DOI: 10.1002/chem.201405989

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Cooperative GeN Bond Activation in Aluminium-Functionalised Aminogermanes and Spontaneous Imine Elimination via an Intermediate Germyl Cation Werner Uhl,*[a] Jens Tannert,[a] Christian Honacker,[a] Marcus Layh,[a] Zheng-Wang Qu,[b] Tobias Risthaus,[b] and Stefan Grimme*[b]

Abstract: Hydrometallation of iPr2NGe(CMe3)(CCCMe3)2 with HM(CMe3)2 (M = Al, Ga) affords alkenyl–alkynylgermanes in which the Lewis-acidic metal atoms are not coordinated by the amino N atoms but by the a-C atoms of the ethynyl groups. These interactions result in a lengthening of the GeC bonds by approximately 10 pm and a comparably strong deviation of the GeCC angle from linearity (154.3(1)8). This unusual behaviour may be caused by steric shielding of the N atoms. Coordination of the metal atoms by the amino groups is observed upon hydrometallation of Et2NGe(C6H5)(CCCMe3)2, bearing a smaller NR2 group. Strong MN interactions lead to a lengthening of the GeN bonds by 10 to 15 pm and a strong deviation of the M atoms from the MC3 plane by 52 and 47 pm, for Al and Ga,

respectively. Dual hydrometallation is achieved only with HAl(CMe3)2. In the product, there is a strong AlN bond with converging AlN and GeN distances (208 vs. 200 pm) and an interaction of the second Al atom to the phenyl group. Addition of chloride anions terminates the latter interaction while the activated GeN bond undergoes an unprecedented elimination of EtN=C(H)Me at room temperature, leading to a germane with a GeH bond. State-of-the-art DFT calculations reveal that the unique mechanism comprises the transfer of the amino group from Ge to Al to yield an intermediate germyl cation as a strong Lewis acid, which induces b-hydride elimination, with chloride binding being crucial for providing the thermodynamic driving force.

Introduction Activation of s-bonds (e.g., CH, HH) by intra- or intermolecular cooperative effects is a very important aspect of catalytic or stoichiometric transformations and crucial for many reactions in research and application.[1] We recently reported the facile synthesis of a variety of highly functionalised silanes or germanes that were generated by hydroalumination or hydrogallation of oligo(alkynyl)silicon or -germanium compounds and demonstrated fascinating aspects of cooperative activation. Mixed alkenyl–alkynylsilanes (1, Scheme 1) and -germanes have been obtained by partial hydrometallation of dialkynylelement compounds.[2–10] They exhibit an interaction of the coordinatively unsaturated Group 13 metal atoms with the a-C atoms of the remaining alkynyl groups. The concomitant weak-

Scheme 1. Compounds obtained by hydrometallation of alkynylsilanes and -germanes (M = Al, Ga; E = Si, Ge; R1 = alkyl, aryl; R2, R3 = CMe3 in many cases).

[a] Prof. Dr. W. Uhl, Dr. J. Tannert, C. Honacker, Dr. M. Layh Institut fr Anorganische und Analytische Chemie Westflische Wilhelms-Universitt Mnster Corrensstrasse 30, 48149 Mnster (Germany) Fax: (+ 49) 251-8336660 E-mail: [email protected]

ening of the SiC or GeC bonds favours the thermally induced rearrangement, which, by 1,1-carbometallation and insertion of the alkynyl C atom into an AlC(vinyl) bond, results in the formation of sila- or germacyclobutenes at elevated temperatures.[6–8] These heterocyclic compounds have interesting fluorescence properties.[11] After hydrometallation, Cl-functionalised alkynylsilanes are known to show strong intramolecular Al···Cl or Ga···Cl interactions (2, Scheme 1),[8] which, in the case of a Si compound, caused a spontaneous and unprece-

[b] Dr. Z.-W. Qu, Dr. T. Risthaus, Prof. Dr. S. Grimme Mulliken Centre of Theortetical Chemistry Institut fr Physikalische und Theoretische Chemie, Universitt Bonn Beringstraße 4, 53115 Bonn (Germany) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201405989. Chem. Eur. J. 2014, 20, 1 – 14

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Full Paper dented 1,3-dyotropic rearrangement and an exchange of the Cl atom by a CMe3 group originally bonded to Al. CH and GeN bond activation has been observed for a germane with an amino and a GaR2 group in a single molecule (3, Scheme 1).[9] This compound shows a strong intramolecular GaN bonding interaction, which results in the formation of a GeNGaC heterocycle (see ref. [10]). Treatment with the alkyne HCCPh at 60 8C leads to ring opening by cleavage of the Ga N bond with approach of the alkyne proton to nitrogen and of the alkyne C atom to gallium. HNEt2, is released and a new GeC bond is formed in the final step. In continuation of these investigations, we have synthesised further amino-functionalised alkynylgermanes, treated them with dialkylmetal hydrides (M = Al, Ga), and observed a unique imine elimination reaction with the transformation of an aminogermane into a hydrogermane.

Results and Discussion Syntheses of the starting dialkynylgermanes

Scheme 2. Syntheses of the starting dialkynylgermanes: A) 4; B) 5.

Three compounds were used as starting materials in these investigations: iPr2NGe(CMe3)(CCCMe3)2 (4), Et2N Ge(C6H5)(CCCMe3)2 (5) and Et2NGe(CCCMe3)3 (6). The synthesis of trisalkynylgermane 6 has been reported previously.[9] We have succeeded now in growing single crystals and determined its structure (Figure 1). In particular the GeN dis-

(Scheme 2). The 13C NMR chemical shifts of the ethynyl groups of all dialkynylgermanes are in narrow ranges at d = 78 (GeC C) and 116 ppm (GeCC). Absorptions at about 2190 and 2150 cm1 in the IR spectra are characteristic of the CC stretching vibrations.

Hydrometallation of the iPr2NGe compound 4 Reactions of the iPr2N germane 4 with equimolar quantities of HM(CMe3)2 (M = Al, Ga) in n-pentane at room temperature gave complete conversion after 3 (M = Al) or 12 h (M = Ga; Scheme 3). Colourless solids of the monohydrometallation products 7 and 8 were isolated in high yields (> 87 %) directly by evaporation of the solvent (7) or by recrystallisation of the crude product from 1,2-difluorobenzene (8). The remaining alkynyl groups of 7 and 8 could not be reduced by treatment with an excess of the hydrides, and even after prolonged reaction times or at elevated temperatures only the monoaddition products were detected by NMR spectroscopy. Several spectroscopic findings ruled out the expected bonding interaction between the amino N and the coordinatively unsaturated Al or Ga atoms. The isopropyl groups of the amino substituents gave single sets of resonances in the NMR

Figure 1. Molecular structure and numbering scheme of 6; displacement ellipsoids are set at the 40 % probability level. Hydrogen atoms have been omitted for clarity. Selected bond lengths [pm] and angles [8]: Ge1N1 181.5(1), Ge1C 189.2(av), CC 119.6 (av); N1-Ge1-C 106.19(5)–113.85(5), C-Ge-C 108.51(5)–111.56(5), Ge-CC 175.7(av), CCC 178.9(av).

tance (181.5(1) pm) is important as a measure for the lengthening and activation of the GeN bond in hydrometallated species. The N atom has a pyramidal environment and the sum of the CNC bond angles is 350.48. Diisopropylaminogermane 4 was obtained in > 80 % yield by treatment of the dichloro compound Cl2Ge(CCCMe3)2[3] with equimolar quantities of LiNiPr2 and reaction of the monochloro intermediate with LiCMe3 (Scheme 2). The synthesis of phenylgermane 5 proceeded by treatment of commercially available H5C6GeCl3 with equimolar quantities of LiNEt2 and reaction of the resulting dichlorogermane with tert-butylethynyllithium in a 1:2 ratio &

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Scheme 3. Reactions of 4 with HM(CMe3)2.

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Full Paper spectra which may indicate a free rotation about the GeN bond. A bridging position of the amino group between Ge and Al/Ga should result in a splitting of the NCH resonances caused by the chirality of the Ge atom (provided that there is no accidental coincidence of the 1H and 13C NMR resonances). The 13C NMR signals of the ethynyl C atoms of the triple bonds of 7 and 8 were shifted to a lower field compared to the starting compound 4 (7: d = 83.0 and 137.5 ppm; 8: d = 84.7 and 124.0 ppm), which is characteristic of metal–alkyne interactions.[4] The pronounced effect observed for the Al compound 7, with a relatively large Dd value of 54 ppm, verified an exceptionally strong coordination of the ethynyl group to the Al atom. The IR spectra exhibited absorptions with relatively low wavenumbers of 2079 (7) and 2108 cm1 (8) for the CC stretching vibrations, which are also characteristic of metal– alkyne interactions.[4] Values of about 2020 cm1 were reported for dimeric alkynyldialkylaluminium or -gallium compounds with the alkynido groups in bridging positions between two Al or Ga atoms.[12] In the NMR spectra two sets of resonances were observed for the M(CMe3)2 groups which correlates to molecular symmetry with a four-membered heterocycle and a chiral environment of the Ge atoms. The interpretation of the spectroscopic data was confirmed by crystal structure determination of 7, which is chiral at the Ge atom and crystallises as a racemic mixture with both enantiomers in the unit cell (the molecule with the (R)-configuration is shown in Figure 2). As predicted, the amino group is in a terminal position. A GeC2Al heterocycle is formed with a remarkably short distance between the Al atom and the a-C atom of the ethynyl group (AlC 227.3(1) pm). This is the shortest Al C(ethyne) separation observed to date for silanes or germanes of this type. The strong AlC(ethyne) interaction results in a lengthening of the Ge1C11 bond (202.3(1) pm) by more than 10 pm compared to related alkynylgermanes, a pyramidalisation of the Al environment with the Al atom 37 pm above the plane of the directly bonded C atoms (C21, C01, C02) and

a relatively strong deviation of the GeCC group from linearity (154.42(9)8). The atoms bonded to N1 (C41, C42, Ge1) are in a plane (sum of the angles = 359.98), which may indicate a hyperconjugative interaction of the lone pair at N with suitable s* orbitals at Ge. The GeC(tert-butyl) bond (GeC31) is in a suitable position, but C31-Ge1-N1-C torsion angles of 56 and 1258 indicate a significant deviation from an ideal conformation for an optimum overlap. Al and H atoms are in a cis arrangement across the C=C double bond, which reflects the kinetically favoured configuration. Rearrangement to yield the thermodynamically favoured trans product[13] is prevented by the intramolecular AlC interaction. The Ge atom is located above the plane of the directly bonded atoms (C31, N1, C21) by 37 pm, and the sum of the bond angles in this group is 351.78. A recent report on the activation of SiF bonds by interactions with different Lewis acids gave an interesting correlation between the planarisation of the R3Si environment and the ionic character of the SiF bond.[14] A higher ionic contribution causes an increasing approach to a coplanar arrangement of the remaining four atoms (Si and three substituents). In a perfectly ionic compound ([R3Si] + and F) the sum of the angles at Si is 3608. For the Ge compound 7, this consideration suggests an intramolecular activation of the GeC(alkyne) bond by the coordination of the a-C atom to Al, which is possibly supported by hyperconjugative interaction to the amino group. The interaction of the alkynyl C atom to Al and Ge may be considered as highly ionic (“ion-like”[14]) with a chelating coordination of the alkynide anion by both Lewis-acidic centres. Crystals of the Ga analogue 8 were obtained from different solvents at different temperatures. In all cases the molecules were disordered across a crystallographic centre of symmetry which prevented a refinement of the structure to reasonable R values. But the preliminary data verified unambiguously the constitution analogous to 7 as shown in Scheme 2. Due to the low quality of the data, we abstain from a detailed discussion. In both structures, we observed the unexpected coordination of the Lewis acids to the a-C atoms of alkynyl groups instead of a bonding interaction to the Lewis-basic N atoms with their lone pairs of electrons. This unusual observation can be attributed to steric shielding of the N atoms by two isopropyl groups, resulting in a fascinating bonding situation that has a strong influence on the GeC(alkynyl) bond and may allow the application of these systems in interesting secondary reactions, such as the insertion of heterocumulenes. As a consequence, we applied smaller NEt2 instead of the bulky NiPr2 groups in further experiments. Hydrometallation of the NEt2Ge compounds 5 and 6 Treatment of the bisalkynylgermane 5 with equimolar quantities of HM(CMe3)2 and recrystallisation of the products from 1,2-difluorobenzene afforded the alkenyl–alkynylgermanes 9 to 10 in high yields (Scheme 4). The crude product of the Al compound 9 always contained the dual addition product 11 as an impurity. Caused by the lower steric shielding of the N atoms by two ethyl groups instead of the isopropyl groups in 7 and 8, we observed a different constitution with the alkynyl groups

Figure 2. Molecular structure and numbering scheme of 7; displacement ellipsoids are set at the 40 % probability level. Hydrogen atoms (except olefinic H, arbitrary radius) have been omitted for clarity. Selected bond lengths [pm] and angles [8]: Ge1N1 183.14(9), Ge1C31 201.4(1), Ge1C11 202.3(1), Ge1C21 194.6(1), C21C22 134.0(2), C11C12 121.4(2), Al1C21 200.2(1), Al1C11 227.3(1); C21-Ge-C11 91.59(4), Ge1-C11-Al1 87.29(4), C11-Al1-C21 83.21(4), Al1-C21-Ge1 97.60(5), Ge1-C11-C12 154.42(9). Chem. Eur. J. 2014, 20, 1 – 14

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Scheme 4. Formation of the monoaddition products 9 and 10.

in terminal positions. Accordingly the 13C NMR shifts of the Gebound alkynyl C atoms (d = 78.0 and 78.4 ppm) were similar to those of the starting compound 5 (d = 77.3 and about 84 ppm in 7 and 8, respectively), and the CC stretching vibrations in the IR spectra were almost unchanged, with the lowest wavenumbers at 2151 and 2147 cm1 (2153 cm1 in 5). The 1H NMR spectrum of the Al compound 9 showed clearly resolved resonances of two different ethyl groups at room temperature which is to be expected for the formation of an AlCGeN heterocycle with a strong AlN bond and the presence of a chiral Ge atom. The diastereotopic CH2 protons gave an instructive spectrum with four doublets of quartets in accordance with an [ABM3]2 spin system of the NEt2 group. In contrast, broad resonances were observed for the Ga compound 10 at room temperature. A splitting pattern comparable to 9 was obtained only upon cooling of a solution in [D8]toluene to 250 K. At 340 K, only a single triplet of the methyl groups and two doublets of quartets for the diastereotopic CH2 hydrogen atoms were detected. The different behaviour of the Al and Ga compounds reflect the acceptor strengths of the metal atoms, and the relatively weak GaN bond may allow a fast rotation about the GeN bond slightly above room temperature. In accordance with molecular symmetry, the tert-butyl groups bound to Al or Ga showed two sets of resonances in the NMR spectra. X-Ray structure determinations (Figure 3) confirmed the interaction between the Lewis-basic N and Lewis-acidic Al or Ga atoms with the formation of almost ideally planar GeCMN heterocycles. The MN distances (Al1-N1 210.2(1) pm; Ga1-N1 224.3(2) pm) are in the range of typical MNM’ bridges.[9, 15] The longer GaN bond length reflects the weaker acceptor capability of Ga compared to Al. The MN interaction results in a significant lengthening of the Ge1N1 bonds [197.2(1) (M = Al) and 194.6(2) pm (M = Ga)] compared to the amino-bis(alkynyl)germane 6 with a terminal amino group (181.5 pm; 183.1 pm in 7). Quantum chemical calculations for comparable compounds have shown that these structural parameters reflect similar Wiberg bond indices for both bonds of the MN Ge group and a considerable weakening of the GeN bond.[9] The sum of the CGeC bond angles is 348.58 and 346.68, respectively, which is smaller than the value (CGeC and N GeC) discussed above for the NiPr2 derivative 7. The Ge atoms are 37.9 and 40.9 pm above the plane of the directly bonded C atoms, the displacement of the Al and Ga atoms from the MC3 planes is 52.0 and 46.7 pm. These results verify that steric effects cause the different molecular constitutions. While the N atom of the diisopropyl derivatives 7 and 8 is highly shielded and not involved in coordinative interaction to &

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Figure 3. Molecular structure and numbering scheme of 9 (structural parameters of the Ga analogue 10 are given in square brackets); displacement ellipsoids are set at the 40 % probability level. Hydrogen atoms (except the olefinic H, arbitrary radius) have been omitted for clarity. Selected bond lengths [pm] and angles [8]: Ge1N1 197.2(1) [194.6(1)], Ge1C11 191.4(1) [191.6(2)], Ge1C21 189.5(2) [189.7(2)], Ge1C31 194.0(1) [194.0(2)], C11 C12 133.7(2) [133.1(3)], C21C22 119.6(2) [119.2(3)], Al1N1 210.2(1) [224.3(2)], Al1C11 199.5(1) [200.6(2)]; C11-Al1-N1 84.29(5) [81.47(6)], Ge1C11-Al1 95.14(6) [97.29(8)], C11-Ge1-N1 90.08(5) [92.01(7)], Ge1-N1-Al1 90.17(5) [89.00(6)].

Al or Ga, the metal atoms are effectively coordinated by the smaller diethylamino group in compounds 9 and 10. Hydrometallation of the terminal alkynyl groups in 9 and 10 should yield bisalkenylgermanes with two Lewis-acidic centres in a single molecule which should give rise to interesting intramolecular donor-acceptor interactions, a possible chelating coordination of the amino group and a further weakening of the GeN bond. The reaction with two equivalents of HGa(CMe3)2 in toluene at room temperature gave, however, almost quantitatively the monohydrogallation product 10 with the gallium-hydride adduct H5C6(H)Ge[C=C(H)CMe3]2(GaCMe3)2[Ga(CMe3)2](m-H)3 formed as a byproduct in trace quantities.[16] In contrast, dual hydroalumination of 5 was achieved by treatment with an excess of 2.3 equivalents of HAl(CMe3)2 in toluene at room temperature for 2 days (Scheme 5), to afford the bisalkene 11 in 72 % yield. The 1 H NMR spectrum of 11 at room temperature shows the resonances of four different tert-butyl groups attached to Al, two complete sets of resonances for the ethyl substituents and two resonances of vinylic H atoms of different alkenyl groups. This pattern is in accordance with the molecular structure shown in Scheme 5 and excludes a fast exchange of the amino ligand between both Al atoms. Complete dissociation of 11 with the formation of the monoaddition product 9 was observed at 80 8C in toluene, as a rare example of a reversible hydroalumination reaction. Accordingly, reaction of 11 with 1-fluoropentane in an NMR experiment afforded 9 and FAl(CMe3)2 by H/F exchange. The monoaddition product was also detected in the mass spectrum. A second decomposition pathway was indicated by the detection of EtN=C(H)Me (see below). The molecular structure of 11 (Figure 4) verifies the reduction of both alkynyl groups and the formation of a bisalkenyl4

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Scheme 5. Dual hydroalumination of dialkynylgermane 5.

Scheme 6. Imine formation.

tion of the halide anion and to influence the accessibility of the GeN bond for secondary reactions such as substitution or elimination. Treatment of 11 with equimolar quantities of [nBu4N]Cl in toluene at room temperature afforded colourless crystals of compound 12 in 84 % yield. 12 had the chloride anion coordinated by both Al atoms (Scheme 6; see below for molecular structure), but the amino group at Ge was replaced by a H atom to form a GeH bond. This group was identified in the 1H NMR spectrum by its characteristic shift of d = 6.85 ppm. Only a single set of resonances was observed for the vinylaluminium groups, which indicates a Cs or C2 symmetry of the molecule in solution. Interestingly we found two almost identical sets of resonances after dissolution of a single crystal in C6D6. One set disappeared almost completely after 7 h at room temperature. On the basis of DFT calculations on various conformers of the anion of 12 (see the Supporting Information, Figure S1), we propose that the boat-like conformer observed for the solid state may convert through hindered GePh bond rotation and ring puckering into a more planar conformer with Cs symmetry that is slightly lower in free energy by 0.7 kcal mol1 in solution (1 kcal = 4.184 kJ); a more twisted conformer is also found with pseudo-C2 symmetry, but it is 2.6 kcal mol1 higher in free energy. In a FT-MS experiment, only one compound was detected, which supports the presence of two isomeric forms in solution. The molecular structure of 12 (Figure 5) consists of an anion with an Al2C2GeCl heterocycle in which the Cl atom is coordinated in a chelating manner by two Al atoms with almost identical AlCl distances (235.0 pm on average).[17] The counterion is the tetra(n-butyl)ammonium cation, which does not have any significant bonding interaction to the anion. A similar structure has been observed only in very few cases with Si- or Ge-centred dialkenyldialuminium compounds, which have comparable AlCl distances of about 234 pm.[6, 18] The central six-membered ring of 12 has a slightly distorted boat confor-

Figure 4. Molecular structure and numbering scheme of 11; displacement ellipsoids are set at the 40 % probability level. Hydrogen atoms (except olefinic H, arbitrary radius) have been omitted for clarity. Selected bond lengths [pm] and angles [8]: Ge1C11 193.4(1), Ge1C21 195.8(1), Ge1C31 197.1(1), Ge1N1 199.69(9), Al1N1 208.2(1), Al1C11 200.1(1), Al2C21 199.4(1), C11C12 134.0(2), C21C22 134.5(2); N1-Ge1-C11 88.05(4), Ge1-C11-Al1 95.58(5), C11-Al1-N1 83.96(4), Al1-N1-Ge1 91.20(4).

germane. A strong AlN interaction (Al1N1 208.2(1) pm) resulted in the formation of an AlCGeN heterocycle. The GeN bond (199.7(1) pm) is slightly longer than that in 9 and considerably elongated (by about 20 pm) compared to alkynylaminogermanes. The second Al atom (Al2) has a short contact to the ortho-CH bond of the phenyl group attached to Ge (Al2···C32 259.9 pm; Al2···H32 224 pm). The two Al atoms deviate from the plane of the three directly bonded C atoms by 52.3 (Al1) and 30.5 pm (Al2). The latter is comparable to values reported for compounds with Al–alkyne interactions. Unique GeN bond activation by the addition of chloride ions Compound 11 has two Al atoms in a molecule, one is coordinated to the N atom, the other one shows an interaction to a CH bond of the phenyl ring attached to Ge. We treated 11 with chloride anions to investigate the strengths of these interactions in competition to AlCl bond formation, to test the capability of 11 to act as a chelating Lewis acid for the coordinaChem. Eur. J. 2014, 20, 1 – 14

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Figure 5. Molecular structure and numbering scheme of the anion of 12; displacement ellipsoids are set at the 40 % probability level. Hydrogen atoms (except H1 at Ge1 and olefinic H, arbitrary radius) and the [nBu4N] + cation have been omitted for clarity. Selected bond lengths [pm] and angles [8]: Ge1C11 194.8(1), Ge1C21 195.8(1), Ge1C31 196.2(1), Ge1H1 145(2), C11C12 134.7(2), C21C22 134.7(2), Al1C11 198.3(1), Al1Cl1 235.37(5), Al2Cl1 234.68(5), Al2C21 199.8(1); Al1-Cl1-Al2 119.97(2), C11-Ge1-C21 115.2(1).

mation with the atoms Al1 and C21 above the plane of the remaining ring atoms by 44 pm and 61 pm, respectively (maximum deviation of 8 pm for the remaining atoms, Ge1, Al2, Cl1, and C11). The GeH bond length of 145(2) pm corresponds to standard values. The fascinating and selective formation of a germane with a GeH bond (12) by replacement of an amino group in the absence of a hydride transfer reagent is, to our knowledge, without precedent in the literature. To investigate the mechanism, we conducted the reaction in a sealed NMR tube in benzene and detected resonances of a second species, which was quantitatively formed as indicated by the integration ratio and was identified as the imine derivative EtN=C(H)Me (13; Scheme 6; for NMR data, see ref. [19]). Compound 13 may be formed by the unexpected spontaneous b-hydride elimination from the Ge-bound diethylamino group. Comparable reactions in which benzophenone reacted with Cl2AlNR2 by formation of the corresponding aluminium diphenylmethanolate were reported,[20] but these were intermolecular processes and the products of the hydride transfer reactions have not been isolated. Dehydrogenation of diethylamine to yield 13 was only observed under drastic reactions conditions in the presence of transition metal catalysts.[21] Recently we reported on the synthesis of the dialkenylgermane 14[9] (Scheme 7), which has a structure[16] closely related to that of compound 11 but the phenyl group attached to gallium is replaced by an alkynyl group. Both compounds show almost the same structural features with a four-membered GeCAlN heterocycle formed by an AlN bond and an intramolecular interaction of the second Al atom to a p-bonding system, the aryl ring in 11 and the alkynyl group in 14. 14 was obtained by the reaction of amino-trisalkynylgermane 6 with two equivalents of HAl(CMe3)2. Despite the similarity of the two compounds, treatment of 14 with [nBu4N]Cl resulted in a different reaction pathway. Rather than forming a Cl-bridged &

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Scheme 7. Synthesis and thermal degradation of the chloride adduct 15.

dialuminium compound analogous to 12 by imine elimination, the Cl atom was coordinated to one of the Al atoms to give compound 15 (Scheme 7, Figure 6). The AlCl bond length (222.2(1) pm) corresponds to standard values for terminal Cl atoms.[22] The second Al atom is part of an AlNGeC heterocycle and involved in an AlN bond (204.7(2) pm; 14: 209.4(2) pm), which results in the longest GeN bond observed to date in these Si or Ge compounds (200.7(2) pm). This lengthening may be influenced by hyperconjugation between the p-bond C31 C32 and suitable s* orbitals at germanium because the torsion angle C32-C31-Ge1-N1 (94.88) approaches the ideal value for an optimum overlap. The GeC bond length to the alkynyl group (191.0(2) pm) is 4 pm shorter than that in compound 14, which has an additional M–alkynyl interaction. The sum of the C-Ge-C bond angles is 350.18, which is in accordance with a relatively high ionic character of the GeN bond.[14] Particularly noteworthy is the large bond angle between the vinylic C atoms (C21-Ge1-C31: 135.0(1)8). A transient chloride adduct, similar to the persistent compound 15, may occur in the initiating step of the spontaneous imine elimination from 11 upon treatment with chloride anions (Scheme 6; see below for DFT calculations). Both adducts differ only by the phenyl or alkynyl substituent attached to Ge. Compared with the alkynyl group, the phenyl group is 6

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Full Paper B2PLYP-D3/def2-QZVP//TPSS-D3/def2-SVP + COSMO-RS(toluene) level of theory. Scheme 8 summarises the most feasible free-energy paths starting from the neutral complexes 11 and its CCCMe3 counterpart 14 (values for 14 shown in parentheses for comparison). Detailed energies and geometries of various intermediates and transition structures as well as some high-lying reaction paths are included in the Supporting Information. Path A shows the Cl coordination to the Lewis-acidic Al atom, which in 11 has a weak contact to the phenyl group with an Al···C distance of 255 pm (239 pm to the CCCMe3 group in 14). The initial Cl binding to the neutral compound 11 (14) is exergonic by 7.1 (5.1) kcal mol1 to form a (a0) in toluene solution. The slightly higher Cl affinity of 11 is consistent with weaker Al···C bonding to the Ph group as compared to the CCCMe3 substituent. Solvent stabilisation effects are Figure 6. Molecular structure and numbering scheme of 15; displacement ellipsoids are set at the 40 % probability level. Hydrogen atoms (except olefinic H, arbitrary radius) have been omitted for clarity. Selected bond lengths [pm] and angles [8]: Ge1C11 191.0(2), Ge1C21 195.0(2), Ge1C31 195.6(2), Ge1N1 200.7(2), C11C12 118.7(3), C21C22 133.6(3), C31C32 134.0(3), Al1C21 199.9(2), Al1N1 204.7(2), Al2C31 204.8(2), Al2Cl1 222.20(9); C21Ge1-N1 87.38(8), Ge1-N1-Al1 92.07(7), N1-Al1-C21 85.01(8), Al1-C21-Ge1 95.28(9).

a relatively soft and less electronegative substituent (sp2 vs. sp hybridised C atoms) and is a better p-electron donor through conjugation to stabilise potential germyl cation intermediates. It may help to enhance the electron density at Ge and to activate the adjacent GeN bond. Compound 15 is thermally very stable and does not show any secondary reaction in toluene at 110 8C after 24 h. Decomposition with gas evolution was only observed when the solid material was heated to 160 8C in a vacuum for 10 min (Scheme 7). The gaseous products were trapped in a Schlenk vessel cooled with liquid N2. The main component was identified by 1H NMR spectroscopy as the imine 13.[19] In a ratio of about 7:1, resonances of a second minor species[19] were observed, which, however, could not be assigned to a specific compound. The residue (16) gave NMR spectra closely related to those of 12. Resonances of the amino group were missing, a singlet with a chemical shift of d = 6.28 ppm in the 1H NMR spectrum indicated the formation of a GeH bond, and the presence of only a single set of resonances for the vinyl groups is in accordance with a Cs-symmetric anion. The 13C NMR signals of the ethynyl group were at d = 88.4 and 112.7 ppm. A 1H–1H ROESY NMR experiment verified the composition of 16 as shown in Scheme 7. Caused by the drastic reaction conditions, several byproducts were formed with 16 as the main component. Purification and generation of single crystals by recrystallisation of 16 was probably prevented by these impurities. Scheme 8. The B2PLYP-D3 predicted free-energy paths (in kcal mol1; R = CMe3) for: A) chloride binding to neutral compound 11; B) ring opening through GeH bond formation; C) ring closure through Z-imine elimination and AlCl bond formation. For comparison, the relative free energies are shown in parentheses when the Ph substituent is replaced by CCCMe3 (14). For each transition state, the imaginary frequency in cm1 is also shown in italics.

Mechanism and quantum chemical calculations To understand the unique and remarkable reaction pathway with GeN bond activation, imine elimination, and GeH bond formation, as well as some substituent effects, state-of-the-art dispersion-corrected DFT calculations were performed at the Chem. Eur. J. 2014, 20, 1 – 14

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Full Paper important for such ionic species, which otherwise would be highly endothermic in the gas phase (see Supporting Information). As the result of AlCl bond formation and cleavage of the weak Al···C interactions, the Ph (CCtBu) and vinyl substituents at Ge become more electropositive, which eventually weakens the endocyclic GeN bond that is elongated by 5.5 (2.8) pm. Starting from the anionic complex a (a0), two ring-opening paths are conceivable through the cleavage of either the GeN (path B) or the AlN bond (see Supporting Information, Scheme S1). The latter, involving a less ionic intermediate (i versus b), is energetically favoured but it is highly hindered by the subsequent hydride transfer step required for imine formation. The ring opening through GeN bond cleavage leads to a four-coordinate Al atom and a three-coordinate, cationic Ge atom (germyl cation[23]), which can be effectively stabilised by an adjacent phenyl group through p-conjugation. The resulting highly Lewis-acidic Ge cation abstracts H from the adjacent amino group to form new GeH and N=C bonds within the intermediate c (c0). The overall ring-opening path B is slightly endergonic by 5.4 (10.2) kcal mol1 and rate-limited by the free-energy barrier of 19.4 (23.1) kcal mol1 for the GeN bond cleavage. Due to geometric constraints, H is selectively abstracted from the bottom ring-side opposite to the Ph (C CtBu) substituent to form selectively the Z-imine bound to the Lewis-acidic Al atom. Whereas the intermediate a was not detected at room temperature, due to relatively facile ring opening, its CCtBu-substituted counterpart a0 showed better kinetic stability (enhanced by about 4 kcal mol1). Starting from the imine adduct c (c0), direct imine elimination from Al is aided by the regeneration of weak Al···C bonding with the electron-rich Ph (CCtBu) substituent, leading to the acyclic intermediate d (d0) in an endergonic step (10.5 (6.6) kcal mol1, path C). Again, the CCtBu substituent is more effective than Ph in forming Al···C bonding interaction. The alternative AlHGe type bonding turns out to be energetically much less favourable (see the Supporting Information, intermediate d’). Before the new AlCl donor–acceptor bond is formed for ring-closing, an intramolecular rotation step is required to adjust the orientation of the existing AlCl bond from trans into cis with respect to the Lewis-acidic Al atom within e (e0), which is hindered by a low barrier of only 6.8 (5.6) kcal mol1. After the intramolecular rotation, the Cl atom attacks the Lewis-acidic Al atom, forming a strong AlClAl bridge and replacing the weak Al···C interaction over a low barrier of only 6.2 (3.3) kcal mol1. Overall, the ring-closing reaction of intermediate e (e0) is exergonic by 5.2 (5.6) kcal mol1 with a low barrier of 17.3 (12.2) kcal mol1, which is kinetically feasible at room temperature. However, taking the initial endergonic ring opening (path B) into account, the imine elimination is almost neutral in free energy from intermediate a but endergonic by 4.0 kcal mol1 from a0 , which, together with the better kinetic stability of a0 discussed above, reasonably explains the higher decomposition temperature required for the CCCMe3-substituted compound 15 compared to the Phsubstituted compound 12. Without Cl binding, the ring opening of the neutral compound 11 would become 6.6 kcal mol1 &

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more endergonic and the reaction would be eventually prevented by very high imine elimination free energy of 28.4 kcal mol1. The initial Cl binding thus plays a crucial role both in activating the endocyclic GeN bond and in providing the thermodynamic driving force for the imine elimination.

Conclusion Amino-functionalised dialkynylgermanes reacted with HM(CMe3)2 (M = Al, Ga) by hydrometallation and formation of mixed alkenyl–alkynylgermanes. Depending on the steric shielding of the N atoms the NiPr2 derivatives showed an intramolecular interaction of the Lewis acidic metal atoms to the aC atom of the unreacted CC triple bonds, while a strong M N bond with the formation of AlNGeC heterocycles and a significant lengthening of GeN bonds was observed for the products having NEt2 groups attached to Ge. The long GeN distance may indicate an activation of these bonds and may facilitate secondary reactions, such as the insertion of heterocumulenes. Some reactions of this type have been reported recently by our group.[9] The bonding in these heterocycles may be described by a chelating coordination of an amido group by two Lewis-acidic atoms (Al and Ge + ). Dual hydroalumination of diethylamino di(tert-butyl)ethynyl phenylgermane afforded a dialkenylgermane, which has a bonding interaction between one of the Al atoms and the amino N atom, while the other metal atom has a narrow contact to a CH bond of a phenyl substituent. Addition of Cl anions and the loss of the Al–phenyl interaction initiated a unique cooperative activation of the GeN bond with the spontaneous release of imine and the formation of a germane with a GeH bond at room temperature. Quantum chemical calculations revealed a lengthening and weakening of the GeN bond upon adduct formation with the chloride anion. The amino group moves completely from Ge to Al with the formation of a germyl cation as an intermediate. The cationic Ge atom is highly Lewis acidic and removes a hydride anion from the diethylamino substituent to afford a Ge H bond and an imine molecule coordinated to Al. Its release is supported by the exergonic formation of an AlClAl bridge. The addition of the Cl anion is crucial to initiate the reaction. However, the phenyl group attached to Ge is essential to stabilise the germyl cation intermediate through p-conjugation for the relatively low activation barrier. Its replacement by a more electronegative alkynyl group enhances considerably the stability of the isolable chloride adduct, and GeH bond formation takes place only at 160 8C. These highly interesting results will stimulate further investigations into the synthesis of similarly reactive germanium or silicon compounds, the search for other suitable leaving groups, such as different amides or alcoholates, and a possible application in catalytic processes.

Experimental Section General methods All manipulations were carried out under purified argon in dried solvents (diethyl ether and toluene with sodium/benzophenone; n-

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Full Paper 25 eV, 298 K): m/z (%): 393 (4) [M] + , 378 (100) [MCH3] + , 336 (57) [MCMe3] + , 293 (97) [MNiPr2] + .

pentane, cyclopentane and n-hexane with LiAlH4 ; pentafluorobenzene and 1,2-difluorobenzene with molecular sieves) using standard Schlenk techniques. NMR spectra were recorded in [D6]benzene or [D8]toluene at ambient probe temperature using the following Bruker instruments: Avance I (1H, 400.13; 13C, 100.61 MHz), Avance III (1H, 400.03; 13C, 100.59 MHz) and referenced internally to residual solvent resonances (chemical shifts d in ppm). 13C NMR spectra were all proton-decoupled. Elemental analyses were determined by the microanalytic laboratory of the Westflische Wilhelms Universitt Mnster. IR spectra were recorded as paraffin mull between KBr, CsBr or CsI plates on a Shimadzu Prestige 21 spectrometer, EI mass spectra on a Varian mass spectrometer (only the most intense peak of the correct isotopic pattern). Solutions of tBuLi in n-pentane and nBuLi in n-hexane, LiNiPr2, HCCCMe3, PhGeCl3 and GeCl4 were used as purchased. LiNEt2,[24] Et2NGe(CCCMe3)3 (6),[9] Cl2Ge(CCCMe3)2,[3] HAl(CMe3)2,[25] HGa(CMe3)2[25] and Et2NGe(CCCMe3)[C{Al(CMe3)2}=C(H)CMe3]2 (14)[9] were synthesised according to literature procedures.

Et2NGe(C6H5)Cl2 : A solution of LiNEt2 (0.98 g, 12.4 mmol) in Et2O (50 mL) was added dropwise at 78 8C to a solution of PhGeCl3 (3.17 g 12.4 mmol) in Et2O (50 mL). The cooling bath was removed and the mixture was stirred for 16 h at room temperature. After filtration the volatiles were removed under reduced pressure. The residue was distilled under reduced pressure (66 8C, 103 mbar) to yield Et2NGe(C6H5)Cl2 as a colourless oil (3.40 g, 94 %). 1H NMR (400 MHz, C6D6, 300 K): d = 7.65 (dd, 3JHH = 7.6 Hz, 4JHH = 1.9 Hz, 2 H, o-Ph), 7.06 (m, 1 H, p-Ph), 7.04 (m, 2 H, m-Ph), 2.94 (q, 3JHH = 7.0 Hz, 4 H, NCH2), 0.93 ppm (t, 3JHH = 7.0 Hz, 6 H, NCH2CH3); 13C NMR (100 MHz, C6D6, 300 K): d = 133.4 (ipso-C), 133.1 (o-C), 132.0 (p-C), 129.2 (m-C), 41.8 (NCH2), 15.3 ppm (NCH2Me); IR (mixture with KBr, measured between CsI plates): n˜ = 1979 (m), 1963 (m), 1909 (m), 1889 (m), 1838 (m), 1819 (m), 1775 (m, n(CHAr), 1657 (m), 1615 (w), 1586 (s), 1484 (vs), 1463 (vs), 1451 (vs), 1435 (vs, phenyl), 1378 (vs), 1367 (sh), 1344 (vs), 1338 (sh), 1308 (vs), 1291 (vs), 1253 (m, d(CH3)), 1192 (sh), 1169 (vs), 1094 (vs), 1071 (vs), 1058 (vs), 1016 (vs), 999 (sh), 968 (s), 903 (vs), 869 (m), 852 (w), 785 (vs), 737 (vs, n(CC), n(CN)), 693 (vs), 679 (sh, phenyl), 609 (vs), 572 (w), 458cm1 (vs, n(GeC), n(GeN), d(CC)); MS (EI + , 25 eV, 298 K): m/z (%): 293 (6) [M] + , 278 (100) [MCH3] + , 258 (7) [MCl] + , 221 (23) [MNEt2] + .

Syntheses iPr2NGe(Cl)(CCCMe3)2 : A solution of LiNiPr2 (0.541 g, 5.05 mmol) in Et2O (25 mL) was added dropwise at 0 8C to a solution of Cl2Ge(CCCMe3)2[3] (1.55 g, 5.07 mmol) in Et2O (50 mL). The cooling bath was removed and the mixture was stirred for 12 h at room temperature. The volatiles were removed under reduced pressure, the residue was extracted with n-hexane (50 mL) and filtered. The solvent of the filtrate was removed under reduced pressure and the residue recrystallised from cyclopentane at 30 8C to give iPr2NGe(Cl)(CCCMe3)2 as a colourless solid (1.76 g, 94 %). 1 H NMR (400 MHz, C6D6, 300 K): d = 3.67 (sept., 3JHH = 6.8 Hz, 1 H, NCH), 1.33 (d, 3JHH = 6.8 Hz, 6 H, NCHMe2), 1.03 ppm (s, 18 H, CMe3); 13 C NMR (100 MHz, C6D6, 300 K): d = 116.3 (CCCMe3), 77.7 (CC CMe3), 48.1 (NCH), 30.1 (CMe3), 28.3 (CMe3), 24.5 ppm (NCHMe2); IR (KBr plates, paraffin): n˜ = 2195 (vs), 2156 (vs), 2127 (sh, n(CC)); 2056 (vw), 1981 (vw), 1956 (vw), 1913 (vw), 1846 (vw), 1830 (vw), 1753 (vw), 1719 (vw), 1701 (vw), 1686 (vw), 1618 (vw), 1572 (w), 1472 (vs), 1395 (vs), 1379 (vs), 1362 (vs, paraffin), 1312 (m), 1254 (vs, d(CH3)); 1179 (vs), 1157 (vs), 1121 (vs), 1015 (vs), 964 (vs), 924 (vs), 862 (s), 843 (vs), 754 (vs, n(CC), n(CN)); 725 (s, paraffin), 691 (w), 606 (m), 554 (m), 515 (vs), 492 (vs), 447 cm1 (s, n(GeC), n(GeN), n(GeCl), d(CC)); MS (EI + , 20 eV, 298 K): m/z (%): 371 (2) [M] + , 356 (100) [MCH3] + , 336 (2) [MCl] + , 314 (3) [MCMe3] + , 271 (10) [MNiPr2] + ; elemental analysis calcd (%) for C18H32ClGeN (370.5): C 58.4, H 8.7, N 3.8; found: C 59.3, H 8.8, N 3.4.

Et2NGe(Ph)(CCCMe3)2 (5): A solution of nBuLi (12.0 mL, 19.2 mmol, 1.6 m in n-hexane) was added dropwise at 78 8C to a solution of H-CCCMe3 (1.56 g, 2.33 mL, 19.0 mmol) in Et2O (50 mL). The cooling bath was removed, the pale yellow mixture was stirred for 16 h at room temperature and added dropwise at 78 8C to a solution of Et2NGe(C6H5)Cl2 (2.78 g, 2.00 mL, 9.5 mmol) in Et2O (50 mL). The cooling bath was removed, and the mixture was stirred for 16 h at room temperature. Filtration and removal of the volatiles yielded a yellow oil which was distilled under reduced pressure (90 8C, 103 mbar) to give compound 5 as a colourless oil (3.04 g, 83 %). 1H NMR (400 MHz, C6D6, 300 K): d = 8.03 (dd, 3JHH = 7.9 Hz, 4JHH = 1.3 Hz, 2 H, o-Ph), 7.23 (d, 3JHH = 7.3 Hz, 2 H, m-Ph), 7.16 (m, 1 H, p-Ph), 3.21 (q, 3JHH = 7.0 Hz, 4 H, NCH2), 1.19 (t, 3JHH = 7.0 Hz, 6 H, NCH2CH3), 1.13 ppm (s, 18 H, CMe3); 13C NMR (100 MHz, C6D6, 300 K): d = 136.8 (ipso-C), 134.0 (o-C), 130.1 (p-C), 128.8 (m-C), 116.5 (CCCMe3), 77.3 (CCCMe3), 42.9 (NCH2), 30.8 (CMe3), 28.4 (CMe3), 15.9 ppm (NCH2Me); IR (CsI plates, paraffin): n˜ = 2186 (s), 2153 (s, n(CC)), 1955 (vw), 1884 (vw), 1817 (vw, n(CHAr)), 1476 (m, paraffin), 1456 (m), 1434 (s, d(CH3)), 1375 (m), 1363 (s, paraffin), 1343 (w), 1292 (w), 1252 (vs, d(CH3)), 1204 (m), 1177 (s), 1097 (s), 1075 (w), 1055 (w), 1017 (s), 965 (vw), 921 (w), 895 (w), 786 (w), 751 (s, n(CC), n(CN)), 737 (s, paraffin), 697 (s, phenyl), 605 (w), 552 (vw), 491 (m), 483 (m), 465 cm1 (m, n(GeC), n(GeN), d(CC)); MS (EI + , 25 eV, 298 K): m/z (%): 385 (4) [M] + , 370 (51) [MCH3] + , 313 (100) [MNEt2] + .

iPr2NGe(CMe3)(CCCMe3)2 (4): A solution of tBuLi (2.65 mL, 4.5 mmol, 1.7 m in n-pentane) was slowly added at 0 8C to a solution of iPr2NGe(Cl)(CCCMe3)2 (1.68 g, 4.5 mmol) in Et2O (25 mL). The mixture was stirred at this temperature for 1 h, the cooling bath was removed and the suspension was stirred for 2 h at room temperature. The volatiles were removed under reduced pressure and the residue was treated with n-pentane (20 mL). After filtration, the solvent was removed and the residue was distilled under reduced pressure (64 8C, 6  103 mbar) to yield 4 as a colourless oil (1.57 g, 89 %). 1H NMR (400 MHz, C6D6, 300 K): d = 3.38 (sept., 3 JHH = 6.9 Hz, 1 H, NCH), 1.33 (d, 3JHH = 6.9 Hz, 6 H, NCHMe2), 1.29 (s, 9 H, GeCMe3), 1.11 (s, 18 H, CCCMe3); 13C NMR (100 MHz, C6D6, 300 K): d = 115.8 (CCCMe3), 78.6 (CCCMe3), 47.8 (NCH), 30.8 (CCCMe3), 28.4 (CCCMe3), 27.0 (GeCMe3), 25.9 (GeCMe3), 24.9 (NCHMe2); IR (KBr plates): n˜ = 2183 (vs), 2151 (vs, n(CC)) 1969 (vw), 1944 (vw), 1558 (vw), 1474 (vs), 1456 (vs), 1393 (vs), 1377 (vs), 1362 (vs, d(CH3), paraffin), 1304 (m), 1252 (vs, d(CH3)); 1180 (vs), 1155 (vs), 1123 (vs), 1016 (vs), 957 (vs), 920 (vs), 883 (vw), 854 (m), 833 (s), 812 (s), 748 (vs, n(CC), n(CN)), 689 (vw), 602 (w), 546 (s), 507 (vs), 488 (vs), 447 cm1 (s, n(GeC), n(GeN), n(GeCl), d(CC)); MS (EI + , Chem. Eur. J. 2014, 20, 1 – 14

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iPr2NGe(CMe3)(CCCMe3)[C{Al(CMe3)2}=C(H)CMe3] (7): Compound 4 (0.245 mL, 0.26 g, 0.66 mmol) was added at 0 8C to a solution of (Me3C)2AlH (0.094 g, 0.66 mmol) in n-pentane (20 mL). The mixture was stirred for 30 min. The cooling bath was removed, and stirring was continued for 3 h at room temperature. All volatiles were removed under reduced pressure to yield analytically pure 7 (0.34 g, 96 %). Single crystals of 7 were obtained by recrystallisation from 1,2-difluorobenzene at 2 8C. M.p. 158 8C (Ar, sealed capillary); 1 H NMR (400 MHz, C6D6, 300 K): d = 7.13 (s, 1 H, C=CH), 3.60 (sept., 3 JHH = 6.9 Hz, 2 H, NCHMe2), 1.40 and 1.36 (each s, 9 H, AlCMe3), 1.35 and 1.33 (each m, overl., 6 H, NCHMe2), 1.31 (s, 9 H, GeCMe3), 1.15 (s, 9 H, CCCMe3), 1.06 ppm (s, 9 H, C=CCMe3); 13C NMR (100 MHz, C6D6, 300 K): d = 164.9 (C=CCMe3), 139.0 (br, C=C CMe3), 137.5 (CCCMe3), 83.0 (CCCMe3), 50.5 (NCHMe2), 36.7 (C=CCMe3), 32.0 and 31.9 (AlCMe3), 31.1 (GeCMe3), 30.5 (CC

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Full Paper (s), 538 (w), 500 (m), 461 cm1 (s, n(GeC), n(AlC), n(GeN), n(AlN), d(CC)); MS (EI + , 20 eV, 343 K): m/z (%): 470 (100) [MCMe3] + , 415 (12) [M2 butene] + , 399 (77) [MCMe3EtN=CHMe] + ; elemental analysis calcd (%) for C30H52AlGeN (526.4): C 68.4, H 10.0, N 2.6; found: C 67.9, H 10.6, N 2.0.

CMe3), 30.2 (GeCMe3), 29.4 (CCCMe3), 28.9 (C=CCMe3), 26.2 and 27.7 (CHMe2), 18.7 and 18.1 ppm (br, AlCMe3); IR (KBr plates, paraffin): n˜ = 2181 (vw), 2145 (w), 2079 (m, n(CC)), 1680 (vw), 1653 (vw), 1595 (m), 1560 (w, n(C=C)), 1458 (vs), 1377 (s, paraffin), 1308 (w), 1246 (m, d(CH3)), 1200 (s), 1177 (m), 1134 (w), 1107 (w), 1055 (vw), 999 (w), 957 (m), 937 (m), 895 (w), 810 (m), 783 (w), 745 (w, n(CC), n(CN)), 719 (s, paraffin), 664 (vw), 581 (m), 501 (w), 471 (w), 447 (w), 420 cm1 (m, n(GeC), n(GeN), n(AlN),n(AlC), d(CC)); MS (EI + , 25 eV, 323 K): m/z (%): 451 (27) [M2 propene] + , 395 (100) [M2 propenebutene] + , 378 (56) [MCMe3NiPr2] + ; elemental analysis calcd (%) for C30H60AlGeN (534.4): C 67.4, H 11.3, N 2.6; found: C 66.8, H 11.3, N 2.1.

Et2NGe(C6H5)(CCCMe3)[C{Ga(CMe3)2}=C(H)CMe3] (10): Compound 5 (0.23 g, 0.60 mmol) was added at room temperature to a solution of (Me3C)2GaH (0.126 g, 0.68 mmol) in toluene (20 mL). The colourless mixture was stirred for 20 h at room temperature, all volatiles were removed under reduced pressure, and the residue was recrystallised from pentafluorobenzene (1.5 mL) to yield 10 as a colourless solid (0.243 g, 71 %). M.p. 112 8C (Ar, sealed capillary); 1H NMR (400 MHz, C7D8, 300 K): d = 7.90 (d, 3JHH = 7.9 Hz, 2 H, o-Ph), 7.18 (pseudo-t, 3JHH = 7.2 Hz, 2 H, m-Ph), 7.13 (s, 1 H, C=CH), 7.11 (m, 1 H, p-Ph), 3.21 and 2.93 (each s br, 2 H, NCH2), 1.49 and 1.45 (each s, 9 H, GaCMe3), 1.18 (s, 9 H, CCCMe3), 1.09 (s, 9 H, C=CCMe3), 0.82 ppm (m br, 6 H, NCH2Me); 1H NMR (400 MHz, C7D8, 340 K): d = 7.83 (d, 3JHH = 6.5 Hz, 2 H, o-Ph), 7.18 (pseudo-t, 2 H, m-Ph), 7.13 (s, 1 H, C=CH), 7.11 (m, 1 H, p-Ph), 3.19 and 2.96 (each dq, 2JHH = 13.8 Hz, 3JHH = 6.9 Hz, 2 H, NCH2), 1.38 and 1.35 (each s, 9 H, GaCMe3), 1.20 (s, 9 H, CCCMe3), 1.04 (s, 9 H, C=CCMe3), 0.84 ppm (t, 3JHH = 6.9 Hz, 6 H, NCH2Me); 1H NMR (400 MHz, C7D8, 190 K): d = 7.90 (s br, 2 H, o-Ph), 7.22 (s, 1 H, C=CH), 7.12 (pseudo-t, 2 H, m-Ph), 7.04 (m, 1 H, p-Ph), 3.81, 3.06, 2.78 and 2.12 (each s br, 1 H, NCH2), 1.63 and 1.58 (each s br, 9 H, GaCMe3), 1.18 (s br, 18 H, CCCMe3 and C=CCMe3), 0.68 and 0.19 ppm (each s br, 3 H, NCH2Me); 13C NMR (100 MHz, C7D8, 300 K): d = 166.2 (C=CCMe3), 145.1 (C=CCMe3), 137.7 (ipso-C), 134.6 (o-C), 130.2 (p-C), 128.7 (mC), 120.4 (CCCMe3), 78.4 (CCCMe3), 42.7 (NCH2), 39.2 (C=C CMe3), 32.6 and 32.5 (GaCMe3), 30.6 (CCCMe3), 29.8 (C=CCMe3), 28.7 (CCCMe3), 27.3 and 25.7 (GaCMe3), 12.6 ppm (NCH2Me); IR (KBr plates, paraffin): n˜ = 2180 (m), 2147 (m, n(CC)), 1954 (vw), 1900 (vw), 1821 (vw), 1763 (vw, n(CHAr)), 1645 (w), 1603 (s), 1553 (m), 1531 (m), 1506 (m, n(C=C), phenyl) 1460 (vs), 1377 (vs, paraffin), 1307 (s), 1288 (s), 1252 (vs, d(CH3)), 1200 (s), 1177 (s), 1136 (s), 1111 (m), 1090 (m), 1070 (m), 1043 (m), 1005 (s), 976 (m), 935 (m), 924 (m), 899 (m), 883 (m), 860 (m), 841 (w), 806 (s), 783 (m, n(CC), n(CN)), 731 (s, paraffin), 700 (s), 675 (w, phenyl), 592 (s), 538 (s), 498 (m), 463 (m), 405 cm1 (m, n(GeC), n(GaC), n(GeN), n(AlN), d(CC)); MS (EI + , 20 eV, 298 K): m/z (%): 512 (69) [MCMe3] + , 441 (100) [MCMe3EtN=CHMe] + ; elemental analysis calcd (%) for C30H52GaGeN (569.1): C 63.3, H 9.2, N 2.5; found: C 63.0, H 9.1, N 2.3.

iPr2NGe(CMe3)(CCCMe3)[C{Ga(CMe3)2}=C(H)CMe3] (8): Compound 4 (0.230 mL, 0.24 g, 0.61 mmol) was added at room temperature to a solution of (Me3C)2GaH (0.11 g, 0.60 mmol) in toluene (25 mL). The mixture was stirred for 12 h. All volatiles were removed under reduced pressure, and the residue was recrystallised from 1,2-difluorobenzene at 2 8C to yield 8 as a colourless solid (0.302 g, 87 %). M.p. 157 8C (Ar, sealed capillary); 1H NMR (400 MHz, C6D6, 300 K): d = 6.66 (s, 1 H, C=CH), 3.63 (sept., 3JHH = 6.9 Hz, 2 H, NCHMe2), 1.43 and 1.40 (each s br, 9 H, GaCMe3), 1.37 (d, 3JHH = 4.9 Hz, 6 H, NCHMe2), 1.36 (d, 3JHH = 5.0 Hz, 6 H, NCHMe2), 1.34 (s, GeCMe3), 1.18 (s, 9 H, CCCMe3), 1.10 ppm (s, 9 H, C=CCMe3); 13 C NMR (100 MHz, C6D6, 300 K): d = 161.7 (C=CCMe3), 142.0 (C= CCMe3), 124.0 (CCCMe3), 84.7 (CCCMe3), 50.2 (NCHMe2), 37.0 (C=CCMe3), 32.03 and 31.96 (GaCMe3), 31.0 (CCCMe3), 30.3 (GeCMe3), 29.4 (GeCMe3), 29.2 (C=CCMe3), 29.0 (CCCMe3), 28.6 and 28.0 (br, GaCMe3), 27.5 and 26.3 ppm (CHMe2); IR (KBr plates, paraffin): n˜ = 2180 (w), 2147 (m), 2108 (w, n(CC)), 1607 (w), 1591 (w), 1562 (w, n(C=C)), 1458 (vs), 1408 (w), 1377 (vs, paraffin), 1362 (vs), 1310 (w), 1250 (s, d(CH3)), 1200 (s), 1179 (s), 1134 (w), 1107 (w), 1011 (w), 955 (m), 941 (w), 922 (w), 899 (w), 874 (w), 810 (m), 783 (w), 745 (m, n(CC), n(CN)), 721 (m, paraffin), 702 (m), 625 (vw), 577 (m), 550 (w), 538 (w), 498 (w), 459 cm1 (w, n(GeC), n(GaC), n(GeN), n(GaN), d(CC)); MS (EI + , 20 eV, 298 K): m/z (%): 520 (2) [MCMe3] + , 477 (4) [MNiPr2] + , 437 (100) [M2 propenebutene] + ; elemental analysis calcd (%) for C30H60GaGeN (577.2): C 62.4, H 10.5, N 2.4; found: C 62.2, H 10.5, N 2.1. Et2NGe(C6H5)(CCCMe3)[C{Al(CMe3)2}=C(H)CMe3] (9): Compound 5 (0.57 g, 1.48 mmol) was added at room temperature to a solution of (Me3C)2AlH (0.23 g, 1.62 mmol) in toluene (30 mL). The colourless mixture was stirred for 16 h at room temperature. All volatiles were removed under reduced pressure, and the residue was recrystallised from pentafluorobenzene (1 mL) to yield 9 as a colourless solid (0.559 g, 72 %). M.p. 126 8C (Ar, sealed capillary); 1H NMR (400 MHz, C7D8, 300 K): d = 7.82 (dd, 3JHH = 7.9 Hz, 4JHH = 1.4 Hz, 2 H, o-Ph), 7.29 (s, 1 H, C=CH), 7.16 (m, 2 H, m-Ph), 7.10 (m, 1 H, p-Ph), 3.47 and 3.27 (each dq, 2JHH = 13.8 Hz, 3JHH = 6.9 Hz, 1 H, NCH2), 2.88 and 2.49 (each dq, 2JHH = 13.8 Hz, 3JHH = 6.9 Hz, 1 H, NCH2), 1.35 and 1.33 (each s, 9 H, AlCMe3), 1.18 (s, 9 H, CCCMe3), 1.02 (s, 9 H, C= CCMe3), 1.00 and 0.62 ppm (each t, 3JHH = 7.0 Hz, 6 H, NCH2Me); 13 C NMR (100 MHz, C7D8, 300 K): d = 168.9 (C=CCMe3), 142.0 (br, C=CCMe3), 137.1 (ipso-C), 134.6 (o-C), 130.4 (p-C), 128.8 (m-C), 120.9 (CCCMe3), 78.0 (CCCMe3), 42.1 and 41.8 (NCH2), 39.3 (C= CCMe3), 32.7 and 32.6 (AlCMe3), 30.5 (CCCMe3), 29.6 (C=C CMe3), 28.7 (CCCMe3), 19.9 and 17.6 (AlCMe3), 12.5 and 12.1 ppm (NCH2Me); IR (CsI plates, paraffin): n˜ = 2185 (m), 2151 (m, n(CC)), 2119 (vw), 1973 (vw), 1956 (vw), 1904 (vw), 1888 (vw), 1836 (vw), 1819 (vw), 1769 (vw, n(CHAr)), 1684 (vw), 1653 (vw), 1599 (m), 1564 (m, n(C=C), phenyl), 1458 (vs), 1379 (vs), 1362 (vs, paraffin), 1339 (s), 1306 (s), 1252 (vs, d(CH3)), 1200 (s), 1092 (s), 1069 (w), 1011 (m), 970 (w), 937 (m), 922 (m), 899 (m), 849 (w), 810 (s), 789 (m), 750 (s), 735 (vs, n(CC), n(CN)), 716 (s, paraffin), 696 (s), 677 (w, paraffin), 586

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Et2NGe(C6H5)[C{Al(CMe3)2}=C(H)CMe3]2 (11): Compound 5 (0.282 g, 0.73 mmol) was added at room temperature to a solution of (Me3C)2AlH (0.238 g, 1.67 mmol) in toluene (25 mL). The colourless mixture was stirred for 48 h at room temperature, all volatiles were removed under reduced pressure, and the residue was recrystallised from 1,2-difluorobenzene (1 mL) at 2 8C to give 11 as a colourless solid (0.352 g, 72 %). M.p. 142 8C (Ar, sealed capillary); 1H NMR (400 MHz, C7D8, 300 K): d = 7.77 (d, 3JHH = 7.1 Hz, 2 H, o-Ph), 7.28 (s, 1 H, NAl-C=CH), 7.25 (pseudo-t, 3JHH = 7.5 Hz, 2 H, m-Ph), 7.01 (t, 3 JHH = 7.5 Hz, 1 H, p-Ph), 6.65 (s, 2 H, Al(aryl)-C=CH), 3.82 and 3.19 (each dq, 2JHH = 14.2 Hz, 3JHH = 7.1 Hz, 1 H, NCH2), 2.95 and 2.90 (each dq overl., 2JHH = 13.6 Hz, 3JHH = 6.9 Hz, 1 H, NCH2), 1.33 and 1.06 (each s, 9 H, NAlCMe3), 1.30 and 0.56 (Al(aryl)-CMe3), 1.18 (s, 9 H, Al(aryl)-C=CCMe3), 1.15 (m overl., 3 H, NCH2Me), 1.11 (s, 9 H, NAl-C=CCMe3), 0.87 ppm (t, 3JHH = 6.9 Hz, 3 H, NCH2Me); 13C NMR (100 MHz, C7D8, 300 K): d = 165.5 (Al(aryl)-C=CCMe3), 165.1 (NAlC=CCMe3), 150.1 (ipso-C), 148.2 (br, NAl-C=CCMe3), 146.8 (Al(aryl)-C=CCMe3), 133.1 (m-C), 131.5 (br, o-C), 130.6 (p-C), 42.7 and 42.3 (NCH2), 39.9 (Al(aryl)-C=CCMe3), 38.1 (NAl-C=CCMe3), 33.0 and 32.7 (NAl-CMe3), 31.9 and 30.6 (Al(aryl)-CMe3), 29.6 (NAl-

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Full Paper C=CCMe3), 29.3 (Al(aryl)C=CCMe3), 20.6 and 20.3 (br, overl., Al(aryl)CMe3), 19.0 and 17.6 (br, NAlCMe3), 13.6 and 12.0 ppm (NCH2Me); IR (CsI plates, paraffin): n˜ = 2027 (vw), 1977 (vw), 1892 (vw), 1838 (vw), 1676 (vw, n(CHAr)), 1595 (m), 1547 (m, n(C=C), phenyl), 1462 (vs), 1377 (vs, paraffin), 1304 (sh), 1287 (w), 1267 (w), 1248 (w, d(CH3)), 1196 (m), 1173 (w), 1155 (sh), 1132 (m), 1109 (m), 1078 (m), 1061 (w), 1043 (m), 1024 (w), 1003 (s), 972 (w), 934 (m), 880 (m), 854 (w), 806 (s), 781 (m), 735 (s, n(CC), n(CN)), 716 (vs, paraffin), 662 (vw, phenyl), 588 (s), 544 (sh), 505 (m), 465 (m), 430 (s), 413 (m), 401 cm1 (s, n(GeC), n(AlC), n(GeN), n(AlN), d(CC)); MS (EI + , 20 eV, 403 K): m/z (%): 612 (17) [MCMe3] + , 470 (100) [MCMe3(Me3C)2AlH] + , 399 (87) [MCMe3(Me3C)2AlHEtN= CHMe] + ; elemental analysis calcd (%) for C38H71Al2GeN (668.6): C 68.2, H 10.7, N 2.1; found: C 67.6, H 10.5, N 1.9.

1 H, NCH2Me (AlCl)), 2.43 (m, 8 H, NCH2Pr), 1.61 and 1.54 (each s, 9 H, NAlCMe3), 1.56 and 1.55 (each s, 9 H, ClAlCMe3), 1.55 (overl., 3 H, NCH2Me) and 1.29 (t, 3JHH = 6.8 Hz, 3 H, NCH2Me (AlCl)), 1.47 (s, 9 H, CCCMe3), 1.46 (s, 9 H, ClAlC=CCMe3), 1.44 (s, 9 H, NAlC=C CMe3), 1.12 (pseudo-quint., 3JHH = 7.2 Hz, 8 H, NCH2CH2), 1.00 (m, 8 H, NCH2CH2CH2), 0.85 ppm (t, 3JHH = 7.2 Hz, 12 H, NCH2CH2CH2Me); 13 C NMR (100 MHz, C6D6, 300 K): d = 165.4 (ClAlC=CCMe3), 157.4 (NAlC=CCMe3 and NAlC=CCMe3), 144.2 (ClAlC=CCMe3), 115.4 (CCCMe3), 88.1 (CCCMe3), 58.4 (NCH2Pr), 42.3 (NCH2Me), 41.9 (NCH2Me, (AlCl)), 40.5 (ClAlC=CCMe3), 38.7 (NAlC=CCMe3), 34.5 and 33.7 (ClAlCMe3), 34.2 and 33.4 (NAlCMe3), 32.0 (ClAlC=CCMe3), 31.0 (CCCMe3), 29.9 (NAlC=CCMe3), 28.7 (CCCMe3), 23.8 (NCH2CH2), 19.8 (NCH2CH2CH2), 19.2 and 18.1 (br, NAlCMe3), 18.6 and 18.1 (br, ClAlCMe3), 14.5 (NCH2Me (AlCl)), 14.0 (NCH2Me), 13.8 ppm (NCH2CH2CH2Me); IR (KBr plates, paraffin): n˜ = 2185 (m), 2153 (m, n(CC)) 1647 (vw), 1593 (m), 1535 (m), 1508 (m, n(C=C)), 1466 (vs), 1379 (vs, paraffin), 1308 (m), 1290 (m), 1252 (m, d(CH3), 1196 (m), 1173 (m), 1152 (m), 1132 (w), 1111 (w), 1070 (w), 1047 (w), 1024 (w), 1005 (m), 955 (w), 934 (m), 883 (m), 864 (m), 808 (s), 797 (s), 777 (m), 743 (s, n(CC), n(CN)), 718 (s, paraffin), 691 (m), 583 (s), 559 (s), 509 (m), 476 (w), 459 (m), 417 cm1 (m, n(GeC), n(AlC), n(GeN), n(AlN), d(CC)); elemental analysis calcd (%) for C54H111Al2ClGeN2 (950.5): C 68.2, H 11.8, N 2.9; found: C 67.7, H 11.7, N 2.9. Thermolysis of 15 (16): Compound 15 (0.08 g, 0.084 mmol) was heated in an NMR tube in vacuo to 160 8C. The solid melted, and gas evolution occurred. The glassy solid was identified by NMR spectroscopy as [nBuN4] + [HGe(CCCMe3)[C{Al(CMe3)2}= C(H)CMe3]2Cl] (16). Attempts to purify the product by recrystallisation and to remove minor quantities of unidentified byproducts were not successful. 1H NMR (400 MHz, C6D6, 300 K): d = 7.47 (s, 2 H, C=CH), 6.26 (s, 1 H, GeH), 2.23 (m, 8 H, NCH2), 1.67 (s, 9 H, C=C CMe3), 1.63 and 1.56 (s, 18 H, AlCMe3), 1.37 (CC- CMe3), 1.05 (pseudo-quint., 3JHH = 7.2 Hz, 8 H, NCH2CH2CH2), 0.89 (m, 8 H, NCH2CH2), 0.82 ppm (t, 3JHH = 7.3 Hz, 12 H, NCH2CH2CH2Me); 13 C NMR (100 MHz, C6D6, 300 K): d = 163.9 (C=CCMe3), 148.5 (C= CCMe3), 112.7 (CCCMe3), 88.4 (CCCMe3), 58.5 (NCH2), 39.2 (C=CCMe3), 33.1 and 33.0 (AlCMe3), 32.2 (C=CCMe3), 31.4 (CC CMe3), 28.6 (CCCMe3), 23.7 (NCH2CH2), 19.7 (NCH2CH2CH2), 17.6 (br AlCMe3), 13.7 ppm (NCH2CH2CH2Me).

[nBu4N] + [HGe(C6H5)[C{Al(CMe3)2}=C(H)CMe3]2Cl] (12): A solution of [nBu4N]Cl (41 mg, 0.15 mmol) and 11 (0.100 g, 0.15 mmol) in toluene (5 mL) was stirred for 3 h. All volatiles were removed under reduced pressure. The oily residue was treated with pentafluorobenzene which initiated immediate crystallisation. The product was dissolved in 1,2 difluorobenzene and pentafluorobenzene (1:5). 12 precipitated as a colourless solid at 2 8C (0.110 g, 84 %). Two almost identical sets of resonances (1:1 ratio) were observed in the 1 H NMR spectra after dissolution of 12 in C6D6 (denoted 12A and 12B). The resonances of species 12B disappeared after about 6 h at room temperature. M.p. 164 8C (Ar, sealed capillary); 1H NMR (400 MHz, C6D6, 300 K): 12A: d = 8.22 (d, 3JHH = 6.9 Hz, 2 H, o-Ph), 7.73 (s, 2 H, C=CH), 7.36 (pseudo-t, 3JHH = 7.5 Hz, 2 H, m-Ph), 7.20 (t, 3 JHH = 7.5 Hz, 1 H, p-Ph), 6.85 (s, 1 H, GeH), 2.07 (m, 8 H, NCH2), 1.63 (s, 9 H, C=CCMe3), 1.60 and 1.36 (each s, 9 H, AlCMe3), 0.96 (pseudo-quint., 3JHH = 7.3 Hz, 8 H, NCH2CH2CH2), 0.79 (m overl., 8 H, NCH2CH2), 0.75 ppm (t overl., 3JHH = 7.3 Hz, 12 H, NCH2CH2CH2Me); 12B: d = 8.05 (d, 3JHH = 7.2 Hz, 2 H, o-Ph), 7.58 (s, 2 H, C=CH), 7.21 (pseudo-t, overl., 2 H, m-Ph), 7.12 (t, 3JHH = 7.3 Hz, 1 H, p-Ph), 6.64 (s, 1 H, GeH), 2.02 (m, 8 H, NCH2), 1.51, 1.46 and 1.24 ppm (each s, 9 H, CMe3); the missing n-butyl resonances overlapped with those of 12A; 13C NMR (100 MHz, C6D6, 300 K): d = 165.3 (C=CCMe3), 149.8 (C=CCMe3), 144.5 (ipso-C), 136.9 (o-C), 127.4 (m-C), 127.3 (p-C), 58.4 (NCH2), 38.5 (C=CCMe3), 33.2 and 32.82 (AlCMe3), 32.77 (C= CCMe3), 23.6 (NCH2CH2), 19.6 (NCH2CH2CH2), 17.8 and 17.5 (br, AlCMe3), 13.6 ppm (NCH2CH2CH2Me); IR (CsI plates, paraffin): n˜ = 2012 (m, n(GeH)), 1955 (vw), 1827 (vw), 1700 (vw, n(CHAr)), 1581 (w), 1531 (m, n(C=C), phenyl), 1459 (vs), 1377 (vs, paraffin), 1305 (m), 1270 (w), 1234 (w, d(CH3)), 1199 (m), 1169 (m), 1110 (vw), 1084 (vw), 1069 (vw), 1060 (vw), 1032 (w), 1004 (w), 933 (w), 900 (w), 849 (w), 833 (w), 810 (m), 779 (m), 754 (m, n(CC)), 721 (m, paraffin), 695 (m), 667 (w, phenyl), 575 (m), 533 (w), 467 (w), 423 cm1 (w, n(GeC), n(AlC), n(AlCl), d(CC)); HRMS (NSI, FT-MS): m/z calcd for C34H62Al2GeCl: 633.3391; found: 633.3413 [PhGe(H)[C(AltBu2)C(H)tBu)]2Cl] ; HRMS (NSI + , FT-MS): m/z calcd for C16H36N: 242.2853; found: 242.2831 [nBu4N] + ; elemental analysis calcd (%) for C50H98Al2ClGeN (875.4): C 68.6, H 11.3, N 1.6; found: C 68.4, H 11.4, N 1.5.

Crystal structure determination Single crystals were obtained by crystallisation under the following conditions: From the oily substance at RT (6), from 1,2-difluorobenzene at 2 8C (7) and 30 8C (15), from pentafluorobenzene at 30 8C (9 and 10) and 2 8C (11), and from a 5:1 mixture of pentafluorobenzene and 1,2-difluorobenzene at 2 8C (12). The crystallographic data was collected with a Bruker APEX II or Bruker D8 Venture diffractometers with multilayer optics and MoKa radiation. The crystals were coated with a perfluoropolyether, picked up with a glass fibre and immediately mounted in the cooled nitrogen stream of the diffractometer. The crystallographic data and details of the final R values are provided in Table 1. All non-hydrogen atoms were refined with anisotropic displacement parameters; hydrogen atoms were calculated on ideal positions and allowed to ride on the bonded atom with U = 1.2 Ueq(C). 7 crystallised with two independent molecules. Disorder of CMe3 groups was observed for 7 (C04, 0.78:0.22), 9 (C32, 0.20:0.47:0.33), 10 (C23, 0.69:0.31), 11 (C04, 0.57:0.43) and 15 (C03, 0.47:0.53). 11 crystallised with half a pentafluorophenyl molecule per formula unit; it was disordered over a centre of symmetry and the positions of six fluorine atoms were refined with site occupancy factors of 5/6. An nbutyl group of the ammonium cation of 11 and 16 was disordered

[Et2NGe(CCCMe3)(C{Al(CMe3)2}=C(H)CMe3)2Cl][nBu4N] + (15): A solution of [nBu4N]Cl (41 mg, 0.15 mmol) and [Et2NGe(CC CMe3)[C{(Al(CMe3)2}=C(H)CMe3]2] 14[9] (0.100 g, 0.15 mmol) in toluene (4 mL) was stirred for 20 min at room temperature. All volatiles were removed under reduced pressure. Recrystallisation of the residue from pentafluorobenzene (0.8 mL) at 30 8C yielded 15 as a colourless solid (0.136 g, 95 %). M.p. 136 8C (Ar, sealed capillary); above 165 8C elimination of EtN=CHMe (13) and formation of 17 (see below); 1H NMR (400 MHz, C6D6, 300 K): d = 7.45 (s, 1 H, ClAlC=CH), 6.96 (s, 1 H, NAlC=CH), 3.97 and 3.62 (each dq, 2JHH = 14.0 Hz, 3JHH = 6.9 Hz, 1 H, NCH2Me], 3.47 and 3.42 (each m overl., Chem. Eur. J. 2014, 20, 1 – 14

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Full Paper Table 1. Crystal data and structure refinement of compounds 6, 7, 9–12 and 15.[a]

Empirical formula T [K] Crystal system Space group a [pm] b [pm] c [pm] a [8] b [8] g [8] V [nm3] Z 1calc [g cm3] m [mm1] crystal size [mm] qmin/qmax [8] Independent reflections Completeness to qmax [%] Parameters R1 (I > 2s(I)) wR2 (all data) Largest diff. peak/hole [e 3]

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15

C22H37GeN 153(2) orthorhombic Pbca 1164.99(6) 2007.7(1) 2073.0(1) 90 90 90 4.8487(4) 8 1.063 1.266 0.69  0.48  0.26 1.96/30.10 7138 [Rint = 0.032] 100 228 0.0274 (6068) 0.0777 0.510, 303

C30H60AlGeN 153(2) triclinic P1¯ 1147.75(7) 1535.97(9) 1921.5(1) 96.447(1) 90.301(1) 101.012(1) 3.3028(3) 4 1.075 0.970 0.31  0.25  0.10 2.13/30.11 19179 [Rint = 0.014] 97.7 664 0.0279 (17021) 0.0780 0.696, 0.344

C30H52AlGeN 120(2) monoclinic P21/c 977.85(2) 1620.05(3) 2031.24(4) 90 99.583(1) 90 3.1729(1) 4 1.102 1.009 0.36  0.28  0.21 2.96/29.58 8881 [Rint = 0.027] 99.8 385 0.0328 (7913) 0.0860 1.189, 0.399

C30H52GaGeN 153(2) monoclinic P21/c 983.28(3) 1621.31(6) 2034.50(7) 90 99.663(1) 90 3.1974(2) 4 1.182 1.799 0.29  0.11  0.08 2.45/28.28 7917 [Rint = 0.024] 99.9 331 0.0312 (6980) 0.0836 0.658, 0.731

C30H71Al2GeN 153(2) triclinic P1¯ 1088.59(5) 1107.20(5) 1777.37(7) 98.772(2) 99.975(2) 99.209(2) 2.0466(2) 2 1.085 0.815 0.51  0.45  0.27 2.73/30.03 11878 [Rint = 0.023] 99.8 399 0.0280 (10668) 0.0761 0.475, 0.299

C50H98Al2ClGeN 153(2) orthorhombic Pbca 2111.5(1) 2134.1(1) 2440.0(1) 90 90 90 10.9951(9) 8 1.058 0.667 0.65  0.21  0.21 1.91/30.15 16185 (Rint = 0.033] 100 542 0.0232 (13173) 0.0891 0.523, 0.491

C54H111Al2ClGeN2 153(2) monoclinic P21/c 1935.8(2) 1589.0(2) 2007.8(2) 90 94.245(3) 90 6.159(1) 4 1.025 0.600 0.41  0.32  0.17 2.40/27.88 14428 [Rint = 0.058] 97.8 619 0.0497 (9926) 0.1375 1.045,-0.441

R1 = S j j Fo j  j Fc j j /S j Fo j ; wR2 = {S[w(Fo2Fc2)2]/S[w(Fo2)2]}1/2 ; [a] Programme shelxL-97;[26] solutions by direct methods, full matrix refinement with all independent structure factors.

energies (in kcal mol1, at 298.15 K and 101 325 Pa) were used unless specified otherwise.

(C63 and C64 in 11: 0.75:0.25; in 15: 0.47:0.53). CCDC-1024579 (6), CCDC-1024580 (7), CCDC-1024581 (9), CCDC-1024582 (10), CCDC1024583 (11), CCDC-1024584 (12), and CCDC-1024585 (15) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

Acknowledgements We are grateful to the Deutsche Forschungsgemeinschaft (Uh 45/9–2 and SFB 813) for generous financial support.

Computational methodology The quantum chemical DFT calculations were performed with the TURBOMOLE suite of programs.[27, 28] The structures are fully optimised at the TPSS-D3/def2-SVP level of theory, which combines the accurate TPSS meta-GGA density functional[29] with the BJdamped D3 dispersion correction[30, 31] and the def2-SVP basis set,[32–35] using the density-fitting RI-J approach[36, 37] to accelerate the calculations. The optimised structures are characterised by frequency analysis at the same level of theory to identify the nature of located stationary points (no imaginary frequency for true minima and only one imaginary frequency for transition state) and to provide thermal corrections according to the modified ideal gas–rigid rotor–harmonic oscillator model.[38] Using the fully optimised geometries, the solvation free energies in toluene are computed by the COSMO-RS solvation model in the COSMOtherm program package using the BP TZVP C30 1201.ctd parameter file,[39] while more reliable total electronic energies are computed at the TPSS-D3 and higher hybrid-meta PW6B95-D3[40] and double-hybrid B2PLYP-D3[41] levels of theory together with the large def2-QZVP basis set.[42] As expected, the TPSS-D3 method tends to slightly underestimate the reaction barriers, while very good agreement (mostly within 1 kcal mol1) between the PW6B95-D3 and B2PLYPD3 methods is observed for the relative energies. The final Gibbs free energies (DG) in toluene solvent are determined from the total electronic energies plus thermal corrections and COSMO-RS solvation free energies. In our discussion, the B2PLYP-D3 Gibbs free

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Keywords: bond activation · density functional calculations · germanium · hydroalumination · imines [1] a) X. Chen, K. M. Engle, D.-H. Wang, J.-Q. Yu, Angew. Chem. Int. Ed. 2009, 48, 5094 – 5115; Angew. Chem. 2009, 121, 5196 – 5217; b) J. WencelDelord, T. Drçge, F. Liu, F. Glorius, Chem. Soc. Rev. 2011, 40, 4740 – 4761; c) R. H. Crabtree in Modern Coordination Chemistry (Eds.: N. Winterton, J. Leigh), RSC Publishing, Cambridge 2002, pp. 31 – 44; d) D. Astruc, Organometallic Chemistry and Catalysis, Springer, Berlin/Heidelberg, 2007; e) I. Ojima, Z. Li, J. Zhu in Chemistry of Organic Silicon Compounds (Eds.: S. Patai, Z. Rappoport), Wiley, New York, USA 2003, Vol. 2, pp. 1678 – 1792; f) K. Miura, A. Hosomi in Main Group Metals in Organic Synthesis (Eds.: H. Yamamoto, K. Oshima), Wiley-VCH, Weinheim, 2004, Vol. 2, pp. 409 – 592; g) T. Akiyama in Main Group Metals in Organic Synthesis (Eds.: H. Yamamoto, K. Oshima), Wiley-VCH, Weinheim, 2004, Vol. 2, pp. 593 – 620; h) H. Yorimitsu, K. Oshima, Inorg. Chem. Commun. 2005, 8, 131 – 142. [2] W. Uhl, M. Rohling, J. Kçsters, New J. Chem. 2010, 34, 1630 – 1636. [3] W. Uhl, S. Pelties, M. Rohling, J. Tannert, Eur. J. Inorg. Chem. 2014, 2809 – 2818. [4] W. Uhl, J. Bohnemann, B. Kappelt, K. Malessa, M. Rohling, J. Tannert, M. Layh, A. Hepp, Z. Naturforsch. 2014, 69b, 1333 – 1347. [5] Further mixed alkenyl-alkynylsilanes and -germanes exhibiting intramolecular Al-C or Ga-C interactions: a) W. Uhl, D. Heller, Z. Anorg. Allg. Chem. 2010, 636, 581 – 588; b) W. Uhl, J. Bohnemann, D. Heller, A. Hepp, M. Layh, Z. Anorg. Allg. Chem. 2012, 638, 68 – 75.

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Received: November 6, 2014 Published online on && &&, 0000

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Full Paper

FULL PAPER & Germanium W. Uhl,* J. Tannert, C. Honacker, M. Layh, Z.-W. Qu, T. Risthaus, S. Grimme* && – && Cooperative GeN Bond Activation in Aluminium-Functionalised Aminogermanes and Spontaneous Imine Elimination via an Intermediate Germyl Cation

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Germane genius: Cooperative activation of a GeN bond by the intramolecular interaction of an amino group with an Al atom facilitates the spontaneous elimination of an imine via an intermediately formed strongly Lewis acidic germyl cation and b-hydride abstrac-

tion, as revealed by a combined experimental and DFT study. The reaction is initiated by the addition of Cl anions and thermodynamically favoured by the chelating coordination of the halide anion by two aluminium atoms.

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