DOI: 10.1002/chem.201500179

Full Paper

& Magnesium Catalysis |Hot Paper|

Organomagnesium-Catalyzed Isomerization of Terminal Alkynes to Allenes and Internal Alkynes Raphal Rochat, Koji Yamamoto, Michael J. Lopez, Haruki Nagae, Hayato Tsurugi,* and Kazushi Mashima*[a]

isomerization of alkynes. Notably, the reactions proceeded through temporally separated autotandem catalysis, thus allowing the isolation of the allene or internal alkyne species in good yields. Mechanistic experiments suggested that the catalytically active tetraalkynyl complexes consist of a tautomeric mixture of alkynyl-, allenyl-, and propargylmagnesium species.

Abstract: Organomagnesium complexes 2 were synthesized from N,N-dialkylamineimine ligands 1 and dibenzylmagnesium by benzylation of the imine moiety. 3-Aryl-1-propynes reacted with 2 to form the corresponding tetraalkynyl complexes, which acted as catalysts for the transformation of these terminal alkynes into allenes and further to internal alkynes under mild conditions. To the best of our knowledge, this example is the first of an organomagnesium-catalyzed

Introduction

Allenes are interesting building blocks for organic synthesis. Various methods for their preparation have been developed, including alkaline-metal-base-mediated or -catalyzed isomerizations of terminal alkynes to allenes. However, these reactions may afford mixtures of allenes and internal alkynes, depending on the substrates and conditions.[6] Therefore, the quest for selective allene-formation reactions by using electropositive organometallics is an important and still ongoing task. Herein, we report that alkylmagnesium complexes bearing monoanionic N,N-bidentate ligands can catalyze the isomerization of terminal alkynes to allenes and further to internal alkynes, and CH activation is a key event in both reactions. To the best of our knowledge, this example is the first homogeneous organomagnesium-catalyzed alkyne isomerization. The reactions from terminal alkynes to allenes and further to internal alkynes notably proceed through a temporally separated autotandem catalysis, so that the macroscopic temporal separation allows for the isolation of the allene or the internal alkyne, according to demand. Furthermore, methyl C(sp3)H bond activation of 1-phenyl-1-propyne by the alkylmagnesium moiety and subsequent tautomerization produces a dimeric alkynylmagnesium complex.

Organomagnesium compounds have become a highly important class of reagent in organic chemistry since the discovery of the Grignard reaction more than 100 years ago. These compounds are powerful and inexpensive reagents that can be readily prepared from metallic magnesium and organic halides, and many applications have been developed.[1] Along with the original synthetic protocol of the Grignard reagent, CH bond activation of functionalized aromatic compounds were recently developed for the synthesis of organomagnesium reagents with functionalized groups (for example, Knochel–Hauser bases).[2] The application of such reagents to the formation of new CC and CE (E = B, O, Si, P, S, Sn, etc.) bonds in addition or substitution reactions has been continuously and intensively studied. However, organomagnesium compounds are used as stoichiometric reagents in the vast majority of these reactions. Besides Lewis acid catalysis and magnesium-initiated polymerization reactions, there are only few reports of homogeneous magnesium catalysis, namely hydroamination,[3] hydroboration,[4] and various coupling reactions (that is, cross-dehydrocoupling of silanes with amines, dehydrocoupling of aminoboranes, coupling of alkynes with carbodiimides, and dehydrocoupling of silanes with 2,2,6,6-tetramethyl-1-piperidinyloxy).[5]

Results and Discussion Preparation and characterization of alkylmagnesium complexes 2 with aminoamido ligands

[a] Dr. R. Rochat, K. Yamamoto, M. J. Lopez, H. Nagae, Dr. H. Tsurugi, Prof. Dr. K. Mashima Department of Chemistry, Graduate School of Engineering Science Osaka University and CREST, JST Toyonaka, Osaka 560-8531 (Japan) E-mail: [email protected] [email protected]

The treatment of [Mg(CH2Ph)2(thf)2] with one equivalent of N1benzylidene-N2,N2-diisopropylethane-1,2-diamine (1 a) in toluene at 60 8C for 18 hours gave monobenzyl complex 2 a in 87 % yield as a product of the intramolecular benzylation of the C=N moiety of the ligand [Eq. (1)]:

Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201500179. Chem. Eur. J. 2015, 21, 1 – 10

These are not the final page numbers! ÞÞ

1

 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

&

&

Full Paper cores.[8] Notable differences between the two complexes are that the MgN1 bond distance in anti-2 a is elongated relative to anti-2 b (2.232(3) versus 2.179(4) , respectively), and the angle N1-Mg-C(benzyl) in anti-2 a is larger than that in anti-2 b (120.42(11) versus 113.52(16)8, respectively) which is due to the steric hindrance of the isopropyl group on the amine nitrogen atom of the ligand. These findings are consistent with the fact that anti-2 a is thermodynamically more stable than syn-2 a. In sharp contrast to the reaction in Equation (1), the reaction of one equivalent of N1-benzylidene-N2,N2-dimethylethane-1,2diamine (1 b) with [Mg(CH2Ph)2(thf)2] (78 8C!room temperature, 3 h) resulted in the formation of a mixture of syn- and anti-conformers of 2 b in 90 % yield (Eq. (2), based on the 1 H NMR resonances). The selective formation of only one isomer at room temperature was not observed; however, prolonged heating of the syn/anti mixture of 2 b in a mixture of toluene and pyridine at 80 8C for 18 hours led to the selective formation of anti-2 b, thus indicating that anti-2 b is thermodynamically more stable than syn-2 b. It is assumed that the isomerization proceeds through the pyridine-induced dissociation of 2 b into monomeric species prior to the facial rearrangement at an elevated temperature. Thus, we isolated anti-2 b in 87 % yield under these reaction conditions. The molecular structure of anti-2 b was determined by a single-crystal X-ray diffraction study (Figure 1), which confirmed that the structure of anti-2 b is essentially the same as that of complex 2 a.

The 1H NMR spectrum of 2 a showed nonequivalent methylene protons for the benzyl moiety attached to the magnesium center. The chemical-shift value of the magnesium-bound benzyl CH2Ph carbon atom was in good accordance with typical benzylmagnesium complexes.[7] The overall molecular structure of 2 a was determined by a single X-ray diffraction study (Figure 1), which revealed the centrosymmetric dimer unit {Mg2(m-N)2}. Both magnesium atoms adopted a distorted-tetrahedral geometry and were bridged by the amido nitrogen atom of the ligand. The two benzyl groups were arranged anti with respect to the {Mg2(m-N)2} core. The bond lengths of Mg N2 and MgN2* (2.13–2.14 ) are consistent with the reported lengths of the bridging MgN(amido) bonds in the {Mg2N2}

Magnesium-catalyzed isomerization of terminal alkynes to allenes and to internal alkynes We first observed that complex 2 b catalytically (2 mol %) transformed 3-phenyl-1-propyne (3 a) into phenylallene (4 a) almost completely within 18 hours at 60 8C. Moreover, the allene was further converted into 1-phenyl-1-propyne (5 a) when the reaction mixture was maintained at 60 8C. Because both isomerization reactions occurred subsequently on a macroscopic level and without any need to the change the catalytic conditions or add reagents, this reaction can be categorized as “temporally separated autotandem catalysis” [Eq. (3)].[9] Such systems are advantageous because the reaction can be terminated after the first or second cycle, thus yielding in our case the allene or internal alkyne, respectively.

Figure 1. ORTEP representations of monobenzyl complexes anti-2 a (top) and anti-2 b (bottom). Ellipsoids are set at 30 % probability. All the hydrogen atoms and solvents have been omitted for clarity. Selected bond lengths [] and angles [8] for anti-2 a: Mg1–N1 2.232(3), Mg1–N2 2.133(2), Mg1–N2* 2.141(3), Mg1–Mg1* 3.0331(18), Mg1–C23 2.204(3); Mg1-N2-Mg1* 90.41(9), N2-Mg1-N2* 89.59(10), N1-Mg1-C23 120.42(11), N2-Mg1-C23 129.11(11). For anti-2 b: Mg1–N1 2.179(4), Mg1–N2 2.132(4), Mg1–N2* 2.144(4), Mg1–Mg1* 2.955(3), Mg1–C19 2.173(5); Mg1-N2-Mg1* 87.46(14), N2-Mg1-N2* 92.54(14), N1-Mg1-C19 113.52(16), N2-Mg1-C19 130.99(16).

&

&

Chem. Eur. J. 2015, 21, 1 – 10

www.chemeurj.org

2

 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

ÝÝ These are not the final page numbers!

Full Paper Table 1. Screening of conditions for the catalytic isomerization of 3phenyl-1-propyne (3 a) to phenylallene (4 a) and further to 1-phenyl-1proypne (5 a), and the formation of the cycloaddition byproduct 6 a.

Figure 2 shows the reaction profile of 3 a in the presence of 2 b (4 mol %) monitored by 1H NMR spectroscopic analysis at 80 8C in [D8]toluene over 34 hours. Initially, 2 b reacted with four equivalents of 3 a to generate the catalytically active spe-

Cat. precursor

T 4a [8C]

5a t1

1[c] 2[c] 3[c] 4[c,d] 5[c,d] 6[c,d] 7[d] 8 9

cies (see below) in a very fast reaction (< 2 min). In the first catalytic cycle, terminal alkyne 3 a was transformed into phenylallene (4 a). After reaching the maximum concentration of 4 a, we observed a shift of one set of 1H NMR signals assigned to a Mg complex (see below), thus indicating a change of the catalyst when switching to the second isomerization cycle (see the Supporting Information for details). In the second stage, 4 a was isomerized further to 1-phenyl-1-propyne (5 a). When 4 a was present at sufficiently high concentrations, a [2+2] cycloaddition reaction occurred as a side reaction to produce mainly 1,2-dimethylene-3,4-diphenylcyclobutane (6 a)[10] in small amounts (< 5 %). Notably, 6 a was only formed in traces when 4 a was heated at 80 8C for 20 hours in the absence of a catalyst. We then investigated the influence of the temperature on the efficiency and product distribution by using 3 a in the presence of 2 a and 2 b as precatalysts (Table 1). We found that higher temperatures are beneficial because they decrease the reaction time while not significantly increasing the formation of the cycloaddition byproducts (less than 10 % in all cases). When 2 a was used as a precatalyst, the catalytic activity was lower (27 % after 7.7 days) than in the case of 2 b owing to steric hindrance around the amine moiety. It is noteworthy that [MgBn2(thf)2] and [MgBn2(TMEDA)] (TMEDA = tetramethylethylenediamine) acted as catalyst precursors for this system as well, but these complexes were much less efficient than the systems of 2 a and 2 b (Table 1, entry 7), thus indicating that www.chemeurj.org

These are not the final page numbers! ÞÞ

40 2.3 d 60 9.5 h 80 4h 100 0.5 h 120 0.35 h 80 7.7 d 80 5d 80 20 h 60 18 h

Yield [%][b] > 95 > 95 86 85 85 2 PhCH=C=CH2 (4 a) > PhCH2CCH (3 a). Depending on the substituent on the C3 fragment however, the series can differ and exclude a catalytic reaction of a terminal to an internal alkyne through the allene.[11] Electron-poor benzylic terminal alkynes were converted into the corresponding allenes much faster than electron-rich alkynes. The rates of isomerization of the allenes to the internal alkynes were in about the same range for all substrates. This finding is consistent with the fact that establishing conjugation of the aromatic ring with the allene system in the first isomerization is the step that is most dependent on the electronic properties of the aromatic group. 3

 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

&

&

Full Paper also possible, as shown by the reaction of two equivalents of 1-phenyl-1-butyne with 2 b for 20 hours at 100 8C, thus producing 1-phenyl-1,2-butadiene after quenching with water. Complex 7 was analyzed by means of X-ray crystallography studies and NMR spectroscopic analysis (Figure 3). The 1H NMR spectrum of 7 showed broad signals when recorded in benzene, but displayed sharp resonances in pyridine, thus indicating syn/anti fluxionality in solution with benzene. Figure 2 shows the molecular structure of 7, which has features that are con-

Table 2. Substrate screening.

Substrate 3

4 t1

Yield [%][b]

5 t2

Yield [%][b]

6 Yield [%][b]

1

3b 9 h

72

25.5 h 67

6

2

3 c 10 h

77

37 h

61

7

3

3d 3 h

75

21.5 h 57

6

4

3 e 12.5 h 47

11 h

64

2

5

3 f 5.5 h

83

27 h

66

6

6

3 g 5.5 h

89

34 h

82

5

7

3h 71

25 h

62

2[c]

8

3i 1 h

52

21 h[d] 11[d]

> 8[c]

9

3 j 29 h

54

28 h

50

8

10

3 k 40 h

58

30 h

63

8

11

3 l 6.3 d[e] 59





12[c]

[a] Reaction mixtures: substrate = 0.5 mmol, [D8]toluene = 0.4 mL, 2 b = 0.02 mmol, 80 8C. The catalyst was generated in situ from complex 2 b and 4 equivalents of the alkyne (relative to 2). [b] Yields were determined by 1H NMR spectroscopic analysis with phenanthrene as an internal standard and were based on the amount of substrate available for isomerization (100 % = 0.42 mmol for 4 and 5, 100 % = 0.21 mmol for 6). [c] Other unknown byproducts were also formed. [d] Terminated owing to poor reactivity and side reactions. [e] Conditions: 4.3 days at 60 8C and 2 days at 80 8C in C6D6.

Mechanistic studies The reaction of 2 b with only two equivalents of 3 a afforded bis-3-phenyl-1-propyne-1-yl dinuclear magnesium complex 7 after 20 minutes at 60 8C. Notably, complex 7 was also obtained by treating 2 b with two equivalents or excess of 5 a for 2 hours at 80 8C, although simple dibenzylmagnesium ([Mg(CH2Ph)2(thf)2]) did not react with 5 a, even upon heating at 100 8C for 12 hours, thus suggesting that the monoanionic aminoamido ligand increased the basicity of the MgC fragment enough to activate the terminal C(sp3)H bond of internal alkynes. The activation of an internal C(sp3)H bond was &

&

Chem. Eur. J. 2015, 21, 1 – 10

www.chemeurj.org

Figure 3. ORTEP representations of intermediate complex 7 (top), dialkynyl complex 12 (middle), and tetraalkynyl complex 13 (bottom). Ellipsoids are set at 30 % probability. All the solvents and hydrogen atoms have been omitted for clarity, except for the hydrogen atoms on the nitrogen atoms. Selected bond lengths [] and angles [8] for 7: Mg1–N1 2.163(3), Mg1–N2 2.103(3), Mg1–N2* 2.132(3), Mg1–C19 2.095(3), C19–C20 1.211(5), C20–C21 1.481(5); Mg1-C19-C20 174.9(3), C19-C20-C21 178.5(4). For 12: Mg1–N1 2.153(5), Mg1–N2 2.094(6), Mg1–N2* 2.134(6), Mg1–C19 2.104(7); Mg1-C19C20 174.2(5). For 13: Mg1–N1 2.208(3), Mg1–N2 2.324(4), Mg1–C19 2.127(4), Mg1–C27 2.401(3), Mg1–C27* 2.181(4), C19–C20 1.217(5), C27–C28 1.218(5); Mg1-C19-C20 171.1(3), Mg1-C27-Mg1* 90.89(13), Mg1-C27-C28 106.5(3), Mg1*-C27-C28 153.9(3), C27-Mg1-C27* 89.11(13), N2-Mg1-C27* 169.44(12).

4

 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

ÝÝ These are not the final page numbers!

Full Paper sistent with its parent complex 2 b, except that the two benzyl moieties on the magnesium atom are substituted with two alkynyl groups. Interestingly, despite the activation of the terminal position of the alkyne and that the benzylic CH2 group remains intact, quenching 7 with an excess of TMSCl (10 equiv) yielded almost solely bis-silylated product 10 a, whereas quenching with two equivalents of TMSCl afforded a mixture of mono- and bis-silylated alkyne and allene products 8 a–11 a (Scheme 1). Accordingly, we concluded that 7 is a tautomeric mixture of alkynyl-, propargyl-, and allenylmagnesium species in solution, among which the bis-3-phenyl-1-propyne-1-ylmagnesium complex was isolated as the thermodynamically most stable tautomer in the solid state (see the Supporting Information).

Scheme 2. Formation of di- (12) and tetraalkynylmagnesium (13) complexes through the deprotonation of phenylacetylene by the MgC and MgN bonds.

adopted a five-coordinated distorted-trigonal planar geometry. It is noteworthy that the bond length of MgN2 in 13 was significantly elongated relative to the analogous bond in 2 b owing to the change from monoanionic to neutral coordination to the metal center,[12] thus indicating that the amidomagnesium moiety in 2 b acts as a proton acceptor to induce deprotonation of phenylacetylene. The formation of the amine group in complex 13 was also confirmed by 1H NMR spectroscopic analysis in which one broad resonance assignable to the amine protons was observed, and by a weak band at n˜ = 3276 cm1 in the IR spectrum. The 13C NMR spectrum of 13 in toluene showed only one set of broad signals for the alkylnylmagnesium moiety, although terminal and bridging alkynyl groups were present in the solid state, thus suggesting that such five-coordinated tetraalkynyl complexes readily dissociate into the corresponding mononuclear complexes in solution owing to the weak bridging nature of the alkynyl group relative to the amido bridge. This finding was further supported by the 13C NMR spectrum of 13 in pyridine, in which there was one set of sharp signals for the alkynyl groups at d = 112.8 and 130.4 ppm, thus indicating that the mononuclear species was stabilized by the coordination of pyridine. Previously, somewhat similar four-coordinated alkyne-bridged dinuclear complexes of Group 2 metals were reported to keep their dimeric nature in non-coordinating solvents.[13] Because the stoichiometric isomerization of 5 a to 3 a by using 2 b seemed to proceed through propargyl and allenyl tautomers of 7, we proposed a plausible pathway for the catalytic reaction outlined in Scheme 3. In the presence of excess amounts of terminal alkyne, 2 b was first converted into 7, followed by the activation of another alkyne through the basic magnesium–amido bond to form a tautomeric mixture of dialkynyl complexes A–C, which were in equilibrium through 1,3-hydride shifts, and acted as key intermediates in the catalytic cycle. The experimental evidence for isomerization in the presence of THF and pyridine supports the proposed mononuclear species. Furthermore, we assumed that the dialkynyl spe-

Scheme 1. Preparation of dialkynyl complex 7 and its reactivity with TMSCl (R = CH(Ph)CH2Ph). TMS = trimethylsilyl.

We then examined the reaction of 2 b with a nonisomerizable terminal alkyne, phenylacetylene, as a model reaction to detect that magnesium species in the catalytic reaction. The acidic C(sp)H hydrogen atom of terminal alkynes is readily deprotonated by MgC bonds. Complex 2 b was treated with two equivalents of phenylacetylene to give dialkynylmagnesium complex 12 after 20 minutes at 60 8C in 61 % yield (Scheme 2), whereas the reaction of 2 b with excess amounts of phenylacetylene afforded the dinuclear tetraalkynylmagnesium complex 13 in 91 % yield, in which the two magnesium centers were bridged by two alkynyl groups and each magnesium atom accommodated one terminal alkynyl moiety. The molecular structures of complexes 12 and 13 were clarified by means of X-ray diffraction studies (ORTEP drawings are shown in Figure 3). Complex 12 possessed a {Mg2(m-N)2} dimer core in which two benzyl groups were replaced with two phenylacetylenyl moieties relative to 2 b. The overall structure of 12 is essentially the same as that of anti-2 b. In contrast, the molecular structure of 13 is centrosymmetric with a four-membered {Mg2(m-C)2} core. The two magnesium centers are bridged by sp-hybridized phenylacetylenyl groups through three-center two-electron bonds, and each magnesium center Chem. Eur. J. 2015, 21, 1 – 10

www.chemeurj.org

These are not the final page numbers! ÞÞ

5

 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

&

&

Full Paper labeled substrates were not expected to be informative in our case because both inter- and intramolecular scrambling on the two alkynyl/allenyl/propargyl fragments of the catalytically active species may occur.

Conclusion The first example of an organomagnesium-catalyzed isomerization of 3-aryl-1-propynes to arylallenes and further to 1-aryl-1propynes is described. Notably, the reactions proceeded through temporally separated autotandem catalysis, thus allowing the isolation of the allene or the internal alkyne species, as desired. In the course of our mechanistic experiments, we observed the stoichiometric magnesium-mediated isomerization of internal alkynes to terminal alkynes. The mechanisms for both type of transformation are proposed to involve alkynyl-, allenyl-, and propargylmagnesium tautomers as key structures. Although stoichiometric magnesium chemistry has a rich past and much progress has been made in the last decades, only few types of organomagnesium-catalyzed reaction have been reported to date. In this context, our work on the magnesium-catalyzed isomerization of the carbon linkage, a fundamental reaction, is an attractive demonstration of the large potential of magnesium chemistry, which is inexpensive and nontoxic.

Scheme 3. Proposed catalytic cycles for the temporally separated autotandem isomerization of phenylpropynes/phenylallene with catalyst precursor 2 b. R = CH(Ph)CH2Ph, R’ = alkynyl, allenyl, propargyl.

Experimental Section cies is involved in the catalytic cycle based on the similar catalytic activities of complexes 13 and 2 b. In the initial period, phenylallene 4 a could be released from allenylmagnesium B by s-bond metathesis with 3 a to regenerate alkynylmagnesium A. After full consumption of 3 a, propargylmagnesium C acted as a key intermediate to produce 1-phenyl-1-propyne (5 a) through C(sp2)H bond cleavage of 4 a. In the presence of one equivalent of phenylacetylene, the isomerization stopped at the allene stage. The formation of 5 a was suppressed because phenylacetylene was acidic enough to protolytically release 4 a from B before allowing further tautomerization to C and the formation 5 a. In the absence of phenylacetylene, 3 a acted as an acid to release 4 a from B, and therefore generated temporal separation of the two isomerization steps. Furthermore, the reaction of 7 with 4 a (2 equiv) produced 5 a as the alkyne-isomerized product, which was clear proof of the involvement of the C(sp2)H bond cleavage step of 4 a. The exact nature of the rearrangements from alkynyl- to allenyl- and to propargylmagnesium species remains unclear. This question was also left unanswered in a recent report in which an alkyne/allene isomerization at heavier Group 2 metal species occurred as the key step in the hydroxyalkylation of alkynes.[14] However, the base-mediated process was proposed to occur through intramolecular 1,3-hydride shifts.[15] As indicated by the screening results with [MgBn2(TMEDA)] (Table 1), the secondary amine moiety on our ligand seems to be important and supposedly assists the 1,3-hydride shifts in the tautomerization processes. Crossover experiments with deuterium&

&

Chem. Eur. J. 2015, 21, 1 – 10

www.chemeurj.org

General procedures All manipulations involving air- and moisture-sensitive organometallic compounds were performed under argon by using standard Schlenk techniques or glove-box techniques. Toluene, hexane, pentane, THF, and diethyl ether were dried and deoxygenated by distillation over sodium benzophenone ketyl under argon or by using Grubbs columns (Glass Counter Solvent Dispensing System; Nikko Hansen & Co., Ltd., Osaka, Japan) and stored over sodium. Magnesium (turnings), N,N-dimethylethane-1,2-diamine, N,N-diisopropylethane-1,2-diamine, benzaldehyde, and CDCl3 were purchased and used as received. The following complexes and substrates were prepared according to reported procedures, and their analytical data were in accordance with the reported values: [{Mg(CH2Ph)2(OEt2)}2] and [Mg(CH2Ph)2(thf)2],[16] [7b] [17] [Mg(CH2Ph)2(TMEDA)], 3-phenyl-1-butyne, 3-(4-methoxyphenyl)-1-propyne,[17a] 3-(4-dimethylaminophenyl)-1-propyne,[17] 3-(4chlorophenyl)-1-propyne,[18] 3-(4-fluorophenyl)-1-propyne,[18b, 19] 3(2-bromophenyl)-1-propyne,[18b, 20] 3-(4-tolyl)-1-propyne,[18] 3-(1,1’biphen-4-yl)-1-propyne,[18] 3-(2-napthtyl)-1-propyne,[18] 3-(2-tolyl)-1propyne,[18] 3-(3,5-bistrifluoromethylphenyl)-1-propyne.[18] Terminal alkynes were distilled, degassed by three freeze–pump–thaw cycles, dried over molecular sieves (4 ; activated for 18 h at 320 8C under vacuum), and stored under argon. [D6]Benzene, [D5]pyridine, [D8]THF, [D8]toluene, PhCH2Cl, 3-phenyl-1-propyne, 4-phenyl-1butyne, phenylacetylene, and pyridine were distilled over CaH2, degassed, and stored under argon. 1H and 13C NMR (400 and 100 MHz, respectively) spectra were measured on a Bruker Avance III-400 spectrometer. The NMR spectra were referenced to the residual solvent signals at dH = 7.16 and dC = 128.0 ppm for C6D6, dH = 8.74 and dC = 150.4 ppm for [D5]pyridine, dH = 3.58 and dC =

6

 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

ÝÝ These are not the final page numbers!

Full Paper 67.2 ppm for [D8]THF, dH = 2.08 and dC = 20.43 ppm for [D8]toluene, and dH = 7.26 and dC = 77.2 ppm for CHCl3. Yields determined from 1 H NMR spectroscopy used an internal standard, a pulse of 308, 1 scan, an acquisition time of 4 s, and a relaxation delay of 10 s. The IR spectra were recorded on a JASCO FT/IR-4200 spectrometer by using air-tight cells. All the melting points were measured in sealed tubes in an argon atmosphere. Low- and high-resolution mass spectra were recorded by JEOL JMS-700. Elemental analyses were performed on a PerkinElmer 2400 microanalyzer at the Faculty of Engineering Science, Osaka University. CCDC 1026445 (anti2 a), 1026446 (anti-2 b), 1026447 (7), 1026448 (12), 1026449 (13), and 1026450 ([{Mg(CH2Ph)2(Et2O)}2]) 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. See the Supporting Information for further details of the X-ray crystallography.

Preparation of complex 2 b (as a mixture of anti-2 b and syn-2 b): A solution of 1 b (522 mg, 2.96 mmol, 2.0 equiv) in toluene (5 mL) was added to a solution of [{Mg(CH2Ph)2(Et2O)}2] (832 mg, 1.48 mmol, 1.0 equiv) or [Mg(CH2Ph)2(thf)2] (1.038 g, 2.96 mmol, 2.0 equiv) in toluene (10 mL) at 78 8C. The mixture was allowed to warm to room temperature and stirred for 3 h. After all the volatiles were removed under reduced pressure, the resulting residue was washed with hexane (3  5 mL) to give 2 b as a white powder (1.02 g, 90 %). Characterization by NMR spectroscopic analysis showed this compound to be a mononuclear species in 1 M.p. > 210 8C (decomp); H NMR (400 MHz, [D5]pyridine. [D5]pyridine, 30 8C): d = 7.56–7.53 (m, 1 H; Ph), 7.48–7.43 (m, 9 H; Ph), 7.30–7.20 (m, 5 H; Ph), 4.10 (dd, J = 9.5, 4.8 Hz, 1 H; NCH(CH2Ph)Ph), 3.51 (dd, J = 12.8, 9.5 Hz, 1 H; NCH(CH2Ph)Ph), 3.27 (ddd, J = 11.1, 6.1, 4.5 Hz, 1 H; NCH2CH2N), 3.04 (s, 2H MgCH2Ph), 2.98 (m, 1 H; NCH(CH2Ph)Ph), 2.91 (ddd, J = 11.1, 7.0, 4.8 Hz, 1 H; NCH2CH2N), 2.47 (m, 2 H; NCH2CH2N), 1.90 ppm (s, 6 H; Me); 13 C NMR (100 MHz, [D5]pyridine, 30 8C): d = 143.6, 141.3, 130.5, 129.9, 128.0, 127.9, 127.9, 127.5, 125.2, 125.1, 67.1, 62.0, 51.5 (MgCH2Ph), 44.7, 44.5, 39.4 ppm; elemental analysis calcd (%) for C50H60Mg2N4 : C 78.43, H 7.90, N 7.32; found: C 78.24, H 8.18, N 7.31.

Preparation of N1-benzylidene-N2,N2-diisopropylethane-1,2-diamine (1 a): Compound 1 a was prepared following the same procedure as for 1 b, thus giving a colorless oil in 76 % yield. 1H NMR (400 MHz, CDCl3, 30 8C): d = 8.24 (br s, 1 H; N=CH), 7.75–7.68 (m, 2 H; Ph), 7.42–7.36 (m, 3 H; Ph), 3.62 (td, J = 7.2 Hz, J = 1.3 Hz, 2 H; NCH2CH2NiPr2), 3.03 (sept, J = 6.5 Hz, 2 H; CH(CH3)2), 2.75 (t, J = 7.2 Hz, 2 H; NCH2CH2NiPr2), 1.02 ppm (d, J = 6.5 Hz, 12 H; CH(CH3)2); 13 C NMR (100 MHz, CDCl3, 30 8C): d = 161.5, 136.6, 130.5, 128.7, 128.1, 63.6, 49.2, 46.3, 21.0 ppm; MS (EI): m/z: 232.3, 217.2, 189.2, 175.2, 114.2, 72.1, 58.1; HRMS (EI): m/z calcd for C15H24N2 : 232.1939; found: 232.1949.

Preparation of complex anti-2 b: Pyridine (63.0 mL, 7.84  101 mmol, 1.0 equiv) was added to a solution of 2 b (300 mg, 7.84  101 mmol, 1.0 equiv) in toluene (10 mL) at room temperature. The mixture was warmed to 80 8C and stirred for 18 h. After all the volatiles were removed under reduced pressure, the resulting residue was washed with hexane (3  5 mL) to give 2 b-anti as a white powder (87 %). 1H NMR (400 MHz, C6D6, 30 8C): d = 7.26– 7.30 (m, 4 H; Ar), 7.16–7.22 (m, 5 H; Ar), 6.98–7.02 (m, 4 H; Ar), 4.26 (dd, J = 12.5, 3.3 Hz, 1 H; NCHPh(CH2Ph)), 3.61 (dd, J = 15.0, 12.5 Hz, 1 H; NCHPh(CH2Ph)), 2.92 (m, 1 H; NCH2CH2N), 2.68 (dd, J = 15.0, 3.3 Hz, 1 H; NCHPh(CH2Ph)), 2.4–2.6 (m, 2 H; NCH2CH2N), 1.93 (d, J = 9.0 Hz, 1 H; CH2Ph), 1.75 (d, J = 9.0 Hz, 1 H; CH2Ph), 1.66 (s, 3 H; Me), 1.60–1.65 (m, 1 H; NCH2CH2N), 1.00 ppm (s, 3 H; Me); 13C NMR (100 MHz, C6D6, 30 8C): d = 156.2, 142.1, 139.7, 129.8, 128.7, 128.6, 126.9, 125.7, 124.4, 117.6, 62.5, 60.5, 47.0, 41.2, 40.1, 39.9, 24.2 ppm.

Preparation of N1-benzylidene-N2,N2-dimethylethane-1,2-diamine (1 b): Benzaldehyde (4.7 mL, 46 mmol, 1.0 equiv) was added to a suspension of N,N-dimethylethane-1,2-diamine (5.0 mL, 46 mmol, 1.0 equiv) and MgSO4 (ca. 5 g) in diethyl ether (20 mL). The reaction mixture was stirred overnight at room temperature, and the MgSO4 was removed by filtration. All the volatiles were removed under reduce pressure to give 1 b as a colorless oil (8.87 g, 85 %). 1 H NMR (400 MHz, CDCl3, 30 8C): d = 8.30 (s, 1 H; N=CH), 7.76–7.66 (m, 2 H; Ph), 7.38 (m, 3 H; Ph), 3.74 (t, J = 7.0 Hz, 2 H; NCH2CH2N(CH3)2), 2.64 (t, J = 7.0 Hz, 2 H; NCH2CH2N(CH3)2), 2.31 ppm (s, 6 H; NCH2CH2N(CH3)2); 13C NMR (100 MHz, CDCl3, 30 8C): d = 161.7, 136.2, 130.5, 128.5, 128.1, 60.1, 59.9, 45.9 ppm; MS (EI): m/z: 176.2, 132.2, 117.1, 91.1, 58.1; HRMS (EI): m/z calcd. for C11H16N2 : 176.1313; found: 176.1310.

Preparation of dialkynyl complex 7: From 3 a: 3-phenyl-1-propyne (12.4 mL, 1.00  101 mmol, 2.0 equiv) was added to a solution of 2 b (38.3 mg, 5.00  102 mmol, 1.0 equiv) in toluene (0.5 mL). The mixture was heated to 60 8C for 20 min. From 5 a: 1-phenyl-1-propyne (13.8 mL, 1.10  101 mmol, 2.2 equiv) was added to a solution of 2 b (38.3 mg, 5.00  102 mmol, 1.0 equiv) in toluene (0.5 mL). The mixture was heated to 80 8C for 2 h. In both cases, the volatiles were removed in vacuo and the remaining oil was washed several times with pentane to give a white-yellow powder. Owing to tautomerization, the NMR spectra could not be unambiguously assigned, even at low temperature and in pyridine. 2D NMR spectra suggested two sets of overlapping signals. M.p. 58 8C (decomp); 1 H NMR (400 MHz, [D5]pyridine, 30 8C): d = 7.77–7.17 (m, Ar), 4.04 (m, 1.3 H), 3.97 (m, 1.7 H), 3.53 (t, J = 11.9 Hz, 1 H), 3.26 (m, 1 H), 2.99 (m, 3.4 H), 2.86 (m, 1 H), 2.58 (m, 1 H), 2.50 (m, 1.5 H), 2.37 (m, 1 H), 2.26 (m, 1.5 H), 1.97 (s, 7.8 H), 1.85 ppm (br s, 1.4 H); 13C NMR (100 MHz, [D5]pyridine, 30 8C): d = 144.9, 143.9, 141.3, 139.5, 131.6, 130.3, 129.9, 129.5, 128.5, 128.4, 128.3, 128.2, 128.1, 128.0, 127.8, 127.6, 127.4, 127.0, 126.2, 125.8, 125.2, 125.1, 124.8, 66.4, 65.3, 65.2, 61.0, 59.0, 51.6, 45.5, 45.4, 45.1, 44.4, 44.4, 38.3, 28.0 ppm (br s); IR (KBr): n˜ = 3059 (w), 3025 (m), 2878 (m), 2842 (m), 2070 (w), 1944 (w), 1869 (w), 1602 (m), 1494 (s), 1453 (s), 1333 (w), 1282 (w), 1181 (w), 1087 (m), 1029 (m), 981 (s), 943 (s), 787 (w), 731 (m), 699 (s), 608 (w), 551 cm1 (w); a satisfactory elemental analysis could not be obtained owing to the high reactivity of the Mg–alkynyl

Preparation of complex anti-2 a: A solution of 1 a (414 mg, 1.78 mmol, 2.0 equiv) in toluene (5 mL) was added to a solution of [{Mg(CH2Ph)2(Et2O)}2] (500 mg, 8.90  101 mmol, 1.0 equiv) or [Mg(CH2Ph)2(thf)2] (624 mg, 1.78 mmol, 2.0 equiv) in toluene (10 mL) at room temperature. The mixture was stirred at 60 8C for 18 h. After all the volatiles were removed under reduced pressure, the resulting residue was washed with hexane (3  5 mL) to give anti-2 a as a white powder (678 mg, 87 %). M.p. > 130 8C (decomp); 1 H NMR (400 MHz, C6D6, 30 8C): d = 7.43–7.40 (m, 2 H; Ph), 7.38–7.32 (m, 4 H; Ph), 7.11–7.07 (m, 2 H; Ph), 7.01–6.95 (m, 4 H; Ph), 6.96– 6.95 (m, 2 H; Ph), 6.90–6.89 (m, 1 H; Ph), 4.59 (dd, J = 12.5, 3.2 Hz, 1 H; NCH(CH2Ph)Ph), 3.70 (dd, J = 16.5, 12.5 Hz, 1 H; NCH(CH2Ph)Ph), 3.38 (m, 1 H; NCH2CH2N), 2.95 (dd, J = 16.5, 3.2 Hz, 1 H; NCH(CH2Ph)Ph), 2.94 (m, 1 H; NCH2CH2N), 2.63 (m, 2 H; NCH2CH2N), 2.53 (br, 2 H; CHMe2), 2.14 (d, J = 9.4 Hz, MgCH2Ph), 1.94 (d, J = 9.4 Hz, MgCH2Ph), 0.70 ppm (br d, J = 6.7 Hz, 12 H; Me); 13C NMR (100 MHz, C6D6, 30 8C): d = 156.1, 142.5, 139.7, 129.8, 128.64, 128.59, 128.50, 127.0, 125.9, 125.2, 118.1, 62.5, 41.3, 27.9 (MgCH2Ph), 20.2 ppm; a satisfactory elemental analysis could not be obtained owing to the high reactivity of the Mg–alkyl moiety: calcd (%) for C58H76Mg2N4 : C 79.35, H 8.73, N 6.38; found: C 78.36, H 8.96, N 6.57. Chem. Eur. J. 2015, 21, 1 – 10

www.chemeurj.org

These are not the final page numbers! ÞÞ

7

 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

&

&

Full Paper moiety: calcd (%) for C54H60Mg2N4 : C 79.71, H 7.43, N 6.89; found: C 78.71, H 7.54, N 6.94.

quenched with a few drops of water and filtered over a short plug of silica with toluene after precipitation of magnesium salts. The crude product was concentrated and purified by chromatography with hexane as the eluent.

Preparation of dialkynyl complex 12: Phenylacetylene (11.0 mL, 1.00  101 mmol, 2.0 equiv) ) was added to a solution of 2 b (38.3 mg, 5.00  102 mmol, 1.0 equiv) in C6D6 (0.5 mL). The mixture was heated to 60 8C for 20 min before it was filtered and the volatiles removed under reduced pressure. The solid was washed with pentane (3  2 mL) to afford dialkyl complex 12 (24.0 mg, 61 %). M.p. 180 8C (decomp); 1H NMR (400 MHz, C6D6, 30 8C): d = 7.89–7.76 (m, 4 H; Ph), 7.35–6.95 (m, 11 H; Ph), 4.48 (m, 1 H; NCHPh(CH2Ph)), 3.57 (m, 1 H; NCHPh(CH2Ph)), 3.31 (m, 1 H; NCHPh(CH2Ph)), 2.68 (m, 1 H; NCH2CH2N), 2.54 (m, 1 H; NCH2CH2N), 1.92 (m, 2 H; NCH2CH2N), 1.72 (s, 3 H; NMe2), 1.55 pm (s, 3 H; NMe2); 13C NMR (100 MHz, C6D6, 30 8C): d = 142.6, 139.6, 131.8, 129.7, 129.0, 128.2, 128.1, 127.7, 127.5, 126.8, 125.8, 125.7, 120.9 (Mg-CCPh), 110.9 (Mg-CCPh), 64.3 (CH), 59.6 (CH2), 46.1 (CH3), 43.4 (CH3), 42.5 (CH2), 41.9 ppm (CH2); IR (KBr): n˜ = 3059 (m), 3025 (m), 2961 (m), 2890 (m), 2846 (m), 2059 (w), 1945 (w), 1869 (w), 1793 (w), 1594 (m), 1495 (m), 1484 (s), 1454 (s), 1357 (w), 1281 (w), 1262 (w), 1199 (m), 1084 (m), 1069 (m), 1023 (m), 938 (w), 852 (w), 779 (m), 758 (s), 695 (s), 597 (w), 547 cm1 (m); a satisfactory elemental analysis could not be obtained owing to the high reactivity of the Mg–alkynyl moiety: calcd (%) for C52H56Mg2N4 : C 79.50, H 7.18, N 7.13; found: C 78.22, H 7.03, N 7.01.

Acknowledgements K.Y. and H.N. express their special thanks for the financial support provided by the JSPS Research Fellowships for Young Scientists. H.T. acknowledges financial support by a Grant-in-Aid for Young Scientists (A) from the Ministry of Education, Culture, Sports, Science, and Technology, Japan. This work was supported by the Core Research for Evolutional Science and Technology (CREST) Program of the Japan Science and Technology Agency. Keywords: alkynes · allenes · CH activation · homogeneous catalysis · magnesium [1] a) V. Grignard, Comptes rendus hebd. sances acad. sci. Paris 1900, 130, 1322 – 1325; b) F. Bickelhaupt, J. Organomet. Chem. 1994, 475, 1 – 14; c) Z. Rappoport, I. Marek, The Chemistry of Organomagnesium Compounds, John Wiley & Sons, Ltd, 2008. [2] A. Frischmuth, A. Unsinn, K. Groll, H. Stadtmller, P. Knochel, Chem. Eur. J. 2012, 18, 10234 – 10238. [3] a) M. Arrowsmith, M. R. Crimmin, A. G. M. Barrett, M. S. Hill, G. KociokKçhn, P. A. Procopiou, Organometallics 2011, 30, 1493 – 1506; b) M. Arrowsmith, M. S. Hill, G. Kociok-Kçhn, Organometallics 2014, 33, 206 – 216; c) A. G. M. Barrett, C. Brinkmann, M. R. Crimmin, M. S. Hill, P. Hunt, P. A. Procopiou, J. Am. Chem. Soc. 2009, 131, 12906 – 12907; d) A. G. M. Barrett, I. J. Casely, M. R. Crimmin, M. S. Hill, J. R. Lachs, M. F. Mahon, P. A. Procopiou, Inorg. Chem. 2009, 48, 4445 – 4453; e) M. R. Crimmin, M. Arrowsmith, A. G. M. Barrett, I. J. Casely, M. S. Hill, P. A. Procopiou, J. Am. Chem. Soc. 2009, 131, 9670 – 9685; f) J. F. Dunne, D. B. Fulton, A. Ellern, A. D. Sadow, J. Am. Chem. Soc. 2010, 132, 17680 – 17683; g) S. R. Neal, A. Ellern, A. D. Sadow, J. Organomet. Chem. 2011, 696, 228 – 234; h) S. Tobisch, Chem. Eur. J. 2011, 17, 14974 – 14986; i) X. Zhang, T. J. Emge, K. C. Hultzsch, Organometallics 2010, 29, 5871 – 5877; j) X. Zhang, T. J. Emge, K. C. Hultzsch, Angew. Chem. Int. Ed. 2012, 51, 394 – 398; Angew. Chem. 2012, 124, 406 – 410; k) P. Horrillo-Martnez, K. C. Hultzsch, Tetrahedron Lett. 2009, 50, 2054 – 2056; l) D. Elorriaga, F. Carrillo-Hermosilla, A. AntiÇolo, I. Lpez-Solera, R. Fern ndez-Gal n, A. Serrano, E. VillaseÇor, Eur. J. Inorg. Chem. 2013, 2940 – 2946. [4] a) M. Arrowsmith, T. J. Hadlington, M. S. Hill, G. Kociok-Kohn, Chem. Commun. 2012, 48, 4567 – 4569; b) M. Arrowsmith, M. S. Hill, T. Hadlington, G. Kociok-Kçhn, C. Weetman, Organometallics 2011, 30, 5556 – 5559; c) M. Arrowsmith, M. S. Hill, G. Kociok-Kçhn, Chem. Eur. J. 2013, 19, 2776 – 2783. [5] a) J. F. Dunne, S. R. Neal, J. Engelkemier, A. Ellern, A. D. Sadow, J. Am. Chem. Soc. 2011, 133, 16782 – 16785; b) D. J. Liptrot, M. S. Hill, M. F. Mahon, D. J. MacDougall, Chem. Eur. J. 2010, 16, 8508 – 8515; c) J. Spielmann, M. Bolte, S. Harder, Chem. Commun. 2009, 6934 – 6936; d) D. J. Liptrot, M. S. Hill, M. F. Mahon, Angew. Chem. Int. Ed. 2014, 53, 6224 – 6227. [6] N. Krause, A. S. K. Hashmi, Modern Allene Chemistry, Wiley-VCH Verlag GmbH; 2008. [7] a) L. F. S nchez-Barba, A. s. Garc s, J. Fern ndez-Baeza, A. Otero, C. Alonso-Moreno, A. n. Lara-S nchez, A. M. Rodrguez, Organometallics 2011, 30, 2775 – 2789; b) P. J. Bailey, R. A. Coxall, C. M. Dick, S. Fabre, L. C. Henderson, C. Herber, S. T. Liddle, D. LoroÇo-Gonz lez, A. Parkin, S. Parsons, Chem. Eur. J. 2003, 9, 4820 – 4828. [8] a) T. K. Panda, K. Yamamoto, K. Yamamoto, H. Kaneko, Y. Yang, H. Tsurugi, K. Mashima, Organometallics 2012, 31, 2268 – 2274; b) T. K. Panda, H. Kaneko, O. Michel, K. Pal, H. Tsurugi, K. W. Tçrnroos, R. Anwander, K. Mashima, Organometallics 2012, 31, 3178 – 3184; c) O. Michel, H. Kaneko, H. Tsurugi, K. Yamamoto, K. W. Tçrnroos, R. Anwander, K. Mashima, Eur.

Preparation of tetraalkynyl complex 13: Phenylacetylene (0.275 mL, 2.50 mmol, 25 equiv) was added to a solution of 2 b (76.6 mg, 1.00  101 mmol, 1.0 equiv) in toluene (3 mL) at room temperature. The mixture was stirred at 60 8C for 20 min. After all the volatiles were removed under reduced pressure, the resulting residue was washed with hexane (5  2 mL), redissolved in benzene, filtered, and dried to give 13 as a white powder (90 mg, 91 %). M.p. 140 8C (decomp); 1H NMR (400 MHz, C6D6, 30 8C): d = 7.99 (d, 4 H; MgCCPh), 7.38 (d, 2 H; NHCHPhCH2Ph), 7.18 (t, 4 H; MgCCPh), 6.95–7.16 (m, 10 H; CHArom), 4.55 (m, 1 H; NHCHPh(CH2Ph)), 4.40 (m, 1 H; NHCHPh(CH2Ph)), 3.17 (m, 1 H; NHCHPh(CH2Ph)), 2.50 (brs, 1 H; NHCHPh(CH2Ph)), 2.27 (s, 6 H; NMe2), 2.12 (m, 1 H; NCH2CH2N), 2.01–2.02 (m, 2 H; NCH2CH2N), 1.64 ppm (m, 1 H; NCH2CH2N); 13C NMR (100 MHz, C6D6, 30 8C): d = 141.3, 139.1, 132.4, 130.3, 128.7, 128.5, 128.3, 128.2, 128.0, 127.6, 126.4, 125.8, 114.6, 65.6, 59.1, 46.2, 44.0, 43.2 ppm; 1H NMR (400 MHz, [D5]pyridine, 30 8C): d = 7.83 (d, J = 7.8 Hz, 4 H; Ph), 7.45 (d, J = 7.8 Hz, 2 H; Ph), 7.33 (t, J = 7.8 Hz, 6 H; Ph), 7.26–7.17 (m, 8 H; Ph), 3.96 (m, 1 H; NHCHPh(CH2Ph)), 2.98 (m, 2 H; NHCHPh(CH2Ph)), 2.50 (m, 2 H; NCH2CH2N), 2.25 (m, 2 H; NCH2CH2N), 2.15 (br s, 1 H; NHCHPh(CH2Ph)), 1.96 ppm (s, 6 H; NMe2); 13C NMR (100 MHz, [D5]pyridine, 30 8C): d = 145.0, 140.7, 139.5, 131.4, 130.4, 129.5, 128.4, 128.3, 127.6, 127.0, 126.2, 124.7, 112.8, 65.3, 59.1, 45.5, 45.4, 45.0 ppm; IR (KBr): n˜ = 3276 (w, NH), 3059 (m), 3025 (m), 2921 (m), 2843 (m), 2063 (w), 1951 (w), 1888 (w), 1810 (w), 1749 (w), 1595 (m), 1484 (s), 1454 (s), 1283 (w), 1246 (w), 1199 (m), 1097 (m), 1069 (m), 1027 (m), 958 (m), 914 (m), 855 (m), 778 (s), 758 (s), 696 (s), 540 (m), 511 cm1 (m); a satisfactory elemental analysis could not be obtained owing to the high reactivity of the Mg–alkynyl moiety: calcd (%) for C68H68Mg2N4 : C 82.51, H 6.92, N 5.66; found: C 79.62, H 6.96, N 5.84. General procedure for the catalytic isomerization: Terminal alkyne 3 (0.50 mmol, 1.0 equiv) was added to a solution of 2 b (15.3 mg, 0.02 mmol, 4 mol %) and phenanthrene as an internal standard (ca. 10 mg) in [D8]toluene (0.4 mL) in a J-Young NMR tube. The reaction mixture was maintained at 80 8C for the specified time and monitored by 1H NMR spectroscopic analysis. For the isolation of the product, the reaction was carried out on a 4.6 mmol scale without phenanthrene. The reaction mixture was

&

&

Chem. Eur. J. 2015, 21, 1 – 10

www.chemeurj.org

8

 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

ÝÝ These are not the final page numbers!

Full Paper

[9] [10] [11]

[12] [13]

J. Inorg. Chem. 2012, 998 – 1003; d) O. Michel, K. Yamamoto, H. Tsurugi, C. Maichle-Mçssmer, K. W. Tçrnroos, K. Mashima, R. Anwander, Organometallics 2011, 30, 3818 – 3825; e) M. Westerhausen, T. Bollwein, N. Makropoulos, S. Schneiderbauer, M. Suter, H. Nçth, P. Mayer, H. Piotrowski, K. Polborn, A. Pfitzner, Eur. J. Inorg. Chem. 2002, 389 – 404; f) K. W. Henderson, R. E. Mulvey, W. Clegg, P. A. O’Neil, J. Organomet. Chem. 1992, 439, 237 – 250; g) V. R. Magnuson, G. D. Stucky, Inorg. Chem. 1969, 8, 1427 – 1433. a) L. Li, S. B. Herzon, Nat. Chem. 2013, 6, 22 – 27; b) D. E. Fogg, E. N. dos Santos, Coord. Chem. Rev. 2004, 248, 2365 – 2379. E. Bustelo, C. Gu rot, A. Hercouet, B. Carboni, L. Toupet, P. H. Dixneuf, J. Am. Chem. Soc. 2005, 127, 11582 – 11583. a) D. S. N. Parker, F. Zhang, R. I. Kaiser, V. V. Kislov, A. M. Mebel, Chem. Asian J. 2011, 6, 3035 – 3047; b) V. B. Kobychev, N. M. Vitkovskaya, N. S. Klyba, B. A. Trofimov, Russ. Chem. Bull. 2002, 51, 774 – 782. V. P. Colquhoun, B. C. Abele, C. Strohmann, Organometallics 2011, 30, 5408 – 5414. a) M. Arrowsmith, M. R. Crimmin, M. S. Hill, S. L. Lomas, D. J. MacDougall, M. F. Mahon, Organometallics 2013, 32, 4961 – 4972; b) A. G. M. Barrett, M. R. Crimmin, M. S. Hill, P. B. Hitchcock, S. L. Lomas, P. A. Procopiou, K. Suntharalingam, Chem. Commun. 2009, 2299 – 2301.

Chem. Eur. J. 2015, 21, 1 – 10

www.chemeurj.org

These are not the final page numbers! ÞÞ

[14] C. Brinkmann, A. G. M. Barrett, M. S. Hill, P. A. Procopiou, S. Reid, Organometallics 2012, 31, 7287 – 7297. [15] A. Maercker, J. Fischenich, Tetrahedron 1995, 51, 10209 – 10218. [16] R. R. Schrock, J. Organomet. Chem. 1976, 122, 209 – 225. [17] a) G. Henrion, T. E. J. Chavas, X. Le Goff, F. Gagosz, Angew. Chem. Int. Ed. 2013, 52, 6277 – 6282; Angew. Chem. 2013, 125, 6397 – 6402; b) L. Van Hijfte, M. Kolb, P. Witz, Tetrahedron Lett. 1989, 30, 3655 – 3656. [18] a) J. Louvel, J. F. S. Carvalho, Z. Yu, M. Soethoudt, E. B. Lenselink, E. Klaasse, J. Brussee, A. P. Ijzerman, J. Med. Chem. 2013, 56, 9427 – 9440; b) A. Carpita, L. Mannocci, R. Rossi, Eur. J. Org. Chem. 2005, 1859 – 1864. [19] R. W. J. Kosley, R. Sher, K. W. Neuenschwander, V. Gurunian, Substituted Phenoxylmethyl Dihydro Oxazolopyrimidinones, Preparation and Use Thereof. Patent WO 2011/034832 A1., Patent No. WO 2011/034832 A1, 2011. [20] K.-S. Masters, M. Wallesch, S. Br se, J. Org. Chem. 2011, 76, 9060 – 9067.

Received: January 15, 2015 Published online on && &&, 0000

9

 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

&

&

Full Paper

FULL PAPER & Magnesium Catalysis

Selective and important: Magnesium complexes bearing aminoamido ligands are precursors for the isomerization of terminal alkynes to allenes and further to internal alkynes through temporally separated autotandem catalysis (see picture). The catalytically active tetraalkynyl complexes consist of a tautomeric mixture of alkynyl-, allenyl-, and propargylmagnesium species.

R. Rochat, K. Yamamoto, M. J. Lopez, H. Nagae, H. Tsurugi,* K. Mashima* && – && Organomagnesium-Catalyzed Isomerization of Terminal Alkynes to Allenes and Internal Alkynes

In a first step, organomagnesium… …catalysts completely transform terminal alkynes into allenes before these are further converted to the final products, internal alkynes, in a second step, allowing for isolation of the intermediate allenes. This is illustrated by three water tanks, symbolizing the substrate, the intermediate product, and the final product, which are connected by tubes that are regulated by linked magnesium stopcocks, allowing only one transformation at a time. For more details, see the Full Paper by H. Tsurugi, K. Mashima, and co-workers on page && ff.

&

&

Chem. Eur. J. 2015, 21, 1 – 10

www.chemeurj.org

10

 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

ÝÝ These are not the final page numbers!

Organomagnesium-catalyzed isomerization of terminal alkynes to allenes and internal alkynes.

Organomagnesium complexes 2 were synthesized from N,N-dialkylamineimine ligands 1 and dibenzylmagnesium by benzylation of the imine moiety. 3-Aryl-1-p...
670KB Sizes 0 Downloads 6 Views