Phosphinimine-substituted boranes and borenium ions.

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Phosphinimine-substituted boranes and borenium ions† Michael H. Holthausen, Ian Mallov and Douglas W. Stephan* The phosphinimines R3PNSiMe3 (R = t-Bu: 1a, R = Cy: 1b, R = Et: 1c, R = Ph: 1d) are reacted with a series of chloro and fluoroboranes (9Cl-9-BBN, (C6F5)2BCl, PhBCl2 and Mes2BF) to access a family of phosphinimine-substituted boranes (2a–d, 3b–d, 4c,d and 6a,b) via Me3SiX elimination (X = Cl, F). The steric

Received 7th August 2014, Accepted 25th August 2014 DOI: 10.1039/c4dt02406k www.rsc.org/dalton

and electronic factors governing the formation of monomeric or dimeric products (7c,d) are presented. In addition, in some cases a Lewis acid mediated exchange of Si-bonded methyl groups for a chloro-substituent was observed (5a,b). Based on the phosphinimine-substituted boranes, a series of borenium ion salts (8b–d, 9c, 10b–d) was prepared upon reaction with MeOTf. All compounds were fully characterized and a number of molecular structures were determined by X-ray diffraction.

Introduction The recent advent of frustrated Lewis pair (FLP) chemistry has drawn significant attention in the chemical community.1 This is based on the ability of non-bonding or weakly-binding combinations of Lewis acids and bases to activate and transform a plethora of small molecules.1 Group XIII-centered compounds are most often used as Lewis acids, with the highly electrophilic B(C6F5)3 being a landmark reagent in FLP chemistry.2 Many FLP-mediated transformations are highly influenced by the steric and electronic features of the employed Lewis acids.3 This has created a surge in interest in the development of facile synthetic protocols for the generation of boranes of distinct steric demand and tuneable Lewis acidity. Phosphinimine-based ligands are valued in transition metal chemistry for their structural diversity,4 and the resulting complexes are used, e.g., as highly effective catalysts for olefin polymerization.5 However, related boron-based compounds featuring phosphinimine substituents have been scarcely investigated.6 Dehnicke and co-workers initially focused on mixtures of BX3 (X = F, Cl, Br) and silylated phosphinimines of type R3PNSiMe3 (R = alkyl, aryl) in various stoichiometries. They reported the formation of four-membered heterocycles of type (R3PNBX2)2 and derivatives thereof.7 In a related fashion, the three-fold phosphinimine-substituted species (Ph3PN)3B was obtained upon reaction of BCl3 and three equivalents Ph3PNLi.8 We utilized the sterically demanding t-Bu3PNLi in

reactions with BCl3 allowing for the preparation of borane t-Bu3PNBCl2.9 Attempts to install a second phosphiniminesubstituent resulted in spontaneous halide elimination and formation of the unique, linear borinium ion salt [(t-Bu3PN)2B][Cl].10 Reacting phosphinimine n-Bu3PNSiMe3 with PhBCl2 results in the formation of n-Bu3PNBClPh via Me3SiCl elimination.9 In addition, we have investigated steric effects that influence reactions between phosphinimines and catechol or pinachol boranes.11 In these cases either monomeric boranes such as R3PNB(O2C2Me4) or dimeric heterocycles of type (R3PNB(O2C6H4)2 are observed. A new approach to phosphinimine-substituted boranes was recently developed in our group based on Staudinger oxidation of phosphines R3P with boron azides R2BN3.12 This is complemented by a report from Bertrand and co-workers who used azidophosphines R2PN3 and Mes2BF to prepare phosphinimine-substituted boranes R2FPNBMes2.13 Herein, we report the preparation and characterization of a series of boranes featuring phosphinimine substituents. This was achieved by reacting silylated phosphinimines of type R3PNSiMe3 with chloro- or fluoroboranes (9-Cl-9-BBN, (C6F5)2BCl, PhBCl2 and Mes2BF). The steric and electronic factors governing the reaction outcome are discussed. Finally, the methylation of the imine-N atom using MeOTf was probed, giving access to a series of phosphinimine-substituted borenium ion salts.

Results and discussion Department of Chemistry, 80 St George St University of Toronto, Toronto, Ontario, M5S3H6 Canada. E-mail: [email protected] † CCDC 1018460–1018471. For crystallographic data in CIF or other electronic format see DOI: 10.1039/c4dt02406k

This journal is © The Royal Society of Chemistry 2014

Initially, we explored the reactions of 9-Cl-9-BBN (9-chloro-9borabicyclo[3.3.1]nonane) with a series of trimethylsilyl-phosphinimines of type 1 featuring substituents R of distinct steric

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Fig. 1 Pov-ray depiction of 2d. C: grey, N: blue, P: orange, B: pink. Hydrogen atoms have been omitted for clarity. Scheme 1 Preparation of phosphinimine-substituted boranes 2a–d and 3b–d (9-Cl-9-BBN = 9-chloro-9-borabicyclo[3.3.1]nonane).

demand (Scheme 1). The reaction progress is easily monitored by the evolution of Me3SiCl in 1H NMR spectra of the reaction mixtures (δ(1H) = 0.19 ppm, d8-toluene). It was found that the reactions involving less sterically demanding 1c,d proceed readily within six hours at ambient temperature. Mixtures containing the more sterically demanding phosphinimines 1a,b were heated to 90 °C for 24 h to achieve complete conversion. The increased steric demand is assumed to impede the adduct formation between 1 and the boron Lewis acid that precedes the Me3SiCl elimination. The respective phosphinimine-substituted boranes 2a–d are isolated in good to excellent yields (69–97%). It is interesting to note that 2a,b,d are solids whereas 2c is a colorless oil with a melting point higher than −35 °C. The 31 P NMR spectra of the compounds dissolved in d8-toluene show resonances at 33.3 (2a), 22.8 (2b), 34.8 (2c), and 6.5 ppm (2d) which are shifted to lower field compared to the resonances of the respective starting materials (32.3 (1a), 17.1 (1b), 15.0 (1c), and −1.8 ppm (1d)).5c The 11B NMR resonances of 2a–d range from 51.8 ppm to 56.1 ppm and appear at lower field compared to B-amino-9BBN derivatives (av. 45 ppm).14 The formulation of boranes of type 2 was further confirmed by the molecular structure of 2d (Fig. 1). In a similar fashion heating mixtures of 1b–d and Mes2BF to 90 °C for two days gave complete conversion to the respective boranes 3b–d which were isolated in good yields (81–94%). It is interesting to note that heating a mixture of Mes2BF and 1a to 90 °C for seven days does not lead to complete conversion to 3a. This is presumably a consequence of the steric demand of the starting materials which hampers the formation of the Lewis acid/base adduct and subsequently, the elimination of Me3SiF. The formation of the latter is indicated in 19F NMR spectra of the reaction mixture (δ(19F) = −156.9 ppm, toluene). The 31P{1H} NMR resonance of 3b (18.8 ppm) is similar to that of 1b whereas that of 3d (4.8 ppm) and 3c (31.5 ppm) is shifted to lower field. The 11B NMR resonances of 3b–d range from 44.4 ppm to

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48.0 ppm and appear in the typical chemical shift range of aminodimesitylboranes.15 In the case of 3c and 3d, X-ray single crystal structure determination was performed and confirmed their formulation (Fig. 2). Important bond lengths and angles of obtained phosphinimine-substituted boranes are summarized in Table 1. The P–N bond lengths of 2d and 3c,d show very little deviation and are comparable to that in related boranes R3PNBCy2 (R = Cy, t-Bu, Ph)12 and other R3PNR′ species.9,16 The N–B bond lengths range between typical N–B single (1.51 Å) and

Fig. 2 Pov-ray depiction of 3c (top) and 3d (bottom). C: grey, N: blue, P: orange, B: pink. Hydrogen atoms have been omitted for clarity.


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Table 1

Paper

Bond length and angles of phosphinimine substituted boranes

2d

3c

3d

6ac

P–Na N–B av. P–C av. B–C(Cl)

1.572(1) 1.409(2) 1.816(1) 1.596(2)

1.571(2) 1.396(4) 1.807(3) 1.605(4)

1.574(1) 1.402(2) 1.813(1) 1.607(2)

P–N–Bb

130.9(1)

140.5(1)

137.3(1)

1.571(4) 1.36(1) 1.884(5) 1.57(1) (1.86(1)) 158.6(4)

a

P–N N–B

av. P–C av. B–C(Cl) P–N–Bb B–N–B N–B–N

7c

7d

1.594(1) 1.539(2) 1.544(2) 1.801(6) 1.613(2) 1.974(1) 133.9(1) 134.9(1) 90.4(1) 89.6(1)

1.597(3) 1.552(4) 1.561(4) 1.80(1) 1.968(3) 1.606(5) 132.6(2) 136.1(2) 89.8(2) 90.4(2)

a

Bond length are reported in Å. b Angles are reported in °. c Average bond length and angles for all formula units in the asymmetric unit are reported.

NvB double bond lengths (1.31 Å) indicating partial delocalization of the lone pair of electrons on nitrogen to the boron atom.5c,9,16 The P–N–B angle in phosphinimine-substituted boranes increases with the steric demand of the substituents (compare 2d: 103.9(1)° and 3d: 137.3(1)°). In a manner similar to 9-Cl-9-BBN, the reaction of phosphinimines 1c and 1d with (C6F5)2BCl provides the respective boranes in good yields (4c: 83% and 4d: 92%; Scheme 2). The 31 1 P{ H} and 11B NMR resonances of both compounds show trends comparable to boranes 2 and 3. Compounds 4a and 4d were previously prepared via Staudinger oxidations of the respective phosphines with (C6F5)2BN3.12 However, this protocol was limited to sterically demanding or weakly Lewis basic phosphines which do not form an adduct with the respective azidoborane. For sterically more demanding 1a,b one methylgroup of the SiMe3-moiety is exchanged for a chloro-group

Scheme 2 Reaction of phosphinimines 1a–d with (C6F5)2BCl giving boranes 4c,d or chloro-functionalized phosphinimines 5a,b.


yielding phosphinimines 5a,b and (C6F5)2BMe. The formation of the latter is indicated in the 11B NMR spectra of the reaction mixture by a low field resonance at 71.2 ppm (toluene).17 The formation of 5a,b is assumed to proceed via methylgroup abstraction giving formally an intermediate of type [R3PNSiMe2][MeBCl(C6F5)2] in which the cation is stabilized by charge delocalization to the P atom. Subsequent chloridetransfer yields the observed products. A related chloro/methylgroup exchange reaction assisted by GaCl3 was recently reported for silylated amino-phosphines and arsines.18 Compounds 5a,b were isolated in 48 and 51% yield, respectively. The molecular structures of 5a as well as starting phosphinimines 1b and 1d19 are depicted in Fig. 3. Compared to the latter two, 5a shows a shorter N–Si bond length (5a 1.628(2) Å, 1b 1.666(1) Å, 1d 1.692(2) Å). This is indicative of hyperconjugation between the lone pair of electrons on the N atom of 5a with the σ*(Si–Cl) orbital. We were also interested in chloro- and phosphinimine-substituted boranes, which could be suitable for further functionalization. Therefore, the reactions of 1a–d with PhBCl2 in 1 : 1 stoichiometry were investigated (Scheme 3).

Fig. 3 Pov-ray depiction of 5a (left), 1b (middle) and 1d (right). C: grey, N: blue, P: orange, Si: yellow, Cl: green. Hydrogen atoms have been omitted for clarity. Selected bond distances [Å] and angles [°]: 5a: P–N 1.550(2), N–Si 1.628(2), Si–Cl 2.116(1), Si–N–P 175.8(1); 1b: P–N 1.546(1), N–Si 1.666(1), Si–N–P 148.0(1); 1d: P–N 1.547(2), N–Si 1.692(2), Si–N–P 138.3(1).

Scheme 3 Reaction of phosphinimines 1a–d with PhBCl2 giving boranes 6a,b or four-membered BN-heterocycles 7c,d.

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Fig. 4 Pov-ray depiction of 6a. C: grey, N: blue, P: orange, B: pink, Cl: green. Hydrogen atoms have been omitted for clarity.

For sterically demanding phosphinimines 1a,b the formation of monomeric boranes 6a,b occurs. The 31P and 11B NMR spectra of the reaction mixture involving 1a show the presence of some amounts of 5a and PhMeBCl (δ(11B) = 68.3 ppm, toluene)20 formed according to the previously presented chloro/methyl-group exchange reaction. However, 6a and 6b were isolated in good yields (83 and 90%) and fully characterized. X-ray single crystal structure determination confirmed a monomeric structure for 6a also in the solid state (Fig. 4). Compound 6a crystallizes with four formula units in the asymmetric unit. Average bond length and angles are reported in Table 1 and bond distances similar to boranes of type 2 and 3 are observed. However, 6a shows a significantly larger P–N–B angle of av. 158.6(4)° compared to 2d, 3c and 3d which might be due to the sterically more demanding t-Bu groups. It is noteworthy that this angle varies widely for each individual molecule of 6a (ranging from 153.4(4) to 168.2(4)°) indicating a shallow energy profile for distortion. The addition of PhBCl2 to toluene solutions of the sterically less demanding phosphinimines 1c,d gave colorless precipitates of 7c,d which were isolated in 63 and 68% yield, respectively (Scheme 3). The 11B NMR spectra of both compounds reveal resonances shifted to higher field (7c: 19.5 ppm and 7d: 23.2 ppm) compared to 6a,b (6a: 33.4 ppm and 6b: 33.9 ppm). The 31P{1H} NMR resonances of 7c,d are shifted to lower field (7c: 53.4 ppm and 7d: 29.3 ppm) compared to ethyl- and phenyl-substituted derivatives of 2, 3 and 4 (av. c: 29.5 ppm, av. d: 8.8 ppm) and are located in the typical chemical shift range of respective amino-phosphonium species.21 Collectively, these data indicate the presence of four-membered (NB)2-heterocycles featuring tetracoordinated borate moieties and phosphoniumyl-substituents at the nitrogen atoms. This is further supported by 13 C NMR data. For 7c a resonance at 16.2 ppm is assigned to the P bonded CH2 moieties and shows a doublet of doublet splitting (1JCP = 65.4 Hz, 5JCP = 3.7 Hz) as a result of a local AA′X3X′3 spin system (A = 31P, X = 13C). The resonance assigned to the CH3 moieties appears as a pseudo-triplet (|2JCP + 6JCP| = 2.3 Hz) indicating that the respective 4J (PAPA′) coupling is comparatively large.22 It is interesting to note, that the previously reported compound n-Bu3PNBClPh shows an 11B NMR chemical shift (11.0 ppm, C6D6)9 comparable to 7c indicating also a dimeric nature of the former.

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Fig. 5 Pov-ray depiction of 7c (top) and 7d (bottom). C: grey, N: blue, P: orange, B: pink, Cl: green. Hydrogen atoms have been omitted for clarity.

X-ray single crystal structure determination confirmed the formulation of 7c,d as four-membered heterocycles (Fig. 5). The chloro-substituents of both compounds are arranged in a trans-fashion. The N atoms reveal a trigonal planar arrangement (angular sums: 7c 359.2(3)°, 7d 358.1(6)°) indicating sp2hybridization. The P–N and B–N bond distances of four-membered heterocycles of type 7 (av. P–N 1.596(4) Å, av. B–N 1.55(1) Å)7b,c are significantly longer compared to those of monomeric boranes of type 2, 3, 4 or 6 (av. P–N 1.57(1) Å, av. B–N 1.39(1) Å). This is in accordance with an increased phosphonium character of the P moieties and less effective donation of electron density from the lone pair of electrons at nitrogen to the boron atom. DART or ESI mass spectroscopy of compounds 2 to 7 showed peaks corresponding to [R3P–NH3]+ and [R3PvNH2]+ usually as the base peaks. Only for 2b, 4c and 5a,b additional peaks for the molecular ion [M–H]+ were observed. A few phosphinimine borane adducts of type R3PNR′–BR3 are known9,16 with some combinations showing FLP-type chemistry.23 However, to the best of our knowledge, related borenium ions of type [R3PNR′–BR2]+ have not been reported in the literature. It was envisioned that the incorporation of a positive charge might enhance the electrophilicity giving access to potentially versatile Lewis acids.24 Such borenium ion salts might be accessible by alkylation of the imine-N atom of phosphinimine-substituted boranes. Initially, the reaction of boranes of type 2 with MeOTf was investigated (Scheme 4). For 2b–d, complete conversion to the respective borenium ion


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Paper Table 2 31P{1H} and 11B NMR parameters of phosphinimine-substituted boranes and borenium ions


P{1H}

2a 2b 2c 2d

31

11

33.3 22.8 34.8 6.5

51.8 53.1 53.4 56.1

31

11

32.3 17.1 15.0 −1.8

— — — —

31

11

41.6 29.9 53.3 29.3

33.4 33.9 19.5 23.2

P{1H}

1a 1b 1c 1d

P{1H}

Scheme 4 Preparation of phosphinimine substituted borenium ion salts 8b–d, 9c and 10b–d (top) and illustration of their potential bonding by resonance structures A and B as well as a dative bonding model C.

6a 6b 7c 7d

P{1H}

9c

salts 8b–d was observed within two hours at ambient temperature. It is interesting to note that methylation of the imine-N atom in 2a does not take place, even after extending the reaction time to several days. This might be a result of the steric demand of the t-Bu-groups on the adjacent P atom. Compounds 8b–d were isolated in excellent yields (95–97%) and fully characterized. Similarly, the reaction of MeOTf with boranes of type 3 yielded the borenium ion salts 10b–d (78–88% yield). The reaction is finished within minutes for the less sterically-demanding 3c while full conversion to 10b and 10d required 48 hours reaction time. It is interesting that boranes of type 6 do not react with MeOTf whereas in the case of C6F5-substituted boranes only conversion of derivative 4c to the respective borenium ion salt 9c was achieved. DART or ESI mass spectroscopy on borenium ion salts 8b–d, 9c and 10b–d revealed only peaks corresponding to [R3P– NMeH2]+ and [R3PvNMeH]+. This indicates a limited stability of the respective B–N bonds. It was speculated that reaction with H2 might proceed via a related B–N bond cleavage yielding R3PNH/[R3PNMeH]+ and R2BH fragments. However, attempts to activate H2 with selected examples of phosphinimine-substituted boranes or borenium ions with or without an external Lewis base proved unsuccessful. The 1H NMR spectra of borenium ion salts 8 to 10 show characteristic doublet resonances for the NMe-groups at approximately 3.1 ppm with a 3JHP coupling constant ranging from 8.7 to 13.1 Hz. It is noteworthy that upon methylation racemic mixtures of 8–10 are formed. Consequently, the 1H and 13C NMR spectra of 10 show two sets of resonances corresponding to two pro-chiral Mes-groups on boron. The 31P{1H} NMR resonances of borenium ion salts are shifted to lower field compared to the respective boranes and show a dependency on the substituents on boron (Table 2). Resonances


P{1H}

B 3a 3b 3c 3d

31

11

— 18.8 22.1 4.8

— 44.4 46.0 48.0

31

11

37.9 23.1 31.5 15.2

— — 33.8 36.2

31

11

43.9 73.3 66.2

62.9 61.7 64.3

31

11

72.7 74.8 47.7

57.5 56.7 58.8

P{1H}

B 5a 5b 4c 4d

P{1H}

B

31

11

80.9

39.0

8b 8c 8d

P{1H}

B 10b 10c 10d

B

B

B

B

corresponding to borenium ion salts of type 8 show a low field shift of av. Δδ(31P) = 39.8 ppm compared to their borane congeners 2b–d. Borenium ion derivatives featuring Mes- (10) and C6F5-substituents (9) show more pronounced low field shifts of av. Δδ(31P) = 53.3 ppm and 49.4 ppm respectively. Interestingly, low field shifts are observed for the 11B NMR resonances of borenium ion salts 8–10 as well, however, those are of smaller magnitude (Table 2, 8: av. Δδ(11B) = 8.8 ppm, 9c: Δδ(11B) = 5.2 ppm and 10: av. Δδ(11B) = 11.5 ppm). The significant low field shift in 31P NMR resonances of borenium ion salts 8–10 correlates to a high phosphonium ion character21 at the P atom of the R3PNMe-substituent. This indicates that a resonance structure featuring a formal positive charge on P (A, Scheme 4) might have a larger contribution than one featuring a P–N double bond and a positive charge on N (B) and might also be more accurate than a dative bonding model with a positive charge centered on the boron atom (C). For 8d, 9c and 10d X-ray single crystal structure determination confirmed the formulation as borenium ion salts (Fig. 6). Significant bond lengths and angles of the borenium ion salts are summarized in Table 3. In all three cases almost trigonal planar environments on nitrogen are observed (angular sum at N: 8d: 359.2(5)°, 9c: 360.0(5)° and 10d: 360.0 (5)°). This indicates effective delocalization of the lone pair of electrons on nitrogen to either the empty p orbital on boron or antibonding σ*(P–C) orbitals on phosphorus. The B–N length in borenium ion salts 8–10 (av. B–N: 1.43(1) Å) are longer than those observed in the respective boranes (av. B–N: 1.39(1) Å). This shows that the donation of electron density from the amine-moieties in 8–10 to the boron atom is less effective than that from the respective imine-environments in 2, 3 and 6. The P–N bond lengths in borenium ion salts 8d, 9c and 10d

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(av. P–N: 1.69(1) Å) are considerably longer than those in the respective boranes 2, 3 and 6 (av. P–N: 1.57(1) Å). This suggests a significant P–N single-bond character and indicates a high share of resonance structure A (Scheme 4). It is interesting to note that this trend is most significant for borenium ion salt 9c featuring a P–N bond length of 1.704(2) Å. This is probably a result of the strong electron withdrawing effect of the C6F5substituents on boron.

Conclusions Combination of haloboranes 9-Cl-9-BBN, Mes2BF, (C6F5)2BCl or PhBCl2 with phosphinimines of type R3PNSiMe3 (R = t-Bu, Cy, Et, Ph) give the respective phosphinimine-substituted boranes of type 2, 3, 4 or 6 via the elimination of Me3SiX (X = Cl, F) in good to excellent yields. In general, higher temperatures and longer reaction times are necessary if sterically more demanding phosphinimines and boranes are utilized. A chloro/methyl-group exchange reaction occurs if strongly Lewis acidic boranes are combined with sterically demanding phosphinimines giving compounds of type 5. In contrast, sterically less demanding phosphinimines and PhBCl2 give dimeric, four-membered heterocycles of type 7. The phosphiniminesubstituted boranes of type 2, 3, and 4 are used for the preparation of phosphinimine-substituted borenium ion salts of type 8–10 upon methylation of the imine-N atom by MeOTf.

Experimental section General remarks

Fig. 6 Pov-ray depiction of 8d (top), 9c (middle) and 10d (bottom). C: grey, N: blue, P: orange, B: pink, Cl: green. Hydrogen atoms have been omitted for clarity.

Table 3 Bond length and angles of phosphinimine substituted borenium ions 8d, 9c and 10d

a

P–N N–B N–C av. P–C av. B–C P–N–Bb a

8d

9c

10d

1.670(2) 1.443(3) 1.497(2) 1.794(1) 1.544(3) 122.2(1)

1.704(2) 1.404(3) 1.509(2) 1.791(2) 1.590(3) 129.5(1)

1.682(2) 1.456(3) 1.503(2) 1.799(2) 1.585(3) 127.2(2)

Bond length are reported in Å. b Angles are reported in °.

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All reactions were carried out under an atmosphere of dry, oxygen-free nitrogen using standard Schlenk techniques or a nitrogen-filled glove box (MBRAUN). All solvents (including deuterated solvents) were dried and stored over molecular sieves under a nitrogen atmosphere before use. Mes2BF, PhBCl2 and MeOTf were commercially available and used as received. (C6F5)2BCl,25 9-Cl-9BBN26 and 1a–d5c were prepared according to literature known methods. 1H (400 MHz), 13C (100 MHz), 11B (128 MHz), 19F (377 MHz), and 31P NMR spectra (163 MHz) were recorded on a Bruker Avance III or a Bruker Avance 500 spectrometer. A Perkin-Elmer analyser was used for carbon, hydrogen and nitrogen elemental analyses. High resolution mass spectrometry was performed in house employing DART or electrospray ionisation techniques in positive ion mode on an AB/Sciex QStarXL mass spectrometer (ESI) or a JEOL AccuTOF model JMS-T1000LC mass spectrometer (DART). Synthesis of R3PN-9BBN (R = t-Bu: 2a, R = Cy: 2b, R = Et: 2c, R = Ph: 2d). These compounds were prepared in a similar manner and, thus, only a general synthetic protocol is given. A solution of 9-chloro-9-borabicyclo[3.3.1]nonane (78 mg, 0.5 mmol, 1.0 eq.) in toluene (3 mL) was added dropwise within five minutes to a solution of the respective phosphinimine 1a–d (0.5 mmol, 1.0 eq.) in toluene (3 mL). The reaction


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mixture was stirred for one day at 90 °C (2a,b) or for six hours at ambient temperature (2c,d). All volatiles were removed in vacuo giving a white solid which was washed with n-hexane (2 × 1 mL). The remaining residue was extracted with n-hexane (5 × 5 mL). All volatiles were removed from the extract yielding 2a,b,d as white solid. For 2c, a white slush was obtained which was suspended in n-hexane. Remaining residue was removed by filtration and removal of all volatiles in vacuo gave 2c as a colorless oil. Single crystals of 2d, suitable for X-ray single crystal structure determination, were obtained by slow diffusion of n-hexane into a toluene solution. 2a: Yield: 89%; 1H NMR (D8-toluene, 26 °C, [ ppm]): δ = 1.23 (27H, d, CH3, 3JHP = 12.9 Hz), 1.39–1.45 (2H, m, CH), 1.66–1.74 (2H, m, CH2), 2.12–2.27 (10H, m, CH2); 11B{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 51.8 (s(br), Δν1/2 = 166 Hz); 13 C{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 24.9 (2C, s, CH2), 29.6 (9C, s, CCH3), 31.3 (2C, s(br)), 34.9 (4C, s, CH2), 39.8 (3C, d, CCH3, 1JCP = 53.2 Hz); 31P{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 33.3 (s); elemental analysis for C20H41BNP: calcd: C 71.2, H 12.2, N 4.2; found: C 70.7, H 11.6, N 3.9; DART MS: m/z: 219.2 (calcd for [t-Bu3PNH3]+: 219.2), 218.2 (calcd for [t-Bu3PNH2]+: 218.2), no peak corresponding to the molecular ion was observed. 2b: Yield: 69%; 1H NMR (D8-toluene, 26 °C, [ ppm]): δ = 0.84–0.98 (9H, m, CH2), 1.12–1.25 (8H, m, CH2), 1.16–1.24 (2H, m, BBN-CH), 1.45–1.56 (6H, m, CH2), 1.75–1.87 (3H, m, CH), 1.46–1.52 (2H, m, BBN-CH2), 1.65–1.74 (7H, m, CH2), 1.89–2.02 (10H, m, BBN-CH2); 11B{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 53.1 (s(br), Δν1/2 = 452 Hz); 13C{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 24.6 (2C, s, BBN-CH2), 26.7 (3C, d, CH2, 4JCP = 1.7 Hz), 27.3 (6C, d, CH2, JCP = 2.9 Hz), 27.4 (6C, d, CH2, JCP = 11.5 Hz), 31.3 (2C, s(br), BBN-CH), 34.9 (4C, s, BBN-CH2), 36.3 (3C, d, CH, 1JCP = 59.9 Hz); 31P{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 22.8 (s); elemental analysis for C26H47BNP: calcd: C 75.2, H 11.4, N 3.4; found: C 74.9, H 10.9, N 3.4; DART MS: m/z: 416.3648 (calcd for MH+: 416.3617). 2c: Yield: 97%; 1H NMR (D8-toluene, 26 °C, [ ppm]): δ = 0.64 (9H, dt, CH3, 3JHH = 7.7 Hz, 3JHP = 16.3 Hz), 1.00 (6H, dquart., CH2, 3JHH = 7.7 Hz, 2JHP = 11.7 Hz), 1.11–1.18 (2H, m, CH), 1.41–1.49 (2H, m, BBN-CH2), 1.85–2.01 (10H, m, BBN-CH2); 11 1 B{ H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 53.4 (s(br), Δν1/2 = 294 Hz); 13C{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 6.1 (3C, d, CH3, 2JCP = 4.7 Hz), 20.2 (3C, d, 1JCP = 63.0 Hz), 24.6 (2C, m, BBN-CH2), 30.6 (2C, s(br), CH), 34.8 (4C, m, BBN-CH2); 31P{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 34.8 (s); an elemental analysis was not performed due to the low melting point; DART MS: m/z: 253.2 (calcd for M+: 253.2), 135.1 (calcd for [Et3PNH3]+: 135.1), 134.1 (calcd for [Et3PNH2]+: 134.1. 2d: Yield: 85%; 1H NMR (D8-toluene, 26 °C, [ ppm]): δ = 1.40–1.48 (2H, m, CH), 1.63–1.72 (2H, m, CH2), 2.01–2.22 (10H, m, CH2), 7.02–7.13 (9H, m, m-Ar, p-Ar), 7.72–7.80 (6H, m, o-Ar); 11B{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 56.1 (s(br), Δν1/2 = 378 Hz); 13C{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 24.5 (2C, s, CH2), 30.1 (2C, s(br), CH), 34.6 (4C, s, CH2), 128.4 (6C, d, m-Ph, 3JCP = 11.9 Hz), 131.2 (3C, d, p-Ph,


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JCP = 2.4 Hz), 132.7 (4C, d, o-Ph, 2JCP = 9.9 Hz), 134.1 (3C, d(br), i-Ph, 1JCP = 99.7 Hz); 31P{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 6.5 (s); elemental analysis for C26H29BNP: calcd: C 78.6, H 7.4, N 3.5; found: C 78.3, H 7.8, N 3.5; DART MS: m/z: 398.2 (calcd for MH+: 398.2), 279.1 (calcd for [Ph3PNH3]+: 279.1), 278.1 (calcd for [Ph3PNH2]+: 278.1). Synthesis of R3PNBMes2 (R = Cy: 3b, R = Et: 3c, R = Ph: 3d). These compounds were prepared in a similar manner and, thus, only a general synthetic protocol is given. A solution of Mes2BF (134 mg, 0.5 mmol, 1.0 eq.) in toluene (3 mL) was added to a solution of the respective phosphinimine (0.5 mmol, 1.0 eq.) in toluene (3 mL). The reaction mixture was stirred for two days at 90 °C. A small amount of a colorless precipitate was formed and removed by filtration. All volatiles were removed in vacuo giving a white solid which was washed with n-hexane or pentane (2 × 1 mL) and dried in vacuo yielding the respective phosphinimine-substituted boranes as white solids. Single crystals of 3c and 3d, suitable for X-ray single crystal structure determination, were obtained by slow diffusion of n-hexane into Et2O solution (3d) or cooling of a saturated pentane solution to −35 °C (3c). 3b: Yield: 94%; 1H NMR (D8-toluene, 26 °C, [ ppm]): δ = 0.72–1.83 (33H, m, C6H11), 2.22 (6H, s, p-CH3), 2.52 (12H, s, o-CH3), 6.79 (4H, s, m-H); 11B{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 44.5 (s(br), Δν1/2 = 1000 Hz); 13C{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 21.7 (2C, s, p-CH3), 24.2 (4C, s, o-CH3), 27.1 (3C, d, CH2, 4JCP = 1.5 Hz), 27.7 (6C, d, CH2, 3JCP = 2.7 Hz), 28.2 (6C, d, CH2, 2JCP = 12.0 Hz), 37.7 (3C, d, CH, 1 JCP = 61.3 Hz), 129.1 (4C, s, m-Mes), 135.8 (2C, s, p-Mes). 140.4 (4C, s, o-Mes), signals for boron-bound carbon atoms were not observed; 31P{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 18.8 ppm (s); elemental analysis for C36H55BNP: calcd: C 79.5, H 10.2, N 2.6; found: C 79.5, H 9.9, N 3.2; ESI MS: m/z: 544.4 (calcd for M+: 544.4). 3c: Yield: 90%; 1H NMR (D8-toluene, 26 °C, [ ppm]): δ = 0.63 (9H, m, CH2CH3), 1.17 (6H, m, CH2CH3), 2.22 (6H, s, p-CH3), 2.46 (12H, s, o-CH3), 6.77 (4H, s, m-H); 11B{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 45.3 (s(br), Δν1/2 = 700 Hz); 13 C{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 6.6 (d, CH2CH3, 2 JCP = 4.8 Hz), 19.6 (d, CH2CH3, 1JCP = 65.0 Hz), 21.8 (2C, s, p-CH3), 24.2 (4C, s, o-CH3), 129.0 (4C, s, m-Mes), 136.1 (2C, s, p-Mes), 140.7 (4C, s, o-Mes), signals for boron-bound carbon atoms were not observed. 31P{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 22.1 (s); elemental analysis for C24H37BNP: calcd: C 75.6, H 9.8, N 3.7; found: C 74.7, H 10.1, N 3.6; DART MS: m/z: 382.3 (calcd for M+: 382.3). 3d: Yield: 81%; 1H NMR (D8-toluene, 26 °C, [ ppm]): δ = 2.18 (6H, s, p-CH3), 2.37 (12H, s, o-CH3), 6.62 (4H, s, m-H), 6.88–9.95 (6H, m, m-Ph), 6.96–7.03 (3H, m, p-Ph), 7.51–7.58 (6H, m, o-Ph); 11B{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 48.0 (s(br), Δν1/2 = 800 Hz); 13C{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 21.2 (2C, s, p-CH3), 23.8 (4C, s, o-CH3), 128.1 (6C, d, m-Ph, 3JCP = 12.1 Hz), 128.4 (4C, s, m-Mes), 130.9 (3C, d, p-Ph, 4JCP = 2.9 Hz), 132.2 (3C, d, i-Ph, 1JCP = 101.6 Hz), 132.8 (6C, d, o-Ph, 2JCP = 9.5 Hz), 135.5 (2C, s, p-Mes), 140.2 (4C, s, o-Mes); 31P{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 4.8 (s);

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elemental analysis for C36H37BNP: calcd: C 82.3, H 7.1, N 2.7; found: C 81.8, H 7.3, N 2.7; ESI MS: m/z: 526.3 (calcd for MH+: 526.3), 279.1 (calcd for [Ph3PNH3]+: 279.1), 278.1 (calcd for [Ph3PNH2]+: 278.1). Synthesis of R3PNB(C6F5)2 (R = Et: 4c, R = Ph: 4d). Both compounds were prepared in a similar manner and, thus, only a general synthetic protocol is given. A solution of (C6F5)2BCl (190 mg, 0.5 mmol, 1.0 eq.) in toluene (3 mL) was added dropwise within five minutes to a solution of the respective phosphinimine (0.5 mmol, 1.0 eq.) in toluene (3 mL). The reaction mixture was stirred for one hour at ambient temperature. All volatiles were removed in vacuo giving, in the case of 1c, a colorless slush which was dissolved in n-pentane (0.5 mL). A small amount of remaining residue was removed by filtration. Removal of all volatiles gave 4c as a colorless oil which solidified after storage for several days at −35 °C (83% yield). For 1d, a white solid was obtained which was washed with n-pentane (2 × 0.5 mL) and dried in vacuo yielding 4d as a white solid. 4c: Yield: 83%; 1H NMR (D8-toluene, 26 °C, [ ppm]): δ = 0.62 (9H, dt, CH3, 3JHH = 7.8 Hz, 3JHP = 16.8 Hz), 1.00 (6H, dquart., CH2, 3JHH = 7.8 Hz, 2JHH = 11.8 Hz); 11B{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 33.8 (s(br), Δν1/2 = 315 Hz); 13C{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 5.4 (3C, d, CH3, 2JCP = 5.3 Hz), 18.3 (3C, d, CH2, 1JCP = 65.3 Hz), 137.5 (4C, m, C6F5), 141.1 (2C, m, C6F5), 146.9 (4C, m, C6F5), signals for boron-bound carbon atoms were not observed; 19F{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = −162.9 (4F, m, m-F), −155.7 (2F, t, p-F, 3JFF = 20.2 Hz), −134.5 (4F, m, o-F); 31P{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 31.5 (s); elemental analysis for C18H15BF10NP: calcd: C 45.3, H 3.2, N 2.9; found: C 45.1, H 3.5, N 2.9; DART MS: m/z: 478.1 (calcd for MH+: 478.1). 4d: Yield: 92%; characterization data were previously reported.12 Synthesis of R3PNSiMe2Cl (R = t-Bu: 5a, R = Cy: 5b). Both compounds were prepared in a similar manner and, thus, only a general synthetic protocol is given. A solution of (C6F5)2BCl (190 mg, 0.5 mmol, 1.0 eq.) in toluene (3 mL) was added dropwise within five minutes to a solution of the respective phosphinimine (0.5 mmol, 1.0 eq.) in toluene (3 mL). The reaction mixture was stirred for one hour at ambient temperature. All volatiles were removed in vacuo giving a white solid which was washed with acetonitrile (3 × 1 mL). Removal of all volatiles yielded 5a,b as white solid. Single crystals of 5a, suitable for X-ray single crystal structure determination, were obtained by slow vaporization of a pentane solution. 5a: Yield: 48%; 1H NMR (C6D6, 26 °C, [ ppm]): δ = 0.66 (6H, s, SiCH3), 1.14 (27H, d, CCH3, 3JHP = 13.0 Hz); 13C{1H} NMR (C6D6, 26 °C, [ ppm]): δ = 7.3 (2C, d, SiCH3, 3JCP = 2.2 Hz), 29.3 (9C, d, CCH3, 2JCP = 0.7 Hz), 39.7 (3C, d, CCH3, 1JCP = 53.9 Hz); 31 1 P{ H} NMR (C6D6, 26 °C, [ ppm]): δ = 37.9 (s); elemental analysis for C14H33ClNPSi: calcd: C 54.3, H 10.7, N 4.5; found: C 54.2, H 10.8, N 4.6; ESI MS: m/z: 310.1885 (calcd for MH+: 310.1882). 5b: Yield: 51%; 1H NMR (C6D6, 26 °C, [ ppm]): δ = 0.71 (6H, s, SiCH3), 1.01–1.16 (9H, m, CH2), 1.28–1.41 (6H, m, CH2),

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1.53–1.76 (12H, m, CH2, CH), 1.81–1.89 (6H, m, CH2); 13C{1H} NMR (C6D6, 26 °C, [ ppm]): δ = 7.6 (2C, d, SiCH3, 3JCP = 3.0 Hz), 26.4 (3C, d, CH2, 4JCP = 1.5 Hz), 26.9 (6C, d, CH2, JCP = 2.9 Hz), 27.2 (6C, d, CH2, JCP = 12.0 Hz), 36.2 (3C, d, CH, 1JCP = 63.0 Hz); 31P{1H} NMR (C6D6, 26 °C, [ ppm]): δ = 23.1 (s); elemental analysis for C14H33ClNPSi: calcd: C 61.9, H 10.1, N 3.6; found: C 61.4, H 10.3, N 3.7; ESI MS: m/z: 388.2344 (calcd for MH+: 388.2351). Synthesis of R3PNBPhCl (R = t-Bu: 6a, R = Cy: 6b). Both compounds were prepared in a similar manner and, thus, only a general synthetic protocol is given. A solution of PhBCl2 (79 mg, 0.5 mmol, 1.0 eq.) in toluene (3 mL) was added to a solution of the respective phosphinimine (0.5 mmol, 1.0 eq.) in toluene (3 mL). The reaction mixture was stirred for twelve hours at 90 °C. All volatiles were removed in vacuo giving a white solid. This was extracted with n-hexane (6 × 3 mL). All volatiles were removed from the extract yielding the respective borane as a white solid. Single crystals of 6a, suitable for X-ray single crystal structure determination, were obtained by slow evaporation of a n-pentane solution. 6a: Yield: 83%; 1H NMR (D8-toluene, 26 °C, [ ppm]): δ = 1.20 (27H, d, CH3, 3JHP = 13.4 Hz), 7.23–7.28 (1H, m, p-Ph), 7.29–7.35 (2H, m, m-Ph), 8.36–8.40 (2H, m, o-Ph); 11B{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 33.4 (s(br), Δν1/2 = 310 Hz); 13C{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 29.5 (9C, s, CH3), 40.3 (3C, d, CCH3, 1JCP = 51.9 Hz), 127.5 (2C, s, o-Ph), 130.0 (1C, s, p-Ph), 135.9 (2C, s, m-Ph), signals for boronbound carbon atoms were not observed; 31P{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 41.6 (s); elemental analysis for C18H32BClNP: calcd: C 63.6, H 9.5, N 4.1; found: C 63.6, H 9.9, N 4.2; DART MS: m/z: 219.2 (calcd for [t-Bu3PNH3]+: 219.2), 218.2 (calcd for [t-Bu3PNH2]+: 218.2), no peak corresponding to the molecular ion was observed. 6b: Yield: 90%; 1H NMR (D8-toluene, 26 °C, [ ppm]): δ = 0.80–0.99 (9H, m, CH2), 1.13–1.27 (6H, m, CH2), 1.31–1.40 (3H, m, CH2), 1.42–1.52 (6H, m, CH2), 1.67–1.76 (6H, m, CH2), 1.77–1.90 (3H, m, CH), 7.07–7.12 (1H, m, p-Ph), 7.13–7.18 (2H, m, m-Ph), 8.30–8.33 (2H, m, o-Ph); 11B{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 33.9 (s(br), Δν1/2 = 730 Hz); 13C{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 26.4 (3C, d, CH2, 4JCP = 1.5 Hz), 27.2 (6C, d, JCP = 2.9 Hz), 27.3 (6C, d, JCP = 12.1 Hz), 35.4 (3C, d, CH, 1JCP = 60.6 Hz), 127.5 (2C, s, m-Ph), 130.2 (1C, s, p-Ph), 136.0 (2C, s, o-Ph), signals for boron-bound carbon atoms were not observed; 31P{1H} NMR (D8-toluene, 26 °C, [ ppm]): δ = 29.9 (s); elemental analysis for C24H38BClNP: calcd: C 69.0, H 9.2, N 3.4; found: C 68.5, H 9.6, N 3.5; DART MS: m/z: 297.2 (calcd for [Cy3PNH3]+: 297.2), 296.2 (calcd for [Cy3PNH2]+: 296.2), no peak corresponding to the molecular ion was observed. Synthesis of (R3PNBPhCl)2 (R = Et: 7c, R = Ph: 7d). Both compounds were prepared in a similar manner and, thus, only a general synthetic protocol is given. A solution of PhBCl2 (79 mg, 0.5 mmol, 1.0 eq.) in toluene (3 mL) was added to a solution of the respective phosphinimine (0.5 mmol, 1.0 eq.) in toluene (3 mL). The reaction mixture was stirred for twelve hours at ambient temperature accompanied by the formation


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of a colorless precipitate. The supernatant was removed and the residue was washed with n-hexane (3 × 3 mL). Removal of all volatiles yielded the respective four-membered heterocycles 7c,d as colorless microcrystalline solids. Single crystals of 7c and 7d·1.5(CH2Cl2) suitable for X-ray single crystal structure determination, were obtained by slow diffusion of n-hexane into CH2Cl2 solutions. 7c: Yield: 63%; 1H NMR (CD2Cl2, 26 °C, [ ppm]): δ = 1.03 (18H, dt, CH3, 3JHH = 7.6 Hz, 3JHP = 18.6 Hz), 1.87 (12H, dquart., CH2, 3JHH = 7.6 Hz, 2JHP = 12.6 Hz), 7.38–7.47 (6H, m, o/p-Ph), 7.74–7.79 (4H, m, m-Ph); 11B{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 19.5 (s(br), Δν1/2 = 311 Hz); 13C{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 5.6 (6C, t, CH3, |2JCP + 6JCP| = 2.3 Hz), 16.2 (6C, dd, CH2, 1JCP = 65.4 Hz, 5JCP = 3.7 Hz), 128.4 (4C, s, o-Ph), 129.1 (2C, s, p-Ph), 132.1 (4C, s, m-Ph), signals for boronbound carbon atoms were not observed; 31P{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 53.3 (s); elemental analysis for C24H40B2Cl2N2P2: calcd: C 56.4, H 7.9, N 5.5; found: C 56.5, H 7.4, N 5.3; ESI MS: m/z: 135.1 (calcd for [Et3PNH3]+: 135.1), 134.1 (calcd for [Et3PNH2]+: 134.1), no peak corresponding to the molecular ion was observed. 7d: Yield: 68%; 1H NMR (CD2Cl2, 26 °C, [ ppm]): δ = 6.84–9.90 (4H, m, m-BPh), 6.96–7.01 (4H, m, o-BPh), 7.01–7.06 (2H, m, p-BPh), 7.43–7.51 (12H, m, m-PPh), 7.51–7.59 (12H, m, o-PPh), 7.63–7.70 (6H, m, p-PPh); 11B{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 23.2 (s(br), Δν1/2 = 675 Hz); 13C{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 122.6 (6C, dd, i-PPh, 1JCP = 108.0 Hz, 5JCP = 3.2 Hz), 127.6 (4C, s, m-BPh), 128.4 (2C, s, p-BPh), 129.5 (12C, t, m-PPh, |3JCP + 7JCP| = 6.7 Hz), 132.7 (4C, s, o-BPh), 134.1 (12C, t, o-PPh, |2JCP + 6JCP| = 5.7 Hz), 134.6 (6C, t, p-Ph, |5JCP + 8 JCP| = 1.3 Hz), signals for boron-bound carbon atoms were not observed; 31P{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 29.3 (s); elemental analysis for C24H20BClNP: calcd: C 72.1, H 5.0, N 3.5; found: C 71.2, H 5.4, N 3.6; ESI MS: m/z: 279.1 (calcd For [Ph3PNH3]+: 279.1), 278.1 (calcd for [Cy3PNH2]+: 278.1), no peak corresponding to the molecular ion was observed. Synthesis of borenium ion salts [R3PNMe-9BBN][OTf ] (R = Cy: 8b, R = Et: 8c, R = Ph: 8d). A solution of MeOTf (82 mg, 0.5 mmol, 1.0 eq.) in toluene (3 mL) was added to a solution of the respective borane (0.5 mmol, 1.0 eq.) in toluene (3 mL). The reaction mixture was stirred for two hours at ambient temperature accompanied by the formation of a colorless precipitate. n-Hexane (3 mL) was added to complete precipitation. The supernatant was removed and the remaining colorless solid was washed with n-hexane (3 × 3 mL) and dried in vacuo yielding the borenium ion salt as microcrystalline material. 8b: Yield: 97%; 1H NMR (CD2Cl2, 26 °C, [ ppm]): δ = 1.35–1.50 (10H, m, BBN-CH2), 1.63–1.74 (8H, m, CH2), 1.77–1.91 (8H, m, BBN-CH), 1.96–2.08 (16H, m, BBN-CH2), 2.70–2.82 (3H, m, CH), 3.21 (3H, d, CH3, 3JHP = 9.3 Hz); 11 1 B{ H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 62.9 (s(br), Δν1/2 = 740 Hz); 13C{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 22.6 (2C, s, BBN-CH2), 25.8 (3C, d, CH2, 4JCP = 1.8 Hz), 27.1 (6C, d, CH2, JCP = 12.4 Hz), 27.8 (6C, d, CH2, JCP = 3.5 Hz), 33.9 (4C, s, BBN-CH2), 35.5 (3C, d, CH, 1JCP = 46.0 Hz), 37.3 (1C, s, CH3),


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121.5 (1C, quart., CF3, 1JCF = 322.1 Hz), signals for boronbound carbon atoms were not observed; 19F{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = −78.9 (s); 31P{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 66.2 (s); elemental analysis for C28H32PF3NO3PS: calcd: C 59.9, H 5.8, N 2.5; found: C 59.4, H 5.7, N 2.5; ESI MS: m/z: 311.3 (calcd for [Cy3PNMeH2]+: 311.3), 310.3 (calcd for [Cy3PNMeH]+: 310.3),), no peak corresponding to the molecular ion was observed. 8c: Yield: 97%; 1H NMR (CD2Cl2, 26 °C, [ ppm]): δ = 1.29–1.45 (2H, m, BBN-CH2), 1.35 (9H, dt, CH3, 3JHH = 7.4 Hz, 3 JHP = 19.1 Hz), 1.58–1.85 (6H, m, BBN-CH, BBN-CH2), 1.94–2.06 (6H, m, BBN-CH, BBN-CH2), 2.52 (6H, dquart., CH2, 3 JHH = 7.4 Hz, 2JHP = 11.6 Hz), 3.18 (3H, d, NCH3, 3JHP = 10.7 Hz); 11B{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 61.7 (s(br), Δν1/2 = 430 Hz); 13C{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 5.9 (3C, d, CH3, 2JCP = 5.1 Hz), 16.5 (3C, d, CH2, 1JCP = 56.3 Hz), 22.8 (4C, s, BBN-CH2), 33.5 (4C, s(br), BBN-CH, BBN-CH2), 35.8 (1C, s, NCH3), 121.4 (1C, quart., CF3, 1JCF = 319.6 Hz); 19F{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = −79.0 (s); 31P{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 73.3 (s); elemental analysis for C16H32PF3NO3PS: calcd: C 46.1, H 7.7, N 3.4; found: C 46.6, H 7.8, N 3.3; ESI MS: m/z: 149.1 (calcd for [Et3PNMeH2]+: 149.1), 148.1 (calcd for [Et3PNMeH]+: 148.1), no peak corresponding to the molecular ion was observed. 8d: Yield: 95%; 1H NMR (CD2Cl2, 26 °C, [ ppm]): δ = 0.62–2.20 (10H, m(br), BBN), 1.24–1.36 (2H, m, BBN), 1.75–1.90 (2H, m, BBN), 3.08 (3H, d, NCH3, 3JHP = 13.1 Hz), 7.75–7.83 (12H, m, o-Ph, m-Ph), 7.85–7.93 (3H, m, p-Ph); 11 1 B{ H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 64.3 (s(br), Δν1/2 = 630 Hz); 13C{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 22.5 (2C, s, CH2-BBN), 33.4 (4C, s, CH2-BBN), 37.6 (1C, d, NCH3, 2JCP = 3.3 Hz), 121.4 (1C, quart., CF3, 1JCF = 321.6 Hz), 121.5 (3C, d, i-Ph, 1 JCP = 100.7 Hz), 130.8 (6C, d, o/m-Ph, JCP = 13.3 Hz), 134.1 (6C, d, o/m-Ph, JCP = 10.5 Hz), 136.0 (3C, d, p-Ar, 4JCP = 3.0 Hz), signals for boron-bound carbon atoms were not observed; 19 1 F{ H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = −78.9 (s); 31P{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 43.9 (s); elemental analysis for C28H32PF3NO3PS: calcd: C 58.0, H 8.7, N 2.4; found: C 57.6, H 8.7, N 2.5; ESI MS: m/z: 293.1 (calcd for [Ph3PNMeH2]+: 293.1), 292.1 (calcd for [Ph3PNMeH]+: 292.1), no peak corresponding to the molecular ion was observed. Synthesis of borenium ion salt [Et3PNMeB(C6F5)2][OTf ] (9c). A solution of MeOTf (82 mg, 0.5 mmol, 1.0 eq.) in toluene (3 mL) was added to a solution of 4c (0.5 mmol, 1.0 eq.) in toluene (3 mL). The reaction mixture was stirred for 48 hours at ambient temperature accompanied by the formation of a colorless precipitate. The supernatant was removed and the remaining colorless solid was washed with toluene (1 × 3 mL) and pentane (2 × 3 mL) and dried in vacuo yielding the borenium ion salt as microcrystalline material. Crystals of 9c suitable for X-ray diffraction analysis were obtained by slow diffusion of n-pentane into a saturated CH2Cl2 solution at −35 °C. Yield: 83%; 1H NMR (CD2Cl2, 26 °C, [ ppm]): δ = 1.30 (9H, dt, CH3, 3JHH = 7.6 Hz, 3JHP = 19.7 Hz), 2.40 (6H, dquart., CH2, 3 JHH = 7.6 Hz, 3JHP = 11.4 Hz), 3.20 (3H, d, NCH3, 3JHP =

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10.7 Hz); 11B{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 39.0 (s(br), Δν1/2 = 700 Hz); 13C{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 5.5 (3C, d, CH3, 2JCP = 5.2 Hz), 14.7 (3C, d, CH2, 1JCP = 54.1 Hz), 110.4 (2C, s(br), C6F5), 120.6 (1C, quart. CF3, 1JCF = 320.0 Hz), 138.2 (4C, d(br), C6F5, 1JCF = 260 Hz), 143.6 (2C, d(br), C6F5, 1 JCF = 260 Hz), 146.3 (4C, d(br), C6F5, 1JCF = 247 Hz); 19F{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = −78.9 (3F, s, CF3), −131.3(4F, m, o-C6F5), −149.8 (2F, m, p-C6F5), −160.2 (4F, m, m-C6F5); 31 1 P{ H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 80.9 (s); elemental analysis for C20H18BF13NO3PS: calcd: C 37.5, H 2.8, N2.2; found: C 37.3, H 3.1, N 2.3; DART MS: m/z: 492.1 (calcd for M+: 492.1). Synthesis of borenium ion salts [R3PNMeBMes2][OTf ] (R = Cy: 10b, R = Et: 10c, R = Ph: 10d). A solution of MeOTf (82 mg, 0.5 mmol, 1.0 eq.) in toluene (3 mL) was added to a solution of the respective borane (0.5 mmol, 1.0 eq.) in toluene (3 mL). The reaction mixture was stirred for 48 hours at ambient temperature accompanied by the formation of a colorless precipitate. The supernatant was removed and the remaining colorless solid was washed with toluene (1 × 3 mL) and pentane (2 × 3 mL) and dried in vacuo yielding the borenium ion salt as microcrystalline material. Compound 10b was isolated as a toluene solvate. Crystals of 10d·CH2Cl2 suitable for X-ray diffraction analysis were obtained by slow diffusion of n-pentane into a saturated CH2Cl2 solution at −35 °C. 10b: Yield: 88%; 1H NMR (CD2Cl2, 26 °C, [ ppm]): δ = 1.05–1.21 (6H, m(br), Cy), 1.24–1.34 (3H, m, Cy), 1.63–1.78 (9H, m, Cy), 1.82–1.93 (6H, m(br), Cy), 1.98–2.09 (6H, m(br), Cy), 2.24 (9H, s(br), o-/p-CH3), 2.27 (3H, s, p-CH3), 2.29 (6H, s, o-CH3), 2.34 (s, C7H8), 2.66 (3H, m, Cy), 3.07 (3H, d, NCH3, 3 JHP = 8.7 Hz), 6.81 (2H, m-Mes), 6.88 (2H, m-Mes), 7.12–7.19 (m, C7H8), 7.22–7.26 (m, C7H8); 11B{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 57.5 (s(br), Δν1/2 = 1300 Hz); 13C{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 21.4 (2C, s, p-CH3), 21.5 (1C, s, C7H8), 24.1 (2C, s, o-CH3), 24.6 (2C, s, o-CH3), 26.0 (3C, d, CH2, 4JCP = 1.8 Hz), 27.5 (6C, d, CH2, 3JCP = 12.3 Hz), 29.4 (6C, d, CH2, 2JCP = 3.9 Hz), 37.9 (3C, d, CH2, 1JCP = 42.6 Hz), 40.8 (1C, s, NCH3), 121.5 (1C, quart. CF3, 1JCF = 321.3 Hz), 125.6 (1C, s, C7H8), 128.5 (2C, s, C7H8), 129.2 (2C, s, m-Mes), 129.4 (2C, s, C7H8), 129.9 (2C, s, m-Mes), 138.4 (1C, s, C7H8), 139.0 (2C, s, o-Mes), 139.6 (1C, s, p-Mes), 140.2 (2C, s, o-Mes), 140.8 (1C, s, p-Mes), signals for boron-bound carbon atoms were not observed; 19 1 F{ H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = −78.9 (s); 31P{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 72.7 (s); elemental analysis for C38H58BF3NO3PS·C7H8: calcd: C 67.6, H 8.3, N 1.8; found: C 67.7, H 9.1, N 2.0; DART MS: m/z: 558.4402 (calcd for M+: 558.4400). 10c: Yield: 82%; 1H NMR (CD2Cl2, 26 °C, [ ppm]): δ = 1.27 (9H, dt, CH2CH3, 3JHH = 7.6 Hz, 3JHP = 19.2 Hz), 2.23 (6H, s, o-CH3), 2.24 (3H, s, o-CH3), 2.25 (6H, dquart., CH2CH3, 3JHH = 7.6 Hz, 2JHP = 11.9 Hz), 2.26 (3H, s, p-CH3), 2.28 (3H, s, p-CH3), 3.15 (3H, d, NCH3, 3JHP = 10.7 Hz), 6.85 (2H, m-Mes), 6.87 (2H, m-Mes); 11B{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 56.7 (s(br), Δν1/2 = 900 Hz); 13C{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 6.9 (9C, d, CH3, 2JCP = 5.2 Hz), 16.1 (6C, d, CH2, 1JCP = 56.0 Hz), 21.2 (1C, s, p-CH3), 21.3 (1C, s, p-CH3), 23.0 (2C, s, o-CH3), 23.9

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(2C, s, o-CH3), 37.5 (1C, d, NCH3, 2JCP = 1.3 Hz), 121.5 (1C, quart., CF3, 1JCF = 321.1 Hz), 129.4 (2C, s, m-Mes), 129.6 (2C, s, m-Mes), 140.2 (1C, s, p-Mes), 140.4 (2C, s, o-Mes), 140.6 (2C, s, o-Mes), 141.3 (1C, s, p-Mes), signals for boron-bound carbon atoms were not observed; 19F{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = −78.9 (s); 31P{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 74.8 (s); elemental analysis for C26H40BF3NO3PS: calcd: C 57.3, H 7.4, N 2.6; found: C 56.8, H 7.9, N 2.9; DART MS: m/z: 396.2990 (calcd for M+: 396.2991). 10d: Yield: 78%; 1H NMR (CD2Cl2, 26 °C, [ ppm]): δ = 1.87 (6H, s, o-CH3), 2.11 (3H, s, p-CH3), 2.25 (3H, s, p-CH3), 2.37 (6H, s, o-CH3), 3.25 (3H, d, NCH3, 3JHP = 11.2 Hz), 6.38 (2H, s, m-Mes), 6.85 (2H, s, m-Mes), 7.56–7.70 (12H, m, o-/m-Ph), 7.77–7.83 (3H, m, p-Ph); 11B{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 58.8 (s(br), Δν1/2 = 1200 Hz); 13C{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 20.5 (1C, s, p-CH3), 20.7 (1C, s, p-CH3), 22.9 (2C, s, o-CH3), 24.0 (2C, s, o-CH3), 41.7 (1C, d, NCH3, 2JCP = 2.3 Hz), 118.3 (3C, d, i-Ph, 1JCP = 100.3 Hz), 121.0 (1C, quart. CF3, 1JCF = 321.3 Hz), 128.6 (2C, s, m-Mes), 129.9 (2C, s, m-Mes), 129.9 (6C, d, m-Ph, 3JCP = 13.2 Hz), 134.1 (6C, d, o-Ph, 2JCP = 10.4 Hz), 135.4 (3C, d, p-Ph, 4JCP = 3.0 Hz), 139.3 (2C, s, o-Mes), 139.7 (1C, s, p-Mes), 139.8 (2C, s, o-Mes), 140.0 (1C, s, p-Mes), signals for boron bond carbon atoms were not observed; 19 1 F{ H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = −78.8 (s); 31P{1H} NMR (CD2Cl2, 26 °C, [ ppm]): δ = 47.7 (s); elemental analysis for C38H40BF3NO3PS: calcd: C 66.2, H 5.9, N 2.0; found: C 66.1, H 6.4, N 2.2; ESI MS: m/z: 539.3028 (calcd for M+: 539.3022). X-ray diffraction studies Crystals were coated in paratone oil and mounted in a cryoloop. Data were collected on a Bruker APEX-2 X-ray diffractometer using graphite monochromated Mo-Kα radiation (0.71073 Å). The temperature was maintained at 150(2) K using an Oxford cryostream cooler for both, initial indexing and full data collection. Data were collected using Bruker APEX-2 software and processed using SAINT and an absorption correction applied using multi-scan27 within the APEX-2 program.28 All structures were solved by direct methods within the SHELXTL package.29 For 10d·CH2Cl2 the solvate molecule and the triflate anion were found to be disordered and were refined over two positions with S.O.F.s of 0.51 : 49 and 0.58 : 0.42, respectively. For 7d·1.5(CH2Cl2) one of the solvate molecules was found to be disordered and was refined over two positions with an S.O. F. of 0.50 : 0.50. For 6a one of the four formula units in the asymmetric unit was found to be disordered and was refined applying several restraints. H atoms were added at calculated positions and refined with a riding model for all structures.

Acknowledgements D.W.S. gratefully acknowledges the financial support of the NSERC of Canada and the award of a Canada Research Chair. M.H.H. thanks the Alexander von Humboldt Foundation for a Feodor Lynen Research Fellowship.


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Notes and references 1 (a) G. Erker and D. W. Stephan, Frustrated Lewis Pairs I: Uncovering and Understanding, Topics in Current Chemistry, 332, Springer Verlag, 2013; (b) G. Erker and D. W. Stephan, Frustrated Lewis Pairs II: Expanding the Scope, Topics in Current Chemistry 334, Springer Verlag, 2013. 2 (a) G. C. Welch, R. R. San Juan, J. D. Masuda and D. W. Stephan, Science, 2006, 314, 1124; (b) L. J. Hounjet, C. Bannwarth, C. N. Garon, C. B. Caputo, S. Grimme and D. W. Stephan, Angew. Chem., Int. Ed., 2013, 52, 7492. 3 M. H. Holthausen, T. Mahdi, C. Schlepphorst, J. J. Weigand and D. W. Stephan, Chem. Commun., 2014, 50, 10038. 4 (a) K. Dehnicke, M. Krieger and W. Massa, Coord. Chem. Rev., 1999, 182, 19; (b) D. W. Stephan, Adv. Organomet. Chem., 2006, 54, 267–291. 5 (a) E. Hollink, P. Wei and D. W. Stephan, Organometallics, 2004, 23, 1562; (b) D. W. Stephan, F. Guerin, R. E. v. H. Spence, L. Koch, X. Gao, S. J. Brown, J. W. Swabey, Q. Wang, W. Xu, P. Zoricak and D. G. Harrison, Organometallics, 1999, 18, 2046; (c) D. W. Stephan, J. C. Stewart, F. Guerin, S. Courtenay, J. Kickham, E. Hollink, C. Beddie, A. Hoskin, T. Graham, P. Wei, R. E. v. H. Spence, W. Xu, L. Koch, X. Gao and D. G. Harrison, Organometallics, 2003, 22, 1937; (d) D. W. Stephan, J. C. Stewart, F. Guerin, R. E. v. H. Spence, W. Xu and D. G. Harrison, Organometallics, 1999, 18, 1116; (e) N. Yue, E. Hollink, F. Guerin and D. W. Stephan, Organometallics, 2001, 20, 4424; (f) D. W. Stephan, Organometallics, 2005, 24, 2548–2560. 6 K. Dehnicke and F. Weller, Coord. Chem. Rev., 1997, 158, 103. 7 (a) F. Heshmatpour, D. Nußhär, R. Garbe, S. Wocadlo, W. Massa and K. Dehnicke, Z. Anorg. Allg. Chem., 1995, 621, 443; (b) M. Möhlen, K. Harms, K. Dehnicke, J. Magull, H. Goesmann and D. Fenske, Z. Anorg. Allg. Chem., 1996, 622, 1692; (c) M. Möhlen, B. Neumüller, N. Faza, C. Müller, W. Massa and K. Dehnicke, Z. Anorg. Allg. Chem., 1997, 623, 1567. 8 M. Möhlen, B. Neumüller and K. Dehnicke, Z. Anorg. Allg. Chem., 1998, 624, 177. 9 S. Courtenay, D. Walsh, S. Hawkeswood, P. Wei, A. Kumar Das and D. W. Stephan, Inorg. Chem., 2007, 46, 3623. 10 S. Courtenay, J. Y. Mutus, R. W. Schurko and D. W. Stephan, Angew. Chem., Int. Ed., 2002, 41, 498.


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11 (a) S. Hawkeswood and D. W. Stephan, Dalton Trans., 2005, 2182; (b) S. Hawkeswood, P. Wei, J. W. Gauld and D. W. Stephan, Inorg. Chem., 2005, 44, 4301. 12 R. L. Melen, A. J. Lough and D. W. Stephan, Dalton Trans., 2013, 42, 8674. 13 G. Alcaraz, A. Baceíredo, F. Dahan and G. Bertrand, J. Am. Chem. Soc., 1994, 116, 1225. 14 (a) H. Nöth and H. Vahrenkamp, Chem. Ber., 1966, 99, 1049; (b) B. Singaram, Heteroat. Chem., 1992, 3, 245. 15 N. M. Brown, F. Davidson and J. W. Wilson, J. Organomet. Chem., 1980, 192, 133. 16 (a) A. Stute, L. Heletta, R. Fröhlich, C. G. Daniliuc, G. Kehr and G. Erker, Chem. Commun., 2012, 48, 11739; (b) N. Kano, K. Yanaizumi, X. Meng and T. Kawashima, Heteroat. Chem., 2012, 23, 429; (c) M. W. P. Bebbington, S. Bontemps, G. Bouhadir and D. Bourissou, Angew. Chem., Int. Ed., 2007, 46, 3333. 17 C. Chen, G. Kehr, R. Fröhlich and G. Erker, J. Am. Chem. Soc., 2010, 132, 13594. 18 (a) A. Schulz, P. Mayer and A. Villinger, Inorg. Chem., 2007, 46, 8316; (b) A. Villinger, A. Westenkirchner, R. Wustrack and A. Schulz, Inorg. Chem., 2008, 47, 9140. 19 The molecular structure of 1d at 300 K was previously reported: F. Weller, H.-C. Kang, W. Massa, T. Rübenstahl, F. Kunkel and K. Dehnicke, Z. Naturforsch., 1995, 50b, 1050. 20 G. Linti, H. Nöth, E. Schneider and W. Storch, Chem. Ber., 1993, 126, 619. 21 L. K. Krannich, R. K. Kanjolia and C. L. Watkins, Magn. Reson. Chem., 1987, 25, 320. 22 E. Niecke, W. Flick and S. Pohl, Angew. Chem., Int. Ed. Engl., 1976, 15, 309. 23 C. Jiang and D. W. Stephan, Dalton Trans., 2013, 42, 630. 24 J. M. Farrell, J. A. Hatnean and D. W. Stephan, J. Am. Chem. Soc., 2012, 134, 15728. 25 D. J. Parks, W. E. Piers and G. P. A. Yap, Organometallics, 1998, 17, 5492. 26 H. C. Brown and S. U. Kulkarni, J. Organomet. Chem., 1979, 168, 281. 27 R. H. Blessing, Acta Crystallogr., Sect. A: Fundam. Crystallogr., 1995, 51, 33. 28 Bruker AXS Inc., Madison, WI. 29 G. M. Sheldrick, Acta Crystallogr., Sect. A: Fundam. Crystallogr., 2008, 64, 112.

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Lewis Base Activation of Lewis Acids - Group 13. In Situ Generation and Reaction of Borenium Ions.

Are boryl radicals from amine-boranes and phosphine-boranes the most stable radicals?

dehydrogenation of amine-boranes.

Synthesis of phosphaguanidines by hydrophosphination of carbodiimides with phosphine boranes.

syn-1,2-carboboration of alkynes with borenium cations.

Radical Reactions of N-Heterocyclic Carbene Boranes with Organic Nitriles: Cyanation of NHC-Boranes and Reductive Decyanation of Malononitriles.

Phosphine catalyzed reduction of CO2 with boranes.

Alkaline-Earth-Catalyzed Dehydrocoupling of Amines and Boranes.

Hydroboration of arynes with N-heterocyclic carbene boranes.

Protein-binding polyhedral boranes II: DL-S-(10-dimethylsulfidooctahydrodecaborane)methionine.

Facile Arylation of Four-Coordinate Boron Halides by Borenium Cation Mediated Boro-desilylation and -destannylation.

Relationship of hypolipidemic and antineoplastic activities of tricyclohexyl- and triphenylphosphine boranes, carboxyboranes, cyanoboranes, and related derivatives.

P-C-Activated Bimetallic Rhodium Xantphos Complexes: Formation and Catalytic Dehydrocoupling of Amine-Boranes.

Protonolysis and thermolysis reactions of functionalised NHC-carbene boranes and borates.

Dynamic Behavior of N-Heterocyclic Carbene Boranes: Boron-Carbene Bonds in B,B-Disubstituted N,N-Dimethylimidazol-2-ylidene Boranes Have Substantial Rotation Barriers.

Catalysis and Mechanism of H2 Release from Amine-Boranes by Diiron Complexes.

Chemical generation of arsane and methylarsanes with amine boranes. Potentialities for nonchromatographic speciation of arsenic.

Synthesis and Suzuki Reactions of N-Heterocyclic Carbene Difluoro(aryl)-boranes.

Electron transport and nonlinear optical properties of substituted aryldimesityl boranes: a DFT study.

Synthesis, cytotoxicity, hypolipidemic and anti-inflammatory activities of amine-boranes and esters of boron analogues of choline and thiocholine.

Hydroboration of Arynes Formed by Hexadehydro-Diels-Alder Cyclizations with N-Heterocyclic Carbene Boranes.

Synthesis of cyclic amine boranes through triazole-gold(I)-catalyzed alkyne hydroboration.

DNA interaction with metal complexes and salts of substituted boranes and hydroborates in murine and human tumor cell lines.

Digitalis: ions, inotropy and toxicity.