Supporting Information for
Supporting Information for
Catalytic Redistribution and Polymerization of Diborazanes: Unexpected Observation of Metal-Free Hydrogen Transfer between Aminoboranes and Amine-Boranes
Alasdair P. M. Robertson, Erin M. Leitao and Ian Manners* School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK
Experimental All manipulations were carried out under an atmosphere of nitrogen gas using standard vacuum line and Schlenk techniques, or under an atmosphere of argon within an MBraun glovebox. All solvents were dried via a Grubbs’ type solvent purification system.1 Deuterated solvents were purchased from Sigma Aldrich Ltd and distilled from potassium (C6D6) or CaH2 (CDCl3, d8-THF). Me2NH∙BH3 and cyclohexene were purchased from Sigma Aldrich Ltd and purified by sublimation and distillation, respectively. MeNH2∙BH3, NH3∙BH3, MeNH-BH2-NHMe-BH3 and Me2ND∙BD3 were synthesized according to literature procedures,2-4 and were all sublimed prior to use. iPr2N=BH2 was synthesized via literature method and purified by distillation prior to use.5 IrH2POCOP was synthesised according to the method of Brookhart and co-workers.6 Me3N (99%, Anhydrous) and MeNH2 (‘standard' grade) were purchased from Sigma Aldrich Ltd and SIP Analytical Ltd, respectively, and were used as received. NMR spectra were recorded using JEOL JNM-ECP300 or JNM-LA300 spectrometers. Chemical shifts were reported relative to residual solvent peaks (1H and 11
standards: BF3·OEt2 ( B). Integration of
11
13
C) or to external
B NMR spectra was performed using ACD Labs
Version 9.13 with an estimated accuracy of ±5%. Gel permeation chromatography (GPC) was performed on a Viscotek VE2001 instrument, using a flow rate of 1 mL/min of THF containing 0.1 w/w % nBu4NBr, calibrated using polystyrene standards. The columns used were of grade GP5000HHR followed by GP2500HHR (Viscotek) at a constant temperature of 30 °C, and a VE 3580 refractometer was employed. GPC samples were prepared by dissolving the sample in the eluent (0.5 mg/mL) and were filtered (Acrodisc, PTFE membrane, 0.45 mm) before analysis. IR spectra were measured using a Perkin-Elmer FT-IR spectrometer. Electrospray ionisation (ESI) mass spectra were recorded using a cone potential 1
of +150 V in a THF/acetonitrile mixture on a Bruker Daltonics Apex IV Fourier transform Ion Cyclotron mass spectrometer. Chemical ionisation (CI) mass spectra were recorded on a VG Analytical AutoSpec mass spectrometer.
Reaction of MeNH2-BH2-NHMe-BH3 with IrH2POCOP: To a solution of MeNH2-BH2NHMe-BH3 (0.490 g, 5.58 mmol) in THF (0.67 mL) was added a solution of 0.3 mol % IrH2POCOP (19.8 mg, 0.033 mmol) [See footnote 7 below] in THF (0.45 mL) at 0 oC. The mixture was stirred for 5 minutes, before warming to 20 oC and stirring for a further 1.5 h. The mixture was then analyzed by 11B NMR spectroscopy which indicated the presence of a single new product with a chemical shift of 6 ppm. The mixture was then diluted with THF (2 mL) and precipitated into hexanes (150 mL) at -78 oC to yield an off-white solid, which was isolated by cannula filtration. Yield: 0.41 g, 86%, 11B NMR (96 MHz, CDCl3): δ -6.3 (br. s, BH2), 1H NMR (300 MHz, CDCl3): δ 2.83 (1H, br. s, NH), 2.24 (3H, br. s, Me), 1.71 (2H, br. s, BH2),
13
C {1H} NMR (76 MHz, CDCl3): δ 35.9 (s, CH3), GPC: Mw = 97,000 Da, PDI =
1.44. See Figs SI-1(a) and (b) for 1H and 11B NMR spectra of isolated products, and Figs SI2(a) and (b) for ESI-MS spectra. Performing an identical experiment in which 2.5 equivalents of cyclohexene (1.14 g, 13.9 mmol) were added to the reaction mixture prior to catalyst addition produced no evidence for formation of MeNH=BCy2 by 11B NMR spectroscopy. The polymeric product was isolated as previously by precipitation into hexanes for further analysis. Multinuclear NMR spectroscopy for the product proved to be identical to that described above for the polymer formed in the absence of cyclohexene. Yield: 0.40 g, 83%, GPC Mw = 180,000 Da, PDI = 1.40. Synthesis of Me3N-BH2-NMe2-BH3: To a 1 M solution of BH3∙THF (70.0 mL, 70.0 mmol) was added solid Me2NH∙BH3 (4.12 g, 70.0 mmol), and the mixture was heated to 60 oC over 48 h. The resulting solution was then vacuum transferred under cooling with liquid nitrogen to yield a ~1 M solution of Me2NB2H5 in THF. 11B NMR (THF, 96 MHz): δ -18.4 (m, BH2). To the distilled solution of Me2NB2H5 was added a 2 M solution of Me3N in THF (43.8 mL, 87.5 mmol) at -78 oC and the mixture was stirred at -78 oC for 15 minutes. The mixture was then warmed to 20 oC, and approximately 30 mL of THF removed under vacuum. Hexanes (30.0 mL) were then added, and the mixture stored at -60 oC for 24 h producing large colorless crystals. The solids were isolated at -78 oC, and dried under high vacuum at 0 o
C over 45 minutes, before storing at -40 oC. Yield: 3.0 g, 33%, 11B NMR (96 MHz, CDCl3):
δ 3.2 (t, JBH = 111 Hz, BH2), -13.0 (q, JBH = 92 Hz, BH3), 1H NMR (300 MHz, CDCl3): δ 2
2.77 (9H, s, NMe3), 2.31 (6H, s, NMe2), 1.58 (3H, br. q, BH3), 1H {11B} NMR (300 MHz, CDCl3): δ 2.77 (9H, s, NMe3), 2.31 (6H, s, NMe2), 1.77 (2H, s, BH2), 1.58 (3H, s, BH3), 13C {1H} NMR (76 MHz, CDCl3): δ 53.1 (s, NMe2), 52.1 (s, NMe3). Thermolysis of Me3N-BH2-NMe2-BH3: A solution of Me3N-BH2-NMe2-BH3 (81 mg, 0.61 mmol) in THF (2 mL) was heated to 70 oC over 18 h before cooling to 20 oC. The mixture was then analyzed by
11
B NMR spectroscopy indicating complete consumption of the
diborazane starting material to produce Me3N∙BH3 [δB -8.8 (q, JBH = 98 Hz, BH3)] and [Me2N-BH2]2 [δB 4.3 (t, JBH = 112 Hz, BH2)]. Repeating the reaction in d8-THF in this case enabled the recording of 1H and 13C {1H} NMR spectra of the reaction mixture. 1H NMR (96 MHz, d8-THF): δ 2.85 (2H, br. q, JBH = 111 Hz, [Me2N-BH2]2), 2.56 (9H, s, Me3N), 2.41 (3H, s, [Me2N-BH2]2), 1.67 (3H, br. q, JBH = 97 Hz, Me3N∙BH3), 13C {1H} NMR (76 MHz, d8-THF): δ 53.3 (s, Me3N∙BH3), 51.2 (s, [Me2N-BH2]2). Reaction of Me3N-BH2-NMe2-BH3 with IrH2POCOP: To a solution of Me3N-BH2-NMe2BH3 (0.29 g, 2.23 mmol) in THF (6 mL) was added a solution of 1 mol % IrH2POCOP (13.2 mg, 0.022 mmol) in THF (1 mL) at 20 oC. The mixture was then stirred for 6 h, and was analyzed by
11
B NMR spectroscopy at 1 h intervals over this period. After 4 h, complete
conversion to [Me2N-BH2]2 and Me3N∙BH3 was observed, with no change in composition apparent after 6 h.
11
B NMR spectroscopic characterization data is identical to that attained
for the analogous thermolytic experiment (vide supra). See Fig. SI-3 for 11B NMR spectra of crude reaction mixture.
Thermolysis of MeNH2-BH2-NHMe-BH3: A solution of MeNH2-BH2-NHMe-BH3 (62 mg, 0.71 mmol), in THF (2 mL) was heated to 70 oC over 18 h before cooling to 20 oC. The mixture was then analyzed by
11
B NMR spectroscopy indicating complete consumption of
the diborazane starting material over this period. 11B NMR (96 MHz, THF): δ 32.8 (d, JBH = 132 Hz, [MeN-BH]3) (3%), -5.2 (t, JBH = 101 Hz, [MeNH-BH2]3) (31%), -18.9 (q, JBH = 94 Hz, MeNH2∙BH3) (66%). Repeating this experiment in the presence of 2.5 equivalents of cyclohexene (0.20 mL, 1.8 mmol) led to the formation of MeNH=BCy2 (δB 44.9 ppm, [THF]) in ca. 50% yield (Calculated via integration versus the peak for MeNH2∙BH3 in the 11B NMR spectrum). See Fig. SI4 for 11B NMR spectra of crude reaction mixture.
3
Isolation of MeNH=BCy2: To a solution of MeNH2-BH2-NHMe-BH3 (0.500 g, 5.70 mmol) in THF (16 mL) was added cyclohexene (1.15 mL, 11.4 mmol) and the mixture then heated to 55 oC over 20 h before cooling to 20 oC. The mixture was then analysed by
11
B NMR
spectroscopy indicating complete consumption of the boron containing starting material. The volatile components of the mixture were then removed under high vacuum to furnish an oily solid which was subsequently extracted with hexanes (20 mL). The hexane fractions were then filtered and the volatiles removed under high vacuum to yield a colorless oil. Yield: 102 mg, 9 %, 11B NMR (96 MHz, C6D6): δ 44.7 (br.s, BCy2), 11B NMR (96 MHz, THF): δ 44.9 (br.s, BCy2), 1H NMR (300 MHz, C6D6): δ 3.21 (1H, br. s, NH), 2.16 (3H, d, JHH = 6 Hz, Me), 1.66-0.66 (22H, m, Cy),
13
C {1H} NMR (76 MHz, C6D6): δ 32.7 (s, Cy), 32.0 (s, Cy),
29.7 (s, CH3), 28.6 (s, Cy), 28.3 (s, Cy), 27.4 (s, Cy), 27.3 (s, Cy), CI-MS 207.2 M+, 70%, CI-MS – High Resolution, M+(calculated) = 207.2158, M+(Measured) = 207.2165.
Attempted Trapping of iPr2N=BH2 with Cyclohexene: To a 0.84 M solution of iPr2N=BH2 (1.0 mL, 0.84 mmol) in THF was added 2.5 equivalents of cyclohexene (0.17 g, 2.1 mmol) and the mixture stirred at 20 oC for 18 h. Analysis of the mixture by 11B NMR spectroscopy indicated solely iPr2N=BH2 in solution. The mixture was then heated to 70 oC over 18 h before analyzing again by 11B NMR spectroscopy, with no change in composition. Ir-Catalysed Polymerization of MeNH2∙BH3 in the Presence of Cyclohexene: To a solution of MeNH2∙BH3 (1.00 g, 22.3 mmol) in THF (1.35 mL) was added a solution of IrH2POCOP (39.5 mg, 0.07 mmol) in THF (0.9 mL) and cyclohexene (4.55 mL, 55.6 mmol) at 0 oC. The mixture was then stirred for 5 minutes before warming to 20 oC and then stirred for an additional 30 minutes. Analysis of the mixture by
11
B NMR spectroscopy indicated
complete conversion of MeNH2∙BH3 to [MeNH-BH2]n, with no evidence of the formation of MeNH=BCy2 (δB 44.9 ppm). The mixture was diluted with THF (4 mL) and was then precipitated into hexanes (150 mL) at -78 oC. The solid products were isolated via filter cannula and then dried for 16 h under high vacuum. Yield: 0.79 g, 83%, 11B NMR (96 MHz, CDCl3): δ -6.9 (br. s, BH2), 1H NMR (300 MHz, CDCl3): δ 2.84 (1H, br. s, NH), 2.26 (3H, br. s, Me), 1.76 (2H, br. s, BH2), 13C {1H} NMR (76 MHz, CDCl3): δ 35.9 (s, Me). Synthesis of Me3N-BH2-NHMe-BH3: To a 1 M solution of BH3∙THF (24 mL, 24 mmol) was added solid MeNH2∙BH3 (1.08 g, 24 mmol), and the mixture was then heated to 60 oC over 24
4
h. The resulting solution was then vacuum transferred under cooling with liquid nitrogen to yield a ~1 M solution of MeNHB2H5 in THF. 11B NMR (96 MHz, THF): δ -23.2 (m, BH2). To the distilled solution of MeNHB2H5 at -78 oC was added a 2 M toluene solution of Me3N (1.5 mL, 30 mmol), and the mixture stirred at this temperature for 15 minutes. The mixture was then warmed to 20 oC and stirred for 1.5 h before the removal of all volatiles under high vacuum to produce the desired product as a colorless solid. Yield: 2.6 g, 94%, 11B NMR (96 MHz, CDCl3): δ 0.1 (t, JBH = 108 Hz, BH2), -17.0 (q, JBH = 92 Hz, BH3), 1H NMR (300 MHz, CDCl3): δ 2.71 (9H, s, NMe3), 2.28 (3H, s, NHMe), 1.50 (3H, br. q, BH3), 1H {11B} NMR (300 MHz, CDCl3): δ 2.71 (9H, s, NMe3), 2.28 (3H, s, NHMe), 1.88 (1H, s, BH), 1.75 (1H, s, BH), 1.50 (3H, s, BH3),
13
C {1H} NMR (76 MHz, CDCl3): δ 51.3 (s, NMe3),
41.4 (s, NHMe). CI-MS: 115.2 (M+-H, 32), 72.1 (Me3N-BH2+, 30), 60.1 (Me3NH+, 100), 58.1 (H3BNHMeBH2+H, 84), CI-MS Accurate Mass: Calculated for M+-H (C4H17B2N2) 115.1578, Found 115.1773.
Reaction of Me3N-BH2-NHMe-BH3 with IrH2POCOP: To a solution of Me3N-BH2NHMe-BH3 (0.284 g, 2.45 mmol) in THF (6.5 mL) was added a solution of 1 mol % IrH2POCOP (14.5 mg, 0.025 mmol) in THF (0.5 mL) at 20 oC. The mixture was then stirred over 48 h, and the reaction progress monitored by
11
B NMR spectroscopy. After 6 h, the
diborazane was completely consumed, with no change in the composition of the mixture over the following 42 h. 11B NMR (96 MHz, THF): δ 32.8 (d, JBH = 134 Hz, [MeN-BH]3) (13%), 2.6 to -7.5 (various overlapping peaks, [MeNH-BH2]x) (28%), -8.5 (q, JBH = 99 Hz, Me3N∙BH3) (51%), -18.7 (br. q, MeNH2∙BH3) (8%) {Composition of the reaction mixture was determined based on integration of the respective signals in the 11B NMR spectrum}. See Fig. SI5(a) and (b) for ESI-MS spectra for isolated polymeric reaction products.
Thermolysis of Me3N-BH2-NHMe-BH3: A solution of Me3N-BH2-NHMe-BH3 (81 mg, 0.70 mmol) in THF (2 mL) was prepared, and heated to 70 oC over 16 h. The mixture was then cooled to ambient temperature and analyzed by 11B NMR spectroscopy.
11
B NMR (96 MHz,
THF): δ 32.8 (d, JBH = 134 Hz, [MeN-BH]3) (15%), 2.1 to -6.6 (various overlapping peaks, [MeNH-BH2]x) (16%), -8.5 (q, JBH = 99 Hz, Me3N∙BH3) (53%), -18.7 (q, JBH = 94 Hz, MeNH2∙BH3) (16%).{Composition of the reaction mixture was determined based on integration of the respective signals in the 11B NMR spectrum}.
5
Reaction of Me3N-BH2-NHMe-BH3 with iPr2N=BH2: To solid Me3N-BH2-NHMe-BH3 (65 mg, 0.56 mmol) was added a 0.28 M THF solution of iPr2N=BH2 (2.0 mL, 0.56 mmol). The clear, colorless mixture was then stirred at 20 oC over 18 h before analysis by
11
B NMR
11
spectroscopy. B NMR (96 MHz, THF): δ 34.6 (t, JBH = 125 Hz, iPr2N=BH2), 33.0 (appears as shoulder on peak due to iPr2N=BH2, [MeN-BH]3), 22.6 (br. s, unknown), 0.5 (t, JBH = 108 Hz, Me3N-BH2-NHMe-BH3), -8.3 (q, JBH = 97 Hz, Me3N∙BH3), -16.2 (q, JBH = 94 Hz, Me3NBH2-NHMe-BH3), -19.1 (q, JBH = 92 Hz, MeNH2∙BH3), -21.7 (q, JBH = 97 Hz, iPr2NH∙BH3). The aminoborane iPr2N=BH2 and corresponding amine-borane iPr2NH∙BH3 were found, via integration of the respective 11B NMR peaks, to be present in a 4:1 ratio. The remainder of the product mixture was as follows: [MeN-BH]3 (9%), Me3N-BH2-NHMe-BH3 (45%), Me3N∙BH3 (17%), MeNH2∙BH3 (8%) and unknowns (21%), with the composition again calculated through integration of the signals within the 11B NMR spectrum. Reaction of NH3∙BH3 with iPr2N=BH2: To solid NH3∙BH3 (0.17 g, 5.6 mmol) was added a 0.28 M THF solution of iPr2N=BH2 (20 mL, 5.6 mmol) producing a clear colorless solution. Within 5 minutes of mixing precipitation of a white solid was observed. The mixture was stirred at 20 oC for 18 h before analysis by 11B NMR spectroscopy, which indicated complete hydrogenation of iPr2N=BH3 to iPr2NH∙BH3. Almost complete consumption of NH3∙BH3 was also observed, with the only soluble products of this reaction identified as minor amounts of [NH-BH]3 and
NH2B2H5 (Based on integration of the
11
B NMR signals of the minor
products versus that of iPr2NH∙BH3, the insoluble, solid product is likely to constitute >50% of the initial boron content present as NH3∙BH3). The solid was collected by decantation of the reaction solution and washed with hexanes (50 mL) before being placed under high vacuum over 16 h. FT-IR (solids): 3228 (N-H stretch), 2294 (B-H stretch) cm-1. Separately, the volatile components of the solution were removed under high vacuum to yield a slightly white oil which was dissolved in CDCl3 for analysis by multinuclear NMR spectroscopy. 11B NMR (96 MHz, CDCl3): δ -22.4 (q, JBH = 92 Hz, iPr2NH∙BH3), 1H NMR (300 MHz, CDCl3): δ 3.23 (1H, br. s, NH), 3.15-3.00 (2H, m, CH), 1.25 (3H, br. q, BH3), 1.16-1.09 (12H, overlapping doublets, CH3), 13C {1H} NMR (76 MHz, CDCl3): δ 51.5 (s, CH), 20.3 (s, CH3), 18.3 (s, CH3). Repeating this experiment on a smaller scale (0.56 mmol of NH3∙BH3) in the presence of 2.5 equivalents of cyclohexene (0.14 mL, 1.4 mmol) led to the formation of NH2=BCy2 (δB 46.9 ppm) in 75% yield (Calculated via integration versus the peak for iPr2NH∙BH3 in the 11B NMR spectrum). 6
Reaction of MeNH2∙BH3 with iPr2N=BH2: To solid MeNH2∙BH3 (0.25 g, 5.6 mmol) was added a 0.28 M THF solution of iPr2N=BH2 (20 mL, 5.6 mmol) producing a clear colorless solution. The mixture was then stirred at 20 oC, and monitored by
11
B NMR spectroscopy
after 30 minutes, 4 h and 21 h respectively. After 30 minutes 75% conversion of iPr2N=BH2 to iPr2NH∙BH3 was observed [δB 34.6 (t, JBH, iPr2N=BH2) and -21.7 (q, JBH, iPr2NH∙BH3)], a process which reached 90% completion over 21 h at 20 oC.
Over the same period,
MeNH2∙BH3 [δB -18.6 (q, JBH = 94 Hz, BH3)] was consumed, with 36% remaining unreacted after 30 minutes, and 25% after 21 h.
11
B NMR (96 MHz, THF): δ 34.6 (t, JBH = 125 Hz,
iPr2N=BH2), 32.8 (shoulder on peaks due to iPr2N=BH2, [MeN-BH]3) (4%), -18.7 (q, JBH = 94 Hz, MeNH2∙BH3) (30%), -21.8 (q, JBH = 99 Hz, iPr2NH∙BH3), -23.1 (m, MeNHB2H5) (6%). The remaining peaks corresponding to dehydrogenation products (~35%) appear as a series of peaks between 2 and -9 ppm, which we tentatively suggest to include [MeNH-BH2]3 [-5.9 (t, JBH = 103 Hz)], and based on ESI-MS evidence (see Fig. SI-7), also [MeNH-BH2]n (~6 ppm). The remainder of the peaks in this region are however unassigned (See Fig. SI-6). No change in composition was apparent by
11
B NMR spectroscopy after stirring for a
further 30 h. Repeating this experiment on a smaller scale (0.56 mmol of MeNH2∙BH3) in the presence of 2.5 equivalents of cyclohexene (0.14 mL, 1.4 mmol) led to the formation of MeNH=BCy2 (δB 44.9 ppm) in 45% yield (Calculated via integration versus the peak for iPr2NH∙BH3 in the 11
B NMR spectrum).
Reaction of Me2NH∙BH3 with iPr2N=BH2: To solid Me2NH∙BH3 (49 mg, 0.83 mmol) was added a 0.83 M solution of iPr2N=BH2 in THF (1.00 mL, 0.83 mmol). The mixture was then stirred over 18 h at 20 oC before analysis by
11
B NMR spectroscopy was carried out.
11
B
NMR (96 MHz, THF): δ 34.7 (t, JBH = 127 Hz, iPr2N=BH2), 4.7 (t, JBH = 113 Hz, [Me2NBH2]2), -13.9 (q, JBH = 97 Hz, Me2NH∙BH3), -21.5 (q, JBH = 97 Hz, iPr2NH∙BH3). At this point, analysis of the peak integrals in the
11
B NMR spectrum indicated 54% conversion of
iPr2N=BH2 to iPr2NH∙BH3, and 58% conversion of Me2NH∙BH3 to [Me2N-BH2]2. The reaction was then allowed to stir for a further 30 h at 20 oC before further analysis by 11
B NMR spectroscopy, which indicated a change in the product distributions, but no change
in the products themselves. After this time period, conversion of iPr2N=BH2 to iPr2NH∙BH3, reached 58% and conversion of Me2NH∙BH3 to [Me2N-BH2]2, 62%.
7
This reaction was also repeated under identical conditions with monitoring by
11
B NMR
spectroscopy every hour, which confirmed a gradual consumption of the starting materials with concomitant growth of peaks corresponding to iPr2NH∙BH3 and [Me2N-BH2]2 respectively (See Fig. SI-8). To gain further mechanistic information, the reaction was also repeated using iPr2N=BH2 and Me2ND∙BD3 which led to an identical product distribution, although requiring significantly longer to reach equilibrium. Strong evidence of an initial transfer of D2 to iPr2N=BH2 to form iPr2ND∙BH2D, present as a broadened triplet at -21.5 ppm in the NMR spectrum, was observed in the
11
11
B
B NMR spectrum after 2 h (Fig. SI-11). After 18 h,
37% conversion of iPr2N=BH2 to iPr2ND∙B(H/D)3 was observed, along with 32% conversion of Me2ND∙BD3 to [Me2N-B(D/H)2]2. Scrambling of hydrogen and deuterium into all components of the reaction mixture was also apparent by
11
B NMR spectroscopy, with the
sharp triplet initially corresponding to iPr2N=BH2 rapidly being broadened into a poorly defined multiplet (See Figs. SI-10 and SI-11). Reaction of [Me2N-BH2]2 with iPr2NH∙BH3: To solid [Me2N-BH2]2 (45 mg, 0.40 mmol) was added iPr2NH∙BH3 (91 mg, 0.79 mmol) in THF (2 mL). The mixture was then stirred over 18 h at 20 oC before analysis by
11
B NMR spectroscopy was carried out.
11
B NMR
(THF, 96 MHz): δ 34.7 (t, JBH = 127 Hz, iPr2N=BH2), 4.7 (t, JBH = 113 Hz, [Me2N-BH2]2), 13.9 (q, JBH = 97 Hz, Me2NH∙BH3), -21.5 (q, JBH = 97 Hz, iPr2NH∙BH3). At this point, analysis of the peak integrals indicated 6% conversion of iPr2NH∙BH3 to iPr2N=BH2 and 7% conversion of [Me2N-BH2]2 to Me2NH∙BH3. The reaction was then allowed to stir for a further 172 h at 20 oC before further analysis by
11
B NMR spectroscopy, which indicated a change in the product distributions, but no
change in the products themselves. After this time period, 35% conversion of iPr2NH∙BH3 to iPr2N=BH2 and 38% conversion of [Me2N-BH2]2 to Me2NH∙BH3 was observed.
8
2.24
Spectroscopic Data ar127183H-3.jdf 3.0
Me
2.0
1.5
# BH2 *
N-H
0.5
#
1.71
2.82
1.0
* 6.0
5.5
5.0
4.5
4.0
3.5 3.0 Chem ical Shi ft (ppm )
2.5
2.0
1.5
1.0
0.5
-6.29
Figure SI-1(a). 1H NMR spectrum (CDCl3) of [MeNH-BH2]n isolated from the reaction of MeNH2-BH2-NHMe-BH3 and 0.3 mol % IrH2POCOP. Peaks marked * and # correspond to residual THF and hexanes respectively. ar127183_B-3.jdf 3.0
[MeNH-BH2 ]n
2.5
2.0
-19.54
Normalized Intensity
Normalized Intensity
2.5
1.5
MeNH2 ∙BH3
1.0
0.5
100
80
60
40
20
0 -20 Chem ical Shi ft (ppm )
-40
-60
-80
-100
Figure SI-1(b). 11B {1H} NMR spectrum (CDCl3) of [MeNH-BH2]n isolated from the catalytic reaction of MeNH2-BH2-NHMe-BH3 and 0.3 mol % IrH2POCOP. 9
Figure SI-2(a). ESI-MS spectrum of [MeNH-BH2]n produced from MeNH2-BH2-NHMeBH3 and 0.3 mol % IrH2POCOP. Repeat unit: 43 m/z.
Figure SI-2(b). Enlarged view of a section of the ESI-MS spectrum of [MeNH-BH2]n produced from MeNH2-BH2-NHMe-BH3 as shown in Figure SI-2(a) above.
10
.0
ar19188B-1.jdf
Me3 N∙BH3
[Me2 N-BH2 ]2
.5
.0
.5
.0
.5
0 64
56
48
40
32
24
16
8 0 -8 -1 6 Ch e m i cal Sh i ft (p p m )
-2 4
-3 2
-4 0
-4 8
-5 6
Figure SI-3. 11B {1H} NMR spectrum (THF) of the reaction of Me3N-BH2-NMe2-BH3 with 1 mol % IrH2POCOP (20 oC, 4 h).
11
-6 4
.
3.0
-18.83
el18533B-3.jdf
(D)
2.0
1.5
1.0
..(B). (C)
.
0.5
-1.97 -5.34 -6.02
44.74
Normalized Intensity
2.5
.
(A) 0
80
70
60
50
40
30
20
10 0 -10 -20 Chem ical Shi ft (ppm )
-30
-40
-50
-60
-70
-80
Figure SI-4. 11B {1H} NMR spectrum (THF) of the reaction mixture from the thermolysis of MeNH2-BH2-NHMe-BH3 (70 oC, THF), in the presence of 2.5 equiv. of cyclohexene. (A) MeNH=BCy2, (B) Unknown species, postulated to be MeNH2∙BCy3, as observed for similar reaction with NH3∙BH3,8 (C) [MeNH-BH2]3 – two isomers, (D) MeNH2∙BH3.
12
Figure SI-5(a). ESI-MS spectrum of [MeNH-BH2]x produced from the catalytic reaction of IrH2POCOP with Me3N-BH2-NHMe-BH3. The spectrum is complicated by multiple distributions of [MeNH-BH2]x, all of repeat unit: 43 m/z. These species are likely to contain different end groups.9
Figure SI-5(b). Enlarged view of a section of the ESI-MS spectrum of [MeNH-BH2]x produced from Me3N-BH2-NHMe-BH3 shown in Figure SI-5(a) above. 13
3.0
ar19323B-3.jdf
(F)
2.5
Normalized Intensity
2.0
1.5
1.0
(E) (C)
(D)
0.5
(G)
(B)
(A) 0
70
60
50
40
30
20
10 0 -10 -20 Chem ical Shi ft (ppm )
-30
-40
-50
-60
-70
Figure SI-6. 11B {1H} NMR spectrum (THF) of the reaction of MeNH2∙BH3 with iPr2N=BH2 (20 oC, THF, 18 h). (A) iPr2N=BH2, (B) [MeN-BH]3, (C) Unknowns “[MeNH-BH2]x”, (D) [MeNH-BH2]3, (E) MeNH2∙BH3, (F) iPr2NH∙BH3, (G) MeNHB2H5. The identity of the peak at 4 ppm is unknown.
14
-80
Figure SI-7(a). ESI-MS spectrum of products of reaction of MeNH2∙BH3 and iPr2N=BH2 at 20 oC in THF. Polymeric product appears to be [MeNH-BH2]x. Repeat unit: 43 m/z.
Figure SI-7(b). Enlarged view of a section of the ESI-MS spectrum of [MeNH-BH2]x shown in Figure SI-7(a) above.
15
4.5 OVERLAY.ESP
.
(C)
4.0
3.5
(B)
Normalized Intensity
3.0
(A)
(D)
2.5
2.0
(E)
1.5
1.0
0.5
40
35
30
25
Figure SI-8. Overlayed
20
11
15
10
5 0 -5 Chem ical Shi ft (ppm )
-10
-15
-20
-25
-30
-35
-40
B {1H} NMR (THF) spectra of the reaction of iPr2N=BH2 with
Me2NH∙BH3 (20 oC, THF). Foremost spectrum corresponds to Time = 0 h, with subsequent spectra recorded at 1 h intervals up to 12 h. (A) iPr2N=BH2, (B) [Me2N-BH2]2, (C) Me2NH∙BH3, (D) iPr2NH∙BH3, (E) Me2N=BH2.
16
3.0
ar91513B-3.jdf
2.5
2.0
1.5
1.0
0.5
(i) (ii)
0 56
48
40
32
Figure SI-9. Overlayed
24
11
16 8 Chem ical Shi ft (ppm )
0
-8
-16
-24
-32
B {1H} NMR spectra of (i) the reaction of iPr2N=BH2 and
Me2NH∙BH3 (20 oC, THF, 48 h), and (ii) the reaction of iPr2NH∙BH3 and ½[Me2N-BH2]2 (20 o
C, THF, 190 h). The spectrum for (ii) is offset for clarity.
17
3.0
el91651B-6.jdf
2.5
Normalized Intensity
2.0
1.5
(B)
(A) 1.0
0.5
0 64
56
48
40
32
24
16 8 0 Chem ical Shi ft (ppm )
-8
-16
-24
-32
-40
Figure SI-10. 11B NMR spectrum (THF) of reaction of iPr2N=BH2 with Me2ND∙BD3 (20 oC, THF, Time = 0 h): (A) iPr2N=BH2, (B) Me2ND∙BD3. 3.0
el19660B-6.jdf
(C) 2.5
Normalized Intensity
2.0
1.5
(A) 1.0
0.5
(D)
(B) 0 64
56
48
40
32
24
16 8 0 Chem ical Shi ft (ppm )
-8
-16
-24
-32
-40
-48
Figure SI-11. 11B NMR spectrum (THF) of reaction of iPr2N=BH2 with Me2ND∙BD3 (20 oC, THF, Time = 2 h): (A) iPr2N=B(H/D)2, (B) [Me2N-B(H/D)2]2, (C) Me2ND∙B(H/D)3, (D) iPr2ND∙B(H/D)3 18
References (1) (2) (3) (4) (5) (6) (7)
(8) (9)
Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.; Timmers, F. J. Organometallics, 1996, 15, 1518. Jaska, C. A.; Temple, K.; Lough, A. J.; Manners, I. J. Am. Chem. Soc. 2003, 125, 9424. Johnson, H. C.; Robertson, A. P. M.; Chaplin, A. B.; Sewell, L. J.; Thompson, A. L.; Haddow, M. F.; Manners, I.; Weller, A. S. J. Am. Chem. Soc. 2011, 133, 11076. Sloan, M. E.; Staubitz, A.; Clark, T. J.; Russell, C. A.; Lloyd-Jones, G. C.; Manners, I. J. Am. Chem. Soc. 2010, 132, 3831. Pasumansky, L.; Haddenham, D.; Clary, J. W.; Fisher, G. B.; Goralski, C. T.; Singaram, B. J. Org. Chem. 2008, 73, 1898. Göttker-Schnetmann, I.; White, P. S.; Brookhart, M. Organometallics. 2004, 23, 1766. In this case a catalyst loading of 0.6 mol % was used relative to the initial diborazane. However as this compound is notionally dimeric, this is a 0.3 mol % loading with respect to the polymerizable components MeNH=BH2 and MeNH2∙BH3 which it redistributes to form. We felt therefore that the polymerization of this substrate was more accurately described as 0.3 mol % in Ir, as discussed in the manuscript. This loading was selected to enable a direct comparison with the previously reported polymerization of MeNH2∙BH3 with 0.3 mol % IrH2POCOP (See ref. 9). All other catalyst loadings are calculated versus the diborazane itself, as within the other diborazanes, e.g. Me3N-BH2-NHMe-BH3, only one polymerizable component is present. Pons, V.; Baker, R. T.; Szymczak, N. K.; Heldebrant, D. J.; Linehan, J. C.; Matus, M. H.; Grant, D. J.; Dixon, D. A. Chem. Commun. 2008, 6597. Staubitz, A.; Sloan, M. E.; Robertson, A. P. M.; Friedrich, A.; Schneider, S.; Gates, P. J.; Schmedt auf der Günne, J.; Manners, I. J. Am. Chem. Soc. 2010, 132, 13332.
19
Catalytic Redistribution and Polymerization of Diborazanes: Unexpected Observation of Metal-Free Hydrogen Transfer between Aminoboranes and Amine-Boranes
Alasdair P. M. Robertson, Erin M. Leitao and Ian Manners* School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK
Experimental All manipulations were carried out under an atmosphere of nitrogen gas using standard vacuum line and Schlenk techniques, or under an atmosphere of argon within an MBraun glovebox. All solvents were dried via a Grubbs’ type solvent purification system.1 Deuterated solvents were purchased from Sigma Aldrich Ltd and distilled from potassium (C6D6) or CaH2 (CDCl3, d8-THF). Me2NH∙BH3 and cyclohexene were purchased from Sigma Aldrich Ltd and purified by sublimation and distillation, respectively. MeNH2∙BH3, NH3∙BH3, MeNH-BH2-NHMe-BH3 and Me2ND∙BD3 were synthesized according to literature procedures,2-4 and were all sublimed prior to use. iPr2N=BH2 was synthesized via literature method and purified by distillation prior to use.5 IrH2POCOP was synthesised according to the method of Brookhart and co-workers.6 Me3N (99%, Anhydrous) and MeNH2 (‘standard' grade) were purchased from Sigma Aldrich Ltd and SIP Analytical Ltd, respectively, and were used as received. NMR spectra were recorded using JEOL JNM-ECP300 or JNM-LA300 spectrometers. Chemical shifts were reported relative to residual solvent peaks (1H and 11
standards: BF3·OEt2 ( B). Integration of
11
13
C) or to external
B NMR spectra was performed using ACD Labs
Version 9.13 with an estimated accuracy of ±5%. Gel permeation chromatography (GPC) was performed on a Viscotek VE2001 instrument, using a flow rate of 1 mL/min of THF containing 0.1 w/w % nBu4NBr, calibrated using polystyrene standards. The columns used were of grade GP5000HHR followed by GP2500HHR (Viscotek) at a constant temperature of 30 °C, and a VE 3580 refractometer was employed. GPC samples were prepared by dissolving the sample in the eluent (0.5 mg/mL) and were filtered (Acrodisc, PTFE membrane, 0.45 mm) before analysis. IR spectra were measured using a Perkin-Elmer FT-IR spectrometer. Electrospray ionisation (ESI) mass spectra were recorded using a cone potential 1
of +150 V in a THF/acetonitrile mixture on a Bruker Daltonics Apex IV Fourier transform Ion Cyclotron mass spectrometer. Chemical ionisation (CI) mass spectra were recorded on a VG Analytical AutoSpec mass spectrometer.
Reaction of MeNH2-BH2-NHMe-BH3 with IrH2POCOP: To a solution of MeNH2-BH2NHMe-BH3 (0.490 g, 5.58 mmol) in THF (0.67 mL) was added a solution of 0.3 mol % IrH2POCOP (19.8 mg, 0.033 mmol) [See footnote 7 below] in THF (0.45 mL) at 0 oC. The mixture was stirred for 5 minutes, before warming to 20 oC and stirring for a further 1.5 h. The mixture was then analyzed by 11B NMR spectroscopy which indicated the presence of a single new product with a chemical shift of 6 ppm. The mixture was then diluted with THF (2 mL) and precipitated into hexanes (150 mL) at -78 oC to yield an off-white solid, which was isolated by cannula filtration. Yield: 0.41 g, 86%, 11B NMR (96 MHz, CDCl3): δ -6.3 (br. s, BH2), 1H NMR (300 MHz, CDCl3): δ 2.83 (1H, br. s, NH), 2.24 (3H, br. s, Me), 1.71 (2H, br. s, BH2),
13
C {1H} NMR (76 MHz, CDCl3): δ 35.9 (s, CH3), GPC: Mw = 97,000 Da, PDI =
1.44. See Figs SI-1(a) and (b) for 1H and 11B NMR spectra of isolated products, and Figs SI2(a) and (b) for ESI-MS spectra. Performing an identical experiment in which 2.5 equivalents of cyclohexene (1.14 g, 13.9 mmol) were added to the reaction mixture prior to catalyst addition produced no evidence for formation of MeNH=BCy2 by 11B NMR spectroscopy. The polymeric product was isolated as previously by precipitation into hexanes for further analysis. Multinuclear NMR spectroscopy for the product proved to be identical to that described above for the polymer formed in the absence of cyclohexene. Yield: 0.40 g, 83%, GPC Mw = 180,000 Da, PDI = 1.40. Synthesis of Me3N-BH2-NMe2-BH3: To a 1 M solution of BH3∙THF (70.0 mL, 70.0 mmol) was added solid Me2NH∙BH3 (4.12 g, 70.0 mmol), and the mixture was heated to 60 oC over 48 h. The resulting solution was then vacuum transferred under cooling with liquid nitrogen to yield a ~1 M solution of Me2NB2H5 in THF. 11B NMR (THF, 96 MHz): δ -18.4 (m, BH2). To the distilled solution of Me2NB2H5 was added a 2 M solution of Me3N in THF (43.8 mL, 87.5 mmol) at -78 oC and the mixture was stirred at -78 oC for 15 minutes. The mixture was then warmed to 20 oC, and approximately 30 mL of THF removed under vacuum. Hexanes (30.0 mL) were then added, and the mixture stored at -60 oC for 24 h producing large colorless crystals. The solids were isolated at -78 oC, and dried under high vacuum at 0 o
C over 45 minutes, before storing at -40 oC. Yield: 3.0 g, 33%, 11B NMR (96 MHz, CDCl3):
δ 3.2 (t, JBH = 111 Hz, BH2), -13.0 (q, JBH = 92 Hz, BH3), 1H NMR (300 MHz, CDCl3): δ 2
2.77 (9H, s, NMe3), 2.31 (6H, s, NMe2), 1.58 (3H, br. q, BH3), 1H {11B} NMR (300 MHz, CDCl3): δ 2.77 (9H, s, NMe3), 2.31 (6H, s, NMe2), 1.77 (2H, s, BH2), 1.58 (3H, s, BH3), 13C {1H} NMR (76 MHz, CDCl3): δ 53.1 (s, NMe2), 52.1 (s, NMe3). Thermolysis of Me3N-BH2-NMe2-BH3: A solution of Me3N-BH2-NMe2-BH3 (81 mg, 0.61 mmol) in THF (2 mL) was heated to 70 oC over 18 h before cooling to 20 oC. The mixture was then analyzed by
11
B NMR spectroscopy indicating complete consumption of the
diborazane starting material to produce Me3N∙BH3 [δB -8.8 (q, JBH = 98 Hz, BH3)] and [Me2N-BH2]2 [δB 4.3 (t, JBH = 112 Hz, BH2)]. Repeating the reaction in d8-THF in this case enabled the recording of 1H and 13C {1H} NMR spectra of the reaction mixture. 1H NMR (96 MHz, d8-THF): δ 2.85 (2H, br. q, JBH = 111 Hz, [Me2N-BH2]2), 2.56 (9H, s, Me3N), 2.41 (3H, s, [Me2N-BH2]2), 1.67 (3H, br. q, JBH = 97 Hz, Me3N∙BH3), 13C {1H} NMR (76 MHz, d8-THF): δ 53.3 (s, Me3N∙BH3), 51.2 (s, [Me2N-BH2]2). Reaction of Me3N-BH2-NMe2-BH3 with IrH2POCOP: To a solution of Me3N-BH2-NMe2BH3 (0.29 g, 2.23 mmol) in THF (6 mL) was added a solution of 1 mol % IrH2POCOP (13.2 mg, 0.022 mmol) in THF (1 mL) at 20 oC. The mixture was then stirred for 6 h, and was analyzed by
11
B NMR spectroscopy at 1 h intervals over this period. After 4 h, complete
conversion to [Me2N-BH2]2 and Me3N∙BH3 was observed, with no change in composition apparent after 6 h.
11
B NMR spectroscopic characterization data is identical to that attained
for the analogous thermolytic experiment (vide supra). See Fig. SI-3 for 11B NMR spectra of crude reaction mixture.
Thermolysis of MeNH2-BH2-NHMe-BH3: A solution of MeNH2-BH2-NHMe-BH3 (62 mg, 0.71 mmol), in THF (2 mL) was heated to 70 oC over 18 h before cooling to 20 oC. The mixture was then analyzed by
11
B NMR spectroscopy indicating complete consumption of
the diborazane starting material over this period. 11B NMR (96 MHz, THF): δ 32.8 (d, JBH = 132 Hz, [MeN-BH]3) (3%), -5.2 (t, JBH = 101 Hz, [MeNH-BH2]3) (31%), -18.9 (q, JBH = 94 Hz, MeNH2∙BH3) (66%). Repeating this experiment in the presence of 2.5 equivalents of cyclohexene (0.20 mL, 1.8 mmol) led to the formation of MeNH=BCy2 (δB 44.9 ppm, [THF]) in ca. 50% yield (Calculated via integration versus the peak for MeNH2∙BH3 in the 11B NMR spectrum). See Fig. SI4 for 11B NMR spectra of crude reaction mixture.
3
Isolation of MeNH=BCy2: To a solution of MeNH2-BH2-NHMe-BH3 (0.500 g, 5.70 mmol) in THF (16 mL) was added cyclohexene (1.15 mL, 11.4 mmol) and the mixture then heated to 55 oC over 20 h before cooling to 20 oC. The mixture was then analysed by
11
B NMR
spectroscopy indicating complete consumption of the boron containing starting material. The volatile components of the mixture were then removed under high vacuum to furnish an oily solid which was subsequently extracted with hexanes (20 mL). The hexane fractions were then filtered and the volatiles removed under high vacuum to yield a colorless oil. Yield: 102 mg, 9 %, 11B NMR (96 MHz, C6D6): δ 44.7 (br.s, BCy2), 11B NMR (96 MHz, THF): δ 44.9 (br.s, BCy2), 1H NMR (300 MHz, C6D6): δ 3.21 (1H, br. s, NH), 2.16 (3H, d, JHH = 6 Hz, Me), 1.66-0.66 (22H, m, Cy),
13
C {1H} NMR (76 MHz, C6D6): δ 32.7 (s, Cy), 32.0 (s, Cy),
29.7 (s, CH3), 28.6 (s, Cy), 28.3 (s, Cy), 27.4 (s, Cy), 27.3 (s, Cy), CI-MS 207.2 M+, 70%, CI-MS – High Resolution, M+(calculated) = 207.2158, M+(Measured) = 207.2165.
Attempted Trapping of iPr2N=BH2 with Cyclohexene: To a 0.84 M solution of iPr2N=BH2 (1.0 mL, 0.84 mmol) in THF was added 2.5 equivalents of cyclohexene (0.17 g, 2.1 mmol) and the mixture stirred at 20 oC for 18 h. Analysis of the mixture by 11B NMR spectroscopy indicated solely iPr2N=BH2 in solution. The mixture was then heated to 70 oC over 18 h before analyzing again by 11B NMR spectroscopy, with no change in composition. Ir-Catalysed Polymerization of MeNH2∙BH3 in the Presence of Cyclohexene: To a solution of MeNH2∙BH3 (1.00 g, 22.3 mmol) in THF (1.35 mL) was added a solution of IrH2POCOP (39.5 mg, 0.07 mmol) in THF (0.9 mL) and cyclohexene (4.55 mL, 55.6 mmol) at 0 oC. The mixture was then stirred for 5 minutes before warming to 20 oC and then stirred for an additional 30 minutes. Analysis of the mixture by
11
B NMR spectroscopy indicated
complete conversion of MeNH2∙BH3 to [MeNH-BH2]n, with no evidence of the formation of MeNH=BCy2 (δB 44.9 ppm). The mixture was diluted with THF (4 mL) and was then precipitated into hexanes (150 mL) at -78 oC. The solid products were isolated via filter cannula and then dried for 16 h under high vacuum. Yield: 0.79 g, 83%, 11B NMR (96 MHz, CDCl3): δ -6.9 (br. s, BH2), 1H NMR (300 MHz, CDCl3): δ 2.84 (1H, br. s, NH), 2.26 (3H, br. s, Me), 1.76 (2H, br. s, BH2), 13C {1H} NMR (76 MHz, CDCl3): δ 35.9 (s, Me). Synthesis of Me3N-BH2-NHMe-BH3: To a 1 M solution of BH3∙THF (24 mL, 24 mmol) was added solid MeNH2∙BH3 (1.08 g, 24 mmol), and the mixture was then heated to 60 oC over 24
4
h. The resulting solution was then vacuum transferred under cooling with liquid nitrogen to yield a ~1 M solution of MeNHB2H5 in THF. 11B NMR (96 MHz, THF): δ -23.2 (m, BH2). To the distilled solution of MeNHB2H5 at -78 oC was added a 2 M toluene solution of Me3N (1.5 mL, 30 mmol), and the mixture stirred at this temperature for 15 minutes. The mixture was then warmed to 20 oC and stirred for 1.5 h before the removal of all volatiles under high vacuum to produce the desired product as a colorless solid. Yield: 2.6 g, 94%, 11B NMR (96 MHz, CDCl3): δ 0.1 (t, JBH = 108 Hz, BH2), -17.0 (q, JBH = 92 Hz, BH3), 1H NMR (300 MHz, CDCl3): δ 2.71 (9H, s, NMe3), 2.28 (3H, s, NHMe), 1.50 (3H, br. q, BH3), 1H {11B} NMR (300 MHz, CDCl3): δ 2.71 (9H, s, NMe3), 2.28 (3H, s, NHMe), 1.88 (1H, s, BH), 1.75 (1H, s, BH), 1.50 (3H, s, BH3),
13
C {1H} NMR (76 MHz, CDCl3): δ 51.3 (s, NMe3),
41.4 (s, NHMe). CI-MS: 115.2 (M+-H, 32), 72.1 (Me3N-BH2+, 30), 60.1 (Me3NH+, 100), 58.1 (H3BNHMeBH2+H, 84), CI-MS Accurate Mass: Calculated for M+-H (C4H17B2N2) 115.1578, Found 115.1773.
Reaction of Me3N-BH2-NHMe-BH3 with IrH2POCOP: To a solution of Me3N-BH2NHMe-BH3 (0.284 g, 2.45 mmol) in THF (6.5 mL) was added a solution of 1 mol % IrH2POCOP (14.5 mg, 0.025 mmol) in THF (0.5 mL) at 20 oC. The mixture was then stirred over 48 h, and the reaction progress monitored by
11
B NMR spectroscopy. After 6 h, the
diborazane was completely consumed, with no change in the composition of the mixture over the following 42 h. 11B NMR (96 MHz, THF): δ 32.8 (d, JBH = 134 Hz, [MeN-BH]3) (13%), 2.6 to -7.5 (various overlapping peaks, [MeNH-BH2]x) (28%), -8.5 (q, JBH = 99 Hz, Me3N∙BH3) (51%), -18.7 (br. q, MeNH2∙BH3) (8%) {Composition of the reaction mixture was determined based on integration of the respective signals in the 11B NMR spectrum}. See Fig. SI5(a) and (b) for ESI-MS spectra for isolated polymeric reaction products.
Thermolysis of Me3N-BH2-NHMe-BH3: A solution of Me3N-BH2-NHMe-BH3 (81 mg, 0.70 mmol) in THF (2 mL) was prepared, and heated to 70 oC over 16 h. The mixture was then cooled to ambient temperature and analyzed by 11B NMR spectroscopy.
11
B NMR (96 MHz,
THF): δ 32.8 (d, JBH = 134 Hz, [MeN-BH]3) (15%), 2.1 to -6.6 (various overlapping peaks, [MeNH-BH2]x) (16%), -8.5 (q, JBH = 99 Hz, Me3N∙BH3) (53%), -18.7 (q, JBH = 94 Hz, MeNH2∙BH3) (16%).{Composition of the reaction mixture was determined based on integration of the respective signals in the 11B NMR spectrum}.
5
Reaction of Me3N-BH2-NHMe-BH3 with iPr2N=BH2: To solid Me3N-BH2-NHMe-BH3 (65 mg, 0.56 mmol) was added a 0.28 M THF solution of iPr2N=BH2 (2.0 mL, 0.56 mmol). The clear, colorless mixture was then stirred at 20 oC over 18 h before analysis by
11
B NMR
11
spectroscopy. B NMR (96 MHz, THF): δ 34.6 (t, JBH = 125 Hz, iPr2N=BH2), 33.0 (appears as shoulder on peak due to iPr2N=BH2, [MeN-BH]3), 22.6 (br. s, unknown), 0.5 (t, JBH = 108 Hz, Me3N-BH2-NHMe-BH3), -8.3 (q, JBH = 97 Hz, Me3N∙BH3), -16.2 (q, JBH = 94 Hz, Me3NBH2-NHMe-BH3), -19.1 (q, JBH = 92 Hz, MeNH2∙BH3), -21.7 (q, JBH = 97 Hz, iPr2NH∙BH3). The aminoborane iPr2N=BH2 and corresponding amine-borane iPr2NH∙BH3 were found, via integration of the respective 11B NMR peaks, to be present in a 4:1 ratio. The remainder of the product mixture was as follows: [MeN-BH]3 (9%), Me3N-BH2-NHMe-BH3 (45%), Me3N∙BH3 (17%), MeNH2∙BH3 (8%) and unknowns (21%), with the composition again calculated through integration of the signals within the 11B NMR spectrum. Reaction of NH3∙BH3 with iPr2N=BH2: To solid NH3∙BH3 (0.17 g, 5.6 mmol) was added a 0.28 M THF solution of iPr2N=BH2 (20 mL, 5.6 mmol) producing a clear colorless solution. Within 5 minutes of mixing precipitation of a white solid was observed. The mixture was stirred at 20 oC for 18 h before analysis by 11B NMR spectroscopy, which indicated complete hydrogenation of iPr2N=BH3 to iPr2NH∙BH3. Almost complete consumption of NH3∙BH3 was also observed, with the only soluble products of this reaction identified as minor amounts of [NH-BH]3 and
NH2B2H5 (Based on integration of the
11
B NMR signals of the minor
products versus that of iPr2NH∙BH3, the insoluble, solid product is likely to constitute >50% of the initial boron content present as NH3∙BH3). The solid was collected by decantation of the reaction solution and washed with hexanes (50 mL) before being placed under high vacuum over 16 h. FT-IR (solids): 3228 (N-H stretch), 2294 (B-H stretch) cm-1. Separately, the volatile components of the solution were removed under high vacuum to yield a slightly white oil which was dissolved in CDCl3 for analysis by multinuclear NMR spectroscopy. 11B NMR (96 MHz, CDCl3): δ -22.4 (q, JBH = 92 Hz, iPr2NH∙BH3), 1H NMR (300 MHz, CDCl3): δ 3.23 (1H, br. s, NH), 3.15-3.00 (2H, m, CH), 1.25 (3H, br. q, BH3), 1.16-1.09 (12H, overlapping doublets, CH3), 13C {1H} NMR (76 MHz, CDCl3): δ 51.5 (s, CH), 20.3 (s, CH3), 18.3 (s, CH3). Repeating this experiment on a smaller scale (0.56 mmol of NH3∙BH3) in the presence of 2.5 equivalents of cyclohexene (0.14 mL, 1.4 mmol) led to the formation of NH2=BCy2 (δB 46.9 ppm) in 75% yield (Calculated via integration versus the peak for iPr2NH∙BH3 in the 11B NMR spectrum). 6
Reaction of MeNH2∙BH3 with iPr2N=BH2: To solid MeNH2∙BH3 (0.25 g, 5.6 mmol) was added a 0.28 M THF solution of iPr2N=BH2 (20 mL, 5.6 mmol) producing a clear colorless solution. The mixture was then stirred at 20 oC, and monitored by
11
B NMR spectroscopy
after 30 minutes, 4 h and 21 h respectively. After 30 minutes 75% conversion of iPr2N=BH2 to iPr2NH∙BH3 was observed [δB 34.6 (t, JBH, iPr2N=BH2) and -21.7 (q, JBH, iPr2NH∙BH3)], a process which reached 90% completion over 21 h at 20 oC.
Over the same period,
MeNH2∙BH3 [δB -18.6 (q, JBH = 94 Hz, BH3)] was consumed, with 36% remaining unreacted after 30 minutes, and 25% after 21 h.
11
B NMR (96 MHz, THF): δ 34.6 (t, JBH = 125 Hz,
iPr2N=BH2), 32.8 (shoulder on peaks due to iPr2N=BH2, [MeN-BH]3) (4%), -18.7 (q, JBH = 94 Hz, MeNH2∙BH3) (30%), -21.8 (q, JBH = 99 Hz, iPr2NH∙BH3), -23.1 (m, MeNHB2H5) (6%). The remaining peaks corresponding to dehydrogenation products (~35%) appear as a series of peaks between 2 and -9 ppm, which we tentatively suggest to include [MeNH-BH2]3 [-5.9 (t, JBH = 103 Hz)], and based on ESI-MS evidence (see Fig. SI-7), also [MeNH-BH2]n (~6 ppm). The remainder of the peaks in this region are however unassigned (See Fig. SI-6). No change in composition was apparent by
11
B NMR spectroscopy after stirring for a
further 30 h. Repeating this experiment on a smaller scale (0.56 mmol of MeNH2∙BH3) in the presence of 2.5 equivalents of cyclohexene (0.14 mL, 1.4 mmol) led to the formation of MeNH=BCy2 (δB 44.9 ppm) in 45% yield (Calculated via integration versus the peak for iPr2NH∙BH3 in the 11
B NMR spectrum).
Reaction of Me2NH∙BH3 with iPr2N=BH2: To solid Me2NH∙BH3 (49 mg, 0.83 mmol) was added a 0.83 M solution of iPr2N=BH2 in THF (1.00 mL, 0.83 mmol). The mixture was then stirred over 18 h at 20 oC before analysis by
11
B NMR spectroscopy was carried out.
11
B
NMR (96 MHz, THF): δ 34.7 (t, JBH = 127 Hz, iPr2N=BH2), 4.7 (t, JBH = 113 Hz, [Me2NBH2]2), -13.9 (q, JBH = 97 Hz, Me2NH∙BH3), -21.5 (q, JBH = 97 Hz, iPr2NH∙BH3). At this point, analysis of the peak integrals in the
11
B NMR spectrum indicated 54% conversion of
iPr2N=BH2 to iPr2NH∙BH3, and 58% conversion of Me2NH∙BH3 to [Me2N-BH2]2. The reaction was then allowed to stir for a further 30 h at 20 oC before further analysis by 11
B NMR spectroscopy, which indicated a change in the product distributions, but no change
in the products themselves. After this time period, conversion of iPr2N=BH2 to iPr2NH∙BH3, reached 58% and conversion of Me2NH∙BH3 to [Me2N-BH2]2, 62%.
7
This reaction was also repeated under identical conditions with monitoring by
11
B NMR
spectroscopy every hour, which confirmed a gradual consumption of the starting materials with concomitant growth of peaks corresponding to iPr2NH∙BH3 and [Me2N-BH2]2 respectively (See Fig. SI-8). To gain further mechanistic information, the reaction was also repeated using iPr2N=BH2 and Me2ND∙BD3 which led to an identical product distribution, although requiring significantly longer to reach equilibrium. Strong evidence of an initial transfer of D2 to iPr2N=BH2 to form iPr2ND∙BH2D, present as a broadened triplet at -21.5 ppm in the NMR spectrum, was observed in the
11
11
B
B NMR spectrum after 2 h (Fig. SI-11). After 18 h,
37% conversion of iPr2N=BH2 to iPr2ND∙B(H/D)3 was observed, along with 32% conversion of Me2ND∙BD3 to [Me2N-B(D/H)2]2. Scrambling of hydrogen and deuterium into all components of the reaction mixture was also apparent by
11
B NMR spectroscopy, with the
sharp triplet initially corresponding to iPr2N=BH2 rapidly being broadened into a poorly defined multiplet (See Figs. SI-10 and SI-11). Reaction of [Me2N-BH2]2 with iPr2NH∙BH3: To solid [Me2N-BH2]2 (45 mg, 0.40 mmol) was added iPr2NH∙BH3 (91 mg, 0.79 mmol) in THF (2 mL). The mixture was then stirred over 18 h at 20 oC before analysis by
11
B NMR spectroscopy was carried out.
11
B NMR
(THF, 96 MHz): δ 34.7 (t, JBH = 127 Hz, iPr2N=BH2), 4.7 (t, JBH = 113 Hz, [Me2N-BH2]2), 13.9 (q, JBH = 97 Hz, Me2NH∙BH3), -21.5 (q, JBH = 97 Hz, iPr2NH∙BH3). At this point, analysis of the peak integrals indicated 6% conversion of iPr2NH∙BH3 to iPr2N=BH2 and 7% conversion of [Me2N-BH2]2 to Me2NH∙BH3. The reaction was then allowed to stir for a further 172 h at 20 oC before further analysis by
11
B NMR spectroscopy, which indicated a change in the product distributions, but no
change in the products themselves. After this time period, 35% conversion of iPr2NH∙BH3 to iPr2N=BH2 and 38% conversion of [Me2N-BH2]2 to Me2NH∙BH3 was observed.
8
2.24
Spectroscopic Data ar127183H-3.jdf 3.0
Me
2.0
1.5
# BH2 *
N-H
0.5
#
1.71
2.82
1.0
* 6.0
5.5
5.0
4.5
4.0
3.5 3.0 Chem ical Shi ft (ppm )
2.5
2.0
1.5
1.0
0.5
-6.29
Figure SI-1(a). 1H NMR spectrum (CDCl3) of [MeNH-BH2]n isolated from the reaction of MeNH2-BH2-NHMe-BH3 and 0.3 mol % IrH2POCOP. Peaks marked * and # correspond to residual THF and hexanes respectively. ar127183_B-3.jdf 3.0
[MeNH-BH2 ]n
2.5
2.0
-19.54
Normalized Intensity
Normalized Intensity
2.5
1.5
MeNH2 ∙BH3
1.0
0.5
100
80
60
40
20
0 -20 Chem ical Shi ft (ppm )
-40
-60
-80
-100
Figure SI-1(b). 11B {1H} NMR spectrum (CDCl3) of [MeNH-BH2]n isolated from the catalytic reaction of MeNH2-BH2-NHMe-BH3 and 0.3 mol % IrH2POCOP. 9
Figure SI-2(a). ESI-MS spectrum of [MeNH-BH2]n produced from MeNH2-BH2-NHMeBH3 and 0.3 mol % IrH2POCOP. Repeat unit: 43 m/z.
Figure SI-2(b). Enlarged view of a section of the ESI-MS spectrum of [MeNH-BH2]n produced from MeNH2-BH2-NHMe-BH3 as shown in Figure SI-2(a) above.
10
.0
ar19188B-1.jdf
Me3 N∙BH3
[Me2 N-BH2 ]2
.5
.0
.5
.0
.5
0 64
56
48
40
32
24
16
8 0 -8 -1 6 Ch e m i cal Sh i ft (p p m )
-2 4
-3 2
-4 0
-4 8
-5 6
Figure SI-3. 11B {1H} NMR spectrum (THF) of the reaction of Me3N-BH2-NMe2-BH3 with 1 mol % IrH2POCOP (20 oC, 4 h).
11
-6 4
.
3.0
-18.83
el18533B-3.jdf
(D)
2.0
1.5
1.0
..(B). (C)
.
0.5
-1.97 -5.34 -6.02
44.74
Normalized Intensity
2.5
.
(A) 0
80
70
60
50
40
30
20
10 0 -10 -20 Chem ical Shi ft (ppm )
-30
-40
-50
-60
-70
-80
Figure SI-4. 11B {1H} NMR spectrum (THF) of the reaction mixture from the thermolysis of MeNH2-BH2-NHMe-BH3 (70 oC, THF), in the presence of 2.5 equiv. of cyclohexene. (A) MeNH=BCy2, (B) Unknown species, postulated to be MeNH2∙BCy3, as observed for similar reaction with NH3∙BH3,8 (C) [MeNH-BH2]3 – two isomers, (D) MeNH2∙BH3.
12
Figure SI-5(a). ESI-MS spectrum of [MeNH-BH2]x produced from the catalytic reaction of IrH2POCOP with Me3N-BH2-NHMe-BH3. The spectrum is complicated by multiple distributions of [MeNH-BH2]x, all of repeat unit: 43 m/z. These species are likely to contain different end groups.9
Figure SI-5(b). Enlarged view of a section of the ESI-MS spectrum of [MeNH-BH2]x produced from Me3N-BH2-NHMe-BH3 shown in Figure SI-5(a) above. 13
3.0
ar19323B-3.jdf
(F)
2.5
Normalized Intensity
2.0
1.5
1.0
(E) (C)
(D)
0.5
(G)
(B)
(A) 0
70
60
50
40
30
20
10 0 -10 -20 Chem ical Shi ft (ppm )
-30
-40
-50
-60
-70
Figure SI-6. 11B {1H} NMR spectrum (THF) of the reaction of MeNH2∙BH3 with iPr2N=BH2 (20 oC, THF, 18 h). (A) iPr2N=BH2, (B) [MeN-BH]3, (C) Unknowns “[MeNH-BH2]x”, (D) [MeNH-BH2]3, (E) MeNH2∙BH3, (F) iPr2NH∙BH3, (G) MeNHB2H5. The identity of the peak at 4 ppm is unknown.
14
-80
Figure SI-7(a). ESI-MS spectrum of products of reaction of MeNH2∙BH3 and iPr2N=BH2 at 20 oC in THF. Polymeric product appears to be [MeNH-BH2]x. Repeat unit: 43 m/z.
Figure SI-7(b). Enlarged view of a section of the ESI-MS spectrum of [MeNH-BH2]x shown in Figure SI-7(a) above.
15
4.5 OVERLAY.ESP
.
(C)
4.0
3.5
(B)
Normalized Intensity
3.0
(A)
(D)
2.5
2.0
(E)
1.5
1.0
0.5
40
35
30
25
Figure SI-8. Overlayed
20
11
15
10
5 0 -5 Chem ical Shi ft (ppm )
-10
-15
-20
-25
-30
-35
-40
B {1H} NMR (THF) spectra of the reaction of iPr2N=BH2 with
Me2NH∙BH3 (20 oC, THF). Foremost spectrum corresponds to Time = 0 h, with subsequent spectra recorded at 1 h intervals up to 12 h. (A) iPr2N=BH2, (B) [Me2N-BH2]2, (C) Me2NH∙BH3, (D) iPr2NH∙BH3, (E) Me2N=BH2.
16
3.0
ar91513B-3.jdf
2.5
2.0
1.5
1.0
0.5
(i) (ii)
0 56
48
40
32
Figure SI-9. Overlayed
24
11
16 8 Chem ical Shi ft (ppm )
0
-8
-16
-24
-32
B {1H} NMR spectra of (i) the reaction of iPr2N=BH2 and
Me2NH∙BH3 (20 oC, THF, 48 h), and (ii) the reaction of iPr2NH∙BH3 and ½[Me2N-BH2]2 (20 o
C, THF, 190 h). The spectrum for (ii) is offset for clarity.
17
3.0
el91651B-6.jdf
2.5
Normalized Intensity
2.0
1.5
(B)
(A) 1.0
0.5
0 64
56
48
40
32
24
16 8 0 Chem ical Shi ft (ppm )
-8
-16
-24
-32
-40
Figure SI-10. 11B NMR spectrum (THF) of reaction of iPr2N=BH2 with Me2ND∙BD3 (20 oC, THF, Time = 0 h): (A) iPr2N=BH2, (B) Me2ND∙BD3. 3.0
el19660B-6.jdf
(C) 2.5
Normalized Intensity
2.0
1.5
(A) 1.0
0.5
(D)
(B) 0 64
56
48
40
32
24
16 8 0 Chem ical Shi ft (ppm )
-8
-16
-24
-32
-40
-48
Figure SI-11. 11B NMR spectrum (THF) of reaction of iPr2N=BH2 with Me2ND∙BD3 (20 oC, THF, Time = 2 h): (A) iPr2N=B(H/D)2, (B) [Me2N-B(H/D)2]2, (C) Me2ND∙B(H/D)3, (D) iPr2ND∙B(H/D)3 18
References (1) (2) (3) (4) (5) (6) (7)
(8) (9)
Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.; Timmers, F. J. Organometallics, 1996, 15, 1518. Jaska, C. A.; Temple, K.; Lough, A. J.; Manners, I. J. Am. Chem. Soc. 2003, 125, 9424. Johnson, H. C.; Robertson, A. P. M.; Chaplin, A. B.; Sewell, L. J.; Thompson, A. L.; Haddow, M. F.; Manners, I.; Weller, A. S. J. Am. Chem. Soc. 2011, 133, 11076. Sloan, M. E.; Staubitz, A.; Clark, T. J.; Russell, C. A.; Lloyd-Jones, G. C.; Manners, I. J. Am. Chem. Soc. 2010, 132, 3831. Pasumansky, L.; Haddenham, D.; Clary, J. W.; Fisher, G. B.; Goralski, C. T.; Singaram, B. J. Org. Chem. 2008, 73, 1898. Göttker-Schnetmann, I.; White, P. S.; Brookhart, M. Organometallics. 2004, 23, 1766. In this case a catalyst loading of 0.6 mol % was used relative to the initial diborazane. However as this compound is notionally dimeric, this is a 0.3 mol % loading with respect to the polymerizable components MeNH=BH2 and MeNH2∙BH3 which it redistributes to form. We felt therefore that the polymerization of this substrate was more accurately described as 0.3 mol % in Ir, as discussed in the manuscript. This loading was selected to enable a direct comparison with the previously reported polymerization of MeNH2∙BH3 with 0.3 mol % IrH2POCOP (See ref. 9). All other catalyst loadings are calculated versus the diborazane itself, as within the other diborazanes, e.g. Me3N-BH2-NHMe-BH3, only one polymerizable component is present. Pons, V.; Baker, R. T.; Szymczak, N. K.; Heldebrant, D. J.; Linehan, J. C.; Matus, M. H.; Grant, D. J.; Dixon, D. A. Chem. Commun. 2008, 6597. Staubitz, A.; Sloan, M. E.; Robertson, A. P. M.; Friedrich, A.; Schneider, S.; Gates, P. J.; Schmedt auf der Günne, J.; Manners, I. J. Am. Chem. Soc. 2010, 132, 13332.
19
