Homogeneous CO Hydrogenation: Ligand Effects on the Lewis Acid ...

the only Re species, but after 2.5 hours a mixture of 2-M 1, and two new species were observed,
identified as Re alkyl 12 and the migratory insertion product [3-M 1] – . After 2.5 hours, there was
more alkyl 12 present than the final product ( 1 H NMR δ 5.14 (d, J PH = 1.9 Hz); 31 P{ 1 H} NMR δ
3.4). After 24 hours, the starting carbene had been almost entirely consumed, and the major
species was the acyl. After 48 hours, the reaction was complete, with only the acyl and residual
[HPt] + remaining. 2D NMR experiments were performed on a reaction carried out in CD 2Cl 2,
which contained a mixture of [3-M 1] - , the alkyl intermediate 12, and small amounts of bridging
alkyl impurities. Details of the crucial correlations that led to the structural assignment of the
products are supplied by the appropriate figures. Typical procedure using NaHBEt 3: To a stirring
~0.6 mL C 6D 5Cl solution of 21.1 mg (0.0265 mmol) [1-M 1][OTf] was added 17.0 mg (0.0265
mmol) [HPt][PF 6] slowly as a solid. The mixture turned yellow with precipitation while it was
allowed to stir for 10 minutes. After 10 minutes, the mixture was filtered through sintered glass,
and 26.5 µL NaHBEt 3 (1.0 M in toluene) was added dropwise. Use of the stronger hydride
source led to a much faster reaction, with complete conversion to in 2.5 hours. The 1 H and 31 P
resonances were at approximately the same chemical shift, but were dramatically broadened
relative to the [HPt] + reactions. Addition of pyridine directly following NaHBEt 3 (in a separate
experiment) led to a moderate decrease in reaction rate, and a sharpening of the signals,
suggesting BEt 3 is leading to broadening, and perhaps rate enhancement. Single crystals suitable
for X-Ray diffraction were grown from this latter experiment, from a THF/pentane mixture at -
35 °C. Characterization of acyl product [3-M 1] - : 1 H NMR (mix of [Pt] 2+ and [HPt] + salts, which
obscure some Ph 2PCH 2B(C 8H 14) resonances, THF-d 8, 600 MHz): δ 0.43 (br, 1H,
Ph 2PCH 2B(C 8H 14)), 0.63 (br, 1H, Ph 2PCH 2B(C 8H 14)), 0.71 (dd, J PH = 9.8 Hz, J HH = 14.4 Hz, 1H,
Ph 2PCH 2B(C 8H 14)), 1.29 (m, 1H), 1.37-1.43 (m, 3H), 1.53 (m, 1H), 4.64 (dd, J PH = 1.9 Hz, J HH =
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