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

Decomposition of 2-M 1.
While searching for ideal conditions to reduce [1-M 1][OTf], a J-Young tube was charged with
19.3 mg (0.0242 mmol) [1-M 1][OTf], 4.0 mg (0.031 mmol) NaHB(OMe) 3, and ~0.6 mL C 6D 5Cl.
The mixture turned yellow and was monitored by NMR spectroscopy, which showed conversion
to two products in a ~2:1 ratio, with the major product being the boroxycarbene 2-M 1. The
product distribution was largely stable for weeks, but after 1 month NMR spectra showed nearly
complete consumption of the carbene and formation of a new species containing three diagnostic
multiplets at 3.94, 5.30, and 6.39. A separate reaction was carried out in C 6H 5Cl under similar
conditions, from which the solvents were removed under vacuum, followed by extraction with
pentane and crystallization from slow pentane evaporation. Crystals of 11 grew only after a few
months, and turned out to be the decomposition product. Although the reaction was fairly clean,
the undesired product was not isolated or purified, and was only characterized as a mixture in the
NMR experiments and by X-Ray crystallography. Similar partial decomposition was observed in
[HPt] + reductions. Partial NMR spectroscopic details: 1 H NMR (C 6D 5Cl, 500 MHz): 3.95 (ddd,
J HH = 8.7 Hz, 14.5 Hz, J PH = 12.0 Hz, Ph 2PCH 2C(O-)(H)-Re), 5.30 (dt, J HH = 8.6 Hz, J PH = 14.5
Hz, Ph 2PCH 2C(O-)(H)-Re), 6.40 (td, J HH = 8.7 Hz, J PH = 5.5, Ph 2PCH 2C(O-)(H)-Re). 31 P{ 1 H}
NMR (C 6D 5Cl, 121 MHz): -54.0 (1P), 1.8 (1P, 4-membered ring). 13 C{ 1 H} NMR (C 6D 5Cl, 75
MHz): 44.13 (J PC = 6.3 Hz, Ph 2PCH 2C(O-)(H)-Re), 52.24 (J PC = 39.3 Hz, Ph 2PCH 2C(O-)(H)-Re),
210.20 (d, J PC = 9.4 Hz, Re=C(O-)O-C(R)H-Re).
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