Organometallics p. 2654 - 2669 (2011)
Update date:2022-08-03
Topics:
Wells, Kyle D.
McDonald, Robert
Ferguson, Michael J.
Cowie, Martin
The complexes [RhOsL(CO)3(dppm)2][CF 3SO3] (L = IMe4 (1,3,4,5-tetramethylimidazol-2- ylidene) (6), PMe3 (8); dppm = μ-Ph2PCH 2PPh2) were prepared by substitution of a carbonyl ligand in [RhOs(CO)4(dppm)2][CF3SO3]. Reaction of 6 with additional IMe4 resulted in deprotonation of a dppm ligand, yielding [RhOs(IMe4)(CO)3(μ- κ1:κ1-Ph2PCHPPh2)(dppm)] (7). Although reaction of 8 with diazomethane at -78 °C yielded the known methylene-bridged [RhOs(PMe3)(CO)3(μ-CH 2)(dppm)2][CF3SO3] (3), compound 6 was unreactive toward diazomethane over a wide temperature range. The methylene-bridged species [RhOs(IMe4)(CO)2(μ-CH 2)(dppm)2][CF3SO3] (9) was obtained by reaction of [RhOs(CO)3(μ-CH2)(dppm) 2][CF3SO3] with IMe4, although [RhOs(CO)3(μ-CH2)(μ-κ1: η2-Ph2PCHPPh2)(dppm)] (10) was also obtained by competing dppm deprotonation by IMe4. Protonation of [RhOsL(CO)2(μ-CH2)(dppm)2][CF 3SO3] (L = IMe4 (9), PMe3 (11)) with triflic acid at -78 °C yielded two isomers in each case. The more abundant isomer, [RhOsL(CO)2(μ-CH3)(dppm)2][CF 3SO3]2, has a bridging agostic methyl group, while the minor isomer has a terminal, Os-bound methyl group. Upon warming, both isomers transformed to species having an Os-bound methyl group and a coordinated triflate ion, subsequently rearranging to the thermodynamic products [RhOsL(CO)2(μ-H)(μ-CH2)(dppm)2][CF 3SO3]2 near ambient temperature. Attempts to prepare an IMe4-containing methyl species directly via triflate ion substitution in [RhOs(CH3)(OSO2CF3)(CO) 3(dppm)2][CF3SO3] by IMe4 instead resulted in deprotonation of the methyl group to give the known product [RhOs(CO)3(μ-CH2)(dppm)2][CF 3SO3]. Addition of methyl triflate to 6 gave no reaction, but protonation of 6 with triflic acid at -78 °C yielded the kinetic isomer of [RhOsH(IMe4)(CO)3(dppm)2][CF 3SO3]2, in which the hydride is terminally bound to Os, and warming this product to ambient temperature resulted in rearrangement to the hydride-bridged, thermodynamic isomer.
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