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Heterobinuclear Hydrido, Alkyl, and Related Complexes of Rh/Os. Site-Specific Reductive Elimination of Methane from a Rh/Os Core and the Structures of [RhOs(CH2CN)(CO)3(dppm)2] and [RhOs(CH3)(CO)3(dppm)2]

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bimetallism, elimination reactions

Abstract (summary)

This paper reports the synthesis and characterization of a series of hydrido, alkyl, alkenyl, and related heterobimetallic complexes of Rh and Os and the site-specific reductive elimination of methane from hydrido methyl complexes. Reaction of[RhOs(C0)3(NCMe)&-H)(dppm)~]~+ (3, dppm= PhzPCHzPPhz) with NaCGCH in acetonitrile yields the acetylide complex [RhOs(CzH)(CO)3(dppm)~] (6) and the cyanomethyl complex [RhOs(CHz- CN)(CO)3(dppm)z] (7). The same reaction under CO instead results in deprotonation of one dppm group to give [RhOs(CO)4(dppm-H)(dppm)] (8, dppm-H = bis(dipheny1phosphino)methanide). The methanide carbon can be alkylated to give [RhOs(CO)4(PhzPCH(CH3)PPhz)(dppm)]+ (9) or protonated to give the known compound [RhOs- (C0)4(dppm)z]+ (2). The methyl complex [RhOs(CH3)(C0)3(dppm)z] (10) is prepared by several routes, and upon protonation yields [R~OS(CO)~&-H)&*-)~-(O-C~H~)P~PCHZPP~~)(~~~~)]+ (14) via methane loss. If the reaction is carried out at -80 "C and slowly warmed, three hydrido methyl intermediates are observed at different temperatures, yielding information about the reductive elimination from these heterobinuclear species, which appears to occur from the Os center. An alkenyl complex analogous to the alkyl species 7 and 10 can be obtained by the reaction of [RhOsH(CO)3(dppm)z] (1) with dimethyl acetylenedicarboxylate resulting in insertion into the Os-H bond and migration of the resulting alkenyl group to Rh yielding [Rh0s(MeO~CC=C(H)COzMe)(C0)3(dppm)~l (18). Protonation of 18 yields [RhOs(R)(C0)3&-H)(dppm)z]+ (19) and alkylation yields [RhOs(R)(CH3)(C0)3(dppm)~]+ (20, R = MeOZCC=C(H)COzMe). Compound 20 has the vinylic moiety bound to Rh with the methyl group on Os. The structures of 7 and 10 have been established by X-ray crystallography. Compound 7 crystallizes in the monoclinic space group C2/c with a = 18.313(3) A, b = 13.279(2) A, c = 22.492(5) A, ,8 = 115.89(1)', and Z = 4; compound 10 crystallizes in the triclinic space group Pi with a = 11.102(2) A, b = 11.684(3) A, c = 10.954(3) A, a = 111.79(2)", ,8 = 93.16(2)', y = 68.18(2)', and Z = 1. Both compounds are disordered at an inversion center, although only the metals and the carbonyl and alkyl groups are disordered. Both models refined acceptably: R = 0.046, R, = 0.058 (7); R = 0.047, R, = 0.077 (10). The geometries of the two complexes are almost identical, having the cyanomethyl or methyl group terminally bound to Rh and having the three carbonyls on Os. One carbonyl forms a semibridging interaction with Rh.

Publication Information

Sterenberg, B. T., & Hilts, R. W. (1995). Heterobinuclear hydrido, alkyl, and related complexes of Rh/Os. Site specific reductive.. Journal of the American Chemical Society, 117(1), 245.



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