Bridging vinylidene complexes of RhMn and evidence for migratory insertions to give terminal vinyl groups

Article abstract of DOI:10.1021/om00005a039

The reaction of the heterobinuclear complex [RhMn(CO)₄(dppm)₂] (1) (dppm = Ph₂PCH₂-PPh₂) with 3-butyn-2-one at -40°C yields the alkyne-bridged product [RhMn(CO)₄(μ-HC₂C-(O)Me)(dppm)₂] (3), which undergoes a 1,2-hydrogen shift, yielding two isomers of the vinylidene-bridged species [RhMn(CO)₄(μ-CC(H)C(O)Me)(dppm)₂] (4) as the temperature is raised. Compound 4 undergoes facile CO loss to give [RhMn(CO)₃(μ-η¹:η ²-CC(H)C(O)Me)-(dppm)₂] (5) in which the ketonic moiety of the bridging vinylidene group coordinates to Mn, filling the open coordination site left vacant by the departing CO. Protonation of the alkyne- or vinylidene-bridged species 3-5 yields a series of vinyl complexes. Addition of methyl triflate to 4 and 5 yields the respective methyl-substituted vinyl complexes, analogous to the protonation products. In the alkylation of 5 at low temperature an intermediate, [RhMn(CH₃)(CO)₃(μ-η¹:η ²-CC(H)C(O)Me)(dppm)₂][SO₃CF₃] (12), having a vinylidene bridge and a methyl group terminally bound to Rh, is obtained. The rearrangement of 12 to a vinyl complex upon warming presents evidence for a migratory insertion involving these groups. The structure of 5 was determined by X-ray crystallography. This compound crystallizes in the monoclinic space group P2₁/n (nonstandard setting of P2₁/c [No. 14]) with a = 14.489(1) A?, b = 15.754(2) A?, c = 24.104(2) A?, β = 91.41(1) A?, V = 5500(1) A?³, and Z = 4. On the basis of 3980 observations the structure has refined to R = 0.058 and R_w = 0.063.