Repercussion of a 1,3-Hydrogen Shift in a Hydride-Osmium-Allenylidene Complex.

An unusual 1,3-hydrogen shift from the metal center to the C atom of the C-chain of the allenylidene ligand in a hydride-osmium(II)-allenylidene complex is the beginning of several interesting transformations in the cumulene. The hydride-osmium(II)-allenylidene complex was prepared in two steps, starting from the tetrahydride dimer [(Os(H···H){κ-,,-[xant(P Pr)]})(μ-Cl)][BF] (). Complex reacts with 1,1-diphenyl-2-propyn-1-ol to give the hydride-osmium(II)-alkenylcarbyne [OsHCl(≡CCH=CPh){κ-,,-[xant(P Pr)]}]BF (), which yields OsHCl(=C=C=CPh){κ-,,-[xant(P Pr)]} () by selective abstraction of the C-H hydrogen atom of the alkenylcarbyne ligand with K BuO. Complex is metastable. According to results of DFT calculations, the migration of the hydride ligand to the C atom of the cumulene has an activation energy too high to occur in a concerted manner. However, the migration can be catalyzed by water, alcohols, and aldehydes. The resulting alkenylcarbyne-osmium(0) intermediate is unstable and evolves into a 7:3 mixture of the hydride-osmium(II)-indenylidene OsHCl(=C){κ-,,-[xant(P Pr)]} () and the osmanaphthalene OsCl(CHPh){κ-,,-[xant(P Pr)]} (). Protonation of with HBF leads to the elongated dihydrogen complex [OsCl(η-H)(=C){κ-,,-[xant(P Pr)]}]BF (), while the protonation of regenerates . In contrast to , complex evolves to a half-sandwich indenyl derivative, [Os(η-IndPh)H{κ-,,-[xant(P Pr)]}][BF]Cl (). Phenylacetylene also provokes the 1,3-hydrogen shift in . However, it does not participate in the migration. In contrast to water, alcohols, and aldehydes, it stabilizes the resulting alkenylcarbyne to afford [Os(≡CCH=CPh)(η-HC≡CPh){κ-,,-[xant(P Pr)]}]Cl ().