A convenient route to binuclear osmium(I) complexes containing diphosphine and arsinophosphine ligands. X-Ray crystal structure of [Os2(MeCO2)2(CO)4(dppm)2]

Abstract

Reaction of the binuclear osmium(I) compound [Os₂(MeCO₂)₂(CO)₄(MeCN)₂] with 1 equivalent of the bidentate groups L–L (L–L = dppm, dppe, or dadpe)[dppm = bis(diphenylphosphino)methane, dppe = 1,2-bis(diphenylphosphino)ethane, and dadpe = 1 -diphenylarsino-2-diphenylphosphino-ethane] yields the osmium(I) polymers [{Os₂(MeCO₂)₂(CO)₄(L–L)}_n] in which two metals are bridged by two carboxylate groups and the binuclear units are linked by diphosphine ligands. Reaction of [Os₂(MeCO₂)₂(CO)₆] in refluxing tetrahydrofuran (thf) with 2 equivalents of dppm yields the neutral diaxially substituted compound [Os₂(MeCO₂)₂(CO)₄(dppm)₂], the X-ray structure of which confirms axial substitution. No evidence for equatorial substitution was found for dppm using alcohols or excess of ligand. Treatment of [Os₂(MeCO₂)₂(CO)₆] in refluxing ethanol with 2 equivalents of dppe or dadpe yields two different types of cationic compounds of formula [Os₂(MeCO₂)(CO)₄(L–L)₂]⁺(L–L = dppe or dadpe) in which an acetate group has been displaced. An edge-sharing bioctahedral structure having two bridging carbonyls and one bridging acetate group with one dppe chelating each metal is suggested in the first case, while either of two possible structures having no bridging carbonyls and one bridging acetate with one dadpe chelating each metal in two possible orientations is suggested for the second.