Osmium: Organometallic Chemistry

Abstract

Organometallic complexes of osmium include those with sigma bonds between the metal and the organic moiety, such as metal–alkyl complexes, or π bonds, such as metal–alkene complexes. The osmium alkyl complexes include homoleptic alkyls and complexes with ancillary carbonyl, cyclopentadienyl, arene, or alkene ligands. Because osmium complexes are stable in higher oxidation states than either ruthenium or iron, oxidative addition of CH bonds to form alkylidene and alkylidyne complexes is very common. Metal–ligand bonds also tend to be stronger in osmium complexes than in complexes of the lighter elements of this group. Because of the stability of OsOs bonds, there are many bimetallic and cluster complexes of osmium and these species have an extensive reaction chemistry. Selective oxidation reactions of unsaturated organic molecules dominates the catalytic chemistry of this metal. Mechanistic studies on the activation of molecular oxygen and oxygen transfer reactions by organoosmium complexes have provided insights into catalytic oxidation chemistry.