Activation of alkynes by diphosphine- and µ-phosphido-spanned heterobimetallic complexes

Abstract

This review deals with the coordination of alkynes as reactive unsaturated substrates on heterobimetallic transition metal complexes LnM–M′Ln in which two transition metal centers interact through a metal–metal bond spanned by a diphosphane ligand such as bis(diphenylphoshino)methane or a bridging phosphido group of the type μ-PR2. Presented are few examples featuring simple π-coordination of the alkyne on M or M′, but the majority of examples involve bimetallic activation associated with synergetic effects of the two adjacent metal centers giving rise to dimetallatetrahedranes, dimetallacyclobutenes, dimetallated olefins, μ-vinylidenes and acetylides species. Covered are also heterobimetallic systems, in which carbon–carbon or carbon-phosphorus couplings have occurred between two alkyne ligands or with carbonyl groups and P-donor ligands present in the coordination sphere of the heterodinuclear scaffold. Furthermore, hydrometallation reactions leading to vinyl-species through insertion of R-CC-H or R-CC-R into a terminal or bridging M–H bond are presented. Included in this review are also selected examples of reactivity studies and transformation of the initially formed heterobimetallic alkyne species, such as addition of electrophiles (H+, R+), generating heterometallic alkenyl and µ-η1:η2-allenyl salts.