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

This review deals with the coordination of alkynes as reactive unsaturated substrates on heterobimetallic transition metal complexes LnM-M'L 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 mu-PR2. Presented are few examples featuring simple pi-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, mu-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-C equivalent to C-H or R-C equivalent to C-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 mu-eta(1):eta(2)-allenyl salts. (C) 2017 Elsevier B.V. All rights reserved.