Mixed Metal Acetylide Complexes

Abstract

Complexes containing C2 hydrocarbyl ligands occupy a very important position in the development of di-, tri- and polynuclear organometallic chemistry. Recognition that monovalent anions of alk-1-ynes, [RCC]¯ are isoelectronic to cyanide ion and CO prompted the first preparation of metal alkynyl complexes in 1953.1,2 Since then, a number of synthetic strategies have been developed and chemistry of metal acetylide complexes has grown tremendously.3-12 Ability of the alkynyl part (-CCR) of the metal acetylides to bind to metal centres in a variety of bonding modes enables a large number of acetylide – bridged polynuclear complexes to be synthesised.13-26 The presence of metal and electron - rich CC moiety in acetylide complexes facilitates cluster growth reactions, and frequently, coupling of acetylide moieties to form polycarbon chains on cluster frameworks is observed.27-30 In this review, focus is given on mixed – metal acetylide complexes which have been prepared from metal – acetylide precursor complexes. Particular emphasis is given on aspects of variation of acetylide bonding on mixed – metal polynuclear frameworks and on reactivity of the polycoordinated acetylide ligand. Since, we recently reviewed oxo - incorporated metal acetylide complexes,31 these are excluded from the present review. A large majority of the acetylide – bridged mixed metal complexes contains metals of the same group of the Periodic Table and, therefore, we have subdivided the review based on different groups. Although, several examples exist of mixed – metal acetylide complexes containing metals from groups 6, 7, 9 and 12, quite surprisingly, we could not find any example of mixed – metal acetylide complexes containing metals only from one of these groups.