Cyclobutadiene complexes of platinum metals

Synthesis and reactivity of the cyclobutadiene complexes of platinum metals are reviewed. Palladium and platinum complexes are well developed and are mainly represented by the half-sandwich compounds such as (C4R4)PtCl2 and their adducts. On the other hand, ruthenium and rhodium complexes have been studied only fragmentarily and are mainly represented by the sandwich compounds such as Cp*Ru(C4R4)X and Cp*Rh(C4R4). Most of the complexes are synthesized via dimerization of internal alkynes by unsaturated metal precursors, although this method often suffers from the side oligomerization of alkynes. Once formed, the cyclobutadiene ligand typically remains intact even under rather harsh conditions, which makes it a promising protecting ligand for metal catalysts. (C) 2017 Elsevier B.V. All rights reserved.