Tetraphenylcyclobutadiene-Transition Metal Complexes

Abstract

The prediction, in 1956 by LONGUET- HIGGINS and ORGEL (1), that while cyclobutadienes are likely to be unstable, their complexes with transition metals would be stable, has been amply confirmed. In 1959 CRIEGEE and SCHRÖDER prepared tetramethylcyclobutadiene nickel chloride (2) and this was quickly followed by the preparation of tetraphenylcyclobutadiene [Ph₄C₄] complexes of iron, [II] (3), nickel, [III] (4), and cobalt, [VI] (5). We have, following the work of MALATESTA et al. (6), recently prepared the tetraphenylcyclobutadiene palladium halides [I] by simple routes from diphenylacetylene (7,8) and characterized these compounds. All of these cyclobutadiene-metal complexes however, were prepared by unique routes, not readily applicable to the synthesis of cyclobutadiene derivatives of other transition metals. We report here the first general syntheses of tetraphenylcyclobutadienetransition metal complexes from [I] by ligand -exchange and ligand -transfer reactions.