1,3-Diphosphacyclobutene Cobalt Complexes.

The synthesis and characterization of rare 1,3-diphosphacyclobutene transition-metal complexes is described. Reactions of the cobalt-hydride complex [Co(P C tBu ) H] (G) with nBuLi, tBuLi, or PhLi afforded [Li(solv) {Co(η -P C tBu HR)(η -P C tBu )}] (1: R=nBu, (solv) =(Et O) ; 2: R=tBu, (solv) =(thf) ; 3: R=Ph, (solv) =(Et O)(thf) ), with an η -coordinated 1,3-diphosphacyclobutene ligand as a result of organyl-anion attack at one of the phosphorus atoms of the bis(1,3-diphosphacyclobutadiene) backbone. In contrast to the reactions with PhLi, the aryl-magnesium compounds p-tolyl magnesium chloride and p-fluorophenyl magnesium bromide deprotonate [Co(P C tBu ) H] to give the magnesium salt [Mg(MeCN) ][Co(η -P C tBu ) ] (4), which contains a bis(1,3-diphosphacyclobutadiene)-cobaltate anion. The [Co(η -P C tBu ) ] anions are well separated from the octahedral [Mg(MeCN) ] cation in the molecular structure of 4. Compound 1 reacts with Me SiCl to give neutral [Co(η -P C tBu HnBu)(η -P C tBu SiMe )] (5, 52 % yield) with an SiMe group attached to one of the P atoms of the previously unfunctionalized backbone.