THE REACTION OF DIPHENYLPHOSPHINE, PPH2H, WITH AN ALKYNE-BRIDGED DICOBALT CARBONYL COMPLEX - THE SYNTHESIS CRYSTAL-STRUCTURE AND REACTIVITY OF THE COMPLEX [CO2(MU-C(CO2ME)=CHCO2ME)(MU-PPH2)(CO)4]

The reaction between [Co2{mu-C2(CO2Me)2}(CO)6] and diphenylphosphine gives the mono- and di-substituted complexes [Co2{mu-C2(CO2Me)2}(CO)6-n(PPh2H)n][n = 1 (1), 2 (2)]. Thermolysis of (1) leads to phosphorus-hydrogen bond cleavage and formation of the phosphido-, vinyl-bridged complex [Co2{mu-C(CO2Me)=CHCO2Me}(mu-PPh2(CO)4] (3) together with the trinuclear cobalt complex [Co3{mu-C2(CO2-Me)2}(mu-PPh2)(CO)7] (4). An X-ray diffraction study of 3 reveals that one of the methylcarboxylate substituents of the vinyl ligand is coordinated via oxygen to cobalt, forming an almost planar M-C-C-C-O five-membered metallacyclic ring. The reactions of (3) with a tertiary phosphine and with phenylacetylene are described.