Reactivity of a (eta(5)-phospholyl)cobalt dicarbonyl complex. Synthesis of [Co-2(eta(5)-(PC4H2Bu2)-Bu-t)(2)(CO)(2)] and [Co-2(eta(5)-(PC4H2Bu2)-Bu-t)(2)(mu-CHCO2Et)(CO)(2)]

Thermolysis of 2,2',5,5'-tetra-tert-butyl-1,1'-biphosphole with Co-2(CO)(8) gives good yields of (2,5-di-tert-butylphospholyl)dicarbonylcobalt (1), a compound which provided access to a range of cobalt phospholyl complexes. Thermolysis with trimethylphosphite produced C12H20PCo(CO)P(OMe)(3) (2), while photolysis with 1,3-cyclohexadiene and 1,5-cyclooctadiene gave the corresponding complexes C12H20PCo(diene) (3, 4). In the absence of a donor ligand, a metal-metal doubly bridged dimer 6 was obtained; this reacted classically with ethyl diazoacetate to give the bridging complex {C12H20PCo(CO)}(2)(mu-CHCO2Et) (7). Prolonged heating of 1 with 3-hexyne in xylene gave the cyclotrimerization product C6Et6; an initial attempt to prepare pyridines by cocyclization of PrCN with PhC=CH gave the cyclobutadiene complex C12H20PCo(1,2-C4H2Ph2) (5).