Reactivity of a (η5-Phospholyl)cobalt Dicarbonyl Complex. Synthesis of [Co2(η5-PC4H2 tBu2)2(CO)2] and [Co2(η5-PC4H2 tBu2)2(μ-CHCO2Et)(CO)2]

Thermolysis of 2,2‘,5,5‘-tetra-tert-butyl-1,1‘-biphosphole with Co2(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 trimethyl phosphite 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(μ-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⋮CΗ gave the cyclobutadiene complex C12H20PCo(1,2-C4H2Ph2) (5).