Reactivity of a (η<SUP>5</SUP>-Phospholyl)cobalt Dicarbonyl Complex. Synthesis of [Co<INF>2</INF>(η<SUP>5</SUP>-PC<INF>4</INF>H<INF>2</INF><SUP>t</SUP>Bu<INF>2</INF>)<INF>2</INF>(CO)<INF>2</INF>] and [Co<INF>2</INF>(η<SUP>5</SUP>-PC<INF>4</INF>H<INF>2</INF><SUP>t</SUP>Bu<INF>2</INF>)<INF>2</INF>(μ-CHCO<INF>2</INF>Et)(CO)<INF>2</INF>]

Thermolysis of 2,2‘,5,5‘-tetra-tert-butyl-1,1‘-biphosphole with Co<INF>2</INF>(CO)<INF>8</INF> gives good yields of (2,5-di-tert-butylphospholyl)dicarbonylcobalt (<BO>1</BO>), a compound which provided access to a range of cobalt phospholyl complexes. Thermolysis with trimethyl phosphite produced C<INF>12</INF>H<INF>20</INF>PCo(CO)P(OMe)<INF>3</INF> (<BO>2</BO>), while photolysis with 1,3-cyclohexadiene and 1,5-cyclooctadiene gave the corresponding complexes C<INF>12</INF>H<INF>20</INF>PCo(diene) (<BO>3</BO>, <BO>4</BO>). In the absence of a donor ligand, a metal−metal doubly bridged dimer <BO>6</BO> was obtained; this reacted classically with ethyl diazoacetate to give the bridging complex {C<INF>12</INF>H<INF>20</INF>PCo(CO)}<INF>2</INF>(μ-CHCO<INF>2</INF>Et) (<BO>7</BO>). Prolonged heating of <BO>1</BO> with 3-hexyne in xylene gave the cyclotrimerization product C<INF>6</INF>Et<INF>6</INF>; an initial attempt to prepare pyridines by cocyclization of PrCN with PhC&tbd1;CΗ gave the cyclobutadiene complex C<INF>12</INF>H<INF>20</INF>PCo(1,2-C<INF>4</INF>H<INF>2</INF>Ph<INF>2</INF>) (<BO>5</BO>).