CARBON-CARBON BOND-CLEAVAGE IN ORGANOCOBALT COMPLEXES WITH AGOSTIC C...H...CO BONDING

The reaction of noncoordinating acid, for example HBF4-OMe2, with the neutral (4-vinylcyclopentene)- and (4-vinylcyclohexene)cobalt(I) complexes [Co(eta-C5R5)((1,2:6,7-eta)-CH2=CHCHCH2CH=CHCH2)][R = H (1), R = Me (2)] and [Co(eta-C5Me5)((1,2:7,8-eta)-CH2=CHCHCH2CH=CHCH2CH2)] (13) affords the cationic ethylcyclopentenyl and ethylcyclohexenyl complexes [Co(eta-C5Me5){(1,2,3-eta)-C5H6(endo-Et-4)}]+ (7), [Co(eta-C5Me5){(1,2,3-eta)-C6H8(endo-Et-4)}]+ 16), and [Co(eta-C5Me5){(1,2,3-eta)-C6H8(endo-Et-5)}]+ (17) in which the other wise electron-deficient metal centers are stabilized by a three-center, two-electron (agostic) interaction. The 4-ethylcyclopentenyl complex readily undergoes disrotatory ''inwards'' ring opening to afford [Co(eta-C5Me5){eta-C5H6(syn-Et-5)}]+ (12) containing an acyclic 5-ethylpentadienyl ligand.