RING-EXPANSION REACTIONS OF LIGAND-BRIDGED DINUCLEAR COBALT COMPLEXES WITH ALKYNES AND WITH ALLENE - CRYSTAL AND MOLECULAR-STRUCTURES OF [CO2(MU-PPH2CHCHC(O)CHCHPPH2)(CO)4]AND [CO2(MU-PPH2CHCHC(O)C(CH2)2)(MU-PPH2)(CO)3]

The bis(phosphido)-bridged complex [Co2(mu-PPh2)2(CO)6] (1) undergoes regiospecific insertion reactions with alkynes, RC=CR', to give, depending on the nature of R and R', new ligand-bridged dinuclear complexes of the type [Co2(mu-PPh2CRCR')(mu-PPh2)(CO)4] (R = R'= CO2Me, 2) or [Co2{mu-PPh2CRCR'C(O)}(mu-PPh2)(CO)4] (R'= R = H, 3a; R'= Ph, R = H, 3b; R'= SiMe3, R = H, 3c; R' = Me, R = H, 3d; R' = CH20H, R = H, 3e; R' = R = CO2Me, 3f). Complexes 3a-f, which contain the mu-PPh2CRCR'C(0) ligand incorporated into a five-membered metallacyclic ring with one of the Co atoms, react regiospecifically with alkynes, R''C=CR''', to give [Co2{mu-PPh2CRCR'C(O)CR''CR'''PPh2}(mu-PPh2)(CO)4] (R'= R = R'' = R''' = H, 4a; R' = R = R''', R'' = Me, 4b; R' = R'' = Ph, R = R''' = H, 4c; R'= Ph, R = R'' = R''' = H, 4d; R' = Ph, R = R''' H, R'' = Me 4e; R'= R = R'' = R''' = CO2Me, 4f, R' = SiMe3, R = R''' = H, R'' = Me, 4g; R' = SiMe3, R = R''' = H, R'' = Ph, 4h), in which the new bridging ligand is part of a nine-membered dimetallacyclic ring. Complex 3a (R = R' = H) also reacts With Edlene to give [Co2{mu-PPh2CHCHC(O)CHCMePPh2}(mu-PPh2)(CO)4] 4b'(an isomer of 4b) and [Co2{mu-PPh2-CHCHC(O)C(CH2)2}(mu-PPh2)(CO)3]5. The structures of 4a and of the hexane solvate of 5 have been determined. Compound 4a crystallizes in the monoclinic space group P2(1)/n with a = 15.586(3) angstrom, b = 18.882(6) angstrom, c = 20.867(7) angstrom, beta = 95.80(3)-degrees, V = 6109.6 angstrom3, and Z = 8, while 5.1/2C6H14 crystallizes in the monoclinic space group P2(1)/a with a = 24.903(8) angstrom, b = 14.674(5) angstrom, c = 9.249(5) angstrom, beta = 96.17(2)-degrees, V = 3360(2) angstrom3, and Z = 4. Final R and R(w) values were 0.032 and 0.036 (4a) and 0.036 and 0.044 (5) based on 4117 (4a) and 2469 (5) observations, respectively.