The reactions of tricobalt alkylidyne complexes [Co 3( μ3−CR)(CO) 9](R = Me, CO 2Me) with the vinyl phosphine ligands PPh 2CHCH 2 and cis-Ph 2PCHCHPPh 2; crystal structure of [Co 3( μ3−CCO 2Me)( μ-Ph 2PCHCHPPh 2)(CO) 7

Abstract

The alkylidyne-capped complexes [ Co 3(μ 3− CR)( CO) 9] ( R = Me 1a, CO 2Me 1b ) react with PPh 2CHCH 2 in heptane at 308 K to give the phosphine-substituted complexes [Co 3( μ 3−CR)(CO) 8(PPh 2CHCH 2)] ( R = Me 2a, CO 2Me 2b ) , [Co 3( μ 3−CR)−(CO) 7(PPh 2CHCH 2) 2] ( R = Me 3a, CO 2Me 3b ) and, in the case of R = CO 2Me, the tris-substituted complex [CO 3( μ 3−CCO 2Me)(CO) 6(PPh 2CHCH 2) 3] 4. Heating of complexes 2a and 2b at 343 K results in loss of a CO group and coordination of the vinyl moiety of the PPh 2CHCH 2 ligand to afford [Co 3( μ 3−CR)( μ−PPh 2CHCH 2)(CO) 7] ( R = Me 5a, CO 2Me 5b ) . In contrast, reaction of [Co 3( μ 3−CR)(CO) 9](R = Me 1 a, CO 2 Me 1 b) with cis-Ph 2PCHCHPPh 2 (dppee) gives [Co 3( μ 3−CR)( μ−Ph 2PCHCHPPh 2)(CO) 7] (R = Me 6 a, CO 2 Me 6 b) in which the dppee ligand bridges two adjacent cobalt atoms via both phosphino moieties. Nuclear magnetic resonance studies on 5a and 5b indicate that two isomeric structures in a ratio of 7:3 are present in solution at 293 K. Conversion of [Co 3( μ 3−CR)( μ−PPh 2CHCH 2)(CO) 7] 5a and 5b back to [Co 3( μ 3−CR)(CO) 8(PPh 2CHCH 2)] 2a and 2b can be achieved by purging with CO at 293 K while further purging at 343 K results in conversion to [Co 3( μ 3−CR)(CO) 9] 1a and 1b. The structure of [Co 3( μ 3−CCO 2Me)( μ−Ph 2PCHCHPPh 2)(CO) 7] 6b was determined by single-crystal X-ray diffraction. All the complexes have been characterized spectroscopically and by elemental analysis.