Synthese und Reaktionsverhalten von (η2-BrCCR)Co2(CO)6. Die Festkörperstruktur von Pentacarbonyl-[μ-(1,2,3,4-η:1,4-η)-1,4-diphenyl-1,3-butadien-1,4-diyl]dicobalt

The reaction of BrCCR (1a, R=nPr; 1b, R=nBu; 1c, R=SiMe3; 1d, R=Ph) with Co2(CO)8 (2) in a 1:1 molar ratio produces the hexacarbonyldicobalt complexes (η2-BrCCR)Co2(CO)6 (3a, R=nPr; 3b, R=nBu; 3c, R=SiMe3; 3d, R=Ph) in moderate yields. Apart from these complexes, pentametallic cobalt clusters of the general composition Co5(CO)12(CCR) (4a, R=nPr; 4b, R=nBu; 4c, R=SiMe3; 4d, R=Ph) are formed. Treatment of 1d with Na[Co(CO)4] (5) yields the butadi-1,3-yne complex [(η2-CCPh)Co2(CO)6]2 (6). A possible reaction mechanism for the formation of complexes 4 and 6 is described. The reaction of 4d with P(OiPr)3 (7) leads to a cluster degradation and the formation of Co2(CO)6[P(OiPr)3]2 (8). In contrast, on addition of HCCPh (9) to 4d the dicarbonyl(η4-tricarbonylcobaltacyclopentadiene) cobalt complex [η5-(PhCCHCHCPh)Co(CO)3]Co(CO)2 (10) is obtained along with (η2-HCCPh)Co2(CO)6 (11). Complex 10 was characterized by single crystal X-ray crystallography. Homobimetallic 10 features a 5-membered PhCCHCHCPhCo(CO)3 ring, which is η5-coordinated to a Co(CO)2 fragment.