Synthesis and reactivity of (eta(2)-BrC Cr)(Co-2(CO)(6). Solid-state structure of pentacarbonyl-(mu-1,2,3,4-eta : 1,4-eta)-1,4-eta-diphenyl-1,3-butadiene-1,4-diyl]cobalt

The reaction of BrC equivalent to CR (1a, R = Pr-n; 1b, R = Bu-n; 1c, R = S iMe3; 1d, R = Ph) with Co-2(CO)(8) (2) in a 1:1 molar ratio produces the he xacarbonyldicobalt complexes (eta (2)-BrC equivalent to CR)Co-2(CO)(6) (3a, R = Pr-n; 3b, R = Bu-n; 3c, R = SiMe3; 3d, R = Ph) in moderate yields. Apa rt from these complexes, pentametallic cobalt clusters of the general compo sition Co-5(CO)(12)(C equivalent to CR) (4a, R = Pr-n; 4b, R = Bu-n; 4c, R = SiMe3; 4d, R = Ph) are formed. Treatment of 1d with Na[Co(CO)(4)] (5) yie lds the butadi-1,3-yne complex [(eta (2)-C equivalent to CPh)Co-2(CO)(6)](2 ) (6). A possible reaction mechanism for the formation of complexes 4 and 6 is described. The reaction of 4d with P(O'Pr)(3) (7) leads to a cluster de gradation and the formation of Co-2(CO)(6)[P(O'Pr)(3)](2) (8). In contrast, on addition of HC equivalent to CPh (9) to 4d the dicarbonyl(eta (4)-trica rbonylcobaltacyclopentadiene) cobalt complex [eta (5)-(PhC equivalent to CH -CH= CPh)Co(CO)(3)]Co(CO)(2) (10) is obtained along with (eta2-HC equivalen t to CPh)Co-2(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 eta5-coordinated to a Co(CO)(2) fragment. (C) 200 1 Published by Elsevier Science B.V.