Cobalt carbonyl clusters incorporating heavy main-group elements: Structure and reactivity

[摘要] Treating $m SbClsb3, SnClsb4.5Hsb2O, or Pb(OAc)sb2.3Hsb2O$ with NaCo(CO)$sb4$ forms the open complexes $m Sb{Co(CO)sb4}sb3, Sn{Co(CO)sb4}sb4$, and Pb$m {$Co(CO)$sb4}sb4$, respectively. The unstable antimony complex was determined to be Sb$m {Co(CO)sb4}sb3$ by the similarity of its infrared spectrum with that of known $m Bi{Co(CO)sb4}sb3$. Isostructural $m Sn{Co(CO)sb4}sb4$ and $m Pb{Co(CO)sb4}sb4$ were characterized by single crystal X-ray diffraction. Each contains a Group 14 element tetrahedrally surrounded by four trigonal bipyramidal Co(CO)$sb4$ groups.Heating solutions of $m Bi{Co(CO)sb4}sb3$ forms BiCo$sb3$(CO)$sb9$, which contains a closed cobalt triangle capped by a bismuth atom. A bridging carbonyl lies along each Co-Co bond. The thermal decomposition is reversible, and a kinetic study of the carbonylation of BiCo$sb3$(CO)$sb9$ indicates this transformation to be first-order with respect to (BiCo$sb3$(CO)$sb9$) and P(CO) in n-hexane (500-900 psi, 50-65 C), with an activation energy of 68+/$-$2 kJ.mol$sp{-1}$.Reducing $m Bi{Co(CO)sb4}sb3 forms lbrack Bi{Co(CO)sb4}sb4brack sp-$. This complex is isostructural to Sn$m {Co(CO)sb4}sb4 and Pb{Co(CO)sb4}sb4$, but it is not isoelectronic, as the bismuth is a hypervalent 10-electron center.Reducing BiCo$sb3$(CO)$sb9$ produces (Bi$sb2$Co$sb4$(CO)$sb{11}$) $sp-$ and (Co(CO)$sb4brack sp-$. Single crystal X-ray analysis (Cp$sb2$Co$sp+$ salt) determined the core structure of the bismuth anion to consist of a Bi$sb2$Co$sb2$ tetrahedron with Co(CO)$sb3$ units capping the two Bi$sb2$Co triangular faces.X-ray analyses of (PPN) (Sb$sb2$Co$sb4$(CO)$sb{11}$) and (PPN) $sb2$ (Sb$sb2$Co$sb4$(CO)$sb{11}$) showed these complexes to have nearly identical frameworks, which are isostructural and isoelectronic to their bismuth homologues. These complexes are electron rich and do not conform to conventional bonding formalisms. Extended Huckel calculations agree with observed structural changes that upon reduction of the monoanion, the added electron enters an antibonding orbital primarily localized between two cobalt atoms bridged by a carbonyl.Treatment of BiCo$sb3$(CO)$sb9$ with PPh$sb3$ gives $m Bi{Co(CO)sb3PPhsb3}sb3.$ $m Bi{Co(CO)sb4}sb3, BiCosb3(CO)sb9$, and $m Sb{Co(CO)sb4}sb3$ all react with PhC$sb2$Ph through an apparent radical mechanism to form Co$sb2$(CO)$sb6{$PhC$sb2$Ph$}$ as the only infrared observable product.

[发布机构] Rice University

[效力级别] chemistry