Cobalt carbene complexes from (butadiene)zirconocene and (cyclopentadienyl)cobalt carbonyls: An example of a nonnucleophilic synthesis of Fischer-type carbene complexes

Article abstract of DOI:10.1021/om00152a022

The (s-cis-/s-trans-η⁴-butadiene)zireonocene equilibrium mixture (17/15 = 55/45) reacts with CpCo(CO)₂ at ambient temperature to give the metallacyclic Fischer-type carbene complex Cp₂Zr(C₄H₆) (OC=)Co(CO)Cp, 20. The (s-trans-diene)metallocene complex reacts much faster with the metal carbonyl than the more nucleophilic (s-cis-C₄H₆) ZrCp₂ isomer. The product of this nonnucleophilic carbene complex forming reaction, 20, was characterized by X-ray diffraction. It crystallizes in the space group P2₁/c with cell constants a = 7.824 (2), b = 15.753 (4), and c = 15.121 (3) A? and β = 99.26 (2)°. Complex 20 is characterized by a rather short Co-C(carbene) bond length of 1.815 (4) A?. At ambient temperature in solution 20 rapidly equilibrates with the starting components Cp₂Zr(butadiene) and CpCo(CO)₂. At equilibrium the carbene complex is favored by 85/15. Substitution of a Cl on the Cp ring of the CpCo moiety shifts the equilibrium ratio further to the side of the zirconoxycarbene complex: (η⁵-C₅H₅)₂Zr-(C ₄H₆)(OC=)Co(CO)(η⁵-C₅H ₄Cl) ? Cp₂Zr(butadiene) + (η⁵-C₅H₄Cl)Co(CO)₂ (>98/2).