The reactions of some diynes with (C₅H₅)Co(CO)₂ and Fe(CO)₅: Inter- or Intra-molecular cyclizations?

Abstract

The reactions of several diynes MeC≡C(CH₂)_nC≡CMe, n = 2-4, with (η- C₅H₅)Co(CO)₂ and Fe(CO)₅ have been compared. A p-benzoquinone complex, (η-C₅H₅)Co[(C₈H₁₀)₂(CO)₂], and three isomers of the cyclopentadienone complex, (η-C₅H₅)Co[(C₈H₁₀)₂CO], are formed in the reaction of (η- C₅H₅)Co(CO)₂ with octa-2,6-diyne. In each complex, the ligand is formed by intermolecular cyclization of two diynes with inclusion of CO. The corresponding reactions with nona-2,7-diyne and deca-2,8-diyne give complexes (η-C₅H₅)Co[(C₉H₁₂)CO] and (C₅H₅)Co[(C₁₀H₁₄)CO] in which a bicyclic cyclopentadienone has been formed by intramolecular condensation of the diyne. Intramolecular cyclization is also achieved when all three diynes are treated with Fe(CO)₅. The reactions with octa- 2,6-diyne and deca-2,8-diyne give metallodiene complexes, Fe₂(CO)₆(diyne), in which the ferracyclopentadiene ring is fused to either a 4- or 6-membered ring. With nona-2,7-diyne, a cyclopentadienone complex of formula Fe(CO)₃[(C₁₀H₁₄)CO] is isolated. In the reactions with Fe(CO)₅,organic products of the type (diyne)₂, (diyne)₃ and [(diyne)CO]₂ are also isolated.