Reactions of But-2-yne and Hexafluorobut-2-yne with Dicarbonyl(η-pentamethylcyclopentadienyl)-cobalt, -rhodium and -iridium. Structure of the iridium complex (η-C₅Me₅)Ir₂(CO)₂(CF₃C₂CF₃)₃H

Abstract

The reactions of but-2-yne and hexafluorobut-2-yne with the complexes (η-C₅Me₅)M(CO)₂, M = CO, Rh, or Ir, have been compared. A cyclopentadienone complex, (η-C₅Me₅)M[C₄Me₄CO]₂ is the major product formed in the reaction of but-2-yne with (η-C₅Me₅)M(CO)₂, M = Co or Rh. The cobalt system also gives some hexamethylbenzene whereas the rhodium system yields the pentadienone-dirhodium complex (q-C₅Me₅)₂Rh₂(MeC₂Me)₂CO. The cyclopentadienone complexes (η-C₅Me₅)M[C₄(CF₃)₄CO], M = CO and Rh, were major products from the reactions of hexa- fluorobut-2-yne with (η-C₅Me₅)M(CO)₂. Hexakis(trifluoromethyl)benzene and the tetrahapto- benzene complexes (η-C₅Me₅)M[η⁴-C₆(CF₃)₆], M = Co or Rh, were minor products from these reactions. Small amounts of the dirhodium complexes (η-C₅Me₅)₂Rh₂(CF₃C₂CF₃)₂(CO)_n, n = 1 or 2, were also isolated from the rhodium system under some reaction conditions.

No products could be isolated from the reaction between (η-C₅Me₅)Ir(CO)₂ and but-2-yne, but the reaction with hexafluorobut-2-yne gives two organoiridium complexes. One complex, (η-C₅Me₅)Ir(CO)₂(CF₃C₂CF₃), incorporates an iridiocyclobutenone ring and one terminal carbonyl. The second, (η-Ir₅Me₅)Ir₂(CO)₂(CF₃C₂CF₃)₃H, has been characterized crystallographically. The compound crystallizes with four molecules in the orthorhombic space group Pnma in a cell of di- mensions a 14.262(5), b 13.293(5), c 15.027(5) Ǻ. The structure has been refined by standard methods to a conventional R factor of 0.072, based on 2061 reflections above background. The environments of the two iridium atoms are markedly different. One forms part of a metallopentadiene ring, and it is also attached to two terminal carbonyls, a σ-bonded C(CF₃)=C(CF₃)H group, and the other iridium atom [Ir-Ir distance 2.737(1) Ǻ]. Overall, this iridium has a distorted octahedral geometry. The second iridium is n-bonded in a conventional sandwich manner to the C₅Me₅ and iridiocycle rings; these two rings have a staggered conformation and are close to parallel.