Spectroscopic studies on C2 hydrocarbon fragments. Part 1. Vibrational studies of cluster-bound vinyl and vinylidene ligands

Abstract

Vibrational assignments of the vinyl and vinylidene groups in [Os₃(CO)₁₀(µ-H)(µ-η²-CHCH₂)](1) and [Os₃(CO)₉(µ-H)₂(µ₃-η²-CCH₂)](3) respectively have been made on the basis of normal co-ordinate analyses of the Os₃(C₂H_n)(n= 2 or 3) fragments and [²H] substitution. π-Co-ordination caused the lowering of the principal ν(CC) vibration to 1 311 and 1 331 cm^–1 in (1) and (3) respectively. The vinyl group frequencies could largely be transferred to assign partially the spectrum of another vinyl complex [Ru₂(CO)₃(η⁵-C₅H₅)₂(µ-η²-CHCH₂)]BF₄(2) with the same co-ordination mode. The vinylidene frequencies in (3) were quite distinct from those of another complex, [Ru₂(CO)₃(η⁵-C₅H₅)₂(µ-CCH₂)](4) which has a different co-ordination mode; a band at 1 586 cm^–1 in (4) is assigned as consisting largely of the ν(CC) mode. Analysis was also made of the Os(µ-H) group in (1) and showed strong mixing between the symmetric ν(Os–H) and out-of-plane bend giving rise to the i.r. active vibrations at 1 285 and 710 cm^–1; the asymmetric ν(Os–H) stretch occurs at 1 394 cm^–1.