Reactions of co-ordinated ligands. Part 26. The reaction of ethylene and acetylene with tri-µ-carbonyl-tris(η5-indenyl)-triangulo-trirhodium; the formation and molecular structure of the bridged vinylalkylidene complex [Rh2(µ-CCH2)(CO)2(η5-C9H7)2], and its protolysis to form a bridged cationic vinyl complex

Abstract

The complex [Rh(CO)₂(η⁵-C₉H₇)] decarbonylates in refluxing heptane to form [Rh₃(µ-CO)₃(η⁵-C₉H₇)₃]. Reaction of the Rh₃ cluster with ethylene affords a high yield of [Rh(CO)(C₂H₄)(η⁵-C₉H₇)], which reforms the Rh₃ cluster in solution. Treatment (60 °C. toluene) of [Rh(CO)(C₂H₄)(η⁵-C₉H₇)] with acetylene affords as the major product the bridged vinylalkylidene complex [Rh₂(µ-CCH₂)(CO)₂(η⁵-C₉H₇)₂]. An X-ray crystallographic study has been carried out on this complex. Crystals are monoclinic, space group P2₁/c, Z= 4, in a unit cell of dimensions a= 13.482(3), b= 9.568(3), c= 14.801(6)Å, and β= 100.69(3)°. The structure has been refined to R 0.021 (R′ 0.021) for 2 999 unique reflections to 2θ⩽ 50°(Mo-K_α, X-radiation). The µ-CCH₂ group symmetrically bridges two Rh(CO)(η⁵-C₉H₇) fragments linked by a Rh–Rh bond [Rh(1)–Rh(2)2.691 (1)Å]. A minor product in this reaction is obtained in higher yield by treating acetylene with [Rh₃(µ-CO)₃(η⁵-C₉H₇)₃, and is characterised as a complex containing two Rh(η⁵-C₉H₇) units linked by a µ-pentadien-3-one fragment. Reaction of this complex with carbon monoxide or heating affords the cyclopentadienone complex, [Rh(η⁴-C₄H₄CO)(η⁵-C₉H₇)]. Reaction of [Rh₂(µ-CCH₂)(CO)₂(η⁵-C₉H₇)₂] with HBF₄–Et₂O gives [Rh₂(µ-CHCH₂)(µ-CO)(CO)(η⁵-C₉H₇)₂][BF₄], there being no evidence for the formation of a bridged alkylidyne complex.