Reactions of co-ordinated ligands. Part 34. Synthesis, structure, and reactivity of cationic dieneruthenium complexes; crystal structures of [Ru(η4-C6H8)(CO)(η-C5H5)][BF4] and [Ru(η3-C6H9)(CO)(η-C5H5)]

Abstract

Ultraviolet irradiation of a solution of [Ru(NCMe)(CO)₂(η-C₅H₅)][BF₄] in MeCN affords [Ru(NCMe)₂(CO)(η-C₅H₅)][BF₄](1) in high yield. The acetonitrile ligands in complex (1) are substitution labile and reaction with buta-1,3-diene, isoprene, 1,4-diphenylbuta-1,3-diene, and cyclohexa-1,3-diene gives the complexes [Ru(η⁴-1,3-diene)(CO)(η-C₅H₅)][BF₄]. An X-ray crystallographic study on the cyclohexa-1,3-diene cation established that the molecule adopts an exo configuration, the C₆ ring showing substantial folding. Whereas trans-penta-1,3-diene reacts with complex (1) to form an analogous complex, cis-penta-1,3-diene affords an isomeric mixture of exo and endo isomers of both the cis- and trans-penta-1,3-diene complexes. This is discussed in terms of a hydrogen-shift process involving a Ru^II→ Ru^IV redox reaction. Cyclo-octa-1,3-diene does not react with complex (1), however, both cyclo-octa-1,5-diene and cyclo-octatetraene react to form [Ru(η⁴-1,5-C₈H₁₂)(CO)(η-C₅H₅)][BF₄] and [Ru(η⁴-C₈H₈)(CO)(η-C₅H₅)][BF₄], u.v. irradiation of the latter complex affording [Ru(η⁶-C₈H₈)(η-C₅H₅)][BF₄]. This is possibly related to a close relationship between the fragments Ru(CO)(η-C₅H₅)⁺ and Cr(CO)₄. Reaction of the buta-1,3-diene and isoprene cations with Li[CuPh₂] and Na[BH₃(CN)] respectively affords η³-allyl complexes. An X-ray crystallographic study on the η³-cyclohexenyl complex, [Ru(η³-C₆H₉)(CO)(η-C₅H₅)], obtained on reaction of the cyclohexa-1,3-diene cation with Na[BH₃(CN)] showed that the C₆ ring adopts a boat conformation. Consideration of this observation along with ¹H n.m.r. data is used to show that nucleophilic reagents attack the opposite face of the C₆ ring to which the ruthenium is bonded. The cyclo-octa-1,5-diene complex reacts with Na[BH₃(CN)] to form a 1,4,5-η³-C₈H₁₃ complex, which does not isomerise to a 1,2,3-η³-bonded species.