Reactions of Ethyne with Some Ruthenium Cluster Complexes Containing dppm

Abstract

In memoriam Luigi M. Venanzi, who was an early mentor of the senior author and who first aroused his interest in organometallic chemistryReactions of ethyne with [Ru 3 (m-dppm)(CO) 10 ] have given isomeric complexes [Ru 3 (m 3 -C 6 H 6 )(CO) 6 (dppm)], one of which, 2, contains the dppm chelating an Ru-atom, together with a hexatrienetriyl ligand attached to the Ru 3 cluster to form a methylideneruthenacyclohexadiene system. The second isomer 3 contains the dppm bridging an RuÀRu bond, with the C 6 H 6 ligand forming a vinylruthenacyclopentadiene system. Also isolated was the open-chain Ru 3 complex 4 containing a ruthenacyclopentadiene attached to the central Ru-atom; the other RuÀRu vector is bridged by a PPh 2 CHPPh 2 C 4 H 5 ligand, formed by a novel insertion of two ethyne molecules into an RuÀP bond. The reaction of ethyne with [Ru 3 (m-H)(m 3 -C 2 H 2 )(CO) 9 ] proceeded by attack at the coordinated alkyne and at the cluster to give a cluster-bonded PPh 2 CH 2 PPh 2 CCH system in 7. Thermolysis of [Ru 3 (m-H)(m 3 -C 2 SiMe 3 )(m-dppm)(CO) 7 ] (8; refluxing MeOH) in the presence of KF gave [Ru 6 (m-CCH 2 ) 2 (m-dppm) 2 (CO) 12 ] (9; 80%); similar reactions carried out with [RuClCp(PPh 3 ) 2 ] also present gave 9 (67%) together with [Ru 3 (m-H)(m 3 -C 2 H)(m-dppm)(CO) 6 (PPh 3 )] (11; 23%). The molecular structures of 2, 3, 4, 7, 9, and 11, some as differently solvated forms, have been determined by single-crystal Xray studies.Helvetica Chimica Acta ± Vol. 84 (2001) 3197 treating [RuClCp(PPh 3 ) 2 ] with a variety of trimethylsilylated alkynes and poly-ynes in the presence of KF in MeOH [7]. It is likely that this reaction proceeds with intermediate formation of the corresponding vinylidene, which is deprotonated by the fluoride (or methoxide) base. We were interested to determine whether similar reactions might be applied to cluster-bonded silylated alkynes or alkynyls. This paper also describes the protodesilylation reaction of [Ru 3 (m-H)(m 3 -C 2 SiMe 3 )(mdppm)(CO) 7 ] [5b], from which an unusual hexanuclear cluster containing vinylidene ligands was isolated.Results and Discussion. ± Reactions of Ethyne with [Ru 3 (m-dppm)(CO) 10 ] (1). Reactions between [Ru 3 (m-dppm)(CO) 10 ] (1) and ethyne were carried out by passing a stream of the gas through a solution of the complex, monitoring the reaction periodically by TLC. The same products were formed either on heating, or from a reaction carried out at room temperature in the presence of Me 3 NO. Thus, from a reaction carried out in refluxing THF for 2 h, four complexes were separated by preparative TLC (Scheme 1). Elemental analyses and mass spectrometry enabled empirical compositions to be established, while single-crystal X-ray studies were required to determine the precise molecular structures of several of the complexes.