Reactivity of the N-heterocyclic carbene complexes [Ru(IMes)2(CO)HX] (X = OH, Cl) with alkynes

Treatment of the 16-electron hydroxy hydride complex [Ru(IMes)2(CO)H(OH)] (1, IMes = 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene) with HCCR affords the alkynyl species [Ru(IMes)2(CO)H(CCR)] (R = Ph 3, SiMe3, 4) and [Ru(IMes)2(CO)(CCR)2] (R = Ph, 5). Deuterium labelling studies show that the mono-alkynyl complexes are formed via hydrogen transfer from a coordinated alkyne ligand to Ru–OH, while bis-alkynyl formation is proposed to take place through hydrogen transfer to Ru–H. Both 3 and 5 readily coordinate CO to give the corresponding dicarbonyl species 6 and 7. Addition of HCCPh to the hydride chloride precursor [Ru(IMes)2(CO)HCl] (2) results in a different reaction pathway involving alkyne insertion into the Ru–H bond to yield the alkenyl chloride complex [Ru(IMes)2(CO)(CHCHPh)Cl] 8. Complexes 3–8 have been structurally characterised by X-ray crystallography.