Rapid Markovnikov addition of HCl to a pendant alkyne: evidence for a quinoidal cumulene†
Abstract
Reaction of cis-[RuCl2(dppm)2]BF4 with TlBF4 and 1,4-diethynyl-benzenes results in the formation of the vinylidene cations trans-[Ru(CCH–C6H2-2,5-R2-4-CCH)Cl(dppm)2]+ (R = H, Me). Subsequent reaction with [NnBu4]Cl results in nucleophilic attack at the coordinated organic ligand, but not at the expected metal-bound carbon atom. Instead, trans-[Ru(CC–C6H2-2,5-R2-4-CClCH2)Cl(dppm)2] was generated which, when coupled with DFT calculations, provides evidence for an intermediate quinoidal cumulene complex.