Reactivity of [TpRuCl(PTA)(PPh3)] with Alkynes and Propargylic Alcohols: Occurrence of Structurally Related Cationic vs Neutral Allenylidene Complexes with the Ruthenium Hydrotris(pyrazolyl)borate Moiety

Abstract

[TpRuCl(PTA)(PPh3)] (1; PTA = 1,3,5-triaza-7-phosphaadamantane) reacts with phenylacetylene, yielding the alkynyl complex [TpRu(C≡CPh)(PTA)(PPh3)] (2) or the neutral vinylidene complex [TpRuCl{C═C(H)Ph}(PTA)] (4), depending on the solvent and the reaction conditions (Tp = hydrotris(pyrazolyl)borate). Protonation of 2 with HOTf (OTf = OSO2CF3) in CH2Cl2 yields the dicationic vinylidene compound [TpRu{C═C(H)Ph}{PTAH}(PPh3)](OTf)2 (3), bearing a N-protonated PTA ligand. Reaction of 1 with 1,1-diphenyl-2-propyn-1-ol affords the new cationic compound [TpRu(C═C═CPh2)(PTA)(PPh3)]PF6 (5) or neutral allenylidene compound [TpRuCl(C═C=CPh2)(PTA)] (6), depending on the reaction solvent (MeOH or toluene, respectively). The reactivity of complexes 5 and 6 toward tertiary phosphines (PTA and PPh2Me) has been investigated. Remarkably, both the cationic and the neutral allenylidene compounds undergo regioselective nucleophilic attack at the allenylidene Cα position to give the σ-allenyl-phosphonium complexes [TpRu{C(L)═C═...