Reactivity of [TpRuCl(PTA)(PPh<sub>3</sub>)] with Alkynes and Propargylic Alcohols: Occurrence of Structurally Related Cationic vs Neutral Allenylidene Complexes with the Ruthenium Hydrotris(pyrazolyl)borate Moiety

[TpRuCl(PTA)(PPh<sub>3</sub>)] (<b>1</b>; PTA = 1,3,5-triaza-7-phosphaadamantane) reacts with phenylacetylene, yielding the alkynyl complex [TpRu(CCPh)(PTA)(PPh<sub>3</sub>)] (<b>2</b>) or the neutral vinylidene complex [TpRuCl{CC(H)Ph}(PTA)] (<b>4</b>), depending on the solvent and the reaction conditions (Tp = hydrotris(pyrazolyl)borate). Protonation of <b>2</b> with HOTf (OTf = OSO<sub>2</sub>CF<sub>3</sub>) in CH<sub>2</sub>Cl<sub>2</sub> yields the dicationic vinylidene compound [TpRu{CC(H)Ph}{PTAH}(PPh<sub>3</sub>)](OTf)<sub>2</sub> (<b>3</b>), bearing a N-protonated PTA ligand. Reaction of <b>1</b> with 1,1-diphenyl-2-propyn-1-ol affords the new cationic compound [TpRu(CCCPh<sub>2</sub>)(PTA)(PPh<sub>3</sub>)]PF<sub>6</sub> (<b>5</b>) or neutral allenylidene compound [TpRuCl(CC=CPh<sub>2</sub>)(PTA)] (<b>6</b>), depending on the reaction solvent (MeOH or toluene, respectively). The reactivity of complexes <b>5</b> and <b>6</b> toward tertiary phosphines (PTA and PPh<sub>2</sub>Me) has been investigated. Remarkably, both the cationic and the neutral allenylidene compounds undergo regioselective nucleophilic attack at the allenylidene C<sub>α</sub> position to give the σ-allenyl-phosphonium complexes [TpRu{C(L)CCPh<sub>2</sub>}(PTA)(PPh<sub>3</sub>)]PF<sub>6</sub> (L = PPh<sub>2</sub>Me (<b>8</b>), PTA (<b>9</b>)) and [TpRuCl{C(L)CCPh<sub>2</sub>}(PTA)] (L = PTA (<b>10</b>), PPh<sub>2</sub>Me (<b>11</b>)), respectively. Noticeably, the reaction goes to completion in the case of the neutral allenylidene complex <b>6</b>, whereas an equilibrium between the phosphonioallenyl adduct and the educt species is observed in the case of the cationic allenylidene compound <b>5</b>. The thermodynamic parameters for such an equilibrium have been determined by NMR methods at different temperatures. Finally, the hydrolysis of the neutral allenylidene <b>6</b> has been briefly considered, showing the formation of the carbonyl compound [TpRuCl(CO)(PTA)] (<b>7</b>).