Selective Synthesis of Indenylruthenium(II) Vinylvinylidene Complexes via Unstable Allenylidene Intermediates: Unexpected Formation of Alkenyl−Phosphonio Complexes (E)-[Ru{C(H)C(PPh3)R}(η5-C9H7)(PPh3)2][PF6] (R = 1-Cyclohexenyl, 1-Cycloheptenyl) through Nucleophilic Addition of Triphenylphosphine on Vinylvinylidene Derivatives

The vinylvinylidene = PPh 3, L 2 = 1,2-bis(diphenylphosphino)ethane (dppe); n = 1 ( 2a, b ), 2 ( 3a, b ), 3 ( 4a, b )) have been prepared by reaction of [RuCl(η 5 -C 9 H 7 )L 2 ] with 1-ethynyl-1-cycloalkanols and NaPF 6 in refluxing methanol. Deprotonation of the vinylidene derivatives with Al 2 O 3 yields the neutral enynyl 6a, b, and 7a, b ). The reaction of the enynyl complex [Ru(C⋮CR)(η 5 -C 9 H 7 )(PPh 3 ) 2 ] (R = 1-cyclohexenyl; 6a ) with MeOSO 2 CF 3 produces the disubstituted vinylvinylidene derivative [Ru{ C C(Me)R}(η 5 -C 9 H 7 )(PPh 3 ) 2 ][CF 3 SO 3 ] (R = 1-cyclohexenyl; 8a ). The crystal structure of 8a was determined by X-ray diffraction methods. In the structure the Ru C C chain is nearly linear (Ru−C(1)−C(2) = 176.2(4)°) with an Ru−C(1) distance of 1.838(5) Å. The indenyl ligand is η 5 -bonded to the metal with the benzo ring orientated “ trans ” with respect to the vinylidene group. When the reaction of [RuCl(η 5 -C 9 H 7 )(PPh 3 ) 2 ] with 1-ethynylcyclohexanol or 1-ethynylcyclopentanol and NaPF 6 takes place in the presence of PPh 3, the alkynyl−phosphonio = 1 ( 11a ), 2 ( 12a )) were obtained via nucleophilic attack of the PPh 3 on C γ of the unstable allenylidene = 1 ( 9a ), 2 ( 10a )). The vinylvinylidene complexes 3a ( n = 2) and 4a ( n = 3) also react with PPh 3, giving the alkenyl−phosphonio = 2 ( 13a ), 3 ( 14a )). The structure of 13a was confirmed by X-ray diffraction methods. A possible mechanism for the formation of 13a and 14a is proposed.