Nucleophilic Addition Reactions to Allenylidene Complexes of Ruthenium Bearing Hemilabile P,N Ligands: Isolation of the Vinylcarbene Complex [Cp*RuCHCHCPh₂(ⁱPr₂PNHPy)][PF₆]

The complex [Cp*RuCCCPh2(iPr2PNHPy)][PF6] (2), prepared by reaction of [Cp*Ru(MeCN)(iPr2PNHPy)][PF6] (1) with HCCC(OH)Ph2, reacts with primary amines, furnishing the corresponding vinylaminocarbenes, which are better formulated as the azoniabutadienyl derivatives [Cp*Ru{C(NHR)CHCPh2}(iPr2PNHPy)][PF6] (R = Cy (6a), Me (6b), CH2CCH (6c)). These species result from the nucleophilic attack of the amine at the Cα atom of the allenylidene ligand. At variance with this, the reaction of 2 with cyclic secondary amines such as piperidine, pyrrolidine, and morpholine yields the Schrock-type vinylcarbene complex [Cp*RuCHCHCPh2(iPr2PNHPy)][PF6] (7), which has been unequivocally characterized by X-ray structure analysis. This vinylcarbene complex is presumably formed by addition of the cyclic amine to the Cγ atom of the allenylidene through the intermediacy of a vinylidene complex. This intermediate vinylidene undergoes a retro-metallo-ene rearrangement, generating 7 plus the product of dehydrogenation of the amine. The reaction of 2 with thiophenol or pentafluorothiophenol afforded the thiocarbenes [Cp*Ru{C(SC6R5)CHCPh2}(iPr2PNHPy)][PF6] (R = H (8H), F (8F)), which have been structurally characterized. Alternatively, the reaction of 2 with pyridine-2-thiol or pyrimidine-2-thiol leads to the thiocarbenes [Cp*Ru{κ2C,N-C(SC5H4N)CHCPh2}(κ1P-iPr2NHPy)][PF6] (9Py) and [Cp*Ru{κ2C,N-C(SC4H3NN)CHCPh2}(κ1-P-iPr2NHPy)][PF6] (9Pym). In these compounds a new five-membered chelate ring has formed, and the iPr2NHPy ligand exhibits hemilabile character, changing its coordination mode from κ2P,N to κ1P.