Phosphinoalkylidene and -alkylidyne Complexes of Titanium: Intermolecular C–H Bond Activation and Dehydrogenation Reactions

The ethylene complex (PNP)­Ti­(η²-H₂CCH₂)­(CH₂^tBu) or (PNP)­TiCH^tBu­(CH₂^tBu) (PNP^– = N­[2-P­(CHMe₂)₂-4-methylphenyl]₂) reacts with H₂CPPh₃ to form the κ²-phosphinoalkylidene (PNP)­TiCHPPh₂(Ph) (1). Compound 1 activates benzene via the transient intermediate [(PNP)­TiCPPh₂] (C). By treatment of (PNP)­TiCH^tBu­(OTf) with LiCH₂PPh₂, 1 or its isotopologue (PNP)­TiCDPPh₂(C₆D₅) (1-d₆) can be produced by an independent route involving intermediate C, which activates benzene or benzene-d₆ and dehydrogenates cyclohexane-d₁₂. Addition of MeOTf to 1 results in elimination of benzene concomitant with the formation of the phosphonioalkylidyne complex, [(PNP)­TiCPPh₂Me­(OTf) (2). Theoretical studies of 2 suggest a resonance structure having dominant Ti–C triple-bond character with some contribution also from a C–P multiple bond.