Neutral and zwitterionic low-coordinate titanium complexes bearing the terminal phosphinidene functionality. Structural, spectroscopic, theoretical, and catalytic studies addressing the Ti-P multiple bond

alpha-Hydrogen abstraction and alpha-hydrogen migration reactions yield novel titanium(IV) complexes bearing terminal phosphinidene ligands. Via an alpha-H migration reaction, the phosphinidene ((tBu)nacnac) Ti = P[Trip]((CH2Bu)-Bu-t) ((tBu)nacnac-= [Ar]NC(Bu-t) CHC(Bu-t) N[Ar], Ar = 2,6-(CHMe2)(2)C6H3, Trip = 2,4,6-(Pr3C6H2)-Pr-i) was prepared by the addition of the primary phosphide LiPH[Trip] to the nucleophilic alkylidene triflato complex ((t)Bunacnac) Ti=(CHBu)-Bu-t(OTf), while alpha-H abstraction was promoted by the addition of LiPH[Trip] to the dimethyl triflato precursor ((t)Bunacnac) Ti(CH3)(2)(OTf) to afford (tBunacnac) Ti=P[Trip](CH3). Treatment of (tBunacnac) Ti=P[Trip](CH3) with B(C6F5)(3) induces methide abstraction concurrent with formation of the first titanium(IV) phosphinidene zwitterion complex (tBunacnac) TidP[Trip] {CH3B(C6F5)(3)}. Complex (tBunacnac)TidP[Trip] {CH3B(C6F5)(3)} [2+2] cycloadds readily PhCCPh to afford the phosphametallacyclobutene [(tBunacnac) Ti(P[Trip] PhCCPh)][CH3B(C6F5)(3)]. These titanium(IV) phosphinidene complexes possess the shortest TidP bonds reported, have linear phosphinidene groups, and reveal significantly upfielded solution P-31 NMR spectroscopic resonances for the phosphinidene phosphorus. Solid state P-31 NMR spectroscopic data also corroborate with all three complexes possessing considerably shielded chemical shifts for the linear and terminal phosphinidene functionality. In addition, high-level DFT studies on the phosphinidenes suggest the terminal phosphinidene linkage to be stabilized via a pseudo Ti=P bond. Linearity about the Ti-P-C-ipso linkage is highly dependent on the sterically encumbering substituents protecting the phosphinidene. Complex (tBunacnac) TidP[Trip] {CH3B(C6F5)(3)} can catalyze the hydrophosphination of PhCCPh with H2PPh to produce the secondary vinylphosphine HP[Ph] PhC=CHPh. In addition, we demonstrate that this zwitterion is a powerful phospha-Staudinger reagent and can therefore act as a carboamination precatalyst of diphenylacetylene with aldimines.