Neutral and Zwitterionic Low-Coordinate Titanium Complexes Bearing the Terminal Phosphinidene Functionality. Structural, Spectroscopic, Theoretical, and Catalytic Studies Addressing the Ti−P Multiple Bond

α-Hydrogen abstraction and α-hydrogen migration reactions yield novel titanium(IV) complexes
bearing terminal phosphinidene ligands. Via an α-H migration reaction, the phosphinidene (tBunacnac)TiP[Trip](CH2tBu) (tBunacnac- = [Ar]NC(tBu)CHC(tBu)N[Ar], Ar = 2,6-(CHMe2)2C6H3, Trip = 2,4,6-iPr3C6H2)
was prepared by the addition of the primary phosphide LiPH[Trip] to the nucleophilic alkylidene triflato
complex (tBunacnac)TiCHtBu(OTf), while α-H abstraction was promoted by the addition of LiPH[Trip] to
the dimethyl triflato precursor (tBunacnac)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)TiP[Trip]{CH3B(C6F5)3}. Complex (tBunacnac)TiP[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 TiP bonds reported, have linear phosphinidene groups, and reveal significantly upfielded solution
31P NMR spectroscopic resonances for the phosphinidene phosphorus. Solid state 31P 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−Cipso linkage is highly dependent on the sterically encumbering substituents protecting the
phosphinidene. Complex (tBunacnac)TiP[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.