Terminal Parent Phosphanide and Phosphinidene Complexes of Zirconium(IV)

The reaction of [Zr(TrenDMBS )(Cl)] [Zr1; TrenDMBS =N(CH2 CH2 NSiMe2 But )3 ] with NaPH2 gave the terminal parent phosphanide complex [Zr(TrenDMBS )(PH2 )] [Zr2; Zr-P=2.690(2) Å]. Treatment of Zr2 with one equivalent of KCH2 C6 H5 and two equivalents of benzo-15-crown-5 ether (B15C5) afforded an unprecedented example (outside of matrix isolation) of a structurally authenticated transition-metal terminal parent phosphinidene complex [Zr(TrenDMBS )(PH)][K(B15C5)2 ] [Zr3; Zr=P=2.472(2) Å]. DFT calculations reveal a polarized-covalent Zr=P double bond, with a Mayer bond order of 1.48, and together with IR spectroscopic data also suggest an agostic-type Zr⋅⋅⋅HP interaction [∡ZrPH =66.7°] which is unexpectedly similar to that found in cryogenic, spectroscopically observed phosphinidene species. Surprisingly, computational data suggest that the Zr=P linkage is similarly polarized, and thus as covalent, as essentially isostructural U=P and Th=P analogues.