Terminal Parent Phosphanide and Phosphinidene Complexes of Zirconium(IV)

The reaction of Zr(Tren^DMBS)(Cl)] Zr1 ; Tren^DMBS=N(CH₂CH₂NSiMe₂Bu^t )₃] with NaPH₂ gave the terminal parent phosphanide complex Zr(Tren^DMBS)(PH₂)] Zr2 ; Zr−P=2.690(2) Å]. Treatment of Zr2 with one equivalent of KCH₂C₆H₅ 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(Tren^DMBS)(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.