Metal-Ligand Cooperativity to Assemble a Neutral and Terminal Niobium Phosphorus Triple Bond (Nb≡P)

Decarbonylation along with P-atom transfer from the phosphaethynolate anion, PCO^- , to the Nb^IV complex [(PNP)NbCl₂ (N^t BuAr)] (1) (PNP=N[2-Pⁱ Pr₂ -4-methylphenyl]₂ ^- ; Ar=3,5-Me₂ C₆ H₃ ) results in its coupling with one of the phosphine arms of the pincer ligand to produce a phosphanylidene phosphorane complex [(PNPP)NbCl(N^t BuAr)] (2). Reduction of 2 with CoCp*₂ cleaves the P-P bond to form the first neutral and terminal phosphido complex of a group 5 transition metal, namely, [(PNP)Nb≡P(N^t BuAr)] (3). Theoretical studies have been used to understand both the coupling of the P-atom and the reductive cleavage of the P-P bond. Reaction of 3 with a two-electron oxidant such as ethylene sulfide results in a diamagnetic sulfido complex having a P-P coupled ligand, namely [(PNPP)Nb=S(N^t BuAr)] (4).

Crystalline Diuranium Phosphinidiide and μ-Phosphido Complexes with Symmetric and Asymmetric UPU Cores

Reaction of [U(TrenTIPS )(PH2 )] (1, TrenTIPS =N(CH2 CH2 NSiPri3 )3 ) with C6 H5 CH2 K and [U(TrenTIPS )(THF)][BPh4 ] (2) afforded a rare diuranium parent phosphinidiide complex [{U(TrenTIPS )}2 (μ-PH)] (3). Treatment of 3 with C6 H5 CH2 K and two equivalents of benzo-15-crown-5 ether (B15C5) gave the diuranium μ-phosphido complex [{U(TrenTIPS )}2 (μ-P)][K(B15C5)2 ] (4). Alternatively, reaction of [U(TrenTIPS )(PH)][Na(12C4)2 ] (5, 12C4=12-crown-4 ether) with [U{N(CH2 CH2 NSiMe2 But )2 CH2 CH2 NSi(Me)(CH2 )(But )}] (6) produced the diuranium μ-phosphido complex [{U(TrenTIPS )}(μ-P){U(TrenDMBS )}][Na(12C4)2 ] [7, TrenDMBS =N(CH2 CH2 NSiMe2 But )3 ]. Compounds 4 and 7 are unprecedented examples of uranium phosphido complexes outside of matrix isolation studies, and they rapidly decompose in solution underscoring the paucity of uranium phosphido complexes. Interestingly, 4 and 7 feature symmetric and asymmetric UPU cores, respectively, reflecting their differing steric profiles.