Ditantalum hydride complexes with bridging (2,6-(Pr2C6H3)-Pr-i)NSiHPh silanimine ligands resulting from PhSiH3-imido ligand coupling. A combined spectroscopic and theoretical investigation

The preparation and characterization of two novel dinuclear tantalum hydrid e complexes featuring bridging silanimine ligands are reported. The reactio n of Cp*(ArN=)Ta-[Si(SiMe3)(3)]H (Cp* = eta(5)-C5Me5; Ar'2,6-(Pr2C6H3)-Pr-i ) with PhSiH3 resulted in formation of [Cp *(ArN=)TaH(mu-H)](2) (4% yield), yellow, paramagnetic Cp*(2)(ArN=)Ta2H2(mu-ArNSiHPh) (1, 18% yield), and da rk green, diamagnetic Cp*2Ta2H2(mu-ArNSiHPh)(2) (2, 71% yield). For 1 and 2 , X-ray structure determinations characterize the ArNSiHPh silanimine ligan d as possessing a Si-N single bond. This is confirmed by molecular orbital calculations that provide an average bond order of 0.7 for the Si-N bond. T he ArNSiHPh fragment is therefore best viewed as a bifunctional silyl-amido ligand. For diamagnetic complex, the X-ray analysis revealed a molecular s tructure possessing nearly exact 2-fold symmetry (the hydride ligands were not located), while NMR spectroscopy indicates that the two Cp*Ta(mu-ArNSiH Ph) fragments in the molecule are chemically inequivalent. To analyze the s tructure and bonding in this compound, a theoretical study based on density functional theory and ab initio molecular dynamics was carried out. Calcul ations of the entire 140-atom dinuclear tantalum system confirm a structure with an asymmetric substitution of the two hydride ligands, with one termi nal and one bridging. The paramagnetic compound 1 exhibits structural featu res that are similar to those for 2. For this complex, the spectroscopic da ta and density functional calculations are consistent with a structure feat uring terminal and bridging hydride ligands.