Ditantalum hydride complexes with bridging (2,6-iPr2C6H3)NSiHPh silanimine ligands resulting from PhSiH3-imido ligand coupling.: A combined spectroscopic and theoretical investigation

The preparation and characterization of two novel dinuclear tantalum hydride complexes featuring bridging silanimine ligands are reported. The reaction 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 dark green, diamagnetic Cp*2Ta2H2(mu-ArNSiHPh)(2) (2, 71% yield). For 1 and 2, X-ray structure determinations characterize the ArNSiHPh silanimine ligand 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. The ArNSiHPh fragment is therefore best viewed as a bifunctional silyl-amido ligand. For diamagnetic complex, the X-ray analysis revealed a molecular structure possessing nearly exact 2-fold symmetry (the hydride ligands were not located), while NMR spectroscopy indicates that the two Cp*Ta(mu-ArNSiHPh) fragments in the molecule are chemically inequivalent. To analyze the structure and bonding in this compound, a theoretical study based on density functional theory and ab initio molecular dynamics was carried out. Calculations of the entire 140-atom dinuclear tantalum system confirm a structure with an asymmetric substitution of the two hydride ligands, with one terminal and one bridging. The paramagnetic compound 1 exhibits structural features that are similar to those for 2. For this complex, the spectroscopic data and density functional calculations are consistent with a structure featuring terminal and bridging hydride ligands.