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(SiMe 3 ) 3 ]H (Cp* = η 5 -C 5 Me 5; Ar = 2,6- i Pr 2 C 6 H 3 ) with PhSiH 3 resulted in formation of [Cp*(ArN )TaH(μ-H)] 2 (4% yield), yellow, paramagnetic Cp* 2 (ArN )Ta 2 H 2 (μ-ArNSiHPh) ( 1, 18% yield), and dark green, diamagnetic Cp* 2 Ta 2 H 2 (μ-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 2, 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(μ-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.