Ditantalum Hydride Complexes with Bridging (2,6-iPr2C6H3)NSiHPh Silanimine Ligands Resulting from PhSiH3-Imido Ligand Coupling. A Combined Spectroscopic and Theoretical Investigation

The prepn. 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* = h5-C5Me5; Ar = 2,6-iPr2C6H3) with PhSiH3 resulted in formation of [Cp*(ArN:)TaH(m-H)]2 (4% yield), yellow, paramagnetic Cp2(ArN:)Ta2H2(m-ArNSiHPh) (1, 18% yield), and dark green, diamagnetic Cp2Ta2H2(m-ArNSiHPh)2 (2, 71% yield). For 1 and 2, x-ray structure detns. characterize the ArNSiHPh silanimine ligand as possessing a Si-N single bond. This is confirmed by MO calcns. that provide an av. 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 anal. revealed a mol. structure possessing nearly exact 2-fold symmetry (the hydride ligands were not located), while NMR spectroscopy indicates that the two Cp*Ta(m-ArNSiHPh) fragments in the mol. are chem. inequivalent. To analyze the structure and bonding in this compd., a theor. study based on d. functional theory and ab initio mol. dynamics was carried out. Calcns. of the entire 140-atom dinuclear tantalum system confirm a structure with an asym. substitution of the two hydride ligands, with one terminal and one bridging. The paramagnetic compd. 1 exhibits structural features that are similar to those for 2. For this complex, the spectroscopic data and d. functional calcns. are consistent with a structure featuring terminal and bridging hydride ligands. [on SciFinder (R)]