Molecular Alumo- and Gallosilicate Hydrides Functionalized with Terminal M(NR₂)₃ and Bridging M(NR₂)₂ (M = Ti, Zr,...

A general synthetic strategy for the systematic synthesis of group 4 M^IV heterometallic complexes LM^III(H)(μ-O)Si(μ-O)(OtBu)₂}M^IV(NR₂)_4- (L = {[HC{C(Me)N(2,6-Pr₂C₆H₃)}₂; M^III = Al or Ga; n = 1 or 2; M^IV = Ti, Zr, Hf; R = Me, Et), based on alumo- or gallosilicate hydride ligands bearing a Si-OH moiety, is presented. The challenging isolation of these metalloligands involved two strategies. On the one hand, the acid-base reaction of LAlH₂ with (HO)₂Si(OtBu)₂ yielded LAlH(μ-O)Si(OH)(OtBu)₂ (1), while on the other hand, the oxidative addition of (HO)₂Si(OtBu)₂ to LGa produced the gallium analog (2). These metalloligands successfully stabilized two hydrogen atoms with different acid-base properties (M^III-H and SiO-H) in the same molecule. Reactivity studies between 1 and 2 and group 4 amides M^IV(NR₂)₄ (M^IV = Ti, Zr, Hf; R = Me, Et) and tuning the reactions conditions and stoichiometry led to isolation and structural characterization of heterometallic complexes 3-11 with a 1:1 or 2:1 metalloligand/M^IV ratio. Notably, some of these molecular heterometallic silicate complexes stabilize for the first time terminal (O₃Si-O-)M^IV(NR₂)₃ moieties known from single-site silica-grafted species. Furthermore, the aluminum-containing heterometallic complexes possess Al-H vibrational energies similar to those reported for modified alumina surfaces, which makes them potentially suitable models for the proposed M^IV species grafted onto silica/alumina surfaces with hydride and dihydride architectures.