Molecular Alumo- and Gallosilicate Hydrides Functionalized with Terminal M(NR₂)₃ and Bridging M(NR₂)₂ (M = Ti, Zr, Hf; R = Me, Et) Moieties

A general synthetic strategy for the systematic synthesis of group 4 M-IV heterometallic complexes LMIII(H)(mu-O)Si( mu-O)(OtBu)(2)} M-n(IV)( NR2)4-n ( L = {[HC{C( Me)N(2,6-(Pr2C6H3)-Pr-i)}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)(2)Si(OtBu)(2) yielded LAlH(mu-O)Si(OH)(OtBu)(2) (1), while on the other hand, the oxidative addition of (HO)(2)Si(OtBu)(2) to LGa produced the gallium analog (2). These metalloligands successfully stabilized two hydrogen atoms with different acid-base properties (MIII-H and SiO-H) in the same molecule. Reactivity studies between 1 and 2 and group 4 amides M-IV(NR2)(411) (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/MIV 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 MIV species grafted onto silica/alumina surfaces with hydride and dihydride architectures.