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

A general synthetic strategy for the systematic synthesis of group 4 M IV heterometallic complexes L M III (H)(μ-O)Si(μ-O)(O t Bu) 2 } n M IV (NR 2 ) 4- n ( L = {[HC{C(Me)N(2,6- i Pr 2 C 6 H 3 )} 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 L AlH 2 with (HO) 2 Si(O t Bu) 2 yielded L AlH(μ-O)Si(OH)(O t Bu) 2 ( 1 ), while on the other hand, the oxidative addition of (HO) 2 Si(O t Bu) 2 to L Ga 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 (NR 2 ) 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 (O 3 Si-O-)M IV (NR 2 ) 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.