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

A general synthetic strategy for the systematic synthesis of group 4 M heterometallic complexes M(H)(μ-O)Si(μ-O)(OBu)}M(NR) ( = {[HC{C(Me)N(2,6-PrCH)}; M = Al or Ga; = 1 or 2; M = 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 AlH with (HO)Si(OBu) yielded AlH(μ-O)Si(OH)(OBu) (), while on the other hand, the oxidative addition of (HO)Si(OBu) to Ga produced the gallium analog (). These metalloligands successfully stabilized two hydrogen atoms with different acid-base properties (M-H and SiO-H) in the same molecule. Reactivity studies between and and group 4 amides M(NR) (M = Ti, Zr, Hf; R = Me, Et) and tuning the reactions conditions and stoichiometry led to isolation and structural characterization of heterometallic complexes - with a 1:1 or 2:1 metalloligand/M ratio. Notably, some of these molecular heterometallic silicate complexes stabilize for the first time terminal (OSi-O-)M(NR) 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 species grafted onto silica/alumina surfaces with hydride and dihydride architectures.