Synthesis and Characterization of Tris(trimethylsilyl)siloxide Derivatives of Early Transition Metal Alkoxides That Thermally Convert to Varied Ceramic-Silica Architecture Materials.

In an effort to generate single-source precursors for the production of metal-siloxide (MSiO ) materials, the tris(trimethylsilyl)silanol (H-SST or H-OSi(SiMe) (1) ligand was reacted with a series of group 4 and 5 metal alkoxides. The group 4 products were crystallographically characterized as [Ti(SST)(OR)] (OR = OPr (2), OBu (3), ONep (4)); [Ti(SST)(OBu )] (5); [Zr(SST)(OBu )(py)] (6); [Zr(SST)(OR)] (OR = OBu (7), ONep, (8)); [Hf(SST)(OBu )] (9); and [Hf(SST)(ONep)(py) ] ( n = 1 (10), n = 2 (10a)) where OPr = OCH(CH), OBu = OC(CH), OBu = O(CH)CH, ONep = OCHC(CH), py = pyridine. The crystal structures revealed varied SST substitutions for: monomeric Ti species that adopted a tetrahedral ( T-4) geometry; monomeric Zr compounds with coordination that varied from T-4 to trigonal bipyramidal ( TBPY-5); and monomeric Hf complexes isolated in a TBPY-5 geometry. For the group 5 species, the following derivatives were structurally identified as [V(SST)(py)] (11), [Nb(SST)(OEt)] (12), [Nb(O)(SST)(py)] (13), 2[H][(Nb(μ-O)(SST))(μ-O)] (14), [NbO(OEt)(SST)·1/5NaO] (15), [Ta(SST)(μ-OEt)(OEt)] (16), and [Ta(SST)(OEt)] (17) where OEt = OCHCH. The group 5 monomeric complexes were solved in a TBPY-5 arrangement, whereas the Ta of the dinculear 16 was solved in an octahedral coordination environment. Thermal analyses of these precursors revealed a stepwise loss of ligand, which indicated their potential utility for generating the MSiO materials. The complexes were thermally processed (350-1100 °C, 4 h, ambient atmosphere), but instead of the desired MSiO , transmission electron microscopy analyses revealed that fractions of the group 4 and group 5 precursors had formed unusual metal oxide silica architectures.