Molecular Routes to Metal Oxides and Metal Silicates. Synthesis and Thermal Decomposition Studies of Eclipsed Mo2[O2Si(OtBu)2]3 and W2(NHMe2)2[O2Si(OtBu)2]2[OSi(OH)(OtBu)2]2

Reaction of Mo 2 (NMe 2 ) 6 with 3 equiv of ( t BuO) 2 Si(OH) 2 afforded a new siloxide complex, Mo 2 [O 2 Si(O t Bu) 2 ] 3 ( 1 ), as the only metal-containing product. An X-ray crystal structure determination reveals that 1 adopts an eclipsed structure with three di- tert- butoxysilanediolato ligands bridging the molybdenum centers in a symmetrical fashion. Lewis acidic complex 1 forms an isolable adduct with pyridine. Reaction of W 2 (NMe 2 ) 6 with 3 equiv of ( t BuO) 2 Si(OH) 2 afforded W 2 (NHMe 2 ) 2 [O 2 Si(O t Bu) 2 ] 2 [OSi(OH)(O t Bu) 2 ] 2 ( 3 ), which was isolated as air-sensitive orange crystals. In this molecule, two O 2 Si(O t Bu) 2 ligands bridge the W⋮W bond in an η 1,η 1 fashion, and OSi(OH)(O t Bu) 2 ligands are coordinated to each W atom. This molecule adopts a highly eclipsed conformation and has a 2-fold axis of symmetry which perpendicularly bisects the tungsten−tungsten bond. Complex 1 undergoes a two-step weight loss (by TGA), which corresponds to the initial loss of isobutene and water (at ca. 200 °C), followed by the loss of molybdenum by evaporation of MoO 3 at 700−1050 °C. The pyrolysis of 1 at 550 °C for 2 h under argon gave a ceramic material with the approximate formula Mo 2 Si 3 O 10 . When the sample was heated at 1200 °C for 1 h, evaporation of MoO 3 occurred and the final ceramic material had a composition of Mo 0.5 Si 3 O 6.5 . Very low carbon contents for these materials are consistent with a clean elimination process during the pyrolysis. The material heated to 550 °C is amorphous, while the material taken to 1200 °C contains MoO 2 as the only crystalline phase. Pyrolysis of 1 in air at 1200 °C resulted in the extensive loss of molybdenum (2.14% Mo; no crystalline phases by XRD). Interestingly, pyrolysis of small crystals of 1 occurs with retention of the crystals' shape and size, despite a great loss in weight (75%). Pyrolysis of 3 at 550 and 1200 °C under argon produced ceramic materials consistent with the formulas W 2.2 Si 4 O 17.4 and W 2.2 Si 4 O 13, respectively. While the 550 °C ceramic is amorphous, the 1200 °C material contains crystalline W and WO 2 (by XRD analysis).