title: Synthesis, structural and spectroscopic characterization, catalytic properties, and thermal transformations of new cyclic di- and trisiloxanediolato tantalum complexes.
abstract: The reaction between Ta(OEt)5 and 1,1,3,3-tetramethyl-1,3-disiloxanediol, (HOSiMe2OSiMe2OH), leads to new siloxy complexes in which the dimeric nature of Ta(OEt)5 is maintained with both bridging ethoxide and disiloxanediolato bridges. With equal amounts of the reagents, two terminal OEt groups are replaced to form [Ta(OEt)2]2(mu-OEt)2(mu-OSiMe2OSiMe2O)2, 1, whereas with an excess of diol, the remaining terminal OEt groups are also replaced but with a trisiloxanediolato unit to form [Ta(OSiMe2OSiMe2OSiMe2O)]2(mu-OEt)2(mu-OSiMe2OSiMe2O)2, 2. Complexes 1 and 2 catalyze the transformation of HOSiMe2OSiMe2OH to polysiloxanes. Thermal treatment of 1 results in the formation of a 1:2 mixture of Ta2O5/SiO2; no new phases are observed. The molecular structures of 1 and 2 are confirmed by X-ray crystallography.
authors.affiliation: Department of Chemistry, University of Texas at El Paso, El Paso, Texas 79968, USA.
authors.forename: Ramesh N
authors.initials: RN
authors.lastname: Kapoor
authors.forename: Francisco
authors.initials: F
authors.lastname: Cervantes-Lee
authors.forename: Charles F
authors.initials: CF
authors.lastname: Campana
authors.forename: Curtis
authors.initials: C
authors.lastname: Haltiwanger
authors.forename: Kent
authors.initials: K
authors.lastname: Abney
authors.forename: Keith H
authors.initials: KH
authors.lastname: Pannell
mesh_terms: D002384:Catalysis; D015392:Chemistry, Inorganic / Q000379:methods*; D018360:Crystallography, X-Ray; D019281:Dimerization; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D013635:Tantalum / Q000737:chemistry*
chemical_list: D009942:Organometallic Compounds; D013635:Tantalum