Dimolybdenum(III) complexes of -OSi(OtBu)3, -O2P(OtBu)2 and-OB[OSi(OtBu)3]2 as single-source molecular precursors tomolybdenum-containing, multicomponent oxide materials

Journal Article · Thu Jan 15 04:00:00 EST 2004 · Chemistry of Materials

DOI:https://doi.org/10.1021/cm030563k· OSTI ID:917046

Fujdala, Kyle L; Tilley, T Don

The following dimolybdenum complexes containing -OSi(O{sup t}Bu){sub 3}, -O{sub 2}P(O{sup t}Bu){sub 2}, and -OB[OSi(O{sup t}Bu){sub 3}]{sub 2} ligands have been synthesized and structurally characterized: Mo{sub 2}(NMe{sub 2}){sub 4}[OSi(O{sup t}Bu){sub 3}]{sub 2} (1), Mo{sub 2}(O{sup t}Bu)4[OSi(O{sup t}Bu){sub 3}]{sub 2} (2), Mo{sub 2}(NMe){sub 4}(OB[OSi(O{sup t}Bu){sub 3}]{sub 2}){sub 2} (3), Mo{sub 2}(NMe{sub 2}){sub 2}[-O{sub 2}P(O{sup t}Bu){sub 2}]{sub 2}[O{sub 2}P(O{sup t}Bu){sub 2}]{sub 2} (4), Mo{sub 2}(NMe{sub 2}){sub 2}[OSi(O{sup t}Bu){sub 3}]{sub 2}[-O{sub 2}P(O{sup t}Bu){sub 2}]{sub 2} (5), and Mo{sub 2}(NMe{sub 2}){sub 2}[-O{sub 2}P(O{sup t}Bu){sub 2}]{sub 2}OB[OSi(O{sup t}Bu){sub 3}]{sub 2} (6). The isolation and structural characterization of trans- and cis-isomers of complexes 4 and 5 (4a and 4b, 5a and 5b, respectively) are also reported. Studies of the thermal decompositions of the complexes (by thermogravimetric analysis and solution 1H NMR spectroscopy) were performed. Xerogels with approximate compositions of 2MoO{sub 1.5}{center_dot}2P{sub 2}O{sub 5} and 2MoO{sub 1.5}{center_dot}2P{sub 2}O{sub 5}{center_dot}2SiO{sub 2} were derived from 4a and 5a or 5b, respectively, via solution thermolyses (toluene). The as-synthesized (and dried) xerogels contain one equiv of HNMe{sub 2} per molybdenum center (by combustion analysis, IR spectroscopy, and thermogravimetric analysis), and these materials have high surface areas (up to 270 m{sup 2} g{sup -1}). Upon calcination at 300 C, the coordinated amines are lost and the surface areas are significantly reduced (to 40 m{sup 2} g{sup -1} and <5 m{sup 2} g{sup -1} for the materials derived from 4 and 5a or 5b, respectively). Solid-state {sup 31}P MAS NMR spectroscopy suggests that the as-synthesized xerogels retain structural features of the starting molecular precursors, as indicated by the presence of resonances that correspond to both bridging and terminal -O{sub 2}P(O{sup t}Bu){sub 2} ligands. Upon calcination at 300 C, the resonances for bridging -O{sub 2}P(O{sup t}Bu){sub 2} groups are replaced by those for PO{sub 4}{sup 3-}. The material derived from 4 exhibits low activity and poor selectivity for the oxidative dehydrogenation (ODH) of propane to propylene. Cothermolyses of 4 and Bi[OSi(O{sup t}Bu){sub 3}]{sub 3} resulted in formation of Bi/Mo/P/Si/O materials with improved performance for the ODH of propane.

• Research Organization: Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
• Sponsoring Organization: USDOE Director. Office of Science. Basic EnergySciences
• DOE Contract Number: AC02-05CH11231
• OSTI ID: 917046
• Report Number(s): LBNL--54417; BnR: KC0302010
• Journal Information: Chemistry of Materials, Journal Name: Chemistry of Materials Vol. 16; ISSN CMATEX; ISSN 0897-4756
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
AMINES
CALCINATION
COMBUSTION
DEHYDROGENATION
MOLYBDENUM
OXIDES
PERFORMANCE
PROPANE
PROPYLENE
PYROLYSIS
SPECTROSCOPY
SURFACE AREA
THERMAL GRAVIMETRIC ANALYSIS
TOLUENE