SILICA HYBRID GEL CATALYSTS CONTAINING GROUP(VIII) TRANSITION-METAL COMPLEXES - PREPARATION, STRUCTURAL, AND CATALYTIC PROPERTIES IN THE SYNTHESIS OF N,N-DIMETHYLFORMAMIDE AND METHYL FORMATE FROM SUPERCRITICALCARBON-DIOXIDE

Sol-gel derived hybrid materials containing group(VIII) transition met al complexes in a porous silica network were prepared and tested for t he catalytic synthesis of N,N-dimethylformamide (dmf) and methyl forma te (mf) from supercritical carbon dioxide, hydrogen, and dimethylamine and methanol/triethylamine, respectively. Bifunctional silylether pho sphines X = Ph2P(CH2)(2)Si(OEt)(3) and Y = Me2P(CH2)(2)Si(OEt)3 were u sed as ligands for the preparation of complexes of the type RuCl2X3, R uCl2Y3, MClX3 (M = Ir, Rh), and MCl2X2 (M = Pt, Pd). The silylether co mplexes were anchored in a silica matrix by co-condensation with Si(OE t)(4). The textural and structural properties of the hybrid gels were characterized by means of P-31 and Si-29 NMR spectroscopy, extended X- ray absorption fine structure (EXAFS), X-ray diffraction (XRD), transm ission electron microscopy (TEM), and nitrogen and argon physisorption . P-31 NMR spectroscopy confirmed nondestructive immobilization of the Ru, Pt, Pd, Rh, and Ir complexes. TFEM and XRD analyses proved the ho mogeneity and noncrystallinity of the materials. The degree of condens ation of the gels and the molecular mixing of the components has been investigated by solid state Si-29 NMR spectroscopy. Textural character ization showed that all gels were micro- to mesoporous. EXAFS measurem ents indicated no metal-metal interactions, confirming that the organo metallic complexes were immobilized as monomers. From all catalysts si lica matrix stabilized ruthenium complexes exhibited highest activitie s at 100% selectivity in dmf synthesis from CO2, H-2, and dimethylamin e. The corresponding turnover frequency (TOF) of 1860 h(-1) exceeded t hose reported so far for heterogeneous catalysts by a factor of 600. I n methyl formate synthesis, TOFs up to 115 h(-1) were reached, (C) 199 8 Academic Press.