Abstract
A heterogeneous hydrosilation catalyst has been prepared by linking a photoactive Pt(C/sub 2/O/sub 4/)L/sub 2/ complex to silica (300 m/sup 2//g) by using the functionalized ligand L = (OMe)/sub 4/Si(CH/sub 2/)/sub 2/PEt/sub 2/. Unreacted surface hydroxyls were capped with inert SiMe/sub 3/ groups in all experiments. The surface-attached oxalate complex has been completely characterized by /sup 13/C, /sup 31/P, and /sup 29/Si CP-MAS solid-state NMR spectroscopies. This shows that the complex binds to the surface with an intact coordination sphere. At maximum loading (5.4 x 10/sup -4/ mol of Pt/g) the NMR data suggest about 75% of the complexes binds to the surface with both L. Ultraviolet irradiation results in the loss of the oxalate ligand as CO/sub 2/ and the formation of a surface-attached PtL/sub 2/ species that can be trapped with CO to yield a supported PtL/sub 2/(CO)/sub 2/ species. On extended irradiation a bridging carbonyl species was observed, in the FTIR spectrum. Scanning and transmission electron microscopy failed to show clustering or polymerization of the complex on the surface down to 20-A resolution. Ultraviolet irradiation of the supported complex in 1-heptene or MeCl/sub 2/SiH generated a catalyst for hydrosilation on addition of MeCl/sub 2/SiH or 1-heptene, respectively.more » The kinetic behavior of the supported catalyst differs from soluble hydrosilation catalysts in its sensitivity toward oxygen, lack of an induction period, and inhibition by coordinating solvents or excess olefin. Addition of Hg, a poison for metallic platinum, to catalysis solutions did not alter the catalytic rate. Thermal activation of the supported oxalate complex (200 /sup 0/C) appears to produce Pt particles (approx.20-A diameter by TEM) on the surface. This sample catalyzes hydrosilation of olefins after a long induction period, and addition of Hg to the catalysis solution quenches all catalytic activity.« less
Published Version
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