Search

The synthesis, characterization, and exploratory chemistry of two classes of alkene-platinum-silyl complexes, which have been postulated as hydrosilation intermediates, are described in this report. The unique dimeric complexes 1, [R(3)Si(mu-Cl)(eta(2)-COD)Pt](2) [R(3)Si = Et(3)Si, MeCl(2)Si, Me(2)ClSi, "(EtO)(3)Si", PhMe(2)Si, and (Me(3)SiO)Me(2)Si; COD = cycloocta-1,5-diene], and the bis-silyl complexes 2, (eta(4)-COD)Pt(SiR(3))(2) (R(3)Si = Cl(3)Si, MeCl(2)Si, Me(2)ClSi, and PhMe(2)Si), are formed from the sequential reaction of 2 and 4 equiv of the corresponding hydrosilanes, respectively, with Pt(COD)Cl(2) in the presence of a small excess of COD. Complexes 1 are stable for many days in solution at room temperature but decompose via slow elimination of chlorosilane. Some of the bis-silyl compounds 2 are stable for extended periods under inert atmosphere and especially below 0 degrees C, either in the solid state or in solution (in the presence of a small excess of free COD). Complexes 2 display catalytic activity as discrete, molecular, and mononuclear species for hydrosilation and isomerization reactions. Compound 2c (R(3)Si = MeCl(2)Si) was fully characterized via multinuclear NMR spectroscopy and X-ray crystal structure analysis. The facile H-transfer rather than Si-transfer to bound COD provides experimental support for the sequence of insertive steps in the Chalk-Harrod catalytic cycle, at least for Pt-catalyzed hydrosilation.

Photooxidation of 1,1,2,2-tetra-tert-butyl-1,2-diphenyldisilane, 1, by triplet sensitizers in CHCl3/CCl4 solutions yields chlorosilane, 2, in high chemical yield. The quantum yield for formation of 2 depends on the energy of the ion radical pair formed following initial electron transfer. Dissociative return electron transfer (DRET) is proposed as the mechanism for the highly efficient Si-Si bond cleavage in 1. DRET may be a useful strategy for the fragmentation of other such bonds in di-, oligo-, and polysilanes as well as other group 4A compounds using a variety of sensitizers with different spectral properties.

We report a new reversed phase liquid chromatography (RPLC) phase with remarkable acid stability using dimethyl(ethylphenylchloromethyl)chlorosilane (1), oligomeric polystyrene (PS), and octylbenzene (C8). This phase Si-1-PS-C8 was prepared using silica modification processes and Friedel-Crafts alkylation chemistry. Under highly aggressive mobile phase conditions, Si-1-PS-C8 exhibited remarkable stability as evinced by only minimal reduction in retention factor (k') after 1400 column volumes at pH = 0.5 and 150 degrees C. The peak shapes for a variety of basic solutes were symmetric using Si-1-PS-C8. Evidence for a highly cross-linked coating of the silica particles was observed using scanning electron microscopy. The remarkable stability of this phase is unparalleled as compared to all other RPLC phases reported to date.

The silylation of silica (Si) surfaces by dimethyldichlorosilane, methyltrichlorosilane, dimethyldiethoxysilane, and methyltriethoxysilane has been studied by solid-state /sup 29/Si and /sup 13/C NMR, by use of cross polarization (CP) and magic-angle spinning (MAS). An earlier formalism for the quantitative analysis of the NRM data has been extended for use with polyfunctional silyating agents and applied in detail to dimethyldichlorosilane reactions. Silylation with ethoxysilane reagents is less amenable to quantitative interpretation but appears to parallel closely the behavior of analogous chlorosilane reagents. With ethoxysilane reagents /sup 13/C NMR is found to be quite useful, especially for determining the fate of ethoxy groups. In all of the cases studied, the products are characterized primarily by single silane-to-surface attachments of each silane silicon atom. The presence of absorbed water is found to play an important role in the course and rate of the silylation reactions, especially those employing ethoxysilane reagents. The NMR data are used to address the question of horizontal and vertical polymerization within the silane phase on the silica surface.