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Heterogeneous platinum catalysts (Pt/Si[O.sub.2]) obtained by the sol-gel process at pH 3 and 9 have been used in the hydrosilylation reaction of 1-alkynes using various silanes. Once the catalysts were activated they were used in the hydrosilylation of 1-alkynes after a short induction period. The product distribution was quite similar in either case but important differences in catalytic activity and turnover reactions were observed. The catalyst obtained in the basic medium after each reaction lost its catalytic activity, so further activation was needed. To understand this behavior, the catalysts were characterized by [sup.29]Si CPMAS NMR, FT IR, and BET surface area measurements. The [sup.29]Si CPMAS NMR studies showed the presence of terminal and bridged hydroxyl groups in the Pt/Si[O.sub.2] catalyst at pH = 9. Similar results were observed by FT IR analysis because of the catalysts' synthetic conditions. Key words: hydrosilylation, sol-gel, Pt/Si[O.sub.2], supported-metal catalysts, phenylacetylene, diphenylacetylene, [sup.29]Si NMR CP-MAS.

PhMeSi[H.sub.2] reduces ethyl benzoate in the presence of a C[p.sub.2]TiM[e.sub.2] (Cp = [[eta].sup.5]-cyclopentadienyl) catalyst to give PhMeSi(OEt)(OC[H.sub.2]Ph) (1). Small to moderate amounts of toluene are also produced, depending on the reaction conditions. Under 40 psi of [H.sub.2] the same reaction gives quantitative reduction of the ester to toluene. PhCHO is reduced, under the same conditions as the ester, to a mixture of PhMeSi[(OC[H.sub.2]Ph).sub.2] and toluene in proportions similar to that observed with the ester. A stoichiometric reaction of PhMeSi[H.sub.2], PhCOOEt, and C[p.sub.2]TiM[e.sub.2] resulted in the formation of known [[C[p.sub.2]Ti(OEt)].sub.2] (2) in 75% isolated yield. A mechanism is proposed in which the C=O of the ester inserts into a Ti-H bond. A Ti-mediated transfer of the ethoxy group from the resulting ([alpha]-ethoxy) benzyloxytitanium intermediate to silicon produces PhMeSi(OEt)H and PhCHO. (1) is generated via hydrosilation of PhCHO by PhMeSi(OEt)H. Both [beta]- and [gamma]-butyrolactones react with PhMeSi[H.sub.2] in the presence of a catalytic amount of C[p.sub.2]TiM[e.sub.2] to produce copolymers-[[[O-PhMeSi-O[(C[H.sub.2]).sub.3]CHR].sub.n-(R = H, 3; R = Me, 4) ([M.sub.w][approximately equal to] 1 x [10.sup.3]; [M.sub.w]/[M.sub.n] [approximately equal to] 1.3). A mechanism analogous to that proposed for the ethyl benzoate reduction is proposed. A reaction of PhMeSi[H.sub.2] and [gamma]-butyrolactone with a stoichiometric amount of C[p.sub.2]TiM[e.sub.2] in the presence of tetrahydofuran (THF) produces C[p.sub.2]Ti ([micro]-H)([micro]-[eta].sup.1], [eta].sup.5]-[C.sub.5][H.sub.4])Ti(O[C.sub.4][H.sub.8])Cp (5) (65% isolated yield) whose structure is determined by X-ray crystallography. Key words: hydrosilation, esters, lactones, titanocene, catalysis.

[La.sup.3+] catalysis of the methanolysis of the esters p-nitrophenyl, 2,4-dinitrophenyl, and phenyl acetate (1-3), phenyl benzoate (4), and ethyl, i-propyl, cyclohexyl, and tert-butyl acetate (5, 6a, 6b, 7) was studied at 25[degrees]C as a function of [sup.s.sub.s]pH and [La[(OTf).sub.3]]. The active form of the catalyst is attributed to a dimethoxy-bridged dimer of stoichiometry [(La.sup.3+]).sub.2][([sup.-.OCH.sub.3]).sub.2], having maximum activity at [sup.s.sub.s]pH 8 to 9. For preparative reactions, the active catalyst can be made in situ simply by adding 0.01 equiv of La[(OTf).sub.3], and 0.01 equiv of Na[OCH.sub.3] to a methanol solution containing the ester (1 M). Strong catalysis of methanolysis of both aryl and alkyl esters was observed, although tert-butyl acetate was inert. At [sup.s.sub.s]pH 8.5, where the catalyst is maximally active, the transesterification reactions are accelerated by 40 000-fold to 18 000 000-fold in the presence of as little as 5 mM catalyst relative to the background reaction depending on the ester structure. A mechanism for catalysis of transesterification is presented wherein the reactive species is generated by breaking a single La--[OCH.sub.3] bond of the dimethoxy-bridged dimer to reveal a nucleophilic metal-bound methoxide--Lewis acid [La.sup.3+] electrophilic pair. Key words: lanthanides, transesterification, methanolysis, catalysis, kinetics.

BINOL-aluminum complexes were successfully employed as mediators and catalysts in asymmetric Baeyer-Villiger rearrangements of cyclobutanones. Good enantioselectivies were achieved with only 15 mol% of the chosen chiral Lewis acid. The enantiomeric excesses obtained have never been reached before in such metal-catalyzed Baeyer-Villiger reactions. Key words: aluminum, asymmetric catalysis, lactones, oxidations, rearrangement.

Phosphate-Zr[O.sub.2]-[Si.sub.2]O catalysts were synthesized by sol-gel method using tributyl phosphite, zirconium propoxide, and tetraethyl orthosilicate as precursors. They were characterized by [N.sub.2] adsorption, [sup.31.P] CP MAS NMR, and DRIFTS. At lower P content, monomeric phosphates were formed on the surface of the catalysts, which were mainly responsible for the isopropanol dehydration activity. At higher P content, polyphosphates were formed, and thus, the dehydration activity decreased. An optimum P content for dehydration activity was found to be at 10 mol%. Key words: sol-gel synthesis, ternary oxides, phosphate, acid catalyst, alcohol dehydration, [sup.31.P] CP MAS NMR, [N.sub.2] adsorption, DRIFTS.

The potentially terdentate NN'N donor ligand 2,6-bis[di-(n-butyl) aminomethyl]pyridine (1) does not form a stable, isolable Ru complex using any standard Ru starting materials. This is in contrast to the dimethylamino derivative 2. In the presence of Zn metal as a reducing agent, the treatment of hydrated ruthenium trichloride with 2 leads instead to the isolation of a diamagnetic Zn(II) complex (3) of general formula [Zn[Cl.sub.2](1)]. Analysis of 3 (NMR, X-ray) reveals the complex to be a mononuclear Zn halide compound containing ligand 1 in an [[eta].sup.3]-NN'N bonding motif. The Zn atom is found to be five-coordinate and in a geometry best described as midway between trigonal bipyramidal and square pyramidal in structure. Similar experiments using 2 produce an analogous Zn species (4) which has likewise been fully characterized (NMR, X-ray) and found to be similar to 3 although the metal is in a distinctly square pyramidal environment. These compounds are viewed as relatives of the class of Zn "pybox" catalysts. Key words: pincer complexes, zinc(II) compounds, X-ray crystal structure.

The hydrosilylation reaction of phenylacetylene, generated on the surface of solid catalysts (such as Pt and Ru) supported on inorganic matrices such as MgO obtained by the sol-gel process, yields vinylsilanes as the main products. The products' distribution, specific activity, and turnover reactions were determined for the case of the hydrosilylation reaction of PhC[equivalent]CH with [R.sub.3]SiH (R = [Ph.sub.3], [Ph.sub.2]Me, and Ph[Me.sub.2]). For [Ph.sub.3]SiH and [Ph.sub.2]MeSiH, the presence of [beta]-trans and [alpha] isomers is observed. Addition of Ph[Me.sub.2] SiH to phenylacetylene leads to the formation of [beta] (cis and trans) and [alpha] isomers. These catalytic systems provide a new synthetic route to Si--C. Key words: vinylsilanes, cataleseur sol-gel, hydrosilylation et phenylacetylene.

Metal-catalyzed coupling reactions are very efficient and reliable methods for the introduction of new carbon-carbon bonds onto molecules attached to a solid support. This review summarizes recent advances in utilizing the three most used methods, the Suzuki reaction, the Heck reaction, and the Stille reaction, in the field of solid phase organic synthesis resulting in small organic molecule libraries. Key words: metal-catalyzed coupling reactions, carbon--carbon bonds, solid phase synthesis, combinatorial chemistry, drug discovery.

Catalytic amination of silyl enol ethers with azo diester compounds was investigated. It was shown that Cu[(OTf).sub.2] or AgOTf had high catalytic activity and that AgOTf was the most efficient among the catalysts tested in the reactions. In asymmetric reactions, the AgCl[O.sub.4]-BINAP system showed high enantioselectivity. In a mixture of toluene or mesitylene and THF, silyl enol ethers reacted with dibenzyl azodicarboxylate (DBnAD) smoothly to afford the corresponding amination adducts in excellent yields with up to 86% ee. Key words: amination, amino acid, asymmetric synthesis, chiral catalyst, silver.

The electrocatalytic hydrogenation (ECH) of [beta]-O-4 lignin model compounds has been carried out at constant current at Raney nickel and palladium-based cathodes in aqueous sodium hydroxide solution at temperatures ranging from 25 to 75[degrees]C. It was found that the hydrogenolysis of phenolic [beta]-arylethyl-aryl ethers with one [beta]-O-4 linkage takes place at both types of electrodes to give a mixture of phenolic compounds. The ECH of 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1-ethanol (model 1) at Raney nickel gives guaiacol (9), acetovanillone (11b), [alpha]-methylvanillyl alcohol (12b), and products derived from their further hydrogenation. The [beta]-O-4 bond is more difficult to cleave upon replacing one hydrogen of the methylene group of 1 by a hydroxymethyl group (see 2). However, model 4 with two [beta]-O-4 linkages obtained by the introduction of an [alpha]-methylvanillyl group at the phenolic position of 1 is hydrogenolysed at the same rate as 1 at Raney nickel. Only the C--O aryl bond attached to the hydroxyethylphenol moiety is cleaved. At palladium, the hydrogenolysis of 1 requires only half of the theoretical amount of electricity due to the generation of chemisorbed hydrogen by dehydrogenation of 1 followed by hydrogenolysis of the resulting ketone. A general reaction scheme is proposed for the ECH of model 1. Key words: Lignins, lignin models, electrocatalytic hydrogenation, Raney nickel electrodes, palladium electrodes.