Bogdan Marciniec

Catalysis of hydrosilylation of carbon-carbon multiple bonds: Recent progress

Recent progress in the catalytic hydrosilylation of organic and organosilicon compounds containing carbon-carbon multiple bonds is reviewed. Related to this, dehydrogenative silylation is also discussed. During the last decade new hydrosilylation catalysts, predominantly homogenous and heterogenous transition methal complexes, have been developed. These catalysts offer not only increased efficiency and turnover rate but also improved regioselectivity and stereoselectivity; moreover, there has been development in the mechanistic rationale behind these improvements. Application and extension of these basic chemical advances are found in many areas including polyorganosiloxane curing, hydrosilylation polymerization, polysiloxane functionalization, and silicon-containing dendrimer development.

Transition metal-siloxide complexes; synthesis, structure and application to catalysis

Abstract Synthesis and structural characterization of molecular transition-metal (TM)-siloxide (TMOSi) complexes by X-ray spectroscopic and other physico-chemical methods reported since 1982 are reviewed. TM siloxides include terminal and/or bridging siloxy ancillary ligands. Stereoselective properties of the two forms of siloxide ligand have been employed as advanced models (e.g. incompletely condensed silsesquioxanes) of catalytically active centers of early-TM complexes (mainly terminal structures) in such reactions as polymerization and metathesis of olefins and/or as precursors for catalysis by low-coordinate and low-oxidation state late-TM-complex catalysts (in the form of bridging structures).

Silicometallics and catalysis

Several processes of silicon substrates (such as hydrosilylation, dehydrogenative silylation and double silylation of alkenes and alkynes, silylative coupling versus cross-metathesis of vinylsilanes with alkenes, polycondensation of divinyl-substituted silicon compounds versus ADMET polymerization, dehydrocoupling of hydrosilanes and silylformylation of acetylene) by transition-metal complexes are briefly overviewed. All the reactions occur via a mechanism involving intermediates containing metal-silicon (i.e. silicometallics versus organometallics) and metal-hydrogen bonds, only occasionally accompanied (sided) by intermediates including metal-carbon bonds.

Ruthenium Carbene Siloxide Complexes Immobilized on Silica: Synthesis and Catalytic Activity in Olefin Metathesis

Ruthenium alkylidene complexes, based on second generation Hoveyda–Grubbs catalysts, have been directly attached to silica through covalent Ru‐O‐Si bonds, characterized by using cross polarization magic angle spinning 13C NMR (CP MAS 13C NMR) spectroscopy, and proved active in selected metathetic transformations. The complexes can be easily recycled and subsequently reused. In the ring closing metathesis (RCM) reaction of diethyl diallyl malonate the heterogenized complex can be recycled up to 15 times.

Cross-metathesis of vinylsilanes with olefins in the presence of Grubbs catalyst

Abstract Effective cross-metathesis of H 2 C C(H)SiR 3 , where SiR 3 =Si(OMe) 3 , Si(OEt) 3 , Si(OSiMe 3 ) 3 , with selected olefins in the presence of (PCy 3 ) 2 Cl 2 Ru( CHPh) ( I ) is described. Treatment of p -substituted styrenes, 1-alkenes and selected allyl derivatives H 2 C CHCH 2 R′ (R′=SiMe 3 , Si(OEt) 3 , Ph, OPh) with an excess of H 2 C C(H)SiR 3 results in the formation of the respective cross-metathesis products with good yields and selectivities. The metallacarbene mechanism of the process is discussed.

Cyclopropanation of activated olefins catalysed by Ru-phosphine complexes

Abstract Two novel ruthenium complexes, RuH 3 [Si(OEt) 3 ](PPh 3 ) 2 and Ru[Si(OEt) 3 ] 2 (PPh 3 ) 2 , have been shown to catalyse the cyclopropanation of activated olefins in high yields.

Catalytic activity of silyloxy-rhodium(I) complexes in hydrosilylation of alkenes

Abstract Silyloxy-rhodium(I) complexes of the general formula [{(diene)Rh(μ-OSiMe3)}2] (I) where diene=cod, nbd, showed much higher catalytic activity in the hydrosilylation of 1-hexene by triethoxysilane than respective chloro-rhodium(I) complexes, [{(diene)Rh(μ-Cl)}2] (II). Kinetic dependence of the rate on the initial concentration of [Rh] and stoichiometric reactions of Rh-complexes with triethoxysilane and 1-hexene allow a distinction between the catalytic cycles of the reactions occurring in the presence of silyloxy-rhodium vs. chloro-rhodium complexes. Direct reaction of triethoxysilane with (I) was followed by next elementary steps, in particular reductive elimination of disiloxane (EtO)3SiOSiMe3 which generates hydridorhodium(I) complex suggested as an intermediate for the catalysis of the hydrosilylation by silyloxy-rhodium complexes.

Synthesis, characterization and some reactions of [(diene)Rh(μ-OSiMe3)]2

Abstract The rhodium(I) complexes of general formula [(diene)Rh(μ-OSiMe 3 )] 2 , (where diene = cod ( I ) and nbd) were synthesized in the reaction of [(diene)RhCl] 2 with sodium trimethylsilanolate. Teh reactions of I with tripenylphosphine gave monomeric and dimeric products, which formula depends on the [Rh]:[P] ratio (i.e. Rh(μ-OSiMe 3 )(cod)PPh 3 and [(PPh 3 ) 2 Rh(μ-OSiMe 3 )] 2 for [Rh]:[P] = 1 : 1 and [(PPh 3 ) 2 Rh(μ-OSiMe 3 )] 2 when [Rh]:[P] = 1 : 2). The reaction of ( I ) with triethylsilane after eliminating triethyltrimethyldisiloxane yielded tetrameric hydride, [codRhH] 4 but, when there was an excess of triethylsilane, also Rh(H) 2 SiEt 3 (cod). The reactions of I with both PPh 3 and Et 3 SiH furnish a mixture of the products mentioned above. All the rhodium complexes were characterized by 1 H, 13 C, 31 P and 29 Si NMR spectroscopy.

Ruthenium and rhodium complex catalysts for metathesis of silicon olefins

Abstract Synthetic, catalytic, kinetic and mechanistic aspects of the olefin metathesis of vinyl (methyl, alkoxy)-substituted silanes, proceeding in the presence of highly active catalytic systems based on complexes of ruthenium and rhodium, as well as those with various hydride-donor cocatalysts and dioxygen activators, are summarized. Divinyldisiloxanes and divinylsilanes gave polymeric products. The experiments have shown some general features of self-metathesis: the requirement of the alkoxy substituent(s) at silicon; the possibility of initiation of the metathesis only by a substrate; the activation of the catalyst by traces of dioxygen and hydride-donor cocatalysts; the inhibition by any solvent as well as the extreme predominance of vinyl-substituted silanes over the higher alkenylsilane. Intermediates isolated from the reaction of RuCl2(PPh3)3 with alkoxy-substituted silanes additionally enabled a discussion of mechanistic pathways for the generation of metal-carbenes responsible for the metathesis of silicon-olefins. The results of preliminary examinations of successful cross-metatheses of vinyltriethoxysilane with 1-alkenes catalyzed by ruthenium complexes are also presented.

New One-Pot Synthesis of (E)-β-Aryl Vinyl Halides from Styrenes

A new, efficient protocol for the highly stereoselective one-pot synthesis of (E)-beta-aryl vinyl iodides and (E)-beta-aryl vinyl bromides from styrenes based on sequential ruthenium-catalyzed silylative coupling-N-halosuccinimide-mediated halodesilylation reactions is reported.