ASYMMETRIC HYDROSILYLATION CATALYZED BY POLYMER—SUPPORTED THIAZOLIDINE RHODIUM CATALYSTS

Asymmetric hydrisilylation catalyzed by polymeric thiazolidine rhodium catalysts was conducted.Almost the same optical yields have been obtained when comb-shaped polymeric ligands and their corresponding monomer complexed rhodium cataltysts were used to asymmetric hydrosilylation of acetophenone.Optical yield of chiral 1-methylbenzyl alcohol reaches as high as 71.5%.Temperature dependence of enantioselective hydrosilylation of acetophenone was discussed.     

Enantioselective metal complex catalysis. 6. Rhodium catalysts for asymmetric hydrosilylation based on chiral phosphites

A study has been made of the asymmetric hydrosilylation of acetophenone by diphenylsilane under the influence of rhodium complexes with chiral phosphites. The enantioselective nature of the reaction depends on the phosphite structure, the acetophenone/rhodium and ligana/rhodium ratios, and the temperature. The maximum optical yield (24%) is attainod on the complex [Rh(COD)Cl]₂/(S, S)-2-ethoxy-4,5-dicarbisopropoxy-1,3-2-dioxophiospholane.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 983–989, May, 1991.     

Chemical assembling of silica surface using a reaction of catalytic hydrosilylation

Chemical assembling of the silica surface modified by dimethylchlorosilane was performed by the catalytic hydrosilylation of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, α-methyl styrene, acetophenone, allyl butyl and allyl glycidyl ethers with dimethylchlorosilane. The effect of the nature of complexes of platinum, palladium, rhodium and ruthenium on the parameters of hydrosilylation was studied. It was shown that the maximum rate of hydrosilylation was observed in the reaction with allyl glycidyl ether, and minimum, with α-methylstyrene; the most effective catalyst of hydrosilylation was [Rh(CO)₂(acac)].     

Synthesis and structural studies on the chiral phosphine-NHC rhodium and palladium complexes for their performances in the metal-catalyzed reactions

Diverse chiral rhodium and palladium complexes ligated with phosphine-functionalized N-heterocyclic carbene ligands based on 1,1′-binaphthyl backbone have been synthesized. The structures of these phosphine-NHC rhodium and palladium complexes have been confirmed by X-ray diffraction analysis. The different sizes of the N-substituents from the NHC-P rhodium complexes had an inverse relationship with their ability of chiral induction, which was accounted by the Rh-catalyzed asymmetric hydrosilylation of acetophenone to afford corresponding chiral alcohol with up to 72% ee. The NHC-P palladium complexes connected with different kinds of coordination anions were also applied in the Suzuki and Heck reactions. The acetate-coordinated NHC-P palladium complex exhibited better catalytic activity to give the products in excellent yield under mild conditions.     

Chiral ligands with pyridine donors in transition metal catalyzed enantioselective cyclopropanation and hydrosilylation reactions

Copper(I) and rhodium(I) complexes prepared in situ from [Cu(OTf)(C₆H₆)_0.5] and [Rh(cod)Cl]₂ with a range of chiral 2,2′-bipyridines, 5,6-dihydro-1,10-phenanthrolines, 1,10-phenanthrolines and 2,2′:6′,2′′-terpyridines were assessed as chiral catalysts for the enantioselective cyclopropanation of styrene with diazoacetates and for the hydrosilylation of acetophenone with diphenylsilane. Enantioselectivities up to 68% in the cyclopropanation and up to 32% in the hydrosilylation were obtained.     

Metal controlled enantioselectivity in the catalytic asymmetric hydrosilylation

The asymmetric hydrosilylation of acetophenone with Ph₂SiH₂ has been investigated in the presence of (S)-amphos as the chiral ligand in combination with the cyclooctadiene-rhodium(I), -iridium(I), -palladium(II), and -platinum(II) chloride complexes.

High activity and optical yields up to 50% ee have been obtained. The product configuration induced by the rhodium system is (S), in all other cases it was (R).     

Bridge functionalized bis-N-heterocyclic carbene rhodium(I) complexes and their application in catalytic hydrosilylation

A series of chelating bridge functionalized bis-N-heterocyclic carbenes (NHC) complexes of rhodium (I) were prepared by reacting the corresponding imidazolium salts with [Rh(COD)Cl]₂ in an in-situ reaction. For the N-methyl substituted complex with a PF₆-anion an X-ray crystal structure was exemplary obtained. All complexes were spectroscopically characterized and tested for the hydrosilylation of acetophenone.     

Conformational analysis,spectral and catalytic properties of 1,3-thiazolidines,ligands for acetophenone hydrosilylation with diphenylsilane

2-Aryl- and 2-furyl-4-carboxy-1,3-thiazolidines were synthesized. Their spectral properties were studied, and conformational analysis was performed. It was shown that they exist in solution as an equilibrium of neutral and zwitter-ion forms. The influence of the nature of substitutents and of their location in a benzene ring of thiazolidines as ligands of rhodium complexes on acetophenone hydrosilylation with diphenylsilane was examined. Thiazolidines containing donor substituents in the para-position of the benzene ring were found to be the most effective; maximal asymmetrical induction (55% ee) was reached in the presence of 2-(4-methoxyphenyl)-4-carboxy-1,3-thiazolidine.     

Rhodium carbene complexes as hydrosilylation catalysts

The catalytic activity of various rhodium carbene complexes has been investigated. These complexes are active for the hydrosilylation of a wide variety of unsaturated organic molecules such as olefins, acetylenes and dienes. Their activity is comparable to other rhodium(I) complexes previously used as hydrosilylation catalysts. The yield of products is found to vary with catalyst, silane and organic substrate.     

Design and Synthesis of Isocyanide Ligands for Catalysis: Application to Rh‐Catalyzed Hydrosilylation of Ketones

New isocyanide ligands with meta‐terphenyl backbones were synthesized. 2,6‐Bis[3,5‐bis(trimethylsilyl)phenyl]‐4‐methylphenyl isocyanide exhibited the highest rate acceleration in rhodium‐catalyzed hydrosilylation among other isocyanide and phosphine ligands tested in this study. ¹H NMR spectroscopic studies on the coordination behavior of the new ligands to [Rh(cod)₂]BF₄ indicated that 2,6‐bis[3,5‐bis(trimethylsilyl)phenyl]‐4‐methylphenyl isocyanide exclusively forms the biscoordinated rhodium–isocyanide complex, whereas less sterically demanding isocyanide ligands predominantly form tetracoordinated rhodium–isocyanide complexes. FTIR and ¹³C NMR spectroscopic studies on the hydrosilylation reaction mixture with the rhodium–isocyanide catalyst showed that the major catalytic species responsible for the hydrosilylation activity is the Rh complex coordinated with the isocyanide ligand. DFT calculations of model compounds revealed the higher affinity of isocyanides for rhodium relative to phosphines. The combined effect of high ligand affinity for the rhodium atom and the bulkiness of the ligand, which facilitates the formation of a catalytically active, monoisocyanide–rhodium species, is proposed to account for the catalytic efficiency of the rhodium–bulky isocyanide system in hydrosilylation.     

聚-4-氧杂-6,7-双二苯膦基庚基硅氧烷铑配合物的合成及其催化硅氢化性能

4-氧杂-6,7-二氯庚基三甲氧基硅烷依次与二苯膦钾、气相法二氧化硅、三氯化铑作用,合成了聚-4-氧杂-6,7-双二苯膦基庚基硅氧烷铑配合物。它对烯烃与取代烯烃的硅氢化反应具有良好的催化活性。     

Cationic rhodium(I)–diolefin complexes containing an optically active C2-symmetric bis(sulfoximine) ligand: Synthesis and catalytic activity

A series of cationic rhodium(I) complexes [Rh(diene)(N^N)][BF₄] (diene = 1,5-cyclooctadiene (cod), norbornadiene (nbd), tetrafluorobenzobarralene (tfb)), containing the optically pure bis(sulfoximine) ligand 1,2-bis(S-methyl-S-phenylsulfonimidoyl)benzene, have been synthesized and fully characterized. The structure of the R,R enantiomer of the ligand, and that of its cyclooctadiene–Rh(I) complex, were confirmed by means of single-crystal X-ray diffraction techniques. Studies on the catalytic activity of these complexes in acetophenone hydrosilylation and dimethyl itaconate hydrogenation are also reported.     

C60正丙胺铂,铑配合物的合成及其催化硅氢化性能

Ｃ６０与正丙胺反应,然后分别与氯亚铂酸钾或三氯化铑配合,制得出含配位氮原子的富勒烯铂,铑 配合物,它们均能有效地催化烯烃与三乙氧基硅烷硅氢加成,铂配合物还对苯乙烯有独特的催化性能,以近１００％的区域选择性得到α－加成产物,对催化机理进行了初步的探讨。     

二氧化硅-聚硅氧烷负载硫杂-15-冠-5铂、铑配合物的合成及其催化硅氧化性能

6－(ω'-十一碳烯氧甲基)-1-硫杂-4,7,1O,13-四氧杂环十五烷与三乙氧基硅烷进行硅氢加成,产物依次以气相法二氧化硅固载、氯亚铂酸钾或三氯化铑络合,合成了相应的二氧化硅-聚硅氧烷负载硫杂-15-冠-5-铂、铑配合物,并研究了它们在烯烃与三乙氧基硅烷的硅氢加成反应中的催化性能.结果表明,二者均为硅氢加成反应的高效催化剂.     

From inconsistent results to high speed hydrosilylation

After noting that the presence of dihydrogen, generated in situ from the partial hydrolysis of a silane with residual water, significantly enhances the rate of the rhodium-catalysed hydrosilylation of acetophenone, we developed a high speed hydrosilylation reaction under dihydrogen pressure.     

SYNTHESIS AND CATALYTIC BEHAVIOR OF POLYSILOXANESUPPORTED FULLERENE PLATINUM OR RHODIUM COMPLEXES*

Two polysiloxanes with pendant fullerene moieties and their platinum or rhodium complexes havebeen prepared from C_(60) via amination with ω-decenylamine, followed by hydrosilylation with triethoxysilaneand immobilization on fumed silica or by hydrosilylation with methyldichlorosilane and polycondensationwith polydimethylsiloxanol, and then by reacting them with potassium chloroplatinite or rhodium chloride inacetone respectively under argon atmosphere. It was found that the four noble metal complexes are effectivecatalysts for the hydrosilylation of olefins with triethoxysilane. The regioselcctivity of platinum complexesfor styrene increases remarkably by introducing C_(60) moiety. Factors influencing catalytic activity and themechanism have been investigated.     

Rhodium-catalysed asymmetric hydrosilylation of ketones using HETPHOX ligands

The HETPHOX ligand class was applied to the rhodium-catalysed asymmetric hydrosilylation of a range of substituted acetophenones. Enantioselective hydrosilylation of acetophenone with the tert-butyl substituted HETPHOX ligand gave (R)-phenylethanol in excellent enantioselectivity (84% ee) and in good conversion (80%). When applied to the hydrosilylation of other ketones conversions up to 93% and enantioselectivities up to 88% were observed.     

Regioselective rhodium-containing catalysts for ring-opening polymerizations and hydrosilylations

Organometallic rhodium complexes are described which are highly efficient initiators for the ring-opening polymerization of expoxides and other heterocyclic compounds. A cocatalyst, consisting of a compound or polymer containing silicon–hydrogen bonds must also be present. These same catalyst–cocatalyst mixtures are also highly active for hydrosilylation reactions. Other complexes bearing phosphine ligands have been discovered, which while active for hydrosilylation, are not catalysts for epoxide polymerizations. Polymer supported rhodium catalysts are also described which permit the synthesis of epoxy-functional silanes in high yields without competing ring-opening polymerization.     

Synthesis of new polymeric rhodium carborane complexes serving as homogeneous catalysts for the hydrosilylation of 1-hexene

The coordination of Rh(PPh₃)₃Cl on a dicarbaundecaborate polyamide gives a new polymeric rhodium hydride complex with catalytic activity in the hydrosilylation of 1-hexene by triethylsilane. The rhodium derivative of 7,9-dicarbanido-undecaborate(11)-7,9-dicarboxyanilide was synthesized as a model of the monomeric unit. Co^III and Ni^IV bis(dicarbollyl) complexes also display catalytic activity in hydrosilylation reactions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 960–962, April, 1991.     

Catalysis of hydrosilylation XIII. Gas-phase hydrosilylation of acetylene by trichlorosilane on functionalised silica supported rhodium and ruthenium phosphine complexes

Gas-phase hydrosilylation of acetylene by tri-chlorosilane catalyzed in a continuous flow apparatus by rhodium and ruthenium phosphine complexes immobilized on the silica via mercapto, phosphine, amine and nitrile ligands has been studied. GLC analysis of the reaction products showed vinyltrichlorosilane to be accompanied by products of double hydrosilylation of acetylene and the redistribution of trichlorosilane followed by the hydrosilylation and hydrogenative hydrosilylation of acetylene with dichlorosilane. A scheme for this complex competitive–consecutive reaction was proposed. The yield and selectivity of vinyltrichlorosilane can be much improved under special reaction conditions, e.g. rate flow of the particular substrates, temperature, given catalyst and others. Kinetic measurements carried out in the range of 115–140°C allowed us to evaluate the activation energy, E_a, for the vinyltrichlorosilane synthesis, which varied between 20.5 and 27.6 kJ mol^?1 for the selected rhodium and ruthenium supported complexes.