Rhodium Catalysts for Enantioselective Hydrosilylation—A New Concept in the Development of Asymmetric Catalysts

Following a survey of the asymmetric hydrogenation of prochiral olefins with transition metal/phosphane catalysts, the problem of chirality transfer from the optically active ligands of the catalyst to the substrate is discussed. A new concept for this chirality transfer is introduced; the conformational analysis of model compounds as well as the development of catalysts for enantioselective hydrosilylation demonstrate the usefulness of this concept.     

Metallo-Carbosiloxan-Dendrimere mit Titanocendichlorid-Endgruppen

The synthesis of titanocenedichloride end-grafted carbosiloxane dendrimers of the 1^st and 2^nd generation is reported. To find the optimal reaction conditions, Me₂ClSiH (1) was reacted with (η⁵-C₅H₄SiMe₂CHCH₂)(η⁵-C₅H₅)TiCl₂ (2). The best result could be obtained with the Karstedt catalyst, whereby exclusively the β-isomer ((η⁵-C₅H₄SiMe₂CH₂CH₂SiMe₂Cl)(η⁵-C₅H₅)TiCl₂, 3) is formed. Under similar conditions Me₃SiOCH(Me)(CH₂)₄SiMe₂H (4) reacts with 2 to give (η⁵-C₅H₄SiMe₂CH₂CH₂SiMe₂(CH₂)₄CH-(Me)OSiMe₃)(η⁵-C₅H₅)TiCl₂ (5). When using MeSi(OCH(Me)(CH₂)₄SiMe₂H)₃ (6), Si(OCH(Me)(CH₂)₄SiMe₂H)₄ (8) and MeSi[O(CH₂)₃SiMe(OCH(Me)(CH₂)₄SiMe₂H)₂]₃ (10) instead of 1 and 4, the respective metallo dendrimers MeSi[OCH(Me)(CH₂)₄-SiMe₂CH₂CH₂SiMe₂(η⁵-C₅H₄)(η⁵-C₅H₅)TiCl₂]₃ (7), Si[OCH(Me)(CH₂)₄SiMe₂CH₂CH₂SiMe₂(η⁵-C₅H₄)(η⁵-C₅H₅)TiCl₂]₄ (9) and MeSi{O(CH₂)₃SiMe[OCH(Me)(CH₂)₄SiMe₂CH₂CH₂SiMe₂(η⁵- C₅H₄)(η⁵-C₅H₅)TiCl₂]₂}₃ (11) can be isolated.Compounds 3, 5, 7, 9 and 11 were characterised by elemental analysis as well as IR and NMR spectroscopy (¹H, ¹³C{¹H}, ²⁹Si{¹H}).     

A NEW TYPE OF CROWN FUNCTIONALIZED POLYSILOXANE AND ITS PLATINUM COMPLEX

A new type of crown functionalized polysiloxane, in which the crown moieties were incorporated into main chain, and its platinum complex were synthesized. The polysiloxane was synthesized from 3, 16-dihydroxy-1- thia - 5, 8, 11, 14- tetraoxacycloheptadecane via etheritication with ω-chloroundecene, followed by hydrosilylation with triethoxysilane, cohydrolysis with D_4, sequentially. Treating the polysiloxane with potassium cholroplatinite, the title complex was obtained. It was found that the platinum complex exhibited high catalytic activity in the hydrosilylation of olefins with triethoxysilane.     

Borane-Catalyzed Tandem Cyclization/Hydrosilylation Towards Enantio- and Diastereoselective Construction of trans-2,3-Disubstituted-1,2,3,4-Tetrahydroquinoxalines

Recent years have witnessed marked progress in the efficient synthesis of various enantioenriched 1,2,3,4-tetrahydroquinoxalines. However, enantio- and diastereoselective access to trans-2,3-disubstituted 1,2,3,4-tetrahydroquinoxalines remains much less explored. Herein we report that a frustrated Lewis pair-based catalyst generated via in situ hydroboration of 2-vinylnaphthalene with HB(C₆F₅)₂ allows for the one-pot tandem cyclization/hydrosilylation of 1,2-diaminobenzenes and 1,2-diketones with commercially available PhSiH₃ to exclusively afford trans-2,3-disubstituted 1,2,3,4-tetrahydroquinoxalines in high yields with excellent diastereoselectivities (>20 : 1 dr). Furthermore, this reaction can be rendered asymmetric by using an enantioenriched borane-based catalyst derived from HB(C₆F₅)₂ and a binaphthyl-based chiral diene to give rise to enantioenriched trans-2,3-disubstituted 1,2,3,4-tetrahydroquinoxalines in high yields with almost complete diastereo- and enantiocontrol (>20 : 1 dr, up to >99 % ee). A wide substrate scope, good tolerance of diverse functionality and up to 20-gram scale production are demonstrated. The enantio- and diastereocontrol are achieved by the judicious choice of borane catalyst and hydrosilane. The catalytic pathway and the origin of the excellent stereoselectivity are elucidated by mechanistic experiments and DFT calculations.     

Half-Sandwich Manganese Complex Bearing Fused Oxazoline-NHC Ligand: Conformational Analysis and Evaluation in Asymmetric Ketone Hydrosilylation

The first manganese complex bearing a chiral N-heterocyclic carbene (NHC) ligand was prepared and studied by spectroscopic methods and X-ray diffraction. While IR spectroscopy revealed the existence of two isomers in solution with distinct ν_CO band patterns, DFT calculations indicated that these isomers correspond to rotamers around the Mn−NHC bond and their different spectroscopic properties were rationalized by the occurrence of attractive π(C=C)⋅⋅⋅π*(C≡O) or σ(C−H)⋅⋅⋅π*(C≡O) intramolecular interligand interactions. The evaluation of this complex in catalytic hydrosilylation of acetophenone using Ph₂SiH₂ under UV irradiation led to the formation of the corresponding (R)-alcohol with low enantioselectivity.     

A multivalent PyBox asterisk ligand

A discrete multivalent PyBox ligand was investigated. An efficient synthesis and the properties of 1 are reported (UV-visible, cyclic voltammetry, NMR, MALDI-Tof). It incorporates a sulfur-rich persulfurated benzene core which was compatible with a metal-catalyzed reaction in spite of donating and oxidizable sulfur atoms. Metal-catalysis with a persulfurated aromatic ligand was demonstrated for the first time in a model reaction: the Rh-enantioselective hydrosilylation of acetophenone. The interesting features were the reactivity and the enantiocatalytic behavior while varying the metal content. This work promotes new thoughts toward chiral supramolecular assemblies or metal nanoparticles stabilized with chiral multivalent ligands.     

超支化聚(β-环糊精)的合成与表征

通过硅氢加成反应, 以ABx型功能化β-环糊精大单体为原料, 采用一步法合成出新型超支化聚(β-环糊精)高分子. ABx大单体由单取代对甲苯磺酰化β-CD依次与烯丙基胺、1,1,3,3-四甲基二硅氧烷(含氢双封头)及丙烯酰氯反应得到. 采用1H NMR, 13C NMR, 29Si NMR和飞行时间质谱对ABx大单体及其聚合物的结构进行了表征. 利用凝胶渗透色谱/多角度激光光散射(SEC/MALLS)联用仪得到了超支化聚(β-环糊精)的分子量、分子量分布及本体黏度.     

AB_2型β-环糊精功能单体及其水溶性超支化聚合物的合成与表征

为了得到结构确定的β-环糊精大单体并用于超支化聚合,通过对β-环糊精上6位伯羟基和2位仲羟基的多步功能化改性得到了同时含有Si—H和—CH CH2基团的AB2型β-环糊精大单体,并利用硅氢加成反应一步法合成了一种新型的水溶性超支化聚合物,其具有β-环糊精空腔和超支化空穴两种疏水单元,从而可构建出一种新颖的超分子体系.采用1H-NMR、13C-NMR、飞行时间质谱和元素分析对AB2单体及其聚合物的结构进行了表征.结果表明,单体和聚合物的结构与所设计的分子结构相符合.凝胶渗透色谱/多角度激光光散射(SEC/MALLS)联用仪测得该聚合物的数均分子量、分子量分布及特性黏数分别为36690、1.887和15.8mL/g.     

Photochemical reactions of [W(CO)4(η-nbd)] with hydrosilanes: Generation of new hydrido complexes of tungsten and their reactivity

Photolysis of the norbornadiene (nbd) complex [W(CO)₄(η⁴-nbd)] (1) creates a coordinatively unsaturated d⁶ species which interacts with the Si-H bond of tertiary and secondary silanes (Cl₃SiH, Et₃SiH, Et₂SiH₂, Ph₂SiH₂) to yield hydride complexes of varying stability. In reaction of complex 1 with Cl₃SiH, oxidative addition of the Si-H bond to the tungsten(0) center gives the seven-coordinate tungsten(II) complex [WH(SiCl₃)(CO)₃(η⁴-nbd)], which has been fully characterized by NMR spectroscopic methods (¹H, ¹³C{¹H}, 2D ¹H-¹H COSY, 2D ¹³C-¹H HMQC and ²⁹Si{¹H}). Reaction of 1 with Et₃SiH leads to the hydrosilylation of the η⁴-nbd ligand to selectively yield endo-2-triethylsilylnorbornene (nbeSiEt₃). The latter silicon-substituted norbornene gives the unstable pentacarbonyl complex [W(CO)₅(η²-nbeSiEt₃)], whose conversion leads to the initiation of ring-opening metathesis polymerization (ROMP). Reaction of secondary silanes (Et₂SiH₂ and Ph₂SiH₂) with 1 leads to the hydrosilylation and hydrogenation of nbd and the formation of bis(silyl)norbornane and silylnorbornane as the major products. In reaction of 1 and Et₂SiH₂, the intermediate dihydride complex [WH(μ-H-SiEt₂)(CO)_x(η⁴-nbd)] was detected by ¹H and ¹³C NMR spectroscopy. As one of the products formed in photochemical reaction of W(CO)₆ with Ph₂SiH₂, the dinuclear complex [{W(μ-η²-H-SiPh₂)(CO)₄}₂] was identified by NMR spectroscopic methods.     

Synthesis and characterization of α-{3-[2-hydroxy-3-(N-methyl-N-hydroxy-ethylamino)propoxy]propyl}-ω-butylpolydimethylsiloxanes.

α-{3-[2-hydroxy-3-(N-methyl-N-hydroxyethylamino)propoxy]propyl}-ω-butylpolydimethylsiloxanes Ⅲ with various moleculax weights were prepared by epoxy addition of α-[3-(2,3-epoxy-propoxy)propyl]-ω-butylpolydimethylsiloxanes Ⅱ and Nmethylmonoethanolamine.At each step.the outcome compounds were characterized through FT-IR and NMR spectra,the results showed that each step was successfully carried out and objective products were achieved.