User-Friendly Platinum Catalysts for the Highly Stereoselective Hydrosilylation of Alkynes and Alkenes.

With a view to addressing the shortcomings of traditional catalysts, a new generation of outstanding N-heterocyclic carbene platinum(0) complexes for the hydrosilylation of unsaturated carbon-carbon bonds is reported. Their discovery and application to the stereoselective addition of various silanes to silylated alkynes, terminal acetylenes, and olefins is presented. Insights into the catalytic cycle and the origin of the stereoselectivity are also discussed.

Highly enantioselective hydroformylation of dihydrofurans catalyzed by hybrid phosphine-phosphonite rhodium complexes.

Unprecedented regio- and enantioselectivities (>91%) are reported for the Rh-catalyzed asymmetric hydroformylation of 2,3- and 2,5-dihydrofuran using tunable hybrid phosphine-phosphonite ligands.

IPr* an easily accessible highly hindered N-heterocyclic carbene.

Herein, we wish to describe the efficient three-step synthesis of a novel highly hindered, but flexible, N-heterocyclic carbene and its coordination chemistry to Ag(i) and Rh(i).

Structure and reactivity of a unique Y-shaped tricoordinate bis(silyl)platinum(II)-NHC complex.

Y not? A unique, three-coordinate Y-shaped bis(silyl)platinum(II) complex was isolated and characterized (see structure; C light gray, N blue, Si pink, Pt dark gray). DFT studies on a model system shed light on the nature of this unusual coordination mode for platinum(II).

Palladium-catalyzed cyclopropanation of alkenyl silanes by diazoalkanes: evidence for a Pd(0) mechanism.

Alkenyl silanes are efficiently converted to the corresponding silyl cyclopropanes in the presence of a slight excess of diazomethane (2-4 equiv) and a low loading of Pd(OAc)(2) (<0.5 mol %). Diazoethane and diazobutane can also be employed and yield silyl cyclopropanes with diastereoselectivities of up to 10:1 for the trans isomer. When conducted on a 4 g scale, the reaction only required a catalyst loading of 5x10(-3) mol %, which corresponds to a turnover frequency of 40,000 h(-1). Competition experiments revealed that vinyl silanes can be selectively cyclopropanated in the presence of an aliphatic terminal alkene and styrene. The complex [Pd(0) (2)(DVTMS)(3)] (38, DVTMS = divinyltetramethyldisiloxane) proved to be an exceptionally active catalyst for the cyclopropanation reaction, giving complete conversion at -35 degrees C in 1 min. Intermolecular and intramolecular competition experiments with DVTMS (36), both with Pd(OAc)(2) and 38, provided strong evidence for a Pd(0)(alkenyl silane)(3) resting state. Detailed density functional calculations on the reaction pathways for the cyclopropanation of trimethylvinylsilane and DVTMS by diazomethane with Pd(0) corroborated the experimental observations.

Highly beta-(E)-selective hydrosilylation of terminal and internal alkynes catalyzed by a (IPr)Pt(diene) complex.

The regioselective hydrosilylation of terminal and internal alkynes catalyzed by the novel (IPr)Pt(AE) ( 7) (IPr = bis(2,6-diisopropylphenyl)imidazo-2-ylidene, AE = allyl ether) complex is presented. The (IPr)Pt(AE) catalyst displays enhanced activity and regioselectivity for the hydrosilylation of terminal and internal alkynes with low catalyst loading (0.1 to 0.05 mol %) when compared to the parent (IPr)Pt(DVDS) complex ( 6) (DVDS = divinyltetramethyldisiloxane). The reaction leads to exquisite regioselectivity in favor of the cis-addition product on the less hindered terminus of terminal and internal alkynes. The solvent effects were examined for the difficult hydrosilylation of benzylpropargyl ether. In light of the observed product distribution and kinetic data, a mechanistic scheme is proposed involving two competing catalytic cycles. One cycle leads to high regioselectivities while the other, having lost the stereodirecting IPr carbene ligand, displays low regiocontrol and activities. The importance of this secondary catalytic cycle is either caused by the strong coordinating ability of the alkyne or by the low reactivity of the silane or both.

Expanding the C2-symmetric bicyclo[2.2.1]hepta-2,5-diene ligand family: concise synthesis and catalytic activity in rhodium-catalyzed asymmetric addition.

New C2-symmetric bicyclo[2.2.1]hepta-2,5-dienes bearing methyl and phenyl substituents at the 2 and 5 positions were prepared enantiomerically pure through a two-step sequence starting from the readily available bicyclo[2.2.1]hepta-2,5-dione. Due to the instability or volatility of these dienes, their isolation was achieved through the formation of the corresponding stable [RhCl(diene)]2 complexes. These chiral rhodium complexes displayed high activity and enantioselectivity (up to 99% ee) in the rhodium-catalyzed 1,4-addition and 1,2-addition of phenylboronic acid to cyclic enones and N-sulfonylimines, respectively.

Second generation N-heterocyclic carbene-Pt(0) complexes as efficient catalysts for the hydrosilylation of alkenes.

A new class of benzimidazolylidene carbene-Pt(0) complexes was developed and used to efficiently catalyse the hydrosilylation of alkenes.