Several chiral ligands containing (R,R)-diaminocyclohexane moieties and pyrrole, furan, or benzene have been synthesized. These ligands were tested in enantioselective zinc-catalyzed hydrosilylation reactions; excellent enantioselectivities were obtained when the ligands containing (R,R)-diaminocyclohexane moieties and furan rings were used. For comparison, zinc chloride combined with different potassium carboxylate salts and ligands were also tested for catalytic hydrosilylation reactions. Chirality 25:275–280, 2013. © 2013 Wiley Periodicals, Inc.

Several carboxylated polyethylene glycols as promoters were applied in the platinum-catalyzed hydrosilylation of alkenes, and polyethylene glycol maleic acid monoester as a promoter for hydrosilylation was investigated. It was found that an improvement of the selectivity was achieved in the presence of carboxylated polyethylene glycol, and the β-adduct as major product was obtained. Additionally, the effect of alkenes and silanes employed on the selectivity was investigated; better selectivity could be achieved when (EtO)₃SiH was used as the hydride than ClMe₂SiH. Copyright © 2011 John Wiley & Sons, Ltd.

A novel series of ladder π-conjugated materials—sila-pentathienoacenes (Si-PTA) are synthesized and characterized. Crystal structures of the compounds show that the length of alkyl chains substituting on the thiophene ring has a significant influence on molecular packing. A densely packed structure with an interfacial distance of about 3.66 Å between the adjacent molecules is observed for the compound with shorter alkyl chains. However, a large interfacial distance (7.99 Å) is obtained for another compound because of the insertion of long alkyl chains between two planes. The investigation of the optical and electrochemical properties shows that the silylene bridge incorporated into the pentathienoacene framework exerts a clear effect on the electronic properties by the σ*–π* conjugation. Although only a slight enhancement is observed for the HOMO levels, with respect to that of pentathienoacene, the LUMO levels are significantly lowered. The observed electronic properties are consistent with the theoretical calculations.

By using functionalized imidazolium salts such as 1-allyl-3-alkylimidazolium or 1-alkyl-3-vinylimidazolium salts as carbene ligand precursors, the reduction of aryl ketones with triethoxysilane may be catalyzed by copper salt/imidazolium salt/KO^tBu systems. The functional substituents attached to the N-heterocyclic carbene (NHC) serve to enhance the catalytic activity. Different copper salts also have an effect on the catalytic activity, with copper(II) acetate monohydrate being superior to copper(I) chloride.

Insertion reactions of dimethylsilylene (Me₂Si:) into the silicon–chlorine bond of various substituted chlorosilanes have been computationally studied by using DFT calculations with a 6-31++G(d,p) basis set. All of the insertions investigated herein were exothermic (more than 40 kcal mol⁻¹) and proceeded via three-membered cyclic transition states (TS) with one substituent of a chlorosilane in the ring plane and two other substituents out of the plane. Among the two possible concerted insertion pathways, the pathway via a TS with a silylene lone-pair orbital approaching a chlorosilane silicon atom was preferred. Important nucleophilic interactions of silylene lone-pair orbitals with anti-bonding σ orbitals of SiY (in plane) were supported by carrying out a natural bond orbital (NBO) analysis of the reaction. A radical pathway through the initial abstraction of chlorine from chlorosilane by the silylene cannot compete with the preferred concerted pathway. Systematic calculations for SiMe₂ insertion into various chlorosilanes (YR₂SiCl; Y (in-plane substituent)=H, Me, NH₂, OH, F, SiH₃, PH₂, SH and Cl; R (out-of-plane substituent)=H, Me, iPr and tBu) have revealed remarkable substituent effects on activation free energies (ΔG^≠). In-plane (Y) substituent effects were mostly electronic. Electron-withdrawing substituents accelerate the insertion through enhanced nucleophilic interaction between silylene lone-pair orbitals with the σ*(SiY) orbital at the TS. The ΔG^≠ values correlate with the σ_I constants as a scale of the inductive effect of Y. Out-of-plane (R) substituent effects are mainly steric, and bulky substituents increase the activation free energy . Correlation of the ΔG^≠ values with Taft’s steric substituent constants (E_s) was observed. There was no significant difference in the out-of-plane substituent effects between the electron-withdrawing Cl and the electron-donating Me groups.