Analysis of an unprecedented mechanism for the catalytic hydrosilylation of carbonyl compounds

This work details an in-depth evaluation of an unprecedented mechanism for the hydrosilylation of carbonyl compounds catalyzed by (PPh3)2Re(O)2I. The proposed mechanism involves addition of a silane Si-H bond across one of the rhenium-oxo bonds to form siloxyrhenium hydride intermediate 2 that reacts with a carbonyl substrate to generate siloxyrhenium alkoxide 4, which, in turn, affords the silyl ether product. Compelling evidence for the operation of this pathway includes the following: (a) isolation and structural characterization by X-ray diffraction of siloxyrhenium hydride intermediate 2, (b) demonstration of the catalytic competence of intermediate 2 in the hydrosilylation reaction, (c) 1H and 31P{1H} NMR and ESI-MS evidence for single-turnover conversion of 2 into 1, (d) observation of intermediate 2 in the working catalyst system, and (e) kinetic analysis of the catalytic hydrosilylation of carbonyl compounds by 1.     

A Synthetic Supramolecular Receptor for the Hydrosulfide Anion

Hydrogen sulfide (H₂S) has emerged as a crucial biomolecule in physiology and cellular signaling. Key challenges associated with developing new chemical tools for understanding the biological roles of H₂S include developing platforms that enable reversible binding of this important biomolecule. The first synthetic small molecule receptor for the hydrosulfide anion, HS^?, using only reversible, hydrogen‐bonding interactions in a series of bis(ethynylaniline) derivatives, is reported. Binding constants of up to 90 300±8700 m ^?1 were obtained in MeCN. The fundamental science of reversible sulfide binding, in this case featuring a key CH???S hydrogen bond, will expand the possibility for discovery of sulfide protein targets and molecular recognition agents.     

Measurement of the ground state 2n pickup probability for 28Si+68Zn and its role in sub-barrier fusion enhancement

The ground state and excited state transfer yields for the 2-neutron pickup channel in the ²⁸Si+⁶⁸Zn system have been measured explicitly. The recoil mass separator at the nuclear Science Centre, New Delhi was used for the measurement. A NaI(T1) detector was used for detecting the deexcitation γ’s from the transfer products. The kinematic coincidence technique was employed for the transfer measurement. Simplified coupled channels calculations show that out of all transfer channels the major contribution to the sub-barrier enhancement comes from the ground state 2 neutron pickup channel with a ground state Q-value of+1.83 MeV.