Substituent effects on Ni-S bond dissociation energies and kinetic stability of nickel arylthiolate complexes supported by a bis(phosphinite)-based pincer ligand.

Pincer complexes of the type [2,6-(R(2)PO)(2)C(6)H(3)]NiSC(6)H(4)Z (R = Ph and i-Pr; Z = p-OCH(3), p-CH(3), H, p-Cl, and p-CF(3)) have been synthesized from [2,6-(R(2)PO)(2)C(6)H(3)]NiCl and sodium arylthiolate. X-ray structure determinations of these thiolate complexes have shown a somewhat constant Ni-S bond length (approx. 2.20 Å) but an almost unpredictable orientation of the thiolate ligand. Equilibrium constants for various thiolate exchange (between a nickel thiolate complex and a free thiol, or between two different nickel thiolate complexes) reactions have been measured. Evidently, the thiolate ligand with an electron-withdrawing substituent prefers to bond with "[2,6-(Ph(2)PO)(2)C(6)H(3)]Ni" rather than "[2,6-(i-Pr(2)PO)(2)C(6)H(3)]Ni", and bonds least favourably with hydrogen. The reactions of the thiolate complexes with halogenated compounds such as PhCH(2)Br, CH(3)I, CCl(4), and Ph(3)CCl have been examined and several mechanistic pathways have been explored.

Tetrabutylammonium tribromide (TBATB): a mild and efficient catalyst for O-isopropylidenation of carbohydrates.

A wide range of O-isopropylidene derivatives can be prepared from the sugars and their derivatives on reaction with acetone at room temperature by employing 2 mol% of tetrabutylammonium tribromide (TBATB) as a catalyst. Good yields, low catalyst loading, mild reaction conditions, and a non-aqueous workup procedure are some major advantages of this protocol.