With petroleum supplies dwindling, there is increasing interest in selective methods for transforming other carbon feedstocks into hydrocarbons suitable for transportation fuel. We report the development of highly productive, well-defined, tandem catalytic systems for the metathesis of n-alkanes. Each system comprises one molecular catalyst (a "pincer"-ligated iridium complex) that effects alkane dehydrogenation and olefin hydrogenation, plus a second catalyst (molecular or solid-phase) for olefin metathesis. The systems all show complete selectivity for linear (n-alkane) product. We report one example that achieves selectivity with respect to the distribution of product molecular weights, in which n-decane is the predominant high-molecular-weight product of the metathesis of two moles of n-hexane.

A catalytic alkane metathesis provides a mild and selective degradation of polyethylene wastes into valuable fuels and waxes.

A trifluoromethyl ketone analogue of arachidonic acid in which the COOH group is replaced with COCF3 (AACOCF3) was prepared and found to be a tight- and slow-binding inhibitor of the 85-kDa cytosolic human phospholipase A2 (cPLA2). Enzyme inhibition was observed when AACOCF3 was tested in assays using either phospholipid vesicles or phospholipid/Triton X-100 mixed micelles. The fact that the inhibition developed over several minutes in both assays establishes that AACOCF3 inhibits by direct binding to the enzyme rather than by decreasing the fraction of enzyme bound to the substrate interface. From the measured values of the inhibitor association and dissociation rate constants, an upper limit of the equilibrium dissociation constant for the Ca(2+).AACOCF3.PLA2 complex of 5 x 10(-5) mole fraction was obtained. Thus, detectable inhibition of cPLA2 by AACOCF3 occurs when this compound is present in the assay at a level of one inhibitor per several thousand substrates. Arachidonic acid analogues in which the COOH group is replaced by COCH3, CH(OH)CF3, CHO, or CONH2 did not detectably inhibit the cPLA2. The arachidonyl ketones AACOCF2CF3 and AACOCF2Cl were found by 19F NMR to be less hydrated than AACOCF3 in phospholipid/Triton X-100 mixed micelles, and compared to AACOCF3 these compounds are also weaker inhibitors of cPLA2. In keeping with the fact that cPLA2 displays substrate specificity for arachidonyl-containing phospholipids, the arachidic acid analogue C19H39COCF3 is a considerably less potent inhibitor compared to AACOCF3.(ABSTRACT TRUNCATED AT 250 WORDS)

This review covers the advance in the development of Fe, Co, and Ni catalysts for the alkene hydrosilylation reaction, as well as the related dehydrogenative silylation reaction. The hydrosilylation of alkene is an important reaction for the synthesis of alkylsilanes that has widespread applications in numerous siliconbased materials, and for decades, this transformation has been relying on the use of Pt catalysts. Recently, the high abundance and low cost, coupled with the environmentally benign nature of the base metals have stimulated enormous research on the development of first-row transition-metal catalysts as replacements for the precious Pt catalysts. Several base-metal catalysts which have emerged during the past 5 years offer high activity, broad substrate scope, and excellent regioselectivity. Both of the anti-Markovnikov and the unusual Markovnikov additions can be achieved in a high degree of regioselectivity. The reactions of acyclic internal olefins catalyzed by the base-metal catalysts reported to date yield linear alkylsilanes via a tandem olefin-isomerization and hydrosilylation process. A few catalysts enable the dehydrogenative silylation of alkenes to form vinylsilanes and/or allylsilanes.