Jay A. Labinger

Other way round: 1H and 13C NMR spectroscopy on isotopically labeled glucose reveals that in the presence of tin-containing zeolite Sn-Beta, the isomerization reaction of glucose in water proceeds by way of an intramolecular hydride shift (see scheme) rather than proton transfer. This is the first mechanistic demonstration of Sn-Beta acting as a Lewis acid in a purely aqueous environment. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

The selective oxidation of alkanes is a topic of considerable interest to both industrial and academic chemists. While the initial discovery occurred more than 25 years ago, new developments in alkane oxidation catalyzed by electrophilic late transition metals have provided important mechanistic insights as well as potentially practical methods for alkane transformations.

Abstract Hydrozirconation has recently been developed as a procedure for functionalizing alkenes, alkynes, and 1,3‐dienes via organozirconium(IV) intermediates. These intermediates react with a variety of electrophilic reagents to give organic products in high yield. Mechanisms of reactions involved in these sequences are discussed.

The scandium hydride complex [(Cp*SiNR)(PMe_3)Sc(µ-H)]_2 (1), ((Cp*SiNR) = ((η^5-C_5Me_4)SiMe_2(η^1-NCMe_3)}) is prepared by hydrogenation of (Cp*SiNR)ScCH(SiMe_3)_2 in the presence of trimethylphosphine. The hydride complex is a catalyst precursor for the polymerization of α-olefins, yielding atactic products of low molecular weight (M, = 3000-7000). GC/MS analysis of volatile, oligomeric products revealed that all scandium centers are active during the polymerization. Selectivity for head-to-tail insertion is high (>99%) and for the tetramer, pentamer, and hexamer formed during propene polymerization, the maximum theoretical numbers of head-to-tail stereoisomers are observed by capillary GC. The stoichiometric reaction between 1 and 2 equiv of ethylene produces the unusual ethylene-bridged dimer [(Cp*SiNR)(PMe_3)Sc]_2(µ,η^2,η^2-C_2H_4) (2) and an equivalent of ethane, whereas the same reaction with propene affords the phosphine-free, alkyl-bridged scandium dimer [(Cp*S~NR)Sc]_2(µ-CH_2CH_2CH_3)_2 (3). The absence of coordinating phosphine allows the latter complex to function as a more active olefin polymerization catalyst precursor. 1 reacts with styrene to form a unique double-insertion product arising from sequential 1,2- and 2,1-styrene insertion. The structure of the catalytic intermediate in solution was determined by low-temperature ^(13)C-NMR studies of the model complexes (Cp*SiNR)(P(^(13)CH_3)_3]ScCH_2CH(CH_3)CHCH_2CH_2CH_3 and (Cp*SiNR)(PMe_3)Sc^(13)CH_2CHCH(^(13)CH_3)_2. One phosphine-bound species is observed in equilibrium with only one phosphine-free species. The symmetry properties of the latter indicate that it is a monomeric, hence 12-electron, scandium alkyl complex. Semiquantitative treatment of equilibrium concentration data supports this conclusion.