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The bio-based substrate and target product 2,5-bishydroxymethylfuran (BHMF) demonstrated to influence the reaction kinetics in the homogeneous reduction of 5-hydroxymethylfurfural (HMF) catalyzed by the Ru-based Shvo's catalyst. A combined experimental and computational study supports an important role of the -CH2OH moiety which may be involved in the catalytic cycle toward the formation of different intermediates from HMF and BHMF. The reaction is selective and leads to quantitative formation of BHMF working under mild conditions. Furthermore, an optimized recycling procedure which avoids the use of water, allows recover and reuse of the catalyst without loss of activity. The mechanistic insights from this work may be extended to provide a general description of the chemistry of the Shvo's catalyst feeding further bio-based molecules. [ABSTRACT FROM AUTHOR]

The novel rhodium(i) complexes [RhCl(NBD)(NHC)] [NBD = norbornadiene, NHC = 1-benzyl-3-R-imidazolin-2-ylidene; R = Me (3a), Bz (3b), Tr (3c), tBu (3d)], containing on one nitrogen the benzyl substituent and on the other increasing bulky alkyl substituents were prepared. All the complexes display restricted rotation around the metal–carbene bond and yield conformational enantiomers. The stereodynamics and racemization barriers about the Rh–carbene have been determined by means of NMR spectroscopy for 3a–c, whereas for the bulkiest 3d only the lower limit (91 kJ mol−1) could be calculated. Whilst the racemization barriers obtained by DFT calculations for 3a,b and 3d matched the experimental values, in the case of 3c the latter (62.3 kJ mol−1) was much smaller with respect to the calculated one (101.7 kJ mol−1). The lower experimental barrier has been attributed to a dissociative pathway that produces a solvated ionic pair in the transition state. The catalytic activity of the neutral rhodium(i) complexes 3a and 3d in the hydrosilylation with HSiMe2Ph of the terminal alkynes PhC≡CH, TolC≡CH, nBuC≡CH, Et3SiC≡CH, and (CPh2OH)C≡CH has been investigated, and compared with the amide-functionalized [RhCl(NBD){1-(2-NHBoc-ethyl)-3-Me-imidazolin-2-ylidene}] (4) and with [RhCl(NBD){1-butyl-3-Me-imidazolin-2-ylidene}] (5). [ABSTRACT FROM AUTHOR]

A convenient method for the bulk preparation of environmentally safe perfluoroalkyl propen-1-yl ethers via isomerization of primary allyl ethers is presented. Herein the solvent-free isomerization was carried out in the presence of two ruthenium(ii) complexes: the ruthenium-hydride [RuClH(CO)(PPh3)3] and the second generation Grubb's type catalyst dichloro[1,3-bis-(2,4,6-trimethylphenyl)-4,5-dimethylimidazol-2-ylidene](thien-2-ylmethylidene)(PCy3) ruthenium(ii) known as CatMETium_RF3™. A variety of reaction parameters such as the catalyst loading, the use of a base and UV photoirradiation have been investigated. We found that the presence of Bu3N is beneficial to both catalytic systems and although CatMETium_RF3™ was shown to be more active than [RuClH(CO)(PPh3)3], the catalytic activity of the latter can also be sensibly improved by UV irradiation. Carrying out the isomerization reaction with 0.1 mol% of [RuClH(CO)(PPh3)3] under UV-irradiation led to a ca. 30% improvement of the conversion compared to the same reaction carried out under sunlight and to a 60% improvement when the reaction is carried out in the dark thus mimicking the conditions present in an autoclave. [ABSTRACT FROM AUTHOR]