The diruthenium(II,II) complex [Ru 2 (L 1 )(OAc) 3 ]Cl (1), spanned by a naphthyridine-diimine ligand and bridged by three acetates, has been synthesized. The catalytic efficacy of complex 1 has been evaluated for the acceptorless dehydrogenation (AD) of alcohols and for the dehydrogenative coupling reactions of alcohols with Wittig reagents. The diruthenium(II,II) complex is an excellent catalyst for AD of a diverse range of alcohols, and it is shown to be particularly effective for the conversion of primary alcohols to the corresponding aldehydes without undesired side products such as esters. Triphenylphosphonium ylides in a one-pot reaction with alcohols afforded the corresponding olefins in high yields with excellent E selectivity. The liberated dihydrogen gas was identified and measured to be 1 equiv with respect to alcohol. Deuteration studies with PhCD 2 OH revealed the absence of isotope scrambling in the product, indicating the involvement of a Ru-monohydride intermediate. Kinetic studies and DFT calculations suggest a low-energy bimetallic β-hydride elimination pathway where rate-limiting intramolecular proton transfer from alcohol to metal-bound hydride constitutes the dehydrogenation step. The general utility of metal−metal bonded compounds for alcohol AD and subsequent coupling reactions is demonstrated here.
The utility and selectivity of the catalyst [Ru(COD)(L(1))Br2] (1) bearing a fused π-conjugated imidazo[1,2-a][1,8]naphthyridine-based abnormal N-heterocyclic carbene ligand L(1) is demonstrated toward selective oxidation of C═C bonds to aldehydes and C≡C bonds to α-diketones in an EtOAc/CH3CN/H2O solvent mixture at room temperature using a wide range of substrates, including highly functionalized sugar- and amino acid-derived compounds.
A ruthenium(II) complex bearing a naphthyridine-functionalized pyrazole ligand catalyzes oxidant-free and acceptorless selective double dehydrogenation of primary amines to nitriles at moderate temperature. The role of the proton-responsive entity on the ligand scaffold is demonstrated by control experiments, including the use of a N-methylated pyrazole analogue. DFT calculations reveal intricate hydride and proton transfers to achieve the overall elimination of 2 equiv of H.
A [RuH(CO)(py-NP)(PPh3)2]Cl (1) catalyst is found to be
effective for catalytic transformation of primary alcohols, including
amino alcohols, to the corresponding carboxylic acid salts and two
molecules of hydrogen with alkaline water. The reaction proceeds via
acceptorless dehydrogenation of alcohol, followed by a fast hydroxide/water
attack to the metal-bound aldehyde. A pyridyl-type nitrogen in the
ligand architecture seems to accelerate the reaction.
Phosphorus ylides are 1,2-dipolar compounds with a negative charge at the carbon atom. This charge is stabilized by the neighboring onium moiety, but can also be shifted towards other substituents...
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