The conversion of alcohols to carbonyl compounds and hydrogen: a survey of homogeneous enzymatic and anthropogenic catalytic dehydrogenation reactions.
Palladium complexes incorporating chiral N-heterocyclic carbene (NHC) ligands catalyze the asymmetric intramolecular α-arylation of amides producing 3,3-disubstituted oxindoles. Comprehensive DFT studies have been performed to gain insight into the mechanism of this transformation. Oxidative addition is shown to be rate-determining and reductive elimination to be enantioselectivity-determining. The synthesis of seven new NHC ligands is detailed and their performance is compared. One of them, L8, containing a tBu and a 1-naphthyl group at the stereogenic centre, proved superior and was very efficient in the asymmetric synthesis of fifteen new spiro-oxindoles and three azaspiro-oxindoles often in high yields (up to 99 %) and enantioselectivities (up to 97 % ee; ee=enantiomeric excess). Three palladacycle intermediates resulting from the oxidative addition of [Pd(NHC)] into the aryl halide bond were isolated and structurally characterized (X-ray). Using these intermediates as catalysts showed alkene additives to play an important role in increasing turnover number and frequency.
Nine new N-heterocyclic carbene gold chloride complexes (10–18) were synthesized starting from bulky chiral imidazolium salts (1–9) developed in this laboratory. Full characterization of all complexes, including the X-ray structures of gold(I)(1,3-bis((S)-1-(2-methoxyphenyl)-2,2-dimethylpropyl)-1H-imidazol-2(3H)-ylidene) chloride (13) and gold(I)(1,3-bis((S)-2,2-dimethyl-1-(naphthalen-1-yl)propyl)-1H-imidazol-2(3H)-ylidene) chloride (16), is reported. The complexes 10–18 were applied in the methoxycyclization of 1,6-enynes using AgNTf2 as an additive. Synthesis of the N-heterocyclic carbene gold triflimidate (19) was achieved by treating complex 12 with AgNTf2. The complex gold(I)(1,3-bis((R)-1-(2-methoxyphenyl)-2,2-dimethylpropyl)imidazolidin-2-ylidene)(1,1,1-trifluoro-N-(trifluoromethylsulfonyl)methylsulfonamido) (19) was isolated and spectroscopically and structurally (X-ray) characterized
A new family of chiral N-heterocyclic carbene borane complexes was synthesized starting from their corresponding imidazolium salts. The complexes were fully characterized. X-ray crystal structures of the complexes were obtained
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