John A. Osborn

Versatile Ligands for Palladium‐Catalyzed Asymmetric Allylic Alkylation

Palladium complexes of the chiral diphosphanes 1 and 2 which possess a rigid backbone and a large bite angle catalyze the alkylation of allyl compounds with both high enantioselectivities and reaction rates, particularly with less sterically demanding substrates. 1: R=Me, X=S; 2: R=H, X=C(CH3 )2 .

The asymmetric hydrogenation of imines using tridentate C2 diphosphine complexes of iridium(I) and rhodium(I)

Abstract We report the synthesis of [M(PNP)(diene)] + complexes (M = Ir or Rh; diene = COD ir NBD), where PNP represents a tridentate diphosphine ligand of C 2 symmetry. These complexes are active catalysts for the hydrogenation of imines. Reduction of prochiral imines in the presence of chiral ligands leads to the corresponding amines with 7 to 55% ee.

Cis-dioxomolybdenum(VI) complexes as new catalysts for the Meyer-Schuster rearrangement

Abstract We describe a new catalytic system for the isomerisation of propargylic alcohols into α,β-ethylenic carbonyl derivatives (Meyer-Schuster rearrangement) 1 , based on the combination of dioxomolybdenum(VI) catalysts and sulfoxides.

Catalytic oxidation of alcohols into aldehydes and ketones by an osmium-copper bifunctional system using molecular oxygen

Abstract The oxidation of allylic and benzylic alcohols to aldehydes can be carried out at room temperature as low as 25°C with molecular oxygen, in the presence of the bifunctional osmium-copper system OsO 4 CuCl acting as the catalyst.

MECHANISTIC IMPLICATIONS OF THE OBSERVATION OF KINETIC RESOLUTION IN A PALLADIUM-CATALYZED ENANTIOSELECTIVE ALLYLIC ALKYLATION

Preferential rotation in substrate-palladium intermediates in a catalyzed asymmetric allylic alkylation is proposed to be responsible for both the observed kinetic resolution of the racemic allylic acetate starting material as well as the high selectivity found in the enantiodiscriminating product-forming step [Eq. (a)].

Asymmetric hydrogenation of imines catalysed by carboxylato(diphosphine)iridium(III) complexes

Abstract The synthesis of three new families of monomeric carboxylato(diphosphine)iridium(III) complexes is described (e.g. diphosphine = diop, binap, bdpp). Some of these complexes catalyse the asymmetric hydrogenation of prochiral imines to amines in good activity and enantioselectivity.

Selective and Environmentally Benign Aerobic Catalytic Oxidation of Alcohols by a Molybdenum-Copper System

The oxidation of activated primary and secondary alcohols to the corresponding aldehydes and ketones can be carried out with molecular oxygen, in the presence of the bimetallic molybdenum–copper system MoO2(acac)2–Cu(NO3)2 as catalyst.

Recent advances in the chemistry of tungsten—carbene complexes

Abstract High oxidation state tungsten—carbene complexes similar to W(CHt-Bu)(OCH2t-Bu)2Br2 were synthesized and their physical and chemical properties analysed and compared. In particular, we discuss in this review (i) the Lewis base character of the halide ligands governing the amount of cationic complex formed in the presence of Lewis acids, (ii) the Lewis acid character of the tungsten center illustrating the availability of a vacant site in these molecules, (iii) the nucleophilicity of the carbene carbon, (iv) the stereochemical non-rigidity of some of the compounds and the barrier to rotation about the tungsten—carbon double bond, and (v) the intermolecular ligand transfer reactions. The activity of these compounds as olefin metathesis catalysts was investigated, in the presence as well as in the absence of Lewis acids. The analysis of its dependence on the steric and electronic features of the ligands allows in particular definition of the relative importance of the properties described above in the catalytic process.

A simple route to molybdenum–carbene catalysts for alkene metathesis

A convenient method for the synthesis of high oxidation state tetra-co-ordinate molybdenum–carbene complexes such as Mo(NBut)(CHBut)[OCH(CF3)2]2, which are catalytically active in alkene metathesis reactions, is reported.

Synthesis and Coordination of the New Chiral Tridentate O,N,O Ligand 2,6-Bis[(1S,2S,5R)-(−)-menthyl]pyridine to Molybdenum(VI) and Vanadium(V) Oxo Complexes: Crystal Structures of [(2,6-Bis{(−)-menthyl}pyridine)MoO2] and [(2,6-Bis{(−)-menthyl}pyridine)VO]2(μ-O)

The novel tridentate chiral ligand 2,6-bis{(−)-menthyl}pyridine (1), was readily prepared from the reaction of 2,6-dilithiopyridine with (−)-menthone. Reaction of 1 with VO(OiPr)3 and [MoO2(acac)2] resulted in the formation of the new metal-oxo complexes [VO(ONO)]2(μ-O) (2) and [MoO2(ONO)] (3) [ONO = (1− 2 H)]. Both metal-oxo compounds 2 and 3 have demonstrated the ability to catalyze the asymmetric oxidation of prochiral olefins with tBuOOH as the oxidant. The compounds 1−3 have been fully characterized by 1H, 13C and 51V (where appropriate) NMR spectroscopy, mass spectrometry, microanalysis and IR spectroscopy. Furthermore, the molecular structures of 2 and 3 have been determined by single-crystal X-ray diffraction.