Combining NHC bis-Phenolate Ligands with Oxophilic Metal Centers: A Powerful Approach for the Development of Robust and Highly Effective Organometallic Catalysts:

The present paper describes an overview of a novel family of tridentate NHC pincer ligand in which two phenoxide moieties are directly connected to the nitrogen atoms of a central N-heterocyclic carbene. It was envisioned that such a structure might be suitable for coordination to a variety of metal centers across the periodic table, including oxophilic metals. Various metal complexes bearing such ligand are indeed readily accessible in high yields via straightforward routes. Interestingly, a robust zirconium-NHC complex was found to polymerize rac-lactide in a highly controlled, living and stereoselective manner to afford heterotactic PLA

Electrochemical Generation of N-Heterocyclic Carbenes for Use in Synthesis and Catalysis

The electrochemical generation of N-heterocyclic carbenes (NHCs) offers a mild and selective alternative to traditional synthetic methods that usually rely on strong bases and air-sensitive materials. The use of electrons as reagents results in an efficient and clean synthesis that enables the direct use of NHCs in various applications. Herein, the use of electrogenerated NHCs in organocatalysis, synthesis and organometallic chemistry is explored

Co-ordination of the chiral N,O-ligand 2-[(1S, 2S,5R)(-)-menthol]pyridine to molybdenum(VI) and vanadium(IV) oxocomplexes - Crystal structures of [MoO2{2-(-)-menthol-pyridine}(2)] and [VO{2-(-)menthol-pyridine}(2)]

Reaction of the chiral 1-pyridin-2-yl-menthol ligand (1) with [VO(acac)(2)] and [MoO2(acac)(2)] results in the formation of the metal-ore complexes [VO(N-O)(2)] (2) and [MoO2(N-O)(2)] (3), where N-O=2-[(-)-menthol]-pyridine. The molecular structures of (2) and (3) have been determined by single-crystal X-ray diffraction, which revealed the expected square-pyramidal geometry for (2) with the pyridine ring nitrogens mutually trans, and the expected slightly distorted octahedral arrangement of (3) with cis di-oxo ligands. Both metal-ore compounds (2) and (3) have demonstrated the ability to catalyse the asymmetric oxidation of prochiral olefins and sulfides with H2O2 or tBuOOH as the oxidant. (C) 1999 Elsevier Science Ltd, All rights reserved

Bis[bis(oxazolinato)] Complexes of Yttrium and Lanthanum: Molecular Structure and Use in Polymerization of (D,L)-Lactide and (D,L)-Γ-Butyrolactone

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Synthesis and coordination of the new chiral tridentate O,N,O ligand2,6-[bis[(1S,2S,5R)-(-)-menthyl]pyridine to molybdenum(VI) andvanadium(V) oxo complexes: Crystal structures of [(2,6-bis{(-)-menthyl}pyridine)MoO2] and [(2,6-bis{(-)-menthyl}pyridine)VO](

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-ore complexes [VO(ONO)](2)(mu-O) (2) and [MoO2(ONO)] (3) [ONO = (1 - 2 H)]. Both metal-ore 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 H-1, C-13 and V-51 (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

Tridentate complexes of group 10 bearing bis-aryloxide N-heterocyclic carbene ligands: Synthesis, structural, spectroscopic, and computational characterization

A series of group 10 complexes featuring chelating tridentate bis-aryloxide N-heterocyclic carbenes were synthesized and characterized by using different techniques. Ni(II), Pd(II), and Pt(II) complexes were isolated in good yields by straightforward direct metalation of the corresponding benzimidazolium or imidazolium precursors in a one-pot procedure. All of the compounds were fully characterized, including single-crystal X-ray diffractometric determination for three of the derivatives. In the solid state, the complexes adopt a typical square-planar coordination geometry around the platinum atom, sizably distorted in order to comply with the geometrical constraints imposed by the bis-aryloxide N-heterocyclic carbene ligand. For platinum and palladium derivatives, a joint experimental and theoretical characterization was performed in order to study the optical properties of the newly prepared complexes by means of electronic absorption and steady-state and time-resolved photophysical techniques as well as density functional theory (DFT) and time-dependent DFT in both vacuum and solvent. When the temperature was lowered to 77 K in frozen glassy matrix, three platinum complexes showed broad and featureless, yet weak, photoluminescence in the green region of the visible spectrum with excited-state lifetimes on the order of a few microseconds. On the basis of joint experimental and computational findings and literature on platinum complexes, such emission was assigned to a triplet-manifold metal-ligand-to-ligand charge transfer (3MLLCT) transition