[PdCl2{8-(di-tert-butylphosphinooxy)quinoline)}]: a highly efficient catalyst for Suzuki-Miyaura reaction

The complex [PdCl2(P-N)] containing the basic and sterically demanding 8-(di-tert-butylphosphinooxy)quinoline ligand (P-N) is a highly efficient catalyst for the coupling of phenylboronic acid with aryl bromides or aryl chlorides. The influence of solvent and base has been investigated, the highest rates being observed at 110 C in toluene with K2CO3 as the base. With aryl bromides the reaction rates are almost independent on the electronic properties of the para aryl substituents, on the contrary, reduced reaction rates are observed when bulky substituents are present on the substrate. Nevertheless the coupling of 2-bromo-1,3,5-trimethylbenzene with phenylboronic acid can be carried out to completion in 2 h using a catalyst loading of 0.02 mol %. Under optimized reaction conditions, turnover frequencies as high as 1900 h(-1) can be obtained in the coupling of 4-chloroacetophenone with phenylboronic acid: lower reaction rates are obtained with Substrates bearing EDG substituents on the aryl group. (C) 2009 Elsevier Ltd. All rights reserved

Synthesis of 4-Isobutylbenzaldehyde an Important Intermediate for the Fragrance (+)- and (-)-Silvial®

The synthesis of 4-isobutylbenzaldehyde, a valuable precursor for the fragrance Silvial® (3-(4-isobutylphenyl)-2-methylpropanal), is reported. Three different synthetic approaches are reported starting either from 4-isobutylbenzoic acid (via benzyl alcohol, or via acyl chloride), or by Suzuki-Miyaura cross-coupling reaction between 4-bromobenzaldehyde and 2-methylpropylboronic acid

Mechanistic understanding of chromium-based oligomerisation catalysts : an EPR and ENDOR investigation

Electron Paramagnetic Resonance (EPR) and Electron Nuclear Double Resonance (ENDOR) spectroscopies have been used to study the fundamental nature of chromium-based selective oligomerisation catalysts. A series of 'pre-catalyst' complexes were fully characterised CW-EPR revealed each complex to possess an axial g matrix (g > ge > g ) and superhyperfine coupling to two equivalent 31P nuclei, consistent with a low-spin cf species of approximate Cjv symmetry, where the metal contribution to the SOMO is primarily dxy. The isotropic component to the 31P coupling was of a larger magnitude in those Cr(I) complexes bearing PNP ligands than those bearing PCP, indicating that the phosphorus 3s character in the SOMO was higher for the former. CW-ENDOR demonstrated that subtle structural differences in the complexes, namely in the phenyl ring conformations, occurred as a function of ligand type. Pulsed experiments proved that the technique is valid and viable for further work on the activated system. Upon activation of the pre-catalyst with an alkylaluminium, four distinct paramagnetic centres were identified. A Cr(I) bis-arene complex was firstly detected it was found to form either via intramolecular co-ordination of the ligand phenyl groups, or preferentially via solvent-based arene co-ordination, if such groups were available. Two further species (I and III) were subsequently observed at low temperatures the spin Hamiltonian parameters extracted for both showed that a significant modification to the structure of the pre-catalyst had occurred. Half-field transitions indicated the possibility of a dimeric nature to Species III. ENDOR measurements detected an exceptionally large proton coupling in the activated system, possibly due to the co ordination of alkyl fragments to the metal centre. A final, fourth paramagnetic centre (Species IV), was detected and classed as an intermediate species, due to the greater similarity between its g and A matrices with those of the parent complex, than the other activated species. Finally, a preliminary investigation into analogous pre-catalyst complexes bearing N-heterocyclic carbene ligands was performed, due to their similar employment in oligomerisation catalysis CW-EPR spectra revealed information on both their electronic and structural natures.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Synthesis and characterization of new pyridine-isourea complexes of Au(III)

New neutral gold(III) complexes having formulae AuX3(pyiuPr) and AuX3(pyiuCy) were synthesized and characterized (X = Cl, Br; pyiuPr = 1,3-diisopropyl-2-((pyridin-2-yl)methyl)isourea; pyiuCy = 1,3-dicyclohexyl- 2-((pyridin-2-yl)methyl)isourea). The N-donor ligands coordinate the metal centre through only one nitrogen atom and DFT calculations support the formation of Au-N(pyridine) bonds. Variable-temperature NMR experiments suggest the formation of intermolecular hydrogen bonds among isourea moieties in CDCl3 solutio

Asymmetric catalysis in fragrance chemistry: a new catalytic approach to non racemic Cyclamen-aldehyde

A new catalytic synthesis of Cyclamen-aldehyde (3-(4-isopropylphenyl)-2-methylpropanal) has been developed. The devised synthetic approach entails as the key step the asymmetric hydrogenation of (E)-3-(4- isopropylphenyl)-2-methyl acrylic acid which has been carried out with ees of about 60% by using a catalytic system prepared by combining in situ [Ru(C6H6)Cl2]2 and (S)-MeO-BIPHEP

The conjugate base of malonaldehyde as antenna-ligand towards trivalent europium and terbium ions

Coordination compounds having formulae [M(MA)3] n and M(MA)(Me2Tp)2 (M = Y, Eu, Tb; MA = conjugate base of malonaldehyde; Me2Tp = tris(3,5-dimethyl-pyrazol-1-yl)borate) were synthesized and characterized. The photoluminescence features of the europium and terbium derivatives were investigated. By comparing the herein reported photoluminescence data with those relative to analogous nitro- and bromomalonaldehyde derivatives, it appears that the conjugate base of malonaldehyde is a more efficient antenna-ligand for the sensitization of Tb(III) luminescence. The experimental data were rationalized on the basis of DFT calculations. Tb(MA)(Me2Tp)2 was used as dopant for the preparation of luminescent plastic materials based on poly(methyl methacrylate)