Using the Colloidal Method to Prepare Au Catalysts for the Alkylation of Aniline by Benzyl Alcohol.

Using the colloidal method, attempts were made to deposit Au NPs on seven different material supports (TiO2, α and γ-Al2O3, HFeO2, CeO2, C, and SiO2). The deposition between 0.8 and 1 wt% of Au NPs can be generally achieved, apart for SiO2 (no deposition) and α-alumina (0.3 wt%). The resultant sizes of the Au NPs were dependent on the nature as well as the surface area of the support. The catalytic activity and selectivity of the supported Au catalysts were then compared in the alkylation of aniline by benzyl alcohol. Correlations were made between the nature of the support, the size of the Au NP, and the H-binding energy. A minimum H-binding energy of 1100 µV K-1 was found to be necessary for high selectivity for the secondary amine. Comparisons of the TEM images of the pre- and post-reaction catalysts also revealed the extent of Au NP agglomeration under the reaction conditions.

Synthesis, Structure and Catalytic Activity of NHC-Ag(I) Carboxylate Complexes.

A general synthetic route was used to prepare 15 new N-heterocyclic carbene (NHC)-Ag(I) complexes bearing anionic carboxylate ligands [Ag(NHC)(O2 CR)], including a homologous series of complexes of sterically flexible ITent ligands, which permit a systematic spectroscopic and theoretical study of the structural and electronic features of these compounds. The complexes displayed a significant ligand-accelerated effect in the intramolecular cyclisation of propargylic amides to oxazolidines. The substrate scope is highly complementary to that previously achieved by NHC-Au and pyridyl-Ag(I) complexes.

Synthesis of Isoindolinones by Pd-Catalyzed Coupling between N-Methoxybenzamide and Styrene Derivatives.

An atom-economical protocol for a tandem process involving Fujiwara-Moritani-aza-Wacker reactions has been developed for the Pd-catalyzed coupling between N-methoxy benzamide and styrene derivatives. The generality of the methodology was demonstrated by the synthesis of a library of 25 3-benzylidene isoindolinones in moderate to good yields. A further 40 3-benzyl derivatives were obtained by telescoping the process with a catalytic hydrogenation reaction.

Atropisomeric [(diphosphine)Au2 Cl2 ] complexes and their catalytic activity towards asymmetric cycloisomerisation of 1,6-enynes.

X-ray crystal structures of two [(diphosphine)Au2 Cl2 ] complexes (in which diphosphine=P-Phos and xylyl-P-Phos; P-Phos=[2,2',6,6'-Tetramethoxy-4,4'-bis(diphenylphosphino)-3,3'-bipyridine]) were determined and compared to the reported structures of similar atropisomeric gold complexes. Correlations between the Au⋅⋅⋅Au distances and torsional angles for the biaryl series of ligands (MeOBIPHEP, SEGPhos, and P-Phos; BIPHEP=2,2'-bis(diphenylphosphino)-1,1'-biphenyl, SEGPhos=[(4,4'-bi-1,3-benzodioxole)-5,5'-diyl]bis[diphenylphosphine]) can be made; these measurements appear to be very dependent upon the phosphorous substituent. Conversely, the same effect was not observed for ligands based on the binaphthyl (BINAP) series. The catalytic activity of these complexes was subsequently assessed in the enantioselective cycloisomerisation of 1,6-enynes and revealed an over-riding electronic effect: more-electron-rich phosphines promote greater enantioselectivity. The possibility of silver acting as a (co-)catalyst was ruled out in these reactions.

New chiral zwitterionic phosphorus heterocycles: synthesis, structure, properties and application as chiral solvating agents.

A family of new chiral zwitterionic phosphorus-containing heterocycles (zPHC) have been derived from methylene-bridged bis(imidazolines). These structures were unambiguously determined, including single-crystal XRD analysis for two compounds. The stability, acid/base and electronic properties of these dipolar phosphorus heterocycles were subsequently investigated. zPHCs can be successfully employed as a new class of chiral solvating agents for the enantiodifferentiation of chiral carboxylic and sulfonic acids by NMR spectroscopy. The stoichiometry and binding constants for the donor-acceptor complexes formed were established by NMR titration methods.

Asymmetric synthesis of 2-alkyl-substituted tetrahydroquinolines by an enantioselective aza-Michael reaction.

An optically active tetrahydroquinoline intermediate (5) was prepared in 8 steps from monoprotected ethylene glycol, using a Pd-catalysed aza-Michael reaction to induce chirality. This can be transformed into three Galipea alkaloids (angustureine, galipeine and cuspareine). The proximity of a benzyloxy group is found to exert profound effects in several steps of the synthesis.

Alternative to benzoquinone for room-temperature Fujiwara-Moritani reactions.

tert-Butyl perbenzoate is a substitute for benzoquinone for mild (room-temperature) Fujiwara-Moritani reactions between acetanilides and butyl acrylate under homogeneous conditions. The system was enhanced further by including Cu(OAc)(2) as a cocatalyst. Methyl methacrylate can be activated toward coupling under these conditions.

Delineating origins of stereocontrol in asymmetric Pd-catalyzed alpha-hydroxylation of 1,3-ketoesters.

Systematic studies of reaction conditions and subsequent optimization led to the identification of important parameters for stereoselectivity in the asymmetric alpha-hydroxylation reaction of 1,3-ketoesters. Enantioselectivities of up to 98% can be achieved for cyclic substrates and 88% for acyclic ketoesters. Subsequently, the combination of cyclic/acyclic ketoester, catalyst, and oxidant was found to have a profound effect on reaction rates and turnover-limiting steps. The stereochemistry of the reaction contradicts that observed for other similar electrophilic substitution reactions. This was rationalized by transition-state modeling, which revealed a number of cooperative weak interactions between oxidant, ligand, and counterion, together with C-H/pi interactions that cumulatively account for the unusual stereoselectivity.

Palladium-catalysed enantioselective alpha-hydroxylation of beta-ketoesters.

Highly enantioselective alpha-hydroxylation of cyclic and acyclic 1,3-ketoesters can be achieved with up to 98% ee using a dicationic palladium(ii) catalyst and dimethyldioxirane as oxidant.

A recyclable copper(ii) catalyst for the annulation of phenols with 1,3-dienes.

Air- and moisture-stable Cu(OTf)(2)-bipy catalyses the addition of phenols to 1,3-dienes under aerobic conditions in a tandem hydroalkoxylation-rearrangement-hydroalkylation sequence, furnishing O-heterocycles in moderate to good yields, and can be recycled without any loss in catalytic activity.

Solvent-dependent nuclearity, geometry and catalytic activity of [(SPhos)Pd(Ph)Cl]2.

The nuclearity and structures of the palladium complex [(SPhos)Pd(Ph)Cl]2 in the solid and solution states are revisited using a combination of Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, NMR spectroscopy, mass spectrometry, DFT calculations and trapping experiments. The complex was tested for its catalytic activity in the coupling reaction between chlorobenzene and n-hexylamine, where different deactivation behaviours were observed in toluene, 1,4-dioxane and DMF.

Copper-catalyzed intermolecular hydroamination of alkenes.

[reaction: see text] Regioselective additions of arylsulfonamides to vinylarenes, norbornene, and cyclohexadiene were achieved using a copper-diphosphine catayst under mild reaction conditions. These processes appear to be ligand-accelerated.

Copper(II)-catalysed addition of O-H bonds to norbornene.

Cu(OTf)2 is an inexpensive, air- and moisture-stable catalyst for the O-H addition of aliphatic and aromatic acids and alcohols to norbornene.

Chemo- and diastereoselectivities in the electrochemical reduction of maleimides.

The electrochemical cathodic reduction of cyclic imides (maleimides) to succinimides can be achieved chemoselectively in the presence of alkene, alkyne, and benzyl groups. The efficiency of the system was demonstrated by using a 3D electrode in a continuous flow reactor. The reduction of 3,4-dimethylmaleimides to the corresponding succinimides proceeds with a 3:2 diastereomeric ratio, which is independent of the nitrogen substituent and electrode surface area. The stereoselectivity of the process was rationalized by using DFT calculations, involving an acid-catalyzed tautomerization of a half-enol occurring through a double hydrogen-transfer mechanism.

Structure and bonding of [(SIPr)AgX] (X = Cl, Br, I and OTf).

A series of iso-structural complexes [(SIPr)AgX] (X = Cl, Br, I, OTf; SIPr = 1,3-bis(2,6-diisopropylphenyl)imidazolidene) were synthesised, including the first example of a N-heterocyclic carbene silver(I) complex containing an O-bound triflate. Bond Energy Dissociation and Natural Orbitals for Chemical Valence bond analyses (BEDA & ETS-NOCV) revealing a significant NHC → M σ-back-donation, which influences the stability and sigma-donicity of these complexes.

Electronic structures of cyclometalated palladium complexes in the higher oxidation states.

The electronic and redox properties of a series of cyclometalated Pd complexes with oxidation states of +2, +3 and +4 were examined using a range of currently available spectroscopic and electrochemical techniques. Changes in metal-ligand bond lengths were established by X-ray crystallography and correctly predicted by DFT calculations, from which the frontier orbitals and partial atomic charges can be obtained. X-ray absorption spectroscopy (XAS) revealed interesting XANES features that suggest a synergistic relationship between metal-ligand interactions. The electrochemical study of the Pd(ii) dimer was found to contain two sequential oxidative potentials indicative of a weak metal-metal interaction.

Models for the Carbonyl-ene Cyclization Reaction: Open and Closed Transition States.

Different cyclization products are formed with different Lewis acids in the ene cyclization of 5-hexenals (see scheme on the right; a: methylaluminum bisphenoxide, b: Me2 AlCl, c: Sc(OSO2 CF3 )3 ). This is not surprising, but it is gratifying that these result can be rationalized with an internally consistent model.