Concise, efficient and practical assembly of bromo-5,6-dimethoxyindole building blocks

A concise, efficient and simple route to a series of bromoindole building blocks is described. The synthetic routes are highlighted by purification-free preparation of o-nitrocinnamate intermediates and clean, modified Cadogan indole syntheses. The scope of this indole synthesis has been explored and expanded through the use of a range of solvents and easily removable phosphine reagents.     

SYNTHESIS OF POLYMERS WITH PHOSPHONIUM END GROUPS BY ATOM TRANSFER RADICAL POLYMERIZATION

The end groups of polymers prepared by atom transfer radical polymerization (ATRP), are well-defined and determined by the initiator used, at least one of them is a halogen end group. The halogen end groups can be transformed to other functionalities such as phosphonium salts as demonstrated in this paper. Kinetic studies with the compounds 1-phenylethyl bromide and methyl 2-bromopropionate, models for the polystyrene and polyacrylate chain ends respectively, indicated that bromine end groups were readily transformed to phosphonium end groups upon the addition of phosphines. Stability tests with the obtained phosphonium salts showed that 1-phenylethyl trialkylphosphonium bromide was stable, even at higher temperatures and in the presence of free phosphines. The stability of the propionate analogue was limited due to the presence of the ester group in the molecule. Polystyrene and poly(methyl acrylate) phosphonium salts were synthesized and the presence of the end groups was demonstrated by ¹H NMR and ESI-MS or MALDI-TOFMS.     

Structural and electronic trends in ortho-metalated dirhodium(II) complexes

Properties of chiral dirhodium catalysts with ortho-metalated aryl phosphine ligands have been studied by a computational quantum chemical density functional theory method. The main aim in the current work was to systematically modify the ligand core of the Rh₂(O₂C R)₂(PC)₂ catalysts (PC is ortho-metalated aryl phosphine) in order to find structural and electronic trends involved with the modifications. The strongest impact on the properties of the active rhodium site was found when electron-withdrawing groups were introduced in the ligand core. The computational approach offers a possibility for a stepwise study of the properties of the catalysts and therefore a tool for further design of the most effective structures.     

X-Ray Photoelectron Spectral (XPS) Studies of Molybdenum (0) and Tungsten (0) Dinitrogen Complexes

The X-ray photoelectron spectra of M(N₂)₂ (dppe)₂, M(N₂)₂ (PMePh₂)₄ and M(N₂)₂ (PMe₂Ph)₄; where M=W or Mo, Ph is phenyl, Me is methyl and dppe is (Ph)₂P-CH₂-CH₂-P(Ph)₂; have been investigated. The N(1s), P(2p_3/2), Mo(3d_5/2) and W(4f_7/2) binding energies do not show significant differences between these complexes. The N(1s) signals show the separation of 1.3-1.4 eV.     

Cone angle radial profiles

Various methodologies have been reported in the literature for the evaluation of the size of a ligand or organic functional group, with the Tolman cone angle methodology proving to be most popular in inorganic chemistry. A procedure to extend the Tolman concept to the measurement of a ligand size, as a profile over a radial distance from the metal (apex), has been developed. The representation of the Tolman cone angle as a function of distance from the metal is termed a cone angle radial profile (CARP). CARPs for PH₃, PMe₃, PEt₃ and PPh₃ have been determined and are described. CARPs for molecules containing the constrained phosphite ligands P(OCH₂)₃CMe, as determined in actual structures (Cambridge Structural Database), have also been evaluated and indicate the invariant shape of the ligand in the different metal environments. The influence of the choice of the H atom van der Waals radius in steric measurements is also discussed.     

A family of simple amide-derived air-stable P,O-ligands for Suzuki cross-coupling of unactivated aryl chlorides

A family of air-stable amide-derived phosphine (Aphos) ligands engineered on simple N,N-dialkyl aryl amide scaffolds has been designed and prepared by one-pot synthesis from the amides in high yields. The Aphos ligands have been used, in analogous to their atropisomeric variations, as hemilabile bidentate P,O-ligands in various Pd-catalyzed C-N and C-C bond forming reactions. We present here our results on the highly efficient Suzuki cross-coupling reactions of unactivated and/or sterically hindered aryl chlorides with arylboronic acids and a relationship of Aphos structures with catalytic efficacy.     

Anab initio investigation of structure and inversion barrier of triisopropylamine and related amines and phosphines

Summary The equilibrium geometry and barrier to pyramidal inversion of triisopropylamine, N(CH(CH₃)₂)₃, is computed at SCF level of theory. For comparison, results for ammonia NH₃ (including a near HF calculation), trimethylamine N(CH₃)₃ and the three analogous phosphine compounds PH₃, P(CH₃)₃ and P(CH(CH₃)₂)₃ are presented as well.     

Synthesis of novel water-soluble linear and heterocyclic phosphino amino acids from 2-phosphinophenols or 2-phosphinophenolethers, formaldehyde and amino acids

Acyclic and cyclic amino acid derivatives of 2-phosphinophenols have been synthesised by reaction of primary phosphinophenols (4-R-2-H₂PC₆H₃OH; R=H, Me, OMe) 1a–c with formaldehyde and amino acids (o- and p-aminobenzoic acid, -lysine) via in situ formed hydroxymethyl species 2a–c. Condensation reactions with glycine did not afford defined products except when the methoxymethyl and tetrahydropyranyl ethers of 1d,e were used instead of the hydroxy compounds. o-Aminobenzoic acid gives rise to linear bis(o-carboxyphenylaminomethyl)phosphines 3a–e. p-Aminobenzoic acid, dependent on the molar ratio, affords bis(p-carboxyphenylaminomethyl)phosphines 4a,d as well as eight-membered heterocyclic 1,5,3,7-diazadiphosphacyclooctanes 5a–e. The aliphatic amino acids glycine and -lysine form six-membered heterocyclic 1,3,5-diazaphosphorinanes 6d and 7a–e, respectively, in presence of excess formaldehyde. -lysine differs from glycine by reaction at the terminal amino group. The structures of the compounds have been elucidated by multinuclear NMR spectroscopy. The salts of the phosphino amino acids are soluble in water. Water solubility increases with the number of hydrophilic groups, i.e. free phenols are more soluble than their ethers. Ligand concentrations in water from 0.1 to 1 M were observed.