Stephen J. Brown

Synthesis of a new family of water-soluble tertiary phosphine ligands and of their rhodium(I) complexes; olefin hydrogenation in aqueous and biphasic media

Abstract The series of phosphonium phosphines [Ph2P(CH2)nPMe3]X (n = 2, 3, 6, 10; X = NO−3, Cl−, PF−6), henceforth II-, III-, VI-, and X-phosphos, respectively, have been prepared and characterized. The ligands react with [NBDRhCl]2 (NBD = norbornadiene) to form the complexes [NBDRhCl(n-phosphos)]X, one of which, [NBDRhCl(II-phosphos)]PF6, has been characterized crystallographically. The 1:1 complexes [NBDRhCl(n-phosphos)]X react with a second equivalent of ligand to form the complexes [NBDRh(n-phosphos)2]X, which form very active olefin hydrogenation catalysts in aqueous and aqueous—organic biphasic systems. The effect of chain length on activity is very significant, the complex of VI-phosphos forming the most active catalyst.

Palladium-catalysed cyclisation–carboformylation. Molecular queuing cascades

Palladium(0)-catalysed tri- and tetra-molecular queuing cascades are described involving five- and six-membered ring formation accompanied by carboformylation of a proximate alkene and employing carbon monoxide (1 atm) and diphenylmethylsilane as the source of the formyl group.

Alumina-supported fluoride reagents for organic synthesis: optimisation of reagent preparation and elucidation of the active species

Reagent loading and drying conditions have been compared for alkali metal fluride (MF)–alumina supported reagents, by reaction studies and a series of analytical techniques. The reaction studies indicate that whereas a combination of low MF loadings and highly efficient drying procedures give the best reagents for catalytic reactions, somewhat higher loadings and more moderate drying conditions give the best reagents for non-catalytic reactions. The analytical studies enable some rationalisation of the reaction results as well as providing important clues concerning the nature of the active-basic species. The formation of OH– on the reagent surface cannot be entirely responsible for the high basicity of the reagents and it seems that co-ordinately unsaturated F– ions on the reagent surface play an important role in the behaviour of the reagents. High MF loadings and high drying temperatures result in significant structural damage to the reagents with resulting loss in activity.

Tetraphenylphosphonium hydrogendifluoride: a new source of fluoride ion

Tetraphenylphosphonium hydrogendifluoride, a soluble and thermally stable reagent, acts as a of source of fluoride ion in a variety of organic reactions.

A Fibre-Optic Coupled Fluorescence Multiwavelength Sensor for Automated Monitoring of Bacteria Culture from Drinking Water

An automated bacteria test combines a solution culture with a fibre-optic coupled fluorescence sensor with miniature spectrometer. A fluorescent product from a selective substrate is extracted into a polymer waveguide contacting the solution.

Tris(3,6-dioxaheptyl)amine alkali-metal cation complexes. A fast atom bombardment mass spectrometry, infrared, and nuclear magnetic resonance study

Tris(3,6-dioxaheptyl)amine (tdoha, industrial name TDA-1) is shown to complex with a series of alkali-metal cations in solution, complexation being observed by fast atom bombardment mass spectrometry (f.a.b.m.s.; observation of a metal–tdoha cation), i.r., and 19F n.m.r. Approximate values of the relative concentrations of the tdoha and crown ether complexes are obtained by f.a.b.m.s. by competitive complexation experiments with a range of cations.

Evidence for the existence of Cu+ and Cu(CN)2– in supported copper cyanide reagents

I.r. analysis of supported CuCN reagents suggests that the active forms of these materials in nucleophilic cyanations contain the ions Cu+ and Cu(CN)2–; this is the first report of an active solid form of CuCN.

High resolution solid state 19F n.m.r. spectroscopy as a tool for the study of ionic fluorides

High resolution solid state 19F n.m.r. spectroscopy has been used for the first time to investigate the bonding in ionic fluorides.

Investigation of cationic hydrogen-bonded systems by fast atom bombardment mass spectrometry

Fast atom bombardment mass spectrometry (FABMS) has been used to investigate the hydrogen-bonding of pyridinium and trialkylammonium ions with a range of electron donors. We have studied the effects of matrix liquid, concentration, nature of the anion, and strength of the hydrogen-bond on the observed intensity of the complex peak. The results may be easily rationalized in hydrogen-bonding terms and are in excellent agreement with those of more ‘conventional’ techniques such as i.r. spectroscopy.