Transition metal complexes, their reactions, and their ability to catalyse valuable processes are at the centre of a variety of research programmes. In particular, the switch from well-understood solution chemistry to often obscure but industrially-relevant heterogeneous catalysis is being explored by examining the reactions of metal complexes whilst supported on silica or clays, or whilst entrapped in the cages of zeolites.
New chiral ligands have been employed to make homochiral complexes of Ti, Zr, V, Cr, Mo, Mn, Fe, Co, Ni and Pd, and the more robust of these have been used as oxidation catalysts for converting prochiral alkenes or sulfides to chiral epoxides or sulfoxides, respectively. An example is [MoO(O2)2(S-(diphenylphosphoryl) binaphthol)] which produces enantiomeric excesses of up to 30% in the epoxidation of 3,3'-dimethylbut-1-ene. Supported by EPSRC, and in collaboration with Drs. Farrugia, Peacock and Stirling, work is in progress to anchor these catalysts on supports in order to improve product separation. See picture.
In common with many palladium complexes, the family of binuclear compounds [Pd2X4(PR3)2] make efficient hydrogenation catalysts for alkenes. When supported on silica, however, the bromo-complexes reveal a remarkable specificity of action, reducing only the C=C bond of PhCH=CHCHO. In collaboration with Dr. Stirling, a range of solid state techniques is being applied to identify the active species and improve the catalyst performance.
The hard base F- is not very compatible with the soft acid centres of organoplatinum compounds, but careful work in strictly anhydrous conditions has shown that organoplatinum fluorides can be synthesised. Along with Prof. Winfield, these compounds are under investigation synthetically and mechanistically as potential F- transfer agents.
