An investigative study into group 6 metal catalysed allylic substitution reactions

We have shown that a number of molybdenum(II) and tungsten(II) complexes are capable of catalysing the C-C bond forming allylic substitution reaction with silyl enol ethers derived from dicarbonyls or simple ketones, aldehydes, and esters as nucleophiles under mild conditions (rt, 1-2 h). Mechanistic and stereochemical experiments are indicative of a Lewis-acid catalysed process. The research was successful in identifying an number of key catalyst structures and properties for our continued investigation into M(II) catalysts. We have subsequently developed a catalytic system based on the chemistry of 2,2'-bipyridine and 1,10-phenanthroline substituted molybdenum(II) complexes {M(CO3 NN(SnCl3) Cl}. These complexes have promoted allylic substitution reactions with cinammyl derived allylic substrates with high levels of regioselectivity, the effect of the ligand, choice of solvent and steric congestion of the nucleophile have been investigated. The above investigation has lead to the development of chiral catalysts for the asymmetric allylic substitution reaction with modest enantioselectivity. Finally, we have prepared and characterised (including X-ray crystal structures) a pair of chiral 2,2'-bipyridyl ligands of C2-symmetry with the aim of introducing complementary chiral environments around a bound metal. These chiral ligands are currently being screened in our laboratory for asymmetric molybdenum catalysed allylic substitution reactions.