Metal catalyst and ligand design
Imidate ligands and Pd and Au catalysts: Since the initial discovery of succinimide ligand effects in Stille cross-couplings (with Prof. R. J. K. Taylor) we have continued to expand the number of palladium-based imidate catalyst systems for a variety of cross-coupling reactions.
We have recently developed AuIII catalyst systems for use in forming 1,5-enynes (from propargyl alcohols and allylic silanes) and their subsequent cycloisomerisation to afford bicyclohexenes.
Alkene (olefin) ligands based on dibenzylidene acetone:
We have comprehensively investigated the role of substituted dibenzylidene acetone ligands in Pd(0)-mediated cross-coupling reactions. The ligands play a role in controlling the flux of active Pd(0) in the catalytic cycle, affecting oxidative addition (primarily, not exclusively). We have written a perspective article on this field, see:
π-Acidic alkene ligand effects in Pd-catalysed cross-coupling processes: Exploiting the interaction of dibenzylidene acetone (dba) and related ligands with Pd(0) and Pd(II).
I J S Fairlamb, Org. Biomol. Chem., 2008, 6, 3645-3656.
Palladacycles: Palladium(II) complexes formed by cyclopalladation are widely referred to as palladacycles. They are used as catalysts and precatalysts in a variety of different bond-forming reactions.
Our group has studied how palladacycles degrade to give activated catalyst species in Suzuki cross-coupling reactions and Carbonylation processes (amido- and methoxy-carbonylation).
For example, the palladacycle shown opposite degrades to give "Pd0-PPh3" species which are highly reactive; our view on these species is that these may be solvated in polar solvents, but in moderately polar solvents they exist as part of soluble Pd clusters, e.g. Pd nanoparticles.
Cu catalysts: In recent studies we have designed a dba-thiophos ligand system capable of forming various Cu(I) complexes, which are active catalysts for alkene cyclopropantion reactions involving carbene intermediates.
Lead reference: Jarvis et al. Dalton Trans., 2011, 40, 3695-3702.