Research - Palladacycles

We recently introduced a series of palladacycles as novel catalysts for organic synthesis. The nitrogen coordinating complexes 1 [1] and 2 [2], readily prepared by highly diastereoselective palladation, catalyse the allylic imidate rearrangement (e.g. 3 into 4) with excellent enantioselectivity [3]. Cobalt-Oxazoline-Palladacycle 1 (COP-Cl) is especially efficient and selective for this reaction [more information]. In this rearrangement, the carbon-palladium bond likely remains intact, with control of the transformation arising from initial coordination of 3 to the palladium(II) centre.
In contrast, phosphapalladacycle 5 is a highly effective precatalyst for the Suzuki coupling of aryl chlorides. [4] These may be performed at room temperature or with low palladium loadings in reactions where the available evidence points to the active catalyst being a monoligated ligated palladium(0) species.
Complementary to this work is our application of monophoshine 6 (TomPhos), which in conjunction with palladium(0) also forms an active catalyst system for the Suzuki coupling of aryl chlorides (and significantly does not form a palladacycle on heating with Pd(OAc)2). [5]
X-ray crystal structure of TomPhos 6
[1] A. M. Stevens and C. J. Richards, Organometallics, 1999, 18, 1346. [2] G. Jones and C. J. Richards, Organometallics, 2001, 20, 1251. [3] L. E. Overman, C. E. Owen, M. M. Pavan and C. J. Richards, Org. Lett., 2003, 5, 1809. [4] F. X. Roca and C. J. Richards, Chem. Commun., 2003, 3002. [5] T. E. Picket, F. X. Roca and C. J. Richards, J. Org. Chem., 2003, 68, 2592.