February 28, 2005
Journal Article

Experimental and Computational Study of Steric and
Electronic Effects on the Coordination of Bulky,
Water-Soluble Alkylphosphines to Palladium under
Reducing Conditions: Correlation to Catalytic Activity

Abstract

The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. Sterically demanding, water-soluble alkylphosphine ligands 2-(di-tert-butylphosphino)- ethyltrimethylammonium chloride (t-Bu-Amphos) and 4-(di-tert-butylphosphino)-N,N-dimethylpiperidinium chloride (t-Bu-Pip-phos) in combination with palladium salts provided active catalysts for the cross-coupling of aryl halides under mild conditions in aqueous solvents, whereas 4-(dicyclohexylphosphino)-N,N-dimethylpiperidinium chloride (Cy-Pipphos) gave a less active catalyst. Catalyst activity increased with increasing cone angle of the ligands, but the ΓΈ electronic parameter determined from the symmetric C-O stretching frequency of LNi(CO)3 did not correlate with catalyst activity. Catalyst activity correlated with other calculated electronic parameters, such as the HOMO-LUMO energy gap of the ligand and the HOMO energy level of the LPd(0) species. Multinuclear NMR spectroscopic studies showed that t-Bu-Amphos and t-Bu-Pip-phos rapidly form L2Pd(0) (L= t-Bu-Amphos or t-Bu-Pip-phos) complexes when reacted with Pd(OAc)2 under reducing conditions over a range of L:Pd ratios. In contrast, the coordination chemistry of Cy-Pip-phos depended on the Cy-Pip-phos:Pd ratio. At =1:1 Cy-Pip-phos:Pd ratio, rapid formation of L2Pd(0) occurred. At higher L:Pd ratios, initial formation of trans-(Cy-Pip-phos)2PdCl2 was observed followed by slow reduction to the Pd(0) complex.

Revised: January 4, 2008 | Published: February 28, 2005

Citation

DeVasher R.B., J.M. Spruell, D.A. Dixon, G.A. Broker, S.T. Griffin, R.D. Rogers, and K.H. Shaughnessy. 2005. "Experimental and Computational Study of Steric and Electronic Effects on the Coordination of Bulky, Water-Soluble Alkylphosphines to Palladium under Reducing Conditions: Correlation to Catalytic Activity." Organometallics 24, no. 5:962-971. doi:10.1021/om049241w