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Williams, B. S.; Dani, P.; Lutz, M.; Spek, A. L.; Van Koten, G. 2001. Development of the first P-stereogenic PCP pincer ligands, their metallation by palladium and platinum, and preliminary catalysis. Helv. Chim. Acta 84: 3519-3530. Full Article

The potentially tridentate P-stereogenic [P*CP*] ligands 1,3-{bis[(tert-butyl)(phenyl)phosphino]methyl}benzene and 1,3-{bis[(tert-butyl)(phenyl)phosphino]methyl}-2-bromobenzene were synthesized as the protected phosphine-borane adducts. Deprotection with a secondary amine affords the free phosphine ligand which can be metalated by Pd and Pt with std. metal synthons. Two of the resultant [P*CP*] metal complexes were characterized by x-ray crystallog. The complexes exhibit a C2 sym. environment about the remaining binding site of the square-planar center, with t-Bu groups filling two quadrants of the open site. The Pd complexes can be converted using a Ag salt to the analogous aquo complex, which is catalytically active in the aldol condensation of Me 2-isocyanoacetate and benzaldehyde. Preliminary results and comparisons with previously reported catalysts with more distal C-stereogenicity are presented.

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