Development of the First P‐Stereogenic PCP Pincer Ligands,Their Metallation by Palladium and Platinum,and Preliminary Catalysis

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 have been synthesized as the protected phosphine‐borane adducts. Deprotection with a secondary amine affords the free phosphine ligand which can be metallated by Pd and Pt with standard metal synthons. Two of the resultant P*CP*] metal complexes have been characterized by X‐ray crystallography. The complexes exhibit a C₂ symmetric 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 by use of a Ag salt to the analogous aquo complex, which is catalytically active in the aldol condensation of methyl 2‐isocyanoacetate and benzaldehyde. Preliminary results and comparisons with previously reported catalysts with more distal C‐stereogenicity are presented.