Preparation of PdCl2 complex of TADDOP the bis(diphenylphosphinite) of TADDOL: Use in enantioselective 1,3-diphenylallylations of nucleophiles and discussion of the mechanism

Article abstract of DOI:10.1002/hlca.19950780703

Reaction of the tartrate-derived diol (R,R)-α,α,α',α'-tetraphenyl-2,2-dimethyl-1,3-dioxolane-4,5-dimethan ol (TADDOL) with chlorodiphenylphosphane gives a new bis(diphenylphosphanyl) ligand (TADDOP). The complex 4 formed with PdCl₂ has been crystallized and its structure determined by X-ray diffraction. The complex is used for Pd-catalyzed enantioselective 1,3-diphenylallylations of various nucleophiles which give products with enantiomer ratios of up to 88:12. Crystallization procedures lead to the enantiomerically pure (> 99:1) product II derived from dimethyl malonate. The structure of the TADDOP complex 4 is compared with those of other transition-metal complexes containing chelating bis(diphenylphosphanyl) ligands. A crystallographic data base search reveals that the structures of transition-metal complexes containing two Ph₂P groups fall into one of two categories: one with approximate C₂ symmetry and the other with C₁ symmetry (20 and 19 examples, resp.). A mechanistic model is proposed which correlates the conformational chirality (δ or λ) of the four Ph groups' arrangement in such complexes with the topicity of nucleophile approach on Pd-bound trans,trans-1,3-diphenylallyl groups.