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Preparation of the PdCl 2 Complex of TADDOP, the Bis(diphenylphosphinite) of TADDOL: Use in enantioselective 1,3‐diphenylallylations of nucleophiles and discussion of the mechanism
Author(s) -
Seebach Dieter,
Devaquet Edmée,
Ernst Alexander,
Hayakawa Michiya,
Kühnle Florian N. M.,
Bernd Schweizer W.,
Weber Beat
Publication year - 1995
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19950780703
Subject(s) - chemistry , nucleophile , enantioselective synthesis , dimethyl malonate , tartrate , ligand (biochemistry) , enantiomer , crystallization , malonate , stereochemistry , chirality (physics) , crystallography , metal , medicinal chemistry , catalysis , organic chemistry , symmetry breaking , chiral symmetry breaking , biochemistry , nambu–jona lasinio model , receptor , physics , quantum mechanics
Reaction of the tartrate‐derived diol ( R , R )‐α,α,α′,α′‐tetraphenyl‐2,2‐dimethyl‐1,3‐dioxolane‐4,5‐dimethanol (TADDOL) with chlorodiphenylphosphane gives a new bis(diphenylphosphanyl) ligand (TADDOP). The complex 4 formed with PdCl 2 has been crystallized and its structure determined by X‐ray diffraction ( Fig.1 ). 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 ( Scheme 2 ). Crystallization procedures lead to the enantiomerically pure (> 99:1) product 11 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 ( Fig.2 ). A crystallographic data base search reveals that the structures of transition‐metal complexes containing two Ph 2 P groups (superpositions in Fig.3 ) fall into one of two categories: one with approximate C 2 symmetry and the other with C 1 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 ( Scheme 3 and Table ).