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Syntheses, Structures, and Catalytic Reactions of Palladium Adducts of Chiral Diphosphines That Contain a Rhenium Stereocenter in the Backbone
Author(s) -
Kromm Klemenz,
Hampel Frank,
Gladysz J. A.
Publication year - 2002
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 - 10.1002/1522-2675(200206)85:6<1778::aid-hlca1778>3.0.co;2-9
Subject(s) - diphosphines , chemistry , stereocenter , palladium , rhenium , chelation , stereochemistry , rhodium , catalysis , medicinal chemistry , crystal structure , ring (chemistry) , adduct , yield (engineering) , enantioselective synthesis , organic chemistry , materials science , metallurgy
Reactions of the title diphosphines [( η 5 ‐C 5 H 4 PPh 2 )Re(NO)(PPh 3 )((CH 2 ) n PPh 2 )] ( n =0, ( R )‐ 1 ; n =1, racemic or ( S )‐ 2 ) with [PdCl 2 (PhCN) 2 ] give the palladium/rhenium chelate complexes [( η 5 ‐C 5 H 4 PPh 2 )Re(NO)(PPh 3 )(( μ ‐CH 2 ) n PPh 2 )PdCl 2 ] ( n =0, ( S )‐ 5 ; n =1, racemic or ( S )‐ 6 ) in 75–92% yield. The crystal structure of racemic 6 shows a twisted‐boat conformation of the chelate ring, giving a chiral pocket very different from that in a related rhodium chelate. However, NOE experiments suggest a similar ensemble of conformations in solution. Catalysts are generated from various combinations of a ) Pd(OAc) 2 and ( R )‐ 1 or ( S )‐ 2 (1 : 2), b ) ( S )‐ 5 or ( S )‐ 6 and ( R )‐ 1 or ( S )‐ 2 (1 : 2), or c ) (i‐Bu) 2 AlH with the preceding recipes. These factors effect the Heck arylation of 2,3‐dihydrofuran with phenyl trifluoromethylsulfonate. In contrast to analogous reactions with ( R )‐binap (=( R )‐2,2′‐bis(diphenylphosphanyl)‐1,1′‐binaphthalene), the major product 2‐phenyl‐2,3‐dihydrofuran is nearly racemic (≤12% ee).