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A New Family of Chelating Diphosphines with a Transition Metal Stereocenter in the Backbone: Novel Applications of “Chiral‐at‐Rhenium” Complexes in Rhodium‐Catalyzed Enantioselective Alkene Hydrogenations
Author(s) -
Kromm Klemenz,
Zwick Bill D.,
Meyer Oliver,
Hampel Frank,
Gladysz John A.
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20010504)7:9<2015::aid-chem2015>3.0.co;2-h
Subject(s) - diphosphines , stereocenter , rhodium , enantioselective synthesis , rhenium , alkene , transition metal , chelation , catalysis , chemistry , iridium , combinatorial chemistry , stereochemistry , organic chemistry
The title compounds are accessed by sequences starting with racemic and enantiomerically pure [( η 5 ‐C 5 H 5 )Re(NO)(PPh 3 )(CH 3 )]. Reactions with chlorobenzene/HBF 4 , PPh 2 H, and t BuOK give the phosphido complex [( η 5 ‐C 5 H 5 )Re(NO)(PPh 3 )(PPh 2 )] ( 3 ). Reactions with Ph 3 C + BF 4 − , PPh 2 H, and t BuOK give the methylene homologue [( η 5 ‐C 5 H 5 )Re(NO)(PPh 3 )(CH 2 PPh 2 )] ( 9 ). Treatment of 3 or 9 with n BuLi or t BuLi and then PPh 2 Cl gives the diphosphido systems [( η 5 ‐C 5 H 4 PPh 2 )Re(NO)(PPh 3 )((CH 2 ) n PPh 2 )] ( n =0/1, 5 / 11 ). Reactions of 5 and 11 with [Rh(NBD)Cl] 2 /AgPF 6 (NBD=norbornadiene) give the rhenium/rhodium chelate complexes [( η 5 ‐C 5 H 4 PPh 2 )Re(NO)(PPh 3 )(( μ ‐CH 2 ) n PPh 2 )Rh(NBD)] + PF 6 − ( n =0/1, 6 + / 12 + PF 6 − ; 30–32 % overall from commercial Re 2 (CO) 10 ). The crystal structures of 6 + PF 6 − and 12 + PF 6 − are compared to those of 3 and 9 , and other rhodium complexes of chelating bis(diphenylphosphines). The chiral pockets defined by the PPh 2 groups show unusual features. Four alkenes of the type ( Z )‐RCH=C(NHCOCH 3 )CO 2 R′ are treated with H 2 (1 atm) and ( R )‐ 6 + PF 6 − or ( S )‐ 12 + PF 6 − (0.5 mol %) in THF at room temperature. Protected amino acids are obtained in 70–98 % yields and 93–82 % ee [( R )‐ 6 + PF 6 − ] or 72–60 % ee [( S )‐ 12 + PF 6 − ]. Pressure and temperature effects are defined, and turnover numbers of >1600 are realized.