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Novel P‐Stereogenic PCP Pincer‐Aryl Ruthenium(II) Complexes and Their Use in the Asymmetric Hydrogen Transfer Reaction of Acetophenone
Author(s) -
Medici Serenella,
Gagliardo Marcella,
Williams Scott B.,
Chase Preston A.,
Gladiali Serafino,
Lutz Martin,
Spek Anthony L.,
van Klink Gerard P. M.,
van Koten Gerard
Publication year - 2005
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.200590048
Subject(s) - chemistry , pincer movement , ruthenium , diphenylphosphine , acetophenone , stereocenter , transfer hydrogenation , medicinal chemistry , aryl , methylene , borane , phosphine , stereochemistry , catalysis , alkyl , enantioselective synthesis , organic chemistry
Achiral P‐donor pincer‐aryl ruthenium complexes ([RuCl(PCP)(PPh 3 )]) 4c , d were synthesized via transcyclometalation reactions by mixing equivalent amounts of [1,3‐phenylenebis(methylene)]bis[diisopropylphosphine] ( 2c ) or [1,3‐phenylenebis(methylene)]bis[diphenylphosphine] ( 2d ) and the N‐donor pincer‐aryl complex [RuCl{2,6‐(Me 2 NCH 2 ) 2 C 6 H 3 }(PPh 3 )], ( 3 ; Scheme 2 ). The same synthetic procedure was successfully applied for the preparation of novel chiral P‐donor pincer‐aryl ruthenium complexes [RuCl(P*CP*)(PPh 3 )] 4a , b by reacting P‐stereogenic pincer‐arenes ( S,S )‐[1,3‐phenylenebis(methylene)]bis[(alkyl)(phenyl)phosphines] 2a , b (alkyl= i Pr or t Bu, P*CHP*) and the complex [RuCl{2,6‐(Me 2 NCH 2 ) 2 C 6 H 3 }(PPh 3 )], ( 3 ; Scheme 3 ). The crystal structures of achiral [RuCl( i Pr, i Pr PCP)(PPh 3 )] 4c and of chiral ( S,S )‐[RuCl( t Bu,Ph PCP)(PPh 3 )] 4a were determined by X‐ray diffraction ( Fig. 3 ). Achiral [RuCl(PCP)(PPh 3 )] complexes and chiral [RuCl(P*CP*)(PPh 3 )] complexes were tested as catalyst in the H‐transfer reduction of acetophenone with propan‐2‐ol. With the chiral complexes, a modest enantioselectivity was obtained.