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Chiral Ruthenium–Sulfene Complexes – Synthesis and C–C Coupling Reactions
Author(s) -
Schenk Wolfdieter A.,
Bezler Jürgen,
Burzlaff Nicolai,
Hagel Michael,
Steinmetz Bernhard
Publication year - 2000
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/(sici)1099-0682(200002)2000:2<287::aid-ejic287>3.0.co;2-v
Subject(s) - chemistry , deprotonation , diazomethane , ruthenium , alkylation , stereochemistry , methylene , enantioselective synthesis , medicinal chemistry , organic chemistry , catalysis , ion
Reaction of the chiral racemic complex [CpRu(mppe)(SO 2 )]PF 6 ( 1 , mppe = Me 2 PC 2 H 4 PPh 2 ) with diazomethane or ‐ethane gave the sulfene complexes [CpRu(mppe)(RHC/SO 2 )]PF 6 (R = H, 2a ; R = Me, 2b ). Treatment of 2a with prochiral enamines or deprotonated β‐oxo esters yielded C–C coupling products with 32–60% de. An analog of 2a , [NmcpRu(mppe)(H 2 C/SO 2 )]PF 6 ( 8 , Nmcp = neomenthylcyclopentadienyl) was prepared in a four‐step synthesis starting from LiNmcp and [RuCl 2 (PPh 3 ) 3 ]. Repeated crystallization of the intermediate [NmcpRu(mppe)Cl] ( 6 ) provided diastereomerically pure 6′ which added methylene stereospecifically to give diastereomerically pure 8′ . Compound 8 turned out to be much less reactive towards nucleophiles than 2a , but still added deprotonated ethyl 2‐methyl‐3‐oxobutanoate with 44% de. The chiral, enantiomerically pure sulfur dioxide complex [CpRu(chir)(SO 2 )]PF 6 [ 10 , chir = ( S , S )‐Ph 2 PCHMeCHMePPh 2 ] was synthesized from [CpRu(chir)Cl] and SO 2 and was characterized by X‐ray crystallography. Reaction of 10 with diazomethane gave the enantiomerically pure sulfene complex [CpRu(chir)(H 2 C/SO 2 )]PF 6 ( 11) . Addition reactions of 11 with N ‐(1‐cyclopentenyl)morpholine, as well as with various enolates derived from β‐oxo esters or 1,3‐diesters proceeded with high yields and 20–90% de. The structure of a diastereomerically pure addition product, [CpRu(chir)(SO 2 CH 2 C(Me){C(O)Me}{C(O)O t Bu}] ( 13d′ ), was determined crystallographically and was shown to have ( R ) configuration at the quaternary carbon atom. After alkylation of one of the S/O functions, the sulfinate ligand was cleaved from the metal center by ligand substitution with acetonitrile, and the resulting acetonitrile complex 15 was converted back into 10 by treatment with SO 2 .