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Novel Ruthenium(II) N‐Heterocyclic Carbene Complexes as Catalyst Precursors for the Ring‐Opening Metathesis Polymerization (ROMP) of Enantiomerically Pure Monomers: X‐ray Structures, Reactivity, and Quantum Chemical Considerations
Author(s) -
Buchmeiser Michael R.,
Wang Dongren,
Zhang Yan,
Naumov Sergej,
Wurst Klaus
Publication year - 2007
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/ejic.200700041
Subject(s) - chemistry , romp , carbene , ruthenium , metathesis , imes , polymerization , reactivity (psychology) , monomer , medicinal chemistry , polymer chemistry , catalysis , stereochemistry , organic chemistry , polymer , medicine , alternative medicine , pathology
Four chiral, enantiomerically pure monomers, exo , exo ‐ N , N ‐(norborn‐5‐ene‐2,3‐dicarbimido)‐ L ‐valine ethyl ester ( exo ‐ 1 ), endo , endo ‐ N , N ‐(norborn‐5‐ene‐2,3‐dicarbimido)‐ L ‐valineethyl ester ( endo ‐ 1 ), exo , exo ‐ N , N ‐(norborn‐5‐ene‐2,3‐dicarbimido)‐ L ‐valine‐ tert ‐butylamide ( exo ‐ 2 ), and endo , endo ‐ N , N ‐(norborn‐5‐ene‐2,3‐dicarbimido)‐ L ‐valine‐ tert ‐butylamide ( endo‐ 2 ), were subjected to ring‐opening metathesis polymerization (ROMP) with Ru(CF 3 CO 2 ) 2 (IMesH 2 )( p ‐cymene) ( 3 ), Ru(CF 3 CO 2 ) 2 (IMes)( p ‐cymene) ( 4 ), RuCl 2 (IMes)( p ‐cymene) ( 5 ), Ru(PCy 3 )(CF 3 CO 2 ) 2 ( p ‐cymene) ( 6 ), Ru(CF 3 CO 2 ) 2 ( p ‐cymene) · CF 3 COOAgPCy 3 ( 6a ), Ru(CF 3 CO 2 ) 2 (PPh 3 )( p ‐cymene) ( 7 ), Ru(CF 3 CO 2 ) 2 (IMes)(PhNC) 3 ( 8 ), and Ru(CF 3 CO 2 ) 2 (IMesH 2 )(PhNC) 3 ( 9 ) (IMes = 1,3‐dimesitylimidazol‐2‐ylidene, IMesH 2 = 1,4‐dimesityl‐4,5‐diyhdroimidazolin‐2‐ylidene, PCy 3 = tricyclohexylphosphane). X‐ray structures of precatalysts 3 and 6 – 9 are presented. Compounds 3 and 4 displayed significant ROMP activity, allowing for the controlled, yet nonliving synthesis of the corresponding polymers with polydispersity indices (PDIs) in the range of 1.17–2.14. In all cases the exo isomers of compounds 1 and 2 were polymerized by preference. While poly( endo ‐ 1 ) was formed in an all‐ trans form, poly( exo ‐ 1 ) and poly( exo ‐ 2 ) were produced in their cis / trans forms with a cis content of around 40 %. Calculations carried out at the B3LYP/LACVP* level suggest two possible mechanisms for the increased reactivity of the 2,3‐R 2 ‐ exo , exo isomers of norborn‐5‐ene‐2,3‐dicarbimido derivatives resulting in the formation of the ROMP‐active Ru IV alkylidene. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)