Stereoselective Olefin Ring‐Opening Cross Metathesis Catalyzed by Molybdenum Imido Alkylidene N‐Heterocyclic Carbene Complexes

Abstract

AbstractThe influence of the structure of cationic molybdenum imido alkylidene N‐heterocyclic carbene (NHC) catalysts, i. e. of [Mo(N‐2‐tert‐butyl‐C6H4) (CHCMe2Ph)(NHC)X+ B(ArF)4−] (NHC=1,3‐di(2‐Pr)imidazol‐2‐ylidene (iPr), 1,3‐dimesitylimidazol‐2‐ylidene (IMes); X=pyrrolide, OCH(CF3)2, B(ArF)4−=tetrakis(3,5‐bis(trifluoromethyl)phenyl)borate) and of [Mo(N‐3,5‐Me2‐C6H3)(CHCMe2Ph)(NHC)(CH3CN)X+ B(ArF)4−] (NHC=1,3‐dimesitylimidazol‐2‐ylidene, 1,3‐dimesitylimidazolin‐2‐ylidene (IMesH2); X=CF3SO3, OCPh(CF3)2) on E/Z‐selectivity in the ring‐opening cross‐metathesis (ROCM) of endo, endo‐2,3‐dicarbomethoxynorborn‐5‐ene (endo, endo‐DCMNBE), exo, exo‐2,3‐dicarbomethoxynorborn‐5‐ene (exo, exo‐DCMNBE), endo, exo‐2,3‐dicarbomethoxynorborn‐5‐ene ((+) DCMNBE) and 2,3‐exo,exo‐bis(acetoxymethyl)‐7‐oxabicyclo[2.2.l]hept‐5‐ene (7‐oxa‐NBE) with 1‐pentene, styrene, allyltrimethylsilane, allyl benzyl ether, allyl phenyl ether and allyl ethyl ether has been studied. With the exception of the ROCM reaction of endo, endo‐DCMNBE with styrene, all other ROCM reactions of endo, endo‐DCMNBE proceeded under thermodynamic control without any post‐metathesis isomerization reactions with full retention of the configuration of the newly formed 1,2‐disubstituted double bond as confirmed by kinetic studies. Similar accounts for selected homometathesis reactions. Catalyst structure‐selectivity correlations based on the buried volume, Vbur, of the N‐imido ligand are presented.magnified image