Synthesis of Methylidene Complexes that Contain a 2,6-Dimesitylphenylimido Ligand and Ethenolysis of 2,3-Dicarbomethoxynorbornadiene

Abstract

Monoalkoxide pyrrolide (MAP) complexes that contain a 2,6dimesitylphenylimido (NAr*) ligand react with ethylene to yield unsubstituted metallacyclobutanes that are in equilibrium with methylidene complexes, W(NAr*)-(CH 2 )(Me 2 Pyr)(OR) (R = t-Bu, OCMe(CF 3 ) 2 , SiPh 3 , or 2,6-Me 2 C 6 H 3 ). Polymerization of 2,3-dicarbomethoxynorbornadiene (DCMNBD) with MCHCMe 2 Ph (M = Mo or W) initiators is slow as a consequence of a slow propagation step. However, W(NAr*)(CH 2 )(Me 2 Pyr)(OR) (R = SiPh 3 or 2,6-dimethylphenyl) complexes react readily with 1 equiv of DCMNBD to give a monoinsertion product. The facile reaction between the monoinsertion product and ethylene then allows these complexes to be catalyts for the ring-opening cross-metathesis (ethenolysis) of DCMNBD and DCMNBE (2,3-dicarbomethoxynorbornene) with minimal formation of polymer.

The Future of Ethenolysis in Biobased Chemistry

“…[50] Tungsten-based catalysts have been designed with bulky ligands to be able to reactw ithn orbornenesa nd are then, after the first insertion, more reactive towards ethylene. In this manner the ethenolysis of norbornenesc an be performed with high selectivity using 1bar ethylene at 60 8Ci nt oluene and 2mol %( 20 000 ppm) W2 after 24 h. [51]…”

Ethenolysis: A Green Catalytic Tool to Cleave Carbon–Carbon Double Bonds

“…The mechanism of ethenolysis follows the general Chauvin mechanism proposed for the olefin metathesis reactions catalyzed by metal alkylidene complexes (Scheme ) . The formation of metallacyclobutane has been reported with various catalysts upon reaction with ethylene at low temperature . The presence of excess ethylene favors the formation of high amounts of metal methylidene species in the reaction medium that contributes to non‐productive metathesis processes but also shifts the equilibrium in the direction of ethenolysis.…”

“…Polymer formation was avoided by premixing ethylene with the catalyst before adding the cyclic olefin. The norbornadiene 25 was selectively transformed into the diene 26 under 1 atm of ethylene in the presence of the tungsten catalyst W3 (Scheme ) Higher ethylene pressure led to a lower amount of diene 26 (Scheme ) …”

ChemInform Abstract: Ethenolysis: A Green Catalytic Tool to Cleave Carbon—Carbon Double Bonds

“…[6] The formation of metallacyclobutane has been reported with variousc atalysts upon reaction with ethylene at low temperature. [7][8][9][10][11][12] The presence of excesse thylene favors the formation of high amountso fm etal methylidene speciesi nt he reactionm edium that contributes to non-productive metathesis processes but also shifts the equilibrium in the direction of ethenolysis. As ac onsequence, the catalytic systemi sv ery efficient due to the presence of activem etal methylidene speciesb ut, conversely, as we will see later,thesevery sensitive species can also be destroyed spontaneously in the presence of functional groupso r impurities in the reaction mixture, thus reducing the productivity of the catalytic system.…”

“…The norbornadiene 25 was selectively transformed into the diene 26 under 1atm of ethylene in the presence of the tungstenc atalyst W3 (Scheme 4) Higher ethylene pressure led to alower amount of diene 26 (Scheme 10). [12] Amino acid motifs embedded in an orbornene scaffold [50] were used to stereoselectively prepare divinylated cis-pentacin [50a] and proline [50b] derivatives (Scheme 11). The reactions were performedi nt he presence of catalysts Ru1-Ru4 a in dry dichloromethane at 20 8Cf or 2h starting from variousn orbornene stereoisomers.…”