Isomerization During Olefin Metathesis: An Assessment of Potential Catalyst Culprits

Two ruthenium hydride complexes commonly proposed as agents of unintended isomerization during olefin metathesis are examined for their activity in isomerization of estragole, a representative allylbenzene. Neither proves kinetically competent to account for the levels of isomerization observed during cross-metathesis of estragole by the second-generation Grubbs catalyst. A structure-activity analysis of selected ruthenium hydride complexes indicates that higher isomerization activity correlates with a more electrophilic metal center.