The Key Role of the Nonchelating Conformation of the Benzylidene Ligand on the Formation and Initiation of Hoveyda–Grubbs Metathesis Catalysts. Issue 29 (12th June 2015)

• Record Type: Journal Article
• Authors: Bieszczad, Bartosz; Barbasiewicz, Michał
• Is Part Of: Chemistry. Volume 21:Issue 29(2015)
• Page Start: 10322
• Page End: 10325
• Publication Date: 2015-06-12
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201501959
• Languages: English
• ISSNs: 0947-6539

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>Experimental studies of Hoveyda–Grubbs metathesis catalysts reveal important consequences of substitution at the 6‐position of the chelating benzylidene ligand. The structural modification varies conformational preferences of the ligand that affects its exchange due to the interaction of the coordinating site with the ruthenium center. As a consequence, when typical S‐chelated systems are formed as kinetic <italic>trans</italic>‐Cl₂ products, for 6‐substituted benzylidenes the preference is altered toward direct formation of thermodynamic <italic>cis</italic>‐Cl₂ isomers. Activity data and reactions with tricyclohexylphosphine (PCy₃) support also a similar scenario for O‐chelated complexes, which display fast <italic>trans</italic>‐Cl₂⇄cis‐Cl₂ equilibrium observed by NMR EXSY studies. The presented conformational model reveals that catalysts, which cannot adopt the optimal nonchelating conformation of benzylidene ligand, initiate through a high‐energy associative mechanism.</p> </abstract>