Geometric and Electronic Structure of a<i>C</i>₁-Symmetric Ruthenium-Aryloxide Metathesis Catalyst: An Experimental and Computational Study

Abstract

Spectroscopic and computational methods were employed to establish the geometric and electronic structure of the Ru-pseudohalide metathesis catalyst RuCl(OC6Br5)(IMes)(py)(═CHPh) 5 (IMes = 1,3-dimesitylimidazol-2-ylidene, py = pyridine). NOESY-NMR and electronic absorption spectroscopic analysis of 5, carried out in parallel with analysis of the known trans- and cis-anionic structures RuCl2(IMes)(py)2(═CHPh) (3a) and Ru(o-cat)(IMes)(py)(═CHPh) 4a (o-cat = ortho-catecholate), confirms the trans-anionic geometry of the bromoaryloxide complex. An additional Ru···Br dative interaction is indicated by DFT analysis. The lower energy barrier to Ru−CNHC rotation vs N−CMes rotation is demonstrated for 4a and 5 and is suggested for the corresponding dichloride catalysts. The location and intensity of the principal visible absorption band is strongly conserved for 3a and 5a and is proposed as a useful signature to facilitate identification of the trans-anionic geometry in related RuX2LL′(═CHPh) species.