Contents lists available at ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica Research paper Spectroscopic characterisation of Grubbs 2nd generation catalyst and its p- cresol derivatives M.R. Swart 3 , Barend C.B. Bezuidenhoudt, C. Marais 2 , E. Erasmus ⁎ ,1 Department of Chemistry, University of the Free State, PO Box 339, Bloemfontein 9300, South Africa ARTICLEINFO Keywords: Grubbs 2nd generation P-cresol XPS UV–vis FTIR ABSTRACT p-CresolderivativesoftheGrubbs2ndgenerationcatalystwerepreparedwitheitherhydrogenbondsbetween p- cresol and the Cl-ligands or ligand exchange between the Grubbs 2nd generation catalyst and thallium p-cre- solate to form Ru-O coordination bonds and TlCl. ATR FTIR and UV–Vis spectroscopic studies revealed a blue shiftincertainbands,indicatingthatcoordinationoccurred.X-rayPhotoelectronSpectroscopywasrecordedfor each of the three Ru-complexes. The binding energy of the Ru 3d 5/2 ,Ru3p 3/2 photoelectron line (found at ca. 281and462eV,respectively)ofthediferentcomplexesshowedtheinfuenceoftheinductiveelectronicefects of the p-cresol interaction with the complexes. The Cl 2p photoelectron lines indicated ionic and covalent en- vironments, representing the TlCl and the Ru-Cl bonds, respectively. The atomic ratio between Ru:P:Cl:N:Tl confrmed the binding modes of p-cresol to the Grubbs 2nd generation catalyst. 1. Introduction Ruthenium-based Grubbs catalysts are extensively being used for a variety of olefn metathesis reactions (e.g. ring-closing, ring-opening, cross- and self-metathesis) under mild conditions [1–5]. The infuence of diferent ligands or the variation of functional groups within the Grubbs catalyst on olefn metathesis is an open area of investigation. Investigation into the electronic properties (imposed by the diferent ligands and variation of functional groups) of the ruthenium centre is thus of importance. The Grubbs 1st generation catalyst is a stable complex exhibiting a deformed square pyramidal crystal structure, with the apical position being occupied by the carbene carbon [6]. The Grubbs 2nd generation catalyst is a modifed version of the Grubbs 1st generation catalyst, wherethemorelabiletricyclohexylphosphine(PCy 3 )ligandisreplaced by 1,3–bis(2,4,6–trimethylphenyl)imidazolinium (H 2 IMes, an N-het- erocyclic carbene ligand), which is a stronger σ-donor. Normallytheadditionofsmallquantitiesofadditiveseitherpoisons the catalyst or have an inhibitory efect on the catalytic process. However,unexpectedly,ithasbeenreportedthattheadditionofphenol to the reaction mixture had a positive efect on metathesis and cross- metathesis catalysed by the Grubbs 1st and 2nd generation catalysts [7,8]. Forman, Tooze and co-workers [7] postulated that phenols may capture PCy 3 after the dissociation thereof from the catalyst, whereas hydrogen bond formation between the phenol and the chloride ligands was proposed to increase the electrophilicity of the carbene [7]. The Fogg group [9,10] furthermore established that free PCy 3 ligand is in- volved in 1,4-addition reactions with acrylates. The formed enolates wereproposedtodeprotonatethemetallocyclobutaneand p-cresol was suggested to protect the catalyst against decomposition by quenching the highly basic enolates through protonation. Using a phenol-func- tionalized polymer resin instead of free phenol, also resulted in im- proved catalytic performance [11]. It may therefore be contemplated that, apart from the formation of hydrogen bonds with the chloride ligands, one or both of the chloride ligands of the catalyst may be substituted by p-cresol or p-cresolate. Aryloxy ligands with electron-withdrawing substituents are known to form σ-bonds with ruthenium, whereas π-interactions and the forma- tion of piano-stool complexes predominates in the absence of electron- withdrawing groups or ortho substituents [12–14]. The σ-π isomerisa- tion could be circumvented by various authors by making use of bi- dentate aryloxy ligands [2,15–20]. Known monodentate aryloxy complexes of ruthenium benzylidenes seem to be limited to those with electron-withdrawing halogen sub- stituents on the aryloxy ligand and pyridine ligands for further stabi- lisation, e.g. Ru(OC 6 F 5 ) 2 (CHPh)(IMes)(py) [21–24] or aryloxy ligands https://doi.org/10.1016/j.ica.2020.120001 Received 24 June 2020; Received in revised form 1 September 2020; Accepted 2 September 2020 ⁎ Corresponding author. E-mail address: Erasmus@ufs.ac.za (E. Erasmus). 1 ORCID: 0000-0003-0546-697X. 2 ORCID: 0000-0003-3846-1956. 3 ORCID: 0000-0001-7843-3357. Inorganica Chimica Acta 514 (2021) 120001 Available online 05 September 2020 0020-1693/ © 2020 Elsevier B.V. All rights reserved. T