Synthesis of latent Grubbs-type ruthenium complex bearing a tridentate anionic bisfluoroalkoxy-carbene and unexpected formation of new complex formed upon coordination of the substrate and occurrence of only first olefin metathesis step; triggering its activity in olefin metathesis reactions by addition of HCl.

Abstract

A Grubbs-type ruthenium complex bearing a tridentate anionic bisfluoroalkoxy-carbene was synthesised and fully characterised. Under standard conditions, it proved to be inactive in olefin metathesis reactions, but the addition of HCl triggers its activity and allows the synthesis of a series of cyclic olefins and ethers as well as a stereoregular polynorbornene with an unexpectedly high content of trans-configured double bonds, as found in commercially available polynorbornene (Norsorex®). Detailed structural studies and DFT calculations showed that the complex enters the catalytic cycle, but instead of performing a full turnover, it is caught as a stable intermediate that does not undergo further reactions. The addition of HCl causes dissociation of the fluoroalkoxy units, resulting in a compound that behaves similarly to standard Grubbs-type complexes. To further understand this phenomenon, the corresponding Hoveyda-Grubbs complex was also obtained and studied in detail; due to the absence of the phosphine ligand, its behaviour was different from that of its Grubbs-type counterpart.