Abstract
Ring-closing metathesis (RCM) is an elegant means of forming cyclic structural elements in both simple and complex molecules. Mechanistically, the reaction cycle is well understood, though subtle details concerning the fate of the catalyst and the appearance of yield-reducing by-products remain to be fully deciphered. We applied real-time analysis using electrospray ionization mass spectrometry (ESI-MS) to probe the RCM reaction, including studying the dynamics of all charged species in the reaction mixture and investigating the nature of the by-products formed. The catalyst of choice was Grubbs’ second-generation catalyst. The principal findings included the fact that for slower reactions, by-products appeared that differed in mass from the starting material and product by increments of CH2; that isomerization reactions were responsible for these by-products; and that the catalyst decomposes to form charged products including [ClPCy3]+, [HPCy3]+, and the imidazolinium salt of the N-heterocyclic carbene (NHC) ligand. In cases where RCM is slow, isomerization reactions play a disproportionate part in affecting yield of the desired product.
Supplementary materials
Title
Supporting Information
Description
Page 2: Experimental procedures
Pages 3-5: Substrate synthesis and tabulated 1H and 13C NMR data
Pages 6-15: 1H and 13C NMR spectra for substrates
Page 16: Tabulated competition experiment rate data
Pages 17-21: Plotted kinetic data from competition experiments
Page 22: Plotted kinetic data for the R7 vs. R7’ rate comparison experiment
Page 23: Expanded mechanistic plot for all R9 side reactions and byproducts
Page 24: Substrate-free GII speciation experiment data
Pages 25-36: X-ray crystallographic data for R5 and R7
Page 37: Supporting information references
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