Why is RCM Favoured Over Dimerisation? Predicting and Estimating Thermodynamic Effective Molarities by Solution Experiments and Electronic Structure Calculations

Abstract

The thermodynamic effective molarities of a series of simple cycloalkenes, synthesised from α,ω‐dienes by reaction with Grubbs’ second generation precatalyst, have been evaluated. Effective molarities were measured from a series of small scale metathesis reactions and agreed well with empirical predictions derived from the number of rotors and the product ring strain. The use of electronic structure calculations (at the M06‐L/6‐311G** level of theory) was explored for predicting thermodynamic effective molarities in ring‐closing metathesis. However, it was found that it was necessary to apply a correction to DFT‐derived free energies to account for the entropic effects of solvation.

The Influence of Structure on Reactivity in Alkene Metathesis

“…0.5 mol L -1 , meaning that for selectivity for cycloalkene over oligomer, reactions must be run at millimolar concentrations. 104 Notably, the rate of As discussed above, Percy and co-workers published a study in which gem-dimethylation of the backbone was found to increase the rate and EM of the cyclisation (see Scheme 18 above). In this case, the target was an eight-membered ring and the substituents were methyl groups rather than bulky esters, which may avoid steric clashes with a bulky catalyst coordinated to a terminus.…”

Olefin cross metathesis and ring-closing metathesis in polymer chemistry

“…High dilutions are required to limit intermolecular cross-linking and promote intramolecular RCM if the reaction mixture is too concentrated, CM will occur promoting ADMET polymerisation and through it extensive cross-linking (Scheme 11). [41][42][43][44] Even with this entropic advantage, ring strain also dictates ring formation. Five, six or seven membered rings are readily Scheme 9 Double cross metathesis based on alkene reactivity to introduce two unique functionalities into the polymer backbone.…”

Toward a Simulation Approach for Alkene Ring-closing Metathesis: Scope and Limitations of a Model for RCM

“…Each experiment was checked for mass balance: the reactions treated in this manuscript all convert diene to cycloalkene (plus ethene) without the formation of oligomers or side-products. 7 …”