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. Complete control: Can classical theory, developed for ring-closing metathesis (RCM) reactions that involve σ-bond formation, describe the thermodynamics of RCM reactions forming π bonds? Empirical theory and modern electronic structure calculations have been employed to predict the outcome of RCM reactions of simple α,ω-dienes with Grubbs' second generation pre-catalysts, resulting in mixtures of cycloalkenes and oligomers (see scheme). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.