Mapping the potential energy surfaces for ring-closing metathesis reactions of prototypical dienes by electronic structure calculations

Abstract

This version is available at https://strathprints.strath.ac.uk/30245/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the Strathprints administrator: strathprints@strath.ac.ukThe Strathprints institutional repository (https://strathprints.strath.ac.uk) is a digital archive of University of Strathclyde research outputs. It has been developed to disseminate open access research outputs, expose data about those outputs, and enable the management and persistent access to Strathclyde's intellectual output. The potential energy surfaces for ring-closing metathesis reactions of a series of simple a,w-dienes which lead to 5-10 membered ring products, have been explored using density functional theory methods. We have investigated both the conformational aspects of the hydrocarbon chain during the course of the reactions, as well as the stationary structures on the corresponding potential energy surfaces. Extensive conformational searches reveal that the reaction proceeds via the conformation that would be expected for the cycloalkene product, though most unexpectedly, cyclohexene forms via complexes in boat-like conformations. The M06-L density functional has been used to map out the potential energy surfaces, and has identified metallocyclobutane fragmentation as being generally the highest barrier along the pathway. The structural variations along the pathway have been discussed for the reactant hydrocarbons of differing chain length to identify points at which cyclisation events may begin to affect reaction rates. Our study provides an excellent starting point from which to begin to learn about the way RCM reaction outcomes are controlled by diene structure. Dalton Transactions

Z-Selectivity in Olefin Metathesis with Chelated Ru Catalysts: Computational Studies of Mechanism and Selectivity

“…Complex 8 easily isomerizes to monodentate intermediates 18 and 18′ and another bidentate metallacycle, 11. 23 Cleavage of the metallacycle requires an activation free energy of 18.7 kcal/mol (12-TS) with respect to the most stable metallacycle intermediate (18). Dissociation of the olefin product leads to 14-electron Ru−alkylidene complex 22, an isomer of 21.…”

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

“…[33] While some cycloalkene major conformers are known from the literature, we explored the energetics of the conformational space via Monte Carlo searches implemented using the conformer distribution routine in the Spartan'08 package [34] (the approach was recently described fully). [6] The same approach was used to find the most stable conformers of cyclic dienes and evaluate their energies. The geometries of all conformers within 4 kcal mol À1 of the lowest were optimised using DFT methods, initially at the B3LYP/6-31G* level of theory.…”

“…Diene-, productand dimer-free energies were calculated at the M06-L/6-311G** level of theory and corrected for solvation effects using a continuum model described previously. [6] Scheme 2 defines the reactions and equilibrium constants of interest, and the calculated free-energy changes for RCM (DG RCM ) and dimerisation (DG Dimer ) are recorded in Table 3.…”

“…[5] We have recently used electronic structure calculations to probe the RCM of simple dienes to cycloalkenes (1 a-f to 3 a-f; n = 1-6 in Scheme 1) in detail. [6] It is generally agreed that the highest free energy barriers are associated with the initial step which converts pre-catalyst 2 into the active 14e catalyst through phosphane dissoci-ation. [7] The view that RCM and cross metathesis (CM) reactions are reversible and thermodynamically controlled processes, which occur after rate-limiting precatalyst activation (initiation), has become widely accepted.…”

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

“…8 We have also modeled the potential energy surfaces for these reactions in some detail using the M06-L functional. 9 It should be possible to interpret the concentration/time data obtained from kinetic experiments using a combination of computational insights and quantitative data obtained from fundamental studies of precatalyst systems. An appropriate kinetic model that takes account of precatalyst initiation and active catalyst decomposition would allow the interpretation of this concentration/time data (which very rarely correspond to a simple kinetic order 8 ) and comparisons between different reaction solvents and precatalyst systems.…”