Issue 25, 2019

A molecular electron density theory study of the insertion of CO into frustrated Lewis pair boron-amidines: a [4 + 1] cycloaddition reaction

Abstract

The insertion of CO into hydrogenated boron-amidine 1 yielding five-membered diazaborolone (5DAB) 3 has been studied within the molecular electron density theory (MEDT) at the DFT ωB97X-D/6-311G(d,p) level. This is a domino process comprised of two consecutive reactions: (i) the dehydrogenation of 1 yielding the frustrated Lewis pair (FLP) boron-amidine 4, which quickly equilibrates with four-membered diazaborolone (4DAB) 2; and (ii) the addition of CO into FLP 4, yielding the final 5DAB 3. Analysis of the Gibbs free energies indicates that the extrusion of H2 demands a high ΔG of 28.6 kcal·mol−1, being endergonic by 6.7 kcal·mol−1. The subsequent addition of CO into FLP 4 presents a low ΔG of 15.0 kcal·mol−1; formation of 5DAB 3 being exergonic by −5.7 kcal·mol−1 from hydrogenated boron-amidine 1. An analysis of the bonding changes along the insertion of CO in a smaller FLP model indicates that this reaction can be considered a [4 + 1] cycloaddition reaction taking place via a five-membered pseudocyclic transition state associated with a two-stage one-step mechanism. Analysis of the conceptual DFT reactivity indices suggests that the initial attack of CO on FLP 4 is an acid/base process in which the carbenoid carbonyl character allows CO to participate as a Lewis base, rather than a nucleophilic/electrophilic interaction. The results arising from the analysis of the Parr functions, however, coincide with this behaviour.

Graphical abstract: A molecular electron density theory study of the insertion of CO into frustrated Lewis pair boron-amidines: a [4 + 1] cycloaddition reaction

Supplementary files

Article information

Article type
Paper
Submitted
08 Apr 2019
Accepted
17 May 2019
First published
24 May 2019

Dalton Trans., 2019,48, 9214-9224

A molecular electron density theory study of the insertion of CO into frustrated Lewis pair boron-amidines: a [4 + 1] cycloaddition reaction

M. Ríos-Gutiérrez, L. R. Domingo, R. S. Rojas, A. Toro-Labbé and P. Pérez, Dalton Trans., 2019, 48, 9214 DOI: 10.1039/C9DT01489F

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