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

Mar Rios-Gutierrez, Luis R. Domingo, René S. Rojas, Alejandro Toro-Labbé, Patricia Perez

Research output: Contribution to journalArticle

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.

Original languageEnglish
Pages (from-to)9214-9224
Number of pages11
JournalDalton Transactions
Volume48
Issue number25
DOIs
Publication statusPublished - 1 Jan 2019

ASJC Scopus subject areas

  • Inorganic Chemistry

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