The Thermochemistry of Alkyne Insertion into a Palladacycle Outlines the Solvation Conundrum in DFT

Abstract

In an effort to determine the thermochemistry of established organometallic transformation, the well documented reaction of alkynes with a palladacycle was investigated by isothermal titration calorimetry (ITC). Although the mechanism of the insertion of unsaturated substrates into the PdÀ C bond of cyclopalladated compounds is known, no information is available so far about their thermochemistry. The enthalpies of the reactions of PhÀ C�CÀ Ph and MeOC(O)À C�C(O)COMe with the bisacetonitrilo salt of the N,N-benzylamine palladacycle were determined by ITC in chlorobenzene after having optimized the conditions to ensure that only the double and a single insertion of alkynes were occurring respectively. The reaction energy profile established by DFT for the double insertion process involving PhÀ C�CÀ Ph confirmed earlier conclusions on the rate determining character of the first insertion. Further computations of reaction enthalpies reveal significant discrepancies between ITC and DFT-D/continuum solvation enthalpies, that are suspected to arise from an unexpected explicit noncovalent interaction of PhCl with the components of the reaction.

Affinity of Telluronium Chalcogen Bond Donors for Lewis Bases in Solution: A Critical Experimental‐Theoretical Joint Study

“…There exist occurrences of good match between COSMO [103] (or other continuous screening solvation models)/DFT-D computed thermochemistry parameters with ITC data for systems implying neutral molecules (or bearing highly delocalized charges). [118][119][120][121] However, significant discrepancies have been often reported for chemical reactions involving salts, [122,123] in which the counter ion is systematically omitted in DFT calculations and the solvent happens to be a discrete actor. The question of solvation addressed using COSMO [103] either fully implicitly or with explicit amount of solvent applied to isolated ions may reputedly produce inaccurate solvation energy contributions.…”

Deciphering the Role of Noncovalent Interactions in the Conformations of Dibenzo‐1,5‐dichalcogenocines

“…This interconversion was detected in the 1 H 2D ROESY spectrum, showing offdiagonal cross-peaks between H in and H out of both conformers (see Figure S2 It is worthy to stress here that solvation might have a significant role on the 2-TeB/2-TeC equilibrium, which cannot satisfactorily be accounted for by theory using static continuum screening models of implicit solvation such as COSMO. [35] This issue was particularly revealed here by conducting the 1 H NMR analysis of 2-Te in toluene-d 8 at 238 K, as a slight difference in the B/C ratio was observed, changing from 89 : 11 in CDCl 3 to 93 : 7 in toluene-d 8 (see Figures S5 and S6 in S. I.)…”

Cover Feature: Deciphering the Role of Noncovalent Interactions in the Conformations of Dibenzo‐1,5‐dichalcogenocines (ChemPlusChem 4/2022)

“…This interconversion was detected in the 1 It is worthy to stress here that solvation might have a significant role on the 2-TeB/2-TeC equilibrium, which cannot satisfactorily be accounted for by theory using static continuum screening models of implicit solvation such as COSMO. [35] This issue was particularly revealed here by conducting the 1 H NMR analysis of 2-Te in toluene-d8 at 238 K, as a slight difference in the B/C ratio was observed, changing from 89:11 in CDCl3 to 93:7 in toluene-d8 (see Figures S5 and S6 in S. I.)…”