Substituent Effects in π‐Hole Regium Bonding Interactions Between Au(p‐X‐Py)₂Complexes and Lewis Bases: Anab initioStudy

Abstract

Long range substituent effects in regium bonding interactions involving Au(I) linear complexes are investigated for the first time. The Au(I) atom is coordinated to two para-substituted pyridine ligands. The interaction energy (RI-MP2/def2-TZVP level of theory) of the π-hole regium bonding assemblies is affected by the pyridine substitution. The Hammett's plot representations for several sets of Lewis bases have been carried out and, in all cases, good regression plots have been obtained (interaction energies vs. Hammett's σ parameter). The Bader's theory of "atoms-in-molecules" has been used to evidence that the electron density computed at the bond critical point that connects the Au-atom to the electron donor can be used as a measure of bond order in regium bonding. Several X-ray structures retrieved from the Cambridge Structural Database (CSD) provide experimental support to the existence of π-hole regium bonding in [Au(Py) 2 ] + derivatives.

Reaction Mechanism and Effect of Substituent in Direct Bromination of Indoles

“…In this way, MESP is able to account for various types of substituent effects, including the classical inductive and resonant effects [28–30] . Likewise, MESP has been used with excellent results to account for long range substituent effects in π‐hole regium bonding interactions [33] …”

“…[27] The molecular electrostatic potential (MESP) has been shown to be a suitable theoretical tool for studying the effects of chemical substituents in π-conjugated molecular systems. [28][29][30][31][32][33] This is because the substituents affect the electron density to some extent and this is noticeably reflected in the MESP. MESP is particularly affected in atomic centers where some kind of chemical activation or deactivation is expected under the presence of a chemical substituent group attached to another atom located in some strategic position of the molecule.…”

Ligand and Substituent Effect on Regium−π Bonding in Cu and Ag π-Conjugated Complexes: A Density Functional Study

“…It has been reported that M 2 –benzene complex (M = Cu, Ag, or Au) undergoes Rg−π interactions whereas MCl–benzene complexes (M = Cu, Ag, or Au) tend to shift toward cation−π interactions . The initial survey of protein data bank (PDB) and Cambridge structural database (CSD) has revealed that Rg−π bonds are present in Au­(I)–protein complexes and dicoordinated linear Au­(I) complexes . A secondary survey of PDB and CSD has discovered that Rg−π bonds of Cu and Ag are also present in biological as well as supramolecular structures, where noble metals (Cu and Ag) act as the Rg−π donor and various aromatic moieties such as pyridine, cyanobenzene, etc., act as the Rg−π acceptor.…”

“…While numerous model studies have been performed on the nature and energetics of the Rg−π bond of Au, , Rg−π bonds of Cu and Ag are still a gray area. Here, we report a detailed computational study to investigate the nature and energetics of Rg−π bonds using the RgL–X model system, where Rg = Cu and Ag; L = CN, NO 2 , OH; and X = π-conjugated system (benzene, cyanobenzene, benzoic acid, pyridine, 2-methoxy aniline, 1,4-dimethoxy benzene, and cyclophane) (Figure ).…”

On the reliability of atoms in molecules, noncovalent index, and natural bond orbital to identify and quantify noncovalent bonds

“…Indeed, quantitative relationships have been derived in certain classes of systems and usefully applied where the binding energy can be simply related to one or more indicators derived from these methods. For example, it is common in the literature to consider the bond critical point density as a measure of bond strength [23][24][25][26][27] and possibly even with spectroscopic perturbations. 28 In an alternate scheme, the energies of some of these bonds are sometimes assessed via a simple relationship with the potential energy density 24,[29][30][31] or other quantities extracted from AIM analysis.…”