The nature of the bonding in symmetrical pincer palladacycles

Abstract

The accuracy of DFT-optimised geometries of the symmetrical pincer palladacycles PdNCN and PdSCS, [ClPd{2,6-(Me2NCH2)2C6H3}] and [ClPd{2,6-(MeSCH2)2C6H3}] respectively, has been evaluated by investigating the performance of eight commonly used density functionals with four combinations of basis set, in reproducing their X-ray crystal structures. It was found that whilst the ωB97XD functional performed best over all, the PBE and TPSS functionals performed best when considering the palladium coordination geometry. The role of the donor atom in the stability and reactivity of the symmetric palladacycles, PdYCY, Y = N, S, or P, has been determined using Bader's Atoms in Molecules method to elucidate the nature of the bonding, and using a model formation reaction, which involves the C-H activation of the pincer ligand YCY by PdCl2. The calculations reveal distinct differences in the bond strength and nature of the interaction of Pd with the donor atoms Y, which support differences in the thermodynamic stability of the palladacycles.

The Trans Influence in Unsymmetrical Pincer Palladacycles: An Experimental and Computational Study

“…which can be used to determine the nature and strength of the interaction; the conclusions regarding the nature of the bonding are in complete agreement with our previous work on the nature of the bonding in symmetrical pincer palladacycles and, so, are not presented again here [36]. In the present work, the focus is on the trans influence and, …”

“…are greater compared to the ρ(r) values for the Pd-P bond in the PdPCP (0.101 a.u.) [36]. This is due to the weaker trans influence of N and S, compared to P, leading to stronger Pd-P bonds in V and VI (Table 3).…”

“…decrease compared to the ρ(r) value of the Pd-N bond in the PdNCN (0.086 a.u.) [36] indicating that P and S exhibit a stronger trans influence than N. to the Pd center, this stronger bond does not exert a trans influence on the amine donor ligand. Thus, it would appear the nature of the donor atom is the sole driver for the trans influence.…”

“…Based on this analysis the ordering of the trans influence series is PMe2 > SMe > NMe2. In order to extend our investigation of the trans influence to unsymmetrical pincer palladacycles, the palladacycles IV-VI have been studied using DFT and QTAIM, and their bond strengths and bond lengths compared to previous results found for symmetrical pincer palladacycles PdNCN, PdSCS and PdPCP [36] (Figure 4). Considering the ρ(r) value at the BCP of the Pd-Y bond in IV-VI, the ρ(r) value of the Pd-P bond of V (0.110 a.u) and VI (0.114 a.u.)…”

“…The SDD ECP basis set was used for Pd, and the 6-31+G(d,p) basis set was used for all other atoms (PBE/6-31+G(d,p) [SDD]). This methodology has been validated in our previous study into the structures of symmetrical pincer palladacycles [36]. The topological analysis using quantum theory of atoms in molecules (QTAIM) was performed using the Multiwfn program [47].…”