Influence of Cis and Trans Ligands in Platinum(II) Complexes on the Ability of the Platinum Center to Activate C−H Bonds. A Density Functional Theory Study

Abstract

We have studied the influence of different ligands X (X ) F, Cl, Br, I, NO 2 , and CN) on the C-H bond activation of CH 4 in trans-PtCl 2 X(CH 4 ) -, 1, and trans-PtClX 2 (CH 4 ) -, 2, where X is either trans (1) or cis (2) to methane. For 1 with X in the trans position, the trans-PtCl 2 Xfragment interacts with CH 4 through the overlap between the empty d σ -based orbital 2a 1 pointing along the Pt-X direction and σ CH on CH 4 . An interaction also takes place between an occupied d σ -based orbital 1b 1 and the empty σ* CH orbital on CH 4 , where the d π metal orbital is positioned perpendicular to the PtCl 2 Xplane. The d σ metal orbital contribution in 2a 1 is antibonding with respect to σ x on X, whereas d π in 1b 1 is antibonding with respect to π x . Through the series F, Cl, Br, I, NO 2 , and CN, the energies of σ x and π x increase. This is mostly an electronegativity effect. The increase in energy causes an increase in the contribution from σ x and π x to 2a 1 and 1b 1 , respectively. As a consequence, the bonding overlaps 〈σ CH |2a 1 〉 and 〈σ CH / |1b 1 〉 will diminish, as only the d-component in 2a 1 and 1b 1 contributes to the overlap. As a result of the decreasing bonding overlaps, the Pt-CH 4 bond strength will decline. It is thus shown that the experimentally established order of trans-labilizing power for the series of ligands X studied here, F < Cl < Br < I < NO 2 < CN, can be related to the orbital energies of σ x and π x and the electronegativity of the elements that are involved in these orbitals. The labilization of the Pt-CH 4 bond in the C-H activation transition state is even larger than in the adduct 1, leading to an increase in the C-H activation barrier along the series F < Cl < Br < I < NO 2 < CN. For 2 with X in the cis position, solvation has the largest influence on trends in the Pt-CH 4 bond for both 2 and the transition state. However C-H activation barriers are quite similar for different X.

Advances in the management of recurrent or metastatic squamous cell carcinoma of the head and neck

“…Extensive kinetic and thermochemical studies 1–17 on square planar complexes of d 8 metals (M = Ni, Pd, Pt) have revealed that the ML bond strength strongly depends on the trans‐ligand T (trans influence) as does the barrier of substitution of L by another ligand Y (trans effect) (Fig. 1).…”

Quantification of mutual trans influence of ligands in Pd(ii) complexes: a combined approach using isodesmic reactions and AIM analysis

“…3 Very often the trans influence has been invoked in organometallic chemistry to explain several reaction pathways. [13][14][15][16][17][18][19][20][21][22][23][24] This influence is not only significant in transition metal complexes and p-block metal compounds, 25-27 but also plays a major role in the stability of hypervalent aryl l 3 -iodanes. 28 Though a number of experimental studies are available, 6,8,29-31 theoretical investigations of trans influence 32-38 are comparatively less.…”

PtII as a proton shuttle during C–H bond activation in the Shilov process

“…11 For this reason, computational quantum chemistry tools may conveniently be used to investigate the atomistic details of C-H activation. Indeed, several theoretical studies focused on Shilov 12,13 and Shilov-type [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] reactions (see e.g. ref.…”