Photocatalytic Reduction of CO 2 into CO with Cyclometalated Pt(II) Complexes of N^C^N Pincer Dipyridylbenzene Ligands: A DFT Study.

In this work, density functional theory (DFT) calculations were employed to study the photocatalytic reduction of CO 2 into CO using a series of Pt(II) square planar complexes with the general formula [Pt(5-R-dpb)Cl] (dpb = 1,3-di(2-pyridyl)benzene anion, R = H, N , N -dimethylaniline,T thiophene, diazaborinine). The CO 2 -into-CO conversion process is thought to proceed via two main steps, namely the photocatalytic/reduction step and the main catalytic step. The simulated absorption spectra exhibit strong bands in the range 280-460 nm of the UV-Vis region. Reductive quenching of the T 1 state of the complexes under study is expected to be favorable since the calculated excited state redox potentials for the reaction with sacrificial electron donors are highly positive. The redox potentials reveal that the reductive quenching of the T 1 state, important to the overall process, could be modulated by suitable changes in the N^C^N pincer ligands. The CO 2 fixation and activation by the three coordinated Pt(II) catalytically active species are predicted to be favorable, with the Pt-CO 2 bond dissociation energies D 0 in the range of -36.9--10.3 kcal/mol. The nature of the Pt-CO 2 bond of the Pt(II) square planar intermediates is complex, with covalent, hyperconjugative and H-bonding interactions prevailing over the repulsive electrostatic interactions. The main catalytic cycle is estimated to be a favorable exergonic process.