Theoretical Studies On The Ir-and Pt-Catalyzed C-H Activation And Ruthenium Catalyzed Water Oxidation

The transition metal-dependent spin orbit coupling (SOC) and outer-core (5s5p)correlation effects in Ir-and Pt-catalyzed C H activation processes are studied hereusing high level ab initio computations. The catalysts involve complexes withoxidation states: Ir(I), Ir(III), Pt(0), and Pt(II). It is demonstrated that for these heavy5d transition metal-containing systems, the SOC effect and outer-core correlationeffect on C H activation are up to the order of~1kcal/mol, and should be included ifchemical accuracy is aimed. The interesting trends in our studied systems are:(1) theSOC effect consistently increases the C H activation barriers and is apparently largerin higher oxidation states (Pt(II) and Ir(III)) than in low-oxidation states (Pt(0) andIr(I)); and (2) the magnitude of outer-core (5s5p) correlation effects is larger in lesscoordinate-saturated system. The effect of basis set on the outer-core correlationcorrection is significant; larger basis sets tend to increase the C H activation barriers.Mononuclear Ru-based water oxidation catalysts (WOCs) constitute animportant class of WOCs for water splitting. In this work, we did a systematic studyof Ru-O2complexes of mononuclear ruthenium WOCs, with a focus on the waterassisted O2release thermodynamics in various electronic states and geometricconformations. Our extensive DFT calculations demonstrate that there are severalfactors that can affect the O2release thermodynamics:(1) steric effect from theligand sphere of Ru;(2) trans effect of ligands trans to O2;(3) oxygen ciscoordinating effect;(4) carbon coordinating effect; and (5) Ru coordination strength.Some of these effects could selectively stabilize/destabilize somestates/conformations of the Ru-O2complexes relative to Ru-OH2complexes, and affect thereby the O2release thermodynamics. The identification and rationalizationof factors for O2release thermodynamics could be helpful to understand better thisfinal step of the ruthenium-catalyzed water oxidation.