The effect of coordination of alkanes, Xe and CO2 (η1-OCO) on changes in spin state and reactivity in organometallic chemistry: a combined experimental and theoretical study of the photochemistry of CpMn(CO)3?

Faraday Discussions Pub Date: 2019-10-14 DOI: 10.1039/C9FD00067D

Abstract

A combined experimental and theoretical study is presented of several ligand addition reactions of the triplet fragment 3CpMn(CO)2 formed upon photolysis of CpMn(CO)3. Experimental data are provided for reactions in n-heptane and perfluoromethylcyclohexane (PFMCH), as well as in PFMCH doped with C2H6, Xe and CO2. In PFMCH we find that the conversion of 3CpMn(CO)2 to 1CpMn(CO)2(PFMCH) is much slower (τ = 18 (±3) ns) than the corresponding reactions in conventional alkanes (τ = 111 (±10) ps). We measure the effect of the coordination ability by doping PFMCH with alkane, Xe and CO2; these doped ligands form the corresponding singlet adducts with significantly variable formation rates. The reactivity as measured by the addition timescale follows the order 1CpMn(CO)2(C5H10) (τ = 270 (±10) ps) > 1CpMn(CO)2Xe (τ = 3.9 (±0.4) ns) ～ 1CpMn(CO)2(CO2) (τ = 4.7 (±0.5) ns) > 1CpMn(CO)2(C7F14) (τ = 18 (±3) ns). Electronic structure theory calculations of the singlet and triplet potential energy surfaces and of their intersections, together with non-adiabatic statistical rate theory, reproduce the observed rates semi-quantitatively. It is shown that triplet adducts of the ligand and 3CpMn(CO)2 play a role in the kinetics, and account for the variable timescales observed experimentally.

Graphical abstract: The effect of coordination of alkanes, Xe and CO2 (η1-OCO) on changes in spin state and reactivity in organometallic chemistry: a combined experimental and theoretical study of the photochemistry of CpMn(CO)3
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