Issue 18, 2019

Carbon dioxide reduction by dinuclear Yb(ii) and Sm(ii) complexes supported by siloxide ligands

Abstract

Two dinuclear homoleptic complexes of lanthanides(II) supported by the polydentate tris(tertbutoxy) siloxide ligand ([Yb2L4], 1-Yb and [Sm2L4], 1-Sm, (L = (OtBu)3SiO)) were synthesized in 70–80% yield and 1-Sm was crystallographically characterized. 1-Yb and 1-Sm are stable in solution at −40 °C but cleave the DME C–O bond over time at room temperature affording the crystal of [Yb2L4(μ-OMe)2(DME)2], 2. The 1-Yb and 1-Sm complexes effect the reduction of CO2 under ambient conditions leading to carbonate and oxalate formation. The selectivity of the reduction towards oxalate or carbonate changes depend on the solvent polarity and on the nature of the ion. For both the lanthanides, carbonate formation is favoured but oxalate formation increases if a non-polar solvent is used. Computational studies suggest that the formation of oxalate is favoured with respect to carbonate formation in the reaction of the dimeric lanthanide complexes with CO2. Crystals of the tetranuclear mixed-valence oxalate intermediate [Yb4L8(C2O4)], 3 were isolated from hexane and the presence of a C2O42− ligand bridging two [YbIIL2YbIIIL2] dinuclear moieties was shown. Crystals of the tetranuclear di-carbonate product [Sm4L83-CO34-O,O′,O′′)2], 4 were isolated from hexane. The structures of 3 and 4 suggest that the CO2 activation in non-polar solvents involves the interaction of two dimers with CO2 molecules at least to some extent. Such a cooperative interaction results in both oxalate and carbonate formation.

Graphical abstract: Carbon dioxide reduction by dinuclear Yb(ii) and Sm(ii) complexes supported by siloxide ligands

Supplementary files

Article information

Article type
Paper
Submitted
05 fev 2019
Accepted
01 mar 2019
First published
14 mar 2019

Dalton Trans., 2019,48, 6100-6110

Carbon dioxide reduction by dinuclear Yb(II) and Sm(II) complexes supported by siloxide ligands

A. R. Willauer, D. Toniolo, F. Fadaei-Tirani, Y. Yang, M. Laurent and M. Mazzanti, Dalton Trans., 2019, 48, 6100 DOI: 10.1039/C9DT00554D

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