Reductive Disproportionation of CO₂ with Bulky Divalent Samarium Complexes

Abstract

The base-free divalent samarium complex Cptt 2Sm (1; Cptt = 1,3-( t Bu)2(C5H3)) has been synthesized in diethyl ether by salt metathesis of SmI2. Crystals of 1 suitable for X-ray study have been obtained by sublimation at 116 °C under reduced pressure. The dissolution of 1 in thf and pyridine solution leads to the solvent adducts Cptt 2Sm­(thf)2 (3) and Cptt 2Sm­(py) (4), respectively, while drying 3 under reduced pressure yields CpttSm­(thf) (5). The reaction of CO2 with the base-free divalent samarium complexes Cptt 2Sm (1) and Cpttt 2Sm (2; Cpttt =1,2,4-( t Bu)3(C5H2)) leads to the clean formation of bridged carbonate samarium dimers [Cpttt 2Sm]2(μ-CO3) (7) and [Cptt 2Sm]2(μ-CO3) (8). This is indicative of the reductive disproportionation of CO2 in both cases with release of CO. This contrasts with the formation of the oxalate-bridged samarium dimer reported from the reaction of CO2 with the Cp*2Sm­(thf)2 complex. Otherwise, the reaction with CO does not proceed with the bulky complexes, while traces of O2 have led to the formation of the original bridged peroxo samarium dimer [Cpttt 2Sm]2(μ-O2) (6). The mechanism for these reactions is studied herein by experiments and also by theoretical computations. The key result is that the different pathways are rather close in energy, which also explains why the nature of the final product, if only one is present, is difficult to predict a priori in this chemistry.

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

“…showed the selective formation of carbonate and CO, when bulky cyclopentadienyls ligands are used as supporting ligands rather than Cp*, as a result of both steric and electronic effects. 9 A similar selectivity towards carbonate formation had been reported for macrocyclic organosamarium(II) complex 3d In contrast we showed previously that both oxalate and carbonate products were formed from the CO2 reduction by a electron-rich mononuclear complex of Yb(II) supported by a polydentate tris(tertbutoxy) siloxide ligand. 8c These studies underline the important role that the nature of the metal and of the supporting ligand play in the CO2 reduction.…”

Small molecule activation with divalent samarium triflate: a synergistic effort to cleave O2

“…while the reaction with CO 2 leads to oxalate or carbonate species depending upon various factors. 11,[28][29][30] The mechanism of the carbonate formation is particularly interesting since it involves a bent CO 2 2fragment, formed in between two lanthanide metal centers, which further reacts with another CO 2 yielding CO and CO 3 2-. 31 The overall reaction is a two-electron disproportionation of CO 2 and has the important drawback of releasing CO, also a pollutant.…”

About the Reaction of C(PPh3)2 with [M(CO)6] (M = Cr, Mo): Unusual Formation of μ‐Carbonato Complexes of Mo under Participation of THF

“…A similar μ.η 1 :η 2 coordination of CO 3 2– is found in two zinc complexes . and various f‐block elements . Other types of bridging modes of the carbonate ligand or bonded in a terminal manner are also reported…”