67530-50-1Relevant articles and documents
How a bifunctional complex drives reactivity of CO2-like molecules: Sodium [N,N′-ethylenebis(salicylaldiminato)]cobaltate(I) promotion of the reductive coupling of molecules resembling CO2
Arena, Francesco,Floriani, Carlo,Chiesi-Villa,Guastini, Carlo
, p. 4589 - 4596 (2008/10/08)
The bifunctional complex [Co(salen)Na(THF)] (1, salen = N,N′-ethylenebis(salicylaldiminato) dianion) promotes the reductive coupling of methyl pyruvate, diethyl ketomalonate, and p-tolylcarbodiimide via a C-C bond formation. Methyl pyruvate is transformed in diastereomeric dimethyl dimethyltartrates and p-tolylcarbodiimide into tetra-p-tolyloxalamidine, while 1 is oxidized to [Co(salen)]. A free-radical pathway involving the homolytic cleavage of a Co-Co σ bond is suggested. Reaction of 1 with diphenylketene, DPK, suggests an alternative pathway for the reductive coupling of CO2-like molecules. The reaction occurs in a 1:1 DPK/Co molar ratio and gives {[Co(salen)]2Na2[Co(salen(DPK)2)]}·3THF (8), which is a trinuclear cobalt(II) complex containing two intact [Co(salen)] units bridged by two Na+ ions to a third cobalt(II) unit, where the metal is surrounded by a hexadentate ligand resulting from the addition of two DPK molecules to the same imino group of the salen ligand. The X-ray analysis shows a rather close proximity between the carbon atoms belonging to the two DPK molecules as in a precoupling stage. Any C-C bond formation between those carbon atoms will restore the original imino functionality in the salen ligand. This may be another plausible pathway leading to a C-C bond between CO2-like molecules. Processes involving reactive sites and electron transfers from an aromatic polydentate ligand surrounding a metal are very important in compounds driving reactions of small molecules. Complex 1 promotes the usual reductive disproportionation of aryl isocyanates, RNCO (R = phenyl, 1-naphthyl). Crystallographic details for complex 8: space group P1 (triclinic); a = 16.313 (2) A?; b = 19.164 (3) A?; c = 15.020 A?; α = 107.16 (2)°; β = 113.23 (2)°; γ = 102.06 (2)°; Z = 2; Dcalcd = 1.410 g cm-3. The final R factor was 0.085 for 2742 observed reflections.
