Organometallic Sn(II) catalyzing adducts of substituted benzaldehydes

Abstract

This paper reports about the electrospray ionization mass spectrometric and quantum chemical study of unique coupling reaction of dihydroxybenzaldehydes in strong basic medium, which in the presence of SnIVCl4 yielded series of condensation products through the homo Dies-Alder reaction of the bicyclohexyl-4,6,4′,6′-tetraene-2,3,2′,3′-tetraone (2). In contrast to the known coupling reaction products catalyzing by diversity of CuI/CuII-, AgI-, Au0/AuIII/AuI-, ZnII-, Pd0/PdIII/PdII- and/or PtII-organometallics, yielding the substituted biphenyls, benzo-[c]-cromenes, condensation products of 5,6,11,12-tetraoxo-tricyclo[6.2.2.02,7]dodeca-3,9-diene-1,4-dicarbaldehyde (14) type from 2,3-dihydroxybenzaldehyde particularly, and/or substituted aldehydes by Reimer–Tiemann reaction, in the presence of SnIVCl4, the formation of above dimeric adducts is chiefly process, explained with SnIV→SnII redox process. The known product 14 is obtained at trace concentrations, producing further dimeric 5,6,11,12,5′,6′,11′,12′-octaoxo-[4,4′]bi[tricyclo[6.2.2.02,7]dodecyl]-3,9,3′,9′-tetraene-1,1′-dicarbaldehyde adduct (15). The catalyzing organometallic precursor is a binuclear SnII-complex (I), where the metal ion is bonded covalently in ClSnC manner. A second metal ion is bidentately coordinated to adjacent OC groups, forming a five membered chelate ring. The Cl− and OH−-terminal ligands completed the SnO3Cl chromophore. The experimentally evidenced complex I exhibited a significant thermodynamics stability of ΔG=−52996.80kcalmol−1, a value different than Δ(ΔG)=|52945| kcalmol−1 towards the corresponding quantities of other structurally proposed analogous of SnII, SnIV or SnII/SnIV organometallics II–IV on the base of the MS elemental compositions and isotopic shapes.