Insertion reaction of carbon dioxide into Sn–OR bond. Synthesis, structure and DFT calculations of di- and tetranuclear isopropylcarbonato tin(iv) complexes

Abstract

The reaction of carbon dioxide with the stannane ⁿBu₂Sn(OⁱPr)₂ and distannoxane [ⁿBu₂(ⁱPrO)Sn]₂O leads to the selective insertion into one Sn–OⁱPr bond generating the corresponding ⁿBu₂Sn(OⁱPr)(OCO₂ⁱPr) and ⁿBu₂(ⁱPrO)SnOSn(OCO₂ⁱPr)ⁿBu₂ species. Both compounds are characterised by multinuclear NMR, FT-IR and single-crystal X-ray crystallography. In the solid state, they adopt a dimeric arrangement with bridging isopropoxy and terminal isopropylcarbonato ligands. The X-ray crystal structure of the dinuclear stannane shows that the Sn₂O₂ ring and the two Sn–OCO₂C fragments are nearby coplanar. The same holds for the ladder-type tetranuclear distannoxane. The dimeric structures are also evidenced by solution NMR in non-coordinating solvents. Interestingly, the assignment of the exo and endo tin resonances of the dimeric distannoxane is unambiguous using a labeled ¹³CO₂ experiment. The stability of the dimeric association has been probed in the stannane series on the basis of DFT calculations.