Triorganotin(iv) cation-promoted dimethyl carbonate synthesis from CO2 and methanol: solution and solid-state characterization of an unexpected diorganotin(iv)-oxo cluster

Abstract

Two novel C,N-chelated organotin(IV) complexes bearing weakly coordinating carborane moieties were prepared by the reaction of the corresponding C,N-chelated organotin(IV) chloride (i.e. L^CNR₂SnCl, R = n-Bu (1) and Ph (2); L^CN = 2-(N,N-dimethylaminomethyl)phenyl)) with monocarba-closo-dodecaborate silver salt (AgCB₁₁H₁₂; Ag·3). Both products of the metathesis, [L^CN(n-Bu)₂Sn]⁺[CB₁₁H₁₂]⁻ (4) and [L^CNPh₂Sn]⁺ [CB₁₁H₁₂]⁻ (5), respectively, were characterized by both multinuclear NMR spectroscopy and elemental analysis. The instability of 4 and 5 towards water is discussed. The solid-state structure of L^CN(n-Bu)₂SnOH·B(C₆F₅)₃ (4a) as a model compound with a Sn–O(H)⋯B linkage is also reported. The evaluation of the catalytic activity of 4 and 5 was carried out within the direct synthesis of dimethyl carbonate (DMC) from methanol and CO₂. While 5 was shown to be definitively inactive, presumably due to cleavage of the Sn–Ph bond, compound 4 exhibits a beneficial action, since it leads to an amount of DMC higher than the stoichiometry (n_DMC/n_Sn(cat) = 1.5). In addition, the solid state structures of [BnNMe₃]⁺[CB₁₁H₁₂]⁻ (6) and [(n-Bu)₂₀Sn₁₀O₂(OMe)₆(CO₃)₂]²⁺·2[CB₁₁H₁₂]⁻ (7), isolated as single-crystals and resulting from the recombination of 4 under the reaction conditions (methanol/CO₂), were established by sc-XRD analyses within the term of this work as well. 6 and 7 were also fully characterized by IR spectroscopy, multinuclear NMR in solution and elemental analysis.