Di-n-butyltin(IV)-catalyzed dimethyl carbonate synthesis from carbon dioxide and methanol: An in situ high pressure 119Sn{1H} NMR spectroscopic study

The reactivity of five di-n-butyltin(IV) complexes, n-Bu2Sn(OR)2 (1), n-Bu2SnO (3), [n-Bu2Sn(OR)]2O (4), (n-Bu2SnO)2(CO2) (6) and (n-Bu2SnO)6[(n-Bu2SnOR)2(CO3)]2 (7) (R = CH3), with CO2, suggested as possible catalyst precursors and key-intermediates for the direct synthesis of dimethyl carbonate from carbon dioxide and methanol, has been investigated using high-pressure 119Sn{1H} NMR (HP-NMR) spectroscopy. Four of the five precursors studied, i.e. 3, 4, 6 and 7 give rise to an identical 119Sn{1H} NMR pattern which can be explicitly attributed to the fingerprint of the dimeric form of the 1-methoxy-3-methylcarbonatotetrabutyldistannoxane {5}2. However, with 1, a new pair of signals is observed in addition to the characteristic 119Sn{1H} NMR resonances of the dimeric hemicarbonato species {2}2 and {5}2, which can be attributed to the in situ formation of an unprecedented species suggested to be the trinuclear carbonato di-n-butyltin(IV) complex, 8.

Graphical abstractThe reactivity of several di-n-butyltin alkoxide and oxide complexes with CO2, known to be implicated in the direct synthesis of dimethyl carbonate promoted by diorganotin(IV) species, was studied by 119Sn{1H} HP-NMR spectroscopy in situ.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Tin(IV) alkoxides promote the formation of organic carbonates from CO2 and alcohols. ► An in situ High Pressure 119Sn{1H} NMR study is carried out to gain more insights. ► The dimer of n-Bu2(CH3O)SnOSn(OC(O)OCH3)n-Bu2 is revealed to be a key-intermediate. ► The in situ formation of a novel trinuclear di-n-butyltin(IV) entity is suspected. ► Dynamic exchanges involving carbonated distannoxanes are observed under CO2 pressure.