The synthesis, characterization, and reactivity of 1,3-dimethoxytetrabutyldistannoxane were investigated in connection to the mechanism of the selective synthesis of dimethyl carbonate from CO2 and methanol. A new distannoxane, 1-methoxy-3-methylcarbonatotetrabutyldistannoxane, resulting from a 1: 1 adduct with CO2 was isolated and characterised by volumetry, multinuclear NMR and IR spectroscopies. When this compound was submitted to 20 MPa Of CO2 at 423 K in toluene no dimethyl carbonate was formed, conversely to dibutyidimethoxystannane. However, when methanol was the solvent, dimethyl carbonate was selectively produced. A promoting effect of Si(OCH3)(4) was evidenced through methoxy-oxo exchange between silicon and tin. For the time, the role of distannoxanes as intermediates for the formation of dimethyl carbonate (DMC) is highlighted. It is suggested that the-Sn-O-Sn-type acido-basic sites may be responsible for methanol activation. (C) 2003 Elsevier B.V. All rights reserved.