The role of mu-hydroxy and mu-alkoxy binuclear complexes in tin(IV)-catalysed urethane formation

It is proposed that at the catalyst concentrations normally used the distannoxane-catalysed formation of urethanes from isocyanates and alcohols involves the monomeric form of the distannoxane rather than the dimeric form as previously suggested, and that the catalytic species of the reaction is a mu-hydroxy binuclear complex that is formed from the alcohol and the distannoxane. Similar oxygen-bridged binuclear species are believed to be involved when other types of tin(IV) compounds are used as catalysts for urethane formation.