Аннотация:Reaction of a number of isocyanates with hexa-n-butyldistannum oxide (for the reactants taken in equimolar ratio) was investigated. Tin carbamates, existing as associates, were shown to be the products of this interaction. The catalytic activity of hexabutyldistannum oxide carbonate, carbamate, and its hydrolysis products were studied in the cyclotrimerization of isocyanates. The carbamate and the products of its interaction with isocyanate were shown to be responsible for the catalysis of trimerization in the presence of hexa-n-butyldistannum oxide.