Efficient organotin catalysts for urethanes: Kinetic and mechanistic investigations

Dibenzyltin bis(2-ethylhexanoate) 1 (4-Y-C6H4CH2)(2)Sn(OC(O)R-1)(2) [Y = H, 1a; MeO, 1b; Cl, 1c; Me, 1d; and R-1 = MeCH2CH2CH2. CH(Et)-] were synthesi zed either from the reaction of corresponding dibenzyltin dichlorides with silver 2-ethylhexanoate or from the reaction of dibenzyltin oxides with 2-e thylhexanoic acid. Compound la was further utilized as a catalyst for the r eaction of mono- and diisocyanates [PhNCO, CH3C6H3-2,4-(NCO)(2) and OCN(CH2 )(6)NCO] with alcohols (primary, secondary, tertiary, cyclohexcyl, alkyl, a llyl, benzyl and aryl) leading to the formation of the corresponding uretha nes, The catalytic efficiencies of 1 vis-g-vis industrially known organotin catalysts have been determined through kinetic studies for the reaction of PhNCO and n-BuOH at various temperatures. Compounds la, Ic and Id show hig her efficiency than dibutyltin bis(2-ethylhexanoate). FTIR studies further provide mechanistic insights into the catalytic cycle, which comprises pre- coordination of isocyanate to tin(IV), formation of stannyl carbamate and g eneration of dibenzyl(alkoxy)carboxylate as the active catalyst. Copyright (C) 2000 John Wiley & Sons, Ltd.