Synergistic effects in the trimerization of isocyanates by organometallic catalysts

Use was made of combinations of organometallic catalysts, having different modes of interacting with the isocyanate group, to obtain strong synergistic effects in catalysing the trimerization of aromatic, aliphatic and strongly hindered isocyanates. The induction period observed in the trimerization of isocyanates with Group 2 catalysts (Pb, Zr and Co-naphthenates) was eliminated in the presence of Group 1 catalysts (tributyltin oxide and Zr(OBu)₄). Group I catalysts in combination with nucleophiles such as KI also showed strong synergistic effects.