SELECTIVE AND EFFICIENT SYNTHESES OF PERHYDRO-1,3,5-TRIAZINE-2,4,6-TRIONES AND CARBODIIMIDES FROM ISOCYANATES USING ZP(MENCH(2)CH(2))(3)N CATALYSTS

With concentrations as low as 0.0033 mol % ZP(MeNCH(2)CH(2))(3)N (Z = lone pair, 1) isocyanates are catalytically trimerized to perhydro-1,3,5-triazine-2,4,6-triones (isocyanurates) at room temperature. This reaction proceeds readily in the presence or absence of solvent, and the catalyst can be recycled at least six times without detectable degradation. Though not as potent a catalyst as 1, the molecule in which Z = Nph (3) also facilitates this reaction, and evidence is adduced that the catalytically active species is the adduct 3.ArNCO (6). In contrast, Ch = P(MeNCH(2)CH(2))(3)N (Ch = O, 4; Ch = S, 5) selectively catalyze the transformation of isocyanates to carbodiimides and do so more efficiently than their acyclic analogues O = P(NMe(2))(3) and (MeO)(2)P(S)Ph, respectively. The crystal structure of 4 is reported for the first time, and details of the crystal structure of [PhN = C(SMe)P(MeNCH(2)CH(2))(3)N]I reported earlier by us in preliminary form are presented. Both structures support the hypothesis that P - N-ax transannulation plays a lead role in the catalytic activities of 1 and 3-5.