Carbodiimides. II. Mechanism of the Catalytic Formation from Isocyanates

Oxo and imido/imido exchange and C–H activation reactions based on pentamethylcylopentadienyl imido tantalum complexes

“…No reaction was observed when the starting complex 1a was added to a solution containing the tantalum(III) complex. Carbodiimides have also been synthesized by coupling isocyanates with elimination of CO 2 , using phosphine oxides [18] and imido vanadium [10] or tungsten [6a] compounds as catalysts.…”

Advances in the Chemistry of Carbodiimides

“…On the other hand, electronwithdrawing groups increase the rate roughly in proportion to their electron-withdrawing power. Thus, for example, the catalyzed conversion of p-nitrophenyl isocyanate into the carbodiimide is almost explosive (107); again, the reaction of the o-chloro compound is about seven times as fast as that of the o-methyl analog, although their mesomeric and steric effects should be similar (479). Thus, the higher the inductive effect (CH3 > H > Cl), the lower is the rate of the reaction.…”

“…A point in favor of this mechanism is Kogon's (364) observation that trimeric isocyanates are formed in excellent yields from the monomers in the presence of metal naphthenates at room temperature. (479), have concluded from their kinetic studies that the catalyzed reaction is of the first order with respect to isocyanate and catalyst over 95% of the reaction in an "open" system. They have put forward the following mechanism.…”

Microwave-mediated and customery synthesis of N-benzoyl- or N-substituted benzoyl-N,N'-dialkylureas from arylcarboxylic acids and N,N'-disubstituted carbodiimides under solvent-free conditions

“…17 We observed the reaction rate enhancement when the phenyl ring of the acid carried an electron-withdrawing group. Increased reaction rate has also been reported earlier by Šlebioda.…”