Catalytic double-bond metathesis without the transition metal

Iminophosphoranes of the type X(3)P=NR (X = Cl, pyrrolyl; R = alkyl, aryl) catalytically metathesize C=N bonds of carbodiimides via an addition/elimination mechanism that, despite the lack of d orbital participation in P-N bonding, conserves the key features of metal-catalyzed olefin metathesis. Diazaphosphetidine intermediates, produced by the formal 2 + 2] addition of carbodiimides to the P=N bond, have been isolated and characterized. All phosphorus-containing species in the complex catalytic reaction mixtures have been identified and their origins explained. The kinetics of addition of diisopropylcarbodiimide to Cl(3)P=NPr(i)() and subsequent elimination were studied, and rate constants were determined: k(add) = 1.7 x 10(-3) (+/-0.1 x 10(-3)) M s(-1) and k(elim) = 4.0 x 10(-4) (+/-0.3 x 10(-4)) s(-1). The rate of these reactions corresponds well with the observed catalytic TOF of 1.44 TO/P/h.