Tantalum-Mediated Cleavage of an NN Bond in an Organic Diazene (Azoarene) to Produce an Imidometal (MNR) Complex: An η 2 -Diazene Complex Is Not an Intermediate

Treatment of methyl tantalocene complexes Cp 2 Ta(L)CH 3 ( 4, L = Cp 2 Ta( S)CH 3, PMe 3, ethylene) with azobenzene or azotoluene (ArN NAr) leads to loss of L and formation of Cp 2 Ta(η 2 -ArN NAr)CH 3 ( 5; the first structurally characterized group V azoarene complex) and Cp 2 Ta( NAr)CH 3 ( 6 ). Mechanistic studies show that complex 5 cannot be an intermediate in the formation of 6; an η 1 -azoarene complex ( 8 ) is suggested as an alternative.