Synthesis, Characterization, and Thermal Rearrangement of Zirconium Tetraazadienyl and Pentaazadienyl Complexes

Reaction of the zirconium dichloro complex [Zr((N2Npy)-N-TBS)Cl-2] (1) with 1 molar equiv of ArNHLi (Ar = Mes, DIPP) yielded the zirconium imido complexes [Zr(N2TBSNpy)(=N-DIPP)(py)] (2; (N2Npy)-N-TBS), [(2-C5H4N) (CH3){CH2NSi (CH3)(2)tBU} DIPP = 2,6-diisopropylphenyl) and [Zr((N2Npy)-N-TBS)(=N-Mes)(py)] (3; Mes = mesityl). The imido complexes are converted to the tetraazadienido complexes [Zr(N2(TBS)N(py)),)((NN2NPh)-N-DIPP)] (4) and Zr- ((N2Npy)-N-TBS) ((NNNPh)-N-Mes-N-2)] (3) by addition of phenyl azide, whereas the reaction of 2 or 3 with mesityl azide gave the alternative product 7, in which the azide is coupled with the CH activated ancillary tripod ligand. Reaction of 1 molar equiv of trimethylsdyl azide or 1-adamantyl azide with the previously reported hydrazinediido complex [Zr(N2(TBS)N(py))(=NNPh2)(py)] (9) at ambient temperature resulted in the formation of the five-membered zirconaacacycles [Zr(N2(TBS)N(py))((NN3NPh2)-N-TMS)] ( 10) and [Zr((N2Npy)-N-TBS)((NN3NPh2)-N-Ad)] (11). Complex 11 was thermally converted into the diazenido complex 12 via loss of 1 molar equiv of molecular N2. The direct formation of the analogous side-on-bonded diazenido analogue 13 was observed upon reaction of 9 with 1 equiv of mesityl azide at ambient temperature. On the basis of N-15 labeling and DFT modeling (DFT(B3PW91/6-31 g(d))) a mechanism for the reaction pathway leading to 12 and 13 is proposed.