Synthesis and Reactivity of Zirconium Hydrazido Complexes Containing Aryloxide Ligation

The reaction of [(ArO)₂Zr(Me)₂] (ArO = 2,6-di-tert-butylphenoxide)with PhNHNHPh (1 equiv) leads to [(ArO)₂Zr(Me)(η²-NPhNHPh)](1) and 1 equiv of methane. Heating a C₆D₆ solution of 1 generates [Zr{OC₆H₃(Bu^t)C(CH₃)₂CH}(OAr)(NPhNHPh)] (2) via cyclometalation of a tert-butyl group of the aryloxide ligand (¹H NMR). Addition of 4-pyrrollidinopyridine (>2 equiv, py′) to 1 results in the formation of the η²-azobenzene complex [(ArO)₂Zr(η²-N₂Ph₂)-(Py′)₂] (3) with the elimination of methane. Solutions of 3 in C₆D₆ slowly convert to the terminal imido complex [(ArO)₂Zr(═NPh) (py′)₂] and free azobenzene. Reaction of 1 with organic isocyanides (1 equiv of RNC; R = Bu^t, 2,6-Me₂C₆H₃) produces a mixed hydrazido, iminoacyl complex [(ArO)₂Zr(η²-NPhNHPh)(η²-MeCNR)], R = Bu^t (4a), 2,6-Me₂C₆H₃ (4b). Compound 4a crystallizes in space group P2₁/c with a = 19.666(5) Å, b = 12.166(3) Å, c = 19139(3) Å, β= 108.01(2)°, and Z = 4. The solid state structure of 4a shows both the hydrazido and iminoacyl groups to be η²-bound to the metal with an PhN—NHPh distance of 1.47(2) Á and Bu^tN—CMe distance of 1.26(2) Å.