Synthesis, Structure, and Insertion Reactivity of Zirconium and Hafnium Amidate Benzyl Complexes

A series of amidate-ligated dibenzyl zirconium and hafnium complexes are accessed through protonolysis reactions of the amide proligands 2,6-dimethylphenylpivaloylamide, [DMP(NO)tBu]H (3), and 1,3-bis(1-adamantylamide)-2,2-dimethylpropane, Ad[O2N2]H2 (5), with Zr(CH2Ph)4 or Hf(CH2Ph)4. The resulting dibenzyl complexes [DMP(NO)tBu]2Zr(CH2Ph)2 (4), Ad[O2N2]Zr(CH2Ph)2(THF) (6), and Ad[O2N2]Hf(CH2Ph)2(THF) (7) are structurally characterized. Insertion reactions of 4 with isocyanides are investigated, resulting in the formation of an η2-iminoacyl species, [DMP(NO)tBu]2Zr(η2-2,6-Me2C6H3NCCH2Ph)2 (8), which undergoes thermal CC coupling to form an enediamido complex, [DMP(NO)tBu]2Zr(η4-ArNC(CH2Ph)C(CH2Ph)NAr) (Ar = 2,6-Me2C6H3) (9). Analogous insertion of tBuNC into the Zr−C bonds of 4 results in the formation of a vinylamido complex, [DMP(NO)tBu]2Zr(N(tBu)CHCHPh)2 (10), through a presumed 1,2-hydrogen migration mechanism from an iminoacyl intermediate similar to 8. Complexes 8 and 9 are also structurally characterized.