Structures and Reactivity of Zr(IV) Chlorobenzene Complexes

The synthesis, structures, and unusual reactivity of (C₅R₅)₂ZrR‘(ClPh)⁺ chlorobenzene complexes are described. The reaction of (C₅R₅)₂ZrR‘₂ with [Ph₃C][B(C₆F₅)₄] in C₆D₅Cl affords [(C₅R₅)₂ZrR‘(ClC₆D₅)][B(C₆F₅)₄] chlorobenzene complexes (1-d₅, R‘ = CH₂Ph and (C₅R₅)₂ = (C₅H₅)₂; 2a−d-d₅, R‘ = Me and (C₅R₅)₂ = rac-(1,2-ethylene(bis)indenyl) (2a), (C₅H₅)₂ (2b), (C₅H₄Me)₂ (2c), (C₅Me₅)₂ (2d, C₅Me₅ = Cp*)). Complexes 1 and 2b,c are thermally robust but are converted to [{(C₅R₅)₂Zr(μ-Cl)}₂][B(C₆F₅)₄]₂ (4b,c) by a photochemical process in ClPh solution. In contrast, 2d undergoes facile thermal ortho-C−H activation to yield [Cp*₂Zr(η²-C,Cl-2-Cl-C₆H₄)][B(C₆F₅)₄] (5), which slowly rearranges to [(η⁴,η-C₅Me₅C₆H₄)Cp*ZrCl][B(C₆F₅)₄] (6) via β-Cl elimination and benzyne insertion into a Zr−C_Cp* bond. The higher thermal reactivity of 2d versus that of 1 and 2b,c is attributed to steric crowding associated with the Cp* ligands of 2d, which forces a ClPh ortho-hydrogen close to the Zr−Me group.