Molecular structures of three coordinate zinc and cadmium complexes that feature β-diketiminato and anilido-imine ligands

Article abstract of DOI:10.1016/j.poly.2010.02.020

A series of zinc and cadmium complexes of the β-diketiminato and anilido-imine classes of ligands, namely [BDI^Ar], [AI^Ar] and [AI^Ar,NPr₂i], have been synthesized and structurally characterized by X-ray diffraction. For example, the zinc and cadmium alkyl compounds [AI^Ar]ZnEt and [AI^Ar]CdMe have been synthesized via the reactions of [AI^Ar]H with Et₂Zn and Me₂Cd, respectively, while [AI^Ar]ZnN(SiMe₃)₂ has been obtained by treatment of [AI^Ar]H with Zn[N(SiMe₃)₂]₂. Single crystal X-ray diffraction studies establish that the metal centers in each of these complexes are trigonal planar. Comparison of the molecular structures of [AI^Ar]CdMe and [BDI^Ar]CdMe demonstrates that the cadmium methyl moiety lies in the plane of the annulated [AI^Ar] ligand, whereas there is considerable displacement for [BDI^Ar]CdMe. [AI^Ar,NPr₂i]Li, an anilido-imine ligand that incorporates a CH₂ CH₂ NPr₂ⁱ tether, has been synthesized via a sequence involving condensation of 2-fluorobenzaldehyde with H₂ NCH₂ CH₂ NPr₂ⁱ, followed by treatment with ArNHLi. X-ray diffraction demonstrates that the lithium has a T-shaped coordination environment which is supplemented by an agostic interaction with a C-H bond of one of the isopropyl groups of the NPr₂ⁱ moiety. However, while the NPr₂ⁱ group of the tether coordinates to lithium in [AI^Ar,NPr₂i]Li, it does not coordinate to the zinc center of [AI^Ar,NPr₂i]ZnMe. The structure of [AI^Ar,NPr₂i]ZnMe is also in marked contrast to that reported for [AI^{Ar, NMe₂}]ZnMe, in which the NMe₂ group does coordinate to the zinc center. The M-C bonds of [AI^Ar,NPr₂i]ZnMe, [BDI^Ar]ZnEt and [BDI^Ar]CdMe are cleaved by B(C₆F₅)₃ to give the perfluorophenyl derivatives [AI^Ar,NPr₂i]ZnC₆F₅, [BDI^Ar]ZnC₆F₅ and [BDI^Ar]CdC₆F₅. Interestingly, the C₆F₅ groups are almost orthogonal to the planes of the chelating ligands in the zinc complexes, [AI^Ar,NPr₂i]ZnC₆F₅ and [BDI^Ar]ZnC₆F₅, whereas the C₆F₅ and [BDI^Ar] ligands of [BDI^Ar]CdC₆F₅ reside in the same plane. In addition to 1:1 [AI^Ar,NPr₂i]ZnX complexes, it is also possible to synthesize the 2:1 complex [AI^Ar,NPr₂i]₂Zn which is consistent with the [AI^Ar,NPr₂i] ligand being less sterically demanding than the [BDI^Ar] ligand.