1,4-Diaza-1,3-dien-Verbindungen elektronenarmer Übergangsmetalle σ-Donor- und π-Akzeptor-Komplexe des Zirconiums und Hafniums mit perphenylsubstituierten DAD-Liganden – ein Strukturvergleich

1,4-Diaza-1,3-diene Compounds of Early Transition Metals. σ-Donor and π-Acceptor Complexes of Zirconium and Hafnium with perphenyl-substituted DAD Ligands – a Comparison of Structures Reaction of 1,4- D i a za-1,3- d ienes (DAD) with the Lewis-acid ZrCl₄ affords σ-donor-complexes of composition ZrCl₄ · DAD. The X-ray analysis of the ( 2c ) (space group P1 , triclinic; a = 11.339(2), b = 11.845(2), c = 12.415(3) Å, α = 107.94(2), β = 107.26(2), γ = 104.73(2)°, Z = 2, R1 = 0.0266) shows that both N-atoms of the s-cis-configurated DAD-ligand occupy two corners of a distorted octahedron. There is only slight difference between the C?N bond lengths of the coordinated and noncoordinated ligand. In the homoleptic DAD-complexes of the type M(DAD)₃ [M = Zr ( 4b ), Hf ( 5b ), R = C₆H₄-4-Me] the DAD-ligands more act as π-acceptor ligands. X-ray analysis shows that the complexes [M = Zr ( 4b ), Hf ( 5b ), R = C₆H₄-4-Me] have the identical structure motive and crystallize in the triclinic space group P1 ( 4b : a = 14.904(1), b = 15.451(2), c = 19.584(4) Å, α = 112.08(1), β = 94.36(1), γ = 97.60(1)°, Z = 2, R1 = 0.0911; 5b a = 14.798(2), b = 18.226(2), c = 22.902(2) Å, α = 71.62(1), β = 72.38(1), γ = 87.27(1)°, Z = 2, R1 = 0.0644). The six N-atoms form a distorted octahedron in both complexes. The planarity of the five-membered rings and the almost similar C?N and C? C bond lengths are typical of the π-acceptor function of the diazadienes in 4b and 5b . The steric hindrance in 4b und 5b results in a dynamical behavior and a asymmetrical distortion at low temperatures as was observed by n.m.r.