Synthesis and structures of dinuclear low-coordinate lithium and zirconium(iv) complexes derived from the diamido ligands 1,3-(CH2C6H3R12)2C6H4 (R1 = Me or Pri)

Abstract

Treatment of 1,3-bis(bromomethyl)benzene with two equivalents of the appropriate compound Li[N(H)C₆H₃R¹₂-2,6] yielded the diamines 1,3-[CH₂N(H)C₆H₃R¹₂-2,6]₂C₆H₄1 [R¹ = Me, abbreviated as H₂(D)] or 2 [R = Prⁱ, abbreviated as H₂(D′)]. The crystalline complex [Li₂(D′)]₂3 was obtained from 2 and 2 LiBuⁿ; the analogue from 1 and 2 LiBuⁿ was an incompletely characterised oil. The binuclear, crystalline zirconium(IV) amides [{Zr(NMe₂)₃}₂(μ-D′)] 4, its D analogue 5 and [{Zr(NMe₂)₂}₂(μ-D)₂] 6 were prepared from [{Zr(NMe₂)₃(μ-NMe₂)}₂] and H₂(D′) [or 2 H₂(D′)], H₂(D) and 2 H₂(D), respectively. The single crystal X-ray molecular structures of complexes 3 and 4 have been elucidated. That of 3 comprises a sixteen-membered, twisted macrocyclic LiNC₅NLiNC₅N core with each of the two-coordinate lithium atoms part of the LiNLiN rhombus. The four-coordinate zirconium atoms in 4 are in an only slightly distorted tetrahedral environment, with the two Zr(NMe₂)₃ units arranged trans to one another across the central aromatic ring. None of 4–6, with MAO, showed catalytic activity for ethylene polymerisation under ambient conditions.