Metal complexes of sexidentate ligands derived from 3-ethoxy-methylenepentane-2,4-dione: reactions with aliphatic diamines and crystal structures of [3,3′-ethylenedithiobis(o-phenyleneiminomethylidyne)bis(pentane-2,4-dionato)(2–)]-nickel(II) and -copper(II)

Abstract

Potentially sexidenatate ligands with [N₂S₂O₂]^2–, [N₄O₂]^2–, and [N₂O₄]^2– donor sets have been prepared from reactions of 3-ethoxymethylenepentane-2,4-dione with 1,2-di(o-aminophenylthio)ethane, 1,2-di(o-aminoanilino)-ethane, and 1,2-di(o-aminophenoxy)ethane. Six-co-ordinate nickel(II) and copper(II) complexes of 3,3′-ethylenedithiobis(o-phenyleneiminomethylidyne)bis[pentane-2,4-dionate(2–)](4a) and (5a) and of 3,3′-ethylenedi-iminobis(o-phenyleneminomethylidyne)bis[pentane-2,4-dionate(2–)] have been characterized and their reactions with ethylenediamine and other diamines have been examined. These result in ligand rearrangement of quadridentate dianionic systems, rather than in formation of cyclic sexidentate ligands. X-Ray structure determination of (4a), space group P2₁/c, a= 8.963(4), b= 29.067(10), c= 9.935(3)Å, β= 106.02(1)°, Z= 4, and isomorphous (5a), a= 8.887(3), b= 28.825(11), c= 10.168(4)Å, β= 106.51(2)°(heavy-atom method, 1 677 and 2 452 four-circle diffractometer data, R 0.056 and 0.060 respectively), shows the ligand to define an irregular octahedral arrangement of donors with the two terminal keto-groups in cis co-ordination sites, suitably positioned for intramolecular reaction with aliphatic diamines.