Isolation and characterization of polydentate ligands derived from the reaction of pentaerythrityltetrabromide and ethylenediamine

Abstract

Reaction of pentaerythrityltetrabromide with ethylenediamine yields three product amines. These have been isolated by separation of the corresponding Ni2+ complexes. The free amine hydrochlorides have been obtained by acid hydrolysis of the Ni2+ species and have been characterized by nuclear magnetic resonance and mass spectroscopy. The crystal structures have been determined for the hexahydrochloride salt of polyamine ligand L1, [H6(L1)]Cl6•4H2O (L1 = C11H28N6, 6,6-bis(4-amino-2-azabutyl)-1,4-diazacycloheptane)(C2/c, a = 15.975) Å, b = 10.723 (1) Å, c = 14.686(1) Å, β = 99.40(1)°, Z = 4), and for the octahydrochloride salt of L2, [H2(L2)Cl8•2H2O (L2 = 5,5-bis(4-amino-2-azabutyl)-1,9-diamino-3,7-diazanonane) (Pccn, a = 12.834(2) Å, b = 16.691(1) Å, c = 14.167(1) Å, Z = 4). Both crystals exhibit strong N—H … Cl,O,N bonding, although in the latter compound the waters of crystallization do not participate in the apparent hydrogen bonding interaction. Both these species are of interest since they represent the precursors to square planar Ni2+ complexes that incorporate the MN4 chromophore. Ring closure of both the free amines L1 and L2 by reaction with diethyl malonate leads to cyclized products that are related to the cyclam ([14-aneN4) tetraaza macrocylic ligands. Keywords: pentaerythrityl, amine, spiro ligand hydrochlorides.