The reaction of 4-chloro-or 4-methyl-2,6-diformylphenol with 7-amino-4-methyl-5-azahept-3-en-2-one leads to either quadridentate mononucleating or heptadentate binucleating Schiff -base ligands, depending on the reaction conditions. Nickel complexes with both types of ligands have been obtained and characterized by i.r., u.v.-visible, n.m.r., and mass spectrometry. An interesting example of impeded pseudo-rotation of a five-membered chelate ring in dinuclear nickel complexes is observed. The single-crystal X-ray structure of [4-chloro-2,6-bis(4-methyl-2-0~0-5,8-diazanona-3,8-dienyl)phenolato(3-)]dinickel(ii) bromide hemihydrate has been determined. It consists of a dinuclear complex cation of twisted bifurcated shape and a bromide anion, with a half-equivalent of water incorporated into the crystal lattice. Crystallographic data: space group C2/c (no. 15), a=22.082(4),b= 11.5,~=22.368(4)A,j3= 118.61(1)",RandR'0.0380and0.0318, respectively.The condensation of a free primary amino group in 7-amino-4-methyl-5-azahept-3-en-2-one (2) with the carbonyl group in ortho-substituted aromatic carbonyl compounds (1) provides an excellent synthetic route to the unsymmetrical quadridentate Schiff-base ligands (3) (Scheme 1) and their transition-metal Our recent studies have revealed that the formation of the unsymmetrical ligand (3) is catalyzed by the intramolecular hydrogen bonding between the hydrogen atom on the X substituent (X = OH, NH2, or NHOCMe) and the carbonyl oxygen atom in (1) and depends on the acidity of this hydrogen atom.-N
CH3 R* CH3Aromatic hydroxydialdehydes of the type (4) can react with two molecules of (2) according to Scheme 2. The first step of this reaction should proceed with ease due to the strong intramolecular hydrogen bond between the acidic phenolic hydrogen and carbonyl oxygen atoms in (4). However the condensation with the second molecule of (2) should be more difficult, since the hydrogen bonding to the more basic imino nitrogen atom is preferred in (9, and the intramolecular catalysis is less effective. This difference in reactivity of the two carbonyl groups in (4) offers the possibility of the preparation of either mononucleating ligands of the type (5), or dinucleating ligands of the type (6), depending on the reaction conditions employed. Indeed, we have found that at room temperature this reaction stops at the stage of the mononucleating ligands (9, whereas at elevated temperature the dinucleating ligands (6) are formed. In this paper we report the preparation of two new R R (4a) R = CI (4b) R=CH3 (5a) R=CI (5b) R=CH3 HiC CH3 (6a) R = C I (6b) R=CH3 Scheme 2.mononucleating ligands (5a) and (5b) and two new binucleating Schiff-base ligands (6a) and (6b) derived from 4-chloro-and 4-methyl-2,6-diformylphenol(4a) and (4b). The ligands have been used for the preparation of mono-and di-nuclear nickel complexes, which have been characterized by spectroscopic t
