Synthesis and molecular structure of bis(2-benzoylimino-benzimidazolinato)copper(II)-dimethylformamide — a metal-containing guanidine derivative 1

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Abstract

Bis(2-benzoylimino-benzimidazolinato)copper(II) (1) as the first neutral chelate of an acylimino-benzimidazoline contains guanidine and amide moieties directly coordinated to a metal atom. The ligands are arranged in trans position. The synthesis of cis-bis(pyridine)bis(N-benzoyl-O-ethyl-N′-m-nitrophenyl-isoureato)nickel(II) (2) is described. The molecular structures of both complexes were determined by X-ray crystal structure analysis.

Introduction

Acylimino(benz)imidazolines which act as ligands in 1 exhibit hypotensive [1], cardiovasculeric [2]as well as herbicidic [3]activities. They are prepared either by condensation of N-dichloromethylene acid amides with diamines 4, 5or by acylation of 2-amino-benzimidazoles [6]with acid chlorides 1, 2, 7. Apart from cationic mixed ligand ruthenium(II) complexes of 1a [RuL2(1a)2]Cl2 (L=dmso; PPh3) [8]and a recently published stepped cubane type complex [Cu4I4(ImNAc)2] with neutral 2-acetylimino-1,3-dimethylimidazoline (ImNAc) [9], no metal complexes are known up to now.

In this paper we report for the first time on the isolation and X-ray structural characterization of the neutral copper(II) complex 1, formed by deprotonation of 1a. Complexes of this type are interesting because they contain the guanidine fragment and simultaneously coordinate through the amide group.

In this respect, complex 2 obtained from the same educt as 1 by reaction with m-nitroaniline is a predecessor for metal-coordinated guanidine moieties. It offers even greater variability by the possibility of replacing the ethoxy group in the coordinated ligands by different amino groups. Though acylisoureas have been known for a long time 10, 11, 12, 13, 14, 15, 16their behavior as ligands was ignored with the exception of our own recent investigation of copper(II) complexes [17]. Thus compound 2 containing two stabilizing pyridine ligands and also characterized by its crystal structure is in fact the first nickel(II) chelate of this type.

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Results and discussion

To synthesize the ligands of the above-mentioned complexes 1 and 2 the same educt N-benzoyl-thiocarbamic acid-O,S-diethylester [18]was reacted either with o-phenylenediamine obtaining 1a or with m-nitroaniline obtaining 2a in good yields. 1a and 2a are characterized by elemental analyses, mass spectra (see Section 3) and 1H NMR and 13C NMR spectra (see Fig. 1).

The reaction of 1a with copper(II) acetate-monohydrate in ethanol yields 1 as a dark green crystalline precipitate (see Fig. 1). It is

2-Benzoylimino-benzimidazoline (1a)

23.7 g (0.1 mol) N-benzoyl-thiocarbamic acid-O,S-diethylester [18]were refluxed with the same molar amount of o-phenylenediamine (10.8 g) in 100 ml ethanol. After this the solution was stirred 24 h at room temperature and left overnight in the refrigerator. The precipitate was filtered and recrystallized from methanol. Colorless crystals. m.p.: 242–243°C (lit.: 241–243°C [4]); yield: 7.1 g (30%). Anal. Calc. for C14H11N3O (237.25 g/mol): C, 70.87; H, 4.67; N, 17.71; O, 6.74. Found: C, 70.72; H,

Supplementary material

Further details of the structure determinations are available on request from Fachinformationszentrum Karlsruhe, D-76344 Eggenstein-Leopoldshafen, Germany, on quoting the depository numbers CSD-380217 (1) and CSD-380218 (2).

Acknowledgements

L.B. would like to thank the Fond der Chemischen Industrie for financial support. M.L. thanks the DAAD Bonn for a grant. We thank Dr. K.H. Hallmeier for recording and discussion of the XPS spectra and Dr. L. Hennig for recording and discussion of the NMR spectra.

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Dedicated to Professor Dr. Joachim Sieler on the occasion of his 60th birthday.

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