J. Chil. Chem. Soc., 52, Nº 3 (2007) 1266 ORGANOMETALLIC 1,5-BENZODIAZEPINE AND 1,5-BENZODIAZE PINIUM COMPOUNDS: SYNTHESIS, CHARACTERIZATION, X-RAY DIFFRACTION STRUCTURES AND THEORETICAL INVESTIGATION CRISTINA GALLARDO a , ALEXANDER TRUJILLO a , MAURICIO FUENTEALBA a , ANDRES VEGA b , DAVID CARRILLO a , CAROLINA MANZUR a, * a Laboratorio de Química Inorgánica, Instituto de Química, Pontificia Universidad Católica de Valparaíso, Avenida Brasil 2950, Valparaíso, Chile; b Facultad de Ecología y Recursos Naturales, Universidad Nacional Andrés Bello, Avenida República 275, Santiago, Chile. (Received 5 th May 2007 – Accepted 25 th June 2007) ABSTRACT The organometallic tridentate ketoamine or enaminone compound, (η 5 -Cp)Fe(η 5 -C 5 H 4 )-C(=O)-CH=C(Me)-NH-C 6 H 4 -o-NH 2 , undergoes an intramolecular cyclocondensation promoted by Cu(ClO 4 ) 2 ⋅6H 2 O (2:1 molar ratio) affording the neutral 2-ferrocenyl-4-methyl-1,5-benzodiazepine, 1. However, when the molar ratio used is 1:1, the ketoamine or enaminone compound transforms into the 2-ferrocenyl-4-methyl-1,5-benzodiazepinium cation, [2] + . The X-ray molecular structure of 1 exhibits a seven-membered ring with a boat conformation, and two folding dihedral angles along the N(1)-N(2) and C(11)-C(13) axes. In the case of [2] + , the structure shows only one folding dihedral angle along the N(1)-N(2) axis. A rationalization of the properties of 1 and [2] + is provided through DFT calculations. Keywords: Organometallic diazepine, organometallic diazepinium, DFT calculations, X-ray structures, ferrocenyl ketoamine, ferrocenyl enaminone. INTRODUCTION It is well known in the literature that reactions of β-diketones with 1,2-diamines generally yield symmetrical 2:1 tetradentate Schiff bases whatever their proportion. 1 However, relatively few studies on tridentate 1:1 condensation products have been reported. 2 These compounds, synthesized by a single condensation reaction of a carbonyl function of a β-diketone with only one amine group of an aliphatic or aromatic 1,2-diamine, are referred to as “half units” or “hemi-Schiff bases” and in solution they can exist as a tautomeric mixture of the keto-amine (enaminone) and keto-imine (iminone) forms (Scheme 1, a and b, respectively). a b Scheme 1. Nowadays, the interest on the development of these “half units”, containing a free NH 2 group at one end of the molecule (Scheme 1), stems from their synthetic potential as precursors for the preparation of unsymmetrical tetradentate Schiff base ligands and their corresponding metal complexes. 3 On the other hand, considering the importance of the ferrocenyl fragment as a strong electron-releasing group 4 and the interesting electronic features exhibited by tridentate ferrocene-based keto-amines and their metal complexes, 5 we have initiated a systematic study on the reactivity of ONN tridentate “half units” synthesized by reaction of ferrocenoylacetone, Fc-C(=O)-CH 2 - C(=O)-Me, Fc= (η 5 -C 5 H 5 )Fe(η 5 -C 5 H 4 )-, with aromatic 1,2 diamines. As part of this work we report herein (i) the cyclocondensation of Fc-C(=O)-CH=C(Me)-NH-C 6 H 4 - o-NH 2 into 2-ferrocenyl-4-methyl-1,5-benzodiazepine, 1, and 2-ferrocenyl- 4-methyl-1,5-benzodiazepinium cation, [2] + , promoted by copper(II), (ii) the molecular structures of complexes 1 and [2] + solved by single crystal X-ray diffraction analysis and, (iii) a DFT calculation which provides a rationalization of the electrochemical and spectroscopic properties of complexes 1 and [2] + . The synthesis of these compounds represents an important entry toward the preparation of organometallic 1,5-benzodiazepine and 1,5-benzodiazepinium compounds with potential pharmacological properties. 6 In fact, many classical members of organic 1,5-benzodiazepines are widely used as antianxiety, analgestic, sedative, antidepresive and hypnotic agents. 7 EXPERIMENTAL SECTION General data Solvents were dried and distilled under dinitrogen by standard methods prior to use. Reagents were purchased from commercial suppliers and used without further purification. Ferrocenoylacetone, Fc-C(=O)-CH 2 -C(=O)- Me, was synthesized according to published procedures with some slight modifications. 8 Ferrocenyl-ketoamine (“half unit”), Fc-C(=O)-CH=C(Me)- NH-C 6 H 4 -o-NH 2 , was synthesized according to a procedure described in our Laboratory. 9 Microanalytical data were obtained on a Perkin Elmer model 2400 elemental analyzer. IR spectra were obtained as KBr disks on a Perkin Elmer model 1600 FT-IR spectrophotometer, in the range of 4000-450 cm - 1 . Electronic spectra were recorded in CH 2 Cl 2 and MeOH solutions with a Spectronic, Genesys 2, spectrophotometer. 1 H-NMR spectra were acquired at 297 K on a multinuclear Bruker AC 400 spectrometer in (CD 3 ) 2 CO; chemical shifts were referenced using the chemical shifts of residual solvent resonances. Variable-temperature 1 H-NMR spectra were recorded in the 223-323 K range. Electrochemical measurements were performed using a Radiometer Analytical model PGZ 100 all-in-one potentiostat, using a standard three-electrode setup with a vitreous carbon working electrode, platinum wire auxiliary electrode and Ag/Ag + (0.1 M AgNO 3 in MeCN) as the reference electrode. MeCN solutions were 1.0 mM in the compound under study and 0.1 M in the supporting electrolyte n-Bu 4 N + PF 6 - with the voltage scan rate = 100 mVs -1 . Under these experimental conditions the Cp 2 Fe 0/+ couple was located at 0.089 V (ΔE = 70 mV). E 1/2 is defined as equal to (E pa + E pc )/2, were E pa and E pc are the anodic and cathodic peak potentials, respectively. Melting points were determined in evacuated capillaries and were not corrected. Caution: complexe 1 and [2] + were synthesized using Cu(ClO 4 ) 2 ⋅6H 2 O as reagent; complex [2] + was isolated as perchlorate salt. Complex [2] + ClO 4 - ·CH 2 Cl 2 was dissolved in different organic solvents (UV-Visible spectroscopy, 1 H NMR spectrommetry, Cyclic Voltammetry) and also handled in solid state (IR) without any incident. In spite of this the impredictable behavior of perchlorate salts necessitates extreme care in their handling. 2-ferrocenyl-4-methyl-1,5-benzodiazepine, 1: A Schlenk tube was charged with a magnetic stirring bar and a solution of 100 mg (0.28 mmol) of the ferrocenyl keto-amine in 20 mL of MeOH, then a solution of 51.5 mg (0.14 mmol) of Cu(ClO 4 ) 2 ⋅6H 2 O dissolved in 10 mL of MeOH, was added drop wise developing immediately a dark red color. The reaction mixture was stirred for 1 h. The resulting solution was concentrated under vacuum until a solid was formed. The brown reddish crude solid was dissolved in 10 mL of CH 2 Cl 2 , filtrated and evaporated to dryness. Suitable single crystals for X-ray diffraction studies were obtained from MeCN. Yield: 58.1 mg (67%). Mp: 157ºC. Anal. Calcd for C 20 H 18 FeN 2 (342.26 gmol -1 ): C, 70.19; H, 5.30; N, 8.19. Found: C, 69.96; H, 5.28; N, 7.98. UV-vis [(λ max , nm (logε)]; CH 2 Cl 2 : 231 (4.03); 284 (3.06); 320 (3.61); 377 (2.81); 462 (2.74). MeOH: 239 (4.00); 280 (2.91); 310 (3.71); 370 (3.00); 453 (2.88). IR (cm -1 , KBr): 3102 (vw), 3078 (w), 3052 (w), ν(C-H) arom; 2963 (w), 2922 (w), 2853 (vw), ν(C-H) aliph; 1634 (m), 1602 (m), 1575 (m), ν(C=N) and ν(C=C). Other very strong bands not attributed