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Boletín de la Sociedad Chilena de Química

versão impressa ISSN 0366-1644

Bol. Soc. Chil. Quím. v.47 n.4 Concepción dez. 2002

http://dx.doi.org/10.4067/S0366-16442002000400014 

ORGANOMETALLIC IRON(II) COMPLEXES CONTAINING
P-SUBSTITUTED ACETOPHENONE-ARYLHYDRAZONE LIGANDS

Carolina Manzur*a, Lorena Millána, Walter Figueroaa,
Jean-René Hamon*b, Jose A. Matac and David Carrilloa

aLaboratorio de Química Inorgánica, Instituto de Química,
Universidad Católica de Valparaíso, Avenida Brasil 2950, Valparaíso, Chile
E-mail address: cmanzur@ucv.cl(C. Manzur)
bUMR 6509 CNRS-Université de Rennes 1, Institut de Chimie de Rennes,
Campus de Beaulieu, F-35042 Rennes-Cedex, France
E-mail address: jean-rene.hamon@univ-rennes1.fr
cDepartamento de Química Inorgánica y Orgánica,
Universitat Jaume I, Apt. 224, E-12080 Castellón, Spain

ABSTRACT

A series of twelve new organometallic acetophenone-hydrazone complexes of general formula [(h 5-Cp)Fe(h 6-o-RC6H4)-NHN=CMe-C6H4-p-R’]+PF6- (Cp= C5H5; R,R’=H,Me, [5]+PF6-; H,MeO, [6]+PF6-; H,NMe2, [7]+PF6-; Me,Me, [8]+PF6-; Me,MeO, [9]+PF6-; Me,NMe2, [10]+PF6-; MeO,Me, [11]+PF6-; MeO,MeO, [12]+PF6-; MeO,NMe2, [13]+PF6-; Cl,Me, [14]+PF6-; Cl,MeO, [15]+PF6-; Cl,NMe2, [16]+PF6-) has been prepared by reaction between their corresponding organometallic hydrazine precursors [(h 5-Cp)Fe(h 6-o-RC6H4)-NHNH2]+PF6- (R=H, [1]+PF6-; Me, [2]+PF6-; MeO, [3]+PF6-; Cl, [4]+PF6-, and aromatic ketones of the type MeC(=O)C6H4-p-R’ (R’=Me, MeO, NMe2) in refluxing ethanol containing concentrated acetic acid. These mononuclear hydrazones were stereoselectively obtained as their trans-isomers about the N=C double bond, and were characterized by elemental analysis or high resolution mass spectrometry, I.R., UV-Vis, and 1H NMR spectroscopies and, in the case of complex [11]+PF6- (R,R'=MeO,Me), by single-crystal X-ray diffraction analysis. The more salient features of this structure are: (i) the concomitant lengthening of the Fe-Cipso and the shortening of the Cipso-N bond distances leading to a slight iminium-cyclohexadienyl character of the coordinated C6 ring, (ii) the intramolecular hydrogen bonding between the benzylic N-H group and the oxygen atom of the ortho-methoxo-substituent, with the N(1)···O(1) separation of ca. 2.627(4) Å, and (iii) the slight deviation of coplanarity between the coordinated and the free phenyl rings (dihedral angle=15.60(0.25)°). Finally, the cyclic voltammetry studies reveal an irreversible one-electron reduction step for compounds [5-7]+PF6-, and the redox potentials clearly indicate that the reduction occurs at the cationic electron acceptor mixed sandwich unit.

KEYWORDS: Mixed sandwiches, organometallic arylhydrazone, acetophenome-arylhydrazone, dipolar chomophores, X-ray structure.

RESUMEN

Se ha preparado una serie de doce nuevos complejos organometálicos que contienen hidrazonas de derivados de la acetofenona como ligandos, de fórmula general: [h 5-Cp)Fe(h 6-o-RC6H4)-NHN=CMe-C6H4-p-R’]+PF6-, (Cp=C5H5; R,R’=H,Me, [5]+PF6-; H,MeO,[6]+PF6-; H,NMe2, [7]+PF6-; Me,Me, [8]+PF6-; Me,MeO, [9]+PF6-; Me,NMe2, [10]+PF6-; MeO,Me, [11]+PF6-; MeO,MeO, [12]+PF6-; MeO,NMe2, [13]+PF6-; Cl,Me, [14]+PF6-; Cl,MeO, [15]+PF6-; Cl,NMe2, [16]+PF6-). Estos compuestos han sido sintetizados mediante reacción de las correspondientes hidracinas organometálicas precursoras [(h 5-Cp)Fe(h 6-o-RC6H4)-NHNH2]+PF6- (R=H,[1]+PF6-; Me, [2]+PF6-; MeO, [3]+PF6-; Cl, [4]+PF6-, con cetonas aromáticas del tipo MeC(=O)C6H4-p-R’ (R’=Me, MeO, NMe2) en ethanol conteniendo ácido acético concentrado a reflujo. Estas hidrazonas mononucleares fueron estereoselectivamente obtenidas como isómeros trans en torno al doble enlace N=C, y fueron caracterizadas mediante análisis elemental o espectrometría de alta resolución, y espectroscopias IR, UV-Vis, y de RMN de 1H y, en el caso del complejo [11]+PF6- (R,R’=MeO,Me), mediante análisis por difracción de rayos-X de mono-cristal. Las características más notables de esta estructura son: (i) la concomitancia con que se produce el alargamiento de la distancia del enlace Fe-Cipso y el acortamiento de la distancia del enlace Cipso-N, que conducen a un ligero carácter iminium-ciclohexadienilo del anillo C6 coordinado, (ii) la presencia de un enlace de hidrógeno intramolecular entre el grupo N-H bencílico y el átomo de oxígeno del grupo metoxo substituyente en posición orto, siendo la separación N(1)× × × O(1) de ca. 2.627(4) Å, y (iii) la ligera desviación de la coplanaridad entre los anillos fenilo coordinado y libre (ángulo diedro=15.60(0.25)°. Finalmente, los estudios de Voltametría Cíclica revelan un paso de reducción mono-electrónico irreversible para los compuestos [5-7]+PF6-, indicando claramente los potenciales redox que la reducción ocurre en la unidad electrón-aceptora catiónica de la unidad sandwich mixto.

PALABRAS CLAVES: Sandwich mixtos, arilhidrozonas organometálicas, arilhidrozonasde acetofenomas, crómosforos, estructuras de rayos-X.

INTRODUCTION

The preparation of organometallic mixed sandwich complexes containing the electron-acceptor cationic moiety [(h 5-Cp)Fe]+ (Cp=C5H5) coordinated to arene ligands, has been an active topic of research both in the development of organometallic1) and metal assisted organic chemistry.2) On the other hand, in the last few years, classical aromatic hydrazones derivatives, containing acceptor and donor groups, e. g. A-NHN=CH-D (Type I) and D-NHN=CH-A (Type II) (A=Acceptor, D=Donor), have extensively been investigated as a potentially attractive class of NLO crystalline materials.3) Considering these two circumstances, we thought it would be interesting to investigate the possibility of synthesizing organometallic entities containing an acceptor group, like the [(h 5-Cp)Fe]+ moiety, coordinated by classical hydrazones containing a donor terminal group. These mononuclear complexes, of the general form [(h 5-Cp)Fe(h 6-aryl)-NHN=CH-D]+, can be viewed as Type I non-rod-shaped dipolar chromophores.3a,b) To the best of our knowledge, complexes of this nature are unknown in the literature. Very recently, we have successfully synthesized organometallic acetone-hydrazones4) of formula [(h 5-Cp)Fe(h 6-p-RC6H4)-NHN=CMe2]+PF6- and formyl-4a,5b) and acetylferrocene-hydrazones5a) of formula [(h 5-Cp)Fe(h 6-p-RC6H4)-NHN=CR-(h 5-C5H4)Fe(h 5-Cp)]+PF6- (R=H, Me), some of which have been crystallographically characterized.4b,5)

Therefore, as part of our current research on the organometallic hydrazone chemistry and as a complementary study to that carried out on aromatic aldehydes6), here we report on the reactivity of organometallic hydrazines [(h 5-Cp)Fe(h 6-o-RC6H4)-NHNH2]+PF6- (R=H, Me, MeO, Cl) toward acetophenones MeC(=O)C6H4-p-R’, bearing a R’ electron-donating group (R’=Me, MeO, NMe2) at the para-position, including: (i) the synthesis and spectroscopic characterization of twelve new organo-iron(II) acetophenone-hydrazone complexes [5-16]+PF6- of general formula [(h 5-Cp)Fe(h 6-o-RC6H4)-NHN=CMe-C6H4-p-R’]+PF6-, (see Scheme 1), and (ii) the X-ray crystal structure of complex [11]+PF6- (R,R’=MeO,Me).


SCHEME 1

RESULTS AND DISCUSSION

Preparation and characterization

The ionic organometallic hydrazones [5-16]+PF6- were prepared, as outlined in Scheme 1, by reacting the respective ortho-substituted organometallic hydrazine precursors [(h 5-Cp)Fe(h 6-o-RC6H4)-NHNH2]+PF6- (R=H, [1]+PF6-; Me, [2]+PF6-; MeO, [3]+PF6-; Cl, [4]+PF6-) with aromatic ketones MeCOC6H4-p-R’ (R’=Me, MeO, NMe2), in refluxing ethanol containing concentrated acetic acid. All complexes were isolated as air stable yellow to red microcrystalline solids after recrystalization from MeCN or CH2Cl2:Et2O 1:1, in yields ranging from 46 to 79%. They are soluble in CH2Cl2, Me2CO, MeCN and DMSO and insoluble in non-polar organic solvents and in water.

The identities of these organometallic hydrazones were confirmed whether by satisfactory elemental analysis or high resolution mass spectrometry, 1H NMR, IR and UV-Vis spectroscopies (see Experimental section). Moreover, the crystalline and molecular structure of complex [11]+PF6- (R,R’=MeO,Me) was determined by single crystal X-ray diffraction analysis (vide infra).

The IR spectra of these complexes are characterized by a sharp medium absorption band in the 3392-3338 cm-1 region assigned to the n (N-H) stretching vibration;7) a strong band in the 1564-1525 cm-1 region which has been attributed to the stretching mode of the C=N group; a very strong n (PF6) band in the 841-828 cm-1 region and a strong d (P-F) band in the 559-557 cm-1 region. On the other hand, the UV-Vis spectra of this new family of mononuclear hydrazones have been recorded in CH2Cl2 (e =8.90) and DMSO (e =47.6). In CH2Cl2, complexes [5,6,8,9,11,12,14,15]+PF6- exhibit similar spectra indicating similar structural features, and are comparable to those exhibited by the organometallic acetone-hydrazones reported elsewhere.4) However, complexes [7,10,13,16]+PF6-, that contain the more electro-donating NMe2 group (see below the Electrochemical section), in para-positions of the free arene, exhibit an additional band in the 340-370 nm region which is attributed to intraligand charge transfer excitations.8) A very weak solvatochromism was observed in DMSO, but its magnitud could not be accurately determined due to the fact that the variations of l max values are too close to the experimental error limits. More interestingly, the 1H NMR spectra exhibit the following features: (i) the presence of only one signal corresponding to the C5H5 proton resonances in the 4.99-5.15 ppm region, revealing that all organometallic hydrazones have been stereoselectively formed as a single isomer, the sterically less hindered conformation with the organometallic moiety and the free phenyl group in the trans arrangement about the N=C double bond is attributed, and confirmed by the crystal structure of compound [11]+PF6- (see below), (ii) a slightly broadened NH proton resonance in the 8.09-9.18 ppm region, and (iii) the presence of two different groups of signals in the ranges 6.00-6.93 and 6.80-8.06 ppm, corresponding to the two types of phenyl protons, those of the coordinated ring being upfield shifted relative to those of the uncomplexed phenyl groups. Finally, the LSIMS+ mass spectra of complexes [9-14]+PF6- exhibit molecular ions (100%) corresponding to the cationic fragment C+ with the characteristic isotopic distribution patterns, and therefore confirm unambiguously the structure of these organometallic materials.

Electrochemical studies

The [(h 5-Cp)Fe(h 6-arene)]+ complexes are known for their interesting redox behavior.9,10) Thus, it is of interest to examine the electronic influence of the para-donating R’ substituents through the hydrazone skeleton, using electrochemistry. Cyclic voltammetry studies were carried with complexes [5-7]+PF6- at room temperature, using a vitreous carbon working electrode in acetonitrile containing 0.1 M n-Bu4N+PF6- as supporting electrolyte. The number of electrons transferred was estimated by comparison with that of the Cp2Fe/Cp2Fe+ couple under similar experimental conditions.

The reduction potentials of the compounds under investigation, are in the expected range for such amino-substituted arene iron complexes.9b) The one-electron irreversible cathodic process, corresponding to the reduction of the Fe(II) to Fe(I)9,10), becomes progressively more cathodic, with Epc (V) from -1.48 for [5]+PF6- to -1.52 for [7]+PF6-, indicating a significant electronic influence of the para-donating substituents on the iron centre (Me<MeO<NMe2) through the hydrazone backbone.

X-ray crystallographic study

Relevant bond distances and angles for compound [11]+PF6- (R,R’=MeO,Me) are reported in Table 1. ORTEP11) view of the cationic moiety [11]+, with the atom labelling scheme is presented in Figure 1.

TABLE 1. Selected bond distances (Å) and angles (º) of cation [11]+.


Distances

     

Fe(1)-C6)

2.166(3)

N(1)-N(2)

1.379(4)

Fe(1)-C(7)

2.138(3)

N(2)-C(13)

1.280(4)

Fe(1)-C(8)

2.071(3)

C(13)-C(14)

1.502(5)

Fe(1)-C(9)

2.057(4)

C(13)-C(15)

1.484(4)

Fe(1)-C(10)

2.064(4)

C(7)-O(1)

1.346(4)

Fe(1)-C(11)

2.082(4)

Fe(1)-CpCNT

1.664

C(6)-N(1)

1.367(4)

Fe(1)-PhCNT

1.555

       

Angles

     

C(6)-N(1)-N(2)

117.9(3)

C(8)-C(7)-O(1)

125.1(3)

N(1)-N(2)-C(13)

117.4(3)

N(2)-C(13)-C(14)

124.2(3)

N(1)-C(6)-C(7)

118.3(3)

N(2)-C(13)-C(15)

116.3(3)

C(6)-C(7)-O(1)

114.5(3)

CpCNT-Fe(1)-PhCNT

178.89


Abbreviations: Cp = C5H5, Ph = o-MeOC6H4, CNT = centroid.


FIG. 1. ORTEP view of the cation [(h 5-Cp)Fe(h 6-o-MeOC6H4)-NHN=C(Me)-C6H4-p-Me]+ ([11]+), with the atom-labelling scheme. Displacement ellipsoids are at the 50% probability level. Hydrogen atoms have been omitted for clarity

The cationic entity displays the classical sandwich structure of the type [CpFe(Arene)]+ with the Fe-Cp and Fe-(Arene) centroid distances of 1.664 and 1.555 Å, respectively. The ring centroid-iron-ring centroid vectors are essentially collinear (Cp-Fe-Arene=178.89°). These values are typical of a h 5-Fe-h 6 coordination.12,13) Likewise, certain structural features of this mononuclear hydrazone are similar to those we have reported elsewhere4b,5), particularly in the following aspects: (i) the elongation of the Fe(1)-C(6) bond (2.166(3) Å) which is 0.098 Å longer than the average of the Fe(1)-C(8-11) bond distances, (ii) the shortening of the C(6)-N(1) bond of 0.070 Å with respect to a single C-N bond13), and (iii) the depyramidalization of the N(1) atom (angle C(6)-N(1)-N(2)=117.9(3)°) as a consequence of the delocalization of the N(1) electron lone-pair to the [CpFe(Arene)]+ fragment. These features we have described for other organometallic hydrazones4b,5) lead us to attribute a partial positive charge on the N(1) atom (iminium resonance form) and, consequently, a cyclohexadienyl-like character of the arene ring with a partial negative charge.14) On the other hand, two additional interesting features were observed in this structure: (i) the unexpected elongation of the Fe(1)-C(7) bond (2.138(3) Å of 0.069 Å with respect to the average bond distance Fe(1)-C(8-11) bond distances of 2.069 Å, and (ii) the strong deviation of the C(6)-C(7)-O(1) bond angle from 120° to 114.5(3)°. These features are probably a consequence of an intramolecular N(1)-H× × × O(1) hydrogen bonding, with a N···O separation of ca. 2.627(4) Å.

Finally, in view of its solid-state structure, it is noteworthy the coordinated and free phenyl rings of [11]+ shows a rather good coplanarity with a dihedral angle between the two phenyl rings of 15.60(25)°. This slight deviation is presumably due to steric hidrance generated by the special close proximity of the benzylic hydrogen and the methyl imine substituent.5a) This nearly coplanar arrangement is important for an efficient p -electron delocalization along the entire hydrazone backbone, and thus might ensure a large molecular nonlinearity in the crystalline solid.3h) This contrasts with the almost thrice greater rotations of the N-methylpyrid-4-yl group by 43.2° out of the coordinated phenyl ring plane in [(h 5-Cp)Fe(h 6-C6H5-N=C5H4NMe)]+.8)

CONCLUDING REMARKS

Utilizing a facile synthetic procedure, we have prepared, under mild conditions, a new homogeneous family of twelve organometallic ketone-hydrazones which can be described as Type I non-rod-shaped dipolar chromophores. One of these hydrazones, [11]+PF6- (R,R’=MeO,Me), was crystallographically characterized by X-ray diffraction analysis, that shows a favourable molecular structure allowing the charge transfer process to extend from the donor to the acceptor termini, and CV studies clearly evidenced the electron releasing effects of the para-R’ substituent of the ketone fragment, =C(Me)-C6H4-p-R’, on the observed reduction potentials of the electron acceptor mixed sandwich for complexes [5-7]+PF6-. Considering the remarkable ONL properties exhibited by classical hydrazones3), it seems probably that the coordination of the electron acceptor [(h 5-Cp)Fe]+ group to hydrazone ligands, o-R-C6H4-NHN=C(Me)-C6H4-p-R’, will be, at least, equivalent to the electron-withdrawing effect of two nitro groups and, consequently, could contribute to the improvement of their ONL responses. Further work will be directed towards the characterization of the second order polarisability b of some selected species of these new class of organometallic hydrazone complexes.

EXPERIMENTAL

General

All manipulations were carried out by using standard Schlenk techniques under an atmosphere of nitrogen with protection of light. Solvents were dried and purified by distillation from standard drying agents prior to use. Microanalyses were obtained on a Perkin-Elmer Model 2400 elemental analyser, and by the Institut de Chimie de Rennes, Microanalysis Service on a Thermo-Finigan Flash EA 1112 CHNS analyzer. IR spectra were obtained as KBr disks on a Perkin Elmer Model 1600 FT-IR spectrophotometer. Electronic spectra were recorded in CH2Cl2 and DMSO solutions with a Spectronic, Genesys 2, spectrophotometer. All the 1H NMR spectra were recorded in acetone-d6 on a multinuclear Bruker DPX 200 spectrometer (200 MHz) at 297K, and all chemical shifts are reported in ppm versus Me4Si (TMS). Mass spectra were recorded at the Centre Régional de Mesures Physiques de l'Ouest (C.R.M.P.O.), Rennes, in a high-resolution ZabSpec TOF VG Analytical spectrometer operating in the LSIMS+ mode. Ions were produced with the standard Cs+ gun at ca. 8 kV, polyethyleneglycol (PEG) was used as internal reference and 3-nitrobenzyl alcohol (NBA) was used as the matrix. All mass measurements refer to peaks for the most common isotopes (1H, 12C, 14N, 16O, 35Cl, 56Fe). 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 and platinum wire auxiliary electrodes and a Ag/AgCl as reference electrode. Acetonitrile solutions were 1.0 mM in the compound under study and 0.1 M in the supporting electrolyte n-Bu4N+PF6-. Melting points were determined in evacuated capillaries and were not corrected. Reagents were obtained as follows: 4-methyl-, 4-methoxo-, and 4-N,N-dimethyl-acetophenone, were purchased from commercial sources and used as received. The hydrazine complexes [(h 5-Cp)Fe(h 6-C6H5)-NHNH2]+PF6-, [1]+PF6- and [(h 5-Cp)Fe(h 6-o-ClC6H4)-NHNH2]+PF6-, [4]+PF6-, were synthesized according to the procedures described elsewhere15) starting from [(h 5-Cp)Fe(h 6-C6H5Cl)]+PF6- 16) and [(h 5-Cp)Fe(h 6-o-Cl2C6H4)]+PF6- 17). Likewise, the hydrazine complexes [(h 5-Cp)Fe(h 6-o-MeC6H4)-NHNH2]+PF6-, [2]+PF6- and [(h 5-Cp)Fe(h 6-o-MeOC6H4)-NHNH2]+PF6-, [3]+PF6-, were prepared according to our previously published procedure4).

Preparation of complexes

[(h 5-Cp)Fe(h 6-C6H5)-NHN=CMe-C6H4-p-Me]+PF6- , [5]+PF6-.

100 mg (0.267 mmol) of [(h 5-Cp)Fe(h 6-C6H5)-NHNH2]+PF6- and 0.030 ml (0.254 mmol) of p-MeC6H4COMe were dissolved in 5.0 ml of EtOH containing 5 drops of glacial acetic acid and refluxed for 4.5 h. The solution was allowed to stand at room temperature and then at -25°C overnight. The orange crystalline solid formed was filtered off and washed with cold EtOH and then with Et2O. Finally, the complex was recrystallized from MeCN:Et2O 1:1. Yield: 103 mg (79% yield). Mp 184ºC, (dec.). C20H21F6FeN2P: calcd C, 49.00; H, 4.32; found C, 48.79; H, 4.19 UV-vis (CH2Cl2): l max (log e )=244(4.32); 292(4.19); 314(4.20); 412(3.22); (DMSO): l max (log e )=320(3.98); 371(4.24); 430(3.58). IR (KBr): 3352 cm-1(m), n (NH); 3103(w), n (CH); 2918(vw), 2861(vw), n (CH); 1556(s), n (C=N); 836(vs), n (PF6) and 557(s), d (P-F). 1H NMR (200 MHz, acetone-d6) d 2.45 (bs, 6H, 2CH3); 5.13 (s, 5H, C5H5); 6.25 (t, 1H, coord-Ph, JH-H=6.0 Hz); 6.41 (pseudo-t, 2H, coord-Ph); 6.61 (d, 2H, coord-Ph, JH-H=6.7 Hz); 7.35 (d, 2H, Ph, JH-H=8.2 Hz); 7.82 (d, 2H, Ph, JH-H=8.3 Hz); 9.18 (s, 1H, NH). Epc = -1.48 V; Epa = 1.26 V, scan rate 100 mVs-1.

[(h 5-Cp)Fe(h 6-C6H5)-NHN=CMe-C6H4-p-OMe]+PF6- , [6]+PF6-.

A mixture of 66.2 mg (0.177 mmol) of [(h 5-Cp)Fe(h 6-C6H5)-NHNH2)]+PF6- and 26.1 mg (0.174 mmol) of p-MeOC6H4COMe in 5.0 ml of EtOH containing 5 drops of glacial acetic acid was refluxed for 3.5 h. The solution was allowed to stand at room temperature and then at -25°C. Standard work up provided 65 mg (74% yield) of a yellow microcrystalline solid which was recrystallised from MeCN by slow diffusion of Et2O at room temperature. Mp 205ºC, (dec.). C20H21F6FeN2OP: calcd C, 47.50; H, 4.18; found C, 47.62; H, 4.24. UV-vis (CH2Cl2): l max (log e )=249(4.28); 294(4.22); 318(4.23); 411(3.31) (DMSO): l max (log e )=297(3.57); 323(3.61); 403(2.72). IR (KBr): 3344 cm-1(m), n (NH); 3344(m), n (NH); 3118(vw), 3096(vw), n (CH); 2966(vw), 2941(vw), 2932(w), 2834(w), n (CH); 1560(s), n (C=N); 1250(m), n (OCH3); 842(vs), 828(vs), n (PF6) and 557(s), d (P-F). 1H NMR (200 MHz, acetone-d6) d 2.41 (s, 3H, CH3); 3.91 (s, 3H, OCH3); 5.10 (s, 5H, C5H5); 6.22 (t, 1H, coord-Ph, JH-H=5.8 Hz); 6.38 (t, 2H, coord-Ph, JH-H=6.3 Hz); 6.56 (pseudo-t, 2H, coord-Ph); 7.06 (d, 2H, Ph , JH-H= 8.9 Hz); 7.96 (d, 2H, Ph, JH-H= 8.9 Hz); 9.13 (s, 1H, NH). Epc = -1.50 V; Epa = 1.50 V, scan rate 100 mVs-1.

[(h 5-Cp)Fe(h 6-C6H5)-NHN=CMe-C6H4-p-NMe2]+PF6- , [7]+PF6-.

To a solution of 77.1 mg (0.206 mmol) of [(h 5-Cp)Fe(h 6-C6H5)-NHNH2)]+PF6- in 5.0 ml of EtOH are added 34.0 mg (0.208 mmol) of p-Me2NC6H4COMe and 5 drops of glacial acetic acid. The solution was refluxed for 4.5 h at room temperature and then at -25°C overnight. Standard work up provided 55 mg (51% yield) of an orange microcrystalline solid which was recrystallised from MeCN by slow diffusion of Et2O at room temperature. Mp 163ºC, (dec.). C21H24F6FeN3P: calcd C, 48.60; H, 4.66; found C, 47.89; H, 4.57. UV-vis (CH2Cl2): l max (log e )=241(4.30); 263(4.19); 325(4.33); 343(4.37); 413(3.66); (DMSO): l max (log e )=268(4.17); 347(3.60); 427(3.66). IR (KBr): 3353 cm-1(m), n (NH); 3109(vw), 3080(vw), n (CH); 2972(vw), 2926(vw), 2861(vw), 2822(vw), n (CH); 1560(s), 1526(m), n (C=N); 842(vs), 831(vs), n (PF6) and 558(s), d (P-F). 1H NMR (200 MHz, acetone-d6) d 2.32 (s, 3H, CH3); 3.01 (s, 6H, N(CH3)2); 5.04 (s, 5H, C5H5); 6.15 (pseudo-t, 1H, coord-Ph); 6.30 (t, 2H, coord-Ph, JH-H=6.0 Hz); 6.48 (d, 2H, coord-Ph, JH-H=5.7 Hz); 6.80 (d, 2H, Ph, JH-H=6.0 Hz); 7.88 (d, 2H, Ph, JH-H=5.7 Hz); 8.98 (s, 1H, NH). Epc = -1.52 V; Epa = 0.69 ;1.50 V, scan rate 100 mVs-1.

[(h 5-Cp)Fe(h 6-o-MeC6H4)-NHN=CMe-C6H4-p-Me]+PF6- , [8]+PF6-.

100 mg (0.258 mmol) of [(h 5-Cp)Fe(h 6-o-MeC6H4)-NHNH2)]+PF6- and 0.03 ml (0.254 mmol) of p-MeC6H4COMe were dissolved in 5.0 ml of EtOH containing 5 drops of glacial acetic acid and refluxed for 4 h. The solution was allowed to stand at room temperature and then at -25°C overnight. Standard work up provided 94 mg (72% yield) of an orange microcrystalline solid which was recrystallised from CH2Cl2 by slow diffusion of Et2O at room temperature. Mp 200ºC, (dec.). C21H23F6 FeN2P: calcd C, 50.02; H, 4.59; found C, 49.58; H, 4.48. UV-vis (CH2Cl2): l max (log e )=245(4.25); 295(4.14); 309(4.15); 412(3.06); (DMSO): l max (log e )=319(4.20); 344(4.11); 402(3.28). IR (KBr): 3392 cm-1(m), n (NH); 3104(w), 3032(vw), n (CH) arom; 2919(vw), 2864(vw), n (CH) aliph; 1548(s), n (C=N); 831(vs), n (PF6) and 557(s), d (P-F). 1H NMR (200 MHz, acetone-d6) d 2.38 (s, 3H, CH3); 2.44 (s, 3H, CH3); 2.64 (s, 3H, CH3); 4.99 (s, 5H, C5H5); 6.09 (t, 1H, coord-Ph, JH-H=6.0 Hz); 6.29 (t, 2H, coord-Ph, JH-H=5.8 Hz); 6.85 (d, 1H, coord-Ph, JH-H=6.9 Hz); 7.28 (d, 2H, Ph, JH-H=8.1 Hz); 7.87 (d, 2H, Ph, JH-H=8.1 Hz); 8,14 (s, 1H, NH).

[(h 5-Cp)Fe(h 6-o-MeC6H4)-NHN=CMe-C6H4-p-OMe]+PF6- , [9]+PF6-.

A mixture of 50.4 mg (0.130 mmol) of [(h 5-Cp)Fe(h 6-o-MeC6H4)-NHNH2)]+PF6- and 20.5 mg (0.137 mmol) of p-MeOC6H4COMe in 5.0 ml of EtOH containing 5 drops of glacial acetic acid was refluxed for 3.5 h. The solution was allowed to stand at room temperature and then at -25°C overnight. Standard work up provided 34 mg (50% yield) of a red-orange microcrystalline solid which was recrystallised from MeCN by slow diffusion of Et2O at room temperature. Mp 185ºC, (dec.). UV-vis (CH2Cl2): l max (log e )=248(4.22); 293(4.16); 315(4.16); 412(3.16); (DMSO): l max (log e )=291(4.01); 321(4.06); 415(3.10). IR (KBr): 3386 cm-1(w), n (NH); 3112(vw), 3085(vw), n (CH); 3009(vw), 2965(vw), 2938(vw), 2845(w), n (CH); 1545(s), n (C=N); 1272(s), n (OCH3); 837(vs), n (PF6) and 559(s), d (P-F). 1H NMR (200 MHz, acetone-d6) d 2.43 (s, 3H, CH3); 2.63 (s, 3H, CH3); 3.87 (s, 3H, OCH3); 4.99 (s, 5H, C5H5); 6.09 (s, 1H, coord-Ph); 6.29 (s, 2H, coord-Ph); 6.83 (s, 1H, coord-Ph); 7.02 (d, 2H, Ph, JH-H=6.1 Hz); 7.94 (d, 2H, Ph, JH-H=6.1 Hz); 8.09 (s, 1H, NH). MS (positive Cs-FAB, m-nitrobenzylic alcohol) : calcd m/z for C21H23FeN2O, C+, 375.1160 ; obsd, 375.1157.

[(h 5-Cp)Fe(h 6-o-MeC6H4)-NHN=CMe-C6H4-p-NMe2]+PF6- , [10]+PF6-.

To a solution of 52.0 mg (0.127 mmol) of [(h 5-Cp)Fe(h 6-o-MeC6H4)-NHNH2)]+PF6- in 5.0 ml of EtOH was added 21.3 mg (0.130 mmol) of p-Me2NC6H4COMe were dissolved and 5 drops of glacial acetic acid. The solution was refluxed for 4.5 h and allowed to stand at room temperature and then at -25°C overnight. Standard work up provided 38 mg (56% yield) of a yellow-orange microcrystalline solid which was recrystallised from CH2Cl2 by slow diffusion of Et2O at room temperature. Mp 159ºC, (dec.). UV-vis (CH2Cl2): l max (log e )=241(4.26); 265(4.12), 320(4.24); 346(4.31), 417(3.68); (DMSO): l max (log e )= 324(4.25), 354(4.35); 433(3.64). IR (KBr): 3388 cm-1(w), n (NH); 3111(w), n (CH); 2890(vw), 2855(vw), 2861(vw), 2806(vw), n (CH); 1545(s), 1525(m), n (C=N); 840(vs), n (PF6) and 557(s), d (P-F). 1H NMR (200 MHz, acetone-d6) d 2.46 (s, 3H, CH3); 2.52 (s, 3H, CH3) ; 2.96 (s, 6H, N(CH3)2); 5.07 (s, 5H, C5H5); 6.17 (pseudo-t, 1H, coord-Ph); 6.37 (pseudo-t, 2H, coord-Ph); 6.93 (d, 1H, coord-Ph, JH-H=6.5 Hz); 7.36 (d, 2H, Ph, JH-H=7.8 Hz); 7.95 (d, 2H, Ph, JH-H=8.1 Hz); 8.22 (s, 1H, NH). MS (positive Cs-FAB, m-nitrobenzylic alcohol) : calcd m/z for C22H26FeN3, C+, 388.1476 ; obsd, 388.1479.

[(h 5-Cp)Fe(h 6-o-MeOC6H4)-NHN=CMe-C6H4-p-Me]+PF6- , [11]+PF6-.

100 mg (0.247 mmol) of [(h 5-Cp)Fe(h 6-o-MeOC6H4)-NHNH2)]+PF6- and 0.030 ml (0.254 mmol) of p-MeC6H4COMe were dissolved in 5.0 ml of EtOH containing 5 drops of glacial acetic acid and refluxed for 4.5 h. The solution was allowed to stand at room temperature and then at -25°C overnight. Standard work up provided 99 mg (77% yield) of an orange microcrystalline solid which was recrystallised from CH2Cl2 by slow diffusion of Et2O at room temperature. Mp 197ºC, (dec.). UV-vis (CH2Cl2): l max (log e )=243(4.33); 285(4.11); 317(4.20); 420(3.16); (DMSO): l max (log e )=284(4.04); 322(4.18); 418(3.15). IR (KBr): 3350 cm-1(m), n (NH); 3100(w), 3098(vw), n (CH); 2980(vw), 2863(vw), n (CH); 1557(s), n (C=N); 1276(s), n (CH3O); 839(vs), n (PF6) and 558(s), d (P-F). 1H NMR (200 MHz, acetone-d6) d 2.38 (s, 3H, CH3); 2.42 (s, 3H, CH3); 4.21 (s, 3H, OCH3); 5.02 (s, 5H, C5H5); 6.01-6.12 (m, 2H, coord-Ph); 6.49 (d, 1H, coord-Ph, JH-H=7.4 Hz); 6.86 (d, 1H, coord-Ph, JH-H=7.4 Hz); 7.29 (d, 2H, Ph, JH-H=7.9 Hz); 7.88 (d, 2H, Ph, JH-H=8.2 Hz); 8.27 (s, 1H, NH). MS (positive Cs-FAB, m-nitrobenzylic alcohol) : calcd m/z for C21H 23FeN2O, C+, 375.1160 ; obsd, 375.1159.

[(h 5-Cp)Fe(h 6-o-MeOC6H4)-NHN=CMe-C6H4-p-OMe]+PF6- , [12]+PF6-.

A mixture of 52.1 mg (0.129 mmol) of [(h 5-Cp)Fe(h 6-o-MeOC6H4)-NHNH2]+PF6- and 19.3 mg (0.129 mmol) of p-MeOC6H4COMe in 5.0 ml of EtOH containing 5 drops glacial acetic acid was refluxed for 3 h. The solution was allowed to stand at room temperature and then at -25°C overnight. Standard work up provided 32 mg (46% yield) of a red-yellow microcrystalline solid which was recrystallised from CH2Cl2 by slow difusión of Et2O at room temperature. Mp 194ºC, (dec.). UV-vis (CH2Cl2): l max (log e )=248(4.35); 289(4.21); 322(4.30); 419(3.32); (DMSO): l max (log e )=291(4.11); 325(4.22); 412(3.23). IR (KBr): 3362 cm-1(m), n (NH); 3114(vw), 3009(w), n (CH); 3004(w), 2956(w), 2839(w), n (CH); 1558(m), n (C=N); 1275(s), n (OCH3); 831(vs), n (PF6) and 557(s), d (P-F). 1H NMR (200 MHz, acetone-d6) d 2.47 (s, 3H, CH3); 3.94 (s, 3H, OCH3); 4.28 (s, 3H, OCH3); 5.08 (s, 5H, C5H5); 6.11 (pseudo-t, 2H, coord-Ph) ; 6.49 (pseudo-t, 1H, coord-Ph) ; 6.77 (pseudo-t, 1H, coord-Ph) ; 7.10 (d, 2H, Ph, JH-H=8.7 Hz); 8.03 (d, 2H, Ph, JH-H=8.6 Hz); 8.29 (s, 1H, NH). MS (positive Cs-FAB, m-nitrobenzylic alcohol) : calcd m/z for C21H23FeN2O2, C+, 391.1109 ; obsd, 391.1118.

[(h 5-Cp)Fe(h 6-o-MeOC6H4)-NHN=CMe-C6H4-p-NMe2]+PF6- , [13]+PF6-.

To a solution of 75.1 mg (0.186 mmol) of [(h 5-Cp)Fe(h 6-o-MeOC6H4)-NHNH2)]+PF6- in 5.0 ml of EtOH was added 30.2 mg (0.185 mmol) of p-Me2NC6H4COMe and 5 drops of glacial acetic acid. The solution was refluxed for 4.5 h and allowed to stand at room temperature and then at -25°C overnight. Standard work up provided 55 mg (54% yield) of an orange microcrystalline solid which was recrystallised from CH2Cl2 by slow diffusion of Et2O at room temperature. Mp 158ºC, (dec.). UV-vis (CH2Cl2): l max (log e )=243(4.26); 269(4.00); 314(4.06); 349(4.17); 425(3.51); (DMSO): l max (log e )= 308 (4.17), 350(4.32), 432(3.52). IR (KBr): 3364 cm-1(w), n (NH); 3091(w), n (CH); 2956(vw), 2889(vw), 2854(vw), 2801(vw), n (CH); 1562(m), n (C=N); 1271(m), n (CH3O); 841(vs), n (PF6) and 558(s), d (P-F). 1H NMR (200 MHz, acetone-d6) d 2.37 (s, 3H, CH3); 3.03 (s, 6H, N(CH3)2); 4.20 (s, 3H, CH3O); 5.00 (s, 5H, C5H5); 6.00-6.05 (m, 2H, coord-Ph); 6.45 (d, 1H, coord-Ph, JH-H=5.6 Hz); 6.80 (s, 2H, Ph); 6.81 (s, 1H, coord-Ph); 7.86 (d, 2H, Ph, JH-H=8.1 Hz); 8.11 (s, 1H, NH). MS (positive Cs-FAB, m-nitrobenzylic alcohol) : calcd m/z for C22H26FeN3O, C+, 404.1425 ; obsd, 404.1433.

[(h 5-Cp)Fe(h 6-o-ClC6H4)-NHN=CMe-C6H4-p-Me]+PF6- , [14]+PF6-.

100 mg (0.244 mmol) of [(h 5-Cp)Fe(h 6-o-ClC6H4)-NHNH2]+PF6- and 0.03 ml (0.254 mmol) of p-MeC6H4COMe were dissolved in 5.0 ml of EtOH containing 5 drops of glacial acetic acid and refluxed for 6 h. The solution was allowed to stand at room temperature and then at -25°C overnight. Standard work up provided 74 mg (58% yield) of an orange microcrystalline solid which was recrystallised from CH2Cl2 by slow diffusion of Et2O at room temperature. Mp 215ºC, (dec.). UV-vis (CH2Cl2): l max (log e )=247(4.20); 297(4.08); 309(4.07); 412(3.05); (DMSO): l max (log e )=315(4.04); 404(3.19). IR (KBr): 3361 cm-1(m), n (NH); 3106(w), 3031(vw), n (CH); 2917(vw), 2857(vw), n (CH); 1552(s), n (C=N); 1126(m), n (C-Cl); 829(vs), n (PF6) and 557(s), d (P-F). 1H NMR (200 MHz, acetone-d6) d 2.39 (s, 3H, CH3); 2.48 (s, 3H, CH3); 5.15 (s, 5H, C5H5); 6.28 (pseudo-t, 1H, coord-Ph); 6.39 (t, 1H, coord-Ph, JH-H=6.0 Hz); 6.77 (d, 1H, coord-Ph, JH-H=5.7 Hz); 7.04 (d, 1H, coord-Ph, JH-H=6.6 Hz); 7.30 (d, 2H, Ph, JH-H=7.9 Hz); 7.90 (d, 2H, Ph, JH-H=8.0 Hz); 8,45 (s, 1H, NH). MS (positive Cs-FAB, m-nitrobenzylic alcohol) : calcd m/z for C20H20ClFeN2, C+, 379.0664 ; obsd, 379.0664.

[(h 5-Cp)Fe(h 6-o-ClC6H4)-NHN=CMe-C6H4-p-OMe]+PF6- , [15]+PF6-.

A mixture of 96.4 mg (0.235 mmol) of [(h 5-Cp)Fe(h 6-o-ClC6H4)-NHNH2]+PF6- and 35.8 mg (0.238 mmol) of p-MeOC6H4COMe in 5.0 ml of EtOH containing 5 drops of glacial acetic acid was refluxed for 4 h. The solution was allowed to stand at room temperature and then at -25°C overnight. Standard work up provided 70 mg (55% yield) of a yellow-red microcrystalline solid which was recrystallised from CH2Cl2 by slow diffusion of Et2O at room temperature. Mp 163ºC, (dec.). C20H20ClF6FeN2OP: calcd C, 44,43; H, 3.73; found C, 44.34; H, 3.64. UV-vis (CH2Cl2): l max (log e )=247(4.44); 295(4.31); 308(4.30); 410(3.32); (DMSO): l max (log e )=298(3.35); 324(3.39); 441(2.38). IR (KBr): 3338 cm-1(w), n (NH); 3096(w), n (CH); 2998(vw), 2965(vw), 2937(w), 2839(w), n (CH); 1564(s), n (C=N); 1251(s), n (OCH3); 842(vs), 829(vs), n (PF6) and 558(s), d (P-F). 1H NMR (200 MHz, acetone-d6) d 2.48 (s, 3H, CH3); 3.88 (s, 3H, OCH3); 5.15 (s, 5H, C5H5); 6.36 (pseudo-t, 1H, coord-Ph); 6.47 (pseudo-t, 1H, coord-Ph); 6.84 (d, 1H, coord-Ph, JH-H=6.2 Hz); 7.11 (d, 2H, Ph, JH-H=9.1 Hz); 7.12 (s, 1H, coord-Ph) ; 8,06 (d, 2H, Ph, JH-H=8.9 Hz); 8,45 (s, 1H, NH).

[(h 5-Cp)Fe(h 6-o-ClC6H4)-NHN=CMe-C6H4-p-NMe2]+PF6- , [16]+PF6-.

To a solution of 70.3 mg (0.172 mmol) of [(h 5-Cp)Fe(h 6-o-ClC6H4NHNH2)]+PF6- in 5.0 ml of EtOH are added 28.0 mg (0.172 mmol) of p-Me2NC6H4COMe and 5 drops of glacial acetic acid. The solution was refluxed for 3.5 h, allowed to stand at room temperature and then at -25°C overnight. Standard work up provided 53 mg (56% yield) of an orange microcrystalline solid which was recrystallised from MeCN by slow diffusion of Et2O at room temperature. Mp 160ºC. C21H23ClF6FeN3P: calcd C,45.55; H, 4.18; found C, 45.42; H, 4.12. UV-vis (CH2Cl2): l max (log e )=244(4.30); 268(4.08), 317(4.15); 369(4.57), 435(3.83); (DMSO): l max (log e )= 320(4.20), 346(4.28); 430(3.57). IR (KBr): 3350 cm-1(w), n (NH); 3108(vw), 3086(w), n (CH); 2921(w), 2861(vw), 2818(vw), n (CH); 1544(s), 1528(m), n (C=N); 1196(m), n (C-Cl); 842(vs), 832(vs), n (PF6) and 558(s), d (P-F). 1H NMR (200 MHz, acetone-d6) d 2.45 (s, 3H, CH3); 3.15 (s, 6H, N(CH3)2); 5.05 (s, 5H, C5H5); 6.23 (pseudo-t, 1H, coord-Ph); 6.37 (pseudo-t, 1H, coord-Ph); 6.61 (d, 2H, coord-Ph, JH-H=6.8 Hz); 7.02 (d, 2H, Ph, JH-H=8.5 Hz); 7.70 (d, 2H, Ph, JH-H=8.5 Hz); 9.05 (s, 1H, NH).

Crystallographic data of [11]+PF6-:

Suitable single crystals for X-ray diffraction studies were grown by slow diffusion of Et2O into a concentrated MeCN solution of [11]+PF6- (R,R’=MeO,Me) at room temperature. A red prism of this complex was mounted on a glass fiber in a random orientation. Data collection was performed at room temperature on a Siemens Smart CCD diffractometer using graphite monochromated Mo-Ka radiation (l =0.71073 Å) with a nominal crystal-to-detector distance of 4.0 cm. A hemisphere of data was collected on the basis of three w -scan runs (starting w = -28°) at values j =0, 90, 180°, with the detector at 2q =28°. In each of these runs, frames (606, 435, 230, respectively) were collected at 0.3° interval and for 30 s per frame. Space group assignements are based on systematic absences, E statistics and successful refinement of the structure. Structure was solved by direct methods with the aid of successful difference Fourier maps and were refined using the SHELXTL 5.1 software package.18) All non-hydrogen were refined anisotropically. Hydrogen atoms were assigned to ideal positions and refined using a riding model. The diffraction frames were integrated using the SAINT19) package and corrected for absorption with SADABS.20)

Crystal data and refinement: C21H23F6FeN2OP, Mr=520.23, unit cell dimensions: a=11.302(3), b=19.767(5), c=11.317(3) Å, b =119.191(5)°, V=2207.1(9) Å 3, monoclinic, P21/c, Z=4, crystal size (mm) : 0.29x0.22x0.19, q range 2.06 to 24.71° at 293(2) K, reflections collected 11986, independent reflections 3766 (Rint=0.0191). Convergence at conventional R1=0.0477, wR2=0.1377 (I>2s (I)). GOF= 1.051.

SUPPLEMENTARY MATERIAL

Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC Nº 186156 for compound [11]+PF6-. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK. Fax: +44-1223-336-033; E-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk.

ACKNOWLEDGEMENTS

The authors thank Drs. P. Jehan and P. Guénot (C.R.M.P.O., Rennes) for mass spectrometry assistance. We greatly appreciate financial support for this work received from the Fondo Nacional de Desarrollo Científico y Tecnológico, FONDECYT, Grant N° 1000281 (C. M.), the Programme International de Coopération Scientifique, CNRS-CONICYT, PICS Nº 922, 2000-02, (D. C., C. M., J.-R. H.) and the Vice-Rectoría de Investigación y Estudios Avanzados, Universidad Católica de Valparaíso, Chile.

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b) Marcen, S., Jiménez, M. V., Dobrinovich, I. T., Lahoz, F. J., Oro, L. A., Ruiz, J., Astruc, D., Organometallics, 21, 326 (2002).         [ Links ]
c) See also references 4b and 8.

For a reference gathering a large number of interatomic and metal-ligand distances obtained from the Cambridge Crystallographic Data Base Centre, see:
13.Orpen, A. G., Brammer, L., Allen, F. H., Kennard, D., Watson, D. G., Taylor, R., J. Chem. Soc., Dalton Trans., S1 (1989). More than 50 X-ray crystal structures of [(h 5-C5H5)Fe(h 6-arene)]+ derivatives can be found in this data base system.        [ Links ]

14. Ruiz, J., Ogliaro, F., Saillard, J.-Y., Halet, J.-F., Varret, F., Astruc, D., J. Am. Chem. Soc., 120, 11693 (1998).        [ Links ]

15. a) Neto, A. F., Miller, J., An. Acad. Brasil. Cienc., 54, 331 (1982).         [ Links ]
b) Lee, C. C., Abd-El-Aziz, A. S., Chowdhury, R. L., Gill, U. S., Piórko, A., Sutherland, R. G., J. Organomet. Chem., 315, 79 (1986).        [ Links ]

16. Nesmeyanov, A. N., Vol'kenau, N. A., Bolesova, I. N., Dokl. Akad. Nauk. SSSR, 166, 607 (1966).        [ Links ]

17. Khand, I. U., Pauson, P. L., Watts, W. E., J. Chem. Soc. C, 2261 (1968).        [ Links ]

18. Sheldrick, G. M., SHELXTL version 5.1, Bruker AXS, Inc., Madison, WI, 1997.        [ Links ]

19. Bruker Analytical X-Ray Systems, SAINT, version 5.0, Madison, WI, 1998.        [ Links ]

20. Sheldrick, G. M., SADABS Empirical Absorption Program, University of Göttingen, Göttingen, Germany, 1996.        [ Links ]

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