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Journal of the Chilean Chemical Society

versão On-line ISSN 0717-9707

J. Chil. Chem. Soc. v.49 n.3 Concepción set. 2004

http://dx.doi.org/10.4067/S0717-97072004000300002 

 

J. Chil. Chem. Soc., 49, N 3 (2004): 205-207

A ONE STEP FUNCTIONALIZATION, COORDINATION OF N3P3Cl6 USING [CpFe(dppe)SC6H4OH]+

 

1C. Díaz,* 2E. Spodine, 3Y. Moreno and 1E. Carrasco

1 Departamento de Química, Facultad de Ciencias, Universidad de Chile, Santiago. Chile.
2 Departamento de Química Inorgánica y Analítica Facultad de Ciencias Químicas y Farmacéuticas Universidad de Chile,Santiago Chile and Centro para la Investigación Interdisciplinaria Avanzada en Ciencias de los Materiales (CIMAT).
3Facultad de Ciencias Químicas, Departamento de Química Analítica e Inorgánica, Universidad de Concepción, Concepción, Chile. E-mail: cdiaz@abello.dic.uchile.cl

(Received: August 6, 2003 - Accepted: Mach 15, 2004)


ABSTRACT

The new iron-thiolate complex [CpFe(dppe)SC6H4OH]PF6 (1), prepared by the oxidative addition of CpFe(dppe)I (2) to HSC6H4OH (3), reacts in one step with N3P3Cl6 (4) in acetone to give the hexanuclear iron-triolate complex N3P3[CpFe(dppe)SC6 H4O]6 (5), the first cyclotriphosphazene containing thiolate groups coordinated to a metal. Electrochemical data suggest the absence of electronic communication between the iron centers. Magnetic properties for the new complexes are discussed.

Keywords: cyclophosphazenes; iron-thiolates; magnetic properties; sulphur ligands.


 

INTRODUCTION

Usually the formation of organometallic derivatives of functionalized cyclophosphazenes with donor atoms involves two steps: the preparation of the organocyclophosphazenes and their reaction with the organometallic [1,2].

As recently reported, the reaction of N3P3(OC6H5 )6-nCln derivatives with W(CO)5PPh2C6H 4OH affords the complexes N3P3(OC6H5 )6-n{OC6H4PPh 2W(CO)5}n [3]. On the other hand, using the previously known selective cleavage of the SH bond in thiolates by CpFe(dppe)I to give the iron (III)-thiolate complexes [4,5],

MeOH

CpFe(dppe)I + HSR →[CpFe(dppe)SR]PF6 (1)

NH4PF6 (1)

we have prepared the respective paramagnetic complex (1) by reaction of CpFe(dppe)I and HSC6H4OH. Complex (1) is a useful precursor for the preparation of the macromolecule N3P3[CpFe(dppe)SC6 H4O]6, to our knowledge the first cyclotriphosphazene containing thiolate groups coordinated to a metal.

EXPERIMENTAL

Materials

The starting precursors N3P3Cl6 and HOC6H4SH were purchased from Aldrich and used as received. CpFe(dppe)I was prepared as reported previously [4,5]. Acetone, diethylether, dichloromethane and n-hexane were dried and purified using standard procedures. All the reactions were carried out under dry nitrogen.

INSTRUMENTS

IR spectra were recorded on a Perkin-Elmer 2000 spectrophotometer. (wavenumbers are in cm-1 ). NMR spectra were recorded on a Bruker AMX-300 instrument; 1H are given in δ relative to TMS and 31P{1H} NMR are given in d relative to external 85% aqueous H3PO4. (Coupling constants are in Hz).

Cyclic voltammetry data were obtained on a Bio Analytical Systems BAS-5O B automated digital potentiostat with a vitreous carbon working electrode, a Pt wire auxiliary electrode and an Ag/AgCl reference electrode.

An approximately 10-3 M solution of the sample in CH2Cl2 with 0.1 M [n-Bu4][PF6] as the electrolyte was used. Ferrocene was added as an internal standard at the end of each experiment. Reported data were converted to one scale of an aqueous saturated calomel electrode (SCE) by addition of 0.4 V to the ferrocene/ferroceniun couple. The electrodes were polished by hand on micro-cloth with diamond paste.

Synthesis of [CpFe(dppe)SC6H4OH]PF6. (1). Cp(dppe)FeI 0.29 g (0.45 mmol) and HOC6H4SH 0.057g (0.45 mmol) in the presence of NH4PF6 0.1g (0.61 mmol) in CH3OH (30 ml) were stirred for 14 h at room temperature. The solvent was evaporated under vacuum and the black solid residue was extracted with dichloromethane (15 ml). Upon addition of a 1:1 mixture of n-hexane-diethyl ether, black microcrystals precipitated, which were washed several times with diethyl ether and dried under reduced pressure. Yield 0.3g, 84%. Anal. found: C 55.74, H 4.47. Calc. for C37H34F6OSP3 Fe, C 55.29, H 4.31. IR (KBr pellets) nOH 3222 ,1504,1500 ,1250,1090; d(CH)ip C5H5; n(PF6) 830; 742, d(CH)op C6H5 692, 524

Synthesis of N3P3[OC6H4 SFe(dppe)(Cp)]6 (5). [CpFe(dppe)SC6H4OH]PF 6 ( 046g, 0.58 mmol) and N3P3Cl6 (0,034 g, 0.09 mmol) in the presence of K2CO3 (0.1 g 0.7337 mmol) in acetone (40 ml) were stirred for 1.5 h. at room temperature. The solvent was evaporated under vacuum and the brown-dark solid residue was extracted with dichloromethane (15 ml). Upon addition of a 1:1 mixture of n-hexane-diethyl ether a brown-dark powder precipitated which was washed several times with diethyl ether and dried under reduced pressure. Yield ca. 60%. Anal. found: C 62.43, H 5.6, N 0.81, S 3.16. Calc. for C222H198O6N3 S6P15Fe6 5CH2Cl2 :C 61.68, H 4.71, N 0.97. S 4.3. IR (KBr pellets) 1720,1579,1270 n(PO-C) ,1236,1165 n(PN), 1120 n(P-OC) ,1096 δ(CH)ip,C5H5, 997, 832, 740, 693 δ(CH)op ,C6H5P, 574, 528. 1NMR (acetone-d6) δ ppm. 8.2-6.8 (several multiplets, C6H5, C6H4), 5.7(CH2Cl2) 4.25 (s,C5H5), 2.97(s,CH2P) 13C{H}(acetone-d6)139.79, 128.89, 117.08, 116.48, SC6H4O.135.14, 134,13, 132.4, 130.13, 129.64. C6H5P, 51 (CH2Cl2) 76.89 C5H5 24.47 CH2. 31P{H}(acetone-d6) 96.5 (s, 12P), 29.16 (s,3P).

RESULTS AND DISCUSSION

As found for other [CpFe(dppe)SR]PF6 complexes [4-7], compound (1) is paramagnetic. The susceptibilities (cm) were measured in the temperature range 5-300 K. Figure 1 shows the cmT and 1/cmT versus temperature profile, which is indicative of normal paramagnetism [8-10].

Fig. 1.- Temperature dependence of cmT , (Δ) and cm-1 (o) for (1)

The value found for the magnetic moment μ = 2.4 BM, higher than those reported for a d5 low spin configuration, can be due to some spin-orbit contribution as is normally observed for Fe (III) low spin systems [8,9,11]. The general profile of the cmT is thus similar to that obtained for Fe(III)-ferricenium salts, which exhibit an appreciable effect of lower symmetry ligand field distortion [10].

Complex (1) reacts with N3P3Cl6 in acetone under reflux and in the presence of K2CO3 to give the new hexametallic complex N3P3[OC6H4 SFe dppe(Cp)]6 (5), See scheme 1.

The IR spectrum of the complex shows the typical bands of the N3P3 ring [12]; n (P-OC) 1096 cm-1, n (PN) 1165,1236, cm-1 and n(PO-C) at 1270 cm-1, as well as the characteristic absorption bands of the CpFe(dppe) fragments [13]: δ(CH)ip,C5H5, 1096 and δ(CH)op C6H5 693 cm-1. However the n(PF6) band is missing, indicating that the iron (III)-thiolate was probably reduced to iron(II)-thiolate. Magnetic measurements as well as the NMR spectrum are in agreement with this. Consistent with the sample's diamagnetism, the 31P-NMR spectrum exhibits two simple signals, one at 96.48 ppm corresponding to dppe bonded to iron [14-16] and one singlet at 29.16 ppm corresponding to the N3P3 ring. The intensity ratio (12:3) is in agreement with the proposed formula. The 1H-NMR spectrum shows the typical singlet of the C5H5 among the phenyl signals. The 13C-NMR spectrum shows the aromatic signals of the OC6H4S moiety as well as those of the dppe. The signal of C5H5 as normally observed for other CpFe(dppe)X complexes appears at 76.89 ppm [14-16]. The CH2 signal appears in its normal position [14-16]. The presence of CH2Cl2 as solvate in the complex (5) is evidenced by the signal at 5.7 ppm in the 1H-NMR spectra as well as by the signal at 51 ppm in the 13C-NMR spectra.

The UV-visible spectrum of (5) shows an absorption pattern similar to those of CpFe(dppe)X complexes (X = Cl, Br, CN) [17]. The N3P3Cl6 does not absorb in the visible region. A weak absorption band at 500 nm and a shoulder near 400 nm were seen for the complex [5]. In contrast, the UV-visible spectrum of (1) shows an intense absorption around 580 nm, typical of the CpFeIII(dppe)-SR chromophore [4-6]. More significantly, the UV-visible spectrum of (5) is similar to that of reduced 17e complexes [CpFe(dppe)-SR]PF6 [18].Unfortunately, no suitable crystals for an X-ray structure determination were obtained.

Thermogravimetric and differential scanning calorimetry curves of complex (5) show an endothermic weight loss at around 50 C, attributable to the loss of CH2Cl2 as solvate molecules.

Scheme 1: Diagram showing the formulas for the reaction of (1) with N3P3Cl6 to give (5)

Electrochemical Studies.

The electrochemical behavior of iron(III)-thiolate complexes has been studied previously [18]. The redox behavior of these complexes is somewhat complex and the voltammogram of the complex [CpFe(dppe)S-C6H4OH]PF6 (1) as well as that of its hexametalated complex (5), both in CH2Cl2, show similar patterns. Both complexes undergo one-electron redox processes at ­0,361 V and ­0.332 V for (1) and (5), respectively, which can be attributed to the reduction of the Fe(III) metal center:

[CpFeIII(dppe)SR]+ + e → [CpFeII(dppe)SR]. (2)

Additionally, other peaks were observed in the cyclic voltammogram of both complex (1) and complex (5).The assignments of those waves are as follow:

Oxidation values of: E00x = 0.572 V for complex (1) and 0.568 V for complex (5) (irreversible waves) were assigned to the oxidation of the thiolate ligand linked to the iron atom:

[CpFeII(dppe)SC6 H4OH]+→[CpFeII (dppe)solv]++HOC6H4 SSC6H4OH+ e (3)

Consistent with this, the oxidation potential values of E00x = 1.3 V for complex (1) and 1.201 V for complex (5) are asssigned to the oxidation of the free dithiophenol, arising from the process shown in equation 3.

HOC6H4SSC 6H4OH→[HOC6H 4SSC6H4OH]++e (4)

Finally, the reduction of the dithiophenol:

HOC6H4SSC 6H4OH+e → 2HOC6H4S (5)

was observed at E0red = -0.950V for complex (1) and not observed for complex (5). A similar behavior was found for the electrochemical study of [CpFeII(dppe)SR][PF6] complexes [18].

An additional peak seen at 0.072 V and 0.099 V for (1) and (5), respectively, not foundd in the voltammogram of [CpFe(dppe)SR]PF6 complexes [18], was not assigned, but it could possibly be related to the same redox process involving the quinone-hydroquinone redox equilibrium of the thiol ligand, probably the oxidation:

HSC6H4OH→[HSC 6H4=O]. + e (6)

In fact, the free ligand HSC6H4OH undergoes an irreversible oxidation at 0.024 V. More detailed electrochemical experiments to understand this aspect are under way.

The observation of a single oxidation wave in complex (5) centered on the metal suggests a lack of electronic communication in the phosphazene ring, in agreement with recent theoretical studies [19] which indicate that these systems are not aromatic. Thus hexametallates of the [N3P3(OC6H4 CH2CN•FeCl2)6][PF 6]6 type also show a single oxidation wave [20].

The formation of complex (5) as a hexametallic neutral complex involves a reduction of the Fe(III) in the [CpFe(dppe)SC6H4OH)]PF6 thiolate complex to the Fe(II) state in compound (5). The absence of a n(PF6) band in the IR spectrum, the normal resolution of the multinuclear NMR spectrum, the magnetic moment close to zero, and the UV-visible spectrum are in agreement with the reduction process. The corresponding oxidation counterpart probably forms part of a secondary product, a solid which could not be identified, insoluble in all solvents. To the best of our knowledge the hexametallic phosphazene compound (5) is the first cyclophosphazene containing a thiolate group coordinated to a metal. The protection of the thiol group by coordination with the Fe(II) organometallic complex, followed by the reaction with a P-Cl group of the phosphazenic compound through the OH bond, followed by hydrolysis constitutes a convenient route to thio-derivatives of phosphazenes which were unknown until now. Experiments along this line are in course.

ACKNOWLEDGEMENTS

Financial support through Fondecyt (1030515), CIMAT FONDAP (11980002) and DIUC 203.021.018-1 projects is gratefully acknowledged.

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