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Boletín de la Sociedad Chilena de Química

Print version ISSN 0366-1644

Bol. Soc. Chil. Quím. vol.47 no.4 Concepción Dec. 2002

http://dx.doi.org/10.4067/S0366-16442002000400028 

REACTIVITY OF[Mo(NHNPh2)(NNPh2)Br2(acac)]
TOWARD-DI-IMINES.
X-REY CRYSTAL STRUCTURE OF[Mo(NNPh2)2Br2(o-phen)]

CARLOS BUSTOS1, MARCIA MATAMALA1, DAPHNE BOYS2 AND
DAVID CARRILLO3

1Laboratorio de Química Inorgánica, Instituto de Química,
Universidad Austral de Chile, Casilla 567, Valdivia, Chile.
2Departamento de Física, Facultad de Ciencias Físicas y Matemáticas,
Universidad de Chile, Casilla 487-3, Santiago, Chile.
3Laboratorio de Química Inorgánica, Instituto de Química,
Universidad Católica de Valparaíso, Avenida Brasil 2950, Valparaíso, Chile

(Received: October 10, 2001 - Acceptr: October 7, 2002)

ABSTRACT

Complex [Mo(NHNPh2)(NNPh2)Br2(acac)], acac=acetylacetonate, reacts in acetonitrile with 1,10-phenanthroline, o-phen, and 2,2’-bipyridine, bpy, to afford complexes [Mo(NNPh2)2Br2(o-phen)], I, and [Mo(NNPh2)2Br2(bpy)], II. These complexes have been characterized by IR, UV-vis and 1H NMR spectroscopies, and elemental analysis. The structure of complex I was solved by single crystal X-ray diffraction. The metal center has a distorted octahedral environment in which the diphenylhydrazido(2-) ligands occupy mutually cis positions but trans to the nitrogen atoms of the o-phen ligand. The bromo ligands occupy mutually trans positions.

KEY WORDS: hydrazido(1-), hydrazido(2-), molybdenum complex, o-phenanthroline, 2,2’-bipyridine, X-ray structure.

RESUMEN

El complejo [Mo(NHNPh2)(NNPh2)Br2(acac)], acac=acetilacetonato, reacciona en acetonitrilo con 1,10-fenantrolina, o-phen, y 2,2’-bipiridina, bpy, para dar origen a los complejos [Mo(NNPh2)2Br2(o-phen)], I, y [Mo(NNPh2)2Br2(bpy)], II. Estos complejos han sido caracterizados por espectroscopías IR, UV-vis y de RMN de 1H, y análisis elemental. La estructura del complejo I fue resuelta por difracción de rayos-X de monocristal. El centro metálico tiene un entorno octaédrico distorsionado, en el cual los ligandos difenilhidrazido(2-) ocupan posiciones mutuamente cis pero trans a los átomos de nitrógeno del ligando o-phen. Los ligandos bromo ocupan posiciones mutuamente trans.

PALABRAS CLAVES: hidrazido(1-), hidrazido(2-), complejo de molibdeno, o-fenantrolina, 2,2’-bipiridina, estructura de rayos-X.

INTRODUCTION

The facile synthesis of molybdenum-complexes containing both organohydrazido(1-), NHNPhR, and organohydrazido(2-), NNPhR, R=Me, Ph, in the same inner coordination sphere of molybdenum [1], and the chemical reactivity exhibited toward (i) tertiary phosphines such as PPh3-xMex, x= 0, 1, 2, and bis-diphenylphosphinoethane (dppe) [2] and (ii) organonitrogen ligands such as 2,2’-bipyridine (bpy) [3], o-phenanthroline (o-phen) [3], trispyrazolylborate (Tp-) [4] and 3,5-dimethylpyrazolylborate (Tp*-) [4], have proved to be suitable starting materials for the synthesis of several complexes containing cis-[MoO(NNPhR)] [3], or cis-[Mo(NNPhR)2] moieties [2-4]. On the other hand, the complexes of formula [MoO(NNPhR)Cl2(di-imine)], R=Me, Ph; di-imine=o-phen, bpy, but not [Mo(NNPhR)2Cl2(di-imine)], have allowed to accede to new trans-dialkyl and trans-diaryl derivatives by reaction with a large excess of Grignard reagents [5]. Aiming to facilitate the nucleophilic substitution of the halo-ligands by alkyl or aryl groups and to accede to organometallic cis-bis{organohydrazido(2-)} complexes, we report herein the chemical reactivity of the precursor [Mo(NHNPh2)(NNPh2)Br2(acac)] [1] toward o-phen and bpy. We describe in this work the synthesis and characterization of trans-dibromo complexes of formulae [Mo(NNPhR)2Br2(o-phen)], I, and [Mo(NNPhR)2Br2(bpy)], II. We describe, also, the X-ray crystal structure of complex I.

RESULTS AND DISCUSSION

The complexes I and II have been prepared in a one-pot reaction by addition of o-phen or bpy to the precursor [Mo(NHNPh2)(NNPh2)Br2(acac)] [1] dissolved in dry acetonitrile. In particular, this type of reaction could occur in two steps [6]: (i) substitution of one coordinated oxygen atom of the acac ligand by the first incoming nitrogen atom of the o-phen or bpy ligands and (ii) concerted elimination of Hacac with the addition of the second incoming nitrogen of the same ligands. As a result, the diphenylhydrazido(1-) ligand, NHNPh2, transforms into the diphenylhydrazido(2-) ligand, NNPh2, which occupies the same position in the metal coordination sphere. While the reaction of the precursor [Mo(NHNPh2)(NNPh2)Br2(acac)] with o-phen or bpy gives the complexes containing the cis-[Mo(NNPh2)2] moiety in high yield, the functionalization of the precursors [MoO2Br2(o-phen)] and [MoO2Br2(bpy)] with 1,1-diphenylhydrazine in excess affords invariably the complexes containing the cis-[MoO(NNPh2)] moiety [5]. Probably, the water molecule eliminated in the first condensation step between the cis-[MoO2] moiety and the NH2 group of the disubstituted hydrazine avoids the second condensation step [3]. The complexes were obtained as dark red, air stable and microcrystalline solids in good yields, and characterized by 1H NMR, IR and UV-vis spectroscopies. The crystalline and molecular structure of I was determined by single crystal X-ray diffraction analysis (vide infra).

The IR spectra of complexes I and II are very similar displaying, respectively, (i) weak absorption bands at 3051 and 3054 cm-1 associated to the n (CH) of the aromatic groups, (ii) characteristic strong and sharp bands at 1587 and 1590 cm-1 assigned to the n (NN) stretching modes of the NNPh2 ligands [7-9], and (iii) very strong absorption bands at 1489 and 1491 cm-1 corresponding to the n (CC) of the aromatic groups. The electronic spectra recorded in CH2Cl2 solutions show two absorption bands in the 270-400 nm region. These bands have also been observed in other cis-{organohydrazido(2-)}molybdenum complexes containing phosphines [2], di-imines [3] and tris-pyrazolylborates [4] ligands and can be attributed to the cis-[Mo(NNPh2)2] chromophore. In addition, these complexes exhibit a broad and weak band centered at ca. 460 nm attributed to a L® Mo charge transfer transition [10]. The 1H NMR spectra of complexes I and II are unexceptional. All the proton resonances of o-phen and bpy ligands and phenyl groups have been attributed unambiguously, despite the overlapping of the broad Hb triplet of the bpy ligand at 7.03 ppm with the broad Hp triplet of the phenyl group at 6.99 ppm in complex II.

The ORTEplot of complex I, together with the atom labeling scheme, is presented in Figure 1, while the selected bond lengths (Å) and angles (°) are presented in Table 1. The geometry about the molybdenum center is best described as distorted octahedral with the bromo ligands occupying mutually trans positions. On the other hand, the diphenylhydrazido(2-) ligands are cis to one another but trans to the nitrogen atoms of the o-phen ligand. Cis bond angles range from 70.55(9)° for N(1)-Mo-N(2) and 107.29(11)° for N(3)-Mo-N(4) and the range of trans bond angles extends from 160,02(10)° for N(1)-Mo-N(3) to 165.27(2)° for Br(1)-Mo-Br(2). To a large extent these distorsions stem from the incorporation of a five-membered ring. A salient feature of the structure of this complex is the preferential inclination of the two bromo ligands toward the nitrogen atoms of the o-phen ligand; thus Br(1) is bent toward the N(2) atom in 79.51(7)° and Br(2) toward the N(1) atom in 80.50(6)°. These inclinations can most probably be ascribed to repulsions between the bromo ligands and one phenyl group of each diphenylhydrazido(2-) ligand. These repulsions can also be observed between both diphenylhydrazido(2-) ligands in which the bond angle N(3)-Mo-N(4) is 107.29(1)°. These structural features have also been observed in similar cis-{oxoorganohydrazido(2-)}- and cis-bis{organohydrazido(2-)}molybdenum complexes [3].

Table 1. Selected bond distances (Å) and angles (°) of complex I.


Mo-Br(1)

2.6093(8)

Mo-Br(2)

2.5993(9)

Mo-N(1)

2.317(2)

Mo-N(2)

2.309(2)

Mo-N(3)

1.773(2)

Mo-N(4)

1.773(2)

N(3)-N(5)

1.323(3)

N(4)-N(6)

1.318(3)

N(5)-C(31)

1.425(4)

N(5)-C(51)

1.437(4)

N(6)-C(41)

1.430(4)

N(6)-C(61)

1.441(3)

Br(1)-Mo-N(1)

86.78(6)

Br(1)-Mo-N(2)

79.51(7)

Br(2)-Mo-N(1)

80.50(6)

Br(2)-Mo-N(2)

89.22(7)

Br(1)-Mo-N(3)

97.48(8)

Br(1)-Mo-N(4)

89.86(8)

Br(2)-Mo-N(3)

92.11(8)

Br(2)-Mo-N(4)

97.96(8)

N(1)-Mo-N(2)

70.55(9)

N(2)-Mo-N(3)

90.95(10)

N(3)-Mo-N(4)

107.29(11)

N(4)-Mo-N(1)

92.18(10)

N(1)-Mo-N(3)

160.02(10)

N(2)-Mo-N(4)

160.03(10)

Br(1)-Mo-Br(2)

165.27(2)

   

Mo-N(3)-N(5)

170.8(2)

Mo-N(4)-N(6)

170.7(2)

N(3)-N(5)-C(31)

119.3(2)

N(3)-N(5)-C(51)

118.0(2)

C(31)-N(5)-C(51)

122.6(2)

N(4)-N(6)-C(41)

120.7(2)

N(4)-N(6)-C(61)

117.3(2)

C(41)-N(6)-C(61)

121.9(2)



Fig. 1. ORTEP view of complex I with the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.

On the other hand, the metrical parameters observed in the cis-[Mo(NNPh2)2] core are similar to those reported in the literature for similar cis-{organohydrazido(2-)}molybdenum complexes [2-5, 7-9,11]. The short Mo-N and N-N bond lengths of 1.773(2) Å for the former and 1.318(3) and 1.323(3) Å for the latter, the nearly linear Mo-N-N bond angles of 170.7(2) and 170.8(2)°, and the nearly planar MoNNC2 unit, is indicative of an extensive delocalization of the p -electron density throughout the {organohydrazido(2-)}molybdenum unit [11].

EXPERIMENTAL

1,10 phenanthroline and 2,2’-bipyridine were obtained from commercial sources and used without further purification. Precursor [Mo(NHNPh2)(NNPh2)Br2(acac)] was synthesized as previously described [1]. Acetonitrile, diethyl ether and chloroform were dried by standard methods. All manipulations were carried out utilizing standard Schlenk techniques. Dinitrogen was used as inert atmosphere.

General preparation of complexes: To a suspension of 1.00 mmol (0.720 g) of complex [Mo(NHNPh2)(NNPh2)Br2(acac)] in dry acetonitrile (25 ml) was added 1.00 mmol of o-phen (0.180 g) or bpy (0.156 g). The reaction mixture was refluxed for 1 h and allowed to stand at room temperature. The dark red solids obtained were filtered off and washed successively with acetonitrile and ethyl ether. The complexes I and II were recrystallized by slow diffusion of ethyl ether in a chloroform solution. In this manner suitable single crystals for X-ray diffraction studies were obtained for I.

Dibromo-cis-{1,1-diphenylhydrazido(2-)}(o-phenanthroline)molybdenum(VI), [Mo(NNPh2)2Br2(o-phen)] (I).

Yield 88%. Anal. Calcd for C36H28MoN6Br2 (Mr 800.41 gmol-1): C, 54.02; H, 3.53; N, 10.50. Found: C, 52.97; H, 3.05; N, 10.46. UV-vis [(CH2Cl2), l max nm (loge )]: 540sh (3.53); 460 (3.62); 295sh (4.57); 275 (4.71); 230 (4.72). IR (cm-1, KBr): 3051(w), n (CH) arom; 1587(s), n (NN); 1489(s), n (CC). 1H NMR (CDCl3) d (ppm), TMS: o-phen resonances: 9.01 (dd, 2H, Ha: Jab= 5.1 Hz, Jac= 1,5 Hz); 8.37 (dd, 2H, Hc: Jcb= 8.1 Hz, Jca= 1.2 Hz); 7.93 (s, 2H, Hd); 7.38 (dd, 2H, Hb: Jba= 8.1 Hz, Jbc= 5.1 Hz). Phenyl resonances: 7.61 (d, 8H, Ho: Jom= 7.5 Hz); 7.16 (t, 8H, Hm: Jmo» Jmp= 8.0 Hz); 7.02 (t, 4H, Hp: Jpm= 7.5 Hz).

Dibromo-cis-[diphenylhydrazido(2-)}-2,2’-bipyridinemolybdenum(VI), [Mo(NNPh2)Br2(bpy)] (II).

Yield 76%. Anal. Calcd for C34H28MoN6Br2 (Mr 776.39 gmol-1): C, 52.60; H, 3.64; N, 10.83. Found: C, 52.11; H, 3.48; N, 10.93. UV-vis [(CH2Cl2), l max nm (loge )]: 520sh (3.56); 460 (3.68); 350sh (4.07); 298 (4.63); 230 (4,60). IR (cm-1, KBr): 3054(w), n (CH) arom; 1590(s), n (NN); 1491(s), n (CC). 1H RMN (CDCl3, d (ppm), TMS): bpy resonances: 8.78 (d br, 2H, Ha: Jab= 4.8 Hz); 8.11 (d br, 2H, Hd: Jdc = 7.8 Hz); 7,90 (t br, 2H, Hc: Jcb» Jcd = 7.8 Hz); 7.03 (t br, 2H, Hb: Jba» Jbc= 6.0 Hz). Phenyl resonances: 7.56 (d br, 8H, Ho: Jom= 7.8 Hz); 7.14 (t br, 8H, Hm: Jmo= 7.8 Hz); 6.99 ( t br, 4H, Hp: Jpm= 7.5 Hz).

Crystallographic data for I: C36H28Br2MoN6, unit cell dimensions: a= 9.923(2), b= 10.623(3), c= 18.149(4) Å, a = 73.22(2), b = 78.22(2), g = 65.27(2)°, V= 1656.0(7) Å3 triclinic, P-1, Z= 2, crystal size(mm): 0.44x0.28x0.16, q range 2.17 to 27.56°at 293(2) K, reflections collected 7981, independent reflections 7547 (Rint= 0.0174). Convergence at conventional R1= 0.0336 [(I>2s (I)], wR2=0.0729 (all data). Intensity data were collected on a Siemens R3m/V four circle diffractometer in q -2q scan mode, using graphite-monochromated Mo-Ka radiation (l = 0.71073 Å). Semi-empirical corrections, via psi-scans, were applied for absorption.

Cell parameters were obtained from 55 reflections with 10£ 2q £ 30°. The structure was solved by direct methods and refined by least-squares procedures with SHELXL-97 [12]. A riding model was applied to all H atoms which were placed at geometrically idealized positions with C-H= 0.96 Å. Isotropic thermal parameters were considered for all H-atoms equal to 1.2 times the equivalent isotropic thermal parameters of the corresponding parent atom.

Crystallographic data for the structural analysis has been deposited with the Cambridge Crystallographic Data Center, CCDC N° 168797 for compound I. 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.uk or http://www.ccdc.cam.ac.uk.

ACKNOWLEDGEMENTS

C.B. greatly appreciates financial support for this work from the Dirección de Investigación, Universidad Austral de Chile (Project S 26/98). C. B. and D. C. acknowledge the Programme International de Coopération Scientifique, CNRS-CONICYT (PICS N° 922, 2000-02). We thanks also Fundación Andes for funding the purchase of the Single-Crystal Diffractometer.

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