The structure of a triosmium carbonyl cluster-phenylarsine oxide derivative

Journal of Organometallic Chemistry 696 (2011) 3436e3439

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The structure of a triosmium carbonyl cluster-phenylarsine oxide derivative Arturo González-Hernández, Simón Hernández-Ortega, Elizabeth Gómez, Juan M. Fernández-G* Instituto de Química, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, Coyoacán 04510, México D.F, Mexico

a r t i c l e i n f o

a b s t r a c t

Article history: Received 17 February 2011 Received in revised form 23 June 2011 Accepted 24 June 2011

The reaction between the dihydride of decacarbonyltriosmium [H2Os3(CO)10] and phenyl arsine oxide (PAO) in benzene yields only one product [Os3(O)9(m-H){m-PhAs(O)OAsPh}] (1), which is characterized by high resolution mass spectrometry (HRMS), Fast Atomic Bombardment Mass Spectrometry (FAB)þ, IR, 1H and 13C NMR, and single crystal X-ray diffraction. The solid state X-ray diffraction study of compound (1) shows that the molecule is polycyclic and has an osmium triangle with a bridging hydride bonded to a PhAs(O)-O-AsPh ligand. Ó 2011 Elsevier B.V. All rights reserved.

Keywords: Crystal structure Triosmium cluster-PAO derivative 1 H and 13C NMR studies

1. Introduction Arsenoxides are a group of compounds used as enzyme inhibitors that act on thiol groups (eSH). Phenylarsine oxide (PAO), a trivalent organoarsenic compound, is one of the most versatile arsenoxides. PAO contains a lone pair of electrons that can establish a covalent bond with vicinal thiol groups (eSH) of proteins, affording stable rings [1]. In addition, it has been suggested that PAO also interacts with eSH/eOH and eSH/eCO2H, pairs [2]. It has been reported that PAO specifically inhibits the activity of tyrosine phosphorylation in leukocytes [3] but has no effect on the enzyme tyrosine-kinase [4]; however, it has been proposed that some aspects of PAO activity are related to other mechanism of action [5]. Due to its wide interactions in several processes, PAO is used intensively in biochemistry and biological studies [6e17]. It is well known that PAO exists in solution as an oligomeric mixture of phenyl cycloarsoxanes, (PhAsO)n (n ¼ 2e5), where rings formed by three or four units are more energetically stable, with four units being the most favored. In the solid state, the phenylcycloarsoxanes (PhAsO)4 are found as cyclotetramers with a chaireboat conformation, where the phenyl substituents occupy equatorial sites [18]. To our knowledge, there is only one report of organometallic derivatives of (PhAsO)4 with Cr(CO)6 or Mo(CO)6 [19]. Therefore, it is interesting to study PAO as a ligand in different metallic environments, especially those of the transition series. Specifically, our

* Corresponding author. Tel.: þ52 55 5622 4470; fax: þ52 55 5616 2203/2217. E-mail address: [email protected] (J.M. Fernández-G). 0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2011.06.029

goal is to obtain organometallic complexes involving MeAs bonds and, hence, understand the chemistry and structure of these MePAO derivatives. In this work, we describe the reaction between the dihydride of decacarbonyltriosmium [H2Os3(CO)10] and phenylarsine oxide (PAO) in benzene (Scheme 1). The reaction product [Os3(CO)9(m-H){m-PhAs(O)-OAsPh}] (1) was purified by preparative TLC and characterized by HRMS, FABþ, IR, 1H and 13C NMR, and single crystal X-ray diffraction. 2. Experimental 2.1. Reagents and techniques Triosmium dodecacarbonyl (Os3(CO)12), phenylarsine oxide (PAO), absolute ethanol (EtOH), methanol (MeOH), n-hexane, benzene (HPLC grade), toluene (HPLC grade), dichloromethane (CHCl2), cyclohexane (C6H12), chloroform (CHCl3) both reactive grade and deuterochloroform (CDCl3) were all obtained from SigmaeAldrich and were used without further purification. Preparative silica gel TLC plates (20  20 cm) were obtained from Merck. The dihydride of decacarbonyltriosmium [H2Os3(CO)10] was prepared as described in the literature [20]. The melting point was determined on a FishereJohns apparatus and is uncorrected. The mass spectrum was obtained using a JEOL Mod. JMS-SX-102A mass spectrometer operated with FABþ (using em-nitrobenzyl alcohol as matrix). IR spectra in solution (cyclohexane) and in solid phase (KBr discs) were recorded on a Nicolet750 spectrometer. NMR data were acquired on a Bruker Avance 300 spectrometer operating at 300 K.

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Scheme 1. Synthesis of [Os3(CO)9(m-H){m-PhAs(O)OAsPh}] (1).

2.2. Crystallography Good quality crystals suitable for X-ray diffraction study were obtained by slow diffusion of n-hexane into a saturated dichloromethane solution of compound (1) at room temperature. 2.3. Data collection and processing A crystal of [Os3(CO)9(m-H){m-PhAs(O)OAsPh}] (1) was mounted on glass fibers. In all cases, the X-ray intensity data were measured at 293 K on a Bruker SMART APEX CCD-based X-ray diffractometer system equipped with a Mo-target X-ray tube (Ka ¼ 0.71073 Å). The detector was placed at a distance of 4.837 cm from the crystals. A total of 1800 frames were collected with a scan width of 0.3 in an exposure time of 10 s/frame. The frames were integrated with the Bruker SAINT software package using a narrow-frame integration algorithm. Analysis of the data showed negligible decay during data collection in all cases. Cell parameters were calculated using least squares fitting for 25 high-angle reflections. Omega scans for several intense reflections indicated acceptable crystal quality. Data were collected for (1) from 1.94 to 25.36 , using a theta scan mode at 293(2) K with a variable scan rate (see Table 1). 2.4. Structure solution and refinement The structure was solved by Direct Method [21]. Anisotropic full-matrix least-squares refinement [22] on F2 was performed for all non-Hydrogen atoms. Weighted R-factors (wR) and all goodnesses of fit parameters (S) are based on F2 and conventional Rfactors (R) are based on F, with F set to zero for negative F2. The observed criterion of F2 > 2s(F2) is used only for calculating Rfactors. Hydrogen atoms attached to C-atoms were placed in idealized positions with isotropic thermal parameters fixed to 1.2 times the value of the attached atom. H atoms attached to N or O atoms were located on a difference Fourier map at an advanced stage of refinement, and their positional parameters were refined. Neutral atom scattering factors and anomalous scattering factors were obtained from the International Tables for X-ray Crystallography [23]. 2.5. Synthetic procedure To a solution of 0.10 g (0.00012 mol) of H2Os3(CO)10 in 70 cm3 of anhydrous benzene stirred under nitrogen atmosphere, 0.40 g (0.0024 mol) of PAO was added, and the mixture was boiled under reflux for 4 h. During this time, a change of color of the solution mixture from purple to light yellow was observed. The mixture was cooled, and the solution was concentrated to dryness under vacuum. A single product was observed by TLC. The residue was purified by preparative TLC plates using a solvent mixture of 3:1 (CH2Cl2/n-hexane) as eluent. Recrystallization by slow diffusion of

n-hexane into a saturated CH2Cl2 solution of the complex (1) yielded light bright yellow crystals. 2.5.1. Nonacarbonyl (m-hydrido)(m-phenylarsine)(m-oxophenylarsine oxide) triosmium [Os3(O)9(m-H){m-PhAs(O)OAsPh}] (1) 1 NMR H (CDCl3, (Yield 60%). M.p. 188e193  C. 300 MHz): 19.32. (1H, s, J187Ose1H ¼ 28.5 Hz, H-hydride), 7.48e7.56 (6H, m, H-12, H-13, H-14, H-18, H-19, H-20,), 7.60 (2H, dd, J ¼ 7.8, 1.8 Hz, H-17, H-21), 7.72e7.77(2H, m, H-11, H-15) ppm; NMR 13C (CDCl3, 75.5 MHz): 128.8 (C-17, C-21), 129.2 (C-15, C-11), 129.34 (C-18, C-20), 129.8 (C-12, C-14), 130.9(C-13), 132.6 (C-19), 138.1 (C-10), 140.4 (C-16), 168.8 (C-3), 168.9 (C-5), 172.2 (C-8), 172.8 (C-9), 176.0 (C-6), 176.1 (C-1), 178.0 (C-7) 178.2 (C-4) 179.6 (C-2) ppm. IR Omax (cyclohexane): 2103(CO)sh, 2086(CO)m, 2057(CO)vs, 2034(CO)vs, 2010(CO)vs, 1986(CO)s, IR Omax (KBr): 738, 573 (AseOeAs), 692(As]O) cm1; MS (FABþ), [m/z] (rel. ab.): [Mþ þ 3](100); [Mþ, 1159] (69); [Mþ  CO, 1131](13), [Mþ  2CO, 1103](11), [Mþ  3CO, 1075](19).

Table 1 Crystallographic data for compound (1). Compound

(1)

Empirical formula Formula weight Temperature (K) Wavelength (MoKa) Crystal system Space group Unit cell dimensions

C21H11As2O11Os3 1159.7433 293(2) 0.71073 Å Triclinic P-1 a ¼ 9.031(1) Å b ¼ 11.097(1) Å c ¼ 14.295(2) Å a ¼ 100.415(1) b ¼ 98.132(1) g ¼ 103.478(2) 1344.7(3) 2 2.864 1038 0.32  0.18  0.07 10  h  10 13  k  13 17  l  17 Bruker Smart APEX AXS CCD area detector 16.635 mm1 1.94e25.36 u scans Analytical 0.3264 and 0.0724 Full-matrix least-squares on F2 11,158 4900 0.0461 4900/0/338 0.921 R1 ¼ 0.0283, wR2 ¼ 0.074 1.249 and 1.540

Volume (Å3) Z Density (calc). Mg m3 F(000) Crystal size (mm) Index ranges

Diffractometer Absorption coefficient q range for data collection Scan mode Absorption correction Max. and min. transmission Refinement method Reflections collected Independent reflections R(int) Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2s(I)] Largest diff. peak and hole (e Å3)

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3. Results and discussion 3.1. Physical and spectroscopic study Nonacarbonyl (m-hydrido)(m-phenylarsine)(m-oxo-phenylarsine oxide) triosmium [Os3(CO)9(m-H){m-PhAs(O)-O-AsPh}] (1) is a bright yellow compound that is soluble in chloroform, dichloromethane benzene and less soluble in n-hexane and n-heptane. Compound (1) is quite stable; it does not react in boiling benzene under nitrogen atmosphere with an additional amount of PAO, PF2Py, ethanedithiol, thiosemicarbazide or N-acetylcysteine. HRMS, analysis of (1) was satisfactory, validating the formula proposed for (1) [Os3(CO)9(m-H){m-PhAs(O)-O-AsPh}], with the following molecular weight for C21H11O11As2Os3: calc. 1159.7514 m/ z, obs. 1159.7510 m/z. Furthermore, the FABþ mass spectrum of (1) shows the expected molecular ion, displaying the characteristic osmium isotopic distribution [(190Os) found M 1159. required 1159]. As is usual with FABþ mass spectrometry, protonated ions and fragments were also recorded [24], in fact the base peak is an (Mþ þ 3) ion. In the fragmentation pattern, we observed three successive loses of CO molecules [m/z](rel. ab.), [Mþ, 1159](69); [Mþ  CO, 1131](13), [Mþ  2CO, 1103](11), [Mþ  3CO, 1075](19). The infrared spectrum in solution (cyclohexane) showed five signals due to terminal neC]O vibrations in the region for MeCO over the range 2083e1962 cm1, in agreement with data described in literature [25]. The infrared spectrum in the solid state (KBr) shows bands due to the phenyl rings and vibrations (AseOeAs) at 738 and 548 cm1 and (As]O) at 692 cm1 [26]. Due to the stability of compound (1), the dimeric subunit PAO group could be considered as a five electron donor, resulting in a saturated triosmium cluster with 48 electrons, similar to other species [27,31].

Fig. 1. Molecular structure of compound (1) in the solid state with atom-numbering schemes. Thermal ellipsoids are drawn at the 50% probability level. Selected bond lengths (Å) and angles ( ) are included.

3.2. Crystal study Crystal and additional data collection parameters and refinement details are given in Table 1. The molecular structure of (1), including atom-numbering schemes with a selection of bond lengths and angles, and the skeletal structure of the polycyclic species (1) including the bridging hydride, are illustrated in Figs. 1 and 2. In the solid state, [Os3(CO)9(m-H){m-PhAs(O)OAsPh}] compound (1) is a polyhedral or polycyclic species and can be seen as two triangles sharing one edge, one of them a slightly scalene osmium triangle Os(1)eOs(2)eOs(3) sharing the Os(2)eOs(3) edge with a third vertex As(2) forming the second triangle, with vertexes Os(2)eOs(3)eAs(2). The As(2) atom is additionally bonded to a phenyl ring and a bridging oxygen atom O(10). The As(1) atom bonds to a bridging oxygen atom O(10), an osmium atom Os(1), a phenyl ring, and a terminal oxygen atom O(11). Therefore, there are three extra cycles in the molecule, two of five members in which the vertexes are Os(2)eAs(2)eO(10)eAs(1)eOs(1) and Os(3)eAs(2)eO(10)eAs(1)eOs(1), and, finally, there is a cycle of six vertexes: Os(2)eOs(3)eAs(2)-O(10)eAs(1)eOs(1). The skeletal framework structure of (1) is similar to other trinuclear ruthenium and osmium carbonyls with different bridging donors [28e31]. The CeO bond lengths (1.128(9)e1.161(8) Å) are in the range of the values described for the terminal CeO bonds in triosmium clusters (1.101e1.27 Å) [27,28]. The three OseOs bond lengths have values in the range for this kind of clusters (2.753e3.104 Å) [25,31]. However, the three bond lengths are different, i.e., Os(1)eOs(3) 2.8770(5) Å, Os(1)eOs(2) 2.8822(4) Å and Os(2)eOs(3) 2.9741(2) Å. Notably, the Os(2)eOs(3) bond is longer due to the presence of the hydride and the two cis carbonyls are bent away from the hydride as is usual in this kind of systems [25,32]. All phenyl CeC, AsePh and As]O bonds (As]O 1.6567(11) Å) are in the range of the values described in literature (As(1)eC(1) 1.8882(12); As(1)eO(1) 1.6617(10) Å) [32].

However, the bond As(1)eO(10) 1.791(4) Å is slightly shorter than As(2)eO(10) 1.820(4) Å, perhaps because As(2) is bridging Os(2)e Os(3) or because As(1) is bonded to an oxygen atom as an “oxo” group, which is somewhat more electronegative than As(2). Additionally, the molecules in the asymmetric unit cell exhibit two main contacts at 2.775 Å between the O(10) molecule and the

Fig. 2. Skeletal structure of the polycyclic molecule (1), including the bridging hydride.

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O(10) molecule of the neighbor, with the same being true for the O(11) molecule and the O(11) molecule of the neighbor. 3.3. NMR spectroscopy The solution structure of [Os3(CO)9(m-H){m-PhAs(O)OAsPh}] (1) obtained by 1H and 13C NMR was determined in CDCl3. Spectral assignments corresponded to the atom-numbering schemes of the molecular structure determined by single crystal X-ray diffraction. The 1H NMR showed a single signal at 19.3 ppm for the hydride; additionally, 187Os satellites were observed and the coupling constant calculated (J187Ose1H ¼ 28.5 Hz). The aromatic region exhibited two sets of signals for ortho protons of the two different aromatic rings bonded to As(1) and As(2), and the meta and para protons were observed as a multiplet. The 13C NMR carbonyl region reveals nine signals in the range of 179e160 ppm, which were assigned by comparison with those reported in the literature [25,31,34], and the low field resonances were assigned to C-2, C-4, and C-7. This assignment is based on the general trend that axial carbonyl resonances shift to lower fields than those of equatorial and by considering that As(1) is more electronegative than As(2), as was observed in IR spectroscopy [26,33]. 4. Concluding remarks The organometallic complex [Os3(CO)9(m-H){m-PhAs(O)OAsPh}] (1) shows a polycyclic geometry resulting from the coordination of a PhAs(O)OAsPh subunit of the PAO tetramer to the triosmium frame and includes a bridging hydride. In the solid state, some supramolecular interactions involving the oxygen atoms, the phenyl rings and oxygen-carbonyl of neighboring molecules were observed. Acknowledgements We wish to thank DGPA-UNAM for financial support of the project IN 210210. We acknowledge Dr. Francisco Javier Pérez-Flores, Eng. Luis Velasco and Q. Eréndira García-Rios for technical assistance. Appendix A. Supplementary material CCDC 812730 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ data_request/cif.

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