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Cyclopentadienyl ruthenium complexes of mixed heterocyclic thiol and Bis(diphenylphosphino)ferrocene ligands
Journal of Molecular Structure 1191 (2019) 1e5
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Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Cyclopentadienyl ruthenium complexes of mixed heterocyclic thiol and Bis(diphenylphosphino)ferrocene ligands € rls b, Hadil Alshurafa a, Mohammad El-khateeb a, *, Hassan Abul-Futouh b, Helmar Go Wolfgang Weigand c a b c
Chemistry Department, Jordan University of Science and Technology, Irbid, 22110, Jordan Department of Pharmacy, Al-Zaytoonah University of Jordan, P.O. Box 130, Amman, 11733, Jordan €t Jena, Humboldt Straße 8, 07743, Jena, Germany Institut für Anorganische und Analytische Chemie, Friedrich-Schiller-Universita
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 February 2019 Received in revised form 19 March 2019 Accepted 1 April 2019 Available online 16 April 2019
Cyclopentadienyl ruthenium complexes bearing mixed heterocyclic thiol and bis(diphenylphsphino) ferrocene (dppf) ligands are presented. The complex-salts [CpRu(dppf)(k1S-HS-het)]PF6 {Cp ¼ h5-C5H5; HS-het ¼ 2-mercaptobenzothiazole (1), 2-mercaptobenzimidazole (2)} were synthesized from the reaction of CpRu(dppf)Cl with the thiol in the presence of KPF6 salt under reflux. Complexes 1 and 2 have been characterized by spectroscopic methods (1H-NMR, 31P{1H}-NMR, MS) and elemental analysis. The solid-state structures of [CpRu(dppf)(k1SeS2C7H5N)]PF6 (1) and [CpRu(dppf)(k1S-SC7H6N2)]PF6 (2) have been determined by X-ray crystallography. The cyclic voltammetry of these two complexes are measured. © 2019 Elsevier B.V. All rights reserved.
Keywords: Ruthenium Heterocyclic thiols X-ray structures Synthesis Characterization
1. Introduction Heterocyclic thiols containing the thioamide moiety are versatile ligands in coordination chemistry and may adopt several coordination modes using either the exocyclic sulfur and/or the endocyclic nitrogen atoms [1e4]. These compounds found applications in biological systems and proved to be antiviral, antibacterial and fungicidal agents [5e8]. We [9e13] and others [14,15] reported several ruthenium complexes of heterocyclic thiolato ligands. The complexes CpRu(PPh3)2(k1SeS-het) [het ¼ furyl, thiopheneyl, 2-imidazolyl, 1-methylimidazolyl, 5-methyl-1,3,5thiadiazolyl, 5-methyl-4H-1,2,4-triazolyl, 2mercaptobenzothiazolyl, 2-mercaptobenzimidazolyl, 2mercaptobenzoxazolyl] are reported from chloride/heterocyclic thiolate exchange reactions of CpRu(PPh3)2Cl and have sulfurcoordinated heterocyclic thiolates [9e12]. On the other hand, the 2-pyridine thiolate and the 2-pyrimidine thiolate coordinated to the Ru through both the N,S-atoms in a chelating fashion forming CpRu(PPh3)(k 2S,NeS-het) (het ¼ 2-pyridine, 2-pyrimidine) while
* Corresponding author. E-mail address: [email protected] (M. El-khateeb). https://doi.org/10.1016/j.molstruc.2019.04.008 0022-2860/© 2019 Elsevier B.V. All rights reserved.
4-mercaptopyridine formed CpRu(PPh3)2(k1SeS-4-py) which has sulfur coordination [13]. Complexes with bis(diphenylphosphino) methane (dppm) or bis(diphenylphosphino)ethane (dppe) (CpRu(k2P,P-dppm)(k 1SeS-het), CpRu(k2P,P-dppe)(k 1SeS-het)) are generated from the one pot reaction of CpRu(PPh3)2Cl, thiolate anions and the corresponding bis(phosphine) ligands for all heterocyclic thiolates mentioned above [12,13]. Ruthenium (II) complexes with the general formula [Ru(k2S,NeS-het)(bipy)(PeP)]PF6 [het ¼ 2-pyrimidine, PeP ¼ dppe, dppf, dppp (¼ 1,3bis(diphenylphosphino)propane] are reported and their activity against some tumor cells are also presented [14]. Indeed, thiols themselves are also good ligands and several ruthenium complex of them are known [16e19]. The complexes [CpRu(L)(L0 )(HSR)]PF6 (R ¼ But, Ph, L, L0 ¼ PPh(OMe)2, PPh2(OMe), P(OMe)3, PPh3, CO) are obtained from CpRu(L)(L0 )Cl, HSR and NH4PF6 [16,17]. 2-Mercaptopyridine, together with other thiols, reacted with CpRu(dppf)Cl to form the thiol salts [CpRu(dppf)(k1SHS-2-py)]BPh4 [18]. The protonation of CpRu(PPh3)2SR with HBF4 produced the corresponding thiol salts [CpRu(PPh3)2(k1S-HSR)]BF4 [19]. In this paper and as a continuing effort in the area of heterocylic thiol/thiolate complexes of ruthenium, we report the full details of the preparation and characterization of heterocylic thiol ruthenium
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complex-salts with bis(diphenylphosphino)ferrocene ligand.
2. Results and discussion 2.1. Synthesis and characterization The ruthenium heterocyclic thiol salts [CpRu(dppf)((k1S-HShet)]PF6 {Cp ¼ h5-C5H5; dppf ¼ 1.10 -bis(diphenylphosphino)ferrocene; HS-het ¼ 2-mercaptobenzothiazole (1), 2mercaptobenzimidazole (2)} are readily prepared from the reaction of the ruthenium chloride and the corresponding heterocyclic thiols in the presences of KPF6 as shown in Equation (1).
for 1 and 2, respectively, one is similar to that observed for the [CpRu(dppf)(kS-HS-2-py)]BPh4 complex of 9.66 ppm [18] and the other is much higher. This is expected result as these peaks are concentration dependent. The 31P{1H}-NMR spectra of complexes 1 and 2 consist of a singlet peak at 48.22 and 47.70 ppm, respectively, arising from the two equivalent P-atoms. This range is similar to the value observed for [CpRu(dppf)(k1S-HS-2-py)]BPh4 (47.7 ppm) [18]. The mass spectra of 1 and 2 displayed the molecular ion peak of the cation followed by another one formed by losing the thiol ligand.
2.2. Molecular structures of 1 and 2
(1)
The thiol complex-salts 1 and 2 are yellow to orange solids, stable to air as solids and in solution. The protonated site of these complexes is the more basic N-atom as proved by the X-ray structure determination of 1 and 2 (vide infra). The identity of these complexes is determined based on their 1H- and 31P{1H}-NMR spectroscopic data, mass spectrometry, elemental analysis and Xray structure determination. The 1H-NMR spectra of complexes 1 and 2 show a singlet in the range of 4.50e4.53 ppm attributable to the protons of the cyclopentadienyl ligand bonded to Ru, while the protons of the Cp-ligands of the ferrocene moiety are present as four-sets of multilplets in the range of 4.00e5.07 ppm. The range of the chemical shift data of CpRu-proton is comparable to those found in the thiolate analogous complexes [9e13] and those of the Cp2Fe-protons are similar to those observed for the reported [CpRu(dppf)L]þ (L ¼ S ¼ C(NH2)2, S]CS2C2H4, S]CS2C2H2, HSpy) complexes [18]. The protons of the phenyl rings of the dppf and the heterocyclic moieties are observed in the aromatic region as expected. The proton on the N-atom appeared at 11.32 and 9.40 ppm
The molecular structures of complexes 1 and 2 are unequivocally confirmed by single-crystal X-ray diffraction analysis. ORTEP views of the structures are shown in Fig. 1 and selected bond lengths (Å) and angles (º) of these complexes are given in Table 1. Both complexes contain one and half dichloromethane molecules per complex molecule. Thiols are bonded to ruthenium through the sulfur atom of the thioimide form with protonated nitrogen atom in which the NeH bond length (0.75(4) Å for 1 and 0.79(3), 0.83(3) Å for 2) is observed. This is expected as the protonated center is the more basic nitrogen atom as observed in similar complexes [10,18]. A notable feature of the structures is that the H atom (located on the N) is hydrogen bonded to one F atom of the PF6 anion. The distance (H/F) is in the range of 2.33(4)-2.53(4) Å for 1 and in the range of 2.26(3)-2.57(3) Å for 2. The RueC(Cp) bond distances of 1 and 2 are in the range of 2.191(2)-2.252(3) Å and are similar to those reported of CpRu-containing systems [9e13,20]. The RueS bond distance of 1 (2.3774(8) Å) is a bit shorter than that of 2 (2.3803(3) Å) and of the corresponding distance of [CpRu(PPh3)(NO)(k1S-HS-2-py)]BF4 (2.3927(7) Å) [10]. The RueP bond lengths of
Fig. 1. Molecular structures (50% probability) of complex 1 (left) and complex 2 (right). All hydrogen atoms are omitted for clarity but those of the N-atoms are shown with arbitrary radius.
H. Alshurafa et al. / Journal of Molecular Structure 1191 (2019) 1e5
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Table 1 Selected bond lengths (Å) and angles (º) for complex [CpRu(dppf)(k 1S eS2C7H5N)]PF6 (1) and [CpRu(dppf)(k 1S-SC7H6N2)]PF6. 1 RueC8 RueC9 RueC10 RueC11 RueC12 RueP1 RueP2 RueS1 S1eC1 S2eC1 N1eC1 N1eH P1eRueS1 P2eRueS1 P1eRueP2 RueSeC1
2 2.212(3) 2.247(3) 2.252(3) 2.232(3) 2.194(3) 2.3092(8) 2.3062(8) 2.3774(8) 1.679(3) 1.720(3) 1.361(3) 0.75(4) 87.95(3) 84.78(3) 97.98(3) 115.74(11)
RueC8 RueC9 RueC10 RueC11 RueC12 RueP1 RueP2 RueS S1eC1 N2eC1 N1eC1 N2eH P1eRueS P2eRueS P1eRueP2 RueSeC1
2.235(2) 2.238(2) 2.224(2) 2.191(2) 2.202(2) 2.3098(7) 2.3044(6) 2.3803(3) 1.695(3) 1.350(3) 1.355(3) 0.79(3) 84.87(2) 88.33(2) 97.99(2) 117.66(9)
1 (2.3092(8), 2.3062(8) Å) are comparable to those of 2 (2.3098(7), 2.3044(6) Å) and are in the same range observed for complexes [CpRu(dppf)(SCX2)]PF6 (X ¼ NH2, SCH, SCH2) [18]. The sulfur atom is sp3-hybridized as indicated from the RueSeC1 angle (1: 115.74(11)º, 2: 117.66(9)º). The P1eRueP2, P1eRueS and P2eRueS bond angles are comparable to those of [CpRu(dppf)(SCX2)]PF6 (X ¼ NH2, SCH, SCH2) [18] and indicated that the coordination around the ruthenium center is distorted octahedral.
wave potentials of complex 2 are shifted to less positive potential (80 and 120 mV, respectively) compared to those of complex 1. However, the half-wave potentials of both complexes show cathodic shifts (~300 and 400 mV, respectively) compared to [CpRu(dppf)Cl] complex [21]. These cathodic shifts can be explained by the difference in electron density added to the metal center by the presence of 2-mercaptobenzothiazole and 2mercaptobenzimidazole relative to Cl.
2.3. Electrochemistry
3. Experimental part
The electrochemical behaviour of complexes 1 and 2 was investigated by cyclic voltammetry (CV). Fig. 2 shows the cyclic voltammetric oxidation of complexes 1 and 2 in CH2Cl2-[n-Bu4N] [BF4] solutions at a scan rate of 0.2 V/s. On initiating the electrochemical scan in the anodic direction, two quasi-reversible anodic events at E1/2 ¼ 0.30 V and 0.63 V for complex 1 and at E1/2 ¼ 0.22 V and 0.51 V for complex 2 were observed. These oxidation peaks are corresponding to one electron transfer similar to the parent complex [CpRu(dppf)Cl] reported in the literature [21]. Moreover, the first oxidation peak of complexes 1 and 2 can be assigned to the metal-centered RuIII/RuII couple, while the second one is correlated to the oxidation of the dppf ligand which is comparable to the corresponding one of the [CpRu(dppf)Cl] complex [21]. The half-
3.1. General Reactions and manipulations were performed under inert atmosphere of nitrogen using Schlenk line techniques. Hexane (Na/ benzophenone), dichloromethane (P2O5) and absolute ethanol (Na) were freshly distilled prior to use. 2-Mercaptobenzoimidazole and 2-mercaptobenzothiazole were used as received (Acros). The complex CpRu(dppf)Cl was prepared as described in the literature [21].1H- and 31P{1H}-NMR spectra were recorded on a Brucker AVANCE 400 MHz spectrometer. Chemical shifts were recorded in ppm using the solvent as reference signal for 1H-NMR (CDCl3 d ¼ 7.26 ppm) and H3PO4 as external reference for 31P{1H}-NMR. Melting points were recorded by Melting Point Apparatus SMP3,
Fig. 2. Cyclic voltammetry of 1.0 mM solution of complexes 1 (left) and 2 (right) in CH2Cl2-[n-Bu4N][BF4] (0.1 M) solutions at 0.2 V/s scan rate. The arrows indicate the scan direction. The potentials E are given in V and referenced to the Fcþ/Fc couple.
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H. Alshurafa et al. / Journal of Molecular Structure 1191 (2019) 1e5
Stuart Scientific. The mass spectra were measured with Finnigan MAT SSQ 710 instrument. Elemental analyses were performed with a Leco CHNS-932 apparatus. 3.2. General procedure for the preparation of [CpRu(dppf)(k1S-HShet)]PF6 1, 2 Heterocyclic thiol (1.00 mmol), CpRu(dppf)Cl complex (1.00 mmol, 0.756 g) and potassium hexaflourophosphate (1.00 mmol, 0.145 g) were dissolved in absolute ethanol (100 mL). The resulting mixture was refluxed for 4 h. Then the volatiles were removed under vacuum and the residue was extracted by 2 5 mL of CH2Cl2. Condensation of the CH2Cl2 solution followed by addition of 40e50 mL hexane gave the product as yellow precipitate. The crude product was washed several times with cooled hexane and recrystallized from CH2Cl2/hexane. [CpRu(dppf)(k 1SeS2C7H5N)]PF6 (1): Yield 73%. M.p.: 262e263 C. 1 H NMR (CDCl3): d 4.00 (m, 2H, PC5H4), 4.14 (m, 2H, PC5H4), 4.48 (m, 2H, PC5H4), 4.55 (s, 5H, C5H5), 5.07 (m, 2H, PC5H4), 7.05 (m, 8H, PPh2), 7.35 (m, 12H, PPh2), 7.21 (d, 2H, C6H4), 7.56 (d, 2H, C6H4) 11.32 (br, 1H, NH). 31P{1H}-NMR (CDCl3) d 48.37. Anal. Calcd. for C46H38F6FeNP3RuS2.1.5CH2Cl2: C, 49.18; H, 3.56; N, 1.21; S, 5.53. Found C, 48.67; H, 3.35; N, 1.18 S, 5.48%. DEI-MS: m/z ¼ 886 [CpRu(dppf)S2C7H5N]þ, 721 [CpRu(dppf)]þ. [CpRu(dppf)(k 1S-SC7H6N2)]PF6 (2): Yield 68%. M.p.: 215e216 C. 1 H NMR (CDCl3): d 4.14 (m, 2H, PC5H4), 4.25 (m, 2H, PC5H4), 4.48 (m, 2H, PC5H4), 4.50 (s, 5H, C5H5), 5.00 (m, 2H, PC5H4), 7.20 (d, 2H, C6H4), 7.24 (d, 2H, C6H4), 7.40 (m, 12H, PPh2), 7.80 (m, 8H, PPh2), 9.40 (br, 1H, NH). 31P{1H}-NMR (CDCl3) d 47.70. Anal. Calcd. for C46H39F6N2P3RuS.1.5CH2Cl2: C, 49.86; H, 3.67; N, 2.44; S, 2.80. Found C, 49.78; H, 3.52; N, 2.30; S, 2.93%. DEI-MS: m/z ¼ 868 [CpRu(dppf)SC7H5N2]þ, 721 [CpRu(dppf)]þ. 3.3. X-ray crystal structure analysis The intensity data were collected on a Nonius KappaCCD diffractometer, using graphite-monochromated Mo-Ka radiation. Data were corrected for Lorentz and polarization effects; absorption was taken into account on a semi-empirical basis using multiple-scans [22e24]. The structures were solved by direct methods (SHELXS [25]) and refined by full-matrix least squares techniques against Fo2 (SHELXL-97 [25]). The hydrogen atoms bonded to the nitrogen atoms of 1 and 2 were located by difference Fourier synthesis and refined isotropically. All other hydrogen atoms were included at calculated positions with fixed thermal parameters. All non-hydrogen atoms were refined anisotropically [25]. XP (SIEMENS Analytical X-ray Instruments, Inc.) was used for structure representations. Crystal Data for 1: [C46H38FeNP2RuS2]þ[PF6]-1.5(CH2Cl2), Mr ¼ 1160.11 g mol-1, yellow prism, size 0.098 0.092 0.084 mm3, monoclinic, space group C 2/c, a ¼ 24.0259(4), b ¼ 12.6098(2), c ¼ 31.1113(6) Å, b ¼ 91.001(1) , V ¼ 9424.1(3) Å3, T ¼ 140 C, Z ¼ 8, rcalcd. ¼ 1.635 gcm3, m (MoKa) ¼ 10.49 cm1, multi-scan, transmin: 0.6939, transmax: 0.7456, F(000) ¼ 4680, 33811 reflections in h(-31/31), k(-16/15), l(-40/40), measured in the range 1.31 Q 27.47, completeness Qmax ¼ 99.6%, 10763 independent reflections, Rint ¼ 0.0365, 9599 reflections with Fo > 4s(Fo), 611 parameters, 0 restraints, R1obs ¼ 0.0451, wR2obs ¼ 0.1023, R1all ¼ 0.0524, wR2all ¼ 0.1067, GOOF ¼ 1.078, largest difference peak and hole: 1.510/1.141 e Å3. Crystal Data for 2: [C46H39FeN2P2RuS]þ[PF6]-.1.5(CH2Cl2), Mr ¼ 1143.07 g mol-1, yellow prism, size 0.112 0.100 0.088 mm3, monoclinic, space group C 2/c, a ¼ 23.7480(5), b ¼ 12.6310(3),
c ¼ 30.9038(6) Å, b ¼ 92.252(1) , V ¼ 9262.8(3) Å3, T ¼ 140 C, Z ¼ 8, rcalcd. ¼ 1.639 gcm3, m (Mo-Ka) ¼ 10.23 cm1, multi-scan, transmin: 0.6917, transmax: 0.7456, F(000) ¼ 4616, 32456 reflections in h(-30/30), k(-16/16), l(-40/40), measured in the range 1.32 Q 27.44 , completeness Qmax ¼ 98.9%, 10473 independent reflections, Rint ¼ 0.0387, 9362 reflections with Fo > 4s(Fo), 633 parameters, 0 restraints, R1obs ¼ 0.0357, wR2obs ¼ 0.0742, R1all ¼ 0.0436, wR2all ¼ 0.0778, GOOF ¼ 1.089, largest difference peak and hole: 0.532/0.603 e Å3. 4. Conclusion In this work, two complex-salts of ruthenium heterocyclic thiols are synthesized. The thiols are bonded to ruthenium through the sulfur atom in a monodentate fashion, while the dppf is bonded to ruthenium in a bidentate form as expected. The proton of the thiol is located at the more basic nitrogen atom leading to the thioimide form. This is evident from the structures of the complexes. Moreover, the electrochemical behaviour of the complexes concluded that both complexes 1 and 2 can be easily oxidized via two quasireversible processes. Possible origins of these processes could be assigned to the metal-centered RuIII/RuII couple and the dppf ligand-centered oxidations. 5. Supporting information available Crystallographic data deposited at the Cambridge Crystallographic Data Center under CCDC-1891036 for 1 and CCDC-1891037 for 2 contain the supplementary crystallographic data excluding structure factors; this data can be obtained free of charge via www. ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Center, 12, Union Road, Cambridge CB2 1EZ, UK; fax: (þ44) 1223-336-033; or [email protected]). Acknowledgements Deanship of Research, Jordan University of Science and Technology is gratefully acknowledged for financial support, under grant No. (282/2017). References [1] G. Kornis, A.R. Katritzky, C.W. Rees (Eds.), Comprehensive heterocyclic chemistry, vol. 6, Pergamon Press, Oxford, 1984, p. 545. [2] I.S. Oae, Organic Sulfur Chemistry: Structure and Mechanism, CRC Press Inc., Florida, 1992. [3] E.S. Raper, Coord. Chem. Rev. 165 (1997) 475. [4] A.R. Katritzky, Z. Wang, R.J. Offerman, J. Heterocycl. Chem. 27 (1990) 139. [5] E. Corral, A.C. Hotze, H. Den Dulk, A. Leczkowska, A. Rodger, M.J. Hannon, J. Reedijk, J. Biol. Inorg. Chem. 14 (2009) 439. [6] G. Von Poelhsitz, A.L. Bogado, M.P. de Araujo, H.S. Selistre-de-Araujo, J. Ellena, E.E. Castellano, A.A. Batista, Polyhedron 26 (2007) 4707. [7] A. Massey, Y.Z. Xu, P. Karran, Curr. Biol. 11 (2001) 1142. [8] Z. Naal, E. Tfouni, A.V. Benedetti, Polyhedron 13 (1994) 133. [9] M. El-khateeb, Trans. Met. Chem. 28 (2001) 267. €rls, W. Weigand, J. Organomet. Chem. 692 [10] M. El-khateeb, K. Damer, H. Go (2007) 2228. [11] M. El-khateeb, M. Al-Noaimi, Z. Al-Amawi, A. Roller, S. Shova, Inorg. Chim. Acta 361 (2008) 2957. [12] D. Taher, S. Mohammad, J.F. Corrigan, D. MacDonald, M. El-khateeb, Inorg. Chim. Acta 363 (2010) 4134. €rls, W. Weigand, Polyhedron [13] M. El-khateeb, K. Shawakfeh, M. Al-Btoosh, H. Go 89 (2015) 70. [14] E.C. Constable, J. Lewis, J. Organomet. Chem. 254 (1983) 105. [15] B. Lima, S. Correa, A.E. Graminha, A.E. Kuznetzov, J. Ellena, F.R. Bavan, C.Q.F. Leite, A. Batista, J. Braz. Chem. Soc. 27 (2016) 30. [16] P.M. Treichel, R.A. Crane, K.N. Haller, J. Organomet. Chem. 401 (1991) 173. [17] P.M. Treichel, M.S. Schmidt, R.A. Crane, Inorg. Chem. 30 (1991) 379. [18] X.L. Lu, J.J. Vittal, E. Tieknik, L.Y. Goh, T.S. Andy Hor, J. Organomet. Chem. 698 (2004) 1444.
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oscillation mode“, in methods in enzymology, in: C.W. Carter, R.M. Sweet (Eds.), Macromolecular Crystallography, Part A, vol. 276, Academic Press, San Diego, USA, 1997, pp. 307e326. [24] SADABS 2016/2 L. Krause, R. Herbst-Irmer, G.M. Sheldrick, D. Stalke, J. Appl. Crystallogr. 48 (2015) [3]. [25] G.M. Sheldrick, Acta Crystallogr. C71 (2015) 3.
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc
Cyclopentadienyl ruthenium complexes of mixed heterocyclic thiol and Bis(diphenylphosphino)ferrocene ligands € rls b, Hadil Alshurafa a, Mohammad El-khateeb a, *, Hassan Abul-Futouh b, Helmar Go Wolfgang Weigand c a b c
Chemistry Department, Jordan University of Science and Technology, Irbid, 22110, Jordan Department of Pharmacy, Al-Zaytoonah University of Jordan, P.O. Box 130, Amman, 11733, Jordan €t Jena, Humboldt Straße 8, 07743, Jena, Germany Institut für Anorganische und Analytische Chemie, Friedrich-Schiller-Universita
a r t i c l e i n f o
a b s t r a c t
Article history: Received 2 February 2019 Received in revised form 19 March 2019 Accepted 1 April 2019 Available online 16 April 2019
Cyclopentadienyl ruthenium complexes bearing mixed heterocyclic thiol and bis(diphenylphsphino) ferrocene (dppf) ligands are presented. The complex-salts [CpRu(dppf)(k1S-HS-het)]PF6 {Cp ¼ h5-C5H5; HS-het ¼ 2-mercaptobenzothiazole (1), 2-mercaptobenzimidazole (2)} were synthesized from the reaction of CpRu(dppf)Cl with the thiol in the presence of KPF6 salt under reflux. Complexes 1 and 2 have been characterized by spectroscopic methods (1H-NMR, 31P{1H}-NMR, MS) and elemental analysis. The solid-state structures of [CpRu(dppf)(k1SeS2C7H5N)]PF6 (1) and [CpRu(dppf)(k1S-SC7H6N2)]PF6 (2) have been determined by X-ray crystallography. The cyclic voltammetry of these two complexes are measured. © 2019 Elsevier B.V. All rights reserved.
Keywords: Ruthenium Heterocyclic thiols X-ray structures Synthesis Characterization
1. Introduction Heterocyclic thiols containing the thioamide moiety are versatile ligands in coordination chemistry and may adopt several coordination modes using either the exocyclic sulfur and/or the endocyclic nitrogen atoms [1e4]. These compounds found applications in biological systems and proved to be antiviral, antibacterial and fungicidal agents [5e8]. We [9e13] and others [14,15] reported several ruthenium complexes of heterocyclic thiolato ligands. The complexes CpRu(PPh3)2(k1SeS-het) [het ¼ furyl, thiopheneyl, 2-imidazolyl, 1-methylimidazolyl, 5-methyl-1,3,5thiadiazolyl, 5-methyl-4H-1,2,4-triazolyl, 2mercaptobenzothiazolyl, 2-mercaptobenzimidazolyl, 2mercaptobenzoxazolyl] are reported from chloride/heterocyclic thiolate exchange reactions of CpRu(PPh3)2Cl and have sulfurcoordinated heterocyclic thiolates [9e12]. On the other hand, the 2-pyridine thiolate and the 2-pyrimidine thiolate coordinated to the Ru through both the N,S-atoms in a chelating fashion forming CpRu(PPh3)(k 2S,NeS-het) (het ¼ 2-pyridine, 2-pyrimidine) while
* Corresponding author. E-mail address: [email protected] (M. El-khateeb). https://doi.org/10.1016/j.molstruc.2019.04.008 0022-2860/© 2019 Elsevier B.V. All rights reserved.
4-mercaptopyridine formed CpRu(PPh3)2(k1SeS-4-py) which has sulfur coordination [13]. Complexes with bis(diphenylphosphino) methane (dppm) or bis(diphenylphosphino)ethane (dppe) (CpRu(k2P,P-dppm)(k 1SeS-het), CpRu(k2P,P-dppe)(k 1SeS-het)) are generated from the one pot reaction of CpRu(PPh3)2Cl, thiolate anions and the corresponding bis(phosphine) ligands for all heterocyclic thiolates mentioned above [12,13]. Ruthenium (II) complexes with the general formula [Ru(k2S,NeS-het)(bipy)(PeP)]PF6 [het ¼ 2-pyrimidine, PeP ¼ dppe, dppf, dppp (¼ 1,3bis(diphenylphosphino)propane] are reported and their activity against some tumor cells are also presented [14]. Indeed, thiols themselves are also good ligands and several ruthenium complex of them are known [16e19]. The complexes [CpRu(L)(L0 )(HSR)]PF6 (R ¼ But, Ph, L, L0 ¼ PPh(OMe)2, PPh2(OMe), P(OMe)3, PPh3, CO) are obtained from CpRu(L)(L0 )Cl, HSR and NH4PF6 [16,17]. 2-Mercaptopyridine, together with other thiols, reacted with CpRu(dppf)Cl to form the thiol salts [CpRu(dppf)(k1SHS-2-py)]BPh4 [18]. The protonation of CpRu(PPh3)2SR with HBF4 produced the corresponding thiol salts [CpRu(PPh3)2(k1S-HSR)]BF4 [19]. In this paper and as a continuing effort in the area of heterocylic thiol/thiolate complexes of ruthenium, we report the full details of the preparation and characterization of heterocylic thiol ruthenium
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complex-salts with bis(diphenylphosphino)ferrocene ligand.
2. Results and discussion 2.1. Synthesis and characterization The ruthenium heterocyclic thiol salts [CpRu(dppf)((k1S-HShet)]PF6 {Cp ¼ h5-C5H5; dppf ¼ 1.10 -bis(diphenylphosphino)ferrocene; HS-het ¼ 2-mercaptobenzothiazole (1), 2mercaptobenzimidazole (2)} are readily prepared from the reaction of the ruthenium chloride and the corresponding heterocyclic thiols in the presences of KPF6 as shown in Equation (1).
for 1 and 2, respectively, one is similar to that observed for the [CpRu(dppf)(kS-HS-2-py)]BPh4 complex of 9.66 ppm [18] and the other is much higher. This is expected result as these peaks are concentration dependent. The 31P{1H}-NMR spectra of complexes 1 and 2 consist of a singlet peak at 48.22 and 47.70 ppm, respectively, arising from the two equivalent P-atoms. This range is similar to the value observed for [CpRu(dppf)(k1S-HS-2-py)]BPh4 (47.7 ppm) [18]. The mass spectra of 1 and 2 displayed the molecular ion peak of the cation followed by another one formed by losing the thiol ligand.
2.2. Molecular structures of 1 and 2
(1)
The thiol complex-salts 1 and 2 are yellow to orange solids, stable to air as solids and in solution. The protonated site of these complexes is the more basic N-atom as proved by the X-ray structure determination of 1 and 2 (vide infra). The identity of these complexes is determined based on their 1H- and 31P{1H}-NMR spectroscopic data, mass spectrometry, elemental analysis and Xray structure determination. The 1H-NMR spectra of complexes 1 and 2 show a singlet in the range of 4.50e4.53 ppm attributable to the protons of the cyclopentadienyl ligand bonded to Ru, while the protons of the Cp-ligands of the ferrocene moiety are present as four-sets of multilplets in the range of 4.00e5.07 ppm. The range of the chemical shift data of CpRu-proton is comparable to those found in the thiolate analogous complexes [9e13] and those of the Cp2Fe-protons are similar to those observed for the reported [CpRu(dppf)L]þ (L ¼ S ¼ C(NH2)2, S]CS2C2H4, S]CS2C2H2, HSpy) complexes [18]. The protons of the phenyl rings of the dppf and the heterocyclic moieties are observed in the aromatic region as expected. The proton on the N-atom appeared at 11.32 and 9.40 ppm
The molecular structures of complexes 1 and 2 are unequivocally confirmed by single-crystal X-ray diffraction analysis. ORTEP views of the structures are shown in Fig. 1 and selected bond lengths (Å) and angles (º) of these complexes are given in Table 1. Both complexes contain one and half dichloromethane molecules per complex molecule. Thiols are bonded to ruthenium through the sulfur atom of the thioimide form with protonated nitrogen atom in which the NeH bond length (0.75(4) Å for 1 and 0.79(3), 0.83(3) Å for 2) is observed. This is expected as the protonated center is the more basic nitrogen atom as observed in similar complexes [10,18]. A notable feature of the structures is that the H atom (located on the N) is hydrogen bonded to one F atom of the PF6 anion. The distance (H/F) is in the range of 2.33(4)-2.53(4) Å for 1 and in the range of 2.26(3)-2.57(3) Å for 2. The RueC(Cp) bond distances of 1 and 2 are in the range of 2.191(2)-2.252(3) Å and are similar to those reported of CpRu-containing systems [9e13,20]. The RueS bond distance of 1 (2.3774(8) Å) is a bit shorter than that of 2 (2.3803(3) Å) and of the corresponding distance of [CpRu(PPh3)(NO)(k1S-HS-2-py)]BF4 (2.3927(7) Å) [10]. The RueP bond lengths of
Fig. 1. Molecular structures (50% probability) of complex 1 (left) and complex 2 (right). All hydrogen atoms are omitted for clarity but those of the N-atoms are shown with arbitrary radius.
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Table 1 Selected bond lengths (Å) and angles (º) for complex [CpRu(dppf)(k 1S eS2C7H5N)]PF6 (1) and [CpRu(dppf)(k 1S-SC7H6N2)]PF6. 1 RueC8 RueC9 RueC10 RueC11 RueC12 RueP1 RueP2 RueS1 S1eC1 S2eC1 N1eC1 N1eH P1eRueS1 P2eRueS1 P1eRueP2 RueSeC1
2 2.212(3) 2.247(3) 2.252(3) 2.232(3) 2.194(3) 2.3092(8) 2.3062(8) 2.3774(8) 1.679(3) 1.720(3) 1.361(3) 0.75(4) 87.95(3) 84.78(3) 97.98(3) 115.74(11)
RueC8 RueC9 RueC10 RueC11 RueC12 RueP1 RueP2 RueS S1eC1 N2eC1 N1eC1 N2eH P1eRueS P2eRueS P1eRueP2 RueSeC1
2.235(2) 2.238(2) 2.224(2) 2.191(2) 2.202(2) 2.3098(7) 2.3044(6) 2.3803(3) 1.695(3) 1.350(3) 1.355(3) 0.79(3) 84.87(2) 88.33(2) 97.99(2) 117.66(9)
1 (2.3092(8), 2.3062(8) Å) are comparable to those of 2 (2.3098(7), 2.3044(6) Å) and are in the same range observed for complexes [CpRu(dppf)(SCX2)]PF6 (X ¼ NH2, SCH, SCH2) [18]. The sulfur atom is sp3-hybridized as indicated from the RueSeC1 angle (1: 115.74(11)º, 2: 117.66(9)º). The P1eRueP2, P1eRueS and P2eRueS bond angles are comparable to those of [CpRu(dppf)(SCX2)]PF6 (X ¼ NH2, SCH, SCH2) [18] and indicated that the coordination around the ruthenium center is distorted octahedral.
wave potentials of complex 2 are shifted to less positive potential (80 and 120 mV, respectively) compared to those of complex 1. However, the half-wave potentials of both complexes show cathodic shifts (~300 and 400 mV, respectively) compared to [CpRu(dppf)Cl] complex [21]. These cathodic shifts can be explained by the difference in electron density added to the metal center by the presence of 2-mercaptobenzothiazole and 2mercaptobenzimidazole relative to Cl.
2.3. Electrochemistry
3. Experimental part
The electrochemical behaviour of complexes 1 and 2 was investigated by cyclic voltammetry (CV). Fig. 2 shows the cyclic voltammetric oxidation of complexes 1 and 2 in CH2Cl2-[n-Bu4N] [BF4] solutions at a scan rate of 0.2 V/s. On initiating the electrochemical scan in the anodic direction, two quasi-reversible anodic events at E1/2 ¼ 0.30 V and 0.63 V for complex 1 and at E1/2 ¼ 0.22 V and 0.51 V for complex 2 were observed. These oxidation peaks are corresponding to one electron transfer similar to the parent complex [CpRu(dppf)Cl] reported in the literature [21]. Moreover, the first oxidation peak of complexes 1 and 2 can be assigned to the metal-centered RuIII/RuII couple, while the second one is correlated to the oxidation of the dppf ligand which is comparable to the corresponding one of the [CpRu(dppf)Cl] complex [21]. The half-
3.1. General Reactions and manipulations were performed under inert atmosphere of nitrogen using Schlenk line techniques. Hexane (Na/ benzophenone), dichloromethane (P2O5) and absolute ethanol (Na) were freshly distilled prior to use. 2-Mercaptobenzoimidazole and 2-mercaptobenzothiazole were used as received (Acros). The complex CpRu(dppf)Cl was prepared as described in the literature [21].1H- and 31P{1H}-NMR spectra were recorded on a Brucker AVANCE 400 MHz spectrometer. Chemical shifts were recorded in ppm using the solvent as reference signal for 1H-NMR (CDCl3 d ¼ 7.26 ppm) and H3PO4 as external reference for 31P{1H}-NMR. Melting points were recorded by Melting Point Apparatus SMP3,
Fig. 2. Cyclic voltammetry of 1.0 mM solution of complexes 1 (left) and 2 (right) in CH2Cl2-[n-Bu4N][BF4] (0.1 M) solutions at 0.2 V/s scan rate. The arrows indicate the scan direction. The potentials E are given in V and referenced to the Fcþ/Fc couple.
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Stuart Scientific. The mass spectra were measured with Finnigan MAT SSQ 710 instrument. Elemental analyses were performed with a Leco CHNS-932 apparatus. 3.2. General procedure for the preparation of [CpRu(dppf)(k1S-HShet)]PF6 1, 2 Heterocyclic thiol (1.00 mmol), CpRu(dppf)Cl complex (1.00 mmol, 0.756 g) and potassium hexaflourophosphate (1.00 mmol, 0.145 g) were dissolved in absolute ethanol (100 mL). The resulting mixture was refluxed for 4 h. Then the volatiles were removed under vacuum and the residue was extracted by 2 5 mL of CH2Cl2. Condensation of the CH2Cl2 solution followed by addition of 40e50 mL hexane gave the product as yellow precipitate. The crude product was washed several times with cooled hexane and recrystallized from CH2Cl2/hexane. [CpRu(dppf)(k 1SeS2C7H5N)]PF6 (1): Yield 73%. M.p.: 262e263 C. 1 H NMR (CDCl3): d 4.00 (m, 2H, PC5H4), 4.14 (m, 2H, PC5H4), 4.48 (m, 2H, PC5H4), 4.55 (s, 5H, C5H5), 5.07 (m, 2H, PC5H4), 7.05 (m, 8H, PPh2), 7.35 (m, 12H, PPh2), 7.21 (d, 2H, C6H4), 7.56 (d, 2H, C6H4) 11.32 (br, 1H, NH). 31P{1H}-NMR (CDCl3) d 48.37. Anal. Calcd. for C46H38F6FeNP3RuS2.1.5CH2Cl2: C, 49.18; H, 3.56; N, 1.21; S, 5.53. Found C, 48.67; H, 3.35; N, 1.18 S, 5.48%. DEI-MS: m/z ¼ 886 [CpRu(dppf)S2C7H5N]þ, 721 [CpRu(dppf)]þ. [CpRu(dppf)(k 1S-SC7H6N2)]PF6 (2): Yield 68%. M.p.: 215e216 C. 1 H NMR (CDCl3): d 4.14 (m, 2H, PC5H4), 4.25 (m, 2H, PC5H4), 4.48 (m, 2H, PC5H4), 4.50 (s, 5H, C5H5), 5.00 (m, 2H, PC5H4), 7.20 (d, 2H, C6H4), 7.24 (d, 2H, C6H4), 7.40 (m, 12H, PPh2), 7.80 (m, 8H, PPh2), 9.40 (br, 1H, NH). 31P{1H}-NMR (CDCl3) d 47.70. Anal. Calcd. for C46H39F6N2P3RuS.1.5CH2Cl2: C, 49.86; H, 3.67; N, 2.44; S, 2.80. Found C, 49.78; H, 3.52; N, 2.30; S, 2.93%. DEI-MS: m/z ¼ 868 [CpRu(dppf)SC7H5N2]þ, 721 [CpRu(dppf)]þ. 3.3. X-ray crystal structure analysis The intensity data were collected on a Nonius KappaCCD diffractometer, using graphite-monochromated Mo-Ka radiation. Data were corrected for Lorentz and polarization effects; absorption was taken into account on a semi-empirical basis using multiple-scans [22e24]. The structures were solved by direct methods (SHELXS [25]) and refined by full-matrix least squares techniques against Fo2 (SHELXL-97 [25]). The hydrogen atoms bonded to the nitrogen atoms of 1 and 2 were located by difference Fourier synthesis and refined isotropically. All other hydrogen atoms were included at calculated positions with fixed thermal parameters. All non-hydrogen atoms were refined anisotropically [25]. XP (SIEMENS Analytical X-ray Instruments, Inc.) was used for structure representations. Crystal Data for 1: [C46H38FeNP2RuS2]þ[PF6]-1.5(CH2Cl2), Mr ¼ 1160.11 g mol-1, yellow prism, size 0.098 0.092 0.084 mm3, monoclinic, space group C 2/c, a ¼ 24.0259(4), b ¼ 12.6098(2), c ¼ 31.1113(6) Å, b ¼ 91.001(1) , V ¼ 9424.1(3) Å3, T ¼ 140 C, Z ¼ 8, rcalcd. ¼ 1.635 gcm3, m (MoKa) ¼ 10.49 cm1, multi-scan, transmin: 0.6939, transmax: 0.7456, F(000) ¼ 4680, 33811 reflections in h(-31/31), k(-16/15), l(-40/40), measured in the range 1.31 Q 27.47, completeness Qmax ¼ 99.6%, 10763 independent reflections, Rint ¼ 0.0365, 9599 reflections with Fo > 4s(Fo), 611 parameters, 0 restraints, R1obs ¼ 0.0451, wR2obs ¼ 0.1023, R1all ¼ 0.0524, wR2all ¼ 0.1067, GOOF ¼ 1.078, largest difference peak and hole: 1.510/1.141 e Å3. Crystal Data for 2: [C46H39FeN2P2RuS]þ[PF6]-.1.5(CH2Cl2), Mr ¼ 1143.07 g mol-1, yellow prism, size 0.112 0.100 0.088 mm3, monoclinic, space group C 2/c, a ¼ 23.7480(5), b ¼ 12.6310(3),
c ¼ 30.9038(6) Å, b ¼ 92.252(1) , V ¼ 9262.8(3) Å3, T ¼ 140 C, Z ¼ 8, rcalcd. ¼ 1.639 gcm3, m (Mo-Ka) ¼ 10.23 cm1, multi-scan, transmin: 0.6917, transmax: 0.7456, F(000) ¼ 4616, 32456 reflections in h(-30/30), k(-16/16), l(-40/40), measured in the range 1.32 Q 27.44 , completeness Qmax ¼ 98.9%, 10473 independent reflections, Rint ¼ 0.0387, 9362 reflections with Fo > 4s(Fo), 633 parameters, 0 restraints, R1obs ¼ 0.0357, wR2obs ¼ 0.0742, R1all ¼ 0.0436, wR2all ¼ 0.0778, GOOF ¼ 1.089, largest difference peak and hole: 0.532/0.603 e Å3. 4. Conclusion In this work, two complex-salts of ruthenium heterocyclic thiols are synthesized. The thiols are bonded to ruthenium through the sulfur atom in a monodentate fashion, while the dppf is bonded to ruthenium in a bidentate form as expected. The proton of the thiol is located at the more basic nitrogen atom leading to the thioimide form. This is evident from the structures of the complexes. Moreover, the electrochemical behaviour of the complexes concluded that both complexes 1 and 2 can be easily oxidized via two quasireversible processes. Possible origins of these processes could be assigned to the metal-centered RuIII/RuII couple and the dppf ligand-centered oxidations. 5. Supporting information available Crystallographic data deposited at the Cambridge Crystallographic Data Center under CCDC-1891036 for 1 and CCDC-1891037 for 2 contain the supplementary crystallographic data excluding structure factors; this data can be obtained free of charge via www. ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Center, 12, Union Road, Cambridge CB2 1EZ, UK; fax: (þ44) 1223-336-033; or [email protected]). Acknowledgements Deanship of Research, Jordan University of Science and Technology is gratefully acknowledged for financial support, under grant No. (282/2017). References [1] G. Kornis, A.R. Katritzky, C.W. Rees (Eds.), Comprehensive heterocyclic chemistry, vol. 6, Pergamon Press, Oxford, 1984, p. 545. [2] I.S. Oae, Organic Sulfur Chemistry: Structure and Mechanism, CRC Press Inc., Florida, 1992. [3] E.S. Raper, Coord. Chem. Rev. 165 (1997) 475. [4] A.R. Katritzky, Z. Wang, R.J. Offerman, J. Heterocycl. Chem. 27 (1990) 139. [5] E. Corral, A.C. Hotze, H. Den Dulk, A. Leczkowska, A. Rodger, M.J. Hannon, J. Reedijk, J. Biol. Inorg. Chem. 14 (2009) 439. [6] G. Von Poelhsitz, A.L. Bogado, M.P. de Araujo, H.S. Selistre-de-Araujo, J. Ellena, E.E. Castellano, A.A. Batista, Polyhedron 26 (2007) 4707. [7] A. Massey, Y.Z. Xu, P. Karran, Curr. Biol. 11 (2001) 1142. [8] Z. Naal, E. Tfouni, A.V. Benedetti, Polyhedron 13 (1994) 133. [9] M. El-khateeb, Trans. Met. Chem. 28 (2001) 267. €rls, W. Weigand, J. Organomet. Chem. 692 [10] M. El-khateeb, K. Damer, H. Go (2007) 2228. [11] M. El-khateeb, M. Al-Noaimi, Z. Al-Amawi, A. Roller, S. Shova, Inorg. Chim. Acta 361 (2008) 2957. [12] D. Taher, S. Mohammad, J.F. Corrigan, D. MacDonald, M. El-khateeb, Inorg. Chim. Acta 363 (2010) 4134. €rls, W. Weigand, Polyhedron [13] M. El-khateeb, K. Shawakfeh, M. Al-Btoosh, H. Go 89 (2015) 70. [14] E.C. Constable, J. Lewis, J. Organomet. Chem. 254 (1983) 105. [15] B. Lima, S. Correa, A.E. Graminha, A.E. Kuznetzov, J. Ellena, F.R. Bavan, C.Q.F. Leite, A. Batista, J. Braz. Chem. Soc. 27 (2016) 30. [16] P.M. Treichel, R.A. Crane, K.N. Haller, J. Organomet. Chem. 401 (1991) 173. [17] P.M. Treichel, M.S. Schmidt, R.A. Crane, Inorg. Chem. 30 (1991) 379. [18] X.L. Lu, J.J. Vittal, E. Tieknik, L.Y. Goh, T.S. Andy Hor, J. Organomet. Chem. 698 (2004) 1444.
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