Steric Control of the Coordination Mode of the
Salicylaldehyde Thiosemicarbazone Ligand.
Syntheses, Structures, and Redox Properties of
Ruthenium and Osmium Complexes
Falguni Basuli,1aShie-Ming Peng,1band Samaresh Bhattacharya*,1a
Inorganic Chemistry Section, Department of Chemistry, Jadavpur University, Calcutta 700032, India, and Department of Chemistry, National Taiwan University, Taipei, Taiwan, ROC ReceiVed May 1, 1997 Introduction
The chemistry of transition metal complexes of thiosemicar-bazones has been receiving considerable attention largely because of their pharmacological properties.2
Thiosemicarba-zones usually bind to a metal ion, either in the neutral thione form (1) or in the anionic thiolate form (2), as bidentate
N,S-donor ligands forming five-membered chelate rings.2,3
How-ever, incorporation of a third donor site (D) into these thiosemicarbazone ligands, linked to the carbonylic carbon via one or two intervening atoms, normally results in D,N,S tricoordination (3).2,4,5 In this note we report the chemistry of
two ruthenium and osmium complexes of the same ligand,Viz. salicylaldehyde thiosemicarbazone (Hsaltsc, where H stands for the dissociable proton). Though free Hsaltsc exists in the thione
form (4),6 it is known to coordinate as a dianionic tridentate
O,N,S donor.5 Reaction of Hsaltsc with [M(PPh
3)3X2] (M) Ru, Os; X)Cl, Br) afforded complexes of the type [M(PPh3)2 -(saltsc)2] where the salicylaldehyde thiosemicarbazone ligand
is coordinated, in spite of having the phenolic oxygen as the potential third donor site, as a bidentate N,S-donor ligand, forming a four-membered chelate ring (5). The steric bulk of
the coligand PPh3appears to be the driving force for this rather
unexpected coordination mode of the salicylaldehyde thiosemi-carbazone ligand. The syntheses, characterization, and cyclic voltammetric properties of these two [M(PPh3)2(saltsc)2]
com-plexes are described here. Experimental Section
Materials. [Ru(PPh3)3Cl2] and [Os(PPh3)3Br2] were synthesized according to reported procedures.7 Salicylaldehyde thiosemicarbazone (Hsaltsc) was prepared by reacting equimolar amounts of salicylalde-hyde and thiosemicarbazide in hot ethanol. Purification of dichlo-romethane and preparation of tetraethylammonium perchlorate (TEAP) for electrochemical work were performed as reported in the literature.8
Preparation of [Ru(PPh3)2(saltsc)2]. To a solution of Hsaltsc (42
mg, 0.22 mmol) in ethanol (40 mL) was added [Ru(PPh3)3Cl2] (100 mg, 0.10 mmol) followed by NEt3(0.22 mg, 0.22 mmol). The resulting mixture was stirred for 30 min at ambient temperature. The yellow precipitate of [Ru(PPh3)2(saltsc)2] was collected by filtration, washed thoroughly with ethanol, and dried in air. Recrystallization of the crude product from 1:1 dichloromethane-hexane solution gave [Ru(PPh3)2
-(saltsc)2] as a golden yellow crystalline solid. Yield: 72%. Anal. Calcd for C52H46N6O2P2S2Ru: C, 61.60; H, 4.54; N, 8.29. Found: C, 61.54; H, 4.59; N, 8.26.
Preparation of [Os(PPh3)2(saltsc)2]. This was prepared by
fol-lowing the above procedure (except that stirring was continued for 2 h at 60°C) using [Os(PPh3)3Br2] instead of [Ru(PPh3)3Cl2]. Yield: 67%. Anal. Calcd for C52H46N6O2P2S2Os: C, 56.62; H, 4.17; N, 7.62. Found: C, 56.54; H, 4.21; N, 7.58.
Physical Measurements. Microanalyses (C, H, N) were performed
using a Perkin-Elmer 240C elemental analyzer. IR spectra were obtained on a Perkin-Elmer 783 spectrometer with samples prepared as KBr pellets. Electronic spectra were recorded on a Simadzu UV-1601 spectrophotometer. Magnetic susceptibilities were measured using a PAR 155 vibrating-sample magnetometer. 1H NMR spectra were obtained on a Bruker AC-200 NMR spectrometer using TMS as the internal standard. Electrochemical measurements were made using a PAR model 273 potentiostat. A platinum-disk working electrode, a platinum-wire auxiliary electrode, and an aqueous saturated calomel reference electrode (SCE) were used in a three-electrode configuration. A platinum-wire gauze electrode was used in the coulometric experi-ments. An RE 0074 X-Y recorder was used to trace the voltammo-grams. Electrochemical measurements were made under a dinitrogen
(1) (a) Jadavpur University. (b) National Taiwan University.
(2) (a) Campbell, M. J. M. Coord. Chem. ReV. 1975, 15, 279. (b) Padhye, S. B.; Kauffman, G. B. Coord. Chem. ReV. 1985, 63, 127. (c) Haiduc, I.; Silvestru, C. Coord. Chem. ReV. 1990, 99, 253. (d) West, D. X.; Padhye, S. B.; Sonawane, P. B. Struct. Bonding 1991, 76, 1. (e) West, D. X.; Liberta, A. E.; Padhye, S. B.; Chikate, R. C.; Sonawane, P. B.; Kumbhar, A. S.; Yerande, R. G. Coord. Chem. ReV. 1993, 123, 49. (3) Tion, Y. P.; Duan, C. Y.; Lu, Z. L.; You, X. Z.; Fun, H. K.;
Kandasamy, S. Polyhedron 1996, 15, 2263.
(4) (a) Souza, P.; Matesanz, I. A.; Fernandez, V. J. Chem. Soc., Dalton Trans. 1996, 3011. (b) Kovala-Demertzi, D.; Domopoulou, A.; Demertzis, M. A.; Valdes-Martinez, J.; Hernandez-Ortega, S.; Espi-nosa-Perez, G.; West, D. X.; Salberg, M. M.; Bain, G. A.; Bloom, P. D. Polyhedron 1996, 15, 2587. (c) Ali, M. A.; Dey, K. K.; Nazimuddin, M.; Smith, F. E.; Butcher, R. J.; Jasinski, J. P.; Jasinski, J. M. Polyhedron 1996, 15, 3331.
(5) (a) De Bolfo, A.; Smith, T. D.; Boas, J. F.; Pilbrow, J. R. Aust. J. Chem. 1976, 29, 2583. (b) Lu, Z.; White, C.; Rheingold, A. L.; Crabtree, R. H. Inorg. Chem. 1993, 32, 3991. (c) West, D. X.; Yang, Y.-H.; Klein, T. L.; Goldberg, K. I.; Liberta, A. E.; Valdes-Martinez, J.; Toscano, R. A. Polyhedron 1995, 14, 1681. (d) West, D. X.; Yang, Y.-H.; Klein, T. L.; Goldberg, K. I.; Liberta, A. E.; Valdes-Martinez, J.; Hernandez-Ortega, S. Polyhedron 1995, 14, 3051.
(6) Chattopadhyay, D.; Mazumdar, S. K.; Banerjee, T.; Ghosh, S.; Mak, T. C. W. Acta Crystallogr. 1988, C44, 1025.
(7) (a) Stephenson, T. A.; Wilkinson, G. J. Inorg. Nucl. Chem. 1966, 28, 945. (b) Hoffman, P. R.; Caulton, K. G. J. Am. Chem. Soc. 1975, 97, 4221.
(8) (a) Sawyer, D. T.; Roberts, J. L., Jr. Experimental Electrochemistry for Chemists; Wiley: New York, 1974; pp 167-215. (b) Walter, M.; Ramaley, L. Anal. Chem. 1973, 45, 165.
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Inorg. Chem. 1997, 36, 5645-5647
S0020-1669(97)00509-0 CCC: $14.00 © 1997 American Chemical Society
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atmosphere. All electrochemical data were collected at 298 K and are uncorrected for junction potentials.
Crystallography of [Ru(PPh3)2(saltsc)2]‚2CH2Cl2. Single crystals
were grown by slow diffusion of hexane into a dichloromethane solution of the complex. Selected crystal data and data collection parameters are given in Table 1. The unit cell dimensions were determined by a least-squares fit of 25 machine-centered reflections (15.18 < 2θ <27.08°). Data were collected on an Enraf-Nonius CAD-4
diffracto-meter using graphite-monochromated Mo KRradiation (λ)0.7107
Å) byθ-2θ scans within the angular range 3.0-45.0°. Three standard
reflections measured every 3600 s of X-ray exposure showed no significant intensity variation over the course of data collection. X-ray data reduction and structure solution and refinement were done using the NRCVAX package. The structure was solved by the Patterson method. Final cycles of refinement converged with discrepancy indices of R)0.049 and Rw)0.049.
Results and Discussion
Reaction of [Ru(PPh3)3Cl2] with Hsaltsc in a 1:2 mole ratio
in the presence of NEt3affords [Ru(PPh3)2(saltsc)2] in decent
yield. It may be noted here that even when a 1:1 mole ratio of the reactants was used, the same bis complex was obtained together with some unreacted [Ru(PPh3)3Cl2], as expected.
Synthesis of [Os(PPh3)2(saltsc)2] was achieved similarly,
al-lowing a relatively longer reaction time and a slightly higher temperature. The complexes are diamagnetic, which corre-sponds to the bivalent state of the metals (low-spin d6, S
)0)
in these complexes.
The molecular structure of [Ru(PPh3)2(saltsc)2] was
deter-mined by X-ray crystallography. A view of the complex molecule is shown in Figure 1, and selected bond distances and angles are listed in Table 2. The two PPh3ligands are in cis
positions as usually observed in bis(triphenylphosphine) com-plexes of ruthenium(II).9 The saltsc ligands are coordinated as
shown in 5 with a bite angle of∼66°, causing severe angular distortion of the RuN2P2S2 coordination sphere from ideal
octahedral geometry. As a result, the P1-Ru-N1, P2-Ru -N4, and S1-Ru-S2 angles deviate significantly from linearity. The phenolic hydrogens are hydrogen-bonded to the azomethine nitrogens as in the case of uncoordinated Hsaltsc.6 The observed
Ru-P and Ru-S distances are quite normal.
9a However, the
Ru-N distances are a bit longer than what is usually observed,9c
which may be attributed to the strong trans effect of the PPh3
ligands. The C-N distances within the chelate ring (C1-N1 and C9-N4) are shorter than a formal single bond (e.g. C1 -N2 and C9-N5) and longer than a formal double bond (e.g. C2-N3 and C10-N6). Similarly the C-S distances (C1-S1 and C9-S2) are intermediate between C(sp
2)
-S (1.76 Å) 10and
CdS (1.63 Å).11 This is in accordance with the resonance
possible in the coordinating part of the saltsc ligand as illustrated in 5.
The structure of [Ru(PPh3)2(saltsc)2] has a C2 symmetry,
which is also reflected in the1H NMR spectrum of this complex
recorded in CDCl3 solution. The aromatic region of the
spectrum is rather complex due to overlap of signals. However, the spectrum clearly shows the azomethine proton signal at 8.89 ppm, the phenolic proton resonance at 10.48 ppm, and the two amine hydrogens at 4.71 ppm. The1H NMR spectrum of
[Os-(PPh3)2(saltsc)2] is almost identical to that of the ruthenium
complex, indicating that [Os(PPh3)2(saltsc)2] has a similar
structure. Electronic spectra of the [M(PPh3)2(saltsc)2]
com-plexes in dichloromethane solution show several intense adsorp-tions in the visible region (Table 3) which are probably due to allowed metal-to-ligand charge-transfer transitions.
Cyclic voltammograms of the [M(PPh3)2(saltsc)2] complexes
were recorded in dichloromethane solution. Each complex shows two oxidative responses on the positive side of SCE (Table 3). The oxidation potentials of the osmium complex are lower than those of the ruthenium analogue, as usually (9) (a) Pramanik, A.; Bag, N.; Lahiri, G. K.; Chakravorty, A. J. Chem.
Soc., Dalton Trans. 1990, 3823. (b) Pierpont, C. G.; Bhattacharya, S. Inorg. Chem. 1991, 30, 1511. (c) Menon, M.; Pramanik, A.; Bag, N.; Chakravorty, A. J. Chem. Soc., Dalton Trans. 1995, 1417.
(10) Collins, R. C.; Davis, R. E. Acta Crystallogr., Sect. B 1978, B34, 283. (11) Arjunan, P.; Ramamurthy, V.; Venkatesan, K. Acta Crystallogr., Sect.
C 1984, C40, 556. Table 1. Crystallographic Data for [Ru(PPh3)2(saltsc)2]‚2CH2Cl2
empirical formula C54H50N6O2P2S2Cl4Ru
fw 1183.97
space group triclinic P1h
a, Å 14.863(3) b, Å 14.830(3) c, Å 16.025(3) R, deg 65.103(17) β, deg 62.503(17) γ, deg 64.950(18) V, Å3 2724.5(9) Z 2 Pcalcd, g cm-3 1.443 Fobsd, g cm -3 1.440 λ, Å 0.7107 crystal size, mm 0.15× 0.30 × 0.35 T,°C 25 µ, cm-1 4.528 Ra 0.049 Rwb 0.049 GOF 1.68 aR )∑||Fo|-|Fc||/∑|Fo|. bR w)[∑w(|Fo|-|Fc|) 2/∑w(F
o)2]1/2. Figure 1. View of the [Ru(PPh
3)2(saltsc)2] molecule.
Table 2. Selected Bond Distances and Bond Angles for
[Ru(PPh3)2(saltsc)2]‚2CH2Cl2 Bond Distances (Å) Ru-S1 2.428(2) C1-S1 1.722(8) Ru-S2 2.425(2) C1-N1 1.320(9) Ru-P1 2.325(2) C1-N2 1.344(9) Ru-P2 2.321(2) C2-N3 1.283(10) Ru-N1 2.152(6) C9-S2 1.719(8) Ru-N4 2.152(6) C9-N4 1.319(9) C9-N5 1.333(9) C10-N6 1.289(10)
Bond Angles (deg)
S1-Ru-S2 161.23(7) S1-Ru-N1 65.96(16)
P1-Ru-N1 161.90(16) S2-Ru-N4 65.52(16)
P2-Ru-N4 161.38(16) P1-Ru-P2 105.95(7)
5646 Inorganic Chemistry, Vol. 36, No. 24, 1997 Notes
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observed.9a,12 The first reversible response is assigned to M(II) -M(III) oxidation. The one-electron nature of this oxidation was verified by constant-potential coulometry. The oxidized solu-tions containing [MIII(PPh
3)2(saltsc)2]+
ions are light green and display voltammograms identical to those of their precursors (except that the M(II)-M(III) couple appears as a reductive response). These oxidized solutions are quantitatively converted
back to yellow solutions of [MII(PPh
3)2(saltsc)2] by coulometric
reduction. The second response is irreversible and is tentatively assigned to M(III)-M(IV) oxidation. The one-electron nature of this oxidation was established by comparing its current height (ipa) with that of the M(II)-M(III) couple.
Variation of steric bulk of the coligand in order to force O,N,S tricoordination of the salicylaldehyde thiosemicarbazone ligand is currently under investigation. The possibility of using these [M(PPh3)2(saltsc)2] complexes as precursors for making
poly-nuclear complexes, utilizing the donor atoms on the pendant part of the N,S-coordinated saltsc ligands, is also being explored. Acknowledgment. Financial assistance received from the Council of Scientific and Industrial Research, New Delhi [Grant No. 01(1408)/96/EMR-II], is gratefully acknowledged, as is financial support from the Third World Academy of Sciences for the purchase of an electrochemical cell system. F.B. thanks the University Grants Commission, New Delhi, for a fellowship.
Supporting Information Available: Tables containing crystal data
and details of the structure determination, atomic coordinates, aniso-tropic thermal parameters, and bond distances and angles (9 pages). Ordering information is given on any current masthead page. IC9705094
(12) (a) Kober, E. M.; Casper, J. V.; Sullivan, B. P.; Meyer, T. J. Inorg. Chem. 1988, 27, 4587. (b) Pramanik, A.; Bag, N.; Lahiri, G. K.; Chakravorty, A. J. Chem. Soc., Dalton Trans. 1992, 101.
Table 3. Electronic Spectral and Cyclic Voltammetric Data
compound electronic spectral dataaλ max, nm (, M-1cm-1) cyclic voltammetric dataa,bE 1/2, V (∆Ep, mV) [Ru(PPh3)2(saltsc)2] 440c(1100), 342 (7400), 0.41 (60), 1.10d 304c(8900), 266 (14 700) [Os(PPh3)2(saltsc)2] 475c(1800), 375c(12 500), 0.21 (60), 1.02d 338 (21 700), 314c (18 200), 272 (22 400)
aIn dichloromethane solution.bSupporting electrolyte TEAP; refer-ence electrode SCE; E1/2)0.5(Epa+Epc), where Epaand Epcare anodic
and cathodic peak potentials, respectively;∆Ep)Epa-Epc; scan rate
50 mV s-1.cShoulder.dE
pavalue.
Notes Inorganic Chemistry, Vol. 36, No. 24, 1997 5647
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![Table 1. Crystallographic Data for [Ru(PPh 3 ) 2 (saltsc) 2 ] ‚ 2CH 2 Cl 2](https://thumb-ap.123doks.com/thumbv2/9libinfo/8665257.195404/2.918.496.812.57.358/table-crystallographic-data-ru-pph-saltsc-ch-cl.webp)
