Comparative study of NS2(S-aryl) pyridine-based dithia-containing ligands with different substituent groups. Reactivity toward Cu(II) and Ru(II)

Article abstract of DOI:10.1021/ic000903t

Ligands LX of the type NS₂ with S-aryl substituents which incorporate the unit 2,6-bis(thiomethyl)pyridine modified with functional groups bonded to the aromatic moieties, either on the phenyl or on the pyridine, are produced. Electron-withdrawing groups, 3-chloro and 4-nitro, that reduce the pyridine basicity have been introduced. Methoxy or methoxycarbonyl substituents have been incorporated on the thiophenyl moieties. The comparative results from the reaction of these ligands with Cu(ClO₄)₂·6H₂O and [RuCl₂(PPh₃)₃] have revealed that their coordination capacity has not been greatly modified as a result of the introduced groups. Complexes of general formulas [Cu(LX)][ClO₄]₂, except for L5, and [RuCl₂(LX)(PPh₃)], have been obtained, respectively. The electronic characteristics of these complexes have been studied by cyclic voltammetry experiments. The structures of 2,6-bis[(2′-methoxycarbonyl)phenylthio-methyl]-4-nitropyridine (L5) and [RuCl₂(L5)(PPh₃)]·2CCl₄ have been characterized by single-crystal X-ray diffraction methods.

Full text of DOI:10.1021/ic000903t

4010
Inorg. Chem. 2001, 40, 4010-4015
Comparative Study of NS2(S-aryl) Pyridine-Based Dithia-Containing Ligands with Different
Substituent Groups. Reactivity toward Cu(II) and Ru(II)
F. Teixidor,*,† P. Angle`s,† C. Vin˜as,† R. Kiveka1s,‡ and R. Sillanpa1a1§
Institut de Cie`ncia de Materials, CSIC, Campus UAB, E-08193 Bellaterra, Spain,
Department of Chemistry, University of Helsinki, Box 55, FIN-00014 Helsinki, Finland, and
Department of Chemistry, University of Turku, FIN-20014 Turku, Finland
ReceiVed August 8, 2000
Ligands LX of the type NS2 with S-aryl substituents which incorporate the unit 2,6-bis(thiomethyl)pyridine modified
with functional groups bonded to the aromatic moieties, either on the phenyl or on the pyridine, are produced.
Electron-withdrawing groups, 3-chloro and 4-nitro, that reduce the pyridine basicity have been introduced. Methoxy
or methoxycarbonyl substituents have been incorporated on the thiophenyl moieties. The comparative results
from the reaction of these ligands with Cu(ClO4)2‚6H2O and [RuCl2(PPh3)3] have revealed that their coordination
capacity has not been greatly modified as a result of the introduced groups. Complexes of general formulas
[Cu(LX)][ClO4]2, except for L5, and [RuCl2(LX)(PPh3)], have been obtained, respectively. The electronic
characteristics of these complexes have been studied by cyclic voltammetry experiments. The structures of 2,6-
bis[(2′-methoxycarbonyl)phenylthio-methyl]-4-nitropyridine (L5) and [RuCl2(L5)(PPh3)]‚2CCl4 have been char-
acterized by single-crystal X-ray diffraction methods.
Introduction
diacetylpyridine,6 or the likes. There exist related tricoordinating
ligands that incorporate two pyridine moieties joined by
nitrogen, e.g., bis(2-pyridylmethyl)amine,7 or a thioether, e.g.,
bis(6-methyl-2-pyridylmethyl)thioether.8 Structurally more re-
lated to the work presented in this paper are the non-imine 2,6-
pyridine derivatives, e.g., 2,6-[bis(dimethylamino)methyl]-
pyridine9 or bis(tert-butylaminomethyl)pyridine.10
Ligands that bind a metal in a 1:1 ratio can be of interest in
membrane transport, especially if the ligand is tethered to a
support.1 Tricoordinating ligands are especially attractive be-
cause they bind the metal in a bichelating way and do not fulfill
all possible coordinating positions, permitting an adequate
release of the metal in the stripping solution. In M/H+ counter-
transport it is also necessary that the carrier is sensitive to H+.
Thus pyridine derivatives are very promising. The tricoordi-
nating terpy ligand complexed to Ru(II)2 or Cu(II)3 has often
been used, but it binds to the metals too strongly to be useful
in transport. Thioethers are too weak coordinating ligands,
although macrocyclic polythioethers form reasonably strong
complexes.4 A ligand combining one base, pyridine, and two
thioether units could be a good choice. There are, however, few
examples of such a combination of donor atoms.5 Tricoordi-
nating ligands incorporating the pyridine moiety are usually the
result of diimine formation from the readily available 2,6-
It has been shown that 2,6-[bis(alkylthio)methyl]pyridine,
NS2(S-alkyl), ligands coordinate in a 1:1 ratio to Zn(II), Cu(II),
and Ni(II).11 The ligand preferentially forces the metal to a
pentacoordinate environment with the counterions in a cis
disposition, although the octahedral arrangement is found in
Ru(II) complexes.5 It was also demonstrated that, when 15-
aza-6-oxa-3,9-dithiabicyclo[9.3.1]pentadeca-1(15),11,13-
triene ligand, a NS2(S-alkyl), was used as ionophore in an all-
solid-state ISE, some discrimination of Cu(II) vs Ni or Co(II)
(Kpot
) 0.1)11 was found. We had also shown that the
Cu,Ni,orCo
NS2(S-aryl) ligands coordinate to Cu(II) much more easily than
to Zn(II) and Ni(II). Thus a marked difference exists between
* Author to whom correspondence should be addressed. Fax: Interna-
tional Code + 93 5805729. E-mail: teixidor@icmab.es.
† Institut de Cie`ncia de Materials, CSIC, Campus UAB.
‡ University of Helsinki.
(5) We revert to refs 2-8 indicated in Vin˜as et al.: Vin˜as, C.; Angle`s,
P.; Sa´nchez, G.; Lucena, N.; Teixidor, F.; Escriche, L.; Casabo´, J.;
Piniella, J. F.; Alvarez-Larena, A.; Kiveka¨s, R.; Sillanpa¨a¨, R. Inorg.
Chem. 1998, 37, 701.
(6) Some examples of application in catalysis: (a) Birtovsek, G. J. P.;
Gibson, V.; Kimberley, B. S.; Maddox, P. J.; McTavish, S. J.; Solan,
G. A.; White, A. J. P.; Williams, D. J. Chem. Commun. 1998, 849.
(b) Bianchini, C.; Lee, H. M Organometallics 2000, 19, 1833.
(7) Thomas, K. R. J.; Velusamy, M.; Palaniandavar, M. Acta Crystallogr.,
Sect. C: Cryst. Struct. Commun. 1998, C54, 741.
§ University of Turku.
(1) (a) Barboiu, M.; Guizard, C.; Hovnanian, N.; Palmeri, J.; Reibel, C.;
Cot, L.; Luca, C. J. Membr. Sci. 2000, 172, 91. (b) Elliott, B. J.; Willis,
W. B.; Bowman, C. N. J. Membr. Sci. 2000, 168, 109 (c) Yahaya, G.
O.; Brisdon, B. J.; England, R.; Hamad, E. Z. J. Membr. Sci. 2000,
172, 253.
(2) Some recent examples where the physical properties of Ru/bipy are
studied: (a) Licini, M.; Gareth W. J. A. Chem. Commun. 1999, 1943.
(b) Constable, E. C.; Housecroft, C. E.; Schofield, E. R.; Encinas, S.;
Armaroli, N.; Barigelletti, F.; Flamigni, L.; Figgemeier, E.; Vos, J.
G. Chem. Commun. 1999, 869. (c) Osawa, M.; Sonoki, H.; Hoshino,
M.; Wakatsuki, Y. Chem. Lett. 1998, 1081.
(3) One example of application of Cu/bipy can be: Jenkins, L. A.; Bashkin,
J. K.; Pennock, J. D.; Florian, J.; Warshel, A. Inorg. Chem. 1999, 38,
3215.
(8) Diebold, A.; Kyritsakas, N.; Fischer, J.; Weiss, R. Acta Crystallogr.,
Sect. C: Cryst. Struct. Commun. 1996, C52, 632.
(9) Abbenhuis, R. A. T. M.; del Rio, I.; Bergshoef, M. M.; Boersma, J.;
Veldman, N.; Spek, A. L.; van Koten, G. Inorg. Chem. 1998, 37, 1749.
(10) Gemel, C.; Folting, K.; Caulton, K. G. Inorg. Chem. 2000, 39, 1593.
(11) (a) Teixidor, F.; Escriche, Ll.; Casabo´, J.; Molins, E.; Miravitlles, C.
Inorg. Chem. 1986, 25, 4060. (b) Teixidor, F.; Casabo´, J.; Escriche,
Ll.; Alegret, S.; Martinez-Fabregas, E.; Molins, E.; Miravitlles, C.;
Rius, J. Inorg. Chem. 1991, 30, 1893. (c) Teixidor, F.; Sanchez-
Castello´, G.; Lucena, N.; Escriche, L.; Kiveka¨s, R.; Sundberg, M.;
Casabo´, J. Inorg. Chem. 1991, 30, 4931.
(4) Mullen, G. E. D.; Went, M. J.; Wocadlo, S.; Powell, A. K.; Blower,
P. J. Angew. Chem., Int. Ed. Engl. 1997, 36, 1205.
10.1021/ic000903t CCC: $20.00 © 2001 American Chemical Society
Published on Web 07/03/2001

NS2(S-aryl) Pyridine-Based Dithia-Containing Ligands
Inorganic Chemistry, Vol. 40, No. 16, 2001 4011
Synthesis of 2,6-Bis(bromomethyl)-4-nitropyridine. A stirred
mixture of 4-nitro-2,6-lutidine (2.66 g, 17.5 mmol), N-bromosuccin-
imide (10.17 g, 56.0 mmol), azobis(isobutyronitrile) (75 mg, radical
initiator), and benzene (100 mL) was refluxed under light (200 W
incandescent bulb) for 12 h. On cooling, a residue formed by
succinimide precipitate was filtered and washed with diethyl ether (2
× 50 mL). The benzene and the diethyl ether filtrates were joined and
washed with sodium carbonate solution and water. The organic layer
was dried over MgSO4 and evaporated under vacuum, and the red oily
residue was chromatographed on silica gel using chloroform/hexane
(3:2) as mobile phase, Rf ) 0.2. Yield: 0.54 g, 1.7 mmol (10%). IR
(KBr): ν 3085 (Caryl-H), 2924 (Calkyl-H), 1545 (NO2) cm-1. 1H NMR
(CDCl3): δ 4.63 (s, 4H, py-CH2-Br), 8.10 (s, 2H, H3py). 13C{1H}
NMR (CDCl3): δ 31.9 (s, py-CH2-Br), 115.6 (s, C3py), 155.4 (s, C2py),
159.9 (s, C4py).
Synthesis of 2,6-Bis(bromomethyl)-3-chloropyridine. Following
the procedure for 2,6-bis(bromomethyl)-4-nitropyridine, 2,6-bis(bro-
momethyl)-3-chloropyridine was prepared, using 3-chloro-2,6-lutidine
(1.02 g, 7.2 mmol), N-bromosuccinimide (3.12 g, 17.3 mmol), azobis-
(isobutyronitrile) (150 mg, radical initiator), and benzene (100 mL).
The mixture was refluxed for 3 h. The final residue was chromato-
graphed on silica gel using chloroform/hexane (1:1) as mobile phase,
NS2(S-alkyl) and NS2(S-aryl) ligands that had been evidenced
in Cu(II) complexes by cyclic voltammetry.12 The NS2(S-aryl)
ligands contain the hard N-donor and soft S-donor atoms but
also a π-system able to accept electron density from the metal.
An improvement of the ligand π-acidity is accompanied by a
reduction of the ligand’s σ-donor ability13 which is related to
its basicity. These characteristics prompted us to study further
the NS2(S-aryl) ligands, to know to what extent substituents in
the pyridine and phenyl groups would modify the σ-donor
capacity, i.e., basicity, of the pyridine ring and their electronic
properties. In this paper we report the synthesis of this type of
NS2(S-aryl) ligand and the reactivity of these ligands toward
Cu(II) and Ru(II). The influence of substituent on the pKA of
the ligands and the reduction potentials (E1/2) of the Cu(II) and
Ru(II) complexes are determined and discussed.
Experimental Section
Materials and Methods. The compounds 4-nitro-2,6-lutidine14 and
3-chloro-2,6-lutidine15 were synthesized as reported. 4-Methoxyben-
zenethiol was commercially available (Aldrich) and used as received.
2,6-Bis[(2′-methoxycarbonyl)phenylthiomethyl]pyridine (L1) and its
Cu(II) complex, [Cu(ClO4)2(L1)]‚H2O, were synthesized as described
previously.12 2,6-Bis[(3′-methoxycarbonyl)phenylthiomethyl]pyridine
(L2), 2,6-bis[(4′-methoxycarbonyl)phenylthiomethyl]pyridine (L3), and
2,6-bis[(4′-methoxyphenyl)thiomethyl]pyridine (L4) and their Ru(II)
complexes, in the form [RuCl2(LX)(PPh3)] (LX ) L1-L4), were
synthesized as described previously,16 as was the starting ruthenium
complex [RuCl2(PPh3)3].17
Rf ) 0.3. Yield: 0.26 g, 0.9 mmol (12%). IR (KBr): ν 3048 (Caryl
-
H), 2966 (Calkyl-H), 581 (C-Br) cm-1. 1H NMR (CDCl3): δ 4.53 (s,
3
2H, py-(CH2)a-Br), 4.68 (s, 2H, py-(CH2)b-Br), 7.40 (d, J(H,H)
3
) 8.4, 1H, H5py), 7.71 (d, J(H,H) ) 8.4, 1H, H4py). 13C{1H} NMR
(CDCl3): δ 30.7 (s, py-(CH2)a-Br), 32.5 (s, py-(CH2)b-Br), 124.5
(s, C5py), 131.0 (s, C3py), 138.6 (s, C4py), 153.5 (s, C6py), 155.2 (s, C2py).
Anal. Calcd for C7H6Br2ClN: C, 28.06; H, 2.00; N, 4.68. Found: C,
28.34; H, 2.00; N, 4.46.
Microanalyses were performed using a Perkin-Elmer 240B mi-
croanalyzer. IR spectra were obtained as KBr pellets on a Nicolet 710-
Synthesis of 2,6-Bis[(2′-methoxycarbonyl)phenylthiomethyl]-4-
nitropyridine (L5). To a stirred solution of sodium metal (0.12 g, 5.1
mmol) in methanol (25 mL) was added thiosalicylic methyl ester (0.85
g, 5.1 mmol), and the mixture was stirred for a further 10 min. The
solution was then added to another solution of 2,6-bis(bromomethyl)-
4-nitropyridine (0.78 g, 2.5 mmol) in methanol (20 mL). After addition,
a yellow precipitate appeared. The mixture was stirred at 30-35 °C
for 30 min. The precipitate was filtered, washed with methanol (2 × 5
mL) and water (2 × 5 mL), redissolved in chloroform, dried over
MgSO4, and vacuum evaporated to afford L5 as a yellow solid. Yield:
1
FT spectrophotometer. The H NMR (300.13 MHz), 13C{1H} NMR
(75.47 MHz), and 31P{1H} NMR (121.5 MHz) spectra were recorded
on a Bruker ARX 300 spectrometer. Chemical shift values for 1H NMR
and 13C{1H} NMR spectra are referenced to an internal standard of
SiMe4 in deuterated solvents. Chemical shift values for 31P{1H} NMR
spectra are referenced relative to external 85% H3PO4. Chemical shifts
are reported in units of parts per million and coupling constants in
hertz.
All ligands and complexes were synthesized under a nitrogen
atmosphere using Schlenk techniques. Solvents were placed under
vacuum to eliminate dissolved oxygen.
0.86 g, 1.8 mmol (71%). IR (KBr): ν 3023 (Caryl-H), 2952 (Calkyl
-
H), 1708 (CdO), 1536 (NO2), 1278, 1250 (C-O-C) cm-1. 1H NMR
(CDCl3): δ 3.67 (s, 6H, -COOCH3), 4.16 (s, 4H, py-CH2-S), 6.92-
7.72 (m, 8H, HPh), 7.80 (s, 2H, H3py). 13C{1H} NMR (CDCl3): δ 38.5
(s, py-CH2-S), 52.2 (s, COOCH3), 114.4-160.4 (Caryl), 166.7 (s,
-COOCH3). Anal. Calcd for C23H20N2O6S2: C, 56.91; H, 4.12; N, 5.77;
S, 13.19. Found: C, 56.95; H, 4.23; N, 5.73; S, 13.19. Crystals suitable
for X-ray diffraction were grown from a carbon tetrachloride solution.
Synthesis of 2,6-Bis[(2′-methoxycarbonyl)phenylthiomethyl]-3-
chloropyridine (L6). L6 was prepared following the same procedure
as for L5, using thiosalicylic methyl ester (0.82 g, 4.9 mmol), sodium
metal (0.11 g, 4.9 mmol), and 3-chloro-2,6-bis(bromomethyl)pyridine
(0.73 g, 2.4 mmol). Yield: 1.01 g, 2.1 mmol (88%). IR (KBr): ν 3062
(Caryl-H), 2953 (Calkyl-H), 1716, 1705 (CdO), 1308, 1274, 1253 (C-
O-C) cm-1. 1H NMR (CDCl3): δ 3.90 (s, 3H, (COOCH3)A), 3.91 (s,
3H, (COOCH3)B), 4.27 (s, 2H, (py-CH2-S)A), 4.43 (s, 2H, (py-CH2-
Cyclic voltammetric measurements were performed on 1-5 mM
solutions of the complexes in dry acetonitrile that contained 0.1 M
[Bu4N][ClO4] as supporting electrolyte at a rate of 20-100 mV s-1
.
Two platinum wires, as working electrode and counter electrode, were
used with a Ag/AgCl/Cl- (0.1 M in acetonitrile) electrode as reference.
In our experimental setup, the Fc+/Fc redox couple was found at 0.820
V with reference to Ag/AgCl/Cl- (0.1 M in acetonitrile). For
comparison purposes potential values could be corrected to normal
hydrogen electrode (NHE) based on the assumption that E1/2 ) 0.340
V for Fc+/Fc in acetonitrile.18 An EG&G Princeton Applied Research
potentiostat-galvanostat model 273a was used.
SAFETY NOTE! Perchlorate salts of metal complexes with organic
ligands are potentially explosive. Small amounts of perchlorate salts
should be prepared and should be handled with great care.
3
3
S)B), 7.12 (ddd, J(H4PhA,H3PhA) ) 7.7 Hz, J(H4PhA,H5PhA) ) 7.8 Hz,
4J(H4PhA,H6PhA) ) 1.4, 1H, H4PhA), 7.18 (ddd, 3J(H4PhB,H3PhB) ) 7.7, 3J
(12) Teixidor, F.; Sa´nchez-Castello´, G.; Lucena, N.; Escriche, Ll.; Kiveka¨s,
R.; Sundberg, M.; Casabo´, J. Inorg. Chem. 1991, 30, 4931.
(13) Toma, H. E.; Creutz, C. Inorg. Chem. 1977, 16, 545.
(14) Ochiai, E. J. Org. Chem. 1953, 534.
(15) (a) Fitton, A. O.; Smalley, R. K. Practical Heterocyclic Chemistry;
Academic Press: London and New York, 1968. (b) Boulton, A. J.;
McKillop, A. M.; Katritzky, A. R.; Rees, C. W. ComprehensiVe
Heterocyclic Chemistry, 1st ed.; Pergamon Press: Oxford, New York,
Toronto, Sydney, Paris, Frankfurt, 1984.
(16) Vin˜as, C.; Angle`s, P.; Sa´nchez, G.; Lucena, N.; Teixidor, F.; Escriche,
Ll.; Casabo´, J.; Piniella, J. F.; Alvarez-Larena, A.; Kiveka¨s, R.;
Sillanpa¨a¨, R. Inorg. Chem. 1998, 37, 701.
(17) Stephenson, T. A.; Wilkinson, G. J. Inorg. Nucl. Chem. 1966, 28,
945.
4
(H4PhB,H5PhB) ) 8.0 Hz, J(H4PhB,H6PhB) ) 1.1, 1H, H4PhB), 7.30 (ddd,
3J(H5PhA,H4PhA) ) 7.8, J (H5PhA,H6PhA) ) 8.2, J(H5PhA,H3PhA) ) 1.7,
3
4
1H, H5PhA), 7.37 (d, 3J(H5py,H4py) ) 8.3, 1H, H5py), 7.38 (dd,
3J(H6PhA,H5PhA) ) 8.2, J (H6PhA,H4PhA) ) 1.4, 1H, H6PhA), 7.48 (ddd,
4
3J(H5PhB,H6PhB) ) 8.1, J (H5PhB,H4PhB) ) 8.0, J(H5PhB,H3PhB) ) 1.7,
1H, H5PhB), 7.58 (d, 3J(H4py,H5py) ) 8.3, 1H, H4py), 7.78 (dd,
3J(H6PhB,H5PhB) ) 8.1, 4J(H4PhB,H6PhB) ) 1.1, 1H, H6PhB), 7.96 (dd,
3
4
3J(H3PhA,H4PhA) ) 7.7, J (H3PhA,H5PhA) ) 1.7, 1H, H3PhA), 7.98 (dd,
4
3J(H3PhB,H4PhB) ) 7.7, 4J (H3PhB,H5PhB) ) 1.7, 1H, H3PhB). 13C{1H} NMR
(CDCl3): δ 36.9 (s, (py-CH2-S)A), 38.1 (s, (py-CH2-S)B), 52.1 (s,
-COOCH3), 122.9-155.3 (Caryl), 166.9 (s, -COOCH3). Subscript A
designates the methylthiophenyl derivative bonded to the pyridine at
position 6, and subscript B designates the methylthiophenyl derivative
(18) Koepp, H. M.; Wendt, H.; Strehlow, H. Z. Elektrochem. 1960, 64,
483.

4012 Inorganic Chemistry, Vol. 40, No. 16, 2001
Teixidor et al.
bonded to the pyridine at position 2. Anal. Calcd for C23H20ClNO4S2:
C, 58.29; H, 4.22; N, 2.96; S, 13.52. Found: C, 58.34; H, 4.30; N,
2.87; S, 14.05.
CH2-S), 54.6 (s, COOCH3), 113.0-135.7 (Caryl), 167.0 (s, COOCH3).
31P{1H} NMR (CDCl3): δ 39.37 (s, PPh3). Anal. Calcd for C43H35-
Cl10N2O6PRuS2: C, 42.09; H, 2.85; N, 2.28; S, 5.22. Found: C, 41.77;
H, 2.86; N, 2.18; S, 4.94.
Synthesis of 2,6-Bis[(4′-methoxyphenyl)thiomethyl]-3-chloropy-
ridine (L7). L7 was prepared following the same procedure as for L5,
using 4-methoxybenzenethiol (0.62 g, 4.4 mmol), sodium metal (0.10
g, 4.4 mmol), and 2,6-bis(bromomethyl)-3-chloropyridine (0.65 g, 2.2
mmol). Yield: 0.77 g, 1.8 mmol (84%). IR (KBr): ν 3020(Caryl-H),
Synthesis of [RuCl2(L6)(PPh3)]. The ligand L6 (47 mg, 0.10 mmol)
and [RuCl2(PPh3)3] (97 mg, 0.10 mmol) were added to a two-necked
round bottom flask. To this mixture was added 12 mL of toluene/diethyl
ether (1:5), and the solution was heated under reflux for 1 h. An orange
solid appeared, which was filtered, washed with diethyl ether and
methanol, and dried under vacuum. Yield: 49 mg, 0.05 mmol (54%).
1
2937(Calkyl-H), 1246, 1033 (C-O-C) cm-1. H NMR (CDCl3): δ
3.77 (s, 3H, (CH3-O)A), 3.78 (s, 3H, (CH3-O)B), 4.04 (s, 2H, (py-
3
1
IR (KBr): ν (CdO) 1722 cm-1. H NMR (CDCl3): δ 3.67 (s, 3H,
CH2-S)A), 4.25 (s, 2H, (py-CH2-S)B), 6.81 (d, J(H3Ph,H2Ph) ) 8.8,
4H, H3Ph), 7.00 (d, 3J(H5py,H4py) ) 8.1, 1H, H4py), 7.25 (d, 3J(H2PhA,H3PhA
)
COOCH3), 3.70 (s, 3H, COOCH3), 4.50-5.50 (m, 4H, py-CH2-S),
7.00-8.10 (m, 25H, Haryl). 13C {1H} NMR (CDCl3): δ 52.4 (s, py-
CH2-S), 54.5 (s, COOCH3), 120.0-136.3 (m, Caryl), 167.0 (s,
COOCH3). 31P{1H} NMR (CDCl3): δ 42.21 (s, PPh3). Anal. Calcd
for C41H35Cl3NO4PRuS2: C, 54.22; H, 3.88; N, 1.54; S, 7.06. Found:
C, 54.01; H, 3.96; N, 1.54; S, 6.78.
) 8.8, 2H, H2PhA), 7.35 (d, 3J(H2PhB,H3PhB) ) 8.8, 2H, H2PhB), 7.50 (d,
3J(H5py,H4py) ) 8.1, 1H, H5py). 13C{1H} NMR (CDCl3): δ 40.3 (s, (py-
CH2-S)A), 41.8 (s, (py-CH2-S)B), 55.3 (s, OCH3), 114.4-159.4
(Caryl). Subscript A designates the methylthiophenyl derivative bonded
to the pyridine at position 6, and subscript B designates the methyl-
thiophenyl derivative bonded to the pyridine at position 2. Anal. Calcd
for C21H20ClNO2S2: C, 60.36; H, 4.79; N, 3.35; S, 15.33. Found: C,
60.51; H, 4.80; N, 3.27; S, 14.93.
Synthesis of [RuCl2(L7)(PPh3)]‚C7H8. The complex [RuCl2(L7)-
(PPh3)]‚C7H8 was prepared following the same procedure as for [RuCl2-
(L6)(PPh3)] using L7 (42 mg, 0.1 mmol) and [RuCl2(PPh)3] (99 mg,
1
Synthesis of [Cu(L2)][ClO4]2‚H2O. The ligand L2 (0.11 g, 0.25
mmol) dissolved in ethyl acetate (4 mL) was added to a solution of
Cu(ClO4)2‚6H2O (0.09 g, 0.25 mmol) in ethyl acetate (2 mL). A violet
solid was obtained, which was filtered, washed with ethyl acetate (4
mL), and vacuum-dried. Yield: 0.15 g, 0.21 mmol (86%). IR (KBr):
ν 1729 (CdO), 1679 (CdO‚‚‚H), 1322, 1279 (C-O-C), 1122, 1090
(ClO4-) cm-1. Anal. Calcd for C23H23Cl2CuNO13S2: C, 38.36; H, 3.20;
N, 1.95; S, 8.89. Found: C, 38.12; H, 3.24; N, 1.81; S, 8.57.
Synthesis of [Cu(L3)][ClO4]2‚H2O‚1/2C4H8O2. The procedure is the
same as before, using L3 (0.11 g, 0.25 mmol) and Cu(ClO4)2‚6H2O
(0.09 g, 0.25 mmol). The complex is a brown solid. Yield: 0.10 g, 0.1
mmol (53.1%). IR (KBr): ν 1729 (CdO), 1294, 1287 (C-O-C), 1151,
1118, 1092 (ClO4-) cm-1. Anal. Calcd for C25H27Cl2CuNO14S2: C,
39.81; H, 3.58; N, 1.86; S, 8.49. Found: C, 39.46; H, 3.40; N, 2.14; S,
8.77.
Synthesis of [Cu(L4)][ClO4]2. The procedure is the same as before,
using L4 (0.10 g, 0.25 mmol) and Cu(ClO4)2‚6H2O (0.09 g, 0.25 mmol).
The complex is a violet solid. Yield: 0.06 g, 0.09 mmol (37%). IR
(KBr): ν 1261, 1180, 1025 (C-O-C), 1115, 1088 (ClO4-) cm-1. Anal.
Calcd for C21H21Cl2CuNO10S2: C, 39.04; H, 3.25; N, 2.17; S, 9.91.
Found: C, 38.87; H, 3.15; N, 2.03; S, 9.56.
Synthesis of [Cu2(L5)2O][ClO4]. The procedure is the same as
before, using L5 (0.12 g, 0.25 mmol) and Cu(ClO4)2‚6H2O (0.09 g,
0.25 mmol). The complex is a deep blue solid. Yield: 0.13 g, 0.17
mmol (68%). IR (KBr): ν 1704 (CdO), 1542, 1357 (NO2), 1289, 1258
(C-O-C), 1120, 1110, 1086 (ClO4-) cm-1. Anal. Calcd for C46H40-
Cl2Cu2N4O21S4: C, 42.14; H, 3.07; N, 4.27; S, 9.78. Found: C, 42.54;
H, 3.10; N, 4.17; S, 9.59.
0.1 mmol). Yield: 72 mg, 0.09 mmol (85%). H NMR (CDCl3): δ
2.38 (s, 3H, CH3Ph), 3.76 (s, 6H, CH3O-), 4.00-5.60 (m, 4H, py-
CH2-S), 6.40-8.00 (m, 30H, Haryl). 13C {1H} NMR (CDCl3): δ 21.5
(s, CH3Ph), 51.9 (s, py-CH2-S), 53.0 (s, py-CH2-S), 54.0 (s, CH3O-
), 55.2 (s, CH3O-), 113.9-140.0 (m, Caryl)
31P{1H} NMR (CDCl3): δ
44.38 (s, PPh3), 47.41 (s, PPh3). Anal. Calcd for C46H43Cl3NO2PRuS2:
C, 58.51; H, 4.56; N, 1.48; S, 6.78. Found: C, 58.07; H, 4.68; N, 1.41;
S, 6.64.
X-ray Studies. Single-crystal data collections for L5 and [RuCl2-
(L5)(PPh3)]‚2CCl4 were performed at ambient temperature on a Rigaku
AFC5S diffractometer using graphite-monochromatized Mo KR radia-
tion. Unit cell parameters were determined by least-squares refinement
of 20 carefully centered reflections. Data obtained were corrected for
Lorentz and polarization effects and for dispersion. Corrections for
empirical absorption (ψ scan) were also applied. A total of 2293 and
8858 unique reflections were collected by the ω/2θ scan mode (2θmax
) 50°) for L5 and [RuCl2(L5)(PPh3)]‚2CCl4, respectively.
Both structures were solved by direct methods by using the
SHELXS-86 program,19 and least-squares refinements and all subsequent
calculations were performed using the SHELX-97 program system.20
For L5, non-hydrogen atoms were refined with anisotropic displace-
ment parameters. Hydrogen atoms were included in the calculations at
fixed distances from their host atoms and treated as riding atoms using
the SHELX-97 default parameters.
For [RuCl2(L5)(PPh3)]‚2CCl4, one of the CCl4 ions is disordered,
showing rotational disorder around the Cl3-C42 bond. Refinement of
the disordered chloride ions with isotropic and the rest of the non-
hydrogen atoms with anisotropic displacement parameters revealed site
occupation parameters 0.588(13) for Cl4a, Cl5a, and Cl6a and 0.412-
(13) for Cl4b, Cl5b, and Cl6b. These site occupation parameters for
the disordered Cl ions were fixed in final refinement, and all non-
hydrogen atoms were refined with anisotropic displacement parameters.
Hydrogen atoms were included in the calculations at fixed distances
from their host atoms and treated as riding atoms using the SHELX-
97 default parameters. Crystallographic data and refinement for the
compounds are presented in Table 1 and selected bond distances and
angles for [RuCl2(L5)(PPh3)]‚2CCl4 in Table 2.
Synthesis of [Cu(L6)][ClO4]2‚H2O. The procedure is as before,
using L6 (0.12 g, 0.25 mmol) and Cu(ClO4)2‚6H2O (0.09 g, 0.25 mmol).
The complex is a violet solid. Yield: 0.16 g, 0.2 mmol (85%). IR
-
(KBr): ν 1710 (CdO), 1260 (C-O-C), 1145, 1118, 1087 (ClO4
)
cm-1. Anal. Calcd for C23H22Cl3CuNO13S2: C, 36.60; H, 2.92; N, 1.86;
S, 8.48. Found: C, 37.00; H, 2.99; N, 1.67; S, 8.51.
Synthesis of [Cu(L7)][ClO4]2‚2H2O‚1/4C4H8O2. The procedure is
as before, using L7 and Cu(ClO4)2‚6H2O in a 0.3 mmol scale. The
complex is a deep blue solid. Yield: 0.08 g, 0.1 mmol (42%). IR
(KBr): ν 1251 (C-O-C), 1145, 1114, 1092 (ClO4-) cm-1. Anal. Calcd
for C22H26Cl3CuNO12.5S2: C, 35.77; H, 3.52; N, 1.90; S, 8.67. Found:
C, 35.96; H, 3.76; N, 1.69; S, 8.33.
Results
The ligands presented in this work have in common the NS2-
(S-aryl) skeleton, but each one differs from the others in the
aromatic ring substituent. Considering substituents on the
pyridine, three distinct bis(bromomethyl)pyridine derivatives
have been utilized as precursors for the ligand synthesis: 2,6-
bis(bromomethyl)pyridine, 2,6-bis(bromomethyl)-3-chloropy-
Synthesis of [RuCl2(L5)(PPh3)]‚2CCl4. To a two-necked round
bottom flask containing 5 mL of toluene were added 48 mg (0.10 mmol)
of ligand L5 and 100 mg (0.10 mmol) of [RuCl2(PPh3)3]. The solution
was heated under reflux for 1 h. After concentration to 2 mL, petroleum
ether was added until precipitation of a deep blue solid took place.
This was filtered, washed with diethyl ether and methanol, and dried
under vacuum. Yield: 66 mg, 0.05 mmol (54%). Crystals suitable for
X-ray diffraction were grown from carbon tetrachloride. IR (KBr): ν
(19) Sheldrick, G. M. SHELXS-86, Program for Crystal Structure Solution;
University of Go¨ttingen: Go¨ttingen, Germany, 1986.
(20) Sheldrick, G. M. SHELX-97, Program for Crystal Structure Refine-
ment; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
1713, 1726 (CdO), 1539 (NO2), 1261 (C-O-C) cm-1 1H NMR
.
(CDCl3): δ 3.69 (s, 6H, COOCH3), 4.50-5.70 (m, 4H, py-CH2-S),
7.00-8.30 (m, 25H, Haryl). 13C {1H} NMR (CDCl3): δ 52.4 (s, py-

NS2(S-aryl) Pyridine-Based Dithia-Containing Ligands
Inorganic Chemistry, Vol. 40, No. 16, 2001 4013
Table 1. Crystallographic Data for L5 and
[RuCl2(L5)(PPh3)]·2CCl4
compd
chem formula
fw
L5
RuCl2(L5)(PPh3)]‚2CCl4
C43H35Cl10N2O6PRuS2
1226.39
C23H20N2O6S2
484.53
21
T, °C
21
λ, Å
0.71069
orthorhombic
P212121 (No. 19)
12.072(3)
25.292(5)
7.377(5)
90
0.71069
triclinic
cryst syst
space group
a, Å
P1h (No. 2)
13.984(3)
15.277(2)
13.508(2)
94.233(17)
118.267(13)
93.462(18)
2519.7(7)
2
1.616
10.04
1232
1.013
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
90
90
2252.4(17)
4
1.429
2.80
1008
1.021
0.0370
0.0796
Z
D
calcd, g cm-3
µ, cm-1
F(000)
GOF on F2
R1a [I > 2σ(I)]
wR2b [I > 2σ(I)]
0.0816
0.1697
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑w(|Fo | - |Fc |)2/
Figure 1. Schematic representation of ligands L1-L7.
2 2
∑w|Fo | ]1/2
.
Scheme 1. Synthetic Procedure for the Pyridine Derivatives
2,6-Bis(bromomethyl)-3-chloropyridine and
2,6-Bis(bromomethyl)-4-nitropyridine
Table 2. Selected Interatomic Distances (Å) and Angles (deg) and
Torsion Angles (deg) for [RuCl2(L5)(PPh3)]‚2CCl4
Ru-Cl1
Ru-Cl2
Ru-S1
2.432(3)
2.424(3)
2.360(3)
Ru-S2
Ru-P
Ru-N1
2.326(3)
2.337(3)
2.125(9)
Cl2-Ru-Cl1
S1-Ru-Cl1
S1-Ru-Cl2
S2-Ru-S1
170.97(12)
79.32(11)
100.45(12)
158.28(11)
N1-Ru-S1
N1-Ru-S2
N1-Ru-P
83.4(3)
81.5(3)
178.7(3)
ridine, and 2,6-bis(bromomethyl)-4-nitropyridine. The last two
2,6-bis(bromomethyl)pyridine derivatives have been synthesized
for the first time in this work. Their syntheses are difficult due
to the electron poverty of pyridine. Thus, the starting compound
for 3-chloro-2,6-lutidine was 2,5-dimethylpyrrole, and the
fragment “CCl” was introduced, resulting in 2,6-dimethyl-3-
chloropyridine.15 In the case of nitropyridine it was necessary
to synthesize first the pyridine oxide. After introduction of the
nitro group, the oxide was removed. The last step to obtain the
bis(bromomethyl)pyridine derivatives was the bromination. This
was accomplished by using N-bromosuccinimide following a
similar procedure to this already described.21 The bis(bromo-
methyl)pyridine derivatives were obtained in 10% yield, after
careful column chromatography separation. The schematic
synthetic procedure is shown in Scheme 1.
The reaction of these bis(bromomethyl)pyridine compounds
with thiophenol derivatives 2-methoxycarbonylthiophenol (thio-
salicylic methyl ester) and 4-methoxybenzenethiol in NaOMe/
MeOH yields the podand ligands: 2,6-bis[(2′-(methoxycarbo-
nyl)phenylthiomethyl]-4-nitropyridine (L5), 2,6-bis[(2′-(meth-
oxycarbonyl)phenylthiomethyl]-3-chloropyridine (L6), and 2,6-
bis[(4′-methoxyphenyl)thiomethyl]-3-chloropyridine (L7), which
were synthesized for the first time in this work. L5 and L6
incorporate electron-withdrawing groups both on the pyridine
and on the phenyl rings, while L7 incorporates an electron-
withdrawing group on the pyridine ring and an electron-donor
group on thiophenyl moieties (-OMe in the para position with
respect to S on thiophenyl groups). A schematic representation
of ligands L1-L7 is shown in Figure 1.
inequality is the result of the presence of a Cl atom in the
pyridine’s 3-position. This produces a chemical shift difference
1
in the corresponding -CH2- groups both in H and in 13C-
{1H} NMR spectra. The same phenomenon is also observed in
the dibromo, 2,6-bis(bromomethyl)-3-chloropyridine, precursor.
Discussion
As it was indicated earlier, the tridentate NS2(S-aryl) pyridine
dithia-containing ligands were chosen due to their copper
affinity, their ligand/copper ratio in the complexation process,
and their ability to coordinate either to copper or to proton
through the pyridinic nitrogen, depending on the solution’s pH.
According to the literature22 the acidity constant of the tridentate
ligand 2,6-bis(methylthiomethyl)pyridine (L) and the formation
All ligands have their arms equal except for L6 and L7. The
(21) Offermann, W.; Vo¨gtle, F. Synthesis 1977, 272.

4014 Inorganic Chemistry, Vol. 40, No. 16, 2001
Teixidor et al.
Table 5. Approximated pKA Values for L1-L7 (except L5)
Table 3. Formal Reduction Potentials (vs Ag/AgCl/Cl- 10-1 M in
CH3CN for the Couple Cu(II)/Cu(I)
ligand
L1
L2
L3
L4
L6
L7
complex
E1/2, V
complex
E1/2, V
pKA
3.8
3.5
3.6
3.9
3.4
3.4
a
b
b
b
b
b
b
[Cu(CH3CN)n][ClO4]2
1.47
1.44
1.40
1.38
1.42
[Cu(L6)][ClO4]2
[Cu(L2)][ClO4]2
[Cu(L7)][ClO4]2
[Cu(L1)][ClO4]2
[Cu(L4)][ClO4]2
1.43
1.33
1.32
1.32
1.26
The approximated pKA’s of ligands L1-L7, except for L5,
were calculated following a procedure similar to the one
described by Ko¨seoglu et al.23 The values obtained are presented
in Table 5. The values range from 3.4 to 3.9, L4 being the ligand
with the highest basicity or, for this case, the highest σ-donor
ability. The pKA’s of L6-L7 are slightly less positive than for
L1-L4, implying that the effect on the pKA by substitution on
the pyridine is stronger than substitution on the thiophenyl group.
Ligands L4 and L7 only differ by a chlorine atom on pyridine,
and pKA(L4) - pKA(L7) ) 0.5, but if the substitution is
produced on the thiophenyl moiety, ∆pKA is less pronounced,
e.g., pKA(L4) - pKA(L3) ) 0.3. This effect is not observed in
the ∆E1/2. For instance the L4 and L7 ruthenium complexes
have an ∆E1/2 ) 40 mV, the complex with L7 having the highest
E1/2 value. For these complexes the difference was on the
pyridine moiety, but if the comparison was between ruthenium
complexes of L4 and L3, where the substitution was on the
phenyl ring, the ∆E1/2 ) 90 mV. Consequently substitution on
pyridine has a greater influence on the pKA than substitution
on the thiophenyl moiety, but the influence on E1/2 for both
substitutions is comparable.
It results, however, that the E1/2 values and the approximated
pKA’s for all these ligands are very similar. The electron-
withdrawing groups introduced on the aromatic moieties do not
considerably alter the electronic properties of the ligand. The
effect of introducing electron-withdrawing groups on the
pyridine moiety is similar to the effect of introducing these
groups on thiophenyl moieties. Thus, the synthetic effort to
obtain the trisubstituted pyridines is not compensated by the
observed electronic modification of the ligand. Synthetically it
is easier to modify the phenyl ring to cause a similar effect.
Although some difference in the E1/2 values for the couples Cu-
(II)/Cu(I) and Ru(III)/Ru(II) are observed for L1 and L5, the
comparative much larger and difficult synthetic work required
to produce substitution on pyridine than on phenyl is not
worthwhile considering the minor difference in the results. In
reality, the same effects can be produced just modifying
adequately the phenyl ring. Also, no major differences are found
upon substitution at the ortho, meta, or para positions in the
phenyl ring, except for the pKA, in which case an electron-
withdrawing substituent in the meta position produces a lower
pKA.
[Cu2(L5)2O][ClO4]a
a
[Cu(L3)][ClO4]2
[Cu(L1)][ClO4]2
[Cu(CH3CN)n][ClO4]2
a
a Initial [Cu(II)] ) 1.50 × 10-3 M. b Initial [Cu(II)] ) 5.04 × 10-3
M.
Table 4. Formal Reduction Potentials (vs Ag/AgCl/Cl- 10-1 M in
CH3CN) for the Couple Ru(III)/Ru(II)
complex
E1/2, V
complex
E1/2, V
[RuCl2(L2)(PPh3)]
[RuCl2(L3)(PPh3)]
[RuCl2(L4)(PPh3)]
[RuCl2(L5)(PPh3)]
1.74
1.75
1.66
1.81
[RuCl2(L6)(PPh3)]
[RuCl2(L7)(PPh3)]
[RuCl2(L1)(PPh3)]
1.76
1.70
1.71
constant of its Cu(II) complex [CuL(H2O)]2+ are log KA ) 4.04
( 0.04 and log KF ) 4.6 ( 0.1, respectively. Thus the system
appears to be very interesting in copper-proton counter-
transport in membranes.
In the following discussion the influence on the pKA of the
substituents on the pyridine and/or on the phenyl groups will
be discussed along with their influence on the electronic
properties. For their study, [Cu(LX)][ClO4]2 and [RuCl2(LX)-
(PPh3)] complexes of L1-L7 have been synthesized. Table 3
presents E1/2 for the Cu(II) NS2(S-aryl) complexes. Values
ranging from 1.26 to 1.44 V vs Ag/AgCl/Cl- (0.1 M in
acetonitrile) are encountered in [Cu(LX)][ClO4]2 (LX ) L1-
L7, for L5 the formula is [Cu2(L5)2O][ClO4]). The ∆E1/2 value
between the complexes [Cu(L4)][ClO4]2 and [Cu(L7)][ClO4]2
is 60 mV, the more positive being [Cu(L7)][ClO4]2. The ligands
L4 and L7 are identical except that L7 has a chlorine atom at
the pyridine 3-position. The chlorine makes the electron pair
less available for coordination, or lowers the pyridine LUMO,
stabilizing more the Cu(I) and consequently increasing E1/2 (Cu-
(II)/Cu(I)).
The same effect is observed comparing L1 with L5 and L6.
The only difference between these ligands is the existence of a
nitro group on the pyridine 4-position for L5 and a chlorine
atom on the pyridine 3-position for L6. Both ligands, L5 and
L6, increase the E1/2 (Cu(II)/Cu(I)) with regard to L1 by 60
and 50 mV, respectively.
Table 4 presents E1/2 for the Ru(II) NS2(S-aryl) complexes.
Values ranging from 1.66 to 1.81 V are encountered in [RuCl2-
(LX)(PPh3)] complexes (LX ) L1-L7). The same trend
observed for the copper complexes is found for the ruthenium
ones. Ligands L5 and L6 increase the E1/2 (Ru(III)/Ru(II)) in
100 and 50 mV respectively with respect to L1. The ∆E1/2
between the [RuCl2(L4)(PPh3)] and [RuCl2(L7)(PPh3)] is ca.
40 mV, being the highest for L7.
Crystal Structure Descriptions. To know the geometrical
arrangement of the free ligand and its complex, the molecular
structures of L5 and its Ru(II) complex were solved. Figures 2
and 3 show a perspective view of L5 and [RuCl2(L5)(PPh3)]‚
2CCl4, respectively.24
In L5 (Figure 2) the substituents connected to C8 and C12
are oriented quite differently. This is indicated by the N1-C8-
C7-S1 and N1-C12-C13-S2 torsion angles, which are 46.4-
(4)° and -121.3(3)°, respectively. The locations of the S atoms
clearly indicate that the conformation observed for L5 in the
solid state is not suitable for tridentate NS2 coordination to a
metal ion.
All of the above discussion has been based on the substituents
on the pyridine ring; however, the substituents on the phenyl
rings can influence the E1/2 change. The Ru(II) complex with
L4 has an E1/2 ) 1.66 V. For this example, the substituent on
the phenyl ring is -OMe, which has an electron-donor effect
(by resonance) since it is placed at the para position with regard
to the sulfur atom. When -OMe is replaced by an electron-
withdrawing group such as -CO2Me (L3), the reduction
potential Ru(III)/Ru(II) increases by 95 mV. The electron-
withdrawing groups bonded to the aromatic moieties of NS2-
(S-aryl) ligands provide an enhanced capacity for stabilizing
low-oxidation states.
In [RuCl2(L5)(PPh3)]‚2CCl4, the metal assumes a distorted
octahedral coordination sphere and the ligand L5 coordinates
(22) Canovese, L.; Chessa, G.; Marangoni, G.; Pitteri, B.; Uguagliati, P.;
Visentin, F. Inorg. Chim. Acta 1991, 186, 79.
(23) Ko¨seoglu, F.; Kilic¸, E.; Uysal, D. Talanta 1995, 42, 1875.
(24) Johnson, C. K. ORTEPII. Report ORNL-5138; Oak Ridge National
Laboratory: Oak Ridge, TN, 1976.

NS2(S-aryl) Pyridine-Based Dithia-Containing Ligands
Inorganic Chemistry, Vol. 40, No. 16, 2001 4015
pyridine derivatives are similar in all of the complexes. Thus
the observed geometrical arrangement of the L5 ligand in
[RuCl2(L5)(PPh3)]‚2CCl4 is a further example of the versatility
of the NS2 coordinating ligands. In the compared complexes,16
the pyridine rings are rotated with respect to the two “substituent
arms” so that C7 and C13 are on the opposite sides of the NS2-
Ru plane. This is a noticeable difference compared with [RuCl2-
(L5)(PPh3)]‚2CCl4. However, all of these complexes show a
common phenomenon. In the case when PPh3 ligand is
coordinated to the metal, the bulky substituent is pushing the
neighboring ligands, and thus the position of the PPh3 ligand
seems to determine the orientations of the Ph groups or Ph
derivatives connected to the S atoms.
Figure 2. Perspective ORTEP20 view of the ligand L5 showing 30%
displacement ellipsoids. Hydrogen atoms are omitted for clarity.
Conclusions
The NS2(S-aryl) ligands reported here are all derivatives of
2,6-bis(phenylthiomethyl)pyridine. Its coordinating sites are the
nitrogen at the pyridine moiety and the two thioethers bonded
to the phenyl rings. The question was whether substituents on
the pyridine moiety would alter more substantially the properties
of the parent ligand than substituents on the phenyl rings. To
achieve these results difficult and time-consuming syntheses of
ligands with substituents on pyridine have been carried out.
Evidence has demonstrated, however, that by adequately choos-
ing the substituents on phenyl similar results can be obtained.
In spite of this possibility, it is clear that the pKA in NS2(S-
aryl) ligands is more dependent on the incorporation of electron-
withdrawing groups on the pyridine than on the phenyl, but
that the pKA lowering with respect to 2,6-bis(phenylthiomethyl)-
pyridine is very different from the case between pyridine and
3-chloropyridine where the pKA of the last is 2.41 units lower.25
Electron-withdrawing substituents on the rings produce a shift
to higher E1/2 both on Cu(II)/Cu(I) and on Ru(III)/Ru(II) couples.
Again, the shift is larger for substitution on the pyridine than
on the S-phenyl ring but, as mentioned, appropriate substituents
shall produce equivalent results.
Figure 3. Simplified ORTEP20 drawing of the complex unit in [RuCl2-
(L5)(PPh3)]‚2CCl4 showing 30% displacement ellipsoids. Phenyl groups
of PPh3 ligand and hydrogen atoms are omitted for clarity.
tridentately via the two S atoms and the N atom of the pyridine
ring to Ru(II). The three remaining coordination positions of
Ru(II) are occupied by two chloride ions and the P atom of
PPh3. The distortion of the coordination sphere is clearly
indicated by variation of the bond angles (Table 2), and
nonplanarity of the atom group Ru, S1, S2, and N1 of the
coordination sphere. The atoms Ru, S1, P, and N1 are
approximately in the same plane, and S2 deviates from the plane
by 0.646(9) Å. Also the orientations of the S atoms with respect
to the pyridine ring are different: the S1 atom is in the same
plane as the pyridine ring, but S2 deviates from (is above) the
plane by 0.812(18) Å.
Acknowledgment. This work was supported by Projects
MAT94-1414-CE and MAT98-0921. P.A. acknowledges the
award of a grant to FIAP-QF95/8.807. R.K. thanks Academy
of Finland for a grant (Project 73533).
Supporting Information Available: Details of the X-ray structure
determinations, in CIF format, of the structures of L5 and [RuCl2(L5)-
(PPh3)]‚2CCl4. This material is available free of charge via the Internet
at http://pubs.acs.org.
IC000903T
In the monomeric Ru(II) complexes of 2,6-bis(phenylthio-
methyl)pyridine derivatives,16 reported recently, the derivatives
exhibit versatile conformations, and different from that in
[RuCl2(L5)(PPh3)]‚2CCl4, even coordination modes of the
(25) Lide, D. R., Ed. in Chief. Handbook of Chemistry and Physics, 73rd
ed.; CRC Press: Boca Raton, Ann Arbor, London, and Tokyo, 1992-
1993.