2-Pyrrolylthiones as monoanionic bidentate N,S-chelators: Synthesis and molecular structure of 2-pyrrolylthionato complexes of nickel(II), cobalt(III), and mercury(II)

Article abstract of DOI:10.1021/ic0004636

The metal-chelating ability of 2-pyrrolylthiones is described. The readily available ligands di-2-pyrrolyl thione (6), 2-thioacetylpyrrole (10), and 2-thiobenzoylpyrrole (11) constitute examples of monoanionic ligands with N,S-donor atom sets, although di-2-pyrrolyl thione (6) could theoretically also achieve chelation through an N,N-donor set. A square planar Ni(II) complex, 14, an octahedral Co(III) complex, 18, and a tetrahedral Hg(II) complex, 17, with the di-2-pyrrolyl thionato chelate have been prepared, and their structures have been characterized by ¹H NMR, UV-vis, MS, IR, elemental analysis, and single-crystal X-ray diffraction. Crystal data for 14: C₁₈H₁₄N₄ -NiS₂·0.28H₂O, trigonal, R3, a = 18.467(1) A, b = 18.467(1) A, c = 26.404(2) A, V = 7797(1) A³; Z = 18, R = 3.2%. Crystal data for 18-mer: C₂₇H₂₁CoN₆ S₃·C₃H₆O (acetone), monoclinic, P21/n, a = 9.569(1) A, b = 23.152(1) A, c = 13.659(1) A, β = 100.882(8)°, V = 2971.6(5) A³, Z = 4, R = 4.3%. Crystal data for 17: C₁₈H₁₄HgN₄S₂, triclinic, P1, a = 8.443(2), b = 14.278(1) A, c = 7.445(1) A, α = 90.561(9)°, β = 97.64(1)°, γ = 104.250(9)°, V = 861.3(2) A³, Z = 2, R = 4.2%. The bond lengths and angles of these metal complexes are comparable to those of known N,S-chelates. A comparison of the structural parameters of the ligand in the metal complexes with those for the free ligand 6 demonstrates the preorganization of the free ligand for complexation and demonstrates the spectator role of the noncoordinating pyrrolic unit. Chelation of Ni(II) by 2-thioacetylpyrrole (10) and 2-thiobenzoylpyrrole (11) to provide complexes 12 and 13 with structures analogous to complex 14 is also described.

Full text of DOI:10.1021/ic0004636

6100
Inorg. Chem. 2000, 39, 6100-6106
2-Pyrrolylthiones as Monoanionic Bidentate N,S-Chelators: Synthesis and Molecular
Structure of 2-Pyrrolylthionato Complexes of Nickel(II), Cobalt(III), and Mercury(II)
Christian Bru1ckner,*,† Steven J. Rettig,‡,§ and David Dolphin‡
Department of Chemistry, University of Connecticut, 55 North Eagleville Road, U-60,
Storrs, Connecticut 06269, and Department of Chemistry, University of British Columbia,
2036 Main Mall, Vancouver, British Columbia, V6T 1Z1 Canada
ReceiVed April 27, 2000
The metal-chelating ability of 2-pyrrolylthiones is described. The readily available ligands di-2-pyrrolyl thione
(6), 2-thioacetylpyrrole (10), and 2-thiobenzoylpyrrole (11) constitute examples of monoanionic ligands with
N,S-donor atom sets, although di-2-pyrrolyl thione (6) could theoretically also achieve chelation through an N,N-
donor set. A square planar Ni(II) complex, 14, an octahedral Co(III) complex, 18, and a tetrahedral Hg(II) complex,
17, with the di-2-pyrrolyl thionato chelate have been prepared, and their structures have been characterized by 1H
NMR, UV-vis, MS, IR, elemental analysis, and single-crystal X-ray diffraction. Crystal data for 14: C18H14N4-
NiS2‚0.28H2O, trigonal, R3h, a ) 18.467(1) Å, b ) 18.467(1) Å, c ) 26.404(2) Å, V ) 7797(1) Å3; Z ) 18, R
) 3.2%. Crystal data for 18-mer: C27H21CoN6S3‚C3H6O (acetone), monoclinic, P21/n, a ) 9.569(1) Å, b )
23.152(1) Å, c ) 13.659(1) Å, â ) 100.882(8)°, V ) 2971.6(5) Å3, Z ) 4, R ) 4.3%. Crystal data for 17:
C18H14HgN4S2, triclinic, P1h, a ) 8.443(2), b ) 14.278(1) Å, c ) 7.445(1) Å, R ) 90.561(9)°, â ) 97.64(1)°, γ
) 104.250(9)°, V ) 861.3(2) Å3, Z ) 2, R ) 4.2%. The bond lengths and angles of these metal complexes are
comparable to those of known N,S-chelates. A comparison of the structural parameters of the ligand in the metal
complexes with those for the free ligand 6 demonstrates the preorganization of the free ligand for complexation
and demonstrates the spectator role of the noncoordinating pyrrolic unit. Chelation of Ni(II) by 2-thioacetylpyrrole
(10) and 2-thiobenzoylpyrrole (11) to provide complexes 12 and 13 with structures analogous to complex 14 is
also described.
Introduction
name Tagamet), used for the treatment of peptic ulcers, is
proposed to exist as a copper(II) chelate under in vivo
conditions.5,6 Other drugs contain N,S-donor group ligands, such
as the copper complex 2.7 The underlying chelate is being used
to complex radioactive metal isotopes, for instance 99mTc or
62Cu, and the complexes find uses as radioimaging agents.8,9
Aryl carboxaldehyde thiosemicarbazones have shown activity
against bacterial and viral infections, tuberculosis, rheumatism,
As recently pointed out by Vahrenkamp and co-workers, the
chemistry of metal complexes with N,S-donor chelates is
experiencing a renaissance.1 This is in part due to their diverse
roles in metalloenzymes and their varied catalytic and pharma-
cological properties. For instance, biomimetic models of met-
alloenzymes such as [NiFe] hydrogenase,2 the blue copper
proteins,3 and aconitases4 often employ, in resemblance to their
natural counterparts, N,S-donor ligands. Cimetidine (1) (trade
(4) Lauble, H.; Kennedy, M. C.; Beinert, H.; Stout, C. D. Biochemistry
1992, 31, 2735.
(5) Greenaway, F. T.; Brown, L. M.; Dabrowiak, J. C.; Thompson, M.
R.; Day, V. M. J. Am. Chem. Soc. 1980, 102, 7782.
(6) Martinez, M. A.; Legros, J. P.; Soto, L.; Sancho, A. Polyhedron 1991,
10, 1031.
(7) John, E. K.; Green, M. A. J. Med. Chem. 1990, 33, 1704.
(8) O’Neil, J. P.; Wilson, S. R.; Katzenellenbogen, J. A. Inorg. Chem.
1994, 33, 319.
(9) Parker, D. Chem. Br. 1994, 10, 818.
(10) Knag, Y.; Yang, N.; Kang, S. O.; Ko, J.; Lee, C.-H.; Lee, Y.-H.
Organometallics 1997, 16, 5522.
(11) Berkessel, A.; Hermann, G.; Rauch, O.-T.; Bu¨chner, M.; Jacobi, A.;
Huttner, G. Chem. Ber. 1996, 129, 1421.
(12) Akbar Ali, M.; Livingstone, S. E. Coord. Chem. ReV. 1974, 13, 101.
(13) Vagg, R. S. Bidentate Ligands. In ComprehensiVe Coordination
Chemistry; Wilkinson, G., Gillard, R. D., McCleverty, J. A., Eds.;
Pergamon: Oxford, 1987; Vol. 2, pp 793-812.
(14) Livingstone, S. E. Other Sulfur-Containing Ligands. In ComprehensiVe
Coordination Chemistry; Wilkinson, G., Gillard, R. D., McCleverty,
J. A., Eds.; Pergamon: Oxford, 1987; Vol. 2, pp 633-660.
(15) McAucliffe, C. A. AdV. Inorg. Chem. Radiochem. 1975, 17, 165.
(16) Kuehn, C. A.; Isied, S. S. Prog. Inorg. Chem. 1980, 27, 153.
(17) Reedijk, S. E. Heterocyclic Nitrogen-Donor Ligands. In ComprehensiVe
Coordination Chemistry; Wilkinson, G., Gillard, R. D., McCleverty,
J. A., Eds.; Pergamon: Oxford, 1987; Vol. 2, pp 73-98.
* To whom correspondence should be addressed. Fax: (860) 486-2981.
E-mail: bruckner@nucleus.chem.uconn.edu.
† University of Connecticut.
‡ University of British Columbia.
§ Deceased on Oct 27, 1998. This paper is dedicated to the memory of
Steven J. Rettig.
(1) (a) Brand, U.; Burth, R.; Vahrenkamp, H. Inorg. Chem. 1996, 35,
1083. For representative examples of current research involving N,S-
donor ligands see, e.g.: (b) Sellmann, D.; Sutter, J. In Sulfur
Coordinated Transition Metal Complexes: Biological and Industrial
Significance; Stiefel, E. J., Matsumoto, K., Eds.; ACS Symposium
Series 653; American Chemical Society: Washington, DC, 1996; p
101. (c) Grapperhaus, C. A.; Darensbourg, M. Y. Acc. Chem. Res.
1998, 31, 451. (d) Hanss, J.; Kru¨ger, H.-J. Angew. Chem., Int. Ed.
Engl. 1998, 37, 360. (e) Musie, G.; Reibenspies, J. H.; Darensbourg,
M. Y. Inorg. Chem. 1998, 37, 302. (f) Sellmann, D.; Utz, J.;
Heinemann, F. W. Inorg. Chem. 1999, 38, 459. (g) Bhattacharyya,
S.; Weakley, T. J. R.; Chaudhury, M. Inorg. Chem. 1999, 38, 633.
(h) Bohle, S. D.; Zafar, A.; Goodson, P. A.; Jaeger, D. A. Inorg. Chem.
2000, 39, 712.
(2) Halcrow, M. A. Angew. Chem., Int. Ed. Engl. 1995, 34, 1193.
(3) (a) Kitajima, N.; Fujisawa, K.; Tanaka, M.; Moro-oka, Y. J. Am. Chem.
Soc. 1992, 114, 9232. (b) Olsson, M. H. M.; Ryde, U.; Roos, B. O.;
Pierloot, K. J. J. Biol. Inorg. Chem. 1998, 3, 109. (c) Messerschmidt,
A. Struct. Bonding (Berlin) 1998, 90, 37.
10.1021/ic0004636 CCC: $19.00 © 2000 American Chemical Society
Published on Web 11/30/2000

2-Pyrrolylthiones as Bidentate N,S-Chelators
Inorganic Chemistry, Vol. 39, No. 26, 2000 6101
Scheme 1
of the reaction a dark green pigment. Its isolation and analysis
led us to discover the complexing action of Ni(II) by di-2-
pyrrolyl thiones.24 This serendipitous finding then initiated a
thorough investigation of the scope and limits of the use of
2-pyrrolylthiones as N,S-donor atom chelating agents for
transition metals.
We now present the preparation and structural characterization
of di-2-pyrrolyl thionato complexes of Ni(II), Co(III), and Hg-
(II). The metals were chosen as representative transition metals
with preferred square planar, octahedral, and tetrahedral coor-
dination environments. N-alkylation of the metal complexes
demonstrates the spectator role of the noncoordinating pyrrolic
unit in di-2-pyrrolyl thionato complexes. This, in turn, launched
the investigation of 2-thioacetylpyrrole (10) and 2-thioben-
zoylpyrrole (11) as N,S-bidentate ligands for Ni(II), the results
of which will also be presented.
Experimental Section
and leprosy.10 Interestingly, their Ni(II) complexes proved also
Instrumentation and Methodologies. Melting points were deter-
mined on a Thomas model 40 micro hot stage, and are uncorrected. IR
spectra were measured with a Perkin-Elmer model 834 FT-IR instru-
ment. 1H NMR and 13C NMR spectra were measured on a Bruker AC-
200 or AMX 500 or a Varian XL-300. The NMR spectra are expressed
on the δ scale and were referenced to residual solvent peaks. UV-vis
spectra were measured on a Hewlett-Packard HP 8452A photodiode
array spectrophotometer in the solvents indicated. Low- and high-
resolution mass spectra were obtained by the University of British
Columbia (UBC) departmental mass spectrometry facilities, and
elemental analyses were performed by the microanalytical laboratory
at UBC.
to be active in the activation of Si-H bonds.11
Materials. The silica gel used for flash chromatography was Merck
silica gel 60, 230-400 mesh. Rf values were measured on Merck silica
TLC aluminum sheets (silica gel 60 F254), while preparative TLC was
performed on precoated 20 × 20 cm (1000 µm thickness) Merck silica
gel glass plates. Dipyrrolylthiones 6-9 were prepared according to
Clezy and Smythe.22 2-Thioacetylpyrrole25 (10) and 2-thiobenzoylpyr-
role26 (11) were prepared by oxygen-to-sulfur exchange from the
corresponding known ketones.27-29 Synthetic procedures and full
analytical and spectroscopic data for 10 and 11 are provided in the
Supporting Information. All reagents and solvents were commercially
available, were of reagent grade or higher, and were used as received.
(SP-4-trans)-Bis(2-pyrrolyl-2′-pyrrolylato-KN-thione-KS)nickel-
(II) (14). General Procedure. Thione 6 (0.5 g, 2.84 mmol) dissolved
in MeOH (10 mL) was mixed with a solution of nickel(II) acetate‚
4H2O (2.5 g, 6.02 mmol) in MeOH (20 mL) and concentrated NH4OH
(0.2 mL). Rapid precipitation of a dark solid occurred. The mixture
was stirred for 12 h and the solid filtered off, dried, and purified by
means of either column chromatography (silica gel-CHCl3) or repeated
(3-4 times) recrystallization by slow solvent exchange on a rotary
evaporator from CH2Cl2 to hexane. Depending on the method chosen,
up to 450 mg (78%) of an analytically pure dark green crystalline
material with a metallic shine was obtained: mp 273 °C dec; Rf )
A review pertaining to the topic of metal complexes of N,S-
bidentate ligands was published by Akbar Ali and Livingston
in 1974.12 More recent reviews cover bidentate ligands in
general13 or certain sulfur-containing ligands.14,15 An exhaustive
review of the reactivity of the metal ion-sulfur bond was
published by Kuehn and Isied in 1980,16 including the trans-
formation of a large number of S,N- and S,O-chelates. In the
present context, a review by Reedijk,17 covering heterocyclic
nitrogen donor ligands, and one by Foulds,18 summarizing the
coordination chemistry of nickel, are of interest as well. A
review of bioinorganic drugs, many of which contain N,S-donor
ligands, was published most recently.19
Examples of N,S-bidentate ligands in which the nitrogen is
part of a heterocycle and the sulfur donor atom is a thione or
thiol include the compounds 3,12 4,20 and thioamide 5.21 To the
best of our knowledge, however, di-2-pyrrolyl thiones such as
6-9 (Scheme 1) have not been described in detail as metal-
complexing agents before, although, in 1969, Clezy and Smythe
noted in their paper describing the synthesis of di-2-pyrrolyl
thiones that “like other members of the thione class [Andrieu,
C., Mollier, Y., Lozac’h, N. Bull. Soc. Chim. Fr., 1965, 2457.]
the dipyrrylthiones form complexes with mercuric chloride”.22
However, they did not provide an analysis or estimate of the
nature of the complexes.
1
0.45 (1:1 CCl4/CH2Cl2); H NMR (500 MHz, acetone-d6) δ 6.36 (dd,
J ) 1.6, 5.8 Hz, 1H), 6.44 (m, 1H), 7.22 (dd, J ) 0.9, 4.5 Hz, 1H),
7.24 (m, 1H), 7.32 (tr, J ) 1.4 Hz, 1H), 7.37 (m, 1H), 11.2 (br s, 1H,
exchangeable with D2O); 13C NMR (75 MHz, acetone-d6) δ 113.4,
(23) Bru¨ckner, C.; Posakony, J. J.; Johnson, C. K.; Boyle, R. W.; James,
B. R.; Dolphin, D. J. Porphyrins Phthalocyanines 1998, 2, 455.
(24) (a) Bru¨ckner, C.; Dolphin, D. Abstracts of Papers, Pacifichem ‘95,
Honululu, HI, Dec 17-22, 1995; INORG 445. (b) Bru¨ckner, C. Ph.D.
Thesis, University of British Columbia, Vancouver, 1996.
(25) Murase, M.; Yoshida, S.; Hosaka, T.; Tobinaga, S. Chem. Pharm.
Bull. 1991, 39, 489.
Our own interests in di-2-pyrrolylthiones lay in their use as
starting materials for the synthesis of 5,15-diphenylporphyrin
by means of the Raney nickel induced hydrodesulfurization of
6, thereby obtaining di-2-pyrrolylmethane.23 Reaction control
of the hydrodesulfurization by TLC revealed at the onset
(26) Lumbroso, H.; Lie´geois, C.; Pappalardo, G. C.; Andrieu, C. G. J. Mol.
Struct. 1984, 112, 85.
(27) Schweizer, E. E.; Light, K. K. J. Org. Chem. 1966, 31, 2912.
(28) Cadamuro, S.; Degani, I.; Dughera, S.; Fochi, R.; Gatti, A.; Piscopo,
L. J. Chem. Soc., Perkin Trans. 1 1993, 273.
(29) Barbero, M.; Cadamuro, S.; Degani, I.; Fochi, R.; Gatti, A.; Regondi,
V. J. Org. Chem. 1988, 53, 2245.
(18) Foulds, G. A. Coord. Chem. ReV. 1990, 98, 1.
(19) Chem. ReV. 1999, 99, 9 (Medicinal Inorganic Chemistry thematic
issue).
(20) Trofimenko, S. Chem. ReV. 1972, 72, 497.
(21) Fukazawa, M.; Kita, M.; Nonoyama, M. Polyhedron 1994, 13, 1609.
(22) Clezy, P. S.; Smythe, G. A. Aust. J. Chem. 1969, 22, 239.

6102 Inorganic Chemistry, Vol. 39, No. 26, 2000
Bru¨ckner et al.
113.5, 117.6, 119.4, 123.3, 128.7, 128.8, 148.9, 151.0, 175.9; UV-vis
(acetone) λmax (log ꢀ) 366 (4.38), 434 (4.75), 530 (4.23) nm; MS (EI,
220 °C) m/e 408 (100, M+), 374 (17.2), 341 (8.5), 288 (76.3), 176
(55.4, ligand+); IR (KBr) 3394 (s), 3343 (s), 1522 (s), 1394 (s), 1381
(s), 1279 (s), 1103 (s), 1066 (m), 1023 (s), 980 (m), 901 (m), 884 (m),
833 (w), 799 (w), 740 (s), 710 (s), 645 (s) cm-1. Anal. for C18H14N4-
NiS2, calcd (found): C, 52.84 (53.10); H, 3.45 (3.46); N, 13.69 (13.35);
S, 15.67 (14.83).
Chromatography on a short column of silica gel with CH2Cl2 as eluent
was used to purify the complex. The first, purple fraction was collected
and evaporated in vacuo to yield 13 as analytically pure microscopically
fine dark purple needles: Rf ) 0.92 (CH2Cl2/CCl4 1:1); dark purple
1
color; mp 234 °C dec; H NMR (200 MHz, dioxane-d8) δ 6.45 (dd, J
) 4.0, 1.5 Hz, 2H), 6.90 (dd, J ) 4.0, 1.5 Hz, 2H), 7.45-7.60 (m,
6H), 7.68 (s, 2H), 7.85 (dd, J ) 8.0, 2 Hz, 4H); UV-vis (CH2Cl2)
λmax (log ꢀ) 312 (4.68), 390 (4.38), 506 (sh), 526 (4.00), 604 (sh) nm;
LR-MS (EI, 150 °C) 430 (100, M+), 397 (19.5), 308 (17.0), 245 (19.1,
MH+ - ligand), 186 (33.6, ligand), 154 (64.3); HR-MS (EI, 150 °C)
m/e calcd for C22H16N259NiS2 430.0108, found 430.0104; IR (KBr) 1548
(s), 1382 (s), 1294 (w), 1062 (m), 969 (m) 762 (m), 758 (w), 688 (m),
684 (m) cm-1. Anal. for C22H16N2NiS2, calcd (found): C, 61.28 (61.17);
H, 3.74 (3.53); N, 6.50 (6.42).
(SP-4-trans)-[(2-Pyrrolyl-2′-pyrrolylato-KN-thione-KS){2-(1-
methyl)pyrrolyl-2′-pyrrolylato-KN-thione-KS}]nickel(II) (15) and
(SP-4-trans)-Bis[2-(1-methyl)pyrrolyl-2′-pyrrolylato-KN-thione-KS]-
nickel(II) (16). Complex 14 (200 mg, 3.94 × 10-4 mol) was suspended
under anhydrous conditions in dry THF (25 mL). A 1.6 M solution of
n-BuLi in THF (3.0 mL, 1.2 equiv) was added by syringe into the
cooled (-78 °C) solution, upon which all remaining solids dissolved.
After the solution was stirred for 1 h, MeI (30 µL, 1.2 equiv) was
injected, and the resulting solution was allowed to warm to rt. MeOH
(1 mL) was added, followed by CHCl3 (50 mL). The mixture was
washed with water and the organic phase dried over Na2SO4 and
subjected to preparative TLC (silica gel, CH2Cl2/CCl4, 1:3). Three
brown bands became visible. They were isolated, eluted with CH2Cl2,
and evaporated to dryness. The least polar compound was starting
material (30 mg, 15% recovery), the second band was the mono-N-
methylated product 15 (125 mg, 61% yield), and the third, most polar
compound was identified as the bis-N-methylated product 16 (20 mg,
9%). The outcome was changed to 14 (5% recovery), 15 (22%), and
16 (55%) if, under otherwise identical conditions, 2.4 equiv of n-BuLi
and MeI were used. Data for 15: mp 200 °C dec; Rf ) 0.85 (1:1 CCl4/
(T-4)-Bis(2-pyrrolyl-2′-pyrrolylato-KN-thione-KS)mercury(II) (17).
17 was prepared from mercury(II) acetate and thione 6 according to
the general procedure. The precipitated crude metal complex was
filtered, dried, loaded onto a short column of silica gel, and eluted with
CH2Cl2. Slow evaporation of the fluorescent yellow CH2Cl2 solution
yielded 17 as analytically pure shiny yellow hexagonal plates (33%
yield). The product is well soluble only in polar solvents such as acetic
acid, pyridine, or DMSO. Data for 17: mp ) 181 °C dec; Rf ) 0.45
1
(CH2Cl2); brilliant yellow color; H NMR (300 MHz, DMSO-d6) δ
4.39 (s, 2H), 6.71 (d, J ) 2.7 Hz, 2H), 6.98 (s, 2H), 7.30 (s, 2H), 7.38
(d, J ) 3.3 Hz, 2H), 7.58 (s, 2H), 11.95 (s, 2H); 13C NMR (75 MHz,
pyridine-d5) δ 112.3, 118.4, 121.8, 127.0, 127.0, 127.7, 146.9, 151.2,
173.4; UV-vis (CH2Cl2) λmax (log ꢀ) 402 (4.77), 452 (4.78) nm; IR
(KBr) 3401 (s), 3334 (s), 1539 (m), 1513 (s), 1481 (m), 1405 (w),
1370 (s), 1347 (s), 1290 (w), 1255 (m), 1195 (w), 1124 (s), 1031 (s),
988 (m), 895 (s), 879 (m), 866 (m), 810 (s), 767 (m), 742 (s), 694 (m)
cm-1. Anal. for C18H14N4HgS2, calcd (found): C, 39.23 (38.88); H,
2.56 (2.61); N, 10.17 (9.85).
1
CH2Cl2); brown color; H NMR (200 MHz, CDCl3) δ 4.07 (s, 3H),
6.23 (s, 1H), 6.25-6.4 (m, 2H), 6.45 (s, 1H), 6.68 (s, 1H), 6.85-7.0
(m, 3H), 7.11 (s, 1H), 7.20 (s, 1H), 7.40-7.45 (m, 2H), 9.6 (br s, 1H);
UV-vis (CHCl3) λmax (rel intens) 368 (0.47), 434 (1.0), 534 (0.33)
nm; LR-MS (EI, 200 °C) m/e 422 (100, M+), 408 (36, M+ - CH2),
246 (28), 189 (88, methylated ligand), 176 (63, non-methylated ligand);
HR-MS (EI, 200 °C) m/e calcd for C18H14N4NiS2 422.0170, found
422.0157. Data for 16: mp ) 220 dec; Rf ) 0.65 (1:1 CH2Cl2/CCl4);
1H NMR (200 MHz, CDCl3) δ 4.01 (s, 3H), 6.23 (s, 1H), 6.32 (s, 1H),
6.68 (s, 1H), 6.85 (s, 1H), 7.00 (s, 1H), 7.47 (s, 1H); 13C NMR (50
MHz, CDCl3) δ 33.2, 105.1, 114.1, 120.8, 127.8, 131.2, 146.2, 149.9,
151.1, 178.0; UV-vis (CH2Cl2) λmax (rel intens) 368 (0.53), 432 (1.0),
543 (0.39) nm; LR-MS (EI, 150 °C) m/e 436 (100, M+), 421 (9.2, M+
- CH3), 403 (6.2), 248 (25.6, M+ - ligand), 189 (ligand+); HR-MS
(EI, 150 °C) m/e calcd for C20H18N4NiS2 436.0326, found 436.0328.
(SP-4-trans)-Bis[2-(3,4-dimethyl)pyrrolyl-2′-(3,4-dimethyl)pyr-
rolylato-KN-thione-KS]nickel(II). This complex was prepared from
thione 8 and nickel(II) acetate in 30% yield as described for the
(OC-6-mer)-Tris(2-pyrrolyl-2′-pyrrolylato-KN-thione-KS)cobalt-
(III) (18-mer) and (OC-6-fac)-Tris(2-pyrrolyl-2′-pyrrolylato-KN-
thione-KS)cobalt(III) (18-fac). Reaction of thione 6 with cobalt(II)
acetate in the presence of oxygen according to the general procedure
produced a solid material which was prepurified by column chroma-
tography (silica-CHCl3) and then subjected to preparative TLC (CH2-
Cl2/CCl4, 1:3, multiple developments). The least polar, brown-orange
band gave 22% 18-mer and the second, orange band 19% 18-fac. Data
for 18-mer: slow evaporation of an acetone solution yielded dark ruby
red X-ray-quality crystals; mp 150 °C dec; Rf ) 0.25 (CH2Cl2/CCl4);
1H NMR (300 MHz, acetone-d6) δ 5.95 (s, 1H), 6.35-6.42 (m, 6H),
6.56 (dd, J ) 1.2, 4.2 Hz, 1H), 7.10-7.20 (m, 3H), 7.24-7.30 (m,
2H), 7.34-7.37 (m, 2H), 7.46 (dd, J ) 1.2, 4.5 Hz, 1H), 7.67 (s, 1H),
7.91 (s, 1H), 11.0 (br s, 3H); 13C NMR (50 MHz, acetone-d6) δ 112.1,
112.2, 112.3, 114.8, 114.9, 115.4, 120.4 (multiplet), 120.7, 123.3, 124.1
(multiplet), 126.9, 127.0 (multiplet), 131.6 (multiplet), 145.8, 147.7,
147.9, 151.1, 151.2, 151.4, 178.2, 178.4, 178.7; UV-vis (CHCl3) λmax
416 nm; LR-MS (FAB, 3-NBA matrix) 643 (3.5, M+ + Co), 585 (5.3,
MH+), 409 (100, M+ - ligand), 343 (23.0), 234 (78.1); LR-MS (FAB,
3-NBA matrix) m/e calcd for C27H21N659CoS3 584.03218, found
584.03505; IR (KBr) 3397 (s), 3345 (s), 1544 (m), 1517 (s), 1420 (s),
1372 (s), 1345 (s), 1308 (m), 1267 (m), 1117 (m), 1105 (m), 1172
(w), 1160 (w), 1031 (m), 997 (m), 908 (m), 878 (m), 815 (m), 747
(m), 698 (w) cm-1. Anal. for C27H21N6CoS3‚1/2H2O, calcd (found): C,
54.63 (54.34); H, 3.74 (3.66); N, 14.16 (13.84). Data for 18-fac: mp
1
formation of 14: Rf ) 0.33 (1:1 CCl4/CH2Cl2); H NMR (200 MHz,
CDCl3) δ 1.80 (s, 3H), 1.85 (s, 3H), 2.02 (s, 3H), 2.10 (s, 3H), 6.76 (s,
1H), 6.78 (s 1H), 7.30 (s, 1H), 8.12 (s, 1H), 9.3 br s (1H); UV-vis
(CHCl3) λmax (rel intens) 360 (sh), 424 (1.0), 508 (0.52); LR-MS (EI,
200 °C) m/e 520 (12.6, M+), 505 (0.9, M+ - CH3), 459 (9.1), 424
(7.8, M+ - dimethylpyrrole), 410 (4.4), 337 (9.1, M+ - ligand), 322
(7.6, M+ - ligand - CH3), 232 (45.1), 184 (100, ligand+); HR-MS
(EI, 200 °C) m/e calcd for C26H30N458NiS2 520.1265, found 520.1259.
(SP-4)-Bis[2-pyrrolylato-KN-thioacetyl-KS]nickel(II) (12). 12 was
prepared in 81% yield from thione 10 and nickel(II) acetate according
to the general procedure. Slow evaporation of a MeOH solution yielded
fine long dark red needles: mp 212-214 °C (phase transitionsas seen
through the microscopesat 177 °C); Rf ) 0.90 (CHCl3); deep red color;
1H NMR (200 MHz, CDCl3) δ 2.84 (s, 3H), 6.25 (d, J ) 4.4 Hz, 1H),
6.81 (m, 1H), 7.42 (s, 1H); 13C NMR (50 MHz, CDCl3) δ 22.7, 119.3,
123.5, 152.3, 155.6, 191.7; UV-vis (log ꢀ) λmax 282 (4.48), 370 (4.32),
474 (3.99), 496 (sh), 578 (3.58) nm; LR-MS (EI, 150 °C) m/e 306
(100, M+), 291 (15.6, M+ - CH3), 246 (18.3), 182 (27.8), 92 (67.0);
HR-MS (EI, 150 °C) m/e calcd for C12H12N258NiS2 305.9795, found
305.9803; IR (KBr) 1569 (s), 1383 (s), 1308 (w), 1150 (w), 1110 (m)
886 (w), 824 (m), 741 (m), 674 (w) cm-1. Anal. for C12H12N2NiS2,
calcd (found): C, 46.94 (47.13); H, 3.94 (3.69); N, 9.12 (8.92).
(SP-4)-Bis(2-pyrrolylato-KN-thiobenzoyl-KS)nickel(II) (13). 13
was prepared in 80% yield from thione 11 (100 mg) and nickel(II)
acetate in the presence of oxygen according to the general procedure.
1
170 °C dec; Rf ) 0.12 (CH2Cl2/CCl4); dark orange color; H NMR
(200 MHz, acetone-d6) δ 5.37 (s, 3H), 5.57 (m, 3H), 5.72 (dd, J ) 1.5,
4.2 Hz, 3H), 6.35 (m, 3H), 6.44 (s, 3H), 6.66 (d, 4.2H, 3H), 11.0 (br
s, 3H); UV-vis (CHCl3) λmax 424 nm; LR-MS (FAB, 3-NBA matrix)
m/e 643 (4.1, M+ + Co), 584 (3.5, MH+), 584 (3.3, M+), 409 (100,
M+ - ligand), 343 (23.2), 234 (76.1); HR-MS (FAB, 3-NBA matrix)
m/e calcd for C27H21N659CoS3: 584.03280, found 584.03184; IR (KBr)
3396 (s), 3343 (s), 1551 (s), 1527 (m), 1429 (s), 1378 (m), 1347 (s),
1304 (m), 1269 (m), 1204 (w), 1121 (m), 1104 (m), 1192 (m), 1165
(m), 1042 (s), 1006 (m), 910 (m), 876 (w), 813 (m), 740 (s), 688 (m)
cm-1. Anal. for C27H21N6CoS3, calcd (found): C, 55.47 (55.04); H,
3.62 (3.72); N, 14.38 (14.11).
X-ray Crystallography. Crystallographic data and selected experi-
mental details are listed in Table 1. Selected bond lengths for the

2-Pyrrolylthiones as Bidentate N,S-Chelators
Inorganic Chemistry, Vol. 39, No. 26, 2000 6103
Table 1. Summary of Crystallographic Dataa
Scheme 2
14‚0.28H2O
18-mer‚Me2CO
17
empirical
formula
mol wt
C18H14N4NiS2‚0.28H2O C27H21CoN6S3‚C3H6O C18H14HgN4S2
414.25
642.70
551.05
cryst syst
space group R3h (no. 148)
a, Å
b, Å
c, Å
trigonal
monoclinic
P21/n (no. 14)
9.569(1)
23.152(1)
13.659(1)
90
100.882(8)
90
2971.6(5)
4
triclinic
P1h (no. 2)
8.443(2)
14.278(1)
7.445(1)
90.561(9)
97.64(1)
104.250(9)
861.3(2)
2
18.467(1)
18.467(1)
26.404(2)
90
90
120
solutions and refinements of the structures.30 Crystals of 14 contain
0.28 water molecule/nickel complex, located on the 3-fold axis. The
population parameter for the oxygen atom was refined. Complex 18-
mer crystallizes as an acetone solvate.
All non-hydrogen atoms were refined with anisotropic thermal
parameters. The hydrogen atoms in the complexes were fixed in
R, deg
â, deg
γ, deg
V, Å3
Z
7797(1)
18
F
calcd, g/cm3 1.588
1.436
Mo (0.710 69)
2.125
Mo (0.710 69)
radiation
(λ, Å)
µ, cm-1
transm
factors
Rb (Rw)c
Cu (1.541 78)
calculated positions (N-H ) 0.91 Å, C-H ) 0.98 Å, BH
)
1.2Bbonded atom). The hydrogen atoms associated with the water molecule
in 14 were not included in the model. Secondary extinction corrections
(Zachariasen type 2 isotropic) were applied where appropriate, the final
values of the extinction coefficient being 2.6(3) × 10-6 for 17. Neutral
atom scattering factors for all atoms and anomalous dispersion
corrections for the non-hydrogen atoms were taken from the Interna-
tional Tables for X-ray Crystallography.31,32
39.47
0.77-1.00
8.11
0.93-1.00
92.10
0.40-1.00
0.032 (0.033)
0.043 (0.038)
0.042 (0.040)
a Obtained at T ) 294 K. b R ) ∑||Fo| - |Fc||/∑|Fo|. c Rw ) (∑w(|Fo|
2
- |Fc|)2/∑w|Fo| )1/2
.
Table 2. Selected Bond Lengths in 14 with Estimated Standard
Deviations in Parentheses
Results and Discussion
Syntheses of the Di-2-pyrrolyl Thiones. The syntheses of
the crystalline, deep orange to red di-2-pyrrolylthiones 6-9 from
thiophosgene and the corresponding pyrroles were performed
according to procedures described in the literature (Scheme
1).22,33 The reaction of the parent unsubstituted pyrrole was, on
the basis of the original procedure, scaled up 10-fold, yielding
∼20 g of crystalline material without any problems in reaction
control or loss of yield. The preparation of 2-thioacetylpyrrole
(10)25 as a red oil and the red solid 2-thiobenzoylpyrrole (11)26
was accomplished by an oxygen-to-sulfur exchange of the
corresponding ketones with P4S10 or Lawesson’s reagent (2,4-
bis(4-methoxyphenyl)-1,3-dithia-2,4-phosphetane-2,4-disul-
fide)34 according to procedures similar to the ones provided in
the literature (Scheme 2). Since the characterization of these
thiones is incomplete in the original literature, we describe
improved synthetic procedures and full analytical and spectro-
scopic data for 10 and 11 in the Supporting Information.
Solution- and Solid-State Structure of Di-2-pyrrolyl Thione
(6). Di-2-pyrrolyl thione (6) could theoretically exist in various
conformations, each in several tautomeric forms (6A-6C).
Dipole moment studies of di-2-pyrrolyl ketone and the corre-
sponding thione 6 have shown, however, that the preferred
solution-state conformation in several nonpolar solvents is the
uniplanar conformation 6B in which the carbonyl or thiocarbonyl
group is on the same side of the molecule as the nitrogens.26
On the basis of IR and UV-vis evidence, Clezy determined
the dominant tautomer to be that of the thione 6A/B rather than
that corresponding to the meso-thioldipyrrin 6C.22 This prefer-
ence is also found in the solid-state structure of both the
thioketone 6 and the corresponding di-2-pyrrolyl ketone.35
bond
distance (Å)
bond
distance (Å)
Ni(1)-S(1)
Ni(1)-S(2)
Ni(1)-N(1)
Ni(1)-N(3)
S(1)-C(9)
S(2)-C(18)
N(1)-C(1)
N(1)-C(4)
N(2)-C(5)
N(2)-C(8)
N(3)-C(10)
N(3)-C(13)
N(4)-C(14)
N(4)-C(17)
C(1)-C(2)
2.1988(9)
2.1740(9)
1.871(2)
1.869(2)
1.724(3)
1.711(3)
1.394(3)
1.332(3)
1.379(4)
1.357(4)
1.387(4)
1.332(4)
1.372(4)
1.349(4)
1.420(4)
C(1)-C(9)
1.380(4)
1.355(4)
1.416(4)
1.377(4)
1.432(4)
1.391(4)
1.356(5)
1.408(4)
1.408(4)
1.360(5)
1.392(4)
1.389(4)
1.415(4)
1.376(5)
1.356(5)
C(2)-C(3)
C(3)-C(4)
C(5)-C(6)
C(5)-C(9)
C(6)-C(7)
C(7)-C(8)
C(10)-C(11)
C(10)-C(18)
C(11)-C(12)
C(12)-C(13)
C(14)-C(15)
C(14)-C(18)
C(15)-C(16)
C(16)-C(17)
Table 3. Selected Bond Lengths in 17 and 18-mer with Estimated
Standard Deviations in Parentheses
17
18-mer
bond
distance (Å)
bond
distance (Å)
Hg(1)-S(1)
Hg(1)-S(2)
Hg(1)-N(1)
Hg(1)-N(3)
S(1)-C(9)
2.457(2)
2.450(2)
2.314(6)
2.330(6)
1.736(7)
1.730(7)
Co(1)-S(1)
Co(1)-S(2)
Co(1)-S(3)
Co(1)-N(1)
Co(1)-N(3)
Co(1)-N(5)
S(1)-C(9)
2.247(1)
2.254(1)
2.232(1)
1.927(3)
1.944(3)
1.908(4)
1.690(4)
1.722(4)
1.709(4)
S(2)-C(18)
S(2)-C(18)
S(2)-C(27)
compounds appear in Tables 2 and 3. The final unit cell parameters
were obtained by least squares on the setting angles for 25 reflections
with 2θ ) 57.6-75.6° for 14, 26.1-38.2° for 17, and 23.0-31.3° for
18-mer. The intensities of three standard reflections, measured every
200 reflections throughout the data collections, remained constant for
the three compounds. The data were processed and corrected for Lorentz
and polarization effects and absorption (empirical, based on azimuthal
scans). The structure of 14 was solved by direct methods, and those of
17 and 18-mer were solved by conventional heavy atom methods, the
heavy atom coordinates being determined from the Patterson function
and those of the remaining non-hydrogen atoms from subsequent
difference Fourier syntheses. Structure analyses of 14 and 17 were
initiated in the centrosymmetric space groups R3h and P1h, respectively,
on the basis of the E statistics and the appearances of the Patterson
functions. These choices were confirmed by the subsequent successful
(30) teXan: Crytal Structure Analysis Package, Molecular Structure Corp.,
The Woodlands, TX, 1985, 1992.
(31) International Tables for X-ray Crystallography; Kynoch Press: Bir-
mingham, U.K., 1974; Vol. IV.
(32) International Tables for Crystallography; Kluwer Academic Publish-
ers: Boston, 1992; Vol. C.
(33) de Groot, J. A.; van der Steen, R.; Fokkens, R.; Lugtenburg, J. Recl.
TraV. Chim. Pays-Bas 1982, 101, 35.
(34) Cava, M. C.; Levinson, M. I. Tetrahedron 1985, 22, 5061.
(35) (a) Norsten, T. B.; McDonald, R.; Branda, N. R. Chem. Commun.
1999, 719. (b) Cf. to the structure of R-substituted di-2-pyrrolyl-
ketones: Sheldrick, W. S.; Becker, W.; Engel, J. Acta Crystallogr.,
Sect. B 1978, 34, 2929.

6104 Inorganic Chemistry, Vol. 39, No. 26, 2000
Bru¨ckner et al.
Figure 1. Optical spectra (CH2Cl2) of Ni(II) complex 14, Hg(II)
complex 17, and Co(III) complexe 18-mer in comparison to that of
the free ligand 6.
Reaction of Di-2-pyrrolyl Thione 6 with Ni(II). A mixture
of a methanol solution of thione 6 with a methanolic nickel(II)
acetate solution results, after the addition of a base such as NH4-
OH, in the quantitative conversion and precipitation of the thione
as nickel complex 14. Recrystallization produces beautiful dark
green crystals with a metallic sheen which are air and water
stable. The mass spectrum and elemental analysis of the pigment
showed the composition C18H14N4NiS2, corroborating the
formulation of 14 as a neutral Ni(II) complex with two
pyrrolythionato ligands. The bis-N-methylated thione 7 is inert
toward Ni(II) under identical conditions, indicating the involve-
ment of at least one pyrrole nitrogen in the coordination action
of 6 with the metal ion. This reaction is unique to pyrrolylthione
6 in that the corresponding pyrrolylketone failed, under identical
conditions, to produce any complex.
The electronic spectrum of the orange solution of complex
14 is shown in Figure 1. The spectrum is dominated by bands
attributable to intraligand p f p* transitions and possibly ligand-
to-metal CT bands. Sharp NMR signals for this Ni(II) complex
could be obtained, indicating the diamagnetic low-spin config-
uration of the Ni(II) ion, characteristic of a (pseudo) square
planar coordination environment of the metal.36 The formation
of a diamagnetic complex with Ni(II) is, given the known
examples of octahedral paramagnetic complexes with N,S-donor
atom chelates, not necessarily expected.6,37 Two modes of
chelation could be attained by thiones of type 14, namely, 14A,
in which the ligand chelates in an N,N-donor fashion like a
dipyrrinato moiety,38-40 or 14B, in which the thione tautomer
Figure 2. ORTEP representation (33% probability level) and number-
ing scheme, top and side views, for bis(di-2-pyrrolylthionato)nickel-
(II) complex 14.
Figure 3. Bond lengths and angle changes of di-2-pyrrolyl thione (6)
upon chelation to Ni(II). The changes were determined by comparison
of the corresponding average bond lengths in the solid-state structure
of 635a and 14.
pendent and nonequivalent pyrrolic units can be clearly distin-
guished in the NMR spectra (1H, 13C, and particularly C,H- and
H,H-COSY) of the complex. High- and low-temperature NMR
studies did not indicate the presence of any dynamic effects
such as intraligand donor exchanges. Thus, isomer 14B is
believed to represent the solution structure of 14. This assign-
ment allows the ligands to adopt a conformation very similar
to the solution- and solid-state conformation of the free ligand.
In principle, cis- and trans-isomers of the square planar Ni(II)
complexe 14B are possible, but electronic factors and interligand
steric interactions make the trans-isomer the most likely. Indeed,
an X-ray crystal structure analysis of 14 confirms this.
A crystal suitable for X-ray crystallography was grown by
slow evaporation of an acetone solution of the nickel complex
14. Crystallographic data and selected bond distances are listed
in Tables 1 and 2. The ORTEP representation and a side view
of the complex are shown in Figure 2. As anticipated, the nickel
center in pigment 14 is coordinated in an almost perfect square
planar fashion by an N,S-donor set, arranged in the trans-
configuration. Upon metalation, the ligands underwent some
bond length changes which can be rationalized by the increased
weight of the limiting resonance structure indicated (Figure 3).
The bond lengths in the noncoordinating pyrrolic unit remain
unchanged upon metal complex formation; it thus appears
nonparticipating in the operation of complexation. The inter-
planar angles between the two pyrrolic units in each chelating
unit in the complex are markedly flattened (23° and 5.3°,
respectively) when compared to that of the free ligand (31.9°).35
N-methylation of Complex 14. The spectator role of the
noncomplexing pyrrolic unit raises the question of whether it
is possible to chemically modify this unit without disturbing
coordinates as an N,S-bidentate chelate. The IR indicates the
presence of a pyrrolic NH functionality (IR (KBr) 3394 (s), 3343
(s) cm-1),41 supporting an N,S-coordination mode. Two inde-
(36) Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M. AdVanced
Inorganic Chemistry, 6th ed.; John Wiley & Sons: New York, 1999.
(37) Smits, J. M. M.; Janssen, R.; Beurskens, P. T.; van Ryin, J.; Reedijk,
J. Polyhedron 1987, 6, 1843.
(38) (a) Bru¨ckner, C.; Karunaratne, V.; Rettig, S. J.; Dolphin, D. Can. J.
Chem. 1996, 74, 2182. (b) Bru¨ckner, C.; Zhang, Y.; Rettig, S. J.;
Dolphin, D. Inorg. Chim. Acta 1997, 236, 279.
(39) Zhang, Y.; Thompson, A.; Rettig, S. J.; Dolphin, D. J. Am. Chem.
Soc. 1998, 120, 13537.
(40) Falk, H. The Chemistry of Linear Oligopyrroles and Bile Pigments;
Springer-Verlag: Wien, New York, 1989.
(41) Hediger, H. J. Infrarotspektroskopie; Akademische Verlagsgesell-
schaft: Frankfurt a.M., 1971.

2-Pyrrolylthiones as Bidentate N,S-Chelators
Inorganic Chemistry, Vol. 39, No. 26, 2000 6105
Scheme 3
the complexation. Another question is whether this unit could
be omitted altogether (vide infra). Both questions can be
answered affirmatively. Deprotonation of complex 14 with BuLi
and subsequent reaction with 1 or 2 equiv of MeI results cleanly
in the formation of the mono- and di-N-methylated products
15 and 16, respectively (Scheme 3). The mass spectra of 15
and 16 show the expected mass gain of 14 and 28 mu, and the
compounds could also be unambiguously identified by their 1H
NMR spectra. The C2 symmetry of 16 is reflected in a simple,
starting-material-like spectrum with an additional signal for the
methyl groups, and the spectrum of compound 15 carrying two
nonequivalent ligands is correspondingly more complex.
Reaction of 2-Thiacetylpyrrole (10) and 2-Thiobenzoylpyr-
role (11) with Ni(II). The recognition of the innocent role of
the noncomplexing pyrrolic unit in all of the dipyrrolylthionato
complexes described raised the question of whether molecules
containing solely the 2-pyrrolylthione moiety would be capable
of forming complexes. Potential ligands of this class are, for
instance, the known compounds 2-thioacetylpyrrole (10)25 and
2-thiobenzoylpyrrole (11).26 Indeed, the Ni(II) complexes 12
and 13 form in high yield upon mixing of basic methanolic
solutions of the pyrrolylthiones 10 and 11, respectively (Scheme
2). Their NMR spectroscopic and analytical data are similar to
those of 14 and allow for their formulation as trans square planar
complexes with a ligand-to-metal ratio of 2:1. The purple
thiobenzoylpyrrolato complex 14 was distinguished by a very
low solubility in noncoordinating solvents, whereas the red
thioacetyl analogue was freely soluble in a variety of solvents.
The pronounced electronic influence of the methyl or phenyl
group on the rest of the complex as compared to the pyrrolyl
group in 14 is demonstrated by their significantly varying optical
spectra, shown in Figure 4. Both spectra exhibit the same general
pattern, with that of the phenyl-substituted complex 14 being
∼25 nm bathochromically shifted as compared to that of the
methyl analogue 13.
Steric Requirements of the 2-Pyrrolylthionato Moiety. In
an attempt to prepare complexes of derivatized di-2-pyrrolyl
thiones, hexamethylpyrrolylthione 9 was mixed with Ni(II) in
the presence of base, as described above. To our surprise, not
a trace of a nickel complex could be detected. Instead, the free
ligand was recovered quantitatively. Due to the electronic
similarity of the ligands, as judged by their similar optical
spectra, electronic arguments do not seem adequate to explain
these findings. The key to understanding the finding lies in the
steric interaction of the R-substituents. On the basis of the X-ray
crystal data of nickel complex 14, a computer-generated model42
in which the R-hydrogens of structure 14 had been replaced
with methyl groups indicated a large overlap of the van der
Waals radii of the R-methyl groups and the sulfur of the
opposing ligand. This makes the achievement of a square planar,
undistorted arrangement impossible. Interestingly, the formation
of a tetrahedral complex, although sterically possible, was not
observed either. The hypothesis that any complex formation is
prevented by the bulk of an R-substituent is strengthened by
Figure 4. Normalized optical spectra (CH2Cl2) of bis(2-thioacetylpyr-
rolato)nickel(II) complex 12, bis(2-thiobenzoylpyrrolato)nickel(II) com-
plex 13, and bis(2-pyrrolylthionato)nickel(II) complex 14.
the smooth complexation of Ni(II) by the R-unsubstituted â,â′-
dimethyl thione 8 to give the corresponding square planar
complex. Its analytical and spectroscopic properties all fall, as
compared to those of 14, within expectation.
Reaction of Thione 6 with Hg(II). To evaluate the propensity
of 6 to coordinate to other metals, it was reacted with Hg(II)
and Co(II and III) (vide infra). Mercury was chosen for its
known thiophilicity and its disposition to form tetrahedral
complexes and to investigate the nature of the complex
mentioned by Clezy.22 The reaction of 6 with mercury(II) acetate
in MeOH produced a fine, bright yellow crystalline precipitate,
providing an elemental analysis indicating the composition
C18H14N4HgS2, corresponding to complex 17 with a ligand-to-
metal stoichiometry of 2:1. Its solubility in solvents such as
acetone or methylene chloride was much lower as compared to
that of the nickel complex 14, and the optical spectrum of the
bright yellow solution, shown in Figure 1, differed significantly
as well. It is, devoid of dd transitions and CT bands, very much
like that of the free ligand. The complex dissolves in DMSO at
sufficient concentration for analysis by NMR spectroscopy. The
pattern expected for one set of equivalent ligands was readily
apparent. These results suggest the expected formation of a
tetrahedral complex with two chelating ligands around the
central metal. However, an oligo- or polymeric structure with
bridging ligands of 2:1 ligand-to-metal stoichiometry could not
be excluded; consequently single crystals were grown by
allowing a dilute solution of 17 in CH2Cl2 to evaporate slowly,
and their X-ray diffraction pattern was analyzed. Crystal data
are listed in Table 1, and selected bond lengths are listed in
Table 3. A stereoview of an ORTEP representation of the
molecule is shown in Figure 5. The structural analysis showed
the molecule as a distorted tetrahedral complex coordinating
through one nitrogen and the sulfur with a dihedral angle of
62.1° between the planes defined by the mercury, the coordi-
nated nitrogen, and the sulfur atom of the respective ligands.
The intraligand bond lengths and bond angles are, with one
exception, equivalent to those observed in the nickel complex.
The two pyrrolic units of the ligands are not uniplanar but angled
by about 40°, a value comparable to that of the free ligand
(31.9°).35 However, the conformations in both the free ligand
and complex 17 may well be governed by crystal packing
effects.
Reaction of Thione 6 with Co(II) and Co(III). Co(II), as
its acetate, was reacted with thione 6 as described above. This
caused rapid precipitation of a dark solid. Chromatography
proved it to be a mixture of two orange low-polarity compounds
(18-mer and 18-fac) in the ratio of ∼4:6 with very similar
optical spectra. The electronic spectrum of 18-mer is shown in
(42) CAChe 4.1, Molecular Modeling Package, MM3 force field, Oxford
Molecular, Beaverton, OR, 1999.
Figure 1. Both compounds have identical mass spectra (M+
)

6106 Inorganic Chemistry, Vol. 39, No. 26, 2000
Bru¨ckner et al.
Figure 6. ORTEP representation (33% probability level) of the tris-
(2,2′-pyrrolylthionato)cobalt(III) complex 18-mer (as its acetone sol-
vate).
Figure 5. Stereoscopic view of the ORTEP representation (33%
probability level) of the bis(2-pyrrolylthionato)mercury(II) complex 17.
compared to those of the uncoordinated ligand are equivalent
to those observed in the Ni(II) and the Hg(II) complexes 14
and 17, respectively. The deviation of the pyrrolic units from
coplanarity within the ligands average to 25°. The propensity
of the NH protons to undergo hydrogen bonding is in this
structure highlighted by the incorporation of one hydrogen-
bonded molecule of acetone per complex into the crystal.
584) corresponding to a molecular formula of C27H21N659CoS3,
i.e., to a complex with a ligand-to-metal stoichiometry of 3:1.
The low polarity of the complexes indicates the presence of
electroneutral complexes of Co(III). The facile aerial oxidation
of Co(II) to Co(III) in the presence of amine ligands is well-
known. Thus, all findings can be rationalized by the formation
of (octahedral) Co(III) trischelates (diamagnetic, d6 low spin).
Complexes 18-mer and 18-fac also form by a ligand exchange
reaction with Co(III)(acac)3 and 6 in refluxing phenol. Unsym-
metrical bidentate ligands forming octahedral complexes may
form two stereoisomeric complexes.43 These isomers, the fac-
and the mer-isomers, can be, in case of the presence of
kinetically inert Co(III) centers, separated by preparative thin-
layer chromatography. Both isomers can be clearly distinguished
by their differing symmetries as seen in their 1H NMR spectra.
The symmetry of the fac-isomer 18-fac (point group C3) bestows
a C3 axis onto the complex, rendering all three ligands
equivalent. Consequently, the 1H NMR spectrum of this isomer
is very similar to that exhibited by the Ni(II) complex 14. The
mer-isomer 18-mer contains no such high-symmetry element
(point group C1), and this renders all three ligands nonequivalent,
reflected in its complex 1H NMR spectrum. The final proof of
the stereochemical assignment was provided by a single-crystal
X-ray structure analysis of 18-mer (as its acetone solvate), the
ORTEP of which is shown in Figure 6. Selected bond lengths
and angles are listed in Table 3. The donor atoms in the
essentially planar ligands form an almost perfect octahedron
around the central metal. All deviations in bond length as
Conclusion
We have shown that 2-pyrrolylthiones can form stable
coordinatively saturated metal complexes with Ni(II), Co(III),
and Hg(II). As shown by a variety of spectroscopic methods
and proven by single-crystal X-ray diffraction studies, the ligand
serves in these complexes as a monoanionic bidentate N,S-
donor. Depending on the metal, square planar, tetrahedral, or
octahedral coordination spheres around the metal center can be
achieved. R-Substituents other than hydrogen on the chelating
moieties introduce too much steric interaction with an opposing
sulfur atom upon chelation to the effect that no chelates for
5-methyl-substituted 2-pyrrolylpyrrole were observed.
This work expands the arsenal of known N,S-donor ligands
by a class which is readily accessible in large quantities. Reports
of the pharmacological activity of compounds containing the
2-pyrrolylthione and 2-indolylthione moieties have appeared in
the literature;25,44 however, their potential chelating ability was
not recognized. In light of our findings it is interesting to
consider the possible importance of metal coordination to the
biological activity of these compounds.
Acknowledgment. We thank the Natural Sciences and
Engineering Council (NSERC) of Canada for financial support.
Supporting Information Available: Details of the preparation for
compounds 10 and 11 and detailed X-ray crystallographic files in CIF
format for complexes 14‚0.28H2O, 18-mer‚Me2CO, and 17. This
material is available free of charge via the Internet at http://pubs.acs.org.
(43) von Zelewsky, A. Stereochemistry of Coordination Compounds;
Wiley: New York, 1996.
(44) (a) Sato; Sunagawa Chem. Pharm. Bull. 1967, 15, 642. (b) Kost, A.
N.; Gorbunova, S. M.; Basova, L. P.; Kiselev, V. K.; Gorbunov, V. I.
Pharm. Chem. J. (Engl. Transl.) 1974, 8, 8. (c) Goerlitzer, K.;
Hoelscher, D. Arch. Pharm. (Weinheim, Ger.) 1986, 319, 120.
IC0004636