Role of O,C,O-ligand in a new coordination mode of organotin compounds to 2-mercapto-1-methylimidazol. Stabilization of its thione form

Article abstract of DOI:10.1016/j.jorganchem.2006.09.056

The reaction of the organotin compound [Ph₂LSn]⁺ [OTf]^- (1), (L(O,C,O) = 2,6-(t-BuOCH₂)₂C₆H₃), with the sodium salt Na(mimt), mimt = 1-methylimidazole-2-thiolate, resulted in the isolation of Ph₂LSn(mimt) (2), where the polar group (mimt) has been stabilized as the thione-tautomeric form by the triorganotin fragment Ph₂LSn. Product 2 was characterized by ¹H, ¹³C and ¹¹⁹Sn NMR and IR spectroscopy, ESI/MS, elemental analyses and X-ray diffraction.

Full text of DOI:10.1016/j.jorganchem.2006.09.056

Journal of Organometallic Chemistry 692 (2007) 908–911
www.elsevier.com/locate/jorganchem
Note
Role of O,C,O-ligand in a new coordination mode of organotin
compounds to 2-mercapto-1-methylimidazol. Stabilization
of its thione form
a
a
a,
*
Jana Martincova , Libor Dostal , Jan Taraba b,1, Roman Jambor
´
´
a
ˇ
Department of General and Inorganic Chemistry, University of Pardubice, na´m. Cs. legiı´ 565, CZ-532 10, Pardubice, Czech Republic
Department of Inorganic Chemistry, Faculty of Science, Masaryk University of Brno, Kotla´rˇska´ 2, CZ-611 37, Brno, Czech Republic
b
Received 29 June 2006; received in revised form 25 August 2006; accepted 29 September 2006
Available online 5 October 2006
Abstract
The reaction of the organotin compound [Ph2LSn]+ [OTf]ꢀ (1), (L(O,C,O) = 2,6-(t-BuOCH2)2C6H3), with the sodium salt Na(mimt),
mimt = 1-methylimidazole-2-thiolate, resulted in the isolation of Ph2LSn(mimt) (2), where the polar group (mimt) has been stabilized as
the thione-tautomeric form by the triorganotin fragment Ph2LSn. Product 2 was characterized by 1H, 13C and 119Sn NMR and IR spec-
troscopy, ESI/MS, elemental analyses and X-ray diffraction.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Organotin; Pincer ligands; S-ligands; NMR; Crystal structure
Organotin compounds containing various mercapto
groups are extensively studied for their biological activities,
most importantly as antitumor agents and their in vitro
potency against trypanozoma cultures was demonstrated
as well [1]. These compounds containing covalent Sn–S
bond are also studied for industrial use, namely as stabiliz-
ers for polyvinyl chlorides [2]. An interesting class of
organotin mercapto derivatives comprises those of general
formula R3Sn(SR0), where R0 contains a donor atom (D)
capable of forming a secondary bond with tin atom [3].
The second donor atom (D) in mercapto groups is most
commonly the nitrogen atom (N) and these ligands are
known to possibly exist in two tautomeric thione and thiol
forms (Scheme 1) [4]. While the thione form of the free
ligand is more favorable and is preferred in solution based
on 1H NMR studies, where the presence of N–H instead of
S–H has been detected, the thiol form of these polar groups
can be found in the chemistry of organotin compounds
resulting in the presence of the Sn–S covalent bond.
In connection with our previous studies that were
focused on hypercoordinated organotin derivatives of
Y,C,Y-pincer ligands containing covalent bond Sn–X,
where X was a monodentate polar group that could not
affect the geometry of the central tin atom [5], we decided
to prepare a triorganotin compound containing 1-methy-
limidazole-2-thiol (Hmimt), which contains a nitrogen
donor atom capable of forming an additional coordination
bond Sn N. Here we report on the use of the triorgano-
tin fragment Ph2LSn containing pincer type ligand L
(L(O,C,O) = 2,6-(t-BuOCH2)2C6H3) on the stabilization
of thione-form in Ph2LSn(mimt) (2) (mimt = 1-methylimi-
dazole-2-thiolate).
The triorganotin compound [Ph2LSn]+[OTf]ꢀ (1) has
been prepared according to literature [5] and stirring a
solution of 1 with sodium salt Na(mimt) in dry degassed
tetrahydrofuran overnight yielded a solid powder (Scheme
2) [6].
*
Corresponding author. Fax: +420 466037068.
E-mail addresses: taraba@chemi.muni.cz (J. Taraba), roman.jam-
bor@upce.cz (R. Jambor).
1
Fax: +420 549492443.
0022-328X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.09.056

J. Martincova´ et al. / Journal of Organometallic Chemistry 692 (2007) 908–911
909
-
NO3
N
N
N
2+
S
SH
N
NH
S
N
R
N
N
H
S
S
H
A
R = Me, Et, Ph
Sn
R
B
S
H
N
N
Scheme 1. Thione (A) and thiol (B) tautomeric forms of the mercapto
ligands.
N
HN
-
NO3
The analytical data show that the polar group (mimt) is
stabilized in a thione form both in solution and solid state.
The value of chemical shift C2 in 13C NMR spectroscopy is
the most informative for thiol–thione tautomeric form
determination [7]. The 13C NMR data revealed broad sig-
nal of C2 at 163.5 ppm for 2 that is comparable to the same
signal of C2 in free ligand (Hmimt) (d 13C(C2) =
160.2 ppm) existing in the thione form in solution [7]. To
the best of our knowledge, such a stabilization of the thione
form of this ligand has been reported in several organotin
cations (d13C(C2) = 157.0 ppm), where free ligand
(Hmimt) has been used as the S-donor ligand for organotin
cations resulting in the Sn–S bond (Chart 1) [8].
Chart 1.
However, the stabilization of the anionic polar group
(mimt)ꢀ in thione form in organotin compounds resulting
in the presence of Sn–N bond is unknown so far. The struc-
turally similar compound Ph3Sn(mimt) contains the cova-
lent bond Sn–S indicating the presence of thiol form of
(mimt)ꢀ (compare d13C(C2) = 138.7 ppm) [7]. The pres-
ence of thione form in 2 was also corroborated by IR spec-
troscopy where bands at 694 and 536 cmꢀ1 assignable to
r(C@S) and p(C@S) were found [8].
Single crystals of 2 were obtained from a toluene solu-
tion at ꢀ5 °C and the molecular structure is shown in
Fig. 1 [9]. The selected bond lengths, and angles of 2 and
related compound Ph3Sn(mimt) are given in Table 1.
The shape of the coordination polyhedron of 2 can be
described as a distorted trigonal bipyramid, with carbon
atoms in equatorial positions. One axial position is occu-
pied by the oxygen donor atom from ligand L, while the
nitrogen atom from mercapto polar group (mimt) is in
the second one (found bonding angle O(1)–Sn(1)–
N(1) = 168.07(8)°). The found bond length Sn(1)–O(1)
Fig. 1. General view (ORTEP) of a molecule showing 50% probability
displacement ellipsoids and the atom-numbering scheme for 2. The
hydrogen atoms are omitted for clarity.
˚
N) = 2.154 A and clearly demonstrates the presence of
covalent bond Sn–N in compound 2. The presence of thi-
one form of (mimt) is also corroborated by bond length
˚
˚
C(17)–S(1) (1.696(2) A) that is comparable to those found
(2.7875(16) A) indicates the presence of medium strong
in organotin cations containing Hmimt in its thione form
[8] and both double bonds C(17)–S(1) (1.696(2) A) and
Sn–O intramolecular interaction in 2. Bond length Sn(1)–
˚
˚
N(1) (2.1518(19) A) is comparable to the
Rcov(Sn,
+
t
O
Bu
t
O
SNa
Bu
Ph
THF
CH3
-
Sn
N
N
SnPh2 OTf
+
Ph
S
NaOTf
-
N
tBu
O
tBuO
C2
N
2
1
CH3
Scheme 2. Preparation and labeling of titled compound 2.

910
J. Martincova´ et al. / Journal of Organometallic Chemistry 692 (2007) 908–911
Table 1
(c) W.T. Piver, Environ. Health Perspect. 4 (1973) 61;
(d) G.J.M. van de Klerk, J.J. Zuckerman (Eds.), Organotin
Compounds, American Chemical Society, Washington, DC, 1976,
p. 1;
(e) P. Yang, M. Guo, Coord. Chem. Rev. 185/86 (1999) 189;
(f) M. Gielen, Coord. Chem. Rev. 151 (1996) 41;
(g) M. Gielen, M. Biesemans, R. Willem, Appl. Organomet.
Chem. 19 (2005) 440;
˚
Selected bond length (A) and angles (°) of 2 and related compound
Ph3Sn(mimt)
Compound
2
Ph3Sn(mimt)
˚
Bond length (A)
Sn(1)–N(1)
Sn(1)–S(1)
C(17)–S(1)
C(18)–C(19)
Sn(1)–O(1)
2.1518(19)
3.5989(10)
1.696(2)
1.340(4)
2.7875(16)
2.920(3)
2.437(1)
1.746(4)
1.321(9)
–
(h) M. Gielen, J. Braz. Chem. Soc. 14 (2003) 870;
(i) M. Gielen, M. Biesemans, R. Willem, E.R.T. Tiekink, Eur. J.
Inorg. Chem. 3 (2004) 445;
(j) M. Gielen, Appl. Organomet. Chem. 16 (2002) 481.
[2] (a) C.J. Evans, S. Karpel, Organotin Compounds in Modern
Technology, Elsevier, Amsterdam, 1985, p. 23;
Bond angle (°)
N(1)–C(17)–S(1)
O(1)–Sn(1)–N(1)
O(1)–Sn(1)–S(1)
127.34(17)
168.08(7)
118.85(4)
123.7(4)
–
–
(b) C.J. Evans, Spect. Chem. 11 (1991) 152.
[3] (a) C.V. Rodarte de Moura, A.P.G. Sousa, R.M. Silva, A. Abras, M.
Horner, A.J. Bortoluzzi, C.A.L. Filgueiras, J.L. Wardell, Polyhedron
18 (1999) 2961, and reference therein;
(b) M.V. Castano, A. Mac´ıas, A. Castineiras, A.S. Gonza´les, E.G.
˚
C(18)–C(19) (1.340(4) A) are well localized in 2. There is no
´
Martınez, J.S. Casas, J. Sordo, J. Chem. Soc., Dalton Trans. 1001
additional interaction between Sn and S as indicated by
interatomic distance Sn(1)–S(1) (3.5989(10) A). The com-
parison of 2 with related Ph3Sn(mimt) (C(17)–S(1) =
(1990).
˚
[4] (a) J. Susperregui, M. Bayle, J.M. Le´ger, G. De´le´ris, J. Organomet.
Chem. 556 (1998) 105;
´
´
(b) A.S. Gonzales, E.G. Martınez, J.S. Casas, J. Sordo, U. Casellato,
R. Graziani, U. Russo, J. Organomet. Chem. 463 (1993) 91;
(c) M.D. Couce, G. Faraglia, U. Russo, L. Sindellari, V. Valle, J.
Organomet. Chem. 513 (1996) 77.
˚
˚
˚
1.746(4) A, Sn(1)–N(1) = 2.920(3) A and Sn(1)–S(1) =
2.437(1) A) also demonstrates the different coordination
mode of the mercapto group (mimt).
˚
´
´
In summary we have reported on the preparation of
Ph2LSn(mimt) (2) containing polar group 1-methylimidaz-
ole-2-thiolate in the thione form, where the presence of
covalent bond Sn–N was determined. Since the structurally
related compound Ph3Sn(mimt) contains this polar group
in traditional thiol form (the presence of covalent bond
Sn–S is usual for organotin compounds containing mer-
capto derivatives) the important role of O,C,O-chelating
ligand in the new coordination mode of organotin frag-
ments towards mercapro derivatives can be proposed and
will be investigated in more detail.
[5] (a) B. Kasˇna´, R. Jambor, L. Dosta´l, A. Ruzˇicˇka, I. Cısarˇova, J.
Holecˇek, Organometallics 23 (2004) 5300;
´
´
´ˇ
´
´
ˇ
´
(b) B. Kasˇna, R. Jambor, L. Dostal, L. Kolarova, I. Cısarova, J.
Holecˇek, Organometallics 25 (2006) 148.
[6] THF solution of Na(mimt) (42 mg; 0.31 mmol) was added to 20 ml of
THF solution of 1 (206 mg; 0.31 mmol) and stirred overnight. Hexan/
CH2Cl2 (15 ml, 2:1) mixture was added after the evaporation of THF,
the suspension was filtrated off and organic solvents evaporated to
give the white powder identified as 2. Yield: 121 mg of 2 (59%).
Characterization: MW = 635.4 g/mol, m.p. 175–178 °C; Elemental
Anal.: Calc. (Found), C 61.03 (61.33); H 6.52 (6.77); ESI/MS: m/z
113, 15% [mimt]ꢀ, m/z 523, 60% [Mꢀmimt]+, m/z 632 [M+H]+, m/z
563, 30% [M+HꢀtBuOH]+, m/z 411, 80% [Mꢀmimtꢀ2butane]+, H
1
NMR d (ppm): 0.88 (18H, s, O-tBu), 3.45 (3H, s, NCH3 (mimt)), 4.53
(4H, s, CH2O), 6.59 (1H, bs, mimt), 6.63 (1H, bs, mimt), 7.4 (9H, m,
Ar–H), 7.8 (4H, m, Ar–H), 13C NMR d (ppm): 27.4 (OCCH3), 34.8
(NCH3), 65.7 (CH2O), 75.1 (OC(CH3)3), 120.3 (C-mimt), 121.5 (C-
mimt), 126.4 (C(3,5)), 128.5 (C(30,50)), 129.5 (C(4)), 129.6 (C(40)),
135.9 (C(1)), (1J(119Sn;13C) = 713 Hz), 137.2 (C(20,60)), 141.5 (C(10)),
Acknowledgements
The authors thank the Ministry of Education of the
Czech Republic (Project Nos. VZ0021627501 and LC523)
for financial support.
(1J(119Sn;13C) = 715 Hz), 147.3 (C(2,6)), 163.5 (SC2),
ppm = ꢀ173.53.
d (
119Sn)
´
[7] (a) J.S. Casas, A. Castineiras, E.G. Martinez, A.S. Gonzales, A.
Appendix A. Supplementary data
´
Sanchez, J. Sordo, Polyhedron 16 (1997) 795;
´
(b) J. Bravo, M.B. Cordero, J.S. Casas, A. Sanchez, J. Sordo,
E.E. Castellano, S. Zukermann, J. Organomet. Chem. 482 (1994)
147;
(c) E. Buncel, A.R. Norris, S.E. Taylor, W.J. Racz, Can. J. Chem.
60 (1982) 3033.
CCDC 610595 contains the supplementary crystallo-
graphic data for 2. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/conts/retrieving.
html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.
2006.09.056.
[8] (a) E.G. Mart´ınez, A.S. Gonza´les, J.S. Casas, J. Sordo, U. Casellato,
R. Graziani, Inorg. Chim. Acta 191 (1992) 75;
(b) J.S. Casas, E.G. Mart´ınez, A.S. Gonza´les, J. Sordo, U. Casellato,
R. Graziani, U. Russo, J. Organomet. Chem. 493 (1995) 107;
´
(c) J.S. Casas, A. Castineiras, E.G. Martinez, A.S. Gonzales, J.
Sordo, E.M.V. Lopez, Polyhedron 15 (1996) 891.
[9] Colorless crystals of 2 were obtained from toluene solution at ꢀ5 °C.
The intensity data were collected on a KUMA KM-4 CCD kappa-
References
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a graphite monochromatized Mo Ka
radiation C32H40N2O2SSn, M = 635.42, triclinic, space group P1,
˚
˚
˚
3
a = 10.256(2) A, b = 10.471(2) A, c = 14.351(3) A, a = 86.78(3)°,
[1] (a) A.G. Davis, Organotin Chemistry, VCH, Weinhein, 1997;
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˚
b = 83.94(3)°, c = 87.24(3)°, U = 1528.7(5) A , Z = 4, q =
1.383 g cmꢀ3, l = 0.934 mmꢀ1, 14,411 reflections collected, of which

J. Martincova´ et al. / Journal of Organometallic Chemistry 692 (2007) 908–911
911
6106 were independent [Rint = 0.0278]. Final R indices [I > 2r(I)]:
R1 = 0.027, wR2 = 0.069. The structure was solved by direct methods
(G.M. Sheldrick: SHELX-97 [10] program package, University of
Goettingen, 1997; G.M. Sheldrick: SHELXTL V 5.1 [11], Bruker AXS
GmbH.) Non-hydrogen atoms were refined anisotropically while
hydrogen atoms were inserted in calculated positions and isotropi-
cally refined assuming a ride-on model.
[10] G.M. Sheldrick: SHELX-97 program package, University of Goettin-
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[11] G.M. Sheldrick: SHELXTL V 5.10, Bruker AXS Inc., Madison, Wl, 1997.