The reactivity of hydrotris(3-methyl-2-thioxo-1-imidazolyl)borate (Tm) towards organotin(IV) acceptors. An unprecedented monodentate coordination mode of Tm ligand

Article abstract of DOI:10.1016/S0020-1693(01)00640-5

The reaction between RSnCl₃ (R = Me, Buⁿ or Ph), R₂SnCl₂ (R = Me, Et, Buⁿ or Ph) and R₃SnCl (R = Me, Buⁿ, Ph or cy) acceptors and equimolar amounts of hydrotris(3-methyl-2-thioxo-1-imidazolyl)borate potassium salt K[Tm] yields the complexes [(Tm)RSnCl₂], [(Tm)R₂SnCl] and [(Tm)R₃Sn], respectively. The NMR data (¹H, ¹¹⁹Sn) showed the mono- and di-organotin derivatives to be five-coordinated in solution, whereas the triorganotin(IV) derivatives are tetrahedral both in solution and in the solid state, as confirmed by X-ray crystallography. The X-ray crystal structure of [(Tm)cy₃Sn] is the first example of a complex containing the Tm-ligand coordinated in monodentate fashion, with the tin in a quasi-regular tetrahedral environment and Sn-S bond being 2.478(1) ?.

Full text of DOI:10.1016/S0020-1693(01)00640-5

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Inorganica Chimica Acta 325 (2001) 20–28
The reactivity of hydrotris(3-methyl-2-thioxo-1-imidazolyl)borate
(Tm) towards organotin(IV) acceptors. An unprecedented
monodentate coordination mode of Tm ligand
C. Santini a,*, M. Pellei a, G. Gioia Lobbia a, C. Pettinari a, A. Drozdov b,
S. Troyanov b
a Dipartimento di Scienze Chimiche, Uni6ersita` degli Studi di Camerino, 6ia S. Agostino 1, I-62032 Camerino, Macerata, Italy
b Department of Chemistry, Moscow State Uni6ersity, Vorobje6y Gory, 119899 Moscow, Russia
Received 4 June 2001; accepted 25 July 2001
Abstract
The reaction between RSnCl3 (R=Me, Bun or Ph), R2SnCl2 (R=Me, Et, Bun or Ph) and R3SnCl (R=Me, Bun, Ph or cy)
acceptors and equimolar amounts of hydrotris(3-methyl-2-thioxo-1-imidazolyl)borate potassium salt K[Tm] yields the complexes
[(Tm)RSnCl2], [(Tm)R2SnCl] and [(Tm)R3Sn], respectively. The NMR data (1H, 119Sn) showed the mono- and di-organotin
derivatives to be five-coordinated in solution, whereas the triorganotin(IV) derivatives are tetrahedral both in solution and in the
solid state, as confirmed by X-ray crystallography. The X-ray crystal structure of [(Tm)cy3Sn] is the first example of a complex
containing the Tm-ligand coordinated in monodentate fashion, with the tin in a quasi-regular tetrahedral environment and SnꢀS
,
bond being 2.478(1) A. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Tm-ligand; Organotin(IV) acceptors; X-ray crystal structures
1. Introduction
the range of analogous soft tripodal ligands is so lim-
ited [4]. By replacing the hard N-donor pyrazole with
the softer S-donor 2-mercapto-1-methylimidazole, the
new tridentate, sulfur-donor ligand, hydrotris(methima-
zolyl)borate anion (Tm) (Fig. 1) has been synthesized
recently by Reglinsky [5] and our group [6]. This com-
pound has been employed to form stable derivatives of
zinc [5], bismute [7], thallium [8,9], ruthenium [10],
The coordination chemistry of organotin acceptors
has been extensively studied due to the interest towards
factors that influence the coordination number and
geometry of the molecule as well as for the important
biological and catalytic properties of these compounds
[1].
Since poly(pyrazol-1-yl)borate ligands (Tp) were dis-
covered and used by Trofimenko in the synthesis of
main group and transition metal derivatives [2], numer-
ous reports of poly(pyrazol-1-yl)borate–tin(IV) com-
plexes appeared [3]. A driving force for much of the
chemistry in this area stems from its biological rele-
vance [1b] and the employment in the selective com-
plexation of anionic and neutral donors by tailor-mode
molecular hosts [1c]. Considering the accepted synthetic
utility of Tp-based ligand systems, it is surprising that
* Corresponding author. Fax: +39-737-637-345.
E-mail address: santini@camserv.unicam.it (C. Santini).
Fig. 1. Structure of the ligand.
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(01)00640-5

C. Santini et al. / Inorganica Chimica Acta 325 (2001) 20–28
21
silver(I) [6,11,12], and copper(I) [13] that have been
2.2. Syntheses
structurally characterized. It is worth noting that in all
the crystal structures reported up to now, this
ligand acts in tetradentate (symmetric bridging with one
azole shared equally between two Ag centers) as in
[Ag(Tm)]2 [12], tridentate as in homoleptic complexes
with Zn, Bi, Tl and Ru [5,7–9] or bidentate mode, as in
the phosphine complexes of copper(I) and silver(I)
[11,13].
The ligand salt potassium hydrotris(3-methyl-2-thi-
oxo-1-imidazolyl)borate, K[Tm], was prepared in accor-
dance with the published procedure [6]. KBH4, NaBH4,
RnSnCl4−n and Hmimt were purchased (Aldrich) and
used as received.
2.2.1. [(Tm)cy3Sn] (1)
As an extension of this research [3a,3b,3c,3d], we
decided to investigate the donating ability of Tm to-
wards tin(IV) and organotin(IV) acceptors with differ-
ent numbers of R-groups linked to metal center. We
have shown that different reaction patterns can take
place depending on the nature and the number of
substituents in the tin(IV) acceptors. In order to gain
insight into the factors controlling the structure and
bonding in these complexes we also determined the
X-ray crystal structure of [(Tm)cy3Sn].
To a chloroform solution (50 ml) of cy3SnCl (1.0
mmol, 0.404 g), K[Tm] (1.0 mmol, 0.390 g) was added
at room temperature. After the addition, the solution
was stirred for 3 h, then the suspension of KCl formed
was separated by filtration and the remaining solution
was concentrated under reduced pressure to give a
colorless precipitate of 1. It was filtered off, washed
with diethyl ether and recrystallized from CHCl3–hex-
ane (1:3) to give complex 1 as a micro-crystalline solid
in 83% yield. M.p.: 210 °C dec. 1H NMR (CDCl3,
293K): l 1.20–2.01 (m, 33H, SnꢀC6H11), 3.61 (s, 9H,
NꢀCH3), 6.62 (sbr, 3H, 4- or 5-CH), 6.84 (sbr, 3H, 4-
1
or 5-CH); H NMR (CD3OH, 293 K): l 1.34–1.92 (m,
33H, SnꢀC6H11), 3.56 (s, 9H, NꢀCH3), 6.54 (d, 3H, 4-
2. Experimental
1
or 5-CH), 6.86 (d, 3H, 4- or 5-CH); H NMR (CDCl3,
223 K): l 1.22–2.02 (m, 33H, SnꢀC6H11), 3.56 (s, 6H,
NꢀCH3), 3.69 (s, 3H, NꢀCH3), 6.67 (sbr, 4H, 4- or
5-CH), 6.86 (s, 1H, 4- or 5-CH), 6.90 (s, 1H, 4- or
5-CH). 119Sn NMR (CDCl3, 293 K): l 45.1. IR (cm−1):
3156w [w(CꢀH)], 2437w [w(BꢀH)], 1550 sh (CꢁC+
CꢁN), 1457sh, 1301sh, 1098m, 1084m, 770m, 741s
(thioamide I–IV), 697m (w CꢁS), 490s [w(SnꢀC)]. Cond.
(CH2Cl2, conc.=1.00×10−3 M): \ 0.34 V−1 cm2
mol−1. Anal. Found: C, 50.2; H, 7.0; N, 11.6; S, 13.2.
Calc. for C30H49BN6S3Sn: C, 50.1; H, 6.9; N, 11.7; S,
13.4%.
2.1. General procedures
The organotin(IV) halides were purchased from Alfa
(Karlsruhe) and Aldrich (Milwaukee) and used as re-
ceived. Solvent evaporations were always carried out
under vacuum by using a rotary evaporator. The sam-
ples for microanalysis were dried in vacuo to constant
weight (20 °C, ca. 0.1 Torr). All syntheses were carried
out under a nitrogen atmosphere. Hydrocarbon sol-
vents were dried by distillation from sodium–potas-
sium, dichloromethane from calcium hydride and
tetrahydrofuran from sodium and benzophenone. All
solvents were degassed with dry nitrogen prior to use.
Elemental analyses (C, H, N, S) were performed in
house with a Fisons model 1106 instrument. IR spectra
were recorded from 4000 to 100 cm−1 with a Perkin–
2.2.2. [(Tm)CH3SnCl2] (2)
Compound 2 was prepared similarly to compound 1,
by using MeSnCl3 (1.0 mmol, 0.240 g) and K[Tm] (1.0
mmol, 0.390 g) in dichloromethane (50 ml) at 298 K. It
was recrystallized from CH2Cl2–petroleum ether (1:5)
1
(yield 66%). M.p.: 220 °C dec. H NMR (acetone, 293
1
2
Elmer System 2000 FT–IR instrument. H and 119Sn
K): l 1.26 (s, 3H, SnꢀCH3, J(119Sn–1H)=108.5 Hz,
NMR spectra were recorded on a VXR-300 Varian
spectrometer operating at room temperature (300 MHz
2J(117Sn–1H)=103.8 Hz), 3.69, 3.73, 3.85 (3 s, 9H,
NꢀCH3), 7.12, 7.22, 7.28, 7.35, 7.38, 7.45 (6 d, 6H, 4- or
5-CH). 119Sn NMR (acetone, 293 K): l −352.7. IR
(cm−1): 3150w, 3123w, 3088w [w(CꢀH)], 2458m, 2226w
[w(BꢀH)], 1555mbr (CꢁC+CꢁN), 1460sbr, 1298m,
1084mbr, 776s, 742sbr (thioamide I–IV), 710m, 690m
(w CꢁS), 512s [w(SnꢀC)], 241s [w(SnꢀCl)]. Anal. Found:
C, 28.3; H, 3.5; N, 15.1; S, 17.2. Calc. for
C13H19BCl2N6S3Sn: C, 28.1; H, 3.4; N, 15.1; S. 17.3%.
1
for H and 111.9 MHz for 119Sn). The chemical shifts
(l) are reported in parts per million (ppm) from SiMe4
(1H calibration by internal deuterium solvent lock) and
SnMe4 (119Sn). Peaks multiplicities are abbreviated: sin-
glet, s; doublet, d; triplet, t; multiplet, m; pseudotriplet,
pt; complex multiplet, mc; broad, br. Melting points are
uncorrected and were taken on an IA 8100 Electrother-
mal instrument and on a capillary apparatus. The
electrical conductance of the solutions was measured
with a Crison CDTM 522 conductimeter at room
temperature.
2.2.3. [(Tm)(CH3)2SnCl] (3)
Compound 3 was prepared similarly to compound 2,
by using Me2SnCl2 (1.0 mmol, 0.220 g) and K[Tm] (1.0

22
C. Santini et al. / Inorganica Chimica Acta 325 (2001) 20–28
mmol, 0.390 g) in dichloromethane (50 ml) at 298 K. It
was recrystallized from CHCl3–ethylacetate (1:3) (yield
75%). M.p.: 144–146 °C. H NMR (CDCl3, 293 K): l
1
was recrystallized from CHCl3–diethyl ether (1:3) (yield
1
80%). M.p.: 170 °C dec. H NMR (CDCl3, 293 K): l
3.41 (br, 9H, NꢀCH3), 6.70 (br, 6H, 4- or 5-CH),
1.02 (s, 6H, SnꢀCH3, 2J(119Snꢀ1H)=75.46 Hz,
2J(117Sn–1H)=74.72 Hz), 3.69 (s, 9H, NꢀCH3), 6.84
(br, 3H, 4- or 5-CH), 7.49 (br, 3H, 4- or 5-CH). 119Sn
NMR (CDCl3, 293 K): l −72.7. IR (cm−1): 3171w,
3130w, 3088w, 3069w [w(CꢀH)], 2467m [w(BꢀH)],
1555m (CꢁC+CꢁN), 1455sbr, 1280sh, 1098mbr,
767sbr (thioamide I–IV), 718s, 694m (w CꢁS), 551m
[w(SnꢀC)], 238s [w(SnꢀCl)]. Cond. (CH2Cl2, conc.=
1.00×10−3 M): \ 0.92 V−1 cm2 mol−1. Anal. Found:
C, 31.4; H, 4.2; N, 15.6; S, 17.9. Calc. for
C14H22BClN6S3Sn: C, 31.4; H, 4.1; N, 15.7; S, 18.0%.
7.31–7.50 (mbr, 10H, SnꢀC6H5). H NMR (CDCl3, 223
1
K): l 3.02 (s, 3H, NꢀCH3), 3.58 (s, 6H, NꢀCH3), 6.47
(s, 1H, 4- or 5-CH), 6.59 (s, 1H, 4- or 5-CH), 6.73 (s,
2H, 4- or 5-CH), 6.89 (s, 2H, 4- or 5-CH), 7.17–7.43
(mbr, 10H, SnꢀC6H5). 119Sn NMR (CDCl3, 293 K): l
−210.9. IR (cm−1): 3151w, 3127w, 3070sh [w(CꢀH)],
2450m [w(BꢀH)], 1556m (CꢁC+CꢁN), 1454sbr, 1300s,
1090mbr, 775sh (thioamide I–IV), 723sbr, 693m (w
CꢁS), 451s [l(Ph)], 272s [w(SnꢀC)], 245s [w(SnꢀCl)].
Cond. (CH2Cl2, conc.=1.02×10−3 M): \ 2.70 V−1
cm2 mol−1. Anal. Found: C, 43.2; H, 4.0; N, 12.6; S,
13.5. Calc. for C24H26BClN6S3Sn: C, 43.6; H, 4.0; N,
12.7; S, 14.5%.
2.2.4. [(Tm)(CH3)3Sn] (4)
Compound 4 was prepared similarly to compound 2,
by using Me3SnCl (1.0 mmol, 0.235 g) and K[Tm] (1.0
mmol, 0.390 g) in dichloromethane (50 ml) at 298 K. It
was recrystallized from diethyl ether–n-hexane (1:1)
(yield 72%). M.p.: 240 °C dec. l 0.67 (s, 9H, SnꢀCH3,
2J(Sn–1H)=57.1 Hz), 3.61 (s, 9H, NꢀCH3), 6.74 (sbr,
3H, 4- or 5-CH), 7.01 (sbr, 3H, 4- or 5-CH). 119Sn
NMR (CDCl3, 293 K): l 147.3. IR (cm−1): 3152w,
3127w, 3070w [w(CꢀH)], 2461m [w(BꢀH)], 1558m
(CꢁC+CꢁN), 1458sbr, 1286s, 1092mbr, 781s, 747sbr
(thioamide I–IV), 678sbr (w CꢁS), 541s [w(SnꢀC)].
Cond. (CH2Cl2, conc.=1.01×10−3 M): \ 0.70 V−1
cm2 mol−1. Anal. Found: C, 34.9; H, 4.8; N, 16.4; S,
18.8. Calc. for C15H25BN6S3Sn: C, 35.0; H, 4.9; N, 16.3;
S, 18.7%.
2.2.7. [(Tm)Ph3Sn] (7)
Compound 7 was prepared similarly to compound 2,
by using Ph3SnCl (1.0 mmol, 0.385 g) and K[Tm] (1.0
mmol, 0.390 g) in dichloromethane (50 ml) at 298 K. It
was recrystallized from CHCl3–hexane (1:3) (yield
79%). M.p.: 127–129 °C. H NMR (CDCl3, 293 K): l
3.48 (br, 9H, NꢀCH3), 6.55 (s, 3H, 4- or 5-CH), 6.66 (s,
3H, 4- or 5-CH), 7.19–7.50 (mbr, 15H, SnꢀC6H5). H
NMR (CDCl3, 223 K): l 3.53 (s, 6H, NꢀCH3), 3.58 (s,
3H, NꢀCH3), 6.54 (s, 2H, 4- or 5-CH), 6.64 (s, 2H, 4-
or 5-CH), 6.70 (s, 1H, 4- or 5-CH), 6.79 (s, 1H, 4- or
5-CH), 7.19–7.50 (mbr, 15H, SnꢀC6H5). 119Sn NMR
(CDCl3, 293 K): l −57.9. IR (cm−1): 3150w, 3130w,
3073w [w(CꢀH)], 2451m [w(BꢀH)], 1557sh, 1551m
(CꢁC+CꢁN), 1463sh, 1300s, 1097mbr, 780sh
(thioamide I–IV), 722sbr, 694m (w CꢁS), 445s [l(Ph)],
268s [w(SnꢀC)]. Cond. (CH2Cl2, conc.=1.01×10−3
M): \ 6.70 V−1 cm2 mol−1. Anal. Found: C, 51.3; H,
4.2; N, 11.8; S, 13.9. Calc. for C30H31BN6S3Sn: C, 51.4;
H, 4.5; N, 12.0; S, 13.8%.
1
1
2.2.5. [(Tm)PhSnCl2] (5)
Compound 5 was prepared similarly to compound 2,
by using PhSnCl3 (1.0 mmol, 0.302 g) and K[Tm] (1.0
mmol, 0.390 g) in dichloromethane (50 ml) at 298 K. It
was recrystallized from CHCl3–diethyl ether (1:3) (yield
1
68%). M.p.: 220 °C dec. H NMR (CDCl3, 293 K): l
3.30 (br, 3H, NꢀCH3), 3.87 (br, 3H, NꢀCH3), 3.96 (br,
3H, NꢀCH3), 6.81 (s, 1H, 4- or 5-CH), 6.96 (s, 2H, 4-
or 5-CH), 6.99 (s, 1H, 4- or 5-CH), 7.05 (s, 2H, 4- or
5-CH), 7.20–7.35 (m, 5H, SnꢀC6H5). 119Sn NMR
(CDCl3, 293K): l −391.3. IR (cm−1): 3143w, 3117w,
3063w [w(CꢀH)], 2459m [w(BꢀH)], 1557m (CꢁC+CꢁN),
1466sbr, 1300m, 1110m, 760s, 750s (thioamide I–IV),
721s, 692m (w CꢁS), 462m, 454s [l(Ph)], 278sh
[w(SnꢀC)], 250sbr [w(SnꢀCl)]. Cond. (CH2Cl2, conc.=
1.00×10−3 M): \ 0.50 V−1 cm2 mol−1. Anal. Found:
C, 34.9; H, 3.5; N, 13.8; S, 15.4. Calc. for
C18H21BCl2N6S3Sn: C, 35.0; H, 3.4; N, 13.6; S, 15.6%.
2.2.8. [(Tm)Et2SnCl] (8)
Compound 8 was prepared similarly to compound 2,
by using (Et)2SnCl2 (1.0 mmol, 0.248 g) and K[Tm] (1.0
mmol, 0.390 g) in dichloromethane (50 ml) at 298 K. It
was recrystallized from CHCl3–hexane (1:3) (yield
1
60%). M.p.: 95–97 °C. H NMR (CDCl3, 293 K): l
1.34 (t, 6H, ꢀCH3 of SnꢀEt), 1.58 (q, 4H, ꢀCH2 of
SnꢀEt), 3.66 (s, 9H, NꢀCH3), 6.81 (br, 3H, 4- or 5-CH),
7.49 (br, 3H, 4- or 5-CH). 119Sn NMR (CDCl3, 293 K):
l −70.8. IR (cm−1): 3128w, 3110w [w(CꢀH)], 2512m
[w(BꢀH)], 1557m, (CꢁC+CꢁN), 1459sbr, 1300s, 1093s,
724br (thioamide I–IV), 676s (w CꢁS), 528s [w(SnꢀC)],
235sbr [w(SnꢀCl)]. Cond. (CH2Cl2, conc.=1.01×10−3
M): \ 0.89 V−1 cm2 mol−1. Anal. Found: C, 33.8; H,
4.8; N, 14.6; S, 16.9. Calc. for C16H26BClN6S3Sn: C,
34.1 H, 4.6; N, 14.9; S, 17.1%.
2.2.6. [(Tm)Ph2SnCl] (6)
Compound 6 was prepared similarly to compound 2,
by using Ph2SnCl2 (1.0 mmol, 0.344 g) and K[Tm] (1.0
mmol, 0.390 g) in dichloromethane (50 ml) at 298 K. It

C. Santini et al. / Inorganica Chimica Acta 325 (2001) 20–28
23
Table 1
13.7; S, 15.3. Calc. for C20H34BClN6S3Sn: C, 38.8; H,
5.5; N, 13.6; S, 15.5%.
Crystallographic data for compound 1
[(Tm)cy3Sn] (1)
2.2.11. [(Tm)Bun3Sn] (11)
Empirical formula
Formula weight
Crystal symmetry
Space group
C30H49BN6S3Sn
719.43
triclinic
Compound 11 was prepared similarly to compound
2, by using (Bun)3SnCl (1.0 mmol, 0.325 g) and K[Tm]
(1.0 mmol, 0.390 g) in dichloromethane (50 ml) at 298
K. It was purified in hexane (yield 37%). M.p.: oil at r.t.
1H NMR (CDCl3, 293 K): l 0.84 (t, 9H, ꢀCH3 of
SnꢀBun), 1.10 (tq, 6H, g-CH2 of SnꢀBun), 1.30 (tt, 6H,
b-CH2 of SnꢀBun), 1.50 (t, 6H, a-CH2 of SnꢀBun), 3.60
(s, 9H, NꢀCH3), 6.63 (s, 3H, 4- or 5-CH), 6.88 (s, 3H,
4- or 5-CH). 119Sn NMR (CDCl3, 293 K): not observed
due to decomposition of 11 in solution. IR (cm−1):
3140w, 3083w [w(CꢀH)], 2465m [w(BꢀH)], 1624w,
1554m (CꢁC+CꢁN), 1452sh, 1329sbr, 1280sh, 1086s,
776m, 740m, 720sbr (thioamide I–IV), 697br, 670m (w
CꢁS), 608sbr [w(SnꢀC)]. Anal. Found: C, 44.6; H, 6.9;
N, 13.0; S, 15.3. Calc. for C24H43BN6S3Sn: C, 44.9; H,
6.8; N, 13.1; S, 15.0%.
(
P1
T (K)
180
,
a (A)
9.3770(1)
10.201(2)
20.362(4)
98.41(3)
91.73(3)
116.54(3)
2
1713.7(5)
0.958
6089
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
Z
3
,
V (A )
v (mm−1
)
Reflections collected
Independent reflections
5189
0.0332, 0.0798
Final R1, wR2 indices [I\2|(I)2]
2.2.9. [(Tm)BunSnCl2] (9)
2.3. X-ray diffraction studies
Compound 9 was prepared similarly to compound 2,
by using BunSnCl3 (1.0 mmol, 0.282 g) and K[Tm] (1.0
mmol, 0.390 g) in dichloromethane (50 ml) at 298 K. It
was recrystallized from CHCl3–hexane (1:3) (yield
The details of crystal data collection and refinement
for complex 1 are given in Table 1.
1
Data collection was carried out on an image plate
diffractometer IPDS (Stoe) using graphite-monochro-
mated Mo Ka radiation. Lattice parameters were
refined using 5000 reflection in the q range of 4–24°.
The structure was solved using SHELXS-86 [14] and
refined with SHELXL-93 programs [15].
Non-hydrogen atoms were refined anisotropically by
full-matrix least-squares techniques based on F2. Hy-
drogen atoms were placed at the calculated positions
and were included in the final refinements in a riding
model.
62%). M.p.: 202–204 °C. H NMR (CDCl3, 293 K): l
0.89 (t, 3H, SnꢀBun), 1.24–1.80 (mbr, 6H, SnꢀBun),
3.67, 3.77, 3.92 (3 s, 9H, NꢀCH3), 6.75, 6.84, 6.97, 7.01,
7.21, 7.45, (6 s, 6H, 4- or 5-CH). 119Sn NMR (CDCl3,
293 K): l −329.3. IR (cm−1): 3157w, 3124w, 3082w
[w(CꢀH)], 2430m, 2213w [w(BꢀH)], 1556m (CꢁC+
CꢁN), 1458sh, 1296m, 1102mbr, 774sh, 742sbr
(thioamide I–IV), 683m (w CꢁS), 600sbr [w(SnꢀC)], 237s
[w(SnꢀCl)]. Anal. Found: C, 32.0; H, 4.3; N, 14.0; S,
15.9. Calc. for C16H25BCl2N6S3Sn: C, 32.1; H, 4.2; N,
14.0; S, 16.1%.
2.2.10. [(Tm)Bun2SnCl] (10)
3. Results and discussion
Compound 10 was prepared similarly to compound
2, by using (Bun)2SnCl2 (1.0 mmol, 0.304 g) and K[Tm]
(1.0 mmol, 0.390 g) in dichloromethane (50 ml) at 298
K. It was recrystallized from CHCl3–hexane (1:3) (yield
3.1. Syntheses and properties
The interaction of the potassium salt of hydrotris(3-
methyl-2-thioxo-1-imidazolyl)borate ligand, K[Tm],
with the appropriate chloroorganotin(IV) acceptors,
SnRnCl3−n (R=Me, Bun or Ph), in dichloromethane at
room temperature, afforded in high yield the complexes
1–11 (Figs. 1–3), in accordance with the following
general equation (Eq. (1)):
1
67%). M.p.: 163–165 °C. H NMR (CDCl3, 293 K): l
0.86 (t, 6H, ꢀCH3 of SnꢀBun), 1.30 (tq, 4H, g-CH2 of
SnꢀBun), 1.56 (tt, 4H, b-CH2 of SnꢀBun), 1.70 (t, 4H,
a-CH2 of SnꢀBun), 3.66 (s, 9H, NꢀCH3), 6.81 (s, 4H, 4-
1
or 5-CH); H NMR (CDCl3, 223 K): l 0.88 (t, 6H,
ꢀCH3 of SnꢀBun), 1.25–1.78 (mbr, 12H, SnꢀBun), 3.66
(br, 9H, NꢀCH3), 6.81 (br, 4H, 4- or 5-CH); 119Sn
NMR (CDCl3, 293 K): l −76.1. IR (cm−1): 3144w,
3109w, 3079w [w(CꢀH)], 2456m [w(BꢀH)], 1559m
(CꢁC+CꢁN), 1461sh, 1300m, 1287m, 1099mbr, 780sbr
(thioamide I–IV), 717sbr, 691m (w CꢁS), 608s, 586m
[w(SnꢀC)]. Cond. (CH2Cl2, conc.=1.02×10−3 M): \
0.99 V−1 cm2 mol−1. Anal. Found: C, 38.7; H, 5.4; N,
CH Cl /r.t.
2
2
K[Tm]+SnRnCl4−n ꢀꢀꢀꢀꢀꢂ [(Tm)RnSnCl3−n]+KCl
1–11
(1)
1
2
3
R=cy
R=CH3
R=CH3
n=3
n=1
n=2

24
C. Santini et al. / Inorganica Chimica Acta 325 (2001) 20–28
4
5
6
7
8
9
10
11
R=CH3
R=Ph
R=Ph
R=Ph
R=Et
n=3
n=1
n=2
n=3
n=2
n=1
n=2
n=3
The conductivity measurements (see Section 2) car-
ried out in CH2Cl2 solutions only for sufficiently stable
derivatives indicate that these compounds are not elec-
trolytes. A similar behavior has been previously ob-
served for analogous organotin(IV) poly(pyrazolyl)-
borates [3a].
R=nBu
R=nBu
R=nBu
3.2. Spectroscopy
All the tin(IV) and organotin(IV) complexes with the
exception of 11, which is an oil, are colorless solids at
room temperature, soluble in chlorinated solvents and
acetone. Prolonged storage in air of solids or their
solutions leads to slow decomposition of complexes,
probably due to the breaking of the BꢀN bond of Tm
ligand, followed by the formation of 1-methyl-2-imida-
zolinethione derivatives and to the hydrolysis of the
SnꢀCl bonds to form tin oxide materials. A similar
process has been previously observed in the case of
tris(pyrazol-1-yl)borate organotin(IV) derivatives [3a].
The reaction between compound 1 and AgNO3 in dry
ethanol results in the complete substitution of tin with
the formation of silver(I) dimeric complex [12]
{[Tm]Ag}2 (Eq. (2)), that is in accordance with the
‘‘soft’’ character of the ligand:
The infrared spectra of derivatives 1–11 (see Section
2) are consistent with the formulations, showing all the
bands required by the presence of organic sulfur donor
[16–18] ligand and tin(IV) and organotin(IV) acceptors.
The K[Tm] salt exhibits weak bands in the region
3200–3000 cm−1 typical of C–H stretching, and some
more intense absorptions due to the ring breathing
mode between 1650 and 1500 cm−1. These bands are
not markedly shifted upon coordination, suggesting a
weak influence of the complexation on the absorptions
within the donor. Changes in the spectrum of the [Tm]
upon coordination are restricted, essentially, to the
thioamide bands: the thioamide I and III bands remain
unchanged upon coordination, while band II is split
and slightly shifted from 1295 cm−1 in K[Tm] to
approximately 1300 cm−1 in the complexes; the
thioamide IV band of the free ligand (730 cm−1) is split
in the complexes into two sharp bands in the range
740–780 cm−1. A slight shift (930 cm−1) occurs also
for the w(CꢁS), from 720 cm−1 in K[Tm] to approxi-
mately 690 cm−1 in organotin derivatives (the band is
split). These facts usually indicate sulfur donation by
the thioxo-imidazole ring [18–20], that is in accordance
with the presence of medium or weak absorptions at
approximately 270–300 cm−1, most likely due to a
Sn–S stretching vibrations. In all the complexes two
sets of thioamide bands have been observed: one due to
the coordinated imidazole ring, another typical for free
ligand absorption.
2[(Tm)cy3Sn]
Ethanol/r.t.
+2AgNO3ꢀꢀꢀꢀꢀꢀꢂ[Ag(Tm)2+2cy3SnNO3
(2)
The B–H stretching vibrations in all complexes are
observed in the region 2430–2460 cm−1, weakly shifted
to lower frequency with respect to the same absorptions
in K[Tm] (2465 cm−1).
The SnꢀC [21] and SnꢀCl [22] stretching vibrations
agree well with the trends previously observed in similar
complexes containing N-donor chelating ligands. In the
spectra of alkyl derivatives 2, 3, 8, 9 and 10 the SnꢀCl
stretching bands are observed between 232 and 241
cm−1, while in the phenyl complexes 5 and 6 these
bands fall in the region 245–250 cm−1, being shifted to
lower frequencies with respect to those reported for
corresponding tris(pyrazolyl)borates [3a].
Fig. 2. Structure proposed for the monoorganotin(IV) derivatives.
The 1H NMR spectra of the organotin(IV) complexes
(1–11) were recorded in CDCl3, acetone and in some
cases in CD3OD due to the solubility of the complexes.
1
The H NMR spectrum of compound 2, recorded at
Fig. 3. Structure proposed for the diorganotin(IV) derivatives.
293 K in acetone solution, shows three sets of signals

C. Santini et al. / Inorganica Chimica Acta 325 (2001) 20–28
25
for the imidazole protons (ratio 1:1:1), suggesting the
presence of three not equivalent azole rings. This be-
havior excludes fluxionality around the central tin atom
in acetone solution; on the other hand the presence of
isomers is also ruled out, as only one SnꢀCH3 signal is
observed.
tion polyhedron from the tetrahedron to the trigonal
bipyramid [27]. In compound 3 we have found that the
tin–proton coupling constants 2J(119Sn–H) and
2J(117Sn–H) are 75.5 and 74.7 Hz, respectively, falling
in the range for five coordinated dimethyltin(IV) species
[32]. On the basis of Lockarts’s equation (Eq. (3))
2
The tin–hydrogen J(119,117Sn–C–H) coupling con-
[MeꢀSnꢀMe]=0.0161×(2J(119Sn–1H))2
stants in various cases can be correlated with the per-
centage of s-character which the Sn atom presents in
−1.32×2J(119Sn–1H)+133.4
(3)
2
the SnꢀC bond [23–25] and hence J(119,117Sn–C–H)
the MeꢀSnꢀMe angle is estimated to approximately
125° [32], which suggests an equatorial disposition of
both Me groups (Fig. 3).
may give information about the coordination number
of tin [26,27]. In compound 2 we have found that the
tin–proton coupling constants 2J(119Sn–H) and
2J(117Sn–H) have a value of 108.5 and 103.5 Hz, re-
spectively, not very different from those reported in
literature [28] for the starting CH3SnCl3 acceptor (100.9
and 96.5–95.5 Hz), and smaller with respect to those
indicated for six-coordinate organotin(IV) complexes
containing N-, O- and S-donor ligands [27,29–33].
Moreover, only one sharp signal is present in the 119Sn
NMR spectra of 2 and the l value (−352.7 ppm) falls
in the range typical for five coordinated tin(IV) species
[33–35].
1
The H NMR spectra of triorganotin(IV) complexes
1, 4, 7, and 11, recorded at 293 K in CDCl3 solution,
show only one set of signals for the imidazole protons,
suggesting a fluxionality around the central tin atom
[33]. However the spectra of 1, 4 and 7, recorded at 223
K in CDCl3, exhibit at least two different groups of
signals for each imidazole proton (ratio 2:1); the more
intense of them is attributable to the dangling non
coordinate imidazole group, in accordance with the
solid-state structure of derivative 1. Moreover, only one
sharp signal is present in the 119Sn NMR spectra of 1,
4 and 7, and the values found (147.3, −57.9 and 45.1
ppm, respectively) are consistent with a tetrahedral and
monomeric structure in solution [40]. In compound 4
we have found that the tin–proton coupling constants
2J(Sn–H) have a value of 57.1 Hz, characteristic for
tetracoordinated trimethyltin(IV) species [32].
A similar behavior is observable in the 1H NMR
spectra of the other monoorganotin(IV) derivatives 5
and 9 recorded at room temperature: in both cases it is
possible to observe three sets of signals for the imida-
zole protons (ratio 1:1:1), suggesting the presence of
three types of imidazole rings. The 119Sn NMR spectra
of 5 and 9 provide an additional support for the five
coordination, the 119Sn chemical shifts being at −391.3
and −329.3 ppm respectively.
On the basis of this experimental evidence of the
monoorganotin(IV) derivatives 2, 5 and 9 we have
proposed the five-coordinate structure in Fig. 2.
The room temperature 1H NMR spectra of the
diorganotin(IV) derivatives 3, 6, 8 and 10 exhibit one
set of signals for the imidazolyl groups, suggesting
highly fluxional species with a rapid exchange of the
[Tm] imidazolyl rings through breaking and formation
of the SnꢀS bonds. On cooling the CDCl3 solutions of
10 to 223 K, no additional signals due to the imidazole
appear but only a broadening occurs. On the contrary,
in the cooled CDCl3 solutions (223 K) of 3 and 6, the
signals of the imidazole protons are split into two
broad subsets in agreement with a five-coordinate tin
environment. The 119Sn NMR chemical shifts of deriva-
tives 3, 6, 8 and 10 are in accordance with those of five
coordinate diorganotin(IV)halides complexes involving
halide or phosphine ligands [36], as well as chelating
S-donors such as ethane-1,2-dithiolate and N,N-di-
ethyldithiocarbamate [37] and O-donors as b-diketo-
nates [38]. However, on the basis of previous reports on
poly(azolyl)borate tin complexes [39] we cannot exclude
the possibility of the structural changes in the coordina-
The probable structures of the triorganotin(IV)
derivatives 1, 4, 7, and 11 are shown in Fig. 4.
All the 1H NMR spectra of the derivatives 1–11
exhibit only one set of signals for the alkyl or aryl
groups linked to tin, excluding the existence of different
isomers in the solution. The tin–proton coupling con-
stants are different from those observed for the starting
organotin(IV) acceptors, clearly indicating the existence
of complexes in solution.
In the spectra of the aryltin(IV) derivatives 5, 6 and
7, the signals of the NꢀCH3 protons are displaced
upfield that can be explained considering the shielding
effect exerted on the NꢀCH3 protons by the aromatic
protons of the phenyl rings linked to tin(IV).
Fig. 4. Structure proposed for the triorganotin(IV) derivatives.

26
C. Santini et al. / Inorganica Chimica Acta 325 (2001) 20–28
,
2.478(1) A that is similar to that in the triphenyltin(IV)
,
derivative of 1-methyl-2-imidazolinethione (2.437(1) A)
[41], and is significantly shorter with respect to that
,
reported for [Me3SnSCN4Ph]3 trimer (2.565(4) A) [42]
with tetrazolethiolato ligand acting in bridging mode.
The coordination of sulfur to tin results in the elonga-
tion of SꢀC distance in the imidazole ring of the ligand
,
involved in coordination that is 0.04 A longer with
respect to the other two. The other distances in Tm− in
1 are very similar to those found in the sodium deriva-
tives [8]. Furthermore, the coordination slightly influ-
ences also the values of CꢀN bonds in the ring; e.g. the
medium CꢀN distance for the coordinated ring is
,
1.345(4) A, whereas they are shorter (1.356(4) and
,
1358(4) A) in the free rings. The deviations in the BꢀN
distances upon coordination are negligible, BꢀN(1)
Fig. 5. Molecular structure of [(Tm)cy3Sn] (1). All hydrogen atoms
except one are omitted for clarity.
,
bond being only 0.01–0.03 A longer than the others.
The structure 1 can be compared with other tin(IV)
complexes containing different mercaptoazoles [40].
Usually in analogous structures tin is coordinated by
both N- and S-atoms, resulting in distorted bipyramidal
or trigonal environment. In the Tm anion not all the
nitrogen atoms are able to coordinate and therefore
cannot be involved in additive coordination to tin. The
two additive sulfur sites available for bonding are not
coordinated to tin, likely due to the steric hindrance of
the bulky cy groups. That is why the coordination
environment of metal in 1 is very similar to that found
in Ph3SnSPh and Ph3SnSC6H4But-p [43]. The 119Sn
NMR chemical shift of 1 confirms the tetrahedral coor-
dination of tin in CDCl3 solution.
Table 2
,
Selected bond distances (A) and angles (°) in 1
SnꢀC(25)
SnꢀC(13)
SnꢀC(19)
SnꢀS(1)
S(3)ꢀC(11)
S(1)ꢀC(3)
S(2)ꢀC(7)
2.158(4)
2.166(3)
2.177(3)
2.478(1)
1.694(3)
1.732(3)
1.685(3)
C(25)ꢀSnꢀC(13)
C(25)ꢀSnꢀC(19)
C(13)ꢀSnꢀC(19)
C(25)ꢀSnꢀS(1)
C(13)ꢀSnꢀS(1)
C(19)ꢀSnꢀS(1)
C(3)ꢀS(1)ꢀSn
N(3)ꢀBꢀN(5)
N(3)ꢀBꢀN(1)
N(5)ꢀBꢀN(1)
109.9(1)
116.9(1)
112.6(1)
108.08(9)
101.24(8)
106.86(9)
100.9(1)
109.1(2)
109.4(3)
109.9(2)
5. Conclusions
We have reported the synthesis and full characteriza-
1
tion (IR, H and 119Sn NMR, conductivity measure-
ments) of a series of novel organotin(IV) complexes
of hydrotris(3 - methyl - 2 - thioxo - 1 - imidazolyl)borate,
K[Tm].
4. Crystal structure
The type of the coordination of Tm-ligand found in
the complexes depends strongly on the Lewis acidity of
organotin acceptors that falls dramatically in the series
SnRCl3ꢀSnR2Cl2ꢀSnR3Cl. The high Lewis acidity of
mono- and diorganotin derivatives results in the forma-
tion of pentacoordinate species with two mercaptoimi-
dazolyl moieties coordinated to tin due to the strong
acceptor character of Cl group. The triorganotin
derivatives free of electron acceptor groups linked to
metal atom can form tetracoordinate species even in the
complexes with potentially polydentate chelating lig-
ands. One of such complexes presented in this work
and structurally characterized is really the first example
of Tm ligand acting in monodentate fashion.
The crystallographic study of [(Tm)cy3Sn] (1) reveals
the compound has the molecular structure shown in
Fig. 5, together with the numbering scheme. Selected
bond lengths and angles are listed in Table 2.
The tin atom in 1 exhibits a tetrahedral coordination
by three cyclohexyl groups and one sulfur atom of the
Tm azole ring. The SnꢀC(cyclohexyl) distances fall in a
,
narrow range from 2.158(4) to 2.177(3) A, typical for
tris(cyclohexyl)tin(IV) derivatives. The tin environment
demonstrates only small deviations from ideal tetrahe-
dral with SꢀSnꢀC angles from 101.24(8) to 108.08(9)°
and CꢀSnꢀC from 109.87(12) to 116.86(12)°. The angle
C(13)ꢀSnꢀS(1) (101.24(8)°) is smaller than the other
two (106.86(9), 108.08(9)°). The SnꢀS(1) distance in 1 is

C. Santini et al. / Inorganica Chimica Acta 325 (2001) 20–28
27
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6. Supplementary material
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Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC No. 171597. Copies of this infor-
mation may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (fax: +44-1223-336-033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
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Acknowledgements
We are grateful to the University of Camerino, Con-
siglio Nazionale delle Ricerche C.N.R.-Rome,
‘CARIMA Foundation’ and Russian Fund of Basic
Research (Grant RFBR 00-03-32662) for financial
support.
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