The synthesis and structural characterization of bis(mercaptoimidazolyl)hydroborato complexes of lithium, thallium and zinc

Article abstract of DOI:10.1039/a908411h

Bidentate [S2]-donor bis(mercaptoimidazolyl) ligands, [BmMe] and [BmMes]~, have been synthesized by reaction of [BH4]~ with 2-mercapto-l-methylimidazole and 2-mercapto-l-mesitylimidazole, respectively. Subsequent treatment with ZnX2 (X = Me, I, NO}) yields a series ofl : 1 [BmR]ZnX complexes, namely [BmMe]ZnMe, [BmMe]ZnI and [BmM"]Zn(NO3), each of which possesses 3-center-2-electron [Zn H-B] interactions. The homoleptic complex, [BmM']2Zn, may be obtained by a redistribution reaction of [BmM']ZnMe in CHC13, and possesses a tetrahedral zinc center which is devoid of a 3-center-2-electron [Zn H-B] interaction. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/a908411h

View Article Online / Journal Homepage / Table of Contents for this issue
The synthesis and structural characterization of
bis(mercaptoimidazolyl)hydroborato complexes of lithium,
thallium and zinc†
Clare Kimblin, Brian M. Bridgewater, Tony Hascall and Gerard Parkin*
Department of Chemistry, Columbia University, New York, New York 10027, USA
Received 21st October 1999, Accepted 28th January 2000
Bidentate [S2]-donor bis(mercaptoimidazolyl) ligands, [BmMe]Ϫ and [BmMes]Ϫ, have been synthesized by reaction of
[BH4]Ϫ with 2-mercapto-1-methylimidazole and 2-mercapto-1-mesitylimidazole, respectively. Subsequent treatment
with ZnX2 (X = Me, I, NO3) yields a series of 1:1 [BmR]ZnX complexes, namely [BmMe]ZnMe, [BmMe]ZnI and
[BmMes]Zn(NO3), each of which possesses 3-center–2-electron [Zn ؒ ؒ ؒ H–B] interactions. The homoleptic complex,
[BmMe]2Zn, may be obtained by a redistribution reaction of [BmMe]ZnMe in CHCl3, and possesses a tetrahedral
zinc center which is devoid of a 3-center–2-electron [Zn ؒ ؒ ؒ H–B] interaction.
Introduction
Acetylacetonato and bis(pyrazolyl)borato are two of the most
commonly employed monoanionic bidentate ligands with a
multi-atom linker between the donor atoms, that respectively
provide [O2] and [N2] coordination to a metal center.1 In con-
trast, monoanionic bidentate [S2] donor ligands of this category
have not found much application, although in zinc chemistry
thiophosphorylamine ligands {N[PR2(S)]2}Ϫ have been studied
in an effort to separate trace quantities of ZnII from aqueous
solutions containing FeIII.2 In this paper, we report the
syntheses of bis(mercaptoimidazolyl)hydroborato ligands and
describe their application to zinc chemistry.
Results and discussion
Reglinski and co-workers have recently reported the synthesis
of the tripodal [S3] tris(2-mercapto-1-methylimidazolyl)borate
ligand, [TmMe]Ϫ,3–5 by reaction of [BH4]Ϫ with 2-mercapto-1-
methylimidazole, a procedure similar to that used in the prep-
aration of tris(pyrazolyl)borato derivatives.6 In view of the
fact that [S2] donor analogs of bis(pyrazolyl)borato [BpRRЈ Ϫ
]
ligands are not common, we considered it worthwhile to syn-
thesize related bis(mercaptoimidazolyl)borato ligands because
they may provide access to an array of interesting chemistry
akin to that for the [BpRRЈ]Ϫ system.6
Significantly, the bis(2-mercapto-1-methylimidazolyl)borate
ligand [BmMe Ϫ
] may be obtained by reaction of LiBH4 with 2
equivalents of 2-mercapto-1-methylimidazole in toluene at
50 ЊC (Scheme 1).7 Since thallium derivatives have proved to be
useful reagents for transferring bis- and tris-(pyrazolyl)borate
ligands,6,8 the thallium complex {[BmMe]Tl}x was prepared by
reaction of [BmMe]Li with Tl(O2CMe), from which the zinc
methyl and iodide complexes, [BmMe]ZnMe and [BmMe]ZnI
were obtained by metathesis with Me2Zn and ZnI2, respectively
(Scheme 2). The more sterically demanding mesityl-substituted
Scheme 1
The molecular structures of {[BmMes]Li}2, {[BmMe]Tl}x,
[BmMe]ZnMe, [BmMe]ZnI and [BmMes]ZnNO3 have been deter-
mined by X-ray diffraction, as illustrated in Figs. 1–6.10
A
[BmMes Ϫ
] ligand was also obtained in an analogous manner by
common feature of each of these structures is that the bidentate
coordination of the two sulfur donor atoms is supplemented, to
varying degrees, by interaction with one of the B–H ligands
(Table 1). For comparison, Zn ؒ ؒ ؒ H–B interactions listed in
the Cambridge Structural Database are observed in the range
1.78–1.98 Å.11 Such 3-center–2-electron [M ؒ ؒ ؒ H–B] inter-
actions are analogous to those observed in the structures of
several bis(pyrazolyl)hydroborato complexes.12,13 Furthermore,
reaction of LiBH4 with 2-mercapto-1-mesitylimidazole,9 from
which the zinc nitrate derivative [BmMes]Zn(NO3) was obtained
by treatment with Zn(NO3)2 (Scheme 3).
† Dedicated to Professor Heinrich Vahrenkamp, a connoisseur and
practitioner of fine zinc chemistry, on the occasion of his 60th birthday.
Happy birthday, Heinrich!
DOI: 10.1039/a908411h
J. Chem. Soc., Dalton Trans., 2000, 891–897
This journal is © The Royal Society of Chemistry 2000
891

View Article Online
Scheme 2
Scheme 3
Fig. 1 Selected bond lengths (Å) and angles (Њ) for {[BmMes]Li}2;
Li(1)–S(1) 2.448(7), Li(1)–S(2) 2.356(7), Li(1)–S(1Ј) 2.413(7), Li(2)–S(3)
2.389(8), Li(2)–S(4) 2.491(8), Li(2)–S(4Ј) 2.518(8), S(1)–C(11) 1.708(4),
S(2)–C(21) 1.702(4), S(3)–C(81) 1.696(4), S(4)–C(91) 1.707(4), Li(1)-
H(1b) 1.86(3), Li(1) ؒ ؒ ؒ Li(1Ј) 3.03(1), Li(2) ؒ ؒ ؒ Li(2Ј) 3.50(2); S(1)–
Li(1)–S(2) 113.6(3), Li(1)–S(1)–Li(1Ј) 77.0(3), S(3)–Li(2)–S(4) 129.0(3),
Li(2)–S(4)–Li(2Ј) 88.7(3).
Fig. 2 Selected bond lengths (Å) and angles (Њ) for {[BmMe]Tl}x,
emphasizing the dinuclear [Tl2S2] core: Tl–S(2) 3.141(2), Tl(1Ј)–S(2)
3.043(1), S(1)–C(11) 1.707(5), S(2)–C(21) 1.712(5); S(2)–Tl–S(2Ј)
90.10(4), Tl(1)–S(2)–Tl(1Ј) 89.90(4).
different from those of bis(pyrazolyl)hydroborato counterparts
since the nitrogen atom of the pyrazolyl group is incapable of
bridging in such a manner. Thus, [BpRRЈ]Tl complexes typically
adopt monomeric structures.12 {[Bp]Tl}2, however, is a notable
exception in that it is dimeric in the solid state,14 although the
dinuclear nature is a result of a weak Tl ؒ ؒ ؒ Tl interaction, and
not due to a bridging pyrazolyl group. The Tl ؒ ؒ ؒ Tl separation
in {[BmMe]Tl}x (4.37 Å) is thus significantly greater than that in
{[Bp]Tl}2 (3.70 Å).
The structural characterization of the heteroleptic 1:1
[BmR]ZnX complexes is of interest in light of the fact that only
homoleptic L2Zn complexes have been previously structurally
characterized11 using related anionic bidentate [S2] donors,
namely [MeC(S)CH2C(S)OEt]2Zn15 and {N[PPri2(S)]2}2Zn.16 In
this regard, the corresponding homoleptic complex, [BmMe]2Zn,
a [Ag ؒ ؒ ؒ H–B] interaction has been reported for the tris(2-
mercapto-1-methylimidazolyl)borate complex [TmMe]AgPCy3,
within which only two of the sulfur atom donors coordinate to
silver.5a,b
While the zinc complexes [BmR]ZnX are strictly mono-
meric in the solid state, the lithium and thallium complexes
{[BmMes]Li}2 and {[BmMe]Tl}x are oligonuclear, with the metal
centers being bridged by sulfur atoms of the mercaptoimid-
azolyl groups (Figs. 1–3). The lithium and thallium complexes
have similar four membered [M2S2] cores, but one of the sulfur
atoms on each of the [BmMe] ligands in the dinuclear thallium
fragment also interacts with another thallium center, thereby
resulting in a polynuclear structure (Fig. 3). Clearly, the
structural motifs adopted by {[BmMes]Li}2 and {[BmMe]Tl}x are
892
J. Chem. Soc., Dalton Trans., 2000, 891–897

View Article Online
Table 1 [M ؒ ؒ ؒ H–B] interactions in {[BmR]M} derivatives
d(M ؒ ؒ ؒ B)/Å
d(M ؒ ؒ ؒ H)/Å
{[BmMes]Li}2
{[BmMe]Tl}x
[BmMe]ZnI
2.80, 3.09a
3.50
2.94
2.88
2.82
1.86, 2.34a
2.69
2.06
[BmMe]ZnMe
[BmMes]Zn(NO3)
[BmMe]2Zn
1.77
1.93b
3.51
3.78
a Values for two independent molecules. b H atom not refined.
Fig. 3 A portion of the polymeric structure of {[BmMe]Tl}x.
Fig. 6 Selected bond lengths (Å) and angles (Њ) for [BmMes]Zn(NO3):
Zn–S(11) 2.267(3), Zn–S(21) 2.268(3), Zn–O(1) 2.241(5), Zn–O(2)
2.065(5), S(11)–C(11) 1.738(10), S(21)–C(21) 1.645(12); S(11)–Zn–
S(21) 127.33(8), O(1)–Zn–O(2) 59.5(2), S(11)–Zn–O(1) 103.1(3), S(11)–
Zn–(O2) 119.7(3), S(21)–Zn–O(1) 98.3(3), S(21)–Zn–(O2) 112.7(3).
Fig. 4 Selected bond lengths (Å) and angles (Њ) for [BmMe]ZnI: Zn–
S(1) 2.287(2), Zn–S(2) 2.292(2), Zn–I 2.548(1), S(1)–C(11) 1.719(5),
S(2)–C(21) 1.723(5); S(1)–Zn–S(2) 118.0(1), S(1)–Zn–I 116.6(1), S(2)–
Zn–I 124.9(1).
Scheme 4
Fig. 5 Selected bond lengths (Å) and angles (Њ) for [BmMe]ZnMe: Zn–
S(1) 2.342(3), Zn–S(2) 2.382(3), Zn–C(1) 1.97(1), S(1)–C(11) 1.724(10),
S(2)–C(21) 1.693(9); S(1)–Zn–S(2) 105.9(1), S(1)–Zn–C(1) 123.0(3),
S(2)–Zn–C(1) 125.3(4).
[BmMe]2Zn and [BmR]ZnX is that the [BmR] ligand in the former
adopts a configuration which results in a “chair-like” eight-
membered ring, as opposed to the “boat-like” rings present in
[BmR]ZnX which allow for a closer proximity between the
metal and B–H group. For comparison purposes the Zn–S
bond lengths in these complexes are summarized in Table
2.17 Thus, the average Zn–S bond length in [BmMe]2Zn (2.34
Å) is comparable to the mean value for tetrahedral [ZnS4]
coordination geometries listed in the CSD (2.35 Å),11 and also
the mean value for the structural site in LADH–NADH–
DMSO (2.35 Å).20,21
may be obtained by a redistribution reaction of [BmMe]ZnMe in
CHCl3 (Scheme 4). The molecular structure of [BmMe]2Zn is
illustrated in Fig. 7 and, as would be expected for a tetrahedral
zinc center, the complex does not possess a 3-center–2-electron
[Zn ؒ ؒ ؒ H–B] interaction; thus, the Zn ؒ ؒ ؒ B separation of 3.78
Å is substantially greater than those in the above [BmR]ZnX
complexes (2.82–2.94 Å). The principal distinction between
J. Chem. Soc., Dalton Trans., 2000, 891–897
893

View Article Online
(CH3)3]: C, 66.0; H, 6.5; N, 12.8. Found: C, 65.7; H, 6.4; N,
12.1%). 1H NMR (CDCl3): δ 2.08 [s, 2 ortho-CH3], 2.33 [s, para-
CH3], 6.63 [d, 3JH–H = 2, 1 H of C3H3N2S], 6.84 [d, 3JH–H = 2, 1 H
of C3H3N2S], 6.99 [s, C6H2Me3], 11–12 [br, 1 H of C3H3N2S].
Synthesis of {[BmMe]Li}2
A mixture of 2-mercapto-1-methylimidazole (10.0 g, 87.6
mmol) and LiBH4 (0.795 g, 36.5 mmol) in toluene (50 mL) was
heated overnight at 50 ЊC. After this period, the volatile com-
ponents were removed in vacuo giving a white solid which
was washed with Et2O (2 × 50 mL) and with CHCl3 (30 mL)
to remove excess 2-mercapto-1-methylimidazole. Yield of
{[BmMe]Li}2ؒCHCl3: 6.0 g, 54% (Calc. for {[BmMe]Li}2ؒCHCl3:
C, 33.4; H, 4.1; N, 18.3. Found: C, 33.6; H, 4.5; N, 18.4%). IR
(KBr disk, cmϪ1): 3121 (s), 2945 (m), 2399 (m), 2379 (m), 2276
(w), 1654 (w), 1628 (w), 1560 (m), 1525 (vw), 1510 (vw), 1458
(s), 1412 (s), 1380 (vs), 1303 (m), 1193 (s), 1119 (vs), 1086 (m),
1040 (w), 1015 (vw), 959 (vw), 884 (vw), 755 (m), 727 (s), 699
(m), 678 (m), 615 (w), 512 (m), 460 (w). NMR spectroscopic
data are listed in Table 3. Crystals for X-ray diffraction were
obtained from chloroform.
Fig. 7 Selected bond lengths (Å) and angles (Њ) for [BmMe]2Zn: Zn–
S(1) 2.336(1), Zn–S(2) 2.344(1), Zn–S(3) 2.330(1), Zn–S(4) 2.338(1),
S(1)–C(11) 1.732(3), S(2)–C(21) 1.724(3), S(3)–C(31) 1.717(3), S(4)–
C(41) 1.726(4); S(1)–Zn–S(2) 115.75(4), S(1)–Zn–S(3) 114.13(4), S(1)–
Zn–S(4) 102.74(3), S(2)–Zn–S(3) 100.59(3), S(2)–Zn–S(4) 108.91(3),
S(3)–Zn–S(4) 115.16(4).
Synthesis of {[BmMe]Tl}x
Table 2 Comparison of Zn–S bond lengths in zinc complexes with
bidentate [S2] ligands
A suspension of {[BmMe]Li}2ؒCHCl3 (7.0 g, 28.4 mmol) and
Tl(O2CMe) (12.4 g, 47.1 mmol) in MeOH (85 mL) was stirred
at room temperature for 1 hour. After this period, the volatile
components were removed in vacuo giving a sticky white solid
which was washed with water (2 × 100 mL) and dried in vacuo.
Yield of {[BmMe]Tl}x: 7.23 g, 71% (Calc. for {[BmMe]Tl}x: C,
21.7; H, 2.7; N, 12.6. Found: C, 21.6; H, 2.5; N, 12.0%). IR
(KBr disk, cmϪ1): 3144 (w), 3116 (m), 3077 (w), 2934 (w), 2665
(vw), 2371 (s), 2078 (vw), 1547 (m), 1453 (s), 1402 (s), 1373 (vs),
1297 (s), 1203 (s), 1181 (s), 1165 (s), 1109 (vs), 1082 (s), 983 (m),
888 (m), 848 (vw), 828 (vw), 749 (s), 728 (s), 701 (m), 678 (m),
651 (w), 606 (vw), 518 (w), 502 (w), 458 (w). NMR spectro-
scopic data are listed in Table 3. Crystals for X-ray diffraction
were obtained from chloroform.
d(Zn–Sav)/Å
Ref.
[BmMe]ZnI
2.29
2.36
2.27
2.34
2.35
2.30
This work
This work
This work
This work
18
[BmMe]ZnMe
[BmMes]Zn(NO3)
[BmMe]2Zn
{N[PPri2(S)]2}2Zn
[MeC(S)CH2C(S)OEt]2Zn
19
Experimental
General considerations
All manipulations were performed using a combination of
glovebox, high-vacuum or Schlenk techniques.22 Solvents were
purified and degassed by standard procedures. 1H NMR
spectra were recorded on Varian VXR-400 and Bruker Avance
400 DRX spectrometers. 13C NMR spectra were recorded on
Varian VXR-300 (75.43 MHz) and Bruker Avance 300wb DRX
(75.47 MHz) spectrometers. 1H and 13C chemical shifts are
reported in ppm relative to SiMe4 (δ = 0) and were referenced
Synthesis of [BmMe]ZnI
A mixture of {[BmMe]Tl}x (660 mg, 1.48 mmol Tl) and ZnI2
(485 mg, 1.52 mmol) in CH2Cl2 was stirred at room temperature
for ca. 3 hours, resulting in the formation of a yellow precipi-
tate. After this period, the mixture was filtered. Removal of the
volatile components from the filtrate in vacuo gave [BmMe]ZnI
as a white solid. Yield of [BmMe]ZnI: 220 mg, 34% (Calc. for
[BmMe]ZnI: C, 22.3; H, 2.8; N, 13.0. Found: C, 22.3; H, 2.8; N,
12.5%). IR (KBr disk, cmϪ1): 3155 (m), 3125 (m), 3087 (w),
2948 (w), 2865 (vw), 2708 (vw), 2439 (m), 2224 (m), 2067 (w),
1559 (s), 1463 (vs), 1439 (m), 1420 (s), 1390 (vs), 1326 (m), 1299
(m), 1261 (w), 1195 ( vs), 1156 (m), 1130 (s), 1088 (s), 1049 (m),
1017 (m), 963 (m), 878 (m), 836 (w), 802 (w), 725 (s), 694 (s), 678
(w), 643 (w), 593.4 (w), 514 (m), 464 (vw). NMR spectroscopic
data are listed in Table 3. Crystals for X-ray diffraction were
obtained from chloroform.
internally with respect to the protio solvent impurity or the 13
C
resonances, respectively. All coupling constants are reported in
Hz. IR spectra were recorded as KBr pellets on Perkin-Elmer
1430 or 1600 spectrophotometers and are reported in cmϪ1
.
C, H, and N elemental analyses were measured using a
Perkin-Elmer 2400 CHN Elemental Analyzer. 2-mercapto-1-
methylimidazole was obtained from Aldrich.
Synthesis of 2-mercapto-1-mesitylimidazole
2-Mercapto-1-mesitylimidazole was prepared using a general
procedure.23 Specifically, a mixture of MesNCS24 (Mes = 2,4,6-
Me3C6H2) (15 g, 0.085 mol) and amino acetaldehyde diethyl
acetal [H2NCH2CH(OEt)2] (12.3 mL, 0.085 mol) in toluene (ca.
60 mL) was stirred at room temperature for 3 hours. After this
period, HCl(aq) (3.2 mL of 14 M, 0.045 mol) was added and
the mixture was refluxed for 7 hours. The volatile components
were removed in vacuo and water (ca. 300 mL) was added to the
residue. The pH was adjusted to 8 by the addition of NaOH
(0.1 M), resulting in the formation of a precipitate. The mixture
was filtered and the precipitate was dried, extracted into CHCl3
(ca. 500 mL), and filtered. The volatile components were
removed in vacuo, and the residue obtained was washed with
Et2O giving 2-mercapto-1-mesitylimidazole as a pale peach
colored powder (13.6 g, 74%) (Calc. for C3H3N2(S)[C6H2-
Synthesis of [BmMe]ZnMe
A suspension of {[BmMe]Tl}x (0.75 g, 1.70 mmol Tl) in benzene
(25 mL) was treated with a solution of ZnMe2 (0.29 g, 3.0
mmol) in toluene (1.5 mL), thereby resulting in the slow form-
ation of a black precipitate. The mixture was stirred for 2 hours,
filtered and the volatile components were removed in vacuo.
Yield of [BmMe]ZnMe 0.45 g (83%). IR (KBr, cmϪ1): 3122 (vs),
2938 (s), 2409 (vs), 2293 (s), 2068 (m), 1578 (w), 1561 (s), 1460
(vs), 1418 (s), 1381 (vs), 1322 (m), 1304 (m), 1227 (m), 1198 (vs),
1120 (vs), 1087 (s), 1043 (m), 1017 (m), 957 (m), 878 (w), 749 (s),
732 (vs), 697 (s), 678 (s), 663 (m), 526 (s), 502 (m), 484 (m), 455
(m). NMR spectroscopic data are listed in Table 3. Crystals for
X-ray diffraction were obtained from benzene.
894
J. Chem. Soc., Dalton Trans., 2000, 891–897

View Article Online
Synthesis of [BmMe]2Zn
A solution of [BmMe]ZnMe (100 mg, 0.19 mmol) in CHCl3 (ca.
5 mL) was allowed to stand at room temperature for 4 days,
depositing [BmMe]2Zn as an off-white precipitate which was
separated by filtration, washed with pentane (ca. 5 mL) and
dried. Yield of [BmMe]2Zn: 54 mg (65%). IR data (KBr, cmϪ1):
3147 (s), 3120 (s), 2946 (s), 2492 (m), 2393 (s), 2291 (m), 1687
(w), 1556 (s), 1459 (s), 1412 (s), 1379 (s), 1326 (m), 1302 (m),
1188 (s), 1171 (s), 1128 (s), 1087 (s), 1042 (m), 1014 (m), 909
(w), 886 (w), 804 (vw), 763 (m), 751 (s), 725 (s), 698 (s), 647 (w),
618 (vw), 601 (vw), 548 (vw), 507 (w), 450 (vw). NMR spectro-
scopic data are listed in Table 3. Crystals for X-ray diffraction
were obtained from CHCl3.
Synthesis of {[BmMes]Li}2
A stirred mixture of 2-mercapto-1-mesitylimidazole (500 mg,
2.29 mmol) and LiBH4 (50 mg, 2.29 mmol) in toluene, was
heated at ca. 115 ЊC for two days in an ampoule (CARE!). The
mixture was allowed to cool to room temperature and filtered.
The volatile components were removed from the filtrate in vacuo
and the white product was washed with pentane (ca. 20 mL)
and dried to give {[BmMes]Li}2 as a white powder (365 mg,
70%). IR (KBr disk, cmϪ1): 2366 (m), 2345 (m), [ν(B–H)].
NMR spectroscopic data are listed in Table 4. Crystals for
X-ray diffraction were obtained from benzene.
Synthesis of {[BmMes]Tl}x
A mixture of 2-mercapto-1-mesitylimidazole (7 g, 0.032 mol)
and LiBH4 (1.4 g, 0.07 mmol) in THF (ca. 50 mL) was heated
at ca. 70 ЊC for 1 day in an ampoule (CARE!). The THF was
removed in vacuo and the product was dissolved in methanol
(ca. 30 mL). Tl(O2CMe) (5.15 g, 0.020 mol) was added to the
solution and the mixture was stirred for 1 hour, resulting in the
formation of a white/beige precipitate. The mixture was stirred
for 1 hour, and the supernatant was decanted. The residue
was dried in vacuo, and washed with diethyl ether, giving
{[BmMes]Tl}x as an off-white powder (4.99 g, 68%). IR data
(KBr disk, cmϪ1): 2361 (s), 2212 (m) [ν(B–H)]. 1H NMR
(d6-DMSO, obtained immediately): δ 1.89 (s, 2 × CH3), 2.27 (s,
1 × CH3), 6.84 (d, 2H), 6.93 (d, 2H), 6.95 (s, 4H).25
Synthesis of [BmMes]ZnNO3
A
mixture of {[BmMes]Li}2 (310 mg, 0.68 mmol) and
Zn(NO3)2ؒ6H2O (400 mg, 1.34 mmol) in MeOH (ca. 15 mL)
was stirred at room temperature for 2 hours. The volatile com-
ponents were removed in vacuo and the residue was extracted
into C6H6 (10 mL). The mixture was filtered and the filtrate was
concentrated. Colorless microcrystals of [BmMes]ZnNO3 were
deposited and were isolated by filtration. The volatile com-
ponents were removed from the filtrate giving [BmMes]ZnNO3 as
a white powder (108 mg, 27%) (Calc. for [BmMes]ZnNO3: C,
50.2; H, 4.9; N, 12.2. Found: C, 50.3; H, 4.8; N, 12.0%). NMR
spectroscopic data are listed in Table 4. Crystals for X-ray
diffraction were obtained from benzene.
X-Ray structure determinations
Crystal data, data collection and refinement parameters are
summarized in Table 5. X-Ray diffraction data for [BmMe]ZnI
and [BmMe]ZnMe were collected on a Siemens P4 diffrac-
tometer. The unit cells were determined by the automatic
indexing of 25 centered reflections and confirmed by examin-
ation of the axial photographs. Intensity data were collected
using graphite monochromated Mo-Kα X-radiation
(λ = 0.71073 Å). Check reflections were measured every 100
reflections, and the data were scaled accordingly and corrected
for Lorentz, polarization and absorption effects. X-Ray diffrac-
tion data for {[BmMe]Tl}x, {[BmMes]Li}2, [BmMes]Zn(NO3) and
J. Chem. Soc., Dalton Trans., 2000, 891–897
895

View Article Online
Table 4 NMR spectroscopic data for {[BmMes]M} derivatives
{[BmMes]Li}2
[BmMes]ZnNO3
a
a
1H NMR
H2B{C3N2H2[C6H2(CH3)3]S}2
1.95, s, ortho
2.30, s, para
6.93, s
1.94, s, ortho
2.34, s, para
6.99, s
H2B{C3N2H2[C6H2(CH3)3]S}2
H2B{C3N2H2[C6H2(CH3)3]S}2
6.90, d, 3JH–H = 2 [2H]
6.60, d, 3JH–H = 2 [2H]
Not observed
6.82, d, 3JH–H = 2 [2H]
7.16, d, 3JH–H = 2 [2H]
3.75, br
H2B{C3N2H2[C6H2(CH3)3]S}2
13C NMR
H2B{C3N2H2[C6H2(CH3)3]S}2
17.9, q, 1JC–H = 127 [o-CH3]
21.1, q, 1JC–H = 127 [ p-CH3]
129.0, d, 1JC–H = 154
134.1, s
17.5, q, 1JC–H = 128 [o-CH3]
21.1, q, 1JC–H = 127 [ p-CH3]
129.4, d, 1JC–H = 158
132.7, s
H2B{C3N2H2[C6H2(CH3)3]S}2
H2B{C3N2H2[C6H2(CH3)3]S}2
135.8, s
138.7, s
135.3, s
140.1, s
117.8, d, 1JC–H = 195
123.4, d, 1JC–H = 186
160.5, s
119.9, d, 1JC–H = 198
124.3, d, 1JC–H = 197
155.6, s
a In CDCl3.
Table 5 Crystal, intensity collection and refinement data
{[BmMe]Tl}x
{[BmMes]Li}2
[BmMe]ZnI
[BmMe]ZnMe
C9H15BN4S2Zn
[BmMes]Zn(NO3)ؒ3C6H6
[BmMe]2Zn
Formula
Formula weight
Crystal symmetry
Space group
a/Å
b/Å
c/Å
α/Њ
C8H12B1N4S2Tl
887.03
Monoclinic
P21/n (no. 14)
8.5696(4)
14.1642(7)
11.3006(5)
90
111.966(1)
90
1272.1(1)
4
C48H56B2Li2N8S4
908.75
C8H12BIN4S2Zn
431.2
C42H46BN5O3S2Zn
809.14
Orthorhombic
Pna21 (no. 33)
24.777(5)
9.451(2)
18.736(4)
90
90
90
4387(2)
4
C16H24B2N8S4Zn
543.66
Monoclinic
P21/n (no. 14)
9.327(1)
14.393(2)
18.520(3)
90
93.811(2)
90
2480.6(6)
4
319.6
Triclinic
Monoclinic
P21/n (no. 14)
11.362(2)
9.937(2)
13.483(3)
90
110.31(2)
90
1427.6(5)
4
Monoclinic
P21/c (no. 14)
7.652(1)
13.822(3)
13.469(2)
90
102.588(7)
90
1390.3(4)
4
¯
P1 (no. 2)
8.135(1)
16.526(3)
20.404(3)
106.379(3)
101.143(3)
97.605(2)
2530.8(6)
2
β/Њ
γ/Њ
V/Å3
Z
Temperature/K
Radiation, λ/Å
Dc/g cmϪ3
µ(Mo-Kα)/mmϪ1
θmax/Њ
203
0.71073
2.316
13.00
28.3
213
0.71073
1.193
0.23
28.3
293
0.71073
2.007
4.16
24.0
293
0.71073
1.527
2.05
22.5
223
0.71073
1.225
0.70
28.3
228
0.71073
1.456
1.348
28.2
No. of data
No. of parameters
2865
154
0.0292
0.0616
1.128
10289
606
0.0718
0.1194
1.038
2226
163
0.0353
0.0799
1.042
1783
163
0.0579
0.1164
1.014
9177
459
0.0838
0.0909
1.066
5607
300
0.0416
0.0919
1.000
a
R1
wR2
a
GOF
2
a R1 = Σ |Fo| Ϫ |Fc| }/Σ|Fo| for [I > 2σ(I)]; wR2 = {Σ[w(Fo2 Ϫ Fc2)2]/Σ[w(Fo )2]}1/2 for [I > 2σ(I)].
[BmMe]2Zn were collected on a Bruker P4 diffractometer
equipped with a SMART CCD detector. The structures were
solved using direct methods and standard difference map tech-
niques, and were refined by full-matrix least-squares procedures
on F2 with SHELXTL (Version 5.03).26 Hydrogen atoms on
carbon were included in calculated positions.
donor ligands. The [BmMe] ligand is, however, insufficiently
bulky to prevent the formation of the homoleptic derivative,
[BmMe]2Zn, which may be obtained by a redistribution reaction
of [BmMe]ZnMe in CHCl3.
Acknowledgements
CCDC reference number 186/1829.
We thank the National Science Foundation (CHE 96-10497) for
support of this research and also the National Science Found-
ation and the U.S. Department of Energy for support via the
Environmental Molecular Sciences Institute at Columbia
University (NSF CHE-98-10367). Dr Tauqir Fillebeen is
thanked for technical assistance.
See http://www.rsc.org/suppdata/dt/a9/a908411h/ for crystal-
lographic files in .cif format.
Conclusion
In summary, the bidentate [S2]-donor bis(mercaptoimidazolyl)
ligands, [BmMe Ϫ and [BmMes]Ϫ, have been synthesized by
]
reaction of [BH4]Ϫ with 2-mercapto-1-methylimidazole and
2-mercapto-1-mesitylimidazole, respectively. Subsequent treat-
ment with ZnX2 (X = Me, I, NO3) yields a series of 1:1
[BmR]ZnX complexes, namely [BmMe]ZnMe, [BmMe]ZnI and
[BmMes]Zn(NO3). The isolation of these 1:1 [BmR]ZnX com-
plexes provides a contrast with the homoleptic L2Zn derivatives
that have previously been obtained using related bidentate [S2]
References
1 Bidentate donors with a single atom linker are also well known, and
include: [RC(O)2]Ϫ, [RC(NRЈ)2]Ϫ and [RC(S)2]Ϫ.
2 J. O. Morley and M. H. Charlton, J. Phys. Chem. A, 1998, 102,
6871.
3 M. Garner, J. Reglinski, I. Cassidy, M. D. Spicer and A. R.
Kennedy, Chem. Commun., 1996, 1975.
896
J. Chem. Soc., Dalton Trans., 2000, 891–897

View Article Online
4 Bis- and tris-(2-mercapto-1-alkylimidazolyl)borate ligands are
14 P. Ghosh, A. L. Rheingold and G. Parkin, Inorg. Chem., 1999, 38,
represented by the abbreviations [BmR] and [TmR], respectively.
5464.
Ϫ
5 For other studies using the [TmMe
]
ligand, see: (a) C. Santini,
15 R. Beckett and B. F. Hoskins, J. Chem. Soc., Dalton Trans., 1975,
908.
16 D. Cupertino, R. Keyte, A. M. Z. Slawin, D. J. Williams and J. D.
Woollins, Inorg. Chem., 1996, 35, 2695.
17 For recent references to tetrahedral zinc complexes with sulfur
ligation, see: B. Muller, A. Schneider, M. Tesmer and H.
Vahrenkamp, Inorg. Chem., 1999, 38, 1900; U. Brand, M. Rombach
and H. Vahrenkamp, Chem. Commun., 1998, 2717; U. Brand and
H. Vahrenkamp, Z. Anorg. Allg. Chem., 1996, 622, 213.
18 D. Cupertino, R. Keyte, A. M. Z. Slawin, D. J. Williams and J. D.
Woollins, Inorg. Chem., 1966, 35, 2695.
19 R. Beckett and B. F. Hoskins, J. Chem. Soc., Dalton Trans., 1975,
908.
20 S. Al-Karadaghi, E. S. Cedergren-Zeppezauer, S. Hövmoller, K.
Petratos, H. Terry and K. S. Wilson, Acta Crystallogr., Sect. D,
1994, 50, 793.
C. Pettinari, G. G. Lobbia, R. Spagna, M. Pellei and F. Vallorani,
Inorg. Chim. Acta, 1999, 285, 81; (b) C. Santini, G. G. Lobbia,
C. Pettinari, M. Pellei, G. Valle and S. Calogero, Inorg. Chem., 1998,
37, 890; (c) J. Reglinski, M. D. Spicer, M. Garner and A. R.
Kennedy, J. Am. Chem. Soc., 1999, 121, 2317.
6 For reviews, see: S. Trofimenko, Chem. Rev., 1993, 93, 943;
G. Parkin, Adv. Inorg. Chem., 1995, 42, 291; N. Kitajima and
W. B. Tolman, Prog. Inorg. Chem., 1995, 43, 419.
7 The syntheses of [BmMe]Li and [BmMe]ZnI have been commun-
icated: C. Kimblin, T. Hascall and G. Parkin, Inorg. Chem., 1997, 36,
5680.
8 C. Janiak, Main Group Met. Chem., 1998, 21, 33; Coord. Chem.
Rev., 1997, 163, 107.
9 2-Mercapto-1-mesitylimidazole is monoclinic, space group P21/c
(No. 14), a = 7.5661(5), b = 20.740(1), c = 7.3572(5) Å, β =
90.000(1)Њ, V = 1154.5(1) Å3, Z = 4, T = 223 K, R1 = 0.0394,
wR2 = 0.1119 [I > 2σ(I)].
21 Furthermore, [Zn(mercaptomethylimidazole)4]2ϩ has a similar co-
ordination geometry. See: I. W. Nowell, A. G. Cox and E. S. Raper,
Acta Crystallogr., Sect. B, 1979, 35, 3047; A. Wilk, M. A. Hitchman,
W. Massa and D. Reinen, Inorg. Chem., 1993, 32, 2483.
22 J. P. McNally, V. S. Leong and N. J. Cooper, in Experimental
Organometallic Chemistry, ed. A. L. Wayda and M. Y. Darensbourg,
American Chemical Society, Washington, DC, 1987, ch. 2, pp. 6–23;
B. J. Burger and J. E. Bercaw, in Experimental Organometallic
Chemistry, ed. A. L. Wayda and M. Y. Darensbourg, American
Chemical Society, Washington, DC, 1987, ch. 4, pp. 79–98; D. F.
Shriver and M. A. Drezdzon, The Manipulation of Air-Sensitive
Compounds, Wiley-Interscience, New York, 2nd edn., 1986.
23 K. Matsuda, I. Yanagisawa and Y. Isomura, Synth. Commun., 1997,
27, 3565.
10 An orthorhombic modification of [BmMe]ZnI was also structurally
characterized: a = 9.075(1), b = 10.800(1), c = 29.261(5) Å, V =
2868.0(8) Å3, Z = 8, T = 293 K, R1 = 0.0490, wR2 = 0.1215
[I > 2σ(I)].
11 CSD Version 5.17. 3D Search and Research Using the Cambridge
StructuralDatabase,F.H.AllenandO.Kennard,Chem.Des.Automat.
News, 1993, 8(1), 1, 31.
12 For example, the “two coordinate” TlI centers in a variety of
[BpRRЈ]Tl complexes are supplemented by weak intramolecular
[Tl ؒ ؒ ؒ H–B] interactions. T. Fillebeen, T. Hascall and G. Parkin,
Inorg. Chem., 1997, 36, 3787; P. Ghosh, T. Hascall, C. Dowling and
G. Parkin, J. Chem. Soc., Dalton Trans., 1998, 3355; C. Dowling,
P. Ghosh and G. Parkin, Polyhedron, 1997, 16, 3469.
24 MesNCS was obtained by a general literature method, see: C. J.
Jochims, Chem. Ber., 1968, 101, 1746.
13 For examples of 3-center–2-electron [M ؒ ؒ ؒ H–B] interactions in
transition metal complexes, see: F. A. Cotton, M. Jeremic and
A. Shaver, Inorg. Chim. Acta, 1972, 6, 543; J. L. Calderon, F. A.
Cotton and A. Shaver, J. Organomet. Chem., 1972, 42, 419; M. O.
Albers, S. F. A. Crosby, D. C. Liles, D. J. Robinson, A. Shaver and
E. Singleton, Organometallics, 1987, 6, 2014; D. L. Reger,
R. Mahtab, J. C. Baxter and L. Lebioda, Inorg. Chem., 1986, 25,
2046; C. A. Kosky, P. Ganis and G. Avitabile, Acta Crystallogr.,
Sect. B, 1971, 27, 1859; R. B. King and A. B. Bond, J. Am. Chem.
Soc., 1974, 96, 1338; D. L. Reger, C. A. Swift and L. Lebioda, J. Am.
Chem. Soc., 1983, 105, 5343; J. C. Calabrese, P. J. Domaille, J. S.
Thompson and S. Trofimenko, Inorg. Chem., 1990, 29, 4429.
25 Note that {[BmMes]Tl}x decomposes over the period of an hour in
Me2SO.
26 G. M. Sheldrick, SHELXTL, An Integrated System for Solving,
Refining and Displaying Crystal Structures from Diffraction Data;
University of Göttingen, Göttingen, Federal Republic of Germany,
1981.
Paper a908411h
J. Chem. Soc., Dalton Trans., 2000, 891–897
897