Homoleptic group 12 metal bis(mercaptoimidazolyl)borate complexes M(BmR)2 (M = Zn, Cd, Hg)

Article abstract of DOI:10.1021/ic025780m

The sodium salt of the bis(2-mercapto-1-methylimidazolyl)borate anion [Bm^Me]^- and those of the new bis(2-mercapto-1-alkylimidazolyl)borates [Bm^R]^- (R = Bz, Bu^t, p-Tol) have been readily obtained from NaBH₄ and the appropriate 2-mercapto-1-alkylimidazoles. To contrast the binding preferences of the group 12 metals in a sulfur-rich environment, the four complete series of homoleptic complexes M[Bm^R]₂ (M = Zn, Cd, Hg), including the first bis(mercaptoimidazolyl)borate derivatives of cadmium and mercury, have been prepared. X-ray diffraction studies of Cd[Bm^Me]₂ and M[Bm^tBu]₂ (M = Zn, Cd, Hg) show the presence of distorted tetrahedral [MS₄] central cores supplemented by two weak vicinal M...H-B bonds, interactions which appear to be a common feature in the coordination chemistry of Bm^R ligands. In the case of zinc, it has been found that only in the presence of bulky ligands, as in Zn [Bm^tBu]₂, may an unexpected expansion in the coordination number from four to six be induced. This observation suggests the viability of octahedral intermediates in the processes whereby certain zinc enzymes transfer or exchange metal ions.

Full text of DOI:10.1021/ic025780m

Inorg. Chem. 2003, 42, 2149−2156
Homoleptic Group 12 Metal Bis(mercaptoimidazolyl)borate Complexes
M(BmR)2 (M ) Zn, Cd, Hg)
Hamsell M. Alvarez, Thuy B. Tran, Mary A. Richter, Dania M. Alyounes, and Daniel Rabinovich*
Department of Chemistry, The UniVersity of North Carolina at Charlotte,
9201 UniVersity City BouleVard, Charlotte, North Carolina 28223
Joseph M. Tanski
Department of Chemistry, Columbia UniVersity, New York, New York 10027
Mariusz Krawiec
Molecular Structure Center, Department of Chemistry, Clemson UniVersity,
Clemson, South Carolina 29634
Received June 8, 2002
Me -
The sodium salt of the bis(2-mercapto-1-methylimidazolyl)borate anion [Bm ] and those of the new bis(2-mercapto-
R -
t
1-alkylimidazolyl)borates [Bm ] (R ) Bz, Bu, p-Tol) have been readily obtained from NaBH and the appropriate
4
2-mercapto-1-alkylimidazoles. To contrast the binding preferences of the group 12 metals in a sulfur-rich environment,
R
the four complete series of homoleptic complexes M[Bm ]2 (M ) Zn, Cd, Hg), including the first bis-
(mercaptoimidazolyl)borate derivatives of cadmium and mercury, have been prepared. X-ray diffraction studies of
tBu
Cd[BmMe]2 and M[Bm ]2 (M ) Zn, Cd, Hg) show the presence of distorted tetrahedral [MS ] central cores
4
supplemented by two weak vicinal M‚‚‚H−B bonds, interactions which appear to be a common feature in the
R
coordination chemistry of Bm ligands. In the case of zinc, it has been found that only in the presence of bulky
tBu
ligands, as in Zn[Bm ]2, may an unexpected expansion in the coordination number from four to six be induced.
This observation suggests the viability of octahedral intermediates in the processes whereby certain zinc enzymes
transfer or exchange metal ions.
Introduction
prepared a number of zinc complexes using the lithium or
thallium reagents M[BmR] (M ) Li, Tl; R ) Me, Mes),7
Santos and co-workers have obtained several BmR derivatives
of rhenium, technetium, and uranium.8,9 Our entry into this
arena was marked by the synthesis of paramagnetic Ni[BmR]2
species as model compounds for the nickel center in the
The coordination chemistry of the tris(mercaptoimid-
azolyl)borate ligand system (Figure 1)1 is expanding at an
accelerated pace, and recent advances include the preparation
of mononuclear zinc hydroxide2 and cadmium thiolate3
complexes and the structural characterization of the first
complete series of group 12 metal derivatives [TmR]MBr
(M ) Zn, Cd, Hg; R ) Me, But).4,5 In contrast, applications
of the related bis(mercaptoimidazolyl)borates (Figure 1)6
have been more sporadic. In this regard, whereas Parkin has
(4) Cassidy, I. D.; Garner, M.; Kennedy, A. R.; Potts, G. B. S.; Reglinski,
J.; Slavin, P. A.; Spicer, M. D. Eur. J. Inorg. Chem. 2002, 1235-
1239.
(5) White, J. L.; Tanski, J. M.; Rabinovich, D. J. Chem. Soc., Dalton
Trans. 2002, 2987-2991.
(6) Kimblin, C.; Hascall, T.; Parkin, G. Inorg. Chem. 1997, 36, 5680-
* To whom correspondence should be addressed. E-mail: drabinov@
email.uncc.edu.
(1) Garner, M.; Reglinski, J.; Cassidy, I.; Spicer, M. D.; Kennedy, A. R.
Chem. Commun. 1996, 1975-1976.
(2) Bridgewater, B. M.; Parkin, G. Inorg. Chem. Commun. 2001, 4, 126-
129.
5681.
(7) Kimblin, C.; Bridgewater, B. M.; Hascall, T.; Parkin, G. J. Chem.
Soc., Dalton Trans. 2000, 891-897.
(8) (a) Garcia, R.; Paulo, A.; Domingos, A.; Santos, I.; Ortner, K.; Alberto,
R. J. Am. Chem. Soc. 2000, 122, 11240-11241. (b) Maria, L.;
Domingos, A.; Santos, I. Inorg. Chem. 2001, 40, 6863-6864. (c)
Garcia, R.; Domingos, A.; Paulo, A.; Santos, I.; Alberto, R. Inorg.
Chem. 2002, 41, 2422-2428.
(3) Bakbak, S.; Incarvito, C. D.; Rheingold, A. L.; Rabinovich, D. Inorg.
Chem. 2002, 41, 998-1001.
10.1021/ic025780m CCC: $25.00 © 2003 American Chemical Society
Published on Web 02/22/2003
Inorganic Chemistry, Vol. 42, No. 6, 2003 2149

Alvarez et al.
Scheme 1
Scheme 2
Figure 1. Tris(mercaptoimidazolyl)borate (TmR) and bis(mercaptoimid-
azolyl)borate (BmR) ligand systems.
active site of NiFe hydrogenases.10 Interestingly, these
complexes exhibit distorted octahedral geometries with
unprecedented [NiS4H2] cores due to the presence of two
fairly strong Ni‚‚‚H-B interactions. Interested in ascertaining
whether such 3-center-2-electron bonds are a standard
feature in BmR chemistry, and prompted by the fact that poly-
(mercaptoimidazolyl)borates are becoming increasingly at-
tractive ligands in bioinorganic chemistry,11 we set out to
prepare new homoleptic BmR complexes of the group 12
metals. Such an endeavor will allow their coordination
preferences in a sulfur-rich environment to be directly
compared and may also provide insight into the subtle
structural factors that govern the processes whereby certain
cysteine-rich metalloproteins (e.g., zinc metallothioneins)12
undergo conformational changes13 or exchange metal ions
with their heavier group congeners.14 We describe in this
paper the preparation of three new bis(mercaptoimidazolyl)-
borate ligands and the synthesis and structures of several
homoleptic complexes of zinc, cadmium, and mercury.
spectroscopy) in almost quantitative yield (ca. 95%). In a
similar fashion, the new bulkier bis(mercaptoimidazolyl)-
borate derivatives Na[BmR] (R ) Bz, But, p-Tol) were also
obtained in 70-90% yield starting from the appropriate
2-mercapto-1-alkylimidazoles. Although repeated attempts
to obtain satisfactory elemental analyses (CHN) for these
compounds have not been successful, they are all sufficiently
pure for further reactions (see later discussion). The yields
in which the Na[BmR] compounds reported here are isolated
compare favorably with those reported for the lithium
derivatives Li[BmR] (R ) Me, 54%; R ) Mes, 70%).7
Perhaps more importantly, a potential advantage of the
Na[BmR] salts over the latter is the ease with which the
sodium halide byproducts can be separated from metathetical
reactions involving metal halides. Na[BmR] (R ) Me, Bz,
But, p-Tol) species are all white, thermally robust, air-stable
solids, only sparingly soluble in toluene but more so in THF,
acetonitrile, dimethyl sulfoxide (DMSO), and methanol. In
addition, the p-tolyl-substituted derivative is soluble in
dichloromethane, Na[BmR] (R ) Bz, But) species are soluble
in chloroform, and the methyl- and tert-butyl-substituted
species are soluble (and stable!) in water. All four Na[BmR]
compounds are spectroscopically similar to the lithium
species Li[BmR],7 featuring also two peaks between 6.7 and
Results and Discussion
The sodium salt of the bis(2-mercapto-1-methylimid-
azolyl)borate anion [BmMe]- was readily prepared from
NaBH4 and 2 molar equiv of 2-mercapto-1-methylimidazole
(methimazole) in refluxing tetrahydrofuran (THF), as il-
lustrated in Scheme 1.15 After partial evaporation of the
solvent and addition of pentane, the desired product was
1
isolated in spectroscopically pure form (i.e., by H NMR
(9) Some complexes containing alkylbis(mercaptoimidazolyl)borate ligands
[H(R)B(mimMe)2]- have also been recently synthesized. See ref 8b
and the following: Garcia, R.; Paulo, A.; Domingos, A.; Santos, I. J.
Organomet. Chem. 2001, 632, 41-48.
(10) Alvarez, H. M.; Krawiec, M.; Donovan-Merkert, B. T.; Fouzi, M.;
Rabinovich, D. Inorg. Chem. 2001, 40, 5736-5737.
(11) See for example refs 2, 10, and the following: (a) Kimblin, C.;
Bridgewater, B. M.; Churchill, D. G.; Parkin, G. Chem. Commun.
1999, 2301-2302. (b) Bridgewater, B. M.; Parkin, G. J. Am. Chem.
Soc. 2000, 122, 7140-7141. (c) Bridgewater, B. M.; Fillebeen, T.;
Friesner, R. A.; Parkin, G. J. Chem. Soc., Dalton Trans. 2000, 4494-
4496. (d) Tesmer, M.; Shu, M.; Vahrenkamp, H. Inorg. Chem. 2001,
40, 4022-4029.
(12) (a) Stillman, M. J. Coord. Chem. ReV. 1995, 144, 461-511. (b)
Nordberg, M. Talanta 1998, 46, 243-254. (c) Vasa´k, M.; Ka¨gi, J. H.
R. In Encyclopedia of Inorganic Chemistry; King, R. B., Ed.; John
Wiley & Sons: New York, 1994; Vol. 4, pp 2229-2241.
(13) Yamamura, T.; Watanabe, T.; Kikuchi, A.; Yamane, T.; Ushiyama,
M.; Hirota, H. Inorg. Chem. 1997, 36, 4849-4859.
1
7.2 ppm for the imidazolyl hydrogens in their H NMR
spectra and usually two distinctive bands of medium intensity
in the 2300-2400 cm-1 range (νB-H) in their solid-state IR
spectra.
The bis(mercaptoimidazolyl)borate complex Zn[BmMe
]
2
was easily obtained by mixing aqueous solutions of zinc(II)
bromide and Na[BmMe] (1:2 ratio) and isolated in pure form
(14) (a) Romero-Isart, N.; Vasa´k, M. J. Inorg. Biochem. 2002, 88, 388-
396. (b) Vasak, M.; Bogumil, R. In Cytotoxic, Mutagenic and
Carcinogenic Potential of HeaVy Metals Related to Human EnViron-
ment; Hadjiliadis, N. D., Ed.; Kluwer Academic Publishers: Boston,
MA, 1997; pp 195-215.
(15) The use of higher boiling point solvents (e.g., toluene) invariably
resulted in the formation of a mixture of Na[BmMe] and Na[TmMe],
even if shorter reactions times are used.
2150 Inorganic Chemistry, Vol. 42, No. 6, 2003

Homoleptic Group 12 Bis(mercaptoimidazolyl)borates
as a white solid in 75% yield. This represents a tangible
improvement over the reported three-step synthesis of
Zn[BmMe]2 (Scheme 2)7 which was, prior to our work, the
only known homoleptic bis(mercaptoimidazolyl)borate com-
plex of the group 12 metals. As an extension of our more
general method, all the M[BmR]2 complexes (M ) Zn, Cd,
Hg; R ) Me, Bz, But, p-Tol) were similarly prepared by
combining aqueous or methanolic solutions of the metal
dihalides MX2 (X ) Cl, Br, or I) with 2 equiv of the
appropriate Na[BmR] reagents (eq 1) and isolated in yields
ranging from 35% to 80%. Most significantly, the four
Figure 2. Molecular structure of Cd[BmMe]2. Selected bond lengths (Å)
and angles (deg): Cd1-S1 2.5089(13), Cd1-S2 2.5716(11), Cd1-H 2.582,
S1-C1 1.735(4), S2-C5 1.708(5); S1-Cd-S1A 114.55(6), S1-Cd1-
S2A 104.31(4), S1-Cd1-S2 119.21(4), S2-Cd1-S2A 94.34(5).
M[BmR]2 triads represent the first complete series of bis-
(mercaptoimidazolyl)borate complexes to be isolated for any
group in the periodic table and include also the first such
derivatives for both cadmium and mercury.
All 12 M[BmR]2 complexes are white, air-stable, dia-
magnetic solids, insoluble in water and only marginally
soluble in methanol. However, they tend to be moderately
soluble in THF and halogenated hydrocarbons and more
soluble in acetone, acetonitrile, and DMSO.16 Unlike the zinc
and cadmium complexes, the mercury compounds are
moderately light-sensitive so their syntheses were performed
in the dark by using glassware wrapped in aluminum foil.
They were all characterized by elemental analyses (CHN)
and IR and multinuclear NMR spectroscopies. For example,
1H NMR data for all the complexes are qualitatively very
similar to those of the corresponding free ligands, with only
modest downfield chemical shifts (0.1-0.5 ppm) observed
for the imidazolyl hydrogens in every case. Likewise,
downfield shifts of up to 6.8 ppm for the imidazolyl carbons
in their 13C NMR spectra were measured upon complexation
to the metals. However, upfield chemical shifts of between
3.8 and 10.4 ppm were found for the thione carbons, a
phenomenon also verified for the tris(mercaptoimidazolyl)-
borate derivatives [TmtBu]MBr (M ) Zn, Cd, Hg)5 and
various other group 12 metal thione complexes.17
Figure 3. Molecular structure of Zn[BmtBu]2. Selected bond lengths (Å)
and angles (deg): Zn-S(11) 2.389(3), Zn-S(12) 2.350(2), Zn-S(21)
2.333(2), Zn-S(22) 2.372(2), Zn‚‚‚H(12) 2.81(7), Zn‚‚‚H(22) 2.47(7),
Zn‚‚‚B(1) 3.445(10), Zn‚‚‚B(2) 3.230(11), S(11)-C(11) 1.737(8), S(12)-
C(18) 1.738(8), S(21)-C(21) 1.735(8), S(22)-C(28) 1.715(7); S(21)-Zn-
S(12) 114.61(9), S(21)-Zn-S(22) 115.82(9), S(12)-Zn-S(22) 116.83(9),
S(21)-Zn-S(11) 109.77(9), S(12)-Zn-S(11) 105.70(9), S(22)-Zn-S(11)
90.52(8), S(21)-Zn-H(22) 71.0(17), S(12)-Zn-H(22) 78.6(18), S(22)-
Zn-H(22) 84.2(18), S(11)-Zn-H(22) 174.4(18), S(21)-Zn-H(12) 66.4(15),
S(12)-Zn-H(12) 64.1(15), S(22)-Zn-H(12) 175.6(15), S(11)-Zn-H(12)
85.1(15), H(22)-Zn-H(12) 100(2).
The molecular structure of Cd[BmMe]2 and those of the
three tert-butyl derivatives M[BmtBu]2 (M ) Zn, Cd, Hg)
have been determined by single-crystal X-ray diffraction
(Figures 2-5). The four isostructural complexes (also
isomorphous for M ) Zn, Hg) present in the solid state
distorted tetrahedral geometries in which a central [MS4] core
is supplemented by two adjacent M‚‚‚H-B interactions of
varying strength (see description later). Unlike the structure
of the closely related nickel compound Ni[BmMe]2,10 whose
geometry is better regarded as distorted octahedral (S-Ni-S
trans ≈ 173°), the S-M-S bond angles in Cd[BmMe]2 and
M[BmtBu]2 (M ) Zn, Cd, Hg) span the approximate range
85-124° and imply an overall geometry much closer to
tetrahedral. The aforementioned 3-center-2-electron M‚‚‚
H-B bonds,18 akin to the better-known “agostic” M‚‚‚H-C
interactions found in metal alkyl complexes,19 are prece-
dented in bis(pyrazolyl)borate (BpRR′) chemistry.20 However,
(16) An interesting exception to these solubility trends is provided by the
M[Bmp-Tol]2 (M ) Zn, Cd) compounds which, unlike their mercury
counterpart, are soluble in benzene.
(17) (a) Bell, N. A.; Branston, T. N.; Clegg, W.; Creighton, J. R.; Cucurull-
Sa´nchez, L.; Elsegood, M. R. J.; Raper, E. S. Inorg. Chim. Acta 2000,
303, 220-227. (b) Popovic, Z.; Matkovic-Calogovic, D.; Soldin, Z.;
Pavlovic, G.; Davidovic, N.; Vikic-Topic, D. Inorg. Chim. Acta 1999,
294, 35-46. (c) Popovic, Z.; Soldin, Z.; Matkovic-Calogovic, D.;
Pavlovic, G.; Rajic, M.; Giester, G. Eur. J. Inorg. Chem. 2002, 171-
180.
(18) For an enlightening introduction to the coordination chemistry of B-H
and other X-H bonds (X ) N, P, S) see: Kubas, G. J. Metal
Dihydrogen and σ-Bond Complexes; Kluwer Academic/Plenum Pub-
lishers: New York, 2001; Chapter 13, pp 417-439.
(19) (a) Brookhart, M.; Green, M. L. H. J. Organomet. Chem. 1983, 250,
395-408. (b) Brookhart, M.; Green, M. L. H.; Wong, L.-L. Prog.
Inorg. Chem. 1988, 36, 1-124.
Inorganic Chemistry, Vol. 42, No. 6, 2003 2151

Alvarez et al.
Table 1. M‚‚‚H-B Interactions in BmR Complexes
complex
d(M‚‚‚H)/Å
d(M‚‚‚B)/Å
reference
{Li[BmMes]}2
1.86, 2.34
1.65
1.86
2.06
1.77
2.80, 3.09
2.83
2.86
2.94
2.88
7
8a
10
7
7
7
7
this work
this work
this work
this work
7
[BmMe]Tc(CO)3
Ni[BmMe
]
2
[BmMe]ZnI
[BmMe]ZnMe
[BmMes]Zn(NO3)
1.93
3.51
2.82
3.78
Zn[BmMe
]
]
2
Zn[BmtBu
2.47, 2.81
2.58
2.49, 2.73
2.62, 3.09
2.69
3.23, 3.45
3.36
3.22, 3.39
3.36, 3.59
3.50
2
Cd[BmMe
Cd[BmtBu
Hg[BmtBu
]
2
]
2
]
2
{Tl[BmMe]}x
substituents in the 3-position of the imidazolyl rings in
Zn[BmtBu]2 results in a measurable change in geometry
relative to Zn[BmMe]2 highlights the impact that remote bulky
substituents may have on the metal’s immediate coordination
sphere and geometry.
Figure 4. Molecular structure of Cd[BmtBu]2. Selected bond lengths (Å)
and angles (deg): Cd-S(11) 2.5407(9), Cd-S(12) 2.5646(9), Cd-S(21)
2.5356(8), Cd-S(22) 2.5954(8), Cd‚‚‚H(1) 2.73(3), Cd‚‚‚H(4) 2.49(3),
S(11)-C(11) 1.732(3), S(12)-C(18) 1.718(3), S(21)-C(21) 1.719(3),
S(22)-C(28) 1.716(3); S(11)-Cd-S(12) 111.87(3), S(11)-Cd-S(22)
114.13(3), S(12)-Cd-S(22) 85.12(3), S(21)-Cd-S(11) 116.44(3), S(21)-
Cd-S(22) 114.30(3), S(21)-Cd-S(12) 110.83(3), H(4)-Cd-S(21) 72.2(7),
H(4)-Cd-S(11) 76.3(7), H(4)-Cd-S(12) 167.0(7), H(4)-Cd-S(22)
82.2(7), S(21)-Cd-H(1) 78.9(6), S(11)-Cd-H(1) 67.1(6), S(12)-Cd-
H(1) 77.7(6), S(22)-Cd-H(1) 161.4(7), H(4)-Cd-H(1) 115.2(9).
The Zn-S bond lengths in Zn[BmtBu]2 (average ) 2.361
Å) are only marginally longer than those in Zn[BmMe]2
(average ) 2.337 Å)7 or other BmR derivatives of zinc,
including [BmMes]Zn(NO3) and [BmMe]ZnI (averages ) 2.268
and 2.290 Å, respectively).7 However, they are within the
values found in a variety of zinc tris(mercaptoimidazolyl)-
borate complexes, typically in the narrow range 2.32-2.37
Å.22 Moreover, the Zn‚‚‚H bond distances in Zn[BmtBu
]
2
(2.47 and 2.81 Å) are clearly longer than the corresponding
values observed in [BmMe]ZnX (1.77 and 2.06 Å for X )
Me and I, respectively), an indication of the relative weakness
of the two Zn‚‚‚H-B interactions. Nevertheless, both values
are smaller than either the sum of van der Waals radii of Zn
and H (ca. 3.25 Å)23 or the Zn‚‚‚H separation in Zn[BmMe]2
(3.51 Å).7 The careful evaluation of M‚‚‚H (or M‚‚‚B)
distances and S-M-S bond angles (or the deviation from
ideal tetrahedral values thereof) may be the simplest way of
assessing the strength of M‚‚‚H-B interactions in these types
of complexes. As exemplified for zinc bis(mercaptoimid-
azolyl)borate complexes, for which the largest number of
[BmR]- derivatives have been structurally characterized (see
Table 1), Zn‚‚‚H-B interactions may be classified as strong
if d(Zn‚‚‚H) e 2.00 Å, weak if 2.00 < d(Zn‚‚‚H) < 3.25 Å,
or negligible/nonexistent if d(Zn‚‚‚H) g 3.25 Å. The value
2.00 Å was chosen as the upper limit for “strong” Zn‚‚‚H-B
interactions since the Zn‚‚‚H distances for such fragments
Figure 5. Molecular structure of Hg[BmtBu]2. Selected bond lengths (Å)
and angles (deg): Hg-S(11) 2.5919(8), Hg-S(12) 2.5557(7), Hg-S(21)
2.5526(7), Hg-S(22) 2.5374(7), Hg‚‚‚H(1) 3.09(3), Hg‚‚‚H(4) 2.62(3),
S(11)-C(11) 1.735(3), S(12)-C(18) 1.736(3), S(21)-C(21) 1.723(3),
S(22)-C(28) 1.730(3); S(22)-Hg-S(21) 112.23(3), S(22)-Hg-S(12)
110.50(2), S(21)-Hg-S(12) 123.89(3), S(22)-Hg-S(11) 112.94(3), S(21)-
Hg-S(11) 94.77(2), S(12)-Hg-S(11) 100.40(3), S(22)-Hg-H(4) 70.4(6),
S(21)-Hg-H(4) 79.0(6), S(12)-Hg-H(4) 82.8(6), S(11)-Hg-H(4) 173.8(6),
S(22)-Hg-H(1) 66.3(5), S(21)-Hg-H(1) 174.2(5), S(12)-Hg-H(1)
61.1(5), S(11)-Hg-H(1) 81.0(5), H(4)-Hg-H(1) 105.2(8).
(21) Analogous M‚‚‚H-B contacts are also present in some TmR
complexes21a-d and in the related bis(mercaptoimidazolyl)(pyrazolyl)-
borate complexes M[pzBmMe
]
2
(M ) Co, Cd).21e See: (a) Santini,
C.; Gioia Lobbia, G.; Pettinari, C.; Spagna, R.; Pellei, M.; Vallorani,
F. Inorg. Chim. Acta 1999, 285, 81-88. (b) Gioia Lobbia, G.; Pettinari,
C.; Santini, C.; Somers, N.; Skelton, B. W.; White, A. H. Inorg. Chim.
Acta 2001, 319, 15-22. (c) Bridgewater, B. M.; Parkin, G. Inorg.
Chem. Commun. 2000, 3, 534-536. (d) Kimblin, C.; Churchill, D.
G.; Bridgewater, B. M.; Girard, J. N.; Quarless, D. A.; Parkin, G.
Polyhedron 2001, 20, 1891-1896. (e) Kimblin, C.; Bridgewater, B.
M.; Churchill, D. G.; Hascall, T.; Parkin. G. Inorg. Chem. 2000, 39,
4240-4243.
such a bonding motif appears to be preValent in the
coordination chemistry of BmR ligands (Table 1).21
For comparison purposes, included in Table 1 is the zinc
complex Zn[BmMe]2 already mentioned, which has a structure
devoid of any significant Zn‚‚‚H-B interactions, has a more
limited range of S-Zn-S bond angles (ca. 101-116°), and
can therefore be described as only slightly distorted tetra-
hedral. The observation that the presence of tert-butyl
(22) (a) See refs 2, 4, 5, and 11c,d. (b) Bakbak, S.; Bhatia, V. K.; Incarvito,
C. D.; Rheingold, A. L.; Rabinovich, D. Polyhedron 2001, 20, 3343-
3348.
(23) Calculated from the van der Waals radii of H (1.20 Å) and Zn (2.05
Å), with the latter value estimated by adding 0.80 Å to its metallic
radius. See: Pauling, L. The Nature of the Chemical Bond, 3rd ed.;
Cornell University Press: Ithaca, NY, 1960; pp 256, 260, and 263.
(20) See for example: Belderra´ın, T. R.; Paneque, M.; Carmona, E.;
Gutie´rrez-Puebla, E.; Monge, M. A.; Ruiz-Valero, C. Inorg. Chem.
2002, 41, 425-428 and references therein.
2152 Inorganic Chemistry, Vol. 42, No. 6, 2003

Homoleptic Group 12 Bis(mercaptoimidazolyl)borates
in the Cambridge Structural Database are in the range 1.73-
1.98 Å.24
mediate the transfer and exchange of metal ions in a variety
of zinc-containing biomolecules.
With regards to the cadmium compounds, the Cd-S bond
lengths in Cd[BmR]2 (averages ) 2.541 and 2.559 Å for R
) Me and But, respectively) are within the 2.48-2.60 Å
range observed for the corresponding values in [TmR]CdX
complexes.25 The Cd‚‚‚H bond distances in these compounds
(2.58 Å for R ) Me, 2.49 and 2.73 Å for R ) But) are
comparable to those in M[pzBmMe]2 (2.55 and 2.58 Å)21e
but significantly longer than those in the only other two
compounds with such interactions that appear in the Cam-
Experimental Section
General Considerations. All reactions were performed in the
air except for the syntheses of the Na[BmR] compounds, which
were carried out under argon using a combination of high-vacuum
and Schlenk techniques.29 Solvents were purified and degassed by
standard procedures, and all commercially available reagents,
including methimazole (Acros), were used as received. The
2-mercapto-1-alkylimidazoles HmimR (R ) Bz, But, p-Tol) were
prepared by the acid-catalyzed cyclization of aminoacetaldehyde
diethyl acetal [H2NCH2CH(OEt)2] and the appropriate alkylisothio-
cyanates (RNCS) following literature procedures.30 1H and 13C
NMR spectra were obtained on General Electric QE 300 or Varian
Gemini (300 MHz) FT spectrometers. Chemical shifts are reported
in ppm relative to SiMe4 (δ ) 0 ppm) and were referenced internally
with respect to the solvent resonances (1H: δ 2.49 for d5-DMSO,
7.24 for CHCl3. 13C: δ 39.5 for DMSO, 77.0 for CDCl3); coupling
constants are given in hertz. IR spectra were recorded as KBr pellets
on Bio-Rad 175C FT or Thermo Mattson Satellite 3000 FT-IR
spectrophotometers and are reported in wavenumbers (cm-1);
relative intensities of the absorptions are indicated in parentheses
(vs ) very strong, s ) strong, m ) medium, w ) weak, sh )
shoulder). Elemental analyses were determined by Atlantic Micro-
lab, Inc. (Norcross, GA).
bridge Structural Database,24 namely [TpMe ]Cd(BH4) (1.973
2
and 2.126 Å)26 and the anionic cadmaborane [Cd(B9H13)2]2
-
(2.213-2.314 Å).27 Similarly, the average Hg-S bond
distance in Hg[BmtBu]2 (2.560 Å) is comparable to the
corresponding values in the only two known [TmR]HgBr
complexes (averages: 2.579 and 2.573 Å for R ) Me and
But, respectively).4,5 However, the strength of the Hg‚‚‚H
contacts in Hg[BmtBu]2 (2.62 and 3.09 Å) is even harder to
quantify: there are no complexes with Hg‚‚‚H-B interac-
tions in the Cambridge Structural Database.24 Nevertheless,
we note that the M‚‚‚H distances in all these cadmium and
mercury complexes are still within the sum of van der Waals
radii of the pertinent atoms (ca. 3.41 and 3.44 Å for Cd‚‚‚H
and Hg‚‚‚H, respectively).
Synthesis of Na[BmMe]. A stirred suspension of NaBH4 (0.500
g, 13.217 mmol) and 2-mercapto-1-methylimidazole (3.018 g,
26.434 mmol) in THF (40 mL) was refluxed for 18 h under an
atmosphere of argon. The resulting slightly cloudy solution was
allowed to cool to room temperature and filtered, and the clear
filtrate was concentrated under reduced pressure to ca. 5 mL, leading
to the formation of a white precipitate. After addition of pentane
(40 mL), the product was isolated by filtration, washed with pentane
(2 × 30 mL), and dried in vacuo for 5 h (3.350 g, 97%). Mp )
220 °C (dec). NMR data (in d6-DMSO): 1H δ 3.33 (s, 6 H, CH3),
Conclusions
In summary, the convenient preparation of Na[BmMe] and
three new bulkier [BmR]- ligands (R ) Bz, But, p-Tol)
expands considerably the range of bis(mercaptoimidazolyl)-
borate ligands available. While this ligand system has been
used in recent years to model the active sites in certain
metalloenzymes (e.g., hydrogenases, alcohol dehydro-
genases), it is also bound to become increasingly attractive
in the study of sulfur-rich proteins such as metallothioneins
and rubredoxins. We have prepared the first four complete
series of homoleptic complexes M[BmR]2 for any given group
in the periodic table, including the first bis(mercaptoimid-
azolyl)borate complexes of both cadmium and mercury.
Cd[BmMe]2 and M[BmtBu]2 (M ) Zn, Cd, Hg) display in the
solid state distorted tetrahedral structures with two ancillary
M‚‚‚H-B interactions, a bonding feature that appears to be
widespread in BmR chemistry. Furthermore, we are currently
extending our work to other metals and have recently verified
that such interactions are also present in related transition
metal derivatives M[BmR]2 (M ) Mn, Fe, Co).28 The
observation that bulky ligands (e.g., [BmtBu]-) are capable
of inducing zinc to expand its coordination number from four
to six (i.e., [ZnS4] to [ZnS4H2]) is particularly significant in
the context of the processes whereby octahedral species could
3
3
6.71 (d, JH-H ) 1.8, 2 H, imidazole H), 6.97 (d, JH-H ) 1.8, 2
H, imidazole H), H2B not located; 13C δ 33.7 (q, JC-H ) 139, 2
1
C, CH3), 115.3 (d, 1JC-H ) 190, 2 C, imidazole C), 123.7 (d, 1JC-H
) 190, 2 C, imidazole C), 163.3 (s, 2 C, CdS). IR data: 3118
(m), 3081 (w), 2939 (w), 2456 (m), 2415 (w), 2358 (w), 2282 (w),
2239 (w), 1656 (w), 1618 (w), 1560 (m), 1455 (s), 1417 (m), 1378
(s), 1319 (w), 1299 (w), 1198 (s), 1165 (w), 1123 (s), 1084 (w),
1040 (w), 968 (w), 886 (w), 870 (w), 759 (w), 733 (s), 697 (w),
682 (w), 649 (w), 621 (w), 521 (w), 503 (w), 452 (w).
Synthesis of Zn[BmMe]2. A stirred solution of ZnBr2 (0.086 g,
0.381 mmol) in H2O (15 mL) was treated with a solution of
Na[BmMe] (0.200 g, 0.763 mmol) in the same solvent (15 mL),
resulting in the formation of a white precipitate. The suspension
was stirred for 15 min, and the product was isolated by filtration
and dried in vacuo for 18 h (0.156 g, 75%). Mp ) 306 °C (dec).
NMR data (in d6-DMSO): 1H δ 3.30 (s, 12 H, CH3), 7.17 (s, 4 H,
imidazole H), 7.21 (s, 4 H, imidazole H), H2B not located; 13C δ
1
1
34.5 (q, JC-H ) 141, 4 C, CH3), 120.3 (d, JC-H ) 193, 4 C,
(24) CSD, version 5.22; October 2001. Allen, F. H.; Kennard, O. 3D Search
and Research Using the Cambridge Structural Database. Chem. Des.
Automat. News 1993, 8, 1, 31-37.
(29) (a) Errington, R. J. AdVanced Practical Inorganic and Metalorganic
Chemistry; Blackie Academic & Professional: London, 1997. (b)
Experimental Organometallic Chemistry; Wayda, A. L., Darensbourg,
M. Y., Eds.; American Chemical Society: Washington, DC, 1987.
(c) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-SensitiVe
Compounds, 2nd ed.; Wiley-Interscience: New York, 1986.
(30) (a) Matsuda, K.; Yanagisawa, I.; Isomura, Y.; Mase, T.; Shibanuma,
T. Synth. Commun. 1997, 27, 3565-3571. (b) Cassidy, C. S.;
Reinhardt, L. A.; Cleland, W. W.; Frey, P. A. J. Chem. Soc., Perkin
Trans. 2 1999, 635-641.
(25) See refs 3, 4, 5, and 22b.
(26) Reger, D. L.; Mason, S. S.; Rheingold, A. L. J. Am. Chem. Soc. 1993,
115, 10406-10407.
(27) Littger, R.; Englich, U.; Spencer, J. T. Inorg. Chem. 1997, 36, 6434-
6436.
(28) Alvarez, H. M.; Richter, M. A.; Tran, T. B.; Churchill, D. G.; Tanski,
J. M.; Rheingold, A. L.; Rabinovich, D. Manuscript in preparation.
Inorganic Chemistry, Vol. 42, No. 6, 2003 2153

Alvarez et al.
imidazole C), 124.1 (d, 1JC-H ) 201, 4 C, imidazole C), 152.8 (s,
4 C, CdS). IR data: 3147 (m), 3120 (m), 3083 (w), 2946 (w),
2493 (w), 2395 (m), 2291 (w), 1556 (m), 1459 (s), 1412 (m), 1379
(s), 1327 (w), 1302 (w), 1188 (s), 1171 (s), 1129 (s), 1086 (w),
1042 (w), 699 (w), 687 (w), 648 (w), 601 (w), 508 (w), 451 (w).
Anal. Calcd for C16H24B2N8S4Zn: C, 35.4; H, 4.5; N, 20.6.
Found: C, 35.5; H, 4.2; N, 20.5%.
Na[BmBz] (0.200 g, 0.483 mmol) in a mixture of water (8 mL) and
methanol (3 mL), resulting in the formation of a white precipitate.
The suspension was stirred for 15 min, and the product was isolated
by filtration and dried in vacuo for 2 h (0.130 g, 63%). Mp ) 230
°C (dec). NMR data (in d6-DMSO): 1H δ 3.47 (br s, 4 H, H2B),
5.00 (s, 8 H, CH2C6H5), 7.20 (s, 4 H, imidazole H), 7.22 (s, 4 H,
1
imidazole H), 7.27 (m, 20 H, CH2C6H5); 13C δ 51.2 (t, JC-H
)
1
Synthesis of Cd[BmMe]2. A stirred solution of CdCl2 (0.105 g,
0.572 mmol) in H2O (15 mL) was treated with a solution of
Na[BmMe] (0.300 g, 1.144 mmol) in the same solvent (15 mL),
resulting in the formation of a white precipitate. The suspension
was stirred for 15 min, and the product was isolated by filtration
and dried in vacuo for 18 h (0.245 g, 72%). Mp ) 273 °C. NMR
data (in d6-DMSO): 1H δ 3.49 (s, 12 H, CH3), 6.98 (s, 4 H,
imidazole H), 7.19 (s, 4 H, imidazole H), H2B not located; 13C δ
140, 4 C, CH2), 117.8 (d, JC-H ) 194, 4 C, imidazole C), 124.6
(d, JC-H ) 195, 4 C, imidazole C), 127.9 (d, JC-H ) 161, 4 C,
Cp in Bz), 128.2 (d, JC-H ) 159, 8 C, Co or Cm in Bz), 128.6 (d,
1
1
1
1JC-H ) 161, 8 C, Co or Cm in Bz), 136.0 (s, 4 C, Cipso in Bz),
155.4 (s, 4 C, CdS). IR data: 3156 (w), 3127 (w), 3062 (w), 3030
(w), 2932 (w), 2483 (m), 2399 (m), 2632 (m), 1558 (w), 1497 (w),
1453 (s), 1429 (m), 1399 (vs), 1356 (m), 1340 (w), 1288 (w), 1216
(m), 1171 (w), 1150 (vs), 1122 (s), 1080 (w), 1060 (w), 1029 (w),
782 (w), 718 (vs), 695 (w), 580 (w), 505 (w), 419 (w). Anal. Calcd
for C40H40B2N8S4Zn: C, 56.7; H, 4.8; N, 13.2. Found: C, 56.4; H,
4.5; N, 13.2%.
1
1
34.6 (q, JC-H ) 141, 4 C, CH3), 120.2 (d, JC-H ) 197, 4 C,
imidazole C), 123.3 (d, 1JC-H ) 195, 4 C, imidazole C), 154.1 (s,
4 C, CdS). IR data: 3160 (w), 3123 (w), 2946 (w), 2407 (m),
2355 (w), 1558 (m), 1458 (s), 1416 (m), 1381 (vs), 1325 (w), 1301
(w), 1193 (s), 1166 (m), 1120 (s), 1087 (w), 1039 (w), 1014 (w),
875 (w), 730 (s), 696 (w), 680 (w), 645 (w), 516 (w), 501 (w), 454
(w), 419 (w). Anal. Calcd for C16H24B2CdN8S4: C, 32.5; H, 4.1;
N, 19.0. Found: C, 32.6; H, 4.3; N, 18.8%.
Synthesis of Cd[BmBz]2. A stirred solution of CdCl2 (0.044 g,
0.241 mmol) in H2O (10 mL) was treated with a solution of
Na[BmBz] (0.200 g, 0.483 mmol) in a mixture of water (10 mL)
and methanol (4 mL), resulting in the formation of a white
precipitate. The suspension was stirred for 15 min and the product
was isolated by filtration and dried in vacuo for 8 h (0.131 g, 61%).
Mp ) 96 °C (dec). NMR data (in d6-DMSO): 1H δ 3.60 (br s, 4
Synthesis of Hg[BmMe]2. In the absence of light, a stirred
solution of HgI2 (0.173 g, 0.381 mmol) in methanol (10 mL) was
treated with a solution of Na[BmMe] (0.200 g, 0.763 mmol) in the
same solvent (15 mL), resulting in the formation of a white
precipitate. The suspension was stirred for 10 min, and the product
was isolated by filtration and dried in vacuo for 4 h (0.195 g, 75%).
Mp ) 150 °C. NMR data (in d6-DMSO): 1H δ 3.34 (s, 12 H, CH3),
7.16 (s, 4 H, imidazole H), 7.18 (s, 4 H, imidazole H), H2B not
H, H2B), 5.22 (s, 8 H, CH2C6H5), 7.03 (s, 4 H, imidazole H), 7.20-
1
7.35 (m, 24 H, imidazole H + CH2C6H5); 13C δ 50.0 (t, JC-H
)
1
141, 4 C, CH2), 119.2 (d, JC-H ) 197, 4 C, imidazole C), 123.9
(d, JC-H ) 195, 4 C, imidazole C), 127.4 (d, JC-H ) 158, 4 C,
Cp in Bz), 127.5 (d, JC-H ) 158, 8 C, Co or Cm in Bz), 128.4 (d,
1
1
1
1JC-H ) 161, 8 C, Co or Cm in Bz), 136.5 (s, 4 C, Cipso in Bz),
154.7 (s, 4 C, CdS). IR data: 3160 (w), 3130 (w), 3083 (w), 3062
(w), 3031 (w), 2929 (w), 2403 (m), 2362 (m), 1559 (m), 1496 (m),
1450 (s), 1427 (m), 1401 (vs), 1358 (w), 1338 (m), 1262 (w), 1220
(m), 1174 (m), 1149 (s), 1114 (s), 1079 (w), 1059 (w), 1029 (w),
960 (w), 875 (w), 806 (w), 779 (w), 722 (vs), 682 (w), 574 (w),
516 (w), 504 (w). Anal. Calcd for C40H40B2CdN8S4: C, 53.7; H,
4.5; N, 12.5. Found: C, 52.9; H, 4.4; N, 12.2%.
located; 13C δ 34.7 (q, 1JC-H ) 141, 4 C, CH3), 120.4 (d, 1JC-H
)
197, 4 C, imidazole C), 124.3 (d, 1JC-H ) 195, 4 C, imidazole C),
152.9 (s, 4 C, CdS). IR data: 3152 (w), 3150 (w), 3123 (w), 3115
(w), 3082 (w), 2945 (w), 2500 (m), 2402 (m), 2360 (m), 2287 (w),
1551 (s), 1457 (s), 1411 (m), 1375 (s), 1326 (m), 1297 (m), 1187
(vs), 1170 (vs), 1123 (vs), 1087 (w), 1041 (w), 1014 (w), 763 (w),
751 (m), 723 (vs), 718 (vs), 648 (w), 600 (w), 505 (m), 451 (m).
Anal. Calcd for C16H24B2HgN8S4: C, 28.3; H, 3.6; N, 16.5.
Found: C, 28.1; H, 3.7; N, 16.2%.
Synthesis of Hg[BmBz]2. In the absence of light, a stirred solution
of Na[BmBz] (0.150 g, 0.362 mmol) in methanol (8 mL) was treated
with a solution of HgI2 (0.049 g, 0.181 mmol) in the same solvent
(5 mL), resulting in the formation of a white precipitate. The
suspension was stirred for 10 min, and the product was isolated by
filtration and dried in vacuo for 2 h (0.060 g, 36%). Mp ) 169 °C
(dec). NMR data (in d6-DMSO): 1H δ 3.60 (br s, 4 H, H2B), 5.08
(s, 8 H, CH2C6H5), 7.20-7.32 (m, 28 H, imidazole H + CH2C6H5);
13C δ 50.1 (t, 1JC-H ) 142, 4 C, CH2), 119.5 (d, 1JC-H ) 197, 4 C,
imidazole C), 124.7 (d, 1JC-H ) 196, 4 C, imidazole C), 127.4 (d,
1JC-H ) 160, 4 C, Cp in Bz), 127.5 (d, 1JC-H ) 160, 8 C, Co or Cm
in Bz), 128.4 (d, 1JC-H ) 160, 8 C, Co or Cm in Bz), 136.4 (s, 4 C,
Cipso in Bz), 153.6 (s, 4 C, CdS). IR data: 3156 (w), 3126 (w),
3062 (w), 3028 (w), 2938 (w), 2486 (m), 2395 (m), 2360 (m), 2343
(m), 1558 (m), 1496 (w), 1451 (m), 1426 (m), 1395 (s), 1352 (m),
1337 (w), 1285 (w), 1214 (m), 1170 (m), 1147 (s), 1116 (s), 1080
(w), 1063 (w), 1029 (w), 922 (w), 780 (w), 715 (vs), 696 (w), 579
(w), 503 (w), 459 (w). Anal. Calcd for C40H40B2HgN8S4: C, 48.9;
H, 4.1; N, 11.4. Found: C, 48.3; H, 4.0; N, 11.2%.
Synthesis of Na[BmBz]. A stirred suspension of NaBH4 (0.099
g, 2.628 mmol) and 2-mercapto-1-benzylimidazole (1.000 g, 5.256
mmol) in THF (30 mL) was refluxed for 18 h under an atmosphere
of argon. The resulting slightly cloudy solution was allowed to cool
to room temperature and filtered, and the clear filtrate was
concentrated under reduced pressure to ca. 5 mL, leading to the
formation of a white sticky solid. After trituration with pentane
(50 mL) for 2 h, the product was isolated by filtration, washed
with pentane (2 × 30 mL), and dried in vacuo for 2 h (0.746 g,
69%). NMR data (in d6-DMSO): 1H δ 5.15 (s, 4 H, CH2C6H5),
3
3
6.84 (d, JH-H ) 1.8, 2 H, imidazole H), 7.02 (d, JH-H ) 1.8, 2
H, imidazole H), 7.20-7.35 (m, 10 H, CH2C6H5), H2B not located;
13C δ 48.7 (t, 1JC-H ) 141, 2 C, CH2C6H5), 116.1 (d, 1JC-H ) 195,
2 C, imidazole C), 117.8 (d, 1JC-H ) 196, 2 C, imidazole C), 127.2
(d, 1JC-H ) 161, 2 C, Cp in Bz), 127.6 (d, 1JC-H ) 159, 4 C, Co or
1
Cm in Bz), 128.3 (d, JC-H ) 160, 4 C, Co or Cm in Bz), 137.5 (s,
2 C, Cipso in Bz), 161.3 (s, 2 C, CdS). IR data: 3130 (m), 3015
(m), 2921 (m), 2818 (m), 2724 (m), 2360 (m), 2339 (m), 1945
(w), 1602 (w), 1573 (vs), 1542 (w), 1495 (s), 1444 (s), 1273 (m),
1208 (m), 1033 (w), 922 (w), 770 (m), 716 (s), 679 (m), 574 (m),
524 (s), 459 (m).
Synthesis of Zn[BmBz]2. A stirred solution of ZnBr2 (0.054 g,
0.241 mmol) in H2O (15 mL) was treated with a solution of
Synthesis of Na[BmtBu]. A stirred suspension of NaBH4 (0.360
g, 9.516 mmol) and 2-mercapto-1-tert-butylimidazole (2.978 g,
19.059 mmol) in THF (40 mL) was refluxed for 22 h under an
atmosphere of argon. The resulting slightly cloudy solution was
allowed to cool to room temperature and filtered, and the clear
filtrate was concentrated under reduced pressure to ca. 5 mL, leading
2154 Inorganic Chemistry, Vol. 42, No. 6, 2003

Homoleptic Group 12 Bis(mercaptoimidazolyl)borates
to the formation of a white sticky solid. After trituration with
pentane (50 mL) for 3 h, the product was isolated by filtration,
washed with pentane (2 × 30 mL), and dried in vacuo for 2 h
(2.670 g, 81%). Mp ) 260 °C (dec). NMR data (in d6-DMSO):
1H δ 1.68 [s, 36 H, C(CH3)3], 6.74 (d, 3JH-H ) 1.7, 2 H, imidazole
2233(w), 1560 (w), 1481 (w), 1426 (m), 1416 (m), 1398 (w), 1360
(vs), 1299 (w), 1259 (m), 1229 (w), 1199 (s), 1169 (s), 1154 (s),
1122 (s), 1058 (w), 1028 (w), 982 (w), 929 (w), 879 (w), 821 (w),
744 (w), 732 (m), 709 (s), 689 (m), 624 (w), 588 (w), 544 (w),
480 (w). Anal. Calcd for C28H48B2HgN8S4: C, 39.7; H, 5.7; N,
13.2. Found: C, 39.7; H, 5.6; N, 13.2%.
H), 6.96 (d, 3JH-H ) 1.7, 2 H, imidazole H), H2B not located; 13
C
1
Synthesis of Na[Bmp-Tol]. A stirred suspension of NaBH4 (0.099
g, 2.617 mmol) and 2-mercapto-1-p-tolylimidazole (0.960 g, 5.046
mmol) in tetrahydrofuran (30 mL) was refluxed for 20 h under an
atmosphere of argon. The resulting slightly cloudy solution was
allowed to cool to room temperature and filtered, and the clear
filtrate was concentrated under reduced pressure to ca. 10 mL,
leading to the formation of a white sticky solid. After trituration
with pentane (4 × 40 mL) for 2 h, the product was isolated by
filtration, washed with pentane (2 × 30 mL), and dried in vacuo
for 3 h (0.968 g, 93%). Mp ) 205 °C (dec). NMR data (in d6-
DMSO): 1H δ 2.32 (s, 6 H, CH3), 3.39 (br s, 2 H, H2B), 6.90 (d,
3JH-H ) 2.3, 2 H, imidazole H), 7.18 (d, 3JH-H ) 2.3, 2 H, imidazole
δ 28.5 [q, JC-H ) 127, 6 C, C(CH3)3], 57.9 [s, 2 C, C(CH3)3],
114.7 (d, 1JC-H ) 193, 2 C, imidazole C), 120.9 (d, 1JC-H ) 193,
2 C, imidazole C), 158.2 (s, 2 C, CdS). IR data: 3186 (w), 3155
(w), 3141 (w), 3126 (w), 3090 (w), 2977 (s), 2925 (w), 2887 (w),
2397 (m), 2350 (m), 2230 (w), 1577 (w), 1568 (w), 1483 (w), 1411
(s), 1397 (m), 1358 (vs), 1315 (w), 1283 (m), 1257 (m), 1228 (m),
1201 (s), 1165 (s), 1118 (s), 1056 (w), 1026 (w), 970 (w), 927
(w), 914 (w), 884 (w), 819 (w), 803 (w), 744 (m), 704 (s), 682 (s),
593 (w), 588 (w), 550 (w), 527 (w), 488 (w), 482 (w).
Synthesis of Zn[BmtBu]2. A stirred solution of ZnCl2 (0.050 g,
0.367 mmol) in methanol (15 mL) was treated with a solution of
Na[BmtBu] (0.254 g, 0.733 mmol) in water (15 mL), resulting in
the formation of a white precipitate. The suspension was stirred
for 20 min, and the product was isolated by filtration and dried in
vacuo for 1 h (0.160 g, 67%). Mp ) 290 °C (dec). NMR data (in
CDCl3): 1H δ 1.67 [s, 36 H, C(CH3)3], 3.56 (br s, 4 H, H2B), 6.73
3
3
H), 7.21 (d, JH-H ) 8.6, 4 H, Ho or Hm in p-Tol), 7.48 (d, JH-H
1
) 8.6, 4 H, Ho or Hm in p-Tol); 13C δ 20.5 (q, JC-H ) 126, 2 C,
1
C6H4CH3), 115.5 (d, JC-H ) 195, 2 C, imidazole C), 125.2 (d,
1JC-H ) 200, 2 C, imidazole C), 125.5 (d, 1JC-H ) 152, 4 C, Co or
Cm in p-Tol), 128.5 (d, 1JC-H ) 158, 4 C, Co or Cm in p-Tol), 135.6
(s, 2 C, Cp in p-Tol), 137.2 (s, 2 C, Cipso in p-Tol), 163.9 (s, 2 C,
CdS). IR data: 3135 (w), 3036 (w), 2921 (w), 2856 (w), 2732
(w), 2612 (w), 2446 (sh), 2360 (m), 2274 (sh), 2129 (w), 2090
(w), 1902 (w), 1872 (w), 1641 (m), 1615 (m), 1589 (m), 1517 (s),
1422 (s), 1363 (s), 1311 (m), 1264 (m), 1191 (m), 1157 (m), 1119
(m), 1101 (m), 1020 (m), 956 (m), 909 (m), 819 (vs), 733 (s), 712
(s), 682 (s), 605 (m), 571 (s), 506 (w), 476 (w).
3
3
(d, JH-H ) 1.2, 4 H, imidazole H), 6.83 (d, JH-H ) 1.2, 4 H,
imidazole H); 13C δ 29.0 [q, 1JC-H ) 127, 12 C, C(CH3)3], 58.5 [s,
4 C, C(CH3)3], 115.3 (d, 1JC-H ) 193, 4 C, imidazole C), 122.9 (d,
1JC-H ) 193, 4 C, imidazole C), 154.5 (s, 4 C, CdS). IR data:
3182 (w), 3152 (w), 2977 (s), 2929 (m), 2450 (m), 2403 (m), 2360
(m), 1560 (m), 1482 (m), 1430 (s), 1399 (m), 1365 (vs), 1301 (w),
1260 (m), 1200 (s), 1171 (s), 1154 (s), 1123 (s), 1059 (w), 819
(w), 731 (m), 709 (s), 688 (s), 545 (w), 479 (w). Anal. Calcd for
C28H48B2N8S4Zn: C, 47.2; H, 6.8; N, 15.7. Found: C, 47.0; H,
7.0; N, 15.5%.
Synthesis of Zn[Bmp-Tol]2. A stirred solution of ZnCl2 (0.037
g, 0.271 mmol) in water (10 mL) was treated with a solution of
Na[Bmp-Tol] (0.225 g, 0.543 mmol) in aqueous methanol (50% v/v,
20 mL), resulting in the formation of a white precipitate. The
suspension was stirred for 20 min, and the product was isolated by
filtration and dried in vacuo for 2.5 h (0.134 g, 58%). Mp ) 140
°C (dec). NMR data (in d6-DMSO): 1H δ 2.33 (s, 12 H, CH3),
3.52 (br s, 4 H, H2B), 7.0-7.5 (m, 24 H, imidazole H and p-Tol
Synthesis of Cd[BmtBu]2. A stirred solution of CdCl2 (0.066 g,
0.360 mmol) in water (15 mL) was treated with a solution of
Na[BmtBu] (0.250 g, 0.722 mmol) in the same solvent (15 mL),
resulting in the formation of a white precipitate. The suspension
was stirred for 30 min, and the product was isolated by filtration
and dried in vacuo for 90 min (0.216 g, 79%). Mp ) 280 °C (dec).
NMR data (in CDCl3): 1H δ 1.69 [s, 36 H, C(CH3)3], 3.64 (br s,
4 H, H2B), 6.69 (d, 3JH-H ) 2.1, 4 H, imidazole H), 6.83 (d, 3JH-H
H); 13C δ 20.6 (q, 1JC-H ) 127, 4 C, C6H4CH3), 120.9 (d, 1JC-H
205, 4 C, imidazole C), 125.2 (d, 1JC-H ) 199, 4 C, imidazole C),
126.1 (d, 1JC-H ) 163, 8 C, Co or Cm in p-Tol), 129.3 (d, 1JC-H
)
)
) 2.1, 4 H, imidazole H), H2B not located; 13C δ 28.9 [q, 1JC-H
127, 12 C, C(CH3)3], 58.5 [s, 4 C, C(CH3)3], 115.3 (d, JC-H
)
)
1
160, 8 C, Co or Cm in p-Tol), 135.1 (s, 4 C, Cp in p-Tol), 137.8 (s,
4 C, Cipso in p-Tol), 153.6 (s, 4 C, CdS). IR data: 3160 (w), 3135
(w), 3041 (w), 2921 (w), 2861 (w), 2411 (m), 2360 (m), 2279 (w),
1899 (w), 1586 (w), 1559 (m), 1517 (vs), 1435 (s), 1367 (vs), 1311
(m), 1273 (m), 1183 (s), 1161 (vs), 1127 (s), 1110 (m), 1041 (w),
1020 (m), 956 (m), 879 (w), 819 (vs), 733 (m), 710 (s), 688 (s),
641 (w), 598 (m), 564 (s), 504 (m), 418 (m). Anal. Calcd for
C40H40B2N8S4Zn: C, 56.7; H, 4.8; N, 13.2. Found: C, 56.7; H,
4.6; N, 13.2%.
193, 4 C, imidazole C), 122.4 (d, 1JC-H ) 193, 4 C, imidazole C),
155.2 (s, 4 C, CdS). IR data: 3182 (w), 3144 (w), 2976 (m), 2927
(w), 2887 (w), 2394 (m), 2362 (w), 1561 (w), 1482 (w), 1426 (m),
1416 (m), 1397 (w), 1364 (vs), 1298 (w), 1258 (w), 1229 (w), 1199
(s), 1169 (s), 1153 (s), 1120 (s), 1057 (w), 1027 (w), 979 (w), 928
(w), 876 (w), 821 (w), 727 (w), 709 (m), 686 (s), 626 (w), 586
(w), 544 (w), 481 (w). Anal. Calcd for C28H48B2CdN8S4: C, 44.3;
H, 6.4; N, 14.8. Found: C, 44.0; H, 6.5; N, 14.5%.
Synthesis of Hg[BmtBu]2. In the absence of light, a stirred
solution of HgI2 (0.164 g, 0.361 mmol) in water (15 mL) was treated
with a solution of Na[BmtBu] (0.250 g, 0.722 mmol) in the same
solvent (15 mL), resulting in the formation of a white precipitate.
The suspension was stirred for 20 min, and the product was isolated
by filtration and dried in vacuo for 90 min (0.189 g, 62%). Mp )
200 °C (dec). NMR data (in CDCl3): 1H δ 1.66 [s, 36 H, C(CH3)3],
Synthesis of Cd[Bmp-Tol]2. A stirred solution of CdCl2 (0.052
g, 0.284 mmol) in water (15 mL) was treated with a solution of
Na[Bmp-Tol] (0.235 g, 0.567 mmol) in methanol (15 mL), resulting
in the formation of a white precipitate. The suspension was stirred
for 15 min, and the product was isolated by filtration and dried in
vacuo for 3 h (0.173 g, 68%). Mp ) 148 °C (dec). NMR data (in
d6-DMSO): 1H δ 2.34 (s, 12 H, CH3), 3.59 (br s, 4 H, H2B), 7.1-
3
3
1
6.72 (d, JH-H ) 2.1, 4 H, imidazole H), 6.83 (d, JH-H ) 2.1, 4
7.5 (m, 24 H, imidazole H and p-Tol H); 13C δ 20.6 (q, JC-H
)
H, imidazole H), H2B not located; 13C δ 29.0 [q, 1JC-H ) 127, 12
127, 4 C, C6H4CH3), 120.7 (d, JC-H ) 199, 4 C, imidazole C),
1
1
C, C(CH3)3], 58.6 [s, 4 C, C(CH3)3], 115.5 (d, JC-H ) 193, 4 C,
124.5 (d, 1JC-H ) 197, 4 C, imidazole C), 126.1 (d, 1JC-H ) 163,
imidazole C), 122.9 (d, 1JC-H ) 193, 4 C, imidazole C), 154.4 (s,
4 C, CdS). IR data: 3181 (w), 3153 (w), 3143 (w), 2979 (m),
2925 (w), 2442 (w), 2396 (m), 2360 (w), 2291 (w), 2269 (w),
8 C, Co or Cm in p-Tol), 129.3 (d, JC-H ) 161, 8 C, Co or Cm in
1
p-Tol), 135.2 (s, 4 C, Cp in p-Tol), 138.0 (s, 4 C, Cipso in p-Tol),
154.9 (s, 4 C, CdS). IR data: 3165 (w), 3135 (w), 3036 (w), 2921
Inorganic Chemistry, Vol. 42, No. 6, 2003 2155

Alvarez et al.
Table 2. Crystallographic Data for Cd[BmMe]2 and M[BmtBu]2 (M ) Zn, Cd, Hg)
C16H24B2CdN8S4‚Me2SO
C28H48B2N8S4Zn
C28H48B2CdN8S4
C28H48B2HgN8S4
fw
668.82
711.97
759.00
847.19
cryst syst
cryst size, mm3
space group
T, K
tetragonal
0.45 × 0.35 × 0.30
P43212 (No. 96)
150(1)
triclinic
monoclinic
0.36 × 0.24 × 0.24
P21/c (No. 14)
243(2)
triclinic
0.30 × 0.18 × 0.05
P1h (No. 2)
243(2)
0.48 × 0.36 × 0.24
P1h (No. 2)
243(2)
a, Å
b, Å
c, Å
10.503(2)
10.503(2)
26.038(5)
90
90
90
2872.6(8)
4
1.546
11.52
29.7
10.031(4)
10.484(4)
18.559(7)
83.741(7)
78.966(7)
71.408(9)
1813.4(12)
2
1.304
9.39
25.51
6721
10.5846(6)
36.021(2)
10.3516(6)
90
110.799(1)
90
3689.5(4)
4
1.366
10.0007(10)
10.6538(11)
18.9510(18)
81.699(2)
76.592(2)
71.855(2)
1860.7(3)
2
1.512
43.91
28.18
7919
R, deg
â, deg
γ, deg
V, Å3
Z
Dc, g cm-3
µ (Mo KR), cm-1
8.49
28.31
8481
θ
max, deg
no. data
4246
no. params
165
405
0.0988/0.2419
0.1695/0.2843
405
0.0405/0.1022
0.0638/0.1086
405
0.0233/0.0572
0.0280/0.0585
R1/wR2 [I > 2σ(I)]a
R1/wR2 (all data)a
0.0397/0.0421b
0.0479/0.0428b
a R1 ) ∑(|Fo| - |Fc|)/∑|Fo|; wR2 ) {∑[w(Fo - Fc )2]/∑[w(Fo )2}1/2
.
b [I > 3σ(I)].
2
2
2
(w), 2856 (w), 2407 (s), 2279 (w), 1898 (w), 1516 (vs), 1426 (s),
1365 (vs), 1311 (m), 1271 (m), 1182 (s), 1157 (vs), 1021 (m), 957
(m), 875 (w), 818 (s), 731 (m), 709 (s), 684 (s), 599 (m), 562 (s),
502 (w), 468 (w). Anal. Calcd for C40H40B2CdN8S4: C, 53.7; H,
4.5; N, 12.5. Found: C, 53.2; H, 4.2; N, 12.4%.
refined. All calculations were performed using the teXsan crystal-
lographic software package.31
Crystals of M[BmtBu
] (M ) Zn, Cd, Hg) suitable for data
2
collection were selected and mounted with epoxy glue on the tip
of thin glass fibers. Data sets for M[BmtBu]2 (M ) Zn, Cd, Hg)
were collected at 243 K on a Bruker P4 diffractometer equipped
with a SMART CCD detector. Absorption corrections were applied
using SADABS. The structures were solved using direct methods
and standard difference map techniques and were refined by full-
matrix least-squares procedures on F2 with SHELXTL (Version
6.10).32 Hydrogen atoms were included in calculated positions,
except for hydrogen atoms on boron, which were located and refined
isotropically.
Synthesis of Hg[Bmp-Tol]2. A stirred solution of HgCl2 (0.058
g, 0.214 mmol) in methanol (10 mL) was treated with a solution
of Na[Bmp-Tol] (0.177 g, 0.427 mmol) in the same solvent (15 mL),
resulting in the formation of a white precipitate. The suspension
was stirred for 15 min, and the product was isolated by filtration
and dried in vacuo for 2 h (0.112 g, 53%). Mp ) 132 °C (dec).
NMR data (in d6-DMSO): 1H δ 2.33 (s, 12 H, CH3), 3.68 (br s, 4
3
H, H2B), 7.10 (d, JH-H ) 8.1, 8 H, Ho or Hm in p-Tol), 7.20 (d,
3JH-H ) 8.1, 8 H, Ho or Hm in p-Tol), 7.34 (s, 4 H, imidazole H),
1
7.44 (s, 4 H, imidazole H); C δ 20.6 (q, JC-H ) 127, 4 C,
Acknowledgment. We thank Research Corporation for
a Cottrell College Science Award, the donors of the
Petroleum Research Fund, administered by the American
Chemical Society, and The University of North Carolina at
Charlotte for generous support of this research. We are also
indebted to Professor Ged Parkin (Columbia University) for
helpful discussions and his generous help with the X-ray
diffraction studies. T.B.T. is particularly grateful to Project
SEED at the American Chemical Society for a summer
stipend, and M.K. also acknowledges generous financial
support from the National Science Foundation (Grant CHE-
9808165) and Clemson University for the purchase of the
X-ray diffractometer.
1
C6H4CH3), 120.9 (d, JC-H ) 199, 4 C, imidazole C), 125.3 (d,
1JC-H ) 201, 4 C, imidazole C), 126.1 (d, 1JC-H ) 164, 8 C, Co or
Cm in p-Tol), 129.2 (d, 1JC-H ) 160, 8 C, Co or Cm in p-Tol), 135.1
(s, 4 C, Cp in p-Tol), 137.9 (s, 4 C, Cipso in p-Tol), 153.8 (s, 4 C,
CdS). IR data: 3164 (w), 3132 (w), 3039 (w), 2922 (w), 2862
(w), 2435 (m), 2399 (m), 2251 (w), 1904 (w), 1586 (w), 1550 (w),
1518 (s), 1429 (s), 1365 (vs), 1312 (w), 1272 (m), 1184 (s), 1155
(vs), 1123 (s), 1107 (s), 1019 (m), 954 (m), 878 (w), 817 (vs), 733
(m), 709 (s), 681 (m), 636 (w), 600 (m), 560 (s), 499 (w), 467 (w).
Anal. Calcd for C40H40B2HgN8S4: C, 48.9; H, 4.1; N, 11.4.
Found: C, 48.1; H, 4.0; N, 11.0%.
X-ray Structure Determinations. A summary of crystal data
collection and refinement parameters for Cd[BmMe]2 and M[BmtBu
]
2
(M ) Zn, Cd, Hg) is given in Table 2. A crystal of the dimethyl
sulfoxide solvate Cd[BmMe]2‚Me2SO suitable for data collection
was selected and mounted with epoxy glue on the tip of a thin
glass fiber. All measurements were made at 150 K on a Rigaku
AFC8 diffractometer equipped with a Mercury CCD area detector.
The lattice solvent (DMSO) molecule in Cd[BmMe]2‚Me2SO is
disordered around the 2-fold axis with the oxygen atom located on
the axis and the sulfur atom disordered over two sites. An absorption
correction was applied, and the data were corrected for Lorentz
and polarization effects. The structure was solved using direct
methods, expanded with Fourier techniques, and refined by full-
matrix least-squares procedures on F. The non-hydrogen atoms were
refined anisotropically, and hydrogen atoms were included but not
Supporting Information Available: X-ray crystallographic files
in CIF format for the structure determinations of Cd[BmMe]2 and
M[BmtBu]2 (M ) Zn, Cd, Hg). This material is available free of
charge via the Internet at http://pubs.acs.org.
IC025780M
(31) teXsan for Windows (Version 1.06): Crystal Structure Analysis
Package; Molecular Structure Corporation, The Woodlands, TX 77381,
1997-1999.
(32) Sheldrick, G. M. SHELXTL, An Integrated System for SolVing, Refining
and Displaying Crystal Structures from Diffraction Data; University
of Go¨ttingen: Go¨ttingen, Germany, 1981.
2156 Inorganic Chemistry, Vol. 42, No. 6, 2003