Synthesis, characterization, and reactivity of alkyldisulfanido zinc complexes

Article abstract of DOI:10.1021/ic900238v

The alkyldisulfanido zinc complexes Tp^{iPr, iPr}Zn(SSR) and Tp^{Ph, Me}Zn(SSR) where Tp^{iPr, iPr} is hydridotris-((3,5- isopropyl) pyrazolyl)borate, Tp^{Ph, Me} is hydridotris-((3-phenyl, 5-methyl)pyrazolyl)borate, and (SSR) is tert-butyldisulfanido or triphenylmethanedisulfanido were synthesized by reaction between the corresponding hydroxo complexes TpZn(OH) and the synthetic persulfide RSSH. All the complexes were characterized by elemental analysis and ¹H NMR spectroscopy, and representative members of the class were also structurally characterized. The reactivity of the alkyldisulfanido TpZn(SSR) complexes with thiols was studied. In the absence of base, a simple exchange reaction between the alkyldisulfanido ligand and the thiol was observed in dichloromethane; when in the presence of base, the corresponding hydrogen(sulfido) complexes TpZn(SH) were obtained. The mechanism of the latter reaction has been studied and does not involve the coordinated alkyldisulfanido group. Reaction of the hydrogen(sulfido) complexes Tp^{iPr, iPr}Zn(SH) with the thiosulfonate PhCH₂S-SO₂CF₃ did not yield the expected alkyldisulfanido complex but benzyltrisulfide and a new complex tentatively assigned as Tp^{lPr, iPr}Zn(O₂SCF₃).

Full text of DOI:10.1021/ic900238v

Inorg. Chem. 2009, 48, 5921–5927 5921
DOI: 10.1021/ic900238v
Synthesis, Characterization, and Reactivity of Alkyldisulfanido Zinc Complexes
Erwan Galardon,† Alain Tomas,‡ Mohamed Selkti,‡ Pascal Roussel,§ and Isabelle Artaud*,†
†
ꢀ
Laboratoire de Chimie et Biochimie Pharmacologique et Toxicologique, UMR 8601 CNRS, Universite Paris
‡
ꢁ
Descartes, 45 rue des Saints Peres, 75270 Paris cedex 06, France, Laboratoire de Cristallographie et RMN
ꢀ
Biologiques, UMR 8015 CNRS, Universite Paris Descartes, 4 avenue de l’Observatoire, 75270 Paris cedex 06,
§
ꢀ
ꢀ
ꢀ
France, and UCCS - Unite de Catalyse et Chimie du Solide, UMR 8012 CNRS, Ecole Nationale Superieure de
Chimie de Lille BP 90108 - 59652 Villeneuve d’Ascq cedex, France
Received February 5, 2009
The alkyldisulfanido zinc complexes TpiPr,iPrZn(SSR) and TpPh,MeZn(SSR) where TpiPr,iPr is hydridotris-((3,5-isopropyl)
pyrazolyl)borate, TpPh,Me is hydridotris-((3-phenyl,5-methyl)pyrazolyl)borate, and (SSR) is tert-butyldisulfanido or
triphenylmethanedisulfanido were synthesized by reaction between the corresponding hydroxo complexes TpZn(OH)
1
and the synthetic persulfide RSSH. All the complexes were characterized by elemental analysis and H NMR
spectroscopy, and representative members of the class were also structurally characterized. The reactivity of the
alkyldisulfanido TpZn(SSR) complexes with thiols was studied. In the absence of base, a simple exchange reaction
between the alkyldisulfanido ligand and the thiol was observed in dichloromethane; when in the presence of base, the
corresponding hydrogen(sulfido) complexes TpZn(SH) were obtained. The mechanism of the latter reaction has been
studied and does not involve the coordinated alkyldisulfanido group. Reaction of the hydrogen(sulfido) complexes
TpiPr,iPrZn(SH) with the thiosulfonate PhCH2S-SO2CF3 did not yield the expected alkyldisulfanido complex but
benzyltrisulfide and a new complex tentatively assigned as TpiPr,iPrZn(O2SCF3).
Introduction
cules.8,9 In biology, hydrodisulfides are generated by several
enzymatic systems,8,9 including cysteine desulfurases, the
physiological implication of which is now clearly assessed.
They use the cofactor pyridoxal 50-phosphate to convert
cysteine to a protein-based cysteinyl persulfide and generate
alanine. The terminal sulfur of the hydrodisulfide, once
transferred to another cysteine in more specific acceptor
proteins, is finally used inthe biosynthesisof severalcofactors
(thiamin, iron-sulfur clusters,...) or thionucleosides (4-
thiouridine,...).8,9 Crystal structures analysis of the oxidized
form of the hybrid cluster protein from sulfate reducing
bacteria,10,11 of the SoxAX protein present in photosynthetic
sulfur bacteria12 as well as of the CO deshydrogenase from
Moorella thermoacetica13 reveals a direct interaction between
a persulfide and a metal center. This finding opens a new
The role of oxidized sulfur species in biology is now well
documented, and in that regard oxidized disulfides have been
recently proposed to be involved in the regulation of various
physiologicalprocesses.1,2 Disulfide monoxides and dioxides,
while usually produced under oxidative stress conditions,
are also involved in the signaling pathways of eukaryotic
cells.3-6 Another emerging class of oxidized sulfur species are
the persulfides (or hydrodisulfides) R-S-S-H,7 which
predominantly serve as sulfur donors to various biomole-
*To whom correspondence should be addressed. E-mail: isabelle.artaud@
parisdescartes.fr.
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Frazao, C.; Saraiva, L. M.; Xavier, A. V.; LeGall, J.; van Dongen, W. M. A. M.;
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(7) We decided to freely use the terms “persulfide” or “hydrodisulfide” to
describe the species RSSH. To refer to the coordinated RSS- and HS-
ligand, we used the denomination “alkyldisulfanido” and “hydrogen(sulfi-
do)”, following the IUPAC recommendations (see “Nomenclature for
inorganic chemistry, IUPAC recommendation 2005” available free of charge
at http://old.iupac.org/publications/books/rbook/Red_Book_2005.pdf).
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r
2009 American Chemical Society
Published on Web 06/10/2009
pubs.acs.org/IC

5922 Inorganic Chemistry, Vol. 48, No. 13, 2009
Galardon et al.
challenging field of investigation for bioinorganic chemists,
since organic persulfides are generally unstable14-17 and
rapidly degraded under the conditions commonly used in
inorganic synthesis, including the presence of redox active
metal cations and the use of basic conditions or of polar
solvents. As part of our ongoing work on the reactivity of
oxidized sulfur species toward metals,18,19 we wish to report
our first results on the study of the interaction between
hydrodisulfides and inorganic complexes. A number of alkyl-
or aryldisulfanido derivatives have been reported in the
literature,20-29 but to the best of our knowledge this work
describes the first direct rational synthesis of alkyldisulfanido
complexes by the simple reaction of a metal complex with a
synthetic persulfide, as well as the first alkyldisulfanido
complexes of zinc to be structurally characterized.
Thiols can react with organic persulfides either at the
sulfenyl (inner) sulfur (Scheme 1a, path (a)) or at the
sulfhydryl (terminal) sulfur14,15 (Scheme 1a, path (b)) leading
to the formation of a disulfide (RSSR0) with release of
hydrogen sulfide, or to a sulfur transfer from the hydrodi-
sulfide (RSSH) to the thiol (R0SH) with formation of a new
hydrodisulfide (R0SSH). In biology, this rich chemistry
(hydrodisulfides are also nucleophiles) make the persulfide
group a versatile reagent for incorporating sulfur along many
metabolic pathways.9 For instance, the release of hydrogen
sulfide upon reduction of the persulfide bond by a thiol is
related to the biosynthesis of 4-thiouridine and of iron-
sulfurclusters30,31 or to thevasoactivity ofgarlic,32 whenpath
(b) is related to the transfer of the active sulfur, generated by
cysteine desulfurases, to the cysteine of a protein acceptor
until the incorporation of the sulfur atom into an end
product.9 Binding the organic persulfide to a metal to give
an alkyldisulfanido complex leads to a more complex situa-
tion with three electrophilic centers, the two sulfurs of the
Scheme 1. Possible Reactions between a Thiol and a Free (1a) or
Metal Bonded (1b) Organic Persulfide
persulfide as described above, and the metal center, thus
adding the possible formation of thiolato complexes
(Scheme 1b) and subsequent reactions. In this regard, the
reactivity of our alkyldisulfanido zinc derivatives toward
thiols is explored in the second part of this paper.
Results and Discussion
Synthesis and Spectroscopic Characterization of the
Alkyldisulfanido Complexes. Several alkyldisulfanido me-
tal derivatives LnM(SSR) have been reported (many if
trithioperoxycarboxylates are classified as persulfides).
They mostly result from unexpected side reactions,20-22
even if some rational routes have also been described,
such as the nucleophilic attack of coordinated hydrogen
(sulfido)23,24 or disulfido25 ligands on either electrophilic
carbon or sulfur centers, sulfur insertion into metal-
carbon bonds,26 or redox processes.27-29 However,
to our knowledge, no alkyldisulfanido complex derived
from the simple reaction of a metal hydroxo complex
with a hydrodisulfide has been reported so far. Hydri-
dotris-(pyrazolyl)borate (Tp) ligands containing a bulky
substituent at the pyrazole 3-position are known to
give access to the stable albeit reactive TpZn-(OH) spe-
cies.33,34 In these complexes, the hydroxide behaves as a
base or a nucleophile. Following this strategy, we used as
scaffold the two sterically restricting ligands TpiPr,iPrK35
and TpPh,MeK, previously reported to yield stable thiola-
to zinc complexes by reaction between TpZn(OH) and
various thiols.36-38 Reaction of equimolar amounts of
the zinc derivatives TpiPr,iPrZn(OH)33 or TpPh,MeZn-
(OH)39 with tert-butyl hydrodisulfide tBuSSH40 or triphe-
nylmethane hydrodisulfide (Ph)3CSSH41 in non-polar
solvents (heptane or dichloromethane) readily affords the
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J. Org. Chem. 1965, 30(8), 2711.
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(18) Bourles, E.; Alves de Sousa, R.; Galardon, E.; Giorgi, M.; Artaud, I.
Angew. Chem., Int. Ed. 2005, 44(38), 6162.
(19) Galardon, E.; Bourles, E.; Artaud, I.; Daran, J.-C.; Roussel, P.;
Tomas, A. Inorg. Chem. 2007, 46(11), 4515.
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Schugar, H. J. J. Am. Chem. Soc. 1986, 108(16), 5015.
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He, G.; Calvo, J. A. M.; Boehmerle, K.; Steinfeld, G.; Brombacher, H.;
Vahrenkamp, H. Inorg. Chem. 2006, 45(18), 7493.
(35) In this paper, TpiPr,iPr refers to hydridotris-((3,5-isopropyl)pyrazolyl)
borate, TpPh,Me refers to hydridotris-((3-phenyl,5-methyl)pyrazolyl)borate,
and Tp refers to both ligands.
metallics 1983, 2(7), 938.
(24) Shaver, A.; Plouffe, P.-Y. Inorg. Chem. 1994, 33(19), 4327.
(25) Lobana, T. S.; Isobe, K.; Kitayama, H.; Nishioka, T.; Doe, M.;
Kinoshita, I. Organometallics 2004, 23(22), 5347.
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Chem. 2003, 42(11), 1604.
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Inorg. Chem. 2005, 44(2), 325.
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Article
Inorganic Chemistry, Vol. 48, No. 13, 2009 5923
Scheme 2. Reaction of the Alkyldisulfanido Complexes with Thiols
under Neutral and Basic Conditions
Figure 1. Complexes used in this work (a: this work,b: ref 42).
new alkyldisulfanido complexes 1, 10 and 2, 20, respectively
(Figure 1). Deprotonation of the persulfide in the vicinity of
the metallic cation is crucial to the success of this reaction,
since hydrodisulfides are rapidly decomposed into poly-
sulfides under alkaline conditions.16 In the case of 10 and 20,
1H NMR analysis of the crude mixtures only reveals the
presence of the expected complexes which are isolated as
analytically pure compounds in yields higher than 80%.
For 1 and 2, yields are lower because the starting complex
TpiPr,iPrZn(OH) cannot be isolated in a pure form because
of its very high solubility.33 Analytically pure alkyldisulfa-
nido complexes are nevertheless obtained by precipitation
in heptane, with yields around 50%. For comparison, we
alsosynthesizedthe thiolatocomplexes 3 and 30 related to1
and 10 (Figure 1). The alkyldisulfanido complexes, like
their thiolato counterparts, are stable for days in the solid
state or in solution in non dissociating solvents.
Structural Characterization of Complexes 2 and 20. The
crystal structures of complexes 2 and 20 are displayed in
Figure 2 (the structures of 10 and 30 are provided in
Supporting Information, Figure S4). Crystal data and
structure refinements are given in Table 1, and selected
bond lengths and angles are listed in Table 2. In all the
compounds, the zinc center is in a trigonally distorted
tetrahedral environment, and bond lengths and angles are
close to those reported for related thiolato complexes.36,37
The Zn-S bonds distance are, however, significantly
˚
shorter (by at least 0.05 A) than those observed in zinc
trithioperoxycarboxylato derivati0ves.43,44 The S-S bond
As above-mentioned, 1H NMR is a good spectroscopic
method to characterize the new alkyldisulfanido com-
plexes, and the analysis of their NMR spectra is straight-
forward. In addition to the classical features attributed to
the TpiPr,iPr and TpPhe,Me ligands, a single peak integrat-
ing for 9H is observed and assigned to the tert-butyl
groups in 1 (δ = 1.45 ppm in C6D6) and 10 (δ = 0.56
ppm in CDCl3). In 10, this signal is shifted upfield relative
to the one in the free persulfide tBuSSH (δ = 1.37 ppm in
CDCl3) and is deshielded relative to the corresponding
signal in the thiolato complex 30 (δ=0.38 ppm in CDCl3).
Shielding of the protons upon coordination of tBuSSH or
tBuSH arises from the pocket created by the phenyl
groups at the 3-pyrazolyl position.42 In the thiolato
complex 30, the protons of the tert-butyl group are
clearly embedded inside the cavity, thus undergoing
the strongest shielding; when in 10 they lie slightly outside
the cavity (see Supporting Information, Figure S4). Free
rotation of the thiolate and hydrodisulfide in the pocket
of the anionic tripod ligand in solution results in a C3
symmetry, with three equivalent pyrazolyl groups and
only one resonance for the tBu moiety. Free rota-
tion is also observed in 1 and 3, but the coordination
of the sulfur-containing ligands induces less variation
of the chemical shifts of the tBu protons. Spectra of
TpiPr,iPrZn(SSC(Ph3)) 2 and TpiPr,iPrZn(SSC(Ph3)) 20 are
less informative because of the number of aromatic
protons in these complexes.
˚
distances in complexes 2 and 2 (2.089 and 2.048 A,
respectively) are within known S-S distances for syn-
thetic45 or protein-bound hydrodisulfide.46 They are also
in the range of reported S-S bond lengths in disulfanido
complexes.11,20,21,24 Increasing the steric bulk of the
persulfide or of the tripodal ligand leads to strongly
distorted complexes, as exemplified by the structure of
complex 20.
Reactivity of the Disulfanido Complexes with Thiols.
The addition of 1 equiv of PhCH2SH to a dichloro-
methane solution of complex 1 or 10 has been monitored
1
by H NMR (Supporting Information, Figure S1) and
yields a mixture containing the starting alkyldisulfanido
complex TpZn(SSR) and the thiolato complex TpZn
(SCH2Ph), as well as the free thiol PhCH2SH and the
free hydrodisulfide RSSH (Scheme 2a). The closely re-
lated thiol/thiolate exchange in parent TpZn(SR) com-
plexes has been studied in detail36,37 and has been shown
to take place via protonation of the coordinated thio-
late by the competing thiol. We did not undertake such
an extensive study but we propose a similar mechanism
to explain our results. This is supported by the lack of
(43) Bonamico, M.; Dessy, G.; Fares, V.; Scaramuz, L J. Chem. Soc. A
1971, 20, 3191.
(44) Fackler, J. P.Jr.; Fetchin, J. A.; Fries, D. C. J. Am. Chem. Soc. 1972,
94(21), 7323.
(45) Franzi, R.; Geoffroy, M.; Bernardinelli, G. Mol. Phys. 1984, 52(4),
947.
(46) Clausen, T.; Kaiser, J. T.; Steegborn, C.; Huber, R.; Kessler, D. Proc.
(42) Rombach, M.; Vahrenkamp, H. Inorg. Chem. 2001, 40(24), 6144.
Natl. Acad. Sci. U.S.A. 2000, 97(8), 3856.

5924 Inorganic Chemistry, Vol. 48, No. 13, 2009
Galardon et al.
1
explanation. Actually, monitoring the reaction by H
NMR shows that the conversion of TpZn(SSR) into
TpZn(SH) proceeds in two steps (Figure 4). A first and
rapid exchange reaction between the alkyldisulfanido
ligand and PhCH2SH affords, as described above, the
complexes 5 or 50. However, under basic conditions,
the released hydrodisulfide is unstable and further re-
acts to yield polysulfides (see below), thus making this
exchange an irreversible process in contrast to the equili-
brium observed in the absence of base. These poly-
sulfides have been reported to generate hydrogen sulfide
by a complex mechanism1.6,32 So, in the second step, the
thiolato ligand is exchanged by hydrogen sulfide and the
resulting complex 4 or 40 is the thermodynamically most
stable product of the reaction since among all the sulfur-
containing organic products in the mixture, hydrogen
sulfide is the most acidic and the less sterically de-
manding. Additional support for this mechanism
arises from the reaction between the thiolato complex
TpiPr,iPrZn(SCH2Ph) (5) and a 1/1 mixture of triphenyl-
methane hydrodisulfide and Et3N (1 equiv.), which pro-
duces complex 4 in a 50% yield. Moreover, no effect of
the cavity is observed on the yields in 4 and 40 obtained
from either 1 and 10 or 2 and 20, essentially reflecting the
different reactivities of the intermediate polysulfides.
Triphenylmethane hydrodisulfide appears under our con-
ditions to be the most efficient precursor of H2S.
Reactivity of the Hydrogen(sulfido) Complexes with
Electrophilic Sulfur-Containing Reagents. The goal of this
study was to investigate the reverse reaction between the
(hydrogen)sulfido complex TpZn(SH) 4 and an electro-
philic sulfur-containing molecule to prepare the related
alkyldisulfanido complexes. While such reactions are well
documented in organometallic chemistry,23,24,49 no such
example has been reported for complexes based on nitro-
gen-containing ligands. For instance, the reaction of
hydrogen(sulfido) ruthenium or tungsten complexes
based on the cyclopentadienyl ligand with alkylthioisoin-
doline-1,3-dione appears a convenient route to access
the corresponding alkyldisulfanido complexes. For this
study, we chose three organic compounds previously used
to transfer the [RS] moiety to a nucleophilic sulfur atom:
the alkylthioisoindoline-1,3-dione PhCH2S-Phth,22 the
thiosulfonate PhCH2S-SO2CF3,50 and the sulfenylthio-
carbonate PhCH2S-SCO2Me.51 Reaction of these com-
pounds with the hydrogen(sulfido) complexes should
promote the intermediate formation of a zinc-bonded
protonated persulfide (Scheme 3) which could be easily
deprotonated by the released phthalimido anion from
PhCH2S-Phth or methylthiocarbonate from PhCH2S-
SCO2Me, while with the thiosulfonate the addition of
an external base will be needed. The hydrogen(sulfido)
zinc complexes based on hydridotris-(pyrazolyl)borate
ligands have earlier been reported to be rather inert
toward electrophiles.42 However, complex 4 was
found to be reactive toward the thiosulfonate, while
no reaction occurred in dichloromethane with the two
other substrates, even after several days. The reaction of
Figure 2. ORTEP views of complexes 2 and 20 showing thermal ellip-
soids at 50% probability and atom labeling. Hydrogen atoms have been
omitted for clarity.
polysulfides formation during the exchange reaction,
which goes against free deprotonated persulfides in solu-
tion. The relative ratio between the alkyldisulfanido and the
thiolato complexes results mainly from steric interactions
between the thiol and the pyrazolyl cavity: when 1 equiv
of the bulky thiol tBuSH is added to 1 or 10 in deutera-
ted dichlomethane (Supporting Information, Figure S2),
a strong preference is noticed for 1 and 10 against 3 and
30 (the ratios 1/3 and 10/30 are greater than 9), whereas with
the less hindered PhCH2SH, the tBuSSH hydrodisulfide
is more or less displaced depending on the size of the
cavity (the ratios 1/5 and 10/5042 are 0.5 and 2, respectively).
A different result is obtained when using, in place of a
thiol, a mixture of a thiol and a base. Addition of 1 equiv
of an equimolar solution of PhCH2SH and Et3N to the
TpiPr,iPrZn(SSR) complexes 1 or 2 results after 18 h in the
formation of the corresponding hydrogen(sulfido) com-
plexes TpiPr,iPrZn(SH) 4 in 40 and 60% yields, respec-
tively (Scheme 2b). Increasing the ratio PhCH2SH/Et3N
to 2 leads to increased yields (74% from 1, 70% from 10,
95% from 2 and 90% from 20) in 4 or 40. Complex 40 has
already been reported and thoroughly characterized by
Vahrenkamp and al.,42 and 4 is a new member of the
TpZn(SH) family.42,47,48 As all the other TpZn(SH)
derivatives, 4 is easily identified by the highly shielded
SH proton in 1H NMR (-1.43 ppm in d2-dichloro-
methane) and its structure has been confirmed by X-ray
diffraction (XRD) analysis (Figure 3). It shows the long-
˚
est Zn-S distance (2.230 A) in the series (average TpZn-
SH42,48 bond lengths of 2.212 A), and other distances and
˚
angles are usual. As already noticed for this family of
compounds,42,47 no ν(SH) is observed by IR spectro-
scopy. In addition to the formation of 4 or 40, the analysis
of the reaction mixture by 1H NMR reveals the presence
of several organic products, among which the main
components are the disulfide PhCH2SSCH2Ph and the
thiol RSH. When an attractive mechanism to explain
these results would be a nucleophilic attack of the depro-
tonated thiol on the sulfenyl sulfur of the alkyldisulfanido
complex followed by protonation of the resulting sulfido
zinc complex (route (a) in Scheme 1b, with R2S- instead
of R2SH), the traces of complexes TpZn(SCH2Ph) 5 or
5042 observed at the end of each reaction goes against this
(49) Shaver, A.; Hartgerink, J. Can. J. Chem. 1987, 65(6), 1190.
(50) Billard, T.; Langlois, B. R.; Large, S.; Anker, D.; Roidot, N.; Roure,
P. J. Org. Chem. 1996, 61(21), 7545.
(47) Looney, A.; Han, R.; Gorrell, I. B.; Cornebise, M.; Yoon, K.; Parkin,
G.; Rheingold, A. L. Organometallics 1995, 14(1), 274.
(51) Brois, S. J.; Pilot, J. F.; Barnum, H. W. J. Am. Chem. Soc. 1970, 92
(48) Ruf, M.; Vahrenkamp, H. Inorg. Chem. 1996, 35(22), 6571.
(26), 7629.

Article
Inorganic Chemistry, Vol. 48, No. 13, 2009 5925
Table 1. - Crystal Data and Structure Refinements for Complexes 2, 20, and 4
2
20
4
formula
fw
T(K)
wavelenght (A)
crystal system
space group
C
46H61BN6S2Zn
C49H43BN6S2Zn
856.19
173(2)
0.71073
triclinic
P1
C27H47BN6SZn
563.95
173(2)
0.71073
monoclinic
P21/n
838.31
296(2)
0.71073
triclinic
P1
˚
unit cell dimension
˚
˚
b (A)
˚
c (A)
a (A)
9.713(1)
11.977(1)
12.926(1)
14.842(1)
98.18(2)
111.25(2)
97.77(2)
2075.8(3)
2
1.370
9.950(1)
14.894(1)
16.308(1)
84.45(1)
89.09(1)
84.25(1)
2336.3(3)
2
1.192
16.036(1)
19.411(1)
90
104.71(2)
90
2995.7(4)
4
1.250
R (deg)
β (deg)
γ (deg)
3
˚
V (A )
Z
d(calc) (Mg/m3)
abs coeff (mm-1
)
0.652
0.50 ꢀ 0.40 ꢀ 0.25
0.736
0.35 ꢀ 0.30 ꢀ 0.20
0.915
crystal size (mm3)
crystal color
0.54 ꢀ 0.25 ꢀ 0.12
Colorless
1.67 - 31.70
-14 < l < 13
-23 < k < 23
-28 < l < 28
79888
colorless
colorless
θ range for data collection (deg)
index ranges
1.77 - 27.00
-11 < h < 12
-19 < k < 19
-20 < l < 20
50349
1.50 - 33.28
-18 < h < 18
-19 < k < 19
-22 < l < 22
83486
reflns collected
indep reflns
10162
15830
10131
[R(int) = 0.045]
99.5%
none
[R(int) =0.0496]
99.0%
none
[R(int) = 0.0376]
99.7%
none
completness to θ max
abs correction
data/restraints/params
GOF on F2
final R indices
10162/1/520
1.022
15830/4/547
1.068
10131/5/353
1.033
R1 = 0.043
wR2 = 0.1214
R1 = 0.066
wR2 = 0.1377
0.881 and -0.487
R1 = 0.028
wR2 = 0.0806
R1 = 0.0331
wR2 = 0.0824
0.563 and -0.282
R1 = 0.028
WR2 = 0.0699
R1 = 0.0420
wR2 = 0.0758
0.454 and -0.508
[I > 2σ(I)]a,b
R indices (all data)a,b
-3
˚
largest peak and hole (e A
)
P
P
P
P
P
aR1 = ||Fo| - |Fc||/ |Fo|. b wR2 = [ w(Fo2 - Fc2)2/ w(Fo2)2]1/2; where w = q/σ2(FO2) + (qp)2 + bp. GOF = S = { [w(Fo2 - Fc2)2]/(n - p)}1/2
.
˚
leads to a complete conversion of 4 into the trisulfide and
the new zinc complex TpiPr,iPrZnX, tentatively assigned as
TpiPr,iPrZn(O2SCF3) since CF3SO2- is the only nucleophile
remaining in solution. To support this hypothesis, trifluor-
omethanesulfonate, a more weakly coordinating ligand
than trifluoromethanesulfinate, has been described to bind
a closely related hydridotris-(pyrazolyl)borate zinc deriva-
tive to form the corresponding TpZn(O3SCF3) complexes,
Table 2. Selected Bond Lengths (A) and Angles (deg)
2
20
4
Zn-S1
2.2447(7)
2.089(1)
2.034(2)
2.035(1)
2.037(1)
92.36(3)
124.06(6)
125.09(6)
121.38(6)
92.68(8)
92.14(8)
92.47(8)
2.2598(4)
2.0485(5)
2.0896(9)
2.1084(9)
2.053(1)
2.2300(4)
S1-S2
Zn1-N1
2.0327(9)
2.039(1)
2.032(1)
Zn1-N2
Zn1-N3
S2-S1-Zn1
N1-Zn1-S1
N2-Zn1-S1
N3-Zn1-S1
N1-Zn1-N2
N2-Zn1-N3
N1-Zn1-N3
107.37(2)
although
no
cry-
113.40(3)
123.68(3)
133.65(3)
89.23(3)
84.88(4)
101.32(4)
124.69(3)
stal structure of this product was reported.52 The formation
of the trisulfide deserves additional comments: its forma-
tion can be rationalized by the mechanism depicted in
Scheme 3, in which the hydrogen(sulfido) ligand first reacts
with the thiosulfonate to give the expected protonated
alkyldisulfanido complex. However, the lack of accessibil-
ity of the zinc-bonded PhCH2SSH ligand prevents its rapid
deprotonation, and thus PhCH2SSH is exchanged with the
trifluoromethane sulfinate anion. Once released in solution,
PhCH2SSH is deprotonated with Et3N and upon reaction
with the remaining thiosulfonate yields the trisulfide. The
reaction of the thiosulfonate with the persulfide anion is
faster than with 4, leading to the observed ratios.
123.56(5)
124.04(3)
92.57(4)
91.09(4)
91.24(4)
sulfenylthiocarbonate with thiols has been proposed to
take place via a 6-membered ring transition state51
which is probably not favored with our bulky complex,
and the steric crowding around the metal may also
contribute to the lack of reaction with PhCH2S-Phth.
Studies in more polar solvents such as methanol or
DMSO were precluded because the starting complex is
poorly soluble in these solvents. Complex 4 reacts
rapidly with an equimolar quantity of the thiosulfonate
PhCH2S-SO2CF3 in the presence of Et3N to give a 1/1/1
mixture of the starting complex, the trisulfide
PhCH2S-S-SCH2Ph and a new zinc derivative, as
detected by 1H NMR (Supporting Information, Figure
S3). Addition of a second equivalent of thiosulfonate
This result highlights the complexity of the synthesis of
alkyldisulfanido complexes, and validates our approach
based on complexes which possess a base within the
coordination sphere of the metal to deprotonate the per-
(52) Brandsch, T.; Schell, F. A.; Weis, K.; Ruf, M.; Muller, B.; Vahren-
kamp, H. Chem. Ber./Recueil 1997, 130(2), 283.

5926 Inorganic Chemistry, Vol. 48, No. 13, 2009
Galardon et al.
Figure 3. ORTEP views of 4 showing thermal ellipsoids at 50% prob-
ability and atom labeling. Hydrogen atoms have been omitted for clarity.
Figure 4. 1H NMR monitoring of the reaction between PhCH2SH and
complex 20 under basic conditions: (A) spectrum of complex 20 (400 μL of
a 15 mM solution in CD2Cl2) recorded at 500 MHz; (B) spectrum
recorded 2 min after the addition of PhCH2SH (2 equiv.) and Et3N
(1 equiv) (complex 50 represents approximately 75% of the total content
of zinc complexes); (C) spectrum recorded after 18 h (complex 40
represents approximately 90% of the total content of zinc complexes). *
indicates the residual solvent peak, TEA the signals corresponding to the
Et3N, and 40 and 50 the characteristic signals from the corresponding
complexes.
sulfide in the vicinity of the metal center and not in the
bulk solution.
Conclusion
This work demonstrates that alkyldisulfanido complexes
can be rationally synthesized by the direct reaction of a
synthetic persulfide and an inorganic complex. The success
of this strategy relies on the nature of the starting complex,
which must contain a base as ligand of the metal center to
avoid the formation of free deprotonated hydrodisulfide in
solution and its further degradation. The alkyldisulfanido
complexes react with thiols under neutral conditions to give
simple exchange reactions; when under basic conditions, the
formation of the corresponding hydrogen(sulfido) deriva-
tives is observed. However, this reaction does not involve the
coordinated alkyldisulfanido group, and further work needs
to be done to direct the reactivity of the nucleophilic reactants
toward the S-S bond rather than the metal center, to more
closely reproduce biologically relevant processes. Attempts
to realize the opposite reaction were unsuccessful, and we
did not observe the formation of alkyldisulfanido zinc com-
plexes by nucleophilic attack of the zinc-bound hydrogen
(sulfido) ligand on substrates containing activated sulfur.
argon at -20 °C (typically 50 mg in 1 mL), and 1 equiv of
the corresponding persulfide was added. After stirring for 1 h,
the white precipitate was filtrated and dried. Pure products were
thus obtained, as indicated by 1H NMR and elemental analysis.
Yields were around 50%, depending on the purity of the starting
hydroxo complexes. TpiPr,iPrZn(SStBu) (1): Anal. Calcd (found)
for C31H55BN6S2Zn: C, 57.09 (56.75); H, 8.50 (8.53); N, 12.89
(12.89). 1H NMR (δ, C6D6): 5.84 (s, 3H), 3.46 (m, 6H),
1.45 (s, 9H), 1.28 (m, 36H). FT-IR (ATR, cm-1): 2545 (νBH).
TpiPr,-iPrZn(SSC(Ph)3) (2): Anal. Calcd (found) for C46H61-
1
BN6S2Zn: C, 65.90 (66.12); H, 7.33 (7.33); N, 10.02 (9.79). H
NMR (δ, CD2Cl2): 7.49 (m, 6H), 7.29 (m, 9H), 5.90 (s, 3H), 3.48
(sept, 3H, 3JH-H=6.8 Hz), 3.39 (sept, 3H,3JH-H=6.8 Hz), 1.28
(d, 18H, 3JH-H=6.8 Hz), 1.15 (d, 18H, 3JH-H=6.8 Hz). FT-IR
(ATR, cm-1): 2547 (νBH).
Disulfanido Complexes 10 and 20. The hydroxo complex
TpPh,MeZn(OH) was dissolved in dichloromethane under argon
at -20 °C (typically 50 mg in 1 mL), and 1 equiv of the
corresponding persulfide was added. After stirring for 1 h, the
solvent was removed, and the white powder washed with
pentane. Pure products were thus obtained, as indicated by 1H
NMR and elemental analysis. Yields were higher than 80%.
Crystals of 10 and 20 suitable for XRD studies were obtained by
layering a benzene solution of the disulfanido complex with
heptane. TpPh,MeZn(SStBu) (10): Anal. Calcd (found) for
C34H37BN6S2Zn: C, 60.95 (61.10); H, 5.57 (5.50); N 12.54
(12.75). 1H NMR (δ, CDCl3): 7.93 (m, 6H), 7.63 (m, 9H), 6.26
(s, 3H), 2.83 (s, 9H), 0.56 (s, 9H). FT-IR (ATR, cm-1): 2545
(νBH). TpPh,MeZn(SSC(Ph)3) (20): Anal. Calcd (found) for
C49H43BN6S2Zn: C, 68.73 (68.42); H, 5.06 (5.17); N 9.82
(9.69). 1H NMR (δ, CD2Cl2): 7.51 (m, 6H), 7.26 (m, 9H),
7.03 (m, 9H), 6.81 (m, 6H), 6.24 (s, 3H), 2.63 (s, 18H). FT-IR
(ATR, cm-1): 2546 (νBH).
Experimental Section
Physical Measurements. 1H NMR spectra were recorded
at 300 K on a Bruker ARX-250 or ADVANCED II-500 spectro-
meter, and chemical shifts are reported in ppm downfield from
TMS. IR spectra were obtained with a Perkin-Elmer Spectrum
One FT-IR spectrometer equipped with a MIRacleTM single
reflection horizontal ATR unit (Zirconium-Selenium crystal).
Elemental analyses were carried out by the microanalysis service
at Gif-sur-Yvette CNRS.
Materials. Solvents were distilled using standard techniques
and treated under argon prior to use when necessary. Chemicals
were purchased from Aldrich or Acros and used as received.
Hydrogen sulfide was purchased from Praxair. tert-Butyl hydro-
disulfide tBuSSH40 and triphenylmethane hydrodisulfide (Ph)3-
CSSH41 were synthesized as previously described. TpPh,-Me
-
Zn(OH)39 and TpiPr,iPrZn(OH)33 were prepared as previously
reported. PhCH2S-SO2CF3 and PhCH2S-SCO2Me were synthe-
sized according to reported procedures.50,53 PhCH2S-Phth was
synthesized by reaction of PhCH2SSO2CF3 with potassium phta-
limide in methanol.
TpiPr,iPrZn(StBu) (3). A 63 mg portion (0.11 mmol) of TpiPr,iPr
-
Zn(OH) was dissolved in 2 mL of heptane under argon at 0 °C, and
1 equiv of tert-butyl mercaptan (12 μL, 0.11 mmol) added. After
stirring for 1 h, the white precipitate was filtered and dried to give
41 mg of 3 (60%). Anal. Calcd (found) for C31H55BN6SZn 1.3
3
Synthesis. Disulfanido Complexes 1 and 2. The crude hydro-
xo complex TpiPr,iPrZn(OH) was dissolved in heptane under
H2O: C, 60.05 (59.94); H, 8.94 (9.11); N, 13.55 (13.61). 1H NMR
(δ, C6D6): 5.99 (s, 3H), 4.08 (sept, 3H, 3JH-H=6.7 Hz), 3.64 (sept,
3H, 3JH-H=6.7 Hz), 1.97 (s, 9H), 1.39 (d, 18H, 3JH-H=6.7 Hz),
1.25 (d, 18H, 3JH-H=6.7 Hz). FT-IR (ATR, cm-1): 2541 (νBH).
(53) Harpp, D. N.; Granata, A. J. Org. Chem. 1980, 45(2), 271.

Article
Inorganic Chemistry, Vol. 48, No. 13, 2009 5927
Scheme 3. Proposed Mechanism for Reaction of 4 with the Thiosulfonate PhCH2S-SO2CF3
TpPh,MeZn(StBu) (30). A 48 mg portion (0.085 mmol) of
TpPh,MeZn(OH) was dissolved in 3 mL of dichloromethane
under argon at 0 °C, and 1 equiv of tert-butyl mercaptan
(10 μL, 85 mmol) added. After stirring for 1 h, the volatiles
were removed, and the product crystallized by slow diffusion of
hexane in a benzene solution of 30 to give 44 mg of colorless
crystals (81%). Anal. Calcd (found) for C34H37BN6SZn: C,
64.01 (63.77); H, 5.85 (5.77); N 13.17 (13.42). 1H NMR
Reactivity of the Hydrogen(sulfido) Complexes. Reactivity
studies were performed as follows: to a 15 mM solution
(400 μL) of the hydrogen(sulfido) complex in CD2Cl2 were
added the corresponding reactants. The progress of the reaction
was monitored by 1H NMR spectroscopy at 27 °C.
X-ray Data Collection and Structural Determination.
Crystal data and experimental conditions are listed in Table 1.
The drawings of the molecules were realized with ORTEP
III.54
3
(δ, CDCl3): 7.71 (d, 6H, J = 8.4 Hz), 7.40 (m, 9H), 6.20 (s,
3H), 2.58 (s, 9H), 0.38 (s, 9H). FT-IR (ATR, cm-1): 2549 (νBH).
Structural Data for 2, 20, and 4. Data were collected with a
Bruker SMART APEX CCD diffractometer. The crystals were
cooled to 173(2) K using the OXFORD CRYOSTREAM
700 low-temperature device for 20 and 4. Intensity measure-
ments were performed using graphite monochromated Mo-KR
TpiPr,iPrZn(SH) (4). A 150 mg portion of crude TpiPr,iPr
-
Zn(OH) was dissolved in 3 mL of heptane under argon at
0 °C, and H2S was passed through the solution for 1 min. The
solution was then filtered, and the white precipitate dried under
vacuum to give 94 mg of pure 5. Crystals suitable for XRD studies
were obtained by layering a benzene solution of 5 with heptane.
Anal. Calcd (found) for C27H47BN6SZn: C, 57.50 (57.76); H, 8.40
(8.38); N 14.90 (15.07). 1H NMR (δ, CD2Cl2): 5.92 (s, 3H), 3.48
(sept, 3H, 3JH-H=6.7 Hz), 3.36 (sept, 3H, 3JH-H=6.7 Hz), 1.28
(d, 18H, 3JH-H=6.7 Hz), 1.26 (d, 18H, 3JH-H=6.7 Hz), -1.43 (s,
1H). FT-IR (ATR, cm-1): 2545 (νBH).
˚
radiation (λ=0.71073 A). Data integration and global cell
refinement were performed with the program SAINT.55 The
structure were solved by direct methods using SHELXS 97.56
Refinement, based on F2, were carried out by full matrix least-
squares with SHELXL-97 software.57 Non-hydrogen atoms
were refined using anisotropic thermal parameters. The hydro-
gen atoms were placed in their geometrically generated posi-
tions and allowed to ride on their parent atoms with an isotropic
thermal parameter 20% higher to that of the atom of attach-
ment. H atoms attached to B atoms were deduced from
a difference Fourier map and were refined with isotropic
temperature factor.
TpiPr,iPrZn(SCH2Ph) (5). A 91 mg portion of crude TpiPr,iPr
-
Zn(OH) was dissolved in 2 mL of heptane under argon at 0 °C, and
20 μL of benzyl mercaptan (0.17 mmol) were added. After stirring
for 1 h, the solution was filtered, and the white precipitate dried
under vacuum to give 48 mg of 5 (44% based on benzyl mercap-
tan). Anal. Calcd (found) for C34H53BN6SZn: C, 62.43 (62.41); H,
8.17 (8.13); N 12.85 (12.89). 1H NMR (δ, CD2Cl2): 7.51 (m, 2H),
7.36 (m, 2H), 7.28 (m, 1H), 5.94 (s, 3H), 4.04 (s, 2H), 3.50 (sept, 3H,
3JH-H =6.7 Hz), 3.32 (sept, 3H, 3JH-H =6.7 Hz), 1.29 (d, 18H,
3JH-H=6.7 Hz), 1.27 (d, 18H, 3JH-H=6.7 Hz). FT-IR (ATR, cm-1):
2546 (νBH).
Reactivity of the Disulfanido Complexes. Reactivity studies
were performed as follows: to a 15 mM solution (400 μL) of the
disulfanido complex in CD2Cl2 were added the corresponding
reactants. The progress of the reaction was monitored by 1H NMR
spectroscopy at 27 °C, and the yields determined after 18 h.
Supporting Information Available: Crystallographic data for
complexes 10, 2, 20, 30, and 4 in CIF format and Figures S1-S4 as
a PDF file. This material is available free of charge via the
Internet at http://pubs.acs.org.
(54) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
(55) Bruker, SAINT, Bruker AXS Inc, Madison, Wisconsin, USA, 2007.
(56) Sheldrick, G. M., SHELXS-97, Program for crystal structure solu-
::
::
tion; University of Gottingen: Gottingen, Germany, 1997.
(57) Sheldrick, G. M., SHELXS-97, Program for crystal structure refine-
ment; University of Gottingen: Gottingen, Germany, 1997.
::