Alkylation of a dimolybdenum SO bridge, subsequent reactions, and characterization of the thioperoxide bridge

Article abstract of DOI:10.1021/ic9002093

The SO bridge of the complex, [Mo₂(NTo)₂(S ₂P(OEt)₂)₂(μ-O₂CMe)(μ-SBn) (μ-SO)], 1, displayed nucleophilicity at O, giving alkylation products [Mo₂(NTo)₂(S₂P(

Full text of DOI:10.1021/ic9002093

Inorg. Chem. 2009, 48,
DOI:10.1021/ic9002093
5027
Alkylation of a Dimolybdenum SO Bridge, Subsequent Reactions, and
Characterization of the Thioperoxide Bridge
Chi MinhTuong,† Whitney K. Hammons,† Ashley L. Howarth,† Kelly E. Lutz,† Ackim D. Maduvu,†
Laura B. Haysley,† Brian R. T. Allred,† Lenore K. Hoyt,†, ‡ Mark S. Mashuta,† and Mark E. Noble*,†
‡
†Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, and Department of
Chemistry, Idaho State University, Pocatello, Idaho 83209
Received February 2, 2009
The SO bridge of the complex, [Mo2(NTo)2(S2P(OEt)2)2(μ-O2CMe)(μ-SBn)(μ-SO)], 1, displayed nucleophilicity at O,
giving alkylation products [Mo2(NTo)2(S2P(OEt)2)2(μ-O2CMe)(μ-SBn)(μ-SOR)]+, 4+, which contained the thioperoxide
bridge. These cations were then subject to nucleophilic attack by two pathways. Debenzylation of the bridge thiolate in
4+ afforded neutral [Mo2(NTo)2(S2P(OEt)2)2(μ-O2CMe)(μ-S)(μ-SOR)], 5; de-esterification of a dithiophosphate ligand
in 4+ gave [Mo2(NTo)2(S2P(dO)(OEt))(S2P(OEt)2)(μ-O2CMe)(μ-SBn)(μ-SO)], 6, which contained a monoester,
dithiophosphate ligand. Complex 1 gave a slow and clean reaction in the crystalline state, further demonstrating its
nucleophilicity by attacking a neighboring molecule in its lattice. X-ray crystallography confirmed the thioperoxide
linkage and revealed structural similarities of the Mo2(μ-SOR) unit to sulfenate esters (RSOR) and related derivatives.
Introduction
emphasis. These have long been considered5-7 to include
SO-bridged species structurally represented as M2(μ-SdO),
as well as sulfinyl-metal complexes represented by MS(dO)-
R. Sulfinyl ligands (S-bound, -S(dO)R) have been known
for some time8 and continue to attract considerable attention,
spurred in large part by biological applications.9-11 Their
complexes are often referred to as sulfenate systems, but this
term can be problematic since the general bonding modes are
not of classical “sulfenate” character. (Unfortunately, the
terminology has become inconsistent between inorganic and
organic usage of these terms and those of related systems.) In
this report, -S(dO)R ligands will be termed sulfinyl ligands,
by direct analogy to acyl (C-bound, -C(dO)R) ligands; in
this manner, -S(dO)R is clearly distinguished from sulfenate
(thioperoxide) and other classical “sulfenyl” (X-SR) charac-
ters. The consideration of MS(dO)R as a sulfoxide analog
rather than as a complex containing a sulfenate ion can more
readily account for various properties and for the stabilization
of the RSO- moiety upon binding to a metal via S.
Sulfur is one of the most interdisciplinary of all elements,
impacting an extensive range of biological, atmospheric,
geochemical, and cosmochemical natural processes, in addi-
tion to human societal and industrial processes. Within the
scope of the general chemistry of sulfur, sulfur/oxygen com-
pounds are among the most common and among the most
important, thus endowing the study of S/O functional units
with tremendous importance. The simplest S1O1 unit traverses
the entire range of main group, transition metal, and organic
chemistry, including biochemical applications therein. This
fundamental SO unit appears at its simplest as diatomic SO
itself, a fleeting molecule at earthly conditions but which
nonetheless does have an astronomical presence.1 The SO unit
appears far more extensively in a variety of compounds
including thionyls, sulfoxides, sulfenic acids and esters, sul-
fines, and numerous metallovariants and complexes of these.
Organic sulfoxides, R2SdO, are among the most numer-
ous compounds which contain the S1O1 unit. While metal
complexes containing molecular sulfoxide ligands are very
well-known,2-4 metallovariants of sulfoxides are the present
(5) Jackson, W. G.; Sargeson, A. M. In Rearrangements in Ground and
Excited States; de Mayo, P., Ed.; Academic Press: New York, 1980; Vol. 2,
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* To whom correspondence should be addressed. E-mail: menoble@
louisville.edu.
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©
2009 American Chemical Society
Published on Web 4/28/2009
pubs.acs.org/IC

5028 Inorg. Chem., Vol. 48, No. 11, 2009
Tuong et al.
While several dimetal sulfoxide analogs, M2(μ-SO), are
known, their numbers, along with those of SO-bridged
complexes of any nuclearity, MxSO,12-19 pale in comparison
to the number of metal-SO2 complexes whose synthesis and
Metal complexes with molecular sulfenate esters, RSOR, as
ligands have also been reported.32,33
In light of the importance and the extensive chemistry of
the SO functional group in nonmetal systems, there is
considerable potential for the SO group in dimetal systems.
Studies of the reactivity of the SO bridge in the Mo2(μ-SO)
complex, [Mo2(NTo)2(S2P(OEt)2)2(μ-O2CMe)(μ-SBn)(μ-SO)],
1, have thus been undertaken. (To = p-tolyl; Bn = benzyl;
other abbreviations are common.) The present report de-
scribes nucleophilic behavior leading to O-alkylation and
the formation of the thioperoxide ligand, ROS-. This
nucleophilicity manifests in solution and even in the crystal
phase, the latter providing an interesting and clean solid-state
reaction of 1. Additional solution reactions are also pre-
sented, including the formation of a dimolybdenum sulfenate
ester analog.
reactivity have been extensively well-developed.12,20,21
A
major reason for the disparity in the studies of SO and SO2
ligand systems is the difficulty of preparation. Due to the
fleeting existence of SO, it is not a simple task to combine free
SO with a metal complex, although precursors containing an
SO equivalent are sometimes used. Dimeric M2(μ-SO)
complexes are sometimes accessible via oxygenation of a
bridge sulfide, M2(μ-S), but these can be hard to control
since there is a facile tendency toward overoxidation to
SO2-bridged products, M2(μ-SO2). Among the known
M2(μ-SO) compounds, there are a few structural varia-
tions,4,22 but the emphasis herein will be on those which have
η1-SO and pyramidal sulfur, and which therefore have some
structural analogy to sulfoxides.
Compared to organic sulfoxides, R2SdO, the isomeric
sulfenate esters, RS-OR, are less common, partly due to
their more reactive nature. Sulfoxide/sulfenate ester isomer-
izations have been of considerable interest for some time, and
both directions are known.23,24 Sulfenate esters are well-
known members of the general family of sulfenyl derivatives
which also includes sulfenic acids, sulfenamides, sulfeni-
mines, sulfenyl halides, and disulfides.25-27 Sulfenate esters
are thioperoxides, and RSOR can be compared to peroxides
ROOR and also to persulfides RSSR.
Results
Relative to organic derivatives, there are few isolable
metallosulfenate ester analogs in any of the various forms,
such as MS-OM, MS-OR,28 or RS-OM,29,30 although the
latter may be the simple salt form for sulfenate anions.31
For simplicity, the dimolybdenum derivatives of general
formula [Mo2(NTo)2(S2P(OEt)2)2(μ-O2CMe)(μ-SR)(μ-SZ)]
will be represented by several abbreviations. The simple
bracket notation {Mo2} will denote the bis(p-tolylimido)-bis
(diethyl dithiophosphato)-μ-acetato-dimolybdenum(V) basic
framework, {Mo2(NTo)2(S2P(OEt)2)2(μ-O2CMe)}3+. Pre-
fixed and suffixed to this {Mo2} bracket term will be the
μ-S bridges, along with their functional groups as appropriate.
By this notation, the dimolybdenum sulfoxide [Mo2(N-
To)2(S2P(OEt)2)2(μ-O2CMe)(μ-SBn)(μ-SO)], 1, is written as
BnS{Mo2}SO. The artwork is also simplified: rotation of the
broadside view above and truncation of ancillary ligands gives
the simplified stick diagram illustrated below.
(12) Schenk, W. A. Angew. Chem., Int. Ed. Engl. 1987, 26, 98–109.
(13) Pandey, K. K. Prog. Inorg. Chem. 1992, 40, 445–502.
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Patai, S., Ed.; John Wiley & Sons: Chichester, U.K., 1990; pp 311-359.
Braverman, S. In The Chemistry of Sulphones and Sulphoxides; Patai, S.,
Rappoport, Z., Stirling, C. J. M., Eds.; John Wiley & Sons: Chichester, U.K.,
1988; pp 717-757.
The corresponding sulfide and μ-SO2 complexes are given
by BnS{Mo2}S, 2, and BnS{Mo2}SO2, 3.
(24) Amaudrut, J.; Wiest, O. J. Am. Chem. Soc. 2000, 122, 3367–3374.
ꢀ
Turecek, F. J. Phys. Chem. A 1998, 102, 4703–4713.
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Wiley & Sons: Chichester, U.K., 1990.
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Pergamon Press: Oxford, U.K., 1979; Vol. 3, pp 261-310.
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383–388.
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Wloszczynski, A. J. Chem. Soc., Dalton Trans. 1994, 2509–2513.
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Article
BnS{Mo2}SO, 1, had been previously prepared17 by
Inorg. Chem., Vol. 48, No. 11, 2009
5029
solution. For this reason, postevaporation workup steps
must be promptly executed until a crystallization step is
reached. This postevaporation sensitivity was not recognized
at the time of the original report. Further details of the
crystal-phase and postevaporative reactions of BnS{Mo2}SO
are given below, following some related reactions.
Solution Reactions. BnS{Mo2}SO, 1, is considerably
nucleophilic. Reaction of 1 with an alkyl halide, RX, in
(CD3)2CO gives O-alkylation, eq 2, resulting in the
cationic complexes BnS{Mo2}SOR+, 4+. Alkylation at
O to give a thioperoxide linkage was definitive by isola-
tion and characterization of the complexes 4+
(vide infra). Alkylation at S to give a sulfinyl bridge
(S(dO)R) was conceivable, but this outcome has never
been identified in the present system of compounds.
oxygenation of the sulfide bridge of BnS{Mo2}S, 2, using
m-chloroperbenzoic acid in CH2Cl2 at -95 ꢀC and under
red-light conditions, eq 1. The low temperature was needed to
limit overoxidation to the SO2-bridged complex BnS{Mo2}-
SO2, 3, although some of that product remained unavoid-
able. Separation required column chromatography. The
synthesis of 1 has been completely revamped, still using
m-ClC6H4CO3H but now in Me2CO at 0 ꢀC in the presence
of excess acids. No special lighting conditions are needed.
The new method is better for avoiding by-production of
BnS{Mo2}SO2, 3. Purification of the desired BnS{Mo2}SO,
1, product from unreacted BnS{Mo2}S, 2, and from small
amounts of some other impurities can be done without
chromatography. The purification takes advantage of the
tenacious binding of BnS{Mo2}SO, 1, to silica gel from
CH2Cl2 solution, while unreacted BnS{Mo2}S and some
impurities wash right through. The desired BnS{Mo2}SO
is then released from the silica gel with Me2CO.
Studies of eq 2 are complicated by secondary reactions.
The cations 4+ are now electrophilic and are themselves
vulnerable to attack by nucleophile, including attack by
the halide anion coproduct. These secondary reactions
parallel those from prior studies, which showed that bis
(thiolate-bridged) cations of general formula R0S{Mo2}-
The peroxide reaction is conducted in the presence of
excess HBF4 and MeCO2H, which keep the nascent product
protonated,34 thus inhibiting a second oxygenation. There is
an additional reason for the excess MeCO2H and that is to
avoid exchange of the carboxylate bridge from the dimolyb-
denum core; otherwise, m-chlorobenzoate exchanges for
acetate to a slight extent. Neutralization of all acids afterward
with aqueous NaHCO3 gives dark-olive BnS{Mo2}SO, 1.
Mechanistically, the peracid/acid/ketone combination could
conceivably involve various peroxy intermediates,35 leaving
open the question of the actual oxidant. This possibility is
noted but was not further investigated.
+
SR0 were subject to nucleophilic attack via two path-
ways, as illustrated by a and b below.36
At the time of the original report,17 BnS{Mo2}SO, 1, was
believed to be photolytically and thermally unstable. Most
issues regarding the instabilities have been eliminated or at
least identified. The compound has good solution stability,
giving 1-2% decomposition after six days in CDCl3
(air-exposed) in the dark. The purified compound is only
slightly light-sensitive: photolysis of a solution in CDCl3 in an
NMR tube in a 12-in., 32-W fluorescent ring lamp for 16 h
yielded 1-2% reaction. This does not warrant reduced light
conditions for normal handling. Crystalline 1 does undergo a
very slow, clean reaction in the solid state, and the compound
is best stored cold. In addition to these very slow processes,
BnS{Mo2}SO, 1, does have one peculiar thermal habit: it
decomposes relatively quickly while standing after evapora-
tion from solution. This decomposition as a film is faster than
as a crystalline solid and faster than when dissolved in
In path a, the nucleophile attacked either of the bridge
thiolates at the R-carbon, cleaving the C-S bond to
produce a neutral sulfide product R0S{Mo2}S, 2; this
was a reversible equilibrium process. In path b, the
nucleophile attacked either dithiophosphate ligand at
either of its ethyl groups, cleaving a C-O bond; this
was an irreversible de-esterification which gave neutral
[Mo2(NTo)2(S2P(OEt)2)(S2PO(OEt))(μ-O2CMe)(μ-SR0)2].
This product contained one dianionic, monoethyl, dithio-
phosphate ligand, (EtO)P(dO)S22-. Given the precedent
of those studies, the analogous reactions for the current
cations 4+ are given by the debenzylation of eq 3 and the
de-ethylation of eq 4.
(34) Protonation and hydrogen bonding studies remain in progress.
(35) Lange, A.; Brauer, H.-D. In Peroxide Chemistry; Waldemar, A., Ed.;
Wiley-VCH Verlag: Weinheim, Germany, 2001; pp 157-176. Renz, M.;
Meunier, B. Eur. J. Org. Chem. 1999, 737–750. Murray, R. W. Chem. Rev.
1989, 89, 1187–1201.
(36) Koffi-Sokpa, E. I.; Calfee, D. T.; Allred, B. R. T.; Davis, J. L.;
Haub, E. K.; Rich, A. K.; Porter, R. A.; Mashuta, M. S.; Richardson, J. F.;
Noble, M. E. Inorg. Chem. 1999, 38, 802–813.

5030 Inorg. Chem., Vol. 48, No. 11, 2009
Tuong et al.
meaning attack at μ-SOR did not occur and eq 2 was
not reversible.
In all of the solution-based de-esterification reactions
of eq 4, two phosphoryl isomers are observed for the
products BnS{Mo2(PdO)}SOR, 6. The isomers arise
from attack at either of the two inequivalent ethyl arms
on each dithiophosphate ligand. Using the tolylimido
ligands as a directional reference, the isomers are denoted
as anti or syn. The anti phosphoryl isomer was shown
above with eq 4; the syn phosphoryl isomer is shown
below. The isomers did not interconvert, and their rela-
tive formation was thus under kinetic control. Attack
at the anti OEt position to give anti PdO is preferred.
For example, the reaction of Cl- with BnS{Mo2}SOMe+
CF3SO3- resulted in 77% of the anti phosphoryl isomer
of BnS{Mo2(PdO)}SOR, 6.
Interestingly, although eqs 3 and 4 complicated the
studies of the nucleophilicity of the μ-SO bridge toward
alkyl halides, these complications do extend the related
chemistry of the system overall. Equation 3 provides a
synthetic entry to the neutral compounds, S{Mo2}SOR,
5. Reactions similar to eqs 2 and 4 provide for a solid-state
reaction of BnS{Mo2}SO, 1, itself, wherein the SO bridge
is the nucleophile and a dithiophosphate ethyl group is
the electrophile. This proved to be the manner of thermal
decomposition of crystalline 1.
Crystal-Phase Reaction of BnS{Mo2}SO, 1. Crystalline
batches of BnS{Mo2}SO, 1, undergo a slow decomposi-
tion in the solid state. Various trials were conducted
to study the effects of different storage atmospheres,
temperatures, and light levels. Of the variables, only
temperature had an effect. As an example, a sample
stored under a vacuum at normal room conditions de-
composed 14% after 159 days, while an air-exposed
sample in the freezer showed no reaction in the same
time. On a shorter time scale, decomposition at room
temperature was ∼1% in 7 days. The reaction was very
clean at room temperature, producing a single product,
BnS{Mo2(PdO)}SOEt, 6 (R = Et). Formally, this is
tantamount to an isomerization: a dithiophosphate ethyl
group ends up on the oxygen of the bridge SO moiety. The
actual mechanism, however, is intermolecular, and it
involves mutual attack between neighboring molecules
within the crystal lattice.
(The bracket notation, {Mo2(PdO)}, and the stick dia-
gram for 6 are modified to denote the presence of the
modified dithiophosphate. For fuller illustration, a
broadside view for this product is given above with
eq 4.) Thus and overall, the reaction of starting sulfoxide
BnS{Mo2}SO, 1, with alkyl halide proceeds first by
O-alkylation, eq 2, to produce cation 4+. Cation 4+
can then undergo debenzylation (eq 3) to give S{Mo2}-
SOR, 5, or cation 4+ can undergo de-ethylation (eq 4) to
produce BnS{Mo2(PdO)}SOR, 6.
As a specific example of the full sequence, the reaction
of BnS{Mo2}SO, 1, with 1 equiv of benzyl bromide after
2 h in (CD3)2CO showed 3% of the cation BnS{Mo2}-
SOBn+, 4+ (eq 2); 15% S{Mo2}SOBn, 5 (eq 2 then
eq 3); and 2% BnS{Mo2(PdO)}SOBn, 6 (eq 2 then
eq 4). A total of 79% BnS{Mo2}SO, 1, remained, and
∼1% was not identified. The product distribution indi-
cated that eq 3 was relatively fast and nascent 4+ more
promptly formed 5. The reaction was also attempted
using ethyl bromide, which gave no observable reaction
after 2 h but yielded ∼2% SMo2SOEt, 5, after 8 h.
Although the cationic complexes 4+ are vulnerable to
nucleophilic counterions, these could be separately pre-
pared in pure form with triflate counterions. This allowed
for a study of eqs 3 and 4 without starting from eq 2. For
-
example, the reaction of BnS{Mo2}SOMe+ CF3SO3
(4+CF3SO3-) in (CD3)2CO with a limiting amount
(0.5 equiv) of PPN+ Cl- gave, after 15 min, a product
distribution of 69% S{Mo2}SOMe, 5, due to debenzyla-
tion (eq 3) and 31% BnS{Mo2(PdO)}SOMe, 6, due to de-
esterification (eq 4). The reaction using BnS{Mo2}SOEt+
gave a similar product distribution. The byproducts BnCl
(eq 3) and EtCl (eq 4) were seen in the 1H NMR spectra.
Notably, there was no evidence for BnS{Mo2}SO, 1,
The crystal structure of BnS{Mo2}SO has been re-
ported previously.17 A re-examination of the packing
has revealed that the molecules pair off in close approach
for nucleophilic attack upon each other, as shown in
Figure 1. The neighboring molecules are related by
inversion. The oxygen atom of one molecule’s SO bridge
is 3.52(1) A from the R-carbon of an ethyl group of a

Article
Inorg. Chem., Vol. 48, No. 11, 2009
5031
While slow at room temperature, the solid reaction is
faster at elevated temperatures. Synthetic procedures
adopted a boiling water bath, and cooking the solid for
135-160 min gave complete reaction. Several impurities
were also observed using the higher temperature, but
these were in the 3-5% range total.
Postevaporation Decomposition of BnS{Mo2}SO, 1.
While the crystalline decomposition of BnS{Mo2}SO, 1,
at room temperature proved to be slow, clean, and tidily
resolved, the sensitivity of this compound to decomposi-
tion following evaporation from solution was more
complicated. This evaporative decomposition was
interesting in that it was much faster than the crystalline
decomposition at room temperature and much faster
than any decomposition in solution. For example, allow-
ing a solution in EtOH to evaporate on a watch glass and
then allowing the residue to stand open to the air
for 3 h resulted in ∼4% decomposition (as determined
by NMR after redissolving in CDCl3). By comparison,
an NMR-tube sample of 1 after 3 h in air-exposed
9:1 EtOH/D2O showed no reaction at all. Thus, evapora-
tion to a film predisposed 1 to decomposition. This
was also peculiar to 1: a similar evaporation trial
using an EtOH solution of BnS{Mo2}SOEt+CF3SO3
-
(4+CF3SO3-) gave no reaction at all after a 3 h stand
time, although such cations, 4+, are activated to nucleo-
philic attack.
Figure 1. Nucleophilic faceoff between adjacent molecules in the crystal
structure of BnS{Mo2}SO, 1. The dashed lines connect an oxygen from
the SO bridge of one molecule to a dithiophosphate R-carbon on the
adjacent molecule. Only one interaction is labeled, but the interactions are
reciprocal.
Numerous studies of solutions of 1 were conducted
involving various evaporation methods followed by a
stand period of various times and conditions. Compar-
ison was made for rotavapping, open-air evaporation,
and stripping on a vacuum line, as well as for various
solvents. Stand periods were conducted open to the air,
open to the air in a jar at 100% relative humidity, open to
dry N2, open to dry O2, and under vacuum conditions,
and for various periods of time. Even the substrate of the
evaporation vessel was studied, using standard (borosili-
cate) glass, polypropylene, or stainless steel. Samples
were then redissolved in CDCl3 and analyzed by NMR
spectroscopy.
dithiophosphate ligand on the adjacent molecule. This
distance is close to but longer than a simple van der Waals
contact (3.32 A37). The angle of the approach, O C-O,
3 3 3
is 166(1)ꢀ, facilitating a backside attack. These interac-
tions are reciprocal for each molecule in the pair. It is this
fortuitous juxtaposition coupled with the inherent nu-
cleophilicity of the bridge (S)O which provides for the
solid-state reaction. While the attacks are mutual between
the neighbors, they may or may not be mechanistically
concerted.
As noted for the solution studies of eq 4, the ethyl arms
of each dithiophosphate ligand are not equivalent, and
de-esterification in solution gave both anti- and syn-BnS-
{Mo2(PdO)}SOR, 6. For the solid-state reaction of BnS-
{Mo2}SO, 1, however, only one isomer of 6 is obtained.
The solid-phase juxtaposition of the bridge (S)O is to the
anti ethyl arm of the dithiophosphate on the neighboring
molecule. This orientation gives product 6 as the anti
phosphoryl isomer only. This configuration was con-
firmed crystallographically for 6 as synthesized in this
manner (vide infra).
The decomposition occurred primarily during the
stand time and not during the evaporation itself.
The primary culprit causing decomposition was moisture,
either atmospheric or water added to the solvent prior
to evaporation. All substrates gave some decomposition,
and glass gave the most. This was attributed to a
simple film effect, since evaporation from polypro-
pylene tended to give less of a film and more small
crystals. Some decomposition was found in all of the
solvents tested, including EtOH, Me2CO, CH2Cl2, and
MeCN.
Although the crystals for the previously reported crys-
tal structure were obtained from CH2Cl2/MeOH, routine
preparations have been more recently obtained from
EtOH/H2O or similar crystallization. Crystals obtained
from EtOH/H2O were examined for unit cell dimensions,
and all of the a, b, c, and β values were within 0.2% of
the values for the unit cell of the published crystal. The
change in crystallization methods produced the same
crystal morphology and is therefore believed to have left
the crystal structure unchanged.
The products of the decomposition clearly resulted
from nucleophilic attack. For a more extensive run which
involved evaporation from EtOH with a stand time of
22 h, 11% total decomposition was obtained. Some
cations, 4+, were present, possibly BnS{Mo2}SOEt+
and BnS{Mo2}SOBn+, but these were not conclusively
resolved. These cations represented the initial products of
the attack of BnS{Mo2}SO, 1, on another molecule of 1
or, more likely, on its hydrate (possibly hydrogen-
bonded34), thereby conceivably explaining the role of
moisture. Identifications of S{Mo2}SOEt, 5, and of
(37) Bondi, A. J. Phys. Chem. 1964, 68, 441–451.

5032 Inorg. Chem., Vol. 48, No. 11, 2009
Tuong et al.
BnS{Mo2(PdO)}SOEt, 6 (major product), were defini-
tive in the mixture; these arose from secondary processes.
Other products were also present in small amounts. While
fuller mechanistic details were not attempted, the general
results did additionally demonstrate the nucleophilicity
of 1. Since the observed rates were not found in solution
even with 10% D2O (and given that crystalline 1 is
prepared from aqueous media), then a film effect and
moisture were jointly responsible. This presumably in-
volved another proximity/orientation effect within the
film.
Syntheses and Characterizations. The various reactions
described herein are substantiated by isolation and char-
acterization of representative compounds of types 4+, 5,
and 6.
Turning now to neutral S{Mo2}SOR, 5 (R = Me, Et),
these were prepared from the debenzylation of the cations
BnS{Mo2}SOR+, 4+, per eq 3. Competition from eq 4
could not be eliminated, and this necessitated some
optimization work. First, the choice of benzyl thiolate
as one bridge in the reactant BnS{Mo2}SOR+, 4+, was
ultimately to allow for facile C-S cleavage; methyl
thiolate or ethyl thiolate bridges could not dealkylate
quickly enough to compete with eq 4. Second, various
nucleophiles were also examined for enhancing the selec-
tivity of S{Mo2}SOR, 5, over the de-esterification
product 6. Tested nucleophiles included Cl-, Br-, and
I- (as PPN+ salts); Ph3P; and Et3N. PPN+I- proved the
most useful reagent for synthetic purposes.
While the methyl and ethyl derivatives S{Mo2}SOMe
and S{Mo2}SOEt were synthesized from cations 4+, it
proved possible to synthesize the benzyl derivative
S{Mo2}SOBn directly from BnS{Mo2}SO, 1, by reaction
with excess benzyl bromide. The one-pot synthesis
combined eq 2 and eq 3, while trying to avoid eq 4. The
ability to isolate product 5 cleanly by this route was only
successful for R = Bn due to the facile kinetics of benzyl
displacement. Interestingly, this reaction is also tanta-
mount to isomerization, but the process is again inter-
molecular.
The isolation of the cations BnS{Mo2}SOR+, 4+,
required the use of relatively non-nucleophilic counter-
ions. Triflate salts were readily prepared from the reac-
tion of BnS{Mo2}SO, 1, with methyl and ethyl triflates,
as per eq 2 with RX = RO3SCF3. The products
4+CF3SO3 were characterized by IR spectroscopy,
-
NMR spectroscopy, and, in the case of 4+(Et)CF3SO3
,
-
X-ray crystallography. The IR spectra showed the
ancillary ligand sets and the triflate anion; no S-O
vibrations from the bridge SOR group could be defini-
tively distinguished from the other absorptions present
in the range of interest. (Reported values for ν(SO) range
from 650 to 760 cm-1 for various RSOR and related
derivatives.32,38-40 The range extends to ∼800 cm-1 with
strong electron withdrawal.41,42
)
31P and 1H NMR
1
spectra gave all of the appropriate resonances. The H
chemical shifts of the R-hydrogens of the thioperoxide
R groups were relatively downfield, consistent with
alkylation at O and not at S. X-ray crystallography
for 4+(Et)CF3SO3- definitively confirmed the S-O-Et
linkage arising from O-ethylation as opposed to a sulfinyl
ligand, S(dO)Et, arising from S-ethylation.
The products S{Mo2}SOR, 5 (R = Me, Et, Bn), were
characterized by IR spectroscopy and NMR spectro-
scopy, along with X-ray crystallography for S{Mo2}-
SOEt. The IR spectra again showed the usual ligand sets
but no definitive S-O vibration. The NMR spectra
showed all of the appropriate resonances. The chemical
shifts of the R groups were relatively downfield again,
indicating that the thioperoxide linkage was preserved
as S-O-R. X-ray crystallography for S{Mo2}SOEt
confirmed the structure. These compounds are isostruc-
tural to the disulfides S{Mo2}SSR, which have been
previously characterized, including the R = Et and Bn
derivatives.43
The NMR spectra of S{Mo2}SOR, 5, again revealed
sulfur invertomers, but now only two isomers were pos-
sible, depending on whether the thioperoxide group was
distal or proximal. The invertomer ratios (distal/proxi-
mal) in CDCl3 were 18 for S{Mo2}SOMe, 3.8 for S{Mo2}-
SOEt, and 3.9 for S{Mo2}SOBn. The latter two ratios are
similar to the invertomer ratios of 4 and 6 for the
disulfides S{Mo2}SSEt and S{Mo2}SSBn, respectively.
The de-esterification product BnS{Mo2(PdO)}SOEt,
6, was synthesized from the thermal decomposition of
The NMR spectra also revealed conformational
isomers in solution associated with facile inversion at
the pyramidal sulfur bridges; these invertomers are com-
mon to BnS{Mo2}SO, 1,17 to previously reported R0S-
+
{Mo2}SR0 cations,36 and to other prior compounds.
The sulfur substituent positions are labeled distal (d)
or proximal (p) relative to the tolylimido rings as a
reference point. Cations 4+ have four possible isomers,
shown below as isomers A-D. The isomer distribution
in CDCl3 for 4+(Me) is 76% A, 16% B, and 9% C; the
distribution for 4+(Et) is the same within integration
error. The presence of isomer D was not definitive
for either compound in CDCl3, but this was present at
∼1% in (CD3)2CO.
(38) Steudel, R.; Schmidt, H.; Baumeister, E.; Oberhammer, H.;
Koritsanszky, T. J. Phys. Chem. 1995, 99, 8987–8993.
(39) Reina, M. C.; Boese, R.; Ge, M.; Ulic, S. E.; Beckers, H.; Willner, H.;
ꢁ
Della Vedova, C. O. J. Phys. Chem. A 2008, 112, 7939–7946.
(40) Brown, C.; Hogg, D. R.; McKean, D. C. Spectrochim. Acta 1970,
26A, 39–42.
(41) Ulic, S. E.; von Ahsen, S.; Willner, H. Inorg. Chem. 2004, 43
5268–5274.
ꢁ
(42) Ulic, S. E.; Della Vedova, C. O.; Hermann, A.; Mack, H.-G.;
Oberhammer, H. Inorg. Chem. 2002, 41, 5699–5705.
(43) Noble, M. E. Inorg. Chem. 1986, 25, 3311–3317.

Article
Inorg. Chem., Vol. 48, No. 11, 2009
5033
crystalline BnS{Mo2}SO, 1. The IR spectrum again
showed the usual ligand set and again gave no clearly
assignable SO band, but now there was a clear phosphoryl
stretch at 1219 cm-1. The NMR spectra were more
complex due to the reduced symmetry within the mole-
cule, which was now asymmetric. In addition, sulfur
invertomers were again observed due to pyramidal
fluxionality. Of the four possible sulfur invertomers,
only two were seen in CDCl3, and these paralleled
isomers A and B, as illustrated above for the cations
4+. Only the anti phosphoryl isomer was produced in the
solid-state reaction, and thus, only one phosphoryl iso-
mer is noted here.
For the dominant sulfur invertomer, the 31P NMR
-
spectrum showed the (EtO)2PS2 ligand at 111.8 ppm
and the (EtO)(O)PS22- ligand at 76.3 ppm. The downfield
peak showed a PP coupling of 1.5 Hz, but this was not
resolved in the upfield peak due to its greater broadness
1
(7 Hz linewidth). In the H NMR spectrum, the loss of
symmetry was particularly apparent in the geminal cou-
pling of inequivalent CH2 protons within each of the SBn
and the SOEt bridge groups.
Figure 2. ORTEP view of the cation BnS{Mo2}SOEt+, 4+(Et).
In addition to the spectroscopic evidence, X-ray crys-
tallography again confirmed the structure.
Within the various compounds 4+, 5, and 6, preliminary
studies of the reactivity of the thioperoxide unit have demon-
strated a reasonable stability. The compounds have an
excellent shelf life. For example, after typical benchtop,
room-temperature, air-exposed storage, solid samples of
BnS{Mo2}SOEt+ (4+) CF3SO3- and of S{Mo2}SOMe (5)
were unchanged after one year. BnS{Mo2}SOEt+CF3SO3
-
is also stable after five days in air-exposed, CDCl3 solution.
Attempts to isomerize the thioperoxide to a sulfinyl ligand
using thermal or photolytic methods have so far been
unsuccessful or, at least, inconclusive. Unfortunately, at the
high temperatures and or UV irradiation required to get any
kind of reaction, the acetate and dithiophosphate coligands
also become reactive, thus rendering these efforts difficult.
Attempts to observe S-O bond homolysis have likewise been
inconclusive, despite the straightforward photohomolysis
previously reported for the disulfides S{Mo2}SSR.44
Figure 3. ORTEP view of the distal isomer of S{Mo2}SOEt, 5(Et).
Crystallographic Studies. Four crystal structures are
presented which contain the O-ethyl thioperoxide ligand,
EtOS-, bridging in μ2-η1(S) fashion. ORTEP views45 are
shown in Figures 2-5, and selected metrical results are
in Tables 1 and 2. Full tabulations are provided in the
Supporting Information. Cations 4+ are represented by
BnS{Mo2}SOEt+; this structure is compared to that
of the precursor BnS{Mo2}SO, 1, for the effects of
alkylation at O. Compounds 5 are represented by two
structures of S{Mo2}SOEt, for which crystals of both
sulfur invertomers were fortuitously obtained. The struc-
ture of this thioperoxide compound is also compared to
that of the disulfide analog, S{Mo2}SSEt.46 Compounds
6 are represented by BnS{Mo2(PdO)}SOEt; in addition
to the thioperoxide ligand, this compound also provides
another structural characterization of a dianionic, mono-
alkyl dithiophosphate ligand. The additional interest
therein lies in the fact that there are few structural studies
known for this ligand,47-49 in stark contrast to the
extensive characterization of monoanionic, dialkyl
dithiophosphate ligands.
Most of the general features of the underlying Mo2-
dithiophosphate-acetate-tolylimido frameworks are
similar to those of prior compounds and will not be
considered here. The emphasis here is the thioperoxide
ligand itself and its effects, if any, on the dimolybdenum
cores. The one exception will include additional descrip-
tion of the monoethyl (EtO)(O)PS22- ligand in 6 since a
prior structure of this ligand type had some disorder.
Throughout, any comparisons of metric data here to data
of prior structures will be done following the numbering
scheme as used in the present report, regardless of the
atom-numbering system used in the previous reports.
(44) Lizano, A. C.; Munchhof, M. G.; Haub, E. K.; Noble, M. E. J. Am.
Chem. Soc. 1991, 113, 9204–9210.
(45) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
(46) Noble, M. E.; Williams, D. E. Inorg. Chem. 1988, 27, 749–752.
(47) Boꢁıllos, E.; Miguel, D. Organometallics 2004, 23, 2568–2572.
(48) Abram, U.; Ritter, S. Inorg. Chim. Acta 1993, 210, 99–105.
(49) Gastaldi, L.; Porta, P.; Tomlinson, A. G. J. Chem. Soc., Dalton
Trans. 1974, 1424–1429.

5034 Inorg. Chem., Vol. 48, No. 11, 2009
Tuong et al.
Table 1. Selected Bond Lengths (A)
4+
5, distal
5, proximal
2.8419(7)
6
Mo(1)-Mo(2) 2.8807(9)
2.8518(7)
2.9109(7)
2.4566(9)
2.4416(10)
2.4433(10)
2.4542(10)
2.5092(10)
2.5386(10)
2.4725(10)
2.4616(10)
1.735(3)
1.734(3)
2.135(2)
2.171(2)
1.655(3)
1.456(5)
1.502(6)
2.0068(14)
1.9912(13)
1.566(3)
Mo(1)-S(1)
Mo(1)-S(2)
Mo(2)-S(1)
Mo(2)-S(2)
Mo(1)-S(3)
Mo(1)-S(4)
Mo(2)-S(5)
Mo(2)-S(6)
Mo(1)-N(1)
Mo(2)-N(2)
Mo(1)-O(1)
Mo(2)-O(2)
S(1)-O(7)
2.4378(17) 2.4401(14) 2.4176(13)
2.4454(18) 2.3457(14) 2.3543(14)
2.4436(19) 2.4565(14) 2.4370(13)
2.4382(17) 2.3439(14) 2.3564(13)
2.4917(17) 2.5176(14) 2.5175(14)
2.5144(19) 2.5695(14) 2.5580(14)
2.4969(19) 2.5173(16) 2.5208(14)
2.495(2)
1.721(6)
1.718(6)
2.156(4)
2.169(5)
1.655(5)
1.466(8)
1.513(12)
2.011(3)
1.998(2)
1.579(5)
1.553(5)
1.431(9)
1.485(10)
1.998(3)
2.014(3)
1.567(7)
1.563(7)
1.570(14)
disa
2.5726(15) 2.5547(13)
1.731(4)
1.737(4)
2.169(3)
2.168(3)
1.654(3)
1.429(6)
1.468(8)
1.732(4)
1.734(4)
2.196(3)
2.199(3)
1.666(4)
1.438(6)
1.499(8)
O(7)-C(32)
C(32)-C(33)
P(1)-S(3)
1.9983(19) 1.994(2)
P(1)-S(4)
1.990(2)
1.574(3)
1.567(3)
1.479(6)
1.459(7)
1.994(2)
1.988(2)
1.577(4)
1.574(4)
disa
1.9923(19)
1.585(4)
1.573(4)
1.451(7)
disa
2.0003(19)
1.9897(19)
1.575(4)
1.569(4)
1.459(6)
1.465(6)
P(1)-O(3)
P(1)-O(4)
1.572(3)
1.461(5)
1.463(4)
2.0560(14)
2.0550(14)
1.595(3)
O(3)-C(17)
O(4)-C(19)
P(2)-S(5)
Figure 4. ORTEP view of the proximal isomer of S{Mo2}SOEt, 5(Et).
P(2)-S(6)
P(2)-O(5)
P(2)-O(6)
1.470(3)
1.451(5)
O(5)-C(21)
O(6)-C(23)
1.443(7)
a Values involving a disorder are not listed here but may be found in
the Supporting Information.
Table 2. Selected Bond and Dihedral Angles (deg)
4+
5, distal 5, proximal
6
S(1)-Mo(1)-S(2)
S(1)-Mo(2)-S(2)
S(3)-Mo(1)-S(4)
S(5)-Mo(2)-S(6)
O(1)-Mo(1)-N(1)
O(2)-Mo(2)-N(2)
Mo(1)-S(1)-Mo(2)
Mo(1)-S(1)-O(7)
Mo(2)-S(1)-O(7)
sum of angles at S(1)
Mo(1)-S(2)-Mo(2)
Mo(1)-S(2)-C(25)
Mo(2)-S(2)-C(25)
S(1)-O(7)-C(32)
S(3)-P(1)-S(4)
107.60(6) 107.15(5) 106.96(5) 107.04(3)
107.65(6) 106.67(5) 106.26(5) 107.07(3)
79.50(6) 77.95(5) 78.10(5)
79.47(7) 77.32(5) 78.15(4)
78.28(3)
79.46(3)
175.1(2) 169.11(15) 170.05(17) 174.20(11)
177.5(2) 165.47(15) 172.72(17) 174.55(11)
72.33(5) 71.24(4) 71.66(4)
72.89(3)
106.87(18) 108.19(13) 108.54(14) 110.07(10)
108.18(19) 113.69(13) 111.85(15) 104.30(10)
Figure 5. ORTEP view of BnS{Mo2(PdO)}SOEt, 6(Et).
287.4(3) 293.1(2) 292.0(2)
72.30(5) 74.91(4) 74.21(4)
110.1(2)
109.3(2)
113.7(5) 116.7(3) 112.0(3)
287.3(2)
72.96(3)
108.86(12)
110.21(12)
114.6(2)
A comparison of the thioperoxide ligand itself among
the four structures shows the S(1)-O(7) bond lengths
to be identical in the three distal isomers (1.655(5) A,
1.654(3) A and 1.655(3) A), while that in the one proximal
isomer (1.666(4) A) was similar within error. The O(7)-C
(32) bond lengths range from 1.429(6) to 1.466(8) A. The
angle at O(7) shows a little flex, 112.0(3)-116.7(3)ꢀ. The
sulfur is distinctly pyramidal in all four cases, with
the sum of angles at S(1) ranging 287.3(2) to 293.1(2)ꢀ.
Aside from this last parameter, the other values are
comparable to metric results reported for several known
RSOR structures and related derivatives.38,39,50-52
105.99(11) 106.72(8) 106.68(8) 105.68(6)
105.40(12) 105.99(9) 106.62(8) 100.19(5)
S(5)-P(2)-S(6)
O(3)-P(1)-O(4)
O(5)-P(2)-O(6)
98.0(3)
98.2(4)
97.12(19) 96.8(2) 95.31(14)
96.6(2) 95.77(19) 106.39(15)
Mo(1)-S(1)-O(7)-C(32) 175.8(4) 156.7(3) 174.0(4)
79.7(4) 96.9(4)
89.0(3)
165.7(2)
Mo(2)-S(1)-O(7)-C(32) 107.8(4)
S(1)-Mo(1)-Mo(2)-S(2) 176.85(8) 178.38(6) 171.24(6) 178.44(4)
For those, S-O bond lengths ran 1.625(2)-1.663(5) A,
O-C(alkyl) bond lengths ran 1.426(3)-1.45(2) A, and
angles at O ran 113(2)-117(2)ꢀ. As a further comparison
of note, there is even some manifestation of the dihedral
preference within the thioperoxide ligand in the present
compounds. Dihedral angles about S-S, S-O, and O-O
bonds have been of considerable interest for many years,
and especially recently for RSOR derivatives.50,51,53
ꢁ
(50) Ulic, S. E.; Kosma, A.; Della Vedova, C. O.; Willner, H.; Oberham-
mer, H. J. Phys. Chem. A 2006, 110, 10201–10205. Ulic, S. E.; Kosma, A.;
ꢁ
Leibold, C.; Della Vedova, C. O.; Willner, H.; Oberhammer, H. J. Phys.
Chem. A 2005, 109, 3739–3744.
(51) Buschmann, J.; Luger, P.; Koritsanszky, T.; Schmidt, H.; Steudel, R.
J. Phys. Chem. 1992, 96, 9243–9250.
(52) Cannon, D.; Low, J. N.; McWilliam, S. A.; Skakle, J. M. S.; Wardell,
J. L.; Glidewell, C. Acta Crystallogr., Sect. C 2001, 57, 600–603. LaPlaca, S.
J.; Ibers, J. A.; Hamilton, W. C. J. Am. Chem. Soc. 1964, 86, 2289–2290.
(53) Du, L.; Yao, L.; Ge, M. J. Phys. Chem. A 2007, 111, 11787–11792.
Du, L.; Yao, L.; Zeng, X.; Ge, M.; Wang, D J. Phys. Chem. A 2007, 111,
4944–4949.

Article
Inorg. Chem., Vol. 48, No. 11, 2009
5035
Experimental and calculated conformations prefer dihe-
dral angles loosely near 90ꢀ ((20ꢀ), although some show
an additional shallow minimum or flat potential near
180ꢀ. Interestingly, the S-O dihedral angles herein are
within or close to those ranges even though the sulfur is
now three-bonded, giving two dihedral values in each
derivative, Mo(1)S-OC and Mo(2)S-OC. Overall, the
thioperoxide ligand structurally parallels organic sulfe-
nate derivatives, even in a bridging arrangement.
sphate) bonds (2.5176(14) and 2.5173(16) vs 2.511(2) and
2.520(1) A). Thus, these two functional groups impart
no difference on the dimolybdenum framework. The
bridge groups do show expected differences internally,
with S-O at 1.654(3) A versus S-S at 2.068(2) A and
O-C at 1.429(6) A versus S-C at 1.789(7) A. Chalcogen
angles for the bridges are 116.7(3)ꢀ for —S-O-C versus
101.5(3)ꢀ for —S-S-C.
The crystal structure of the de-esterified product BzS-
{Mo2(PdO)}SOEt, 6, is the same as its major solution
invertomer, again with both sulfur bridge substituents in
distal orientation. An important feature of this structure
lies in the definitive confirmation of conformation re-
garding the phosphoryl bond; this is in the anti position,
reflecting the mode of attack in the crystal phase reaction
of the precursor BnS{Mo2}SO, 1. A second importance
Turning now to the individual compounds, the general
structure of the cation in BnS{Mo2}SOEt+CF3SO3- is the
same as its major solution invertomer, with both bridge
sulfur groups in distal orientation. Comparison of the
crystal structure to that of the precursor BnS{Mo2}-
SO, 1, reveals several effects of the alkylation at O. As
expected, S(1)-O(7) lengthens considerably, from 1.515
(4) A in 1 to 1.655(5) A in 4+. Both of the Mo-S(1)-O(7)
angles decrease upon alkylation (113.1(2)ꢀ and 113.7(2)ꢀ
in 1 vs 106.87(18)ꢀ and 108.18(19)ꢀ in 4+), consistent with
reduced steric demand upon changing from SdO to S-O.
There is a corresponding effect on the pyramidicity of
the sulfur: the sum of the angles at S(1) decreases from
299.2(3)ꢀ in 1 to 287.4(3)ꢀ in 4+. This effect is specific to
the thioperoxide S(1) bridge: by comparison, the sum of
the angles at the benzyl thiolate sulfur, S(2), are more
similar for the two compounds, 293.9(3)ꢀ in 1 versus 291.7
(3)ꢀ in 4+. Mo-S(1) bond lengths are also close between
the two compounds, 2.429(1) A and 2.428(1) A in 1 versus
2.4378(17) A and 2.4436(19) A in 4+. The Mo-S(dithio-
phosphate) bonds which are trans to S(1) (namely, Mo-
(1)-S(3) and Mo(2)-S(5)) contract a bit, 2.523(2) A for
each in 1 versus 2.4917(17) A and 2.4969(19) A in 4+;
this suggests a weakened trans influence upon alky-
lation at O.
2-
lies in the (EtO)OPS2 ligand itself. The thioperoxide
bridge in neutral 6 shows no significant changes relative
to that in cation 4+. The primary changes in comparing
the overall structures of 6 and 4+ arise from converting
-
one monoanionic (EtO)2PS2 to a dianionic (EtO)(O)-
PS22-, and these changes parallel a prior comparison for
EtS{Mo2(PdO)}SEt36 which were not related to a thio-
peroxide bridge. A key feature of that compound as well
as 6 is that they both contain a typical, monoanionic,
diethyl dithiophosphate along with a dianionic, mono-
ethyl dithiophosphate in otherwise equivalent environ-
ments; this allows a direct comparison of the two ligand
types. Such a comparison for the prior compound, EtS-
{Mo2(PdO)}SEt, was limited due to some disorder in the
phosphoester functionality, but this is not the case for the
present BzS{Mo2(PdO)}SOEt, 6.
The (EtO)(O)PS2
2-
ligand of 6 possesses longer
P(2)-S bonds (2.0560(14) and 2.0550(14) A) than the
-
Beyond these comparisons, there are other modest
differences between BnS{Mo2}SOEt+ and BnS{Mo2}-
SO, but these differences are similar when comparing
another cation, MeS{Mo2}SMe+,36 to BnS{Mo2}SO.
Thus, those additional differences are not a consequence
of the thioperoxide link.
P(1)-S bonds in the (EtO)2PS2 ligand (2.0068(14) and
1.9912(13) A); this is consistent with formal bond orders
of 1 versus 1.5. On the other hand, the dianion is a better
donor than the monoanion, which gives shorter Mo-S
(dithiophosphate) bonds: 2.4725(10) and 2.4616(10) A
for Mo(2)-S(5,6) versus 2.5092(10) and 2.5386(10) A for
2-
Two crystal structures of S{Mo2}SOEt, 5, were ob-
tained, differing in the invertomer orientation of the
thioperoxide bridge. Chronologically, the proximal
isomer was first, although this was not the dominant
solution isomer. By varying solvent combinations, a
crystal and a structure of the distal isomer were also
obtained. The principal structural differences between
the two isomers are parallel to the differences previously
reported for the closely related (but not isomeric) dimo-
lybdenum sulfenimines, S{Mo2}SNdCHCMe3 (distal)
and S{Mo2}SNdCMe2 (proximal).54 Thus, these differ-
ences are not associated with the thioperoxide ligand per
se. The major reason for the specific interest in the distal
isomer was in its isostructural relationship to the distal
structure of the disulfide complex, S{Mo2}SSEt,46 there-
by allowing a direct comparison of the ethyl thioperoxide
EtOS- bridge to the ethyl persulfide EtSS- bridge. The
{Mo2} frameworks are relatively unchanged: Mo-S(1)
bond lengths are similar (2.4401(14) and 2.4565(14) in 5 vs
2.446(1) and 2.451(1) A), as are trans Mo-S(dithiopho-
Mo(1)-S(3,4). Within the (EtO)(O)PS2 ligand itself,
the phosphoryl P(2)dO(6) bond is much shorter, 1.470(3)
A, compared to the ester P(2)-O(5) bond of 1.595(3) A;
the latter is long compared to P(1)-O(3,4) lengths of
-
1.566(3) and 1.572(3) A in the diester (EtO)2PS2
.
(P)O-C bond lengths are the same within error between
the two dithiophosphate ligands, 1.451(5)-1.463(4) A.
The phosphoryl linkage opens the OPO angle to 106.39
(15)ꢀ for P(2) from 95.31(14)ꢀ for P(1); the SPS angle
respectively closes to 100.19(5)ꢀ from 105.68(6)ꢀ. These
results extend the resonance discussion, as had been
presented for EtS{Mo2(PdO)}SEt.36
Discussion
The complex BnS{Mo2}SO, 1, is somewhat of a paradox-
ical mix of nucleophilic character combined with weak
electrophilic character. The SO bridge is considerably
nucleophilic at O, reacting with classical electrophiles such
as alkyl halides but also slowly on another molecule of its
own type in its own crystal phase. In solution, alkylation at O
gives an activated cation with enhanced electrophilicity at the
benzyl thiolate and dithiophosphate ester sites.
(54) Haub, E. K.; Richardson, J. F.; Noble, M. E. Inorg. Chem. 1992, 31,
4926-4932.

5036 Inorg. Chem., Vol. 48, No. 11, 2009
Tuong et al.
While organic sulfoxides are nucleophilic at both S and O,
no evidence has been seen in BnS{Mo2}SO, 1, for alkylation
at S to produce a sulfinyl product, BnS{Mo2}S(dO)R+,
although sulfinyl-bridged dimetal systems are indeed
known.55-57 This relative lack of reactivity at S may be
kinetic or thermodynamic. Kinetic factors arise from the
overhanging ortho positions of the imido rings, which pro-
vide some steric interference at the bridge sulfur positions.
Although reaction at S is not seen in this work, the oxygena-
tion of BnS{Mo2}SO, 1, to BnS{Mo2}SO2, 3, had shown in
prior work that the SO sulfur atom was not completely inert
and that some reactivity at that site did still exist.17 In
contrast, the sulfur of the thiolate bridge has not shown
any nucleophilicity inany work todate, and infact, this sulfur
tends to be dealkylated in some of these derivatives.
There is some precedent for O-alkylation at metal-SO sites
among various MxSyOz systems. O-alkylation of a tri-iron
SO2 bridge was accomplished using MeO3SCF3;58 a similar
reaction with AcCl was proposed to give O-acetylation.16
O-alkylation of an Ir-S2O ligand was reported using
MeO3SF.28 O-alkylations of sulfinyl or sulfonyl ligands are
also known (or proposed), using alkyl halides or Et3O+
derivatives.32,59,60 In addition to alkylation at O, sulfinyl
metal systems, MS(dO)R, can also alkylate at S.61
Given the fundamental interest in the nucleophilicity of the
SO functional group and its importance in the chemistry of
organic sulfoxides, there is broad potential among either
metallo forms, M2(SO) or MS(dO)R, considering the possi-
ble variations in the metal, the d-electron count, coligands,
M-S π bonding/antibonding character, and other factors,
along with the interplay of such factors toward enhancing the
classical polarized bond form (δ+)S-O(δ-) of the sulfoxide
linkage.9,62 Difficulties in synthetic methodologies, however,
impede such studies. Unfortunately, one of the best known
reactions for these systems is further oxygenation to M2(SO2)
or MS(dO)2R (or other products); such reactions are often
facile and difficult to avoid synthetically. The protonation/
deprotonation method reported herein proved very effective
in protecting BnS{Mo2}SO, 1, from the second oxygenation.
As a ligand, the -SOR thioperoxide bridge has proven to
be fairly robust in the present systems so far, even outlasting
some coligands under somewhat energetic conditions. The
failure to achieve isomerization to a sulfinyl ligand may be an
experimental difficulty or it may represent a thermodynamic
preference, an outcome which is known for some sulfenate
ester-sulfoxide conversions.23,24,41,63
Given the thioperoxide/sulfenate ester RSOR connection,
the present compounds S{Mo2}SOR, 5, can be considered
dimolybdenum sulfenate ester analogs. This consideration
(moreso for 5 than for 4+ or 6 given the background of prior
work) follows previous analogies of dimolybdenum sulfenyl
types such as the primary sulfenamide S{Mo2}SNH2,54,64
sulfenimines S{Mo2}SNdCZ2,54 sulfenyl halides S{M2}SX
(more stable for M = W than for M = Mo),65 and disulfides
S{Mo2}SSR.43,46 Despite the fact that the sulfur is three-
bonded in these complexes, other structural, spectroscopic,
and chemical properties parallel such properties in RSNH2,
RSNdCZ2, RSX, and RSSR.
The sulfenate character of the current system contrasts
sharply with various sulfinyl ligand complexes which are
termed sulfenates. There is reasonable cause for more uni-
form terminology for the various sulfur oxygenates within
the inorganic and organic domains which span the general
chemistry of sulfur.
Experimental Section
Reactions and manipulations were conducted open to the
air, except as noted. BnS{Mo2}S, 2, was prepared as pre-
viously reported43 or by an analogous procedure using BnCl
in benzene instead of BnBr in CH2Cl2. m-Chloroperbenzoic
acid was prepared for use by drying a small portion (<1 g)
of the commercial impure reagent (containing water and
m-chlorobenzoic acid) in a desiccator for several days. The
peracid/acid content for each portion was then assessed from
1
the H NMR spectrum, and this was converted to mass
percent. PPN+I- was prepared from PPN+Cl-.66 Where
indicated, “dry” CH2Cl2 was simply syringed from a settled
slurry of solvent, CaCl2, and NaHCO3. Other solvents and
reagents were used as received. Silica gel was Davisil grade
644. Except whereindicated, operations were conducted open
to the air. 31P{1H} and 1H NMR spectra were obtained on
a Varian Inova500 spectrometer; results are reported relative
to external 85% H3PO4 and internal Me4Si, respectively.
Solution reactions were monitored by NMR spectroscopy
in (CD3)2CO, except as noted. NMR characterization data
were obtained in CDCl3 and are reported below; values for
the minor sulfur invertomers are given in parentheses
when these were confidently discernible. When three or more
isomers could be assigned, these were given by A for the
major isomer, followed by B-D parenthetically for the other
isomers. The A-D labels follow those diagrammed in the
Results for 4+. Infrared spectra were obtained on a Mattson
Galaxy Series FTIR 5000 spectrometer by diffuse reflectance
on KBr powder.
BnS{Mo2}SO, 1. This preparation is greatly improved over
the prior method,17 and no light exclusion is necessary.
A solution of BnS{Mo2}S, 2 (0.3701 g, 0.375 mmol) in 7.0 mL
Me2CO was chilled in an ice water bath. Separately, a solution of
m-chloroperbenzoic acid (0.0719 g, 88%, 0.37 mmol) in 1.8 mL
of Me2CO was likewise chilled. To the stirring, red-orange
solution of 2 were added in close succession MeCO2H (86 μL),
HBF4 (48% aqueous, 98 μL), and then, dropwise, the cold
solution of m-chloroperbenzoic acid. Two rinses (0.5 mL each)
with Me2CO were used to facilitate the quantitative transfer of
the peracid solution. The solution color changed to orange-
yellow during the addition.
(55) Vasyutinskaya, E. A.; Eremenko, I. L.; Pasynskii, A. A.; Nefedov, S.
E.; Yanovskii, A. I.; Struchkov, Y. T. Russ. J. Inorg. Chem. 1991, 36,
964–972.
(56) Kramer, A.; Lingnau, R.; Lorenz, I.-P.; Mayer, H. A. Chem. Ber.
::
1990, 123, 1821–1826. Messelhauser, J.; Gutensohn, K. U.; Lorenz, I.-P.;
Hiller, W. J. Organomet. Chem. 1987, 321, 377–388.
(57) Silverthorn, W. E. J. Organomet. Chem. 1980, 184, C25–C27.
(58) Karet, G. B.; Norton, D. M.; Stern, C. L.; Shriver, D. F. Inorg. Chem.
1994, 33, 5750–5753.
(59) Schenk, W. A.; Bezler, J.; Burzlaff, N.; Hagel, M.; Steinmetz, B. Eur.
J. Inorg. Chem. 2000, 287–297.
(60) Bellefeuille, J. A.; Grapperhaus, C. A.; Buonomo, R. M.;
Reibenspies, J. H.; Darensbourg, M. Y. Organometallics 1998, 17,
4813–4821.
After stirring cold for 3 min, a solution (unchilled) of NaH-
CO3 (0.2518 g, 3.00 mmol) in 4.0 mL of H2O was slowly added,
(61) Gainsford, G. J.; Jackson, W. G.; Sargeson, A. M. J. Am. Chem. Soc.
1982, 104, 137–141.
(62) Schenck, W. A.; Frisch, J.; Adam, W.; Prechtl, F. Inorg. Chem. 1992,
31, 3329–3331.
(63) Gildersleeve, J.; Rascal, R. A.; Kahne, D. J. Am. Chem. Soc. 1998,
(64) Noble, M. E. Inorg. Chem. 1990, 29, 1337–1342.
(65) Lee, J. Q.; Sampson, M. L.; Richardson, J. F.; Noble, M. E. Inorg.
Chem. 1995, 34, 5055–5064.
120, 5961–5969.
(66) Martinsen, A.; Songstad, J. Acta Chem. Scand. A 1977, 31, 645–650.

Article
Inorg. Chem., Vol. 48, No. 11, 2009
5037
causing the color to go very dark. The solution was removed
from the ice bath. Additional H2O (10 mL) was added dropwise,
and the slurry was stirred for 5 min and then filtered. The solid
was washed (1:2 Me2CO/H2O) and then suction-dried to give an
olive solid (0.3662 g, 99% crude yield). The 31P NMR spectrum
revealed 96 mol % purity.
(ppm): 115.0, (114.8). 1H NMR (ppm): (6.60 d), 6.56 d, 6.46 d
(6.45 d), To-H; (4.33 q), 4.20 q, SOCH2; 4.18 m, 4.08 m,
POCH2; (2.08 s), 2.08 s, To-CH3; (1.36 t), 1.36 t, SOCCH3;
1.32 t, (1.22 t), 1.21 t, POCCH3; 1.25 s, (1.18 s), O2CCH3.
Invertomer ratio: 3.8.
S{Mo2}SOBn, 5(Bn). To a solution of BnS{Mo2}SO,
1 (0.0996 g, 0.0993 mmol) in 2 mL of Me2CO was added BnBr
(47 μL, 0.40 mmol). The solution was stirred for 2.9 h. Pre-
cipitation using 1:1 EtOH/H2O (6 mL), followed by filtration,
washing (1:1 EtOH/H2O), and suction-drying, gave an orange
powder (0.0570 g, 57%). 31P NMR (ppm): 114.9, (114.8).
1H NMR (ppm): 7.46 d, 7.29-7.39 m, BnH; 6.54 d, (6.53 d),
6.45 d, (6.32 d), To-H; (5.24 s), 5.14 s, Bn-CH2; 4.19 dq,
4.09 m, POCH2; 2.08 s, (2.05 s), To-CH3; 1.32 t, (1.23 t), 1.22 t,
POCCH3; (1.17 s), 1.04 s, O2CCH3. Invertomer ratio: 3.9.
Crude product (0.3510 g) and silica gel (3.5113 g) were stirred
together for several minutes in 15 mL of CH2Cl2, and the
mixture was then filtered. The silica gel fraction was washed
with CH2Cl2 (25 mL). The orange silica gel fraction, without
drying, was then washed slowly and in several portions with a
total of 38 mL of Me2CO; this released the product, giving an
olive filtrate and a pale yellow silica remainder. The olive filtrate
was rotavapped. The residue was promptly dissolved in 8.0 mL
of EtOH, and this solution was treated slowly with 8.0 mL of
H2O. Filtration and washing yielded very dark crystals of
1 (0.2983 g, 84% calcd overall yield). The compound was
typically stored at freezer temperatures of -15 ꢀC or so.
BnS{Mo2}SOMe+CF3SO3-, 4+(Me)CF3SO3-. In a
glovebag under N2, BnS{Mo2}SO, 1 (0.1611 g, 0.1606 mmol)
was dissolved in 1.5 mL of dry CH2Cl2. To this olive solution
was added CF3SO3Me (20 μL, 0.18 mmol), quickly lightening
the color. The stoppered flask was removed from the glovebag,
and the solution was stirred for 4 min to give a yellow-orange
solution. After opening to the air, the solution was rotavapped.
The residue was dissolved in 1.2 mL of EtOH, and then 2.4 mL
of H2O were added. The slurry was stirred for 1.4 h and filtered.
The product was washed (1:3 EtOH/H2O) and suction-dried
to give a yellow powder (0.1775 g, 95%). 31P NMR (ppm):
BnS{Mo2(PdO)}SOEt, 6. Dark olive BnS{Mo2}SO,
1 (0.1215 g, 0.121 mmol) was placed into the bottom of a tared
tube of dimensions ∼16 ꢀ 200 mm. The bottom portion of the
tube was immersed into a boiling water bath for 150 min. The
tube was then briefly immersed in water at room temperature
and then dried. The product was an orange-brown solid
(0.1207 g, 99%), which was 97 mol % by its 31P NMR spectrum.
Crude product (0.0926 g) was combined with silica gel (1.39 g)
in CH2Cl2 (4.6 mL) and stirred briefly. The slurry was filtered,
and the silica gel fraction was washed with CH2Cl2 and then
suction-dried. This was washed in portions with 20 mL (total) of
Me2CO, and the combined filtrates were then rotavapped. The
residue was dissolved in diglyme (1.2 mL). The addition of H2O
(1.8 mL) and stirring for 2.0 h gave a slurry which was then
filtered. Washing (1:2 EtOH/H2O) and suction-drying gave
a yellow powder (0.0710 g, 77% recovery). A trace impurity
(∼0.5 mol %) remained in the 31P NMR spectrum, while some
1
(109.9 C), (109.7 B), 109.1 (A). H NMR (ppm): 7.65 d (A),
(7.60 d), 7.55 t (A), 7.47 t (A), Bn-H; (6.82 br), (6.74 br),
(6.65 d), 6.62 d (A), 6.58 d (A), To-H; (4.79 s, C), 3.96 s (A),
(3.61 s, B), Bn-CH2; (4.37 s, B), 4.23 s (A), SOCH3; 4.26 m,
4.07 dq, POCH2; (2.21 s), 2.13 s (A), To-CH3; 1.52 s (A),
(1.47 s), O2CCH3; 1.44 t (A), 1.24 t (A), POCCH3. Invertomer
distribution: 76% A, 16% B, 9% C.
1
diglyme (∼1 mol %) lingered in the H NMR spectrum. 31P
NMR (ppm): (112.2), 111.8 (JPP = 1.5 Hz), (EtO)2P; (76.5),
76.3, (EtO)(O)P. 1H NMR (ppm): 7.75 d, (7.70, d), 7.50 t, 7.40 t,
Bn-H; (6.63 d), 6.55 d, 6.48 d, 6.47 d, 6.39 d, To-H; 4.47 dq,
4.36 dq, SOCH2; 4.23 dq, 4.03 dq, P(OCH2)2; 4.18 d, 3.81 d,
(3.47 d), Bn-CH2; 3.83 dq, PO(OCH2); (2.10 s), 2.09 s, (2.05 s),
2.03 s, To-CH3; (1.53 t), 1.41 t, SOCCH3; 1.43 s, O2CH3; 1.39 t,
1.21 t, P(OCCH3)2; 1.02 t, (1.02 t), PO(OCCH3). Invertomer
ratio: 5.
BnS{Mo2}SOEt+CF3SO3-, 4+(Et)CF3SO3-. The re-
-
action steps followed those for 4+(Me)CF3SO3 above, using
1 (0.1049 g, 0.1046 mmol) and CF3SO3Et (15 μL, 0.12 mmol) in
1.5 mL of dry CH2Cl2. After the reaction and then rotavapping,
Et2O (2.0 mL) and pet ether (1.5 mL) were added, and this
mixture was then stirred for 1.5 h. The slurry was filtered, and
the product was then washed (3:2 Et2O/pet ether) and suction-
dried to give a yellow powder (0.1109 g, 90%). 31P NMR (ppm):
X-Ray Crystallography. The crystal for the proximal iso-
mer of 5(Et) was mounted on a glass fiber, while the crystals
for the other structures were mounted on a CryoLoop with
Paratone oil. Data were collected on a Bruker SMART APEX
CCD diffractometer using monochromated Mo KR radiation.
The SMART software package (v. 5.632) was used for data
collection. Frame data were processed using SAINT (v. 6.45a);
raw hkl data were corrected for absorption using SADABS
(v. 2.10). The structures were solved by Patterson methods using
SHELXS-90 and refined by least-squares methods on F2 using
SHELXL-99 incorporated into the SHELXTL (v. 6.14) suite of
programs. Information specific to each structure is given below
and summarized in Table 3. More extensive information is given
in the Supporting Information. Crystallographic data for the
structural analyses have also been deposited with the Cambridge
Crystallographic Data Centre (CCDC), and those numbers
are given for each structure below.
1
(110.0 C), (109.7 B), 109.2 (A). H NMR (ppm): 7.65 d (A),
(7.60 d), 7.55 t (A), 7.47 t (A), Bn-H; (6.80 br), (6.74 br),
(6.65 d), 6.61 d (A), 6.57 d (A), To-H; (4.77 s, C), 3.96 s (A),
(3.61 s, B), Bn-CH2; (4.57 q, B), 4.47 q (A), SOCH2; 4.25 m,
4.07 dq, POCH2; (2.21 s, C), (2.14 s, B), 2.13 s (A), To-CH3;
(1.64 t, B), 1.50 t (A), SOCCH3; 1.50 s (A), O2CCH3; 1.43 t (A),
1.24 t (A), POCCH3. Invertomer distribution: 75% A,
16% B, 9% C.
S{Mo2}SOMe, 5(Me). PPN+I- (0.0641 g, 0.0963 mmol)
-
was added to a solution of BnS{Mo2}SOMe+CF3SO3
(4+(Me)CF3SO3-, 0.0936 g, 0.0793 mmol) in Me2CO (0.9
mL) plus THF (0.6 mL). Through 4 min of stirring, the PPN+I-
dissolved, and the solution turned red-orange. Then, 1:1
EtOH/H2O (3.0 mL) was added. The slurry was filtered; the
solid was washed (2:1 EtOH/H2O) and suction-dried to give a
red-orange, crystalline product (0.0536 g, 72%). 31P NMR
Crystals of BnS{Mo2}SOEt+CF3SO3 (4+(Et)CF3SO3
)
-
-
were obtained from layering n-C7H16 onto a solution in
MeCCl3. The carbon atoms of one dithiophosphate OEt group
were modeled with a 50% disorder (C23a-C24a and C23b-
C24b) as was the methyl atom (C20a and C20b) of another OEt
group. The triflate anion was disordered but was accurately
modeled using two half-occupancy fluorine groups (F1a-F3a,
and F1b-F3b) and two half-occupancy oxygen groups (O10a-
O12a, and O10b-O12b); the carbon and sulfur of the anion
were full-occupancy. All non-hydrogen atoms except those
involved in set b of the disordered anion were refined anisotro-
1
(ppm): 114.9, (114.8). H NMR (ppm): 6.57 d, 6.47 d, To-H;
4.19 m, 4.07 m, POCH2; 3.95 s, SOCH3; 2.08 s, To-CH3; 1.33 t,
1.21 t, POCCH3; 1.28 s, (1.18 s), O2CCH3. Invertomer ratio: 18.
S{Mo2}SOEt, 5(Et). The synthesis followed that of 5(Me)
above, using 4+(Et)CF3SO3- (0.1775 g, 0.150 mmol) in Me2CO
(1.0 mL) plus THF (1.0 mL) and PPN+I- (0.1204 g,
0.181 mmol), stirring for 5 min. Precipitation with 1:1 EtOH/
H2O (4 mL), followed by filtration, washing (2:1 EtOH/H2O),
and drying, gave a red-orange solid (0.0878 g, 62%). 31P NMR

5038 Inorg. Chem., Vol. 48, No. 11, 2009
Tuong et al.
Table 3. Selected Crystal Data and Refinement Results
BnS{Mo2}SOEt+ (4+) CF3SO3
S{Mo2}SOEt (5), distal
S{Mo2}SOEt (5), proximal
BnS{Mo2(PdO)}SOEt (6)
-
formula
fw
T, ꢀC
wavelength, A
cryst syst
space group
a, A
b, A
c, A
C
34H49F3Mo2N2O10P2S7
1180.99
C26H42Mo2N2O7P2S6
940.80
25
C26H42Mo2N2O7P2S6
940.80
C31H44Mo2N2O7P2S6
1002.86
-173
0.71073
monoclinic
Cc
18.917(4)
10.906(2)
24.231(4)
104.856(4)
4832.0(15)
1.623
-173
0.71073
monoclinic
P21/c
20.448(2)
19.771(2)
9.470(1)
97.819(2)
3792.8(7)
1.648
-173
0.71073
monoclinic
P21/n
12.940(3)
13.775(3)
23.200(5)
94.521(4)
4122.6(14)
1.616
0.71073
monoclinic
P21/c
17.668(4)
9.900(2)
23.167(5)
90.073(4)
4052.1(14)
1.542
4
1.047
β, deg
V, A3
Dcalcd, g/cm3
Z
4
0.951
4
1.118
4
1.035
abs coeff, mm-1
cryst size, mm3
cryst habit
abs corrn
max/min transmission
final R1 (I > 2σ(I))a
final wR2 (I > 2σ(I))b
GOFc
0.25 ꢀ 0.20 ꢀ 0.02
yellow plate
SADABS
0.989/0.725
0.0505
0.30 ꢀ 0.10 ꢀ 0.05
red-orange needle
SADABS
0.941/0.673
0.0455
0.35 ꢀ 0.25 ꢀ 0.15
orange rhomb prism
SADABS
0.895/0.733
0.0510
0.29 ꢀ 0.22 ꢀ 0.08
orange plate
SADABS
0.914/0.787
0.0355
0.1175
1.03
0.0857
1.03
0.1085
1.06
0.0753
1.02
P
P
P
P
P
a
R1 = ||Fo| - |Fc||/ |Fo|. b wR2 ={ [w(Fo2 - Fc2)2]/ [w(Fo2)2]}1/2, where w = q/σ2(Fo2) + (qp)2 + bp. c GOF = S={ [w(Fo2 - Fc2)2]/(n - p)}1/2
.
pically. Hydrogen atoms were placed in their geometrically
generated positions and refined as a riding model. Methyl H’s
were included as fixed contributions with U(H) = 1.5 ꢀ Ueq
(attached C atom), while the torsion angle which defines its
orientation was allowed to refine on the attached C atom.
Methylene and phenyl H’s were included as fixed contributions
with U(H) = 1.2 ꢀ Ueq (attached C atom). For all 9175 unique
reflections (R(int) = 0.045), the final anisotropic, full matrix
least-squares refinement on F2 for 455 variables converged at
(for I > 2σ(I)) R1 = 0.0505 and wR2 = 0.1175 with a GOF of
1.03 (CCDC No. 710480).
atoms attached to parent carbon atoms were positioned geome-
trically (C-H = 0.95-0.99 A) and refined using a riding model
as described above for 4+(Et)CF3SO3-. For all 8687 unique
reflections (R(int) = 0.043), the final anisotropic, full matrix
least-squares refinement on F2 for 423 variables converged at
(for I > 2σ(I)) R1 = 0.0510 and wR2 = 0.1085 with a GOF of
1.06 (CCDC No. 710481).
Crystals of BnS{Mo2(PdO)}SOEt, 6, were obtained by stor-
ing a test tube containing a solution in Et2O inside a closed jar
with a layer of n-C12H26 in the bottom of the jar. All non-
hydrogen atoms were refined anisotropically. Hydrogen atoms
were placed in their geometrically generated positions and
refined as a riding model as described above for 4+(Et)
CF3SO3-. For all 7717 unique reflections (R(int) = 0.045),
the final anisotropic, full matrix least-squares refinement on F2
for 422 variables converged at (for I > 2σ(I)) R1 = 0.0355 and
wR2 = 0.0753 with a GOF of 1.02 (CCDC No. 710483).
Crystals of distal S{Mo2}SOEt, 5(Et), were obtained from
layering a solution in MeCN onto H2O. The disorder in a
dithiophosphate OEt group was modeled using two sets of
50% occupancy carbon atoms (C21a-C22a and C21b-
C22b). All other non-hydrogen atoms were refined anisotropi-
cally. Hydrogen atoms were placed in their geometrically gen-
erated positions and refined as a riding model as described above
for 4+(Et)CF3SO3-. For all 7235 unique reflections (R(int) =
0.047), the final anisotropic, full matrix least-squares refinement
on F2 for 455 variables converged at (for I > 2σ(I)) R1 = 0.0455
and wR2 = 0.0857 with a GOF of 1.03 (CCDC No. 710482).
Crystals of proximal S{Mo2}SOEt, 5(Et), were obtained from
layering EtOH onto a solution in 1,2,3-trichloropropane. The
disordered dithiophosphate OEt group was modeled using two
sets of carbon atoms; C19a-C20a were refined anisotropically
at 80% occupancy and C19b-C20b isotropically at 20%. All
non-hydrogen atoms were refined anisotropically. All hydrogen
Acknowledgment. This work was supported in part by the
Office of the Vice President for Research at the University of
Louisville. M.S.M. thanks the Kentucky Research Challenge
Trust Fund for an upgrade of the X-ray facilities.
Supporting Information Available: Additional crystallo-
graphic refinement details and data, including CIF files.
This material is available free of charge via the Internet at
http://pubs.acs.org.