Oxygenation of zinc dialkyldithiocarbamate complexes: Isolation, characterization, and reactivity of the stoichiometric oxygenates

Article abstract of DOI:10.1021/ic060671j

S-oxygenation of dithiocarbamate (DTC) complexes has been implicated in their function as industrial anti-oxidants, as well as in their use as pesticides and most recently in their cumulative toxicity, but little is known of the species generated. Several S-oxygenated derivatives of N,N-disubstituted DTCs have been synthesized, characterized by a variety of methods, and their structure and reactivity examined. Low-temperature reaction of bis(N,N-diethyldithiocarbamato)zinc(II), Zn(deDTC)₂ 1, with oxygenating reagents (hydrogen peroxide, m-chloroperbenzoic acid, urea hydrogen peroxide) yields mono-oxygenated DTC complexes (N,N- peroxydiethyldithiocarbamato)(N,N-diethyldithiocarbamato)zin(II), Zn(O-deDTC)(deDTC), 2 and bis(N,N-peroxydiethyldithiocarbamato)zinc(II), Zn(O-deDTC)₂, 3. The tetraoxygenated derivative bis(N,N- diethylthiocarbamoylsulfinato)zinc(II), Zn(O₂-deDTC)₂, 4, was cleanly obtained by initial reaction of the DTC salts with stoichiometric oxidant prior to complexation with Zn(II). X-ray crystallographic analysis of 2, 3, and 4 show that the peroxydithiocarbamate ligands are S,O-bound. Similar derivatives were obtained from the homoleptic dimethyl and pyrollidine DTC Zn complexes. These oxygenated species display unique ¹H and ¹³C NMR variable-temperature spectra, as the symmetry of DTC ligand is broken upon oxygenation; total line shape analysis (TLSA) was used to compare the energetic parameters for rotation about the C-N bond in several derivatives. Compounds 2, 3, and 4 were deoxygenated by alkyl phosphine, regenerating the parent dithiocarbamate 1. The peroxydithiocarbamate complexes were susceptible to base-catalyzed hydrolytic decomposition, giving ligand-based products indicative of S-oxidation and S-extrusion.

Full text of DOI:10.1021/ic060671j

Inorg. Chem. 2006, 45, 6064−6072
Oxygenation of Zinc Dialkyldithiocarbamate Complexes: Isolation,
Characterization, and Reactivity of the Stoichiometric Oxygenates
Daniel F. Brayton, Kristine Tanabe, Mariya Khiterer, Kian Kolahi, Joseph Ziller, John Greaves, and
Patrick J. Farmer*
Department of Chemistry, UniVersity of California, IrVine, California 92697-2025
Received April 19, 2006
S-oxygenation of dithiocarbamate (DTC) complexes has been implicated in their function as industrial anti-oxidants,
as well as in their use as pesticides and most recently in their cumulative toxicity, but little is known of the species
generated. Several S-oxygenated derivatives of N,N-disubstituted DTCs have been synthesized, characterized by
a variety of methods, and their structure and reactivity examined. Low-temperature reaction of bis(N,N-diethyl-
dithiocarbamato)zinc(II), Zn(deDTC)2 1, with oxygenating reagents (hydrogen peroxide, m-chloroperbenzoic acid,
urea hydrogen peroxide) yields mono-oxygenated DTC complexes (N,N-peroxydiethyldithiocarbamato)(N,N-
diethyldithiocarbamato)zin(II), Zn(O-deDTC)(deDTC), 2 and bis(N,N-peroxydiethyldithiocarbamato)zinc(II), Zn(O-
deDTC)2, 3. The tetraoxygenated derivative bis(N,N-diethylthiocarbamoylsulfinato)zinc(II), Zn(O2-deDTC)2, 4, was
cleanly obtained by initial reaction of the DTC salts with stoichiometric oxidant prior to complexation with Zn(II).
X-ray crystallographic analysis of 2, 3, and 4 show that the peroxydithiocarbamate ligands are S,O-bound. Similar
derivatives were obtained from the homoleptic dimethyl and pyrollidine DTC Zn complexes. These oxygenated
species display unique 1H and 13C NMR variable-temperature spectra, as the symmetry of DTC ligand is broken
upon oxygenation; total line shape analysis (TLSA) was used to compare the energetic parameters for rotation
about the C−N bond in several derivatives. Compounds 2, 3, and 4 were deoxygenated by alkyl phosphine,
regenerating the parent dithiocarbamate 1. The peroxydithiocarbamate complexes were susceptible to base-catalyzed
hydrolytic decomposition, giving ligand-based products indicative of S-oxidation and S-extrusion.
Scheme 1
Introduction
Dithiocarbamates (DTCs) are strong metal chelators used
industrially as pesticides, vulcanization accelerators, and
lubricants.1-5 Disulfiram (DSF), a disulfide derivative of N,N-
diethyldithiocarbamate (deDTC), is clinically used in alcohol
aversion therapy because of its inhibition of aldehyde
dehydrogenase, a crucial enzyme in the physiological detoxi-
fication of ethanol.6 This activity has been attributed to
S-oxygenated derivatives of DSF formed by xenobiotic
transformations,7 Scheme 1. In this hypothesis, alkylated
* To whom correspondence should be addressed. E-mail: pfarmer@uci.edu.
(1) Reid, E. E. Organic Chemistry of BiValent Sulfur; Chemical Publishing
Co.: New York City, 1962.
(2) Becker, R. K., A. Lubr. Sci. 1996, 8, 95-117.
(3) Becker, R. K., A. Z. Kristallogr. - New Cryst. Struct. 1995, 210,
769-774.
(4) Shelkova, R. G. K. m., G. N.; Dzyubina, M. A.; Il’in, K. V.; Parenago,
O. P. Neftekhimiya 1990, 30, 244-251.
(5) Parenago, O. P. K. m., G. N.; Bakulin, V. N.; Shelkova, R. G.;
Zaimovskaya, T. A. Neftekhimiya 1995, 35, 219-227.
(6) DeMaster, E. G.; Redfern, B.; Nagasawa, H. T. Biochem. Pharmacol.
1998, 55, 2007-2015.
DTCs are oxygenated within the liver, ultimately generating
monothiocarbamates (MTCs) by sulfur extrusion from a
sulfine intermediate. Further oxygenation produces sulfoxide
and sulfone MTC derivatives (MTC-MeSO and MTC-
6064 Inorganic Chemistry, Vol. 45, No. 15, 2006
10.1021/ic060671j CCC: $33.50
© 2006 American Chemical Society
Published on Web 06/28/2006

Oxygenation of Zinc Dialkyldithiocarbamate Complexes
Scheme 2
Figure 1. UV-vis absorbance spectra of compounds 1, 2, 3, and 4 at
0.025 mM in CH2Cl2.
MeSO2), which substantial evidence implies are the active
agents in ALDH inhibition in vivo.7,8
Recently, we and others have shown that nanomolar
concentrations of DSF induce apoptotic cell death in
metastatic melanoma cells,9 and DSF has shown some
success in clinical trials.10 The anti-melanoma activity of DSF
is metal ion dependent, and we have shown that one possible
active agent is Cu(deDTC)2, formed by cannibalistic decom-
position of DSF.11
Previous investigations of the activity of both DSF and
other DTC derivatives have focused on biotransformations
of the DTC ligand itself, but little consideration was given
to what effect metal-uptake might induce.7,8,12,13 The evidence
for the bioactivation of DSF by S-oxygenation is attributed
to alkylated forms, and we postulated that similar reactivity
may occur upon oxygenation of DTC metal complexes. In a
recent report, the reaction of an inert Ru-DTC complex with
O-atom transfer agents yielded products of both S-oxygen-
ation and S-extrusion key to the transformations in Scheme
1;14 a kinetically inert Ru complex was investigated in hopes
of trapping and characterizing various intermediates formed
from the initial oxygenated intermediates. In this report, we
examine synthetic aspects of the S-oxygenation of Zn DTC
complexes, as well as forming Zn complexes using pre-
oxygenated free DTCs, to assay the stability and reactivity
of the resulting products.
Figure 2. Infrared spectra (KBr pellet) of Zn(deDTC)(O-deDTC)2, 2, and
Zn(O2-deDTC)2, 4; tentatively assigned νSO stretching frequencies are
indicated.
with regard to their function as antioxidants and vulcanizing
agents in polymeric materials, but relatively few oxygenated
dithiocarbamate complexes have been reported that are
analogous to those described here.3-5,14-19 Scheme 2 il-
lustrates the compounds identified in this study, which
include the peroxydithiocarbamate derivatives Zn(O-deDTC)-
(deDTC), 2, Zn(O-deDTC)2, 3, the dioxygenated dithiocar-
bamoylsulfinato Zn(O2-deDTC)2, 4, and analogous deriva-
tives of pyrollidine and dimethyl-substituted dithiocarbamates.
Electronic and Vibrational Spectra. Shown in Figure 1
are equilmolar absorbance spectra for the isolated complexes
1, 2, 3, and 4 which demonstrate the change in absorbance
of DTC derivatives upon sequential oxygenation. The
peroxydithiocarbamate complexes have a distinct absorbance
at 325 nm, similar to bands observed in other sulfenate metal
complexes, M-S(O)R, that have been attributed to the S-O
chromophore.20,21 The band apparent in spectra of the mono-
oxygenate 2, roughly doubles in that of the homoleptic bis-
O-deDTC species, 3, but disappears in that of the homoleptic
bis-O2-deDTC complex, 4. A previous kinetic study at-
tributed a distinctive band at ca. 300 nm to the dioxygenated
DTC ligand22 but is not observe for crude or purified samples
of 4.
Results and Discussion
The oxygenation and oxidative decomposition of metal
dithiocarbamate complexes have been previously investigated
(7) Madan, A.; Faiman, M. D. Drug Metab. Dispos. 1994, 22, 324-330.
(8) Hart, B. W.; Faiman, M. D. Biochem. Pharmacol. 1992, 43, 403-
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N. B.; Meyskens, F. L. Mol. Cancer Ther. 2002, 1, 197-204.
(10) Brar, S. S.; Grigg, C.; Wilson, K. S.; Holder, W. D.; Dreau, D.; Austin,
C.; Foster, M.; Ghio, A. J.; Whorton, A. R.; Stowell, G. W.; Whittall,
L. B.; Whittle, R. R.; White, D. P.; Kennedy, T. P. Mol. Cancer. Ther.
2004, 3, 1049-1060.
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J. J. Med. Chem. 2004, 47, 6914-6920.
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Chem. Commun. 1977, 99-100.
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Nobel, C. S. I.; Orrenius, S.; Slater, A. F. G. Arch. Biochem. Biophys.
1998, 353, 73-84.
(18) Reck, G.; Becker, R. Acta Crystallogr. E 2003, 59, M489-M490.
(19) Reck, G.; Becker, R.; Walther, G. Z. Kristallogr. 1995, 210, 769-
774.
(13) Stefan, C.; Nobel, I.; Burgess, D. H.; Zhivotovsky, B.; Burkitt, M. J.;
Orrenius, S.; Slater, A. F. G. Chem. Res. Toxicol. 1997, 10, 636-
643.
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3109-3118.
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(14) Ng, S.; Ziller, J. W.; Farmer, P. J. Inorg. Chem. 2004, 43, 8301-
8309.
Inorganic Chemistry, Vol. 45, No. 15, 2006 6065

Brayton et al.
Figure 4. Variable-temperature 1H NMR of Zn(deDTC)(O-deDTC) 2 (+50
to -50 °C, from top to bottom).
Figure 3. 1H NMR spectra of each isolated diethyl zinc compounds 1, 2,
3, and 4.
Figure 2 displays infrared spectra obtained for compounds
2 and 4. Strong vibrational bands in the IR spectrum are
expected for the sulfenate (960-1000 cm-1) and sulfinate
(1250-1050 and 1080-1030 cm-1) moieties.14,20-24 The
prominent band at 816 cm-1 in the spectrum of 2 is not
apparent in the spectra of the parent 1 (Supporting Informa-
tion, S1) and is tentatively assigned to the sulfenic ν(SO)
stretch. A similar band at 804 cm-1 was reported for the
S,O-bound form Ru(bpy)2(O-dmDTC)+; a band at 1030 cm-1
was assigned to the sulfenic ν(SO) stretch of the S,S-bound
form.14 Likewise, two strong bands at 1066 and 1002 cm-1
are apparent in the spectra of 4 and are attributed to the
asymmetric and symmetric ν(SO2) stretches of the sulfinato
group. Similar bands at 1144 and 1048 cm-1 were assigned
to ν(SO2) for the S,S-bound thiocarbamate-sulfinato, Ru-
(bpy)2(O2-dmDTC)+; the lower-energy absorbances observed
for the S,O-bound 4 are expected due to the difference in
coordination mode.14
1
Figure 5. Variable-temperature H NMR of Zn(dmDTC)(O-dmDTC), 6
(+60 to -60 °C, from top to bottom).
Scheme 3
Table 1. Parameters for Zn(deDTC)(O-deDTC) and
Zn(dmDTC)(O-dmDTC) Complexes
∆Gq
∆Hq
∆Sq
Ea
compound
(kcal/mol) (kcal/mol) (kcal/mol) (kcal/mol)
Zn(O-deDTC)(deDTC), 2
Zn(O-deDTC)2, 3
Zn(O-dmDTC)(dmDTC), 6
12.25
18.5
11.9
15.0
12.2
15.9
9.2
23
13.2
15.6
12.7
16.5
1
1H NMR. H NMR spectra can differentiate the degree
or -50 °C, allows the degree of oxygenation to be quantified.
Similar behavior is observed for the dimethyl peroxydithio-
carbamate, 5, Figure 5, as well as for the Ru-bound
peroxydithiocarbamate complex.14
of oxygenation within the DTC-derived ligands, Figure 3
and Scheme 2, but not between possible mixtures of
complexes; the N-alkyl-based signals are unaffected by the
nature of the second ligand on the metal ion, i.e., a 1:1
mixture of Zn(O-pDTC)2 and Zn(pDTC)2 is indistinguishable
from a sample of Zn(O-pDTC)(pDTC). The parent DTC
complexes are known to undergo rapid ligand exchange
between metal centers, and such exchange processes are
evident in mixtures of the peroxydithiocarbamate complexes
(vide supra).
Broadening of the N-alkyl resonances due to hindered
rotation about the C-N bond is well documented in DTC
complexes, Scheme 3.25-28 Rate constants for the exchange
of N-alkyl groups were determined by total line shape
analysis (TLSA) as described in the Experimental Section,
and activation parameters obtained from the least-squares
straight lines of the log(k/T) vs 1/T and log k vs 1/T
(Supporting Information, S2) and given in Table 1. The ∆Hq
values obtained fall within the range (10-19 kcal) previously
reported for rotation about the C-N bond in DTC deriva-
tives.25-28 The range of ∆Sq values is much broader (from
-13 to +17 cal), and thus, ∆Gq varies accordingly.25-28 To
our knowledge, this is the first time that these parameters
have been obtained for oxygenated DTC ligands, and more
generally, the first example of such exchange processes being
affected by insertion into a ligand-to-metal bond.
Significant line broadening also makes assignment of
product distributions difficult at room temperature, but high-
1
or low-temperature H NMR allows better integration to
assess the degree of oxygenation. This is illustrated by the
methylene peaks of 2, Figure 4. At -50 °C, three separate
quartets are observed at 3.34, 3.83, and 3.89 ppm. The 3.34
and 3.89 peaks coalesce into a broad signal at room
temperature (∼25 °C). As the temperature rises to +50 °C,
the broad signal sharpens into a quartet peak at 3.67 ppm
while the quartet at 3.83 remains relatively stationary. The
integration values for these peaks at the two extremes, +50
(25) Pignolet, L. H.; Lewis, R. A.; Holm, R. H. J. Am. Chem. Soc. 1971,
93, 360.
(26) Femec, D. A.; Silver, M. E.; Fay, R. C. Inorg. Chem. 1989, 28, 2789-
(23) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coor-
dination Compounds; Wiley: New York City, 1977.
(24) Farmer, P. J.; Reibenspies, J. H.; Lindahl, P. A.; Darensbourg, M. Y.
J. Am. Chem. Soc. 1993, 115, 4665-4674.
2796.
(27) Fay, R. C.; Weir, J. R.; Bruder, A. H. Inorg. Chem. 1984, 23, 1079-
1089.
(28) Paparizos, C.; Fackler, J. P. Inorg. Chem. 1980, 19, 2886-2889.
6066 Inorganic Chemistry, Vol. 45, No. 15, 2006

Oxygenation of Zinc Dialkyldithiocarbamate Complexes
Figure 6. ESI-MS spectra of a ca. 1:1 mixture of Zn(dmDTC)2, 5, and
Zn(O-deDTC)2, 3, indicating the presence of a mixed complex, Zn(dmDTC)-
(O-deDTC), 7, formed by ligand exchange.
Figure 7. Crystal structure determination solved as a 3:1 mixture of 2
and 3.
Mass Spectroscopy. The unique isotopic envelope of Zn
allowed ready identification of Zn-containing species in ESI-
MS spectra. In the homoleptic complexes, the parent ion
peaks were the most abundant (Supporting Information,
S3): M + H+ (m/z 361) for Zn(deDTC)2 1; M + H+ (m/z
393) and M + Na+ (m/z 415) for Zn(O-deDTC)2 3; and M
+ Na+ (m/z 447) for Zn(O2-deDTC)2 4. However, when an
analytically pure sample (by NMR and EA) of the singly
oxygenated compound 2 was analyzed, a distribution of
peaks obtained corresponding to 2 (plus H+ and Na+ at m/z
377 and 399), 3 (plus H+ and Na+ at m/z 393 and 431) and
4 (plus Na+ at m/z 447), with those attributed to the
homoleptic compounds more prominent than those of 2
(Supporting Information, S4). Smaller peaks are also apparent
that may be rationalized as mixed oxygenates, e.g., m/z 431
as M + Na+ for [Zn(O-deDTC)(O2-deDTC)].
Ligand exchange is facile in solutions of DTC metal
complexes29-31 and is also seen for the oxygenated deriva-
tives. ESI MS of equal molar solution of the homoleptic
peroxy-diethyldithiocarbamate 3, Zn(O-deDTC)2, and the
dimethyldithiocarbamate 5, Zn(dmDTC)2, showed prominent
peaks corresponding to the mixed complex Zn(dmDTC)(O-
deDTC), 7, Figure 6.
Scheme 4
different bonding angles, labeled in Table 1 as IR1, IR2, and
Iâ1, as in the original paper.14,17-19
As previously observed, oxygenation of the DTC ligand
expands the bidentate chelation from a four-member to a
five-member ring, Scheme 4; the S-bound tautomer, which
is the apparent kinetic product of oxygenation of the Ru-
(bpy)2(dmDTC)+ is not observed in the Zn complexes.14 The
dimeric 2:3 is formed by bridging of the sulfenic oxygens
between the two metal ions; the Zn2O2 core is rectangular
with Zn-O bond lengths of 2.12 and 2.05 Å. The parent
Zn(deDTC)2 complexes are also dimeric in the solid state,32,33
with one sulfur of a DTC bridging between two zinc atoms,
forming a Zn2S2 four-membered ring. All of these dimeric
structures have a center of symmetry and crystallize in the
P21/n space group; a comparison of the crystallographic
parameters and Zn-ligand bond lengths are given in the
Supporting Information (S5).
Solid-State Structures. Crystallographic characterization
of the diethyl peroxydithiocarbamate adducts has proved
difficult; crystals of homoleptic compound 3 did not diffract,
and three structural determinations of purified compound 2,
each showing significant disorder, attributed to partial
oxygenation of the second dithiocarbamate ligand. The best
refinement, shown in Figure 7, was solved as a 75:25 mixture
of dimeric compounds 2 and 3. Crystallographic disorder
was also observed in previous reported structures of per-
oxydithiocarbamate complexes: the Cr(deDTC)2(O-deDTC)
has O-atom disordered through three positions in the pseudo-
octahedral complex; likewise, three different homologues of
the dibutyl-peroxydithiocabamate complex Zn(O-dbDTC)2
were reported, with similar bond lengths but decidedly
The crystal structure of the sulfinato 4 is monoclinic and
in the P2/n space group, with two independent half-molecules
present in the unit cell. Each molecule is hydrogen-bonded
to the next through the Zn-bound water interacting with the
noncoordinated sulfinato oxygens. The representation shown
in Figure 8 illustrates the hydrogen bonding between the
nonbridging sulfinic oxygens and the water molecule coor-
dinated to the complex below, producing linear chains within
the crystal lattice. Hydrogen atoms of the coordinated water
were located from a difference map and refined. The
hydrogen bond (O-H‚‚‚O) Hwater to ODTC distances are 1.902
and 1.828 Å; the Owater to ODTC distances are 2.690 and 2.693
Å. The general form of the chelate is analogous to the
recently reported structure for bis-(diisobutyldithiocarbam-
(29) Palazzot, M.; Duffy, D. J.; Edgar, B. L.; Que, L.; Pignolet, L. H. J.
Am. Chem. Soc. 1973, 95, 4537-4545.
(30) Norman, V.; Duffy, W. G. M. a. D. L. U. Inorg. Chim. Acta 1982,
64, L19-93.
(31) Drabent, K.; Latosgrazynski, L. Polyhedron 1985, 4, 1637-1641.
(32) Simonsen, S. H.; Ho, J. W. Acta Crystallogr. 1953, 6, 430-430.
(33) Bonamico, M.; Mazzone, G.; Vaciago, A.; Zambonel, L. Acta
Crystallogr. 1965, 19, 898-909.
Inorganic Chemistry, Vol. 45, No. 15, 2006 6067

Brayton et al.
Table 2. Selected Bond Lengths (Å) for S-Oxygenated
Dithiocarbamate Derivatives Complexed to Metal Ions
M-ligand
N-C
C-S
Bridging
C-Sox
S-O
IR1 Zn-(O-dbDTC)a 1.338(18) 1.669(9)
IR2 Zn-(O-dbDTC)a 1.334(18) 1.691(9)
1.726(9)
1.744(9)
1.586(8)
1.581(7)
Iâ1 Zn-(O-dbDTC)a 1.371(19) 1.663(16) 1.733(15) 1.551(11)
2 Zn-(O-deDTC)
1.326(3)
1.709(2)
1.743(2)
1.5973(15)
Nonbridging
IR1 Zn-(O-dbDTC)a 1.309(16) 1.717(9)
IR2 Zn-(O-dbDTC)a 1.343(17) 1.719(9)
1.726(11) 1.45(11)
1.730(11) 1.543(9)
Iâ1 Zn-(O-dbDTC)a 1.318(18) 1.694(15) 1.742(17) 1.503(17)
Cr-(O-deDTC)b
Ru-(O-dmDTC)c
3 Zn-(O-deDTC)
1.324(8)
1.350(16) 1.701(12) 1.717(12) 1.588(9)
1.335(3) 1.456(8) 1.835(3) 1.562(6)
1.680(6)
1.754(8)
1.53(1)
S,O-Bound
4 Zn-(O2-deDTC) 1.3098(17) 1.6792(13) 1.8947(13) 1.5068(9)
Zn-(O2-dbDTC)d
1.303(4)
1.676(3)
1.899(3)
1.465(3)
1.509(3)
S,S-Bound
1.286(9)
Ru-(O2-dmDTC)c
1.698(8)
1.862(7)
1.470(5)
a IR1, IR2, Iâ1: three isoforms of Zn(O-dbDTC)2.19 b Cr-(O-deDTC):
Cr-(O-deDTC)(deDTC)2.17 c Ru-(O-dmDTC): Ru(bpy)2(O-dmDTC)(BF4);
Ru-(O2-dmDTC): Ru(bpy)2(O2-dmDTC)(BF4).14 d Zn-(O2-dbDTC): Zn-
(O2-dbDTC)2.18
Figure 8. Crystal structure determination of 4 [Zn(O2-deDTC)2(H2O)].
oylsulfinato)Zn(II); the sulfinato was S,O-bound to the metal
ion but without acoordinated water the Zn was four-
coordinate, close to Td symmetry.18
As in the parent complex 1, the C2NCS2 framework
remains substantially planar in complexes 2, 3, and 4,
indicating significant C-N double bond character remains
after S-oxygenation. The sulfenic oxygens of the mono-
oxygenated ligands in the 2:3 structures are coplanar with
the C2NCS2 framework, implying π-delocalization extends
through the oxygen. Such planarity is not seen for the sulfinic
oxygens of 4, in which the S-O bonds are ca. 26° from the
average C2NCS2 plane.
Figure 9. 1H NMR spectra of the products of the reaction of compound
1 with 2 equiv of UHP, which yielded a mixture of the dithiocarbamate
(A), peroxydithiocarbamate (B), and thiocarbamoylsulfinate (C) ligands.
mono-, and dioxygenated ligands.
The effect of S-oxygenation on delocalization within the
DTC framework may be qualitatively compared by examina-
tion of the C-N and C-S bond lengths within the various
characterized oxygenated derivatives, limited by the crystal-
lographic disorder. In general, oxygenation lengthens the
C-S bond of the oxygenated sulfur, Table 2, and cor-
respondingly shortens the C-S bond of the non-oxygenated
sulfur. This effect is larger for the bridging ligands, where
the oxygen is further coordinated to two cationic metal ions.
The localization of the double bond is even more evident in
the dioxygenated sulfinato ligands, and the bonding param-
eters are similar for both the Zn-S,O-bound complexes as
well as the S,S bound tautomer found in Ru(bpy)2(N,N′-
dimethylthiocarbamylsulfinate-S,S)+.14
Synthetic Routes to the Oxygenated Derivatives. While
the oxygenation of dithiocarbamates is facile, controlling the
level of oxidation is often difficult, as is purification of the
mixtures generated. For the Zn dithiocarbamates studied here,
the combination of rapid ligand exchange with decomposition
during chromatography on both silica and alumina made
obtaining pure compounds challenging.
plexation gave the best control over oxygenation. The
homoleptic peroxydithiocarbamate complex, 3, could only
be obtained by the latter route, and likewise, the highest
yields of 4 were obtained by initial ligand oxygenation prior
to zinc complexation. For both routes, urea hydrogen
peroxide (UHP) proved the superior reagent to cleanly
generate the peroxydithiocarbamate derivatives; as a stable
solid, it allowed better control over the stoichiometry of
oxygenation with decidedly fewer side-products than with
mCPBA or other oxidants.
Oxygenations of the Zn-bound DTC complexes themselves
are more difficult to control. Treatment of 1 with 1 equiv of
UHP in chloroform yielded the singly oxygenated complex
2 in greater than 90% yield by 1H NMR; isolated yields are
lower, ca. 50-60% as much product is lost during purifica-
tion. But treatment of 1 with 2 equiv of UHP yielded a
mixture of mono- and dioxygenated ligands observable by
NMR, Figure 9. Using high-temperature NMR (60 °C) to
assay the product mixture gave the distribution as ca. 35%
O-deDTC to 25% O2-deDTC with 40% deDTC unreacted,
Supporting Information, Table S6. Identical ligand distribu-
tions were obtained by stoichiometric reactions of 1 equiv
of UHP with purified 2. These results are consistent with
the initial oxygenation of 1 yielding predominantly the mixed
complex, 2, in which the peroxydithiocarbamates are perhaps
Two general synthetic routes were used. The reaction of
the homoleptic Zn DTC complexes with O-atom transfer
reagents typically generated mixtures of products, whereas
initial oxygenation of the free DTC ligand prior to com-
6068 Inorganic Chemistry, Vol. 45, No. 15, 2006

Oxygenation of Zinc Dialkyldithiocarbamate Complexes
Scheme 6
Scheme 7
Figure 10. 1H NMR of a reaction mixture of 2 with mCPBA left for over
a week, substantial conversion back to the starting Zn(deDTC)2 1 and DSF,
along with unknown byproducts.
Scheme 5
Organic thiosulfinates (RS(O)SR) are known to undergo
facile O-atom transfer and disproportionations.34,35 The
unstable Vic-disulfoxides (RS(O)S(O)R) have only been
observed spectroscopically; attempted isolations by chroma-
tography inevitably yield mixtures of disulfides and thio-
sulfonates. Previous studies of the electron-ionization MS
of alkyl dithiocarbamates suggested that formation of a 2,2-
diethyl thiooximinium cation, Scheme 6,36 is catalyzed by
carboxylates, e.g., mCPBA.37 Indeed, an ion at m/z 116
corresponding to the sulfonium is abundant in ESI-MS
spectra of yellow byproduct, which shifts to m/z 117 in
samples 13C-labeled at the thiocarbonyl, and this peak is
prominent in the ESI-MS of the oxygenated complexes.
Promotion of decomposition by O-donor Lewis bases is also
supported by the generation of the yellow byproducts upon
elution of purified samples of 2 and 3 on silica under both
aerobic and anaerobic conditions. As a test for the sensitivity
of the Zn-oxygenates to such Lewis base reactivity,
exposure of the homoleptic peroxydithiocarbamate complex
3 in CDCl3 to pH 10 borate buffer under biphasic conditions
also results in the slow generation of the yellow byproducts,
stabilized by bridging between two Zn in the dimeric form
seen in the solid state. Comparison of the product yields upon
further oxygenation shows that the rate of oxygenation of
the O-deDTC is over twice that of deDTC. Thus, the
reactivity of the Zn-bound peroxydithiocarbamates varies
with its coordination mode, with the nonbridging form much
more susceptible to oxygenation than the similarly coordi-
nated dithiocarbamate.
Oxygenations with mCPBA proved to be even more
problematic. The reaction of 1 with 1 equiv of mCPBA
yielded the isolated mono-oxygenated 2 in modest yield by
1H NMR, but the reaction mixture was yellow and byprod-
ucts were evident. If reaction mixtures were left for long
periods of time, substantial conversion back to the starting
1 was observed, Figure 10. Considerable side reactions were
observed when more than 1 equiv of mCPBA was reacted
with 1; to follow this reactivity, 13C-labeled 1 at the
thiocarbonyl Zn(deDTC)2 was reacted and the product
mixture followed by ESI MS and 13C and 1H NMR,
Supporting Information, S7. The thiocarbonyl peak of starting
complex 1 appears in the 13C spectra at 202 ppm, indepen-
dently synthesized homoleptic peroxydithiocarbamate 3 at
208, and the sulfinato thiocarbamate 4 at 212 ppm. Upon
reaction of a 3:1 mixture of mCPBA and 1, the initial
formation of 2 is readily identifiable, but DSF and various
oxygenated products and sulfur extruded analogues are seen
to increase over time, as indicated by multiple peaks from
190 to 130 ppm (typical of monothiocarbamates), as well as
corresponding peaks in the 1H NMR between 3 and 3.5 ppm.
1
as well as the parent 1, as characterized by H NMR,
Supporting Information, S8.
Oxygenation vs Oxidation. The formation of DSF during
oxygenations by mCPBA, as well as from the base-catalyzed
decompositions of the oxygenated products, suggests the
possible involvement of S-based radicals, i.e., Scheme 7.
Disulfides may be formed by either one- or two-electron
oxidation pathways, by coupling of S-radicals, or by nu-
cleophilic attack of a thiol on a sulfenic acid equivalent. For
all reactions described here, essentially identical results were
obtained in the presence or absence of air, which argues
against radical intermediates, Path B. A reviewer requested
further investigations of possible radical reactivity; we
therefore looked at the oxidation of 1 both electrochemically
and by bulk reaction.
The electrochemistry of DTC compounds has been well
studied38 and reviewed.39 The electrochemical oxidations of
the DTCs described here were investigated in MeCN, Figure
Similar yellow byproducts were also observed during puri-
fication of isolated peroxydithiocarbamate 2 or 5 on silica
chromatography, during washings, or during aqueous work-
ups. ESI-MS spectra of the yellow band shows it to be a
mixture of multiple oxygenated and sulfur-extruded versions
of the disulfide form of the ligand, characterized by [(de-
DTC)2 (16]+ ions, and this is consistent with 1H NMR spec-
tra of these samples. A similar yellow product mixture is
generated from 1:1 reaction of DSF with mCPBA, Scheme
5.
(34) Cullis, C. F.; Hopton, J. D.; Trimm, D. L. J. Appl. Chem.-USSR 1968,
18, 330.
(35) Cullis, C. F.; Trimm, D. L. Discuss. Faraday Soc. 1968, 144.
(36) Riter, L. S.; Meurer, E. C.; Handberg, E. S.; Laughlin, B. C.; Chen,
H.; Patterson, G. E.; Eberlin, M. N.; Cooks, R. G. Analyst 2003, 128,
1112-1118.
(37) Segall, Y.; Casida, J. E. J. Agric. Food Chem. 1983, 31, 242-246.
(38) Nieuwpoort, A.; Dix, A. H.; Porskamp, P. A. T. W.; Vanderlinden, J.
G. M. Inorg. Chim. Acta 1979, 35, 221-226.
(39) Bond, A. M.; Martin, R. L. Coord. Chem. ReV. 1984, 54, 23-98.
Inorganic Chemistry, Vol. 45, No. 15, 2006 6069

Brayton et al.
Figure 11. Cyclic voltammograms of DTC derivatives: (a) Na(deDTC);
(b) compound 1; (c) Na(O-deDTC); (d) compound 3; (e) compound 4.
Conditions: ca. 5 mg sample in MeCN, 0.1 M TBAHFP, 100 mV/s scan
rate, PG working electrode, Pt counter electrode, referenced to a Ag/AgCl
electrode via a Luggin capillary connector.
Figure 12. Deoxygenations of 4 by stoichiometric reactions with PEt3.
1H NMR spectra of product of (a) compound 4, Zn(O2-deDTC)2, displaying
only resonances of the thiocarbamylsulfinate ligand (C); (b) 4 plus ca. 2
equiv of PEt3; (c) 4 plus ca. 4 equiv of PEt3; (d) authentic sample of 1,
Zn(deDTC)2, with a single resonance of the dithiocarbamate ligand (A).
No peaks attributable to a peroxydithiocarbamate ligand (ca. 3.65 ppm)
were observed in spectra b and c.
Scheme 8
of the free deDTC ligand, which would be more susceptible
to oxidation. In reactions with excess CAN, in the absence
or presence of O-atom donors such as O2 or OPPh3, no
identifiable oxygenates were seen by NMR or ESI-MS. Thus,
radical reactivity is not implicated in the formation or
reactivity of the S-oxygenated DTC complexes.
Scheme 9
O-Atom Transfer Reactivity. The formation of the parent
dithiocarbamate 1 during decomposition of the S-oxygenates
also implies that these compounds may act as O-atom donors;
this ability was assayed against the series of aryl and alkyl
phosphines shown in Scheme 8. These test reactions were
performed at room temperature on the NMR scale, initiated
by stoichiometric addition of the phosphine to the Zn
complex in chloroform. Oxygen-exchange was confirmed by
observation of the phosphine oxide in the 31P NMR spectra
and the appearance of the unoxygenated parent Zn dithio-
11. The irreversible oxidation of the sodium salt of deDTC
occurs at ∼300 mV vs Ag/AgCl; by contrast, its Zn complex
1 shows no definable oxidation until ca. 1600 mV. A positive
shift in oxidation potential due to thermodynamic stability
of the chelate form is predicted by the Nernst equation, the
overall binding affinity (â2) in water has been reported as
1011.6 mol-2,40 and it is likely larger in MeCN. The mono-
oxygenated DTC ligand, as prepared by peroxidation of Na-
(deDTC) in MeCN, shows a broad, irreversible oxidation
with two features at ca. 400 and 700 mV; its homoleptic Zn
complex, compound 3, also shows a two-featured oxidation
shifted to 1000 and 1300 mV. The homoleptic Zn complex
dioxygenated DTC, 4, yields no observable oxidation within
the solvent window.
Stoichiometric chemical oxidation of 1 with cerium
ammonium nitrate, CAN, under aerobic conditions yields
only DSF and a white precipitate, presumably Zn(NO3)2. The
reaction is quite slow, but over a 3 day period, the
characteristic NMR signals of DSF are seen to grow in,
Supporting Information, S9. The slow oxidation rate may
be due to low solubility of CAN in CDCl3 or to slow release
1
carbamate complex in the H NMR spectra. The oxygen-
exchange reactivity was highly dependent on the phos-
phine: both PPh3 and PPh2Me were unable to deoxygenate
any of the S-oxygenated compounds. The dependence on
phosphine follows the well-characterized trend in basicity
of arene and alkyl phosphines.41-43 However, unexpectedly,
relatively little difference in donor ability was seen between
the S-oxygenates: both PPhMe2 and PEt3 stoichiometrically
deoxygenates compounds 2 and 3, as well as the sulfinato
derivative 4. The ease in deoxygenation of the sulfinato 4
was counter to the reactivity of the tautomeric S,S-bound
sulfinate in Ru(bpy)2(N,N′-dimethylthiocarbamoylsulfinato)+,
which did not react with PEt3 under similar conditions.14
(41) Capps, K. B.; Wixmerten, B.; Bauer, A.; Hoff, C. D. Inorg. Chem.
1998, 37, 2861-2864.
(42) Nolan, S. P.; Hoff, C. D. J. Organomet. Chem. 1985, 290, 365-373.
(43) Cucullu, M. E.; Luo, L. B.; Nolan, S. P.; Fagan, P. J.; Jones, N. L.;
Calabrese, J. C. Organometallics 1995, 14, 289-296.
(40) Scharfe, R. R.; Sastri, V. S.; Chakraba, C. Anal. Chem. 1973, 45, 413-
415.
6070 Inorganic Chemistry, Vol. 45, No. 15, 2006

Oxygenation of Zinc Dialkyldithiocarbamate Complexes
Voltammetric experiments were performed using Bioanalytical
Systems (BAS) CV-50W voltammetric analyzer under PC control.
Solutions were prepared with ∼5 mg of each compound in 5 mL
of 0.1 M TBAF in dry CH2Cl2. A glassy carbon electrode was used
for the working electrode, with Pt wire as auxiliary. An Ag/AgClaq
reference electrode was connected to the analyte solution via a
Luggin capillary connector. All samples were purged with N2(g)
for 5-10 min before the experiments were preformed.
Some difference between sulfenic and sulfinic oxygens in
O-atom transfers was discernible by following stoichiometric
additions of PEt3 to the sulfinato 4, Figure 12; the addition
of ca. 2 equiv of phosphine to the homoleptic sulfinato 4
generated ca. equal mixtures of 4 with the fully deoxygenated
1; no evidence of peroxydithiocarbamates 2 or 3 was
observed. As the peroxydithiocarbamate ligand should be
formed by bimolecular reaction of one phosphine with one
sulfinato, the absence of accumulated peroxydithiocarbamate
suggests that it reacts with phosphine faster than the
corresponding thiocarbamate-sulfinate.
Conclusions. The work shown here introduces a series
of new oxygenated DTC compounds and outlines the effect
of metal coordination on pathways of ligand oxidation. In
addition to crystallographic characterization of structures of
both forms of the oxygenated dithiocarbamate complexes,
we describe their independent synthesis, characterization, and
reactivity, as well identification of several decomposition
products.
Many previous studies of Zn DTC oxygenates have
focused on their application as antioxidants in rubber
formulation and vulcanization accelerants at elevated
temperatures.3-5,15,16 Likewise, it has been long postulated
that the bioactivity of dithiocarbamate derivatives such as
DSF derives from S-oxygenation and extrusion.14 The
Phoenix-like ability of the oxygenated forms to regenerate
the parent DTC complex upon decomposition recalls the
recent demonstration that Cu-catalyzed decomposition of the
deDTC disulfide, DSF, generates the highly cytotoxic Cu-
(deDTC)2 in high yield.11 Similarly, the widely used DTC-
based pesticides Ziram, Zn(dmDTC)2, and Thiuram (dm-
DTC)2, undergo analogous decomposition reactions to those
described for the diethyl analogues. The decomposition
pathways illustrated here are likely relevant to both the
biological and antioxidant activity of these widely used DTC
derivatives.
Synthesis of Zn(OS2NC5H10)(S2NC5H10), 2. Zn(deDTC)2 (0.500
g, 1.386 mmol) was dissolved in 250 mL of CHCl3, and in a
separate round-bottom flask mCPBA (0.310 g, 1.386 mmol) was
dissolved in a 250 mL 1:1 mixture of CHCl3 and CH3CN, and both
solutions were cooled to 4 °C. The mCPBA solution was then added
dropwise in an addition funnel to the stirred solution of Zn(deDTC)2.
After the mixture was stirred for 10-12 h, the solvent was removed
under vacuum. The resulting solid was collected and washed with
three 20 mL portions of ice cold CH3CN to yield 0.412 g (79%) of
1
a white solid. H NMR (500.22 MHz, CDCl3): δ 1.28 (t, 3 H,
-CH3, J ) 7.2 Hz), 1.33 (t, 3 H, -CH3, J ) 7.2 Hz), 3.65 (broad,
2H, -CH2-), 3.87 (q, 2 H, -CH2, J ) 7.1 Hz). IR(cm-1): 819
(VS-O), 885 (VS-O). Anal. Calcd. for H20C10ON2S4Zn: C, 31.78;
H, 5.33; N, 7.41. Found: C, 31.55; H, 5.20; N, 7.32. Variable-
temperature (-40 to +50 °C) 1H NMR was performed for energetic
parameters and to confirm the oxidized product.
Synthesis of Zn(OS2NC5H10)2, 3. A stirred solution of Na-
(deDTC) (0.2749 g, 1.605 mmol) in 50 mL of MeOH was cooled
in an ice bath, and UHP (0.1478 g, 1.571 mmol) was added after
5 min. Upon UHP dissolution, the mixture turned yellow and ZnCl2
(0.1094 g, 0.802 mmol) was immediately added. Once the mixture
was no longer yellow, a white precipitate was collected, washed
with 20 mL of MeOH, and dried under vacuum yielding 0.1734 g
(56%) of a white solid. 1H NMR at +25 °C (500.04 MHz,
CDCl3): δ 3.64 (bs, 2H, -CH2-), 1.29 (t, 3H, -CH3, J ) 7.1
1
Hz). H NMR at +50 °C: δ 3.66 (q, 2H, -CH2-, J ) 6.8 Hz),
1.29 (t, 3H, -CH3, J ) 7.0 Hz). 1 H NMR at -50°C (500.04 MHz,
CDCl3): δ 3.88 (q, 2H, -CH2-, J ) 7.0 Hz), 3.34 (q, 2H, -CH2-,
J ) 7.0 Hz), 1.27 (t, 3H, -CH3, J ) 6.8 Hz), 1.19 (t, 3H, -CH3,
J ) 7.0 Hz). IR (cm-1): 823 (VS-O), 886 (VS-O). Anal. Calcd for
C10H20S4N2O2Zn: C, 30.49; H, 5.12; N, 7.11. Found: C, 30.27;
H, 5.12; N, 6.96.
Synthesis of Zn(O2S2NC5H10)2‚H2O, 4. A stirred solution of
Na(deDTC) (0.500 g, 2.22 mmol) in 10 mL of acetone was cooled
to 4 °C, and 30% H2O2 (1 mL, 10 mmol) was added dropwise
over a 15 min period. The reaction mixture turned yellow and was
left to stir for 30 min before being allowed to warm to room
temperature. CHCl3 (2 mL), deionized H2O (2 mL), and Zn(OAc)2
(0.225 g, 1.03 mmol) were added to the reaction mixture and left
to stir for another 30 min. Stirring was then stopped, and the mixture
was left to stand for 48 h until all the solvent had evaporated.
Extractions from the residue with chloroform yielded 0.0877 g
(19%) of a white solid. 1H NMR (500.22 MHz, CDCl3): δ 1.40 (t,
3H, -CH3, J ) 3.5 Hz), 1.42 (t, 3H, -CH3, J ) 3.5 Hz), 3.92 (q,
-CH2-, J ) 7.0 Hz), 4.14 (q, -CH2-, J ) 7.0 Hz). IR(cm-1):
1002 (VS-O), 1065 (VS-O). Anal. Calcd for H22C10O5N2S4Zn: C,
27.05; H, 4.99. Found: C, 27.22; H, 4.98.
Synthesis of Zn(OS2NC3H6)(S2NC3H6), 6. Zn(dmDTC)2 (0.474
g, 1.540 mmol) was dissolved in 200 mL of CHCl3, and in a
separate round-bottom flask mCPBA (0.347 g, 1.540 mmol) was
dissolved in 200 mL of a 1:1 CHCl3 and CH3CN mixture, and both
solutions were cooled 4 °C. The mCPBA solution was then added
dropwise in an addition funnel to the stirred solution of Zn-
(dmDTC)2. After the mixture was stirred for 10-12 h, the solvent
was removed under vacuum. The resulting solid was collected and
Experimental Section
Abbreviations. DSF, tetraethylthiuram disulfide; deDTC, di-
ethyldithiocarbamate; dmDTC; dimethyldithiocarbamate, UHP, urea
hydrogen peroxide; mCPBA, meta-chloroperoxybenzoic acid; pDTC,
pyrrolidinedithiocarbamate; PEt3, triethylphosphine; PPhMe2, dim-
ethylphenylphosphine; PPh2Me, methyldiphenylphosphine; PPh3,
triphenylphosphine.
Materials. All common laboratory solvents were reagent grade.
KOH, NaOH, and ZnCl2 were purchased from Fisher and used as
received. All other chemicals were purchased from Aldrich Chemi-
cal Co. Solvents in the nitrogen glovebox were dried using standard
techniques. Where anaerobic techniques were required, a dry
glovebox and standard Schlenk techniques were used.
Physical Measurements. Mass spectra were determined by
Micromass LCT. UV-vis spectra were recorded by Perkin-Elmer
1
Lambda 900. H, 13C, and 31P NMR spectra were recorded using
Bruker Avance 400 and 500 MHz spectrometers. Chemical shifts
are referenced via the solvent signal. Infrared spectra were recorded
as KBr pellets on Impact 410 from Nicolet. Elemental analyses
were performed by Atlantic Microlab, Norcross, GA or Desert
Analytics, Phoenix, AZ. All single-crystal X-ray diffraction struc-
tures were solved at the X-ray Crystallography Facility at UCI.
Inorganic Chemistry, Vol. 45, No. 15, 2006 6071

Brayton et al.
washed with three 10 mL portions of ice cold CH3CN to yield 0.170
g (34%) of a white solid. 1H NMR (500.22 MHz, CDCl3): δ 3.31
(broad s, -CH3), 3.48 (s, -CH3), +50 °C: δ 3.31 (s, 3H, -CH3).
1H NMR at -50 °C (500.04 MHz, CDCl3): δ 3.56 (t, 3H, -CH3),
3.48 (s, -CH3), 3.08 (s, -CH3). Anal. Calcd for H12C6ON2S4Zn:
C, 22.39; H, 3.75. Found: C, 22.61; H, 3.65. Variable-temperature
(-40 to +50 °C) 1H and 13C NMR were also done to confirm the
oxidized product.
the resulting solid was collected and washed with 50 mL of water
to yield a white solid. Each solid was analyzed by H NMR to
1
identify and determine the yields of oxygenated products. The
procedure described above was varied in the amounts of 1, 2, and
UHP used, as is outlined in the Supporting Information, Table S6.
Reactions of Zn(deDTC)2 with Stoichiometric mCPBA. In a
typical reaction, aliquots of 1, 2, 3, or 4 equiv of mCPBA (each
212 g, 0.949 mmol) in 30 mL of CHCl3 were added dropwise at 0
°C to a 50 mL CHCl3 solution of Zn(deDTC)2 (0.342 g, 0.945
mmol). Upon addition, the reaction mixture turned yellow and the
color intensified with increasing equivalents of mCPBA. After the
reaction was allowed to stir for ∼12 h, the solvent was removed.
The resulting solid was collected and washed with three 20 mL
portions of ice cold MeCN to yield an off white solid. Each solid
Synthesis of Zn(OS2NC5H8)(S2NC5H8). A solution of Zn-
(pDTC)2 (0.5122 g, 1.431 mmol) was dissolved in 125 mL of CH2-
Cl2 and degassed for 30 min. A solution of UHP (0.1325 g, 1.408
mmol) in 40 mL of MeOH was degassed for 15 min. After the
Zn(pDTC)2 was cooled to 4 °C, the UHP solution was added
dropwise over a period of 5 min. The reaction was left to stir at 4
1
1
°C and periodically monitored in situ by H NMR. After 5 days,
was analyzed by ESI-MS and H NMR to identify and determine
the reaction solvent was evaporated and an off white solid obtained.
A CHCl3/H2O extraction was performed; stripping the solvent
resulted in white solid which was washed with 20 mL of MeCN
and dried by vacuum to give 0.2586 g (49.1%) of a white solid. 1H
NMR 25 °C (500.04 MHz, CDCl3): δ 3.91(bs, 2H, -CH2-), 3.76
the yields of oxygenated and/or oxidized products.
Reactions of DSF and Stoichiometric mCPBA. DSF (0.107
mg, 0.362 mmol) was added to CH2Cl2 at 0 °C, and mCPBA
(0.0801 mg, 0.3622 mmol) in 20 mL of CH2Cl2 was added dropwise
over 20 min. The reaction turned yellow after the first several drops
and slowly intensified upon further addition. The reaction was
1
(t, 2H,-CH2-), 3.21 (bs, 2H, -CH2-), 2.08 (m, 2H, -CH2-). H
1
NMR -50°C (500.04 MHz, CDCl3): δ 3.91(t, 2H, -CH2-), 3.76
(t, 2H, -CH2-), 3.21 (t, 2H, -CH2-), 2.12 (m, 2H, -CH2-),
2.06 (m, 2H, -CH2-), 2.02 (m, 2H, -CH2-). Anal. Calcd for
C10H16S4N2OZn: C, 32.11; H, 4.31; N, 7.49. Found: C, 32.34; H,
54.26; N, 7.75.
Synthesis of Zn(OS2NC5H8)2. A solution of (NH4)(pDTC)
(0.3621 g, 2.204 mmol) was dissolved in 50 mL of MeOH and
cooled in an ice bath. UHP (0.2006 g, 2.132 mmol) was then added
to the pDTC solution. Once the UHP dissolved and the mixture
turned yellow, ZnCl2 (0.1578 g, 1.157 mmol) was added to the
mixture. Upon vigorous stirring of the mixture, a white solid
precipitated, which was collected by vacuum filtration and washed
with 50 mL each of both MeOH and MeCN, yielding 0.3025 g
(72.8%) of white solid. 1H NMR 25 °C (500.04 MHz, CDCl3): δ
3.99 (t, 2H), 2.18 (m, 2H), 2.04 (m, 2H). Anal. Calcd for
C10H16S4N2O2Zn: C, 30.80; H, 4.14; N, 7.19. Found: C, 30.94;
H, 4.34; N, 7.08.
monitored by H and 13C NMR and ESI-MS.
Chemical Oxidation of Zn(deDTC)2 with CAN. An NMR tube
charged with Zn(deDTC)2 (0.011 mg, 0.0303 mmol) and CAN
(0.016 g, 0.0303 mmol) in CDCl3 was monitored by 1H NMR over
the course of a week. Integrating the methylene protons estimates
a product distribution at about a 10:9 ratio, DSF to Zn(deDTC)2.
Reactivity with Phosphines. Solutions of PEt3, PPh3, PPhMe2,
and PPh2Me were prepared and add to separate solutions of the
oxygenated zinc compounds 2-6 in CDCl3. The solutions were
periodically refluxed for up to 2 weeks and monitored by TLC,
ESI-MS, and 1H and 31P NMR. For PPh3 and PPh2Me, no reaction
or decomposition was ever observed. For PEt3 and PPhMe2, the
O-atom abstraction from zinc compounds 2-6 was complete before
NMR spectra could be taken. To verify assignments, each phosphine
solution was prepared anaerobically in an NMR tube to obtain the
PR3 chemical shift values, then to each sample excess mCPBA was
added to obtain the corresponding P(O)R3 chemical shift values.
Synthesis of 13C-Labeled Zn(S2NC5H10)2, 1. To an aqueous
solution of (C2H5)2NH (0.908 g, 12.4 mmol) and NaOH (0.491,
12.4 mmol), 13CS2 (1.000 g, 12.9 mmol) was added dropwise via
an addition funnel over a 10 min period. The mixture was allowed
to stir for an hour before being frozen in a dry ice-acetone bath
and lyophilized overnight. The resulting solid was collected and
washed with Et2O (20 mL), yielding 0.412 g (85%) of an off white
solid. Addition of the 13C-labeled deDTC (0.398 g, 1.629 mmol)
to a stirred solution of ZnCl2 (0.107 g, 0.790 mmol) in 50 mL of
MeOH produced a white solid precipitate, which was collected by
vacuum filtration and washed with water, yielding 0.520 g of white
solid (90%).
Reactions of 1 and 2 with Stoichiometric UHP. In a typical
reaction, an aliquot of UHP (0.025 g, 0.276 mmol) in 20 mL of
MeOH was added dropwise at 0 °C to a 50 mL CH2Cl2 solution of
Zn(deDTC)2 (0.052 g, 0.138 mmol). The reaction mixture was
allowed to stir overnight or longer. After the solvent was stripped,
Acknowledgment. This research was supported by the
American Cancer Society Research Scholar grant (P.J.F.,
RSG-03-251-01). K.T., M.K., and K.K. acknowledge funding
from the Undergraduate Research Opportunities Program at
UC Irvine. We especially thank Szeman Ng for assistance
and inspiration.
Supporting Information Available: Total line shape analysis
of 1H NMR of compounds 1, 3, and 5; crystallographic and metric
parameters for compounds 1, 2:3, and 4; ESI-MS spectra for 1, 2,
3, and 4 matched with the isotopic models; NMR characterizations
of the reaction of UHP with 3, the decomposition of 3 when exposed
to pH 10 buffer in biphasic mixture; and 13C NMR of the byproduct
mixture described in the text. This material is available free of
charge via the Internet at http://pubs.acs.org.
IC060671J
6072 Inorganic Chemistry, Vol. 45, No. 15, 2006