Electrochemical and structural characterization of tri- and dithioether copper complexes

Article abstract of DOI:10.1002/ejic.201000960

Tri- and dithioethers tris(2-tert-butyl-4-methylphenylthiomethyl)amine (1), bis(2,4-dimethylphenylthio)methane (2), and bis(2-tert-butyl-4- methylphenylthio)methane (3) were developed to evaluate their coordination properties toward Cu⁺. The th

Full text of DOI:10.1002/ejic.201000960

FULL PAPER
DOI: 10.1002/ejic.201000960
Electrochemical and Structural Characterization of Tri- and Dithioether
Copper Complexes
Paulina R. Martínez-Alanis,[a] Víctor M. Ugalde-Saldívar,[b] and Ivan Castillo*[a]
Keywords: Copper / Sulfur / Tripodal ligands / Voltammetry
Tri- and dithioethers tris(2-tert-butyl-4-methylphenylthio-
methyl)amine (1), bis(2,4-dimethylphenylthio)methane (2),
and bis(2-tert-butyl-4-methylphenylthio)methane (3) were
developed to evaluate their coordination properties toward
plexes revealed that the sulfur-rich coordination environ-
ment results in high redox potentials for the Cu2+/Cu+ cou-
ple, which is close to the first oxidation potential of the li-
gands. Thus, chemical (Cu2+) or electrochemical oxidation of
the thioethers resulted in oxidative decomposition of the li-
gands with concomitant reduction to Cu+, in agreement with
the electrochemical results. Bulk electrolyses of the tri- and
dithioethers 1–3 enabled us to confirm that the corresponding
disulfides are the major oxidation products. The cathodic
peak potentials for the Cu+/Cu0 couple of the complexes al-
lowed us to determine the relative stability of the thioether/
Cu+ complexes.
–
Cu+. The thioethers associate weakly with Cu+ when ClO4
–
or PF6 are the counterions, while the reactions with CuI af-
ford crystalline products in the case of nitrilotrithioether 1
and dithioether 2. The solid-state structures of the complexes
[(1)CuI]2 and [(2)(CuI)4(CH3CN)2]2·2THF·4CH3CN are char-
acterized by the chelating-bidentate coordination mode of 1
and the bridging nature of 2 spanning two Cu4I4 cuboidal
clusters. Electrochemical studies of the thioether/Cu+ com-
redox potentials for sulfur-rich coordination environments.
With regard to inorganic model systems, the ethylene-
bridged tripodal NS3 ligands employed by the group of Ro-
rabacher form stable Cu+ and Cu2+ complexes,[1c,6] and
their electronic properties resemble those of type 1 copper
sites in metalloenzymes with redox potentials in the order
of 0.28 V relative to the ferrocinium/ferrocene (Fc+/Fc) cou-
ple. Related tripodal ligands with N2S2 coordination envi-
ronments have redox potentials as high as 0.54 V (vs. Fc+/
Fc).[7] In the case of methylene-bridged anionic and neutral
tripodal trithioethers E(CH2SR)3 (E = B, C, Si), reactions
with Cu+ afford monomeric, oligomeric, and polymeric
complexes,[8] but attempts to prepare cupric analogues have
been unsuccessful. This has prevented the determination of
the Cu2+/Cu+ redox potential in the latter systems; in ad-
dition, the reduction of Cu2+ to Cu+ has been observed
with methylene-bridged tripodal ligands,[8b] which is cou-
pled with ligand-based oxidation, indicating that there is an
intrinsic reactivity of the E–CH2–S linker.
Introduction
Thioether ligands have been intensively studied in recent
years because of their involvement in bioinorganic systems,
particularly in the active sites of copper-containing metallo-
enzymes.[1] A growing number of copper complexes featur-
ing thioether ligation have been developed, mainly aimed at
understanding the role of sulfur-based donors in biological
and chemical systems.[2] These include the exhaustively
studied blue copper proteins,[1b,1c,3] in which the presence
of thiolate and thioether donors play a key role in their
characteristic fast electron-transfer kinetics. Thioether do-
nors have recently been identified in copper trafficking,[1a,1j]
in addition to the predominant thiolate-based Cu+ metall-
ochaperones. Moreover, the presence of methionine residues
as thioether ligands in several types of copper monooxygen-
ases,[1e,1f,1i,4] as well as the involvement of cysteine in the
generation of the active site of galactose oxidase,[5] have fur-
ther spurred the interest in copper–sulfur systems. The pres-
ence of sulfur donors around copper centers modulates the
In this context, we recently reported the synthesis of an
redox potential of the Cu2+/Cu+ couple, resulting in high nitrilotrithioether ligand (LMe in Scheme 1), as well as its
reactivity toward Cu+ and Cu2+ [9]
To further investigate the
.
reactivity of methylene-bridged thioethers, we have pre-
pared related sulfur-containing ligands. The nitrilotrithio-
ether (1 in Scheme 1) allowed us to investigate the steric
effects of the bulky tert-butyl groups in the ortho positions,
while the dithioethers ArS–CH2–SAr that lack the potential
nitrogen donor at the bridging position (2 and 3, Ar = sub-
stituted aromatic group) provided information on the effect
of the heteroatom on the ease of oxidation of the ArS–
[a] Instituto de Química, Universidad Nacional Autónoma de
México, Circuito Exterior, Ciudad Universitaria,
México, D. F., 04510, México
Fax: +52-55-56162217
E-mail: joseivan@unam.mx
[b] Facultad de Química, División de Estudios de Posgrado,
Universidad Nacional Autónoma de México, Ciudad Universitaria,
México, D. F., 04510, México
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201000960.
212
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 212–220

Characterization of Tri- and Dithioether Copper Complexes
Scheme 1. Tri- and dithioether ligands 1–3, and disulfides 4 and 5.
CH2–E moiety (E = N, S). Thus, we report herein on the 1:1 stoichiometry [(1)Cu]+ (see Figure S1 in the Supporting
study of the electrochemical and structural properties of the Information); analysis of the same sample after 24 h of ex-
ligands and their Cu+ complexes. In addition, we also re- posure to air revealed a new peak at m/z = 234, which could
port on the chemical (Cu2+) and electrochemical oxidation correspond to the product of oxidative C–C bond forma-
reactions of the sulfur-containing ligands, which result tion (see below).
mainly in the formation of the disulfides 4 and 5, as well as
minor amounts of C–C bond formation products.
Employment of CuI allowed the isolation of a complex
upon treatment with 1 equiv. of 1; reactions with different
Cu/ligand ratios resulted in the same product, the combus-
tion analysis being consistent with a 1:1 stoichiometry. The
ESI mass spectra of the complex contain peaks correspond-
ing to copper-containing species at m/z = 1251 [(1)2Cu]+,
Results and Discussion
The sterically encumbered nitrilotrithioether tris(2-tert- fragmentation peaks at m/z = 1102 and 954, attributable
butyl-4-methylphenylthiomethyl)amine (1), which features to the sequential loss of 2-tBu-4-Me–C6H3 groups, and the
tert-butyl groups in one of the ortho positions of the phenyl- species [(1)Cu]+ at m/z = 657 (see Supporting Information
thioether moieties, was prepared by acid-catalyzed conden- Figure S2). Although 1H and 13C NMR spectra are charac-
sation of 2-tert-butyl-4-methylbenzenethiol and hexameth- terized by small shifts of the signals corresponding to the
ylenetetramine (Scheme 2), in an analogous fashion to the ligand, confirmation of the formation of the copper com-
previously reported LMe [9]
Compound 1 interacts weakly plex was obtained by X-ray crystallography. Single crystals
.
with Cu+ centers in solution, as evidenced by 1H NMR of [(1)CuI]2 were obtained in the monoclinic space group
spectroscopy. The analyses of the 1H NMR spectra of [D3]- P21/c by cooling concentrated acetonitrile solutions to
acetonitrile solutions of 1 with varying amounts of –20 °C. A crystallographic inversion center generates the di-
[Cu(CH3CN)4]PF6 (0.5–2.0 equiv.) reveal only marginal meric structure of the complex, which is characterized by
changes in the signals corresponding to the ligand. Reac- bridging iodido ligands, defining a rhomboidal Cu2I2 core
tions of the related nitrilotrithioether LMe with equimolar with an average Cu–I distance of 2.625(1) Å and an I–Cu–I
amounts of [Cu(CH3CN)4]PF6 and [Cu(CH3CN)4]ClO4 angle of 121.10(1)°. The deviation from an ideal tetrahedral
had previously resulted in microcrystalline solids, but in the geometry around Cu1 is also reflected in the compressed
case of compound 1 isolation of the corresponding cuprous S1–Cu1–S2 angle of 90.15(2)°, as well as the corresponding
complexes appears to be precluded by the increased steric S1–Cu1–I1 and S2–Cu1–I1 angles of 112.77(2) and
bulk of the ligand; attempts to precipitate or crystallize the 108.28(2)°, respectively. The average Cu–S bond length of
complexes resulted in the recovery of the Cu+ starting mate- 2.336(1) Å is within the range of related complexes (Fig-
rials. Extended reaction times of 1 with the aforementioned ure 1);[10] a list of selected bond lengths and angles for all
copper salts results in ligand decomposition. Nonetheless, compounds is presented in Table 1. The crystallographically
freshly prepared acetonitrile solutions allowed the detection related copper centers are at a distance of 2.582(1) Å, which
of a peak at m/z = 657 by electrospray-ionization mass spec- is considerably shorter than the sum of the van der Waals
trometry (ESI-MS), which corresponds to a complex with a radii (2.80 Å),[11] and is only comparable to that reported
Scheme 2. Acid-catalyzed synthesis of tri- and dithioether ligands.
Eur. J. Inorg. Chem. 2011, 212–220
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
213

P. R. Martínez-Alanis, V. M. Ugalde-Saldívar, I. Castillo
FULL PAPER
by Hor and coworkers of 2.525(2) Å.[12] In the latter com- Table 1. Selected bond lengths [Å] and angles [°].
plex, the Cu+ centers have amino and thioether ligands, and
the Cu2I2 cores differ from those of [(1)CuI]2 in the triply
bridging mode of the iodido ligands. In [(1)CuI]2 the nitro-
gen atom on the ligand does not participate in bonding to
[(1)CuI]2
Cu1–I1
Cu1–I1*
Cu1–S1
2.658(1)
2.591(1)
2.334(1)
2.338(1)
2.582(1)
I1–Cu1–I1*
S1–Cu1–S2
I1–Cu1–S1
I1–Cu1–S2
121.10(1)
90.15(2)
112.77(2)
108.28(2)
copper, and the sum of the angles of 348.6° attests to its Cu1–S2
Cu1···Cu1*
Cu1–I1–Cu1* 58.90(1)
nearly planar geometry. In the related solid-state structure
of [LMe(CuI)2(CH3CN)], all thioether groups of LMe coor-
dinate to two independent Cu centers in a μ-κ1,κ2 fashion,
while in the case of 1 only two of the thioether sulfur atoms
coordinate to Cu1. We attribute this behavior to the in-
creased steric hindrance conferred to the ligand by the tert-
butyl groups in the ortho positions.
[(2)(CuI)4(CH3CN)2]2·2THF·4CH3CN
Cu1–I1
Cu1–I2
Cu1–I3
Cu2–I1
Cu2–I2
Cu2–I4
2.760(1)
2.660(1)
2.592(1)
2.687(1)
2.674(1)
2.615(1)
2.689(1)
2.736(1)
2.688(1)
2.690(1)
2.689(1)
2.692(1)
2.304(1)
2.327(1)
1.972(4)
1.985(5)
2.679(1)
2.697(1)
2.687(1)
2.689(1)
2.737(1)
2.650(1)
I1–Cu1–I2
I1–Cu1–I3
I2–Cu1–I3
I1–Cu2–I2
I1–Cu2–I4
I2–Cu2–I4
I1–Cu3–I3
I1–Cu3–I4
I3–Cu3–I4
I2–Cu4–I3
I2–Cu4–I4
I3–Cu4–I4
S1–Cu1–I1
S1–Cu1–I2
S1–Cu1–I3
S2–Cu2–I1
S2–Cu2–I2
S2–Cu2–I4
N1–Cu3–I1
N1–Cu3–I3
N1–Cu3–I4
N2–Cu4–I2
N2–Cu4–I3
N2–Cu4–I4
113.40(2)
113.00(2)
113.42(2)
115.36(2)
112.49(2)
111.67(2)
110.73(2)
110.10(2)
116.37(2)
109.40(2)
108.80(2)
117.87(2)
93.10(3)
109.54(3)
112.71(4)
100.41(3)
104.63(3)
111.40(3)
109.1(1)
Cu3–I1
Cu3–I3
Cu3–I4
Cu4–I2
Cu4–I3
Cu4–I4
Cu1–S1
Cu2–S2
Cu3–N1
Cu4–N2
Cu1···Cu2
Cu1···Cu3
Cu1···Cu4
Cu2···Cu3
Cu2···Cu4
Cu3···Cu4
102.9(1)
107.2(1)
114.0(1)
103.0(1)
103.8(1)
the chemical oxidation by Cu2+ (see Electrochemical Stud-
ies section).
Figure 1. ORTEP diagram of [(1)CuI]2 at the 50% probability level;
hydrogen atoms were removed for clarity.
Reaction of 1 with Cu2+ salts resulted in oxidation of the
ligand, with concomitant reduction to Cu+.[8b] For example,
when 1–3 equiv. of Cu(ClO4)2·6H2O were added to aceto-
nitrile solutions of 1 the corresponding disulfide (2-tBu-4-
MeC6H3S)2 (4) was detected by 1H NMR spectroscopy; the
solid-state structure of 4 characterized it unambiguously
(see Figure S3 in the Supporting Information). An ESI-MS
analysis of the samples revealed the presence of disulfide–
copper complexes: when 2 equiv. of Cu2+ were employed
the species at m/z = 957, 779, and 599 were assigned to the
complexes [(4)2Cu(SC6H3-2-tBu-4-Me)]+, [(4)2Cu]+, and
[(4)Cu(SC6H3-2-tBu-4-Me)]+, respectively (see Supporting
Information Figure S4). Repeated attempts to isolate the
products resulted in the recovery of Cu+ as [Cu(CH3CN)4]-
ClO4 and the disulfide 4. While ligand hydrolysis mediated
by the Lewis-acidic cupric ion may be invoked, the oxidat-
ive degradation pathway proposed in Scheme 3 is supported
by cyclic voltammetry measurements on solutions of 1 in
Scheme 3. Proposed mechanism for the formation of the C–C cou-
pling product by oxidation of 1.[9]
In contrast to the reported Cu2+ oxidation of LMe, no
the presence of Cu+, in which the first oxidation potential C–C bond formation products were isolated from the chem-
of 1 is below the value of the Cu2+/Cu+ couple. This allows ical or electrochemical oxidations of 1. Nonetheless, FAB+
us to postulate that the interaction with Cu2+ would likely mass spectra of the reaction mixtures are characterized by
result in the oxidation of 1, with concomitant reduction of the presence of a peak at m/z = 234 (see Supporting Infor-
copper. Moreover, the electrochemical oxidation of 1 in the mation Figure S5), which could arise from the Mannich-
absence of copper affords the same products observed in type attack of one of the electrochemically active N–CH2–
214
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 212–220

Characterization of Tri- and Dithioether Copper Complexes
S groups on the ortho position of the thioether generated P21/n, with compound 2 bridging two distorted cuboidal
according to Scheme 3.
Cu4I4 moieties, in an analogous fashion to the macrocyclic
The different reactivities of the trithioethers 1 and LMe structures reported with bridging bidentate amines.[14] The
could in principle be ascribed to the steric effect exerted by iodido ligands coordinate the Cu+ ions in a μ3 fashion, with
the ortho tert-butyl groups in the former, compared to that Cu1 and Cu2 having additional thioether ligands from the
of the ortho methyl groups in the latter. For example, substi- S1 and S2 atoms, respectively. The sulfur donors corre-
tution of a tert-butyl for a methyl group in related ligands spond to two molecules of the ligand 2, which are related
has resulted in higher oxidation potentials for the corre- by a crystallographic inversion center; this symmetry ele-
sponding Cu complexes.[7] An additional feature of the ni- ment also generates the second Cu4I4 fragment. Cu3 and
trilotrithioethers 1 and LMe is the presence of the central Cu4 have additional nitrogen donors from molecules of ace-
nitrogen atom, which may direct the oxidative decomposi- tonitrile, so that all Cu+ ions have pseudo-tetrahedral coor-
tion by stabilizing the resulting iminium cations. In order dination geometries, with I3S and I3N donor sets; an OR-
to verify the role of the N atom we prepared dithioethers TEP diagram of [(2)(CuI)4(CH3CN)2]2·2THF·4CH3CN is
that can potentially act as ligands toward copper ions, but presented in Figure 2, and selected bond lengths and angles
that lack the central nitrogen atom. The study of the elec- are given in Table 1. The complex is characterized by
trochemical properties of the dithioether/Cu+ systems, as average bond lengths of Cu–I 2.681(1) Å, Cu–S 2.316(1) Å,
well as their chemical (Cu2+) and electrochemical oxidation and Cu–N 1.979(5) Å, all of which are within the range
processes by cyclic voltammetry, revealed that the N–CH2– of reported values;[10d,10f,10g,15] the bond angles around the
S moiety in the nitrilotrithioethers is characterized by lower copper centers vary from 93.10(3) to 117.87(2)°. The four
oxidation potentials than that of the S–CH2–S groups in Cu and four I atoms define distorted tetrahedra within the
the dithioethers.
Cu4I4 units, with average distances for Cu–Cu of 2.690(1)
Thus, we explored the coordination properties of the di- and I–I of 4.463(1) Å. Although the luminescent properties
thioether compounds bis(2,4-dimethylphenylthio)methane of the complex are beyond the scope of this work, in related
(2), and bis(2-tert-butyl-4-methylphenylthio)methane (3) to- systems a Cu–Cu distance in the range of 2.77–2.80 Å ap-
ward Cu+ salts. As in the case of 1, 1H NMR spectroscopic pears to be required for luminescence.[10g,13,15b,15c,16]
analyses of solutions of 2 with various amounts of
[Cu(CH3CN)4]PF6 and [Cu(CH3CN)4]ClO4 revealed small
displacements of the ligand-derived signals. Although the
association of 2 with Cu+ appears to be weak, ESI-MS re-
vealed the presence of Cu+ complexes of 2: the base peak
at m/z = 639 was assigned to the species [(2)2Cu]+, while
the peak at m/z = 351 corresponds to the complex [(2)Cu]+
(see Supporting Information Figure S6). Despite these ob-
servations we were unable to isolate the copper complexes
of 2 present in solution, and resorted to cyclic voltammetry
measurements to confirm complex formation by monitor-
ing the addition of Cu+ to solutions of 2 (see Electrochemi-
cal Studies section).
Reactions of 2 with CuI resulted in the formation of two
products with different stoichiometries, based on combus-
tion analysis; when relatively high ligand to copper ratios
were employed (from 2:1 to 1:1), the solid isolated was con-
sistent with the empirical formula [(2)(CuI)2(CH3CN)2].
While the structures of CuI/thioether complexes are hard
to predict, a tentative proposal would correspond to a coor-
dination polymer with bridging dithioethers, akin to those
Figure 2. ORTEP diagram of [(2)(CuI)4(CH3CN)2]2·2THF·
4CH3CN at the 50% probability level, hydrogen atoms and the
solvate molecules of CH3CN and THF were removed for clarity.
reported with bis(arylthio)methanes (aryl = phenyl, p-
tolyl).[13] The steric hindrance exerted by the additional
In an analogous fashion to the reactions of the nitrilotri-
methyl groups in the ortho position of the aromatic groups thioethers LMe and 1 with Cu2+, treatment of 2 with Cu2+
of 2 may preclude the extended ordering required for the salts resulted in oxidation of the ligand and reduction of
formation of adequate crystals. When the ratio of 2 to cop- copper. Addition of 2 equiv. of Cu(ClO4)2·6H2O to acetoni-
per was low (from 1:2 to 1:4), the product isolated corre- trile solutions of 2 resulted in the formation of the disulfide
sponded to the formula [(2)(CuI)4(CH3CN)2]; the yield of (2,4-Me2C6H3S)2 (5) as the only organic product, as de-
1
this product was optimized by using 4 equiv. of CuI per tected by H NMR spectroscopy. [Cu(CH3CN)4]ClO4 was
ligand. Colorless X-ray quality crystals of [(2)(CuI)4- recovered in nearly quantitative yield, based on the amount
(CH3CN)2]2·2THF·4CH3CN were obtained by cooling a of Cu(ClO4)2·6H2O employed. When only 1 equiv. of Cu-
concentrated solution in 1:1 acetonitrile/THF to –20 °C. (ClO4)2·6H2O was employed, ESI-MS analyses of the sam-
The complex crystallizes in the monoclinic space group ples allowed the detection of mixed dithioether (ArSCH2-
Eur. J. Inorg. Chem. 2011, 212–220
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
215

P. R. Martínez-Alanis, V. M. Ugalde-Saldívar, I. Castillo
FULL PAPER
SAr)/disulfide (ArSSAr)–copper complexes; for example,
In contrast to the behavior of 1 and 2 toward CuI, no
the species at m/z = 761, 639, 625, 611, and 351 were crystalline products were obtained in the reactions with 3,
assigned to the complexes [(2)(5)Cu(SC6H3-2,4-Me2)]+, even when the less sterically demanding CuBr and CuCl
[(2)2Cu]+, [(2)(5)Cu]+, [(5)2Cu]+, and [(2)Cu]+, respectively were employed. Two factors can be identified in the stability
(see Supporting Information Figure S7). Among the species of the complexes: the degree of steric hindrance exerted by
detected, the peaks at m/z = 501, 487, and 473 can be as- the ortho substituents of the arylthioethers, and the size of
signed to the successive loss of methylene groups, and the the chelate that may be formed upon complexation of Cu+.
tentative formulae [(2)Cu(SC6H3-2,4-Me2)]+ and [(5)Cu- In the case of 3, both considerations appear to disfavor
(SC6H3-2,4-Me2)]+ for the latter two species. Intriguingly, thioether coordination to the copper centers: the steric in-
the peak at m/z = 501 would correspond to the species [(2) fluence of the bulky ortho tert-butyl groups as well as the
Cu(SC6H3-2,4-Me2)]+ plus the mass of an additional meth- proximity of the sulfur atoms, which do not allow the for-
ylene group; while the coordination of the very reactive car- mation of a four-member chelate in [(2)(CuI)4(CH3CN)2]2.
bosulfonium ion [2,4-Me2C6H3S=CH2]+ as ligand appears
Treatment of 3 with 1–2 equiv. of Cu(ClO4)2·6H2O for
unlikely,[17] an alternative formulation would correspond to ESI-MS analysis revealed a different behavior from that of
a product of C–C bond formation between the latter frag- 2. In this case an unidentified species was detected at m/z
ment and an aromatic ring of the dithioether 2 (see = 1501, with a poorly defined isotopic pattern. Fragmenta-
Scheme 4). This would clearly represent a minor reaction tion of this species gives rise to two peaks at m/z = 679
manifold, since no products of this type could be isolated and 971; the latter was assigned to the mixed dithioether/
or detected by 1H NMR spectroscopy. Oxidative C–C bond disulfide complex [(3)(4)Cu(SC6H3-2-tBu-4-Me)]+ (see Fig-
formation starting from 2 (or 3) would be disfavored by ure S9 in the Supporting Information). The absence of
the intermolecular nature of the reaction, compared to the other peaks corresponding to Cu complexes of 3 or 4 is
intramolecular reaction starting from 1, outlined in consistent with the low stability determined by cyclic vol-
Scheme 3.
tammetry.
Electrochemical Studies
Further evidence of the oxidative nature of the ligand
decomposition reactions was obtained from cyclic voltam-
metry measurements and bulk electrolysis experiments.
Compounds 1–3 were characterized electrochemically in an
acetonitrile solution at a concentration of 1 mm and a scan
rate of 0.100 Vs–1. Under these conditions the observed oxi-
dation signals behave irreversibly, and therefore most of the
cathodic peaks are not well defined. In the case of 1 five
oxidation processes were identified as Iap, IIap, IIIap, IVap,
and Vap (see Table 2), with anodic peak potentials (Eap) at
0.65, 1.04, 1.42, 1.61, and 1.96 V relative to the Fc+/Fc cou-
ple, respectively. Compound 2 presented four oxidative pro-
cesses at 0.92, 1.08, 1.63, and 2.02 V, while 3 is charac-
terized by only three oxidation processes, with Eap at 0.95,
1.53, and 1.92 V. With regard to the interaction of the thio-
ethers with Cu+, comparison of the voltammograms of an
acetonitrile solution of [Cu(CH3CN)4]ClO4, and 2 plus
2 equiv. of [Cu(CH3CN)4]ClO4, reveals that the potential
peak reduction process from Cu+ to Cu0 is shifted from
–0.97 to –1.07 V (ΔE = 105 mV, see Figure 3). We attribute
this behavior to the coordination of 2 to Cu+, which results
in the stabilization of the cuprous complex, and hence a
Scheme 4. Proposed mechanism of oxidative C–C bond formation
from 2.
The sterically hindered dithioether bis(2-tert-butyl-4-
methylphenylthio)methane (3) appears to behave as 2 in its
interaction with Cu+ ions, based on spectroscopic evidence.
Thus, 1H NMR spectra of mixtures of 3, and either
[Cu(CH3CN)4]PF6 or [Cu(CH3CN)4]ClO4 in acetonitrile
are characterized by small changes in the chemical shifts
of the ligand-derived signals. Mass spectra contain peaks
ascribed to Cu+ complexes of 3, including those at m/z =
807 and 435, which were assigned to [(3)2Cu]+ and [(3)-
Cu]+, respectively. The base peak at m/z = 823 corresponds
to the product of air oxidation of [(3)2Cu]+, namely
[(3)2CuO]+. Fragmentation of the latter complex gives rise
to [(3)CuO]+, detected at m/z = 451 (see Supporting Infor-
mation Figure S8). Thus, the cuprous complexes of 3 are
more easily oxidized by dioxygen in the ionization chamber
than those of 2.
Table 2. Redox potentials of the compounds LMe and 1–3 (V, E vs.
Fc+/Fc).
Iap
IIap
IIIap
IVap
Vap
LMe
1
2
3
0.56[a]
0.65
0.92
–
–
–
–
1.96
–
1.04
1.08
1.53
1.42
1.63
1.92
1.61
2.02
–
0.95
–
[a] Taken from ref.[9]
216
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 212–220

Characterization of Tri- and Dithioether Copper Complexes
more negative reduction potential. Solutions of 1 and 3
with 2 equiv. of Cu+ also presented a shift in the reduction
peak potentials from Cu+ to Cu0 (ΔE = 202 mV for 1, and
ΔE = 14 mV for 3, see Supporting Information Figures S10
and S11), suggesting that the complex 1/Cu is the most
stable, while 3/Cu presents the weakest thioether/Cu inter-
action, in agreement with the inaccessibility of isolable cu-
prous complexes of 3. Attempts to characterize the CuI
complexes of 1–3 electrochemically were precluded by the
complexity of the anodic region of the voltammograms.
Figure 4. Cyclic voltammograms of 2 before (gray line) and after
(black line) electrolysis.
revealed the peaks corresponding to the disulfides 4 and 5
as the main products of the electrochemical oxidation, and
the disappearance of the characteristic E–CH2–S singlets (E
= N, S) between δ = 4.29 and 4.49 ppm of 1–3 (see Fig-
ures S15 and S16, Supporting Information). Thus, ligand
decomposition to the corresponding disulfides is an oxidat-
ive process, which can be carried out by chemical (Cu2+) or
electrochemical methods.
Comparison of the first anodic peak potentials (Iap,
Table 2) of compounds LMe and 1–3 reveals that the nitrilo-
trithioethers are more easily oxidized than the dithioethers.
This can be attributed to the presence of the central nitro-
gen atom in LMe and 1, which upon oxidation results in the
formation of iminium ions. In contrast, the oxidation of 2
and 3 gives rise to the less stable carbosulfonium ions. Thus,
it seems plausible to propose that the nitrogen-stabilized
iminium species are more easily generated due to their rela-
tive stability, resulting in lower oxidation potentials for the
nitrilotrithioethers.
Figure 3. Cyclic voltammograms of 2 plus 2 equiv. of [Cu(CH3-
CN)4]ClO4 (black line) and [Cu(CH3CN)4]ClO4 (gray line).
Comparison of the products of the chemical oxidation of
the thioethers with Cu2+, with those of the electrochemical
oxidation of 1–3 was achieved by chronopotentiometry. The
compounds were electrolyzed by applying a current of
100 μA to 1 mm solutions of the thioethers in a 0.1 m
(C4H9)4NPF6 acetonitrile solution. The effectiveness of this
method was confirmed by measuring the voltammograms
of the solutions before and after electrolysis, which revealed
close to 90% completion. Figure 4 shows a representative
example of the cyclic voltammograms obtained for 2; the
first oxidation corresponds to 1e– processes for 1 and 2. In
the case of 3, the first oxidation wave decreases by 47%
Conclusions
In summary, the thioether/Cu+ systems derived from li-
after electrolysis, and the fact that only three anodic peaks gands 1–3 and different cuprous salts are present in solution
are observed for this compound suggests that the peak at as a rapidly interconverting mixture of complexes with dif-
Eap = 0.95 V involves more than one oxidative process (see ferent stoichiometries. The chelate ring size of four does not
Figures S12 and S13, Supporting Information).
support copper complexation and gives rise instead to a six-
Upon electrolysis the products of oxidation of the thio- membered ring in [(1)CuI]2, with 1 acting as a bidentate
1
ethers were analyzed by mass spectrometry and H NMR thioether. The instability of four-membered chelates renders
spectroscopy. The high concentration of the supporting 2 as a bridging ligand toward CuI clusters, although ex-
electrolyte in the solutions gave rise to spectra partially ob- tended bridging to generate coordination polymers appears
scured by the signals corresponding to the [(C4H9)4N]+ cat- to be restricted by the steric influence of the ortho methyl
ion at m/z = 242 in all mass spectra (see Figure S14, Sup- groups. Dithioether 3 appears to be both restricted to form
porting Information). The low abundance of the other chelates and too sterically congested to afford isolable Cu+
peaks in the spectra did not allow the identification of li- complexes, either as discrete or polymeric species. Chemical
gand-derived fragments. Nonetheless, the 1H NMR spectra or electrochemical oxidation of 1 results mainly in the disul-
Eur. J. Inorg. Chem. 2011, 212–220
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
217

P. R. Martínez-Alanis, V. M. Ugalde-Saldívar, I. Castillo
FULL PAPER
a JEOL Eclipse 300 spectrometer in CDCl3 with tetramethylsilane
as an internal standard, or in CD3CN referenced relative to the
residual solvent protons at 300 (1H) or 75 MHz (13C). Mass spectra
were obtained with a JEOL JMS-SX-102A mass spectrometer at
an accelerating voltage of 10 kV, with a nitrobenzyl alcohol matrix
and Xenon atoms at 6 keV (FAB+), or a Bruker Daltonics Esquire
6000 spectrometer with ion trap (Electrospray). Elemental analyses
were performed at the microanalytical facility of the Instituto de
Química.
fide 4, although a small amount of intramolecular C–C
bond formation appears to take place. Compounds 2 and 3
are also oxidized to the disulfides 5 and 4, respectively.
These observations are supported by bulk electrolysis of the
ligands, which also results in the formation of the disulfides.
Mass spectrometry appears to indicate that intermolecular
C–C bond formation occurs in the oxidation of 2, as pro-
posed in Scheme 4, although the amount of product formed
would be negligible. This is probably because of the instabil-
ity of the reactive [ArS=CH2]+, which would readily decom-
pose in the presence of nucleophiles. The oxidation poten-
tials determined for the thioether/Cu+ complexes are high
(see Table 2), as expected for copper centers in sulfur-rich
coordination environments. Furthermore, the thioethers
employed do not support cupric complexes, since reactions
with Cu2+ lead to the oxidation of 1–3. Thus, in thioether
coordination environments Cu+ is favored over Cu2+, and
it is likely that ligand-promoted reduction of the metal cen-
ter can occur in these systems.
Warning! Metal perchlorates are potentially explosive and should
be handled with extreme care.
Electrochemical Studies: Measurements were made under N2 in an-
hydrous acetonitrile with a potentiostat-galvanostat EG&G PAR
model 263A with a glassy carbon working electrode and a platinum
wire auxiliary electrode. Potentials were recorded vs. a pseudo-ref-
erence electrode of AgBr(s)/Ag(wire) immersed in a 0.1 m (C4H9)4-
NBr acetonitrile solution. The working electrode was polished with
alumina and washed with acetonitrile prior to measurements. All
voltammograms were started from the current null potential (Ei =
0) and were scanned in both directions, positive and negative, and
obtained at a scan rate of 0.100 Vs–1. In agreement with IUPAC
convention, the voltammogram of the Fc+/Fc system was obtained
to establish the values of the anodic (Eap), and cathodic (Ecp) peak
potentials. The electrolytic domain under the working conditions
was –2.2 to 3.2 V relative to AgBr(s)/Ag(wire). Bulk electrolyses
were performed with a high-surface platinum wire as the auxiliary
electrode and a platinum minigrid as the working electrode.
Experimental Section
General: Compounds were manipulated under an atmosphere of
dinitrogen in a glovebox or by vacuum-line and Schlenk techniques.
Solvents were dried by standard methods and distilled under N2
prior to use. CuI, [Cu(CH3CN)4]PF6, Cu(ClO4)2·6H2O, hexamethy-
lenetetramine, 2,4-dimethylthiophenol, para-formaldehyde, and p-
toluenesulfonic acid were used as received from commercial suppli-
X-ray Crystallography: Selected crystallographic data are presented
in Table 3. Single crystals were mounted at 173 K on a Bruker
ers. [Cu(CH3CN)4]ClO4 and 2-tert-butyl-4-methylthiophenol were SMART diffractometer equipped with an Apex CCD area detector.
prepared according to literature procedures.[18,19] Melting points
were determined with an Electrothermal Mel-Temp apparatus and
are uncorrected. Infrared spectra were recorded with a Bruker Ten-
sor 27 spectrophotometer in the 4000–400 cm–1 region as CH2Cl2
solutions or by using KBr disks. NMR spectra were recorded with
Frames were collected by omega scans, and integrated with the
Bruker SAINT software package using the appropriate unit cell.[20]
The structures were solved using the SHELXS-97 program,[21] and
refined by full-matrix least-squares on F2 with SHELXL-97.[22]
Weighted R factors, Rw, and all goodness of fit indicators, S, were
Table 3. Summarized crystallographic data.
[(1)CuI]2
[(2)(CuI)4(CH3CN)2]2·2THF·4CH3CN
4
Empirical formula
Mr [gmol–1]
Temperature [K]
Crystal system
Space group
Crystal size [mm]
a [Å]
b [Å]
c [Å]
β [°]
C72H102Cu2I2N2S6
1568.80
100(2)
monoclinic
P21/c
0.132ϫ0.258ϫ0.348
16.630(2)
14.794(2)
15.185(2)
95.394(2)
90
3719.3(8)
2
1.610
1.85 to 25.42
–20 Յ h Յ 19
–17 Յ k Յ 17
–18 Յ l Յ 18
1.401
391
29845
C58H80Cu8I8N8O2S4
2573.06
100(2)
monoclinic
P21/n
0.102ϫ0.196ϫ0.242
16.434(2)
14.014(2)
18.041(2)
97.336(s)
90
4121.1(8)
2
5.161
1.79 to 25.38
–18 Յ h Յ 19
–16 Յ k Յ 16
–21 Յ l Յ 21
2.074
451
33441
C22H30S2
358.58
298(2)
orthorhombic
P212121
0.190ϫ0.200ϫ0.380
8.567(1)
12.899(1)
37.925(2)
90
γ [°]
90
4190.8(4)
8
V [Å3]
Z
μ(Mo-Kα) [mm–1]
θ range
0.255
1.67 to 25.00
–10 Յ h Յ 10
–15 Յ k Յ 15
–45 Յ l Յ 45
1.137
449
34044
hkl range
Dcalc [kgm–3]
Refined parameters
Total reflections
Unique reflections
R1 [IϾ2σ(I)]
6832
0.0286
7547
0.0306
7400
0.0463
wR2
Goodness of fit
0.0680
1.063
0.0643
1.049
0.0730
0.913
218
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 212–220

Characterization of Tri- and Dithioether Copper Complexes
4
based on F2. The observed criterion of (F2 Ͼ2σF2) was used only
for calculating the R factors. All non-hydrogen atoms were refined
with anisotropic thermal parameters in the final cycles of refine-
ment. Hydrogen atoms were placed in idealized positions, with C–
H distances of 0.93 and 0.98 Å for sp2- and sp3-hybridized carbon
atoms, respectively. The isotropic thermal parameters of the hydro-
gen atoms were assigned the values of Uiso = 1.2 times the thermal
parameters of the parent non-hydrogen atom.
2 H, Ar), 7.24 (d, J = 1.38 Hz, 2 H, Ar), 7.01 (m, 2 H, Ar), 4.39
(s, 2 H, SCH2S), 2.29 (s, 6 H, ArCH3), 1.42 [s, 18 H, ArC-
(CH3)3] ppm. 13C NMR (75 MHz, CDCl3): δ = 151.20 (Ar), 138.26
(Ar), 134.71 (Ar), 132.19 (Ar), 129.02 (Ar), 128.64 (Ar), 44.04
(SCH2S), 37.42 (ArCH3), 31.36 [ArC(CH3)3], 21.67 [ArC-
(CH ) ] ppm. IR (KBr): ν = 2972, 2924, 2874, 1592, 1454, 1395,
˜
3 3
1364, 1248, 1242, 1193, 1046, 904, 879 cm–1. C23H32S2 (372.63):
calcd. C 74.14, H 8.66; found C 74.28, H 8.72.
CCDC-782635 (for [(1)CuI]2), -782636 (for [(2)(CuI)4(CH3-
CN)2]2), -782637 (for 4) contain the crystallographic data for this
article. These data can be obtained free of charge from the Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[(1)CuI]2: CuI (91 mg, 0.48 mmol) was added to a solution of 1
(285 mg, 0.48 mmol) in CH3CN (10 mL) and the mixture was
stirred under N2 for 12 h. The solution was concentrated to ca.
4 mL, and cooling to –25 °C afforded [(1)CuI]2 (243 mg, 83.6%)
1
as colorless crystals; m.p. 196–199 °C (dec). H NMR (300 MHz,
CD3CN): δ = 7.27 (d, 3J = 7.80 Hz, 3 H, Ar), 7.22 (d, 4J = 1.80 Hz,
3 H, Ar), 6.89 (m, 3 H, Ar), 4.50 (s, 6 H, NCH2S), 2.27 (s, 9 H,
ArCH3), 1.45 [s, 27 H, ArC(CH3)3] ppm. 13C NMR (75 MHz,
CDCl3): δ = 151.43 (Ar), 137.81 (Ar), 135.93 (Ar), 131.96 (Ar),
128.70 (Ar), 128.33 (Ar), 62.85 (NCH2S), 37.26 (ArCH3), 31.20
Tris(2-tert-butyl-4-methylphenylthiomethyl)amine (1): 2-tert-Butyl-
4-methylthiophenol (0.60 g, 3.33 mmol), hexamethylenetetramine
(0.09 g, 0.63 mmol), and p-toluenesulfonic acid (0.02 g) were placed
in a sealed vessel under N2, and then heated to 115–120 °C for 2 d.
After cooling to room temperature and removing volatile materials
(primarily NH3) under vacuum, another portion of 2-tert-butyl-4-
methylthiophenol (0.20 g, 1.11 mmol) was added, and the mixture
was heated to 115–120 °C for a further 18 d. The yellow oil ob-
tained was washed with MeOH, dissolved in hexanes, and filtered.
The components were separated by flash column chromatography
on silica gel, eluting with hexanes followed by 9:1 hexanes/CH2Cl2
[ArC(CH ) ], 21.41 [ArC(CH ) ] ppm. IR (KBr): ν = 3039, 2960,
˜
3 3
3 3
2918, 2867, 1597, 1562, 1468, 1447, 1394, 1359, 1332, 1257, 1210,
1125, 1090, 1041, 924, 876, 810, 705, 665, 631, 471 cm–1.
C72H102Cu2I2N2S6 (1568.87): calcd. C 55.12, H 6.55, N, 1.79; found
C 54.83, H 6.32, N 1.93.
[(2)(CuI)4(CH3CN)2]2: CuI (276 mg, 1.44 mmol) was added to a
solution of 2 (105 mg, 0.36 mmol) in CH3CN (10 mL) and the mix-
ture was stirred under N2 for 12 h. The solution was concentrated
to ca. 2 mL, and cooling to –25 °C afforded [(2)(CuI)4(CH3CN)4]2
(236 mg, 57.9%) as a colorless crystalline product. M.p.Ͼ300 °C.
1H NMR (300 MHz, CD3CN): δ = 7.32 (d, 3J = 7.95 Hz, 2 H, Ar),
7.06 (s, 2 H, Ar), 7.02 (d, 3J = 7.95 Hz, 2 H, Ar), 4.30 (s, 2 H,
SCH2S), 2.28 (s, 12 H, ArCH3) ppm. 13C NMR (75 MHz, CDCl3):
δ = 139.86 (Ar), 138.32 (Ar), 132.08 (Ar), 131.99 (Ar), 131.43 (Ar),
128.28 (Ar), 40.08 (SCH2S), 21.02 (ArCH3), 20.62 (ArCH3) ppm.
1
afforded 1 (0.25 g, 33.4%) as a colorless oil. H NMR (300 MHz,
3
4
CDCl3): δ = 7.27 (d, J = 7.70 Hz, 3 H, Ar), 7.16 (d, J = 1.52 Hz,
3
4
3 H, Ar), 6.86 (dd, J = 7.70, J = 1.52 Hz, 3 H, Ar), 4.49 (s, 6 H,
NCH2S), 2.29 (s, 9 H, ArCH3), 1.48 [s, 27 H, ArC(CH3)3] ppm. 13
C
NMR (75 MHz, CDCl3): δ = 150.71 (Ar), 136.60 (Ar), 135.17 (Ar),
131.28 (Ar), 127.68 (Ar), 127.39 (Ar), 62.18 (NCH2), 36.66
(ArCH ), 30.90 [ArC(CH ) ], 21.54 [ArC(CH ) ] ppm. IR (KBr): ν
˜
3
3 3
3 3
= 2961, 2920, 2869, 1726, 1690, 1597, 1453, 1395, 1261, 1213, 1100,
1043, 919, 878, 810, 688, 636, 475 cm–1. FAB+ MS: m/z = 592 (1+),
536 ([1 – tBu]+), 414 ([ArSCH2]2NCH2+). C36H51NS3 (593.99):
calcd. C 72.79, H 8.65; found C 72.59, H 8.90.
IR (KBr): ν = 3008, 2971, 2945, 2915, 2857, 2731, 1599, 1478, 1447,
˜
1378, 1278, 1230, 1195, 1149, 1050, 874, 830, 803, 724, 652, 617,
540, 441 cm–1. C42H52Cu8I8N4S4 (2264.74): calcd. C 22.27, H 2.31,
N 2.47; found C 22.65, H 2.50, N 2.12.
Bis(2,4-dimethylphenylthio)methane (2): 2,4-Dimethylthiophenol
(2.00 g, 14.47 mmol), para-formaldehyde (0.22 g, 7.23 mmol), and
p-toluenesulfonic acid (0.05 g) were heated to reflux in toluene
(20 mL) for 14 h. After cooling to room temperature, the solution
was washed with a saturated aqueous Na2CO3 solution (20 mL),
and twice with brine (20 mL). The organic phase was dried with
Na2SO4, concentrated under reduced pressure, and the solid ob-
tained was crystallized from hexanes to afford of 2 (1.71 g, 82.2%)
Bis(2-tert-Butyl-4-methylphenyl) Disulfide (4): On a preparative
scale, the disulfide is best synthesized by air oxidation of the corre-
sponding arylthiol. A CH2Cl2 solution of the thiol[19] is left stand-
ing exposed to air for 72 h, and the sole product is the disulfide in
quantitative yield. The compound was crystallized by slow evapo-
ration of a concentrated hexane solution at 4 °C; the solid melts
readily on handling. 1H NMR (300 MHz, CD3CN): δ = 7.55 (d, 3J
1
as a colorless solid; m.p. 29–30 °C. H NMR (300 MHz, CD3CN):
3
3
4
3
δ = 7.31 (d, J = 7.95 Hz, 2 H, Ar), 7.06 (s, 2 H, Ar), 7.01 (d, J =
7.95 Hz, 2 H, Ar), 4.29 (s, 2 H, SCH2S), 2.28 (s, 12 H,
ArCH3) ppm. 13C NMR (75 MHz, CDCl3): δ = 140.20 (Ar), 138.65
(Ar), 132.47 (Ar), 132.32 (Ar), 131.82 (Ar), 128.59 (Ar), 40.33
= 7.98 Hz, 2 H, Ar), 7.15 (d, J = 1.35 Hz, 2 H, Ar), 6.92 (d, J =
7.98 Hz, 2 H, Ar), 2.29 (s, 6 H, ArCH3), 1.48 (s, 18 H,
ArCH3) ppm. 13C NMR (75 MHz, CDCl3): δ = 148.95 (Ar), 137.00
(Ar), 132.80 (Ar), 131.68 (Ar), 127.58 (Ar), 127.51 (Ar), 36.54
(SCH S), 21.35 (ArCH ), 20.94 (ArCH ) ppm. IR (KBr): ν = 2971,
˜
(ArCH ), 31.08 [ArC(CH ) ], 21.46 [ArC(CH ) ] ppm. IR (KBr): ν
2
3
3
˜
3
3 3
3 3
2922, 2863, 1602, 1479, 1448, 1403, 1380, 1225, 1202, 1055, 1036,
878 cm–1. C17H20S2 (288.47): calcd. C 70.78, H 6.99; found C 70.52,
H 6.91.
= 2963, 2927, 2871, 1593, 1460, 1398, 1364, 1344, 1300, 1239, 1193,
1162, 1096, 1056, 1018, 902 cm–1.
Supporting Information (see also the footnote on the first page of
this article): Additional spectroscopic and mass spectrometry data,
cyclic voltammograms, and an ORTEP diagram of 4.
Bis(2-tert-butyl-4-methylphenylthio)methane (3): 2-tert-Butyl-4-
methylthiophenol (0.52 g, 2.88 mmol), para-formaldehyde (43 mg,
1.44 mmol), and p-toluenesulfonic acid (10 mg) were heated to re-
flux in toluene (10 mL) for 14 h. After cooling to room temperature
the solution was washed with a saturated aqueous Na2CO3 solution
(10 mL) and twice with brine (10 mL). The organic phase was dried
with Na2SO4, concentrated under reduced pressure, and the prod-
uct obtained was purified by flash column chromatography on sil-
ica gel. Eluting with hexanes afforded 3 (0.34 g, 63.5%) as a color-
Acknowledgments
The authors thank Rubén A. Toscano and Simón Hernández-Or-
tega for crystallographic work, Rocío Patiño Maya for IR spectro-
scopic measurements, Carmen Márquez and Luis Velasco for mass
1
3
less oil. H NMR (300 MHz, CD3CN): δ = 7.44 (d, J = 7.98 Hz, spectrometry data, and Eréndira García-Ríos for combustion
Eur. J. Inorg. Chem. 2011, 212–220
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
219

P. R. Martínez-Alanis, V. M. Ugalde-Saldívar, I. Castillo
FULL PAPER
Rheingold, Chem. Commun. 1996, 1081–1082; c) H. W. Yim,
L. M. Tran, E. D. Dobbin, D. Rabinovich, L. M. Liable-Sands,
C. D. Incarvito, K.-C. Lam, A. L. Rheingold, Inorg. Chem.
1999, 38, 2211–2215; d) H. W. Yim, L. M. Tran, E. E. Pullen,
D. Rabinovich, L. M. Liable-Sands, T. E. Concolino, A. L.
Rheingold, Inorg. Chem. 1999, 38, 6234–6239; e) P. J. Schebler,
B. S. Mandimutsira, C. G. Riordan, L. M. Liable-Sands, C. D.
Incarvito, A. L. Rheingold, J. Am. Chem. Soc. 2001, 123, 331–
332; f) C. Ohrenberg, L. M. Liable-Sands, A. L. Rheingold,
C. G. Riordan, Inorg. Chem. 2001, 40, 4276–4283; g) T.
Weidner, A. Krämer, C. Bruhn, M. Zharnikov, A. Shaporenko,
U. Siemeling, F. Träger, Dalton Trans. 2006, 2767–2777; h) J. A.
DuPont, M. B. Coxey, P. J. Schebler, C. D. Incarvito, W. G.
Dougherty, G. P. A. Yap, A. L. Rheingold, C. G. Riordan, Or-
ganometallics 2007, 26, 971–979.
analyses. P. R. M. A. thanks the Consejo Nacional de Ciencia y
Tecnología (CONACyT) for financial support (Beca 27252).
[1]
a) L. A. Finney, T. V. O’Halloran, Science 2003, 300, 931–936;
b) E. I. Solomon, R. K. Szilagyi, S. D. George, L. Basumallick,
Chem. Rev. 2004, 104, 419–458; c) D. B. Rorabacher, Chem.
Rev. 2004, 104, 651–697; d) E. A. Lewis, W. B. Tolman, Chem.
Rev. 2004, 104, 1047–1076; e) S. T. Prigge, B. A. Eipper, R. E.
Mains, L. M. Amzel, Science 2004, 304, 864–867; f) J. P. Klin-
man, J. Biol. Chem. 2006, 281, 3013–3016; g) J. Shearer, P. Soh,
S. Lentz, J. Inorg. Biochem. 2008, 102, 2103–2113; h) A. V.
Davis, T. V. O’Halloran, Nature Chem. Biol. 2008, 4, 148–151;
i) S. I. Chan, S. S.-F. Yu, Acc. Chem. Res. 2008, 41, 969–979; j)
A. V. Davis, T. V. O’Halloran, Nat. Chem. Biol. 2008, 4, 148–
151; k) R. A. Himes, K. D. Karlin, Curr. Opin. Chem. Biol.
2009, 13, 119–131.
[9] R. Huerta, A. Flores-Figueroa, V. M. Ugalde-Saldívar, I. Cas-
tillo, Inorg. Chem. 2007, 46, 9510–9512.
[10] a) B. Norén, Å. Oskarsson, Acta Chim. Scan. A 1987, 41, 12–
17; b) J. Ramos, V. M. Yartsev, S. Golhen, L. Ouahab, P.
Delhaes, J. Mater. Chem. 1997, 7, 1313–1319; c) H. W. Yim, D.
Rabinovich, K.-C. Lam, J. A. Golen, A. L. Rheingold, Acta
Crystallogr., Sect. E: Struct. Rep. Online 2003, 59, m556–m558;
d) M. Heller, W. S. Sheldrick, Z. Anorg. Allg. Chem. 2004, 630,
1869–1874; e) W. Lu, Z.-M. Yan, J. Dai, Y. Zhang, Q.-Y. Zhu,
D.-X. Jia, W.-J. Guo, Eur. J. Inorg. Chem. 2005, 2339–2345; f)
T. H. Kim, Y. W. Shin, S. S. Lee, J. Kim, Inorg. Chem. Commun.
2007, 10, 11–14; g) T. H. Kim, Y. W. Shin, J. H. Jung, J. S. Kim,
J. Kim, Angew. Chem. Int. Ed. 2008, 47, 685–688.
[2]
a) T. Osako, Y. Ueno, Y. Tachi, S. Itoh, Inorg. Chem. 2004, 43,
6516–6518; b) R. C. Pratt, L. M. Mirica, T. D. P. Stack, Inorg.
Chem. 2004, 43, 8030–8039; c) C. Belle, W. Rammal, J.-L.
Pierre, J. Inorg. Biochem. 2005, 99, 1929–1936; d) N. W. Aboe-
lella, B. F. Gherman, L. M. R. Hill, J. T. York, N. Holm, V. G.
Young Jr., C. J. Cramer, W. B. Tolman, J. Am. Chem. Soc. 2006,
128, 3445–3458; e) L. Q. Hatcher, D.-H. Lee, M. A. Vance,
A. E. Milligan, R. Sarangi, K. O. Hodgson, B. Hedman, E. I.
Solomon, K. D. Karlin, Inorg. Chem. 2006, 45, 10055–10057;
f) L. Zhou, K. M. Nicholas, Inorg. Chem. 2008, 47, 4356–4367;
g) G. Y. Park, Y. Lee, D.-H. Lee, J. S. Woertink, A. A. N. Sarje-
ant, E. I. Solomon, K. D. Karlin, Chem. Commun. 2010, 91–
93.
[11] A. Bondi, J. Phys. Chem. 1964, 68, 441–451.
[12] S. Q. Bai, L. L. Koh, T. S. A. Hor, Inorg. Chem. 2009, 48, 1207–
1213.
[3]
[4]
a) R. H. Holm, P. Kennepohl, E. I. Solomon, Chem. Rev. 1996,
96, 2239–2314; b) K. Paraskevopoulos, M. Sundararajan, R.
Surendran, M. A. Hough, R. R. Eady, I. H. Hillier, S. S. Has-
nain, Dalton Trans. 2006, 3067–3076.
a) S. T. Prigge, R. E. Mains, B. A. Eipper, L. M. Amzel, Cell
Mol. Life Sci. 2000, 57, 1236–1259; b) S. I. Chan, V. C.-C.
Wang, J. C.-H. Lai, S. S.-F. Yu, P. P.-Y. Chen, K. H.-C. Chen,
C.-L. Chen, M. K. Chan, Angew. Chem. Int. Ed. 2007, 46,
1992–1994.
[13] a) H. N. Peindy, F. Guyon, A. Khatyr, M. Knorr, C.
Strohmann, Eur. J. Inorg. Chem. 2007, 1823–1828; b) P. D. Har-
vey, M. Knorr, Macromol. Rapid Commun. 2010, 31, 808–826.
[14] R.-H. Wang, M.-C. Hong, J.-H. Luo, R. Cao, J.-B. Weng, Eur.
J. Inorg. Chem. 2002, 3097–3100.
[15] a) J. San Filippo Jr., L. E. Zyontz, J. Potenza, Inorg. Chem.
1975, 14, 1667–1671; b) M. Knorr, F. Guyon, A. Khatyr, C.
Däschlein, C. Strohmann, S. M. Aly, A. S. Abd-El-Aziz, D.
Fortin, P. D. Harvey, Dalton Trans. 2009, 948–955; c) C. Xie,
L. Zhou, W. Feng, J. Wang, W. Chen, J. Mol. Struct. 2009, 921,
132–136.
[5] a) S. J. Firbank, M. S. Rogers, C. M. Wilmot, D. M. Dooley,
M. A. Halcrow, P. F. Knowles, M. J. McPherson, S. E. V. Phil-
lips, Proc. Natl. Acad. Sci. USA 2001, 98, 12932–12937; b)
M. M. Whittaker, J. W. Whittaker, J. Biol. Chem. 2003, 278,
22090–22101.
[16] M. Knorr, A. Pam, A. Khatyr, C. Strohmann, M. M. Kubicki,
Y. Rousselin, S. M. Aly, D. Fortin, P. D. Harvey, Inorg. Chem.
2010, 49, 5834–5844.
[6] a) E. A. Ambundo, M.-V. Deydier, A. J. Grall, N. Aguera-Vega,
L. T. Dressel, T. H. Cooper, M. J. Heeg, L. A. Ochrymowycz,
D. B. Rorabacher, Inorg. Chem. 1999, 38, 4233–4242; b) E. A.
Ambundo, L. A. Ochrymowycz, D. B. Rorabacher, Inorg.
Chem. 2001, 40, 5133–5138; c) E. A. Ambundo, Q. Yu, L. A.
Ochrymowycz, D. B. Rorabacher, Inorg. Chem. 2003, 42, 5267–
5273.
[7] a) S. Torelli, C. Belle, C. Philouze, J.-L. Pierre, W. Rammal,
E. Saint-Aman, Eur. J. Inorg. Chem. 2003, 2452–2457; b) W.
Rammal, H. Jamet, C. Philouze, J.-L. Pierre, E. Saint-Aman,
C. Belle, Inorg. Chim. Acta 2009, 362, 2321–2326.
[17] G. A. Olah, K. K. Laali, Q. Wang, G. K. S. Prakash, Onium
Ions, Wiley, New York, 1998.
[18] T. C. Deivaraj, J. J. Vittal, J. Chem. Soc., Dalton Trans. 2001,
322–328.
[19] A. Flores-Figueroa, V. Arista-M., D. Talancón-Sánchez, I. Ca-
stillo, J. Braz. Chem. Soc. 2005, 16, 397–403.
[20] Bruker AXS, SAINT Software Reference Manual, v. 6.23C,
Madison, Wisconsin, USA, 2002.
[21] G. M. Sheldrick, SHELXS-97, Crystal Structure Solution, Uni-
versity of Göttingen, Germany, 1990.
[22] G. M. Sheldrick, SHELXL-97, Crystal Structure Refinement,
University of Göttingen, Germany, 1997.
[8] a) P. Ge, B. S. Haggerty, A. L. Rheingold, C. G. Riordan, J.
Am. Chem. Soc. 1994, 116, 8406–8407; b) C. Ohrenberg, M. M.
Saleem, C. G. Riordan, G. P. A. Yap, A. K. Verma, A. L.
Received: September 8, 2010
Published Online: December 1, 2010
220
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 212–220