Activation of dichloromethane by a V(iii) thiolate complex: An example of S-based nucleophilic reactivity in an early transition metal thiolate

Article abstract of DOI:10.1039/c2cc37801a

A V^III thiolate complex activated C-Cl bond in dichloromethane via S-based nucleophilic attack. The reaction products, a V^III-Cl species (major one) and a V^IV binding to a CH₂ containing ligand (minor one) were obtained. The work demonstrates sulfur donors in the early-transition metal thiolates having strong nucleophilic characteristics.

Full text of DOI:10.1039/c2cc37801a

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Activation of dichloromethane by a V(III) thiolate
complex: an example of S-based nucleophilic reactivity
in an early transition metal thiolate†
Cite this: Chem. Commun., 2013,
49, 1109
Received 27th October 2012,
Accepted 17th December 2012
a
a
Tzu-Tso Chen,z Yu-Sen Chen,z Ya-Ho Chang,a Jung-Ching Wang,a Yi-Fang Tsai,a
Gene-Hsiang Lee,b Tin-Shen Kuoc and Hua-Fen Hsu*a
DOI: 10.1039/c2cc37801a
www.rsc.org/chemcomm
A VIII thiolate complex activated C–Cl bond in dichloromethane via
The increasing interest in vanadium sulfur complex stems from
S-based nucleophilic attack. The reaction products, a VIII-Cl species its biological relevance, specifically, the interaction between vana-
(major one) and a VIV binding to a CH2 containing ligand (minor one) dium ion and cysteine or glutathione as well as the finding of
were obtained. The work demonstrates sulfur donors in the early- vanadium nitrogenase.9 For examples, cysteine and glutathione
transition metal thiolates having strong nucleophilic characteristics.
might act as reductants for the intracellar reduction of vanadium
ion in vanadocyte of ascidians.10 Amavadin, a natural VIV complex
The non-innocent nature of cysteine bioligand has yielded a wide likely plays a role in the fungus defensive system through the specific
range of sulfur-based reactivity in biological systems, such as the oxidation of some thiols to disulfide.11 In the cases of vanadium ion
post-translational modifications of nitrile hydratase,1 cysteine dioxy- interacting with organic thiolate ligands, the sulfur donors mainly
genase,2 and ZnII-dependent thiolate methylation proteins. The last behave as innocent ligands and act as structural support. However,
one has involved S-alkylation of cysteine identified in DNA repair in several examples, the thiolate ligands are not innocent and
protein Ada,3 methionine synthase,4 and farnesyl transferase.5 In display several types of reactivity.12 These include the formation of
synthetic examples, the alkylation of metal bound sulfur donor has a disulfide bond coupled with the reduction of vanadium ion,12a,b
been mostly found in various late-transition metal thiolates, for the oxygenation of the bound sulfur in a VV-thiolate resulting in a
instance, in the cases of CuI, NiII, ZnII, FeII, RuII and PtII complexes.6 corresponding sulfenate compound12c and the generation of a
These comply with a hypothesis that the nucleophilicity of the metal metal–thiyl radical that further cleaves the C–O bond of methanol,
bound sulfur donor is a result of the four-electron destabilizing consequently leading to the methylation of the bound thiolate.12b,d It
interaction of lone pairs on thiolate sulfur and fulfilled metal was proposed that a vanadyl(IV) cis-dithiolate complex reacting with
d-orbitals.7a Recently, a more detailed mechanism has been devel- 1,3-dibromopropane might generate an S-alkylated product, however
oped through studies involving zinc compounds or enzymes.7b–d no direct evidence was provided for this chemistry.13 At this work, we
These state that the active nucleopile might involve a dissociated/ report a VIII-thiolate complex that shows S-based nucleophilic
unbound thiolate or bound thiolate. Alternatively, the pathway reactivity with dichloromethane (Scheme 1). Such reactivity is rare
might be based on a s-bond metathesis reaction with a four-center for early-transition metal thiolates and unprecedented for the exist-
transition state. By contrast, the alkylation of the bound sulfur in the ing vanadium thiolate complexes.
early-transition metal thiolates has not been widely observed and
investigated. The only reported example is a dimeric molybdenum obtained from the reaction of VCl3(thf)3 and [PS2SH00 2ꢀ
A six-coordinate VIII complex, [VIII(PS2SH00)2][PPh4] (1), was
in a
= P(C6H3-3-SiMe3-2-S)2(C6H3-3-SiMe3-2-SH)).
]
complex that undergoes nucleophilic attack on dibromomethane to 1 : 2 ratio ([PS2SH00 2ꢀ
]
+
form a methylene-brideged thioether core.8
The addition of the counterion, PPh4 , to the reaction mixture,
followed by layering with ether, gave the crystalline solid of 1ꢁ
0.103CH3OHꢁ0.455THF (60% yield). The X-ray crystallographic
data shows 1 as a distorted octahedral vanadium center by way
a Department of Chemistry, National Cheng Kung University, Tainan 701, Taiwan.
E-mail: konopka@mail.ncku.edu.tw; Fax: +886-62740552;
Tel: +886-62757575-65336
of its binding to two [PS2SH00 2ꢀ
ligands where thiol groups remain
]
b Department of Chemistry, National Taiwan University, Taipei 116, Taiwan
unbound (Fig. 1).§ The electron density of the hydrogen atoms
c Department of Chemistry, National Taiwan Normal University, Taipei 116, Taiwan in the unbound thiols was not found in diffraction map,
† Electronic Supplementary Information (ESI) available: Experimental details, IR
however, the distance of 3.642 Å between S2 and S6 atoms
indicates the presence of intramolecular hydrogen bonding
spectrum of 1, UV-vis-NIR spectrum of 3, X-ray structural parameters and selected
bond distances and angles of 1 and 3. CCDC 895276 and 895067. For ESI and
interaction. The containing thiol groups in 1 were also supported
crystallographic data in CIF or other electronic format see DOI: 10.1039/
by an IR spectrum that gave an S–H stretching band at 2312 cmꢀ1
c2cc37801a
‡ T.-T. C and Y.-S. C. contributed equally.
(Fig. S1 in the ESI†). In addition, FAB-mass data show a set of
c
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Chem. Commun., 2013, 49, 1109--1111 1109

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Scheme 1
Fig. 2 Thermal ellipsoid plot (35% probability) of [VIV((PS300)2CH2] (3). H atoms
are omitted for clarity.
peaks at 1195 m/z, consistent with the calculated mass of the
isotope pattern of [VIII(PS2SH00)2]ꢀ (the anion of 1).
The isolation of 2 and 3 from the reaction of 1 with dichloro-
methane is consistent with activation and cleavage of the C–Cl
bond and insertion of the methylene moiety of dichloromethane
between two S-donors of two different PS300 ligands, forming a
methylene-bridged thioether core contained in [VIV((PS300)2CH2)]
(3). Confidence in this interpretation of the nature of the reaction
was enhanced by ESI-MS spectrometric investigations. Thus,
complex 3 gives rise to a set of molecular ion peaks at 1208 m/z
(M + H)+, consistent with the theoretical isotope pattern. When
CD2Cl2 was used instead of CH2Cl2 in the reaction, the molecular
ion peaks were shifted by 2 m/z with the same isotope pattern
(Fig. 3), unequivocally meaning that the bridged methylene
moiety is from the cleavage of dichloromethane.
Dissolving complex 1 in CH2Cl2 yielded a reddish-brown
solution, but the color gradually turned to yellow in 24 h.
Continuously layered with hexane, the crystals of [VIII(PS300)Cl]-
[PPh4] (2) ([PS300]3ꢀ = P(C6H3-3-SiMe3-2-S)3) were precipitated in
3–5 days (70% yield based on vanadium).
When methanol was used instead of hexane to layer on
dichloromethane solution of 1, the crystalline form of
[VIV((PS300)2CH2)] (3), was produced (8% yield based on vana-
dium) (Scheme 1). In control experiments, the reaction carried
in the absence of light gave the same products, excluding the
involvement of the photolysis. Complex 2 has been reported
previously by our laboratory.14 It consists of a five-coordinate
VIII center ligated by a chloride and a PS300 ligand, forming a
trigonal bipyramidal geometry. The X-ray crystallographic
structure of 3 was obtained and it adopts a seven-coordinate
VIV center by binding to a ((PS300)2CH2) ligand, where a methylene
group is bridged between two thiolates of two PS300 ligands (Fig. 2).
The geometry found in 3 is a distorted pentagonal bipyramid with
S2 and S6 thiolato groups in axial positions (S2–V1–S6 = 168.07
deg). The equatorial plane is constructed by two phosphine donors
(P1 and P2), two thiolates (S1 and S3) and one thioether (S5).
The conversion of 1 in dichloromethane solution to 2 was also
demonstrated by UV-vis-NIR and 1H NMR spectroscopic studies. As
shown in Fig. 4, the electronic spectrum of 1 in CH2Cl2 slowly
changed to the one with characteristic bands similar to those
in 2 during a 24 hour observation. A nearly complete conversion
Fig. 3 ESI-MS spectrum of complex 3 (top) and complex 3 isolated from the
reaction of 1 and CD2Cl2 (bottom). The molecular ion peaks display isotopic
distribution at 1207 m/z (top) and 1209 m/z (bottom), consistent with the
formulation of C55H74P2S6Si6V1 and C55D2H72P2S6Si6V1, respectively.
Fig. 1 Thermal ellipsoid plot (35% probability) of 1ꢁ0.103CH3OHꢁ0.455THF. The
H atoms except H3 and H6, cation (PPh4+), and solvated molecules are omitted
for clarity.
c
1110 Chem. Commun., 2013, 49, 1109--1111
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thiolates also have strong nucleophilic characteristics reacting
with a weak electrophile such as dichloromethane. Whether the
active nucleophile of this reaction involves a bound thiolate or a
dissociated thiolato ligand is still obscure with the current data.
The kinetic study and theoretic calculation of this chemistry are
undergoing to provide the further mechanistic information.
This work was supported by National Science Council in
Taiwan (NSC 99-2113-M006-004-MY3).
Notes and references
§ Crystal
data
for
1ꢁ0.103CH3OHꢁ0.455THF:
CCDC-895276,
%
C79.93H98.07O0.56P3S6Si6V, M = 1572.52, triclinic, space group P1 (no.
2), a = 13.2824(2) Å, b = 16.9608(3) Å, c = 20.7372(3) Å, a = 80.6212(11)1,
Fig. 4 Variation in UV-vis-NIR spectrum of 1 in CH2Cl2 (3.18 ꢂ 10ꢀ4 M). The
spectrum was taken every 6 hour during a 24 hour time period. Inset: UV-vis-NIR
spectrum of 2 in CH2Cl2.
b = 86.5684(12)1, g = 70.7773(7)1, V = 4352.15(12) Å3, Z = 2, d(calcd)
=
1.200 Mg mꢀ3, T = 150 K, 67094 reflection collected, 19900 indepen-
dent, Rint = 0.0565, R1 = 0.0560, wR2 = 0.1456 for all data. Crystal data for
3: CCDC-895067, C55H74P2S6Si6V, M = 1208.92, monoclinic, space group
P21/c (no. 14), a = 26.551(8) Å, b = 11.965(4) Å, c = 21.288(6) Å, a = 901,
b = 104.2(5)1, g = 901, V = 6556.03(300) Å3, Z = 4, d(calcd) = 1.225 Mg mꢀ3
,
T = 296(2) K, 16135 reflection collected, 7071 independent, Rint = 0.1902,
R1 = 0.0634, wR2 = 0.1151 for all data.
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Chem. Commun., 2013, 49, 1109--1111 1111