Methyl transfer from rhenium to coordinated thiolate groups

Article abstract of DOI:10.1002/1521-3773(20021018)41:20<3807::AID-ANIE3807>3.0.CO;2-Z

Methylation of a thiolate group, which has only been observed in vitamin B₁₂ and its mimics, has been accomplished with [MeReO₃] and [MeReO(edt)PPh₃] (edt = 1,2-ethanedithiolato; see scheme). The proposed mechanism involves the formation of [MeRe^VIIO(edt)₂] through two stepwise condensation reactions; nucleophilic attack of a thiolate ligand on the methyl group leads to the product.

Full text of DOI:10.1002/1521-3773(20021018)41:20<3807::AID-ANIE3807>3.0.CO;2-Z

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[10] D. Ozkaya, W. Z. Zhou, J. M. Thomas, P. A. Midgley, V. J. Keast, S.
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and related complexes also convert thiols to thioethers
[Eq. (1)]:[5]
CoIIIꢀCH3 þ RSH ! ½CoIŠꢀ þ RSCH3 þ Hþ
ð1Þ
[13] D. S. Shephard, T. Maschmeyer, G. Sankar, J. M. Thomas, D. Ozkaya,
B. F. G. Johnson, R. Raja, R. D. Oldroyd, Eur. J. Chem. 1998, 4, 1214.
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P. Deschamps, J. Philibert), Hermann, Paris, 1966, p. 1509.
[17] W. Reuter in X-ray Opticsand Microanalysis (Eds.: G Shimoda, K.
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[18] E. D. Boyes, Microsc. Microanal. 2000, 6, 307.
There are, however, a lack of precedents in the literature for
similar conversions that do not involve organocobalt com-
plexes. In this work, new reactions of rhenium complexes have
been examined, and sound evidence for the analogous
conversion has now been obtained.
[19] R. A. Crowther, D. J. de Rosier, A. Klug, Proc. R. Soc. London Ser. A
1970, 317, 319.
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[25] M. Weyland, PhD thesis, University of Cambridge, 2002.
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7882.
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[29] J. C. Russ, The Image Processing Handbook, 3rd ed., IEEE Press,
Piscataway, 2000.
MeReO3 (MTO, 2)[6] reacts with the readily-oxidized 2-
(mercaptomethyl)thiophenol (mtpH2), to yield a disulfide
[Eq. (2)]:
2 MeReO3 þ 4 mtpH2 ! fMeReOðmtpÞg2 ð4Þ þ 2 ð6Þ þ 4 H2O
ð2Þ
With 1,2-ethanedithiol (edtH2), however, a quite different
result was obtained. As ReVII was reduced to ReV, one
edtH2 molecule was transformed to HS(CH2)2SMe, which
remains coordinated to the rhenium(v) center through both
sulfur atoms in a k2 fashion [Eq. (3)]:
[30] P. Gilbert, J. Theor. Biol. 1972, 36, 105.
[31] P. R. Buseck, R. E. Dunin-Borkowski, B. Devouard, R. B. Frankel,
M. R. McCartney, P. A. Midgley, M. Posfai, M. Weyland, Proc. Natl.
Acad. Sci. USA 2001, 98, 13490.
MeReO3 þ 2 edtH2 ! 1 þ 2 H2O
ð3Þ
Details of the synthesis and characterization of the dark-red
complex 1 are given in the Experimental Section. A similar
reaction starting with [MeReO(edt)(PPh3)] (3)[7] gave the
same product in lower yield. Crystals of 1 suitable for X-ray
diffraction could not be obtained. We have formulated the
composition of 1 to be [ReO(k2-edt)(k2-edtMe)] based on
elemental analysis and spectroscopic data. An alternative
formulation as an organorhenium(vii) compound, [Me-
ReO(edt)2], could not be ruled out by these data. However,
the evidence is in favor of structure 1 as the CH3 resonance
appears at d ¼ 1.90 ppm, which is further downfield than
would be expected for a methyl group coordinated to a
ReVII center. Indeed, the proposed mechanism suggests that
[MeReO(edt)2] lies on the pathway to 1.
Methyl Transfer from Rhenium to Coordinated
Thiolate Groups**
Xiaopeng Shan, Arkady Ellern, and
James H. Espenson*
A prominent reaction of vitamin B12 is the conversion of
d,l-homocystein, HS(CH2)2CHNH2CO2H, to l-methionine,
MeS(CH2)2CHNH2CO2H, with methylcobalamin and meth-
4]
ylcobinamide.[1 Methyl bis(dimethylglyoximato)cobalt(iii)
[*] Prof. J. H. Espenson, X. Shan, Dr. A. Ellern
Department of Chemistry
Chemical methods were therefore used to obtain informa-
Iowa State University
tion about the molecular structure of 1, particularly with
Ames, IA 50011 (USA)
Fax : (þ 1)515-294-5233
ꢀ
respect to whether the Me Re interaction present in the
E-mail: espenson@iastate.edu
starting material is retained. The reaction of 1 with H2O2 in
wet acetonitrile gave ReO4ꢀ ions, which are easily recognized
from the characteristic UV spectrum. The same product was
[**] This work was supported by the US National Science Foundation,
Grant No. CH-9982004. We are grateful to Professor G. M. Miller for
a discussion concerning crystallography and to Professor D. J. Dare-
nsbourg for the gift of 1,3,5-triaza-phosphaadamantane.
ꢀ
obtained from 5, another compound that lacks a Me Re
ꢀ
bond. In contrast, several compounds that do contain a Me
Supporting information for this article is available on the WWW under
http://www.angewandte.org or from the author.
Re bond (2, 3, and 4) cleanly reacted with H2O2 to form
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[MeReO(k2-O2)2(OH2)], with a characteristic absorption
maximum at 360 nm (e ¼ 1200). Thus, these results suggest
[8]
ꢀ
that no Me Re bond exists in 1.
The reaction of compound 1 with phosphanes (PZ3, in
general) yields a new series of compounds, [ReO(k2-edt)(k1-
edtMe)(PZ3)] (7) in which the thioether arm has been
displaced. One such compound, where PZ3 ¼ 1,3,5-triaza-
phosphaadamantane (PTA),[9] has been characterized crystal-
lographically; the molecular structure is displayed in Figure 1.
Phosphanes are generally much stronger Lewis bases than
Scheme 1. Proposed mechanism for the formation of 1 (RDS ¼ rate-
determining step).
final step appears to involve nucleophilic attack of the
coordinated thiolate sulfur atom on the methyl group of the
intermediate. Precedents for this mechanism, aside from those
found in organocobalt systems, are rare. While the transfer of
a phenyl group to the oxo group of an intermediate species
([TpRe(O)2Ph]þ, Tp ¼ hydrotris(1-pyrazolyl)borate) repre-
sents a distantly related example,[11] a more relevant case is
the thermal decomposition of [MeReO(k2-O2)2(OH2)], which
yields MeOOH and [HReO4].[12]
In summary, a novel transformation of the [MeRe(edt)]
complex to give a [Re(thiolate methylthioether)] complex
(1) has been discovered and established. This transformation
is without precedent, aside from the homocystein-to-methio-
nine transformation found for vitamin B12 and its mimics.
Furthermore, the thioether group can be replaced by a
phosphane; the derivative with PTA was characterized
crystallographically. All of these reactions proceed to equili-
brium, but owing to the chelate effect, the equilibrium
constants are smaller by a factor of 105 than the analogous
values of K for the displacement of a nonchelated RSR’
group.
Figure 1. The molecular structure of [ReO(k2-edt)(k1-edtMe)(PTA)]. The
methyl group at S4 was disordered; the structure was refined at 50%
occupancy of the two sites. Selected bond lengths [pm] and angles [8] are:
Re-O 170.0(5), Re-S3 230.54(17), Re-P 242.25(18), S4-C10 181.0(9), S4-
C11A 175.6(17), S4-C11B 184.0(4); O-Re-S3 110.68(19), O-Re-P 97.3(2),
S2-Re-P 153.94(6), S1-Re-S3 133.58(7), C10-S4-C11A 102.7(7), C10-S4-
C11B 104.3(17), C11A-S4-C11B 133.1(14). The structure was drawn with
the CrystalMaker program.[13]
thioethers and will, to a great extent, displace RSR’ groups. In
keeping with this fact, the equilibrium constant for PPh3 [K4,
Eq. (4)] is 6 î 105 (C6H6, 258C),[10] whereas the equilibrium
constant for Equation (5) (K5) is 8.0 under the same
conditions. The large difference in these values arises from
the chelate effect, and illustrates its very substantial impor-
tance in this case.
Experimental Section
1: Dimethylsulfoxide (0.2 mmol) was added to 2 (0.5 mmol) in toluene
(5 mL). 1,2-Ethanedithiol (0.5 mmol) was added to this mixture, where-
upon the solution turned red. After 4 h, hexanes (10 mL) were layered on
top of the solution, which yielded a deep-red solid (87% yield) which was
purified by recrystallization from dichloromethane/hexanes. Elemental
analysis (%) calcd for C5H11OReS4: C 14.95, H 2.76, S 31.94; found: C
15.16, H 2.82, S 32.09; 1H NMR (400 MHz, [D6]benzene, 258C): d ¼ 3.55
(m, 1H; CH2), 3.36 (m, 1H; CH), 2.70 (m, 1H; CH2), 2.51 (m, 2H; CH2),
2.11 (m, 1H; CH2), 1.92 (m, 1H; CH2), 1.90 (s, 3H; CH3), 0.84 ppm (m, 1H;
CH2); 13C NMR (100 MHz, [D6]benzene, 258C): d ¼ 45.6, 45.0, 43.5, 36.2,
22.3 ppm; UV/Vis (C6H6): lmax (e) ¼ 510 (160), 389 nm (3400).
MeReOðedtÞðMe2SÞ þ PPh3¼MeReOðedtÞPPh3 þ Me2S K4
1 þ PPh3¼ReOðꢀ2 ꢀ edtÞðꢀ1 ꢀ edtMeÞðPPh3Þ K5
ð4Þ
ð5Þ
The formation of 1, as shown in reaction (3), follows the net
1:2 stoichiometry given. It is a sequential process that obeys
the rate law [Eq. (6)]:
[ReO(k2-edt)(k1-edtMe)(PTA)]: A 1:1 reaction between 1 and PTA in
toluene gave dark, shiny single crystals after recrystallization from toluene/
hexanes. Elemental analysis (%) calcd for C11H23ON3PReS4: C 23.65, H
4.15, N 7.52, S 22.96, P 5.54; found: C 23.57, H 4.12, N 7.55, S 23.25, P 5.61;
1H NMR (400 MHz, [D6]benzene, 258C): d ¼ 4.34 (m, 1H; CH2), 4.21 (m,
7H; CH2), 3.86 (m, 6H; CH2); 3.43 (m, 1H; CH2), 3.34 (m, 1H; CH2), 3.20
(m, 1H; CH2), 2.97 (m, 1H; CH2), 2.41 (m, 2H; CH2), 1.98 ppm (s, 3H;
CH3); 13C NMR (100 MHz, [D6]benzene, 258C): d ¼ 72.5 (d, J(C,P) ¼
7 Hz), 51.9 (d, J(C,P) ¼ 16 Hz), 43.6 (d, J(C,P) ¼ 8 Hz), 42.0(s), 37.2(s),
35.5 (d, J(C,P) ¼ 9 Hz), 15.3 ppm (s); 31P NMR (162 MHz, [D6]benzene,
258C): d ¼ ꢀ74.0 ppm; UV/Vis (C6H6): lmax (e) ¼ 386 (1900), 318 (1600; sh),
d½1Š=dt ¼ k ½2Š ½edtH2Š
ð6Þ
with k ¼ 7.3 î 10ꢀ2 Lmolꢀ1 sꢀ1 (Me2SO, 258C). Clearly the first
condensation step is rate determining, as the methylation step
occurs more rapidly and is not manifest in the kinetics. The
sequential mechanism proposed is given in Scheme 1. The
3808
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interactions for the recognition of analytes.[2] These interac-
tions are, however, attenuated drastically in a highly polar
medium such as water, because of the competing solvation
effect.[3] The detection of anions such as phosphate in water is,
hence, a challenging task.[4] We report herein a colorimetric
sensor that can detect phosphate anions in an aqueous
solution of neutral pH values. The sensor is easy to assemble
and shows a high sensitivity and excellent selectivity for
phosphate ions over other anions.
262 nm (3800). CCDC-190226 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crys-
tallographic Data Centre, 12, Union Road, Cambridge CB21EZ, UK; fax:
(þ 44)1223-336-033; or deposit@ccdc.cam.ac.uk).
Received: June 13, 2002
Revised: August 1, 2002 [Z19200]
[1] J. R. Guest, S. Friedman, D. D. Woods, E. L. Smith, Nature 1962, 195,
340.
In assembling the sensor, we took advantage of metal
ligand interactions. Such interactions are so highly favorable
that they occur even in polar media. Furthermore, the metal
ion can present some geometrical preferences, thus imparting
selective binding tendencies towards anions of a given
shape.[5] 2,6-Bis(bis(2-pyridylmethyl)aminomethyl)-4-methyl-
phenol (H-bpmp) was reported to form a crystalline dinuclear
complex with CoII,[6] and Seo et al. reported that the phenyl-
phosphonate anion binds to the dinuclear complex of CoIII
with H-bpmp by bridging the two metal ions.[7] These reports
led us to explore the metal complex of H-bpmp as a receptor
for phosphate ions. The dinuclear ZnII complex of H-bpmp
was readily obtained by dissolving H-bpmp and zinc perchlo-
rate in water; the complex is colorless and has a good water
solubility, which are features desirable for using the complex
as a receptor for a water-soluble chemosensor. We chose
pyrocatechol violet, a catechol-type pH-sensitive dye, as the
chromogenic indicator for the sensor. Catechols are known to
coordinate to the two metal ions in a phenoxo-bridged
binuclear metal complex.[8] Furthermore, it is known that the
yellow color of pyrocatechol violet at neutral pH may change
to blue when it binds to a metal ion.[9] Therefore, the
displacement of the receptor-bound pyrocatechol violet by a
phosphate anion would be communicated visually as well as
spectrophotometrically. The competition approach[10] used for
assembling the present sensor is schematically illustrated in
Figure 1.
[2] J. R. Guest, S. Friedman, M. J. Dilworth, D. D. Woods, Ann. N. Y.
Acad. Sci. 1964, 112, 774.
[3] M. L. Ludwig, R. G. Matthews, Annu. Rev. Biochem. 1997, 66, 269.
[4] R. G. Matthews, Acc. Chem. Res. 2001, 34, 681.
[5] G. N. Schrauzer, R. J. Windgassen, J. Am. Chem. Soc. 1967, 89, 3067.
[6] W. A. Herrmann, R. M. Kratzer, R. W. Fischer, Angew. Chem. 1997,
109, 2767; Angew. Chem. Int. Ed. Engl. 1997, 36, 2652.
[7] G. Lente, X. Shan, I. A. Guzei, J. H. Espenson, Inorg. Chem. 2000, 39,
3572.
[8] Each compound was treated with 30% hydrogen peroxide to give a
final concentration of 38 mm H2O2 in acetonitrile. The final spectra
from these procedures confirming the two indicated ReVII products
are given in the Supporting Information.
[9] D. J. Darensbourg, T. J. Decuir, J. H. Reibenspies, NATO ASI Ser. Ser.
3 1995, 5, 61.
[10] This equilibrium constant applies to the analogue of 3, with mtp
instead of edt, where mtpH2 is 2-(mercaptomethyl)thiophenol. The
terms contributing to K1 are given in the Supporting Information.
[11] S. N. Brown, J. M. Mayer, J. Am. Chem. Soc. 1996, 118, 12119.
[12] W.-D. Wang, J. H. Espenson, Inorg. Chem. 1997, 36, 5069.
[13] D. Palmer, CrystalMaker, 2.0 ed., Hollywell, Bicester, 1999.
Naked-Eye Detection of Phosphate Ions in
Water at Physiological pH: A Remarkably
Selective and Easy-To-Assemble Colorimetric
Phosphate-Sensing Probe**
Min Su Han and Dong H. Kim*
Phosphate anions are one of most important constituents of
living systems. Together with heterocyclic bases and sugars,
phosphates make up the genes, the hereditary elements of
living systems. In addition, phosphate ions and their deriva-
tives play pivotal roles in signal transduction and energy
storage in biological systems.[1] Numerous sensors for anions,
including phosphate ions, have been devised, but most of
them use organic solvents as the detection medium because
these sensors rely on hydrogen-bonding and electrostatic
Figure 1. A schematic representation of the phosphate anion sensor.
[*] Prof. D. H. Kim, M. S. Han
The sensing ensemble was prepared by simply mixing H-
bpmp,[11] zinc perchlorate, and pyrocatechol violet[12] in a 1:2:1
molar ratio in an aqueous solution of 10 mm HEPES buffer
pH 7.0 (HEPES ¼ 2-[4-(2-hydroxyethyl)-1-piperazinyl]etha-
nesulfonic acid). Figure 2a shows the UV/Vis spectra ob-
tained when the solution of [Zn2(H-bpmp)]3þ was titrated into
the aqueous buffer (pH 7.0) solution of the indicator (50 mm).
Center for Integrated Molecular Systems
Division of Molecular and Life Sciences
Pohang University of Science and Technology
San 31 Hyojadong, Pohang 790-784 (Korea)
Fax : (þ 82)54-279-5877 or (þ 82)54-279-8142
E-mail: dhkim@postech.ac.kr
[**] This work was supported by the Korea Science and Engineering
Foundation, and M.S.H. is a recipient of a BK21 fellowship from the
Ministry of Education and Human Resources, Republic of Korea.
The color change from yellow (lmax ¼ 444 nm) to blue (lmax
¼
624 nm) observed upon the addition of [Zn2(H-bpmp)]3þ is
ascribed to the binding of pyrocatechol violet to the ZnII ions
Supporting information for this article is available on the WWW under
http://www.angewandte.org or from the author.
Angew. Chem. Int. Ed. 2002, 41, No. 20
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0044-8249/02/4120-3809 $ 20.00+.50/0
3809