Copper-mediated cleavage of disulfides by tertiary phosphines: A new route to As-S anions

Article abstract of DOI:10.1039/b610228j

The synthesis of [(PhAs)₂(-S₂)(-S)] and its reactions to form novel Cu(i) complexes are reported, together with a new cleavage reaction of disulfides by Cu(i) thiolates and tertiary phosphines. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b610228j

View Article Online / Journal Homepage / Table of Contents for this issue
COMMUNICATION
www.rsc.org/dalton | Dalton Transactions
Copper-mediated cleavage of disulfides by tertiary phosphines: a new route to
As–S anions†
Robert Langer,a Weifeng Shia and Alexander Rothenberger*a,b
Received 17th July 2006, Accepted 24th August 2006
First published as an Advance Article on the web 31st August 2006
DOI: 10.1039/b610228j
The synthesis of [(PhAs)2(l-S2)(l-S)] and its reactions to form
novel Cu(I) complexes are reported, together with a new
cleavage reaction of disulfides by Cu(I) thiolates and tertiary
phosphines.
In comparison to the chemistry of phosphorus chalcogenides the
related area of arsenic chalcogenides is less developed. This is
illustrated by a large number of ca. 1750 compounds containing
P–E–metal (E = S, Se, Te) structural motifs in comparison
to less than 100 hits for analogous arsenic compounds [As–
E–metal (E = S, Se, Te)].1,2 Amongst the metal complexes
containing arsenic–chalcogenide-based ligands, As–S ligands are
predominant. Synthetic routes to metal complexes with As–S
ligands include the transformation of As–S precursors in the
coordination sphere of a transition metal or synthesis in melts.3–9
Alternatively, preformed As–S ligands can directly be reacted with
metal complexes in ligand exchange reactions.10–12 The interest
in this type of chemistry has so far been motivated mainly by
structural features of previously unknown compounds in addition
to the biological role of arsenic which is known to bind to S
atoms of cysteine sites in proteins.13–16 The present investigation
builds on recent results where metal salts containing P–S and
P–Se anions were obtained in one-pot syntheses from metal
salts and chalcogen transfer reagents.17–19 In the following at
first the optimised synthesis of an arsenic compound analogous
to Lawesson’s reagent (L. R.) [ArP(S)(l-S)]2 (Ar = 4-anisyl) is
described and then, the transformation of an As–S heterocyclic
compound to the first representatives of coinage metal complexes
containing As–S anions is demonstrated.
Scheme 1 Synthesis of Group 15 chalcogen transfer reagents.
back-donation).25 The high-yield preparation of [(PhAs)2(l-S2)(l-
S)] was achieved by an adapted procedure, originally used for
the preparation of As4S5, in which PhAs(O)(OH)2 was dissolved
in concentrated hydrochloric acid and reacted with H2S at low
temperature.26
When [(PhAs)2(l-S2)(l-S)] is reacted with the Cu(I) thiolate
CuSCy (Cy = Cyclohexyl, C6H11) in the presence of the tertiary
phosphine PEt3, [Cu4{Ph(S)As–As(S)Ph}2(PEt3)4] (1) is formed in
moderate yield (Scheme 2). The structural analysis showed that
1 consists of a centrosymmetric arrangement of four [Cu(PEt3)]-
units held together by two [Ph(S)As–As(S)Ph]-dianions (Fig. 1).‡§
The phosphorus chalcogenide heterocyclic compounds L. R.
or Woollins’ reagent (W. R.) [PhP(Se)(l-Se)]2 are easily accessible
(Scheme 1).20–22 For arsenic analogs, however, compounds of the
type [RAs(S)(l-S)]2 (R = organic group) are unknown. [(PhAs)2(l-
S2)(l-S)] is the closest related As–S reagent to L. R. and it is
obtained by treating solutions of PhAs(O)(OH)2 with H2S(g)
(Scheme 1).23,24 In the course of the reaction H2S is partially
oxidised to unidentified polysulfanes whilst As(V) is reduced to
As(III). The formation of As–S heterocycliccompounds containing
Scheme 2 Synthesis of 1.
The phenyl substituents at As(1,2) are in a gauche-conformation
and form the organic shell of 1 together with ethyl substituents of
the tertiary phosphine. S(1) and S(2) each bridge two Cu atoms.
Cu(1) is four-coordinated, interacting with the stereochemically
active lone-pair at As(1), two S atoms and one phosphine ligand.
Cu(2) is three-coordinated by S atoms and one phosphine ligand.
The lone-pair at As(2) is not involved in metal coordination and is
pointing towards the periphery of the arrangement. The formation
of [Ph(S)As–As(S)Ph]2− anions in the course of the reaction was
surprising and a comparison of starting materials and product
reveals that in 1 the bridging S atom between arsenic atoms
is missing. Instead, formation of a As–As bond and cleavage
of the disulfide bridge, present in the starting material, were
observed. This rather complex transformation can be regarded
=
As S double bonds has so far not been observed (and a theoretical
study describes hypothetical As–S double bonds as polarized r-
bonds, with the bond strength depending on the electrostatic
interactions between the As and S atoms rather than on p-
aInstitut fu¨r Anorganische Chemie der Universita¨t Karlsruhe, Geb. 30.45,
Engesserstr. 15a, 76131, Karlsruhe, Germany. E-mail: ar252@chemie.uni-
karlsruhe.de
bInstitut fu¨r Nanotechnologie, Forschungszentrum Karlsruhe GmbH, Post-
fach 3640, 76021, Karlsruhe, Germany
† In memory of Dr Alex Hopkins.
This journal is
The Royal Society of Chemistry 2006
Dalton Trans., 2006, 4435–4437 | 4435
©

View Article Online
Fig. 2 Solid-state structure of 2 (phenyl groups of triphenylphosphine
˚
ligands were omitted). Selected bond lengths [A] and angles
Fig. 1 Solid-state structure of 1 (disordered components of one PEt3
ligand are omitted). Selected bond lengths [A] and angles [ ]: As(1)–Cu(1)
[◦]: As(1)–Cu(1) 2.4144(9), As(2)–Cu(2) 2.4122(9), As(3)–Cu(3)
2.4076(9), As(4)–Cu(4) 2.4331(9), As(1)–S(1) 2.2548(16), As(1)–S(2)
2.2106(14), As(2)–S(3) 2.2104(14), As(2)–S(1) 2.2549(15), As(3)–S(5)
2.2167(15), As(3)–S(4) 2.2608(15), As(4)–S(6) 2.2069(16), As(4)–S(4)
2.2614(15), Cu–P 2.2390(18)–2.2504(17), Cu–S 2.3171(14)–2.3793(16);
S(2)–As(1)–S(1) 104.55(5), S(3)–As(2)–S(1) 103.89(5), S(5)–As(3)–S(4)
103.72(6), S(6)–As(4)–S(4) 103.82(6), S(2)–As(1)–Cu(1) 110.87(4),
S(1)–As(1)–Cu(1) 104.40(5), S(3)–As(2)–Cu(2) 110.91(4), S(1)–As(2)–
Cu(2) 105.05(5), S(5)–As(3)–Cu(3) 111.11(4), S(4)–As(3)–Cu(3)
103.47(5), S(6)–As(4)–Cu(4) 111.34(4), S(4)–As(4)–Cu(4) 102.95(4),
As(2)–S(1)–As(1) 90.44(5).
◦
˚
2.4533(8), As(1)–As(2) 2.4648(8), As(1)–S(1) 2.2096(15), As(2)–S(2)
2.2185(16), Cu(1)–P(1) 2.201(3), Cu(2)–P(2) 2.2089(19), Cu(1)–S(1A)
2.3201(17), Cu(1)–S(2A) 2.3450(16), Cu(2)–S(1) 2.2542(15), Cu(2)–S(2A)
2.3121(16); S(1)–As(1)–Cu(1) 111.65(4), S(1)–As(1)–As(2) 102.90(4),
Cu(1)–As(1)–As(2) 116.17(3), S(2)–As(2)–As(1) 95.32(4). Symmetry op-
erations: −x + 1, −y + 1, −z (A).
as a multiple reduction of the neutral As–S starting material in
which desulfuration and formation of the As–As bond can be
=
explained by oxidation of the tertiary phosphine PEt3 to Et3P S
27
=
(solid samples of 1 were contaminated with Et3P S). Similar
reactions were observed for trithiophosphonates.28 In order to
study the cleavage of the disulfide bridge in [(PhAs)2(l-S2)(l-
S)] and to understand the role of the anions in Cu(I) thiolates,
several reactions of [(PhAs)2(l-S2)(l-S)] with tertiary phosphines
and a range of Cu(I) thiolates were performed. In the case of a
mixture of [(PhAs)2(l-S2)(l-S)], CuSEt and PPh3 this resulted in
the formation of crystals of [Cu4{Ph(S)As–S–As(S)Ph}2(PPh3)4]
(2) (Scheme 3, Fig. 2).
formation of [Ph3P(SEt)]+(SEt)− and 2. The [Ph3P(SEt)]+-ion was
observed in MALDI-TOF experiments. A broader application of
these findings could be the copper-mediated cleavage of all kinds
of disulfides. In this context a couple of model reactions were
performed (Scheme 4). The cleavage of MeS–SMe by CuSEt/PEt3
or CuSEt/PPh3 was investigated and the 31P NMR of reaction mix-
tures recorded. Several P-containing species [R3P S,27 R3P(SEt)+,
=
R3PCu (R = Et, Ph)] were detected in the two separate reactions
indicating that the nature of the organic substituent of phosphines
does not seem to have an influence on the course of the reaction.
Clearly, more studies are required in order to optimise this Cu-
mediated reductive cleavage reaction of disulfides for synthetic
purposes.29,30
Scheme 3 Synthesis of 2.
In the solid state 2 forms a cage arrangement consisting of
four [Cu(PPh3)]-units, in which the Cu atoms are chelated by
[Ph(S)As–S–As(S)Ph]2− anions. The core composition found in 2
can be described as two dimerised norbornane-like [Cu2{Ph(S)As–
S–As(S)Ph}(PPh3)2}]-arrangements consisting of five-membered
[CuS2As2] and [Cu2S2As] rings (with additional organic groups
and phosphine ligands). In contrast to 1 where formation of a As–
As bond and cleavage of the disulfide bridge were observed now the
reaction of [(PhAs)2(l-S2)(l-S)], CuSEt and PPh3 resulted in the
formation of [Ph(S)As–S–As(S)Ph]2− anions. During the reaction
the disulfide bridge in [(PhAs)2(l-S2)(l-S)] was cleaved but the
sulfur bridge between As atoms was retained. Mechanistically
this observation can be rationalised by oxidation of PPh3 and
Scheme 4 Competing desulfurization and reductive Cu-mediated disul-
fide cleavage of Me2S2 (R = Et, Ph).
The presented work showed that As–chalcogenides can be
converted into unusual anions. Desulfurization and reductive
cleavage both occurred in reactivity studies of the disulfides
[(PhAs)2(l-S2)(l-S)] and Me2S2 with mixtures of Cu(I) thiolates
and tertiary phosphines.
4436 | Dalton Trans., 2006, 4435–4437
This journal is
The Royal Society of Chemistry 2006
©

View Article Online
+
−
=
PPh3), 29 (s, [Ph3PSEt] [EtS] ), −5.1 (s, PPh3); m/z (MALDI-TOF,
We thank the DFG Center for Functional Nanostructures
(W. S.) and the Forschungszentrum Karlsruhe (A. R.) for financial
support. A. R. thanks Prof. D. Fenske for his support.
S
2,6-dihydroxyacetophenone) 322.8 (100%) (C20H20PS, [Ph3PSEt]+ requires
323.1), 323.8 (25), 324.8 (8).
Reactions o◦f Cu(I) thiolates/tertiary phosphines with Me2S2: dP (162 MHz;
+
=
CDCl3; 23 C; 65% H3PO4) 54.9, 52.4 (s, S PEt3), 40.2 [s, Et3P(SEt) ],
+
=
−11.5 (br., CuPEt3) and 43.4 (s, S PPh3), 29.2 [s, Ph3P(SEt) ], −5.1 (s,
Notes and references
PPh3).
1 F. H. Allen, Acta Crystallogr., Sect. B, 2002, 58, 380–388.
2 I. J. Bruno, J. C. Cole, P. R. Edgington, M. Kessler, C. F. Macrae, P.
McCabe, J. Pearson and R. Taylor, Acta Crystallogr., Sect. B, 2002, 58,
389–397.
‡ All structures were solved by direct methods and refined using
SHELXTL with anisotropic thermal parameters for heavy atoms (Ta-
ble 1).31 Disordered components were refined with isotropic thermal
parameters.
3 A. J. Dimaio and A. L. Rheingold, Inorg. Chem., 1990, 29, 798–804.
4 H. Brunner, B. Nuber, L. Poll and J. Wachter, Angew. Chem., Int. Ed.
Engl., 1993, 32, 1627–1628.
5 I. Didbaridze, G. Khelashvili, A. Chubinidze and R. Gigauri, Bull.
Georgian Acad. Sci., 1998, 157, 56–59.
6 S. Lo¨ken and W. Tremel, Eur. J. Inorg. Chem., 1998, 283–289.
7 Y. An, X. Li, X. Liu, M. Ji and C. Jia, Inorg. Chem. Commun., 2003, 6,
1137–1139.
8 R. G. Iyer and M. G. Kanatzidis, Inorg. Chem., 2004, 43, 3656–3662.
9 M.-L. Fu, G.-C. Guo, L.-Z. Cai, Z.-J. Zhang and J.-S. Huang, Inorg.
Chem., 2005, 44, 184–186.
§ Crystal data for 1: C48H80As4Cu4P4S4, M = 1463.08, triclinic, a =
˚
11.8503(9), b = 12.4641(9), c = 12.6238(10) A, a = 63.637(6), b = 64.437(6),
◦
3
¯
˚
c = 77.138(6) , U = 1506.0(2) A , T = 100(2) K, space group P1 (no.
2), Z = 1, l(Mo-Ka) = 3.849 mm−1, 13441 reflections measured, 6856
unique (Rint = 0.0594) which were used in all calculations. wR2 (all data)
= 0.0.1454, R1 = 0.0525 {I > 2r(I)}.
Crystal data for 2: C108H105As4Cu4O3P4S6 M = 2321.00, monoclinic, a
◦
˚
= 26.626(2), b = 19.8281(9), c = 19.0953(10) A, b = 99.870(5) , U =
3
˚
9931.9(10) A , T = 100(2) K, space group P21/c (no. 14), Z = 4, l(Mo-Ka)
= 2.410 mm−1, 31368 reflections measured, 20179 unique (Rint = 0.0670)
which were used in all calculations. wR2 (all data) = 0.1174, R1 = 0.0516
{I > 2r(I)}.
10 O. M. Kekia and A. L. Rheingold, Organometallics, 1998, 17, 726–730.
11 W. S. Sheldrick and I. M. Mu¨ller, Coord. Chem. Rev., 1999, 182, 125–
173.
CCDC reference numbers 611503 and 611504. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/b610228j
12 L. H. Doerrer, J. C. Green, M. L. H. Green, I. Haiduc, C. N. Jardine,
S. I. Pascu, L. Silaghi-Dumitrescu and D. J. Watkin, J. Chem. Soc.,
Dalton Trans., 2000, 3347–3355.
All operations were carried out in an atmosphere of purified dinitrogen.
All solvents were dried over the appropriate drying agent and freshly
distilled prior to use. Cu(I) thiolates were synthesized according to a
published procedure.32 PhAs(O)(OH)2 was obtained from Strem Chem-
icals. [(PhAs)2(l-S2)(l-S)]: The published synthesis for [(PhAs)2(l-S2)(l-
S)] was modified as follows.23,24 9.7 g (48.0 mmol) of PhAs(O)(OH)2
was dissolved in a mixture of 50 mL H2O and 100 mL concentrated
hydrochloric acid. The solution was stirred and cooled in an ice bath.
H2S (g) was passed through the cold reaction mixture for 90 min. A pale
yellow precipitate formed which was recrystallised from DME (DME =
1,2-dimethoxyethane) to give [(PhAs)2(l-S2)(l-S)]; 8.2 g, yield 85%, mp
142 ◦C. Found: C, 35.98; H, 2.48. C12H10As2S3 requires C, 36.01; H,
2.52%. The identity of the compound was confirmed by repeated unit-
cell determination of crystals.
13 D. J. Cline, C. Thorpe and J. P. Schneider, J. Am. Chem. Soc., 2003,
125, 2923–2929.
14 O. M. Nidhubhghaill and P. J. Sadler, Struct. Bonding, 1991, 78, 129–
190.
15 A. von Do¨llen and H. Strasdeit, Eur. J. Inorg. Chem., 1998, 61–66.
16 T. G. Carter, E. R. Healey, M. A. Pitt and D. W. Johnson, Inorg. Chem.,
2005, 44, 9634–9636.
17 W. Shi, M. Shafaei-Fallah, C. E. Anson and A. Rothenberger, Dalton
Trans., 2005, 3909–3912.
18 W. Shi and A. Rothenberger, Eur. J. Inorg. Chem., 2005, 2935–2937.
19 W. Shi, R. Ahlrichs, C. E. Anson, A. Rothenberger, C. Schrodt and M.
Shafaei-Fallah, Chem. Commun., 2005, 5893–5895.
20 B. S. Pedersen, S. Scheibye, K. Clausen and S. O. Lawesson, Bull. Soc.
Chim. Belg., 1978, 87, 293–297.
21 M. J. Pilkington, A. M. Z. Slawin, D. J. Williams, P. T. Wood and J. D.
Woollins, Heteroat. Chem., 1990, 1, 351.
22 I. P. Gray, P. Bhattacharyya, A. M. Z. Slawin and J. D. Woollins,
Chem.–Eur. J., 2005, 11, 6221–6227.
23 A. W. Cordes, M. C. Malmstrom and P. D. Gwinup, Inorg. Chem., 1972,
11, 836–838.
24 C. A. Applegate, E. A. Meyers, R. A. Zingaro and A. Merijanian,
Phosphorus, Sulfur Silicon Relat. Elem., 1988, 35, 363–370.
25 J. A. Dobado, H. Martinez-Garcia, J. M. Molina and M. R. Sundberg,
J. Am. Chem. Soc., 1998, 120, 8461–8471.
26 G. Brauer, Handbuch der pra¨parativen anorganischen Chemie, Ferdi-
nand Enke Verlag, Stuttgart, 1975.
1: A mixture of [(PhAs)2(l-S2)(l-S)] 200 mg (0.50 mmol) and CuSCy
179 mg (1.00 mmol) was dissolved in 10 mL THF. The reaction mixture
was stirred for 1 day. A brown precipitate formed together with a yellow
solution. Upon addition of 0.3 mL PEt3 (2.00 mmol) a yellow solution
was obtained. The reaction mixture was filtered and concentrated under
reduced pressure to a volume of ca. 2 mL and layered with 15 mL hexane.
After three days yellow crystals of 1 were obtained; 107 mg, yield 29%, mp
120 ◦C (decomp.). Found: C, 39.50; H, 5.55. C48H80As4Cu4P4S4 requires
C, 39.40; H, 5.51%; tmax/cm−1 (KBr) 3039 w (C–H, ar.), 2956 s, 2927 m,
=
2872 m, 1454 m, 1433 m (C–H, alkyl), 1576 w, 1474 m, 734 s, 689 s (C C),
1413 m (P–C), 1328 w (As–C); dH (400 MHz; CDCl3; 23 ◦C) 1.24, 1.88 (m,
PCH2CH3), 7.08–7.49 (m, 20H, ArH); dC (100 MHz; CDCl3; 25 ◦C) 6.5
(d, 2JPC = 4.5 Hz, CH3), 23.0 (d, 1JPC = 51.6 Hz, P–CH2); dP (162 MHz;
CDCl3; 23 ◦C; 65% H3PO4) 54.9, 52.4 (s, S PEt3), −11.5 (br., CuPEt3).
=
2: A mixture of [(PhAs)2(l-S2)(l-S)] 200 mg (0.50 mmol) and CuSEt
124 mg (1.00 mmol) was dissolved in 10 mL THF. The yellow solution
was stirred for 15 h at room temperature. 524 mg (2.00 mmol) PPh3 were
dissolved in 5 mL THF and added to the reaction mixture. The reaction
was then filtered and layered with hexane. After one day yellow crystals of
2 were obtained; 105 mg, yield 20%, mp 167 ◦C. Found: C, 54.84; H, 3.92.
27 G. Baccolini, C. Boga and M. Mazzacurati, J. Org. Chem., 2005, 70,
4774–4777.
28 D. Fenske, A. Rothenberger and M. S. Fallah, Eur. J. Inorg. Chem.,
2005, 59–62.
29 D. N. Harpp, J. G. Gleason and J. P. Snyder, J. Am. Chem. Soc., 1968,
C
108H105As4Cu4O3P4S6 (−3 thf) requires C, 54.78; H, 3.88%; tmax/cm−1
90, 4181–4182.
30 T. Oku, Y. Furusho and T. Takata, Org. Lett., 2003, 5, 4923–4925.
31 G. M. Sheldrick, Shelxtl v. 5.1, University of Go¨ttingen, Germany,
1997.
=
(KBr) 3040 m (C–H), 1574 w, 1479 m, 739 s, 695 s (C C), 1429 s (P–C),
1308 w (As–C); dH (400 MHz; CDCl3; 23 ◦C) 6.9–7.3 (m, 80 H, ArH); dC
(100 MHz; CDCl3; 23 ◦C) 127.8–134.3 (ArC); dP (162 MHz; CDCl3; 23 ◦C;
65% H3PO4) −3.6 (s, CuPPh3). The mother liquor was evaporated and the
solid residue analysed. dP (162 MHz; CDCl3; 23 ◦C; 65% H3PO4) 43 (s,
32 L. M. Nguyen, M. E. Dellinger, J. T. Lee, R. A. Quinlan, A. L.
Rheingold and R. D. Pike, Inorg. Chim. Acta, 2005, 358, 1331–1336.
This journal is
The Royal Society of Chemistry 2006
Dalton Trans., 2006, 4435–4437 | 4437
©