New approach to sulfonated diphosphine complexes: Synthesis and amphoteric behaviour of zwitterionic [Mn+(CO4{(PPh2) 2C(H)SO3-}]

Article abstract of DOI:10.1039/b507600e

Oxidation of the thioketone residue in the complex [Mn(CO) ₄{(PPh₂)₂C=S}]⁺ (2) with hydrogen peroxide affords the sulfonate derivative [Mn(CO)₄{(PPh ₂)₂C(H)SO₃}] (3),

Full text of DOI:10.1039/b507600e

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New approach to sulfonated diphosphine complexes: synthesis and
amphoteric behaviour of zwitterionic [Mn+(CO4{(PPh2)2C(H)SO3 }]
2
Javier Ruiz,*a Mario Ceroni,a Maril´ın Vivanco,a Marta P. Gonzalo,a Santiago Garc´ıa-Grandab and
Francisco van der Maelenb
Received (in Cambridge, UK) 1st June 2005, Accepted 26th July 2005
First published as an Advance Article on the web 5th September 2005
DOI: 10.1039/b507600e
Thus, the treatment of a dichloromethane solution of 2.ClO4
with threefold excess of H2O2 (30% solution in H2O) lead to the
formation of 3 after 1 h of stirring at room temperature.
Compound 3 was isolated in 70% yield after crystallization. The
spectroscopic data of 3 reveal the presence of the new sulfonate
functionalized diphosphine ligand. The IR spectrum in KBr shows
bands at 1250, 1236 and 1038 cm21 for the S–O stretching modes;5
the 1H NMR spectrum of a CD2Cl2 solution of 3 shows a triplet at
6.50 ppm (2JPH 5 13 Hz) assigned to the P2CH proton, and the
13C NMR spectrum presents a triplet at 75.6 ppm (1JPC 5 13 Hz)
for the central carbon atom of the diphosphine.6
Oxidation of the thioketone residue in the complex
[Mn(CO)4{(PPh2)2CLS}]+ (2) with hydrogen peroxide affords
the sulfonate derivative [Mn(CO)4{(PPh2)2C(H)SO3}] (3), which
shows amphoteric behaviour in reversible acid–base processes,
and is easily chlorinated to give [Mn(CO)4{(PPh2)2C(Cl)SO3}]
(8).
We have recently reported that the disulfide complex
[Mn(CO)4{(PPh2)2C–S–S–C(PPh2)2}Mn(CO)4)] (1)1 undergoes
oxidative cleavage of the sulfur–sulfur bond to give the mono-
nuclear thioketone derivative [Mn(CO)4{(PPh2)2CLS}]+ (2)
(Scheme 1).2 Compound 2 features interesting reactivity patterns
toward reducing agents, being able to regenerate the sulfur–sulfur
bond to give 1 after reaction with Na.2 Beside this electron-
acceptor behaviour, we have now found that the thione residue of
Colourless single crystals of 3 suitable for an X-ray analysis were
obtained from slow diffusion of hexane into a dichloromethane
solution of the compound.{ The structure is shown in Fig. 1
˚
together with selected bond distances and angles. The S1–O (1.44 A
˚
on average) and S1–C5 (1.80 A) bond lengths, as well as the
2
can be oxidized with hydrogen peroxide affording the
different bond angles around the sulfur atom are typical for
zwitterionic complex [Mn(CO)4{(PPh2)2C(H)SO3}] (3), that incor-
porates a sulfonate functionality at the central carbon atom of the
diphosphine (Scheme 1). Sulfonated diphosphines have attracted
widespread interest in recent years as they greatly increase the
solubility of their corresponding metal complexes in aqueous
media;3 in most cases sulfonation is carried out on the aryl
substituents at phosphorus by severe treatment with H2SO4–SO3
mixtures.3,4 By contrast, the methodology provided herein allows
sulfonation to take place at the carbon backbone of the
diphosphine (dppm) and under very mild conditions.
Fig. 1 A view of the crystal structure of 3. For clarity most hydrogen
˚
atoms of phenyl groups are not shown. Selected bond lengths (A) and
Scheme 1 Synthesis of the diphosphinothioketone complex 2 and its
oxidation to the sulfonate derivative 3; [Mn] 5 [Mn(CO)4].
angles (u): P1–C5 1.848(15), P2–C5 1.874(12), C5–S1 1.807(14), S1–O5
…
1.448(10), S1–O6 1.461(13), S1–O7 1.422(12), O5 H11 2.416(13),
aDepartamento de Qu´ımica Orga´nica e Inorga´nica, Facultad de
Qu´ımica, Universidad de Oviedo, Oviedo, 33071, Spain.
E-mail: jruiz@fq.uniovi.es; Fax: +34 98510 3446; Tel: +34 985102977
bDepartamento de Qu´ımica F´ısica y Anal´ıtica, Facultad de Qu´ımica,
Universidad de Oviedo, Oviedo, 33071, Spain
…
…
O6 H13 2.414(14), O7 H19 2.502(13); P1–C5–P2 96.2(7), C5–S1–O5
105.9(7), C5–S1–O6 104.5(8), C5–S1–O7 106.8(8), O5–S1–O6 112.9(7),
…
O6–S1–O7 111.1(9), O7–S1–O5 114.7(8), C11–H11 O5 155.4(14), C13–
… …
H13 O6 150.6(10), C19–H19 O7 149.0(8).
4860 | Chem. Commun., 2005, 4860–4862
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Scheme 2 Proposed mechanism for the formation of 3, involving sulfine
(4), sulfene (5), and sulfonic acid (6) intermediates.
Scheme 3 Amphoteric behaviour of complex 3, and chlorination
reaction at the central carbon atom of the diphosphine to yield 8.
uncoordinated sulfonate groups, and can be compared with those
usually found in organic aminosulfonic acids, which exist as
zwitterions (ammoniosulfonate).7 Owing to the presence of the
sulfonate group the solubility of complex 3 in polar solvents is
dramatically increased with respect to the analogous dppm parent
complex.8
direct reaction of this complex with SO3 sources such as SO3.DMF
results in the instantaneous formation of the cationic complex
[Mn(CO)4{(PPh2)2CH2}]+ instead of 3.
The P2CH group in the anionic ligand [(PPh2)2C(H)SO3]2 in 3
is acidic enough as to be readily deprotonated by treatment with
KOH in CH2Cl2 (Scheme 3), yielding the potassium salts of
complex 7 that formally contains the dianionic diphosphine
[(PPh2)2CSO3]22. The spectroscopic data of 7 (Table 1) show
strong lowering in the frequencies of the IR bands of carbonyl and
sulfonate groups with respect to those of 3; similarly, the
phosphorus signal in the 31P NMR spectrum is strongly shifted
Most sulfonate compounds of transition metals contain the
sulfonate group either as an external anion of the corresponding
cationic complex, or as a ligand coordinated to the metal through
the oxygen atoms in a variety of coordination modes.9 In this
regard, complex 3 is a remarkable example of a neutral sulfonato
complex lacking a metal–oxygen bond. This circumstance allows
+
to higher field. Protonation of 7 with a weak acid (NH4 ) readily
three of the phenyl groups to point towards the oxygen atoms of
…
turns it into 3, which can be further protonated with an strong
acid (HBF4) affording the cationic complex 6 (Scheme 3), which
the sulfonate in order to establish three intramolecular C–H
O
2
hydrogen bonds,10 which stabilize the uncoordinated –SO3
residue (Fig. 1). To the best of our knowledge, diphosphino-
methylsulfonates are unknown, although other phosphorus-
substituted methylsulfonates have been described in the literature,
remarkably the a-phosphono methylsulfonates of general formula
{P(O)(OR9)2C(H)(R)SO3K} that are potent squalene synthase
inhibitors and so potential selective cholesterol lowering agents,11
as well as the 1,1-bis(phosphono)methylsulfonate {(P(O)(OR)2)2-
C(H)SO3Na}, which is used in the preparation of supercharged
analogues of nucleotides.12
contains
the
sulfonic
acid–substituted
diphosphine
[(PPh2)2C(H)SO3H]. Complex 6 is readily transformed to 3 in
the presence of traces of water, thus precluding isolation of pure
solid samples of this compound. Obviously, 6 features IR and 31P
NMR bands at higher frequencies than those of 7 and 3 (Table 1).
The easy dissociation of the P2CH proton in complex 3 allows
the diphosphine to be doubly functionalized at the central carbon
atom. A preliminary example is provided by the treatment of a
dichloromethane solution of 3 with concentrated hydrochloric
acid-30% H2O2 system,16 affording [Mn(CO)4{(PPh2)2C(Cl)SO3}]
(8) (Scheme 3). The reduction of electronic density on the metal
atom produced by chlorination of the diphosphine is reflected in
the spectroscopic data of 8 (Table 1), especially in the very low-
field signal at 68 ppm in the 31P NMR spectrum.
It has been described that controlled oxidation of thioketones
with H2O2 can lead to the formation of sulfines.13 Oxidation of
certain thiones with oxygen to afford ketones appears to proceed
through the formation of sulfene intermediates.14 Considering all
the above, a likely mechanism for the formation of 3 is proposed in
Scheme 2; this implies the formation of the sulfine and sulfene
intermediates 4 and 5, respectively, followed by the hydrolysis of
the last to afford the sulfonic acid functionality in complex 6, as
typically occurs with transient sulfenes which are trapped by
water.15 Compound 6 would be finally deprotonated by water
yielding 3.
To summarize, we have reported herein that the thione residue
in the complex [Mn(CO)4{(PPh2)2CLS}]+ (2) can be oxidized with
H2O2 under mild conditions to yield a sulfonate functionality;
which provides an unprecedented access to sulfonated dipho-
sphines of dppm-type. The method allows sulfonation of the
diphosphine to take place at the carbon backbone, in opposition to
most known experimental procedure to obtain sulfonated dipho-
sphines based on severe treatment with oleum, that introduce the
sulfonate group at the aryl substituents of the phosphorus atoms.
Complex 3 can be viewed as an SO3 adduct of the dipho-
sphinomethanide complex [Mn(CO)4{(PPh2)2CH}]. Nevertheless,
Table 1 Selected spectroscopic data for the new compounds
Complex
Ligand
IR(nCO)a
IR(nSO)b
31P NMRc
7
3
6
8
[(PPh2)2CSO3]22
[(PPh2)2C(H)SO3]2
[(PPh2)2C(H)SO3H]
[(PPh2)2C(Cl)SO3]2
c
2073, 1990, 1962
1180, 1161, 1016
1250, 1238, 1038
—
0.8
28.0
31.3
68.0
2090, 2026, 2010, 1999
2095, 2034, 2014
2093, 2027, 2016, 1998
1263, 1247, 1046
a
b
CH2Cl2, cm21
.
KBr, cm21
. CD2Cl2, d.
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6 The NMR data of compound 3 are similar to those of other
tetracarbonylmanganese(I) complexes containing C-functionalized
dppm: J. Ruiz, V. Riera, M. Vivanco, S. Garc´ıa-Granda and
M. R. D´ıaz, Organometallics, 1998, 17, 4562.
We thank the Spanish Ministerio de Ciencia y Tecnolog´ıa (PGE
and FEDER funding, Project BQU2003-01011) for financial
support.
7 (a) M. A. Leonard and P. J. Squattrito, Acta Crystallogr., Sect. C, 1997,
53, 648; (b) L. Skrzypek and K. Suwinska, Heterocycles, 2002, 57, 2035;
(c) M. Canagaratna, J. A. Phillips, H. Goodfriend and K. R. Leopold,
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8 The compound [Mn(CO)4(dppm)]ClO4 is only very slightly soluble in
acetone, whereas complex 3 is extremely soluble in this solvent. 3 is also
very soluble in 1 : 2 acetone–water mixtures, although it is not soluble in
pure water.
Notes and references
{ Crystal data for 3: C29H21MnO7P2S, M 5 630.40, orthorhombic, space
˚
group P212121, a 5 10.714(4), b 5 14.256(2), c 5 18.824(7) A, V 5
3
2875(2) A , rcalcd 5 1.456 g cm23, T 5 293 K, Z 5 4, l 5 1.54184 A,
m 5 5.854 mm21, 11310 reflections measured, 2227 unique (Rint 5 0.083),
1478 observed [I . 2s(I)], R1 5 0.077, wR2 5 0.177 [I . 2s(I)], largest diff.
˚
˚
peak and hole 0.757 and 20.497 e A23. The structure showed a rather large
˚
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C18) had to be isotropically refined in order to prevent them from going
non-positive definite. CCDC 274156. See http://dx.doi.org/10.1039/
b507600e for crystallographic data in CIF or other electronic format.
…
˚
10 The C–H O distances in 3 (average value 2.44 A) is even shorter
˚
than the mean distance of 2.55 A found in similar hydrogen bonds
2
…
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4862 | Chem. Commun., 2005, 4860–4862
This journal is ß The Royal Society of Chemistry 2005