Reactivity of thiophosphinous acid bound to ruthenium

Article abstract of DOI:10.1016/j.jorganchem.2008.06.019

The thiophosphinous acid coordinated to ruthenium through the phosphorus atom in [CpRu(PPh₃)₂(PH₂SH)]CF₃SO₃ (1) is deprotonated in the presence of proton sponge to yield the neutral compound [CpRu(PPh₃)₂(PH₂S)] (2), where the thiophosphinite, PH₂S^-, anion remains bound to the metal through the phosphorus atom. The parent complex 1 is easily restored in the presence of a weak acid. The sulfur of the coordinated anion may be alkylated with CF₃SO₃Me to yield [CpRu(PPh₃)₂(PH₂SCH₃)]CF₃SO₃ (3), the methyl thioester of the acid being bound to ruthenium through the phosphorus. The new compounds have been characterized by elemental analyses, IR and multinuclear NMR spectroscopy. The crystal structure of 2 · CH₃CN has been determined by X-ray diffraction methods.

Full text of DOI:10.1016/j.jorganchem.2008.06.019

Journal of Organometallic Chemistry 693 (2008) 3011–3014
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Reactivity of thiophosphinous acid bound to ruthenium
Massimo Di Vaira a, Maurizio Peruzzini b, Stefano Seniori Costantini a, Piero Stoppioni a,
*
a Dipartimento di Chimica, Università di Firenze, via della Lastruccia 3, 50019 Sesto Fiorentino, Firenze, Italy
b ICCOM CNR, Via Madonna del Piano 10, 50019 Sesto Fiorentino, Firenze, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 5 May 2008
Received in revised form 17 June 2008
Accepted 17 June 2008
Available online 25 June 2008
The thiophosphinous acid coordinated to ruthenium through the phosphorus atom in
[CpRu(PPh3)2(PH2SH)]CF3SO3 (1) is deprotonated in the presence of proton sponge to yield the neutral
compound [CpRu(PPh3)2(PH2S)] (2), where the thiophosphinite, PH2Sꢀ, anion remains bound to the metal
through the phosphorus atom. The parent complex 1 is easily restored in the presence of a weak acid. The
sulfur of the coordinated anion may be alkylated with CF3SO3Me to yield [CpRu(PPh3)2(PH2SCH3)]CF3SO3
(3), the methyl thioester of the acid being bound to ruthenium through the phosphorus. The new com-
pounds have been characterized by elemental analyses, IR and multinuclear NMR spectroscopy. The crys-
tal structure of 2 ꢁ CH3CN has been determined by X-ray diffraction methods.
Keywords:
Ruthenium
Thiophosphinous acid
Reactivity
Ó 2008 Elsevier B.V. All rights reserved.
Cyclopentadienyl complexes
X-ray structure
1. Introduction
We have recently found that the plain hydrolysis of tetraphos-
phorus trisulfide, P4S3, g1:1 doubly metallated to two CpRu(PPh3)2
A large number of aromatic and aliphatic mono- and poly-pho-
phane sulfides have been synthesized and have been frequently
used to assist organic transformations [1]. However, the simple
ternary P, S and H derivatives, which are the parent compounds
of substituted phosphine sulfides, are quite elusive due to their
instability. As a result, the properties of the simplest compounds
of this class, the thiophosphinous acid, PH2SH (I), and its sulfide
tautomer, S@PH3 (II), are practically unknown in the free state.
The former compound has been obtained in very poor yield at very
low temperature and under harsh reaction conditions [2] or has
been trapped in solid argon matrices [3]. At the same time, many
theoretical studies have been undertaken to address the structures
of the simplest phosphorus thiohydrides, the pathways for hydro-
gen migration accounting for the different thiohydride tautomers
and eventually the energetics of these transformations [4–8].
ruthenium fragments through the apical and one of the basal phos-
phorus atoms, yields different products including PH2SH, which is
stabilized through coordination, via the phosphorus atom, to the
CpRu(PPh3)2 unit [9]. [CpRu(PPh3)2(PH2SH)]CF3SO3 (1), which
was authenticated by X-ray methods, is quite stable both in the so-
lid state and in dichloromethane solution. As it may be prepared in
quite good amount, it appears to be a useful synthon for gaining
some insight on the reactivity of the metal-coordinated PH2SH
molecule. In this article we report that, once coordinated to ruthe-
nium, PH2SH may be easily deprotonated in the presence of non
nucleophilic bases, such as proton sponge, to yield the neutral
compound [CpRu(PPh3)2(PH2S)] (2); reversibly, the parent complex
1 may be quantitatively restored by reacting 2 with a weak acid.
The thiolate sulfur atom in 2 undergoes plain alkylation with
methyl triflate to afford [CpRu(PPh3)2(PH2SCH3)]CF3SO3 (3), which
is a rare example of coordinated methyl ester of the parent thi-
ophosphinous acid. Compounds 2 and 3 have been characterized
by elemental analyses and NMR measurements. The crystal struc-
ture of 2 ꢁ CH3CN has been determined by X-ray diffraction
methods.
S
H
P
P
S
H
H
H
H
H
I
II
2. Results and discussion
The tetraphosphorus trisulfide cage molecule, P4S3, coordinated
to two ruthenium fragments through its apical and one of the basal
phosphorus atoms in [{CpRu(PPh3)2}2(
(CF3SO3)2 (4), Fig. 1, undergoes selective hydrolysis to yield several
l,g
1:1–Papical–Pbasal–P4S3)]-
* Corresponding author. Tel.: +39 055 4573281.
E-mail address: piero.stoppioni@unifi.it (P. Stoppioni).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.06.019

3012
M.D. Vaira et al. / Journal of Organometallic Chemistry 693 (2008) 3011–3014
Fig. 1. The dimetal cation in the strucutre of (4) [9].
products among which the thiophosphinous acid, PH2SH, is quan-
titatively obtained [9]. This molecule, highly reactive and practi-
cally unknown as a free species [3], is likely produced via metal-
mediated tautomerization of the phosphane sulfide (II) generated
from the hydrolysis of 4 and is stabilized by coordination to the
ruthenium center via the phosphorus atom, yielding the compound
[CpRu(PPh3)2(PH2SH)]CF3SO3 (1) [10].
The coordinated thiophosphinous acid readily undergoes
deprotonation by treatment of 1, dissolved in CH3CN, with the stoi-
chiometric amount of the non nucleophilic base 1,8-bis-(dimethyl-
amino)-naphthalene, i.e. proton sponge, giving the neutral
complex [CpRu(PPh3)2(PH2S)], (2) (Scheme 1). Complex 2 was iso-
lated as a yellow microcrystalline solid, stable under an inert atmo-
sphere and soluble in common organic solvents such as acetone
and dichloromethane.
gaged in a weak hydrogen bond interaction with a C–H moiety of a
phenyl group (Table 1 and Fig. 2), with an Hꢁ ꢁ ꢁS separation of
2.781(2) Å. Since a symmetrical, minimum energy conformation
may be attained by interaction of the thiophosphinite sulfur atom
with a phenyl group of the other triphenylphosphane, the exis-
tence of these two alternative settings may rationalise some fea-
tures of the 1H NMR signals due to the PH2 group, which are
discussed below.
The 31P{1H} NMR spectrum of 2 in CDCl3 exhibits the expected
A2M spin system, in which A and M are the phosphorus atoms of
the triphenylphosphane molecules and of the PH2Sꢀ anion, respec-
tively. Both resonances are downfield shifted with respect to those
observed in the parent compound 1 [9]; such shift is particularly
enhanced for the resonances ascribed to the phosphorus of the an-
ion. In keeping with the31P{1H} NMR pattern, the 1H spectrum in
the PH2 region is consistent with an AA’MXX’ spin system (where
A, A’ and M are the phosphorus atoms of the triphenylphosphanes
and the PH2Sꢀ anion, respectively, and X, X’ are the hydrogen
atoms of the PH2 group). This pattern can be successfully simulated
0
Crystals of the CH3CN solvate of 2 suitable for a crystallographic
study were grown by slow evaporation of an acetonitrile solution
of 1 containing the proton sponge. A view of complex 2 is shown
in Fig. 2. The metal atom in 2 is in a pseudo-octahedral coordina-
tion environment formed by the atoms of the Cp ring, by the two
triphenylphosphane P atoms and by the phosphorus atom of the
PH2Sꢀ thiophosphinite anion. Both the coordination geometry
and the overall molecular conformation are closely similar to those
found for the parent complex cation containing the PH2SH ligand
[9].
only assuming an exchange process between PA and PA (kexch
=
46.7 sꢀ1). The nature of the dynamic process, however, is not clear
although it is likely due to the presence of the formal negative
charge on the sulfur atom and the consequent interaction high-
lighted in Fig. 2. This conclusion follows from the absence of any
detectable dynamic process in the NMR spectrum of the compound
[CpRu(PPh3)2(PH2SCH3)]CF3SO3 3, see below. [CpRu(PPh3)2(PH2-
SH)]CF3SO3 is readily restored by adding the stoichiometric
amount of triphenylphosphonium triflate, [PPh3H]CF3SO3, to a
CHCl3 solution of 2. Such result, according to the weak acidity of
the phosphonium salt (pka = 11.2), highlights a pronounced basic
character of the sulfur of the PH2Sꢀ thiophosphinite anion.
However, the Ru–P distance involving the PH2Sꢀ ligand in com-
pound 2 (Table 1) is 0.047 Å longer than that formed by PH2SH in 1
[9]. This significant metrical change, which occurs on going from 1
to 2, is clearly related to differences in P–S bonding, the P–S bond
length in 2 being 0.098 Å shorter than that in 1. The lengthening of
the Ru—PðPH
distance with respect to the Ru—PðPH
one, is
2SÞ
2SHÞ
accompanied by a small shortening of the triphenylphosphane
Ru–P distances, by 0.04 Å in the mean. The sulfur atom in 2 is en-
The addition of methyl trifluoromethansulfonate to a solution of
2 in CH2Cl2 yields [CpRu(PPh3)2(PH2SCH3)]CF3SO3 (3), see Scheme
Scheme 1.

M.D. Vaira et al. / Journal of Organometallic Chemistry 693 (2008) 3011–3014
3013
Fig. 2. A view of the complex molecule in the structure of [CpRu(PPh3)2(PH2S)] ꢁ CH3CN (2). Thermal ellipsoids are shown at the 30% probability level. Only the ipso carbon
atoms of phenyl groups and the one involved in the weak C–Hꢁ ꢁ ꢁS interaction discussed in the text are labelled.
NMR spectra were run at room temperature on a Bruker Avance
400 DRX spectrometer. 19F and 31P chemical shifts are relative to
external CFCl3 and to 85% H3PO4, respectively. 1H chemical shifts
are relative to tetramethylsilane as external reference and were
calibrated against the residual solvent resonance. Coupling con-
stants of 2 were obtained from 1D 31P{1H}, 1H and 1H{31P} NMR
spectra with the aid of computer simulation using the gNMR pro-
gram [12]. Chemical shifts are relative to tetramethylsilane (1H),
Table 1
Selected bond lengths (Å) and angles (°) for [CpRu(PPh3)2(PH2S)] ꢁ CH3CN (2)
Ru–P(1)
Ru–P(2)
Ru–P(3)
2.304(2)
2.333(2)
2.297(2)
Ru–C(Cp)
P(3)–S
Sꢁ ꢁ ꢁH(62)
Ru–P(3)–S
C(62)–H(62)ꢁ ꢁ ꢁS
2.231–2.250
2.011(2)
2.781(2)
P(1)–Ru–P(2)
P(1)–Ru–P(3)
P(2)–Ru–P(3)
102.48(6)
92.33(6)
90.21(6)
119.24(9)
166.0(4)
CFCl3
( (
19F) and H3PO4 85% 31P) as external standards at
0.00 ppm, with downfield values taken as positive; coupling con-
stants are in Hertz. IR spectra were recorded on a Perkin–Elmer
Spectrum BX FT-IR system spectrometer in nujol mull between so-
dium chloride plates. Analytical data for carbon, hydrogen and
phosphorus were obtained from the Microanalytical Laboratory
of the Department of Chemistry of the University of Firenze. The
complex [CpRu(PPh3)2(PH2SH)]CF3SO3 (1) was synthesized accord-
ing to literature method [9]. Trifluoromethansulfonic acid, methyl
trifluoromethansulfonate and 1,8-bis-(dimethylamino)-naphtha-
lene, proton sponge, were purchased from Aldrich and used as re-
ceived apart for proton sponge which was purified by sublimation
prior the use.
1. Compound 3 is stable under nitrogen in both the solid state and
solution. The 31P NMR spectrum yields an A2M spin system, in
which A are the phosphorus atoms of the triphenylphosphane
and M the phosphorus of PH2SCH3. The NMR parameters are sim-
ilar to those observed both for 1 and 2. Such data show that the
methylthioester, PH2SCH3, retains its coordination to the metal
through the phosphorus atom. The presence of the methylated sul-
fur atom is confirmed by the occurrence of a three-proton reso-
nance at 2.31 ppm doubled by a 10.3 Hz coupling with the
neighbouring thiophosphinite P atom. Remarkably, the PH2 portion
of the spectrum does not show any fluxional behaviour and ap-
pears as a first order doublet of triplets. This behaviour corrobo-
rates the hypothesis that the scrambling process in 2 may be
traced back to the engagement of a high-energy lone pair of the
deprotonated sulfur atom, which should not be available in the
case of 3.
The chemistry here presented shows that the coordinated thi-
ophosphinous acid, PH2SH, stabilised by coordination to suitable
organometallic platforms, may undergo simple chemical transfor-
mations resulting in the formation of new and unprecedented
coordinated species like the PH2Sꢀ anion and the methylthioester
PH2SCH3. Also, the present results show that the tautomerization
processes via fast and low-energy mobility pathways, causing
instability of PH2SH as a free molecule [4], are blocked by coordi-
nation of the phosphorus atom to the metal.
3.1. [PPh3H]CF3SO3
One equivalent of trifluromethansulfonic acid was added to tri-
phenylphosphane (520 mg, 2.0 mmol) dissolved in toluene (8 ml);
the salt was precipitated by cooling the resulting suspension with
an ice bath. Yield: 670 mg, 81%. Anal. Calc. for C19H16F3O3PS: C,
55.3; H, 3.9; P, 7.5%; M, 412.3. Found: C, 55.1; H 4.0; P, 7.2%.
3.2. [CpRu(PPh3)2(PH2S)] (2)
Proton sponge (43 mg, 0.2 mmol) dissolved in CH3CN (5 ml)
was added to
a solution of [CpRu(PPh3)2(PH2SH)]CF3SO3 (1)
(181 mg, 0.2 mmol) in CH3CN (10 ml). A yellow microcrystalline
material was obtained by stirring the resulting solution for 1 h.
The solid was separated from the solution, washed with cold
CH3CN (2 ml) and dried under vacuum. Yield: 118 mg, 78%. Anal.
Calc. for C41H37P3RuS: C, 65.1; H, 4.9; P, 12.3%; M, 755.8. Found:
3. Experimental
All reactions and manipulations were performed under an
atmosphere of dry oxygen-free argon. The solvents were purified
according to standard procedures [11]. The 1H, 19F and 31P{1H}
C, 65.1; H 5.0; P, 12.2%. IR (
(CDCl3, 298 K): dH 7.40–7.10 (30H, m, Ph), 6.19 (2H, AA’MXX’ spin
m
max/cmꢀ1): (PH) 2305 s. 1H NMR

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M.D. Vaira et al. / Journal of Organometallic Chemistry 693 (2008) 3011–3014
refined by full-matrix least-squares on F2 values [15]. All non-
hydrogen atoms were refined anisotropically. All hydrogens bound
to carbons were placed in idealized positions, each riding on the
respective carrier atom, with its temperature factor linked to the
overall U of the latter. The positions of the PH2S hydrogens were
allowed to refine, with a geometrical restraint on P–H distances.
Programs used for crystallographic calculations included PARST
[16] and ORTEP was used for drawings [17].
Table 2
Crystal data and structure refinement parameters for [CpRu(PPh3)2(PH2S)] ꢁ CH3CN
(2)
Formula
C43H40NP3RuS
796.80
Monoclinic
P21/c
12.0041(3)
13.1006(4)
24.7880(10)
90
100.768(3)
90
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
a
(°)
4. Supplementary material
b (°)
c
(°)
V (Å3)
3829.5(2)
4
CCDC 686518 contains the supplementary crystallographic data
for 2. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/da-
ta_request/cif.
Z
Crystal size (mm)
0.18 ꢂ 0.20 ꢂ 0.60
l
(Mo K
a )
, mmꢀ1
0.621
T (K)
170(2)
Reflections collected
26228
Independent reflections
7085
4673 [0.0856]
445 [1]
0.0608; 0.1547
0.0915; 0.1651
1.090
Acknowledgement
Reflections with I > 2
No. of parameters [restraints]
R1; wR2 [I > 2 (I)]
r(I) [Rint
]
We acknowledge financial support by the Ministero dell’Uni-
versità e della Ricerca Scientifica e Tecnologica (Rome).
r
R1; wR2 [all data]
Goodness-of-fit
References
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1
1
2
3
JXX ¼ 18:2, 3JXA
¼
JX A ¼ 1:8,
0
0
0
0
system,
JXM ¼ JX M ¼ 350:1,
JXA ¼ 10:8, PH2), 4.48 (5H, s, C5H5); 31P{1H} NMR (CDCl3,
3
3
0
0
JX A
¼
2
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CH3CN solution of 1 and proton sponge overnight.
3.3. [CpRu(PPh3)2(PH2SCH3}]CF3SO3 (3)
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(113 mg, 0.15 mmol) in CH2Cl2 (10 ml). The resulting solution was
stirred at room temperature for 15 min; after than the solvent was
removed under reduced pressure leaving a yellow residue. The yel-
low solid was washed with diethylether and dried under vacuum.
Yield 117 mg, 85%. Anal. Calc. for C43H40F3O3P3RuS2: C, 56.1; H, 4.4;
P, 10.1%; M, 919.8. Found: C, 56.0; H 4.5; P, 9.5%. IR (
m
max/cmꢀ1):
(PH) 2290 s. 1H NMR (CDCl3, 298 K): dH 7.40–6.80 (30H, m, Ph),
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1
3
5.49 (2H, dt, JHP 370.3, JHP 6.0, PH2), 4.58 (5H, s, C5H5), 2.31
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3
d, JPP 47.4, PPh3), 3.2 (1P, t, PH2SCH3); 19F NMR (CDCl3, 298 K):
2
dF, ꢀ75.5 (s, CF3SOꢀ).
3
3.4. X-ray crystallography of [CpRu(PPh3)2(PH2S)].CH3CN (2)
X-ray diffraction data for 2, as the acetonitrile solvate, were col-
lected at 170(2) K on an Oxford Diffraction Xcalibur 3 CCD diffrac-
tometer, using Mo K
the main data collection and structure refinement parameters are
given in Table 2. Lattice constants were obtained from the setting
angles of 15460 reflections in the h range 3.7–28.0°. Intensity data
were corrected for absorption by a multi-scan procedure [13]. The
structure was solved by direct methods, with SIR-97 [14], and was
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a radiation (k = 0.71073 Å). Crystal data and