Getting a clue to the hydrolytic activation of white phosphorus: The generation and stabilization of P(OH)2PHPHPH(OH) at ruthenium centers

Article abstract of DOI:10.1021/ic801859z

The bimetallic compound [{CpRu(PPh₃)₂} ₂(μ,η^1:1-P₄)][CF₃SO ₃]₂, in which the tetrahedral P₄ is bound to two CpRu(PPh₃)₂ fragments, slo

Full text of DOI:10.1021/ic801859z

Inorg. Chem. 2009, 48, 1091-1096
Getting a Clue to the Hydrolytic Activation of White Phosphorus: The
Generation and Stabilization of P(OH)2PHPHPH(OH) at Ruthenium
Centers
Pierluigi Barbaro,† Massimo Di Vaira,‡ Maurizio Peruzzini,† Stefano Seniori Costantini,‡
and Piero Stoppioni*,‡
ICCOM CNR, Via Madonna del Piano, 10, 50019, Sesto Fiorentino, Firenze, Italy, and
Dipartimento di Chimica, UniVersita` di Firenze, Via della Lastruccia, 3,
50019 Sesto Fiorentino, Firenze, Italy
Received September 30, 2008
The bimetallic compound [{CpRu(PPh3)2}2(µ,η1:1-P4)][CF3SO3]2, in which the tetrahedral P4 is bound to two
CpRu(PPh3)2 fragments, slowly reacts under mild conditions with a moderate excess of water (1:20) to yield a
mixture of compounds. Among the hydrolysis products, the new, remarkably stable complexes [{CpRu(PPh3)}{CpRu-
(PPh3)2}{µ1,4:3,η2:1-P(OH)2PHPHPH(OH)}](CF3SO3)2 (2) and [{CpRu(PPh3)2}{CpRu(PPh3){P(OH)3)}(µ,η1:1-P2H4)]-
(CF3SO3)2 (3) have been isolated. In the former, the previously unknown 1,1,4-tris(hydroxy)tetraphosphane molecule,
P(OH)2PHPHPH(OH), is 1,4- and, respectively, 3-coordinated to the CpRu(PPh3) and the CpRu(PPh3)2 moieties;
in the latter, the diphosphane P2H4 is stabilized through coordination to two different metal fragments. All of the
compounds were characterized by elemental analyses and IR and NMR spectroscopy. The crystal structure of 2
was determined by X-ray analysis. The formation of the hydroxytetraphosphane, containing the tetraphosphorus
entity, provides a clue to the hydrolytic activation of the P4 molecule.
Introduction
final aim of developing a true catalytic cycle that directly
converts the feedstock species into valuable chemical
products.
The activation and functionalization of small, readily
available molecules represent important processes for the
advancement of knowledge on chemical reactivity which,
in addition, may open the way to many industrial applica-
tions. This is particularly important at the present time, when
more and more stringent European legislation requires that
local industries devote increasing attention to the environ-
mental impact of any newly implemented processes.
A simple, small molecule that has received comparatively
less attention is elemental white phosphorus, which only
recently has become the target of controlled metal-mediated
activation.6,7 P4 is indeed readily available and provides the
key entry to many aspects of phosphorus chemistry. More-
over, it represents the basis for the preparation of the myriad
organophosphorus compounds, which are among the chemi-
cal specialties with the largest worldwide production.8
Organophosphorus compounds are synthesized commercially
from P4, which, upon oxidation with chlorine to PCl3 or PCl5,
is straightforwardly transformed into the target products.
A huge number of studies have focused on the activation
of simple molecules, either largely available in nature, such
as CH4,1 CO2,2 and N2,3 or easily produced in industrial
plants, such as H2 or NH3.5 Very often, transition metal
4
reagents are employed to carry out these processes, with the
(4) Heinekey, D. M.; Lledo´s, A.; Lluch, J. M. Chem. Soc. ReV. 2004, 33,
175–182.
* To whom correspondence should be addressed. Fax: (+39)0554573385:
E-mail: piero.stoppioni@unifi.it.
(5) Kol, M.; Schrock, R. R.; Kempe, R.; Davis, W. M. J. Am. Chem.
Soc. 1994, 116, 4382–4390.
†
ICCOM CNR.
Universita` di Firenze.
‡
(6) Peruzzini, M.; Gonsalvi, L.; Romerosa, A. Chem. Soc. ReV. 2005, 34,
(1) (a) Jones, W. D. Acc. Chem. Res. 2003, 36, 140–146. (b) Crabtree,
R. H. Chem. ReV. 1995, 95, 987–1007.
(2) Castro-Rodriguez, I.; Meyer, K. Chem. Commun. 2006, 1353–1368.
(3) (a) Fryzuk, M. D.; Kozak, C. M.; Bowdridge, M. R.; Patrick, B. O.;
Rettig, S. J. J. Am. Chem. Soc. 2002, 124, 8389–8397. (b) Fryzuk,
M. D.; Johson, S. A. Coord. Chem. ReV. 2000, 200-202, 379–409.
1038–1047.
(7) (a) Peruzzini, M.; Abdreimova, R. R.; Budnikova, Y.; Romerosa, A.;
Scherer, O. J.; Sitzmann, H. J. Organomet. Chem. 2004, 689, 4319–
4331. (b) Ehses, M.; Romerosa, A.; Peruzzini, M. Top. Curr. Chem.
2002, 220, 108–140. (c) Cummins, C. C. Angew. Chem., Int. Ed. 2006,
45, 862–870.
10.1021/ic801859z CCC: $40.75  2009 American Chemical Society
Inorganic Chemistry, Vol. 48, No. 3, 2009 1091
Published on Web 01/05/2009

Barbaro et al.
Recently, the activation of white phosphorus has been
accomplished with either heterocyclic carbenes9 or highly
nucleophilic main group compounds.10 These studies have
disclosed new opportunities in this area, allowing achieve-
ment of the partial degradation of the molecule and its
functionalization via the insertion of organic fragments into
assembled polyphosphorus units, without the involvement
of any transition metal. The use of readily available reagents,
effective for the direct incorporation of phosphorus atoms
from P4 into inorganic or organic molecules, would be more
profitable, and this goal may be pursued through mild metal-
catalyzed reactions that, avoiding hazardous processes, may
furthermore provide an environmental benefit. Achieving the
coordination of the intact tetrahedral molecule of white
phosphorus and studying its reactivity is mandatory for this
purpose.
Previous work from our group has highlighted the utility
of the CpRRuL2 platform (CpR ) C5H5, C5Me5; L )
phosphane) to coordinate the intact P4 molecule, yielding
stable mononuclear11 or dinuclear12 cationic complexes
[{CpRRuL2}n(η1-P4)]Yn (n ) 1, 2; Y ) PF6, CF3SO3).
Furthermore, these mono- or bimetallic compounds, which
may be easily obtained in gram amounts, have been found
to be useful for investigating the reactivity of the coordinated
P4 under mild reaction conditions. Unexpectedly, the reactiv-
ity of the coordinated tetraphosphorus molecule in the
ruthenium cyclopentadienyl derivatives is spectacularly
modified with respect to that of the free molecule. An
interesting feature in this respect is the straightforward
reactivity toward water of the coordinated P4 molecule, which
readily undergoes disproportionation at room temper-
ature.11b,c,12 By studying the hydrolysis of the bimetallic
[{CpRu(PPh3)2}2(µ,η1:1-P4)][CF3SO3]2 (1) compound, which
contains the doubly metallated P4 bridging ligand, intriguing
features have appeared.12 Remarkably, both the nature of
the products and the time needed to complete the hydrolysis
are strongly affected by the relative amounts of the complex
and water. Thus, the addition of 100 equiv of water to 1
equiv of 1 in THF hydrolyzes the coordinated P4 ligand in
a few hours, yielding a mixture of diphosphane, P2H4, and
phosphorus oxoacids, H3PO2 and H3PO3. While the diphos-
phane molecule is stabilized through end-on/end-on coor-
dination to two CpRu(PPh3)2 fragments,12 the oxo derivatives
are obtained as either free molecules or as ligands P-
coordinated to ruthenium after their tautomerization to the
pyramidal species, PH(OH)2 and P(OH)3.13 In contrast to
this chemistry, quick quenching of the hydrolyzed THF
solution of the dinuclear derivative 1, carried out using a
large excess of water, affords selectively phosphorous acid,
H3PO3, and a bimetallic compound containing the unprec-
edented 1-hydroxytriphosphane molecule, stabilized as a
bridging ligand between two CpRu(PPh3)2 fragments.14
Herein, we report a further breakthrough in this type of
reactivity, showing that the reaction of the doubly coordi-
nated P4 may be significantly slowed down by reducing the
amount of water and that, among the several products which
are formed by hydrolysis under these conditions, the previ-
ously unknown 1,1,4-tris(hydroxy)tetraphosphane, P(OH)2-
PHPHPH(OH), is generated. The formation of this intriguing
molecule, which is stabilized through coordination to two
nonequivalent {CpRu} platforms, besides its intrinsic interest,
provides an important clue to the understanding of the initial
steps of the coordinated P4 hydrolytic degradation.
Results and Discussion
Compound 1 in THF is completely hydrolyzed within 6
days in the presence of 20 equiv of water. Reactions carried
out on different batches are reproducible with respect to both
the amount and nature of the products obtained. The 31P{1H}
NMR spectrum of the solid obtained after workup (see
Experimental Section) shows the presence of a mixture of
several compounds. The two most abundant species are
identifiedas[{CpRu(PPh3)}{CpRu(PPh3)2}{µ1,4:3,η2:1-P(OH)2-
PHPHPH(OH)}]2+ (2) and [{CpRu(PPh3)2}{CpRu(PPh3)-
{P(OH)3)}(µ,η1:1-P2H4)]2+ (3), Scheme 1; their fractional
amounts (35% and 30%, respectively) have been estimated
with reference to the four P atoms of the educt species 1 by
careful integration of the 31P NMR resonances. The remain-
ing minor species are the known complex cations
[CpRu(PPh3)2{PH(OH)2}]+ (4),13 [CpRu(PPh3)2{P(OH)3}]+
(5),13 [CpRu(PPh3)2(PH3)]+ (6),11b [{CpRu(PPh3)2}2(µ,η1:1-
P2H4)]2+ (7),12 and the free phosphorous acid, H3PO3, which
were identified by comparing the 31P NMR spectrum of the
reaction mixture originating from the hydrolysis of 1 with
those of pure samples.11b,12 Notably, the 1-hydroxytriphos-
phane complex [{CpRu(PPh3)2}2{µ1:3,η1:1-PH(OH)PHPH2}]2+
(8), previously obtained in the presence of excess water,14
has never been detected among the hydrolysis products of 1
obtained by the present procedure. The new complexes 2
and 3 were separated as yellow solids from the reaction
mixture by careful selective precipitation. Both compounds
are air-stable in the solid state and soluble in common organic
solvents such as acetone, dichloromethane, and chloroform,
(8) (a) Corbridge, D. E. C. Phosphorus. An Outline of its Chemistry,
Biochemistry and Technology. In Studies in Inorganic Chemistry, 5th
ed.; Elsevier: New York, 1995; Vol. 20. (b) Emsley, J. The 13th
Element: The Sordid Tale of Murder, Fire, and Phosphorus; Wiley:
New York, 2002.
(9) (a) Masuda, J. D.; Schoeller, W. W.; Donnadieu, B.; Bertrand, G.
Angew. Chem., Int. Ed. 2007, 119, 7052–7055. (b) Masuda, J. D.;
Schoeller, W. W.; Donnadieu, B.; Bertrand, G. J. Am. Chem. Soc.
2007, 129, 14180–14181.
(10) (a) Xiong, Y.; Yao, S.; Brym, M.; Driess, M. Angew. Chem., Int. Ed.
2007, 46, 4511–4513. (b) Fox, A. R.; Wright, R. J.; Rivard, E.; Power,
P. P. Angew. Chem., Int. Ed. 2005, 44, 7729–7733. (c) Kraus, F.;
Aschenbrenner, J. C.; Korber, N. Angew. Chem., Int. Ed. 2003, 42,
4030–4033. (d) Chan, W. T. K.; Garc´ıa, F.; Hopkins, A. D.; Martin,
L. C.; McPartlin, M.; Wright, D. S. Angew. Chem., Int. Ed. 2007, 46,
3084–3086. (e) Peng, Y.; Fan, H.; Zhu, H.; Roesky, H.; Magull, J.;
Hughes, C. Angew. Chem., Int. Ed. 2004, 43, 3443–3445.
(11) (a) de los Rios, I.; Hamon, J.-R.; Hamon, P.; Lapinte, C.; Toupet, L.;
Romerosa, A.; Peruzzini, M. Angew. Chem., Int. Ed. 2001, 40, 3910–
3912. (b) Di Vaira, M.; Frediani, P.; Seniori Costantini, S.; Peruzzini,
M.; Stoppioni, P. Dalton Trans. 2005, 2234, 2236. (c) Di Vaira, M.;
Peruzzini, M.; Seniori Costantini, S.; Stoppioni, P. J. Organomet.
Chem. 2006, 691, 3931–3937.
(13) Akbayeva, D. N.; Di Vaira, M.; Seniori Costantini, S.; Peruzzini, M.;
Stoppioni, P. Dalton Trans. 2006, 389–395.
(12) Barbaro, P.; Di Vaira, M.; Seniori Costantini, S.; Peruzzini, M.;
Stoppioni, P. Chem.sEur. J. 2007, 13, 6682–6690.
(14) Barbaro, P.; Di Vaira, M.; Seniori Costantini, S.; Peruzzini, M.;
Stoppioni, P. Angew. Chem., Int. Ed. 2008, 47, 4425–4427.
1092 Inorganic Chemistry, Vol. 48, No. 3, 2009

Generation and Stabilization of P(OH)2PHPHPH(OH)
Scheme 1
Figure 1. A view of the cation in the structure of 2, with 30% probability
ellipsoids. Hydrogen atoms of the phenyl and cyclopentadienyl rings are
not shown for clarity.
but they are insoluble in diethyl ether and n-hexane.
Recrystallization of 2 from acetone and n-hexane afforded
yellow crystals suitable for X-ray diffraction, while attempts
to grow single crystals of 3 were unsuccessful.
An overall view of the dimetal cation in the structure of
2 is shown in Figure 1, and its core is presented in Figure 2.
The P(OH)2PHPHPH(OH) unit is coordinated with its two
hydroxylated ends to the metal atom bearing only one
triphenylphosphane coligand, and it bonds the other metal
atom, coordinated by both triphenylphosphanes of the
original CpRu(PPh3)2 fragment, through one of the central
atoms of the tetraphosphorus chain. The 2.312(1) Å Ru1-P1
bond distance, formed by the triphenylphosphane to the
former metal atom (Figure 2), is 0.040 Å smaller than the
2.352 Å mean of the Ru2-P2 and Ru2-P3 distances formed
by the two PPh3 ligands with the other metal atom. On the
other hand, the latter distances are in line with those
previously found, for analogous bond types, in the dimetal
cations containing the PH(OH)PHPH2 and P2H4 units
(2.345 and 2.360 Å, respectively, mean values). As far as
the coordinating bonds formed by the P(OH)2PHPHPH(OH)
unit in 2 are concerned, the Ru1-P4 and Ru1-P7 bonds to
Ru1 are, again, shorter (by 0.062 Å, in the mean) than the
single Ru2-P5 bond formed with Ru2. Possibly, the overall
shorter Ru-P distances around Ru1 are due to the lower
steric requirements of one PPh3 ligand, compared to those
of the two triphenylphosphanes linked to Ru2 (there were
two coordinating PPh3 ligands also in the other,12,14 above-
mentioned, cations). The three P-P distances in the
P(OH)2PHPHPH(OH) unit, spanning the 2.226-2.244 Å
range, are rather closely grouped, the longest one being
formed by the two central, nonhydroxylated, P atoms. The
five-membered ring formed by the four atoms of the
tetraphosphane unit and Ru1 is in the envelope conformation,
with the P4, P6, P7, and Ru1 atoms lying in a plane (P7
deviates most from the plane, by 0.121(1) Å), whereas P5
Figure 2. The core of the cation in the structure of 2, with 30% probability
ellipsoids. Selected bond lengths (Å) and angles (deg): Ru1-P4 2.240(1),
Ru1-P7 2.235(1), Ru2-P5 2.300(1), P4-P5 2.232(2), P5-P6 2.244(2),
P6-P7 2.226(2), P4-O1 1.598(4), P7-O2 1.585(4), P7-O3 1.579(4),
P4-Ru1-P7 88.45(5), Ru1-P4-P5 109.04(7), P4-P5-P6 92.10(7),
P5-P6-P7 97.65(7), P6-P7-Ru1 116.92(7).
is significantly displaced from it. The hinge angle between
the above plane and that passing through the P5, P4, and P6
atoms is 124.3(1)°.
14
12
In keeping with the X-ray structural analysis, the 31P{1H}
spectrum of 2 shows a second-order AA′CFNQS spin system,
in which A, A′, and C are the triphenylphosphane P atoms
and F, N, Q, and S are the phosphorus atoms of the bridging
1,1,4-tris(hydroxy)tetraphosphane; the labels of the P atoms
are sketched in Scheme 1. The NMR parameters of 2 were
obtained by computer simulation of the experimental spec-
trum (Figure 3). The chemical shifts of the phosphane P
atoms of the CpRu(PPh3)2 fragment (PA, PA′) are in the range
observed for [CpRu(PPh3)2(L)]+ complexes,11-15 while the
signal of the phosphane P atom of the CpRu(PPh3) moiety
(PC) is appreciably downfield-shifted (δ 56.5). The NMR
resonances of the tetraphosphane chain in the P(OH)2-
PHPHPH(OH) bridging ligand exhibit chemical shifts span-
(15) Ru¨ba, E.; Simanko, W.; Mauthner, K.; Soldouzi, K. M.; Slugovc, C.;
Mereiter, K.; Schmid, R. Organometallics 1999, 18, 3843–3850.
Inorganic Chemistry, Vol. 48, No. 3, 2009 1093

Barbaro et al.
on the basis of elemental analysis and 1H and 31P NMR data,
the latter being obtained through computer simulation of the
experimental spectrum. The dinuclear complex cation con-
tains the diphosphane, P2H4, molecule bridging two non-
equivalent ruthenium moieties, namely, CpRu(PPh3)2 and
CpRu(PPh3)(P(OH)3. The latter is likely formed by substitu-
tion of a molecule of phosphorous acid, coordinating through
the P lone pair as a result of H3PO3 T P(OH)3 tautomer-
ization,13 for one of the triphenylphosphane ligands of the
parent compound 1. Such substitution, certainly promoted
by the well-known mobility of a PPh3 ligand in the
CpRu(PPh3)2 moiety, has been observed also for the com-
pounds [CpRu(PPh3)2{PR(OH)2}]CF3SO3 [R ) H (4), OH
(5)], which undergo replacement of a coordinated triph-
enylphosphane molecule under mild conditions by a PR(OH)2
species (H3PO2 or H3PO3 tautomer).13 In the 31P NMR
spectra of these compounds, the signal of the remaining
phosphane is downfield-shifted with respect to that of the
parent CpRu(PPh3)2 fragment.13 An analogous downfield
shift is observed for the PPh3 ligand of the CpRu-
(PPh3){P(OH)3} fragment in 5. Thus, the 31P NMR spectrum
of 3 exhibits a second-order AA′CFNQ spin system (labels
as in Scheme 1) in which AA′ and C are the triphenylphos-
phane P atoms, F is the phosphorus atom of the coordinated
P(OH)3 ligand, and N and Q are the nonequivalent P atoms
of the bridging diphosphane. The resonances of the CpRu(P-
Ph3)2 triphenylphosphane P atoms (PA and PA′) occur at the
expected frequencies, and the low-field shift of the PC
multiplet of the CpRu(PPh3)(P(OH)3) moiety is comparable
to that of the PC atom in 2 where the CpRu(PPh3) fragment
is bound to the hydroxylated PS and PF atoms. The P(OH)3
ligand exhibits a shift analogous to that observed for 5.
Finally, the two nonequivalent P2H4 atoms (PN and PQ) yield
two distinct multiplets whose chemical shifts are slightly
downfield with respect to that exhibited by the P2H4 molecule
symmetrically bound to two CpRu(PPh3)2 units in 7.12 In
Figure 3. Computed (bottom) and experimental (top) 31P{1H} NMR spectra
of 2.
ning a range of more than 300 ppm, with the signals of the
oxygenated P atoms (PF, PS) falling at the low-field end of
the range (δF 168.4, δS 183.4) and the multiplet of the
nonmetallated P-H phosphorus (PQ) at the high-field end
(δQ -126.5). The signal of the metallated P-H atom (PN),
at ca. 31 ppm, shows a coordination chemical shift of about
1
160 ppm with respect to PQ. In the H NMR spectrum, the
hydrogens bound to PF, PN, and PQ yield broad multiplets
(δF 5.80, δN 3.61, δQ 1.40) with H-P coupling constants
that are in the range observed for 1-hydroxytriphosphane.14
The 1,1,4-tris(hydroxy)tetraphosphane molecule, stabilized
in 2 by µ1,4:3,η2:1-coordination to two {CpRu} moieties, is
particularly intriguing as it represents an additional mem-
ber of the practically unknown family of polyhydroxy-
phosphanes, that is, compounds of general formula
PnH[(n+2)-m](OH)m (m e n + 2),16 which may be formally
related to the slightly more investigated, but still elusive,
family of polyphosphorus hydrides (PnHn+2),17 by substitution
of OH groups for one or more H atoms of the hydrides. The
latter linear phosphanes are formally isoelectronic with the
corresponding alkanes but are quite reactive, undergoing
exothermic decomposition through disproportionation, even
at low temperatures. Remarkably, no compound formed by
their reaction with oxygen has been fully characterized, as
they spontaneously ignite, yielding, as the final product,
phosphoric acid.
1
the H NMR spectrum, the hydrogens bound to PN and PQ
yield broad multiplets (δ 5.22, 4.61, 4.48, and 4.04) with
H-P coupling constants that are in the range observed for
7.14 The two cyclopentadienyls yield two resonances (δ 4.89
and 4.80), as expected for two nonequivalent metal frag-
ments. Therefore, although the structure of 3 could not be
authenticated by crystallographic methods, there is strong
evidence for the present assignment, based on the analysis
of the 31P{1H}, 31P NMR, and 1H spectra and the comparison
with the NMR parameters of 7. In view of the existence of
a small amount of compound 7 among the minor products
of the present hydrolysis process, it may be assumed that 3
is formed from 7 by substitution of the P(OH)3 molecule
for a phosphane ligand.
The numerous species containing up to four phosphorus
atoms, that is, PH3,11b,c PH(OH)2,12,13 P(OH)3,12,13 P2H4,12
PH2PHPH(OH),14 and the present P(OH)2PHPHPH(OH),
obtained by the various processes of hydrolysis of 1 and
stabilized by coordination to one or two metal moieties, may
be assumed as thermodynamic sinks along the degradation
pathway of the dimetallated P4 ligand. Their number suggests
The [{CpRu(PPh3)2}{CpRu(PPh3)(P(OH)3)}(µ,η1:1-P2H4)]-
[CF3SO2]2 formula and the structure of 3 have been assigned
(16) To the best of our knowledge, no free polyhydroxophosphane
PnH[(n+2)-m](OH)m with n > 1 is known. The tris(hydroxy)phosphane
PH(OH)PHPH2, stabilized as the µ,η1,η1-ligand, has been reported in
[{CpRu(PPh3)2}2(µ1:3,η1:1-PH(OH)PHPH2)]CF3SO3 (ref 14).
(17) Baudler, M.; Glinka, K. Chem. ReV. 1994, 94, 1273–1297.
1094 Inorganic Chemistry, Vol. 48, No. 3, 2009

Generation and Stabilization of P(OH)2PHPHPH(OH)
Scheme 2
that several routes may be activated during the hydrolysis
of 1, depending on the reaction conditions, particularly the
amount of added water.
resulting in the intermediate B. From this point on, the
process would be straightforward and the formation of 2
would be brought about by coordination of the pending
PH(OH) end of the opened tetraphosphane to the ruthenium
center already coordinated by the distal P(OH)2 end, with
associated decoordination of a triphenylphosphane ligand.
By contrast, the alternative addition of the third water
molecule across the 3,4-P-P bond in A yields, after passing
through C and the addition of a fourth water molecule, the
triphosphorus chain featuring the 1-hydroxytriphosphane,
PH(OH)PHPH2, ligand, which has been characterized in the
complex [{CpRu(PPh3)2}2{µ1:3,η1:1-PH2PHPH(OH)}]2+ (8).14
One equivalent of P(OH)3 accompanies the formation of 8,
which, once released in the reaction medium, retrotautomer-
izes to the more stable oxyacid form, H3PO3.13,14
The progressive addition of three or four water molecules,
besides being controlled by the electronic properties of the
coordinated P4 molecule and ensuing species, is clearly
affected by the reaction conditions. In our hands, the
hydrolysis of the doubly metallated molecule is in fact
specific in the presence of a large amount of water, going
with almost complete regioselectivity to the formation of 8,14
with no detectable amount of the tetraphosphane species
found in 2.
Therefore, although no rigorous and comprehensive mecha-
nistic picture of the hydrolysis of the dimetallated P4 in 1
may be proposed in the absence of an in-depth kinetic study
and of a reliable energetic profile of the reaction, possibly
backed up by theoretical modeling of the process, it seems
nevertheless to be possible to trace some hypotheses about
the initial steps of the process, particularly those leading to
the formation of compound 2, which is the main focus of
the present paper. Indeed, the P(OH)2PHPHPH(OH) formula
suggests that the species sandwiched in 2 may result from
the addition of three water molecules to P4 without complete
disruption of the cage. A trivial assignment of oxidation
numbers shows that a disproportionate reshuffle occurs,
yielding the oxidation numbers +2, -1, -1, and 0 for the
four P atoms of the molecule, in the above order. A pictorial
description of a possible route for the stepwise addition of
three water molecules to 1, with the cleavage of three P-P
bonds, however without total disruption of the diruthenium-
tetraphosphorus assembly, is shown in Scheme 2. Whatever
the detailed order of addition, one may assume that the first
two water molecules add across the P-P bond connecting
the pair of unmetallated P atoms and that connecting the
metallated pair, yielding the (undetected) species 1,2-
(dihydroxy)tetraphosphacyclobutane (A) 1,3-dicoordinated
to two {CpRu(PPh3)2} moieties. Then, in order that the
formation of the 1,1,4-tris(hydroxy)tetraphosphane found in
2 is rationalized, the addition of the third water molecule to
A should take place with complete 1,4-regioselectivity,
Experimental Section
All reactions and manipulations were performed under an
atmosphere of dry, oxygen-free argon. The solvents were purified
1
according to standard procedures. H, 19F, and 31P NMR spectra
were run on Bruker Avance 400 DRX spectrometers, equipped with
variable-temperature control units accurate to (0.1 °C. 19F and 31
P
chemical shifts are relative to external CFCl3 and to 85% H3PO4,
Inorganic Chemistry, Vol. 48, No. 3, 2009 1095

Barbaro et al.
respectively. 1H chemical shifts are relative to tetramethylsilane as
external reference and were calibrated against the residual solvent
resonance. Downfield values are reported as positive, coupling
constants (Hz) of 2 and 3 and were obtained from 1D 31P{1H}, 1H,
and 1H{31P} NMR spectra with the aid of computer simulation using
the gNMR program.18 19F NMR spectra of compounds 2 and 3
yielded a singlet at -75.5 ppm for the triflate anion. Nujol mull
infrared spectra were run on a Perkin-Elmer Spectrum BX FT-IR
spectrometer with samples between NaCl discs. Microanalyses were
carried out at the Microanalytical Laboratory of the Department of
Table 1. Crystal Data, Data Collection, and Structure Refinement
Parameters for 2a
empirical formula
C66H61F6O9P7Ru2S2
1595.20
130(2)
fw (g mol-1
temp (K)
)
cryst system
space group
a (Å)
monoclinic
P21/c
14.493(1)
b (Å)
18.021(1)
c (Å)
26.931(1)
ꢀ (deg)
91.635(6)
7030.9(8)
Chemistry of the University of Firenze. [{CpRu(PPh3)2}2(µ,η1:1
-
V (Å3)
P4)][CF3SO3]2 (1) was prepared according to the literature method.12
Hydrolysis of 1. A 20-fold excess of water (0.21 mL, ca. 12
mmol) was added to a Schlenk flask charged with [{CpRu(P-
Ph3)2}2(µ,η1:1-P4)](CF3SO3)2 (1) (1.08 g, 0.60 mmol) and THF (120
mL), and the resulting solution was stirred at room temperature.
The parent compound 1, as observed by carrying out the 31P NMR
spectrum on small aliquots of the solution, is completely hydrolyzed
after 6 days. The solvent was then removed under reduced pressure
to yield an orange solid.
Z
4
Fcalcd (g cm-3
)
1.507
6.133
123158
µ (mm-1
reflns collected
)
independent reflns
13824 (Rint ) 0.0692)
obsd reflns [I > 2σ(I)]
data/restraints/params
final R indices [I > 2σ(I)]
R indices (all data)
9600
13824/86/928
R1 ) 0.0508, wR2 ) 0.1328
R1 ) 0.0780, wR2 ) 0.1586
1.042
goodness-of-fit on F2
largest difference peak and hole/e Å-3
1.412 and -0.829 e Å-3
[{CpRu(PPh3)}{CpRu(PPh3)2}{µ1,4:3,η2:1-P(OH)2PHPHPH(OH)}]-
[CF3SO3]2 (2). The crude hydrolyzed mixture, obtained as described
above, was dissolved in acetone (30 mL), and n-hexane was added
up to saturation (ca. 5 mL). The resulting solution separated within
two days yielding yellow crystals, which were collected on a glass
frit, washed with a 1:1 acetone/n-hexane mixture (20 mL), and
dried. Yield: 40 mg, 0.025 mmol, 4%. Elem anal. (%) calcd for
C66H61F6O9P7Ru2S2 (1595.2): C, 49.7; H, 3.9; P, 13.6. Found: C,
49.2; H, 4.0; P, 13.3. IR (NaCl, cm-1): ν(O-H) 3058 (br); ν(P-H)
2307 (br). 31P{1H} NMR (161.89 MHz, CD2Cl2, 0 °C) δ 183.4
(m, PS, 1J(PS-PQ) 199.5, 2J(PS-PC) 42.0, 2J(PS-PF) 28.0, 2J(PS-PN)
15.0, 1P), 168.4 (m, PF, 2J(PF-PC) 40.0, 1J(PF-PN) 126.0, 2J(PF-PQ)
25.0, 3J(PF-PA′) 8.0, 1J(PF-H) 391.0, 1P), 56.5 (m, PC, 3J(PC-PN)
16.0, 1P), 45.0 (m, PA, 2J(PA-PA′) 33.0, 2J(PA-PN) 39.0, 3J(PA-PQ)
7.0, 1P), 39.3 (m, PA′, 2J(PA′-PN) 35.0, 1P), 30.9 (m, PN, 1J(PN-PQ)
a CCDC reference number 000000. For crystallographic data in CIF or
other electronic format see the Supporting Information.
angles of 33 910 reflections in the θ range 3.9-72.1°. Intensity
data were corrected for absorption by a multiscan procedure (max/
min transmission factor values: 1.000/0.650).19 The structure was
solved by direct methods, with SIR-97,20 and was refined by full-
matrix least-squares on F2 values, with SHELXL-97.21 The
asymmetric unit contains one dimetal cation and two triflate anions,
one of which, disorderly arranged, was refined as consisting of two
complementary fractions, imposing similarity restraints on geom-
etries. In the final cycles, all non-hydrogen atoms, including those
of the disordered anion, were assigned anisotropic temperature
factors. Hydrogen atoms were in calculated positions, riding, except
for those bound to phosphorus or oxygen atoms, whose positions,
identified on ∆F Fourier maps, were allowed to refine, with some
restraints on distances; the hydrogen temperature factors were linked
to the equivalent isotropic thermal parameters of the respective
carrier atoms, according to the expression UH ) 1.2UC,Peq, or UH
1
1
263.0, J(PN-H) 365, 1P), -126.5 (m, PQ, J(PN-H) 195.0, 1P).
1H NMR (400.13 MHz, CD2Cl2, 0 °C): δ 7.70-6.90 (m, 45H,
C6H5), 5.80 (brm, 1H, HPF), 4.88 (s, 5H, C5H5), 4.86 (s, 5H, C5H5),
3.61 (brm, 1H, HPN), 1.40 (brm, 1H, HPQ).
eq
) 1.5UO for the hydroxyl hydrogens. Although large voids are
present in the structure, possibly due to the irregular shape of the
rather large cation, no chemically significant residual density was
found in those regions, the highest ∆F peaks lying instead in
proximity of the heavy atom positions. Programs used in the
crystallographic calculations included PARST,22 the WinGX pack-
age,23 and ORTEP.24
[{CpRu(PPh3)2}{CpRu(PPh3)(P(OH)3)}{µ,η1:1-P2H4}][CF3SO3]2 (3).
After the separation of 2, the yellow solution was carefully
concentrated to half volume under argon to yield a yellow
precipitate which was separated from the solution. The solvent of
the solution was removed at reduced pressure. The remaining solid
was dissolved in the minimum amount of CH2Cl2, and n-hexane
was added. The yellow solid which separated overnight was
collected on a glass frit, washed with n-hexane, and dried.
Yield: 50 mg 0.032 mmol, 5%. Elem anal. (%) calcd for
C66H62F6O9P6Ru2S2 (1565.2): C, 50.6; H, 4.0; P, 11.9. Found: C,
49.9; H, 4.3; P, 11.5. IR (NaCl, cm-1): ν(O-H) 3055 (br); ν(P-H)
2322 (br). 31P{1H} NMR (161.89 MHz, CD2Cl2, 0 °C): δ 134.3
Acknowledgment. Financial support by the Italian Min-
istero dell′Istruzione, dell′Universita` e della Ricerca, is
gratefully acknowledged. This work has been carried out
within the frame of COST ACTION CM0802 of the
European Community.
2
2
3
(m, PF, J(PF-PC) 54.5, J(PF-PQ) 72.5, J(PF-PM) 4.0, 1P), 50.9
(m, PC, 2J(PC-PQ) 38.0, 3J(PC-PM) 16.5, 1P), 41.7 (m, PA,
2J(PA-PA′) 29.5, 3J(PA-PQ) 7.0, 2J(PA-PM) 45.0, 1P), 40.8 (m, PA′,
Supporting Information Available: Crystallographic data for
2 in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
3J(PA′-PQ) 7.0, J(PA′-PM) 44.0, 1P), -54.1 (m, PQ, J(PQ-PM)
2
1
1
1
1
64.0, J(PQ-H) 353.0, 1P), -55.8 (m, PM, J(PM-H) 350.0). H
NMR (400.13 MHz, CD2Cl2, 0 °C): δ 7.70-6.90 (m, 45H, C6H5),
5.22 (brm, 1H, HPN), 4.89 (s, 5H, C5H5), 4.81 (s, 5H, C5H5), 4.61
(brm, 1H, HPQ), 4.48 (brm, 1H, HPN), 4.04 (brm, 1H, HPQ).
Crystallography. X-ray diffraction data for 2 were collected at
130 K on an Oxford Diffraction Xcalibur PX Ultra CCD diffrac-
tometer, using Cu KR radiation (λ ) 1.5418 Å). Crystal data and
the main data collection and structure refinement parameters are
given in Table 1. Lattice constants were obtained from the setting
IC801859Z
(19) ABSPACK routine in the CrysAlisPro package: CrysAlisPro; Oxford
Diffraction Ltd.: Abingdon, Oxfordshire, England, 2006.
(20) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giacovazzo,
C.; Guagliardi, A.; Moliterni, A. G.; Polidori, G.; Spagna, R. J. Appl.
Crystallogr. 1999, 32, 115–119.
(21) Sheldrick, G. M. Shelxl97; University of Go¨ttingen: Go¨ttingen,
Germany, 1997.
(22) Nardelli, M. J. Appl. Crystallogr. 1995, 28, 659.
(23) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837–838.
(24) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
(18) Budzelaar, P. H. M.; gNMR V4.0, Cherwell Scientific Publishing:
Oxford, England, 1995-1997.
1096 Inorganic Chemistry, Vol. 48, No. 3, 2009