Easy hydrolysis of white phosphorus coordinated to ruthenium

Article abstract of DOI:10.1039/b504795a

The P₄ molecule bound to ruthenium as an η¹- ligand in [CpRu(PPh₃)₂(η¹-P₄)]Y (Y = PF₆, CF₃SO₃) undergoes an easy reaction with water in exceedingly mild con

Full text of DOI:10.1039/b504795a

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C O M M U N I C A T I O N
Easy hydrolysis of white phosphorus coordinated to ruthenium
Massimo Di Vaira,a Piero Frediani,b Stefano Seniori Costantini,a Maurizio Peruzzinic and
Piero Stoppioni*a
a Dipartimento di Chimica, Universita` di Firenze, via della Lastruccia n. 3, 50019,
Sesto Fiorentino, Firenze, Italy. E-mail: piero.stoppioni@unifi.it
b Dipartimento di Chimica Organica “Ugo Schiff”, Universita` di Firenze, via della Lastruccia n.
13, 50019, Sesto Fiorentino, Firenze, Italy. E-mail: piero.frediani@unifi.it
c ICCOM CNR, Via Madonna del Piano, snc, 50019, Sesto Fiorentino, Firenze, Italy.
E-mail: mperuzzini@iccom.cnr.it
Received 6th April 2005, Accepted 19th May 2005
First published as an Advance Article on the web 31st May 2005
1
The P4 molecule bound to ruthenium as an g -ligand in
the phosphine complexes [CpRu(PPh3)2(PH3)]Y (Y = PF6 3a,
1
[CpRu(PPh3)2(g -P4)]Y (Y = PF6, CF3SO3) undergoes an
CF3SO3 3b).
easy reaction with water in exceedingly mild conditions to
yield PH3, which remains coordinated to the [CpRu(PPh3)2]
fragment, and oxygenated derivatives.
Reaction of [CpRu(PPh3)2Cl] (1) under argon in CH2Cl2–
THF with one equivalent of P4 in the presence of chloride
scavengers (TlPF6 or AgCF3SO3), leads to precipitation of TlCl
or AgCl and coordination of the P4 molecule (Scheme 1) to
1
yield the orange [CpRu(PPh3)2(g -P4)]Y complexes in excellent
In recent years the chemistry of white phosphorus in the presence
of transition-metal fragments has been widely investigated and
many compounds containing Px units originating either from
the degradation of the P4 tetrahedron or reaggregation of
fragments thereof have been synthesized and characterized.1
The compounds, besides having unique geometric and electronic
properties,2 have also been found to be useful building blocks
for networks of inorganic coordination compounds.3 Previous
studies have shown that it is easier to cleave bond(s) of the cage
than attaining coordination by the intact P4 molecule.2,4 Indeed,
until some years ago, only a few compounds, thermally unstable
and difficult to handle, containing the intact molecule had
been described.5,6 Accordingly, the reactivity of the coordinated
molecule had not been investigated. Recently rhenium,7 iron8
and ruthenium8 complexes containing the intact P4 molecule
bound to the metal have been described. These tetrahedro-
tetraphosphorus complexes are readily obtained and possess
stability and solubility properties that make them suitable
as starting materials for investigating the reactivity of the
coordinated P4 molecule and comparing the chemistry of the
coordinated ligand with the free, highly reactive, molecule. Such
a topic is of particular interest in view of the central role of the
P4 molecule in the synthesis of organophosphorus derivatives.9
The P4 allotrope, which is activated only in harsh conditions,10 is
in fact the starting material for the production of a large variety
of organophosphorus compounds which rival the chemistry of
carbon in terms of complexity and applications.9
yield (>95%).† The compounds exhibit an exceptional stability
1
in comparison to the few known g -P4 derivatives5,6 as well as to
the free phosphorus molecule and, in this regard, they behave
as the related Cp* analogous derivatives.8 The P4 molecule
remains firmly coordinated to the metal in solution yielding a
temperature-invariant and anion independent first-order A2FM3
spin pattern in the 31P NMR spectra. The four phosphorus atoms
of the cage yield the FM3 part of the spectrum with the PF atom
coordinated to the metal featuring a quartet of triplets, due
to the coupling to PM and PA, respectively, significantly shifted
downfield with respect to the signal of the free P4 (d −526.9 ppm);
the three naked P atoms yield a doublet at −487.0 ppm.
The chemical shift of the naked PM atoms is similar to that
1
shown by [Cp*Ru(dppe)(g -P4)]BPh4, whereas the signal of the
coordinated phosphorus (d −348.2) is shifted at lower frequency
with respect to that of the Cp* derivative (d −308.46).8 The X-
ray structure of the complex cation in 2a is shown in Fig. 1.‡ The
P–P distances formed by the coordinating phosphorus atom are
˚
consistently shorter by an average of 0.043 A than those among
the distal P atoms, similarly to what has been found for the
1
[Cp*Fe(dppe)(g -P4)]+ cation8 and, to a lesser extent, for the
1
[W(CO)3(PCy3)2(g -P4)] complex.6
When a solution of 2a or 2b in acetone or THF is treated with
excess water (1 : 100), unexpected hydrolysis of the P4 ligand
occurs at room temperature, affording [CpRu(PPh3)2(PH3)]Y
(Y = PF6 3a, CF3SO3 3b) in substantially quantitative ruthenium
yield within 1 h.§ The reaction, intriguing in view of the well
known stability of elemental phosphorus in water, is promoted
by subtle changes in the properties of the metal fragment
Herein, we describe the synthesis and characterization of new
1
tetraphosphorus complexes [CpRu(PPh3)2(g -P4)]Y (Y = PF6
2a, CF3SO3 2b) and report on the astonishing hydrolysis of
the coordinated tetraphosphorus molecule, which takes place
under exceedingly mild conditions to yield one equivalent of
1
from those of [Cp*Ru(dppe)(g -P4)]PF6, whose solutions are
indefinitely stable at room temperature in the presence of water.8
Scheme 1
T h i s j o u r n a l i s
2 2 3 4
D a l t o n T r a n s . , 2 0 0 5 , 2 2 3 4 – 2 2 3 6
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
©

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˚
of the 2.25–2.49 A range of values found for distances formed by
the PH3 ligand with various metal atoms. The P–H distance in
˚
3a of 1.27(2) A is at the short end of the range of P–H distances
15–17
˚
recently reported (1.3–1.5 A).
Complex 3a may be independently synthesized in almost
quantitative yield by reaction of 1 in THF with gaseous PH3
in the presence of TlPF6.¶
Studies are in progress to highlight the reaction mechanism,
the nature of the red solid accompanying the formation of 3a
and 3b, and the scope of this surprising reaction, by extending
the reactivity studies of 2a and 2b towards other nucleophiles.
In this respect, preliminary tests confirm that methanol and
other simple reagents may also easily react with coordinated P4,
thus paving the way to still unexplored paths of phosphorus
chemistry.
Notes and references
† A solution of [CpRu(PPh3)2Cl] (1) (2.00 g, 2.75 mmol) and TlPF6
(960 mg, 2.75 mmol) in a mixture of CH2Cl2 (90 cm3) and THF (140 cm3)
was added at room temperature to a solution of white phosphorus
(380 mg, 3.07 mmol) in THF (30 cm3) under argon. The resulting
slurry was stirred at room temperature for 4 h; the precipitated TlCl
1
Fig. 1 View of the [CpRu(PPh3)2(g -P4)]+ cation in 2a. In this and the
following ORTEP diagram thermal ellipsoids are at the 20% probability
level and hydroge◦n atoms are not shown for clarity. Selected bond lengths
1
was filtered off and [CpRu(PPh3)2(g -P4)]PF6 2a was obtained as orange
microcrystals by evaporating the solvent under reduced pressure (2.50 g,
95%). The solid was recrystallized from CH2Cl2–hexane (Found: C
51.3; H, 3.8. C41H35F6P7Ru requires C 51.3; H 3.7%). 2b was obtained
through the same procedure as 2a using AgCF3SO3 as chloride scavenger
(Found: C 52.1; H, 3.9. C42H35F3O3P6RuS requires C 52.3; H 3.7%). dP
(121.5 MHz, (CD3)2CO, 25 ◦C, 85% H3PO4; complex cation A2FM3
pattern) 39.0 (2P, d, 2J(PAPF) 64 Hz, PA), −348.2 (1P, tq, 1J(PFPM)
235 Hz, PF), −487.0 (3P, d, PM), −143.10 (1P, sept, 1J(PF) 714 Hz, PF6,
only for 2a). dH (300.0 MHz, (CD3)2CO, 25 ◦C, TMS) 7.60–7.10 (30H,
m, Ph), 5.04 (5H, s, Cp).
˚
(A) and angles ( ): Ru–P1 2.364(1), Ru–P2 2.360(1), Ru–P3 2.269(2),
P3–P4 2.154(2), P3–P5 2.145(2), P3–P6 2.141(2), P4–P5 2.180(2), P4–P6
2.200(3), P5–P6 2.189(3); P1–Ru–P2 104.54(4), P1–Ru–P3 94.70(5),
P2–Ru–P3 90.10(5).
The single P-atom hydrogenation leading to 3a and 3b is
accompanied (as revealed by NMR in solution) by formation
of H3PO3 (ca. 100% with respect to 3a or 3b), while the rest
of the P4 atoms yield a red solid of difficult characterization,
featuring a broad 31P NMR resonance at ca. 43 ppm in CD2Cl2.
The nature of this solid, which contains hydrogen, phosphorus
and oxygen in a ca. 1 : 1 : 2.5 ratio, according to XPS and
elemental analysis, has not been clarified by mass spectrometry
and variable-temperature 1D- and 2D-NMR measurements.
The strict similarity in reactivity of 2a and 2b rules out any
involvement of the anion in the hydrolysis. Complexes 3a and
‡ Crystal data: 2a: C41H35F6P7Ru, M = 959.55, monoclinic, space
˚
group P21/c, a = 11.611(5), b = 14.619(4), c = 24.489(5) A, b =
94.95(3)◦, U = 4141(2) A , Z = 4, T = 293 K, l(Mo-Ka) =
3
˚
0.706 mm−1. 28874 reflections collected, 11949 unique, 6783 (I >
2rI), Rint = 0.033. Final residual was R1 = 0.067 for data with I >
2rI and wR2 = 0.203 for all data. 3a: C41H38F6P4Ru, M = 869.66,
monoclinic, space group P21/c, a = 10.107(1), b = 18.603(2), c =
◦
3
˚
˚
20.228(3) A, b = 95.95(3) , U = 3782.8(8) A , Z = 4, T = 293 K,
l(Mo-Ka) = 0.643 mm−1. 31410 reflections collected, 12180 unique,
8354 (I > 2rI ), Rint = 0.024. PH3 H atom positions refined with one
constraint. Final residual was R1 = 0.055 for data with I > 2rI and
wR2 = 0.173 for all data. CCDC reference numbers 262402 (2a) and
262404 (3a). See http://www.rsc.org/suppdata/dt/b5/b504795a/ for
crystallographic data in CIF or other electronic format.
3b represent rare examples of metal PH3 derivatives.11–17
A
view of the complex cation [CpRu(PPh3)2(PH3)]+, which was
authenticated by X-ray diffraction analysis,‡ is reported in
˚
Fig. 2. The 2.283(1) A Ru–P(PH3) distance in 3a is at the low end
§ Distilled water (1.08 g, 60 mmol) was added to a solution of
1
[CpRu(PPh3)2(g -P4)]PF6 2a (576 mg, 0.60 mmol) in THF or acetone
(50 cm3) and the solution was stirred at room temperature for 2 h
under argon. The solvent was removed under reduced pressure and
the remaining red solid was extracted twice with acetone (2 × 5 cm3)
leaving a reddish solid. [CpRu(PPh3)2(PH3)]PF6 3a was obtained as a
yellowish solid by concentrating the acetone solution. The crude 3a was
recrystallized from CH2Cl2–hexane (420 mg, 80%) (Found: C 56.5; H,
4.5. C41H38F6P4Ru requires C 56.6; H 4.4%). 3b was obtained through the
same workup as 3a (Found: C 57.5; H, 4.6. C42H38F3O3P3RuS requires C
57.7; H 4.4%). dP (121.4 MHz, (CD3)2CO, 25 ◦C, H3PO4; complex cation
A2F pattern) 44.7 (2P, d, 2J(PAPF) 51 Hz, PA), −113.2 (1P, t, PF), −143.1
(1P, sept, 1J(PF) 714 Hz, PF6, only for 3a). dP (121.5 MHz, (CD3)2CO,
25 ◦C, 85% H3PO4; hydrogen coupled, complex cation A2FX3 pattern)
44.8 (2P, d, 2J(PAPF) 51 Hz, PA), −113.1 (1P, qt, 1J(PFH) 358, PF), −143.1
(1P, sept, 1J(PF) 714 Hz, PF6, only for 2a). dH (300.0 MHz, (CD3)2CO,
25 ◦C, TMS) 7.46–7.10 (30H, m, Ph), 4.91 (5H, s, Cp), 4.52 (3H, dt,
1J(HPF) 357 Hz, 3J(HPA) 6 Hz, PH3). The red solid (60 mg) yields a
1 : 1 : 2.5 ratio between hydrogen, phosphorus and oxygen (XPS and
elemental analysis). dP (121.4 MHz, CD2Cl2, 25 ◦C, 85 % H3PO4) broad
band centered at 43.0.
¶ PH3 was gently bubbled for
5 min through a solution of
[CpRu(PPh3)2Cl] (730 mg, 1.00 mmol) and TlPF6 (350 mg, 1.00 mmol)
in a mixture of CH2Cl2 (20 cm3) and THF (30 cm3). The resulting
slurry was stirred at room temperature for 1 h; the precipitated TlCl was
filtered off and yellow microcrystals of 3a were obtained by evaporating
the solvent under reduced pressure. The solid was recrystallized from
CH2Cl2–hexane (850 mg, 98%).
Fig. 2 Structure of the [CpRu◦(PPh3)2(PH3)]+ cation in 3a. Selected
˚
bond lengths (A) and angles ( ): Ru–P1 2.283(1), Ru–P2 2.357(1),
Ru–P3 2.335(1), P1–H 1.27(2); P1–Ru–P2 90.53(3), P1–Ru–P3 95.43(3),
P2–Ru–P3 100.59(3), H–P1–H 94(2).
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2 2 3 5

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2 2 3 6
D a l t o n T r a n s . , 2 0 0 5 , 2 2 3 4 – 2 2 3 6