Reaction of a bulky phosphite with [Ru3(CO)12]: The molecular structure of one of the decomposition products

Article abstract of DOI:10.1016/j.ica.2007.08.008

Mono- and bis-substituted phosphite complexes [Ru₃(CO)_12-x L_x] (L = tris(2,4-di-tert-butylphenyl) phosphite; x = 1, 2) were synthesized by simple substitution reactions, and were characterized by spectroscopic methods. The monosubstituted ruthenium complex disproportionates in acetone producing a mononuclear ruthenium complex as one of the decomposition products. Single crystal X-ray diffraction analysis established the molecular structure of this new compound.

Full text of DOI:10.1016/j.ica.2007.08.008

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Inorganica Chimica Acta 361 (2008) 335–340
www.elsevier.com/locate/ica
Reaction of a bulky phosphite with [Ru3(CO)12]: The molecular
structure of one of the decomposition products
a
b,
b
a,
*
Abraham O. Magwaza , Reinout Meijboom *, Alfred Muller , Ipe J. Mavunkal
a
Department of Chemistry, University of Botswana, P.O. Box 0704, Gaborone, Botswana
Department of Chemistry, University of the Free State, P.O. Box 339, Bloemfontein 9300, South Africa
b
Received 21 May 2007; received in revised form 20 July 2007; accepted 12 August 2007
Available online 21 August 2007
Abstract
Mono- and bis-substituted phosphite complexes [Ru3(CO)12ꢀx Lx] (L = tris(2,4-di-tert-butylphenyl) phosphite; x = 1, 2) were synthe-
sized by simple substitution reactions, and were characterized by spectroscopic methods. The monosubstituted ruthenium complex dis-
proportionates in acetone producing a mononuclear ruthenium complex as one of the decomposition products. Single crystal X-ray
diffraction analysis established the molecular structure of this new compound.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Ruthenium; Phosphite; Cluster; Crystal structure
1. Introduction
mula [M3(CO)12ꢀxLx] (x = 1–3) have been synthesized and
characterized [5]. Many of these phosphine substituted
metal carbonyl complexes have been shown to display cat-
alytic properties [6]. Although a large number of phosphine
derivatives have been synthesized and their properties stud-
ied in detail, similar phosphite complexes are scarce.
Ligand modification is known to bring about interesting
features in the resulting compounds [7], and the bulkiness
of ligands, for example has been shown to direct the reac-
tion pathways in many instances. We focused our interest
first to investigate the reactivity of tris(2,4-di-tert-butylphe-
nyl) phosphite (1) towards CO substitution in the triangu-
lar complexes [M3(CO)12] (M = Ru, Os). Herein, we report
the synthesis and characterization of the above phosphite
substituted complexes of triruthenium dodecacarbonyl
complex.
Transition metal carbonyl cluster compounds have been
widely investigated in the past decades [1]. These complexes
provide interesting scaffolds for organic substrates to adopt
multi-center bonding that could be crucial for their subse-
quent reactivity. Diverse geometries with varying number
of electron counts in these cluster complexes provide good
platforms for a number of interesting transformations that
may not be possible in mononuclear complexes. It is con-
ceivable that the diverse transformations that are possible
on metal cluster complexes make them good candidates
as catalysts [2]. Apart from their potential application in
homogeneous as well as heterogeneous catalysis, transition
metal carbonyl clusters have generated interest in diverse
areas such as materials science, etc. [3].
Substitution chemistry of the triangular metal complexes
[M3(CO)12] (M = Fe, Ru, Os) have been studied in detail
[4], and numerous phosphine substituted complexes of for-
2. Experimental
2.1. Reagents and general procedures
*
Corresponding authors. Tel.: +267 355 2481; fax: +267 355 2836 (I.J.
Mavunkal); tel.: +27 50 401 9526; fax: +27 50 444 6384 (R. Meijboom).
E-mail addresses: meijboomr.sci@mail.ufs.ac.za (R. Meijboom), ma-
vunkal@mopipi.ub.bw (I.J. Mavunkal).
All syntheses of air and moisture sensitive compounds
were performed using standard Schlenk techniques under
0020-1693/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.08.008

336
A.O. Magwaza et al. / Inorganica Chimica Acta 361 (2008) 335–340
prepurified N2 [8]. Dichloromethane was pre-dried by pas-
sage over alumina (neutral, Brockmann grade I) and subse-
quently distilled over CaH2 [9]. [Ru3(CO)12] (Strem),
tris(2,4-di-tert-butylphenyl) phosphite (Aldrich), were used
as received. Me3NO (Aldrich) was sublimed prior to use.
NMR spectra were recorded on a Bruker Avance
300 MHz spectrometer (1H: 300 MHz, 13C: 75.5 MHz,
31P: 121.46 MHz) at ambient temperature, and were refer-
enced relative to TMS (1H and 13C) or 85% H3PO4 (31P),
using the residual protonated impurities in the solvent
(1H NMR: CDCl3: d 7.27) or external 85% H3PO4 (31P).
Infrared spectra were recorded in solution cells of sodium
chloride windows (optical pathlength 0.1 mm) on a Per-
kin-Elmer 2000 FTIR spectrometer. Mass spectrometric
analyses were carried out on a Finnigan LCQ Deca spec-
trometer. Elemental analyses were performed on a Vario
Elemental Analyzer.
2.3. Reaction of 2 with acetone
In an attempt to recrystallize 2 from acetone, a large
amount of black precipitate was formed, as well as well-
shaped colourless needles. Single crystal X-ray diffraction
of the compound revealed 4.
Counter intuitively, recrystallisation of 3 from acetone
did not result in the formation of 4.
2.4. Structure determination
Crystals of [Ru(CO){P(O-2,4-tBu2C6H2)(O-2,4-tBu2-
C6H3)2}(OH2){OC(CH3)2}][O2P(O-2,4-tBu2C6H3)2]
(4),
were grown from acetone as described above. X-ray diffrac-
tion data for 4 were collected on a Bruker X8 APEX II dif-
fractometer using Mo Ka (0.71073 A) radiation with / and
x-scans at 100(2) K. All reflections were merged and inte-
grated using SAINT [10] and were corrected for Lorentz,
polarization and absorption effects using SADABS [10]. The
structures were solved by the direct method using SIR97 [11]
and refined through full-matrix least-squares cycles using
˚
2.2. Reaction of [Ru3(CO)12] with P(O-2,4-tBu2C6H3)3
A mixture of [Ru3(CO)12] (0.104 g,0.162 mmol) and
P(O-2,4-tBu2C6H3)3 (1, 0.409 g, 0.632 mmol) was heated
under reflux in dichloromethane (100 cm3) for 3 h. The
color of the reaction mixture changed from light yellow
to dark red during this time. After cooling, the mixture
was left stirring overnight. The volatiles were removed in
vacuo and the residue dissolved in minimum amount of
hexane. A short silica gel column (1.5 cm · 10 cm) was
used to separate the products formed. The major red frac-
tion, which followed unreacted [Ru3(CO)12] and the phos-
phite ligand, was eluted using hexane and was identified as
the monosubstituted product (2) using spectroscopic meth-
ods. After evaporation of the solvent, 2 was obtained as a
dark red solid (0.110 g; 54%); mCO/cmꢀ1: 2084 (w), 2035 (s),
2013 (s), 2004 (s), 1989 (sh), 1948 (w), 1942 (w), 1813 (w);
dH(CDCl3, 300 MHz): 7.49 (d), 7.36 (d), 6.97 (dd), 1.54
(s), 1.26 (s); dC{H}(CDCl3, 75.5 MHz): 204.4 (–CO),
148.1, 146.3, 138.1, 124.7, 123.3, 119.5 (Ar), 35.1
(–CMe3), 34.1 (–CMe3), 31.3 (–CMe3), 30.5 (–CMe3);
Table 1
Crystal data and structural refinement for 4
4
Empirical formula
Formula weight
Temperature (K)
Wavelength (A)
Crystal system
Space group
C77H118O11P2Ru
1382.72
100(2)
0.71073
triclinic
˚
ꢀ
P1
Unit cell dimensions
˚
a (A)
15.855(5)
16.153(5)
16.688(5)
110.129(5)
99.882(5)
94.148(5)
3913(2)
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
Volume (A )
Z
2
d
P{H}(CDCl3, 121.46 MHz): 128; m/z(ES): 1260 (M+), (at
Dcalc (Mg/m3)
1.173
0.295
1484
0.28 · 0.09 · 0.09
1.32–28.32
Absorption coefficient (mmꢀ1
F(000)
)
least 6 clear peaks corresponding to CO losses were also
observed).
Crystal size (mm3)
The second, yellow band was eluted using 5% dichloro-
methane in hexane and was identified as the bis-substituted
product (3). After evaporation of the solvent, 3 was obtained
as a yellow powder (0.039 g, 13%); Ru3C94O16P2H126
requires: C, 60.15; H, 6.77. Found: C, 60.28; H, 6.57%.
h Range for data collection (ꢁ)
Index ranges
ꢀ21 6 h 6 21, ꢀ21 6 k 6 21,
ꢀ22 6 l 6 22
Reflections collected
58442
Independent reflections [Rint
Completeness to h = 28.32ꢁ
Absorption correction
Maximum and minimum
transmission
]
19421 [0.0542]
99.7%
semi-empirical from equivalents
0.9739 and 0.9219
m
CO/cmꢀ1: 2084 (w), 2030 (m), 2017 (s), 1983 (w), 1948 (w),
1942 (w), 1813 (br, w); dH(CDCl3, 300 MHz): number of
overlapping signals observed between 7.93 and 7.00, 1.59,
1.57, 1.44, 1.28, 1.26, 1.19 (the signals observed between
1.59 and 1.19 are due to the methyl protons); dC{H}(CDCl3,
75.5 MHz): aromatic signals observed between 170 and
110 ppm, the aliphatic signals were observed between 29
and 36 ppm; dP{H}(CDCl3, 121.46 MHz): 148 (d), 126 (d);
m/z(ES): 1877 (M+), (10 peaks corresponding to subsequent
CO losses observed in the mass spectrum).
Refinement method
full-matrix least-squares on F2
19421/14/900
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
1.080
R1 = 0.0452, wR2 = 0.1073
R1 = 0.0710, wR2 = 0.1271
Largest difference in peak and hole 0.887 and ꢀ0.555
ꢀ3
˚
(e A
)

A.O. Magwaza et al. / Inorganica Chimica Acta 361 (2008) 335–340
337
the SHELXL 97 [12] software package with R(jFoj ꢀ jFcj)2
being minimized. All non-H atoms were refined with aniso-
tropic displacement parameters. Aromatic and methyl H
atoms were placed in geometrically idealized positions (C–
from the resonance for the CO carbons) adequately sup-
port the formation of the mono-substituted product 2.
Electrospray mass spectrometry carried out on the red frac-
tion confirmed the suggested molecular formula of 2 as
[Ru3(CO)11{P(OR)3}] (R = ꢀ2,4-di-tert-butylphenyl). A
molecular ion peak around 1260 with subsequent peaks
corresponding to CO losses establishes the molecular for-
mula suggested for this fraction. Our attempts to obtain
meaningful elemental analyses were unfortunately not suc-
cessful. Spectroscopic evidence suggests the formation of
other species upon standing and meaningful elemental
analysis could not be carried out as it was difficult to obtain
a sample with adequate purity. Formation of other species
upon standing also prevented the growth of good single
crystals for X-ray analysis of 2.
˚
H = 0.97–0.98 A) and constrained to ride on their parent
atoms, with Uiso(H) = 1.2Ueq(C) for aromatic and
1.5Ueq(C) for methyl H atoms. The protons of the coordi-
nated aqua moiety were located and refined from the Fou-
rier difference map. The deepest residual electron–density
ꢀ3
˚
˚
hole (ꢀ0.555 e A ) is located 0.29 A from H3A, and the
ꢀ3
˚
˚
highest peak (0.887 e A ) 1.39 A from C77A. The acetone
solvate molecule was modelled disordered over two posi-
tions with a 69.7/30.3% occupancy. The solvate molecule
was restrained to keep the refinement stable.
The DIAMOND [13] Visual Crystal Structure Information
System software was used for the graphics. Crystal data
and details of data collection and refinement are given in
Table 1.
Proton and carbon NMR spectra of the second (yellow)
fraction are indicative of it being the di-substituted prod-
uct, [Ru3(CO)10{P(OR)3}2], 3. Careful examination of both
1
the H and 13C{H} NMR spectra clearly suggest that this
3. Results and discussion
particular product exist in the various possible isomeric
forms. Overlap of multiple signals in the aromatic region
as well as six methyl signals (three sets) in the H NMR
1
3.1. Synthesis and spectroscopy
suggests the compound existing in at least three isomers
(in approximately 2:1.2:1 ratio). This assumption is further
supported by the number of resonances observed in the
13C{H} NMR spectrum. Six resonances each for the quar-
ternary carbon atoms and the methyl carbon atoms of the
tert-butyl group are due to the various isomers being pres-
ent. In a monosubstituted complex, preference for the axial
or equatorial positions in the trimetal unit would depend
largely on the nature of the ligand involved [14]. Additional
ligands create the possibility of the various axial–equatorial
Reaction of an excess of phospite (1) with [Ru3(CO)12]
in dichloromethane under reflux produced mono and bis
substituted products (Scheme 1).
The two fractions collected were characterized by spec-
troscopic methods as well as by elemental analyses. IR
spectroscopy of the first, red band, which is presumed to
be the mono-substituted compound [Ru3(CO)11{P(OR)3}]
(2) (R = -2,4-di-tert-butylphenyl) showed bands in the
infrared spectrum that can be assigned as absorption due
to terminal CO groups. The second, yellow, product (3)
showed a simpler IR m(CO) spectrum.
combinations.
A ‘Star-of-David’ disorder has been
reported for the known phosphite complex [Ru3(CO)10-
{P(OMe)3}2] [15]. Two signals, at d 148 and 126 ppm, in
the 31P{H} NMR spectrum provides additional evidence
to the bis-substituted complex. These two signals appear
as doublets with a coupling constant of 72 Hz. Electro-
spray mass spectrometric analysis shows the expected
molecular ion peak at m/z 1877 along with a number of
peaks corresponding to subsequent loss of CO molecules.
Elemental analysis confirms the molecular formula
deduced from the various spectroscopic data.
The red compound (2) initially appeared to decompose
in acetone solution over a period of several days. Upon
inspection of a sample, colorless needles were observed
between the black decomposition product. X-ray diffrac-
tion showed these colorless crystals to be compound 4.
1
The H NMR spectrum of 2 consists of two sets of res-
onances due to the aromatic and aliphatic protons. As
expected, three sets of resonances are observed for the three
aromatic protons, which show a very small shift upon coor-
dination of the phosphite ligand to the metal. However, the
methyl signals from the tert-butyl groups experience signif-
icant change in their chemical shift compared to that of the
free ligand. The two signals for the methyl groups in the
coordinated ligand (in 2) are observed at d 1.54 and
1.26 ppm, as opposed to d 1.40 and 1.31 ppm for the free
ligand. A single resonance at d 128 ppm in the 31P{H}
NMR spectrum and the expected number of resonances
in the 13C{H} NMR spectrum (six signals for the aromatic
carbons and four signals for the tert-butyl carbons apart
Ru
Ru
Ru
CO
excess L
+
L =
P
O
3
Ru
Ru
L Ru
Ru
Ru
Ru
L
L
Scheme 1. Reaction of [Ru3(CO)12] with P(O-2,4-tBu2C6H3)3 (L).

338
A.O. Magwaza et al. / Inorganica Chimica Acta 361 (2008) 335–340
t
-Bu
t
-Bu
t
-Bu
t
-Bu
O
t
-Bu
O
t
-Bu
Ru
2
O
O
P
O
t-Bu
O
P
t-Bu
Ru
O
O
O
t-Bu
OH2
C
CO
Ru
Ru L
O
t
-Bu
L =
P
O
4
Scheme 2. Reaction of 3 with acetone. L = P(O-2,4-tBu2C6H3)3.
˚
We are currently in the process of exploring ways to syn-
thesize compound 4 independently and will report the
details later (see Scheme 2).
to the Ru–C bond distance of 2.12(4) A, reported previ-
ously [16] for a dimeric ortho-metallated structure.
Classical intra- and inter-molecular hydrogen bonding is
observed between the coordinated aqua (O2) and the
P(1) = O(10) oxygen (see Table 3). These interactions cause
a pseudo-dimerisation between two molecules situated
around the inversion center. The same P(1) = O(10) oxygen
shows an intermolecular close contact with the coordinated
acetone moiety (Table 3).
3.2. Solid state structure of 4
A molecular diagram showing the numbering scheme
of the title compound [Ru(CO){P(O-2,4-tBu2C6H2)(O-2,
4-tBu2C6H3)2}(OH2){OC(CH3)2}][O2P(O-2,4-tBu2C6H3)2]
(4), is presented in Fig. 1, with selected bond lengths, angles
and torsion angles in Table 2 and the hydrogen bonding
interactions in Table 3. The compound 4, crystallizes in
The ruthenium atom in 4 is in a formal oxidation state
of 2+. Intermolecular ring-closure is observed in the struc-
ture of 4, accounting for one electron. The complete Ru
fragment is cationic with the PO2(OR)2 moiety functioning
as a mono-anionic ligand. Clearly these reactions were nec-
essary in order to stabilize the charge on ruthenium.
Surprisingly no disorder of the tert-butyl groups was
found in the structure of 4. Previously, we reported the
structures of Co [17] and Rh [18] compounds containing
the same phosphite ligand. In solving these structures we
ꢀ
the triclinic space group P1 with Z = 2. The molecule lies
on a general position in the asymmetric unit. All angles
within the Ru coordination polyhedron show a slightly dis-
torted octahedral environment (Table 2). Intermolecular
ring closing of the coordinated phophite ligand via agnostic
intermediates is well known for ruthenium compounds.
˚
The Ru–C(39) bond distance of 2.066(3) A is comparable
Fig. 1. Molecular structure of 4 (50% probability). H atoms have been omitted for clarity.

A.O. Magwaza et al. / Inorganica Chimica Acta 361 (2008) 335–340
339
Table 2
˚
Selected interatomic bond distances (A) and angles (ꢁ) for 4
Distances
Ru–C(1)
Ru–C(39)
Ru–O(8)
P(1)–O(7)
P(1)–O(9)
P(2)–O(4)
1.817(3)
2.066(3)
2.1468(17)
1.5880(17)
1.6005(18)
1.5997(19)
Ru–P(2)
2.1783(8)
Ru–O(2)
Ru–O(1)
P(1)–O(8)
P(1)–O(10)
2.1979(18)
2.2175(18)
1.4940(18)
1.4950(18)
Angles
O(3)–C(1)–Ru
C(34)–C(39)–Ru
O(6)–P(2)–Ru
177.0(2)
119.70(17)
109.60(7)
C(2)–O(1)–Ru
C(39)–C(34)–O(6)
138.53(18)
116.6(2)
Torsion angles
C(39)–Ru–P(2)–O(6)
O(8)–Ru–P(2)–O(6)
O(1)–Ru–P(2)–O(6)
ꢀ0.63(10)
ꢀ92.58(9)
ꢀ172.57(9)
O(2)–Ru–P(2)–O(4)
O(2)–Ru–P(2)–O(6)
O(2)–Ru–P(2)–O(5)
ꢀ134.2(4)
ꢀ22.6(4)
96.5(4)
Table 3
a phosphite ligand, leading to the formation of [{P(O-
2,4-tBu2C6H3)3}2Ru{O@C(CH3)2} (CO)3]. This intermedi-
ate is unstable and intermolecular CH activation with the
concomitant loss of one CO starts the oxidation process.
Cyclometallation in Ru(II) compounds is fairly common
[20]. The Ru(I) intermediate is further oxidised by the trip-
hosphite ligand which is reduced to a diphosphite ligand
(see Scheme 3).
˚
Selected inter- and intra-molecular hydrogen interactions (A) and angles
(ꢁ) for, 4
D–H. . .A
d(D–H) d(H. . .A) d(D. . .A) \(DHA)
O(2)–H(1W) . . . O(10)
O(2)–H(2W) . . . O(10)#1 0.78(4)
C(3)–H(3A) . . . O(10)#1
C(38)–H(38) . . . O(2)
0.97(4)
1.74(4)
2.00(4)
2.56
2.681(3)
2.754(3)
3.156(3)
3.176(3)
161(3)
162(4)
119.3
120.4
0.98
0.95
2.59
Symmetry transformations used to generate equivalent atoms: #1 ꢀx + 1,
ꢀy + 1, ꢀz + 1.
4. Conclusions
The reaction of [Ru3(CO)12] clusters with the bulky
phosphite P(O-2,4-tBu2C6H3)3 in dichloromethane under
reflux produced the mono-phosphite cluster [Ru3(CO)11L]
and the bis-phosphite cluster [Ru3(CO)10L2]. The former
cluster compound is unstable in acetone solution and
decomposes to form metallic ruthenium and a monometal-
lic ruthenium compound. An X-ray crystallographic analy-
sis establishes cyclometallation in this monometallic
ruthenium decomposition product.
observed that especially the 4-tert-butyl groups tend to dis-
order over two different positions.
3.3. Possible mechanism for the formation of 4
Compound 2 in solutions of hexane or methylene chlo-
ride undergoes disproportionation forming small amounts
of the bis-substituted complex 3 along with small amounts
of decomposition products. Cleavage of metal–metal
bonds, initiated by solvation of acetone, has been suggested
in a number of mechanistic studies [19]. It is conceivable
that coordination of an acetone molecule, upon the
metal–metal cleavage, caused a complete degradation of
the triangular cluster. Free phosphite in the reaction mix-
ture is a logical result of the degradation of the cluster,
which then could add to a ruthenium fragment containing
Acknowledgements
Financial assistance from the Research and Publication
Committee, University of Botswana, South African Na-
tional Research Foundation, THRIP and the Research
Fund of the University of the Free State and SASOL is
t-Bu
t
-Bu
t
-Bu
t
-Bu
t
-Bu
O
O
Ru
2
t
-Bu
CO
O
OCMe2
L
O
P
O
t-Bu
OC
OC
O
P
t
-Bu
Ru
L
Ru
O
O
O
t-Bu
OH2
C
Ru
Ru
L
O
CO
t
-Bu
L =
P
O
4
3
Scheme 3. Possible mechanism for the formation of 4.

340
A.O. Magwaza et al. / Inorganica Chimica Acta 361 (2008) 335–340
[5] (a) Y.L. Shi, Y.-C. Gao, Q.-Z. Shi, D.L. Kershner, F. Basolo,
Organometallics 6 (1987) 1528;
(b) S.E. Kabir, M.B.H. Howlader, Ind. J. Chem., Sec. A 28 (1989)
47.
[6] (a) G. Gervasio, R. Giordano, D. Marabello, E. Sappa, J. Organo-
met. Chem. 588 (1999) 83;
gratefully acknowledged. Part of this material is based on
work supported by the South African National Research
Foundation (SA NRF, GUN 2038915). Opinions, findings,
conclusions or recommendations expressed in this material
are those of the authors and do not necessarily reflect the
views of the NRF. We (R.M., A.M.) are grateful to Profes-
sor A. Roodt (University of the Free State) for the freedom
to pursue our own research within his group.
(b) B. Fontal, M. Reyes, T. Suarez, F. Bellandi, N. Ruiz, J. Mol.
Catal. A 149 (1999) 87.
[7] P. Braunstein, J. Organomet. Chem. 689 (2004) 3953.
[8] (a) D.F. Shriver, M.A. Drezdzon, The Manipulation of Air-sensitive
Compounds, Wiley-Interscience, New York, 1986;
(b) R.J. Errington, Advanced Practical Inorganic and Metallorganic
Chemistry, Blackie Academic, London, 1997.
Appendix A. Supplementary material
[9] D.D. Perrin, W.L.F. Armarego, Purification of Laboratory Chemi-
cals, Pergamon Press, Oxford, 1988.
[10] Bruker, 2004. SAINT-PLUS (Version 7.12), XPREP and SADABS (Version
2004/1). Bruker AXS Inc., Madison, WI, USA.
[11] A. Altomare, M.C. Burla, M. Camalli, G.L. Cascarano, C. Giaco-
vazzo, A. Guagliardi, A.G.G. Moliterni, G. Polidori, R. Spagna, J.
Appl. Cryst. 32 (1999) 115.
[12] G.M. Sheldrick, SHELXL97, Program for Solving Crystal Structures,
University of Go¨ttingen, Go¨ttingen, Germany, 1997.
[13] K. Brandenburg, H. Putz, DIAMOND, 2005, Version 3.0c. Crystal
Impact GbR, Bonn, Germany.
CCDC 647378 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.ica.2007.08.
008.
[14] A.J. Deeming, in: E.W. Abel, F.G.A. Stone, G. Wilkinson (Eds.),
Comprehensive Organometallic Chemistry II, vol. 7, Pergamon Press,
Oxford, UK, 1995.
References
[15] M.I. Bruce, J.G. Matisons, B.W. Skelton, A.H. White, J. Chem. Soc.,
Dalton Trans. (1983) 2375.
[16] M.I. Bruce, J. Howard, I.W. Nowell, G. Shaw, P. Woodward, J.
Chem. Soc. Chem. Commun. (1972) 1041.
[17] R. Meijboom, M. Haumann, A. Roodt, L. Damoense, Helv. Chim.
Acta 88 (2005) 676.
[18] R. Crous, M. Datt, D. Foster, L. Bennie, C. Steenkamp, J. Huyser, L.
Kirsten, G. Steyl, A. Roodt, Dalton Trans. (2005) 1108.
[19] D. Blazina, S.B. Duckett, P.J. Dyson, B.F.G. Johnson, J.A.B.
Lohman, C.J. Sleigh, J. Am. Chem. Soc. 123 (2001) 9760.
[20] L.N. Lewis, J.F. Smith, J. Am. Chem. Soc. 108 (1986) 2728.
[1] (a) P. Braunstein, L.A. Oro, P.R. Raithby (Eds.), Metal Clusters in
Chemistry, Wiley-VCH, New York, 1999;
(b) P.J. Dyson, J.S. McIndoe (Eds.), Transition Metal Carbonyl
Cluster Chemistry, Gordon and Breach, Amsterdam, 2000.
[2] R. Whyman, in: B.F.G. Johnson (Ed.), Transition Metal Clusters,
Wiley Interscience, Chichester, 1980.
[3] S. Dehnen, M. Melullis, Coord. Chem. Rev. 251 (2007) 1259.
[4] K.H. Whitmire, in: E.W. Abel, F.G.A. Stone, G. Wilkinson (Eds.),
Comprehensive Organometallic Chemistry II, vol. 7, Pergamon Press,
Oxford, UK, 1995.