Ruthenium carbonyl clusters derived from pyrazolyl substituted diphosphazanes: Crystal and molecular structure of a triruthenium cluster featuring a triply bridging μ3-η1: η1:η1 coordination mode of pyrazolate moiety

Article abstract of DOI:10.1016/j.jorganchem.2005.06.047

The radical initiated reactions of Ru₃(CO)₁₂ with pyrazolyl substituted diphosphazanes Ph₂PN(R)PPh(N₂C ₃HMe₂-3,5) [R = (S)-*CHMePh (1) or CHMe₂ (2)] proceed via P-N(pyrazole) bond rupture resulting in the formation of phosphido clusters, [Ru₃(CO)₅(μ_sb-CO) ₂(μ₃-N,N′-η¹:η¹: η¹-N₂C₃HMe₂-3,5){μ-P, P′-Ph₂PN(R)PPh}] [R = (S)-*CHMePh (3) or CHMe₂ (4)]. The pyrazolate moiety adopts an unusual triply bridging μ₃-η¹:η¹:η¹-mode of coordination in these clusters.

Full text of DOI:10.1016/j.jorganchem.2005.06.047

Journal of Organometallic Chemistry 691 (2006) 224–228
www.elsevier.com/locate/jorganchem
Ruthenium carbonyl clusters derived from pyrazolyl substituted
diphosphazanes: Crystal and molecular structure of a
triruthenium cluster featuring a triply bridging l3-g1:g1:g1
q
coordination mode of pyrazolate moiety
,1
*
Thengarai S. Venkatakrishnan, Munirathinam Nethaji, Setharampattu S. Krishnamurthy
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012, India
Received 14 February 2005; accepted 28 June 2005
Available online 4 October 2005
Abstract
The radical initiated reactions of Ru3(CO)12 with pyrazolyl substituted diphosphazanes Ph2PN(R)PPh(N2C3HMe2-3,5) [R = (S)-
*CHMePh (1) or CHMe2 (2)] proceed via P–N(pyrazole) bond rupture resulting in the formation of phosphido clusters,
[Ru3(CO)5(lsb-CO)2(l3-N,N0-g1:g1:g1-N2C3HMe2-3,5){l-P,P0-Ph2PN(R)PPh}] [R = (S)-*CHMePh (3) or CHMe2 (4)]. The pyrazolate
moiety adopts an unusual triply bridging l3-g1:g1:g1-mode of coordination in these clusters.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Ruthenium carbonyl clusters; P–N ligands; Phosphane–phosphido clusters, Chirality; l3-g1:g1:g1-Pyrazolyl coordination
1. Introduction
reactions of metal carbonyl clusters with various ligands
is cluster degradation; use of bidentate ligands of the type
L–X–L (where L carries a group 14, 15 or 16 donor atom
and X is C, N or O) can obviate this difficulty to a large ex-
tent [1].
There has been an increasing interest in the area of metal
clusters in recent years for a variety of reasons, especially
the use of metal clusters in catalysis [1]. Homogeneous
catalysis by metal clusters holds great promise as it has
the advantage of cooperative effects of several metal atoms
held in close proximity to each other. The reactivity and
selectivity of the cluster catalysts can be altered by appro-
priate ligand design. The synthesis of a large number of me-
tal carbonyl clusters bearing a variety of ligands and the
use of some of these clusters in homogeneous catalysis
are well documented [1–3]. A major impediment in the
Recently, we have reported the synthesis and character-
ization of ruthenium carbonyl clusters of diphosphazanes
bearing axially chiral 1,10-binaphthylene-2,20-dioxy moiety
[4], and found that the cluster nuclearity is preserved by
diphosphazanes containing a strong p-acceptor phospho-
rus and also bearing sterically bulky substituents. We have
also reported the chalcogen bridged ruthenium carbonyl
clusters derived from diphosphazane mono- and dichalcog-
enides [5]. In an attempt to prepare chiral clusters bearing a
stereogenic phosphorus centre, and in continuation of our
research program on the organometallic chemistry of
diphosphazane ligands [6], we report here the reactions of
pyrazolyl substituted diphosphazanes Ph2PN(R)PPh-
(N2C3HMe2-3,5) [R = (S)-*CHMePh (SCRP)-(1) or CHMe2
(2)] with Ru3(CO)12.
q
Part 24 of the series ‘‘Organometallic chemistry of diphosphazanes’’;
for Part 23, see [5b].
*
Corresponding author. Tel.: +91 80 2293 2401; fax: +91 80 2360 0683/
23601552.
E-mail address: sskrish@ipc.iisc.ernet.in (S.S. Krishnamurthy).
INSA Senior Scientist.
1
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.06.047

T.S. Venkatakrishnan et al. / Journal of Organometallic Chemistry 691 (2006) 224–228
225
3
2. Experimental
N2C3HMe2-3,5), 1.33 (d, J(H,H) = 7.0 Hz, CH3, CHMe-
Ph). 31P{1H} NMR (CDCl3, ppm) for 3a and 3b: 3a (major
2
2.1. General
diastereomer) 333.4 (d, J(P,P) = 43.6 Hz, PPh), 76.0 (d,
PPh2); 3b (minor diastereomer) 333.9 (d, 2J(P,P) =
All reactions and manipulations were carried out under
an atmosphere of dry nitrogen using standard Schlenk and
vacuum-line techniques. The solvents were purified by
standard procedures and distilled under nitrogen prior to
use. The NMR spectra (1H, 31P{1H}) were recorded in
CDCl3 at 298 K using Bruker Avance-400 MHz spectrom-
eters. IR spectra were recorded using a Bruker FT-IR spec-
trometer as a thin film on a KBr disk. Elemental analyses
were carried out using a Perkin–Elmer 2400 CHN analyser.
Melting points were recorded in a Buchi B-540 melting
point apparatus and were uncorrected. The ligands
(SCRP)-1 [7] and 2 [8] were prepared by previously reported
procedures. Me3NO (Aldrich) and Ru3(CO)12 (Strem
Chemicals) were used as received.
43.6 Hz, PPh), 72.7 (d, PPh2).
2.4. Ru3(CO)5(lsb-CO)2{l3-N,N0-g1:g1:g1-N2C3HMe23,5}-
{l-P,P0-Ph2PN(R)PPh}] (R = CHMe2) (4):
Yield: 0.009 g (12%). Anal. Calc. for C33.5H32N3O8-
P2Ru3Cl: C, 40.0; H, 3.2; N, 4.2; Found: C, 39.2; H, 2.6;
N, 4.3%. M.p 186–188 ꢁC (d). IR (neat, mCO cmꢀ1):
2042(s), 1990(vs), 1976(w, sh), 1957(w, br), 1929(m),
1887(m, br), 1793(s, br, lsb-CO). 1H NMR (400 MHz,
CDCl3, ppm): 5.28 (s, CH, N2C3HMe2-3,5), 3.30 (m, CH,
CHMe2), 1.63, 1.43 (s, CH3, N2C3HMe2-3,5), 0.95, 0.80
(d, 3J(H,H) = 7.0 Hz, CH3, CHMe2). 31P{1H} NMR
2
(CDCl3, ppm): 331.3 (d, J(P,P) = 43.0 Hz, PPh), 69.0 (d,
PPh2).
2.2. Ru3(CO)5(lsb-CO)2{l3-N,N0-g1:g1:g1-N2C3HMe23,5}-
{l-P,P0-Ph2PN(R)PPh}] (3, 4)
2.5. X-ray crystallography
To a solution of Ru3(CO)12 (0.050 g, 7.82 · 10ꢀ5 mol) in
THF (6 cm3) were added a few drops of Bruce catalyst [9]
using a syringe until the solution darkened. Immediately
the ligand (0.040 g of 1 or 0.035 g of 2, 7.82 · 10ꢀ5 mol)
was added. The resulting solution was heated under reflux
for 2 h. The 31P{1H} NMR spectrum of the reaction mix-
ture revealed the presence of several products. Solvent
was evaporated from the reaction mixture in vacuo to ob-
tain a dark colored residue. The residue was dissolved in
dichloromethane (2 cm3) and subjected to chromato-
graphic separation by thin layer chromatography over sil-
ica gel using CH2Cl2/petrol (1:1 v/v) as eluant. The red
orange band at Rf = 0.70 was isolated and the product ex-
tracted into dichloromethane. Evaporation of the solvent
afforded a dark red residue which was crystallized from
dichloromethane–petrol to yield the compounds, [Ru3-
(CO)5(lsb-CO)2{l3-N,N0-g1:g1:g1-N2C3HMe2-3,5}{l-P,P0-
Ph2PN(R)PPh}] [R = (S)-*CHMePh (3) or CHMe2 (4)] as
dark red orange solids. Efforts to isolate the other prod-
uct(s) from the reaction mixture were unsuccessful.
The crystal was mounted on a glass fibre and the inten-
sity data was obtained at room temperature from a Bruker
SMART APEX CCD diffractometer equipped with fine fo-
cus 1.75 kW sealed tube Mo Ka X-ray source with increas-
ing x (width of 0.3ꢁ/frame) at a scan speed of 5 s/frame.
The SMART [10a] software was used for cell-refinement
and data acquisition and the SAINT [10b] software was used
for data reduction. Lorentzian and polarization corrections
were made on the intensity data. An absorption correction
was made on the intensity data using the SADABS [10c] pro-
gram. The structure was solved using SHELXTL [10d] and the
WINGX graphical user interface [11]. Least-square refine-
ments were performed by the full-matrix method with
SHELXL-97 [12]. All non-hydrogen atoms were refined aniso-
tropically and hydrogen atoms were refined isotropically
and were fixed at idealised positions. The carbon atom
C(21) attached to C(19) was disordered over two sites
and was modelled with 50:50 occupancy. Hence, the hydro-
gen atom bound to C(19) was not fixed. The lattice held
water and the solvent dichloromethane molecules were re-
fined separately during final refinement cycles. The carbon
and chlorine atoms of the solvent dichloromethane were re-
fined isotropically. The hydrogen atoms of the lattice held
dichloromethane and water were not located.
2.3. Ru3(CO)5(lsb-CO)2{l3-N,N0-g1:g1:g1-N2C3HMe23,5}-
{l-P,P0-Ph2PN(R)PPh}] (R = (S)-*CHMePh)-
{(SCRP)-(3a) and (SCSP)-(3b)}
Yield: 0.008 g (10%). Anal. Calc. for C38H31N3O7P2Ru3:
C, 45.3; H, 3.1; N, 4.2; Found: C, 44.7; H, 3.1; N, 4.0%.
M.p. 181–183 ꢁC (d). IR (neat, mCO cmꢀ1): 2040(w),
2025(m), 1991(vs), 1976(w), 1953(sh), 1930(w), 1892(w,
br), 1791(s, br, lsb-CO). 1H NMR (400 MHz, CDCl3,
ppm) for 3a and 3b: 3a (major diastereomer) 5.27 (s, CH,
N2C3HMe2-3,5), 3.90 (m, CH, CHMePh), 1.59, 1.46 (s,
CH3, N2C3HMe2-3,5), 1.44 (d, 3J(H,H) = 7.0 Hz, CH3,
CHMePh); 3b (minor diastereomer) 5.23 (s, CH,
N2C3HMe2-3,5), 4.20 (m, CH, CHMePh), 1.38 (s, CH3,
3. Results and discussion
In contrast to the reactivity of diphosphazanes reported
earlier [4], the unsymmetrical pyrazolyl substituted diphos-
phazanes Ph2PN(R)PPh(N2C3HMe2-3,5) [R = (S)-*CHMe-
Ph (SCRP)-(1), CHMe2 (2)] display a different type of
reactivity towards Ru3(CO)12. The reaction of Ru3(CO)12
with an equimolar quantity of the diphosphazane 1 or 2
in the presence of benzophenone-ketyl radical in boiling
THF results in the formation of several products from

226
T.S. Venkatakrishnan et al. / Journal of Organometallic Chemistry 691 (2006) 224–228
which the phosphido clusters, [Ru3(CO)5(lsb-CO)2(l3-
N,N0-g1:g1:g1-N2C3HMe2-3,5){l-P,P0-Ph2PN(R)PPh}]
[R = (S)-*CHMePh (3) or CHMe2 (4)] could be isolated in
low yields after chromatographic separation (Scheme 1).
These clusters have been characterized by elemental analy-
ses, IR and NMR (1H and 31P{1H}) spectroscopic tech-
niques. The molecular structure of 4 has been determined
by single crystal X-ray crystallography [13]. Evidently, P–
N(pyrazolyl) bond has cleaved to give phosphido and pyr-
azolate moieties which bind to the Ru centres. The infrared
spectrum of the cluster 3 or 4 displays bands in the region
2042–1790 cmꢀ1. The band at 1790 cmꢀ1 is assigned to the
semi-bridging carbonyl ligand. The 31P{1H} NMR spec-
trum of cluster 4 displays an AX spin system. The
‘‘PPh2’’ phosphorus appears as a doublet at 69.0 ppm while
the ‘‘PPh’’ phosphorus resonates very much downfield at
331.3 ppm. The chemical shift of PPh2 phosphorus is very
much downfield shifted compared to the free ligand. The
reaction of the diastereomerically pure diphosphazane
(SCRP)-Ph2PN((S)-*CHMePh)PPh (N2C3HMe2-3,5) (1)
with Ru3(CO)12 gives a mixture of two diastereomeric
clusters, 3a and 3b. The formation of two diastereomers
arises due to P–N bond rupture, which can lead to either
retention (RP) or inversion (SP) of configuration at the
phosphorus. Tentatively, the major diastereomer 3a is as-
signed the SCRP configuration and the minor diastereomer
3b the SCSP configuration. The 31P{1H} NMR spectrum of
the mixture consists of two AX spin systems. The ‘‘PPh’’
phosphorus of the major and minor diastereomers appear
at 333.4 and 333.9 ppm, respectively while the resonances
at 76.0 and 72.7 ppm are assigned to the ‘‘PPh2’’ phospho-
rus of the major and minor diastereomers respectively. The
1H NMR spectrum displays two sets of resonances
corresponding to the two diastereomers. From the relative
integrated intensities of the two sets of signals in the 1H and
31P NMR spectra of the reaction mixture, we can estimate
that the two diastereomers are formed in the ratio 1.0:2.2.
Attempts to separate the diastereomers were unsuccessful.
The structure of 4 has been determined by a single crys-
tal X-ray diffraction study (Fig. 1). The compound crystal-
lises in the space group C2/c. The molecule has a triangular
arrangement of three ruthenium atoms bearing a triply
bridging pyrazolate group, two semi-bridging carbonyl li-
gands and a diphosphorus species in both chelating and
bridging mode of coordination. One of the nitrogen atoms
of the pyrazolate group is bonded to one ruthenium while
the other nitrogen atom is bonded to the other two ruthe-
nium centres. To our knowledge, such a l3-g1:g1:g1 mode
of coordination of a pyrazolate ligand has been observed
previously only in two instances, viz for a thallium complex
and a trinuclear rhenium complex [14]. This unusual fea-
ture may be contrasted with the common l-g1:g1 and the
other less-common (l-g1:g2, l-g2:g2, l3-g1:g2:g1, etc.),
Fig. 1. Molecular structure of [Ru3(CO)5(lsb-CO)2(l3-N,N0-g1:g1:g1-
N2C3HMe2-3,5){l-P,P0-Ph2PN(CHMe2)PPh}] Æ 0.5 CH2Cl2 Æ H2O (4).
Thermal ellipsoids are shown at 30% probability level. The carbon atom
C(21a), lattice held solvent molecules (dichloromethane and water) and
the hydrogen atoms are not shown for clarity.
R
PPh2
N
R
N
Ph
(i)
P
Ru
+
Ru3(CO)12
Ph2P
P
Ph
Ru
N
N
Ru
N
N
R = (S)-*CHMePh (SCRP) (1)
R = CHMe2 (2)
= CO
_
.
3 a; R = (S)-*CHMePh (SCRP)
b; R = (S)-*CHMePh (SCSP)
4; R = CHMe2
(i) Ph2CO, THF, 70 0C, 2 h
Scheme 1. Reaction of pyrazolyl substituted diphosphazanes, Ph2PN(R)PPh(N2C3HMe2-3,5) with Ru3(CO)12
.

T.S. Venkatakrishnan et al. / Journal of Organometallic Chemistry 691 (2006) 224–228
227
bridging modes of binding observed in pyrazolate coordi-
nation chemistry [15,16]. The pyrazolate group in 4 is
inclined at an angle of 80.1(2)ꢁ to the triruthenium plane
and the two nitrogen atoms of this group are at a distance
graphic Data Centre as supplementary publication no.
CCDC-259131. Copies of the data can be obtained free
of charge from the Director, CCDC, 12, Union Road,
Cambridge, CB2 1EZ, UK (fax: +44 1223 336033); e-mail:
deposit@ccdc.cam.ac.uk or www: http://www.ccdc.cam.
ac.uk.
˚
of 1.716(4) and 1.957(4) A from the Ru3 plane. The phos-
phido phosphorus atom of the bidentate diphosphorus
ligand occupies the equatorial position and is coordinated
to two ruthenium centres. The ‘‘PPh2’’ phosphorus occu-
pies a pseudo-axial position. The span angle of the
‘‘P–N–P’’ backbone is 99.3(2)ꢁ and the bite angle at
Ru(1) is 69.03(5)ꢁ. The coordination geometry around
Ru(2) and Ru(3) ruthenium centres can be regarded as dis-
torted octahedral. All the Ru–Ru bond distances are differ-
Acknowledgments
We thank the Department of Science and Technology,
New Delhi, India for financial support and for the data col-
lection using the CCD X-ray facility, IISc, Bangalore set up
under IRHPA program.
˚
ent. The longest Ru–Ru bond [2.916(2) A] is the one that
bears the bidentate ligand; the phosphido phosphorus is
doubly coordinated to these two ruthenium centres. The
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˚
˚
1005.22; Unit cell dimensions a = 34.80(3) A, b = 13.35(1) A,
˚
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4. Supplementary material
Crystallographic data for the structure reported in this
paper has been deposited with the Cambridge Crystallo-

228
T.S. Venkatakrishnan et al. / Journal of Organometallic Chemistry 691 (2006) 224–228
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(i) M.A. Bennett, D.E. Berry, T. Dirnberger, D.C.R. Hockless, E.
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[18] The reaction of the diphosphazane monosulfide, Ph2(S)PN(CHMe2)-
PPh(N2C3HMe2-3,5) [8] with Ru3(CO)12 in the presence of TMNO
also gives a phosphido cluster which is formulated as [Ru3(CO)4-
(l-CO)(l3-S){l-P,P0-Ph2PN(R)PPh}(l3-N,N0-g1:g1:g1-N2C3HMe2-3,
5)] on the basis of IR {2048(s), 1981(vs), 1805(m, br)} and 31P NMR
{331.3 (d, 2J(P,P) = 43.0 Hz, PPh), 69.0 (d, PPh2)} spectroscopic
data; such a cluster is formed as a result of P–N bond cleavage and
oxidative sulfur transfer [5].
(b) G.B. Deacon, A. Gitlits, P.W. Roesky, M.R. Burgstein, K.C.
¨
Lim, B.W. Skelton, A.H. White, Chem. Eur. J. 7 (2001) 127;
(c) G.B. Deacon, C.M. Forsyth, A. Gitlits, R. Harika, P.C. Junk,
B.W. Skelton, A.H. White, Angew. Chem. Int. Ed. 41 (2002) 3249;
(d) C. Yelamos, M.J. Heeg, C.H. Winter, Inorg. Chem. 37 (1998) 3892.
[17] (a) D. Cauzzi, C. Graiff, C. Massera, G. Predieri, A. Tiripicchio, J.
Cluster Sci. 12 (2001) 259;
´
(b) E. Simon-Manso, C.P. Kubiak, Inorg. Chem. Commun. 6 (2003)
1096;