Chalcogen-capped ruthenium carbonyl clusters derived from diphosphazane mono- and dichalcogenides of the type X2P(E)N(R)PX2 and X2P(E)N(R)P(E)X2 (E = S or Se)

Article abstract of DOI:10.1016/j.jorganchem.2005.05.041

Reactions of Ru₃(CO)₁₂ with diphosphazane monoselenides Ph₂PN(R)P(Se)Ph₂ [R = (S)-*CHMePh (L⁴), R = CHMe₂ (L⁵)] yield mainly the selenium bicapped tetraruthenium clusters [Ru

Full text of DOI:10.1016/j.jorganchem.2005.05.041

Journal of Organometallic Chemistry 690 (2005) 4001–4017
www.elsevier.com/locate/jorganchem
Chalcogen-capped ruthenium carbonyl clusters derived from
diphosphazane mono- and dichalcogenides of the
q
type X2P(E)N(R)PX2 and X2P(E)N(R)P(E)X2 (E = S or Se)
,1
*
Thengarai S. Venkatakrishnan, Setharampattu S. Krishnamurthy
Munirathinam Nethaji
,
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012, India
Received 4 March 2005; accepted 6 May 2005
Available online 14 July 2005
Abstract
Reactions of Ru3(CO)12 with diphosphazane monoselenides Ph2PN(R)P(Se)Ph2 [R = (S)- CHMePh (L4), R = CHMe2 (L5)] yield
*
mainly the selenium bicapped tetraruthenium clusters [Ru4(l4-Se)2(l-CO)(CO)8{l-P,P-Ph2PN(R)PPh2}] (1, 3). The selenium mono-
capped triruthenium cluster [Ru3(l3-Se)(lsb-CO)(CO)7{j2-P,P-Ph2PN((S)- CHMePh)PPh2}] (2) is obtained only in the case of L4.
*
An analogous reaction of the diphosphazane monosulfide (PhO)2PN(Me)P(S)(OPh)2 (L6) that bears a strong p-acceptor phosphorus
shows a different reactivity pattern to yield the triruthenium clusters, [Ru3(l3-S)(l3-CO)(CO)7{l-P,P-(PhO)2PN(Me)P(OPh)2}] (9)
(single sulfur transfer product) and [Ru3(l3-S)2(CO)5{j2-P,P-(PhO)2PN(Me)P(OPh)2}{l-P,P-(PhO)2PN(Me)P(OPh)2}] (10) (double
sulfur transfer product). The reactions of diphosphazane dichalcogenides with Ru3(CO)12 yield the chalcogen bicapped tetraruthe-
nium clusters [Ru4(l4-E)2(l-CO)(CO)8{l-P,P-Ph2PN(R)PPh2}] [R = (S)- CHMePh, E = S (6); R = CHMe2, E = S (7); R = CHMe2,
*
E = Se (3)]. Such a tetraruthenium cluster [Ru4(l4-S)2(l-CO)(CO)8{l-P,P-(PhO)2PN(Me)P(OPh)2}] (11) is also obtained in small
quantities during crystallization of cluster 9. The dynamic behavior of cluster 10 in solution is probed by NMR studies. The struc-
tural data for clusters 7, 9, 10 and 11 are compared and discussed.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Ruthenium; Cluster compounds; P ligands; Chalcogen clusters; Cluster dynamics; X-ray crystallography
1. Introduction
clusters have the ability to add or remove ligands or
electrons while still retaining their integrity. Such chal-
cogen bridged clusters can be regarded as models for
extended inorganic solids [4] and have been utilized
for cluster growth reactions [5] and synthesis of hetero-
metallic clusters [6]. Chalcogen bridged clusters bearing
phosphorus ligands are synthesized by one of the fol-
lowing routes: (1) treatment of a zero-valent metal car-
bonyl of the type M3(CO)12 (M = Fe, Ru, Os) with a
phosphine chalcogenide R3P(E) (E = S, Se) in the pres-
ence of Me3NO as a decarbonylating agent [7], (2)
reaction of a chalcogen-bridged cluster with a phos-
phine [8], (3) reaction of a phosphine substituted
cluster with H2S [9a] and (4) reaction of phosphine
Chalcogen bridged transition metal clusters bearing
mono- and bidentate phosphorus ligands [1–3] have
been the subject of several recent publications. In such
clusters, the chalcogen element plays an important role
in stabilizing the bonding network. Furthermore, these
q
Part 23 of the series ‘‘Organometallic chemistry of diphospha-
zanes’’; for Part 22, see [19e].
*
Corresponding author. Tel.: +91 80 22932401; fax: +91 80
23600683/23601552.
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.2005.05.041

4002
T.S. Venkatakrishnan et al. / Journal of Organometallic Chemistry 690 (2005) 4001–4017
substituted hydrido cluster with elemental chalcogen
[9b]. The first route takes advantage of the reactivity
of the P@E bond to undergo oxidative addition across
the M3 core thereby transferring the chalcogen to the
transition metal with concomitant coordination of the
phosphine ligand. In the case of bidentate ligands,
the ligand can coordinate either in a chelating or bridg-
ing fashion depending on the reaction conditions, the
bite angle of the diphosphine and the transition metal
employed.
2. Experimental
2.1. General
All reactions and manipulations were carried out un-
der 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, 13C{1H} and 31P{1H})
were recorded in CDCl3 at 298 K using Bruker ACF-
200, Bruker AMX-400 or Bruker Avance-400 spectrome-
ters. Two-dimensional 31P–31P COSY, 31P–31P phase sen-
sitive NOESY, 1H–1H ROESY and 31P–1H COSY
spectra were recorded either on a Bruker AMX-
400 MHz or Bruker Avance-400 MHz spectrometer
using standard pulse sequences. IR spectra were recorded
using a Bruker FT-IR spectrometer; for this purpose, the
sample was spread 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 diphosphazane ligands X2PN(R)PX2 (X = Ph,
Chalcogen(E) bridged carbonyl clusters bearing
monophosphines of the type PR3 (R = Ph [7,8b,8e, 10],
p-tolyl [10a], C6H4 (OMe-4) [10b] or C6H2{(OMe)3-
2,4,6} [11]) and PR2R0 (R = Me, R0 = Ph [8a]; R = Ph,
R0 = benzyl [10b], Me [5], OMe [5], 2-thienyl [12a], (2-
pyridyl)-2-thienyl [12b] or 2-pyridyl [12c]) have been
investigated to obtain both tri- and tetranuclear clusters
of different structural types. Extensive studies have also
been reported on a variety of chalcogen bridged car-
bonyl clusters bearing diphosphines of the type
(Ph2P)2R (R = C „ C, E = Se, M = Ru [8d]; R = CH2,
E = S, M = Os [9a]; R = CH2, E = Se, M = Fe [13a],
Ru [8e,13b,13c], Os [9b]; R = CH2, E = Te, M = Ru
[8b]; R = (CH2)2, E = Se, M = Fe [13a], Ru [8e,13d];
R = (CH2)3, E = Se, M = Ru [8c]; R = (C5H4)2 Fe,
E = Se, M = Fe [13a], Ru [13d,13e]; R = C6H4{(CH2)2-
1,2)}, E = S, M = Ru [11]; R = C6H4 (CH2)2-1,2),
E = Se, M = Fe, Ru [14]; R = C5H2O2, E = S, M = Ru
[15]). Chalcogen bridged heterometallic clusters bear-
ing both mono- and diphosphines have been reported
recently by Predieri [5] and Braunstein [16]. On the
other hand, there are only two reports [17] on the
analogous chalcogen bridged clusters bearing diphos-
phazanes as ancillary ligands. Woollins and co-work-
ers studied the reactivity of diphosphazane
dichalcogenides R2P(E)N(H)P(E)R2 (R = Ph, E = S
or Se; R = iPr, E = S) towards Ru3(CO)12 to obtain
the closo clusters [Ru4(l4-E)2(l-CO)(CO)8{l-P,P-
R2PN(H)PR2}] as the main products. In these clusters,
the diphosphazane R2PN(H)PR2 adopts a bridging
mode of co-ordination [17a]. Raghuraman et al.
reported the reactivity of diphosphazane monosulfides
R = (S)- CHMePh (L1) [21a], CHMe2 (L2) [21b];
*
R = Me, X = OPh (L3) [21c,21d]) and the chalcogenides
Ph PN((S)- CHMePh)P(Se)Ph (L4) [22] and Ph P(S)-
*
2
2
2
N((S)- CHMePh)P(S)Ph (L7) [23] were prepared by
*
2
previously reported procedures. Me3NO (Aldrich),
C6D6 (Aldrich), Ru3(CO)12 (Strem chemicals) were used
as received.
2.1.1. Synthesis of Ph2P(Se)N(CHMe2)PPh2 (L5)
The title compound was prepared by following the
same procedure as that for L4. Elemental selenium
(0.056 g, 0.705 mmol) was added to a solution of
Ph2PN(CHMe2)PPh2 (0.301 g, 0.705 mmol) in THF
(10 cm3). The reaction mixture was stirred at 25 ꢁC for
18 h and solvent was evaporated to obtain an oil. Meth-
anol (5–10 cm3) was added to precipitate the title com-
pound. Yield: 42%. M.p. 124–125 ꢁC. Anal. Calc. for
C27H27NP2Se: C, 64.0; H, 5.3; N, 2.8. Found: C, 64.0;
H, 5.3; N, 1.8%.
Ph2P(S)N(R)PPh2 (R = (S)- CH-MePh or CHMe2)
*
2.1.2. Synthesis of (PhO)2P(S)N(Me)P(OPh)2 (L6)
towards Ru3(CO)12 and isolated sulfur-monocapped
clusters, [Ru3(l3-S)(lsb-CO)(CO)7{j2-P,P-Ph2PN(R)-
PPh2}] in which the diphosphazane adopts a chelating
mode of coordination [17b]. Recently we have studied
the radical initiated substitution of CO in Ru3(CO)12
by axially chiral diphosphazanes in which the
diphosphazane adopts a bridging mode of coordina-
tion [18]. As a part of our research program [17b–
19] on the organometallic chemistry of ‘‘P–N–P’’ type
ligands [20], we report here the results of our investi-
gations on the reactions of chiral and achiral
diphosphazane mono- and dichalcogenides with
Ru3(CO)12.
A
mixture of (PhO)2PN(Me)P(OPh)2 (1.000 g,
2.16 mmol) and elemental sulfur (0.069 g, 2.16 mmol)
was dissolved in acetonitrile (35 cm3) and the mixture
heated under reflux for 10 h. Evaporation of solvent
from the reaction mixture resulted in an oil. The oil
was dissolved in hot methanol and kept at 0 ꢁC over-
night to obtain a colorless air-sensitive solid of L6.
Yield: 70%. M.p. 132–133 ꢁC. Anal. Calc. for
C25H23NO4P2S: C, 60.5; H, 4.6; N, 2.8; S, 6.5. Found:
C, 60.5; H, 4.6; N, 2.9; S, 6.4%. The analogous disulfide
was synthesized by the reaction of L6 with elemental sul-
fur but attempts to obtain the compound in a pure form
were unsuccessful. The NMR spectroscopic data for the

T.S. Venkatakrishnan et al. / Journal of Organometallic Chemistry 690 (2005) 4001–4017
4003
1
disulfide were as follows. H NMR (CDCl3, 400 MHz):
Evaporation of solvent resulted in an oil. The oil was
dissolved in hot methanol and the solution kept at
0 ꢁC to give the diphosphazane dichalcogenides as color-
less solids. E = S (L8): Yield: 25%. M.p. 189–190 ꢁC.
Anal. Calc. for C27H27NP2S2: C, 66.0; H, 5.5; N, 2.9.
Found: C, 65.9; H, 5.3; N, 3.3%. E = Se (L9): Yield:
36%. M.p. 188–190 ꢁC. Anal. Calc. for C27H27NP2Se2:
C, 55.4; H, 4.6; N, 2.4. Found: C, 54.9; H, 4.3; N, 1.8%.
The spectroscopic data for the diphosphazane chalc-
ogenides L4ꢀL9 are presented in Table 1.
3
7.4–7.2 (m, aryl protons), 3.59(t, J(P,H) = 12 Hz, Me,
N–Me). 31P{1H} NMR (CDCl3, 162 MHz): 61.6(s).
2.1.3. Synthesis of Ph P(S)N((S)- CHMePh)P(S)Ph
*
2
2
(L7)
The title compound L7 was prepared by following the
literature procedure. However, in addition to L7, the
reaction also gave another known dichalcogenide
Ph2P(S)N(H)P(S)Ph2 as described below.
A mixture of L1 (0.200 g, 0.41 mmol) and elemental
sulfur (0.026 g, 0.82 mmol) was heated under reflux in
THF (10 cm3) for 8 h. Solvent was evaporated to dry-
ness and the resulting oil was subjected to column chro-
matography (a column of dimensions 20 · 1.5 cm was
used) using benzene–petroleum ether (b.p. 60–80 ꢁC)
(35:65 v/v) as eluant. Evaporation of the solvent from
the first fractions gave the title compound as a colorless
solid. Yield: 30%. M.p. 123–125 ꢁC. Further elution fol-
lowed by evaporation of the eluant afforded a solid
which displayed a singlet at 57.2 ppm in its 31P NMR
spectrum. The 1H NMR spectrum of this compound
showed a singlet at 4.38 ppm (1H) and a multiplet at
7.9–7.3 ppm (20H). Colorless single crystals of the prod-
uct were obtained by slow evaporation of its benzene
solution. Preliminary X-ray crystallographic study gave
the cell parameters which were close to those reported
for Ph2P(S)N(H)P(S)Ph2 [24]. Attempts to obtain the ti-
tle compound exclusively by the reaction of Ph2PN((S)-
2.1.5. General procedure for the synthesis of clusters 1–11
In a typical reaction, a 50 cm3 double-necked round
bottom flask was charged with Ru3(CO)12 (0.050 g,
0.078 mmol) and diphosphazane mono- or dichalcoge-
nide (0.078 mmol) under nitrogen. The mixture was dis-
solved in toluene (20 cm3). Me3NO (0.006 g, 0.009
mmol, 1.1 eq.) was added and the solution heated under
reflux for 1.5 h (in the case of diphosphazane dichalcog-
enides, the reaction employed 2.2 molar equivalents of
Me3NO and the reaction time was 2.5 h). At the end
of the reaction, solvent was evaporated from reaction
mixture and the residue dissolved in dichloromethane
(2 cm3) and subjected to preparative scale thin-layer
chromatography over silica-gel using dichlorometh-
ane–petroleum ether (b.p. 60–80 ꢁC) (1:1 v/v) as eluant.
The eluted bands were separated and the product was
extracted into dichloromethane. The dichloromethane
solvent was evaporated and the residue crystallised from
dichloromethane solution layered with petroleum ether.
The infrared spectroscopic and NMR (1H, 31P) data for
the ruthenium carbonyl clusters are presented in
Table 2. The remaining data are listed below.
CHMePh)P(S)Ph [17b] with elemental sulfur also
*
resulted in the same mixture of products.
2
2.1.4. Synthesis of Ph2P(E)N(CHMe2)P(E)Ph2 [E = S
(L8), Se (L9)]
A
mixture of Ph2PN(CHMe2)PPh2 (1.000 g,
2.1.6. [Ru4(l4-Se)2(l-CO)(CO)8{l-P,P-Ph2PN((S)-
2.34 mmol) and two equivalents of chalcogen (0.150 g,
for E = S, 0.370 g for E = Se, 4.68 mmol) in benzene
(35 cm3) was heated under reflux at 80 ꢁC for 1 day.
CHMePh)PPh }] (1)
*
2
The reaction of Ru3(CO)12 with L4 mainly gave the
tetraruthenium cluster 1 (Rf = 0.70) and the triruthenium
Table 1
1H and 31P NMRa data for the ligands L4–L9
31P{1H}
2JA-X(Hz)
Ddb
1H
CHc
CH3
d
PA
PX
PA
PX
L4
L5
L6
L7
L8
L9
a
68.5(d)e,f
51.3(s, br)g
7.0
50.8
102.1
–
+16.3
+15.5
ꢀ3.0
ꢀ0.9
5.30
4.07
–
1.85
1.24
3.26i
1.73
1.26
1.28
64.3(d)e,h
60.0(d)e
54.3(d)g
+5.5
ꢀ75.5
ꢀ
132.5(d)g
69.8(s, br)e
67.2(s, br)e
68.0(s, br)e
–
–
–
+17.6
+18.4
+19.2
5.30
4.13
4.21
–
ꢀ
–
ꢀ
Recorded in CDCl3.
b
Dd = dP(chalcogenide derivative)ꢀdP(parent diphosphazane)
.
c
CH-protons of the CHMePh or CHMe2 appear as multiplets.
CH3 protons of the CHMePh or CHMe2 are doublets with 3J(H,H) = 7.0 Hz.
P(V) phosphorus.
d
e
f
J(P–Se) = 759.5 Hz.
P(III) phosphorus.
g
h
J(P–Se) = 750.0 Hz.
Recorded in C6D6 (200 MHz), N–CH3 (dd, 3J(P,H) = 11.3, 1.7 Hz).
i

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T.S. Venkatakrishnan et al. / Journal of Organometallic Chemistry 690 (2005) 4001–4017
Table 2
NMRa (1H and 31P) and IR data for the ruthenium carbonyl clusters synthesised in the present study
31P{1H}
Ddb
1H
IR (mCO cmꢀ1
)
CHc
CH3
d
1
82.8(s)
65.6(s)
+30.6e
4.95(m)
4.55(m)
3.93(m)
3.76(m)g
–
1.02(d, br)
1.24(d)
0.48(d)
2043(m), 2005(s), 1959(m, br), 1854(w), 1809(m, br, l-CO)
2056(m), 2044(sh), 2014(s), 1984(m), 1946(sh), 1874(w)
2059(m), 2040(m), 2002(s), 1961(w), 1809(w, br, l-CO)
2078(sh), 2061(m), 2043(w), 2027(sh), 1990(w, br)g
–
2
+13.4e
3
82.5(s)
86.2(s)
+33.7f
4a
4b
+37.4f
0.36(d)
0.82(d)
95.3,84.2
+46.5, 35.4f
(d, 2J(P,P) = 52.8 Hz)
85.2(s)
81.2(s)
6
7
8
+33.0e
4.95(m)
3.95(m)
4.20(m)
1.28(d)
0.38(d)
1.23, 0.38(d)
2046(m), 2009(s), 1965(m), 1813(m, br)
2060(m), 2040(m), 2003(s), 1961(w), 1809(w, br, l-CO)
2065(s), 2030(m), 1991(s)
+32.4f
94.4, 84.6
(d, 2J(P,P) = 56.4 Hz)
143.8(s)
+45.6, +35.8e
9
10
+8.3h
–
–
–
3.11(t)i
3.23 (t),k 2.88 (br),l
2.47 (t)m
2080(m), 2033(m), 2007(w, sh), 1821(w), 1701(m, l3-CO)
2079(w), 2057(w) 2037(w, sh), 2020(w), 1997(m), 1951(w, br)
j
a
b
c
Recorded in CDCl3.
Dd = d(complex) – d(free diphosphazane).
CH-protons of the CHMePh or CHMe2 appear as multiplets.
CH3 protons of the CHMePh or CHMe2 are doublets with 3J(H,H) = 7.0 Hz.
Free ligand is L1.
Free ligand is L2.
d
e
f
g
h
i
4a + 4b.
Free ligand is L3.
3J(P,H) = 7.0 Hz.
j
Exists as two isomers 10 and 10a; see Fig. 6 for assignment of resonances.
3J(P,H) = 7.0 Hz, N–CH3, bridging diphosphazane of 10 and 10a.
N–CH3, chelating diphosphazane of 10.
3J (P,H) = 10.0 Hz, N–CH3, chelating diphosphazane of 10a.
k
l
m
cluster 2 (Rf = 0.90) as the isolable products of which 1 is
the major product. Analytical data for 1: Yield: 20%.
M.p. 172–173 ꢁC (dec). Anal. Calc. for C41H29NO9P2-
Se2Ru4: C, 37.7; H, 2.2; N, 1.1. Found: C, 38.1; H, 2.2;
N, 0.9%. 13C{1H} NMR (CDCl3, 100 MHz): 202.9(br,
CO, Ru–CO), 197.6(s, CO, Ru–CO), 66.2(s, CH,
CHMePh), 22.4(s, Me, CHMePh).
2.1.8. [Ru4(l4-S)2(l-CO)(CO)8{l-P,P-Ph2PN((S)-
CHMePh)PPh }] (6)
2
The reaction of Ru3(CO)12 with L7 gave the tetraru-
*
thenium cluster 6 (Rf = 0.70) as the only isolable prod-
uct. Yield: 13%. M.p. 179–181 ꢁC (dec). Anal. Calc.
for C41H29NO9P2S2Ru4: C, 40.7; H, 2.4; N, 1.2. Found:
C, 40.0; H, 2.3; N, 1.0%.
2.1.7. [Ru4(l4-Se)2(l-CO)(CO)8{l-P,P-Ph2PN-
(CHMe2)PPh2}] (3)
2.1.9. [Ru4(l4-S)2(l-CO)(CO)8{l-P,P-Ph2PN-
(CHMe2)PPh2}] (7)
The reaction of Ru3(CO)12 with L5 gave a mixture of
several products from which the tetraruthenium cluster 3
(Rf = 0.70) and the triruthenium cluster 4 (Rf = 0.80)
were isolated and characterised. Analytical data for 3:
Yield: 30%. M.p. 181–183 ꢁC (dec). Anal. Calc. for
C37H29NO9P2Se2Ru4Cl2: C, 33.5; H, 2.2; N, 1.1. Found:
C, 33.0; H, 2.5; N, 1.7%. 13C{1H} NMR (CDCl3,
100 MHz): 199.0(br, CO, Ru–CO), 197.2(br, CO, Ru–
CO), 61.3(t, 2J(P,C) = 4.6 Hz, CH, CHMe2), 23.9(s,
Me, CHMe2). Another compound 5 with an Rf value
of 0.90 was also isolated from the reaction mixture which
was tentatively formulated as a diruthenium species
bearing a bridging diphosphazane. The spectroscopic
data for compound 5 are as follows. IR (neat, mCO
cmꢀ1): 2053(s), 2039(w), 2011(m), 1999(m), 1986(m).
1H NMR (CDCl3, 400 MHz): 7.8–7.4 (m, aryl protons),
The reaction of Ru3(CO)12 with L8 gave the tetraru-
thenium cluster 7 (Rf = 0.70) and the triruthenium clus-
ter 8 (Rf = 0.80). Analytical data for 7: Yield: 28%. M.p.
188–190 ꢁC (dec). Anal. Calc. for C37H29NO9P2S2-
Ru4Cl2: C, 36.0; H, 2.4; N, 1.1. Found: C, 35.8; H,
2.0; N, 0.6%.
2.1.10. [Ru3(l3-S)(l3-CO)(CO)7{l-P,P-(PhO)2-
PN(Me)P(OPh)2}] (9) and [Ru3(l3-S)2(CO)5-
{l-P,P-(PhO)2PN(Me)P(OPh)2}{j2-P,P-(PhO)2-
PN(Me)P(OPh)2}] (10)
The reaction of Ru3(CO)12 with L6 gave the triruthe-
nium clusters 9 (Rf = 0.90) and 10 (Rf = 0.70) as the iso-
lable products. Even when the reaction was carried out
in the presence of 2 equivalents of L6, both the clusters
9 and 10 were obtained and isolated. Cluster 10 was also
formed in the reaction of 9 with L6 in boiling toluene in
the presence of Me3NO and could be isolated from the
3
3.50 (m, CH, CHMe2), 0.48 (d, J(H,H) = 7.0 Hz, Me,
CHMe2). 31P{1H} NMR (CDCl3, 162 MHz): 82.5(s).

T.S. Venkatakrishnan et al. / Journal of Organometallic Chemistry 690 (2005) 4001–4017
4005
reaction mixture by PTLC. Analytical data for 9: Yield:
45%. M.p. 181–183 ꢁC (dec). Anal. Calc. for
C33H23NO12P2SRu3: C, 38.7; H, 2.2; N, 1.4; S, 3.1.
Found: C, 37.5; H, 2.7; N, 1.5; S, 3.1%. 13C{1H}
NMR (CDCl3, 100 MHz): 199.1(s, CO, Ru–CO),
143.0 ppm but no cross-peaks to any other resonances.
These correlations indicate the presence of a four spin
system. Based on these results and comparison of the
NMR chemical shifts (see Table 2), one of the compo-
nents of this mixture was tentatively formulated as
[Ru3(l3-S)2(CO)5{j2-P,P-(PhO)2PN(Me)P(OPh)2)}{j2-
2
194.9(s br, CO, Ru–CO), 30.8(t, J(P,C) = 3.7 Hz, Me,
N–Me). Analytical data for 10: Yield: 9%. M.p. 201–
205 ꢁC (dec). Anal. Calc. for C55H46N2O13P4S2Ru3:
C, 46.0; H, 3.2; N, 2.0. Found: C, 45.8; H, 2.9; N,
1.5%. 13C{1H} NMR (CDCl3, 100 MHz): 199.2(d,
2J(P,C) = 11.0 Hz, CO, Ru–CO, adjacent to bridging
diphosphazane), 198.5(m br, CO, Ru–CO), 196.7(m br,
CO, Ru–CO), 195.1(br, CO, Ru–CO), 192.9(t,
2J(P,C) = 12.9 Hz, CO, Ru–CO, adjacent to chelating
P,P-Ph PN(R)PPh }] (R = (S)- CHMePh). Attempts to
*
2 2
obtain a pure compound from this material by frac-
tional crystallization were unsuccessful.
2.1.12. Reaction of [Ru3(l3-S)(l3-CO)(CO)7{l-P,P-
(PhO)2PN(Me)P(OPh)2}] (9) with Ph2PN((S)-
CHMePh)P(S)Ph
*
2
Ph PN((S)- CHMePh)P(S)Ph (0.041 g, 7.82 · 10ꢀ5
*
2
2
2
diphosphazane), 30.4(br, Me, N–Me), 30.3(t, J(P,C) =
3.7 Hz, Me, N–Me), 29.8(br, Me, N–Me), 29.5(br, Me,
N–Me).
mol) and Me3NO (0.006 g, 9.00 · 10ꢀ5 mol) were added
to a toluene (20 cm3) solution of cluster 9 obtained from
the reaction of Ru3(CO)12 with L6. The mixture was
heated under reflux for 1 h. Solvent was evaporated;
the residue was dissolved in dichloromethane (2 cm3)
and subjected to preparative scale thin-layer chromatog-
raphy [dichloromethane–petroleum ether (b.p. 60–
80 ꢁC) (1:1 v/v) as eluant] to isolate a solid which
displayed the following spectroscopic features.
2.1.11. Reaction of [Ru3(l3-S)(lsb-CO)(CO)7{j2-P,P-
Ph PN((S)- CHMePh)PPh }] (A) with
*
2
2
(PhO)2PN(Me)P(S)(OPh)2 (L6)
The ruthenium cluster A was prepared as reported
previously [17b]. A mixture of Ru3(CO)12 (0.050 g,
7.82 · 10ꢀ5 mol) and diphosphazane monosulfide
1
IR (neat, mCO cmꢀ1): 2016(m), 1989(s), 1948(s). H
Ph PN((S)- CHMePh)P(S)Ph (0.041 g, 7.82 · 10ꢀ5
NMR (CDCl3, 400 MHz): 7.9–6.6 (m, aryl protons),
3
4.65 (m, CH, CHMePh), 3.21 (t, J(P,H) = 7.0 Hz, Me,
*
2
2
mol) was dissolved in toluene (20 cm3). Me3NO
(0.006 g, 9.00 · 10ꢀ5 mol) was added and the reaction
mixture was heated to 105 ꢁC for 1 h. The reaction mix-
ture was cooled to ambient temperature and the solvent
evaporated to dryness. The dark red residue which con-
sisted essentially of A (31P NMR evidence) was dissolved
in toluene (20 cm3); L6 (0.039 g, 7.82 · 10ꢀ5 mol) and
Me3NO (0.006 g, 9.00 · 10ꢀ5 mol) were added and the
mixture was heated under reflux for 1 h. Solvent was
evaporated; the residue was dissolved in dichlorometh-
ane (2 cm3) and subjected to preparative scale thin-layer
chromatography [dichloromethane-petroleum ether
(b.p. 60–80 ꢁC) (1:1 v/v) as eluant] to isolate a solid sam-
ple for which the following spectroscopic data were
obtained.
N–Me), 1.10 (d, 3J(H,H) = 7.0 Hz, Me, CHMePh).
31P{1H} NMR (CDCl3, 162 MHz): 143.0 (m), 132.0
(m) [diphosphazane bearing phenoxy substituents in
bridging mode], 78.0ꢀ72.0 (m), 68.0 (d) [diphosphazane
bearing phenyl substituents in chelating mode].
Attempts to obtain a pure compound from this mate-
rial by fractional crystallization were unsuccessful. One
of the components of this mixture was tentatively
formulated as [Ru3(l3-S)2(CO)5{l-P,P-(PhO)2PN(Me)-
P(OPh) )}{j2-P,P-Ph PN(R)PPh }] (R = (S)- CHMePh)
*
2
2
2
from the observed 31P chemical shifts.
2.2. X-ray crystallography
IR (neat, mCO cmꢀ1): 2036(s), 1982(s). 1H NMR
(CDCl3, 400 MHz): 7.5–6.5 (m, aryl protons), 4.55 (m,
The crystals were mounted on a glass fiber and the
intensity data for all the clusters were obtained at room
temperature from a Bruker SMART APEX CCD dif-
fractometer equipped with fine focus 1.75 kW sealed
tube Mo Ka X-ray source with increasing x (width of
0.3ꢁ per frame) at a scan speed of n s/frame (n = 15 for
1, n = 10 for 3, n = 9 for 7, n = 15 for 9, n = 5 for 10
and n = 6 for 11). The SMART [25a] software was used
for cell-refinement and data acquisition and the SAINT
[25b] software was used for data reduction. Lorentzian
and polarization corrections were made on the intensity
data. An absorption correction was made on the inten-
sity data using the SADABS [25c] program. Pertinent
crystallographic data are summarized in Table 3. All
the structures were solved using SHELXTL [25d] and the
WinGX graphical user interface [26]. Least-square
3
CH, CHMePh), 3.30 (t br, J(P,H) = 7.0 Hz, Me, N–
Me), 2.94 (dd, 3J(P,H) = 16.0, 6.0 Hz, Me, N–Me),
1.33 (s br, Me, CHMePh). 31P{1H} NMR (CDCl3,
162 MHz): 149.9 (m), 143.0 (m), [diphosphazane bearing
phenoxy substituents in bridging mode], 105.1 (m),
103.3 (m) [diphosphazane bearing phenoxy substituents
in chelating mode], 85.0 (s br), 81.4 (d), 78.7 (d,
2J(P,P) = 71.3 Hz) [diphosphazane bearing phenyl sub-
stituents in chelating mode]. The 31P–31P COSY spec-
trum of the sample showed the following correlations:
(a) cross-peaks between the resonances centered at
105.1 and 81.4 ppm; (b) cross-peaks between the reso-
nances at d 103.3 and 85.0 as well as 78.7 ppm and (c)
cross-peaks between the resonances at 149.9 and

Table 3
Details of X-ray crystallographic data collection for the cluters 7, 9, 10 and 11
7 Æ CH2Cl2
9
10
11 Æ 0.5C6H6 Æ H2O
Empirical formula
Formula weight
C36H27NO9P2S2Ru4.CH2Cl2
1232.85
C33H23NO12P2SRu3
1022.73
C55H46N2O13P4S2Ru3
1434.15
Monoclinic, P21/n
C34H23NO13P2S2Ru4.0.5C6H6.H2O
1240.94
Monoclinic, C2/c
ꢀ
ꢀ
Crystal system, Space group
Unit cell dimensions
Triclinic, P1
Triclinic, P1
˚
a (A)
12.979(3)
13.138(3)
11.390(11)
11.507(11)
11.973(3)
25.117(7)
20.249(5)
24.778(5)
17.034(3)
22.335(4)
˚
b (A)
˚
c (A)
15.324(3)
81.351(3)
15.057(14)
78.761(13)
a (ꢁ)
b (ꢁ)
c (ꢁ)
66.286(3)
63.586(3)
2141(1)
77.447(14)
79.832(15)
1871(3)
104.735(5)
90.138(4)ꢁ
3
˚
Volume (A )
5889(3)
4
1.618
9427(3)
8
1.749
Z
2
1.912
2
1.816
Density (calcd) (mg/mm3)
Absorption coefficient (mmꢀ1
)
1.733
0.9383 and 0.7617
1204
1.398
0.9793 and 0.4630
1004
1.002
0.9073 and 0.5788
2872
1.473
0.6972 and 0.4850
4856
Maximum and minimum transmission
F(000)
Crystal size, (mm)
0.300 · 0.083 · 0.070
1.45–27.6ꢁ
ꢀ17 6 h 6 16,
ꢀ17 6 k 6 16,
ꢀ20 6 l 6 19
25,222
0.650 · 0.130 · 0.020
1.82–26.0ꢁ
ꢀ14 6 h 6 14,
ꢀ14 6 k 6 13,
ꢀ18 6 l 6 19
19,082
0.613 · 0.203 · 0.099
1.32–27.0ꢁ
ꢀ15 6 h 6 15,
ꢀ32 6 k 6 31,
ꢀ26 6 l 6 26
47,991
0.540 · 0.070 · 0.040
1.45–27.5ꢁ
ꢀ31 6 h 6 31,
ꢀ21 6 k 6 22,
ꢀ29 6 l 6 29
40,858
h range for data collection
Index ranges
Reflections collected
Independent reflections [Rint
Refinement method
]
9956[0.0292]
Full-matrix least-squares on F2
9956/0/622
7492[0.0311]
Full-matrix least-squares on F2
7492/0/561
12,891[0.0638]
Full-matrix least-squares on F2
12,891/0/712
0.933
11,121[0.0898]
Full-matrix least-squares on F2
11,121/0/525
1.064
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices all data
1.000
1.106
R1 = 0.0306, wR2 = 0.0796
R1 = 0.0421, wR2 = 0.0839
0.878 and ꢀ0.667
R1 = 0.0449, wR2 = 0.1018
R1 = 0.0586, wR2 = 0.1088
1.260 and ꢀ0.687
R1 = 0.0389, wR2 = 0.0637
R1 = 0.0661, wR2 = 0.0688
0.460 and ꢀ0.460
R1 = 0.0680, wR2 = 0.1140
R1 = 0.1399, wR2 = 0.1309
0.794 and ꢀ0.559
ꢀ3
˚
Largest different peak and hole (e A
)

T.S. Venkatakrishnan et al. / Journal of Organometallic Chemistry 690 (2005) 4001–4017
4007
refinements were performed by the full-matrix method
with SHELXL-97 [27]. All non-hydrogen atoms were re-
fined anisotropically and hydrogen atoms were refined
isotropically. The solvent molecules in 3 (dichlorometh-
ane) and 11 (water oxygen) were disordered and were
thus refined isotropically with shared occupancy factors;
the carbon atoms of the solvent benzene in 11 were re-
fined isotropically.
ogenides L5–L9 were characterized by elemental analy-
ses, melting point and NMR spectroscopic techniques
(see Table 1).
The 31P chemical shift of the pentavalent phosphorus
in the diphosphazane mono- and dichalcogenides lies in
the region ꢁ67–70 ppm. For the monoselenides,
Ph P(Se)N(R)PPh [R = (S)- CHMePh (L4) or CHMe
*
2
2
2
(L5)], the 31P chemical shifts of the pentavalent phospho-
rus lie downfield as compared to the parent diphosphaz-
ane (L1 or L2). On the other hand, the 31P chemical shift
of the pentavalent phosphorus in L6 is upfield shifted
[Dd = dP (chalcogenide derivative) – dP (parent diphosp-
hazane) = ꢀ 75.5] compared to the trivalent phosphorus.
This reverse trend may be related to the strong p-accep-
tor character of the phosphorus in L6, which is also
reflected in the large coupling constant between the
3. Results and discussion
3.1. Synthesis of diphosphazane mono- and
dichalcogenides and their NMR spectra
The diphosphazane mono- and dichalcogenides are
prepared by the treatment of the respective diphosphaz-
ane with elemental chalcogen (S8 or Se) in the appropri-
ate ratio as reported in the literature [17b,28]. The
1
two phosphorus nuclei. The H NMR spectrum (C6D6)
of L6 shows a doublet of doublets for the N(Me) pro-
tons. The 31P NMR spectra of the diphosphazane
dichalcogenides Ph2P(E)N(CHMe2)P(E)Ph2 [E = S (L8)
or Se (L9)] display a broad singlet at ꢁ68.0 ppm.
diphosphazane chalcogenides Ph PN((S)- CHMePh)P-
*
2
(Se)Ph (L4) [22] and Ph P(S)N((S)- CHMePh)P(S)Ph
*
2
2
2
(L7) [23] are known compounds. The synthesis of the
new diphosphazane chalcogenides L5, L6, L8 and L9 is
shown in Scheme 1. The reaction of a diphosphazane
that bears a strong p-acceptor phosphorus (PhO)2PN-
(Me)P(OPh)2 (L3) with one equivalent of elemental
sulfur in boiling acetonitrile affords the diphosphazane
monosulfide (PhO)2PN(Me)P(S)(OPh)2 (L6). During
the synthesis of the known diphosphazane disulfide
3.2. Reactivity of L4 and L5 towards Ru3(CO)12
The reaction of Ru3(CO)12 with L4 in toluene in the
presence of Me3NO yields a mixture of several prod-
ucts of which only two ruthenium containing species
1 and 2 could be isolated by TLC (Scheme 2).
Compound 1 is the diphosphazane bridged selenium
bicapped tetraruthenium cluster, [Ru4(l4-Se)2(CO)8-
Ph P(S)N((S)- CHMePh)P(S)Ph (L7) [23], we find that
*
2
2
the reaction also yields the disulfide Ph2P(S)N(H)-
P(S)Ph2 (see Section 2). Evidently, N–C bond rupture
occurs during the oxidation of the trivalent phosphorus
by the chalcogen. Recently, Manso et al. [23] investi-
gated the reaction of L7 with [Rh(1,5-COD)(l-Cl)]2 in
the presence of AgBF4 in which N–C bond rupture
occurs to yield the complex, [Rh(1,5-COD){j2-S,S-
Ph2P(S)N(H)P(S)Ph2}]BF4. The diphosphazane chalc-
(l-CO){l-P,P-Ph PN((S)- CHMePh)PPh }] as revealed
*
2 2
by X-ray crystallography (see Sections 2.2 and 5). The
31P NMR spectrum of 1 displays a singlet that lies very
much downfield as compared to the 31P chemical shift
of the free ligand [Dd = dP (complex)ꢀdP (parent
diphosphazane) = +30.6] (see Table 2). The 13C NMR
spectrum displays a broad resonance at 202.9 ppm and
a singlet at 197.6 ppm for the metal bound carbonyls.
Me
N
X2P
S
PX2
R
(i)
R
N
N
X = OPh (L6)
(iii)
PX2
E
X2P
E
X2P
PX2
CHMe2
N
(ii)
R = (S)-*CHMePh, X = Ph (L1)
R = CHMe2, X = Ph (L2)
R = Me, X = OPh (L3)
X = Ph
E = S, R = (S)-*CHMePh (L7)
X2P
Se
X = Ph (L5)
PX2
E = S, R = CHMe2 (L8)
E = Se, R = CHMe2 (L9)
(i) 1/8 S8, MeCN, 85 0C, 10h
(ii) 1/8 Se8, THF, 25 0C, 18h
(iii) 2 eq. E, [THF, 65 0C, 8h (for L7), Benzene, 80 0C, 1d (for L8 and L9)]
Scheme 1. Synthesis of various diphosphazane mono- and di-chalcogenides.

4008
T.S. Venkatakrishnan et al. / Journal of Organometallic Chemistry 690 (2005) 4001–4017
R
N
Se
Ph2
P
Ph
2P
Ru
PPh2
Ru
N R
Ru
Ru
E = Se, R = (S)-*CHMePh, (1)
E = Se, R = CHMe2, (3)
P
Ph2
E
E
Ru
Ru
Ru
R = (S)-*CHMePh (2)
= CO
(i)
Ru3(CO)12
(ii)
R
N
Ph2
P
Ru(CO)3
Ph
2P
Ru
PPh2
Ru
(OC)
2 Ru
CHMe2
N
E
Ru(CO)2
(OC)3Ru
(OC)2Ru
Ph2P
PPh2
Ru(CO)2
E
E
E
E
E
PPh2
Ru
Ru
N
CHMe2
E = Se (4b)
S (8)
E = S, R = (S)-*CHMePh (6)
E = S, R = CHMe2 (7)
E = Se, R = CHMe2 (3)
E = Se (4a)
(i) L4 or L5, Toluene, 1.1 eq. Me3NO, 105 0C, 1.5 h
(ii) L7, L8 or L9, Toluene, 2.2 eq. Me3NO, 105 0C, 2.5 h
Scheme 2. Reactions of Ru3(CO)12 with diphosphazane mono- and dichalcogenides.
Cluster 2 is assigned the chelated arachno structure,
[Ru (CO) (l -Se)(l -CO){j2-P,P-Ph PN((S)- CH-
MePh)PPh2}] (2) [Dd = +13.4] by comparison of the
NMR chemical shifts and carbonyl stretching frequen-
cies in its infrared spectrum with the data reported for
the sulfur analogue, the structure of which has been
confirmed by X-ray crystallography [17b].
The reaction of Ph2PN(CHMe2)P(Se)Ph2 (L5) with
Ru3(CO)12 results in the formation of several products
of which the selenium bicapped tetraruthenium cluster
3 is the major one. The structure of 3 has been confirmed
by single crystal X-ray diffraction (see below). The other
two products 4 and 5 could be characterised by spectro-
scopic data only. The 31P NMR spectrum of 4 displays a
singlet and two doublets (11:1 ratio) that may be as-
cribed to the presence of two isomers (4a and 4b) in solu-
tion. A similar feature is observed in the case of the nido
clusters, [M3(CO)7(l3-E)2{l-P,P-diphosphine}] (diphos-
phine = dppm [13b], dppe [13a], dppa [17a]). The ratio
of the intensities in the 31P NMR spectrum of 4 indicates
that the isomer in which the bridging diphosphine occu-
pies the basal sites (4a) is favored presumably because of
less steric repulsion experienced in this arrangement.
Cluster 5 displays a singlet at 82.5 ppm indicating that
the diphosphazane adopts a bridging mode of coordina-
tion and is probably a diruthenium species. Attempts to
crystallize 4 and 5 were unsuccessful as the products de-
graded slowly. Complex 3 is also obtained from the
reaction between the diselenide L9 and Ru3(CO)12 (see
below).
*
3
7
3
sb
2
3.3. Reactivity of diphosphazane dichalcogenides L7–L9
towards Ru3(CO)12
The reaction of Ru3(CO)12 with diphosphazane
dichalcogenides (L7–L9) in boiling toluene in the
presence of Me3NO yield mainly the diphosphazane
bridged chalcogen bicapped tetraruthenium clusters,

T.S. Venkatakrishnan et al. / Journal of Organometallic Chemistry 690 (2005) 4001–4017
4009
[Ru4(l4-E)2(CO)8 (l-CO){l-P,P-Ph2PN(R)PPh2}] [R =
13C NMR spectrum displays resonances at 199.0 and
194.9 ppm, which can be assigned to the metal bound
carbonyl ligands. Crystallization of the compound from
a mixture of benzene and petroleum ether over a period
of two months at ambient temperature gave 9 as thin
yellow needle-shaped crystals suitable for X-ray diffrac-
tion. In addition, a tiny quantity of dark red crystals was
also obtained. A single crystal X-ray study was carried
out on the dark red crystals; the structure was found
to be the sulfur bicapped tetraruthenium closo octahe-
dral cluster 11 (Fig. 3).
(S)- CHMePh, E = S (6); R = CHMe , E = S (7);
*
2
R = CHMe2, E = Se (3)], respectively. The clusters 4b
(see previous section) and 8 are also isolated from the
reactions of Ru3(CO)12 with L9 and L8, respectively.
The IR and NMR data for the clusters are given in Ta-
ble 2. The structures of the clusters 3 and 7 were estab-
lished by single crystal X-ray diffraction studies (see
Sections 2.2 and 5). The 31P NMR spectrum of 3 or 7
shows a singlet for the magnetically equivalent bridging
phosphorus nuclei. An absorption at ꢁ1810 cmꢀ1 in the
infrared spectrum is assigned to the bridging carbonyl li-
gand. The 31P NMR spectra of 4b and 8 exhibit two
doublets. Attempts to obtain single crystals of 4b and
8 were unsuccessful. Based on the IR spectroscopic data
and 31P NMR chemical shifts, we tentatively assign a
structure in which the diphosphazane acts as a bridging
ligand.
The reactions of diphosphazane monosulfides
Ph PN(R)P(S)Ph (R = (S)- CHMePh or CHMe ) with
*
2
2
2
Ru3(CO)12 give sulfur monocapped triruthenium clus-
ters, [Ru3(l3-S)(lsb-CO)(CO)7{j2-P,P-Ph2PN(R)PPh2}]
in which the diphosphazane acts as a chelating ligand
[17b]. The reaction of the cluster [Ru3(3-S)(lsb-CO)-
(CO) {j2-P,P-Ph PN((S)- CHMePh)PPh }] (A) with
*
7
2
2
(PhO)2PN(Me)P(S)(OPh)2 (L6) in boiling toluene in
the presence of Me3NO as decarbonylating agent gave
a mixture of products which could not be separated
and isolated in a pure state. However, based on
31P–31P COSY spectrum and observed 31P chemical
shifts (see Section 2), one of the products is tentatively
identified as [Ru3(l3-S)2(CO)5{j2-P,P-(PhO)2PN(Me)-
3.4. Reactivity of the diphosphazane monosulfide L6
towards Ru3(CO)12
The oxidative decarbonylation of Ru3(CO)12 by
Me3NO in the presence of L6 proceeds through a differ-
ent pathway to yield two products 9 and 10 correspond-
ing to single and double oxidative transfer of sulfur
respectively (Scheme 3). Clusters 9 and 10 were sepa-
rated by thin layer chromatography and their structures
determined by X-ray crystallography (Figs. 1 and 2). A
singlet is observed in the 31P{1H} NMR spectrum of
cluster 9. The infrared spectrum of 9 shows a band at
1701 cmꢀ1 for the triply bridging carbonyl group. The
P(OPh) )}{j2-P,P-Ph PN((S)- CHMePh)PPh }] in which
*
both the diphosphazane ligands adopt chelating mode
2
2
2
of coordination.
The reaction of [Ru3(l3-S)(l3-CO)(CO)7{l-P,P-
(PhO)2PN(Me)P(OPh)2}] (9) with the diphosphazane
monosulfide, Ph PN((S)- CHMePh)P(S)Ph in boiling
*
2
2
toluene in the presence of Me3NO as decarbonylating
(OPh)2
P
(OPh)2
S
P
Me
Ru
Ru
N
Me N
Ru
S
(i)
P(OPh)2
+
S
P
Ru3(CO)12
(PhO)2P
(OPh)2
Ru
Ru
N
Ru
Me
P
9
(OPh)2
(i)
(ii)
10
10
= CO
Me
N
(PhO)
2P
P(OPh)2
(i ) L6, toluene, 1.1 eq Me3NO, 105 0C, 1h
Ru
Ru
(ii) Crystallisation, 2 months
+
S
9
S
Ru
Ru
11
Scheme 3. Reactivity of diphosphazane monosulfide (PhO)2PN(Me)P(S)(OPh)2 (L6) towards Ru3(CO)12
.

4010
T.S. Venkatakrishnan et al. / Journal of Organometallic Chemistry 690 (2005) 4001–4017
Fig. 3. An ORTEP view of the molecular structure of [Ru4(CO)8(l4-
S)2(l-CO){l-P,P-(PhO)2PN(Me)P(OPh)2}] (11). Thermal ellipsoids are
drawn at 30% probability level. Hydrogen atoms and lattice held
solvent molecules (benzene and water) are not shown for clarity.
Fig. 1. An ORTEP view of the molecular structure of [Ru3(CO)7(l3-
S)(l3-CO){l-P,P-(PhO)2PN(Me)P(OPh)2}] (9). Thermal ellipsoids are
drawn at 30% probability level. Hydrogen atoms are not shown for
clarity.
of Me3NO did not proceed and the starting material (A)
was recovered unchanged.
3.5. NMR spectrum and dynamic behavior of 10
Cluster 10 represents the first example of a chalcogen
bridged carbonyl cluster bearing two bidentate phos-
phorus ligands in two different coordination modes.
As evident from the structure of 10 (Fig. 2), all the four
phosphorus nuclei are magnetically non-equivalent.
Hence, one would expect the 31P NMR spectrum to
consist of 32 lines. But the actual spectrum is more com-
plicated (Fig. 4). A homonuclear 31P–31P COSY experi-
ment shows that the complexity is due to the presence of
two isomers (1:4 ratio) each giving rise to an AMRX
spin system. The COSY spectrum is illustrated in Fig.
5. The 31P chemical shifts and coupling constants for
only the major isomer (10) could be determined accu-
rately; for the minor isomer (10a) only the chemical
shifts could be determined as the resonances were not
well resolved. The values calculated directly from the
spectrum for 10 agree closely with those obtained by
computer simulation using the LEQUOR program
[29]. The 31P NMR spectrum (recorded in acetone-d6)
does not show any change in the temperature range
ꢀ90 to +50 ꢁC.
Fig. 2. An ORTEP view of the molecular structure of [Ru3(CO)5(l3-
S)2{l-P,P-(PhO)2PN(Me)P(OPh)2}{j2-P,P-(PhO)2PN(Me)P(OPh)2}]
(10). Thermal ellipsoids are drawn at 30% probability level. Hydrogen
atoms are not shown for clarity.
agent also gave a mixture of products which could not
be separated and isolated in a pure form. Based on IR
and NMR spectroscopic data (see Section 2), one of
the products can be tentatively identified as [Ru3(l3-
S)2(CO)5{l-P,P-(PhO)2PN(Me)P(OPh)2}{j2-P,P-Ph2PN((S)-
The assignment of the 31P NMR chemical shifts for
the major isomer 10 is based on the following two trends
noted in the literature: (a) the 31P chemical shifts of
bridging diphosphazanes are downfield shifted com-
pared to those of the chelating ones [17b] (also see data
for compounds given in Table 2) (b) within a chelating
diphosphine, the chemical shift of the phosphorus that
CHMePh)PPh }] in which the incoming diphosphazane
*
adopts a chelating mode of coordination. Further reaction
2
of [Ru (l -S)(l -CO)(CO) {j2-P,P-Ph PN((S)- CHMe-
Ph)PPh2}] (A) with the diphosphazane monosulfide
*
3
3
sb
7
2
Ph PN((S)- CHMePh)P(S)Ph orPh P(S)in the presence
*
2
2
3

T.S. Venkatakrishnan et al. / Journal of Organometallic Chemistry 690 (2005) 4001–4017
4011
Fig. 4. The 31P NMR spectrum (162 MHz, CDCl3, 20 ꢁC) of 10.
Fig. 5. The 31P–31P COSY spectrum (162 MHz, CDCl3, 20 ꢁC) of 10.
3
3
occupies the axial position lies downfield compared to
that present at the equatorial position [13d]. Based on
these two correlations, the 31P resonances centered at
151.1(dt, PA1) and 142.7(ddd, PM1) ppm are assigned
to the phosphorus nuclei of the bridging diphosphazane
ent coupling constants [2J (P,P), J(P,P)trans, J(P,P)cis].
The other phosphorus [P(4) in Fig. 2] present at the base
of the square pyramid would also have three coupling
constants [2J(P,P), 4J(P,P),4J(P,P)], of which the two
long-range coupling constants will be weak (probably
equal in magnitude). Therefore the resonance centered
at d 142.7(ddd) is assigned to the phosphorus at the apex
of the square pyramid and that at d 151.1(dt) is assigned
to the phosphorus at the base of the square pyramid.
Fig. 6 shows the assignment of 31P chemical shifts to
the phosphorus nuclei in 10 and 10a.
and those centered at 110.3(dt, PR1) and 109.4(q, PX1
)
are assigned to the axial and equatorial phosphorus nu-
clei of the chelating diphosphazane, respectively. Con-
sidering the X-ray crystal structure and the relevant
torsion angles (see Fig. 2 and the X-ray crystal structure
section), the phosphorus nuclei of the bridging diphosp-
hazane located at the apex of the square pyramid [P(3)
in Fig. 2] would be expected to have three widely differ-
A homonuclear 31P–31P phase-sensitive NOESY
experiment, (Fig. 7) reveals that the two isomers undergo

4012
T.S. Venkatakrishnan et al. / Journal of Organometallic Chemistry 690 (2005) 4001–4017
(OPh)2
P
PR
(OPh)2
P
PX
Me
S
PA
S
Me
N
Ru
PA
Ru
Ru
S
N
Ru
P(OPh)2
S
P(OPh)2
N
P
P
(OPh)2
(OPh)2
PX
N
Ru
PR
Me
Ru
P
Me
(OPh)2
P
(OPh)2
PM
= CO
PM
10
10a
Major isomer 10
PA, 151.1 (dt, 2J(A-M) = 112.4 Hz, 4J(A-R) = 4J(A-X) = 13.8 Hz)
PM, 142.7 (ddd, 2J(M-A) = 112.4 Hz, 3J(M-R) = 48.2 Hz, 3J(M-X) = 13.8 Hz)
PR, 109.3 (dt, 3J(R-M) = 48.2 Hz, 4J(R-A) = 2J(R-X) = 16.1 Hz)
PX, 108.1 (q, 2J(X-R) = 3J(X-M) = 4J(X-A) = 13.8 Hz)
Minor isomer 10a
PA, 146.5
PM, 144.5
PR, 111.9
PX, 101.8
Fig. 6. Assignment of 31P chemical shifts to phosphorus nuclei in the two isomers 10 and 10a.
Fig. 7. The 31P–31P phase sensitive NOESY spectrum (162 MHz, CDCl3, 20 ꢁC) of 10.
exchange in solution. The exchange process can be
explained on the basis of a reversible skeletal rearrange-
ment brought about by the migration of a Ru–Ru bond
across the ruthenium triangle [13a] as shown in Scheme
4. Depending on which of the two Ru–Ru bonds
(Ru1–Ru2 or Ru2–Ru3) migrates to the basal plane of
the square pyramid linking the two non-bonded Ru
atoms (Ru1 and Ru3), different exchange behavior
would be observed. Isomerization via path A would
result in the exchange of PA1, PM1, PR1 and PX1 with
A2, PM2, PX2 and PR2, respectively. This pathway leads
P
to the isomer (10a) which differs significantly from the
solid-state structure in that the bridging diphosphazane
links the two non-bonded ruthenium atoms in the basal
plane. Isomerisation via path B would result in the
exchange of PA1, PM1, PR1 and PX1 with PM3, PA3, PX3
and PR3, respectively. The isomer obtained in this way
(100) is similar to 10 and differs only in the number of

T.S. Venkatakrishnan et al. / Journal of Organometallic Chemistry 690 (2005) 4001–4017
4013
X2
R1
Expected exchange
behavior
P
P
S
S
Ru
Ru
Me
N
Me
N
Ru
Ru
PA1
PM1
PR1
PX1
PA2
PM2
PX2
PR2
S
S
A2
P
P
A1
P
P
Path A
R2
X1
N
Ru
Ru
N
Me
= CO
P
P
Me
M2
M1
10
10a
Path B
Path C
PA3
PM3
PR3
PX3
PM2
PA2
PR2
PX2
PA1
PM3
PA3
PX3
PR3
X3
P
PM1
PR1
PX1
S
Ru
Me
N
Ru
S
M3
P
P
R3
N
Ru
Me
P
A3
PA1
PA2
PM1
PM2
PR1
PR2
PX1
PX2
10'
Exchange behavior as shown by 31P-31P NOESY
Scheme 4. Reversible skeletal rearrangements occurring in the cluster [Ru3(l3-S)2(CO)5{j2-P,P-(PhO)2PN(Me)P(OPh)2}{l-P,P-(PhO)2PN(Me)-
P(OPh)2}] (10).
carbonyls at the ruthenium centers. Because of the simi-
larity in the structures of 10 and 100, the 31P chemical
two triplets that correspond to the methyl protons of
the chelating diphosphazane of the two isomers.
shifts of the phosphorus nuclei in 100 (PA3, PM3, PR3
,
P
X3) would be close to those of 10 (PA1, PM1, PR1, PX1
)
3.6. Crystal and molecular structures of the
tetraruthenium clusters 1, 3, 7 and 11
and hence separate resonances for 100 are not observed.
This supposition is supported by the observation of the
exchange peaks A1–M3, M1–A3, R1–X3 and X1–R3 in
the 31P–31P phase-sensitive NOESY spectrum (Fig. 7)
at the same position as the correlation peaks observed
for the A1–M1 and R1–X1 in the COSY spectrum
(Fig. 5). The direct exchange peaks observed for the
phosphorus nuclei of the chelating diphosphazane (R1
exchanging with R2, X1 exchanging with X2) can be ac-
counted for by the isomerisation of 100 to 10a via path
C. The observed exchange behavior (see Scheme 4)
clearly shows that isomerization occurs by all the three
pathways; however, among the three possible isomers
as noted above, resonances of only two distinct isomers
are observed in the 31P NMR spectrum.
The structures of the clusters 1, 3, 7 and 11 as re-
vealed by X-ray crystallography show an octahedral
arrangement of four ruthenium atoms and two chalco-
gens in which the four metals form the square plane.
The diphosphazane adopts a bridging mode of coordi-
nation and lies trans to the doubly bridging carbonyl
ligand. All these clusters are isostructural and show
similar trends in their structural parameters. For a
comparison of the structural features of these tetraru-
thenium clusters, selected data of 7 and 11 only are
included here (see Table 4). The data for the clusters 1
and 3 are given in Section 5. The molecular structure
of 11 is shown in Fig. 3. The Ru–Ru edge bridged by
the diphosphazane in these closo octahedral clusters is
The 1H NMR spectrum of 10 displays only three trip-
lets in the ratio 5:4:1 for the methyl protons attached to
nitrogen (two triplets are expected for each isomer). The
downfield triplet is assigned to the methyl protons of the
bridging diphosphazane of both the isomers based on
heteronuclear 31P–1H COSY experiment. The other
two triplets arise from the methyl protons of the chelat-
ing diphosphazane of the two isomers. A 1H–1H
ROESY spectrum shows exchange peaks between the
˚
shorter (ꢁ0.08–0.13 A) than the other two edges that
do not contain a bridging ligand. It is also shorter
˚
(ꢁ0.04–0.07 A) than the edge bridged by the carbonyl
ligand reflecting the short span angle of the diphosphaz-
ane. Such a trend in the bond lengths is also observed in
˚
dppa [Ph2PN(H)PPh2] (0.08–0.10 and 0.02 A) clusters,
[Ru4(l4-E)2(l-CO)(CO)8{l-P,P-dppa}] (E = S, Se) [17a].
However, in the dppm [Ph2PCH2PPh2] [13b] analogue,

4014
T.S. Venkatakrishnan et al. / Journal of Organometallic Chemistry 690 (2005) 4001–4017
Table 4
Comparison of structural parameters in the clusters 7, 9, 10 and 11
7
9
10
11
˚
Bond distances (A)
Ru(1)–Ru(2)
Ru(1)–Ru(4)
Ru(2)–Ru(3)
Ru(3)–Ru(4)b
Ru–S(1)Æaveæ
Ru–S(2)Æaveæ
Ru–P
2.690(1)a
2.771(1)
2.824(1)
2.769(2)a
2.827(1)
2.696(1)a
2.791(1)
2.798(1)
–
–
–
2.809(2)
2.809(2)
2.370(2)
2.722(1)a
2.755(1)
2.469(1)
2.480(1)
2.742(1)
2.486(2)
2.468(2)
2.386(1)
2.393(1)
–
2.289(1), 2.332(1)
1.716(2)
1.876(4)
2.263(2), 2.266(2)
1.673(4)
1.913(5)
2.207(1), 2.272(1)c 2.253(1), 2.237(1)d
1.668(2),c 1.675(2)d
1.898(4)
2.249(2) 2.244(2)
1.670(5)
1.878(7)
P–NÆaveæ
Ru–C(O)Æaveæ
Ru–C(O)Æaveæ (bridging)
C–O(l)
2.044(4)
1.157(4)
2.177(5)
1.189(5)
–
–
2.042(7)
1.155(7)
Bond angles (ꢁ)
P–N–P
P–N–C
118.5(1)
116.8(2) 124.2(2)
137.2(3), 138.1(3)
121.4(2)
119.3(4) 119.2(4)
132.1(3) 132.8(4) 131.5(4)
98.6(2),c 120.9(2)d
122.4(3)
118.3(4) 119.2(4)
137.2(6), 138.4(3)
130.2(2), 130.8(2)c 118.9(2), 120.1(2)d
Ru–C–O(l)
a
–
Edge bridged by diphosphazane.
Edge bridged by carbonyl ligand.
Chelating diphosphazane.
b
c
d
Bridging diphosphazane.
while the edge bridged by the diphosphine is shorter
(symmetrically bridging in the clusters 1 and 7, semi-
bridging in the previously reported cluster [17b]). The
˚
than the other two ‘‘non-bridged’’ edges (0.06 A), the
edge bridged by dppm is longer than that bridged by
˚
carbonyl ligand (0.02 A). Though the span angle of
˚
mean Ru–S distances in cluster 7 is longer (ꢁ0.11 A)
than that in the sulfur monocapped cluster. This
indicates an overall expansion of the cluster core upon
going from arachno tetrahedral to closo octahedral
framework.
dppm (115.2(2)ꢁ) is shorter than that of the diphospha-
zanes used here, this reverse trend in bond distance is
probably due to the less p-back bonding to the phospho-
rus center in dppm as compared to P–N–P analogues.
The Ru–P, Ru–E (E = S or Se), Ru–C(O), C–O and
P–N distances are unexceptional and are comparable
to literature values [13b,17]. The Ru–P bond in cluster
11, in which the diphosphazane bears a strong p-accep-
tor phosphorus, is shorter than that in the clusters 1, 3,
and 7 (see Table 4 and Section 5). The strong p-acceptor
nature of the phosphorus in 11 is also responsible for the
3.7. Crystal and molecular structures of the triruthenium
clusters 9 and 10
The structure of [Ru3(l3-S)(l3-CO)(CO)7{l-P,P-
(PhO)2PN(Me)P(OPh)2}] (9) (Fig. 1) consists of an isos-
celes triangle of triruthenium framework with a triply
bridging sulfur, a triply bridging carbonyl group and a
bridging diphosphazane ligand. This cluster is a 48 elec-
tron species, in which the cluster core has a trigonal
bipyramidal geometry consisting of 3 ruthenium atoms,
a triply bridging sulfur and a triply bridging carbonyl li-
gand. To the best of our knowledge, there are only two
reports on the ‘‘structural characterization ’’ of [M3(l3-
E)(l3-CO)L9] (L = 2eꢀ donor ligand) family of clusters
bearing phosphorus donor ligands, viz. [Os3(l3-Se)-
(l3-CO)(CO)7{l-P,P-Ph2PCH2PPh2}] [9b] and [Ru3-
(l3-Se)(l3-CO)(CO)7(PPh3)2] [10b]. Other reports [30]
on this family of clusters do not bear phosphorus donor
ligands. The bonding parameters are listed in Table 4.
The Ru–Ru edge bridged by the diphosphazane is
˚
shortening of P–N bond distance by ꢁ0.04 A as
compared to 7. The sum of the angles at nitrogen in this
cluster and in all the clusters reported in this paper is
close to 360ꢁ revealing planar geometry around the
nitrogen atom.
The contrast in the cluster skeletal framework of the
‘‘closo octahedral’’ chalcogen bicapped tetraruthenium
clusters, [Ru4(l4-E)2(l-CO)(CO)8{l-P,P-Ph2PN(R)PPh2}]
[E = Se, R = (S)- CHMePh (1) or E = S, R = CHMe
*
(7)] with that of the sulfur monocapped ‘‘arachno tetra-
2
hedral’’ triruthenium cluster [Ru3(l3-S)(lsb-CO)(CO)7-
{j2-P,P-Ph PN((S)- CHMePh)PPh }] (A) [17b] is
*
2
2
noteworthy. The Ru–Ru edges that do not bear a bridg-
ing ligand in the clusters 1 or 7 are longer than those in
the sulfur monocapped cluster. The edge bridged by the
˚
0.04 A shorter than the other two edges. The triply
˚
bridging sulfur lies at 1.736 A above the triruthenium
˚
˚
plane while the carbonyl group is located at 1.460 A
carbonyl ligand in 1 or 7 is shorter (ꢁ0.04–0.06 A) than
that in the monocapped cluster. This shortening can be
attributed to the different coordination modes of the
bridging carbonyl ligand in the two types of clusters
below the triruthenium plane. There is a slight asymme-
try in the coordination of the triply bridging carbonyl
and sulfur to the triruthenium core. The triply bridging

T.S. Venkatakrishnan et al. / Journal of Organometallic Chemistry 690 (2005) 4001–4017
4015
sulfur (4 electron donor) is closer to Ru(1) and Ru(3)
while the triply bridging carbonyl (2 electron donor) is
closer to Ru(2) and is slightly farther from the other
two ruthenium centers. The span angle of the diphosp-
hazane is slightly greater than that seen in the other
structures reported in this paper and is closer to that
in 11, because of which the Ru–Ru edge bridged by
the diphosphazane is longer than that in the clusters 1,
3 and 7 (see Table 4 and Section 5). The Ru–S distances
are shorter than those in the closo structures 7 and 11.
The C–O bond distance of the triply bridging carbonyl
When we compare the values of the Ru–Ru edge
bridged by the diphosphazane that bears the same
diphosphazane ligand as in clusters 9, 10 and 11, we find
that on going from a trigonal bipyramidal geometry (9)
to an octahedral geometry (11) through the square pyra-
midal gemometry (10), there is a gradual decrease in the
Ru–Ru edge bridged by the diphosphazane, a trend that
implies a gradual closing of the cluster framework. Con-
comitantly, the mean Ru–S distance shows a gradual in-
crease along the sequence 9, 10 and 11.
˚
(1.189(6) A) is longer than that observed in 1, 3 and 7
˚
(1.16 A) and is close to that reported in literature for a
triply bridging carbonyl [9b,10b].
4. Conclusions
The molecular structure of 10 (Fig. 2) represents a 50-
electron square pyramidal open nido triruthenium cluster
that bears two diphosphazane ligands in different coordi-
nation modes (one chelating and the other bridging
mode of binding). The bite angle at Ru(1) is 68.8ꢁ while
the span angle of the chelating and bridging diphosphaz-
ane units are 98.6ꢁ and 120.9ꢁ, respectively. The Ru–Ru
A variety of chalcogen bridged ruthenium carbonyl
clusters have been synthesized from the reaction of
Ru3(CO)12 with a range of diphosphazane mono- and
dichalcogenidesbyvaryingthechalcogenandthep-accep-
tor capability of the phosphorus centers. In general, it is
found that diphosphazane monosulfides bearing a less
p-acceptorphosphorus give risetosulfur monocappedtri-
ruthenium clusters in which the diphosphazane adopts a
chelating mode of coordination [17b]. On the other hand,
diphosphazane monoselenides afford the bicapped
tetraruthenium clusters in which the diphosphazane is in
bridgingmodeofcoordinationinadditiontomonocapped
triruthenium clusters. Diphosphazane dichalcogenides
give mainly chalcogen bicapped tetraruthenium clusters
as the main products irrespective of the nature of the chal-
cogen. Diphosphazane monosulfide derived from a
diphosphazane bearing a strong p-acceptor phosphorus
showsadifferenttypeofreactivity.Stepwisesulfurtransfer
occurs to give successively a sulfur monocapped Ru3 clus-
ter containing a l3-CO and a bridging diphosphazane and
a sulfur bicapped Ru3 cluster containing both chelating
and bridging diphosphazane. Preliminary experiments
on the synthesis of sulfur bicapped ruthenium carbonyl
clusters bearing two different diphosphazane ligands re-
veal that, at least one of the diphosphazanes should be a
strongp-acceptor[e.g.(PhO)2PN(Me)P(OPh)2].Monoch-
alcogenides (e.g. L4, L5 and Ph2PN(R)P(S)Ph2) derived
from a diphosphazane in which the p-acceptor capability
ofthephosphoruscentersislowdonotgiveachalcogenbi-
cappedcluster bearing twodiphosphazanemoieties. Also,
irrespectiveofthenatureofthep-acceptorcapabilityofthe
phosphorus centers in the diphosphazane monosulfide,
second sulfur transfer occurs to give a cluster in which
the second diphosphazane adopts a chelating mode of
coordination.
˚
edge that bears the bridging diphosphazane is 0.1 A
shorter than the other edge. The torsion angles
P(1)–Ru(1)–Ru(2)–P(3) and P(2)–Ru(1)–Ru(2)–P(3)
[100.6(1)ꢁ and ꢀ155.9(1)ꢁ, respectively] indicate that
P(1) is pseudo-trans to P(3) while P(2) is cisoid to P(3).
The presence of two strongly p-accepting phosphorus
centers almost trans to each other on either side of the
Ru(1)–Ru(2) bond elongates it compared to Ru(2)–
Ru(3) distance. Hence, there is a considerable shortening
of Ru(1)–P(1) bond at the pseudo-axial position com-
pared to the other Ru–P distances. The Ru–S bond dis-
tances are similar to those in 9 but shorter than those
in 11. Other bond-distances and bond-angles are similar
to those observed in other structures. The packing in the
lattice consists of a weak hydrogen bond network involv-
ing the hydrogen atoms on the phenyl rings and the
oxygen atoms of the carbonyl group. The solid-state
structure is the favored isomer in solution also because,
in this geometry, there is a subtle balance of the p-accept-
ing capability of the phosphorus nuclei present at each
ruthenium center. On the other hand, in the minor iso-
mer that exists in solution, the presence of two strongly
p-acceptor phosphorus mutually trans to each other
could probably weaken the cluster framework. At this
stage it is worth noting that the solid state structure of
the triruthenium dppa cluster, [Ru3(l3-S)2(CO)7(l-P,P-
dppa)] is the one in which the dppa ligand bridges two
non-bonded ruthenium atoms [17a] corresponding to
the minor isomer 10a. The Ru. . .Ru non-bonded
distance in 10 and [Ru3(l3-S)2(CO)7(l-P,P-dppa)] are
˚
3.653 and 3.561 A, respectively. The smaller span angle
5. Supplementary material
of the ligand in 10 (120.9) compared to that of the dppa
ligand (137.7) in [Ru3(l3-S)2(CO)7(l-P,P-dppa)] may be
responsible for the bridging of the two bonded ruthe-
nium centers in 10 by the diphosphazane ligand.
Crystallographic data for the structures reported in
this paper have been deposited with the Cambridge Crys-
tallographic Data Centre as supplementary publication

4016
T.S. Venkatakrishnan et al. / Journal of Organometallic Chemistry 690 (2005) 4001–4017
[11] D. Belletti, C. Graiff, V. Lostao, R. Pattacini, G. Predieri, A.
Tiripicchio, Inorg. Chim. Acta 347 (2003) 137–144.
[12] (a) D. Cauzzi, C. Graiff, C. Massera, G. Predieri, A. Tiripicchio,
Inorg. Chim. Acta 300–302 (2000) 471–476;
nos. CCDC-252278 (1), -252279 (3), -252280 (7), -252281
(9), -252282 (10) and -252283 (11) contain the supple-
mentary crystallographic data for this paper. Copies of
the data can be obtained free of charge from the Direc-
tor, CCDC, 12, Union Road, Cambridge, CB2 1EZ,
UK (Fax: +44 1223 336033; deposit@ccdc.cam.ac.uk
or http://www.ccdc.cam.ac.uk
(b) D. Cauzzi, C. Graiff, C. Massera, G. Predieri, A. Tiripicchio,
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(b) D. Cauzzi, C. Graiff, G. Predieri, A. Tiripicchio, C. Vignali, J.
Chem. Soc. Dalton Trans. (1999) 237–241;
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We thank the Department of Science and Technol-
ogy, New Delhi, India for financial support and for
the data collection using the CCD X-ray facility, IISc,
Bangalore set up under IRHPA program. We also thank
Dr. N. Suryaprakash and Ms. Anu Joy (Sophisticated
Instruments Facility, Indian Institute of Science, Banga-
lore) for simulation of the NMR spectrum of compound
10.
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