Addition of primary phosphines to the unsaturated triosmium cluster [(μ-H)Os3(CO)8{Ph2PCH2P(Ph)C 6H4}]: Synthesis of triosmium clusters bearing dppm, phosphide and phosphinidene ligands via P-H bond activation

Article abstract of DOI:10.1016/j.jorganchem.2005.06.005

Treatment of the electronically unsaturated cluster [(μ-H)Os ₃(CO)₈{Ph₂PCH₂P(Ph)C ₆H₄}] (1) with primary phosphines PPhH₂ and PCyH₂ gives the phosphido bridged compounds [(μ-H)Os ₃(CO)₈(μ-PPhH)(μ-dppm)] (2) and [(μ-H)Os ₃(CO)₈(μ-PCyH)(μ-dppm)] (3), respectively, by P-H bond activation of the phosphines and demetallation of the phenyl ring of the diphosphine ligand. Thermolysis of 2 and 3 in refluxing octane at 128 °C results in the formation of the phosphinidene compounds [(μ-H) ₂Os₃(CO)₇(μ₃-PPh)(μ-dppm)] (4) and [(μ-H)₂Os₃(CO)₇(μ₃-PCy) (μ-dppm)] (5), respectively, by further P-H bond cleavage of the phosphido groups. All the compounds have been characterized by infrared, ¹H NMR, ³¹P{¹H} NMR and mass spectroscopic data together with single-crystal X-ray diffraction studies for 4. Compound 4 consists of a triangular cluster of osmium atoms with a symmetrically capped phosphinidene ligand and a bridging dppm ligand.

Full text of DOI:10.1016/j.jorganchem.2005.06.005

Journal of Organometallic Chemistry 690 (2005) 4206–4211
www.elsevier.com/locate/jorganchem
Note
Addition of primary phosphines to the unsaturated triosmium
cluster [(l-H)Os3(CO)8{Ph2PCH2P(Ph)C6H4}]: Synthesis
of triosmium clusters bearing dppm, phosphide and
phosphinidene ligands via P–H bond activation
a
a
a,
*
Shamsuddin M. Azad , Kazi A. Azam , Shariff E. Kabir
,
a
b
Madhu S. Saha , G.M. Golzar Hossain
a
Department of Chemistry, Jahangirnagar University, Savar, Dhaka-1342, Bangladesh
School of Chemistry, Cardiff University, Main College Building, Cardiff CF10 3AT, United Kingdom
b
Received 21 May 2005; received in revised form 29 May 2005; accepted 3 June 2005
Abstract
Treatment of the electronically unsaturated cluster [(l-H)Os3(CO)8{Ph2PCH2P(Ph)C6H4}] (1) with primary phosphines PPhH2
and PCyH2 gives the phosphido bridged compounds [(l-H)Os3(CO)8(l-PPhH)(l-dppm)] (2) and [(l-H)Os3(CO)8(l-PCyH)(l-
dppm)] (3), respectively, by P–H bond activation of the phosphines and demetallation of the phenyl ring of the diphosphine ligand.
Thermolysis of 2 and 3 in refluxing octane at 128 ꢀC results in the formation of the phosphinidene compounds [(l-H)2Os3(CO)7(l3-
PPh)(l-dppm)] (4) and [(l-H)2Os3(CO)7(l3-PCy)(l-dppm)] (5), respectively, by further P–H bond cleavage of the phosphido groups.
All the compounds have been characterized by infrared, 1H NMR, 31P{1H} NMR and mass spectroscopic data together with single-
crystal X-ray diffraction studies for 4. Compound 4 consists of a triangular cluster of osmium atoms with a symmetrically capped
phosphinidene ligand and a bridging dppm ligand.
ꢁ 2005 Elsevier B.V. All rights reserved.
Keywords: Triosmium clusters; Primary phosphine; Phosphide; Phosphinidene; X-ray structure
1. Introduction
ligand (l2-PR2) acts as a robust and flexible bridge
and keeps the integrity of the metal framework in a great
variety of reactions including decarbonylation [2], oxi-
dation [3], and protonation [4] thus leading to many
new metal–metal bonded substrates. In case of a pri-
mary phosphine, the l2-PRH ligand on thermolysis or
photolysis can lead to further oxidative addition result-
ing in the formation of phosphinidene (l3-PR) moiety in
the presence of more than two metal centers [5]. Trinu-
clear complexes of the type [(l-H)M3(CO)10(l-PR2)]
(M = Fe, Ru, Os; R = organic residue) have been exten-
sively investigated by several groups [6–8].
The scission of a P–H bond of a secondary or pri-
mary phosphine within the coordination sphere of a
transition metal di- and polynuclear compound either
thermally or photochemically leading to the formation
of bridging hydrido and phosphido ligands has been
the subject of numerous studies [1]. The phosphide
*
Corresponding author. Present address: Department of Chemistry,
University of Montana, Missoula, MT 59812, USA. Tel.: +406 243
2592; fax: +406 243 4227.
During the past few years, we have been studying
the reactions of the coordinatively unsaturated trios-
E-mail address: skabir_ju@yahoo.com (S.E. Kabir).
0022-328X/$ - see front matter ꢁ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.06.005

S.M. Azad et al. / Journal of Organometallic Chemistry 690 (2005) 4206–4211
4207
mium cluster [(l-H)Os3(CO)8{Ph2PCH2P(Ph)C6H4}]
2.1. Reaction of [(l-H)Os3(CO)8{Ph2PCH2P(Ph)-
C6H4}] (1) with PPhH2
(1) with a wide variety of small inorganic and organic
molecules to afford many interesting and potentially
useful compounds [9]. A few years ago, we reported
that 1 reacts with PPh2H at ambient temperature
to give [(l-H)Os3(CO)8{l3-g3-Ph2PCH2P(Ph)C6H4}-
(PPh2H)] and [Os3(CO)8(l-dppm)(PPh2H)2] [10]. We
also found that [Os3(CO)10(l-dppm)], the precursor
of 1, gives completely different products, [Os3(CO)9-
(l-dppm)(Ph2PH)] and [H(l-H)Os3(CO)7(l-dppm)-
(l-PPh2)2] when treated with PPh2H at 110 ꢀC.
Bo¨ttcher et al. reported that bulky phosphines, such
as, tBu2PH reacts with [Os3(CO)10(l-dppm)] and
[Ru3(CO)10(l-dppm)] to give exclusively the electron
deficient compounds [(l3-H)(l-H)Os3(CO)5(l-dppm)-
(l-PtBu2)2] [11] and [(l3-H)(l-H)Ru3(l-CO)(CO)4-
(l-dppm)(l-PtBu2)2] [12], respectively. Interestingly,
the reaction of [Ru3(CO)10((l-dppm)] with less bulky
phosphine Cy2PH leads to the electronically saturated
compound [(l-H)2Ru3(CO)6(l-dppm)(l-PCy2)2] [12].
Recently, we have reported that [Ru3(CO)10(l-dppm)]
reacts with PPh2H in refluxing heptane to give four
triruthenium compounds, [Ru3(CO)6(l-CO)(l3-CH2P-
A 10% hexane solution of PPhH2 (0.014 g, 0.127
mmol) was added to a CH2Cl2 solution (25 mL) of 1
(0.075 g, 0.064 mmol) and the reaction mixture was stir-
red at room temperature for 30 min during which time
the color changed from green to yellow. The solvent
was removed under reduced pressure and the residue
chromatographed by TLC on silica gel. Elution with
cyclohexane/CH2Cl2 (2:1, v/v) developed one band
which afforded [(l-H)Os3(CO)8(l-PPhH)(l-dppm)] (2)
(0.049 g, 60%) as orange crystals after recrystallization
from CH2Cl2/hexane at À4 ꢀC. Anal. Calc. for
C39H29O8Os3P3: C, 36.33; H, 2.27. Found: C, 36.55;
H, 2.45%. IR (mCO, CH2Cl2): 2066 s, 2020 s, 1991 vs,
1933 m cmÀ1
;
1H NMR (CDCl3): d 7.66–7.08 (m,
1
25H), 6.17 (d, 1H, JP–H = 413.5), 5.56 (m, 1H),
2
4.67 (m, 1H), À18.24 (ddd, 1H, JP–H = 17.6, 7.8,
3JP–H = 4.4 Hz); 31P{1H} NMR (CD2Cl2): d À14.1
2
3
(dd, 1P, JP–P = 20.4, JP–P = 3.6 Hz), À20.4 (dd, 1P,
2
2JP–P = 41.3, 20.6 Hz), À28.5 (dd, 1P, JP–P = 41.3,
3JP–P = 3.6 Hz); FAB MS: m/z 1288 (M+).
Ph)(l-PPh2)2],
[(l-H)Ru3(CO)6(l3-g2-PPh2CH2PPh)-
(l-PPh2)2], [(l-H)2Ru3(CO)5(l-dppm)(l3-PPh)(l-PPh2)2],
and [(l-H)2Ru3(CO)6(l-dppm)(l-PPh2)2] formed by
the cleavage of P–C and P–H bonds of the ligands
[13]. Herein, we report our findings on the synthesis
and characterization of [(l-H)Os3(CO)8(l-PPhH)-
(l-dppm)] (2) and [(l-H)Os3(CO)8(l-PCyH)(l-dppm)]
(3) along with the results of our experiments on the
thermolysis of 2 and 3 to give [(l-H)2Os3(CO)7-
(l3-PPh)(l-dppm)] (4) and [(l-H)2Os3(CO)7(l3-PCy)-
(l-dppm)] (5), respectively.
2.2. Reaction of [(l-H)Os3(CO)8{Ph2PCH2P(Ph)-
C6H4}] (1) with PCyH2
A similar reaction between a 10% hexane solution of
PCyH2 (0.021 g, 0.181 mmol) and 1 (0.105 g, 0.089
mmol) followed by similar chromatographic separation
afforded [(l-H)Os3(CO)8(l-PCyH)(l-dppm)] (3) (0.052
g, 45%) as yellow crystals after recrystallization from
CH2Cl2/hexane at À4 ꢀC. Anal. Calc. for C39H35O8-
Os3P3: C, 36.16; H, 2.73. Found: C, 36.29; H, 2.95%.
IR (mCO, CH2Cl2): 2065 s, 2021 s, 1990 vs, 1933 m cmÀ1
;
1H NMR (CDCl3): d 7.49–7.19 (m, 25H), 5.24 (ddt, 1H,
2
3
2. Experimental
1JP–H = 381.7, JP–H = 4.0, JP–H = 2.0 Hz), 5.18 (m,
1H), 5.14 (m, 1H), 2.06–0.45 (m, 11H), À18.61 (ddd,
2
3
All reactions were carried out under an atmosphere
of dry nitrogen, using standard Schlenk techniques. Sol-
vents were dried and distilled under nitrogen from
appropriate drying agents and degassed prior to use.
Phenylphosphine and cyclohexylphosphine were pur-
chased as 10% hexane solution from Strem and used
as received. The starting cluster [(l-H)Os3(CO)8{Ph2-
PCH2P(Ph)C6H4}] (1) was prepared according to the
literature method [14]. Infrared spectra were recorded
on a Shimadzu FT-IR 8101 spectrophotometer. 1H
and 31P{1H} NMR spectra were recorded on a Bruker
DPX 400 spectrometer. Chemical shifts for the
31P{1H} NMR spectra are relative to 85% H3PO4. Fast
atom bombardment mass spectra were obtained on a
JEOL SX-102 spectrometer using 3-nitrobenzyl alcohol
as matrix and CsI as calibrant. Elemental analyses were
carried out at the microanalytical Laboratories, Univer-
sity College London.
1H, JP–H = 15.6, 9.6, JP–H = 4.4 Hz); 31P{1H} NMR
2
3
(CD2Cl2): d À1.8 (dd, 1P, JP–P = 20.6, JP–P = 4.0
2
3
Hz), À26.2 (dd, 1P, JP–P = 40.0, JP–P = 4.0 Hz),
2
À28.5 (dd, 1P, JP–P = 40.0, 20.6 Hz); FAB MS: m/z
1294 (M+).
2.3. Thermolysis of [(l-H)Os3(CO)8(l-PPhH)-
(l-dppm)] (2)
An octane solution (30 mL) of 2 (0.025 g, 0.019
mmol) was heated to reflux at 128 ꢀC for 4 h. The sol-
vent was removed under reduced pressure and the resi-
due chromatographed by TLC on silica gel. Elution
with cyclohexane/CH2Cl2 (7:3, v/v) gave a single band
which afforded [(l-H)2Os3(CO)7(l3-PPh)(l-dppm)] (4)
(0.018 g, 75%) as pale yellow crystals from hexane/
CH2Cl2. Anal. Calc. for C38H29O7Os3P3: C, 36.19; H,
2.32. Found: C, 36.37; H, 2.49%. IR (mCO, CH2Cl2):

4208
S.M. Azad et al. / Journal of Organometallic Chemistry 690 (2005) 4206–4211
2053 vs, 2024 vs, 1985 vs, 1927 m cmÀ1 1H NMR
;
Table 1
Crystal data and structure refinement for [(l-H)2Os3(CO)7(l3-PPh)-
(l-dppm)] Æ 1/2H2O (4)
(CD2Cl2): d 7.59–6.99 (m, 25H), 4.64 (m, 1H), 3.02 (m,
2
1H), À19.77 (dd, 1H, JP–H = 19.6, 10.8 Hz), À20.56
2
(dd, 1H, JP–H = 29.6, 10.8 Hz); 31P{1H} NMR
Empirical formula
Formula weight
Temperature (K)
C38H30O7.5Os3P3
1270.13
150(2)
0.71073
Monoclinic
P21/n
2
(CD2Cl2): d 124.0 (dd, 1P, JP–P = 14.3, 3.2 Hz), À14.3
2
(dd, 1P, JP–P = 48.9, 14.5 Hz), À25.0 (dd, 1P,
˚
Wavelength (A)
2JP–P = 48.9, 3.2 Hz); FAB MS: m/z 1260 (M+).
Crystal system
Space group
Unit cell dimensions
a (A)
2.4. Thermolysis of [(l-H)Os3(CO)8(l-PCyH)-
(l-dppm)] (3)
˚
11.210 (4)
21.454(6)
18.523(6)
˚
b (A)
˚
c (A)
A similar thermolysis to that above of 3 (0.035 g,
0.027 mmol) in refluxing octane for 5 h followed by sim-
ilar chromatographic separation developed two bands.
The first band afforded unreacted 3 (0.004 g) while the
second band gave [(l-H)2Os3(CO)7(l3-PCy)(l-dppm)]
(5) (0.017 g, 50%) as pale yellow crystals from hexane/
CH2Cl2 at À4 ꢀC. Anal. Calc. for C38H35O7Os3P3: C,
36.01; H, 2.79. Found: C, 36.25; H, 2.93%. IR (CO,
a (ꢀ)
b (ꢀ)
c (ꢀ)
90
104.08(2)
90
4321(2)
3
˚
Volume (A )
Z
4
Density (calculated) (mg/m3)
Absorption coefficient (mmÀ1
F(000)
1.952
8.954
2364
0.45 · 0.15 · 0.15
2.41–25.35
)
Crystal size (mm3)
h Range for data collection (ꢀ)
Index ranges
1
CH2Cl2): 2051 vs, 2023 vs, 1984 vs, 1925 m cmÀ1; H
À13 6 h 6 13, À25 6 k 6 6,
NMR (CDCl3): d 7.56–7.19 (m, 20H), 4.34 (m, 1H),
3.53 (m, 1H), 2.04–1.24 (m, 11H), À19.59 (dd, 1H,
0 6 1 6 22
Absorption correction
Reflections collected
Independent reflections
Completeness to theta = 25.35
Maximum and minimum
transmission
w scan
2
2JP–H = 18.0, 8.8 Hz), À20.84 (dd, 1H, JP–H = 31.2,
8201
10.4 Hz); 31P{1H} NMR (CD2Cl2): d 124.0 (dd, 1P,
7831 [R(int) = 0.0341]
98.9%
0.3469 and 0.1074
2
2JP–P = 14.3, 3.2 Hz), À14.3 (dd, 1P, JP–P = 48.9, 14.5
2
Hz), À25.0 (dd, 1P, JP–P = 48.9, 3.2 Hz); FAB MS:
m/z 1266 (M+).
Refinement method
Full-matrix least-squares on F2
7831/0/469
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
Largest difference in peak
and hole (e AÀ3
1.086
2.5. X-ray crystallography
R1 = 0.0558, wR2 = 0.1719
R1 = 0.0874, wR2 = 0.1989
3.704 and À3.574
Single crystals of 4 suitable for X-ray diffraction were
grown by slow diffusion of hexane into a dichlorometh-
ane solution at À4 ꢀC. Crystallographic data were
collected at 150 K, on a CAD4 diffractometer using
graphite monochromatised Mo Ka radiation (k =
)
by usual workup and chromatographic separation gave
exclusively the phosphido bridged compounds [(l-
H)Os3(CO)8(l-PPhH)(l-dppm)] and [(l-H)Os3(CO)8(l-
PCyH)(l-dppm)] (3) in 60% and 45% yields, respectively
(Scheme 1). Compounds 2 and 3 have been character-
ized by mass spectrometry, elemental analysis and by
1H, 31P{1H} NMR and IR spectroscopy. A partial
determination of the molecular structure of compound
2 was made [18], but the poor quality of the data pre-
cludes discussion of the structural details. The X-ray
analysis is, however, consistent with the proposed struc-
ture with two short Os–Os bonds one of which is
bridged by the dppm ligand and a longer Os–Os bond,
bridged by the hydride and the phosphide group. Fur-
thermore, the spectroscopic properties of 2 are in agree-
ment with the solid state structure being maintained in
solution. Unfortunately, suitable single crystals could
not be grown for compound 3 also. The infrared spectra
of 2 and 3 are very similar and show bands characteris-
tics of terminal carbonyl ligands. The close similarity of
the IR spectra in the carbonyl region of 2 and 3 indicate
that they are isostructural. The mass spectra exhibit
˚
0.71073 A). The unit cell parameters were determined
from all observed reflections in a h-range of 3–10ꢀ and
refined using the entire data set. The structures were
solved by direct methods (SHELXS-97) [15] and refined
on F2 by full matrix least-squares (SHELXL-97) [16] using
all unique data and corrected for absorption by using
the semi empirical w-scan methods [17]. All nonhydro-
gen atoms were refined anisotropically. The hydrogen
atoms were included in calculated positions (riding mod-
el) with Uiso set at 1.2 times the Ueq of the parent atom.
Final difference maps did not show any residual electron
density of stereochemical significance. The details of the
data collection and structure refinement are given in
Table 1.
3. Results and discussion
The reactions of the unsaturated cluster [(l-H)Os3-
(CO)8{Ph2PCH2P(Ph)C H4}] (1) with two equivalents
6
of PPhH2 and PCyH2 at ambient temperature followed

S.M. Azad et al. / Journal of Organometallic Chemistry 690 (2005) 4206–4211
4209
Ph
l-PRH ligand could be achieved. On heating either 2
or 3 at 128 ꢀC in octane, compounds [(l-H)2Os3(CO)7-
(l3-PPh)(l-dppm)] (4) and [(l-H)2Os3(CO)7(l3-PCy)-
(l-dppm)] (5) were obtained in 75% and 50% yields,
respectively. Compounds 4 and 5 have been character-
ized by elemental analysis, mass spectrometry and by
P
(CO)3
Os
CH2
Os(CO)3
PHR
PPh2
H
PRH2 (R = Ph, Cy)
Os(CO)2
PPh2
(CO)3Os
Ph2P
(CO)3Os
Os(CO)2
25 o
C
H
1
CH2
1
IR, H, 31P{1H} NMR spectroscopy. In addition, com-
2, R = Ph
3, R = Cy
pound 4 has been the subject of a single crystal X-ray
structure determination.
128 o
C
-CO
The solid-state structure of 4 is depicted in Fig. 1,
crystal data and structure refinement parameters are gi-
ven in Table 1, and selected bond distance and angles
are listed in the caption. The structure is based on the
previously reported compound [(l-H)2Os3(CO)9(l3-
PPh)] which was synthesized by the thermolysis of either
[Os3(CO)11(PPhH2)] or [(l-H)Os3(CO)9(l2-PPhH)] in
refluxing nonane [19]. The molecular structure of 4 con-
sists of a triangular core of osmium atoms with two sim-
ilar but significantly elongated Os–Os bond distances,
(CO)3
Os
PR
H
Os(CO)2
PPh2
(CO)2Os
Ph2P
H
CH2
4, R = Ph
5, R = Cy
Scheme 1.
˚
Os(1)–Os(2) = 2.9617(10), Os(1)–Os(3) = 2.9714(10) A,
and one shorter Os–Os bond, Os(2)–Os(3) =
˚
molecular ion peaks (m/z 1288 for 2; 1294 for 3) corre-
sponding to their proposed formulations and fragmen-
tation peaks due to the sequential loss of eight
carbonyl ligands. The 1H NMR spectra confirm the for-
mation of a bridging hydrido and phosphido ligands by
activation of a P–H bond by showing characteristic P–H
2.8498(12) A. The seven terminal carbonyl ligands are
distributed so that two are bonded to each of Os(1)
and Os(2) and three bonded to Os(3). The Os(1)–Os(2)
edge is simultaneously bridged by a hydride and the
dppm ligand. The other hydride ligand spans the
Os(1)–Os(3) edge. The position of the hydride ligands
were located but not refined. The elongation of the
Os(1)–Os(2) and Os(1)–Os(3) edges are also consistent
with the hydrides being bridged on these edges while
1
(a doublet at d 6.17, JP–H = 413.5 Hz for 2 and a dou-
1
2
blet of doublets of triplets at d 5.24, JP–H = 381.7, JP–
3
H = 4.0, JP–H = 2.0 Hz for 3) and hydride resonances
2
3
{d À18.24 (ddd, 1H, JP–H = 17.6, 7.8, JP–H = 4.4 Hz
2
for 2 and d À18.61 (ddd, 1H, JP–H = 15.6, 9.6,
3JP–H = 4.4 Hz) for 3}. In the case of the cyclohexyl-
phosphine compound 3, in addition to the P–H cou-
pling, another coupling arises from a-hydrogen atom
of the cyclohexyl group (JH–H = 4.0 Hz). The chemical
shifts and coupling constants of these resonances in 2
and 3 are in agreement with the proposed structures
and the data reported for the related phosphido bridged
triosmium compounds [(l-H)Os3(CO)10(l-PPhH)] and
[(l-H)Os3(CO)10(l-PCyH)] which were synthesized from
the Me3NO initiated reactions of [Os3(CO)12] with
PPhH2 and PCyH2, respectively [18]. In addition to phe-
nyl resonances, the multiplets at d 5.56 and 4.67 for 2
and d 5.18 and 5.14 for 3 are due to the methylene
protons of the dppm ligands. In the 31P{1H} NMR spec-
tra of 2 and 3, there are three doublet of doublets, one
2
3
Fig. 1. ORTEP drawing of [(l-H)2Os3(CO)7(l3-PPh)(l-dppm)] (4).
Thermal ellipsoids are drawn at the 50% probability level. Selected
bond distances (A) and angles (ꢀ): Os(1)–Os(3) = 2.9714(10), Os(2)–
Os(3) = 2.8498(12), Os(1)–Os(2) = 2.9617(10), Os(2)–P(3) = 2.332(4),
Os(3)–P(1) = 2.341(4), Os(1)–P(1) = 2.354(4), Os(2)–P(1) = 2.333(4),
Os(1)–P(2) = 2.332(4), Os(2)–Os(1)–Os(3) = 57.41 (3), Os(2)–Os(3)–
Os(1)=61.12(2), Os(3)–Os(2)–Os(1)=61.464(18), P(2)–Os(1)–Os(2) =
91.35(9), P(1)–Os(2)–Os(3) = 52.55(4), P(1)–Os(2)–Os(1) = 51.12(9),
due to l-PRH ligand (d-14.1, JP–P = 20.4, JP–P 3.6
Hz for 2 and d-1.8, JP–P = 20.6, JP–P 4.0 Hz for 3)
and two due to the dppm ligand (d-20.4, JP–P = 41.3,
2
3
˚
2
2
3
20.6 Hz, À28.5, JP–P = 41.3, JP–P = 3.6 Hz for 2; d-
2
3
2
26.2, JP–P = 40.0, JP–P = 4.0 Hz, À28.5, JP–P = 40.0,
20.6 Hz for 3), indicating that all the 31P nuclei are non-
equivalent and coupled to each other.
Os(3)–P(1)–Os(1) = 78.54(11), P(2)–C(26)–P(3) = 116.1(7),
P(1)–
Thermolysis of compounds 2 and 3 was carried out to
ascertain whether further P–H bond cleavage of the
Os(1)–Os(3) = 50.54(9), P(3)–Os(2)–Os(1) = 92.88(9), P(1)–Os(3)–
Os(1) = 50.93(9), Os(2)–P(1)–Os(1) = 78.39(11).

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S.M. Azad et al. / Journal of Organometallic Chemistry 690 (2005) 4206–4211
the short Os(2)–Os(3) edge carries no hydride. An inter-
esting feature of the structure is that the phosphinidene
ligand, PPh, almost symmetrically caps the Os3 triangle
{Os(1)–P(1) = 2.354(4), Os(2)–P(1)= 2.333(4) and Os(3)–
P(1) = 2.341(4) A}. This observation is in contrast to
that reported for [(l-H)2Os3(CO)9(l3-PPh)] in which
4. Conclusion
In this paper, we have demonstrated that the elec-
tronically unsaturated cluster [(l-H)Os3(CO)8{Ph2PCH2-
P(Ph)C6H4}] (1) reacts with two equivalents of PPhH2
and PCyH2 at room temperature to give the phosphido
bridged compounds [(l-H)Os3(CO)8(l-PPhH)(l-dppm)]
(2) and [(l-H)Os3(CO)8(l-PCyH)(l-dppm)] (3), respec-
tively. The formation of 2 and 3 from 1 involves oxida-
tive addition of PRH2 followed by demetallation of the
phenyl ring of the diphosphine ligand. These results are
in sharp contrast to those obtained from the reaction of
PPh2H with 1 which afforded two phosphine-substituted
compounds, [(l-H)Os3(CO)8{l3-g3-Ph2PCH2P(Ph)C6-
H4}(PPh2H)] and [Os3(CO)8(l-dppm)(PPh2H)2] [10]. It
leads one to think of the P–H bond activation in terms
of acid/base chemistry rather than an enhanced oxida-
tive cleavage (or addition) due to rapid kinetics, whose
origin undoubtedly lies in the greater accessibility of 1ꢀ
versus 2ꢀ P–H bonds towards cleavage at a metal
center(s). When refluxed in octane at 128 ꢀC, a further
P–H bond activation in both 2 and 3 occurs resulting
in the formation of the dihydrido phosphinidene
compounds [(l-H)2Os3(CO)7(l3-PPh)(l-dppm)] (4) and
[(l-H)2Os3(CO)7(l3-PCy)(l-dppm)] (5), respectively.
˚
the phosphinidene ligand asymmetrically caps the Os3
˚
triangle {2.309(8)–2.358(10) A} [18]. The dppm ligand
bridges in equatorial sites at Os(1) and Os(2) with both
the phosphorus nuclei on the same side of the Os3 plane.
The Os–P bond distances involving the dppm ligand
˚
{Os(1)–P(2) = 2.332(4), Os(2)–P(3) = 2.332(4) A) are
also symmetric and very similar to the Os–P distances
involving the phosphinidene ligand. All other features
of the molecular geometry are within the expected range.
Individual Os–CO distances range from 1.859(15) to
˚
1.928(17) A, C–O bond lengths range from 1.116(18)
˚
to 1.172(18) A and Os–C–O angles are in the range
˚
172.4(12)–178.1(13) A. The cluster is electron precise
with 48 electrons as expected for a closed triangular
cluster.
The spectroscopic data of 4 are consistent with the
solid state structure being maintained in solution. Fur-
thermore, on the basis of close similarity of the spectro-
scopic data between 4 and 5, a similar structure may be
ascribed for 5. Both compounds 4 and 5 exhibit car-
bonyl stretching bands in the region 2053–1921 cmÀ1
,
indicating that all the carbonyl groups are terminal.
The mass spectra exhibit molecular ion peaks (m/z
1260 for 4; 1266 for 5) and fragmentation peaks due
to the sequential loss of seven carbonyl ligands. In addi-
tion to phenyl and cyclohexyl proton resonances, the 1H
NMR spectra of 4 and 5 in the aliphatic region shows
two equally intense multiplets (d 4.64 and 3.02 for 4;
4.34 and 3.53 for 5) for the diastereotopic methylene
protons of the dppm ligand. The hydride region of the
spectra contain two double doublets (d À19.77,
Acknowledgement
The support of this research by the Ministry of
Science and Technology, Government of the Peoples
Republic of Bangladesh is gratefully acknowledged.
Appendix A. Supplementary data
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC No. 271515 for the compound 4.
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road
Cambridge, CB2 1EZ, UK (Fax: +44 1223 336033;
email: deposit@ccdc.cam.ac.uk or www: http://www.
ccdc.cam.ac.uk). Supplementary data associated with
this article can be found, in the online version at
doi:10.1016/j.jorganchem.2005.06.005.
2
2JP–H = 19.6, 10.8 Hz and À20.56, JP–H = 29.6, 10.8
2
Hz for 4; d À19.59, JP–H = 18.0, 8.8 Hz and À20.84,
2JP–H = 31.2, 10.4 Hz for 5), indicating the presence of
two nonequivalent hydride ligands each coupled to
two nonequivalent phosphorus nuclei. Consistent with
this the 31P{1H} NMR spectrum of 4 contains three
equal intensity doublet of doublets at d 124.0 (2JP–P
=
14.3, 3.2 Hz), À14.3 (2JP–P = 48.9, 14.5 Hz), and
À25.0 (2JP–P = 48.9, 3.2 Hz) for the three magnetically
non-equivalent phosphorus atoms. The deshielded reso-
nance at d 124.4 is readily assigned to the phosphinidene
moiety while the two remaining resonances at d 51.4 and
19.30 are due to the bridging dppm ligand. A similar
31P{1H} NMR is found for 5 with resonances appearing
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˚
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˚
˚
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˚
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