Synthesis and characterization of the dinuclear polyhydrides [Os 2H7PPhiPr2)4] and [Os2H6(PPhiPr2)4]

Article abstract of DOI:10.1021/ic900111s

The dinuclear osmium polyhydride [Os₂H₇(PPh _iPr₂)₄][HC(SO₂CF₃)2] (1) was synthesized by the protonation of [OsH₆(PPhⁱPr ₂)₂] with bis(trifluoromethylsulfonyl) methane. Treatment with amine bases was not able to deprotonate 1, but reaction with potassium hydride gave the corresponding neutral polyhydride [Os₂H ₆(PPhⁱPr₂)4] (2). Single crystal X-ray diffraction revealed that 1 and 2 both crystallize in the P2₁/c space group and are classical polyhydrides containing similar OS(μ-H) ₃OS cores with Os-Os distances of 2.5431(1) A and 2.5448(2) A, respectively. These structures represent rare examples of dinuclear osmium polyhydrides with six or more hydride ligands.

Full text of DOI:10.1021/ic900111s

Inorg. Chem. 2009, 48, 7977–7983 7977
DOI: 10.1021/ic900111s
Synthesis and Characterization of the Dinuclear Polyhydrides [Os2H7(PPhiPr2)4]þ
and [Os2H6(PPhiPr2)4]
Bradley G. Anderson,* Sarah A. Hoyte, and John L. Spencer*
School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington, New Zealand
Received January 19, 2009
The dinuclear osmium polyhydride [Os2H7(PPhiPr2)4][HC(SO2CF3)2] (1) was synthesized by the protonation of
[OsH6(PPhiPr2)2] with bis(trifluoromethylsulfonyl)methane. Treatment with amine bases was not able to deprotonate 1,
but reaction with potassium hydride gave the corresponding neutral polyhydride [Os2H6(PPhiPr2)4] (2). Single crystal
X-ray diffraction revealed that 1 and 2 both crystallize in the P21/c space group and are classical polyhydrides containing
˚
˚
similar Os(μ-H)3Os cores with Os-Os distances of 2.5431(1) A and 2.5448(2) A, respectively. These structures
represent rare examples of dinuclear osmium polyhydrides with six or more hydride ligands.
Introduction
[Os2H6(PPhiPr2)4] (2) (Scheme 1), as well as the X-ray crystal
structures of both species.
Dinuclear transition metal polyhydride complexes have
been known since complexes of the type Re2H8P4 (where P is
a phosphorus-donor ligand such as a phosphine) were first
reported by Chatt and Coffey in 1969.1 Since then homo- and
heterodinuclear polyhydrides of a range of metals including
molybdenum, ruthenium, and platinum have been synthe-
sized.2 Of these species, many of the most interesting com-
plexes have a relatively large hydride count of between six
and nine hydride ligands. A high hydride count means these
complexes require a low number of ancillary ligands for
stabilization, giving them a versatile chemistry based around
loss of molecular hydrogen and reaction with donor mole-
cules.2
Much of the research in this field has focused on dinuclear
polyhydrides of rhenium and ruthenium,3-6 with compara-
tively little work reported on similar diosmium polyhydrides.
Consequently there are few reports of diosmium compounds
with high hydride counts, such as the pentahydride
[Cp*2Os2H5]þ.7
Experimental Section
All reactions were carried out using degassed solvents and
standard Schlenk techniques under a nitrogen atmosphere.
Starting materials were purchased from Sigma-Aldrich and
used without further purification unless otherwise stated.
Bis(trifluoromethylsulfonyl)methane8 and [OsH6(PPhiPr2)2]9
were synthesized via previously reported methods. NMR
solvents were purchased from Sigma-Aldrich and stored under
nitrogen. NMR spectra were measured on Varian Unity Inova
300 and 500 MHz NMR spectrometers, with chemical shift
values δ referenced to the residual solvent peaks for 1H and to
85% H3PO4 for 31P. All IR spectra were obtained on a Perkin-
Elmer Spectrum One FT-IR Spectrometer using KBr disks.
Elemental analyses were performed by the Campbell Micro-
analytical Laboratory, University of Otago, New Zealand.
Protonation of [OsH6(PPhiPr2)2] - Synthesis of [Os2H7-
(PPhiPr2)4][HC(SO2CF3)2] (1). H2C(SO2CF3)2 (49 mg, 0.17 mmol)
was reacted with [OsH6(PPhiPr2)2] (101 mg, 0.17 mmol) in dichloro-
methane (5 mL) for 20 h. The solvent was removed in vacuo, leaving
a dark yellow oil. Addition of diethyl ether (15 mL) yielded the
product as air stable dark red microcrystals (0.11 g, 86%). 1HNMR
(CD2Cl2): δ 7.22 ppm (m, 20H, PC6H5), 3.90 (s, 1H, HC-
(SO2CF3)2), 2.00 (br s, 8H, PCH), 1.00 (br s, 48H, CH3), -8.93
(q, JP-H=8.4 Hz, 3H, bridging OsH), -12.92 (t, JP-H=28 Hz, 4H,
terminal OsH). 31PNMR(CD2Cl2):δ50.1ppm(s).IR(KBr, cm-1):
v(OsH) 2140 (w, br). Elemental Analysis: C51H84O4F6P4S2Os2
requires C, 42.4; H, 5.9%. Found: C, 42.5; H, 6.0%.
Herein we report the synthesis and characterization of the
dinuclear osmium heptahydride, [Os2H7(PPhiPr2)4]þ (1),
synthesized via the protonation of a mononuclear precursor
rather than the photochemical methods conventionally used
to produce diosmium polyhydrides. We also report the
deprotonation of 1 to form the first diosmium hexahydride,
*To whom correspondence should be addressed. E-mail: andersbrad@
myvuw.ac.nz (B.G.A.), john.spencer@vuw.ac.nz (J.L.S.).
(1) Chatt, J.; Coffey, R. S. J. Chem. Soc. A 1969, 1963–1972.
(2) Hlatky, G. G.; Crabtree, R. H. Coord. Chem. Rev. 1985, 65, 1–48.
(3) Allison, J. D.; Walton, R. A. J. Am. Chem. Soc. 1984, 106, 163–168.
(4) Ito, J.; Shima, T.; Suzuki, H. Organometallics 2004, 23, 2447–2460.
(5) Suzuki, H. Eur. J. Inorg. Chem. 2002, 2002, 1009–1023.
(6) Chaudret, B.; Devillers, J.; Poilblanc, R. Organometallics 1985, 4,
1727–1732.
Deprotonation of [Os2H7(PPhiPr2)4]þ - Synthesis of [Os2H6-
(PPhiPr2)4] (2). [Os2H7(PPhiPr2)4][HC(SO2CF3)2] (300 mg, 0.21
mmol) was added to a suspension of potassium hydride (27 mg,
0.67 mmol) in sodium-dried THF (20 mL). The mixture was
(8) Koshar, R. J.; Mitsch, R. A. J. Org. Chem. 1973, 38, 3358–3363.
(9) Connelly, N. G.; Howard, J. A. K.; Spencer, J. L.; Woodley, P. K.
J. Chem. Soc., Dalton Trans. 1984, 2003–2009.
(7) Kameo, H.; Suzuki, H. Organometallics 2008, 27, 4248–4253.
r
2009 American Chemical Society
Published on Web 07/13/2009
pubs.acs.org/IC

7978 Inorganic Chemistry, Vol. 48, No. 16, 2009
Anderson et al.
Scheme 1
stirred for 1 hour, after which the supernatant liquid was
removed and dried in vacuo to yield a dark brown expanded
oil. Recrystallization from diethyl ether yielded dark red micro-
crystals that decomposed when exposed to the atmosphere.
1H NMR (C6D6): δ 7.51 ppm (m, 8H, PC6H5), 6.91 (m, 12H,
bis(trifluoromethylsulfonyl)methane was observed in the
1H NMR spectrum at 3.90 ppm in a 1:1 ratio with 1. This
chemical shift was consistent with previous observations
of non-coordinated HC(SO2CF3)2
cationic nature of the product.
,
- 11 and confirmed the
PC6H5), 2.07 (sext, JH-H=6.9 Hz, 8H, PCH), 1.29 (dd, JP-H
=
Performing the protonation reaction in situ in an NMR
tube showed that initially an intermediate species (3)
was formed, which displayed a 31P NMR resonance at
15.0 Hz, JH-H=6.9 Hz, 24H, CH3), 1.05 (dd, JP-H=15.0 Hz,
JH-H = 6.9 Hz, 24H, CH3), -12.63 (s, 6H, OsH). 31P NMR
(C6D6): δ 48.2 ppm (s).
1
33.8 ppm and a broad singlet H NMR resonance at
Observation of the Protonation Intermediate [OsH7-
(PPhiPr2)2]þ (3). Dichloromethane-d2 was added to a mixture
of [OsH6(PPhiPr2)2] (20 mg, 0.034 mmol) and H2C(SO2CF3)2
(10 mg, 0.036 mmol) in a stoppered NMR tube under nitrogen
at 195 K. Quantitative formation of 1 was complete after about
30 min, at which point the yellow solution was analyzed by
NMR. Above approximately 253 K 3 reacts irreversibly to form
a dark red solution of 1. 1H NMR (CD2Cl2, 243 K): δ 7.64 ppm
(m, 4H, PC6H5), 7.54 (m, 6H, PC6H5), 3.85 (br s, 1H, HC-
(SO2CF3)2), 2.44 (m, 4H, PCH), 1.03 (m, 12H, CH3), 0.99 (m,
12H, CH3), -6.49 (s, 7H, OsH). 31P NMR (CD2Cl2, 243 K): δ
33.8 ppm (s).
-6.49 ppm. After 3 h at room temperature, this species
had been completely replaced by 1. Further investigation
revealed that 3 was indefinitely stable in CD2Cl2 solution
below 253 K. Repeating this reaction at 193 K allowed
formation of 3 without further reaction to form 1. Inte-
gration of the signals indicated that 3 had seven hydride
and two phosphine ligands, suggesting the chemical for-
mula [OsH7(PPhiPr2)2]þ.
Measurement of the spin-lattice relaxation time
T1 performed on 3 gave a value of 22.0 ms12 at 193 K
(the lower temperature limit of the probe). Obtaining
T1 values at 193 K (22.0 ms), 203 K (27.6 ms), 213 K
(35.0 ms), and 243 K (69.7 ms) allowed us to estimate that
T1 min would be in the vicinity of 17 ms at 170 K. This is
significantly shorter than T1 min for the starting material
(116 ms).13 Care needs to be exercised when assigning
non-classical structures on the basis of T1 measurements.
It has been demonstrated that metal-hydride and ligand-
hydride interactions can contribute significantly to the
observed hydride relaxation rate (Robs, 1/T1), leading
to a low T1 min value without the presence of a mole-
cular hydrogen ligand.13 This has led to classical poly-
hydrides being mistakenly characterized as molecular
hydrogen species14,15 on the basis of short T1 min values
(<100 ms).16 For 3 the metal-hydride and ligand-hydride
interactions can be approximated by using the values
from [OsH6(PPhiPr2)2] (adjusted to 300 MHz)13 and are
responsible for less than 7% of the value of Robs, meaning
that the observed T1 should be predominantly due to H-
H dipole interactions among the hydride ligands. With a
T1 of 22.0 ms (193 K) and a predicted T1 min of 17 ms,
significantly lower than the <35 ms value associated with
non-classical polyhydrides,15 we are confident that
[OsH7(PPhiPr2)2]þ possesses a non-classical structure.
X-ray Structure Analysis. Red block crystals of 1 were
obtained after two days from the slow diffusion of diethyl ether
into a dichloromethane solution of 1. Dark red block crystals
of 2 were obtained by recrystallization from diethyl ether. X-ray
diffraction data was collected on a Bruker SMART CCD
diffractometer using Mo KR radiation. Data was reduced
using Bruker SAINT software. Absorption correction was
performed using the SADABS program. The structures were
solved by direct methods using SHELXS97 and refined using
SHELXL97.10 All atoms were located during refinement.
Results
Protonation of [OsH6(PPhiPr2)2] - Synthesis and Char-
acterization of [Os2H7(PPhiPr2)4][HC(SO2CF3)2]. The
reaction of [OsH6(PPhiPr2)2] with 1 equiv of H2C(SO2-
CF3)2 in CH2Cl2 yielded dark red microcrystals of 1 upon
removal of the solvent and treatment with diethyl ether.
NMR analysis of 1 showed a signal in the 31P NMR
spectrum at 50.1 ppm and two hydride resonances at
-9.82 (quintet) and -12.93 ppm (triplet) in the 1H NMR
spectrum.
The coupling patterns of these hydride resonances
suggested a hydride-bridged dinuclear species. The ob-
servation of hydride environments coupled to two and
four phosphorus atoms (a triplet and a quintet) indicated
the presence of bridging and terminal hydrides. Integra-
tion of the hydride resonances against those of the
(11) Siedle, A. R.; Newmark, R. A.; Pignolet, L. H. Inorg. Chem. 1986, 25,
3412–3418.
(12) All T1 measurements performed at 300 MHz, with literature values
adjusted to 300 MHz for comparison.
(13) Desrosiers, P. J.; Cai, L.; Lin, Z.; Richards, R.; Halpern, J. J. Am.
Chem. Soc. 1991, 113, 4173–4184.
(14) Cotton, F. A.; Luck, R. L. J. Am. Chem. Soc. 1989, 111, 5757–5761.
(15) Luo, X. L.; Crabtree, R. H. Inorg. Chem. 1989, 28, 3775–3777.
(16) Hamilton, D. G.; Crabtree, R. H. J. Am. Chem. Soc. 1988, 110, 4126–
4133.
1
phosphine ligands in the H NMR spectrum indicated
that four phosphine ligands, three bridging hydrides and
four terminal hydrides were present. Upon lowering the
temperature to 193 K the two hydride resonances broa-
dened, but did not decoalesce. The conjugate base of
(10) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112–122.

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7979
Table 1. Crystallographic Data for [Os2H7(PPhiPr2)4][HC(SO2CF3)2] (1):
chemical formula
formula weight
C51H84O4F6P4S2Os2
1443.58
17.1709(5)
22.0917(6)
16.7632(4)
90
112.3520(10)
90
5881.1(3)
4
P21/c
˚
a, A
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
3
˚
V, A
Z
space group
T, K
97
λ
0.71073
1.63
4.556
0.0200
0.0466
dcalcd, g cm-3
μ, cm-1
R1 (I > 2σ(I)]a
wR2 (all data)a
˚
Selected Bond Distances (A) and Angles (deg) for Complex 1
Os(1)-Os(2)
2.54306(12) Os(1)-P(1)
2.3179(5) Os(2)-P(3)
2.3250(5) Os(1)-H(1A)
2.3209(5)
Os(1)-P(2)
2.3233(5)
1.837
1.744
1.734
1.398
1.519
Os(2)-P(4)
Os(2)-H(1A)
Os(2)-H(2A)
Os(2)-H(3A)
Os(1)-H(5A)
Os(2)-H(7A)
1.906
1.770
1.786
1.512
1.564
Os(1)-H(2A)
Os(1)-H(3A)
Os(1)-H(4A)
Os(2)-H(6A)
Figure 1. ORTEP diagram of 1 showing 50% probability thermal
ellipsoids. Non-hydride H-atoms and the HC(SO2CF3)3 anion have
been omitted for clarity.
-
The NMR data obtained for 3 is similar to that
reported for an analogous cationic heptahydride,
[OsH3(H2)2(PiPr3)2]þ.17 This compound displayed a T1 min
of 12.2 ms (169 K), compared to a value of 119 ms for the
parent [OsH6(PiPr3)2] species. The bis(dihydrogen) struc-
ture was elucidated on the basis of T1 min data and JHD
coupling values in the η2-HD ligand of the d6 isotopomer.
Given the similarities between the two compounds, the
structure of 3 is thought to be the bis(dihydrogen) poly-
hydride [OsH3(H2)2(PPhiPr2)2]þ.
Os(2)-Os(1)-P(1)
Os(1)-Os(2)-P(3)
P(1)-Os(1)-P(2)
124.758(13) Os(2)-Os(1)-P(2)
122.520(12) Os(1)-Os(2)-P(4)
112.276(17) P(3)-Os(2)-P(4)
122.851(12)
124.364(12)
112.998(17)
Os(2)-Os(1)-H(4A) 118.73
Os(1)-Os(2)-H(6A) 121.36
P(1)-Os(1)-H(4A) 74.81
P(2)-Os(1)-H(4A) 70.91
P(3)-Os(2)-H(6A) 70.81
P(4)-Os(2)-H(6A) 72.68
H(4A)-Os(1)-H(5A) 121.31
Os(1)-H(1A)-Os(2) 85.57
Os(1)-H(3A)-Os(2) 92.51
Os(2)-Os(1)-H(5A) 119.90
Os(1)-Os(2)-H(7A) 121.77
P(1)-Os(1)-H(5A) 74.93
P(2)-Os(1)-H(5A) 76.02
P(3)-Os(2)-H(7A) 73.24
P(4)-Os(2)-H(7A) 76.09
H(6A)-Os(2)-H(7A) 116.74
Os(1)-H(2A)-Os(2) 92.72
X-ray Crystal Structure of [Os2H7(PPhiPr2)4][HC-
(SO2CF3)2]. Crystals of a quality sufficient for use in
X-ray analysis were grown by the inward diffusion of diethyl
ether into a dichloromethane solution of the crude reaction
product. Single crystal X-ray crystallography confirmed the
proposed structure of 1, showing a diosmium species com-
posed of two OsP2H2 fragments bridged by a (μ-H)3 face
P
P
P
a Definition of R indices: R1= ||Fo|-|Fc||/ |Fo|; wR2=[ w(Fo
-
2
P
Fc2)2/ w(Fo2)2]1/2
.
is presumably due to the constraints of the crystal packing
rather than any association.
Deprotonation of [Os2H7(PPhiPr2)4][HC(SO2CF3)2] -
Synthesis and Characterization of [Os2H6(PPhiPr2)4].
Crystals of 1 were added to a suspension of potassium
hydride in tetrahydrofuran (THF), producing a solution
that formed a dark brown expanded oil when the solvent
was removed under vacuum. Recrystallization from di-
ethyl ether yielded dark red microcrystals of 2. The 31P
NMR spectrum of 2 showed a single peak at 48.2 ppm and
˚
(Figure 1). The Os-Os distance of 2.5431(1) A (Table 1) is
consistent with the Os2(μ-H)3 structure, being similar to the
Os-Os distances in the hydride-bridged species
[Os2H4(PMePh2)5] and [Os2H3(PMe2Ph)6]þ (2.551(1) and
18,19
˚
2.558(1) A, respectively).
The two OsP2H2 units are
staggered about the Os-Os bond, having an average torsion
angle of 61.77°. The average P-Os-P angle is 112.6°, and
˚
the average Os-P bond length is 2.32 A (Table 1). In the
1
a singlet hydride resonance at -12.63 ppm in the H
starting material [OsH6(PPhiPr2)2] the P-Os-P angle is
NMR spectrum at room temperature. Integration data
indicated that 2 contained four phosphine ligands and six
hydrides.
20
˚
155.2(1)° and Os-P distance is 2.342(7) A.
The HC(SO2CF3)2 counterion is non-coordinating.
-
˚
The nearest contact of 2.50 A between O(4) of the SO2CF3
group and an aromatic H on C(40) is similar to that
To confirm that six hydride ligands were present, elucida-
tion of the P-H coupling patterns was attempted by per-
forming selective proton-decoupled 31P NMR spectrosco-
py. However, the 31P resonance remained a singlet both at
room temperature and at 348 K. In contrast, resolution of
the P-H coupling was achieved using variable temperature
1H NMR. Upon increasing the temperature to 333 K, the
hydride peak showed coupling to four phosphorus nuclei
(quintet, JP-H=2.5 Hz) (Figure 2), demonstrating that 2is a
dinuclear polyhydride with rapidly exchanging bridging and
terminal hydrides. Low temperature 1H NMR spectroscopy
observed in [OsH3(PPh3)4][HC(SO2CF3)2] (2.47 A)11 and
˚
(17) Smith, K.-T.; Tilset, M.; Kuhlman, R.; Caulton, K. G. J. Am. Chem.
Soc. 1995, 117, 9473–9480.
(18) Bruno, J. W.; Huffman, J. C.; Green, M. A.; Zubkowski, J. D.;
Hatfield, W. E.; Caulton, K. G. Organometallics 1990, 9, 2556–2567.
(19) Green, M. A.; Huffman, J. C.; Caulton, K. G. J. Organomet. Chem.
1983, 243, C78–C82.
(20) Howard, J. A. K.; Johnson, O.; Koetzle, T. F.; Spencer, J. L. Inorg.
Chem. 1987, 26, 2930–2933.

7980 Inorganic Chemistry, Vol. 48, No. 16, 2009
Anderson et al.
Scheme 2
Very recently a brief report25 has appeared describing the
thermal decomposition of [OsH3(H2)2(PiPr3)2]þ at reflux
in toluene, leading to the formation of [Os2H7(PiPr3)4]þ
which is similar to 1.
This difference in reactivity is most likely due to the
different electronic effects of the diisopropylphenyl and
the triisopropyl phosphine ligands, with PPhiPr2 being a
poorer σ-donor than PiPr3 (σ-donor capacity, χd=10 for
PPhiPr2, 3.45 for PiPr3,).26 This means the PPhiPr2 ligand
produces an [OsH3(H2)2P2]þ intermediate (3) with a less
electron rich osmium atom, reducing the amount of
Os-H2 backbonding and making H2 more labile. This trend
of complexes with stronger σ-donor ligands exhibiting
reduced H2 dissociation has previously been observed for
[OsH5(PPh3)3]þ and [OsH5(PPhMe2)3]þ species, with the
more weakly donating PPh3 ligand promoting H2 elimina-
tion 2 orders of magnitude faster than the more strongly
donating PPhMe2.27 Thus, the increased propensity for H2
dissociation with the less donating PPhiPr2 ligand facilitates
the formation of 1 in a reaction that involves the loss of three
molecules of hydrogen (Scheme 2).
Figure 2. Variable temperature 1H NMR spectra of 2.
confirmed the presence of six hydride ligands, with the
observation of three broad singlet resonances at -10.45,
-12.95, and -21.02 ppm in a 3:2:1 ratio at 193 K (Figure 3).
This allows a formulation of 2 as an unsymmetrical di-
nuclear polyhydride with three bridging and three terminal
hydrides.
X-ray Crystal Structure of [Os2H6(PPhiPr2)4]. Recrys-
tallization of 2 from diethyl ether yielded dark red rec-
tangular prisms of sufficient quality for single crystal
X-ray diffraction analysis. The dimer is unsymmetrical,
composed of OsP2H and OsP2H2 fragments sharing a
common (μ-H)3 face (Figure 4). The six-coordinate Os(1)
is a distorted octahedron, with a P(1)-Os(1)-P(2) angle
of 105.29(3)°, while the additional terminal hydride at the
seven-coordinate osmium forces a P(3)-Os(2)-P(4) an-
gle of 113.76(3)° (Table 2). The Os-Os distance is con-
sistent with other trihydride-bridged diosmium structures
Compounds 1 and 2 could be assigned Os-Os triple-
bonds within the Os2(μ-H)3 cores on the basis of the EAN
rule, Os-Os distances in the solid state structures and
consistency with similar work.4,18,19,28 However it must
be noted that for similar 30-electron species [Cp*2Ru2-
(μ-H)4] and [(η6-C6Me6)2Ru2(μ-H)3]þ, quantum mechanical
computations have demonstrated that there is minimal
direct orbital interaction between the metal centers, with
the metal-metal distancesin the solidstate structures being
a result of the geometric constraints imposed by the brid-
ging hydrides.29,30 Assigning these type of structures a
metal-metal triple bond can be useful in rationalizing
bond lengths and observed reactivities;30 however, com-
parisons betweenthese structuresand those with unbridged
Os-Os triple bonds should be made with caution.
at 2.5447(2) A,18 and is very similar to the Os-Os bond
˚
length in 1 (only 0.06% difference between the two).
Discussion
Synthesis of [Os2H7(PPhiPr2)4]þ (1). The protonation
of [OsH6(PPhiPr2)2] to form 1 represents the first example
of dinuclear osmium polyhydride formation through the
protonation of a mononuclearprecursor. Thisprotonation
is analogous to the chemistry of rhenium polyhydrides,
where polyhydrides of the type ReH7P2 can be protonated
to form Re2H9P4 .
þ 21,22 It is also similar to the protonation
of the osmium halohydride OsH2Cl2P2,þwhich forms the
chloride-bridged P2H2Os(μ-Cl)3OsH2P2 through elimi-
nation of HCl.23
Previously, dinuclear osmium polyhydrides such as Os2-
H4P6, Os2H4P5, and [Cp*2Os2H4] have been generated by
photolysis rather than protonation,18,24 with cationic di-
nuclear osmium polyhydrides obtained through the proto-
nation of these photolysis products.7,19 Where the proto-
nation of mononuclear osmium polyhydrides has been
attempted, the products are reported to be mononuclear
polyhydrides.11,17 In a reaction analogous to that of the
formation of 1, [OsH6(PiPr3)2] was protonated with HBF4 to
yield the non-classical polyhydride [OsH3(H2)2(PiPr3)2]þ.17
The structure of 1 (and the recently prepared25 [Os2H7-
(PiPr3)4]þ) is interesting in two respects. It has the highest
reported oxidation state for osmium in a Os2(μ-H)3 config-
uration (Os4þ).31 The other examples of bimetallic Os2-
(μ-H)3 osmium species all contain Os2þ 18,19,32,33
while
,
an Os5 cluster contains a (μ-H)3 face bridging Os2þ and
Os3þ atoms.34 High oxidation state M2(μ-H)3 bridges are
uncommon for ruthenium species as well, the highest
(26) Fernandez, A. L.; Wilson, M. R.; Prock, A.; Giering, W. P.
Organometallics 2001, 20, 3429–3435.
(27) Jessop, P. G.; Morris, R. H. Coord. Chem. Rev. 1992, 121, 155–284.
::
ꢀ
(28) Tschan, M. J.-L.; Cherioux, F.; Therrien, B.; Suss-Fink, G. Eur. J.
Inorg. Chem. 2007, 2007, 509–513.
ꢀ
(21) Bravo, J.; Castro, J.; Garcıa-Fontan, S.; Iglesias, M.; Rodrıguez-
(29) Koga, N.; Morokuma, K. J. Mol. Struct. 1993, 300, 181–189.
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(22) Love, J. B. Heterobimetallic Polyhydride and Alkyl Polyhydride
Complexes of Rhenium. PhD Thesis, University of Salford, Salford, U.K.,
1993.
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Olivan, M. Organometallics 2009, ASAP DOI: 10.1021/om9002544.
(31) Results of a Cambridge Structural Database search for the Os2(μ-H)3
structural unit.
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469–479.
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Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7981
Figure 3. Variable temperature 1H (left) and 31P (right) NMR spectra of 2.
Table 2. Crystallographic Data for [Os2H6(PPhiPr2)4] (2):
chemical formula
formula weight
C48H82P4Os2
1163.42
17.9836(6)
15.1146(5)
18.9267(6)
90
106.994(2)
90
4919.9(3)
4
P21/c
˚
a, A
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
3
˚
V, A
Z
space group
T, K
119
λ
0.71073
1.57
5.321
0.0318
0.0715
dcalcd, g cm-3
μ, cm-1
R1 (I > 2σ(I)]a
wR2 (all data)a
˚
Selected Bond Distances (A) and Angles (deg) for Complex 2
Os(1)-Os(2)
2.54471(18) Os(1)-P(1)
2.2645(7)
Os(1)-P(2)
2.2736(8)
2.3169(8)
1.735
Os(2)-P(3)
2.3113(8)
1.712
1.872
1.810
1.398
1.412
Figure 4. ORTEP diagram of 2 showing 50% probability thermal
ellipsoids. Non-hydride H-atoms omitted for clarity.
Os(2)-P(4)
Os(1)-H(1A)
Os(1)-H(2A)
Os(1)-H(3A)
Os(2)-H(4A)
Os(1)-H(6A)
Os(2)-H(1A)
Os(2)-H(2A)
Os(2)-H(3A)
Os(2)-H(5A)
being Ru3þ in [Ru2H6(PiPr3)4].35,36 Second, 1 (along with
[OsH7(PiPr3)4]þ) has the highest hydride content of all repor-
ted diosmium species (7 hydride ligands), surpassing the
previous mark of 5 hydride ligands in [Cp*2Os2H5][BF4].3
Compound 1, however, has fewer hydrides per osmium than
Bronger’s monoosmium [OsH7]3- and [OsH9]3- species.37
Synthesis of [Os2H6(PPhiPr2)4] (2). Deprotonation of
the dinuclear polyhydride 1 was viewed as a route to
the synthesis of the neutral hexahydride 2, as reversible
protonation has been observed for dinuclear rhenium
octahydrides of the type Re2H8P4.38 The correspond-
ing dinuclear ruthenium hexahydrides Ru2H6P4 have
been known in the literature since 1985,6 and can be
1.663
1.663
1.323
Os(2)-Os(1)-P(1)
Os(1)-Os(2)-P(3)
P(1)-Os(1)-P(2)
Os(2)-Os(1)-H(4A) 117.12
Os(1)-Os(2)-H(6A) 120.38
P(3)-Os(2)-H(5A) 69.22
P(4)-Os(2)-H(5A) 86.13
P(2)-Os(1)-H(6A) 76.20
Os(1)-H(1A)-Os(2) 95.16
Os(1)-H(3A)-Os(2) 94.14
119.80(2)
126.11(2)
105.29(3)
Os(2)-Os(1)-P(2)
Os(1)-Os(2)-P(4)
P(3)-Os(2)-P(4)
130.06(2)
119.59(2)
113.76(3)
Os(2)-Os(1)-H(5A) 120.12
P(3)-Os(2)-H(4A)
P(4)-Os(2)-H(4A)
P(1)-Os(1)-H(6A)
H(4A)-Os(1)-H(5A) 122.39
Os(1)-H(2A)-Os(2) 91.91
82.97
60.04
90.92
P
P
P
a Definition of R indices: R1= ||Fo|-|Fc||/ |Fo|; wR2=[ w(Fo
-
2
P
Fc2)2/ w(Fo2)2]1/2
.
produced by thermolysis of the appropriate mono-
nuclear hexahydride.39 Compound 2 has also been pro-
duced by the reaction of [OsH6(PPhiPr2)2] with cyclo-
hexa-1,3-diene in hexane at 328 K.40
(35) Results of a Cambridge Structural Database search for the Ru2-
(μ-H)3 structural unit.
(36) Abdur-Rashid, K.; Gusev, D. G.; Lough, A. J.; Morris, R. H.
Organometallics 2000, 19, 1652–1660.
::
(37) Bronger, W.; Sommer, T.; Auffermann, G.; Muller, P. J. Alloys
This deprotonation was initially attempted using
piperidine, DBU, and triethylamine, as these bases
Compd. 2002, 330-332, 536–542.
(38) Moehring, G. A.; Fanwick, P. E.; Walton, R. A. Inorg. Chem. 1987,
26, 1861–1866.
(39) Arliguie, T.; Chaudret, B.; Morris, R. H.; Sella, A. Inorg. Chem.
1988, 27, 598–599.
(40) Steel, C. E.; Spencer, J. L. unpublished results.

7982 Inorganic Chemistry, Vol. 48, No. 16, 2009
Anderson et al.
have been shown to deprotonate rhenium and osmium
polyhydrides.17,38 However, these attempts were unsuc-
cessful, and deprotonation was only achieved using po-
tassium hydride. This indicates that the pKa of 1 is greater
than that of piperidine-Hþ,41 and thatþ13i8s less acidic than
the dirhenium polyhydrides Re2H9P4
.
While isoelectronic ruthenium polyhydrides of the
type Ru2H6P4 have been shown to possess a non-classical
terminal dihydrogen ligand,6,39,42 2 has solely classical
terminal hydrides. It is stable under a nitrogen atmo-
sphere rather than displaying the facile exchange of N2 for
H2 seen in the non-classical ruthenium polyhydrides, and
has a nearest contact between terminal hydride ligands of
˚
˚
2.4 A, significantly longer than even the 1.357(7) A
observed for an elongated non-classical H2 ligand.43 It
has been observed for Ru2H6P4 species that replacing
PPh3 with more basic PiPr3 ligands induces a change from
a non-classical to a classical structure.36 This introduces
the possibility that Os2H6P4 species with less basic or
chelating phosphines may adopt non-classical structures.
Attempts to synthesize the corresponding dinuclear
octahydride Os2H8P4 from the reaction of 1 with lithium
aluminum hydride were unsuccessful.
Figure 5. ORTEP diagram of 1 viewed along the Os-Os bond. 50%
probability thermal ellipsoids with non-hydride H-atoms and the HC-
(SO2CF3)3- anion have been omitted for clarity.
with three bridging hydrides and a non-coordinating anion.
The major difference between this structure and similar
structures with the M(μ-H)3M core is the asymmetry in
the molecule. For example, the isoelectronic [Re2H7-
(PPh2Me)4]- contains a center of inversion between the
two metal atoms, with the phosphine ligands eclipsed when
viewed along the metal-metal bond.48 In contrast, the
phosphine ligands in 1 are staggered with a torsion angle
of 61.8° when viewed along the osmium-osmium bond
(Figure 5). This greater degree of asymmetry in 1 com-
pared to similar compounds is most likely due to the steric
demand of the PPhiPr2 ligands. This leads to 1 having larger
P-M-P angles and smaller terminal H-M-H angles
when compared to [Re2H7(PPh2Me)4]-,49 as the isopropyl
groups force the phosphorus atoms apart, allowing the
hydrides to inhabit some of this space. The steric bulk of
the ligand introducing torsion about the metal-metal bond
is also seen when comparing 2 to its corresponding ruthe-
nium polyhydride [Ru2H6(PiPr3)4]. Increasing the steric
bulk of the ligand from PPhiPr2 (cone angle 155°)26 to PiPr3
(cone angle 160°)50 results in an increase in the torsion
angles between phosphine ligands on opposite ends of the
molecule (P(2)-Os(1)-Os(2)-P(3) and P(1)-Os(1)-Os-
(2)-P(4)) from 38.95(4)° and 76.49(3)° to 57.3° and 79.2°,
respectively.36
Significance of Dinuclear Osmium Polyhydrides. As
mentioned earlier, the protonation of a mononuclear poly-
hydride to form a dinuclear polyhydride has previously been
observed in rhenium chemistry. Other established transition
metal polyhydride chemistry may be transferable to these
dinuclear osmium polyhydrides. One such example of this
may be the formation of mixed polyhydride-phosphine
clusters. Rhenium polyhydrides of the type Re2H8P4 have
been shown to react with [Au(PPh3)]þ to form the tri- and
tetranuclear clusters [Re2H8(PPh3)4Au(PPh3)]þ and [Re2H8-
(PPh3)4{Au(PPh3)}2]þ.38 It has been demonstrated that
osmium hexahydrides can react with metallic Lewis acids
in a similar manner to rhenium heptahydrides,9 introducing
the possibility that 2maybeabletoreactwith[Au(PPh3)]þ in
the same way as the isoelectronic Re2H8P4 to produce a
multinuclear polyhydride-phosphine cluster. Hydride-con-
taining transition metal clusters are currently of particular
interest, as they often display reversible binding of dihydro-
gen, giving them relevance in the field of hydrogen storage.44
Moreover, osmium polyhydride species such as
[OsH6(PiPr3)2] have been observed to activate sp2 and
sp3 carbon-hydrogen bonds.45,46 Coupled with the ob-
servation that multinuclear transition metal polyhydrides
can also cleave a variety of C-H and C-C bonds,5,47 this
gives these new dinuclear osmium polyhydride species
potential applications in small molecule activation.
Comparison of Solid State Structures of 1 and 2. The struc-
ture adopted by 1 in the solid state comprises OsH2P2 units
Compared to the crystal structure of 1, 2 is less symme-
trical about the central P2Os-OsP2 core because it is
composed of OsHP2 and OsH2P2 units rather than two
OsH2P2 units. The OsH2P2 unit of 2 is similar to those of
˚
1 with an average Os-P bond length of 2.31 A (com-
˚
pared to 2.32 A for 1) and an average P-Os-P angle of
113.8° (compared to 112.6° for 1). The OsHP2 unit has a
˚
shorter average Os-P bond length (2.27 A) and a smaller
P-Os-P bond angle (105.3°) because of the decreased
steric demands of being a seven-coordinate rather than an
eight-coordinate center. These differences in the P2Os-
OsP2 core are evident when viewed along the Os-Os
bond (Figure 6). In 2, P(2) is closer to eclipsing P(3)
(P-Os-Os-P torsion of 38.95(4)°) and P(1) is further
(41) Crampton, M. R.; Robotham, I. A. J. Chem. Res. 1997, 22–23.
(42) Prechtl, M. H. G.; Ben-David, Y.; Giunta, D.; Busch, S.; Taniguchi,
::
Y.; Wisniewski, W.; Gorls, H.; Mynott, R. J.; Theyssen, N.; Milstein, D.;
Leitner, W. Chem.;Eur. J. 2007, 13, 1539–1546.
(43) Brammer, L.; Howard, J. A. K.; Johnson, O.; Koetzle, T. F.; Spencer,
J. L.; Stringer, A. M. J. Chem. Soc., Chem. Commun. 1991, 241–243.
(44) Weller, A. S.; McIndoe, J. S. Eur. J. Inorg. Chem. 2007, 2007, 4411–
4423.
(45) Barrio, P.; Esteruelas, M. A.; Onate, E. Organometallics 2004, 23,
3627–3639.
(46) Baya, M.; Eguillor, B.; Esteruelas, M. A.; Lledos, A.; Olivan, M.;
Onate, E. Organometallics 2007, 26, 5140–5152.
(47) Shima, T.; Ichikawa, T.; Suzuki, H. Organometallics 2007, 26, 6329–
6337.
(48) Hinman, J. G.; Abdur-Rashid, K.; Lough, A. J.; Morris, R. H. Inorg.
Chem. 2001, 40, 2480–2481.
(49) For 1, avg P-Os-P=112.64°, avg H-Os-H=119.04°. For [Re2H7-
(PPh2Me)4], P-Re-P=105.70°, H-Re-H=136.86°.
(50) Tolman, C. A. Chem. Rev. 1977, 77, 313–348.

Article
Inorganic Chemistry, Vol. 48, No. 16, 2009 7983
degree of symmetry between the two ends of the molecule,
and giving the OsP2H2 unit of 2 a larger P-Os-P angle
of 113.76(3)°.
Conclusion
In this paper we report the synthesis of two dinuclear
osmium polyhydrides with a high hydride count. We have
synthesized the dinuclear polyhydride [Os2H7(PPhiPr2)4]-
[HC(SO2CF3)2] (1) from the protonation of [OsH6-
(PPhiPr2)2] with H2C(SO2CF3)2. This is a rare example
of the protonation of an osmium polyhydride resulting in
a dinuclear structure, with this reactivity being attributed
to facile loss of H2 from the observed intermediate
[OsH3(H2)2(PPhiPr2)2]þ (3). The cationic species 1 can
also be deprotonated with potassium hydride to yield the
first diosmium hexahydride [Os2H6(PPhiP2)2] (2). X-ray
diffraction study reveals both 1 and 2 to be classical
polyhydrides with a P2Os(μ-H)3OsP2 core and a stag-
gered arrangement of the phosphine ligands.
These species represent the extension of established rhe-
nium and ruthenium chemistry to high hydride count os-
mium polyhydrides. This may provide the potential to adapt
successful polyhydride chemistry to similar osmium species,
which have demonstrated utility in reactions such as C-H
activation.
Figure 6. ORTEP diagram of 2 viewed along the Os-Os bond. 50%
probability thermal ellipsoids with non-hydride H-atoms omitted for
clarity.
staggered from P(4) (P-Os-Os-P torsion of 76.49(3)°),
creating a compound with two distinct P-Os-Os-P faces.
However, it is 1 that is asymmetric about the ends of the
molecule. In 1, Os(1) has PPhiPr2 ligands which are
oriented with the isopropyl groups pointing inward
(toward the Os2(μ-H)3 core), while Os(2) has PPhiPr2
ligands in which the phenyl groups point inward, appear-
˚
ing to be π-stacked (closest C-C contact of 3.2 A between
C(2) and C(14)). This means the P-Os-P angle for Os(2)
is very slightly larger than for Os(1), 113.00(2)° compared
to 112.28(2)°. This difference between the two ends of the
molecule may be a consequence of having to accommo-
date the HC(SO2CF3)2- counterion into the crystal pack-
ing. In the neutral 2, both ends of the molecule have one
phosphine with a phenyl group pointing inward and one
with an isopropyl group pointing inward, providing a
Acknowledgment. We thank Dr Jan Wikaira at the
University of Canterbury for collecting the single crystal
X-ray data.
Supporting Information Available: X-ray crystallographic
files in CIF format for [Os2H7(PPhiPr2)4][HC(SO2CF3)2] (1)
and [Os2H6(PPhiPr2)4] (2). This material is available free of
charge via the Internet at http://pubs.acs.org.