Synthesis and characterization of osmium(IV) polyhydride complexes of stoichiometry (C5Me5)OsH3(L). Crystal structures of (C5Me5)OsH3(AsPh3) and (C5Me5)OsH3(PPha)

Article abstract of DOI:10.1021/om060463z

Addition of Lewis bases to solutions of (C₅Me₅) ₂Os₂Br₄ in ethanol affords mononuclear osmium(III) complexes with the general formula (C₅Me ₅)OsBr₂(L), where L is AsPh₃, PPh₃, P(c-Hx)₃, PEt₃, pyridine, or tetrahydrothiophene. These paramagnetic complexes react with sodium borohydride in ethanol to afford the osmium(IV) trihydrides (C₅Me₅)OsH₃(L), where L is AsPh₃, PPh₃, P(c-Hx)3, or PEt₃. X-ray diffraction and NMR studies of the trihydride complexes show that they adopt classical structures (i.e., lacking molecular dihydrogen ligands). Unlike their ruthenium analogues, these osmium(IV) trihydrides show no evidence of quantum tunneling phenomena, probably because the H-Os-H bending motion is characterized by a steep potential energy well.

Full text of DOI:10.1021/om060463z

4792
Organometallics 2006, 25, 4792-4798
Synthesis and Characterization of Osmium(IV) Polyhydride
Complexes of Stoichiometry (C5Me5)OsH3(L). Crystal Structures of
(C5Me5)OsH3(AsPh3) and (C5Me5)OsH3(PPh3)
Christopher L. Gross and Gregory S. Girolami*
School of Chemical Sciences, The UniVersity of Illinois at Urbana-Champaign,
600 South Mathews AVenue, Urbana, Illinois 61801
ReceiVed May 26, 2006
Addition of Lewis bases to solutions of (C5Me5)2Os2Br4 in ethanol affords mononuclear osmium(III)
complexes with the general formula (C5Me5)OsBr2(L), where L is AsPh3, PPh3, P(c-Hx)3, PEt3, pyridine,
or tetrahydrothiophene. These paramagnetic complexes react with sodium borohydride in ethanol to afford
the osmium(IV) trihydrides (C5Me5)OsH3(L), where L is AsPh3, PPh3, P(c-Hx)3, or PEt3. X-ray diffraction
and NMR studies of the trihydride complexes show that they adopt classical structures (i.e., lacking
molecular dihydrogen ligands). Unlike their ruthenium analogues, these osmium(IV) trihydrides show
no evidence of quantum tunneling phenomena, probably because the H-Os-H bending motion is
characterized by a steep potential energy well.
Introduction
Results
The discovery of dihydrogen complexes1-3 and of quantum
exchange coupling between classical hydride ligands4,5 has
stimulated great interest in the bonding of hydrogen atoms to
metal centers. One aspect of interest is how the structures and
properties of metal hydride complexes depend on the identity
of the metal center. One trend that is becoming apparent is that
there are significant differences between the behavior of second-
and third-row metal complexes. For example, the second-row
transition metal complexes (C5H5)2NbH3 and [(C5H5)2MoH3]-
[BF4] have classical polyhydride structures but exhibit pro-
nounced quantum exchange with JHH couplings as large as 1000
Hz.6,7 In contrast, the third-row analogues of these species,
(C5H5)2TaH3 and [(C5H5)2WH3][BF4], exhibit classical behavior
Synthesis of the Osmium(III) Complexes (C5Me5)OsBr2(L).
Addition of Lewis bases to the diruthenium complex (C5Me5)2-
Ru2Cl4 yields mononuclear ruthenium(III) complexes of stoi-
chiometry (C5Me5)RuCl2(PR3),9,13 and we find that the dios-
12
mium complex (C5Me5)2Os2Br4 reacts similarly. Thus,
(C5Me5)2Os2Br4 reacts with Lewis bases in ethanol or tetrahy-
drofuran to afford mononuclear adducts with the general formula
(C5Me5)OsBr2(L). Among the Lewis bases that give such
products are triphenylarsine, triphenylphosphine, tricyclohexyl-
phosphine, triethylphosphine, pyridine, and tetrahydrothiophene:
1/2 (C5Me5)2Os2Br4 + L- f (C5Me5)OsBr2(L)
1, L ) AsPh3
1
in their H NMR spectra.6,7
Ruthenium complexes of the form (C5R5)RuH3(L) were
among the first to exhibit quantum exchange, and they have
been the subject of several studies.8-11 Comparisons between
these compounds and their osmium analogues would be of
considerable interest. We now describe the synthesis and
characterization of the first extensive series of half-sandwich
osmium(IV) trihydrides, (C5Me5)OsH3(L). Portions of this work
have been communicated previously.12
2, L ) PPh3
3, L ) P(c-Hx)3
4, L ) PEt3
5, L ) NC5H5
6, L ) SC4H8
(1) Jessop, P. G.; Morris, R. H. Coord. Chem. ReV. 1992, 121, 155-
284.
(2) Heinekey, D. M.; Oldham, W. J., Jr. Chem. ReV. 1993, 93, 913-
926.
1
These complexes are all paramagnetic, and their H NMR
resonances are broad and shifted from their diamagnetic
1
positions by up to ∼30 ppm. The diagnostic feature in the H
(3) Kubas, G. J. Acc. Chem. Res. 1988, 21, 120-128.
(4) Heinekey, D. M.; Millar, J. M.; Koetzle, T. F.; Payne, N. G.; Zilm,
K. W. J. Am. Chem. Soc. 1990, 112, 909-919.
(5) Zilm, K. W.; Heinekey, D. M.; Millar, J. M.; Payne, N. G.; Neshyba,
S. P.; Duchamp, J. C.; Szczyrba, J. J. Am. Chem. Soc. 1990, 112, 920-
929.
(6) Heinekey, D. M. J. Am. Chem. Soc. 1991, 113, 6074-6077.
(7) Camanyes, S.; Maseras, F.; Moreno, M.; Lledo´s, A.; Lluch, J. M.;
Bertra´n, J. J. Am. Chem. Soc. 1996, 118, 4617-4621.
(8) Heinekey, D. M.; Payne, N. G.; Sofield, C. D. Organometallics 1990,
9, 2643-2645.
(9) Arliguie, T.; Border, C.; Chaudret, B.; Devillers, J.; Poilblanc, R.
Organometallics 1989, 8, 1308-1314.
(10) Arliguie, T.; Chaudret, B.; Jalon, F. A.; Otero, A.; Lopez, J. A.;
Lahoz, F. J. Organometallics 1991, 10, 1888-1896.
(11) Sabo-Etienne, S.; Chaudret, B. Chem. ReV. 1998, 98, 2077-2091.
NMR spectra of these complexes is a broad resonance between
δ 25 and 35 for the methyl protons of the C5Me5 ring.
The 1H NMR spectrum of the PPh3 compound 2 features six
resonances for the phosphine phenyl protons with ratios of
approximately 4:4:2:2:2:1. This pattern suggests that rotation
about the Os-P bond axis is slow on the NMR time scale: two
of the phenyl groups are equivalent (and give ortho, meta, and
para resonances with intensities of 4:4:2, respectively) but are
(12) Gross, C. L.; Wilson, S. R.; Girolami, G. S. J. Am. Chem. Soc.
1994, 116, 10294-10295.
(13) Suzuki, H.; Lee, D. H.; Oshima, N.; Moro-Oka, Y. Organometallics
1987, 6, 1569-1575.
10.1021/om060463z CCC: $33.50 © 2006 American Chemical Society
Publication on Web 08/25/2006

Osmium(IV) Polyhydride Complexes
Organometallics, Vol. 25, No. 20, 2006 4793
different from the third (which gives ortho, meta, and para
resonances with intensities of 2:2:1). Our ability to observe the
slow-exchange spectrum is doubtlessly assisted here by the
paramagnetism: the chemical shift difference between the two
ortho environments, for example, is over 30 ppm. Interestingly,
the IR spectrum is entirely consistent with a four-legged piano
stool structure of Cs symmetry (structure B).
1
the H NMR spectrum of the AsPh3 complex 1 is not in the
slow-exchange limit; only two very broad phenyl resonances
are observed. One possibility is that the AsPh3 complex is less
crowded than the PPh3 complex, a conclusion that is consistent
with the smaller steric demand of the AsPh3 ligand caused by
the longer Os-As bond.
The mass spectra of these complexes fall into two classes:
in some cases (compounds 1-4) an intense peak for the
molecular ion is observed, whereas in other cases (compounds
5 and 6) peaks due to (C5Me5)OsBr2 and the free ligand are
seen and no molecular ion is present. Presumably, the Lewis
bases in the latter complexes are bound more weakly.
The 1H NMR spectra of 8-11 all feature two hydride
resonances in a ratio of 1:2. For example, the PPh3 complex 9
is characterized by two doublets at δ -13.77 (2JHP ) 7.8 Hz)
and δ -14.28 (2JHP ) 33.5 Hz), the latter being the more
intense. The 1:2 intensity ratios confirm that these compounds
adopt four-legged piano stool geometries in which one of the
hydride ligands is “transoid” to the phosphine ligand and two
are “cisoid”. Two other osmium complexes are known that adopt
a similar structure: the unsubstituted cyclopentadienyl com-
pound (C5H5)OsH3[P(i-Pr)3]14 and the carbonyl compound (C5-
Me5)OsH3(CO).15 For the phosphine compounds 9-11, the 2JHP
value for the transoid hydride ligand is significantly smaller
than that for the cisoid hydrides. Similar behavior has long been
known4,8,16 and is related to the fact that the transoid H-Os-P
angle in such four-legged piano stool structures is closer to 100°
The synthesis of (C5Me5)OsBr2[P(c-Hx)3] (3) is best carried
out at room temperature. Under these conditions, a small amount
(∼5%) of a second compound is formed. This second com-
pound, which can be synthesized in pure form by treatment of
(C5Me5)2Os2Br4 with tricyclohexylphosphine in refluxing etha-
nol, is the diamagnetic osmium(IV) hydride (C5Me5)OsBr2H-
[P(c-Hx)3] (7), where the hydride ligand most likely arises by
abstraction from the ethanol solvent. The hydride resonance
appears in the 1H NMR spectrum as a doublet at δ -14.28 with
2JHP ) 36.6 Hz. Within the presumed four-legged piano stool
structure, the hydride ligand is probably cisoid to the phosphine
ligand, as judged from comparisons of 2JHP with those observed
in complexes of stoichiometry (C5Me5)OsH3(L) (see below).
A similar compound, (C5H5)OsCl2H[P(i-Pr)3], has been de-
scribed previously and assigned a similar structure.14
Synthesis of Pentamethylcyclopentadienyl Osmium(IV)
Trihydrides. Treatment of the bromoosmium(III) complexes
(C5Me5)OsBr2(L) with sodium borohydride in ethanol affords
the osmium(IV) trihydrides, (C5Me5)OsH3(L), where L is AsPh3
(8), PPh3 (9), P(c-Hx)3 (10), or PEt3 (11). Whereas the first
two of these complexes are best made in refluxing ethanol, the
latter two are best prepared at room temperature. The mechanism
by which the osmium(IV) products 8-11 are generated from
(C5Me5)OsBr2(PR3) and NaBH4 in ethanol is undoubtedly
similar to that proposed by Suzuki et al. for the corresponding
ruthenium complex (C5Me5)RuH3(PPh3).13
2
rather than 180° (see below). The JHH coupling constant
between the hydrides in 8-11 is too small to be resolved; we
place an upper limit of 1 Hz for each. The significance of the
2
near-zero magnitude of JHH will be discussed below.
Some samples of 11 also contained traces of the dihydride
complex (C5Me5)OsH2Br(PEt3); the 1H NMR spectrum showed
only a single resonance for the hydride ligand, with a JPH
coupling constant of 36.4 Hz. This spectrum is consistent with
a transoid geometry. Some similar compounds of the type
(C5H5)OsH2X(PR3), where X ) Cl14,17 or SiPh2OTf,18 are
known; the former exists as a 20:1 mixture of the transoid and
cisoid isomers in dichloromethane, and the latter was seen to
adopt only the transoid structure.
Crystallographic Studies of the Osmium(IV) Trihydrides.
We have carried out X-ray diffraction studies of both the AsPh3
compound 8 and the PPh3 compound 9 (Tables 1-3). The results
confirm that both compounds adopt the four-legged piano stool
structures proposed from the NMR results (Figures 1 and 2).
The Os-As distance of 2.3666(4) Å for 8 and the Os-P bond
distance of 2.2628(8) Å measured for 9 are consistent with the
larger size of arsenic relative to phosphorus. Otherwise, the
structures are remarkably similar.
(C5Me5)OsBr2(L) + xs NaBH4 EtOH8 (C5Me5)OsH3(L)
8, L ) AsPh3
9, L ) PPh3
The hydride atoms were located in both compounds. In 8,
the closest H‚‚‚H distance of 1.57 Å (corresponding to a
H-Os-H angle of 65°) is too long to suggest that there are
any bonds between the hydrogen atoms. A similar conclusion
is reached for 9. In both compounds the three Os-H distances
are equal within experimental error, averaging 1.58 Å for 8 and
1.52 Å for 9. This finding agrees with the neutron diffraction
study of [(C5H5)IrH3(PMe3)]+, which showed that the three
Ir-H distances are also virtually identical.4 Suzuki has noted
that, for the complexes (C5Me5)RuH3(PPh3) and (C5Me5)IrH3-
10, L ) P(c-Hx)3
11, L ) PEt3
All four complexes exhibit three Os-H stretching bands in
their infrared spectra: for example, for the AsPh3 complex 8,
the bands appear at 2090, 2052, and 2026 cm-1. The IR spectra
of 8-11 feature an osmium hydride bending band at ∼800
cm-1. The presence of three Os-H stretching bands is incon-
sistent with a trigonal bipyramidal structure of pseudo-C3V
symmetry in which the Cp* and Lewis base occupy the axial
sites (structure A). Such a structure should give rise to only
two Os-H stretching bands in the IR spectrum. In contrast,
(15) Hoyano, J. K.; Graham, W. A. G. J. Am. Chem. Soc. 1982, 104,
3722-3723.
(16) Faller, J. W.; Anderson, A. S. J. Am. Chem. Soc. 1970, 92, 5852-
5860.
(17) Baya, M.; Buil, M. L. Esteruelas, M. A.; On˜ate, E. Organometallics
2004, 23, 1416-1423.
(18) Glaser, P. B.; Tilley, T. D. Organometallics 2004, 23, 5799-5812.
(14) Baya, M.; Crochet, P.; Esteruelas, J. A.; Gutie´rrez-Puebla, E.; Ruiz,
N. Organometallics 1999, 18, 5034-5043.

4794 Organometallics, Vol. 25, No. 20, 2006
Gross and Girolami
Table 1. Crystal Data for (C5Me5)Os(AsPh3)H3 (8) and
(C5Me5)Os(PPh3)H3 (9)
Table 3. Selected Bond Distances and Angles for
(C5Me5)Os(PPh3)H3 (9)a
(C5Me5)Os(AsPh3)H3
(C5Me5)Os(PPh3)H3
Distances (Å)
Os-H(1)
Os-H(2)
Os-H(3)
Os-C(1)
Os-C(2)
Os-C(3)
Os-C(4)
Os-C(5)
Os-P
1.58(4)
1.47(4)
1.51(4)
P-C(31)
1.843(3)
1.438(5)
1.437(5)
1.449(5)
1.426(5)
1.421(5)
1.499(5)
1.500(5)
1.500(5)
1.501(5)
1.503(5)
formula
fw
C28H33AsOs
634.66
198(2)
0.71073
Siemens SMART
0.32 × 0.32 × 0.08
triclinic
C28H33OsP2
590.71
198(2)
0.71073
Siemens SMART
0.32 × 0.23 × 0.12
triclinic
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(1)-C(5)
C(1)-C(6)
C(2)-C(7)
C(3)-C(8)
C(4)-C(9)
C(5)-C(10)
temp, K
wavelength, Å
diffractometer
size, mm
cryst syst
space group
a, Å
2.289(4)
2.225(3)
2.217(3)
2.279(3)
2.322(3)
2.2628(8)
1.843(3)
1.840(3)
P1h
P1h
8.5812(3)
9.2527(3)
17.3789(6)
93.041(3)
101.095(1)
113.856(1)
1225.16(7)
2
9.0638(1)
9.1459(2)
16.6003(1)
94.827(1)
101.359(1)
115.217(1)
1198.47(3)
2
P-C(11)
P-C(21)
b, Å
c, Å
R, deg
Angles (deg)
â, deg
H(1)-Os-H(2)
H(1)-Os-H(3)
H(2)-Os-H(3)
Cn-Os-H(1)
Cn-Os-H(2)
Cn-Os-H(3)
Cn-Os-P
64(2)
119(2)
68(2)
120(1)
128(1)
119(1)
136.7(1)
H(1)-Os-P
H(2)-Os-P
H(3)-Os-P
C(11)-P-Os
C(21)-P-Os
C(31)-P-Os
76(2)
95(2)
74(1)
117.6(1)
117.0(1)
115.7(1)
γ, deg
V, Å3
Z
d
calcd, g cm-3
1.720
6.556
620
1.21-28.24
7931
5560
4874
1.637
5.399
584
2.51-28.30
7911
5438
5174
µ, mm-1
F(000)
θ range, deg
a Cn ) centroid of C5Me5 ring.
no. of rflns measd
no. of indep rflns
no. of reflns with
I g 2σ(I)
no. of params
absorp corr
387
288
face-indexed
0.132-0.690
0.0268
0.0759
1.057
ellipsoidal
0.243-0.543
0.0221
0.0548
1.113
transmn coeff range
R1(I g 2σ(I))a
wR2(all data)a
GOF (F2)
∆F(max/min), e Å-3
0.722/-1.179
0.684/-1.156
2
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|, wR2) {∑[w(Fo - Fc )2]/∑[w(Fo )2]}1/2
.
Table 2. Selected Bond Distances and Angles for
(C5Me5)Os(AsPh3)H3 (8)a,b
Distances (Å)
Os-H(1)
Os-H(2)
Os-H(3)
Os-C(1A)
Os-C(2A)
Os-C(3A)
Os-C(4A)
Os-C(5A)
Os-As
1.60(5)
1.53(6)
1.62(5)
2.31(2)
2.25(2)
2.17(2)
2.22(1)
2.30(1)
2.3666(4)
1.955(3)
1.957(4)
As-C(31)
1.956(4)
1.42(2)
1.43(2)
1.40(2)
1.42(1)
1.44(2)
1.51(2)
1.49(2)
1.49(2)
1.48(2)
1.54(2)
C(1A)-C(2A)
C(2A)-C(3A)
C(3A)-C(4A)
C(4A)-C(5A)
C(1A)-C(5A)
C(1A)-C(6A)
C(2A)-C(7A)
C(3A)-C(8A)
C(4A)-C(9A)
C(5A)-C(10A)
Figure 1. ORTEP diagram of (C5Me5)OsH3(AsPh3), 8. The 30%
probability density surfaces are shown for all atoms except for the
hydrogen atoms, which are represented by arbitrarily sized spheres.
As-C(11)
As-C(21)
Angles (deg)
H(1)-Os-H(2)
H(1)-Os-H(3)
H(2)-Os-H(3)
Cn-Os-H(1)
Cn-Os-H(2)
Cn-Os-H(3)
Cn-Os-As
60(3)
123(3)
70(3)
114(1)
129(1)
118(1)
134.4(2)
H(1)-Os-As
H(2)-Os-As
H(3)-Os-As
C(11)-As-Os
C(21)-As-Os
C(31)-As-Os
83(2)
97(2)
78(2)
118.2(1)
117.4(1)
117.0(1)
a Cn ) centroid of C5Me5 ring. b The C5Me5 ring was disordered over
two positions. The values given in the table for distances and angles
involving C5Me5 carbons are for the major (52%) position.
(SnPh3), the M-H bond distance to the hydride transoid to the
EPh3 ligand is shorter than the other two by ∼0.1 Å, and he
has proposed that the greater trans influence of H vs PR3 may
be responsible for this difference.13 In fact, the 0.1 Å difference
in bond lengths in these latter two compounds amounts to only
about twice the estimated standard deviation. It is therefore more
accurate to say that the M-H distances are equal within error
for trihydride complexes of this type.
Deuteration Studies of the Osmium(IV) Trihydrides. Isoto-
pologues of 8 and 9 in which the hydride sites are selectively
deuterated can be synthesized by treatment of (C5Me5)OsBr2(L)
Figure 2. ORTEP diagram of (C5Me5)OsH3(PPh3), 9. The 30%
probability density surfaces are shown for all atoms except for the
hydrogen atoms, which are represented by arbitrarily sized spheres.

Osmium(IV) Polyhydride Complexes
Organometallics, Vol. 25, No. 20, 2006 4795
with NaBD4 in ethanol-d1. Resonances due to small amounts
of the dideuterated and monodeuterated isotopologues showed
that the H-D coupling was too small to measure (<2 Hz).
Replacing one hydrogen atom by a deuterium atom causes the
resonance due to the remaining hydrogen atoms to be shifted
upfield by 33 ppb at room temperature.19
The Os-H bending band at 795 cm-1 in the IR spectrum of
the AsPh3 complex 8 is shifted upon deuteration to 575 cm-1
(νH/νD ) 1.38). Similarly, for the PPh3 complex 9, this band is
shifted upon deuteration from 798 to 579 cm-1 (νH/νD ) 1.38).
for example, 2JHH is 219 Hz at 153 K and increases to 374 Hz
at 173 K for the triphenylphosphine derivative [(C6H6)OsH3-
(PPh3)][BF4]. Other classes of osmium(IV) trihydrides are
known, some of which also exhibit quantum exchange
coupling.22-35
2
The presence of large JHH couplings in (C5Me5)RuH3(PR3)
and [(C6H6)OsH3(PR3)][BF4] complexes, but not in compounds
8-11, is consistent with the proposal that quantum exchange
couplings decrease as the metal center becomes more electron
rich (i.e., as the frontier molecular orbitals become higher in
energy) and the classical hydride structures are relatively
stabilized.4,7,11,14 The osmium C5Me5 complexes are more
electron rich than the Ru C5Me5 analogues owing to general
trends involving second-row vs third-row metals, and are more
electron rich than the Os arene compounds owing to the different
donor properties of the ligand sets.
Protonation of the osmium(IV) hydrides 8-11 should make
the metal center less electron rich and should give rise to
molecular dihydrogen complexes. This expectation has been
confirmed: we have described elsewhere that protonation of
the (C5Me5)OsH3(L) complexes affords cationic osmium tet-
rahydrides, which actually are molecular dihydrogen complexes
of stoichiometry [(C5Me5)Os(H2)H2(L)]+.36,37
Discussion
Exchange and Exchange Couplings in Ruthenium and
Osmium Analogues. At room temperature, the 1H NMR
spectrum of the ruthenium compounds of the type (C5Me5)-
RuH3(PR3) shows a single Ru-H resonance, a doublet owing
to coupling to the 31P nucleus.9,13 At lower temperatures, this
resonance changes to a AB2X pattern (A,B ) H; X ) P) owing
to slowing of a thermally activated exchange process. Similar
behavior was seen for the unsubstituted cyclopentadienyl
analogue (C5H5)RuH3(PPh3), and the barrier for exchange
calculated to be 9.5 kcal/mol.8
In contrast, even at room temperature the osmium complexes
8-11 show no evidence of exchange, and sharp 1H NMR
resonances characteristic of AB2 or AB2X (X ) 31P) spin
patterns are seen. From these observations, we can set lower
limits of ∼15 kcal/mol on the free energy of activation for
exchange of the hydride ligands in 8-11. The osmium carbonyl
(C5Me5)OsH3(CO) shows no evidence of exchange at room
temperature either.15 Interestingly, the unsubstituted cyclopen-
tadienyl compound (C5H5)OsH3[P(i-Pr)3], whose 1H NMR
spectrum at low temperature is very similar to those of 8-11,
shows exchange of the two different hydride environments at
Experimental Section
All operations were carried out under argon or vacuum by using
standard Schlenk techniques. Solvents were distilled under nitrogen
from magnesium (ethanol and methanol), calcium hydride (dichlo-
romethane), sodium benzophenone (diethyl ether, pentane), or
barium oxide (pyridine). The osmium compound (C5Me5)2Os2Br4
was synthesized as described elsewhere.12 Triethylphosphine was
prepared by a literature route.38 Sodium borohydride (Aldrich),
sodium borodeuteride (Aldrich), deuterium oxide (Cambridge), tert-
butyl alcohol (Fisher), triphenylarsine (Aldrich), triphenylphosphine
(Aldrich), tri(cyclohexyl)phosphine (Strem), and tetrahydrothiophene
(Aldrich) were used without further purification.
higher temperatures with a barrier of 15 kcal mol-1 14
. Theoreti-
cal studies suggested that the exchange process takes place
through a dihydrogen transition state.
For the ruthenium compounds (C5Me5)RuH3(PR3), the AB2X
patterns seen at low temperature are affected by quantum
exchange coupling between the hydride ligands; the value of
(22) Esteruelas, M. A.; Jean, Y.; Lledo´s, A.; Oro, L. A.; Ruiz, N.;
Volatron, F. Inorg. Chem. 1994, 33, 3609-3615.
(23) Buil, M. L.; Espinet, P.; Esteruelas, M. A.; Lahoz, F. J.; Lledo´s,
A.; Mart´ınez-Ilarduya, J. M.; Maseras, F.; Modrego, J.; On˜ate, E.; Oro, L.
A.; Sola, E.; Valero, C. Inorg. Chem. 1996, 35, 1250-1256.
(24) Esteruelas, M. A.; Lahoz, F. J.; Lo´pez, A. M.; On˜ate, E.; Oro, L.
A.; Ruiz, N.; Sola, E.; Tolosa, J. I. Inorg. Chem. 1996, 35, 7811-7817.
(25) Demachy, I.; Esteruelas, M. A.; Jean, Y.; Lledo´s, A.; Maseras, F.;
Oro, L. A.; Valero, C.; Volatron, F. J. Am. Chem. Soc. 1996, 118, 8388-
8394.
2
the JHH coupling constant is unusually large, e.g., 290 Hz at
2
190 K for the PPh3 compound.8 For comparison, the JHH
coupling constants in the osmium complexes 8-11 are too small
to observe (<1 Hz), and thus the contributions from quantum
exchange coupling must be negligible.20 Slightly larger, but still
2
small JHH coupling constants of 8.9 and 3.4 Hz, respectively,
(26) Gusev, D. G.; Kuhlman, R.; Renkema, K. B.; Eisenstein, O.; Caulton,
K. G. Inorg. Chem. 1996, 35, 6775-6793.
(27) Castillo, A.; Esteruelas, M. A.; On˜ate, E.; Ruiz, N. J. Am. Chem.
Soc. 1997, 119, 9691-9698.
(28) Kuhlman, R.; Clot, E.; Leforestier, C.; Streib, W. E.; Eisenstein,
O.; Caulton, K. G. J. Am. Chem. Soc. 1997, 119, 10153-10169.
(29) Barea, G.; Esteruelas, M. A.; Lledo´s, A.; Lo´pez, A. M.; On˜ate, E.;
Tolosa, J. I. Organometallics 1998, 17, 4065-4076
(30) Castillo, A.; Barea, G.; Esteruelas, M. A.; Lahoz, F. J.; Lledo´s, A.;
Naseras, F.; Modrego, J.; On˜ate, E.; Oro, L. A.; Ruiz, N.; Sola, E. Inorg.
Chem. 1999, 38, 1814-1824.
(31) Rickard, C. E. F.; Roper, W. R.; Woodgate, S. D.; Wright, L. J. J.
Organomet. Chem. 2000, 609, 177-183.
(32) Barrio, P.; Castarlenas, R.; Esteruelas, M. A.; Lledo´s, A.; Maseras,
F.; On˜ate, E.; Toma´s, J. Organometallics 2001, 20, 442-452.
(33) Ferrando-Miguel, G.; Wu, P.; Huffman, J. C.; Caulton, K. G. New
J. Chem. 2004, 29, 193-204.
(34) Yousufuddin, M.; Wen, T. B.; Mason, S. A.; McIntyre, G. J.; Jia,
G.; Bau, R. Angew. Chem., Int. Ed. 2005, 44, 7227-7230.
(35) Guilera, G.; McGrady, G. S.; Steed, J. W.; Jones, A. L. Organo-
metallics 2006, 25, 122-127.
(36) Gross, C. L.; Young, D. M.; Schultz, A. J.; Girolami, G. S. J. Chem.
Soc., Dalton Trans. 1997, 3081-3082.
(37) Webster, C. E.; Gross, C. L.; Young, D. M.; Girolami, G. S.; Schultz,
A. J.; Hall, M. B.; Eckert, J. J. Am. Chem. Soc. 2005, 127, 15091-15101.
have been noted for the related osmium compounds (C5Me5)-
OsH3(CO)15 and (C5H5)OsH3[P(i-Pr)3].14 These trends, in which
compounds 8-11 have higher exchange barriers and smaller
2JHH coupling constants, are consistent with electronic factors,
as discussed below.
In addition, it is interesting to compare complexes 8-11 with
cationic osmium complexes of the general formula [(C6H6)-
OsH3(L)][BF4].21 These cations are isoelectronic with complexes
8-11 and also adopt a four-legged piano stool structures. The
arene complexes exhibit quantum exchange couplings between
2
the hydride resonances with JHH values as large as 400 Hz;
(19) The sign and magnitude of the secondary isotope shift are similar
to those observed for other classical polyhydrides. See: Luo, X. L.; Crabtree,
R. H. J. Am. Chem. Soc. 1990, 112, 4813-4821.
(20) A reviewer has suggested that the near-zero 2JHH couplings for 8-11
are the result of the fortuitous cancellation of the contributions of magnetic
and quantum exchange contributions to J. This may be true, but the absolute
magnitudes of each are certainly both small.
(21) Heinekey, D. M.; Harper, T. G. P. Organometallics 1991, 10, 2891-
2895.

4796 Organometallics, Vol. 25, No. 20, 2006
Gross and Girolami
Elemental analyses were performed by the University of Illinois
Microanalytical Laboratory. Field desorption mass spectra were
recorded on a Finnigan-MAT 731 mass spectrometer from samples
loaded as solutions in dichloromethane. The IR spectra were
recorded on a Perkin-Elmer 1700 FT-IR instrument as Nujol mulls
osmium(III), (C5Me5)OsBr2(PEt3) (4). To a solution of (C5Me5)2-
Os2Br4 (0.196 g, 0.20 mmol) in tetrahydrofuran (40 mL) at -78
°C was added triethylphosphine (0.03 mL, 0.20 mmol). The solution
was stirred at -78 °C for 2 h and then was slowly warmed to room
temperature. After 2 h at room temperature, the solvent was
removed under vacuum, and the residue was extracted with diethyl
ether (3 × 20 mL). The extracts were filtered, combined, concen-
trated to ca. 1 mL, and cooled to -20 °C to afford red-orange
crystals. Yield: 0.183 g (79%). Anal. Calcd for C16H30Br2OsP: C,
31.9; H, 5.01; Br, 26.5; P, 5.13. Found: C, 32.2; H, 5.05; Br, 26.1;
1
between KBr plates. The H and 31P NMR data were recorded on
a Varian Unity 400 spectrometer at 400 and 161 MHz, respectively;
13C NMR spectra were recorded on a Varian Unity 500 spectrometer
at 101 MHz. Some NMR spectra were recorded on General Electric
QE-300, GN-300, or GN-500 instruments. Chemical shifts are
reported in δ units (positive shifts to high frequency) relative to
SiMe4 (1H and 13C) or H3PO4 (31P).
1
P, 5.07. MS(FD): 603 (M+). H NMR (C6D6, 22 °C): δ 31.4 (s,
fwhm ) 320 Hz, C5Me5), 7.8 (s, fwhm ) 210 Hz, PCH2CH3),
-3.7 (s, fwhm ) 60 Hz, PCH2CH3). IR (cm-1): 1421 (m), 1415
(m), 1306 (w), 1263 (m), 1149 (w), 1072 (w), 1051 (m), 1036 (s),
1026 (s), 1003 (m), 978 (w), 948 (w), 895 (w), 792 (w), 761 (s),
750 (s), 742 (m), 729 (s), 719 (s), 692 (w), 673 (w), 667 (w), 657
(w), 629 (w), 616 (w), 601 (w), 535 (w), 529 (w), 422 (m).
(Pentamethylcyclopentadienyl)dibromo(triphenylarsine)-
osmium(III), (C5Me5)OsBr2(AsPh3) (1). To a mixture of (C5Me5)2-
Os2Br4 (0.25 g, 0.26 mmol) and triphenylarsine (0.17 g, 0.56 mmol)
was added ethanol (25 mL). The solution was heated to reflux for
1.5 h. The resulting brown-orange solid was collected by filtration
and dried under vacuum. Yield: 0.35 g (83%). Anal. Calcd for
C28H30AsBr2Os: C, 42.5; H, 3.82; Br, 20.2. Found: C, 42.0; H,
3.81; Br, 20.0. MS(FD): 793 (M+). 1H NMR (CD2Cl2, 22 °C): δ
27 (s, fwhm ) 470 Hz, C5Me5), 4 (s, fwhm ) 650 Hz, AsPh3), -8
(s, fwhm ) ∼700 Hz, AsPh3). IR (cm-1): 3067 (w), 3057 (w),
3048 (w), 2178 (w), 1965 (w), 1901 (w), 1814 (w), 1580 (w), 1572
(w), 1483 (s), 1434 (s), 1306 (w), 1272 (w), 1186 (w), 1173 (w),
1161 (w), 1077 (m), 1024 (m), 999 (w), 968 (w), 873 (w), 843
(w), 782 (w), 748 (s), 740 (s), 735 (s), 668 (w), 616 (w), 481 (m),
474 (m), 462 (m), 414 (w).
(Pentamethylcyclopentadienyl)dibromo(pyridine)osmium-
(III), (C5Me5)OsBr2(py) (5). To a solution of (C5Me5)2Os2Br4 (0.26
g, 0.27 mmol) in ethanol (30 mL) was added pyridine (0.05 mL,
0.62 mmol). The solution was stirred at room temperature for 1.5 h.
The resulting orange microcrystalline precipitate was collected by
filtration and dried under vacuum. Yield: 0.23 g (75%). Anal. Calcd
for C15H20Br2NOs: C, 31.9; H, 3.57; Br, 28.3; N, 2.48. Found: C,
31.6; H, 3.43; Br, 28.5; N, 2.41. MS(FD): 485 (M+ - C5H5N), 79
1
(C5H5N). H NMR (CD2Cl2, 22 °C): δ 26 (s, fwhm ) 260 Hz,
C5Me5), 10 (s, fwhm ) 240 Hz, o-py), 7.9 (s, fwhm ) 20 Hz,
p-py), 5.2 (s, fwhm ) 40 Hz, m-py). IR (cm-1): 3069 (w), 3053
(m), 2170 (w), 2013 (w), 1988 (w), 1957 (w), 1929 (w), 1597 (m),
1575 (w), 1506 (w), 1476 (s), 1439 (s), 1403 (w), 1360 (w), 1351
(w), 1342 (w), 1332 (w), 1230 (w), 1210 (w), 1153 (w), 1144 (w),
1100 (w), 1064 (w), 1057 (m), 1035 (m), 1027 (m), 1009 (w), 983
(w), 952 (w), 768 (s), 698 (s), 604 (w), 582 (w), 534 (w), 434 (w).
(Pentamethylcyclopentadienyl)dibromo(triphenylphosphine)-
osmium(III), (C5Me5)OsBr2(PPh3) (2). To a mixture of (C5Me5)2-
Os2Br4 (0.54 g, 0.56 mmol) and triphenylphosphine (0.29 g, 1.1
mmol) was added ethanol (40 mL). The solution was heated to
reflux for 30 min. The resulting red-orange solid was collected by
filtration and dried under vacuum. Yield: 0.56 g (67%). Anal. Calcd
for C28H30Br2OsP: C, 45.0; H, 4.05; P, 4.14. Found: C, 45.1; H,
(Pentamethylcyclopentadienyl)dibromo(tetrahydrothiophene)-
osmium(III), (C5Me5)OsBr2(SC4H8) (6). To a solution of (C5Me5)2-
Os2Br4 (0.28 g, 0.29 mmol) in ethanol (20 mL) was added a solution
of tetrahydrothiophene (0.60 mL, 6.8 mmol) in ethanol (10 mL).
The solution was heated to reflux for 17 h and then filtered. The
filtrate was concentrated to ca. 5 mL and cooled to -20 °C to afford
red-orange crystals. Yield: 0.17 g (51%). Anal. Calcd for C14H23-
Br2OsS: C, 29.3; H, 4.04; Br, 27.9; S, 5.59. Found: C, 29.5; H,
4.26; Br, 27.4; S, 6.05. MS(FD): 485 (M+ - SC4H8), 88 (SC4H8).
1H NMR (C6D6, 22 °C): δ 35 (s, fwhm ) 640 Hz, R-H of SC4H8),
25 (s, fwhm ) 240 Hz, C5Me5), 18 (s, fwhm ) 320 Hz, R-H of
SC4H8), 11 (s, fwhm ) 210 Hz, â-H of SC4H8), 3 (s, fwhm ) 200
Hz, â-H of SC4H8). IR (cm-1): 1506 (w), 1421 (w), 1399 (w),
1308 (w), 1266 (w), 1254 (w), 1208 (w), 1193 (w), 1153 (w), 1133
(w), 1076 (m), 1031 (sh), 1025 (m), 962 (w), 879 (w), 802 (w),
772 (w), 749 (w), 605 (w), 534 (w), 521 (w), 514 (w), 474 (w),
435 (m), 403 (m).
1
4.17; P, 4.22. MS(FD): 747 (M+). H NMR (CD2Cl2, 22 °C): δ
28.0 (s, fwhm ) 470 Hz, C5Me5), 21.5 (s, fwhm ) 300 Hz, o-CH),
12.2 (s, fwhm ) 120 Hz, m-CH), 11.0 (s, fwhm ) 120 Hz, p-CH),
3.7 (s, fwhm ) 60 Hz, m′-CH), 3.2 (s, fwhm ) 60 Hz, p′-CH),
-11.2 (s, fwhm ) 300 Hz, o′-CH). IR (cm-1): 3066 (w), 3054
(w), 3044 (w), 1960 (w), 1891 (w), 1571 (w), 1481 (s), 1437 (s),
1433 (s), 1311 (w), 1185 (w), 1161 (w), 1156 (w), 1093 (m), 1089
(m), 1069 (w), 1028 (m), 1022 (m), 996 (w), 973 (w), 755 (m),
750 (m), 746 (m), 741 (m), 697 (s), 691 (m), 621 (w), 526 (s), 513
(s), 502 (m), 498 (m), 458 (w), 448 (w), 437 (w), 431 (w).
(Pentamethylcyclopentadienyl)dibromo(tricyclohexylphos-
phine)osmium(III), (C5Me5)OsBr2[P(c-Hx)3] (3). To a mixture
of (C5Me5)2Os2Br4 (0.26 g, 0.27 mmol) and tricyclohexylphosphine
(0.15 g, 0.53 mmol) was added ethanol (30 mL). The solution was
stirred at room temperature for 3.5 h, the solvent was removed under
vacuum, and the residue was extracted with pentane (2 × 20 mL)
and diethyl ether (5 × 20 mL). The extracts were filtered, and the
filtrates were combined, concentrated to ca. 20 mL, and cooled to
-20 °C to afford an orange solid. Yield: 0.29 g (70%). Anal. Calcd
for C28H48Br2OsP: C, 43.9; H, 6.32; Br, 20.9; P, 4.05. Found: C,
(Pentamethylcyclopentadienyl)dibromohydrido(tricyclohex-
ylphosphine)osmium(IV), (C5Me5)OsBr2H[P(c-Hx)3] (7). To a
mixture of (C5Me5)2Os2Br4 (0.23 g, 0.24 mmol) and tricyclohexyl-
phosphine (0.13 g, 0.48 mmol) was added ethanol. The solution
was heated to reflux for 40 min and then cooled to room
temperature. The solution was filtered, and the filtrate was
concentrated to ca. 5 mL and cooled to -20 °C to afford an orange
powder. Yield: 0.26 g (71%). Anal. Calcd for C28H49Br2OsP: C,
43.9; H, 6.44; Br, 20.8; P, 4.04. Found: C, 44.0; H, 6.70; Br, 20.1;
P, 3.84. MS(FD): 768 (M+), 686 (M+ - HBr). 1H NMR (CD2Cl2,
22 °C): δ 2.42 (m, c-Hx), 2.15 (m, c-Hx), 1.96 (m, c-Hx), 1.79 (s,
C5Me5), 1.70 (m, c-Hx), 1.46 (m, c-Hx), 1.26 (m, c-Hx), -14.28
(d, 2JHP ) 36.6 Hz, Os-H). IR (cm-1): 2166 (w), 2146 (w), 1324
(w), 1298 (w), 1274 (w), 1218 (w), 1203 (w), 1179 (w), 1116 (w),
1073 (m), 1050 (w), 1024 (m), 1008 (m), 974 (w), 955 (w), 915
(w), 890 (w), 851 (m), 819 (w), 809 (w), 777 (w), 744 (w), 707
(w), 697 (w), 610 (w), 522 (w), 513 (m), 478 (w), 470 (w).
1
41.0; H, 5.89; Br, 23.7; P, 3.76. MS(FD): 767 (M+). H NMR
(C7D8, 22 °C): δ 24 (s, fwhm ) 470 Hz, C5Me5), 1.2 (br m, c-Hx),
0.6 (s, fwhm ) 300 Hz, c-Hx), -0.5 (s, fwhm ) 100 Hz, c-Hx),
-3 (s, fwhm ) 450 Hz, c-Hx). IR (cm-1): 2028 (br, w), 1404
(w), 1358 (m), 1341 (w), 1328 (m), 1303 (w), 1277 (w), 1266 (w),
1222 (w), 1204 (w), 1173 (m), 1154 (w), 1121 (w), 1115 (w), 1108
(w), 1074 (m), 1053 (w), 1043 (w), 1025 (m), 1020 (sh), 1004
(m), 997 (m), 972 (w), 912 (w), 888 (w), 848 (m), 820 (w), 735
(w), 729 (w), 721 (w), 697 (w), 682 (w), 607 (w), 598 (w), 528
(w), 512 (m), 505 (m), 486 (m), 477 (w), 459 (w).
(Pentamethylcyclopentadienyl)dibromo(triethylphosphine)-
(38) Luetkens, M. L.; Sattelberger, A. P.; Murray, H. H.; Basil, J. D.;
Fackler, J. P. Inorg. Synth. 1989, 26, 7-12.

Osmium(IV) Polyhydride Complexes
Organometallics, Vol. 25, No. 20, 2006 4797
(Pentamethylcyclopentadienyl)trihydrido(triphenylarsine)-
osmium(IV), (C5Me5)OsH3(AsPh3) (8). To a mixture of (C5Me5)-
OsBr2(AsPh3) (0.64 g, 0.81 mmol) and sodium borohydride (0.20
g, 5.3 mmol) was added ethanol (25 mL). The solution was heated
to reflux for 3.5 h, the solvent was removed under vacuum, and
the residue was extracted with diethyl ether (4 × 20 mL). The
extracts were filtered and the filtrates were combined, concentrated
to ca. 20 mL, and cooled to -20 °C to afford off-white crystals.
Additional crops of crystals were obtained by further concentrating
and cooling the supernatant. Yield: 0.37 g (72%). Anal. Calcd for
C28H33AsOs: C, 53.0; H, 5.24; As, 11.8. Found: C, 52.4; H, 4.99;
concentrated to ca. 20 mL, and cooled to -20 °C to afford pale
orange crystals. Additional crops of crystals were obtained by
further concentrating and cooling the supernatant. Yield: 1.19 g
(76%). MS(FD): 595 (M+). IR (cm-1): 3050 (m), 2173 (w), 2131
(w), 1954 (w), 1903 (w), 1811 (w), 1478 (m), 1433 (s), 1309 (w),
1264 (w), 1180 (w), 1121 (w), 1092 (s), 1070 (w), 1030 (m), 922
(w), 851 (w), 807 (w, br), 748 (m), 725 (w), 697 (s), 689 (m), 633
(w), 579 (m), 541 (s), 524 (m), 506 (m), 491 (w), 430 (w).
(Pentamethylcyclopentadienyl)trihydrido(tricyclohexyl-
phosphine)osmium(IV), (C5Me5)OsH3[P(c-Hx)3] (10). To a mix-
ture of (C5Me5)OsBr2[P(c-Hx)3] (0.71 g, 0.93 mmol) and NaBH4
(0.18 g, 4.8 mmol) was added ethanol (30 mL). The solution was
stirred at room temperature for 30 min, the solvent was removed
under vacuum, and the residue was extracted into pentane (2 × 20
mL). The extracts were filtered, and the filtrates were combined,
concentrated to ca. 2 mL, and cooled to -20 °C to afford off-
white crystals. Yield: 0.19 g (34%). Anal. Calcd for C28H51OsP:
C, 55.2; H, 8.44; P, 5.09. Found: C, 54.6; H, 8.37; P, 4.60. MS-
1
As, 11.3. MS(FD): 636 (M+). H NMR (CD2Cl2, 25 °C): δ 7.37
(m, AsPh3, 15H), 1.99 (s, C5Me5, 15H), -13.92 (s, Os-H, 1H),
-14.57 (s, Os-H, 2H). 13C{1H} NMR (C7D8, 25 °C): δ 141.2 (s,
i-C), 133.1 (s, o-C), 129.1 (s, p-C), 128.0 (s, m-C), 90.7 (s, C5-
Me5), 12.3 (s, C5Me5). IR (cm-1): 3064 (m), 3048 (m), 2720 (w),
2090 (m), 2052 (s), 2026 (s), 1952 (w), 1814 (w), 1581 (w), 1572
(w), 1480 (s), 1434 (s), 1310 (w), 1304 (w), 1271 (w), 1261 (w),
1181 (m), 1153 (w), 1082 (m), 1076 (s), 1026 (m), 1000 (m), 921
(w), 916 (w), 862 (m), 795 (s), 739 (s), 696 (s), 683 (s), 668 (m),
628 (w), 618 (w), 565 (w), 520 (w), 476 (s), 472 (s), 468 (s).
1
(FD): 610 (M+). H NMR (CD2Cl2, 25 °C): δ 2.10 (s, C5Me5,
15H), 1.80 (“d”, c-Hx, 12H), 1.65 (m, c-Hx, 3H), 1.46 (m, c-Hx,
3H), 1.20 (m, c-Hx, 18H), -15.26 (d, 2JHP ) 33.6 Hz, Os-H, 2H),
2
-15.48 (d, JHP ) 4.4 Hz, Os-H, 1H). 13C{1H} NMR (CD2Cl2,
(Pentamethylcyclopentadienyl)trideuterido(triphenylarsine)-
osmium(IV), (C5Me5)OsD3(AsPh3) (8-d3). To a mixture of (C5-
Me5)OsBr2(AsPh3) (0.99 g, 1.4 mmol) and sodium borodeuteride
(0.24 g, 5.8 mmol) was added ethanol-d1 (30 mL). The solution
was heated to reflux for 45 min, the solvent was removed under
vacuum, and the residue was extracted into diethyl ether (4 × 20
mL). The extracts were filtered, and the filtrates were combined,
concentrated to ca. 10 mL, and cooled to -20 °C to afford pale
orange crystals. Additional crops of crystals were obtained by
further concentrating and cooling the filtrates. Yield: 0.53 g (60%).
MS(FD): 630 (M+). IR (cm-1): 3063 (w), 3048 (w), 2049 (w),
1954 (w), 1889 (w), 1582 (w), 1480 (m), 1434 (s), 1313 (w), 1306
(w), 1277 (w), 1263 (w), 1181 (w), 1082 (w), 1076 (m), 1026 (w),
1000 (w), 918 (w), 850 (w), 802 (w, br), 739 (s), 696 (s), 668 (m),
629 (w), 615 (w), 575 (m), 492 (w), 475 (m), 469 (m).
2
1
25 °C): δ 90.8 (d, JCP ) 7.5 Hz, C5Me5), 39.8 (d, JCP ) 27.6
2
Hz, 1-C), 30.3 (s, 3-C), 28.1 (d, JCP ) 10.1 Hz, 2-C), 27.3 (s,
4-C), 12.8 (s, C5Me5). 31P{1H} NMR (CD2Cl2, 25 °C): δ 34.8 (s).
IR (cm-1): 2113 (w), 2095 (m), 2078 (s), 1344 (w), 1325 (w),
1294 (w), 1262 (w), 1223 (w), 1196 (w), 1171 (w), 1154 (w), 1126
(w), 1109 (w), 1070 (m), 1033 (m), 1006 (m), 916 (w), 898 (w),
887 (w), 851 (w), 844 (m), 823 (m), 800 (s), 735 (m), 702 (w),
680 (w), 523 (s), 494 (w).
(Pentamethylcyclopentadienyl)trihydrido(triethylphosphine)-
osmium(IV), (C5Me5)OsH3(PEt3) (11). To a mixture of (C5Me5)-
OsBr2(PEt3) (1.0 g, 1.66 mmol) and sodium borohydride (0.31 g,
8.2 mmol) was added ethanol (30 mL). The solution was stirred at
room temperature for 1 h, and the color of the solution became
yellow. The solvent was removed under vacuum, the residue was
extracted with pentane (3 × 30 mL), and the extracts were filtered.
The filtrates were combined and taken to dryness to yield off-white
crystals. Yield: 0.50 g (67%). Anal. Calcd for C16H32OsP: C, 43.0;
(Pentamethylcyclopentadienyl)trihydrido(triphenylphosphine)-
osmium(IV), (C5Me5)OsH3(PPh3) (9). To a mixture of (C5Me5)-
OsBr2(PPh3) (0.48 g, 0.64 mmol) and sodium borohydride (0.12 g,
3.2 mmol) was added ethanol (25 mL). The solution was stirred at
room temperature for 15 h, and the color of the solution gradually
became a lighter orange. The solvent was removed under vacuum,
the residue was extracted with diethyl ether (3 × 20 mL), and the
extracts were filtered. The filtrates were combined, concentrated
to ca. 5 mL, and cooled to -78 °C to yield off-white crystals.
Additional crops of crystals were obtained by further concentrating
and cooling the supernatant. Yield: 0.27 g (71%). Anal. Calcd for
C28H33OsP: C, 56.9; H, 5.63; P, 5.24. Found: C, 56.4; H, 5.62; P,
1
H, 7.45. Found: C, 42.1; H, 7.17. MS(FD): 443 (M+ - H2). H
NMR (C6D6, 25 °C): δ 2.07 (s, C5Me5, 15H), 1.34 (dq, 2JHP ) 9.2
Hz, 3JHH ) 7.6 Hz, PCH2, 6H), 0.84 (dt, 3JHP ) 7.2 Hz, 3JHH ) 7.6
Hz, PCH2CH3, 9H), -13.72 (d, 2JHP ) 7 Hz, Os-H, 1H), -14.66
(d, 2JHP ) 33.2 Hz, Os-H, 2H). 13C{1H} NMR (C6D6, 25 °C): δ
2
1
90.4 (d, JCP ) 2.2 Hz, C5Me5), 22.6 (d, JCP ) 37 Hz, PCH2),
12.1 (s, C5Me5), 8.3 (s, PCH2CH3). 31P{1H} (C6D6, 25 °C): δ 9.7
(s). IR (cm-1): 2089 (m), 2073 (m), 2032 (m), 1410 (m), 1032 (s),
814 (s), 778 (s), 747 (s), 638 (s), 452 (s). Some samples of 11 also
contained traces of the dihydride complex (C5Me5)OsH2Br(PEt3),
1
5.01. MS(FD): 592 (M+). H NMR (CD2Cl2, 25 °C): δ 7.36 (m,
1
which had the following H NMR resonances: δ 1.76 (s, C5Me5,
2
PPh3, 15H), 1.91 (s, C5Me5, 15H), -13.77 (d, JHP ) 8 Hz, Os-
2
3
15H), 1.50 (dq, JHP ) 9.2 Hz, JHH ) 7.6 Hz, PCH2, 6H), 0.80
(dt, 3JHP ) 7.6 Hz, 3JHH ) 7.6 Hz, PCH2CH3, 9H), -11.18 (d, 2JHP
) 36.4 Hz, Os-H, 2H).
2
H, 1H), -14.28 (d, JHP ) 33.5 Hz, Os-H, 2H). 13C{1H} NMR
1
2
(CD2Cl2, 25 °C): δ 141.1 (d, JCP ) 51.7 Hz, i-C), 133.7 (d, JCP
4
3
) 10.8 Hz, o-C), 129.1 (d, JCP ) 2.1 Hz, p-C), 127.7 (d, JCP
)
Crystallographic Studies.39 Single crystals of (C5Me5)OsH3-
(PPh3), 9, grown from diethyl ether, were mounted on glass fibers
with Paratone-N oil (Exxon) and immediately cooled to -75 °C in
a cold nitrogen gas stream on the diffractometer. [Single crystals
of (C5Me5)OsH3(AsPh3), 8, grown from diethyl ether, were treated
similarly. Subsequent comments in brackets will refer to this
compound.] Standard peak search and indexing procedures gave
rough cell dimensions, and least-squares refinement using 6537
[4582] reflections yielded the cell dimensions given in Table 1.
Data were collected with an area detector by using the measure-
ment parameters listed in Table 1. The average values of the
9.7 Hz, m-C), 92.5 (d, JCP ) 2.3 Hz, C5Me5), 11.7 (s, C5Me5).
31P{1H} (CD2Cl2, 25 °C): 26.1 (s). IR (cm-1): 3057 (m), 2721
(w), 2101 (m, sh), 2068 (s), 2049 (s), 1954 (w), 1902 (w), 1814
(w), 1169 (w), 1580 (w), 1570 (w), 1479 (s), 1434 (s), 1306 (w),
1265 (w), 1180 (m), 1154 (w), 1092 (s), 1071 (m), 1030 (m), 1000
(w), 919 (w), 871 (w), 849 (w), 798 (s), 748 (s), 697 (s), 620 (w),
540 (s), 511 (s), 456 (m).
(Pentamethylcyclopentadienyl)trideuterido(triphenylphos-
phine)osmium(IV), (C5Me5)OsD3(PPh3) (9-d3). To a mixture of
(C5Me5)OsBr2(PPh3) (1.97 g, 2.64 mmol) and sodium borodeuteride
(0.51 g, 12.3 mmol) was added ethanol-d1 (40 mL). The solution
was heated to reflux for 25 min, the solvent was removed under
vacuum, and the residue was extracted into diethyl ether (5 × 20
mL). The extracts were filtered, and the filtrates were combined,
(39) For a description of the crystallographic programs and procedures
used, see: Brumaghim, J. L.; Priepot, J. G.; Girolami, G. S. Organometallics
1999, 18, 3139-2144.

4798 Organometallics, Vol. 25, No. 20, 2006
Gross and Girolami
normalized structure factors suggested the choice P1h, which was
confirmed by successful refinement of the proposed model. The
measured intensities were reduced to structure factor amplitudes
and their esd’s by correction for background, scan speed, and
Lorentz and polarization effects. Corrections for crystal decay were
unnecessary, but an empirical absorption correction was applied,
the maximum and minimum transmission factors being 0.543 and
0.243 [for 8, 0.690 and 0.132]. Systematically absent reflections
were deleted and symmetry equivalent reflections were averaged
to yield the set of unique data. The 0 0 1 reflection was obscured
by the beam stop and was therefore omitted from the least-squares
“idealized” positions (methyl hydrogens were optimized by rotation
about the C-C bonds) with C-H ) 0.98 Å, and their displacement
factors were set equal to 1.5 times Ueq for the attached carbon atom.
Phenyl hydrogens were fixed in “idealized” positions with C-H
) 0.95 Å, and their displacement factors were set equal to 1.2 times
Ueq for the attached carbon atom. The osmium-bound hydrogen
atoms were located in the difference Fourier map, and their locations
were independently refined with individual isotropic displacement
factors. Successful convergence was indicated by the maximum
shift/error of 0.004 [0.002] for the last cycle. Final refinement
parameters are given in Table 1. [For 8, an isotropic extinction
parameter was refined to a final value of x ) 3.9(3) × 10-6, where
Fc is multiplied by the factor k[1 + Fc2xλ3/sin 2θ]-1/4, with k being
the overall scale factor. An extinction correction was not necessary
for 9.] The largest peak in the final Fourier difference map (0.68 e
Å-3) was located 1.21 Å from the osmium atom and 2.11 Å from
the phosphorus atom. [For 8, the largest peak in the final Fourier
difference map (0.72 e Å-3) was located 0.76 Å from the osmium
atom.] A final analysis of variance between observed and calculated
structure factors showed no apparent errors.
2
refinement. Two reflections (4 4 8 and 0 6 13) with Fo < -3σ-
2
(Fo ) were suppressed, and the remaining 5436 data were used in
the least-squares refinement. [For 8, the 0 0 1 reflection was
obscured by the beam stop and was therefore omitted, leaving 5559
unique data.]
The structure was solved using Patterson methods (SHELXTL).
The correct positions for the osmium, phosphorus, and six phenyl
carbon atoms were deduced from a sharpened Patterson map [for
8, only the Os and As atoms were found]. Subsequent least-squares
refinement and difference Fourier calculations revealed the positions
of the remaining non-hydrogen atoms. [For 8, the C5Me5 ring was
disordered over two positions; the site occupancy factors for the
two positions refined to 0.52(1) and 0.48(1). The displacement
factors for the overlapping ring carbons were restrained to near-
isotropic values, and equivalent carbon-carbon bond distances were
restrained to be approximately equal.] The quantity minimized by
Acknowledgment. We thank the National Science Founda-
tion (Grants CHE 00-76061 and CHE 04-20768) for support of
this work, and Dr. Scott Wilson and Ms. Teresa Prussak-
Wieckowska of the University of Illinois Materials Chemistry
Laboratory for collecting the crystallographic data for 8 and 9.
We thank Dr. Julia L. Brumaghim for preparing and character-
izing compound 11. C.L.G. thanks the University of Illinois at
Urbana-Champaign for a departmental fellowship.
2
the least-squares program was ∑w(Fo - Fc2)2, where w ) {[σ-
2
(Fo )]2 + (0.0130P)2 + 2.0848P}-1 and P ) (Fo2 + 2Fc2)/3 [for 8,
2
w ) {[σ(Fo )]2 + (0.0167P)2 + 1.56P}-1 ]. The analytical
approximations to the scattering factors were used, and all structure
factors were corrected for both real and imaginary components of
anomalous dispersion. In the final cycle of least-squares, indepen-
dent anisotropic displacement factors were refined for the non-
hydrogen atoms. The methyl hydrogen atoms were placed in
Supporting Information Available: X-ray crystallographic files
in CIF format for (C5Me5)OsH3(AsPh3) (8) and (C5Me5)OsH3(PPh3)
(9) are available free of charge via the Internet at http://pubs.acs.org.
OM060463Z