Complex formation and rearrangement reactions of the phosphine hydride anions [OsH3(PPh3)3] and [IrH 2(PPh3)3]

Article abstract of DOI:10.1021/om050391w

[OsH₄(PPh₃)₃] (1) reacts with KH in THF in the presence of 18-crown-6 to form [K(THF)(18-crown6)][OsH₃(PPh ₃)₃] (2), characterized by NMR spectroscopy and X-ray crystallography; cation-anion contact is achieved through three Os-H-...K moieties. In contrast, [IrH₃(PPh₃)₃] (6) reacts with KH and 18crown-6 in THF with redistribution of ligands to produce the known bis-phosphine complex [K(18crown-6)][IrH₄(PPh₃) ₂] (7). This reaction has been followed by NMR spectroscopy, and [IrH₂(PPh₃)₃]has been identified as a likely intermediate. K[OsH₃(PPh₃)₃] (3) reacts with Bu₃ⁿSnCl to form the tinosmium complex [OsH ₃(SnBu₃ⁿ)(PPh3)3] (8), characterized by NMR spectroscopy and X-ray crystallography. The molecule contains a seven-coordinate osmium center, which can be described approximately as a distorted fac-[OsH₃(PPh₃)] arrangement, with the SnBu ₃ⁿ moiety capping the OsH₃ face.

Full text of DOI:10.1021/om050391w

122
Organometallics 2006, 25, 122-127
Complex Formation and Rearrangement Reactions of the Phosphine
Hydride Anions [OsH3(PPh3)3]- and [IrH2(PPh3)3]-
Gemma Guilera,† G. Sean McGrady,*,‡ Jonathan W. Steed,*,§ and Aled L. Jones‡
European Synchrotron Radiation Facility, 6 Rue Jules Horowitz, Grenoble Cedex 9, France,
Department of Chemistry, UniVersity of New Brunswick, Fredericton, N.B. E3B 6E2, Canada, and
Department of Chemistry, UniVersity of Durham, South Road, Durham DH1 3LE, U.K.
ReceiVed May 16, 2005
[OsH4(PPh3)3] (1) reacts with KH in THF in the presence of 18-crown-6 to form [K(THF)(18-crown-
6)][OsH3(PPh3)3] (2), characterized by NMR spectroscopy and X-ray crystallography; cation-anion contact
is achieved through three Os-H‚‚‚K moieties. In contrast, [IrH3(PPh3)3] (6) reacts with KH and 18-
crown-6 in THF with redistribution of ligands to produce the known bis-phosphine complex [K(18-
crown-6)][IrH4(PPh3)2] (7). This reaction has been followed by NMR spectroscopy, and [IrH2(PPh3)3]-
has been identified as a likely intermediate. K[OsH3(PPh3)3] (3) reacts with Bun SnCl to form the tin-
3
osmium complex [OsH3(SnBun )(PPh3)3] (8), characterized by NMR spectroscopy and X-ray crystal-
3
lography. The molecule contains a seven-coordinate osmium center, which can be described approximately
as a distorted fac-[OsH3(PPh3)] arrangement, with the SnBun moiety capping the OsH3 face.
3
Here we report a study of the coordination chemistry of
phosphine polyhydride complexes of Os and Ir and of their
conjugate anions stabilized by [K(18-crown-6)]+. These new
materials have electronic and steric properties distinct from those
reported by Morris et al.5,6 We have focused on complexes
containing three phosphine ligands instead of two, at the same
time using the electronically less basic phosphine PPh3.
Introduction
Even though transition metal hydrides have been known for
over seven decades, they remain highly topical in such diverse
fields as organometallic chemistry,1 bioinorganic chemistry,2
supramolecular chemistry,3 and hydrogen storage.4 Transition
metal hydrides have the advantage of containing at least one
hydrogen atom with tunable electronic characteristics. This
feature enables them to take part in intermolecular noncovalent
bonding interactions, including electrostatic and van der Waals
interactions, and especially hydrogen bonding. For example,
recent elegant work by Morris and co-workers exploited
proton-hydride interactions to control the formation of su-
pramolecular structures containing anions such as [OsH4(PPri3)2]-
and [IrH5(PPri3)2]-.5,6 In particular, noncovalent interactions
between metal hydrides and either acidic hydrogen (unconven-
tional hydrogen bonding)7 or other metals8 have become topical.
Morris’ work shows that the M-H‚‚‚K+ interaction is significant
and that it may play a role in metal hydride reactivity.
Results and Discussion
Ionic Derivatives of [OsH4(PPh3)3]. The complex [OsH4-
(PPh3)3] (1) was synthesized by the literature procedure9 as an
off-white precipitate. Characterization data were in agreement
with those previously reported. The yellow, oxygen- and water-
sensitive solid [K(THF)(18-crown-6)][OsH3(PPh3)3] (2) was
prepared in 62% yield by reacting 1 with an excess of KH in
THF in the presence of 18-crown-6. In this reaction, the role of
the crown ether is to enhance the solubility of KH in THF and
to impart stability to the final complex, but it may also serve as
a C-H hydrogen bond donor. This reaction resulted in the
formation of only the fac-isomer of [OsH3(PPh3)3]-, as evi-
denced by 1H and 31P{1H} NMR spectroscopy and X-ray
crystallography. Complex 2 is very soluble in THF and only
sparingly soluble in toluene, and decomposes slowly in chlo-
* Corresponding authors. E-mail: smcgrady@unb.ca; jon.steed@
durham.ac.uk.
† European Synchrotron Radiation Facility.
‡ University of New Brunswick.
§ University of Durham.
(1) Guilera, G.; McGrady, G. S. Chem. Soc. ReV. 2003, 383.
(2) (a) Autissier, V.; Clegg, W.; Harrington, R. W.; Henderson, R. A.
Inorg. Chem. 2004, 43, 3098. (b) Cammack, R.; Vliet, P. In Bioinorganic
Catalysis, 2nd ed.; Reedijk, J., Bouwman, E., Eds.; Marcel Dekker: New
York, 1999.
(3) (a) Braga, D.; Grepioni, F. J. Chem. Soc., Chem. Commun. 1996,
571. (b) Desiraju, G. R. J. Chem. Soc., Dalton Trans. 2000, 3745.
(4) (a) Peruzzini, M.; Poli, R. Recent AdVances in Hydride Chemistry;
Elsevier Science: Amsterdam, 2001. (b) Grochala, W.; Edwards, P. P.
Chem. ReV. 2004, 104, 1283.
1
rinated solvents. The H NMR spectrum (d8-THF) of 2 shows
the distinctive mirror-symmetry patterns characteristic of an
AA′A′′XX′X′′ spin system for the octahedrally coordinated
anion. This multiplet, centered at -11.3 ppm, clearly differs
from the precursor 1 (-8.1 ppm). The singlet observed in the
31P{1H} NMR spectrum (d8-THF) at 24.6 ppm also differs from
that of the starting material (23.8 ppm).
(5) (a) Abdur-Rashid, K.; Gusev, D. G.; Landau, S. E.; Lough, A. J.;
Morris, R. H. J. Am. Chem. Soc. 1998, 120, 11826. (b) Abdur-Rashid, K.;
Gusev, D. G.; Lough, A. J.; Morris, R. H. Organometallics, 2000, 19, 834.
(6) Gusev, D. G.; Lough, A. J.; Morris, R. H. J. Am. Chem. Soc. 1998,
120, 13138.
(7) (a) Crabtree, R. H.; Siegbahn, P. E. M.; Eisenstein, O.; Rheingold,
A. L.; Koetzle, T. F. Acc. Chem. Res. 1996, 29, 348. (b) Custelcean, R.;
Jackson, J. E. Chem. ReV. 2001, 101, 1963. (c) Fung, W. K.; Huang, X.;
Man, M. L.; Ng, S. M.; Hung, M. Y.; Lin, Z.; Lau, C. P. J. Am. Chem.
Soc. 2003, 125, 11539.
The reaction was monitored in a 5 mm NMR tube closed
with a Teflon valve, with the hope of identifying any intermedi-
ate dihydrogen species. The tube was filled with equimolar
amounts of 1 and 18-crown-6 and an excess of KH in d8-THF
and was shaken vigorously, and 1H and 31P{1H} NMR spectra
were measured every 30 min at 213 K. However, reaction did
(9) Ahmad, N.; Levion, J. J.; Robinson, S. D.; Utteley, M. F. Inorg.
Synth. 1974, 15, 57.
(8) Braga, D.; Grepioni, F.; Desiraju, G. R. Chem. ReV. 1998, 98, 1375.
10.1021/om050391w CCC: $33.50 © 2006 American Chemical Society
Publication on Web 11/22/2005

Phosphine Hydride Anions
Organometallics, Vol. 25, No. 1, 2006 123
not commence at this low temperature and had to be encouraged
by gentle warming. Once it had clearly started, the mixture was
cooled again and its progress was followed by NMR spectros-
copy. The spectra revealed a gradual transformation from
starting material to product, without any evidence of intermedi-
ate species and implying extraction of a hydride from Os by
KH in a conventional acid-base reaction.
The osmium complex 2 is extremely sensitive to proton
sources, which cleanly and rapidly regenerate [OsH4(PPh3)3].
Indeed, in the absence of the stabilizing crown ether, the anion
of K[OsH3(PPh3)3] (3), which is very unstable in solution, easily
reverts to the starting tetrahydride complex 1. The proclivity
of anionic [OsH3(PPh3)3]- in complex 2 to react with proton
sources was studied by NMR spectroscopy, employing the weak
acid (CF3)2CHOH (HFIP) as the proton source. Variable-
temperature NMR studies of complex 2 in d8-THF solution
showed no evidence of fluxionality over the range 293-180
K. Upon addition of a single equivalent of HFIP, the yellow
solution became colorless and the tetrahydride was completely
regenerated, even at low temperatures. However, upon addition
of 3, 5, 15, 35, and more equivalents of HFIP, the peak at -8.1
ppm assigned to the tetrahydride 1 remained unaltered, and no
further species appeared. This observation is remarkable, since
addition of an excess of HFIP at low temperature to 1 in CD2Cl2
resulted in protonation and led to the formation of [OsH5-
(PPh3)3]+(4). This new cationic species was characterized by
the appearance of a peak at -5.7 ppm in the 1H NMR spectrum,
with a T1 value of 269 ms at 190 K, much smaller than that of
the parent tetrahydride 1 (T1 ) 1738 ms).
Disagreement has arisen in the literature over the formulation
of the analogous compound [OsH5(PMe2Ph)3]+, either as a
nonclassical trihydride-dihydrogen complex10,11 or as a dodeca-
hedral pentahydride.12 On the basis of our T1 measurements for
[OsH5(PPh3)3]+, we consider it to contain five classical hydride
ligands. The short relaxation time for the hydride resonance of
4 relative to the classical tetrahydride complex 1 can be
accounted for by the proximity of five fluxional hydride ligands
in the cation. The close approach of these hydrides can induce
dipole-dipole interactions and may even result in the formation
of transient elongated dihydrogen ligands. Such a description
accords with the interpretation of Esteruelas and Lledo´s, who
carried out DFT calculations on the model complex [OsH5-
(PH3)3]+.13 Their optimized geometries revealed that the struc-
tures containing nonclassical hydrides are energetically very
similar to those that are classical and that their energy is
practically independent of the separation between the H atoms
involved in the nonclassical interaction. As a consequence,
Esteruelas and Lledo´s described [OsH5(PH3)3]+ as a species
containing hydrogen atoms moving freely in a wide region
within the metal coordination sphere.
Figure 1. (a) X-ray crystal structure of [K(THF)(18-crown-6)]-
[OsH3(PPh3)3] (2). All non-hydride H atoms are omitted for clarity.
Selected average bond lengths (Å): Os-P ) 2.3273(13), Os-K
) 3.5829(13), Os-H ) 1.64(5), K-H ) 2.86(5). Selected average
angles (deg): P-Os-P ) 105.45(5), K-Os-H ) 49.7(16),
H-Os-H ) 83(2). (b) [K(18-crown-6)][OsH3(PPh3)3] (2) viewed
along the Os‚‚‚K axis. The staggered arrangement of the hydrides
with respect to the phosphine ligands is revealed.
days after addition of HFIP to 2. This quintet at -9.9 ppm is
clearly the known [OsH3(PPh3)4]+ (5);14 there was no evidence
at this stage of the initially formed pentahydride cation 4. It is
not clear to us why complex 2 is only protonated to the neutral
[OsH4(PPh3)3] (1) in the presence of excess acid, but the
rearrangements and ligand exchanges that clearly take place in
the formation of 5 from 1 via 4 reveal a complicated series of
reactions occurring under acid conditions.
Diffraction quality yellow crystals of 2 were obtained by slow
diffusion of hexane into a THF solution of the complex under
an Ar atmosphere. The complex crystallizes in the triclinic space
group P1h, with two molecules per asymmetric unit. The crystal
structure reveals the fac-configuration deduced spectroscopically
for the anion (Figure 1), with the three hydrides pointing toward
the potassium cation, which is drawn slightly out of the plane
of the crown ether. The ion pair is held together through
electrostatic interactions, enhanced by the anionic nature of the
metal hydride moieties. The two molecules of the asymmetric
unit are well separated, with no unusually short nonbonding
intermolecular interactions present, and the two crown ether
ligands are displaced away from each other and face in different
directions, as can be seen in Figure 2.
The structure adopted by 2 contrasts with that of the crown-
ether-free complex K[OsH3(PMe2Ph)3],15 which also contains
more basic and sterically less demanding phosphine ligands.
This complex adopts a dimeric structure in the crystal, as shown
in Figure 3. In this case, the naked potassium ion and the more
electron-rich Os-H moieties favor a more ionic arrangement.
The two monomers are intimately connected by the interaction
of the pyramidal K+ in one monomer with one Os-H moiety
from its partner unit, assisted by the encapsulation of K+ by
two phenyl rings of the phosphine ligands.
In an attempt to study further the reaction between 1 and
1
HFIP, a H NMR spectrum was recorded at room temperature
2 days after addition of the acid. Two peaks were observed in
the spectrum: the original quartet at -8.1 ppm assigned to 1
along with a quintet at -9.9 ppm. The latter feature was the
only one remaining after 5 days: it collapsed to a singlet when
phosphorus-decoupled. The same feature was also observed 3
The molecular structure of 2 reveals that the potassium ion
does not occupy a direct coordination site at osmium, as
indicated by the Os‚‚‚K distances of 3.54 and 3.63 Å, which
are larger than the sum of the covalent radii for K and Os (3.29
(10) Johnson, T. J.; Huffman, J. C.; Caulton, K. G.; Jackson, A.;
Eisenstein, O. Organometallics 1989, 8, 2073.
(11) Johnson, T. J.; Albinati, A.; Koetzle, T. F.; Ricci, J.; Eisenstein,
O.; Huffman, J. C.; Caulton, K. G. Inorg. Chem. 1994, 33, 4966.
(12) Maseras, F.; Koga, N.; Morokuma, K. J. Am. Chem. Soc. 1993,
115, 8313.
(13) Esteruelas, M. A.; Lledo´s, A.; Mart´ın, M.; Maseras, F.; Ose´s, R.;
Ruiz, N.; Toma`s, J. Organometallics 2001, 20, 5297.
(14) Harding, P. A.; Robinson, S. D.; Henrick, K. J. Chem. Soc., Dalton
Trans. 1988, 415.
(15) (a) Huffman, J. C.; Green, M. A.; Kaiser, S. L.; Caulton, K. G. J.
Am. Chem. Soc. 1985, 107, 5111. (b) Siedle, A. R.; Newmark, R. A.;
Pignolet, L. H. Inorg. Chem. 1986, 25, 3412.

124 Organometallics, Vol. 25, No. 1, 2006
Guilera et al.
number of H‚‚‚K interactions is variable according to the shape
and size of the anion, and the H-atom positions are not well
defined in some cases. The cation-anion interaction draws the
potassium ion out of the plane of the crown ether by 0.7 to 1.2
Å, with M‚‚‚K distances in the range 3.4-3.8 Å. It is notable
also that the [OsH3(PPh3)3] anion in 2 bears a striking structural
resemblance to the isoeletronic neutral congener fac-[IrH3(PPh2-
Me)3], whose structure has been determined by neutron dif-
fraction.21 Here, the Ir-H bond distances are 1.627(5) Å and
the H-Ir-H angles 83.4(2)°. The cation-anion interaction in
2 thus appears to be purely electrostatic and causes a negligible
effect on the geometry of the anion.
Ionic Derivatives of [IrH3(PPh3)3]. We also investigated the
reaction of [IrH3(PPh3)3] (6) with KH and 18-crown-6, with the
aim of forming an iridium analogue of 2. Complex 6 was
prepared in a two-step reaction following the literature method.22
A mixture of mer- and fac-isomers of 6 was obtained, as
evidenced by 1H and 31P NMR spectroscopy. This pale yellow
complex is quite stable in the solid state, but decomposed
gradually in solution.
Figure 2. Asymmetric unit of [K(THF)(18-crown-6)][OsH3(PPh3)3]
(2). All non-hydride H atoms are omitted for clarity.
A mixture of 6, KH, and 18-crown-6 in THF was warmed to
313 K and stirred for 4 days, during which time the yellow
slurry changed through green to deep red in color. Unexpectedly,
this produced the known Ir(V) bis-phosphine complex [K(18-
crown-6)][IrH4(PPh3)2] (7) as a white solid, extremely air-
sensitive in both the solid state and solution. Complex 7 shows
a complicated multiplet pattern at -12.6 ppm (3H) in the
hydride region of the 1H NMR spectrum in d8-THF and a broad
doublet of triplets at -12.9 ppm (1H), revealing two different
environments for the hydride ligands. The 31P{1H} NMR
spectrum also shows two different singlet phosphine resonances,
at 26.9 and 12.8 ppm. White crystals were obtained by slow
diffusion of hexane into a THF solution of 7, and X-ray
diffraction confirmed these to be [K(18-crown-6)][IrH4(PPh3)2]
Figure 3. X-ray crystal structure of dimeric K2[OsH3(PMe2Ph)3]2.12
All non-hydride H atoms are omitted for clarity.
1
as reported by Morris and co-workers.20 We note that the H
NMR and 31P spectra obtained by us in d8-THF differ
significantly from those described for complex 7 by Morris et
al. in d6-benzene, which showed a triplet of triplets at -11.9
ppm and a multiplet at -12.3 ppm, each integrating to 2H. This
difference presumably arises from interference by the basic THF
solvent, which can coordinate to the open face of the cation in
7 and lower the symmetry of the hydride ligand environment
in the solvated ion pair.
Å). Generally, as in the highly symmetric complex [K(18-crown-
6)]SCN, the crown ether adopts a D3d geometry in which K+
lies at the center of the crown, with K‚‚‚O distances of 2.80 Å.16
In complex 2, the crown ether ligand also adopts a D3d geometry
and K+ remains equidistant from the six oxygen donor atoms.
However, the potassium is attracted out of the plane of the crown
and toward the osmium (K-crown centroid ) 0.73 Å).
All Os-P distances in 2 are very similar, with an average
value of 2.31 Å. The average P-Os-P angle is 105.5°, slightly
wider than those in K[OsH3(PMe2Ph)3]2 (97.4°),15 on account
of the larger cone angle of PPh3.17 Likewise, all P-Os-K angles
are equivalent (113.2°) and slightly smaller than those observed
for K2[OsH3(PMe2Ph)3]2. Average values for the Os-H and
K-H distances are 1.64(5) and 2.86(5) Å, respectively, although
the former may be in reality somewhat larger and the latter
correspondingly smaller on account of the inaccurate location
of H atoms by X-ray methods. The average value for the Os-
H-K angle (102.3°) shows this moiety to be far from linear,
as is the case also with K[OsH3(PMe2Ph)3]2.
Morris et al. obtained complex 7 and its PPri3 analogue using
Ir(III) or Ir(V) precursors with two phosphine ligands, as
described in eqs 1 and 2. In contrast, we prepared 7 from an
Ir(III) tris-phosphine precursor (eq 3). It is noteworthy that H2
is added to stabilize the product in eq 1, whereas H2 is released
in eq 2. Our synthesis (eq 3) involved neither addition nor
release of H2 from solution, but instead proceeded through a
ligand redistribution process.
THF, H2
[IrHCl2(PPri3)2] + KH + 18-crown-6
8
[K(18-crown-6)][IrH4(PPri3)2] (1)
The structure we have determined for 2 is in accord with
those reported for similar complexes in the literature, viz., [K(18-
crown-6)][RuH3(PPh3)3],18 [K(18-crown-6)][WH5(PMe3)3],19
[K(18-crown-6)][ReH2(PMe3)4],19 and [K(18-crown-6)][IrH4-
(PR3)2] (R ) Ph or Pri).20 In these other systems, a maximum
of three M-H moieties point toward the K+ ion, although the
THF, -H2
[IrH5(PPh3)2] + KH + 18-crown-6
8
[K(18-crown-6)][IrH4(PPh3)2] (2)
[IrH3(PPh3)3] + KH + 18-crown-6 THF8
(16) Seiler, P.; Dobler, M.; Dunitz, J. D. Acta Crystallogr., Sect. B:
Struct. Crystallgr. Cryst. Chem. 1974, 30, 2744.
(17) Tolman, C. A. Chem. ReV. 1977, 77, 313.
(18) Chan, A. S. C.; Shieh, H.-S. J. Chem. Soc., Chem. Commun. 1985,
1379.
[K(18-crown-6)][IrH4(PPh3)2] (3)
In an attempt to characterize intermediates involved in the
1
formation of 7 according to eq 3, we monitored the H NMR

Phosphine Hydride Anions
Organometallics, Vol. 25, No. 1, 2006 125
white, air- and water-sensitive crystalline material. The 1H NMR
spectrum of 8 in d8-THF showed a pseudoquartet centered at
-11.4 ppm, and the 31P{1H} NMR spectrum displayed a singlet
at 13.3 ppm. A single crystal of the complex was analyzed by
X-ray crystallography.
Complex 8 crystallizes in the monoclinic space group P21/n.
The molecular structure of 8, shown in Figure 4, consists of a
seven-coordinate osmium center with facially disposed phos-
phines and hydrides approximately occupying the vertexes of
an octahedron. The hydride ligands were located in a difference
Fourier map, and the positions of two were refined freely while
the third was allowed to refine with loose restraints. Description
of the nature of the OsH3Sn moiety is far from clear-cut, and
much discussion has arisen around the interpretation of similar
moieties in other transition metal hydride complexes.25 The
structure may be considered to contain an Os(III) trihydride
center that is covalently bound to the Sn atom. Indeed, the Os-
Sn distance of 2.6538(7) Å is slightly less than the sum of the
covalent radii (2.66 Å), implying a covalent bond between these
two atoms. Alternatively, complex 8 may be described
Figure 4. Hydride region of the 1H NMR spectrum for the reaction
between [IrH3(PPh3)3] (6), KH, and [18-crown-6] in d8-THF. (a)
Early stage and (b) later stage, showing the presence of the product
[K(18-crown-6)][IrH4(PPh3)2] (7).
as consisting of the two ionic fragments, [SnBun ]+ and
3
spectrum of the reaction mixture as a function of time, as
depicted in Figure 5. The hydride region showed several species
to be present. The starting materials mer- and fac-[IrH3(PPh3)3]
were evident, as was the product [K(18-crown-6)][IrH4(PPh3)2]
(7), which showed hydride signals in a 3:1 ratio. In addition, a
quartet centered at -11.6 ppm (JHP ) 20 Hz) may be assigned
as either [IrH2(PPh3)3]- or [IrH4(PPh3)3]-. We prefer the former
suggestion on account of the stability of 18-electron five-
coordinate complexes of Ir(I).23
[OsH3(PPh3)3]-. This arrangement then corresponds to Os(II)
instead of the more unusual Os(III). A further possibility is to
view 8 as a σ-bond complex, in accord with other similar group
8 hydride complexes with group 14 ligands. For example, the
tin-iron complex [FeH3(PBunPh2)3(SnPh3)] was reported by
Schubert et al., who interpreted its NMR spectra in terms of
an η2-HSn moiety that interacts with the metal center of
the [FeH2(PBunPh2)3] fragment.26 The second-row congener
[RuH3(SiCl2Me)(PPh3)3] contains a SiR3 moiety instead of SnR3,
but otherwise is structurally rather similar to complex 8.27 This
seven-coordinate Ru complex contains three Ru-H ligands,
which engage in secondary interactions with the Si atom only
1.9 Å away, and may be described as [RuH2(η2-HSiCl2Me)-
(PPh3)3], where the Si-H bond is almost fullysalbeit not
completelyscleaved. In 8, the average H‚‚‚Sn distances of 2.3
Å are only 0.1 Å larger than their H‚‚‚Si counterparts in the Ru
analogue. However, we can expect oxidative addition to be more
advanced in the Os complex, owing to the more electron-rich
metal center and the weaker E-H and stronger M-H bonds
involved.
Accordingly, we propose the following process to explain
the formation of 7 through eq 3. The first step involves
abstraction of a proton from mer- or fac-[IrH3(PPh3)3] by KH,
with the formation of H2. The resulting tris-phosphine inter-
mediate [K(18-crown-6)][IrH2(PPh3)3] is then responsible for
1
the feature at -11.6 ppm in the H NMR spectrum, which
displays a characteristic quartet (JHP ) 20 Hz). However, the
steric requirements of the crown ether and the three geminal
PPh3 ligands in this intermediate are considerable, and [K(18-
crown-6)][IrH2(PPh3)3] rapidly loses a phosphine ligand. The
newly formed H2 can now bind to Ir at the vacated coordination
site to form [K(18-crown-6)][IrH4(PPh3)2] (7), possibly via a
transient dihydrogen complex.
Despite the imprecise location of the H atoms, the geometry
of the OsSnR3 moiety of complex 8 affords a diagnosis of the
nature of the Os-Sn bond. The angles C-Sn-C [103.2(5)°,
105.0(5)°, and 102.0(5)°] and C-Sn-Os [116.6(4)°, 113.6(3)°,
and 114.9(3)°] define a tetrahedral geometry at Sn, and the
closest nonbonded C‚‚‚C distances (3.9 Å) between the phenyl
groups on the phosphine ligands and the butyl groups at Sn
provide no evidence for steric crowding influencing this
geometry. Flattening of the SnC3 moiety would imply a positive
change on Sn and a significant electrostatic component in the
Covalent Derivatives of [OsH4(PPh3)3]. In view of the subtle
yet apparently significant influence of the [K(18-crown-6)]+
countercation on the reactivity of polyhydride anions, we
decided to explore the effects of replacing this A-metal cation
with the much more coordinating and covalent R3Sn+ moiety.
Monoanionic transition metal complexes react with halides of
group 14 forming a wide range of products. Tin-osmium
derivatives are of particular interest on account of their catalytic
role in important processes such as hydroformylation, olefin
hydrogenation, and organic coupling reactions.24 A THF solution
bonding between Sn and Os: in the limit [SnBun ]+ may be
3
expected to be trigonal planar, as has been demonstrated recently
of trihydride 3 reacted with Bun SnCl with elimination of HCl
3
for the free silylium cation [Mes3Si]+.28 However, the observed
to produce the novel complex [OsH3(SnBun )(PPh3)3] (8) as a
3
(25) (a) Esteruelas, M. A.; Lledos, A.; Maresca, O.; Olivan, M.; Onate,
E.; Tajada, M. A. Organometallics 2004, 23, 1453. (b) Knorr, M.; Gilbert,
S.; Shubert, U. J. Organomet. Chem. 1988, 347, C17. (c) Gilbert, S.; Knorr,
M.; Mock, S.; Shubert, U J. Organomet. Chem. 1994, 480, 241. (d) Bull,
M.; Espinet, P.; Esteruelas, M. A.; Lahoz, F. J.; Lledo´s, A.; Martinez-
Ilarduya, J. M.; Maseras, F.; Modrego, J.; On˜ate, E.; Oro, L. A.; Sola, E.;
Valero, C. Inorg. Chem. 1996, 35, 1250. (d) Rickard, C. E. F.; Roper, W.
R.; Woodgate, S. D.; Wright, L. J. J. Organomet. Chem. 2000, 609, 177.
(26) (a) Schubert, U.; Gilbert, S.; Mock, S. Chem. Ber. 1992, 125, 835.
(b) Gilbert, S.; Knorr, M.; Mock, S.; Schubert, U. J. Organomet. Chem.
1994, 480, 241.
(19) Berry, A.; Green, M. L. H.; Bandy, J. A.; Prout, K. J. Chem. Soc.,
Dalton Trans. 1991, 2185.
(20) Landau, S. E.; Groh, K. E.; Lough, A. J.; Morris, R. H. Inorg. Chem.
2002, 41, 2995.
(21) Bau, R.; Schwerdtfeger, C. J.; Garlaschelli, L.; Koetzle, T. F. J.
Chem. Soc., Dalton Trans. 1993, 3359.
(22) (a) Vaska, L. J. Am. Chem. Soc. 1961, 83, 765. (b) Park, S.; Lough,
A. J.; Morris, R. H. Inorg. Chem. 1996, 35, 3001.
(23) Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M.
AdVanced Inorganic Chemistry, 6th ed.; Wiley-Interscience: New York,
1999.
(27) Yardy, N. M.; Lemke, F. R.; Brammer, L. Organometallics 2001,
20, 5670.
(24) Holt, M. S.; Wilson, W. L.; Nelson, J. H. Chem. ReV. 1989, 89, 11.

126 Organometallics, Vol. 25, No. 1, 2006
Guilera et al.
Figure 5. (a) X-ray crystal structure of [OsH3(SnBun )(PPh3)3] (8). All non-hydride H atoms are omitted for clarity. Selected bond distances
3
(Å): Os-P 2.375(2), Os-Sn 2.6538(7), Os-H(av) 1.67(7), H‚‚‚Sn(av) 2.3. Selected angles (deg): P-Os-P(av) 104.87(8), H(1)-Os-
H(2) 90.3, H(1)-Os-H(3) 115.5, H(2)-Os-H(3) 90.3, Sn-Os-H(1) 63.5, Sn-Os-H(2) 57.9, Sn-Os-H(1) 60(3), C(55)-Sn-C(59)
103.2(5), C(55)-Sn-C(63) 102.0(5), C(59)-Sn-C(63) 105.0(5), C(55)-Sn-Os 116.6(4), C(59)-Sn-Os 114.9(3), C(55)-Sn-Os 113.6(3).
The n-butyl groups are disordered, although only one conformation is depicted for clarity. (b) Representation of the skeleton of complex
8, which contains the disordered n-butyl groups.
standard Schlenk and glovebox techniques. All solvents were
distilled under an Ar atmosphere, employing as drying agents CaH2
(pentane, hexane), Na/benzophenone (Et2O, THF, toluene), or Mg
turnings/I2 (MeOH, EtOH). After distillation, solvents were de-
angles show the Sn-Os bond to be covalent in character, albeit
with a certain degree of polarity, and complex 8 is best described
as seven-coordinate [OsH3(SnBun )(PPh3)3].
3
gassed to completion by vigorous passage of Ar and stored over
activated molecular sieves. Deuterated solvents were degassed, then
stored over sodium (d6-benzene, d8-toluene, d8-THF). KH was
Summary
The hydrido tris-phosphine complex [OsH4(PPh3)3] (1) reacts
with KH in THF in the presence of 18-crown-6 to form
[K(THF)(18-crown-6)][OsH3(PPh3)3] (2). The structure of 2,
determined by X-ray crystallography, shows three hydrides to
point toward the potassium cation, in an arrangement similar
to that reported by Morris et al. for the hydrido bis-phosphine
complex [K(18-crown-6)][IrH4(PPh3)2] (7).29 In contrast, at-
tempts to prepare an Ir analogue of 2 from [IrH4(PPh3)3] (6)
resulted instead in ligand redistribution and the unexpected
formation of 7. A study of this reaction by NMR spectroscopy
identified [IrH2(PPh3)3]- as a likely intermediate in this process.
purchased as an oil suspension: before use, it was washed several
times with pentane, thoroughly dried in vacuo, and stored in a
glovebox. Crown ethers were thoroughly dried before used by
dissolving them in THF over dried molecular sieves and were stored
in a glovebox. Elemental analyses were performed at Birkbeck
College and the University of North London (London, UK) or by
Galbraith Laboratories, (Knoxville, TN). All quoted yields are for
products obtained as crystalline material.
FT-IR spectra were recorded using a Perkin-Elmer Spectrum One
spectrometer with a beam-condensing accessory and employing a
diamond compression cell. Spectra were recorded for a neat sample
of solid material contained between the diamond optics. Routine
1H and 31P NMR spectra were recorded using a Bruker AV360
spectrometer operating at 360 and 145 MHz, respectively, a Bruker
AV400 spectrometer (400 and 162 MHz), or a Bruker DRX500
spectrometer (500 and 202.5 MHz). Complex 8 was characterized
using a Varian Oxford300 spectrometer operating at 300 (1H), 121
(31P), and 112 (119Sn) MHz. Maestre and XWin-Plot programs were
used for graphical representations.
For spin-lattice relaxation time (T1) measurements, 5 mm NMR
tubes were loaded in a glovebox and transferred to a Schlenk line,
where the appropriate volume of the corresponding deuterated
solvent was added. Acid reagents were added by syringe at 195 K,
and the NMR tube was rapidly inserted into the probe of the
spectrometer, which had been precooled to ca. 180 K. Samples were
allowed at least 10 min to equilibrate at each temperature. The
conventional inversion-recovery method (180-τ-90) was used
to determine the T1 relaxation time as a function of temperature.
Relaxation times were calculated by using a nonlinear three-
parameter fitting routine. The pulses were calibrated at each
temperature. In each experiment, the waiting period was much
longer than the expected relaxation time, and 16 variable delays
were employed.
The tin-osmium complex [OsH3(SnBun )(PPh3)3] (8) was
3
prepared by reaction of KOsH3(PPh3)3 with Bun SnCl. Complex
3
8 possesses a covalent Sn-Os bond in a seven-coordinate
environment at osmium, which is best described as a distorted
fac-[OsH3(PPh3)] arrangement with the SnBun3 moiety capping
the OsH3 face, rather than as a σ-bond complex containing an
Os(η2-HSn) moiety.
The results we report here show that the stability and
reactivity of anionic phosphine polyhydride complexes depends
strongly on the nature and steric bulk of the countercation, as
well as on that of the phosphine ligands. Under appropriate
circumstances, both phosphine and hydride ligands can be labile,
and complex rearrangements can occur. Loss of a phosphine
ligand is a common first step in many transition-metal-mediated
catalytic processes,23 but reversible binding and release of H2
is a less common phenomenon. These results have wider
implications in areas such as hydrogenation catalysis and the
mechanistic study of H2 activation.30
Experimental Section
General Procedures. Unless otherwise stated, all operations
were carried out under strictly inert atmosphere conditions using
[Na2OsCl6‚xH2O] and (NH4)2IrCl6 were purchased from Strem.
All other starting materials were purchased from Sigma-Aldrich.
The complexes [OsH4(PPh3)3],23 [IrHCl2(PPh3)3],22a and [IrH3-
(PPh3)3]22b were each prepared by literature methods.
(28) Kim, K.-C.; Reed, C. A.; Elliott, D. W.; Mueller, L. J.; Tham, F.;
Lin, L.; Lambert, J. B. Science 2002, 297, 825.
(29) Landau, S. E.; Groh, K. E.; Lough, A. J.; Morris, R. H. Inorg. Chem.
2002, 41, 2995.

Phosphine Hydride Anions
Organometallics, Vol. 25, No. 1, 2006 127
Synthesis and Characterization. [K(THF)(18-crown-6)][OsH3-
(PPh3)3] (2). A mixture of [OsH4(PPh3)3] (1.12 g, 1.15 mmol), THF
(12 mL), KH (0.23 g, 5.75 mmol), and 18-crown-6 (0.46 g, 1.73
mmol) was stirred for 5 days under an Ar atmosphere. During this
time, the brown slurry became yellow. All solids were removed
by filtration, and the yellow product was crystallized from the filtrate
by slow diffusion of hexane at 233 K. Yield: 62% (0.96 g, 0.71
mmol). Anal. Calc for C70H80OsP3O7K: C, 62.02; H, 5.95. Found:
cooled to 195 K and HFIP (1.37 µL, 13.3 µmol) was added via a
syringe. 1H NMR spectra were recorded at 180, 190 (T1 (269 ms),
230, 260, and 293 K. This reaction was also studied in d8-THF
because [OsH4(PPh3)3] decomposes slowly in CD2Cl2. In the
hydride region of the 1H NMR spectrum peaks were visible at -8.10
(1) and -5.74 ppm, assigned to the OsH5 moiety of [OsH5(PPh3)3]+
(4). After 3 days 1H, 1H{31P}, and 31P{1H} NMR spectra (d8-THF)
were measured at 293 K, showing a quintet at -9.90, a singlet at
-9.90, and a singlet at 37.83 ppm, respectively.
1
C, 62.12; H, 6.28. IR (solid, cm-1): νOsH 1920 (s). H NMR (d8-
THF): δ 7.70-6.70 (m, 45H, phenyl H), 3.45 (s, 24H, crown),
Reaction between [K(THF)(18-crown-6)][OsH3(PPh3)3] and
[(CF3)2CHOH]. A 5 mm NMR tube was charged with [K(THF)-
(18-crown-6)][OsH3(PPh3)3] (13 mg, 10.1 µmol) and 0.7 mL of
d8-THF. HFIP (1.26 µL, 12.2 µmol) was added via a syringe to
-11.27 (m, 3H, OsH). 31P{1H} NMR (d8-THF): δ 24.55 (s).
K[OsH3(PPh3)3] (3). A mixture of [OsH4(PPh3)3] (0.24 g, 0.24
mmol) and KH (0.08 g, 1.96 mmol) in THF (7 mL) was stirred for
12 h under an Ar atmosphere, during which time the brown slurry
became yellow. All solids were removed by filtration, and the
yellow solution was removed in vacuo to leave a very unstable
yellow solid, which was washed with hexane. Yield: 80% (0.2 g,
0.20 mmol). Anal. Calc for C54H48OsP3K: C, 63.64; H, 4.75.
Found: C, 63.83; H, 4.94. IR (solid, cm-1): νOsH 1913 (s). The
1
the precooled tube, and the H and 31P{1H} NMR spectra were
recorded at 200 K. These revealed the transformation of 2 (1H
-11.27; 31P 24.55) into 1 (1H -8.07; 31P 23.80). Subsequent
aliquots of HFIP (1.58, 5.25, 14.07, 35.7, and 52.5 µL) were added,
and the spectra re-recorded at 200 K, but no further change was
observed in the hydride region. After 3 days 1H and 31P{1H} NMR
spectra (d8-THF) were recorded at 298 K, showing a quintet at
-9.90 ppm and a singlet at 37.83 ppm, respectively.
1
product was identified by H and 31P NMR spectroscopy, which
revealed a mixture of complexes 3 and 1, because 3 is unstable in
1
X-ray Structural Determinations. Air-sensitive crystals were
transferred in a glovebox into a vessel containing perfluoropolyalkyl
ether. Crystals were mounted on a thin glass fiber and cooled on
the diffractometer to 100-120 K using an Oxford Cryostream
Liquid N2 device. Approximate unit cell dimensions were deter-
mined by the Nonius Collect program31 from five index frames of
width 2° in φ using a Nonius KappaCCD diffractometer (graphite
monochromatic Mo KR radiation, λ ) 0.71073 Å), with a detector-
to-crystal distance of 30 mm. The Collect program was then used
to calculate a data collection strategy to 99.5% completeness for θ
) 27.5° using a combination of 0.5-2° φ and ω scans of 10-60
s deg-1 exposure time (depending on crystal quality). Crystals were
indexed using the DENZO-SMN package,32 and positional data
were refined along with diffractometer constants to give the final
unit cell parameters. Integration and scaling (DENZO-SMN,
Scalepack32) resulted in unique data sets corrected for Lorentz and
polarization effects and for the effects of crystal decay and
absorption, by a combination of averaging of equivalent reflections
and an overall volume and scaling correction. Structures were solved
using SHELXS-9733 and developed via alternating least-squares
cycles and difference Fourier synthesis (SHELXL-97) with the aid
of the program XSeed.34 In general, unless stated, all non-hydrogen
atoms were modeled anisotropically, while hydrogen atoms were
assigned an isotropic thermal parameter 1.2 times that of the parent
atom (1.5 for terminal atoms) and allowed to ride. POV-Ray was
used for the molecular graphics.
solution. H NMR (d8-THF): δ 7.80-6.70 (m, 45H, phenyl H),
-11.45 (m, 3H, OsH). 31P{1H} NMR (d8-THF): δ 25.71 (s, 2P),
24.53 (s, 1P).
[K(18-crown-6)][IrH4(PPh3)2] (7). A mixture of [IrH3(PPh3)3]
(0.48 g, 0.49 mmol), THF (10 mL), KH (0.1 g, 2.45 mmol), and
18-crown-6 (0.19 g, 0.73 mmol) was gently warmed and stirred
for 4 days under an Ar atmosphere. The pale yellow slurry became
green and finally deep red. The solution was filtered, and hexane
was layered above. This solution was kept at 233 K for 7 days,
during which time it turned green and small colorless crystals
appeared. Yield: 45% (0.13 g, 0.22 mmol). Anal. Calc for C48H58-
IrO6P2K: C, 56.29; H, 5.71. Found: C, 56.46; H, 5.92. IR (solid,
cm-1): 1992 (m), νIrH; 1717 (m), νIrH. 1H NMR (d8-THF): δ 7.60-
6.90 (m, 30H, phenyl H), 3.82 (s, 24H, crown H), -12.56 (t of t,
2JHH ) 5.1 Hz, 2JHP ) 13.3 Hz, 3H, HA of AA′A′′BXX′), -12.89
(d of t, 1H, HB). 31P{1H} NMR (d8-THF): δ 26.94 (s, 1P, PX),
12.84 (s, 1P, PX′).
[OsH3(Bun Sn)(PPh3)3] (8). A mixture of [OsH4(PPh3)3] (0.25
3
g, 0.26 mmol) and KH (0.05 g, 1.27 mmol) in THF (10 mL) was
stirred at 303 K for 1 day. The resulting yellow solution was filtered
into a Schlenk vessel, and Bu3SnCl (0.07 mL, 0.26 mmol) was
added via a syringe. The solution was stirred for 12 h, whereupon
it changed from yellow to brown. The brown oily product obtained
after removal of solvent in vacuo was extracted with 15 mL of
light petroleum, resulting in a clear yellow solution. This solution
was kept at 233 K, and white crystals were obtained after 3 days.
Yield: 56% (0.18 g, 0.14 mmol). Anal. Calc for C66H75OsP3Sn:
1
Acknowledgment. We are grateful to NSERC (Canada) and
EPSRC (UK) for financial support and to Prof. Susan Gibson
for provision of a studentship (to G.G.).
C, 62.41; H, 5.95. Found: C, 62.68; H, 6.10. H NMR (d8-THF):
δ 7.68-6.89 (m, 45 H, phenyl H), 2.46-0.79 (m, 27H, butyl H),
-11.48 (q, 3H, JHP ) 27). 31P{1H} NMR (d8-THF): δ 13.3 (s).
119Sn{1H} (d8-THF): δ -41.4 (s).
Supporting Information Available: X-ray crystallographic files
in CIF format for complexes 2 and 8. This material is available
free of charge via the Internet at http://pubs.acs.org.
Reactions Monitored by NMR Spectroscopy. Reaction be-
tween [OsH4(PPh3)3], KH, and 18-crown-6. [OsH4(PPh3)3] (0.04
g, 41 µmol), KH (8.2 mg, 0.21 mmol), and 18-crown-6 (16.1 mg,
61.2 µmol) were placed in a 5 mm NMR tube with 1 mL of THF-
d8. The solution was warmed slightly with a water bath and
transferred rapidly to the spectrometer probe precooled to 200 K.
1H NMR spectra were recorded at 200, 230, 270, and 293 K and
again after 24 h at 293 K, which revealed the direct conversion of
1 into 2 (simultaneous disappearance of the peak at -8.10 and
growth of the peak at -11.27 ppm).
OM050391W
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Etienne, S.; Chaudret, B.; Limbach, H.-H. J. Am. Chem. Soc. 2004, 126,
8366. (b) Sandoval, C. A.; Ohkuma, T.; Muniz, K.; Noyori, R. J. Am. Chem.
Soc. 2003, 125, 13490. (c) Voges, M. H.; Bullock, R. M. J. Chem. Soc.,
Dalton Trans. 2002, 759. (d) Liang, F.; Schmalle, H. W.; Berke, H. Inorg.
Chem. 2004, 43, 993.
(31) Hooft, R. Collect; Nonius BV: Delft, The Netherlands, 1988.
(32) Otwinowski, Z.; Minor, W. Scalepack; Carter, C. W., Sweet, R.
M., Eds.; Academic Press: New York, 1997; p 307.
(33) Sheldrick, G. M. SHELXS-97; University of Go¨ttingen: Germany,
1997.
Reaction between [OsH4(PPh3)3] and (CF3)2CHOH. A 5 mm
NMR tube was charged with [OsH4(PPh3)3] (13 mg, 13.3 µmol)
and 0.7 mL of CD2Cl2. H NMR spectra were recorded at 190 K,
1
as was the relaxation time T1 (1738 ms). Further spectra were
recorded at 230, 260, and 293 K. Subsequently, the NMR tube was
(34) Barbour, L. J. J. Supramol. Chem. 2001, 1, 189.