Protonation of metal hydrides by strong acids. Formation of an equilibrium mixture of dihydride and dihydrogen complexes from protonation of Cp*Os(CO)2H. Structural characterization of [CpW(CO)2(PMe3(H)2</s

Article abstract of DOI:10.1021/om950976y

Cp^*Os(CO)₂H is protonated by triflic acid (HOTf) in CD₂ Cl₂ solution to give an equilibrium mixture (87:13) of the dihydride [ Cp^*Os(CO)₂(H)₂]⁺OTf^- and the

Full text of DOI:10.1021/om950976y

2504
Organometallics 1996, 15, 2504-2516
P r oton a tion of Meta l Hyd r id es by Str on g Acid s.
F or m a tion of a n Equ ilibr iu m Mixtu r e of Dih yd r id e a n d
Dih yd r ogen Com p lexes fr om P r oton a tion of
Cp *Os(CO)2H. Str u ctu r a l Ch a r a cter iza tion of
[Cp W(CO)2(P Me3)(H)2]+OTf-
R. Morris Bullock,* J eong-Sup Song,† and David J . Szalda‡
Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000
Received December 19, 1995X
Cp*Os(CO)2H is protonated by triflic acid (HOTf) in CD2Cl2 solution to give an equilibrium
mixture (87:13) of the dihydride [Cp*Os(CO)2(H)2]+OTf- and the dihydrogen complex [Cp*Os-
(CO)2(η2-H2)]+OTf-. The acidity of these protonated species is roughly comparable to HOTf,
since only partial protonation was observed, e.g., 36% protonation with 1.2 equiv of HOTf.
In the absence of acid, the T1 of the hydride ligand of Cp*Os(CO)2H is 5.9 s at -80 °C.
When all of the Cp*Os(CO)2H is protonated by excess HOTf, the T1 (-80 °C) of the terminal
hydride ligands of [Cp*Os(CO)2(H)2]+OTf- is 2.8 s, while the T1 of the dihydrogen ligand of
[Cp*Os(CO)2(η2-H2)]+OTf- is 19 ms (-80 °C). The observed T1 values of the Os-H resonance
of Cp*Os(CO)2H decreased significantly under conditions of partial protonation, indicating
intermolecular proton transfer among [Cp*Os(CO)2(η2-H2)]+OTf-, [Cp*Os(CO)2(H)2]+OTf-,
Cp*Os(CO)2H, and HOTf. IR spectra indicate that the two CO ligands of [Cp*Os(CO)2(H)2]+
(and hence the hydrides as well) are trans to each other in the four-legged piano stool
geometry. Two resonances for HOTf are observed in the NMR spectra and are assigned as
[HOTf]n (hydrogen bonded to itself) and TfOH‚‚‚OTf- in which HOTf is hydrogen bonded to
an OTf- counterion. [CpW(CO)3(H)2]+OTf- and [Cp*W(CO)3(H)2]+OTf- were formed by
protonation of CpW(CO)3H and Cp*W(CO)3H. Protonation of the phosphine-substituted
tungsten hydrides CpW(CO)2(PR3)H (R ) Me, Cy, Ph) by HOTf or [H(Et2O)2]+ BAr′4- (Ar′ )
3,5-bis(trifluoromethyl)phenyl) gives dihydrides [CpW(CO)2(PR3)(H)2]+ which were isolated
and fully characterized. The structure of [CpW(CO)2(PMe3)(H)2]+OTf- was determined by
single-crystal X-ray diffraction and reveals weak hydrogen bonds between one hydride on
W and two of the fluorines on the triflate anion.
In tr od u ction
Protonation of neutral metal hydrides is frequently
used to prepare cationic metal dihydrides1 and/or dihy-
drogen complexes.2 Our studies on protonation of metal
hydrides arose out of our work on the ionic hydrogena-
tion of alkenes,3 alkynes,4 and ketones,5 in which a
strong acid and a transition metal hydride are used to
hydrogenate unsaturated organic substrates. Ionic
hydrogenation of Me2CdCMe2 by HOTf and CpW-
(CO)3H (eq 1) involves formation of a carbenium ion by
protonation of the alkene; subsequent hydride transfer
from CpW(CO)3H produces the organic hydrogenation
product along with Cp(CO)3WOTf as the organometallic
product. In some cases, protonation of the metal hy-
dride competed with protonation of the alkene. At-
tempted use of CpW(CO)2(PMe3)H as a hydride donor
in ionic hydrogenation failed because [CpW(CO)2-
(PMe3)(H)2]+OTf-, the cationic dihydride generated from
protonation by HOTf, was not sufficiently acidic to
transfer a proton to the olefin. Other metal hydrides
failed to be useful as hydride donors for a different
reasonsCpMo(CO)2(PPh3)H, Cp*Fe(CO)2H, and Cp*Mo-
(CO)3H (Cp* ) η5-C5Me5) rapidly formed H2 and M-OTf
from their reaction with HOTf (eq 2). Cationic dihy-
drides (or dihydrogen complexes) are presumed inter-
mediates that decompose by loss of H2, but they were
not observed for these hydrides. On the other hand,
several metal hydrides were efficient hydride donors in
the presence of HOTf; this is possible in cases where
the cationic dihydride (or dihydrogen complex) has
† Present address: Department of Chemistry, Sun Moon University,
Asan City, Chungnam, South Korea 336-840.
‡ Research Collaborator at Brookhaven National Laboratory. Per-
manent address: Department of Natural Sciences, Baruch College,
New York, NY 10010.
X Abstract published in Advance ACS Abstracts, May 1, 1996.
(1) For a review of polyhydride complexes, see: Hlatky, G. G.;
Crabtree, R. H. Coord. Chem. Rev. 1985, 65, 1-48.
(2) For reviews of dihydrogen complexes, see: (a) Heinekey, D. M.;
Oldham, W. J ., J r. Chem. Rev. 1993, 93, 913-926. (b) J essop, P. G.;
Morris, R. H. Coord. Chem. Rev. 1992, 121, 155-284. (c) Crabtree, R.
H. Acc. Chem. Res. 1990, 23, 95-101. (d) Kubas, G. J . Acc. Chem. Res.
1988, 21, 120-128. (e) Kubas, G. J . Comments Inorg. Chem. 1988, 7,
17-40.
(3) (a) Bullock, R. M.; Rappoli, B. J . J . Chem. Soc., Chem. Commun.
1989, 1447-1448. (b) Bullock, R. M.; Song, J .-S. J . Am. Chem. Soc.
1994, 116, 8602-8612.
(4) Luan, L.; Song, J .-S.; Bullock, R. M. J . Org. Chem. 1995, 60,
7170-7176.
(5) Song, J .-S.; Szalda, D. J .; Bullock, R. M.; Lawrie, C. J . C.; Rodkin,
M. A.; Norton, J . R. Angew. Chem., Int. Ed. Engl. 1992, 31, 1233-
1235.
S0276-7333(95)00976-9 CCC: $12.00 © 1996 American Chemical Society

Protonation of Metal Hydrides by Strong Acids
Organometallics, Vol. 15, No. 10, 1996 2505
sufficient kinetic acidity to transfer a proton to the
organic substrate and also has adequate thermal stabil-
ity on the time scale of the hydrogenation reaction.
Three such hydrides, Cp*Os(CO)2H, CpW(CO)3H, and
Cp*W(CO)3H, form observable protonation products. In
this paper we report that protonation of Cp*Os(CO)2H
by HOTf gives an equilibrium mixture of the dihydride
[Cp*Os(CO)2(H)2]+OTf- and the dihydrogen complex
[Cp*Os(CO)2(η2-H2)]+OTf-. Protonation of CpW(CO)3H
and Cp*W(CO)3H gives dihydrides that have also been
characterized. Each of these three hydrides were only
partially protonated by 1 equiv of HOTf, indicating that
their protonated forms are extremely acidic. Phosphine-
substituted tungsten compounds CpW(CO)2(PR3)H (R
) Me, Ph, Cy; Cy ) cyclohexyl) are protonated to give
dihydrides that are much less acidic; the characteriza-
tion of these compounds is also reported, along with the
crystal structure of [CpW(CO)2(PMe3)(H)2]+OTf-.
F igu r e 1. IR spectrum from protonation of Cp*Os(CO)2H
by excess HOTf. The dots show the observed spectrum, and
the solid lines show the fitting of the four separate bands
and their sum.
of these bands using the relationship6 tan2 θ ) Ia/Is,
where 2θ is the OC-M-CO angle and Ia and Is are the
relative intensities of the asymmetric and symmetric
bands. The experimental value of Ia/Is ) 2.19 leads to
a predicted OC-Os-CO angle of 112°, indicating that
the carbonyls (and hence the hydrides) are trans to each
other, as drawn in eq 3.
While we find no spectroscopic evidence for the cis
isomer of our cationic Os dihydride, the isoelectronic
neutral Re dihydride was shown to exist as a mixture
of both isomers. Casey and co-workers7 characterized
the cis and trans isomers of Cp*Re(CO)2(H)2; the trans
isomer is thermodynamically favored over the cis isomer
(97:3 ratio). From the IR intensities, the OC-Re-CO
angles were estimated as 106° for the trans isomer and
92° for the cis isomer. The extensive series of Ru
dihydrogen complexes of general formula [CpRuL2(η2-
H2)]+ (L2 ) chelating diphosphine) studied by Heinekey8
and by Morris9 also convert to trans-dihydride isomers.
A trans geometry of hydrides was verified in the crystal
Resu lts a n d Discu ssion
F or m a tion of [Cp *Os(CO)2(H)2]+ a n d [Cp *Os-
(CO)2(η2-H2)]+ by P r oton a tion of Cp *Os(CO)2H.
Addition of excess HOTf to a solution of Cp*Os(CO)2H
(δ -14.21) in CD2Cl2 produced an 87:13 mixture of the
dihydride complex [Cp*Os(CO)2(H)2]+OTf- (δ -10.00)
and the dihydrogen complex [Cp*Os(CO)2(η2-H2)]+OTf-
1
(δ -7.24), as observed by H NMR spectra at -80 °C
(eq 3). The protonation of Cp*Os(CO)2H was also
structures of [CpOs(PPh3)2(H)2]+OTf- 10 and [Cp*Fe-
- 11
(iPr2PCH2CH2PiPr2)(H)2]+BPh4
.
Ab initio calcula-
tions12 predict a greater stability for the trans forms of
both [CpOs(CO)2(H)2]+ and [CpRu(PH3)2(H)2]+.
The other two bands (2091 and 2040 cm-1) in the IR
spectrum (Figure 1) are assigned as the carbonyl
stretching vibrations of the dihydrogen complex [Cp*Os-
(CO)2(η2-H2)]+OTf-. The maximum absorbance of these
two bands are nearly identical, but the lower energy
band has a significantly larger bandwidth. The relative
areas of these two bands are in a ratio of 1.0:2.0, leading
to a calculated OC-Os-CO angle of 109° based on these
IR intensities.
(6) (a) King, R. B.; Riemann, R. H. Inorg. Chem. 1976, 15, 179-
183. (b) Brown, T. L.; Darensbourg, D. J . Inorg. Chem. 1967, 6, 971-
977. (c) Beck, W.; Melnikoff, A.; Stahl, R. Angew. Chem., Int. Ed. Engl.
1967, 4, 692-693.
studied by IR spectroscopy. Addition of HOTf (7 equiv)
to a solution of Cp*Os(CO)2H (0.02 M) in CH2Cl2
resulted in four bands in the metal carbonyl region.
Figure 1 shows the observed IR spectrum along with a
fitting that enabled a determination of the areas of the
individual bands which are partially overlapped in the
spectrum. The two most intense bands, at 2118 and
2068 cm-1, are assigned as the symmetric and asym-
metric carbonyl stretching vibrations of the dihydride
complex [Cp*Os(CO)2(H)2]+OTf-. An estimate of the
OC-M-CO angle can be made from the relative areas
(7) Casey, C. P.; Tanke, R. S.; Hazin, P. N.; Kemnitz, C. R.;
McMahon, R. J . Inorg. Chem. 1992, 31, 5474-5479; Inorg. Chem. 1994,
33, 5978.
(8) Chinn, M. S.; Heinekey, D. M. J . Am. Chem. Soc. 1990, 112,
5166-5175.
(9) J ia, G.; Lough, A. J .; Morris, R. H. Organometallics 1992, 11,
161-171.
(10) (a) Angelici, R. J . Acc. Chem. Res. 1995, 28, 51-60. (b) Rottink,
M. K.; Angelici, R. J . J . Am. Chem. Soc. 1993, 115, 7267-7274.
(11) J ime´nez-Tenorio, M.; Carmen Puerta, M.; Valerga, P. Organo-
metallics 1994, 13, 3330-3337.
(12) Lin, Z.; Hall, M. B. Organometallics 1992, 11, 3801-3804.

2506 Organometallics, Vol. 15, No. 10, 1996
Bullock et al.
The ν(CO) bands of the dihydrogen complex [Cp*Os-
(CO)2(η2-H2)]+OTf- both appear about 27 cm-1 lower in
energy than the bands of the dihydride [Cp*Os(CO)2-
(H)2]+OTf-. This is consistent with the higher formal
oxidation state of the dihydride [Os(IV)] compared to
the dihydrogen complex [Os(II)] and was observed
previously in other dihydride/dihydrogen equilibria.
Kubas and co-workers found13 that the high-energy ν-
(CO) band of (H)2W(CO)3(PCy3)2 appeared at 25 cm-1
higher energy than the high energy ν(CO) band of the
corresponding dihydrogen complex (η2-H2)W(CO)3(PCy3)2;
the lower energy bands of this dihydride/dihydrogen
pair were separated by a larger amount (∼60 cm-1). IR
spectra in liquid Xe show substantially higher energies
(50-90 cm-1) for the ν(CO) bands of CpNb(CO)3(H)2
compared to the dihydrogen analog CpNb(CO)3(η2-H2).14
High Acid ity of Ca tion ic Dih yd r id es a n d Dih y-
d r ogen Com p lexes. Since the hydride Cp*Os(CO)2H
is the conjugate base of both the dihydride and the
dihydrogen complex, thermodynamics requires that the
less abundant (more energetic) of the pair be the
stronger acid. Thus the thermodynamic acidity of the
dihydrogen complex [Cp*Os(CO)2(η2-H2)]+OTf- is greater
than that of the dihydride [Cp*Os(CO)2(H)2]+OTf-.
Only 36% of the initial Cp*Os(CO)2H was protonated
after addition of 1.2 equiv of HOTf, indicating that the
dihydride and dihydrogen species are extremely strong
acids, being roughly comparable to HOTf.
spanning a wide range of thermodynamic acidities.
Complexes with strongly electron donating phosphines
have relatively low acidity; a pKa of 16.3 ( 0.3 (aqueous
pKa scale) was found9 for [Cp*Ru(PMe3)2(H)2]+. Of most
relevance to our present study is their prediction16 of a
pKa of -6 (aqueous pKa scale) for the dicarbonyl complex
[CpRu(CO)2(η2-H2)]+. Thus, from our work and previous
reports, the collective evidence indicates that extremely
high acidities can result from dihydrides or dihydrogen
complexes, particularly in carbonyl compounds without
phosphines.
Com p a r ison of HBF 4‚OEt2 vs HOTf a s Acid s in
th e P r oton a tion of Cp *Os(CO)2H. Rela tive Kin etic
Acid ity of Dih yd r id e a n d Dih yd r ogen Com p lexes.
Protonation of Cp*Os(CO)2H by HBF4‚OEt2 was exam-
ined under conditions similar to those used with HOTf.
The extent of protonation of Cp*Os(CO)2H was compa-
rable for the two acids, but significant differences were
1
observed in the H NMR line widths. Using HOTf as
the acid, the line width (ω1/2 ) 7 Hz) observed at -80
°C for the dihydride resonance of [Cp*Os(CO)2(H)2]+OTf-
was the same as that found for the hydride resonance
of Cp*Os(CO)2H; the resonance for the H2 ligand of
[Cp*Os(CO)2(η2-H2)]+OTf- was much broader (ω1/2 ≈ 70
Hz). Similar observations were made in the partial
protonation of Cp*Os(CO)2H by HBF4‚OEt2 but only at
the lowest temperature attempted (-98 °C). At -89 °C,
the NMR spectrum exhibited a significantly larger line
width (ω1/2 ≈ 32 Hz) for the hydride resonance of Cp*Os-
(CO)2H compared to the dihydride resonance of [Cp*Os-
Heinekey and co-workers previously reported15 the
synthesis of highly acidic cationic dihydrogen complexes
by protonation of metal hydrides. Protonation of Cp*Re-
(CO)(NO)H with HBF4‚OEt2 produced a 7:93 mixture
-
(CO)2(H)2]+BF4 (ω1/2 ≈ 10 Hz); the dihydrogen reso-
nance of [Cp*Os(CO)2(η2-H2)]+BF4- was very broad (ω1/2
≈ 200 Hz) at this temperature. When this solution was
warmed to -75 °C, the dihydrogen resonance of [Cp*Os-
(CO)2(η2-H2)]+BF4- had broadened into the baseline; the
line width for the hydride resonance of Cp*Os(CO)2H
had increased to ω1/2 ≈ 90 Hz, but the dihydride
-
of the dihydride [Cp*Re(CO)(NO)(H)2]+BF4 and the
-
dihydrogen complex [Cp*Re(CO)(NO)(η2-H2)]+BF4
,
for which they estimated a pKa of about -2 in CH2Cl2.
The ruthenium dihydrogen complex [Cp*Ru(CO)2(η2-
H2)]+BF4-, which is the Ru analog of the Os complex
reported in this paper, was also prepared.15 Their Ru
compound exists solely as a dihydrogen complex, whereas
in the Os compound we find the dihydride form pre-
dominates over the dihydrogen tautomer. As is often
found for 3rd row vs 2nd row organometallic compounds,
a much higher thermal stability was found for the Os
compounds, where we observe slow decomposition over
a period of many days at room temperature (see below).
In contrast, the Ru compound [Cp*Ru(CO)2(η2-H2)]+
begins to decompose at temperatures as low as -38 °C.15
The Ru hydride Cp*Ru(CO)2H was reported to be fully
protonated by 1.2 equiv of HBF4‚OEt2, whereas we find
only partial protonation of Cp*Os(CO)2H by ∼1.1 equiv
of either HBF4‚OEt2 or HOTf. The relative thermody-
namic basicities of the Ru and Os compounds are
surprising, particularly in view of studies by Rottink
and Angelici10 on enthalpies of protonation of an exten-
sive series of Ru and Os compounds of the type CpM-
(PR3)2X (X ) halide or hydride). They found that the
Os compounds in this series were usually 6-8 kcal/mol
more basic than analogous Ru compounds.
-
resonance of [Cp*Os(CO)2(H)2]+BF4 was not substan-
tially broadened (ω1/2 ≈ 8 Hz). The onset of line
broadening is observed at a lower temperature for the
BF4- complex compared to the OTf- complex, implying
-
that kinetics of deprotonation by Et2O (in the BF4
complex) are faster than deprotonation by OTf-.
These 1H NMR line-broadening experiments indicate
a higher kinetic acidity of the dihydrogen complex
[Cp*Os(CO)2(η2-H2)]+ compared to the tautomeric di-
hydride complex [Cp*Os(CO)2(H)2]+. Microscopic re-
versibility thus requires that the kinetic protonation site
be at the Os-H bond to give the dihydrogen complex
rather than direct protonation at the metal to produce
the dihydride. In several cases it was previously
shown8,9,17-19 that the initial site of protonation of a
metal hydride is at the M-H bond to give a dihydrogen
complex as the kinetic product, prior to isomerization
to the dihydride tautomer (or an equilibrium mixture
of dihydride and dihydrogen complexes). We were not
successful at measuring the rate of conversion of the
dihydrogen complex to the dihydride/dihydrogen equi-
librium mixture; when Cp*Os(CO)2H was protonated at
-78 °C and an NMR spectrum was promptly recorded
Morris and co-workers have systematically examined
the pKa values of a series of ruthenium complexes9,16
(13) Kubas, G. J .; Unkefer, C. J .; Swanson, B. I.; Fukushima, E. J .
Am. Chem. Soc. 1986, 108, 7000-7009.
(16) J ia, G.; Morris, R. H. J . Am. Chem. Soc. 1991, 113, 875-883.
(17) Parkin, G.; Bercaw, J . E. J . Chem. Soc., Chem. Commun. 1989,
255-257.
(14) George, M. W.; Haward, M. T.; Hamley, P. A.; Hughes, C.;
J ohnson, F. P. A.; Popov, V. K.; Poliakoff, M. J . Am. Chem. Soc. 1993,
115, 2286-2299.
(18) Hamon, P.; Toupet, L.; Hamon, J .-P.; Lapinte, C. Organome-
tallics 1992, 11, 1429-1431.
(15) Chinn, M. S.; Heinekey, D. M.; Payne, N. G.; Sofield, C. D.
Organometallics 1989, 8, 1824-1826.
(19) Henderson, R. A.; Oglieve, K. E. J . Chem. Soc., Dalton Trans.
1993, 3431-3439.

Protonation of Metal Hydrides by Strong Acids
Organometallics, Vol. 15, No. 10, 1996 2507
protonated samples) is much smaller than that found
for pure Cp*Os(CO)2H provides evidence that the rate
of proton exchange is faster than its relaxation rate.20
Exchange is apparently taking place between the hy-
dride and one (or more) species with a lower actual T1
value. This suggests that the dihydrogen complex
[Cp*Os(CO)2(η2-H2)]+OTf-, with a T1 value of 19 ms, is
involved in these proton transfer reactions.
Equations 4-6 show protonation of Cp*Os(CO)2H by
three different proton donors, giving the dihydrogen
1
F igu r e 2. Observed H NMR T1 values (-80 °C, 300 MHz)
from protonation of Cp*Os(CO)2H (0.092 M) by HOTf
(∼0.3-2.5 equiv). 9 ) Cp*Os(CO)2H, [ ) [Cp*Os(CO)2-
(H)2]+, b ) TfOH‚‚‚OTf- at δ 17.09, and 2 ) HOTf at δ
12.24.
complex as the kinetic product. The proton transfer
equilibria operative in our experiments may be pre-
dominately mediated by OTf- as the base. Thus depro-
tonation of the dihydrogen complex by OTf- to regener-
ate Cp*Os(CO)2H and HOTf (the reverse of eq 4),
followed by reprotonation of another molecule of Cp*Os-
(CO)2H, provides a mechanism for proton exchange
among [Cp*Os(CO)2(η2-H2)]+, HOTf, and Cp*Os(CO)2H.
This mechanism can account for the “T1 averaging” and
line-broadening involving these species and avoids the
requirement of a direct metal-to-metal proton transfer
as shown in eq 5. The degenerate proton transfer
exchange in eq 5 may occur as well but would likely
involve a higher barrier21 in view of steric requirements.
Protonation of Cp*Os(CO)2H by the dihydride [Cp*Os-
(CO)2(H)2]+OTf- (eq 6) would presumably also involve
a significant barrier to proton transfer. Furthermore,
this process would not be very efficient at lowering the
at the same temperature, the equilibrium between
dihydrogen complex and dihydride was established
before the spectrum was completed.
P r oton Exch a n ge P r ocesses d u r in g P a r tia l P r o-
t on a t ion of Cp *Os(CO)2H . Ob ser va t ion of “T1
Aver a gin g”. The hydride ligand of Cp*Os(CO)2H has
an extremely long T1 of 51 s at 23 °C. This very slow
relaxation rate requires that long pulse delays and/or
1
small pulse angles be utilized in H NMR studies of this
and other metal hydrides in experiments where accurate
integrations are needed. Most of the T1 measurements
reported in this paper were carried out at -80 °C, where
relaxation is much faster than at room temperature. The
true T1 for the hydride ligand of Cp*Os(CO)2H (with no
added acid) is 5.9 s at -80 °C.
Information about proton exchange reactions was
obtained from experiments involving partial protonation
of Cp*Os(CO)2H. HOTf was added at room temperature
in several portions (∼0.4 equiv with each addition) to a
solution of Cp*Os(CO)2H (0.092 M) in CD2Cl2; NMR
spectra and T1 values were measured at -80 °C follow-
ing each incremental addition of HOTf. As the overall
conversion to protonated products increased, the ratio
of [Cp*Os(CO)2(H)2]+OTf-:[Cp*Os(CO)2(η2-H2)]+OTf- re-
mained constant at 87((2):13((2). Figure 2 shows the
changes in observed T1 values at different concentra-
tions of acid. Most notable are the substantial changes
obs
T1 for the hydride, since the T1 of the dihydride (2.8
s) is only a factor of two different from than that of the
hydride. In principle, other faster processes could be
occurring but not detected in our experiments; these “T1
averaging” experiments are most sensitive for detection
of exchange processes where one compound exchanges
with a second species having a significantly lower T1.
obs
In these experiments we found “averaging” of T1
values due to the intermolecular proton exchange rate
being faster than the relaxation rate. T1 averaging has
been observed previously for intramolecular exchange
of hydride and dihydrogen sites. In their study of the
interconversion of dihydride and dihydrogen forms of
[Cp*Ru(dppm)(η2-H2)]+,9 Morris and co-workers found
averaging of the T1 values of the Ru(η2-H2) and Ru(H)2
resonances; complete averaging was observed above 40
°C, with T1 values for both sites being 86 ms. More
commonly observed than averaging between an H2
ligand and the two terminal M-H ligands of its dihy-
dride tautomer are examples where a compound exhib-
its averaging of the T1 values between an η2-H2 ligand
and one (or more) terminal hydrides that are present
in addition to the dihydrogen ligand. Morris and co-
obs
in the T1 values of the hydride resonance of Cp*Os-
(CO)2H. After the first addition of HOTf, only 9% of
obs
the Cp*Os(CO)2H had been protonated, but the T1 of
the Os-H resonance dropped to 1.2 s (cf. 5.9 s with no
obs
acid). The T1 continued to decrease as the amount
obs
of protonation increased, decreasing to T1 ) 0.17 s
when 72% of the initial Cp*Os(CO)2H had been proto-
nated. When sufficient acid had been added to com-
pletely convert Cp*Os(CO)2H to [Cp*Os(CO)2(H)2]+OTf-
and [Cp*Os(CO)2(η2-H2)]+OTf-, however, a T1 measure-
ment of the dihydride resonance of [Cp*Os(CO)2-
(H)2]+OTf- gave a value of 2.8 s. In sharp contrast to
this long T1 value, the dihydrogen ligand of [Cp*Os-
(CO)2(η2-H2)]+OTf- had a short T1 of 19 ms.
In these spectra, separate resonances were observed
at -80 °C for the hydride (δ -14.21), the dihydride (δ
-10.00), and the dihydrogen complex (δ -7.24), indicat-
ing that the rate of proton exchange is slow on the
chemical shift time scale.20 The observation that the
T1obs for the hydride ligand of Cp*Os(CO)2H (in partially
(20) For an informative discussion of the different exchange time
scales and their effect on the observed spectrum, see: Sanders, J . K.;
Hunter, B. K. Modern NMR Spectroscopy; Oxford University Press:
Oxford, U.K., 1987; pp 218-219.
(21) For a weak-interaction model of proton transfer self-exchange
between metals, see: Creutz, C.; Sutin, N. J . Am. Chem. Soc. 1988,
110, 2418-2427.

2508 Organometallics, Vol. 15, No. 10, 1996
Bullock et al.
workers reported intramolecular exchange between η2-
H2 ligands and terminal hydrides in an extensive series
of Fe, Ru, and Os complexes of general formula [M(H)-
(η2-H2)(R2PCH2CH2PR2)2]+.22 Crabtree and co-workers
reported an early example of T1 averaging in [Ir(H)(η2-
H2)(PPh3)2(7,8-benzoquinolate)]+.23 Luo and Crabtree
later observed averaging of T1 values in the dihydrogen/
dihydride complex [ReH2(η2-H2)(CO)(PMe2Ph)3]+, which
exists in equilibrium with its eight-coordinate tetrahy-
dride form [ReH4(CO)(PMe2Ph)3]+.24
[CpW(CO)3(H)2]+, which was first reported26 over 30
years ago from protonation of CpW(CO)3H by BF3/H2O/
obs
CF3CO2H. The T1
for the dihydride resonance of
obs
[CpW(CO)3(H)2]+ was 1.8 s. The T1 for the hydride
resonance of CpW(CO)3H in this partially protonated
sample was 3.7 s, which is much smaller than the T1
value of 11.2 s measured separately (with no acid added)
for CpW(CO)3H at -80 °C. (For comparison, the hy-
dride ligand of CpW(CO)3H has T1 ) 85 s at 29 °C.)
When a CD2Cl2 solution of the related Cp* complex
Cp*W(CO)3H (0.1 M) was treated at room temperature
with HOTf (1.1 equiv), an NMR spectrum recorded at
-78 °C indicated a 1:1 ratio of Cp*W(CO)3H to [Cp*W-
(CO)3(H)2]+OTf- (eq 7). The T1 measured at -78 °C for
Rate constants for the exchange between η2-H2 ligands
and terminal hydrides ligands have been determined
in many cases, and a recent review discusses this topic
in detail.2b Quantitative evaluation of the observed T1
data has been carried out in certain cases where reliable
values of T1 in the absence of exchange are available.
For slower exchanges, complete line shape analysis of
NMR line-broadening data can be used to obtain rate
constants. For the protonation of Cp*Os(CO)2H re-
ported here the hydride, dihydride, and dihydrogen
resonances were well-separated at -80 °C, the temper-
ature at which our T1 measurements were carried out,
but coalescence was observed at higher temperatures.
In the intramolecular exchange cases previously re-
ported, the exchanging sites were generally limited to
an η2-H2 ligand and hydride sites. The intermolecular
proton transfer exchanges observed in our Os system
are more complicated to analyze, since there are five
exchanging sites: Os(H), Os(H)2, Os(η2-H2), and two
HOTf sites (see below). We cannot determine specific
rate constants for proton transfer from our data, but
approximate limits on the overall rate constant for
proton exchange in the system may be estimated from
the relaxation rates of the Os(η2-H2) and Os-H sites in
the absence of exchange. The proton exchange rate
must be greater than the relaxation rate of the Os-H
site, or else no T1 averaging would have been observed.
For the estimated upper limit, the proton exchange rate
cannot greatly exceed the relaxation rate of the Os(η2-
H2) site, or else the observed T1 values would have been
more similar, approaching the limit of relaxation coa-
lescence.25 The limits obtained in this way are 1/T1-
[Os(η2-H2)] ) 1/(19 ms) ) 52 s-1 and 1/T1(OsH) ) 1/(5.9
s) ) 0.17 s-1, corresponding to ∆G‡(-80 °C) between 9.6
the W-H resonance of Cp*W(CO)3H (δ -7.03) was 0.87
s (compared to T1 ) 6.4 s determined at -80 °C with
no acid present), and the T1 measured for the dihydride
(δ -2.33) was 0.52 s. The protonation of Cp*W(CO)3H
was completed by the addition of more HOTf (4 equiv
total). An IR spectrum of the cationic dihydride [Cp*W-
(CO)3(H)2]+OTf- exhibited three ν(CO) bands at room
temperature in CH2Cl2 (2119 s, 2075 vs, 2057 s cm-1),
all of which appear at higher energy than the bands for
the neutral hydride Cp*W(CO)3H (2006 s, 1909 s cm-1).
The observation that HOTf (1.2 equiv) caused only
∼16% protonation of CpW(CO)3H implies that the
cationic dihydride [CpW(CO)3(H)2]+OTf- is a stronger
acid than HOTf. The analogous Cp* complex Cp*W-
(CO)3H has a slightly higher basicity, since it was 50%
protonated upon addition of 1.2 equiv of HOTf. The
difference in basicity in CpW(CO)3H compared to Cp*W-
(CO)3H is in the expected direction, but the magnitude
of the effect is smaller here than in previously reported
examples of Cp/Cp* pairs. The anion [Cp*Mo(CO)3]-
is 4.4 kcal/mol more basic than [CpMo(CO)3]- (i.e., the
pKa of Cp*Mo(CO)3H (17.1) in CH3CN is larger than
that of CpMo(CO)3H (pKa ) 13.9).27 Angelici and co-
workers studied enthalpies of protonation of several
classes of organometallic compounds by titration calo-
rimetry and found that the Cp* ligand increases metal
basicity (compared to Cp analogs) by 5.5-9.0 kcal/mol.10
Decom p osition to Meta l Tr ifla tes. All of the metal
hydrides we have examined are very rapidly protonated
by HOTf. As described earlier,3b H/D exchange was
observed at low temperature following addition of HOTf
to either CpW(CO)3D or CpMo(CO)3D. Decomposition
of these partially protonated metal hydrides to H2 and
metal triflates (eq 2) does occur but on a far slower time
scale than that at which the proton transfer equilibrium
is established. For example, formation of Cp(CO)3WOTf
was incomplete after 2 weeks at room temperature
and 11.8 kcal mol-1
.
The T1 values in the present study were measured at
a single temperature, as opposed to minimum T1 values
obtained from variable-temperature studies. Notwith-
standing the effect of exchange on the observed T1
values, the large T1 value found for [Cp*Os(CO)2(H)2]+
supports its assignment as a dihydride rather than a
dihydrogen complex.2
P r oton a tion of Cp W(CO)3H a n d Cp *W(CO)3H.
When HOTf (1.2 equiv) was added at room temperature
to a CD2Cl2 solution of CpW(CO)3H (0.1 M), an NMR
spectrum at -80 °C indicated 16% conversion to a new
complex exhibiting a slightly broadened (ω1/2 ) 12 Hz)
resonance at δ -2.07 that integrated as two protons.
These resonances are assigned to the cationic dihydride
following protonation of CpW(CO)3H with HOTf.3
A
CD2Cl2 solution of Cp*W(CO)3H (0.1 M) that had been
treated with HOTf (4 equiv) was only 48% decomposed
to Cp*(CO)3WOTf after 2.5 days at room temperature.
An even slower rate of decomposition was observed
when Cp*Os(CO)2H was reacted with HOTf. When a
(22) Earl, K. A.; J ia, G.; Maltby, P. A.; Morris, R. H. J . Am. Chem.
Soc. 1991, 113, 3027-3039.
(23) Crabtree, R. H.; Lavin, M.; Bonneviot, L. J . Am. Chem. Soc.
(26) Davison, A.; McFarlane, W.; Pratt, L.; Wilkinson, G. J . Chem.
Soc. 1962, 3653-3666.
(27) (a) Moore, E. J .; Sullivan, J . M.; Norton, J . R. J . Am. Chem.
Soc. 1986, 108, 2257-2263. (b) For a review of proton transfer reactions
of metal hydrides, see: Kristja´nsdo´ttir, S. S.; Norton, J . R. In
Transition Metal Hydrides; Dedieu, A., Ed.; VCH: New York, 1992.
1986, 108, 4032-4037.
(24) Luo, X.-L.; Crabtree, R. H. J . Am. Chem. Soc. 1990, 112, 6912-
6918.
(25) Lambert, J . B.; Keepers, J . W. J . Magn. Reson. 1980, 38, 233-
244.

Protonation of Metal Hydrides by Strong Acids
Organometallics, Vol. 15, No. 10, 1996 2509
Ta ble 1. Cr ysta llogr a p h ic Da ta fr om th e X-r a y
Diffr a ction Stu d y of [Cp W(CO)2(P Me3)(H)2]+OTf-
CD2Cl2 solution of Cp*Os(CO)2H (0.10 M) was treated
with HOTf (2.8 equiv), 32% of the [Cp*Os(CO)2(H)2]+OTf-
+ [Cp*Os(CO)2(η2-H2)]+OTf- mixture remained after 20
days. The decomposition products were Cp*Os(CO)2-
OTf (23%) and 41% of a second product tentatively
identified as the bimetallic bridging hydride complex
{[Cp*Os(CO)2]2(µ-H)}+OTf- (see Experimental Section
for further details).
formula
mol wt
space group
a, Å
C11H16F3O5PSW
532.12
P212121
8.105(3)
13.650(3)
15.336(2)
1696.6(7)
4
b, Å
c, Å
V, Å3
F or m a tion of [Cp W(CO)2(P R3)(H)2]+OTf- by P r o-
ton a tion of Cp W(CO)2(P R3)H (R ) Me, Cy, P h ). The
PMe3 ligand is a strong electron donor, and substitution
of CO by PMe3 is known to greatly increase the basicity
of the metal and decrease the thermodynamic acidity
of metal hydrides. The pKa of CpW(CO)3H in MeCN is
16.1, while that of CpW(CO)2(PMe3)H is 26.6.27 Proto-
nation of CpW(CO)2(PMe3)H by HOTf gives the dihy-
dride [CpW(CO)2(PMe3)(H)2]+OTf- (eq 8). Similarly,
Z
F(calcd), g cm-3
temp, K
2.083
200 K
radiation
Mo KR
µ, cm-1
72.1
transm factor: max, min (ψ scans)
reflcns collcd
0.9979, 0.6594
2832
unique reflcns (Fo > 0)
reflcns used (Fo > 3σ(Fo))
2θ limits (deg)
no. of variables
Ra
2508
2140
4-60
200
0.031
Rw
0.032
max shift/error, final cycle
e0.01
a
2
R ) ∑||Fo| - |Fc||/∑|Fo|; Rw ) {∑[w(|Fo| - |Fc|)2/∑[w|Fo| ]}1/2
.
(PPh3)(H)2]+ BAr′4-, was also isolated and characterized
(see Experimental Section).
As was done for the osmium compounds, the inte-
grated intensities of the IR bands of the carbonyl ligands
in these tungsten dihydrides allowed estimates6 of the
OC-W-CO angles. Estimated OC-W-CO angles were
reaction of CpW(CO)2(PMe3)H with Brookhart’s acid,28
-
[H(Et2O)2]+BAr′4 (Ar′ ) 3,5-bis(trifluoromethyl)phe-
nyl), led to the isolation of [CpW(CO)2(PMe3)(H)2]+
-
92° for [CpW(CO)2(PPh3)(H)2]+BAr′4 and 93° for
-
BAr′4
.
The dihydride [CpW(CO)2(PMe3)(H)2]+ was
[CpW(CO)2(PCy3)(H)2]+BAr′4-. The OC-W-CO angle
estimated from the IR bands of [CpW(CO)2(PMe3)(H)2]+O-
Tf- is 96°, which suggests that steric congestion in the
PPh3 and PCy3 complexes may decrease the OC-W-
CO angle, relative to the dihydride with the smaller
PMe3 ligand. The angle of 96° estimated from IR
intensities is larger than the angle of 90.4(4)° found in
the crystal structure (see below). Sutton and co-workers
found that OC-M-CO angles estimated from IR data
also exceeded those found in crystal structures.30 For
cis-Cp*Re(CO)2I2 the OC-Re-CO angle of 80° esti-
mated from the IR intensities was only slightly larger
than the angle of 78(1)° determined crystallographically.
For trans-Cp*Re(CO)2Br2 a much larger difference was
found: an OC-Re-CO angle of ∼115° was estimated from
IR intensities, compared to 104.3(6)° found in the X-ray
structure.30
Str u ctu r al Ch ar acter ization of [CpW(CO)2(P Me3)-
(H)2]+OTf-; Obser va tion of Wea k Hyd r ogen -Bon d -
in g In ter a ction s. Our structural characterization of
[CpW(CO)2(PMe3)(H)2]+OTf- by single crystal X-ray
diffraction verifies the geometry about tungsten sug-
gested by Tilset.29 Table 1 lists information on the data
collection and refinement, and Table 2 gives selected
bond distances and angles. The tungsten hydrides were
located but not refined. As shown in the ORTEP
diagram in Figure 3, the overall geometry can be viewed
as a distorted octahedron, if the Cp ligand is thought of
as occupying a single coordination site. One of the
tungsten hydrides is nearly trans to the Cp, with a Cp-
(centroid)-W-H angle of 167°. A view from above the
Cp ligand is shown in Figure 4.
isolated in analytically pure form with both the OTf-
and BAr′4 counterions. This same dihydride was
-
previously prepared and characterized as the BF4- salt
by Tilset and co-workers.29 They first observed it (along
with CpW(CO)2(PMe3)(NCMe)+) as a product of the
oxidation of CpW(CO)2(PMe3)H by Cp2Fe+ in MeCN;
they independently prepared it by protonation of CpW-
(CO)2(PMe3)H with HBF4‚Et2O. Our spectroscopic data
-
for the OTf- and BAr′4 salts are in good agreement
-
with those reported for the BF4 salt. Tilset reported
-
that the two hydrides of [CpW(CO)2(PMe3)(H)2]+BF4
were nonequivalent at -112 °C and suggested the
structure drawn in eq 8. A fluxional process renders
the two hydrides equivalent at room temperature. We
measured T1 ) 2.4 s for the hydrides at 22 °C. This
averaged value for the two hydrides is so large that it
is clear that the compound is a dihydride in solution as
well as in the solid. As suggested by Tilset,29 the
fluxional process that makes the two hydrides equiva-
lent might involve the dihydrogen complex [CpW(CO)2-
(PMe3)(η2-H2)]+ as an intermediate, but no direct evi-
dence for this dihydrogen complex was obtained.
The dihydride [CpW(CO)2(PCy3)(H)2]+OTf-, with the
more sterically demanding tricyclohexylphosphine ligand,
was also isolated. This compound is thermally unstable
in solution, releasing H2 and producing Cp(CO)2-
(PCy3)WOTf; in CD2Cl2 at room temperature the de-
composition is half complete in about 16 h. Even as a
solid, [CpW(CO)2(PCy3)(H)2]+OTf- turns dark when
stored at room temperature. In contrast, [CpW(CO)2-
(PCy3)(H)2]+ BAr′4-, with the BAr′4- counterion, is much
more stable, and has been obtained in analytically pure
form. A dihydride with a PPh3 ligand, [CpW(CO)2-
The crystal structure reveals a network of weak
hydrogen bonds between the tungsten complex and the
triflate anions; details of angles and distances of these
(28) Brookhart, M.; Grant, B.; Volpe, A. F., J r. Organometallics 1992,
11, 3920-3922.
(29) Ryan, O. B.; Tilset, M.; Parker, V. D. J . Am. Chem. Soc. 1990,
112, 2618-2626.
(30) Einstein, F. W. B.; Klahn-Oliva, A. H.; Sutton, D.; Tyers, K. G.
Organometallics 1986, 5, 53-59.

2510 Organometallics, Vol. 15, No. 10, 1996
Bullock et al.
Ta ble 2. Selected Bon d Len gth s a n d An gles for
[Cp W(CO)2(P Me3)(H)2]+OTf-
Metal Coordination Sphere Distances (Å)
W-C(1)
W-C(2)
W-P
2.029(10)
2.023(10)
2.487(2)
W-Cp(CEN)a
W-H(1)b
1.983(10)
1.83
1.62
W-H(2)b
Metal Coordination Sphere Angles (deg)
C(1)-W-C(2)
90.4(4) Cp(CEN)a-W-C(1) 110.5(4)
C(1)-W-P
131.7(3) Cp(CEN)a-W-C(2) 115.4(4)
C(2)-W-P
84.7(3) Cp(CEN)a -W-P
114.9(3)
76
137
H(1)-W-C(1)
H(1)-W-C(2)
H(1)-W-P
61
76
71
H(2)-W-C(1)
H(2)-W-C(2)
H(2)-W-P
75
H(1)-W-Cp(CEN)a 167
H(2)-W-Cp(CEN)a 107
H(1)-W-H(2)
63
a
b
Cp(CEN) designates the centroid of the Cp ring. H(1) and
H(2) were located in the final difference Fourier map but were
not refined.
F igu r e 5. ORTEP drawing of the packing of [CpW(CO)2-
(PMe3)(H)2]+OTf-, showing the weak hydrogen-bonding
interactions (W-H‚‚‚F and C-H‚‚‚O). Two oxygens of one
triflate form a hydrogen bond to adjacent C-H bonds on
the Cp, while the remaining three C-H bonds are hydrogen
bonded to oxygens on three other triflate anions. To
improve the clarity of the figure, four of these hydrogen
bonds are shown on the Cp near the middle of the figure,
while the 5th C-H‚‚‚O hydrogen bond is shown at the
bottom of the figure.
the two fluorines, thus providing further evidence for
the existence of this three-centered hydrogen bond.31
F igu r e 3. ORTEP drawing of [CpW(CO)2(PMe3)(H)2]+. The
thermal ellipsoids are at the 50% probability level, and the
hydrogen atoms on the Cp and PMe3 ligands are omitted.
Participation of metal hydrides in hydrogen bonds has
been a subject of substantial recent interest. Infrared
spectroscopic data has been presented as evidence for
hydrogen bonding of phosphine oxides to cationic hy-
dride complexes of Os32 and Re.33 Another recent report
of an O‚‚‚H-M hydrogen bond involves [(dppe)2(η1-
OCOMe)WH3]+, where structural and spectroscopic
indicated that one of the hydrides of this cationic
tungsten complex was involved in a hydrogen bond with
an oxygen of the acetate ligand.34 In these O‚‚‚H-M
interactions, as with the F‚‚‚H-M interaction in [CpW-
(CO)2(PMe3)(H)2]+OTf-, the metal hydride acts as the
hydrogen bond donor. All of these examples involve
cationic metal hydrides; a Raman and IR spectroscopic
study revealed no evidence for hydrogen bonding of the
neutral hydride HCo(CO)4 to amine bases prior to
deprotonation.35
F igu r e 4. ORTEP drawing of [CpW(CO)2(PMe3)(H)2]+
viewed through the center of the Cp ring. The thermal
ellipsoids are at the 50% probability level, and the hydrogen
atoms on the Cp and PMe3 ligands are omitted.
Metal hydrides have also been shown to be involved
in hydrogen bonds where the metal hydride is the
hydrogen bond acceptor. Several examples of intramo-
lecular N-H‚‚‚H-M hydrogen bonding have been dis-
covered.36,37 Intermolecular hydrogen bonding has been
found between indole (and other N-H donors) and Re
and W polyhydrides,38 and a three-centered hydrogen
bond between indole and two hydrides of Re(PPh3)H5
are tabulated in the Supporting Information. Figure 5
is an ORTEP diagram of four [CpW(CO)2(PMe3)(H)2]+
cations and four OTf- anions, showing the hydrogen
bonding. The tungsten hydride trans to the Cp ligand
is involved in a weak hydrogen bond with two of the
fluorines on a triflate anion. The hydride is a hydrogen
bond donor in this three-centered hydrogen bond, with
the fluorines as hydrogen bond acceptors. The H‚‚‚F
separations for these interactions are 2.59 Å and 2.82
Å; the one with the shorter distance is also more linear
(W-H-F angles of 162° vs 152°). The sum of the van
der Waals radii for H and F is 2.55 Å, so these H‚‚‚F
interactions are quite weak. The tungsten hydride (H1)
lies only 0.06 Å out of the plane defined by the W and
(31) J effrey, G. A.; Saenger, W. Hydrogen Bonding in Biological
Structures; Springer-Verlag: New York, 1991; p 21.
(32) Epstein, L. M.; Shubina, E. S.; Krylov, A. N.; Kreindlin, A. Z.;
Rybinskaya, M. I. J . Organomet. Chem. 1993, 447, 277-280.
(33) Peris, E.; Crabtree, R. H. J . Chem. Soc., Chem. Commun. 1995,
2179-2180.
(34) Fairhurst, S. A.; Henderson, R. A.; Hughes, D. L.; Ibrahim, S.
K.; Pickett, C. J . J . Chem. Soc., Chem. Commun. 1995, 1569-1570.
(35) Kristja´nsdo´ttir, S. S.; Norton, J . R.; Moroz, A.; Sweany, R. L.;
Whittenburg, S. L. Organometallics 1991, 10, 2357-2361.

Protonation of Metal Hydrides by Strong Acids
Organometallics, Vol. 15, No. 10, 1996 2511
was recently structurally characterized by neutron
diffraction.39 Spectroscopic data were recently pub-
lished40 for intermolecular ROH‚‚‚H-M interactions
between acidic alcohols and tungsten hydrides.
resonance of cis-Cp*Re(CO)2(H)(D) appears 0.056 ppm
upfield of the dihydride resonance of cis-Cp*Re(CO)2-
(H)2.7
In an NMR spectrum recorded at -80 °C following
addition of DOTf to a CD2Cl2 solution of Cp*Os(CO)2H,
the resonance due to [Cp*Os(CO)2(H)2]+OTf- at
δ -10.006 exhibited a shoulder at δ -9.987. This
additional resonance is assigned to [Cp*Os(CO)2(H)-
(D)]+OTf-, indicating an unusual downfield shift of
0.019 ppm upon partial deuteration. This resonance
assigned to the Os(H)(D) complex was not well-resolved
but was reproducible. Precedent for a downfield shift
of a dihydride in equilibrium with its dihydrogen
tautomer comes from Heinekey’s report15 of a downfield
shift of 0.027 ppm upon partial deuteration of [Cp*Re-
(CO)(NO)(H)2]+, which was shown to be in equilibrium
with [Cp*Re(CO)(NO)(η2-H2)]+. In both of these cases
the resonance for the dihydrogen ligand is downfield of
that due to the dihydride. Downfield shifts upon partial
deuteration have also been reported for Os(PTol3)3(H)4,46
(tBu3SiO)4Ta2(H)4,47 cis-IrH(η2-H2)Cl2(PiPr3)2,48 and
IrH4[HB(3,5-Me2pz)3].49
In addition to the hydrogen bonding of the W-H bond
to the fluorines on the triflate, the crystal structure also
indicates the existence of weak C-H‚‚‚O hydrogen
bonds,41 where the oxygens atoms of the triflate behave
as hydrogen bond acceptors. Each of the five hydrogens
on the Cp ring are hydrogen bonded to an oxygen of a
triflate. The C‚‚‚O distances range from 3.246 to 3.497
Å; C-H‚‚‚O angles range from 138 to 154°. These
distances and angles are in the range found for other
C-H‚‚‚O hydrogen-bonding interactions. Although each
of these individual hydrogen bonds is weak, collectively
they can have a substantial impact on the overall crystal
structure. The influence of hydrogen bonding in orga-
nometallic complexes has been recognized recently, and
insightful analyses of the impact of C-H‚‚‚O hydrogen
bonding interactions on the crystal structures of orga-
nometallic complexes have been reported.42
Isotop ic Effects on th e Ch em ica l Sh ifts of P a r -
tia lly Deu ter a ted Dih yd r id es. We previously noted3b
that the hydride resonance of [CpW(CO)3(H)(D)]+OTf-
appears at δ -2.12, indicating an upfield shift of 0.05
ppm upon partial deuteration of the dihydride [CpW(C-
O)3(H)2]+OTf- (δ -2.07). Protonation of CpW(CO)2(P-
Me3)H by DOTf gives [CpW(CO)2(PMe3)(H)(D)]+OTf-,
which exhibits a doublet (δ -2.541, J PH ) 38 Hz) at 25
°C. This resonance is 0.062 ppm upfield of the doublet
for [CpW(CO)2(PMe3)(H)2]+OTf- (δ -2.479). The mag-
nitude of the isotope effects on the chemical shift, as
well as the sign (upfield upon partial deuteration) that
we find for these W hydrides, is similar to examples
reported for a series of other dihydrides and polyhy-
drides. Crabtree and co-workers reported isotope effects
on chemical shifts for partial deuteration of a large
series of Re polyhydride complexes; upfield shifts of
0.002-0.03 ppm for each deuterium were typically
observed.43 Heinekey and co-workers found upfield
shifts of up to 0.075 ppm upon partial deuteration of
[Cp*Ir(PPh3)(H)3]+.44 The trihydride complex CpRu-
(PPh3)(H)3 exhibits an upfield isotope shift of 0.023 ppm
upon substitution of one H by D,45 and the hydride
Isotope effects on chemical shift50 caused by geminal
substitution of H for D on a metal are normally <0.1
ppm. Much larger changes in chemical shift can be
observed in cases where isotopic perturbation of reso-
nance occurs, in which there is a nonstatistical occupa-
tion of D vs H in chemically distinct sites. Partial
deuteration of complexes containing both hydride and
dihydrogen ligands24,51 or dihydrides with chemically
inequivalent hydride sites52,53 can lead to observed
chemical shift changes in the range of 0.2 ppm or
greater due to isotopic perturbation of resonance.
Dep en d en ce of th e NMR Ch em ica l Sh ift of HOTf
on Con cen tr a tion a n d Tem p er a tu r e. NMR spectra
in our experiments show resonances due to HOTf, in
addition to the resonances due to the organometallic
hydride complexes discussed above. The solutions of
partially protonated Cp*Os(CO)2H exhibited NMR reso-
nances at -80 °C for HOTf at δ 12.24 and 17.09, both
of which were somewhat broadened singlets (ω1/2 ≈ 16
Hz). As further additions of HOTf were made, the
relative integrations of the δ 12.24:δ 17.09 resonances
remained constant at 75((3):25((3). The acid reso-
nances changed their chemical shift and broadened
when a sufficient excess HOTf had been added to
(36) (a) Peris, E.; Lee, J . C., J r.; Crabtree, R. H. J . Chem. Soc., Chem.
Commun. 1994, 2573. (b) Lee, J . C., J r.; Peris, E.; Rheingold, A. L.;
Crabtree, R. H. J . Am. Chem. Soc. 1994, 116, 11014-11019. (c) Peris,
E.; Lee, J . C., J r.; Rambo, J . R.; Eisenstein, O.; Crabtree, R. H. J . Am.
Chem. Soc. 1995, 117, 3485-3491.
(37) (a) Park, S.; Ramachandran, R.; Lough, A. J .; Morris, R. H. J .
Chem. Soc., Chem. Commun. 1994, 2201-2202. (b) Lough, A. J .; Park,
S.; Ramachandran, R.; Morris, R. H. J . Am. Chem. Soc. 1994, 116,
8356-8357.
(38) Peris, E.; Wessel, J .; Patel, B. P.; Crabtree, R. H. J . Chem. Soc.,
Chem. Commun. 1995, 2175-2176.
(39) Wessel, J .; Lee, J . C., J r.; Peris, E.; Yap, G. P. A.; Fortin, J . B.;
Ricci, J . S.; Sini, G.; Albinati, A.; Koetzle, T. F.; Eisenstein, O.;
Rheingold, A. L.; Crabtree, R. H. Angew. Chem., Int. Ed. Engl. 1995,
34, 2507-2509.
(40) Shubina, E. S.; Belkova, N. V.; Krylov, A. N.; Voronstov, E. V.;
Epstein, L. M.; Gusev, D. G.; Niedermann, M.; Berke, H. J . Am. Chem.
Soc. 1996, 118, 1105-1112.
(41) For leading references on C-H‚‚‚O hydrogen bonds, see: (a)
Taylor, R.; Kennard, O. J . Am. Chem. Soc. 1982, 104, 5063-5070. (b)
Desiraju, G. R. Acc. Chem. Res. 1991, 24, 290-296. (c) Steiner, T.;
Saenger, W. J . Am. Chem. Soc. 1992, 114, 10146-10154. (d) Steiner,
T.; Saenger, W. J . Am. Chem. Soc. 1993, 115, 4540-4547.
(42) (a) Braga, D.; Grepioni, F.; Sabatino, P.; Desiraju, G. R.
Organometallics 1994, 13, 3532-3543. (b) Braga, D.; Grepioni, F.;
Biradha, K.; Pedireddi, V. R.; Desiraju, G. R. J . Am. Chem. Soc. 1995,
117, 3156-3166. (c) Braga, D.; Grepioni, F. Acc. Chem. Res. 1994, 27,
51-56.
(43) (a) Hamilton, D. G.; Luo, X.-L.; Crabtree, R. H. Inorg. Chem.
1989, 28, 3198-3203. (b) Luo, X.-L.; Crabtree, R. H. J . Am. Chem.
Soc. 1990, 112, 4813-4821. (c) Luo, X.-L.; Michos, D.; Crabtree, R. H.
Organometallics 1992, 11, 237-241.
(44) Heinekey, D. M.; Millar, J . M.; Koetzle, T. F.; Payne, N. G.;
Zilm, K. W. J . Am. Chem. Soc. 1990, 112, 909-919.
(45) Baird, G. J .; Davies, S. G.; Moon, S. D.; Simpson, S. J .; J ones,
R. H. J . Chem. Soc., Dalton Trans. 1985, 1479-1486.
(46) Desrosiers, P. J .; Cai, L.; Lin, Z.; Richards, R.; Halpern, J . J .
Am. Chem. Soc. 1991, 113, 4173-4184.
(47) Miller, R. L.; Toreki, R.; LaPointe, R. E.; Wolczanski, P. T.; Van
Duyne, G. D.; Roe, D. C. J . Am. Chem. Soc. 1993, 115, 5570-5588.
(48) Albinati, A.; Bakhmutov, V. I.; Caulton, K. G.; Clot, E.; Eckert,
J .; Eisenstein, O.; Gusev, D. G.; Grushin, V. V.; Hauger, B. E.; Klooster,
W. T.; Koetzle, T. F.; McMullan, R. K.; O’Loughlin, T. J .; Pe´lissier, M.;
Ricci, J . S.; Sigalas, M. P.; Vymenits, A. B. J . Am. Chem. Soc. 1993,
115, 7300-7312.
(49) Paneque, M.; Poveda, M.; Taboada, S. J . Am. Chem. Soc. 1994,
116, 4519-4520.
(50) Hansen, P. E. Annu. Rep. NMR Spectrosc. 1983, 15, 105-234.
(51) Heinekey, D. M.; Oldham, W. J ., J r. J . Am. Chem. Soc. 1994,
116, 3137-3138.
(52) Bianchini, C.; Laschi, F.; Peruzzini, M.; Ottaviani, F. M.; Vacca,
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1994, 116, 8388-8389.

2512 Organometallics, Vol. 15, No. 10, 1996
Bullock et al.
protonate all of the Cp*Os(CO)2H; the resonances then
equilibrium mixture of the dihydride [Cp*Os(CO)2-
(H)2]+OTf- and the dihydrogen complex [Cp*Os(CO)2-
(η2-H2)]+OTf-. The kinetic and thermodynamic acidity
of the dihydrogen complex are greater than the dihy-
dride. Protonation of the phosphine-substituted tung-
sten compounds CpW(CO)2(PR3)H (R ) Me, Cy, Ph)
gives dihydrides that are much less acidic. The crystal
structure of [CpW(CO)2(PMe3)(H)2]+OTf- reveals the
presence of a weak hydrogen bond; one tungsten hydride
is a hydrogen bond donor to two fluorines on the triflate
anion.
appeared at δ 12.01 (ω1/2 ≈ 70 Hz) and δ 16.04 (ω1/2
≈
35 Hz). An additional change is that the relative
intensities had interchanged (28:72 ratio).
obs
The T1
for the two resonances of HOTf were
typically about 0.17 s and did not undergo major
changes in as the protonation proceeded (see Figure 2).
After the final addition of HOTf, when all of the hydride
obs
had been protonated, the T1 values of the two HOTf
resonances increased to about 0.4 s.
The chemical shift of HOTf in CD2Cl2 was examined
in order to help interpret these observations. A CD2-
Cl2 solution of HOTf (0.04 M) exhibited a singlet at
δ 8.13. The chemical shift of HOTf was linearly de-
pendent on concentration up to 0.22 M, increasing to
δ 8.70 at [HOTf] ) 0.22 M (see Figure 6 in the
Experimental Section for a plot of chemical shift vs
concentration). The downfield shift of the HOTf peaks
with increasing concentration is consistent with the
expected effect of increased hydrogen-bonding (of HOTf
with itself). Above 0.22 M, the singlet for HOTf
continued to move further downfield with increasing
concentration, but additional broad resonances were
observed at δ 11.5 and 11.8.
NMR spectra of HOTf at low temperature exhibit
similar features. Whereas a singlet was observed at
δ 8.37 for a solution of HOTf (0.1 M) in CD2Cl2 at 22
°C, the same solution at -50 °C exhibited broad
resonances at δ 11.4 and 10.9, in addition to the main
peak at δ 9.23. These broad resonances accounted for
a total of 31% of the initial intensity of the peak
observed at 22 °C, and the singlet that moved to δ 9.23
upon cooling accounted for 66% of the initial intensity.
HOTf has low solubility (∼8 mM) at -80 °C, but the
solubility increases in the presence of OTf- anions. A
T1 value of 1.5 s was determined at -80 °C for HOTf
(0.09 M) in the presence of PPN+OTf- (0.09 M). The
chemical shift (δ 17.15) of this resonance is far downfield
of the resonance for pure HOTf, implicating hydrogen
bonding of HOTf to an OTf- counterion.
The NMR experiments on HOTf described above,
carried out in the absence of metal hydrides, provide
an explanation for the observation that two separate
resonances were observed in the low-temperature ex-
periments involving protonation of metal hydrides. On
the basis of the similarity of the chemical shift to similar
broadened resonances observed for HOTf at high con-
centrations or low temperatures, the resonance near
δ 12 is thought to be due to excess HOTf, hydrogen-
bonded to itself in aggregates [(HOTf)n] or possibly not
fully dissolved in solution at the low temperatures of
the experiments. In our protonation experiments, OTf-
counterions are present as a result of partial deproto-
nation of the HOTf by the metal hydrides. Thus the
resonance near δ 17 is assigned as TfOH‚‚‚OTf-, in
which HOTf is hydrogen-bonded to an OTf- counterion,
based on the similarity of chemical shift to the HOTf/
PPN+OTf- mixture described above.
Exp er im en ta l Section
Gen er a l Meth od s. All manipulations were carried
out under an atmosphere of argon using Schlenk or
vacuum-line techniques or in a Vacuum Atmospheres
drybox. 1H NMR chemical shifts were referenced to the
residual proton peak of CD2Cl2 at δ 5.32. Solutions used
for T1 measurements were degassed by three or four
freeze-pump-thaw cycles on a high-vacuum line. The
T1 measurements were carried out on a Bruker AM-
300 (300 MHz for 1H) using the standard inversion-
recovery pulse sequence, 180°-τ-90°. Actual NMR
probe temperatures were determined54 using the mea-
sured difference in chemical shifts of the methyl and
OH protons in MeOH. Line widths of NMR resonances
(full width at half-maximum height) are abbreviated as
ω1/2. Elemental analyses were carried out by Schwarz-
kopf Microanalytical Laboratory (Woodside, NY). Cp*Os-
(CO)2H was prepared by a modification of the method
reported by Graham.55 Cp*Os(CO)2H was purified by
column chromatography on silica gel using hexane as
eluent and was further purified by sublimation at 65
°C. Cp*W(CO)3H,56 CpW(CO)3H,57 CpW(CO)2(PMe3)H,58
and [H(Et2O)2]+ BAr′4- 28 [Ar′ ) 3,5-bis(trifluoromethyl)-
phenyl] were prepared by literature methods. CpW-
(CO)2(PPh3)H was prepared by a minor modification of
a reported method,59 by refluxing a hexane solution of
CpW(CO)3H with an equimolar amount of PPh3 for 5
h. HOTf was distilled and stored under Ar. PPN+OTf-
was prepared from reaction of AgOTf and PPN+Cl- in
CH2Cl2, followed by recrystallization from CH2Cl2/Et2O.
P r oton a tion of Cp *Os(CO)2H To Give [Cp *Os-
(CO)2(H)2]+OTf- a n d [Cp *Os(CO)2(η2-H2)]+OTf-. T1
Mea su r em en ts. Cp*Os(CO)2H (22.8 mg, 0.0596 mmol)
was placed in an NMR tube equipped with a J . Young
valve, and CD2Cl2 was added to give a volume of 0.65
mL. 1,2-Dichloroethane (3 µL, internal standard) was
added. The chemical shifts of Cp*Os(CO)2H are tem-
perature dependent. 1H NMR of Cp*Os(CO)2H at 22
°C in CD2Cl2: δ 2.20 (s, Cp*), δ -14.08 (s, OsH). 1H
NMR of Cp*Os(CO)2H at -80 °C in CD2Cl2: δ 2.13 (s,
Cp*), δ -14.21 (s, OsH). The T1 of the hydride (with
no acid added) was found to be 5.9 s at -80 °C. HOTf
was added at room temperature in 2 µL (0.023 mmol)
increments. After each addition of HOTf, the solution
(54) Van Geet, A. L. Anal. Chem. 1970, 42, 679-680.
(55) Hoyano, J . K.; May, C. J .; Graham, W. A. G. Inorg. Chem. 1982,
21, 3095-3099.
Con clu sion s
The tungsten hydride Cp*W(CO)3H and the osmium
hydride Cp*Os(CO)2H are only partially protonated by
1 equiv of HOTf, giving protonated species having aci-
dities comparable to that of HOTf. The resultant tung-
sten complex is a dihydride, [Cp*W(CO)3(H)2]+OTf-,
while the protonation of the osmium complex gives an
(56) Kubas, G. J .; Kiss, G.; Hoff, C. D. Organometallics 1991, 10,
2870-2876.
(57) Keppie, S. A.; Lappert, M. F. J . Chem. Soc. A 1971, 3216-3220.
(58) Kalck, P.; Poilblanc, R. J . Organomet. Chem. 1969, 19, 115-
121.
(59) Bainbridge, A.; Craig, P. J .; Green, M. J . Chem. Soc. A 1968,
2715-2718.

Protonation of Metal Hydrides by Strong Acids
Organometallics, Vol. 15, No. 10, 1996 2513
Ta ble 3. T1 Da ta fr om P r oton a tion of
Ta ble 4. Lin e Wid th s of Hyd r id e, Dih yd r id e, a n d
Dih yd r ogen Reson a n ces fr om P r oton a tion of
Cp *Os(CO)2H by HBF 4‚OEt2
Cp *Os(CO)2H
obs
T1 (s)
ω
1/2(HOs)
ω
1/2((H)2Os)
(δ -10.00)
ω
1/2((η2H2)Os)
(δ -7.25)
equiv of
%
δ -14.21, δ -10.00, δ 12.24, δ 17.09,
temp (°C)
(d -14.23)
HOTfa protonationb hydride dihydride HOTf
HOTf
-75
-89
-98
90
32
16
8
10
15
very broad
200
100
0.33
0.73
1.2
1.5
2.3
9
21
36
49
66
72
1.2
0.99
0.79
0.88
1.0
1.0
1.2
0.21
0.17
0.15
0.16
0.15
0.16
0.32
0.19
0.16
0.18
0.15
0.16
0.60
0.38
0.33
0.19
0.17
at 22 °C; after 20 days, the sum of [Cp*Os(CO)2-
(H)2]+OTf- + [Cp*Os(CO)2(η2-H2)]+OTf- was 32% of the
initial amount of Cp*Os(CO)2H. While clean decompo-
sition to metal triflates is observed3 from reaction of
many metal hydrides with HOTf, the metal triflate
Cp*Os(CO)2OTf (δ 2.00)60 was not the sole product
observed here, since it formed in only 23% yield after
20 days in this experiment. The other decomposition
2.5
a
Equiv of HOTf determined by integration of the two HOTf
b
resonances plus the two protonated products. % protonation
includes dihydride and dihydrogen complexes, as a percentage of
total [Os].
was freeze-pump-thawed three times on a high-
vacuum line, and the tube was refilled with argon.
NMR spectra were recorded at -80 °C, the intensities
of the resonances were integrated vs the internal
standard, and T1 values were determined. 1H NMR of
[Cp*Os(CO)2(H)2]+OTf- at -80 °C in CD2Cl2: δ 2.38 (s,
Cp*), δ -10.00 (s, Os(H)2). 1H NMR of [Cp*Os(CO)2(η2-
H2)]+OTf- at -80 °C in CD2Cl2: δ 1.92 (s, Cp*), δ -7.24
(br, ω1/2 ≈ 70 Hz, η2-H2). Typical line widths for the
hydride and dihydride resonances were 7 Hz. Broad
resonances (ω1/2 ≈ 15-20 Hz) were observed for HOTf
at δ 12.24 and δ 17.09. The relative integrations of the
δ 12.24:δ 17.09 peaks remained constant at 75((3):25-
((3); the resonance at 12.24 typically integrated to 1.5-
1.7 H compared to the sum of [Cp*Os(CO)2(H)2]+ and
[Cp*Os(CO)2(η2-H2)]+. Results of the T1 measurements
at -80 °C are found in Table 3. Addition of more HOTf
(6 µL, total of 18 µL added) resulted in complete
protonation of Cp*Os(CO)2H. The acid resonances
1
product formed in 41% yield after 20 days and had H
NMR resonances (δ 2.20, 30 H, Cp*; δ -19.60, 1 H, µ-H)
consistent with a tentative assignment as a bimetallic
cation with a bridging hydride, {(µ-H)[Cp*Os(CO)2]2}+-
OTf-. This product has the same Cp* chemical shift at
22 °C as pure samples of Cp*Os(CO)2H, but it is
straightforward to distinguish it from the Cp*Os(CO)2H,
since, under these conditions at 22 °C with excess acid
present, the Cp* peaks of [Cp*Os(CO)2(H)2]+OTf- and
[Cp*Os(CO)2(η2-H2)]+OTf- appear as a coalesced singlet
at δ 2.44. The resonances assigned to {(µ-H)[Cp*Os-
(CO)2]2}+OTf- are similar to those (δ 2.06, 30 H, Cp*,
and -17.65, 1 H, µ-H) reported61 for the analogous Ru
-
complex {(µ-H)[Cp*Ru(CO)2]2}+BF4
.
Precedent for
formation of a bridging hydride by decomposition of a
dihydrogen complex comes from thermal decomposition
of [Cp*Ru(CO)2(η2-H2)]+BF4-, which gives15 {(µ-H)[Cp*-
Ru(CO)2]2}+BF4-. Similarly, protonation of Cp*Re(CO)-
(NO)H with HBF4‚OEt2 gives a equilibrium mixture of
dihydride and dihydrogen complexes that decompose to
{(µ-H)[Cp*Re(CO)(NO)]2}+BF4-, while protonation of
Cp*Re(CO)(NO)H with HOTf ultimately leads to Cp*Re-
(CO)(NO)OTf as a decomposition product.15
P r ot on a t ion of Cp *Os(CO)2H b y H BF 4‚OE t 2.
Cp*Os(CO)2H (21.0 mg, 0.0549 mmol) was placed in an
NMR tube equipped with a screw cap, and CD2Cl2 was
added to give a volume of 0.65 mL. HBF4‚OEt2 (8.5 µL,
∼0.058 mmol, ∼1.1 equiv) was added at room temper-
ature, and NMR spectra were recorded at -75, -89, and
-98 °C. Line widths (ω1/2 in Hz) of hydride resonances
are found in Table 4.
P r oton a tion of Cp W(CO)3H To Give [Cp W(CO)3-
(H)2]+OTf-. T1 Mea su r em en ts. CpW(CO)3H (21.3
mg, 0.0638 mmol) was placed in an NMR tube, and CD2-
Cl2 was added to give a volume of 0.62 mL. 1,2-
Dichloroethane (4 µL, internal standard) was added.
The chemical shifts of CpW(CO)3H are temperature
dependent. 1H NMR of CpW(CO)3H at 22 °C in CD2-
Cl2: δ 5.52 (s, Cp), δ -7.32 (s with W satellites; J WH
37 Hz, WH). 1H NMR of CpW(CO)3H at -80 °C in CD2-
Cl2: δ 5.49 (s, Cp), δ -7.45 (s with W satellites, J WH
obs
obs
moved to δ 12.01 (T1 ) 0.37 s) and δ 16.03 (T1
0.42 s) (28:72 relative areas).
)
T1 Mea su r em en ts of Cp *Os(CO)2H a t 23 °C. In a
separate experiment carried out similarly to that de-
scribed above, a T1 measurement was carried out on a
solution of Cp*Os(CO)2H in CD2Cl2. The T1 of the
hydride was determined to be 51 s at 23 °C, and that of
the CH3 groups of the Cp* ligand was measured as 5.1
s.
IR Spectr a of [Cp*Os(CO)2(H)2]+OTf- an d [Cp*Os-
(CO)2(η2-H2)]+OTf-. Cp*Os(CO)2H (15 mg, 0.039 mmol)
was dissolved in CH2Cl2 (2.0 mL, volumetric flask). IR
of Cp*Os(CO)2H in CH2Cl2: ν(CO) 1990 (s), 1923 (s)
cm-1. HOTf (25 µL, 0.28 mmol, 7.2 equiv) was added,
and an IR spectrum was recorded (0.1 mm path length;
NaCl windows). As shown in Figure 1, IR bands
(absorbance) were observed at 2118 (0.25), 2090 (0.13),
2069 (0.39), and 2042 (0.12) cm-1
. Fitting of these
partially overlapping bands gave the following band
maxima (relative areas in parentheses; arbitrary
units): 2118 (3.13), 2091 (1.00), 2068 (6.87), 2040 (1.99)
cm-1. As described in the text, the OC-Os-CO angles
estimated from the intensities of these IR bands are
112° for [Cp*Os(CO)2(H)2]+OTf- and 109° for [Cp*Os-
(CO)2(η2-H2)]+OTf-.
Decom p osition P r od u cts F or m ed fr om Cp *Os-
(CO)2H + HOTf. Cp*Os(CO)2H (23.2 mg, 0.0607
mmol) was placed in an NMR tube, and CD2Cl2 was
added to give a volume of 0.61 mL. 1,2-Dichloroethane
(2 µL, internal standard) was added. HOTf (15 µL, 0.17
mmol, 2.8 equiv) was added, giving complete protona-
tion of Cp*Os(CO)2H. This solution decomposed slowly
)
)
37 Hz, WH). At -80 °C, the T1 of the hydride was
determined to be 11.2 s and the T1 of the Cp was 7.6 s.
HOTf (7 µL, 0.079 mmol, 1.2 equiv) was added, and an
(60) The metal triflate complex Cp*(CO)2OsOTf is formed cleanly3
from the ionic hydrogenation of Me2CdCMe2 by HOTf and Cp*(CO)2-
OsH. IR (CH2Cl2) of Cp*(CO)2OsOTf: 2034 (s), 1976 (s) cm-1
.
(61) Stasunik, A.; Malisch, W. J . Organomet. Chem. 1984, 270, C56-
C62.

2514 Organometallics, Vol. 15, No. 10, 1996
Bullock et al.
Ta ble 5. T1 Da ta (-80 °C) a n d Assign m en ts fr om
Ta ble 7. T1 Da ta (-78 °C) a n d Assign m en ts fr om
P r oton a tion of Cp *W(CO)3H by Excess HOTf
P r oton a tion of Cp W(CO)3H by HOTf
obs
chem shift (δ)
T1 (s)
assgnt
chem shift (δ)
T1 (s)
assgnt
14.19
5.92
5.50
-2.07
-7.45
1.8
7.2
7.6
1.8
3.7
HOTf
13.1
2.32
-2.33
1.9
0.76
0.49
HOTf
Cp of CpW(CO)3H
Cp of [CpW(CO)3(H)2]+
W(H)2
Cp* of [Cp*W(CO)3(H)2]+
W(H)2
WH
solution of [Cp*W(CO)3(H)2]+OTf- turned red as it
slowly decomposed to Cp*(CO)3WOTf (δ 2.08, 48% yield
after 2.5 days at 22 °C).
Ta ble 6. T1 Da ta (-78 °C) a n d Assign m en ts fr om
P r oton a tion of Cp *W(CO)3H by HOTf (1.1 Equ iv)
IR Sp ectr u m of [Cp *W(CO)3(H)2]+OTf-. Cp*W-
(CO)3H (9.7 mg, 0.024 mmol) was dissolved in CH2Cl2
(1.0 mL). IR of Cp*W(CO)3H: ν(CO) 2006 (s), 1909 (s)
cm-1. HOTf (20 µL, 0.22 mmol, 9.4 equiv) was added,
and the IR spectrum of [Cp*W(CO)3(H)2]+ exhibited ν-
obs
chem shift (δ)
T1 (s)
assgnt
16.8
12.1
2.33
2.11
0.33
0.34
0.72
0.78
0.52
0.87
HOTf‚‚‚OTf-
HOTf
Cp* of [Cp*W(CO)3(H)2]+
Cp* of Cp*W(CO)3H
-2.33 (ω1/2 ) 25 Hz)
-7.03 (ω1/2 ) 5 Hz)
W(H)2
WH
(CO) bands at 2119 (s), 2075 (vs), and 2057 (s) cm-1
.
P r epar ation of [CpW(CO)2(P Me3)(H)2]+OTf-. HOTf
(105 µL, 1.19 mmol) was added to a solution of CpW-
(CO)2(PMe3)H (384 mg, 1.00 mmol) in CH2Cl2 (10 mL).
The solution was stirred for 10 min at 22 °C, during
which time it turned from yellow to colorless. Et2O (10
mL) and hexane (30 mL) were added by vacuum
transfer to produce a white precipitate, which was
collected by filtration, washed with Et2O (30 mL), and
dried under vacuum to give [CpW(CO)2(PMe3)(H)2]+O-
Tf- (522 mg, 0.98 mmol, 98%). 1H NMR (CD2Cl2): δ
5.70 (s, 5H, Cp), 1.88 (d, J PH ) 9.6 Hz, 9H, PMe3), -2.48
(d, J PH ) 40 Hz, 2H, W(H)2). 13C NMR (CD2Cl2, 250
K): 202.0, 200.4 (br, CO), 120.7 (q, J CF ) 318.9 Hz, CF3),
88.2 (Cp), 23.5 (d, J PC ) 38.9 Hz, PMe3). 31P{1H} NMR
NMR spectrum recorded at -80 °C indicated that 16%
of the CpW(CO)3H had been protonated to form [CpW-
(CO)3(H)2]+OTf-. 1H NMR of [CpW(CO)3(H)2]+OTf- at
-80 °C in CD2Cl2: δ 5.92 (s, Cp), δ -2.07 (s, ω1/2 ) 12
Hz, W(H)2). The resonance observed at δ 14.19 (ω1/2
)
12 Hz) is assigned to HOTf. Results of T1 measure-
ments on this solution at -80 °C are found in Table 5.
T1 Mea su r em en t of Cp W(CO)3H a t 29 °C. In a
separate experiment carried out similarly to that de-
scribed above, a T1 measurement was carried out on a
solution of CpW(CO)3H (0.1 M) in CD2Cl2. The T1 of
the hydride was determined to be 85 s at 29 °C, and
that of the Cp ligand was measured as 52 s.
1
(CD2Cl2): δ -32.3 (s, J PW ) 204 Hz). IR (CH2Cl2): ν-
P r oton a tion of Cp *W(CO)3H To Give [Cp *W-
(CO)3(H)2]+OTf-. T1 Mea su r em en ts. Cp*W(CO)3H
(24.0 mg, 0.0594 mmol) was placed in an NMR tube,
and CD2Cl2 was added to give a volume of 0.63 mL. 1,2-
Dichloroethane (3 µL, internal standard) was added.
The chemical shifts of Cp*W(CO)3H are temperature
dependent. 1H NMR of Cp*W(CO)3H at 22 °C in CD2-
(CO)asym 2073 (rel intensity 1.0), 2016 (rel intensity 1.25)
cm-1; calculated6 OC-W-CO ) 96°. Anal. Calcd for C11-
H16F3O5PSW: C, 24.83; H, 3.03. Found: C, 25.13; H,
3.24.
Collection a n d Red u ction of X-r a y Da ta . Crystals
of [CpW(CO)2(PMe3)(H)2]+OTf- were prisms grown from
slow diffusion of hexane into a CH2Cl2 solution at -50
°C. A crystal (0.28 × 0.30 × 0.48 mm) was coated with
petroleum jelly and sealed inside a glass capillary. The
diffraction data measured on an Enraf Nonius CAD-4
diffractometer indicated orthorhombic symmetry with
systematic absences h00, h ) 2n + 1, 0k0, k ) 2n + 1,
and 00l, l ) 2n + 1 consistent with the space group
P212121.
1
Cl2: δ 2.20 (s, Cp*), δ -6.86 (s, J WH ) 40 Hz, WH). H
NMR of Cp*W(CO)3H at -80 °C in CD2Cl2: δ 2.12 (s,
Cp*), δ -7.03 (s with W satellites, J WH ) 40 Hz, WH).
The T1 of the hydride was determined to be 6.4 s at -80
°C. HOTf (6 µL, 0.068 mmol, 1.1 equiv) was added, and
the color of the solution turned from pale yellow to
slightly darker yellow. The NMR spectrum at -36 °C
exhibited a single broad (ω1/2 ) 59 Hz) Cp* resonance
at δ 2.23; separate resonances were observed for the
dihydride [Cp*W(CO)3(H)2]+OTf- (δ -2.27, ω1/2 ) 80 Hz)
and for the hydride (δ -6.95, ω1/2 ) 70 Hz). At -57 °C,
separate Cp* resonances were observed for the hydride
(δ 2.14) and dihydride (δ 2.36). Along with resonances
for the hydride (δ -6.98) and dihydride (δ -2.29)
observed at -57 °C, broad resonances were observed at
δ 16.4 and 12.2. Further cooling of the solution to -78
°C and integration of the resonances indicated that the
ratio of Cp*W(CO)3H to [Cp*W(CO)3(H)2]+OTf- was 1:1.
A resonance at δ 16.8 (ω1/2 ) 25 Hz) integrated to 1.0
proton compared to the dihydride, and the resonance
at δ 12.1 (ω1/2 ) 40 Hz) integrated to 0.4 protons
compared to the dihydride. Results of T1 measurements
on this solution at -78 °C are found in Table 6.
Deter m in a tion a n d Refin em en t of th e Str u ctu r e.
The structure62 was solved by standard heavy-atom
Patterson methods using absorption-corrected data. In
the least-squares refinement, anisotropic temperature
parameters were used for all the non-hydrogen atoms
and the quantity ∑w(|Fo| - |Fc|)2 was minimized.
Hydrogen atoms were placed at calculated (X-H ) 0.95
Å) positions and allowed to “ride” on the atom to which
they were attached. (The two hydrogen atoms coordi-
nated to the tungsten were not included in the refine-
ment.) A common isotropic thermal parameter was
refined for the hydrogen atoms. In the final difference
Fourier map the peaks were less than (1 e-/Å3. Two
peaks, 1.83 and 1.62 Å from the tungsten, were observed
Additional HOTf (15 µL, making a total of 4 equiv of
HOTf added per Cp*W(CO)3H) was added, and the
NMR spectrum indicated complete conversion to [Cp*W-
(CO)3(H)2]+OTf-. Results of T1 measurements on this
solution at -78 °C are found in Table 7. This yellow
(62) Sheldrich, G. M. 1976, SHELX76. Crystal Structure refinement
program, Cambridge University, England. Neutral atom scattering
factors were taken from: International Tables for X-Ray Crystal-
lography; Kynoch Press: Birmingham, England, 1974; Vol. IV, pp 99-
100. Anomalous dispersion effects were taken from: Cromer, D. T.;
Liberman, D. J . Chem. Phys. 1970, 53, 1891-1898.

Protonation of Metal Hydrides by Strong Acids
Organometallics, Vol. 15, No. 10, 1996 2515
in reasonable positions to be the two coordinated
hydrogen atoms. The handedness of the structure was
checked, and the model which resulted in the lower Rw
value is reported here.
was stirred for 5 min at 22 °C, during which time the it
became colorless. Hexane (30 mL) was added by
vacuum transfer, and slow evaporation of the solvent
gave a white air-sensitive precipitate, which was col-
lected by filtration, washed with hexane (30 mL), and
dried under vacuum to give [CpW(CO)2(PCy3)-
-
P r ep a r a tion of [Cp W(CO)2(P Me3)(H)2]+BAr ′4
.
CH2Cl2 (10 mL) was vacuum-transferred into a flask
containing CpW(CO)2(PMe3)H (82 mg, 0.21 mmol) and
[H(Et2O)2]+BAr′4- (202 mg, 0.200 mmol), and the solu-
tion was stirred for 10 min at 22 °C, during which time
it turned from yellow to colorless. Hexane (30 mL) was
added, and slow evaporation of the solvent under
vacuum gave a white, air-sensitive precipitate, which
was collected by filtration, washed with hexane (50
mL), and dried under vacuum to give [CpW(CO)2-
-
(H)2]+BAr′4 (397 mg, 0.273 mmol, 99%). 1H NMR
(CD2Cl2): δ 7.73 (br, 8H, o-H), 7.57 (br, 4H, p-H), 5.56
(s, 5H, Cp), 1.97-1.78 (m, 33H, PCy3), -2.61 (d, J ) 38
Hz, 2H, W(H)2). 13C NMR (CD2Cl2, 250 K): 201.4 (br,
CO), 161.8 (1:1:1:1 quartet, J BC ) 50 Hz, ipso-C), 134.8
2
(s, o-C), 128.8 (br, q, J CF ) 31 Hz, m-C), 124.6 (q, J CF
1
) 272 Hz, CF3), 117.6 (p-C), 87.4 (Cp), 39.6 (d, J PC
)
24.7 Hz, C-1 of PCy3), 30.2 (s, C-3 of PCy3), 27.3 (d, 2J PC
) 10.6 Hz, C-2 of PCy3), 25.9 (s, C-4 of PCy3). 31P{1H}
NMR (CD2Cl2): δ 30.0 (s, J PW ) 205 Hz). IR (CH2-
-
(PMe3)(H)2]+BAr′4 (228 mg, 0.183 mmol, 92%). 1H
1
NMR (CD2Cl2): δ 7.73 (br, 8H, o-H), 7.58 (br, 4H, p-H),
5.48 (s, 5H, Cp), 1.79 (d, J ) 10.5 Hz, 9H, PMe3), -2.42
(d, J ) 41 Hz, 2H, W(H)2). 13C NMR (CD2Cl2, 250 K):
201.4 (br, CO), 161.5 (1:1:1:1 quartet, J BC ) 50.2 Hz,
Cl2): ν(CO)asym 2069 (rel intensity 1.0), ν(CO)sym 2013
(rel intensity 1.09) cm-1; calculated6 OC-W-CO ) 93°.
Anal. Calcd for C57H52BF24O2PW: C, 47.19; H, 3.61.
Found: C, 46.89; H, 3.54.
2
ipso-C), 134.5 (o-C), 128.4 (br, q, J CF ) 29 Hz, m-C),
1
-
P r ep a r a t ion of [Cp W(CO)2(P P h 3)(H )2]+BAr ′4
.
124.2 (q, J CF ) 272 Hz, CF3), 117.3 (p-C), 87.3 (Cp),
23.6 (d, J PC ) 39 Hz, PMe3). 31P{1H} NMR (CD2Cl2,
CH2Cl2 (5 mL) was vacuum-transferred into a flask
containing Cp(CO)2(PPh3)WH (135 mg, 0.238 mmol) and
[H(Et2O)2]+BAr′4- (200 mg, 0.198 mmol). The solution
was stirred for 5 min at 22 °C, and hexane (10 mL) was
added by vacuum transfer. Slow evaporation of the
solvent under vacuum gave a white precipitate, which
was collected by filtration, washed with hexane (20 mL),
and dried under vacuum to give [CpW(CO)2(PPh3)-
1
295 K): δ -32.4 (s, J PW ) 208 Hz). IR (CH2Cl2): ν-
(CO)asym 2079 (rel intensity 1.0), ν(CO)sym 2023 (rel
intensity 1.33) cm-1; calculated6 OC-W-CO ) 98°.
Anal. Calcd for C42H28BF24O2PW: C, 40.47; H, 2.26.
Found: C, 40.57; H, 2.37.
P r ep a r a tion of Cp W(CO)2(P Cy3)H. A solution of
CpW(CO)3H (1.0 g, 3.0 mmol) and PCy3 (820 mg, 2.92
mmol) in toluene (50 mL) was heated under reflux for
15 h. The solvent was evaporated under vacuum, and
the residue was washed with hexane (60 mL) to give a
pale yellow solid (1.68 g, 2.86 mmol, 98%). 1H NMR
(CD2Cl2): δ 5.31 (s, 5H, Cp), 1.85-1.24 (br, m, 33H,
P(C6H11)3), -7.65 (br d, J PH ) 65 Hz, 1H, WH). IR (CH2-
Cl2): ν(CO) 1915 (vs), 1821 (s) cm-1. Anal. Calcd for
C25H39O2PW: C, 51.20; H, 6.70. Found: C, 51.19; H,
6.54.
-
(H)2]+BAr′4 (277 mg, 0.193 mmol, 98%). 1H NMR
(CD2Cl2): δ 7.74 (br, 8H, o-H), 7.57 (br, 4H, p-H), 7.56-
7.31 (m, 15H, PPh3), 5.37 (s, 5H, Cp), -1.33 (d, J ) 38
Hz, 2H, W(H)2). 13C NMR (CD2Cl2, 250 K): 201.4 (br,
CO), 161.8 (1:1:1:1 quartet, J BC ) 51 Hz, ipso-C), 134.8
2
(s, o-C), 132.9 (d, J PC ) 10 Hz, o-C of PPh3), 132.4 (s,
1
p-C of PPh3), 131.8 (d, J PC ) 57 Hz, ipso-C of PPh3),
3
2
129.6 (d, J PC ) 11 Hz, m-C of PPh3), 128.4 (br, q, J CF
1
) 32 Hz, m-C), 124.6 (q, J CF ) 273 Hz, CF3), 117.6 (p-
C), 89.4 (Cp). 31P{1H} NMR (CD2Cl2): δ 17.3 (s, J PW
1
P r epar ation of [CpW(CO)2(P Cy3)(H)2]+OTf-. HOTf
(50 µL, 0.56 mmol) was added to a solution of
CpW(CO)2(PCy3)H (300 mg, 0.512 mmol) in CH2Cl2 (10
mL). The solution was stirred for 5 min at 22 °C, during
which time the color changed from yellow to pale yellow.
Hexane (30 mL) was added by vacuum transfer. The
resulting air- and temperature-sensitive white precipi-
tate was collected by filtration, washed with hexane (30
mL), and dried under vacuum to give [CpW(CO)2-
(PCy3)(H)2]+OTf- (340 mg, 0.462 mmol, 90%). This
compound is thermally unstable. In CD2Cl2 solution,
it decomposes with an approximate halflife of 16 h at
room temperature, and it eventually turns black even
when stored as a solid. 1H NMR (CD2Cl2): δ 5.65 (s,
5H, Cp), 1.94-1.24 (br, m, 33H, P(C6H11)3), -2.78 (br,
d, J PH ) 38 Hz, 2H, W(H)2). 13C NMR (CD2Cl2, 220 K):
203.0 (br, CO), 119.0 (q, J CF ) 316 Hz, CF3), 87.3 (Cp),
38.8 (d, 1J PC ) 24 Hz, C-1 of PCy3), 29.6 (s, C-3 of PCy3),
26.9 (d, 2J PC ) 8.5 Hz, C-2 of PCy3), 25.5 (s, C-4 of PCy3).
) 205 Hz). IR (CH2Cl2): ν(CO)asym 2078 (rel intensity
1.0), ν(CO)sym 2025 (rel intensity 1.08) cm-1; calculated6
OC-W-CO ) 92°.
T1 Mea su r em en t of HOTf a t 25 °C. An 0.1 M
solution of HOTf in CD2Cl2 was prepared by adding
HOTf (5.5 µL, 0.062 mmol) to CD2Cl2 (0.61 mL). The
solution was freeze-pump-thawed three times on a
high-vacuum line, and a T1 measurement at 25 °C gave
a value of 9.4 s.
Con cen t r a t ion Dep en d en ce of t h e 1H NMR
Ch em ica l Sh ift of HOTf in CD2Cl2. NMR spectra
were recorded at 22 °C on a CD2Cl2 solution (0.62 mL)
in which HOTf was added in 2 µL increments. The
chemical shift of the HOTf peak as a function of
concentration is shown in Figure 6; the plot is linear (R
) 0.997) up to [HOTf] ) 0.22 M. The concentration of
HOTf in the plot represents the concentration of HOTf
added to the solution, although the data suggest that
some of it may not be dissolved in solution above [HOTf]
) 0.22 M. The equation is ppm ) 3.09(ppm/M)[HOTf]
+ 8.04 ppm, indicating a chemical shift of δ 8.04 for
HOTf at infinite dilution in CD2Cl2. Above [HOTf] )
0.22 M, the chemical shift continued to move downfield
as [HOTf] increased, but the change was nonlinear.
Broad resonances at δ 11.8 and δ 11.5 were observed
above this concentration. The resonance at δ 11.8 was
1
31P{1H} NMR (CD2Cl2): δ 30.1 (s, J PW ) 207 Hz). IR
(CH2Cl2): ν(CO)asym 2068 (rel intensity 1.0), ν(CO)sym
2011 (rel intensity 1.08) cm-1; calculated6 OC-W-CO
) 92°.
-
P r ep a r a t ion of [Cp W(CO)2(P Cy3)(H )2]+BAr ′4
.
CH2Cl2 (10 mL) was vacuum-transferred into a flask
containing CpW(CO)2(PCy3)H (190 mg, 0.324 mmol) and
[H(Et2O)2]+BAr′4- (280 mg, 0.276 mmol). The mixture

2516 Organometallics, Vol. 15, No. 10, 1996
Bullock et al.
4.5 s for the aromatic protons of PPN+). When the
solution was cooled to -80 °C, the HOTf resonance
moved to δ 17.15, but the T1 of HOTf remained at 1.5 s
(T1 ≈ 1.0 s for the aromatic protons of PPN+ at -80
°C). The integration of HOTf at -80 °C dropped to 73%
of the amount at 25 °C, and broad resonances were
observed around δ 12 at -80 °C.
1
Tem per atu r e Depen den ce of th e H NMR Ch em i-
ca l Sh ift of HOTf in CD2Cl2. A singlet (δ 8.37, ω1/2
)
3 Hz) was observed at 22 °C for a CD2Cl2 solution (0.59
mL) containing HOTf (5 µL, 0.1M). At -50 °C, the
chemical shift of the singlet had changed to δ 9.23, and
the integrated intensity of this peak (relative to 1,2-
dichloroethane internal standard) dropped to 66% of the
initial value. Broad resonances were observed at δ 11.4
(ω1/2 ≈ 40 Hz, 19%) and at δ 10.9 (12%), indicating a
mass balance of 97% of the initial intensity of the
resonance that was measured at 22 °C. At -80 °C a
singlet was observed at δ 9.00 which accounted for only
8% of the initial intensity.
F igu r e 6. Plot of 1H NMR chemical shift vs concentration
of HOTf (CD2Cl2; 22 °C).
Ta ble 8. 1H NMR Ch em ica l Sh ifts of HOTf in th e
P r esen ce of P P N+OTf- (0.09 M)
µL of HOTf [HOTf] δ (ppm) µL of HOTf [HOTf] δ (ppm)
added
(M)
of HOTf
added
(M)
of HOTf
6
12
0.10
0.20
16.19
14.11
18
24
0.31
0.41
13.11
12.62
Ack n ow led gm en t. This research was carried out
at Brookhaven National Laboratory under Contract DE-
AC02-76CH00016 with the U.S. Department of Energy
and supported by its Division of Chemical Sciences,
Office of Basic Energy Sciences. We thank Prof. J ack
Norton, Prof. Michael Heinekey, Prof. Lee Brammer, Dr.
Mark Andrews, Dr. Thomas Koetzle, and Dr. Gerald
Cook for helpful comments and the reviewers for helpful
suggestions on the organization of the paper.
initially larger, but the resonance at 11.5 increased in
relative intensity as [HOTf] increased. When 18 µL
HOTf had been added, the solution was cloudy and the
resonances at δ 11.8 and 11.5 were of equal peak
heights, with both having ω1/2 ≈ 60 Hz.
Effect of Ad d ed P P N+OTf- on th e Ch em ica l
Sh ift of HOTf in CD2Cl2. NMR spectra were recorded
on a CD2Cl2 solution (0.66 mL) containing PPN+OTf-
(41 mg, 0.060 mmol, 0.09 M; PPN ) bis(triphenylphos-
phine)nitrogen(1+), Ph3PNPPh3) in which HOTf was
added in 6 µL increments. The resonance was observed
as a broad singlet, and the chemical shifts are found in
Table 8.
Su p p or tin g In for m a tion Ava ila ble: Tables giving ad-
ditional experimental details of the X-ray diffraction structure,
final anisotropic thermal parameters for the non-hydrogen
atoms, calculated hydrogen atom positions, complete inter-
atomic distances and angles, atomic coordinates and thermal
parameters, and a table of distances and angles for the
hydrogen-bonding interactions (8 pages). This material is
contained in many libraries on microfiche, immediately follows
this article in the microfilm version of the journal, can be
ordered from the ACS, and can be downloaded from the
Internet; see any current masthead page for ordering informa-
tion and Internet access instructions.
Effect of P P N+OTf- on th e T1 of HOTf in CD2Cl2.
HOTf (5.5 µL, 0.062 mmol, 0.095 M), PPN+OTf- (41 mg,
0.060 mmol, 0.09 M), and 1,2-dichloroethane (3 µL,
internal standard) were added to CD2Cl2 (0.65 mL) in
an NMR tube. The solution was freeze-pump-thawed
three times on a high-vacuum line, and a T1 measure-
ment at 25 °C for HOTf (δ 16.11) gave T1 ) 1.5 s (T1 ≈
OM950976Y