Activation of C(sp2)-H and Reduction of C=E (E = CH, N) bonds with an osmium-hexahydride complex: Influence of E on the behavior of RCH=E-py substrates

Article abstract of DOI:10.1021/om0497036

The activation of C-H bonds by transition metal compounds was investigated. It was found that the short-lived intermediate species OsH ₂(η²-H₂)(PⁱPr₃ ) ₂ reacts with RCH double bond E-py or

Full text of DOI:10.1021/om0497036

Organometallics 2004, 23, 3627-3639
3627
Activa tion of C(sp 2)-H a n d Red u ction of CdE (E ) CH,
N) Bon d s w ith a n Osm iu m -Hexa h yd r id e Com p lex:
In flu en ce of E on th e Beh a vior of RCHdE-p y Su bstr a tes
Pilar Barrio, Miguel A. Esteruelas,* and Enrique On˜ate
Departamento de Quı´mica Inorga´nica, Instituto de Ciencia de Materiales de Arago´n,
Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain
Received April 26, 2004
The hexahydride complex OsH6(PiPr3)2 (1) reacts with 2-vinylpyridine to give the trihydride
derivative OsH3(NC5H4-o-CHdCH)(PiPr3)2 (2). The â- and γ-positions of the pyridine ring
are quantitatively and selectively deuterated by addition of 1 (5%) to toluene-d8 and benzene-
d6 solutions of 2. Under hydrogen atmosphere, 2 reacts with HBF4‚OEt2 to afford [HNC5H4-
o-Et]BF4 and regenerate 1. Under argon atmosphere, the addition of HBF4‚OEt2 to
dichloromethane solutions of 2 leads to the hydride-dihydrogen [OsH(η2-H2)(η2-CH2dCH-
o-C5H4N)(PiPr3)2]BF4 (3), which catalyzes the hydrogenation of 2-vinylpyridine to 2-ethylpy-
ridine. In dichloromethane 3 evolves into the neutral chloro-dihydrogen compound Os(NC5H4-
o-CHdCH)Cl(η2-H2)(PiPr3)2 (4). Complex 1 also reacts with N-methylene-2-pyridinamine and
(E)-N-(phenylmethylene)-2-pyridinamine. The reaction with the first pyridinamine leads to
a 3:1 mixture of the trihydride complexes OsH3(NC5H4-o-NCH3)(PiPr3)2 (5) and OsH3(NC5H4-
o-NdCH)(PiPr3)2 (6), while the reaction with the second one selectively affords OsH3(NC5H4-
o-NCH2Ph)(PiPr3)2 (7). Similarly to 2, the addition of 1 (5%) to toluene-d8 and benzene-d6
solutions of 6 produces the quantitative and selective deuteration of the â- and γ-positions
of the pyridine ring. The addition of HBF4‚OEt2 to diethyl ether solutions of 5 leads to [OsH3-
(NC5H4-o-NHCH3)(PiPr3)2]BF4 (8). Isotope labeling experiments suggest that the reduction
of the CdC double bond of 2-vinylpyridine takes place by concerted addition of a dihydrogen
ligand, while the reduction of the CdN double bond of N-methylene-2-pyridinamine occurs
by sequential addition of H- and H+. In solution the hydride ligands of these compounds
undergo two different site exchange processes. Their activation parameters have been
calculated by 1H NMR spectroscopy. Complexes 2, 3, and 5 have been characterized by X-ray
diffraction analyses.
In tr od u ction
niscent species of the intermediates proposed by Murai
for the insertion of olefins into ortho-CH bonds of
ketones and imines4 and for the arylation of aromatic
ketones with arylboronates.5
In addition to aromatic ketones and imines, interme-
diate OsH2(η2-H2)(PiPr3)2 activates cyclohexylmethyl
ketone and aromatic and alkyl aldehydes. The reaction
with cyclohexylmethyl ketone affords the cyclohexenyl-
The activation of C-H bonds by transition metal
compounds is a type of reaction of general interest due
to its connection with the functionalization of nonacti-
vated organic molecules.1 Although it is rare with high-
valent metal complexes, we have recently shown that
the saturated d2 hexahydride OsH6(PiPr3)2 can be
thermally activated to generate the unsaturated short-
lived dihydride-dihydrogen OsH2(η2-H2)(PiPr3)2, which
activates ortho-CH bonds of aromatic ketones and
imines3 and ortho-CF bonds of partially fluorinated
ketones.2 The reactions give complexes that are remi-
keto complex OsH3{C6H8C(O)CH3}(PiPr3)2, as a result
of a triple C(sp3)-H activation of the cyclohexyl sub-
stituent.6 The reactions with aldehydes lead to acyl
species, as a consequence of C(sp2)-HR activation
processes. These acyl derivatives are highly unstable
and rapidly evolve to different types of isolated com-
* Corresponding author. E-mail: maester@posta.unizar.es.
(1) (a) Shilov, A. E.; Shul’pin, G. B. Chem. Rev. 1997, 97, 2879. (b)
J ia, C.; Kitamura, T.; Fujiwara, Y. Acc. Chem. Res. 2001, 34, 633. (c)
Ritleng, V.; Sirlin, C.; Pfeffer, M. Chem. Rev. 2002, 102, 1731.
(2) Barrio, P.; Castarlenas, R.; Esteruelas, M. A.; Lledo´s, A.;
Maseras, F.; On˜ate, E.; Toma`s, J . Organometallics 2001, 20, 442.
(3) Barea, G.; Esteruelas, M. A.; Lledo´s, A.; Lo´pez, A. M.; On˜ate,
E.; Tolosa, J . I. Organometallics 1998, 17, 4065.
(4) Kakiuchi, F.; Murai, S. Acc. Chem. Res. 2002, 35, 826.
(5) Kakiuchi, F.; Kan, S.; Igi, K.; Chatani, N.; Murai, S. J . Am. Chem.
Soc. 2003, 125, 1698.
(6) Barrio, P.; Castarlenas, R.; Esteruelas, M. A.; On˜ate, E. Orga-
nometallics 2001, 20, 2635.
10.1021/om0497036 CCC: $27.50 © 2004 American Chemical Society
Publication on Web 06/16/2004

3628 Organometallics, Vol. 23, No. 15, 2004
Barrio et al.
pounds, including OsH2(CO)2(PiPr3)2, OsHPh(CO)2-
(PiPr3)2, and OsH3(κ2-O2CR)(PiPr3)2.7
Hydride complexes of platinum group metals have
shown to be effective reducing agents for the transfor-
mation of olefins to alkanes. It is assumed that two
hydrides are transferred sequentially to the olefin. The
transfer of the first of them yields hydride-alkyl species,
which evolve into the alkane by intramolecular reduc-
tive elimination (eqs 1 and 2).8
The mechanism of the addition of molecular hydrogen
to transition metal complexes goes through a dihydro-
gen intermediate. The kinetic acidity of dihydrogen
complexes is much greater than their corresponding
dihydrides.9 In agreement with this, there is increasing
evidence showing that polar CdX bonds (X ) N, O) can
be also reduced by an ionic mechanism involving the
rapid and reversible protonation of the substrate, fol-
lowed by the hydride transfer from the metal (eqs 3 and
4).10
F igu r e 1. Molecular diagram of complex OsH3(NC5H4-o-
CHdCH)(PiPr3)2 (2).
In this paper, we report the results of this study.
Resu lts a n d Discu ssion
1. Rea ction s of OsH6(P iP r 3)2 w ith 2-Vin ylp yr i-
d in e. Treatment under reflux of toluene solutions of the
hexahydride OsH6(PiPr3)2 (1) with 1.6 equiv of 2-vi-
nylpyridine affords after 5 h orange solutions, from
which the trihydride OsH3(NC5H4-o-CHdCH)(PiPr3)2 (2)
was isolated as a yellow solid in 83% yield (eq 5).
Complex 2 is the result of the C(sp2)-H bond activation
of the CH2 olefinic group of the substituent of the
pyridine, by the short-lived intermediate OsH2(η2-H2)-
(PiPr3)2. The formation of ethylpyridine or organome-
tallic products resulting from the insertion of the vinyl
substituent of the substrate into any of the Os-H bonds
of the starting complex was not observed during the
reaction.
At first glance, the short-lived dihydride-dihydrogen
OsH2(η2-H2)(PiPr3)2 has all the qualities to be an active
species for the following reactions: (i) the activation of
C(sp2)-H bonds of olefins and aldimines, in a manner
similar to the previously mentioned activations; (ii) the
reduction of olefins according to eqs 1 and 2, due to its
hydride character; and (iii) the reduction of aldimines
according to eqs 3 and 4, or by a similar pathway,
because its dihydrogen ligand is expected to be fairly
acidic.
Ruthenium- and osmium-polyhydride complexes have
shown to be useful templates to carbon-carbon and
carbon-heteroatom coupling reactions. The processes
involve the entry, in a consecutive and controlled way,
of organic molecules into the metallic center of the
polyhydride. The field needs much more research effort,
mainly on the control of the products from the first step
of the global process.11 Our interest in learning to
control the products of these reactions prompted us to
study the reactivity of the hexahydride OsH6(PiPr3)2
toward olefin and aldimine substrates containing a
pyridyl group. This substituent was used in order to
facilitate stable metallacycles, resulting from C(sp2)-H
activation reactions.12
Figure 1 shows a view of the molecular geometry of
2. Selected bond distances and angles are listed in Table
1. The coordination geometry around the osmium atom
can be rationalized as a distorted pentagonal bipyramid
with the two phosphorus atoms of the triisopropylphos-
phine ligands occupying axial positions (P(1)-Os-P(2)
) 165.12(4)°). The osmium sphere is completed by the
hydride ligands and the metalated group, which acts
with a bite angle of 75.40(18)°.
The bond length Os-C(7) (2.073(5) Å) is as expected
for an Os-C(sp2) single bond and similar to those found
in other alkenyl-osmium complexes (between 1.99(1)
and 2.195(5) Å).13 The C(6)-C(7) bond length of 1.347(7)
(7) Barrio, P.; Esteruelas, M. A.; On˜ate, E. Organometallics 2004,
23, 1340.
(8) Chaloner, P. A.; Esteruelas, M. A.; J oo´, F.; Oro, L. A. Homoge-
neous Hydrogenation; Kluwer Academic Publisher: Dordrecht, 1994.
(9) J essop, P. G.; Morris, R. H. Coord. Chem. Rev. 1992, 121, 155.
(10) Papish, E. T.; Magee, M. P.; Norton, J . R. In Recent Advances
in Hydride Chemistry; Peruzzini, M., Poli, R., Eds.; Elsevier: Amster-
dam, 2001; Chapter 2, pp 39-74.
(11) Esteruelas, M. A.; Lo´pez, A. M. In Recent Advances in Hydride
Chemistry; Peruzzini, M., Poli, R., Eds.; Elsevier: Amsterdam, 2001,
Chapter 7, pp 189-248.
(12) J un, C.-H.; Moon, C. W.; Lee, D.-Y. Chem. Eur. J . 2002, 8, 2423.
(13) See for example: (a) Werner, H.; Esteruelas, M. A.; Otto, H.
Organometallics 1986, 5, 2295. (b) Werner, H.; Weinand, R.; Otto, H.
J . Organomet. Chem. 1986, 307, 49. (c) Espuelas, J .; Esteruelas, M.
A.; Lahoz, F. J .; Oro, L. A.; Valero, C. Organometallics 1993, 12, 663.

Osmium-Hexahydride Complex
Organometallics, Vol. 23, No. 15, 2004 3629
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for th e Com p lex
OsH3(NC5H4-o-CHdCH)(P iP r 3)2 (2)
Os-P(1)
Os-P(2)
Os-N
Os-C(7)
Os-H(01)
2.3380(13)
2.3253(13)
2.148(4)
2.073(5)
1.43(4)
Os-H(02)
Os-H(03)
N-C(1)
C(1)-C(6)
C(6)-C(7)
1.45(4)
1.43(4)
1.371(5)
1.422(7)
1.347(7)
P(1)-Os-P(2)
P(1)-Os-N
P(1)-Os-C(7)
P(1)-Os-H(01)
P(1)-Os-H(02)
P(1)-Os-H(03)
P(2)-Os-N
165.12(4)
97.36(10) N-Os-H(03)
92.53(13) C(7)-Os-H(01)
94.6(16)
88.0(16)
83.5(16)
N-Os-H(02)
145.1(16)
152.0(16)
146.8(16)
139.0(16)
76.6(16)
74(2)
C(7)-Os-H(02)
C(7)-Os-H(03)
H(01)-Os-H(02)
97.46(10) H(01)-Os-H(03) 136(2)
63(2)
115.7(3)
P(2)-Os-C(7)
P(2)-Os-H(01)
P(2)-Os-H(02)
P(2)-Os-H(03)
N-Os-C(7)
92.39(13) H(02)-Os-H(03)
88.9(16)
79.1(16)
84.0(16)
Os-N-C(1)
Os-C(7)-C(6)
118.4(4)
114.5(4)
116.0(4)
N-C(1)-C(6)
75.40(18) C(1)-C(6)-C(7)
71.5(16)
N-Os-H(01)
Å agrees well with the average carbon-carbon double
bond distances in vinyl groups (1.35(2) Å).14 In ac-
cordance with the sp2 hybridization at C(6) and C(7),
the angles C(7)-C(6)-C(1) and C(6)-C(7)-Os are
116.0(4)° and 118.4(4)°, respectively.
The spectroscopic data of 2 are consistent with the
structure shown in Figure 1. The IR spectrum in KBr
contains two bands at 2173 and 2118 cm-1, correspond-
ing to the hydride ligands. In the 13C{1H} NMR spec-
trum in toluene-d8 at room temperature, the resonances
due to the CHdCH substituent of the pyridine are
observed at 203.9 and 158.6 ppm. The first of them,
assigned to the OsCH-carbon atom, appears as a triplet
with a C-P coupling constant of 6.4 Hz. The second one,
corresponding to the HCpy-carbon atom, is observed as
a singlet. In agreement with the mutually trans disposi-
tion of the phosphine ligands, the 31P{1H} NMR spec-
trum in toluene-d8 contains a singlet at 26.8 ppm, which
is temperature invariant between 363 and 193 K.
In contrast to the 31P{1H} NMR spectrum, the 1H
NMR spectrum is temperature-dependent. In toluene-
d8 at 363 K, it shows in the hydride region a single broad
resonance centered at -9.4 ppm. This observation is
consistent with the operation of two thermally activated
site exchange processes, which proceed at rates suf-
ficient to lead to the single resonance. Consistent with
this, lowering the sample temperature produces broad-
ening of the resonance. Between 343 and 333 K, the first
decoalescence occurs, and at about 223 K, the second
one takes place. At 193 K, three broad resonances at
-5.05 (HA), -11.33 (HB), and -12.20 (HC) are observed.
In the low-field region of the spectrum, the resonance
corresponding to the OsCH-proton of the substituent of
the pyridine appears at 11.47 ppm (HD), while the
HCpy-proton displays a doublet at 7.91 ppm (HE). The
resonance HD is observed as a double doublet by spin
F igu r e 2. Left: Variable-temperature 1H{31P} NMR
spectra (300 MHz) in the high-field region of OsH3(NC5H4-
o-CHdCH)(PiPr3)2 (2). Right: Simulated spectra and rate
constants (s-1) for the intramolecular hydrogen site-
exchange processes.
NMR spectrum at 193 K, which shows the cross signals
between both resonances. On the basis of this spectrum,
the resonance HC was assigned to the hydride ligand
disposed cisoid to the OsCH-carbon atom of the sub-
stituent of the pyridine. In agreement with this, the
saturation of HD increases the intensities of HC (2%) and
HE (12%), while HA and HB do not show any NOE effect.
1
In the H{31P} NMR spectrum, the resonances HA, HB,
and HC are simplified to doublets. The resonances HA
and HB show a HA-HB coupling constant of 25 Hz.
The T1 values of the hydrogen nuclei of the OsH3 unit
of 2 were determined over the temperature range 253-
183 K. T1(min) values of 108 ( 3 ms for HA, 102 ( 2 ms
for HB, and 114 ( 1 ms for HC were obtained at 203 K.
They support the trihydride character of the complex
and suggest that the central atom of the OsH3 unit is
HB. So, HA is the hydride situated cisoid to the nitrogen
atom of the pyridine.
coupling with HE (J H
) 10 Hz) and HC (J H
) 8
D-HE
C-HD
Hz). The spin coupling between the hydride HC and the
vinylic proton HD was confirmed by a 1H-1H COSY
(d) Bohanna, C.; Callejas, B.; Edwards, A. J .; Esteruelas, M. A.; Lahoz,
F. J .; Oro, L. A.; Ruiz, N.; Valero, C. Organometallics 1998, 17, 373.
(e) Esteruelas, M. A.; Garc´ıa-Yebra, C.; Oliva´n, M.; On˜ate, E.; Tajada,
M. A. Organometallics 2000, 19, 5098. (f) Baya, M.; Esteruelas, M. A.;
On˜ate, E. Organometallics 2001, 20, 4875.
(14) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson,
D. G.; Taylor, R. J . Chem. Soc., Dalton Trans. 1989, S1.
1
Figure 2 shows the H{31P} NMR spectra of 2 in the
hydride region, as a function of the temperature. Line-

3630 Organometallics, Vol. 23, No. 15, 2004
Barrio et al.
shape analyses of these spectra allow the calculation of
the rate constants for the thermal exchange processes
at different temperatures. The activation parameters
obtained from the corresponding Eyring analysis are
∆Hq ) 9.1 ( 0.2 kcal‚mol-1 and ∆Sq ) 1.1 ( 0.7
cal‚mol-1‚K-1 for the HA/HB exchange and ∆Hq ) 14.1
( 0.6 kcal‚mol-1 and ∆Sq ) -1.9 ( 1.2 cal‚mol-1‚K-1
for the HB/HC exchange. The values for the entropy of
activation, close to zero, are in agreement with an
intramolecular process, whereas the values for the
enthalpy of activation lie in the range reported for
thermal exchange processes in related osmium-trihy-
dride complexes.2,3,15
Under argon atmosphere the addition of 1.0 equiv of
HBF4‚OEt2 to a diethyl ether solution of 2 produces the
precipitation of the cationic hydride-dihydrogen complex
[OsH(η2-H2)(η2-CH2dCH-o-C5H4N)(PiPr3)2]BF4 (3), as a
result of the formal protonation of the OsCH-carbon
atom of the substituent of the pyridine of 2, and the
conversion of the HB and HC hydrides into an elongated
dihydrogen ligand (eq 8).
In addition to the vinylic resonances, four signals at
9.57 (d), 7.06 (d), 6.85 (dd), and 6.09 (dd) ppm are
observed in the low-field region of the 1H NMR spec-
trum. They were assigned to the pyridinic protons HR,
Hâ′, Hγ, and Hâ (see Figure 2), respectively, on the basis
of their multiplicities and the 1H-1H COSY NMR
spectrum at 193 K. The addition of 0.05 equiv of 1 to
an NMR tube containing toluene-d8 or benzene-d6
solutions of 2 produces after 10 h the extinction of the
resonances at 6.85 (Hγ) and 6.09 (Hâ) ppm, whereas the
resonances at 9.57 (HR) and 7.06 (Hâ′) are converted into
singlets. Changes in the vinylic, phosphine, and hydride
resonances are not observed. In the 13C{1H} NMR
spectrum of these solutions, the resonances correspond-
ing to the CHâ- and CHγ-carbon atoms of the pyridine
(132.4 and 115.5 ppm) appear as 1:1:1 triplets with C-D
coupling constants of 24.3 and 24.6 Hz, respectively. The
2H NMR spectrum in benzene of the residue resulting
from removing the deuterated solvent under reduced
pressure shows two singlets at 6.98 and 6.20 ppm.
Resonances in the high-field region are not observed.
The above-mentioned facts indicate that the hexahy-
dride 1 selectively catalyzes the H/D exchange between
the less handicapped â- and γ-positions of the pyridine
of 2 and the deuterated solvent, in the presence of the
hydride ligands of the OsH3 unit (eq 6). The process
should involve C-Hâ and C-Hγ activations of the
pyridine and C-D activations of the deuterated solvent
on the short-lived intermediate OsH2(η2-H2)(PiPr3)2.
Complex 3 was isolated as a white solid in 92% yield
and characterized by elemental analyses, MS, IR, and
1H, 31P{1H}, and 13C{1H} spectroscopy, and by an X-ray
crystallographic study. The structure has two chemically
equivalent but crystallographically independent mol-
ecules in the asymmetric unit. A drawing of the cation
of one of them is shown in Figure 3. Selected bond
distances and angles for both molecules are listed in
Table 2.
The coordination geometry around the osmium atom
could be rationalized as being derived from a highly
distorted octahedron with the two phosphorus atoms of
the triisopropylphosphine ligands occupying pseudo-
trans positions (P(1)-Os(1)-P(2) ) 152.45(4)° in mol-
ecule a and 149.88(4)° in molecule b) at opposite sides
of an ideal coordination plane defined by the nitrogen
atom, the midpoint (M) of the carbon-carbon double
bond of the substituent of the pyridine (N(1)-Os(1)-M
) 68.8° in molecule a and 69.0° in molecule b), the
hydride, and the dihydrogen ligand. The strong devia-
tion of the P(1)-Os(1)-P(2) angle from the ideal value
of 180° is most probably a result of a large steric
hindrance between the phosphines and the substituent
of the pyridine. The vinyl group lies almost parallel to
the phosphorus-phosphorus vector, the dihedral angle
between the P(1)-Os(1)-P(2) and C(2)-Os(1)-C(3)
planes being 22.85° in molecule a and 19.86° in molecule
b.
The intrinsic asymmetry of the olefin produces a loss
of symmetry in the cation, which is seen in the struc-
tural parameters by the two different Os-P distances.
The Os(1)-P(1) bond length (2.3857(12) Å in molecule
a and 2.3827(11) Å in molecule b) is approximately 0.01
Å longer than the Os(1)-P(2) bond length (2.3740(11)
Å in molecule a and 2.3724(11) Å in molecule b). This
fact can also be observed in the 31P{1H} NMR spectrum,
which shows an AB spin system centered at 20.1 ppm,
and defined by ∆ν ) 189 Hz and J AB ) 157 Hz.
The osmium-vinyl coordination exhibits Os-C dis-
tances of 2.222(4) (molecule a ) and 2.220(4) (molecule
b) Å (Os(1)-C(2)) and 2.225(4) (molecule a ) and 2.220(4)
Under hydrogen atmosphere, complex 2 is stable and
does not evolve into 1 and 2-vinylpyridine, or 2-ethylpyr-
idine, even at 80 °C. However, at room temperature in
dichloromethane and in the presence of 1.0 equiv of
HBF4‚OEt2, the formation of 1 and the tetrafluoroborate
salt of 2-ethylpyridinium takes place after 4 h, according
to eq 7.
(15) (a) Esteruelas, M. A.; Lahoz, F. J .; Lo´pez, A. M.; On˜ate, E.; Oro,
L. A.; Ruiz, N.; Sola, E.; Tolosa, J . I. Inorg. Chem. 1996, 35, 7811. (b)
Castillo, A.; Esteruelas, M. A.; On˜ate, E.; Ruiz, N. J . Am. Chem. Soc.
1997, 119, 9691. (c) Castillo, A.; Barea, G.; Esteruelas, M. A.; Lahoz,
F. J .; Lledo´s, A.; Maseras, F.; Modrego, J .; On˜ate, E.; Oro, L. A.; Ruiz,
N.; Sola, E. Inorg. Chem. 1999, 38, 1814.

Osmium-Hexahydride Complex
Organometallics, Vol. 23, No. 15, 2004 3631
dihydrogen resonance corresponds to a hydrogen-
hydrogen distance of 1.35 Å (slow spinning).9,18
Treatment of 2 with DBF4 yields 3 partially deuter-
ated, including the dihydrogen position. The H-D
coupling constant for the η2-HD resonance, obtained
from the 2H NMR spectrum at 253 K, is 4.7 Hz.
According to the standard equation,19 this value allows
the calculation of a separation between the hydrogen
atoms of the dihydrogen ligand of 1.34 Å, which agrees
well with that obtained from the T1 study.
The deuterium distribution in the partially deuterated
complex 3 is 0.17 at the dihydrogen, 0.09 at the hydride,
0.50 at C(3) (0.25 at each position), and 0.24 at C(2).
The presence of deuterium at the osmium atom and at
all positions of the olefinic group, equally distributed,
suggests that the protonation of 2 initially occurs on one
of its hydride ligands. From a classical point of view,
one could argue that the amounts of deuterium at C(2)
and C(3) are the result of Markovnikov and anti-
Markovnikov insertion equilibria equally favored. How-
ever, it should be noted that the stability of the resulting
metallacycles should be very different. So, classical
consecutive insertion equilibria cannot explain the
observed deuterium distribution.
J ia and co-workers have recently shown that the
dihydrogen ligand can be transferred to an olefin by a
process similar to the [2 + 2] cycloaddition between
olefins.20 In this context, it should be noted that dihy-
drogen and olefins are similar in terms of their bonding
interaction with transition metal centers.21 Dihydrogen
forms metal-ligand σ bonds by donating its σ-bonding
electron pair to an empty orbital of the metal and
metal-ligand π bonds by back-donation of metal dπ
electrons to the σ* orbital.22 Olefins form metal-ligand
σ bonds by donating their π-bonding electron pairs to
empty orbitals of the metal and metal-ligand π bonds
by back-donation of metal dπ electrons to the π* orbit-
als.23
F igu r e 3. Molecular diagram of the cation of complex
[OsH(η2-H2)(η2-CH2dCH-o-C5H4N)(PiPr3)2]BF4 (3).
(molecule b) Å (Os(1)-C(3)), which agree well with those
found in other osmium-olefin complexes (between 2.13
and 2.28 Å).16 Similarly, the olefinic bond distance C(2)-
C(3) (1.395(5) Å in molecule a and 1.415(5) Å in molecule
b) is within the range reported for transition metal
olefin complexes (between 1.340 and 1.445 Å).17 In
accordance with the coordination of the C(2)-C(3)
double bond to the osmium atom, in the 13C{1H} NMR
spectrum, the resonances due to C(2) and C(3) are
observed at 42.8 and 46.7 ppm, respectively.
1
In the high-field region of the H NMR spectrum, in
dichloromethane-d2 at 253 K, the hydride ligand gives
rise to a double doublet at -4.55 ppm, with H-P
coupling constants of 23.7 and 16.8, whereas the elon-
gated dihydrogen displays an apparent triplet at -13.30
ppm with a H-P coupling constant of 11.4 Hz. The cis
disposition of the latter with regard to the coordinated
olefin group was inferred from a NOESY 1H NMR
experiment at 253 K. The spectrum shows cross-peaks
between the hydride resonance and the HR signal of the
pyridine ring (δ 8.16) and between the dihydrogen
resonance and two of those corresponding to the olefinic
protons (δ 4.16 and 3.13).
A variable-temperature 300 MHz T1 study between
253 and 173 K of these resonances gives T1(min) values
of 129 ( 6 ms for the hydride resonance and 48 ( 2 ms
for the dihydrogen resonance, at 193 K. These values
support the hydride-elongated dihydrogen character of
the complex. In particular, the T1(min) value of the
A transfer of this type allows us to rationalize our
observations. Scheme 1 shows the elemental steps for
the protonation of 2, which could lead to the obtained
deuterium distribution in 3.
The addition of D+ to one of the hydride ligands of 2
should afford a deuterated a intermediate with 0.25
deuterium atom in each position of the OsH4 unit, as a
consequence of exchange processes between the hy-
drides and between the hydrides and the dihydrogen.
Thus, the migration of one of the hydrides from the
metallic center to the metalated carbon atom of the
substituent of the pyridine in 2 should initially move
0.25 deuterium atom to C(3). Then, the subsequent
concerted addition of the dihydrogen ligand to the
(16) (a) J ohnson, T. J .; Albinati, A.; Koetzle, T. F.; Ricci, J .;
Eisenstein, O.; Huffman, J . C.; Caulton, K. G. Inorg. Chem. 1994, 33,
4966. (b) Edwards, A. J .; Esteruelas, M. A.; Lahoz, F. J .; Lo´pez, A. M.;
On˜ate, E.; Oro, L. A.; Tolosa, J . I. Organometallics 1997, 16, 1316. (c)
Edwards, A. J .; Elipe, S.; Esteruelas, M. A.; Lahoz, F. J .; Oro, L. A.;
Valero, C. Organometallics 1997, 16, 3828. (d) Buil, M. L.; Esteruelas,
M. A.; Garc´ıa-Yebra, C.; Gutie´rrez-Puebla, E.; Oliva´n, M. Organome-
tallics 2000, 19, 2184. (e) Esteruelas, M. A.; Garc´ıa-Yebra, C.; Oliva´n,
M.; On˜ate, E. Organometallics 2000, 19, 3260. (f) Baya, M.; Esteruelas,
M. A.; On˜ate, E. Organometallics 2002, 21, 5681. (g) Esteruelas, M.
A.; Gonza´lez, A. I.; Lo´pez, A. M.; On˜ate, E. Organometallics 2003, 22,
414. (h) Barrio, P.; Esteruelas, M. A.; On˜ate, E. Organometallics 2003,
22, 2472. (i) Esteruelas, M. A.; Lledo´s, A.; Oliva´n, M.; On˜ate, E.; Tajada,
M. A.; Ujaque, G. Organometallics 2003, 22, 3753. (j) Baya, M.; Buil,
M. L.; Esteruelas, M. A.; On˜ate, E. Organometallics 2004, 23, 1416.
(17) Allen, F. H.; Davis, J . E.; Galloy, J . J .; J ohnson, O.; Kennard,
O.; Macrae, C. F.; Mitchell, E. M.; Mitchel, G. F.; Smith, J . M.; Watson,
D. G. J . Chem. Inf. Comput. Sci. 1991, 31, 187.
(18) (a) Earl, K. A.; J ia, G.; Maltby, P. A.; Morris, R. H. J . Am. Chem.
Soc. 1991, 113, 3027. (b) Desrosiers, P. J .; Cai, L.; Lin, Z.; Richards,
R.; Halpern, J . J . Am. Chem. Soc. 1991, 113, 4173.
(19) Maltby, P. A.; Schlaf, M.; Steinbeck, M.; Lough, A. J .; Morris,
R. H.; Klooster, W. T.; Koetzle, T. F.; Srivastava, R. C. J . Am. Chem.
Soc. 1996, 118, 5396.
(20) (a) Liu, S. H.; Huang, X.; Ng, W. S.; Wen, T. B.; Lo, M. F.; Zhou,
Z. Y.; Williams, I. D.; Lin, Z.; J ia, G. Organometallics 2003, 22, 904.
(b) J ia, G.; Lin, Z.; Lau, C. P. Eur. J . Inorg. Chem. 2003, 2551.
(21) Maseras, F.; Lledo´s, A.; Clot, E.; Eisenstein, O. Chem. Rev.
2000, 100, 601.
(22) Kubas, G. J . Dihydrogen and σ-donor Complexes; Kluwer
Academic/Plenum Press: New York, 2001.
(23) Crabtree, R. H. The Organometallics Chemistry of The Transi-
tion Metals, 3rd ed.; Wiley: New York, 2001.

3632 Organometallics, Vol. 23, No. 15, 2004
Barrio et al.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles (d eg) for th e Com p lex
[OsH(η2-Η2)(η2-CH2dCH-o-C5H4N)(P iP r 3)2]BF 4 (3)
molecule a
molecule b
molecule a
molecule b
Os(1)-P(1)
2.3857(12)
2.3740(11)
2.168(3)
2.222(4)
152.45(4)
92.73(8)
103.7
76.0(13)
68(2)
87.5(13)
102.42(9)
103.7
80.4(13)
90(2)
89.4(13)
68.8
92.4(12)
154.0(18)
2.3827(11)
2.3724(11)
2.161(3)
2.220(4)
149.88(4)
92.53(9)
108.2
81.0(13)
77.4(17)
82.0(12)
100.92(9)
101.8
71.7(12)
80.5(17)
97.9(12)
69.0
92.5 (11)
158.4(15)
Os(1)-C(3)
N(1)-C(1)
2.225(4)
1.358(4)
1.478(5)
1.395(5)
152.4(12)
2.220(4)
1.360(4)
1.466(5)
1.415(5)
150.5(12)
Os(1)-P(2)
Os(1)-N(1)
Os(1)-C(2)
C(1)-C(2)
C(2)-C(3)
N(1)-Os(1)-H(03)
P(1)-Os(1)-P(2)
P(1)-Os(1)-N(1)
P(1)-Os(1)-Ma
P(1)-Os(1)-H(01)
P(1)-Os(1)-H(02)
P(1)-Os(1)-H(03)
P(2)-Os(1)-N(1)
P(2)-Os(1)-Ma
P(2)-Os(1)-H(01)
P(2)-Os(1)-H(02)
P(2)-Os(1)-H(03)
N(1)-Os(1)-Ma
N(1)-Os(1)-H(01)
N(1)-Os(1)-H(02)
Ma-Os(1)-H(01)
Ma-Os(1)-H(02)
Ma-Os(1)-H(03)
H(01)-Os(1)-H(02)
H(01)-Os(1)-H(03)
H(02)-Os(1)-H(03)
Os(1)-N(1)-C(1)
Os(1)-C(2)-C(3)
Os(1)-C(2)-C(1)
Os(1)-C(3)-C(2)
N(1)-C(1)-C(2)
C(1)-C(2)-C(3)
161.3
130.8
84.7
159.3
132.2
85.1
67.0(15)
114.3(14)
48.2(14)
97.8(2)
71.9(2)
91.9(2)
71.6(2)
106.3(3)
114.1(4)
67.3(15)
115.0(14)
47.8(14)
97.9(2)
71.4(2)
92.2(2)
71.4(2)
106.4(3)
113.6(4)
a
M represents the midpoint of the C(2)-C(3) double bond.
Sch em e 1
plex into the 14-electron monohydride, it should be
noted the similarity between both equilibria. Direct
experimental evidence for the existence of related 14-
electron transition metal complexes has been reported
by Caulton and co-workers.25 They prove that agostic
interactions are not inevitable in this type of unsatur-
ated species, but that a triplet state with half-filling of
two orbitals is another way to make the best outcome
of an otherwise electron-deficient situation.26
In agreement with an accessible species b, complex
3 is an active catalyst for the hydrogenation of 2-vi-
nylpyridine to 2-ethylpyridine, in dichloromethane, at
room temperature and under hydrogen atmospheric
pressure (eq 9). However its stability under the reaction
coordinated olefin group in 3 could give a 14-e- unsat-
urated species b, containing in the resulting ethyl
substituent of the pyridine 0.50 deuterium atom at the
methyl group and 0.25 deuterium atom at the CH2
group. The remaining 0.25 deuterium atom should lie
at the hydride position. Finally, the concerted extraction
of H2 from the ethyl substituent of the pyridine in b
should afford 3, which could distribute 0.25 deuterium
atom between the positions of the OsH3 unit by means
of a hydride-dihydrogen exchange process, to show the
observed deuterium distribution. The extraction of H2
instead D2 or HD is in agreement with the higher
strength of the alkyl-D bond in comparison with the
alkyl-H bond.24
conditions is very low, and it rapidly undergoes deac-
tivation. Using a 1:100 catalyst:substrate molar ratio,
after 1, 4, and 50 h, the yields of the reaction are 10%,
20%, and 39%, respectively. The resulting species from
the deactivation process is the elongated dihydrogen
complex Os(NC5H5-o-CHdCH)Cl(η2-H2)(PiPr3)2 (4). This
1
is supported by the H and 31P{1H} NMR spectra of the
residue obtained from removing the volatiles of the
catalytic mixture, after 50 h of reaction, which show the
characteristic resonances of 4. This complex is formed
by reaction of the catalyst with the solvent. Thus, we
have observed that in the absence of 2-vinylpyridine,
under argon, the dichloromethane solutions of 3 evolve
into 4 (eq 10).
We have recently reported that the trihydride-isopro-
penyl complex OsH3(SnPh2Cl){η2-CH2dC(CH3)PiPr2}(Pi-
Pr3) activates ortho-CH bonds of aromatic ketones and
imines via the 14-electron monohydride intermediate
OsH(SnPh2Cl)(PiPr3)2, which is formed by reversible
transfer of two hydrides from the metallic center to the
olefin group of the isopropenylphosphine.16i Although
from an intimate point of view, the transformation from
3 to b appears to be significantly different from the
conversion of the trihydride-isopropenylphosphine com-
Complex 4 was isolated as a yellow oil and character-
ized by MS, IR, and 31P{1H}, 13C{1H}, and 1H NMR
(24) Connors, K. A. Chemical Kinetics. The Study of Reaction Rates
in Solution; VCH Publisher: New York, 1990.

Osmium-Hexahydride Complex
Organometallics, Vol. 23, No. 15, 2004 3633
spectroscopy. In agreement with the mutually trans
disposition of the phosphine ligands, the 31P{1H} NMR
spectrum contains a singlet at 9.02 ppm. In the 13C{1H}
NMR spectrum, the resonances due to the CHdCH
substituent of the pyridine are observed at 180.6 and
151.1 ppm. The first of them, assigned to the OsCH-
carbon atom, appears as a triplet with a C-P coupling
constant of 6.1 Hz. The second one, corresponding to
the pyCH-carbon atom, is observed as a singlet. In the
1H NMR spectrum the vinylic resonances are observed
at 7.32 (CH) and 10.06 (OsCH) ppm. The CH-proton
displays a doublet, while the OsCH resonance is ob-
served as a double (J H-H ) 7.3 Hz) triplet (J H-H ) 4.6
Hz) by spin coupling with the CH-proton and the
1
dihydrogen ligand. The latter was confirmed by a H-
1H COSY NMR spectrum, which shows the cross-peaks
between the OsCH signal and the dihydrogen resonance
(δ -7.71; J H-P ) 12.5 Hz).
A variable-temperature 300 MHz T1 study of the
dihydrogen resonance gives a T1(min) value of 39 ( 1 ms
at 193 K. The treatment of 4 with methanol-d4 yields
F igu r e 4. Molecular diagram of complex OsH3(NC5H4-o-
NCH3)(PiPr3)2 (5).
the partially deuterated derivative Os(NC5H5-o-CHd
spectroscopy, and by an X-ray crystallographic study.
The structure has two chemically equivalent but crys-
tallographically independent molecules in the asym-
metric unit. A drawing of one of them is shown in Figure
4. Selected bond distances and angles for both molecules
are listed in Table 3.
The coordination geometry around the osmium atom
can be rationalized as a distorted pentagonal bipyramid
with the two phosphorus atoms of the triisopropylphos-
phine ligands occupying axial positions (P(1)-Os-P(2)
) 170.67(3)° (molecule a ) and 171.50(3)° (molecule b)).
The osmium sphere is completed by the hydride ligands
and the chelate nitrogen donor group, which acts with
a bite angle of 60.85(11)° in molecule a and 60.60(11)°
in molecule b.
The spectroscopic data of 5 are consistent with the
structure shown in Figure 4. The IR spectrum in KBr
contains two bands at 2134 and 2116 cm-1, correspond-
ing to the hydride ligands. In the 13C{1H} NMR spec-
trum, the most noticeable feature is the presence of a
singlet at 36.0 ppm, due to the methyl group of the
chelate ligand. In agreement with the mutually trans
disposition of the phosphine ligands, the 31P{1H} NMR
spectrum shows a singlet at 26.4 ppm, which is tem-
perature invariant between 353 and 193 K.
CH)Cl(η2-HD)(PiPr3)2 (4-d 1), which has a H-D coupling
constant of 6.3 Hz. T1(min) and J (H-D) values suggest
that the separation between the hydrogen atoms of the
dihydrogen ligand is about 1.32 Å.9,18,19
2. Rea ction s of OsH6(P iP r 3)2 w ith N-Meth ylen e-
2-p yr id in a m in es. The replacement of the CH group
of the substituent of the pyridine by a nitrogen atom
has a marked influence on the reactions of this type of
organic substrates with the short-lived intermediate
OsH2(η2-H2)(PiPr3)2. The substitution produces an in-
crease of the electrophilic character of the terminal
group of the double bond, which favors the migration
of a hydride ligand to the carbon atom. Thus, in contrast
to 2-vinylpyridine, the treatment under reflux of toluene
solutions of 1 with 1.4 equiv of N-methylene-2-pyridin-
amine leads after 5 h to a mixture of the trihydride
derivatives OsH3(NC5H4-o-NCH3)(PiPr3)2 (5) and OsH3-
(NC5H4-o-NdCH)(PiPr3)2 (6) in a 3:1 molar ratio, ac-
cording to the 1H and 31P{1H} NMR spectra of the
residue obtained from removing the reaction solvent
under reduced pressure (eq 11).
In contrast to the 31P{1H} NMR spectrum, the 1H
NMR spectrum is temperature-dependent. The behavior
of the hydride ligands of 5 with the temperature is
similar to that found for 2. In toluene-d8, at 353 K, the
spectrum contains a triplet at -11.88 ppm with a H-P
coupling constant of 13.5 Hz. Lowering the sample
temperature leads to broadening of the resonance.
Between 273 and 263 K, the first decoalescence occurs,
and between 223 and 213, the second one. At 183 K, an
Complex 5 was obtained as a pure yellow solid in 52%
yield by crystallization of the above-mentioned residue
in toluene-methanol and characterized by elemental
1
ABCX2 (X ) 31P) spin system is observed. The H{31P}
1
analysis, MS, IR, and H, 31P{1H}, and 13C{1H} NMR
spectrum is simplified to the expected ABC spin system,
which is defined by δA ) -10.97, δB ) -11.65, δC
)
(25) (a) Huang, D. J .; Streib, W. E.; Eisenstein, O.; Caulton, K. G.
Angew. Chem., Int. Ed. Engl. 1997, 36, 2004. (b) Cooper, A. C.; Streib,
W. E.; Eisenstein, O.; Caulton, K. G. J . Am. Chem. Soc. 1997, 119,
9069. (c) Huang, D.; Streib, W. E.; Bollinger, J . C.; Caulton, K. G.;
Winter, R. F.; Scheiring, T. J . Am. Chem. Soc. 1999, 121, 8087. (d)
Huang, D.; Bollinger, J . C.; Streib, W. E.; Folting, K.; Young, V., J r.;
Eisenstein, O.; Caulton, K. G. Organometallics 2000, 19, 2281.
(26) Watson, L. A.; Ozerov, O. V.; Pink, M.; Caulton, K. G. J . Am.
Chem. Soc. 2003, 125, 8426.
-12.24, J AC ) 11.6 Hz, J BC ) 24.7 Hz, and J AB ) 0.
The activation parameters obtained from the corre-
sponding Eyring analysis are ∆Hq ) 9.9 ( 0.5 kcal‚mol-1
and ∆Sq ) -0.3 ( 1.5 cal‚mol-1‚K-1 for the HB-HC
exchange and ∆Hq ) 12.6 ( 0.3 kcal‚mol-1 and ∆Sq )
2.4 ( 0.8 cal‚mol-1‚K-1 for the HA-HC exchange. In

3634 Organometallics, Vol. 23, No. 15, 2004
Barrio et al.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles (d eg) for th e Com p lex OsH3(NC5H4-o-NCH3)(P iP r 3)2 (5)
molecule a
molecule b
molecule a
molecule b
Os(1)-P(1)
2.3377(9)
2.3228(10)
2.152(3)
2.151(3)
1.50(4)
2.3390(9)
2.3335(9)
2.158(3)
2.140(3)
1.49(5)
171.50(3)
93.54(8)
92.42(8)
88.9(16)
87(2)
90.0(15)
94.89(8)
92.72(8)
90.0(16)
85(2)
83.1(15)
60.60(11)
89.4(16)
Os(1)-H(02)
1.34(5)
1.53(4)
1.376(4)
1.324(5)
1.432(4)
148(2)
152.7(16)
152.7(15)
150(2)
1.29(5)
1.56(4)
1.375(4)
1.322(4)
1.449(4)
152(2)
151.8(16)
150.0(16)
148(2)
Os(1)-P(2)
Os(1)-H(03)
Os(1)-N(1)
N(1)-C(1)
Os(1)-N(2)
N(2)-C(1)
Os(1)-H(01)
N(2)-C(6)
P(1)-Os(1)-P(2)
P(1)-Os(1)-N(1)
P(1)-Os(1)-N(2)
P(1)-Os(1)-H(01)
P(1)-Os(1)-H(02)
P(1)-Os(1)-H(03)
P(2)-Os(1)-N(1)
P(2)-Os(1)-N(2)
P(2)-Os(1)-H(01)
P(2)-Os(1)-H(02)
P(2)-Os(1)-H(03)
N(1)-Os(1)-N(2)
N(1)-Os(1)-H(01)
170.67(3)
94.76(8)
92.30(8)
94.3(14)
78.2(18)
84.4(15)
94.54(8)
92.90(8)
84.5(14)
93.5(18)
87.7(15)
60.85(11)
92.2(15)
N(1)-Os(1)-H(02)
N(1)-Os(1)-H(03)
N(2)-Os(1)-H(01)
N(2)-Os(1)-H(02)
N(2)-Os(1)-H(03)
H(01)-Os(1)-H(02)
H(01)-Os(1)-H(03)
H(02)-Os(1)-H(03)
Os(1)-N(1)-C(1)
Os(1)-N(2)-C(1)
Os(1)-N(2)-C(6)
N(1)-C(1)-N(2)
C(1)-N(2)-C(6)
91.9(16)
57(2)
115(2)
91.3(16)
62(3)
119(2)
59(2)
56(2)
95.0(2)
96.5(2)
141.6(3)
107.7(3)
121.8(3)
94.9(2)
97.4(2)
139.7(3)
107.0(3)
122.9(3)
agreement with the trihydride character of the complex,
T1(min) values of 109 ( 2 (δA), 94 ( 1 (δB), and 87 ( 1
(δC) ms were found at 208 K.
ment of a hydrogen atom in the latter by a phenyl group
favors the insertion with regard to the C-H activation.
Thus, the treatment under reflux of toluene solutions
of 1 with 1.3 equiv of (E)-N-(phenylmethylene)-2-pyr-
idinamine selectively affords after 5 h the trihydride
Complex 6 was characterized by 13C{1H}, 1H, and
31P{1H} NMR spectroscopy. The 13C{1H} NMR spectrum
reveals a significant contribution of the aminocarbene
resonance form to the structure of the complex. Thus,
the OsCN resonance appears at 251.7 ppm as a triplet
with a C-P coupling constant of 4.6 Hz. The behavior
of the hydride ligands with the temperature is similar
to those found for 2 and 5. In toluene-d8 at 343 K, the
1H NMR spectrum shows a broad resonance centered
at -9.1 ppm for the three hydride ligands. Between 323
and 313 K, the first decoalescence takes place, and
between 223 and 218, the second one. At 193 K, an
OsH3(NC5H4-o-NCH2Ph)(PiPr3)2 (7), as result of the
insertion of the CdN double bond of the organic
substrate into one of the Os-H bonds of the starting
complex (eq 13). The role of the phenyl group is double.
On one hand it increases the electrophilic character of
the carbon atom of the CdN double bond, favoring the
migration of the hydride ligand; on the other its steric
hindrance prevents the coordination of the activated
CPh group to the osmium atom.
ABCX2 (X ) 31P) spin system with δA ) -5.77, δB
)
-10.53, and δC ) -11.33 is observed. In the low-field
region of the spectrum the OsCH-proton displays at
14.30 ppm a doublet (J H-H ) 9 Hz), by spin coupling
with the HC hydride ligand. The estimated activation
enthalpies for the site exchange processes of the hydride
ligands are 9 kcal‚mol-1 for the HA-HB exchange and
15 kcal‚mol-1 for the HB-HC exchange. The trihydride
character of 6 is supported by T1(min) values of 94 ( 5
(δA), 85 ( 4 (δB), and 126 ( 2 (δC) ms. The 31P{1H} NMR
spectrum contains a singlet at 30.8 ppm.
Complex 6 can also be selectively deuterated at the
â- and γ-positions of the pyridine ring (eq 12). Thus, the
addition of 0.05 equiv of 1 to toluene-d8 or benzene-d6
solutions of 6 produces the extinction of the Hγ and Hâ
resonances (7.01 and 6.16 ppm), in the 1H NMR
spectrum, while the HR and Hâ′ resonances are con-
verted into singlets.
Complex 7 was isolated as a yellow solid in 75% yield.
Its spectroscopic data agree well with those of 5. The
IR spectrum in KBr shows the ν(Os-H) vibrations at
2117 and 2102 cm-1. In the 13C{1H} NMR spectrum the
C(sp3) carbon atom of the benzyl group displays a singlet
at 54.6 ppm. At 343 K, the 1H NMR spectrum in
toluene-d8 shows a triplet at -12.04 ppm, with a H-P
coupling constant of 13.5 Hz, for the three hydride
ligands. The first decoalescence of this resonance occurs
between 273 and 263 K, whereas the second one is
observed at 213 K. At 193 K, the spectrum shows an
ABCX2 (X ) 31P) spin system. The 1H{31P} NMR
spectrum is simplified to the expected ABC spin system
with δA ) -10.89, δB ) -12.11, δC ) -12.32, J AC ) 11.8
Hz, J BC ) 22.3 Hz, and J AB ) 0. The activation
parameters for the site exchange processes between the
hydride ligands are ∆Hq ) 10.8 ( 1.1 kcal‚mol-1 and
∆Sq ) 0.3 ( 3.2 cal‚mol-1‚K-1 for the HB-HC exchange
and ∆Hq ) 12.7 ( 0.3 kcal‚mol-1 and ∆Sq ) 3.4 ( 0.8
cal‚mol-1‚K-1 for the HA-HC exchange. In agreement
with the trihydride character of the complex, T1(min)
values of 96 ( 2 (δA) and 80 ( 2 (δB and δC) were found
at 223 K, before the second decoalescence. The 31P{1H}
NMR spectrum shows a singlet at 25.0 ppm.
Complex 5 is the result of the insertion of the CdN
double bond of N-methylene-2-pyridinamine into one of
the Os-H bonds of the short-lived intermediate OsH2-
(η2-H2)(PiPr3)2, while complex 6 is a consequence of the
C-H activation of the terminal CH2 group. The replace-

Osmium-Hexahydride Complex
Organometallics, Vol. 23, No. 15, 2004 3635
Sch em e 2
Under atmospheric hydrogen pressure, 2-vinylpyri-
dine and the studied pyridinamines show significant
differences in reactivity. The toluene solutions of 5 and
7 are stable under hydrogen atmosphere. The addition
of 1.0 equiv of HBF4‚OEt2 to the diethyl ether solutions
of 5 affords the cationic trihydride derivative [OsH3-
(NC5H4-o-NHCH3)(PiPr3)2]BF4 (8) as a result of the
formal addition of the proton of the acid to the CH3N-
nitrogen atom of 5 (eq 14). In contrast to 3, the
dichloromethane solutions of 8 are also stable under
hydrogen atmosphere, even in the presence of N-meth-
ylene-2-pyridinamine. So, the catalytic reduction of the
CdN double bond of this organic substrate is not
achieved.
Complex 8 was isolated as a white solid in 82% yield.
In agreement with the presence of a NH group in the
complex, its IR spectrum in KBr shows a ν(N-H) band
at 3264 cm-1, along with the ν(Os-H) vibrations at 2157
and 2122 cm-1. In the 13C{1H} NMR spectrum, the
methyl group of the amino substituent of the pyridine
gives rise to a singlet at 42.1 ppm. The 31P{1H} NMR
spectrum is temperature dependent. In dichloromethane-
d2 at 303 K, the spectrum shows a singlet at 27.4 ppm.
Lowering the sample temperature produces broadening
of the resonance. At 198 K, an AB spin system centered
at 25.2 ppm and defined by ∆ν ) 429 Hz and J AB ) 245
Hz is observed. This behavior suggests that in solution
the nitrogen atom of the methylamino substituent is
involved in a dynamic process of inversion of its con-
figuration. Line-shape analyses of the 31P{1H} NMR
spectra allows the calculation of the rate constants of
the process at different temperatures. The activation
parameters obtained from the corresponding Eyring
resonance at -12.81 ppm for the three hydride ligands.
Between 283 and 273 K, the first decoalescence occurs,
and between 243 and 233 K the second one. At 193 K,
the characteristic ABCX2 (X ) 31P) spin system for this
type of derivatives is observed. The ABC spin system
in the 1H{31P} NMR spectrum is defined by δA ) -10.59,
δB ) -12.65, δC ) -15.19, J AB ) 63.7 Hz, J BC ) 15.9
Hz, and J AC ) 0 Hz. The activation parameters for the
exchanges are ∆Hq ) 10.4 ( 0.5 kcal‚mol-1 and ∆Sq )
0.9 ( 1.5 cal‚mol-1‚K-1 for the HA-HB exchange and
∆Hq ) 14.1 ( 0.6 kcal‚mol-1 and ∆Sq ) 8.5 ( 1.3
cal‚mol-1‚K-1 for the HB-HC exchange. In accordance
with the trihydride character of 8, T1(min) values of 71
( 3 (δA), 69 ( 3 (δB), and 101 ( 1 (δC) ms were obtained
at 203 K.
Treatment of 5 with DBF4 yields 8 partially deuter-
ated. According to the 2H NMR spectrum of this species,
the deuterium atom is distributed as follows: 0.07 and
0.14 at the R- and â′-position respectively, of the
pyridine ring, 0.47 at the nitrogen atom of the methyl-
amino substituent, 0.27 at the methyl group, and 0.05
at the hydride positions.
analysis are ∆Hq ) 18.9 ( 0.3 kcal‚mol-1 and ∆Sq
)
23.2 ( 0.7 cal‚mol-1‚K-1. The value of the activation
entropy is consistent with an unsaturated intermediate
containing the nitrogen donor ligand coordinated as
monodentated (eq 15).
The observed deuterium distribution can be rational-
ized according to Scheme 2. The initial addition of the
acid to one of the hydride ligands of 5 should afford a
dihydride-dihydrogen intermediate d , with half of the
atoms of the dihydrogen being deuterium. The transfer
of one of these atoms to the CH3-N nitrogen atom should
give 8 with 0.5 deuterium at the methylamino nitrogen
atom. Since this is the amount found at this atom, the
migration from the dihydrogen appears to be faster than
the site exchange processes between the dihydrogen and
the hydrides. The remaining 0.50 deuterium should
initially lie in the hydride positions. It could be distrib-
uted between the R, â′, and methyl positions of the
pyridine via the unsaturated intermediates c and g
through reversible C-H activation processes (interme-
diates e, f, and h ). The formation of η2-C, N-pyridyl
complexes, related to intermediate f, by reaction of a
polyhydride compound with pyridines has been recently
The dynamic equilibrium shown in eq 15 is also
supported by the 1H NMR spectrum. In dichloromethane-
d2 at 303 K, the spectrum shows two broad resonances
at 5.27 and 3.19 ppm for the NH and methyl protons of
the methylamino substituent, respectively. At temper-
atures lower than 293 K, these resonances are split into
a quartet and a doublet, respectively, with a H-H
coupling constant of 5.9 Hz. Like in the trihydride
compounds previously mentioned, the hydrides of 8 are
involved in two different site exchange processes. At 303
K, the spectrum in the high-field region contains a broad

3636 Organometallics, Vol. 23, No. 15, 2004
Barrio et al.
shown.27 In addition, it should be noted that the amount
of deuterium at the carbon atoms of the pyridine
increases (CR < Câ′ < C-methyl) as the number of
members, and therefore the stability, of the heteromet-
allacycles of f, h , and e increases.
Equations 11 and 14 represent the ionic stoichiomet-
ric reduction of the CdN double bond of N-methylene-
2-pyridinamine. The hydride transfer together with the
addtion of H+, in a subsequent reaction, have been
proposed by Ba¨ckvall and co-workers as the key elemen-
tal steps for the [Ru2(CO)4(µ-H)(C4Ph4COHOCC4Ph4)]-
catalyzed transfer hydrogenation of imines by 2-pro-
panol in benzene.28 Stoichiometric ionic reductions of
carbonyl groups,29 olefins,30 and imines31 have also been
reported.
1 equiv of the corresponding aldehyde, benzaldehyde (1.6 mL,
0.016 mol) or paraformaldehyde (0.5 g, 0.016 mol), were solved
in 8 mL of toluene. A catalytic quantity of p-toluenesulfonic
acid was added. In both cases, the resulting solution was
heated under reflux overnight with a Dean-Stark apparatus
as water collector. Then the solvent was removed in vacuo,
and pentane was added to afford a white solid, which was
washed with further portions of pentane and dried in vacuo.
Yield: 1.89 g (65%) for (E)-N-(phehylmethylene)-2-pyridin-
amine and 0.92 g (54%) for N-methylene-2-pyridinamine. Data
for N-methylene-2-pyridinamine (py-NdCH2): Anal. Calcd for
C6H6N2: C 67.90, H 5.70, N 26.40. Found: C 67.90, H 5.67, N
1
26.50. IR (KBr, cm-1): ν(CdN) 1591 (s). H NMR (300 MHz,
C6D6, 293 K): δ 8.16, 6.98, 6.88, and 6.25 (all m, 1H, py), 5.45
(s, 2H, CH2). 13C{1H} NMR (75.42 MHz, C6D6, 293 K): δ 158.0
(s, Cipso(py)), 148.1, 137.5, 114.2, and 108.4 (all s, py), 60.0 (s,
CH2). MS (EI): m/z 106 (M+ - H).
1H, 2H, 19F, 31P{1H}, and 13C{1H} NMR spectra were
recorded on either a Varian UNITY 300, Varian Gemini 2000,
Bruker AXR, or Bruker Avance 300 MHz instrument. Chemi-
cal shifts (expressed in parts per million) are referenced to
residual solvent peaks (1H, 13C{1H}), external 85% H3PO4 (31P-
{1H}), or external CFCl3 (19F). Coupling constants, J and N
(N ) J P-H + J P′-H for 1H and N ) J P-C + J P′-C for 13C{1H})
are given in hertz. Infrared spectra were run on a Perkin-
Elmer 1730 spectrometer as solids (KBr pellet). C, H, and N
analyses were carried out in a Perkin-Elmer 2400 CHNS/O
analyzer. For organometallic compounds, mass spectra analy-
ses were performed with a VG Austospec instrument. In FAB+
mode, ions were produced with the standard Cs+ gun at ca.
30 kV, and 3-nitrobenzyl alcohol (NBA) was used in the matrix.
For the organic products, GC-MS analyses were run on an
Agilent 5973 mass selective detector interfaced to an Agilent
6890 series gas chromatograph system. Samples were injected
into a 30 m × 250 µm HP-5MS 5% phenyl methyl siloxane
column with a film thickness of 0.25 µm (Agilent).
Con clu d in g Rem a r k s
This study reveals that the short-lived intermediate
species OsH2(η2-H2)(PiPr3)2, generated by thermal ac-
tivation of the hexahydride OsH6(PiPr3)2, reacts with
RCHdE-py organic substrates (E ) CH, N) to give
derivatives resulting from C(sp2)-H activation or inser-
tion reactions. They are competitive and depend on the
nature of both E and R, which determine the polarity
of the CdE double bond and the steric hindrance of the
RCH group.
For E ) N the migration of a hydride ligand from the
metal to the RCH-carbon atom is favored with regard
to the C-H activation. On the other hand, for E ) CH
the C(sp2)-H activation of the RCH group is preferred
over the hydride migration. Bulky substituents at the
RCH group prevent the coordination of the RC-carbon
atom to the metal, favoring the insertion of the double
bond.
In the presence of HBF4 both CdC and CdN double
bonds are reduced. However, isotope labeling experi-
ments suggest that there are strong differences between
the intimate details of each process. The CdC double
bond, less polar than CdN, appears to undergo the
concerted addition of a dihydrogen ligand, while the Cd
N double bond adds H- and H+ in a sequential manner.
1
Kin etic An a lysis. Complete line-shape analyses of the H-
{31P} NMR spectra of the complexes 2, 5, 7, and 8 were
achieved using the program gNMR (Cherwell Scientific Pub-
lishing Limited). The rate constants for various temperatures
were obtained by fitting calculated to experimental spectra by
full line-shape iterations. The transverse relaxation time, T2,
was estimated at the lowest interval of temperatures using
the resonances corresponding to the hydride ligands. The
activation parameters ∆Hq and ∆Sq were calculated by least-
squares fit of ln(k1/T) versus 1/T (Eyring equation). Error
analysis assumed a 10% error in the rate constant and 1 K in
the temperature. Errors were computed by published meth-
ods.33
Exp er im en ta l Section
All reactions were carried out with rigorous exclusion of air
using Schlenk-tube techniques. Solvents were dried by the
usual procedures and distilled under argon prior to use. The
starting materials OsH6(PiPr3)2 and DBF4‚D2O were prepared
by the published methods.32 The aldimines were synthesized
as follows: 1 equiv of 2-aminopyridine (1.5 g, 0.016 mol) and
P r ep a r a tion of OsH3(NC5H4-o-CHdCH)(P iP r 3)2 (2). A
colorless solution of OsH6(PiPr3)2 (212.6 mg, 0.412 mmol) in
15 mL of toluene was treated with 1.6 equiv of 2-vinylpyridine
(71 µL, 0.659 mmol) and heated under reflux for 5 h. The
resulting orange solution was filtered through Celite and dried
in vacuo. Pentane was added to afford a yellow solid, which
was washed with further portions of pentane at 223 K and
(27) Ozerov, O. V.; Pink, M.; Watson, L. A.; Caulton, K. G. J . Am.
Chem. Soc. 2004, 126, 2105.
dried in vacuo. Yield: 211.0 mg (83%). Anal. Calcd for C25H51
-
(28) Samec, J . S. M.; Ba¨ckvall, J .-E. Chem. Eur. J . 2002, 8, 2955.
(29) (a) Gaus, P. L.; Kao, S. C.; Youngdahl, K.; Darensbourg, M. Y.
J . Am. Chem. Soc. 1985, 2428. (b) Gibson, D. H.; El-omrani, Y. S.
Organometallics 1985, 4, 1473. (c) Geraty, S. M.; Harkin, P.; Vos, J .
G. Inorg. Chim. Acta 1987, 131, 217. (d) 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. (e) Bakhmutov, V. I.; Vorontsov,
E. V.; Antonov, D. Y. Inorg. Chim. Acta 1998, 278, 122.
(30) (a) Bullock, R. M.; Rappoli, B. J . J . Chem. Soc., Chem. Commun.
1989, 1447. (b) Bullock, R. M.; Song, J .-S. J . Am. Chem. Soc. 1994,
116, 8602.
NOsP2: C 48.60, H 8.32, N 2.27. Found: C 48.40, H 8.02, N
2.01. IR (KBr, cm-1): ν(OsH) 2173 (m), 2118 (m); ν(CdC) 1599
(s). 1H NMR (300 MHz, C7D8, 293 K, plus COSY): δ 11.51
(double virtual quartet, J H-H ) 10 Hz, J H-H(OsH ) 3 Hz, 1H,
)
3
OsCHD), 9.57 (d, J H-H ) 7.1 Hz, 1H, HR py), 7.91 (d, J H-H
)
10 Hz, 1H, dCHE), 7.06 (d, J H-H ) 7.1 Hz, 1H, Hâ′ py), 6.85
and 6.09 (both dd, J H-H ) J H-H ) 7.1 Hz, 1H, Hγ and Hâ py),
1.87 (m, 6H, PCH), 1.24 and 0.99 (both dvt, N ) 12.9 Hz, J H-H
) 6.6 Hz, 18H, PCHCH3), -8.22 (br, 2H, OsH), -12.22 (br,
1H, OsH). 1H{31P} NMR (300 MHz, C7D8, 193 K (plus 1H
COSY), only variable-temperature signals): low-field (OsCHD),
(31) (a) Minato, M.; Fujiwara, Y.; Ito, T. Chem. Lett. 1995, 647. (b)
Minato, M.; Fujiwara, Y.; Koga, M.; Matsumoto, M.; Kurishima, S.;
Natori, M.; Sekizuka, N.; Yoshioka, K.; Ito, T. J . Organomet. Chem.
1998, 569, 139.
(32) Aracama, M.; Esteruelas, M. A.; Lahoz, F. J .; Lo´pez, J . A.;
Meyer, U.; Oro, L. A.; Werner, H. Inorg. Chem. 1991, 30, 288.
(33) Morse, P. M.; Spencer, M. D.; Wilson, S. R.; Girolami, G. S.
Organometallics 1994, 13, 1646.

Osmium-Hexahydride Complex
δ 11.47 (dd, J H ) 10 Hz, J H
Organometallics, Vol. 23, No. 15, 2004 3637
C ) 8 Hz, 1H, OsCHD); high-
-H
obtained. Yield: 81.6 mg (67%). 2H NMR (46.03 MHz, CH2Cl2,
253 K): δ 4.2 (s, 0.24D, CDpy), 3.4 and 3.1 (both s, 0.25D,
CDH), -4.5 (br, 0.09D, OsD), -13.3 (t(1:1:1)dd, J H-D ) 4.7 Hz,
J P-D ) J P′-D ≈ 2 Hz, 0.17D, Os(η2-HD)).
-H
D
E
D
field region (OsH3 unit), δ -5.05 and -11.33 (both d, J H
-H
A
B
) 25 Hz, 1H, HA and HB), -12.20 (d, J H
) 8 Hz, 1H, HC).
-H
C
D
31P{1H} NMR (121.42 MHz, C7D8, 293 K): δ 26.8 (s). 13C{1H}
NMR (75.42 MHz, C7D8, 293 K): δ 203.9 (t, J P-C ) 6.4 Hz,
OsCH), 169.6 (s, Cipso), 158.6 (s, CH), 132.4, 127.2, 119.3, and
115.5 (all s, py), 27.7 (vt, N ) 24.4 Hz, PCH), 20.1 and 19.8
(both s, PCHCH3). MS (FAB+): m/z 613 (M+ - 2H). T1(min) (ms,
OsH3, 300 MHz, C7D8, 203 K): 108 ( 3 (-5.05 ppm, 1H), 102
( 2 (-11.33 ppm, 1H), 114 ( 1 (-12.20 ppm, 1H).
Ca ta lytic Hyd r ogen a tion of 2-Vin ylp yr id in e. A solution
of 3 (114.0 mg, 0.162 mmol) and 2-vinylpyridine (1.75 mL, 16.2
mmol) in 15 mL of dichloromethane was stirred under a
hydrogen atmosphere. The reaction was monitored by GC-
MS. The products were identified by comparison of their mass
spectra with those of the G1045B Spectral Library (Willey 7N,
Agilent Technologies, 2000). The yields of formation of 2-eth-
ylpyridine after 1, 4, and 50 h were 10%, 20%, and 39%,
respectively. After 50 h, the reaction was stopped and the
resulting solution was concentrated in vacuo. The 1H and
31P{1H} NMR spectra of the residue obtained, in CD2Cl2,
revealed the formation of 4.
The addition of 0.05 equiv of OsH6(PiPr3)2 to an NMR tube
containing 2 in toluene-d8 or benzene-d6 gives, after 10 h, the
complex 2 partially deuterated in the pyridine ring. H NMR
1
(300 MHz, C6D6 or C7D8, 293 K, pyridine ring): δ 9.57 (s, 1H,
2
HR py), 7.06 (s, 1H, Hâ′ py). H NMR (300 MHz, C6H6, 293 K):
δ 6.98 and 6.20 (both s, 1D, Dγ and Dâ py). 13C{1H} NMR (75.42
MHz, C7D8, 293 K, Cγ and Câ of the pyridine ring, no changes
in the other signals): δ 115.5 (t(1:1:1), J C-D ) 24.6 Hz), 132.4
(t(1:1:1), J C-D ) 24.3 Hz).
P r ep a r a tion of Os(NC5H4-o-CHdCH)Cl(η2-H2)(P iP r 3)2
(4). A yellow solution of 3 (203.1 mg, 0.288 mmol) in 15 mL of
dichloromethane was heated under reflux for 16 h. The yellow
solution was filtered through Celite and dried in vacuo.
Pentane was added to afford a yellow oil, which was washed
with further portions of pentane at 223 K and dried in vacuo.
Yield: 63.2 mg (34%). IR (KBr, cm-1): ν(OsH) 2174 (m); ν(Cd
Rea ction of 2 w ith HBF 4‚OEt2 a n d H2. A yellow solution
of 2 (20.0 mg, 0. 032 mmol) in CD2Cl2 in an NMR tube was
treated with 1.0 equiv of HBF4‚OEt2 (4 µL, 0.032 mmol), and
the tube was sealed under hydrogen atmosphere. After 4 h,
the 1H and 31P{1H} NMR spectra of the resulting solution
revealed the formation of complex 1 and [HNC5H5-o-CH2CH3]-
BF4. Data for [HNC5H5-o-CH2CH3]BF4: 1H NMR (300 MHz,
CD2Cl2, 293 K): δ 12.99 (br, 1H, NH), 8.66 (d, J H-H ) 7.7 Hz,
1H, py), 8.51 (vt, J H-H ) 7.7 Hz, 1H, py), 7.89 (d, J H-H ) 7.7
Hz, 1H, py), 7.87 (vt, J H-H ) 7.7 Hz, 1H, py), 3.14 (quartet,
1
C) 1602 (s). H NMR (300 MHz, C6D6, 293 K, plus COSY): δ
10.57 (d, J H-H ) 6.7 Hz, 1H, HR py), 10.06 (dt, J H-H ) 7.3 Hz,
J H-H ) 4.6 Hz, 1H, OsCH), 7.32 (d, J H-H ) 7.3 Hz, 1H, CH),
6.98 (d, J H-H ) 6.7 Hz, 1H, Hâ′ py), 6.92 and 6.48 (both vt,
J H-H ) 6.7 Hz, 1H, Hâ and Hγ py), 2.30 (m, 6H, PCH), 1.08
and 0.96 (both dvt, N ) 12.6 Hz, J H-H ) 6.9 Hz, 18H, PCCH3),
-7.71 (td, J H-P ) 12.5 Hz, J H-H ) 4.6 Hz, 2H, OsH). 31P{1H}
NMR (121.42 MHz, C6D6, 293 K): δ 9.02 (s). 13C{1H} NMR
(75.42 MHz, C6D6, 293 K, plus APT): δ 180.6 (t, J P-C ) 6.1
Hz, OsCH), 167.8 (s, Cipso), 151.1 (s, dCH), 134.6, 125.1, 118.5
and 114.3 (all s, py), 25.6 (vt, N ) 23.7 Hz, PCH), 19.5 and
19.4 (both s, PCCH3). MS (FAB+): m/z 651 (M+ - 2H). T1(min)
(ms, OsH2, 300 MHz, CD2Cl2, 193 K): 39 ( 1 (-7.75 ppm, 2H).
J H-H ) 7.5 Hz, 2H, CH2), 1.43 (t, J H-H ) 7.5 Hz, 3H, CH3). 19
NMR (282.33 MHz, CD2Cl2, 293 K): δ -151.0 (br).
F
P r ep a r a t ion of [OsH (η2-H 2)(η2-CH2dCH -o-C5H 4N)(P i-
P r 3)2]BF 4 (3). A yellow solution of 2 (131.4 mg, 0.213 mmol)
in 30 mL of diethyl ether was treated with 1 equiv of HBF4‚
OEt2 (29 µL, 0.213 mmol) and stirred for 40 min at room
temperature. During the course of the reaction a white solid
formed. The solvent was removed, and the solid was washed
with further portions of diethyl ether and dried in vacuo.
Yield: 137.6 mg (92%). Anal. Calcd for C25H52BF4NOsP2: C
42.55, H 7.43, N 1.98. Found: C 42.37, H 7.85, N 1.97. IR (KBr,
cm-1): ν(OsH) 2152 (s), 2098 (m); ν(CdC) 1603 (s); ν(BF4) 1050
Os(NC5H4-o-CHdCH)Cl(η2-HD)(PiPr3)2 was obtained from
4 stirred in CD3OD for 1 day. 1H NMR (300 MHz, CD3OD,
293 K, high-field region): δ -7.71 (tt(1:1:1) d, J H-P ) 12.5 Hz,
J H-D ) 6.3 Hz, J H-H ) 4.6 Hz).
Rea ction of OsH6(P iP r 3)2 w ith N-Meth ylen e-2-p yr id in -
a m in e. A colorless solution of OsH6(PiPr3)2 (207.0 mg, 0.401
mmol) in 15 mL of toluene was treated with 1.4 equiv of
N-methylene-2-pyridinamine (59.4 mg, 0.560 mmol) and heated
under reflux for 5 h. The resulting orange solution was filtered
(br). 1H NMR (300 MHz, CD2Cl2, 293 K): δ 8.18 (d, J H-H
)
7.0 Hz, 1H, HR py), 7.74 and 7.22 (both vt, J H-H ) 7.0 Hz, 1H,
Hâ and Hγ py), 7.04 (d, J H-H ) 7.0 Hz, 1H, Hâ′ py), 4.23 (br,
1H, CH2), 3.40 (br, 1H, CH2), 3.16 (d, J H-H ) 7.8 Hz, 1H, CH),
2.42 and 2.21 (both m, 3H, PCH), 1.16 (dvt, N ) 12.6 Hz, J H-H
) 6.9 Hz, 27H, PCHCH3), 0.92 (br, 9H, PCCH3), -4.53 (br,
1
through Celite and dried in vacuo. The H and 31P{1H} NMR
1
spectra of the residue, in benzene-d6, indicated the formation
of two products: 5 and 6 in a 3:1 ratio. Methanol was added
to afford complex 5 as a yellow solid, which was washed with
further portions of methanol at 223 K and dried in vacuo.
Complex 6 was the major component in the supernatant
solution, but it could not be isolated purely.
1H, OsH), -13.29 (br, 2H, OsH). H NMR (300 MHz, CD2Cl2,
253 K): δ 8.16 (d, J H-H ) 7.0 Hz, 1H, HR py), 7.72 and 7.21
(both vt, J H-H ) 7.0 Hz, 1H, Hâ and Hγ py), 7.03 (d, J H-H
)
7.0 Hz, 1H, Hâ′ py), 4.16 (ddd, J H-P ) 8.1 Hz, J H-H ) 8.1 Hz,
J H-H ) 7.6 Hz, 1H, CHpy), 3.36 (dd, J H-P ) 13.2 Hz, J H-H
)
8.1 Hz, 1H, CH cis to py), 3.13 (d, J H-H ) 7.6 Hz, 1H, CH trans
to py), 2.40 and 2.18 (both m, 3H, PCH), 1.13 (dvt, N ) 12.6
Hz, J H-H ) 6.9 Hz, 27H, PCCH3), 1.13 (dvt, N ) 12.6 Hz, J H-H
Da ta for OsH3(NC5H4-o-NCH3)(P iP r 3)2 (5). Yield: 129.3
mg (52%). Anal. Calcd for C24H52N2OsP2: C 46.43, H 8.44, N
4.51. Found: C 46.56, H 8.24, N 4.92. IR (KBr, cm-1): ν(OsH)
2134 (s), 2116 (s). 1H NMR (300 MHz, C7D8, 293 K): δ 7.88 (d,
J H-H ) 7.0 Hz, 1H, HR py), 6.88 and 5.87 (both vt, J H-H ) 7.0
Hz, 1H, Hâ and Hγ py), 5.55 (d, J H-H ) 7.0 Hz, 1H, Hâ′ py),
3.05 (s, 3H, CH3), 1.93 (m, 6H, PCH), 1.14 and 1.08 (both dvt,
N ) 12.5 Hz, J H-H ) 6.3 Hz, 18H, PCHCH3), -11.88 (br, 3H,
) 6.9 Hz, 9H, PCCH3), -4.55 (dd, J H-P ) 23.7 Hz, J H-P′
)
16.8 Hz, 1H, OsH), -13.30 (dd, J H-P ) J H-P′ ) 11.4 Hz, 2H,
OsH2). 31P{1H} NMR (121.42 MHz, CD2Cl2, 293 K): AB spin
system, δ 20.1, ∆ν ) 189 Hz, J AB ) 157 Hz. 19F NMR (282.33
MHz, CD2Cl2, 293 K): δ -155.4 (br). 13C{1H} NMR (75.42
MHz, CD2Cl2, 233 K, plus APT): δ 165.6 (s, Cipso), 149.1, 136.7,
124.5, and 122.9 (all s, py), 46.7 (s, CH2), 42.8 (s, CH), 27.9 (d,
J C-P ) 25.5 Hz, PCH), 27.0 (d, J C-P ) 26.3 Hz, PCH), 19.7,
19.6, 19.3, and 18.5 (all s, PCHCH3). MS (FAB+): m/z 610 (M+
- 10H). T1(min) (ms, OsH3, 300 MHz, CD2Cl2, 193 K): 129 ( 6
(-4.58 ppm, 1H), 48 ( 2 (-13.35 ppm, 2H).
OsH). H{31P} NMR (300 MHz, C7D8, 183 K, in the high-field
1
region): δ -10.97 (d, J H-H ) 11.6, 1H), -11.65 (d, J H-H ) 24.7,
1H), -12.24 (dd, J H-H ) 24.7, J H-H ) 11.6, 1H). 31P{1H} NMR
(121.42 MHz, C7D8, 293 K): δ 26.4 (s). 13C{1H} NMR (75.42
MHz, C7D8, 293 K): δ 167.5 (s, Cipso), 149.2, 133.1, 102.9, and
102.1 (all s, py), 36.0 (s, CH3), 27.3 (vt, N ) 23.0 Hz, PCH),
P r ep a r a t ion of [OsH (η2-H 2)(η2-CH2dCH -o-C5H 4N)-
(P iP r 3)2]BF 4 P a r tia lly Deu ter a ted . This complex was pre-
pared as described for 3 starting from 2 (106.1 mg, 0.172 mmol)
and DBF4‚D2O (33 µL, 0.173 mmol). A white solid was
20.3 and 20.1 (both s, PCHCH3). MS (FAB+): m/z 619 (M+
-
3H). T1(min) (ms, OsH3, 300 MHz, C7D8, 208 K): 109 ( 2 (-10.97
ppm, 1H), 94 ( 1 (-11.65 ppm, 1H), 87 ( 1 (-12.24 ppm, 1H).

3638 Organometallics, Vol. 23, No. 15, 2004
Ta ble 4. Cr ysta l Da ta a n d Da ta Collection a n d Refin em en t for 2, 3, a n d 5
Barrio et al.
2
3
5
Crystal Data
formula
molecular wt
C
25H51NOsP2
C25H52BF4NOsP2‚0.5(C4H10O)
742.69
C24H52N2OsP2
620.82
617.81
color and habit
symmetry, space group
a, Å
orange, irregular block
triclinic, P1h
7.5678(6)
dark red, irregular block
triclinic, P1h
8.947(2)
orange, irregular block
monoclinic, P21/c
7.7832(7)
b, Å
c, Å
12.1370(10)
15.4192(13)
79.5480(10)
89.0740(10)
82.6080(10)
1381.1(2)
11.992(3)
32.215(8)
84.276(4)
83.400(4)
69.593(4)
3211.2(13)
4
38.317(3)
18.7027(17)
R, deg
â, deg
γ, deg
V, Å3
Z
96.8040(10)
5538.4(9)
8
1.489
2
D
calc, g cm-3
1.486
1.536
Data Collection and Refinement
diffractometer
λ(Mo KR), Å
Bruker Smart APEX
0.71073
monochromator
scan type
graphite oriented
ω scans
µ, mm-1
4.744
3, 57
100
4.112
4.733
3, 57
100
2θ, range, deg
3, 57
temp, K
100
no. of data collected
no. of unique data
no. of params/restraints
16 410
6356 (Rint ) 0.0442)
307/0
0.0351
0.0603
0.848
39 261
14 903 (Rint ) 0.0410)
734/10
0.0307
0.0516
0.777
67 277
13 337 (Rint ) 0.0372)
563/54
0.0269
0.0599
0.946
R1 [F2 > 2σ(F2)]
a
b
wR2 [all data]
Sc [all data]
R1(F) )∑||Fo| - |Fc||/∑|Fo|. wR2(F2) ) {∑[w(Fo - Fc2)2]/∑[w(Fo2)2]}1/2
.
c Goof ) S ) {∑[Fo - Fc2)2]/(n - p)}1/2, where n is the number
a
b
2
2
of reflections, and p is the number of refined parameters.
1H, Hγ py), 6.84 (vt, J H-H ) 7.5 Hz, 1H, p-Ph), 5.93 (vt, J H-H
) 6.7 Hz, 1H, Hâ py), 5.82 (d, J H-H ) 6.7 Hz, 1H, Hâ′ py), 4.58
(s, 2H, CH2), 1.91 (m, 6H, PCH), 1.11 and 1.01 (both dvt, N )
12.7 Hz, J H-H ) 6.5 Hz, 18H, PCHCH3), -11.92 (br, 3H, OsH).
1H{31P} NMR (300 MHz, C7D8, 193 K, in the high-field
region): δ -10.89 (d, J H-H ) 11.8, 1H), -12.11 (d, J H-H ) 22.3,
1H), -12.32 (dd, J H-H ) 22.3, J H-H ) 11.8, 1H). 31P{1H} NMR
(121.42 MHz, C7D8, 293 K): δ 25.0 (s). 13C{1H} NMR (75.42
MHz, C7D8, 293 K, plus HETCOR): δ 168.4 (s, Cipso(py)), 149.4
(s, py), 142.9 (s, Cipso(Ph)), 133.1 (s, p-Ph), 128.5 (s, o-Ph), 128.1
(s, m-Ph), 126.5, 103.9, and 103.7 (all s, py), 54.6 (s, CH2), 27.5
(vt, N ) 23.0 Hz, PCH), 20.5 and 19.8 (both s, PCHCH3). MS
(FAB+): m/z 698 (M+). T1(min) (ms, OsH3, 300 MHz, C7D8, 223
K): 96 ( 2 (-10.90 ppm, 1H), 80 ( 2 (-12.22 ppm, 2H).
Da ta for OsH3(NC5H4-o-NdCH)(P iP r 3)2 (6). 1H NMR (300
MHz, C7D8, 293 K): δ 14.26 (virtual quartet, J H-H(OsH ) 3
)
3
Hz, 1H, OsCH), 9.40 and 7.85 (d, J H-H ) 6.8 Hz, 1H, HR and
Hâ′ py), 7.01 and 6.16 (both dd, J H-H ) J H-H ) 6.8 Hz, 1H, Hγ
and Hâ py), 1.70 (m, 6H, PCH), 0.93 and 0.92 (both dvt, N )
12.7 Hz, J H-H ) 7.0 Hz, 18H, PCHCH3), -8.19 (br, 2H, OsH),
1
-11.42 (br, 1H, OsH). H{31P} NMR (300 MHz, C7D8, 193 K,
only variable-temperature signals): low-field (OsCH), δ 14.30
(d, J H-H ) 9 Hz, 1H, OsCH); high-field region, δ -5.77 and
-10.53 (both d, J H
) 22 Hz, 1H, HA and HB), -11.33 (d,
-H
A
B
J H-H ) 9 Hz, 1H, OsH3). 31P{1H} NMR (121.42 MHz, C7D8,
293 K): δ 30.8 (s). 13C{1H} NMR (75.42 MHz, C7D8, 293 K): δ
251.7 (t, J C-P ) 4.6 Hz, OsC), 172.5 (s, Cipso), 155.6, 134.7,
119.3, and 116.3 (all s, py), 27.9 (vt, N ) 25.7 Hz, PCH), 19.8
and 19.7 (both s, PCHCH3). T1(min) (ms, OsH3, 300 MHz, C7D8,
213 K): 94 ( 5 (-5.77 ppm, 1H), 85 ( 4 (-10.53 ppm, 1H),
126 ( 2 (-11.33 ppm, 1H).
P r ep a r a tion of [OsH3(NC5H4-o-NHCH3)(P iP r 3)2]BF 4 (8).
A yellow solution of 5 (129.0 mg, 0.208 mmol) in 30 mL of
diethyl ether was treated with 1 equiv of HBF4‚OEt2 (29 µL,
0.213 mmol) and stirred for 40 min at room temperature.
During the course of the reaction a white solid formed. The
solvent was removed, and the solid was washed with further
portions of diethyl ether and dried in vacuo. Yield: 121.5 mg
(82%). Anal. Calcd for C24H53BF4N2OsP2: C 40.68, H 7.54, N
3.95. Found: C 40.54, H 7.73, N 4.01. IR (KBr, cm-1): ν(NH)
3264 (m); ν(OsH) 2157 (s), 2122 (m); ν(BF4) 1050 (br). 1H NMR
(300 MHz, CD2Cl2, 293 K): δ 8.47 (d, J H-H ) 7.1 Hz, 1H, HR
py), 7.86 and 7.45 (both vt, J H-H ) 7.1 Hz, 1H, Hγ and Hâ py),
The addition of 0.05 equiv of OsH6(PiPr3)2 to an NMR tube
containing 6 in toluene-d8 or benzene-d6 gives, after 10 h,
1
complex 6 partially deuterated in the pyridine ring. H NMR
(300 MHz, C6D6 or C7D8, 293 K, pyridine ring): δ 9.40 (s, 1H,
2
H
R py), 7.85 (s, 1H, Hâ′ py). H NMR (300 MHz, C6H6, 293 K):
δ 7.12 and 6.27 (both s, 1D, Dγ and Dâ py). 13C{1H} NMR (75.42
MHz, C7D8, 293 K, Cγ and Câ of the pyridine ring, no changes
in the other signals): δ 116.3 (t(1:1:1), J C-D ) 24.4 Hz), 134.7
(t(1:1:1), J C-D ) 23.9 Hz).
P r ep a r a tion of OsH3(NC5H4-o-NCH2P h )(P iP r 3)2 (7). A
colorless solution of OsH6(PiPr3)2 (173.1 mg, 0.335 mmol) in
15 mL of toluene was treated with 1.3 equiv of (E)-N-
(phenylmethylene)-2-pyridinamine (79.2 mg, 0.435 mmol) and
heated under reflux for 5 h. The resulting yellow solution was
filtered through Celite and dried in vacuo. Pentane was added
to afford a yellow solid, which was washed with further
portions of pentane at 223 K and dried in vacuo. Yield: 175.1
mg (75%). Anal. Calcd for C30H56N2OsP2: C 51.70, H 8.10, N
4.02. Found: C 51.63, H 8.05, N 4.17. IR (KBr, cm-1): ν(OsH)
2117 (s), 2102 (s). 1H NMR (300 MHz, C7D8, 293 K): δ 7.96 (d,
J H-H ) 6.7 Hz, 1H, HR py), 7.40 (d, J H-H ) 7.5 Hz, 2H, o-Ph),
7.18 (vt, J H-H ) 7.5 Hz, 2H, m-Ph), 7.09 (vt, J H-H ) 6.7 Hz,
7.42 (d, J H-H ) 7.1 Hz, 1H, Hâ′ py), 5.42 (br quartet, J H-H
)
5.9 Hz, 1H, NH), 3.28 (d, J H-H ) 5.9 Hz, 3H, CH3), 2.10 (m,
6H, PCH), 1.19 and 0.96 (both dvt, N ) 13.4 Hz, J H-H ) 6.7
Hz, 18H, PCHCH3), -12.80 (br, 3H, OsH). 1H{31P} NMR (300
MHz, CD2Cl2, 193 K, in the high-field region): δ -10.59 (d,
J H
) 63.7 Hz, 1H), -12.65 (dd, J H
) 63.7 Hz, J H
-H
A
-H -H
) 15.9 Hz, 1H). 31P{1H}
B
A
B
B
C
) 15.9 Hz, 1H), -15.19 (d, J H
-H
B
C
NMR (121.42 MHz, CD2Cl2, 303 K): δ 27.4 (s). 31P{1H} NMR
(121.42 MHz, CD2Cl2, 198 K): ΑΒ spin system, δ 25.2, ∆ν )
429 Hz, J AB ) 245 Hz. 19F NMR (282.33 MHz, CD2Cl2, 293 K):
δ -154.9 (br). 13C{1H} NMR (75.42 MHz, CD2Cl2, 293 K, plus
APT): δ 161.5 (s, Cipso), 150.1, 137.6, 127.1, and 120.3 (all s,
py), 42.1 (s, CH3), 27.6 (vt, N ) 25.5 Hz, PCH), 20.3 and 19.4

Osmium-Hexahydride Complex
Organometallics, Vol. 23, No. 15, 2004 3639
(both s, PCHCH3). MS (FAB+): m/z 621 (M+ - 2H). T1(min) (ms,
OsH3, 300 MHz, CD2Cl2, 203 K): 71 ( 3 (-10.59 ppm, 1H),
69 ( 3 (-12.65 ppm, 1H), 101 ( 1 (-15.19 ppm, 1H).
3 and 5 the asymmetric unit shows two independent, but
chemically equivalent molecules, and a solvent molecule of
diethyl ether was observed in 3. In the last cycles of anisotropic
refinement, the shape and size of some thermal ellipsoids
suggest the presence of disorder in a phosphine ligand of
molecule a in 5 due to a rotation about the P-Os bond. This
ligand was refined with two moieties with isotropic thermal
parameters and complementary occupancy factors. The hy-
drogen atoms for nondisordered groups were observed or
calculated and refined using a restricted riding model or freely.
Hydride ligands were located, but not all of them refined
appropriately, and some restraints were used in 2 (thermal
parameters) and 3 (Os-H bonds). All the highest electronic
residuals were observed in the close proximity of the Os centers
and make no chemical sense. Crystal data and details of the
data collection and refinement are given in Table 4.
P r epar ation of [OsH3(NC5H4-o-NHCH3)(P iP r 3)2]BF4 P ar -
tia lly Deu ter a ted . This complex was prepared as described
for 8 starting from 5 (78.6 mg, 0.127 mmol) and DBF4‚D2O
(24 µL, 0.127 mmol). A white solid was obtained. Yield: 32.8
mg (36%). 2H NMR (46.03 MHz, CH2Cl2, 293 K): δ 8.5 (s,
0.07D, DR py), 7.4 (s, 0.14D, Dâ′ py), 5.4 (s, 0.47D, ND), 3.3 (s,
0.27D, CDH2), -12.4 (br, 0.05D, OsD).
Str u ctu r a l An a lysis of Com p lexes 2, 3, a n d 5. Suitable
crystals for X-ray diffraction were obtained by slow diffusion
of pentane into a saturated solution of 2 in toluene, diethyl
ether into a saturated solution of 3 in dichloromethane, or
methanol into a saturated solution of 5 in toluene. X-ray data
were collected for all complexes on a Bruker Smart APEX CCD
diffractometer equipped with a normal focus, 2.4 kW sealed
tube source (molybdenum radiation, λ ) 0.71073 Å) operating
at 50 kV and 40 (2) or 30 (3 and 5) mA. Data were collected
over the complete sphere by a combination of four sets. Each
frame exposure time was 10 (3) or 20 (2 and 5) s covering 0.3°
in ω. Data were corrected for absorption by using a multiscan
method applied with the SADABS34 program. The structures
for all compounds were solved by the Patterson method.
Refinement, by full-matrix least squares on F2 with
SHELXL97,35 was similar for all complexes, including isotropic
and subsequently anisotropic displacement parameters. For
Ack n ow led gm en t . Financial support from the
MCYT of Spain (Proyect BQU2002-00606 and PPQ2000-
0488-P4-02) is acknowledged. P.B. thanks the “Minis-
terio de Educacio´n, Cultura y Deporte” for her grant.
Su p p or tin g In for m a tion Ava ila ble: Tables of positional
and displacement parameters, crystallographic data, and bond
lengths and angles. This material is available free of charge
via the Internet at http://pubs.acs.org.
OM0497036
(35) SHELXTL Package, v. 6.10; Bruker-AXS: Madison, WI, 2000.
Sheldrick, G. M. SHELXS-86 and SHELXL-97; University of Go¨tin-
gen: Go¨tingen, Germany, 1997.
(34) Blessing, R. H. Acta Crystallogr., Sect. A 1995, 51, 33. SADABS,
Area-detector absorption correction; Bruker-AXS: Madison, WI, 1996.