Synthesis and characterization of OsX{NH=C(Ph)C6H4}H2(PiPr 3)2 (X = H, Cl, Br, I): Nature of the H2 unit and its behavior in solution

Article abstract of DOI:10.1021/om9802820

The hexahydride OsH₆(PⁱPr₃)₂ (1) reacts with benzophenone imine to give the trihydride derivative OsH₃{NH=C(Ph)C₆H₄}(PⁱPr ₃)₂ (2). The three hydride ligands and the bidentate group of 2 are situated in the equatorial plane of a pentagonal-bipyramidal arrangement of ligands around the metallic center. In solution, two thermally activated exchange processes take place between these hydride ligands, one of them faster than the other one. The reaction of 2 with HCl leads to OsH₃Cl(NH=CPh₂)(PⁱPr₃)₂ (3), which evolves in solution into the elongated dihydrogen compound OsCl{NH=C(Ph)C₆H₄}(η²-H₂)(P ⁱPr₃)₂ (4). Complex 4 and the related compounds OsX{NH=C(Ph)C₆H₄}(η²-H₂)(P ⁱPr₃)₂ (X = Br (5), I (6)) can be also prepared by protonation of 2 with HBF₄·OEt₂ in dichloromethane and subsequent treatment with NaX (X = Cl, Br, I). The structure of 4 has been determined by X-ray diffraction. The geometry around the osmium atom can be described as a distorted octahedron, with the triisopropylphosphine ligands occupying two relative trans positions. The remaining perpendicular plane is formed by the mutually cis disposed chloro and dihydrogen ligands and the metalated benzophenone imine group, which has a bite angle of 75.1(1)°. The H₂ unit of 4-6 shows a restricted rotational motion in solution. Thus, the ¹H NMR spectra in the high-field region are a function of the temperature. Lowering the sample temperature leads to a broadening of the dihydrogen resonances. At 213 K, decoalescence occurs, and at 193 K, two signals are clearly observed. Theoretical calculations suggest that the transition states for the hydrogen exchanges in 2 and 4-6 present dihydrogen-like nature.

Full text of DOI:10.1021/om9802820

Organometallics 1998, 17, 4065-4076
4065
Syn th esis a n d Ch a r a cter iza tion of
OsX{NHdC(P h )C6H4}H2(P iP r 3)2 (X ) H, Cl, Br , I): Na tu r e
of th e H2 Un it a n d Its Beh a vior in Solu tion
Guada Barea,† Miguel A. Esteruelas,*,‡ Agust´ı Lledo´s,*,† Ana M. Lo´pez,‡
Enrique On˜ate,‡ and J ose´ I. Tolosa‡
Departamento de Quı´mica Inorga´nica, Instituto de Ciencia de Materiales de Arago´n,
Universidad de Zaragoza, CSIC, 50009 Zaragoza, Spain, and Unitat de Qu´ımica Fı´sica,
Departament de Quı´mica, Universitat Auto`noma de Barcelona,
08193 Bellaterra, Barcelona, Spain
Received April 14, 1998
The hexahydride OsH6(PiPr3)2 (1) reacts with benzophenone imine to give the trihydride
derivative OsH3{NHdC(Ph)C6H4}(PiPr3)2 (2). The three hydride ligands and the bidentate
group of 2 are situated in the equatorial plane of a pentagonal-bipyramidal arrangement of
ligands around the metallic center. In solution, two thermally activated exchange processes
take place between these hydride ligands, one of them faster than the other one. The reaction
of 2 with HCl leads to OsH3Cl(NHdCPh2)(PiPr3)2 (3), which evolves in solution into the
elongated dihydrogen compound OsCl{NHdC(Ph)C6H4}(η2-H2)(PiPr3)2 (4). Complex 4 and
the related compounds OsX{NHdC(Ph)C6H4}(η2-H2)(PiPr3)2 (X ) Br (5), I (6)) can be also
prepared by protonation of 2 with HBF4‚OEt2 in dichloromethane and subsequent treatment
with NaX (X ) Cl, Br, I). The structure of 4 has been determined by X-ray diffraction. The
geometry around the osmium atom can be described as a distorted octahedron, with the
triisopropylphosphine ligands occupying two relative trans positions. The remaining
perpendicular plane is formed by the mutually cis disposed chloro and dihydrogen ligands
and the metalated benzophenone imine group, which has a bite angle of 75.1(1)°. The H2
1
unit of 4-6 shows a restricted rotational motion in solution. Thus, the H NMR spectra in
the high-field region are a function of the temperature. Lowering the sample temperature
leads to a broadening of the dihydrogen resonances. At 213 K, decoalescence occurs, and at
193 K, two signals are clearly observed. Theoretical calculations suggest that the transition
states for the hydrogen exchanges in 2 and 4-6 present dihydrogen-like nature.
In tr od u ction
several distinct spectroscopic features: for example low
T1(min) and high J (HD) constants for the M(HD)
isotopomer. These have helped to characterize the
complexes, to estimate the hydrogen-hydrogen dis-
tance, and hence, to get information on the amount of
stretching of the hydrogen-hydrogen bond.1f,2
Hydrides have the hydrogen-hydrogen distances
expected for two ligands occupying the usual stereo-
chemical positions in coordination polyhedra (>1.6 Å).
Such distances usually result in little communication
between the nuclei: a long T1(min) (>90 ms at 200
MHz) and very small J (HD) constant for the M(H)(D)
There are two well-established classes of compounds
with more than one hydrogen atom in the coordination
sphere of a transition metal: nonclassical dihydrides
(or dihydrogens) and classical hydrides.1
Dihydrogen compounds contain a hydrogen molecule
coordinated to the metal, and the separation between
the hydrogen atoms is between 0.8 and 1.0 Å. This
range appears suitable to include complexes with a
rapidly spinning dihydrogen unit whose properties are
perturbed little from those of free dihydrogen gas. Thus,
the molecular hydrogen, when coordinated, exhibits
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1996, 118, 5396. (g) Hush, N. S. J . Am. Chem. Soc. 1997, 119, 1717.
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† Universitat Auto`noma de Barcelona.
‡ Universidad de Zaragoza.
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Comments Inorg. Chem. 1988, 7, 17. (c) Henerson, R. H. Transition
Met. Chem. 1988, 13, 474. (d) Crabtree, R. H.; Hamilton, D. G. Adv.
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1990, 23, 95. (f) J essop, P. G.; Morris, R. H. Coord. Chem. Rev. 1992,
121, 155. (g) Crabtree, R. H. Angew. Chem., Int. Ed. Engl. 1993, 32,
789. (h) Heinekey, D. M.; Oldham, J . Chem. Rev. 1993, 93, 913. (i)
Morris, R. H. Can. J . Chem. 1996, 74, 1907.
S0276-7333(98)00282-9 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 08/15/1998

4066 Organometallics, Vol. 17, No. 18, 1998
Barea et al.
1
isotopomer.1,3 Variable-temperature H NMR spectra
of the interesting points of this dihydrogen complex lies
in the fact that the activation barrier for the rotation
of the dihydrogen ligand is relatively high (ca. 10 kcal
mol-1). As a consequence of this, the rotation of the HD
molecule in the isotopomer [Nb(η5-C5Me5)2(η2-HD)(PMe2-
Ph)]CF3CO2 is blocked on the NMR time scale. In the
of some of these compounds have revealed dynamic
behaviors associated with thermally activated exchange
processes, involving the hydride positions. Theoretical
studies on the hydride exchange processes in the tri-
hydrides [CpIrH3L]+ (L ) PH3, CO),4 OsH3(η2-H2BH2)-
(PH3)2,5 and [CpMH3]n+ (M ) Mo, W, n ) 1; M ) Nb,
Ta, n ) 0)6 suggest that the exchange takes place
through a transition state, which is reached by a
shortening of the hydrogen-hydrogen distance and a
lengthening of the M-H distance, and from a geo-
metrical point or view, the exchange presents a η2-H2
complex-like nature.
In addition to these two types of compounds, there is
a group of complexes that is difficult to classify, with
hydrogen-hydrogen distances between 1.0 and 1.5 Å.
These compounds are seen as frozen structures at
various points on the reaction profile path for the
oxidative addition-reductive elimination of molecular
hydrogen at the metallic center. Thus, it is assumed
that the potential energy versus the hydrogen-hydro-
gen distance plot for such a complex has a minimum at
the equilibrium hydrogen-hydrogen distance.1f An
indicator of a complex containing a ligand of this type
(elongated dihydrogen, also referred as to “stretched”)
is the J (HD) value in the M(HD) isotopomer. It has
been proposed that when this coupling falls between 5
and 25 Hz, such a form of the ligand is present.7
The spectroscopic properties of an elongated dihydro-
gen complex might also be explained by the averaging
of the properties of a dihydride compound and a complex
with a rotating dihydrogen ligand, caused by a low-
energy bond-splitting/bond-forming process. In such a
case, a potential surface with a double well must be
found.1f
1
high-field region of the H NMR spectrum of [Nb(η5-C5-
Me5)2(η2-H2)(PMe2Ph)]CF3CO2, a single resonance is
observed for the two hydrogen atoms at high tempera-
tures. When the temperature is lowered, decoalescence
is not observed. However, a slowly rotating HD unit in
the isotopomer [Nb(η5-C5Me5)2(η2-HD)(PMe2Ph)]CF3CO2
enables the observation of two interconverting rotamers.
Subsequently, a similar phenomenon was observed for
[Ta(η5-C5H5)2(η2-HD)(CO)]BF4 (J (HD) ) 27.5 Hz)9 and
[Nb(η5-C5H4SiMe3)2(η2-H2)(CNR)]+ (J (HD) ) 30 Hz).10
As a part of the work of our groups on osmium
polyhydride chemistry,3c,5,11 in this paper we report the
synthesis and characterization of complexes of formula
OsX{NHdC(Ph)C6H4}H2(PiPr3)2 (X ) H, Cl, Br, I), a
theoretical study on OsH2 interactions in these systems,
and the behavior of the H2 unit in solution.
Resu lts a n d Discu ssion
1. OsH3{NHdC(P h )C6H4}(P iP r 3)2. Recently, we
have reported that the hexahydride compound OsH6(P-
iPr3)2 (1) reacts with tetrafluorobenzobarrelene, 2,5-
norbornadiene, and 1,3-cyclohexadiene to afford the
dihydride diolefin derivatives OsH2(η4-TFB)(PiPr3)2,
OsH2(η4-NBD)(PiPr3)2, and OsH2(η4-cyclohexadiene)(P-
iPr3)2, respectively. The protonation of OsH2(η4-TFB)(P-
iPr3)2 and OsH2(η4-NBD)(PiPr3)2 leads to the trihydride
diolefin cations [OsH3(η4-TFB)(PiPr3)2]+ and [OsH2(η4-
NBD)(PiPr3)2]+, while under the same conditions, the
complex OsH2(η4-cyclohexadiene)(PiPr3)2 yields the di-
hydride cyclohexenyl derivative [OsH2(η3-C6H9)(P-
iPr3)2]+, which shows an agostic interaction between the
osmium center and one of the two endo-CH bonds
adjacent to the π-allyl unit.3c
Previously, we had observed that complex 1 reacts
with 2,2′-biimidazole to give the trihydride compound
OsH3(Hbiim)(PiPr3)2, which affords the heterobimetallic
complexes (PiPr3)2H3Os(µ-biim)M(COD) by reaction with
the dimers [M(µ-OMe)(COD)]2 (M ) Rh, Ir).11c
Continuing with the study of the reactivity of 1, we
have now carried out the reaction of this complex with
benzophenone imine. Treatment under reflux of a
toluene solution of 1 with ca. 1 equiv of benzophenone
imine leads after 6 h to a red solution, from which the
Rotational motion of the elongated dihydrogen struc-
ture is assumed to be restricted. However, only very
recently has this been proven. In 1995, J alo´n, Otero,
Chaudret, and co-workers8 reported the preparation of
the complex [Nb(η5-C5Me5)2(η2-H2)(PMe2Ph)]CF3CO2
(J (HD) ) 15 Hz) by protonation at low temperature of
the corresponding neutral hydridoniobium complex. One
(3) (a) Bakhmutov, V. I.; Vorontsov, E. V.; Vymenits, A. B. Inorg.
Chem. 1995, 34, 214. (b) Gusev, D. G.; Kuhlman, R. L.; Renkema, K.
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Castillo, A.; Esteruelas, M. A.; On˜ate, E.; Ruiz, N. J . Am. Chem. Soc.
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Am. Chem. Soc. 1995, 117, 1069.
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F.; Oro, L. A.; Valero, C.; Volatron, F. J . Am. Chem. Soc. 1996, 118,
8388.
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Bertran, J . J . Am. Chem. Soc. 1996, 118, 4617.
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5166. (b) Collman, J . P.; Wagenknecht, P. S.; Hembre, R. T.; Lewis,
N. S. J . Am. Chem. Soc. 1990, 112, 1294. (c) Michos, D.; Luo, X.-L.;
Howard, J . A. K.; Crabtree, R. H. Inorg. Chem. 1992, 31, 3914. (d)
Albinati, A.; Bakhmutov, V. I.; Caulton, K. G.; Clot, E.; Eckert, J .;
Eisenstein, O.; Gusev, D. G.; Grushim, 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. (e) Hasegawa, T.; Li, Z.; Parkin, S.; Hope, H.; McMullan,
R. K.; Koetzle, T. F.; Taube, H. J . Am. Chem. Soc. 1994, 116, 4352. (f)
Li, Z.-W.; Taube, H. J . Am. Chem. Soc. 1994, 116, 9506. (g) Schlaf,
M.; Lough, A. J .; Maltby, P. A.; Morris, R. H. Organometallics 1996,
15, 2270. (h) Chin, R. M.; Barrera, J .; Dubois, R. H.; Helberg, L. E.;
Sabat, M.; Bartucz, T. Y.; Lough, A. J .; Morris, R. H. Harman, W. D.
Inorg. Chem. 1997, 36, 3553. (i) Gelabert, R.; Moreno, M.; Lluch, J .
M.; Lledo´s, A. J . Am. Chem. Soc. 1997, 119, 9840.
trihydride complex OsH3{NHdC(Ph)C6H4}(PiPr3)2 was
isolated as a red solid in 80% yield (eq 1).
(9) Sabo-Etienne, S.; Chaudret, B.; Abou el Makarim, H. A.; Bar-
thelat, J .-C.; Daudey, J .-P.; Ulrich, S.; Limbach, H.-H.; Mo¨ıse, C. J .
Am. Chem. Soc. 1995, 117, 11602.
(10) Antin˜olo, A.; Carrillo-Hermosilla, F.; Fajardo, M.; Garc´ıa-Yuste,
S.; Otero, A.; Camanyes, S.; Maseras, F.; Moreno, M.; Lledo´s, A.; Lluch,
J . M. J . Am. Chem. Soc. 1997, 119, 6107.
(11) (a) Esteruelas, M. A.; J ean, Y.; Lledo´s, A.; Oro, L. A.; Ruiz, N.;
Volatron, F. Inorg. Chem. 1994, 33, 3609. (b) Buil, M. L.; Espinet, P.;
Esteruelas, M. A.; Lahoz, F. J .; Lledo´s, A.; Mart´ınez-Ilarduya, J . M.;
Maseras, F.; Modrego, J .; On˜ate, E.; Oro, L. A.; Sola, E.; Valero, C.
Inorg. Chem. 1996, 35, 1250. (c) 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.
(8) J alo´n, F. A.; Otero, A.; Manzano, B. R.; Villasen˜or, E.; Chaudret,
B. J . Am. Chem. Soc. 1995, 117, 10123.

OsX{NHdC(Ph)C6H4}H2(PiPr3)2
Organometallics, Vol. 17, No. 18, 1998 4067
The spectroscopic data for 2 agree well with the
structure proposed in eq 1. The IR spectrum in Nujol
shows the ν(NH) vibration at 3348 cm-1 along with
three bands at 2143, 2106, and 1942 cm-1, correspond-
ing to the ν(Os-H) vibrations. In the region δ 195-
175 the 13C{1H} NMR spectrum contains two triplets
at 194.6 (J (PC) ) 5.6 Hz) and 179.9 (J (PC) ) 3.0 Hz)
ppm. The triplet at 179.9 ppm was assigned to the
carbon atom of the CdN group by comparison of this
spectrum with those previously reported for the com-
plexes Os(C2Ph){NHdC(Ph)C6H4}(CO)(PiPr3)2 (δ 185.7;
J (PC) ) 2.9 Hz),12 [Ru{N(Ph)dC(R)C6H4}(η6-C6Me6)-
(PMe3)]BF4 (R ) H (δ 175.3), R ) CH3 (δ 180.4)),13 [Os-
{NHdC(Ph)C6H4}(η6-C6H3Me3)(PiPr3)]PF6 (δ 191.72,
J (PC) ) 1.5 Hz),14 Ru(η5-C5H5){NHdC(Ph)C6H4}(PPh3)
(δ 183.24, J (PC) ) 2.0 Hz)15 and OsH{NHdC(Ph)C6H4}-
(CO)(PiPr3)2 (δ 181.2),16 while the triplet at 194.6 ppm
was assigned to the aromatic carbon bonded to the
osmium. In agreement with the mutually trans disposi-
tion of the phosphine ligands, the 31P{1H} NMR spec-
trum in toluene-d8 shows a singlet at 26.8 ppm, which
is temperature-invariant between 353 and 193 K. At
F igu r e 1. 1H{31P} NMR spectra (300 MHz, toluene-d8) in
the high-field region of OsH3{NHdC(Ph)C6H4}(PiPr3)2 (2):
(a) observed; (b) simulated.
1
room temperature the H NMR spectrum in toluene-d8
exhibits an NH resonance at 10.25 ppm, along with the
expected resonances for the protons of the metalated
and nonmetalated phenyl rings, and the typical reso-
nances for the triisopropylphosphine protons. Further-
more, in the high-field region, the spectrum contains
two broad resonances at -9.07 (2H) and -9.87 (1H)
ppm.
In contrast to the 31P{1H} NMR spectrum, the 1H
NMR spectrum is temperature-dependent. At 353 K,
the spectrum shows in the hydride region a single triplet
resonance at -9.39 ppm with a P-H coupling constant
of 15.4 Hz. This observation is consistent with the
operation of two thermally activated site exchange
processes, which proceed at rates sufficient to lead to a
single hydride resonance. Consistent with this, lower-
ing the sample temperature leads to broadening of the
resonance. At 283 K, the first decoalescence occurs, and
at 223 K, the second one takes place. At this temper-
ature, an ABCX2 spin system (X ) 31P) is observed,
which becomes well-resolved at 193 K. The 1H{31P}
spectra (Figure 1) are simplified to the expected ABC
spin system. The values of the chemical shifts of the A
(δ -7.3), B (δ -9.9), and C (δ -10.5) sites as well as
the values of H-H coupling constants (J (AB) ) 0.0 Hz,
J (AC) ) 15.0 Hz, J (BC) ) 13.5 Hz) show no significant
temperature dependence. This is in contrast with that
observed for the related trihydride complexes OsH3-
(Hbiim)(PiPr3)2 (Hbiim ) 2,2′-biimidazole)11c and [OsH3-
(η4-diolefin)(PiPr3)2]BF4 (diolefin ) 2,5-norbornadiene,
tetrafluorobenzobarrelene),3c where the H-H coupling
constants are very sensitive to temperature, as a result
of a quantum-mechanical exchange process.
(12) Esteruelas, M. A.; Lahoz, F. J .; Lo´pez, A. M.; On˜ate, E.; Oro,
L. A. Organometallics 1995, 14, 2496.
(13) Martin, G. C.; Boncella, J . M. Organometallics 1989, 8, 2968.
(14) Daniel, T.; Mu¨ller, M.; Werner, H. Inorg. Chem. 1991, 30, 3118.
(15) Werner, H.; Daniel, T.; Knaup, W.; Nu¨rnberg, O. J . Organomet.
Chem. 1993, 362, 309.
(16) (a) Daniel, T.; Werner, H. Z. Naturforsch., B 1992, 4, 1707. (b)
Albe´niz, M. J .; Buil, M.; Esteruelas, M. A.; Lo´pez, A. M. J . Organomet.
Chem. 1997, 545-546, 495.
To assign the hydride resonances to the hydride
ligands of 2, we have carried out a NOESY experiment,
at 193 K. As a result of this experiment (Figure 2), we

4068 Organometallics, Vol. 17, No. 18, 1998
Barea et al.
Ta ble 1. Selected Geom etr ica l P a r a m eter s (Å a n d
d eg) of th e B3LYP Op tim ized Str u ctu r es of th e
OsH2X{NHdC(H)C6H4}(P H3)2 (X ) H (2t)) a n d
OsX{NHdC(H)C6H4}(η2-H2)(P H3)2 (X ) Cl (4t), Br
(5t), I (6t)) System s
2t (X ) H) 4t (X ) Cl) 5t (X ) Br) 6t (X ) I)
Os-H(1)
Os-H(2)
Os-X
1.635
1.633
1.671
2.146
2.320
1.015
1.723
1.722
2.532
1.633
1.607
2.534
2.126
2.334
1.023
1.483
2.695
2.737
1.632
1.610
2.688
2.129
2.340
1.019
1.475
2.783
2.841
1.632
1.611
2.873
2.134
2.341
1.019
1.465
2.894
3.020
Os-N
Os-P
N-Hn
H(1)-H(2)
H(1)-X
X‚‚‚Hn
H(1)-Os-X
H(1)-Os-H(2)
H(1)-Os-N
H(1)-Os-C(3)
X-Os-H(2)
X-Os-N
X-Os-C(3)
H(2)-Os-N
H(2)-Os-C(3)
N-Os-C(3)
N-Os-P
62.8
63.6
77.3
54.5
75.8
54.2
74.3
53.7
142.8
142.0
126.4
80.0
159.2
153.6
78.4
75.2
93.6
91.6
172.6
122.8
157.3
126.8
131.8
80.0
155.9
148.2
72.3
75.9
92.8
92.5
173.3
121.3
156.8
127.2
130.1
81.0
156.9
148.9
73.0
75.9
92.8
92.5
173.3
120.1
156.8
127.2
128.0
82.5
158.5
149.5
73.5
76.0
92.9
92.5
173.2
121.1
1
F igu r e 2. Partial view of the H NOESY NMR spectrum
(300 MHz, dichloromethane-d2) of OsH3{NHdC(Ph)C6H4}(P-
iPr3)2 (2) at 193 K.
C(3)-Os-P
P-Os-P
Os-N-Hn
assigned the resonance C to the central hydride ligand
(H(1)), the resonance B to the hydride ligand disposed
trans to the nitrogen atom (H(2)), and the resonance A
to the hydrido ligand disposed trans to the ortho-
metalated phenyl ring (H(3)).
T1 values of the hydrogen nuclei of the OsH3 unit were
determined in toluene-d8 as solvent over the tempera-
ture range 283-198 K. The T1(min) values of the three
hydrides H(3) (89 ms), H(2) (114 ms), and H(1) (90 ms)
occur at the same temperature (223 K). These values
are in agreement with those previously found for the
hydride ligands of the complexes OsH3(Hbiim)(PiPr3)2
(77 and 86 ms)11c and [OsH3(η4-diolefin)(PiPr3)2]BF4
(diolefin ) TFB (69 and 118 ms), NBD (64 ms and 85
ms))3c and support the trihydride character of 2.
F igu r e 3. Optimized structure of OsH3{NHdC(Ph)C6H4}-
(PH3)2 (2t).
the charge density over the atomic domain.17 In agree-
ment with the hydride nature of 2t, the Bader net
charges are negative, similar to those obtained with the
same methodology in the Os(IV) complex OsH4(PH3)3.18
However, the charge that each hydride bears is detect-
ably different: -0.19e for H(1), -0.24e for H(2), and
-0.29e for H(3). Therefore, it seems to be clear that in
the site trans to the C atom less electronic density is
transferred from the ligand to the metal.
To obtain a more complete structural description of
complex 2, we have also performed theoretical calcula-
tions on the model system OsH3{NHdC(H)C6H4}(PH3)2
(2t). The geometry of 2t has been fully optimized at
the B3LYP level. The main geometrical parameters are
collected in the first column of Table 1, and the structure
is depicted in Figure 3.
The spectra shown in Figure 1 indicate that, between
the hydride ligands of 2, two thermally activated site
exchange processes take place. One of them is faster
than the other one. The slower exchange process
involves the hydride ligand disposed trans to the
nitrogen atom (H(2)) and the central hydrido ligand
(H(1)), while the faster exchange process takes place
between H(1) and the hydride ligand located trans to
the ortho-metalated phenyl ring (H(3)).
The characterization of 2t as a trihydride species is
confirmed, with H-H distances of 1.72 Å. The complex
presents a quite regular pentagonal-bipyramidal geom-
etry, with the three hydride ligands and the bidentate
group in the equatorial plane. Bond angles between the
equatorial ligands are very close to the ideal value of
72°. The metal-hydride bond distances for the central
hydride (H(1); 1.635 Å) and the terminal hydride trans
to the N atom (H(2); 1.633 Å) are practically the same,
while the separation Os-H(3) (trans to C) is appreciably
longer (1.671 Å). This fact suggests a weaker M-H(3)
bond and thus a lesser electron donation in this site.
To verify that the three hydrides are different from an
electronic point of view, we have computed the atomic
charges for the three hydrogen atoms, by integration of
Line shape analysis of the spectra shown in Figure 1
allows the calculation of the rate constants for both
(17) (a) Bader, R. F. W.; Nguyen-Dang, T. T. Adv. Quantum Chem.
1981, 14, 63. (b) Biegler-Ko¨ning, F. W.; Bader, R. F. W.; Tang, T. H. J .
Comput. Chem. 1982, 3, 317.
(18) Maseras, F.; Lledo´s, A.; Costas, M.; Poblet, J . M. Organome-
tallics 1996, 15, 2947.

OsX{NHdC(Ph)C6H4}H2(PiPr3)2
Organometallics, Vol. 17, No. 18, 1998 4069
Ta ble 2. Ra te Con sta n ts (s-1) for th e
In tr a m olecu la r Site-Exch a n ge P r ocesses in
Ta ble 3. Selected Geom etr ica l P a r a m eter s (Å a n d
d eg) of th e B3LYP Tr a n sition -Sta te Str u ctu r es of
OsH3{NHdC(P h )C6H4}(P iP r 3)2 (2)
th e OsX{NHdC(H)C6H4}(η2-H2)(P H3)2 (X ) Cl) a n d
T (K) k[H(1)-H(3)] k[H(1)-H(2)] T (K) k[H(1)-H(3)] k[H(1)-H(2)]
OsH2X{NHdC(H)C6H4}(P H3)2 (X ) H) System s
2t-TStN (X ) H) 2t-TStC (X ) H) 4t-TS (X ) Cl)
213
223
233
243
253
263
273
283
160
385
980
293
303
313
323
333
343
353
69 000
120 000
200 000
300 000
480 000
760 000
1100 000
650
1 100
3 000
Os-H(1)
Os-H(2)
Os-X
1.721
1.721
1.718
2.098
2.325
1.016
0.906
2.465
2.465
1.788
1.667
1.788
2.142
2.316
1.018
2.442
0.869
2.442
1.732
1.732
2.565
2.080
2.352
1.018
0.891
3.192
3.192
2 400
5 500
10 500
20 500
39 000
9 000
15
70
210
350
28 000
85 000
260 000
Os-N
Os-P
N-Hn
H(1)-H(2)
H(1)-X
H(2)-X
H(1)-Os-X
H(1)-Os-H(2)
H(1)-Os-N
H(1)-Os-C(3)
X-Os-H(2)
X-Os-N
X-Os-C(3)
H(2)-Os-N
H(2)-Os-C(3)
N-Os-C(3)
N-Os-P
91.6
30.5
162.7
94.1
91.6
96.7
174.1
162.7
94.1
77.4
88.2
99.1
160.2
28.1
89.9
95.1
164.0
89.9
95.1
164.0
174.9
97.9
77.0
99.5
85.9
157.0
94.0
29.8
164.1
95.5
94.0
91.6
170.2
164.1
95.5
78.6
88.3
95.8
167.1
C(3)-Os-P
P-Os-P
Despite the geometrical similarity of the two transi-
tion states, the activation barriers for the two processes
are very different, in agreement with the spectra shown
in Figure 1. The transition state 2t-TStN, in which the
dihydrogen ligand lies trans to the nitrogen atom, is
found 20.1 kcal mol-1 above the trihydride minimum,
whereas 2t-TStC, in which the dihydrogen ligand is
trans to the ortho-metalated phenyl ring, is only 12.3
kcal mol-1 above the minimum.
The motion corresponding to the evolution dihydride-
dihydrogen involves the approach of the hydrogen atoms
and their estrangement from the metallic center. To
understand the origin of the energetic difference be-
tween 2t -TSt N and 2t -TSt C, we have optimized the
geometry of 2t with a H(1)-H(3) distance of 0.90 Å, a
value very close to that found in 2t-TStC, but imposed
the coplanarity of the OsH3 unit. This structure is 5.3
kcal mol-1 above the minimum. The structure of 2t
with a H(1)-H(2) distance of 0.90 Å is 10.5 kcal mol-1
above the minimum. Thus, the difference in energy
between the transition states is already found between
the two dihydrogen structures before the twist. It is
clear that the approach of H(1) to H(3) is easier than
that of H(1) to H(2).
F igu r e 4. Transition-state structures for the hydrogen
exchange processes in 2t: (top) 2t-TStN; (bottom) 2t-TStC.
thermal exchange processes at different temperatures
(Table 2). The activation parameters obtained from the
Eyring analysis are ∆Hq ) 18.2((0.7) kcal mol-1 and
∆Sq ) 17((2) cal K-1 mol-1 for the H(1)-H(2) exchange
and ∆Hq ) 8.9((0.2) kcal mol-1 and ∆Sq ) -5.8((0.6)
cal K-1 mol-1 for the H(1)-H(3) exchange.
To find the transition states of these processes and
the mechanism of the exchanges, theoretical calcula-
tions were carried out. The transition states (2t-TStN
for the H(1)-H(2) exchange and 2t-TStC for the H(1)-
H(3) exchange) were calculated by a complete optimiza-
tion of the geometry of 2t with H(1) and H(2) (2t-TStN)
and H(1) and H(3) (2t-TStC) twisted 90° with respect
to the position in the minimum. The structures found
in this way are shown in Figure 4. Selected bond
distances and angles are collected in Table 3.
Both transition states can be described as octahedral
osmium(II) species containing dihydrogen ligands. The
Os(η2-H2) nature is supported by the hydrogen-hydro-
gen distances between the exchanging atoms, 0.906 Å
in 2t-TStN and 0.896 Å in 2t-TStC. This agrees well
with the mechanism initially proposed by Limbach et
al.19 for the hydrogen exchange in trihydride complexes
and theoretically corroborated for the OsH3(η2-H2BH2)-
(PR3)2 system5 and iridium trihydride4 and metallocene
trihydride complexes.6
An energy decomposition analysis20 is also useful in
understanding where the difference comes from. In the
planar hydride-dihydrogen structures the energies of
the two MHL4 fragments are very different. The
fragment OsH{NHdC(H)C6H4}(PH3)2 with the hydride
trans to C lies 18 kcal mol-1 above the same fragment
with the hydride trans to N, and although the first
fragment interacts more strongly with the H-H unit
(20) We consider the species MHL4(η2-H2) at a particular value of
the H-H distance between 0.80 and 1.80 Å has been built from two
separate fragments (the H2 molecule and the MHL4 fragment), each
one at its equilibrium geometry. Thus, the process to obtain MHL4-
(η2-H2) at each hydrogen-hydrogen distance can be decomposed into
three terms, ∆Estret(H2), ∆Edef(MHL4), and ∆Eint, and at each point the
variation in the total energy (∆Etot) can be obtained by adding the three
(19) Limbach, H. H.; Scherer, G.; Maurer, M.; Chaudret, B. Angew.
Chem., Int. Ed. Engl. 1992, 31, 1369.
contributions: ∆Etot ) ∆Estret(H2) + ∆Edef(MHL4) + ∆Eint
.

4070 Organometallics, Vol. 17, No. 18, 1998
Barea et al.
(∆Eint ) -49.6 kcal mol-1) than does the second one
(∆Eint ) -36.8 kcal mol-1), the term does not balance
the intrafragment destabilization.
Sch em e 1
Once a dihydrogen structure has been reached, the
energies associated with their rotations are similar (7
kcal mol-1 for the dihydrogen trans to C, and 9.6 kcal
mol-1 for the dihydrogen trans to N). These energies
mainly come from the loss of the metal-dihydrogen
interaction in the transition states, with respect to the
planar hydrido-dihydrogen structures. For instance,
this interaction, which is -49.6 kcal mol-1 when the
dihydrogen unit H(1)-H(2) is in the equatorial plane,
diminishes to -39.1 kcal mol-1 in 2t-TStN.
2. OsX{NHdC(P h )C6H4}(η2-H2)(P iP r 3)2 (X ) Cl,
Br , I). According to the charge which each hydride
ligand of 2 bears, it seems to be clear that in the site
trans to the C atom of the metalated group less electron
density is transferred from the ligand to the metal.
Therefore, one should expect that an electronegative
ligand will prefer to occupy this position. To confirm
this, we carried out the reaction of 2 with HCl. In this
context, it should be mentioned that a general procedure
to generate hydride-halide compounds is the treatment
of polyhydride precursors with hydrohalic acids.21
Complex 2 reacts at room temperature with HCl in
toluene to give OsH3Cl(NHdCPh2)(PiPr3)2 (3), which can
be isolated at -78 °C as an orange solid in 35% yield.
In methanol, complex 3 is unstable and rapidly evolves
into OsCl{NHdC(Ph)C6H4}(η2-H2)(PiPr3)2 (4), by loss of
molecular hydrogen. In toluene at room temperature,
complex 3 is stable. However, at 60 °C, it quantitatively
affords 4 after 2 weeks (Scheme 1).
Complex 4 can be also synthesized by protonation of
a dichloromethane solution of 2 with HBF4 and subse-
quent treatment with NaCl in methanol. By this
procedure, complex 4 was obtained in 77% yield. Simi-
IR spectrum in Nujol shows the ν(N-H) vibration at
3321 cm-1 and the absorptions due to the Os-H bonds
at 2176 and 2122 cm-1. In the 13C{1H} NMR spectrum,
the resonance due to the CdN carbon atom appears at
169.6 ppm as a triplet with a P-C coupling constant of
2.6 Hz. The 31P{1H} NMR spectrum in toluene-d8,
which is temperature-invariant, shows a singlet at 27.2
larly to 4 the complexes OsX{NHdC(Ph)C6H4}(η2-H2)(P-
iPr3)2 (X ) Br (5), I (6)) can be obtained in 80% yield by
treatment of the resulting solution from the protonation
of 2, with methanol solutions of NaBr and NaI, respec-
tively (eq 2).
1
ppm. In the H NMR spectrum, at room temperature,
the NH resonance is observed at 12.42 ppm. In the
high-field region, the spectrum contains a broad reso-
nance at -11.97 ppm. This spectrum is temperature-
dependent. Between 253 and 243 K, a decoalescence
of the hydride resonance takes place, and two broad
resonances at about -9 (1H) and -13 (2H) ppm are
observed. Although a second decoalescence does not
occur between 243 and 193 K, lowering the sample
temperature leads to a broadening of the resonance at
about -13 ppm. These observations suggest that,
similarly to the hydride ligands of 2, the hydride ligands
of 3 undergo two thermally activated site exchange
processes, one of them faster than the other one.
The T1 values of the hydride ligands of the OsH3 unit
of 3 were also determined over the temperature range
293-193 K. T1(min) values of 78 and 82 ms were
obtained at 233 K. These values support the trihydride
character of 3.
The spectroscopic data for 4-6 also support the
structure proposed in eq 2. The IR spectra show the
ν(NH) band at about 3330 cm-1. The presence of the
ortho-metalated benzophenone imine group is also sup-
ported by the 13C{1H} NMR spectra, which contain
The spectroscopic data for 3 are consistent with the
structure proposed for this complex in Scheme 1. The
(21) Hlatky, G. G.; Crabtree, R. H. Coord. Chem. Rev. 1985, 65, 1.

OsX{NHdC(Ph)C6H4}H2(PiPr3)2
Organometallics, Vol. 17, No. 18, 1998 4071
Figu r e 6. Molecular diagram of OsCl{NHdC(Ph)C6H4}(η2-
H2)(PiPr3)2 (4). Thermal ellipsoids are shown at 50%
probability.
decoalescence occurs and, at 193 K, two signals are
clearly observed.
The T1 values of the high-field-region resonances were
determined over the temperature range 213-293 K. The
T1(min) values for the three compounds, 49 (4) and 50
(5 and 6) ms, occur at the same temperature (233 K).
These values correspond to hydrogen-hydrogen dis-
tances of 1.08 Å (fast spinning) or 1.36 Å (slow
spinning).1f
The partially deuterated dihydrogen derivatives OsX-
{NHdC(Ph)C6H4}(η2-HD)(PiPr3)2 (X ) Cl (4-d ), Br (5-
d ), and I (6-d )) were prepared according to eq 2 using
methanol-d4 instead of methanol. They have H-D
coupling constants of 6.3 (4-d ), 6.6 (5-d ), and 6.8 (6-d )
Hz. According to eq 3, these values allow us to calculate
a separation between the hydrogen atoms of the dihy-
drogen ligands of 4-6 of 1.31 Å, suggesting that the
coordinated hydrogen molecules in these derivatives are
in a slow-rotation regime, in agreement with the
observed decoalescence.
F igu r e 5. Variable-temperature 1H NMR spectra (300
MHz, toluene-d8) in the high-field region of OsCl{NHd
C(Ph)C6H4}(η2-H2)(PiPr3)2 (4).
triplets at about 177 (J (PC) ) 2.8 Hz) and 173 (J (PC)
≈ 5 Hz) ppm, assigned to the CdN and Os-C carbon
atoms, respectively. The 31P{1H} NMR spectra of the
three compounds, which are temperature-invariant,
show singlets at 6.8 (4), 3.3 (5), and -2.2 (6) ppm.
Under off-resonance conditions, they are split into
triplets. At room temperature, in dichloromethane-d2
as solvent, the 1H NMR spectra contain a broad NH
resonance at about 10.8 ppm, and in the high-field
region double triplets at -6.52 (J (PH) ) 12.9 Hz, J (HH)
) 2.7 Hz; 4), -6.99 (J (PH) ) 12.7 Hz, J (HH) ) 3.0 Hz;
5), and -7.93 (J (PH) ) 12.7 Hz, J (HH) ) 2.9 Hz; 6) ppm
correspond to the H2 unit. The multiplicity of these
resonances is the result of the nuclear spin coupling
between the dihydrogen ligands and the phosphorus and
NH nuclei. The nuclear spin coupling between the
dihydrogen ligand and the NH proton was confirmed
d(H-H) ) -0.0167[J (HD)] + 1.42
(3)
The X-ray diffraction study on a single crystal of 4
confirms the structure proposed for 4-6 in eq 2. A view
of the molecular geometry of 4 is shown in Figure 6.
Selected bond distances and angles are listed in Table
4. The hydrogen atoms H(1) and H(2) were located in
the difference Fourier maps and refined as isotropic
atoms together with the rest of the non-hydrogen atoms
of the structure, giving Os-H(1) and Os-H(2) distances
of 1.53(4) and 1.42(4) Å, respectively. The H(1)-H(2)
distance is 1.22(5) Å.
The osmium atom is coordinated in a somewhat
octahedral fashion with the two triisopropylphosphine
ligands in trans positions (P(1)-Os-P(2) ) 162.31(4)°).
An ideal equatorial plane is formed by the atoms C(3)
and N of the ortho-metalated benzophenone imine group
coordinating with the osmium atom to form a five-
membered ring (C(3)-Os-N ) 75.1(1)°) and the chloro
and dihydrogen ligands, which align along the Cl-M-C
axis, cis-disposed. The five-membered metallacycle is
almost planar. The deviations from the best plane are
-0.0001(2) (Os), -0.036(4) (C(1)), 0.007(4) (C(2)), 0.011-
(4) (C(3)), and 0.027(4) (N) Å.
1
by H-COSY NMR experiments.
In contrast to the 31P{1H} NMR spectra, the H NMR
1
spectra are temperature-dependent. The three com-
pounds display the same behavior. Figure 5 shows the
1H NMR spectrum of 4 in the high-field region as a
function of the temperature, in toluene-d8 as solvent,
where the J (HH) coupling constant is not observed.
Lowering the sample temperature leads to broadening
of the resonance. At very low temperature (213 K)

4072 Organometallics, Vol. 17, No. 18, 1998
Barea et al.
Ta ble 4. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for th e Com p lex
diffraction for 4. The main discrepancy is found in the
H(1)-H(2) distance (1.483 Å), which is about 0.25 Å
longer than that determined from the X-ray diffraction
study and is 0.17 Å longer than the hydrogen-hydrogen
distance calculated according to eq 3. In this context,
it should be mentioned that a recent theoretical study
on the elongated dihydrogen complexes [Ru(η5-C5H5)(η2-
H2)(R2PCH2PR2)]+ has revealed that the experimental
H-H distance, determined by a neutron diffraction
study, cannot be explained with pure electronic struc-
ture results.7i The main reason lies in the shape of the
potential energy surface corresponding to the stretch
of the H-H unit of the complex, which is very anhar-
monic.
OsCl{NHdC(P h )C6H4}(η2-H2)(P iP r 3)2 (4)
Os-H(1)
Os-H(2)
Os-Cl
Os-P(1)
Os-P(2)
Os-N
1.53(4)
1.42(4)
N-C(1)
1.291(5)
1.451(5)
1.484(6)
1.431(6)
1.417(5)
0.96
C(1)-C(2)
C(1)-C(8)
C(2)-C(3)
C(3)-C(4)
N-Hn
2.482(1)
2.387(1)
2.3806(9)
2.097(3)
2.069(4)
1.22(5)
Os-C(3)
H(1)-H(2)
Cl-Hn
Cl-H(1)
2.81
2.72(4)
Cl-Os-P(1)
Cl-Os-P(2)
Cl-Os-N
Cl-Os-C(3)
Cl-Os-H(1)
Cl-Os-H(2)
P(1)-Os-P(2)
P(1)-Os-N
P(1)-Os-C(3)
P(1)-Os-H(1)
P(1)-Os-H(2)
P(2)-Os-N
P(2)-Os-C(3)
P(2)-Os-H(1)
87.88(3)
87.92(3)
82.48(9)
157.5(1)
82(1)
P(2)-Os-H(2)
N-Os-C(3)
88(1)
75.1(1)
164(1)
147(2)
121(1)
N-Os-H(1)
N-Os-H(2)
C(3)-Os-H(1)
C(3)-Os-H(2)
H(1)-Os-H(2)
Os-N-C(1)
Let us analyze structural changes caused in the
complexes by the substitution of a hydride ligand (2t)
by a chloride ligand (4t). The most remarkable fact is
the diminution of the H(1)-H(2) distance from 1.72 Å
(2t) to a value that falls in the range of a stretched-
dihydrogen complex (1.48 Å) in 4t. This is in contrast
with that previously observed in the complexes trans-
[RuX(η2-H2)L2]+ 25 and trans-[OsX(η2-H2)L2]+ (X ) H,
Cl),2b,f,26 where a change of the trans ligand from hydride
to chloride increases the H-H distance and the hydride
character of the dihydrogen ligand. For instance, the
complex trans-[OsH(η2-H2)(dppe)2]+ has a H-H distance
of 0.99 Å according to NMR studies,2b while neutron
diffraction studies of trans-[OsCl(η2-H2)(dppe)2]+ have
revealed an elongated H‚‚‚H ligand with RH-H ) 1.22
Å.2f The different behavior of a chloride ligand in trans
and cis positions with respect to a dihydrogen unit can
be interpreted by considering that in the trans position
the strong π-donor nature of Cl dominates, raising the
energy of dπ orbitals and increasing back-donation to
the σ*(H2) orbital. On the other hand, in the cis position
the weak σ-donor character predominates, transferring
less electronic density to the metal than a hydride and
thus rendering less basic the metal center. Following
this analysis, in 4t less electronic density would be
transferred from the metal to the H(1)-H(2) unit that
in 2t. The Bader net atomic charges computed in 4t
for H(1) (-0.18e) and H(2) (-0.15e) reveal that a
noticeable diminution (0.10e), with respect to those of
the same two atoms in 2t, has occurred. Charges
calculated for H(1) and H(2) in 4t are very similar to
those computed with the same method for the dihydro-
gen unit of the elongated-dihydrogen complex trans-[Os-
(HCO2)(η2-H2){NH2(CH2)2NH2}2]+ (-0.18e and -0.17e).18
130(2)
72(2)
49(2)
162.31(4)
96.32(8)
96.29(9)
82(1)
121.7(3)
112.8(4)
121.9(3)
114.1(3)
116.2(2)
129.5(3)
114.2(4)
N-C(1)-C(2)
N-C(1)-C(8)
C(1)-C(2)-C(3)
Os-C(3)-C(2)
Os-C(3)-C(4)
C(2)-C(3)-C(4)
82(1)
100.15(8)
94.15(9)
80(1)
F igu r e 7. Optimized structure of OsCl{NHdC(H)C6H4}-
(η2-H2)(PH3)2 (4t).
The Os-N bond length of 2.097(3) Å and the Os-C(3)
bond distance of 2.069 Å are typical for Os-N and Os-
C(aryl) single bonds, respectively, and are in agreement
with the values previously found for the complexes Os-
(C2Ph){NHdC(Ph)C6H4}(CO)(PiPr3)2 (2.106(7) and 2.089-
(7) Å),12 Os{NHdC(Ph)C6H4}(η6-C6H3Me3)(PiPr3)]PF6
(2.083(4) and 2.072(4) Å),22 OsH{(C6H3-p-Me)(p-tolyl)-
CNNC(p-tolyl)2}(CO)2(PPh3) (2.119(5) and 2.100(7) Å),23
and fac-Os{C,N-3-Me[2-(MeC6H4)NCMe3]C6H3}(2-Me-
C6H4)(CN-tBu)3 (2.193(24) and 2.077(20) Å).24
At first glance the decoalescence observed in Figure
5 could be due to a restricted rotational motion of the
elongated dihydrogen ligand or, alternatively, to a low-
energy bond-splitting/bond-forming process. Previously,
we have pointed out that for an elongated-dihydrogen
compound (also for those with a restricted rotational
motion of the dihydrogen ligand) a plot of the potential
We have also carried out a theoretical determination
of the structure of complexes 4-6, taking the OsX{NHd
C(H)C6H4}(η2-H2)(PH3)2 (X ) Cl (4t), Br (5t), I (6t))
system as a model. Selected geometrical parameters are
collected in Table 1, and the structure of 4t is shown in
Figure 7. Because the three complexes present very
similar geometries, we will focus our discussion on 4t.
Bond distances and angles for the non-hydrogen
atoms of 4t agree well with those determined by X-ray
energy versus the hydrogen-hydrogen distance (RH-H
)
should have one minimum at the equilibrium hydrogen-
hydrogen distance, while for a low-energy bond-split-
ting/bond-forming process, a potential surface with a
double well must be expected.
(22) Werner, H.; Daniel, T.; Braun, T.; Nu¨rnberg, O. J . Organomet.
Chem. 1994, 480, 145.
(23) Gallop, M. A.; Rickard, C. E. F.; Roper, W. R. J . Organomet.
Chem. 1990, 395, 333.
(24) Arnold, J .; Wilkinson, G.; Hussain, B.; Hurthouse, M. B.
Organometallics 1989, 8, 1362.
(25) Chin, B.; Lough, A. J .; Morris, R. H.; Schweitzer, C. T.;
D’Agostino, C. Inorg. Chem. 1994, 33, 6278.
(26) Mezzetti, A.; Del Zotto, A.; Rigo, P.; Farnetti, E. J . Chem. Soc.,
Dalton Trans. 1991, 1525.

OsX{NHdC(Ph)C6H4}H2(PiPr3)2
Organometallics, Vol. 17, No. 18, 1998 4073
takes place in 4t with an energy barrier29 of 11.0 kcal
mol-1, which is substantially lower than in 2t (20.1 kcal
mol-1). The explanation for this fact can be found in
Figure 8. To cause H(1) and H(2) to approach at a
distance of 0.90 Å costs only 4.0 kcal mol-1 in 4t, while
10.5 kcal mol-1 is necessary in 2t. The presence of a
cis-chloride ligand instead of a hydride facilitates the
approach between H(1) and H(2). Once the dihydrogen
ligands are formed, the rotational barriers are similar
(7.0 (4t) and 9.6 (2t) kcal mol-1).
Con clu d in g Rem a r k s
This study has revealed that the hexahydride OsH6(P-
iPr3)2 reacts with benzophenone imine to give the
derivative OsH3{NHdC(Ph)C6H4}(PiPr3)2 containing
three hydride ligands and a bidentate group in the
equatorial plane of a pentagonal-bipyramidal arrange-
ment of ligands around the metallic center. In solution
two thermally activated exchange processes take place
between the hydride ligands, one of them faster than
the other one. The slower exchange process involves
the hydride ligand disposed trans to the nitrogen atom
and the central hydride ligand, while the faster one
takes place between the latter and that located trans
to the ortho-metalated phenyl ring.
F igu r e 8. Energy profile for the lengthening of the H(1)-
H(2) distance in the complex OsCl{NHdC(H)C6H4}(η2-H2)-
(PH3)2 (4t).
In the transitions state of both processes, the ex-
changing atoms form a dihydrogen unit, which is
twisted 90° with regard to the position of the minimum.
The difference in energy between them is a consequence
of the difference in energy needed for the exchanging
atoms to approach before the twist.
In the site trans to the phenyl ring of the metalated
group of 2, less electron density is transferred from the
ligand to the metal. In agreement with this, the hydride
ligand located in this position can be replaced by
electronegative ligands such as chloride, bromide, and
iodide. This change of ligands produces significant
disruptions in the interaction between the other two
hydrogen ligands and the osmium atom. Thus, in the
F igu r e 9. Transition-state structure for the hydrogen
exchange process in 4t: 4t-TS.
To clarify this point, we have calculated the potential
energy profile for the H(1)-H(2) stretch in 4t. Accord-
ing to the curve depicted in Figure 8 the nature of the
elongated dihydrogen of the H2 unit of 4 is confirmed.
Furthermore, since the curve does not have a double
well, without the shadow of a doubt, a low-energy bond-
splitting/bond-forming process must be totally rejected.
The latter is in agreement with the ln T1 vs 1/T plot,
which has the usual V-shape and does not show any
distortion that would be expected for a tautomeric
equilibrium, where the ratio of the two tautomers should
be temperature-dependent.28
new compounds, OsX{NHdC(Ph)C6H4}(η2-H2)(PiPr3)2,
the H2 unit forms an elongated dihydrogen ligand,
which in solution shows a restricted rotational motion.
The transition states for the hydrogen exchange in these
compounds also present a dihydrogen-like nature.
The transition state for the hydrogen exchange in 4t
(4t-TS) has been located with the same methodology as
that used for the other transition states. It also
presents a dihydrogen-like nature (H(1)-H(2) ) 0.891
Å). Despite the different H(1)-H(2) distances in 2t and
4t, the geometry of 4t-TS (Figure 9, Table 3) is similar
to that of 2t-TStN. However, the hydrogen exchange
In conclusion, the ligand X of the complexes OsX-
{NHdC(Ph)C6H4}H2(PiPr3)2 determines the nature of
the H2 unit and, as a consequence, the energy barrier
for the rotational motion of the H2 unit in solution.
Exp er im en ta l Section
(27) At each fixed value of RH-H the rest of the geometrical
parameters have been optimized at the B3LYP level.
P h ysica l Mea su r em en ts. Infrared spectra were recorded
as Nujol mulls on polyethylene sheets using a Nicolet 550
spectrometer. NMR spectra were recorded on a Varian UNITY
300, Varian GEMINI 2000 300 MHz, or on a Bruker ARX 300.
The probe temperature of the NMR spectrometers was cali-
brated at each temperature against a methanol standard in
the range 293-193 K and against ethylene glycol in the range
353-303 K. For the T1 measurements the 180° pulses were
calibrated at each temperature. 1H and 13C{1H} chemical
(28) (a) Kubas, G. J .; Unkefer, C. J .; Swanson, B. I.; Fukushima, E.
F. J . Am. Chem. Soc. 1986, 108, 7000. (b) Kubas, G. J .; Ryan, R. R.;
Unkefer, C. J . J . Am. Chem. Soc. 1987, 109, 8113. (c) Conroy-Lewis,
F. M.; Simpson, S. J . J . Am. Chem. Soc., Chem. Commun. 1987, 1675.
(d) Chinn, M. S.; Heinekey, D. M. J . Am. Chem. Soc. 1987, 109, 5865.
(e) Chinn, M. S.; Heinekey, D. M.; Payne, N. G.; Sofield, C. D.
Organometallics 1989, 8, 1824. (f) Cappellani, E. P.; Maltby, P. A.;
Morris, R. H.; Schweitzer, C. T.; Steele, M. R. Inorg. Chem. 1989, 28,
4437. (g) Arliguie, T.; Chaudret, B. J . Chem. Soc., Chem. Commun.
1989, 155. (h) Khalsa, G. R. K.; Kubas, G. J .; Unkefer, C. J .; Van Der
Sluys, L. S.; Kubat-Martin, K. A. K. J . Am. Chem. Soc. 1990, 112, 189.
(i) Luo, X.-L.; Crabtree, R. H. J . Am. Chem. Soc. 1990, 112, 6912. (j)
Luo, X.-L.; Crabtree, R. H. J . Am. Chem. Soc. 1990, 112, 6912. (k) Luo,
X.-L.; Michos, D.; Crabtree, R. H. Organometallics 1992, 11, 237.
q
(29) The value of ∆G293 estimated by NMR spectroscopy for the
rotation of the H2 unit in 4 is 12 kcal mol-1
.

4074 Organometallics, Vol. 17, No. 18, 1998
Barea et al.
shifts were measured relative to partially deuterated solvent
peaks but are reported relative to tetramethylsilane. 31P{1H}
chemical shifts are reported relative to H3PO4 (85%). The
coupling constants J and N (N ) J (PH) + J (P′H) for 1H and
N ) J (PC) + J (P′C) for 13C{1H}) are given in hertz. C, H, and
N analyses were carried out in a Perkin-Elmer 2400 CHNS/O
analyzer. Mass spectral analyses were performed with a VG
Auto Spec instrument. The ions were produced (FAB+ mode)
with the standard Cs+ gun at ca. 30 kV, and 3-nitrobenzyl
alcohol (NBA) was used as the matrix.
Syn th esis. All reactions were carried out with exclusion
of air using standard Schlenk techniques. Solvents were dried
by known procedures and distilled under argon prior to use.
The complex OsH2Cl2(PiPr3)2 was prepared according to the
literature method.30
Kin etic An a lysis. Complete line shape analysis of the 1H-
{31P} NMR spectra of 2 was achieved using the program
DNMR6 (QCPE, Indiana University). The rate constants for
various temperatures were obtained by visually matching
observed and calculated spectra. In the temperature range
213-243 K the rate for the site exchange process H(1)-H(2)
was fixed at 0 s-1, and the resonance corresponding to the H(2)
hydride ligand was used to estimate the T2 value. The rate
values obtained for the site exchange process H(1)-H(3) were
extrapolated for the rest of the temperature values (253-353
K). With these rate values the T2 value was estimated and
the rates for the site exchange process H(1)-H(2) at each point
of the temperature range 253-353 K were computed. The
activation parameters ∆Hq and ∆Sq were calculated by a least-
squares fit of ln(k/T) vs 1/T (Eyring equation). Error analysis
assumed a 10% error in the rate constant and 1 K error in
the temperature. Errors were computed by published meth-
ods.31
the resulting orange solution was filtered through Kieselguhr
and concentrated to dryness. Ten milliliters of pentane was
added and evaporated until an orange solid began to precipi-
tate. The suspension was stored at -78 °C for 1 h, and the
orange solid obtained was separated by decantation and dried
in vacuo: yield 36.1 mg (35%). IR (Nujol): ν(NH) 3321 cm-1
,
ν(OsH) 2176, 2122 cm-1 1H NMR (300 MHz, C6D6, 293 K): δ
.
12.42 (br, 1 H, NH), 7.71 (m, 2 H, Ph), 7.66 (m, 2 H, Ph), 7.24
(m, 1 H, Ph), 7.12 (m, 1 H, Ph), 6.93 (m, 4 H, Ph), 2.18 (m, 6
H, PCH), 1.29 [dvt, N ) 13.2 Hz, J (HH) ) 6.9 Hz, 18 H,
PCCH3], 0.93 [dvt, N ) 12.6 Hz, J (HH) ) 6.9 Hz, 18 H,
PCCH3], -11.97 (br, 3 H, OsH3). 31P{1H} NMR (121.42 MHz,
C6D6, 293 K): δ 27.2 (s).13C{1H} NMR (75.42 MHz, C6D6, 293
K): δ 169.6 [t, J (PC) ) 2.6 Hz, NdC], 140.1, 138.6, 130.7,
130.0, 129.8, 129.5, 129.2, 127.7, 127.3 (all s, Ph), 24.7 [vt, N
) 23.4 Hz, PCH], 20.6, 19.5 (both s, PCCH3). Anal. Calcd for
C
31H56ClNOsP2: C, 50.97; H, 7.72; N, 1.91. Found: C, 50.62;
H, 7.42; N, 1.84. T1 (ms, OsH3, 300 MHz, C7D8): 165 (293 K),
93 (253 K), 78, 82 (233 K), 92, 96 (213 K), 197, 224 (193 K).
P r ep a r a t ion of OsCl{NH dC(P h )C6H 4}(η2-H 2)(P iP r 3)2
(4). A solution of 2 (120 mg, 0.17 mmol) in 5 mL of CH2Cl2
was treated with HBF4 (23.5 µL, 0.17 mmol). The resulting
red solution obtained was evaporated to dryness, and the
residue was treated with a solution of NaCl (16.4 mg, 0.17
mmol) in 8 mL of methanol. The red solid obtained was
separated by decantation, washed with methanol, and dried
in vacuo: yield 97.1 mg (77%). IR (Nujol): ν(NH) 3329 cm-1
ν(OsH) 2251, 2160 cm-1 1H NMR (300 MHz, CD2Cl2, 293 K):
,
.
δ 10.8 (br, 1 H, NH), 7.86 (m, 1 H, Ph), 7.58-7.50 (m, 5 H,
Ph), 7.35 (m, 1 H, Ph), 6.75 (m, 2 H, Ph), 2.92 (m, 6 H, PCH),
1.16 [dvt, N ) 12.7 Hz, J (HH) ) 7.0 Hz, 18 H, PCCH3], 0.95
[dvt, N ) 12.6 Hz, J (HH) ) 6.9 Hz, 18 H, PCCH3], -6.52 [td,
J (PH) ) 12.9 Hz, J (H-NH) ) 2.7 Hz, 2 H, OsH2]. 31P{1H}
NMR (121.42 MHz, CD2Cl2, 293 K): δ 6.8 (s, t in off-resonance).
13C{1H} NMR (75.42 MHz, CD2Cl2, 293 K): δ 176.0 [t, J (PC)
) 2.8 Hz, NdC], 172.8 [t, J (PC) ) 5.0 Hz, Os-C], 145.8, 143.8,
138.0, 130.6, 130.5, 129.7, 129.1, 128.7, 118.3 (all s, Ph), 24.7
(vt, N ) 24.8 Hz, PCH), 19.6, 19.0 (both s, PCCH3). Anal.
Calcd for C31H54ClNOsP2: C, 51.11; H, 7.47; N, 1.92. Found:
C, 50.81; H, 7.37; N, 1.87. MS (FAB+): m/e 727 (M+ - 2 H).
T1 [ms, Os(η2-H2), 300 MHz, C7D8]: 127 (293 K), 92 (273 K),
66 (253 K), 51 (238 K), 49 (233 K), 58, 61 (223 K), 67, 69 (213
K).
P r ep a r a tion of OsH3{NHdC(P h )C6H4}(P iP r 3)2 (2).
A
suspension of OsH2Cl2(PiPr3)2 (200 mg, 0.35 mmol) in 16 mL
of toluene was first treated with NaBH4 (133 mg, 3.5 mmol)
and then dropwise with 1.0 mL of methanol. After it was
stirred for 15 min at room temperature, the solution was
filtered through Kieselguhr and concentrated to dryness. The
white residue obtained was dissolved in 10 mL of toluene and
treated with 74.5 mg (0.42 mmol) of benzophenone imine. The
sample was heated under reflux for 6 h. The resulting red
solution was filtered by Kieselguhr and concentrated to
dryness. Addition of methanol caused the precipitation of a
red solid, which was separated by decantation, washed with
methanol, and dried in vacuo: yield 193.3 mg (80%). IR
P r ep a r a tion of OsCl{NHdC(P h )C6H4}(η2-HD)(P iP r 3)2
(4-d ) a n d OsCl{NHdC(P h )C6H4}(η2-D2)(P iP r 3)2 (4-d 2). A
suspension of 2 (35 mg, 0.05 mmol) in 3 mL of MeOD was
treated first with HBF4 (7.1 µL, 0,05 mmol). After 10 min, a
solution of NaCl (4.4 mg, 0.05 mmol) in 3 mL of MeOD was
added to the red solution obtained. The red solid formed was
separated by decantation and dried in vacuo. 1H{31P} NMR
(300 MHz, CD2Cl2, 293 K): δ -6.51 [td, J (HD) ) 6.3 Hz, J (H-
NH) ) 2.7 Hz, OsHD].
Rea ction of 4 w ith Na BH4. A solution of 4 (75 mg, 0.10
mmol) in 10 mL of toluene was first treated with NaBH4 (38.8
mg, 1.02 mmol) and then dropwise with 0.8 mL of methanol.
After it was stirred at room temperature for 20 min, the
sample was filtered through Kieselguhr and concentrated to
dryness. The addition of methanol caused the precipitation
of a red solid, which was separated by decantation, washed
with methanol, and dried in vacuo. The red solid obtained
was characterized as 2 by 1H and 31P NMR spectroscopy.
Yield: 63 mg (83%).
(Nujol): ν(NH) 3348 cm-1, ν(OsH) 2143, 2106, 1942 cm-1 1H
.
NMR (300 MHz, C6D6, 293 K): δ 10.25 (br, 1 H, NH), 8.93 [d,
J (HH) ) 7.5 Hz, 1 H, Ph], 7.68 [d, J (HH) ) 7.5 Hz, 1 H, Ph],
7.47 (m, 2 H, Ph), 7.17-6.93 (m, 5 H, Ph), 1.82 (m, 6 H, PCH),
1.01 [dvt, N ) 12.6 Hz, J (HH) ) 6.9 Hz, 18 H, PCCH3], 0.98
[dvt, N ) 12.6 Hz, J (HH) ) 6.9 Hz, 18 H, PCCH3], -9.07 (br,
2 H, OsH3), -9.87 (br, 1 H, OsH3). 31P{1H} NMR (121.42 MHz,
C6D6, 293 K): δ 26.8 (s). 13C{1H} NMR (75.42 MHz, C6D6, 293
K): δ 194.6 [t, J (PC) ) 5.6 Hz, Os-C], 179.9 [t, J (PC) ) 3.0
Hz, NdC], 147.4, 142.4, 140.2, 130.8, 128.9, 128.4, 128.3, 118.3
(all s, Ph), 27.7 (vt, N ) 25.6 Hz, PCH), 20.1, 19.9 (both s,
PCCH3). Anal. Calcd for C31H55NOsP2: C, 53.66; H, 7.98; N,
2.01. Found: C, 53.25; H, 7.46; N, 2.00. T1 (ms, OsH3, 300
MHz, C7D8): 283, 312 (283 K), 198, 182 (253 K), 102, 124, 129
(233 K), 99, 117, 105 (228 K), 89, 114, 90 (223 K), 98, 119, 100
(218 K), 107, 121, 106 (213 K), 179, 182, 167 (198 K).
P r ep a r a tion of OsH3Cl(NHdCP h 2)(P iP r 3)2 (3). A solu-
tion of 2 (100 mg, 0.14 mmol) in 10 mL of toluene was treated
with 1.2 mL (0.14 mmol) of a toluene-0.12 M HCl solution.
After the mixture was stirred for 30 min at room temperature,
P r ep a r a t ion of OsBr {NH dC(P h )C6H 4}(η2-H 2)(P iP r 3)2
(5). A solution of 2 (100 mg, 0.14 mmol) in 5 mL of CH2Cl2
was treated with HBF4 (19.6 µL, 0.14 mmol). The resulting
red solution obtained was evaporated to dryness, and the
residue was treated with a solution of NaBr (23.0 mg, 0.14
mmol) in 8 mL of methanol. The red solid obtained was
separated by decantation, washed with methanol, and dried
(30) Aracama, M.; Esteruelas, M. A.; Lahoz, F. J .; Lo´pez, J . A.;
Meyer, U.; Oro, L. A.; Werner, H. Inorg. Chem. 1991, 30, 288.
(31) Morse, P. M.; Spencer, M. O.; Wilson, S. R.; Girolami, G. S.
Organometallics 1994, 13, 1646.

OsX{NHdC(Ph)C6H4}H2(PiPr3)2
Organometallics, Vol. 17, No. 18, 1998 4075
in vacuo: yield 88 mg (80%). IR (Nujol): ν(NH) 3324 cm-1
,
Ta ble 5. Cr ysta l Da ta a n d Da ta Refin em en t
ν(OsH) 2260, 2171 cm-1 1H NMR (300 MHz, C6D6, 293 K): δ
.
Deta ils for OsCl{NHdC(P h )C6H4}(η2-H2)(P iP r 3)2 (4)
11.11 (br, 1 H, NH), 8.12 [d, J (HH) ) 7.2 Hz, 1 H, Ph], 7.57
[d, J (HH) ) 7.2 Hz, 2 H, Ph], 7.52 [d, J (HH) ) 7.2 Hz, 1 H,
Ph], 7.13 (m, 3 H, Ph), 6.84 (m, 2 H, Ph), 2.43 (m, 6 H, PCH),
1.14 [dvt, N ) 12.9 Hz, J (HH) ) 6.9 Hz, 18 H, PCCH3], 0.92
[dvt, N ) 12.9 Hz, J (HH) ) 6.9 Hz, 18 H, PCCH3], -6.78 [t,
J (PH) ) 12.3 Hz, 2 H, OsH2]. 31P{1H} NMR (121.42 MHz,
C6D6, 293 K): δ 3.3 (s, t in off-resonance). 13C{1H} NMR (75.42
MHz, C6D6, 293 K): δ 176.6 [t, J (PC) ) 2.8 Hz, NdC], 173.9
[t, J (PC) ) 4.8 Hz, Os-C], 145.4, 143.6, 138.1, 130.8, 130.6,
129.4, 129.2, 128.0, 118.8 (all s, Ph), 25.0 [vt, N ) 24.8 Hz,
formula
fw
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
C31H54ClNOsP2
728.34
P1h (No. 2)
8.759(2)
11.102(2)
17.608(4)
74.31(1)
76.93(1)
83.15(2)
Z
2
λ, Å
0.71073
1.509
223.0(2)
4.182
0.0275
0.0745
0.985
F(caclcd), g cm-3
T (K)
µ, mm-1
R1a
wR2b
Sc
R1(F) ) ∑||Fo| - |Fc||/∑|Fo|. wR2(F2) ) {∑[w(Fo - Fc2)2]/
a
b
2
PCH], 19.5, 18.9 (both s, PCCH3). Anal. Calcd for C31H54
-
∑[w(Fo2)2]}1/2
.
c S ) {∑[w(Fo - Fc2)2]/(n - p)}1/2, where n is the
number of observed reflections and p is the number of parameters
2
BrNOsP2: C, 48.17; H, 7.04; N, 1.81. Found: C, 47.99; H, 6.99;
N, 1.77. MS (FAB+): m/e 771 (M+ - 2 H). T1 [ms, Os(η2-H2),
300 MHz, C7D8]: 95 (293 K), 72 (273 K), 53 (253 K), 51 (238
K), 50 (233 K), 57, 57 (223 K).
refined.
used in the refinement. Three orientation and intensity
standards were monitored every 55 min; no significant varia-
tion was observed. Reflections were also corrected for absorp-
tion by a semiempirical method (ψ scans).32
The structure was solved by Patterson (osmiun atom) and
conventional Fourier techniques. Anisotropic thermal param-
eters were used for all non-hydrogen atoms; hydrogens were
included in calculated positions33 and refined riding on linked
atoms with a common isotropic thermal parameter. Hydride
ligands were refined as free isotropic atoms with a common
isotropic thermal parameter. Final R1(F, Fo > 4.0σ(Fo)) and
wR2(F2, all reflections) values were 0.0275 and 0.0745. All
calculations were performed by the SHELXTL v. 5.0 system
of computer programs.33
P r ep a r a tion of OsBr {NHdC(P h )C6H4}(η2-HD)(P iP r 3)2
(5-d) an d OsBr {NHdC(P h )C6H4}(η2-D2)(P iP r 3)2 (5-d2). This
mixture was prepared analogously as described for 4-d and
4-d 2, but using NaBr (5.1 mg, 0.05 mmol). 1H{31P} NMR (300
MHz, CD2Cl2, 293 K): δ -6.99 [td, J (HD) ) 6.6 Hz, J (H-NH)
) 3.0 Hz, OsHD].
P r ep a r a tion of OsI{NHdC(P h )C6H4}(η2-H2)(P iP r 3)2 (6).
A solution of 2 (100 mg, 0.14 mmol) in 5 mL of CH2Cl2 was
treated with HBF4 (19.6 µL, 0.14 mmol). The resulting red
solution obtained was evaporated to dryness, and the residue
was treated with a solution of NaI (32.0 mg, 0.14 mmol) in 8
mL of methanol. The red solid obtained was separated by
decantation, washed with methanol, and dried in vacuo: yield
94 mg (80%). IR (Nujol): ν(NH) 3329 cm-1, ν(OsH) 2255, 2164
Com p u ta tion a l Deta ils. Calculations were performed
with the GAUSSIAN 94 series of programs.34 Geometry
optimizations were carried out using density functional theory
(DFT)35 with the B3LYP functional,36 which has already been
used with success to study several dihydrogen and polyhydride
systems.7i,37,38 Cs symmetry has been maintained in the
geometry optimizations. A quasirelativistic effective core
potential operator was used to represent the 60 innermost
electrons of the osmium atom39a as well as the electron core of
Br and I atoms.39b The basis set for the metal atoms was that
associated with the pseudopotential,39a with a standard dou-
ble-ú LANL2DZ contraction.34 P and Cl atoms were described
with the 6-31G(d) basis set.40a The basis set for the hydrogen
atoms directly attached to the metal was a double ê supple-
mented with a polarization p shell.40b,c The 6-31G basis set
was used for the other H atoms, as well as for carbon and
cm-1 1H NMR (300 MHz, C6D6, 293 K): δ 11.16 (br, 1 H, NH),
.
8.13 [d, J (HH) ) 7.2 Hz, 1 H, Ph], 7.57 [d, J (HH) ) 7.2 Hz, 2
H, Ph], 7.52 [d, J (HH) ) 7.2 Hz, 1 H, Ph], 7.11 (m, 3 H, Ph),
6.89 [dd, J (HH) ) 7.2 Hz, 1 H, Ph], 6.81 [dd, J (HH) ) 7.2 Hz,
1 H, Ph], 2.50 (m, 6 H, PCH), 1.15 [dvt, N ) 13.2 Hz, J (HH)
) 6.9 Hz, 18 H, PCCH3], 0.90 [dvt, N ) 12.3 Hz, J (HH) ) 6.6
Hz, 18 H, PCCH3], -7.72 [t, J (PH) ) 12.6 Hz, 2 H, OsH2].
31P{1H} NMR (121.42 MHz, C6D6, 293 K): δ -2.2 (s, t in off-
resonance). 13C{1H} NMR (75.42 MHz, C6D6, 293 K): δ 177.9
[d, J (PC) ) 2.8 Hz, NdC], 174.6 [t, J (PC) ) 5.1 Hz, Os-C],
144.7, 142.8, 137.8, 131.1, 130.3, 129.5, 129.2, 119.1 (all s, Ph),
26.4 (vt, N ) 25.0 Hz, PCH), 20.0, 19.4 (both s, PCCH3). Anal.
Calcd for C31H54INOsP2: C, 45.41; H, 6.63; N, 1.70. Found:
C, 45.20; H, 6.77; N, 1.64. MS (FAB+): m/e 819 (M+ - 2 H).
T1 [ms, Os(η2-H2), 300 MHz, C7D8]: 99 (293 K), 75 (273 K), 56
(253 K), 51 (238 K), 50 (233 K), 65, 64 (223 K), 68, 66 (213 K).
(32) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.,
Sect. A 1968, 24, 351.
P r ep a r a tion of OsI{NHdC(P h )C6H4}(η2-HD)(P iP r 3)2 (6-
(33) Sheldrick, G. M. SHELXTL version 5.0; Siemens Analytical
Automation, Inc., Analytical Instrumentation. Madison, WI, 1994.
(34) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.;
J ohnson, B. G.; Robb, M. A.; Cheeseman, J . R.; Keith, T. A.; Petersson,
G. A.; Montgomery, J . A.; Raghavachari, K.; Al-Laham, M. A.;
Zakrzewski, V. G.; Ortiz, J . V.; Foresman, J . B.; Ciolowski, J .; Stefanov,
B. B.; Nanayakkara, A.; Challacombe, M.; Peng, C. Y.; Ayala, P. Y.;
Chen, W.; Wong, M. W.; Andre´s, J . L.; Replogle, E. S.; Gomperts, R.;
Martin, R. L.; Fox, D. J .; Binkley, J . S.; Defrees, D. J .; Baker, J .;
Stewart, J . J . P.; Head-Gordon, M.; Gonza´lez, C.; Pople, J . A. Gaussian
94; Gaussian Inc., Pittsburgh, PA, 1995.
(35) (a) Parr, R. G.; Yang, W. Density Functional Theory of Atoms
and Molecules; Oxford University Press: Oxford, U.K., 1989. (b)
Ziegler, T. Chem. Rev. 1991, 91, 651.
(36) (a) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
(b) Becke, A. D. J . Chem. Phys. 1993, 98, 5648. (c) Stephens, P. J .;
Devlin, F. J .; Chabalowski, C. F.; Frisch, M. J . J . Phys. Chem. 1994,
98, 11623.
d ) a n d OsI{NHdC(P h )C6H4}(η2-D2)(P iP r 3)2 (6-d 2). This
mixture was prepared analogously as described for 4-d and
4-d 2, but using NaI (7.5 mg, 0.05 mmol). 1H{31P} NMR (300
MHz, CD2Cl2, 293 K): δ -7.93 [td, J (HD) ) 6.8 Hz, J (H-NH)
) 2.9 Hz, OsHD].
X-r a y Str u ctu r e An a lysis of OsCl{NHdC(P h )C6H4}(η2-
H2)(P iP r 3)2 (4). Crystals suitable for the X-ray diffraction
study were obtained by slow diffusion of methanol into a
saturated solution of 4 in dichloromethane. A summary of
crystal and refinement data is reported in Table 5. A yellow
irregular prism of approximate dimensions 0.57 × 0.55 × 0.44
mm was mounted on a glass fiber at -50 °C. A set of randomly
searched reflections in the range 20 e 2θ e 40° showed strong
reflections, from which a group of 67 were carefully centered
and used to obtain by least-squares methods the unit cell
dimensions. A Siemens-STOE AED four-circle diffractometer
was used for data acquisition (ω/2θ scans), with graphite-
monochromated Mo KR radiation and 2θ range 3 e 2θ e 50°
(-10 e h e 10, -13 e l e 13, -6 e k e 20). A total of 8170
reflections were measured; 5648 were unique, and 5647 were
(37) (a) Maseras, F.; Lledo´s, A.; Costas, M.; Poblet, J . M. Organo-
metallics 1996, 15, 2947. (b) Gelabert, R.; Moreno, M.; Lluch, J . M.;
Lledo´s, A. Organometallics 1997, 16, 3805.
(38) (a) Bacskay, G. B.; Bytheway, I.; Hush, N. S. J . Am. Chem. Soc.
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(39) (a) Hay, P. J .; Wadt, W. R. J . Chem. Phys. 1985, 82, 299. (b)
Wadt, W. R.; Hay, P. J . J . Chem Phys. 1985, 82, 284.

4076 Organometallics, Vol. 17, No. 18, 1998
Barea et al.
nitrogen atoms.40b The basis set for the Br and I atoms was
that associated with the pseudopotential,39b with a standard
double-ú LANL1DZ contraction,34 supplemented with a set of
d-polarization functions.40d
and PB95-0639-CO2-01). The use of the computational
facilities of the Centre de Supercomputacio´ i Comuni-
cations de Catalunya (C4) are gratefully appreciated.
Helpful discussions with Prof. J . M. Lluch (UAB, Bel-
laterra, Spain) are also acknowledged.
Ack n ow led gm en t. We acknowledge financial sup-
port from the DGES of Spain (Project Nos. PB95-0806
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates and equivalent isotropic displacement coefficients,
anisotropic thermal parameters, experimental details of the
X-ray study, bond distances and angles, and interatomic
distances for 4 (15 pages). Ordering information is given on
any current masthead page.
(40) (a) Francl, M. M.; Pietro, W. J .; Hehre, W. J .; Binkley, J . S.;
Gordon, M. S.; Defrees, D. J .; Pople, J . A. J . Chem. Phys. 1982, 77,
3654. (b) Hehre, W. J .; Ditchfield, R.; Pople. J . A. J . Chem. Phys. 1972,
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213. (d) Ho¨llwarth, A.; Bo¨hme, M.; Dapprich, S.; Ehlers, A. W.; Gobbi,
A.; J onas, V.; Ko¨hler, K. F.; Stegman, R.; Veldkamp, A.; Frenking, G.
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OM9802820