Reactions of MH(OTf)(NBD)(PPh3)2(M = Ru, Os) with H2

Article abstract of DOI:10.1021/om000369x

Treatment of RuHCl(NBD)(PPh₃)₂(NBD = norbornadiene) with AgOTf produced RuH-(OTf)(NBD)(PPh₃)₂. Reaction of RuH(OTf)(NBD)(PPh₃)₂with H₂in benzene gave norbornene and [(η⁶

Full text of DOI:10.1021/om000369x

Organometallics 2000, 19, 4523-4530
4523
Rea ction s of MH(OTf)(NBD)(P P h 3)2 (M ) Ru , Os) w ith H2
Shu Tak Lo,† Zhitao Xu,† Ting Bin Wen,† Weng Sang Ng,† Sheng Hua Liu,†
Zhong Yuan Zhou,‡ Zhenyang Lin,*,† Chak Po Lau,*,‡ and Guochen J ia*,†
Department of Chemistry, The Hong Kong University of Science and Technology,
Clear Water Bay, Kowloon, Hong Kong, and Department of Applied Biology & Chemical
Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
Received May 1, 2000
Treatment of RuHCl(NBD)(PPh3)2 (NBD ) norbornadiene) with AgOTf produced RuH-
(OTf)(NBD)(PPh3)2. Reaction of RuH(OTf)(NBD)(PPh3)2 with H2 in benzene gave norbornene
and [(η6-C6H6)RuH(PPh3)2]OTf. The same reaction in CD2Cl2 in the presence of added PPh3
produced norbornane and [RuH(PPh3)4]OTf. Reaction of OsH3Cl(PPh3)3 with norbornadiene
produced OsHCl(NBD)(PPh3)2, which was converted to OsH(OTf)(NBD)(PPh3)2 on treatment
with AgOTf. Reaction of OsH(OTf)(NBD)(PPh3)2 with H2 in benzene gave norbornane and
[(η6-C6H6)OsH(PPh3)2]OTf. In dichloromethane, OsH(OTf)(NBD)(PPh3)2 reacted with H2 in
the presence of added PPh3 to produce norbornane and [OsH3(PPh3)4]OTf. Supported by
computational studies, it is assumed that the dihydrogen complexes [MH(H2)(NBD)(PPh3)2]+
(M ) Ru, Os) were involved in the hydrogenation reactions. Two reaction pathways for the
conversion of [RuH(H2)(NBD)(PH3)2]+ to [RuH(NBE)(PH3)2]+ (NBE ) norbornene) have been
studied by density functional theory calculations. The results show that the first hydrogen
transferred to the olefin ligand is more likely from the hydride ligand rather than from the
dihydrogen ligand.
In tr od u ction
and OsH(H2)(CtCPh)(CO)(P(i-Pr)3)2.6b Hydrogen trans-
fer from H2 to the â-carbon of vinylidene ligands has
been proposed for the reactions of OsH2Cl2(P(i-Pr)3)2
with HCtCR to give the carbyne complex OsHCl2(t
CCH2R)(P(i-Pr)3)2 via the intermediates OsCl2(H2)(Cd
CHR)(P(i-Pr)3)2.7
Oxidative coupling reactions of coordinated olefins
and acetylenes are among the most common organome-
tallic reactions.8 In principle, a coordinated dihydrogen
ligand may also undergo oxidative coupling reactions
with unsaturated substrates such as olefins and acety-
lenes. However, examples of these reactions or even
olefin-dihydrogen complexes are still very rare. Cou-
pling between H2 and olefin ligands has been proposed
Since the first report of dihydrogen complexes in
1984,1 this unique class of complexes have been inten-
sively investigated, especially their preparation, char-
acterization, and structural and catalytic properties.2
A relatively less studied aspect of the chemistry of
dihydrogen complexes is their reactivities toward or-
ganic ligands (e.g., alkyls, vinyls, vinylidenes, and
olefins), although such study should help to clarify the
mechanisms of reactions mediated by dihydrogen com-
plexes and to further develop new catalytic reactions
based on dihydrogen complexes. It has been shown that
a coordinated dihydrogen ligand in LnM(H2)R could
transfer one of the hydrogen atoms of the dihydrogen
ligand to the R-carbons of alkyl or vinyl ligands R to
form LnMH and RH. Such a reactivity has been invoked
in the catalytic hydrogenation of olefins using M(CO)6
+
(M ) Cr, Mo, and W)9 and [TpRu(PPh3)x(CH3CN)3-x
]
(x ) 1, 2)10 and in the protonation reaction of Cp*RuH-
(NBD).11 Reported olefin-dihydrogen complexes are
limited to M(H2)(η4-NBD)(CO)3 (M ) Cr, Mo, and W)
and M(H2)(η2-NBD)(CO)4 (M ) Mo and W), which have
been detected by IR spectroscopy,9 and [Cp*Ru(H2)-
(COD)]+, which has been detected by NMR spectros-
copy.11
3
to explain the catalytic activity of RuHCl(PPh3)3 and
[MH(H2)(PP3)]+ (M ) Fe, Ru; PP3 ) P(CH2CH2PPh2)3)4
for hydrogenation of olefins and acetylenes. The reac-
tions are also thought to be involved in the reactions of
some d0 alkyl complexes with H2 to give hydride
complexes and alkanes.5 Alkynyl-dihydrogen complexes
6a
have been reported for [Ru(H2)(CtCPh)(dippe)2]BPh4
† The Hong Kong University of Science and Technology.
‡ The Hong Kong Polytechnic University.
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10.1021/om000369x CCC: $19.00 © 2000 American Chemical Society
Publication on Web 09/27/2000

4524 Organometallics, Vol. 19, No. 22, 2000
Lo et al.
Sch em e 1
Sch em e 2
To further model reactions of coordinated dihydrogen
ligand with olefin and alkyl ligands, we have investi-
gated the reactions of hydrogen with MH(OTf)(NBD)-
(PPh3)2 (M ) Ru, Os). As triflate has been recognized
as a facile leaving group that can be readily displaced
under mild conditions12 and a number of dihydrogen
complexes of the type [MH(H2)(L4)]+ (M ) Ru, Os; L4 )
mono- to tetradentate phosphorus ligands) have previ-
ously been well characterized,13 one might expect that
reactions of H2 with MH(OTf)(NBD)(PPh3)2 (M ) Ru,
Os) may produce the dihydrogen complexes [MH(H2)-
(NBD)(PPh3)2]+. The latter dihydrogen complexes may
undergo hydrogen transfer reactions to hydrogenate the
NBD ligand. Complexes [MH(H2)(NBD)(PPh3)2]+ are
interesting because both η2-H2 and hydride ligands are
present on the same metal center having an olefin
moiety. Thus this provides a good opportunity to study
whether hydrogen transfer from the η2-H2 or the hydride
ligand to the olefin ligand is easier.
Rea ction of H2 w ith Ru H(OTf)(NBD)(P P h 3)2.
Complex 2 in benzene reacted with H2 to give nor-
bornene (3) and the known hydride complex [(η6-C6H6)-
RuH(PPh3)2]OTf (4).15-17 As triflate is a good leaving
group, the hydrogenation reaction is likely initiated by
formation of the dihydrogen complex [RuH(H2)(NBD)-
(PPh3)2]+ through displacement of the triflate anion with
a H2 molecule. To detect the intermediate, we have
carried out the hydrogenation in dichloromethane at low
temperature. It was shown that complex 2 in CD2Cl2
reacted with H2 to give norbornane (5) and a mixture
of phosphorus-containing species, which proved to be
difficult to purify and characterize. In the presence of
added PPh3, complex 2 reacted with H2 to give norbor-
nane (5) and [RuH(PPh3)4]OTf 18 (6) (Scheme 1). We
have not been able to detect the dihydrogen intermedi-
ate even when the reactions were carried out at low
temperature.
Resu lts a n d Discu ssion
P r ep a r a tion of Ru H(OTf)(NBD)(P P h 3)2. The com-
plex RuH(OTf)(NBD)(PPh3)2 (2) was prepared by treat-
ing RuHCl(NBD)(PPh3)2 (1) with AgOTf (Scheme 1). In
P r epar ation of OsH(OTf)(NBD)(P P h 3)2. For analo-
gous dihydrogen complexes, osmium analogues are
usually thermally more stable than their ruthenium
counterparts.2 Thus we have prepared the analogous
complex OsH(OTf)(NBD)(PPh3)2, hoping that its sub-
sequent reaction with H2 would give the observable
dihydrogen complex [OsH(H2)(NBD)(PPh3)2]+.
1
the H NMR spectrum in CD2Cl2, the CH2 protons of
the NBD exhibited a singlet at 0.89 ppm and the bridge-
head protons of NBD displayed two signals at 2.98 and
4.35 ppm. The NMR data suggest that the hydride is
trans to the OTf ligand and that the two PPh3 ligands
are cis to each other. A similar structure has been
previously proposed for RuHCl(NBD)(PPh3)2.14
The synthetic route to the new osmium complex OsH-
(OTf)(NBD)(PPh3)2 (8) is outlined in Scheme 2. Reaction
19
of OsH3Cl(PPh3)3 with NBD led to the formation of
OsHCl(NBD)(PPh3)2 (7). The procedure is similar to that
used to prepare RuHCl(NBD)(PPh3)2.20 Complex 8 was
then obtained in high yield by treating 7 with AgOTf.
Complex 7 has been characterized by NMR spectros-
copy as well as elemental analysis. In particular, the
31P NMR spectrum in CD2Cl2 showed a singlet at -12.1
ppm, indicating that the two PPh3’s are equivalent. In
the 1H NMR spectrum in CD2Cl2, five NBD proton
signals were observed: the olefinic protons displayed
(12) Beck, W.; Su¨nkel, K. Chem. Rev. 1988, 88, 1405.
(13) See for example: (a) Schlaf, M.; Lough, A. J .; Morris, R. H.
Organometallics 1997, 16, 1253. (b) Bianchini, C.; Masi, D.; Peruzzini,
M.; Casarin, M.; Maccato, C.; Rizzi, G. A. Inorg. Chem. 1997, 36, 1061.
(c) Ayllo´n, J . A.; Gervaux, C.; Sabo-Etienne, S.; Chaudret, B. Organo-
metallics 1997, 16, 2000. (d) Rocchini, E.; Mezzetti, A.; Ru¨egger, H.;
Burckhardt, U.; Gramlich, V.; Del Zotto, A.; Martinuzzi, P.; Rigo, P.
Inorg. Chem. 1997, 36, 711. (e) Gusev, D. G.; Hu¨bener, R.; Orama, O.;
Berke, H. J . Am. Chem. Soc. 1997, 117, 3716, and references therein.
(f) Albertin, G.; Antoniutti, S.; Baldan, D. Bordgnon, E. Inorg. Chem.
1995, 34, 6205. (g) Cappellani, E. P.; Drouin, S. D.; J ia, G.; Maltby, P.
A.; Morris, R. H.; Schweitzer, C. T. J . Am. Chem. Soc. 1994, 116, 3375.
(h) Field, L. D.; Hambley, T. W.; Yau, B. C. K. Inorg. Chem. 1994, 33,
2009. (i) J ia, G.; Drouin, S. D.; J essop, P. G.; Lough, A. J .; Morris, R.
H. Organometallics 1993, 12, 906. (j) Bianchini, C.; Linn, K. Masi, D.
Peruzzini, M.; Polo, A.; Vacca, A.; Zanobini, F. Inorg. Chem. 1993, 32,
2366. (k) Michos, D.; Luo, X. L.; Crabtree, R. H. Inorg. Chem. 1992,
31, 4245. (l) Bianchini, C.; Perez, P. J .; Peruzzini, M.; Zanoboni, F.;
Vacca, A. Inorg. Chem. 1991, 30, 279. (m) Earl, K. A.; J ia, G.; Maltby,
P. A.; Morris, R. H. J . Am. Chem. Soc. 1991, 113, 3027. (m) Bautista,
M. T.; Cappellani, E. P.; Drouin, S. D.; Morris, R. H.; Schweitzer, C.
T.; Sella, A.; Zubkowski, J . J . Am. Chem. Soc. 1991, 113, 4876. (n)
Amendola, P.; Antoniutti, S.; Albertin, G.; Bordignon, E. Inorg. Chem.
1990, 29, 318.
(14) Dekleva, T. W.; J ames, B. R. J . Chem. Soc., Chem. Commun.
1983, 1350.
(15) Harding, P. A.; Robinson, S. D. J . Chem. Soc., Dalton Trans.
1988, 415.
(16) Werner, R.; Werner, H. Chem. Ber. 1982, 115, 3781.
(17) Cole-Hamilton, D. J .; Young, R. J .; Wilkinson, G. J . Chem. Soc.,
Dalton Trans. 1976, 1995.
(18) Sanders, J . R. J . Chem. Soc., Dalton Trans. 1973, 743.
(19) Ferrando, G.; Caulton, K. G. Inorg. Chem. 1999, 38, 4168.
(20) Hallman, P. S.; McGarvey, B. R.; Wilkinson, G. J . Chem. Soc.
(A) 1968, 3143.

Reactions of MH(OTf)(NBD)(PPh3)2 withH2
Organometallics, Vol. 19, No. 22, 2000 4525
As indicated by its NMR spectroscopic data, complex
8 must have a geometry similar to that of complex 7.
Reported complexes closely related to 7 and 8 are the
osmium dihydrido diolefin complexes OsH2(η4-diolefin)-
(P(i-Pr)3)2 (diolefin ) COD, NBD, TFB).23 Unlike com-
plexes 7 and 8, the two phosphine ligands are trans to
each other in OsH2(η4-diolefin)(P(i-Pr)3)2.
Reaction of H2 with OsH(OTf)(NBD)(P P h 3)2. Com-
plex 8 in benzene reacted with H2 to give norbornane
(5) and the known hydride complex [η6-C6H6)OsH-
(PPh3)2]OTf (9)17 (see Scheme 2). On the contrary,
ruthenium complex 2 reacted with H2 in benzene to give
norbornene. In CD2Cl2 at room temperature, complex
8 reacted with H2 to give norbornane and a mixture of
uncharacterized phosphorus-containing species. If com-
plex 8 in CD2Cl2 was allowed to react with H2 at low
temperature, a mixture of unstable hydride species was
produced as indicated by 1H NMR. However, the ex-
pected hydride complex [OsH(H2)(NBD)(PPh3)2]+ or
[OsH3(NBD)(PPh3)2]+ could not be identified. In the
presence of added PPh3, complex 8 reacted with H2 to
give to norbornane and [OsH3(PPh3)4]+ (10).24
F igu r e 1. Molecular structure for OsHCl(NBD)(PPh3)2
showing 40% probability of thermal ellipsoids
Ta ble 1. Cr ysta l Da ta a n d Refin em en t Deta ils for
OsHCl(NBD)(P P h 3)2
formula
fw
C43H39ClP2Os
843.33
Com m en ts on th e P ossible Mech a n ism s for th e
Hyd r ogen a tion of NBD. As triflate can be displaced
easily, it is reasonable to assume that the first step of
the reaction is to displace the triflate anion in MH(OTf)-
(NBD)(PPh3)2 with a H2 molecule to give dihydrogen
complexes [MH(H2)(NBD)(PPh3)2]+ (11) or the hydride
complexes [MH3(NBD)(PPh3)2]+ (M ) Ru, Os). We favor
the formulation of dihydrogen complexes, as a number
of complexes of the type [MH(H2)(L4)]+ (M ) Ru, Os; L
) phosphines) have previously been well characterized
and as NBD is a better π acceptor than phosphines.
Once the dihydrogen complexes were formed, the NBD
can be hydrogenated by transfer of a hydrogen atom
either from the hydride or the dihydrogen ligand to the
olefin ligand followed by transfer of the second one to
give norbornene. Insertions of olefins to M-H bonds and
hydrogen transfer from the η2-H2 ligand to coordinated
olefins are all known reactions. The norbornane is
presumably formed by further hydrogenation of nor-
bornene. We noted that the NBD ligand in RuH(OTf)-
(NBD)(PPh3)2 in benzene is hydrogenated to nor-
bornene, but that in OsH(OTf)(NBD)(PPh3)2 in benzene
is hydrogenated to norbornane. The difference could be
attributed to the stronger bonding of NBE to osmium
relative to ruthenium.
cryst syst
space group
a, Å
b, Å
c, Å
monoclinic
P21/n
12.9154(11)
18.0172(15)
15.3078(13)
100.854(2)
3498.4(5)
4
1.601
3.844
0.71073
1.76-27.51
23 217
8026 (Rint ) 6.14%)
6509 (I > 2σ(I))
456
R1 ) 3.42%, wR2 ) 8.09%
0.972
2.253
-0.826
â, deg
V, Å3
Z
d
calc, g cm-3
abs coeff, mm-1
radiation, Mo KR, Å
θ range, deg
no. of reflns collected
no. of ind reflns
no. of obsd reflns
no. of params refined
final R indices (obsd data)
goodness of fit
largest diff peak, e Å-3
largest diff hole, e Å-3
two signals at 3.02 and 3.22 ppm; the bridge-head
protons also displayed two signals at 3.48 and 4.11 ppm;
the CH2 protons showed only one signal at 0.69 ppm.
The pattern of the NBD H signals implies that the two
PPh3 ligands are cis to each other and that the hydride
is trans to the chloride.
1
The structure of 7 has been confirmed by an X-ray
diffraction study. The molecular geometry of 7 is
depicted in Figure 1. The crystallographic details and
selected bond distances and angles are given in Tables
1 and 2, respectively. The structure of 7 can be viewed
as a distorted octahedron in which two vertexes are
occupied by the double bonds of the norbornadiene
ligand. The two PPh3 ligands are cis to each other,
although P(1)-Os(1)-P(2) angle (101.21(2)°) is signifi-
cantly distorted from 90°. The norbornadiene ligand is
symmetrically coordinated to osmium with the double
bonds trans to the PPh3 ligands. The CdC bonds of
norbornadiene are significantly lengthened relative to
free NBD, and the CdC bond distances are similar to
those observed in RuCl2(NBD)(PPh3)2.21 The Os-C bond
distances are close to those observed in osmium olefin
complexes such as OsCl2(η4-COD)(η2-CH2dCMeP(i-
Pr)2)22 and OsCl2(η4-TFB)(η2-CH2dCMeP(i-Pr)2) (TFB
) tetrafluorobenzobarrelene).22
St r u ct u r es of [MH(H2)(NBD)(P H3)2]+ (M ) R u ,
Os). Although dihydrogen complexes [MH(H2)(NBD)-
(PPh3)2]+ (M ) Ru, Os) are the likely intermediates for
the reactions of MH(OTf)(NBD)(PPh3)2 with H2, we have
not been able to characterize them experimentally. Thus
a computational study was carried out in order to see if
the dihydrogen complexes are reasonable species. To
find out the ground-state structures of [MH(H2)(NBD)-
(PPh3)2]+, density functional calculations have been
carried out for the model complexes [MH(H2)(NBD)-
(PH3)2]+. The optimization on the structure of [RuH-
(21) Bergbreiter, D. E.; Bursten, B. E.; Bursten, M. S.; Cotton, F.
A. J . Organomet. Chem. 1981, 205, 407.
(22) 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.
(23) Castillo, A.; Esteruelas, M. A.; On˜ate, E.; Ruiz, N. J . Am. Chem.
Soc. 1997, 119, 9691.
(24) Siedle, A. R.; Newmark, R. A.; Pignolet, L. H. Inorg. Chem.
1986, 25, 3412.

4526 Organometallics, Vol. 19, No. 22, 2000
Lo et al.
Ta ble 2. Selected Bon d Dista n ces a n d An gles for OsHCl(NBD)(P P h 3)2
Bond Distances (Å)
Os(1)-P(1)
Os(1)-C(1)
Os(1)-C(4)
C(1)-C(5)
C(4)-C(5)
Os(1)-H(1)
2.3918(11)
2.211(4)
2.203(4)
1.543(6)
1.546(6)
1.727
Os(1)-P(2)
2.3739(10)
2.206(4)
1.410(6)
1.529(6)
1.553(6)
Os(1)-Cl(1)
Os(1)-C(3)
C(3)-C(4)
C(3)-C(6)
C(6)-C(7)
2.4997(10)
Os(1)-C(2)
C(1)-C(2)
C(2)-C(6)
C(5)-C(7)
2.209(4)
1.397(6)
1.531(6)
1.539(6)
Bond Angles (deg)
P(1)-Os(1)-P(2)
101.18(4)
P(1)-Os(1)-Cl(1)
91.94(4)
P(1)-Os(1)-C(1)
P(1)-Os(1)-C(3)
P(2)-Os(1)-Cl(1)
P(2)-Os(1)-C(2)
P(2)-Os(1)-C(4)
Cl(1)-Os(1)-C(2)
Cl(1)-Os(1)-C(4)
C(1)-Os(1)-C(3)
C(2)-Os(1)-C(3)
C(3)-Os(1)-C(4)
98.75(12)
148.97(11)
87.40(4)
148.17(12)
94.91(12)
120.23(11)
80.97(11)
76.59(16)
63.68(6)
P(1)-Os(1)-C(2)
P(1)-Os(1)-C(4)
P(2)-Os(1)-C(1)
P(2)-Os(1)-C(3)
Cl(1)-Os(1)-C(1)
Cl(1)-Os(1)-C(3)
C(1)-Os(1)-C(2)
C(1)-Os(1)-C(4)
C(2)-Os(1)-C(4)
93.83(12)
162.12(12)
158.17(12)
90.60(12)
83.11(11)
117.42(11)
37.23(15)
64.25(17)
76.02(16)
36.93(15)
F igu r e 2. Schematic illustration of the two reaction pathways together with calculated relative energies (kcal/mol) and
free energies (kcal/mol, in parentheses) for species involved in the reaction
(H2)(NBD)(PH3)2]+ (12) shows that complex 12 is indeed
a typical dihydrogen complex in which the nonclassical
η2-H2 ligand is trans to the hydride ligand and has a
short H-H distance of 0.793 Å (see discussion in the
next section). As expected, the distances between Ru
and the two hydrogen atoms of the dihydrogen ligand
are much longer (∼1.95 Å) than that between Ru and
the terminal hydride ligand (1.595 Å). A similar opti-
mized structure was obtained for [OsH(H2)(NBD)-
(PH3)2]+, in which the two hydrogen atoms of the
dihydrogen ligand are separated by 0.831 Å. It should
be noted that the related complex [OsH3(NBD)(P(i-
Pr)3)2]+ is known to adopt a trihydride structure.23
However, the complex is different from ours in that the
phosphine is more electron donating and the two steri-
cally more demanding phosphines prefer to be trans to
each other.
Th eor etica l Stu d y on th e Rea ction P a th w a ys of
th e Con ver sion of [Ru H(H2)(NBD)(P H3)2]+ to [Ru -
H(NBE)(P H3)2]+. As mentioned previously, hydrogena-
tion of the NBD ligand in [MH(H2)(NBD)(PPh3)2]+ can
be initiated by transfer of a hydrogen to the olefin ligand
from either the hydride or the dihydrogen ligand. To
clarify whether hydrogen transfer from the η2-H2 or the
hydride ligand to the olefin ligand in [MH(H2)(NBD)-
(PPh3)2]+ is more likely the first step for the hydrogena-
tion reactions, density functional theory calculations
have been carried out for all stable and transition
structures for the two reaction pathways involved in the
conversion of the model complex [RuH(H2)(NBD)-
(PH3)2]+ to [RuH(NBE)(PH3)2]+ (NBE ) norbornene).
Figure 2 shows the two possible reaction pathways
studied here for the conversion of [RuH(H2)(NBD)-

Reactions of MH(OTf)(NBD)(PPh3)2 withH2
Organometallics, Vol. 19, No. 22, 2000 4527
F igu r e 3. Optimized structures with selected geometry parameters (and relative stability). The hydrogen atoms, which
are not directly involved in the hydrogenation, have been omitted for the purpose of clarity
(PH3)2]+ to [RuH(NBE)(PH3)2]+.25 Path 1 starts with the
hydrogen transfer from the hydride ligand (Ha) followed
by the cleavage of the dihydrogen ligand to form a cis
dihydride intermediate 13; then the second hydrogen
transfers from one (Hb) of the two hydride ligands to
complete the hydrogenation and gives a coordinated
NBE complex 14. By contrast, the second pathway (path
2) starts with the first hydrogen transfer from the
dihydrogen ligand (Hb) to form a trans (or nearly trans)
dihydride intermediate 13′; the second hydrogen trans-
fers from the original hydride ligand (Ha) to form the
same norbornene (NBE) complex 14 as in path 1.
Figure 2 also shows the relative reaction energies and
free energies (in brackets) calculated for all the species
(stable and transition structures). It is clear that the
relative free energies do not differ too much from the
relative reaction energies. These results suggest that
the entropy contribution is not important because the
reaction paths involve only structural rearrangement
(25) Another possible pathway is the concert hydrogen transfer from
both hydride and dihydrogen ligands. However, we were not able to
locate the transition state in our calculations.

4528 Organometallics, Vol. 19, No. 22, 2000
Lo et al.
within the molecules. Therefore, we will use the reaction
energies for discussion since the differences between the
reaction energies and free energies are small.
overall activation energies of path 2 are higher than
those of path 1.
Now we come to the second question why the activa-
tion energies required for the first hydrogen transfer
are much higher than those for the second hydrogen
transfer for both reaction pathways. Carefully examina-
tion of the geometrical changes during the relevant
hydrogen transfer steps provides helpful information to
the understanding of this problem. The geometrical
changes from the reactant to the first transition struc-
tures (TS1 and TS1′) are quite significant. The Ru-
Hb/Hb-Hc distances change from 1.951/0.793 Å to 1.795/
0.841 Å for path 1 and to 1.736/1.387 Å for path 2. These
remarkable changes give rise to higher activation ener-
gies required for the first hydrogen transfers in both
paths. However, TS2 and TS2′ are structurally similar
to 13 and 13′, respectively. The similarity leads to small
changes in their stabilities and therefore the activation
energies required for the second hydrogen transfers turn
out to be much smaller.
For both reaction pathways, the reaction barriers of
the first hydrogen transfer (10.3 and 16.9 kcal/mol) are
much higher than those of the second hydrogen transfer
(2.5 and 1.8 kcal/mol), indicating that the first hydrogen
transfer is the rate-determining step. Overall, the
reaction barriers of path 1 are significantly lower than
those of path 2, suggesting that path 1 is the main
channel of the hydrogenation of NBD in this Ru
complex. The low activation energy (10.3 kcal/mol) of
path 1 is in agreement with the experimental observa-
tion that the NBD ligand is hydrogenated rapidly and
that the dihydrogen complex [RuH(H2)(NBD)(PPh3)2]+
could not be observed.
One may ask why the overall activation energy of
path 1 is significantly lower than that of path 2, and
why the reaction barriers for the first hydrogen transfer
of both pathways are much higher than those of the
second hydrogen transfer. To answer these questions,
the calculated geometries of the related structures are
examined below.
Su m m a r y a n d Con clu sion s
The NBD ligand in MH(OTf)(NBD)(PPh3)2 (M ) Ru,
Os) is hydrogenated on treatment with H2 gas. Forma-
tion of the dihydrogen complexes [MH(H2)(NBD)-
(PPh3)2]+ is likely the first event of the hydrogenation
reactions, although the dihydrogen complexes could not
be observed experimentally. Density functional calcula-
tions on the model complexes [MH(H2)(NBD)(PH3)2]+
confirm that [MH(H2)(NBD)(PH3)2]+ indeed adopts the
dihydrogen form. Hydrogenation of the NBD ligand in
[MH(H2)(NBD)(PPh3)2]+ can be initiated by first trans-
fer of a hydrogen atom to the olefin ligand either from
the hydride (path 1) or from the dihydrogen ligand (path
2). The density functional theory calculations at the
BLYP level on the reaction pathways for the conversion
of [RuH(H2)(NBD)(PH3)2]+ to [RuH(H2)(NBE)(PH3)2]+
found that the pathway (path 1) in which the first
hydrogen transfer is from the hydride ligand has a lower
reaction barrier than the other one (path 2) in which
the first hydrogen transfer is from the dihydrogen
ligand. The overall reaction barrier of path 1 is calcu-
lated to be low (the relative free energy is only 11.0 kcal/
mol at room temperature). In good agreement with the
experimental observations, this result indicates that the
hydrogenation of NBD through the first reaction path-
way (path 1) can go rapidly at room temperature. The
higher reaction barrier of the second pathway is due to
the trans influence of the trans dihydride transition
states and intermediate involved. It is also found that
the activation energies required for the first hydrogen
transfer are much higher than that required for the
second hydrogen transfer in both pathways. These
differences in activation energies are related to the
different degree of the geometry changes during the two
steps of hydrogen transfers. The first hydrogen transfers
in both pathways lead to significant geometry changes,
especially for the Ru-H bond lengths, while the second
hydrogen transfers do not cause remarkable geometry
changes.
Figure 3 shows the optimized structures with selected
structural parameters for all related species. The reac-
tant (12) is a typical dihydrogen complex in which the
nonclassical η2-H2 ligand is trans to the hydride ligand
(Ha) and has a short Hb-Hc distance of 0.793 Å. The
first transition state (TS1) of path 1 is also a nonclas-
sical complex with a slightly longer Hb-Hc distance
(0.841 Å). However, the first transition state (TS1′) of
path 2 has a much longer Hb-Hc distance (1.387 Å) and
typical Ru-hydride distances (see Figure 3 for details),
especially Ru-Ha and Ru-Hc. The short Ru-H dis-
tances suggest that TS1′ could be considered as a
trihydride with two hydride ligands (Ha and Hc) trans
(or nearly trans) to each other. The high relative energy
of this trihydride structure, compared with that of TS1,
reveals that the strong trans influence between Ha and
Hc (or Hb) plays an important role in this transition
state. The trans influence of a hydride ligand weakens
the metal-ligand interaction at the position trans to it
and thus destabilizes the system.26
As the first hydrogen moves closer to the olefin ligand,
TS1 gives a cis dihydride intermediate (13) with a weak
agostic interaction between the Ru center and Ha while
TS1′ gives a trans dihydride intermediate (13′). The
higher energy of 13′ is again due to the strong trans
influence between Ha and Hc. This strong trans influ-
ence is also reflected by the relevant structural param-
eters that the Ru-H distances in 13′ (Ru-Ha and Ru-
Hc) are longer than those in 13 (Ru-Hb and Ru-Hc).
The second hydrogen transfer in path 1 gives a cis
dihydride transition structure (TS2) while that in path
2 leads to a trans dihydride transition structure (TS2′).
The higher relative energy of TS2′ can be easily related
to the trans influence between Ha and Hc.
It is obvious that the high relative energies of
structures TS1′, 13′, and TS2′ are all related to the
trans influence between the hydride ligands in these
species. Such a trans influence also explains why the
Exp er im en ta l Section
All manipulations were carried out under a nitrogen atmo-
sphere using standard Schlenk techniques. Solvents were
(26) (a) Lin, Z.; Hall, M. B. J . Am. Chem. Soc. 1992, 114, 6102. (b)
Xu, Z.; Bytheway, I.; J ia, G.; Lin, Z. Organometallics 1999, 18, 1761.

Reactions of MH(OTf)(NBD)(PPh3)2 withH2
Organometallics, Vol. 19, No. 22, 2000 4529
distilled under nitrogen from sodium benzophenone (hexane,
ether, THF) or sodium (benzene) or calcium hydride (CH2Cl2).
The starting materials RuHCl(NBD)(PPh3)2,20 OsCl2(PPh3)3,27
and OsH3Cl(PPh3)3 were prepared according to literature
methods. All other reagents were used as purchased from
Aldrich Chemical Co.
Microanalyses were performed by M-H-W Laboratories
(Phoenix, AZ). 1H, 13C{1H}, and 31P{1H} NMR spectra were
collected on a J EOL EX-400 spectrometer (400 MHz) or a
Bruker ARX-300 spectrometer (300 MHz). 1H and 13C NMR
chemical shifts are relative to TMS, and 31P NMR chemical
shifts are relative to 85% H3PO4. MS spectra were recorded
on a Finnigan TSQ7000 spectrometer.
R u H (OTf)(NBD)(P P h 3)2. A mixture of RuHCl(NBD)-
(PPh3)2 (1.25 g, 1.66 mmol) and AgOTf (0.60 g, 2.7 mmol) in
THF (35 mL) was stirred for 0.5 h. The solvent was then
removed completely under vacuum. Addition of 50 mL of 10%
MeOH aqueous solution to the residue produced a yellow solid,
which was collected by filtration, washed with water, and dried
under vacuum for 3 h. The solid was then extracted with 8:1
benzene/hexane. The extraction was filtered through a column
of Celite. The volume of the filtrate was reduced to ca. 1 mL
under vacuum. A pale yellow solid was formed when 40 mL of
hexane was added. The solid was collected on a filter frit,
washed with hexane, and dried under vacuum. Yield: 0.94 g,
60%. Anal. Calcd for C44H39F3O3P2SRu: C, 60.89; H, 4.53.
Found: C, 60.75; H, 5.13. 1H NMR (300.13 MHz, C6D6): δ
-13.64 (t, J (PH) ) 22.5 Hz, 1 H, RuH), 0.89 (s, 2 H, CH2),
2.98 (s, 1 H, bridge-head CH), 3.61 (s, 2 H, olefinic protons),
4.35 (br s, 3 H, two olefinic protons and one bridge-head CH
proton), 7.00-7.60 (m, 30 H, PPh3). 31P{1H} NMR (121.49
MHz, C6D6): δ 41.5 (s).
Rea ction of Ru H(OTf)(NBD)(P P h 3)2 w ith H2 in CD2Cl2
in th e P r esen ce of P P h 3. A mixture of RuH(OTf)(NBD)-
(PPh3)2 (20 mg, 0.023 mmol) and PPh3 (30 mg, 0.11 mmol) in
CD2Cl2 (0.7 mL) in an NMR tube was allowed to stand under
H2 atmosphere for 1 h. The mixture was occasionally shaken.
Then 1H and 31P{1H} NMR spectra were collected. 31P{1H}
NMR (121.49 MHz, CD2Cl2): δ - 6.0 (s, free PPh3), 28.3 (s,
br, [RuH(PPh3)4](OTf)18). 1H NMR (300.13 MHz, CD2Cl2): δ
-8.00 (quintet, J (PH) ) 20.4 Hz, [RuH (PPh3)4](OTf)18), 0.90-
2.19 (m, norbornane), 6.77-7.90 (m, PPh3). Using a residual
solvent signal at 5.32 ppm as the internal standard, the yield
of norbornane was determined to be 81%. The volatile portion
of the reaction mixture can be separated by vacuum transfer.
A 1H NMR spectrum of the vacuum-transferred solution shows
that norbornane is the only volatile organic product formed
in the reaction.
Rea ction of Ru H(OTf)(NBD)(P P h 3)2 w ith H2 in Ben -
zen e. A solution of RuH(OTf)(NBD)(PPh3)2 (0.35 g, 0.40 mmol)
in benzene (30 mL) was stirred under a H2 atmosphere for 1
h. The volume of the reaction mixture was then reduced to
ca. 1 mL. Addition of hexane (50 mL) to the residue produced
a white solid. The solid was collected by filtration, washed with
hexane, and dried under vacuum. The solid was identified to
be [(η6-C6H6)RuH(PPh3)2]OTf.15-17 Yield: 0.31 g, 91%. 1H NMR
(300.13 MHz, acetone-d6): δ -8.83 (t, J (PH) ) 36.9 Hz, RuH),
5.93 (s, 6 H, C6H6), 7.46-7.85 (m, Ph). 31P{1H} NMR (121.49
MHz, C6D6): δ 51.0 (s).
Id en tifica tion of NBE F or m ed fr om th e Rea ction of
Ru H(OTf)(NBD)(P P h 3)2 w ith H2 in C6D6. A C6D6 solution
(1 mL, contains 0.03% v/v TMS) of RuH(OTf)(NBD)(PPh3)2 (50
mg, 0.023 mmol) was allowed to stand under a H2 atmosphere
for 0.5 h. The mixture was occasionally shaken. Then 1H and
31P{1H) NMR spectra were collected. 31P{1H} NMR (121.49
MHz, C6D6): δ 51.0 (s, [(η6-C6D6)RuH(PPh3)2]OTf)15-17). 1H
NMR (300.13 MHz, C6D6): δ 0.79-1.74 (m, 6 H, CH2), 2.73 (s,
2 H, bridge-head proton), 5.93 (s, 2 H, olefinic CH proton),
6.89-7.48 (m, PPh3). Using the TMS signal as the internal
standard, the yield of norbornene was determined to be 90%.
The volatile portion of the reaction mixture can be separated
by vacuum transfer. A 1H NMR spectrum of the vacuum-
transferred solution shows that norbornene is the only volatile
organic product formed in the reaction.
Rea ction of OsH(OTf)(NBD)(P P h 3)2 w ith H2 in CD2Cl2
in th e P r esen ce of P P h 3. A mixture of OsH(OTf)(NBD)-
(PPh3)2 (20 mg, 0.021 mmol) and PPh3 (0.30 mg, 0.11 mmol)
in CD2Cl2 (0.7 mL) in an NMR tube was allowed to stand under
a H2 atmosphere for 1 h. The mixture was occasionally shaken.
Then 1H and 31P{1H} NMR spectra were collected. 31P{1H}
NMR (121.49 MHz, CD2Cl2): δ -6.0 (s, free PPh3), -0.8 (br,
[OsH3(PPh3)4](OTf)24). 1H NMR (300.13 MHz, CD2Cl2): δ -9.83
(quintet, J (PH) ) 19.6 Hz, [OsH3(PPh3)4](OTf)24), 0.92-2.07
(m, norbornane), 6.71-7.41 (m, PPh3). Using residual solvent
proton signal at 5.32 ppm as the internal standard, the yield
of norbornane was determined to be 90%. The volatile portion
of the reaction mixture can be separated by vacuum transfer.
A 1H NMR spectrum of the vacuum-transferred solution shows
that norbornane is the only volatile organic product formed
in the reaction.
19
OsHCl(NBD)(P P h 3)2. A mixture of OsH3Cl(PPh3)3 (1.32 g,
1.30 mmol) and NBD (1.0 mL, 9.3 mmol) in benzene (35 mL)
was stirred for 8 h to give a brown solution, which was filtered
through a column of Celite. The solvent of the filtrate was then
removed completely under vacuum. Addition of hexane (30 mL)
to the residue produced a brown solid. After stirring for 0.5 h,
the solid was collected by filtration, washed with hexane, and
dried under vacuum. Yield: 0.98 g, 89%. Anal. Calcd for C43H39
-
ClP2Os: C, 61.24; H, 4.66. Found: C, 61.34; H, 4.82. 1H NMR
(300.13 MHz, C6D6): δ -12.13 (t, J (PH) ) 22.5 Hz, 1 H, OsH),
0.69 (s, 2 H, CH2), 3.02 (d, J (HH) ) 3.5 Hz, 2 H, olefinic CH
protons), 3.22 (s, 2 H, olefinic CH protons), 3.48 (s, 1 H, bridge-
head CH proton), 4.11 (s, 1 H, CH), 7.00-7.80 (m, 30 H, PPh3).
31P{1H} NMR (121.49 MHz, C6D6): δ 2.8 (s). 13C{1H} NMR
(75.47 MHz, C6D6): δ 41.0 (d, J (PC) ) 4.6 Hz, olefinic CH),
45.1 (s, bridge-head CH), 47.4 (d, J (PC) ) 15.9 Hz, olefinic
CH), 49.2 (s, CH2), 62.1 (t, J (PC) ) 5.4 Hz, bridge-head CH),
127.0-134.7 (m, Ph).
OsH(OTf)(NBD)(P P h 3)2. A mixture of OsHCl(NBD)(PPh3)2
(0.95 g, 1.1 mmol) and AgOTf (0.65 g, 2.95 mmol) in THF (25
mL) was stirred for 0.5 h. The solvent was then removed
completely under vacuum. Addition of 50 mL of 10% MeOH
aqueous solution to the residue produced a yellow solid, which
was collected by filtration, washed with water, and dried under
vacuum for 3 h. The solid was then extracted with 8:1 benzene/
hexane. The extraction was filtered through a column of Celite.
The volume of the filtrate was reduced to ca. 1 mL under
vacuum. A pale yellow solid was formed when 40 mL of hexane
was added. The solid was collected on a filter frit, washed with
hexane, and dried under vacuum. Yield: 0.63 g, 61%. Anal.
Calcd for C44H39F3O3P2SOs: C, 55.22; H, 4.11. Found: C,
55.49; H, 5.25. 1H NMR (300.13 MHz, C6D6): δ -17.57 (t,
J (PH) ) 21.0 Hz, 1 H, OsH), 0.68 (s, 2 H, CH2), 3.26 (s, 1 H,
bridge-head CH proton), 3.44 (s, 2 H, olefinic CH proton), 3.90
(d, J (HH) ) 3.3 Hz, 2 H, olefinic CH proton), 4.73 (s, 1 H,
bridge-head CH proton), 7.10-7.90 (m, 30 H, PPh3). 31P{1H}
NMR (121.49 MHz, C6D6): δ 12.5 (s).
Rea ction of OsH(OTf)(NBD)(P P h 3)2 w ith H2 in C6D6.
A C6D6 solution (1 mL, contains 0.03% v/v TMS) of OsH(OTf)-
(NBD)(PPh3)2 (20 mg, 0.021 mmol) in an NMR tube was
allowed to stand under a H2 atmosphere for 30 min. The
mixture was occasionally shaken. Then 1H and 31P{1H) NMR
spectra were collected. 31P{1H} NMR (121.49 MHz, C6D6): δ
6.1 (s, [(η6-C6D6)OsH(PPh3)2]OTf)17). 1H NMR (300.13 MHz,
C6D6): δ -11.35 (t, J (PH) ) 17.5 Hz, [(η6-C6D6)OsH(PPh3)2]-
OTf), 1.00-1.44 (m, 8 H, CH2 of norbornane), 2.15 (s, 2 H, CH
of norbornane), 6.80-7.43 (m, [(η6-C6D6)OsH(PPh3)2]OTf)17).
Using the TMS signal as the internal standard, the yield of
norbornane was determined to be 91%. The volatile portion of
the reaction mixture can be separated by vacuum transfer. A
(27) Hoffmann, P. R.; Caulton, K. G. J . Am. Chem. Soc. 1975, 97,
4221.

4530 Organometallics, Vol. 19, No. 22, 2000
Lo et al.
1H NMR spectrum of the vacuum-transferred solution shows
that norbornane is the only volatile organic product formed
in the reaction. Pure samples of [(η6-C6H6)OsH(PPh3)2]OTf can
be obtained on preparative scale from the reaction of OsH-
(OTf)(NBD)(PPh3)2 in C6H6 with H2.
theory. For C and H atoms the 6-31G standard basis set was
used, while Ru, Os, and P were represented by the LANL2DZ
effective core potentials,30 which include a double-ú basis set
to describe the valence electrons explicitly. Additionally, to
better describe the electronic properties of both hydride and
dihydrogen ligands, polarization functions with úp ) 0.1131
have also been added to the standard basis set for the H atoms
of these two ligands. The calculations were performed using
the Gaussian 98 program32 installed on Pentium III personal
computers with Linux (Red Hat) operating systems.
Cr ysta llogr a p h ic An a lysis for OsHCl(NBD)(P P h 3)2.
Suitable crystals of OsHCl(NBD)(PPh3)2 for X-ray diffraction
study were grown by layering of hexane on a CH2Cl2 solution
of 7. A brown prismatic single crystal having approximate
dimensions of 0.12 × 0.10 × 0.06 mm was mounted in a glass
fiber and used for X-ray structure determination. Intensity
data were collected on a Bruker SMART CCD area detector
using graphite-monochromated Mo KR radiation (λ ) 0.71073
Å). The intensity data were corrected for SADABS (Siemens
area detector absorption28) (from 0.6555 to 0.8022 on I). The
structure was solved by direct methods and refined by full-
matrix least-squares analysis on F2 using the SHELXTL
(version 5.10) program package.29 All non-hydrogen atoms
were refined anisotropically. The H atoms of the phenyl rings
of the PPh3 ligands were introduced at calculated positions
and refined via a riding model. The H atoms of the NBD were
located from the difference Fourier map and refined with
isotropic thermal parameters. The metal-bound hydrido ligand
could be located satisfactorily in a final difference Fourier
synthesis with reasonable Os-H bond distance and was
constrained to ride on the Os atom. The largest difference peak
and hole 2.253/-0.826 e Å-3 are in the vicinity of the Os atom.
Further details are given in Table 1.
Ack n ow led gm en t. The authors acknowledge finan-
cial support from the Hong Kong Research Grants
Council.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic details, bond distances and angles, atomic coordi-
nates and equivalent isotropic displace coefficients, and aniso-
tropic displacement coefficients for OsHCl(NBD)(PPh3)2. The
material is available free of charge via the Internet at
http://pubs.acs.org.
OM000369X
(30) Hay, P. J .; Wadt, W. R. J . Chem. Phys. 1985, 82, 299.
(31) Huzinaga, S. Gaussian Basis Sets for Molecular Calculations;
Elsevier Science Pub. Co.: Amsterdam, 1984.
(32) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J . R.; Zakrzewski, V. G.; Montgomery, J . A.,
J r.; Stratmann, R. E.; Burant, J . C.; Dapprich, S.; Millam, J . M.;
Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J .;
Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo,
C.; Clifford, S.; Ochterski, J .; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J . B.; Cioslowski, J .; Ortiz, J . V.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.;
Fox, D. J .; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; J ohnson, B. G.; Chen,
W.; Wong, M. W.; Andres, J . L.; Head-Gordon, M.; Replogle, E. S.;
Pople, J . A. Gaussian 98 (Revision A.7); Gaussian, Inc.: Pittsburgh,
PA, 1998.
Com p u ta tion a l Deta ils. In the calculations, the PPh3
ligand has been modeled using a PH3 group. Geometry
optimizations have been carried out for all stable species
(reactant, intermediates, and product) and transition states
involved in the two possible reaction paths. All calculations
have been carried out at the BLYP level of density functional
(28) Sheldrick, G. M. SADABS, Empirical Absorption Correction
Program; University of Go¨ttingen: Germany, 1996.
(29) SHELXTL Reference Manual (Version 5.1); Bruker Analytical
X-Ray Systems Inc.: Madison, WI, 1997.