Synthesis and characterization of dihydrogen(olefin)osmium complexes with (E)-Ph2P(CH2)2CH=CH (CH2)2PPh2

Article abstract of DOI:10.1002/1099-0682(200207)2002:7<1697::AID-EJIC1697>3.0.CO;2-O

Treatment of [OsClH₃(PPh₃)₃] with (E)-Ph₂P(CH₂)₂CH= CH(CH₂)₂PPh₂ produced [OsClH(PPh₃){Ph₂P(CH₂)₂CH= CH(CH₂)₂PPh₂}], which reacted with HOTf to give the dihydrogen(olefin) complex [OsCl(H₂)(PPh₃){Ph₂P (CH₂)₂CH= CH(CH₂)₂PPh₂}]OTf. Treatment of the latter complex with H₂ did not result in hydrogenation of the olefin double bond, but gave the (hydrido)dihydrogen complex [OsH(H₂)-(PPh₃){Ph₂P (CH₂)₂CH=CH(CH₂)₂ PPh₂}]OTf. A density functional theory study suggested that hydrogenation of the double bond in [OsCl(H₂)(PPh₃){Ph₂P (CH₂)₂CH= CH(CH₂)₂PPh₂}]OTf was thermodynamically feasible but kinetically unfavorable. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.

Full text of DOI:10.1002/1099-0682(200207)2002:7<1697::AID-EJIC1697>3.0.CO;2-O

FULL PAPER
Synthesis and Characterization of Dihydrogen(olefin)osmium Complexes with
(E)-Ph2P(CH2)2CH؍CH(CH2)2PPh2
Sheng Hua Liu,[a] Xin Huang,[a] Zhenyang Lin,*[a] Chak Po Lau,*[b] and Guochen Jia*[a]
Keywords: Dihydrogen / Diphosphane / Hydride / Osmium
Treatment of [OsClH3(PPh3)3] with (E)-Ph2P(CH2)2CH=
CH(CH2)2PPh2 produced [OsClH(PPh3){Ph2P(CH2)2CH=
CH(CH2)2PPh2}], which reacted with HOTf to give the dihy-
drogen(olefin) complex [OsCl(H2)(PPh3){Ph2P(CH2)2CH=
(PPh3){Ph2P(CH2)2CH=CH(CH2)2PPh2}]OTf. A density func-
tional theory study suggested that hydrogenation of the
double
bond
in
[OsCl(H2)(PPh3){Ph2P(CH2)2CH=
CH(CH2)2PPh2}]OTf was thermodynamically feasible but
CH(CH2)2PPh2}]OTf. Treatment of the latter complex with H2 kinetically unfavorable.
did not result in hydrogenation of the olefin double bond, but ( Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany,
gave the (hydrido)dihydrogen complex [OsH(H2)- 2002)
Introduction
In addition, there are reports that hydrogenation may
also proceed through hydrogen transfer from a coordinated
dihydrogen ligand to an olefin ligand. The complexes
[M(H2)(η4-NBD)(CO)3] and [M(H2)(η2-NBD)(CO)4] (M ϭ
Cr, Mo, and W) have been proposed as the intermediates
in the photocatalytic hydrogenation of norbornadiene with
[M(CO)6].[12,13] Dihydrogen(olefin) complexes have also
been proposed (but not detected) as the intermediates in
Since the first report of dihydrogen complexes by Kubas
and his co-workers in 1984,[1] this unique class of complexes
has been intensively investigated, especially with regard to
their preparation, characterization, and structural and cata-
lytic properties.[2Ϫ4] Previous studies have established that
dihydrogen complexes may have their own individual react-
ivity and play active roles in catalytic reactions. In catalytic
hydrogenation reactions, there are several possible ways in
which dihydrogen complexes may play active roles. Among
them, intramolecular hydrogen transfer from a coordinated
dihydrogen ligand to the α-carbon atom of a σ-bonded car-
bon ligand has been recognized as one of the key steps in
the catalytic cycles. In particular, (alkyl)dihydrogen and (al-
kenyl)dihydrogen complexes have been proposed or inferred
as the key intermediates in the hydrogenation of olefins and
acetylenes under catalysis by group-8 metal complexes such
catalytic
[Ru(Tp)(PPh3)x(CH3CN)3Ϫx
hydrogenation
of
olefins
with
ϩ
]
(x ϭ 1, 2),[8] and in the pro-
tonation reaction of [Ru(Cp*)H(NBD)].[14a] However, well-
characterized dihydrogen(olefin) complexes are rare.[12Ϫ14]
Reported dihydrogen(olefin) complexes include [M(H2)(η2-
NBD)(CO)4] (M ϭ Mo and W),[12] [M(H2)(η4-NBD)(CO)4]
(M ϭ Cr, Mo, and W),[12] and [Fe(H2)(CO)3(MeO2CCHϭ
CHCO2Me)],[13] which have been detected by IR spectro-
scopy, and [Ru(Cp*)(H2)(COD)]ϩ, which has been detected
by NMR spectroscopy.[14a] In this paper we wish to report
the synthesis and characterization of new dihydrogen-
(olefin) complexes.
as [MH(H2)(PP3)]ϩ [M
CH2PPh2)3],[5] [OsClH(CO){P(iPr)3}2],[6]
ϭ
Fe, Ru; PP3
ϭ
P(CH2-
[RuClH-
(PPh3)3],[7] and [RuH(Tp)(L)(PPh3)] [Tp ϭ hydrotris(1-pyr-
azolyl)borate; L ϭ PPh3, CH3CN].[8] As model complexes
for reactions involving intramolecular hydrogen transfer
from a coordinated dihydrogen ligand to the α-carbon atom
of a σ-bonded carbon ligand, several well-characterized di-
hydrogen complexes containing σ-bonded carbon ligands
(such as alkynyl,[9] alkenyl,[10] and aryl[11]) have been syn-
thesized in recent years.
Results and Discussion
Synthesis and Characterization of
[OsClH(PPh3){Ph2P(CH2)2CH؍CH(CH2)2PPh2}]
Complexes of the type [MCl(H2)L4]ϩ (M ϭ Ru, Os; L ϭ
phosphane, CO, pyridine) are known to contain a dihydro-
gen ligand.[15,16] One might therefore expect that pro-
tonation of [MClH(olefin)(PR3)3] might produce dihydro-
gen complexes [MCl(H2)(olefin)(PR3)3]ϩ. To test this pos-
sibility, we prepared the hydrido(olefin) complex
[OsClH(PPh3)(Ph2P(CH2)2CHϭCH(CH2)2PPh2], hoping
that subsequent protonation would produce the corres-
[a]
Department of Chemistry, The Hong Kong University of
Science and Technology,
Clear Water Bay, Kowloon, Hong Kong
Department of Applied Biology & Chemical Technology, The
[b]
Hong Kong Polytechnic University,
Hung Hom, Kowloon, Hong Kong
Eur. J. Inorg. Chem. 2002, 1697Ϫ1702  WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 1434Ϫ1948/02/0707Ϫ1697 $ 20.00ϩ.50/0
1697

S. H. Liu, X. Huang, Z. Lin, C. P. Lau, G. Jia
FULL PAPER
ponding dihydrogen(olefin) complex. Osmium metal and ture in which the hydride ligand is trans to a chloride ligand.
the bidentate phosphane ligand with an olefinic func- During the course of this work, the closely related complex
tionality in the backbone were used in the project because [OsClH(PPh3)(Ph2PϪC6H3MeϪCHϭ
of the expectation that such systems may give thermally CHϪC6H3MeϪPPh2)] was reported.[19]
stable dihydrogen(olefin) complexes.
The ligand (E)-Ph2P(CH2)2CHϭCH(CH2)2PPh2 (2)[17]
Synthesis and Characterization of
was prepared by treatment of (E)-Br(CH2)2CHϭ
[OsCl(H2)(PPh3){Ph2P(CH2)2CH؍CH(CH2)2PPh2}]OTf
CH(CH2)2Br (1) with excess KPPh2 in THF (Scheme 1).
Protonation of complex 3 with HOTf produced the dihy-
drogen(olefin) complex [OsCl(H2)(PPh3)(Ph2P(CH2)2CHϭ
CH(CH2)2PPh2)]OTf (4). Complex 4 was unstable and de-
composed under vacuum. The compound could therefore
not be isolated as a pure solid, so it was characterized in
situ. The 31P{1H} NMR spectrum of complex 4 (in
CD2Cl2) exhibited the PPh3 signal at δ ϭ Ϫ8.9 ppm and
the PPh2 signals at δ ϭ 14.2 and 16.8 ppm. The 31P signals
of the PPh2 groups at δ ϭ 14.2 and 16.8 ppm had a large
2JP,P coupling constant (243.6 Hz), indicating that the PPh2
1
Ligand 2 was characterized by H, 13C{1H}, and 31P{1H}
NMR spectroscopy and by elemental analysis. In particular,
1
the H NMR spectrum (in C6D6) showed the olefinic pro-
ton signal at δ ϭ 5.4 ppm, while the 31P{1H} NMR spec-
trum (in C6D6) showed a singlet at δ ϭ Ϫ17.0 ppm. The
closely related ligand (E)-(tBu)2P(CH2)2CHϭCH(CH2)2-
P(tBu)2 has also been reported previously.[18]
1
groups were trans to each other in 4. The H NMR spec-
trum (in CD2Cl2) exhibited a broad signal attributable to a
dihydrogen ligand at δ ϭ Ϫ9.57 ppm. The broad hydride
signal had a T1 (min) of 27.0 ms (at 300 MHz) at 258 K.
The short T1 (min) value strongly suggested that complex 4
contained
a dihydrogen ligand. Further support for
the existence of the dihydrogen ligand in 4 was provided by
the 1H NMR spectrum of the HD isotopomer
[OsCl(HD)(PPh3){Ph2P(CH2)2CHϭCH(CH2)2PPh2}]ϩ,
which was generated in situ by protonation of complex 3
with DOTf. The 1H NMR spectrum of the HD isotopomer
(in CD2Cl2) displayed the HD signal as a 1:1:1 triplet at δ ϭ
Ϫ9.58 ppm, with a 1J(HD) coupling constant of 14.1 Hz. A
˚
d(HH) of 1.18 A was obtained by application of the rela-
1
tionship d(HH) ϭ Ϫ0.0167J(HD) ϩ 1.42 and J(HD) ϭ
14.1 Hz.[15a] On the basis of the T1 (min) of 27 ms, the
Scheme 1
˚
HϪH bond length was calculated to be 1.13 A for a non-
[20]
˚
spinning H2 or 0.98 A for a spinning dihydrogen ligand.
Treatment of a benzene solution of [OsClH3(PPh3)3] with
ligand 2 for 5 h produced [OsClH(PPh3){Ph2P(CH2)2CHϭ
CH(CH2)2PPh2}] (3), which was isolated as a gray solid in
ca. 79% yield. The structure of complex 3 could readily be
Treatment of [OsCl(H2)(PPh3){Ph2P(CH2)2CH؍
CH(CH2)2PPh2}]OTf with H2
We tried to hydrogenate the coordinated olefin double
assigned by its H, 13C{1H}, 31P{1H}, and H-31P-COSY bond in 4 by storing a solution of 4 in CD2Cl2 under H2.
1
1
NMR spectra and by elemental analysis. The 31P{1H} However,
the
expected
hydrogenated
product
NMR spectrum (in C6D6) showed three doublets of doub- [OsClHx(PPh3){Ph2P(CH2)6PPh2}]ϩ was apparently not
2
lets at δ ϭ Ϫ7.7, 7.3, and 23.8 ppm. A large JP,P coupling produced from the reaction, as indicated by in situ NMR
(290.6 Hz) for the 31P signals at δ ϭ 7.3 and 23.8 ppm was studies. Instead, the fluxional (hydrido)dihydrogen complex
observed, indicating that two of the phosphorus atoms in 3 [OsH(H2)(PPh3){Ph2P(CH2)2CHϭCH(CH2)2PPh2}]OTf
were trans to each other. A 1H-31P-COSY NMR experi- (5) was slowly produced under these reaction conditions. A
ment suggested that the two trans-disposed phosphorus molecule of HCl in 4 was thus apparently replaced by a H2
atoms were associated with the two PPh2 groups of ligand molecule in the reaction. Mechanistically, complex 5 could
1
2. In the H NMR spectrum (in C6D6), the olefinic proton be formed by initial displacement of ClϪ in 4 with an H2
signals appeared at δ ϭ 3.88 ppm, significantly upfield from molecule to give the dicationic dihydrogen complex
their counterparts in free ligand 2, confirming that the ol- [Os(H2)2(PPh3){Ph2P(CH2)2CHϭCH(CH2)2PPh2}]2ϩ
, fol-
efin double bond was coordinated to the osmium center. lowed by deprotonation.
Complex 3 exhibited a hydride signal at δ ϭ Ϫ16.40 ppm
The presence of a coordinated CHϭCH moiety in 5 was
2
(dt, JP,H ϭ 27.0, 15.0 Hz). The magnitude of the coupling supported by the 13C NMR spectrum (in CD2Cl2), which
constants indicated that the hydride ligand was cis to the displayed the coordinated olefinic CH carbon signals at δ ϭ
three phosphorus atoms. The chemical shift of the hydride 56.9 and 65.7 ppm. The 31P{1H} NMR spectrum (in
signal was quite strongly upfield, consistently with a struc- CD2Cl2) at 230 K showed the PPh3 signal at δ ϭ 4.0 ppm
1698
Eur. J. Inorg. Chem. 2002, 1697Ϫ1702

Dihydrogen(olefin)osmium Complexeswith (E)-Ph2P(CH2)2CHϭCH(CH2)2PPh2
FULL PAPER
and the PPh2 signals at δ ϭ 29.1 and 36.5 ppm. The two complex. The HϪH distance in the dihydrogen complex is
˚
PPh2 groups in 5 had to be trans to each other for the large calculated to be 1.011 A, which is close to the experiment-
2JP,P coupling constant (201.7 Hz) observed for the PPh2 ally predicted value in 4 based on the 1J(HD) coupling con-
signals at δ ϭ 29.1 and 36.5 ppm. In the room-temperature stant and T1 (min) value. In a similar manner to complex
1H NMR spectrum (in CD2Cl2), a broad hydride signal was 4Ј, complex 5Ј is another dihydrogen(olefin) species. In 5Ј,
˚
observed at δ ϭ Ϫ5.30 ppm. When the temperature was the HϪH distance is significantly shorter (0.853 A), due to
below 275 K, the hydride signal was split into two with a the presence of the strongly trans-influencing hydride li-
1
relative intensity ratio of 1:2. For example, the H NMR gand, which gives weaker OsϪH2 interaction.
spectrum at 230 K showed a doublet of triplets at δ ϭ
Ϫ6.70 ppm (2JP,H ϭ 33.0, 19.5 Hz) and a broad singlet at
δ ϭ Ϫ4.74 ppm, corresponding to one and two hydrogen
atoms, respectively. T1 measurements showed that the broad
hydride signal at δ ϭ Ϫ4.74 ppm had a T1 (min) of 10.1 ms
(on 300 MHz) at 232 K. The short T1 (min) value strongly
suggested that complex 5 contained a dihydrogen ligand.
Furthermore,
a
partially deuterated sample of
[OsD3ϪxHx(PPh3){Ph2P(CH2)2CHϭCH(CH2)2PPh2}]ϩ (in
CD2Cl2 at 235 K) showed a 1:1:1 triplet at δ ϭ Ϫ4.69 ppm
1
with a J(HD) coupling constant of 26.7 Hz. The d(HH)
˚
value in 5 was estimated to be 0.97 A by application of the
relationship d(HH)
ϭ Ϫ0.0167 J(HD) ϩ 1.42 and
1J(HD) ϭ 26.7 Hz.[15a] On the basis of the T1 (min) of 10.1
˚
ms, the HϪH bond length was calculated to be 1.04 A for
[20]
˚
a nonspinning H2 or 0.83 A for a spinning H2 ligand.
The HϪH distance in the (hydrido)dihydrogen complex 5
was shorter than that in the (chloro)dihydrogen complex 4;
a similar trend has been observed for [MX(H2)(dppe)2]ϩ
(M ϭ Ru, Os; X ϭ H, Cl).[15a]
Deprotonation of complex 5 with NEt3 produced the
neutral
dihydride
complex
trans-[OsH2(PPh3)-
{Ph2P(CH2)2CHϭCH(CH2)2PPh2}] (6), which could also
be obtained by treatment of complex 3 with NaBH4. Com-
plex 5 was regenerated when 6 was treated with HOTf. The
geometry of complex 6 could readily be assigned from its
Figure 1. Optimized structures together with selected bond
˚
lengths [A]
1
NMR spectroscopic data. In particular, the H NMR spec-
trum (in CD2Cl2) displayed only one hydride signal at δ ϭ
Experimentally, it is interesting that under H2 the coord-
Ϫ9.13 ppm, indicating that the molecule had high sym- inated η2-H2 did not hydrogenate the olefin unit. The calcu-
metry. Consistently with the structure, the 31P{1H} NMR lated free energy change (∆G0) for the process of 4Ј ϩ H2
spectrum (in CD2Cl2) showed a doublet at δ ϭ 41.2 ppm Ǟ 7Ј (see Figure 1 for 7Ј, the hydrogenated product featur-
for the PPh2 groups and a triplet at δ ϭ 17.6 ppm for the ing an agostic interaction) is ca. Ϫ1.0 kcal/mol. This result
PPh3 ligand; the 13C{1H} NMR showed the coordinated suggests that the hydrogenation is thermodynamically feas-
olefinic CH carbon signal at δ ϭ 37.6 ppm.
ible, and we therefore feel that kinetic factors are probably
responsible for the hydrogenation not occurring. Careful ex-
amination of the structure of complex 4Ј (Figure 1) allows
Structural Study Using Quantum Chemical Calculations
To obtain a better understanding of the interesting chem- one to see that the orientation of the coordinated ϪHCϭ
istry described above, we calculated the structures of com- CHϪ unit is in such a manner that one olefinic carbon
plexes [OsClH(PH3){H2P(CH2)2CHϭCH(CH2)2PH2}] (3Ј), atom (Ca) is closer to the η2-H2 ligand while the other is
[OsCl(H2)(PH3){H2P(CH2)2CHϭCH(CH2)2PH2}]ϩ
and
(4Ј), further away. The hydrogenation of a coordinated olefin by
[OsH(H2)(PH3){H2P(CH2)2CHϭCH(CH2)2PH2}]ϩ an η2-H2 unit can occur through the formation of an agos-
(5Ј), by the density functional theory B3LYP technique. The tic intermediate by transfer of one hydrogen atom of the H2
calculated structures of complexes 3Ј, 4Ј, and 5Ј should pro- ligand to one of the two olefinic carbon atoms. A reductive
vide enlightening geometric information regarding com- elimination then follows, to complete the hydrogenation
plexes 3, 4, and 5. We also calculated the structure of process. If the transfer of one H atom from the η2-H2 ligand
[OsCl(H2)(PH3){H2P(CH2)6PH2}]ϩ (7Ј), a model complex to the closer olefinic carbon atom (Ca) in 4Ј is regarded as
for a hydrogenated product of complex 4. The optimized the first step, it is found that the assumed agostic species
structures are shown in Figure 1. Complex 3Ј is a typical does not correspond to a stationary point in the potential
hydrido(olefin) complex with strong OsϪolefin interaction. energy surface. An agostic structure can be calculated
˚
The protonated species 4Ј is confirmed to be a dihydrogen (optimized) by fixing the CaϪH bond length at 1.20 A.
Eur. J. Inorg. Chem. 2002, 1697Ϫ1702
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S. H. Liu, X. Huang, Z. Lin, C. P. Lau, G. Jia
FULL PAPER
THF. The reaction mixture was stirred at room temperature for 3 h.
A deep red solid was obtained after the solvent had been removed.
Addition of water (10 mL) and methanol (40 mL) to the reaction
mixture gave a pale yellow solid. The solid was collected on a filter
frit, washed with MeOH/H2O (4:1, 6 ϫ 50 mL) and MeOH (4 ϫ
40 mL), and dried under vacuum. Yield, 4.2 g, 76%. 1H NMR
(300.13 MHz, C6D6): δ ϭ 2.03Ϫ2.08 (m, 4 H, CH2CH2PPh2),
2.14Ϫ2.24 (m, 4 H, CH2PPh2), 5.38Ϫ5.41 (m, 2 H, HCϭCH),
7.12Ϫ7.52 ppm (m, 20 H, Ph). 31P{1H} NMR (121.5 MHz, C6D6):
δ ϭ Ϫ17.0 ppm (s, PPh2). 13C{1H} NMR (75.48 MHz, C6D6): δ ϭ
However, the partially optimized structure is 20 kcal/mol
higher in energy than complex 4Ј and adopts a pseudopen-
tagonal-bipyramidal (PB) structure in which the equatorial
plane is formed by one hydride ligand, the chloride ion, the
PH3 molecule, the CaϪH agostic ligand, and the bonded
Cb alkyl moiety. In the PB structure, the hydride ligand and
the bonded Cb alkyl moiety are separated by the CaϪH
agostic ligand. In such a ligand arrangement, reductive
elimination starting from the high-energy partially optim-
ized structure is difficult. Considering the PB structure, one 28.0 (d, JP,C ϭ 12.8 Hz, CH2CH2PPh2), 28.9 (d, JP,C ϭ 17.7 Hz,
CH2CH2PPh2), 128.1 (s, p-Ph), 128.2 (d, JP,C ϭ 6.2 Hz, m-Ph),
130.2 (d, JP,C ϭ 13.3 Hz, ϭCH), 132.6 (d, JP,C ϭ 18.6 Hz, o-Ph),
139.2 ppm (d, JP,C ϭ 14.6 Hz, ipso-Ph). C30H30P2 (452.52): calcd.
C 79.63, H 6.68; found C 79.72, H 6.56.
might also take account of the possibility of pushing the
CaϪH agostic ligand away and then binding an additional
H2 molecule so that reductive elimination becomes possible.
Calculations showed that such a structure was again not a
stationary point and had an even higher energy, due to the
crowded ligand environment. When the transfer of one H
[OsClH(PPh3){Ph2P(CH2)2CH؍CH(CH2)2PPh2}] (3): A mixture
of [OsClH3(PPh3)3] (1.37 g, 1.35 mmol) and (E)-Ph2P(CH2)2CHϭ
atom from the η2-H2 ligand to the further olefinic carbon CH(CH2)2PPh2 (0.71 g, 1.6 mmol) in benzene (110 mL) was stirred
for 5 h. The volume of the reaction mixture was reduced to ca.
7 mL under vacuum. A gray solid was formed when hexane
(60 mL) was added. The solid was collected by filtration, washed
with hexane (3 ϫ 15 mL), and dried under vacuum. Yield: 1.0 g,
atom (Cb) was considered as the first step, we found that
the activation energy (50 kcal/mol) was too high for such a
transfer under the given reaction conditions. The high ac-
tivation energy for such a process was not surprising, be-
cause of the geometric separation of the H and the Cb
atoms. A concerted process in which both hydrogen atoms
in the η2-H2 ligand would transfer simultaneously to the
two olefinic carbon atoms seemed unlikely on the basis of
our previous calculations on related systems.[21]
1
79%. H NMR (300.13 MHz, C6D6): δ ϭ Ϫ16.40 (dt, JP,H ϭ 27.0,
15.0 Hz 1 H, OsϪH), 1.96Ϫ3.88 [m, 10 H, Ph2P(CH2)2CHϭ
CH(CH2)2PPh2], 6.87Ϫ8.55 ppm (m, 35 H, Ph). 31P{1H} NMR
(121.50 MHz, C6D6): δ ϭ Ϫ7.7 (dd, JP,P ϭ 15.0, 14.2 Hz PPh3), 7.3
(dd, JP,P ϭ 290.6, 15.0 Hz, PPh2), 23.8 ppm (dd, JP,P ϭ 290.6,
14.2 Hz, PPh2). 13C{1H} NMR (75.48 MHz, C6D6): δ ϭ 28.1Ϫ33.5
(m, CH2CH2PPh2), 56.4 (m, HCϭ), 56.7 (d, JP,C ϭ 21.9 Hz, ϭCH),
126.8Ϫ143.0 ppm (m, Ph). C48H46ClP3Os (941.47): calcd. C 61.24,
H 4.93; found C 61.06, H 5.13.
Conclusion
[OsCl(H2)(PPh3){Ph2P(CH2)2CH؍CH(CH2)2PPh2}]OTf (4): Be-
cause of its low stability, the compound was not isolated but was
characterized in situ. HOTf (5 µL, 0.06 mmol) was added to a
CD2Cl2 solution (0.5 mL) containing [OsClH(PPh3){Ph2P-
(CH2)2CHϭCH(CH2)2PPh2}] (20 mg, 0.021 mmol) in an NMR
The dihydrogen(olefin) complex [OsCl(H2)(PPh3){Ph2P-
(CH2)2CHϭCH(CH2)2PPh2}]OTf has been prepared and
characterized by NMR spectroscopy. Treatment of
[OsCl(H2)(PPh3){Ph2P(CH2)2CHϭCH(CH2)2PPh2}]OTf
with H2 produced the (hydrido)dihydrogen complex
1
tube. H, 13C, and 31P NMR spectra were measured immediately.
1H NMR (300.13 MHz, CD2Cl2): δ ϭ Ϫ9.57 (br, OsϪH2),
2.15Ϫ3.10 (m, 8 H, CH2CH2PPh2), 4.77 (br, 1 H, HCϭ), 5.58 (br,
1 H, ϭCH), 6.86Ϫ7.82 ppm (m, 35 H, Ph). 31P{1H} NMR
(121.50 MHz, CD2Cl2): δ ϭ Ϫ8.9 (dd, JP,P ϭ 14.1, 15.5 Hz, PPh3),
14.2 (dd, JP,P ϭ 243.6, 15.5 Hz, PPh2), 16.8 ppm (dd, JP,P ϭ 243.6,
[OsH(H2){Ph2P(CH2)2CHϭCH(CH2)2PPh2}]OTf
rather
than the hydrogenated products. A computational study
suggested that the hydrogenation was thermodynamically
feasible but kinetically unfavorable. This work provides rare
examples of dihydrogen(olefin) complexes that are charac-
terizable by NMR spectroscopy.
14.1 Hz, PPh2). 13C{1H} NMR (75.48 MHz, CD2Cl2):
δ ϭ
28.6Ϫ37.4 (m, CH2CH2PPh2), 89.0 (br, HCϭ), 96.0 (br, ϭCH),
118.8Ϫ137.2 ppm (m, Ph). T1 [ms] of Os(H2) (300 MHz, CD2Cl2)
(temperature) ϭ 35.2 (298 K), 31.3 (273 K), 29.1 (263 K), 27.0
(258 K), 27.5 (253 K), 29.5 (243 K), 32.5 (233 K).
Experimental Section
[OsCl(HD)(PPh3){Ph2P(CH2)2CH؍CH(CH2)2PPh2}]OTf ([D1]-4):
The compound was prepared similarly, except that DOTf was used
instead of HOTf. The η2-HD signal was observed after cancellation
of the η2-H2 peak at δ ϭ Ϫ9.57 ppm by the inversion-recovery
method. H NMR (300.13 MHz, CD2Cl2): δ ϭ Ϫ9.58 ppm [1:1:1
triplet, J(HD) ϭ 14.1 Hz, Os(HD)].
General: All manipulations were carried out at room temperature
under nitrogen by standard Schlenk techniques unless otherwise
stated. Solvents were distilled under nitrogen from sodium/benzo-
phenone (hexane, diethyl ether, THF, benzene) or calcium hydride
(dichloromethane, CHCl3). The starting materials Br(CH2)2CHϭ
CH(CH2)2Br[22] and [OsClH3(PPh3)3][23] were prepared by literat-
ure methods. Microanalyses were performed by M-H-W Laborat-
ories (Phoenix, AZ). 1H, 13C{1H}, and 31P{1H} NMR spectra were
measured with 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.
1
Characterization
of
[OsH(H2)(PPh3){Ph2P(CH2)2CH؍CH-
(CH2)2PPh2}]OTf (5): Because of its low stability, this compound
was not isolated but was characterized in situ. Method A: HOTf (5
µL, 0.06 mmol) was added to a CD2Cl2 solution (0.5 mL) con-
taining [OsH2(PPh3){Ph2P(CH2)2CHϭCH(CH2)2PPh2}] (20 mg,
0.020 mmol) in an NMR tube. NMR spectra were then measured
(E)-Ph2P(CH2)2CH؍CH(CH2)2PPh2 (2):
A THF solution of
KPPh2 (50 mL, 0.50 , 25 mmol) was added slowly to a solution immediately. Method B: A CD2Cl2 solution (0.5 mL) containing
of (E)-Br(CH2)2CHϭCH(CH2)2Br (3.00 g, 12.4 mmol) in 30 mL of
[OsClH(PPh3){Ph2P(CH2)2CHϭCH(CH2)2PPh2}]
(20 mg,
1700
Eur. J. Inorg. Chem. 2002, 1697Ϫ1702

Dihydrogen(olefin)osmium Complexeswith (E)-Ph2P(CH2)2CHϭCH(CH2)2PPh2
FULL PAPER
0.021 mmol) and TlOTf (20 mg, 0.057 mmol) in an NMR tube was
also added to the standard basis set for H atoms of these two li-
gands. The standard 6Ϫ31G basis set was used for all other atoms.
1
stored under H2 for 5 h. H, 13C, and 31P NMR spectra were then
measured. Method C: A CD2Cl2 solution of 4 was stored under H2
1
for 18 h, and H and 31P{1H} NMR spectra were then measured.
1H NMR (300.13 MHz, CD2Cl2, 230 K): δ ϭ Ϫ6.70 (dt, JP,H
ϭ
Acknowledgments
The authors acknowledge financial support from the Hong Kong
Research Grants Council.
33.0, 19.5 Hz, 1 H, OsϪH), Ϫ4.74 (br, 2 H, OsH2), 1.60Ϫ3.80 [m,
10 H, Ph2P(CH2)2CHϭCH(CH2)2PPh2], 6.86Ϫ7.70 ppm (m, 35 H,
1
Ph). H NMR (300.13 MHz, CD2Cl2, 298 K): δ ϭ Ϫ5.30 (br, 3 H,
OsϪH, OsϪH2), 1.60Ϫ3.80 [m, 12 H, Ph2P(CH2)2CHϭ
CH(CH2)2PPh2], 6.86Ϫ7.64 ppm (m, 35 H, Ph). 31P{1H} NMR
(121.50 MHz, CD2Cl2, 230 K): δ ϭ 4.0 (dd, JP,P ϭ 11.0, 12.8 Hz,
PPh3), 29.1 (dd, JP,P ϭ 201.7, 12.8 Hz, PPh2), 36.5 ppm (dd, JP,P ϭ
201.7, 11.0 Hz, PPh2). 31P{1H} NMR (121.50 MHz, CD2Cl2,
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298 K): δ ϭ 4.4 (dd, JP,P ϭ 12.4, 12.5 Hz, PPh3), 29.8 (br. d JP,P
181.5 Hz, PPh2), 36.2 ppm (br. d, JP,P ϭ 181.5 Hz, PPh2). 13C{1H}
NMR (75.48 MHz, CD2Cl2, 233 K): 28.6Ϫ35.1 (m,
ϭ
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(272 K), 12.2 (252 K), 10.1 (232 K), 14.2 (213 K); δ ϭ Ϫ6.58: 14.9
(272 K), 65.16 (252 K), 204.9 (232 K), 301.5 (213 K).
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a
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HD signal was observed after cancellation of the η2-H2 peak at
δ ϭ Ϫ4.74 ppm by the inversion-recovery method. 1H NMR
(300.13 MHz, CD2Cl2, 235 K): δ ϭ Ϫ4.69 ppm [1:1:1 triplet,
J(HD) ϭ 26.7 Hz, Os(HD)].
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{Ph2P(CH2)2CHϭCH(CH2)2PPh2}] (0.50 g, 0.53 mmol) in 20 mL
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benzene (20 mL). The volume of the extracted solution was reduced
to ca 3 mL. A yellow solid was formed when hexane (40 mL) was
added. The solid was collected by filtration, washed with hexane
(3 ϫ 15 mL), and dried under vacuum. Yield: 0.25 g, 52%. The
complex was also produced when complex 5 was treated with NEt3.
1H NMR (300.13 MHz, CD2Cl2): δ ϭ Ϫ9.13 (dt, JP,H ϭ 29.7,
12.6 Hz, 2 H, OsϪH), 1.80Ϫ2.74 [m, 10 H, Ph2P(CH2)2CHϭ
CH(CH2)2PPh2], 6.74Ϫ7.80 ppm (m, 35 H, Ph). 31P{1H} NMR
(121.50 MHz, CD2Cl2): δ ϭ 17.6 (t, JP,P ϭ 15.1 Hz, PPh3), 41.2
ppm (d, JP,P ϭ 15.0 Hz, PPh2). 13C NMR (75.48 MHz, CD2Cl2):
δ ϭ 30.4 (t, JP,C ϭ 13.5 MHz, CH2P), 34.2 (t, JP,C ϭ 7.3 MHz,
CH2CH2P), 37.6 (d, JP,C ϭ 12.1 MHz, HCϭ), 126.8Ϫ143.1 ppm
(m, Ph). C48H47P3Os·3H2O (961.06): calcd. C 59.99, H 5.56 (the
water was probably from the solvents); found C 59.98, H 6.00.
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