Exchange Couplings between a Hydride and a Stretched Dihydrogen Ligand in Ruthenium Complex

Full text of DOI:10.1021/ja971603m

4228
J. Am. Chem. Soc. 1998, 120, 4228-4229
Scheme 1. New Orthometalated Ruthenium Complexes
Exchange Couplings between a Hydride and a
Stretched Dihydrogen Ligand in Ruthenium
Complexes
Yannick Guari, Sylviane Sabo-Etienne, and Bruno Chaudret*
Laboratoire de Chimie de Coordination CNRS
205 route de Narbonne, 31077 Toulouse Cedex, France
ReceiVed May 19, 1997
Over 10 years after the Kubas discovery, the chemistry of
dihydrogen has proven to be far more complex than originally
thought. Thus coordinated dihydrogen can be unstretched,
stretched, electrophilic, or even superacidic.1 The study of the
reactivity of stretched dihydrogen derivatives, which are known
in particular in the chemistry of rhenium, ruthenium, and osmium,
has remained relatively unexplored.1c,2 We have studied for a
few years the reactivity of ruthenium dihydrogen complexes and
have demonstrated that, whereas dihydrogen substitution and
hydrogen transfer is easy on RuH2(H2)2(PCy3)2 (1),3 the related
complexes RuH(H2)(LX)(PCy3)2 (LX ) o-OC5H4N, pyO, 2; LX
) o-NHC5H4N, pyNH, 3) which accommodate a stretched
dihydrogen ligand are found to be much less reactive.4 In
addition, stretched dihydrogen ligands may experience a high
ing H2 by CO in 5 leads to RuH(CO)(ph-py)(PiPr3)2 (6). Full
characterization of the complexes is given in the Supporting
Information. The similarity of 31P and 13C NMR data (triplets
for metalated carbon respectively at 197.0 ppm, JP-C ) 10.6 Hz
and 192.0 ppm, JP-C ) 13.1 Hz) demonstrates that 5 and 6 are
1
isostructural. The only difference is their high-field H NMR
spectra: broad triplet at -8.59 ppm for 5 (JP-H ) 12.3 Hz, 3 H;
T1 min ) 22 ms at 258 K, 400 MHz, C7D8) and sharp triplet at
-12.50 ppm (JP-H ) 24.6 Hz, 1 H; T1 min ) 202 ms at 233 K,
250 MHz, C7D8) for 6. The calculation of the H-H bond length
in 5, using 6 as a reference for all effects other than H-H
distance,12 gives a value of 1.08 Å (slow rotation hypothesis, 0.83
Å for rapid rotation hypothesis), close to that found by X-ray
5
rotation barrier that we have demonstrated, at least in the case
of tantalum 6 and niobium,7 to be related to the existence of large
quantum mechanical exchange couplings.6,8,9
Exchange couplings have been previously observed in di- and
trihydride complexes8,9 and in tantalum6 and niobium7 dihydrogen
complexes. We now report the synthesis of a series of hydrido
orthometalated dihydrogen complexes showing exchange cou-
plings as well as preliminary catalytic activity for the coupling
of ethylene to functional arenes (Murai’s reaction).10
Phenylpyridine reacts rapidly at room temperature in pentane
with 1 to yield the new compound RuH(H2)(Ph-py)(PCy3)2
(Ph-py ) o-C6H4C5H4N, 4) as a slightly soluble orange powder
(see Scheme 1). The analogous and more soluble triisopropyl-
phosphine derivative RuH(H2)(Ph-py)(PiPr3)2 (5) could be pre-
pared directly from Ru(COD)(COT) (COD ) 1,5 cyclooctadiene,
COT ) 1,3,5-cyclooctatriene), PiPr3, and dihydrogen.11 Substitut-
i
and NMR for RuHI(H2)(PR3)2 (R ) Cy, Pr), 1.03 Å,11,13 and
much less than that found for 2 and 3, ca.1.3 Å.4 In the 1H NMR
spectra of 4 and 5 we observe at low temperature the decoales-
cence of the high-field signal into an AB2 spin system at -12.1
and -6.1 ppm (∆Gq 39.8 kJ mol-1) displaying quantum mechan-
ical exchange couplings clearly visible for 5 between 218 K
(JHA-HB ) 308 Hz) and 188 K (JHA-HB ) 141 Hz; see Figure 1).
After the decoalescence, the relaxation time of HA is always
observed to be longer than that of HB (198 K: HB δ-6.1, 69 ms;
HA δ-12.1, 87 ms; 208 K: HB δ-6.2, 34 ms; HA δ-12.2, 38 ms) but
both signals remain in exchange as evidenced by T1 averaging.14
4 displays similar features, but they are more difficult to observe
because of low solubility and the large correlation time of PCy3
complexes. As stated above, complexes 5 and 6 display very
* E-mail: Chaudret@lcc-toulouse.fr.
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Kuhlman, R.; Sini, G.; Eisenstein, O.; Caulton, K. G. J. Am. Chem. Soc. 1994,
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1995, 14, 1082. (c) Borowski A.; Sabo-Etienne, S.; Christ, M. L.; Donnadieu
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N.; Murai S. Chem. Lett. 1996, 113 and references therein.
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S0002-7863(97)01603-X CCC: $15.00 © 1998 American Chemical Society
Published on Web 04/16/1998

Communications to the Editor
J. Am. Chem. Soc., Vol. 120, No. 17, 1998 4229
L ) H2, 7; L ) CO, 8; X ) C(O)Ph, L ) H2, 9; L ) CO, 10).
Whereas 7 reacts stoichiometrically with triethoxyvinylsilane at
room temperature to give the monoinsertion product MeC(O)-
C6H4(CH2)2Si(OEt)3, catalytic insertion of ethylene (20 bar) is
achieved at room temperature with both acetophenone and
benzophenone using 1 or 7 as the catalyst precursor (see eq 1).20-22
Acetophenone gave selectively the monoinsertion product, whereas
benzophenone led mainly to the bis-insertion product, 2,2′-
diethylbenzophenone. Up to 19 turnovers could be achieved in
48 h in the case of benzophenone. Interestingly, complex 10 does
not show any stoichiometric or catalytic activity, which substanti-
ates the suggestion by Trost that CO must be excluded from the
complex during the reaction.16
In conclusion, we describe the synthesis of a new series of
ruthenium hydride and dihydrogen derivatives which, besides
being a rare case of a dihydrogen complex incorporating a sp2
metal carbon σ bond,23 displays two novel features. After de-
coalescence of the hydride and dihydrogen signals,24 it is possible
to observe in these complexes, for the first time, exchange coup-
lings between a hydride and protons of a coordinated dihydrogen
molecule. The second novel feature is the coupling of ethylene
to functional arenes which is catalytic at room temperature in
the presence of our complexes (Murai’s reaction occurs at 135
°C). The mild conditions could significantly increase the scope
of this reaction and confirm that complexes such as 7 are true
intermediates in the catalytic cycle postulated by Murai.
Figure 1. High-field {31P}1H NMR spectrum of 5 (400 MHz, C7D8) at
variable temperatures (asterisks denote impurities).
similar spectroscopic features. The chemical shift after decoa-
lescence and, more importantly, the H-P coupling constant of
HA (-12.1 ppm, t, JP-H ) 22.5 Hz for 5) are also very similar to
those of the hydride of 6, which suggests that the HA signal in 4
and 5 is due to the hydride. The HB signal would result from the
coordinated dihydrogen molecule, in agreement with the lower
T1 measured for HB compared to HA below the decoalescence
temperature. The calculated H-P coupling constant of HB (ca.
7 Hz) is also in agreement with this proposal. The origin of this
novel phenomenon is the presence of an exchange process
between the hydride and one of the hydrogens of the dihydrogen
molecule, the barrier for this process being 39.8 kJ‚mol-1. A
possibility for explaining it involves the presence of a weak
bonding interaction between the hydride and the coordinated
dihydrogen molecule as previously proposed by Eisenstein et al.15
Compounds 4-6 are reminiscent of the intermediates proposed
by Murai for the insertion of olefins into aromatic C-H bonds
located in ortho position relative to a coordinating group such as
ketone, amine, or pyridine.10 A similar reaction has recently been
Acknowledgment. We are grateful to SHELL International Chemicals
B.V. (Amsterdam) for financial support of this work.
Supporting Information Available: Experimental data for com-
pounds 4-10, 1H NMR spectra of the partially deuterated 5, and scheme
showing the exchange process in 5 (7 pages, print/PDF). See any current
masthead page for ordering information and Web access instructions.
JA971603M
(17) Complexes of this type have however been previously isolated: (a)
Cole-Hamilton, D. J.; Wilkinson, G. NouV. J. Chim. 1977, 1, 141. (b) Halpern,
J. Pure Appl. Chem. 1987, 59, 173. (c) Linn, D. E.; Halpern, J. J. Organomet.
Chem. 1987, 330, 155. Rhodium-catalyzed coupling of olefins with 2-phen-
ylpyridines was also reported: Lim, Y.-G.; Kim, Y. H.; Kang, J.-B. J. Chem.
Soc., Chem. Commun. 1994, 2267.
(18) For selected recent papers, see: (a) Ryabov, A. E. Chem. ReV. 1990,
90, 403. (b) Pfeffer, M. Pure Appl. Chem. 1992, 3, 335. (c) Vicente, J.; Abad,
J.-A.; Fernande-de-Bobadilla, R.; Jones, P. G.; de Arrelano, M. C. R.
Organometallics 1996, 15, 1422.
(19) Ferstl, W.; Sakodinskaya, I. K.; Beydoun-Sutter, N.; Le Borgne, G.;
Pfeffer, M.; Ryabov, A. D. Organometallics 1997, 16, 411.
used by Trost et al. for elaborating conjugated alkenes.16
A
mechanism is proposed which involves the intermediacy of an
orthometalated species but which has not been substantiated by
the isolation of any intermediate.17 Such a chemistry can find
useful applications in organic synthesis.18,19 These studies led
us to prepare the analogous complexes using acetophenone and
benzophenone, namely RuH(L)(o-C6H4X)(PCy3)2 (X ) C(O)Me;
(20) Ninety-seven percent conversion of 10 equiv of Ph2CO under 20 bar
of C2H4 using 1 in pentane solution is achieved in 48 h at 20 °C, leading to
the bis-insertion product (C17H18O) and to the monoinsertion product (C15H14O)
in 96 and 4% selectivity, respectively. When 10 equiv of PhCOMe is added
to 1 or 7 in toluene solution under 20 bar of C2H4, 100% conversion after 22
h using 1 or 80% conversion after 27 h using 7 is observed. All the organic
products have been characterized by GC-MS.
(21) Catalytic insertion of olefins into aromatic C-H bonds has previously
been shown by Jordan to be catalyzed by zirconium complexes at room
temperature: Jordan, R. F.; Taylor, D. F. J. Am. Chem. Soc. 1989, 111, 778.
(22) Murai et al. have recently reported an asymmetric C-H olefin coupling
occurring at 25 °C: Fujii, N.; Fumitoshi, K.; Yamada, A.; Murai, S. Chem.
Lett. 1997, 425.
(23) Li, Z.-W.; Taube, H. J. Am. Chem. Soc. 1994, 116, 6, 11584.
(24) Few systems containing cis hydride and dihydrogen ligands have led
to a decoalescence but not to observable exchange couplings: (a) Crabtree,
R. H.; Lavin, M.; Bonneviot, L. J. Am. Chem. Soc. 1986, 108, 4032. (b)
Bianchini, C.; Perez, P. J.; Peruzzini, M.; Zanobini, F.; Vacca, A. Inorg. Chem.
1991, 30, 279.
(14) It was possible to determine on the spectrum that the line width of
the HD signal was larger than that of the
H signal in RuH(HD)-
(Ph-py)(PiPr3)2 and was compatible with an H-D coupling of up to ca. 25
Hz. Furthermore, it was possible to determine that under the same conditions
(C7D8, 400 MHz) at 188 and 193 K the JH-H couplings were respectively ca.
124 and 149 Hz for RuH(HD)(Ph-py)(PiPr3)2 and ca. 141 and 168 Hz for
RuH(H2)(Ph-py)(PiPr3)2. It is noteworthy that the influence of partial deu-
teration on exchange couplings is the reverse of the usual observation in
dihydridodeutero complexes of iridium or ruthenium.9 (a) Heinekey, D. M.;
Millar, J. M.; Koetzle, T. F.; Payne, N. G.; Zilm, K. W. J. Am. Chem. Soc.
1990, 112, 909. (b) Manzano, B.; Jalon, F.; Matthes, J.; Sabo-Etienne, S.;
Chaudret, B.; Ulrich, S.; Limbach, H. H. J. Chem. Soc., Dalton Trans. 1997,
3153.
(15) Van Der Sluys, L. S.; Eckert, J.; Eisenstein, O.; Hall, J. H.; Huffman,
J. C.; Jackson, S. A.; Koetzle, T. F.; Kubas, G. J.; Vergamini, P. J.; Caulton,
K. G. J. Am. Chem. Soc. 1990, 112, 4831.
(16) Trost, B. M.; Imi, K.; Davies, I. W. J. Am. Chem. Soc. 1995, 117,
5371.