Catalytic activity of bis-phosphine ruthenium(II) - Arene compounds: Chemoselective hydrogenation and mechanistic insights

Article abstract of DOI:10.1021/om7005112

Bis-phosphine ruthenium(II)-arene complexes have been found to be highly active and chemoselective catalysts for the hydrogenation of aldehydes in the presence of olefinic bonds. Mechanistic studies, including comparisons with a structural analogue, reactions of an isolated hydride complex, base poisoning experiments, and a computational analysis, help rationalize the preferential hydrogenation of C=O bonds, which is suggested to proceed via an ionic outer-sphere mechanism.

Full text of DOI:10.1021/om7005112

Organometallics 2007, 26, 4357-4360
4357
Catalytic Activity of Bis-phosphine Ruthenium(II)-Arene
Compounds: Chemoselective Hydrogenation and Mechanistic
Insights
Adrian B. Chaplin and Paul J. Dyson*
Institut des Sciences et Inge´nierie Chimiques, Ecole Polytechnique Fe´de´rale de Lausanne (EPFL),
CH-1015 Lausanne, Switzerland
ReceiVed May 23, 2007
Summary: Bis-phosphine ruthenium(II)-arene complexes haVe
been found to be highly actiVe and chemoselectiVe catalysts for
the hydrogenation of aldehydes in the presence of olefinic bonds.
Mechanistic studies, including comparisons with a structural
analogue, reactions of an isolated hydride complex, base
poisoning experiments, and a computational analysis, help
rationalize the preferential hydrogenation of CdO bonds, which
is suggested to proceed Via an ionic outer-sphere mechanism.
reduction of aldehydes together with a mechanistic and com-
putational study.
Results and Discussion
Initial experiments, with styrene, benzaldehyde, and 3-phe-
nylpropionaldehyde as substrates, demonstrated that 1a is an
active precatalyst, with comparable conversions, for the hydro-
genation of both CdC and CdO bonds in toluene at 50 °C
under 50 bar of H2 (Table 1). Competition experiments with
1a indicated, however, a high preference for the hydrogenation
of benzaldehyde over styrene (82% CdO selectivity). This
selectivity was further confirmed by experiments using 1a for
the hydrogenation of trans-cinnamaldehyde, with CdO selectiv-
ity approaching 100%. Similar selectivity was observed for 1b
and 1c, with the activity increasing in the order 1b > 1a > 1c.
In base poisoning experiments using NEt3, carried out to aid
mechanistic investigations, benzaldehyde hydrogenation was
dramatically reduced, whereas styrene hydrogenation was
enhanced. Large decreases in activity and changes in selectivity
were also observed for the competition experiment and hydro-
genation of trans-cinnamaldehyde using 1a. Furthermore, ad-
dition of mercury, a selective poison for heterogeneous catalysis,
did not inhibit catalytic activity significantly (Table 1).7
In addition to the bis-phosphine complexes 1, the catalytic
activity of a structural analogue, [Ru(κ2-PPh2C6H4O)(OCMe2)-
(p-cymene)]PF6 (2),8 containing instead a more strongly bound
anionic chelating P,O ligand and a labile acetone ligand, was
determined in an attempt to assess the role of the chloride ligand
during catalysis. Complex 2 was prepared by chloride abstraction
from [RuCl(κ2-PPh2C6H4O)(p-cymene)]6 in CH2Cl2-acetone
with AgPF6 (solid-state structure in Figure 1) and showed similar
activity for the hydrogenation of benzaldehyde and 3-phenyl-
propionaldehyde, but much reduced activity for the hydrogena-
tion of styrene (although in the presence of NEt3 activity is
comparable).9 Correspondingly, a high CdO selectivity was
found for the reduction of trans-cinnamaldehyde using 2.
The reactivity of complex 1b with H2 was examined in situ
using a high-pressure sapphire NMR tube under similar condi-
tions (i.e., THF, 50 °C, 50 bar of H2). Formation of the hydride
complex, [RuHCl(PPh3)(p-cymene)] (3), presumably following
phosphine dissociation and dihydrogen coordination, is observed
together with anion hydrolysis and other minor products.
Following optimization, 3 was prepared in 66% isolated yield
Introduction
The catalytic chemoselective reduction of carbonyl groups
in the presence of olefinic bonds is a particularly challenging
task, since most common catalysts are selective for the reduction
of CdC bonds,1 and the discovery of active catalysts for this
process is of ongoing importance. The most successful catalysts
for this process are arguably ruthenium-based diamino-bis-
phosphine (or diphosphine) complexes, selective for the reduc-
tion of ketone and aldehyde groups.1,2 With these catalysts, Cd
O bonds in R,â-unsaturated carbonyl compounds can be reduced
with a selectivity of >99% with TONs up to 10 000. Other
notable examples are ruthenium-PPh2(C6H4-3-SO3Na) or P(C6H4-
3-SO3Na)3 systems, which show pH-tunable selectivity for the
hydrogenation of unsaturated aldehydes under biphasic condi-
tions,1,3,4 although other catalysts are also known.1,5 Following
earlier work in our group involving the investigation of
phosphine dissociation characteristics and prescreening for
catalytic activity,6 we report here the activity of the air- and
moisture-stable bis-phosphine ruthenium(II)-arene complexes,
[RuCl(PR3)(PR′3)(p-cymene)]PF6 (1a, R ) Ph, P′ ) p-tol; 1b,
R ) R′ ) Ph; 1c, R ) R′ ) p-tol), for the chemoselective
* Corresponding author. E-mail: paul.dyson@epfl.ch.
(1) (a) Handbook of Homogeneous Hydrogenation; de Vries, J. G.,
Elsevier, C. J., Eds.; Wiley-VCH: Weinheim 2007; Vol 1. (b) Noyori, R.;
Ohkuma, T. Angew. Chem., Ind. Ed. 2001, 40, 40.
(2) (a) Wu, J.; Ji, J.-X.; Guo, R.; Yeung, C.-H.; Chan, A. S. C. Chem.-
Eur. J. 2003, 9, 2963. (b) Ohkuma, T.; Koizumi, M.; Doucet, H.; Pham,
T.; Kozawa, M.; Murata, K.; Katayama, E.; Yokozawa, T.; Ikariya, T.;
Noyori, R. J. Am. Chem. Soc. 1998, 120, 13529. (c) Ohkuma, T.; Ooka,
H.; Ikariya, T.; Noyori, R. J. Am. Chem. Soc. 1995, 117, 10417.
(3) (a) Joo´, F. Acc. Chem. Res. 2002, 35, 738. (b) Joo´, F.; Kova´cs, J.;
Be´nyei, A. C.; Katho´, A. Angew. Chem., Int. Ed. 1998, 37, 969.
(4) These systems have also been the subject of a number of theoretical
investigations: (a) Rossin, A.; Kova´cs, G.; Ujaque, G.; Lledo´s, A.; Joo´, F.
Organometallics 2006, 25, 5010. (b) Kova´cs, J.; Ujaque, G.; Lledo´s, A.;
Joo´, F. Organometallics 2006, 25, 862. (c) Joubert, J.; Delbecq, F.
Organometallics 2006, 25, 854.
(5) Further examples include: (a) Mebi, C. A.; Nair, R. P.; Frost, B. J.
Organometallics 2007, 26, 429. (b) Li, R.-X.; Wong, N.-B.; Li, H.-J.; Mak,
E. C. W.; Yang, Q.-C.; Tin, K.-C. J. Organomet. Chem. 1998, 571, 223.
(c) Bianchini, C.; Farnetti, E.; Graziani, M.; Peruzzini, M.; Polo, A.
Organometallics 1993, 12, 3753.
(7) Anton, D. R.; Crabtree, R. H. Organometallics 1983, 2, 855.
(8) Although [Ru(PPh3)(κ2-PPh2C6H4O)(p-cymene)]PF6 would be a
better model, dissociation of triphenylphosphine is not facile (see ref 6)
and instead a labile acetone ligand was used.
(9) In comparison to the bis-phosphine complexes, 2 is significantly air-
sensitive and the preparation of catalyst solutions in a glovebox was required.
(6) Chaplin, A. B.; Dyson, P. J. Organometallics 2007, 26, 2447.
10.1021/om7005112 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 07/13/2007

4358 Organometallics, Vol. 26, No. 17, 2007
Notes
Table 1. Catalytic Activity of 1 and 2a
Scheme 1
selectivity/%
substrate
TON
CdO
CdC
1a
styrene
styrene
styrene
styrene
benzaldehyde
benzaldehyde
560
400
950
890
650
630
20
800
600
140
740f
640f
50f
1a/Hgb
1a/NEt3
c
1a/NEt3/Hgb,c
1a
1a/Hgb
c
1a/NEt3
benzaldehyde
1ad
1a
3-phenylpropionaldehyde
1:1 styrene-benzaldehydee
1:1 styrene-benzaldehydee
trans-cinnamaldehyde
trans-cinnamaldehyde
trans-cinnamaldehyde
trans-cinnamaldehyde
trans-cinnamaldehyde
styrene
styrene
benzaldehyde
3-phenylpropionaldehyde
trans-cinnamaldehyde
82
10
>99
>99
46
18
90
<1
<1
54
<1
2
c
1a/NEt3
1a
1a/Hgb
mational isomer are proposed to equilibrate through a 16 VE
phenethyl complex via a â-hydride elimination-olefin insertion
process.11 Other precedents for this process are known for
ruthenium(II)-arene complexes.13 Addition of HCl(g) to a
solution of 3 and benzaldehyde in C6D6 at ambient temperature
resulted in the formation of [RuCl2(PPh3)(p-cymene)], 5,14
together with H2 and benzyl alcohol in a ca. 7:3 ratio. Thus,
HCl acts as a Lewis acid, activating the aldehyde to hydride
transfer from the metal. Formation of H2 occurs as a side product
by protonation of 3 and is quantitative in the absence of
benzaldehyde.
c
1a/NEt3
1b
1c
2d
810f
500f
120
820
760
870
1000f
>99
98
c,d
2/NEt3
2d
2d
2d
>99
<1
a Conditions: 5.0 × 10-6 mol of precatalyst, sub:cat ) 1000:1, 2 mL of
toluene, 100 mg of octane (internal standard), 50 bar of H2, 50 °C, 2 h.
b
Conversion determined by GC. Values averaged over duplicate runs. 0.1
mL of Hg. 5 equiv of NEt3. Prepared under N2. Total sub:cat ) 2000:1.
fPh(CH2)3OH < 0.01%.
c
d
e
Catalytic cycles for the hydrogenation of aldehydes and
alkenes, depicted in Figure 2, are proposed on the basis of the
above experimental observations and supported by a computa-
tional analysis (see Experimental Section). Both mechanisms
involve initial phosphine dissociation, a key process identified
in an earlier study,6 and coordination of dihydrogen. An ionic
outer-sphere mechanism is proposed for the hydrogenation of
aldehydes,1a,15 i.e., proton transfer to the aldehyde from a dihy-
drogen complex followed by hydride transfer from the resulting
hydride complex (e.g., 3). Similar ionic mechanisms have been
established for the hydrogenation of imminium salts with CpRu-
(P-P)H (P-P ) diphosphine)16 and ketones with [CpM(CO)2-
(PR3)(OCEt2)]+ (M ) Mo, W).17 The protonation of the
aldehyde is a key step in the proposed cycle, enhancing the
electrophilicity of the carbonyl carbon and thus promoting
hydride transfer from the metal (cf. reactions of 3 in Scheme
1); calculated Lowdin atomic charges illustrate the activation
of the carbonyl carbon, whose charge increases from +0.09 in
benzaldehyde to +0.21 in intermediate D (Figure 2).18 This
mechanism accounts for the dramatic inhibition of the catalytic
activity on addition of NEt3, which acts as a competitive base.
In the case of alkenes, heterolytic cleavage of the dihydrogen
complex, C, and loss of HCl is suggested, leading to an olefin-
hydride complex (e.g., 4), consistent with the increased activity
on addition of NEt3.19 â-Hydride elimination from the olefin-
Figure 1. Ball-and-stick representations of 2 (left, counterion
omitted for clarity) and 3 (right, selected molecule from asymmetric
cell). Key bond lengths (Å) and angles (deg): 2, Ru1-P1, 2.3463-
(9); Ru1-O1, 2.056(2); Ru1-O2, 2.126(2); Ru1-Cav, 2.21(3); P1-
Ru1-O1, 81.89(7); P1-Ru1-O2, 82.84(6); O1-Ru1-O2, 84.07-
(9); 3, Ru1-Cl1, 2.4226(6); Ru1-P1, 2.2919(7); Ru1-H1, 1.48(3);
Ru1-Cav, 2.26(6), Cl1-Ru1-P1, 87.48(2); Cl1-Ru1-H1, 75.2-
(11); P1-Ru1-H1, 86.2(11).
from [RuCl(PPh3)2(p-cymene)]BPh4 using the aforementioned
conditions, with PPh3, C6H6, and BPh3 as side products. The
structure of 3 has been confirmed by NMR spectroscopy and
X-ray diffraction (Figure 1). The hydride resonance is located
2
at -7.44 ppm (CD2Cl2, 293 K, JPH ) 53 Hz, T1 ) 1.75 s).
Analogous C6Me6 and PCy3 complexes have been reported,10
although this appears to be the first hydride complex of this
type to be characterized in the solid state by X-ray diffraction.
Both at ambient temperature and at 50 °C, 3 showed no reaction
with either styrene or benzaldehyde in C6D6 (Scheme 1).
However, the olefin-hydride complex 4 (and its conformational
isomer)11,12 may be prepared in good yield (82%) from 3 by
reaction with styrene and AgPF6 in CD2Cl2. 4 and its confor-
(13) (a) Faller, J. W.; Fontaine, P. P. Organometallics 2007, 26, 1738.
(b) Umezawa-Vizzini, K.; Lee, T. R. Organometallics 2004, 23, 1448.
(14) Bennett, M. A.; Smith, A. K. J. Chem. Soc., Dalton Trans. 1974,
233.
(15) (a) Clapham, S. E.; Hadzovic, A.; Morris, R. H. Coord. Chem. ReV.
2004, 248, 2201. (b) Bullock, R. M. Chem.-Eur. J. 2004, 10, 2366.
(16) (a) Guan, H.; Iimura, M.; Magee, M. P.; Norton, J. R.; Zhu, G. J.
Am. Chem. Soc. 2005, 127, 7805. (b) Guan, H.; Iimura, M.; Magee, M. P.;
Norton, J. R.; Janak, K. E. Organometallics 2003, 22, 4084. (c) Magee, M.
P.; Norton, J. R. J. Am. Chem. Soc. 2001, 123, 1778.
(17) (a) Kimmich, B. F. M.; Fagan, P. J.; Hauptman, E.; Bullock, R. M.
Chem. Commun. 2004, 1014. (b) Voges, M. H.; Bullock, R. M. J. Chem.
Soc., Dalton Trans. 2002, 7509. (c) Bullock, R. M.; Voges, M. H. J. Am.
Chem. Soc. 2000, 122, 12594.
(10) (a) Bennett, M. A.; Latten, J. L. Inorg. Synth. 1989, 26, 180, and
references therein (b) Demerseman, B.; Mbaye, M. D.; Se´meril, D.; Toupet,
L.; Bruneau, C.; Dixneuf, P. J. Eur. J. Inorg. Chem. 2006, 1174.
(11) Faller, J. W.; Chase, K. J. Organometallics 1995, 14, 1592.
(12) The conformational isomer of 4, 4′, differs by the orientation of
the styrene ligand; the phenyl group instead points toward the methyl group
of the p-cymene ligand. 4 is the major isomer (4:4′ ) 8.2:1 (ref 11); 8.3:1
(this work)).
(18) Additional Lowdin atomic charges (carbonyl carbon): TSCD, +0.17;
TSDB, +0.18; benzyl alcohol, -0.04.
(19) Consistent with the base poisoning experiments, using the more basic
solvent THF, instead of toluene, higher activities for the hydrogenation of
styrene are observed under equivalent conditions using 1a also (see ref 6).

Notes
Organometallics, Vol. 26, No. 17, 2007 4359
Figure 2. Proposed catalytic cycles for the hydrogenation of aldehydes (left) and alkenes (center) with calculated energies (right). Calculations
a
were carried out using a model system, where [Ru] ) Ru(PPh3)(C6H6) and R ) R′ ) Ph. E is a (computed) intermediate in the heterolytic
cleavage of dihydrogen in C.
h. The solution was then filtered through dry Celite, washing with
CH2Cl2 (4 × 5 mL). Acetone (20 mL) was then added to the filtrate,
which was then concentrated to ca. 10 mL. Addition of pentane
(50 mL) gave the product as a microcrystalline orange solid, which
was filtered, washed with pentane (3 × 10 mL), and dried under a
stream of nitrogen. Yield: 0.27 g (86%). Crystals suitable for X-ray
diffraction were grown by layering a CH2Cl2-acetone (∼1:1 v/v)
solution of the complex with pentane. 1H NMR (CD2Cl2): δ 7.45-
7.79 (m, 10H, PPh2), 7.20-7.28 (m, 1H, H14), 7.13-7.20 (m, 1H,
H12), 6.93-6.99 (m, 1H, H15), 6.64-6.71 (m, 1H, H13), 5.96 (br,
1H, H3), 5.75 (br, 1H, H6), 5.34 (br, 1H, H2), 4.97 (br, 1H, H5),
2.60 (sept, 3JHH ) 6.9, 1H, H8), 2.16 (s, 6H, H18), 2.11 (s, 3H, H7),
hydride complex followed by dihydrogen coordination and
σ-bond metathesis close the catalytic cycle. A related mechanism
has been established for RuCl2(PPh3)3, whose catalytic activity
is similarly increased by addition of bases such as NEt3, which
promote heterolytic cleavage of dihydrogen, leading to the active
catalyst RuHCl(PPh3)3.1,20 This pathway should be less signifi-
cant for the chelating complex 2, and correspondingly lower
activity is observed for the hydrogenation of styrene (without
NEt3). Furthermore, the calculated energy barrier for the
heterolytic cleavage in the alkene cycle (C f E) is 3.5 times
larger than proton transfer to the aldehyde (C f D), in line
with the observed selectivity.
3
3
1.28 (broad d, JHH ≈ 7, 3H, H9), 1.10 (br d, JHH ∼ 7, 3H, H10).
To conclude, bis-phosphine ruthenium(II)-arene complexes
exhibit both high activity and chemoselectivity for the catalytic
hydrogenation of aldehydes. From the evidence presented herein
an ionic outer-sphere mechanism is proposed for this process.
2
13C{1H} NMR (CD2Cl2): δ 229 (C17), 177.6 (d, JPC ) 20, C16),
127-135 (m, PPh2), 133.5 (s, C14), 132.7 (s, C12), 119.1 (d, JPC
)
3
1
9, C15), 116.6 (d, JPC ) 8, C13), 112.4 (d, JPC ) 56, C11), 106.0
(br, C4), 97.6 (s, C1), 88.7 (br, C3), 88 (C2 + C6), 81.4 (br, C5), 31
(C8 + C18), 22.3 (br, C9), 21.2 (br, C10), 17.7 (s, C7). 31P{1H} NMR
1
Experimental Section
(CD2Cl2): δ 56.2 (s, 1P, RuPPh3), -144.3 (sept, JPF ) 711, 1P,
PF6). 31P{1H} NMR (OC(CD3)2): δ 55.7 (s, 1P, RuPPh3), -144.1
General Methods. All organometallic manipulations were
carried out under a nitrogen atmosphere using standard Schlenk
techniques or in a dry-nitrogen glovebox. CH2Cl2, toluene, pentane,
diethyl ether, and THF were dried catalytically under nitrogen using
a solvent purification system, manufactured by Innovative Technol-
ogy Inc. Octane and acetone were distilled from CaH2 and CaSO4,
respectively, and stored over molecular sieves under nitrogen. CD2-
Cl2 and C6D6 were distilled from CaH2 and K, respectively, and
stored under nitrogen. All other solvents were p.a. quality and
saturated with nitrogen prior to use. [RuCl(PPh3)(P(p-tol)3)(p-
cymene)]PF6,6 [RuCl(PPh3)2(p-cymene)]PF6,6 [RuCl(P(p-tol)3)2(p-
cymene)]PF6,6 [RuCl-(κ2-PPh2C6H4O)(p-cymene)],6 and [RuCl2-
(PPh3)(p-cymene)]14 were prepared as described elsewhere. Styrene,
benzaldehyde, 3-phenylpropionaldehyde, and trans-cinnamaldehyde
were saturated with nitrogen and stored over molecular sieves. All
other chemicals are commercial products and were used as received.
NMR spectra were recorded on a Bruker Avance 400 spectrometer
at room temperature (293 K), unless otherwise stated (see Sup-
porting Information for NMR labelling schemes). The T1 relaxation
measurement was preformed at 400 MHz by the standard inver-
sion-recovery method. High-pressure in situ NMR measurements
were performed in sapphire NMR tubes.21 Chemical shifts are given
in ppm and coupling constants (J) in Hz. Microanalyses were
performed at the EPFL.
1
(sept, JPF ) 708, 1P, PF6). Anal. Calcd for C31H34F6O2P2Ru
(715.62 g mol-1): C, 52.03; H, 4.79. Found: C, 52.07; H, 4.65.
Preparation of [RuCl(PPh3)2(p-cymene)]BPh4. A suspension
of [RuCl2(PPh3)(p-cymene)] (0.300 g, 0.53 mmol), PPh3 (0.277 g,
1.06 mmol), and NaBPh4 (0.22 g, 0.64 mmol) in MeOH (30 mL)
was stirred at 35 °C for 2 h. The resulting precipitate was then
isolated by filtration, washed with EtOH (2 × 15 mL), and extracted
with CH2Cl2 (60 mL) through Celite. Addition of MeOH (50 mL)
and slow concentration gave the product as a microcrystalline
orange solid. Yield: 0.51 g (86%). NMR data were in agreement
with analogous compounds;6,22 selected data are included for
1
reference. H NMR (CDCl3): δ 6.74-7.48 (m, 50H, Ph), 5.06-
5.12 (m, 2H, H2), 4.82 (d, 3JHH ) 6.2, 1H, H3), 2.67 (sept, 3JHH
)
3
6.9, 1H, H8), 1.23 (d, JHH ) 7.0, 6H, H7), 0.50 (s, 3H, H5). 31P-
{1H} NMR (CDCl3): δ 20.8 (s, RuPPh3). 11B{1H} NMR (CDCl3):
δ 86.7 (s, BPh4). Anal. Calcd for C70H64BClF6P2Ru (1114.56 g
mol-1): C, 75.44; H, 5.79. Found: C, 75.62; H, 5.76.
Preparation of [RuHCl(PPh3)(p-cymene)] (3). In a glovebox,
a 300 mL capacity autoclave, containing a Teflon liner and glass
vessel, was charged with [RuCl(PPh3)2(p-cymene)]BPh4 (0.70 g,
0.22 mmol), THF (30 mL), and a magnetic stirrer bar. The autoclave
was removed from the glovebox, flushed with H2 (3 × 15 bar),
and pressurized with H2 (50 bar). The system was heated at 50 °C
for 90 min and cooled and the pressure partially released (to ca. 5
bar) before being placed back into the glovebox. The remaining
pressure was released, the solution transferred into a round-bottom
flask, and the solvent removed in vacuo. The residue was then
extracted with diethyl ether (20 mL) and the filtered solution
reduced to dryness. The residue was then suspended in a mixture
of pentane (50 mL) and diethyl ether (2 mL), stirred briefly, filtered,
and washed with pentane (20 mL) to afford the product as a bright
Preparation of [Ru(κ2-PPh2C6H4O)(OCMe2)(p-cymene)]PF6
(2). A suspension of [RuCl(κ2-PPh2C6H4O)(p-cymene)] (0.238 g,
0.43 mmol) and AgPF6 (0.121 g, 0.48 mmol) in a mixture of CH2-
Cl2-acetone (5:1 v/v, 18 mL) was stirred in the dark at RT for 1
(20) (a) Crabtree, R. H. The Organometallic Chemistry of the Transition
Metals; Wiley-Interscience: Hoboken, 2005. (b) Chaloner, P. A.; Esteruelas,
M. A.; Joo´, F.; Oro, L. A. Homogenous Hydrogenation; Kluwer Aca-
demic: Dordrecht, 1994.
(21) Cusanelli, A.; Frey, U.; Richens, D. T.; Merbach, A. E. J. Am. Chem.
Soc. 1996, 118, 5265.
(22) Lalrempuia, R.; Carroll, R. J.; Kollipara, M. R. J. Coord. Chem.
2003, 56, 1499.

4360 Organometallics, Vol. 26, No. 17, 2007
Notes
yellow, air-sensitive powder. Yield: 0.23 g (66%). Crystals suitable
for X-ray diffraction were grown by layering a diethyl ether solution
of the complex with pentane in a glovebox. 1H NMR (CD2Cl2): δ
samples using a Varian chrompack CP-3380 gas chromatograph,
with species verified by comparison to authentic samples.
Computational Methods. All geometry optimizations and
frequency calculations were carried out using the Gaussian03 suite
of programs.23 Geometries were optimized and verified by harmonic
analysis using the ONIOM approach,24 with the phenyl groups
constituting the low layer; all other atoms where included in the
high layer. The model chemistry of the low layer was HF, and the
LanL2MB basis set was used for all atoms; LanL2MB pseudopo-
tentials were used for Ru, P, and Cl. B3LYP was used for the high
layer, with the 6-31G(d,p) basis set used for all atoms except Ru,
for which the LanL2DZ basis set was used; LanL2DZ pseudopo-
tentials were used for Ru, P, and Cl. Energies were calculated by
single-point SCF calculation on the full optimized geometry at the
B3LYP level using the high-layer basis sets, with the LanL2DZ
pseudopotential for Ru, and are not zero-point-corrected. A pruned
grid consisting of 75 radial shells and 302 angular points was used
for all calculations. Energies for the small molecules used in this
study are compiled in Table S1, with the optimized geometries and
energies of A-F listed in Table S2.
3
7.30-7.77 (m, 15H, PPh3), 5.68 (2, JHH ) 6.2, 1H, H3), 5.12 (d,
3JHH ) 5.5, 1H, H6), 4.89 (d, 3JHH ) 6.1, 1H, H2), 4.10 (d, 3JHH
)
3
5.5, 1H, H5), 2.17 (sept, JHH ) 6.9, 1H, H8), 2.03 (s, 3H, H7),
1.26 (d, 3JHH ) 6.8, 3H, H9), 1.15 (d, 3JHH ) 6.8, 3H, H10), -7.44
(d, 2JPH ) 53, 1H, Ru-H, T-1 ) 1.75 s). 13C{1H} NMR (CD2Cl2):
δ 136.8 (d, 1JPC ) 46, PPh3), 133.8 (d, 2JPC ) 11, PPh3), 129.6 (d,
4JPC ) 2, PPh3), 127.8 (d, 3JPC ) 10, PPh3), 109.3 (d, 2JPC ),2 C4),
2
2
104.0 (s, C1), 91.9 (d, JPC ) 5, C2), 89.4 (d, JPC ) 2, C6), 87.3
(d, 2JPC ) 7, C3), 80.1 (d, 2JPC ) 1, C5), 31.2 (s, C8), 24.0 (s, C10),
22.6 (s, C9), 18.5 (s, C7). 31P{1H} NMR (CD2Cl2) δ 52.5 (s,
RuPPh3). 31P NMR (CD2Cl2): δ 52.5 (d, 2JPH ) 54, RuPPh3). Anal.
Calcd for C28H30ClPRu (534.04 g mol-1): C, 62.97; H, 5.66.
Found: C, 63.03; H, 5.67.
Reactions of [RuHCl(PPh3)(η6-p-cymene)] (3). Reactions of
3 were carried out in a screw-cap NMR tube, with the samples
prepared in a glovebox. Yields were calculated from integration of
NMR spectroscopic data. (a) Attempted reaction with styrene: A
solution of 3 (4 mg) and styrene (1 µL, 1.2 equiv) in C6D6 (0.5
mL) was heated at 50 °C for 15 min. (b) Reaction with styrene
and AgPF6: A suspension of 3 (7.0 mg), styrene (2 µL, 1.3 equiv),
and AgPF6 (5.3 mg, 1.6 equiv) in CD2Cl2 (0.5 mL) was stirred in
the absence of light at RT for 20 min and then filtered through
Celite into a screw-cap NMR tube and analyzed by NMR
spectroscopy. (c) Reaction with benzaldehyde: A solution of 3 (10.0
mg) and benzaldehyde (2 µL, 1.1 equiv) in C6D6 (0.5 mL) was
heated at 50 °C for 15 min. No reaction was observed by NMR
spectroscopy. HCl(g) (10 mL, excess) was bubbled through the
cooled solution, resulting in the solution turning red instantly. The
solution contained [RuCl2(PPh3)(p-cymene)] (5, verified further by
31P{1H} NMR), H2, PhCH2OH (5:PhCH2OH ≈ 7:3), and PhCHO
Acknowledgment. This work was supported by the EPFL
and the Swiss National Science Foundation. We thank the New
Zealand Foundation for Research, Science and Technology for
a Top Achiever Doctoral Fellowship (A.B.C.) and Dr. R.
Scopelliti and Dr. E. Solari for technical support.
Supporting Information Available: Crystallographic details,
X-ray data and tables; optimized geometries and energies; NMR
labelling schemes and spectra of 3; crystallographic information
for 2 and 3 in CIF format. This material is available free of charge
via the Internet at http://pubs.acs.org.
OM7005112
1
as identified by H NMR spectroscopy. Bubbling N2 through the
(23) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K.
N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;
Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich,
S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A.
D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A.
G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.;
Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham,
M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian
03, Revision D.01; Gaussian, Inc.: Wallingford, CT, 2004.
solution removed the peak corresponding to H2. (d) Reaction with
HCl(g): HCl(g) (10 mL, excess) was bubbled through a solution
of 3 (5.0 mg) in C6D6 (0.5 mL), which turned red immediately.
Catalytic Procedures. All catalytic experiments were conducted
using a home-built multicell autoclave containing an internal
temperature probe. Each glass reaction vessel was charged with
the precatalyst (5.0 × 10-6 mol), substrate (0.005 mol, S:C ) 1000:
1), internal standard (100 mg of octane), and solvent (2 mL of
toluene) and then placed inside the autoclave and sealed. This
procedure was carried out either in air (general procedure for 1) or
in a glovebox (for 2). Following flushing with H2 (3 × 10 bar),
the autoclave was heated to 50 °C under H2 (5 bar, ca. 10 min)
and then maintained at 50 bar for the duration of the catalytic run
(2 h). The autoclave was then cooled to ambient temperature (<5
min) using an external water-cooling system, and then the pressure
was released. Conversions were determined by GC analysis of the
(24) (a) Dapprich, S.; Koma´romi, I.; Byun, K. S.; Morokuma, K.; Frisch,
M. J. J. Mol. Struct. (THEOCHEM) 1999, 462, 1. (b) Vreven, T.;
Morokuma, K. J. Comput. Chem. 2000, 21, 1419.