The first Ru(ν3-PCP) complexes of the electron-rich pincer ligand l,3-bis((dicyclohexylphosphino)methyl)benzene: Structure and mechanism in transfer hydrogenation catalysis

Article abstract of DOI:10.1021/om040025x

Mild routes to the first Ru(ν³-pincer) derivatives of bis((dicyclohexylphosphino)methyl)benzene are reported. RuCl(ν³- PCP)(PPh₃) (3·PPh₃; PCP = [2,6-(Cy ₂PCH₂)₂C₆H₃]) is formed quantitatively on reaction of the PC(H)P-arene ligand with RuCl ₂(PPh₃)₃ at 22°C in the presence of base. Treatment of 3·PPh₃ with KHB^sBu₃ under nitrogen atmosphere generates RuH(ν³-PCP)(PPh₃)(N ₂), 4, as a mixture of conformational isomers in which the hydride and N₂ ligands are trans or cis (4a or 4b, respectively). On exposure to H₂, 4a/b undergo immediate, quantitative exchange of bound N ₂ for ν₂-H₂, affording the corresponding isomers of RuH(ν³-PCP)(PPh₃)(H₂), 5a/b. Complex 3·PPh₃ resists displacement of PPh₃ by H₂ at 22 °C, but on exposure to CO, readily yields RuCl(ν³-PCP)(CO)₂, 6. Transfer hydrogenation of ketones is efficiently catalyzed by 3·PPh₃ and 4, in a pathway involving loss of PPh₃ and (for 3) exchange of chloride for hydride. The duration of pretreatment of 3·PPh₃ with base (KOH, BuOK) in refluxing 2-propanol is critical to activity, and indirect evidence supports formation of a catalytically active dihydride species during this process. X-ray crystal structures are reported for 3, 4a, 5a, and 6.

Full text of DOI:10.1021/om040025x

Organometallics 2004, 23, 4047-4054
4047
Th e F ir st Ru (η3-P CP ) Com p lexes of th e Electr on -Rich
P in cer Liga n d
1,3-Bis((d icycloh exylp h osp h in o)m eth yl)ben zen e:
Str u ctu r e a n d Mech a n ism in Tr a n sfer Hyd r ogen a tion
Ca ta lysis
Dino Amoroso,† Amir J abri, Glenn P. A. Yap, Dmitry G. Gusev,‡
Eduardo N. dos Santos,§ and Deryn E. Fogg*,†
Center for Catalysis Research and Innovation, Department of Chemistry, University of Ottawa,
Ottawa, Ontario, Canada K1N 6N5
Received March 2, 2004
Mild routes to the first Ru(η3-pincer) derivatives of bis((dicyclohexylphosphino)methyl)-
benzene are reported. RuCl(η3-PCP)(PPh3) (3‚PPh3; PCP ) [2,6-(Cy2PCH2)2C6H3]) is formed
quantitatively on reaction of the PC(H)P-arene ligand with RuCl2(PPh3)3 at 22 °C in the
presence of base. Treatment of 3‚PPh3 with KHBsBu3 under nitrogen atmosphere generates
RuH(η3-PCP)(PPh3)(N2), 4, as a mixture of conformational isomers in which the hydride
and N2 ligands are trans or cis (4a or 4b, respectively). On exposure to H2, 4a /b undergo
immediate, quantitative exchange of bound N2 for η2-H2, affording the corresponding isomers
of RuH(η3-PCP)(PPh3)(H2), 5a /b. Complex 3‚PPh3 resists displacement of PPh3 by H2 at 22
°C, but on exposure to CO, readily yields RuCl(η3-PCP)(CO)2, 6. Transfer hydrogenation of
ketones is efficiently catalyzed by 3‚PPh3 and 4, in a pathway involving loss of PPh3 and
(for 3) exchange of chloride for hydride. The duration of pretreatment of 3‚PPh3 with base
t
(KOH, BuOK) in refluxing 2-propanol is critical to activity, and indirect evidence supports
formation of a catalytically active dihydride species during this process. X-ray crystal
structures are reported for 3, 4a , 5a , and 6.
In tr od u ction
introduction of chirality. Examples of alkylphosphine
pincer complexes in group 8 chemistry are confined,
however, to tert-butyl10-12 and isopropyl13 PCP ligands.
In view of the profound influence of pincer ligand
properties and chelate bite angles on structure and
reactivity,12,14a and motivated by the remarkably high
transfer-hydrogenation activity of the cyclohexylphos-
phine complex [RuH3(dcypb)(CO)]- (dcypb ) 1,4-bis-
(dicyclohexyl)phosphinobutane),15 we undertook inves-
tigation of the chemistry of the cyclohexyl-PCP pincer
systems, group 9 and 10 complexes of which have been
studied by the Cross14 and Park16 groups. We recently
Organometallic complexes containing monoanionic,
terdentate pincer ligands have been intensively studied
over the past decade, driven in large part by the
potential of such species in catalysis.1-6 While group 9
and 10 metal complexes with aryl- and alkyl-PCP
ligands have received much attention, the PCP pincer
chemistry of group 8 metals has focused principally on
the important family of arylphosphine derivatives. Such
ruthenium pincer complexes exhibit versatile catalytic
activity in (e.g.) transfer hydrogenation, Kharasch ad-
dition, atom-transfer radical polymerization (ATRP),
ring-opening metathesis polymerization (ROMP), and
oxidative coupling of arenes with alkenes.1-3,6-9 Electron-
rich alkylphosphine derivatives can expand opportuni-
ties for modulating activity and selectivity, and for
(7) van de Kuil, L. A.; Grove, D. M.; Gossage, R. A.; Zwikker, J . W.;
van Koten, G. Organometallics 1997, 16, 4985.
(8) Gossage, R. A.; van de Kuil, L. A.; van Koten, G. Acc. Chem.
Res. 1998, 31, 423.
(9) del Rio, I.; van Koten, G. Tetrahedron Lett. 1999, 40, 1401.
(10) (a) Gusev, D. G.; Madott, M.; Dolgushin, F. M.; Lyssenko, K.
A.; Antipin, M. Y. Organometallics 2000, 19, 1734. (b) Gusev, D. G.;
Dolgushin, F. M.; Antipin, M. Y. Organometallics 2000, 19, 3429.
(11) (a) Gusev, D. G.; Maxwell, T.; Dolgushin, F. M.; Lyssenko, M.;
Lough, A. J . Organometallics 2002, 21, 1095. (b) Reinhart, B.; Gusev,
D. G. New J . Chem. 1999, 23, 1.
(12) Farrington, E. J .; Viviente, E. M.; Williams, B. S.; van Koten,
G.; Brown, J . M. J . Chem. Soc., Chem. Commun. 2002, 308.
(13) van der Boom, M. E.; Kraatz, H.-B.; Hassner, L.; Ben-David,
Y.; Milstein, D. Organometallics 1999, 18, 3873.
(14) (a) Cross, R. J .; Kennedy, A. R.; Muir, K. W. J . Organomet.
Chem. 1995, 487, 227. (b) Cross, R. J .; Kennedy, A. R.; Manojlovic-
Muir, L.; Muir, K. W. J . Organomet. Chem. 1995, 493, 243. (c) Kennedy,
A. R.; Cross, R. J .; Muir, K. W. Inorg. Chim. Acta 1995, 231, 207. (d)
Kennedy, A. R.; Cross, R. J .; Muir, K. W. Inorg. Chim. Acta 1995, 231,
195.
* Corresponding author. E-mail: dfogg@science.uottawa.ca. Fax:
(613) 562-5170.
† Present address: Promerus L.L.C., 9921 Brecksville Rd., Brecks-
ville, OH 44141-3829.
‡ Department of Chemistry, Wilfrid Laurier University, Waterloo,
ON, Canada N2L 3C5.
§ On sabbatical leave from Departamento de Qu´ımica, ICEx, Uni-
versidade Federal de Minas Gerais, 31270-901 Belo Horizonte, Brazil.
(1) Albrecht, M.; Kocks, B. M.; Spek, A. L.; van Koten, G. J .
Organomet. Chem. 2001, 624, 271.
(2) Albrecht, M.; van Koten, G. Angew. Chem., Int. Ed. 2001, 40,
3750.
(3) van der Boom, M. E.; Milstein, D. Chem. Rev. 2003, 103, 1759.
(4) Vigalok, A.; Milstein, D. Acc. Chem. Res. 2001, 34, 798.
(5) J ensen, C. M. J . Chem. Soc., Chem. Commun. 1999, 2243.
(6) Milstein, D. Pure Appl. Chem. 2003, 75, 445.
(15) Drouin, S. D.; Amoroso, D.; Yap, G. P. A.; Fogg, D. E.
Organometallics 2002, 21, 1042.
10.1021/om040025x CCC: $27.50 © 2004 American Chemical Society
Publication on Web 07/22/2004

4048 Organometallics, Vol. 23, No. 17, 2004
Amoroso et al.
Ch a r t 1
Sch em e 1
F igu r e 1. ORTEP diagram of 3‚THF; thermal ellipsoids
set at the 30% probability level. Hydrogen atoms and THF
solvate are omitted for clarity. Key structural parameters
are summarized in Table 2.
reported the first ruthenium complex of 1,3-bis(dicyclo-
hexylphosphino)methyl)benzene, 1,3-(Cy2PCH2)2C6H4,
an η2-PC(H)P-arene complex bearing an alkylidene
ligand.17 Here we describe a mild route to η3-pincer
Ru(II) derivatives containing a chloride or hydride
ligand, their reactivity toward small molecules, includ-
ing N2, H2, and CO, and their high activity in transfer
hydrogenation of aryl ketones.
F igu r e 2. ORTEP diagrams of 4a ‚Et2O (left) and 5a
(right); ellipsoids set at the 30% probability level. Non-
hydridic hydrogen atoms and solvent molecule (4a ) are
omitted for clarity. Hydride and dihydrogen ligands are not
located for 5a . Key parameters are given in Table 2.
Additional values for 4a (distances in Å, angles in deg):
Ru-N(1), 2.014(4); N(1)-N(2), 1.111(6); H(1)-Ru-N(1),
173(1); Ru-N(1)-N(2), 178.3(4).
Resu lts a n d Discu ssion
Convenient access to an η3-pincer derivative of the
bulky ligand 1,3-(CH2PtBu2)2C6H4 has been established
from [RuCl2(COD)]n.10a RuX[η3-2,6-(PtBu2CH2)2C6H3]-
(CO) (1a , X ) Cl) was obtained in good yields from these
precursors by decarbonylation of isoamyl alcohol in
the presence of NEt3 as base. Attempts to access Ru-
(η3-PCP) complexes via the corresponding reaction of
1,3-(Cy2PCH2)2C6H4 were frustrated by formation of PP-
bridged species.18 We find that RuCl2(PPh3)3 functions
as a much more tractable precursor to the desired pincer
complexes, as earlier found for the synthesis of RuX-
[η3-2,6-(CH2PPh2)2C6H3](PPh3) (2a , X ) Cl; Chart 1).19,20
Thus, we observe quantitative formation of RuCl(η3-
PCP)(PPh3)‚PPh3 (3‚PPh3) on reaction of RuCl2(PPh3)3
with the PC(H)P-arene ligand at room temperature in
the presence of NEt3 (Scheme 1; isolated yield ca. 80%).
The added base serves to scavenge the HCl liberated.
While it has previously been noted that the RuCl2(η2-
PC(H)P-arene) intermediate can be sufficiently acidic
to be deprotonated by NEt3,10,21,22 the driving force for
activation of the C-H (arene) bond in the present
reaction is sufficient that 3 is observed at 22 °C even in
the absence of added base. Direct cyclometalation of
electron-donating alkylphosphine pincer ligands typi-
cally requires forcing temperatures.2 Optimum yields
of 1a , for example, require refluxing at 120 °C for 24
h.10a Reaction of RuCl2(PPh3)3 with 1,3-(iPrCH2)2C6H4
similarly requires thermolysis at 110 °C in THF using
a pressure vessel.13
Spectroscopic and microanalytical data for 3‚PPh3 are
consistent with a square pyramidal structure, with a
basal PCP ligand and a PPh3 ligand, occupying the apical
site. A doublet of virtual triplets is observed for one of
2
the methylene protons in each “elbow” (δ 2.90; J HH
)
16.7 Hz, vJ HP ) 5.2 Hz) and a broad doublet for the other
(δ 2.55; 2J HH ) 12.2 Hz). The 31P NMR spectrum (Table
1) consists of an A2X spin system, indicating trans-
disposition of the two equivalent PCy2 groups, and a
singlet for free PPh3 at -5.46 ppm. While the latter
signal does not diminish perceptibly on trituration or
reprecipitation, a crystal structure determination re-
veals the complex devoid of “solvating” PPh3 (Figure 1).
(16) (a) Yun, J . G.; Seul, J . M.; Lee, K. D.; Kim, S.; Park, S. Bull.
Korean Chem. Soc. 1996, 17, 311. (b) Ryu, S. Y.; Yang, W.; Kim, H. S.;
Park, S. Bull. Korean Chem. Soc. 1997, 18, 1183. (c) Park, S. Bull.
Korean Chem. Soc. 2000, 21, 1251. (d) Park, S. Bull. Korean Chem.
Soc. 2002, 23, 132. (e) Seul, J . M., Park, S. J . Chem. Soc., Dalton Trans.
2002, 1153.
(17) Amoroso, D.; Snelgrove, J . L.; Conrad, J . C.; Drouin, S. D.; Yap,
G. P. A.; Fogg, D. E. Adv. Synth. Catal. 2002, 344, 757.
(18) Gusev, D. G. Personal communication.
(19) Karlen, T.; Dani, P.; Grove, D. M.; Steenwinkel, P.; van Koten,
G. Organometallics 1996, 15, 5687.
(20) (a) J ia, G.; Lee, H. M.; Xia, H. P.; Williams, I. D. Organome-
tallics 1996, 15, 5453. (b) J ia, G.; Lee, H. M.; Williams, I. D. J .
Organomet. Chem. 1997, 534, 173.
(21) Vigalok, A.; Uzan, O.; Shimon, L. J . W.; Ben-David, Y.; Martin,
J . M. L.; Milstein, D. J . Am. Chem. Soc. 1998, 120, 12539.
(22) (a) Crocker, C.; Errington, R. J .; McDonald, W. S.; Odell, K. J .;
Shaw, B. L.; Goodfellow, R. J . J . Chem. Soc., Chem. Commun. 1979,
498. (b) Crocker, C.; Errington, R. J .; Markham, R.; Moulton, C. J .;
Odell, K. J .; Shaw, B. L. J . Am. Chem. Soc. 1980, 102, 4373.
Hydride derivatives of Ru-pincer complexes are
thought to be key intermediates in transfer hydrogena-
tion via 2a ,2,3 and are also of interest for their potential
as precursors to alkylidene derivatives.17,23 In undertak-
ing transformation of 3‚PPh3 to the hydride, we chose
to use KBHsBu3, in preference to more conventional
hydride sources, in the hope of circumventing deproto-
nation of the pincer “arms”2 or formation of borohydride
complexes.10b Addition of KHBsBu3 to 3‚PPh3 under
nitrogen atmosphere resulted in clean transformation
into two new products (ratio 1:1), the 31P NMR signals
for which correlate by EXSY-NMR. Two A2X patterns
(23) Wilhelm, T. E.; Belderrain, T. R.; Brown, S. N.; Grubbs, R. H.
Organometallics 1997, 16, 3867.

First Ru(η3-PCP) Cyclohexyl Pincer Complexes
Organometallics, Vol. 23, No. 17, 2004 4049
Ta ble 1. Su m m a r y of Key NMR Da ta for Com p lexes 3-5a
compd
solvent
δ
P(A) PCP
δ
P(B) PPh3
2J PP
δH, RuH
2J HP cis
2J HP trans
δH, Ru(H2)
3
C6D6
2:1 PrOH/C7D8
35.7
37.0
59.6
60.5
54.6
55.5
68.1
68.9
71.1
71.8
80.9
81.2
45.0
45.6
28.8
29.4
56.6
57.0 (br s)
37.1
32
31
17
17
14
14
18
16
14
15
i
4a b
4b
5a
C6D6
-12.2 (q)
-8.05 (dt)
-8.70 (q)
-10.64 (dt)
19.5 (s)
21.8 (s)
18.9 (s)
21.7 (s)
i
2:1 PrOH/C7D8
C6D6
90
-
i
2:1 PrOH/C7D8
C6D6
-4.34 (s)
-7.08 (s)
i
2:1 PrOH/C7D8
5b
C6D6
80
i
2:1 PrOH/C7D8
37.8 (br s)
a
b
300 MHz (1H); 121 MHz (31P); 295 K, J in Hz. All PCP signals doublets; all PPh3 signals triplets, unless otherwise noted. Spectra
at 253 K; unresolved at 295 K.
Sch em e 2
Sch em e 3
of dinitrogen adducts has been reported10b in related
Ru[η3-2,6-(PtBu2CH2)2C6H3] chemistry, and we earlier
noted the potency of N2 as a stabilizing ligand in
Ru-dcypb complexes.25
are observed, confirming retention of bound PPh3: that
for 4b is well resolved at room temperature (295 K),
while the doublet for the PCP ligand within 4a emerges
only on cooling to 253 K. These species could not be
separated, but were isolated as a mixture in 87% yield.
On the basis of X-ray analysis for 4a (Figure 2),
supported by spectroscopic and microanalytical data for
the mixture, we identify the products as conformational
isomers of RuH(η3-PCP)(PPh3)(N2), 4 (4a , hydride trans
to N2; 4b, hydride cis to N2; Scheme 2).
Exchange of bound N2 for H2 is facile for 4a /b, but
not for chloride complex 3. Complex 3 undergoes no
spectroscopically observable reaction under 1 atm H2
after 1 h at RT. After 24 h, a new A2B system is
apparent in the 31P NMR spectrum, but this accounts
for only 7% of the total integrated intensity (δ 53.6 (d),
2
23.2 (t), J PP ) 16.3 Hz). The multiplicity indicates
NMR evidence excludes the possibility that the 4a -
4b equilibrium involves reversible coordination of N2,
i.e., assignment of 4b as square pyramidal RuH-
(η3-PCP)(PPh3). The downfield location of the hydride
signal (δRuH -8.05, doublet of triplets; Table 1) indicates
that this ligand is not trans to an empty coordination
site (for which δRuH values of -25 to -30 ppm are expec-
ted10b,24), while its multiplicity confirms that the hydride
ligand is trans to one phosphorus ligand and cis to two
others. In comparison, the hydride signal for 4a is poorly
resolved at room temperature, appearing as a very
broad resonance centered at -12 ppm, barely visible
above the baseline. The breadth of the peak suggests
increased lability for N2 trans to hydride. The signal
resolves into a quartet on cooling to 253 K: its multi-
plicity and the magnitude of the coupling constant (2J PH
) 19.5 Hz; Table 1) indicate a cis relationship between
the hydride ligand and all three phosphorus nuclei. Both
hydride signals display the long T1(min) relaxation
times characteristic of hydride ligands: 359 ms for 4a
(278 K, 500 MHz) and 333 ms for 4b (282 K, 500 MHz).
Observation of only two IR bands for ν(Ru-H) and
ν(NtN) (2114, 2134 cm-1) may indicate the presence
of a single isomer in the solid state.
retention of PPh3, as well as the pincer ligand, within
the coordination sphere, and the structure is tentatively
assigned as RuCl(η3-PCP)(PPh3)(H2). Under the same
conditions, the N2 ligand in 4a /b is displaced within
minutes by H2 (Scheme 3). The reaction yields RuH-
(η3-PCP)(PPh3)(H2), 5a /b, again as a mixture of two
conformational isomers, with hydride trans (5a ) or cis
(5b) to dihydrogen: the cis isomer predominates by a
ratio of 3:1. (The high stability of hydride cis to H2 has
been noted26 and may provide a driving force for
exchange in the case of 4, versus 3.) Four distinct sets
of 1H NMR resonances appear in the hydride region for
5a /b. Again, the downfield location of the hydride
signals (-8.70, -10.64 ppm) argues for a coordinatively
saturated structure. Coupling to three cis 31P nuclei
splits the hydride signal for 5a into a quartet, while that
for 5b appears as a doublet of triplets, split by one trans
and two cis 31P nuclei. The dihydrogen ligands give rise
to two broad singlets, each integrating to twice the
intensity of the corresponding hydride. The T1(min)
relaxation time for the dihydrogen ligand in 5b is longer
than that in 5a , as expected for a dihydrogen ligand
perturbed by interaction with a cis-hydride (5a , 20 ms;
5b, 24 ms; both at 265 K, 500 MHz). 31P NMR analysis
reveals two A2X patterns, which do not correlate in
EXSY-NMR experiments, indicating that exchange
between 5a and 5b is slow on the NMR time scale.
Indeed, binding of H2 is sufficiently strong in 5a that
crystals could be grown by evaporation of a benzene
Retention of N2 within the coordination sphere in 4a
and 4b contrasts with formation of a coordinatively
unsaturated product on reaction of 2a with sodium
hydride under nitrogen atmosphere.20b Facile formation
(24) The high trans influence of hydride is manifested in a strong
site preference: this ligand normally takes up the apical site in square
pyramidal complexes, for which these diagnostic upfield chemical shifts
are observed. See, for example: Marchenko, A. V.; Huffman, J . C.;
Valerga, P.; Tenorio, M. J .; Puerta, M. C.; Caulton, K. G. Inorg. Chem.
2001, 40, 6444.
(25) Amoroso, D.; Yap, G. P. A.; Fogg, D. E. Can. J . Chem. 2001,
79, 958.
(26) Kubas, G. J ., Ed. Metal Dihydrogen and σ-Bond Complexes.
Structure, Theory and Reactivity; Kluwer Academic/Plenum Publish-
ers: New York, 2001.

4050 Organometallics, Vol. 23, No. 17, 2004
Amoroso et al.
Ta ble 2. Su m m a r y of Key Str u ctu r a l P a r a m eter s
for Com p lexes 3-6
3
4a
5a
6
Ru-C(19)
Ru-P(1)
Ru-P(2)
Ru-P(3)
Ru-X(1) (X )
H, Cl)
2.061(4)
2.129(5)
2.133(4)
2.112(4)
2.3247(10) 2.3433(12) 2.3434(11) 2.3649(14)
2.3522(10) 2.3578(12) 2.3148(10) 2.3698(13)
2.1996(10) 2.3655(12) 2.3617(10)
2.4520(10) 1.60(4)
2.447(4),
2.447(4)
P(1)-Ru-P(2) 154.21(4) 154.95(5) 158.36(4) 160.76(4)
P(1)-Ru-P(3) 95.60(4)
101.15(4) 98.06(4)
P(1)-Ru-C(19) 82.26(11) 77.61(12) 79.12(11) 78.88(13)
P(2)-Ru-P(3) 102.63(4) 102.30(4) 103.02(4)
F igu r e 3. ORTEP diagram for 6. Selected bond lengths
(Å) and angles (deg) (where two values are given, the
second is for the mirror image complex); other values shown
in Table 2: Ru(1)-C(34), 1.837(11), 1.859(11); Ru(1)-C(33),
1.912(5); Ru(1)-Cl(1), 2.447(4), 2.447(4); C(33)-O(1),
1.167(5); C(34)-O(2), 1.187(11), 1.166(11); C(33)-Ru-
C(19), 177.7(2); C(34)-Ru-C(33), 90.4(6), 88.3(6); C(34)-
Ru-Cl(1), 178.8(5), 178.6(7); C(34)-Ru-C(19), 91.4(6),
89.9(6); C(19)-Ru-Cl(1), 88.66(16), 89.12(16); 78.88(13).
P(2)-Ru-C(19) 80.29(11) 77.68(12) 79.31(11) 81.88(13)
P(3)-Ru-C(19) 88.13(11) 198.96(12) 170.88(10)
exerted by the dicyclohexylphosphine moiety versus
diphenylphosphine: the P(1)-Ru-P(2) angle is 4° larger
in 3 than in 2a (154.21(4)° versus 150.4(1)°),20b and the
C(19)-Ru-Cl angle is contracted by ca. 10° (151.42(11)°
versus 161.6(1)°).
The coordination geometry about Ru in 4a and 6 is
distorted octahedral, as is that deduced for 5a , for which
the crystal quality did not permit location of the hydride
and dihydrogen ligands.27 In all three complexes, the
pincer ligand occupies one meridian, and the site trans
to the activated ring carbon C(19) is taken up by PPh3
(4a , 5a ) or CO (6).28 The trans influence of the aryl
carbon may contribute to the ca. 0.16 Å increase in the
Ru-P(3) bond length in 4a and 5a , versus 3 (in which
the PPh3 group is trans to the vacant site). Likewise,
the slight increase in the Ru-C(19) distance in 4a , 5a ,
and 6, versus 3, may reflect the stronger trans influence
of phosphine and carbonyl, versus chloride, though a
change in metal hybridization associated with the lower
coordination number in 3 may also account for these
changes. While the P(1)-Ru-P(2) angle of 154.95(5)°
in 4a is very close to that in 3, the values in 5a and 6
(158.36(4)°, 160.76(4)°) are significantly less com-
pressed. In the case of 6, this can be attributed to
replacement of the PPh3 ligand by a sterically unde-
manding carbonyl group.
Sch em e 4
solution of 5a /b in a N2-filled drybox over a period of 3
days. X-ray analysis revealed the structure shown in
Figure 2.
The PPh3 ligand in 3‚PPh3, though unperturbed by
exposure to H2, is readily displaced by carbon monoxide
(Scheme 4). The deep green color of 3‚PPh3 dissipates
within minutes of exposure to 1 atm CO (RT, benzene),
giving a pale yellow solution. Displacement of PPh3 and
formation of six-coordinate RuCl(η3-PCP)(CO)2 (6) are
confirmed by spectroscopic, microanalytical, and X-ray
data. In situ 31P{1H} NMR analysis reveals a singlet
for (free) PPh3 and another singlet, of equal integrated
intensity, for the equivalent 31P nuclei of the pincer
ligand (δP 62.4). The PPh3 singlet disappears on repre-
cipitation of the product from CH2Cl2/diethyl ether, and
6 is isolated in 88% yield. The presence of two inequiva-
lent carbonyl ligands is indicated by the appearance of
two strong ν(CO) bands in the IR spectrum (2018, 1945
cm-1), and two characteristically downfield 13C{1H}
NMR triplets (199.8 ppm (t, 2J CP ) 12 Hz), 198.2 (t, 2J CP
) 7 Hz)), the multiplicity of which confirms that only
two 31P nuclei remain in the coordination sphere. Both
the IR and the 13C NMR data are consistent with cis-
disposition of the CO ligands, as also found for RuCl-
[η3-2,6-(PPh2CH2)2C6H3](CO)2.20b X-ray quality crystals
were obtained by slow evaporation of a benzene solution;
an ORTEP diagram is shown in Figure 3.
X-r a y Da ta for 3, 4a , 5a , a n d 6 (for key, common
structural parameters, see Table 2). Square pyramidal
3 is isostructural with 2a :20b consistent with the spec-
troscopic data, the chloride and η3-PCP ligands are sited
in the basal plane, with PPh3 occupying the apical site
(Figure 1). The single Ru-C bond to the ipso carbon lies
in the aromatic plane of the [2,6-(CH2PCy2)2C6H3]
ligand, with a bond length (2.061(4) Å) essentially
identical to that in 2a (2.070(4) Å). Unsurprisingly, some
manifestations are seen of the greater steric pressure
The Ru-H distance (1.60(4) Å) in 4a is comparable,
within experimental error, with the value of 1.73(7) Å
observed for RuX[η3-2,6-(PtBu2CH2)2C6H3](CO) (1b, X
) H).10b Ru-N (2.014(4) Å) and N-N (1.111(6) Å)
distances correlate well with literature values for
related complexes (av Ru-N ) 2.10 Å; av N-N ) 1.13
Å).10b,29 The C-O bond distance for the nondisordered
CO ligand in 6 is within the usual range.30-33
Tr a n sfer Hyd r ogen a tion via P CP Com p lexes.
Ru(II) complexes of both NCN and PCP pincer ligands
catalyze the transfer hydrogenation of ketones.1,3,34
(27) One cyclohexyl group was also conformationally disordered,
with a 50/50 site occupancy distribution.
(28) In complex 6, the remaining carbonyl and chloride ligands are
disordered; the electron density is distributed over C(34), O(2), and
Cl(1) and the positions are arbitrarily assigned. The excess of electron
density at C(34) results in an unusually small ellipsoid.
(29) Hidai, M.; Mizobe, Y. Chem. Rev. 1995, 95, 1115.
(30) Maddock, S. M.; Rickard, C. E. F.; Roper, W. R.; Wright, L. J .
Organometallics 1996, 15, 1793.
(31) Gottschalk-Gaudig, T.; Folting, K.; Caulton, K. G. Inorg. Chem.
1999, 38, 5241.
(32) Batista, A. A.; Zukerman-Schpector, J .; Porcu, O. M.; Queiroz,
S. L.; Araujo, M. P.; Oliva, G.; Souza, D. H. F. Polyhedron 1994, 13,
689.
(33) Wilkes, L. M.; Nelson, J . H.; Mitchener, J . P.; Babich, M. W.;
Riley, W. C.; Helland, B. J .; J acobson, R. A.; Cheng, M. Y.; Seff, K.;
McCusker, L. Inorg. Chem. 1982, 21, 1376.

First Ru(η3-PCP) Cyclohexyl Pincer Complexes
Organometallics, Vol. 23, No. 17, 2004 4051
Ta ble 3. Tr a n sfer Hyd r ogen a tion of
Ben zop h en on ea
Ta ble 4. Tr a n sfer Hyd r ogen a tion of Acetop h en on e
Usin g 3.P P h 3 a s P r eca ta lysta
entry
precatalyst
additiveb
time (h)
conversion (%)
pretreatment timeb
(min)
TOFc
(h-1
entry
additive
KOH
)
1
2
3
4
5
2b
4a /b
4a /b
3‚PPh3
3‚PPh3
KOH
108
96
24
24
40
98
88
90
91
92
6
7
8
9
10
11
12f
0
10
60
60
60
60
60
300
450
1300
1200
320
KOH
KOH/H2
KOH
KOH
KOH
tBuOK
KOH + NBu4Cld
a
Conditions: 20 mmol of Ph2CO, [Ru] ) 0.1 mol %, 20 mL of
e
KOH + PPh3
480
2500
iPrOH, reflux (82 °C), N2 atmosphere, unless otherwise noted.
tBuOK/H2
b
[KOH]/[Ru] ) 20.
a
Conditions: 2.0 mmol of acetophenone, [Ru] ) 0.1 mol %, 2.0
mL of PrOH, reflux (82 °C), N2 atmosphere, unless otherwise
i
RuX[η3-2,6-(PPh2CH2)2C6H3](PPh3) (2b, X ) OTf), with
its weakly bound triflate ligand, has demonstrated
particularly high activity, as well as versatility toward
a range of substrates, including aryl and diaryl ketones
targeted as precursors to pharmaceutically desirable
benzhydrols.34 Anionic [RuH(OiPr)(η3-PCP)(PPh3)]-, gen-
erated during pretreatment of 2a or 2b with KOH in
refluxing 2-propanol, was proposed as the resting state
in catalysis; a ruthenium hydride species was presumed
to be the active catalyst. We find that in the absence of
base, “preformed” monohydrides 4a /b display lower
activity for benzophenone reduction than 2b (Table 3,
entries 1, 2). Performance increases dramatically in the
presence of KOH (entry 3), consistent with the generally
accepted requirement for isopropoxide ion.34-37 Given
this requirement for added base, however, use of the
robust chloride complex 3 is preferred over hydride 4.
Activity is significantly higher for reactions carried out
under H2 rather than N2 (entries 4, 5), suggesting that
both H2- and transfer-hydrogenation pathways are
implicated.
To gain mechanistic insight into the transfer hydro-
genation catalyzed by 3.PPh3, we undertook more
detailed studies of ligand, base promoter, and reaction
conditions. For the sake of both convenience and added
insight, we chose to study the more reactive (and
enolizable) substrate acetophenone, for which we moni-
tored reactions by gas chromatography. Turnover fre-
quencies (TOF) were evaluated at 20% conversion, to
minimize the influence on the rate of decreases in
substrate concentration, increases in product concentra-
tion, and catalyst decomposition. Results are sum-
marized in Table 4.
b
noted. Precatalyst heated in the presence of base before addition
of substrate. c Mol substrate converted per mol Ru per hour at 20%
d
conversion. 2.0 mol % NBu4Cl. e 0.8 mol % PPh3. f Reaction and
pretreatment under H2 (1 atm).
etophenone, 82 °C), control experiments in the absence
of Ru result in only 2% reduction of acetophenone after
4 h.42
We find that catalyst activity is very sensitive to the
duration of pretreatment, during which the precatalyst
is heated at reflux in the presence of base (base: Ru )
20:1), prior to addition of substrate. After only 10 min
of pretreatment, activity increases by 50% relative to
reactions carried out without this initial heating step.
Activity increases by 4-fold after 1 h (entries 6-8),
declining thereafter. Approximately identical activity
was found using KOH or tBuOK, although the base
strength varies by 3 orders of magnitude (pKa KOH )
16; pKa tBuOK ) 19; entries 8, 9). This suggests that
the base is not involved in the rate-determining step,
but rather promotes formation of the catalytically active
species, most probably in a rapid preequilibrium involv-
ing formation of isopropoxide ion.36,37
Addition of the soluble ammonium chloride NBu4Cl
(20 equiv per Ru) reduces the activity to the level of the
system without pretreatment (entries 10, 6). Excess
chloride is presumed to coordinate to the metal center
via exchange with a hydride ligand. Its inhibiting effect
is consistent with the earlier report that complex 2b,
containing the weakly coordinating triflate ion, is much
more active than its chloride analogue 2a .34 Addition
of PPh3 to the system (8 equiv per Ru) also diminishes
activity, suggesting that an equilibrium involving loss
of PPh3 precedes the rate-determining step and that
excess PPh3 can compete with the substrate for vacant
sites. Both the bound and the solvating PPh3 present
in the precatalyst 3‚PPh3 will thus diminish the overall
activity of the system.
At high concentrations, strong bases such as alkali
hydroxides can promote hydrogen transfer to ke-
tones,38-40 a process related to the classical Meerwein-
Pondorff-Verlay reduction. While harsh conditions are
typical, rates can be significant even at 82 °C. LePage
and J ames, for example, report 60% conversion of
acetophenone to 1-phenylethanol within 4 h at 34 mol
% NaOH in refluxing 2-propanol.41 Under our standard
conditions (0.02 M KOH, or 2 mol % relative to ac-
Finally, we note that under hydrogen atmosphere
catalyst activity is approximately double that observed
under nitrogen atmosphere, presumably due to a H2-
hydrogenation pathway.
NMR Exp er im en ts u n d er Ca ta lytica lly Releva n t
Con d ition s. In view of the marked dependence of
catalytic activity on pretreatment time, we undertook
an in situ 31P{1H} NMR study of the precursor 3‚PPh3
under pretreatment conditions. KOtBu was employed
in preference to KOH in order to ensure solubility of
the base without stirring. These experiments are sum-
(34) Dani, P.; Karlen, T.; Gossage, R. A.; Gladiali, S.; van Koten, G.
Angew. Chem., Int. Ed. 2000, 39, 743.
(35) Aranyos, A.; Csjernyik, G.; Szabo´, K. J .; Ba¨ckvall, J .-E. J . Chem.
Soc., Chem. Commun. 1999, 351.
(36) Chowdhury, R.; Ba¨ckvall, J .-E. J . Chem. Soc., Chem. Commun.
1991, 1063.
(37) Morton, D.; Cole-Hamilton, D. J . J . Chem. Soc., Chem. Com-
mun. 1988, 1154.
(38) Berkessel, A.; Schubert, T. J . S.; Mueller, T. N. J . Am. Chem.
Soc. 2002, 124, 8693.
(39) Walling, C.; Bollyky, L. J . Am. Chem. Soc. 1964, 86, 3750.
(40) Ba¨ckvall, J .-E. J . Organomet. Chem. 2002, 652, 105.
(41) LePage, M. D.; J ames, B. R. J . Chem. Soc., Chem. Commun.
2000, 1647.
(42) While the presence of base can trigger aldol condensation of
ketones, only traces of heavier byproducts (<1%) were observed even
over the combined time scale of pretreatment and reduction experi-
ments (ca. 3.5 h), reaching 3% after 19 h.

4052 Organometallics, Vol. 23, No. 17, 2004
Amoroso et al.
fact that the activity observed for catalysis under H2 is
only double that under N2, despite a 100-fold increase
in concentration of 5a /b, argues against identification
of the dihydrogen complex(es) as the active species.)
Ba¨ckvall recently proposed that a Ru(H)2 complex is
formed as the true catalytic species in transfer hydro-
genation via related Ru systems,40 and our observations
provide strong circumstantial support for the accessibil-
ity of such an entity. The absence of spectroscopic
evidence for either a PPh3-free or a dihydride species
points toward operation of a highly active catalyst
present in low concentration. Favored candidates in-
clude Ru(H)2[η2-PC(H)P](L), formed by elimination of
the activated pincer carbon, and anionic [Ru(H)2(η3-
PCP)(L)]- (L ) ketone). In favor of the former are its
coordinative unsaturation and the enhanced flexibility
of such η2-pincer ligands (both factors that would
facilitate substrate entry and hence, catalytic activity).
In addition, the ease with which the η3-PCP structure
could be regenerated would give access to a stable
resting state, accounting for the thermal stability of the
catalyst, as well as the spectroscopic invisibility of the
η2-species.
F igu r e 4. In situ 31P{1H} NMR spectra of precursor
3‚PPh3 under transfer-hydrogenation conditions (2:1 2-pro-
panol/C7D8, N2 atmosphere, 20 equiv KOH): (a) before
addition of base, 22 °C; (b) 10 min after adding base, 22
°C; (c) after 10 min at 82 °C (spectrum measured at 82 °C);
(d) after 1 h at 82 °C (spectrum measured at 22 °C); (e)
after 3 days at 82 °C (spectrum measured at 22 °C).
Con clu sion s
The foregoing describes facile routes to the first group
8 complexes of a bulky, electron-rich η3-pincer ligand
containing cyclohexylphosphine groups. RuCl(η3-PCP)
(PPh3), 3, prepared via room-temperature reaction of
RuCl2(PPh3)3 with the PC(H)P ligand, provides a con-
venient entry point into complexes RuH(η3-PCP)(PPh3)-
(L) (L ) N2, H2). The triphenylphosphine ligand is
retained within all of these complexes, being displaced
only by carbon monoxide or, as judged from the catalytic
data, under transfer-hydrogenation conditions. Both
chloride and hydride complexes serve as precatalysts
for transfer hydrogenation of ketones, with activity
comparable to that of the arylphosphine complex 2b:
we speculate that a PPh3-free dihydride species such
as Ru(H)2[η2-PC(H)P](ketone) may be the most active
catalyst in each case. While the activity of related
species containing the flexible dcypb ligand is higher
by several orders of magnitude (TOF 9600 h-1 for
reduction of benzophenone), the robustness and tun-
ability of the pincer ligand scaffold offer enhanced
potential for asymmetric catalysis, and we are currently
pursuing development of chiral, PPh3-free versions of
these systems.
marized in Figure 4. After 10 min in the presence of
base and 2-propanol at ambient temperatures (nitrogen
atmosphere), the signals for 3 have nearly disappeared,
being replaced by two new A2B patterns assigned to 4b
and 4a (ratio 1:1; chemical shifts confirmed with
authentic samples). The signals due to 4b progressively
diminish as the NMR probe is warmed: at 82 °C, they
are no longer observed. After 1 h at 82 °C, the spectrum
is essentially unchanged: resonances for 4a dominate
the spectrum, accompanied by a new A2B pattern for
unknown 7 (<5% integrated intensity) at δ 57.3 and
45.0 (2J PP ) 23 Hz) and emerging signals for 5a /b. As
the probe is cooled back to room temperature, the
signals for 4b reappear, and a 1:1 integration relative
to 4a is reestablished (implying that the equilibrium
favors 4a at elevated temperatures), but the new signals
remain. Heating the NMR sample for 3 days at 82 °C
resulted in a color change from red to pale yellow:
dominating the 31P NMR spectrum are signals assigned
to hydride complexes 5b and 5a (chemical shifts con-
firmed by comparison to authentic samples).
The catalytic data indicate that the most active
catalytic species is formed by loss of both choride and
triphenylphosphine ligands from 3 and that maximum
activity requires a “pretreatment” period (reaction with
base in refluxing 2-propanol) as long as 1 h. The in situ
NMR experiments, however, show complete conversion
of 3 to monohydrides 4a /b in <10 min even at room
temperature. It may be inferred that the monohydride
complexes are not the catalytically most active species,
but a resting state which delivers this species, as van
Koten has proposed.34 Furthermore, the emergence of
dihydrogen complexes 5a /b under nitrogen strongly
suggests the intermediacy of a dihydride species. (The
Exp er im en ta l Section
Gen er a l P r oced u r es. All reactions were carried out at 22
°C under nitrogen atmosphere using standard Schlenk or
drybox techniques, unless stated otherwise. Reactions with H2
were carried out under 1 atm pressure, using Praxair UHP
grade H2, passed through a Deoxo cartridge and Drierite
column in series. CO (Praxair) was used as received. Dry,
oxygen-free solvents were obtained using an Anhydrous
Engineering solvent purification system and stored over Linde
4 Å molecular sieves. CDCl3, C6D6, and toluene-d8 were
dried over activated sieves (Linde 4 Å) and degassed by
43
consecutive freeze/pump/thaw cycles. RuCl2(PPh3)3 and 1,3-
10
(Cy2PCH2)2C6H4 were prepared as previously described.
(43) Hallman, P. S.; Stephenson, T. A.; Wilkinson, G. Inorg. Synth.
1970, 12, 237.

First Ru(η3-PCP) Cyclohexyl Pincer Complexes
Organometallics, Vol. 23, No. 17, 2004 4053
Ta ble 5. Deta ils of Cr ysta l Da ta a n d Str u ctu r e Refin em en t
3‚THF
4a ‚Et2O
5a
C56H74P3Ru
6
formula
fw
C
54H74ClOP3Ru
C54H77N2OP3Ru
964.16
C34H51ClO2P2Ru
690.21
968.56
941.13
temperature
wavelength
cryst syst, space group
unit cell dimens
203(2) K
0.71073 Å
triclinic, P1h
293(2) K
0.71073 Å
triclinic, P1h
203(2) K
0.71073 Å
monoclinic, P2(1)/c
a ) 18.886(3) Å
R ) 90°
203(2) K
0.71073 Å
triclinic, P1h
a ) 12.9390(8) Å
R ) 99.9870(10)°
b ) 14.2861(9) Å
â )100.7430(10)°
c ) 14.9545(9) Å
γ ) 93.3590(10)°
2662.9(3) Å3
2, 1.208 g/cm3
0.469 mm-1
a ) 11.3988(10) Å
R ) 91.4430(10)°
b ) 11.4641(10) Å
â ) 92.0320(10)°
c ) 19.3073(16) Å
γ ) 99.1330(10)°
2488.3(4)Å3
a ) 11.082(2) Å
R ) 94.222(2)°
b ) 11.568(2) Å
â ) 91.744(2)°
c ) 14.228(2) Å
γ ) 115.517(2)°
1637.8(4) Å3
2, 1.400 g/cm3
0.687 mm-1
724
b ) 14.2595(19) Å
â ) 107.256(2)°
c ) 19.073(3) Å
γ ) 90°
volume
4905.4(11) Å3
4, 1.274 g/cm3
0.453 mm-1
1996
Z, calcd density
absorp coeff
F(000)
2, 1.287 g/cm3
0.451 mm-1
1024
1024
cryst size, mm
θ range for data
collection
0.10 × 0.10 × 0.10
0.10 × 0.10 × 0.05
0.10 × 0.10 × 0.10
0.10 × 0.07 × 0.02
1.41 to 28.72°
1.06 to 26.37 °
1.13 to 28.71 °
1.44 to 28.74°
limiting indices
-17e h e 16,
-14 e h e 14,
-25 e h e 24,
-14 e h e 14,
-19 e k e 18, 0 e l e 20
20833/11993 [R(int) )
0.0299]
-14 e k e 14, 0 e l e 24
22227/10024 [R(int) )
0.0657]
0 e k e 19, 0 e l e 25
43750/11732 [R(int) )
0.0480]
-15 e k e15, 0 e l e 18
12803/7413 [R(int) )
0.0616]
no. of reflns collected/
unique
completeness to θ
max. and min. transmn
refinement method
86.8% to θ ) 28.72
0.928075 and 0.843640
full-matrix least-
squares on F2
98.3% to θ ) 26.37
0.928075 and 0.779621
full-matrix least-
squares on F2
92.5% to θ ) 28.71
1.000000 and 0.925298
full-matrix least-
squares on F2
87.3% to θ ) 28.74
0.928076 and 0.643412
full-matrix least-
squares on F2
no. of data/restraints/
params
11 993/0/518
10 024/0/553
11 732/36/527
7413/2/388
goodness-of-fit on F2
Ra
1.027
0.0515
1.024
0.0565
1.028
0.0580
1.025
0.0530
b
Rw
0.0766
0.0976
0.0976
0.0878
largest diff peak and
hole
1.709 and -0.428 e A-3
0.709 and -0.944 e A3
0.709 and -0.944 e A3
2.519 and -0.807 e A-3
R ) ∑||Fo| - |Fc||/∑||Fo|. Rw ) [∑wδ2/∑wFo
] .
a
b
2 1/2
Potassium tri(sec-butyl)borohydride was purchased from Al-
drich and used as received. 1H NMR (300 or 500 MHz) spectra
were recorded on a Bruker Avance-300 or AMX-500 spectrom-
eter; 31P NMR (121 MHz) and 13C NMR (75 MHz) on the
Bruker Avance-300. All 2D experiments were carried out on
the Avance-300 instrument. Solid state NMR spectra were
recorded on a Bruker ASX-200 MHz spectrometer (81 MHz
for 31P). IR spectra were measured on a Bomem MB100 IR
spectrometer. Microanalyses were carried out by Guelph
Chemical Laboratories Ltd., Guelph, Ontario.
in 4 mL of toluene was stirred for 24 h at RT under N2, then
stripped to a red oil, which crystallized on addition of 2-pro-
panol. Reprecipitation from hexanes/2-propanol afforded 100
mg (87%) of isomers 4a +4b. X-ray quality crystals of 4a were
obtained by slow evaporation of a diethyl ether solution. 1H
NMR (C6D6): δ 7.96 (t, Ar, J HH ) 7.5 Hz, 3H), 7.50 (t, Ar, J HH
3
) 7.0 Hz, 3H), 7.34 (d, CHmetaPCP, J HH ) 6.9 Hz, 2H), 7.24
3
(t, CHparaPCP, J HH ) 6.9 Hz, 1H), 7.15 (t, Ar, J HH ) 7.2 Hz,
2
3H), 7.04 (m, Ar, 6H), 3.48 (d, ArCHHP, J HH ) 14.9 Hz, 1H),
2
2
3.33 (d, ArCHHP, J HH ) 14.9 Hz, 1H), 3.01 (br d, J HH ) 16
Ru Cl(η3-P CP )(P P h 3)‚P P h 3 (3‚P P h 3). A mixture of RuCl2-
(PPh3)3 (0.505 g, 0.53 mmol), 1,3-(Cy2PCH2)2C6H4 (0.268 g, 0.54
mmol), and NEt3 (1 mL, excess) in 5 mL of toluene was stirred
under N2 for 18 h at 22 °C. Quantitative reaction was evident
by 31P{1H} NMR. The product was filtered through Celite,
stripped to an oil, and treated with cold 2-propanol to
precipitate a green solid. The solid was filtered off, washed
with 3 × 5 mL each of cold 2-propanol and hexanes, and dried
under vacuum. Yield of 3‚PPh3: 0.478 g (79%; isolated yields
are limited by the high solubility of the complex). X-ray quality
crystals of 3 deposited on slow evaporation of an ether solution.
(A solvating THF molecule is present, owing to earlier at-
2
Hz, 1H), 0.9-2.5 (br, Cy, 44H), -8.05 (dt, RuH, 4b, J HP
)
2
21.8 Hz, J HP ) 90 Hz), -12.2 (br s, RuH, 4a ). The signal at
-12.2 ppm resolves into a quartet (2J HP ) 19.5 Hz) in C7D8 at
253 K. Hydride T1(min): 333 ms (4b, 282 K, 500 MHz), 359
ms (4a , 278 K, 500 MHz). 31P{1H} NMR (C6D6): δ 59.6 (br s,
2
2P; 4a , PCP), 54.6 (d, 2P, J PP ) 14 Hz; 4b, PCP), 45.0 (t, 1P,
2J PP ) 17 Hz; 4a , PPh3), 28.8 (t, 1P, J PP ) 14 Hz; 4b, PPh3).
2
The signal at 59.6 ppm resolves into a doublet (2J PP ) 17 Hz)
in C7D8 at 253 K. IR (Nujol): ν(N2) 2134 (m), ν(RuH) 2114 (m)
cm-1. Anal. Calcd for C50H67N2P3Ru: C, 67.47; H, 7.59; N, 3.15.
Found: C, 67.56; H, 7.77; N, 3.14.
Ru H(η3-P CP )(H2)(P P h 3) (5). NMR-Sca le Exp er im en t.
A solution of 4b and 4a , generated by treating a C6D6 solution
(∼1 mL) of 3 (25 mg, 0.22 µmol) with KHBsBu3 (43.1 µL of a
1.0 M solution in Et2O), was placed under an atmosphere of
H2. Within minutes, the originally red/brown solution had
become yellow in color and no starting material was spectro-
tempts to crystallize the sample from THF/hexanes.) 1H NMR
3
(CDCl3): δ 7.0-8.2 (m, Ar, 30H), 6.79 (d, CHmetaPCP, J HH
)
7.1 Hz, 2H), 6.68 (t, CHparaPCP, 3J HH ) 7.2 Hz, 1H), 2.90 (dvt,
2
v
ArCHHP, J HH ) 16.7 Hz, J HP ) 5.2 Hz, 2H), 2.55 (br d,
ArCHHP, 2J HH ) 12.2 Hz, 2H), 0.7-2.2 (br, Cy, 44H). 31P{1H}
NMR (CDCl3): δ 80.9 (t, Ru-PPh3, 2J PP ) 32 Hz), 35.7 (d, PCP,
2J PP ) 32 Hz), -5.46 (s, PPh3 solvate). Solid state 31P{1H} CP/
MAS NMR (80.9 MHz): 82.7 (br s, Ru-PPh3), 34.1 (br s, PCP),
-6.1 (s, PPh3 solvate). Anal. Calcd for C68H81ClP4Ru: C, 70.48;
H, 7.05. Found: C, 70.37; H, 7.02. All analytical methods, with
the exception of X-ray diffraction, consistently reveal the
presence of 1 equiv of free PPh3 even after multiple reprecipi-
tations.
1
scopically observable. H NMR (C6D6): δ -4.34 (br s, Ru(H2),
5a ), -7.08 (br s, Ru(H2), 5b), -8.70 (q, RuH, 5a , 2J HP,cis ) 18.9
2
2
Hz), -10.64 (dt, RuH, 5b, J HP,cis ) 21.7 Hz, J HP,trans ) 80.1
Hz.) Dihydrogen T1(min) values at 500 MHz: 5a , 20 ms (265
K); 5b, 24 ms (265 K). 31P{1H} NMR (C6D6): δ 71.1 (d, 2P, 2J PP
2
) 15 Hz; 5b, PCP), 68.1 (d, 2P, J PP ) 18 Hz; 5a , PCP), 56.6
2
2
(t, 1P, J PP ) 18 Hz; 5a , PPh3), 37.1 (t, 1P, J PP ) 14 Hz; 5b,
PPh3). X-ray quality crystals of 5a were obtained by slow
evaporation of a benzene solution.
Ru H(η3-P CP )(N2)(P P h 3) (4). A mixture of 3‚PPh3 (150 mg,
0.13 mmol) and KHBsBu3 (136 µL of a 1.0 M solution in Et2O)

4054 Organometallics, Vol. 23, No. 17, 2004
Amoroso et al.
Ru Cl((η3-P CP )(CO)2 (6). A solution of 3 (83 mg, 0.093
mmol) in benzene (5 mL) was placed under an atmosphere of
CO, stirred at 294 K for 24 h, and then concentrated to
dryness. The yellow residue was redissolved in CH2Cl2 (∼0.25
mL) and cooled to -35 °C. Addition of cold Et2O (-35 °C,
1 mL) afforded a pale yellow solid, which was filtered off,
washed with cold Et2O (-35 °C, 3 × 1 mL), and dried under
vacuum. Yield: 56 mg (88%). 31P{1H} NMR (CDCl3): δ 62.4
(s). 1H NMR (CDCl3): δ 7.0 (m, Ar, 2H), 6.85 (m, Ar, 1H), 3.65
(m, CH2, 2H), 3.35 (m, CH2, 2H), 2.5 (m, aliphatic, 2H), 1.1-
2.2 (br, aliphatic, 42H). 13C{1H} NMR (CDCl3): δ 199.8 (t, 2J CP
diffraction data and unit-cell parameters for 5a were uniquely
consistent with the reported space group P21/ c (No. 14). The
structures were solved by direct methods, completed with
difference Fourier syntheses, and refined with full-matrix
2
least-squares procedures based on F
.
For complex 3, two molecules of THF solvent were found at
half-occupancy severely disordered in the asymmetric unit. For
4a ‚Et2O, one molecule of diethyl ether solvent was located in
the asymmetric unit. One cyclohexyl group in 5a and the
chloride and carbonyl ligands in 6 were found disordered with
a refined site occupancy of 50/50. All non-hydrogen atoms were
refined with anisotropic displacement coefficients, except the
solvent atoms for 3‚THF and the disordered cyclohexyl carbon
atoms for 5a , which were refined isotropically. All non-hydridic
hydrogen atoms were treated as idealized contributions. All
scattering factors are contained in the SHELXTL 6.12 program
library.45 Table 5 compiles the data for the structure deter-
minations.
Crystallographic data (excluding structure factors) have
been deposited with the Cambridge Crystallographic Data
Centre as CCDC publications 183904 (3‚THF), 232518
(4a ‚Et2O), 232519 (5a ), and 232520 (6). These data can be
obtained free of charge on application to the CCDC at 12 Union
Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033;
e-mail: deposit@ccdc.cam.ac.uk.
2
) 12 Hz, CO), 198.2 (t, J CP ) 7 Hz, CO). IR (Nujol, cm-1):
ν(CO) 2018 (s), 1945 (s). Anal. Calcd for C56H104N2Cl4P4Ru2:
C, 59.04; H, 7.44. Found: C, 59.16; H, 7.45. X-ray quality
crystals were obtained by slow evaporation of a benzene
solution.
Rep r esen ta tive P r oced u r e for Tr a n sfer Hyd r ogen a -
t ion . A toluene solution of 3‚PPh3 (0.10 mL, 0.020 M) was
mixed with KOH in 2-propanol (0.20 mL, 0.20 M) and heated
at 82 °C under N2. A color change from dark green to red
occurred within 5 min. After 1 h at reflux, a solution of
acetophenone in 2-propanol (1.7 mL, 1.18 M) was added by
syringe. The reaction was monitored for 4 h, sampling every
10 min for the first hour and every 30 min thereafter.
Conversions were determined by gas chromatography.
Con d ition s for in Situ NMR Exp er im en t. A solution of
3‚PPh3 (6 µmol) in 0.3 mL of C7D8 was mixed with a solution
of KOtBu (0.12 mmol) in 0.6 mL of 2-propanol and heated at
82 °C under N2. The solution was monitored by 31P{1H} NMR
spectroscopy over 3 days.
Str u ctu r a l Deter m in a tion for 3‚THF , 4a ‚Et2O, 5a , a n d
6. Suitable crystals were selected, mounted on thin glass fibers
using paraffin oil, and cooled to the data collection tempera-
ture. Data were collected on a Bruker AXS SMART 1k CCD
diffractometer using 0.3° ω-scans at 0°, 90°, and 180° in φ.
Initial unit-cell parameters were determined from 60 data
frames collected at different sections of the Ewald sphere.
Semiempirical absorption corrections based on equivalent
reflections were applied.44 No symmetry higher than triclinic
was observed in the diffraction data for 3‚THF, 4a ‚Et2O, or 6,
and solution in the centrosymmetric space group option, P1h
[No. 2], yielded chemically reasonable and computationally
stable results of refinement. Systematic absences in the
Ack n ow led gm en t. We thank Dr. Melanie Eelman
for her assistance. This work was supported by the
Natural Sciences and Engineering Research Council of
Canada, the Canada Foundation for Innovation, the
Ontario Innovation Trust, and the Conselho Nacional
de Desenvolvimento Cientifico e Tecnologico of Brazil
(in the form of a sabbatical fellowship to E.S.).
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data collection and refinement parameters, atomic coordinates,
bond lengths and angles, anisotropic displacement parameters,
and hydrogen coordinates for complexes 3, 4a , 5a , and 6. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM040025X
(45) Sheldrick, G. M. SHELXTL 6.12; Bruker AXS: Madison, WI,
2001.
(44) Blessing, R. Acta Crystallogr. 1995, A51, 33-38.