Terdentate RuX(CNN)(PP) (X = Cl, H, OR) complexes: Synthesis, properties, and catalytic activity in fast transfer hydrogenation

Article abstract of DOI:10.1021/om060408q

Terdentate ruthenium(II) complexes of general formula RuX(CNN)(dppb) (X = chloride, hydride, alkoxide; dppb = Ph₂P(CH₂) ₄PPh₂), where CNN is a deprotonated 2-aminomethyl-6- arylpyridine ligand, have been prepared. The orthometalated derivative RuCl(b)(dppb) (1) has been obtained by reaction of RuCl₂(PPh ₃)(dppb) with N,N-dimethyl-2-aminomethyl-6-(4-methylphenyl)pyridine (Hb) in 2-propanol and in the presence of triethylamine by elimination of PPh₃ and HCl. Similarly, RuCl(a)(dppb) (2) and the chiral analogue RuCl(c)(dppb) (3), containing primary amine ligands, have been isolated starting from 2-aminomethyl-6-(4-methylphenyl)pyridine (Ha) and (R)-2,2-dimethyl-1-(6- phenylpyridin-2-yl)-propylamine (Hc), respectively. The synthesis of the functionalized pyridines Ha-Hc is here described, whereas the crystal structure of 3 has been determined through an X-ray diffraction experiment. Treatment of 1-3 with sodium or potassium isopropoxide gives the corresponding hydrides RuH(b)(dppb) (4), RuH(a)(dppb) (5), and RuH(c)(dppb) (6) from the ruthenium isopropoxide complexes, via a β-H elimination process. Studies in solution show that the isopropoxides bearing a NH donor group are in equilibrium with the corresponding hydrides (5 and 6). Reaction of 5 with benzophenone leads to the alkoxide Ru(OCHPh₂)(a)(dppb) (7), which has been proven to interact with benzhydrol in C₆D₆, leading to the adduct 7·(HOCHPh₂), the alkoxide ligand, and the alcohol being in rapid exchange. Complexes 2 and 3 display a remarkable high catalytic activity for the transfer hydrogenation of ketones to alcohol in 2-propanol using a very small amount of catalyst. With the chiral complex 3 (0.005 mol %) methyl-aryl ketones can be quickly reduced (TOF ranging from 5.4 × 10⁵ to 1.4 × 10⁶ h^-1) with an enatiomeric excess up to 88%.

Full text of DOI:10.1021/om060408q

Organometallics 2006, 25, 4611-4620
4611
Terdentate RuX(CNN)(PP) (X ) Cl, H, OR) Complexes: Synthesis,
Properties, and Catalytic Activity in Fast Transfer Hydrogenation
Walter Baratta,*,† Marco Bosco,‡ Giorgio Chelucci,§ Alessandro Del Zotto,† Katia Siega,†
Micaela Toniutti,† Ennio Zangrando, and Pierluigi Rigo†
Dipartimento di Scienze e Tecnologie Chimiche, UniVersita` di Udine, Via Cotonificio 108,
I-33100 Udine, Italy, Serichim S.r.l., P.le F. Marinotti 1, I-33050 TorViscosa, Italy,
Dipartimento di Chimica, UniVersita` di Sassari, Via Vienna 2, I-07100 Sassari, Italy, and
Dipartimento di Scienze Chimiche, UniVersita` di Trieste, Via L. Giorgieri 1, I-34127 Trieste, Italy
ReceiVed May 12, 2006
Terdentate ruthenium(II) complexes of general formula RuX(CNN)(dppb) (X ) chloride, hydride,
alkoxide; dppb ) Ph2P(CH2)4PPh2), where CNN is a deprotonated 2-aminomethyl-6-arylpyridine ligand,
have been prepared. The orthometalated derivative RuCl(b)(dppb) (1) has been obtained by reaction of
RuCl2(PPh3)(dppb) with N,N-dimethyl-2-aminomethyl-6-(4-methylphenyl)pyridine (Hb) in 2-propanol
and in the presence of triethylamine by elimination of PPh3 and HCl. Similarly, RuCl(a)(dppb) (2) and
the chiral analogue RuCl(c)(dppb) (3), containing primary amine ligands, have been isolated starting
from 2-aminomethyl-6-(4-methylphenyl)pyridine (Ha) and (R)-2,2-dimethyl-1-(6-phenylpyridin-2-yl)-
propylamine (Hc), respectively. The synthesis of the functionalized pyridines Ha-Hc is here described,
whereas the crystal structure of 3 has been determined through an X-ray diffraction experiment. Treatment
of 1-3 with sodium or potassium isopropoxide gives the corresponding hydrides RuH(b)(dppb) (4),
RuH(a)(dppb) (5), and RuH(c)(dppb) (6) from the ruthenium isopropoxide complexes, via a â-H
elimination process. Studies in solution show that the isopropoxides bearing a NH donor group are in
equilibrium with the corresponding hydrides (5 and 6). Reaction of 5 with benzophenone leads to the
alkoxide Ru(OCHPh2)(a)(dppb) (7), which has been proven to interact with benzhydrol in C6D6, leading
to the adduct 7‚(HOCHPh2), the alkoxide ligand, and the alcohol being in rapid exchange. Complexes 2
and 3 display a remarkable high catalytic activity for the transfer hydrogenation of ketones to alcohol in
2-propanol using a very small amount of catalyst. With the chiral complex 3 (0.005 mol %) methyl-aryl
ketones can be quickly reduced (TOF ranging from 5.4 × 105 to 1.4 × 106 h-1) with an enatiomeric
excess up to 88%.
containing a diphosphine, prepared from 2-aminomethyl-6-(4-
methylphenyl)pyridine of formula RuX(CNN)(dppb) (X ) Cl,
H; dppb ) Ph2P(CH2)4PPh2), in which the CNN moiety is
connected to the metal via a sp2 aryl-carbon σ bond and one
sp2 and one sp3 N donor site, giving two stable five-membered
cyclometalated rings.3 To the best of our knowledge the
ruthenium complex 2 (Figure 1) is the most active transfer
hydrogenation catalytic precursor (TOF and TON up to 2.5 ×
106 h-1 and 1.7 × 105) for the reduction of ketones in basic
2-propanol reported to date.4
Introduction
The reduction of ketones using catalytic hydrogen-transfer
conditions, with 2-propanol as hydrogen source, has been largely
investigated in the last years, and several ruthenium complexes
have proven to be efficient catalyst precursors in transfer
hydrogenation.1 Many efforts have been made for designing
highly efficient catalysts for selective transformations, but for
large-scale application increasing activity and productivity of
catalytic reactions is still a target of primary importance.2
In the search for new catalytic systems we have recently
reported on novel terdentate complexes of ruthenium(II),
The pincer terdentate ligand is designed to combine the
2-aminomethylpyridine (ampy) moiety, which shows a particu-
larly high ligand acceleration effect in the ruthenium(II) transfer
hydrogenation of ketones,5 and 2-phenylpyridine derivatives,
* To whom correspondence should be addressed. E-mail: inorg@
dstc.uniud.it.
† Universita` di Udine.
‡ Present address: Sigea S.r.l., Area Science Park, Padriciano 99, I-34012
Trieste, Italy.
(2) (a) Blaser, H.-U.; Malan, C.; Pugin, B.; Spindler, F.; Steiner, H.;
Studer, M. AdV. Synth. Catal. 2003, 345, 103. (b) Blaser, H.-U.; Pugin, B.;
Spindler, F. J. Mol. Catal. A: Chem. 2005, 231, 1. (c) Blaser, H.-U.;
Schmidt, E. In Asymmetric Catalysis on Industrial Scale; Blaser, H.-U.,
Schmidt, E., Eds.; Wiley-VCH: Weinheim, 2004; p 1. (d) Everaere, K.;
Mortreux, A.; Carpentier, J. F. AdV. Synth. Catal. 2003, 345, 67. (e) Wills,
M.; Palmer, M.; Smith, A.; Kenny, J.; Walsgrove, T. Molecules 2000, 5, 4.
(f) Palmer, M. J.; Wills, M. Tetrahedron: Asymmetry 1999, 10, 2045.
(3) Baratta, W.; Chelucci, G.; Gladiali, S.; Siega, K.; Toniutti, M.;
Zanette, M.; Zangrando, E.; Rigo, P. Angew. Chem., Int. Ed. 2005, 44, 6214.
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Soc., Dalton Trans. 1999, 589. (b) Yang, H.; Alvarez, M.; Lugan, N.;
Mathieu, R. J. Chem. Soc., Chem. Commun. 1995, 1721. (c) Yang, H.;
Alvarez-Gressier, M.; Lugan, N.; Mathieu, R. Organometallics 1997, 16,
1401.
§ Universita` di Sassari.
Universita` di Trieste.
(1) (a) Zassinovich, G.; Mestroni, G.; Gladiali, S. Chem. ReV. 1992, 92,
1051. (b) Noyori, R.; Hashiguchi, S. Acc. Chem. Res. 1997, 30, 97. (c)
Gladiali, S.; Alberico, E. In Transition Metals for Organic Synthesis, 2nd
ed.; Beller, M., Bolm, C., Eds.; Wiley-VCH: Weinheim, 2004; Vol. 2, p
145. (d) Noyori, R.; Yamakawa, M.; Hashiguchi, S. J. Org. Chem. 2001,
66, 7931. (e) Pa`mies O.; Ba¨ckvall, J. E. Chem. Eur. J. 2001, 7, 5052. (f)
Ba¨ckvall, J. E. J. Organomet. Chem. 2002, 652, 105. (g) Samec, J. S. M.;
Ba¨ckvall, J. E.; Andersson, P. G.; Brandt, P. Chem. Soc. ReV. 2006, 35,
237. (h) Clapham, S. E.; Hadzovic, A.; Morris, R. H. Coord. Chem. ReV.
2004, 248, 2201. (i) Gladiali, S.; Alberico, E. Chem. Soc. ReV. 2006, 35,
226.
10.1021/om060408q CCC: $33.50 © 2006 American Chemical Society
Publication on Web 08/08/2006

4612 Organometallics, Vol. 25, No. 19, 2006
Baratta et al.
Figure 2.
presence of the -NH2 group is crucial in enhancing the activity
of the catalysts, in agreement with the “NH effect” extensively
described by Noyori and co-workers.11 Evidence has been
provided in systems containing the RuH/NH2 motif (bifunctional
catalysts) of a mechanism involving a concerted transfer of a
proton and of a hydride to the substrate, without coordination
of either alcohol or ketone to the metal and without formation
of a ruthenium alkoxide.11,12 It should be noted that in the case
of complex 2 containing the CNN ligand, the corresponding
hydride reacts with ketones to give the corresponding alkoxides,3
thus suggesting a possible different mechanism from that
proposed by Noyori.
As part of our current work dealing with the chemistry of
ruthenium complexes containing CNN ligands, we report herein
the synthesis and characterization of complexes of formula RuX-
(CNN)(dppb) (X ) Cl, H, or alkoxide) prepared from the
2-aminomethyl-6-arylpyridine-type ligands Ha-Hc (Figure 2).
In addition to the ligand Ha containing the NH2 group, the
N,N-dimethyl analogue Hb has been synthesized to prepare the
corresponding ruthenium complex RuCl(b)(dppb) (1) (Figure
1), with the aim to gain more insights in the mechanism of
transfer hydrogenation. Because asymmetric reduction of prochiral
ketones via hydrogen transfer represents an attractive route for
preparation of optically active alcohols, we have also isolated
the chiral analogue (R)-2,2-dimethyl-1-(6-phenylpyridin-2-yl)-
propylamine (Hc), by introducing chirality at the C-NH2 carbon
atom. The resulting new chiral ruthenium derivative RuCl(c)-
(dppb) (3) (Figure 1), which has also been characterized by a
structural X-ray analysis, displays a very high catalytic activity
for asymmetric transfer hydrogenation (TOF up to 1.4 × 106
h-1, ee up to 88%) with very low loading (0.005 mol %). The
reactivity of the ruthenium alkoxide complexes Ru(OR)(CNN)-
(dppb) and their role as key species in the catalytic transfer
hydrogenation is discussed.
Figure 1.
which are known to easily give access to CN orthometalated
ruthenium species. Complexes of monoanionic C-aryl ligands,
such as 2, belong to the class of pincer metal complexes
containing P- and N-donor atoms (ZCZ′; Z, Z′ ) N, P),6 which
have recently attracted much attention because of their relevance
in a number of metal-mediated organic transformations.7 In
particular, ruthenium complexes containing monoanionic ter-
dentate NCN and PCP ligands of the type [C6H3(CH2ZR2)2-
2,6]- (Z ) N or P) are active catalysts in base-cocatalyzed
hydrogen-transfer reactions of ketones with 2-propanol.8 In the
ligand the central aryl-carbon σ bond is complemented by two
sp3 N- or P-donor atoms. The presence of a metal-carbon bond
generally gives compounds with a high degree of thermal
stability and prevents to a large extent the metal dissociation
from the ligand. Fine-tuning of the catalytic properties of these
complexes can also be achieved by controlling the electronic
and steric properties of the substituents of the ZCZ′ ligand.
So far the majority of investigations with nitrogen-containing
pincer ligands have been focused on the NCN-type, while the
CNN motif has received much less attention. As a matter of
fact, only a few CNN complexes have been described, namely,
those prepared from BrC6H4(CH2N(Me)CH2CH2NMe2)-26a and
more recently the palladium(II) and platinum (II) derivatives
obtained from 6-phenyl-2-(2-aminoisopropyl)pyridine.9 It should
be noted that despite the importance that Ru compounds have
as mediators and catalysts of organic transformations,10 no
examples of “pincer” CNN Ru catalysts have been reported
before our communication.3
As found for several other ruthenium(II) complexes, the
catalytic activity of 2 in transfer hydrogenation is promoted by
addition of a base (iPrOH/NaOH), which leads to the formation
of the corresponding hydride, which is an active catalytic
species. It is worth pointing out that for the CNN ligands the
Results and Discussion
Synthesis of the Ligands Ha-Hc. The asymmetric 2,6-
functionalized pyridine ligands Ha and Hb were prepared
according to Scheme 1.
(5) (a) Baratta, W.; Da Ros, P.; Del Zotto, A.; Sechi, A.; Zangrando, E.;
Rigo, P. Angew. Chem., Int. Ed. 2004, 43, 3584. (b) Baratta, W.; Del Zotto,
A.; Esposito, E.; Sechi, A.; Toniutti, M.; Zangrando, E.; Rigo, P.
Organometallics 2004, 23, 6264. (c) Baratta, W.; Herdtweck, E.; Siega,
K.; Toniutti, M.; Rigo, P. Organometallics 2005, 24, 1660. (d) Baratta,
W.; Schu¨tz, J.; Herdtweck, E.; Herrmann, W. A.; Rigo, P. J. Organomet.
Chem. 2005, 690, 5570.
(6) (a) Rietveld, M. H. P.; Grove, D. M.; van Koten, G. New J. Chem.
1997, 21, 751. (b) Albrecht, M.; van Koten, G. Angew. Chem., Int. Ed.
2001, 40, 3750. (c) van der Boom, M. E.; Milstein, D. Chem. ReV. 2003,
103, 1759. (d) Singleton, J. T. Tetrahedron 2003, 59, 1837.
(7) (a) Ohff, M.; Ohff, A.; van der Boom, M. E.; Milstein, D. J. Am.
Chem. Soc. 1997, 119, 11687. (b) Miyazaki, F.; Yamaguchi, K.; Shibasaki,
M. Tetrahedron Lett. 1999, 40, 7379. (c) Gibson, S.; Foster, D. F.; Eastham,
G. R.; Tooze, R. P.; Cole-Hamilton, D. J. Chem. Commun. 2001, 779. (d)
Gupta, M.; Hagen, C.; Kaska, W. C.; Cramer, R. E.; Jensen, C. M. J. Am.
Chem. Soc. 1997, 119, 840. (e) Liu, F.; Pak, E. B.; Singh, B.; Jensen, C.
M.; Goldman, A. S. J. Am. Chem. Soc. 1999, 121, 4086. (f) Dani, P.; Karlen,
T.; Gossage, R. A.; Gladiali, S.; van Koten, G. Angew. Chem., Int. Ed.
2000, 39, 743. (g) Conner, D.; Jayaprakash, K. N.; Cundari, T. R.; Gunnoe,
T. B. Organometallics 2004, 23, 2724. (h) Amoroso, D.; Jabri, A.; Yap, G.
P. A.; Gusev, D. G.; dos Santos, E. N.; Fogg, D. E. Organometallics 2004,
23, 4047.
Thus, oxidation of 2-(4-methylphenyl)pyridine with hydrogen
peroxide in glacial acetic acid leads to the corresponding
N-oxide, which by treatment with dimethylcarbamyl chloride
and trimethylsilyl cyanide in dichloromethane gives 2-cyano-
6-(4-methylphenyl)pyridine in almost quantitative yield. Sub-
sequent reduction of the cyano group with LiAlH4 in THF-
Et2O leads in 46% yield to the amino pyridine ligand Ha, which
was finally converted into the N,N-dimethylamine ligand Hb
by reaction with formaldehyde in an aqueous solution of formic
acid (58% yield). The procedure described herein for the
synthesis of Ha is more straightforward with respect to the routes
reported for related 2-pyridylamines containing an aryl sub-
(11) (a) Haack, K.-J.; Hashiguchi, S.; Fujii, A.; Ikariya, T.; Noyori, R.
Angew. Chem., Int. Ed. Engl. 1997, 36, 285. (b) Yamakawa, M.; Ito, H.;
Noyori, R. J. Am. Chem. Soc. 2000, 122, 1466.
(8) Dani, P.; Karlen, T.; Gossage, R. A.; Gladiali, S.; van Koten, G.;
Angew. Chem., Int. Ed. 2000, 39, 743.
(9) Song, D.; Morris, R. H.; Organometallics 2004, 23, 4406.
(10) Naota, T.; Takaya, H.; Murahashi, S.-I. Chem. ReV. 1998, 98, 2599.
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Alonso, D. A.; Brandt, P.; Nordin, S. J. M.; Andersson, P. G. J. Am. Chem.
Soc. 1999, 121, 9580. (c) Rautenstrauch, V.; Hoang-Cong, X.; Churlaud,
R.; Abdur-Rashid, K.; Morris, R. H. Chem. Eur. J. 2003, 9, 4954.

Terdentate RuX(CNN)(PP) (X ) Cl, H, OR) Complexes
Organometallics, Vol. 25, No. 19, 2006 4613
Scheme 1
the two N-methyl groups give a relatively sharp singlet at δ
1.77. Upon cooling, the latter signal broadens, revealing a
coalescence temperature of about -50 °C and leading at -90
°C to two resonances at δ 1.79 and 1.29 for two nonequivalent
methyl groups, indicating that the dynamic process involving
the methyl groups can be frozen out. The approximation to the
Eyring equation ∆Gq ) RTc[22.96 + ln(Tc/∆ν)]17 (∆ν ) 100
Hz) affords a relatively low value for ∆Gq
(10.5 ( 0.2
223
kcal/mol) of the fluxional process. The 13C{1H} NMR spectrum
at room temperature shows one signal for the CH2 at δ 70.7
and one single resonance for the two Me groups at δ 50.7,
shifted downfield of δ 4.1 and 5.0, respectively, compared to
the free ligand, and indicating that the NMe2 group is coordi-
nated to the metal center. Conversely, the 13C{1H} NMR
spectrum at -90 °C reveals two signals at δ 50.6 and 50.0 for
two N-methyl groups, whereas the orthometalated carbon
resonance appears at low field15a,18 at δ 174.6 as a doublet of
doublets (2J(CP) ) 17.8 and 7.5 Hz).19 Addition of [PPh4]Cl
to 1 in CD2Cl2, aiming to prevent a possible chloride dissociation
from the complex, does not affect the 1H and 31P NMR spectra.
Therefore, these data suggest that 1 exhibits a hemilabile
terdentate CNN ligand with the NMe2 group that undergoes an
easy pyramidal inversion at the nitrogen atom through decoor-
dination from the Ru metal center, favored by the presence of
the aryl group, exerting a strong trans influence.20 Despite the
fact the N-alkyl substituents are expected to increase the
σ-donating properties of the N atom, it is generally accepted
that the metal-nitrogen bond is intrinsically weaker for tertiary
amine ligands, compared to the primary or secondary ones. This
has been ascribed to different factors, such as elongation due
to the steric hindrance and elimination of intra- or intermolecular
M-N-H‚‚‚X hydrogen bonds with a decrease of the outer
sphere solvation energy of the complex.21
stituent in the 6-position of the pyridine ring, using 6-bromopi-
colylaldehyde13 or 2,6-dibromopyridine9 as starting compounds.
The optically active ligand Hc has been obtained in high yield
by trifloroacetic acid-mediated hydrolysis of the recently de-
scribed (SS,R)-N-(p-toluenesulfinyl)-2,2-dimethyl-1-(6-phenylpy-
ridin-2-yl)propylamine, in turn accessible in 98% de via dia-
stereoselective reduction of the related enantiopure N-p-tolu-
enesulfinylpyridyl ketimine14 (eq 1).
CNN Ruthenium(II) Chloride Complexes. It is well known
that cyclometalated CN and CNN ruthenium complexes involv-
ing the 2-phenylpyridine and the 6-phenyl-2,2′-bipyridine motifs
have been prepared through direct metalation in the ortho
position of the aryl group, resulting in stable five-membered
chelate rings.15 Alternatively, some CN complexes have also
been obtained in high yield via transmetalation using Ar2Hg.16
We have found that when the functionalized pyridine Hb,
displaying a NMe2 group, is allowed to react with RuCl2(PPh3)-
(dppb) in 2-propanol at reflux and in the presence of triethyl-
amine, the orthometalated ruthenium(II) complex 1 is easily ob-
tained by displacement of PPh3 and elimination of HCl (eq 2).
Reaction of RuCl2(PPh3)(dppb) with the ligand Ha, showing
a NH2 group instead of NMe2, leads to complex 2, which was
isolated in high yield (eq 2). By comparison with 1, the reaction
for 2 requires a shorter time (2 h) to be completed, suggesting
that orthometalation occurs more easily. The VT 1H NMR
measurements of 2 (CDCl2CDCl2) show that the broad reso-
nance at δ 3.41 (at 20 °C), attributable to one NH2 proton, which
undergoes H/D exchange in basic (NaOH) D2O, is still distinct
at 60 °C, indicating that decoordination of the NH2 moiety in 2
is more hindered compared to that of the NMe2 group in 1.
(13) Chang, C.; Lim, K.; Chen, Q.; Zubieta, J.; Canary, J. W. Inorg.
Chem. 1995, 34, 2562.
(14) (a) Chelucci, G.; Baldino, S.; Chessa, S. Tetrahedron 2006, 62, 619.
(b) Chelucci, G.; Baldino, S.; Solinas, R.; Baratta, W. Tetrahedron Lett.
2005, 46, 5555.
(15) (a) Toner, A. J.; Gru¨ndemann, S.; Clot, E.; Limbach, H. H.;
Donnadieu, B.; Sabo-Etienne, S.; Chaudret, B. J. Am. Chem. Soc. 2000,
122, 6777. (b) Guari, Y.; Sabo-Etienne, S.; Chaudret, B. J. Am. Chem. Soc.
1998, 120, 4228. (c) Bardwell, D. A.; Cargill Thompson, A. M. W.; Jeffery,
J. C.; McCleverty, J. A.; Ward, M. D. J. Chem. Soc., Dalton Trans. 1996,
873. (d) Bonnefous, C.; Chouai, A.; Thummel, R. P. Inorg. Chem. 2001,
40, 5851.
(16) Clark, A. M.; Rickard, C. E. F.; Roper, W. R.; Wright, L. J.
Organometallics 1999, 18, 2813.
(17) Gu¨nther, H. NMR Spectroscopy: Basic Principles, Concepts, and
Applications in Chemistry, 2nd ed.; John Wiley & Sons: New York, 1995;
Chapter 9.
(18) Koizumi, T.; Tomon, T.; Tanaka, K. Organometallics 2003, 22, 970,
and references therein.
(19) Attempts to detect at room temperature the orthometalated carbon
signal of 1 failed, probably because of the fluxional behavior of this complex.
(20) (a) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. ReV.
1973, 10, 335. (b) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke R.
G. In Principles and Application of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987. (c) Toledo, J. C.; Lima
Neto, B. S.; Franco, D. W. Coord. Chem. ReV. 2005, 249, 419.
(21) Meyerstein, D. Coord. Chem. ReV. 1999, 185-186, 141.
In the solid state the yellow, thermally stable derivative 1
can be kept in air, but in solution it is fairly oxygen sensitive
and decomposes if air is admitted. The 31P{1H} NMR spectrum
of 1 in CD2Cl2 shows two doublets at δ 50.8 and 35.5 with
2J(PP) ) 37.3 Hz, and these data do not change significantly
in the range of temperatures between +30 and -90 °C. In the
1H NMR spectrum at room temperature the protons of the NCH2
moiety are at δ 3.50 and 3.09 with 2J(HH) ) 13.6 Hz, whereas

4614 Organometallics, Vol. 25, No. 19, 2006
Baratta et al.
Table 1. Crystal Data and Details of Structure Refinements
of 3
formula
fw
C44H47ClN2P2Ru
802.30
cryst syst
space group
a (Å)
orthorhombic
P 212121
12.047(3)
15.900(3)
21.476(5)
4113.7(16)
4
1.295
0.555
1664
b (Å)
c (Å)
V (Å3)
Z
D
calc (g cm-3
)
µ(Mo KR) (mm-1
F(000)
)
θ range
1.59-29.66
no. of reflns collected
no. of unique reflns
no. of observed reflns I > 2σ(I)
no. of params refined
Flack parameter
47 070
10 978 [Rint ) 0.0360]
9416
451
-0.020(19)
0.975
0.0340
0.0832
0.685, -0.311
Figure 3. Molecular structure of 3 (ORTEP drawing, thermal
ellipsoids at 40% probability level).
goodness-of-fit (F2)
R1 (I > 2σ(I))a
(2.055(2) Å) compared to the corresponding values measured
in cis-RuCl2(diphosphine)(ampy) complexes (2.138(2)-2.148-
(2) Å).5c This fact may be ascribed to the geometrical constraints
of the terdentate ligand, showing narrow C(1)-Ru-N(1) and
N(1)-Ru-N(2) bond angles (80.97(10)°, 75.50(9)°). In addi-
tion, the Ru-N amino bond distance (2.221(2) Å) is similar to
that of 2 (2.246(3) Å) and significantly longer than that found
in the aforementioned ampy complexes (2.104(3)-2.116(2) Å)
that display the NH2 group trans to a chloride, in agreement
with the higher trans influence of the aryl compared to the
chloride ligand. The carbon bearing the tBu group and the amino
nitrogen N(2) are displaced by +0.059(4) and -0.647(4) Å,
respectively, from the best-fit plane through the terdentate
ligand. This arrangement leads one N-H bond to be almost
parallel to the Ru-Cl bond (H-N(2)-Ru-Cl dihedral angle
of about 8.2°, with a H‚‚‚Cl distance of 2.62 Å), suggesting a
possible intramolecular hydrogen bond interaction.23 As for 2,
there is also a relatively short contact between the pyridine
nitrogen atom and the ipso carbon atom C(21) of the phosphine
phenyl (3.12 Å), indicating a stacking between the pyridine and
phenyl rings. Similar features have also been observed in 2 and
in cis-RuCl2(diphosphine)(ampy) complexes. Consequently,
solid-state studies and NMR data in solution for 1-3 are
consistent with the relatively weak σ-donation of the amino
group to the ruthenium center in the CNN ligands, because of
the trans influence of the aryl group, with the Ru-NH2 bond
being stronger than the Ru-NMe2 one.
CNN Ruthenium(II) Hydride Complexes. The chemistry
of transition metal hydrides continues to attract a great deal of
attention because of the unique M-H bonding properties (e.g.,
insertion reactions, acidic vs hydridic character, hydrogen-
bonding interactions) that allow the use of these species in
stoichiometric reactions and catalysis.24 Among the different
procedures for obtaining late transition metal hydride complexes,
a method generally employed entails the reaction of halide
precursor complexes with sodium or potassium alkoxides
displaying a hydrogen in the â-position. The resulting covalent
metal alkoxides are generally reactive intermediates that undergo
a facile â-hydrogen elimination reaction, affording hydride
complexes (alkoxide route).25 When the ruthenium complex 1
wR2a
∆F (e Å-3
)
2
2
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|, wR2 ) [∑w(Fo - Fc )2/∑w(Fo )2]1/2
.
Table 2. Selected Bond Distances (Å) and Angles (deg) for 3
Ru-C(1)
Ru-N(1)
Ru-N(2)
2.047(3)
2.055(2)
2.221(2)
Ru-P(1)
Ru-P(2)
Ru-Cl(1)
2.251(1)
2.295(1)
2.498(1)
C(1)-Ru-N(1)
C(1)-Ru-N(2)
C(1)-Ru-P(1)
C(1)-Ru-P(2)
C(1)-Ru-Cl(1)
N(1)-Ru-N(2)
N(1)-Ru-P(1)
N(1)-Ru-P(2)
80.97(10)
154.71(9)
86.70(7)
105.54(7)
88.95(7)
75.50(9)
92.70(6)
170.64(6)
N(1)-Ru-Cl(1)
N(2)-Ru-P(1)
N(2)-Ru-P(2)
N(2)-Ru-Cl(1)
P(1)-Ru-P(2)
P(1)-Ru-Cl(1)
P(2)-Ru-Cl(1)
C(12)-N(2)-Ru
82.86(6)
103.37(6)
96.86(6)
79.15(6)
94.36(3)
174.23(3)
90.46(2)
109.63(16)
The 13C{1H} NMR resonance of the terdentate ligand of 2
presents a signal at δ 52.5 for the NH2CH2 moiety, shifted
downfield by about δ 4.3 compared to the free ligand, similarly
to 1. The resonance of the orthometalated carbon is at δ 181.8,
strongly shifted downfield with respect to the free ligand a (∆δ
2
54.8) and coupled with two phosphorus atoms with J(CP) )
16.3 and 7.8 Hz, as for 1.
According to eq 2, the chiral complex 3 can be prepared
by reaction of RuCl2(PPh3)(dppb) with the ligand Hc. The
31P{1H} NMR spectrum displays two doublets similar to those
of 2, indicating that 3 is present in solution as a single
stereoisomer with chirality at the metal center.22 The H and
1
13C NMR data are related to those of 2 and are in agreement
with the formation of a terdentate CNN complex. The molecular
structure of 3 was confirmed by X-ray analysis carried out on
a single crystal. Crystallographic data are summarized in Table
1, and selected bond distances and angles are reported in Table
2. The ruthenium center of 3 is in a pseudo-octahedral
environment with the orthometalated c ligand bound to the metal
in a terdentate fashion, forming two five-membered chelate rings
t
(Figure 3).With respect to the terdentate ligand plane, the Bu
group bound to the chiral carbon atom (R configuration) is
pointing to the side of the chloride, away from the phosphine
phenyl groups. The solid-state structural features of 3 are closely
related to those described for 2.3 The Ru-N1 bond length of
the pyridine trans to the phosphorus atom is significantly shorter
(23) (a) Steiner, T. Angew. Chem., Int. Ed. 2002, 41, 48. (b) Brammer,
L. Dalton. Trans. 2003, 3145. (c) Peris. E.; Lee, G. C.; Rambo, J. R.;
Eisenstein, O.; Crabtree, R. H. J. Am. Chem. Soc. 1995, 117, 3485. (d)
Yap, G. P. A.; Rheingold, A. L.; Das, P.; Crabtree, R. H. Inorg. Chem.
1995, 34, 3474. (e) Aullo´n, G.; Bellamy, D.; Brammer, L.; Bruton, E. A.;
Orpen, A. G. Chem. Commun. 1998, 653.
(22) (a) Cyr, P. W.; Patrick, B. O.; James, B. R. Chem. Commun. 2001,
1570. (b) Fogg, D. E.; James, B. R. Inorg. Chem. 1997, 36, 1961. (c)
Schlu¨nken, C.; Esteruelas, M. A.; Lahoz, F. J.; Oro, L. A.; Werner, H.
Eur. J. Inorg. Chem. 2004, 2477. (d) Pinto, P.; Marconi, G.; Heinemann,
F. W.; Zenneck, U. Organometallics 2004, 23, 374.
(24) Jacobsen, H.; Berke H. In Recent AdVances in Hydride Chemistry;
Peruzzini, M., Poli R., Eds.; Elsevier: Amsterdam, 2001; Chapter 4, p 89.

Terdentate RuX(CNN)(PP) (X ) Cl, H, OR) Complexes
Organometallics, Vol. 25, No. 19, 2006 4615
Scheme 2
is treated with 1.5 equiv of NaOiPr in 2-propanol-toluene at
room temperature, the solution quickly turns red, affording an
intermediate alkoxide, as inferred by 31P{1H} NMR spectros-
copy (δ 46.4 and 35.8, 2J(PP) ) 32.5 Hz, C6D6 (10% in volume)
as inside lock) (Scheme 2).
reaction is carried out in a single solvent, slow or poor
conversion is observed. It is likely that the favorable effect of
2-propanol, which displays good polarity favoring the dissocia-
tion of the chloride, for the ruthenium alkoxide formation may
be due to an acid/conjugate base metathesis approach, according
to the route suggested by Bergman for the preparation of late
transition metal amido complexes using NaNH2 in the presence
of its conjugate acid NH3 in THF.28 Employment of potassium
isopropoxide with 2 leads the reaction to be completed at room
temperature in a few minutes, suggesting that the reactivity is
affected by the different ion pairing of potassium vs sodium
isopropoxide in 2-propanol.29 We want to point out that, by
contrast to 4, heating the ruthenium isopropoxide solution re-
sults in the reversible formation of the hydride 5, as inferred
by 31P{1H} NMR spectroscopy. As a matter of fact, a solution
prepared from 2 and NaOH (molar ratio ) 1/2) in 2-propanol-
C6D6 shows the presence of the Ru-isopropoxide as essentially
the only product at 20 °C, whereas at higher temperatures the
Ru-H/Ru-alkoxide ratio increases (i.e., about 1:2 at 60 °C),
indicating that the formation of the hydride is an endothermic
process. Due to the lability of this system, the hydride complex
5 can be isolated from the reaction mixture by shifting the
equilibrium reaction to the right, removing acetone through
evaporation of the 2-propanol-toluene media (Scheme 2). The
1H NMR spectrum of 5 shows the hydride signal at δ -5.58
(dd, 2J(HP) ) 89.1, 26.4 Hz), close to that of the NMe2
derivative 4, with two broad resonances at δ 2.75 and 1.02 for
the nonequivalent NH2 protons. A 1H-1H NOESY experiment
shows contacts of the Ru-H with two different ortho phenyl
protons and with both N-H protons, but no exchange has been
apparently observed. The Ru-H stretching bands of 5 and 4 are
1743 and 1811 cm-1, respectively, and these low wavelengths
are in agreement with the presence of a phosphine trans to
hydride. Furthermore, the significantly lower value for 5
compared to 4 can be ascribed to a possible RuH‚‚‚HN hydrogen
bonding interaction. Complex 5 can be easily protonated by
weak acids, such as CH3COOH, leading to the corresponding
acetate derivative via elimination of dihydrogen, as will be
described elsewhere. Dissolution of 5 in CHCl3 or CH2Cl2
results in the fast conversion into the chloride 2, indicating that
the hydride 5 is highly active and halogenated solvents cannot
be employed. Examination of the reactivity of the hydrides 4
and 5 with acetone in C6D6 in the presence of 2-propanol shows
As will be described in a further part of this work, all
ruthenium alkoxides of this type assume a red-orange color and
are characterized by a 2J(PP) of about 32-34 Hz, which differ
significantly from those of the chloride and hydride complexes.
Heating of this solution above 50 °C results in the slow and
irreversible formation of the hydride complex 4 through
elimination of acetone. The 31P{1H} NMR spectrum of 4 in
C6D6 at room temperature exhibits two doublets at δ 62.5
and 30.4, the latter being trans to the hydride as proven by a
1H-coupled 31P NMR measurement, with a significantly small
phosphorus-phosphorus coupling constant (2J(PP) ) 15.5 Hz),
compared to that of the chloride analogue (2J(PP) ) 37.3 Hz).
1
The H NMR signal for the hydride appears as a doublet of
doublets at δ -5.79 with 2J(HP) ) 87.7 and 28.6 Hz, in
agreement with the data reported for other ruthenium hydride
complexes bearing the phosphorus atoms trans and cis to the
hydride, respectively.26 At room temperature the CH2NMe2
moiety presents two doublets at δ 3.25 and 2.61 (2J(HH) )
13.3 Hz) for the nonequivalent methylene protons, whereas the
methyl groups show two resonances at δ 2.13 and 2.10, at
variance with 1. This clearly indicates that replacement of
the chloride with a hydride leads to a stronger coordinated
NMe2 amino group, and this is likely to be ascribed to the lesser
steric hindrance of H vs Cl. In addition, for the chloride deriv-
ative a π-donation of the adjacent lone pairs of the halide can
also promote the opening of the arm trans to the aryl group,
destabilizing the six-coordinate complex vs the corresponding
16-electron species.27
Reaction of 2 with NaOiPr in 2-propanol-toluene gives at
50 °C a red solution containing a ruthenium alkoxide species
as the main product, as inferred by 31P{1H} NMR spectroscopy
2
(δ 54.3 and 44.6, J(PP) ) 34.2 Hz, C6D6 lock) (Scheme 2).
The use of a mixture of 2-propanol-toluene (1:1 in volume) is
necessary for the solubilization of both the ruthenium chloride
2 and sodium isopropoxide, leading quickly to the ruthenium
alkoxide and formation of NaCl. As a matter of fact, when the
(25) (a) Nolan, S. P.; Belderrain, T. R.; Grubbs R. H. Organometallics
1997, 16, 5569. (b) Esteruelas M. A.; Sola. E.; Oro L. A.; Werner H.; Meyer
U. J. Mol. Catal. 1988, 45, 1. (c) Chaudret, B. N.; Cole-Hamilton, D. J.;
Nohr, R. S.; Wilkinson, G. J. Chem. Soc., Dalton Trans. 1977, 1546.
(26) (a) Bianchini, C.; Frediani, P.; Masi, D.; Peruzzini, M.; Zanobini,
F. Organometallics 1994, 13, 4616. (b) Hsu, G. C.; Kosar, W. P.; Jones,
W. D. Organometallics 1994, 13, 385. (c) Drouin, S. D.; Amoroso, D.;
Yap, G. P. A.; Fogg, D. E. Organometallics 2002, 21, 1042.
(28) Kaplan, A. W.; Ritter, J. C. M.; Bergman, R. G. J. Am. Chem. Soc.
1998, 120, 6828.
(29) (a) Bradley, D. C.; Mehrotra, R. C.; Rothwell, I. P.; Singh, A. In
Alkoxo and Aryloxo DeriVatiVes of Metals; Academic Press: New York,
2001; Chapter 2. (b) Bagno, A.; Montanari, S.; Paradisi, C.; Scorrano, G.
Eur. J. Org. Chem. 2000, 1953. (c) Crampton, M. R.; Gibson, B.; Gilmore,
F. W. J. Chem. Soc., Perkin Trans. 2 1979, 91.
(27) Caulton, K. G. New J. Chem. 1994, 18, 25.

4616 Organometallics, Vol. 25, No. 19, 2006
Baratta et al.
Scheme 3
that the two complexes have a substantially different behavior.
As a matter of fact, the presence of the NH2 group in 5 leads to
the thermodynamically stable and kinetically labile isopropoxide
species, with respect to the hydride-acetone system. For the
NMe2 derivative 4 the â-hydrogen elimination is a relatively
slow and irreversible process, the reaction being completely
shifted to the right. The stability of the isopropoxide bearing a
NH2 group can be tentatively ascribed to the lesser steric
bulkiness of the H vs Me, in combination with the possible
formation of a O‚‚‚H hydrogen bond.
alkoxide 7. Furthermore, the doublet at δ ) 5.50 (3J(HH) )
7.6 Hz) is for one proton of the pyridine in the position 5, as
1
established via a H-1H COSY experiment, shifted upfield
compared to those in 2 and 5 and which may be due to a possible
interaction between the pyridine ring and a phenyl of the
alkoxide. The 13C NMR spectrum of the complex in benzene-
d6 displays a signal at 80.1, shifted downfield compared to
benzhydrol (∆δ ) 4.0). This value can be compared with those
of other transition metal alkoxide complexes, which show a
similar trend.32 Addition of benzhydrol in about 1:1 molar ratio
results in the formation of a new species, 8, which can be
ascribed to an alkoxide-alcohol adduct, in equilibrium with
the original alkoxide 7.33,34 Interestingly, this new complex 8
displays two doublets in the 31P NMR spectrum at δ ) 55.0
Similarly to 2, treatment of the chiral precursor 3 with
potassium isopropoxide in 2-propanol-toluene at room tem-
perature affords a mixture of the ruthenium isopropoxide species
(31P{1H} NMR: δ 53.6 and 46.2 with 2J(PP) ) 34.6 Hz, C6D6
lock) and the ruthenium hydride 6 (31P{1H} NMR: δ 64.8 and
2
and 42.8 with a J(PP) ) 34.2 Hz, a value identical to that of
2
the alkoxide 7. Addition of alcohol leads to the increase of the
signals for 8, with a high-field resonance that shifts progressively
to lower field (δ up to 45.0). In the 1H NMR spectrum the signal
at δ ) 5.45 is for the benzhydrol OCH moiety, which is in
rapid exchange with the coordinated OCH group at 4.80, as
revealed through a 1H 1D sel-NOESY experiment. As a matter
of fact, the latter signal is converted into that of benzhydrol in
70 ms (plateau, 40% conv.), following an exponential behavior.
This clearly indicates that the alkoxide in Ru(amine)(alkoxide)
exchanges rapidly with alcohol, and this process can be possibly
mediated via a RuOR‚‚‚HOR hydrogen bond, according to the
studies of Bergman and other authors.33 By increasing the
temperature to about 50 °C the two OCH signals (and also the
low-field NH resonance) disappear in the baseline, leading at
70 °C to only one broad signal at δ ) 5.10. The NCH2 group
shows a singlet at δ ) 3.22 for the two protons, apparently not
coupled with the NH protons, probably because of their fast
exchange, whereas the carbon signal is, at δ ) 52.0, almost
identical to that of 7, indicating that the nitrogen is coordinated
as amine to ruthenium. At room temperature the CH3 groups
of the tolyl moiety of 7 and 8 are at δ ) 2.28 and 2.35, while
at higher temperature they broaden, leading to a singlet at δ )
2.29 at 70 °C. Also in the 31P NMR spectra the signals of 7
and 8 broaden when the temperature is increased, and at about
70 °C the two species lead only to two resonances at δ ) 57.2
and 39.5, indicating that these complexes are involved in a fast
exchange process. Furthermore, at temperatures higher than 70
°C, the spectra show the signals of the hydride 5, which
equilibrates with the species 7 and 8. The reversible insertion
of a ketone into the metal-hydride bond has been described
previously by Hoffmann on a rhenium isopropoxide system.35
On the other hand, there are only a few reports on stable
ruthenium alkoxides obtained through Ru-H insertion of ketones,
namely, those containing electron-withdrawing group, such as
35.3 with J(PP) ) 16.5 Hz) in 4:1 molar ratio, respectively.
Likewise to the alkoxide prepared from 2, heating the solution
results in shifting the equilibrium toward the hydride complex,
with a Ru-isopropoxide/Ru-H molar ratio of about 1.5:1 and
1:3 at 50 and 70 °C, respectively. The hydride 6 shows a doublet
2
of doublets at δ -5.59 (dd, J(HP) ) 89.8, 26.1 Hz), which
are values very close to those of the hydrides 4 and 5. Attempts
to isolate 6 by removing acetone failed, leading to a mixture of
6 (about 70%) and the isopropoxide as main products.
Reaction of the Ruthenium Hydride 5 with Ketones.
Insertion of unsaturated compounds into a metal-hydrogen bond
is a fundamental step of stoichiometric and catalytic transforma-
tions.30 However, insertion of ketones into a Ru-H bond is
sparingly documented,31 whereas the reverse â-hydrogen elimi-
nation is a well-exploited procedure for the synthesis of ruthen-
ium hydrides.25 Reaction of the hydride 4 with an equimolar
amount of different ketones, such as acetone or benzophenone,
results in no formation of the corresponding alkoxides, as
observed by NMR measurements. By contrast when complex
5 in d8-toluene is treated with benzophenone, insertion of the
carbonyl group into the Ru-H bond occurs promptly, as
depicted in Scheme 3.
The 31P NMR spectrum of 7 shows two doublets at δ ) 57.0
and 37.3, showing a 2J(PP) ) 34.2 Hz, which is similar to those
of the ruthenium isopropoxide intermediates obtained from 1
and 2. In the 1H NMR spectrum the resonance at 4.80 is for the
alkoxide CH group, and by cooling at 0 °C it turns into a doublet
4
1
with a J(HP) ) 3.7 Hz, as inferred through a H{31P} NMR
experiment, which indicates that the alkoxide is directly bound
to ruthenium. The broad signal at δ ) 5.30 is for one proton of
the amine group at low field, compared to the other amine proton
(δ ) 1.45), and this large difference may be consistent with a
NH‚‚‚O hydrogen bond interaction, which could stabilize the
(30) (a) Espinet, P.; Albe´niz, A. C. In Fundamentals of Molecular
Catalysis; Current Methods in Inorganic Chemistry Vol. 3; Kurosawa, H.,
Yamamoto, A., Eds.; Elsevier: Amsterdam, 2003; Chapter 6, p 293. (b)
Koga, N.; Morokuma, K. Chem. ReV. 1991, 91, 823.
(31) (a) Hayashi, Y.; Komiya, S.; Yamamoto, T.; Yamamoto, A. Chem.
Lett. 1984, 1363. (b) Daley, C. J. A.; Bergens, S. H. J. Am. Chem. Soc.
2002, 124, 3680.
(32) (a) Sanford, M. S.; Henling, L. M.; Day, M. W.; Grubbs, R. H.
Angew. Chem., Int. Ed. 2000, 39, 3451. (b) Liang, F.; Schmalle, H. W.;
Fox, T.; Berke, H. Organometallics 2003, 22, 3382. (c) Chen, Z.; Schmalle,
H. W.; Fox, T.; Berke, H. Dalton Trans. 2005, 580.
(33) Fulton, J. R.; Holland, A. W.; Fox, D. J.; Bergman, R. G. Acc. Chem.
Res. 2002, 35, 44.

Terdentate RuX(CNN)(PP) (X ) Cl, H, OR) Complexes
Organometallics, Vol. 25, No. 19, 2006 4617
CF3,31a or ketoesters, which can lead to bidentate alkoxides.31b
Although it has been well established that NH hydrogens
increase the activity of ruthenium catalysts in hydrogenation,
far less is known about the role of these hydrogen in stabilizing
Ru-O species, such as alkoxides or carboxylates. Interestingly,
Koike and Ikariya have reported that the presence of NH
hydrogens allows insertion of carbon dioxide into the Ru-H
bond.36 Furthermore, these authors and Morris have given
evidence of the formation of ruthenium alkoxide-amine spe-
cies.37
Table 3. Catalytic Transfer Hydrogenation of Methyl-Aryl
Ketones with Complex 3a
Addition of acetophenone to the hydride 5 in C6D6 leads to
the corresponding alkoxide Ru(OCHMePh)(a)(dppb) with 31P
NMR data (δ ) 56.1 and 37.9; 2J(PP) ) 34.3 Hz) that resemble
those of 7, whereas addition of 1-phenylethanol (2 equiv) leads
2
to a new alcohol adduct at δ ) 54.5 and 41.6 with a J(PP) )
33.8 Hz in equilibrium with the alkoxide. By addition of
subsequent amounts of alcohol the latter resonance shifts to
lower field (to 46.2) as for 8, the four doublets being relatively
broad (∆ν1/2 ≈ 70 Hz), indicating that a rapid exchange process
occurs between the alkoxide and the alkoxide-alcohol adduct.
Therefore, our NMR data show that the Ru alkoxides of the
type Ru(OR)(CNN)(PP) are in rapid exchange with alcohols
(<0.1 s) and also with the corresponding hydrides, allowing
very fast equilibration of the alcohol and ketone species. This
represents a central point for the transfer hydrogenation catalysis
in which Ru-alkoxides are effective key species. Since the
exchange between the alkoxide 7 and the corresponding alcohol
adduct 8 is very fast compared to the â-hydrogen elimination
reaction, we cannot rule out that the presence of alcohol could
be fundamental in facilitating the formation of the hydride 5.
This point has been raised by Milstein for the trans-HIr(OCH3)-
(C6H5)(PMe3)3 system, which leads to the corresponding dihy-
dride without requiring a vacant cis coordination site and
possibly through a hydrogen-bonding network with methanol.38
Catalytic Transfer Hydrogenation with 1-3. The catalytic
precursor 2 has been shown to be extremely active for the
selective reduction of a large number of ketones to alcohols in
2-propanol and in the presence of NaOH.3 Thus, acetophenone
has been quantitatively converted in 5 min using 0.005% mol
of 2 in refluxing 2-propanol, with a remarkable speed (TOF of
1.1 × 106 h-1). The robust frame of 2 allows the reaction to be
carried out even at lower catalyst loading. Different ketones,
such as acetophenone and benzophenone, have been easily
reduced using 0.001 mol % of 2, indicating that this protocol
can be applied for the medium-scale preparation of alcohols
and, therefore, may be of interest for industrial applications. It
is noteworthy that most of the described hydrogen-transfer
catalysts work with relatively higher loading (>0.01% mol) and
lead to incomplete conversion of substrate when the amount of
catalyst is reduced.
a Conditions: reactions were carried out at 82 °C, ketone 0.1 M in
2-propanol, ketone/Ru/NaOiPr ) 20000/1/400. b The conversion and ee
were determined by GC analysis. c Turnover frequency (moles of ketone
converted to alcohol per mole of catalyst per hour) at 50% conversion.
d Complex 3 was prepared in situ by treatment of RuCl2(PPh3)(dppb) with
the ligand Hc (1:2 molar ratio) in 2-propanol at reflux for 10 min.
used for 2, complex 1 (0.005 mol %, NaOH 2 mol %) leads
only to 30% conversion of acetophenone after 3 h. As re-
ported in the previous part, when 1 reacts with sodium
isopropoxide, the hydride 4 is easily formed, but this species
does not give insertion of ketones and no formation of ruthenium
alkoxides has been observed by NMR measurements. This
provide additional evidence for the key role of alkoxides in the
fast transfer hydrogenation and suggests that the effectiveness
of complexes containing an amino NH group could be related
to their ability to favor the formation of ruthenium alkoxides.
When the chiral complex 3 is used, again fast reduction of
different methyl-aryl ketones is observed under the same experi-
mental conditions employed for 2, and the results are reported
in Table 3.
The values of the rate of reduction are comparable to those
of 2, leading to the corresponding alcohols in a few minutes
(TOF in the range 5.4 × 105 to 1.4 × 106 h-1) and with fairly
good to good enantiomeric excess (70-88%), the best result
being obtained with 2-methoxyacetophenone. These data indi-
cate that 3 can be employed for the fast enatioselective reduction
of prochiral ketones using very low catalyst loading (substrate/
catalyst up to 20 000). Furthermore, the same catalytic perfor-
mance can be obtained generating the catalyst in situ, by reaction
of RuCl2(PPh3)(dppb) with the ligand Hc (2 equiv) in 2-propanol
at reflux, showing that the formation of 3 is quite straightforward
(Table 3).
It is significant that complex 1, which shows a NMe2 group
instead of NH2, displays a much lower catalytic activity for
the reduction of ketones. Under identical catalytic conditions
(34) (a) Kim, Y. J.; Osakada, K.; Takenaka, A.; Yamamoto, A. J. Am.
Chem. Soc. 1990, 112, 1096. (b) Osakada, K.; Ohshiro, K.; Yamamoto, A.
Organometallics 1991, 10, 404. (c) Kegley, S. E.; Schaverien, C. J.;
Freudenberger, J. H.; Bergman, R. G.; Nolan, S. P.; Hoff, C. D. J. Am.
Chem. Soc. 1987, 109, 6563.
(35) (a) Hoffman, D. M.; Lappas, D.; Wierda, D. A. J. Am. Chem. Soc.
1989, 111, 1531. (b) Hoffman, D. M.; Lappas, D.; Wierda, D. A. J. Am.
Chem. Soc. 1993, 115, 10538.
(36) Koike, T.; Ikariya, T. AdV. Synth. Catal. 2004, 346, 37.
(37) (a) Koike, T.; Ikariya, T. Organometallics 2005, 24, 724. (b) Abdur-
Rashid, K.; Clapham, S. E.; Hadzovic, A.; Harvey, J. N.; Lough, A. J.;
Morris, R. H. J. Am. Chem. Soc. 2002, 124, 15104.
As regards the mechanism of the transfer hydrogenation of
ketones mediated by RuX(CNN)(PP) complexes, the first step
is the reaction of the chloride catalytic precursor with alkaline
isopropoxides, affording the ruthenium isopropoxide derivative.
This species gives the ruthenium hydride, which then reacts with
the ketone substrate, affording the corresponding ruthenium
(38) Blum, O.; Milstein, D. J. Organomet. Chem. 2000, 593-594, 479.

4618 Organometallics, Vol. 25, No. 19, 2006
Baratta et al.
alkoxide.39 Subsequent reaction with 2-propanol, which is
present in large excess, leads to the formation of the ruthenium
isopropoxide, which closes the cycle. This route is supported
by stoichiometric reactions that show that the ruthenium
isopropoxide CNN complexes, formed by chloride displacement,
are in equilibrium with the hydrides (such as 5, 6), when a NH2
group is present. This shows that for the above complexes the
alkoxide â-elimination and the insertion of ketones into the
Ru-H bond is a relatively easy and rapid process. Furthermore,
the fast exchange of the alkoxide with alcohol, as observed for
5, which is likely to occur via hydrogen bond interactions,
indicates that the last step of the catalytic cycle also takes place
rapidly. Therefore, these studies show that the Ru(OR)(CNN)-
(PP) complexes bearing a NH donor group display rapid hydride/
alkoxide and alkoxide/alcohol equilibrium processes as well as
fast catalytic transfer hydrogenation.
52.3 mol). The solution was stirred at room temperature for 3 days
and then heated under reflux for 9 h. After cooling, a 10% solution
of K2CO3 was added and stirring continued for 15 min. The organic
phase was separated and dried (Na2SO4), the solvent was evapo-
rated, and the residue was purified by flash chromatography
(petroleum ether-EtOAc, 95:5). Yield: 9.23 g (96%). Mp: 131-
132 °C. Anal. Calcd for C13H10N2: C, 80.39; H, 5.19; N, 14.42.
Found: C, 80.52; H, 5.17; N, 14.44. 1H NMR (200.1 MHz, CDCl3,
20 °C): δ 7.94-7.91 (m, 3H), 7.88 (t, J(HH) ) 9.6 Hz, 1H), 7.59
(dd, J(HH) ) 1.2, 1.2 Hz, 1H), 7.31 (dd, J(HH) ) 0.6, 0.6 Hz,
2H), 2.42 (s, 3H; CH3).
Synthesis of 2-Aminomethyl-6-(4-methylphenyl)pyridine (Ha).
2-Cyano-6-(4-methylphenyl)pyridine (0.970 g, 5.00 mmol) was
added portionwise to a solution prepared by mixing anhydrous Et2O
(10 mL) with a 1 M solution of LiAlH4 in THF (6.92 mL, 6.92
mmol). The mixture was stirred at room temperature for 1 h and
then heated at 40 °C for 3 h. After cooling, a 40% aqueous solution
of NaOH (5 mL) was cautiously added, and stirring continued for
1 h. The organic phase was separated and dried (Na2SO4), and the
solvent was evaporated. The residue was purified by flash chro-
matography (methanol). Yield: 0.46 g (46%). Mp: 59-60 °C. Anal.
Calcd for C13H14N2: C, 78.75; H, 7.12; N, 14.13. Found: C, 78.66;
Concluding Remarks
In summary, we have described a novel class of terdentate
complexes of formula RuCl(CNN)(dppb) also with a chiral CNN
moiety that are extremely active catalysts for transfer hydro-
genation in basic conditions. Reaction of these complexes with
MOiPr (M ) Na, K) leads to the corresponding isopropoxides,
which, when a NH2 group is present, are in equilibrium with
the hydrides. These complexes react with ketones with formation
of alkoxides, which are in rapid exchange with the alcohol.
Because the new highly active catalysts RuCl(CNN)(PP) can
be easily prepared combining 6-aryl-2-aminomethylpyridines
with a large number of commercially available diphosphines,
this new group of complexes appears to be very promising for
application in homogeneous catalysis. Work is in progress to
extend this chemistry to chiral diphosphines for obtaining very
fast enantioselective catalysts.
1
H, 7.14; N, 14.14. H NMR (200.1 MHz, CDCl3, 20 °C): δ 7.92
(d, J(HH) ) 8.1 Hz, 2H), 7.68 (t, J(HH) ) 7.5 Hz, 1H), 7.57 (d,
J(HH) ) 7.5 Hz, 1H), 7.27 (d, J(HH) ) 8.1 Hz, 2H), 7.15 (d,
J(HH) ) 7.5, 1H), 4.01 (s, 2H; CH2), 2.40 (s, 3H; CH3), 1.86 (s,
2H; NH2).
Synthesis of N,N-Dimethyl-2-aminomethyl-6-(4-methylphen-
yl)pyridine (Hb). 2-Aminomethyl-6-(4-methylphenyl)pyridine (Ha)
(0.30 g, 1.5 mmol) was slowly added to a cooled (0 °C) 90%
aqueous solution of formic acid (0.460 g, 9.0 mmol). Then a 35%
aqueous solution of formaldehyde (0.283 g, 3.3 mmol) was added,
and the resulting mixture was heated at 70 °C for 4 h. After cooling,
the mixture was basified with a 10% aqueous solution of NaOH
(10 mL) and then extracted with CH2Cl2 (3 × 20 mL). The
combined organic phase was dried (Na2SO4), the solvent was
evaporated, and the residue was purified by flash chromatography
(CH2Cl2-MeOH, 9:1), affording a pale yellow oil. Yield: 0.197 g
(58%). Anal. Calcd for C15H18N2: C, 79.61; H, 8.02; N, 12.38.
Found: C, 79.93; H, 8.05; N, 12.39. 1H NMR (200.1 MHz, CDCl3,
20 °C): δ 7.90 (d, J(HH) ) 8.1 Hz, 2H), 7.68 (t, J(HH) ) 7.5 Hz,
1H), 7.55 (d, J(HH) ) 7.5 Hz, 1H), 7.32 (d, J(HH) ) 7.5 Hz, 1H),
7.25 (d, J(HH) ) 8.1 Hz, 2H), 3.67 (s, 2H; CH2), 2.39 (s, 3H;
CH3), 2.34 (s, 6H; NMe2).
Experimental Section
All reactions were carried out under an argon atmosphere using
standard Schlenk techniques. The solvents were carefully dried by
standard methods and distilled under argon before use. The
ruthenium complex RuCl2(PPh3)(dppb)40 and (SS,R)-N-(p-toluene-
sulfinyl)-2,2-dimethyl-1-(6-phenylpyridin-2-yl)propylamine14 were
prepared according to literature procedures, whereas all other
chemicals were purchased from Aldrich and used without further
purification. NMR measurements were recorded on a Bruker AC
200 spectrometer and a Bruker AVANCE 400 spectrometer
equipped with a 5 mm multinuclear z-gradient probe. 2D COSY,
2D HSQC, and 1D sel-NOESY experiments were performed using
the standard pulse sequences from the Bruker library. Chemical
Synthesis of (R)-2,2-Dimethyl-1-(6-phenylpyridin-2-yl)pro-
pylamine (Hc). Trifluoroacetic acid (1.4 g, 12.2 mmol) was added
dropwise to a cooled (0 °C) solution of (SS,R)-N-(p-toluenesulfinyl)-
2,2-dimethyl-1-(6-phenylpyridin-2-yl)propylamine (1.12 g, 2.96
mmol, 98% de) in CH3OH (12 mL). After 24 h stirring at room
temperature, H2O (10 mL) was added and the MeOH was
evaporated under vacuum. The aqueous residue was taken up in
CH2Cl2 (100 mL), and the resulting solution was washed with 10%
NaOH (3 × 10 mL). The organic phase was dried over anhydrous
Na2SO4, and the solvent was evaporated under vacuum. The residue
was purified by flash chromatography (methanol), obtaining a
yellow oil. Yield: 0.67 g (94%). [R]25D ) -39.4 (c 0.13, CHCl3).
Anal. Calcd for C16H20N2: C, 79.96; H, 8.39; N, 11.66. Found: C,
1
shifts, in ppm, are relative to TMS for H and 13C{1H}, whereas
85% H3PO4 was used for 31P{1H}. Infrared measurements were
obtained using a Brucker Vector 22 FT-IR spectrometer. Elemental
analyses (C, H, N) were carried out with a Carlo Erba 1106
elemental analyzer.
Synthesis of 2-Cyano-6-(4-methylphenyl)pyridine. 2-(4-Meth-
ylphenyl)pyridine was converted into the N-oxide by oxidation with
30% hydrogen peroxide in glacial acetic acid at 70 °C for 13 h
according to Ochiai41 (84% yield, mp 119-120 °C). To a solution
of the N-oxide (9.21 g, 49.7 mmol) in anhydrous CH2Cl2 (130 mL)
were added dropwise in sequence dimethylcarbamyl chloride (5.35
g, 4.58 mL, 49.7 mol) and trimethylsilyl cyanide (5.19 g, 6.97 mL,
1
79.65; H, 8.41; N, 11.64. H NMR (200.1 MHz, CDCl3, 20 °C):
δ 8.03 (d, J(HH) ) 7.2 Hz, 2H), 7.66-7.58 (m, 2H), 7.49-7.37
(m, 3H), 7.10 (d, J(HH) ) 7.2 Hz, 1H), 3.72 (s, 1H; CHN), 1.99
(s, 2H; NH2), 0.97 (s, 9H; CMe3).
Synthesis of 1. To a suspension of RuCl2(PPh3)(dppb) (0.400
g, 0.465 mmol) in 2-propanol (4 mL) were added the ligand Hb
(0.148 g, 0.654 mmol) and triethylamine (0.9 mL, 6.46 mmol). The
mixture was refluxed overnight, and the orange precipitate was
filtered, washed with methanol, and dried under reduced pressure.
Yield: 0.260 g (71%). Anal. Calcd for C43H45ClN2P2Ru: C 65.52;
(39) (a) Aranyos, A.; Csjernyik, G.; Szabo´, K. J.; Ba¨ckvall, J. E. Chem.
Commun. 1999, 351. (b) Martin-Matute, B.; Edin, M.; Bogar, K.; Kaynak,
F. B.; Ba¨ckvall, J. E. J. Am. Chem. Soc. 2005, 127, 8817.
(40) Jung, C. W.; Garrou, P. E.; Hoffman, P. R.; Caulton, K. G. Inorg.
Chem. 1984, 23, 726.
(41) Ochiai, E. J. Org. Chem. 1953, 18, 548.

Terdentate RuX(CNN)(PP) (X ) Cl, H, OR) Complexes
Organometallics, Vol. 25, No. 19, 2006 4619
H, 5.75; N 3.55. Found: C, 65.21; H, 5.68; N, 3.32. 1H NMR (200.1
MHz, CD2Cl2, 20 °C): δ 8.19-6.60 (m, 24H; aromatic protons),
6.19 (t, J(HH) ) 8.0 Hz, 2H; m-Ph), 3.50 (d, J(HH) ) 13.6, 1H;
CH2N), 3.09 (d, J(HH) ) 13.6 Hz, 1H; CH2N), 3.24-0.90 (m,
8H; CH2), 2.20 (s, 3H; CH3), 1.77 (s, 6H; N(CH3)2). 13C{1H} NMR
(50.3 MHz, CD2Cl2, 20 °C): 164.2 (s; NCC), 157.6 (s; NCCH2),
150.2-116.5 (m; aromatic carbons), 70.7 (s, CH2N), 50.7 (s,
N(CH3)2), 34.5 (d, J(CP) ) 23.3 Hz; CH2P), 32.5 (d, J(CP) ) 32.0
Hz; CH2P), 27.1 (s; CH2), 21.8 (s; CH2), 21.6 (s, CH3).31P{1H}
NMR (81.0 MHz, CD2Cl2, 20 °C): δ 50.8 (d, J(PP) ) 37.3 Hz),
35.5 (d, J(PP) ) 37.3 Hz).
Synthesis of 2. The synthesis of 2 was carried out in a way
similar to that described for 1, using Ha instead of Hb. To a
suspension of RuCl2(PPh3)(dppb) (1.17 g, 1.36 mmol) in 2-propanol
(15 mL) were added the ligand Ha (0.300 g, 1.51 mmol) and
triethylamine (1.9 mL, 13.6 mmol). The mixture was refluxed for
2 h, and the yellow precipitate was filtered, washed with methanol,
and dried under reduced pressure. Yield: 810 mg (78%). Anal.
Calcd for C41H41ClN2P2Ru: C, 64.77; H, 5.44; N, 3.68. Found:
C, 64.36; H, 5.52; N, 3.70. 1H NMR (200.1 MHz, CD2Cl2, 20 °C):
δ 8.10-6.57 (m, 24H; aromatic protons), 6.00 (t, J(HH) ) 8.1 Hz,
2H; m-Ph), 4.12 (dd, J(HH) ) 15.5, 4.4 Hz, 1H; CH2N), 3.72 (td,
J(HH) ) 15.5, 4.1 Hz, 1H; CH2N), 3.41 (m, 1H; NH2), 3.05 (m,
2H; CH2P), 2.46-0.90 (m, 7H; NH and CH2), 2.23 (s, 3H; CH3).
13C{1H} NMR (50.3 MHz, CD2Cl2, 20 °C): δ 181.8 (dd, J(CP) )
16.3, 7.8 Hz; CRu), 163.2 (s; NCC), 155.9 (s; NCCH2), 149.2-
116.0 (m; aromatic carbons), 52.5 (d, J(CP) ) 2.7 Hz; CH2N), 33.4
(d, J(CP) ) 26.3 Hz; CH2P), 30.7 (d, J(CP) ) 31.6 Hz; CH2P),
26.8 (s; CH2), 22.1 (s; CH2), 21.8 (s, CH3). 31P{1H} NMR (81.0
MHz, CD2Cl2, 20 °C): δ 57.3 (d, J(PP) ) 38.3 Hz), 42.6 (d, J(PP)
) 38.3 Hz).
72.9 (s, CH2N), 33.4 (d, J(CP) ) 18.1, 5.0 Hz; CH2P), 31.6 (d,
J(CP) ) 22.5 Hz; CH2P), 27.0 (s; CH2), 23.1 (s; CH2), 22.1 (s;
CH3). 31P{1H} NMR (81.0 MHz, C6D6, 20 °C): δ 62.5 (d, J(PP)
) 15.5 Hz), 30.4 (d, J(PP) ) 15.5 Hz). IR (Nujol): 1811 cm-1
(br, Ru-H).
Synthesis of 5. Complex 2 (516 mg, 0.679 mmol) was suspended
in toluene (10 mL), and 10 mL of a solution of NaOiPr (0.1 M,
1.00 mmol) in 2-propanol was added. After 1 h at 60 °C the solution
was concentrated, stirred at room temperature, and after addition
of toluene filtered on Celite (fine frit). The filtrate was evaporated,
and the solid was precipitated from toluene and filtered, affording
a bright orange product, which was dried under reduced pressure.
Yield: 395 mg (80%). Anal. Calcd for C41H42N2P2Ru: C, 67.85;
1
H, 5.83; N, 3.86. Found: C, 66.80; H, 5.63; N, 3.57. H NMR
(200.1 MHz, C6D6, 20 °C): δ 8.55-5.90 (m, 26H; aromatic
protons), 3.10-0.9 (m, 12H; CH2 and NH2), 2.30 (s, 3H; CH3),
-5.58 (dd, J(HP) ) 89.1, 26.4 Hz, 1H; RuH). 13C{1H} NMR (50.3
MHz, C6D6, 45 °C): δ 189.1 (s; CRu), 163.0 (s; NCC), 154.8 (s;
NCCH2), 149.2-113.2 (m; aromatic carbons), 52.1 (d, J(CP) )
2.8 Hz; CH2N), 32.5 (d, J(CP) ) 13.8 Hz; CH2P), 30.0 (d, J(CP)
) 21.3 Hz; CH2P), 27.0 (s; CH2), 22.8 (s; CH2), 22.0 (s; CH3).
31P{1H} NMR (81.0 MHz, C6D6, 45 °C): δ 65.7 (d, J(PP) )
17.2 Hz), 34.6 (d, J(PP) ) 17.2 Hz). IR (Nujol): 1743 cm-1 (br,
Ru-H).
Synthesis of 7. To a suspension of 5 (160 mg, 0.220 mmol) in
toluene (2 mL) was added benzophenone (45 mg, 0.247 mmol),
and the solution was stirred for 15 min. The solution was
concentrated and addition of pentane afforded a dark orange
precipitate, which was filtered and dried under reduced pressure.
Yield: 140 mg (70%). Anal. Calcd for C54H52N2OP2Ru: C, 71.43;
1
H, 5.77; N, 3.09. Found: C, 70.51; H, 5.39; N, 2.81. H NMR
(200.1 MHz, C6D6, 20 °C): δ 8.40-5.80 (m, 35H; aromatic
protons), 5.58 (d, J(HH) ) 7.2 Hz, 1H; aromatic proton), 5.35 (br
s, 1H; NH2), 4.86 (s, 1H; OCH), 3.20-2.60 (m, 5H), 2.25 (s, 3H;
CH3), 2.10-0.9 (m, 6H). 13C{1H} NMR (50.3 MHz, C6D6, 20
°C): δ 187.6 (s; CRu), 163.8 (s; NCC), 157.4 (s; NCCH2), 155.7-
112.4 (m; aromatic carbons), 80.1 (s; OCH), 52.0 (s; CH2N), 31.6
(d, J(CP) ) 29.2 Hz; CH2P), 30.9 (d, J(CP) ) 26.7 Hz; CH2P),
27.0 (s; CH2), 22.6 (s; CH2), 22.1 (s; CH3). 31P{1H} NMR (81.0
MHz, C6D6, 20 °C): δ 57.0 (d, J(PP) ) 34.2 Hz), 37.3 (d, J(PP)
) 34.2 Hz).
Typical Procedure for the Catalytic Transfer Hydrogenation.
The ruthenium complex 3 (3.2 mg, 4.0 µmol) was dissolved in 8
mL of 2-propanol. The ketone (2 mmol) was dissolved in 19 mL
of 2-propanol, and the solution was heated to reflux under argon.
By addition of NaOiPr (0.1 M, 0.4 mL) and the solution containing
the ruthenium complex (0.2 mL) the reduction of the ketone starts
immediately (3 0.005 mol %, NaOiPr 2 mol %), and the yield was
determined by GC analysis using a MEGADEX-ETTBDMS-â
chiral column.
X-ray Structure Determination of 3. Data collection for 3 was
carried out at 293(2) K on a Nonius DIP-1030H system, with
graphite-monochromatized Mo KR radiation. A total of 30 frames
were collected, each with an exposure time of 20 min, over a half
of reciprocal space with a rotation of 6° about æ, the detector being
at 80 mm from the crystal. Cell refinement, indexing, and scaling
of the data set were carried out using the programs Denzo and
Scalepack.42 The structure was solved by Patterson and Fourier
analyses and refined by the full-matrix least-squares method based
on F2 with all observed reflections.43 Anisotropic temperature factors
were obtained for all non-H atoms of the complex. The contribution
of hydrogen atoms at calculated positions was included in the final
cycles of refinements. All the calculations were performed using
Synthesis of 3. The synthesis of 3 was carried out in a way
similar to that described for 1, using Hc instead of Hb. To a
suspension of RuCl2(PPh3)(dppb) (1.35 g, 1.57 mmol) in 2-propanol
(20 mL) were added the ligand Hc (0.470 g, 1.96 mmol) and
triethylamine (2.20 mL, 15.8 mmol). The mixture was refluxed
overnight, and the light brown precipitate was filtered, washed
with methanol, and dried under reduced pressure. Yield: 1.07 g
(85%). Anal. Calcd for C44H47ClN2P2Ru: C 65.87; H, 5.90; N
1
3.49. Found: C, 65.61; H, 5.78; N, 3.32. H NMR (200.1 MHz,
CD2Cl2, 20 °C): δ 8.16-6.57 (m, 25H; aromatic protons), 5.93 (t,
J(HH) ) 8.6 Hz, 2H; m-Ph), 3.40 (d, J(HH) ) 13.1, 1H; CHN),
3.22 (dd, J(HH) ) 13.2, 9.5 Hz, 1H; NH2), 3.04 (m, 2H; PCH2),
2.30-1.05 (m, 7H; PCH2, CH2 and NH2), 0.95 (s, 9H; C(CH3)3).
13C{1H} NMR (50.3 MHz, CD2Cl2, 20 °C): 183.6 (dd, J(CP) )
16.3, 7.7 Hz; CRu), 165.1 (s; NCC), 156.5 (s; NCCH2), 150.2-
116.5 (m; aromatic carbons), 72.2 (d, J(CP) ) 2.53 Hz; CHN),
35.1 (s, CCH3), 33.3 (d, J(CP) ) 24.8 Hz; CH2P), 30.6 (d, J(CP)
) 32.0 Hz; CH2P), 27.2 (s; C(CH3)3), 26.9 (s; CH2), 21.8 (s; CH2).
31P{1H} NMR (81.0 MHz, CD2Cl2, 20 °C): 56.8 (d, J(PP) ) 38.8
Hz), 43.7 (d, J(PP) ) 38.8 Hz).
Synthesis of 4. Complex 1 (0.200 g, 0.254 mmol) was suspended
in toluene (4.0 mL), and 4.0 mL of a solution 0.1 M of NaOiPr in
2-propanol (0.4 mmol) was added. After 2 h at 60 °C the solution
was concentrated, stirred at room temperature for 30 min, and
filtered on Celite (fine frit). The solvent was eliminated under
reduced pressure, and the solid was extracted with pentane,
affording an orange product, which was dried under reduced
pressure. Yield: 0.099 g (52%). Anal. Calcd for C43H46N2P2Ru:
C, 68.51; H, 6.15; N, 3.72. Found: C, 68.33; H, 6.02; N, 3.51. 1H
NMR (200.1 MHz, C6D6, 20 °C): δ 8.50-6.10 (m, 26H; aromatic
protons), 3.25 (d, J(HH) ) 13.3 Hz, 1H; CH2N), 2.83 (m, 2H;
PCH2), 2.61 (d, J(HH) ) 13.3 Hz, 1H; CH2N), 2.23-0.90 (m, 6H;
CH2), 2.18 (s, 3H; CH3), 2.13 (s, 3H; N(CH3)2), 2.10 (s, 3H;
N(CH3)2), -5.79 (dd, J(HP) ) 87.7, 28.6 Hz, 1H; RuH). 13C{1H}
NMR (50.3 MHz, C6D6, 20 °C): δ 184.5 (s br; CRu), 163.6
(s; NCC), 154.3 (s; NCCH2), 148.7-114.8 (m; aromatic carbons),
(42) Otwinowski Z.; Minor, W. In Processing of X-ray Diffraction Data
Collected in Oscillation Mode; Carter, C. W., Jr., Sweet, R. M., Eds.;
Methods in Enzymology, Volume 276: Macromolecular Crystal-lography,
Part A; Academic Press: New York, 1997; p 307.

4620 Organometallics, Vol. 25, No. 19, 2006
Baratta et al.
the WinGX System, Ver 1.70.00.44 Details of the X-ray experiment,
data reduction, and final structure refinement calculation are
summarized in Table 1.
measurements and Mr. P. Polese for carrying out the elemental
analyses.
Supporting Information Available: Tables of crystal and data
collection parameters, atomic coordinates, bond lengths, bond
angles, and thermal displacement parameters for 3 in cif format.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Acknowledgment. This work was supported by the
Ministero dell’Istruzione, dell’Universita` e della Ricerca (MIUR).
The authors also thank Dr. P. Martinuzzi for assistance in NMR
(43) Sheldrick, G. M. SHELX97 Programs for Crystal Structure Analysis
(Release 97-2); University of Go¨ttingen: Germany, 1998.
(44) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
OM060408Q