Pincer CNN ruthenium(II) complexes with oxygen-containing ligands (O 2CR, OAr, OR, OSiR3,O3SCF3): Synthesis, structure, and catalytic activity in fast transfer hydrogenation

Article abstract of DOI:10.1021/om900274r

The pincer complexes [RuX(CNN)(dppb)] (5-11: X = carboxylate, phenoxide, alkoxide, silanolate, triflate; HCNN = l-[6-(4'-methylphenyl)pyridin-2-yl] methanamine; dppb = Ph₂P(CH₂)₄PPh₂), containing the Ru-NH₂

Full text of DOI:10.1021/om900274r

Organometallics 2009, 28, 4421–4430 4421
DOI: 10.1021/om900274r
Pincer CNN Ruthenium(II) Complexes with Oxygen-Containing Ligands
(O2CR, OAr, OR, OSiR3, O3SCF3): Synthesis, Structure, and Catalytic
Activity in Fast Transfer Hydrogenation
Walter Baratta,*,† Maurizio Ballico,† Alessandro Del Zotto,† Eberhardt Herdtweck,‡
Santo Magnolia,† Riccardo Peloso,† 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, Department Chemie, Lehrstuhl fu€r Anorganische Chemie, Technische Universitat Munchen,
€
Lichtenbergstrasse 4, 85747 Garching, Germany, and Dipartimento di Scienze Chimiche, Universita di
€
§
ꢀ
Trieste, Via L. Giorgieri 1, I-34127 Trieste, Italy
Received April 10, 2009
The pincer complexes [RuX(CNN)(dppb)] (5-11: X=carboxylate, phenoxide, alkoxide, silano-
late, triflate; HCNN=1-[6-(40-methylphenyl)pyridin-2-yl]methanamine; dppb=Ph2P(CH2)4PPh2),
containing the Ru-NH2 functionality and a monodentate oxygen donor ligand, have been prepared
in high yield starting from [RuCl(CNN)(dppb)] (1) via substitution of the chloride with sodium or
thallium compounds or protonation of the alkoxide [Ru(OiPr)(CNN)(dppb)] n(iPrOH) (3). In the
solid state the formate 5 shows intermolecular NH O hydrogen bonds, whereas the acetate 6
3
3 3 3
displays an intramolecular interaction, as inferred from X-ray studies. Addition of phenol and
alcohol compounds to the phenoxide and alkoxide complexes leads to fast ligand exchange through
hydrogen bond interactions. The corresponding pincer complexes [RuX(CNN0)(dppb)] (12, 13b:
X = phenoxide, alkoxide; HCNN0 = N,N-dimethyl-1-[6-(40-methylphenyl)pyridin-2-yl]methanamine),
containing the Ru-NMe2 moiety, have been obtained from [RuCl(CNN0)(dppb)] (4) and sodium
phenoxide or alkoxide. All the NH2 complexes 5-11 are highly active catalysts in the transfer
hydrogenation of ketones in 2-propanol with NaOiPr, affording complete conversion in a few
minutes and achieving TOF values of up to 3.8 ꢀ 106 h-1 with 0.005 mol % of catalyst.
Introduction
development of highly efficient systems characterized by
appropriate designed chiral ligands containing the NH2
function (bifunctional catalysis).3 The high activity of [(η6-
arene)RuH(H2NCHPhCHPhNTs)]3b in the TH is due to the
concerted delivery of a Ru-H hydride and an amine N-H
proton to the ketone substrate, affording a 16-electron
ruthenium amide species and the alcohol, through an outer-
sphere mechanism. Notably, DFT calculations indicate that
the reaction of the ketone with the amino Ru hydride leads to
an amino Ru alkoxide, which is regarded as a catalyst reser-
The catalytic hydrogenation (HY)1 with H2 and transfer
hydrogenation (TH)2 with 2-propanol or formic acid are
fundamental transformations of current academic and in-
dustrial relevance for the preparation of alcohols from
carbonyl compounds through environmentally benign reac-
tion conditions. In the late 1990s, Noyori and co-workers
made a significant breakthrough in both reactions by the
*To whom correspondence should be addressed. E-mail: inorg@uniud.it.
(1) (a) The Handbook of Homogeneous Hydrogenation; de Vries, J. G.,
Elsevier, C. J., Eds.; Wiley-VCH: Weinheim, Germany, 2007; Vols. 1-3.
(b) Asymmetric Catalysis on Industrial Scale; Blaser, H.-U., Schmidt, E.,
Eds.; Wiley-VCH: Weinheim, Germany, 2004. (c) Transition Metals for
Organic Synthesis, 2nd ed.; Beller, M., Bolm, C., Eds.; Wiley-VCH:
Weinheim, Germany, 2004; p 29. (d) Blaser, H.-U.; Malan, C.; Pugin, B.;
Spindler, F.; Steiner, H.; Studer, M. Adv. Synth. Catal. 2003, 345, 103.
(e) Ohkuma, T.; Kitamura, M.; Noyori, R. In Catalytic Asymmetric
Synthesis; Ojima, I., Ed.; Wiley-VCH: New York, 2000; Chapter 1 .
(2) (a) Baratta, W.; Rigo, P. Eur. J. Inorg. Chem. 2008, 4041. (b) Wang,
C.; Wu, X.; Xiao, J. Chem. Asian J. 2008, 3, 1750. (c) Morris, D. J.; Wills, M.
Chim. Oggi 2007, 25, 11. (d) Ikariya, T.; Blacker, A. J. Acc. Chem. Res.
voir, stabilized by an intramolecular NH O hydrogen
3 3 3
bond.4 A realistic modeling of the TH in solution with arene
Ru amine species has been proposed by Handgraaf and
Meijer to lead to a concerted solvent-mediated mechanism
with the substrate appearing as alkoxide-like intermediate.5
Interestingly, Hamilton and Bergens provided evidence of
the formation of the ruthenium alkoxide [RuH(OR)-
(BINAP)(dpen)], from [Ru(H)2(BINAP)(dpen)] and ketone,
as a putative step in the catalytic HY of carbonyl com-
pounds.6
€
2007, 40, 1300. (e) Samec, J. S. M.; Backvall, J. E.; Andersson, P. G.; Brandt,
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Chem., Int. Ed. 1998, 37, 1703. (b) Haack, K. J.; Hashiguchi, S.; Fujii, A.;
Ikariya, T.; Noyori, R. Angew. Chem., Int. Ed. Engl. 1997, 36, 285.
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J. Am. Chem. Soc. 1999, 121, 9580. (b) Yamakawa, M.; Ito, H.; Noyori, R.
J. Am. Chem. Soc. 2000, 122, 1466. (c) Petra, D. G. I.; Reek, J. N. H.;
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r
2009 American Chemical Society
Published on Web 07/08/2009
pubs.acs.org/Organometallics

4422 Organometallics, Vol. 28, No. 15, 2009
Baratta et al.
Recently, we found that the phosphane ruthenium com-
plexes cis-[RuCl2(PP)(Pyme)]7 (PP=diphosphane), based on
1-(pyridin-2-yl)methanamine (Pyme), are among the most
efficient asymmetric TH catalysts.3b,8 A more productive
system, obtained using 1-[6-(40-methylphenyl)pyridin-2-yl]metha-
namine (HCNN), is the terdentate CNN complex [RuCl-
(CNN)(dppb)]9 (1: dppb = Ph2P(CH2)4PPh2) which pro-
motes the TH of ketones and aldehydes in basic 2-propanol
with extremely high TOF10 and TON values (Figure 1).11
The chiral version of this complex, namely [RuCl(CNN*)-
(PP)] (HCNN*=1-substituted 1-(6-arylpyridin-2-yl)metha-
namine; PP = Josiphos), afforded high rate, productivity,
and enantioselectivity in the TH and also HY of alkyl-aryl
ketones.12 Surprisingly, the analogous osmium complexes
[OsCl2(PP)(Pyme)] and [OsCl(CNN*)(PP)] were proven to
show similar or even higher activity in the asymmetric HY
and TH of ketones.13 The identical sense and degree of
enantioselectivity for both HY and TH reactions suggests
the involvement of the same metal hydride intermediates.14
Evidence has been provided that the ruthenium hydride 2 in
the presence of acetone rapidly equilibrates with the alcohol
adduct isopropoxide 3 (<1 s, room temperature) and these
species are involved in the TH of acetophenone (Figure 1).15
It is worth noting that this reversible reaction is a fundamental
step in TH and only a few examples have been reported.16
In addition, metal alkoxide complexes easily give adduct
formation and substitution reactions with protic com-
pounds, on account of the highly polarized M-O bond
and hydrogen bond formation.17
In this context we were interested in the study of pincer Ru
complexes displaying the NH2 functionality and an oxygen
donor ligand in a cis arrangement, and we report here
the preparation and characterization of the complexes
[RuX(CNN)(dppb)] (X=carboxylate, phenoxide, alkoxide,
silanolate, triflate). All these compounds, containing a
Ru-O bond, have been found to be highly active catalysts in
the ketone TH in basic 2-propanol, leading to complete
conversion within 5 min with 0.005 mol % of Ru at 82 °C.
A comparison with the NMe2 derivatives has been provided.
Results and Discussion
Carboxylate Complexes. Transition-metal formates can be
prepared by insertion of CO2 into the metal-hydride
bond.18 Conversely, the thermal decomposition of formates
provides a route to achieve M-H complexes by elimination
of carbon dioxide.19 With regard to ruthenium complexes
involved in the catalytic TH and HY reactions, it is worth
noting that [Ru(O2CH)(NN)(p-cymene)]20 (NN=TsNCHPh-
CHPhNH2) decomposes to the corresponding hydride at
T>-30 °C, whereas the derivatives [RuH(O2CH)(PPh3)2-
(NN)] (NN = H2NCMe2CMe2NH2, Pyme)21 are stable at
room temperature. The CNN pincer formate complex
[Ru(O2CH)(CNN)(dppb)] (5) has been prepared by reaction
of 1 with HCOOTl in THF at 35 °C and isolated in 76% yield
(eq 1).
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The H NMR signal of one NH2 proton is significantly
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Article
Organometallics, Vol. 28, No. 15, 2009 4423
Figure 1
Figure 2. Diamond23 ball and stick plot of compound 5 in the solid state. The dotted lines indicate the possible inter- and
intramolecular hydrogen bonds.
stretching of 5 appears at 1611 cm-1, in agreement with the
presence of a monodentate formate ligand.18a,22 It is worth
noting that compound 5 is apparently stable in C6D6 at room
temperature and no significant formation of the hydride 2
by β-hydrogen elimination was observed, even at 60 °C by
NMR. Conversely, in CD2Cl2 compound 5 converts par-
tially into 1 in a few days, possibly through the hydride 2,
which is chlorinated by the solvent.9b The molecular struc-
ture of 5 was confirmed by X-ray analysis carried out on a
single crystal (Figure 2). The selected bond distances and
angles are reported in Table 1.
N-H bond to be almost parallel to the Ru-O1 bond (H2-
N2-Ru-O1 dihedral angle of about 8°, with a H2 O1
3 3 3
distance of 2.41 A), suggesting a possible weak intramole-
cular hydrogen bond interaction between N2-H2 and O1.24
In order to prepare ruthenium derivatives displaying a
Ru-O bond, we found that the isopropoxide species
[Ru(OiPr)(CNN)(dppb)] n(iPrOH) (3), obtained from the
3
chloride 1 and NaOiPr (1.5 equiv) in 2-propanol, is a suitable
intermediate which undergoes fast protonation with acidic
H-O compounds. An excess of NaOiPr was used to achieve
the complete chloride displacement of 1 and to preserve
complex 3 during the filtration on Celite to remove NaCl.
The acetate derivative [Ru(O2CCH3)(CNN)(dppb)] (6) was
easily prepared in 88% yield, by reaction of 3 with acetic acid
in excess, also to eliminate the remaining NaOiPr (Scheme 1).
The two resonances of the NH2 group are at δ 8.40 and
1.41, as inferred from a 1H-1H COSY experiment, the low-
field resonance being consistent with an intramolecular N-
Unexpectedly, the atom O2 is not involved in an intramo-
lecular hydrogen bond interaction with a N-H proton, but it
points toward a N-H proton of another molecule of the
complex via an intermolecular hydrogen bond (N2 O20=
3 3 3
2.869(3) A), building up a one-dimensional infinite chain
parallel to the crystallographic b axis. The methylene carbon
C6 and the amino nitrogen N2 are displaced by -0.135(3)
and þ0.341(2) A, respectively, from the best-fit plane
through the terdentate ligand. This arrangement leads one
H
O hydrogen bond interaction with the acetate ligand.
3 3 3
(23) Brandenburg, K.; Diamond, Version 3.1d; Crystal Impact GbR,
Bonn, Germany, 2006.
(24) (a) Steiner, T. Angew. Chem., Int. Ed. 2002, 41, 48. (b) Brammer,
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Chem. 2000, 39, 5632. (b) Albeniz, M. J.; Esteruelas, M. A.; Lledos, A.;
~
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Maseras, F.; Onate, E.; Oro, L. A.; Sola, E.; Zeier, B. J. Chem. Soc., Dalton
L. Dalton Trans. 2003, 3145. (c) Aullon, G.; Bellamy, D.; Brammer, L.;
Trans. 1997, 181.
Bruton, E. A.; Orpen, A. G. Chem. Commun. 1998, 653.

4424 Organometallics, Vol. 28, No. 15, 2009
Baratta et al.
˚
Table 1. Selected Bond Distances (A) and Angles (deg) of
Complexes 5 and 6
formate 5
acetate 6 1.5C6H6
3
Ru-O1
Ru-N1
Ru-N2
Ru-C7
Ru-P1
Ru-P2
2.170(2)
2.050(2)
2.218(2)
2.060(3)
2.2907(9)
2.2396(9)
2.162(2)
2.058(2)
2.236(3)
2.060(3)
2.2879(11)
2.2496(10)
O1-Ru-N1
O1-Ru-N2
O1-Ru-C7
O1-Ru-P1
O1-Ru-P2
N1-Ru-N2
N1-Ru-C7
N1-Ru-P1
N1-Ru-P2
N2-Ru-C7
N2-Ru-P1
N2-Ru-P2
C7-Ru-P1
C7-Ru-P2
P1-Ru-P2
87.29(8)
77.35(8)
92.48(10)
85.84(6)
179.34(6)
76.60(9)
79.64(11)
171.11(7)
92.52(7)
154.49(11)
96.37(6)
103.22(6)
106.28(10)
86.86(9)
94.41(3)
85.32(9)
85.66(10)
83.23(10)
87.81(7)
168.19(7)
76.99(11)
79.70(12)
170.77(7)
92.40(7)
154.88(12)
96.37(8)
105.14(8)
105.61(10)
84.96(8)
Figure 3. Diamond ball and stick plot of compound 6 in the
solid state. The dotted line indicates a possible intramolecular
hydrogen bond.
95.56(4)
of 4-fluoro-3-methylphenol is heated, the two 19F NMR
signals broaden (Δν1/2=208, 385 Hz, for δ -138.9, -132.6,
respectively, at 60 °C). The 19F NMR spectra show that
during addition of 4-fluoro-3-methylphenol the former
resonance decreases and with 10 equiv of the phenol dis-
appears, leading to a broad signal at δ -130.0, close to that
of the free phenol. In the 31P NMR spectrum the doublets
at δ 60.4 and 38.6 (2J(PP)=36.9 Hz) broaden and shift to
δ 59.9 and 43.4, respectively. These data are in agreement
with a dynamic process involving a rapid exchange of the
phenoxide with the phenol, possibly through a hydrogen
bond interaction, as reported for other phenoxide com-
plexes.17a,26 In addition to the protonation reaction, a second
important feature of the isopropoxide 3 is the fast and
reversible β-hydrogen elimination that leads to the hydride
2 and acetone.15a Thus, the alkoxide 9 can be promptly
prepared in 92% yield at room temperature by reaction of
3 with 1 equiv of 3,30-dinitrobenzophenone, in 2-propanol/
toluene (Scheme 1). It is worth noting that the presence of
electron-withdrawing groups in the alkoxide ligand stabilizes
The carbonyl stretch of 6 appears at 1713 cm-1, which is
at higher wavelength with respect to that of the formate 5
(Δν=102 cm-1). The molecular structure of 6 obtained from
an X-ray analysis is shown in Figure 3, and the selected bond
distances and angles are reported in Table 1.
In contrast to the case for the formate 5, the solid-state
study of 6 revealed the presence of an intramolecular
hydrogen bond interaction of the acetate with an axial
N-H proton, leading to a six-membered cycle (N2 O2=
3 3 3
2.817(5) A). Also in 6 one N-H bond is almost parallel to
the Ru-O1 bond (H1a-N2-Ru-O1 dihedral angle of
about -4°, with an H O distance of 2.61 A). Intramole-
3 3 3
cular hydrogen bonds have been observed for acetate com-
plexes containing the NH2 function.20,25 Attempts to pre-
pare the formate 5 by protonation of 3 with formic acid in
2-propanol failed, resulting in a mixture of different species,
including 5, and decomposition of HCO2H. The data in
solution and in the solid state for the formate 5 and acetate 6
indicate that the carboxylate ligands interact with the N-H
functionality by hydrogen bonds. Both Ru-O and CdO
oxygen atoms are involved in the interaction, with the latter
moiety leading to both inter- and intramolecular hydrogen
bonds in the solid state.
1
9 with respect to β-hydrogen elimination. In the H NMR
spectrum the doublet at δ 5.20 is for the OCH group,
showing a coupling constant with a phosphorus atom
(4J(HP)=3.1 Hz), indicating that the alkoxide is directly bound
to the metal center. The broad signal at δ 4.69 is for one
Phenoxide and Alkoxide Complexes. The phenoxide com-
plexes [Ru(OAr)(CNN)(dppb)] can be quickly prepared in
high yield by protonation of 3 with phenols. Treatment of 3
with 1 equiv of 4-nitrophenol in a 2-propanol/toluene (1:1)
mixture at room temperature leads to the complex 7 in 87%
proton of the NH2 group, consistent with a NH O hydro-
3 3 3
gen bond that stabilizes the alkoxide 9. It is worth noting
that these Ru-O bond containing complexes are moisture
sensitive and therefore must be stored under an inert atmo-
sphere. Moreover, these compounds are characterized by
1
yield (Scheme 1). In the H NMR spectrum the meta and
ortho protons of the phenoxide appear as doublets at δ 8.00
and 5.92 (3J(HH)=9.3 Hz), the latter resonance being shifted
upfield with respect to the free 4-nitrophenol (Δδ 1.04),
whereas one NH2 proton appears at δ 3.50.
Similarly to the synthesis of 7, treatment of 3 with 4-fluoro-
3-methylphenol leads to the complex 8 in 91% yield. In the
19F NMR spectrum the coordinated phenoxide shows a
resonance at δ -138.9, shifted upfield compared to the
free phenol at δ -132.6. When a solution of 8 with 1 equiv
a certain degree of intramolecular N-H O hydrogen
3 3 3
bonding, but no proton transfer leading to the formation
of the corresponding 16-electron Ru amide species was
observed.
(26) (a) Clapham, S. E.; Guo, R.; Zimmer-De Iuliis, M.; Rasool, N.;
Lough, A. J.; Morris, R. H. Organometallics 2006, 25, 5477. (b) Koike, T.;
Ikariya, T. Organometallics 2005, 24, 724. (c) Kapteijn, G. M.; Dervisi, A.;
Grove, D. M.; Kooijman, H.; Lakin, M. T.; Spek, A. L.; van Koten, G. J. Am.
Chem. Soc. 1995, 117, 10939. (d) Osakada, K.; Ohshiro, K.; Yamamoto, A.
Organometallics 1991, 10, 404. (e) Kim, Y. J.; Osakada, K.; Takenaka, A.;
Yamamoto, A. J. Am. Chem. Soc. 1990, 112, 1096. (f) 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.
(25) (a) Kuznetsov, V. F.; Yap, G. P. A.; Alper, H. Organometallics
2001, 20, 1300. (b) Wong, W.-K.; Lai, K.-K.; Tse, M.-S.; Tse, M.-C.; Gao,
J.-X.; Wong, W.-T.; Chan, S. Polyhedron 1994, 13, 2751.

Article
Organometallics, Vol. 28, No. 15, 2009 4425
Scheme 1
Silanolate and Triflate Complexes. Silicone greases, which
was easily prepared in high yield (74%) by treatment
of 1 with NaOSiMe3 in toluene at room temperature in 1 h
(eq 2).
are widely used in the laboratory for lubricating glassware
and for operations that require low pressure, are poly-
siloxanes of the chemical formula [R2SiO]n (R=alkyl, aryl).
Interestingly, we observed that the alkoxide 3 slowly reacts
with silicone grease, leading to a series of new complexes,
displaying in the 31P{1H} NMR spectra doublets centered
at about δ 60 and 40 with 2J(PP)=36-37 Hz and 1H NMR
singlets close to δ 0. These species can be reconverted to 3
using an excess of sodium isopropoxide in alcohol. It is worth
noting that treatment of polysiloxanes with strong bases
affords silanolates27 and that silanols R3SiOH display a
higher acidity28 than the corresponding alcohols and there-
fore can react with the alkoxide ligands. A number of
examples of reactions in which silicone grease became in-
volved as a reactant (e.g., “R2SiO” insertion into the M-X
bond) has been reviewed.29 On account of these results
and the implications in catalysis, we decided to prepare a
pincer ruthenium complex displaying a Ru-OSi bond.30
The ruthenium silanolate [Ru(OSiMe3)(CNN)(dppb)] (10)
Complex 10 displays two 31P NMR doublets at δ 59.3
and 39.8 (2J(PP)=36.8 Hz). In the 1H NMR spectrum one
NH2 proton appears at δ 4.50, which is consistent with a
NH O hydrogen bond interaction, whereas the OSiMe3
3 3 3
signal is shifted upfield at δ -0.17. Interestingly, treatment of
the silanolate 10 with 1 equiv of NaOiPr in 2-propanol leads
promptly to the quantitative formation of 3. These results
suggest that when silicon grease is employed during the
catalytic TH, the use of an excess of base has a beneficial
effect, inhibiting the formation of pincer Ru silanolates.
The triflate ligand can be regarded as one of the less coordi-
nating oxygen donor ligands, affording complexes character-
ized by an ionic or highly polarized covalent M-O bond,31
ꢂ
(27) Sefcı
ꢂ
´
k, J.; Rankin, S. E.; Kirchner, S. J.; McCormick, A. V.
J. Non-Cryst. Solids 1999, 258, 187.
(28) Damrauer, R.; Simon, R.; Krempp, M. J. Am. Chem. Soc. 1991,
113, 4431.
(29) Haiduc, I. Organometallics 2004, 23, 3.
(30) (a) Marciniec, B.; Maciejewski, H. Coord. Chem. Rev. 2001, 223,
301. (b) Johnson, T. J.; Folting, K.; Streib, W. E.; Martin, J. D.; Huffman,
J. C.; Jackson, S. A.; Eisenstein, O.; Caulton, K. G. Inorg. Chem. 1995, 34,
488. (c) Poulton, J. T.; Folting, K.; Streib, W. E.; Caulton, K. G. Inorg. Chem.
1992, 31, 3190.
(31) (a) Lawrance, G. A. Chem. Rev. 1986, 86, 17. (b) Beck, W.; S€unkel,
K. Chem. Rev. 1988, 88, 1405.

4426 Organometallics, Vol. 28, No. 15, 2009
Baratta et al.
and several ruthenium derivatives have been reported.32 The
pincer triflate complex [Ru(O3SCF3)(CNN)(dppb)] (11) is
formed in 80% yield by treatment of 1 with 1 equiv of
CF3SO3Tl in CH2Cl2 at room temperature (2 h) (eq 3).
1-[6-(40-methylphenyl)pyridin-2-yl]methanamine), which re-
acts with 4-fluoro-3-methylphenol, affording the phenoxide
12 in 82% yield (Scheme 2).
In the 1H NMR spectrum of 12, the CH2N protons appear
as two doublets, whereas the two N-methyl groups give a
relatively sharp singlet at δ 1.97. This can be ascribed to the
hemilabile terdentate ligand containing the NMe2 group,
which undergoes a pyramidal inversion at the nitrogen atom,
through decoordination from the Ru metal center, favored
by the presence of the ortho-metalated aryl group that exerts
a strong trans influence.35 Despite the fact the N-alkyl
substituents should 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 com-
pared to the primary or secondary ligands.36 The 31P{1H}
NMR spectrum of 12 shows two doublets at δ 52.4 and 39.7
and a small singlet at δ 33.2, the last signal being consistent
with the presence of a five-coordinate species. The presence
of a NMe2 function, instead of NH2, excludes the forma-
tion of a 16-electron amide species. Addition of 4-fluoro-
3-methylphenol results in a slight broadening of the 31P
NMR doublets and an increase of the singlet, which pro-
gressively shifts downfield (δ 35.4 with ArOH/12=5). The
19F NMR spectrum shows two broad signals at δ -139.6 (for
12) and -138.0, with the latter resonance shifting to the value
for the free phenol (δ -132.6). These data are consistent with
the presence of an equilibrium between 12 and a cationic five-
coordinate species, with the phenoxide stabilized by a hydro-
gen bond with the free phenol (Scheme 2).24a,37
Attempt to prepare 11 using CF3SO3Ag failed, leading to a
blue solution containing uncharacterized species, possibly as
a result of a redox process. Complex 11 is thermally stable
and highly soluble in different organic solvents (CH2Cl2,
iPrOH, benzene). The broad resonance at δ 4.21 (toluene-d8)
is for one NH2 proton involved in an intramolecular
N-H O triflate hydrogen bond interaction.33 The 19F{1H}
3 3 3
NMR spectrum of 11 shows a broad singlet at δ -73.5,
shifted downfield with respect to the free triflate anion
(δ ∼-80.0).34 Upon heating, the two 31P doublets (δ 68.3 and
43.0) broaden and coalesce at 100 °C to an averaged peak at
δ 51.5. At this temperature the 1H NMR spectrum shows a
triplet at δ 3.52 (J(HH) = 4.8 Hz) for the two NCH2 protons,
suggesting the existence of a fast equilibrium of 3 with a five-
coordinate cationic species resulting from the dissociation of
the triflate. Below 0 °C, the NMR measurements reveal the
presence of an equilibrium between two six-coordinate tri-
flate complexes. At -60 °C, the 31P{1H} NMR spectrum
shows two doublets at δ 64.1 and 42.8 (2J(PP)=41.2 Hz) in
addition to two doublets at δ 68.4 and 43.6 (2J(PP)=42.2 Hz)
in a 1:2 molar ratio, whereas the 19F{1H} NMR spectrum
displays two singlets at δ -73.6 and -72.8 (1:2 ratio). This
has tentatively been ascribed to the formation at low tem-
perature of two diastereomer complexes which may arise
The alkoxide derivative 13b, lacking β-hydrogens, was
isolated in 74% yield by reaction of KOtBu with 4 in
1
toluene/tBuOH (Scheme 2). In the H NMR spectrum of
13b in C6D6, the protons of the CH2N group appear as two
doublets, whereas the two N-methyl groups give a relatively
sharp singlet at δ 2.00. The 31P{1H} NMR spectrum of 13b
displays two doublets at δ 48.3 and 35.4 and a small singlet at
δ 32.1. Similarly to 12, addition of tBuOH to 13b results in a
slight broadening of the doublets and an increase of the
singlet, which shifts downfield (up to δ 34.6). As for 12, these
data are consistent with an equilibrium involving the com-
plex 13b and a cationic five-coordinate species in which the
alkoxide interacts with the alcohol. Attempts to isolate
the related isopropoxide [Ru(OiPr)(CNN0)(dppb)] (13a)
failed, on account of the slow conversion to the hydride
[RuH(CNN0)(dppb)], possibly through a β-hydrogen elim-
ination reaction.9b
These data suggest that the NMe2 six-coordinate alkoxide
and phenoxide ruthenium complexes react with ROH and
ArOH, respectively, leading to an equilibrium reaction in
which five-coordinate species are formed. When a NH2
function is present on the ruthenium center, the formation
of five-coordinate species is prevented by stabilization of the
labile six-coordinate alkoxide and phenoxide species
from a N-H O triflate hydrogen bond33 with a chiral
3 3 3
sulfur atom. Notably, the formation of diastereomer com-
plexes [Ru(OR)(CNN)(PP)] with alkoxide ligands has pre-
viously been established by 31P and 19F NMR measure-
ments.15a Complex 11, showing a highly polarized Ru-O
bond, promptly reacts with 1 equiv of NaOiPr in 2-propanol
at room temperature, leading to the alcohol adduct 3.
NMe2 Phenoxide and Alkoxide Ru Complexes. The reac-
tivity of the NMe2 derivative 4 toward alkaline alkoxide and
phenoxide was also investigated, and the properties of the
resulting Ru-O bond containing complexes were compared
to those of the related NH2 derivatives. Treatment of 4 with
KOiPr in toluene/2-propanol leads to the intermediate
[Ru(OiPr)(CNN0)(dppb)] (13a:9b HCNN0 = N,N-dimethyl-
€
(32) (a) Geldbach, T. J.; Ruegger, H.; Pregosin, P. S. Magn. Reson.
Chem. 2003, 41, 703. (b) Belli Dell'Amico, D.; Calderazzo, F.; Grazzini, A.;
Labella, L.; Marchetti, F. Inorg. Chim. Acta 2002, 334, 411. (c) Bickley, J. F.;
Higgins, S. J.; Stuart, C. A.; Steiner, A. Inorg. Chem. Commun. 2000, 3, 211.
(d) Feher, F. J.; Baldwin, R. K.; Ziller, J. W. Acta Crystallogr. 2000, C56,
633. (e) Mahon, M. F.; Whittlesey, M. K.; Wood, P. T. Organometallics 1999,
18, 4068. (f) Blosser, P. W.; Gallucci, J. C.; Wojcicki, A. Inorg. Chem. 1992,
31, 2376.
(33) (a) Pavlik, S.; Mereiter, K.; Puchberger, M.; Kirchner, K.
Organometallics 2005, 24, 3561. (b) Fossey, J. S.; Matsubara, R.; Vital, P.;
Kobayashi, S. Org. Biomol. Chem. 2005, 3, 2910. (c) Arnold, D. I.; Cotton,
F. A.; Matonic, J. H.; Murillo, C. A. Polyhedron 1997, 16, 1837. (d) Feazell,
R. P.; Carson, C. E.; Klausmeyer, K. K. Eur. J. Inorg. Chem. 2005, 3287.
(34) Jones, V. A.; Sriprang, S.; Thornton-Pett, M.; Kee, T. P.
J. Organomet. Chem. 1998, 567, 199.
through NH O hydrogen bonds. Thus, for complexes
displaying the X-M-N-H motif, the intramolecular
3 3 3
H X interaction may play a significant role in the stabi-
lization of these species.
3 3 3
(35) (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.
(36) Meyerstein, D. Coord. Chem. Rev. 1999, 185-186, 141.
(37) Buzzeo, M. C.; Zakharov, L. N.; Rheingold, A. L.; Doerrer,
L. H. J. Mol. Struct. 2003, 657, 19.

Article
Organometallics, Vol. 28, No. 15, 2009 4427
Scheme 2
The silanolate (10) and the labile triflate complexes (11)
,
Table 2. Catalytic Transfer Hydrogenation of MeCOPh (0.1 M)
in 2-Propanol with Pincer Ru Complexes (Ru=0.005 mol %,
NaOiPr=2 mol %)
afford similar values (TOF=9.4 ꢀ 105 and 9.3 ꢀ 105 h-1
respectively), close to those of the alkoxide complexes. The
catalytic and stoichiometric studies on 10 may suggest that
the use of an excess of NaOiPr has a positive effect on
catalysis, preventing the formation of Ru silanolate com-
plexes from accidental reaction with silicon grease. It is
worth noting that the compounds 5, 6, 10, and 11 should
be considered better catalytic precursors, with respect to the
moisture-sensitive phenoxide and alkoxide compounds 7-9.
The highly active acetate 6 has been proven to efficiently
catalyze the quantitative reduction of different substrates,
namely 3-bromoacetophenone, 2-acetonaphthone, and cy-
clohexanone in less than 1 min and with TOFs in the range
of (1.7-3.8) ꢀ 106 h-1, the latter being the highest value
reported to date (Table 3).
complex
T (°C)
Conv. %a
Time (min)
TOF (h-1
)
5
6
7
8
82
82
82
82
82
82
82
82
82
40
40
40
97
97
98
96
98
97
98
98
98
94
92
92
2 min
2 min
5 min
5 min
5 min
5 min
5 min
5 min
5 min
2 h
1.4 ꢀ 106
1.8 ꢀ 106
1.1 ꢀ 106
6.0 ꢀ 105
8.7 ꢀ 105
8.0 ꢀ 105
1.0 ꢀ 106
9.4 ꢀ 105
9.3 ꢀ 105
2.3 ꢀ 104
1.8 ꢀ 104
2.1 ꢀ 104
9
9a
9b
10
11
1
9b
11
2 h
2 h
a The conversion was determined by GC analysis.
In addition, the substrate 5-hexen-2-one has quickly and
quantitatively been reduced to the corresponding alcohol
without hydrogenation of the CdC bond. The phenoxide
(12) and the alkoxide complexes (13b) displaying the NMe2
group are poor catalysts in 2-propanol, leading to incom-
plete conversion of acetophenone (25 and 30% after 2 h,
respectively), likely through a inner-sphere mechanism in-
volving NMe2 displacement,2e,9a,9b indicating that the pre-
sence of the NH2 functionality is crucial for obtaining high
performance. In order to investigate the influence of the
ligand X of [RuX(CNN)(dppb)] in the catalysis, the activity
of 1 was compared with that of the more labile alkoxide (9b)
and triflate complexes (11) at 40 °C. Compound 1 shows a
TOF=2.3ꢀ104 h-1, a value slightly higher than those found
for 9b and 11 (TOF=1.8ꢀ104 and 2.1ꢀ104 h-1), indicating
that the displacement of X by OiPr in 2-propanol is a rapid
step even at low temperature. This result is in agreement with
our kinetic studies, which showed that the chloride 1, the
hydride 2, and the isopropoxide 3 display much the same
activity in basic media, C-H bond cleavage being the rate-
determining step.15b It is worth noting that the Ru-O pincer
TH of Ketones Catalyzed by Pincer Ru Complexes. All the
NH2 pincer complexes containing a Ru-O bond have
been found to be exceptionally active catalysts for TH of
acetophenone in 2-propanol and in the presence of NaOiPr
(2 mol %) (eq 4).
Complete conversion has been achieved within 5 min using
0.005 mol % of the pincer complexes at 82 °C (Table 2).
The formate (5) and acetate derivatives (6) display turn-
over frequencies10 of 1.4ꢀ106 and 1.8ꢀ106 h-1, respectively.
These values are higher than that of the chloride 1 (TOF=
1.1 ꢀ 106 h-1 9a
)
and indicate that these carboxylate species
are among the most efficient TH systems.11 The phenoxides 7
and 8 give TOF values of 1.1ꢀ106 and 6.0ꢀ105 h-1, whereas
the rate for the alkoxides 9a9a and 9b15a ranges from 8.0 ꢀ
105 to 1.0 ꢀ 106 h-1 (Figure 4).

4428 Organometallics, Vol. 28, No. 15, 2009
Baratta et al.
species. Apparently, the carboxylate, silanolate, and triflate
compounds appear to be superior catalytic precursors, with
respect to the moisture-sensitive alkoxide and phenoxide
complexes.
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 complexes 1, 4, 9a,9b and 9b15a were prepared
according to literature procedures, whereas all other chemicals
were purchased from Aldrich and used without further purifica-
tion. NMR measurements were recorded on a Bruker AC 200
spectrometer. 2D COSY experiments were performed using the
standard pulse sequences from the Bruker library. Chemical
shifts, in ppm, are relative to TMS for 1H and 13C{1H}, whereas
85% H3PO4 was used for 31P{1H} and CFCl3 for 19F{1H}.
Infrared measurements were obtained using a Bruker Vector 22
FT-IR spectrometer. Elemental analyses (C, H, N) were carried
out with a Carlo Erba 1106 elemental analyzer.
Figure 4
Table 3. Catalytic Transfer Hydrogenation of Ketones (0.1 M)
with Complex 6 (0.005 mol %, NaOiPr=2 mol %) at 82 °C
Synthesis of 5. Complex 1 (340 mg, 0.447 mmol) was dissolved
in THF (20 mL), and HCOOTl (400 mg, 1.604 mmol) was
added. The resulting suspension was stirred overnight at 35 °C
and filtered on Celite, and the solid on the frit was washed
with CH2Cl2 (4ꢀ5 mL). The filtrate was concentrated (3 mL),
and pentane was added (10 mL). The orange precipitate was fil-
tered, washed with pentane (2ꢀ2 mL), and dried under reduced
pressure. Yield: 260 mg (76%). Anal. Calcd for C42H42N2O2-
P2Ru: C, 65.44; H, 5.50; N, 3.64. Found: C, 65.01; H, 5.70; N,
3.32. 1H NMR (200.1 MHz, CD2Cl2, 20 °C): δ 8.02-7.92
(m, 3H; aromatic protons and HCO2), 7.58 (t, J(HH)=7.6 Hz,
3H; aromatic protons), 7.52-7.10 (m, 14H; aromatic protons),
7.03 (d, J(HH)=8.1 Hz, 1H; aromatic proton), 6.79 (t, J(HH)=
7.9 Hz, 2H; aromatic protons), 6.63 (d, J(HH)=6.6 Hz, 2H;
aromatic protons), 6.16 (td, J(HH)=11.3, 5.3 Hz, 1H; NH2),
6.02 (t, J(HH) = 8.0 Hz, 2H; aromatic protons), 4.13 (dd,
a The conversion was determined by GC analysis.
complexes 5-11 show no catalytic activity without base and
an excess of NaOiPr is crucial to achieve fast TH. These
catalytic results suggest that, in basic 2-propanol solutions,
the derivatives 5-11 are catalytic precursors and give rapid
displacement of the oxygen-containing ligand, affording the
catalytically active hydride (2) and isopropoxide species (3),
in agreement with the previously proposed inner-outer
sphere mechanism involving 2-propanol.15
3
2J(HH) = 15.1 Hz, J(HH) = 4.4 Hz, 1H; CH2N), 3.75-3.55
(m, 1H; CH2N), 3.20-2.80 (m, 2H; PCH2), 2.20 (s, 3H; CH3),
2.50-0.75 (m, 7H; CH2 and NH2). 13C{1H} NMR (50.3 MHz,
CD2Cl2, 20 °C): δ 182.8 (dd, 2J(C,P)=16.3, 8.1 Hz; CRu), 171.0
(s; HCO2), 163.7 (s; NCC), 158.4 (s; NCCH2), 148.9-115.0
(m; aromatic carbon atoms), 52.8 (d, 3J(C,P)=3.0 Hz; CH2N),
1
1
31.8 (d, J(C,P)=24.0 Hz; CH2P), 31.3 (d, J(C,P)=32.1 Hz;
CH2P), 26.5 (s; CH2), 22.1 (s; CH2), 21.7 (s, CH3). 31P{1H}
NMR (81.0 MHz, CD2Cl2, 20 °C): δ 60.0 (d, 2J(PP)=38.3 Hz),
42.7 (d, 2J(PP)=38.3 Hz). IR (Nujol): ν 1611 cm-1 (asymmetric
ν(OCO)).
Concluding Remarks
In summary, we have isolated and characterized a series of
pincer complexes containing a Ru-O bond of formula
[RuX(CNN)(dppb)] (X=carboxylate, phenoxide, alkoxide,
silanolate, triflate). The solid-state structures and the studies
in solution revealed that the six-coordinate NH2 pincer
complexes are stabilized by intramolecular and intermole-
Synthesis of 6. To a suspension of 1 (218 mg, 0.287 mmol) in
toluene (4.8 mL) was added 4.8 mL of a 2-propanol solution
of NaOiPr (0.1 M, 0.480 mmol), and the mixture was stirred at
60 °C for 2 h. The suspension was kept at -20 °C for 6 h and
filtered on Celite. Acetic acid (35.0 μL, 0.612 mmol) was added
to the filtrate, and the solution was stirred for 30 min at room
temperature, concentrated to 5 mL, and kept at -20 °C for 2 h.
After filtration on Celite, the solution was concentrated (1 mL)
and addition of pentane (5 mL) afforded an orange precipitate,
which was filtered and dried under reduced pressure. Yield:
197 mg (88%). Anal. Calcd for C43H44N2O2P2Ru: C, 65.89;
cular N-H O bond interactions. Reaction of the phen-
3 3 3
oxide and alkoxide complexes with phenol and alcohol
compounds leads to the fast exchange of the ligands. Con-
versely, the phenoxide and alkoxide NMe2 pincer complexes,
which are not stabilized by intramolecular hydrogen bonds,
react with H-O acidic compounds, leading to five-coordi-
nate species. While the NMe2 derivatives display poor
catalytic activity in transfer hydrogenation, all the NH2
pincer complexes are highly active catalysts, with TOF
values in the range of 6.0ꢀ105 to 3.8ꢀ106 h-1 for the reduc-
tion of ketones in basic 2-propanol. These data suggest that
the pincer ruthenium complexes with a Ru-O bond can
be used as efficient catalytic precursors, on account of their
fast conversion into the catalytically active Ru-H/Ru-OiPr
1
H, 5.66; N, 3.57. Found: C, 65.58; H, 5.82; N, 3.39. H NMR
(200.1 MHz, C6D6, 20 °C): δ 8.40 (br s, 1H; NH2), 8.31 (t,
J(HH)=8.6 Hz, 2H; aromatic protons), 7.89 (s, 1H; aromatic
proton), 7.74 (t, J(HH)=7.8 Hz, 2H; aromatic protons), 7.46-
6.97 (m, 11H; aromatic protons), 6.93 (d, J(HH)=7.7 Hz, 1H;
aromatic proton), 6.72 (t, J(HH)=7.8 Hz, 2H; aromatic protons),
6.65 (t, J(HH) = 8.0 Hz, 2H; aromatic protons), 6.47 (t, J(HH)=
7.3 Hz, 2H; aromatic protons), 6.16 (d, J(HH)=7.2 Hz, 1H;
aromatic proton), 6.07 (t, J(HH)=8.1 Hz, 2H; aromatic protons),
3.87 (dd, 2J(HH)=15.5 Hz, 3J(HH)=4.3 Hz, 1H; CH2N), 3.24

Article
Organometallics, Vol. 28, No. 15, 2009 4429
(m, 1H; CH2N), 3.05 (m, 1H; CH2P), 2.85 (m, 1H; CH2P), 2.34
(s, 3H; CH3), 2.10-1.50 (m, 5H; CH2), 1.72 (s, 3H; CH3CO),
1.41 (br s, 1H; NH2), 0.84 (m, 1H; CH2). 13C{1H} NMR (50.3
MHz, C6D6, 20 °C): δ 183.4 (dd, 2J(C,P)=16.0, 8.3 Hz; CRu),
181.5 (s, CORu), 163.9 (s; NCC), 159.3 (s; NCCH2), 148.8-
(d, 2J(PP)=36.9 Hz). 19F{1H} NMR (188.3 MHz, C6D6, 20 °C):
δ -138.9 (s).
Synthesis of 9. The preparation of 9 was carried out in a
way similar to that described for 8, using compound 1 (100 mg,
0.131 mmol), 2.0 mL of a 2-propanol solution of NaOiPr (0.1 M,
0.200 mmol), and 3,30-dinitrobenzophenone (40 mg, 0.147 mmol),
resulting in a dark yellow product. Yield: 121 mg (92%). Anal.
Calcd for C54H50N4O5P2Ru: C, 64.99; H, 5.05; N, 5.61. Found:
C, 64.93; H, 5.01; N, 5.58. 1H NMR (200.1 MHz, C6D6, 20 °C): δ
8.47 (s, 1H; aromatic proton). 7.93 (m, 5H; aromatic protons),
7.57 (td, J(HH)=7.9, 1.8 Hz; 2H; aromatic protons), 7.45 (dd,
J(HH)=7.9, 1.8 Hz, 1H; aromatic proton), 7.40-6.85 (m, 14H;
aromatic protons), 6.78 (td, J(HH)=7.2, 1.3 Hz, 2H; aromatic
protons), 6.59 (t, J(HH)=7.8 Hz, 2H; aromatic protons), 6.40
(m, 2H; aromatic protons), 6.23 (m, 2H; aromatic protons), 5.88
(t, J(HH)=8.0 Hz, 2H; aromatic protons), 5.53 (d, J(HH)=6.8 Hz,
1H; aromatic proton), 5.20 (d, J(HP)=3.1 Hz, 1H; OCH), 4.69
(br s, 1H; NH2), 3.19 (m, 2H; CH2N, CH2P), 2.84 (m, 2H;
CH2N, CH2P), 2.35 (s, 3H; CH3), 2.03 (m, 2H; CH2), 1.85-1.15
(m, 5H; CH2, NH2). 13C{1H} NMR (50.3 MHz, C6D6, 20 °C): δ
186.9 (m; CRu), 163.9 (s; NCC), 157.2 (s; NCCH2), 157.1 (s;
C-NO2), 154.8 (d, J(C,P)=3.0 Hz; C-NO2), 149.1-115.0 (m;
aromatic carbon atoms), 80.3 (s, OCH), 52.2 (d, 3J(C,P) =
2.7 Hz; CH2N), 32.5 (m; CH2P), 31.8 (m; CH2P), 26.9 (s;
CH2), 23.0 (s; CH2), 22.3 (s, CH3). 31P{1H} NMR (81.0 MHz,
3
115.4 (m; aromatic carbon atoms), 52.7 (d, J(C,P)=2.8 Hz,
1
1
CH2N), 31.6 (d, J(C,P)=24.6 Hz; CH2P), 31.3 (d, J(C,P)=
31.9 Hz; CH2P), 26.2 (s; CH2), 25.9 (d, 4J(C,P) = 3.7 Hz;
CH3CO), 22.2 (s; CH2), 22.1 (s, CH3). 31P{1H} NMR (81.0 MHz,
2
2
C6D6, 20 °C): δ 60.8 (d, J(PP)=38.3 Hz), 44.6 (d, J(PP)=
38.3 Hz). IR (Nujol): ν 1713 cm-1 (asymmetric ν(OCO)).
Synthesis of 7. To a suspension of complex 1 (105 mg, 0.138
mmol) in toluene (2.1 mL) was added 2.1 mL of a 2-propanol
solution of NaOiPr (0.1 M, 0.21 mmol), and the mixture was
stirred at 60 °C for 2 h. The mixture was kept at -20 °C over-
night, affording the precipitation of NaCl, which was eliminated
by filtration on Celite. The compound 4-nitrophenol (21 mg,
0.151 mmol) was added, and the red solution was stirred for 1 h
at room temperature. The solvent was eliminated, toluene
(2 mL) was added, and the mixture was kept at -20 °C for 2 h.
After filtration on Celite, the resulting solution was concen-
trated (1 mL), and addition of pentane (10 mL) afforded a red-
orange product which was filtered and dried under reduced
pressure. Yield: 104 mg (87%). Anal. Calcd for C47H45N3O3-
P2Ru: C, 65.42; H, 5.26; N, 4.87. Found: C, 65.33; H, 5.37; N,
4.82. 1H NMR (200.1 MHz, C6D6, 20 °C): δ 8.16 (ddd, J(HH)=
9.7, 7.7, 2.0 Hz, 2H; aromatic protons), 8.0 (d, 3J(HH)=9.3 Hz,
2H; aromatic protons), 7.73 (m, 3H; aromatic protons), 7.45-
6.90 (m, 13H; aromatic protons), 6.64 (t, J(HH)=7.4 Hz, 1H;
aromatic proton), 6.45 (t, J(HH)=8.6 Hz, 2H; aromatic protons),
6.37 (t, J(HH)=8.8 Hz, 2H; aromatic protons), 6.00 (t, J(HH)=
2
2
C6D6, 20 °C): δ 57.3 (d, J(PP)=34.9 Hz), 40.4 (d, J(PP)=
34.9 Hz). IR (Nujol): ν 1526 (asymmetric ν(NO2)), 1352 cm-1
(symmetric ν(NO2)).
Synthesis of 10. The complex 1 (100 mg, 0.132 mmol) and
NaOSiMe3 (19 mg, 0.169 mmol) were suspended in toluene
(2 mL), and the mixture was stirred at room temperature for 1 h.
The suspension was kept at -20 °C overnight and filtered on
Celite, and the solution was concentrated (1 mL). Addition of
pentane (5 mL) afforded an orange precipitate, which was
filtered, washed with pentane (2 ꢀ 2 mL), and dried under
reduced pressure. Yield: 80 mg (74%). Anal. Calcd for C44H50-
N2OP2RuSi: C, 64.92; H, 6.19; N, 3.44. Found: C, 65.20; H,
3
8.1 Hz, 2H; aromatic protons), 5.92 (d, J(HH)=9.3 Hz, 2H;
aromatic protons), 5.79 (d, J(HH)=7.5 Hz, 1H; aromatic proton),
3.50 (m, 1H; NH2), 3.35-2.80 (m, 4H; CH2N and CH2P), 2.27
(s, 3H; CH3), 2.30-0.80 (m, 7H; CH2, NH2). 13C{1H} NMR
2
(50.3 MHz, C6D6, 20 °C): δ 182.6 (dd, J(C,P)=17.1, 7.5 Hz;
CRu), 177.9 (s; C-O), 163.9 (s; NCC), 156.6 (s; NCCH2),
149.4-115.4 (m; aromatic carbon atoms), 51.8 (d, 3J(C,P) =
2.8 Hz; CH2N), 31.0 (d, 1J(C,P) = 25.1 Hz; CH2P), 30.9 (d,
1J(C,P) = 32.2 Hz; CH2P), 26.6 (s; CH2), 22.1 (d, 2J(C,P) =
1.5 Hz; CH2), 22.0 (s, CH3). 31P{1H} NMR (81.0 MHz, C6D6,
20 °C): δ 62.1 (d, 2J(PP)=38.5 Hz), 41.6 (d, 2J(PP)=38.5 Hz). IR
(Nujol): ν 1495 (asymmetric ν(NO2)), 1342 cm-1 (symmetric
ν(NO2)).
1
5.93; N, 3.47. H NMR (200.1 MHz, C6D6, 20 °C): δ 8.43 (t,
J(HH)=8.0 Hz, 2H; aromatic protons), 7.94 (t, J(HH)=7.6 Hz,
2H; aromatic protons), 7.84 (s, 1H; aromatic proton), 7.41-6.58
(m, 16H; aromatic protons), 6.50 (t, J(HH)=6.2 Hz, 2H; aromatic
protons), 6.02 (m, 3H, aromatic protons), 4.50 (broad s, 1H;
NH2), 3.32 (m, 2H; CH2), 2.95 (m, 2H; CH2), 2.30 (s, 3H; CH3),
2.12-0.87 (m, 7H; CH2 and NH2), -0.17 (s, 9H; SiMe3).
13C{1H} NMR (50.3 MHz, C6D6, 20 °C): δ 185.0 (dd, 2J(C,P)=
15.9, 8.4 Hz; CRu), 164.4 (s; NCC), 156.9 (s; NCCH2), 149.3-
Synthesis of 8. To a suspension of 1 (148 mg, 0.195 mmol) in
toluene (3 mL) was added 3 mL of a 2-propanol solution of
KOiPr (0.1 M, 0.300 mmol), and the mixture was stirred at 60 °C
for 2 h. The suspension was kept at -20 °C for 2 h and KCl was
eliminated by filtration on Celite. 4-Fluoro-3-methylphenol
(31 μL, 0.279 mmol) was added, and the solution was stirred
for 30 min at room temperature. The solvent was eliminated,
and the residue was dissolved in toluene (2 mL). Evaporation of
the solvent afforded an orange solid which was dried under
reduced pressure. Yield: 150 mg (91%). Anal. Calcd for C48H47F-
N2OP2Ru: C, 67.83; H, 5.57; N, 3.30. Found: C, 68.01; H, 5.39;
N, 3.12. 1H NMR (200.1 MHz, C6D6, 20 °C): δ 8.61 (t, J(HH)=
8.1 Hz, 2H; aromatic protons), 8.07 (t, J(HH) = 8.1 Hz, 2H
aromatic protons), 7.85 (s, 1H; aromatic proton), 7.54-6.40 (m,
21H; aromatic protons), 6.15 (t, J(HH)=7.9 Hz, 2H; aromatic
protons), 5.90 (d, J(HH)=7.0 Hz, 1H; aromatic proton), 4.47
(broad s, 1H; NH2), 3.45-2.80 (m, 5H; CH2N, CH2P), 2.30
3
115.1 (m; aromatic carbon atoms), 51.8 (d, J(C,P)=2.7 Hz;
1
1
CH2N), 31.3 (d, J(C,P)=23.6 Hz; CH2P), 30.8 (d, J(C,P)=
29.5 Hz; CH2P), 27.0 (s; CH2), 22.3 (s; CH2), 22.1 (s; CH3), 4.8
(s; SiMe3). 31P{1H} NMR (81.0 MHz, C6D6, 20 °C): δ 59.3
(d, 2J(PP)=36.5 Hz), 39.8 (d, 2J(PP) = 36.5 Hz).
Synthesis of 11. Complex 1 (154 mg, 0.203 mmol) was
dissolved in dichloromethane (5 mL), and CF3SO3Tl (72 mg,
0.204 mmol) was added. The orange suspension was stirred at
room temperature for 2 h and filtered on Celite to eliminate
TlCl, and the filtrate was reduced to 1 mL. Addition of pentane
afforded a yellow precipitate, which was filtered, washed with
pentane, and dried under reduced pressure. Yield: 142 mg
(80%). Anal. Calcd for C42H41F3N2O3P2RuS: C, 57.73; H,
4.73; N, 3.21. Found: C, 57.65; H, 4.89; N, 3.01. 1H NMR
(200.1 MHz, CD2Cl2, 20 °C): δ 7.91 (m, 2H; aromatic protons),
7.60-7.20 (m, 16H; aromatic protons), 7.06 (d, J(HH)=8.0 Hz,
2H; aromatic protons), 6.83 (d, J(HH)=7.7 Hz, 2H; aromatic
protons), 6.73 (d, J(HH)=7.5 Hz, 2H; aromatic protons), 6.06
(m, 2H; aromatic protons), 4.18 (m, 1H; NH2), 3.81 (m, 1H;
CH2N), 3.61 (m, 1H; CH2N), 3.05 (m, 2H; PCH2), 2.20 (s, 3H;
CH3), 2.30-0.80 (m, 7H; NH2 and CH2). 13C{1H} NMR
(50.3 MHz, CD2Cl2, 20 °C): δ 178.1 (t, 2J(C,P)=12.6 Hz; CRu),
164.8 (s; NCC), 158.7 (s; NCCH2), 149.7-116.4 (m; aro-
4
(s, 3H; CH3), 2.05 (d, J(HF)=1.5 Hz, 3H; FCCCH3), 2.24-
1.01 (m, 6H; NH2, CH2). 13C{1H} NMR (50.3 MHz, C6D6,
20 °C): δ 185.4 (dd, 2J(C,P)=16.0, 7.8 Hz; CRu), 164.0 (s; NCC),
156.4 (s; NCCH2), 152.5 (d, 1J(CF)=220.6 Hz; C-F), 148.7-
3
114.9 (m; aromatic carbon atoms), 52.0 (d; J(C,P)=2.8 Hz,
1
1
CH2N), 31.4 (d, J(C,P)=30.0 Hz; CH2P), 30.6 (d, J(C,P)=
25.1 Hz; CH2P), 26.9 (s; CH2), 22.2 (s; CH2), 22.0 (s;
CH3), 15.0 (d, 3J(CF) = 1.6 Hz; FCCCH3). 31P{1H} NMR
2
1
(81.0 MHz, C6D6, 20 °C): δ 60.4 (d, J(PP) = 36.9 Hz), 38.6
matic carbon atoms), 119.8 (q, J(CF)=320.0 Hz; CF3), 52.9

4430 Organometallics, Vol. 28, No. 15, 2009
Baratta et al.
Table 4. Crystallographic Data for Complexes 5 and 6
(s; CH2N), 31.9 (s; CH2P), 31.2 (s; CH2P), 26.8 (s; CH2), 22.7
(s; CH2), 21.7 (s; CH3). 31P{1H} NMR (81.0 MHz, CD2Cl2,
20 °C): δ 65.4 (br s), 42.5 (d, 2J(PP) = 30.7 Hz). 19F NMR
(188.3 MHz, CD2Cl2, 20 °C): δ -77.6 (s). 1H NMR (200.1 MHz,
toluene-d8, 20 °C): δ 8.07 (m, 2H; aromatic protons), 7.80-
7.65 (m, 3H; aromatic protons), 7.37 (t, J(HH) = 6.9 Hz, 2H;
aromatic protons), 7.26-7.05 (m, 5H; aromatic protons), 7.02
(m, 1H; aromatic proton), 6.98 (m, 4H; aromatic protons), 6.87
(d, J(HH)=7.6 Hz, 1H; aromatic proton), 6.78 (d, J(HH)=4.3 Hz,
2H; aromatic protons), 6.65 (t, J(HH)=7.0 Hz, 1H; aromatic
proton), 6.44 (t, J(HH)=6.8 Hz, 2H; aromatic protons), 6.20 (m,
1H; aromatic proton), 5.99 (t, J(HH)=8.3 Hz, 2H; aromatic
protons), 4.21 (m, 1H; NH2), 3.61 (m, 1H; CH2N), 3.21 (m, 1H;
CH2N), 2.95 (m, 2H; CH2P), 2.26 (s, 3H; CH3), 2.30-0.70 (m,
7H; NH2 and CH2). 13C{1H} NMR (50.3 MHz, toluene-d8,
20 °C): δ 178.2 (dd, 2J(C,P)=18.1, 7.0 Hz; CRu), 164.4 (s; NCC),
158.5 (s; NCCH2), 149.5-116.3 (m; aromatic carbon atoms
and CF3), 52.6 (d, 3J(C,P)=1.8 Hz; CH2N), 31.7 (d, 1J(C,P)=
35.4 Hz; CH2P), 30.8 (d, 1J(C,P) = 32.1 Hz; CH2P), 26.4
(s; CH2), 22.0 (s; CH2), 21.9 (s, CH3). 31P{1H} NMR (81.0 MHz,
toluene-d8, 20 °C): δ 68.3 (d, 2J(PP) = 42.5 Hz), 43.0 (d,
2J(PP) = 42.5 Hz). 19F NMR (188.3 MHz, toluene-d8, 20 °C):
δ -73.5 (s).
formate 5
acetate 6 1.5C6H6
3
empirical formula
C42H42N2O2-
P2Ru
769.79
153(1)
monoclinic
P21/n
11.2659(5)
11.5008(14)
27.682(2)
90
C52H53N2O2-
P2Ru
formula wt
T (K)
cryst syst
Space group
a (A)
b (A)
c (A)
R (deg)
β (deg)
900.97
293(2)
triclinic
P1
11.815(4)
13.204(4)
17.016(4)
84.26(3)
72.34(2)
66.90(3)
2326.2(12)
2
2.09-28.28
0.447
938
1.286
35 379
10 080/0.051
5902
538
94.279(5)
90
γ (deg)
V (A3)
3576.7(5)
4
2.83-25.36
0.567
1592
1.430
63 721
6553/0.077
4329
443
0.0331/0.0636 0.0415/0.0966
0.0701/0.0706 0.0735/0.1053
0.928
þ0.69/-0.64
Z
θ range data collection (deg)
μ (mm-1
F(000)
)
Dcalcd (g cm-3
)
no. of rflns collected
no. of indep rflns/Rint
no. of obsd rflns (I > 2σ(I))
no. of params
R1/wR2 (I > 2σ(I))
R1/wR2 (all data)
Synthesis of 12. The preparation of 12 was carried out in a
way similar to that described for 8, using compound 4 (100 mg,
0.127 mmol) instead of 1, 1.9 mL of a 2-propanol solution of
KOiPr (0.1 M, 0.190 mmol), and 4-fluoro-3-methylphenol (16 μL,
0.144 mmol). Yield: 91 mg (82%). Anal. Calcd for C50H51-
FN2OP2Ru: C, 68.40; H, 5.85; N, 3.19. Found: C, 68.15; H, 5.69;
N, 3.27. 1H NMR (200.1 MHz, C6D6, 20 °C): δ 8.23 (t, J(HH)=
9.0 Hz, 2H; aromatic protons), 8.19 (t, J(HH)= 8.8 Hz, 2H;
aromatic protons), 7.84-6.35 (m, 21H; aromatic protons), 6.33
(d, J(HH) = 7.3 Hz, 1H; aromatic proton), 6.24 (t, J(HH) =
8.0 Hz, 2H; aromatic protons), 6.08 (m, 1H; aromatic proton),
3.78 (d, J(HH)=14.7 Hz, 1H; CH2N), 3.24 (d, J(HH)=14.7 Hz,
1H; CH2N), 2.17 (s, 3H; CH3), 2.11 (br s, 3H; FCCCH3),
1.97 (br s, 6H; NMe2), 2.98-0.77 (m, 8H; CH2). 31P{1H}
GOF (on F2)
0.875
þ0.32/-0.24
largest diff peak and hole (e A-3
)
Crystallographic Studies of Compounds 5 and 6. Clear orange
crystals were mounted on a glass fiber in both cases. X-ray data
of compound 5 were collected on an Oxford Xcalibur system
and those of 6 1.5C6H6 on a Nonius DIP-1030H system by
3
using Mo KR radiation (λ=0.710 73 A). Data were processed
and corrected for Lorentz and polarization and for absorption
effects with the Crysalis suite of programs38 and the Denzo/
Scalepack packages,39 respectively. Both of the structures were
solved by direct methods followed by difference Fourier calcu-
lations. Hydrogen atoms were placed in ideal positions (riding
model). All calculations were performed with the WinGX
program system.40 Crystal and refinement data are summarized
in Table 4.
2
NMR (81.0 MHz, C6D6, 20 °C): δ 52.4 (d, J(PP)=34.2 Hz),
2
39.7 (d, J(PP)=34.2 Hz). 19F{1H} NMR (188.3 MHz, C6D6,
20 °C): δ -139.6 (s).
Synthesis of 13b. The complex 4 (110 mg, 0.140 mmol) was
suspended in 2.0 mL of a toluene/tBuOH mixture (1:1 by
volume), and KOtBu (24 mg, 0.214 mmol) was added. The
mixture was stirred for 2 h at room temperature, giving a dark
red solution, which was kept at -20 °C overnight and filtered on
Celite. The solvent was eliminated, toluene (2.0 mL) was added,
and the resulting solution was concentrated (1 mL). Addition of
pentane (5.0 mL) afforded a dark red product, which was
filtered and dried under reduced pressure. Yield: 86 mg (74%).
Anal. Calcd for C47H54N2OP2Ru: C, 68.35; H, 6.59; N, 3.39.
Found: C, 68.23; H, 6.41; N, 3.48. 1H NMR (200.1 MHz, C6D6,
20 °C): δ 8.66 (m, 2H; aromatic protons), 8.38 (t, J(HH) =
7.8 Hz, 2H; aromatic protons), 7.97-5.87 (m, 22H; aro-
matic protons), 3.95 (d, J(HH)=13.7 Hz, 1H; CH2N), 2.83 (d,
J(HH)=13.7 Hz, 1H; CH2N), 2.60-0.76 (m, 8H; CH2), 2.20
(s, 3H; CH3), 2.00 (br s, 6H; NMe2), 1.35 (s, 9H; CMe3). 31P{1H}
Acknowledgment. This work was supported by the
ꢀ
the Regione Friuli Venezia Giulia. We thank Johnson-
Matthey/Alfa Aesar for a generous loan of ruthe-
nium and Mr. P. Polese for carrying out the elemental
analyses.
Ministero dell’Universita e della Ricerca (MIUR) and
Supporting Information Available: CIF files giving crystal and
data collection parameters, atomic coordinates, bond lengths,
bond angles, and thermal displacement parameters for 5 and 6.
This material is available free of charge via the Internet at http://
pubs.acs.org.
2
(38) CrysAlis Data Collection Software and Data Processing Software
for Oxford Xcalibur diffractometer, Version 1.171; Oxford Diffraction
Ltd., Oxfordshire, U.K., 2005.
NMR (81.0 MHz, C6D6, 20 °C): δ 48.3 (d, J(PP)=31.1 Hz),
35.4 (d, 2J(PP)=31.1 Hz).
Typical Procedure for the Catalytic Transfer Hydrogenation.
The ruthenium complex (2.5 μmol) was dissolved in 5 mL of
2-propanol. The ketone (2.0 mmol) was dissolved in 2-propanol
(final volume 19.4 mL), and the solution was heated to reflux
under argon. By addition of NaOiPr (0.1 M, 0.4 mL, 0.04 mmol)
and the solution containing the ruthenium complex (0.2 mL,
0.10 μmol), the reduction of the ketone starts immediately and
the yield was determined by GC analysis (complex 0.005 mol %,
NaOiPr 2 mol %).
(39) Otwinowski, Z.; Minor, W. Processing of X-ray Diffraction
Data Collected in Oscillation Mode. In Macromolecular Crystallogra-
phy, Part A; Carter, C. W., Jr., Sweet, R. M., Eds.; Academic Press: New
York, 1997; Methods in Enzymology Vol. 276, pp 307-326.
(40) (a) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi,
A.; Burla, M. C.; Polidori, G.; Camalli, M. SIR92. J. Appl. Crystallogr.
€
1994, 27, 435. (b) Sheldrick, G. M. SHELXL-97; University of Gottingen,
€
Gottingen, Germany, 1998. (c) Spek, A. L.; PLATON; Utrecht University,
Utrecht, The Netherlands, 2008. (d) Farrugia, L. J. J. Appl. Crystallogr.
1999, 32, 837.