pH-dependent selective transfer hydrogenation of α,β-unsaturated carbonyls in aqueous media utilizing half-sandwich ruthenium(II) complexes

Article abstract of DOI:10.1021/om060892x

Half-sandwich ruthenium(II) PTA complexes bearing the 1,2-dihydropentalenyl (C₈H₉^-, Dp) and indenyl (C₉H ₇^-, Ind) ancillary ligands have been synthesized and characterized using multinuclea

Full text of DOI:10.1021/om060892x

Organometallics 2007, 26, 429-438
429
pH-Dependent Selective Transfer Hydrogenation of r,â-Unsaturated
Carbonyls in Aqueous Media Utilizing Half-Sandwich
Ruthenium(II) Complexes
Charles A. Mebi, Radhika P. Nair, and Brian J. Frost*
Department of Chemistry, UniVersity of NeVada, Reno, NeVada 89557
ReceiVed September 28, 2006
-
Half-sandwich ruthenium(II) PTA complexes bearing the 1,2-dihydropentalenyl (C8H9 , Dp) and indenyl
-
(C9H7 , Ind) ancillary ligands have been synthesized and characterized using multinuclear NMR
spectroscopy and X-ray crystallography. The complexes DpRu(PTA)(PPh3)Cl, DpRu(PTA)2Cl, IndRu-
(PTA)(PPh3)Cl, and [IndRu(PTA)2(PPh3)]Cl were obtained in good to excellent yields. The solid-state
structures of these compounds exhibit piano stool geometries with η5-coordination of the indenyl and
dihydropentalenyl moieties. DpRu(PTA)2Cl is water-soluble (S25°C ) 43 mg/mL), while the mixed
phosphine compounds are slightly soluble in acidic solutions. The Ru-H complexes, Cp′Ru(PTA)(PPh3)H
(Cp′ ) Ind, Cp), have been synthesized in good yield and spectroscopically and structurally characterized.
The ruthenium hydrides undergo an H/D exchange reaction with CD3OD with relative rates CpRu(PTA)-
(PPh3)H . IndRu(PTA)(PPh3)H > CpRu(PTA)2H. The air-stable Cp′Ru(PTA)(PR3)Cl complexes (Cp′
) Cp, Dp, Ind; PR3 ) PPh3 or PTA) exhibit activity in the regioselective transfer hydrogenation of
R,â-unsaturated carbonyls in aqueous media with HCOONa, HCOOH, or isopropanol/Na2CO3 serving
as the hydrogen source. They were found to be effective in the selective reduction of the carbonyl
functionality of cinnamaldehyde and the CdC bond of benzylidene acetone and chalcone. IndRu(PTA)-
(PPh3)Cl was less active than Cp′Ru(PTA)(PPh3)Cl (Cp′ ) Cp or Dp). Results of the transfer hydrogenation
of unsaturated substrates using CpRu(PTA)(PPh3)H are also reported.
have reported pH-dependence of the regioselective hydrogena-
tion of R,â-unsaturated carbonyls.
Introduction
Aqueous biphasic catalysis has been of interest in academic
and industrial circles since the early 1970s when Manassen and
Joo´ independently developed the field.1,2 Water is probably the
most desirable “green” solvent, as it is nonflammable, inex-
pensive, abundant, and environmentally benign.3 Apart from its
role as solvent in aqueous catalysis, water is reported to be
actively involved in a variety of reactions through coordination
to a metal center and/or proton transfer.4 The ability to vary
the activity and selectivity of a water-soluble catalyst by
modulating conditions, such as pH, is another unique aspect of
aqueous phase catalysis.4a-7 For example, Joo´3a,6-9 and others10-12
We13,14 and others15,16 have recently reported that CpRu-
(PTA)2X (X ) Cl or H) complexes, where PTA ) 1,3,5-triaza-
7-phosphaadamantane, are active in the catalytic reduction of
R,â-unsaturated ketones in aqueous or biphasic environments
using H2 as the reductant. The ability of complexes such as
these to undergo H/D exchange with solvent, such as D2O and
CD3OD, has been reported.14,17,18 Herein, we report the prepara-
tion and characterization of a series of Cp′Ru(PTA)(PPh3)Cl
complexes bearing 1,2-dihydropentalenyl (η5-C8H9-, Dp) or
indenyl (η5-C9H7-, Ind) ancillary ligands: DpRu(PTA)(PPh3)-
Cl (3), IndRu(PTA)(PPh3)Cl (5), [IndRu(PTA)2(PPh3)]Cl (6),
and DpRu(PTA)2Cl (4). The use of these compounds as transfer
hydrogenation catalysts employing formic acid or sodium
* Corresponding author. E-mail: Frost@chem.unr.edu.
(1) Joo´, F.; Beck, M. Magy. Ke´m. Foly. 1973, 79, 189-191.
(2) Manassen, J. Catalysis: Progress in Research; Plenum Press:
London, 1973.
(7) Joo´, F.; Kovacs, J.; Benyei, A. Cs.; Katho, A. Angew. Chem., Int.
Ed. 1998, 37, 969-970.
(3) (a) Joo´, F. Acc. Chem. Res. 2002, 35, 738-745. (b) Joo´, F. Aqueous
Organometallic Catalysis; Catalysis by Metal Complexes 23; Kluwer
Academic Publishers: Boston, 2001. (c) Aqueous Organometallic Chemistry
and Catalysis; Horvath, I. T., Joo´, F., Eds.; NATO ASI Series 3; High
Technology; Kluwer: Dordrecht, The Netherlands, 1995. (d) Joo´, F.; Katho´,
A. In Aqueous Phase Organometallic Catalysis, 2nd ed.; Wiley-VCH:
Weinheim, Germany, 2004. (e) Adams, D. J.; Dyson, P. J.; Tavener, S. J.
Chemistry in AlternatiVe Reaction Media; Wiley: Chichester, U.K., 2004.
(4) For example see: (a) Yin, C.; Xu, Z.; Yang, S.-Y.; Ng, S. M.; Wong,
K. Y.; Lin, Z.; Lau, C. P. Organometallics 2001, 20, 1216-1222. (b)
Laghmari, M.; Sinou, D. J. Mol. Catal. 1991, 66, L15-L18. (c) Kova´cs,
G.; Schubert, G.; Joo´, F.; Pa´pai, I. Organometallics 2005, 24, 3059-3065.
(d) Chu, H. S.; Xu, Z.; Ng, S. M.; Lau, C. P.; Lin, Z. Eur. J. Inorg. Chem.
2000, 993-1000. (e) Ohnishi, Y.; Nakao, Y.; Sato, H.; Sakaki, S.
Organometallics 2006, 25, 3352-3363. (f) Joo´, F.; Nadasdi, L.; Benyei,
A. Cs.; Darensbourg, D. J. J. Organomet. Chem. 1996, 512, 45-50.
(5) Joo´, F.; Kovacs, J.; Benyei, A. Cs.; Nadasdi, L.; Laurenczy, G. Chem.
Eur. J. 2001, 7, 193-199.
(8) Kova´cs, G.; Ujaque, G.; Lledo´s, A.; Joo´, F. Organometallics 2006,
25, 862-872.
(9) Papp, G.; Kovacs, J.; Benyei, A. Cs.; Laurenczy, G.; Nadasdi, L.;
Joo´, F. Can. J. Chem. 2001, 79, 635-641.
(10) Joubert, J.; Delbecq, F. Organometallics 2006, 25, 854-861.
(11) Grosselin, J. M.; Mercier, C.; Allmang, G.; Grass, F. Organome-
tallics 1991, 10, 2126-2133.
(12) Hernandez, M.; Kalck, P. J. Mol. Catal. A 1997, 116, 131-146.
(13) Mebi, C. A.; Frost, B. J. Organometallics 2005, 24, 2339-2346.
(14) Frost, B. J.; Mebi, C. A. Organometallics 2004, 23, 5317-5323.
(15) Bolano, S.; Gonsalvi, L.; Zanobini, F.; Vizza, F.; Bertolasi, V.;
Romerosa, A.; Peruzzini, M. J. Mol. Cat. A 2004, 224, 61-70.
(16) Akbayeva, D. N.; Gonsalvi, L.; Oberhauser, W.; Peruzzini, M.;
Vizza, F.; Brueggeller, P.; Romerosa, A.; Sava, G.; Bergamo, A. Chem.
Commun. 2003, 264-265.
(17) Belkova, N. V.; Besora, M.; Epstein, L. M.; Lledo´s, A.; Maseras,
F.; Shubina, E. S. J. Am. Chem. Soc. 2003, 125, 7715-7725.
(18) Kova´cs. G.; Schubert, G.; Joo´, F.; Pa´pai, I. Organometallics 2005,
24, 3059-3065.
(6) Joo´, F.; Kovacs, J.; Benyei, A. Cs.; Katho, A. Catal. Today 1998,
42, 441-448.
10.1021/om060892x CCC: $37.00 © 2007 American Chemical Society
Publication on Web 12/10/2006

430 Organometallics, Vol. 26, No. 2, 2007
Mebi et al.
solid washed with diethyl ether, affording 76 mg of 3 as orange
formate as the reducing agent is described. Also reported is the
synthesis and reactivity of the mixed phosphine hydrides CpRu-
(PTA)(PPh3)H (7) and IndRu(PTA)(PPh3)H (8).
1
crystals (50% yield). H NMR (400 MHz, CDCl3): δ 7.58-7.34
2
(complex m, PPh3); 4.41, 4.23 (AB quartet, J(HAHB) ) 13.2 Hz,
2
6H NCH2N); 3.92 (d, J(HAHB) ) 14.4 Hz 3H, PCH2N), 3.65 (d,
2J(HAHB) ) 14.4 Hz 3H, PCH2N); 4.24, 3.73, 3.29 (s, 3H Cp); 2.40-
Experimental Section
1.96 (m, 6H Cp(CH2)3). 31P{1H} NMR (162 MHz, CDCl3): δ 43.2
2
2
ppm (d, PPh3, Jpp ) 45.2 Hz); -39.6 ppm (d, PTA, Jpp ) 45.2
Hz). Anal. Calc for C32H36ClN3P2Ru: C, 58.14; H, 5.49; N, 6.36.
Found: C, 58.41; H, 5.39; N, 6.35. Crystals of 3 obtained from
the aforementioned procedure were suitable for X-ray diffraction,
details of which may be found in Table 1.
Materials and Methods. Unless otherwise noted all manipula-
tions were performed on a double-manifold Schlenk vacuum line
under nitrogen or in a nitrogen-filled glovebox. Solvents were
freshly distilled from standard drying reagents (Na/benzophenone
for THF and hexanes; Mg/I2 for methanol) or dried with activated
molecular sieves and degassed with nitrogen, prior to use. Water
was distilled and deoxygenated before use. All reagents were
obtained from commercial sources, checked by NMR and GC/MS,
and used as received. Tetrakis(hydroxymethyl)phosphonium chlo-
ride was obtained from Cytec and used without further purification.
DpRu(PPh3)2Cl,19 1,3,5-triaza-7-phosphaadamantane (PTA),20,21
CpRu(PPh3)2Cl,22 IndRu(PPh3)2Cl,23 and CpRu(PTA)2Cl14,16 were
prepared as described in the literature. GC/MS analyses were
obtained using a Varian CP 3800 GC (DB5 column) equipped with
a Saturn 2200 MS and a CP 8400 auto-injector. All NMR spectra
were recorded on either a Varian Unity Plus 500 FT-NMR
spectrometer, a Varian NMR System 400, a GN 300 FT-NMR/
Scorpio spectrometer, or a QE 300 FT-NMR/Aquarius spectrometer.
1H and 13C NMR spectra were referenced to residual solvent relative
to TMS. Phosphorus chemical shifts are relative to an external
reference of 85% H3PO4 in D2O with positive values downfield of
the reference. IR spectra were recorded on a Perkin-Elmer 2000
FT-IR spectrometer in a 0.1 mm CaF2 cell for solutions or as a
KBr pellet for solid samples. X-ray crystallographic data were
collected at 100((1) K on a Bruker APEX CCD diffractometer
with Mo KR radiation (λ ) 0.71073 Å) and a detector-to-crystal
distance of 4.94 cm. A full sphere of data were collected utilizing
four sets of frames, 600 frames per set with 0.3° rotation about ω
between frames, and an exposure time of 10 s per frame. Data
integration, correction for Lorentz and polarization effects, and final
cell refinement were performed using SAINTPLUS and corrected
for absorption using SADABS or TWINABS. The structures were
solved using direct methods followed by successive least-squares
refinement on F2 using the SHELXTL 5.12 software package.24
Crystallographic data and data collection parameters are listed in
Table 1.
Synthesis of (η5-C8H9)Ru(PTA)2Cl] (4). To 100 mL of toluene
was added 173 mg (0.23 mmol) of DpRu(PPh3)2Cl along with
78 mg (0.5 mmol) of PTA under nitrogen. The solution was heated
to reflux for 3 h, affording DpRu(PTA)2Cl as a yellow precipitate
in 98.5% yield (124 mg, 0.23 mmol). 1H NMR (300 MHz,
2
CDCl3): δ 4.59, 4.51 (AB quartet, J(HAHB) ) 12.8 Hz, 12H
2
NCH2N); 4.18, 4.17 (m, 3H Cp); 4.16 (d, J(HAHB) ) 15.6 Hz, 6H
PCH2N); 4.02 (d, 2J(HAHB) ) 15.6 Hz, 6H PCH2N); 2.50-1.96 (m,
1
6H, Cp(CH2)3). H NMR (300 MHz, D2O): δ 4.52 (br s, 12H
NCH2N); 4.33 (s, 2H , Cp); 4.23 (s, 1H, Cp); 4.09, 3.93 (AB quartet,
2J(HAHB) ) 15.9 Hz, 12H PCH2N); 2.38-1.63 (m, 6H Cp(CH2)3).
31P NMR (162 MHz, CDCl3): δ -27.32 ppm (s), 31P{1H} NMR
(162 MHz, D2O): δ -27.15 ppm (s); -26.76 ppm (s). Anal. Calc
for C20H33N6P2ClRu: C, 43.20; H, 5.98; N, 15.12. Found: C, 43.30;
H, 5.75; N, 14.85. Crystals of 4 suitable for X-ray diffraction were
obtained by diffusion of diethyl ether into a dichloromethane
solution of DpRu(PTA)2Cl. Crystallographic details are reported
in Table 1.
Synthesis of (η5-C9H7)Ru(PTA)(PPh3)Cl (5). A mixture of
IndRu(PPh3)2Cl (1.00 g, 1.3 mmol) and PTA (204 mg, 1.3 mmol)
in 105 mL of toluene was refluxed for 5 h under nitrogen. The
solvent was removed under vacuum and the residue washed several
times with diethyl ether and air-dried, affording 5 as an orange-
1
red solid (312 mg, 72% yield). H NMR (300 MHz, CD2Cl2): δ
7.49-7.23 (m, 19H, PPh3 and indenyl); 7.01 (t, 1H, indenyl); 6.77
(d, 2H, indenyl) 4.35, 4.18 (AB quartet, 2J(HAHB) ) 12.9 Hz, PTA,
2
6H, NCH2N), 3.91 (d, J
) 15.0 Hz, PTA, 3H, PCH2N);
(HAHB)
2
3.54 (d, J
) 15.0 Hz, PTA, 3H, PCH2N). 31P{1H} NMR
(HAHB)
2
(162 MHz, CD2Cl2): δ 50.8 ppm (d, PPh3, JPP ) 42.8 Hz),
-22.6 ppm (d, PTA, 2JPP ) 42.8 Hz). Anal. Calc for C33H34N3P2-
ClRu: C, 59.06; H, 5.11; N, 6.26. Found: C, 58.17; H, 5.04; N,
6.35. X-ray-quality crystals of 5 were grown by slow diffusion of
diethyl ether into a dichloromethane solution of (η5-C9H7)Ru(PTA)-
(PPh3)Cl. Crystallographic details are presented in Table 1.
Synthesis of (η5-C5H5)Ru(PTA)(PPh3)Cl (1). CpRu(PTA)-
(PPh3)Cl was synthesized by a slightly modified procedure from
that recently reported.25 A dichloromethane solution of CpRu-
(PPh3)2Cl (194 mg, 0.27 mmol) and PTA (41 mg, 0.26 mmol) was
stirred for 14 h under nitrogen. The reaction mixture was pulled
dry under vacuum and washed with diethyl ether, affording 52 mg
(0.084 mmol) of 1 as an orange powder in 62% yield. Spectroscopic
data for CpRu(PTA)(PPh3)Cl obtained via this method are identical
to those reported in the literature.25
Synthesis of [(η5-C9H7)Ru(PTA)2(PPh3)]Cl (6). A mixture of
IndRuCl(PPh3)2 (300 mg, 0.39 mmol) and PTA (122 mg, 0.78
mmol) was refluxed under nitrogen in 40 mL of toluene for 4 h.
The resulting yellow precipitate was filtered and dried under
1
vacuum, yielding 197 mg of 6 (62% yield). H NMR (300 MHz,
CD2Cl2): δ 7.4-7.07 (m, 19H, PPh3 and indenyl), 7.02 (t, 1H,
indenyl); 6.75 (d, 2H, indenyl), 4.40 (s, 12H, PCH2N); 4.1, 3.8
(AB quartet, 2J(HAHB) ) 14 Hz, PTA, 12H, NCH2N). 31P{1H} NMR
(162 MHz, CD2Cl2): δ 48.9 ppm (t, PPh3), -34.1 ppm (d, PTA),
2JPP ) 30.1 Hz. Anal. Calc for C39H46N6P3ClRu: C, 56.55; H, 5.60;
N, 10.15. Found: C, 56.62; H, 5.60; N, 10.87. [(η5-C9H7)Ru(PTA)2-
(PPh3)](SnCl3) was synthesized by stirring a mixture of 6 (58 mg,
0.07 mmol) and SnCl2‚2H2O (316 mg, 0.14 mmol) in 40 mL of
dichloromethane for 14 h under nitrogen. The solution was filtered
to remove excess SnCl2‚2H2O and the solvent evaporated under
vacuum, leaving a light brown solid. X-ray-quality crystals of [(η5-
C9H7)Ru(PTA)2(PPh3)](SnCl3) were grown by slow diffusion of
diethyl ether into a dichloromethane solution of the ruthenium
complex.
Synthesis of (η5-C8H9)Ru(PTA)(PPh3)Cl (3). A mixture of
DpRu(PPh3)2Cl (173 mg, 0.23 mmol) and PTA (36 mg, 0.23 mmol)
in 80 mL of toluene was refluxed for 2 h under nitrogen. After
cooling to room temperature, the solvent was evaporated and the
(19) Kirss, R. U.; Ernst, R. D.; Arif, A. M. J. Organomet. Chem. 2004,
689, 419-428.
(20) Daigle, D. J. Inorg. Synth. 1998, 32, 40-45.
(21) Daigle, D. J.; Pepperman, A. B. Jr.; Vail, S. L. J. Heterocycl. Chem.
1974, 11, 407-408.
(22) Joslin, F. L.; Mague, J. T.; Roundhill, D. M. Organometallics 1991,
10, 521-524.
(23) Oro, L. A.; Ciriano, M. A.; Campo, M.; Foces-Foces, C.; Cano, F.
H. J. Organomet. Chem. 1985, 289, 117-131.
(24) XRD Single-Crystal Software; Bruker Analytical X-ray Systems:
Madison, WI, 1999.
Synthesis of (η5-C5H5)Ru(PTA)(PPh3)H (7). CpRu(PTA)-
(PPh3)Cl (30 mg, 0.05 mmol) and HCO2Na (7 mg, 0.10 mmol)
were refluxed for 1 h under nitrogen in 10 mL of methanol. The
(25) Romerosa, A.; Campos-Malpartida, T.; Lidrissi, C.; Saoud, M.;
Serrano-Ruiz, M.; Peruzzini, M.; Garrido-Ca´rdenas, J. A.; Garc´ıa-Maroto,
F. Inorg. Chem. 2006, 45, 1289-1298.

Table 1. Crystallographic Data for Complexes 3-8; Cp′Ru(PTA)(PR3)X, Where Cp′ ) η5-C5H5 (Cp), η5-C8H9, η5-C9H7 (Ind); X ) Cl or H
(η5-C8H9)Ru(PTA)(PPh3)Cl
(η5-C8H9)Ru(PTA)2Cl
IndRu(PTA)(PPh3)Cl
CpRu(PTA)(PPh3)H
IndRu(PTA)(PPh3)H
(3)
(4)
(5)
[IndRu(PPh3)(PTA)2](SnCl3)
(7)
(8)
empirical formula
fw
C32H36ClN3P2Ru
661.10
C20H33ClN6P2Ru
555.98
C33H34N3P2ClRu
671.09
C39H46N6P3Cl3SnRu
1102.76
C29H33N3P2Ru
586.59
C33H35N3P2Ru
636.65
color
T (K)
orange
100(2)
yellow
100(2)
yellow
100(2)
orange
100(2)
pale yellow
100(2)
pale yellow
100(2)
wavelength (Å)
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
volume (Å3)
Z
0.71073
monoclinic
P21/c
17.0102(6)
9.5281(3)
19.0872(7)
90
115.6030(10)
90
2789.80(17)
4
1.574
0.801
1360
0.16 × 0.11 × 0.04
2.16-27.50
-22 e h e 22
-12 e k e 12
-24 e l e 24
35 712
0.71073
orthorhombic
Pna21
18.2731(8)
17.5230(8)
6.9254(3)
90
0.71073
monoclinic
P21/c
16.9997(9)
9.6556(5)
18.9784(10)
90
115.7220(10)
90
2806.5(3)
4
1.588
0.798
1376
0.34 × 0.09 × 0.03
2.17-25.99
-20 e h e 20
-11 e k e 11
-23 e l e 23
31 312
0.71073
monoclinic
P21/c
14.0277(10)
11.7222(8)
26.5468(19)
90
95.6880(10)
90
4343.7(5)
4
1.6
1.379
2216
0.14 × 0.02 × 0.03
1.90-27.50
-18 e h e 18
-15 e k e 15
-34 e l e 34
41 651
0.71073
triclinic
P1h
0.71073
triclinic
P1h
9.6416(4)
11.0933(5)
12.6741(6)
99.4450(10)
102.0990(10)
96.1810(10)
1293.24(10)
2
1.506
0.754
604
0.25 × 0.22 × 0.03
1.67-30.00
-13 e h e 13
-15 e k e 15
-17 e l e 17
20 067
9.9727(7)
10.4488(7)
15.4665(13)
95.4810(10)
90.6990(10)
117.4650(10)
1420.58(18)
2
1.488
0.693
656
0.16 × 0.12 × 0.03
2.21-32.35
-14 e h e 14
-15 e k e 15
-23 e l e 23
25 339
90
90
2217.51(17)
4
1.665
0.993
1144
0.46 × 0.05 × 0.03
2.23-32.28
-27 e h e 27
-26 e k e 26
-10 e l e 10
35 112
D
calcd (Mg/m3)
abs coeff (mm-1
F(000)
)
cryst size (mm3)
θ range (deg)
index ranges
no. of reflns collected
no. of indep reflns
6416
7893
5505
9982
7527
9979
Rint ) 0.0916
6416/0/352
0.811
Rint ) 0.0535
7893/1/271
1.033
Rint ) 0.1148
5505/0/395
0.983
Rint ) 0.2002
9982/0/505
0.904
Rint ) 0.0263
7527/0/352
1.012
Rint ) 0.0622
9979/36/375
1.004
no. of data/restraints/params
GOF on F2
final R indices
[I > 2σ(I)]
R1 ) 0.0364
wR2 ) 0.0721
R1 ) 0.0663
wR2 ) 0.0759
616215
R1 ) 0.0345
wR2 ) 0.0729
R1 ) 0.0417
wR2 ) 0.0761
616220
R1 ) 0.0403
wR2 ) 0.0866
R1 ) 0.0692
wR2 ) 0.0934
616217
R1 ) 0.0641
wR2 ) 0.1045
R1 ) 0.1542
wR2 ) 0.1221
616216
R1 ) 0.0288
wR2 ) 0.0695
R1 ) 0.0344
wR2 ) 0.0714
616218
R1 ) 0.0548
wR2 ) 0.1228
R1 ) 0.0886
wR2 ) 0.1378
616219
R indices
(all data)
CCDC no.

432 Organometallics, Vol. 26, No. 2, 2007
Mebi et al.
solvent was removed under vacuum and the resulting solid extracted
with 5 mL of CH2Cl2. Removal of the CH2Cl2 under reduced
pressure afforded 25 mg (0.04 mmol, 88% yield) of the ruthenium
hydride 7 as a pale yellow powder. Alternatively, 7 may be obtained
by washing the residue with deoxygenated water to remove the
Scheme 1
1
sodium salts. H NMR (400 MHz, DMSO-d6): δ 7.34-7.19 (m,
15H, Ph); 4.39 (s, 5H Cp); 4.05, 3.82 (AB quartet, 2J(HAHB) ) 12.4
2
Hz, 6H, NCH2N); 3.13 (s, 6H, PCH2N); -13.16 ppm (dd, JPH
)
35.2 Hz (PTA), 32.4 Hz (PPh3), 1H, RuH). 31P NMR (162 MHz,
DMSO-d6): δ 68.80 ppm (t, PPh3, JPP ) 36.8 Hz, JPH ) 32.4
Hz); -23.69 ppm (t, PTA, JPP ) 36.8 Hz, JPH ) 35.2 Hz). IR
(KBr): ν(Ru-H) 1925 cm-1 (br). Yellow crystals of CpRu(PTA)-
(PPh3)H suitable for X-ray diffraction were obtained by slow
evaporation of the solvent from a concentrated methanol solution
of 7 at room temperature for 1 h (see Table 1 for details).
2
2
2
2
Scheme 2
Synthesis of (η5-C9H7)Ru(PTA)(PPh3)H (8). A mixture of
IndRu(PTA)(PPh3)Cl (134 mg, 0.2 mmol) and CH3ONa (0.2 mmol)
was refluxed under nitrogen for 5 h in 40 mL of MeOH. The
resulting yellow solution was cooled to room temperature and
filtered, and the solvent was removed under vacuum, resulting in
118 mg of 8 as a pale yellow solid (92% yield). 1H NMR
(400 MHz, CD3OD): δ -16.3 (dd, 2JPTA-H ) 32.0 Hz, 2JPPh3-H
)
2
29.2 Hz, 1H, RuH); 4.30 (d, J(HAHB) ) 12.5 Hz, 3H, NCH2N),
4.06 (d, 2J(HAHB) ) 12.5 Hz, 3H, NCH2N); 4.66 (s, 6H, PCH2N); δ
7.58-7.13 (m, PPh3 indenyl, 19H). 31P{1H} NMR (162 MHz, CD3-
2
OD): δ 62.7 ppm(d, PPh3, JPP ) 29.0 Hz), -23.3 ppm (d, PTA,
Table 2. 31P{1H} Chemical Shifts and Coupling Constants
for the Series of Cp′Ru(PTA)(PR3)Cl Complexes (Cp′ ) Cp,
Dp, Ind; PR3 ) PTA or PPh3) in CDCl3
2JPP ) 29.0 Hz). IR (KBr): ν(Ru-H) 1977 cm-1 (br). X-ray-quality
crystals of (η5-C9H7)Ru(PTA)(PPh3)H were grown by slow diffu-
sion of diethyl ether into a methanol solution of 8.
complex
31P{1H} NMR
2JPP, Hz
Transfer Hydrogenation Procedure. The transfer hydrogena-
tion reactions were carried out in a 20 mL Schlenk tube with a
Teflon valve. The reactions were conducted in acidic or basic
conditions using HCOOH (formic acid), HCOONa (sodium for-
mate), or Na2CO3/isopropanol as the hydrogen source. Each
catalytic run was repeated at least twice to ensure reproducibility.
Method A (Acidic Medium). In a typical catalytic run 5 mol
% catalyst and the substrate were treated with 40 µL of 88%
HCOOH in 2 mL of water. The resultant solution was stirred at
80 °C in an oil bath. The solution was cooled to room temperature
and the product(s) extracted with hexanes (2 × 3 mL). The hexanes
CpRu(PPh3)2Cl
CpRu(PTA)(PPh3)Cl (1)
40.15
48.4 (PPh3)
-34.5 (PTA)
-25.65
45.0
CpRu(PTA)2Cl (2)a,14,16
DpRu(PPh3)2Clb,19
DpRu(PTA)(PPh3)Cl (3)
41.4
43.2 (PPh3)
-39.6 (PTA)
-27.3
45.2
DpRu(PTA)2Cl (4)
IndRu(PPh3)2Cl23
IndRu(PTA)(PPh3)Cl (5)
47.4
50.8 (PPh3)
-22.6 (PTA)
48.9 (PPh3)
-34.1 (PTA)
42.8
30.1
[IndRu(PTA)2(PPh3)]Cl (6)
1
layer was analyzed by GC-MS and H NMR spectroscopy, and
the peaks were identified by comparison with authentic samples.
Yields were determined by H NMR integrations of all products
a In CD2Cl2. b In C6D6.
1
and remaining starting material.
Cl with aminophosphines, Ph2PNHR (R ) Ph, C6H11).26 We
have obtained CpRu(PTA)(PPh3)Cl cleanly in modest yield
(62%) by stirring equimolar amounts of PTA and CpRu(PPh3)2-
Cl in CH2Cl2 at room temperature for 14 h. Cp′Ru(PTA)(PPh3)-
Cl, Cp′ ) η5-C8H9 (3) or η5-C9H7 (5), complexes were prepared
by refluxing equimolar amounts of PTA and Cp′Ru(PPh3)2Cl
in toluene, affording 3 in 50% yield and 5 in 72% yield. The
bis-PTA complex DpRu(PTA)2Cl (4) was obtained as a yellow
precipitate in >98% yield by refluxing a toluene solution of
PTA (0.5 mmol) and DpRu(PPh3)2Cl (0.23 mmol) for 3 h,
Scheme 1. Attempts to synthesize IndRu(PTA)2Cl in an
analogous manner resulted in the formation of the cationic
species [IndRu(PTA)2(PPh3)]Cl (6) in 89% yield, Scheme 2.
The spectroscopic data for compounds 3-6 support the
formulation of the complexes27 and were confirmed by X-ray
crystallography (Vide infra). The 31P{1H} NMR spectra of the
Method B (Basic Medium). In a typical run, the ruthenium
complex, unsaturated carbonyl, and HCOONa in mole ratio of
1:20:500 were dissolved in 2 mL of water or a mixture of water/
methanol (2:3 mL). Alternatively the catalyst, substrate, and Na2-
CO3 in 1:20:212 mole ratio were dissolved in 7 mL of water/
isopropanol (4:3 mL). The reaction temperature, workup, and
analysis are the same as in method A.
Results and Discussion
Preparation of Cp′Ru(PTA)(PR3)Cl Complexes, Cp′ )
Cp, Dp, Ind; PR3 ) PTA or PPh3. The synthesis of a series
of half-sandwich Ru(II) complexes, of the type Cp′Ru(PTA)-
(PR3)Cl, Cp′ ) Cp, Dp, Ind; PR3 ) PTA or PPh3, was
accomplished in good to excellent yields. The complexes CpRu-
(PTA)2Cl14,16 and CpRu(PTA)(PPh3)Cl25 have been previously
synthesized by addition of PTA to CpRu(PPh3)2Cl in toluene.
In our hands, the reaction of PTA with CpRu(PPh3)2Cl in
refluxing toluene afforded the monosubstituted complex CpRu-
(PTA)(PPh3)Cl (1) in low yield and the disubstituted complex
CpRu(PTA)2Cl (2) in high yield as a precipitate irrespective of
the stoichiometric proportions of the reactants. This observation
is consistent with that described for the reaction of CpRu(PPh3)2-
Cp′Ru(PTA)(PPh3)Cl complexes each consist of two doublets
2
due to coupling of the inequivalent phosphorus nuclei: Jpp
)
45.0 Hz, 1; 45.2 Hz, 3; 42.8 Hz, 5; Table 2. The indenyl complex
[IndRu(PTA)2(PPh3)]Cl also exhibits two sets of resonances in
(26) Priya, S.; Balakrishna, M. A.; Mobin, S. M.; McDonald, R. J.
Organomet. Chem. 2003, 688, 227-235.
(27) See Supporting Information for details.

Half-Sandwich Ruthenium(II) Complexes
Organometallics, Vol. 26, No. 2, 2007 433
Figure 1. 31P{1H} NMR spectra of 2 and 4 in D2O: (a)
CpRu(PTA)2Cl (-25.50 ppm) and [CpRu(PTA)2(OH2)]+ (-26.05
ppm); (b) in 0.027 M KCl only CpRu(PTA)2Cl is observed; (c)
DpRu(PTA)2Cl (-26.76 ppm) and [DpRu(PTA)2(OH2)]+ (-27.15
ppm); (d) in 0.027 M KCl only DpRu(PTA)2Cl is observed.
Figure 2. Thermal ellipsoid (50% probability) representation of
DpRu(PTA)(PPh3)Cl (3) with the atomic numbering scheme.
Scheme 3
the 31P{1H} NMR spectrum; 48.9 (t, PPh3, 2JPP ) 30.1 Hz) and
2
-34.1 ppm (d, PTA, JPP ) 30.1 Hz). The 31P{1H} NMR
spectrum of DpRu(PTA)2Cl (4) in CDCl3 contains a single
resonance at -27.3 ppm corresponding to an ∼2 ppm downfield
shift from CpRu(PTA)2Cl14,16 and an ∼7 ppm upfield shift from
1
the Cp* analogue, Cp*Ru(PTA)2Cl (-34.23 ppm).16 The H
NMR spectrum of 4 exhibits a classic AB pattern for the NCH2N
protons of PTA centered at 4.51 and 4.59 ppm; the PCH2N and
C5H3 resonances overlap between 4.00-4.17 ppm. A set of
broad multiplets were observed for the Cp(CH2)3 protons
between 2.50 and 1.96 ppm.
Figure 3. Thermal ellipsoid (50% probability) representation of
IndRu(PTA)(PPh3)Cl (5) with the atomic numbering scheme.
consistent with protonation of a PTA ligand (-10.59 ppm, d,
2
PTAH, JPP ) 16 Hz, 1H+; -7.77 ppm, br, PTAH, 3H+) and
The bis-PTA complexes, CpRu(PTA)2Cl (2) and DpRu-
(PTA)2Cl (4), are soluble in aqueous solution; S25°C ) 40 mg/
mL16 and S25°C ) 43 mg/mL, respectively. 1H and 31P{1H} NMR
spectra of 2 and 4 in aqueous solution both contain two sets of
resonances (Figure 1), the relative heights of which are
concentration-dependent: 31P NMR (D2O): 2, δ -25.50 and
-26.05 ppm; 4, δ -26.76 and -27.15 ppm. The two resonances
observed in aqueous solution indicate the existence of two
species presumably due to the partial hydrolysis of the ruthe-
nium-chloride bond and the formation of the corresponding
aqua complex, Scheme 3. The solid-state structures of two
[CpRu(PR3)2(OH2)]+ cations have been reported: a water-
soluble silver containing polymer of [CpRu(PTA)2(OH2)]+ 28
and an alkyne hydration catalyst [CpRu(PPh2Ar)2(OH2)]+
(where Ar ) 4-tert-butyl-N-methylimidazole).29 As depicted in
Scheme 3, the chloride and aqua complexes are in equilibrium;
addition of Cl- shifts the equilibrium to the left, decreasing the
concentration of the aqua complex (Keq ) 6.18 × 10-4 for 2
and 5.08 × 10-4 for 4).
a very small shift in the PPh3 resonance (55.34 ppm, d, PPh3,
2JPP ) 16 Hz, 1H+; 59.60 ppm, br, PPh3, 3H+). The mixed
phosphine indenyl complex 5 is essentially insoluble even in
acidic solution. As observed for compound 2,13 DpRu(PTA)2Cl
can be protonated at a PTA nitrogen to afford [DpRu-
(PTAH)2Cl]2+ or [DpRu(PTAH)(PTA)Cl]+. Protonation results
in a shift in the 31P{1H} NMR spectrum of 9.6 ppm to
-17.71 ppm, similar in magnitude to the chemical shift
difference between CpRu(PTA)2Cl and [CpRu(PTAH)2Cl]2+ (∆
) 10.05 ppm).13
Structure of Cp′Ru(PTA)(PR3)Cl Complexes, Cp′ ) Dp,
Ind; PR3 ) PTA or PPh3. Thermal ellipsoid representations
of the solid-state structures of DpRu(PTA)(PPh3)Cl (3) and
IndRu(PTA)(PPh3)Cl (5), along with the atomic numbering
schemes, are depicted in Figures 2 and 3, respectively. The
structure of CpRu(PTA)(PPh3)Cl was recently reported;25 how-
ever, we report here a different crystal morphology resulting in
slightly different bond lengths and angles.27 Orange plates of
DpRu(PTA)(PPh3)Cl suitable for X-ray diffraction were ob-
tained by slow evaporation of a toluene solution. X-ray-quality
crystals of IndRu(PTA)(PPh3)Cl were obtained as orange-red
rods by slow diffusion of diethyl ether into a dichloromethane
solution of the complex. All three piano stool complexes, Cp′Ru-
(PTA)(PPh3)Cl (Cp′ ) Cp, Dp, Ind), consist of an η5-Cp′ ligand
bound to ruthenium along with one PTA, one PPh3, and a chlor-
ide ligand. The Ru-Cl distances are comparable and observed
to be between 2.445 and 2.466 Å, Table 3. The Ru-P distances
vary between 2.247 and 2.314 Å for the series depending on
the phosphine and ancillary Cp′ ligand. A slight increase in the
P1-Ru-P2 bond angle is observed as the Cp′ ligand changes:
Cp 95.39(4); Dp 97.80(3); Ind 98.19(4). The Cp-ML2 angle
between the plane defined by the Cp′ ligand and the plane
The mixed phosphine complex 1 is insoluble in water (S25°C
) 1.5 mg/mL),25 as are compounds 3 and 5. In acidic solutions;
however, complexes 1 and 3 become soluble in aqueous
solution, presumably due to protonation of the PTA ligand,
affording the cationic species [Cp′Ru(PTAH)(PPh3)Cl]+, Cp′
) Cp (1H+), Dp (3H+). The formation of [Cp′Ru(PTAH)-
(PPh3)Cl]+ was observed, by 31P{1H} NMR spectroscopy.
Treatment of Cp′Ru(PTA)(PPh3)Cl with HCO2H in water (pH
e 3) resulted in a substantial shift in the 31P{1H} NMR spectrum
(28) Lidrissi, C.; Romerosa, A.; Saoud, M.; Serrano-Ruiz, M.; Gonsalvi,
L.; Peruzzini, M. Angew. Chem., Int. Ed. 2005, 44, 2568-2572.
(29) Grotjahn, D. B.; Incarvito, C. D.; Rheingold, A. L. Angew. Chem.,
Int. Ed. 2001, 40, 3884-3887.

434 Organometallics, Vol. 26, No. 2, 2007
Mebi et al.
Table 3. Selected Bond Lengths [Å] and Angles [deg] for a Series of Cp′Ru(PTA)(PR3)Cl Complexes; Cp′ ) Cp, Dp, or Ind;
and PR3 ) PTA or PPh3
CpRu(PTA)(PPh3)Cla
CpRu(PTA)2Cl14
DpRu(PTA)(PPh3)Cl
DpRu(PTA)2Cl
IndRu(PTA)(PPh3)Cl
(1)
(2)
(3)
(4)
(5)
Ru-Cl
2.4664(10)
2.3139(11)
2.3041(11)
1.861
95.39(4)
90.27(3)
91.68(3)
51.9
2.445(2)
2.258(3)
2.247(3)
1.846
96.85(5)
91.61(7)
86.46(7)
55.3
2.4529(8)
2.2923(9)
2.3089(9)
1.842
97.80(3)
88.06(3)
93.57(3)
54.3
2.4523(7)
2.2645(7)
2.2571(7)
1.855
93.20(2)
89.83(2)
87.03(2)
54.2
2.4465(9)
2.2931(10)
2.2697(10)
1.890
98.19(4)
90.03(3)
91.99(3)
51.4
Ru-P1
Ru-P2
Ru-Cp′cent
P1-Ru-P2
P1-Ru-Cl
P2-Ru-Cl
Cp-ML2
a See Supporting Information for the crystallographic details and ref 25 for a different polymorph of this compound.
Figure 5. Thermal ellipsoid (50% probability) representation of
the cation of [IndRu(PTA)2(PPh3)](SnCl3) along with the atomic
numbering scheme. Selected bond lengths (Å) and angles (deg):
Ru1-P1 ) 2.3076(19); Ru1-P2 ) 2.2576(18); Ru1-P3 ) 2.3456-
(19); Ru1-Indcent ) 1.936; P1-Ru1-P2 ) 92.99(7); P1-Ru1-
P3 ) 97.47(7); P2-Ru1-P3 ) 95.56(7).
Figure 4. Thermal ellipsoid (50% probability) representation of
DpRu(PTA)2Cl (4) with the atomic numbering scheme.
defined by P1-Ru1-P2 varies slightly between the Cp, Dp,
and Ind complexes (Table 3). The distance between the Ru and
the Cp′ plane (Cpcent) is observed between 1.84 and 1.89 Å,
consistent with standard Ru-Cp′ distances.
Scheme 4
Yellow needles of 4 suitable for X-ray diffraction were
obtained by slow diffusion of diethyl ether into a dichlo-
romethane solution of DpRu(PTA)2Cl. A thermal ellipsoid
representation is depicted in Figure 4 showing the piano stool
geometry of 4 with two PTA ligands, a chloride, and an η5-
coordinated C8H9- ancillary ligand. The PTA ligands are bound
through the phosphorus as expected, with a P-Ru-P bond angle
of 93.20(2)°, slightly smaller than that reported for the Cp
analogue (96.85(5)°)14 and similar to that reported for Cp*Ru-
(PTA)2Cl (93.30(5)°).16 This suggests that Cp* and Dp ligands
may have similar stereoelectronic influence on the metal center.
The Ru-P (2.264, 2.257 Å), Ru-Cl (2.452 Å), and Ru-Cpcent
(1.855 Å) distances for 4 are comparable to those of the Cp
and Cp* analogues, Table 3.14,16 The saturated portion of the
η5-C8H9 (Dp) ligand of 4 has an endo-conformation with an
envelope angle of 28.4°, defined as the dihedral angle between
the C5H3 plane and that of C18-C19-C20, slightly larger than
that reported for DpRu(PPh3)2Cl (26.4°).19 The envelope angle
in DpRu(PTA)(PPh3)Cl was found to be 29.5°, larger than that
observed for either DpRu(PPh3)2Cl or 4. The (N)C-N distances
for the triazacyclohexane ring of the PTA ligands in complexes
1-5 are consistent with nonprotonated PTA ligands (N-C(N)
) 1.447-1.480 Å).30
a triplet at 48.9 ppm (2JPP ) 30.1 Hz) for the PPh3 ligand and
a doublet at -34.1 ppm (2JPP ) 30.1 Hz) for the two PTA
ligands. A thermal ellipsoid representation of the structure of
[IndRu(PTA)2(PPh3)](SnCl3) may be found in Figure 5 along
with the atomic numbering scheme and selected bond lengths
and angles. The structure is not unusual, with the indenyl ligand
bound to ruthenium in a η5-fashion and the two PTA ligands
and one PPh3 bound in a classic piano stool fashion about the
metal. It is interesting that the two PTA ligands are not
equivalent, with one Ru-PPTA distance significantly shorter:
Ru-PPTA ) 2.3076(19) and 2.2576(18) Å. The triphenylphos-
phine ligand exhibits the longest Ru-P bond length at 2.3456-
(19) Å, Ru-P3. A complete listing of bond lengths and angles
may be found in the Supporting Information.
Structure of [IndRu(PTA)2(PPh3)](SnCl3). Due to difficul-
ties related to crystal growth of [IndRu(PTA)2(PPh3)]Cl (6),
[IndRu(PTA)2(PPh3)](SnCl3) was synthesized by stirring a
mixture of [IndRu(PTA)2(PPh3)]Cl with an excess of SnCl2‚2H2O.
Spectroscopically, both 6 and [IndRu(PTA)2(PPh3)](SnCl3) are
identical; the 31P{1H} NMR spectra of both compounds contain
Cp′Ru(PTA)(PPh3)H Complexes (Cp′ ) Cp, Dp, Ind):
Synthesis and Reactivity. The air-sensitive ruthenium hydrides,
Cp′Ru(PTA)(PPh3)H (Cp′ ) Cp, In), were obtained in good
yield by the reaction of Cp′Ru(PTA)(PPh3)Cl with sodium
formate or sodium methoxide in refluxing methanol, Scheme
4. The 1H NMR spectra show characteristic Ru-H resonances
(30) Darensbourg, D. J.; Decuir, T. J.; Reibenspies, J. H. Aqueous
Organometallic Chemistry and Catalysis; Horvath, I. T., Joo´, F., Eds.;
NATO ASI Ser., Ser. 3; High Technology; Kluwer: Dordrecht, The
Netherlands, 1995; pp 61-80.
2
at -13.2 ppm (2JPTA-H ) 36.0 Hz, JPPh3-H ) 33.0 Hz) for 7
2
and at -16.3 ppm (2JPTA-H ) 32.0 Hz, JPPh3-H ) 29.2 Hz)
for 8. Table 4 contains detailed 31P{1H} data on the series of

Half-Sandwich Ruthenium(II) Complexes
Organometallics, Vol. 26, No. 2, 2007 435
Table 4. 31P{1H} NMR Chemical Shifts and Coupling
Constants for a Series of Cp′Ru(PTA)(PPh3)H and
Cp′Ru(PTA)2H Complexes (Cp′ ) Cp, Dp, Ind)
chemical shift,
complex
ppm
2JPP, Hz
2JPH, Hz
36.6
32.4 (PPh3)
35.2 (PTA)
33.2
CpRu(PTA)2H14,a
-12.0
CpRu(PTA)(PPh3)H (7)b
68.80 (PPh3)
-23.69 (PTA)
67.76
36.8
CpRu(PPh3)2Hb
IndRu(PTA)(PPh3)H (8)c
62.7 (PPh3)
-23.3 (PTA)
64.5
-17.8
68.39 (PPh3)
-25.90 (PTA)
29.0
37.0
29.2 (PPh3)
32.0 (PTA)
33.9
36.0
32.0 (PPh3)
36.0 (PTA)
IndRu(PPh3)2H23
DpRu(PTA)2Hb
DpRu(PTA)(PPh3)Hb
Figure 6. Thermal ellipsoid (50% probability) representation of
CpRu(PTA)(PPh3)H (7) with the atomic numbering scheme.
b
c
a In D2O. In DMSO-d6. In CD3OD.
Scheme 5. H/D Exchange between Cp′Ru(PTA)(PR3)H and
CD3OD; Cp′ ) η5-(C5H5), η5-(C9H7), or η5-(C8H9) and PR3
) PTA or PPh3
Ru-H complexes. The 31P{1H} spectrum of CpRu(PTA)-
(PPh3)H recorded in DMSO-d6 contained resonances at
68.80 ppm (d, PPh3, 2JPP ) 36.8 Hz) and -23.69 ppm (d, PTA,
2JPP ) 36.8 Hz). The 31P{1H} NMR spectrum of IndRu(PTA)-
(PPh3)H in CD3OD contained signals at 62.7 ppm (d, PPh3)
2
Figure 7. Thermal ellipsoid (50% probability) representation of
IndRu(PTA)(PPh3)H (8) with the atomic numbering scheme.
and -23.3 ppm (d, PTA), JPP ) 29.0 Hz. The preparation of
DpRu(PTA)(PR3)H (PR3 ) PTA or PPh3) via analogous
methods leads to the formation of the respective Ru-H complex
along with an unidentified species and is still under investigation.
Preliminary 1H NMR spectroscopic results in DMSO-d6 reveal
the Ru-H resonances for DpRu(PTA)2H at δ -14.13 ppm (t,
Table 5. Selected Bond Lengths [Å] and Angles [deg] for
CpRu(PTA)(PPh3)H (7) and IndRu(PTA)(PPh3)H (8)
IndRu(PTA)(PPh3)H
CpRu(PTA)(PPh3)H
Ru-H
1.52(4)
2.2564(8)
2.2539(8)
1.929
97.59(3)
83.1(15)
82.7(15)
69.9
1.53(2)
2.2543(4)
2.2449(4)
1.894
97.703(16)
81.4(8)
81.6(8)
72.7
2
2JPH ) 36.0 Hz) and at δ -12.88 ppm (t, JPPh3-H ) 32.0 Hz,
Ru-P1
2JPTA-H ) 36.0 Hz) for DpRu(PTA)(PPh3)H.
Ru-P2
We have previously reported that CpRu(PTA)2H undergoes
H/D exchange with D2O, t1/2 ) 127 min at 25 °C; in CD3OD
no H/D exchange was observed over the course of weeks at
room temperature.14 Interestingly, CpRu(PTA)(PPh3)H under-
goes rapid H/D exchange (t1/2 , 10 min) with CD3OD, affording
CpRu(PTA)(PPh3)D; however, much slower H/D exchange (t1/2
≈ 5.5 days, kobs ≈ 0.12 day-1) was observed for IndRu(PTA)-
(PPh3)H in CD3OD at 25 °C (Scheme 5). Electronic differences
alone between CpRu(PTA)(PPh3)H and IndRu(PTA)(PPh3)H are
not likely responsible for this difference.31 The formation of
Cp′Ru(PTA)(PPh3)D was confirmed by the disappearance of
the hydride resonance in the 1H NMR spectrum, a slight isotopic
shift, and a change in the splitting of the 31P{1H} NMR
resonances, and by IR spectroscopy. The ν(Ru-H) of IndRu-
(PTA)(PPh3)H, CpRu(PTA)(PPh3)H, and DpRu(PTA)(PPh3)H
varies a great deal with the electronic nature of the Cp′ ligand
(Ind > Cp > Dp): ν(Ru-H) ) 1977, 1925, and 1898 cm-1
respectively. Isotopic labeling has been used to identify the IR
bands as ν(Ru-H); deuteration of 7 results in the disappearance
of the absorption band at 1925 cm-1 and appearance of a new
absorbance at 1385 cm-1 for CpRu(PTA)(PPh3)D assigned to
the ν(Ru-D) stretch. The observed isotopic shift (540 cm-1
for 7) is close to the calculated value based on Hooke’s law
(554 cm-1).32
Ru-Cp′cent
P1-Ru-P2
P1-Ru-H
P2-Ru-H
Cp-ML2
Solid-State Structure of CpRu(PTA)(PPh3)H (7) and
IndRu(PTA)(PPh3)H (8). Single-crystal X-ray diffraction was
performed on suitable crystals of CpRu(PTA)(PPh3)H (7) and
IndRu(PTA)(PPh3)H (8), Table 1. Both sets of crystals were
grown by slow evaporation of a concentrated methanol solution
of the Ru-H. Thermal ellipsoid plots of 7 and 8 are presented
in Figures 6 and 7, respectively; along with the atomic
numbering scheme, selected bond lengths and angles may be
found in Table 5. The structures of the Cp′Ru(PTA)(PPh3)H
complexes are similar to those of the parent Ru-Cl complexes
with the notable difference of a significant increase in the Cp-
ML2 angle as the chloride ligand is replaced by the much smaller
and electronically different hydride. The Cp-ML2 angle was
found to be 72.7° and 69.9°, respectively, for 7 and 8, which
compares favorably with the value of 67.8° reported by us for
the CpRu(PTA)2H complex.14 This is ∼20° larger than the
values reported for compounds 1 and 5 and consistent with the
mean value of 67.6° reported for a series of Cp′M(L)2H
complexes.33 The change in Cp-ML2 angle from the Ru-Cl
to the Ru-H complexes can be ascribed to both an electronic
effect and the smaller steric requirement of H- versus Cl-.
Transfer Hydrogenation of r,â-Unsaturated Substrates.
Selective transfer hydrogenation of R,â-unsaturated carbonyls
(31) The details of this unexpectedly large variation in the rate of H/D
exchange in the Cp and Ind complexes are currently under further
investigation; a change in mechanism or possibly an acidic impurity may
be involved.
(32) Drago, R. S. Physical Methods for Chemists, 2nd ed.; Saunders:
Philadelphia, 1992.
(33) Lemke, F. R.; Brammer, L. Organometallics 1995, 14, 3980-3987.

436 Organometallics, Vol. 26, No. 2, 2007
Mebi et al.
Table 6. Selective Transfer Hydrogenation of Cinnamaldehyde by Complexes 1-5 and 7 with HCOOH or HCOONA as
Hydrogen Donorf
b
c
a 100 µL of 88% HCOOH. 0.9 mmol (61.2 mg) of HCO2Na used in lieu of HCO2H, pH ≈ 9. 2 mmol of cinnamaldehyde, 0.03 mmol of catalyst,
22 mmol of HCO2Na, 6 mL of H2O, 80 °C, 5 h.15 d5 mol % of catalyst, 3.7-4.0 µL of cinnamaldehyde, 150 µL of 88% HCOOH, 2 mL of H2O, 1 mL of
MeOH, 24 h. No catalyst, 4.0 µL of cinnamaldehyde, 60 µL of HCO2H, 80 °C, 12 h. f General conditions: 5 mol % of catalyst, 4.0-4.5 µL of cinnamaldehyde,
e
40 µL of 88% HCO2H, 2 mL of H2O, 6 h, 80 °C, pΗ ≈ 3.
Table 7. Selective Transfer Hydrogenation of Benzylidene Acetone by 1-5 and 7 Using HCOOH or HCOONa as the Reducing
Agentg
b
d
a 0.9 mmol (61.2 mg) of HCO2Na in lieu of HCO2H, pH ≈ 9. 25 h. c 6 h. 0.75 mmol of substrate, 7.5 × 10-3 mmol of catalyst, 7.5 mmol of HCO2Na,
f
3 mL of MeOH, 3 mL of H2O, 90 °C, 6 h.15 e 150 µL of HCOOH, 2 mL of H2O, 1 mL of MeOH. 100 µL of HCOOH, 12 h. g General conditions: 5 mol
% of catalyst; 4.3 mg of benzylidene acetone; 40 µL of 88% HCO2H; 2 mL of H2O; 24 h at 80 °C; pH ≈ 3.
Table 8. Selective Transfer Hydrogenation of Chalcone by Compounds 1, 2, 4, 5, and 7 Using HCOOH, HCOONA, or
CH3CH(CH3)OH as Reducing Agentf
b
c
d
a 61.2 mg of HCO2Na (0.9 mmol) used in place of HCO2H. 6 h. HCO2Na 61.2 mg (0.9 mmol); 5.3 mg of PTA added. 38.2 mg of Na2CO3, 4 mL of
H2O, 3 mL of isopropanol in place of HCO2H. e 150 µL of 88% HCOOH, 2 mL of H2O, 1 mL of MeOH, 24 h. f General conditions: 5 mol % of catalyst,
7.6 mg of chalcone, 40 µL of 88% HCO2H, 2 mL of H2O, 3 mL of MeOH, 80 °C, 13 h.
(cinnamaldehyde, benzylidene acetone, and chalcone) has been
accomplished using compounds 1-5 and 7 under acidic and
basic conditions with various hydrogen donors. The results are
contained in Tables 6-8. The hydrogenation products of these
substrates are presented in Scheme 6. Cinnamaldehyde and
benzylidene acetone were hydrogenated in aqueous solution,
while chalcone was reduced utilizing a mixture of water and
methanol for solubility reasons.
Scheme 6. Hydrogenation Pathway for the Unsaturated
Substrates (R ) H, Me, Ph)
Transfer Hydrogenation of Cinnamaldehyde. Cinnamal-
dehyde was reduced under aqueous conditions utilizing Cp′Ru-
(PTA)(PR3)Cl (Cp′ ) Cp, Dp, Ind; PR3 ) PTA or PPh3)
compounds with formic acid or sodium formate as the reducing
agent (Table 6). Entries 1, 2, 7, and 10 in Table 6 describe results
of the transfer hydrogenation of cinnamaldehyde with the mixed

Half-Sandwich Ruthenium(II) Complexes
Organometallics, Vol. 26, No. 2, 2007 437
phosphine complexes Cp′Ru(PTA)(PPh3)Cl (Cp′ ) Cp, Dp, Ind)
using HCOOH as hydrogen donor. The complexes selectively
reduce the CdO bond prior to reduction of the CdC bond.
However, increasing the [HCOOH] afforded hydrocinnamyl
alcohol as the only detectable product (>99% selectivity, entry
2). Replacing CpRu(PTA)(PPh3)Cl with CpRu(PTA)(PPh3)H
had little effect on catalysis, indicating it is a competent reaction
intermediate, entry 3. A decrease in catalyst loading led to
decreased formation of hydrocinnamyl alcohol but no change
in the total conversion (see Supporting Information). A signifi-
cant dependence of hydrocinnamaldehyde selectivity on catalyst
concentration has been reported for [Ir(COD)Cl]2 stabilized by
hydro(pyrazolyl)borate ligands.34 Compared to CpRu(PTA)-
(PPh3)Cl and DpRu(PTA)(PPh3)Cl, IndRu(PTA)(PPh3)Cl is less
active for the reduction of cinnamaldehyde; Table 6, entries 1,
7, and 10. CpRu(PTA)2Cl in the presence of formic acid reduced
cinnamaldehyde all the way down to hydrocinnamyl alcohol
with high conversion (89.5%), Table 6, entry 4. Under basic
conditions (HCOONa used in lieu of HCOOH) a different
product distribution was obtained: 48.1% hydrocinnamaldehyde
and 51.9% hydrocinnamyl alcohol at slightly lower total
conversion (69.6%), Table 6, entry 5. Under different catalytic
conditions, specifically a higher sodium formate concentration,
Peruzzini et al. reported 85.6% selective olefin reduction with
CpRu(PTA)2Cl at low conversion (11.1%), as shown in entry
6.15 DpRu(PTA)2Cl selectively reduces cinnamaldehyde to
cinnamyl alcohol in >99% conversion with formic acid as
hydrogen source (entry 8); replacing HCOOH with HCOONa
results in exclusive formation of the double hydrogenation
product, dihydrocinnamyl alcohol (entry 9). In the absence of
catalyst, no formation of hydrogenation products was detected
replacement of HCOOH for HCOONa, only the olefin reduction
product was obtained in 83.7% yield (entry 7).
Transfer Hydrogenation of 1,3-Diphenylpropenone. The
reduction of chalcone (1,3-diphenylpropenone) using Cp′Ru-
(PTA)2Cl (Cp′ ) Cp or Dp), Cp′Ru(PTA)(PPh3)Cl (Cp ) Cp
or Ind), or CpRu(PTA)(PPh3)H is presented in Table 8. Formic
acid, sodium formate, or Na2CO3/isopropanol were employed
as reducing agents. All the complexes selectively hydrogenate
the CdC bond (>65% selectivity) irrespective of the reducing
agent with the percent conversion ranging from 14 to 93%. The
total conversion and selectivity for CdC bond reduction were
highest in acidic solution (HCOOH, entries 1, 3, 5, 9, 10). In
basic media, hydrogenation continues onto the double hydro-
genation product, 1,3-diphenylpropan-1-ol, thus lowering the
selectivity for the CdC bond reduction product, 1,3-diphenyl-
propan-1-one (entries 2, 4, 6, 8). The presence of free PTA
dramatically lowers the % conversion for the hydrogenation of
chalcone, suggesting that dissociation of PTA from DpRu-
(PTA)2Cl may be involved in the mechanism (entry 7).
Hydride complexes have often been implicated as the active
catalyst in hydrogenation reactions. Indeed, we have shown
previously, with CpRu(PTA)2Cl, that under the catalytic condi-
tions described the generation of CpRu(PTA)2H is possible.14
As a consequence, CpRu(PTA)(PPh3)H was tested as a catalyst
for the reduction of chalcone, resulting in selective CdC
hydrogenation with small amounts of 1,3-diphenylprop-2-enol
(8.3%) detected, entry 10. The use of CpRu(PTA)(PPh3)H as
the catalyst resulted in improved selectivity and higher activity
relative to CpRu(PTA)(PPh3)Cl (Table 8 entry 2), indicating
that the hydride may, in fact, be the active catalyst.
1
by GC-MS or H NMR spectroscopy (entry 11).
Conclusions
The difference in product distribution observed between
CpRu(PTA)2Cl and DpRu(PTA)2Cl (Table 6, entry 4 and 8)
can be attributed to the influence of the different ancillary ligand;
that is, Dp is a more sterically hindered and electron-donating
ligand than Cp. Karam et al. recently observed a remarkable
effect of steric and electronic properties of ancillary ligands on
selective hydrogenation of cinnamaldehyde.34 They reported a
change in the selectivity toward the unsaturated alcohol using
the more sterically demanding and electron-donating ligand Tp*
in lieu of Tp.
Transfer Hydrogenation of Benzylidene Acetone. The
results of hydrogenation of benzylidene acetone by Cp′Ru-
(PTA)(PR3)Cl (Cp′ ) Cp, Dp, Ind; PR3 ) PTA or PPh3) with
HCOOH or HCOONa as the hydrogen donor are presented in
Table 7. In the presence of formic acid, CpRu(PTA)(PPh3)Cl
catalyzed the transfer hydrogenation of benzylidene acetone,
affording 55.9% 4-phenylbutan-2-one and 34.7% 1,3-diphenyl-
propan-1-ol (entry 1). Under the same conditions, DpRu(PTA)-
(PPh3)Cl (entry 5) and IndRu(PTA)(PPh3)Cl (entry 8) selectively
reduced the CdC bond of benzylidene acetone, with IndRu-
(PTA)(PPh3)Cl demonstrating lower activity. In the presence
of either formic acid (entry 2) or sodium formate (entry 3),
CpRu(PTA)2Cl selectively reduces the CdC bond of ben-
zylidene acetone, affording 4-phenylbutan-2-one. Similar regi-
oselectivity has been reported for the reduction of benzylidene
acetone using Cp*Ru(PTA)2Cl as the catalyst and sodium
formate as the reducing agent.15 Hydrogenation of benzylidene
acetone with DpRu(PTA)2Cl as the catalyst resulted in 58.7%
CdC reduction and 41.3% CdO hydrogenation in 81.4% total
yield (entry 6) with HCOOH as the hydrogen donor. Upon
We have presented here the synthesis, characterization, and
reactivity of a series of ruthenium(II) PTA complexes bearing the
cyclopentadienyl (Cp), 1,2-dihydropentalenyl (Dp), and indenyl
(Ind) ancillary ligands. DpRu(PTA)2Cl and CpRu(PTA)2Cl are
water-soluble and exhibit significant Ru-Cl bond hydrolysis in
aqueous solution, while the mixed phosphine complexes, Cp′Ru-
(PTA)(PPh3)Cl, are somewhat soluble in acidic solution due to
protonation of a PTA nitrogen, forming [Cp′Ru(PTAH)(PPh3)-
Cl]+. The Cp′Ru(PTA)(PPh3)H complexes have been prepared
and undergo an H/D exchange reaction with CD3OD with t1/2
< 10 min when Cp′ ) Cp and t1/2 ≈ 5.5 days when Cp′ ) Ind.
Compounds 1-5 and 7 were tested as catalysts for the
selective transfer hydrogenation of unsaturated substrates in
aqueous media. The mixed phosphine complexes, Cp′Ru(PTA)-
(PPh3)Cl, selectively reduced the CdO bond of cinnamaldehyde,
and the CdC bonds of benzylidene acetone and chalcone in
the presence of formic acid (pH e 3). The indenyl complex 5
was less active than either the Cp (1) or Dp (3) analogues. Under
acidic conditions (HCO2H) DpRu(PTA)2Cl was selective toward
hydrogenation of the CdC bond in chalcone and the CdO bond
in cinnamaldehyde and was not selective with benzylidene
acetone as the substrate. In the presence of HCOONa, DpRu-
(PTA)2Cl selectively reduced the CdC bond of benzylidene
acetone. In the presence of either formic acid or sodium formate
CpRu(PTA)2Cl afforded the saturated carbonyl or saturated
alcohol, consistent with results previously reported.15 The results
of this study indicate that the regioselectivity of reduction of
unsaturated substrate depends on the ancillary ligand of the
catalyst, the substrate, and the pH of the solution.
Acknowledgment. The authors would like to thank the
Donors of the American Chemical Society Petroleum Research
(34) Lo´pez-Linares, F.; Agrifoglio, G.; Labrador, AÄ .; Karam, A. J. Mol.
Catal. 2004, 207, 115-120.

438 Organometallics, Vol. 26, No. 2, 2007
Mebi et al.
details of 1 and full bond lengths and angles for compounds 1 and
3-8; and crystallographic data in cif format are available free of
charge via the Internet at http://pubs.acs.org.
Fund for providing partial support of this project. Financial
support from the National Science Foundation (CHE-0226402)
is acknowledged for funding the X-ray diffractometer.
Supporting Information Available: 31P and 1H NMR spectra
of all compounds as well as IR spectra for 7 and 8; crystallographic
OM060892X