mer-[RuCl3(P-P)H2O] (P-P = dppb or diop) as a starting material for the synthesis of binuclear complexes. Crystallographic structures of [(dppb)ClRu-μ(Cl)3-RuCl(dppb)] and [(η6-C6H6)Ru-μ(Cl)3- RuCl(dppb)].: Imine hydrogenation using mono- and binuclear ruthenium complexes

Article abstract of DOI:10.1016/j.poly.2004.09.028

In this work the reactvity of mer-[RuCl₃(P-P)H₂O] (P-P = chiral and achiral chelating ditertiary phosphine) with H₂, ruthenium(II) and ruthenium(III) complexes was studied. Several new and known complexes (Ru₂(II,II) and Ru₂(II,III)) were isolated. The activity of some complexes was tested for the hydrogenation of imines and the results are discussed. X-ray structures of [(dppb)ClRu-(μ-Cl) ₃-RuCl(dppb)] (5) and [(η⁶-C₆H ₆)Ru-(μ-Cl)-RuCl(dppb)] are presented. The reactivity of the mer-[RuCl₃(dppb)H₂O] complex (1) with di-hydrogen shows that the products formed depend on the conditions of the reaction, i.e., solvents and presence or absence of a base. The new mixed-valence complexes [(diop)ClRu-(μ-Cl)₃-RuCl(dppb)] (3), [(binap)ClRu-(μ-Cl) ₃-RuCl(dppb)] (4), [(PPh₃)₂ClRu-(μ-Cl) ₃-RuCl(dppb)] (6), [(dppn)ClRu-(μ-Cl)₃-RuCl(dppb)] (7), [(P-ptol₃)₂ClRu-(μ-Cl)₃-RuCl(dppb)] (8), [(SbPh₃)₂ClRu-(μ-Cl)₃-RuCl(dppb)] (9), [(η⁶-C₆H₆)Ru-(μ-Cl)₃- RuCl(dppb)] (11) and the known mixed-valence [(dppb)ClRu-(μ-Cl) ₃-RuCl(dppb)] (5) and [(diop)ClRu-(μ-Cl)₃-RuCl(diop)] (10) were synthesized from complexes (1) or (2) using a methodology developed in our research group. The known complexes [(dppb)ClRu-(μ-Cl) ₂-RuCl(dppb)] (12), [(dppb)(CO)Ru-(μ-Cl)₃-RuCl(dppb)] (13) and [H₂NEt₂][(dppb)ClRu-(μ-Cl)₃- RuCl(dppb)] (14) were synthesized by changing the reaction conditions between mer-[RuCl₃(dppb)H₂O] (1) and di-hydrogen. The crystal structures of (5) and (11) were determined by single-crystal X-ray diffraction. Some of the complexes described here are effective pre-catalysts for the hydrogenation of imines. Preliminary results on the homogeneous hydrogenation of the imines Ph-CH₂-NCH-Ph and Ph-NCH-Ph are presented.

Full text of DOI:10.1016/j.poly.2004.09.028

Polyhedron 23 (2004) 3163–3172
www.elsevier.com/locate/poly
mer-[RuCl3(P–P)H2O] (P–P = dppb or diop) as a starting material
for the synthesis of binuclear complexes.
Crystallographic structures of [(dppb)ClRu–l(Cl)3–RuCl(dppb)] and
[(g6-C6H6)Ru–l(Cl)3–RuCl(dppb)].
Imine hydrogenation using mono- and binuclear
ruthenium complexes
b
c
c
Marcio P. de Araujo a, ,1, Eliana M.A. Valle , Javier Ellena , Eduardo E. Castellano ,
*
´
d
Eduardo N. dos Santos , Alzir A. Batista
b,
*
a
´ ´
Instituto de Quımica, Universidade Estadual Paulista ‘‘Julio de Mesquita Filho’’, CP 355, CEP 14800-900 Araraquara (SP), Brazil
b
´
Departamento de Quımica, Universidade Federal de Sa˜o Carlos, CP 676, CEP 13565-905 Sa˜o Carlos (SP), Brazil
c
´
Instituto de Fısica de Sa˜o Carlos, Universidade de Sa˜o Paulo, CEP 13560-970 Sa˜o Carlos (SP), Brazil
d
´
Departamento de Quımica, ICEX, Universidade Federal de Minas Gerais, CEP 31270-901 Belo Horizonte (MG), Brazil
Received 16 April 2004; accepted 30 September 2004
Available online 13 November 2004
Abstract
The reactivity of the mer-[RuCl3(dppb)H2O] complex (1) with di-hydrogen shows that the products formed depend on the conditions
of the reaction, i.e., solvents and presence or absence of a base. The new mixed-valence complexes [(diop)ClRu–(l-Cl)3–RuCl(dppb)]
(3), [(binap)ClRu–(l-Cl)3–RuCl(dppb)] (4), [(PPh3)2ClRu–(l-Cl)3–RuCl(dppb)] (6), [(dppn)ClRu–(l-Cl)3–RuCl(dppb)] (7),
[(P-ptol3)2ClRu–(l-Cl)3–RuCl(dppb)] (8), [(SbPh3)2ClRu–(l-Cl)3–RuCl(dppb)] (9), [(g6-C6H6)Ru–(l-Cl)3–RuCl(dppb)] (11) and
the known mixed-valence [(dppb)ClRu–(l-Cl)3–RuCl(dppb)] (5) and [(diop)ClRu–(l-Cl)3–RuCl(diop)] (10) were synthesized from
complexes (1) or (2) using a methodology developed in our research group.
The known complexes [(dppb)ClRu–(l-Cl)2–RuCl(dppb)] (12), [(dppb)(CO)Ru–(l-Cl)3–RuCl(dppb)] (13) and [H2NEt2][(dppb)-
ClRu–(l-Cl)3–RuCl(dppb)] (14) were synthesized by changing the reaction conditions between mer-[RuCl3(dppb)H2O] (1) and di-
hydrogen. The crystal structures of (5) and (11) were determined by single-crystal X-ray diffraction. Some of the complexes described
here are effective pre-catalysts for the hydrogenation of imines. Preliminary results on the homogeneous hydrogenation of the imines
Ph–CH2–N@CH–Ph and Ph–N@CH–Ph are presented.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Keywords: Mixed valent Ru(II)/Ru(III) complexes; Binuclear ruthenium complexes; Catalysis; Imine hydrogenation
*
1. Introduction
Corresponding authors. Tel.: +55 16 2608285/41 3613177; fax:
+55 16 2608350/41 3613186.
E-mail addresses: mparaujo@quimica.ufpr.br (M.P. de Araujo),
Ru(P–P) (P–P = di-tertiary phosphine) chemistry is
very interesting and attractive [1–3, and references there-
in]. The ability of ruthenium complexes containing a sin-
gle chelating di-tertiary phosphine per Ru atom to
daab@power.ufscar.br (A.A. Batista).
1
´
Has recently moved to Universidade Federal do Parana, Centro
´ ´
Politecnico, Jd das Americas, CP 19081, CEP 81531-990, Curitiba
(PR) Brazil.
0277-5387/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2004.09.028

3164
M.P. de Araujo et al. / Polyhedron 23 (2004) 3163–3172
catalyze the hydrogenation of styrene and imines with
practically 100% conversion is described in the literature
[4,5]. Thus the high efficiency of these complexes as pre-
catalysts in hydrogenation reactions assumes crucial
importance in finding out simple routes for their
synthesis.
Face-sharing bi-octahedral complexes are of great
importance due to two facts: (1) these species are poten-
tial catalysts in hydrogenation reactions [4,5]; (2) at least
three different oxidation states can be generated in solu-
tion [6]. Due to these facts binuclear ruthenium phos-
removed from the system by evacuating the autoclave
and refilling it up with Ar three times, and purging three
times with H2 before adjusting it to the desired pressure.
Conversions of imines to amines were determined by 1H
NMR experiments.
IR spectra (cmꢁ1) were recorded as CsI pellets in the
4000–200 cmꢁ1 region, on a Bomen–Michelson 102
instrument; UV–Visible (UV–Vis) and near-infrared
(NIR) spectra were recorded in solution on a Hewlett-
Packard 8452A diode array or Cary 500 spectrophotom-
eters, respectively, and are presented as kmax(nm)/emax
(Mꢁ1 cmꢁ1). Cyclic voltammetry (CV) experiments were
carried out at room temperature in CH2Cl2 containing
0.10 mol lꢁ1 Bu4NþClOꢁ4 (TBAP) (Fluka Purum) using
a BAS-100B/W Bioanalytical Systems Instruments.
The working and auxiliary electrodes were stationary
Pt foils, and the reference electrode was Ag/AgCl, 0.10
mol lꢁ1 TBAP in CH2Cl2, a medium in which ferrocene
is oxidized at 0.43 V (Fc+/Fc).
All NMR experiments were run on BRUKER,
DRX400 9.4 Tesla equipment, in a BBO 5 mm probe
at 298 K, using CDCl3 (1H) and CH2Cl2(31P{1H}) as a
solvent, TMS and H3PO4 85% for internal and external
reference for 1H and 31P, respectively. Effective magnetic
moments (leff) were determined at room temperature
(ꢂ25 ꢁC) by the Gouy method using a Johnson Matthey
magnetic susceptibility balance.
phine
complexes
containing
a
face-sharing
bioctahedral Ru–(l-Cl)3–Ru core have received consid-
erable attention [1,2,6–8].
In this work, we present the synthesis of a series of
binuclear complexes based on the reactivity of the
mer-[RuCl3(P–P)H2O] complexes and their synthesis is
summarized in Eq. (1):
½RuCl3ðP–PÞH2Oꢀ þ ½RuCl2ðP–PÞ0PR3ꢀ
! ½ðP–PÞClRu–ðl-ClÞ –RuClðP–PÞ0ꢀ þ H2O þ PR3
3
ð1Þ
PR3 = PPh3 (triphenylphosphine), P-ptol3 (tri-p-tolyl-
phosphine); (P–P) = dppb (1,4-bis(diphenylphosph-
ino)butane) or S-diop ((2S–2S)-o-isopropylidene-2,
3-dihydroxy-1,4-bis(diphenylphosphino)butane); (P–P)0
= dppb, S-diop, S-binap ((S)-2,20-bis (diphenylphosph-
ino)1,10-binaphthyl), dppn (1,5-bis(diphenylphosphino)
pentane), (PPh3)2, (P-ptol3)2 or (SbPh3)2 (triphenyl-
stibine).
Elemental analyses were performed in the Chemis-
try Department of Universidade Federal de Sa˜o
Carlos.
2.2. X-ray crystallographic analysis of [(dppb)ClRu–
(l-Cl)3–RuCl(dppb)] (5) and [(g6-C6H6)Ru–(l-Cl)–
RuCl- (dppb)] (11)
2. Experimental
2.1. Materials and instrumentation
X-ray data of crystals of compounds (5) and (11)
were measured on an Enraf-Nonius Kappa-CCD dif-
fractometer with graphite monochromated Mo Ka
All manipulations were carried out under purified Ar
using standard Schlenk techniques. Reagent grade sol-
vents were appropriately distilled and dried before use.
RuCl3 Æ nH2O, dppb, PPh3, P-ptol3, dppn, S-diop, S-bi-
nap, dpae (1,2-bis(diphenylarsino)ethane), dppe
˚
(k = 0.71073 A) radiation. Data were collected up to
50ꢁ in 2h, with a redundancy of 4. The final unit cell
parameters were based on all reflections. Data collec-
tions were carried out using the COLLECT program
[16]. Integration and scaling of the reflections were per-
formed with the HKL Denzo-Scalepack system of pro-
grams [17]. Absorption corrections were carried out
using the multi-scan method [18].
The structures were solved by direct methods with
SHELXS-97 [19]. Models were refined by full-matrix
least-squares on F2 using SHELXL-97 [20]. All hydrogen
atoms were stereochemically positioned and refined with
the riding model [21].
Data collection and experimental details for com-
plexes (5) and (11) are summarized in Table 1. Relevant
interatomic bond lengths and bond angles are listed in
Table 2. ORTEP projections of the structures are shown
in Figs. 1 and 2.
(1,2-bis(diphenylphosphino)ethane),
1,3-cyclohexadi-
ene, benzonitrile (PhCN) were used as received from
Aldrich. Imines were prepared by condensation of the
appropriate aldehyde and amines [5] and stored under
Ar in the dark. mer-[RuCl3(dppb)H2O] (1) [1], mer-
[RuCl3(S-diop)H2O] (2) [1], [RuCl2(S-diop)PPh3] [9],
[RuCl2(S-Binap)PPh3] [10], [RuCl2(dppb)PPh3] [11],
[RuCl2(PPh3)3] [12], [Ru2Cl4(dppn)3] [13], [RuCl2(P-
ptol3)3] [14], [RuCl2(SbPh3)3] [12] and [(g6-
C6H6)RuCl(dpae)]Cl [15] were prepared according to
the above mentioned literature procedures.
Hydrogenation reactions were carried out in a stain-
less steel autoclave equipped with a high-pressure regu-
lator and connected to a vacuum line. Oxygen was

M.P. de Araujo et al. / Polyhedron 23 (2004) 3163–3172
3165
Table 1
Crystallographic data for complexes (5) and (11)
(5)
(11)
Empirical formula
Formula weight
Temperature (K)
C56H56P4Cl5Ru2
1232.28
120(2)
[C34H34P2Cl4Ru2] Æ C2H4Cl2
947.44
120(2)
0.71073
˚
Wavelength (A)
0.71073
monoclinic
P21/c
Crystal system
Space group
Unit cell dimensions
triclinic
ꢀ
P1
˚
a (A)
13.2450(4)
20.3790(7)
23.0640(8)
10.4240(1)
12.5350(1)
15.6530(2)
100.467(1)
96.164(1)
112.293(1)
1825.67(3)
2
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
–
117.912(1)
–
5501.2(3)
3
˚
Volume (A )
Z
4
1.488
Dcalc (Mg/m3)
1.724
1.381
Absorption coefficient (mmꢁ1
F (0 0 0)
Crystal size (mm)
)
0.944
2500
948
0.28 · 0.10 · 0.02
1.35–25.00
0.20 · 0.04 · 0.01
2.53–25.00
h range for data (ꢁ)
Collection index ranges
Reflections collected
Independent reflections
ꢁ15 6 h 6 15, ꢁ20 6 k 6 24, ꢁ27 6 l 6 27
17,640
ꢁ12 6 h 6 12, ꢁ14 6 k 6 14, ꢁ18 6 l 6 18
12,205
9613 (Rint = 0.0523)
99.5
Multiscan
6442 (Rint = 0.0178)
100.0
Multiscan
Completeness to h = 25.00ꢁ (%)
Absorption correction
Maximum and minimum transmission
Refinement method
0.9906 and 0.8336
full-matrix least-squares on F2
9613/604
0.9729 and 0.6984
full-matrix least-squares on F2
6442/433
Data/parameters
Goodness-of-fit on F2
1.096
1.143
Final R indices [I > 2r(I)]
R indices (all data)
Largest differential peak and hole (eA
R1 = 0.0443, wR2 = 0.1000
R1 = 0.0862, wR2 = 0.1347
0.497 and ꢁ0.717
R1 = 0.0291, wR2 = 0.0878
R1 = 0.0358, wR2 = 0.1106
0.842 and ꢁ1.519
ꢁ3
˚
)
2.3. Reactivity of mer-[RuCl3(dppb)H2O] with other
Ru(II) or Ru(III) complexes
4.23. Found: C, 60.39; H, 4.56%. UV–Vis (CH2Cl2):
340 (3440), 398 (2840), 534 (1780). leff 1.95 lB/dimer.
The procedure for the preparation of binuclear com-
plexes is similar to that used for complex (3):
2.3.3. [(dppb)ClRu–(l-Cl)3–RuCl(dppb)] (5)
Complex (1) (0.0353 g, 0.0542 mmol) and
[RuCl2(dppb)PPh3] (0.0466 g, 0.0542 mmol). Yield
(0.0467 g, 70%). Anal. Calc. for C56H56Cl5P4Ru2: C,
54.58; H, 4.58. Found: C, 54.51; H, 4.77%. UV–Vis
(CH2Cl2): 374 (3500), 436 (2730), 550 (1850). leff 2.01
lB In this case to a dichloromethane solution of (5)
n-hexane was added until cloudiness and it was left
undisturbed in a freezer. After 2 days a crop of red-
dish-brown crystals suitable for X-ray analysis were
recovered.
2.3.1. [(S-diop)ClRu–(l-Cl)3–RuCl(dppb)] (3)
A suspension of (1) (0.0848 g, 0.1301 mmol) and
[RuCl2(S-diop)PPh3] (0.1214 g, 0.1301 mmol) in CH2Cl2
(50 ml) was stirred at room temperature for 3 h. The
solution volume was reduced to ꢂ5 ml and addition of
n-hexane (10 ml) precipitated a brown solid, which
was collected, washed well with methanol and n-hexane,
and dried under vacuum. Yield (0.1528 g, 90%). Anal.
Calc. for C59H60O2Cl5P4Ru2: C, 54.33; H, 4.64. Found:
C, 54.34; H, 4.64%. UV–Vis (CH2Cl2): 372 (3400), 448
(1930), 525 (1380). leff 1.80 lB/dimer.
2.3.4. [(PPh3)2ClRu–(l-Cl)3–RuCl(dppb)] (6)
Complex (1) (0.0450 g, 0.0690 mmol) and
[RuCl2(PPh3)3] (0.0662 g, 0.0690 mmol). Yield (0.0615
g, 67%). Anal. Calc. for C64H58Cl5P4Ru2: C, 57.78; H,
4.39. Found: C, 57.90; H, 4.66%. UV–Vis (CH2Cl2):
378 (3650), 444 (1930), 536 (1720). leff 1.78 lB/dimer.
2.3.2. [(S-binap)ClRu–(l-Cl)3–RuCl(dppb)] (4)
Complex (1) (0.0294 g, 0.0450 mmol) and [RuCl2(S-
Binap)PPh3] (0.0476 g, 0.0450 mmol). Yield (0.0488 g,
76%). Anal. Calc. for C72H60Cl5P4Ru2: C, 60.54; H,

3166
M.P. de Araujo et al. / Polyhedron 23 (2004) 3163–3172
Table 2
6
˚
Selected bond distances (A) and bond angles (ꢁ) of the [(dppb)ClRu–(l-Cl)3–RuCl(dppb)] (5) and [(g -C6H6)Ru–(l-Cl)3–RuCl(dppb)] Æ C2H4Cl2 (11)
complexes
(5)
(11)
Bond distances
Ru(1)–Ru(2)
Ru(1)–Cl(11)
Ru(1)–Cl(1)
Ru(1)–Cl(2)
Ru(1)–Cl(3)
Ru(2)–Cl(21)
Ru(2)–Cl(1)
Ru(2)–Cl(2)
Ru(2)–Cl(3)
Ru(1)–P(1)
Ru(1)–P(2)
Ru(2)–P(3)
Ru(2)–P(4)
3.174(6)
Ru(1)–Ru(2)
Ru(1)–Cl(1)
Ru(1)–Cl(2)
Ru(1)–Cl(3)
Ru(1)–Cl(4)
Ru(2)–Cl(2)
Ru(2)–Cl(3)
Ru(2)–Cl(4)
Ru(2)–C(21)
Ru(2)–C(25)
Ru(2)–C(26)
Ru(1)–P(1)
Ru(1)–P(2)
3.314(1)
2.3627(15)
2.3402(15)
2.4607(14)
2.4422(14)
2.3927(14)
2.4877(15)
2.3729(15)
2.4829(13)
2.3293(16)
2.3236(15)
2.2957(15)
2.2809(16)
2.3865(7)
2.4936(8)
2.4343(8)
2.5960(8)
2.4144(8)
2.4208(8)
2.4231(8)
2.158(4)
2.176(3)
2.164(4)
2.2777(8)
2.2463(8)
Bond angles
P(2)–Ru(1)–P(1)
P(3)–Ru(2)–P(4)
P(2)–Ru(1)–Cl(1)
P(1)–Ru(1)–Cl(1)
P(2)–Ru(1)–Cl(11)
P(1)–Ru(1)–Cl(11)
P(2)–Ru(1)–Cl(3)
P(1)–Ru(1)–Cl(3)
Cl(1)–Ru(1)–Cl(11)
Cl(1)–Ru(1)–Cl(3)
Cl(11)–Ru(1)–Cl(3)
Ru(1)–Cl(1)–Ru(2)
95.33(6)
93.02(5)
91.83(5)
96.76(5)
98.00(5)
87.62(6)
91.45(5)
172.65(6)
168.85(6)
85.82(5)
88.65(5)
82.14(5)
P(2)–Ru(1)–P(1)
P(2)–Ru(1)–Cl(1)
P(1)–Ru(1)–Cl(1)
P(2)–Ru(1)–Cl(3)
P(1)–Ru(1)–Cl(3)
Cl(1)–Ru(1)–Cl(3)
Cl(1)–Ru(1)–Cl(2)
Cl(3)–Ru(1)–Cl(2)
P(2)–Ru(1)–Cl(4)
P(1)–Ru(1)–Cl(4)
Ru(2)–Cl(2)–Ru(1)
Ru(2)–Cl(3)–Ru(1)
93.58(3)
98.30(3)
88.36(3)
94.86(3)
101.44(3)
163.07(3)
88.42(3)
80.92(2)
165.09(3)
99.54(3)
84.94(2)
86.10(3)
54.93; H, 4.69. Found: C, 55.34; H, 4.73%. UV–Vis
(CH2Cl2): 380 (2390), 445 (1750), 525 (1040). leff 1.83
lB/dimer.
2.3.6. [(P-ptol3)2ClRu–(l-Cl)3–RuCl(dppb)] (8)
Complex (1) (0.0125 g, 0.0192 mmol) and [RuCl2
(P-ptol3)3] (0.0208 g, 0.0192 mmol). Yield (0.0190 g,
70%). Anal. Calc. for C70H70Cl5P4Ru2: C, 59.43; H,
4.99. Found: C, 59.29; H, 4.66%. UV–Vis (CH2-
Cl2): 379 (3820), 437 (2840), 527 (1710). leff 1.79 lB/
dimer.
2.3.7. [(SbPh3)2ClRu–(l-Cl)3–RuCl(dppb)] (9)
Complex (1) (0.0958 g, 0.1470 mmol) and
[RuCl2(SbPh3)3] (0.1809 g, 0.1470 mmol). Yield
(0.1166 g, 75%). Anal. Calc. for C64H58Cl5Sb2P2Ru2:
C, 50.84; H, 3.87. Found: C, 51.02; H, 3.98%. UV–Vis
(CH2Cl2): 379 (3470), 443 (2340), 530 (1470). leff 1.85
lB/dimer.
Fig. 1. ORTEP view of the complex [(dppb)ClRu–(l-Cl)3–
RuCl(dppb)] (5), showing the atom labelling and the 50% probability
ellipsoids.
2.3.8. [(S-diop)ClRu–(l-Cl)3–RuCl(S-diop)] (10)
Complex (2) (0.0250 g, 0.0345 mmol) and [RuCl2-
(S-diop)PPh3] (0.0322 g, 0.0345 mmol). Yield (0.0356
g, 75%). Anal. Calc. for C62H64O4Cl5P4Ru2: C, 54.10;
H, 4.69. Found: C, 54.15; H, 4.67%. UV–Vis (CH2Cl2):
377 (3350), 446 (1950), 540 (1390). leff 1.79 lB/dimer.
2.3.5. [(dppn)ClRu–(l-Cl)3–RuCl(dppb)] (7)
Complex (1) (0.1035 g, 0.1588 mmol) and
[Ru2Cl4(dppn)3] (0.1322 g, 0.0794 mmol). Yield
(0.1583 g, 80%). Anal. Calc. for C57H58Cl5P4Ru2: C,

M.P. de Araujo et al. / Polyhedron 23 (2004) 3163–3172
3167
2.4.2. [(dppb)(CO)Ru–(l-Cl)3–RuCl(dppb)] (13)
A suspension of (1) (0.083 g, 0.1273 mmol) in N,N0-
dimethylacetamide (20 ml) was stirred under H2 (1
atm) for 24 h, at room temperature. To the obtained or-
ange solution methanol (30 ml) was added and stirred
under H2 for 3h. An orange solid was collected and
washed well with methanol and dried under vacuum.
Yield (0.0741 g, 95%). Anal. Calc. for C57H56OCl4-
P4Ru2: C, 55.89; H, 4.61. Found: C, 55.35; H, 4.67%.
IR (cmꢁ1) 1970 m(CO). 31P{1H}, ppm: d PA 53.90 (d),
PB 53.35 (d) (2JPAPB 45 Hz), PC 47.71 (d), PD 35.07
(d) (2JPCPD 30 Hz).
2.4.3. [H2NEt2][(dppb)ClRu–(l-Cl)3–RuCl(dppb)]
(14)
Fig. 2. ORTEP view of the complex [(g6-C6H6)Ru–(l-Cl)3–
RuCl(dppb)]. C2H4Cl2 (11), showing the atom labelling and the 50%
probability ellipsoids.
A suspension of (1) (0.100 g, 0.1534 mmol) in CH2Cl2
(10 ml) and an excess of triethylamine (1 ml) was stirred
under H2 (1 atm) for 24 h, at room temperature. The or-
ange solution volume was reduced (ꢂ5 ml) and passed
through a Celiteꢂ. Addition of n-hexane precipitated a
brown solid that was collected, washed well with meth-
anol and dried under vacuum. Yield (0.0862 g, 86%).
Anal. Calc. for C60H68NCl5P4Ru2: C, 55.16; N, 1.07;
H, 5.24. Found: C, 55.23; N, 1.07; H, 5.15%. 31P{1H},
ppm: d 49 (s). 1H (CDCl3): d 1.22 (br, s, 6H,
CH3H2NEt2), 1.35 (br, m, 4H, CH2), 1.64 (br, m, 4H,
CH2), 2.05 (br, m, 4H, CH2), 2.82 (br, m, 4H, CH2),
2.92 (br, m, 4H, CH2H2NEt2), 6.9–7.5 (m, 40H, Ph),
7.9 (br, s, 2H, NH2).
2.3.9. [(g6-C6H6)Ru–(l-Cl)3–RuCl(dppb)] (11)
A suspension of (1) (0.0200 g, 0.0307 mmol) and [(g6-
C6H6)RuCl(dpae)]Cl (0.0226 g, 0.0307 mmol) in 1,
2-dichloroethane (30 ml) was refluxed for 24 h.
Surprisingly, a crop of red crystals was obtained during
the reaction and crystals suitable for X-ray analysis
were separated from the solution Addition of n-hexane
to the solution yielded a brown solid that was washed
well with n-hexane and dried under vacuum. The red
crystals and the brown solid are the same compound
as proved by 31P{1H}, 1H NMR and elemental
analysis.
3. Results and discussion
Yield (0.0208 g, 80%). Anal. Calc. for
C34H34Cl4P2Ru2: C, 48.13; H, 4.04. Found: C, 48.17;
The magnetic moments of the mixed-valent com-
plexes (3–10) leff = 1.78–2.01 are consistent with one un-
paired electron per molecule.
1
H, 4.08%. 31P{1H}, ppm: d PB 54.00 (s). H (CDCl3):
d 1.27 (br, s, 2H, CH2), 1.81 (br, m, 2H, CH2), 2.04
(br, m, 2H, CH2), 3.12 (br, m, 2H, CH2), 6.20 (s, 6H,
g6-C6H6), 7.20–7.65 (m, 20H, Ph).
The X-ray structure of (5) (Fig. 1) shows that the Ru
cation is in an approximate C2 environment, as was re-
ported by Nicholson [22] for [(PnBu3)2ClRu–(l-Cl)3–
RuCl(PnBu3)2]; this local symmetry is lower than that
in [(chiraphos)ClRu–(l-Cl)3–RuCl(chiraphos)], previ-
ously determined [23], which belongs to an approximate
C2v point group in which one octahedron was rotated by
120ꢁ about the Ru–Ru vector, as compared with the sit-
uation in the complex (5). The bridging chlorides trans
to the phosphorus atoms (Ru(2)–Cl(1) = 2.4877(15);
2.4. Reactivity of mer-[RuCl3(dppb)H2O] with
dihydrogen
2.4.1. [(dppb)ClRu–(l-Cl)2–RuCl(dppb)] (12)
A suspension of (1) (0.0990 g, 0.1519 mmol) in
CH2Cl2 (20 ml) and methanol (5 ml) was stirred under
H2 (1 atm) for 48 h at room temperature (RT). The vol-
ume of the orange solution was reduced (ꢂ10 ml) and
addition of methanol (30 ml) precipitated an orange so-
lid that was collected, washed well with methanol and
dried under vacuum. Yield (0.0907 g, >99%). Anal. Calc.
for C56H56Cl4P4Ru2: C, 56.20; H, 4.72. Found: C, 56.12;
H, 4.60%. 31P{1H}, ppm: d PA 55.30 (d), PB 63.50 (d)
(2JPAPB 30 Hz).
Ru(2)–Cl(3) = 2.4839(13);
Ru(1)–Cl(2) = 2.4607(14)
˚
and Ru(1)–Cl(1) = 2.4422(14) A) show longer Ru–Cl
distances than the bridging chlorides trans to the termi-
nal chlorides (Ru(1)–Cl(1) = 2.3402(15) and Ru(2)–
˚
Cl(2) = 2.3729(15) A). This fact can be attributed to
the strong trans influence of the phosphine ligands.
˚
The Ru–Ru distance (3.174(6) A) is well outside of the
˚
range (2.28–2.95 A) usually found for a Ru–Ru bond
[24–30] and shorter than that found for the chiraphos
1H (CDCl3): d 1.35 (br, m, 4H, CH2), 1.64 (br, m, 4H,
CH2), 2.05 (br, m, 4H, CH2), 2.62 (br, m, 4H, CH2), 6.9–
7.7 (m, 40H, Ph).
˚
analog (3.25 A) [23]. The Ru–Cl–Ru bond angles

3168
M.P. de Araujo et al. / Polyhedron 23 (2004) 3163–3172
(81.48ꢁ, average) are larger than the expected value for
two octahedra sharing one face (70.5ꢁ). The bond angles
P(1)–Ru–P(2) = 95.33(6)ꢁ and P(3)–Ru–P(4) = 93.02(2)ꢁ
are within the range of other Ru(dppb) core complexes
[31,32].
The X-ray structure of (5) is similar to the [(dcypb)Cl-
Ru–(l-Cl)3–RuCl(dcypb)] [33] complex, which adopts
the same approximate C2 point group (considering the
local symmetry only). As observed for complex (5)
The cyclic voltammetric studies of mixed-valence
complexes (3–10) synthesized in this work only reveal
two reversible one-electron transfer processes, which
correspond to the couples designated in Eq. (2).
þeꢁ
½RuðIIÞ–Cl3–RuðIIÞꢁꢀ ꢀ ½RuðIIÞ–Cl3–RuðIIIÞꢀ
E1=2ð1Þ
ꢁeꢁ
ꢁ ½RuðIIIÞ–Cl3–RuðIIIÞþꢀ
ð2Þ
E1=2ð2Þ
[(dcypb)ClRu–(l-Cl)3–RuCl(dcypb)]
also
presents
The observation of only two redox processes in com-
plexes such as [(PPh3)2ClRu–(l-Cl)3–RuCl(dppb)] avoid
the possibility of the presence of two symmetrically
longer Ru–Cl bond lengths for chlorides trans to phos-
phorus than for chlorides trans to chlorides. The Ru–
Ru distance for [(dcypb)ClRu–(l-Cl)3–RuCl(dcypb)]
mixed-valence
complexes
[(PPh3)2ClRu–(l-Cl)3–
˚
(3.278 A) is higher than for complex (5).
RuCl(PPh3)2] and [(dppb)ClRu–(l-Cl)3–RuCl(dppb)].
Of note is the electrochemical behavior of
[(SbPh3)2ClRu–(l-Cl)3–RuCl(dppb)] (discussed below)
in which only two redox processes are observed with a
separation DE1/2 = 0.21 V. If two symmetrically mixed-
valence complexes had been formed, the observation
of well separated (DE1/2 = 0.62 V) redox processes due
to [(dppb)ClRu–(l-Cl)3–RuCl(dppb)] in addition to
the observed processes should be expected, but this is
not the case. The same argument can be used for the
complex [(S-diop)ClRu–(l-Cl)3–RuCl(dppb)].
Fig. 3 shows the cyclic voltammogram of the
[(dppb)ClRu–(l-Cl)3–RuCl(dppb)] (5) complex. The
separations between half-wave potential E1/2(1) and
E1/2(2) for the complexes in Table 3 are small when com-
pared with those found for unsymmetric complexes such
as [(PPh3)2(CO)Ru–(l-Cl)3–RuCl2(PPh3)] [7] (1.57 V)
and [(AsPh3)2(CO)Ru–(l-Cl)3–RuCl2(AsPh3)] [8] (1.66
V). This observation suggests that in symmetric species
(same donor atoms) there is a stronger contribution of
the metal–metal interaction, increasing the half-wave
potential separations; for unsymmetric complexes (dif-
ferent donor atoms) such as [(PPh3)2(CO)Ru–(l-Cl)3–
RuCl2(PPh3)] this separation is mainly due to the ligand
characteristics since the orbital energies of the metal cen-
ters are different, the metal–metal interactions are weak
and each metal center behaves as a monomer.
The reaction of mer-[RuCl3(dppb)H2O] (1) and [(g6-
C6H6)RuCl(dpae)]Cl produces the binuclear complex
(11). The possible mechanism for this reaction involves
the formation of the intermediate ‘‘RuCl2(dppb)’’ since
the reduction of the mer-[RuCl3(dppb)H2O] (1) complex
by the dpae ligand generates this Ru(II) species which
can be dimerized forming the binuclear [(dppb)ClRu–
(l-Cl)2–RuCl(dppb)] [2] (12) complex, similar to that
found for the dissolution of [RuCl2(dppb)(PPh3)] [11],
which once in solution dissociates PPh3 and dimerizes.
The 31P{1H} NMR spectrum of the triply chloride-
bridged [(g6-C6H6)Ru–(l-Cl)3–RuCl(dppb)] complex
shows only a singlet at d 54.0 ppm in CDCl3.
The electrochemical behavior of (1) is well docu-
mented and the products formed after partial and
exhaustive electrolysis were described elsewhere by our
research group and collaborators [1]. This reaction is
similar to the one of [RuCl2(dppb)(PPh3)] with [(g6-
cymene)RuCl2]2 producing [(g6-cymene)ClRu–(l-Cl)3–
RuCl(dppb)] [32], which strongly confirms our suggestion
regarding the mechanism involved in our reaction.
The binuclear arene complex (11) presents two dis-
torted octahedra sharing one face as in [(dppb)ClRu–
(l-Cl)3–RuCl(dppb)]. The Ru–P bond lengths
˚
(2.2463(8) and 2.2777(8) A) are slightly smaller than
those found for complex (5) and are in the expected
range for Ru(II)–P bond lengths [32–35]. The Ru–Cl
bond lengths for the bridged chlorides are longer than
for terminal ones (see Table 2).
The most relevant manifestation of metal–metal
interaction is the separation of electrochemical couples
[36–38]. In complexes with similar donor atoms coordi-
nated to both metal centers this separation is related to
the comproportionation constant (Kc). In binuclear
complexes with apparent similar donor atoms in both
metal sites, an increase in the metal–metal interaction
is accompanied by increasing separation of electrochem-
ical couples. Separation of electrochemical couples DE1/2
of about 0.60 V [39] (for complexes with a similar coor-
dination sphere) show a strong metal–metal interaction
and high comproportionation constant and can be con-
sidered as belonging to the Class III classification [40].
Fig. 3. Cyclic voltammetry of (5). CH2Cl2, 0.10 mol lꢁ1 (TBAP) E1/2 vs
Ag/AgCl.

M.P. de Araujo et al. / Polyhedron 23 (2004) 3163–3172
3169
Table 3
Electrochemical data for the mixed-valence complexes
Complexes
E1/2 1(V)
E1/2 2(V)
DE1/2 (V)
Kc
[(S-diop)ClRu–(l-Cl)3–RuCl(dppb)] (3)
[(S-binap)ClRu–(l-Cl)3–RuCl(dppb)] (4)
[(dppb)ClRu–(l-Cl)3–RuCl(dppb)] (5)
[(PPh3)2ClRu–(l-Cl)3–RuCl(dppb)] (6)
[(dppn)ClRu–(l-Cl)3–RuCl(dppb)] (7)
[(P-ptol3)2ClRu–(l-Cl)3–RuCl(dppb)] (8)
[(SbPh3)2ClRu–(l-Cl)3–RuCl(dppb)] (9)
[(S-diop)ClRu–(l-Cl)3–RuCl(S-diop)] (10)
0.0
0.58
0.69
0.70
0.67
0.56
0.66
0.61
0.79
0.58
0.60
0.62
0.58
0.56
0.58
0.21
0.61
6.8 · 109
1.5 · 1010
3.2 · 1010
6.8 · 109
3.1 · 109
6.8 · 109
3.1 · 103
2.2 · 1010
0.09
0.08
0.09
0.0
0.08
0.40
0.18
The electrochemical behaviors of the mixed valence
complexes are similar to those found in the literature
with the general formula [L2ClRu–(l-Cl)3–RuClL2]
(L = arsines and phosphines) [41,42]. The separation of
the half-wave potentials (Table 3) are ca. 0.60 V which
give Kc values in the range (109–1010), greater than the
value for the classical Creutz-Taube mixed valence ions
type of complexes (7–103) [38,43]. Complex (9) is the only
one in our series that shows a different behavior
where the separation between half-wave potentials
(DE1/2 = 0.21 V) is too small; this can be attributed to
the fact that for each metal center there are different do-
nor atoms coordinated. This behavior is also reflected in
the intervalence charge transfer energy detected in the
near infrared region (Table 4), where the intervalence
charge transfer bands are shifted to higher energy values.
These binuclear complexes show two intervalence
charge transfer absorptions in the near-IR spectra.
One suggestion for this behavior in this kind of triply-
chlorine-bridged mixed valence di-ruthenium(II,III)
compound was given by James et al. [23], who proposed
that the second absorption at higher energy is due to the
presence of a tetranuclear species in solution. We do not
believe that this applies to our case as the structure pro-
posed for the tetranuclear species is very different from
the dimer and if tetramers were formed in solution a dif-
ferent behavior in the cyclic voltammetry experiments
would be expected, a fact we did not observe. Another
suggestion based on the work developed by Heath
et al. [6] ascribes the presence of the second absorption
in the near-IR spectra to another transition in binuclear
complexes of the type [(R3P)3Ru–(l-Cl)3–Ru(PR3)3],
described as r ! r* and d* ! r*.
We are thus inclined to suggest that the two absorp-
tions observed in our experiments belong to the same
complexes in solution.
The presence of donor solvents as methanol, acetonit-
rile, dimethylsulfoxide make the intervalence charge
transfer bands (near-infrared region) disappear due to
disproportionation of the dimers into Ru(II) and
Ru(III) species and this behavior was previously ob-
served for similar systems [23].
3.1. Reactivity of mer-[RuCl3(dppb)H2O] with
dihydrogen
The reactivity of mer-[RuCl3(dppb)H2O] (1) with H2
is dependent upon the reaction conditions. Thus, the
reaction in CH2Cl2/MeOH leads to the formation of
the known [2] complex [(dppb)ClRu–(l-Cl)2–
RuCl(dppb)] (12) (identified by 31P{1H} NMR and ele-
mental analysis). The AB quartet [d PA 55.30 (d) and d
2
PB 63.50 (d); JPAPB, 30 Hz] for the doubly chloride-
bridged [(dppb)ClRu–(l-Cl)2–RuCl(dppb)] (12) com-
plex is in agreement with those reported in the literature
[2]. In this case the PB phosphorus atom is trans to the
bridged chloride (see Fig. 4).
An ‘‘in situ’’ 31P{1H} NMR experiment was done
using complex mer-[RuCl3(dppb)H2O] (1) in CH2Cl2/
MeOH (1:1) and H2 (1 atm). After 24 h of reaction, a
mixture of complexes was detected by 31P{1H} NMR
experiments, namely [(dppb)ClRu–(l-Cl)2–RuCl(dppb)]
2
(12) [2] (dPA = 63.5, dPB = 55.3 ppm; JAB = 30 Hz),
[(dppb)(g2-H2)Ru–(l-Cl)3–RuCl(dppb)] [3] (dPA = 55.8,
2
d
PB = 40.6; JAB = 34 Hz; dPC = 54.2, dPD = 52.1 ppm;
2JCD = 45 Hz) and [(dppb)ClRu–(l-Cl)3–RuCl(dppb)]ꢁ
Table 4
Near infrared spectral data for the mixed-valence complexes in CCl4
Complexes
kmax (nm)
e (Mꢁ1 cmꢁ1
)
[(S-diop)ClRu–(l-Cl)3–RuCl(dppb)] (3)
[(S-binap)ClRu–(l-Cl)3–RuCl(dppb)] (4)
[(dppb)ClRu–(l-Cl)3–RuCl(dppb)] (5)
[(PPh3)2ClRu–(l-Cl)3–RuCl(dppb)] (6)
[(dppn)ClRu–(l-Cl)3–RuCl(dppb)] (7)
[(P-ptol3)2ClRu–(l-Cl)3–RuCl(dppb)] (8)
[(SbPh3)2ClRu–(l-Cl)3–RuCl(dppb)] (9)
[(S-diop)ClRu–(l-Cl)3–RuCl(S-diop)] (10)
1860/961
1900/980
1856/980
1856/978
1736/967
1889/970
1648/849
1858/968
940/930
780/720
1180/890
740/880
520/495
770/728
640/665
1145/890

3170
M.P. de Araujo et al. / Polyhedron 23 (2004) 3163–3172
P
P
Cl
P'
OC
P
Cl
Cl
Cl
Cl
Ru
Ru
P
Ru
Ru
P
Cl
Cl
P'
Cl
P
Cl
(i)
(ii)
Cl
P
P
P
Cl
Cl
Cl
Cl
P
P
(iii)
(vi)
Ru
Cl
P
Cl
Ru
P
Ru
Cl
OH
2
Cl
Cl
Ru
Ru
P
P
R
3
Cl
R P
Cl
3
(iv)
(v)
P
P
P
Cl
Cl
Cl
+
Cl
[H NEt ]
2
Ru
2
Ru
Ru
P
Ru
P
P
Cl
Cl
Cl
Cl
Cl
Fig. 4. General scheme for the reactivity of mer-[RuCl3(dppb)H2O] (1): (i) in DMA (24 h, RT); (ii) [RuCl2(dppb)(PPh3)] in CH2Cl2 (3 h, RT); (iii) H2
in CH2Cl2/MeOH (48 h, RT); (iv) H2 in CH2Cl2 and NEt3 (excess, 24 h, RT); (v) [RuCl(g6-C6H6)(dpae)] in ClCH2CH2Cl under reflux;
(v) [RuCl2(PR3)3] in CH2Cl2 (3 h, RT).
(14) [3] (dPA,B = 49 ppm). Evacuation of H2 from the
NMR tube and refilling it with Ar led to the observation
of the presence of [(dppb)ClRu–(l-Cl)2–RuCl(dppb)]
(12) and [(dppb)ClRu–(l-Cl)3–RuCl(dppb)]ꢁ (14).
Complex (12) was also identified as being key in the
reactivity of mer-[RuCl3(dppb)H2O] (1) in the formation
of [(dppb)(CO)Ru–(l-Cl)3–RuCl(dppb)] (13) [2], since in
a short reaction time (2–3 h) of (1) with H2, complex
(12) appears as a by-product, while keeping the reaction
going for a longer period (24 h) only complex (13) was
obtained. In the [(dppb)(CO)Ru–(l-Cl)3–RuCl(dppb)]
complex m(CO) at 1972 cmꢁ1 is present in the IR spec-
trum and an AB quartet is present in the 31P{1H}
NMR spectrum. For this complex the signals at d PA
53.90 (d), d PB 53.35 (d) (2JPAPB 45 Hz) can be assigned
to the resonances of the (l-Cl)3–RuCl(dppb)] side of the
molecule while d PC 47.71 (d), d PD 35.07 (d) (2JPCPD 30
Hz) belong to the [(dppb)(CO)Ru–(l-Cl)3 part of the
same molecule. On the other hand, stirring complex
(14) in methanol leads to the formation of (12) (under
these conditions chloride dissociation is observed).
Similar reactivity of (1) was found upon electrochem-
ical reduction [1,44]. Complex (12) is obtained in quanti-
tative yield and in this case the mixed-valence compound
(5) is the intermediate, as proved by partial electrolysis.
Complex (14) can be synthesized in high yield by the
reaction of mer-[RuCl3(dppb)H2O] with H2 in CH2Cl2
and triethylamine (excess). This procedure has advan-
tages over the published synthesis [3], since it uses mild
conditions, short reaction time, gives a high yield and
the resulting solution is phosphine free. The symmetric
[H2NEt2][(dppb)ClRu–(l-Cl)3–RuCl(dppb)] complex,
as expected, shows only a singlet at d 49.00 ppm.
We have tried to synthesize complex (12) as described
by James et al. [2] using the reaction of the mixed va-
lence complex (5) with H2 in DMA. In this case the
product obtained quantitatively was the carbonyl spe-
cies (13), formed by DMA decarbonylation. Similar
behavior was found as described before for complex
(1) under the same conditions. The desired penta-coordi-
nated double chloride-bridged (12) was synthesized from
complex (1) or (5) in a solvent mixture (CH2Cl2/MeOH)
and H2. We found that this route was clean since com-
plex (12) was obtained quantitavely.
Reactivity of mer-[RuCl3(dppb)(H2O)] is sumarized
in Fig. 4.
3.2. Homogeneous hydrogenation of imines
We have performed studies on the hydrogenation of
imines catalyzed by some of the complexes described
in this work. Hydrogenation of imines is less studied
than for alkenes and carbonyl substrates and as a conse-
quence is less understood. Yet, it is an important path-
way for the synthesis of amines and is particularly
important for the enantioselective reductions of imines
that are only achieved in good enantiomeric excess
employing homogeneous catalysts [45].

M.P. de Araujo et al. / Polyhedron 23 (2004) 3163–3172
3171
Table 5
Hydrogenation of the imines Ph–CH2–N@CH–Ph (15) and Ph–N@CH–Ph (16)
Entry
Complexes
Yield(%) (15)a
Yield(%) (16)a
1
2
3
4
5
6
7
a
[(dppb)ClRu–(l-Cl)3–RuCl(dppb)] (5)
[(PPh3)2ClRu–(l-Cl)3–RuCl(dppb)] (6)
[(dppn)ClRu–(l-Cl)3–RuCl(dppn)] (7)
[(P-ptol3)2ClRu–(l-Cl)3–RuCl(dppb)] (8)
mer-[RuCl3(dppb)H2O] (1)
99
99
ndb
100
93
49
ndb
15
23
40
24
22
[(dppb)(4-Phpy)Ru–(l-Cl)3–RuCl(dppb)]c
[(dppb)(PhCN)Ru–(l-Cl)3–RuCl(dppb)]c
75
80
1000 psi H2, MeOH (10 ml), [Ru] = 1.3 · 10ꢁ4 mol lꢁ1, [Ru]/[imine] = 1/200, 24 h, rt.
Not determined.
Synthesized as described in [9].
b
c
In Table 5 the results for the hydrogenation of N-
complexes are good precursors for inorganic synthesis
and there are at least three reasons for this: (1) the ruthe-
nium(III) species are air stable and easy to handle, (2)
they can be easily reduced chemically or electrochemi-
cally leading to chloride dissociation [1,44], and (3)
products will not be contaminated with free
triphenylphosphine.
A wide range of binuclear mixed valence diruthe-
nium(II,III) complexes can be synthesized from them
and some of their derivatives present high activity in
imines hydrogenation.
benzylidene-benzylamine (Ph–CH2–N@CH–Ph) and
N-benzylidene-aniline (Ph–N@CH–Ph) are presented.
It is evident that for the mixed valence Ru(II)–Ru(III)
complexes (Entries 1 and 4) the Ph–CH2–N@CH–Ph
(15) is reduced at a higher rate than Ph–N@CH–Ph
(16). A similar behavior is presented by (1) (entry 5)
which in a first step generates (5) under the reaction con-
ditions. Considering the results for the hydrogenation of
(16) (entries 1, 3 and 4), the ligand dppb seems to be
important on the stabilization/activity of the catalytic
system as its substitution by dppn decreased the yield
of the hydrogenated products.
Asymmetric hydrogenation of imines and ketones
studies using (3), (4) and (2) and other chiral ruthenium
complexes are currently ongoing in our laboratory.
For the reduction of the aldimines R–N@CHPh;
R = methyl, isopropyl, cyclohexyl, benzyl (15), phenyl
(16), catalyzed by (5) James et al. [5] have found that
the rate of hydrogenation decreased in the order ben-
zyl > methyl > isopropyl ꢂ cyclohexyl > phenyl. It has
been pointed out that the rate of hydrogenation de-
creased with the bulkiness of R. Since the rate of the
reduction of (15) was higher than the reduction of
CH3N@CHPh [5], this suggests that the electronic effects
play an important role in the process. Indeed, another
correlation can be done: as the positive inductive effect
of R increased, the rate of hydrogenation decreased. A
distinct interpretation should be given for (16) as the
lone electron pair on nitrogen is conjugated to the aro-
matic ring (negative mesomeric effect). Thus, even
though the mixed valence complexes are reduced to
Ru(II) complexes in the presence of dihydrogen and a
base (imine), it seems that the Ru(III) centre plays an
important role for the hydrogenation of the imines
studied.
5. Supplementary material
Coordinates and other crystallographic data have
been deposited with the CCDC, deposition number
CCDC 203371 for complex (5) and CCDC 203372 for
complex (11). Copies of this information may be ob-
tained free of charge from The Director, CCDC, 12 Un-
ion Road, Cambridge, CB2 1EZ (fax: +44 1223 336033;
e-mail: deposit@ccdc.cam.ac.uk or at www: http://
www.ccdc.cam.ac.uk).
Acknowledgements
We thank CNPq (Conselho Nacional de Desenvolvi-
´
´
mento Cientıfico e Tecnologico) and FAPESP (Funda-
c¸a˜o de Amparo a Pesquisa do Estado de Sa˜o Paulo)
`
A more detailed study taking into account not only
the catalyst role, but also the role of the substrate should
be carried out in order to elucidate these effects.
for financial support.
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