Coordination chemistry and catalytic activity of ruthenium(II) complexes containing a phospha-macrocyclic ligand

Article abstract of DOI:10.1016/j.poly.2012.06.079

Substitution of [RuCl₂(CO)₃(THF)], [RuCl ₂(dmso)₄] and [RuCl₂(PPh₃) ₃] with a macrocyclic ligand, 2,3,4,5,6,7,8,9-octahydro-1,9-diphenyl- 1H-5,1,9-benzazadiphosphacyclo undecine (11-P₂NH), provided [Ru(11-P₂NH)Cl₂(CO)] (3), [Ru(11-P₂NH)Cl ₂(dmso)] (4) and [Ru(11-P₂NH)Cl₂(CH ₃CN)] (5), respectively. These complexes were characterized by elemental analyses as well as NMR spectroscopy. The structure of 3 was further confirmed by X-ray diffraction analysis. The octahedral geometry around the ruthenium center is in agreement with the Werner's "coordination" bonding concepts. The chelate rings of the macrocycle toward Ru(II) center adopting into chair conformations were revealed. Furthermore, these ruthenium complexes were found to be active for N-alkylation of dibenzylamine with alcohols.

Full text of DOI:10.1016/j.poly.2012.06.079

Polyhedron 52 (2013) 1024–1029
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Coordination chemistry and catalytic activity of ruthenium(II) complexes
containing a phospha-macrocyclic ligand
⇑
⇑
Chun-Chin Lee, Hsiao-Ching Huang, Shiuh-Tzung Liu , Yi-Hung Liu, Shie-Ming Peng, Jwu-Ting Chen
Department of Chemistry, National Taiwan University, Taipei, Taiwan 106, ROC
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 6 July 2012
Substitution of [RuCl2(CO)3(THF)], [RuCl2(dmso)4] and [RuCl2(PPh3)3] with a macrocyclic ligand, 2,3,4,5,6,
7,8,9-octahydro-1,9-diphenyl-1H-5,1,9-benzazadiphosphacyclo undecine (11-P2NH), provided [Ru(11-
P2NH)Cl2(CO)] (3), [Ru(11-P2NH)Cl2(dmso)] (4) and [Ru(11-P2NH)Cl2(CH3CN)] (5), respectively. These
complexes were characterized by elemental analyses as well as NMR spectroscopy. The structure of 3
was further confirmed by X-ray diffraction analysis. The octahedral geometry around the ruthenium cen-
ter is in agreement with the Werner’s ‘‘coordination’’ bonding concepts. The chelate rings of the macro-
cycle toward Ru(II) center adopting into chair conformations were revealed. Furthermore, these
ruthenium complexes were found to be active for N-alkylation of dibenzylamine with alcohols.
Ó 2012 Elsevier Ltd. All rights reserved.
Dedicated to Alfred Werner on the 100th
Anniversary of his Nobel prize in Chemistry
in 1913.
Keywords:
Phosphine
Macrocyclic ligand
Catalysis
Amination
Ruthenium
1. Introduction
the coordination chemistry of 11-P2NH toward Ru(II) and the cat-
alytic activity of the resulting complexes.
Multidentate macrocyclic ligands represent an important class
of direct extension of Werner’s chelating ligands in coordination
chemistry [1–4]. Among this context, phospha-macrocycles exhibit
strong binding behavior toward transition metal ions [5–26].
Moreover, by suitable modification of donor atoms in the macrocy-
clic ligands, coordination behavior and geometry can be controlled
[1–26]. For example, in the macrocycles 11-P2X which have a soft
donor, i.e. phosphorus, sulfur or arsenic as shown in Chart 1, the X
position was found to readily react with W(CO)6 to yield tridentate
facial complexes. In contrast, only the bidentate complexes were
formed when X was a hard donor such as oxygen or nitrogen
[14]. Ciampolini and coworkers also found that the stereochemis-
try at phosphorus centers can influence the coordination behavior
of the metal ions [25,26]. In their findings, the macrocycle b-18-
P4O2 behaved as a tetra-dentate ligand toward cobalt(II) ions,
2. Experimental
2.1. Methods and materials
All reactions, manipulations and purifications steps were per-
formed under a dry nitrogen atmosphere. Tetrahydrofuran was
distilled under nitrogen from sodium benzophenone ketyl. Dichlo-
romethane and acetonitrile were dried over CaH2 and distilled un-
der nitrogen. Other chemicals and solvents were of analytical grade
and were used after degassed process. Ligand 11-P2NH was pre-
pared accordingly to the method reported previously [15].
Nuclear magnetic resonance spectra were recorded on a Bruker
AVANCE 400 spectrometer. Chemical shifts are given in parts per
million relative to Me4Si for 1H and 13C NMR, and relative 85%
H3PO4 for 31P NMR. Infrared spectra were measured on a Nicolet
Magna-IR 550 spectrometer (Series-II).
whereas
ions to yield [(
c
-18-P4O2, acting as a hexadenate, reacted with Co(II)
c
-18-P4O2)Co]2+ [25].
As part of our research project on the coordinating capability of
multi-dentate toward transition metal ions, we have reported the
coordination chemistry of a phospha-macrocycle 11-P2NH toward
[FeCp(CO)2Cl] (Scheme 1), resulting in 1. The amine moiety of the
macrocycle in 1 could be slowly converted into a coordinating
imine [24]. Continuing our interest in this context, we explore
2.2. Synthesis and characterization
2.2.1. Complex 3
A mixture of 11-P2NH (101 mg, 0.26 mmol) and RuCl2(CO)3
(THF) (85 mg, 0.26 mmol) in THF (2 mL) was heated at refluxing
temperature for 12 h. During the reaction, light yellow precipitates
formed. Upon filtration, the solid product was washed with trace
amount of THF and re-crystallized from CH2Cl2 and methanol to
⇑
Corresponding authors. Tel.: +886 2 2366 0352; fax: +886 2 3366 8671.
E-mail addresses: stliu@ntu.edu.tw (S.-T. Liu), jtchen@ntu.edu.tw (J.-T. Chen).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.06.079

C.-C. Lee et al. / Polyhedron 52 (2013) 1024–1029
1025
(9.15 ꢁ 10ꢀ4 mol) was placed in flask under the atmospheric pres-
sure of nitrogen (or hydrogen) and was heated by an oil bath at
110–150 °C for a period of time. After the completion of the reac-
tion, brine (3 mL) and CH2Cl2 (5 mL) were added. The organic layer
was separated and the aqueous layer was extracted with CH2Cl2.
The combined organic extracts were dried over magnesium sulfate
and concentrated. Products were characterized by NMR spectros-
copy and the data were consistent with those reported. Product
yields were obtained by the 1H NMR integration compared to the
internal standard. Spectral data of these compounds are essentially
similar to those reported as listed below:
O
Ph
Ph
Ph
Ph
Ph
O
O
Ph
Ph
Ph
Ph
P
P
P
P
P
P
P
P
P
P
X
O
Ph
11-P2X
γ-18-P4O2
β-18-P4O2
X = PPh, S, AsPh,
NPh, O
Chart 1. Various phospha-macrocycles.
Ph
P
2.2.4.1. N,N-Dibenzyl(4-chlorobenzyl)amine. 1H NMR (400 MHz,
CDCl3) d 3.47 (s, 2H), 3.54 (s, 4H), 7.22–7.37 (m, 14H). 13C NMR
(400 MHz, CDCl3) d 57.16, 57.87, 126.92, 128.23, 128.38, 128.65,
129.96, 132.44, 138.13, 139.36.
Ph
CpFe(CO)2Cl
Ph
Ph
Fe
N
Ph
Fe
HN
P
P
P
P
P
N
H
Ph
2
11-P2NH
1
2.2.4.2. N,N-Dibenzyl(4-methylbenzyl)amine. 1H NMR (400 MHz,
CDCl3) d 2.25 (s, 3H), 3.44 (s, 2H), 3.46 (s, 4H), 7.08 (d, J = 7.6 Hz,
2H), 7.13–7.19 (m, 2H), 7.23–7.28 (m, 6H), 7.35–7.38 (m, 4H). 13C
NMR (400 MHz, CDCl3) d 21.07, 57.56, 57.83, 126.75, 128.14,
128.66, 128.75, 128.86, 136.34, 136.45, 139.74.
Scheme 1. .
yield white crystalline solids (117 mg, 76%): IR (KBr): 1984 cmꢀ1
CO); 1H NMR (400 MHz, d6-DMSO): d 8.05–7.26 (m, 14H, Ar H),
(
t
3.99 (s, 1H, NH–), 3.49 (t, J = 7 Hz, 2H, –CH–),3.10–1.34 (m, 10H,
–CH–); 13C NMR (100 MHz): d 199.8 (s, CO), 144.1 (m), 133.3,
133.1 (t, JC–P = 8.7 Hz), 132.2 (d, JC–P = 8.7 Hz), 131.3, 129.8 (d, JC–
P = 11.8 Hz), 129.5 (t, JC–P = 5.5 Hz), 52.3. 25.1, 22.8; 31P NMR
(161 MHz, CDCl3): d 69.2.:ESI-MS m/z: 556.19 ([MꢀCl]+, calc. for
2.2.4.3. N,N-Dibenzyl(4-methoxybenzyl)amine. 1H NMR (400 MHz,
CDCl3) d 3.41 (s, 2H), 3.45 (s, 4H), 3.73 (s, 3H, OCH3), 6.82–6.87
(m, 2H), 7.11–7.21 (m, 2H), 7.27–7.32 (m, 6H), 7.31–7.41 (m,
4H); 13C NMR (400 MHz, CDCl3) d 57.5, 58.0, 58.2, 113.8, 126.9,
127.1, 128.3, 128.6, 129.0, 139.8, 158.6.
C
25H27ClNOP2Ru: 556.03). Anal. Calc. for C25H27Cl2NOP2Ru: C,
50.77; H, 4.60; N, 2.37. Found: C, 50.54; H, 4.45; N, 2.07%.
2.2.4.4.
N,N-Dibenzyl(1-naphthalylmethyl)amine. 1H
NMR
2.2.2. Complex 4
(400 MHz, CDCl3) d 3.54 (s, 4H), 3.64 (s, 2H), 7.14–7.18 (m, 2H),
7.23–7.28 (m, 4H), 7.35–7.46 (m, 6H), 7.47–7.53 (m, 1H), 7.73–
7.76 (m, 4H). 13C NMR (400 MHz, CDCl3) d 57.93, 58.05, 125.47,
125.85, 126.84, 127.15, 127.36, 127.63, 127.85, 128.24, 128.73,
132.74, 133.33, 137.25, 139.59.
A mixture of 11-P2NH (103 mg, 0.27 mmol) and RuCl2(dmso)4
(130 mg, 0.27 mmol) in THF (2 mL) was heated at refluxing tem-
perature for 12 h. Upon filtration, the crude product was obtained
as light yellow solids. Re-crystallization from THF/methanol gave
light yellow solids (141 mg, 82%): 1H NMR (400 MHz, CDCl3): d
7.80–7.33 (m, 14H, Ar H), 4.29 (s, 1H, NH–), 4.00 (m, 2H, –CH–),
2.83 (m, 2H, –CH–), 2.59 (m, 2H, –CH–), 2.44 (m, 2H, –CH–), 2.11
(s, 6H,dmso), 1.97 (m, 2H, –CH–), 1.39 (m, 2H, –CH–); 13C NMR
(100 MHz): d 144.9 (t, JC–P = 23.0 Hz), 134.6 (m), 133.3, 131.0 (t,
2.2.4.5. N,N-Dibenzyl-1-hexanamine. 1H NMR (400 MHz, CDCl3) d
0.84, 1.26 (m, 11H), 2.42 (t, 2H), 3.54 (s, 4H), 7.26 (m, 10H).
2.2.4.6. N,N-Dibenzyl-3-phenylpropan-1-amine. 1H NMR (400 MHz,
CDCl3) d 1.74–1.87 (m, 2H), 2.46 (t, J = 7.1 Hz, 2H), 2.54 (t,
J = 8.1 Hz, 2H), 3.54 (s, 2H), 7.08–7.19 (m, 3H), 7.15–7.38 (m,
12H). 13C NMR (400 MHz, CDCl3) d 29.04, 33.56, 52.93, 58.37,
125.58, 126.74, 128.13, 128.23, 128.37, 128.85, 139.83, 142.52.
J
C–P = 8.4 Hz), 130.8, 129.9, 127.6 (t, JC–P = 4.5 Hz), 55.4, 46.0, 29.5,
24.1; 31P NMR (161 MHz, CDCl3): d 72.5. ESI-MS m/z: 606.22
([MꢀCl]+, calcd. for C26H33ClNOP2RuS: 606.05). Anal. Calc. for
C
26H33Cl2NOP2RuS: C, 48.68; H, 5.18; N, 2.18. Found: C, 48.28; H,
5.01; N, 1.89%.
2.3. X-ray crystallographic analysis
2.2.3. Complex 5
A mixture of 11-P2NH (99 mg, 0.26 mmol) and RuCl2(PPh3)3
(249 mg, 0.26 mmol) in CH3CN (2 mL) was heated at refluxing tem-
perature for 12 h. During the reaction, light yellow solids precipi-
tated. Upon filtration, the desired product was obtained as light
yellow solids, which was then washed with THF (0.5 mL) and ether
(0.5 mL). (117 mg, 76%): 1H NMR (400 MHz, CDCl3): d 7.88–7.24
(m, 14H, Ar H), 3.86 (s, 1H, NH–), 3.58 (m, 2H, –CH–), 2.99 (m,
2H, –CH–), 2.65 (m, 2H, –CH–), 2.37–2.20 (m, 4H, –CH–), 1.40 (m,
2H, –CH–), 0.91 (s, 3H,CH3CN); 13C NMR (100 MHz): d 143
(t, JC–P = 24.0 Hz), 134.3, 133.1, 131.7 (t, JC–P = 8 Hz), 131.0, 130,
127.6, 123.3, 54.3, 28.5 (m), 23.9, 4.8; 31P NMR (161 MHz, CDCl3):
d 81.8. ESI-MS m/z: 569.23 ([MꢀCl]+, calc. for C26H30ClN2P2Ru:
569.06). Anal. Calc. for C26H30Cl2N2P2Ru: C, 51.66; H, 5.00; N,
4.63. Found: C, 51.37; H, 4.76; N, 4.38%.
Crystals suitable for X-ray determination were obtained for 3 by
recrystallization from CH2Cl2/MeOH at room temperature. Cell
parameters were determined either by a Siemens SMART CCD dif-
fractometer. Crystal data of these complexes are listed in Table 1.
The structure was solved using the SHELXS-97 program [27] and re-
fined using the SHELXL-97 program [28] by full-matrix least-squares
on F2 values.
3. Results and discussion
3.1. Synthesis and characterization of ruthenium(II) complexes
The macrocyclic ligand 11-P2NH was prepared according to the
previous reported methods [15]. A series of ruthenium(II) com-
plexes containing 11-P2NH were prepared as shown in Scheme 2.
Complexation of 11-P2NH with [RuCl2(CO)3(THF)], at a 1:1 ratio,
under refluxing THF afforded a single substitution product of Ru(II)
complex 3. Treatment of 11-P2NH with equal molar amount of
2.2.4. Catalysis
Typical procedure for N-alkylation of dibenzylamine with an
alcohol: a mixture of dibenzylamine (3.05 ꢁ 10ꢀ4 mol), catalysts
(1ꢂ2 mol
%
based on amine) and NaBAr’4 in 3 eq. alcohol

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C.-C. Lee et al. / Polyhedron 52 (2013) 1024–1029
Table 1
Crystal data of 3.
C(4)
Formula
C25H27Cl2NOP2Ru
C(3)
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
591.39
orthorhombic
Pnma
10.6483(3)
18.3861(4)
12.9231(3)
O(1)
C(1)
C(2)
C(2A)
P(1A)
C(8)
P(1)
a
b (°)
(°)
90
90
90
Ru(1)
C(7A)
C(6A)
Cl(1)
Cl(1A)
c
(°)
C(7)
V (Å3); Z
2530.09(11), 4
1.553
Dcalc (Mg/m3)
F(000)
1200
C(6)
Crystal size (mm3)
Reflections collected
Independent reflections
h range (°)
0.25 ꢁ 0.20 ꢁ 0.15
N(1)
15435
C(5A)
C(5)
2997(Rint = 0.0265)
3.15–27.49
Fig. 1. ORTEP Plot of Complex 3 (Drawn with 30% probability ellipsoids).
Refined method
Full-matrix least-squares on F2
0.629
Goodness of fit on F2
R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0248, wR2 = 0.0765
R1 = 0.0353, wR2 = 0.0832
Table 2
Selected bond distances (Å) and bond angles (°) of 3.
Ru(1)–N(1)
Ru(1)–P(1)
Ru(1)–Cl(1)
Ru(1)–C(1)
C(1)–O(1)
2.230(2)
2.2428(6)
2.4757(5)
1.849(3)
1.135(4)
N(1)–Ru(1)–P(1)
P(1)–Ru(1)–P(1A)
C(1)–Ru(1)–N(1)
P(1)–Ru(1)–Cl(1A)
Cl(1)–Ru(1)–Cl(2)
94.42(7)
85.64(3)
173.87(14)
176.21(2)
89.02(3)
RuCl2(CO)3(THF)
RuCl2(PPh3)3
N
Ru
ACN
5
P
P
N
P
P
11-P2N
ACN, Δ
THF, Δ
Ph
Ph
Ph
Ph
Ru
Cl
Cl
Cl
Cl
RuCl2(DMSO)4
CO
THF, Δ
dmso
3
peaks at m/z = 606.22 [4-Cl]+ and 569.23[5-Cl]+, respectively. These
observations well suggest the proposed structures for 4 and 5.
ACN
dmso
N
P
P
3.2. X-ray structural analysis of complex 3
Ph
Ph
Ru
Cl
Cl
The ORTEP plot of 3 is shown in Fig. 1, while some selected dis-
tances and angles are summarized in Table 2. The coordination
sphere of the ruthenium metal is in slightly distorted octahedral
geometry, with one face occupied by two chlorides and carbonyl
and the other face by two phosphorus atoms and the nitrogen do-
nor from the macrocyclic 11-P2NH. This geometry around the
ruthenium center is in agreement with the Werner’s ‘‘coordina-
tion’’ bonding concepts [29]. The metal–ligand bond distances
[Ru–P = 2.2428(6) and Ru–N = 2.230(2) Å] and bond angles [P(1)–
Ru(1)–P(1A) = 85.64(3)° and P(l)–Ru–N(1) = 94.42(7)°] are all in
the normal ranges for an Oh feature (Table 2). The macrocyclic
conformation in 3 consists of one five- and two six-membered
chelating rings. The five membered ring is attributed to o-phenyl-
enebisphosphine-Ru, while both six-membered ones are consti-
tuted by Ru–N–C–C–C–P. Examination of those dihedral angles
resulting from the ring [Ru–N(1)–C(5)–C(6)–C(7)–P(1)] reveals
alternating + gauche/-gauche configuration of a typical chair form
(Table 3). That deviation from the ideal 60° is due to the constraint
of the bond lengths within the ring (e.g. Ru–P or Ru–N versus C–C).
dmso
4
Scheme 2. Complexation of 11-P2NH toward Ru(II) ions.
[RuCl2(dmso)4] [dmso:(CH3)2S=O] gave a ruthenium macrocyclic
complex 4 in excellent yield. Similarly, substitution reaction of
[RuCl2(PPh3)3] with 11-P2NH generated the desired complex 5 in
76% yield. Furthermore, dissolving 3 in dimethylsulfoxide readily
underwent the replacement of a dmso for a carbonyl to yield the
complex 4. Complex 4 was not converted back to 3 in the atmo-
sphere of CO. However, complexes 4 and 5 are interconvertable
to each other in suitable solvents (Scheme 2).
All complexes were obtained as yellow solids, which were char-
acterized by elemental analysis, IR and NMR spectroscopy. The 31
P
NMR spectra of 3–5 in CDCl3 show only one resonance signal at d
69.2, 72.5 and 81.8, respectively, indicating that both phosphorus
donors of 11-P2NH are bonded to the metal center in a symmetrical
manner. Comparing with that of the free ligand 11-P2NH, the 31P
resonance signals for all complexes are shifted down-field, in
agreement with a metal-bound coordination shift. The IR spectrum
for 3 shows a stretching frequency at 1984 cmꢀ1, corresponding to
the terminal carbonyl ligand bound to the ruthenium ion. In addi-
tion, 13C NMR resonance at 199.8 ppm also supports the existence
of a Ru-CO moiety. ESI-MS of 3 shows a peak at m/z = 556.19 cor-
responding to the fragment of [3-Cl]+. The molecular configuration
of 3 is unequivocally confirmed by X-ray crystallographic analysis.
(See Section 3.2).
3.3. Conformational analysis of complex 4 by NMR Spectroscopy
We were not able to acquire the crystal structures for com-
plexes 4 and 5. However, the conformational analysis of the six-
Table 3
Torsional angles for six-membered chelate rings for 3.
P(1)–Ru(1)–N(1)–C(5)
Ru(1)–N(1)–C(5)–C(6)
N(1)–C(5)–C(6)–C(7)
C(5)–C(6)–C(7)–P(1)
C(6)–C(7)–P(1)–Ru(1)
C(7)–P(1)–Ru(1)–N(1)
31.8
ꢀ55.0
75.9
As for the complex 4, the observation of a singlet (d 2.11 ppm)
with integration of 6H in its 1H NMR spectrum provides a convinc-
ing evidence for the coordination of dmso to the metal center,
whereas the coordination of acetonitrile in 5 displays one set of
methyl resonance at d 0.91 ppm. ESI-MS spectra of 4 and 5 show
ꢀ70.3
48.6
ꢀ28.0

C.-C. Lee et al. / Polyhedron 52 (2013) 1024–1029
1027
(ax)
Ph
P
(ax)
H3
H
N
Ru
1H
(eq)
H6
H4
(eq)
(eq)
H2
(ax)
H5
(ax)
H1
H5
H2
H6
H4
NH
H3
ppm
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
ppm
Fig. 2. COSY spectrum of 4.
membered chelate ring may be achieved by the NMR analysis. The
1H and 13C signals assignments were based on the COSY and HSQC
spectra. Fig. 2 shows the COSY spectrum of 4 in the region of 0–
4.5 ppm. One can easily assign the chemical shift of each proton
on the ring denoted as H1–H6, respectively, as indicated in the
Fig. 2.
Both geminal and vicinal proton–proton coupling constants
were determined by first-order approximation from the 400 MHz
proton spectrum of 4 and are summarized in Table 4. The constants
J(H2–H3) and J(H3–H5), which are substantially larger than 10 Hz,
are considered to be affected by a dihedral angle close to 180°. The
constants J(H1–H4), J(H4–H5) and J(H4–H6) are around 6 Hz, indi-
cating the smaller dihedral angles among these C–H bonds. These
results suggest that the six-membered chelate rings in 4 are in
the chair conformations. Unlike complex 4, the ill-resolved split-
ting patterns in 5 cause the determination for the coupling con-
stants and conformation difficult.
Table 4
Coupling Constants of all protons in the six-membered chelate ring for 4.a
Geminal coupling
Vicinal couplingb
J(H1ꢂH2) = 13.8
J(H3ꢂH4) = 14.9
J(H5ꢂH6) = 16.4
J(H1ꢂH4) = 5.9
J(H2ꢂH3) = 14.3
J(H3ꢂH5) = 13.8
J(H4ꢂH5) = 5.8
J(H4ꢂH6) = 5.6
a
In CDCl3; in Hz.
J(H2–H4), J(H1–H3), and J(H3–H6) are not able to be resolved.
b
investigated the catalytic activity of ruthenium complexes 3–5 to-
ward N-alkylation of dibenzylamine with various alcohols. Under
the typical reaction conditions commonly applied for the amina-
tion, the results of the coupling reaction of dibenzylamine with
benzyl alcohol using various ruthenium complexes (Eq. (1)) are
listed in Table 5.
3.4. Catalysis
½Ruꢃ
It has been revealed that ruthenium complexes may serve suit-
able catalysts for N-alkylation of amines with alcohols, which in-
ðPhCH2Þ2NH þ PhCH2OH !ðPhCH2Þ3N
ð1Þ
volves
a
series of tandem reactions including oxidation of
The activities of the catalysts were substantially influenced by
the ruthenium complexes and additives. A screening test suggested
that carrying out the reaction at 110 °C with the use of ruthenium
alcohols, condensation of amines with carbonyl compounds and
reduction of imines as illustrated in Scheme 3 [30]. Thus we also

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C.-C. Lee et al. / Polyhedron 52 (2013) 1024–1029
Table 6
[Ru(II)]
N-alkylation of dibenzylamines with alcohols catalyzed by 3.a
R
R
OH
Entry
Alcohol
Product
Yield
H
R
OH
β-elimination
[Ru]
1
2
3
4
p-ClC6H4CH2OH
p-MeC6H4CH2OH
p-MeOC6H4CH2OH
p-ClC6H4N(CH2Ph)2
p-MeC6H4N(CH2Ph)2
p-MeOC6H4N(CH2Ph)2
100%
100%
100%
97%
O
[Ru]
R
H
CH2OH
CH2N(CH2Ph)2
O
[Ru]-H
R2
R1
H
N
R
5
6
7
8
CH3(CH2)5OH
C6H5(CH2)3OH
C6H5CH = CH2CH2OH
C6H5CH(OH)CH3
CH3(CH2)5N(CH2Ph)2
C6H5(CH2)3N(CH2Ph)2
C6H5(CH2)3N(CH2Ph)2
–
33%
37%
88%
–
R1
N
R2
NHR1R2
R
aReaction conditions: dibenzylamine (3.05 ꢁ 10ꢀ4 mol), 3 (1 mol % based on amine)
NaBAr’4 (2 mol %) and benzyl alcohol (9.15 ꢁ 10ꢀ4 mol) at 110 °C for 24 h.
Scheme 3. Catalytic pathway of Ru-catalyzed N-alkylation of amines with alcohols.
(Table 6, entry 8). Subjecting cinnamyl alcohol to the same condi-
tions resulted in the formation of the product of C=C reduction,
C6H5CH2CH2CH2N(CH2C6H5)2 in high yield (88%), indicating the
reduction of C=C bonds well competes with that of C=N bonds.
complexes containing phosphine-amine tridentates provided bet-
ter yields of amine products evidenced by the entries 5, 6, 9 and
10 (Table 5). Among them, the ruthenium complex 3 with the mac-
rocyclic 11-P2NH gives the best activity, indicating that the stabil-
ization of the facial coordination mode of 11-P2NH toward the
metal center might play a crucial role on activity. Apparently, aux-
iliary ligands e.g. dmso versus CO, can also influence the activity
(Table 5, entries: 6 versus 7 and 9 versus 11).
It has been known that the yields of amine products often
increases as the reaction proceeds under ambient pressure of molec-
ular hydrogen, presumably due to the acceleration of imine-reduc-
tion. However, in this study, the case of hydrogen is not necessary
(Table 5, entries 7, 10, 14), suggesting that the in situ generated
ruthenium hydrides ought to be active enough for the reduction
of C=N bonds.
4. Summary
We have successfully prepared and structurally characterized
a series of ruthenium complexes containing a macrocyclic ligand
11-P2NH. The structures of these complexes were unambiguously
determined by spectroscopic methods as well as X-ray single crys-
tal analysis for 3. The facial coordination mode of 11-P2NH toward
Ru(II) constitutes a macrocycle with the fuse of a five-membered
and two six-membered chelate rings. The latter ones adopt into
chair conformations. Unlike the known iron complex 1, the
amine-donor in ruthenium complexes 3–5 does not undergo the
oxidation to form the imine moiety. Complex 3 appears to be cat-
alytically active for N-alkylation of dibenzylamine with various
alcohols.
The reaction scope with respect to various alcohols was investi-
gated (Table 6). Under the optimized reaction conditions, various
substituted benzyl alcohol to yield the corresponding amines in
excellent yields (Table 6, entries 1–4) except the secondary alcohol
Table 5
Reductive amination catalyzed by Ru(II) complexes.a
Entry
[Ru] catalyst
Additiveb
Temp. (°C)
Time
Yieldc
1
2
3
4
5
6
7
8
6 (1 mol%)d
6 (1 mol%)
7 (1 mol%)d
7 (1 mol%)
8 (1 mol%)e
8 (2 mol%)
9 (1 mol%)e
3 (1 mol%)
3 (1 mol%)
3 (1 mol%)
4 (1 mol%)
4 (1 mol%)
5 (1 mol%)
5 (1 mol%)
–
110
110
110
110
110
120
110
110
110
110
110
150
110
150
24
24
24
24
24
24
24
24
24
24
24
24
24
24
trace
45%
21%
trace
56%
57%
24%
43%
67%
63%
<10%
35%
trace
34%
NaBAr’4
NaBAr’4
–
NaBAr’4
NaBAr’4,
NaBAr’4, H2 (1 atm)
-
9
NaBAr’4,
10
11
12
13
14
NaBAr’4, H2 (1 atm)
,
NaBAr’4,
NaBAr’4,
NaBAr’4
NaBAr’4, H2 (1 atm)
aReaction conditions: dibenzylamine (3.05 ꢁ 10ꢀ4 mol), catalysts (1–2 mol % based on amine), in 3 eq. benzyl alcohol (9.15 ꢁ 10ꢀ4 mol).
b
NaBAr’4 = NaB[(3,5-(CF3)2C6H3)]4; 2 mol %.
c
Yield based on 1H NMR integration with mesitylene as the internal standard.
d
Ref. [31].
Ref. [32].
e
Ph2
P
Ph2
P
Ph2
P
Ru(dmso)2Cl2
Ph2
P
Ru(CO)2Cl2
Ru(dmso)2Cl
O
Ru(CO)2Cl
O
N
N
N
N
H2
H2
7
9
6
8
.

C.-C. Lee et al. / Polyhedron 52 (2013) 1024–1029
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Acknowledgment
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Appendix A. Supplementary data
HSQC spectrum of 4, COSY spectrum of 5, tables of atomic coor-
dinates, isotropic and anisotropic thermal parameters, and bond
distances and angles are available. In addition, CCDC 880893 con-
tains the supplementary crystallographic data for complex 3. These
data can be obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223–336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary
data associated with this article can be found, in the online version,
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