Synthesis of tridentate 2,6-bis(imino)pyridyl aminechlorohydro ruthenium(II) complexes: The convenient use of amine hydrochlorides to generate metal-hydride

Article abstract of DOI:10.1016/j.jorganchem.2010.12.015

The reaction of low-valent ruthenium complexes with 2,6-bis(imino)pyridine ligand, [η²-N₃]Ru(η⁶-Ar) (1) or {[N₃]Ru}₂(μ-N₂) (2) with amine hydrochlorides generates six-coordinate chlorohydro ruthenium (II) complexes with amine ligands, [N₃]Ru(H)(Cl)(amine) (4). Either complex 1 or 2 activates amine hydrochlorides 3, and the amines coordinate to the ruthenium center to give complex 4. This is a convenient and useful synthetic approach to form ruthenium complexes with amine and hydride ligands using amine hydrochloride.

Full text of DOI:10.1016/j.jorganchem.2010.12.015

Journal of Organometallic Chemistry 696 (2011) 1895e1898
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Note
Synthesis of tridentate 2,6-bis(imino)pyridyl aminechlorohydro ruthenium(II)
complexes: The convenient use of amine hydrochlorides to generate
metal-hydride
,
Jin Kyung Kim b, Donald H. Berry c, Hyojong Yoo a
*
a Institute for Applied Chemistry and Department of Chemistry, Hallym University, Chuncheon, Gangwon-do 200-702, Republic of Korea
b Los Alamos National Laboratory, Mail Stop E529, Los Alamos, NM 87545, USA
c Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA
a r t i c l e i n f o
a b s t r a c t
The reaction of low-valent ruthenium complexes with 2,6-bis(imino)pyridine ligand, [h h
2-N3]Ru( 6-Ar)
Article history:
Received 4 September 2010
Received in revised form
7 December 2010
(1) or {[N3]Ru}2(m-N2) (2) with amine hydrochlorides generates six-coordinate chlorohydro ruthenium
(II) complexes with amine ligands, [N3]Ru(H)(Cl)(amine) (4). Either complex 1 or 2 activates amine
hydrochlorides 3, and the amines coordinate to the ruthenium center to give complex 4. This is
a convenient and useful synthetic approach to form ruthenium complexes with amine and hydride
ligands using amine hydrochloride.
Accepted 9 December 2010
Keywords:
Ó 2011 Elsevier B.V. All rights reserved.
Bis(imino)pyridine ligand
Ruthenium(II)-amine complex
Ruthenium-hydride
1. Introduction
(H)(Cl)(amine) (4). In particular, we use amine hydrochloride salts
instead of using amines or ammonia gas to generate ruthenium
Late transition metal complexes bearing bis(imino)pyridine
ligands have drawn much attention recently due to their possible
use in catalysis and in other chemical transformations [1e6]. Bis
(imino)pyridyl transition metal complexes are effective catalysts
for polymerization of ethylene [2e6], hydrosilylation [7,8], epoxi-
dation [9], cyclopropanation [9], etc. Tridentate bis(imino)pyridine
ligands form mer geometry, which provide spatial advantages for
the interaction of transition metal centers with other ligands
[2e11]. Ruthenium complexes with 2,6-bis(imino)pyridine ligands
have been reported as well [9e12]. In particular, novel low-valent
complexes with amine and hydride ligands. The precursor amine
hydrochloride salts are commercially available and easy to handle;
therefore, this method is expected to be applicable for the gener-
ation of stable and potentially useful transition metal complexes
with amine and hydride ligands [14,15]. Proposed formation
mechanisms for these transformations are also discussed.
ruthenium complexes of the 2,6-bis(imino)pyridine ligands, [h2
N3]Ru(
6-Ar) (1) and {[N3]Ru}2(
-N2) (2), where Ar ¼ C6H6 or
C6H5(CH3), and [N3] 2,6-(MesN]CMe)2C5H3N, have been
-
h
m
¼
synthesized and characterized (Fig. 1) [11,12]. These low-valent Ru
(0) complexes show interesting reactivities toward SieCl bond
activation as a route to silyl and silylene complexes [12,13], and the
coordination of other donating ligands (e.g. CO and PR3) to generate
a variety of [N3]Ru(II) families [11,13].
Here, we describe the reaction of low-valent bis(imino)pyridyl
ruthenium complexes with amine hydrochlorides to form [N3]Ru
* Corresponding author. Tel.: þ82 33 248 2072; fax: þ82 33 256 3421.
E-mail address: hyojong@hallym.ac.kr (H. Yoo).
Fig. 1. Low-valent ruthenium complexes of the 2,6-bis(imino)pyridine ligands, 1 and 2.
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.12.015

1896
J.K. Kim et al. / Journal of Organometallic Chemistry 696 (2011) 1895e1898
Table 1
2. Results and discussion
Crystallographic Data for [N3]Ru(H)(Cl)((CH3)2NH), 4a.
Treatment of either [N3]Ru(0) complex 1 or 2 with excess
dimethylamine hydrochloride ((CH3)2NH$HCl (3a); about 14 equiv.)
in toluene at room temperature leads to formation of [N3]Ru(H)(Cl)
((CH3)2NH) (4a) in one day (eq. (1)).
Formula
C35H51N4ClRu
Formula weight
Crystal class
Space group
Z
664.32
Triclinic
P1 (#2)
2
Cell constants
a
b
c
a
8.2645(10) Å
13.5201(14) Å
16.513(2) Å
71.591(8)ꢀ
b
79.949(9)ꢀ
g
81.082(9)ꢀ
V
m
1713.9(3) Å3
5.64 cmꢁ1
Crystal size, mm
Dcalc
F(000)
0.42 ꢂ 0.12 ꢂ 0.08
1.287 g/cm3
700
Radiation
Mo-Ka
(
l
¼ 0.71069 Å)
Diffractometer: Rigaku Mercury CCD
Scan type
Rotation width
Exposure
4
and
u
rotations
0.5ꢀ
30 s
824
Complex 4a has been isolated in 59% yield, as a dark green solid.
The solid-state structure of 4a was determined by a single-crystal
X-ray diffraction study (Fig. 2 and Table 1), and exhibits a six-
coordinate, pseudo-octahedral geometry with a trans arrangement
of hydride and chloride ligands (H1eRu1eCl1 ¼ 168.9(13)ꢀ). The
dimethylamine ((CH3)2NH) ligand is cis to the chloride and hydride
(H1eRu1eN4 ¼ 84.5(12)ꢀ, Cl1eRu1eN4 ¼ 85.31(8)ꢀ) and trans to
Total number of images
2
q
range
5.04e54.96ꢀ
Hkl collected
ꢁ9 ꢃ h ꢃ 10; ꢁ17 ꢃ k ꢃ 17;
ꢁ21 ꢃ l ꢃ 19
No. reflections measured
No. unique reflections
No. observed reflections
No. reflections used in refinement
No. parameters [25]
19,144
7583 (Rint ¼ 0.0334)
6711 (F > 4
7583
s)
the pyridine ligand (N2eRu1eN4
¼
176.13(10)ꢀ). The trans
402
w ¼ 1/[
Weighting scheme
s
2(F2o) þ 0.0937P2 þ 0.6261P],
N1eRu1eN3 bond angle is 156.13(10)ꢀ, which reflects a typical bis
(imino)pyridyl complex and shows the constraints of the chelating
ligand [9e12]. The mesityl ligands are oriented approximately
where P ¼ (F2o þ 2Fc2)/3
R1 ¼ 0.0512, wR2 ¼ 0.1352
R1 ¼ 0.0566, wR2 ¼ 0.1426
1.041
R indices (F > 4s)
R indices (all data)
GOF
perpendicular to the [N3] ligand plane, and form
a pocket
surrounding the dimethylamine ligand. The 1H NMR spectrum of 4a
Final Difference Peaks, e/Å3
þ2.428, ꢁ1.221
C26
in solution is consistent with the solid state structure, and exhibits
four resonances determined as the imine methyls, two pairs of
o-mesityl methyls, and p-mesityl methyls, consistent with mirror
symmetry in the plane bisecting pyridine. A single 1H NMR reso-
C22
C21
C23
nance for the ruthenium hydride (
d
ꢁ19.72, singlet) indicates
C18
C20
a trans hydride-chloride arrangement [11,12]. A single 1H NMR
resonance for inequivalent NeCH3 groups is observed at room
C25
N3
C24
C19
temperature (
d
2.25, doublet, 3JHH ¼ 6.3 Hz), which shows that the
C7
C6
rotation of dimethylamine ligand around RueN bond is not
hindered in solution on the NMR time scale.
C27
Treatment of either [N3]Ru(0) complex 1 or 2 with excess
ammonium chloride (NH4Cl (3b); about 53 equiv.) in THF at room
temperature leads to formation of [N3]Ru(H)(Cl)(NH3) (4b) in one
day (eq. (1)). Complex 4b was isolated in 45% yield, as a dark green
solid. Although attempts to grow crystals for a single-crystal X-ray
diffraction study were not successful, the structure of 4b is most
likely similar to that of 4a: a six-coordinate, pseudo-octahedral
geometry with a trans arrangement of hydride and chloride ligands,
based on the 1H NMR experimental results. A single resonance for
C5
C3
C29
C28
H1
C4
N2
N4
Ru1
Cl1
C2
C1
N1
C14
C9
C8
the NH3 ligand (
observed.
d
2.63) and a ruthenium hydride (
d
ꢁ19.69) are
C10
C17
Reaction of 4a with excess P(CH3)3 (8 equiv.) in benzene-d6 at
room temperature leads to rapid displacement of dimethylamine
and formation of Ru(II) phosphine complex, [N3]Ru(H)(Cl)(P(CH3)3)
(5) [16]. Further reaction with additional P(CH3)3 to form probable
Ru(0) complex such as the bis(phosphine) complex [N3]Ru(PMe3)2
[16] and the dimethylamine hydrochloride salt 3a, is not observed
at room temperature. Complex 4a is not able to reduce even in the
presence of excess P(CH3)3.
C16
C13
C11
C12
C15
Fig. 2. ORTEP drawing of [N3]Ru(H)(Cl)((CH3)2NH), 4a with 30% probability thermal
ellipsoids.

J.K. Kim et al. / Journal of Organometallic Chemistry 696 (2011) 1895e1898
1897
3.3. Synthesis of [N3]Ru(H)(Cl)((CH3)2NH) (4a)
2-N3]Ru(
A toluene solution (5 mL) of [
h
h
6-C6H5(CH3)) (1)
(31 mg, 0.053 mmol) and dimethylamine hydrochloride, 3a (60 mg,
0.75 mmol) was stirred under nitrogen at 25 ꢀC for 1 day. The
reaction mixture was filtered under N2 to filter out excess 3a as
a white solid, and then reduced in volume to approximately 0.5 mL
in vacuo. The product was multiply recrystallized from pentane/
toluene at room temperature, yielding 18 mg of dark green 4a (59%
3
yield). 1H NMR of 4a (benzene-d6): 7.25 (d, JHH ¼ 7.9 Hz, 2H,
PyeHm), 6.93 (t, 3JHH ¼ 7.9 Hz,1H, PyeHp), 6.84 and 6.73 (s, each 2H,
MeseHm), 3.98 (m, 1H, NH), 2.69, 2.14, 1.95, and 1.88 (s, each 6H,
MeseCH3o,p, ImeCH3), 2.25 (d, 3JHH ¼ 6.3 Hz, 6H, NeCH3), ꢁ19.72 (s,
1H, RueH).
Formation of ruthenium amine complexes 4a and 4b is most
likely the result of ionic oxidative addition of hydrochloride (HCl)
from amine hydrochlorides followed by the addition of amine to
the ruthenium center [17]. Oxidative addition of HCl by the [N3]Ru
(0) complexes can yield the intermediate structure 6. Finally,
coordination of amines to ruthenium can lead to formation of 4a
and 4b (Scheme 1).
3.4. Reaction of 4a with P(CH3)3
An NMR tube was loaded with a benzene-d6 solution (0.3 mL) of
4a (6 mg, 0.010 mmol), and the solution was degassed in vacuo. At
ꢁ196 ꢀC, P(CH3)3 (0.08 mmol, 8 equiv.) was added, and the NMR
tube was sealed. The reaction mixture was then warmed to room
temperature and the reaction was monitored via 1H NMR spec-
troscopy. The color of the reaction mixture immediately changed
from green to purple. After 5 min, all 4a were consumed, and
changed to [N3]Ru(H)(Cl)(P(CH3)3) (5) [16].
In conclusion, low-valent bis(imino)pyridyl ruthenium
complexes show interesting reactivities toward the amine hydro-
chloride salts to generate hydrochloro ruthenium(II)-amine
complexes, [N3]Ru(H)(Cl)(amine) (4). Either [N3]Ru(0) complexes
[h h m-N2) (2) activates amine hydro-
2-N3]Ru( 6-Ar) (1) or {[N3]Ru}2(
chlorides 3, and the amines coordinate to the ruthenium center to
give complex 4. The synthetic methods can be further applied to
generate other transition metal-amine hydride complexes which
are useful for catalysis.
3.5. Synthesis of [N3]Ru(H)(Cl)(NH3) (4b)
A THF solution (5 mL) of [h h
2-N3]Ru( 6-C6H5(CH3)) (1) (31 mg,
3. Experimental
0.053 mmol) and ammonium chloride, 3b (150 mg, 2.8 mmol) was
stirred under nitrogen at 25 ꢀC for 1 day. The reaction mixture was
filtered under N2 to filter out excess 3b as a white solid, and then
pumped out in vacuo. The product was multiply recrystallized from
pentane/toluene at ꢁ78 ꢀC, yielding 13 mg of green 4b (45% yield).
3.1. General methods
All manipulations were performed in Schlenk-type glassware on
a dual-manifold Schlenk line or in a nitrogen-filled Vacuum
Atmospheres glovebox [18]. All glassware was oven-dried prior to
use. 1H NMR spectra were obtained at 300, 360 and 500-MHz on
Bruker DMX-300, AM-360, and AMX-500 FT NMR spectrometers,
respectively. 31P{1H} NMR spectra were recorded with broadband
1H decoupling at 121.5 MHz on Bruker DMX-300 spectrometers. All
NMR spectra were recorded at 303 K unless stated otherwise.
Chemical shifts are reported relative to tetramethylsilane for 1H
and external 85% H3PO4 for 31P resonances.
3
1H NMR (benzene-d6): 7.28 (d, JHH ¼ 7.5 Hz, 2H, PyeHm), 6.95 (t,
3JHH ¼ 7.5 Hz, 1H, PyeHp), 6.83 and 6.74 (s, each 2H, MeseHm), 2.63
(s, 3H, NH3), 2.64, 2.17, 1.96, and 1.82 (s, each 6H, MeseCH3o,p
ImeCH3), ꢁ19.69 (s, 1H, RueH).
,
3.6. Single crystal X-ray diffraction analysis
Suitable X-ray quality crystals of 4a were grown from benzene.
Fig. 1 is an ORTEP [20] representation of the molecule with 30%
probability thermal ellipsoids displayed. X-ray intensity data were
collected on a Rigaku Mercury CCD area detector employing
3.2. Materials
graphite-monochromated Mo-Ka radiation (
l
¼ 0.71069 Å) at
Hydrocarbon solvents were dried over Na/K alloy-benzophe-
none. Benzene-d6, toluene-d8, cyclohexane-d12, and tetrahydro-
furan-d8 were dried over Na/K alloy. Chloroform-d was dried over
molecular sieves. C2H4 (Airco) was used as received. Triethylsilane
a temperature of 143 K. Preliminary indexing was performed from
a series of twelve 0.5ꢀ rotation images with exposures of 30 s.
Oscillation images were processed using CrystalClear [21],
producing a listing of unaveraged F2 and (F2) values, which were
s
(Aldrich) was dried over Na prior to use. Ruthenium complexes [h2
-
thenpassed to the CrystalStructure [22] program package for further
processing and structure solution on a Dell Pentium III computer.
The intensity data were corrected for Lorentz and polarization
effects and for absorption using REQAB. The structure was solved by
direct methods (SIR97) [23]. Refinement was by full-matrix least
N3]Ru(h m-N2) (2) [11], P(CH3)3 [19]
6-C6H5(CH3)) (1) [11], {[N3]Ru}2(
were synthesized according to the literature procedures. Amine
hydrochloride salts, 3a and 3b (Aldrich) were dried in vacuo prior to
use.
Scheme 1. Proposed formation mechanism of complex 4.

1898
J.K. Kim et al. / Journal of Organometallic Chemistry 696 (2011) 1895e1898
squares based on F2 using SHELXL-97 [24]. All reflections were used
during refinement (F2’s that were experimentally negative were
replaced by F2 ¼ 0). Non-hydrogen atoms were refined anisotropi-
cally and hydrogen atoms were refined using a “riding” model,
except hydride hydrogen atoms, which were refined isotropically.
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Acknowledgments
[12] H. Yoo, P.J. Carroll, D.H. Berry, J. Am. Chem. Soc. 128 (2006) 6038e6039.
[13] H. Yoo, Ph. D. Thesis, University of Pennsylvania, 2006.
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273e287.
This research was supported by Hallym University Research
Fund, 2010 (HRF-2010-018). The diffraction data collection was
carried out by Dr. Patrick J. Carroll at Department of Chemistry,
University of Pennsylvania.
[15] A.C. Bowman, S.C. Bart, F.W. Heinemann, K. Meyer, P.J. Chirik, Inorg. Chem. 48
(2009) 5587e5589.
[16] 1H NMR resonances were compared with those of [Nx3yl]Ru complexes iso-
lated. (Ref. [11]).
Appendix. Supplementary material
[17] J.P. Collman, L.S. Hegedus, J.R. Norton, R.G. Fink, Principles and Application of
Organotransition Metal Chemistry. University Science Books, Mill Valley, CA,
1987.
[18] A.L. Wayda, M.Y. Darensbourg (Eds.), Experimental Organometallic Chemistry,
American Chemical Society, Washington, DC, 1987.
X-ray crystallographic data (in CIF format) and 1H NMR spectra
of purified samples associated with this article can be found in the
online version at doi:10.1016/j.jorganchem.2010.12.015.
[19] M.L. Luetkens, A.P. Sattelberger, H.H. Murray, J.D. Basil, J.P. Fackler, Inorg.
Synth. 26 (1989) 7.
[20] ORTEP-II: A Fortran Thermal Ellipsoid Plot Program for Crystal Structure
Illustrations. C.K. Johnson, 1976, ORNL-5138.
[21] CrystalClear. Rigaku Corporation, 1999.
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P
P
P
P
P
[25] R1
¼
jjFoj ꢁ jFcjj/ jFoj, wR2 ¼ { w(F2o ꢁ Fc2)2/ w(Fo2)2}1/2, GOF ¼ {
w
(F2o ꢁ F2c)2/(n ꢁ p)}1/2, where n ¼ the number of reflections and p ¼ the
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