Ruthenium Bisammine Complex and Its Reaction with Aryl Azides

Article abstract of DOI:10.1021/acs.organomet.7b00403

A ruthenium bisammine complex was formed in the reaction of ruthenium 1,4-dibenzyltetraazadiene complex with primary amines at room temperature, which was a versatile precursor for the synthesis of various Ru(II) complexes through ligand exchange reactions. In the reaction with azidobenzene, ruthenium 1,4-diphenyltetraaza-1,3-diene complex was formed, while ruthenium imido complexes were given in the reaction with bulky aryl azides such as 2-azido-1,3-dimethylbenzene and 2-azido-1,3-diisopropylbenzene. The ruthenium imido complexes showed high catalytic activity in the reaction of alkyl azides with primary amines to afford N-substituted imines.

Full text of DOI:10.1021/acs.organomet.7b00403

Article
pubs.acs.org/Organometallics
Ruthenium Bisammine Complex and Its Reaction with Aryl Azides
Jin Yong Park, Yongjin Kim, Dae Young Bae, Young Ho Rhee,* and Jaiwook Park*
Department of Chemistry, POSTECH (Pohang University of Science and Technology), Pohang 37673, Republic of Korea
S
* Supporting Information
ABSTRACT: A ruthenium bisammine complex was formed in
the reaction of ruthenium 1,4-dibenzyltetraazadiene complex
with primary amines at room temperature, which was a versatile
precursor for the synthesis of various Ru(II) complexes through
ligand exchange reactions. In the reaction with azidobenzene,
ruthenium 1,4-diphenyltetraaza-1,3-diene complex was formed,
while ruthenium imido complexes were given in the reaction
with bulky aryl azides such as 2-azido-1,3-dimethylbenzene and
2-azido-1,3-diisopropylbenzene. The ruthenium imido com-
plexes showed high catalytic activity in the reaction of alkyl
azides with primary amines to afford N-substituted imines.
give N-hexylbenzylideneimine at room temperature. This
observation prompted us to carry out the stoichiometric
reaction of n-hexylamine with the ruthenium dibenzyltetraaza-
diene complex 2 that is formed as the major product in the
reaction of 1 with benzyl azide in the absence of n-hexylamine.
In general, metal tetraazadiene complexes are quite stable, and
there are few reports on the reactions of the reaction of metal
tetraazadiene complexes.6 Interestingly, we found that the
complex 2 readily reacted with n-hexylamine to produce a new
ruthenium complex along with N-hexylbenzylideneimine in
quantitative yield at room temperature (Scheme 2). Herein we
INTRODUCTION
■
In 2007, Severin and co-workers reported a dimeric ruthenium
half-sandwich complex [Cp^RuCl2]2 (1) (Cp^ = η 5-1-
methoxy-2,4-di-tert-butyl-3-neopentylcyclopentadienyl) con-
taining sterically demanding cyclopentadienyl ligand, which
was formed in the simple reaction of Ru(III) chloride complex
with t-butylacetylene in methanol.1 They observed that the Cp^
ligand endows interesting catalytic activities to the ruthenium
complex.2,3 Arenes are produced from the reaction of alkynes
(Scheme 1a),2 while hydrobenzamides are formed in the
Scheme 1. Catalytic Reactions Using [Cp^RuCl2]2: (a)
Reaction of Alkynes; (b) Reaction of Benzyl Azide; (c)
Synthesis of Enamide
Scheme 2. Formation of Ruthenium Bisammine Complex in
the Reaction of Ruthenium Tetraazadiene Complex with n-
Hexylamine
report that the new ruthenium complex is a ruthenium
bisammine complex (3)7 and that is an active precursor for
the synthesis of various Cp^Ru(II) complexes (4−6) (Scheme
3). Notably, aryl azides reacted with 3 to give the
corresponding ruthenium 1,4-diaryltetraazadiene complexes 7.
reaction of benzyl azide (Scheme 1b).3 The catalytic activity of
1 for the transformation of benzyl azide attracted our attention,
because N−H benzaldimine was proposed as the key
intermediate.3,4 In fact, we found that its catalytic activity is
not only limited to the reaction with benzyl azides but also
effective for that with alkyl azides to generate the corresponding
N−H imines.5 Various N-acetyl enamides can be synthesized
by the catalytic transformation of alkyl azides in the presence of
acetic anhydride (Scheme 1c).5a
RESULTS AND DISCUSSION
■
The ruthenium dibenzyltetraazadiene complex 2 did not react
with benzyl azide at room temperature, but it acted as a catalyst
for the reaction of benzyl azide with primary amines to give N-
Recently, we observed that the ruthenium complex 1
catalyzes the reaction of benzyl azide with n-hexylamine to
Received: May 31, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.7b00403
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Scheme 3. Ligand Exchange Reactions of Ruthenium
Bisammine Complex
Scheme 5. Reaction of Ruthenium Bisammine Complex with
Aryl Azides
benzylimines. In a stoichiometric reaction of 2 with benzyl-
amine, 2 equivalents of benzylamine were consumed to
produce N-benzylidene-1-phenylmethanamine and a new
ruthenium complex quantitatively (Scheme 4). At first we
Scheme 4. Trapping of Ammonia Liberated in Ligand
Exchange Reaction of the Ruthenium Bisammine Complex
complexes (9).13 Interestingly, the reaction with (1-azidoethyl)-
benzene to form 9a was highly diastereoselective. The
complexes 7a−c, 8a,b, and 9a,b were characterized by NMR
and high-resolution mass spectrometry. Fortunately, we
succeeded in obtaining single crystals of 7a, 8a, and 9a suitable
for X-ray diffraction analysis (Figure 1). Selected bond
distances of the complexes are listed in Table 1. The molecular
structure of 7a reveals that the tetraazadiene moiety exists as a
dianionic resonance form to show short N2−N3 bond and
longer N1−N2 and N3−N4 bonds.14 In contrast, that of 9a
shows a highly distorted tetraazadiene moiety: N2−N3 bond is
longer than the N1−N2 bond but shorter than the N3−N4
bond. The Ru−N bond (1.7459(19) Å) in 8a is clearly shorter
than those in the tetraazadiene complexes and comparable to
that (1.718(3) Å) of an analogous ruthenium imido complex
[Cp^RuCl(NAd)].12 The coordination mode of the imido
ligand in 8a (Ru−N−C angle 168.76(16)o) is almost linear.
Then, ruthenium complexes (1−3, 7a, and 8a) were tested as
catalysts for the reaction of benzyl azide with n-hexylamine
(Table 2). N-Hexylbenzylideneimine was obtained in 83% yield
using the dimeric ruthenium complex 1 at room temperature
for 24 h (entry 1). The dibenzyltetraazadiene complex 2
showed a better reactivity (entry 2), while the ruthenium
bisammine complex 3 was significantly less reactive (entry 3).
The low reactivity of 3 is consistent with the predominant
formation of 3 in the stoichiometric reaction of 2 and n-
hexylamine as shown in Scheme 2. The diaryltetraazadiene
complex 7a was inactive, indicating that the formation of N−H
imines from the corresponding tetraazadiene moiety is essential
for the generation of active catalytic species (entry 4). The
catalytic activity of the coordinatively unsaturated ruthenium
imido complex 8a was best (entry 5).
The scope of the catalytic reaction for the synthesis of N-
substituted imines was investigated using 2 as the catalyst at 70
°C, which is more practical and convenient than 8a for
preparation and manipulation (Table 3). Generally, N-
substituted imines (10a−c) were formed in high yields by
the reaction of benzyl azide with a linear amine, branched one,
and t-butylamine in 1 h. The reactions of (1-azidoethyl)-
benzene with n-hexylamine and 2-butylamine were also
successful to give the corresponding N-substituted imines
(10d,e) in high yields, while 1-phenylethanimine was observed
in the reaction using t-butylamine.5a
On the basis of the generation of N−H imines from benzyl
azide and the transimination reaction of N−H imines with
primary amines,4a a pathway for the formation of the ruthenium
bisammine complex 3 in the reaction of 2 with an amine is
proposed in Scheme 6. The ruthenium tetraazadiene complex 2
thought that the ruthenium complex is [Cp^RuCl]2,8 but later
we realized that it is monomeric and contains ammonia as
ligands. The proton signal of the coordinated ammonia was
observed as a broad peak at 2.4 ppm in the 1H NMR spectrum9
of the reaction mixture in tetrahydrofuran-d8 (THF-d8), in
contrast to the free ammonia of which protons appear at 0.45
ppm (Figure S1 in the Supporting Information). The ligation of
ammonia on the ruthenium center 3 was supported further by
the formation of 4-methoxybenzamide in the reaction with
(isopropyl carbonic) 4-methoxybenzoic anhydride after the
ligand exchange reaction of 3 with 1,2-bis(diphenylphosphino)-
ethane.
Then we tried to isolate the ruthenium bisammine complex 3
using polymer-bound benzylamine in the reaction with 2. A
solution of 3 was obtained successfully by simple filtration after
the reaction, but 3 was decomposed during concentration.
However, the solution was useful to obtain analytically pure
products in the ligand exchange reactions. Furthermore, the
addition of aryl azides to the solution provided ruthenium 1,4-
diaryltetraazadiene complexes (7a−c). Although several
ruthenium complexes containing imido ligands have been
reported, which are coordinated to one or two ruthenium
centers,10,11 only one cyclopentadienyl ruthenium imido
complex, [Cp^RuCl(NAd)] (Ad = adamantyl), has been
reported by Severin and co-workers without reactivity
investigation.12 This result inspired us that the use of bulky
aryl azides would give the ruthenium imido complexes, which
are less sterically congested than the corresponding ruthenium
tetraazadiene complexes. Actually, ruthenium imido complexes
(8a,b) were formed in the reaction with bulky aryl azides such
as 2-azido-1,3-diisopropylbenzene and 2-azido-1,3-dimethyl-
benzene (Scheme 5). The ruthenium imido complex 8a
reacted not only with benzyl azide but also with (1-
azidoethyl)benzene to form unsymmetrical tetraazadiene
B
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Table 2. Catalytic Activity Comparison in the Reaction of
a
Benzyl Azide with n-Hexylamine
entry
[Ru]
yield (%)
1
2
3
4
5
1
2
83b
91
62
0
3
7a
8a
95
a
A solution of azide (0.25 mmol), amine (1.2 equiv), and ruthenium
catalyst (2.0 mol %) in THF (1.0 mL) was stirred. The yield was
estimated by 1H NMR using dibromomethane as an internal standard.
b
1.0 mol % of 1 was used.
Table 3. Catalytic Reaction of Alkyl Azides with Primary
a,b
Amines
a
A solution of azide (0.25 mmol), amine (1.2 equiv) and 2 (2.0 mol
b
%) in THF (1.0 mL) was stirred at 70 °C for 1 h. The yields were
estimated by 1H NMR using dibromomethane as an internal standard.
c
1-Phenylethanimine was formed in >95% yield.
Scheme 6. Reaction Pathway for the Formation of
Ruthenium Bisammine Complex
Figure 1. Graphical representation of the molecular structure of
complex 7a (top), 8a (middle), and 9a (bottom). Thermal ellipsoids
are at the 50% probability level. Hydrogen atoms are omitted for
clarity.
Table 1. Selected Bond Distances (Å) of Complexes 7a, 8a,
and 9a
7a
8a
9a
Ru1−N1
Ru1−N4
Ru1−Cl1
N1−N2
N2−N3
N3−N4
2.0027(18)
1.9618(16)
2.3674(8)
1.325(2)
1.7459(19)
1.9924(18)
1.9741(19)
2.3677(7)
1.308(3)
-
2.3626(8)
-
-
-
1.310(2)
1.323(3)
1.336(2)
1.341(2)
CONCLUSION
■
In summary, a new ruthenium bisammine complex was
obtained in the reaction of a ruthenium dibenzyltetraazadiene
complex with primary amines, which was utilized as an efficient
precursor for the synthesis of various Ru(II) complexes
containing a sterically demanding cyclopentadienyl ligand.
Notably, its reactivity toward aryl azides provided novel
ruthenium 1,4-diaryltetraaza-1,3-diene complexes and ruthe-
nium imido complexes. In addition, we investigated the
catalytic reaction of alkyl azides with various primary amines
to synthesize N-substituted imines.
is in equilibrium with a ruthenium imido species (B), which is
converted to a ruthenium N−H imine complex (C). Amine is
reacted with the N−H imine to produce a benzylidene imine
and a ruthenium species containing ammonia (D), from which
another ruthenium imido species (E) is formed. Then, the
nitrene moiety in E is converted to N−H imine, and the second
reaction with amine gives the ruthenium bisammine complex 3.
C
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[Cp^RuCl(nbd)] (6).1a Norbornadiene (35 μmol, 3.6 μL) was
added to a solution of complex 3 (23 μmol) in THF (0.80 mL), and
the mixture was stirred at ambient temperature for 18 h. After the
solvent was removed, the residue was dissolved with hexane and
filtered by a Celite pad. The solution was concentrated and dried
under vacuum to afford an orange solid (11 mg, 95%). 1H NMR (300
MHz, CD2Cl2): δ 5.18 (m, 1H, CHCH, nbd), 4.82 (s, 1H, Cp^-H),
4.67 (m, 1H, CHCH, nbd), 4.47 (m, 1H, CHCH, nbd), 3.71 (s,
3H, OCH3), 3.68−3.58 (m, 3H, CHCH, nbd, CH bridge, nbd),
2.55 (d, J = 16.4 Hz, 1H, Cp^-CH2), 2.35 (d, J = 16.4 Hz, 1H, Cp^-
CH2), 1.26 (m, 2H, CH2, nbd), 1.19 (s, 9H, t-Bu), 1.16 (s, 9H, t-Bu),
1.14 (s, 9H, t-Bu). 13C NMR (75 MHz, CD2Cl2): δ 85.4, 79.0, 78.5
(C10, C11, C12), 63.2, 60.2 (CHCH, nbd), 56.8 (C9), 55.5
(bridging C, nbd), 50.7 (C8), 48.8 (CH2, nbd), 38.3 (C7), 35.0, 33.9,
31.4 (C4, C5, C6), 33.2, 32.7, 31.3 (C1, C2, C3).
EXPERIMENTAL SECTION
■
General Procedures. Air-sensitive manipulations were carried out
with standard Schlenk techniques under argon atmosphere.
Commercial chemicals used without further purification. Flash column
chromatography was carried out on silica gel (230−400 mesh) as the
stationary phase. 1H and 13C NMR spectra were recorded with Bruker
1
(300 MHz, 500, 600, and 850 MHz) spectrometer. H NMR spectra
were referenced to residual CDCl3 (7.26 ppm), CD2Cl2 (5.32 ppm),
THF-d8 (3.58 ppm) and reported as follows; chemical shift,
multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, sept =
septet, m = multiplet, and br = broad). Chemical shift of 13C NMR
spectra were measured relative to CDCl3 (77.23 ppm), CD2Cl2 (54.00
ppm), THF-d8 (67.57 ppm). Mass spectral data were obtained from
the Korea Basic Science Institute (Daegu) on a Jeol JMS 700 high
resolution mass spectrometer. Elemental analyses were performed by
the Korea Basic Science Institute (Busan) on a Vario-Micro Cube
elemental analyzer. Ruthenium complexes 11a and 23 were synthesized
according to the literature procedure.
[Cp^RuCl(PhNNNNPh)] (7a). Azidobenzene (46 μmol, 5.5 mg)
was added to a solution of complex 3 (23 μmol) in THF (0.80 mL),
and the mixture was stirred at ambient temperature for 2 h. After the
solvent was removed, the residue was purified by flash chromatography
on silica gel, using hexane/ethyl acetate as eluent. The product was
1
isolated as a red-yellow solid (14 mg, 96%). H NMR (300 MHz,
CDCl3): δ 8.54 (d, J  6.17 Hz, 2H, Ar), 7.90 (s, 2H, Ar), 7.48−7.39
(m, 6H, Ar), 4.78 (s, 1H, Cp^-H), 3.89 (s, 3H, OCH3), 2.26 (d, J =
16.0 Hz, 1H, Cp^-CH2), 1.25 (d, 1H, overlap, Cp^-CH2), 1.22 (s, 9H,
t-Bu), 0.95 (s, 9H, t-Bu), 0.71 (s, 9H, t-Bu). 13C NMR (150 MHz,
CDCl3): δ 156.1, 151.9, 129.3, 128.8, 128.5, 128.3, 124.9, 123.4 (Ar),
109.2, 101.8, 95.7 (C10, C11, C12), 65.4 (C8), 57.8 (C9), 38.9 (C7),
35.2, 32.4 (C4, C5, C6), 32.2, 31.3 (C1, C2, C3). HRMS (FAB) Calcd
for C31H44ClN4ORu [M + H]+ 625.2247, Found 625.2245. Anal.
Calcd (%) for C31H43ClN4ORu: C, 59.65; H, 6.94; N, 8.98. Found: C,
60.08; H, 6.88; N, 8.65. Single crystals were obtained from a CH2Cl2/
hexane solution by slow evaporation.
[Cp^RuCl{(4-MeOC6H4)NNNN(4-MeOC6H4)}] (7b). 1-Azido-4-
methoxybenzene (46 μmol, 6.9 mg) was added to a solution of
complex 3 (23 μmol) in THF (0.80 mL), and the mixture was stirred
at ambient temperature for 2 h. After the solvent was removed, the
residue was purified by flash chromatography on silica gel, using
hexane/ethyl acetate as eluent. The product was isolated as a red solid
(14 mg, 83%). 1H NMR (300 MHz, CDCl3): δ 8.55 (s, 2H, Ar), 7.86
(s, 2H, Ar), 6.99−6.91 (m, 4H, Ar), 4.77 (s, 1H, Cp^-H), 3.89 (s, 3H),
3.89 (s, 3H), 3.88 (s, 3H), 2.23 (d, J = 16.2 Hz, 1H, Cp^-CH2), 1.30
(s, 9H, t-Bu), 1.25 (d, 1H, overlap, Cp^-H), 0.96 (s, 9H, t-Bu), 0.69 (s,
9H, t-Bu). 13C NMR (213 MHz, CDCl3): δ 160.1, 159.7, 150.7, 149.9,
126.3, 124.7, 114.3, 113.6 (Ar), 107.4, 101.3, 95.0 (C10, C11, C12),
64.8 (C8), 57.8 (C9), 56.0, 55.8 (OCH3), 38.9 (C7), 35.1 (C4, C5,
C6), 32.2, 31.7, 31.3 (C1, C2, C3). HRMS (FAB) Calcd for
C33H48ClN4O3Ru [M + H]+ 685.2485, Found 685.2463. Anal. Calcd
(%) for C33H47ClN4O3Ru: C, 58.57; H, 6.86; N, 7.70. Found: C,
57.92; H, 6.92; N, 8.19.
[Cp^RuCl{(4-CF3C6H4)NNNN(4-CF3C6H4)}] (7c). 1-Azido-4-
(trifluoromethyl)benzene (46 μmol, 8.6 mg) was added to a solution
of complex 3 (23 μmol) in THF (0.80 mL), and the mixture was
stirred at ambient temperature for 2 h. After the solvent was removed,
the residue was dissolved with hexane and filtered by a Celite pad. The
solution was concentrated and dried under vacuum to afford a yellow
solid (16 mg, 92%). 1H NMR (300 MHz, CDCl3): δ 8.68 (d, J = 7.56
Hz, 2H, Ar), 7.99 (s, 2H, Ar), 7.78−7.68 (m, 4H, Ar), 4.83 (s, 1H,
Cp^-H), 3.91 (s, 3H, OCH3), 2.20 (d, J = 14.8 Hz, 1H, Cp^-CH2),
1.25 (d, 1H, overlap, Cp^-CH2), 1.22 (s, 9H, t-Bu), 0.96 (s, 9H, t-Bu),
0.72 (s, 9H, t-Bu). 13C NMR (125 MHz, CDCl3): δ 158.4, 131.1,
130.9, 130.6, 129.9, 126.7, 125.8, 125.4, 123.5, 123.0 (Ar), 103.1, 96.8
(C10, C11, C12), 65.5 (C8), 58.1 (C9), 38.9 (C7), 35.3, 32.6 (C4, C5,
C6), 32.1, 31.4 (C1, C2, C3). HRMS (FAB) Calcd for
C33H42ClF6N4ORu [M + H]+ 761.1995, Found 761.1993. Anal.
Calcd (%) for C33H41ClF6N4ORu: C, 52.14; H, 5.44; N, 7.37. Found:
C, 52.07; H, 5.25; N, 7.21.
General Procedure for Synthesis of [Cp^RuCl(NH3)2] (3).
Method A: using benzylamine. Benzylamine (46 μmol, 5.0 μL) was
added to a solution of complex 2 (23 μmol, 15 mg) in THF (0.50
mL), and the mixture was stirred at ambient temperature for 1 h. The
red solution was obtained.
Method B: using polymer-bound benzylamine. Polymer-bound benzyl-
amine (50 μmol, 24 mg) was added to a solution of complex 2 (23
μmol, 15 mg) in THF-d8 (0.80 mL), and the mixture was shaken at
ambient temperature for 4 h. The resulting polymeric material was
removed by filtration under argon atmosphere, and the red solution
1
1
was obtained. H NMR (300 MHz, THF-d8): δ 3.71 (s, H, Cp^-H),
3.64 (s, 3H, OCH3), 2.74 (d, J = 16.0 Hz, 1H, Cp^-CH2), 2.50 (d, J =
16.0 Hz, 1H, Cp^-CH2), 2.44 (br, 6H, NH3), 1.45 (s, 9H, t-Bu), 1.42
(s, 9H, t-Bu), 1.08 (s, 9H, t-Bu). 13C NMR (125 MHz, THF-d8): δ
124.3 (C13), 82.6, 72.9, 71.0 (C10, C11, C12), 57.1 (C9), 45.1 (C8),
39.0 (C7), 34.3, 33.5, 31.9 (C4, C5, C6), 32.9, 32.7, 32.4 (C1, C2,
C3).
[Cp^RuCl(dppe)] (4).1a 1,2-Bis(diphenylphosphino)ethane (23
μmol, 9.2 mg) was added to a solution of complex 3 (23 μmol) in
THF (0.80 mL), and the mixture was stirred at ambient temperature
for 2 h. After the solvent was removed, the residue was dissolved with
hexane and filtered by a Celite pad. The solution was concentrated and
dried under vacuum to afford an orange solid (18 mg, 98%). 1H NMR
(300 MHz, CD2Cl2): δ 7.92−7.82 (m, 4H, Ph), 7.42−7.20 (m, 16H,
Ph), 4.39 (s, 1H, Cp^-H), 3.14 (s, 3H, OCH3), 2.90 (m, 2H, Cp^-
CH2), 2.62 (m, 2H, P-CH2−CH2−P), 2.28 (m, 2H, P-CH2−CH2−P),
1.21 (s, 9H, t-Bu), 1.15 (s, 9H, t-Bu), 0.98 (s, 9H, t-Bu). 13C NMR (75
MHz, CD2Cl2): δ 142.3−127.4 (4 Ph), 132.1 (C13), 105.4, 93.5, 93.4
(C10, C11, C12), 57.5 (C9), 56.1 (C8), 39.4 (C7), 34.4, 34.0, 32.3
(C4, C5, C6), 33.5, 32.5, 32.2 (C1, C2, C3), 30.3 (dppe).
[Cp^RuCl(CO)2] (5).1b A solution of complex 3 (23 μmol) in THF
(0.80 mL) was stirred at ambient temperature under an atmosphere of
CO (1 atm) for 2 h. After the solvent was removed, the residue was
purified by flash chromatography on silica gel, using hexane/ethyl
acetate as eluent. The product was isolated as a yellow solid (11 mg,
1
99%). H NMR (300 MHz, CDCl3): δ 4.84 (s, 1H, Cp^-H), 3.77 (s,
3H, OCH3), 2.94 (d, J = 16.2 Hz, 1H, Cp^-CH2), 2.38 (d, J = 16.2 Hz,
1H, Cp^-CH2), 1.49 (s, 9H, t-Bu), 1.38 (s, 9H, t-Bu), 1.14 (s, 9H, t-
Bu). 13C NMR (75 MHz, CDCl3): δ 198.8, 198.4 (CO), 151.2 (C13),
111.4, 98.5, 95.9 (C10, C11, C12), 61.6 (C9), 58.4 (C8), 37.8 (C7),
34.5, 33.4 (C4, C5, C6), 32.5, 32.3 (C1, C2, C3).
[Cp^RuCl{N(2,6-iPr2C6H3)}] (8a). 2-Azido-1,3-diisopropylbenzene
(46 μmol, 9.3 mg) was added to a solution of complex 3 (23 μmol) in
THF (0.80 mL), and the mixture was stirred at ambient temperature
for 4 h. After the solvent was removed, the residue was purified by
D
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flash chromatography on silica gel, using hexane/ethyl acetate as
eluent. The product was isolated as an orange solid (10 mg, 71%). 1H
NMR (300 MHz, CD2Cl2): δ 7.60 (t, J = 7.76 Hz, 1H, Ar), 7.01 (d, J =
7.76 Hz, 2H, Ar), 4.51 (s, 1H, Cp^-H), 4.10−3.96 (m, 2H, CH), 3.45
(s, 3H, OCH3), 3.10 (d, J = 15.9 Hz, 1H, Cp^-CH2), 2.44 (d, J = 15.9
Hz, 1H, Cp^-CH2), 1.54 (s, 9H, t-Bu), 1.51 (s, 9H., t-Bu), 1.25−1.20
(m, 12H, i-Pr), 1.18 (s, 9H, t-Bu). 13C NMR (75 MHz, CD2Cl2): δ
158.4, 142.1, 139.7, 131.6, 125.3 (Ar, C13), 106.9, 97.4, 95.5 (C10,
C11, C12), 69.9 (C9), 57.4 (C8), 39.6 (C7), 34.6, 33.9, 33.4 (C4, C5,
C6), 32.9, 32.5, 32.4 (C1, C2, C3), 29.0 (CH), 24.0, 23.3 (i-Pr).
HRMS (FAB) Calcd for C31H50ClNORu [M]+ 589.2624, Found
589.2627. Anal. Calcd (%) for C31H50ClNORu: C, 63.19; H, 8.55; N,
2.38. Found: C, 63.46; H, 8.14; N, 2.19. Single crystals were obtained
from a diethyl ether by slow evaporation.
[Cp^RuCl{N(2,6-Me2C6H3)}] (8b). 2-Azido-1,3-dimethylbenzene
(46 μmol, 6.8 mg) was added to a solution of complex 3 (23 μmol) in
THF (0.80 mL), and the mixture was stirred at ambient temperature
for 2 h. After the solvent was removed, the residue was dissolved with
hexane and filtered by a Celite pad. The solution was concentrated and
dried under vacuum to afford an orange solid (6.4 mg, 52%). 1H NMR
(300 MHz, CD2Cl2): δ 7.42 (t, J = 7.57 Hz, 1H, Ar), 6.94 (d, J = 7.57
Hz, 2H, Ar), 4.53 (s, 1H, Cp^-H), 3.44 (s, 3H, OCH3), 3.09 (d, J =
15.9 Hz, 1H, Cp^-CH2), 2.46 (d, J = 15.9 Hz, 1H, Cp^-CH2), 2.23 (s,
6H, CH3), 1.53 (s, 9H, t-Bu), 1.51 (s, 9H, t-Bu), 1.18 (s, 9H, t-Bu).
13C NMR (75 MHz, CD2Cl2): δ 161.3, 140.0, 131.2, 130.5, 130.2 (Ar,
C13), 106.6, 98.1, 95.9 (C10, C11, C12), 70.2 (C9), 57.4 (C8), 40.0
(C7), 34.4, 34.0, 33.6 (C4, C5, C6), 33.0, 32.6, 32.4 (C1, C2, C3),
20.6 (CH3). HRMS (FAB) Calcd for C27H42ClNORu [M]+ 533.1998,
Found 533.2001. Anal. Calcd (%) for C27H42ClNORu: C, 60.82; H,
7.94; N, 2.63. Found: C, 60.56; H, 7.17; N, 2.83.
Anal. Calcd (%) for C38H57ClN4ORu: C, 63.18; H, 7.95; N, 7.76.
Found: C, 63.36; H, 7.18; N, 7.50.
Trapping of Ammonia Liberated in Ligand Exchange
Reaction of the Ruthenium Bisammine Complex. In an NMR
tube filled with argon gas complex 2 (46 μmol, 30 mg) and
benzylamine (92 μmol, 10 μL) were dissolved in THF-d8 (1.0 mL),
and the resulting solution was shaken at ambient temperature for 2 h.
Then 1,2-bis(diphenylphosphino)ethane (46 μmol, 18 mg) was added
to the solution, and the mixture was shaken at ambient temperature for
2 h. Then (isopropyl carbonic) 4-methoxybenzoic anhydride15 (92
μmol, 22 mg) was added to the solution and the mixture was shaken at
ambient temperature for 6 h. The yield of product was determined by
1H NMR by using dibromomethane as an internal standard. After the
solvent was removed, the residue was purified by flash chromatography
on silica gel, using hexane/ethyl acetate as eluent. The 4-
methoxybenzamide16 was isolated as a white solid (11 mg, 78%). H
1
NMR (300 MHz, CDCl3): δ 7.80−7.75 (m, 2H), 6.99−6.91 (m, 2H),
5.88 (br, 2H), 3.85 (s, 3H). 13C NMR (75 MHz, CDCl3): δ 169.0,
162.9, 129.5, 126.0, 114.1, 55.7.
General Procedure for Synthesis of N-Substituted Imines.
Alkyl azide (0.25 mmol) and primary amine (0.30 mmol) was added
to a solution of ruthenium complex 2 (2.0 mol %, 3.3 mg) in THF (1.0
mL), and the mixture was stirred at 70 °C for 1 h. After the solvent
1
was removed, the yield of N-substituted imine was determined by H
NMR in CDCl3 by using dibromomethane as an internal standard.
N-Hexylbenzylideneimine (10a).4a 1H NMR (300 MHz,
CDCl3): δ 8.27 (s, 1H, NCH), 7.75−7.71 (m, 2H, Ar), 7.41−
7.39 (m, 3H, Ar), 3.61 (t, J = 7.0, 1.2 Hz, 2H, N−CH2), 1.75−1.66 (m,
2H, N−CH2−CH2), 1.42−1.26 (m, 6H, (CH2)3-CH3), 0.92−0.88 (m,
3H, CH3). 13C NMR (75 MHz, CDCl3): δ 160.8, 136.6, 130.6, 128.7,
128.2, 62.0, 31.8, 31.1, 27.2, 22.8, 14.2.
[Cp^RuCl{Ph(CH3)CHNNNN(2,6-iPr2C6H3)}] (9a). (1-
Azidoethyl)benzene (44 μmol, 6.5 mg) was added to a solution of
complex 5a (22 μmol, 13 mg) in THF (1.0 mL), and the mixture was
stirred at ambient temperature for 24 h. After the solvent was
removed, the residue was purified by flash chromatography on silica
gel, using hexane/ethyl acetate as eluent. The product was isolated as
N-Benzylidenebutan-2-amine (10b).17 1H NMR (300 MHz,
CDCl3): δ 8.27 (s, 1H, NCH), 7.76−7.73 (m, 2H, Ar), 7.42−7.39
(m, 3H, Ar), 3.26−3.16 (m, 1H, CH), 1.68−1.58 (m, 2H, CH2) 1.27
(d, J = 6.3 Hz, 3H, CH−CH3), 0.86 (t, J = 7.4 Hz, 3H, CH2−CH3).
13C NMR (75 MHz, CDCl3): δ 158.9, 136.8, 130.5, 128.7, 128.3, 68.4,
30.9, 22.4, 11.2.
1
an pale green solid (13 mg, 80%). H NMR (300 MHz, CD2Cl2): δ
N-Benzylidene-2-methylpropan-2-amine (10c).18 1H NMR
(300 MHz, CDCl3): δ 8.28 (s, 1H, NCH), 7.77−7.73 (m, 2H, Ar),
7.44−7.37 (m, 3H, Ar), 1.30 (s, 9H, t-Bu). 13C NMR (75 MHz,
CDCl3): δ 155.4, 137.4, 130.4, 128.7, 128.1, 57.4, 29.9.
7.63−7.61 (m, 2H, Ar), 7.39−7.18 (m, 6H, Ar), 6.13 (q, J = 6.81 Hz,
1H, N−CH), 4.69 (s, 1H, Cp^-H), 4.14 (m, 1H, CH), 3.56 (s, 3H,
OCH3), 2.08 (d, J = 6.75 Hz, 3H, CH3), 2.09−2.03 (s, 1H, overlap,
Cp^-CH2), 1.84 (m, 1H, CH), 1.70 (d, J = 14.8 Hz, 1H, Cp^-CH2),
1.31−1.28 (m, 6H, i-Pr), 1.13 (d, J = 6.67 Hz, 3H, i-Pr), 1.05 (s, 9H, t-
Bu), 1.01 (s, 9H, t-Bu), 0.83 (s, 9H, t-Bu), 0.79 (d, J = 6.61 Hz, 3H, i-
Pr). 13C NMR (150 MHz, CD2Cl2): δ 152.3, 145.0, 144.4, 142.6,
129.0, 128.8, 127.5, 123.8, 123.0 (Ar), 99.4, 98.1 (C10, C11, C12),
79.1 (N−CH), 63.5 (C8), 58.2 (C9), 36.7 (C7), 34.9, 34.5, 32.7 (C4,
C5, C6), 32.9, 32.1, 31.5 (C1, C2, C3), 28.7, 28.0 (CH), 27.2 (CH3),
27.9, 26.4, 23.1, 21.9 (i-Pr). HRMS (FAB) Calcd for C39H60ClN4ORu
[M + H]+ 737.3499, Found 737.3497. Anal. Calcd (%) for
C39H59ClN4ORu: C, 63.61; H, 8.08; N, 7.61. Found: C, 63.20; H,
7.92; N, 6.97. Single crystals were obtained from a CH2Cl2/hexane
solution by slow evaporation.
N-(1-Phenylethylidene)hexan-1-amine (10d).19 1H NMR (300
MHz, CDCl3): δ 7.79−7.76 (m, 2H, Ar), 7.39−7.36 (m, 3H, Ar), 3.48
(t, J = 7.1 Hz, 2H, N−CH2), 2.23 (s, 3H, C−CH3), 1.80−1.71 (m, 2H,
N−CH2−CH2), 1.47−1.31 (m, 6H, (CH2)3-CH3), 0.95−0.90 (m, 3H,
CH2−CH3). 13C NMR (75 MHz, CDCl3): δ 164.9, 141.7, 129.4,
128.3, 126.7, 52.4, 32.0, 31.1, 27.6, 22.8, 15.5, 14.2.
N-(1-Phenylethylidene)butan-2-amine (10e). 1H NMR (300
MHz, CDCl3): δ 7.77−7.74 (m, 2H, Ar), 7.40−7.34 (m, 3H, Ar),
3.64−3.54 (m, 1H, N−CH), 2.24 (s, 3H, C−CH3), 1.69−1.59 (m, 2H,
CH2), 1.18 (d, J = 6.3 Hz, 3H, CH−CH3), 0.90 (t, J = 7.4 Hz, 3H,
CH2−CH3). 13C NMR (75 MHz, CDCl3): δ 162.9, 142.2, 129.3,
128.3, 126.8, 57.5, 31.3, 21.3, 15.6, 11.4. HRMS (EI) Calcd for
C12H17N 175.1361, Found 175.1361.
[Cp^RuCl{BnNNNN(2,6-iPr2C6H3)}] (9b). Benzyl azide (22 μmol,
2.9 mg) was added to a solution of complex 5a (22 μmol, 13 mg) in
THF (1.0 mL), and the mixture was stirred at ambient temperature for
4 h. After the solvent was removed, the residue was purified by flash
chromatography on silica gel, using hexane/ethyl acetate as eluent.
ASSOCIATED CONTENT
■
S
* Supporting Information
1
The product was isolated as an pale green solid (14 mg, 89%). H
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.7b00403.
NMR (300 MHz, CD2Cl2): δ 7.58−7.56 (m, 2H, Ar), 7.42−7.16 (m,
6H, Ar), 5.66 (d, J = 16.0 Hz, 1H, N−CH2), 5.44 (d, J = 16.0 Hz, 1H,
N−CH2), 4.76 (s, 1H, Cp^-H), 4.01 (m, 1H, CH), 3.72 (s, 3H,
OCH3), 2.00 (d, J = 15.3 Hz, 1H, Cp^-CH2), 1.85 (m, 1H, CH), 1.63
(d, J = 16.1 Hz, 1H, Cp^-CH2), 1.26 (d, J = 6.68 Hz, 3H, i-Pr), 1.19 (s,
9H, t-Bu), 1.19−1.13 (m, 6H, i-Pr), 1.13 (s, 9H, t-Bu), 1.02 (s, 9H, t-
Bu), 0.71 (d, J = 6.61 Hz, 3H, i-Pr). 13C NMR (213 MHz, CD2Cl2): δ
151.9, 144.9, 142.3, 137.6, 130.6, 128.8, 128.0, 123.6, 122.8 (Ar),
109.7, 102.7, 96.2 (C10, C11, C12), 72.3 (N−CH2), 63.0 (C8), 58.4
(C9), 36.3 (C7), 35.0, 32.8 (C4, C5, C6), 32.8, 32.5, 31.6 (C1, C2,
C3), 28.7, 27.9 (CH), 28.2, 26.3, 22.9, 21.8 (i-Pr). HRMS (FAB)
Calcd for C38H58ClN4ORu [M + H]+ 723.3343, Found 723.3340.
Characterization including NMR spectroscopic data and
X-ray crystallographic data (PDF)
XYZ coordinates of all structures (XYZ)
Accession Codes
CCDC 1552955−1552957 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
E
DOI: 10.1021/acs.organomet.7b00403
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
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(8) Dutta, B.; Scopelliti, R.; Severin, K. Organometallics 2008, 27,
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(9) We obtained 1H NMR spectra of the complex 3 at various
temperatures (Figure S3). Interesting fluxional behavior was observed
due to the dynamic exchange of NH3 and the restricted rotation of t-
butyl groups and the Cp^ ring.
AUTHOR INFORMATION
Corresponding Authors
*E-mail: yhrhee@postech.ac.kr.
*E-mail: pjw@postech.ac.kr.
■
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ORCID
Young Ho Rhee: 0000-0002-2094-4426
Jaiwook Park: 0000-0002-1135-3317
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the National Research Foundation
of Korea (NRF) grant funded by the Korea government
(MSIP) (2015R1A2A2A01008130).
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DOI: 10.1021/acs.organomet.7b00403
Organometallics XXXX, XXX, XXX−XXX