Cycloruthenation of aryl imines and N-heteroaryl benzenes via C-H bond activation with Ru(II) and acetate partners

Article abstract of DOI:10.1016/j.jorganchem.2015.02.050

The reaction of arylimines with [RuCl₂(p-cymene)]₂ and 4 equiv. of KOAc at room temperature in methanol leads to the formation of N-Ru-C cycloruthenates RuCl(arylimine-_kC,N)(p-cymene) 3a-3d via ortho C-H activation/deprotonation by acetate. The presence of the stable Ru-Cl bond rather than a labile Ru-OAc bond is crucial for the isolation of the complexes. This preparative method of cyclometallates was applied to 2-phenyloxazoline, and benzo[h]quinoline and to the improved synthesis of 2-phenylpyridine and 1-phenylpyrazole derivatives. The molecular structures of three cycloruthenates are reported.

Full text of DOI:10.1016/j.jorganchem.2015.02.050

Accepted Manuscript
Cycloruthenation of aryl imines and N-heteroaryl benzenes via C-H bond activation
with Ru(II) and acetate partners
Bin Li, Christophe Darcel, Thierry Roisnel, Pierre H. Dixneuf
PII:
S0022-328X(15)00145-X
10.1016/j.jorganchem.2015.02.050
JOM 18957
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 23 December 2014
Revised Date: 26 February 2015
Accepted Date: 27 February 2015
Please cite this article as: B. Li, C. Darcel, T. Roisnel, P.H. Dixneuf Cycloruthenation of aryl imines
and N-heteroaryl benzenes via C-H bond activation with Ru(II) and acetate partners, Journal of
Organometallic Chemistry (2015), doi: 10.1016/j.jorganchem.2015.02.050.
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ACCEPTED MANUSCRIPT
Graphical abstract synopsis
(N-Ru-C)-cycloruthenates are easily prepared at room temperature on reaction of
arylimines with [RuCl2(p-cymene)]2 and KOAc in methanol, via ortho arene C-H
activation/deprotonation by acetate. The presence of a Ru-Cl remaining bond, instead
of a Ru-OAc bond, is crucial for compound isolation. This preparative method was
applied to 2-phenyl oxazoline, benzo[h]quinoline, 2-phenylpyridine and
1-phenylpyrazole derivatives.

ACCEPTED MANUSCRIPT
Cycloruthenation of aryl imines and N-heteroaryl benzenes
via C-H bond activation with Ru(II) and acetate partners
Bin Li,a,b Christophe Darcel,a* Thierry Roisnel, c Pierre H. Dixneufa*
aInstitut des Sciences Chimiques de Rennes, UMR 6226 CNRS-Université de Rennes 1,
Team “Organometallics: Materials and Catalysis” Centre for Catalysis and Green Chemistry,
Campus de Beaulieu, 35042 Rennes, France
bSchool of Chemical & Environmental Engineering, Wuyi University, Jiangmen 529020, Guangdong
Province, P.R. China
cInstitut des Sciences Chimiques de Rennes, UMR 6226 CNRS – Université de Rennes 1, Centre de
Diffractométrie X, Campus de Beaulieu, 35042 Rennes, France.
In the memory of professor Alexander Shilov
for his creative and inspiring work on C-H bond activation
Abstract. The reaction of arylimines with [RuCl2(p-cymene)]2 and 4 equiv. of KOAc at room
temperature in methanol leads to the formation of N-Ru-C cycloruthenates
RuCl(arylimine-kC,N)(p-cymene) 3a-3d via ortho C-H activation/deprotonation by acetate.
The presence of the stable Ru-Cl bond rather than a labile Ru-OAc bond is crucial for the
isolation of the complexes. This preparative method of cyclometallates was applied to
2-phenyl oxazoline, and benzo[h]quinoline and to the improved synthesis of
2-phenylpyridine and 1-phenylpyrazole derivatives. The molecular structures of three
cycloruthenates are reported.
Keywords: N-Ru-C cycloruthenates, C-H bond activation, C-H bond deprotonation,
arylimines, ruthenium-acetate.
1 Introduction
Since the initial creative work of Alexander Shilov on C-H bond activation of alkanes with
Pt(II) and Pt(IV) 1,2 catalysts leading especially to alcohols,2 many transition metal complexes
have been shown to promote the activation of C-H bonds via various processes and to further
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lead to catalytic functionalizations of aromatic systems and alkanes.3 Among these molecular
metal catalysts, after the useful contribution of ruthenium(0) species in the Murai reaction,4
the easily prepared, inexpensive and stable ruthenium(II) complexes are now offering easy
and diverse catalytic functionalizations of sp2 C-H 5,6 as well as sp3 C-H 7 bonds.
Ruthenium(II)-catalyzed sp2C-H bond functionalization of functional aromatic
compounds has known since 2001 a tremendous development due to the control of direct
(hetero)arylation with aryl and heteroaryl halides for the preparation of polyfunctional
molecules and polydentate ligands8-11 and for the access to polyfunctional alkenes via catalytic
alkenylation.5,12 For catalytic functionalization of arene C-H bonds the mechanism based on
kinetics was shown13,14 to be favoured by nitrogen containing functional/directing groups and
to take place via an initial, easy ortho C-H bond deprotonation by carbonate only10a,11 or by
carboxylate10b-10e as a proton shuttle to form a cyclometallated ruthenium(II) intermediate.
The oxidative addition of arylhalide to the orthometallacycle followed by the reductive C-C
bond formation is a more energy demanding step,13,14 that can be also performed in water as
solvent.15
The first preparations of (N,C)-cyclometallated ruthenium(II) complexes were made by
transmetallations from mercury salts.16 Then they were performed more directly by C-H bond
deprotonation of N-containing functional arenes as reported by Pfeffer et al.17 and Davies et
al..18 Thus the cyclometallated ruthenium(II) complexes arising from the deprotonation of
arylmethylamines,16a,17a,b,e 1-aminotetralin,17f and N-containing heterocycles such as
phenylpyrrolidine,17e phenylpyridine,11a,b,c,18a oxazolines,18c,d pyrazole18d were successfully
isolated. By contrast the preparation of cycloruthenates of arylimines with ruthenium(II)
complexes was not straightforward in spite of the easiness of their Ru(II)-catalyzed ortho
arylations.19-21 Cationic ruthenium(II) cyclometallated benzylideneanilines PhC(R)=NPh (R =
H, Me) were first obtained on reaction with RuCl2(PMe3)(C6Me6)/ 2AgBF4.22 By contrast
benzodiazepine reacted with [RuCl2(p-cymene)]2 and NEt3 to generate the (N,C)-ruthenacycle
involving the benzodiazepine arylimine moiety.23
Davies18a showed that the acetate ligand of RuCl(OAc)(p-cymene) complex could
promote the formation at room temperature of (N,C)-cyclometallated complexes from
aldimines but only when they contained a N-alkyl group and in the presence of an excess of
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benzaldehyde.18 This methodology could not be used for the preparation of cyclometallated
ruthenium(II) complexes from arylideneanilines,18d which easily led by contrast to their
rhodium and iridium cyclometallated derivatives. For the later the regioselectivity of C-H
bond deprotonation was shown to be mostly sensitive to steric effects.18a,18b,24
Orthometallation of aryloxazolines appeared less favorable than that of alkylimines. It
occurred only with iridium complexes and not with ruthenium or rhodium derivatives. 18d
The ruthenium(II) catalyzed direct ortho C-H bond diarylations of N-arylimines with
arylhalides by action of both acetate and PPh3 ligands were successfully performed in NMP,20
and more surprisingly in water with higher activity of the catalyst. 21 The first step of this
reaction is expected to be the formation of the orthometallated intermediate via the C-H bond
deprotonation, which motivated the search for the conditions to form and isolate the N-aryl
imine cycloruthenation intermediates.
We now describe the general and facile access to a variety of cyclometallated ruthenium(II)
complexes first of arylimines, following our preliminary report,25 on reaction with
[RuCl2(p-cymene)]2 at room temperature in the presence of KOAc in methanol. It will be
shown that these complexes are stable when a Ru-Cl bond is retained. This ortho C-H bond
activation by deprotonation with acetate can be applied to functional arenes equipped of a
nitrogen-containing heterocyclic directing group such as pyridine, pyrazole, oxazoline and
benzo[h]quinoline and three of these cyclometallate complexes are characterized by X-ray
structure analysis.
2 Experimental
2.1 General
All reagents were obtained from commercial sources and used as received. THF and
dichloromethane were dried over Braun MB-SPS-800 solvent purification system, and stored
under an argon atmosphere. Methanol (anhydrous, HPLC grade, Aldrich) was used as
received. Technical grade petroleum ether (40-60 °C b.p.) and ethyl acetate were used for
chromatography column. Analytical TLC was performed on Merck 60F254 silica gel plates
(0.25 mm thickness). Column chromatography was performed on Acros Organics Ultrapure
silica gel (mesh size 40-60µm, 60A).
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1H NMR spectra were recorded in CDCl3 at ambient temperature on Bruker DPX-200,
AVANCE I 300, AVANCE III 400 spectrometers at 200.1, 300.1 and 400.1 MHz, using the
solvent as the internal standard (CDCl3, 7.26 ppm). 13C NMR spectra were obtained at 50, 75
and 100 MHz and referenced to the internal solvent signals (CDCl3, central peak at 77.2 ppm).
Chemical shift (δ) and coupling constants (J) are given in ppm and in Hz, respectively. The
peak patterns are indicated as follows: s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet,
and br. for broad. Infrared spectra were recorded on a Bruker IFS28 spectrometer using KBr
pellets. HRMS were measured on Waters Q-TOF 2, at the CRMPO (Centre régional de
mesures physiques de l'Ouest), Université de Rennes 1.
2.2 General procedures for the reactions of imines with [RuCl2(p-cymene)]2
[RuCl2(p-cymene)]2 (0.1 mmol, 61.2 mg), imine (0.2 mmol), KOAc (0.4 mmol, 40 mg) and
methanol (5 mL) were introduced in a dried Schlenck tube under argon, equipped with
magnetic stirring bar and the mixture was stirred at ambient temperature for 20 h. The solvent
was then evaporated under vacuum and the desired product was purified by chromatography
column on silica gel (0.5 mol% Et3N) with a mixture of petrol ether/ethyl acetate as the
eluent.
[RuCl{C6H4-1-C(H)=N(4-CH3C6H4-kC,N)}(p-cymene)] (3a)
This compound was prepared from the imine 2a. The complex 3a was purified by
chromatography column on silica gel with a mixture of petroleum ether/ethyl acetate as the
eluent (75:25), and was isolated as a orange solid (83 mg, 90 %). Rf (petroleum ether/EtOAc
70:30) = 0.45.
1H NMR (400 MHz, CDCl3): δ = 8.20 (d, 1H, J = 7.6 Hz, H6), 8.10 (s, 1H, H7), 7.66 (d, 2H, J
= 8.4 Hz, H11), 7.54 (d, 1H, J = 7.6 Hz, H3), 7.23-7.17 (m, 3H, H10, H4 or H5), 7.02 (t, 1H, J =
7.4 Hz, H4 or H5), 5.48 (d, 1H, J = 6.0 Hz, cymene), 5.22 (d, 1H, J = 6.0 Hz, cymene), 4.87 (d,
1H, J = 6 Hz, cymene), 4.83 (d, 1H, J = 6.0 Hz, cymene), 2.43-2.36 (m, 4H, H13, CHMeMe’),
2.08 (s, 3H, Me cymene), 0.99 (d, 3H, J = 6.8 Hz, CHMeMe’), 0.85 (d, 3H, J = 6.8 Hz,
CHMeMe’). The protons H3, H6, H10 have been assigned from a COSY experiment. 13C{1H}
NMR (100 MHz, CDCl3): δ =189.2 (C-Ru), 171.7, 152.8, 146.2, 139.3, 137.3, 130.3, 129.8,
129.4, 122.6, 122.3, 102.5, 100.7, 92.7, 89.6, 82.9, 82.4, 31.0, 23.1, 21.6, 21.3, 18.9. IR: v
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(C=N) 1579 cm-1. HRMS (ESI): m/z calcd for C24H26N35ClNa102Ru [M+ Na]+ 488.0695,
found 488.0708. m/z calcd for C24H26N102Ru [M- Cl]+ 430.1109, found 430.1112.
[RuCl{(4-OMeC6H4)-1-C(H)=N(4-CH3C6H4-kC,N)}(p-cymene)] (3b)
This compound was prepared from the imine 2b (45 mg, 0.2 mmol). The complex 3b was
purified by chromatography column on silica gel with a mixture of petroleum ether/ethyl
acetate as the eluent (70:30), and was isolated as a red solid (77 mg, 77 %). Rf (petroleum
ether/EtOAc 70:30) = 0.30.
1H NMR (300 MHz, CDCl3): δ = 7.97 (s, 1H, H7), 7.72 (d, 1H, J = 2.4 Hz, H6), 7.63 (d, 2H, J
= 8.4 Hz, H11), 7.48 (d, 1H, J = 8.4 Hz, H3), 7.19 (d, 2H, J = 8.4 Hz, H10), 6.56 (dd, 1H, J =
2.4 Hz, J = 8.4 Hz, H4), 5.44 (d, 1H, J = 6.0 Hz, cymene), 5.18 (d, 1H, J = 5.7 Hz, cymene),
4.83 (m, 2H, cymene), 3.92 (s, 3H, OMe), 2.41-2.35 (m, 4H, H13, CHMeMe’), 2.08 (s, 3H,
Me cymene), 0.99 (d, 3H, J = 6.9 Hz, CHMeMe’), 0.85 (d, 3H, J = 6.9 Hz, CHMeMe’).
13C{1H} NMR (75 MHz, CDCl3): δ =191.5 (C-Ru), 170.2, 160.3, 152.8, 139.7, 136.8, 131.1,
129.3, 123.6, 122.3, 109.0, 102.3, 100.1, 92.4, 89.2, 83.0, 82.2, 55.3, 30.9, 23.1, 21.6, 21.2,
18.9. IR: v (C=N) 1582 cm-1. HRMS (ESI): m/z calcd for C25H28NO35ClNa102Ru [M+ Na]+
518.0801, found 518.0817. m/z calcd for C25H28NO102Ru [M- Cl]+ 460.1214, found 460.1212.
[RuCl{(4-ClC6H4)-1-C(H)=N(4-CH3C6H4-kC,N)}(p-cymene)] (3c)
This compound was prepared from the imine 2c (45.8 mg, 0.2 mmol). The complex 3c was
purified by chromatography column on silica gel with a mixture of petroleum ether/ethyl
acetate as the eluent (75:25), and was isolated as a red solid (52 mg, 52 %). Rf (petroleum
ether/EtOAc 70:30) = 0.65.
1H NMR (300 MHz, CDCl3): δ = 8.15 (d, 1H, J = 1.8 Hz, H6), 8.06 (s, 1H, H7), 7.63 (d, 2H, J
= 8.1 Hz, H11), 7.45 (d, 1H, J = 7.8 Hz, H3), 7.22 (d, 2H, J = 8.1 Hz, H10), 7.01-6.97 (m, 1H,
H4), 5.47 (d, 1H, J = 6.0 Hz, cymene), 5.22 (d, 1H, J = 6.0 Hz, cymene), 4.90 (d, 1H, J = 6.0
Hz, cymene), 4.85 (d, 1H, J = 6.0 Hz, cymene), 2.42-2.33 (m, 4H, H13, CHMeMe’), 2.10 (s,
3H, Me cymene), 0.98 (d, 3H, J = 6.9 Hz, CHMeMe’), 0.85 (d, 3H, J = 6.9 Hz, CHMeMe’).
13C{1H} NMR (75 MHz, CDCl3): δ =190.5 (C-Ru), 170.8, 152.5, 144.5, 138.5, 137.6, 136.0,
130.4, 129.5, 123.0, 122.2, 103.1, 100.9, 92.9, 89.4, 83.7, 82.6, 31.0, 23.0, 21.7, 21.3, 19.0. IR:
v (C=N) 1578 cm-1. HRMS (ESI): m/z calcd for C24H25N35Cl2Na102Ru [M+ Na]+ 522.0305,
found 522.0323. m/z calcd for C24H25 N35Cl 102Ru [M- Cl]+ 464.0719, found 464.0719.
[RuCl{C6H4-1-C(CH3)=N(4-OCH3C6H4-kC,N)}(p-cymene)] (3d)
This compound was prepared from the imine 2d (45 mg, 0.2 mmol). The complex 3d was
purified by chromatography column on silica gel with a mixture of petroleum ether/ethyl
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acetate (70:30) as the eluent, and was isolated as a red solid (72 mg, 73 %). Rf (petroleum
ether/EtOAc 70:30) = 0.35
1H NMR (300 MHz, CDCl3): δ = 8.20 (d, 1H, J = 7.5 Hz, H3 or H6), 7.46 (d, 1H, J = 7.5 Hz,
H3 or H6), 7.30-7.18 (m, 3H, H11, H4 or H5), 7.05-6.96 (m, 3H, H10, H4 or H5), 5.33 (d, 1H, J =
6.0 Hz, cymene), 4.95 (d, 1H, J = 6.0 Hz, cymene), 4.63 (d, 2H, J = 6.0 Hz, cymene), 3.91 (s,
3H, OMe), 2.57-2.48 (m, 1H, CHMeMe’), 2.27 (s, 3H, H14), 2.02 (s, 3H, Me cymene), 1.01 (d,
3H, J = 6.9 Hz, CHMeMe’), 0.83 (d, 3H, J = 6.9 Hz, CHMeMe’). 13C{1H} NMR (100 MHz,
CDCl3): δ =188.3 (C-Ru), 179.6, 157.8, 147.4, 146.4, 139.3, 130.1, 128.3, 121.9, 116.5, 114.8,
102.9, 102.6, 92.8, 90.4, 80.3, 80.2, 55.6, 30.8, 23.0, 21.3, 18.8, 16.9. IR: v (C=N) 1578 cm-1.
HRMS (ESI): m/z calcd for C25H28NO35ClNa102Ru [M+ Na]+ 518.0801, found 518.0811. m/z
calcd for C25H28NO 102Ru [M- Cl]+ 460.1214, found 460.1211.
2.3 Reaction of 2-phenyl-2-oxazoline with [RuCl2(p-cymene)]2: preparation of complex 5.
This compound was prepared from 2-phenyl-2-oxazoline 4 (0.2 mmol, 26.3 µL). The desired
complex 5 was purified by chromatography column on silica gel with a mixture of petroleum
ether/ethyl acetate (30:70) as the eluent, and was isolated as a green solid (32.7 mg, 40%). Rf
(petroleum ether/EtOAc 30:70) = 0.25
1H NMR (300 MHz, CDCl3): δ = 8.15 (d, 1H, J = 7.5 Hz, H3 or H6), 7.35 (d, 1H, J = 7.5 Hz,
H3 or H6), 7.22 (t, 1H, J = 7.5 Hz, H4 or H5), 6.98 (t, 1H, J = 7.5 Hz, H4 or H5), 5.56 (d, 1H, J
= 5.7 Hz, cymene), 5.46 (d, 1H, J = 5.7 Hz, cymene), 5.19 (d, 1H, J = 5.7 Hz, cymene), 4.99
(d, 1H, J = 5.7 Hz, cymene), 4.78-4.67 (m, 2H, H11), 4.26-4.08 (m, 2H, H10), 2.55 (sept, 1H, J
= 6.9 Hz, CHMeMe’), 2.06 (s, 3H, Me cymene), 1.10 (d, 3H, J = 6.9 Hz, CHMeMe’), 1.00
(d, 3H, J = 6.9 Hz, CHMeMe’). 13C{1H} NMR (75 MHz, CDCl3): δ = 182.7 (C-Ru), 174.2,
139.3, 130.9, 130.7, 126.4, 122.3, 101.3, 99.3, 88.1, 87.5, 81.8, 81.0, 70.8, 54.4, 31.2, 22.8,
22.2, 19.1. IR: v (C=N) 1632 cm-1. HRMS (ESI): m/z calcd for C19H22NO35ClNa102Ru [M+
Na]+ 440.0331, found 440.0336; m/z calcd for C19H22NO 102Ru [M- Cl]+ 382.0745, found
482.0755.
2.4 Reaction of benzo[h]quinoline with [RuCl2(p-cymene)]2 : preparation of complex 7.
This compound was prepared from benzo[h]quinolone 6 (0.2 mmol, 35.8 mg). The desired
complex 7 was purified by chromatography column on silica gel with a mixture of petroleum
ether/ethyl acetate (50:50) as the eluent, and was isolated as a dark green solid (41.9 mg,
47 %). Rf (petroleum ether/EtOAc 1:1) = 0.20.
1H NMR (300 MHz, CDCl3): δ = 9.48 (d, 1H, J = 5.1 Hz, H2), 8.41 (d, 1H, J = 6.9 Hz), 8.18
(d, 1H, J = 7.8 Hz), 7.78 (d, 1H, J = 8.7 Hz), 7.63-7.42 (m, 4H), 5.74 (d, 1H, J = 5.7 Hz,
cymene), 5.66 (d, 1H, J = 6.0 Hz, cymene), 5.30 (d, 1H, J = 6.0 Hz, cymene), 5.13 (d, 1H, J =
6.0 Hz, cymene), 2.50 (m, 1H, CHMeMe’), 2.04 (s, 3H, Me cymene), 0.97 (d, 3H, J = 6.9 Hz,
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CHMeMe’), 0.84 (d, 3H, J = 6.9 Hz, CHMeMe’). 13C{1H} NMR (75 MHz, CDCl3): δ =178.4
(C-Ru), 155.3, 152.5, 140.5, 136.6, 135.4, 133.9, 129.7, 129.3, 126.9, 122.8, 121.1, 120.9,
101.5, 99.6, 89.7, 89.3, 83.6, 82.5, 30.9, 22.7, 21.8, 18.9. HRMS (ESI): m/z calcd for
C23H22N35ClNa102Ru [M+ Na]+ 472.0382, found 472.0390. m/z calcd for C23H22N102Ru [M-
Cl]+ 414.0796, found 414.0797.
2.5 Reaction of 2-Phenylpyridine with [RuCl2(p-cymene)]2 : preparation of complex 9. [13,
18b]
This compound was prepared from 2-phenylpyridine 8 (0.2 mmol, 29 µL). The desired
complex 9 was purified by chromatography column on silica gel with a mixture of petroleum
ether/ethyl acetate (30/70) as the eluent, and isolated as a dark green solid (81 mg, 94 %). Rf
(petroleum ether/EtOAc 30:70) = 0.35.
1H NMR (400 MHz, CDCl3): δ = 9.16 (d, 1H, J = 5.2 Hz, H12), 8.09 (d, 1H, J = 7.6 Hz, H3),
7.65-7.53 (m, 3H, H9, H10, H6), 7.11 (t, 1H, J = 7.2 Hz, J = 7.2 Hz, H4), 6.99-6.94 (m, 2H, H5,
H11), 5.52-5.48 (m, 2H, cymene), 5.10 (d, 1H, J = 5.6 Hz, cymene), 4.91 (d, 1H, J = 5.6 Hz,
cymene), 2.37 (sept, 1H, J = 6.8 Hz, CHMeMe’), 1.98 (s, 3H, Me cymene), 0.91 (d, 3H, J =
6.8 Hz, CHMeMe’), 0.81 (d, 3H, J = 6.8 Hz, CHMeMe’). 13C{1H} NMR (100 MHz, CDCl3):
δ = 181.5 (C-Ru), 165.4, 154.7, 143.5, 139.7, 136.7, 129.5, 124.0, 122.6, 121.5, 118.9, 100.8,
100.6, 90.9, 89.7, 84.3, 82.3, 30.9, 22.6, 21.8, 18.9.
2.6 Reaction of 1-phenyl-1H-pyrazole with [RuCl2(p-cymene)]2 : preparation of complex
11.[18d]
This compound was prepared from 1-phenyl-1H-pyrazole (0.2 mmol, 26.4 µL). The desired
complex 10 was purified by chromatography column on silica gel with a mixture of petroleum
ether/ethyl acetate (30:70) as the eluent, and was isolated as a greenish solid (65.0 mg, 79 %)
Rf (petroleum ether/EtOAc 30:70) = 0.40.
1H NMR (300 MHz, CDCl3): δ = 8.15 (d, 1H, J = 7.2 Hz, H6), 8.06 (d, 1H, J = 2.1 Hz, H11),
7.91 (d, 1H, J = 2.7 Hz, H9), 7.19-7.01 (m, 3H, H3, H4, H5), 6.47 (t, 1H, J = 2.7 Hz, H10), 5.57
(d, 2H, J = 6.0 Hz, cymene), 5.30 (d, 1H, J = 6.0 Hz, cymene), 5.09 (d, 1H, J = 6.0 Hz,
cymene), 2.47-2.44 (sept, 1H, J = 6.9 Hz, CHMeMe’), 2.06 (s, 3H, Me cymene), 0.97 (d, 3H,
J = 6.9 Hz, CHMeMe’), 0.93 (d, 3H, J = 6.9 Hz, CHMeMe’). 13C{1H} NMR (75 MHz,
CDCl3): δ = 161.9 (C-Ru), 142.2, 141.9, 140.2, 126.1, 125.0, 123.2, 111.5, 108.4, 100.09,
100.08, 88.7, 88.2, 84.2, 82.2, 30.7, 22.5, 22.0, 18.9.
2.7 Preparation of complex 12
[RuCl2(p-cymene)]2 (0.1 mmol, 61.2 mg), 1-phenyl-1H-pyrazole (0.2 mmol, 26.4 µL),
diphenylacetylene (0.2 mmol, 35.6 mg), KOAc (0.4 mmol, 40 mg) and methanol (5 mL) were
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introduced in a dried Schlenck tube under Argon, equipped with magnetic stirring bar and was
stirred at ambient temperature for 20 h. The solvent was then evaporated under vacuum and
the desired product was purified by chromatography column on silica gel with a mixture of
petrol ether/ethyl acetate (1:1) as the eluent. The complex 1218e was isolated as a dark green
solid in 67% (79.3 mg).
1H NMR (300 MHz, CDCl3): δ = 8.59 (d, 1H, J = 1.5 Hz, H11), 7.88 (d, 1H, J = 1.5 Hz, H9),
7.39-7.14 (m, 7H), 6.97-6.87 (m, 4H), 6.81-6.74 (m, 3H), 6.52 (t, 1H, J = 2.4 Hz, H10), 5.57
(d, 1H, J = 5.1 Hz, cymene), 4.66 (d, 1H, J = 5.1 Hz, cymene), 4.52 (d, 1H, J = 5.1 Hz,
cymene), 3.51 (d, 1H, J = 5.1 Hz, cymene), 2.83 (sept, J = 6.9 Hz,1H, CHMeMe’), 2.47 (s,
3H, Me cymene), 1.25 (d, 3H, J = 6.9 Hz, CHMeMe’), 1.10 (d, 3H, J = 6.9 Hz,
CHMeMe’).13C{1H} NMR (75 MHz, CDCl3): δ =183.3 (C-Ru), 152.5, 146.7, 146.0, 144.1,
137.7, 137.5, 133.7, 133.4, 131.6, 128.5, 128.2, 127.2, 126.3, 125.9, 125.5, 124.7, 123.1,
110.3, 107.8, 103.8, 96.4, 81.1, 78.9, 75.3, 31.4, 23.6, 23.2, 19.6.
2.8 Catalytic arylation of imine 2a with Ru(II)-OAc catalytic system in NMP
[RuCl2(p-cymene)]2 (0.025 mmol, 15.3 mg), KOAc (0.1 mmol, 10 mg) and K2CO3 (1.5 mmol,
208 mg) were introduced in a dried Schlenck tube under argon, equipped with magnetic
stirring bar. Imine 2a (0.5 mmol), phenylbromide (1.25 mmol), NMP (2 mL) and tetradecane
(10 ꢀL) as the internal standard for gas chromatography, were added in the Schlenck tube
o
which was then placed in the oil bath at 160 C. The reaction mixture was stirred for the
specified time. Then, the conversion of the reaction was analyzed by gas chromatography. The
reaction mixture was diluted with 30 mL of diethyl ether, washed with water (20 mL × 3), and
dried over MgSO4. The solvent was then evaporated under vacuum and the desired product
was purified by chromatography using a silica gel column. The solvent was then evaporated
under vacuum and the product was purified by chromatography using a silica gel column. The
silica gel was previously stirred for 1h in 200 mL of petroleum ether containing 1 mol% Et3N
(99:1). The products were eluted with a mixture of petroleum ether/ethyl acetate. The product
was thus obtained and the mono and diarylated products ratio was determined by 1H NMR.
N-[(o,o’-Diphenyl)benzylidene]-p-toluidine (14)
Green solid, yield = 75%, 1H NMR (200 MHz, CDCl3): δ = 8.36 (s, 1H), 7.61-7.40 (m, 13H),
7.10 (d, 2H, J = 8.2 Hz), 6.62 (d, 2H, J = 8.1 Hz), 2.33 (s, 3H). 13C NMR (50 MHz, CDCl3):
δ = 161.0, 150.0, 143.0, 141.5, 135.7, 134.3, 130.5, 130.15, 129.9, 129.5, 128.5, 127.5, 120.60,
21.38. GC: tR = 30.5 min. MS (EI): m/z: 346 (100, M+ - H), 254 (16), 241 (15), 91 (10), 65
(11); HRMS (ESI): m/z calcd for C26H21N (M+ H+) 348.1746, found 348.1742.
8

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2.8 X-ray crystallography
Crystals of complexes 3a, 3b and 7 were mounted on Bruker APEX2 single crystal X-ray
diffractometer using monochromated Mo Kα radiation (λ = 0.71073Å). The structures were
solved by direct methods using the program SHELXS-97 26. Refinement and all further
calculations were carried out using SHELXL-97 27. The H-atoms were included in calculated
positions and treated as riding atoms using the SHELXL default parameters. The non H atoms
were refined anisotropically, using weighted full-matrix least-square on F2. Figures of
complexes 3a, 3b and 7 were drawn with ORTEP.
3 Results and discussion
3.1 Synthesis of [RuCl(aryl imine)(p-cymene)] complexes 3a-3d
The reaction of the [RuCl2(p-cymene)]2 complex 1 was first performed with 2 equivalents
of aldimine 2a in the presence of various amounts of KOAc and K2CO3 in THF or methanol
as an attempt to produce cyclometallated complex 3a. The choice of solvent is crucial as with
2 equiv. of KOAc no transformation was observed in THF, but in methanol at room
temperature 36% of complex 3a were formed. The increase to 4 equiv of KOAc led to the
complete formation of the orange complex 3a which was isolated in 90% yield after 20h at
room temperature (Scheme 1). It is noteworthy that the addition of K2CO3 disfavoured the
formation of 3a and this is consistent with the kinetic studies of the reaction of
Ru(OAc)2(arene) with 2-phenylpyridine13 and 1-phenylpyrazole14 showing that the reaction
was autocatalysed by the freed AcOH, and thus that the rate of ortho C-H bond activation was
decreased by K2CO3. Only 10% yield of complex 3a was obtained in water as solvent likely
due to the low solubility of the ruthenium complex 1 and substrates in water. The
cycloruthenation of substituted aryl imines 2b-d with [RuCl2(p-cymene)]2 1 in methanol in
the presence of 4 equiv. of KOAc at room temperature for 20 h led to the isolation of red
complexes 3b (77%), 3c (52%), and 3d in 73% isolated yields (Scheme 1). The struture of
3a-3d was based on 1H, 13C NMR and the X-ray struture analysis of compounds 3a and 3b.
9

ACCEPTED MANUSCRIPT
The ruthenium complex 3a, or its analogous derivative with a Ru-OAc bond instead of a
Ru-Cl bond, was not detected in the reaction of Ru(OAc)2(p-cymene) and aryl imine 2a.
However the unstable cyclometallate arising from the interaction of 2-phenyl pyridine with
Ru(OAc)2(p-cymene) at 27°C in acetonitrile was observed.13 Thus the aryl imine 2a was
reacted with Ru(OAc)2(p-cymene) in methanol but in the presence of one equiv. of KCl and
then 66% yield of the complex 3a was isolated (Scheme 2). This result shows that the
complex 3a containing a Ru–Cl bond is more stable than its parent compound containing the
Ru–OAc bond.
This result, along with the formation of complexes 3a–3d from complex 1 or in situ
formed Ru(OAc)2(p-cymene) complex, also shows that the Ru(II)-OAc bonds easily
dissociate leading to free external anion OAc- which is able to deprotonate, on cooperative
action of the Ru(II) centre, the neighbour ortho C-H bond of the substrate coordinated to this
Ru(II) centre.13,14
10

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3.2 Synthesis of [RuCl(N-containing heterocycle)(p-cymene)] complexes 5, 7, 9 and 11.
The previous mild conditions for cyclometallation of aryl imines, with [RuCl2(p-cymene)]2
in the presence of excess KOAc at room temperature, led us to apply this method for the
synthesis and isolation of cycloruthenate complexes from arenes possessing a nitrogen
containing heterocycle as directing group. Thus the heterocycle 2-phenyloxazoline 4 was
reacted with [RuCl2(p-cymene)]2 in the presence of 4 equiv. of KOAc in methanol at room
temperature
and
led
to
the
formation
of
the
green
complex
[RuCl(o-C6H4-2-oxazoline)(p-cymene)] 5, which was isolated in 40% (Scheme 3).
The related complex with Ru-OAc bond was observed during the kinetic study of
Ru(OAc)2(p-cymene) with the same oxazoline derivative 4 in acetonitrile,14 which was shown
not to be stable as it readily led to the dissociation of the Ru-OAc bond and to the formation
of the complex [Ru(NCCD3)(o-C6H4-2-oxazoline)(p-cymene)]+(AcO-) in the absence of
choride anion and then to [Ru(NCCD3)4(o-C6H4-2-oxazoline)] +(AcO-) by displacement of the
arene.
The heterocycle benzo[h]quinoline 6 was also reacted with [RuCl2(p-cymene)]2 1 in
methanol under the same conditions and afforded to the green cyclometallated complex 7
isolated in 47% (Scheme 3).
We applied the above conditions to the synthesis of the known dark green cycloruthenate
complex 9 arising from 2-phenyl pyridine 8. Indeed 2-phenyl pyridine 8 readily reacts in
methanol with [RuCl2(p-cymene)]2 1 to afford the dark green complex 9 isolated in 94% yield
11

ACCEPTED MANUSCRIPT
(Scheme 3). This cyclometallate complex 9 was previously prepared by A. Jutand et al. via
the cyclometallation of 2-phenylpyridine with [RuCl2(p-cymene)]2 in the presence of KOAc
in CH3CN,13 and by Davies et al. with an excess of NaOAc in dichloromethane (61%).18b This
complex 9 is very stable with respect to its analogous complex containing a Ru-OAc bond.
The reaction of 1-phenylpyrazole 10 with Ru(OAc)2(p-cymene) was studied in details in
acetonitrile
and
shown
to
give
at
27°C
the
orthometallate
[Ru(OAc)(o-C6H4-2-NNC3H3)(p-cymene)].14 Thus 1-phenylpyrazole 10 was also reacted with
[RuCl2(p-cymene)]2 with 4 equiv. KOAc in methanol and the green cyclometallated
ruthenium(II) complex 11 was formed and isolated in 79% yields (Scheme 3). The complex
11 was previously prepared by Davies et al. from the reaction of [RuCl2(p-cymene)]2 and
1-phenylpyrazole in the presence of an excess of NaOAc in dichloromethane (64%).[18d]
Thus the above results show that arenes containing a functional imine group and a
12

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nitrogen functional group easily react with [RuCl2(p-cymene)]2 in methanol with 4 equiv of
KOAc
[RuCl(o-C6H4-N-heterocycle)(p-cymene)] in a good yield. It contrasts with their ready
reaction with Ru(OAc)2(p-cymene) which leads to unstable
at
room
temperature
to
produce
isolable
cycloruthenate
[Ru(OAc)(o-C6H4-N-heterocycle)(p-cymene)] complex with labile Ru-OAc bond. These
reactions definitely point out the key role of acetate or carboxylate in general for the
deprotonation of ortho arene C-H bonds.
3.3 Characterization of the Ru(II)-cyclometallated complexes
1
The H NMR spectrum of 3a shows the cyclometallated phenyl H6 and H3 protons as two
inequivalent doublets at δ = 8.20 ppm and δ = 7.54 ppm, respectively, and that the CH=N
proton gives a singlet at δ = 8.10 ppm. (Fig. 1) The isopropyl group of the p-cymene is
observed as two inequivalent doublets at δ = 0.85 ppm and at δ = 0.99 ppm, and the four
aromatic protons of the p-cymene are observed as inequivalent doublets between δ = 4.83 and
5.49 ppm as expected for a p-cymene ligand in a chiral-at-metal Ru-(II) complex centre.
1
The H NMR spectra of ruthenium complexes 3b and 3c are similar to that of 3a except
that the phenyl H6 proton was observed as a doublet at δ = 7.71 ppm or δ = 8.15 ppm for 3b or
3c, respectively. The H4 and H3 protons were observed as two doublets at δ = 6.54 ppm and δ
1
= 7.46 ppm for 3b, at δ = 7.21 ppm and δ = 7.43 ppm for 3c. The H NMR spectrum of
ruthenium complex 3d is similar to that of 3a except that the C-CH3 protons in p-cymene
were observed as a singlet at δ = 2.27 ppm.
13

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The 1H NMR spectrum of complex 5 clearly shows that coordination and cyclometallation
of the ligand has occurred. The CH2-N protons and CH2-O protons were observed as
multiplets between δ = 4.08 and δ = 4.78 ppm. The H6 proton was observed as a doublet at δ =
8.14 ppm. The 1H NMR spectrum of complex 7 shows for the H2 proton a doublet at δ = 9.46
ppm. The 1H NMR spectrum of complex 9 showed that the CH=N proton is shifted to a lower
field at δ = 9.20 ppm as compared to that of the free ligand δ = 8.72 ppm. The signals for the
p-cymene ligand in complexes 5, 7, 9, and 11 revealed that they are coordinated in a chiral
ruthenium complex.
13
In the C NMR spectra, the expected number of carbons can be seen and the metallated
carbon atoms of cyclometallated ruthenium(II) imine complexes 3a-3d are observed at 189.2,
191.5, 190.5 and 188.3 ppm, respectively, at more lower field than that of cyclometallated
ruthenium(II) heterocycle complexes 5, 7, 9 and 11 (182.7, 178.4, 181.5 and 161.9 ppm). The
CH=N carbon of complexes 3a, 3b, 3c are observed at 8.10, 7.97 and 8.06 pm, respectively.
The v(C=N) free imine of 2a absorption at 1621 cm-1 decreases to 1579 cm-1 as expected by
coordination of the aryl aldimine nitrogen in complex 3a.
3.4 X-ray structure analysis of complexes 3a, 3b and 7.
Crystal of 3a, 3b and 7, obtained from EtOH/EtOAc solvents, were suitable for X-ray
diffraction. The ORTEP view of complexes 3a, 3b and 7 are shown in Fig. 2.
The summary of the data collection and refinement parameters are given in Table 1
whereas selected bond lengths and bond angles are given in Table 2. Each of the structure of
3a, 3b and 7 shows the expected piano stool geometry. As to be seen in Table 1, the Ru-Cl
bond lengths of imine complexes 3a and 3b (2.4161(4) Å and 2.4183(6) Å) appeared slightly
longer than that of benzo[h]quinoline complex 7 (2.3999(11) Å), and the same observation
was made for the Ru-C bond lengths. However the Ru-N bonds of imine complexes 3a and
3b (2.1115(15) Å and 2.0966(19) Å) are longer than that of complex 7 (2.0883(3) Å). On the
other hand, the chelate bite angles C-Ru-Cl and Cl-Ru-N appear slightly larger in more
flexible arylimine cyclometallated ruthenium(II) complexes 3a and 3b than for the rigid
cyclometallated benzo[h]quinoline in complex 7 (Table 1).
14

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3a
3b
7
Fig. 2 Molecular structure and atom numbering scheme for 3a, 3b and 7 with 50%
displacement ellipsoids, all H atoms are omitted for clarity.
Table 1. Selected bond distances and angles of complexes 3a, 3b and 7
Complex
bond distances (Å)
Ru-N
2.0463(17) 2.1115(15) 2.4161(4)
angles (o)
C-Ru-Cl
87.54(5)
85.80(6)
83.98(11)
Ru-C
Ru-Cl
C-Ru-N
77.75(6)
77.94(8)
Cl-Ru-N
87.96(4)
86.39(5)
86.37(11)
3a
3b
7
2.048(2)
2.054(4)
2.0966(19) 2.4183(6)
2.088(3)
2.3999(11) 78.97(15)
Table 2. Crystallographic data for 3a, 3b and 7
Complex
3a
3b
7
Empirical formula
Formula weight
T (K)
C24H26ClNRu
464.98
C25H28ClNORu
495.00
C23H22ClNRu
448.94
150(2)
150(2)
150(2)
λ(Å)
0.71073
0.71073
Monoclinic
0.71073
Orthorhombic
Crystal system
Monoclinic
15

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Color, habit
Crystal size (mm)
Space group
a (Å)
Orange, prism
Orange, prism
0.47 × 0.43 × 0.26
P 21/n
Orange, prism
0.43 × 0.15 × 0.08
P c a b
0.58×0.29 × 0.17
P 21/n
10.9423(3)
8.1961(2)
23.3753(7)
90
11.7681(12)
7.7852(9)
25.379(3)
90
7.9390(17)
14.829(2)
31.719(5)
90
b (Å)
c (Å)
α (o)
β (o)
102.0690(10)
90
103.000(5)
90
90
γ (o)
90
V (Å3)
2050.06(10)
4
2265.6(4)
4
3734.2(11)
8
Z
Absorption coefficient 0.903
(mm-1)
0.825
0.989
θ range (o)
3.13-27.47
3.09-27.41
2.91-27.48
Index range
-14≤h≤11, -10≤k≤9,
-27≤l≤30
-13≤h≤15, -9≤k≤10,
-32≤l≤21
-10≤h≤6, -19≤k≤17,
-41≤l≤40
Reflections collected
Independent
15025
16551
16104
4670 (0.0304)
5114 (0.0520)
4167 (0.0478)
reflections (Rint)
Data/restraints/parame 4670 / 0 / 248
ters
5114 / 0 / 267
4167 / 0 / 238
Goodness-of-fit on F2
1.032
0.959
1.113
Final
R
indices R1=0.0230,
wR2=0.0538
R1=0.0291,
wR2=0.0715
R1=0.0324,
wR2=0.0735
0.416 and -0.581
R1=0.0468,
wR2=0.0974
R1=0.0584,
wR2=0.1023
2.024 and -1.231
[I>2σ(I)]
R indices (all data)
R1=0.0262,
wR2=0.0553
Largest diff. peak and 0.451 and -0.399
hole (e. Å3)
3.5 One pot Ru(II) cyclometallation of 1-phenylpyrazole and alkyne insertion
The insertion of an alkyne into a cycloruthenate Ru-C bond is not straightforward, 18a thus we
attempted the direct reaction of the heterocycle 10 with complex 1 and KOAc, under the
cyclometallation formation conditions but in the presence of one equivalent of
diphenylacetylene in methanol. This reaction led directly to the formation of the complex 12 ,
which was isolated in 67% yield after 20 h at room temperature, and corresponds to the
insertion product of the alkyne into the cyclometallated C-Ru bond of intermediate 11,
(Scheme 4). This complex was previously obtained by Davies by insertion of
diphenylacetylene into the complex 11 and obtained in 42%.18a Our results in Scheme 4 show
that alkyne insertion complex can be synthesized more efficiently directly from
16

ACCEPTED MANUSCRIPT
phenylpyrazole, alkyne and ruthenium complex 1 than via two steps : the cyclometallation
followed by the alkyne insertion.18a Whereas in 13C NMR the (C1-Ru) carbon singlet of 11 is
at δ 161.9 ppm, for the new cyclometallated complex 12 the =C(Ph)-Ru carbon atom appears
as a singlet at δ = 183.3 ppm. It is suggested that the alkyne insertion takes place on reaction
with the in situ generated Ru-OAc containing intermediate, analogous to 11, instead of
insertion into the Ru-C bond of the 18 electrons complex 11. The easy Ru-OAc bond
dissociation should allow the alkyne coordination and insertion, before final exchange of the
acetate by chloride leading to the stable Ru-Cl bond and complex 12.
Cl
Ru
N
Ph
Ph
N
N
KOAc (4 equiv.)
MeOH, r.t., 20 h
N
2
+ 2
+ [RuCl2(p-cymene)]2
2
Ph
Ph
12: 67%
1
10
Scheme 4. Ruthenium(II) cyclometallation of 1-phenylpyrazole with diphenylacetylene
3.6 From stoichiometric to catalytic diarylation of aryl imines
The synthesis of cyclometallated ruthenium(II) imine complexes 3 after ortho C-H bond
activation via C-H deprotonation led us to search for the functionalization of the (Ru-C)
carbon of a cyclometallated aryl imine with aryl halide. First we showed that the reaction of
cyclometallated ruthenium(II) complex 3a with 2 equiv. of arylbromide required the presence
of acetate and thus the reaction was performed in the presence of 2 equiv. of KOAc, 2 equiv.
of K2CO3 in NMP at 130oC for 24 h. Under these conditions 85% GC-yield of mixed-arylated
imines were formed with the ratio of mono-/di- arylated compound of 60:40. (Scheme 5)
17

ACCEPTED MANUSCRIPT
Scheme 5 Reaction of cyclometallated complex 3a with phenyl bromide
Based on this result, we have searched for the direct catalytic diarylation of imine 2a with
phenyl bromide by using in situ generated ruthenium(II)-carboxylate catalyst (Table 3).
Whereas [RuCl2(p-cymene)]2 1 alone in NMP at 120 °C for 48 h gives as expected a low
conversion of 45%, the ruthenium complex 1 with 2 equiv. KOAc per Ru atom leads to 85 %
conversion (Table 3, entries 1, 2). With in situ prepared Ru(OAc)2(p-cymene)10a,b in NMP
the reaction needed to be performed at 160 °C for 48 h to reach complete diarylation (entry
3,4, 5) and the diarylated imine 14 was isolated in 75 % yield (entry 4). NMP appeared to be
the best solvent for this transformation as DMAc and DCE could not improve the conversion
into diarylated imine 14 under similar conditions (entries 6, 7). The above observations led us
to explore favourable conditions and scope for catalytic diarylation of aryimines.20
Table 3 Optimisation for the direct arylation of aldimine 2a with Ru(II)/KOAc catalytic
system.[a]
Entry
Solvent
Additives
(mol%)
Temp (°C)
Time
Conv.
(%)b
Mono/di
(h)
48
48
48
48
24
48
48
13/14
14:86
15:85
10:90
0:100
23:77
15:85
40:60
1
2
3
4
5
6
7
NMP
NMP
NMP
NMP
NMP
DMAc
DCE
-
120
120
140
160
160
160
120
45
KOAc(20)
KOAc(20)
KOAc(20)
KOAc(20)
KOAc(20)
KOAc(20)
85
90
100(75)c
50
88
20
[a] Imine (0.5 mmol), PhBr (1.25 mmol), [RuCl2(p-cymene)]2 (5 mol%), additives, 3 equiv K2CO3, solvent
(2 mL), 10 µL of tetradecane as the internal standard. [b] Conversion of imine. [c] in parenthesis, isolated
yields of purified purified diarylated product 14.
18

ACCEPTED MANUSCRIPT
4 Conclusion
We have described the easy preparation of new cyclometallated N-containing ruthenium(II)
complexes especially derivatives of aryl imines, 2-phenyl oxazoline, benzo[h]quinoline and
the improved synthesis of cycloruthenate derivatives of 2-phenylpyridine and
1-phenylpyrazole via C-H bond activation via deprotonation simply with KOAc at room
temperature in methanol. X-ray struture analysis of complexes 3a, 3b and 7 comfirmed the
struture of the cyclic N-Ru-C complexes and show the expected piano stool geometry and
chirality-at-metal of the complexes. We have shown the efficient diect catalytic diarylation of
an arylimine by arylbromide promoted by the association of [RuCl2(p-cymene)]2 with 4 equiv.
of KOAc, shown before to afford the Ru(OAc)2(p-cymene) catalyst.
5 Acknowledgements
The authors are grateful to CNRS, the French Ministry for Research, the Institut Universitaire
de France (P.H.D.), the ANR program 09-Blanc-0101-01, and the support by Science
Foundation for Young Teachers of Wuyi University (No:2014zk04), Ministry of Human
Resources and Social Security of the People's Republic of China (MOHRSS) to Dr Bin Li.
Appendix A. Supplementary material
CCDC 891360 for 3a, 1039989 for 3b, 1039990 for 7 contain the supplementary
crystallographic data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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Highlights
Room temperature (N-Ru-C)-cycloruthenation of arylimines.
Key role of acetate for C-H bond activation/deprotonation.
Ru-Cl remaining bond is crucial for cycloruthenate isolation.