Reactions of ketones with coordinated nitriles on β-diketonato ruthenium complexes leading to formation of compounds with new carbon-carbon bonds

Article abstract of DOI:10.1016/j.ica.2005.01.005

The reactions of [Ru(acac)₂(CH₃CN)₂] with four ketones (acetone, ethyl methyl ketone, acetylacetone and monochloroacetone), and the reactions of [Ru(acac)₂(C ₆H₅CN)₂] with two ke

Full text of DOI:10.1016/j.ica.2005.01.005

Inorganica Chimica Acta 358 (2005) 2207–2216
www.elsevier.com/locate/ica
Reactions of ketones with coordinated nitriles on
b-diketonato ruthenium complexes leading to formation
of compounds with new carbon–carbon bonds
a,
a
a
a
Takeshi Hashimoto *, Shuhei Hara , Yumi Shiraishi , Mayumi Yamauchi ,
b
Karuppannan Natarajan , Kunio Shimizu
a
a
Department of Chemistry, Faculty of Science and Technology, Sophia University, 7-1 Kioicho, Chiyoda-ku, Tokyo 102-8554, Japan
b
Department of Chemistry, Bharathiar University, Coimbatore 641 046, India
Received 28 June 2004; accepted 11 January 2005
Abstract
The reactions of [Ru(acac)2(CH3CN)2] with four ketones (acetone, ethyl methyl ketone, acetylacetone and monochloroacetone),
and the reactions of [Ru(acac)2(C6H5CN)2] with two ketones (acetone and ethyl methyl ketone) yielded six novel compounds of
b-ketiminato ruthenium complexes: [Ru(acac)2(mhmk)], [Ru(acac)2(ehmk)], [Ru(acac)2(mAmk)], [Ru(acac)2(mClmk)], Ru(a-
cac)2(mhbk)], and [Ru(acac)2(ehbk)] (mhmk = 4-iminopentane-2-one mono anion, ehmk = 5-iminohexane-3-one mono anion,
mAmk = 3-(1-iminoethyl)-2,4-pentanedione mono anion, mClmk = 3-chloro-4-imino-pentane-2-one mono anion, mhbk = 1-phe-
nyl-1-iminobutane-3-one mono anion, ehbk = 1-phenyl-1-iminopentane-3-one mono anion). All the new complexes have been char-
acterized by elemental analyses, 1H NMR, MS and electronic spectral data. Crystal and molecular structures for the six b-ketimine
complexes have been solved by single crystal X-ray diffraction studies. A mechanism involving the attack of ketones on the coor-
dinated nitrile has been proposed. The electrochemical redox behavior of the b-ketimine complexes has been elucidated.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Bis(acetylacetonato)bis(acetonitrile)ruthenium complex; b-Ketimine; Reaction of ligated nitrile; Ketone; Cyclic voltammetry
1. Introduction
for quite some time due to the occurrence of insertion
and coupling reactions and nucleophilic and electro-
philic attacks [1]. Recently, the reactions of H2O and
CH3OH on coordinated nitrile in a nitrosyl ruthenium
complex have been reported to give imido-type com-
plexes [2]. Moreover, hydrolysis of nitriles to amide
has been shown to be enhanced by the coordination
of nitriles to various metal centers [3]. The formation
of b-diketimine chelate has been reported by prior
insertion of nitrile into a M–C bond before the attack
of nucleophilic methylene at the electrophilic carbon of
the other coordinated nitrile on scandium [4]. Chro-
mium alkyls react with an excess of nitrile to form
mononuclear b-diketiminato complexes by a similar
Nitriles are isoelectronic with N2, CO, isocyanide
and alkynes and they have been known to form tran-
sition metal complexes. Owing to their weak r and p-
acceptor ability, these samples can be easily substituted
to give a variety of coordination and organometallic
compounds. Among the reactions, those on coordi-
nated nitriles leading to the formation of other organic
compounds have attracted the attention of chemists
*
Corresponding author. Tel.: +81332383371; fax: +81332383361.
E-mail address: t-hasimo@sophia.ac.jp (T. Hashimoto).
0020-1693/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.01.005

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T. Hashimoto et al. / Inorganica Chimica Acta 358 (2005) 2207–2216
insertion of nitrile into the Cr–C bond [5]. Very reac-
tive methylidenetitanocene reacts with nitrile to yield
b-diketiminato complex [6]. Oxo- and sulfidozircono-
cene intermediates, [Cp*ZrX] (X = O, S), cycloadd
nitriles to form six-membered metallocycles via initial
formation of aza-oxo-metallacycle, followed by subse-
quent insertion of a second nitrile into the Zr–N bond
[7]. Nakamura and co-workers [8] have reported the
formation of b-ketimine chelates by the reaction of
cis- and trans-[PtCl2(NCPh)2] with thallium acetylacet-
onate complex by a mechanism involving the nucleo-
philic attack of the b-diketonate carbanion on the
coordinated nitrile carbon atom. This is probably the
first known direct attack of the coordinated nitrile
leading to the formation of b-ketimine chelate as all
other reactions involve nitrile insertion into M–C bond
prior to the attack on coordinated nitrile. Only one
b-ketimine chelate formation has been reported on rhe-
nium by the attack of 2-oxoalkyl group on coordi-
nated nitrile [9]. Though vinylimido complexes react
with unsaturated organic species allowing cross cou-
pling of nitriles with ketones to afford new carbon–car-
bon bonded compounds, no such reaction of acetone
on coordinated nitrile ligand has been shown to give
such compounds [6,10]. Moreover, to our knowledge
there is no report of a reaction of ketone on coordi-
nated nitrile ligand leading to b-ketimine with new
C–C bond formation. Hence, we report in this paper
the reactions of various ketones on the coordinated ni-
trile in a b-diketonato ruthenium complex with the for-
mation of b-ketiminate. We have reported a short
communication about the reaction of acetone on coor-
dinated acetonitrile in b-diketonato ruthenium complex
([Ru(acac)2(CH3CN)2]) with the formation of b-ketim-
inato complex [11]. These reactions, besides being
novel, are not only the first report of the reaction of
a ketone on the coordinated nitrile ligand but also
are a new and simple method for the formation of
b-ketimine on ruthenium ion.
2. Results and discussion
2.1. Reactions of coordinated nitrile with ketone
The reactions of ketones (acetone, methylethyl ke-
tone, monochloroacetone, and acetylacetone) with the
ruthenium precursors, [Ru(acac)2(AN)2] or [Ru(a-
cac)2(BN)2] (AN, acetonitrile; BN, benzonitrile) yielded
the six novel compounds (1–6) with new carbon–carbon
bonds (Fig. 1). The reaction of diethyl ketone with
[Ru(acac)2(AN)2] or [Ru(acac)2(BN)2] did not produce
any b-ketiminato complex. Furthermore, the methylene
group, except in the methyl group adjacent to carbonyl
in methyl ethyl ketone, monochloroacetone, and acety-
lacetone group, did not react with carbon in nitrile.
These results suggested that only the methyl carbon
adjacent to carbonyl in ketone can make the C–C bond
Fig. 1. The formation reactions of the b-ketiminato ruthenium(III) complexes and their structural formulas.

T. Hashimoto et al. / Inorganica Chimica Acta 358 (2005) 2207–2216
2209
with the carbon in nitrile. These reactions are quite no-
vel as these can be best described as reactions between a
coordinated ketone and a coordinated nitrile on a com-
plex. This is probably the first report on the reactions of
ketone on coordinated nitrile with the formation of
b-ketiminato chelate though such a chelate was obtained
elsewhere [4] by prior insertion of nitrile into M–C bond
before the attack on coordinated nitrile. However, a rhe-
nium enolate complex, [(CO)4(PPh3)Re(H2CCOO-
C2H5)], on reaction with PPh3 in the presence of
trimethylamine oxide and acetonitrile yielded a b-ketim-
inato complex [9]. The mechanism proposed for this for-
mation involves a rearrangement of enolate from carbon
bonding to one with oxygen bonding prior to the forma-
tion of b-ketiminate.
On careful examination of all the reactions of various
ketones with [Ru(acac)2(AN)2] or [Ru(acac)2(BN)2], it
appears that the presence of an electron withdrawing
group on the carbon atom of the ketone which attacks
the coordinated nitrile is necessary for the formation of
b-ketiminate. This has been further confirmed by the fact
that diethyl ketone, which contains an electron-donating
methyl group, does not react with [Ru(acac)2(AN)2].
Moreover, deprotonation of coordinated ketone and
oxidation of ruthenium are necessary steps for the for-
mation of a nucleophile, and the reaction is facilitated
by an electron-withdrawing group on the carbon atom.
Based on the above observations and on the structures
of the complexes formed, the mechanism shown in Fig. 2
has been suggested. The first step is the coordination of
ketone by the replacement of one of the coordinated nitr-
iles (step 1). A nucleophilic center could be generated by
the deprotonation of an alkyl group (step 2). The process
is facilitated by the presence of electron withdrawing
group on it and by the tautomerism of coordinated ke-
tone. The coordinated ketones react with the coordi-
nated nitrile on the ruthenium complex, leading to the
formation of b-ketiminato chelates with new carbon–
carbon bond (step 3). Then, the migration of H+ from
the carbon to nitrogen and the oxidation of ruthe-
nium(II) to (III) may take place (step 4). A similar mech-
anism has been proposed for the diketiminate formation
on scandium [4]. However, it is to be pointed out that a
direct reaction takes place between water and the coordi-
nated nitrile on ruthenium nitrosyl complex with the for-
mation of methylcarboxyimidato complex [2], where
water attacks the electophilic nitrile carbon.
2.2. Structures of b-ketiminato complexes
The crystal and molecular structures of all new com-
plexes except [Ru(acac)2(mhmk)] (1), which has been
reported [11], have been determined by single crystal
X-ray diffraction studies. Three selected ORTEP plots
are given in Figs. 3–5. All the crystal structure data
Fig. 3. Molecular structure of [Ru(acac)2(mAmk)] (3).
Fig. 2. A presumed formation scheme of b-ketiminato ruthenium(III) complexes with the reaction between [Ru(acac)2(RCN)2] (R = CH3 or C6H5)
and ketones.

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T. Hashimoto et al. / Inorganica Chimica Acta 358 (2005) 2207–2216
are given in Table 1 and the important bond lengths and
bond angles are given in Tables 2–6. The structures of all
the complexes can be described as distorted octahedrons
with b-ketiminate ligand and ruthenium atom in almost
one plane. The general structural features are very sim-
ilar to that of [Ru(acac)3] [12] and there seems to be no
difference in structures irrespective of different substitu-
ents on the b-ketiminate chelate rings. The Ru–O
lengths observed for acac and that of b-ketiminate are
almost the same in all the complexes. However, the
Ru–N distance is slightly shorter and is similar to the
distance found in salen complexes [10]. The C–O bond
lengths of b-ketiminate ligand are slightly longer than
the C–O lengths seen in acetylacetonate. The C–N bond
length in b-ketiminate is exactly the same as that of C–O
Fig. 4. Molecular structure of [Ru(acac)2(mClmk)] (4).
˚
˚
(1.29 A). However, a C–N distance of 1.303 A has been
Table 2
˚
Selected bond lengths (A) and angles (°) of [Ru(acac)2(ehmk)] (2)
˚
Bond length (A)
Bond angle (°)
Ru–N
1.983(3)
1.999(2)
2.078(3)
2.034(3)
2.023(3)
2.003(3)
1.302(5)
1.416(6)
1.365(6)
1.291(5)
1.513(6)
1.518(7)
O2–Ru–N
O1–Ru–O4
O3–Ru–O5
O2–Ru–O3
O4–Ru–O5
O1–Ru–N
Ru–N–C1
N–C1–C2
C1–C2–C3
C2–C3–O1
C3–O1–Ru
178.6(1)
177.52(9)
178.82(7)
91.32(9)
91.97(8)
92.1(1)
Ru–O1
Ru–O2
Ru–O3
Ru–O4
Ru–O5
N–C1
125.9(3)
122.4(4)
127.4(4)
126.3(4)
122.6(2)
C1–C2
C2–C3
O1–C3
C1–C4
C3–C5
Fig. 5. Molecular structure of [Ru(acac)2(ehbk)] (6).
Table 1
Crystallographic data for b-ketiminato complexes
Complexes
[Ru(acac)2(ehmk)] (2)
[Ru(acac)2(mAmk)] (3)
[Ru(acac)2(mClmk)] (4)
[Ru(acac)2(mhbk)] (5)
[Ru(acac)2(ehbk)] (6)
Formula
C
411.44
16H24NO5Ru
C17H24NO6 Ru
439.45
triclinic
C15H21NO5ClRu
431.86
triclinic
C20H24NO5Ru
459.48
triclinic
C42H52N2O10Ru2
947.02
triclinic
Formula weight
Crystal system
Space group
triclinic
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
P1 ð#2Þ
P1 ð#2Þ
P1 ð#2Þ
P1 ð#2Þ
P1 ð#2Þ
Color of crystal
Unit cell dimensions
red
red
brown
red
red
˚
a (A)
8.648(6)
11.115(8)
11.906(9)
104.849(5)
108.781(5)
108.676(5)
2
9.778(1)
10.309(1)
11.189(2)
109.771(3)
110.217(4)
96.712(2)
2
9.113(2)
10.234(2)
11.387(3)
113.094(5)
108.080(5)
93.554(4)
2
9.7438(2)
10.0464(4)
11.6869(1)
80.957(13)
66.709(9)
81.81(1)
2
10.142(3)
11.931(4)
18.418(6)
98.863(4)
98.435(4)
98.699(4)
2
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
Z
3
˚
V (A )
940.5(12)
1.453
960.5(2)
1.519
907.9(3)
1.580
1033.66(5)
1.476
2143.3(13)
1.467
Dcalc (g cmꢀ3
F0 0 0
)
422.00
8.55
25
450.00
8.47
25
438.00
10.32
25
470.00
7.87
25
972.00
7.62
25
l(Mo Ka) (cmꢀ1
T (°C)
)
R1 (>2.00)
R (all data)
Rw (all data)
GOF
0.040
0.044
0.039
0.042
0.061
0.072
0.044
0.052
0.049
0.062
0.097
0.985
0.096
1.035
0.121
0.943
0.100
0.918
0.102
0.856

T. Hashimoto et al. / Inorganica Chimica Acta 358 (2005) 2207–2216
2211
Table 3
N, which are trans to each other. The bond lengths of
O1–C3 and N–C1 in all the complexes are in between
those for single and for double bonds, indicating the
presence of alternative single and double bonds in the
b-ketiminato ring. The C1–C2 bond lengths are longer
than that of C2–C3, corresponding to single and double
bonds, respectively. All the above observations confirm
that there is delocalization of electrons in the b-ketimi-
nato ring.
˚
Selected bond lengths (A) and angles (°) of [Ru(acac)2(mAmk)] (3)
˚
Bond length (A)
Bond angle (°)
Ru–N
1.971(3)
1.988(2)
2.072(3)
2.025(2)
2.019(2)
2.004(2)
1.308(4)
1.431(3)
1.393(5)
1.291(4)
1.512(5)
1.510(5)
1.220(5)
1.485(4)
1.513(4)
O3–Ru–N
O1–Ru–O5
O4–Ru–O6
O3–Ru–O4
O5–Ru–O6
O1–Ru–N
Ru–N–C1
N–C1–C2
C1–C2–C3
C2–C3–O1
C3–O1–Ru
178.40(8)
177.6(1)
179.91(9)
90.62(9)
91.40(8)
91.28(9)
128.0(2)
122.8(3)
125.3(3)
126.1(2)
126.0(2)
Ru–O1
Ru–O3
Ru–O4
Ru–O5
Ru–O6
N–C1
C1–C2
C2–C3
O1–C3
C1–C6
C2–C4
C4–O2
C4–C5
C3–C7
1
2.3. H NMR spectra of b-ketiminato complexes
1
The H NMR spectral data and the assignments are
given in the experimental section. The chemical shifts
for all the complexes have been observed over a wide
range up to ꢀ34.60 ppm. This is characteristic of para-
magnetic shifts due to the presence of RuIII, which is a
d5 system with one unpaired electron. There are many
factors apart from electron density that affect the chem-
ical shifts of these systems. Especially in the case of
mixed ligand complexes, both metal–ligand interactions
and ligand–ligand interactions have to be considered.
The paramagnetic shifts in all the ruthenium(III) com-
plexes can arise from both the contact interaction and
the pseudo-contact interaction [14]. All the methyne
proton signals have been shifted to upper field from
the corresponding signals of the diamagnetic ruthe-
nium(II) complexes [15–17]. The methyl protons of the
acac showed singlets in the range from 5.70 to
ꢀ6.31 ppm and those of the b-ketiminate showed sing-
lets around ꢀ12.58 to ꢀ22.4 ppm. The methyne protons
of acac showed two types of singlets in the range from
0.26 to ꢀ15.2 ppm and from ꢀ16.35 to ꢀ29.7 ppm for
the presence of two types of acac in the complexes.
The methyl protons of b-ketiminate showed singlets in
the range from ꢀ28.2 to ꢀ34.6 ppm. In the case of the
ethyl group in the b-ketiminate, the signal due to the ter-
minal methyl protons has been shifted to lower field
(4.63–8.15 ppm) due to the effect of the ring current.
The signal due to the presence of phenyl group has also
been shifted to lower field (5.58–10.32 ppm). The methyl
protons of the c-acetyl group showed a singlet at
12.5 ppm. No signal could be observed either for the
proton on the nitrogen atom or the methyne proton of
the b-ketiminate though the former could be due to
the fast exchange of proton with deuterium.
Table 4
˚
Selected bond lengths (A) and angles (°) of [Ru(acac)2(mClmk)] (4)
˚
Bond length (A)
Bond angle (°)
Ru–N
1.970(3)
1.983(3)
2.060(4)
2.020(3)
2.017(3)
1.997(3)
1.312(7)
1.418(6)
1.389(7)
1.288(5)
1.513(8)
1.507(6)
1.760(6)
O2–Ru–N
O1–Ru–O4
O3–Ru–O5
O2–Ru–O3
O4–Ru–O5
O1–Ru–N
Ru–N–C1
N–C1–C2
C1–C2–C3
C2–C3–O1
C3–O1–Ru
178.3(1)
178.9(1)
178.4(1)
90.7(1)
Ru–O1
Ru–O2
Ru–O3
Ru–O4
Ru–O5
N–C1
91.5(1)
91.7(1)
127.5(3)
121.6(5)
128.3(5)
123.8(4)
126.5(3)
C1–C2
C2–C3
O1–C3
C1–C4
C3–C5
C2–Cl
Table 5
˚
Selected bond lengths (A) and angles (°) of [Ru(acac)2(mhbk)] (5)
˚
Bond length (A)
Bond angle (°)
Ru–N
1.983(3)
1.997(2)
2.073(3)
2.032(2)
2.014(2)
2.000(2)
1.314(4)
1.413(4)
1.384(5)
1.277(4)
1.488(5)
1.518(5)
O2–Ru–N
O1–Ru–O4
O3–Ru–O5
O2–Ru–O3
O4–Ru–O5
O1–Ru–N
Ru–N–C1
N–C1–C2
C1–C2–C3
C2–C3–O1
C3–O1–Ru
176.21(9)
177.70(9)
179.7(1)
90.68(9)
92.67(9)
92.6(1)
Ru–O1
Ru–O2
Ru–O3
Ru–O4
Ru–O5
N–C1
124.5(2)
122.7(3)
127.6(3)
125.9(3)
123.6(2)
C1–C2
C2–C3
O1–C3
C1–C4
C3–C10
2.4. Electronic spectra of b-ketiminato complexes
The electronic spectra of the complexes have been
measured either in acetonitrile or in dichloromethane.
The band positions and their molar absorption coeffi-
cients are given in Table 7. The general features of the
electronic spectra are the same as those of [Ru(acac)3]
[18]. Three to four bands have been observed in the
range from 573 to 240 nm for the complexes. The bands
observed in rhodium ketiminate complex [13], which
contains a phenyl group on the nitrogen atom. The
Ru–O length trans to Ru–N is slightly longer than other
Ru–O lengths in all the complexes. This may be due to
the fact that there is less back bonding into O than into

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T. Hashimoto et al. / Inorganica Chimica Acta 358 (2005) 2207–2216
Table 6
˚
Selected bond lengths (A) and angles (°) of [Ru(acac)2 (ehbk)] (6)
˚
Bond length (A)
Bond angle (°)
Ru–N
1.986(2)
1.996(2)
2.058(2)
2.027(2)
2.016(2)
2.011(2)
1.316(3)
1.417(4)
1.383(4)
1.287(3)
1.497(4)
1.528(5)
1.503(5)
1.976(3)
1.999(3)
2.072(2)
2.041(2)
2.023(3)
1.996(2)
1.324(4)
1.410(5)
1.383(5)
1.282(5)
1.495(5)
1.525(8)
1.40(1)
O2–Ru–N
O1–Ru–O4
O3–Ru–O5
O2–Ru–O3
O4–Ru–O5
O1–Ru–N
Ru–N–C1
N–C1–C2
C1–C2–C3
C2–C3–O1
C3–O1–Ru
177.2(1)
177.52(7)
177.32(8)
91.10(8)
92.74(9)
91.65(9)
126.1(1)
122.2(2)
127.2(3)
125.8(3)
124.1(2)
177.0(1)
176.3(1)
178.95(9)
90.60(9)
92.50(8)
91.5(1)
Ru–O1
Ru–O2
Ru–O3
Ru–O4
Ru–O5
N–C1
125.2(2)
122.3(3)
126.6(4)
125.7(4)
122.3(3)
C1–C2
C2–C3
O1–C3
C1–C4
C3–C10
C10–C11
Table 7
Electronic spectral data of b-diketonato- and b-ketiminato complexes in acetonitrle
Complexes
kmax (nm) (log10 (ꢀ/molꢀ1 dm3 cmꢀ1))
b-Diketonato complexes
[Ru(acac)3] [19]
271 (4.18)
270 (4.45)
290 (4.27)
347 (3.87)
391 (4.25)
353 (sh)
505 (3.16)
502 (3.22)
[Ru(acac)2(BN)2]
[Ru(acac)2(bhma)]
227 (4.49)
248 (sh)
b-Ketiminato complexes
[Ru(acac)2(mhmk)] (1) [11]
[Ru(acac)2(ehmk)] (2)
[Ru(acac)2(mAmk)] (3)
[Ru(acac)2(mClmk)] (4)
[Ru(acac)2(mhbk)] (5)
[Ru(acac)2(ehbk)] (6)
274 (4.38)
272 (4.26)
272 (4.21)
271 (4.15)
272 (4.16)
273 (4.16)
351 (4.13)
344 (3.97)
350 (3.93)
358 (3.92)
370 (3.86)
373 (3.86)
559 (3.69)
530 (3.65)
546 (3.30)
591 (3.25)
570 (2.95)
571 (3.00)
240 (4.08)
242 (4.06)
around 570 and 350 nm have been assigned to MLCT
transitions and the bands around 250 nm to LMCT
transitions.
ence in electronegativity between N and O atoms. The
electronegativity of N atom is less compared to that of
O atom; hence, there may be higher electron density
on ruthenium containing b-ketiminate ligand compared
to the density on acetylacetonate ligand. In other words,
the ring consisting of ruthenium and b-ketiminate
(OÙN) has higher electron density than the ring consist-
ing of ruthenium and acetylacetonate (OÙO). Fig. 7 was
the substituent effects of the b-ketiminate on E1/2 to-
gether with that of b-diketonate. Linear relationships
2.5. Electrochemistry of b-ketiminato complexes
The cyclic voltammograms of all the b-ketiminato
complexes are shown in Fig. 6; these are almost identical
in nature except for their redox potentials. Analyses of
the cyclic voltammograms showed that both the oxida-
tion and reduction reactions were reversible one-elec-
tron transfer processes corresponding to RuIII ! RuIV
and RuIII ! RuII, respectively. The reversible half-wave
potentials (E1/2) of the oxidation and the reduction are
given in Table 8. The E1/2 of the oxidation process was
in the range from 0.36 to 0.44 V and reduction process
was in the range from ꢀ1.23 to ꢀ1.36 V. The E1/2 of
the b-ketiminato complexes showed significant negative
shifts in their reductions as well as their oxidations when
compared to those of corresponding b-diketonato com-
plexes. The large negative shifts are attributable to the
replacement of O donor atom by NH donor group in
b-ketiminate ligand. This may be explained by the differ-
were obtained between E1/2 value and the sum of Ham-
P
mett constant ( rpmp [19]) of the substituents on the
b-diketonate and b-ketiminate in the complexes as well
as in the case of b-diketonato complexes. Here, rpmp rep-
resents a combination of the Hammett constants for the
meta (rm) and the para position (rp) [20]. Furthermore,
the slopes of the straight lines for E1/2 (ox) and E1/2 (red)
rpmp (b-diketonato complex: oxida-
P
against
tion = 0.30 V; reduction = 0.16 V, b-ketiminato com-
plexes: oxidation = 0.34 V; reduction = 0.18 V) were
nearly the same for b-diketonato and b-ketiminato com-
plexes. Furthermore, the C–C bond lengths of b-ketimi-
nate in the b-diketonato ruthenium(III) complexes were

T. Hashimoto et al. / Inorganica Chimica Acta 358 (2005) 2207–2216
2213
P
P
Fig. 7. Dependence of E1/2 on rpmp
.
rpmp is the sum of Hammett
substituent constants [19,20] on b-ketiminate (s) or b-diketonate (n).
Slope (b-ketiminate): oxidation; 0.18 V, reduction 0.34 V. Slope
(b-diketonato): oxidation; 0.16 V, reduction; 0.30 V.
Fig. 6. Cyclic voltammograms of b-ketiminato ruthenium complexes
in acetonitrile solution containing 0.1 mol dmꢀ3 tetraethylammonium
perchlorate. Potential scan rate = 0.1 V sꢀ1. The concentration of
complexes except complex 4 is 1 mmol dmꢀ3. The concentration of
complex 4 is 0.5 mmol dmꢀ3. (a) [Ru(acac)2(ehmk)] (1); (b) [Ru(aca-
c)2(ehmk)] (2); (c) [Ru(acac)2(mAmk)] (3); (d) [Ru(acac)2(mClmk)] (4);
(e) [Ru(acac)2(mhbk)] (5); (f) [Ru(acac)2(ehbk)] (6).
between single and double bonds. Such results mean
that the six member ring consisting of ruthenium(III)
and b-ketiminate is conjugated as well as that of ruthe-
nium(III) and b-diketonate.
3. Experimental
Table 8
3.1. General
a
Reversible half-wave potentials (E1/2 of the b-diketonato- and b-
ketiminato complexes in 0.1 mol dmꢀ3 (C2H5)4NClO4–CH3CN at
P
25 °C and rpmpb[19])
For synthetic experiments, commercially available
reagent grade solvents and chemicals were used. [Ru
(acac)2(AN)2] was prepared by the literature methods
[21–23] and [Ru(acac)2(BN)2] was prepared by a similar
method, as described in the syntheses section. Spectro-
scopic grade acetonitrile from Dojin Chemical Labora-
tories was used for spectroscopic work. Dehydrated
acetonitrile and dichloromethane from Kanto Chemical
Co. Inc., were used for voltammetric studies. The sup-
porting electrolyte, tetraethylammonium perchlorate
(TEAP) (special polarographic grade), was purchased
from Nakarai Chemicals Co. Ltd.
P
ꢀ1.02
ꢀ0.85
ꢀ0.65
Complexes
rpmp
E1/2(red) (V)
E1/2(ox) (V)
b-Diketonato complexes
[Ru(acac)3]
ꢀ1.16
ꢀ1.11
ꢀ1.11
0.60
0.62
0.62
[Ru(acac)2(bhma)]
[Ru(acac)2(mClma)] [19]
b-Ketiminato complexes
[Ru(acac)2(mhmk)] (1) [11]
[Ru(acac)2(ehmk)] (2)
[Ru(acac)2(mAmk)] (3)
[Ru(acac)2(mClmk)] (4)
[Ru(acac)2(mhbk)] (5)
[Ru(acac)2(ehbk)] (6)
ꢀ1.02
ꢀ1.00
ꢀ0.64
ꢀ0.65
ꢀ0.86
ꢀ0.84
ꢀ1.34
ꢀ1.36
ꢀ1.22
ꢀ1.23
ꢀ1.27
ꢀ1.29
0.37
0.36
0.44
0.42
0.40
0.39
1H NMR spectra were recorded in CDCl3 with a
JEOL Lambda Spectrophotometer (SiMe4 as internal
reference). UV–Vis spectra were recorded on a Hitachi
a
vs. Fc|Fc+.
P
P
b
rpmp
substitutes) [19].
=
rp (for b-position substitutes) + Rrm (for c-position

2214
T. Hashimoto et al. / Inorganica Chimica Acta 358 (2005) 2207–2216
Model U-3210 spectrometer. IR spectra were recorded
with a Shimadzu FT-IR-8600PC spectrophotometer
and EI- and FAB-MS spectra were measured with a
JEOL JMS-SX102A spectrometer.
it was cooled to room temperature, an aqueous solution
of KHCO3 (1.2 mol dmꢀ3) was added and the mixture
was refluxed for 30 min. Then, the solvent was evapo-
rated and the residue was chromatographed on a silica
gel column. The red fraction eluted with toluene/2-pro-
panol (4:1 v/v) was collected and chromatographed
again. The red fraction obtained by eluting with tolu-
ene/2-propanol (29:1 v/v) yielded the red crystals of
[Ru(acac)2(bhma)]. Yield: 0.25 g (68% based on Ru).
FAB-Mass: m/z+ = 460 (M+). Anal. Calc. for
C20H23O6Ru (460.46): C, 52.17; H, 5.03. Found: C,
52.97; H, 4.99%.
The voltammograms were measured with BAS100W
(BAS Corp.). All the voltammograms were measured
in 0.1 mol dmꢀ3 TEAP–AN and dichloromethane
(DM) solutions and all the potentials were measured
against Ag|AgCl (3 mol dmꢀ3 aqueous NaCl solution)
reference electrode obtained from BAS Corp. The refer-
ence electrode was connected to the test solution
through 0.1 mol dmꢀ3 TEAP–AN or DM solution with
a Vycor plug filled with the supporting electrolyte solu-
tion. All the electrode potentials were determined
against the half-wave potential of the ferrocene/ferrici-
nium+ (Fc|Fc+) couple as an internal standard. The
average potential of the reference electrode at 25 °C
was ꢀ0.47 V in AN and ꢀ0.52 V in DM. A platinum
disk of diameter 1.6 mm embedded in Teflon from
BAS Corp was used as the test electrode. A spiral plat-
inum wire was used as the auxiliary electrode. The
reversible half-wave potentials were determined from
the mid-point potential of cyclic voltammograms,
(Epa + Epc)/2, where Epa and Epc are the potentials of
the anodic and cathodic peaks, respectively.
3.3.2. Preparation of [Ru(acac)2(C6H5CN)2]
1.0 g (2.5 mmol) of [Ru(acac)3] was dissolved in a
mixture of ethanol–water (14:1 v/v, 150 cm3) and then
0.52 g (5.0 mmol) of benzonitrile was added to the solu-
tion. The solution was refluxed with stirring for 10 min
under an argon atmosphere. Zn powder activated with
hydrochloric acid was added to the resulting solution.
The solution color turned from red to brown. Then,
the solution was refluxed for 30 min. The solvent was
then evaporated under vacuum and the residue was
chromatographed on silica gel column. Brown crystals.
Yield: 1.26 g (97% based on Ru). FAB-Mass:
m/z+ = 506
(M+),
403
(M–C6H5CN).
FT-IR:
3.2. X-ray crystallography
m(C„N) = 2197 cmꢀ1. Anal. Calc. for C24H24N2O4Ru
(505.53): C, 57.02; H, 4.79; N, 5.54. Found: C, 57.25;
H, 4.63; N, 5.36%. 1H NMR (500 MHz, CDCl3):
d = 1.82, 1.88 (each s, 3H, acacÕs b-CH3), 4.64 (s, 2H,
acacÕs c-H), 7.35, 7.41, 7.62 (10H, phenyl–H of BN).
Crystal data and structure determination parameters
are given in Table 1. Single crystals of the complexes
suitable for diffraction studies were grown by the vapor
diffusion of n-hexane into a solution of the complex in
benzene or dichloromethane. Single crystal data collec-
tions were performed at 298 K with a Rigaku AFC8
Mercury-CCD diffractometer using graphite-mono-
3.3.3. Preparation of [Ru(acac)2(b-ket)]
Six novel compounds of b-ketimine complexes,
[Ru(acac)2(b-ket)] (b-ket: b-ketiminate mono anion),
have been synthesized from the reaction between [Ru(a-
cac)2(RCN)2] (R = CH3 or C6H5) [21–23] and ketones
(Fig. 1). The similar procedure was used to synthesize
all b-ketiminato complexes.
˚
chromated Mo Ka (k = 0.7170 A) radiation. The data
were collected and processed using the CrystalClear
software package of Rigaku Corp [24]. The structures
were solved by direct methods [25] or Patterson meth-
ods [26] and were expanded using Fourier techniques
[27]. For all complexes, empirical absorption correc-
tions were applied using Lorentz-polarization and
absorption. The non-hydrogen atoms were refined
anisotropically. All hydrogen atoms were refined using
the riding model. All calculations were performed using
the CrystalStucture crystallographic software packages
[28,29].
3.3.3.1. [Ru(acac)2(mhmk)] (1). In a typical experi-
ment, [Ru(acac)2(AN)2] (0.38 g; 1.0 mmol) was added
to acetone (300 cm3) and this mixture was stirred at
40 °C for 24 h. During the course of the reaction, the
color of the solution turned from yellowish orange to
violet. The solvent was then evaporated under vacuum
and the residue was chromatographed on a silica gel
column. A purple fraction that eluted with benzene–
acetonitrile (4:1 v/v) was collected and it was again chro-
matographed. A pure purple fraction was eluted with
benzene–acetonitrile (4:1 v/v). The solvent was evapo-
rated to yield purple [Ru(acac)2(mhmk)]. The formation
of b-ketiminate has been supported by the appearance
of a sharp band due to m(N–H) at 3263 cmꢀ1 in the
FT-IR spectrum of complex 1. However, we could not
observe any signal due to the proton on the N atom in
3.3. Syntheses
3.3.1. Preparation of [Ru(acac)2(bhma)]
[Ru(acac)2(bhma)] (Hbhma = 1-phenyl-1,3-butanedi-
one). To a solution of [Ru(acac)2(AN)2] (0.30 g,
0.79 mmol) in ethanol (100 cm3), 0.38 g (2.36 mmol) of
1-phenyl-1,3-butanedione (Hbhma) was added, then
the mixture was heated under reflux for 30 min. After

T. Hashimoto et al. / Inorganica Chimica Acta 358 (2005) 2207–2216
2215
its 1H NMR spectrum. This may be due to fast exchange
with deuterium. Purple crystals, Yield: 0.14 g (35%
based on Ru). FAB-Mass: m+/z = 398 (M+). FT-IR
mClmk), ꢀ19.2 (s, 3H, N–CH3 of mClmk), ꢀ34.6 (s,
3H, O–CH3 of mClmk).
Spectrum: m(N–H) = 3263 cmꢀ1
.
Anal. Calc. for
3.3.3.5. [Ru(acac)2(mhbk)] (5). The reaction was car-
ried out by the same procedure as described for 1 with
[Ru(acac)2(BN)2] (0.40 g; 0.87 mmol) in acetone
(50 cm3) and the solution was stirred at 30 °C for 24 h.
The color of the solution turned to brown from orange.
After the usual work up, the brown fraction containing
5 was obtained. Yield: 0.14 g (38% based on Ru). FAB-
C15H22NO5Ru (397.41): C, 45.33; H, 5.58; N, 3.40.
Found: C, 45.53; H, 5.82; N, 3.22%. 1H NMR
(500 MHz, CDCl3): d = ꢀ1.09, ꢀ2.62, 1.7, 4.55 (each
s, 3H, acacÕs b-CH3), ꢀ29.5, ꢀ20.9 (each s, 3H, mhmkÕs
b-CH3), ꢀ6.76 (s, 1H, acacÕs c-H), ꢀ22.1 (s, 1H, acacÕs
c-H), the c-H of the b-ketiminate could not be observed.
Mass: m+/z = 459 (M+). FT-IR: m(N–H) = 3278 cmꢀ1
.
Anal. Calc. for C20H24NO5Ru (459.48): C, 52.28; H,
3.3.3.2. [Ru(acac)2(ehmk)] (2). The reaction was car-
ried out by the same procedure as described for 1 with
[Ru(acac)2(AN)2] (0.19 g; 0.5 mmol) in ethylmethyl ke-
tone (100 cm3) and stirred at 30 °C for 10 h. The color
of the solution turned to violet. The residue was sub-
jected to chromatographic separation as described for
1 and a reddish purple fraction containing 2 was ob-
tained. Yield: 0.07 g (34% based on Ru). FAB-Mass:
m+/z = 412 (M+). FT-IR: m(N–H) = 3263 cmꢀ1. Anal.
Calc. for C16H24NO5Ru (411.44): C, 46.71; H, 5.88; N,
1
5.26; N, 3.05. Found: C, 52.61; H, 5.34; N, 2.92%. H
NMR (500 MHz, CDCl3) d = ꢀ1.82, 0.02, 1.0, 2.01
(acacÕs b-CH3), ꢀ15.2, ꢀ16.35 (2H, methyne proton of
acac),ꢀ29.3(s, 3H, O–CH3 of mhbk). 5.66, 5.67, 10.04,
10.09 (phenyl–H of bhmk).
3.3.3.6. [Ru(acac)2(ehbk)] (6). The reaction was car-
ried out in a similar manner to that described for 5 with
[Ru(acac)2(BN)2] (0.40 g; 0.87 mmol) in ethyl methyl ke-
tone (50 cm3). After the usual work up, the brown frac-
tion containing 6 was obtained. Yield: 0.11 g (25% based
on Ru). FAB-Mass: m+/z = 473 (M+). FT-IR: m(N–H) =
3280 cmꢀ1. Anal Calc. for C21H26NO5Ru (473.50): C,
53.27; H, 5.53; N, 2.96%. Found: C, 53.19; H, 5.44; N,
1
3.40. Found: C, 46.86; H, 5.84; N, 3.34%. H NMR
(500 MHz, CDCl3): d = ꢀ6.31, ꢀ5.96, 3.66, 5.70 (each
s, 12H, acacÕs b-CH3), 0.26, ꢀ29.7 (2H, methyne proton
of acac) ꢀ19.45, ꢀ30.7 (each s, 2H, CH2 of ehmk), 8.15
(s, 3H, N–CH3 of ehmk), ꢀ22.4 (s, 3H, O–CH3 of
ehmk).
1
2.87%. H NMR (500 MHz, CDCl3) d = ꢀ3.51, ꢀ3.36,
2.84, 3.84 (each s, 12H, acacÕs b-CH3), ꢀ6.71, ꢀ26.3
(s, 2H, methyne proton of acac), 5.59, 5.60, 10.32 (5H,
phenyl–H of ehbk). ꢀ29.8, ꢀ20.3 (each s, 2H, CH2 of
ehbk), 4.63(s, 3H, O–CH3 of ehbk).
3.3.3.3. [Ru(acac)2(mAmk)] (3). The reaction was car-
ried out in a similar manner to that described for 2 with
[Ru(acac)2(AN)2] (0.50 g; 1.3 mmol) in acetylacetone
(100 cm3). The color of the solution turned to violet.
After the usual work up, the reddish-purple fraction ob-
tained by chromatographic separation yielded 3. Yield:
0.06 g (10% based on Ru) FAB-Mass: m+/z = 440
4. Conclusion
(M+). FT-IR: m(Ac of mAmk C@O) = 1672 cmꢀ1
,
Six novel compounds of b-ketiminato ruthenium
complexes were synthesized from the reaction of coordi-
nated organonitrile with bis(acetylacetonato)ruthe-
nium(II) in ketones. The reaction mechanism was
presumed to proceed as follows: the reaction started
by the substitution of coordinated nitrile to ketone
and then new carbon–carbon bonding was formed be-
tween the carbon in the nitrile and neighboring methy-
lene carbon on the carbonyl group of ketone. The
b-ketiminato complexes were oxidized and reduced with
reversible one-electron transfer electrode processes cor-
responding to RuIII ! RuIV and RuIII ! RuII, respec-
tively. The reversible half-wave potentials (E1/2) of the
b-ketiminato complexes showed significant negative
shifts in their reductions as well as their oxidations when
compared to those of the corresponding b-diketonato
complexes. The negative shifts are attributable to the
differences of the electronegativity between the coordi-
nated atoms O and N. The effects of the substituent in
b-ketiminato complexes on the half-wave potential
could be interpreted by the strength of electron donor
m(N–H) = 3256 cmꢀ1. Anal. Calc. for C17H24NO6Ru
(439.45): C, 46.46; H, 5.50; N, 3.19. Found: C, 46.20;
H, 5.41; N, 3.16%. 1H NMR (500 MHz, CDCl3):
d = ꢀ3.98, ꢀ3.06, 2.17, 3.78 (each s, 12H, acacÕs
b-CH3), ꢀ7.01, ꢀ26.4 (s, 2H, methyne proton of acac),
12.5 (s, 3H, c-Ac–CH3 of mAmk), ꢀ12.5 (s, 3H,
N–CH3 of mAmk), ꢀ28.2 (s, 3H, O–CH3 of mAmk).
3.3.3.4. [Ru(acac)2(mClmk)] (4). The reaction was
carried out in a similar manner to that described for 2
with [Ru(acac)2(AN)2] (0.10 g; 0.26 mmol) in monochlo-
roacetone (25 cm3). The color of the solution turned to
violet. After the usual work up, the green fraction ob-
tained yielded purple crystals 4. Yield: 0.01 g (9% based
on Ru). FAB-Mass: m+z = 432 (M+). FT-IR: m (N–H) =
3254 cmꢀ1. Anal. Calc. for C15H21ClNO5Ru (431.85):
Calc: C, 52.28; H, 5.26; N, 3.05. Found: C, 52.61; H,
5.34; N, 2.92%. 1H NMR (500 MHz, CDCl3):
d = ꢀ2.80, ꢀ2.04, 1.98, 3.74 (each s, 12H, acacÕs
b-CH3), ꢀ3.29, ꢀ23.4 (each s, 2H, methyne proton of

2216
T. Hashimoto et al. / Inorganica Chimica Acta 358 (2005) 2207–2216
Park, Organometallics 19 (2000) 4043;
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ability of substituents. Linear relationships were ob-
tained between E1/2 value and the Hammett constant
of the substituents on b-ketiminate and the slopes of
the lines of E1/2 (ox) and E1/2 (red) were nearly the same
as those of b-diketonato and b-ketiminato complexes.
From such results, it may be concluded that the six
member ring consisting of ruthenium(III) and b-ketimi-
nate is conjugated as well as that of ruthenium(III) and
b-diketonate. The structures of the b-ketiminato com-
plexes obtained here were very similar to those of
b-diketonato complexes.
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5. Supplementary material
Crystallographic data of complexes 2–6 (excluding
structure factors) for the structures reported in this pa-
per have been submitted to the Cambridge Crystallo-
graphic Data Centre (CCDC) as Supplementary
Publication Nos. CCDC-242421–242425. Copies of the
data can be obtained free of charge on application to
the CCDC, 12 Union Road, Cambridge, CB2 1EZ,
UK (Fax: +44 1223 336033; e-mail: deposit@ccdc.cam.
ac.uk). The ORTEP diagram and selected structure fac-
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Acknowledgments
We thank Professor F.S. Howell, Department of
Chemistry, Sophia University, for correcting this manu-
script. This study was supported by Grants-in-Aid for
Scientific Research (No. 15750056) from the Ministry
of Education, Science, Sport and Culture of Japan.
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