Reactions of pentaammineruthenium complexes with 1,2- and 1,4-dicyanobenzene and cyanobenzamides: Evidences of neighboring group participation

Article abstract of DOI:10.1016/j.ica.2004.09.008

The spectral (UV-Vis and IR) and electrochemical behavior of the nitrile bonded complexes [Ru(NH₃)₅L]²⁺ (L = 1,4-dicyanobenzene (1,4-dcb), 1,2-dicyanobenzene (1,2-dcb)), [Ru(NH ₃)₅(NHC(OH)-bz-4-CN)]³⁺, [Ru(NH ₃)₅(NHC(O)-bz-2-CN)]²⁺ and [Ru(NH ₃)₅(NH(C)NHC(O)bz)]³⁺ (NH(C)NHC(O)-bz = 3-imino-1-oxo-isoindoline) are described. Oxidation of [Ru(NH₃) ₅L]²⁺, at 0 ≤ pH ≥ 6, is followed by hydrolysis of the coordinated nitrile to give amide complexes in which the amide is through the nitrogen, with pH-dependent rate constants. The estimated values of the rate constant of hydrolysis (k_obs) at 25 °C are 2.9 × 10 ^-3 s^-1 for [Ru(NH₃)₅(1,4-dcb)] ³⁺ and 5.6 × 10^-3 s^-1 for [Ru(NH ₃)₅(1,2-dcb)]³⁺ at pH 4.65. Reduction of [Ru(NH₃)₅(NHC(O)-bz-4-CN)]²⁺ and [Ru(NH ₃)₅(NHC(O)-bz-2-CN)]²⁺ is followed by two reactions, one is an aquation forming [Ru(NH₃)₅(OH ₂)]²⁺ and free ligand, and the other an intramolecular linkage isomerization forming [Ru(NH₃)₅(NC-bz-4-NH ₂C(O))]²⁺ and [Ru(NH₃)₅(NC-bz-2- NH₂C(O))]²⁺. The oxidized1,2-cyanobenzamide complex [Ru(NH₃)₅(NHC(OH)-bz-2-CN)]³⁺ undergoes an amide to nitrile intramolecular linkage isomerization, followed by a cyclization reaction resulting in [Ru(NH₃)₅(NH-(C)(HN-C(O)-2-bz))] ³⁺ ((NH-(C)(HN-C(O)-2-bz)) = 3-imino-1-oxo-isoindoline bonded through the exocyclic nitrogen) (pK_a = 4.3). The rates of these reactions, which occur with neighboring group participation, increase with acidity. The reduced form, [Ru(NH₃)₅(NH-(C)(HN-C(O)-2-bz))] ²⁺, is relatively substitution inert.

Full text of DOI:10.1016/j.ica.2004.09.008

Inorganica Chimica Acta 358 (2005) 2909–2920
www.elsevier.com/locate/ica
Reactions of pentaammineruthenium complexes with
1,2- and 1,4-dicyanobenzene and cyanobenzamides:
q
evidences of neighboring group participation
a,
Elia Tfouni , Antonio Marcos de Souza Macedo , Luciana nunes Cardoso ,
a
b
*
ˆ
Kleber Queiroz Ferreira , Erica Cristina de Oliveira , Zenis Novais da Rocha
ˆ
b
b
b
´
ˆ
a
´ ˆ
Departamento de Quımica da Faculdade de Filosofia, Ciencias e Letras de Ribeira˜o Preto, Universidade de Sa˜o Paulo, Av.Bandeirantes,
3900, 14040901 Ribeirao Preto, Brazil
´
Instituto de Quımica da, Universidade Federal da Bahia, Brazil
b
Received 30 July 2004; accepted 7 September 2004
Dedicated to the memory of Professor Rex. E. Shepherd
Abstract
The spectral (UV–Vis and IR) and electrochemical behavior of the nitrile bonded complexes [Ru(NH3)5L]2+ (L = 1,4-dicyano-
benzene (1,4-dcb), 1,2-dicyanobenzene (1,2-dcb)), [Ru(NH3)5(NHC(OH)-bz-4-CN)]3+, [Ru(NH3)5(NHC(O)-bz-2-CN)]2+ and
[Ru(NH3)5(NH(C)NHC(O)bz)]3+ (NH(C)NHC(O)-bz = 3-imino-1-oxo-isoindoline) are described. Oxidation of [Ru(NH3)5L]2+
,
at 0 6 pH P 6, is followed by hydrolysis of the coordinated nitrile to give amide complexes in which the amide is through the nitro-
gen, with pH-dependent rate constants. The estimated values of the rate constant of hydrolysis (kobs) at 25 ꢀC are 2.9 · 10ꢀ3 sꢀ1 for
[Ru(NH3)5(1,4-dcb)]3+ and 5.6 · 10ꢀ3 sꢀ1 for [Ru(NH3)5(1,2-dcb)]3+ at pH 4.65. Reduction of [Ru(NH3)5(NHC(O)-bz-4-CN)]2+ and
[Ru(NH3)5(NHC(O)-bz-2-CN)]2+ is followed by two reactions, one is an aquation forming [Ru(NH3)5(OH2)]2+ and free ligand, and
the other an intramolecular linkage isomerization forming [Ru(NH3)5(NC-bz-4-NH2C(O))]2+ and [Ru(NH3)5(NC-bz-2-NH2C(O))]2+
.
The oxidized1,2-cyanobenzamide complex [Ru(NH3)5(NHC(OH)-bz-2-CN)]3+ undergoes an amide to nitrile intramolecular linkage
isomerization, followed by a cyclization reaction resulting in [Ru(NH3)5(NH-(C)(HN-C(O)-2-bz))]3+ ((NH-(C)(HN-C(O)-2-bz)) =
3-imino-1-oxo-isoindoline bonded through the exocyclic nitrogen) (pKa = 4.3). The rates of these reactions, which occur with neigh-
boring group participation, increase with acidity. The reduced form, [Ru(NH3)5(NH-(C)(HN-C(O)-2-bz))]2+, is relatively substitution
inert.
ꢁ 2004 Elsevier B.V. All rights reserved.
Keywords: Ruthenium; dicyanobenzene; Cyanobenzamide; Neighboring group participation; Nitrile hydrolysis
1. Introduction
A general feature, the hydrolysis of nitriles in aqueous
solutions, is greatly enhanced by coordination of RCN in
q
Taken in part from: E.C. Oliveira, M.Sc. Dissertation, Univer-
sidade de Sa˜o Paulo, Ribeira˜o Preto, Brazil, 1998. A.M.S. Maceˆdo,
a metal complex as demonstrated by 106–108-fold in-
crease in the rates of hydrolysis compared to the uncoor-
M.Sc. Dissertation, Universidade Federal da Bahia, Salvador, Brazil,
dinated ligand [1–9]. These rates can be lower, though, in
2002.
*
cases where the metal ion is capable of p back-bonding,
such as with ruthenium(II) ammines. This reaction is
Corresponding author. Tel.: +55166023748; fax: +55166331851.
E-mail address: eltfouni@usp.br (E. Tfouni).
0020-1693/$ - see front matter ꢁ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.09.008

2910
E. Tfouni et al. / Inorganica Chimica Acta 358 (2005) 2909–2920
important in fundamental chemistry [10–12], and in
industry [13,14]. Amides are used in a wide variety of
industrial applications as lubricant; detergent additives,
drug stabilizers, and monomers [14], in the industrial
conversion of nitriles to amides, such as acrylonitrile to
acrilamide [13], and in biochemistry, as in nitrile hydra-
tase [15–17]. Reactions of coordinated organonitriles
and catalysis aspects to amide formation were reviewed
recently [2].
the work. All other materials were of reagent grade
and were used without further purification.
2.2. Complexes synthesis
2.2.1. RuCl(NH3)5]Cl2
This compound was prepared as described [28] with
slight modifications [11]. Average yield: 85%.
In general, the hydrolysis results in coordinated
amide complexes. However, the reactivity of the coordi-
nated nitrile is not restricted to hydrolysis, as exempli-
fied by several reactions [2,7,18] of nitrile complexes
and of their products. Oxygen–nitrogen linkage isomeri-
zation occurs for amido bonded complexes, which re-
sult, from the hydrolysis of the coordinated nitrile
[19,20]. Linkage isomerizations also occur in bifunc-
tional nitriles, such as 4-cyanopyridine and acrylonitrile
[9,21–23]. Deprotonation reactions leading to further
reactions [18] and oxidative dehydrogenation of a-
carbon of 4-pyridylacetonitrile were also reported [24].
A chelation reaction for the products of the hydrolysis
of [Ru(NH3)5(2-NCpy)]3+ (2-NCpy = 2-cyanopyridine)
had been reported [25]. For cobalt complexes, other
reactions have been reported. Intramolecular cyclization
of the coordinated 2-cyanobenzamide, resulting in a
complex of 3-imino-1-oxo-isoindoline bonded through
the exocyclic nitrogen and deprotonated at the endocy-
clic nitrogen, was reported for [Co(NH3)5(1,2-dcb)]3+
(1,2-dcb = 1,2-dicyanobenzene) [26]. The same reaction
had been inferred for ruthenium in acidic pH [27].
In our studies related to coordinated nitriles, we re-
cently drew our attention to dinitriles, such as malonit-
rile, fumaronitrile, succinonitrile, 1,4-dicyanobenzene
(1,4-dcb), and 1,2-dicyanobenzene, investigating linkage
isomerization reactions. In view of the reported prelim-
inary and complicated nature of the reactions involved
with the 1,2-dicyanobenzene ruthenium complex [27],
we decided to further investigate the behavior of
[Ru(NH3)5(1,2-dcb)]2+ and, for comparison purposes,
also of [Ru(NH3)5(1,4-dcb)]2+. Thus, in this paper the
synthesis and reactions of these two complexes and the
reactions of their products are described.
2.2.2. Ru(NH3)5(1,2-dcb)](BF4)2 Æ H2O
This compound was synthesized by the method de-
scribed for other pentaammineruthenium(II) complexes
with azine ligands with some modifications [29,30]. 100
mg (0.342 mmol) of [RuCl(NH3)5]Cl2 was suspended in
deaerated water (5 mL) and argon was bubbled through
the mixture. After dissolution, Zn(Hg) was added to the
solution, with continuous argon bubbling and protection
from light. After the solution became bright orange, 10
mL of a deaerated solution of 260 mg (2.00 mmol) of
1,2-dicyanobenzene in 1:1 acetone:ethanol was added.
After 2 h, the mixture was filtered over a freshly prepared
and deaerated NaBF4 solution (0.15 g/0.15 mL). The sol-
vent was removed under reduced pressure to give an or-
ange solid, which was washed several times with doubly
distilled, cold and deaerated water, to extract the orange
complex. Then, the orange filtrate was evaporated to dry-
ness under reduced pressure to give an orange solid with a
color more intense than the first solid. This solid was
washed with cold and deaerated water/ethanol (1:1 mix-
ture), and finally washed with cold and deaerated ethanol
and vacuum dried. Average yield: 83%. Elemental Anal.
Calc. for RuC8H21N7B2F8O: C, 18.99; N, 19.38; H,
4.18. Found: C, 18.55; N, 18.95; H, 4.10%. IR: mmax
/
cmꢀ1 (nujol) = 2230 (mCN free); 2180 (mCN coordinated).
1H NMR: dH/ppm (dmso-d6) = 8.01 (d); 7.76 (t); 7.68
(t); 7.43 (d).
2.2.3. Ru(NH3)5(1,4-dcb)](BF4)2 Æ 2H2O
This compound was synthesized by the same proce-
dure used for the 1,2-dcb complex, but using 200 mg
(1.54 mmol) of 1,4-dicyanobenzene. Average yield: 65–
75%. Elemental Anal. Calc. for RuC8H23N7B2F8O2: C,
18.34; N, 18.71; H, 4.42. C, 17.91; N, 18.55; H, 4.30%.
IR: mmax/cmꢀ1 (nujol) = 2233 (mCN free); 2182 (mCN
coordinated).
2. Experimental
2.2.4. Ru[(NH3)5(NHC(OH)-bz-4-CN)](BF4)3
2.1. Chemicals and reagents
50 mg (1.0 mmol) of [Ru(NH3)5(1,4-dcb)](BF4)2 Æ 2-
H2O was dissolved in 1 mol Lꢀ1 HCl solution and then
0.5 mL of 30% H2O2 was added. After 24 h, ꢁ10 mL of
acetone was added dropwise. The yellow solid formed
was collected by filtration and washed with ethanol
and vacuum dried. Average yield: 62%. Elemental anal-
ysis was consistent with RuC8H21N7OB3F12. Anal.
Calc.: C, 16.21; N, 16.54; H, 3.57. Found: C, 15.73; N,
16.92; H, 3.84%. IR: mmax/cmꢀ1 (nujol) = 2233 (mCN
Ruthenium trichloride (RuCl3 Æ 3H2O) (Strem) was
the starting material for ruthenium complexes syntheses.
Reagent grade 1,4-dicyanobenzene and 1,2-dicyanoben-
zene (Aldrich) were used as supplied. Sodium tetrafluo-
roborate (Aldrich) was recrystallized from hot water.
Acetone and ethanol (Aldrich) grade P.A were used as
supplied. Doubly distilled water was used throughout

E. Tfouni et al. / Inorganica Chimica Acta 358 (2005) 2909–2920
2911
free); 1630 (mC@O). This product was also prepared in
solution by oxidation with controlled potential electrol-
ysis of [Ru(NH3)5(1,4-dcb)]2+ (10ꢀ3 mol Lꢀ1 of com-
plex) in 0.1 mol Lꢀ1ꢀ HCl/KCl solution or 1 mol Lꢀ1
CH3CO2H=CH3CO2 (pH 4.65) at +500 mV versus
Ag/AgCl.
auxiliary electrode and quartz cell with 0.030 cm optical
path. Successive spectra were recorded during the redox
processes of the complexes at 25 ꢀC.
3. Results and discussion
3.1. [Ru(NH3)5(1,4-dcb)]2+ and [Ru(NH3)5(1,2-dcb)]2+
complexes
2.2.5. Ru(NH3)5(3-imino-1-oxo-isoindoline-exo-N)]
(BF4)3, [Ru(NH3)5(NH-(C)(HN-C(O)-2-bz))](BF4)3
This compound was isolated after chemical oxidation
of [Ru(NH3)5(1,2-dcb)]2+. About 50 mg (1.0 mmol) of
[Ru(NH3)5(1,2-dcb)](BF4)2 Æ H2O was dissolved in 1
mol Lꢀ1 HCl solution and then 0.5 mL of 30% H2O2
was added. After 24 h, ꢁ10 mL of acetone was added
dropwise. The yellow solid formed was collected by fil-
tration and washed with ethanol and vacuum dried.
Average yield: 45%. Elemental Anal. Calc. for RuC8H21-
N7OB3F12: C, 16.21; N, 16.54; H, 3.57. Found: C, 15.97;
N, 16.35; H, 5.33%. IR: mmax/cmꢀ1 (nujol) = 1630
(mC@O); 1610 (mC@N).
The known pentaammineruthenium(II) complex with
1,4-dcb complex and the new complex with 1,2-dcb were
synthesized following the procedure described for other
pentaammine nitrile complexes. The electronic spectrum
(Table 1) in aqueous solution of [Ru(NH3)5(1,4-dcb)]2+
(1A) is similar to that previously reported [31,32], and
the spectrum of [Ru(NH3)5(1,2-dcb)]2+ (1A) is similar
to that of 1,4-dcb and similar to those of other pentaam-
mines [29]. The spectra are dominated by an absorption
band of high absorptivity in the visible range assigned to
a metal to ligand charge transfer (MLCT) transition and
UV bands assigned as internal ligand (IL) in analogy to
analogous nitrile complexes. Compared to the MLCT
band of [Ru(NH3)5(bzn)]2+ (bzn = benzonitrile) [32],
which appears at 376 nm, the MLCT band of
[Ru(NH3)5(1,2-dcb)]2+ is red shifted to 430 nm due to
the electron-withdrawing nature of the nitrile substitu-
ent in the aromatic ring. A further red shift to 442 nm
is observed for the MLCT band of [Ru(NH3)5(1,4-
dcb)]2+. Inspection of Table 1 shows that the energy of
the MLCT band in the dicyanobenzene complexes de-
pends on the relative ring positions of the cyano groups,
as for cyanopyridine complexes [33,34] and could be ex-
plained likewise.
The redox potentials (Table 1), in aqueous solution of
[Ru(NH3)5(1,4-dcb)]2+ (1A) and [Ru(NH3)5(1,2-dcb)]2+
(1B) are +360 mV versus Ag/AgCl (+582 mV versus
NHE) and +400 mV versus Ag/AgCl (ꢁ+600 mV versus
NHE), respectively, and they are similar to those previ-
ously reported [27]. These potentials are assigned to the
Ru(III/II) processes and are larger than those of the
analogous benzonitrile complex (+485 mV versus
NHE) [35] for the presence of a second electron-with-
drawing group in the aromatic group. These reduction
potentials reflect the relative Ru(II) to Ru(III) affinity
ratios for the nitrile ligands, and, as for the MLCT
bands energies, can be explained in terms of the elec-
tron-withdrawing ability of the groups and ring
positions.
This product was also prepared in solution by oxida-
tion with controlled potential electrolysis of [Ru(NH3)5
(1,2-dcb)]2+ (10ꢀ3 mol Lꢀ1 of complex) in 0.1 mol Lꢀ1
HCl/KCl solution or 1 mol Lꢀ1 CH3CO2H=CH3CO2
ꢀ
(pH 4.65) at +550 mV versus Ag/AgCl.
2.3. Physical measurement
The electronic absorption spectra were recorded
using Hewlett Packard Models 8452 A and 8453 record-
ing spectrophotometers using quartz cells. IR absorp-
tion spectra were recorded in 4000–400 cmꢀ1 range
using a Bomem MB-102 spectrophotometer. Spectra
were taken in KBr discs.
Cyclic voltammetry (CV), differential pulse polarog-
raphy (dpp) and constant potential electrolysis measure-
ments were taken with PARC, Model 273, potentiostat/
galvanostats. All tests were carried out using a conven-
tional three electrodes cell. Glassy carbon was used as
working electrode for cyclic voltammetry and differen-
tial pulse polarography, and platinum gauze for coul-
ometry. Ag/AgCl and platinum wire were used as
reference and auxiliary electrodes, respectively. Electro-
chemical data were obtained iꢀn aqueous solutions of 1
mol Lꢀ1 CH3CO2H=CH3CO2 (pH 4.65) or 0.10 mol
L
ꢀ1 KCl/HCl. All solutions were deaerated by bubbling
high purity argon and thermostated using a Haake,
Model FK, ultracryostat. In the CVs and dpps, no ano-
dic or cathodic peaks in the absence of complexes in the
potential range studied were observed. The reported Ef
values ( 10 mV) are the arithmetic mean of Epa and Epc
values.
3.2. Chemical and electrochemical reactivities of
[Ru(NH3)5(1,4-dcb)]2+ (1A) and [Ru(NH3)5(1,2-
dcb)]2+ (1B)
The spectroelectrochemical measurements were car-
ried out using a gold mini-grid working electrode, Ag/
AgCl as reference electrode and platinum wire as an
The CVs of [Ru(NH3)5(1,4-dcb)]2+ (1A) and
[Ru(NH3)5(1,2-dcb)]2+ (1B), from +0.6 to ꢀ1.1 V versus

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E. Tfouni et al. / Inorganica Chimica Acta 358 (2005) 2909–2920
Table 1
Electronic absorption data and reduction potentials of some pentaammineruthenium(II) amide or nitrile complexes and related species in aqueous
solutions
Complex or pentaammine ligand
kmax/nm (loge)
Ef/mV vs. NHE Ref.
MLCT
IL
c
1,4-dcb
442 (4.19)
463
430 (3.90)
250 (4.45)
582a,b
[31,32]
c
1,2-dcb
bzn
4-NCpy
257 (4.19); 236 (4.09)
249 (4.21); 226 (4.17)
253 (3.95)
622a,b
485d
592b
376 (3.93); 347 (3.84)(sh)
425 (3.73)
424 (4.00)
[32,35]
[33]
[36]
[12]
[12]
[33]
[12]
[33]
[22]
422 (4.05)
408 (3,97)
253 (4.22); 212 (4.09)
256 (4.18); 222 (3.94)
256 (4.18); 222 (3.94)
255 (4.29); 218 (4.05)
336(sh) (3.58), 255 (4.97), 219 (3.87)
260 (3.57)
2-NCpy
3-NCpy
562e
549e
408 (3.82)
398 (3.98)
401 (3.75)
NHCO-4-py
475 (loge = 4.06)g
695 (3.84)g
421 (3.90),
408 (3.96)
NHCO-1-methyl-4-pyh
NC-bz-4-NH2C(O) (8A)h
NC-bz-2-NH2C(O) (9B)h
NH2C(O)-bz-2-CN (4B)h
N-(C)(HNC(O)-2-bz) (12B)
ꢀ130f
557b,e
547b,e
[22]
c
239 (4.31)
240 (4.26)
246 (4.26)
225 (4.27)
256 (2.84)
c
d
d
535 (3.52)
533 (3.99)b,c
ꢁꢀ178b,e
297b,e,h
ꢀ28h
trans-[RuCl(cyclam)(NH2CO-4pyH)]2 + h 550 (2.65), 357 (3.02)b
trans-[RuCl(cyclam)(OCNH2-4pyH)]2 + h ꢁ495 (2.82)sh, 357 (3.31), 312 (3.13)b 256 (3.63), 228 (3.66)
[19]
[19]
ꢀ148h
bzn, benzonitrile.
a
0.1 mol Lꢀ1HCl, pH 1.
b
1 mol Lꢀ1 CH3CO2H=CH3CO2 solution, pH 4.65.
ꢀ
c
d
e
f
This work and Ef values vs. Ag/AgCl converted to NHE by adding +222 mV.
0.1 mol Lꢀ1 p-toluenosulfonic acid/potassium p-toluenosulfonate.
0.1 mol Lꢀ1 KCl.
In aqueous pH 11 0.01 mol Lꢀ1 phosphate buffer.
Data obtained from the reaction solution.
0.1 mol Lꢀ1 HCl/KCl.
g
h
Ag/AgCl, in deaerated aqueous solution, in 1 mol Lꢀ1
These hydrolysis reactions are slow enough as to have
the pairs of peaks of the 1,2-dcb and 1,4-dcb complexes
with a reversible profile according to the criteria of
Nicholson and Shain [38]. At scan rates smaller than
50 mV sꢀ1, peaks dependent on the more positive anodic
peak start to appear at ꢀ380 mV (Epc) and ꢀ140 mV
(Epa), for the 1,4-dcb complex, as a result of the coordi-
nated nitrile hydrolysis reaction, to form the corre-
sponding Ru(III) amide (Eq. (2)), resulting from the
oxidation of the nitrile complex (Eq. (1)). The cathodic
peak at ꢀ380 mV corresponds to the reduction of the
Ru(III) complex with the coordinated amide bonded
through the N atom (Eq. (3)). The anodic peak at
ꢀ140 mV is dependent on the ꢀ380 mV cathodic peak
and corresponds to the oxidation of [Ru(NH3)5(OH2)]2+
formed from the aquation reaction of the reduced amide
complex (Eqs. (4) and (5)).
CH3CO2H=CH3CO2 at pH 4,65, and in 0.1 mol Lꢀ1
ꢀ
HCl/KCl at pH 1, show one-pH independent pair of
peaks with Ef = +360 and +400 mV versus Ag/AgCl
for Ru3+/2+ in the 1,4-dcb and 1,2-dcb complexes,
respectively (Eq. (1)).
ꢀeꢀ
þeꢀ
nþ
½RuðNH3Þ ðNCRÞꢂ ꢀ ½RuðNH3Þ ðNCRÞꢂðnþ1Þþ
ð1Þ
5
5
The monoelectronic process assigned is further sup-
ported by controlled potential electrolyses of 1 · 10ꢀ3
mol Lꢀ1 aqueous solutions of [Ru(NH3)5(1,4-dcb)]2+
or [Ru(NH3)5(1,2-dcb)]2+, in the same above conditions,
at E = +550 mV versus Ag/AgCl, which show consump-
tion of 1 F molꢀ1 and orange to yellow color change
in both cases. However, oxidation of Ru(II) in
[Ru(NH3)5(1,2-dcb)]2+ or [Ru(NH3)5(1,4-dcb)]2+
, in
aqueous media, is followed by hydrolysis of the coordi-
nated nitrile to the corresponding amide (Eq. (2)), with
the resulting amide complex coordinated through the
amide nitrogen, as for other nitriles with ruthenium am-
mines [6,9,36,37].
3þ
½RuðNH3Þ ðNHCðOHÞRÞꢂ
5
þeꢀ
2þ
ꢀ ½RuðNH3Þ ðNHCðOHÞRÞꢂ
ð3Þ
ð4Þ
5
ꢀeꢀ
2þ
nþ
½RuðNH3Þ ðNHCðOHÞRÞꢂ
½RuðNH3Þ ðNCRÞꢂ
5
5
nþ
þ H2O ꢀ ½RuðNH3Þ ðOH2Þꢂ2þ þ NH2COR
þ H2O ꢀ ½RuðNH3Þ ðNHCðOHÞRÞꢂ
ð2Þ
5
5

E. Tfouni et al. / Inorganica Chimica Acta 358 (2005) 2909–2920
2913
ꢀeꢀ
þeꢀ
of [Ru(NH3)5(1,4-dcb)]2+ with K2S2O8 also leads to
bleaching of the MLCT band. In both oxidations, the
coordinated nitrile in the 1,4-dcb Ru(III) complex
undergoes hydrolysis to amide forming [Ru(NH3)5(NH-
C(O)-bz-4-CN)]3+ (3A). The other nitrile group does not
undergo hydrolysis, as evidenced by the presence of the
nitrile stretching band at 2230 cmꢀ1 in the infrared spec-
tra of this latter complex (3A). The UV–Vis spectrum
(Table 2) of [Ru(NH3)5(NHC(O)-bz-4-CN)]3+ (3A) is
pH dependent, as those of other pentaammineruthe-
nium(III) amide complexes [20]. Amide bonded Ru(III)
ammine complexes display pH-dependent absorption
bands in the 300–400 nm range assigned as LMCT tran-
sitions [6,22,39,40], arising from different modes of
bonding of the amide in these complexes, including N
and O linkage isomers. In general, in acidic medium,
the substitution inert complexes with the amide N coor-
dinated to Ru(III) have absorptions lower in energy
than the corresponding substitution labile O linkage iso-
mers, which can undergo amide aquation. Accordingly,
the absorption bands of [Ru(NH3)5(NHC(O)-bz-4-
CN)]2+ in the 300–400 nm range can be assigned as
LMCT as for other related amide complexes with the
2þ
3þ
½RuðNH3Þ ðOH2Þꢂ ꢀ ½RuðNH3Þ ðOH2Þꢂ
ð5Þ
5
5
This behavior is consistent with that reported for
other ruthenium ammine nitriles [5,9,10,37]. The rates
of hydrolysis of the coordinated nitriles are pH depend-
ent, and, accordingly, the cyclic voltammogram profile
is pH dependent. The peaks corresponding to the
formed amide are only seen in the CV at scan rates be-
low 50 mV sꢀ1 for the 1,4-dcb, and not observed for the
1,2-dcb complex, preventing a good estimate of the rates
by the method of Nicholson and Shain [38]. Actually,
the pH-dependent reactions undergone by the 1,2-dcb
complex upon oxidation are more complicated than
those of the 1,4-dcb complex (see ahead) and they
should be considered in the interpretations of its CVs.
The small rate of hydrolysis of the coordinated nitrile
allowed to have the UV–Vis spectrum of [Ru(NH3)5(1,4-
dcb)]3+ (2A) recorded during electrochemical oxidation
of [Ru(NH3)5(1,4-dcb)]2+ at pH 4.65. This spectrum
shows decrease of the MLCT band at 442 nm and
appearance of a band at 279 nm (Table 2), which can
be assigned as ligand to metal charge transfer (LMCT)
in the formed [Ru(NH3)5(1,4-dcb)]3+ (2A). Oxidation
Table 2
Electronic absorption data of some pentaammineruthenium(III) amide or nitrile complexes
Ligand
kmax/nm (loge)
Ref.
NHC(OH)-bz-4-NC (3A0)
388 (3.69), 320 (4.0), sh285; 234.a
388 (3.77), 320 (3.89), 235 (4.38)b
b384 (3.19); 326 (3.70); 236 (4.01)
385 (3.03), 327(3.93), 319 (3.93)a
385 (3.56), 315 (3.41), 278 (3.43), 227 (4.02)b
279b
*
*
*
*
*
*
*
NHC(O)-bz-2-CN (3B)
1,4-dcb
NH-(C)(HN-C(O)-2-bz) (12B)
331 (3.89), 321 (3.89), 295 (3.74)a
516 (2.88), 376 (3.72), 325 (3.69), 275(sh) (3.72), 220 (4.46)c
383 (3.54), 249 (3.36)d
NHC(O)CH3
NHC(OH)CH3
NHCOC6H5
[6]
[6]
322 (3.19)e
393 (3.61), 314 (3.56), 270 (3.58), 228 (3.97)f
385 (3.17), 320 (3.54), 270 (3.42), 219 (3.97)g
386 (3.51), 306 (3.49), 270 (3.57)h
386i
[6]
[6]
NHC(OH)C6H5
NHCO-4-py
[22]
[36]
[9,12]
[22]
[36]
[22]
[37]
[39]
384 (3.57), 262 (3.71), 228 (3.61)b
358 (3.67), 264 (3.67)j
NHCO-4-pyH
NHCO-4-pyCH3
NHCHO
358 (3.48)d
358 (3.70), 268 (3.67), 220 (3.86)h
350k
383 (3.58)l
a
pH 1.
CH3CO2H/CH3CO2Na solution, pH 4.65.
b
c
pH 7.
1.0 mol Lꢀ1 NaClO4.
1 mol Lꢀ1 HClO4.
d
e
f
H2O, pH ꢁ 8 (NaHCO3).
g
2 M HClO4.
In aqueous, pH 6.8, phosphate buffer.
h
i
0.1 mol Lꢀ1 LiClO4.
j
In 0.1 mol Lꢀ1 triflic acid.
k
0.1 mol Lꢀ1 CF3CO2H/CF3CO2Na.
l
In HCONH2 acidified with mol Lꢀ1 CF3SO3H (1 mol Lꢀ1).
This work.
*

2914
E. Tfouni et al. / Inorganica Chimica Acta 358 (2005) 2909–2920
amide N-bonded to Ru(III), such as acetamide [6]. As
for other amide complexes, these absorptions bands
are shifted to higher energies at lower pHs as a result
of protonation of the coordinated amide. The pKa for
the protonated form of this complex (Eq. (6)),
[RuIII(NH3)5(NHC(OH)-bz-4-CN)]3+, is 1.8, a value
that is close to those found (ꢁ2.5) for other nitrogen
bonded amide ruthenium complexes [20].
3.3. Reactions of [Ru(NH3)5(1,4-cyanobenzamido)]2+
(3A)
The CV of [Ru(NH3)5(NHC(O)-bz-4-CN)]2+ (3A)
formed by controlled potential electrolysis at +500 mV
versus Ag/AgCl of [Ru(NH3)5(1,4-dcb)]2+ (1A) and sub-
sequent hydrolysis of [Ru(NH3)5(1,4-dcb)]2+ (2A), in 0.1
mol Lꢀ1 KCl solution at pH 4.8, scanned at 100 mV sꢀ1
,
shows one cathodic peak at ꢀ290 mV assigned to the
reduction of Ru(III) in [Ru(NH3)5(NHC(O)-bz-4-
CN)]2+. Dependent on this cathodic peak, one anodic
peak at ꢀ110 mV, attributed to the oxidation of Ru(II)
in [Ru(NH3)5(OH2)]2+, and a pair of peaks at +370 mV
(anodic) and +300 mV (cathodic), with Ef = +335 mV
versus Ag/AgCl, assigned to [Ru(NH3)5(NC-bz-4-
NH2C(O))]2+ (8A) appear.
Reduction of [Ru(NH3)5(NHC(O)-bz-4-CN)]2+ in the
presence of 10-fold excess of 4-acetylpyridine (4-acpy) is
followed by two reactions (Scheme 1). One is aquation
(ꢁ45%), resulting in free 1,4-cyanobenzamide and
[Ru(NH3)5(OH2)]2+, which reacts with acpy forming
[Ru(NH3)5(4-acpy)]2+, the amount of which was calcu-
lated by the electronic absorption band at 526 nm [41].
The other reaction is a N-amide to N-nitrile linkage
isomerization reaction (ꢁ55%), to give [Ru(NH3)5(NC-
bz-4-NH2C(O))]2+ (8A). These reactions are similar to
those that occur for [Ru(NH3)5(NHC(O)4-py)]2+, ob-
tained after hydrolysis of [(NH3)5Ru(4-NCpy)]3+, and
could be explained likewise. For [Ru(NH3)5(NHC(O)4-
½RuðNH3Þ ðNHCðOHÞ-bz-4-CNÞꢂ3þ ꢀ
5
2þ
½RuðNH3Þ ðNHCðOÞ-bz-4CNÞꢂ þ Hþ
ð6Þ
5
The rate constant of hydrolysis (kobs) of the coordi-
nated nitrile of [Ru(NH3)5(1,4-dcb)]3+ (2A), generated
by chemical oxidation of [Ru(NH3)5(1,4-dcb)]2+ (1A),
was estimated as 2.9 · 10ꢀ3 sꢀ1 at pH 4.65. This value
is consistently larger than the value of 2 · 10ꢀ4 sꢀ1 re-
ported for this complex in the pH range 0–2 [27]. This
value is also larger than that of the benzonitrile complex
(2 · 10ꢀ4 sꢀ1) at pH 5 [12] because of the presence of the
electron-withdrawing nitrile group in position 4 of the
ring, turning the coordinated nitrile more prone to
nucleophilic attack. This is further illustrated by the lar-
ger values with 1-R-4-cyanopyridinium complexes, as
for instance, 0.16 and 0.71 sꢀ1, for 4-mcp and 4-bcp,
respectively [37], which come from the presence of the
positive charge introduced by the substituent in the 4
position.
C
N
-
III
C
N
- e
(NH3)5Ru
C
N
-
+e
(NH3)5RIuI
C
N
H
(2A)
H2O
(1A)
C
N
+
H
+
H
-
-
e
N
III
C
N
H
(NH3)5Ru
-
e
+
II
N
O
(3A)
(NH ) Ru
3 5
(4A)
O
kis
kaq
O
CO NH2
[Ru(NH3)5(OH2)]2+
II
NH2
C
(NH3)5Ru
+
(5A)
N C
CN
II
(NH3)5Ru NC
(6A)
(8A)
O
NH2
(7A)
Scheme 1.

E. Tfouni et al. / Inorganica Chimica Acta 358 (2005) 2909–2920
2915
py)]2+, reduction to RuII[(NH3)5(NHC(O)-4-py)]+ is fol-
lowed by an amido to pyridinyl linkage isomerization
competitive with aquation, forming [Ru(NH3)5(isn)]2+
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
,
[Ru(NH3)5(OH2)]2+ and free isonicotinamide (isn)
[9,12,22,23]. The linkage isomerization occurs through
a series of stepwise g2-bonded (NH3)5Ru(II) isonicotin-
amide complexes [22,23] and presumably, the same type
of mechanism should be occurring for the isomerization
with 1,4-cyanobenzamide. The UV–Vis spectrum of the
nitrile linkage isomer [Ru(NH3)5(NC-bz-4-NH2C(O))]2+
(8A) displays a band at 421 nm (loge = 3.90) and 239 nm
(loge = 4.31) (Table 1), assigned as MLCT and IL,
respectively. Compared with that of [Ru(NH3)5(1,4-
dcb)]2+, the MLCT band is blue shifted, since the amide
group is less electron-withdrawing than the nitrile
group.
I
F
400
600
800
wavelenght (nm)
Fig. 1. Successive spectra during oxidation of [Ru(NH3)5(1,2-dcb)]2+
by controlled potenꢀtial electrolysis at +550 mV (vs. Ag/AgCl) in
[Ru(II)] = 2.93 · 10ꢀ3 mol Lꢀ1. I, initial spectrum; F, final spectrum.
CH3CO2H=CH3CO solution, pH 4.65, l = 1 mol Lꢀ1 at 25 ꢀC.
3.4. Reactions of [Ru(NH3)5(1,2-dcb)]2+ after
oxidation
2
The reactions undergone by [Ru(NH3)5(1,2-dcb)]2+
,
nm, respectively, and the appearance of absorption
bands at 385 nm (loge = 3.56), 315 nm (loge = 3.41),
278 nm (loge = 3.43) and 227 nm (loe = 4.02) (see Fig.
1).
As for [Ru(NH3)5(NHC(O)-bz-4-CN)]2+ (3A), the
pH-dependent absorption bands (Table 2) in the 300–
400 nm range can be assigned to the amido nitrogen
bonded [Ru(NH3)5(NHC(O)-bz-2-CN)]2+ (3B) complex.
The pKa of the protonated form, [Ru(NH3)5(NHC(OH)-
bz-2-CN)]3+ (3B0), is 1.5, close to those of other analo-
gous complexes [20,22].
after oxidation, are largely pH dependent. As aforesaid,
the CVs of this complex show a reversible pair of peaks
with Ef = +400 mV versus Ag/AgCl in the pH range 1–
5.6 corresponding to the [Ru(NH3)5(1,2-dcb)]3+/2+ proc-
ess. However, unlike [RuII(NH3)5(1,4-dcb)]2+, for which,
at scan rates smaller than 50 mV sꢀ1, peaks dependent
on the more positive anodic peak start to appear, as a
result of the coordinated nitrile hydrolysis reaction, to
form the corresponding Ru(III) amide, the CVs only
show one pair of peaks. On one hand, at first, it could
be imagined that this behavior could be resulting from
a specific rate constant of hydrolysis in the 1,2-dcb com-
plex smaller than that of 1,4-dcb. On the other hand, the
CV profile is different from those previously reported in
the pH 0–2 range [27], suggesting that the reactions are
different. As a matter of fact, the difference is arising
from the reactions involved and the different experimen-
tal conditions, as will be seen. In the reported CVs [27],
the 1,2-dcb complex is already in the oxidized form and
the outcome should be resulting from the elapsed time
from dissolution and CV scan, during which time reac-
tion products already had been formed. The estimated
rates of reaction of the oxidized 1,2-dcb complex in
The rate constant value (kobs) for the hydrolysis reac-
tion of the coordinated nitrile of the chemically oxidized
[Ru(NH3)5(1,2-dcb)]3+ (2B) is 5.6 · 10ꢀ3 sꢀ1 at pH 4.65
as estimated by spectral monitoring of the formation of
[Ru(NH3)5(NHC(O)-bz-2-CN)]2+. This value is nearly
twice that of the 1,4-dcb complex and consistently one
order of magnitude larger than those reported for the
pH 0–2 range (2 · 10ꢀ4 and 6 · 10ꢀ4
s
ꢀ1) for 1,4-dcb
and 1,2-dcb, respectively [27]. However, it should be
noted that subsequent reactions occur at these lower
pHs.
3.5. Reactions of [Ru(NH3)5(1,2-cyanobenzamido)]2+
(3B) and [Ru(NH3)5(1,2-cyanobenzamide)] (4B) at
pH 4.65
the pH 0–2 range were reported as 6 · 10ꢀ4
s
ꢀ1, which
are larger than those of the 1,4-dcb complex, and would
explain the reason for the appearance of more than one
pair of peaks since the 1,2-dcb complex screened was al-
ready in the oxidized form [27]. However, the differential
pulse polarogram (dpp) of [Ru(NH3)5(1,2-dcb)]2+ at pH
5.6 shows one cathodic peak of relatively low intensity
at negative potential assigned to the reduction of
[Ru(NH3)5(NHC(O)-bz-2-CN)]3+ (3A).
The CV scanned after electrochemical oxidation
(electrolysis) at +550 mV versus Ag/AgCl of
[Ru(NH3)5(1,2-dcb)]2+ (1B) to [Ru(NH3)5(1,2-dcb)]3+
(2B) and after the hydrolysis of the coordinated nitrile
forming [Ru(NH3)5(NHC(O)-bz-2-CN)]2+ (3B), in
ꢀ
CH3CO2H=CH3CO2 at pH 4.65, shows one cathodic
The UV–Vis spectra, recorded during electrochemical
oxidation of [Ru(NH3)5(1,2-dcb)]2+, at pH 4.65, show
decrease of the MLCT and IL bands at 430 and 257
peak (1c) at ꢀ410 mV versus Ag/AgCl, which corre-
sponds to the reduction of [Ru(NH3)5(NHC(O)-bz-2-
CN)]2+ (3B). One anodic peak at ꢀ130 mV (2a), with

2916
E. Tfouni et al. / Inorganica Chimica Acta 358 (2005) 2909–2920
a barely seen corresponding cathodic peak, and a pair of
peaks at +360 mV (4a) and +290 mV (4c) versus Ag/
AgCl (Ef = +325 mV versus Ag/AgCl) dependent on 1c
also appear. Repetitive cycles (Fig. 2) result in CVs dis-
playing more peaks. There are cathodic peaks at +40
mV (3c) and at ꢀ190 mV (2c), more pronounced in
the second scan and one anodic peak (3a) at +110
mV, with decrease of the 1c peak current intensity.
The pairs of peaks 4a/4c (Ef = +325 mV, DEp = 70
mV) and 2a/2c (Ef = ꢀ160 mV, DEp = 60 mV) are
dependent on peak 1c. The pair of peaks 2a/2c can be
assigned to [Ru(NH3)5(OH2)]3+/2+ [35,37] and it indi-
cates that dissociation of coordinated amide in Ru(II)
complex is taking place (Scheme 2). Peaks 4a/4c are as-
signed to [Ru(NH3)5(NC-bz-2-NH2C(O))]3+/2+ (9A).
The pair of peaks 3a/3c (Ef = +75 mV; DEp = 70 mV)
is dependent on 4a and is assigned to [Ru(NH3)5(NH-
(C)(HN-C(O)-2-bz))](BF4)3 (12A) (see ahead).
Controlled potential electrolysis of [Ru(NH3)5-
(NHC(O)-bz-2-CN)]2+ (3B) (1 mol Lꢀ1 CH3CO2H=
CH3CO2ꢀ, pH 4.65) at ꢀ500 mV versus Ag/AgCl, with
simultaneous UV–Vis spectrophotometrical monitoring,
showed that upon reduction of 3B, the absorption bands
of 3B are bleached and absorption bands at 408 nm
(loge = 3.96) and 246 nm (loge = 4.26) (Table 1) are
developed. The consumption of ca 1 F molꢀ1 suggests
that monoelectronic charge-transfer occurred. Chemical
reduction of 3B with Zn(Hg) develops a transient purple
color which turns orange. The UV–Vis spectra show
first bands at 535 and 408 nm. The band intensity at
535 nm decreases with increase of the intensity of the
408 nm band. As for other similar complexes, the band
at 535 nm (Table 1) can be assigned to a MLCT transi-
tion in the intermediate [Ru(NH3)5(NH2C(O)-bz-2-
CN)]2+ (4B) complex. Conceivably, the final product
could be a cis-tetraammine, since it can be formed by
reduction of pentaammineruthenium(II) with substitu-
tion of labile ligands, in the presence of ortho chelating
ligands [25,42,43]. For instance, oxidation of the closely
related nitrile-bonded [Ru(NH3)5(2-NCpy)]2+ in aque-
ous solution is followed by hydrolysis to the corre-
sponding amide complex [Ru(NH3)5(NHC(O)2-py)]2+
[9,25]. Reduction of this Ru(III)-amide complex results
in addition to aquation (30%), in a chelation reaction
(70%), to give cis-[(NH3)4RuII(2-pca)] (2-pca = pico-
linamide), with displacement of one coordinated cis-
ammonia [9,25]. Thus, it is reasonable to expect similar
reactions after reduction of [Ru(NH3)5(NHC(O)-bz-
2-CN)]2+ (3B) to [Ru(NH3)5(NH2C(O)-bz-2-CN)](4B).
However, the spectra are not consistent with a cis-
tetraammine species [25,42–46] and, thus, by anal-
ogy to [Ru(NH3)5(NHC(O)-bz-4-CN)]2+ (3B) and
[Ru(NH3)5(NHC(O)-4-py)]2+ [9,22,23], reduction of 3B
to 4B should be followed by amide aquation, forming
free 1,2-cyanobenzamide (6B) and [Ru(NH3)5(OH2)]2+
(5B), and by amide-N to nitrile-N bonded linkage
isomerization reaction, forming Ru(NH3)5(NC-bz-
2-NH2C(O))]2+ (9B) (Scheme 1). The UV–Vis spectra
and CV results support this assumption. The band at
408 nm (Table 1) can be assigned to a Ru(II)–NC
MLCT transition in [Ru(NH3)5(NC-bz-2-NH2C(O))]2+
(9B). Peaks 4a/4c (Ef = +325 V versus Ag/AgCl) (Figs.
2 and 3), are consistent with [Ru(NH3)5(NC-bz-
2-NH2C(O))]3+/2+ (10B/9B) and peaks 2a/2c with
[Ru(NH3)5(OH2)]3+/2+
.
Upon reduction of [Ru(NH3)5(NHC(O)-bz-2-CN)]2+
(3B), the [Ru(NH3)5(NC-bz-2-NH2C(O))]2+ (9B) com-
plex is formed in 53% and the other 47% corresponds
to aquation (5B), as calculated spectrophotometrically
by the spectra of [Ru(NH3)5(4-acpy)]2+ and [Ru(N-
H3)5(isn)]2+, formed in the presence of 10-fold excess
of 4-acetylpyridine or isonicotinamide, from reaction
of the aqua species, [Ru(NH3)5(OH2)]2+, resulting from
the reduction of 3B. The CVs of [Ru(NH3)5(NHC(O)-
bz-2-CN)]2+ (3B) during electrolysis at ꢀ500 mV (reduc-
tion) are consistent with the reactions outlined and
resemble those of Fig. 2. They show the pairs of peaks
2a/2c ([Ru(NH3)5(OH2)]3+/2+), 4a/4c ([Ru(NH3)5(NC-
bz-2-NH2C(O))]3+/2+), and, in the beginning, the catho-
dic peak 1c, with the corresponding anodic peak at ꢀ370
10
4a
2a
5
3a
0
4c
3c
2c
-5
-10
-15
-20
-25
mV for Ru3+/2+ in [Ru(NH3)5(NHC(O)-bz-2-CN)]3+/2+
.
Again, dependent on 4a, appears the pair of peaks 3a/
3c. The current peaks 2a/2c [Ru(NH3)5(OH2)]2+/3+ de-
crease with exhaustive electrolysis probably due to
some recombination of the aqua species with the free
1,2-cyanobenzamide to form [Ru(NH3)5(NC-bz-2-
NH2C(O))]2+ to which the pair of peaks 4a/4c are as-
signed, and contributing to increase its current intensity.
At the end, only peaks 4a/4 and 3a/3c are displayed,
with peaks 2a/2c barely seen.
1c
-600
-400
-200
0
200
400
600
E (mV vs Ag / AgCl)
Fig. 2. Repetitive cyclic voltammogram of 1.29 · 10ꢀ3ꢀ mol Lꢀ1
[Ru(NH3)5(NHC(O)-bz-2-CN)]2+ in CH3CO2H=CH3CO2 aqueous
However, the I–E profiles for [Ru(NH3)5(NC-bz-2-
NH2C(O))]2+ ion (9B), obtained in solution from reduc-
solution, pH 4.65, m = 100 mV sꢀ1
.

E. Tfouni et al. / Inorganica Chimica Acta 358 (2005) 2909–2920
2917
-
-e
II
III
(NH3)5Ru
N
C
N
C
(NH3)5Ru
-
+e
2B
1B
C
C
N
N
H O
2
H
H
H
-e-
+e
III
H+
II
(NH3)5Ru
N
+
-
(NH3)5Ru
N
-
3B
O
C
O
C
4B
N
N
H O
2
H
III
(NH3)5Ru
N
H
N
O
H
C
II
CN
O
OH
(NH ) Ru
3 5
N
II
NH
+
2
[(NH ) Ru(OH )]
NC
3 5
2
5B
H
III
6B
(NH ) Ru
N
3 5
7B
O
NH
C
-
-
e
II
II
+e-
(NH3)5RIuII
(NH3)5Ru
(NH3)5Ru NC
NC
C
NC
O
O
NH
10B
2
CONH2
8B
NH
2
9B
III
5Ru
(NH )
II
Ru
3
H
III
(NH3)5
H
(NH )
H
5Ru
-
N
3
N
C
N
C
-e-
C
O
-
+ H+
+ OH
N
H
+e-
N
H
C
O
NH2
11B
C
O
C
12B
13B
O
Scheme 2.
tion of [Ru(NH3)5(NHC(O)-bz-2-CN)]2+ (3B), at pH
4.65 and at scan rates of 100 mV sꢀ1 (Fig. 3) and 500
mV sꢀ1, show, in addition to 4a/4c, a pair of peaks
(3a/3c) with Ef = +75 mV versus Ag/AgCl.
This pair of peaks (3a/3c) is dependent on the oxida-
tion of [Ru(NH3)5(NC-bz-2-NH2C(O))]2+ (9B) (4a) and
is shown also in the I–E profiles of [Ru(NH3)5(NH2-
C(O)-bz-2-CN)]2+ (4B) (at pHs 1 and 4.65) and
[Ru(NH3)5(NHC(O)-bz-2-CN)]2+ (3B) (pH 1) ions,
where these complexes result in [Ru(NH3)5(NC-bz-2-
NH2C(O))]2+
(9B) and [Ru(NH3)5(NC-bz-2-
NH2C(O))]3+ (10B). The potential of the pair 3a/3c
agrees with that previously reported, assigned by infer-
ence to [Ru(NH3)5(3-imino-1-oxo-isoindoline-exo-
N)]3+/2+ (12B/13B). Thus, it is reasonable to conclude
that oxidation of 9B to 10B is followed by a reaction
with a rate constant higher than the rate constant of
hydrolysis of [Ru(NH3)5(1,2-dcb)]3+. This result is not

2918
E. Tfouni et al. / Inorganica Chimica Acta 358 (2005) 2909–2920
30
4a
3a
15
10
5
25
20
15
10
5
3a
0
-5
0
-10
-15
-20
-25
-30
-35
-5
4c
3c
3c
-10
-600
-400
-200
0
200
400
600
-400
-200
0
200
400
E (mV vs Ag / AgCl)
E (mV vs Ag / AgCl)
Fig. 3. Repetitive cyclic voltammograms after chemical reduction of
1.29 · 10ꢀ3 Lꢀ1 [Ru(NH3)5(NHC(O)-bz-2-CN)]2+
mol in
CH3CO2H=CH3CO aqueous solution, pH 4.65, m = 100 mVsꢀ1
Fig. 4. Cyclic voltammograms after electrochemical oxidation of
[(NH3)5Ru(NC-bz-2-NH2C(O))]2+ at +500 mV, at pH 4.65.
[(NH3)5Ru(NC-bz-2-NH2C(O))]2+ was obtained in solution by electr-
ochemical oxidation ꢀof 1.0 · 10ꢀ3 mol Lꢀ1 [(NH3)5Ru(1,2-dcb)]2+, in
CH3CO2H=CH3CO2 solution, followed by reduction.
ꢀ
.
2
unexpected, since the rate of hydrolysis of the coordi-
nated nitrile in [Ru(NH3)5(NC-bz-2-NH2C(O))]3+
(10B) should be smaller than for [Ru(NH3)5(1,2-
dcb)]3+ (1B) because of the decrease of r electron-
withdrawing properties of amide compared to that
of the remote nitrile [47]. Thus, formation of
[Ru(NH3)5(NHC(O)-bz-2-NH2C(O))]3+ (11B) would oc-
cur in minor extension compared to [Ru(NH3)5(3-imino-
1-oxo-isoindoline-exo-N)]3+ (12B).
dependence allowed the calculation of a pKa of 4.3.
Consistently, the spectra after oxidation match those
of [Ru(NH3)5(NH-(C)(HN-C(O)-2-bz))]3+ (12B), which
result from an intramolecular cyclization of the coordi-
nated 2-cyanobenzamide of [Ru(NH3)5(NC-bz-2-
NH2C(O))]3+ (10B).
The reaction of nitrile bonded pentaammin(2-cyano-
benzamide)cobalt(III), in aqueous base, had been stud-
ied [48,49] and it was recently confirmed that the data
are more consistent with an intramolecular cyclization
of the coordinated 2-cyanobenzamide, resulting in a
complex of 3-imino-1-oxo-isoindoline bonded through
the exocyclic nitrogen and deprotonated at the endocy-
clic nitrogen [26]. The same reaction had been inferred
for ruthenium in acidic pH [27]. Thus, in analogy to pen-
taammine(2-cyanobenzamide)cobalt(III), in addition to
the described reactions, another reaction has occurred
for the ruthenium complexes, as previously inferred by
Schaffer and Taube [27], presumably an intramolecular
cyclization of the coordinated 2-cyanobenzamide to 3-
imino-1-oxo-isoindoline-exo-N, resulting in [Ru(NH3)5-
(NH-(C)(HN-C(O)-2-bz))]3+ (12B), for which the pair of
peaks 3a/3c in the CVs can be assigned.
The cyclic voltammogram (Fig. 4) scanned after elec-
trolysis of [Ru(NH3)5(NC-bz-2-NH2C(O))]2+ (9B) at
+500 mV at pH 4.65, with scan rates of 25–200 mV
s
ꢀ1, showed a behavior different from another penta-
ammine amido complexes [9,19,21–23,25,37]. There is
only one pair of peaks, 3a/3c, with Ef = ꢀ75 mV ver-
sus Ag/AgCl (DE = 70 mV), assigned to [Ru(NH3)5-
(NH-(HN-C(O)-2-bz))]3+/2+ (12B–13B). Oxidation of
[Ru(NH3)5(NC-bz-2-NH2C(O))]2+ (9B) to Ru[(NH3)5-
(NC-bz-2-NH2C(O))]3+ (10B) is followed by an
intramolecular cyclization of the ligand, forming
[Ru(NH3)5(NH-(HN-C(O)-2-bz))]3+ (11B), with possible
minor hydrolysis of the coordinated nitrile to amide in
[Ru(NH3)5(NC-bz-2-NH2C(O))]3+ (10B), since this rate
should be much smaller than in [Ru(NH3)5(1,2-dcb)]3+
(2B).
Controlled potential electrolysis of [Ru(NH3)5(NC-
bz-2-NH2C(O))]2+ (9B), obtained in
1
mol Lꢀ1
3.6. Reactions of [Ru(NH3)5(1,2-cyanobenzamido)]2+
(3B) and [Ru(NH3)5(1,2-cyanobenzamide)] (4B) at
pH 1
ꢀ
CH3CO2H=CH3CO2 solution from reduction of 3B,
at pH 4.65 and at +500 mV, with simultaneous UV–
Vis spectrophotometrical monitoring, showed that upon
oxidation of 9B, the absorption bands at 408 and 246
nm (Table 1) are bleached and showed absorption bands
(Table 2) at 516 nm (loge = 2.88), 376 nm (loge = 3.72),
325 nm (loge = 3.69), 275(sh) (loge = 3.72), and 220 nm
(loge = 4.46). These bands are pH dependent (Table 2),
and at pH 1 they appear at 331 nm (loge = 3.89), 321 nm
(loge = 3.89), and 295 nm (loge = 3.74). This pH
Oxidation of [Ru(NH3)5(1,2-dcb)]2+ (1B) at pH 1 re-
sults in an apparent different behavior. The CV scanned
right after controlled potential electrolysis at +550 mV
versus Ag/AgCl to oxidize [Ru(NH3)5(1,2-dcb)]2+ in
HCl/KCl 0.1 mol Lꢀ1 (pH 1) is similar to that at 4.65.
There are peaks attributed to [Ru(NH3)5(1,2-dcb)]3+/2+
(1B/2B) due to the slower rate of hydrolysis at this

E. Tfouni et al. / Inorganica Chimica Acta 358 (2005) 2909–2920
2919
pH; to reduction of [Ru(NH3)5(NHC(O)-bz-2-CN)]2+
(3B) to the aqua species [Ru(NH3)5(OH2)]3+/2+; to the
nitrile bonded cyanobenzamide [Ru(NH3)5(NC-bz-
NH2C(O))]3+/2+ (9B–10B) and to the cyclized ligand
in N-bonded diamide complexes, [Ru(NH3)5(NHC(O)-
bz-2-NH2C(O))]2+ (11B). The rate of hydrolysis of the
coordinated nitrile is accelerated by the presence of elec-
tron-withdrawing substituents R on the nitrile (NC-R)
[26]. Compared to the dinitrile complex, the rate of
hydrolysis of coordinated nitrile in [Ru(NH3)5(NC-bz-
2-NH2C(O))]3+ should be smaller, since the amide group
is less electron-withdrawing than the nitrile. For
[Ru(NH3)5(1,2-dcb)]3+ (1B), the rate constants (kobs) of
hydrolysis are 5.6 · 10ꢀ3 sꢀ1 at pH 4.65 and 2 · 10ꢀ4
[27], at pH 0–2, so it is expected that the rate of hydrol-
ysis for [Ru(NH3)5(NC-bz-2-NH2C(O))]3+ (10B) should
be smaller.
Chemical reduction of [(NH3)5Ru(NH-(C)(HN-
C(O)-2-bz))]3+ (12B) by Zn(Hg) resulted in a color
change from yellow to purple (13B). The absorptions
change from 516, 371, 325, 275, 220 nm for the oxidized
form at pH 1, to 533 (loge = 3.99), and 225 nm
(loge = 4.27) for the reduced form, which can be as-
signed to [(NH3)5Ru(NH-(C)(HN-C(O)-2-bz))]2+ (13B)
(during reduction a transient band at 285 nm devel-
oped). The reduced form is easily oxidized to regenerate
12B in the presence of air. Both oxidized and reduced
forms have the same I–E profiles, with peaks at
Epa = +110 mV and Epc = +40 mV. If [Ru(NH3)5(NH-
C(O)-bz-2-NH2C(O))]2+ (11B) had been formed, it
would have rapidly been aquated upon reduction to re-
sult in [RuII(NH3)5(OH2)]2+ and free amide, as occurs
with (4B) and other amides with ruthenium(II) penta-
ammine. Reduction of 12B in the presence of pyridine
(py), isonicotinamide (isn), pyrazine (pz), 2-acetylpyri-
dine (2-acpy), or bipyridine (bpy) resulted in only minor
amounts of [Ru(NH3)5(L)]2+ (L = py, izn, pz) or
[Ru(NH3)4(L)]2+ (L = 2-acpy, bpy). Also, the spectral
features are consistent with a pentaammine, ruling out
possible cis-tetraammines. However, although phtali-
mide could have been formed instead of the exo
bonded ligand (3-imino-1-oxo-isoindoline-exo-N) in
[Ru(NH3)5(NH-(C)(HN-C(O)-2-bz))]3+ (12B), the pH
dependence of the spectrum is more consistent with this
latter species.
complex
[Ru(NH3)5(NH-(C)(HN-C(O)-2-bz))]3+/2+
(12B/13B). However, letting the reactions to proceed
for 1 h results in the CV profile similar to that of Fig.
4 and with an UV–Vis spectrum that corresponds to
[Ru(NH3)5(NH-(C)(HN-C(O)-2-bz))]3+ (12B).
As at pH 4.65 (Fig. 2), after oxidation of 1B, results
in [Ru(NH3)5(NHC(O)-bz-2-CN)]2+ (3B). However, at
pH 1, this complex (3B) (protonated at the amide
group, [Ru(NH3)5(NHC(OH)-bz-2-CN)]3+; pKa = 1.5)
rearranges to form the nitrile bonded isomer,
[Ru(NH3)5(NC-bz-NH2C(O))]3+ (10B) (Scheme 2),
which in its turn undergoes a reaction to form
[Ru(NH3)5(NH-(C)(HN-C(O)-2-bz))]3+ (12B). The
roughly estimated rate constant values (kobs) for this last
reaction, from the decrease of current intensities of peak
4a as a function of time, are 1.7 · 10ꢀ2 sꢀ1 at pH 2.5,
2 · 10ꢀ2 sꢀ1 at pH 1.5, and 4.6 · 10ꢀ2 sꢀ1 at pH 0.2.
These values indicate that the rate of the cyclization
reaction increases with increasing acidity of the medium,
while this trend is inverse for the analogous Co(III)
complex, for which these values are three order of mag-
nitude smaller, as expected [27]. The rate constant value
(kobs) of the linkage isomerization reaction (3B–10B)
was roughly estimated as 2 · 10ꢀ3 sꢀ1 at pH 1.5, a value
that is smaller than that for cyclization, and should in-
crease with increased acidity. Thus, after isomerization,
cyclization to 12B occurs relatively fast. At pH 4.65,
these rates are small enough to allow the identification
of [Ru(NH3)5(NHC(O)-bz-2-CN)]2+ (3B). That cycliza-
tion involves a rearrangement similar to that suggested
for the amido-N to nitrile-N bonded linkage isomeriza-
tion reaction in [Co(NH3)5(2-cyanobenzamido)]3+
[26,47] in acidic medium. In aqueous acid, the amido
bonded cobalt complex is protonated at the amide
group (pKa = 0.4) and rearranges rapidly (kH = 0.3
s
ꢀ1) to form the nitrile-bonded isomer and then the cyc-
lyzed ligand complex [50]. The reason for the smaller
rate (2 · 10ꢀ3 sꢀ1 at pH 1.5) of this reaction for the
Ru complex is unclear. The disappearance of the pair
of peaks 4a/4c is consistent with the hydrolysis of the
oxidized 1,2-dcb complex, forming first the amide
bonded 1,2-cyanobenzamide (peak 1c), followed by the
appearance of the pair of peaks at Ef = +325 mV from
the nitrile bonded 1,2-cyanobenzamide complex, result-
ing from the isomerization reaction of the amido bonded
complex, and then results in the final product (12B,
13B).
For [Ru(NH3)5(NHC(OH)-bz-2-CN)]2+ (3B), there
are two important possible reactions to be considered.
One reaction is the isomerization reaction to form
[Ru(NH3)5(NC-bz-2-NH2C(O))]3+ (10B/12B) followed
by hydrolysis of the coordinated nitrile group, resulting
In an attempt to get structural evidence to further
support the assignments for the reaction products of
1
[Ru(NH3)5(1,2-dcb)]2+, H and 13C NMR spectra were
run in D2O and DMSO. The spectral analyses are com-
plicated by the large dependence on pH. The spectra
show that there are several products whose intensities
and chemical shifts change dramatically with pH. To
avoid the pH dependence, the spectra were run in
DMSO, and preliminary results show an apparent
inconsistency with those in D2O, which could come
from the different nature of the solvent. In addition to
a more complete study of the spectra in D2O, at different
pDs, and DMSO, a chemical and electrochemical study
in DMSO would be required to elucidate the reactivity
in both solvents, since they may vary with solvent.

2920
E. Tfouni et al. / Inorganica Chimica Acta 358 (2005) 2909–2920
[7] B.N. Storhoff, H.C. Lewis, Coord. Chem. Rev. 23 (1977) 1.
4. Conclusions
[8] R.A. Michelin, M. Mozzon, R. Bertani, Coord. Chem. Rev. 147
(1996) 299.
The reactions undergone by [Ru(NH3)5(1,4-dcb)]2+
(1A) are basically similar to those of [Ru(NH3)5(1,4-
dcb)]2+, i.e., oxidation of this complex in aqueous solu-
tion is followed by nitrile hydrolysis to form the amido
nitrogen bonded [Ru(NH3)5(NHC(O)-bz-4-CN)]2+ (3A).
This complex, upon reduction, undergoes two reactions.
One is amide aquation, forming [Ru(NH3)5(OH2)]2+ and
1,4-cyanobenzamide. The other reaction is a linkage
isomerization reaction, forming the nitrile bonded
[Ru(NH3)5(NC-bz-4-NH2C(O))]2+ (8A). Similar reac-
tions occur for [Ru(NH3)5(1,2-dcb)]2+ (1B). The rate
constants (kobs) of the nitrile hydrolysis are pH depend-
ent, as for other coordinated nitriles, the higher the pH
the larger the rate. However, in addition to those reac-
tions, the results suggest that [Ru(NH3)5(1,2-dcb)]2+
(1B), after oxidation, forming [Ru(NH3)5(NHC(O)-bz-
2-CN)]2+ (3B), an amide to nitrile linkage isomerization
followed by an intramolecular cyclization reaction of the
coordinated 2-cyanobenzamide occur, resulting in a
complex of 3-imino-1-oxo-isoindoline bonded through
the exocyclic nitrogen, [Ru(NH3)5(NH-(C)(HN-C(O)-
2-bz))]3+ (12B), as occurs for the similar cobalt complex.
The rates of these reactions are pH dependent and con-
trary to hydrolysis, the more acidic the medium, the lar-
ger the rate constant values. The reduced species
[Ru(NH3)5(NH-(C)(HN-C(O)-2-bz))]2+ (13B) is easily
oxidized and is relatively substitution inert. As for the
cobalt complex, these reactions are consistent with
neighboring group participation and illustrate the rich-
ness involved in the chemistry of coordinated nitriles,
including ruthenium.
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The authors thank FAPESP, CAPES, CNPq, and the
PADCT program for grants and fellowships. We thank
´
Profs. Dr. Bruce McGarvey, Gil Valdo Jose da Silva and
Ms. Virginia Helena Betarello for help in NMR meas-
´
urements, and Prof. Dr. Angelica M. Lucchese for help-
ful discussions concerning phtalamide and phtalimide.
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