Cp*Ru+ complexes of benzylideneaniline and salicylideneaniline

Article abstract of DOI:10.1016/S0020-1693(01)00733-2

The reaction product of Cp*Ru(CH₃CN)₃⁺ OSO₂CF₃^- with salicylaldehyde yielded (1) which reacted with a series of aniline derivatives to produce air-stable solids. These products were characterized by ¹H and ¹³C NMR spectrometry and UV - Vis spectroscopy. Solvatochromism studies of these products revealed that the p-NH₂ and p-N(CH₃)₂ derivatives exhibit relatively large values of molecular hyperpolarizability and have the potential to exhibit nonlinear optical properties. These derivatives were further studied by electrochemical investigations.

Full text of DOI:10.1016/S0020-1693(01)00733-2

www.elsevier.com/locate/ica
Inorganica Chimica Acta 328 (2002) 210–217
Cp*Ru+ complexes of benzylideneaniline and salicylideneaniline
Dale E. Wheeler a,*, Nicholas W. Baetz a, Grant N. Holder a, Scott T. Hill b,
Steven Milos c, Kraig A. Luczak d
a A.R. Smith Department of Chemistry, Appalachian State Uni6ersity, Boone, NC 28608, USA
b Department of Chemistry, Alma College, Alma, MI 48802, USA
c Northwestern Memorial Hospital, Chicago, IL 60611, USA
d National Starch and Chemical Company, Bridgewater, NJ 08807, USA
Received 13 June 2001; accepted 18 October 2001
Abstract
The reaction product of Cp*Ru(CH3CN)3+ OSO2CF3− with salicylaldehyde yielded (1) which reacted with a series of aniline
derivatives to produce air-stable solids. These products were characterized by 1H and 13C NMR spectrometry and UV–Vis
spectroscopy. Solvatochromism studies of these products revealed that the p-NH2 and p-N(CH3)2 derivatives exhibit relatively
large values of molecular hyperpolarizability and have the potential to exhibit nonlinear optical properties. These derivatives were
further studied by electrochemical investigations. © 2002 Elsevier Science B.V. All rights reserved.
Keywords: Ruthenium; Benzylideneaniline; Salicylideneaniline; Nonlinear optical materials; Electrochemistry
bridging electron donor and acceptor groups. This arti-
cle reports our efforts to increase the conjugation
within these materials by reacting the salicylaldehyde
complex Cp*Ru(h6-o-OHꢀC6H4CHO)+ OSO2CF3− (1)
with several aniline derivatives.
1. Introduction
It is well established that aniline derivatives react
with aromatic aldehydes to form imines [1], commonly
called Schiff bases. Our previous studies [2] demon-
strated facile reactivity of the formyl group in benzalde-
hyde upon coordination of the aromatic ring to a
Cp*Ru+ moiety (Cp*=C5Me5). The enhanced elec-
trophilic character of the formyl carbon is believed to
be due to the electron withdrawing effect of the coordi-
nated Ru(II).
Our interest in benzylideneaniline complexes having a
single h6-coordinated Cp*Ru+ is their potential as
nonlinear optical (NLO) materials. Basic features of
NLO organometallic materials include the presence of a
highly conjugated and polarizable p electron system
and the occurrence of an intermolecular charge transfer
band [3]. Extended donor/acceptor aromatic systems
such as in benzylideneanilines [4] have demonstrated
strong second harmonic generation characteristics
shown to arise from the conjugated p electron system
2. Experimental
All synthetic procedures were carried out under a dry
nitrogen atmosphere with glassware fitted with Teflon
solvent seal connections using standard Schlenk tech-
niques. All solvents were freshly distilled prior to use.
Methanol was dried over Mg/I2, diethyl ether was dried
over calcium hydride, methylene chloride was predried
over P2O5, distilled, and dried over calcium hydride.
4-Hydroxyaniline, 4-chloroaniline, 1,4-phenylenedi-
amine, and 4-methoxyaniline were purified by recrystal-
lization prior to use. Salicylaldehyde, benzaldehyde,
and aniline were distilled prior to use. 4-N,N-dimethy-
laminoaniline was purchased from Aldrich Chemical
Co. and used without further purification.
Methylene chloride was used as the reaction solvent
because of the solubility of the starting materials and
products. Diethyl ether was used to precipitate the
* Corresponding author. Tel.: +1-828-262 6805; fax: +1-828-262
6558.
E-mail address: wheelerde@appstate.edu (D.E. Wheeler).
0020-1693/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(01)00733-2

D.E. Wheeler et al. / Inorganica Chimica Acta 328 (2002) 210–217
211
products from solution. Products were collected by
filtration and dried under vacuum.
Elemental analyses were performed by Galbraith Labo-
ratories in Knoxville, TN.
Synthetic procedures, 1H and 13C data for
Cp*Ru(h6-C6H5CHꢁNC6H4OH-p)+ OSO2CF3− (13),
Cp*Ru(h6-C6H5CHꢁNC6H4Cl-p)+ OSO2CF3− (14),
and Cp*Ru(h6-C6H5CHꢁNC6H4NH2-p)+ OSO2CF3−
(15) have been previously reported [2]. The procedure
for the synthesis of Cp*Ru(h6-C6H5CHO)+ OSO2CF3−
(2) was also previously reported [7].
2.1. Cp*Ru(p6-o-OHC6H4CHO)+ OSO2CF3− (1)
Cp*Ru(NCCH3)3+ OSO2CF3− (1) [7] (4.00 g, 7.87
mmol) was dissolved in 40 ml CH2Cl2. Salicylaldehyde,
o-OHC6H4CHO, (1.00 g, 8.19 mmol) was added to the
solution and the mixture was stirred overnight resulting
in a pale yellow solution. The solvent was removed
under vacuum and 25 ml diethyl ether was added to the
resulting solid. The mixture was stirred and then filtered
and the cream colored powder was dried under vac-
uum. 3.53 g, 88% yield. Anal. Found: C, 42.12; H, 4.34.
C18H21F3O5RuS. Calc.: C, 42.60; H, 4.17%.
The 1H NMR spectra (Table 1) were measured at 300
MHz and 13C NMR spectra (Table 2) at 75.5 MHz
with a Bruker AC-F 300 FT NMR spectrometer at
Appalachian State University. UV–Vis spectra (Table
3) were recorded on a Shimadzu Model UV 2401
Spectrophotometer at Appalachian State University.
Table 1
1H NMR data
Imine proton
(1H, s)
Non-coordinated aromatic
ring protons
Coordinated aromatic ring Other protons
protons
Cp* methyl protons
(15H, s)
1
6.36 (1H, d, 3JHH=6.3
Hz)
CHO
10.33 (1H, s)
1.89
6.02 (1H, d, 3JHH=5.7
Hz)
5.83 (1H, t, 3JHH=5.8 Hz)
5.63 (1H, t, 3JHH=5.7 Hz)
6.42 (2H, d, 3JHH=5.7Hz)
5.96–6.00 (3H, m)
6.51 (2H, d, 3JHH=6.3
Hz)
5.96–6.06 (3H, m)
6.45 (2H, d, 3JHH=5.7
Hz)
3
4
8.33
8.42
7.34–7.36 (2H, m)
1.87
1.91
7.20–7.24 (3H, m)
7.32 (2H, d, 3JHH=9.0Hz)
OCH3
3.81
(3H, s)
(6H, s)
6.92 (2H, d, 3JHH=9.0Hz)
7.24 (2H, d, 3JHH=9.0 Hz)
5
6
8.36
8.98
N(CH3)2 2.99
1.89
1.87
6.69 (2H, d, 3JHH=8.1 Hz)
7.35–7.45 (5H, m)
5.92–6.01 (3H, m)
6.64 (1H, d, 3JHH=4.8
Hz)
5.83 (1H, d, 3JHH=5.1
Hz)
5.77–5.72 (2H, m)
6.64 (1H, d, 3JHH=4.5
Hz)
7
9.03
7.40 (5H, s)
1.86
5.82 (1H, d, 3JHH=5.1
Hz)
5.77–5.72 (2H, m)
6.16 (1H, d, 3JHH=5.0
Hz)
5.57–5.65 (3H, m)
6.64 (1H, d, 3JHH=5.0
Hz)
5.68–5.77 (3H, m)
6.18 (1H, m)
5.62–5.57 (3H, m)
6.56 (1H, d, 3JHH=5.3
Hz)
8
9
8.58
8.96
7.22 (2H, d, 3JHH=8.7 Hz)
OH
3.81
3.83
3.61
(1H, broad)
(3H, s)
1.73
1.86
6.77 (2H, d, 3JHH=9.0 Hz)
7.47 (2H, d, 3JHH=7.2 Hz)
OCH3
NH2
6.94 (2H, d, 3JHH=7.2 Hz)
7.21 (2H, d, 3JHH=8.7 Hz)
6.63 (2H, d, 3JHH=8.4 Hz)
7.44 (2H, d, 3JHH=9.3 Hz)
10
11
8.58
8.86
(2H, broad)
(6H, s)
1.76
1.84
N(CH3)2 3.01
6.69 (2H, d, 3JHH=8.7 Hz)
5.71–5.69 (2H, m)
5.61 (1H, m)
12
13
8.92
Pyrene (9H)
6.35 (1H, d, 3JHH=5.7
Hz)
1.76
8.28, 8.25, 8.14–8.07 (m)
8.02–7.91(m)
5.67-5.56 (3H, m)
All spectra were taken in 9:1 CDCl3:CD3OD. The internal reference of residual CHCl3 was set equal to 7.24 ppm.

212
D.E. Wheeler et al. / Inorganica Chimica Acta 328 (2002) 210–217
Table 2
13C NMR data
Imine carbon
Non-coordinated aromatic ring carbons
Coordinated aromatic ring carbons
Cp* carbons Other carbons
(i-OH)
1
3
4
5
6
7
8
9
133.5 87.7
93.5
85.2 81.9 80.3 77.8 97.2, 10.3
CHO 190.5
155.5
152.1
148.0
161.6
162.1
158.5
161.8
154.0
154.0
159.2
149.0
159.8
150.6
146.1
144.7
156.1
159.8
148.1
151.0
139.7
128.6
126.0
125.0
129.3 127.6 120.8
142.0 123.1 114.8
137.6 123.2 112.4
88.0 87.6 86.2
88.0 87.8 86.2
87.8 87.7 85.9
97.5, 10.2
97.5, 10.6
97.3, 10.7
94.5
95.4
OCH3 55.6
N(CH3)2 40.4
129.8 129.1 121.5 133.1 87.2
134.7 130.0 123.0 132.9 87.2
137.7 122.8 116.3 132.6 86.3
138.6 123.1 115.0 133.6 87.3
136.0 122.9 115.3 133.2 86.3
134.0 123.3 112.6 133.6 87.0
131.5 131.2 130.7 132.1 86.4
128.1 127.1 126.5
86.8 85.1 79.8 77.8 96.4, 10.2
86.7 84.1 79.9 77.7 96.5, 10.2
86.2 84.5 80.0 77.5 95.9, 10.1
86.4 85.9 80.1 77.7 96.1, 10.1
86.0 84.5 80.4 77.4 96.0, 10.0
86.0 84.5 80.6 77.7 95.8, 9.9
85.9 84.8 80.7 77.3 96.2, 10.0
OCH3 55.6
10
11
12
N(CH3)2 40.6
125.9 125.7 125.6
124.2 121.1 114.9
Spectra for compounds 1, 4, 5, 6, 7, and 11 were taken in CDCl3 with the reference set to 77.00 ppm. Spectra for compounds 3, 8, 9, and 10 were
taken in 1:1 CDCl3 and CD3OD with the reference set to 77.00 ppm.
Table 3
UV–Vis spectral data
Compound
Solvent umax
Molar absorptivity constant (in CH3OH)
CH2Cl2
C6H5Br
H2O
CH3OH
3
4
5
6
7
329.7
357.0
429.6
328.5
334.5
357.2
360.3
396.0
442.2
334.8
354.1
387.6
330.3
356.2
422.4
328.8
336.0
354.8
360.2
391.1
431.4
332.6
352.8
386.7
*
339.8
382.6
*
324.5
348.3
411.3
319.9
326.3
345.5
341.5
367.4
391.4
326.4
353.1
387.1
3800
9700
19 000
8500
*
*
*
*
8900
8
9
11 300
10 800
9800
16 900
5700
10
11
13
14
15
*
317.1
340.9
362.5
10 400
15 400
*, umax was not observed in these solutions. Note: Absorbance values ranged from 0.5 to 1.0.
2.2. Cp*Ru(p6-C6H5CHꢁNC6H5)+ OSO2CF3− (3)
Methoxyaniline (0.0455 g, 0.369 mmol) was added and
the reaction was stirred for 4 h. Diethyl ether was
added (ca. 10 ml) to complete the precipitation of the
product from the cloudy white solution. The resulting
pale yellow powder was filtered and dried under vac-
uum, 0.17 g, 78% yield. Anal. Found: C, 49.84; H, 4.59.
C25H28F3NO4RuS. Calc.: C, 50.33; H, 4.73%.
Cp*Ru(h6-C6H5CHO)+ OSO2CF3− (2) (0.172 g,
0.349 mmol) was dissolved in 20 ml of CH2Cl2. Freshly
distilled aniline (20 drops, ca. 10 mmol) was added and
the reaction was stirred for 4 h. Diethyl ether was
added (ca. 15 ml) to the clear rose-colored solution
until the precipitation of the product was complete. The
white powdered solid was filtered and dried under
vacuum, 0.14 g, 70% yield. Anal. Found: C, 50.43; H,
4.47. C24H26F3NO3RuS. Calc.: C, 50.88; H, 4.63%.
2.4. Cp*Ru(p6-C6H5CHꢁNC6H4N(CH3)2-p)+
OSO2CF3− (5)
Cp*Ru(h6-C6H5CHO)+ OSO2CF3− (2) (0.210 g,
0.427 mmol) was dissolved in 20 ml of CH2Cl2. p-N,N-
dimethylaminoaniline (0.072 g, 0.53 mmol) was added
and the reaction was stirred overnight. Diethyl ether
was added (ca. 15 ml) to the dark green solution and a
green solid precipitated from solution. The green pow-
2.3. Cp*Ru(p6-C6H5CHꢁNC6H4OCH3-p)+ OSO2CF3−
(4)
Cp*Ru(h6-C6H5CHO)+ OSO2CF3− (2) (0.182 g,
0.369 mmol) was dissolved in 15 ml of CH2Cl2. p-

D.E. Wheeler et al. / Inorganica Chimica Acta 328 (2002) 210–217
213
der was filtered and dried under vacuum, 0.18 g, 70%
yield. Anal. Found: C, 50.79; H, 5.01. C26H31F3N2-
O3RuS. Calc.: C, 51.22; H, 5.13%.
82% yield. Anal. Found: C, 48.70; H, 4.39.
C25H28F3NO5RuS. Calc.: C, 49.01; H, 4.61%.
2.9. Cp*Ru(p6-o-OHC6H4CHꢁNC6H4NH2-p)+
OSO2CF3− (10)
2.5. Cp*Ru(p6-o-OHC6H4CHꢁNC6H5)+ OSO2CF3−
(6)
Cp*Ru(NCCH3)3+ OSO2CF3− (1) (0.203 g, 0.401
mmol) was dissolved in 20 ml of CH2Cl2. 1,4-
Phenylenediamine (0.0437 g, 0.404 mmol) was added to
the solution of 1 and the reaction mixture was stirred
for about 4 h. The addition of about 10 ml of diethyl
ether induced a green precipitate to form from the pale
green solution. The yellow green powdered product was
filtered and dried under vacuum, 0.18 g, 72% yield.
Anal. Found: C, 47.92; H, 4.33. C24H27F3N2O4RuS.
Calc.: C, 48.24; H, 4.55%.
Cp*Ru(NCCH3)3+ OSO2CF3− (1) (0.203 g, 0.399
mmol) was dissolved in 20 ml of CH2Cl2. Freshly
distilled aniline (20 drops, ca. 10 mmol) was added and
the reaction was allowed to stir overnight. The product
was precipitated from the pale yellow solution by
adding approximately 10 ml of diethyl ether. The white
powdered solid was filtered and dried under vacuum,
0.18 g, 76% yield. Anal. Found: C, 49.06; H, 4.38.
C24H26F3NO4RuS. Calc.: C, 49.48; H, 4.50%.
2.6. Cp*Ru(p6-o-OHC6H4CHꢁNC6H4Cl-p)+
OSO2CF3− (7)
2.10. Cp*Ru(p6-o-OHC6H4CHꢁNC6H4N(CH3)2-p)+
OSO2CF3− (11)
Cp*Ru(NCCH3)3+ OSO2CF3− (1) (0.198 g, 0.391
mmol) was dissolved in 20 ml of CH2Cl2. p-Chloroani-
line (0.0516 g, 0.405 mmol) was added to the solution
of 1 and the reaction mixture was stirred for 4 h.
Precipitation of the product from the pale yellow solu-
tion occurred as approximately 10 ml of diethyl ether
was added to the reaction solution. The white pow-
dered solid was filtered and dried overnight under
vacuum, 0.20 g, 83% yield. Anal. Found: C, 46.33; H,
3.84. C24H25ClF3NO4RuS. Calc.: C, 46.72; H, 4.08%.
Cp*Ru(NCCH3)3+ OSO2CF3− (1) (0.204 g, 0.402
mmol) was dissolved in 20 ml of CH2Cl2. p-N,N-
dimethylaniline (0.074 g, 0.543 mmol) was added to the
solution of 1 and the reaction mixture was stirred
overnight. A green solid precipitated from solution as
approximately 10 ml of diethyl ether was added to the
dark green solution. The green powdered product was
filtered and dried under vacuum for several hours, 0.18
g, 74% yield. Anal. Found: C, 49.55; H, 4.75.
C26H31F3N2O4RuS. Calc.: C, 49.91; H, 4.99%.
2.7. Cp*Ru(p6-o-OHC6H4CHꢁNC6H4OH-p)+
OSO2CF3− (8)
2.11. Cp*Ru(p6-o-OHC6H4CHꢁNC16H9)+ OSO2CF3−
(12)
Cp*Ru(NCCH3)3+ OSO2CF3− (1) (0.202 g, 0.398
mmol) was dissolved in 20 ml of CH2Cl2. p-Hydrox-
yaniline (0.0460 g, 0.425 mmol) was added to the
solution of 1 and the reaction mixture was stirred
overnight. About 10 ml of diethyl ether was added to
the golden colored reaction solution inducing the pre-
cipitation of a pale yellow powder. The product was
filtered and dried under vacuum, 0.17 g, 72% yield.
Anal. Found: C, 47.81; H, 4.26. C24H26F3NO5RuS.
Calc.: C, 48.16; H, 4.38%.
Cp*Ru(NCCH3)3+ OSO2CF3− (1) (0.158 g, 0.310
mmol) was dissolved in 15 ml of CH2Cl2. 1-Aminopy-
rene (0.069 g, 0.32 mmol) was added to the solution of
1 and the reaction mixture was stirred overnight. Pre-
cipitation of the product occurred as approximately 10
ml of diethyl ether was added to the reaction solution.
The orange powdered product was filtered and dried
under vacuum, 0.16 g, 73% yield. Anal. Found: C,
57.42; H, 4.11. C34H30F3NO4RuS. Calc.: C, 57.78; H,
4.28%.
2.8. Cp*Ru(p6-o-OHC6H4CHꢁNC6H4OCH3-p)+
OSO2CF3− (9)
3. Results and discussion
Cp*Ru(NCCH3)3+ OSO2CF3− (1) (0.133 g, 0.263
mmol) was dissolved in 15 ml of CH2Cl2. p-
Methoxyaniline (0.0324 g, 0.263 mmol) was added to
the solution of 1 and the reaction mixture was stirred
overnight. Precipitation of the yellow product occurred
as approximately 10 ml of diethyl ether was added to
the golden brown solution. The bright yellow powder
was filtered and dried under vacuum overnight, 0.13 g,
The first reported derivative exhibiting NLO proper-
ties was 4-nitro-4%-methylbenzylideneaniline [5]. The
crystal structure of this compound revealed the
molecule to be nearly planar [5] and had a SHG
efficiency 100 times urea. 4-Dimethylamino-4%-nitroben-
zylideneaniline and 4-nitro-4%-dimethylaminobenzylide-
neaniline also have near planar structures [6], which
promote the maximum conjugation of the strong elec-

214
D.E. Wheeler et al. / Inorganica Chimica Acta 328 (2002) 210–217
tron donating and accepting groups. This paper reports
the synthesis of several air-stable benzylideneanilines of
the general formula Cp*Ru(h6-C6H5CHꢁNC6H4X-p)+
from the reaction of Cp*Ru(h6-C6H5CHO)+ (2) with
various p-substituted anilines. These products would
possess a polar extended conjugated p system if the
h6-benzylideneaniline part of the complex was planar.
The results of solvatochromism studies of these com-
plexes (see Table 3) are an indication of the molecular
hyperpolarizability (i). Large values of i are associ-
ated with chromophores comprised of electron donors
and acceptors linked by a conjugated p system. Our
studies revealed that the benzylideneaniline complexes
with the strongest electron donating groups (X=NH2
(15) and N(CH3)2 (5)) are green and that (15) exhibited
the greatest solvatochromism. The complexes where
X=Cl (14), or H (3), were white powders and exhib-
ited little solvatochromism, indicating that the benzyli-
dene ligand may not be planar.
imine bond. Electron density in the uncoordinated ring
may also decrease if the salicylideneaniline ligand is
planar and the electron withdrawing effects of the
ruthenium is felt throughout the entire delocalized p
system. The solvatochromism properties of these com-
plexes were determined (see Table 3).
3.1. Electrochemical studies
3.1.1. Voltammetric beha6ior
All compounds were examined on a BioAnalytical
Systems, Inc. 100 B/W electrochemical workstation uti-
lizing glassy carbon and platinum disk electrodes in
acetonitrile (dried over CaH2) and 0.1 M tetra-N-buty-
lammonium hexafluorophosphate (TBAH) supporting
electrolyte. All potentials are referenced to the Ag/Ag+
couple and are uncorrected for liquid junction.
3.2. Cp*Ru(p6-o-OHC6H4CHO)+ OSO2CF3− (1)
To increase the probability of a planar ligand, an
o-OH group was added to the aromatic aldehyde,
which would allow the possibility of hydrogen bonding
with nitrogen. This would fix the ligand into a planar
configuration and promote greater delocalization of p
electrons. These complexes would exhibit greater solva-
Observed voltammetric processes consisted of two
reductions at Ep,1= −1.060 V and Ep,2= −1.920 V.
These potentials shifted cathodically with increasing
scan rate and did not exhibit behavior characteristic of
reversibility (anodic/cathodic current ratioB1) at any
scan rate up to 3 V s−1. A wave at Ep,ox= +1.080 V,
present only after scanning past Ep,2, represents the
decomposition product of a chemical reaction following
the second reduction and is also not reversible. This
electroactive decay product decomposes slowly, as evi-
denced by the rapid diminution of iox/ip,2 at scan rates
B0.300 V s−1. At scan rates \0.300 V s−1, this ratio
became constant within experimental error. Significant
adsorption of the electroactive product formed from
the reaction following E1 was observed.
tochromism indicating
a
potentially greater SHG
efficiency.
The
salicylaldehyde
complex
Cp*Ru(h6-o-
OHꢀC6H4CHO)+ OSO2CF3− (1) was synthesized using
the published procedure of Fagen, et al. [7]. Reactions
of (1) with a variety of aniline derivatives produced a
series of products with the general formula Cp*Ru(h6-
o-OHꢀC6H4CHꢁNC6H4X-p)+ OSO2CF3−. See Scheme
1.
Curiously, only one of the ꢀNH2 groups in 1,4-
phenylenediamine reacted with (1), even when a 2:1
ratio of amine:aldehyde was used. It is believed that the
second p-amino group is unreactive toward (1) due to a
decrease in the nucleophilic character of the nitrogen
lone pair electrons. The decrease in the electron density
of the uncoordinated ring may be due to the loss of the
available nitrogen lone pair upon reaction forming the
3.3. Cp*Ru(p6-o-OHC6H4CHꢁNC6H4N(CH3)2-p)+
OSO2CF3− (11)
The cyclic voltammogram for this compound is
shown in Fig. 1a. Initial anodic scan exhibited a one-
electron transfer at a half-wave potential Eox,2=0.987
Scheme 1. This scheme shows the general reaction of Cp*Ru(h6-o-OHC6H4CHO)+OSOCF3− (1) with various p-substituted anilines to give
products 6–11.

D.E. Wheeler et al. / Inorganica Chimica Acta 328 (2002) 210–217
215
ond reduction does not exhibit surface enhancement.
However, the increase in current magnitude does not
justify an assignment of two-electron stoichiometry, as
current magnitude in that case must be 2.83 times
higher than ip,1. As for (11), an oxidation coupled to
Ep,2 appears, though shifted to −0.132 V, a cathodic
shift of 0.320 V. Comparison of ip,2 to the current of
this coupled wave displays variation from 0.042 (0.100
V s−1) to 0.5 (1 V s−1). This indicates the chemical
reaction following Ep,2 is much faster in the absence of
RuCp*. Though the RuCp* moiety does not appear to
be electroactive within our potential window, it does
have an effect on the energy of the electron-transfer
process. Compared with uncomplexed salicyl-
ꢁNꢀC6H4ꢀN(Me)2, there are anodic shifts between
0.500 and 0.700 V for both reductions, corresponding
to a stabilization of the ligand LUMO following com-
plexation of the RuCp* moiety. Potential differences
between Ep,1 and Ep,2 for (11) and salicyl-
ꢁNꢀC6H4ꢀN(Me)2 are 0.920 V (complex) versus 0.750 V
(salicyl-ꢁNꢀC6H4ꢀN(Me)2), indicating the effect of
RuCp* to be greater on Ep,1. This might indicate the
first reduction corresponds to the ring/double bond
system bound directly to the RuCp* while the latter is
a ring-centered reduction of the uncoordinated ring.
Interestingly, current ratios rise for the oxidation Eox,2
following addition of RuCp*, indicating that the rate
constant of the decomposition reaction following the
oxidation of the dimethylamino nitrogen is lowered by
the presence of RuCp*. An anodic shift of 0.120 V is
observed for Eox,2 following complexation. Kinetics of
the chemical reactions following electron-transfer ap-
pear faster on Pt than glassy carbon as indicated by
differences in the rate of change of current ratio with
scan rate.
Fig. 1. Full cycle voltammetric scan (MeCN/0.1 M TBAH), glassy
carbon electrode (A=0.109 cm2) of: (a) (11); (b) salicyl-N-C6H4-
N(Me)-p; (c) (10); Scan rates in all cases=0.300 V s−1
.
V. The process is not fully reversible, though current
ratios approached unity with increasing scan rates;
separation between anodic and cathodic peak potentials
(DEp) was 0.130 V at 0.100 V s−1 and increases with
scan rate. Initial cathodic scan reveals a non-reversible
reduction at Ep,1= −1.130 V, similar to that seen in 1,
as well as a reduction at Ep,2= −2.050 V. A low-cur-
rent reduction is observed at −0.845 V for all com-
plexes. This amounts to a ‘shoulder’ on Ep,1 and may be
a prepeak resulting from adsorption of the product of
the chemical reaction following the −1.130 V reduc-
tion. Current magnitude for the first and second reduc-
tions do not show an equivalence, with ip,1 between 0.55
and 0.65 of ip,2. This is insufficient to justify the second
reduction as a two-electron process. However, close
examination of the second reduction shows a signifi-
cantly different waveshape than that displayed by the
first reduction and characteristic of surface adsorption,
which amply justifies the current inequities between the
two processes. An oxidation, not observed on initial
anodic scan, appeared at 0.190 V only after scanning
through Ep,2. This is identical behavior to 1, though the
potential for the coupled peak (Eox,1) is shifted cathodi-
cally by 0.900 V. This is the oxidation of a product of
a rather slow chemical reaction following Ep,2. Current
3.4. Cp*Ru(p6-o-OHC6H4CHꢁNC6H4NH2-p)+
OSO2CF3− (10)
The substitution of amino—for dimethylamino—re-
sults in a marked increase in the rate of decomposition
following oxidation of amino moiety, as Eox,2 exhibits
much lower current ratios at any scan rate. (Fig. 1c).
Other electron-transfer processes seemed unaffected
save for a shift of about 0.050–0.100 V relative to the
magnitude of iox,1 varies from 0.19 of ip,2 (0.050 V s−1
to equivalence at 2 V s−1
)
dimethylamino derivative;
Eox,2=1.085 V, Ep,1=
.
−1.150 V, Ep,2= −2.100 V. One would expect peak
shifts on the basis of inductive effect to be in an anodic
direction for 11 relative to 10. Cathodic and anodic
peak potentials shift in opposing directions, with all
electron-transfers shifting to more extreme values; this
indicates a difference in electron-transfer mechanism
related to the active hydrogens of the amine group. The
ꢀNH2 functionality can give rise to proton transfers not
possible for the ꢀN(Me)2 group.
Comparison of the cyclic voltammetry of (11) with
uncomplexed ligand salicyl-ꢁNꢀC6H4ꢀN(Me)2 (Fig. 1b)
indicates all electron-transfers are ligand based. The
process Eox,2 corresponds to electrochemical oxidation
of the amino group on the uncoordinated ring. This
oxidation approaches reversibility as scan rates in-
crease, though DEp approaches 0.250 V at 3 V s−1
.
Current magnitude exhibited by the initial reduction is
0.46–0.6 that of the second reduction, though the sec-

216
D.E. Wheeler et al. / Inorganica Chimica Acta 328 (2002) 210–217
3.5. Cp*Ru(p6-C6H5CHꢁNC6H4N(CH3)2-p)+
OSO2CF3− (5)
corresponding to the reduction of products formed
following decomposition of the anion Ep,3. The current
magnitudes of Ep,4 and Ep,5 decrease with increasing
scan rate, indicating the scan is outrunning the reaction
in which these products are formed and, therefore, that
the rate constant for the formation of these processes is
relatively slow on the voltammetric time scale. The first
reduction appears more reversible than the correspond-
ing process in 11. The narrow shape of the forward
wave of Ep,3 and its large magnitude (i8w) are indica-
tive of moderate adsorption on the electrode surface.
This is observed only on glassy carbon; the voltammet-
ric curve has the characteristic diffusion-controlled
shape on platinum as well as a magnitude similar to the
other electron-transfer processes (i8w1/2) [8]. On plat-
inum, two non-reversible reductions were observed at
The effect of the highly active ꢀOH group was exam-
ined by comparing the voltammetry of 11 and 5, two
compounds which differ only by the presence or ab-
sence of the hydroxyl group attached to the metalated
ring. The reductive mechanism (Fig. 2a) is far more
complex than 11, probably due to the loss of stabiliza-
tion provided by H-bonding between the imine nitrogen
and the hydroxyl group. Removal of ꢀOH results in a
disproportionately large-magnitude reduction at Ep,3
=
−1.570 V followed by fast decomposition to multiple
electroactive products. Processes Ep,1 and Ep,2 show
similar peak potentials to 11. Two additional processes
are observed (Ep,4= −2.092 and Ep,5= −2.188 V),
Ep,4= −1.560 and Ep,5= −2.246 V. That these pro-
cesses are observed only on glassy carbon implies their
formation depends on some surface chemical process or
these are strongly adsorbed products of a reaction
following E3. Anodically, (Fig. 3a) the first oxidation
shows excellent reversibility at all scan rates, intimating
the significant function of ꢀOH in the chemical decom-
position following oxidation.
3.6. Cp*Ru(p6-C6H5CHꢁNC6H4NH2-p)+ OSO2CF3−
(15)
The reduction of this compound (Fig. 2b) exhibits
two waves of equal current magnitude at Ep,1
=
−1.620 and Ep,2= −2.250 V. The most extreme re-
duction shows some reversibility, unlike processes at
similar potentials in 10 and 5. Ep,1 and Ep,2 behavior is
typical of the electrochemical ‘ECE’ mechanism. Lig-
and-based reduction (radical anion formation) is imme-
diately followed by bond cleavage. The reversible
reduction at −2.250 V is typical of a ring-based one-
electron reduction [9]. Anodically (Fig. 3b), two oxida-
tions of equal current magnitude are observed at
Fig. 2. Reductive voltammetry (MeCN/0.1 M TBAH) of: (a) 5; and
(b) 15. Scan rate=0.300 V s−1
.
Eox,1=0.896 and Eox,2=1.805 V. The first oxidation
does not exhibit the same degree of reversibility as 5;
there is an obvious following chemical reaction to
produce at least one electroactive product sufficiently
long-lived to be reduced at 0.413 V. Diagnostic criteria
for the first oxidation are essentially the same as 10,
emphasizing the reactivity of the oxidized—amino moi-
ety compared with the—dimethylamino derivative. Re-
duction of 15 parallels 5 in the appearance of a
reduction of Ep,3= −1.620 V which is absent in the
salicyl derivative. As this potential is shifted cathodi-
cally by 0.040 V relative to 5, a direction in opposition
to expectations, one must suspect surface or intermolec-
ular effects. Current magnitude for this reduction is
much reduced on glassy carbon compared with corre-
sponding process in 5, leading one to the conclusion
that the potential of the dimethylamino—derivative is
Fig. 3. Oxidative voltammetry (MeCN/0.1 M TBAH) of: (a) (5); and
(b) (15). Scan rates in all cases=0.300 V s−1
.

D.E. Wheeler et al. / Inorganica Chimica Acta 328 (2002) 210–217
217
being lowered by substantial adsorption onto the elec-
Acknowledgements
trode surface.
We thank Johnson–Matthey for their generous loan
of RuCl3·×H2O through participation in their Metal
Loan program. We also thank Appalachian State Uni-
versity for their monetary support of this project.
4. Summary of electrochemical results
One can deduce from the observations that:
(a) The compounds exhibit ligand-based electron-trans-
fers only.
References
(b) Initial reductions are followed by chemical reac-
tions, with some of the reactive fragments gener-
ated by bond cleavage from formed radical anions
sufficiently long lived to be oxidized at scan rates
\0.300 V s−1; the hydroxyl moiety appears to
prevent electrochemical reduction of the double
bond possibly through H-bonding with the imine
nitrogen.
(c) The oxidation at approximately 900–1000 mV is
due to the amine on the uncoordinated ring. Once
oxidized, 10 decomposes much more quickly than 5
due to the ease with which H+ is lost from the
ꢀNH2 group.
(d) Pronounced adsorption occurs in the absence of the
hydroxyl group. Voltammetric behavior is more
complex on glassy carbon electrode than platinum.
The complete electron-transfer mechanisms for these
compounds will be presented in full in a future
publication.
[1] S. Patai, The Chemistry of the Carbon–Nitrogen Double Bond,
Wiley, New York, 1970, pp. 64–83.
[2] D.E. Wheeler, S.T. Hill, S. Milos, J.D. Williams, J.D. Johnson, J.
Organometallic Chem. 530 (1997) 83.
[3] (a) J.W. Perry, in: S.R. Marder, J.E. Sohn, G.D. Stucky, (Ed.),
Materials for Nonlinear Optics—Chemical Perspectives, ACS
Symposium Series 455, American Chemical Society, Washington,
DC, 1991, pp. 67–88;
(b) D.F. Eaton, in: S.R. Marder, J.E. Sohn, G.D. Stucky, (Ed.),
Materials for Nonlinear Optics—Chemical Perspectives, ACS
Symposium Series 455, American Chemical Society, Washington,
DC, 1991, pp. 128–156;
(c) J.-M. Lehn, in: S.R. Marder, J.E. Sohn, G.D. Stucky, (Ed.),
Materials for Nonlinear Optics—Chemical Perspectives, ACS
Symposium Series 455, American Chemical Society, Washington,
DC, 1991, pp. 436–445.
[4] (a) S.A. Jenekhe, C.-J. Yang, H. Vanherzeele, J.S. Meth, Chem.
Mater. 3 (1991) 985;
(b) J. Zyss, in: J.L. Bredas, R.R. Chance (Eds.), Journal of
Conjugated Polymeric Materials: Opportunities in Electronics,
Optoelectronics, and Molecular Electronics, Kluwer Academic
Publishers, The Netherlands, 1990, p. 545;
(c) J.C. Dubois, in: J.L. Bredas, R.R. Chance (Eds.), Journal of
Conjugated Polymeric Materials: Opportunities in Electronics,
Optoelectronics, and Molecular Electronics, Kluwer Academic
Publishers, The Netherlands, 1990, p. 321;
5. Conclusions
(d) J.F. Wolfe, S.P. Ermer, S.M. Lovejoy, D.S. Leung, K.P. Aron,
G.A. Hansen, S.P. Bitler, in: Nonlinear Optical Properties of
Polymers, Materials Research Society Symposium Proceedings
173, Materials Research Society, Pittsburgh, 1990, 499.
[5] O.S. Filipenko, V.D. Shigorin, V.I. Ponomarev, L.O. Atovmyan,
Z.S. Safina, B.L. Tanopol’skii, Sov. Phys. Crystallogr. 22 (1977)
305.
[6] F. Skrabal, J. Straiger, H. Zollinger, Helv. Chim. Acta 58 (1975)
800.
[7] P.J. Fagen, M.D. Ward, J.C. Calabrese, J. Am. Chem. Soc. 111
(1989) 1698.
The facile reaction of Cp*Ru(h6-p-OHC6H4CHO)+
OSO2CF3− (1) with a variety of aniline derivatives and
primary amines yields air-stable solids. Solva-
tochromism studies of these products revealed that the
ꢀNH2 and ꢀN(CH3)2 derivatives, (10, 11) exhibit the
greatest change in umax between solvents. Large values
of Dumax indicate potential molecular hyperpolarizabil-
ity within the compounds. Therefore, products (10, 11)
are the most likely in this series of complexes to exhibit
nonlinear optical properties. Further studies of these
complexes are ongoing.
[8] R.S. Nicholson, I. Shain, Anal. Chem. 36 (4) (1964) 706.
[9] C.P. Andrieux, J.-M. Saveant, R.T. Tallec, C.J. Tardy, Am.
Chem. Soc, 1997, 119, 2424; and many others.