Synthesis and characterization of copper(I) and copper(II) flavonolate complexes with phthalazine ligand, and their oxygenation and relevance to quercetinase

Article abstract of DOI:10.1016/S0020-1693(39)60540-7

Copper(I) and copper(II) flavonolate (fla) complexes with 1,4-(di-2′-pyridyl)aminophthalazine ligand (PAPH₂) have been prepared by the reaction of copper salts with flavonol and the ligand in acetonitrile or dichloromethane. The copper(II) cent

Full text of DOI:10.1016/S0020-1693(39)60540-7

Inorganica Chimica Acta 256 (1997) 9–14
Synthesis and characterization of copper(I) and copper(II) flavonolate
complexes with phthalazine ligand, and their oxygenation and relevance
to quercetinase
U
b,
a
b
´
Eva Balogh-Hergovich ,Jo´zsef Kaizer ,Ga´bor Speier
a Research Group for Petrochemistry of the Hungarian Academy of Sciences, 8201 Veszpre´m, Hungary
b Department of Organic Chemistry, University of Veszpre´m, 8201 Veszpre´m, Hungary
Received 14 February 1996; revised 27 May 1996
Abstract
Copper(I) and copper(II) flavonolate (fla) complexes with 1,4-(di-29-pyridyl)aminophthalazine ligand (PAPH2) have been prepared by
the reaction of copper salts with flavonol and the ligand in acetonitrile or dichloromethane. The copper(II) centers are bound to the tetradentate
phthalazine ligand resulting in both mononuclear and binuclear complexes. Flavonol is oxygenated to the corresponding depside catalyzed
by flavonolato copper(II) phthalazine complexes.
Keywords: Copper complexes; Flavonolate complexes; Phthalazine complexes
1. Introduction
onuclear and binuclear complexes with copper, cobalt, nickel
and zinc salts [13–21]. Catecholase and phenolase activity
was reported for some copper(II) phthalazine derivatives
[13,14]. Here we report the preparation of some copper(I)
and copper(II) flavonolate complexes with 1,4-(di-29-pyri-
dyl)aminophthalazine (PAPH2, 3) ligand and their catalytic
activity in the oxygenation of flavonol.
The degradation of quercetin (1c,3 9,49,5,7-tetrahydroxy-
flavonol) in living systems to the correspondingdepside(2c)
and carbon monoxide is performed by the dioxygenase
quercetinase (Eq. (1)) [1–4].
(1)
The catalytic center of this enzyme contains copper(II) ion,
but the ligand environment around CuII has not been encoun-
tered. Studies on structural and functional models have been
carried out to elucidate the mechanism of the reaction. Base
catalyzed oxygenation of quercetin and related 3-hydroxyfla-
vones under aqueous [5] and non-aqueous [6] conditions,
photosensitized oxygenations [7] and reaction with superox-
ide [8] have been investigated. Co(salen) proved a good
catalyst in the oxygenation of flavonols [9,10]. Copper(I)
[11] and copper(II) [12]flavonolatecomplexeswithsimple
ligands were also successfully used for the oxygenation of
flavonols. Aminophthalazines have been shown to formmon-
2. Experimental
Solvents used for the reactions were purified by literature
methods [22] and stored under argon. 3-Hydroxyflavone
[5], 3-hydroxy-49-methoxyflavone [5], PAPH2 [21],
mesityl copper(I) [23], Cu(OMe)2 [24] and
[Cu(CH3CN)4]ClO4 [25] were prepared by literature
methods.
2.1. Preparation of [Cu2(ClO4)2(fla)2(PAPH2)] (4a)
[Cu(CH3CN)4]ClO4 (0.328 g, 1 mmol) was dissolved in
acetonitrile (20 ml). Flavonol (1a) (0.238 g, 1 mmol) and
U Corresponding author.
0020-1693/97/$17.00 q 1997 Elsevier Science S.A. All rights reserved
PII S0020-1693(39)60540-1

´
E. Balogh-Hergovich et al. / Inorganica Chimica Acta 256 (1997) 9–14
10
PAPH2 (0.158 g, 0.5 mmol) were added and stirred under
argon for 1 h and then under dioxygen for 4 h. A light yellow
crystalline solid formed, which was filtered, washed with
acetonitrile and dried in vacuum (0.48 g, 88%). The product
was recrystallized from acetonitrile. Compound 4b was pre-
pared similarly using 49-methoxyflavonol (1b). Attempts to
obtain suitable single crystals of the compounds 4a or 4b for
X-ray analysis failed and only thin needles could be obtained.
determined at room temperature with a Bruker B-E 10B8
magnetic balance. EPR spectra were obtained with a JEOL
JES-FE3X spectrometer. Electrochemical measurements
were carried out under argon atmosphere at roomtemperature
in acetonitrile with 0.1 mol dmy3 tetraethylammonium per-
chlorate as supporting electrolyte, using platinum working
electrode, platinum auxiliary electrode and Ag/AgCl refer-
ence electrode with a BAS CV-1B cyclic voltammograph.
Potentials are given relative to SCE referenced to the internal
ferrocene/ferrocenium potential taken as 0.425 V [26]. GC
analyses were performed on anHP5830Agaschromatograph
equipped with a flame ionization detector and CP SIL8CB
column. GC-MS measurementswere recorded onanHP5890
II, 5971 GC/MSD at 75 eV. Analytical data for the com-
plexes are given in Table 1.
2.2. Preparation of [Cu2(fla)2(PAP)] (5a)
A mixture of Cu(OMe)2 (0.126 g, 1 mmol), flavonol
(0.238 g, 1 mmol) and PAPH2 (0.158 g, 0.5 mmol) in
dichloromethane (30 ml) was refluxed under argon for 4 h.
The dark red solution was allowed to stand for one night. The
red crystalline product was filtered, washed with dichloro-
methane and dried under vacuum. Compound 6a was pre-
pared in a similar manner reacting equimolar amounts of
reagents at room temperature. Compounds 5b and 6b were
prepared similarly from 49-methoxyflavonol.
3. Results and discussion
3.1. Characterization of the complexes
2.3. Preparation of [Cu2(fla)2(OH)(PAPH)] (7a)
In a series of binuclear copper(I) and copper(II) com-
plexes involving tetradentate aminophthalazine ligands the
metal centers are bridged by a diazine entity (_N–N_).
By reacting molar quantities of [Cu(CH3CN)4]ClO4,
flavonol or 49-OMe-flavonol and a half mole quantity of
PAPH2 in acetonitrile with dioxygen at room temperature
the complexes [Cu2(ClO4)2(fla)2(PAPH2)] (4a) and
[Cu2(ClO4)2(49-MeOfla)2(PAPH2)] (4b) were obtained.
Compounds 4a and 4b have very similar IR and electronic
spectra. The presence of a p–pU charge transfer absorption
above 26 000 cmy1 has been used to indicate the presence of
neutral PAPH2, while the observation of a single band below
26 000 cmy1 implies an anionic ligand [21]. Compound 4a
and 4b have charge transfer absorption at 30 200 and 29 400
cmy1 (Table 2), implying the presence of the neutral PAPH2
ligand. The band at 24 783 cmy1 indicates the presence of
the flavonolate ligand [12]. The very weak band at 12 000
cmy1 can be assigned to a d–d transition in the copper(II)
centers. In the IR spectra single NH stretching absorption
occurs at 3315 and 3340 cmy1, suggesting the presence of
one type of NH group. The ligand is therefore expected to
exist in the tautomeric form 3. Two bands associated with
CN stretching frequencies of the neutral ligand are observed
above 1600 cmy1. Similar absorptions were obtained for
copper tetrafluoroborate PAPH2 complexes [18]. Previous
studies have shown that the presence of an IR band above
1000 cmy1, associated with the ring breathing mode of the
pyridine ring in PAPH2, indicates the coordination of this
group to the metal centers [21]. Absorptions at 1011 and
1020 cmy1 indicate the tetradentate coordination of the
PAPH2 ligand in both complexes. The strong absorption at
1557 cmy1 in 4a can be assigned to nCO of the coordinated
flavonolate ligand. The decrease of ;40 cmy1 of the nCO
band compared to that of flavonol is due to chelation and
formation of a stable five-membered ring [12]. Two major
A mixture of [Cu(mes)]5 (0.183 g, 0.2 mmol), flavonol
(0.238 g, 1 mmol) and PAPH2 (0.158 g, 0.5 mmol) in
acetonitrile (30 ml) was stirred at room temperature under
dioxygen for 2 h. The orange product was filtered, washed
with acetonitrile and dried. Compound 8a was prepared sim-
ilarly, reacting equimolar amounts of reagents under argon.
Compounds 7b and 8b were prepared in a similar way from
49-methoxyflavonol.
2.4. Reaction of flavonol with dioxygen in the presence of
copper flavonolate complexes
In a typical procedure, to a solution of [Cu2(ClO4)2-
(fla)2(PAPH2)] (0.111 g, 0.1 mmol) in DMF (20 ml) fla-
vonol (0.119 g, 0.5 mmol) was added and the mixture stirred
under dioxygen at 1008C for 8 h. GC analyses were made to
determine the conversion of the substrate. GC analyses of the
solution after treating with an ether solution of diazomethane
gave the yields of the products. Products were identified by
comparison of their mass spectra with referencespectra[12].
The catalytic reactions were also followed by electronic
spectra in the range 50 000–20 000 cmy1. In these experi-
ments the copper complex and flavonol were dissolved under
argon atmosphere in DMF, and the solution was heated to
1008C. The argon was then replaced with dioxygen and con-
sumption of flavonol was analyzed periodically (about every
10 min) at 29 069 cmy1
.
2.5. Physical measurements
Electronic spectra were recorded with a ShimadzuUV-160
(Carl Zeiss) spectrometer, and IR spectra with a Specord IR-
75 (Carl Zeiss) spectrometer. Magnetic susceptibilitieswere

´
E. Balogh-Hergovich et al. / Inorganica Chimica Acta 256 (1997) 9–14
11
Table 1
Characterization of flavonolato copper phthalazine complexes
Complex
M.p.
Color
Yield
Analytical data a (%)
(8C)
(%)
CHN
4a [Cu2(ClO4)2(fla)2(PAPH2)]
4b [Cu2(ClO4)2(49MeOfla)2(PAPH2)]
5a [Cu2(fla)2(PAP)]
298–300
290–294
300–304
305–308
193–195
196–198
245–250
235–240
190–195
205–210
yellow
yellow
red
88
84
75
72
73
68
74
76
82
85
51.80
(51.71)
50.72
(51.11)
62.97
(63.08)
59.45
(60.69)
64.40
(64.53)
63.20
(63.39)
61.77
(61.86)
60.30
2.79
(2.89)
3.04
(3.08)
3.19
(3.31)
3.33
(3.61)
3.40
(3.61)
3.90
(3.75)
3.47
(3.46)
3.66
7.65
(7.54)
6.99
(7.15)
9.25
(9.19)
8.67
(8.84)
13.40
(13.68)
12.81
(13.05)
8.94
(9.02)
8.61
5b [Cu2(49MeOfla)2(PAP)]
6a [Cu(fla)(PAPH)]
red
orange
orange
orange
orange
yellow
yellow
6b [Cu(49MeOfla)(PAPH)]
7a [Cu2(fla)2(OH)(PAPH)]
7b [Cu2(49MeOfla)2(OH)(PAPH)]
8a [Cu(fla)(PAPH2)]
(60.53)
64.21
(64.44)
62.97
(3.65)
3.57
(3.76)
3.78
(8.47)
13.32
(13.65)
12.83
8b [Cu(49MeOfla)(PAPH2)]
(63.29)
(3.90)
(13.02)
a Theoretical values in parentheses.
IR absorptions are observed at 1103 and 1060 cmy1 associ-
ated with the perchlorate group, suggesting that the anion is
coordinated to copper [20]. For complexes4aand 4bslightly
reduced room temperature magnetic moments are observed
(Table 2), indicative of systems involving weak antiferrom-
agnetic exchange between the metal centers. Efficient bridg-
ing exchange groups are therefore considered to be absent in
these complexes. EPR spectra recorded on solid samples
Table 2
Spectroscopic data of flavonolato copper phthalazine complexes
Complex
Infrared (cmy1
(Nujol)
)
UV–Vis (cmy1
(DMF)
)
meff b (BM)
(r.t.)
g c
4a
4b
5a
5b
6a
6b
7a
7b
8a
8b
3315(NH), 1634, 1612(CN), 1557(CO)
1103, 1068(ClO4), 1011(py)
3340(NH), 1637, 1605(CN), 1556(CO)
1107, 1060(ClO4), 1020(py)
38240(61960), 30211(28870), 24783(32160)
38610(75060), 29411(30780), 24570(31220)
1.56
1.65
1.83
1.74
1.71
1.65
1.41
1.39
diam.
diam.
2.1263
2.1346
2.1132
2.1265
2.0787 d
2.0958
2.1170
2.1273
1614(CN), 1541(CO), 1012(py)
37878(48709), 30120(28058), 24154(32828),
23068(34900), 21367(26094), 12836(67) a
38314(27183), 29673(15020), 24096(17890)
23063(18670), 21505(12670)
37593(30676), 27173(15527), 25445(19896),
24509(20065), 23255sh(13800)
37593(26639), 26954(16149), 25773(16770)
24509(15596), 23207sh(11042)
37593(41887), 30211(25000), 24242(32244)
23174(31580)
37593(44857), 29717(26250), 23809(34642)
23014(37178)
38161(37887), 29325(18616), 27359(18926)
25641(20236), 24509(20581)
37593(28952), 28571(16544), 25773(18805)
24390(19944)
1608(CN), 1549(CO), 1004,
1020(py)
3360(NH), 1614(CN), 1541(CO),
1024w, 1004s(py)
3400(NH, 1608(CN), 1548(CO),
1028s, 1008s(py)
3310(NH), 1614(CN), 1545(CO)
1028w, 1003s(py)
3330(NH), 1608(CN), 1545(CO)
1031s, 1003w(py)
3227(NH), 1614(CN), 1558(CO)
1016w, 988s(py)
3231(NH), 1621(CN), 1548(CO)
1028s, 994s(py)
a CH2Cl2.
b meff per copper atom.
c Solid sample.
d In CH3CN, gHs2.0504, g≤s2.2384, AN s16.5 G.

´
E. Balogh-Hergovich et al. / Inorganica Chimica Acta 256 (1997) 9–14
12
show isotropic spectra, which are not very informative; they
are listed in Table 2. Cyclic voltammetry of complex 4a
(y0.295 and y0.635 V versus SCE) and of 4b (y0.325
and y0.725 VversusSCE)gavetworedoxwavesatnegative
potentials, which may be associated with two-step, one-elec-
tron transfers. Similar results were obtained for binuclear
copper(II) complexes with a macrocyclicligand(y0.52and
y0.91 V versus SCE) [27]. Spectroscopic and other data
indicate complexes 4a and 4b to be binuclear involving two
five-coordinate copper(II) centers bound to the same PAPH2
ligand, two flavonolate ligands, and two monodentate per-
chlorates (Fig. 1). The involvement of the perchlorate anion
in the coordination is not unusual. Five-coordinate cop-
per(II) centers and a monodentate perchloratewereproposed
for the [Cu2(PAPH)(OH)2(H2O)(ClO4)] [20] and
[Cu(bpy)(fla)(ClO4)] [28] complexes.
Fig. 1. Proposed structure for complexes 4a and 4b.
Compund 5a has charge transfer bands at 23 068 and
21 367 cmy1, suggesting the presence of the deprotonated
PAP ligand. The band at 24 154 cmy1 is associated with
flavonolate. The presence of a weak d–d band at 12 800 cmy1
is structurally not very informative. The pyridine ring
breathing absorption in the IR spectrum at 1012 cmy1 is
characteristic of tetradentate coordination of the PAP ligand.
The IR band for nCO of the flavonolate is at 1541 cmy1.A
four-coordinate, binuclear structure is expected for this com-
pound. The magnetic moment supports this structure. Cyclic
voltammetry of the complex shows a one-step redox process
at positive potential (0.675 V versus SCE). Positive redox
potentials have been obtained for binuclear copper(II) com-
plexes of cryptate ligands [29,30] and other ligands with NS
donor sets [31], which have magnetically isolated metalcen-
ters without an oxygen bridging group. The binuclear,
hydroxo-bridged copper(II) complexes of some quadri-
dentate pyridazine and phthalazine thioether ligands exhibit
two-electron transfer at positive potentials as well [14,15].
For the other complexes rather poorly defined cyclic voltam-
mograms were obtained. Compound 5b is suggested to have
a similar structure.
In the reaction between equimolar amounts of Cu(OMe)2,
flavonol and PAPH2 in dichloromethane an orange product,
6a, is formed. Compound 6acontainsthedeprotonatedPAPH
ligand and flavonolate (Table 2). The very weak band at
11 100 cmy1 can be assigned to a d–d transition. The IR band
at 1004 cmy1 can be assigned to coordinated pyridine.
PAPH2 exhibits a pyridine ring breathing absorption at 987
cmy1. Thus both pyridine residues of the ligand are coordi-
nated to copper. The strong absorption at 1541 cmy1 shows
coordination of the flavonolate [12]. A five-coordinatestruc-
ture is suggested for compound 6a, with deprotonated PAPH
and one flavonolate ligand (Fig. 2). This structure requires
the PAPH ligand to be tridentate [21]. The ambient temper-
ature EPR spectrum is isotropic, whilst in acetonitrile at low
temperature an axial spectrum was obtained, very similar to
that obtained for pentacoordinate copper complexes of nitro-
gen-donor ligands [32]. Compound 6b is believed to have a
similar structure.
Fig. 2. Proposed structure for complexes 6a and 6b.
Fig. 3. Proposed structure for complexes 7a and 7b.
Compound 7a was prepared by the reaction of
[Cu(mes)]5, flavonol and PAPH2 in acetonitrile. The charge
transfer region of the electronic spectra exhibits bands of an
anionic PAPH and a flavonolate ligand. The weak d–d band
at 11 400 cmy1 is structurally not very informative. The IR
band at 1545 cmy1 shows the coordination of the flavonol.
The band at 1003 cmy1 indicates the tetradentate coordina-
tion of PAPH. For complex 7a a reduced room temperature
magnetic moment was observed, due to antiferromagnetic
exchange between copper(II) centers. Considerably reduced
magnetic moments are observed forPAPH2 complexeswhere
the copper centers are bridged by oxygen groups, e.g. meth-
oxide or hydroxide [15]. A rather broad weak absorption
around 3600 cmy1 is associated with the hydroxide bridge.
Considering all the data, complex 7a can be represented as a
binuclear system involving two five-coordinate copper(II)
centers, atetradentatePAPH, twoflavonolateandahydroxide
bridge (Fig. 3). Compound 7b is assumed to have a similar
structure.
Reacting molar quantities of [Cu(mes)]5, flavonol and
PAPH2 in acetonitrile under argon a diamagnetic compound,
8a, was obtained. The p–pU transition at 25 641 cmy1 indi-
cates the presence of the neutral PAPH2 ligand. The band at
24 509 cmy1 is associated with flavonolate. The IR band at
1016 cmy1 can be assigned to the ring breathing absorption
of coordinated pyridine. The band at 988 cmy1 shows that
one pyridine ring of the PAPH2 ligand is not coordinated.
The coordination of the flavonol is expected from the nCO at
1558 cmy1. A mononuclear structure with four-coordinate

´
E. Balogh-Hergovich et al. / Inorganica Chimica Acta 256 (1997) 9–14
13
Table 3
Oxygenation of flavonol by flavonolato copper(II) phthalazine complexes
Complex
Time
Solvent
Conversion a
Products a (%)
(h)
(%)
2a
9
10
11
0
[Cu2(8C3lO4)2(7fl8a1)2(PFAP48H4)] (M4a) 8
D
2
[Cu2(fla)2(PAP)] (5a)
[Cu2(fla)2(PAPH)(OH)] (7a)
[Cu(fla)(PAPH)] (6a)
8
8
8
DMF
DMF
DMF
100
69
27
27
32
48
36
34
26
20
25
18
17
9
8
a Determined by GLC.
Fig. 4. Proposed structure for complexes 8a and 8b.
Fig. 5. Time dependence of the consumption of flavonol during the catalytic
oxidation with flavonolato copper phthalazine complexes. [Cu]0s
0.5=10y4 M, [flaH]0s8=10y4 M, pO s1 bar, 1008C, DMF.
2
(6a versus 4a, 5a, 7a) which may be explained by mono-
nuclear or binuclear catalysis. However a detailed kinetic
investigation is necessary to disclose these mechanistic dif-
ferences in the catalytic processes. These are now in progress
in our laboratory. The oxygenation results show howeverthat
copper flavonolate complexes containing phthalazine N-
donor ligands catalyze the oxidative cleavage of 3-hydroxy-
flavone leading to identical products to those found in the
enzyme reaction.
Scheme 1.
copper(I) is expected for complex 8a (Fig. 4). A similar
structure is suggested for compound 8b.
3.2. Dioxygenation of flavonol by flavonolato copper(II)
phthalazine complexes
Catalytic oxygenation of flavonol was carried out using
the flavonolato copper(II) phthalazine complexes discussed
before. Conversions and composition of the products are
shown in Scheme 1 and Table 3.
Acknowledgements
We thank the Hungarian Research Fund (OTKA T-7443,
T-16285 and T-2326) for financial support.
We find now that the oxygenation of flavonol using fla-
vonolato copper(II) phthalazine catalysts resultsinoxidative
cleavage of the heterocyclic ring to give depside (2a) and
CO as primary products. Secondary products derived from
2a such as salicylic acid (9), benzoic acid (10) and N,N-
dimethylbenzamide (11) due to hydrolysis and amidation of
2a by DMF were also formed. The oxidation is selective, no
other products were obtained. Different products were
obtained in the oxidation of flavonol catalyzed by CuCl and
CuCl2 [33,34]. It can be seen from theseresultsthatbinuclear
complexes are better and more selective catalysts than mono-
nuclear ones. The time dependence of the consumption of
flavonol in some of the oxygenation reactions was followed
also spectroscopically (Fig. 5). Preliminarykineticmeasure-
ments of the oxygenation reactions show that the flavonolato
copper(II) phthalazine complexes have a different behavior
References
[1] D.W. Westlake, G. Talbot, E.R. Blakely and F.J. Simpson, Can. J.
Microbiol., 5 (1959) 62.
[2] F.J. Simpson, G. Talbot and D.W.S. Westlake, Biochem. Biophys. Res.
Commun., 2 (1959) 621.
[3] S. Hattori and I. Noguchi, Nature, 184 (1959) 1145.
[4] T. Oka, F.J. Simpson and H.G. Krishnamurthy, Can. J. Microbiol., 16
(1977) 493.
[5] A. Nishinaga, T. Tojo, H. Tomita and T. Matsuura, J. Chem. Soc.,
Perkin Trans. I, (1979) 2511.
[6] V. Rajananda and S.B. Brown, Tetrahedron Lett., 22 (1981) 4331.
[7] T. Matsuura, H. Matsushima and R. Nakashima, Tetrahedron Lett., 26
(1970) 435.
[8] M.M.A. El-Sukkary and G. Speier, J. Chem. Soc., Chem. Commun.,
(1981) 745.

´
E. Balogh-Hergovich et al. / Inorganica Chimica Acta 256 (1997) 9–14
14
[9] A. Nishinaga, T. Tojo and T. Matsuura, J. Chem. Soc., Chem.
[22]
[23]
[24]
[25]
[26]
[27]
D.D. Perrin, W.L. Armarego and W.L. Perrin, Purification of
Laboratory Chemicals, Pergamon, New York, 2nd edn., 1990.
T. Tsuda, T. Yazawa, K. Watanabe, T. Fujii and T. Saegusa, J. Org.
Chem., 46 (1981) 192.
R.W. Adams, E. Bishop, R.L. Martin and G. Winter, Aust. J. Chem.,
19 (1966) 207.
B.J. Hathaway, D.G. Holah and J.D. Postlethwaite, J. Chem. Soc.,
(1961) 3215.
A.B.P. Lever, E.R. Milaeva and G. Speier, in C.C. Leznoff and A.B.P.
Lever (eds.), Phthalocyanines, Vol. 3, VCH, New York, 1993, p. 8.
R.R. Gagne, C.A. Koval and T.J. Smith, J. Am. Chem. Soc., 99 (1977)
8367.
G. Speier et al., unpublished results.
J.-P. Gisselbrecht, M. Gross, A.H. Alberts and J.-M. Lehn, Inorg.
Chem., 19 (1980) 1386.
Y. Agnus, R. Louis, J.-P. Gisselbrecht and R. Weiss, J. Am. Chem.
Soc., 106 (1984) 93.
J.-M. Latour, D. Limosin and P. Rey, J. Chem. Soc., Chem. Commun.,
(1985) 464.
Commun., (1974) 896.
[10] A. Nishinaga, T. Kuwashige, T. Tsutsui, T. MashinoandK.Maruyama,
J. Chem. Soc., Dalton Trans., (1994) 805.
[11] G. Speier, V. Fu¨lo¨p and L. Pa´rka´nyi, J. Chem. Soc., Chem. Commun.,
(1990) 512.
´
[12] E. Balogh-Hergovich, G. Speier and G. Argay, J. Chem. Soc., Chem.
Commun., (1991) 551.
[13] A.B.P. Lever, B.S. Ramaswamy and S.R. Pickens, Inorg. Chim. Acta,
46 (1980) L59.
[14] T.C. Woon, R. McDonald, S.K. Mandal, L.K. Thompson, S.P.Connors
and A.W. Addison, J. Chem. Soc., Dalton Trans., (1986) 2381.
[15] L.K. Thompson, S.K. Mandal, L. Rosenberg, F.L. Lee and E.J. Gabe,
Inorg. Chim. Acta, 133 (1987) 81.
[16] D.V. Bautista, J.C. Dewan and L.K. Thompson, Can. J. Chem., 60
(1982) 2583.
[17] L.K. Thompson, A.W. Hanson and B.S. Ramaswamy, Inorg. Chem.,
23 (1984) 2459.
[18] J.C. Dewan and L.K. Thompson, Can. J. Chem., 60 (1982) 121.
[19] F.W. Hartstock and L.K. Thompson, Inorg. Chim. Acta, 72 (1983)
227.
[20] L.K. Thompson, F.W. Hartstock, L. Rosenberg and T.C. Woon, Inorg.
Chim. Acta, 91 (1985) 1.
[21] L.K. Thompson, V.T. Chacko, J.A. Elvidge, A.B.P. Lever and R.V.
Parish, Can. J. Chem., 47 (1969) 4141.
[28]
[29]
[30]
[31]
[32]
[33]
[34]
A.W. Addison, P.J. Burke, K. Henrick, T.N. Rao and E. Sinn, Inorg.
Chem., 22 (1983) 3645.
M. Utaka and A. Takeda, J. Chem. Soc., Chem. Commun., (1985)
1824.
´
E. Balogh-Hergovich and G. Speier, J. Mol. Catal., 71 (1992) 1.