First Schiff base of vinylamine and an a-diketone: A novel N,N donor ligand with extensive conjugation. Synthesis, properties and its copper(i) complexes f

Article abstract of DOI:10.1039/a909726k

Exhaustive methylation of 8,8a-diphenyl-l,2,3,5,6,8a-hexahydroimidazo[l,2-fl]pyrazine by NaH and CH3I in dehydrated tetrahydrofuran yielded 4,5-diphenyl-3,6-diazaocta-l,3.5,7-tetraene (i). Using 1 as an N,N donor ligand, cationic copper(i) complexes of the type [Cu(l)j]X-H₂O (X^- = C1O^4-, n = 1.5; X^- = PF6~, n = 0) and [Cu(l)(PPh3)2]X (X' = C1O4₄^- or PF₆^-) have been synthesized. Compound 1 and its copper(i) complexes have been thoroughly characterised by 'H NMR (300 MHz). The Cu^m potential in [Cu(l)2]X-H₂O is rather high, 0.92 V vs. SCE in CH2C12 at a glassy carbon electrode. This indicates that 1 is a potential n acid which preferentially stabilises copper(i) much more than copper(n). It is photoluminescent in fluid solution, its emission being somewhat quenched in [Cu(1)₂]X-mH₂O. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/a909726k

View Article Online / Journal Homepage / Table of Contents for this issue
First Schiff base of vinylamine and an ꢀ-diketone: a novel N,N
donor ligand with extensive conjugation. Synthesis, properties
and its copper(I) complexes†
Goutam K. Patra, Susanta Samajdar and Dipankar Datta*
Department of Inorganic Chemistry, Indian Association for the Cultivation of Science,
Calcutta 700 032, India. E-mail: icdd@mahendra.iacs.res.in
Received 10th December 1999, Accepted 5th April 2000
Published on the Web 26th April 2000
Exhaustive methylation of 8,8a-diphenyl-1,2,3,5,6,8a-hexahydroimidazo[1,2-a]pyrazine by NaH and CH3I in
dehydrated tetrahydrofuran yielded 4,5-diphenyl-3,6-diazaocta-1,3,5,7-tetraene (1). Using 1 as an N,N donor
Ϫ
Ϫ
ligand, cationic copper() complexes of the type [Cu(1)2]XؒnH2O (XϪ = ClO4 , n = 1.5; XϪ = PF6 , n = 0) and
[Cu(1)(PPh3)2]X (XϪ = ClO4Ϫ or PF6 ) have been synthesized. Compound 1 and its copper() complexes have
Ϫ
been thoroughly characterised by 1H NMR (300 MHz). The CuII/I potential in [Cu(1)2]XؒnH2O is rather
high, 0.92 V vs. SCE in CH2Cl2 at a glassy carbon electrode. This indicates that 1 is a potential π acid which
preferentially stabilises copper() much more than copper(). It is photoluminescent in fluid solution, its
emission being somewhat quenched in [Cu(1)2]XؒnH2O.
A few Schiff bases of vinylamines are known.1,2 Since vinyl-
amine is not readily available,3 these have been obtained
circuitously, mainly by thermolysis (dehydrogenation or de-
hydrohalogenation) of appropriate precursors.1,2 Moreover, the
known Schiff bases of vinylamine can in principle be syn-
thesized by condensing it with appropriate monoketones. So
far, no Schiff base of vinylamine is known which can be derived
from an α-diketone. However such Schiff bases are envisaged to
be very important from the co-ordination chemistry point of
view as these can provide novel bidentate N-donor ligands
with extensive conjugation. Herein we report the synthesis
and properties of the first example, 4,5-diphenyl-3,6-diazaocta-
1,3,5,7-tetraene 1, which in principle can be obtained by 1ϩ2
condensation of benzil and vinylamine.
Results and discussion
The novel Schiff base 1 has been obtained as a hemihydrate
during our attempt to methylate 8,8a-diphenyl-1,2,3,5,6,8a-
hexahydroimidazo[1,2-a]pyrazine (DPHP) with sodium hydride
and methyl iodide. A tentative mechanism for the reaction
is proposed in Scheme 1. The reaction can be described
Fig. 1 A line drawing of the stereo view of the minimum energy gas
phase structure of compound 1 as obtained by AM1 calculations
together with the labelling scheme for the vinyl protons.
as exhaustive methylation of DPHP. In this mechanism,
the bridge-head N is proposed to be methylated first yielding
a hitherto unknown triaza macrocycle 7-methyl-2,3-diphenyl
1,4,7-triazanona-1,3-diene. Subsequently this
N atom is
proposed to undergo further methylation and finally leaves
as trimethylamine resulting in 1.
The minimum energy gas phase structure of 1 as obtained
by AM1 calculations4 (using MOPAC, version 1.10) is described
in Fig. 1. The dihedral angle N᎐C–C᎐N is calculated as 98Њ
᎐
᎐
(O᎐C–C᎐O dihedral angle in benzil in the solid state5 is 70Њ).
᎐
᎐
The lone pairs on the two imino N atoms in Fig. 1 are syn to
each other. The other two possible geometric isomers, where the
nitrogen lone pairs can be in anti-anti or in syn-anti orient-
ations, are slightly higher in energy. The 1H NMR spectrum of
1ؒ0.5H2O in CDCl3 (supplementary material) shows that the C2
axis of symmetry predicted theoretically for 1 in the gas phase
Scheme 1 A proposed reaction mechanism.
† Supplementary data available: 300 MHz 1H NMR spectrum of
1ؒ0.5H2O in CDCl3 available from BLDSC (SUPP. NO. 57702, 2 pp.).
See Instructions for Authors, Issue 1 (http://www.rsc.org/dalton).
DOI: 10.1039/a909726k
J. Chem. Soc., Dalton Trans., 2000, 1555–1558
This journal is © The Royal Society of Chemistry 2000
1555

View Article Online
Fig. 3 300 MHz spectrum of [Cu(1)(PPh3)2]ClO4 in CDCl3 (reference:
TMS) in the region δ 5–6. For the assignments of the peaks and the
J values, see Results and discussion.
Fig. 2 300 MHz 1H NMR spectrum of [Cu(1)2]ClO4ؒ1.5H2O in CDCl3
(reference: TMS) in the region δ 5–8. The peak marked by an asterisk is
due to the solvent. For the assignments of the other peaks, see Experi-
mental section.
(Fig. 1) prevails at least in solution. The phenyl protons reson-
ate in the region δ 7.82–7.78 and 7.43–7.37. The double doublet
around δ 6.87 is assigned to HX, the doublet around δ 5.68
with higher J value to the proton trans to HX, i.e. HA, and the
doublet around δ 5.14 with lower J value to the proton cis to
HX, i.e. HB; JAX = 14.4 and JBX = 7.2 Hz; JAB is not observed.
The assignments of the vinyl protons in 1 have been made in
keeping with those in other vinyl compounds.6
In the IR spectrum, compound 1 shows a very strong and
sharp band at 1550 cmϪ1 with no band appearing at an energy
above it up to 2940 cmϪ1. This we assign as ν(C᎐N). The occur-
᎐
rence of the C᎐N stretching frequency at such a low energy is
᎐
due to the conjugation present in 1. This conjugation suggests
that 1 is a potential π acid that can bind a transition metal ion
through the N atoms and stabilise lower oxidation state(s) of
the metal. Accordingly we wanted to synthesize air stable
copper() complexes of 1 in the first instance. Reaction of
Fig. 4 Cyclic voltammogram (scan rate = 50 mV sϪ1) of [Cu(1)2]PF6 in
CH2Cl2 (0.1 mol dmϪ3 Bu4NClO4) at a planar glassy carbon electrode.
complexes [Cu(1)(PPh3)2]X increases to ca. 50% when [Cu-
(CH3CN)4]X, 1 and PPh3 are allowed to react directly in 1:1:2
[Cu(CH3CN)4]X (XϪ = ClO4 or PF6Ϫ) with 1 in 1:2 molar
Ϫ
stoichiometry in dehydrated methanol under
a dry N2
proportion in dehydrated methanol under a dry N2 atmosphere
yields homoleptic copper() complexes of formulation
[Cu(1)2]XؒnH2O (XϪ = ClO4Ϫ, n = 1.5; XϪ = PF6Ϫ, n = 0) which
are bluish black in the solid state. Many copper() complexes
can be prepared by treating a copper() salt with a ligand in
appropriate proportion in dehydrated alcohol in the presence
of the reducing agent hydrazine hydrate, see ref. 7 for an
example. Such a synthetic approach has been found to be
ineffective in our case. Our homoleptic copper() complexes are
quite stable towards aerial oxidation, for at least seven days
in the solid state, about 3 h in methanol and about 6 h in
dichloromethane. If a solution of [Cu(1)2]XؒnH2O is allowed
to stand in air, slowly the intensity of the blue colour
decreases to a faint blue. That the ligand moiety remains intact
in [Cu(1)2]XؒnH2O is evident from the 1H NMR spectrum (see
Experimental section and Fig. 2); the vinyl protons of free
1 are uniformly shifted downfield by ca. 0.3 ppm on binding
CuI with the J values remaining more or less unchanged. The
bis complexes of copper(), [Cu(1)2]XؒnH2O, show an intense
MLCT band in solution around 615 nm giving rise to a deep
blue colour. The rather low energy of this band indicates the
presence of an accessible low-lying π* orbital in 1 which arises
because of the extensive conjugation possible in 1 in the
chelated mode.
atmosphere. It is really interesting that these two phosphine
complexes are completely devoid of the 615 nm band.
However, they do not obey Beer’s law. This can be understood
from their NMR spectra (Fig. 3) which show that in a solution
of [Cu(1)(PPh3)2]X the ligand partially dissociates from
the metal [eqn. (2)]. The NMR spectra of the complexes
[Cu(1)(PPh3)2]ϩ
[Cu(PPh3)2]ϩ ϩ 1
(2)
[Cu(1)(PPh3)2]ClO4 and [Cu(1)(PPh3)2]PF6 are identical with
the phenyl protons and the HX protons resonating in the region
δ 7.96–6.75. Doublets observed (Fig. 3) at δ 5.68 (J = 14.4) and
5.14 (J = 7.0 Hz) are assigned respectively to the HA and HB
protons of free 1. The doublets (Fig. 3) at δ 5.39 (J = 15.0) and
5.04 (J = 7.5 Hz) are respectively assigned to the HA and
HB protons of 1 in the chelated mode. Existence of the
species [Cu(PPh3)2]ϩ, invoked in eqn. (2), is known in the solid
state.8
The electrochemical behaviour of the complexes [Cu(1)2]-
ClO4ؒ1.5H2O and [Cu(1)2]PF6 has been examined by cyclic
voltammetry in dichloromethane at a glassy carbon electrode.
Identical voltammograms are obtained for the two complexes
(Fig. 4). These show a quasireversible CuII/I couple with an E of
₁
₂

In order to assess whether compound 1 is a stronger π acid
than PPh3, we treated [Cu(1)2]XؒnH2O with the phosphine in
1:2 molar proportion in dehydrated methanol under a N2
atmosphere. It is found that PPh3 displaces 1 to give rise to
[Cu(1)(PPh3)2]X (XϪ = ClO4Ϫ or PF6Ϫ) in ca. 30% yield [reaction
(1)]. Subsequently we found that the yield of phosphine
0.92 V vs. SCE (saturated calomel electrode). The peak-to-peak
separation for this couple in cyclic voltammetry varies from 210
to 635 mV as the scan rate is changed from 10 mV sϪ1 to 1 V sϪ1
.
The high potential of the CuII/I couple in [Cu(1)2]XؒnH2O
shows that our ligand 1 is capable of stabilising CuI much more
than CuII. For a ready appraisal of the magnitude of the poten-
tial, we mention that this couple in [Cu(bipy)2]ϩ has a potential
of ca. 0.01 V vs. SCE in 50% 1,4-dioxane–water.9 The highest
potential for the CuII/I couple in a CuIN4 chromophore reported
[Cu(1)2]XؒnH2O ϩ 2 PPh3 →
[Cu(1)(PPh3)2]X ϩ 1 ϩ n H2O (1)
1556
J. Chem. Soc., Dalton Trans., 2000, 1555–1558

View Article Online
were procured commercially. Copper was estimated grav-
imetrically as CuSCN. Microanalyses were performed by a
Perkin-Elmer 2400II elemental analyser. Molar conductance
was determined by a Systronics (India) direct reading conduct-
ivity meter (model 304). The melting point of 1ؒ0.5H2O was
determined by an apparatus from CBC Power System
(Calcutta, India) and is uncorrected. IR spectra (KBr disc) were
recorded on a Perkin-Elmer 783 spectrophotometer, UV–VIS
spectra on a Shimadzu UV-160A spectrophotometer, 1H NMR
spectra (in CDCl3) by a Brucker DPX300 spectrometer and EI
(electron impact) mass spectra on a Finnigan-Mat 1020 instru-
ment. All the photoluminescnce studies were performed in air
using a Hitachi F-4500 spectrofluorimeter. Cyclic voltammetry
was performed at a planar EG&G PARC G0229 glassy carbon
milli electrode using an EG&G PARC electrochemical analysis
system (model 250/5/0) in purified and anhydrous dichloro-
methane under a dry nitrogen atmosphere in conventional three
electrode configurations. Under the experimental conditions
employed here, the ferrocene–ferrocenium couple appears at
0.468 V vs. SCE with a peak-to-peak separation of 114 mV at a
Fig.
5
Emission spectra of compound 1ؒ0.5H2O (——) and
[Cu(1)2]ClO4ؒ1.5H2O (– – – –) in methanol at room temperature on
excitation at 290 nm. The absorbance at 290 nm in both cases is 0.04.
so far is 1.55 V vs. SCE.10 It is now believed that the CuII/I
potential in a CuIN4 chromophore increases with the π acidity
of the ligand and the extent of tetrahedral distortion in the
corresponding CuIIN4 chromophore.9–12 Both the factors may
be operative in our case. Incidentally, so far, we have not been
able to isolate any homoleptic copper() complex of 1. Upon
treating Cu(ClO4)2ؒ6H2O with 1 in 1:2 molar proportion in
dehydrated methanol, initially a light green colour develops
which changes to a faint blue on standing; from the reaction
mixture, finally only the ligand can be recovered.
The Schiff base 1 shows a broad, featureless, intense band at
275 nm in its absorption spectrum in methanol. Upon excita-
tion at 290 nm (within the envelope of the 275 nm band) at
room temperature in methanol it gives rise to a weak emission
band with the maximum at 370 nm (Fig. 5). The emission quan-
tum yield (φ) is determined to be 8.2 × 10Ϫ3 with reference to
2-methylindole.13 This emission is somewhat quenched in the
scan rate of 50 mV sϪ1
.
Syntheses
4,5-Diphenyl-3,6-diazaocta-1,3,5,7-tetraene
hemihydrate
(1ؒ0.5H2O). To a 25 ml solution of 0.56 g (2 mmol) of DPHP,
synthesized by a previously published procedure,20 in dehy-
drated tetrahydrofuran was added 0.072 g (3 mmol) of NaH
and stirred for 3 h. Then the mixture was cooled to 0 ЊC and 0.4
ml of CH3I (6 mmol) was added and stirred for 12 h at 0 ЊC.
After two hours’ of stirring, another 0.4 ml of CH3I was added.
Then the reaction mixture was warmed to room temperature
and filtered. Solvent was removed completely from the filtrate at
room temperature under reduced pressure to obtain a yellow
mass. It was extracted with 50 ml of diethyl ether. The light
yellow ether layer was washed thoroughly thrice with 100 ml of
water and then dehydrated by adding anhydrous sodium sulfate.
Complete removal of ether yielded 1ؒ0.5H2O as a pale yellow
solid. It was recrystallised from n-hexane and stored in the
dark. Yield 0.30 g (55%) mp 100–104 ЊC (Found: C, 80.34; H,
6.34; N, 10.34. C18H17N2O0.5 requires C, 80.26; H, 6.37; N,
10.40%). EI MS: m/z 260 (1ϩ, 42%). IR/cmϪ1 (KBr): 1550vs
copper() complex [Cu(1)2]ClO4ؒ1.5H2O in methanol (λexcitation
,
290 nm; λemission, 370 nm; Fig. 5; φ, 3.3 × 10Ϫ3). The change of
anion from perchlorate to hexafluorophosphate has negligible
effect on φ ([Cu(1)2]PF6 in methanol: λexcitation, 290 nm; λemission
,
370 nm; φ, 3.4 × 10Ϫ3). Quenching of the fluorescence of an
organic fluorophore by a transition metal is a very common
phenomenon; only in some rare cases, transition metals
can induce enhancement of the fluorescence of an organic
fluorophore.14
(C᎐N). δ (300 MHz, CDCl , TMS) 7.82–7.78 (m, 4 H, phenyl),
᎐
H
3
7.43–7.37 (m, 6 H, phenyl), 6.91–6.83 (dd, 2 H, J = 7.2 and 14.4,
HX), 5.68 (d, 2 H, J = 14.4, HA), 5.14 (d, 2 H, J = 7.2 Hz, HB)
and 1.64 (br, H2O). UV–VIS λmax/nm (ε/dm3 molϪ1 cmϪ1):
(CH3OH) 275 (32 300) and 222 (24 800).
Concluding remarks
Here we have shown that methylation of 8,8a-diphenyl-
1,2,3,5,6,8a-hexahydroimidazo[1,2-a]pyrazine yields a new N,N
donor ligand 1 which can be regarded as a 1ϩ2 Schiff base of
benzil and vinylamine. Considering the procedures used by
others to generate molecules which can be called 1 ϩ 1 Schiff
bases of vinylamine and appropriate mono ketones,1,2 we feel
that given the molecule 1 it will not be very easy to devise a
suitable synthetic route. However, a few 1 ϩ 2 Schiff bases of
2,6-diacetylpyridine and some primary amines containing
olefinic groups are known.15 Here we have also demonstrated by
synthesising its bis copper() complexes with a rather high
potential CuII/I couple that 1 is a potential π acid and capable of
stabilising lower oxidation states of a transition metal. This π
acidity arises because of the extensive conjugation present in 1.
In order to determine the π-acid strength of 1 electrochemically
(to be precise, in terms of Chatt’s ligand constant16 and Lever’s
ligand constant17), we are at present engaged in developing its
ruthenium() chemistry.
[Cu(1)2]ClO4ؒ1.5H2O. To a solution of 0.26 g (1 mmol) of
compound 1ؒ0.5H2O in 20 ml of dehydrated methanol, 0.165 g
(0.5 mmol) of solid [Cu(CH3CN)4]ClO4 was added and stirred
for 6 h under a dry N2 atmosphere. (Within 5 min of stirring,
the yellow solution became blue.) Then the reaction mixture
was added to 200 ml of diethyl ether dropwise with constant
stirring. Shining dark microneedles started separating. The
mixture was kept in a refrigerator for 30 min. Then the bluish
black compound was filtered off, washed with 10 ml of diethyl
ether, dried in vacuo over fused CaCl2 and stored in vacuum.
Yield 0.075 g (20%) (Found: C, 60.81; H, 4.89; Cu, 8.91; N,
7.89. C36H35ClCuN4O5.5Cl requires C, 60.81; H, 4.97; Cu, 8.94;
N, 7.88%). IR/cmϪ1 (KBr): 1600br (C᎐N) and 1090vs (br)
᎐
(ClO4). ΛM (CH3OH): 90 ΩϪ1 cm2 molϪ1 (1:1 electrolyte). δH
(300 MHz, CDCl3, TMS) 7.38–7.32 (m, 6 H, phenyl), 7.10–7.08
(m, 4 H, phenyl), 7.22–7.15 (dd, 2 H, J = 7.1 and 14.4, HX), 5.99
(d, 2 H, J = 14.4, HA), 5.43 (d, 2 H, J = 7.1 Hz, HB) and 1.63 (br,
H2O). UV–VIS λmax/nm (ε/dm3 molϪ1 cmϪ1): (CH3OH) 615
(6500), 427 (2000), 293 (23 200) and 214 (39 600); (Nujol mull)
630, 435, 370 and 265 nm.
Experimental
General
The complexes [Cu(CH3CN)4]ClO4 and [Cu(CH3CN)4]PF6
[Cu(1)2]PF6. This was synthesized by a procedure similar to
that described for [Cu(1)2]ClO4ؒ1.5H2O by starting with 0.5
were synthesized by reported procedures.18,19 All other reagents
J. Chem. Soc., Dalton Trans., 2000, 1555–1558
1557

View Article Online
mmol [Cu(CH3CN)4]PF6. Yield 0.145 g (40%) (Found: C,
59.21; H, 4.40; Cu, 8.67; N, 7.71. C36H32CuF6N4P requires C,
59.28; H, 4.42; Cu, 8.72; N, 7.68%). IR/cmϪ1 (KBr): 1600br
(C᎐N), 830vs (br) (PF ). ΛM (CH3OH): 95 ΩϪ1 cm2 molϪ1 (1:1
electrolyte). δH (300 MHz, CDCl3, TMS) 7.39–7.32 (m, 6 H,
phenyl), 7.08–7.06 (m, 4 H, phenyl), 7.22–7.15 (dd, 2 H, J = 7.1
and 14.4, HX), 5.99 (d, 2 H, J = 14.4, HA) and 5.44 (d, 2 H,
J = 7.1 Hz, HB). UV–VIS λmax/nm (ε/dm3 molϪ1 cmϪ1): (CH3-
OH) 618 (7500), 426 (2000), 279 (28 000) and 208 (45 700);
(Nujol mull) 635, 430, 360 and 265 nm.
cmϪ1): (CH3OH; c, 0.056 mol dmϪ3) 460 (1200), 268 (32 600)
and 216 (60 750); (Nujol mull) 475 and 270 nm.
CAUTION: Though while working with the perchlorate
compounds described here we have not met with any incident,
care should be taken in handling them as perchlorates are
potentially explosive. These should not be prepared and stored
in large amounts.
᎐
6
Acknowledgements
D. D. thanks the Department of Science and Technology, New
Delhi, India for financial support.
[Cu(1)(PPh3)2]ClO4. To a solution of 0.26 g (1 mmol) of
compound 1ؒ0.5H2O in 20 ml of dehydrated methanol, 0.165 g
(0.5 mmol) of solid [Cu(CH3CN)4]ClO4 was added and stirred
under a dry N2 atmosphere. Within 5 min of stirring the yellow
solution became blue. After stirring for 1 h, 0.26 g (1 mmol) of
solid PPh3 was added and the reaction stirred for 2 h main-
taining the N2 atmosphere. (Within 2 min of the addition of
PPh3, the blue mixture became reddish.) Then the solvent was
evaporated under reduced pressure at 50 ЊC. The reddish yellow
residue was triturated with diethyl ether to obtain a light yellow
solid. It was filtered off, washed with diethyl ether, dried in
vacuo over fused CaCl2 then recrystallised from dichloro-
methane–hexane (65–70 ЊC fraction from light petroleum).
Yield 0.26 g (≈55%) (Found: C, 68.36; H, 5.00; Cu, 6.62; N,
2.91. C54H46ClCu N2O4P2 requires C, 68.40; H, 4.90; Cu, 6.70;
References
1 Y.-M. Malecot, J.-L. Ripoll and A. Thuillier, J. Chem. Res. (S),
1983, 86 and references therein.
2 M. Sugie, H. Takeo and C. Matsumura, J. Am. Chem. Soc., 1989,
111, 906 and references therein.
3 Y. Hamada, K. Hashiguchi, M. Tsuboi, Y. Koga and S. Kondo,
J. Mol. Spectrosc., 1984, 105, 93 and references therein.
4 M. J. S. Dewar, E. G. Zoebisch, E. F. Healy and J. J. P. Stewart,
J. Am. Chem. Soc., 1985, 107, 3902.
5 C. J. Brown and R. Sadanaga, Acta Crystallogr., 1965, 18, 158.
6 P. S. Kalsi, Spectroscopy of Organic Compounds, Wiley Eastern, New
Delhi, 1993, pp. 238–244.
7 J. P. Naskar, S. Hati, D. Datta and D. A. Tocher, Chem. Commun.,
1997, 1319.
8 H. J. Gysling, Inorg. Synth., 1979, 19, 93.
9 B. R. James and R. J. P. Williams, J. Chem. Soc., 1961, 2007.
10 M. T. Miller, P. K. Gantzel and T. B. Karpishin, Angew. Chem., Int.
Ed., 1998, 37, 1556 and references therein.
11 D. Datta and A. Chakravorty, Inorg. Chem., 1983, 22, 1085.
12 S. Chowdhury, G. K. Patra, M. G. B. Drew, N. Chattopadhyay and
D. Datta, J. Chem. Soc., Dalton Trans., 2000, 235 and references
therein.
N, 2.95%). IR/cmϪ1 (KBr): 1580br (C᎐N) and 1080vs (br)
᎐
(ClO4). ΛM (CH3OH): 101 ΩϪ1 cm2 molϪ1 (1:1 electrolyte). δH
(300 MHz, CDCl3, TMS): 7.96–6.75 (phenyl protons ϩ the HX
protons); other protons, see Fig. 3 and Results and discussion.
UV–VIS λmax/nm (ε/dm3 molϪ1 cmϪ1): (CH3OH; concentration
c, 0.058 mol dmϪ3) 460 (1350), 268 (31 000) and 214 (55 400);
(Nujol mull) 470 and 270 nm.
13 H.-T. Yu, J. Colucci, M. L. McLaughlin and M. D. Barkley, J. Am.
Chem. Soc., 1992, 114, 8449.
14 P. Purkayastha, N. Chattopadhyay, G. K. Patra and D. Datta, Indian
J. Chem., Sect. A, 2000, 39, in press.
15 S. M. Nelson, A. Lavery and M. G. B. Drew, J. Chem. Soc., Dalton
Trans., 1986, 911.
16 D. Datta, J. Chem. Soc., Dalton Trans., 1986, 1907.
17 J. P. Naskar, S. Hati and D. Datta, Proc. Indian Acad. Sci. (Chem.
Sci.), 1996, 108, 101.
18 P. Hemmerich and C. Sigwart, Experientia, 1963, 19, 488.
19 G. J. Kubas, Inorg. Synth., 1979, 19, 90.
[Cu(1)(PPh3)2]PF6. This was synthesized by a procedure
similar to that given for [Cu(1)(PPh3)2]ClO4 by starting with 0.5
mmol [Cu(CH3CN)4]PF6. Yield 0.25 g (≈50%) (Found: C,
65.30; H, 4.69; Cu, 6.45; N, 2.78. C54H46CuF6N2P3 requires C,
65.27; H, 4.67; Cu, 6.40; N, 2.82%). IR/cmϪ1 (KBr): 1590br
(C᎐N) and 830vs (br) (PF ). ΛM (CH3OH): 102 ΩϪ1 cm2 molϪ1
(1:1 electrolyte). δH (300 MHz, CDCl3, TMS): 7.96–6.75
(phenyl protons ϩ the HX protons); other protons, see Fig. 3
and Results and discussion. UV–VIS λmax/nm (ε/dm3 molϪ1
᎐
6
20 S. B. Majumder, M. Mukherjee, G. K. Patra, D. Datta and
M. Helliwell, Acta Crystallogr., Sect. C, 1999, 55, 668.
1558
J. Chem. Soc., Dalton Trans., 2000, 1555–1558