Stable mixed phenanthroline copper(I) complexes. Key building blocks for supramolecular coordination chemistry

Article abstract of DOI:10.1039/a701509g

A simple procedure is presented that is used to synthesise, for the first time, pure mixed phenanthroline copper(I) complexes that do not exchange ligands.

Full text of DOI:10.1039/a701509g

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Stable mixed phenanthroline copper(i) complexes. Key building blocks for
supramolecular coordination chemistry†
Michael Schmittel* and Andrea Ganz
Institut fu¨r Organische Chemie der Universita¨t Wu¨rzburg, Am Hubland, D-97074 Wu¨rzburg, Germany
A simple procedure is presented that is used to synthesise,
for the first time, pure mixed phenanthroline copper(I)
complexes that do not exchange ligands.
Indeed, after mixing 1 equiv. of 2a with [Cu(MeCN)4]+ at
280 °C in CD2Cl2 and adding 1 equiv. of 1a complex
[Cu(1a)(2a)]+ formed almost quantitatively. However, upon
raising the temperature (T > 250 °C) increased formation of
[Cu(1a)2]+ was observed. Mixing [Cu(2a)2]+ with 2 equiv. of
ligand 1a led to formation of the mixed complex [Cu(1a)(2a)]+
besides the symmetrical complex [Cu(1a)2]+ in a ratio of 1:2
remaining constant at 220 °C over several days. Apparently,
the thermodynamics of the copper(i) complex equilibria follows
qualitatively the course depicted in Fig. 1, but isolation of
[Cu(1a)(2a)]+ is precluded because of the rather low barrier for
[Cu(1a)(2a)]+ ? [Cu(1a)2]+.
Our current interest in the coordination chemistry of phenan-
throline ligands1–7 stems from their fascinating potential to
allow for the construction of the novel redox-active structures A
as well as nanotubes B (Scheme 1) through the simple self-
assembly of (i) CuI as coordinating metal ion with a tetrahedral
geometry, (ii) a macrocyclic bisphenanthroline with exo-
coordination sites, and (iii) either a macrocyclic bisphenanthro-
line with endo-coordination sites (for A) or linear 3,8-linked
oligophenanthrolines (for B).
As a prerequisite for the successful construction of such
novel topologies a strategy is needed for the defined synthesis of
mixed phenanthroline copper(i) complexes according to eqn.
(1) while avoiding the formation of the two symmetrical
complexes, eqn. (2).
From the above results the use of 2,9-disubstituted phenan-
throlines 1b–d is proposed the steric congestion of which
through larger groups (X = Me, OMe) precludes formation of
symmetrical complexes [Cu(1)2]+. Indeed, when we reacted
[Cu(MeCN)4]+ with 2 equiv. of sterically encumbered 2,9-di-
substituted phenanthrolines 1b–d, formation of [Cu(1b–d)2]+
was not observed! Now the reaction of [Cu(MeCN)4]+ with 1
equiv. of each, 1b–d and 2a–c, resulted in the almost
L1 + L2 + Cu+ ? [CuL1L2]+
(1)
(2)
2 L1 + 2 L2 + Cu+ ? [CuL1 ]+ + [CuL2 ]+
2
2
R
Remarkably, there is no report so far on the clean formation
of mixed-phenanthroline copper(i) species8 except for oli-
gomeric phenanthroline complexes9 and in cases where the
geometrical constraints of a phenanthroline with endo-coordi-
nation sites embedded in a cyclic ring system prevent formation
of symmetrical complexes3,10 according to eqn. (2).
Z
X
R′
X
X
N
N
N
N
Herein, we report, for the first time, on a general strategy to
synthesise mixed phenanthroline copper(i) complexes using
acyclic ligands and its use for the preparation of a model
complex of A demonstrating the feasibility of our approach.
The synthesis of phenanthrolines 1–4 is straightforward,11–14
or is described elsewhere.15 As expected, the symmetrical
copper(i) complexes [Cu(1a)2]BF4 and [Cu(2a)2]BF4 formed
quantitatively within seconds by mixing 2 equiv. of the ligands
with [Cu(MeCN)4]BF4 in MeCN.16
R′
Z
X
R
1a Z = Ph, X = H
b Z = H, X = Me
c Z = H, X = OMe
d Z = Me, X = Me
2a R = H, R′ = H
b R = C≡CH, R′ = H
c R = H, R′ = C≡CH
O
O
O
N
N
In order to synthesise mixed complexes of type [CuL1L2]+
several mechanistic investigations using low-temperature NMR
techniques on the influence of solvent, temperature and
sequence of addition of the phenanthroline ligand were
undertaken. The results proposed that the preparation of the
mixed-ligand complex could possibly be achieved by adding 1
equiv. of the 4,7-disubstituted 2a to [Cu(MeCN)4]+ followed by
addition of 1a at low temperature in dichloromethane as solvent.
O
O
O
O
O
3
O
O
O
O
O
O
N
N
N
N
2,9-disub. phen
4,7-disub. phen
3,8-disub. phen
4,7-disub. phen
+
+
(e.g. Cu )
O
O
O
+
+
(e.g. Cu )
M
M
B
A
Scheme 1 Schematic representation of the ball-type structure A and
nanotube B as examples of interesting topologies resulting from mixed
phenanthroline copper(i) complexes with tetrahedral coordination
O
O
O
O
4
Chem. Commun., 1997
999

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Me
Me
Me
Me
O
O
O
O
O
Me
N
O
Me
N
O
N
N
N
N
+
+
Cu
Cu
O
N
O
N
Me
Me
O
O
O
O
O
O
Me
Me
Me
Me
[Cu2(1d)2(4)]2+
2,9-disubstituted phenanthrolines with X = Me or OMe,
however, we have prevented the formation of [Cu(1b–d)2]+ and
forced the system to form the mixed-ligand complexes solely.
As a consequence of such controlled ligand exchange processes
the straightforward self-assembly of structures A and B should
now be possible.
Financial support from the DFG and the Fonds der Chem-
ischen Industrie is gratefully acknowledged. We are grateful to
Professor Dr U. Lu¨ning (Kiel) for the generous gift of
phenanthrolines 1b, c and to Dr M. Hederich and Professor Dr
P. Schreier (Wu¨rzburg) for recording the ESIMS spectra.
E
relative
2
1
L
L
= 2a–c
= 1a
2
+
[CuL
]
2
1
2 +
[CuL L ]
1
+
[CuL
]
2
reaction coordinate
Fig. 1 Energy diagram for the complexation equilibria of [CuL1L2]+
complexes in solution
Footnotes
Table 1 Half-wave potentials E1/2 (V vs. Fc–Fc+)‡ of mixed-ligand
copper(i) complexes determined by cyclic voltammetry in dichloromethane
at v = 100 mV s21 (electrolyte: NBun4PF6) and yields after purification
* E-mail: mjls@chemie.uni-wuerzburg.de
† New building blocks for sensors and supramolecular arrays, Part 4; for
Part 3 see ref. 7(a).
‡ All potentials are referred to the ferrocene–ferrocenium redox couple. By
addition of +0.39 V the values vs. SCE can be obtained.
Copper(i) complex
Yield (%)
E1/2
DEp/mV
References
[Cu(1a)2]BF4
[Cu(2a)2]BF4
95
83
86
97
86
81
92
+0.40
20.05
+0.36
+0.04
+0.30
+0.21
+0.20
70
150a
60
70
70
130a
220a
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[Cu(1c)(2a)]BF4
[Cu(1d)(2a)]BF4
[Cu(1d)(3)]BF4
[Cu2(1d)2(4)][BF4]2
a Large peak broadening because of slow heterogeneous electron transfer.
quantitative formation of the unsymmetrical complexes
[Cu(1b–d)(2a–c)]+ that could easily be isolated at room
temperature. All compounds were characterised by NMR,
elemental analysis and/or ESI mass spectra.
Cyclic voltammetry investigations on the novel mixed
complexes revealed fully or quasi-reversible waves for CuI "
CuII indicating that the complexes remain intact despite the
redox process.
The mixed-complex preparation technique was then used for
the first time with macrocyclic phenanthroline ligands with exo-
coordination sites in order to probe our concept for the
preparation of precursors to the novel supramolecular systems
A and B. Reaction of [Cu(MeCN)4]+ with 1 equiv. of 3 and 1c
or 1d each provided [Cu(1c)(3)]+ and [Cu(1d)(3)]+, whereas
with 1 equiv. of 4 and 2 equiv. of 1d the complex
[Cu2(1d)2(4)]2+ was furnished.
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immediate formation of a mixture of [Cu(1d)(2a)]+ and
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phenanthroline 1d to the complex [Cu(1c)(3)]+ also led to a
mixture of [Cu(1d)(3)]+ and unreacted [Cu(1c)(3)]+ in a ratio of
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Received in Cambridge, UK, 4th March 1997; Com.
7/01509G
1000
Chem. Commun., 1997