Synthesis of bis(phosphinoferrocenyl) copper complexes from zwitterionic quinonoid ligands and their structural and redox properties?

Article abstract of DOI:10.1021/ic802042w

Reactions of N,N'-di-n-butyl-2-amino-5-alcoholate-1,4- benzoquinonemonoiminium L¹, or N,N'-diisopropyl-2-amino-5- al∞holate-1,4-benzoquinonemonoiminium L² with [{(dppf)Cu} ₂(μ-CI)₂] (dppf = 1,1'-bis(diphenylphos

Full text of DOI:10.1021/ic802042w

Inorg. Chem. 2009, 48, 2534-2540
Synthesis of Bis(phosphinoferrocenyl) Copper Complexes from
Zwitterionic Quinonoid Ligands and Their Structural and Redox
Properties†
Pierre Braunstein,*,‡ Denis Bubrin,§ and Biprajit Sarkar*,‡,§
Laboratoire de Chimie de Coordination, Institut de Chimie (UMR 7177 CNRS), UniVersite´ de
Strasbourg, 4 rue Blaise Pascal, F-67070 Strasbourg Ce´dex, France, and Institut fu¨r
Anorganische Chemie, UniVersita¨t Stuttgart, Pfaffenwaldring 55, D-70550 Stuttgart, Germany
Received October 24, 2008
Reactions of N,N′-di-n-butyl-2-amino-5-alcoholate-1,4-benzoquinonemonoiminium L1, or N,N′-diisopropyl-2-amino-5-
alcoholate-1,4-benzoquinonemonoiminium L2 with [{(dppf)Cu}2(µ-Cl)2] (dppf ) 1,1′-bis(diphenylphosphino)ferrocene) or
[{(dispf)Cu}2(µ-Cl)2] (dispf ) 1,1′-bis(diisopropylphosphino)ferrocene) led to the formation of the heterodinuclear complexes
[(dppf)(CuL1-H)] (2), [(dppf)(CuL2-H)] (3), [(dispf)(CuL1-H)] (4), and [(dispf)(CuL2-H)] (5). The crystal structure of L2 was
determined by X-ray diffraction and shows that the molecule exists in a 6π + 6π zwitterionic form, with two chemically
connected but electronically nonconjugated π-subunits. The crystal structures of complexes 2-4 show a distorted tetrahedral
coordination environment for the Cu(I) center and a more localized π-system for the ligands. Cyclic voltammetry on the
ligands and complexes indicates various redox processes. The first oxidation of the complexes leads to an electron
paramagnetic resonance supported formulation where the ligand radical is bound to Cu(I). UV-visible spectroscopy of
the ligands and the complexes is also reported and discussed.
Scheme 1
Introduction
The copper/quinone interactions play an important role in
different areas of chemistry1 and are relevant to current
research areas as diverse as biochemical systems,2-4 mo-
lecular devices,5-7 and photochemical charge transfer.8 The
bis-chelating quinonoid ligand 2,5-dihydroxy-1,4-benzo-
quinone (a, Scheme 1) has been much used in coordination
chemistry, and it has allowed the preparation of hundreds
of metal complexes, including molecular boxes for supramo-
lecular chemistry.9
Recently, such ligands have attracted much attention as
spacers in polynuclear complexes because they combine
metal-based and ligand-based redox activity.10-13 The related
ligands (b, Scheme 1) with a N, O, N, O donor set have
†
Dedicated to Prof. Ingo-Peter Lorenz on the occasion of his 65th
birthday, with our warmest congratulations and best wishes.
* To whom correspondence should be addressed. E-mail: braunstein@
also become popular as spacers for the study of metal-metal
interactions14,15 and the formation of magnetic materials16
chimie.u-strasbg.fr.
‡
Universite´ de Strasbourg.
Universita¨t Stuttgart.
and in homogeneous catalysis.17,18 In contrast, the ligands
§
(1) Kaim, W. Dalton Trans. 2003, 761.
(2) da Silva, G. F. Z.; Ming, L.-J. Angew. Chem., Int. Ed. 2007, 46, 3337.
(3) Decker, H.; Schweikardt, T.; Tuczek, F. Angew. Chem., Int. Ed. 2006,
45, 4546.
(10) Ward, M. D. Inorg. Chem. 1996, 35, 1712.
(11) Kitagawa, S.; Kawata, S. Coord. Chem. ReV. 2002, 224, 11.
(12) Leschke, M.; Melter, M.; Lang, H. Inorg. Chim. Acta 2003, 350, 114.
(13) Carbonera, C.; Dei, A.; Le´tard, J.-F.; Sangregorio, C.; Sorace, L.
Angew. Chem., Int. Ed. 2004, 43, 3136.
(4) Lee, Y.; Sayre, L. M. J. Am. Chem. Soc. 1995, 117, 3096.
(5) Pierpont, C. G.; Lange, C. W. Prog. Inorg. Chem. 1994, 41, 331.
(6) Pierpont, C. G. Coord. Chem. ReV. 2001, 216-217, 95.
(7) Hendrickson, D. N.; Pierpont, C. G. Top. Curr. Chem. 2004, 234, 63.
(8) Kunkely, H.; Vogler, A. J. Photochem. Photobiol., A 2002, 147, 149.
(9) Therrien, B.; Su¨ss-Fink, G.; Govindaswamy, P.; Renfrew, A. K.;
Dyson, P. J. Angew. Chem., Int. Ed. 2008, 47, 3773.
(14) Kar, S.; Sarkar, B.; Ghumaan, S.; Janardanan, D.; van Slageren, J.;
Fiedler, J.; Puranik, V. G.; Sunoj, R. B.; Kaim, W.; Lahiri, G. K.
Chem. Eur. J. 2005, 11, 4901.
(15) Cotton, F. A.; Jin, J.-Y.; Li, Z.; Murillo, C. A.; Reibenspies, J. H.
Chem. Commun. 2008, 211.
2534 Inorganic Chemistry, Vol. 48, No. 6, 2009
10.1021/ic802042w CCC: $40.75  2009 American Chemical Society
Published on Web 02/18/2009

Bis(phosphinoferrocenyl) Copper Complexes
with N, N, N, N donor atoms (c, Scheme 1)19 have been
much less used in coordination chemistry,20 with a few new
examples appearing in recent years.19,21-24
p- to the o-quinone form associated with the migration of a
proton from one nitrogen center to another.
Over the past few years our laboratory has developed a
very efficient and facile access to zwitterionic N-substituted
benzoquinonemonoimines (d, Scheme 1).25,26 Following the
synthesis of the first member of this unique family of
molecules,27,28 which are rare examples of potentially
antiaromatic zwitterions being more stable than their canoni-
cal form and have therefore aroused the interest of numerous
theoreticians,28-32 we have developed a very general,
straightforward, and “green” route to prepare such
ligands.25,26 Metalation of these ligands with various metal
complex precursors has shown their potential in homoge-
neous catalysis33 and supramolecular chemistry.26 Further-
more, the possibility of including a donor atom into the R
group of such ligands (d, Scheme 1) and the enhanced
catalytic activity of the resulting metal complexes was also
shown.34 Recently, these ligands have been found to be
exceptionally good facilitators of electronic communication
between two quadruply bonded dimolybdenum units.15
Complexes of Cu(I) with o-quinonemonoimines are known
in the literature.35 In addition, the interactions of the O,O-
chelating o-quinones (including the one-electron reduced
o-semiquinone form) with Cu(I) have been studied in the
context of valence tautomerism and their biological rel-
evance.36-38 To the best of our knowledge, there is only
one Cu(I) complex reported so far with the ligands shown
in Scheme 1, only with ligands of type c.20 This complex,
1, was formed through a metal-induced tautomerism of the
A similar proton migration was also observed with
W(CO)4 complexes of such ligands,39 and these observations
were consistent with earlier studies on the proton dynamics
in azophenine.40,41 Considering the rich potential of the
zwitterionic ligands d (Scheme 1) in coordination and redox
chemistry and the importance of Cu/quinone complexes in
chemistry5,6 and biochemistry,2,3 we set out to react the
ligands L1 and L2 (Scheme 1, d with R ) n-butyl or i-propyl,
respectively) with the diphosphine Cu(I) complexes [{(dppf)-
Cu}2(µ-Cl)2] (dppf ) 1,1′-bis(diphenylphosphino)ferrocene)
and [{(dispf)Cu}2(µ-Cl)2] (dispf ) 1,1′-bis(diisopropyl
phosphino)ferrocene), respectively. We have used dppf and
dispf as ancillary ligands because their redox-active group
and their chelation ability should provide additional stability
to the resulting metal complexes.42 In the following, results
obtained from X-ray crystallography, cyclic voltammetry,
electron paramagnetic resonance (EPR) spectroscopy, and
ultraviolet-visible (UV-vis) spectroscopy on the ligands
and the resulting heterodinuclear complexes will be dis-
cussed.
Results and Discussion
(16) Margraf, G.; Kretz, T.; Fabrizi de Biani, F.; Laschi, F.; Losi, S.;
Zanello, P.; Bats, J. W.; Wolf, B.; Langer, K. R.; Lang, M.; Prokofiev,
A.; Assmus, W.; Lerner, H.-W.; Wagner, M. Inorg. Chem. 2006, 45,
1277.
(17) Zhang, D.; Jin, G.-X. Organometallics 2003, 22, 2851.
(18) Scheuermann, S.; Kretz, T.; Vitze, H.; Bats, J. W.; Bolte, M.; Lerner,
H.-W.; Wagner, M. Chem. Eur. J. 2008, 14, 2590.
(19) Siri, O.; Braunstein, P.; Rohmer, M.-M.; Be´nard, M.; Welter, R. J. Am.
Chem. Soc. 2003, 125, 13793.
Ligand Synthesis. The ligand L2 was synthesized in a
straightforward way from 4,6-diaminoresorcinol dihydro-
chloride and excess of isopropyl amine in water. This
synthesis is similar to that reported earlier for L1 and related
ligands.25,26 The ligands were characterized by H NMR
1
spectroscopy, elemental analysis, and in the case of L2, by
(20) (a) Rall, J.; Stange, A. F.; Hu¨bler, K.; Kaim, W. Angew. Chem., Int.
Ed. 1998, 37, 2681. (b) Braunstein, P.; Demessence, A.; Siri, O.;
Taquet, J.-P. C. R. Chim. 2004, 7, 909.
X-ray crystallography.
(21) Frantz, S.; Rall, J.; Hartenbach, I.; Schleid, T.; Zalis, S.; Kaim, W.
Chem. Eur. J. 2004, 10, 149.
(22) Siri, O.; Taquet, J.-P.; Collin, J.-P.; Rohmer, M.-M.; Be´nard, M.;
Braunstein, P. Chem. Eur. J. 2005, 11, 7247.
(23) Taquet, J.-P.; Siri, O.; Braunstein, P.; Welter, R. Inorg. Chem. 2006,
45, 4668.
(24) Siri, O.; Braunstein, P.; Taquet, J.-P.; Collin, J.-P.; Welter, R. Dalton
Trans. 2007, 1481.
(25) Yang, Q. Z.; Siri, O.; Braunstein, P. Chem. Commun. 2005, 2660.
(26) Yang, Q. Z.; Siri, O.; Braunstein, P. Chem. Eur. J. 2005, 11, 7237.
(27) Siri, O.; Braunstein, P. Chem. Commun. 2002, 208.
(28) Braunstein, P.; Siri, O.; Taquet, J.-P.; Rohmer, M.-M.; Be´nard, M.;
Welter, R. J. Am. Chem. Soc. 2003, 125, 12246.
(29) Sawicka, A.; Skurski, P.; Simons, J. Chem. Phys. Lett. 2002, 362,
527.
(30) Le, H. T.; Nam, P. C.; Dao, Y. L.; Veszpremi, T.; Nguyen, M. T.
Mol. Phys. 2003, 101, 2347.
(31) Delaere, D.; Nam, P. C.; Nguyen, M. T. Chem. Phys. Lett. 2003, 382,
349.
(32) Haas, Y.; Zilberg, S. J. Am. Chem. Soc. 2004, 126, 8991.
(33) Taquet, J.-P.; Siri, O.; Braunstein, P.; Welter, R. Inorg. Chem. 2004,
43, 6944.
(34) Yang, Q. Z.; Kermagoret, A.; Agostinho, M.; Siri, O.; Braunstein, P.
Organometallics 2006, 25, 5518.
(35) Speier, G.; Csihony, J.; Whalen, A. M.; Pierpont, C. G. Inorg. Chim.
Acta 1996, 245, 1.
Crystal data and details of the structure determination are
listed in Table 1. The structural parameters of L2 confirm
its zwitterionic nature, with a fully delocalized π-system
within each of the O1-C1-C2-C3-O2 and N1-C6-C5-
C4-N2 moieties (Figure 1). The corresponding pairs of
C-O, C-N, and C-C bond lengths are very similar (Table
2). The C1-C6 and C3-C4 distances of 1.538(2) and
1.533(2) Å, respectively, correspond clearly to single bonds
and indicate a lack of conjugation between the two “6π
halves” of the ligand which is thus best described as a
zwitterionic 6π + 6π electron molecule.26,28
Synthesis of the Complexes. The precursor complex
[{(dispf)Cu}2(µ-Cl)2] was synthesized from CuCl and dispf
Inorganic Chemistry, Vol. 48, No. 6, 2009 2535

Braunstein et al.
Table 1. Crystal Data and Details of the Structure Determination for L2 and 2-4
crystal data
L2
2
3
4
formula
C12H18N2O2
222.28
orthorhombic
P212121
5.7087(8)
14.096(2)
15.390(3)
90
90
90
1238.5(3)
4
1.192
C48H49N2CuFeO2P2
867.22
monoclinic
P21/n
11.344(4)
23.552(11)
15.910(7)
90
98.34(3)
90
4206(3)
4
1.370
0.97
1808
C46H45N2CuFeO2P2
839.19
monoclinic
P21/n
10.488(2)
23.362(4)
16.579(3)
90
98.600(17)
90
4016.3(14)
4
1.391
1.01
1752
C36H57N2CuFeO2P2
731.17
formula weight (g ·mol-1
)
crystal system
space group
a [Å]
b [Å]
c [Å]
R [deg]
ꢀ [deg]
γ [deg]
V [Å3]
triclinic
j
P1
11.5638(4)
16.3723(7)
20.7837(5)
92.505(2)
105.466(2)
97.362(2)
3748.6(2)
4
Z
density (calcd) [g ·cm-3
]
1.296
1.07
1552
µ(Mo KR) [mm-1
F(000)
]
0.08
480
temperature (K)
θ min–max [deg]
data set [h; k; l]
173(2)
173(2)
173(2)
173(2)
1.96–27.98
0/7; -1/18; -1/20
2003, 1938, 0.027
1624
1938, 160
0.0378, 0.0968, 0.995
2.01–26.00
-13/13; -6/29; -19/19
8672, 8247, 0.086
2528
8247, 478
0.0782, 0.1861, 0.714
1.52–26.00
-3/12; -8/28; -20/20
8854, 7883, 0.077
3744
7883, 491
0.0516, 0.1050, 0.737
2.35–26.00
-13/14; -20/16; -25/25
20834, 14654, 0.040
8449
14654, 815
0.0683, 0.1166, 1.039
tot., unique data, R(int)
observed data [I > 2σ(I)]
No. reflns, No. params
R, wR2, GOF [I > 2σ(I)]
1
by a procedure similar to that already reported for
[{(dppf)Cu}2(µ-Cl)2].43 This compound was characterized
by 1H and 31P{1H} NMR spectroscopy and elemental
analysis. The heterodinuclear bis(phosphinoferrocenyl) cop-
per complexes 2-5 were prepared as outlined in Scheme 2.
Monodeprotonation of L1 or L2 with equimolar amounts of
KOtBu followed by reaction with [{(dppf)Cu}2(µ-Cl)2] or
[{(dispf)Cu}2(µ-Cl)2] afforded the products in high yields.
These complexes were characterized by H and 31P{1H}
NMR spectroscopy and elemental analysis. Metalation of L1
and L2 results in the localization of their π-system (see
discussion of crystal structures below). Slow diffusion of
n-hexane into a dichloromethane solution of 2-4 afforded
crystals suitable for X-ray diffraction. Crystal data and details
of the structure determination are listed in Table 1. Selected
bond lengths and angles are given in Tables 2 and 3,
respectively.
The copper center in complexes 2-4 (Figures 2-4) adopts
a distorted tetrahedral geometry as seen from the O1-Cu-P1
and N1-Cu-P2 angles (103.1(2)° and 116.6(2)° for 2,
107.8(1)° and 120.3(1)° for 3, and 104.6(1)° and 115.4(1)°
for 4, respectively, Table 3). In all three compounds, the
Cu-O1 and Cu-P1 distances are slightly longer than the
Cu-N1 and Cu-P2 distances, and accordingly, the O1-Cu-
P1 angle is smaller than the N1-Cu-P2 angle (Table 3).
In complexes 2-4, examination of the respective bond
distances within the N1-C6-C5-C4-N2 moiety reveals
an alternation of single and double bonds,44 which is
consistent with two conjugated but localized π-systems
(Table 2). This result is in agreement with the localization
of the π-system found in other metal complexes with such
ligands.28,33 In keeping with related crystallographic struc-
tures previously described,26,28,33 the C1-C6 and C3-C4
distances of 1.50(1) Å for 2, 1.520(7) Å and 1.534(7) Å for
Figure 1. Oak Ridge thermal ellipsoid plot (ORTEP) view of L2. Thermal
ellipsoids enclose 50% of the electron density.
Table 2. Comparison among Selected Interatomic Distances (Å) in L2,
2 and 3, and One of the Two Molecules of 2 and 3, and One of the
Two Molecules of 4
L2
2
3
4
(36) Rall, J.; Kaim, W. J. Chem. Soc., Faraday Trans. 1994, 90, 2905.
(37) Rall, J.; Wanner, M.; Albrecht, M.; Hornung, F. M.; Kaim, W. Chem.
Eur. J. 1999, 5, 2802.
(38) Ye, S.; Sarkar, B.; Niemeyer, M.; Kaim, W. Eur. J. Inorg. Chem.
2005, 4735.
(39) Braunstein, P.; Demessence, A.; Siri, O.; Taquet, J.-P. C. R. Chim.
2004, 7, 909.
(40) Rumpel, H.; Limbach, H.-H. J. Am. Chem. Soc. 1989, 111, 5429.
(41) Rumpel, H.; Limbach, H.-H.; Zachmann, G. J. Phys. Chem. 1989,
93, 1812.
(42) Femoni, C.; Iapalucci, M. C.; Longoni, G.; Svensson, P. H.; Zanello,
P.; Fabrizi de Biani, F. Chem. Eur.sJ. 2004, 10, 2318.
(43) Diez, J.; Gamasa, M. P.; Gimeno, J.; Aguirre, A.; Garc´ıa-Granda, S.
Organometallics 1999, 18, 662.
(44) van Bolhuis, F.; Kiers, C. T. Acta Crystallogr., Sect. B: Struct. Sci.
1978, 34, 1015.
Cu-O1
Cu-N1
Cu-P1
Cu-P2
C1-C2
C1-C6
C2-C3
C3-C4
C4-C5
C5-C6
C1-O1
C6-N1
C3-O2
C4-N2
2.084(5)
2.001(8)
2.261(2)
2.245(3)
1.39(1)
1.50(1)
1.42(1)
1.50(1)
1.34(1)
1.43(1)
1.284(9)
1.30(1)
1.243(8)
1.35(1)
2.084(3)
2.062(4)
2.273(2)
2.264(1)
1.385(7)
1.520(7)
1.393(7)
1.534(7)
1.369(6)
1.423(6)
1.292(6)
1.309(6)
1.252(5)
1.342(6)
2.113(3)
2.037(3)
2.269(1)
2.247(1)
1.387(5)
1.514(6)
1.397(5)
1.502(6)
1.376(5)
1.421(5)
1.272(5)
1.313(5)
1.254(4)
1.330(5)
1.398(2)
1.538(2)
1.401(2)
1.533(2)
1.393(2)
1.395(2)
1.251(2)
1.321(2)
1.252(2)
1.322(2)
2536 Inorganic Chemistry, Vol. 48, No. 6, 2009

Bis(phosphinoferrocenyl) Copper Complexes
Scheme 2
Table 3. Selected Bond Angles (deg) in 2 and 3 and One of the Two
Molecules of 4
for 2 and 3, with phenyl substituents on the phosphorus
atoms, occurs at 0.32 and 0.35 V, respectively. This shift
can be explained by the superior donor properties of the
i-propyl group compared to the phenyl group. A similar shift
of all other redox processes to more negative potentials is
also observed on going from 4 or 5 to 2 or 3 (Table 4).
The first oxidation as well as the reduction processes in
the complexes are centered on ligand L1 or L2 (see EPR
section below). The second oxidation is tentatively assigned
to the oxidation of the ferrocene center in the complexes,
by analogy with data for other Cu(I) complexes with the
dppf ligand.45 The second reduction wave observed for the
ligands L1 or L2 is not seen in the complexes, probably
because it lies outside the potential window of the solvent.
In the UV-vis spectrum of L1 or L2, two main bands are
observed at around 350 and 330 nm, with high molar
extinction coefficients (Figure 6, Table 5). Such bands have
been previously observed for a related ligand.28 The first band
is assigned to a π f π* transition and the second one to a
vibrational excitation on top of the electronic transition.29
The complexes also display the intraligand bands observed
for the free ligands. In addition, all the complexes exhibit a
band around 420 nm (Figure 6). This transition is due to a
metal-to-ligand charge transfer (MLCT). The position as well
as the intensity of the bands is very similar for all the
complexes (Table 5).
The electrochemically generated one-electron oxidized
form of the complexes shows an EPR signal at 233 K with
g values around 2.03 (Figure 7, Table 6). The spectra could
be simulated with 14N (I ) 1) couplings of around 6 G and
63,65Cu (I ) 3/2) couplings of around 11 G (Table 6).
Attempts to simulate the EPR spectrum by using two
different N atoms led to the same best fit as when considering
one N atom, probably because of the poor spectral resolution
due to the need to record the EPR spectrum at 233 K. The
g value as well as the hyperfine coupling constants point to
a species with a radical ligand bound to the Cu(I) center, by
analogy with other complexes which have a radical ligand
bound to Cu(I).46 Even though there is a non-negligible
contribution of the Cu center to the singly occupied molecular
orbital (SOMO), the unpaired electron clearly is predomi-
nantly located at the ligand, leading to a formulation
[(dispf)CuI(L1•)]+ for 4+ and similarly for the other com-
plexes.
2
3
4
O1-Cu-N1
O1-Cu-P1
O1-Cu-P2
N1-Cu-P2
N1-Cu-P1
P1-Cu-P2
78.9(3)
103.1(2)
118.9(2)
116.6(2)
122.3(2)
112.02(9)
79.57(14)
107.8(1)
110.0(1)
120.3(1)
122.8(1)
110.19(5)
79.20(12)
104.59(9)
107.94(9)
115.4(1)
125.8(1)
114.38(5)
3, and 1.514(6) Å and 1.502(6) Å for 4, respectively,
correspond to single bonds and indicate the lack of conjuga-
tion between the two 6π-subunits. As reported earlier,
monodeprotonation of ligands of the type L1 or L2 leads to
monometallic complexes where the π-systems become more
localized.33,39 The only Cu(I) complex which was earlier
reported in the literature20 with the N, N, N, N-type ligand
c (Scheme 1), 1, has a different bonding pattern than the
complexes described here. In 1, the chelating N-donor centers
have to adopt a o-quinonediimine form because of proton
migration, whereas such a situation is not necessary for
complexes 2-5 because the ligands L1 and L2 in these
complexes exist in a monodeprotonated form.
Electrochemistry, UV-Vis Spectroscopy, and EPR
Spectroscopy. Ligands L1 and L2 show one irreversible
oxidation and two irreversible reduction waves in CH2Cl2/
0.1 M Bu4NPF6. The reversibility of the cyclic voltammetric
responses did not improve even at lower temperatures or with
higher scan rates. The potentials of the redox processes are
almost identical for both ligands (Table 4).
Complexes 2-5display a reversible oxidation at 233 K
in CH2Cl2/0.1 M Bu4NPF6. They also show a further
irreversible oxidation and an irreversible reduction (Figure
5). All of the processes, including the first oxidation, are
irreversible at room temperature. Compared to the free
ligands, the potentials of the complexes are all shifted to
more negative values (Table 4), confirming the π-donor
character of the Cu(I) center. The effect of the N-substituents
(n-butyl vs i-propyl) on the redox potentials of the complexes
is marginal. On comparing complexes with the same ligands
but different substituents on the phosphorus atoms (2 and 4
for example), one notices a fairly large shift of the redox
potentials. The first oxidation process for 4 and 5, with
i-propyl substituents on the phosphorus atoms, occurs at
-0.09 and -0.03 V, respectively, whereas the same process
(45) Roy, S.; Sieger, M.; Singh, P.; Niemeyer, M.; Fiedler, J.; Duboc, C.;
Kaim, W. Inorg. Chim. Acta 2008, 361, 1699.
Inorganic Chemistry, Vol. 48, No. 6, 2009 2537

Braunstein et al.
Figure 2. ORTEP view of 2. Thermal ellipsoids enclose 30% of the electron density. Isotropically refined atoms are depicted as white spheres with an
arbitrary radius.
Figure 3. ORTEP view of 3. Thermal ellipsoids enclose 50% of the electron density.
Conclusion
of the ligands shows signals typical of a ligand radical bound
to a Cu(I) center. In view of the differences in the ligand
bonding patterns of complex 120 compared to our complexes,
it will be interesting to study the reactions of our ligands
with Cu(I) precursors in the absence of a base. Further studies
are in progress.
The ligands L1 and L2, synthesized from 4,6-diaminore-
sorcinol dihydrochloride and the respective primary amine,
were reacted with the Cu(I) complex [{(dppf)Cu}2(µ-Cl)2]
or [{(dispf)Cu}2(µ-Cl)2], and the heterodinuclear, bis(diphe-
nylphosphino)ferrocene copper complexes 2-5 were ob-
tained in good yields. Whereas the π-system of the free
ligands is delocalized over the upper and lower half of the
molecules, the complexes display increased bond localization.
Cyclic voltammetry of the complexes show ligand- and
ferrocene-centered oxidations and a ligand-centered reduc-
tion. EPR spectroscopy of the one-electron oxidized form
Experimental Section
General Considerations. The ligands were synthesized under
normal atmospheric conditions using reagent grade solvents. For
the metal complexes, all manipulations were carried out using
Schlenk techniques under an argon atmosphere. The solvents used
for metal complex synthesis were dried and distilled under argon
2538 Inorganic Chemistry, Vol. 48, No. 6, 2009

Bis(phosphinoferrocenyl) Copper Complexes
Figure 4. ORTEP view of 4. The unit cell contains two independent but very similar molecules. Thermal ellipsoids enclose 50% of the electron density.
The isopropyl group attached to P2 shows disorder.
Table 4. Redox Potentials of Ligands and Complexesa
b
c
c
compound
E1/2 (ox1)
Epa (ox2)
Epc (red1)
Epc (red2)
L1
L2
2
3
4
0.91b
0.89b
0.32
0.35
-0.09
-0.03
n.o.d
n.o.
0.70
0.68
0.42
0.44
-1.64
-1.62
-1.99
-1.92
-2.43
-2.46
-2.24
-2.19
n.o.
n.o.
n.o.
5
n.o.
a Electrochemical potentials from cyclic voltammetry in CH2Cl2/0.1 M
(Bu4N)PF6 at 233 K. The Fc0/Fc+ couple was used as an internal standard.
b Anodic peak potential for irreversible oxidation. c Cathodic peak potential
for irreversible reduction. d n.o. ) not observed.
Figure 6. UV-vis spectra of L2 (black) and 3 (red) in CH2Cl2.
Table 5. UV-Vis Data of Ligands and Complexes in CH2Cl2
compound
λ (ε)a
L1
L2
2
3
4
332 (29100), 351 (32400), 515sh
336 (29400), 356 (32200), 515sh
330 (32400), 344sh, 422 (10900)
332 (32900), 345sh, 424 (11000)
332 (32500), 348sh, 426 (11200)
334 (32700), 347sh, 420 (10800)
5
a Wavelength in nanometers; molar extinction coefficient in M-1cm-1
.
tometer. Cyclic voltammetry was carried out in 0.1 M Bu4NPF6
solution using a three-electrode configuration (glassy carbon
working electrode, Pt counter electrode, Ag wire as pseudorefer-
ence) and a PAR 273 potentiostat and function generator. The
ferrocene/ferrocenium (Fc/Fc+) couple served as internal reference.
Elemental analyses were performed with a Perkin-Elmer Analyzer
240.
Figure 5. Cyclic voltammogram of 4 in CH2Cl2/0.1 M Bu4NPF6 at 233 K.
Scan rate ) 100 mV/s. The Fc0/Fc+ couple was used as an internal standard.
and degassed by common techniques prior to use. 4,6-Diaminore-
sorcinol dihydrochloride was purchased from Acros, CuCl and 1,1′-
bis(diisopropylphosphino)ferrocene from Strem, and 1,1′-bis(diphe-
nylphosphino) ferrocene from Alfa Aesar. The complex [{(dppf)-
Cu}2(µ-Cl)2]43 and the ligand L1 were prepared according to
reported procedures.25,26
Synthesis of N,N′-Diisopropyl-2-amino-5-alcoholate-1,4-benzo-
quinonemono iminium (L2). 4,6-Diaminoresorcinol dihydrochloride
(0.500 g, 2.35 mmol) was dissolved in water (7 mL), and an excess
of isopropylamine (7 equiv) was added dropwise to this solution.
The solution was stirred under air for 90 min. The purple precipitate
thus formed was filtered, washed with cold water, and dried in air.
Instrumentation. The 1H and 31P{1H} NMR spectra were
recorded at 250.13 and 101.26 MHz, respectively, on a Brucker
AC250 instrument. EPR spectra in the X-band were recorded with
a Bruker System EMX. UV-vis near-infrared (NIR) absorption
spectra were recorded on a Shimadzu UV 3101 PC spectropho-
1
3
Yield: 0.365 g (70%). H NMR (CDCl3, 298 K) δ: 1.34 (d, J )
6.5 Hz, 12H, CH3-CH-NH), 3.84 (sept., 2H, CH3-CH-NH), 5.12
Inorganic Chemistry, Vol. 48, No. 6, 2009 2539

Braunstein et al.
-16.2. Anal. Calcd for C46H45N2CuFeO2P2: C, 65.84; H, 5.40; N,
3.34. Found: C, 65.51; H, 5.61; N, 3.19%.
Synthesis of [(dispf)Cu(L1)] (4). This compound was synthe-
sized similarly to [(dppf)Cu(L1)] by using [{(dispf)Cu}2(µ-Cl)2]
and L1. Yield: 75%. 1H NMR (CDCl3, 298 K) δ: 0.94 (t, 3J ) 7.3
3
Hz, 3H, CH3-CH2-CH2-CH2-NH), 0.99 (t, J ) 7.4 Hz, 3H,
3
3
CH3-CH2-CH2-CH2-N), 1.07 (dd, JHH ) 7.1 Hz, JPH ) 14.3
Hz, 12H, P-CH-CH3), 1.20 (dd, 3JHH ) 7.1 Hz, 3JPH ) 14.7 Hz,
12H, P-CH-CH3), 1.37-1.85 (m, 8H, CH3-CH2-CH2-CH2),
2.07 (m, 4H, P-CH-CH3), 3.11 (m, 2H, CH3-CH2-CH2-
CH2-NH), 3.78 (m, 2H, CH3-CH2-CH2-CH2-N), 4.36 (m, br,
8H, ferrocene ring H), 5.20 (s, 1H, N-C-CH), 5.61 (s, 1H,
O-C-CH), 6.32 (t, br, 1H, NH). 31P{1H} NMR (CDCl3, 298 K)
δ: -1.0. Anal. Calcd for C36H57N2CuFeO2P2: C, 59.13; H, 7.86;
N, 3.83. Found: C, 59.28; H, 7.63; N, 3.95%.
Figure 7. X-band EPR spectrum of electrochemically generated 4•+ in
CH2Cl2/0.1 M Bu4NPF6 at 233 K (black ) experimental, red ) simulated).
Table 6. X-Band EPR Data of the Electrochemically Generated First
Oxidized Form of the Complexes at 233 K in CH2Cl2/0.1 M (Bu4N)PF6
a (N)a
a (Cu)a
Synthesis of [(dispf)Cu(L2)] (5). This compound was synthe-
compound
g
sized similarly to [(dppf)Cu(L1)] by using [{(dispf)Cu}2(µ-Cl)2]
2•+
3•+
4•+
5•+
2.0315
2.0320
2.0290
2.0282
6
5.8
6
10.8
11.3
11
and L2. Yield: 70%. 1H NMR (CDCl3, 298 K) δ: 1.06 (dd, 3JHH
)
3
3
7.1 Hz, JPH ) 14.0 Hz, 12H, P-CH-CH3), 1.16 (dd, JHH ) 7.1
6.3
11.2
Hz, 3JPH ) 14.3 Hz, 12H, P-CH-CH3), 1.25 (d, 3J ) 6.5 Hz, 6H,
a Hyperfine coupling constants in gauss obtained from simulation.
3
CH3-CH-NH), 1.41 (d, J ) 6.4 Hz, 6H, CH3-CH-N), 2.10
(m, 4H, P-CH-CH3), 3.59 (m, 1H, CH3-CH-NH), 4.12 (m, 1H,
CH3-CH-N), 4.34 (t, br, 4H, ferrocene ring H), 4.48 (s, br, 4H,
ferrocene ring H), 5.26 (s, 1H, N-C-CH), 5.59 (s, 1H, O-C-CH),
6.26 (d, br, 1H, NH). 31P{1H} NMR (CDCl3, 298 K) δ: -1.4. Anal.
Calcd for C34H53N2CuFeO2P2: C, 58.08; H, 7.60; N, 3.98. Found:
C, 57.91; H, 7.70; N, 4.02%.
(s, 1H, N-C-CH), 5.45 (s, 1H, O-C-CH), 8.09 (s, br, 2H, NH).
Anal. Calcd for C12H18N2O2: C, 64.84; H, 8.16; N, 12.60. Found:
C, 64.65; H, 8.18; N, 12.47%.
Synthesis of [{(dispf)Cu}2(µ-Cl)2]. This compound was syn-
thesized by a procedure identical to that reported for [{(dppf)Cu}2-
1
1
(µ-Cl)2] by using dispf instead of dppf. Yield: 90%. H NMR
(CDCl3, 298 K) δ: 1.27 (m, 48H, CH3), 2.22 (m, br, 8H, CH), 4.26
(s, br, 8H, ferrocene ring H), 4.39 (t, br, 8H, ferrocene ring H).
31P{1H} NMR (CDCl3, 298 K) δ: -1.5. Anal. Calcd for
C44H72Cl2Cu2Fe2P4: C, 51.08; H, 7.01. Found: C, 50.95; H, 7.21%.
Synthesis of [(dppf)Cu(L1)] (2). To solid KOtBu (0.0112 g, 0.10
mmol) in a Schlenk flask was added L1 (0.025 g, 0.10 mmol) and
tetrahydrofuran (10 mL). The color changed immediately from
purple to orange. The solution was stirred overnight at room
temperature under an argon atmosphere, and then the solvent was
removed under vacuum. Then solid [{(dppf)Cu}2(µ-Cl)2] (0.0653
g, 0.05 mmol) and dichloromethane (15 mL) were added. The color
changed immediately to red. The solution was stirred at room
temperature for 4 h. It was then filtered over Celite to remove KCl.
The volume of the solution was reduced by removing dichlo-
romethane under reduced pressure. Finally, a four-fold excess of
n-hexane was added to the solution which was left overnight at 4
°C. The red crystalline material which precipitated was filtered and
Crystal Structure Determination. Single crystals were grown
by layering a dichloromethane solution of the compound with
n-hexane at room temperature (L2) or at 4 °C (2-4). A suitable
crystal was selected under a layer of viscous hydrocarbon oil,
attached to a glass fiber, and instantly placed in a low-temperature
N2 stream. Except for 4, the X-ray intensity data were collected at
173 K using a Siemens P4 diffractometer. For 4, the intensity data
were collected at 173(2) K on a Kappa CCD diffractometer
˚
(graphite monochromated Mo-KR radiation, λ ) 0.71073 A).
Calculations were performed with the SHELXTL PC 5.0347 and
SHELXL-97 program48 system installed on a local PC. The
2
structures were solved by direct methods and refined on Fo by
full-matrix least-squares refinement. Unless otherwise stated, aniso-
tropic thermal parameters were included for all non-hydrogen atoms.
Acknowledgment. We are grateful to the Ministe`re de la
Recherche (Paris) for a postdoctoral grant to B.S. and to the
CNRS and the ANR (07-BLAN-0274-04) for funding. B.S. is
also indebted to the Landesstiftung Baden-Wu¨rttemberg for
financial support through the Eliteprogramme for Postdocs and
to Kathrin Schellmann for experimental help. We thank Dr. R.
1
washed with n-hexane. Yield: 0.035 g (85%). H NMR (CDCl3,
298 K) δ: 0.63 (t, 3J ) 7.3 Hz, 3H, CH3-CH2-CH2-CH2-NH),
3
0.93 (t, J ) 7.3 Hz, 3H, CH3-CH2-CH2-CH2-N), 1.02-1.72
Pattacini for crystal structure determination of 4.
(m, 8H, CH3-CH2-CH2-CH2), 3.09 (m, 2H, CH3-CH2-CH2-
CH2-NH), 3.35 (m, 2H, m, 2H, CH3-CH2-CH2-CH2-N), 4.26
(s, br, 4H, ferrocene ring H), 4.33 (s, br, 4H, ferrocene ring H),
5.16 (s, 1H, N-C-CH), 5.65 (s, 1H, O-C-CH), 6.32 (t, br, 1H,
NH), 7.20-7.55 (m, 20H, phenyl H). 31P{1H} NMR (CDCl3, 298
K) δ: -15.3. Anal. Calcd for C48H49N2CuFeO2P2: C, 66.48; H, 5.69;
N, 3.23. Found: C, 66.25; H, 5.73; N, 3.38%.
Supporting Information Available: Crystallographic data for
all structures in this paper in CIF format. This material is available
free of charge via the Internet at http://pubs.acs.org. Files have been
deposited with the Cambridge Crystallographic Data Centre, CCDC
705553-705556. Copies of this information may be obtained free
of charge from The Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, U.K. (fax, +44-1223-336033; e-mail, deposit@ccdc.
cam.ac.uk; online, http://www.ccdc.cam.ac.uk).
Synthesis of [(dppf)Cu(L2)] (3). This compound was synthesized
similarly to [(dppf)Cu(L1)] but using L2 instead of L1. Yield: 80%.
1H NMR (CDCl3, 298 K) δ: 0.86 (d, 3J ) 6.4 Hz, 6H,
IC802042W
3
CH3-CH-NH), 1.23 (d, J ) 6.5 Hz, 6H, CH3-CH-N), 3.55
(46) Schwach, M.; Hausen, H.-D.; Kaim, W. Chem. Eur. J. 1996, 2, 446.
(47) SHELXTL PC 5.03; Siemens Analytical X-Ray Instruments Inc.:
Madison, WI, 1994.
(48) Sheldrick, G. M. Program for Crystal Structure Solution and Refine-
ment; Universita¨t Go¨ttingen: Go¨ttingen, 1997.
(m, 1H, CH3-CH-NH), 3.81 (m, 1H, CH3-CH-N), 4.34 (d, br,
4H, ferrocene ring H), 4.36 (d, br, 4H, ferrocene ring H), 5.18 (s,
1H, N-C-CH), 5.64 (s, 1H, O-C-CH), 6.24 (d, br, 1H, NH),
7.25-7.52 (m, 20H, phenyl H). 31P{1H} NMR (CDCl3, 298 K) δ:
2540 Inorganic Chemistry, Vol. 48, No. 6, 2009