Multistep redox properties of 2,2′-bipyridylboronium substituted ferrocenes

Article abstract of DOI:10.1016/S0022-328X(01)00942-1

A high-yield synthesis and the X-ray crystal structure analysis of the dinuclear complex [FcB(bipy)OC₆H₄O(bipy)BFc](PF₆)₂, 6(PF₆)₂, which consists of two ferrocenyl moieties, two 2,2′-bipyridylboronium substituents and a hydroquinone linker, is described. The compound is perfectly stable toward air and moisture. 6(PF₆)₂ exhibits a ferrocene-centered two-electron oxidation wave and two separate bipyridylboronium-centered two-electron reduction steps. No oxidation of the hydroquinone spacer takes place in the solvent window. 6(PF₆)₂ is thus able to accept or deliver up to six electrons. Attempts to connect two [FcB(bipy)] fragments using glycol rather than hydroquinone as the bridging element gave the mononuclear complex [FcB(bipy)O(CH₂)₂OH]PF₆ only. A similar reaction scheme that was applied for the generation of [FcB(bipy)O(CH₂)₂OH]PF₆ was employed to synthesize the diol {1,1′-[HO(CH₂)₂OB(bipy)]2fc}(PF₆)₂; fc=[(C₅H₄)₂Fe]. This compound is able to store up to five electrons and may find use as a monomer for the generation of cationic, redox-active polyesters and polyurethanes.

Full text of DOI:10.1016/S0022-328X(01)00942-1

Journal of Organometallic Chemistry 637–639 (2001) 390–397
www.elsevier.com/locate/jorganchem
Multistep redox properties of 2,2%-bipyridylboronium substituted
ferrocenes
Li Ding a, Kuangbiao Ma a, Michael Bolte b, Fabrizia Fabrizi de Biani c, Piero Zanello c,
Matthias Wagner a,*
a Institut fu¨r Anorganische Chemie, J.W. Goethe-Uni6ersita¨t Frankfurt, Marie-Curie-Strasse 11, D-60439 Frankfurt (Main), Germany
b Institut fu¨r Organische Chemie, J.W. Goethe-Uni6ersita¨t Frankfurt, Marie-Curie-Strasse 11, D-60439 Frankfurt (Main), Germany
c Dipartimento di Chimica dell’Uni6ersita`, Via Aldo Moro, I-53100 Siena, Italy
Received 17 January 2001; received in revised form 23 April 2001; accepted 23 April 2001
Abstract
A high-yield synthesis and the X-ray crystal structure analysis of the dinuclear complex [FcB(bipy)OC6H4O(bipy)BFc](PF6)2,
6(PF6)2, which consists of two ferrocenyl moieties, two 2,2%-bipyridylboronium substituents and a hydroquinone linker, is
described. The compound is perfectly stable toward air and moisture. 6(PF6)2 exhibits a ferrocene-centered two-electron oxidation
wave and two separate bipyridylboronium-centered two-electron reduction steps. No oxidation of the hydroquinone spacer takes
place in the solvent window. 6(PF6)2 is thus able to accept or deliver up to six electrons. Attempts to connect two [FcB(bipy)]
fragments using glycol rather than hydroquinone as the bridging element gave the mononuclear complex [FcB-
(bipy)O(CH2)2OH]PF6 only. A similar reaction scheme that was applied for the generation of [FcB(bipy)O(CH2)2OH]PF6 was
employed to synthesize the diol {1,1%-[HO(CH2)2OB(bipy)]2fc}(PF6)2; fc=[(C5H4)2Fe]. This compound is able to store up to five
electrons and may find use as a monomer for the generation of cationic, redox-active polyesters and polyurethanes. © 2001
Elsevier Science B.V. All rights reserved.
Keywords: Ferrocene; 2,2%-Bipyridylboronium cations; Oligonuclear complexes; Cyclic voltammetry; X-ray crystal structure analysis
1. Introduction
Similar to the related electron acceptor Diquat (Fig.
1), the 2,2%-bipyridylboronium moieties behave as re-
versible two-step redox systems in DMF solution [9].
Transition metal-based polymers are of considerable
current interest due to the fact that numerous speci-
mens belonging to this class of compounds possess
promising electronic and magnetic properties or show
pronounced non-linear optical effects [1–7]. Among all
the versatile building blocks used today, metallocenes
exhibit particularly intriguing features, and much effort
has been focused on the synthesis of poly(metallocene)s.
Although the discovery of ring-opening polymerization
(ROP) led to a breakthrough in poly(metallocene) syn-
thesis [2], the development of this area still offers
considerable synthetic difficulties.
We have recently reported on the facile synthesis of
ferrocene derivatives bearing up to four 2,2%-bipyridyl-
boronium substituents (A1–A3, Fig. 1) [8].
* Corresponding author. Fax: +49-69-798-29260.
E-mail address: matthias.wagner@chemie.uni-frankfurt.de (M.
Wagner).
Fig. 1. Highly redox-active ferrocene derivatives bearing 2,2%-
bipyridylboronium substituents.
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00942-1

L. Ding et al. / Journal of Organometallic Chemistry 637–639 (2001) 390–397
391
are substituted easily by various nucleophiles (e.g.
amines, alcohols) [8]. Difunctional nucleophiles can
thus be expected to act as efficient bridging elements in
the synthesis of larger aggregates of A.
This paper focuses on the reactions of mono- (1Br)
and diborylated (2Br2) ferrocenes with glycol and hy-
droquinone (Scheme 1).
The resulting complexes will supply valuable infor-
mation about the electrochemical behavior of the mate-
rial. Moreover, they will help to evaluate the
perspective of our approach regarding polymer
synthesis.
2. Results and discussion
2.1. Syntheses
The shortest possible bridge between two borylated
ferrocene units would be a boron–boron bond or a
single atom between the two boron centers. However,
up to now, attempts to connect diborylated ferrocenes
2Br2 via BꢀOꢀB linkers by controlled hydrolysis of their
BꢀBr bonds always led to the ansa-bridged complex
3Br2 as the result of an intra- rather than an inter-
molecular reaction [10]. No polymeric material could be
isolated, irrespective of the experimental conditions ap-
plied. The reaction of 2Br2 with aniline in the presence
of triethylamine, on the other hand, was much slower
and stopped at the monoborylamine stage without for-
mation of diborylamine linkers [11]. For our purposes,
O-nucleophiles thus appear to be superior over N-nu-
cleophiles, however, the size of the bridging unit has to
be increased in order to disfavor ansa-ferrocene
formation.
On the basis of these considerations, two equivalents
of 1Br were treated with one equivalent of glycol and
triethylamine in CH2Cl2. The reaction, which proceeded
reluctantly and was accompanied by the formation of
undesired side products (e.g. CꢀB bond cleavage), gave
the 1:1 complex 4PF6 as a major component of the
resulting mixture. The aimed-for dinuclear aggregates
were not formed. To prove the chemical composition of
4PF6, the bromo derivative 1Br was dissolved in neat
glycol in the presence of triethylamine. The resulting
mixture was added dropwise to an aqueous solution of
NH4PF6. By this method, an analytically pure sample
of the air and moisture stable compound 4PF6 was
obtained in good yield. In an analogous way, 5(PF6)2
can be synthesized from glycol and 2Br2.
Scheme 1. (i)+exc. glycol, r.t.; (ii) +exc. NH4PF6, H2O, r.t. (iii)
+exc. glycol, r.t.; (iv) +exc. NH4PF6, H2O, r.t. (v) +0.5 equivalent
hydroquinone, +one equivalent NEt3, −40 °C; (vi) +exc.
NH4PF6, H2O, r.t. (vii) +one equivalent hydroquinone/NEt3, r.t.
(viii) +exc. NH4PF6, H2O, r.t.
Compounds A, which are highly soluble in polar sol-
vents (e.g. DMF, DMSO, acetonitrile), can thus accept
or deliver three (A1) to nine (A3) electrons [8]. Conse-
quently, oligomeric aggregates of these redox-active
compounds might be useful in the development of
novel electron storage media.
Oligomerization of A might be achieved, for example,
by linking the individual monomers via their boron
atoms. Bromo substituents R at the boron centers of A
As a consequence of the results obtained with the
aliphatic diol, the aryl alcohol hydroquinone was cho-
sen as an alternative bridge to generate the desired
ferrocene-containing aggregates. Reaction of 1Br with
hydroquinone in a molar ratio of 2:1 led to the air- and
moisture-stable dinuclear complex 6Br2. The corre-

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L. Ding et al. / Journal of Organometallic Chemistry 637–639 (2001) 390–397
sponding salt 6(PF6)2 is moderately soluble in polar
solvents like DMSO and acetonitrile. Aiming at the
next higher trimeric complex, we have first isolated
7PF6 from 1Br and hydroquinone (Scheme 1) and then
treated two equivalents of 7PF6/triethylamine with one
equivalent of 2Br2 in acetonitrile. The resulting material
was insoluble in all common solvents and thus not
characterized any further.
the chelating bipy ligands appear at lower field com-
pared to free 2,2%-bipyridine). In the 1H-NMR spec-
trum, the dinuclear complex 6(PF6)2 and the
monomeric compound 7Br exhibit characteristic differ-
ences. The hydroquinone bridge of the former gives rise
to only one resonance [l(1H)=6.03] due to the high
symmetry of the molecular framework, while the 1,4-
phenylene spacer of the latter shows two signals
[l(1H)=6.34 and 6.26] because of its less symmetric
environment. An analogous pattern is observed in the
13C-NMR spectra of both compounds.
2.2. NMR spectroscopy
The 11B-NMR signals of all products reported here
lie in the range from −3.7 to 12.3 ppm, which is
typical of tetracoordinate boron nuclei [12]. The H-
2.3. Molecular structures of 4PF6, 6(PF6)2 and 7PF6 in
the solid state
1
and 13C-NMR spectra of 4PF6, 5(PF6)2, 6(PF6)2 and
7Br exhibit the same general features for the ferrocene
and [B(R)bipy] fragments (bipy: 2,2%-bipyridine): similar
to the starting materials 1Br and 2Br2 [8], the ferrocene
moieties give rise to only one set of signals. The same is
true for the bipy ligands. This finding points towards an
unhindered rotation about the BꢀC and the BꢀO axes
in the respective compounds. All chemical shifts lie in
the usually observed ranges (e.g. the proton signals of
X-ray-quality crystals of 4PF6 (orthorhombic;
Pna21), 6(PF6)2 (monoclinic; P21/c) and 7PF6 (mono-
clinic; P21/c) were grown by gas phase diffusion of
diethyl ether into their acetonitrile solutions (Tables 1
and 2; Figs. 2–4).
As has already been deduced from the NMR spectra,
tetracoordinate boron atoms are present in all the
molecular structures. The dinuclear compound 6(PF6)2
Table 1
Crystal data and structure refinement details of 4PF6, 6(PF6)2 and 7PF6
4PF6
6(PF6)2
7PF6
Empirical formula
Formula weight (g mol−1
Temperature (K)
Crystal system
C22H22BF6FeN2O2P
558.05
173
Orthorhombic
Pna21
C46H38B2F12Fe2N4O2P2×2 C2H3N
1184.17
173
Monoclinic
P21/c
C26H22BF6FeN2O2P×0.5C4H10O
643.15
173
Monoclinic
P21/c
)
Space group
Unit cell dimensions
,
a (A)
18.172(1)
14.506(1)
8.558(1)
90
90
90
2255.9(3)
4
1.643
8.8453(9)
19.484(2)
14.549(1)
90
102.811(4)
90
2445.0(4)
2
1.608
11.393(2)
16.545(2)
14.961(2)
90
91.64(1)
90
2819.0(7)
4
1.515
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
V (A )
3
,
Z
Dcalc (g cm−3
)
Crystal size (mm)
Radiation (Mo–Ka) (A)
Number of total reflections
Number of unique reflections
Rint
0.65×0.25×0.05
0.71073
27502
4461
0.52×0.12×0.08
0.71073
47187
6310
0.097
0.50×0.10×0.10
0.71073
16924
5324
0.077
,
0.055
Number of parameters
320
8.13
344
7.54
376
6.63
v (cm−1
)
Final R1 a[I\2|(I)]
Final R1 a(all data)
Final wR2 b[I\2|(I)]
Final wR2 b(all data)
Goodness-of-fit on F2 c
0.0418
0.0530
0.0937
0.0997
1.067
0.0601
0.1484
0.0905
0.1134
1.015
0.0526
0.1002
0.1094
0.1272
1.025
a R1=ꢀ(ꢁFoꢂ−ꢂFcꢁ)/ꢀꢂFoꢂ.
b wR2=[ꢀw(F2o−F2c)2/ꢀw(F2o)2.
c Goodness-of-fit=[ꢀw(Fo2−F2c)2/(NO−NV)]1/2
.

L. Ding et al. / Journal of Organometallic Chemistry 637–639 (2001) 390–397
393
Table 2
conformations with torsion angles between both pyridyl
rings ranging from 0.3(4) to 3.4(4)°. Coordination of
the small boron centers results in a distortion of the
chelating bipy ligands. In the case of 6(PF6)2, for exam-
ple, the angles C(23)ꢀC(22)ꢀC(32) and C(33)ꢀC(32)ꢀ
C(22) on the outer frame of the aromatic system are
stretched to values of 129.5(3) and 129.2(3)°, respec-
tively. Consequently, the angles N(21)ꢀC(22)ꢀC(32) and
N(31)ꢀC(32)ꢀC(22) on the inside of the five-membered
heterocycle are compressed to values of 109.1(3) and
109.6(3)°, respectively. The B(OR)bipy substituents in
4PF6 and 7PF6 are turned away from the central iron
atom with torsion angles O(1)ꢀB(1)ꢀC(11)ꢀC(12) of
,
Selected bond lengths (A), bond angles (°) and torsion angles (°) of
4PF6, 6(PF6)2 and 7PF6
4PF6
6(PF6)2
7PF6
B(1)ꢀO(1)
1.397(5)
1.570(5)
1.631(5)
1.628(5)
1.352(5)
1.354(5)
1.471(5)
1.434(4)
1.581(5)
1.599(4)
1.609(4)
1.355(4)
1.358(4)
1.460(4)
1.431(5)
1.573(6)
1.613(5)
1.631(5)
1.354(4)
1.347(4)
1.463(5)
B(1)ꢀC(11)
B(1)ꢀN(21)
B(1)ꢀN(31)
N(21)ꢀC(22)
N(31)ꢀC(32)
C(22)ꢀC(32)
N(21)ꢀB(1)ꢀN(31)
N(21)ꢀB(1)ꢀO(1)
N(31)ꢀB(1)ꢀO(1)
N(21)ꢀB(1)ꢀC(11)
N(31)ꢀB(1)ꢀC(11)
O(1)ꢀB(1)ꢀC(11)
B(1)ꢀN(21)ꢀC(22)
B(1)ꢀN(31)ꢀC(32)
N(21)ꢀC(22)ꢀC(32)
N(31)ꢀC(32)ꢀC(22)
C(23)ꢀC(22)ꢀC(32)
C(33)ꢀC(32)ꢀC(22)
O(1)ꢀB(1)ꢀC(11)ꢀC(12)
92.9(3)
113.0(3)
113.4(3)
108.0(3)
111.8(3)
115.4(3)
113.9(3)
113.9(3)
109.1(3)
109.3(3)
128.7(4)
128.9(4)
148.3(4)
94.7(2)
108.5(3)
108.6(3)
112.4(3)
112.4(3)
117.7(3)
113.3(3)
112.6(3)
109.1(3)
109.6(3)
129.5(3)
129.2(3)
−99.9(4)
2.3(3)
93.4(3)
112.5(3)
110.0(3)
113.6(3)
111.3(3)
114.2(3)
113.6(3)
113.8(3)
109.8(3)
109.0(3)
128.3(3)
129.2(3)
40.3(5)
N(21)ꢀC(22)ꢀC(32)ꢀN(31) −3.4(4)
C(23)ꢀC(22)ꢀC(32)ꢀC(33) −4.7(6)
0.3(4)
0.9(7)
2.5(5)
Fig. 3. Plot of 6(PF6)2; thermal ellipsoids are drawn at the 50%
probability level.
Fig. 2. Plot of 4PF6; thermal ellipsoids are drawn at the 50%
probability level.
possesses somewhat shorter BꢀN bond lengths
,
,
[BꢀN(21) 1.599(4) A; BꢀN(31) 1.609(4) A] than the
,
monomeric complexes 4PF6 [BꢀN(21) 1.631(5) A;
,
,
BꢀN(31) 1.628(5) A] and 7PF6 [BꢀN(21) 1.613(5) A;
,
BꢀN(31) 1.631(5) A]. The B(1)ꢀO(1) bonds in the hy-
,
droquinone-containing species [6(PF6)2: 1.434(4) A;
,
7PF6:1.431(5) A] are longer than the boron–oxygen
bond in the glycol derivative 4PF6 [1.397(5) A]. The
2,2%-bipyridylboronium fragments exhibit almost planar
,
Fig. 4. Plot of 7PF6; thermal ellipsoids are drawn at the 50%
probability level. Ether molecule omitted for clarity.

394
L. Ding et al. / Journal of Organometallic Chemistry 637–639 (2001) 390–397
Table 3
Formal electrode potentials (V, vs. SCE) and peak-to-peak separations (mV) for the redox changes exhibited by 4PF6, 6(PF6)2 and 7PF6
Complex
Oxidation processes
Reduction processes
Solvent
a
b
b
b
Ep
E°%
DEp
E°%
DEp
E°%
DEp
4PF6
–
–
+0.45
+0.44
+0.41
+0.50 e
+0.44 e
+0.40
+0.42
+0.49
+0.39
60
63
60
66
61
64
66
60
78
−0.85
−0.84
−0.86
−0.78
−0.86
−1.02
−0.99
–
72
63
50
99
45
64
70
–
−1.48
−1.66 a,b
−1.73 a,b
−1.48 a,b,f
−1.60 a,b,f
−1.71
−1.79 a
–
68
–
–
–
–
66
–
–
DMF c
CH2Cl2
CH2Cl2
DMF c
CH2Cl2
DMF c
CH2Cl2
DMF c
CH2Cl2
d
d
7PF6
6(PF6)2
+1.34 b
–
–
–
–
–
–
d
d
d
A1 g
FcH
–
–
–
–
a Peak-potential value for irreversible process.
b Measured at 0.1 V s−1
.
c [NEt4]PF6 (0.1 mol dm−3) supporting electrolyte.
d [NBu4]PF6 (0.2 mol dm−3) supporting electrolyte.
e Two-electron processes.
f Averaged value (see text).
g R=Me.
148.3(4) and 40.3(5)°, respectively. A different confor-
mation is observed for 6(PF6)2. Here, each Bbipy sub-
stituent is placed in a position close to the central iron
atom of the attached ferrocenyl unit (Fe···COG=
The electrochemical properties of 7PF6 are similar to
those of 4PF6, except for the presence of a further
irreversible anodic process attributable to the oxidation
of the hydroquinone substituent (Table 3). Again, the
reduction processes appear to be accompanied by
chemical complications.
,
3.801 A, COG: center of gravity of the B(1)N(21)-
C(22)C(32)N(31) ring; O(1)ꢀB(1)ꢀC(11)ꢀC(12)=
Finally, Fig. 5, which shows the cyclic voltammetric
behavior of 6(PF6)2 in DMF solution, exhibits a coulo-
metrically measured two-electron oxidation, a first two-
electron reduction wave displaying features of chemical
reversibility and a second irreversible reduction wave
(Table 3). The latter is split into two very close maxima.
The anodic step can easily be assigned to the concomi-
tant oxidation of the two ferrocenyl units, which are
apparently not electronically communicating. Exhaus-
tive two-electron oxidation causes the original violet
solution (umax=545 nm) to turn blue (umax=627 nm).
The cathodic pattern indicates a lack of electronic
interaction between the two bipyridylboronium units,
too, since the first electron addition to the two groups
proceedes simultaneously. Only the second electron ad-
−99.9(4)°). The two FcBbipy moieties in 6(PF6)2 adopt
a sterically favorable s-trans conformation with respect
to the hydroquinone bridge [Fc: (C5H5)Fe(C5H4)].
Both in 4PF6 and in 7PF6, the cationic moiety is
bound to the respective PF−6 counterion via an OH···F
hydrogen bridge.
2.4. Electrochemistry
Paralleling the behavior of A1 (R=Me) [8], complex
4PF6 exhibits both a ferrocene-centered one-electron
oxidation and two separate 2,2%-bipyridylboronium-cen-
tered one-electron reductions (Table 3). In dichloro-
methane, as well as in dimethylformamide solutions,
the oxidation step possesses features of chemical re-
versibility in the short time range of cyclic voltammetry
as well as during macroelectrolysis. Upon one-electron
removal, the original violet solution (umax=528 nm)
assumes the blue color (umax=625 nm) typical of iron-
centered ferrocenium species. The reduction processes
also display features of chemical reversibility in cyclic
voltammetry (Table 3), even though they are affected
by electrode adsorption phenomena, which required
cleaning of the electrode surface after each cycle. In
addition, the second reduction step is accompanied by
chemical complications, which are, however, retarded
in DMF compared to CH2Cl2.
Fig. 5. Cyclic voltammogram recorded at a platinum electrode on a
DMF solution containing [NEt4](PF6) (0.1 mol dm−3) and 6(PF6)2
(0.9×10−3 mol dm−3). Scan rate 0.2 V s−1
.

L. Ding et al. / Journal of Organometallic Chemistry 637–639 (2001) 390–397
395
dition causes a slight coulombic effect. In contrast to
7PF6, no oxidation of the hydroquinone spacer takes
place in the solvent window.
dried in vacuo. Yield: 0.19 g, 67%. X-ray quality crys-
tals were grown by gas phase diffusion of Et2O into an
actonitrile solution of 4PF6 at ambient temperature.
11B-NMR (128.3 MHz, CD3CN): l 9.4 (h1/2=130
1
Hz). H-NMR (400.0 MHz, CD3CN): l 9.01 (d, 2H,
3. Conclusions
3J(HH)=5.0 Hz, bipy-6,6%), 8.65 (m, 4H, bipy-
3,3%,4,4%), 8.13 (vtr, 2H, 3J(HH)=5.0 Hz, bipy-5,5%),
4.20, 3.89 (2×n.r., 2×2H, C5H4), 3.92 (s, 5H, C5H5),
3.47, 3.13 (t, 2×2H, 3J(HH)=4.8 Hz, ꢀCH2CH2ꢀ),
2.66 (br, 1H, OH). 13C-NMR (100.6 MHz, CD3CN): l
146.7 (bipy-4,4%), 145.6 (bipy-2,2%), 145.1 (bipy-6,6%),
130.0 (bipy-5,5%), 123.9 (bipy-3,3%), n.o. (C5H4-ipso),
71.9, 70.8 (C5H4), 69.3 (C5H5), 66.0, 63.5 (ꢀCH2CH2ꢀ).
FABMS: m/z 558 [M+; 4%], 413 [(M+−PF6); 100%].
Anal. Found: C, 47.17; H, 4.22; N, 5.00. Calc. for
C22H22BF6FeN2O2P (558.05): C, 47.35; H, 3.97; N,
5.02.
Complexes 1Br and 2Br2 with one and two
[B(Br)bipy]+ substituents covalently attached to a fer-
rocene core are promising building blocks for the syn-
thesis of larger, highly redox-active aggregates. The
reaction of two equivalents of 1Br with one equivalent
of hydroquinone, for example, gives the dinuclear spe-
cies 6(PF6)2, in which the monomeric units are linked
via their boron atoms by a [ꢀOꢀC6H4ꢀOꢀ] bridge. Ac-
cording to cyclic voltammetry, 6(PF6)2 undergoes three
redox transitions resulting in an overall transfer of six
electrons. From 2Br2 and excess glycol, the 2-hydroxy-
ethoxy substituted complex 5(PF6)2 is obtained. Work
is in progress to polymerize this compound using well-
established polyester or polyurethane chemistry.
4.3. Synthesis of 5(PF6)2
5(PF6)2 was synthesized similar to 4PF6 from 2Br2
(0.28 g, 0.33 mmol), glycol (5 ml), NEt3 (0.07 g, 0.67
mmol) and NH4PF6 (0.22 g, 1.35 mmol).Yield: 0.20 g,
65%.
4. Experimental
11B-NMR (128.3 MHz, CD3CN): l 10.4 (h1/2=230
1
4.1. General considerations
Hz). H-NMR (400.0 MHz, CD3CN): l 9.04 (d, 4H,
3J(HH)=5.0 Hz, bipy-6,6%), 8.64 (m, 8H, bipy-
3,3%,4,4%), 8.13 (vtr, 4H, 3J(HH)=5.0 Hz, bipy-5,5%),
3.97, 3.72 (2×n.r., 2×4H, C5H4), 3.47, 3.08 (m, t,
2×4H, 3J(HH)=4.8 Hz, ꢀCH2CH2ꢀ), 2.79 (br, 2H,
OH). 13C-NMR (100.6 MHz, CD3CN): l 146.8 (bipy-
4,4%), 145.5 (bipy-2,2%), 145.2 (bipy-6,6%), 130.0 (bipy-
5,5%), 123.9 (bipy-3,3%), n.o. (C5H4-ipso), 72.0, 71.3
(C5H4), 65.7, 63.4 (ꢀCH2CH2ꢀ). FABMS: m/z 785
[(M+−PF6); 100%]. Anal. Found: C, 43.67; H, 3.67;
N, 5.88. Calc. for C34H34B2F12FeN4O4P2 (930.06): C,
43.91; H, 3.68; N, 6.02.
All reactions and manipulations of air-sensitive com-
pounds were carried out in dry, oxygen-free Ar using
standard Schlenk ware. Solvents were freshly distilled
under N2 from Na/K alloy-benzophenone (toluene,
hexane) or from CaH2 (CH2Cl2, CH3CN) prior to use.
NMR: JEOL JMN-GX 400, Bruker ACP 200, Bruker
DPX 250 spectrometer. 11B-NMR spectra are reported
relative to external BF3·Et2O. Unless stated otherwise,
all NMR spectra were run at ambient temperature;
abbreviations: s=singlet; d=doublet; t=triplet; vtr=
virtual triplet; m=multiplet; n.r.=multiplet expected
1
in the H-NMR spectrum but not resolved; n.o.=sig-
4.4. Synthesis of 6(PF6)2
nal not observed, bipy=2,2%-bipyridine, ph=phenyl-
ene ring of hydroquinone. Elemental analyses were
performed by the microanalytical laboratory of the
University of Frankfurt. 1Br and 2Br2 were synthesized
according to literature procedures [8].
A slurry of hydroquinone (0.11 g, 0.97 mmol) in 20
ml of CH2Cl2 was treated with neat NEt3 (0.20 g, 1.98
mmol) and cooled to −40 °C. 1Br (0.99 g, 1.93 mmol)
in 40 ml of CH2Cl2 was slowly added, the resulting blue
mixture was allowed to warm to r.t. and stirred for 12
h. Insoluble material was collected on a frit (G3),
dissolved in water (200 ml) and added dropwise to
excess NH4PF6 (0.65 g, 4.00 mmol) in water (50 ml).
The resulting purple precipitate was isolated by filtra-
tion, triturated with Et2O (150 ml) and dried in vacuo.
Yield: 1.30 g, 61%. X-ray quality crystals were grown
by gas phase diffusion of Et2O into an actonitrile
solution of 6(PF6)2 at ambient temperature.
4.2. Synthesis of 4PF6
1Br (0.26 g, 0.51 mmol) was dissolved in glycol (5 ml)
at room temperature (r.t.), and neat NEt3 (0.05 g, 0.50
mmol) was added to the resulting purple solution. The
mixture was stirred for 12 h and diluted with 20 ml of
H2O. The clear purple solution was added dropwise
into an aqueous solution of NH4PF6 (0.17 g, 1.04
mmol), whereupon 4PF6 precipitated as a microcrys-
talline solid. The precipitate was isolated by filtration,
triturated with H2O (3×10 ml) and Et2O (10 ml) and
11B-NMR (64.2 MHz, CD3CN): l 12.3 (h1/2=1625
1
Hz). H-NMR (250.1 MHz, CD3CN): l 9.02 (d, 4H,
3
3J(HH)=5.6 Hz, bipy-6,6%), 8.62 (vtr, 4H, J(HH)=

396
L. Ding et al. / Journal of Organometallic Chemistry 637–639 (2001) 390–397
8.0 Hz, bipy-4,4%), 8.50 (d, 4H, 3J(HH)=8.0 Hz,
bipy-3,3%), 8.10 (m, 4H, bipy-5,5%), 6.03 (s, 4H, ph),
4.25, 3.95 (2×n.r., 2×4H, C5H4), 3.99 (s, 10H,
C5H5). 13C-NMR (62.9 MHz, CD3CN): l 150.9 (ph-
ipso), 146.9 (bipy-4,4%), 145.0 (bipy-2,2%), 144.9 (bipy-
6,6%), 130.0 (bipy-5,5%), 123.6 (bipy-3,3%), 122.0
(ph-CH), n.o. (C5H4-ipso), 71.7, 70.9 (C5H4), 69.1
(C5H5). FABMS of 6(PF6)2: m/z 1102 [M+; 2%], 957
[(M+−PF6); 20%], 812 [(M+−2PF6); 7%]. Anal.
Found: C, 50.33; H, 3.68; N, 5.08. Calc. for
C46H38B2F12Fe2N4O2P2 (1102.07): C, 50.13; H, 3.48;
N, 5.08.
and polarization terms; an empirical absorption cor-
rection was applied [13]. The structure was solved by
direct methods [14] and refined against F2 with full-
matrix least-squares methods [15]. Hydrogen atoms
bonded to C were calculated in ideal positions (riding
model). The hydroxyl-H atom was refined freely. A
total of 320 parameters refined, 13.9 data per parame-
ter, w=1/[|2(Fo2)+(0.0473P)2+1.8562P] where P=
(F2o+2F2c)/3, shift/error B0.001 in the last cycle of
−3
,
refinement, residual electron density +0.613 e A
/
−0.387 e A−3, R1=0.0418, wR2=0.0937 [I\2|(I)],
minimized function was ꢀw((F2o)−(Fc2))2.
,
4.5. Synthesis of 7Br and 7PF6
4.7. Crystal data of 6(PF6)2
A CH2Cl2 (60 ml) solution of 1Br (0.13 g, 0.26
mmol) was added dropwise with stirring at r.t. to
hydroquinone (0.03 g, 0.27 mmol) and NEt3 (0.03 g,
0.30 mmol) in 10 ml of CH2Cl2. The resulting mix-
ture was stirred overnight, whereupon a purple micro-
crystalline solid slowly precipitated. Insoluble material
was collected on a frit, triturated with Et2O (2×20
ml) and dried in vacuo. Yield: 0.10 g, 71%.
A red needle of 6(PF6)2 was mounted on top of a
glass filament on a CCD Diffraction System (Bruker
AXS). Final lattice parameters were obtained by
least-squares refinement of 510 reflections. Data were
collected with a crystal-to-detector distance of 40 mm
(1.78°BqB28.70°). Data were corrected for Lorentz
and polarization terms; an empirical absorption cor-
rection was applied [13]. The structure was solved by
direct methods [14] and refined against F2 with full-
matrix least-squares methods [15]. Hydrogen atoms
were calculated in ideal positions (riding model). A
total of 344 parameters refined, 18.3 data per parame-
ter, w=1/[|2(Fo2)+(0.0382P)2+0.991P] where P=
11B-NMR (64.2 MHz, Me2SO-d6): l −3.7 (h1/2
=
772 Hz). 1H-NMR (250.1 MHz, Me2SO-d6): l 9.45
(d, 2H, 3J(HH)=5.4 Hz, bipy-6,6%), 8.98 (d, 2H,
3J(HH)=8.0 Hz, bipy-3,3%), 8.87 (s, 1H, OH), 8.81
(vtr, 2H, 3J(HH)=8.0 Hz, bipy-4,4%), 8.32 (vtr, 2H,
3J(HH)=6.6 Hz, bipy-5,5%), 6.34 (d, 2H, 3J(HH)=
9.0 Hz, ph-2,6), 6.26 (d, 2H, 3J(HH)=9.0 Hz, ph-
3,5), 4.27, 4.11 (2×n.r., 2×2H, C5H4), 3.99 (s, 5H,
C5H5). 13C-NMR (62.9 MHz, Me2SO-d6): l 152.1
(ph-4), 147.3 (ph-1), 146.4 (bipy-4,4%), 144.6 (bipy-
2,2%), 144.0 (bipy-6,6%), 129.3 (bipy-5,5%), 123.2 (bipy-
3,3%), 120.9 (ph-2,6), 115.6 (ph-3,5), n.o. (C5H4-ipso),
71.1, 69.7, (C5H4), 68.2 (C5H5). Anal. Calcd. for
C26H22BBrFeN2O2 (541.03)×H2O (18.02): C, 55.86;
H, 4.33; N, 5.01. Found: C, 55.50; H, 4.35; N, 5.10.
7Br (0.07 g, 0.13 mmol) was dissolved in 20 ml of
H2O and added to an aqueous solution of NH4PF6
(0.04 g, 0.25 mmol), whereupon 7PF6 precipitated.
The precipitate was isolated by filtration, triturated
with H2O (2×10 ml) and Et2O (10 ml) and dried in
vacuo. X-ray quality crystals were grown by gas
phase diffusion of Et2O into an actonitrile solution of
7PF6 at ambient temperature.
(F2o+2F2c)/3, shift/error B0.001 in the last cycle of
−3
,
refinement, residual electron density +0.425 e A
,
−0.431 e A−3, R1=0.0601, wR2=0.0905 [I\2|(I)],
minimized function was ꢀw((F2o)−(Fc2))2.
,
4.8. Crystal data of 7PF6
A brown–black needle of 7PF6·0.5C4H10O was
mounted on top of a glass filament on a CCD Dif-
fraction System (Bruker AXS). Final lattice parame-
ters were obtained by least-squares refinement of 5419
reflections. Data were collected with a crystal-to-de-
tector distance of 40 mm (1.79°BqB25.68°). Data
were corrected for Lorentz and polarization terms; an
empirical absorption correction was applied [13]. The
structure was solved by direct methods [14] and
refined against F2 with full-matrix least-squares meth-
ods [15]. Hydrogen atoms bonded to C were calcu-
lated in ideal positions (riding model). The
hydroxyl-H atom was refined freely. A total of 376
parameters refined, 14.2 data per parameter, w=1/
[|2(Fo2)+(0.0570P)2+0.6507P] where P=(Fo2 +2F2c)/
4.6. Crystal data of 4PF6
A black needle of 4PF6 was mounted on top of a
glass filament on a CCD Diffraction System (Bruker
AXS). Final lattice parameters were obtained by
least-squares refinement of 7864 reflections. Data were
collected with a crystal-to-detector distance of 50 mm
(1.8°BqB26.02°). Data were corrected for Lorentz
3, shift/error B0.024 in the last cycle of refinement,
−3
,
residual electron density +0.720 e A
, −0.442
e A−3, R1=0.0526, wR2=0.1094 [I\2|(I)], mini-
mized function was ꢀw((F2o)−(Fc2))2.
,

L. Ding et al. / Journal of Organometallic Chemistry 637–639 (2001) 390–397
397
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Acknowledgements
This work was supported by the ‘Deutsche
Forschungsgemeinschaft’ and the ‘Fonds der Chemis-
chen Industrie’. L.D. is grateful to the Alexander von
Humboldt foundation for a postdoc grant. P.Z. ac-
knowledges financial funding by the University of Siena
(PAR 1999).
[11] K. Ma, M. Wagner, unpublished results.
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