Synthesis and electrochemistry of ferrocenyldiazabutadiene metal carbonyl complexes (Fc-DAB)M(CO)4 [M = Cr,Mo,W]

Article abstract of DOI:10.1016/S0020-1693(99)00418-1

The synthesis, characterization (UV-Vis, IR, MS, NMR), and electrochemistry (CV, DPV) of ferrocenyl diazabutadienes and their chromium, molybdenum, and tungsten tetracarbonyl complexes are reported in this study. The properties of these compounds are compared to those of p-methoxyphenyl diazabutadiene analogues, (a) allowing the clear distinction between ferrocene-based and diazabutadiene metal carbonyl localized redox processes in these multimetallic complexes, and (b) showing that the electronic interaction between the peripheral ferrocenyl substituents increases upon complexation to the Group 6 transition metal tetracarbonyl moieties. (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(99)00418-1

www.elsevier.nl/locate/ica
Inorganica Chimica Acta 300–302 (2000) 16–22
Synthesis and electrochemistry of ferrocenyldiazabutadiene metal
carbonyl complexes (Fc-DAB)M(CO)4 [M=Cr,Mo,W]
Benno Bildstein a,*1, Michael Malaun a, Holger Kopacka a, Marco Fontani b,
Piero Zanello b,*2
a Institut fu¨r Allgemeine, Anorganische und Theoretische Chemie, Uni6ersita¨t Innsbruck, Innrain 52a, A-6020 Innsbruck, Austria
b Dipartimento di Chimica dell’Uni6ersita` di Siena, Via Aldo Moro, I-53100 Siena, Italy
Received 25 May 1999; accepted 30 July 1999
Abstract
The synthesis, characterization (UV–Vis, IR, MS, NMR), and electrochemistry (CV, DPV) of ferrocenyl diazabutadienes and
their chromium, molybdenum, and tungsten tetracarbonyl complexes are reported in this study. The properties of these
compounds are compared to those of p-methoxyphenyl diazabutadiene analogues, (a) allowing the clear distinction between
ferrocene-based and diazabutadiene metal carbonyl localized redox processes in these multimetallic complexes, and (b) showing
that the electronic interaction between the peripheral ferrocenyl substituents increases upon complexation to the Group 6
transition metal tetracarbonyl moieties. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Electrochemistry; Chromium complexes; Molybdenum complexes; Tungsten complexes; Ferrocene; Diimine ligands
pounds upon complexation with transition metal frag-
ments. Therefore, it was of general interest to study the
electronic influence of ferrocenyl substituents in these
ligand systems and metal complexes. Here we report on
the synthesis, properties and electrochemical behavior
of metal carbonyl Fc-DAB complexes (Fc-
DAB)M(CO)4 with M=Cr, Mo, W, and the compari-
son of their properties with analogous para-
methoxyphenyl-DAB [p-MeOC6H4-DAB] compounds.
The p-methoxyphenyl moiety has been chosen as the
most ‘ferrocene-like’ reference group because non-linear
optical measurements [6] have shown comparable
donor capacities for ferrocenyl and p-methoxyphenyl
groups.
1. Introduction
The coordination chemistry of 1,4-diaza-1,3-butadi-
ene (R-DAB) ligands has attracted much interest due to
their unusual electron donor and acceptor properties
[1,2] and, more recently, due to their application in
olefin homo- and co-polymerizations [3]. With the latter
goal in mind we have been investigating the use of
N,N%-diferrocenyldiazabutadiene (Fc-DAB; Fc=ferro-
cenyl) in nickel and palladium complexes as precata-
lysts for the cationic polymerization of olefins [4] with
the intention to take advantage of the steric bulk of the
N-ferrocenyl substituents in these complexes to sup-
press chain-termination processes. In addition, Fc-DAB
has been proven to be the key starting material for the
synthesis of N,N%-diferrocenyl-N-heterocyclic Wan-
zlick/Arduengo carbenes [5]. On the other hand, the
presence of two redox-active ferrocenyl groups per
DAB ligand results in conjugated oligometallic com-
2. Results and discussion
2.1. Synthesis and characterization
Scheme 1 gives an overview of the compounds of this
study. The ferrocenyl DAB ligands 1–3 have been
prepared by condensation of glyoxal with the corre-
sponding aminoferrocenes as was recently published [4].
1*Corresponding author. Tel.: +43-512-507 5141; fax: +43-512-
507 2934/2662; e-mail: benno.bildstein@uibk.ac.at
2*Corresponding author. Tel.: +43-512-507 5141; fax: +43-512-
507 2934/2662; e-mail: zanello@unisi.it
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(99)00418-1

B. Bildstein et al. / Inorganica Chimica Acta 300–302 (2000) 16–22
17
(5a,b,c), show an additional long wavelength band (umax
(nm)/m: 5a: 649/7000; 5b: 581/12000, 702/11000; 5c:
578/8400, 729/6300) clearly visible for 5b and 5c but
unresolved in the case of 5a. Obviously this additional
MLCT transition is due to the presence of the N-ferro-
cenyl substituents, but a precise assignment cannot be
given at this point.
The p-acceptor strength of the Fc-DAB ligand is
slightly inferior to that of the p-MeOC6H4-DAB ligand,
as evidenced by the IR wCꢀO frequencies of complexes
5a,b,c in comparison to 6a,b,c (see Section 4). Interest-
ingly, the Fc-DAB complexes 5a,b,c are much more
soluble than the analogous p-MeOC6H4-DAB com-
pounds 6a,b,c, allowing full characterization by NMR
spectroscopy in the case of the former, but preventing
detection of the quaternary 13C NMR signals for 6b
and 6c. In addition, the Fc-DAB complexes 5a,b,c show
the molecular ions in the FAB or EI mass spectra,
respectively, in contrast to p-MeOC6H4-DAB com-
pounds 6a,b,c, which gave only low-mass fragment
signals of no analytical value.
Similarly, p-MeOC6H4-DAB (4), a known compound
[7], was synthesized from p-anisidine and glyoxal. In
contrast to 4 and other purely organic DAB ligands
[1,2] which are yellow to orange compounds, the ferro-
cenyl DAB compounds 13 have an intense dark purple
color (1: umax=524 nm, 2: umax=537 nm [4,5]) indicat-
ing metal-to-ligand charge transfer (MLCT) which is to
be expected for molecules incorporating redox-active
ferrocenyl groups and a DAB backbone with two low-
lying antibonding p* orbitals [8]. In the following, only
the DAB ligand 1 has been used for metal complex
formation, because this ferrocenyl DAB compound is
the most easily available and the 1%-ferrocenyl substi-
tuted ligands 2 and 3 have been synthesized mainly for
increasing the steric bulk of the ligands [4].
Reaction of 1 or 4 with photochemically generated
substitution-labile M(CO)5(THF) (M=Cr, Mo, W)
yielded the corresponding heterometallic complexes
(Fc-DAB)M(CO)4
(5a,b,c)
and
(p-MeOC6H4-
DAB)M(CO)4 (6a,b,c), respectively, as dark green or
blue air-stable compounds.
Fig. 1 shows a comparison of the UV–Vis spectra of
all six metal carbonyl complexes. The compounds (p-
MeOC6H4-DAB)M(CO)4 (6a,b,c) have a moderately in-
tense broad MLCT band centered at 600 nm (umax
(nm)/m: 6a: 619/7000; 6b: 593/10000; 6c: 579/12000),
characteristic for such (R-DAB)M(CO)4 complexes
with an organic R-DAB ligand, and which has been
shown to consist of four separate electronic transitions
[1,8]. In contrast, the complexes (Fc-DAB)M(CO)4
The 1H and 13C NMR chemical shifts of the
ꢁNꢀCHꢁCHꢀNꢁ subunit in the complexes 5a,b,c and
6a,b,c are slightly shielded/deshielded (l(1H) 5a/5b/
5c=8.47/8.43/8.81 ppm; l(1H) 6a/6b/6c=8.31/8.38/
8.68 ppm; l(13C) 5a/5b/5c=154.3/152.6/154.4 ppm;
l(13C) 6a=158.2 ppm) in comparison to those of the
free ligands Fc-DAB 1 and p-MeOC6H4-DAB 4 (l(1H)
1/4=8.33/8.33 ppm; l(13C) 1/4=157.8/157.3 ppm),
similar to other (DAB)M(CO)4 complexes [8].
Scheme 1. Overview of compounds 1–6 (cHex=cyclohexyl).

18
B. Bildstein et al. / Inorganica Chimica Acta 300–302 (2000) 16–22
3. Electrochemistry
Fig. 2 illustrates the redox behavior of Fc-DAB 1 in
dichloromethane solution either in cyclic or differential
pulse voltammetry. It exhibits two essentially over-
lapped oxidations with features of chemical reversibility
as well as an irreversible reduction. In agreement with
the presence of two ferrocenyl subunits, controlled po-
tential coulometry (Ew= +0.8 V) confirmed that the
overall oxidation process consumes two electrons per
molecule. Exhaustive oxidation made the original violet
solution turn yellow–brown, but in spite of the appar-
ent chemical reversibility of the oxidation process in the
short times of cyclic voltammetry, a final cyclic voltam-
mogram did not reveal any presence of Fc-DAB con-
geners. It is noteworthy that the sequential oxidations
of the two ferrocenyl units occur at potential values
differing by only 60 mV, whereas in Fc(CHꢀCH)2Fc
they are separated by about 130 mV [9]; the low
conjugation operated by nitrogen atoms with respect to
carbon atoms is hence reflected in a low, if any, elec-
tronic communication between the ferrocenyl units.
As far as the reduction step is concerned, in confir-
mation of the conceivable assignment to a diazabutadi-
ene centerd process, p-MeOC6H4-DAB (4) afforded a
quite similar irreversible response. Based on the relative
peak height, we assume that such reduction also in-
volves a two-electron process. It seems interesting to
point out that, as Fig. 2 shows, the backward profile
after traversing the reduction step gives rise to a minor
reversible peak-system at E°%= +0.05 V, which is just
coincident with that of an authentic sample of ferro-
cenylamine, indicating partial chemical decomposition
following the two electron addition.
Fig. 1. Comparison of the UV–Vis spectra of R-DAB-M(CO)4
compounds 5a,b,c (R=Fc, ——) and 6a,b,c (R=p-MeOC6H4,
·········) in CH2Cl2 solution.
A qualitatively similar behavior was displayed by the
1%-substituted ferrocenyl DAB compounds 2 and 3, but
in both cases the dication generated by macroelectroly-
sis appeared more stable as compared to 1. In both
cases the color of the solution turned from violet to
green upon oxidation and displayed a broad UV–Vis
band centerd at about 600 nm, typical of ferrocenium
species.
The formal electrode potentials of the redox changes
exhibited by the DAB ligands 1–4 are summarized in
Table 1. In spite of the fact that the trimethylsilyl
substituents slightly increase the separation between the
two sequential oxidations of the ferrocene units, a
rough use of the Kcom values could justify the assump-
tion that in all cases the electrogenerable monocations
are localized mixed-valent species.
More complicated appeared the voltammetric re-
sponses exibited by the metallacomplexes (Fc-
DAB)M(CO)4 (5a,b,c) (M=Cr, Mo, W), but the
availability of the related complexes (p-MeOC6H4-
DAB)M(CO)4 (6a,b,c) facilitated their interpretation.
Fig. 2. Cyclic and differential pulse voltammograms of a CH2Cl2
solution containing Fc-DAB 1 (1.4 mmol l−1) and NBu4PF6 (0.2 mol
l
−1). Scan rates: cyclic voltammogram, 0.2 V s−1; DPV, 0.004 V
s−1
.
Fig.
3 shows the voltammetric profiles of (Fc-

B. Bildstein et al. / Inorganica Chimica Acta 300–302 (2000) 16–22
19
Table 1
Formal electrode potentials (in V, vs. SCE) for the redox changes of DAB ligands 1, 2, 3, 4 in CH2Cl2 solution
a
a
Compound
E°%(2+/+)
E°%(+/0)
DE°%
Kcom
Ep(0/2−) b
1
2
3
4
+0.52
+0.54
+0.55
–
+0.46
+0.46
+0.46
–
0.06
0.08
0.09
–
10
22
33
–
−1.69
−1.73
−1.75
−1.67
–
Fe(C5H5)2
–
+0.38
–
–
a Peak potential value in DPV.
b Measured at 0.2 V s−1
.
DAB)W(CO)4 (5c) and its related complex (p-
MeOC6H4-DAB)W(CO)4 (6c). Apart from slight ad-
sorption phenomena occurring in correspondence of the
most anodic process (Fig. 3a), based on the voltammet-
ric features of (p-MeOC6H4-DAB)W(CO)4 (6c) it is
quite clear that in the case of (Fc-DAB)W(CO)4 (5c)
the first irreversible oxidation at Ep=0.5 V (accompa-
nied by its backward peak at Ep −0.2 V) and the
reversible reduction process at Ep= −1.0 V have to be
assigned to the redox processes of the metal fragment
(DAB)W(CO)4, which, if we assume that the reduction
process at Ep= −1.6 V remains centered on the DAB
fragment, should involve four- and two-electron trans-
fers, respectively. Quite interestingly, the separation
between the one-electron oxidations of the two ferro-
cenyl units of 5c is significantly higher than in Fc-DAB
1 itself, i.e. 180 mV versus 60 mV, indicating that the
formation of the W-DAB metallacycle notably in-
creases the electronic communication between the pe-
ripheral ferrocene moieties. (Fc-DAB)Mo(CO)4 (5b)
gives rise to a voltammetric picture qualitatively similar
to that of the tungsten analogue 5c, but the separation
between the two ferrocenyl-centred oxidations is
slightly decreased to 140 mV.
based on the relevant Kcom values, the mixed-valent
FeIIFeIII species should become partially delocalized
complexes.
4. Experimental
4.1. General
Reactions of air-sensitive materials were carried out
using standard Schlenk techniques and vacuum-line
Finally, as Fig. 4 illustrates, also (Fc-DAB)Cr(CO)4
(5a) affords a response somewhat similar to that of
(Fc-DAB)M(CO)4 (5b,c) (M=Mo, W), even if the first
(DAB)Cr(CO)4-centred, (likely) two-electron oxidation
is reversible, as was also observed for (p-MeOC6H4-
DAB)Cr(CO)4 (6a). However, it is interesting to note
that the separation between the two sequential oxida-
tions of the ferrocene groups further decreases to 120
mV, thus suggesting that the ability of the metallacycle
(DAB)M(CO)4 to favor the interaction between the two
ferrocenyl donor units decreases according to the se-
quence: CrBMoBW. The same trend has been de-
duced from resonance Raman experiments of other
(DAB)M(CO)4 complexes [8]. All the pertinent electro-
chemical data are compiled in Table 2.
It has to be noted that the presence of the M(CO)4
fragment exerts a significant electron-withdrawing ef-
fect on the Fc-DAB frame making the oxidation of the
two ferrocenyl groups to shift toward more positive
potential values by about 0.15–0.25 V. In addition,
Fig. 3. Cyclic (a) and differential pulse (b) voltammograms of (Fc-
DAB)W(CO)4 (5c) (0.8 mmol l−1); (c) cyclic voltammogram of
(p-MeOC6H4-DAB)W(CO)4 (6c) (0.9 mmol l−1). CH2Cl2 solutions
containing NBu4PF6 (0.2 mol l−1) supporting electrolyte. Scan rates:
cyclic voltammogram, 0.2 V s−1; DPV, 0.004 V s−1
.

20
B. Bildstein et al. / Inorganica Chimica Acta 300–302 (2000) 16–22
4.2. Electrochemistry
Materials and apparatus for electrochemical mea-
surements have been described elsewhere [10]. Differen-
tial pulse voltammograms were recorded under a pulse
amplitude of 50 mV. All the potential values are re-
ferred to the saturated calomel electrode (SCE).
4.3. Synthesis of Fc-DAB-M(CO)4 complexes
(5a: M=Cr, 5b: M=Mo, 5c: M=W)
A THF solution of an excess of the corresponding
metal hexacarbonyl M(CO)6 (Cr: 0.6 g, 2.7 mmol; Mo:
1 g, 3.79 mmol; W: 0.823 g, 2.3 mmol) was photolyzed
for 2 h with a 150 W high pressure mercury lamp. To
the resulting solution of M(CO)5(THF) was added a 15
ml THF solution of Fc-DAB 1 (Cr: 0.14 g, 0.33 mmol;
Mo: 0.2 g, 0.47 mmol; W: 0.25 g, 0.59 mmol) and the
mixture was stirred over night at ambient temperature,
resulting in a blue–green solution. Work up: Solvent
and volatile materials were removed in vacuo and the
residue was chromatographed (Al2O3, ether/n-hexane)
yielding a mixture of the product and the correspond-
ing metal hexacarbonyl. Sublimation at reduced pres-
sure removed the metal hexacarbonyl, yielding the pure
product as a dark green powder (5a: 0.182 g, 0.31
mmol, 94%; 5b: 0.238 g, 0.38 mmol, 80%; 5c: 0.245 g,
0.34 mmol, 58%).
Fig. 4. Cyclic (a) and differential pulse (b) voltammograms of (Fc-
DAB)Cr(CO)4 (5a) (0.8 mmol l−1); (c) cyclic voltammogram of
(p-MeOC6H4-DAB)Cr(CO)4 (6a) (1.1 mmol l−1). CH2Cl2 solutions
containing NBu4PF6 (0.2 mol l−1) supporting electrolyte. Scan rates:
Data for 5a: m.p. 180°C, dec. Anal. Found: C, 53.03;
H, 3.44. Calc. for C26H20CrFe2N2O4: C, 53.10; H,
3.43%. IR (KBr): cm−1 2004s (wCꢀO), 1910s (wCꢀO),
1885s (wCꢀO), 1823 (wCꢀO), 1636m, 1466m, 1437m,
1412w, 1261w, 1107m, 1053w, 1034w, 1003w, 821w,
652w, 619w, 540w, 522w, 490w, 474w. MS (FAB):
cyclic voltammogram, 0.2 V s−1; DPV, 0.004 V s−1
.
manipulations. Solvents were carefully deoxygenated,
purified, and dried prior to use. Standard instrumenta-
tion and methods were as recently published [5]. The
ferrocenyl DAB ligands 1–3 were synthesized by con-
densation of aqueous glyoxal with the corresponding
aminoferrocenes [4,5]. p-Methoxyphenyl-DAB (4) was
analogously prepared by condensation of glyoxal with
p-anisidine and had spectral properties in concordance
with published data [7].
1
m/z(%) 588(100) (M+). H NMR (CDCl3): l 4.33 (s,
10H, Cpunsubst), 4.52 (m, 4H, Cpsubst), 5.01 (m, 4H,
Cpsubst), 8.47 (s, 2H, NꢀCHCHꢁN). 13C NMR (CDCl3):
l 65.3 (Cpsubst), 69.2 (Cpsubst), 71.1 (Cpunsubst), 90.7
(C(1) of Cpsubst), 154.3 (NꢀCHꢁCHꢀN). UV–Vis
(CH2Cl2): umax(nm)/m 376/13000, 649/7000. CV
(CH2Cl2): −1.11, +0.44, +0.70, +0.82 V.
Table 2
Comparison of the formal electrode potentials (V, vs. SCE; CH2Cl2 solution) for the redox changes of the (Fc-DAB)M(CO)4 complexes 5a, 5b,
5c and of the (p-MeOC6H4-DAB)M(CO)4 complexes 6a, 6b, 6c
Complex
Ferrocenyl oxidations
(DAB)M(CO)4 oxidation/reduction
a
a
E°1%
E°2%
DE°%
Kcom
E°o% x
E°r%ed
5a
6a
5b
6b
5c
6c
+0.70
+0.82
0.12
–
0.14
–
0.18
–
106
–
232
–
1100
–
+0.44
+0.43
−1.11
−1.12
−1.00
−1.12
−0.96
−0.92
–
+0.61
–
+0.72
–
–
+0.75
–
+0.90
–
+0.54 b
+0.70 b
+0.51 b
+0.73 b
a Peak potential value in DPV.
b Peak potential value for irreversible processes (measured at 0.2 V s−1).

B. Bildstein et al. / Inorganica Chimica Acta 300–302 (2000) 16–22
21
Data for 5b: m.p. \200°C, dec. Anal. Found: C,
49.23; H, 3.18. C26H20Fe2MoN2O4. Calc.: C, 49.41; H,
3.19. IR (KBr): cm−1 2006s (wCꢀO), 1914s (wCꢀO), 1889s
(wCꢀO), 1825 (wCꢀO), 1636m, 1557w, 1478s, 1431w,
1412w, 1107w, 1053w, 1034w, 1001w, 958w, 821w,
642w, 598w, 540w, 517w, 486m. MS (FAB): m/z(%)
632(60) (M+), 606(42) (M+−CO), 578(37) (M+−
NMR (CD2Cl2): l 56.0 (OCH3), 114.4 (C6H4), 123.7
(C6H4), 158.2 (NꢀCHꢁCHꢀN). UV–Vis (CH2Cl2):
umax(nm)/m 396/12000, 619/7000. CV (CH2Cl2): −1.12,
+0.43 V.
Data for 6b: m.p. \150°C, dec. Anal. Found: C,
50.28; H, 3.38. C20H16MoN2O6. Calc.: C, 50.43; H,
3.39. IR (KBr): cm−1 3015w, 2934w, 2842w, 2022s
(wCꢀO), 1946s (wCꢀO), 1881s (wCꢀO), 1809s (wCꢀO), 1601m,
1505s, 1479m, 1464w, 1443w, 1298w, 1254s, 1173s,
1
2CO), 548(20) (M+−3CO), 520(100) (M+−4CO). H
NMR (CDCl3): l 4.34 (s, 10H, Cpunsubst), 4.58 (m, 4H,
Cpsubst), 5.07 (m, 4H, Cpsubst), 8.43 (s, 2H,
NꢀCHꢁCHꢁN). 13C NMR (CDCl3): l 65.4 (Cpsubst),
70.01 (Cpsubst), 71.4 (Cpunsubst), 90.0 (C(1) of Cpsubst),
152.6 (NꢀCHꢁCHꢀN). UV–Vis (CH2Cl2): umax(nm)/m
379/24000, 581/12000, 702/11000. CV (CH2Cl2):
−1.00, +0.54, +0.61, +0.75 V.
1
1113w, 1026m, 835m, 557w, 540w. H NMR (CD2Cl2):
l 3.88 (s, 6H, OCH3), 7.01 (d, 4H, J=9 Hz, C6H4),
7.54 (d, 4H, J=9 Hz, C6H4), 8.38 (s, 2H,
NꢀCHꢁCHꢁN). 13C NMR (CD2Cl2): l not observed,
overlapped by solvent peak: (OCH3), 114.6 (C6H4),
124.1 (C6H4), not observed: (NꢀCHꢁCHꢀN). UV–Vis
(CH2Cl2): umax(nm)/m 425/14000, 593/10000. CV
(CH2Cl2): −1.12, +0.70 V.
Data for 5c: m.p.\180°C, dec. Anal. Found: C,
43.25; H, 2.78. C26H20Fe2N2O4W. Calc.: C, 43.37; H,
2.80. IR (KBr): cm−1 1998s (wCꢀO), 1885s (wCꢀO), 1823
(wCꢀO), 1472s, 1429m, 1246s, 1107m, 1036w, 1003w,
958w, 868w, 821s, 571w, 544w, 519w, 499w, 488w,
472w, 374m. MS (EI, 70 eV): m/z(%) 720(31) (M+),
Data for 6c: m.p. \150°C, dec. Anal. Found: C,
42.46; H, 2.84. C20H16N2O6W. Calc.: C, 42.58; H, 2.86.
IR (KBr): cm−1 3052w, 2981w, 2932w, 2842w, 2014s
(wCꢀO), 1937s (wCꢀO), 1879s (wCꢀO), 1809s (wCꢀO), 1601m,
1505s, 1464s, 1443w, 1298m, 1254s, 1173m, 1113w,
1
606(100) (M+−4CO). H NMR (CDCl3): l 4.34 (s,
1
10H, Cpunsubst), 4.60 (m, 4H, Cpsubst), 5.10 (m, 4H,
Cpsubst), 8.81 (s, 2H, NꢀCHꢁCHꢁN). 13C NMR (dmso-
d6): l 65.9 (Cpsubst), 69.8 (Cpsubst), 71.5 (Cpunsubst),
154.41 (NꢀCHꢁCHꢀN). UV–Vis (CH2Cl2): umax(nm)/m
383/13000, 578/8400, 729/6300. CV (CH2Cl2): −0.96,
+0.51, +0.72, +0.90 V.
1024m, 835m, 557w, 542w. H NMR (CD2Cl2): l 3.88
(s, 6H, OCH3), 7.01 (d, 4H, J=9 Hz, C6H4), 7.49 (d,
4H, J=9 Hz, C6H4), 8.68 (s, 2H, NꢀCHꢁCHꢁN). 13C
NMR (CD2Cl2): l not observed, overlapped by solvent
peak: (OCH3), 114.5 (C6H4), 124.6 (C6H4), not ob-
served: (NꢀCHꢁCHꢀN). UV–Vis (CH2Cl2): umax(nm)/m
422/13000, 579/12000. CV (CH2Cl2): −0.92, +0.73 V.
4.4. Synthesis of p-MeOC6H4-DAB-M(CO)4
complexes (6a: M=Cr, 6b: M=Mo, 6c: M=W)
Acknowledgements
A THF solution of 1.5 mole equiv. of the corre-
sponding metal hexacarbonyl M(CO)6 (2.8 mmol; Cr:
0.615 g, Mo: 0.738 g, W: 0.983 g) was photolyzed for 2
h with a 150 W high pressure mercury lamp. To the
resulting solution of M(CO)5(THF) was added 0.5 g
(1.9 mmol) p-An-DAB 4 and the mixture was stirred
for 48 h at ambient temperature, resulting in a blue–
purple solution. Work up: Solvent and volatile materi-
als were removed in vacuo and the residue was
chromatographed (Al2O3, ether/n-hexane) yielding a
mixture of the product and the corresponding metal
hexacarbonyl. Sublimation at reduced pressure re-
moved the metal hexacarbonyl, yielding the pure
product as a dark blue-purple powder (6a: 0.516 g, 1.2
mmol, 64%; 6b: 0.648 g, 1.4 mmol, 73%; 6c: 0.536 g, 1.0
mmol, 51%).
B.B. acknowledges partial funding of this work by
the European HCM-project ‘Electron and Energy
Transfer in Model Systems and their Implications for
Molecular Electronics’ (Grant No. CHRX-CT94-0538).
P.Z. gratefully acknowledges the financial support of
the University of Siena (ex quota 60%). We thank
Professor Karl–Hans Ongania from the Institute of
Organic Chemistry of the University of Innsbruck for
measurement of FAB mass spectra.
References
[1] G. van Koten, K. Vrieze, Advan. Organometal. Chem. 21 (1982)
151.
[2] K. Vrieze, G. van Koten, in: G. Wilkinson, R.D. Gillard, J.A.
McCleverty (Eds.), Comprehensive Coordination Chemistry, vol.
2, Pergamon, Oxford, 1987, p. 206.
[3] L.K. Johnson, C.M. Moore, S.D. Arthur, J. Feldman, E.F.
McCord, S.J. McLain, K.A. Kreutzer, M.A. Bennett, E.B.
Coughlin, S.D. Ittel, A. Parthasarathy, D.J. Tempel, M.
Brookhart, Patent WO 96/23010.
[4] B. Bildstein, M. Malaun, A. Hradsky, A. Gonioukh, W. Mickl-
itz, Patent pending DE 19920486.1 (1999).
Data for 6a: m.p.\150°C, dec. Anal. Found: C,
55.40; H, 3.72. C20H16CrN2O6. Calc.: C, 55.56; H, 3.73.
IR (KBr): cm−1 2932w, 2842w, 2014s (wCꢀO), 1943s
(wCꢀO), 1883s (wCꢀO), 1809s (wCꢀO), 1601m, 1503s, 1476s,
1464m, 1443w, 1298w, 1252s, 1173m, 1026m, 835m,
1
684w, 652w, 617w, 544w. H NMR (CD2Cl2): l 3.88 (s,
6H, OCH3), 7.01 (d, 4H, J=9 Hz, C6H4), 7.42 (d, 4H,
J=9 Hz, C6H4), 8.31 (s, 2H, NꢀCHꢁCHꢁN). 13C

22
B. Bildstein et al. / Inorganica Chimica Acta 300–302 (2000) 16–22
[5] B. Bildstein, M. Malaun, H. Kopacka, M. Mitterbo¨ck, K.
[8] L.H. Staal, D.J. Stufkens, A. Oskam, Inorg. Chim. Acta 26
(1978) 255.
[9] A.-C. Ribou, J.-P. Launay, M.L. Sachtleben, H. Li, C.W.
Spangler, Inorg. Chem. 36 (1996) 3735.
[10] P. Zanello, F. Laschi, M. Fontani, C. Mealli, A. Ienco, K.
Tang, X. Jin, L. Li, J. Chem. Soc., Dalton Trans. (1999)
965.
Wurst, K.-H. Ongania, G. Opromolla, P. Zanello, Organometal-
lics 18 (1999) 4325.
[6] V. Alain, A. Fort, M. Barzoukas, C.-T. Chen, M. Blanchard-
Desce, S.R. Marder, J.W. Perry, Inorg. Chim. Acta 242 (1996)
43.
[7] J.M. Klerks, D.J. Stufkens, G. van Koten, K. Vrieze, J.
Organomet. Chem. 181 (1979) 271.
.
.