Ethynylferrocene compounds of 1,3,5-tribromobenzene

Article abstract of DOI:10.1021/om9701027

The new compounds 1,3-dibromo-5-(ferrocenylethynyl)benzene (1), 1-bromo-3,5-bis(ferrocenylethynyl)benzene (2), and 1,3,5-tris(ferrocenylethynyl)benzene (3) have been synthesized by palladium-catalyzed cross-coupling reactions and characterized, and the cr

Full text of DOI:10.1021/om9701027

2646
Organometallics 1997, 16, 2646-2650
Eth yn ylfer r ocen e Com p ou n d s of 1,3,5-Tr ibr om oben zen e
Herbert Fink,† Nicholas J . Long,*,† Angela J . Martin,† Giuliana Opromolla,‡
Andrew J . P. White,† David J . Williams,† and Piero Zanello‡
Department of Chemistry, Imperial College of Science, Technology and Medicine,
South Kensington, London, SW7 2AY U.K., and Dipartimento di Chimica dell’ Universita di
Siena, Pian dei Mantellini, 44, I-53100, Siena, Italy
Received February 11, 1997X
The new compounds 1,3-dibromo-5-(ferrocenylethynyl)benzene (1), 1-bromo-3,5-bis(ferro-
cenylethynyl)benzene (2), and 1,3,5-tris(ferrocenylethynyl)benzene (3) have been synthesized
by palladium-catalyzed cross-coupling reactions and characterized, and the crystal structures
of 1 and 3 have been determined; electrochemical studies show chemically reversible
oxidations with single-step one-electron, two-electron, and three-electron processes per
molecule, respectively, indicating that in 2 and 3 the iron(II) centers do not electronically
communicate with each other.
In tr od u ction
With their importance in the field of materials sci-
ence,9 there is currently great interest in the chemistry
of ferrocenyl and ferrocenylene oligomers and polymers
and their precursors. Here we report the utilization of
palladium-mediated cross-coupling methodology to the
reaction of ethynylferrocene with a 1,3,5-trisubstituted
aromatic species to give, via a simple single-step syn-
thetic procedure, a series of novel precursors for the
production of interesting and potentially exciting cross-
linked metal-aromatic polyyne networks.
Carbon-rich organometallics containing rigid π-con-
jugated chains are of increasing interest due to their
uses in the syntheses of unsaturated organic species,1
organometallic polymers,2 and π-conjugated bi- or mul-
timetallic systems.3 These organometallic assemblies
are key design targets for the study of electron-transfer
processes,4 the fabrication of nanostructured materials,5
the formation of liquid crystalline organometallic poly-
mers,6 the construction of molecular devices,7 and the
creation of dendrimers containing inorganic or organo-
metallic fragments.8
Resu lts a n d Discu ssion
The compounds 1,3-dibromo-5-(ferrocenylethynyl)-
benzene (1), 1-bromo-3,5-bis(ferrocenylethynyl)benzene
(2), and 1,3,5-tris(ferrocenylethynyl)benzene (3) (along
* To whom correspondence should be addressed. E-mail: n.long@
ic.ac.uk.
† Imperial College of Science, Technology and Medicine.
‡ Universita di Siena.
X Abstract published in Advance ACS Abstracts, May 1, 1997.
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S0276-7333(97)00102-7 CCC: $14.00 © 1997 American Chemical Society

Ethynylferrocene Compounds of 1,3,5-Tribromobenzene
Organometallics, Vol. 16, No. 12, 1997 2647
Sch em e 1. Syn th eses of 1-3
F igu r e 1. Solid state structure of 1.
Ta ble 1. Exp er im en ta l Da ta for th e Ra tio of
Rea cta n ts a n d Yield of P r od u cts
ratio of reagents (mol)
yields of products (%)
FcCtCH
C6H3Br3
1
2
3
4
F igu r e 2. Solid state structure of 3.
1
2
3
1
1
1
46
36
14
36
12
60
angles of 178(1) and 179(1)°) to the dibromophenyl ring,
which adopts a coplanar orientation with respect to the
substituted cyclopentadienyl ring. There is distinct
bond ordering within the CsCtCsC linkage with
single-bond lengths of 1.45(1) and 1.43(1) Å and a CtC
distance of 1.16(1) Å. The molecules pack within the
crystal to form stacks that extend in the 110 plane, the
dibromophenyl ring of one molecule being π-stacked
with the unsubstituted cyclopentadienyl ring of a lattice-
translated molecule (interplanar separation 3.47 Å,
centroid‚‚‚centroid distance 3.52 Å). The opposite face
of the dibromophenyl ring is approached edge-on by the
ferrocenyl group of another molecule, the Fe‚‚‚centroid
distance being 4.78 Å.
The X-ray analysis of 3 confirms the tris(ferrocenyl-
acetylide) structure of the complex (Figure 2). Two of
the substituted cyclopentadienyl rings are essentially
coplanar with the 1,3,5-trisubstituted benzenoid nucleus
(twist angles of between 1 and 2°), while the third (that
associated with Fe(1)) is oriented orthogonally (twist
angle ca. 86°). This geometry is in contrast to the
almost all-planar, up-up-down arrangement observed
in the related chromium tricarbonyl aryl complex.8j
Interestingly, in 3 the pair of “in-plane” ferrocenyl
moieties (associated with Fe(3) and Fe(5)) have normal
eclipsed conformations for their C5 rings, while in the
orthogonally aligned unit, the rings are almost perfectly
staggered. The geometries of the CsCtCsC linkages
are, in two instances, essentially linear with angles
within the C(3)- - -C(37) and C(5)- - -C(57) chains in the
range 175.0(9)-178.5(10)° and CtC distances of
1.187(11) and 1.182(11) Å, respectively. For the third
linkage, to the orthogonally oriented ferrocenyl unit,
33
with the coupled dimer of ethynylferrocene, 1,4-difer-
rocenylbutadiyne (4)) were formed by the simple cross-
coupling (“Heck-Cassar-Sonogashira-Hagihara”) reac-
tion10 of ethynylferrocene11 and 1,3,5-tribromobenzene
(Scheme 1). This versatile single-step reaction was
performed with different ratios of reagents, and depend-
ing on this ratio, the yields of the substitution products
could be controlled (Table 1). The reactions were
monitored by infrared spectroscopy, which showed that
the ν(CtC) stretching frequencies of the compounds are
shifted by ca. 100 cm-1 to higher wavenumber, indicat-
ing a strengthening of the CtC bond. After purification
by column chromatography, the compounds were iso-
lated as orange or orange-red air- and moisture-stable,
microcrystalline solids. The solubility of 1-3 in chloro-
carbon solvents decreases with increasing molecular
weight. Eventually, orange crystals were obtained by
slow evaporation of saturated solutions of 1 in n-hexane
and 3 in benzene. The shape and geometry of these
species are crucial to their utilization as precursors for
building multidimensional metal-carbon networks.
The X-ray structural analysis of 1 shows (Figure 1)
the ferrocenyl unit to have a characteristic eclipsed
conformation and to be bonded linearly (CsCtCsC
(10) (a) Cassar, I. J . Organomet. Chem. 1975, 93, 253. (b) Dieck,
H. A.; Heck, R. F. J . Organomet. Chem. 1975, 93, 259. (c) Heck, R. F.
Org. React. 1982, 27, 345. (d) Sonogashira, K.; Tohda, Y.; Hagihara,
N. Tetrahedron Lett. 1975, 4467. (e) Alami, M.; Ferri, F.; Linstrumelle,
G. Tetrahedron Lett. 1993, 6403.
(11) Doisneau, G.; Balavoine, G.; Fillebeen-Kahn, T. J . Organomet.
Chem. 1992, 425, 113.

2648 Organometallics, Vol. 16, No. 12, 1997
Fink et al.
Ta ble 2. F or m a l Electr od e P oten tia ls (in V),
P ea k -to-P ea k Sep a r a tion s (in m V), a n d Ma xim u m
Wa velen gth s of th e Oxid ized Sp ecies (in n m )
Exh ibited by th e P r esen t Eth yn ylfer r ocen esa
b
b
b
complex
E°0/+ ∆Ep
E°′0/2+ ∆Ep
E°′0/3+ ∆Ep
λmax
FcCtCH +0.53
97
81
698
760
762
772
628
1
+0.54
2
3
+0.51
88
+0.49
74
FcH
+0.39
95
a
In dichloromethane solutions containing [NBu4][PF6] as sup-
porting electrolyte (0.2 mol dm-3). Fc ) (C5H5)Fe(C5H4). Meas-
b
ured at 0.2 V s-1
.
F igu r e 3. Cyclic voltammetric responses recorded at a
platinum electrode on CH2Cl2 solutions containing 1 (1.1
× 10-3 mol dm-3) and 3 (0.4 × 10-3 mol dm-3), respectively
([NBu4][PF6] (0.2 mol dm-3) supporting electrolyte; scan
rate 0.1 V s-1).
from unsubstituted ferrocene (as is the case for
FcCtCPh17), then the explanation of the slightly nega-
tive shift which occurs upon progressive insertion of
ethynylferrocenyl units around the central benzene is
less obvious. The resulting decrease in overall electronic
unsaturation could stem either from the removal of the
electron-withdrawing bromide substituents or from the
electron delocalization within the central bis- or tris-
(ethynyl)benzene fragments. The fact that 2 and 3
exhibit single-step oxidation processes is of relevance,
as this implies that the central benzenoid nucleus does
not allow the relevant peripheral ferrocenyl subunits
to communicate electronically with each other. This
conclusion is further supported by the fact that all the
complexes reported in Table 2 display roughly similar
peak-to-peak separations (bearing in mind that they are
likely to be affected by the presence of uncompensated
solution resistances, as is evident from the oxidation
step of ferrocene). For molecules with multiple, non-
interacting sites a peak-to-peak separation matching
that of a one-electron step is consistent with theory.18
As expected, IVET transitions are not observed in the
partially oxidized species, due to the presence of single-
step multielectron processes.
there is a noticeable bending at C(11) (170.4(10)°), the
angle at C(12) remaining linear (179.1(11)°). The
C(11)-C(12) bond exhibits a slight shortening at
1.145(11) Å. Adjacent “trimers” pack back-to-back with
one of the C5H4 rings of one molecule aligned essentially
parallel to and overlapping the benzenoid nucleus of the
other and vice versa (mean interplanar separation 3.51
Å, centroid‚‚‚centroid separation 3.71 Å). These back-
to-back pairs form a stepped-stack arrangement with
their neighbors in the crystal such that the iron atoms
of the in-plane ferrocenyl moieties of one molecule lie
almost in the plane of the benzenoid nucleus of the next.
In view of the interest in assessing the existence of
electronic interactions among linked ferrocene subunits
in oligoferrocene molecules,12 we have examined the
electrochemical behavior of 1-3. Despite the fact that
2 and 3 contain multiple ferrocenyl subunits, cyclic
voltammetry on their dichloromethane solutions dis-
plays only a single anodic process with features of
chemical reversibility, as is seen for 1. Figure 3 gives
a comparative picture of the cyclic voltammetric re-
sponses exhibited by 1 and 3. Controlled-potential
coulometric tests show the consumption of one, two, and
three electrons per molecule for 1-3, respectively. As
As far as bis(ferrocenyl) complexes related to 2 are
concerned, 1,4-bis(â-ferrocenylvinyl)benzene also un-
dergoes a single-step two-electron oxidation,19 whereas
1,4-diferrocenylbutadiyne (4), which lacks the benzene
bridge between the two ferrocenylethynes, exhibits two
separated (by about 100 mV) one-electron oxidations.15
In the field of tris(ferrocene) molecules, it is worth
noting that the closely related triferrocenylbenzene
behaves similarly to 3 (E°′0/3+ ) +0.1 V, vs Fc/Fc+, in
confirmation of the stability of the cations [1]+, [2]2+
,
and [3]3+, cyclic voltammograms recorded on the olive
green solutions resulting from the exhaustive oxidation
of the relevant neutral yellow-orange species display
voltammetric profiles complementary to the original
ones. Analysis13 of the cyclic voltammetric responses
exhibited by 1 with scan rate increasing from 0.02 to
1.00 V s-1 is diagnostic of a simple, electrochemically
reversible, one-electron oxidation (ip,c /ip,a is constantly
equal to 1, ip,av1/2 is constant and ∆Ep departs slightly
from the theoretical value of 59 mV, as in the oxidation
process of ferrocene).
(14) For recent articles on the chemistry of ethynylferrocene,
consult: (a) Sato, M.; Shintate, H.; Kawata, Y.; Sekino, M.; Katada,
M.; Kawata, S. Organometallics 1994, 13, 1956. (b) Sato, M.; Hayashi,
Y.; Shintate, H.; Katada, M.; Kawata, S. J . Organomet. Chem. 1994,
471, 179. (c) Sato, M.; Mogi, E.; Kamakura, S. Organometallics 1995,
14, 3157. (d) Colbert, M. C. B.; Ingham, S. L.; Lewis, J .; Long, N. J .;
Raithby, P. R. J . Chem. Soc., Dalton Trans. 1994, 2215. (e) Colbert,
M. C. B.; Edwards, A. J .; Lewis, J .; Long, N. J .; Page, N. A.; Parker,
D. G.; Raithby, P. R. J . Chem. Soc., Dalton Trans. 1994, 2589. (f)
Onitsuka, K.; Tao, X.-Q.; Sonogashira, K. Bull. Chem. Soc. J pn. 1994,
67, 2611. (g) Wiegand, W.; Robl, C. Chem. Ber. 1993, 126, 1807. (h)
Russo, M. V.; Furlani, A.; Licoccia, S.; Paolesse, R.; Chiesi-Villa, A.;
Guastini, C. J . Organomet. Chem. 1994, 469, 245. (i) Koridze, A. A.;
Zdanovich, V. I.; Kizas, O. A.; Yanovsky, A. I.; Struchkov, Y. T. J .
Organomet. Chem. 1994, 464, 197. (j) Bunz, U. H. F. J . Organomet.
Chem. 1995, 494, C8
Table 2 gives the electrochemical and the associated
spectroscopic parameters of the complexes studied here.
If the unsaturation of the ethynyl substituent can
account for the fact that the electron removal from
either ethynylferrocene14-16 or 1 is more difficult than
(15) Levanda, C.; Bechgaard, K.; Cowan, D. O. J . Org. Chem. 1976,
41, 2700.
(16) Kasahara, Y.; Hoshino, Y.; Kajitani, M.; Shimizu, K.; Sato, G.
P. Organometallics 1992, 11, 1968.
(17) Sato, M.; Mogi, E.; Katada, M. Organometallics 1996, 14, 4837.
(18) Flanagan, J . B.; Margel, S.; Bard, A. J .; Anson, F. C. J . Am.
Chem. Soc. 1978, 100, 4248.
(19) Morrison, W. H., J r.; Krogsrud, S.; Hendrickson, D. N. Inorg.
Chem. 1973, 12, 1998.
(12) Selected references include: (a) Beer, P. D.; Tite, E. L.; Ibbotson,
A. J . Chem. Soc., Dalton Trans. 1991, 1691. (b) Rulkens, R.; Lough,
A. J .; Manners, I. J . Am. Chem. Soc. 1994, 116, 797. (c) Bildstein, B.;
Denifi, P.; Wurst, K.; Andre´, M.; Baumgarten, M.; Friederich, J .;
Ellmerer-Mu¨ller, E. Organometallics 1995, 14, 4334.
(13) Brown, E. R.; Sandifer, J . In Physical Methods of Chemistry:
Electrochemical Methods; Rossiter, B. W., Hamilton, J . F., Eds.;
Wiley: New York, 1986; Vol. 2, Chapter 4.

Ethynylferrocene Compounds of 1,3,5-Tribromobenzene
Organometallics, Vol. 16, No. 12, 1997 2649
CH2Cl2 solution ([NBu4][BF4] 0.1 mol dm-3)),20 as do
tris(ferrocene) molecules in which the ferrocene units
are appended to triaza crown ether21 or borazine22 rings.
In contrast, tris(ferrocenes) having ferrocenyl units
either appended to cyclopropene23 or linked to open-
chain frames24 display separated one-electron-oxidation
steps. The lack of communication between the ferrocene
units in similar systems has been noted previously25 and
the nature of the chain length and the element type
between the units proven to be crucial.
Ta ble 3. Cr ysta l Da ta a n d Da ta Collection a n d
Refin em en t P a r a m eter s for 1 a n d 3a
data
1
3
formula
solvent
fw
C18H12Br2Fe
C42H30Fe3
0.5 PhH
741.3
444.0
color, habit
cryst size (mm)
lattice type
space group
cell dimens
a (Å)
orange-red prisms thin yellow plates
0.27 × 0.20 × 0.15 0.13 × 0.10 × 0.02
monoclinic
monoclinic
P21/n
C2/c
9.352(1)
14.165(1)
11.856(1)
93.39(1)
1567.9(3)
4
21.628(7)
12.750(2)
25.880(4)
110.01(2)
6706(3)
8
b (Å)
c (Å)
Exp er im en ta l Section
â (deg)
All preparations were carried out using standard Schlenk
techniques.26 All solvents were distilled over standard drying
agents under nitrogen directly before use, and all reactions
were carried out under an atmosphere of nitrogen. Alumina
gel (neutral-grade II) was used for chromatographic separa-
tions.
All NMR spectra were recorded on Bruker instruments,
operating at 250.1 MHz. Chemical shifts are reported in δ
using CDCl3 (1H, δ 7.25 ppm) as reference. Infrared spectra
were recorded using NaCl solution cells (CH2Cl2) using a
Perkin-Elmer 1710 Fourier transform IR spectrometer. Mass
spectra were recorded using positive FAB methods, on a Kratos
MS60 spectrometer. Microanalyses were carried out in the
Department of Chemistry, Imperial College of Science, Tech-
nology and Medicine. Materials and apparatus for electro-
chemical measurements have been described elsewhere.27 All
the potential values are referred to the saturated calomel
electrode (SCE).
Rep r esen ta tive Rea ction To Syn th esize 1-3. The
following procedure is representative for all the reactions
performed to synthesize compounds 1-3, and only the ratio
of the reagents or the scale of the reaction was changed, not
the procedure itself. Catalytic amounts of CuI (0.010 g),
Pd(OAc)2 (0.011 g), and PPh3 (0.030 g) in diisopropylamine (50
mL) were stirred at 0 °C for 10 min. The mixture was then
treated with ethynylferrocene (0.100 g, 0.47 mmol) and 1,3,5-
tribromobenzene (0.074 g, 0.23 mmol) and stirring continued
at 0 °C for 1 h before warming to room temperature and then
heating under reflux for 2 h. After filtration and evaporation
to dryness, the residue was washed with dilute HCl, Na2CO3
(10%), and water and then subjected to column chromatogra-
phy on alumina using a hexane-dichloromethane (4:1) solvent
system. Successive bands of orange 1 (0.037 g, 36%), orange
2 (0.048 g, 36%), and orange-red 3 (0.020 g, 12%) were
subsequently obtained as microcrystalline solids after removal
of the solvent in vacuo.
V (Å3)
Z
Dc (g cm-3
F(000)
)
1.881
1.468
864
Mo KR
6.05
3048
radiation used
Cu KRb
10.51
µ (mm-1
)
θ range (deg)
no. of unique reflns
measd
2.2-25.0
3.6-60.0
2730
4591
obsd, |Fo| > 4σ(|Fo|) 1572
2580
abs cor semiempirical
semiempirical
0.91, 0.48
431
0.072
0.155
0.064, 30.103
0.60, -0.68
max, min transmissn
no. of variables
R1c
0.27, 0.20
190
0.049
wR2d
0.089
weighting factors A, Be 0.034, 0.217
largest diff peak,
0.44, -0.38
hole (e Å-3
)
a
Details in common: graphite-monochromated radiation, ω-
scans, Siemens P4 diffractometer, 293 K, refinement based on F2.
Rotating-anode source. c R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2
)
b
d
{∑[w(Fo - Fc2)2]/∑[w(Fo2)2]}1/2
.
e w-1 ) σ2(Fo2) + (AP)2 + BP.
2
1: mp 189-191 °C. Anal. Calcd for C18H12FeBr2: C, 48.71;
H, 2.73. Found: C, 48.64; H, 2.81. ν (CtC) (cm-1): 2211
(CH2Cl2). 1H NMR (CDCl3): δ 4.25 (s, 5H, C5H5 ring), 4.28 (t,
J ) 2.0 Hz; 2H, H3, H4 Cp ring), 4.50 (t, J ) 2.0 Hz; 2H, H2,
H5 Cp ring), 7.55 (d, J ) 1.3 Hz; 2H, H2, H6 Ph ring), 7.60 (d,
J ) 1.3 Hz; 1H, H4 Ph ring). MS (FAB + ve): m/ z (relative
intensity, %) 444 (M+, 40).
2: mp 217-220 °C dec. Anal. Calcd for C30H21Fe2Br: C,
62.98; H, 3.77. Found: C, 63.30; H, 4.01. ν (CtC) (cm-1):
2216 (CH2Cl2). 1H NMR (CDCl3): δ 4.24 (s, 10H, C5H5 ring),
4.25 (t, J ) 2.0 Hz; 4H, H3, H4 Cp ring), 4.89 (t, J ) 2.0 Hz;
4H, H2, H5 Cp ring), 7.51 (d, J ) 1.3 Hz; 1H, H4 Ph ring), 7.53
(d, J ) 1.3 Hz; 2H, H2, H6 Ph ring). MS (FAB + ve): m/ z
(relative intensity, %) 574 (M+, 4).
(20) Nakashima, T.; Kunitake, T. Bull. Chem. Soc. J pn. 1972, 45,
2892.
(21) Beer, P. D.; Crowe, D. B.; Ogden, M. I.; Drew, M. G. B.; Main,
B. J . Chem. Soc., Dalton Trans. 1993, 2107.
(22) Kotz, J . C.; Painter, W. J . J . Organomet. Chem. 1971, 32, 231.
(23) Fry, A. J .; J ain, P. S.; Krieger, R. L. J . Organomet. Chem. 1981,
214, 381.
(24) (a) Brown, G. M.; Meyer, T. J .; Cowan, D. O.; Le Vanda, C.;
Kaufman, F.; Roling, P. V.; Rausch, M. D. Inorg. Chem. 1975, 14, 506.
(b) Atzkern, H.; Hiermeier, J .; Kohler, F. H.; Steck, A. J . Organomet.
Chem. 1991, 408, 281. (c) Pannell, K. H.; Dementiev, V. V.; Li, H.;
Cervantes-Lee, F.; Nguyen, M. T.; Diaz, A. F. Organometallics 1994,
13, 3644.
(25) (a) Dement’ev, V. V.; Cervantes-Lee, F.; Parkanyi, L.; Sharma,
H.; Pannell, K. H. Organometallics 1993, 12, 1983. For further reading
on electrical communication in ferrocenyl polymers, consult: (b)
Kapoor, R. N.; Crawford, G. M.; Mahmoud, J .; Dementiev, V. V.;
Nguyen, M. T.; Diaz, A. F.; Pannell, K. H. Organometallics 1995, 14,
4944. (c) Foucher, D. A.; Honeyman, C. H.; Nelson, J . M.; Tang, B. Z.;
Manners, I. Angew. Chem. 1993, 105, 1853; Angew. Chem., Int. Ed.
Engl. 1993, 32, 1709. (d) Nguyen, M. T.; Diaz, A. F.; Dement’ev, V.
V.; Pannell, K. H. Chem. Mater. 1993, 5, 1389. (e) Brandt, P. F.;
Rauchfuss, T. B. J . Am. Chem. Soc. 1992, 114, 1926.
(26) Shriver, D. F. In Manipulation of Air-Sensitive Compounds;
McGraw-Hill: New York, 1969.
3: mp 254-256 °C dec. Anal. Calcd for C42H30Fe3: C,
71.82; H, 4.34. Found: C, 71.70; H, 4.25. ν (CtC) (cm-1):
2214 (CH2Cl2). 1H NMR (CDCl3): δ 4.24 (m, 21H, C5H5 rings
and H2, H5 Cp ring), 4.49 (t, J ) 2.0 Hz; 6H, H3, H4 Cp ring),
7.51 (s, 3H, H2, H4, and H6 Ph ring). MS (FAB + ve): m/ z
(relative intensity, %) 702 (M+, 3).
X-r a y Cr ysta llogr a p h y. Table 3 provides a summary of
the crystal data, data collection, and refinement parameters
for 1 and 3, which were solved by direct methods and the
heavy-atom method, respectively. Except for the disordered
solvent molecules in 3, where the carbon atoms were refined
isotropically, all of the non-hydrogen atoms in both structures
were refined anistropically using full-matrix least squares
based on F2. All of the C-H hydrogen atoms in each structure
were placed in calculated positions, assigned isotropic thermal
parameters, U(H) ) 1.2Ueq(C), and allowed to ride on their
parent atoms. Computations were carried out using the
SHELXTL PC program system.28
(27) Togni, A.; Hobi, M.; Rihs, G.; Rist, G.; Albinati, A.; Zanello, P.;
Zech, D.; Keller, H. Organometallics 1994, 13, 1224.
(28) SHELXTL PC version 5.03; Siemens Analytical X-Ray Instru-
ments, Inc., Madison, WI, 1994.

2650 Organometallics, Vol. 16, No. 12, 1997
Fink et al.
The crystallographic data (excluding structure factors) for
the structures reported in Table 3 have been deposited with
the Cambridge Crystallographic Data Centre. Copies of the
data can be obtained free of charge on application to The
Director, CCDC, 12 Union Road, Cambridge, CB12 1EZ U.K.
Universita¨t of Marburg, Germany) and P.Z. gratefully
acknowledges the financial support of MURST of Italy
(quota 40%).
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data and structure refinement details, positional and thermal
parameters, and bond distances and angles for 1 and 3 (14
pages). Ordering information is given on any current mast-
head page.
(Fax, Int. code
chemcrys.cam.ac.uk.).
+
(1223)336-033; e-mail, teched@
Ack n ow led gm en t. We thank the EPSRC (student-
ship to A.J .M.) and the European Commission (ERAS-
MUS exchange studentship to H.F. from the Philipps-
OM9701027