New carbene and vinylidene chelate complexes of cyclopentadienylcobalt bearing a phosphorus tether

Article abstract of DOI:10.1016/S0022-328X(00)00676-8

The {η⁵[2-(di-tert-butylphosphanyl-P)ethyl]cyclopentadienyl}cobalt chelate was treated with trimethylsilylethyne to give the corresponding alkyne complex along with the trimethylsilylvinylidene complex. In a similar way, the bis(trimethylsilyl)ethyne complex was obtained. Silyl migration to give the bis(trimethylsilyl)vinylidene complex was observed at elevated temperature and represents the first cobalt example of this reaction. As the first cobalt vinylidene complex the bis(trimethylsilyl)vinylidene complex was characterized by an X-ray structure analysis. Reaction of the cobalt chelate with an Arduengo type carbene unexpectedly gave a non-chelated cobalt complex bearing the carbene ligand and ethene at the same metal atom. This complex was also structurally characterized.

Full text of DOI:10.1016/S0022-328X(00)00676-8

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 617–618 (2001) 412–422
New carbene and vinylidene chelate complexes of
cyclopentadienylcobalt bearing a phosphorus tether
Jan Foerstner a, Alf Kakoschke a, Richard Goddard b, Jo¨rg Rust b, Rudolf Wartchow c,
Holger Butenscho¨n a,*
a Institut fu¨r Organische Chemie, Uni6ersita¨t Hanno6er, Schneiderberg 1B, D-30167 Hanno6er, Germany
b Max-Planck-Institut fu¨r Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mu¨lheim an der Ruhr, Germany
c Institut fu¨r Anorganische Chemie, Uni6ersita¨t Hanno6er, Callinstraße 9, D-30167 Hanno6er, Germany
Received 26 July 2000; accepted 15 September 2000
Abstract
The {h5[2-(di-tert-butylphosphanyl-P)ethyl]cyclopentadienyl}cobalt chelate was treated with trimethylsilylethyne to give the
corresponding alkyne complex along with the trimethylsilylvinylidene complex. In a similar way, the bis(trimethylsilyl)ethyne
complex was obtained. Silyl migration to give the bis(trimethylsilyl)vinylidene complex was observed at elevated temperature and
represents the first cobalt example of this reaction. As the first cobalt vinylidene complex the bis(trimethylsilyl)vinylidene complex
was characterized by an X-ray structure analysis. Reaction of the cobalt chelate with an Arduengo type carbene unexpectedly gave
a non-chelated cobalt complex bearing the carbene ligand and ethene at the same metal atom. This complex was also structurally
characterized. © 2001 Elsevier Science B.V. All rights reserved.
chemistry of self-organizing and supramolecular materi-
als [15–29].
1. Introduction
Most of the work in the field of Fischer type carbene
complexes has involved Group 6 metals, with emphasis
on chromium and tungsten [5]. Catalytic applications
recently focus on ruthenium carbene complexes. Some
metals, however, have been rather neglected.
We have contributed to the chemistry of cyclopenta-
dienylcobalt complexes bearing a pendant phosphane
ligand. This chemistry allows for the preparation of
stable alkyne [30], bicyclopropyilidene [31], and 3,3-
diphenylvinylcarbene complexes [32], facilitates new re-
arrangement reactions of strained cyclopropene ligands
[32,33], and even allows the complete cleavage of a
phosphorus carbon triple bond in a phosphaalkyne
[34]. We wish to report here the syntheses and some
structures of new cobalt vinylidene and carbene
complexes.
Since their discovery by Fischer in 1964 [1], carbene
complexes of almost all the transition metals have been
prepared. While in the sixties and in the seventies of the
last century many structural and theoretical aspects of
carbene complexes were investigated, the last decades
have been dominated by applications of carbene com-
plexes in organic chemistry. Prominent examples are
the Do¨tz benzanellation reaction [2–7] and metathesis
reactions catalyzed by carbene complexes [8–14]. The
variety of carbene ligands has also broadened signifi-
cantly. In addition to typical Fischer or Schrock type
carbene complexes, bearing alkynyl or vinyl carbene,
vinylidene and cumulenylidene ligands, bidendate car-
bene ligands and carbene ligands, that are stable with-
out a metal (Arduengo carbenes) have been reported.
Many of the complexes of these ligands show interest-
ing chemical properties, and the most highly unsatu-
rated ones, in particular, are now being applied to the
2. Vinylidene complexes
* Corresponding author. Fax: +49-511-762 4616.
E-mail address: holger.butenschoen@mbox.oci.uni-hannover.de (H.
Butenscho9 n).
The chemistry of cyclopentadienylmetal complexes in
which a pendant phosphane ligand is used to facilitate
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00676-8

J. Foerstner et al. / Journal of Organometallic Chemistry 617–618 (2001) 412–422
413
chelation is a rapidly growing field [35]. In many
cases, the presence of the bridge leads to the stabiliza-
tion of complexes that are not otherwise observed
in the usual chemistry of cyclopentadienyl metal
complexes. Thus in contrast to non-chelating systems,
the reaction of the cobalt chelate 2, which is easily
obtained from chloride 1, with ethyne gave vinylidene
complex 3, which has been fully characterized and
represents the first vinylidene complex of a cyclopenta-
dienylcobalt system. 3 is obtained in higher yield if it is
prepared from 1 with Na/Hg as the reducing reagent
[30,36].
As the chemistry of cyclopentadienylcobalt com-
plexes with alkynes is dominated by cyclooligomeriza-
tion reactions [37], cobalt vinylidene complexes are
rarely observed. The only other examples are those
reported by Bianchini upon the reaction of a cobalt(0)
tripod complex with terminal alkynes [38–40]. Subse-
quently we reported the synthesis of the tert-
butylvinylidene complex corresponding to 3 upon
reaction of 3,3-dimethyl-1-butyne with 1 and Na/Hg
[30].
In order to perform a codimerization reaction, the
vinylidene complex 3 was treated with diphenylethyne
and bis(trimethylsilyl)ethyne at 140°C in a sealed tube.
The reaction with diphenylethyne gave, after chromato-
graphic work-up in air, a cyclobutadiene complex, the
phosphane oxide 7. The corresponding phosphane is a
known compound [34]. Apparently the reaction in-
volves a displacement of the vinylidene ligand by
diphenylethyne. Decomplexation of the phosphane arm
enables the coordination of a second diphenylethyne
ligand followed by cyclization. A reversed order of
steps seems less likely, since the vinylidene ligand is not
involved in the coupling process.
The reaction of 1 with bis(trimethylsilyl)ethyne gave
the bis(trimethylsilyl)vinylidene complex 8 as the only
product in 48% yield. This is in accord with the obser-
vation that bis(trimethylsilyl)ethyne does not usually
cyclooligomerize. To confirm that this is indeed the
result of a silylalkyne complexation, followed by a silyl
migration, the bis(trimethylsilyl)ethyne complex 9 was
prepared from the chloride
1 and bis(trimethyl-
silyl)ethyne in 93% yield.
When cobalt(II) chloride
1 was treated with
trimethylsilylethyne and Na/Hg in THF at tempera-
tures between −50 and 20°C for 2 h, a mixture of the
alkyne and vinylidene complexes 4 and 5 was obtained
in 79% overall yield. Extension of the reaction time to
24 h gave trimethylsilylvinylidene complex 5 as the only
product in 54% yield. 4 and 5 were characterized spec-
troscopically. Attempts to deprotonate 5 failed (BuLi at
−78 and 20°C, t-BuLi at −78°C).
The chemistry of the vinylidene complex 3 was briefly
explored. Although many attempted reactions resulted
in the formation of decomposed material only, some
reactions with sources of CO (CO gas, arenetricar-
bonylchromium complex, diironenneacarbonyl) re-
sulted in the formation of the known carbonyl complex
6 [41,42].

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The DSC (differential scanning calorimetry) analysis
Cp ring, the ethylene bridge, P, and C6 and C7 of the
vinylidene ligand. The relatively high ratio of maximum
to minimum principle mean square atomic displace-
ments of atom C5 (3.0) indicates that the ethylene chain
linking the Cp ring to the P atom may be disordered,
but attempts to refine the structure in the acentric space
group Pna21 or using a disordered model were unsuc-
cessful, suggesting that deviations from ideal symmetry
are slight. The Cp–Co–P angle [120.4(6)°] is, however,
comparable with that found in structures of other
cobalt complexes containing the 2-(di-tert-butyl-phos-
phino)ethylcyclopentadienyl group (mean, 121°). The
of 9 does not show a melting point of the complex, but
rather reveals that a highly exothermic reaction occurs
at 86°C. In an analogous experiment, 9 was heated in
toluene at 110°C for 1 h, and a clean rearrangement
was observed, resulting in
a 93% yield of the
bis(trimethylsilyl)vinylidene complex 8. Alternatively, 8
was obtained from 9 photochemically within 18 h at
20°C in 56% yield. 7–9 have been characterized spec-
troscopically. The IR spectrum of alkyne complex 9
brought to light an interesting property of the com-
1
pound. Whereas the H-NMR spectrum indicated the
,
pure compound, the IR spectrum (KBr) exhibited an
unmistakable vinylidene absorption at 1595 cm−1 in
addition to the alkyne absorption at 1749 cm−1. More
importantly, its relative intensity increased when the
pressure during the preparation of the KBr pellet was
increased or applied for a longer time. This clearly
indicates, at least qualitatively, that the silyl migration
in the reaction of 9 to 8 is facilitated by pressure.
Although a more detailed interpretation of this effect
must be based on quantitative investigation, it is worth
mentioning that the effect indicates a negative activa-
tion volume, which is in accord with an insertion of
cobalt with formation of a Me3Si–Co–CꢀC–SiMe3
fragment.
Crystallization of 8 from toluene gave crystals suit-
able for an X-ray structure analysis (Fig. 1). 8 is the
first neutral cobalt vinylidene complex to be structurally
characterized. The molecules crystallize in the cen-
trosymmetric space group Pnma with an exact mirror
plane passing through the Co atom, the centroid of the
CꢁC double bond distance (C6–C7) is 1.319(4) A and is
similar to those in other vinylidene complexes (1.25–
,
1.41 A) [43,44]. The CoꢁC bond length (Co–C6) at
1.724(3) A is shorter than those observed in Co carbene
complexes (mean, 1.881 A) and almost as short as the
,
,
Co–C bond in the analogous carbonyl complex, car-
bonyl(h5 - 2 - (di - tert - butylphosphino)ethylcyclopenta-
,
dienyl)cobalt(I) (6) [1.702(3) A], indicating considerable
double bond character in this bond. It is also similar to
that in the cobalt tripod cation [(PP3)Co{CꢁC(H)Ph}]+
,
[1.71(3) A] [30], though the high error associated with
this latter bond distance prevents a useful comparison.
The Cp–Co–C6 angle at 136(1)° and the P–Co–C6
angle at 103.2(1)° are respectively smaller and larger
than the corresponding angles in the CO complex 6
[140.8(1) and 97.2(1)°]. This, together with the smaller
than expected Co–C6–C7 angle of 172.6(3)°, is proba-
bly the result of repulsive steric interaction between the
tert-butyl groups on the P atom and the methyl groups
on the Si atoms. Unfortunately, we have not been able
,
Fig. 1. Structure of 8 in the crystal. Selected bond lengths (A) and angles (°) (Cp is the centroid of the cyclopentadienyl ligand; the numbering
scheme is arbitrary): Co–C1 2.069(3), Co–C2 2.091(3), Co–C3 2.055(4), Co–Cp 1.68(1), C3–C4 1.499(6), C4–C5 1.434(7), C5–P 1.854(4), Co–P
2.160(1), Co–C6 1.724(3), C6–C7 1.319(4), C7–Si 1.870(2), C6–Co–P 103.2(1), Cp–Co–P 120.4(3), Cp–Co–C6 136(1), Co–C6–C7 172.6(3),
C6–C7–Si 117.84(8), Si–C7–Si* 124.3(2).

J. Foerstner et al. / Journal of Organometallic Chemistry 617–618 (2001) 412–422
415
to obtain crystals of the bis(trimethylsilyl)ethyne com-
plex 9, but a computer simulation of 9 based on the
geometry of the analogous diphenylethyne complex, in
which the phenyl groups are bent by 13° out of the
coordination plane away from the phosphine [39], indi-
cates that 9 is highly sterically crowded, suggesting that
the rearrangement of 9 to 8 probably results in a
considerable loss of steric repulsion.
Although the observation of such silyl migrations
from silylalkyne to silylvinylidene ligands in mononu-
clear metal complexes is rare, there is some literature
precedence. The reaction was first mentioned by
Sakurai in 1987, who reported the effect in a man-
ganese complex [45]. In 1991 Werner et al. reported this
type of reaction in coordinatively unsaturated rhodium
complexes [46–49]. Connelly et al. found the reaction
to take place in an arene chromium complex, and, most
interestingly, that a one-electron oxidation of the
bis(trimethylsilyl)vinylidene complex favored the re-
verse reaction back to the alkyne complex. More re-
cently Berke found that the reaction also works with an
18-electron iron system [50]. The reaction of 9 to 8 is
the first example using cobalt.
3. Carbene complexes
As in the case for the non-bridging cobalt vinylidene
complexes, non-bridging cobalt carbene complexes are
also comparatively rare [51,52]. Recently, metal com-
plexes of stable heterocyclic carbenes (Arduengo type
carbenes) have gained in importance in processes such
as hydroformylation and catalytic ring closing metathe-
sis [53–55]. Complexes with carbene ligands of this type
had previously been prepared from the respective alke-
nes, like 13, which gives the cobalt complex 14 upon
reaction with CpCo(CO)2 [56].
The mononuclear bis(trimethylsilyl)butadiyne com-
plex 10 was obtained in 72% yield by treatment of the
ligand with an equimolar amount of 1 and Na/Hg.
Heating of 10 at 110°C in toluene for 5 days resulted in
some decomposition and a poor yield of a product,
which on the basis of its IR and MS data has been
tentatively characterized as the cyclobutadiene complex
11. Irradiation of 10 also did not give a vinylidene
complex. Treatment of bis(trimethylsilyl)butadiyne with
two equivalents of 1 and Na/Hg presumably gives the
dinuclear vinylidene complex 12, which has only been
incompletely characterized and which decomposed dur-
ing the 13C-NMR measurement. The identification of
12 is strongly based on the IR spectrum, which in
contrast to that of 10 does not show an alkyne absorp-
tion band but instead an intense absorption at 1607
cm−1, which we attribute to the vinylidene valence
In an attempt to attach an Arduengo type carbene to
the cobalt chelate, 1,3-diisopropyl-3,4-dimethyl-2,3-di-
hydro-1H-imidazol-2-ylidene (15) [57] was treated with
the ethene complex 2. In accord with all other experi-
ments in which 2 was used for ligand exchange reac-
tions with monodendate ligands, it was anticipated that
the ethene ligand would be replaced by the Arduengo
carbene. The reaction took place between −30 and
20°C and unexpectedly gave a 42% yield of the non-
chelated complex 16. Instead of loss of the ethene
ligand, the phosphane side arm became uncoordinated.
Complexes like 16, which bears a carbene and an
ethene ligand at one metal atom, are rarely observed
[58–61]. Formally such a complex represents the very
first step of a metathesis reaction.
16 has been characterized spectroscopically. The car-
bene carbon atom shows a broad 13C-NMR signal at
l=241.4 (w1/2:220 Hz), possibly the highest chemical
shift observed for the carbene carbon atom of an
Arduengo type carbene complex so far and a value
considerably higher than that found for 14 (l=207.38,
218.46 for CO and carbene carbon atoms) [56]. This
may be a result of backbonding or anisotropy effects
associated with the ethene ligand. The ethene ligand in
16 produces a signal at l=14.9 (w1/2:170 Hz). The
ethene ligand in 2 resonates at l=22.3. The signals of
the carbene ligand and that of the ethene ligand are
1
vibration. In addition, the H-NMR spectrum shows a
singlet for the trimethylsilyl groups at l=0.39 and
doublet at l=1.30 for the tert-butyl groups (3JP,H=13
Hz). The chelated cobalt systems give rise to an AA%BB%
line system and two multiplets for the ethylene bridges.
These data and the number of signals are in accord
with the formation of 12.

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J. Foerstner et al. / Journal of Organometallic Chemistry 617–618 (2001) 412–422
So far no intramolecular cyclization of the ethene
and the Co,C double bonds with formation of a cobal-
tacyclobutane has yet been observed for 16. Conse-
quently, no metathetic activity has been found.
4. Conclusions
The synthesis of silylvinylidene chelate complexes has
been reported. These include the first observation of a
silyl migration with vinylidene formation at a cobalt
atom. Bis(trimethylsilyl)cobalt chelate 8 was prepared
and strucuturally characterized. The synthesis of a car-
bene complex with an ethene ligand at the same metal
gave 16, which also was structurally characterized.
Structural and spectroscopic data indicate that the
ethene and carbene ligands compete for electron density
from the metal.
extraordinarily broad, presumably due to the cobalt
quadrupol moment (Fig. 2). In the 31P-NMR spectrum
a signal at l=29.7 indicates an uncoordinated phos-
phane side arm. 16 was crystallized from pentane, and
a suitable crystal has been subjected to a crystal struc-
ture analysis (Fig. 3).
5. Experimental
The analysis confirms the constitution of 16, in which
the phosphane side arm is uncoordinated and the car-
bene and the ethene ligand are simultaneously attached
to one cobalt atom. The bond length C27–C28
5.1. General
All operations involving air sensitive materials were
performed under argon using standard Schlenk tech-
niques. Diethyl ether, THF, benzene, and toluene were
dried over Na/K–benzophenone. Silica gel was heated
at reduced pressure and then put under normal pressure
with argon. This was repeated five times. Starting mate-
rials were either purchased or prepared according to
literature procedures. IR: Bruker ISS 25, Perkin–Elmer
,
[1.355(13) A] in the ethene ligand is shorter than the
C,C bond length in the ethene ligand of 2 [1.396(5)]
[36]. The cobalt carbene bond length Co1–C16
,
[1.929(8) A] is longer than the corresponding bond in
,
the structurally characterized complex 17 [1.902(3) A]
[56] but shorter than that in the Fischer carbene
,
cobalt(I) complex 18 [1.989(4) A], which has also been
structurally characterized [62]. Usually the carbene
metal bonds in Arduengo carbene complexes are longer
than those in Fischer type carbene complexes [53].
However, since 16 represents a carbene complex with
ethene as a ligand at the same metal atom, such a
comparison is difficult. It appears that the molecular
geometry is a result of a competition between the
electron donating and accepting properties of the two
ligands. Thus, the relatively short bond length in the
ethene ligand and the relatively short metal–carbene
bond indicate that a back donation to the carbene is
preferred. The isopropyl groups are bent away from the
ethene ligand, presumably for steric reasons, causing
a slight distortion of the carbene ligand, which is bent
out of planarity by about 3° [C16–N2–C17–C18
−2.6(19)°, C16–N1–C18–C17 −3.6(19)°].
1
FT 580, FT 1710. H-NMR: Bruker AVS 200 (200.1
MHz), AVS 400 (400.1 MHz). 13C-NMR: Bruker AVS
200 (50.3 MHz), AVS 400 (100.6 MHz). Spectra were
obtained with the DEPT and with the APT techniques.
+ and − indicate positive (C, CH2) and negative
phase (CH, CH3), respectively. 31P-NMR: H decoupled,
Bruker AVS 400 (161.9 MHz), 85% aqu. H3PO4 as
external standard. MS, FAB-MS, HRMS: Finnigan
AM 400, Fisons VG Autospec. Elemental analyses:
Haeraeus CHN-Rapid. Melting points: Bu¨chi appara-
tus according to Dr Tottoli, uncorrected.
5.2. {[2-Di(tert-butylphosphanyl-P)ethyl]cyclopenta-
dienyl}chlorocobalt(II) (2) [30]: impro6ed procedure
At 0°C 25.7 ml (41.1 mmol) of a 1.6 M solution of
butyllithium in hexane was added dropwise to a stirred
solution of 6.00 g (41.1 mmol) of di-tert-butylphos-
phane in 150 ml of THF. After completed addition, the
pale yellow solution was stirred for 1 h. At 25°C 3.78 g
(41.1 mmol) of spiro[2.4]hepta-4,6-diene [63] was added
dropwise. The mixture was heated at reflux until it
became colorless. At −50°C 5.34 g (41.1 mmol) of

J. Foerstner et al. / Journal of Organometallic Chemistry 617–618 (2001) 412–422
417
Fig. 2. 13C-NMR signals of the carbene (left) and the ethene ligands (right) in 16.
anhydrous cobalt(II)chloride was added to the obtained
solution of lithium [2-di(tert-butylphosphanyl)ethyl]-
cyclopentadienide. The mixture was warmed to 25°C
over 4 h and stirred at 25°C for another hour. After
condensation of the THF into a cold trap the residue
was extracted five times with 50 ml of diethyl ether each
time. The combined organic extracts were filtered
through a P4 frit covered with a 3 cm thick layer of
Celite. After solvent condensation into a cold trap 10.1
g (30.5 mmol, 74%) of 2 was obtained as a black–violet
solid.
diethyl ether until the filtrate remained colorless. After
solvent removal into a cold trap the residue was
separated by column chromatography (petroleum
ether–diethyl ether 3:1).
Fraction I: 169 mg (0.043 mmol, 38%) of 4 as
blue–green crystals (m.p. 106°C). IR (film): w˜ =3295
cm−1 (m, ꢀC–H), 3080 (m, Cp–H), 2960 (s, CH2,
CH3), 2898 (s, CH2, CH3), 2864 (s, CH2, CH3), 1715 (s,
CꢀC), 1601 (s), 1472 (s), 1385 (m, t-Bu), 1365 (s, t-Bu),
1240 (s), 1180 (m), 1168 (m), 1038 (m, Cp–R),
5.3. {p5:p1-[2-(Di-tert-butylphosphanyl-P)ethyl]cyclo-
pentadienyl}(trimethylsilylethyne)cobalt(I) (4) and
{p5:p1-[2-(di-tert-butylphosphanyl-P)ethyl]-
cyclopentadienyl}(trimethylsilyl-1-ethenylidene)cobalt(I)
(5)
(a) 110 mg (0.11 mmol) of trimethylsilylethyne was
added dropwise to a −50°C cold solution of 374 mg
(0.11 mmol) of 2 in 20 ml of THF. After 5 min 20.0 g
of sodium amalgam was added, and the solution was
slowly warmed to −45°C. After stirring the mixture at
this temperature for 10 min it was warmed slowly to
20°C and then stirred for 1 h. The THF was condensed
into a cold trap, and the residue was taken up with
diethyl ether and filtered through a P4 frit covered with
a 3 cm thick layer of Celite. The Celite was washed with
,
Fig. 3. Structure of 16 in the crystal. Selected bond lengths (A) and
angles (°): Co1–C1 2.07(2), Co1–C2 2.03(2), Co1–C3 2.07(2), Co1–
C4 2.04(2), Co1–C5 2.08(2), Co1–C16 1.929(8), Co1–C27 1.97(2),
Co1–C28 1.91(2), C16–N1 1.39(2), C16–N2 1.35(2), C27–C28
1.355(13), Co1–C27–C28 67.2(13), Co1–C28–C27 71.9(13), C27–
Co1–C16 91.6(6), C28–Co1–C16 95.2(7)

418
J. Foerstner et al. / Journal of Organometallic Chemistry 617–618 (2001) 412–422
by comparison of the spectroscopic data (1H-NMR,
IR).
1017 (m, Cp–R), 930 (m), 860 (s, C–Si), 845 (s, C–Si),
790 (s, Cp), 752 (s), 672 (s), 620 (m), 585 (m), 492 (m).
1H-NMR (200 MHz, [D6]benzene): l=0.55 (s, 9H,
12-H), 1.21 (d, 18H, 9-H, 3JP,H=11.5 Hz), 1.6–1.95
(m, 5H, 6-H, 7-H, 10-H), 3.85 [m, 2H, 2(5)-H or
3(4)-H], 6.03 [m, 2H, 2(5)-H or 3(4)-H]. 13C-NMR (100
MHz, [D6]benzene): l=1.2 (s, C-12), 25.3 (d, C-6,
5.4. Reaction of 3 with diphenylethyne
585 mg (1.82 mmol) of 3 and 160 mg (0.90 mmol) of
diphenylethyne in 20 ml of toluene in a sealed glass
ampule were heated at 140°C for 5 days. The solvent
was condensed into a cold trap at reduced pressure, and
the residue was chromatographed on silica gel
(petroleum ether–diethyl ether 1:1). Oxidation in air
gave 270 mg (0.41 mmol, 45%) of [h5-2-(di-tert-
butylphosphoranyl)ethylcyclopentadienyl](h4-tetra-
phenylcyclobutadiene)cobalt(I) (7) as a yellow, micro-
crystalline powder (m.p. 78°C).
1
2JC,P=6.8 Hz), 29.8 (s, C-9), 34.7 (d, C-8, JC,P=6.4
1
Hz), 37.1 (d, C-7, JC,P=19.3 Hz), 76.4 [s, C-2(5) or
C-3(4)], 80.3 (s, C-2(5) or C-3(4)], 108.3 (d, C-1, 3JC,P
=
7.2 Hz), signals for C-10, C-11 were not observed. MS
(70 eV, 90 °C): m/z (%): 394 (41) [M+], 378 (11)
[M+−CH4], 336 (35) [M+−Si(CH3)2], 321 (12) [M+
−Si(CH3)3], 296 (35) [M+−C5H10Si], 279 (53) [M+−
Si(CH3)2–C4H8], 265 (34) [M+−Si(CH3)3–C4H8], 239
(88) [M+−C5H10Si–C4H9], 183 (100) [M+−C5H10Si–
C4H9–C4H8], 137 (43), 118 (35), 106 (35), 91 (34), 73
(49).
IR (KBr): w˜ =3080 cm−1 (w), 3056 (m), 3026 (w),
2961 (m, CH2, CH3), 2870 (m, CH2, CH3), 1598 (m),
1499 (s), 1475 (m), 1445 (m), 1309 (w), 1157 (br., m,
t-Bu), 1025 (w, Cp–R), 817 (m, Cp), 772 (m, arom.),
745 (m, arom.), 698 (s, arom.), 590 (m), 565 (m).
1H-NMR (200 MHz, CDCl3): l=1.12 (d, 18H, 9-H,
3JP,H=13 Hz), 1.6–1.75 (m, 2H, 6-H), 2.20–2.40 (m,
2H, 7-H), 4.52 [s, 4H, 2(5)-H, 3(4)-H], 7.20 [m, 12H,
11(15)-H, 13-H], 7.44 [m, 8H, 12(14)-H]. MS (70 eV,
190°C): m/z (%): 669 (100) [M+], 506 (78) [M+−
P(O)tBu2], 416 (17), 327 (18) [M+−2(C4H8)–3(C6H5)],
312 (73) [M+−Ph4C4], 256 (12), 237 (10), 178 (16)
[C14H+10], 150 (15), 105 (7). Anal. Calc. for C43H46CoOP
(668.74): C 77.23, H 6.93. Found: C 76.32, H 7.00%.
Fraction II: 183 mg (0.46 mmol, 41%) of 5, brown
oil. IR (film): w˜ =3095 cm−1 (w, Cp–H), 2950 (s, CH2,
CH3), 2900 (m, CH2, CH3), 2870 (m, –CH2–, CH3),
1605 (br. m, vinylidene), 1475 (m), 1392 (w, t-Bu), 1370
(m, t-Bu), 1247 (m), 1149 (br. m), 840 (br. s, C–Si), 818
(s, Cp), 760 (w), 495 (w). 1H-NMR (200 MHz,
[D6]benzene): l=0.37 (s, 9H, 12-H), 1.30 (d, 18H, 9-H,
3JP,H=12.7 Hz), 1.72–1.85 (m, 2H, 6-H), 2.15–2.22
4
(m, 2H, 7-H), 2.62 (d, 1H, 11-H, JP,H=9.6 Hz), 4.61
[br. s, 2H, 2(5)-H or 3(4)-H], 4.91 [br. s, 2H, 2(5)-H or
3(4)-H]. 13C-NMR (100 MHz, [D6]benzene): l=1.2 (s,
C-12), 25.1 (d, C-6, 2JC,P=5.7 Hz), 29.8 (d, C-9,
1
2JC,P=2.8 Hz), 35.7 (d, C-8, JC,P=14.6 Hz), 40.2 (d,
5.5. {p5:p1-[2-(Di-tert-butylphosphanyl-P)ethyl]cyclo-
pentadienyl}[bis(trimethylsilyl)6inylidene]cobalt(I) (8)
from 3
1
C-7, JC,P=17.8 Hz), 80.3 [s, C-2(5) or C-3(4)], 81.36
2
[d, C-2(5) or C-3(4), JC,P=5.1 Hz], 108.3 (s, C-11),
3
110.5 (d, C-1, JC,P=7.6 Hz), 302.4 (br., C-10, w1/2
=
100 Hz). 31P-NMR (162 MHz, [D6]benzene): l=115.2.
MS (70 eV, 90 °C): m/z (%): 394 (43) [M+], 378 (8)
[M+−CH4], 336 (25) [M+−Si(CH3)2], 321 (32) [M+
−Si(CH3)3], 296 (47) [M+−C5H10Si], 279 (53), 265
(22) [M+−Si(CH3)3–C4H8], 239 (79) [M+−C5H10Si–
C4H9], 183 (100) [M+−C5H10Si–C4H9–C4H8], 137
(65), 118 (25), 106 (36), 91 (24), 73 (62). HRMS
(C20H36PSiCo): calc. 394.16559; found 394.16554.
(b) To a stirred solution of 204 mg (0.63 mmol) 2 in
30 ml of THF 60 mg (0.63 mmol) trimethylsilylethyne
was added at −30°C. After removing the ice-bath and
warming up to 25°C, the solution was stirred for 24 h
at ambient temperature. During this time the color
changed to reddish brown. After removal of all
volatiles into a cold trap, the residue was taken up with
50 ml of a 2:1 mixture of diethylether and pentane.
Filtration through a frit covered with a 2 cm layer of
Celite and washing the filter pad once with a small
amount of diethyl ether gave a red solution, which was
evaporated to dryness, affording 132 mg (0.34 mmol,
54%) of 5 as a red–brown powder. This was identified
A solution of 120 mg (0.37 mmol) of 3 and 94 mg
(0.37 mmol) of bis(trimethylsilyl)ethyne in 20 ml of
toluene in a sealed tube was heated at 140°C for 5 days.
Chromatography at silica gel (petroleum ether–diethyl
ether 3:1) followed by recrystallization from toluene
gave 83 mg (0.18 mmol, 48%) of {h5:h1-[2-(di-tert-
butylphosphanyl-P)ethyl]cyclopentadienyl}[bis(trime-
thylsilyl)vinylidene]cobalt(I) (8), which was identified
spectroscopically (see below).
5.6. {p5:p1-[2-(Di-tert-butylphosphanyl-P)ethyl]cyclo-
pentadienyl}[p2-bis(trimethylsilyl)ethyne]cobalt(I) (9)
153 mg (0.90 mmol) of bis(trimethylsilyl)ethyne was
added dropwise at −50°C to a solution of 290 mg
(0.88 mmol) of 1 in 20 ml of THF. After 5 min 14.0 g
of Na/Hg was added, and the mixture was stirred at
−45°C for 10 min and then stirred for 1 h at 20°C. The
THF was condensed into a cold trap, and the residue
was taken up with diethyl ether and filtered through a
P4 frit covered with a 3 cm thick layer of Celite. The

J. Foerstner et al. / Journal of Organometallic Chemistry 617–618 (2001) 412–422
419
Celite was washed with diethyl ether until the solution
became colorless. The diethyl ether was condensed into
a cold trap. Crystallization from diethyl ether gave 379
mg (0.81 mmol, 93%) of 9 as blue–green crystals [m.p.
(DSC) 86°C, exothermic reaction to 8].
117.2. MS (70 eV, 160 °C): m/z (%): 466 (4) [M+], 393
(6) [M+−SiMe3], 295 (27) [M+−C8H19Si2], 239 (6)
[M+−C8H18Si2–C4H8], 183 (9) [M+−C8H18Si2–
C4H8–C4H9], 170 (15) [C8H18Si+2 ], 155 (100) [C8H18Si+2
–CH3], 137 (4), 106 (7), 91 (6), 75 (27). Anal. Calc. for
C23H44Si2PCo (466.68): C 59.20, H 9.51. Found: C
59.21, H 9.40%.
IR (KBr): w˜ =3095 cm−1 (w, Cp), 2953 (s, CH2,
CH3), 2898 (s, CH2, CH3), 1749 (s, alkyne, compl.),
1594 (m), 1557 (m), 1474 (s), 1367 (m, t-Bu), 1243 (s),
1182 (w), 1147 (m), 1019 (Cp–R), 932 (w), 854 (br. s,
C–Si), 792 (m), 754 (m), 687 (m), 672 (m), 467 (w).
1H-NMR (200 MHz, [D6]benzene): l=0.54 (s, 18H,
11-H), 1.21 (d, 18H, 9-H, 3JP,H=12.0 Hz), 1.80 (m, 4H,
6-H, 7-H), 3.65+5.69 [AA%BB% line system, 4H, 2(5)-H,
3(4)-H, ꢀJ=4.0 Hz]. 13C-NMR (50 MHz, [D6]benzene,
APT): l=2.5 (−, s, C-11), 25.2 (+, d, C-6, 2JC,P=7.4
5.8. Crystal structure analysis of 8
C23H44CoPSi2, MW=466.7, dark red prism 0.28×
0.46×0.53 mm, orthorhombic Pnma [no. 62], a=
,
18.694(1), b=14.808(1), c=9.600(1) A, U=2657.4(4)
,
,
3
A , T=293 K, Z=4, Dx=1.17 g cm−3, u=0.71073
A, v(Mo–Ka)=0.803 mm−1, Enraf–Nonius CAD-4
2
Hz), 29.9 (−, d, C-9, JC,P=4.2 Hz), 34.3 (+, d, C-8,
diffractometer, 2.39BqB27.41°, 3147 independent
measured reflections, 2307 with I\2|(I). Structure
solved by direct methods and refined by least-squares
using Chebyshev weights on F2o to R1=0.040 [I\
2|(I)], wR2=0.141, 133 parameters, H atoms riding,
1
1JC,P=5.2 Hz), 38.5 (+, d, C-7, JC,P=20.0 Hz), 78.9
2
[−, d, C-2(5) or C-3(4), JC,P=8.6 Hz], 79.2 (−, s,
3
C-2(5) or C-3(4)], 106.9 (+, d, C-1, JC,P=6.7 Hz),
2
115.0 (+, br. d, C-10, JC,P=5.3 Hz). 31P-NMR (81
MHz, [D6]benzene): l=96.6. MS (70 eV, 50 °C) m/z
(%): 466 (2) [M+], 295 (31) [M+−C8H19Si2], 240 (6)
[M+−C8H18Si2–C4H8], 184 (8) [M+−C8H18Si2–
2(C4H8)], 170 (12) [C8H18Si+2 ], 155 (100) [C8H18Si2+–
CH3], 137 (4), 107 (3), 97 (5), 73 (23). Anal. Calc. for
C23H44Si2PCo (466.68): C 59.25, H 9.51. Found: C
59.92, H 9.17%.
S=0.928, residual electron density +0.415/−0.609 e
−3
,
A
.
5.9. [p2-Bis(trimethylsilyl)butadiyne]{p5:p1-[2-(di-tert-
butylphosphanyl-P)ethyl]cyclopentadienyl}cobalt(I) (10)
101 mg (0.52 mmol) of bis(trimethylsilylbutadiyne
was added to 173 mg (0.52 mmol) of 1 in 30 ml of
THF. 20.0 g of Na/Hg was added, and the mixture was
warmed to −45°C. After 10 min the mixture was
slowly warmed to 20°C and stirred for 1 h. The THF
was condensed into a cold trap, the residue was taken
up with diethyl ether and filtered through a P4 frit
covered with a 3 cm thick layer of Celite. The Celite
was washed with diethyl ether until the filtrate became
colorless. The diethyl ether was condensed into a cold
trap. 184 mg (0.38 mmol, 72%) of 10, green, viscous oil.
IR (film): w˜ =3094 cm−1 (w, Cp), 2958 (s, CH2,
CH3), 2894 (s, CH2, CH3), 2104 (s, CꢀC), 2070 (s,
CꢀC), 1777 (s, CꢀC coord.), 1562 (m), 1473 (s), 1398
(m, t-Bu), 1388 (m, t-Bu), 1368 (m, t-Bu), 1245 (s),
1182 (m), 1065 (m, Cp–R), 1027 (m, Cp–R), 839 (br. s,
C–Si), 756 (s), 698 (m), 672 (m), 654 (w), 577 (w), 467
(m). 1H-NMR (200 MHz, [D6]benzene): l=0.42 (s,
9H, 16-H or 17-H), 0.50 (s, 9H, 16-H or 17-H), 1.09 (d,
5.7. {p5:p1-[2-(Di-tert-butylphosphanyl-P)ethyl]cyclo-
pentadienyl}[bis(trimethylsilyl)6inylidene]cobalt(I)
(8) from 9
74 mg (0.16 mmol) of 9 in 10 ml of toluene was
heated at 110°C for 1 h. The mixture was filtered
through a P4 frit covered with a 3 cm thick layer of
Celite, which was washed with toluene until the filtrate
became colorless. The volume of the solution was re-
duced to 5 ml. Crystallization at −30°C gave 69 mg
(0.15 mmol, 93%) of 8 as red crystals [m.p. 137°C
(DSC)].
IR (KBr): w˜ =3095 cm−1 (w, Cp–H), 2953 (m,
–CH2–, CH3), 2898 (m, –CH2–, CH3), 1595 (s, vinyli-
dene), 1473 (m), 1367 (w, t-Bu), 1244 (m), 1153 (w),
1019 (w, Cp–R), 862 (s, C–Si), 840 (s, C–Si), 805 (m,
Cp), 758 (w), 685 (w), 624 (w), 580 (w), 528 (w), 468
(w). 1H-NMR (200 MHz, [D6]benzene): l=1.30 (d,
3
9H, 9-H or 11-H, JP,H=12.0 Hz), 1.46 (d, 9H, 9-H or
3
3
18H, 9-H, JP,H=13.0 Hz), 1.75 (dt, 2H, 6-H, J=7.0
11-H, JP,H=12.0 Hz), 1.60–1.90 (m, 4H, 6-H, 7-H),
Hz, 3JP,H=19.0 Hz), 2.15 (dt, 2H, 7-H, J=7 Hz,
2JC,P=8.0 Hz), 4.71+5.06 [AA%BB% line system, 2×
2H, 2(5)-H, 3(4)-H, ꢀJ=4.0 Hz]. 13C-NMR (100 MHz,
3.62 (m, 1H, 2-H or 3-H or 4-H or 5-H), 4.31 (m, 1H,
2-H or 3-H or 4-H or 5-H), 5.11 (m, 1H, 2-H or 3-H or
4-H or 5-H), 5.80 (m, 1H, 2-H or 3-H or 4-H or 5-H).
13C-NMR (50 MHz, [D6]benzene, APT): l=0.5 (−,
C-16 or C-17), 1.3 (−, s, C-16 or C-17), 25.3 (+, d,
2
[D6]benzene): l=2.5 (s, C-12), 25.2 (d, C-6, JC,P=5.7
2
1
Hz), 29.9 (d, C-9, JC,P=4.3 Hz), 35.5 (d, C-8, JC,P
=
1
2
2
13.4 Hz), 39.8 (d, C-7, JC,P=18.9 Hz), 81.1 [d, C-2(5)
or C-3(4), 2JC,P=4.7 Hz], 81.3 [s, C-2(5) or C-3(4)],
109.7 (d, C-1, 3JC,P=7.0 Hz), 110.5 (s, C-11), 298.4
(br., C-10). 31P-NMR (81 MHz, [D6]benzene): l=
C-6, JC,P=6.9 Hz), 29.4 (−, d, C-9 or C-11, JC,P=
2
4.0 Hz), 30.1 (−, d, C-9 or C-11, JC,P=4.0 Hz), 34.6
1
(+, d, C-8 or C-10, JC,P=3.6 Hz), 35.3 (+, d, C-8 or
C-10, 1JC,P=10.2 Hz), 37.0 (+, d, C-7, 1JC,P=20.2

420
J. Foerstner et al. / Journal of Organometallic Chemistry 617–618 (2001) 412–422
Hz), 77.4 (−, C-2 or C-3 or C-4 or C-5), 78.9 (−, d,
C-2 or C-3 or C-4 or C-5, JC,P=8.9 Hz) 80.5 (−, C-2
(81 MHz, [D6]benzene): l=29.2, 56.5, 69.9, 106.8,
114.8.
2
or C-3 or C-4 or C-5), 83.5 (−, d, C-2 or C-3 or C-4
or C-5, 2JC,P=7.6 Hz), 96.4 (+, d, C-12 or C-13,
2JC,P=8.8 Hz), 103.2 (+, s, C-14 or C-15), 103.9 (+,
5.12. {p5[2-(Di-tert-butylphosphanyl-P)ethyl]cyclopenta-
dienyl}-(1,3-diisopropyl-4,5-dimethyl-2-dehydro-
1H-imidazol-2-ylidene)(p2-ethene)cobalt (I) (16)
3
s, C-14 or C-15), 110.8 (+, d, C-1, JC,P=7.3 Hz).
31P-NMR (81 MHz, [D6]benzene): l=94.0. MS (70 eV,
50 °C): m/z (%): 490 (10) [M+], 434 (2) [M+−C4H8],
393 (2) [M+−C2SiMe3], 375 (2) [M+−2(C4H9)], 296
(49) [M+−Me3SiC4SiMe3], 240 (8) [M+−Me3-
SiC4SiMe3–C4H8], 195 (10) [Me3SiC4SiMe3H+], 179
(45) [Me3SiC4SiMe+3 –CH4], 162 (7), 147 (7), 106 (9), 84
(30), 74 (100) [HSiCH+3 ]. HRMS (C25H44PSi2Co): calc.
490.2051; found 490.2044.
422 mg (2.35 mmol) of 1,3-diisopropyl-3,4-dimethyl-
2,3-dihydro-1H-imidazol-2-ylidene (15) was added at
−50°C to 760 mg (2.35 mmol) of 2 in 75 ml of
pentane. After stirring for 3 h and warming up to 20°C
the mixture was filtered through a P4 frit covered with
a 3 cm thick layer of Celite. Crystallization from the
filtrate at −30°C gave 493 mg (0.98 mmol, 42%) of 16,
red crystals (m.p. 134°C, dec.).
5.10. Thermolysis of 10
IR (KBr): w˜ =3688 (w) cm−1, 2960 (s, CH3, –CH2–),
1668 (m), 1640 (m), 1600 (m), 1464 (m), 1396 (m),
1368 (m), 1188 (w), 1132 (m), 1080 (m), 1020 (m), 912
(w), 808 (m), 756 (w), 654 (w), 516 (w). 1H-NMR (400.1
122 mg (0.25 mmol) of 10 in 10 ml of toluene was
heated at 110°C for 5 days. The color of the mixture
changed from green to brown. The toluene was con-
densed into a cold trap, and the residue was taken up
with diethyl ether and filtered through a P4 frit. After
solvent removal into a cold trap 67 mg of a brown–
black oil was obtained, which was tentatively character-
ized as the cyclobutadiene complex 11.
IR (film): w˜ =2956 (s), 2925 (s), 2875 (m), 2110 (w),
2060 (w), 2000 (w), 1472 (m), 1399 (w), 1368 (w), 1247
(m), 1020 (w), 842 (s), 758 (w). MS (70 eV, 170 °C): m/z
(%): 684 (4), 628 (2), 540 (4), 295 (20), 239 (35), 183
(48), 147 (100), 73 (37).
3
MHz, [D6]benzene): l=1.15 (d, JP,H=10.3 Hz, 18H,
3
9-H, 13-H), 1.33 (d, JH,H=6.1 Hz, 12H, 17-H, 19-H),
1.62 (s, 6H, 21-H, 23-H), 1.78–2.00 (m, 4H, 14-H), 2.35
(m, 2H, 6-H or 7-H), 2.75 (m, 2H, 6-H or 7-H), 4.14
(m, 2H, 16-H, 18-H), 4.53 (s, 1H, 2-H or 3-H or 4-H or
5-H), 4.92 (s, 1H, 2-H or 3-H or 4-H or 5-H), 5.24 (s,
1H, 2-H or 3-H or 4-H or 5-H), 5.45 (s, 1H, 2-H or 3-H
or 4-H or 5-H). 13C-NMR (100.6 MHz, [D6]benzene,
APT): l=10.2 (−, s, C-21, C-23), 14.9 (+, m, C-14,
w1/2:170 Hz), 22.5 (−, s, C-17, C-19), 23.0 (+,
1
1JC,P=23.1 Hz, C-8 or C-12), 25.0 (+, JC,P=7.0 Hz,
2
C-7), 30.0 (−, JC,P=14.0 Hz, C-9, C-13), 34.8 (+, d,
5.11. Bis(6inylidene) complex 12
2JC,P=7.0 Hz, C-6), 53.5 (−, s, C-16, C-18), 79.0 (−,
2
s, C-2 or C-3 or C-4 or C-5), 80.0 (−, d, JC,P=5.1
64 mg (0.33 mmol) of bis(trimethylsilyl)butadiyne
was added to 219 mg (0.66 mmol) of 1 at −50°C. After
5 min 15.0 g of Na/Hg was added and the mixture was
warmed to −45°C. After 10 min the mixture was
slowly warmed to 20°C and stirred for 1 h. The solution
was separated from the Na/Hg, and the THF was
condensed into a cold trap. The residue was taken up
with diethyl ether and filtered through a P4 frit covered
with a 3 cm thick layer of Celite. The Celite was washed
with diethyl ether until the filtrate was colorless. After
solvent condensation into a cold trap 171 mg (0.22
mmol, 66%) of 12 was obtained, as a brown, microcrys-
talline powder.
2
Hz, C-2 or C-3 or C-4 or C-5), 80.6 (−, d, JC,P=5.7
3
Hz, C-2 or C-3 or C-4 or C-5), 109.7 (+, d, JC,P=6.4
Hz, C-1), 124.6 (+, s, C-20, C-22), 241.4 (+, m, C-15,
w1/2:220 Hz). 31P{1H}-NMR ([D6]benzene): l=29.7
(s). MS (70 eV, 90°C): m/z (%) 506 (8) [M++2], 505
(11) [M++1], 504 (31) [M+], 478 (1) [M+−C2H4], 421
(1) [M+−C2H4–C3H7N], 364 (1) [M+−C2H4–
(C3H7N)2], 296 (5) [M+−C11H20N2], 281 (24), 240 (4),
196 (47), 154 (26), 112 (100), 91 (16), 73 (24), 65 (2).
5.13. Crystal structure analysis of 16
IR (KBr): w˜ =3095 cm−1 (w, Cp), 2961 (s, –CH2–,
CH3), 2951 (m, –CH2–, CH3), 1607 (br, m, vinylidene),
1475 (m), 1367 (m, t-Bu), 1261 (s), 1098 (br., s), 1028
(br., s, Cp–R), 843 (br., s, C–Si), 802 (s, Cp), 755 (w),
C28H50N2PCo, molecular weight 504.60, crystal sys-
tem orthorhombic, space group Pna21, a=23.805(2),
,
b=11.073(1), c=11.130(1) A, h=90, i=90, k=90°,
3
cm−3
,
,
V=2933.8(4) A , Z=4,
d
ber=1.142
g
1
450 (w), 419 (w). H-NMR (200 MHz, [D6]benzene):
F(000)=1096 e, v=6.56 cm−1, red crystal, crystal size
0.33×0.30×0.11 mm, Stoe IPDS (area detector)
3
l=0.39 (s, 18H, 12-H), 1.30 (d, 36H, 9-H, JP,H=13
,
Hz), 1.62 (m, 4H, 6-H), 2.20 (m, 4H, 7-H), 4.62+5.31
[AA%BB% line system, 2×2H, 2(5)-H, 3(4)-H, ꢀJ=3.0
Hz]. The sample decomposed during the 13C-NMR
measurement. 31P-NMR of the decomposed material
diffractometer, T=300(2) K, Mo–Ka=0.71073 A,
2qmin=2.03°, 2qmax=20.96°, 10376 measured reflec-
tions (923; −10–11; 911), 3085 independent, 1434
observed (I\2|) reflections, completeness of data

J. Foerstner et al. / Journal of Organometallic Chemistry 617–618 (2001) 412–422
421
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99.7%, R(I)=0.1441, absorption correction none, ex-
tinction correction none, refinement program SHELXL
-
93, full-matrix least-squares on F2, R(F,F\4|( f ))
=0.1360, wR(F2,all)=0.1551, minimum/maximum
−3
,
residual electron density −0.406/0.538 e A
.
6. Supplementary material
Crystallographic data (without structural factors) of
the structures described in this publication have been
deposited with the Cambridge Crystallographic Data
Centre, CCDC nos. 147197 (8) and 146998 (16). Copies
of the data can be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (Fax: +44-1223-336033; e-mail: deposit@
ccdc.cam.ac.uk or www: http//www.ccdc.cam.ac.uk).
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Am. Chem. Soc. 115 (1993) 8509.
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P.H. Dixneuf, Organometallics 14 (1995) 5263.
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P.H. Dixneuf, J. Chem. Soc. Chem. Commun. (1994) 859.
[28] D. Touchard, P. Haquette, A. Daridor, L. Toupet, P.H.
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Acknowledgements
This work was supported by the Deutsche
Forschungsgemeinschaft and the Fonds der Chemis-
chen Industrie. We are indebted to BASF AG,
Chemetall GmbH, and Degussa-Hu¨ls AG for donations
of chemicals.
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