η1-Vinylidene to η2-Alkyne Isomerization of Tungsten and Molybdenum Complexes

Article abstract of DOI:10.1002/ejic.200300314

The thermal isomerizations of η¹-vinylidene complexes [(η⁵-C₅H₅)(CO)(NO)W=C=CHR] [5a, R = Si(CH₃)₂C(CH₃)₃; 5c, R = C(CH ₃)₃] as well as [(η⁵-C₅H ₅)(CO)(NO)Mo=C=CHC(CH₃)₃] (8), to the corresponding η²-1-alkyne complexes [(η⁵-C ₅H₅)(CO)(NO)W(η²-H-C≡C-R)] [7a, R = Si(CH₃)₂C(CH₃)₃; 7c, R = C(CH ₃)₃] and [(η⁵-C₅H ₅)(CO)(NO)Mo{η²-H-C≡C-CHC(CH₃) ₃}] (9) has been investigated. Activation parameters for the isomerization of 5a in [D₆]benzene and 8 in [D₈]toluene and [D₅]ethanol were determined. In [D₈]toluene η ¹-vinylidene complex 5a undergoes a single step 1,2-shift of the silyl group from C_β to C_αm. However, complex 8 shows dichotomous behavior. The isomerization 8 → 9, dependent upon the solvent applied, occurs by means of two different pathways: in a nonpolar solvent, 8 tautomerizes via the 1,2-migration of the hydrogen atom to 9 and in ethanol this tautomerization proceeds by a multi-step process via deprotonation-protonation and subsequent reductive elimination. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejic.200300314

FULL PAPER
η1-Vinylidene to η2-Alkyne Isomerization of Tungsten and Molybdenum
Complexes
Junes Ipaktschi,*[a] Javad Mohsseni-Ala,[a] and Sascha Uhlig[a]
Keywords: Vinylidene ligands / Alkyne ligands / Isomerization / Kinetics / Isotope effects
The thermal isomerizations of η1-vinylidene complexes [(η5-
C5H5)(CO)(NO)W=C=CHR] [5a, R = Si(CH3)2C(CH3)3; 5c, R =
C(CH3)3] as well as [(η5-C5H5)(CO)(NO)Mo=C=CHC(CH3)3]
(8), to the corresponding η2-1-alkyne complexes [(η5-
shift of the silyl group from Cβ to Cα. However, complex 8
shows dichotomous behavior. The isomerization 8 Ǟ 9, de-
pendent upon the solvent applied, occurs by means of two
different pathways: in a nonpolar solvent, 8 tautomerizes via
C5H5)(CO)(NO)W(η2-H−CϵC−R)] [7a, R = Si(CH3)2C(CH3)3; the 1,2-migration of the hydrogen atom to 9 and in ethanol
7c,
R
=
C(CH3)3] and [(η5-C5H5)(CO)(NO)Mo{η2-
this tautomerization proceeds by a multi-step process via de-
H−CϵC−CHC(CH3)3}] (9) has been investigated. Activation protonation-protonation and subsequent reductive elimina-
parameters for the isomerization of 5a in [D6]benzene and 8
tion.
in [D8]toluene and [D5]ethanol were determined. In [D8]tol-
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
uene η1-vinylidene complex 5a undergoes a single step 1,2- Germany, 2003)
Introduction
A great deal of attention has been devoted to the iso-
merization of transition metal η1-vinylidene and η2-1-al-
kyne complexes over the past two decades.[1] Thus, it is now
well established that the thermodynamic stabilities and
properties of such derivatives are essentially a function of
the nature of both the metal center and its ancillary li-
gands.[1,2] It is well-known that η1-vinylidene complexes of
electron-rich transition metals are thermodynamically more
Scheme 1. Alternative pathways for the η2-1-alkyne Ǟ η1-vinyl-
stable than the corresponding η2-1-alkyne derivatives.[1,3]
This fact is widely used in the preparation of η1-vinylidene
complexes.[4]
idene rearrangement
rely been described in the literature.[5] Bly et al.[5g,5h] have
observed the isomerization of the cationic complexes [Fe(ϭ
CϭCR1R2)(η5-C5H5)(CO)2]ϩOTfϪ to the corresponding
The mechanism of the η2-1-alkyne Ǟ η1-vinylidene re-
arrangement has been extensively studied both experimen-
tally and theoretically.[2,4,5Ϫ8] Two alternative pathways are
discussed so far in the literature (Scheme 1): via either an
intramolecular 1,2-hydrogen shift (AϪBϪD)[2,4e,6a,6b] or by
the formation of a hydride alkynyl species C and concomi-
tant 1,3-hydrogen shift.[4a,4c,4d,4f,5a,8,6b] Electron-rich metal
complexes favor the AϪCϪD[4a,4d,8b] pathway whereas elec-
tron poor complexes prefer the AϪBϪD[4e,5a,6a] pathway.
The reaction order for the 1,3-hydrogen shift is also a
matter of active debate. Recent experimental and theoretical
studies demonstrated a bimolecular mode for this pro-
cess[4c,4a,4d,9] while others support a unimolecular reac-
tion.[2]
η2-alkyne
derivatives
[Fe(η2-R1CϵCR2)(η5-C5H5)-
(CO)2]ϩOTfϪ by an alkyl shift from the β- to α-carbon
atom. In the same way, Connelly et al.[5b,5g,5i] have observed
η1-vinylidene Ǟ η2-alkyne rearrangements induced by one-
electron oxidation of the 18-electron complexes [MϭCϭ
C(SiMe3)2(η6-C6R6)(CO)2]ϩ (M ϭ Cr, Mo).
To shed some light on the mechanism of the η1-vinyl-
idene Ǟ η2-alkyne isomerization we have studied the ther-
mal isomerization of the tungsten η1-vinylidene complexes
5aϪc, as well as of the molybdenum derivatives 8.
The isomerization of η1-vinylidene transition metal com-
plexes into the corresponding η2-alkyne complexes has ra-
Results
[a]
Synthesis and Characterization of 5a,b
Institute of Organic Chemistry, Justus-Liebig University,
Heinrich-Buff-Ring 58, 35392 Giessen, Germany
Fax: (internat.) ϩ49-(0)641-9934309
The reaction of the tungsten carbonyl complex 1 with
lithium alkynyl 2a,b in THF at Ϫ30 °C led to a deep green
E-mail: junes.ipaktschi@org.chemie.uni-giessen.de
Eur. J. Inorg. Chem. 2003, 4313Ϫ4320
DOI: 10.1002/ejic.200300314
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4313

J. Ipaktschi, J. Mohsseni-Ala, S. Uhlig
FULL PAPER
solution of the lithium metalate 3a,b (Scheme 2). Treatment alkyne ratios of the interconversion of 8, 5a,b and 5c after
of this solution with dilute HCl resulted, after purification heating in toluene for 24 h are reported in Table 1. Longer
through chromatography, in the formation of the η1-vinyl- reaction times lead to the decomposition of 5b and 5c.
idene complexes 5a,b as a mixture of two rotamers. It is Interestingly the isomerization rate of 8 is highly dependent
interesting to note that, after protonation the CϪSi bond is on the nature of the solvent. In ethanol as the solvent the
cleaved, in the course of the reaction of 3b, yielding the transformation occurs quantitatively after heating for 2 h at
η1-vinylidene complex 6 (21% yield).[10] This behavior has 79 °C.[13]
precedents in the literature, i.e., the formation of [CpRuϭ
Table 1. Product ratios of the thermal interconversion of the η1-
vinylidenes 8, 5aϪc after 24 h at 110 °C
CϭCH2(dippe)][BPh4]
from
[CpRuCl(dippe)]
with
HϪCϵCϪSiMe3,[4g] and the formation of [CpFeϭCϭ
CH2(dppm)][BF4] from [CpFeϪCϵCϪSiMe3(dppm)].[11]
η1-Vinylidene complexes
Product ratio[a]
η2-alkyne:
η1-vinylidene[b]
[Mo{ϭCϭCHC(CH3)3}(η5-C5H5)-
(CO)(NO)] (8)
100:0
79:21
63:37
6:94
[W{ϭCϭCHSi(CH3)2C(CH3)3}(η5-C5H5)-
(CO)(NO)] (5a)
[W{ϭCϭCHSi(C6H5)2CH3}(η5-C5H5)-
(CO)(NO] (5b)
[W{ϭCϭCHC(CH3)3}(η5-C5H5)(CO)-
(NO)] (5c)
[a]
[b]
All reactions were carried out in toluene.
The product ratios
were determined by measuring the relative peak integration of the
1H NMR signals of the η2-alkyne and η1-vinylidene complexes in
the crude product spectra.
Also a quantitative isomerization to 9 is observed by tre-
ating the THF solution of 8 at room temperature with 10%
aqueous NaOH for 20 min (Scheme 3).
Scheme 2. Synthesis of vinylidene complexes 5 and 6 from the tung-
sten complexes 1
Compound 5a is an orange crystalline solid, whereas 5b
is a dark red oil. These η1-vinylidenes can be stored under
argon at Ϫ20 °C for several months. Their unequivocal
characterization was achieved by means of standard spec-
troscopic techniques and, in particular, by the 13C NMR
signal at δ ϭ 331Ϫ335 ppm that is characteristic for the α-
carbon atom of the η1-vinylidene moiety.
Scheme 3. Base-catalyzed isomerization of vinylidene complexes 8
Kinetic Studies
Upon treatment of the deep green solution of lithium me-
talate 3a,b with methyltrifluoromethanesulfonate at Ϫ30
°C, the η2-alkynes 4a,b were obtained (Scheme 2). We sup- a) Isomerization in a Nonpolar Solvent
pose that the alkylation of the metalate anion occurs at the
The isomerization rates of 8 to 9 were measured at fixed
β-carbon atom generating the corresponding η1-vinylidene
complexes, which then isomerize by migration of the silyl
group to 4a,b. Structural assignment of the η2-alkynes 4a,b
are based on NMR spectroscopic data and by the charac-
teristic CϵC stretching vibration in IR spectra, respec-
tively.[12]
temperatures between 80 °C and 140 °C in [D8]toluene
while the rate of transformation of 5a to 7a was measured
between 130 °C and 150 °C in [D6]benzene by varying the
starting concentration of the η1-vinylidene complexes.[14]
The results indicate that the η1-vinylidene Ǟ η2-alkyne iso-
merization is first-order. The first-order rate constants
measured at five different temperatures are listed in Table 2
and 3. From the Eyring plot, we derived the activation par-
Isomerization of η1-Vinylidene Complexes
Molybdenum-vinylidene complex 8 and tungsten deriva- ameters for 8 Ǟ 9: ∆H# ϭ 29.0 Ϯ 0.5 (kcal·molϪ1) and
tives 5a,b rearrange under refluxing toluene to the corre- ∆S# ϭ Ϫ1.8 Ϯ 0.2 (cal/mol·K) and for 5a Ǟ 7a: ∆H#
ϭ
sponding η2-alkyne complexes 9 and 7a,b. Whereas the 27.2 Ϯ 0.4 (kcal·molϪ1) and ∆S# ϭ Ϫ9.7 Ϯ 0.9 (cal/mol·K).
tungsten η1-vinylidene complex 5c with a tert-butyl group For the rearrangement of [RuCp(HϪCϵCϪMe)(PMe3)2]PF6
at the β-carbon atom, is much more stable than 5a,b and 8 to [RuCp(ϭCϭCHMe)(PMe3)2]PF6 the kinetic study in
and rearranges very poorly upon heating at 110 °C to the CH3CN by Bullock gave ∆H# ϭ 23.4 Ϯ 0.3 kcal·molϪ1 and
corresponding η2-alkyne complex 7c. The η1-vinylidene/η2- ∆S# ϭ 3.9 Ϯ 0.9 (cal/mol·K).[15]
4314
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Vinylidene to Alkyne Isomerization of Tungsten and Molybdenum Complexes
Table 2. Rates of the isomerization and kinetic deuterium isotope effect of 5a to 7a and 5a-D to 7a-D in [D6]benzene
FULL PAPER
Temp. (°C)
104kH (sϪ1
)
r[a]
104kD (sϪ1
)
r[a]
kH/kD
130
135
140
145
150
1.174
1.731
2.706
4.037
6.067
0.999
0.999
0.998
0.999
0.999
0.957
1.482
2.310
3.414
4.939
0.999
0.999
0.999
0.999
0.999
1.227
1.168
1.172
1.182
1.228
average: 1.196 Ϯ 0.030
[a]
Correlation coefficient for the first-order plot.
the η1-vinylidene ligand in the transition state during the
migration of the silyl group. Contrary, for the later iso-
merization, kH/kD suggests that the bond to the isotopically
substituted hydrogen atom is being broken in the rate-de-
termining step. The 1,2-shift of the silyl group is also sup-
ported by the comparison of the isomerization ability of 5a
and 5b versus 5c where the reaction rate decreases in the
order: Si(CH3)2C(CH3)3 Ͼ Si(C6H5)2(CH3) Ͼ C(CH3)3.[17]
Table 3. Rates of the isomerization and kinetic deuterium isotope
effect of 8 to 9 and 8-D to 9-D in [D8]toluene
Temp. (°C) 105kH (sϪ1
)
r[a]
105kD (sϪ1
)
r[a]
kH/kD
80.0
90.2
106.2
121.4
139.6
0.558
1.733
11.483
43.883
236.516
0.999
0.998
0.999
0.998 22.070
0.999 123.489
0.280
0.920
5.266
0.999 2.0
0.998 1.9
0.999 2.2
0.998 2.0
0.999 1.9
average:
2.00 Ϯ 0.2
b) Isomerization in Ethanol
In order to obtain more information on the mechanism
of the η1-vinylidene Ǟ η2-alkyne isomerization we exam-
ined the isomerization of 8 in ethanol as the solvent. The
isomerization rate of 8 in C2D5OH, measured in a 0.1 
solution at fixed temperatures between 60 °C and 100 °C,
is much faster than the reaction rate in [D8]toluene. The
pseudo first-order rate constants are listed in Table 4. From
Eyring plots we have obtained the activation parameters for
the isomerization 8 Ǟ 9 in C2D5OH, ∆S# ϭ Ϫ21.3 Ϯ 0.5
(cal/mol·K) and ∆H# ϭ 19.6 Ϯ 1.6 kcal·molϪ1. Compared
to the isomerization in [D8]toluene, the most striking point
of the thermodynamics of the reaction, is the high negative
value of ∆S# in C2D5OH. This leads one to suppose, that
in toluene and ethanol two different mechanisms govern the
reaction. This presumption is further strongly supported by
the large differences of the kinetic isotope effect for k8Ǟ9
measured in C2D5OH and k8-DǞ9-D in C2D5OD versus the
k8Ǟ9/k8-DǞ9-D measured in [D8]toluene as the solvent. The
k8Ǟ9/k8-DǞ9-D ratio also shows a large temperature depen-
dency in ethanol contrary to the value in toluene. From
extrapolation of the reaction rate the values kH/kD ϭ 15.7
at 60 °C and kH/kD ϭ 7.1 at 100 °C, are obtained.
[a]
Correlation coefficient for the first-order plot.
Principally the isomerization of 5a to 7a can occur either
by migration of the silyl group or of the hydrogen atom
from Cβ to Cα, however, a priori it is not possible to differ-
entiate between one or the other reaction path. In order to
distinguish between these two possibilities, we determined
the kinetic deuterium isotope effect for the conversion of
[(η5-C5H5)(CO)(NO)WϭCϭCDSi(CH3)2C(CH3)3] (5a-D)
to [(η5-C5H5)(CO)(NO)W{η2-DCϵCSi(CH3)2C(CH3)3}]
(7a-D) and as a comparison the kinetic deuterium isotope
effect for the transformation 8-D to 9-D (Scheme 4).
Table 4. Rates of the isomerization and kinetic deuterium isotope
effect of 8 to 9 in [D5]ethanol and 8-D to 9-D in [D6]ethanol (kH/
kD ϭ 15.7 at 60 °C and 7.1 at 100 °C)
Scheme 4. Thermal isomerization of 5a-D and 8-D
8 Ǟ 9
8-D Ǟ 9-D
Temp. (°C) 104 kH (sϪ1
)
r[a]
Temp. (°C) 104 kD (sϪ1
)
r[a]
The k5aǞ7a/k5a-DǞ7a-D in [D8]toluene was found to be
1.20 Ϯ 0.03 and k8Ǟ9/k8-DǞ9-D ϭ 2.00 Ϯ 0.2 (Table 2 and
3), both effects show very minor temperature dependency.
The kinetic isotope effect for the former reaction is in the
range of normal secondary isotope effects,[16] and is the re-
sult of a hybridization change from sp2 to sp of the Cβ of
59.0
69.0
79.3
88.5
97.6
1.070
2.200
4.450
8.833
24.920
0.998 83.7
0.998 94.4
0.999 106.2
0.999 116.2
0.998 125.0
0.717
2.233
5.417
12.867
25.68
0.998
0.999
0.998
0.999
0.999
[a]
Correlation coefficient for the first-order plot.
Eur. J. Inorg. Chem. 2003, 4313Ϫ4320
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J. Ipaktschi, J. Mohsseni-Ala, S. Uhlig
FULL PAPER
H/D Exchange
Theoretical studies on vinylidene transition metal com-
plexes have identified the electron density on the Cβ
atom,[18] and the protonation of vinylidene complexes to
the carbyne derivatives occurs via another mechanism.[9,19]
In order to distinguish between these two possibilities we
investigated the exchange rate in the presence of D2O and
C6D5OD, respectively. While after 3 h at 45 °C the H/D
exchange in 10 molar D2O/[D8]THF was complete, no ex-
change occurred in the presence of C6D5OD. The result of
this experiment clearly shows that the H/D exchange occurs
by a dissociative pathway.
The η1-Vinylidene derivatives 8 and 5a undergo H/D ex-
change at the Cβ atom without isomerization. Treatment of
tetrahydrofuran solutions of 5a at room temperature and 8
at 45 °C with D2O produces the corresponding deuterated
derivatives 8-D and 5a-D (Scheme 5).
Discussion
Our kinetic study of the isomerization of 8 Ǟ 9 and 5a
Ǟ 7a suggests that the η1-vinylidene Ǟ η2-alkyne isomeriz-
ation of the molybdenum and tungsten complexes studied
here, follows two different pathways.
In nonpolar solvents such as toluene or benzene, starting
from the η1-vinylidene 5a, a 1,2-shift of the silyl group takes
place by forming the transition state 10 (Scheme 7). Slipp-
age processes of the silyl group as well as the metal, fol-
lowed by CϪSi σ bonding and π coordination of the metal
center generated the η2-alkyne complexes 7. The magnitude
of the kinetic isotope effect and the activation entropy ob-
served for the isomerization 5a Ǟ 7a are in good agreement
with an isomerization mechanism of least motion; namely,
the 1,2-silyl group shifts in a concerted fashion.[20,21] In the
same manner the thermal tautomerization of 8 in nonpolar
solvents occurs by a 1,2-migration of the hydrogen atom
leading to the transition state 11, followed by a slippage of
the metal to yield the η2-1-alkyne complex 9. The observed
kinetic isotope effect supports the isomerization pathway,
DǞBǞA (Scheme 1) with an asymmetrically bonded tran-
sition state in a single-step hydrogen or silyl transfer reac-
tion for both transformations depicted as 10 and 11.[22,23]
Scheme 5. H/D exchange of vinylidene complexes 8 and 5a
Besides the deprotonation-deuteration pathway, it is con-
ceivable that the H/D exchange occurs by the prior addition
of deuterium to yield a carbyne derivative (Scheme 6).
Scheme 6. Alternative mechanisms for the H/D exchange of vinyl-
idene complexes
Scheme 7. Postulated transition states 10 and 11 and structure of gold complexes 12
Scheme 8. Postulated mechanism for the isomerization of vinylidene complexes 8 in ethanol
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Vinylidene to Alkyne Isomerization of Tungsten and Molybdenum Complexes
FULL PAPER
diluted with 20 mL of water led to a dark red solution. After the
reaction mixture was allowed to reach room temperature, the THF
was removed under reduced pressure. The residue was extracted
with diethyl ether, washed with saturated aqueous sodium chloride
and dried with magnesium sulfate. The dark red oil was filtered
through silica gel (n-pentane/diethyl ether, 5:1) to remove decompo-
sition products. Chromatography on silica gel (n-pentane/diethyl
ether, 5:1) yielded 341 mg (21%) of 5b as dark red oil and 230 mg
(15%) of the unsubstituted vinylidene complex 6 as orange crys-
tals.[12]
Additionally we have recently synthesized and structurally
characterized the gold-tungsten complex 12 which has simi-
lar structural features to 10 and 11 and shows a fluxional
behavior.[24]
Contrary to the isomerization in nonpolar solvents, the
kinetic data of the isomerization 8 Ǟ 9 in ethanol suggests
a two-step dissociation-addition process (Scheme 8). The
high value of k8Ǟ9/k8-DǞ9-D and its temperature depen-
dency supports this mode of isomerization and suggests
that it is even more likely that a tunneling process takes
place for this reaction.[22,23] According to this data we sup-
pose that the tautomerization of 8 occurs via a depro-
tonation step generating the η1-alkynyl complex 13 followed
by the protonation on molybdenum to the hydrido-alkynyl
complex 14 which undergoes reductive elimination to the
η2-1-alkyne isomer 9. The NaOH catalyzed isomerization
Compound 5b: Two rotamers (5:2) were found in the NMR spectra.
1H NMR (CDCl3, 25 °C): δ ϭ 7.65Ϫ7.38 (m, 10 H, C6H5), 6.02
and 5.93 (2 s, 2:5, 1 H, CβH), 5.73 and 5.40 (2 s, 2:5, 5 H, Cp),
0.71 and 0.69 (2 s, 5:2, 3 H, CH3) ppm. 13C NMR (CDCl3, 25
°C): δ ϭ 334.9 and 333.6 [1JCϪW ϭ 183.1 Hz, Cα], 212.3 (1JCϪW
ϭ
202.6 Hz), 212.0 (CO), 136.0Ϫ127.9 (C6H5), 118.3 and 117.2
[2JCϪW ϭ 34.5 Hz, Cβ], 95.4 and 95.3 (Cp), Ϫ2.0 and Ϫ2.2 (CH3)
of 8 (see Scheme 3) is in agreement with this hypothesis as ppm. IR (KBr): ν˜ ϭ 1990 (s, CϭO), 1636 (s, NϵO), 1595 (s, Cϭ
C) cmϪ1. MS (70 eV): m/z ϭ 529 [Mϩ, 184W], 501 [Mϩ Ϫ CO], 471
it supports a deprotonation-protonation process. All at-
tempts to isolate the hydrido-alkynyl complex were unsuc-
[Mϩ Ϫ CO Ϫ NO]. C21H19NO2SiW: calcd. C 47.65, H 3.62, N 2.65;
found C 47.28, H 3.32, N 2.89. High-resolution mass spectrum:
cessful.
m/z calcd. for C21H19NO2Si182W [Mϩ] 527.0668, found 527.0667.
The tautomerization of η2-1-alkyne via hydrido-alkynyl
Compound 6: 1H NMR (CDCl3, 25 °C): δ ϭ 5.87 (s, 5 H, Cp), 5.28
complexes is often postulated in the literature as a con-
certed 1,3-hydrogen shift.[1,4f] However, this mechanism was
2
(3JW-H ϭ 6 Hz), 5.21 [2 d, 2 H, JH,H ϭ 19 Hz, CH2] ppm. 13C
found to be, in general, energetically too costly.[4b,4h] Our NMR (CDCl3, 25 °C): δ ϭ 341.2 (Cα), 209.9 (CO), 112.2 (Cβ), 96.3
(Cp) ppm. IR (KBr): ν˜ ϭ 1998 (CO), 1635 (NO), 1591 (CϭC)
cmϪ1. IR (CCl4): ν˜ ϭ 2008 (CO), 1654 (NO), 1618 (CϭC) cmϪ1
MS (70 eV): m/z ϭ 333 [Mϩ, 184W], 305 [Mϩ Ϫ CO], 275 [Mϩ
CO Ϫ NO]. C14H11NO2W: calcd. C 28.86, H 2.12, N 4.21; found
C 29.17, H 1.74, N 4.29. High-resolution mass spectrum: m/z calcd.
for C14H11NO2186W [Mϩ] 335.0021, found 335.0027.
results, however, support the findings that isomerization via
a hydrido-alkynyl complex proceeds in a nonconcerted fa-
shion.
.
Ϫ
Experimental Section
[(η5-C5H5)(CO)(NO)W؍C؍CDSi(CH3)2C(CH3)3] (5a-D): A solu-
tion of vinylidene 5a (300 mg) in THF (5 mL) and D2O (5 mL) was
stirred for 2 h at room temperature. After removal of THF and
D2O under reduced pressure, the residue was dried under vacuum
for several hours. Spectroscopically pure orange crystals of 5a-D
were obtained (m.p. 60 °C). C14DH20NO2SiW: calcd. C 37.51, H
4.50, N 3.12; found C 37.32, H 4.53, N 3.28. Two rotamers were
General Remarks: All reactions were carried out under argon
(99.99%, by MesserϪGriesheim) with the use of standard Schlenk
techniques. Solvents were purified by standard methods and dis-
tilled under argon prior to use. Literature methods were used to
prepare
[(η5-C5H5)Mo(CO)2(NO)]
and
[(η5-C5H5)W-
(methyl-
[(η5-C5H5)(CO)(NO)MoϭCϭCHC-
(CO)2(NO)],[25]
(tert-butyldimethylsilyl)acetylene,[26]
1
diphenylsilyl)acetylene,[26]
found in the NMR spectra. H NMR (CDCl3, 25 °C): δ ϭ 5.76 (s,
(CH3)3] (8);[12] 7c, and 5c[12] and [(η5-C5H5)(CO)(NO)WϭCϭ
CHSi(CH3)2C(CH3)3] (5a).[27] All other compounds were commer-
cially available. NMR spectra were obtained with a Bruker AM
400 spectrometer (1H NMR, 400.13 MHz. 13C NMR,
100.61 MHz). Proton and carbon chemical shifts are reported in
ppm relative to the residual proton resonance (δ ϭ 7.24 ppm) or
the carbon multiplet (δ ϭ77.0 ppm) of the NMR solvent CDCl3.
5 H, Cp), 0.91 and 0.89 [2 s, 3:2, 9 H, C(CH3)3], 0.13, 0.10 and
0.09 (3 s, overlapping, diastereotopic methyl groups,
6 H,
Si[CH3)2C(CH3)3] ppm. 13C NMR (CDCl3, 25 °C): δ ϭ 333.0 and
331.0 (Cα), 213.8 and 212.0 (CO), 118.5 (1JCϪD ϭ 20.8 Hz) and
117.5 (1JCϪD ϭ 22.2 Hz) (Cβ), 95.4 and 95.2 (Cp), 26.1 [C(CH3)3],
17.6 and 17.1 [C(CH3)3], Ϫ4.4, Ϫ4.5 and Ϫ4.8 [Si(CH3)2C(CH3)3]
ppm. IR (KBr): ν˜ ϭ 1999 and 1975 (s, CϭO), 1635 and 1617 (s,
NϵO), 1584 (s, CϭC) cmϪ1. MS (70 eV): m/z ϭ 448 [Mϩ, 184W],
420 [Mϩ Ϫ CO]. High-resolution mass spectrum: m/z calcd. for
C14DH20NO2Si182W [Mϩ] 446.0887, found 446.0884.
1
When [D6]benzene is used as solvent for a H NMR spectrum, the
shifts are reported in ppm relative to the residual proton resonance
at δ ϭ 7.17 ppm. 13C DEPT experiments were run with the Bruker
AM 400 spectrometer. MS measurements (70 eV) were performed
with a Varian MAT 311-A. IR spectra were recorded with a Bruker
FT-IR IFS 85. Microanalyses were done with a Carlo Erba 1104
elemental analyzer.
Synthesis of the η2-Alkyne Complexes. [(η5-C5H5)(CO)(NO)W{η2-
H3C؊CϵC؊Si(CH3)2C(CH3)3}] (4a): The preparation of 4a is
analogous to that of 5a, but, instead of diluted HCl, (0.5 mL,
4.5 mmol) trifluoromethanesulfonate was used. This solution was
stirred for 1 h at Ϫ30 °C. After usual workup the dark red oil was
Synthesis of the Vinylidene Complexes. [(η5-C5H5)(CO)(NO)W؍
C؍CHSi(C6H5)2CH3] (5b): At Ϫ78 °C nBuLi (3 mL, 4.5 mmol; a chromatographed on silica gel (n-pentane/diethyl ether, 3:1) to yield
solution of 1.5 mmol/mL in hexane) was added to a solution of
(methyldiphenylsilyl)acetylene (1.00 g, 4.5 mmol) in THF (10 mL).
This solution was added dropwise to [(η5-C5H5)(CO)2(NO)W]
927 mg (67%) of 4a as orange crystals (m.p. 119 °C). C15H23NO2-
SiW: calcd. C 39.06, H 5.03, N 3.04; found C 39.02, H 4.73, N
2.78. Two rotamers were found in the NMR spectra. 1H NMR
(1.0 g, 3.0 mmol) in THF (60 mL) at Ϫ30 °C, whereby the color (CDCl3, 25 °C): δ ϭ 5.65 and 5.60 ppm (2 s, 6:1, 5 H, Cp), 2.92
changed from orange to deep green. The reaction mixture was
stirred for 4 h at Ϫ30 °C. Addition of 1 mL of concentrated HCl
and 2.87 (2 s, 1:6, 3 H, CϵCCH3), 0.96 and 0.90 [2 s, 6:1, 9 H,
C(CH3)3], 0.30 (2JHϪSi ϭ 6.3 Hz), 0.24 and 0.16 [3 s, overlapping,
Eur. J. Inorg. Chem. 2003, 4313Ϫ4320
www.eurjic.org
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4317

J. Ipaktschi, J. Mohsseni-Ala, S. Uhlig
diastereotopic methyl groups, 6 H, Si(CH3)2C(CH3)3] ppm. 13C ppm. IR (KBr): ν˜ ϭ 1983 (s, CϭO), 1699 (m, CϵC), 1594 (s, NϵO)
FULL PAPER
NMR (CDCl3, 25 °C): δ ϭ 220.0 (CO), 122.5 (alkyne C), 95.9 and
cmϪ1. MS (70 eV): m/z ϭ 529 [Mϩ, 184W], 501 [Mϩ Ϫ CO], 471
95.8 (Cp), 90.7 (alkyne C), 26.6 and 26.5 [C(CH3)3], 20.6 and 18.6 [Mϩ Ϫ CO Ϫ NO]. High-resolution mass spectrum: m/z calcd. for
[C(CH3)3], 18.2 and 15.7 (CϵCCH3), Ϫ3.8 and Ϫ3.9 C21H19NO2Si182W [Mϩ] 527.0668, found 527.0681.
[Si(CH3)2C(CH3)3] ppm. IR (KBr): ν˜ ϭ 1986 (s, CϭO), 1827 (m,
[(η5-C5H5)(CO)(NO)W{η2-H؊CϵC؊C(CH3)3}] (7c): The prep-
aration of 7c is analogous to that of 7a, but, instead of complex
5a, vinylidene 5c (1000 mg) was used. Chromatography on silica
gel with 10:1 n-pentane/diethyl ether yielded 24 mg (2%) of 7c as
light orange crystals and 563 mg (56%) of the starting material 5c
as orange crystals. C12H15NO2W: calcd. C 37.04, H 3.89, N 3.60;
found C 37.32, H 3.70, N 3.40. Two rotamers were found in the
CϵC), 1558 (s, NϵO) cmϪ1. MS (70 eV): m/z ϭ 461 [Mϩ, 184W],
433 [Mϩ Ϫ CO]. High-resolution mass spectrum: m/z calcd. for
C15H23NO2Si182W [Mϩ] 459.0981, found 459.0974.
[(η5-C5H5)(CO)(NO)W{η2-H3C؊CϵC؊Si(C6H5)2CH3}] (4b): The
preparation was carried out as described for 4a, but, instead of
(tert-butyldimethylsilyl)acetylene, (1.00 g, 4.5 mmol) (methyldi-
phenylsilyl)acetylene was used. After usual workup the dark red oil
was chromatographed on silica gel (n-pentane/diethyl ether, 7:1) to
yield 760 mg (47%) of 4b as a dark red oil. C22H21NO2SiW: calcd.
C 48.63, H 3.90, N 2.58; found C 48.90, H 3.58, N 2.77. Two rota-
NMR spectra. 1H NMR (CDCl3, 25 °C): δ ϭ 7.45 (2JHϪW
ϭ
8.0 Hz) and 6.98 (2JHϪW ϭ 9.2 Hz) (2 s, 1:6, 1 H, CϵCH), 5.77
and 5.68 (2 s, 6:1, 5 H, Cp), 1.35 and 1.32 [2 s, 6:1, 9 H, C(CH3)3]
ppm. 13C NMR (CDCl3, 25 °C): δ ϭ 215.5 (CO), 133.7 (1JCϪW
ϭ
1
52.0 Hz) and 124.4 (1JCϪW ϭ 13.6 Hz) (alkyne C), 96.4 and 96.0
(Cp), 91.0 (1JCϪW ϭ 43.1 Hz) and 88.1 (1JCϪW ϭ 8.9 Hz) (alkyne
C), 36.4 and 34.6 [C(CH3)3], 31.9 and 31.0 [C(CH3)3] ppm. IR
mers were found in the NMR spectra. H NMR (CDCl3, 25 °C):
2
δ ϭ 7.62Ϫ7.33 (m, 10 H, C6H5), 5.57 and 5.37 [2 s, 1:8, JHϪW
ϭ
9.5 Hz, , 5 H, Cp], 2.88 and 2.82 (2 s, 8:1, 3 H, CϵCCH3), 0.83
(2JHϪSi ϭ 6.6 Hz) and 0.79 [2 s, 8:1, 3 H, Si(C6H5)2CH3] ppm. 13C
NMR (CDCl3, 25 °C): δ ϭ 219.1 (1JCϪW ϭ 183.1 Hz) and 217.5
(CO), 136.8Ϫ127.8 (C6H5), 127.4 [1JCϪW ϭ 13.9 Hz, alkyne C],
96.0 and 95.8 (Cp), 90.7 [1JCϪW ϭ 38.9 Hz, alkyne C], 20.4 and
(KBr): ν˜ ϭ 1977 (s, CϭO), 1736 (m, CϵC), 1556 (s, NϵO) cmϪ1
.
MS (70 eV): m/z ϭ 389 [Mϩ, 184W], 361 [Mϩ Ϫ CO]. High-resolu-
tion mass spectrum: m/z calcd. for C12H15NO2182W [Mϩ] 387.0585,
found 387.0553.
15.5 (CϵCCH3), Ϫ2.0 (1JCϪSi
ϭ
56.9 Hz) and Ϫ2.9
Isomerization of 8 to 9 with NaOH: 10% aqueous NaOH (3 mL)
was added to a solution of 8 (0.4 mmol) in THF (10 mL). After
the reaction mixture was stirred for 20 min at room temperature,
the organic layer was separated and the solvent was removed under
reduced pressure. The residue was dissolved in diethyl ether and
dried with MgSO4. The diethyl ether was removed under reduced
[Si(C6H5)2CH3] ppm. IR (KBr): ν˜ ϭ 1966 (s, CϭO), 1806 (s, CϵC),
1575 (s, NϵO) cmϪ1. MS (70 eV): m/z ϭ 543 [Mϩ, 184W], 515 [Mϩ
Ϫ CO], 485 [Mϩ Ϫ CO Ϫ NO]. High-resolution mass spectrum:
m/z calcd. for C22H21NO2Si182W [Mϩ] 541.0820, found 541.0817.
[(η5-C5H5)(CO)(NO)W{η2-H؊CϵC؊Si(CH3)2C(CH3)3} (7a): A
solution of vinylidene 5a (300 mg) in toluene (30 mL) was heated
for 24 h under reflux. After removal of the solvent under reduced
pressure at room temperature, the dark red oily residue was chrom-
atographed on silica gel (n-pentane/diethyl ether, 7:1) to yield
152 mg (51%) of 7a as orange crystals (m.p. 66 °C). C14H21NO2-
SiW: calcd. C 37.60, H 4.73, N 3.13; found C 37.87, H 4.57, N
2.90. Two rotamers were found in the NMR spectra. 1H NMR
(CDCl3, 25 °C): δ ϭ 8.74 (2JHϪW ϭ 7.8 Hz) and 8.12 [2s, 1:5,
2JHϪW ϭ 8.8 Hz, 1 H, CϵCH], 5.67 and 5.62 (2 s, 5:1, 5 H, Cp),
0.97 and 0.93 [2 s, 5:1, 9 H, C(CH3)3], 0.32 (2JHϪSi ϭ 6.1 Hz), 0.27,
0.25 (6.0 Hz) and 0.18 [4 s, diastereotopic methyl groups, 5:1:5:1, 6
H, Si(CH3)2C(CH3)3] ppm. 13C NMR (CDCl3, 25 °C): δ ϭ 219.2
1
pressure, and the H NMR spectrum of the residue was collected.
8 was 100% isomerized to 9.
Treatment of 8 with D2O and C6D5OD: 8 (0.6 mL, 0.1 mmol) and
D2O (0.2 mL, 10 mmol) in [D8]THF (1 mL) were heated at 45 °C.
At regular time intervals the probe was cooled to Ϫ20 °C, which
was followed by the measuring of the relative peak integration of
1
the H NMR CβϪH signal [([D8]THF) δ ϭ 5.93 and 5.91 ppm] of
8. After 3 h the H/D exchange was complete. The same experiment
with perdeuterated phenol (C6D5OD) instead of D2O showed no
exchange.
[(η5-C5H5)(CO)(NO)Mo{η2-H-CϵC-C(CH3)3}] (9): At Ϫ30 °C, a
solution of 7.5 mmol of (tert-butylethynyl)lithium in THF (15 mL)
was added dropwise to an orange solution of (η5-C5H5)Mo-
(CO)2(NO) (1.24 g, 5 mmol) in THF (50 mL). The progress of the
reaction was monitored by IR spectroscopy. After complete disap-
pearance of [(η5-C5H5)Mo(CO)2(NO)], at 5 °C, saturated aq. so-
dium carbonate (30 mL) was added to the deep green reaction mix-
ture, whereby the color changed to red. The solution was concen-
trated under vacuum and extracted with diethyl ether. The organic
and 218.4 [1JCϪW ϭ 178.4 Hz, CO], 121.9 and 115.7 [1JCϪW
ϭ
15.4 Hz, CϵCH], 105.1 (1JCϪW ϭ 40.3 Hz) and 97.1 (CϵCH), 95.9
(Cp), 26.5 and 26.4 [C(CH3)3], 18.2 and 17.8 [C(CH3)3], Ϫ3.6
(1JCϪSi ϭ 52.2 Hz), Ϫ4.1 (1JCϪSi ϭ 54.5 Hz), Ϫ4.5 and Ϫ4.8
[Si(CH3)2C(CH3)3] ppm. IR (KBr): ν˜ ϭ 1965 (s, CϭO), 1713 (m,
CϵC), 1565 (s, NϵO) cmϪ1. MS (70 eV): m/z ϭ 447 [Mϩ, 184W],
419 [Mϩ Ϫ CO]. High-resolution mass spectrum: m/z calcd. for
C14H21NO2Si182W [Mϩ] 445.0825, found 445.0824.
[(η5-C5H5)(CO)(NO)W{η2-H؊CϵC؊Si(C6H5)2CH3}] (7b): The layer was dried with MgSO4. The diethyl ether was removed under
preparation of 7b is analogous to that of 7a, but, instead of com-
plex 5a, vinylidene 5b (300 mg) was used. Chromatography on silica
gel (n-pentane/diethyl ether, 7:1) yielded 60 mg (20%) of 7b as dark
red oil and 40 mg (13%) of the starting material 5b as orange crys-
reduced pressure and the residue was chromatographed (silica gel,
pentane) to yield 714 mg (47%) of 9, as orange crystals, m.p. 71Ϫ72
°C (dec, pentane:dichloromethane, 10:1). C12H15MoNO2: calcd. C
47.85, H 5.02, N 4.65; found C 47.84, H 4.83, N 4.72. Two rotamers
1
tals. C21H19NO2SiW: calcd. C 47.65, H 3.62, N 2.65; found C (ratio 1:5). H NMR (CDCl3, 25 °C): δ ϭ 6.69 and 6.09 ppm (2 s,
47.20, H 3.34, N 2.86. Two rotamers were found in the NMR spec-
1:5, 1 H, CϵCH), 5.65 and 5.55 (2 s, 5:1, 5 H, Cp), 1.37 and 1.34
tra. 1H NMR (CDCl3, 25 °C): δ ϭ 9.10 (2JHϪW ϭ 7.4 Hz) and 8.54
[2 s, 5:1, 9 H, C(CH3)]. 13C NMR (CDCl3, 25 °C): δ ϭ 226.7 (Cϭ
(2JHϪW ϭ 8.8 Hz) (2s, 1:5, 1 H, CϵCH), 7.64 and 7.33 (m, 10 H, O), 128.0 (CϵC), 97.0 and 96.7 (Cp), 80.5 (CϵC), 35.8 [C(CH3)3],
C6H5), 5.59 and 5.38 (2 s, 5:1, 5 H, Cp), 0.84 (2JHϪSi ϭ 6.5 Hz) 32.2 and 31.3 (CH3) ppm. IR (KBr): ν˜ ϭ 1982 (CϭO), 1785
and 0.83 (2 s, 5:1, 3 H, CH3) ppm. 13C NMR (CDCl3, 25 °C): δ ϭ (CϵC), 1581 (NϭO) cmϪ1. MS (70 eV): m/z ϭ 301 [Mϩ, 96Mo],
217.6 (1JCϪW ϭ 177.6 Hz) and 217.0 (CO), 136.4Ϫ126.7 (C6H5),
273 [Mϩ Ϫ CO], 243 [Mϩ Ϫ CO Ϫ NO]. High resolution mass
120.1 [1JCϪW ϭ 15.3 Hz, CϵCH], 105.2 [1JCϪW ϭ 40.2 Hz, spectrum calcd. for C12H1592MoNO2 [Mϩ]: m/z ϭ 297.0171, found
CϵCH], 96.0 and 95.9 (Cp), Ϫ1.9 (1JCϪSi ϭ 58.3 Hz), Ϫ2.9 (CH3)
4318
m/z ϭ 297.0141.
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2003, 4313Ϫ4320

Vinylidene to Alkyne Isomerization of Tungsten and Molybdenum Complexes
FULL PAPER
[4]
[4a]
η2-alkyne Ǟ η1-vinylidene isomerization:
Jimenez-Tenorio, M. C. Puerta, P. Valerga, Eur. J. Inorg. Chem.
2001, 2391Ϫ2398.
Fukushima, A. Horiuchi, Y. Wakatsuki, J. Am. Chem. Soc.
2001, 123, 11917Ϫ11924.
teruelas, A. M. Lopez, J. Modrego, E. Onate, Organometallics
E. Bustelo, M.
Kinetic Studies of the η1-Vinylidene Ǟ η2-Alkyne Isomerization of
´
8 Ǟ 9; 8-D Ǟ 9-D in [D8]Toluene and 5a Ǟ 7a and 5a-D Ǟ 7a-D
in [D6]Benzene: A typical experiment was done in the following
way. 8 or 8-D (0.8 mL, 0.1 ) in [D8]toluene as well as a weighted
amount of the vinylidene 5a or 5a-D (in the range of 20Ϫ120 mg)
in [D6]benzene (0.8 mL) (measured with a gas-tight syringe) were
placed in a dried sealable NMR tube. The solution was freeze-
pump-thaw degassed and the NMR tube was sealed under vacuum.
The sample was then placed into a thermostat at a fixed tempera-
ture (reproducibility Ϯ 0.1 °C). At regular time intervals, the tube
was removed and the reaction quenched at room temperature. The
reaction time was followed by measuring the relative peak inte-
[4b]
M. Tokunaga, T. Suzuki, N. Koga, T.
[4c]
M. Baya, P. Crochet, M. A. Es-
´
ˇ
[4d]
´
2001, 20, 4291Ϫ4294.
E. Bustelo, I. De los Rıos, M. Ji-
´
menez-Tenorio, M. C. Puerta, P. Valerga, Monatsheft. Chem.
[4e]
2000, 131, 1311Ϫ1320.
meno, E. Perez-Carren˜o, S. Garcıa-Granda, Organometallics
V. Cadierno, M. P. Gamasa, J. Gi-
´
´
[4f]
´
E. Perez-Carren˜o, P. Paoli, A. Ienco,
1999, 18, 2821Ϫ2832.
[4g]
C. Mealli, Eur. J. Inorg. Chem. 1999, 1315Ϫ1324.
I. De los
Rıos, M. Jimenez-Tenorio, M. C. Puerta, P. Valerga, J. Am.
´
´
[4h]
Chem. Soc. 1997, 119, 6529Ϫ6538.
Y. Wakatsuki, N. Koga,
1
gration of the H NMR of the cyclopentadienyl signals of 8 (δ ϭ
H. Yamazaki, K. Morokuma, J. Am. Chem. Soc. 1994, 116,
5.18 and 5.16 ppm); 9 (δ ϭ 5.06 and 4.92 ppm); 8-D (δ ϭ 5.18 and
5.16 ppm); 9-D (δ ϭ 5.06 and 4.92 ppm); tert-butyl signals of 5a
(δ ϭ 0.95 ppm); 7a (δ ϭ 1.01 and 0.99 ppm); 5a-D (δ ϭ 0.94 ppm)
and 7a-D (δ ϭ 1.01 and 0.99 ppm).
8105Ϫ8111.
[5]
[5a]
η1-vinylidene Ǟ η2-alkyne isomerization:
´
C. Garcıa-Yebra,
´
´
´
C. Lopez-Mardomingo, M. Fajardo, A. Antin˜olo, A. Otero, A.
Rodrıguez, A. Vallat, D. Lucas, Y. Mugnier, J. J. Carbo, A.
´
[5b]
Lledos, C. Bo, Organometallics 2000, 19, 1749Ϫ1765.
I. M.
First-order rate constants were derived from least-squares best-fit
lines of the ln(%) versus time plots. The uncertainty in the isomeriz-
ation rate constants was derived from the slope of the best-fit line.
Uncertainties in the activation enthalpies and entropies were calcu-
lated from the uncertainties in the slope of the best-fit line of the
Eyring plot.
´
Bartlett, N. G. Connelly, A. J. Martın, A. G. Orpen, T. J. Paget,
A. L. Rieger, P. H. Rieger, J. Chem. Soc., Dalton Trans. 1999,
691Ϫ698.
[5c]
´
M. P. Gamasa, J. Gimeno, C. Gonzalez-
´
Bernando, J. Borge, S. Garcıa-Granda, Organometallics 1997,
16, 2483Ϫ2485. [5d] H. Katayama, K. Onitsuka, F. Ozawa, Or-
[5e]
ganometallics 1996, 15, 4642Ϫ4645.
N. G. Connelly, W. E.
Geiger, C. Lagunas, B. Metz, A. L. Rieger, P. H. Rieger, M. J.
Kinetic Studies of the η1-Vinylidene Ǟ η2-Alkyne. Isomerization of
8 Ǟ 9 in [D5]Ethanol and 8-D Ǟ 9-D in [D6]Ethanol: The kinetic
studies of isomerization of 8 Ǟ 9 in [D5]ethanol and 8-D Ǟ 9-D
in [D6]ethanol are analogous to that for the isomerization of 8 Ǟ
9 and 8-D Ǟ 9-D in [D8]toluene. The time course of the reaction
Shaw, J. Am. Chem. Soc. 1995, 117, 12202Ϫ12208. [5f] P. Nom-
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C22ϪC25.
R. S. Bly, Z. Zhong, C. Kane, R. K. Bly, Or-
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N. G. Connelly,
A. G. Orpen, A. L. Rieger, P. H. Rieger, C. J. Scott, G. M.
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[6a] F. De Angelis, A. Sgamellotti, N. Re, Organometallics 2002,
1
was followed by measuring the relative peak integration of the H
NMR of cyclopentadienyl signals 8 [(C2D5OH) δ ϭ 5.83 and 5.81
ppm], 9 [(C2D5OH) δ ϭ 5.70 and 5.60 ppm], 8-D [(C2D5OD) δ ϭ
5.82 and 5.81 ppm] and 9-D [(C2D5OD) δ ϭ 5.67 and 5.59 ppm].
Uncertainties in the activation enthalpies and entropies were calcu-
lated from the uncertainties in the slope of the best-fit line of the
Eyring plot.
[6]
21, 2715Ϫ2723. [6b] R. Stegmann, G. Frenking, Organometallics
[6c]
´
I. De los Rıos, M. J. Tenorio, M. C.
1998, 17, 2089Ϫ2095.
Puerta, P. Valerga, J. Am. Chem. Soc. 1997, 119, 6529Ϫ6538.
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Y. Wakatsuki, N. Koga, H. Werner, K. Morokuma, J. Am.
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For earlier theoretical studies see: J. Silvestre, R. Hoffmann,
[7]
Helv. Chim. Acta 1985, 68, 1461.
[8] [8a]
´
M. Baya, P. Crochet, M. A. Esteruelas, E. Gutierrez-Puebla,
´
ˇ
A. M. Lopez, J. Modrego, E. Onate, N. Vela, Organometallics
Acknowledgments
We gratefully acknowledge financial support from the Deutsche
Forschungsgemeinschaft.
[8b]
´
E. Bustelo, M. Jimenez-Tenorio, M.
2000, 19, 2585Ϫ2596.
C. Puerta, P. Valerla, Organometallics 1999, 18, 4563Ϫ4573. [8c]
´
M. Olivan, E. Clot, O. Eisenstein, K. G. Caulton, Organomet-
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M. Baya, M. A. Esteruelas, E. Onate, Organometallics 2001,
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The formation of complex 18 can be explained by cleavage of
the CϪSi bond of the methyldiphenyl-substituted vinylidene
complex 17b.
[9]
ˇ
[1]
[1a]
For comprehensive reviews see:
M. C. Puerta, P. Valerga,
[10]
Coord. Chem. Rev. 1999, 193Ϫ195, 977Ϫ1025. [1b] C. Bruneau,
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M. P. Gamasa, J. Gimeno, E. Lastra, B. M. Martın, A. Anillo,
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www.eurjic.org
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4319

J. Ipaktschi, J. Mohsseni-Ala, S. Uhlig
FULL PAPER
Third Edition; Plenum Press: New York, London, 1990; pp.
216Ϫ218.
Rh(η2-FcCϵCSiMe3) {PCH(CH3)2}2Cl] (∆H# ϭ 22.7 Ϯ 0.1
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The values of activation entropy are in the typical range for
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[21]
Received May 28, 2003
Early View Article
[trans-Rh{ϭCϭC(Fc)SiMe3}{PCH(CH3)2}2Cl]
to
[trans-
Published Online October 10, 2003
4320
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2003, 4313Ϫ4320