Intermolecular insertion of the carbene ligand of pentacarbonyl tungsten benzylidenes into the M-H bond of transition metal hydrido complexes

Article abstract of DOI:10.1016/S0022-328X(98)00942-5

The strongly electrophilic carbene complexes [(CO)₅W=C(H)C₆H₄R-p] (2) [R=H (a), Me (b), OMe (c)] react with the terminal transition metal hydrides [(CO)₅MnH] (3) and [Cp(CO)₃WH] (5) by a formal transfer and insertion of the carbene ligand into the M-H bond (M=Mn, W) to give the benzyl complexes [(CO)₅MnCH₂C₆H₄R-p] (4a-c) and [Cp(CO)₃WCH₂C₆H₄R-p] (6a-c). Similarly, 6a is formed when solutions of [(CO)₅Cr=C(H)Ph] (7a) or [Cp(CO)₂Mn=C(H)Ph] (8a) are treated with 5. The analogous reaction of 2c with [Cp*(CO)₃WH] (9) (Cp=C₅Me₅) affords [Cp*(CO)₃WCH₂C₆H₄OMe-p] (10). In contrast, the reactions of 2b with [Cp₂WH₂] (11) and PNP[(CO)₄FeH] (13) afford binuclear complexes, [Cp₂W(H)(CH₂C₆H₄Me-p)W(CO) ₅] (12) and PNP[(CO)₄Fe(CH₂C₆H₄Me-p)W(CO) ₅] (14). Spectroscopic data confirm the existence of a Fe-W bond in the structure of 14 while in complex 12 the W(CO)₅ fragment is coordinated to the W-H bond of the second metal center in a three center two electron mode. In contrast to 3, 5, 9, 11, and 13, the μ-hydrido complexes [H₃Mn₃(CO)₁₂], [HW₂(CO)₉(NO)], and NEt₄[HW₂(CO)₁₀] show no comparable reaction with the benzylidene complexes 2. Kinetic measurements of the reaction of 2c with 5 reveal second-order kinetics, first-order in the concentrations of the benzylidene complex 2c and the metal hydride 5. The activation enthalpy ΔH^≠ is small (ΔH^≠=19±3 kJ mol^-1), the activation entropy ΔS^≠ strongly negative (ΔS^≠=-120±10 J mol^-1 K^-1). The kinetic isotope effect for the reaction of 2c with [Cp(CO)₃WX] (X=H, D) is k^H/k^D=2.6±0.4. The reaction rate increases (a) with increasing electrophilicity of the carbene carbon atom and (b) with decreasing steric demand of the ligands at the metal hydride. The reaction mechanism is discussed on the basis of an associative rate-determining step with an early transition state.

Full text of DOI:10.1016/S0022-328X(98)00942-5

Journal of Organometallic Chemistry 572 (1999) 105–115
Intermolecular insertion of the carbene ligand of pentacarbonyl
tungsten benzylidenes into the M–H bond of transition metal hydrido
complexes
Helmut Fischer *, Holger Jungklaus
Fakulta¨t fu¨r Chemie, Uni6ersita¨t Konstanz, Fach M727, D-78457 Konstanz, Germany
Received 21 July 1998
Abstract
The strongly electrophilic carbene complexes [(CO)5WꢀC(H)C6H4R-p] (2) [R=H (a), Me (b), OMe (c)] react with the terminal
transition metal hydrides [(CO)5MnH] (3) and [Cp(CO)3WH] (5) by a formal transfer and insertion of the carbene ligand into the
M–H bond (M=Mn, W) to give the benzyl complexes [(CO)5MnCH2C6H4R-p] (4a–c) and [Cp(CO)3WCH2C6H4R-p] (6a–c).
Similarly, 6a is formed when solutions of [(CO)5CrꢀC(H)Ph] (7a) or [Cp(CO)2MnꢀC(H)Ph] (8a) are treated with 5. The analogous
reaction of 2c with [Cp*(CO)3WH] (9) (Cp*=C5Me5) affords [Cp*(CO)3WCH2C6H4OMe-p] (10). In contrast, the reactions of 2b
with [Cp2WH2] (11) and PNP[(CO)4FeH] (13) afford binuclear complexes, [Cp2W(H)(CH2C6H4Me-p)W(CO)5] (12) and
PNP[(CO)4Fe(CH2C6H4Me-p)W(CO)5] (14). Spectroscopic data confirm the existence of a Fe–W bond in the structure of 14 while
in complex 12 the W(CO)5 fragment is coordinated to the W–H bond of the second metal center in a three center two electron
mode. In contrast to 3, 5, 9, 11, and 13, the v-hydrido complexes [H3Mn3(CO)12], [HW2(CO)9(NO)], and NEt4[HW2(CO)10] show
no comparable reaction with the benzylidene complexes 2. Kinetic measurements of the reaction of 2c with 5 reveal second-order
kinetics, first-order in the concentrations of the benzylidene complex 2c and the metal hydride 5. The activation enthalpy DH"
is small (DH" =1993 kJ mol−1), the activation entropy DS" strongly negative (DS" = −120910 J mol−1
K
−1). The kinetic
isotope effect for the reaction of 2c with [Cp(CO)3WX] (X=H, D) is kH/kD=2.690.4. The reaction rate increases (a) with
increasing electrophilicity of the carbene carbon atom and (b) with decreasing steric demand of the ligands at the metal hydride.
The reaction mechanism is discussed on the basis of an associative rate-determining step with an early transition state. © 1999
Elsevier Science S.A. All rights reserved.
Keywords: Carbene complexes; Hydrido complexes; Insertion reactions; Activation parameters; Labeling experiments
1. Introduction
Thus, the interaction of carbene complexes as model
systems with FTS substrates such as hydrogen or car-
bon monoxide is of fundamental interest. Therefore,
reactions of carbene complexes with CO have been
investigated in detail [2]. Recently we have shown that
CO insertion into the metal carbene bond follows either
an intramolecular [3] or an intermolecular pathway [4]
depending on the electrophilicity of the carbene com-
plexes. In contrast, there are only few reports on the
reactions of carbene complexes with hydrogen [5].
Brady and Pettit observed a dissociative chemisorption
of H2 under heterogeneous FTS reaction conditions [6].
Carbene ligands of transition metal carbene com-
plexes are versatile building blocks in organic synthesis
[1]. The transfer of carbene ligands to alkynes, olefins,
or imines affords, e.g., carbo- and heterocycles. In
addition, transition metal bound carbenes are assumed
to be important intermediates in several catalytic pro-
cesses, e. g. in the Fischer Tropsch Synthesis (FTS) and
related reactions.
* Corresponding author. Tel.: +49-7531-88-2783; fax: +49-7531-
88-3136; e-mail: hfischer@dg6.chemie.uni-konstanz.de.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)00942-5

106
H. Fischer, H. Jungklaus / Journal of Organometallic Chemistry 572 (1999) 105–115
The reaction was proposed to proceed via formation of
metal hydrides. Subsequently, the interest also focused
on the interaction of hydrido and carbene ligands in
homogeneous systems. The intramolecular coupling of
a carbene and a hydrido ligand in carbene hydrido
complexes is now well established [7,8]. In contrast,
information on intermolecular coupling reactions are
rather scarce [9,10].
Nevertheless, based on the results of our investiga-
tions on the reaction of benzylidene(pentacarbonyl)
complexes with CO [4] we found these carbene com-
plexes also useful precursors to get an insight into the
intermolecular mechanisms of carbene–hydrido ligand
interaction.
Scheme 2.
Substitution of the metal ligand fragments (CO)5Cr
or Cp(CO)2Mn for (CO)5W in 2a had no influence on
the type of products in the reaction with 5. Thus,
treatment of [(CO)5CrꢀC(H)Ph] (7a) with 5 afforded 6a
(42%) and [Cr(CO)6] while the analogous reaction of
[Cp(CO)2MnꢀC(H)Ph] (8a) gave 6a (4%) and [CpMn-
(CO)3]. In contrast to 2a, the less electrophilic carbene
complexes [(CO)5WꢀC(Ph)C6H4OMe-p] and [(CO)5Wꢀ
C(OMe)C6H4Me-p] either decomposed or remained un-
changed when their solutions were stirred with equimo-
lar amounts of 5 at ambient temperature.
2. Results
2.1. Reactions of benzylidene complexes with transition
metal hydrido complexes
The isolated yields of analytically pure compounds
4a–c and 6a–c varied considerably (11–54%, based on
the h-methoxybenzyl tungstates 1a–c) depending on
workup conditions and the stationary phase used in
chromatography. The yields of the benzylidene com-
plexes 2a–c in the synthesis from 1a–c and HBF4 ·Et2O
(Scheme 1) usually are in the range 50–80%. Therefore,
the carbene transfer/M–H insertion in the reaction with
the hydrido complexes 3 and 5 can be assumed to
proceed in most cases almost quantitatively. This as-
sumption is supported by the absence of w(CO) absorp-
tions in the IR spectra of the reaction mixtures in
addition to those derived from the reaction products
mentioned above.
The starting carbene complexes (benzylidene com-
plexes) were generated as shown in Scheme 1. Treat-
ment of solutions of the h-methoxybenzyl tungstates
1a–c [11] (obtained by addition of the hydride of
[HB(OiPr)3]− to the carbene carbon of the correspond-
ing methoxycarbene complexes [(CO)5WꢀC(OMe)
C6H4R-p]) with HBF4 ·Et2O at −78°C gave rise to the
elimination of methanol and formation of the benzyli-
dene complexes 2a–c [12]. Rapid chromatography of
these solutions on silica gel at −70°C afforded solu-
tions of 2a–c. Due to the low thermal stability of these
complexes, 2a–c were not isolated in a pure form.
Instead, the solutions were immediately used for the
subsequent reactions with metal hydrides.
Substitution of the sterically more demanding pen-
tamethylcyclopentadienide for the cyclopentadienide
ligand in 5 did not alter the product distribution. The
major product in the reaction of 2c with
[Cp*(CO)3WH] (9) was 10 (Scheme 4). After chro-
matography, complex 10 was isolated in 53% yield.
All complexes 4a–c, 6a–c, and 10 were identified and
characterized by their IR, NMR and mass spectra; their
purity was established by elemental analysis.
When a solution of [(CO)5MnH] (3) was added to
2a–c in pentane/dichloromethane rapid reactions were
observed. Judged by the color change of the solutions
from deep red to yellow the reactions were complete
within seconds even at −78°C. Workup of the reaction
mixtures by column chromatography yielded [W(CO)6]
and [(CO)5MnCH2C6H4R-p] (4a–c) in addition to
small amounts of [Mn2(CO)10] (Scheme 2).
The reactions of 2a–c with [Cp(CO)3WH] (5) pro-
ceeded similarly fast giving [Cp(CO)3WCH2C6H4R-p]
(6a–c) and [W(CO)6] (Scheme 3).
Complex 2a also rapidly reacted with [(CO)4CoH].
The IR spectrum of the product mixture indicated the
formation of several CO-containing complexes. How-
Scheme 1.
Scheme 3.

H. Fischer, H. Jungklaus / Journal of Organometallic Chemistry 572 (1999) 105–115
107
[Cp2MoH2 ·Mo(CO)5] obtained by reaction of
[Cp2MoH2] with [(CO)5Mo(THF)] [14]. The weak ab-
sorption at 1970 cm−1 can either be assigned to the B1
mode of the W(CO)5 fragment or to the W–H stretch-
ing mode. Although the B1 mode is formally IR-forbid-
den for a C4v symmetric (CO)5M fragment, the band is
often observed with low intensity in mononuclear
M(CO)5 complexes due to a lowering of the symmetry.
The alternative assignment to the W–H stretching vi-
bration is supported by the observation of a W–H
stretching mode in the adduct [Cp2WH2 ·BCl3] at 1967
cm−1 [15].
Scheme 4.
ever, it was not possible to separate the reaction prod-
ucts and characterize them. In contrast, 2b did not react
with [Cp2Zr(H)Cl]n. When the reaction was monitored
by IR spectroscopy complete decomposition of 2b
within 2.3 h and formation of the characteristic ther-
molysis products of 2b, namely [W(CO)6] and
[{(CO)5W}2{v-C(H)C6H4Me-p}], was observed. The
failure of a reaction between 2b and the zirconium
complex is presumably due to the poor solubility of the
zirconium complex in pentane/dichloromethane even at
room temperature. As a consequence, the rate of the
insertion reaction is rather slow and the competing
decomposition dominates.
1
The H-NMR spectrum of 12 in [D8]toluene showed
resonances at l= −23.42, 2.23, 2.36, 4.04, 6.50, and
6.91 in a 1:3:2:10:2:2 ratio as expected for a dicyclopen-
tadienyl(hydrido)(p-methylbenzyl)tungsten
complex.
Two sets of satellites of the W–H resonance indicate a
bistungsten complex. This conclusion is also confirmed
by the strong low-field shift of the methylene protons
(l=2.36) when compared to the mononuclear deriva-
tive [Cp2W(H)CH2C6H4Me-p] (l=0.52 in [D6]benzene
[16]). In contrast, the hydrido signal of 12 (l= −
23.42) is at a significantly higher field than that of
[Cp2W(H)CH2C6H4Me-p] (l= −11.54 in [D6]benzene
[16]) or of [Cp2W(H)2] (l= −12.28 in [D6]benzene
[17]). Similar high-field shifts are characteristic for
The reaction of the benzylidene complexes with the
dihydrido complex [Cp2WH2] (11) took a different
course than the reactions with the monohydrido species
3, 5, or 9. When 11 was added to a solution of 2b in
pentane/dichloromethane the color of the solution im-
mediately turned yellow and a green-black precipitate
cationic
v-hydrido
complexes
[18]
such
as
[{Cp(CO)3W}2(v-H)]+ (l= −24.77 in conc. H2SO4
[19]). The 1J(1H–183W) coupling constants (J=70.8
and 36.0 Hz) are in the range usually observed for
1J(1H–183W) in [Cp2W(R)H] complexes [18] (e.g.,
1J(1H–183W)=73.2 Hz in [Cp2W(H)2] [15] and ca. 72
Hz in [Cp2WH2 ·AlEt3] [20]) and in neutral [(CO)5W(v-
H)MLn] complexes (e.g., 1J(1H–183W)=39.5 Hz
[LnM=W(CO)3(NO){P(OMe)3}] [21], 42.5 Hz [LnM=
Ta(CO)Cp2] [22], and 46 Hz [LnM=AuPPh3] [23]).
These NMR spectroscopic data indicate a three-center
two-electron H bridge like that in [Cp2(CO)Nb(v-
H)W(CO)5] [24]. Based on these data and on theoretical
considerations, the most likely structure of 12 is that
shown in Scheme 5. However, the alternative structure
12A cannot be completely ruled out.
1
(12) formed (Scheme 5). The H- and 13C-NMR spectra
of the precipitate indicated a 1:1 adduct of 2b and 11.
Purification of the new compound 12 by chromatogra-
phy or by recrystallization failed since 12 quickly de-
composed in solution even at −78°C.
Scheme 5.
When 2b was employed in a 2-fold excess there was
no indication of the transfer of two benzylidene units to
one molecule of 11 to form either the known complex
[Cp2W(CH2C6H4Me-p)2] [13] or its W(CO)5 adduct.
Only complex 12 was isolated independent of whether
pentane or polar solvents were used.
When a solution of 2b was treated with the trihy-
drido complex [Cp2NbH3] an as yet unidentified brown
precipitate formed insolubly in common organic sol-
vents. There was no indication of an insertion of the
benzylidene ligand into the M–H bond of the hydrido
complex.
Although it was not possible to isolate complex 12 in
a pure form, the IR and NMR spectroscopic data
allowed one to establish the constitution of 12. The IR
spectrum in the range between 2100 and 1900 cm−1
exhibited absorptions at 2067, 1969, and 1926 cm−1
.
These absorptions are characteristic for a neutral pen-
tacarbonyl metal fragment and are similar to those of
The reaction of the anionic hydrido complex
PNP[(CO)4FeH] (13) [PNP=bis(triphenylphospho-

108
H. Fischer, H. Jungklaus / Journal of Organometallic Chemistry 572 (1999) 105–115
Scheme 7.
2.2. Mechanistic in6estigations
Scheme 6.
The most feasible mechanism for the insertion of the
benzylidene ligand of 2a–c, 7a, and 8a into the M–H
bond of 3, 5, 9, 11, and 13 is a concerted reaction.
Labeling experiments support this assumption. Treat-
ment of the monodeuterated benzylidene complex
[(CO)5WꢀC(D)Ph] (2aD, 100% d1) with 3 gave 4aD
(100% d1) (Scheme 7). When the analogous reaction of
the deuterated benzylidene complex [(CO)5WꢀC
(D)C6H4OMe-p] (2cD, 100% d1) with 3 was quenched
with a 100-fold excess of PMe3 after one half-life only
the monodeuterated complex 6cD and the adduct
[(CO)5W–C(D)(PMe3)C6H4OMe-p] were detected. The
formation of [(CO)5W–C(H)(PMe3)C6H4OMe-p] by a
H/D exchange was not observed. Similarly, the reaction
of the deuterido complex [Cp(CO)3WD] (5D, 81% d1)
with 2b selectively afforded 6bD (60% d1) (Scheme 8).
Most likely, the small reduction of the degree of deuter-
ation is caused by traces of HBF4. Small amounts of
HBF4 are usually present in the solutions of the ben-
zylidene complexes when they are obtained by in situ
generation (see Scheme 1). HBF4 presumably reacts
with 5D by H/D exchange to form [Cp(CO)3WH] which
then with 2b affords undeuterated 6b.
ranylidene)ammonium] with the p-methylbenzylidene
complex 2b proceeded similarly to the reactions of
2a–c, 7a, and 8a with 3, 5, and 9. Addition of a
solution of 13 in CH2Cl2 to 2b in CH2Cl2 at −65°C
instantaneously gave a brown-green reaction mixture.
Removal of the solvent and chromatographic workup
did not afford a mononuclear alkyl complex similar to
4a–c, 6a–c, and 10 but rather its W(CO)5 adduct
PNP[(CO)4(CH2C6H4Me-p)Fe·W(CO)5] (14) in 6%
yield (Scheme 6). Presumably, complex 14 is formed by
insertion of the p-methylbenzylidene ligand of 2b into
the Fe–H bond of 13 to give [(CO)4Fe(CH2C6H4Me-
p)]− and subsequent addition of the W(CO)5 fragment
to the tetracarbonyl(p-methylbenzyl)ferrate. An alter-
native pathway involves initial nucleophilic addition of
the anion in 13 to the carbene carbon atom of 2b to
form an ylide complex [(CO)5W{v-C(C6H4Me-
p)H}Fe(H)(CO)4]− and subsequent fast rearrangement
to 14. On the basis of steric considerations the former
pathway seems more likely. In addition, there is no
indication for an ylide complex intermediate. Neverthe-
less, the latter pathway cannot completely be excluded
since in other cases 13 has been reported to act as an
iron nucleophile [25].
The structure of 14 as a heterobimetallic complex
with a Fe–W bond was deduced from the spectroscopic
data. The IR and UV–vis spectra agree well with those
of the related dinuclear complex PNP[(CO)4(H)Fe–
W(CO)5] [26]. The 13C-NMR spectrum exhibits three
FeCO resonances (l=211.1, 214.4, and 222.2) indica-
tive of a rigid (CO)4Fe fragment similar to that in
[cis-(CO)4FeI2] [27] and NEt4[Ph3AuFe(CO)4 ·W(CO)5]
[28]. In contrast, complex 13 [29], PNP[cis-
(CO)3{P(OPh)3}FeH] [30], and PNP[(CO)4(H)Fe–
W(CO)5] [26] show only one 13C-NMR signal for the
four iron-bound carbonyl ligands. This was explained
by rapid CO exchange ([26]a) and by magnetic and
electronic degeneration [30].
Unlike terminal hydrido complexes, v-hydrido com-
pounds did not react with the benzylidene complexes 2.
Solutions of 2b remained unchanged when treated at
low temperature with [H3Mn3(CO)12], [HW2(CO)9
(NO)], or NEt4[HW2(CO)10]. Warming of the mixtures
only resulted in decomposition of 2b giving predomi-
nantly [W(CO)6] and [{(Co)5W}2{v-C(H)C6H4Me-p}].
Scheme 8.
The reaction sequence involving (a) dissociation of
H+ from the terminal metal hydrides LnM–H, (b)
nucleophilic addition of the resulting metallate to the
carbene carbon atom in 2a–c, 7a, and 8a to form a
binuclear carbene-bridged complex and (c) protolytic
cleavage of the W–C bond to give the final product can
be excluded. Sequential reaction of 2b with the metal-
late NEt4[(CO)5Mn] and HBF4 ·Et2O did not afford 4b.
An alternative mechanism involving (a) heterolytic
cleavage of the metal hydride bond to give LnM+ and
H−, (b) addition of H− to the carbene carbon atom to
form a benzyl metallate and (c) transfer of the benzyl
ligand to LnM+ can likewise be excluded. When
NEt4[(CO)5W–CH2Ph]
was
treated
with
[(CO)5Mn]BF4, compound 4a was not detected among
the reaction products.

H. Fischer, H. Jungklaus / Journal of Organometallic Chemistry 572 (1999) 105–115
109
Fig. 2. Plot of ln(k2/T) versus 1/T for the reaction of 2c with 5 in
Fig. 1. Plot of kobs versus concentration of complex 5 for the reaction
of 2c with 5 in pentane.
pentane.
ln(k2/T) versus 1/T (Fig. 2) yields the activation
parameters. The activation enthalpy DH" is small
(1993 kJ mol−1), the activation entropy DS" strongly
Radical intermediates in the reaction of terminal
metal hydrides with benzylidene complexes are also
unlikely. Addition of two equivalents of galvinoxyl as a
radical scavenger to a solution of 2c prior to the
reaction with 3 did not prevent the formation of 4c (see
Scheme 3).
negative (−120910 J mol−1
K
−1). The influence of
the solvent on the reaction rate is small. When pentane
was replaced by polar dichloromethane as the solvent,
the reaction accelerated only by about 10% (k2=
360(10) l mol−1 s−1 at −8.4°C).
2.3. Kinetic in6estigations
When [Cp(CO)3WH] (5) was replaced by the deute-
ride [Cp(CO)3WD] (5D, 75% d1) in the reaction with 2c
in pentane at −8.4°C a positive kinetic isotope effect
of kH2 /k2D=2.790.4 was observed (kD2 =180910 l
Kinetic investigations were performed of the reaction
of 2c with 3 in pentane using stopped-flow techniques
and pseudo first-order conditions ([3]0/[2c]0]10). The
progress of the reaction was followed by monitoring the
decrease of MLCT absorption of the carbene complex
at umax=496 nm as a function of time. Fig. 1 shows
plots of kobs (Table 1) versus [5] at different tempera-
tures between−8.4 and 8.7°C.
The reaction of 2c with 5 follows a second-order rate
law first-order in the concentrations of the benzylidene
complex 2c and the hydrido complex 5. Second-order
rate constants k2 calculated from these plots are (stan-
dard deviation in brackets): k2=340(20) l mol−1 s−1
(at −8.4°C) 410(20) l mol−1 s−1 (at −4.0°C) 420(20)
l mol−1 s−1 (at −0.2°C) 550(30) l mol−1 s−1 (at
4.2°C) and 620(90) l mol−1 s−1 (at 8.7°C). The plot of
mol−1 −1).
s
The influence of the electrophilicity of the carbene
carbon atom and of the steric requirements of the
spectator ligands in the metal hydride were also deter-
mined. Reduction of the electrophilicity of the carbene
carbon atom by substitution of OMe for the p-methyl
substituent in 2b led to a decrease of the reaction rate in
pentane at −9.5°C by 76%. When the cyclopentadi-
enide ligand in 5 was replaced by the sterically more
demanding pentamethylcyclopentadienide in 9 in the
reaction with 2c the reaction rate decreased by 68%
(k2=440(20) l mol−1 s−1 (for 5), 140(10) l mol−1 s−1
(for 9), both in pentane at 3.2°C).
Table 1
Rate constants (103 ·kobs) for the reaction of 2c with 5 in pentane
([2c]0=0.0375 mM)
3. Discussion
The strongly electrophilic benzylidene complexes 2a–
c, (CO)5CrꢀC(H)Ph and Cp(CO)2MnꢀC(H)Ph react
with a series of terminal hydrido complexes by insertion
of the carbene ligand into the metal hydrido bond. In
contrast, the reactions of the cationic iron carbene
complexes [Cp(CO)2FeꢀC(OMe)R]PF6 (R=H, Me,
Ph) with [Cp(PPh3)(CO)FeH] afford iron h-alkoxyalkyl
complexes [Cp(CO)2FeꢀC(OMe)(H)R] by transfer of
H− from the hydride complex to the carbene ligand
Temperature (°C) [5]0 (mM)
0.375
0.500
0.635
0.750
8.7
4.2
0.2
−4.0
−8.4
0.227(10)
0.200(3)
0.169(14)
0.142(5)
0.115(6)
0.308(5)
0.279(8)
0.222(5)
0.198(5)
0.154(3)
0.418(10)
0.352(12)
0.273(7)
0.240(1)
0.203(9)
0.448(5)
0.405(4)
0.325(9)
0.300(4)
0.240(5)

110
H. Fischer, H. Jungklaus / Journal of Organometallic Chemistry 572 (1999) 105–115
−1291 cal mol−1 K−1 for the reaction of [HM-
n(CO)5] with H2CꢀC(Me)Ph [43]) DS" for the reaction
of 2c with 3 is strongly negative (−120910 J mol−1
whereas the phosphine-substituted carbene complexes
[Cp(PPh3)(CO)FeꢀC(OMe)R]PF6 (R=H, Me) remain
unaltered when treated with [Cp(PPh3)(CO)FeH] [31].
Substitution of [Cp(dppe)FeH] for [Cp(PPh3)(CO)Fe–
H] as the reducing agent leads to dealkylation and
formation of [Cp(PPh3)(CO)FeꢀC(O)R] [31]. When
K
−1). These observations render a radical mechanism
rather unlikely.
IR-spectroscopic studies of metal carbonyl hydrides
suggest that the M–H bond is polarized with the
negative charge on the hydrogen [44]. The approximate
charges on hydrogen are −0.8 for [HMn(CO)5] and
−0.75 for [HCo(CO)4] [45] as derived from the results
of X-ray photoelectron spectroscopic studies. There-
fore, the most probable pathway involves initial nucle-
ophilic attack of the metal hydride LnMH on the
carbene carbon atom. Interaction of the M–H | bond
with the LUMO of the carbene complex which is
predominantly localized on the carbene carbon atom
could lead to an elongation of the W–C(carbene) bond
and a tilting of the carbene substituent away from the
approaching metal hydride. The nucleophilic attack is
followed by electrophilic interaction of LnM with the
carbene carbon atom, presumably from the direction
opposite to the (CO)5W fragment. W–C(carbene) bond
dissociation then completes the reaction (Scheme 9).
The proposal of a rate-limiting nucleophilic attack of
the metal hydride on the carbene carbon is supported
by the second-order rate law and by the decrease of the
reaction rate when the electrophilicity of the carbene
carbon atom (2b“2c) is reduced.
The strongly negative activation entropy indicates a
highly ordered transition state. Steric interactions be-
tween the co-ligands do not play a significant role as
the reaction rate increases only by a factor of about
three when the bulky pentamethylcyclopentadienide lig-
and in 9 is replaced by the sterically less demanding
cyclopentadienide group (in complex 5). The deuterium
isotope effect (2.690.4) is indicative of significant M–
H(D) bond breaking and still less developed C–H(D)
bond formation in the transition state for insertion
(early transition state).
[Cp(PEt3)(CO)FeꢀC(H)Me]BF4
is
treated
with
[Cp(PR3)(CO)Fe–H] (R=Et, Ph) at −78°C an instan-
taneous reaction is observed. However, it was not pos-
sible to identify the products [32].
There are many examples for the insertion of unsatu-
rated molecules or fragments into the M–H bond of
metal hydrides ([1]b, [33]). Intermolecular insertions of
carbene ligands into activated X–H bonds (X=C [34],
Si [32,35,36], Ge [36,37], Sn [36,37], P [38], O [39], Se
[40], Cl [39], Br [41]) are also well established. However,
mechanistic investigations on the latter reactions are
very scarce.
Several reaction pathways are conceivable for the
insertion of the benzylidene ligand into the M–H bond.
On the basis of the mechanistic investigations and of
the kinetic results (second-order rate law, strongly neg-
ative activation entropy) mechanisms involving a rate-
determining CO, H+, or H− dissociation or a
rate-limiting intramolecular rearrangement can be
discarded.
A radical mechanism has to be taken into account as
hydrogen atom transfer to unsaturated substrates such
as substituted styrenes, anthracenes, allenes, and dienes
is an important reactivity pattern exhibited by many
transition metal hydrides. The stoichiometric hydro-
genation of olefins by metal hydrides has been studied
in detail [42]. These reactions follow a second-order
rate law and proceed by a stepwise process. The first
hydrogen transfer is rate-determining. An inverse iso-
tope effect was found for those hydrogenation reactions
that proceed by sequential hydrogen atom transfers
from metal hydrides to unsaturated substrates. In addi-
tion, H/D exchange between metal deuteride and alkene
in the recovered educts and CIDNP effects in the
1H-NMR spectra of the reaction of [HMn(CO)5] with
h-methylstyrene were observed [43].
Similar to these hydrogenations, the reaction of 2c
with 3 follows second-order kinetics. However, several
observations do not agree with a radical mechanism. In
contrast to these radicalic hydrogenation reactions nei-
ther D/H exchange in recovered 2cD nor ‘cage escape’
products such as [Cp(CO)3W]2 and ArCH2CH2Ar
’
(derived from the rather long-lived radicals Cp(CO)3W
’
and PhCH2 ) are observed. Furthermore, the radical
scavenger galvinoxyl does not influence the reaction.
Instead of an inverse isotope effect a normal isotope
effect (kH2 /kD2 =2.690.4) is observed in the reaction of
2c with 3. Whereas the activation entropies for the
hydrogenation of olefins are usually small (e.g. DS"
=
Scheme 9.

H. Fischer, H. Jungklaus / Journal of Organometallic Chemistry 572 (1999) 105–115
111
The insertion of a carbene ligand into the M–H
4.2. Generation of carbene complexes 2a–c
bond of metal hydrides is related to the reactions of
complexes 2 with olefins to form cyclopropanes [46,47].
The reaction characteristics for the reaction of 2c with
vinyl acetate are similar to those of the reaction with 5:
small activation enthalpy, strongly negative activation
entropy, small solvent effect, similar influence of the
substituent at the carbene carbon atom (2b react 4.1
times faster with [(CO)5MnH] and 3.8 times faster with
vinyl acetate than 2c). Based on the results of a kinetic
study [47] and on HMO calculations performed with
the model system (CO)5CrꢀCH2+H2CꢀCH2 [48], an
associative mechanism with an early transition state
was proposed. The calculations indicated that the least-
energy pathway involves initial nucleophilic attack of
one carbon of the olefin on the carbene carbon fol-
lowed by an electrophilic attack of the second olefinic
carbon on the carbene carbon from the direction oppo-
site to the metal (‘backside ring closure’). A similar
mechanism was also proposed for the cyclopropanation
of olefins by cationic iron carbene complexes
[Cp(CO)LFeꢀC(R)H]+ (L=CO, PPh3; R=Me, aryl)
[49] and the backside ring closure was verified by
labeling studies [50].
The carbene complexes 2a–c were freshly prepared
prior to the reactions with the metal hydrides. A typical
example
is
as
follows:
3.50
mmol
of
NEt4[(CO)5WC(H)(OMe)C6H4R-p] (2.01 g (1a), 2.06 g
(1b), 2.12 g (1c)) was dissolved in 25 ml of CH2Cl2 and
7.25 mmol of HBF4 (1.00 ml of a 54% solution in Et2O)
was rapidly added at −90°C while vigorously stirring
the solution. The yellow solution immediately turned
deep red. After 1 min, 25 ml of pentane (precooled to
−78°C) was added and the solution was chro-
matographed at −78°C on silica gel. With pentane/
CH2Cl2 (3/1 (2a), 2/1 (2b), 1/1 (2c)), the dark red
fraction containing 2a–c was eluted and immediately
used for the subsequent reactions with metal hydrides.
4.3. Reaction of 2a with [(CO)5MnH] (3)
At −78°C, 0.75 mmol (0.15 g) of 3 was added to a
solution of 2a in pentane/CH2Cl2 (3/1), freshly pre-
pared from 0.35 mmol (0.20 g) of 1a and 0.72 mmol of
HBF4 (0.10 ml of a 54% solution in Et2O). Within
seconds the deep red solution turned yellow. The sol-
vent was removed in vacuo. The residue was dissolved
in 5 ml of CH2Cl2 and chromatographed at 0°C on
silica gel. First, a band containing [(CO)6W] and
[(CO)10Mn2] was eluted with pentane. Then, 4a was
eluted with pentane/THF (10/1). The solvent was re-
moved in vacuo and the residue recrystallized at
−34°C from 2 ml of pentane.
4. Experimental section
4.1. General
All manipulations were performed under argon using
standard Schlenk techniques. Solvents were dried by
refluxing over sodium/benzophenone ketyl or CaH2 and
freshly distilled under argon prior to use. To remove
water and oxygen, silica gel for flash chromatography
(J.T. Baker) and Al2O3 (basic, Merck) was kept in
vacuo at room temperature for 4 h and then stored
under argon. The complexes 2a–c [12], 3 [51], 5 [51], 7a
4a: Colorless crystals (24 mg, 24% based on 1a). All
spectroscopic and analytical data agree with reported
values [63].
4.4. Reaction of 2b with [(CO)5MnH] (3)
The reaction of 3.00 mmol (0.59 g) of 3 with 2b,
prepared from 1.34 mmol (0.79 g) of 1b and 2.77 mmol
of HBF4 (0.38 ml of a 54% solution in Et2O), and the
chromatographic workup were carried out analogously
to Section 4.3.
[12], 8a [52],
9
[53], 11 [51], 13 [54],
[(CO)5WꢀC(Ph)C6H4OMe-p] [55], [(CO)5WꢀC(OMe)-
C6H4Me-p] [56], [(CO)4COH] [57], [(Cp2ZrHCl)n] [58],
[Cp2NbH3] [51], [H3Mn3(CO)12] [51], [HW2(CO)9(NO)]
[59], NEt4[HW2(Co)10] [60], NEt4[Mn(CO)5] [61],
[(CO)5Mn]BF4 [62], and NEt4[(CO)5WCH2Ph] ([46]a)
were synthesized according to literature procedures.
The monodeuterated complexes [(CO)5WꢀC(D)Ph],
[(CO)5WꢀC(D)C6H4OMe-p], and [Cp(CO)3WD] were
prepared analogously to [(CO)5WꢀC(H)Ph] [12] and
[Cp(CO)3WH] [51], respectively. NMR spectra were
recorded with Bruker WM250 or Bruker AC250 spec-
trometers at room temperature in CDCl3 unless other-
wise stated. Chemical shifts are reported relative to
TMS. Other instrumentation: IR, Perkin-Elmer 983G
or Bio-Rad FTS 60 spectrophotometer; UV–vis, Perkin
Elmer Lambda 15; MS, Finnigan MAT 312 (EI, 70
eV); elemental analyses, Heraeus CHN-O-RAPID.
4b: Colorless crystals (80 mg, 20% based on 1b), m.p.
47°C. IR (pentane/THF 10/1): w(CO) 2108 w, 2016 vs,
1
2010 vs, 1990 s cm−1. H-NMR: l 2.26 (s, 3H, CH3),
2.39 (s, 2H, CH2), 6.96–7.00 (m, 2H, C6H4), 7.04–7.08
(m, 2H, C6H4). EI-MS: m/z (%) 300 (7) [M+], 160 (84)
[M+ –5CO], 105 (100) [CH2C6H4CH3-p]. Anal. Found:
C, 52.15; H, 3.09; C13H9MnO5 (300.2) calc.: C, 52.02;
H, 3.02.
4.5. Reaction of 2c with [(CO)5MnH] (3)
The reaction of 4.50 mmol (0.88 g) of 3 with 2c,
prepared from 1.80 mmol (1.10 g) of 1c and 3.77 mmol
of HBF4 (0.52 ml of a 54% solution in Et2O), and the

112
H. Fischer, H. Jungklaus / Journal of Organometallic Chemistry 572 (1999) 105–115
6c: Yellow crystals (0.16 g, 11% based on 1c), m.p.
107°C. IR (pentane): w(CO) 2016 s, 1935 s, 1926 vs
chromatographic workup were carried out analogously
to Section 4.3.
4c: Colorless crystals (120 mg, 21% based on 1c). All
spectroscopic and analytical data agree with reported
values [64].
1
cm−1. H-NMR: l 0 2.98 (s, 2H, CH2), 3.76 (s, 3H,
OCH3), 5.27 (s, 5H, Cp), 6.71–6.75 (m, 2H, C6H4),
7.07–7.11 (m, 2H, C6H4). EI-MS: m/z (%) 454 (1)
[M+], 370 (17) [M+ –3CO], 121 (100) [CH2C6H4OCH3-
p+]. Anal. Found: C, 42.23; H, 3.16; C16H14O4W
(454.1) calc.: C, 42.31; H 3.11.
4.6. Reaction of 2a with [Cp(CO)3WH] (5)
At −40°C, a solution of 1.95 mmol (0.65 g) of 5 in
10 ml of CH2Cl2 was added to a solution of 2a in 100
ml of pentane/CH2Cl2 (3/1), obtained from 2.14 mmol
(1.26 g) of 1a and 4.43 mmol of HBF4 (0.61 ml of a
54% solution in Et2O). The dark red solution immedi-
ately turned yellow. Then, 10 g of basic Al2O3 was
added and the solvent was removed in vacuo. The
residue (reaction products adsorbed on Al2O3) was
placed on top of a column filled with Al2O3 and chro-
matographed at −30°C. First, with pentane [(CO)6W]
and then, with pentane/CH2Cl2 (5/2), a yellow band
containing 6a was eluted. The solvent of the yellow
fraction was removed in vacuo and the residue was
recrystallized at −30°C from 2 ml of methanol.
6a: Yellow crystals (0.49 g, 54% based on 1a), m.p.
86°C. All spectroscopic and analytical data agree with
reported values [65].
4.9. Reaction of [(CO)5CrꢀC(H)Ph] (7a) with
[Cp(CO)3WH] (5)
At −78°C, a solution of 0.33 mmol (0.11 g) of 5 in
15 ml of pentane was added to a solution of 7a,
obtained from 0.28 mmol (0.20 g) of PNP-
[(CO)5CrC(H)(OMe)Ph] and 0.58 mmol of HBF4 (0.08
ml of a 54% solution in Et2O). The solution turned
yellow. Chromatography and recrystallization as de-
scribed in Section 4.6 gave complex 6a.
6a: Yellow crystals (50 mg, 42% based on PNP-
[(CO)5Cr–C(H)(OMe)Ph]). All spectroscopic and ana-
lytical data agree with reported values [65].
4.10. Reaction of [Cp(CO)2MnꢀC(H)Ph] (8a) with
[Cp(CO)3WH] (5)
At ambient temperature, a green-brown solution of
0.34 mmol (0.09 g) of 8a in 17 ml of pentane was added
to a solution of 0.34 mmol (0.12 mg) of 5 in 17 ml of
pentane. The progress of the reaction was followed by
IR spectroscopy. The absorptions of 8a disappeared
within 5 min. After a few further min a red-black
precipitate formed. The reaction mixture was filtered
through a 3 cm-layer of kieselguhr. The filtrate was
concentrated in vacuo to a volume of ca. 3 ml and then
chromatographed at −20°C with pentane/CH2Cl2 (3/1)
on flash silica gel. First, a colorless fraction containing
[Cp(CO)3Mn] and then a yellow fraction containing 6a
were collected.
4.7. Reaction of 2b with [Cp(CO)3WH] (5)
The reaction of 2b, obtained from 2.12 mmol (1.25 g)
of 1b and 4.39 mmol of HBF4 (0.60 ml of a 54%
solution in Et2O), with 2.12 mmol (0.71 g) of 5 and the
chromatographic workup were carried out analogously
to Section 4.6.
6b: Yellow crystals (0.17 g, 18% based on 1b), m.p.
103°C. IR (pentane): w(CO) 2016 s, 1933 s, 1927 vs
cm−1 1H-NMR: l 2.26 (s, 3H, CH3), 2.96 (s, 2H,
.
CH2), 5.27 (s, 5H, Cp), 6.95–6.99 (m, 2H, C6H4),
7.04–7.08 (m, 2H, C6H4). EI-MS: m/z (%) 438 (2)
[M+], 354 (42) [M+ –3CO], 105 (100) [CH2C6H4CH3-
p+]. Anal. Found: C, 43.68; H, 3.23; C16H14O3W
(438.1) calc.: C, 43.86; H, 3.22.
6a: Yellow crystals (6 mg, 4% based on 8a). All
spectroscopic and analytical data agree with reported
values [65].
4.8. Reaction of 2c with [Cp(CO)3WH] (5)
4.11. Reaction of 2c with [Cp*(CO)3WH] (9)
At −50°C, a solution of 4.49 mmol (1.50 g) of 5 in
10 ml of CH2Cl2 was added to a solution of 2c in 100
ml of pentane/CH2Cl2 (1/1), obtained from 3.31 mmol
(2.00 g) of 1c and 6.85 mmol of HBF4 (0.94 ml of a
54% solution in Et2O). The solution immediately turned
yellow and a yellow-brown precipitate formed. The
solution was decanted. When the volume of the solu-
tion was reduced in vacuo to a few ml yellow crystals of
6c formed. Recrystallization of the yellow-brown pre-
cipitate from 5 ml of methanol afforded additional
crystals of 6c.
At −60°C, a solution of 0.25 mmol (0.11 g) of 2c in
20 ml of CH2Cl2 was added to a solution of 0.25 mmol
(0.10 g) of 9 in 20 ml of CH2Cl2. The solution immedi-
ately turned yellow. The solvent was evaporated in
vacuo and the residue was chromatographed on Al2O3
at 0°C. With pentane/CH2Cl2 (10/1) [(CO)6W] was
eluted and then with pentane/CH2Cl2 (1/1) complex 10.
The solvent was removed in vacuo and the residue
recrystallized from pentane/CH2Cl2 (40/1).
10: Yellow crystals (0.07 g, 53% based on 1c), m.p.
149°C. IR (pentane): w(CO) 2006 s, 1915 vs cm−1
.

H. Fischer, H. Jungklaus / Journal of Organometallic Chemistry 572 (1999) 105–115
113
1
1H-NMR: l 2.02 (s, 15H, CH3), 2.18 (s, 2H, CH2), 3.74
(s, 3H, OCH3), 6.67–6.71 (m, 2H, C6H4), 7.06–7.10 (m,
2H, C6H4). EI-MS: m/z (%) 524 (2) [M+], 440 (19)
[M+ –3CO], 121 (100) [CH2C6H4OCH3-p+]. Anal.
Found: C, 47.90; H, 4.63; C21H24O4W(254.3) calc.: C,
48.11; H, 4.61.
m): 406 nm (3.488). H-NMR (238 K): l 2.21 (s, 3H,
CH3), 2.35 (s, 2H, CH2), 6.91–6.94 (m, 2H, C6H4),
7.10–7.13 (m, 2H, C6H4), 7.48 (m, 24H, o,m-H of
PNP–Ph), 7.66 (br, 6p-H of PNP–Ph). 13C-NMR (238
K): l 13.3 (CH2), 21.0 (CH3), 125.6, 126.5, 127.4, 128.1,
131.0, 131.8, 133.6 (C6H4 and Ph), 204.6 (cis-WCO,
lJ(WC)=127.3 Hz), 206.3 (trans-WCO), 211.1, 214.4,
222.2 (FeCO). MS (FAB, negative modus): m/z (%) 597
(67) [M−], 492 (100) [M− –CH2C6H4CH3-p], 464 (30),
436 (18), 408 (8), 324 (5) [M− –CH2C6H4CH3-p-nCO]
(n=1, 2, 3, 6), 245 (5) [(CO)3FeCH2C6H4CH3]. Anal.
Found C, 54.98; H, 3.59; N, 1.18; C53H39FeNO9P2W
(1135.5) calc.: C, 56.06; H, 3.46; N, 1.23. Complex 14 is
thermolabile and quickly decomposed at room
temperature.
4.12. Reaction of 2b with [Cp2WH2] (11)
At −78°C, a solution of 0.79 mmol (0.25 g) of 11 in
25 ml of pentane was added to a solution of 2b in 100
ml of pentane, obtained from 1.24 mmol (0.73 g) of 1b
and 2.56 mmol of HBF4 (0.35 ml of a 54% solution in
Et2O). The solution immediately turned yellow and a
green-black precipitate formed. The precipitate was
washed several times with 10 ml portions of pentane
precooled to −78°C. The resulting powder of 12 was
dried in vacuo for several hours at −78°C. Due to fast
decomposition in solution, it was not possible to recrys-
tallize 12 and obtain the complex in a pure form.
12: Black powder (80 mg, 13% based on 11). IR
4.14. Mechanistic studies
4.14.1. Reaction of 3 with [(CO)5WꢀC(D)Ph] (2aD)
At −70°C, 0.75 mmol (0.15 g) of complex 3 was
added to a solution of 2aD, prepared from 0.35 mmol
(0.20 g) of NEt4[(CO)5W–C(D)(OMe)Ph] (1aD) (100%
1
(toluene): w(CO) 2067 w, 1969 w, 1926 s cm−1. H-
1
NMR ([D8]toluene, 238 K): l −23.42 (1H, W–H–W,
1J(WH)=70.8 Hz, 2J(WH)=36.0 Hz), 2.23 (s, 3H,
CH3), 2.36 (s, 2H, CH2), 4.04 (s, 10H, Cp), 6.50–6.53
(m, 2H, C6H4), 6.90–6.94 (m, 2H, C6H4). 13C-NMR
([D6]acetone, 238 K): l −13.8 (CH2), 20.6 (CH3), 86.1
(Cp), 128.2, 128.6, 131.6, 153.5 (C6H4), 199.2 (cis-CO,
1J(WC)=129.0 Hz), 199.8 (trans-CO). EI-MS: m/z (%)
419 (1) [Cp2WCH2C6H4CH3-p+], 352 (4) [W(CO)6+],
314 (27) [Cp2W+], 268 (20) [W(CO)3+], 106 (82)
[(CH3)2C6H4+].
monodeuterated based on the H-NMR spectrum). Af-
ter
workup
analogously
to
Section
4.3
[(CO)5MnC(H)(D)Ph] (4aD) was recrystallized from 2
ml of pentane.
4aD: Yellow crystals (20 mg, 20% based on 1aD).
1H-NMR: l 2.31 (s, 1H, CHD), 6.89 (s, 1H, p-H of
1
Ph), 7.09 (s, 4H, o,m-H of Ph). Based to the H-NMR
spectrum 4aD was 100% monodeuterated at the
methylene carbon atom.
4.14.2. Reaction of 5 with [(CO)5WꢀC(D)C6H4OMe-p]
(2cD) and PMe3
4.13. Reaction of 2b with PNP[(CO)4FeH] (13)
At −80°C, a solution of 0.018 mmol (0.008 g) of
2cD (100% monodeuterated) was added to a solution of
0.06 mmol (0.02 g) of 5 and thoroughly mixed. After 60
s, 1.84 mmol (0.14 g) of PMe3 was added. The solution
immediately turned yellow. The solvent was removed in
vacuo and the residue was analyzed by H-NMR spec-
troscopy. The spectrum showed no proton resonance in
the range expected for [(CO)5WC(H)(PMe3)C6H4OMe-
p]
At −65°C, a solution of 0.96 mmol (0.68 g) of 13 in
50 ml of CH2Cl2 was added to a solution of 2b in 100
ml of CH2Cl2, obtained from 2.97 mmol (1.75 g) of 1b
and 6.15 mmol of HBF4 (0.85 ml of a 54% solution in
Et2O). The solution turned brown-green. The solvent
was completely removed in vacuo at −45°C and the
residue was dissolved at room temperature in the mini-
mum volume of ether possible. The solution was
quickly chromatographed on a 10 cm-layer of basic
Al2O3. With ether [(CO)6W] was eluted and then, with
CH2Cl2, the product 14 as a brown-red fraction. The
solvent was removed in vacuo at −50°C. The residue
was dissolved in a few millilitres of acetone precooled
to −30°C. Pentane (precooled to −30°C) was slowly
added until the solution got slightly cloudy. When the
solution was cooled to −74°C a red-brown precipitate
(14) formed which was washed with pentane (precooled
to −78°C) and dried in vacuo.
1
4.14.3. Reaction of 2b with [Cp(CO)3WD] (5D)
The reaction of 0.047 mmol (0.020 g) of 2b in 20 ml
of CH2Cl2 with 0.051 mmol (0.017 g) of 5D (81%
monodeuterated) at −60°C and the chromatographic
workup were carried out analogously to Section 4.6.
After workup the methylene carbon atom of the result-
ing product 6bD was 60% monodeuterated as deter-
mined by NMR spectroscopy.
14: Red-brown powder (60 mg, 6% based on 13). IR
(CH2Cl2): w(CO) 2060 w, 2006 w, 1946 vs, 1940 sh,
1909 m, 1855 vw, br cm−l. UV–vis (CH2Cl2): umax (1g
4.14.4. Reaction of 2b with NEt4[(CO)5Mn] and HBF4
At −60°C, a solution of 0.68 mmol (0.22 g) of
NEt4[(CO)5Mn] in 10 ml of CH2Cl2 was added to a

114
H. Fischer, H. Jungklaus / Journal of Organometallic Chemistry 572 (1999) 105–115
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[8] See e.g. (a) M.J. Winter, Polyhedron 8 (1989) 1583. (b) V.A.
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solution of 2b, obtained from 1.40 mmol (0.80 g) of lb
and 2.90 mmol of HBF4 (0.40 ml of a 54% solution in
Et2O). Within 3 min the reaction mixture turned orange
and a yellow precipitate formed. Based on the IR
spectrum of the solution, the reaction of 2b with
NEt4[Mn(CO)5] was complete. The reaction product
was unstable and rapidly decomposed at ambient tem-
perature in the IR cuvette. When 2.90 mmol of HBF4
(0.4 ml of a 54% solution in Et2O) were added to the
mixture at −60°C the yellow compound decomposed.
4b was not detected among the decomposition
products.
[10] P.J. Brothers, W.R. Roper, Chem. Rev. 88 (1988) 1293.
[11] C.P. Casey, S.W. Polichnowski, H.E. Tuinstra, L.D. Albin, J.C.
Calabrese, Inorg. Chem. 17 (1978) 3045.
4.14.5. Reaction of [(CO)5Mn(BF4)] with
NEt4[(CO)5WCH2Ph]
[12] (a) C.P. Casey, T.J. Burkhardt, J. Am. Chem. Soc. 96 (1974)
7808. (b) H. Fischer, S. Zeuner, K. Ackermann, J. Chem. Soc.
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A
solution of 0.21 mmol (0.117 g) of
NEt4[(CO)5WCH2Ph] in 10 ml of CH2Cl2 was added at
ambient temperature to filtered solution of
a
[(CO)5Mn]BF4 in 15 ml of CH2Cl2, freshly prepared
from 0.21 mmol (0.059 g) of [(CO)5MnBr] and 0.30
mmol (0.059 g) of AgBF4. The mixture turned black
and a metallic shiny precipitate formed. The IR spec-
trum of the solution did not show absorptions due to
4a.
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4.15. Kinetic studies
All reactions were performed with a HI-TECH SFA-
11 stopped-flow apparatus using pseudo-first order con-
ditions. The ratio of the hydrido and the carbene
complex concentration was at least 10:1. The reactions
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Acknowledgements
Support of this work by the Fonds der Chemischen
Industrie is gratefully acknowledged.
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