Molybdenum alkylidene complexes with linked cycloheptatrienyl-phosphane ligands for potential use in olefin metathesis

Article abstract of DOI:10.1016/S0022-328X(03)00767-8

The synthesis of cycloheptatrienyl molybdenum complexes incorporating the linked cycloheptatrienyl-phosphane ligand [2-(diisopropylphosphanyl) phenyl]cycloheptatrienyl, o-i Pr₂P-C₆H₄- C₇H₆, is described. Reaction of the 17-electron dibromide [(o-iPr₂PC₆H₄-η ⁷-C₇H₆)MoBr₂(P-Mo)] (1) with NaBH₄ furnishes a tetrahydroborate complex, which can be directly converted into the acetate complex [(o-iPr₂PC ₆H₄-η⁷-C₇H₆) Mo(η²-O₂CCH₃)( P-Mo )] (2). The acetate ligand can be cleaved upon treatment with diazoalkanes, N₂CHR, in the presence of Me₃SiCl affording the molybdenum alkylidenes [(o-iPr₂PC₆H₄ -η⁷-C₇H₆)MoCl(=CHR)(P-Mo)] (4a, R=Ph; 4b, R=SiMe₃). Complexes 4 might serve as a source for the preparation of potential olefin metathesis catalysts of the type [(o-iPr₂PC₆H₄-η⁷-C ₇H₆)Mo(=CHR)(P-Mo)]⁺ by halide abstraction. CH₂ insertion into the metal-carbon bond of the diphenylacetylene complex 5 resulted in the formation of the cationic η³-vinylcarbene complex 6, which can be regarded as an alkene adduct of a 16-electron complex of just that kind. In addition, the X-ray crystal structures of 2 and 6 are reported.

Full text of DOI:10.1016/S0022-328X(03)00767-8

Journal of Organometallic Chemistry 684 (2003) 322Á328
/
www.elsevier.com/locate/jorganchem
Molybdenum alkylidene complexes with linked cycloheptatrienylÁ
/
phosphane ligands for potential use in olefin metathesis
Matthias Tamm a,*, Bernd Dreßel a, Thomas Lugger b
¨
a Anorganisch-chemisches Institut, Lehrstuhl fur Anorganische Chemie, Technische Universitat Munchen, Lichtenbergstr. 4, D-85747 Garching,
¨
¨
¨
Germany
b Institut fur Anorganische und Analytische Chemie, Westfalische Wilhelms-Universitat, Wilhelm-Klemm-Str. 8, D-48149 Munster, Germany
¨
¨
¨
¨
Received 12 March 2003; received in revised form 5 June 2003; accepted 5 June 2003
Dedicated to Professor Ernst Otto Fischer on the occasion of his 85th birthday
Abstract
The synthesis of cycloheptatrienyl molybdenum complexes incorporating the linked cycloheptatrienylÁ
/phosphane ligand [2-
(diisopropylphosphanyl)phenyl]cycloheptatrienyl, o-iPr2P-C6H4-C7H6, is described. Reaction of the 17-electron dibromide [(o-
iPr2PC6H4-h7-C7H6)MoBr2(P-Mo)] (1) with NaBH4 furnishes a tetrahydroborate complex, which can be directly converted into the
acetate complex [(o-iPr2PC6H4-h7-C7H6)Mo(h2-O2CCH3)(P-Mo)] (2). The acetate ligand can be cleaved upon treatment with
diazoalkanes, N2CHR, in the presence of Me3SiCl affording the molybdenum alkylidenes [(o-iPr2PC6H4-h7-C7H6)MoCl(Ä
/
CHR)(P-Mo)] (4a, Rꢀ
/
Ph; 4b, Rꢀ
/
SiMe3). Complexes 4 might serve as a source for the preparation of potential olefin metathesis
catalysts of the type [(o-iPr2PC6H4-h7-C7H6)Mo(Ä
/
CHR)(P-Mo)]ꢁ by halide abstraction. CH2 insertion into the metalÁ
/
carbon
bond of the diphenylacetylene complex 5 resulted in the formation of the cationic h3-vinylcarbene complex 6, which can be regarded
as an alkene adduct of a 16-electron complex of just that kind. In addition, the X-ray crystal structures of 2 and 6 are reported.
# 2003 Elsevier B.V. All rights reserved.
Keywords: Cycloheptatrienyl complexes; Molybdenum; Alkylidene complexes; Olefin metathesis; Diazoalkanes
1. Introduction
plexes [RuCl2(Ä
/
CHR)(PPh3)2] (Rꢀalkyl, aryl) [7],
/
which are among the most important (pre)catalysts for
all types of olefin metathesis reactions [8]. The phenyl-
carbene complex I is even commercially available and
constitutes a versatile starting material for further
catalyst design by substitution of PPh3 for other ligands
among which stable N-heterocyclic carbenes [9,10]
proved to be extremely useful for boosting the catalytic
activity [11]. Although exceedingly sensitive towards
dioxygen and moisture, Schrock’s molybdenum-based
Since the first successful isolation and characteriza-
tion of a stable transition metal carbene complex by
Fischer and Maasbol in 1964 [1], numerous preparative
¨
routes for the synthesis of Fischer and Schrock type
carbene complexes have been developed [2,3]. Among
many other possible carbene sources, diazoalkanes are
particularly useful for the preparation of non-heteroa-
tom-stabilized carbene complexes due to their stability
and ease of availability [4]. Established and extensively
studied by Herrmann [5], diazoalkanes were frequently
used in the synthesis of transition metal carbenes [6].
Recently, this method could be employed in the
preparation of Grubbs-type ruthenium alkylidene com-
alkylidene complexes of the general formula [Mo(Ä
/
CHCMe2Ph)(ÄNAr)(OR2)] represent the second impor-
/
tant class of potent molecular olefin metathesis cata-
lysts, and the highly active compound II can also be
obtained from commercial sources [12]. It is also
noteworthy in this context that recent work by Hof-
mann involves cationic ruthenium carbene complexes
such as III, which exhibit much higher ring-opening
metathesis polymerization (ROMP) activity in solution
than any other Ru system [13] (Fig. 1).
* Corresponding author. Tel.: ꢁ
13473.
E-mail address: matthias.tamm@ch.tum.de (M. Tamm).
/
49-89-289-13080; fax: ꢁ49-89-289-
/
0022-328X/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00767-8

M. Tamm et al. / Journal of Organometallic Chemistry 684 (2003) 322Á
/
328
323
course of the metathesis polymerization by the Chauvin
mechanism [17].
Our preparative route for making these alkylidene
complexes available is outlined in Scheme 1. The 17-
electron dibromide 1 is easily accessible [14d], and it can
be reduced employing hydride sources such as NaBH4
or NaH. Thus, treatment with sodium borohydride
results in the formation of the tetrahydroborate complex
[(o-iPr2PC6H4-h7-C7H6)Mo(h2-BH4)(P-Mo)] exhibiting
a bidentate M(m2-H2BH2) ligation [14b], whereas chiral-
at-metal monohydride complexes of the type [(o-
iPr2PC6H4-h7-C7H6)MoHL(P-Mo)] (Lꢀ
/phosphines,
imidazol-2-ylidenes) are formed on reaction with so-
dium hydride in the presence of suitable Lewis bases L
[14c]. In a similar fashion, the acetate complex 2 can be
prepared in high yield by addition of a large excess of
NaBH4 to an ethanolic solution of 1, followed by
quenching this reaction mixture with acetic acid. In its
1H-NMR spectrum 2 exhibits three cycloheptatrienyl
resonances at 5.61, 4.55 and 4.50 ppm in a 2:2:2 ratio
indicating that its structure is essentially Cs symmetric.
Accordingly, the 13C-NMR spectrum displays four
resonances for the C7H6 carbon atoms. The resonances
observed for the acetate ligand at 1.60 ppm (CH3) and at
Fig. 1. Alkylidene transition metal complexes for use in olefin
metathesis.
In continuation of our work on complexes containing
linked cycloheptatrienylÁphosphane ligands [14], we
/
became interested in cationic 16-electron molybdenum
alkylidene complexes of type IV and their potential use
in olefin metathesis. With Brunner, we have indepen-
dently emphasized the similarity between the isoelec-
tronic and isolobal fragments [(h-C5R5)Ru] and [(h-
180.3 ppm (3JC,P
ꢀ1.3 Hz, COO) and 22.8 ppm (CH3),
/
respectively, are in good agreement with the values
found for related carboxylate transition metal com-
plexes [18].
C7H7)Mo] [14Á16], which has prompted us to pursue a
/
general study on the possibility of replacing frequently
used ruthenium catalysts by analogous but much
cheaper molybdenum systems [14]. Consequently, we
propose that alkylidene complexes such as IV can be
regarded as a link between the two most popular
catalyst systems I and II and might additionally exhibit
a similar reactivity as observed for the cationic system
III. In this contribution, we wish to present a prelimin-
ary report on the syntheses of molybdenum carbenes of
type
(Rꢀ
[(o-iPr2PC6H4-h7-C7H6)MoCl(Ä
Ph, SiMe3), which could provide the 16-electron
complex fragments IV upon chloride abstraction.
/
CHR)(P-Mo)]
/
2. Results and discussion
We had previously reported on the use of paramag-
netic dialkyl complexes of the type [(o-R2PC6H4-h7-
C7H6)Mo(CH2SiMe3)2(P-Mo)] (Rꢀ
ROMP of norbornene [14a]. We proposed that 17-
electron alkylidene complexes
[(o-R2PC6H4-h7-
C7H6)Mo(ÄCHSiMe3)(P-Mo)] could have formed as
/Ph, iPr) in the
/
the active species by intramolecular a-deprotonation
and elimination of Me4Si. However, we have not yet
been able to prove the formation of such complexes.
From our present point of view, cationic 16-electron
metal carbenes such as IV are more likely to be
catalytically active as they would allow to coordinate
an additional alkene ligand and to further describe the
Scheme 1.

324
M. Tamm et al. / Journal of Organometallic Chemistry 684 (2003) 322Á328
/
Instead, characterization of the reddish-brown com-
pound isolated from the reaction mixture indicates the
formation of the diazoalkane complex 3 [22]. This
assumption could be supported by X-ray diffraction
analysis revealing that the N2CPh2 ligand is coordinated
through the terminal nitrogen atom [23].
Due to our failure to convert 3 into a diphenylalk-
ylidene complex, the monosubstituted N2CHPh was
used instead leading to an instantaneous evolution of
dinitrogen and the formation of the phenylcarbene
complex 4a in good yield. Similarly, the trimethylsilyl-
carbene derivative 4b was quantitatively isolated em-
ploying N2CHSiMe3. Indicative of metal alkylidene
formation are the low-field 13C NMR resonances of 4a
Fig. 2. ORTEP drawing of 2 with thermal ellipsoids drawn at 50%
˚
probability. Selected bond lengths [A] and angles [8]: C1Ã
/
C2 1.414(2),
C5 1.392(3),
O1 1.265(2), C20ÃO2 1.265(2),
C2 2.2760(15), MoÃC3 2.2463(17), MoÃ
C5 2.3068(17), MoÃC6 2.2371(17), MoÃ
2.2599(17), MoÃO1 2.2174(12), MoÃ
2.4710(4); O1ÃC20ÃO2 118.52(15).
C1Ã
C5Ã
MoÃ
2.3014(17), MoÃ
/
C7 1.419(2), C2Ã
C6 1.413(3), C6ÃC7 1.418(2), C20Ã
C1 2.2495(14), MoÃ
/
C3 1.413(2), C3Ã
/
C4 1.420(3), C4Ã
/
and 4b [24], which are observed at 318 (2JC,P
and 354 ppm (2JC,P
23 Hz), respectively. In their H-
NMR spectra, both complexes exhibit characteristic
doublets for the MoÄCHR protons at 13.61 (4a,
3JH,P
26 Hz) and 15.35 ppm (4b, JH,Pꢀ32 Hz). In
ꢀ
/
23 Hz)
/
/
/
/
1
ꢀ
/
/
/
/
/
C4
C7
/
/
/
/
/
O2 2.2189(11), MoÃP
/
/
3
/
/
ꢀ
/
/
4a and 4b, the pseudotetrahedrally coordinated molyb-
denum center has four different ligands, and so the
complexes are obtained as racemic mixtures of two
enantiomers. As these representatives of so-called
‘‘chiral-at-metal’’ half-sandwich compounds [15,25] are
configurationally stable, the diastereotopic cyclohepta-
trienyl hydrogen atoms of each complex give rise to six
To confirm the spectroscopic results, a single crystal
of 2 was subjected to X-ray diffraction analysis. The
molecular structure is depicted in Fig. 2, and it reveals
that the cycloheptatrienylÁphosphane ligand does in-
/
deed coordinate in chelating h7:h1-fashion with an
almost perfectly perpendicular orientation of the six-
and seven-membered rings. The molybdenum atom is
symmetrically bound to the seven ring-carbon atoms
1
different H-NMR resonances. Accordingly, seven 13C-
NMR resonances are observed for the C7H6 carbon
atoms together with six resonances each for the phen-
ylene-bridge as well as for the isopropyl groups. Finally,
one single 31P-NMR resonance is found for each
complex at 50.3 (4a) and 51.7 ppm (4b).
˚
with the shortest bond to C6 [2.2371(17) A] and the
˚
longest bond to C5 [2.3068(17) A]. The two MoÃ
/
O
˚
bonds are almost identical [MoÃ
/
O1 2.2174(12) A, MoÃ
/
2
˚
O2 2.2189(11) A] confirming the h -coordination mode
for the acetate group. It should be noted that the
positions of all hydrogen atoms could be refined for 2.
Therefore, it is possible to establish the angles between
the centroid of the cycloheptatrienyl ring, the C7 carbon
atoms and the adjacent hydrogen atoms revealing a
significant out-of-plane displacement for the C7 hydro-
gen atoms. The average bending is about 98 toward the
molybdenum center, and such a deviation has been
attributed to a reorientation of the large seven-mem-
bered ring for a better metal overlap [19,20].
Complexes 4 are ideal precursors for the generation of
16-electron alkylidene complexes of type IV (vide
supra), and treatment of 4a or 4b with halide abstracting
agents such as trimethylsilyl triflate or complex silver(I)
and thallium(I) salts should result in the formation of
the cations [(o-iPr2PC6H4-h7-C7H6)Mo(Ä
/
CHR)(P-
Mo)]ꢁ (Rꢀ
/
Ph, SiMe3). In fact, preliminary studies
indicate that a highly active ROMP catalyst can be
generated upon addition of TlPF6 to a solution of 4b in
dichloromethane. An initial experiment has been carried
out in the following manner: A solution of 4b (3 mg, 6
mmol) in CH2Cl2 (0.5 ml) was treated with an excess of
TlPF6 (10 mg, 29 mmol). The resulting mixture was
filtered to remove thallium(I) chloride and added to a
solution of norbornene (300 mg, 3.18 mmol). Rapid
formation and precipitation of poly(norbornene) could
be observed, and the reaction seemed to be over within
90 s. These reactions are currently under further
investigation, and we hope to present novel homoge-
neous cycloheptatrienyl transition metal catalysts in the
near future.
Werner and coworkers have shown that reaction of
the
ruthenium
methallyl
complex
[(h-
C5H5)Ru(PPh3)(h3-2-MeC3H4)] with acetic acid leads
to the formation of the closely related acetate complex
[(h-C5H5)Ru(PPh3)(h2-O2CCH3)] [18]. Cleavage of the
carboxylate ligand is observed on treatment with diaryl
diazoalkanes in the presence of halide sources such as
[Et3NH]Cl or Me3SiCl, and ruthenium alkylidene com-
plexes of type [(h-C5H5)RuCl(PPh3)(Ä/CRR’)] are
formed [18b,21]. We anticipated that 2 should react in
a similar manner to produce alkylidene complexes [(o-
iPr2PC6H4-h7-C7H6)MoCl(Ä
tion of 2 with diphenyl diazoalkane in the presence of
Me3SiCl, however, did not give the desired product.
/CRR’)(P-Mo)]. The reac-
By chance, we have been able to isolate and crystal-
lographically characterize a complex, which can be
regarded as an olefin adduct of a type IV complex.

M. Tamm et al. / Journal of Organometallic Chemistry 684 (2003) 322Á
/
328
325
Recrystallization of the diphenylacetylene complex 5
[26] from CH2Cl2 afforded single crystals of the
alkylidene complex 6, which must have formed by
insertion of a methylene group, CH2, into one of the
acetylenic molybdenumÁcarbon bonds (Scheme 2). It is
/
a matter of fact that the CH2 moiety must stem from the
dichloromethane solvent, the mechanism of its insertion,
however, cannot yet be fully explained. The spectro-
scopic characterization of 6 is still in progress, but the
structural parameters give clear evidence for the forma-
tion of a h3-vinylcarbene complex (vide infra) [27,28].
Dinuclear complexes containing exactly the same alky-
lidene ligand, the 1,2-diphenylpropenylidene, have been
described previously. Interestingly, they have either
formed by addition of CH2 (from diazoalkane) to a
dinuclear diphenylacetylene complex or by addition of
just the same alkyne to a bridged methylene complex
[29,30].
Fig. 3. ORTEP drawing of 6 with thermal ellipsoids drawn at 50%
probability. The hydrogen atoms have been omitted for clarity.
˚
Selected bond lengths [A] and angles [8] for molecule 1 [molecule 2]:
Mo1Ã
C27 1.969(6) [1.969(6)], Mo1Ã
C20 71.3(3) [75.9(4)], C300ÃC20Ã
Mo1 85.8(4) [84.2(4)], C300ÃMo1Ã
/
C300 2.368(6) [2.384(6)], Mo1Ã
P1 2.5467(16) [2.5611(15)]; Mo1Ã
C27 113.1(5) [114.5(5)], C20Ã
C27 65.1(2) [64.6(2)].
/
C20 2.336(6) [2.319(6)], Mo1Ã
C300Ã
C27Ã
/
/
/
/
/
/
/
/
The molecular structure of the cation in 6 is shown in
Fig. 3. The asymmetric unit contains two independent
complexes 6, and the two cations exhibit an identical
/
/
3. Conclusion
˚
alkylidene bond length of 1.969(6) A,
molybdenumÁ
/
which is comparable to values for related cationic
vinylidene complexes, such as [(h7-C7H7)Mo(Ä
CÄ
CH2CH2CH2OH, 1.91(1) A; RÄ
Ph, 1.93(1) A] [24b,31]. The only other structurally
characterized carbene derivative of any cycloheptatrie-
nyl metal system, the cyclic oxacarbene complex [(h7-
With this contribution, we have presented a prelimin-
ary account of the preparation of cycloheptatrienyl
molybdenum alkylidene complexes, which might allow
the generation and isolation of cationic 16-electron
/
/
˚
CHR)(dppe)]PF6 [RÄ
/
/
˚
complexes of the type [(o-iPr2PC6H4-h7-C7H6)Mo(Ä
/
CHR)(P-Mo)]ꢁ for applications in olefin metathesis in
the near future. With these systems, we hope to show
again that cycloheptatrienyl complexes can indeed be
potentially useful for applications in homogeneous
transition metal catalysis. This work is part of our
general goal to extend the chemistry of cycloheptatrienyl
complexes and to raise their level of significance in
comparison with that of cyclopentadienyl and benzene
complexes.
C7H7)Mo(Ä
plays a longer MoÃ
Surprisingly, the carbonÁ
the MoÄC(Ph)ÃC(Ph)ÄCH2 moiety of the two indepen-
/
CCH2CH2CH2O)(dppe)(Mo-O)]PF6
dis-
C bond length of 2.04(3) A [24b].
carbon bond distances within
˚
/
/
/
/
/
dent cations differ quite significantly (Fig. 3), the
formulation of 6 as a h3-vinylcarbene complex, how-
ever, is unequivocally justified.
4. Experimental
All operations were performed in an atmosphere of
dry Ar by using Schlenk and vacuum techniques.
Solvents were dried by standard methods and distilled
prior to use. The synthesis of 1 has been described
previously [14d]. The diazoalkanes were prepared ac-
cording to published procedures [4]. Elemental analyses
(C, H, N) were performed on a Heraeus CHNO-Rapid
elemental analyzer. EI and ESI mass spectra were
recorded on a Varian MAT 212 or on a Micromass
1
Quattro LCZ mass spectrometer, respectively. H- and
13C-NMR spectra were measured on Bruker AC 200,
Bruker AMX 400 or Varian U 600 spectrometers using
the solvent as internal standard, whereas 31P-NMR
measurements were run on a Bruker AC 200 spectro-
Scheme 2.

326
M. Tamm et al. / Journal of Organometallic Chemistry 684 (2003) 322Á328
/
meter using aqueous H3PO4 (85%) as an external
reference. IR spectra were recorded on a Bruker Vector
22 instrument. For the atomic numbering schemes used
in Section 4, see Fig. 2.
CHPh), 152.8 (d, 2JC,P
7.0 Hz, ipso-C6H5), 138.3 (d, JC,P
ꢀ
/
29.0 Hz, C-8), 149.6 (d, 3JC,P
ꢀ
/
2
ꢀ33.9 Hz, C-9),
/
131.9 (s, o-C6H5), 131.3 (s, C-13), 131.1 (s, C-12), 129.2
2
(s, p-C6H5), 128.8 (d, JC,P
ꢀ6.7 Hz, C-10), 128.7 (d,
/
3JC,P
2JC,P
ꢀ
/
3.8 Hz, C-11), 127.9 (s, m-C6H5), 107.9 (d,
2.0 Hz, C-1), 102.3 (s, C7H6), 97.0 (t, 2 C,
4.1. [(o-iPr2P-C6H4-h7-C7H6)Mo(O2CCH3)(P-Mo)]
(2)
ꢀ
/
C7H6), 93.7 (d, C7H6), 84.7 (s, C7H6), 81.6 (s, C7H6),
1
15.6 Hz, iPr: CH), 24.6 (d, JC,P
1
25.1 (d, JC,P
ꢀ
/
ꢀ15.6
/
A solution of 1 (500 mg, 0.93 mmol) in EtOH was
treated at 0 8C with NaBH4 (250 mg, 6.52 mmol) and
stirred for 3 h at ambient temperature, followed by
quenching the reaction mixture with acetic acid. The
solvent was removed in vacuo, and the residue was
extracted with Et2O/hexane (1:1). After evaporation of
the solvent, 2 could be isolated as a light green solid.
Hz, iPr: CH), 18.6 (s, iPr: CH3), 18.3 (m, 2C, iPr: CH3),
17.3 (s, 2C, iPr: CH3). 31P-NMR (THF-d8, 81 MHz): d
50.3. MS (EI): m/z (%)ꢀ
/
505(28) [Mꢁ].
4.3. [(o-iPr2PC6H4-h7-C7H6)MoCl(Ä
Mo)] (4b)
/
CHSiMe3)(P-
Purification by recrystallization from Et2OÁ
/
hexane was
possible, affording green crystals of 2. Yield: 350 mg
A solution of 2 (150 mg, 0.34 mmol) in 20 ml of
toluene was treated with 0.1 ml Me3SiCl and stirred for
30 min at r.t. The reaction mixture was cooled to 0 8C,
and a solution of N2CHSiMe3 in hexane (0.23 ml of a 2
M solution, 0.46 mmol) was added. After stirring for 3 h
at ambient temperature, the solvent was removed in
vacuo, and the residue was extracted with hexane.
Purification by recrystallization from hexane afforded
1
(86%). H-NMR (benzene-d6, 600 MHz): d 7.92 (t, 1H,
C6H4), 7.29 (d, 1H, C6H4), 7.61 (m, 2H, C6H4), 5.61 (s,
2H, C7H6), 4.55 (m, 2H, C7H6), 4.50 (s, 2H, C7H6), 2.05
(sep., 2H, iPr: CH), 1.60 (s, 3H, O2CCH3), 1.04 (dd, 6H,
iPr: CH3), 0.66 (dd, 6H, iPr: CH3). 13C-NMR (benzene-
3
d6, 150.7 MHz): d 180.3 (d, JC,P
ꢀ
/
1.3 Hz, O2C), 158.0
36.0 Hz, C-9),
1.5 Hz, C-10), 128.9 (s,
(d, 3JC,P
131.6 (s, C-11), 130.3 (d, 2JC,P
C-13), 128.8 (s, C-12), 109.3 (d, JC,P
ꢀ
/
25.5 Hz, C-8), 136.4 (d, 2JC,P
ꢀ
/
brown crystals of 4b. Yield: 99% (170 mg). H-NMR
3
(THF-d8, 400 MHz): d 15.35 (d, 1H, JH,P
1
ꢀ
/
ꢀ32 Hz,
/
3
ꢀ
/2.6 Hz, C-1),
CHSiMe3), 7.43 (m, 1H, C6H4), 7.35 (m, 1H, C6H4),
7.30 (m, 2H, C6H4), 5.40 (t, 1H, C7H6), 5.19 (dd, 2H,
C7H6), 4.74 (t, 1H, C7H6), 4.38 (t, 1H, C7H6), 4.27 (t,
1H, C7H6), 2.47 (sep., 1H, iPr: CH), 2.30 (sep., 1H, iPr:
CH), 1.23 (dd, 3H, iPr: CH3), 1.06 (dd, 3H, iPr: CH3),
2
3
93.5 (d, JC,P 5.9 Hz, C-4,5), 85.5 (d, JC,P
1
C-3,6), 79.9 (s, C-2,7), 23.7 (d, 2C, JC,P
ꢀ
/
ꢀ/1.8 Hz,
ꢀ/16.4 Hz, iPr:
CH), 22.8 (s, O2CCH3), 18.7 (s, 2C, iPr: CH3), 18.6 (s,
2C, iPr: CH3). 31P-NMR (benzene-d6, 81 MHz): d 67.8.
MS (EI): m/z (%)ꢀ
/
438 (78) [Mꢁ]. IR (CH2Cl2): n˜
/
0.80 (m, 6H, iPr: CH3), 0.00 (s, 9H, SiMe3). 13C-NMR
2
(THF-d8, 100.6 MHz): d 352.1 (d, JC,P
(OCOasym)ꢀ1532, n˜(OCOsym)ꢀ
/
/
/
1454 cmꢂ1
.
Anal.
ꢀ23.3 Hz,
/
2
calc. for C21H27MoO2P (438.41): C, 57.53; H, 6.20.
Found C, 57.30; H, 6.15%.
CHSiMe3), 152.6 (d, JC,P
2JC,P
35.0 Hz, C-9), 130.0 (s, 2C, C6H4), 127.4 (dd, 2C,
C6H4), 103.3 (d, JC,P
ꢀ/28.1 Hz, C-8), 135.8 (d,
ꢀ
/
2
ꢀ2.1 Hz, C-1), 99.7 (s, C7H6),
/
4.2. [(o-iPr2PC6H4-h7-C7H6)MoCl(Ä
Mo)] (4a)
/CHC6H5)(P-
97.7 (s, C7H6), 95.9 (d, C7H6), 91.6 (d, C7H6), 82.5 (s,
C7H6), 81.0 (s, C7H6), 29.4 (s, 2 C, iPr: CH), 18.0 (d,
2
2JC,P
CH3), 16.5 (d, JC,P
ꢀ
/
2.8 Hz, iPr: CH3), 16.9 (d, JC,P
2
ꢀ3.4 Hz, iPr:
/
A solution of 2 (200 mg, 0.45 mmol) in 20 ml of
toluene was treated with 0.1 ml Me3SiCl and stirred for
30 min at room temperature (r.t.). The reaction mixture
was cooled to 0 8C, and a freshly prepared solution of
PhHCN2 in hexane (6.4 ml of a 0.1 M solution, 0.64
mmol) was added. After stirring for 3 h at ambient
temperature, the solvent was removed in vacuo and the
residue extracted with hexane. Purification by recrys-
tallization from hexane afforded dark green crystals of
ꢀ5.4 Hz, iPr: CH3), 16.0 (s, iPr:
/
CH3), 0.1 (s, 3C, SiMe3). 31P-NMR (benzene-d6, 81
MHz): d 51.6.
4.4. X-ray crystallography
All data sets were collected at ꢂ
/
120 8C with a Bruker
AXS APEX diffractometer equipped with a rotating
˚
Ka radiation (lꢀ0.71073 A). Empiri-
anode using MoÁ
/
/
1
4a. Yield 80% (184 mg). H-NMR (THF-d8, 600 MHz):
3
d 13.61 (d, 1H, JH,P
cal absorption correction with SADABS [32] was applied
to the raw data. Structure solution in all cases with
SHELXS [33] and refinement with SHELXL [34] with
anisotropic thermal parameters for all atoms. Hydrogen
atoms for 2 and for the cation in 6 were located by
difference Fourier techniques and were refined with
isotropic thermal parameters, the hydrogen atoms for
the BPh4 counterions in 6 were added to the structure
model on calculated positions and are unrefined. ORTEP
ꢀ26 Hz, CHPh), 7.68 (m, 2H,
/
C6H4), 7.62 (d, 2H, o-C6H5), 7.53 (m, 2H, C6H4), 7.31
(t, 2H, m-C6H5), 7.04 (t, 2H, p-C6H5), 5.55 (t, 1H,
C7H6), 5.40 (d, 1H, C7H6), 5.15 (t, 1H, C7H6), 4.94 (t,
1H, C7H6), 4.43 (t, 1H, C7H6), 4.24 (t, 1H, C7H6), 2.79
(sep., 1H, iPr: CH), 2.52 (sep., 1H, iPr: CH), 1.41 (dd,
6H, iPr: CH3), 0.95 (dd, 6H, iPr: CH3). 13C-NMR
2
(THF-d8, 150.7 MHz): d 317.5 (d, JC,P
ꢀ23.1 Hz,
/

M. Tamm et al. / Journal of Organometallic Chemistry 684 (2003) 322Á
/
328
327
Kreissl, U. Schubert, K.Weiss, Transition Metal Carbene Com-
plexes, VCH Publishers, Weinheim, Germany, 1983.
Table 1
Crystallographic data for 2 and 6
[3] J. Organomet. Chem. 617Á618 (2001), Special Issue ‘‘Transition
/
2
6
Metal Complexes of Carbenes and Related Species in 2000’’ (Ed.:
G. Bertrand).
[4] B. Eistert, M. Regitz, G. Heck, H. Schwall, in: E. Muller (Ed.),
¨
Formula
Formula weight (amu)
C
21H27MoO2P
C58H56BMoP
890.75
9.8870(18)
17.054(3)
27.011(5)
90
438.34
15.0825(15)
14.373(2)
18.223(3)
90
Methoden der Organischen Chemie (Houben-Weyl), vol. 10/4,
Georg Thieme Verlag, Stuttgart, 1968, p. 473.
[5] (a) W.A. Herrmann, Angew. Chem. 86 (1974) 556; Angew. Chem.
Int. Ed. Engl. 13 (1974) 599.;
˚
a (A)
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
V (A )
Dcalc (g cmꢂ1
(b) W.A. Herrmann, Chem. Ber. 108 (1975) 486;
(c) W.A. Herrmann, Chem. Ber. 108 (1975) 3412;
(d) W.A. Herrmann, B. Reiter, H. Biersack, J. Organomet. Chem.
97 (1975) 245;
90
90
93.349(3)
90
3
˚
3950.6(10)
1.474
4546.6(14)
1.301
)
(e) W.A. Herrmann, J. Plank, M.L. Ziegler, K. Weidenhammer,
Angew. Chem. 90 (1978) 817; Angew. Chem. Int. Ed. Engl. 17
(1978) 777.
Crystal system
Space group
Z
Orthorhombic
Pbca
Monoclinic
P21
8
0.756
5758
4
0.362
11 846
[6] (a) W.A. Herrmann, Angew. Chem. 90 (1978) 855; Angew. Chem.
Int. Ed. Engl. 17 (1978) 800.;
m (mmꢂ1
)
Unique data
(b) W.A. Herrmann, Adv. Organomet. Chem. 20 (1982) 159.
[7] (a) P. Schwab, M.B. France, J.W. Ziller, R.H. Grubbs, Angew.
Chem. 107 (1995) 2179; Angew. Chem. Int. Ed. Engl. 34 (1995)
2039.;
Observed data {I ꢀ
R1 (obs. data) (%)
R2 (all data) (%)
Goodness-of-fit
/2s(I)}
4901
10 204
2.57, wR1ꢀ
3.27, wR2ꢀ
1.050
334
/6.36
4.26, wR1ꢀ
/
9.16
9.76
/6.65
5.52, wR2ꢀ
/
0.998
1387
(b) P. Schwab, R.H. Grubbs, J.W. Ziller, J. Am. Chem. Soc. 118
(1996) 100.
[8] (a) A. Furstner, Angew. Chem. 112 (2000) 3140; Angew. Chem.
¨
Number of variables
˚
Res. electr. dens. (e A
ꢂ3
)
0.596/ꢂ
/0.223
0.411/ꢂ0.607
/
Int. Ed. Engl. 39 (2000) 3012.;
(b) M.R. Buchmeiser, Chem. Rev. 100 (2000) 1565;
(c) M. Schuster, S. Blechert, ChiuZ 35 (2001) 24.
[9] A.J. Arduengo, III, R.L. Harlow, M. Kline, J. Am. Chem. Soc.
113 (1991) 361.
[35] was used for all drawings. Additional crystal-
lographic data are listed in Table 1.
[10] (a) D. Bourissou, O. Guerret, F.P. Gabbaı, G. Bertrand, Chem.
¨
Rev. 100 (2000) 39;
5. Supplementary material
(b) A.J. Arduengo, III, Acc. Chem. Res. 32 (1999) 913;
(c) A.J. Arduengo, III, R. Krafczyk, ChiuZ 32 (1998) 6;
(d) W.A. Herrmann, C. Kocher, Angew. Chem. 109 (1997) 2256;
¨
Angew. Chem. Int. Ed. Engl. 36 (1997) 2162.
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC nos. 205582 (2) and 205583 (6).
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
[11] (a) T.M. Trnka, R.H. Grubbs, Acc. Chem. Res. 34 (2001) 18;
(b) W.A. Herrmann, Angew. Chem. 114 (2002) 1342; Angew.
Chem. Int. Ed. Engl. 41 (2002) 1290.
[12] R.R. Schrock, J.S. Murdzek, G.C. Bazan, J. Robbins, M.
DiMare, M. O’Regan, J. Am. Chem. Soc. 112 (1990) 3875.
[13] (a) S.M. Hansen, M.A.O. Volland, F. Rominger, F. Eisentrager,
¨
Cambridge CB2 1EZ, UK (Fax: ꢁ44-1223-336033; e-
/
mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
P. Hofmann, Angew. Chem. 111 (1999) 1360; Angew. Int. Ed.
Engl. 38 (1999) 1273.;
(b) S.M. Hansen, F. Rominger, M. Metz, P. Hofmann, Chem.
Eur. J. 5 (1999) 557;
Acknowledgements
(c) C. Adlhart, M.A.O. Volland, P. Hofmann, P. Chen, Helv.
Chim Acta 83 (2000) 3306.
[14] (a) M. Tamm, K. Baum, T. Lugger, R. Frohlich, K. Bergander,
¨
¨
This work was financially supported by the Deutsche
Forschungsgemeinschaft and by the Fonds der Che-
mischen Industrie. M.T. is grateful to Professor W.A.
Herrmann (Munich) for the appointment to temporarily
represent the Chair of Inorganic Chemistry at the
Eur. J. Inorg. Chem. (2002) 918;
(b) M. Tamm, B. Dreßel, V. Urban, T. Lugger, Inorg. Chem.
¨
Commun. 5 (2002) 837;
(c) M. Tamm, B. Dreßel, T. Lugger, R. Frohlich, S. Grimme, Eur.
¨
¨
J. Inorg. Chem. (2003) 1088;
(d) M. Tamm, B. Dreßel, K. Baum, T. Lugger, T. Pape, J.
¨
Technische Universitat Munchen.
¨
¨
Organomet. Chem. 677 (2003) 1.
[15] (a) H. Brunner, J. Klankermayer, M. Zabel, Eur. J. Inorg. Chem.
(2002) 2494;
References
(b) H. Brunner, J. Klankermayer, M. Zabel, Organometallics 21
(2002) 5746.
[16] M. Tamm, T. Bannenberg, B. Dreßel, R. Frohlich, C. Holst,
¨
[1] E.O. Fischer, A. Maasbol, Angew. Chem. 76 (1964) 645; Angew.
¨
Chem. Int. Ed. Engl. 3 (1964) 580.
Inorg. Chem. 41 (2002) 47.
[17] J.-L. He´rrison, Y. Chauvin, Makromol. Chem. 141 (1970) 161.
[18] (a) T. Daniel, N. Mahr, T. Braun, H. Werner, Organometallics 12
(1993) 1475;
[2] For an excellent book, which has been dedicated to Prof. Dr. E.O.
Fischer on the occasion of his 65th birthday and which covers the
older literature, see: K.H. Dotz, H. Fischer, P. Hofmann, F.R.
¨

328
M. Tamm et al. / Journal of Organometallic Chemistry 684 (2003) 322Á328
/
(b) H. Werner, T. Braun, T. Daniel, O. Gevert, M. Schulz, J.
[26] Complex 5 has been prepared in a similar manner as described for
analogous phenyl- and tert-butylacetylene complexes in Ref.
[14c].
Organomet. Chem. 541 (1997) 127.
[19] M.L.H. Green, D.K.P. Ng, Chem. Rev. 95 (1995) 439.
[20] M. Elian, M.M.L. Chen, D.M.P. Mingos, R. Hoffmann, Inorg.
Chem. 15 (1976) 1148.
[27] T.M. Trnka, M.W. Day, R.H. Grubbs, Organometallics 20 (2001)
3845 (and references cited therein).
[28] For a leading review on h3-vinylcarbene complexes, see: T.
Mitsudo, Bull. Chem. Soc. Jpn. 71 (1998) 1525.
[21] T. Braun, O. Gevert, H. Werner, J. Am. Chem. Soc. 117 (1995)
7291.
[29] R.E. Colburn, A.F. Dyke, S.A.R. Knox, K.A. MacPherson, A.G.
Orpen, J. Organomet. Chem. 239 (1982) C15.
[30] J. Muller, B. Passon, J. Pickardt, J. Organomet. Chem. 236 (1982)
¨
[22] (a) Y. Mizobe, Y. Ishii, M. Hidai, Coord. Chem. Rev. 139 (1995)
281;
(b) M. Dartiguenave, M.J. Menu, E. Deydier, Y. Dartiguenave,
C11.
H. Siebald, Coord. Chem. Rev. 178Á/180 (1998) 623.
[31] R.L. Beddoes, C. Bitcon, R.W. Grime, A. Ricalton, M.W.
Whiteley, Dalton Trans. (1995) 2873.
[32] SMART, Bruker AXS, 2000.
[23] R. Frohlich, Universitat Munster, private communication (2002).
¨
¨
¨
[24] (a) R.W. Grime, M.W. Whiteley, Dalton Trans. (1994) 1671;
(b) R.L. Beddoes, R.W. Grime, Z.I. Hussain, M.W. Whiteley,
Dalton Trans. (1996) 3893.
[33] G.M. Sheldrick, SHELXS-97, Acta Crystallogr. Sect. A 46 (1990)
467.
[34] G.M. Sheldrick, SHELXL-97, Universitat Gottingen, Gottingen,
[25] (a) H. Brunner, Eur. J. Inorg. Chem. (2001) 905;
(b) H. Brunner, Angew. Chem. 111 (1999) 1248; Angew. Chem.
Int. Ed. Engl. 38 (1999) 1194.
¨
¨
¨
Germany, 1997.
[35] L.J. Farrugia, ORTEP-3, University of Glasgow, 1999.