Unusual thermal reactivity of [W(≡CPh)(NCMe) (I·2-C60)(I·5-C 5Ph5)] in chlorobenzene involving activation of all ligands

Article abstract of DOI:10.1002/anie.201105542

A tung(sten) twister: Heating 1 in chlorobenzene affords 2, 3, C ₆Ph₆, and C₆₀, and involves C-H bond activation and C-C bond formation of the ligands, as well as chlorine atom abstraction from the solvent. C₆Ph₆ is presumably generated from insertion of the benzylidyne ligand into the C₅Ph₅ ring. Compound 3 is an air-stable, 17-electron species, with the phenyldichloromethyl ligand having a unique I·³-allyl-type bonding motif. Copyright

Full text of DOI:10.1002/anie.201105542

Communications
DOI: 10.1002/anie.201105542
Structure Elucidation
2
5
ꢀ
Unusual Thermal Reactivity of [W( CPh)(NCMe)(h -C60)(h -C5Ph5)]
in Chlorobenzene Involving Activation of All Ligands**
Wen-Yann Yeh*
In memory of Yasushi Mizobe
One of the most fascinating aspects pertaining to organome-
solution from dark green to brown. The products were
separated by thin-layer chromatography (TLC; silica gel) to
afford C60 (67%), [WCl(NC(Me)C60)(h6-C5Ph4(o-C6H4)CPh)]
(3; 25%), [WCl(h3-CCl2Ph)(h5-C5Ph5)] (4; 18%), and C6Ph6
(35%) [Eq. (2)]. For comparison, thermolysis of 2 was carried
À
À
tallic chemistry concerns the C H bond activation and C C
bond formation of organic substrates at transition-metal
centers,[1] because these processes hold the promise of leading
to efficient and catalytic methods for the selective conversion
of hydrocarbon feedstocks into functionalized organic com-
pounds.[2] In particular, complexes containing metal–carbon
multiple bonds (alkylidenes and alkylidynes) are important
and undergo numerous reactions, several of which are useful
in alkyne/alkene metathesis[3] and cyclization reactions,[4] as
well as in the synthesis of complicated organic molecules.[5]
Recently, the availability of gram quantities of the fullerene
C
60 has facilitated the study of the reactivity of this intriguing
molecule.[6,7] Subsequent work has been extensive, and many
attempts have been made to coordinate fullerenes to metals,[8]
and to incorporate metal-binding groups into their struc-
tures.[9] Investigation of the reactivity of fullerene-bound
organometallic compounds also becomes an attractive
research topic.[10] It was recently described that C60 induced
alkyne–alkyne coupling and alkyne scission reactions of
[W(NCMe)(C2Ph2)3] to produce [W(h3-NCMeC60)(h6-
2
5
ꢀ
C6Ph6)] (1) and [W( CPh)(NCMe)(h -C60)(h -C5Ph5)] (2)
[Eq. (1)].[11] Compound 2 contains a terminal benzylidyne
out in refluxing xylene to yield C60 (75%), C6Ph6 (42%), and a
new olive-colored complex, which was characterized as
[WH(NC(Me)C60)(h6-C5Ph4(o-C6H4)CPh)] (5; 25%), and
converted into 3 in refluxing chlorobenzene. Two reaction
routes, depicted in Scheme 1, can be proposed. Apparently,
thermal reaction of 2 is dominated by dissociation of the labile
acetonitrile and the weakly coordinated C60 ligands, thus
5
ꢀ
likely generating the reactive species [W( CPh)(h -C5Ph5)]
(A), which can either abstract three chlorine atoms from the
solvent to yield 4, or have the benzylidyne ligand inserted into
the cyclopentadienyl ring to release hexaphenylbenzene. In
À
contrast, C H bond activation of one periphery phenyl group
moiety and might be able to undergo additional ligand
activation/insertion reactions. Presented herein are results
concerning the thermal reactivity of 2, which leads to quite
striking products.
A chlorobenzene solution of compound 2 was heated to
reflux under dinitrogen to result in a change in the color of the
on the tungsten atom, with concomitant [1+2] cycloaddition
of the acetonitrile ligand to one 6:6-ring junction of C60, would
generate B, which would then undergo benzylidyne insertion
to afford 5. Subsequent H/Cl atom exchange from 5 to 3
probably involves oxidative addition of one Ph–Cl bond and
reductive elimination of a benzene molecule.
Compound 3 forms an air-stable, dark-brown solid. The
MALDI mass spectrum shows the molecular ion peak at
m/z 1513, and the isotope distribution matches the calculated
pattern for the compound containing one chlorine atom.
Crystals of 3 suitable for an X-ray diffraction study were
grown from toluene/CS2/n-hexane (1:1:1) at room temper-
ature. An ORTEP diagram of 3 is depicted in Figure 1, where
the tungsten atom is linked to an imido, a benzylidene, and an
[*] Dr. W.-Y. Yeh
Department of of Chemistry
National Sun Yat-Sen University, Kaohsiung 804 (Taiwan)
E-mail: wenyann@mail.nsysu.edu.tw
[**] The author is grateful for support of this work by the National
Science Council of Taiwan and thanks Mr. Ting-Shen Kuo (National
Taiwan Normal University, Taipei) for X-ray diffraction analysis.
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Angew. Chem. Int. Ed. 2011, 50, 12046 –12049

1.401(9)–1.46(1) ꢀ. It is inter-
À
esting that the ortho C H bond
of one phenyl group is activated
and coupled with the benzyli-
dyne carbon atom to generate a
benzylidene species with the
W1-C36 double bond distance
of 2.003(8) ꢀ, which is length-
ened by approximately 0.2 ꢀ
ꢀ
compared to that of the W C
distance in
2
(1.78(1) ꢀ).[11]
Moreover, the C60 molecule is
not ligated to the tungsten
atom, but to one 6:6-ring junc-
tion undergoing a [1+2] cyclo-
addition with the acetonitrile
ligand to yield an imido moiety.
The
distances
C43-C44
1.51(1) ꢀ, C43-C45 1.54(1) ꢀ,
and C43-C46 1.55(1) ꢀ are typ-
À
ical C C single bond lengths,
whereas the C45-C46 distance
(1.64(1) ꢀ) is substantially
Scheme 1. Proposed pathways for the thermal reaction of 2.
longer, likely due to the ring strains. We note that the
acetonitrile ligand is inserted into one 6:5-ring junction in 1 to
give a ring-opened fulleroid structure.[11] One chlorine atom is
bonded to tungsten with Cl1-W1 2.367(2) ꢀ, and is presum-
ably abstracted from the chlorobenzene solvent. Further-
more, for the complex to satisfy the 18-electron rule, the
resulting imido RN group is best considered as a four-electron
donor, thus giving rise to a formal N W bond.[12] This feature
ꢀ
is supported by the short N1-W1 distance of 1.747(6) ꢀ,
À
whereas the N W single bond distance is 2.17(3) ꢀ for
[W(NCMe)(C2Ph2)3].[13] A related conversion of nitriles into
imidos through azavinylidenes in tungsten carbonyl com-
plexes was previously reported.[14]
The 13C{1H} NMR spectrum of 3 displays a downfield
resonance at d = 272.4 ppm for the benzylidene carbon atom.
Because of the chirality at the pseudo-tetrahedral tungsten
atom and the rigidity of the complex, signals at d = 124.3,
124.0, 119.5, 118.9, and 116.7 ppm were recorded for the five
cyclopentadienyl ring carbon atoms, signals at d = 82.3, 80.7,
and 68.6 ppm for the three cyclopropanyl carbon atoms, and
signals within the range of d = 163.6–135.9 ppm for the rest of
the remaining fifty carbon resonances on the C60 core (with
some signals being coincident).
Figure 1. Molecular structure of 3. Thermal ellipsoids shown at 30%
probability. Selected bond distances [ꢀ]: C1–W1 2.449(7), C8–W1
2.506(7), C15–W1 2.432(7), C22–W1 2.351(8), C29–W1 2.370(7), C36–
W1 2.003(8), N1–W1 1.747(6), Cl1–W1 2.367(2), C1–C8 1.44(1), C1–
C29 1.46(1), C8–C15 1.401(9), C15–C22 1.46(1), C22–C29 1.454(9),
C43–C44 1.51(1), C43–C45 1.54(1), C43–C46 1.55(1), C45–C46 1.64(1),
N1–C43 1.435(9). Selected bond angles [8]: C36-W1-N1 100.4(3), C36-
W1-Cl1 96.3(2), Cl1-W1-N1 101.3(2), W1-N1-C43 173.3(5), N1-C43-C44
115.7(6), N1-C43-C45 114.6(6), N1-C43-C46 114.7(6).
Compound 5 is isomeric to 1 and 2, with the ESI mass
spectrum showing the molecular ion peaks around m/z 1477.
The 1H and 13C{1H} NMR spectra of 5 bear a close
1
resemblance to 3, except that a far downfield H signal at
d = 9.16 ppm with 183W satellites (1J(W-H) = 159 Hz) is
recorded, and is assigned to the H-W resonance. These
spectral data indicate a similar coordination environment for
the tungsten atom of 3 and 5. Although hydride signals are
most commonly found upfield of Me4Si (TMS),[15] this is not
always the case. For example, a hydride resonance at d =
20.4 ppm has been reported for [W2H(m-C4Me4)(m-CPh)-
h5-C5Ph5 group, as well as a chlorine atom. The cyclopenta-
dienyl ring is coordinated to the tungsten atom asymmetri-
cally, with the C-W bond lengths varying from 2.351(8) ꢀ for
C22-W1 through 2.506(7) ꢀ for C8-W1 (average 2.422 ꢀ),
and the C-C bond lengths within the ring are in the range of
1
(OiPr)4],[16] and at d = 10.8 ppm with J(W-H) = 115 Hz for
[17]
ꢀ
[TpWH(CO)(PhC CMe)].
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Communications
Compound 4 forms an air-stable, greenish brown crystal-
Compound 4 is formally a 17-electron species by counting
the neutral h5-C5Ph5 and the h3-CCl2Ph ligand as a five-
electron donor and the chlorine atom as a one-electron donor,
thus suggesting that it is paramagnetic. This was confirmed by
employing a variation of the Evans NMR method[19] which
revealed a magnetic moment indicative of one unpaired
electron (meff = 1.66 BM). The observed air-stability of this
paramagnetic mononuclear complex can be attributed to
protection by the bulky C5Ph5 ligand and the electronic
stabilization by three p-donating chlorine atoms.
line solid. The ESI mass spectrum displays the molecular ion
peaks around m/z 823, and the isotope distribution matches
the calculated pattern. Crystals of 4·CS2 suitable for an X-ray
diffraction study were grown from CS2/n-hexane (1:1) at
À208C. The Cl2 and C36–C42 atoms are disordered at their
sites, and are shown with 65% occupancy for 4 in Figure 2a.
In summary, an unusual thermal reactivity of 2 has been
À
À
revealed, and it involves C H bond activation and C C bond
formation within the ligands, and chlorine atom abstraction
from the solvent. The [1+2] cycloaddition of acetonitrile to
one 6:6-ring junction of C60, and the benzylidyne insertion
into the cyclopentadienyl ring are novel. Mostly, the air-
stable, 17-electron compound 4 bearing an h3-CCl2Ph struc-
ture is unprecedented and unique. Finally, this work suggests
that chlorobenzene, which has been widely used for the
reactions of organometallic compounds and fullerenes
because of solubility and temperature concerns, might not
be an innocent solvent.[20]
Experimental Section
Details on the reaction procedures, characterization data, and
structural determination for the new compounds are given in the
Supporting Information. CCDC 837439 for 3 and 837438for 4 contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Received: August 5, 2011
Revised: September 24, 2011
Published online: October 14, 2011
Figure 2. a) Molecular structure of 4·CS2. Thermal ellipsoids shown at
30% probability. The hydrogen atoms and crystal solvent have been
artificially omitted. The phenyldichloromethyl group is disordered at
two sites (inset), and the ORTEP diagram displays the atoms with
65% occupancy; b) Skeleton of the [PhCCl2W] unit, showing an h3-allyl-
type bonding structure. Selected bond distances [ꢀ]: C1–W1 2.446(4),
C8–W1 2.433(4), C15–W1 2.368(4), C22–W1 2.390(4), C29–W1
2.395(4), C36–W1 2.252(7), Cl1–W1 2.194(1), Cl2–W1 2.274(2), Cl3–
W1 2.266(1), C36–Cl2 1.739(7), C36–Cl3 1.701(7), C1–C8 1.420(6), C1–
C29 1.447(6), C8–C15 1.441(6), C15–C22 1.430(6), C22–C29 1.441(6).
Selected bond angles [8]: C36-W1-Cl1 91.6(2), C36-W1-Cl2 45.2(2),
C36-W1-Cl3 44.2(2), Cl1-W1-Cl2 109.78(6), Cl1-W1-Cl3 108.72(5), Cl2-
W1-Cl3 78.33(7), W1-C36-C37 130.5(5).
À
À
Keywords: C C coupling · C H activation · fullerenes ·
structure elucidation · tungsten
.
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À
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