The first transition metal complex of tetrafluorobenzyne: Ir(η5-C5Me5) (PMe3)(η2-C6F4) [11]

Full text of DOI:10.1021/ja010992o

J. Am. Chem. Soc. 2001, 123, 7443-7444
7443
Scheme 1
The First Transition Metal Complex of
Tetrafluorobenzyne: Ir(η5-C5Me5)(PMe3)(η2-C6F4)
Russell P. Hughes,*,§ Alex Williamson,§
Roger D. Sommer,| and Arnold L. Rheingold|
Scheme 2a
Departments of Chemistry, 6128 Burke Laboratory
Dartmouth College, HanoVer, New Hampshire 03755
UniVersity of Delaware, Newark, Delaware 19716
ReceiVed April 19, 2001
While tetrafluorobenzyne 1 has been proposed as an intermedi-
ate in many organometallic transformations, no stable metal
complex of this ligand has been prepared, either by in situ
generation of the tetrafluorobenzyne ligand1-4 or by reaction of
exogenous tetrafluorobenzyne with a metal complex.5,6 Attempts
to prepare transition metal complexes of the hydrocarbon parent,
benzyne, have been more successful, and η2 complexes of both
early and late transition metals have been isolated and crystal-
lographically characterized. These compounds (inter alia) have
been the subjects of recent reviews.7,8 Here we report the synthesis,
and the complete structural characterization of, a mononuclear
iridium complex of tetrafluorobenzyne that shows a significantly
different distribution of intraring bond lengths than do its
hydrocarbon analogues.
a R ) H, F; X ) Cl, Br.
Scheme 3
The principal method for synthesis of metal complexes of
benzyne involves an ortho carbon-hydrogen bond activation of
a phenyl ligand and elimination of RH (R ) CH3, C6H5) as shown
in Scheme 1. Representative examples of compounds prepared
by this approach include 2,9 3,10 4,11 and 5.12 An alternative route
4,5-difluorobenzyne complexes of nickel, characterized only by
their solution spectra and their reactivity patterns.7,14
Our successful approach is shown in Scheme 3. Pentafluo-
rophenyl complex 7 is prepared by oxidative addition of iodo-
pentafluorobenzene to Ir(C5Me5)(CO)2 in the manner used to
prepare perfluoroalkyl-iridium analogues.15 This reaction requires
prolonged refluxing in benzene, while the corresponding per-
fluoroalkyl iodides react at room temperature.15 Choice of solvent
(5) Roe, D. M.; Massey, A. G. J. Organomet. Chem. 1970, 23, 547-550.
(6) Roe, D. M.; Massey, A. G. J. Organomet. Chem. 1969, 20, P1-P2.
(7) Bennett, M. A.; Wenger, E. Chem. Ber./Recl. 1997, 130, 1029-1042.
(8) Jones, W. M.; Klosin, J. AdV. Organomet. Chem. 1998, 42, 147-221.
(9) McLain, S. J.; Schrock, R. R.; Sharp, P. R.; Churchill, M. R.; Youngs,
W. J. J. Am. Chem. Soc. 1979, 101, 263-265.
to group 10 complexes of benzyne has been by reduction of ortho-
halogenated aryl derivatives, as shown in Scheme 2 for nickel
complexes 6.13 Neither route has afforded tetrafluorobenzyne
complexes, although the latter has been used to prepare some
(10) Buchwald, S. L.; Watson, B. T.; Huffman, J. C. J. Am. Chem. Soc.
1986, 108, 7411-7413.
(11) Buijink, J. K. F.; Kloetstra, K. R.; Meetsma, A.; Teuben, J. H.; Smeets,
W. J. J.; Spek, A. L. Organometallics 1996, 15, 2523-2533.
(12) Hartwig, J. F.; Bergman, R. G.; Andersen, R. A. J. Am. Chem. Soc.
1991, 113, 3404-3418.
§ Dartmouth College.
| University of Delaware.
(1) Edelbach, B. L.; Kraft, B. M.; Jones, W. D. J. Am. Chem. Soc. 1999,
121, 10327-10331.
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Organometallics 1985, 4, 1992-2000.
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36, 43-53.
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A. C. J. Chem. Soc., Dalton Trans. 1998, 271-278.
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Organomet. Chem. 1979, 182, 121-141.
(15) Hughes, R. P.; Smith, J. M.; Liable-Sands, L. M.; Concolino, T. E.;
Lam, K.-C.; Incarvito, C.; Rheingold, A. L. J. Chem. Soc., Dalton Trans.
2000, 873-879.
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N. Dokl. Akad. Nauk SSSR 1981, 259, 127-131 [Chem.].
10.1021/ja010992o CCC: $20.00 © 2001 American Chemical Society
Published on Web 07/07/2001

7444 J. Am. Chem. Soc., Vol. 123, No. 30, 2001
Communications to the Editor
Table 1. Bond Lengths (Å) for the Benzyne Ligands in Complexes 2-5 and the Tetrafluorobenzyne Ligand in 11
C(11)-C(12)
C(12)-C(13)
C(13)-C(14)
C(14)-C(15)
C(15)-C(16)
C(16)-C(11)
29
1.346(5)
1.364(8)
1.368(5)
1.355(3)
1.332(6)
1.374(7)
1.410(5)
1.389(8)
1.384(5)
1.382(3)
1.386(6)
1.357(7)
1.362(2)
1.383(9)
1.385(5)
1.372(3)
1.383(7)
1.393(8)
1.403(2)
1.380(9)
1.404(5)
1.411(4)
1.390(8)
1.355(9)
1.375(6)
1.377(9)
1.382(5)
1.363(4)
1.383(7)
1.418(9)
1.408(6)
1.406(8)
1.398(5)
1.398(4)
1.389(6)
1.360(7)
310
411
512
6a,13
11
a R ) H.
Figure 2. Resonance structures for an η2-benzyne complex.
shown. The19F NMR of 11 exhibits a classic AA′XX′ pattern for
the four fluorines, with an additional 31P coupling to the “ortho”
set.
An ORTEP diagram of the molecular structure of 11 is shown
in Figure 1, along with some representative bond lengths and
angles. The fluorinated ligand adopts the expected conformation,
with the Ir-P bond bisecting the axis of the coordinated carbon
atoms. A comparison of the intraring bond distances of this
complex with those in previously characterized benzyne com-
plexes is provided in Table 1. The coordinated C-C bond distance
of 1.374(7) Å is significantly longer than the corresponding
distances in either the d8 analogue 5 or the d10 analogue 6 (R )
H). In addition, the distribution of bond lengths around the
tetrafluorobenzyne ring in 11 is significantly different from those
of its benzyne relatives. Figure 2 illustrates the resonance
structures for an (η2-benzyne)metal complex; the pattern of bond
distances in 11 appears to be more consistent with the pair of
resonance structures shown in Figure 2B, while those in other
benzyne complexes either favor those in Figure 2A or a
delocalized structure or are not significantly different enough to
allow a distinction.7,8
Figure 1. ORTEP plot for 11 with ellipsoids drawn at the 30% probability
level. Selected bond lengths (Å) and angles (deg): Ir(1)-C(12), 2.046-
(5); Ir(1)-C(11), 2.058(5); Ir(1)-P(1), 2.2573(13); C(13)-F(1), 1.358-
(6); C(14)-F(2), 1.355(6); C(15)-F(3), 1.351(6); C(16)-F(4), 1.361(6);
C(12)-Ir(1)-C(11), 39.1(2); C(16)-C(11)-C(12), 120.6(5); C(13)-
C(12)-C(11), 122.4(5); C(12)-C(13)-C(14), 117.5(5); C(15)-C(14)-
C(13), 121.2(5); C(14)-C(15)-C(16), 120.3(5); C(11)-C(16)-C(15),
117.8(5). C-C distances in the benzyne ring are given in Table 1.
is also important; no reaction is observed in refluxing hexane,
and refluxing toluene affords products that do not contain C6F5
ligands. Carbonyl displacement with PMe3 affords 8, which can
be converted to the corresponding aqua cation 9 using AgOTf in
moist toluene.16,17 As observed with analogous perfluoroalkyl-
(aqua) complexes, treatment of 9 with 1,8-bis(dimethylamino)-
naphthalene (Proton Sponge) cleanly affords the hydride 10.16,18
This hydride is obtained less cleanly by direct reaction of 8 with
NaBH4, and has also been prepared recently by Bergman by
reaction of the nucleophilic anion [Ir(C5Me5)(PMe3)H]-Li+ with
hexafluorobenzene.19 Finally, treatment of the hydride 10 with
an excess of n-BuLi affords the benzyne complex 11, presumably
via deprotonation to give 12, followed by elimination of LiF, as
Finally, while compound 11 is air-sensitive, it shows no
reactivity toward H2, CO, C2H4, or CH2dCHCO2Me after several
hours at 70 °C, making it significantly less reactive than many
other reported compounds of its hydrocarbon relatives.7,8 Further
reactivity studies of this compound and its relatives will be
reported in due course.
Acknowledgment. R.P.H. is grateful to the National Science Founda-
tion for generous financial support.
(16) Hughes, R. P.; Smith, J. M. J. Am. Chem. Soc. 1999, 121, 6084-
6085.
(17) Hughes, R. P.; Lindner, D. C.; Smith, J. M.; Zhang, D.; Incarvito, C.
D.; Lam, K.-C.; Liable-Sands, L. M.; Sommer, R. D.; Rheingold, A. L., J.
Chem. Soc., Dalton Trans. 2001. In press.
(18) Hughes, R. P.; Kovacik, I.; Lindner, D. C.; Smith, J. M.; Willemsen,
S.; Zhang, D.; Guzei, I. A.; Rheingold, A. L. Organometallics 2001. In press.
(19) Peterson, T. H.; Golden, J. T.; Bergman, R. G. Organometallics 1999,
18, 2005-2020.
Supporting Information Available: Synthetic and spectroscopic data
for compounds 7-11; tables of crystal data, atomic coordinates, structure
solution and refinement, bond lengths and angles, and anisotropic thermal
parameters for 11 (PDF). This material is available free of charge via
the Internet at http://pubs.acs.org.
JA010992O