Decarbonylation of aryl ketones mediated by bulky cyclopentadienylrhodium Bis(ethylene) complexes

Article abstract of DOI:10.1021/om030563u

The cleavage of C-C bonds of diaryl ketones and aryl alkyl ketones mediated by bulky (1,2,4-triisopropyl-3,5-dimethylcyclopentadienyl)rhodium bis(ethylene) (1) and (1,2,4-tri-tert-butylcyclopentadienyl)rhodium bis(ethylene) (2) is reported. The reactions

Full text of DOI:10.1021/om030563u

Organometallics 2004, 23, 527-534
527
Deca r bon yla tion of Ar yl Keton es Med ia ted by Bu lk y
Cyclop en ta d ien ylr h od iu m Bis(eth ylen e) Com p lexes
Olafs Daugulis and Maurice Brookhart*
Department of Chemistry, University of North Carolina at Chapel Hill,
Chapel Hill, North Carolina 27599-3290
Received August 5, 2003
The cleavage of C-C bonds of diaryl ketones and aryl alkyl ketones mediated by bulky
(1,2,4-triisopropyl-3,5-dimethylcyclopentadienyl)rhodium bis(ethylene) (1) and (1,2,4-tri-tert-
butylcyclopentadienyl)rhodium bis(ethylene) (2) is reported. The reactions using 2 proceed
at 120-150 °C, and the products of the decarbonylation are the (tri-tert-butylcyclopentadi-
enyl)rhodium carbonyl dimer 4, the carbonyl ethylene complex 7, biphenyls (from benzophe-
nones), and toluenes (from acetophenones). Use of â-phenylpropiophenone as substrate results
initially in dehydrogenation to form the η4-enone complex 13, followed by decarbonylation
at higher temperatures to yield stilbene.
In tr od u ction
systems such as strained cyclic ketones,8a-f diketones,8g-i
alkynyl ketones,8j and functionalized ketones or their
derivatives possessing a chelating group that directs the
bond activation step.8k,l Relatively few examples of C-C
bond cleavage of nonactivated ketones have been re-
ported. Ito, Murakami, et al. have demonstrated that
cyclopentanones and cyclododecanone upon thermolysis
(110-150 °C, days) in the presence of stoichiometric
(PPh3)3RhCl yield cyclobutanes and cycloundecane.8a,b
Decarbonylation of cyclohexanone8m and cleavage of
acetone to produce methane have also been reported.8n
The protocol developed by J un1d,f,4 results in the cleav-
age of C-C bonds in nonactivated ketones; however, the
actual cleavage step occurs in a chelate-activated picol-
ylketimine.
Transition-metal-mediated cleavage of C-C bonds is
substantially more difficult than C-H bond cleavage for
both kinetic and thermodynamic reasons and represents
a significant challenge.1 Success in activating C-C
bonds has often relied on use of special substrates.
There are numerous reports of metal-mediated cleavage
of C-C bonds of molecules possessing significant ring
strain, particularly cyclopropane derivatives.1e,2,3 Use of
directing groups to facilitate access of the metal center
to the C-C bond has been a successful strategy.
Prominent examples include catalytic C-C bond cleav-
age in 2-amino-3-picolylimines1d,f,4 and stoichiometric
and catalytic C-C bond cleavage in phosphine-based
pincer complexes.1a,g,5 Aromatization and cooperative
effects in metal clusters have also been used to facilitate
C-C bond cleavage.6 Several reports describing the
C-C bond cleavage in nitriles have appeared recently.7
The cleavage of C(O)-CR bonds of ketones by transi-
tion metals8 has generally been confined to activated
Much of our recent work on C-H bond activation and
incorporation of C-H activation processes into catalytic
cycles has involved the use of Cp*Rh(I) and Cp*Co(I)
moieties.9 J ones has shown that Cp*Rh(C2H4)2 and
2
2
Cp*Co(C2H4)2 can be used to cleave Csp -Csp bonds in
(6) (a) Ohki, Y.; Suzuki, H. Angew. Chem., Int. Ed. 2000, 39, 3463.
(b) Older, C. M.; Stryker, J . M. J . Am. Chem. Soc. 2000, 122, 2784. (c)
Takemori, T.; Inagaki, A.; Suzuki, H. J . Am. Chem. Soc. 2001, 123,
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J ones, W. D. J . Am. Chem. Soc. 2002, 124, 9547. (c) Miller, J . A.;
Dankwardt, J . W. Tetrahedron Lett. 2003, 1907. C-C bond activation
in diphenylacetylene: (d) Mu¨ller, C.; Iverson, C. N.; Lachicotte, R. J .;
J ones, W. D. J . Am. Chem. Soc. 2001, 123, 9718.
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10.1021/om030563u CCC: $27.50 © 2004 American Chemical Society
Publication on Web 12/31/2003

528 Organometallics, Vol. 23, No. 3, 2004
Daugulis and Brookhart
Sch em e 1
strained hydrocarbons.10 Spurred by the results of these
studies, we have investigated the possibility of using
bulky cyclopentadienylrhodium(I) fragments generated
from thermolysis of bis(ethylene) complexes for cleavage
of C-C bonds of aryl ketones. We report here the studies
of these cleavage reactions employing (1,2,4-triisopropyl-
3,5-dimethylcyclopentadienyl)rhodium bis(ethylene) (1)
and (1,2,4-tri-tert-butylcyclopentadienyl)rhodium bis-
(ethylene) (2).
F igu r e 1. ORTEP view of 1. Selected interatomic dis-
tances (Å): Rh(1)-C(1) ) 2.101(3), Rh(1)-C(2) ) 2.118-
(3), Rh(1)-C(3) ) 2.1271(24), Rh(1)-C(4) ) 2.1314(25),
C(1)-C(2) ) 1.387(6), C(3)-C(4) ) 1.376(4).
The reaction of ethylene complexes 1 and 2 with tert-
butyl vinyl ether at 120 °C in hexanes or without solvent
affords the carbonyl dimers 3 and 4 as intensely blue-
violet crystalline materials. Isobutylene and methane
were observed in the crude reaction mixtures by NMR
spectroscopy. In the case of the reaction of 2, the main
byproduct in the crude reaction mixture was identified
as the dicarbonyl complex 5, independently synthesized
from chlorodicarbonylrhodium dimer and (1,2,4-tri-tert-
butylcyclopentadienyl)potassium. Like Cp*Rh(CO)2 (6),13
5 slowly loses CO under vacuum, forming 4. The
reaction of 2 with CO at 70 °C yields the carbonyl
ethylene complex 7. At 80 °C, the substitution is
nonselective and substantial amounts of 5 are formed.
Complex 7 is unstable at room temperature in solution
and slowly loses ethylene, forming the highly colored
carbonyl dimer 4.
Resu lts a n d Discu ssion
Syn th esis of th e Rh od iu m Com p lexes. Two meth-
ods summarized in Scheme 1 were used to synthesize
the bulky cyclopentadienylrhodium ethylene complexes.
(1,2,4-Triisopropyl-3,5-dimethylcyclopentadienyl)rhod-
ium bis(ethylene) (1) was prepared in a two-step syn-
thesis starting from RhCl3‚nH2O in 63% yield. (1,2,4-
Tri-tert-butylcyclopentadienyl)rhodium bis(ethylene) (2)
was prepared in good yield (76%) from chlorobis-
(ethylene)rhodium dimer and (1,2,4-tri-tert-butylcyclo-
pentadienyl)potassium. Both substances are yellow
solids and stable under inert atmosphere at room
temperature.
Crystals of 1 suitable for an X-ray structure deter-
mination were grown from acetone solution at -30 °C.
The ORTEP diagram of 1 is shown in Figure 1. The
CdC bond lengths of complexed ethylene in 1 are
1.387(6) and 1.376(4) Å, in the same range as for other
cyclopentadienylrhodium ethylene complexes (typically
1.36-1.43 Å)11 but elongated compared to free ethylene
(1.339 Å).12 The Rh-ethylene (Rh-C1 and Rh-C2)
distances of ca. 2.1 Å are close to values reported in the
literature.11 The rhodium center is partially shielded by
the isopropyl groups that are situated perpendicular to
the cyclopentadiene ring.
Deca r bon yla tion of Keton es Med ia ted by 1 a n d
2. The thermolysis of Cp*Rh(C2H4)2 (8)14 and Cp*Rh-
(C2H3TMS)2 (9)9a with 3-(trifluoromethyl)acetophenone
in C6D12 at 120 °C produced complicated mixtures
containing multiple Cp* signals, and mostly ketone
ortho-alkylation products were observed. Thermolysis
of Cp*Rh(C2H4)2 with 4,4′-dimethylbenzophenone also
yielded ortho-alkylation products in a mixture with 4,4′-
dimethylbiphenyl. Multiple Cp* signals were observed
1
in the reaction mixture by H NMR spectroscopy. On
Several rhodium-containing intermediates and prod-
ucts of the decarbonylation reactions (see below) were
prepared independently and characterized (Scheme 2).
the other hand, the corresponding reactions using the
more hindered derivative 1 afforded dimer 3 and de-
carbonylation products, biphenyls or toluenes. Since the
NMR spectra of these reaction mixtures were compli-
cated in the alkyl region (multiple Me and i-Pr signals),
the tri-tert-butyl-substituted complex 2 was synthesized
and tested in the decarbonylation reactions. Qualitative
comparison of the rate of decarbonylation (3.4 equiv of
3-methylbenzophenone, 0.1 M Rh complex in C6D12, 120
°C) showed that both Rh complexes decarbonylate this
substrate at about equal rates (10-15% conversion to
the carbonyl dimers 3 and 4 in 1 h). As a consequence,
(9) (a) Lenges, C. P.; White, P. S.; Brookhart, M. J . Am. Chem. Soc.
1999, 121, 4385. (b) Lenges, C. P.; Brookhart, M. J . Am. Chem. Soc.
1999, 121, 6616. (c) Diaz-Requejo, M. M.; DiSalvo, D.; Brookhart, M.
J . Am. Chem. Soc. 2003, 125, 2038. (d) Lenges, C. P.; White, P. S.;
Brookhart, M. J . Am. Chem. Soc. 1998, 120, 6965.
(10) (a) Perthuisot, C.; J ones, W. D. J . Am. Chem. Soc. 1994, 116,
3647. (b) Perthuisot, C.; Edelbach, B. L.; Zubris, D. L.; J ones, W. D.
Organometallics 1997, 16, 2016.
(11) (a) Arthurs, M.; Piper, C.; Morton-Blake, D. A.; Drew, M. G. B.
J . Organomet. Chem. 1992, 429, 257. (b) Mu¨ller, J .; Qiao, K. Z. Anorg.
Allg. Chem. 1995, 621, 1293. (c) Mu¨ller, J .; Ha, K.; Lettau, O.; Schubert,
R. Z. Anorg. Allg. Chem. 1998, 624, 192. (d) Day, V. W.; Stults, B. R.;
Reimer, K. J .; Shaver, A. J . Am. Chem. Soc. 1974, 96, 1227. (e) Gaede,
P. E.; Moran, P. H.; Richarz, A.-N. J . Organomet. Chem. 1998, 559,
107.
(13) Nutton, A.; Maitlis, P. M. J . Organomet. Chem. 1979, 166, C21.
(14) Maitlis, P. M.; Moseley, K.; Kang, J . W. J . Chem. Soc. A 1970,
2875.
(12) Tables of Interatomic Distances and Configuration in Molecules
and Ions; Sutton, L. E., Ed.; The Chemical Society: London; 1958.

Decarbonylation of Aryl Ketones
Organometallics, Vol. 23, No. 3, 2004 529
Sch em e 2
Sch em e 3
Ta ble 1. Deca r bon yla tion of Keton es Med ia ted by
2a
further experiments were carried out using 2 which
gave substantially simplified NMR spectra.
conversn (%)b to
Several benzophenones and acetophenones were de-
carbonylated using complex 2 in cyclohexane-d12. Reac-
tions were monitored by 1H NMR spectroscopy, and
conversions were determined by reference to a capillary
insert containing a mixture of C2H2Cl4 and C2D2Cl4. In
addition, two preparative thermolyses were carried out,
from which decarbonylation products were isolated.
Scheme 3 illustrates the general reactions observed.
Table 1 summarizes the in situ experiments. Reactions
were carried out at 120 °C with 0.05 mmol of 2 and 0.2
mmol of ketone 10. The extent of decarbonylation is best
quantitatively monitored by watching the formation of
rhodium carbonyl complexes 4 and 7, although the
biaryls or methyl arenes 11 can also be detected. In the
early stages of reaction, the ethylene carbonyl complex
7 is the major product, but at 120 °C this complex
converts to the carbonyl dimer 4. Except in the case of
10a , in addition to the decarbonylated organic products,
ortho ethylation of the aryl ring occurs via insertion of
ethylene into the ortho C-H bond. We have reported
similar ortho-alkylation reactions using Cp*Rh(C2H3-
Si(CH3)3) as a catalyst.9b
entry
ketone
time, h
12
4
7
4 + 7
1
2
3
4
5
6
7
8
10a
10a
10a
10b
10b
10b
10c
10c
10c
10d
10d
10d
10e
10e
10e
10f
10f
10f
7
13
26
1
3
10.5
1
3
10.5
1
3
10.5
1
0
0
0
28
53
68
14
48
74
15
42
61
16
33
50
<2
11
34
<2
<2
24
22
21
<5
31
25
11
23
15
<5
20
11
5
<2
11
<2
<2
<2
<2
50
74
73
45
73
85
38
57
66
36
44
55
ND
22
36
ND
ND
ca. 26
25
35
35
30
42
42
28
37
37
6
20
27
<2
ca. 10
18
9
10
11
12
13
14
15
16
17
18
7
36
1
7
36
a
Conditions: 0.5 mL of C6D12, 0.05 mmol of 2, 0.2 mmol of 10,
b
120 °C. Conversion to 12 with respect to the initial amount of
10 and to 4 and 7 with respect to the initial amount of 2.
doubt due to the presence of CF3 groups adjacent to each
ortho C-H bond. At 7 h complexes 4 and 7 are present
at approximately equal concentrations, but at 26 h
Entries 1-3 summarize the results for 3,5,3′,5′-
tetrakis(trifluoromethyl)benzophenone (10a ). As noted
above, no ortho-ethylation product 12 is observed, no

530 Organometallics, Vol. 23, No. 3, 2004
Daugulis and Brookhart
Sch em e 4
virtually all of 7 has been converted to 4. Decarbo-
nylation is essentially complete after 13 h.
three inequivalent tert-butyl resonances at δ 0.69, 1.17,
and 1.41 and characteristic signals for the vinyl hydro-
gens of the bound enone at δ 3.4 (d, J H-H ) 8.3 Hz) and
5.95 (dd, J H-H ) 8.3 Hz, J H-Rh ) 0.8 Hz). While Cp*Rh-
(C2H3SiMe3)2 is known to catalyze intramolecular hy-
drogen transfer,9c formation of 13 is the first observation
of intermolecular hydrogen transfer mediated by these
systems. Further heating of the reaction mixture at 150
°C results in C-C activation and formation of stilbene
along with complexes 4 and 7. Thermolysis of 2 with
chalcone at 120 °C results in clean formation of 13 and
serves to confirm its structural assignment. Further-
more, suitable crystals for an X-ray structure determi-
nation were grown from acetone solution of 13 at -30
°C. The ORTEP diagram of 13 is shown in Figure 2.
The enone binds to the rhodium fragment in an η4
fashion through the O(1)-C(2)-C(3)-C(4) atoms. In
comparison to free chalcone,15 the C(2)-O(1) bond is
elongated from 1.204(6) to 1.304(4) Å and C(3)-C(4)
from 1.319(6) to 1.429(5) Å. The length of the C(2)-C(3)
bond is somewhat shortened from 1.478(6) to 1.437(5)
Å. The enone moiety is almost planar (O(1)-C(2)-C(3)-
C(4) ) -2.7°). Iron and ruthenium enone complexes are
common and have been crystallographically character-
ized;16 however, no rhodium(I) η4-enone complexes ap-
pear to have been crystallographically characterized. An
η4-acrolein-rhodium complex has been spectroscopically
characterized.17
Mech a n istic Con sid er a tion s. At this stage only a
somewhat speculative discussion of the reaction mech-
anism is possible (Scheme 5). Complexation of the
ketone to the rhodium fragment must precede the C-C
activation step. The isolation of intermediate 13 prior
to decarbonylation and formation of stilbene suggests
that in the case of benzophenone or acetophenone the
complex formed prior to C-C bond cleavage is the
enone-type complex 14, involving η2 coordination of the
arene. In fact, the Cp*Rh complex 18, exhibiting this
mode of coordination, has been isolated and char-
acterized.9b From 14 oxidative addition would yield 15,
which upon deinsertion would produce 16.18 Reductive
elimination from 16 (possibly preceded by CO loss)19
leads to hydrocarbon product and the rhodium species
17, which can form 4 and 7. Complex 7 is relatively
unstable and upon prolonged heating loses ethylene and
Entries 4-6 summarize results for 3,3′-bis(trifluo-
romethyl)benzophenone (10b). In this case a significant
amount of ortho-ethylation product 12b is observed.
After 1 h, ca. 45% decarbonylation has occurred, with
the major Rh product being the mononuclear complex
7. Decarbonylation proceeds to ca. 85% in 10.5 h, with
dimer 4 now being the major Rh carbonyl species. A
preparative-scale reaction was carried out in toluene
(135 °C, 23 h), and the biaryl 11b was isolated in ca.
82% yield.
Entries 7-9 and 10-12 summarize results for ben-
zophenone (10c) and 4,4′-dimethylbenzophenone (10d ),
respectively. The behavior of these ketones is similar
to that of 10a . For example, after 3 h ca. 50% decarbo-
nylation has occurred and ca. 40% ortho-ethylated
product is observed. In a preparative-scale reaction
employing 10d in cyclohexane-d12 (120 °C, 17 h), 4,4′-
dimethylbiphenyl (11d ) was isolated in 62% yield along
with the ortho-ethylated product 12d in 66% yield. Only
a trace (<2%) of an impurity tentatively assigned as
2-ethyl-4,4′-dimethylbiphenyl (arising from the decar-
bonylation of 12d ) was observed.
Entries 13-15 and 16-18 summarize results for
4-(trifluoromethyl)acetophenone (10e) and acetophe-
none (10f). The decarbonylations are substantially
slower than in the case of benzophenones, and the
conversions attained are lower. For example, 7 h is
necessary to obtain 22% conversion in the case of 10e,
and in the case of 10f after 36 h ca. 26% conversion was
observed. The thermolysis of acetophenones 10e and 10f
was studied also at 150 °C. After 4 h (0.05 mmol of 2,
0.2 mmol of ketone, 0.5 mL of C6D12) 47% and 38%
conversion to 4 was observed, respectively. Only trace
amounts of 7 were observed.
For benzophenones, the reaction rate is not strongly
dependent on the electronic properties of the aryl group.
However, in the case of acetophenones, the decarbonyl-
ation is substantially faster for the electron-withdraw-
ing trifluoromethyl-substituted substrate 10e. The ther-
molysis of 2 and benzophenone (10c) was carried out
at 120 °C using two different ketone concentrations. As
expected, the reaction is faster if a higher concentration
of benzophenone is used (ethylene dissociation is revers-
ible;9 see Scheme 5). Using 3.5 equiv of ketone (0.05
mmol of 2, 0.5 mL of C6D12), 10% conversion to 4 and
23% conversion to 7 was observed in 1 h. If 10 equiv of
ketone was used, 27% conversion to 4 and 23% conver-
sion to 7 was observed in 1 h.
(15) Rabinovich, D. J . Chem. Soc. B 1970, 11.
(16) (a) Vichi, E. J . S.; Raithby, P. R.; McPartlin, M. J . Organomet.
Chem. 1983, 256, 111. (b) Marcuzzi, A.; Linden, A.; von Philipsborn,
W. Helv. Chim. Acta 1993, 76, 976. (c) Zhang, W.-Y.; J akiela, D. J .;
Maul, A.; Knors, C.; Lauher, J . W.; Helquist, P.; Enders, D. J . Am.
Chem. Soc. 1988, 110, 4652.
(17) Hidai, M.; Ishimi, K.; Iwase, M.; Uchida, Y. Bull. Chem. Soc.
J pn. 1972, 45, 2935.
(18) Maitlis et al. have shown that Cp*Rh(Ph)(CO)(Me) thermally
eliminates acetophenone (27%) and toluene (9%): Sunley, G. J .;
Fanizzi, F. P.; Saez, I. M.; Maitlis, P. M. J . Organomet. Chem. 1987,
330, C27.
While decarbonylations of acetophenones and ben-
zophenones occur at 120 °C, we were surprised to find
that thermolysis of 2 and â-phenylpropiophenone at 120
°C did not yield any carbonyl dimer 4. Instead, slow
formation (50% conversion, 35 h) of the enone (chalcone)
complex 13 is observed (Scheme 4). Complex 13 exhibits
(19) (a) Milstein, D. Acc. Chem. Res. 1984, 17, 221. (b) Bartlett, K.
L.; Goldberg, K. I.; Borden, W. T. J . Am. Chem. Soc. 2000, 122, 1456.

Decarbonylation of Aryl Ketones
Organometallics, Vol. 23, No. 3, 2004 531
carbonyl dimer 4. The organic products of the reaction
are biphenyls (from benzophenones) or toluenes (from
acetophenones). If ketones possessing â-hydrogens are
used as substrates, dehydrogenation to unsaturated
ketones precedes the C-C activation. The rhodium η4-
enone complex 13 has been isolated and crystallo-
graphically characterized. Future investigations will
involve attempts to develop catalytic reactions and in-
depth studies of the reaction mechanism.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All the operations related to
catalysts were carried out under an argon atmosphere using
standard Schlenk techniques. The 1H and 13C spectra were
recorded using Bruker 300, 400, or 500 MHz spectrometers
and are referenced against residual solvent peaks (1H, 13C).
Flash chromatography was performed using 60 Å silica gel
(SAI). Elemental analyses were performed by Atlantic Micro-
lab Inc. of Norcross, GA. Yields in the preparative decarbo-
nylation reactions (leading to 4, 7, 11, and 12) were calculated
with respect to 2.
Ma ter ia ls. Anhydrous solvents were used in the reactions.
Solvents were distilled from drying agents or passed through
alumina columns under an argon or nitrogen atmosphere.
NMR solvents were vacuum-transferred from P2O5 and de-
gassed by repeated freeze-pump-thaw cycles. The following
starting materials were made using literature procedures:
1,2,4-triisopropyl-3,5-dimethylcyclopentadiene,21 1,2,4-tri-tert-
butylcyclopentadiene,22 benzylpotassium,23 and chlorobis(eth-
ylene)rhodium dimer.24
F igu r e 2. ORTEP view of 13. Selected interatomic dis-
tances (Å) and angles (deg): C(2)-O(1) ) 1.304(4), C(3)-
C(4) ) 1.429(5), Rh(1)-O(1) ) 2.1663(23), Rh(1)-C(2) )
2.137(3), Rh(1)-C(3) ) 2.137(4), Rh(1)-C(4) ) 2.174(3),
C(2)-C(3) ) 1.437(5); O(1)-C(2)-C(3)-C(4) ) -2.7.
Sch em e 5
1,2,4-iP r 3-3,5-Me2Cp Rh (C2H4)2 (1). To a solution of RhCl3‚
nH2O (0.66 g, 2.31 mmol, Next Chimica) in methanol (30 mL)
was added 1,2,4-triisopropyl-3,5-dimethylcyclopentadiene (1.20
g, 5.45 mmol). The mixture was refluxed for 66 h. Methanol
was evaporated, and the residue was suspended in toluene and
evaporated (2 × 30 mL). After that, the residue was suspended
in hexanes and filtered. After drying, a reddish yellow solid
(0.90 g) was obtained. This material (mostly (1,2,4-triisopropyl-
3,5-dimethylcyclopentadienyl)rhodium dichloride dimer) was
used further without additional purification. The material
obtained as above (1.23 g) was mixed with Zn powder (2.50 g,
38.2 mmol, Aldrich) and THF (20 mL). Ethylene was slowly
purged through the magnetically stirred mixture for 15 h. The
color changed from reddish to blue to violet. The solvent was
evaporated, the residue was extracted with pentane (2 × 10
mL), and the extracts were filtered through a pad of alumina
(3 × 2.2 cm) in pentane. The solution was evaporated and the
residue crystallized from acetone at -78 °C. Two crops of the
product were collected: (1) 0.57 g of dark yellow crystals; (2)
0.19 g of dark yellow crystals. Total yield: 0.76 g (63.4% from
1
rhodium trichloride). H NMR (C6D6): δ 2.67 (septet, 2H; J )
forms 4. Species of the type 16 have been shown to be
resting states in catalytic hydroacylation reactions of
olefins by aryl aldehydes, which suggests the revers-
ibility of steps B and C.20 In the hydroacylation reac-
tions, catalyst deactivation occurs by formation of
[Cp*RhCO]2, which is also consistent with Scheme 5.
7.2 Hz); 2.48 (septet, 1H; J ) 7.2 Hz); 2.31-2.14 (m, 4H;
complexed ethylene); 1.51 (s, 6H); 1.48-1.35 (m, 4H; complexed
ethylene); 1.32 (d, 6H; J ) 7.2 Hz); 1.25 (d, 6H; J ) 7.2 Hz);
1.20 (d, 6H; J ) 7.2 Hz). 13C{1H} NMR (C6D6) δ 110.3 (d, J Rh-C
) 4.9 Hz); 109.6 (d, J Rh-C ) 4.4 Hz); 94.3 (d, J Rh-C ) 4.3 Hz);
43.1 (d, J Rh-C ) 13.6 Hz); 26.5; 26.1; 24.5; 24.2; 24.1; 10.6. Anal.
Calcd for C20H35Rh: C, 63.48; H, 9.32. Found: C, 63.54; H,
9.55. The structure was verified by X-ray crystallography.
1,2,4-tBu 3Cp Rh (C2H4)2 (2). To a solution of 1,2,4-tri-tert-
butylcyclopentadiene (0.933 g, 4.0 mmol) in THF (10 mL) was
added a solution of benzylpotassium (0.535 g, 4.1 mmol) in
Su m m a r y
The cleavage of C-C bonds in diaryl and aryl alkyl
ketones mediated by bulky cyclopentadienylrhodium
ethylene complexes 1 and 2 has been investigated. The
reactions proceed at 120-150 °C, and the initial product
of the decarbonylation is the carbonyl ethylene complex
7, which is converted to the cyclopentadienylrhodium
(21) Quindt, V.; Saurenz, D.; Schmitt, O.; Scha¨r, M.; Dezember, T.;
Wolmersha¨user, G.; Sitzmann, H. J . Organomet. Chem. 1999, 579, 376.
(22) Dehmlow, E. V.; Bollmann, C. Z. Naturforsch., B 1993, 48b,
457.
(23) Schlosser, M.; Hartmann, J . Angew. Chem., Int. Ed. Engl. 1973,
12, 508.
(20) Lenges, C. P.; Brookhart, M. Unpublished results, 1999.
(24) Cramer, R. Inorg. Synth. 1974, 15, 14.

532 Organometallics, Vol. 23, No. 3, 2004
Daugulis and Brookhart
THF (10 mL) at 0 °C. Benzylpotassium has an intense red
color, and the exact stoichiometry can easily be determined
by the color change (intense red to colorless) in the deproto-
nation. To a solution of chlorobis(ethylene)rhodium dimer
(0.778 g, 2.0 mmol) in THF (10 mL) was added dropwise a
suspension of (1,2,4-tri-tert-butylcyclopentadienyl)potassium
at -40 °C. The solution was stirred at that temperature for 2
h and then warmed to 0 °C and evaporated. The residue was
dissolved in diethyl ether, and the solution was filtered
through a pad of alumina (3 × 2.2 cm) in diethyl ether. The
solvent was evaporated and the residue crystallized from
acetone at -78 °C. The product was obtained as yellow crystals
(1.19 g, 75.9%). 1H NMR (C6D6): δ 4.72 (s, 2H); 3.08-2.93 (m,
4H; complexed ethylene); 1.30 (s, 18H); 1.26 (s, 9H); 1.19-
1.05 (m, 4H; complexed ethylene). 13C{1H} NMR (C6D6): δ
116.5 (d, J Rh-C ) 4.9 Hz); 114.2 (d, J Rh-C ) 3.9 Hz); 85.6 (d,
J Rh-C ) 4.1 Hz); 38.2 (d, J Rh-C ) 13.2 Hz); 34.3; 33.2; 33.1;
31.5. Anal. Calcd for C23H37Rh: C, 64.27; H, 9.50. Found: C,
64.38; H, 9.76.
[1,2,4-iP r 3-3,5-Me2Cp Rh (CO)]2 (3). The mixture of 1 (0.19
g, 0.5 mmol) and tert-butyl vinyl ether (1.5 mL, Aldrich) was
heated at 120 °C in a Kontes flask for 15 h. The color changed
from yellow to deep ink blue. The solution was evaporated and
the residue recrystallized from hexanes at -30 °C. Dark blue-
violet crystals were obtained (0.07 g, 40.0%). 1H NMR
(C6D12): δ 2.65 (septet, 2H; J ) 7.2 Hz); 2.19 (septet, 1H; J )
7.2 Hz); 1.96 (s, 6H); 1.14 (d, 6H; J ) 7.2 Hz); 1.13 (d, 6H; J
) 7.2 Hz). 13C{1H} NMR (C6D6): δ 250.5 (t, J Rh-C ) 54.6 Hz);
113.7 (d, J Rh-C ) 6.7 Hz); 112.3 (d, J Rh-C ) 7.8 Hz); 100.6 (d,
J Rh-C ) 4.9 Hz); 25.7; 25.6; 24.4; 23.6; 22.9; 9.8 (d, J Rh-C ) 2.8
Hz). IR (solution in C6D12): νCO 1746 cm-1. Anal. Calcd for
h at 70 °C. The yellow solution was evaporated (Schlenk flask
kept at 0 °C at the end). Assay by H NMR showed that the
1
reaction mixture at that point contained 6% 5, 7% 2, and 87%
7. The residue was recrystallized from acetone at -30 °C. A
yellow powder that liquefies at room temperature was ob-
tained; yield 0.22 g (73%). This material was contaminated
with a few percent of 5 and 7. The compound is stable at 0 °C
under an inert temperature; however, in solution or neat at
room temperature it decomposes to 4. 1H NMR (C6D12): δ 5.04
(s, 2H); 2.86 (br s, 2H); 2.27 (br s, 2H); 1.39 (s, 18H); 1.17 (s,
9H). 13C{1H} NMR (C6D12) δ 192.3 (d, J Rh-C ) 84.3 Hz); 118.6
(d, J Rh-C ) 4.3 Hz); 117.1 (d, J Rh-C ) 4.1 Hz); 85.3 (d, J Rh-C
)
3.6 Hz); 34.7; 32.9; 32.3; 31.5 (d, J Rh-C ) 12.9 Hz); 31.2. IR
(solution in C6D12): νCO 1972 cm-1. Anal. Calcd for C20H33
-
RhO: C, 61.22; H, 8.48. Found: C, 61.32; H, 8.53.
Gen er a l P r oced u r e for th e NMR-Sca le Deca r bon yla -
tion of Keton es. In the glovebox, a Teflon-stoppered NMR
tube (J . Young) was charged with the rhodium complex 2 (0.05
mmol, 0.0196 g), ketone (0.2 mmol), a capillary insert contain-
ing a mixture of tetrachloroethane and tetrachloroethane-d2
(external standard for NMR, 5.20 ppm), and cyclohexane-d12
(0.5 mL, Cambridge Isotope Laboratories). After the NMR
spectrum is recorded, the mixture was heated at 120 °C with
periodic monitoring of the conversion by NMR spectroscopy
(integration of [1,2,4-tBu3CpRh(CO)]2 resonances at 4.97, 1.31,
and 0.97 ppm and 1,2,4-tBu3CpRh(CO)(ethylene) resonances
at 5.03, 1.38, and 1.16 ppm vs the capillary standard). Some
unidentified 1,2,4-tBu3Cp-containing species were observed in
the reaction mixtures during the reaction. Occasionally the
reaction mixtures were separated on silica gel to compare the
spectra of products with the spectra of authentic samples
purchased from commercial suppliers.
C
34H54Rh2O2: C, 58.29; H, 7.77. Found: C, 58.42; H, 7.94.
Deca r bon yla tion of 3,5,3′,5′-Tetr a k is(tr iflu or om eth yl)-
ben zop h en on e (10a ). The NMR spectra were recorded at 70
°C due to the insolubility of 3,5,3′,5′-tetrakis(trifluoromethyl)-
benzophenone (Lancaster) in the reaction mixture at room
temperature. At initial stages of the reaction the ketone was
not completely soluble in C6D12, even at 120 °C.
[1,2,4-tBu 3Cp Rh (CO)]2 (4). A mixture of 2 (0.15 g, 0.38
mmol), tert-butyl vinyl ether (0.20 mL, 1.52 mmol, Aldrich),
and hexanes (5 mL) was heated in a Kontes flask for 8 h. The
color changed from yellow to dark ink blue. The solvent was
removed under vacuum and the residue heated (120 °C) under
vacuum for 2 h followed by recrystallization from hexanes at
-30 °C. Dark blue-violet crystals were obtained (0.05 g, 35.9%).
1H NMR (C6D12): δ 4.97 (s, 1H); 1.31 (s, 18H); 0.97 (s, 9H).
13C{1H} NMR (C6D6): δ 245.7 (t, J Rh-C ) 54.5 Hz); 119.4 (d,
J Rh-C ) 5.9 Hz); 115.9 (d, J Rh-C ) 8.3 Hz); 94.5; 34.0; 33.1;
31.2; 30.5. IR (solution in C6D12): νCO 1754 cm-1. Anal. Calcd
for C36H58Rh2O2: C, 59.34; H, 8.02. Found: C, 59.60; H, 8.18.
The major byproduct observed was 1,2,4-tBu3CpRh(CO)2 (com-
parison of crude reaction mixture NMR with an authentic
sample).
The following data points were acquired (time, conversion
to 1,2,4-tBu3CpRh(CO)(C2H4), conversion to [1,2,4-tBu3CpRh-
(CO)]2 with respect to 1,2,4-tBu3CpRh(C2H4)2): 3 h, 19%, 9%;
7 h, 22%, 28%; 9 h, 30%, 36%; 13 h, 21%, 53%; 26 h, ND, 68%.
After the thermolysis the reaction mixture was chromato-
graphed (silica gel) in hexanes to elute 3,5,3′,5′-tetrakis-
(trifluoromethyl)biphenyl (1H NMR spectrum compared with
an authentic sample purchased from Maybridge) followed by
2/1 hexanes/toluene to elute a mixture of unreacted 3,5,3′,5′-
tetrakis(trifluoromethyl)benzophenone and [1,2,4-tBu3CpRh-
(CO)]2. Rf(3,5,3′,5′-tetrakis(trifluoromethyl)biphenyl, hexanes)
) 0.36. Rf(3,5,3′,5′-tetrakis(trifluoromethyl)benzophenone, 2/1
hexanes/toluene) ) 0.53. Rf([1,2,4-tBu3CpRh(CO)]2, 2/1 hex-
anes/toluene) ) 0.43. No ortho-ethylation product (or any other
organic product besides biphenyl and unreacted benzophenone)
was observed.
Decar bon ylation of 3,3′-Bis(tr iflu or om eth yl)ben zoph e-
n on e (10b). The ketone was purchased from Aldrich. The
following data points were acquired (time, conversion to 1,2,4-
tBu3CpRh(CO)(C2H4), conversion to [1,2,4-t-Bu3CpRh(CO)]2
with respect to 1,2,4-tBu3CpRh(C2H4)2, conversion to 2-ethyl-
5,3′-bis(trifluoromethyl)benzophenone with respect to 3,3′-bis-
(trifluoromethyl)benzophenone: 1 h, 31%, 14%, 25%; 2 h, 36%,
41%, 35%; 3 h, 25%, 48%, no further change in the amount of
ethylated benzophenone; 4.5 h, 20%, 58%; 6.5 h, 18%, 69%;
10.5 h, 11%, 74%.
1,2,4-tBu 3Cp Rh (CO)2 (5). (1,2,4-Tri-tert-butylcyclopenta-
dienyl)potassium was prepared as in the case of 2 from 1,2,4-
tri-tert-butylcyclopentadiene (0.385 g, 1.65 mmol) and ben-
zylpotassium (0.230 g, 1.7 mmol) in THF (15 mL) at 0 °C. The
suspension of the potassium salt was added dropwise to the
suspension of chlorodicarbonylrhodium dimer (0.32 g, 0.82
mmol, Strem) in THF (5 mL) at -78 °C. The solution was
stirred for 10 min at -78 °C and then warmed to room
temperature and stirred for 30 min. The color of the mixture
at this point was dark brown. The solvent was evaporated,
the residue was dissolved in pentane, and this solution was
filtered through Celite. After evaporation and crystallization
from acetone at -78 °C a yellow solid that liquefies at room
temperature was obtained; yield 0.52 g (80.8%). 1H NMR
(C6D12): δ 5.28 (s, 1H); 1.36 (s, 18H); 1.16 (s, 9H). 13C{1H} NMR
(C6D12): δ 194.0 (d, J Rh-C ) 83.0 Hz); 119.7 (d, J Rh-C ) 4.3
Hz); 119.1 (d, J Rh-C ) 3.9 Hz); 85.8 (d, J Rh-C ) 3.5 Hz); 34.9;
32.5; 32.4; 30.6. IR (solution in C6D12): νCO 2032, 1968 cm-1
.
After the thermolysis the reaction mixture was chromato-
graphed (silica gel) in hexanes to elute 3,3′-bis(trifluorometh-
yl)biphenyl (1H NMR shifts compared with literature values)25
followed by 5/1 hexanes/dichloromethane to elute a mixture
Anal. Calcd for C19H29RhO2: C, 58.16; H, 7.45. Found: C,
58.84; H, 7.60. The compound slowly decomposes under
vacuum, producing 4.
1,2,4-tBu 3Cp Rh (CO)(C2H4) (7). Complex 2 (0.30 g, 0.77
mmol) was dissolved in toluene (20 mL), and CO was slowly
bubbled through the solution for 6 h at 75 °C and then for 29
(25) Lourak, M.; Vanderesse, R.; Fort, Y.; Caubere, P. J . Org. Chem.
1989, 54, 4840.

Decarbonylation of Aryl Ketones
Organometallics, Vol. 23, No. 3, 2004 533
of 2-ethyl-5,3′-bis(trifluoromethyl)benzophenone and [1,2,4-
tBu3CpRh(CO)]2. After that, unreacted 3,3′-bis(trifluorometh-
yl)benzophenone was eluted. Rf(3,3′-bis(trifluoromethyl)-
biphenyl, hexanes) ) 0.39. Rf(2-ethyl-5,3′-bis(trifluoromethyl)-
benzophenone, 4/1 hexanes/dichloromethane) ) 0.28. Rf([1,2,4-
t-Bu3CpRh(CO)]2, 4/1 hexanes/dichloromethane) ) 0.35. Rf-
(3,3′-bis(trifluoromethyl)benzophenone, 4/1 hexanes/dichlo-
romethane) ) 0.19.
Deca r bon yla tion of Ben zop h en on e (10c). The ketone
was purchased from Aldrich. The following data points were
acquired (time, conversion to 1,2,4-tBu3CpRh(CO)(C2H4), con-
version to [1,2,4-tBu3CpRh(CO)]2 with respect to 1,2,4-tBu3-
CpRh(C2H4)2, conversion to the known 2-ethylbenzophenone26
with respect to benzophenone: 1 h, 23%, 15%, 30%; 2 h, 19%,
25%, 38%; 3 h, 15%, 42%, no further change in the amount of
ethylated benzophenone; 4.5 h, 11%, 46%; 6.5 h, 8%, 50%; 10.5
h, <5%, 61%.
observed. The mixture was then heated at 150 °C for 18 h.
The color changed to greenish blue, and the formation of [1,2,4-
tBu3CpRh(CO)]2 (ca. 70% conversion) was observed by 1H
NMR. After that, the mixture was chromatographed on silica
gel with hexanes as eluent. After a trace of unreacted 2 and
7, stilbene (0.016 g) was eluted, contaminated with <5% of
bibenzyl. The column was dried out, and the residual mixture
was left on the silica gel for 1 day to decompose the rhodium
complexes. After that, elution with toluene/hexane (1/2) af-
forded a mixture of starting ketone with unidentified impuri-
ties followed by impure chalcone (0.027 g). The 1H NMR
spectra of chalcone and stilbene were compared with the
spectra of commercial materials (Aldrich). Rf(stilbene, hexanes)
) 0.34. Rf(chalcone, 1/1 hexanes/toluene) ) 0.15.
A mixture of chalcone (0.108 g, 0.52 mmol, Aldrich) and
1,2,4-tBu3CpRh(C2H4)2 (0.20 g, 0.52 mmol) was heated in
1
hexanes (1 mL) for 18 h at 120 °C. At this point assay by H
Deca r bon yla tion of 4,4′-Dim eth ylben zop h en on e (10d ).
The ketone was purchased from Aldrich. The following data
points were acquired (time, conversion to 1,2,4-tBu3CpRh(CO)-
(C2H4), conversion to [1,2,4-tBu3CpRh(CO)]2 with respect to
1,2,4-tBu3CpRh(C2H4)2, conversion to 2-ethyl-4,4′-dimethyl-
benzophenone with respect to 4,4′-dimethylbenzophenone: 1
h, 20%, 16%, 28%; 2 h, 13%, 29%, 37%; 3 h, 11%, 33%, no
further change in the amount of ethylated benzophenone; 4.5
h, 9%, 35%; 6.5 h, 7%, 40%; 10.5 h, 5%, 50%.
Deca r bon yla tion of 4-(Tr iflu or om eth yl)a cetop h en on e
(10e). The ketone was purchased from Aldrich. The following
data points were acquired (time, conversion to 1,2,4-tBu3CpRh-
(CO)(C2H4), conversion to [1,2,4-tBu3CpRh(CO)]2 with respect
to 1,2,4-tBu3CpRh(C2H4)2, conversion to the mixture of 2-ethyl-
4-(trifluoromethyl)acetophenone and 2,6-diethyl-4-(trifluoro-
methyl)acetophenone with respect to 4-(trifluoromethyl)-
acetophenone: 1 h, <2%, <2%, 6%; 4 h, 11%, 4%, 16%; 7 h,
11%, 11%, 20%; 11 h, 10%, 20%, 25%; 15 h, 7%, 23%, 27%; 23
h, 4%, 30%, no further change in the amount of ethylated
acetophenones; 36 h, <2%, 34%.
After thermolysis the reaction mixture was chromato-
graphed (silica gel) in hexanes followed by 4/1 hexanes/toluene
and then 3/1 hexanes/toluene. [1,2,4-tBu3CpRh(CO)]2 was
eluted, followed by a mixture of the known 2-ethyl-4-(trifluo-
romethyl)acetophenone and 2,6-diethyl-4-(trifluoromethyl)-
acetophenone.27 After that 4-(trifluoromethyl)acetophenone
was eluted. Rf(hexanes) ) 0.39. Rf(2-ethyl-4-(trifluoromethyl)-
acetophenone and 2,6-diethyl-4-(trifluoromethyl)acetophenone,
4/1 hexanes/toluene) ) 0.20. Rf([1,2,4-tBu3CpRh(CO)]2, 4/1
hexanes/toluene) ) 0.38. Rf(4-(trifluoromethyl)acetophenone,
4/1 hexanes/toluene) ) 0.13. 4-(Trifluoromethyl)toluene was
not isolated due to volatility; it was observed in the crude
reaction mixture by NMR.
Deca r bon yla tion of Acetop h en on e (10f). The ketone was
purchased from Aldrich. The following data points were
acquired (time, conversion to 1,2,4-tBu3CpRh(CO)(C2H4), con-
version to [1,2,4-tBu3CpRh(CO)]2 with respect to 1,2,4-tBu3-
CpRh(C2H4)2, conversion to 2-ethylacetophenone28 with respect
to acetophenone: 1 h, <2%, <2%, <2%; 4 h, <2%, <2%, <10%;
7 h, 7%, <2%, <10%; 11 h, 9%, 4%, ND; 15 h, 7%, 9%, ND; 23
h, 5%, 17%, ND; 36 h, <2%, 24%, 18%.
NMR showed >95% conversion to the product, which was
identical with the product obtained by the thermolysis of
â-phenylpropiophenone and 1,2,4-tBu3CpRh(C2H4)2 at 120 °C.
The reaction mixture was evaporated and the residue twice
recrystallized from acetone at -30 °C to afford 0.188 g (66.4%)
of rust-colored crystals. The structure was verified by X-ray
1
crystallography. H NMR (C6D12): 7.99-7.87 (m, 2H); 7.36-
7.19 (m, 5H); 7.14-7.04 (m, 2H); 7.02-6.92 (m, 1H); 5.95 (dd,
1H; J 1 ) 8.3 Hz, J 2 ) 0.8 Hz); 4.25 (d, J ) 1.9 Hz); 3.85 (d, J
) 1.9 Hz); 3.4 (d, J ) 8.3 Hz); 1.41 (s, 9H); 1.17 (s, 9H); 0.89
(s, 9H).
13C{1H} NMR (C6D12): 144.9; 139.1; 130.5 (d, J Rh-C
5.9 Hz; CdO); 129.6; 128.5; 128.1; 127.1; 125.5; 116.1 (d, J Rh-C
)
) 6.1 Hz); 114.1 (d, J Rh-C
) 7.4 Hz); 110.8 (d, J Rh-C ) 7.9 Hz);
81.7 (d, J Rh-C
) 5.4 Hz); 77.8 (d, J Rh-C ) 8.7 Hz); 71.9 (d, J Rh-C
) 6.6 Hz); 61.0 (d, J Rh-C
) 13.9 Hz); 34.1; 33.5; 33.3; 32.5; 31.4;
30.8. The signal of one aromatic carbon could not be located.
Anal. Calcd for C32H41RhO: C, 70.58; H, 7.59. Found: C, 70.41;
H, 7.65.
P r ep a r a tive-Sca le Deca r bon yla tion of 4,4′-Dim eth yl-
ben zop h en on e (10d ). In the glovebox a Teflon-stoppered
NMR tube (J . Young) was charged with the rhodium complex
2 (0.059 g, 0.15 mmol), 4,4′-dimethylbenzophenone (0.106 g,
0.50 mmol, Aldrich), and cyclohexane-d12 (0.5 mL) and heated
at 120 °C for 17 h. The reaction mixture was purified by
chromatography in hexanes as eluent to give 4,4′-dimethylbi-
phenyl (0.017 g, 62% based on 2). The elution was continued
using 3/1 hexanes/toluene to give [1,2,4-tBu3CpRh(CO)]2 (0.02
g, 37%). After that, elution was continued with 1/1 hexanes/
toluene to give 2-ethyl-4,4′-dimethylbenzophenone (0.047 g,
66%) and unreacted 4,4′-dimethylbenzophenone (0.029 g, 27%).
The 1H NMR spectrum of 4,4′-dimethylbiphenyl was compared
with the spectrum of the commercial material (Aldrich). Rf-
(4,4′-dimethylbiphenyl, hexanes) ) 0.28. Rf(2-ethyl-4,4′-dim-
ethylbenzophenone, toluene) ) 0.39. Rf(4,4′-dimethylbenzophe-
none, toluene) ) 0.31.
Characterization data for 2-ethyl-4,4′-dimethylbenzophe-
1
none are as follows. H NMR (CDCl3): δ 7.72-7.66 (m, 2H);
7.24-7.20 (m, 2H); 7.16 (d, 1H; J ) 7.7 Hz); 7.13 (s, 1H); 7.02
(d, 1H; J ) 7.7 Hz); 2.64 (q, 2H; J ) 7.5 Hz); 2.40 (s, 3H); 2.38
(s, 3H); 1.14 (t, 3H; J ) 7.5 Hz). 13C{1H} NMR (CDCl3): δ
198.4; 143.8; 143.2; 140.2; 135.8; 135.7; 130.3; 130.2; 129.0;
128.7; 125.7; 26.4; 21.6; 21.4; 16.0. Anal. Calcd for C17H18O:
C, 85.67; H, 7.61. Found: C, 85.13; H, 7.62.
Deca r bon yla tion of â-P h en ylp r op iop h en on e: P r ep a -
r a tion of th e Ch a lcon e Ad d u ct 13. In the glovebox a Teflon-
stoppered NMR tube (J . Young) was charged with the rhodium
complex 2 (0.097 g, 0.25 mmol), â-phenylpropiophenone (0.052
g, 0.25 mmol, Lancaster), and cyclohexane-d12 (0.5 mL, Cam-
bridge Isotopes). The mixture was thermolyzed at 120 °C for
35 h. At that point the mixture was red-brown and an
incomplete conversion (ca. 50%) to intermediate 13 was
P r ep a r a tive-Sca le Deca r bon yla tion of 3,3′-Bis(tr iflu o-
r om eth yl)ben zop h en on e (10b). In the glovebox a Kontes
flask was charged with the rhodium complex 2 (0.098 g, 0.25
mmol), 3,3′-bis(trifluoromethyl)benzophenone (0.318 g, 1.0
mmol, Aldrich), and toluene (3 mL). The reaction mixture was
heated at 135 °C for 23 h. Crude NMR showed the presence
of only 10b, 11b, 12b, 4, and 7 in the reaction mixture at that
point. The reaction mixture was purified by chromatography
in hexanes, eluting 3,3′-bis(trifluoromethyl)biphenyl contami-
nated with 7 (0.07 g of impure material, contained 0.06 g of
biphenyl (82.2%) and 0.01 g of 7). The elution was continued
(26) Kobayashi, K.; Mannami, T.; Kawakita, M.; Tokimatsu, J .;
Konishi, H. Bull. Chem. Soc. J pn. 1994, 67, 582.
(27) Busch, S.; Leitner, W. Adv. Synth. Catal. 2001, 343, 192.
(28) Fleming, I.; Morgan, I. T.; Sarkar, A. K. J . Chem. Soc., Perkin
Trans. 1 1998, 2749.

534 Organometallics, Vol. 23, No. 3, 2004
Daugulis and Brookhart
Ta ble 2. Cr ysta llogr a p h ic Da ta Collection
P a r a m eter s for 1 a n d 13
rhodium complex. Elution with 6/1 hexanes/dichloromethane
afforded 2-ethyl-5,3′-bis(trifluoromethyl)benzophenone (0.103
g) contaminated with <5% of an impurity (most likely 2,2′-
diethyl-5,5′-bis(trifluoromethyl)benzophenone).
1
13
formula
mol wt
C
370.4
20H35Rh
C32H41RhO
544.6
Characterization data for 2-ethyl-5,3′-bis(trifluoromethyl)-
1
benzophenone are as follows. H NMR (CDCl3): δ 8.1 (s, 1H);
cryst syst
space group
a, Å
monoclinic
P21/n
orthorhombic
Fdd2
31.3052(7)
39.2724(9)
8.9197(2)
7.90 (d, 1H; J ) 7.8 Hz); 7.86 (d, 1H; J ) 7.8 Hz); 7.70 (d, 1H;
J ) 8.0 Hz); 7.61 (t, 1H; J ) 7.8 Hz); 7.51 (s, 1H); 7.50 (d, 1H;
J ) 8.0 Hz); 2.70 (q, 2H; J ) 7.6 Hz); 1.18 (t, 3H; J ) 7.6 Hz).
13C{1H} NMR (CDCl3): δ 195.6; 147.3; 138.0; 137.7; 133.3;
131.6 (q, J C-F ) 33.1 Hz); 130.3; 130.1 (q, J C-F ) 3.4 Hz); 129.4;
128.2 (q, J C-F ) 33.0 Hz); 127.4 (q, J C-F ) 3.6 Hz); 126.6 (q,
J C-F ) 3.8 Hz); 125.0 (q, J C-F ) 3.8 Hz); 123.8 (q, J C-F ) 272.3
Hz); 123.5 (q, J C-F ) 272.7 Hz); 26.4; 15.5. Anal. Calcd for
9.0105(3)
16.5882(6)
12.8672(4)
95.933(1)
1912.93(11)
4
b, Å
c, Å
â, deg
V, Å3
10966.1(4)
16
1.319
Z
calcd density, Mg/m3
F(000)
1.314
795.83
4560.13
cryst dimens, mm
temp, °C
radiation (λ), Å
2θmax, deg
µ, mm-1
0.25 × 0.25 × 0.10 0.30 × 0.10 × 0.10
C
17H12F6O: C, 58.97; H, 3.49. Found: C, 59.25; H, 3.63.
-100
0.710 73
65.0
-100
0.710 73
56.0
X-r a y Cr ysta l Str u ctu r es (1, 13). Diffraction data were
collected on a Bruker SMART 1K diffractometer using the
ω-scan mode. Refinement was carried out with the full-matrix
least-squares method based on F (NCRVAX) with anisotropic
thermal parameters for all non-hydrogen atoms. Hydrogen
atoms were inserted in calculated positions and refined riding
with the corresponding atom. Complete details of X-ray data
collection are given in Table 2.
0.89
0.64
total no. of rflns
total no. of unique rflns
35 313
6953
42 823
6529
no. of obsd data (I > 2.5σ(I)) 5741
5499
306
no. of refined params
331
RF, %
Rw, %
GOF
0.034
0.042
1.7561
0.033
0.032
1.1250
Ack n ow led gm en t. We are grateful to the NIH
(Grant No. GM 28938) for support of this research and
to Dr. Peter S. White for X-ray structures of 1 and 13.
using 6/1 hexanes/dichloromethane to give a mixture of [1,2,4-
tBu3CpRh(CO)]2 and 2-ethyl-5,3′-bis(trifluoromethyl)benzophe-
none. After that, impure 3,3′-bis(trifluoromethyl)benzophenone
(0.142 g) was eluted. The 1H NMR shift values of 3,3′-bis-
(trifluoromethyl)biphenyl were compared with the literature
values.25 The fraction containing the ethylated benzophenone
was adsorbed on silica gel and kept for 24 h to decompose the
Su p p or tin g In for m a tion Ava ila ble: Tables giving X-ray
crystallographic data for 1 and 13. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM030563U