Rhodium mediated C-H Bond functionalisation leading to carboxylate: Derivatives

Article abstract of DOI:10.1002/chem.201001453

Selective functionalisation of 15-cyclooctadiene either to a carboxylic acid or to a γ-lactone is achieved by a novel sequence of reactions involving quantitative oxygenation with oxygen and C-C coupling with carbon monoxide (see graphic). The rhodium hydroxy-alkyl-allyl complex shown is the active intermediate that promotes the elimination of the organic compounds.

Full text of DOI:10.1002/chem.201001453

COMMUNICATION
DOI: 10.1002/chem.201001453
À
Rhodium Mediated C H Bond Functionalisation Leading to Carboxylate
Derivatives
Cristina Tejel,* M. Pilar del Rꢀo, Josꢁ A. Lꢂpez, and Miguel A. Ciriano[a]
Carboxylic acids, their esters and lactones are among the
most common functional groups and a large number of fine
chemicals are accessible from these functionalities.[1] Typical
organic synthetic procedures[2] towards carboxylic acid syn-
thesis include the oxidation of alcohols and aldehydes and
the hydrolysis of nitriles, although the carboxylation of or-
1,3-diphenyltriazenide) with molecular oxygen to give dinu-
clear 2-rhoda(III)oxetane complex 1, [{Rh(PhN3Ph)-
(OC8H12)}2] (Scheme 1).[6a] Diffusion of carbon monoxide
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
À
ganic substrates containing C X bonds is, perhaps, the best
established approach to carboxylic acids that is mediated by
transition metal complexes.[3] From an atom economy per-
À
À
spective, the direct functionalisation of C H bonds to C
CO2R groups is a highly desirable alternative, since it avoids
classical functional group manipulations. Although scarce,
such palladium-catalysed reactions have recently been re-
ported.[4] From a formal point of view, a COO moiety could
À
be inserted into a C H bond by combining oxygenation and
carbonylation, involving simply O2 and CO as attractive and
cheap substrates. In this field, 2-metallaACTHNUTRGNEUNG
oxetanes[5] emerge
as valuable candidates to test this possibility, since they can
be obtained by oxygenation of olefins with dioxygen.[6] Al-
though the reactivity of 2-metallaoxetanes is currently in its
Scheme 1. Elimination reactions from 2-rhodaACTHNUTRGENUG(N III)oxetane complex 1 on
reaction with carbon monoxide under different conditions. i) slow diffu-
sion and ii) vigorous stirring. The two nitrogen atoms in 1 and 6 represent
the anionic PhN3Ph ligand. The numbering scheme shown is used for
NMR characterisation.
infancy,[7] two of them have been reported as suitable for C
À
X (X=N, O) bond formation, as shown by the reactions of
2-rhoda- and 2-platinaACHTNUTGRNEUNG
oxetanes with acetonitrile[8] and
carbon monoxide,[9] respectively. Herein, we describe new
reactions leading to carboxylic acids and lactones, involving
À
the stoichiometric functionalisation of an allylic C H bond
through a solution of 1 in dichloromethane at room temper-
ature gave carbonyl complex 3, [{Rh(CO)2ACTHNGUTERNU(NG m-PhN3Ph)}2],
quantitatively, along with 4-cyclooctenone (2, 65%). Al-
in 1,5-cyclooctadiene (COD) with carbon monoxide and di-
oxygen, which proceeds through a discrete 2-rhodaoxetane
intermediate.
À
though complex 1 contains three different types of metal X
We have previously reported the selective reaction of
[RhACHTUNGTRENNUNG(C8H12)ACHTUNGTRENNUNG(PhN3Ph)] (C8H12 =1,5-cyclooctadiene, PhN3Ph=
s bond (X=O, N, C), each, in principle, suitable for carbon
monoxide insertion, the reaction predominantly leads to
elimination of the oxygenated fragment as 4-cyclooctenone
(2). The way in which 2 is eliminated upon exposure of 1 to
CO should be similar to that in previously reported reac-
tions of complex 1 with phosphanes.[10] The second organic
compound produced by the reaction (35% yield) was identi-
fied as cycloocta-2,6-diene carboxylic acid 4 (see the Experi-
mental Section). As the most relevant resonance, the proton
[a] Dr. C. Tejel, Dr. M. P. del Rꢀo, Dr. J. A. Lꢁpez, Prof. M. A. Ciriano
Departamento de Quꢀmica Inorgꢂnica
Instituto de Ciencia de Materiales de Aragꢁn (ICMA)
CSIC-Universidad de Zaragoza, Pedro Cerbuna 12
50009-Zaragoza (Spain)
Fax : (+34)976-761-187
E-mail: ctejel@unizar.es
À
from the COOH moiety, unobserved at room temperature,
was located as a sharp singlet (d=13.67 ppm) at À708C in
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201001453.
Chem. Eur. J. 2010, 16, 11261 – 11265
ꢃ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
11261

[D8]toluene, whereas the carboxylic carbon appeared at the
usual chemical shift (d=180.7 ppm) in the 13C{1H} attached
proton test (APT) spectrum.
On raising the temperature of the reaction, the amount of
carboxylic acid 4 produced increases until it becomes the
major product at 608C in C6D6, provided that carbon mon-
oxide is allowed to diffuse slowly through a solution of 1
(Scheme 1). Noticeably, the slow diffusion and dilution of
carbon monoxide is crucial for the regioselective synthesis
of 4. If a solution of 1 is heated at 608C and then mixed
with CO at 08C under vigorous shaking a different product
À
Scheme 2. The
possible
stereoisomers
of
[RhACTHNGURTENNU(G PhN3Ph)ACHTUNGTRENNUNG(HO
C8H11)(CO)]. Isomers 6b and 6c were not observed. The two nitrogen
atoms on rhodium represent the triazenide ligand.
is formed, that is, the new 8-oxabicycle
G
Figure 1 shows the DFT optimised geometry of 6a. The
9-one (5, Scheme 1). Again [{Rh(CO)2A(m-PhN3Ph)}2] (3) is
C
hydroxy–alkyl–allyl moiety behaves as a fac-tridentate
the only rhodium containing product. Prolonged heating
[1008C, CO (3 bar)] gave a mixture, probably the thermody-
namic one, containing 5 and two isomeric oxabicycles con-
taining the olefinic bonds in positions 2 and 4 (5b), and 3
and 5 (5c). Compound 5 was identified on the basis of its
spectroscopic data (see the Experimental Section and Sup-
porting Information). From the six CH signals observed in
the 13C{1H} APT NMR spectrum four of them correspond to
the olefinic carbons, while those at d=40.3 and 76.9 ppm
correspond to C1 and C7, which are bound to the C=O and
O, respectively. As expected, the carboxylic carbon (C9) was
observed at a typical chemical shift (d=176.3 ppm).
Monitoring the reactions by 1H NMR spectroscopy al-
lowed the observation of the common active species leading
to 4 and 5. This species was found to be eighteen-electron
À
ligand; a chelating triazenide ligand and one carbonyl group
complete an almost octahedral environment around rhodi-
Figure 1. The DFT calculated structure of 6a. Selected distances [ꢄ]:
À
À
À
À
À
Rh C1 2.094, Rh C4 2.200, Rh C5 2.181, Rh C6 2.337, Rh N1 2.244,
À
À
Rh N3 2.188, Rh C9 1.906. Only the ipso carbons of the phenyl groups
rhodiumACHTUNGTRENNUNG(III) complex [RhACHTNURTGEG(NNNU PhN3Ph)ACHTNGUTNERN(UGN HO C8H11)(CO)] (6,
are shown for clarity.
Scheme 1), which was isolated in a separate experiment by
working quickly at 08C to prevent the elimination reaction.
The phenyl groups in 6 are non-equivalent and the allyl
moiety was clearly identified by sharp resonances at d=
um. The strong trans influence of the alkyl carbon (C1) is
clearly demonstrated by the considerable elongation of the
1
À
5.45, 4.71 and 4.53 ppm in the H NMR spectrum. The alkyl
Rh N1 bond trans to it (2.244 ꢄ) in comparison with the
À
carbon bound to rhodium produces a sharp doublet at d=
other Rh N bond (2.188 ꢄ), which is trans to the allylic C4
À
54.8 ppm [J
N
atom. Within the allyl group, the Rh C4 bond is found to
À
whereas the carbon bearing the hydroxyl group gives a
sharp singlet at d=87.3 ppm. The terminal carbonyl group
bound to rhodium was identified by a strong n(CO) stretch-
ing band at 2083 cmÀ1 in the IR spectrum.
be shorter (2.200 ꢄ) than the Rh C6 bond (2.337 ꢄ). The
optimised geometries of isomers 6b (+4.0 kcalmolÀ1) and
6c (+4.3 kcalmolÀ1) are clearly higher in energy (see the
Supporting Information).
Complex
rhodaoxetane
droxy–alkyl–allyl species [Rh
lowed by coordination of carbon monoxide. We have previ-
ously reported (as a coordination polymer) the hydroxy–
6
is the result of the isomerisation of
Starting from an isolated sample of 6a, carboxylic acid 4
and oxabicycle 5 were synthesised and the new organic com-
pounds were isolated (see the Experimental Section). More-
over, we have verified that carbon monoxide is not needed
for the formation of carboxylic acid 4 from 6a, except for
liberation from rhodiumꢅs coordination sphere, whereas the
formation of lactone 5 requires carbon monoxide as a re-
agent. Furthermore, when the reaction of 6a with 13CO was
carried out under the two different experimental conditions
13CO was found to only be fully incorporated into the prod-
ACHTUNGTRENNUNG(III) complex 1 into 16-valence-electron hy-
À
G
N
À
alkyl–allyl species [Rh
N
G
CO ligand, which was formed in the reaction of [Rh
ACHTUNGTRENNUNG(PhN3Ph)] with oxygen through isomerisation of the 2-rho-
daoxetane intermediate.[6a] Related isomerisation reactions
have previously been reported for similar 2-metallaoxetane
complexes,[6,5 g] but follow-up reactivity for these species
have not been described. In principle, complex 6 could exist
in three different isomeric forms, as shown in Scheme 2, but
the reaction selectively produces isomer 6a, in which the
carbonyl group is in close proximity to the hydroxyl group
(as evidenced by NOESY spectroscopy; see the Supporting
Information).
uct [{RhACTHUNGTRENNUG 2ACHTUNGTRENNUGN
(13CO) (m-PhN3Ph)}2] (3-13CO) in both cases, indi-
cating that the carbonyl group in both 4 and 5 is that already
coordinated to rhodium in complex 6a. In reverse order, the
reaction of labelled complex 6a-13CO with unlabelled
carbon monoxide gave either 4-13CO or 5-13CO as the only
labelled compounds. The selectivity observed in the label-
ling experiments indicates that 4 and 5 come from an intra-
11262
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Chem. Eur. J. 2010, 16, 11261 – 11265

À
Rhodium Mediated C H Bond Functionalisation
COMMUNICATION
molecular reaction undergone by 6a and suggests that both
reactions proceed through a common intermediate which
would result from the coupling of the carbonyl group (13CO)
with C4 (A, Scheme 3). This step is possible through a
ganic compound and the rhodium complex, [{Rh(CO)2ACHTUNGTRENNUNG(m-
PhN3Ph)}2]. A similar sequence of reactions involving C1
would give a four-membered b-lactone ring, which is disfav-
oured due to ring-strain.
In summary, rhodium complexes containing a hydroxy–
alkyl–allyl moiety are suitable intermediates for the regiose-
lective synthesis of either carboxylic acids or g-lactones. In
these reactions, carbon monoxide is incorporated into the
À
organic fragment, along with the formation of new C C and
À
C O bonds. The oxygenation of 1,5-cyclooctadiene to [Rh-
À
G
(HO C8H11)] by O2, together with the carbon
monoxide reactions described here, disclose a new sequence
of stoichiometric reactions for the regioselective functionali-
À
sation of allylic C H bond, which is currently a major chal-
lenge in chemistry.[12] Further studies into the reaction mech-
anisms and to uncover synthetic applications of this new re-
action are underway.
Experimental Section
[{Rh(CO)2ACHTUNGRTNEUNN(G m-PhN3Ph)}2] (3): A suspension of [RhACHTUNTGERNNU(G PhN3Ph)ACHTUNGTRENNUNG(C8H12)]
(100.0 mg, 0.25 mmol) in toluene (5 mL) was warmed for 2 h at 808C
under a CO atmosphere. The resulting red solution was evaporated to
dryness, left under vacuum for one day and the red residue was washed
with cold hexane (2 mL). Yield: 73.7 mg (85%); 1H NMR (500 MHz,
Scheme 3. The formation of 4 and 5 from 6a. [Rh] represents the rho-
dium(triazenide) fragment. The numbering follows convention and corre-
sponds to that in Figure 1.
C6D6, 258C): d=7.66 (dd, 3J
(H,H)=7.8 Hz, 8H; Hm), 6.88 ppm (tt, 3J
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
G
13C{1H} NMR (500 MHz, C6D6, 258C): d=185.9 (d, J
ACHTUNGTRENNUNG
CO), 152.1 (Cipso), 128.9 (Cm), 125.8 (Cp), 122.9 ppm (Co).
À
[Rh
G
E
A
suspension of [{Rh
G
change in the coordination mode of the h3-allyl group to a
s-allyl group, perhaps assisted by the hydroxyl moiety, to
A
1008C for 1.5 h to ensure the full transformation of 1 into [RhACHTUNGTRENNUNG(PhN3Ph)-
(HO C8H11)]. The suspension was cooled to 08C and the argon atmos-
À
allow the carbonyl insertion into the Rh C4 bond. Prece-
E
phere replaced by carbon monoxide. After stirring for 15 min, the result-
ing brown solution was concentrated to 3 mL and hexane (10 mL) was
added under a CO atmosphere to precipitate a brown solid. The mother
liquor was decanted and the solid was washed with cold hexane (3ꢆ
2 mL) and dried under vacuum. Yield: 70.3 mg (76%); 1H NMR
dents for reactions of this type, assisted by hemilabile li-
gands, are known in palladium chemistry.[11]
À
The route to 4 from A requires cleavage of the C OH
bond in the organic moiety. A viable possibility involves a b-
hydroxy elimination reaction from coordinatively unsaturat-
ed acyl intermediate A, to give rhodiumhydroxo(h2,h2-cyclo-
octa-2,5-dien-1-carbonylate)-complex B (Scheme 3). Prece-
dents for b-hydroxy elimination within the coordination
sphere of platinum are known.[5a,7a] Reductive elimination of
the hydroxyl and carbonyl groups, to produce the COOH
group, gives diene ligand 4, which, according to the experi-
mental data, is eventually replaced by carbon monoxide in
the rhodium complex. This mechanism, proceeding via a b-
hydroxy elimination from coordinatively unsaturated inter-
mediate A, should be stopped by CO coordination, which
drives the reaction to form intermediate C (Scheme 3) and,
thus, readily explains why this reaction path is suppressed by
the presence of CO.
(500 MHz, C6D6, 258C): d=7.52 (d, 3J
(H,H)=7.9 Hz, 2H; Hm), 7.17 (t, 3J(H,H)=7.9 Hz, 2H; Hm’), 7.12 (d, 3J-
(H,H)=7.9 Hz, 2H; Ho’), 7.01 (t, 3J(H,H)=7.6 Hz, 1H; Hp), 6.92 (tt, 3J-
(H,H)=1.2 Hz, 1H; Hp’), 5.48–5.42 (m, 1H; H6), 4.71 (t, 3J-
(H,H)=8.0 Hz, 1H; H5), 4.56–4.50 (m, 1H; H4), 2.99 (d, 3J
(H,H)=
3.0 Hz, 1H; H2), 2.84 (d, 3J(H,H)=6.3 Hz, 1H; H1), 2.06–2.00 (m, 1H;
(H,H)=6.8 Hz, 2H; Ho), 7.27 (t, 3J-
ACHTUNGTRENNUNG
R
N
ACHUTNGREN(NUG H,H)=7.1, JACHTGNUTRENNUNG
G
H8a), 1.50–1.46 (m, 1H; H3a), 1.36–1.30 (m, 1H; H7a), 1.14 (dt, 3J
ACHTUNGTRENNUNG(H,H)=
14.7, 4.6 Hz, 1H; H3b), 0.91 (brs, 1H; OH), 0.86–0.82 (m, 1H; H7b), 0.80–
0.76 ppm (m, 1H; H8b); 13C{1H} NMR (500 MHz, C6D6, 258C): d=190.9
(d, J
(C,Rh)=76 Hz, Rh CO), 151.4 (Cipso), 149.1 (Cipso), 129.4 (Cm’),
129.2 (Cm), 123.8 (Cp), 123.6 (Cp’), 118.4 (Co), 117.0 (Co’), 106.9 (d, J-
R
T
(C3), 21.8 ppm (C7); elemental analysis calcd (%) for C21H22N3O2Rh: C
55.89, H 4.91, N 9.31; found: C 55.97, H 5.05, N 9.18.
4-Cyclooctanone (2):
(20.0 mg, 0.024 mmol) in CD2Cl2 (0.5 mL) was connected to a balloon
filled with CO and left undisturbed at room temperature. After 48 h,
complete disappearance of 1 was observed while the reaction mixture
contained 4-cyclooctanone (2, 65%), cycloocta-2,6-diene carboxylic acid
(4, 35%) and [{Rh(CO)
Cycloocta-2,6-diene carboxylic acid (4): A suspension of [{Rh
(OC8H12)}2] (20.0 mg, 0.024 mmol) was warmed at 608C in C6D6 (0.5 mL)
under argon and the evolution of the reaction monitored by 1H NMR to
Starting from C (Scheme 3), independent of the exact
order of steps, the formation of 5 would require nucleophilic
attack of the hydroxyl group on the acyl group to form a
À
protonated g-lactone ring. b-Hydride elimination of the C8
H bond, along with the acidic proton, would give dihydro-
gen and compound 5, probably coordinated to rhodium. Fi-
nally, replacement of 5 by carbon monoxide renders the or-
AHCTUNGTRENNUNG
ensure the complete transformation of 1 into [RhACTHNGURTEN(NNUG PhN3Ph)ACHTGNUTRENNUNG
Chem. Eur. J. 2010, 16, 11261 – 11265
ꢃ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
11263

C. Tejel et al.
Then, it was connected to a balloon filled with CO and argon in approxi-
mately equimolar amounts and left undisturbed for 1 h at 608C (slow,
dilute diffusion). The resulting dark red solution contained equimolar
for the rhodium atom and 6–311GACTHNGUTER(NNUG d,p) for the remaining atoms. Zero-
point vibration energy (ZPVE) and thermal corrections (298 K, 1 atm) to
the energy have been estimated on the basis of the frequency calcula-
tions.
amounts of
(500 MHz, C6D6, 258C): d=5.77 (dd, 3J
5.55–5.49 (m, 1H; H3), 5.46–5.42 (m, 2H; H6,7), 3.60–3.54 (m, 1H; H1),
2.68–2.60 (m, 1H; H8a), 2.45 (dt, 3J(H,H)=16.1, 3.7 Hz, 1H; H8b), 2.20–
3
and 4, by NMR, as the only products. 4: 1H NMR
AHCTUNGTRENNUNG
(H,H)=11.5, 6.6 Hz, 1H, H2),
AHCTUNGTRENNUNG
2.14 (m, 1H; H4a), 2.15–2.13 (m, 1H; H5a), 2.03–1.95 (m, 1H; H4b), 1.87–
1.81 ppm (m, 1H; H5b); 13C{1H} NMR (500 MHz, C6D6, 258C): d=180.7
(COOH), 130.5 (C2), 129.6 (C7), 126.5 (C7), 126.4 (C2), 45.3 (C1), 30.9
(C8), 27.9 (C5), 27.6 ppm (C4). In an independent experiment, acid 4 was
isolated as follows: a solution of 6 (100 mg) in toluene (5 mL) was left
under argon for two days at room temperature or for 3 h at 608C. The
1H NMR spectrum of the resulting brown-red solution showed unre-
solved signals in the d=6–2 ppm region. Shaking this solution with CO
for 5 min resulted in a dark-red solution showing well-resolved multiplets
in the 1H NMR spectrum, which corresponds to the quantitative forma-
Acknowledgements
Generous financial support from MICINN/FEDER (Project CTQ2008-
03860) and GA (Gobierno de Aragꢁn, PM 36/2007) is gratefully ac-
knowledged. M.P.R. thanks GA for a fellowship. Authors thank Dr. B. de
Bruin for useful discussions and M. V. Mendoza for experimental assis-
tance.
Keywords: carbon monoxide · carboxylic acids · lactones ·
metallaoxetanes · rhodium
tion of organic compound 4 and [{Rh(CO)2ACTHNUTRGNEUNG(m-PhN3Ph)}2] (3). The solu-
tion was added to and shaken with a solution of aqueous NaHCO3 (1.0 g
in 25 mL). The aqueous phase was separated, acidified with aqueous HCl
(1m) and extracted with diethyl ether (15 mL). After drying with MgSO4,
evaporation of the organic extract under vacuum gave acid 4 as a pale
yellow oil (15 mg), which was characterized by high-resolution mass spec-
trometry and NMR spectroscopy (see the Supporting Information).
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Gooßen, K. Gooßen, N. Rodriguez, M. Blanchot, C. Linder, B. Zim-
mermann, Pure Appl. Chem. 2008, 80, 1725–1733.
8-Oxabicycle
ACHTUNGTRENNUNG[5.2.1]deca-2,5-dien-9-one (5): A suspension of [{Rh-
A
E
[2] M. A. Ogliaruso, J. F. Wolfe in Synthesis of Carboxylic Acids, Esters
and Their Derivatives (Eds.: S. Patai, Z. Rappopot), Wiley, New
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(0.5 mL) under argon and the progress of the reaction monitored by
1H NMR to ensure complete transformation of 1 into [Rh
(PhN3Ph)
G
À
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C8H11)]. Then, it was cooled in an ice bath, saturated with CO by three
vacuum/CO cycles and vigorously stirred under carbon monoxide for 6 h
at 08C to prevent isomerisation into oxabicycles 5b and 5c. 5:1H NMR
(500 MHz, C6D6, 258C): d=5.60–5.52 (m, 2H, H3,5), 5.46–5.40 (m, 1H;
H2), 5.25–5.18 (m, 1H; H6), 4.35–4.32 (m, 1H, H7), 2.98–2.92 (m, 1H;
H4a), 2.70–2.66 (m, 1H, H1), 2.17–2.11 (m, 1H; H4b), 1.54–1.50 ppm (m,
2H; H10a,10b); 13C{1H} NMR (500 MHz, C6D6, 258C): d=176.3 (CO2),
133.8 (C5), 132.9 (C3), 129.8 (C6), 128.6 (C2), 76.9 (C7), 40.3 (C1), 31.6
(C10), 24.2 ppm (C4). In a separate experiment, 5 was isolated as follows:
a brown-green solution of 6 (100 mg) in toluene (5 mL) was shaken
under an atmosphere of carbon monoxide at 08C for 6 h. The solution
was concentrated under vacuum and subjected to chromatography on a
column of silica gel by using a 1:10 mixture of ethyl acetate/hexane as
eluent. Complex 3 emerged first and then a brownish band was collected.
Evaporation of the solvent gave 5 as a tan oil, which was characterised
by high-resolution mass spectrometry and NMR spectroscopy (see the
Supporting Information).
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8-Oxabicycle
3,5-dien-9-one (5c): A suspension of [{Rh
N
ACHUTGTNREN[NUG 5.2.1]ACHTUNGTNERdNUGN eca-
A
ACHTUNGTRENNUNG
0.048 mmol) in toluene (2 mL) was warmed at 1008C in a low-pressure
reactor under CO (3 bar) for 2 h. The solvent was evaporated to dryness
and the residue dissolved in C6D6 (0.5 mL), which showed a mixture of 5,
5b and 5c (38:48:14) by NMR spectroscopy (see the Supporting Informa-
tion). 5b: 1H NMR (500 MHz, C6D6, 258C): d=5.82–5.74 (m, 1H; H4),
5.54–5.48 (m, 1H; H3), 5.43–5.37 (m, 1H, H2), 5.22–5.16 (m, 1H, H5),
4.06–3.98 (m, 1H, H7), 2.74–2.70 (m, 1H, H1), 2.23–2.17 (m, 1H; H6a),
1.88–1.82 (m, 1H; H6b), 1.42–1.38 ppm (m, 2H; H10a,10b); 13C{1H} NMR
(500 MHz, C6D6, 258C): d=174.9 (CO2), 129.7 (C4), 127.1 (C2), 126.8
(C5), 126.6 (C3), 72.2 (C7), 40.7 (C1), 33.4 (C6), 31.2 ppm (C10). 5c:
1H NMR (500 MHz, C6D6, 258C): d=5.87–5.81 (m, 1H; H4), 5.41–5.35
(m, 1H; H5), 5.36–5.28 (m, 1H; H3), 5.31–5.25 (m, 1H; H6), 4.29–4.23 (m,
1H; H7), 2.13–2.09 (m, 1H; H1), 2.01–1.94 (m, 2H; H2a,2b), 1.38–1.34 (m,
1H; H10a), 1.30–1.26 ppm (m, 1H; H10b); 13C{1H} NMR (500 MHz, C6D6,
258C): d=177.7 (CO2), 130.5 (C4), 130.0 (C3), 127.5 (C6), 126.5 (C5), 75.4
(C7), 35.4 (C1), 28.3 (C2), 28.2 ppm (C10).
Computational details: The computational method used was density
functional theory (DFT) with the B3LYP exchange-correlation function-
al,[13–15] and the Gaussian 03[16] program package. The basis sets used for
full optimisation of the structures and for calculation of the single-point
energies are of triple-zeta quality: LanL2TZ(f)[17] effective core potential
11264
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À
Rhodium Mediated C H Bond Functionalisation
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Received: May 26, 2010
Published online: August 18, 2010
Chem. Eur. J. 2010, 16, 11261 – 11265
ꢃ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
11265