Formation of indanone from an iridanaphthalene complex

Article abstract of DOI:10.1021/om400702b

The first example of evolution of an iridanaphthalene into an indanone through an intermediate indenyl is reported, serving as a good example of starting material to obtain indanones. Two new iridanaphthalenes are obtained by intramolecular C-H activation of a phenyl ring of a carbene ligand in [IrCp*{=C(OMe)CH=CPh₂}(L)]PF₆ (L = PPh ₂Me, PMe₃) complexes. It is demonstrated that these iridanaphthalene complexes can undergo a thermal reaction to give indenyl complexes and 3-phenylindanone.

Full text of DOI:10.1021/om400702b

Communication
pubs.acs.org/Organometallics
Formation of Indanone from an Iridanaphthalene Complex
†
,†
†
†
†
‡
M. Talavera, S. Bolan
̃
o,* J. Bravo, J. Castro, S. Garcıa
́
-Fontan
́
, and J. M. Hermida-Ramon
́
†
‡
Departamento de Quım
́
ica Inorganica and Departamento de Quımica Fısica, Universidad de Vigo, Campus Universitario,
́ ́ ́
E-36310 Vigo, Spain
*
S Supporting Information
ABSTRACT: The first example of evolution of an iridanaph-
thalene into an indanone through an intermediate indenyl is
reported, serving as a good example of starting material to
obtain indanones. Two new iridanaphthalenes are obtained
by intramolecular C−H activation of a phenyl ring of a
carbene ligand in [IrCp*{C(OMe)CHCPh }(L)]PF
2
6
(
L = PPh Me, PMe ) complexes. It is demonstrated that these
2 3
iridanaphthalene complexes can undergo a thermal reaction to
give indenyl complexes and 3-phenylindanone.
etallacyclic aromatic compounds incorporating transition
M
metals are a subject of great interest, since they display a
behavior that includes properties from both aromatic organic
and organometallic compounds. Although many metallaben-
zenes of osmium, iridium, platinum, and ruthenium are known,
to the best of our knowledge only two metallanaphthalenes
1
2
have been reported, one with osmium and another with iridium.
The importance of this type of metal-organic functionality is
emphasized by the fact that metal cyclopentadienyls can be
3
formed from transitory metallabenzenes. Analogously, an
osmanaphthalene has been proposed as intermediate leading to
4
an indenyl complex.
Recently, we have reported that the new (methoxy)-
alkenylcarbeneiridium complex [IrCp*Cl{C(OMe)CH
CPh }(PPh Me)]PF (1a) reacts with amines to undergo the
2
2
6
unexpected cleavage of the O−CH bond instead of the usual
3
5
aminolysis. This peculiar behavior has prompted us to further
explore the reactivity of these types of compounds. Here, we
report that treatment of [IrCp*Cl{C(OMe)CHCPh }-
2
(
L)]PF (L = PPh Me (1a), PMe (1b)) with AgPF gives high
6 2 3 6
Figure 1. ORTEP view of the cation [IrCp*{C(OMe)CHC(o-
+
yields of the iridanaphthalene complexes [IrCp*{C(OMe)-
CHC(o-C H )(Ph)}(L)]PF (L = PPh Me (2a), PMe (2b))
C H )(Ph)}(PPh Me)] (2a) drawn at the 50% probability level. P1
6
4
2
represents a PPh Me ligand, and the hydrogen atoms are not shown.
2
6
4
6
2
3
Selected bond lengths (Å) and angles (deg): Ir−P(1), 2.2968(9);
Ir−CT, 1.9306(2); Ir−C(11), 1.966(4); Ir−C(22), 2.068(3); C(11)−
Ir−C(22), 89.52(14). CT refers to the centroid of the Cp* ligand.
through an intramolecular C−H activation of one of the phenyl
rings of the carbene ligand (eq 1).
coordination sphere is completed with a pentamethylcyclopen-
tadienyl (Cp*) and a phosphane ligand.
The NMR spectra support the solid-state structures of 2a,b
see the Supporting Information).
(
Remarkably, the iridanaphthalene moiety is not stable and
refluxing 2 in 1,2-dichloroethane or toluene for 24 h gives
-phenylindanone (4) (eq 2). The same transformation occurs
3
also at longer reaction times in dichloromethane at 35 °C (eq 2).
The structures of both iridanaphthalene complexes have been
confirmed by single-crystal X-ray diffraction (see the Supporting
Information). Figure 1 shows the complex cation 2a. The iridium
atom becomes part of a metallanaphthalene moiety and the metal
Received: July 17, 2013
Published: July 30, 2013
©
2013 American Chemical Society
4058
dx.doi.org/10.1021/om400702b | Organometallics 2013, 32, 4058−4060

Organometallics
Communication
Scheme 1. Proposed Mechanism for the Formation of 3 and 4
6
The nature of 4, which was isolated in excellent yield, was
1
13
1
confirmed by H and C{ H} NMR spectroscopy (see the
Supporting Information). The transformation of 2 to give 4 is, to
the best of our knowledge, the first example of indanone forma-
tion from a metallanaphthalene. We prepared a solution of 2
(
0.013 M) in dichloromethane, and in order to shed light on
the mechanism of this reaction the transformation of 2 into 4
was followed at 35 °C by NMR spectroscopy. After 8 days,
31
1
integration of the P{ H} peaks showed a partial transformation
3
of 2 into the new complex [IrCp*{η -(C H )(OMe)(Ph)}(L)]-
9
5
1
PF (3) (3:7 ratio). H NMR confirms the presence of 4 in
6
addition to 2 and 3. Extraction of 4 with diethyl ether gives 3a
(
(
L = PPh Me) (or 3b (L = PMe )) contaminated with 2a (30%)
or 2b (5%)).
Multidimensional and multinuclear NMR analysis of the
2
3
5
ligand (PPh Me), to a η -pentamethylcyclopentadienyl ligand,
2
3
and to η -1-methoxy-3-phenylindene (Figure 3). The noteworthy
mixture formed by 2 and 3 confirms the formulation of 3 as the
indenyl complex. The H NMR spectrum for 3a shows the pre-
sence of signals at 3.84 (s, 3H, OCH ) and 6.01 (d, 1H, J
1
3
=
3
H−P
2
1
0.8 Hz, C -H) ppm, while for 3b the same signals appear at 3.78
3
2
(
s, 3H, OCH ) and 5.96 (d, 1H, J
= 10.7 Hz, C -H) ppm.
3
H−P
13
1
The C{ H} NMR spectrum for 3a reveals the existence of
resonances at 49.4 (s, C ), 56.3 (s, C -H), 132.3 (s, C ), 161.0
3
2
9
8
1
(
s, C ), and 186.3 (s, C ) ppm, while the peaks for 3b appear at
3
2
9
8
5
0.1 (s, C ), 55.3 (s, C -H), 132.3 (s, C ), 161.3 (s, C ) and 185.5
1
1
13
(
s, C ) ppm. The { H, C} HMBC NMR experiment further
confirms the existence of the indenyl ligand, showing correlations
3
2
3
1
8
9
between η -C H and C , C , C , and C (Figure 2).
3
Figure 3. ORTEP view of the cation [IrCp*{η -(C H )(OMe)(Ph)}-
9
5
+
(
PPh Me)] (3a) drawn at the 20% probability level. P1 represents a
2
PPh Me ligand, and the hydrogen atoms are not shown. Selected bond
2
lengths (Å) and angles (deg): Ir−CT, 1.896(2); Ir−P(1), 2.280(7); Ir−
C(11), 2.92(2); Ir−C(12), 2.17(2); Ir−C(13), 2.25(2); CT−Ir−C(12),
1
42.6(6); CT−Ir−C(13), 133.6(7); CT−Ir−C(14), 106.9(5). CT
refers to the centroid of the Cp* ligand.
geometrical feature of the structure is the strongly slipped indenyl
group, in which the average of the Ir−C(14) and Ir−C(15)
distances is 3.23(3) Å. This value is 24% longer than the average
value of the Ir−C(11), Ir−C(12), and Ir−C(13) distances,
1
13
Figure 2. Section of the { H, C} HMBC NMR experiment of 3a
3
2
3
1
8
9
showing correlations between η -C H and C , C , C , and C resonances.
Signals marked with an asterisk correspond to the presence of 2a as an
impurity.
2
.45(2) Å. On the other hand, the C(12)−C(13) and C(12)−
C(11) distances are 1.42(3) Å, as expected. Bond distances and
Since chemical shifts ranging between 140 and 160 ppm are
angles are given in the Supporting Information.
8
9
3
7
typical for C and C in η -indenyl ligands, the NMR data
suggest the structure displayed in Scheme 1 for complex 3,
The interception of complex 3 along the transformation of
complex 2 shed light on the possible mechanism for the forma-
tion of 4. The iridanaphthalene 2 could undergo carbene migratory
3
showing an η hapticity of the indenyl ligand. The crystal
8
structure of 3a confirms that this formulation is retained in the
solid state, with the iridium atom coordinated to a phosphane
insertion, leading to the 16e intermediate A (not observed), which
1
3
after switching from η to η hapticity leads to the more stable
4
059
dx.doi.org/10.1021/om400702b | Organometallics 2013, 32, 4058−4060

Organometallics
8e complex 3, stabilized with respect to A by aromatization of the
Communication
1
(5) Talavera, M.; Bolan
̃
o, S.; Bravo, J.; Castro, J.; Garcıa
́
́
-Fontan, S.;
Hermida-Ramo
om400565c.
́
n, J. M. Organometallics, DOI: doi.org/10.1021/
benzene ring. Formation of 4 from 3 recalls the formation of indene
7a
from the indenyl complex, but in our case the final product is an
(
6) van der Waals, A. C. L. M.; Klunder, A. J. H.; van Boren, F. R.;
Zwanenburg, B. J. Mol. Catal. A: Chem. 1998, 134, 179−189.
7) (a) Habib, A.; Tanke, R. S.; Holt, E. M.; Crabtree, R. H.
Organometallics 2003, 8, 1225−1231. (b) Rerek, M. E.; Basolo, F. J. Am.
Chem. Soc. 1984, 106, 5908−5912. (c) Merola, J. S.; Kacmarcik, R. T.;
Engent, D. V. J. Am. Chem. Soc. 1986, 108, 329−331.
(8) Formation of Cp complexes from metallabenzenes is known, and
also this rearrangement was proposed for obtaining an indenyl osmium
complex (see refs 3 and 4).
indanone (Scheme 1). This implies not only the heterolytic
cleavage of the O−CH bond but also the hydrogenation of the
3
(
remaining double bond. The solvent does not seems to play any
role in the reaction, since it occurs irrespective of solvent polarity
(
dichloromethane, 1,2-dichloroethane, methanol, chloroform, and
toluene) and in aprotic solvents (carbon tetrachloride) or when the
presence of water is rigorously avoided. In keeping with this
9
hypothesis, repeating the reaction in deuterated solvents (CD Cl ,
2
2
(
9) All solvents were dried by the usual procedures (Perrin, D. D.;
CDCl ) does not result in any deuterium incorporation in the final
3
Armarego, W. L. F. Purification of Laboratory Chemicals, 3rd ed.;
Butterworth/ Heinemann: London/Oxford, 1988) and, prior to use,
distilled under argon.
products. Therefore, complex 3 is the only species initially involved
in the formation of 4, and the methyl group possibly bonded to the
iridium atom after the heterolytic cleavage of the O−CH bond
3
(
10) (a) Senaiar, R. S.; Teske, J. A.; Young, D. D.; Deiters, A. J. Org.
seems to be involved in the hydrogenation.
Chem. 2007, 7801−7804. and references therein (b) Gilmer, J. F.;
Simplicio, A. L.; Clancy, J. M. Eur. J. Pharm. Sci. 2005, 24, 315−323 and
references therein.
In summary, we have synthesized the iridanaphthalene 2 by a
intramolecular C−H activation of one phenyl ring of the carbene
ligand in complex 1 and shown that 2 selectively transforms into
the indenyl compound 3. When the reaction is carried out at low
concentration in a low-boiling-point solvent, a mixture of 2 and
3
is formed, suggesting a rationale for the mechanism of the
evolution from to 2 to 4. The formation of the indanone 4 from
compound 2 suggests that indenyl complexes could be relevant
intermediates to obtain these organic compounds, which are
important for their medical applications. Further studies tackling
the preparation of other iridanaphthalenes are in progress in our
laboratory, aimed at addressing the full scope of the reaction.
10
ASSOCIATED CONTENT
Supporting Information
■
*
S
Text, figures, tables, and CIF files giving experimental procedures
and full spectroscopic data for all new compounds and crystallo-
graphic data for compounds 2a·BPh , 2b·BPh , 2b·PF , and
4
4
6
3
a·BPh . This material is available free of charge via the Internet
4
at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
E-mail for S.B.: bgs@uvigo.es.
■
*
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENTS
We thank the University of Vigo CACTI services for collecting
X-ray data and recording NMR spectra.
■
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■
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