Synthesis, characterization, and catalytic properties of new electrophilic iridium(III) complexes containing the (R)-(+)-2,2,′-binaphthyl Ligand

Article abstract of DOI:10.1021/ic100300y

The oxidative addition of MeI to the Ir(I) square-planar complex IrI(CO)((R)-(+)-BINAP) where (R)-(+)-BINAP = (R)-(+)-2,2′- bis(diphenylphosphino)-1,′-binaphthyl)) results in the formation of two diastereomers in a 2:1 ratio of the Ir(III) oxidative addit

Full text of DOI:10.1021/ic100300y

Inorg. Chem. 2010, 49, 4331–4342 4331
DOI: 10.1021/ic100300y
Synthesis, Characterization, and Catalytic Properties of New Electrophilic Iridium(III)
Complexes Containing the (R)-(+)-2,20-Bis(diphenylphosphino)-1,10-binaphthyl Ligand
Abdurrahman C. Atesin, Jing Zhang, Tulaza Vaidya, William W. Brennessel, Alison J. Frontier,* and Richard Eisenberg*
Department of Chemistry, University of Rochester, Rochester, New York 14627
Received February 12, 2010
The oxidative addition of MeI to the Ir(I) square-planar complex IrI(CO)((R)-(þ)-BINAP) where (R)-(þ)-BINAP = (R)-(þ)-
2,20-bis(diphenylphosphino)-1,10-binaphthyl)) results in the formation of two diastereomers in a 2:1 ratio of the Ir(III) oxidative
addition product IrI2(CO)(Me)((R)-(þ)-BINAP) (4a and 4b) in a 85% overall yield. Upon iodide abstraction from the
diastereomeric mixture with 2 equiv of AgSbF6 in the presence of diethyl isopropylidene malonate (DIM), two diastereomers of
the dicationic complex [Ir(CO)(Me)(DIM)((R)-(þ)-BINAP)][SbF6]2 (5) are formed in a 90% yield with a ratio of 9:1. One
diastereomer of the diiodide complex 4 and one diastereomer of the dicationic complex 5 have been characterized by X-ray
diffraction. An anion exchange reaction of 5 with NaBAr4f- (BAr4f- = B(3,5-(CF3)2C6H3)4) affords [Ir(CO)(Me)(DIM)-
((R)-(þ)-BINAP)][BAr4f]2 (6) in quantitative yield. Both 5 and 6 are active Lewis acid catalysts for the polarized Nazarov
f
cyclization and the Diels-Alder reaction. In the Nazarov cyclization, when NaBAr4 is added as a cofactor for the reaction
catalyzed by 5 or 6, the resultant oxyallyl cation intermediate from the 4π conrotation undergoes a Wagner-Meerwein
rearrangement to afford spirocyclic cyclopentenones in modest to good yields.
Introduction
occupied by a weakly coordinating solvent molecule. Charge is
balanced in these systems by essentially non-coordinating ani-
ons. Over the past decade, research by Eisenberg and co-
workers have focused on the development of cationic iridium-
(III) complexes fulfilling these criteria with adjacent coordina-
tion sites occupied by readily dissociatable chelating ligands that
allow for substrate activation through coordination and possi-
bly chelation to the metal center. In the course of developing
such reactive systems, the d6 iridium(III) dicationic complex
[Ir(Me)(CO)(dppe)(DIB)][BArf4]2, 1 (dppe=1,2-bis(diphenyl-
Electrophilicly driven reactions promoted by cationic com-
plexes of the platinum group elements in nonpolar, aprotic
media comprise an important class of transition metal catalyzed
reactions. Recent developments in the electrophilic chemistry of
platinum group metal complexes include catalysis of R-olefin
polymerization by cationic palladium(II) systems and C-H
bond activation using cationic platinum(II) and iridium(III)
complexes.1 In the majority of these studies, the metal com-
plexes have an alkyl ligand and at least one labile binding site
phosphino)ethane, DIB = 1, 2-diiodobenzene and BArf4-
B(3,5-(CF3)2C6H3)4) was prepared and fully characterized.2
=
*To whom correspondence should be addressed. E-mail: eisenberg@
chem.rochester.edu (R.E.).
(1) (a) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. Rev. 2000, 100,
1169. (b) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. J. Am. Chem. Soc. 1995,
117, 6414. (c) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283.
(d) Drent, E.; Budzelaar, P. H. M. Chem. Rev. 1996, 96, 663. (e) Rix, F. C.; Brookhart,
M.; White, P. S. J. Am. Chem. Soc. 1996, 118, 4746. (f) Arndtsen, B. A.; Bergman,
R. G. Science 1995, 270, 1970. (g)Tellers, D. M.; Bergman, R. G. J. Am. Chem. Soc.
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Organometallics Chemistry; Springer GmbH: New York, 2009; Vol. 26, p 179.
Complex 1 exhibited electrophilic behavior leading to the
initiation of cationic polymerization or oligomerization of
different electron-rich olefins.2,3 Subsequently, 1 was found
to be an efficient catalyst for promoting Nazarov cyclization
(2) Albietz, P. J.; Cleary, B. P.; Paw, W.; Eisenberg, R. J. Am. Chem. Soc.
2001, 123, 12091.
(3) Albietz, P. J.; Cleary, B. P.; Paw, W.; Eisenberg, R. Inorg. Chem. 2002,
41, 2095.
r
2010 American Chemical Society
Published on Web 04/02/2010
pubs.acs.org/IC

4332 Inorganic Chemistry, Vol. 49, No. 9, 2010
Atesin et al.
Scheme 1
Additionally, through the use of a chiral analogue of 1, it was
hypothesized that asymmetric induction could be achieved.
In this report, we describe the synthesis and characterization
of chiral iridium(III) complexes containing R-(þ)-BINAP
(R)-(þ)-2,20-bis(diphenylphosphino)-1,10-binaphthyl), includ-
ing two salts of the same cation, [Ir(CO)(Me)(DIM)(R)-(þ)-
BINAP)][SbF6]2 (5) and[Ir(CO)(Me)(DIM)(R)-(þ)-BINAP)]-
f
[BAr4 ]2 (6) (DIM = diethyl iso-propylidenemalonate), and a
study of their catalytic properties. In addition to catalyzing the
Nazarov cyclization, the Ir(III) salts 5 and 6 are found to
catalyze spirocycle formation as shown in Scheme 1 in the
presence of specific additives in the reaction solutions.
Results and Discussion
Synthesis and Characterization of IrI2(CO)(Me)(R)-(þ)-
BINAP). According to the reported procedure,15 reaction
of (n-Bu4N)[Ir(CO)2I2] with (R)-(þ)-BINAP (R)-(þ)-2,20-
bis(diphenylphosphino)-1,10-binaphthyl) in toluene results in
the formation of IrI(CO)((R)-(þ)-BINAP) (3) in 85% yield.
Because of the chiral nature of (R)-(þ)-BINAP ligand,
oxidative addition of MeI to 3 gives two diastereomers of
IrI2(CO)(Me)((R)-(þ)-BINAP), denoted 4a and 4b, that
differ in the chirality at the metal center following trans
oxidative addition to yield a product with two iodides cis to
each other, as well as the BINAP chelate with cis P donors.
When 10 equiv of MeI are used, as described for synthesis of
IrI2(CO)(Me)(dppe),16 the reaction proceeds very slowly, and
leads to only 25% conversion after 12 h at room temperature.
31P{1H} NMR spectroscopy of the reaction mixture shows
the formation of the two diastereomers 4a and 4b at early
stages of the reaction, but significant decomposition occurs
before the reaction is complete. This observation is in contrast
to the reported syntheses of analogous complexes IrI2(CO)-
(Me)(dppe)16 and IrI2(CO)(Me)(duphos) (duphos=1, 2-bis-
(2,5-di-iso-propyl-phospholano)benzene).17 In both cases, the
reaction was complete in several hours. However, for the
oxidative addition of MeI to 3, it was found that using MeI as
the solvent results in complete reaction within 3 h, giving 4a
and 4b in 85% yield with a product ratio of 2:1 (eq 1). A
similar ratio of 4a/4b is observed during early stages of the
reaction (0.5 h). In the 31P{1H} NMR spectrum, 4a exhibits a
pair of doublets at δ-25.6 and -30.8 (2JPP =21Hz) while4b
shows δ -23.0 and -26.6 (2JPP = 23 Hz).
of polarized aryl vinyl and divinyl ketones to form five-
membered carbocycles,4 as well as a tandem reaction se-
quences involving Nazarov cyclization and subsequent
Michael addition under mild conditions at substantially
higher rates than other Lewis acid catalysts.5
Within the past decade interest in the polarized Nazarov
cyclization has attracted considerable attention because of
the reaction’s potential application in the synthesis of natural
products and bioactive molecules containing highly functio-
nalized five-membered carbocycles. Catalysis of Nazarov
cyclization has been reported with simple transition metal
complexes such as Cu(OTf)2,6 Sc(OTf)3,7 Pd(MeCN)2Cl2,8
Cu(SbF6)2,9 Fe(ClO4)3 Al2O3,10 and V(salen)Cl2/AgSbF6 in
3
good to excellent yields.11 For derivatives of these catalysts to
which a chelating chiral ligand has been added, moderate to
good enantioselectivities have been reported, such as with
Sc(pybox)(OTf)3,12 Cu(pybox)(OTf)2,13 and Ni(bis{(R)-1-
[(S)-2-(diphenylphosphino)ferrocenyl]ethyl}-cyclohexylphos-
phine)(THF)][ClO4]2.14
In a study by Huang and Frontier reported in 2007,9 when
substrate 2a (Scheme 1) was treated with stoichiometric
amounts of Cu(SbF6)2, an unusual spirocycle product 2c
was obtained in good yield, while in other reactions with a
catalytic amount of the metal promoter, only a mixture of the
spirocycle product 2c and the Nazarov product 2b were
observed to form, with the ratio favoring 2b. It was proposed
that the spirocycle forms through a Wagner-Meerwein re-
arrangement of the intermediate carbocation generated in the
reaction sequence. These observations, along with the high
substrate reactivity observed for the Ir(III) cationic complex 1
suggested that 1 might catalyze the reaction of 2a to form
the spirocycle product 2c under appropriate conditions.
(4) (a) Janka, M.; He, W.; Frontier, A. J.; Eisenberg, R. J. Am. Chem. Soc.
2004, 126, 6864. (b) Janka, M.; He, W.; Frontier, A. J.; Flaschenreim, C.;
Eisenberg, R. Tetrahedron 2005, 61, 6193.
(5) Janka, M.; He, W.; Frontier, A. J.; Eisenberg, R. J. Am. Chem. Soc.
2006, 128, 5312–5313.
(6) (a) He, W.; Herrick, I. R.; Atesin, T. A.; Caruana, P. A.; Kellenberger,
C. A.; Frontier, A. J. J. Am. Chem. Soc. 2008, 130, 1003. (b) He, W.; Sun, X.;
Frontier, A. J. J. Am. Chem. Soc. 2003, 125, 14278.
(7) Malona, J. A.; Colbourne, J. M.; Frontier, A. J. Org. Lett. 2006, 8, 5661.
(8) Bee, C.; Leclerc, E.; Tius, M. A. Org. Lett. 2003, 5, 4927.
(9) Huang, J.; Frontier, A. J. J. Am. Chem. Soc. 2007, 129, 8060.
(10) (a) Fujiwara, M.; Kawatsura, M.; Hayase, S.; Nanjo, M.; Itoh, T.
Adv. Syn. Catal. 2009, 351, 123. (b) Kawatsura, M.; Higuchi, Y.; Hayase, S.;
Nanjo, M.; Itoh, T. Synlett. 2008, 1009.
(11) Walz, I.; Bertogg, A.; Togni, A. Eur. J. Org. Chem. 2007, 2650.
(12) (a) Liang, G.; Gradl, S. N.; Trauner, D. Org. Lett. 2003, 5, 4931.
(b) Liang, G.; Trauner, D. J. Am. Chem. Soc. 2004, 126, 9544.
(13) Aggarwal, V. K.; Belfield, A. J. Org. Lett. 2003, 5, 5075.
(14) Walz, I.; Togni, A. Chem. Commun. 2008, 4315.
(15) Atesin, A. C.; Duckett, S. B.; Flaschenriem, C.; Brennessel, W. W.;
Eisenberg, R. Inorg. Chem. 2007, 46, 1196.
(16) Cleary, B. P.; Eisenberg, R. Inorg. Chim. Acta 1995, 270, 1970.
(17) Mesfin, J.; Atesin, A. C.; Fox, D. J.; Flaschenriem, C.; Brennessel, W.
W.; Eisenberg, R. Inorg. Chem. 2006, 45, 6559.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4333
Table 1. Crystal Data, Data Collection, and Structure Refinement Parameters for IrI2(CO)(Me)((R)-BINAP), 4b, and [Ir(CO)(Me)(DIM)((R)-BINAP)][SbF6]2, 5
empirical formula
formula weight
temperature
C51 H47 Cl2 I2 Ir O2 P2
1270.73
100.0(1) K
0.71073 A
orthorhombic
P212121
C71.50 H87 Cl F12 Ir O5 P2 Sb2
1787.50
100.0(1) K
˚
˚
0.71073 A
wavelength
crystal system
space group
unit cell dimensions
tetragonal
P43212
˚
a, A
12.2235(15)
14.4669(18)
26.899(3)
4756.7(10)
4
1.774
21.483(2)
21.483(2)
33.421(7)
15424(4)
8
1.540
2.567
7120
˚
b, A
˚
c, A
˚
volume, A
3
Z
density (calculated), Mg/m3
absorption coefficient, mm-1
F(000)
4.324
2464
crystal color, morphology
crystal size, mm3
θ range for data collection
index ranges
yellow, block
0.38 ꢀ 0.26 ꢀ 0.12
1.60 to 30.51°
-17 e h e 17
-20 e k e 20
-38 e l e 38
74776
14345 [R(int) = 0.0434]
12949
multiscan
0.5950 and 0.2704
14345/4/515
1.039
R1 = 0.0325, wR2 = 0.0780
R1 = 0.0382, wR2 = 0.0797
colorless, block
0.24 ꢀ 0.18 ꢀ 0.10
1.47 to 32.58°
-28 e h e 32
-32 e k e 32
-50 e l e 50
208563
28041 [R(int) = 0.0918]
22417
multiscan
0.7833 and 0.5778
28041/0/723
1.060
R1 = 0.0561, wR2 = 0.1446
R1 = 0.0718, wR2 = 0.1516
reflections collected
independent reflections
observed reflections
absorption correction
max. and min transmission
data/restraints/parameters
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
When a higher initial concentration of Ir(CO)I-
((R)-(þ)-BINAP) was employed in the MeI oxidative
addition reaction, product precipitation commenced
during the course of the reaction. The precipitate con-
tains a mixture of 4a and 4b in ratio of 1:19, as deter-
mined by its 31P{1H} NMR spectrum, while the mother
liquor was enriched with 4a in a ratio of 4:1 to 4b. Dark
orange crystals suitable for X-ray diffraction were ob-
tained by slow diffusion of diethyl ether into a solution
of 4b in dichloromethane at room temperature. Crystal-
lographic data collection and refinement parameters are
shown in Table 1, and complete structural details may be
found in the CIF supplied in the Supporting Informa-
tion. A POV-Ray drawing of the structure of 4b is shown
in Figure 1 with selected bond distances and angles given
in Table 2.
The crystal structure of 4b confirms the geometry
around the Ir(III) center as essentially octahedral, with a
slight distortion in the axial methyl and iodide ligand
positions to give a trans angle of 163.47(13)°. The analo-
gous duphos and dppe complexes,16,17 on the other hand,
have less pronounced deviations from linearity in their
respective trans Me-Ir-I angle with values of 178.7(4)°
and 171.11(8)°. The two Ir-P bond lengths of 2.4091(12)
A and 2.3169(10) A are consistent with the trans structural
influences of CO and iodide ligands, respectively. Other
bond distances in the structure of 4b are similar to those
reported for IrI2(CO)(Me)(dppe)16 and IrI2(CO)(Me)-
(duphos).17
Figure 1. POV-Ray view of4b showingthe labeling ofthe atomsaround
the Ir atom. Displacement ellipsoids are drawn at the 50% level. Hydro-
gens have been removed for clarity.
˚
Table 2. Selected Bond Lengths (A) and Angles (deg) of 4b
˚
˚
˚
Bond Length (A)
Ir(1)-P(1)
Ir(1)-C(1)
Ir(1)-I(1)
2.409 (1)
1.938(6)
2.8157(5)
Ir(1)-P(2)
Ir(1)-C(2)
Ir(1)-I(2)
2.317(1)
2.161(6)
2.7390(4)
Synthesis and Characterization of [Ir(CO)(Me)(DIM)-
((R)-(þ)-BINAP)][SbF6]2 (5) and [Ir(CO)(Me)(DIM)((R)-
Bond Angle (deg)
f
P(1)-Ir(1)-P(2)
P(2)-Ir(1)-C(1)
C(2)-Ir(1)-I(1)
C(1)-Ir(1)-P(1)
O(1)-C(1)-Ir(1)
91.20(4)
97.1 (2)
163.5 (1)
170.0 (1)
170.1(5)
P(1)-Ir(1)-I(2)
C(1)-Ir(1)-I(2)
I(1)-Ir(1)-I(2)
P(2)-Ir(1)-I(2)
89.38(3)
82.0(2)
88.41(1)
176.29(3)
(þ)-BINAP)][BAr4 ]2 (6). When a mixture of diastereo-
mers of 4a and 4b (2:1) is reacted with 2 equiv of AgSbF6
in the presence of excess diethyl isopropylidene malo-
nate (DIM) in dichloromethane, two diastereomers of

4334 Inorganic Chemistry, Vol. 49, No. 9, 2010
Atesin et al.
[Ir(CO)(Me)(DIM)((R)-(þ)-BINAP)]2þ form in a 90%
yield with a ratio of 9:1 (eq 2). The 31P{1H} NMR spec-
-
trum of the SbF6 salt of [Ir(CO)(Me)(DIM)(R)-(þ)-
BINAP)]2þ, denoted as 5, exhibits two pairs of doublets at
δ 3.1 and -11.9 for the major isomer (2JPP = 6 Hz) and δ
7.3 and -14.0 (2JPP = 10 Hz) for the minor isomer. The 1H
NMR spectrum of 5 shows four multiplets (integration of
one proton each) centered at 4.97, 4.74, 4.60, and 4.31,
respectively, corresponding to four inequivalent methylene
protons of the DIM ligand.
Figure 2. POV-Ray view of 5 showing the labeling of the atoms
around the Ir atom. Displacement ellipsoids are drawn at the 50%
level. Hydrogens and the anions SbF6 have been removed for
clarity.
f -
The (BAr4 ) salt (BArf4- = B(3,5-(CF3)2C6H3)4) of
[Ir(CO)(Me)(DIM)((R)-(þ)-BINAP)]2þ is obtained quan-
titatively by the reaction of 5 with NaBAr4f in dichloro-
methane (eq 2). This salt is denoted as 6. The 31P{1H}
NMR spectrum of 6 shows the same chemical shifts and
diastereomeric ratio as those of 5. The 19F{1H} NMR
spectrum of 6 also exhibits a singlet peak at δ -63.2,
confirming the presence of the BAr4f- counteranion.
Yellow crystals of one of the diastereomers of 5 suitable
for X-ray diffraction were obtained by slow diffusion
of hexanes into a concentrated dichloromethane solution
of 5 at room temperature. Crystallographic data collec-
tion and refinement parameters are shown in Table 1,
and complete structural details may be found in the
CIF supplied in the Supporting Information. A POV-
Ray drawing of the structure of 5 is shown in Figure 2
with selected bond distances and angles given in
Table 3.
-
ligand, whereas in 4b the methyl ligand is cis to the two
phosphines.
Initial Catalytic Studies of [Ir(CO)(Me)(DIM)((R)-(þ)-
BINAP)]2þ in 5 and 6. The electrophilic behavior and
catalytic activity of the Ir(III) cation in 5 were examined
using previously employed substrates for the Nazarov
cyclization and the Diels-Alder reaction. For the Nazarov
cyclization, the reaction with substrate 7a proceeded
rapidly (<5 min at room temperature (rt)) using only
2 mol % of 5 leading to product 7b, as shown in eq 3.
The product was identified by 1H NMR spectroscopy that
showed it to have the same spectrum as that previously
reported for 7b by Frontier et al.6b This initial success
stimulated studies described below with substrates cap-
able of generating quarternary C centers upon Nazarov
cyclization.
In the crystal structure of 5, the iridium(III) center adopts a
distorted octahedral coordination geometry, defined by two
phosphorus atoms of (R)-(þ)-BINAP, two oxygen atoms of
DIM, a carbonyl, and the methyl ligand. The coordination
geometry is necessarily chiral at iridium as a consequence
of the two bidentate ligands. The six-membered chelate ring
formed by the DIM ligand possesses a boat conforma-
tion, which is similar to that observed in the complex
and
18
[Cu(S,S-t-Bu-box)-((MeO2C)2CdCH(Ph))][SbF6]2
in the dppe analogue of 5.4b The bond distance of Ir(1)-P(1)
(2.443(2) A) is significantly longer than that of Ir(1)-P(2)
(2.307(1) A), consistent with the larger trans structural
˚
Catalysis of the Diels-Alder reaction was alsoexamined
using either isoprene (8) or 2,3-dimethylbutadiene (9) and
methacrolein (10) asthedienophile. Bothof these reactions
proceeded rapidly and were complete in less than 5 min
(eqs 4 and 5). The products 11 and 12 were identified by 1H
NMR spectroscopy and comparison of the observed reso-
nances with literature values. However, for the Diels-
Alder product obtained with 2,3-dimethylbutadiene,
further reaction was observed that is consistent with the
˚
influence of CO compared to the carbonyl oxygen of DIM.
Finally, we note a structural difference between 4b and 5 in
the relative positions of the CO and methyl ligands. In 5 the
carbonyl is cis to the two phosphines of the (R)-(þ)-BINAP
(18) Evans, D. A.; Rovis, T.; Kozlowski, M. C.; Downey, C. W.; Tedrow,
J. S. J. Am. Soc. Chem. 2000, 122, 9134.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4335
˚
Table 3. Selected Bond Lengths (A) and Angles (deg) of [Ir(CO)(Me)-
(DIM)(R-(þ)-BINAP)][SbF6]2, 5
˚
Bond Length (A)
Ir(1)-P(1)
Ir(1)-C(1)
Ir(1)-O(2)
C(1)-O(1)
2.443(2)
1.861(6)
2.130(4)
1.111(7)
Ir(1)-P(2)
Ir(1)-C(2)
Ir(1)-O(3)
2.307(1)
2.138(7)
2.125(4)
Bond Angle (deg)
P(1)-Ir(1)-P(2)
P(2)-Ir(1)-C(2)
O(2)-Ir(1)-O(3)
C(2)-Ir(1)-P(1)
O(1)-C(1)-Ir(1)
94.14(5)
92.1(2)
83.6(2)
172.2(2)
176.8(5)
P(1)-Ir(1)-O(2)
C(2)-Ir(1)-O(2)
O(2)-Ir(1)-P(2)
O(3)-Ir(1)-C(1)
93.0(1)
81.0(2)
172.6(1)
173.6(2)
significant electrophilicity of the Ir(III) cation [Ir(CO)-
(Me)(DIM)((R)-(þ)-BINAP)]2þ. Specifically, the alde-
hyde resonance of product 12 was observed to diminish
over time and disappeared completely after 5 h at ambient
temperature. As that resonance decreased in intensity,
three methyl resonances, two singlets, and one doublet
were observedto grow in asshown inFigure 3. The identity
of the new product was established based on an earlier
report by Baldwin and Lusch who observed essentially the
same change using SnCl4 as the Lewis acid.19 The mechan-
ism proposed by Baldwin, which is shown in Scheme 2,
yields the bicyclic ketone 13 as the final product and relies
on the considerable electrophilicity of the SnCl4 catalyst to
promote the rearrangement. The observation of 13 as the
final product in the reaction catalyzed by 5 supports the
notion of [Ir(CO)(Me)(DIM)((R)-(þ)-BINAP)]2þ as highly
electrophilic. The fact that the same rearrangement is not
seen when isoprene is used supports the carbocation nature
of the rearrangement.
Figure 3. 1H NMR spectra showing the conversion of 12 to 13 overtime
in CD2Cl2.
Scheme 2
with rapid E-Z interconversion of the substrate followed
by electrocyclization of the Z substrate. The results of
different runs are summarized in Table 4. It was found that
the catalytic activities of 5 and 6 are comparable to that of
1. In each product, a quarternary center is created at the C1
position upon Nazarov cyclization. As seen previously,
cyclization of substrates with aryl substituents at the C5
position (see Table 4 equation for substrate position
numbering) occurs more rapidly than with alkyl substi-
tuents at that position.
Catalysis of spirocycle formation for the substrate 2a
by the Ir(III) complexes is also seen to occur, as shown in
Table 5. For a dilute solution (5 mM) of 2a in dichloro-
methane, reaction with 10% mol of the Ir(III) dppe
dication 1 yields the Nazarov product 2b in 48% isolated
yield while the spirocycle product 2c is found to form in
only 9% yield. However, when the amount of 1 is
increased to stoichiometric (1:1 catalyst:substrate), the
spirocycle product 2c forms in 61% yield while 2b is
obtained in just ∼6% yield. In earlier studies by Huang
and Frontier,9 the formation of spirocycle 2c had been
reported in reactions with Cu(OTf)2 and Cu(SbF6)2 and
became selective for the spirocycle product when the
Cu(II) salts were present in stoichiometric amounts
relative to 2a. With the Ir(III) salts 5 and 6 as the catalysts,
the formation of 2c also increases with greater amounts
of the catalyst, but only leads to a product ratio of 2c/2b
of ∼ 1:1 ratio when stoichiomeric amounts of 5 or 6 are
used.
Nazarov Cyclization Catalysis Leading to Quarternary
Carbon Generation and Spirocycle Formation. β-Keto-
ester alkylidene substrates having a methyl substituent
at the C1 position were next chosen for Nazarov cycliza-
tion and possible spirocycle formation. It was thus found
that when a mixture of E and Z diastereomers of these
substrates is treated with catalytic amounts of the Ir(III)
catalyst 1, 5, or 6 (10% mol), a single diastereomer from
Nazarov cyclization is isolated as the product with the
configuration corresponding to a conrotatory cycliza-
tion of the Z isomer. This observation is in agree-
ment with results reported previously using the same
substrates in the presence of Cu(OTf)2.6a The fact that
only a single diastereomeric product forms is consistent
In previous studies, it had been reported that the
addition of simple salts to catalytic Nazarov reactions
(19) Baldwin, J. E.; Lusch, M. J. J. Org. Chem. 1979, 44, 1923.

4336 Inorganic Chemistry, Vol. 49, No. 9, 2010
Atesin et al.
Table 4. Nazarov Cyclizations Leading to Quarternary Carbon Formation
a Reaction conditions: substrate (5 mM) and catalyst (0.5 mM) in dichloromethane. b Isolated yield. c In 1,2-dichloroethane; TMP = 2,4,6-
trimethoxyphenyl; PMP = 4-methoxyphenyl; PNP= 4 -nitrophenyl.
f
affected the yield and rates of cyclization. For example,
stoichiomeric amounts of LiClO4 were found to be essen-
tial for efficient cyclization of heteroaryl vinyl ketones
with Sc(OTf)3 or In(OTf)3 as the catalyst,7 and in a recent
report, addition of AgSbF6 to solutions containing
[IrBr(CO)((R)-(þ)-BINAP)(DIM)][SbF6]2 as the cata-
lyst, which significantly enhanced that Ir(III) catalyst’s
activity.20 Therefore, a study was undertaken to deter-
mine the effect of different additives on the relative rates
and product distributions of 2c and 2b using the Ir(III)
complexes 1, 5, or 6 as electrophilic catalysts. The results
of this study are shown in Table 6.
carried out in the presence of 1 equiv of NaBAr4 in
dichloromethane, spirocycle product 2c is obtained in
78% yield accompanied by 2b in 14% yield. Similarly, 2c
is obtained as the major product with catalysts 5 and 6 in
75% and 80% yield, respectively, with 2b as the minor
product in yields of 13% and 12% (Table 6, entries 3 and
6). Control experiments show that Nazarov cyclization of
f
2a does not occur with 1 equiv of NaBAr4 in the absence
of the Ir(III) complex, nor does spirocycle formation take
place when the Nazarov product 2b is treated with
NaBAr4 .
f
f
When the amount of NaBAr4 is reduced to 0.5 equiv of
In contrast with the product ratio obtained in the
reaction of 2a with 10 mol % 1 that yielded 48% 2b and
9% 2c (entry 1 in Table 5), when the same reaction is
2a and the reaction carried out under the same conditions,
the yield of 2c decreases to 66% while that of 2b increases
to 22% (Table 6, entry 5). Moreover, when 15-crown-5,
which is known to complex Naþ, is added to the reaction
along with NaBAr4 , formation of spirocycle 2c decreases
further to a 25% yield while that of the Nazarov product
f
(20) Vaidya, T.; Atesin, A. C.; Herrick, I. R.; Frontier, A. J.; Eisenberg, R.
Angew. Chemie., Int. Ed., in press.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4337
Table 5. Formation of 2b and 2c Catalyzed by Ir(III) Complexes 1, 5, and 6
entry
catalyst (mol)
time (h)
temp. (°C)
yield of 2b (%)/(ee)
yield of 2c (%)/(ee)
ratio 2b/2c
1
2
3
4
5
6
1 (10%)
1 (100%)
5 (10%)
5 (100%)
6 (10%)
6 (100%)
4
4
4
12
4
22
22
22
22
22
22
48
6
62
9
61
13
42
5.6/1
1/11
4.8/1
1/1.3
7.9/1
1/1.4
32
51 /(15% ee)
17 /(15% ee)
7 /(6%ee)
24 /(4%ee)
4
Table 6. Effects of Additives on Formation of 2b and 2c Catalyzed by 6a
catalyst
(10 mol %)
temperature
(°C)
yield of
2b (%)
yield
of 2c (%)
ratio
2b/2c
entry
additive (mol)
solvent
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
time (h)
1
2
3
4
5
6
7
1
none
NaBAr4f (100%)
NaBAr4f (100%)
NaBAr4f (100%)
none
4
6
4
4
4
4
4
22
22
22
22
22
22
22
13
0
12
51
22
78
0
75
7
66
1/6
5
6
6
6
6
1/6.3
7.9/1
1/3
1/6.1
2.9/1
NaBAr4f (50%)
NaBAr4f (100%)
NaBAr4f (100%) þ
15-crown-5 (100%)
NaBAr4f (100%)
NaBAr4f (100%)
KBAr4f (100%)
ZnCl2 (100%)
13 /(7% ee)
72
80 /(6% ee)
25
8
9
6
6
6
6
6
6
6
6
CH3NO2
CH2Cl2 /ether(3/1)
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
4
2
22
22
22
22
22
22
22
22
0
70
0
15
0
4.6/1
1/3
10
11
12
13
14
15
2.5
1.5
1.5
4
1.5
1.5
24 /(8% ee)
16
19 /(8% ee)
6
77
66
75 /(6% ee)
59
74 /(6% ee)
68
16
15
1/3.8
1/3.8
1/11
4.9/1
4.5/1
ZnBr2 (100%)
ZnI2 (100%)
Mg(OTf)2 (100%)
TlPF6 (100%)
a Reaction conditions catalyst (10 mol %), 2a (5 mM), catalyst (0.5 mM) and additive (s) (5 mM) in dichloromethane.
2b grows to 72% yield (Table 6, entry 7). These observa-
tions support the notion that Naþ influences the relative
selectivity for formation of 2b and 2c, which in turn leads
to the hypothesis that binding of Naþ to carbonyl oxygen
atoms of 2a influences positively the formation of 2c. We
hypothesize that by Naþ coordination, overall carbonyl
oxygen basicity is reduced for proton abstraction to
complete the Nazarov cyclization sequence, thus favoring
the Wagner-Meerwein rearrangement to give 2c. This
notion is further supported by the observation that in
solvents containing carbonyl O atoms, the formation of
2c is not observed (Table 6, entries 8 and 9). Use of
intact (eq 6). Likewise, when 2c was dissolved in dichloro-
methane (5 mM) in the presence of 6 (0.5 mM) and
NaBAr4 (5 mM) at room temperature, no 2b was seen
after 24 h and 2c was recovered quantitatively (eq 7).
These results indicate that any change in the ratios of
Nazarov-to-spirocycle products must occur during the
catalytic cycle and not subsequent to product elimination.
f
f
KBAr4 and ZnX2 (where X = Cl, Br, I) as additives also
leads to predominant formation of 2c (60-75% yield),
whereas addition of Mg(OTf)2 or TlPF6 to the reaction
system affords Nazarov product 2b as the major product
(66-77% yield) (Table 6, entries 10 to 15). As with
f
NaBAr4 , control experiments reveal that none of these
additives is found to promote the cyclization of 2a in the
absence of the iridium(III) complexes (1, 5, or 6).
To determine whether 2b and 2c interconvert under the
reaction conditions used for their formation, 2b was
dissolved in dichloromethane (5 mM) in the presence of
f
the Ir(III) catalyst 6 (0.5 mM) and NaBAr4 (5 mM) at
room temperature. However, after 24 h only 5% conver-
sion to 2c was observed while 95% of 2b was recovered
The basis of spirocycle formation has been put forward
previously9 and is outlined in Scheme 3. Catalysis of

4338 Inorganic Chemistry, Vol. 49, No. 9, 2010
Atesin et al.
Scheme 3
Nazarov cyclization by electrophilic complexes proceeds
by initial coordination that activates the substrate to the
4π conrotatory electrocyclization. Once 5-membered ring
closure is achieved, the subsequent steps involve proton
loss adjacent to the carbocation center and subsequent
proton addition elsewhere in the molecule. The branch
point to spirocycle formation exists when, following
electrocyclization, proton loss is slow or inhibited. Under
that condition, a ring contraction can occur yielding a
spirocyclic carbocation. The migrating ability of the
hydrogen atom (as hydride) or the R substituent on the
C atom adjacent to the cationic carbon then determines
the specific spirocycle that is produced, following disso-
ciation of the catalyst-product complex.
alkylidene β-ketoesters with aryl, alkyl, and cinnamyl
substitutents at the C5 position were examined using 6 as
the catalyst and 1 equiv of NaBAr4 (Table 4). For
f
substrate 2a having a 2,4,6-trimethoxyphenyl substituent,
the spirocycle product that forms in 80% yield has the
2,4,6-trimethoxyphenyl (TMP) substituent remaining
bound to the C5 carbon. No evidence is seen in this
reaction of aryl group migration. However, in the corre-
sponding reaction with substrate 14a in which the C5
substituent is 4-methoxyphenyl (PMP), the spirocycle
formed in 48% yield corresponds to the one in which only
the PMP group has migrated. In this case, no evidence is
observed in support of the isomeric spirocycle in which
hydride migration occurs.
The observations described above indicate that in
catalytic amounts, the Ir(III) cationic complexes are
unable to bind to all carbonyl functionality on reactants
and products to inhibit facile proton loss so that Nazarov
cyclization is the result of the catalysis. However, when
the catalyst is present in stoichiometric amounts or other
Lewis acids are added to the reaction system to bind all
available carbonyl groups on substrates and products,
then proton loss from the cyclized Nazarov intermediate
is inhibited, at which point Wagner-Meerwein ring con-
traction to form a more stable intermediate becomes
competitive. The use of NaBAr4f as an effective additive
to the reaction for spirocycle formation takes advantage
of the modest but significant Lewis acidity of Naþ and the
When substrate 15a or 16a is heated in 1,2-dichloro-
ethane with 10% mol of 6 and 1 equiv of NaBAr4 , the
f
only spirocycle product is 15c or 16c, respectively, with no
evidence of isomeric 15d or 16d, respectively. These
results are consistent only with a hydride shift from C5
to C1 leading to the spirocycle product in 45% or 60%
yield, respectively. Finally, the cinnamyl-containing sub-
strates 17a and 18a when reacted with 6 and 1 equiv of
f
NaBAr4 yield 17b and 18b as the major products in 43%
and 35% yields, respectively. With regard to the spiro-
cycle products for these substrates, yields are poor (14%
and 13%, respectively), but products 17d and 18d indicate
that the migration of the cinnamyl group from C5 to C1
occurs. If the reaction with 17a and 18a is conducted using
f-
f
non-coordinating and non-basic behavior of the BAr4
anion.
6 but without 1 equiv of NaBAr4 as additive, only the
Nazarov product is seen (Table 4). The migration ten-
dencies for the C5 substituents in spirocycle formation
that are seen in the present study are in full agreement
with the previously published work that employed a
stoichiometric amount of [Cu(bisoxazoline)](SbF6)2 as
the catalyst.9
Results Regarding Asymmetric Induction. While the
cationic complex [Ir(CO)(Me)(DIM)((R)-(þ)-BINAP)]2þ
in 5 and 6 is chiral, the use of either salt to promote the
conversion of 2a to 2b and 2c yielded results in which
A final series of studies regarding spirocycle formation
was conducted in which the substituent at the C5 position
of the Nazarov substrate was varied tosee whether or not it
migrated to the substrate C1 position during spirocycle
formation. Previously, Huang and Frontier9 had found
that the migration tendency of alkyl, aryl, and cinnamyl
substituents at the C5 position differed, with only the aryl
group migrating to give a product having two adjacent
quarternary centers. In the studies reported here, different

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4339
f 21
f 22
product enantiomeric excesses were less than 15%. The basis
for this poor enantioselectivity is likely unselective binding of
the substrate carbonyl oxygen atoms to the two adjacent but
inequivalent binding sites at the iridium center, similar to
what has been observed previously at lower temperatures by
1H NMR spectroscopy regarding Nazarov substrate binding
to complex 1.4b These studies showed that the Nazarov
divinyl β-ketoester substrates chelated to the iridium(III)
center through the two carbonyl oxygen atoms, and because
of the inequivalence of the two Ir binding sites, two substrate-
catalyst diastereomers were observed with little preference for
one diastereomer over the other (shown as 19 and 20). This
meant that even if the chirality at the Ir(III) center was
sufficient to control the direction of conrotation in the
Nazarov electrocyclization, unselective substrate binding
would lead to poor enantioselectivity.
Ir(CO)I(R)-(þ)-BINAP),15 NaBAr4 , and KBAr4
were
synthesized according to the published procedures. Known
Nazarov substrates (2a, 7a, 14a-18a) were prepared and char-
acterized as reported before.6a,9 All solvents (dichloromethane,
tetrahydrofuran (THF), toluene, hexanes, and diethyl ether) were
purified and dried under nitrogen by conventional methods.23
Dichloromethane-d2 and benzene-d6 were purchased from Cam-
bridge Isotope Laboratories, degassed and stored in a dry glovebox
prior to use. 1H NMR, 31P{1H} NMR, and 13C{1H} NMR spectra
were recorded on either a Bruker Avance 400 MHz or a Bruker
Avance 500 MHz spectrometer. H and 13C{1H} chemical shifts
1
are reported in parts per million after referencing to the appro-
priate solvent resonances. 31P{1H} chemical shifts are reported
relative to an external 85% solution of phosphoric acid. Elemental
analyses were done at Quantitatives Technologies Inc. (QTI) or
Desert Analystic Inc. X-ray crystal structures were obtained using
a Bruker SMART APEX II CCD Platform diffractometer, solved
using SIR97, and refined with SHELXL-97.
Synthesis of IrI2(CO)(Me)((R)-(þ)-BINAP), 4. The complex
Ir(CO)I((R)-(þ)-BINAP) (100 mg, 0.103 mmol) was dissolved
in MeI (10 mL) and the solution was stirred at room temperature
for 3 h. The color of the solution turned from dark red to yellow.
After removal of the solvent to half its amount (5 mL), diethyl ether
(20 mL) was added slowly to precipitate a yellow solid, which was
filtered, washed with diethyl ether (3 ꢀ 1.5 mL), and dried under
vacuum. A mixture of 4a and 4b was obtained (0.098 g, 85% yield).
The 31P{1H} NMR spectrum of the yellow solid in CD2Cl2 shows
the presence of 4a and 4b in a ratio of 2:1. Anal. Calcd for C46H35
I2IrOP2: C, 49.70, H, 3.17. Found: C, 50.01, H, 3.05.
1
4a: H NMR (CD2Cl2, ppm): δ 8.50-6.00 (32 H, m, over-
lapping naphthyl and aryl H), 2.15 (dd, 3H, JPH = 3.5 Hz, 5.4
Hz, CH3); 31P{1H} (CD2Cl2, ppm): δ -25.59 (d, JPP = 20.9 Hz,
1P), -30.78 (d, JPP = 20.9 Hz, 1P).
1
4b: H NMR (CD2Cl2, ppm): δ 8.50-6.00 (32 H, m, over-
Conclusions
lapping naphthyl and aryl H), 1.24 (dd, 3H, JPH = 4.3 Hz, 6.0
Hz, CH3); 31P{1H} (CD2Cl2, ppm): δ -23.01 (d, JPP = 23.5 Hz,
1P), -26.56 (d, JPP = 23.5 Hz, 1P).
The synthesis and catalytic activity of the new elec-
trophilic dicationic complex [Ir(CO)(Me)(DIM)((R)-(þ)-
BINAP)]2þ which has been isolated as its SbF6- salt 5 and
Synthesis of [Ir(CO)(Me)(DIM)((R)-(þ)-BINAP)][SbF6]2, 5.
Into an oven-dried round-bottom flask was placed a mixture of
diastereomers 4a and 4b (in a 2:1 ratio) (100 mg, 0.090 mmol),
and DIM (90 μL, 0.45 mmol) in CH2Cl2 (50 mL). AgSbF6 was
then added to the rapidly stirred solution followed by 5 mL of
CH2Cl2. After 5 min of stirring in the dark, the resulting AgI
precipitate was removed by filtration, and the yellow filtrate was
concentrated under vacuum to about 5 mL. Diethyl ether (20
mL) was then added slowly to yield a yellow solid. This yellow
solid was filtered and washed with diethyl ether (3 ꢀ 1.5 mL). A
mixture of two diastereomers of 5 was obtained (0.098 g, 85%
yield) in a ratio of 9:1 as determined by 31P{1H} NMR spec-
troscopy. Anal. Calcd for C56H51F12IrO6P2Sb2: C, 43.97, H,
3.36. Found: C, 43.83, H, 3.30.
f-
BAr4 salt 6 have been described. The structure of the
cationic complex has been confirmed crystallographically,
and its strong electrophilic nature coupled with the weak
binding ability of diethyl isopropylidenemalonate makes
the iridium(III) center of 5 or 6 a strong Lewis acid catalyst
for polarized Nazarov cyclizations and the Diels-Alder
cycloaddition reaction. A carbocation rearrangement of
the Diels-Alder product formed between methacrolein
and 2,3-dimethylbutadiene that has previously been re-
ported supports the notion of the high degree of Lewis
acidity for the Ir(III) cation [Ir(CO)(Me)(DIM)((R)-(þ)-
BINAP)]2þ. Catalysis of the Nazarov cyclization using 5
or 6 with substrates capable of generating a quarternary center
upon ring closure proceeds readily along with minor amounts
of a spirocyclic product. However, through the addition of
metal salts to the reaction solutions, the ratio of Nazarov to
spirocycle products are found to be adjustable with a stoichio-
Major Isomer. 1H NMR (CD2Cl2, ppm): δ 8.20-6.10 (32H,
m, overlapping naphthyl and aryl H), 4.97 (m, 1H, CH3-
CH2O), 4.74 (m, 1H, CH3-CH2O), 4.60 (m, 1H, CH3-CH2O),
4.31 (m, 1H, CH3-CH2O), 2.33 (s, 3H, CH3(CH3)C=), 2.02 (s,
3H, CH3(CH3)C=), 1.55 (t, JHH = 7.5 Hz, CH3-CH2O), 1.35 (t,
3H, JHH = 7.5 Hz, CH3-CH2O), 1.01 (dd, 3H, JPH = 3.5 Hz, 5.4
Hz, CH3); 31P{1H} (CD2Cl2, ppm): δ 3.10 (d, JPP = 6.3 Hz, 1P),
-11.92 (d, JPP = 6.3 Hz, 1P).
f
metric amount of NaBAr4 being particularly effective in
biasing the system to spirocycle formation.
Minor Isomer. 1H NMR (CD2Cl2, ppm): All the signals were
overlapped with major isomer which could not be identified.
31P {1H} (CD2Cl2, ppm): δ 7.34 (d, JPP = 10.1 Hz, 1P), -14.04
(d, JPP = 10.1 Hz, 1P).
Experimental Section
General Methods. Unless otherwise stated, all the reac-
tions and manipulations were performed in oven-dried glass-
ware under purified nitrogen atmosphere using either stan-
dard Schlenk techniques or an inert-atmosphere glove-
f
Synthesis of [Ir(CO)(Me)(DIM)((R)-(þ)-BINAP)][BAr4 ]2, 6.
To an oven-dried round-bottom flask was added complex 5
(126 mg, 0.082 mmol) in CH2Cl2 (20 mL). NaBAr4 (153 mg,
f
box. [n-Bu4N][Ir(CO)2I2],16 [IrMe(CO)(dppe)(DIB)](BAr4 )2,2
f
(23) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. G.; Timmers, F. J.
Organometallics 1996, 15, 1518.
(21) Yakelis, N. A.; Bergman, R. G. Organometallics 2005, 24, 3579.
(22) Buschmann, W. E.; Miller, J. S. Inorg. Synth. 2002, 33, 83.

4340 Inorganic Chemistry, Vol. 49, No. 9, 2010
Atesin et al.
0.173 mmol) was then added to the rapidly stirred solution
followed by 2 mL of CH2Cl2. After stirring at room temperature
for 1 h, the mixture was filtered, and the yellow filtrate was
concentrated under vacuum to about 4 mL. Hexanes (20 mL)
were then added slowly. The yellow oil thus formed was
decanted from the solvent, dissolved in CH2Cl2 (2 mL), and
filtered through a pad of Celite to remove small amounts of
NaSbF6. Upon addition of hexanes (10 mL) to the filtrate, a
yellow oil formed, which was separated from the solvent and
stirred in hexanes (10 mL) to yield a yellow solid, that was
filtered, washed with hexanes (3 ꢀ 1 mL), and dried under
vacuum for several hours. The yellow solid 6 was obtained in 220
mg (97%). The 31P{1H} NMR spectrum of 6 shows the same
signals as did 5 with the same ratio of the isomers. The 19F{1H}
NMR spectrum of 6 shows a strong signal of δ at -63.2
1H NMR and MS data are given below for the different
products detected in the catalytic reactions. All of these com-
pounds, except for 15c, have been reported previously in the
literature, and references to their initial reports are cited.
Methyl 5-(2-furyl)-7-oxo-2,3,4,5,6,7-hexahydrocyclopenta-[b]-
pyran-6-carboxylate (7b).6b 1H NMR(400 MHz, CDCl3) δ 1.94
(m, 2H), 2.19 (m, 1H), 2.27 (m, 1H), 3.52 (d, J = 2 Hz, 1H, 3.76
(s, 3H), 4.13 (m, 2H), 4.35 (d, J = 2 Hz, 1H), 6.17 (d, J = 3.2 Hz,
1H), 6.31 (t, J = 1.2 Hz, 1H), 7.33 (d, J = 1.2 Hz, 1H); 13C{1H}
(CDCl3, 100 MHz) δ 21.1, 22.2, 40.8, 52.8, 55.6, 66.9, 107.2, 110.3,
142.4, 144.7, 149.4, 151.7, 168.4, 192.0. Elemental Analysis Calcd.
for C14H14O5: C, 64.12%, H, 5.38%; Found: C, 64.00%, H,
5.51%.
f
corresponding to the BAr4 anion. This complex was used
directly without further characterization.
General Procedures for Catalytic Reactions Involving Ir(III)
Complexes 1, 5, and 6. (a) In a glovebox, a J-Young tube was
charged with catalyst complex 1, 5, or 6 (0.005 mmol) and the
particular substrate (0.05 mmol) in CD2Cl2 (0.7 mL) and was
sealed with a Teflon cap. The J-Young tube was then brought to
the desired temperature, and the ensuing reaction was monitored
1,4-Dimethyl-3-cyclohexene-1-carboxaldehyde (11).24 1H NMR
(CD2Cl2, ppm): δ 9.51 (s, 1H), 5.45 (m, 1H), 2.44-2.30 (m, 1H),
2.08-1.98 (m, 2H), 1.96-1.81 (m, 2H), 1.52 (bs, 3H), 1.57
(m, 1H), 1.09 (s, 3H); MS (e/z) 138.11.
1
by H NMR spectroscopy. Each experiment was repeated two
times. The product was purified by flash column chromato-
1
graphy on silica gel and confirmed by its H NMR spectrum
relative to that reported previously for known Nazarov cyclization
products.
(b) In a glovebox, a dried 20 mL vial was charged with 6 (0.005
mmol), a substrate (0.05 mmol), and an additive (0.05 mmol)
if examined (Table 6) in CH2Cl2 (10 mL) or 1, 2-dichloro-
ethane and sealed with a Teflon cap. The solution was stirred
at room temperature or higher for several hours (shown in
Table 6), and the ensuing reaction was monitored by thin layer
chromatography. After the substrate was consumed, the solu-
tion was taken to dryness and the residue was passed through a
small silica gel column to remove the metal complex. The
organic products were collected and confirmed by their 1H
NMR data as compared to reported known samples. The yields
of the Nazarov products were estimated by comparison of their
1H NMR resonances using mesitylene (10 μL) as an internal
standard. Each experiment was repeated two times.
1,3,4-Trimethyl-3-cyclohexene-1-carbaldehyde (12).25 1H NMR
(CD2Cl2, ppm): δ 9.42 (s, 1H), 2.28-2.18 (m, 1H), 2.00-1.93 (m,
2H), 1.76 (m, 2H), 1.64 (bs, 3H), 1.60 (bs, 3H), 1.44 (m, 1H), 1.00
(s, 3H); MS (e/z) 152.13.
1,3-exo-4-Trimethylbicyclo[2.2.l]heptan-2-one (13).19 1H NMR
(CD2Cl2, ppm): δ 1.84 (q, 1H, J = 7.1 Hz), 1.67-1.54
(m, 1H), 1.46-1.38 (m, 2H), 1.37-1.32 (m, 2H), 1.31-1.24
(m, 1H), 1.15 (s, 3H), 1.10 (s, 3H), 0.96 (d, 3H, J = 7.2 Hz); MS
(e/z) 152.12.
(c) In a glovebox, a dried 20 mL vial was charged with 6 (0.005
mmol), substrate 2c (0.05 mmol), and NaBAr4f (0.05 mmol) in
CH2Cl2 (10 mL) and sealed with a Teflon cap. The solution was
stirred at room temperature for 24 h, and the resulting solution
was monitored by thin layer chromatography. No 2b was seen to
form after 24 h.
(d) In a glovebox, a dried 20 mL vial was charged with 6 (0.005
mmol), substrate 2b (0.05 mmol), and NaBAr4f (0.05 mmol) in
CH2Cl2 (10 mL) and sealed with a Teflon cap. The solution was
stirred at room temperature for 24 h, and the resulting solution
was monitored by thin layer chromatography. The solution was
then taken to dryness, and the residue was passed through a
small silica gel column to remove any metal complexes. The
organic products were collected and confirmed by their 1H
NMR data as compared to reported samples. The yield of the
Methyl 3a-Methyl-1-oxo-3-(2,4,6-trimethoxyl-phenyl)-2,3,3a,
4,5,6-hexahydro-1H-indene-2-carboxylate Ester (2b).6b 1H
NMR (400 MHz, CDCl3): δ 6.74 (t, J = 4 Hz, 1H), 6.15
(s, 2H), 4.90 (d, J = 13.2 Hz, 1H), 4.05 (d, J = 13.2 Hz, 1H),
3.81 (s, 3H), 3.77 (s, 6H), 3.66 (s, 3H), 2.21 (m, 2H), 1.63-1.71
(m, 4H), 1.24 (s, 3H), 13C{1H} (CDCl3, 100 MHz): δ 200.0,
170.6, 159.9, 144.8, 134.4, 105.9, 91.5, 55.1, 52.1, 45.6, 41.9,
34.1, 25.5, 20.6, 18.1.
1
2c (5%) was obtained by comparing its H NMR resonances
against mesitylene (10 μL) as an internal standard. Each experi-
ment was repeated twice.
(e) In a glovebox, a dried 20 mL vial was charged with a
substrate (0.05 mmol) and an additive (0.05 mmol) in CH2Cl2
(10 mL) or 1,2-dichloroethane and sealed with a Teflon cap. The
solution was stirred at room temperature or higher for a
specified time (the reaction conditions are the same as the entries
in Table 6, but without the catalyst), and the resulting reaction
was monitored by thin layer chromatography. Neither Nazarov
cyclization product nor spirocycle product was observed to
form in these control reactions.
Methyl 3-(4-Methoxy-phenyl)-3a-methyl-1-oxo-2,3,3a4,5,6-
hexahydro-1H-indene-2-carboxylate (14b).6a 1H NMR (400
MHz, CDCl3): δ 0.80 (s, 3 H), 1.51 (m, 1 H), 1.67 (m, 1 H),
(24) Roberston, J.; Fowler, T. G. Org. Biomol. Chem. 2006, 4, 4307.
(25) Teo, Y.; Loh, T. Org. Lett. 2005, 7, 2539.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4341
1.85 (m, 2 H), 2.29 (m, 1 H), 2.35 (m, 1H), 3.44 (d, 1H, J = 13.1
Hz), 3.70 (s, 3H), 3.82 (s, 3H), 3.92 (d, 1H, J = 13.1 Hz), 6.84 (t,
1H, J = 3.6 Hz), 6.90 (d, 2H, J = 8.8 Hz), 7.18 (d, 2H, J = 8.8
Hz); 13C{1H} NMR (100 MHz, CDCl3): δ 17.9, 20.3, 25.4, 34.5,
40.6, 52.4, 54.9, 55.2, 56.2, 113.7, 128.2, 129.1, 135.4, 144.5,
158.7, 169.8, 197.8; HRMS calculated for C19H22O4 (MþH)þ:
315.1591, Found: 315.1594.
J = 8.6 Hz), 6.55 (d, 1H, J = 15.7 Hz), 7.02 (t, 1H, J = 3.6 Hz),
7.33 (m, 5H); 13C{1H} NMR (100 MHz, CDCl3): δ 18.6, 24.8,
27.3, 28.3, 38.4, 45.9, 52.3, 52.8, 58.0, 125.4, 126.2, 127.5, 128.4,
133.9, 136.6, 139.8, 146.5, 169.7, 198.0; HRMS calculated for
C21H24O3 (MþH)þ: 325.1798, Found: 325.1799.
Methyl 4-Methyl-1-oxo-3-(2,4,6-trimethoxy)phenylspiro[4,4]non-
2-ene-2-carboxylate (2c).9 1H NMR (400 MHz, CDCl3) δ: 0.89
(d, 3H, J = 7.2 Hz), 1.64-1.68 (m, 4H), 1.67-1.86 (m, 4H), 3.29
(q, 1H, J = 7.2 Hz), 3.65 (s, 3H), 3.72 (s, 6H), 3.82 (s, 3H), 6.12
(s, 2H); 13C{1H} NMR (100 MHz, CDCl3) (ppm): δ 15.99,
25.33, 25.39, 30.72, 40.17, 48.25, 51.39, 55.33, 55.63, 59.56,
90.64, 105.64, 131.89, 157.87, 162.48, 164.25, 178.48, 207.94;
HRMS (ESI) for [C21H27O6]þ Calcd: 375.1802, Found:
375.1802.
Methyl 3-(4-Nitrophenyl)-3a-methyl-1-oxo-2,3,3a,4,5,6-hexa-
hydro-1H-indene-2-carboxylate (15b).6a 1H NMR (400 MHz,
CDCl3): δ 0.81 (s, 3 H), 1.69 (m, 4 H), 2.31 (m, 2 H), 3.60 (d, 1H,
J = 12.8 Hz), 3.71 (s, 3H), 3.98 (d, 1H, J = 12.8 Hz), 6.88 (t, 1H,
J = 3.6 Hz), 7.43 (d, 2H, J = 8.8 Hz), 8.22 (d, 2H, J = 8.8 Hz);
13C{1H} NMR (100 MHz, CDCl3): δ 17.9, 20.6, 25.4, 34.6, 40.9,
52.8, 55.4, 55.8, 123.7, 129.0, 136.6, 143.5, 144.3, 147.3, 169.1,
196.6; HRMS calculated for C18H20NO5 (MþH)þ: 330.1341,
Found: 330.1337.
Methyl 4-(4-Methoxyphenyl)-4-methyl-1-oxo-spiro[4,4]non-
2-ene-2-carboxylate (14d).9 1H NMR (400 MHz, CDCl3): δ
0.87 (m, 1H), 1.23 (m, 1H), 1.34 (m, 1H), 1.47 (s, 3H), 1.57 (m,
2H), 1.75 (m, 1H), 1.85 (m, 1H), 1.95 (m,1H), 3.78 (s, 3H), 3.85
(s, 3H), 6.85 (d, 2H, J = 7.2 Hz), 7.06 (d, 2H, J = 7.2 Hz), 8.37
(s, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ (ppm): 24.29,
25.00, 25.22, 30.89, 36.08, 51.65, 52.09, 55.26, 66.15, 113.88,
128.20, 132.65, 134.00, 158.61, 162.86, 175.85, 207.10; HRMS
(ESI) for [C19H23O4]þ Calcd. 315.1591, Found 375.1589.
Methyl 3a-Methyl-1-oxo-3-propyl-2,3,3a,4,5,6-hexahydro-
1H-indene-2-carboxylate (16b).6a 1H NMR (400 MHz, CDCl3):
δ 0.94 (t, 3H, J = 7.2 Hz), 0.99 (s, 3H), 1.33 (m, 2H), 1.35 (m,
2H), 1.45 (m, 1H), 1.79 (m, 2H), 1.98 (m, 1H), 2.21 (m, 2H), 2.31
(m, 1H), 3.15 (d, 1H, J = 11.9 Hz), 3.77 (s, 3H), 6.70 (t, 1H, J =
3.6 Hz); 13C{1H} NMR (100 MHz, CDCl3): δ 14.4, 18.1, 19.7,
21.4, 25.3, 32.1, 34.8, 39.2, 50.0, 58.8, 134.2, 145.2, 171.1, 199.5;
HRMS calculated for C15H22O3 (MþNa)þ: 273.1461, Found:
273.1463.
Methyl 4-Methyl-3-(4-nitrophenyl)spiro[4,4]non-2-ene-2-car-
boxylate (15c). 1H NMR (400 MHz, CD2Cl2): δ 1.00 (d, 3H,
JHH = 7.2 Hz), 1.69-1.78 (m, 4H), 1.86-1.96 (m, 4H), 3.14
(q, 1H, JHH = 7.2 Hz), 3.66 (s, 3H), 7.56 (d, 2H, JHH = 8.8 Hz),
8.29 (d, 2H, JHH = 8.8 Hz); 13C{1H} NMR (100 MHz, CD2Cl2)
(ppm): δ 16.3, 25.46, 30.05, 30.91, 41.00, 49.29, 52.46, 60.28,
124.09, 128.67, 133.40, 141.13, 148.89, 164.31, 175.95, 207.00;
IR(thin film): 2960, 1739, 1728, 1596, 1521, 1347, 1270; HRMS
calculated for C18H20NO5 (MþH)þ: 330.1341, Found: 300.1330:
Methyl 3a-Methyl-1-oxo-3-styryl-2,3,3a,4,5,6-hexahydro-
1H-indene-2-carboxylate (17b).6a 1H NMR (400 MHz, CDCl3):
δ 1.08 (s, 3 H), 1.37 (m, 1H), 1.82 (m, 2H), 1.97 (m, 2H), 2.36 (m,
2H), 2.99 (dd, 1H, J1 = 12.2 Hz, J2 = 8.0 Hz), 3.56 (d, 1H, J =
12.2 Hz), 3.77 (s, 3H), 6.24 (dd, 1H, J1 = 15.8 Hz, J= 8.0 Hz), 6.54
(d, 1H, J = 15.8 Hz), 6.80 (t, 1H, J = 3.6 Hz), 7.27 (d, 2H,
J = 6.5 Hz), 7.35 (d, 2H, J = 6.5 Hz); 13C{1H} NMR (100 MHz,
CDCl3): δ 17.8, 20.5, 25.3, 34.3, 40.3, 52.3, 53.8, 57.2, 125.7, 126.2,
127.5, 128.4, 133.0, 135.1, 136.1, 144.2, 169.7, 198.0; HRMS
calculated for C20H22O3 (MþH)þ: 311.1642, Found: 311.1632.
Methyl 4-Methyl-1-oxo-3-propylspiro[4,4]non-2-ene-2-carboxy-
late (16c).9 1H NMR (400 MHz, CDCl3) δ (ppm): 0.97 (t, 3H,
J = 7.5 Hz), 1.09 (d, 3H, J = 7.5 Hz), 1.39-1.44 (m, 1H), 1.45-
1.55 (m, 1H), 1.54-1.64 (m, 4H), 1.78-1.86 (m, 4H), 2.40-2.44
(m, 1H), 2.61 (q, 1H, J = 7.2 Hz), 2.97-3.00 (m, 1H), 3.82 (s, 3H);
13C{1H} NMR (100 MHz, CDCl3) (ppm): δ 14.22, 15.83, 21.14,
25.05, 25.25, 30.22, 31.89, 40.45, 48.12, 51.74, 59.52, 129.89, 164.24,
Methyl 3a-Methyl-1-oxo-3-styryl-1,2,3,3a,4,5,6,7-octahydro-
azulene-2-carboxylic Methyl Ester (18b).6a 1H NMR (400 MHz,
CDCl3): δ 1.13 (s, 3 H), 1.47 (m, 4H), 1.98 (m, 2H), 2.30 (m, 1 H),
2.51 (m, 1H), 3.45 (dd, 1H, J1 = 8.6 Hz, J2 = 8.6 Hz), 3.55
(d, 1H, J = 16.1 Hz), 3.75 (s, 3H), 6.18 (dd, 1H, J1 = 8.6 Hz,

4342 Inorganic Chemistry, Vol. 49, No. 9, 2010
Atesin et al.
189.76, 207.41; HRMS (ESI) for [C15H23O3]þ Calcd: 251.1642,
Found: 251.1644.
regions of reciprocal space were surveyed for each sample: four
major sections of frames were collected with 0.50° steps in ω at
four different j settings and a detector position of -33° in 2θ.
The intensity data were corrected for absorption,27 and final
cell constants were calculated from the xyz centroids of ap-
proximately 4000 strong reflections from the actual data
collection after integration.28 Structures were solved using
SIR9729 and refined using SHELXL-97.30 Space groups were
determined based on systematic absences, intensity statistics,
and Cambridge Structural Database frequencies.31 Direct-
methods solutions were calculated which provided most non-
hydrogen atoms from the difference Fourier map. Full-matrix
least-squares (on F2)/difference Fourier cycles were performed
which located the remaining non-hydrogen atoms. Non-hy-
drogen atoms were refined with anisotropic displacement
parameters, and hydrogen atoms were placed in ideal positions
and refined as riding atoms with relative isotropic displace-
ment parameters. All refinements were run to mathematical
convergence.
Methyl 4-Methyl-1-oxo-4-[(E)-2-phenylvinyl]spiro[4,4]non-2-
ene-2-carboxylate (17d).9 1HNMR (400 MHz, CDCl3) (ppm):
δ 1.32 (s, 3H), 1.50-1.86 (m, 8H), 3.85 (s, 3H), 6.01 (d, 1H, J =
16.0 Hz), 6.31 (d, 1H, J = 16.0 Hz), 7.28-7.34 (m, 5H), 8.19 (s,
1H). 13C {1H}NMR (100 MHz, CDCl3): δ: 22.70, 24.67, 24.94,
32.18, 34.39, 50.41, 52.05, 65.49, 126.24, 127.86, 128.65, 130.28,
132.07, 133.03, 136.44, 162.72, 174.57, 206.31; HRMS (ESI) for
[C20H23O3]þ Calcd: 311.1642, Found: 311.1648.
Structure 4b is a pentane and dichloromethane solvate. In
structure 5 the atoms of the cation and one SbF6 anion lie in
general positions, while the second anion has two independent
positions coincident with crystallographic 2-fold axes. While
the co-crystallized dichloromethane solvent of 5 could be
located and modeled, the n-hexane solvent was found highly
disordered in channels and had to be removed from the model
using program PLATON, function SQUEEZE,32 which deter-
Methyl 4-Methyl-1-oxo-4-[(E)-2-phenylvinyl]spiro[4,5]dec-2-
ene-2-carboxylate (18d).9 1H NMR (400 MHz, CDCl3) δ
(ppm): 1.20-1.95 (m, 10 H), 1.31 (s, 3H), 3.87 (s, 3H), 6.09 (d,
1H, J = 16.0 Hz), 6.24 (d, 1H, J = 16.0 Hz), 7.31-7.33 (m, 5H),
8.12 (s, 1H); 13C{1H} NMR (100 MHz, CDCl3) (ppm): δ 22.05,
22.11, 22.57, 25.58, 30.20, 32.67, 51.78, 52.07, 56.83, 126.27,
127.86, 128.70, 129.00, 130.10, 132.47, 136.54, 162.87, 173.55,
206.43; HRMS (ESI) for [C21H25O3]þ Calcd: 325.1798, Found:
325.1794.
3
˚
mined there to be 418 electrons in 5207 A removed per unit
cell.
Acknowledgment. The authors thank the National Science
Foundation (Grants CHE-0556225 and CHE-0847851) for
support of this work.
Supporting Information Available: X-ray crystallographic
data of 4b and 5 in CIF format. This material is available free
of charge via the Internet at http://pubs.acs.org.
€
(27) Sheldrick, G. M. SADABS, version 2008/1; University of Gottingen:
Crystal Structure Determinations. Each crystal was placed
onto the tip of a glass fiber and mounted on a Bruker SMART
Platform diffractometer equipped with an APEX II CCD area
detector. All data were collected at 100.0(1) K using MoKR
radiation (graphite monochromator).26 Data collections were
carried out with frame exposure times of 20 (4b) and 60 (5)
seconds at a detector distance of 5 cm. Randomly oriented
€
Gottingen, Germany, 2008.
(28) SAINT, version 7.60A; Bruker AXS: Madison, WI, 2003.
(29) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. SIR97: A new program for solving and refining crystal structures; Istituto di
Cristallografia, CNR: Bari, Italy, 1999.
(30) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
(31) Allen, F. Acta Crystallogr. 2002, B58, 380.
(32) Spek, A. L. PLATON: A multipurpose crystallographic tool, version
300106; Utrecht University: Utrecht, The Netherlands, 2006.
(26) APEX2, version 1.0-22; Bruker AXS: Madison, WI, 2004.