Isolation and characterization of a nucleophilic allylic indium reagent

Article abstract of DOI:10.1021/om900096r

Transmetalation between allylic stannanes and indium halides gave allylic indium dihalides. The bond length of In - C is 2.172 A, which is close to the reported average indium - carbon bond length. The isolated allylic indium dibro-mide with two phthalan

Full text of DOI:10.1021/om900096r

1998
Organometallics 2009, 28, 1998–2000
Isolation and Characterization of a Nucleophilic Allylic Indium
Reagent
Makoto Yasuda, Masahiko Haga, and Akio Baba*
Department of Applied Chemistry and Center for Atomic and Molecular Technologies, Graduate School of
Engineering, Osaka UniVersity, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
ReceiVed February 8, 2009
or dienes with hydroindium;5 (ii) transmetalation of a parent
Summary: Transmetalation between allylic stannanes and in-
dium halides gaVe allylic indium dihalides. The bond length of
In-C is 2.172 Å, which is close to the reported aVerage
indium-carbon bond length. The isolated allylic indium dibro-
mide with two phthalan ligands showed nucleophilicity for a
carbonyl compound.
allylic metal species with indium halides.6 Only a few reports
have proffered a structural discussion of allylic indiums. Araki
and Butsugan generated the allylic indium species using a
reductive method and considered the species as allylindium
sesquihalide3a,c or allylindium dihalide,3b by NMR spectroscopic
analysis. Chan employed a reductive method and proved the
formation of allylindium(I) in aqueous media and allylindium(I)/
allylindium dibromide in organic solvent or ionic liquid.3f,k In
the reaction system using allylstannane and InCl3, the generation
of allylic indium species via transmetalation was assumed by
observing the halostannane byproduct.6b Despite extensive
synthetic studies on allylic indium, the pure isolation and X-ray
analysis of allylic indium7 with the potential for nucleophilic
allylation have never been reported, as far as we know. Recently
a reactive propargylic indium, a system related to the allylic
indium, was investigated on the basis of X-ray crystallographic
characterization.8 The establishment of a structural discussion
of allylic indium is indispensable for the development of the
chemistry of allylic indium and, furthermore, for other related
organometallic nucleophiles. In this communication, introducing
bulky substituents and external ligands realized the isolation of
an allylic indium compound from the corresponding stannane
with indium trihalide. Herein, we describe its structural analysis
on the basis of X-ray crystallography and reactivity of the
isolated allylic indium species.
Reactions of allylic indium species have been extensively
studied in recent years, in particular for the alkylation of
carbonyl compounds.1 A number of reports have appeared
regarding stereoselective reactions and aqueous media reactions
using allylic indium species.2 The methods used to generate
allylic indium can be classified into two types: (i) a reductive
process using either allylic halides with low-valent indium3,4
* To whom correspondence should be addressed. E-mail: baba@
chem.eng.osaka-u.ac.jp.
(1) Auge´, J.; Germain, N. L.; Uziel, J. Synthesis 2007, 1739–1764.
(2) (a) Li, C. J. Chem. ReV. 1993, 93, 2023–2035. (b) Li, C. J.
Tetrahedron 1996, 52, 5643–5668. (c) Loh, T. P.; Chua, G. L. Chem.
Commun. 2006, 2739–2749.
(3) Examples using organo halides with low-valent indium species: (a)
Araki, S.; Ito, H.; Butsugan, Y. J. Org. Chem. 1988, 53, 1833–1835. (b)
Araki, S.; Ito, H.; Katsumura, N.; Butsugan, Y. J. Organomet. Chem. 1989,
369, 291–296. (c) Araki, S.; Shimizu, T.; Johar, P. S.; Jin, S.; Butsugan, Y.
J. Org. Chem. 1991, 56, 2538–2542. (d) Li, C. J.; Chan, T. H. Tetrahedron
Lett. 1991, 32, 7017–7020. (e) Kim, E.; Gordon, D. M.; Schmid, W.;
Whitesides, G. M. J. Org. Chem. 1993, 58, 5500–5507. (f) Isaac, M. B.;
Chan, T. H. Tetrahedron Lett. 1995, 36, 8957–8960. (g) Paquette, L. A.;
Rothhaar, R. R. J. Org. Chem. 1999, 64, 217–224. (h) Chan, T. H.; Yang,
Y. J. Am. Chem. Soc. 1999, 121, 3228–3229. (i) Loh, T. P.; Tan, K. T.;
Hu, Q.-Y. Tetrahedron Lett. 2001, 42, 8705–8708. (j) Huang, J. M.; Xu,
K. C.; Loh, T. P. Synthesis 2003, 755–764. (k) Tan, K. T.; Chng, S. S.;
Cheng, H.-S.; Loh, T. P. J. Am. Chem. Soc. 2003, 125, 2958–2963. (l)
Min, J. H.; Jung, S. Y.; Wu, B.; Oh, T. J.; Lah, M. S.; Koo, S. Org. Lett.
2006, 8, 1459–1462. (m) Law, M. C.; Cheung, T. W.; Wong, K. Y.; Chan,
T. H. J. Org. Chem. 2007, 72, 923–929. (n) Yadav, J. S.; Reddy, B. V. S.;
Vishnumurthy, P.; Biswas, S. K. Tetrahedron Lett. 2007, 48, 6641–6643.
(o) Babu, S. A.; Yasuda, M.; Baba, A. J. Org. Chem. 2007, 72, 10264–
10267. (p) Tan, K. L.; Jacobsen, E. N. Angew. Chem., Int. Ed. 2007, 46,
1315–1317. (q) Colombo, F.; Cravotto, G.; Palmisano, G.; Penoni, A.; Sisti,
M. Eur. J. Org. Chem. 2008, 2801–2807. (r) Hirashita, T.; Daikoku, Y.;
Osaki, H.; Ogura, M.; Araki, S. Tetrahedron Lett. 2008, 49, 5411–5413.
(4) Examples using organo halides with low-valent indium mediated
by other metals: (a) Li, X. R.; Loh, T. P. Tetrahedron: Asymmetry 1996, 7,
1535–1538. (b) Araki, S.; Kamei, T.; Hirashita, T.; Yamaura, H.; Kawai,
M. Org. Lett. 2000, 2, 847–849. (c) Anwar, U.; Grigg, R.; Rasparini, M.;
Savic, V.; Sridharan, V. Chem. Commun. 2000, 645–646. (d) Anwar, U.;
Grigg, R.; Sridharan, V. Chem. Commun. 2000, 933–934. (e) Takemoto,
Y.; Anzai, M.; Yanada, R.; Fujii, N.; Ohno, H.; Ibuka, T. Tetrahedron Lett.
2001, 42, 1725–1728. (f) Anzai, M.; Yanada, R.; Fujii, N.; Ohno, H.; Ibuka,
T.; Takemoto, Y. Tetrahedron 2002, 58, 5231–5239. (g) Kang, S. K.; Lee,
S. W.; Jung, J.; Lim, Y. J. Org. Chem. 2002, 67, 4367–4379. (h) Araki, S.;
Kambe, S.; Kameda, K.; Kirashita, T. Synthesis 2003, 751–754. (i) Cooper,
I. R.; Grigg, R.; MacLachlan, W. S.; Sridharan, V.; Thornton-Pett, M.
Tetrahedron Lett. 2003, 44, 403–405. (j) Miyabe, H.; Yamaoka, Y.; Naito,
T.; Takemoto, Y. J. Org. Chem. 2004, 69, 1415–1418. (k) Grigg, R.;
Blacker, J.; Kilner, C.; McCaffrey, S.; Savic, V. Tetrahedron 2008, 64,
8177–8181. (l) Cleghorn, L. A. T.; Grigg, R.; Savic, V.; Simic, M.
Tetrahedron 2008, 64, 8731–8737.
We chose a transmetalation method to investigate an allylic
indium species, because the method would simply give the
desired allylic indium and a reductive method could generate
two types of species.3 The mixture of allyltributylstannane (1a)
with either InCl3 or InBr3 was examined in acetonitrile. The
NMR spectra of the mixture showed halostannane but no allylic
signals, perhaps because the generated allylindium species was
unstable. Changing the solvent to THF, which was expected to
stabilize the indium species by coordination, gave a reasonable
NMR spectrum. The formation of halostannane and the appear-
ance of allylic signals without satellites by 119Sn coupling
indirectly proved the generation of an allylindium species (see
the Supporting Information). The substituted allylic stannane
(5) (a) Hayashi, N.; Honda, H.; Yasuda, M.; Shibata, I.; Baba, A. Org.
Lett. 2006, 8, 4553–4556. (b) Hayashi, N.; Honda, H.; Shibata, I.; Yasuda,
M.; Baba, A. Synlett 2008, 1407–1411.
(6) (a) Marshall, J. A.; Hinkle, K. W. J. Org. Chem. 1995, 60, 1920–
1921. (b) Yasuda, M.; Miyai, T.; Shibata, I.; Baba, A. Tetrahedron Lett.
1995, 36, 9497–9500. (c) Marshall, J. A. Chem. ReV. 1996, 96, 31–47. (d)
Inoue, K.; Shimizu, Y.; Shiata, I.; Baba, A. Synlett 2001, 1659–1661. (e)
Donnelly, S.; Thomas, E. J.; Arnott, E. A. Chem. Commun. 2003, 1460–
1461.
(7) A dinuclear complex of allylindium including a PInPIn core was
reported, but its nucleophilicity was not discussed: Culp, R. D.; Cowley,
A. H.; Decken, A.; Jones, R. A. Inorg. Chem. 1997, 36, 5165–5172.
(8) Xu, B.; Mashuta, M. S.; Hammond, G. B. Angew. Chem., Int. Ed.
2006, 45, 7265–7267.
10.1021/om900096r CCC: $40.75
2009 American Chemical Society
Publication on Web 03/12/2009

Communications
Organometallics, Vol. 28, No. 7, 2009 1999
Scheme 1. Generation and Isolation of Allylic Indium
cinnamyltributylstannane (1b) also showed similar results, even
in an acetonitrile solvent. Although evaporation of the volatiles
of the mixture unfortunately led to the decomposition of the
allylic indium species, the addition of external ligands stabilized
the active allylic indium species and enabled the isolation of a
sample that, when solidified,9 was appropriate for X-ray analysis.
After various combinations of allylic stannanes, indium halides,
external ligands, and solvents were examined, the use of 1c, a
new type of allylic stannane, and InBr3 and phthalan in
acetonitrile successfully isolated the allylic indium species
(Scheme 1). The allylic stannane 1c, bearing bulky substituents
(tert-butylphenyl) at the γ-position, was mixed with InBr3 in
acetonitrile to quantitatively give Bu3SnBr, as confirmed by
NMR. Allylic signals corresponding to the allylic indium species
2 were also observed (2.20 ppm, InCH2, CD3CN). After the
addition of 3 equiv of phthalan (1,3-dihydroisobenzofuran )
L) to the mixture, removing the volatiles gave a yellow viscous
oil, which was then mixed with hexane to give two layers. The
upper layer (hexane layer) was pipetted out to remove the
byproduct Bu3SnBr. The yellow residue was cooled to -25 °C
to be solidified. The obtained solid was washed with hexane to
give a pale yellow solid, which was confirmed to be the allylic
indium species 3 (29% isolated) without contamination by a
tin residue. The NMR spectrum in CDCl3 showed allylic protons
at 2.53 ppm. The spectrum also showed that 2 equiv of phthalan
was included as ligands, because the signals of its methylenes
(8H) appeared at a lower chemical shift (5.20 ppm) as compared
with that of free phthalan (5.10 ppm). It is noted that this pure-
isolation experiment first clarified the precise structure around
indium, including ligand (or sometimes solvent) coordination
that is often neglected.
A suitable crystal for X-ray analysis was obtained after
recrystallization of 3 from acetonitrile at -25 °C to give 4. The
ORTEP drawing of 4 is shown in Figure 1. One of the ligands
was exchanged from phthalan to acetonitrile after recrystalli-
zation. Indium has a trigonal-bipyramidal coordination sphere
with two bromines and an allylic group in the equatorial plane
and two ligands, phthalan and acetonitrile, in axial positions.
The sum of the bond angles in the equatorial plane is 359.7°
(Br(1)-In(1)-Br(2) ) 112.64(5)°, Br(2)-In(1)-C(1) )
122.4(3)°, C(1)-In(1)-Br(1) ) 124.7(3)°). Two axial ligands
and indium are in a small bent line (O(1)-In(1)-N(1) )
169.7(3)°). The bond length of In-C(1) is 2.172(12) Å, which
is close to the reported average indium-carbon bond length
(2.184 Å).
Figure 1. ORTEP drawing of allylic indium dibromide 4 (all
hydrogens and solvent are omitted for clarity). Selected bond lengths
(Å): In(1)-C(1) ) 2.172(12), C(1)-C(2) ) 1.481(15), C(2)-C(3)
) 1.299(14), C(3)-C(4) ) 1.518(16), C(3)-C(14) ) 1.502(14),
In(1)-Br(1) ) 2.5031(15), In(1)-Br(2) ) 2.5179(14), In(1)-O(1)
) 2.429(7), In(1)-N(1) ) 2.362(9). Selected bond angles (deg):
Br(1)-In(1)-Br(2) ) 112.64(5), Br(2)-In(1)-C(1) ) 122.4(3),
C(1)-In(1)-Br(1) ) 124.7(3), O(1)-In(1)-N(1) ) 169.7(3).
Scheme 2. Ligand Exchange on Allylic Indium
appeared at the chemical shifts corresponding to its free form
(see the Supporting Information). These results suggest that the
ligand exchange on indium readily occurred from phthalan to
acetonitrile, giving the doubly acetonitrile coordinated allylic
indium 2 as shown in Scheme 2. It was found that the species
2 observed in Scheme 1 was also the doubly acetonitrile
coordinated one. During the recrystallization process, compound
4, bearing phthalan and acetonitrile, was crystallized.
The isolated allylic indium 3 was mixed with benzaldehyde
in dichloromethane at room temperature for 2 h and gave the
homoallylic alcohol 5 in 15% yield through carbon-carbon
bond formation in a SE2′ manner (eq 1). Surprisingly, complex
3 still has the potential for nucleophilic attack, in spite of the
bulky substituents that should retard the addition of allylic
indium 3 to a carbonyl compound. The use of acetonitrile as a
solvent, in which acetonitrile coordinates to the indium center
in situ, also gave the same level of yield. This fact indicates
that phthalan provides minimal stabilization for the species. As
a practical method, we also employed the reaction system
starting from the allylic stannane 1c/InBr3/benzaldehyde in
acetonitrile. It gave the product 5 in 12% yield, which was
similar to the result of eq 1.
The direct observation of compound 4 in solution by NMR
studies was not successful because the obtained sample amount
was too small. Instead, the isolated compound 3 in CD3CN was
investigated using 1H NMR. The results showed chemical shifts
that were almost the same as those of 2 in CD3CN, as described
in Scheme 1. Additionally, the signals of the phthalan moiety
(9) Yasuda, M.; Kiyokawa, K.; Osaki, K.; Baba, A. Organometallics
2009, 28, 132–139.

2000 Organometallics, Vol. 28, No. 7, 2009
Communications
In summary, the allylic indium dibromide complex was
isolated in a pure form and analyzed by X-ray crystallography.
The indium center has trigonal-bipyramidal coordination ge-
ometry with two external ligands. This study will help develop
indium-mediated synthetic chemistry based on structural modi-
fication. A structural analysis of the allylic indium species
generated by a reductive system3 is now under investigation.
20036036, “Synergistic Effects for Creation of Functional
Molecules”) and for Scientific Research (No. 19550038) from
the Ministry of Education, Culture, Sports, Science and
Technology of Japan. We thank Dr. Nobuko Kanehisa for
valuable advice regarding X-ray crystallography.
Supporting Information Available: Text, figures, tables, and
a CIF file giving experimental procedures and X-ray data for 4.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Acknowledgment. This work was supported by a Grant-
in-Aid for Scientific Research on Priority Areas (No.
18065015, “Chemistry of Concerto Catalysis”, and No.
OM900096R