AlMe3-promoted oxidative cyclization of η2-alkene and η2-ketone on nickel(0). Observation of intermediate in methyl transfer process

Article abstract of DOI:10.1021/ja0542486

AlMe3 can promote the oxidative cyclization of η²-alkene and η²-ketone on nickel(0) to give an intriguing nickel-aluminum dinuclear complex having a bridging methyl group, which might be an intermediate for the nickel-catalyzed cyclo

Full text of DOI:10.1021/ja0542486

Published on Web 08/23/2005
AlMe3-Promoted Oxidative Cyclization of η2-Alkene and η2-Ketone on
Nickel(0). Observation of Intermediate in Methyl Transfer Process
Sensuke Ogoshi,* Mizu Ueta, Tomoya Arai, and Hideo Kurosawa*
Department of Applied Chemistry, Faculty of Engineering, Osaka UniVersity, Suita, Osaka 565-0871, Japan
Received June 28, 2005; E-mail: ogoshi@chem.eng.osaka-u.ac.jp
Ketones and aldehydes can be employed as one of the two π
components in the nickel-catalyzed three-component coupling, with
alkylmetals as the third component (Scheme 1).1 The oxidative
cyclization on nickel(0) to give a nickelacycle intermediate was
assumed as a key step. However, so far, only scattered studies on
the oxidative cyclization on nickel(0) have been reported. Recently,
we reported a spontaneous oxidative cyclization of η2:η2-enalnickel
and the acceleration of the cyclization by the addition of Me3SiOTf
as a Lewis acid.2 Montgomery and Schlegel suggested that ZnMe2
can play a dual Lewis basic/Lewis acidic role in the nickel-catalyzed
coupling reaction of enone and alkyne with ZnMe2 based on their
experimental and computational study.3 Here, we report that AlMe3
promotes oxidative cyclization of an η2:η2-2-allylacetophenone- or
η2:η2-2-allylbenzophenone nickel complex to lead to the formation
Figure 1. Molecular structure of 2b. Cyclohexyl groups are omitted.
of a nickelahydrofuran, having a significant interaction between
nickel and an aluminum-methyl bond. Moreover, the catalytic
application of this oxidative cyclization is also reported.
Scheme 1. Nickel-Catalyzed Three-Component Coupling
Reaction
The reaction of 2-allylacetophenone (1a) or 2-allylbenzophenone
(1b) with Ni(cod)2 and PCy3 gave an η2:η2-1,5-enonenickel complex
(2a, 2b) quantitatively (Scheme 2).4 1H, 13C, and 31P NMR spectra
indicate that both CdC and CdO bonds coordinate to Ni(0) in
η2-fashion. The molecular structure of 2b was also confirmed by
the X-ray diffraction analysis, showing that all of the atoms expected
to participate in the oxidative cyclization (Ni, C1, C2, C10, O) are
on the same plane and the atom distance between C2 and C10 is
2.7 Å (Figure 1). Neither 2a nor 2b was converted into the
nickelacycle by heating at 60 °C or by addition of Me3SiOTf, which
was efficient for the oxidative cyclization of the aldehyde analogues
on nickel(0).2
Figure 2. Molecular structure of 3b. Cyclohexyl groups are omitted.
Scheme 2. AlMe3-Promoted Oxidative Cyclization
The reaction of 2a or 2b with AlMe3 in C6D6 proceeded very
rapidly to give a deep-orange solution of cyclized compound 3a or
3b (quantitative).5 Both complexes 3a and 3b could be isolated,
and the molecular structure of 3b confirmed by X-ray diffraction
analysis shows a unique nickelacycle structure having a bridging
methyl group (Figure 2; C2-C10 1.536(8) Å, Ni-C1 1.925(6) Å,
Ni-O 1.893(4) Å, Ni-C17 2.292(6) Å, Al-C17 2.037(7) Å, Al-
C18 1.970(6) Å, Al-C19 1.961(9) Å, Ni-Al 2.691(1) Å, Al-O
1.796(5) Å, <Ni-C17-Al 76.6(2)°, <Ni-O-Al 93.7(2)°). This
structure is very intriguing because the bond sequence Ni-C4-
Al-O-Ni could be regarded as a nice model for the transmeta-
lation.6 The bridging methyl group and the other two methyl groups
exchange one another very rapidly in a solution at room temperature
1
since in H NMR spectrum of 3a the only resonance of AlMe3
was observed at δ -0.89. However, three different broad resonances
for AlMe3 appeared (δ -0.15, -0.50, -2.10) at -80 °C in toluene-
d8, which is consistent with the molecular structure in the solid
state. Not only is the structural evidence for 3b relevant for
describing the role of AlMe3 in the promotion of the 2 to 3
conversion but also is the nature of 3b consistent with the role of
ZnMe2 proposed by Montgomery and Schlegel in other oxidative
cyclization processes. A molecular orbital description for a bridging
Zn-C-Ni interaction and a direct Zn-Ni interaction was provided
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J. AM. CHEM. SOC. 2005, 127, 12810-12811
10.1021/ja0542486 CCC: $30.25 © 2005 American Chemical Society

C O M M U N I C A T I O N S
Scheme 3. Formation of η3-Allylmethylnickel Complex
complex is a nice model as an intermediate in the transmetalation
process. Moreover, the cycloisomerization can proceed catalytically
in THF, which encourages us to use a simple alkene or ketone as
one component in the nickel-catalyzed multicomponent coupling
reaction. Further studies are in progress in our group.
Acknowledgment. Partial support of this work through the
Asahi Glass Foundation (S.O.), Grants-in-Aid for Scientific Re-
search from Ministry of Education, Science, and Culture, Japan,
and the Japanese Government’s Special Coordination Fund for
Promoting Science and Technology is gratefully acknowledged.
Supporting Information Available: Experimental procedures
(PDF) and crystallographic information (CIF). This material is available
free of charge via the Internet at http://pubs.acs.org.
Scheme 4. Nickel-Catalyzed Cycloisomerization
References
(1) Acetylene: (a) Oblinger, E.; Montgomery, J. J. Am. Chem. Soc. 1997,
119, 9065-9066. (b) Miller, K.; Huang, W.; Jamison, T. F. J. Am. Chem.
Soc. 2003, 125, 3442-3443. (c) Mahandru, G. M.; Liu, G.; Montgomery,
J. J. Am. Chem. Soc. 2004, 126, 3698-3699. Diene: (d) Takimoto, M.;
Hiraga, Y.; Sato, Y.; Mori, M. Tetrahedron Lett. 1998, 4543-4546. (e)
Kimura, M.; Ezoe, A.; Shibata, K.; Tamaru, Y. J. Am. Chem. Soc. 1998,
120, 4033-4034. (f) Kimura, M.; Fujimatsu, H.; Ezoe, A.; Shibata, K.;
Shimizu, M.; Matsumoto, S.; Tamaru, Y. Angew. Chem, Int. Ed. 1999,
38, 397-400. Allene: (g) Kang, S.; Yoon, S. Chem. Commun. 2002,
2634-2635. Review: (h) Montgomery, J. Angew. Chem, Int. Ed. 2004,
43, 3890-3908. Book: (i) Modern Organonickel Chemistry; Tamaru, Y.,
Eds.; Wiley-VCH: Weinheim, Germany, 2005.
in that work, and the corresponding structural features involving
AlMe3 are now documented in compound 3b.
Neither 3a nor 3b underwent further reaction in benzene, but
treatment of these with THF or pyridine resulted in intriguing
transformation involving two transmetalation steps. Thus, 6 equiv
of THF-d8 or 1 equiv of pyridine was added to a solution of 3 in
C6D6 to lead to the generation of an unexpected η3-allylnickel
complex (4a, 4b)7 concomitant with the evolution of methane gas
and insoluble white precipitates (Scheme 3). The complex 4 might
be generated via transmetalation in 3 and methane elimination to
give an intermediate A, followed by the oxidative addition of an
allyloxyaluminum unit and the second transmetalation. The treat-
ment of 4a or 4b with carbon monoxide led to the formation of
the corresponding acylated compound 5a or 5b, quantitatively.8
We conceived that the allyloxyaluminum compound might be
released from the intermediate A in Scheme 3 prior to the oxidative
addition if the starting material (1a, 1b) is present in excess to trap
the Ni(0) unit. We then found a catalytic cycloisomerization of 1,5-
enone compounds, as shown in Scheme 4. Thus, in THF, in the
presence of a catalytic amount of Ni(cod)2 and PCy3, both 1a and
1b reacted with AlMe3 to give allyl alcohols 6a and 6b, respectively,
by protonation of the reaction mixture.9 The evolution of CH4 as a
gas was observed during the reaction, and the formation of 4a was
(2) Ogoshi, S.; Oka, M.; Kurosawa, H. J. Am. Chem. Soc. 2004, 126, 11082-
11083.
(3) Hratchian, H. P.; Chowdhury, S. K.; Gutie´rrez-Garc´ıa, V. M.; Amara-
singhe, K. K. D.; Heeg, M. J.; Schlegel, H. B.; Montgomery, J.
Organometallics 2004, 23, 4636-4646.
(4) Selected spectral data for 2a: 1H NMR (C6D6) δ 1.93 (d, J ) 4.2 Hz,
3H, CH3CdO), 2.31 (dd, J ) 12.4, 6.5 Hz, 1H, -CH2-CHdCH2), 2.50
(m, 1H, -CH2-CHdCH2), 2.55 (m, 1H, -CH2-CHdCH2), 3.36 (m,
1H, -CH2-CHdCH2), 3.69 (dt, J ) 17.3, 4.9 Hz, 1H, -CH2-CHdCH2).
31P NMR (C6D6): δ 38.6 (s). 13C NMR (C6D6): δ 30.5 (s, -COCH3),
36.5 (s, -CH2CHdCH2), 49.5 (d, JCP ) 3.1 Hz, -CH2CHdCH2), 72.9
(d, JCP ) 9.1 Hz, -CH2CHdCH2), 112.1 (d, JCP ) 9.2 Hz, -COCH3).
Anal. calcd for C29H45NiOP: C, 69.75; H, 9.08. found: C, 69.71; H, 9.15.
(5) Selected spectral data for 3a: 1H NMR (C6D6) δ -0.89 (s, 9H, -Al-
(CH3)3), 0.97-1.83 (m, 39H, Cy, including 2H of -NiCH2CH- at δ 1.32
and 1.58, 1H of -NiCH2CH- at δ 1.67, and 3H of -C(CH3)OAl(CH3)3
at δ 1.74, 2.90 (dd, J ) 15.2, 7.2 Hz, 1H, -CHCH2C6H4-), 3.38 (dd,
J ) 15.4, 6.0 Hz, 1H, -CHCH2C6H4-). 31P NMR (C6D6): δ 31.8 (s).
13C NMR (C6D6): δ -13.1 (brs, Al(CH3)3), 18.7 (d, JCP ) 28.2 Hz,
-NiCH2-), 26.6 (s, -C(CH3)OAl(CH3)3, 38.8 (s, -CH2C6H4-), 59.6
(d, JCP ) 3.0 Hz, -NiCH2CH-), 91.1 (s, -C6H4C(CH3)-).
(6) Nickel(0) complexes having bridging methyl group: (a) Kaschube, W.;
Po¨rschke, K.-R.; Angermund, K.; Kru¨ger, C.; Wilke, G. Chem. Ber. 1988,
121, 1921. (b) Wilke, G. Angew. Chem., Int. Ed. Engl. 1988, 27, 185-
206.
(7) Selected spectral data for 4a: 1H NMR (toluene-d8) δ -0.70 (d, JHP
)
4.3, 3H, Ni-CH3), 0.87 (m, 3H, -C6H4CCH3), 1.00-2.09 (m, 34H,
including 1H of NiCH2-), 2.82 (brs, 1H, NiCH2-), 3.23 (d, J ) 20.3,
1H, -CH2Ar-), 3.46 (d, J ) 20.3, 1H, -CH2Ar-). 31P NMR (toluene-
d8): δ 50.2 (s). 13C NMR (toluene-d8): δ -2.9 (d, JCP ) 16.0, Ni-CH3),
14.7 (s, -C6H4CCH3), 34.9 (s, -C6H4CCH3), 41.5 (s, -CH2CCH2-),
41.6 (s, -CH2CCH2-), 88.1 (d, JCP ) 19.0 Hz, -CH2CCH2-).
(8) Selected spectral data for 5a: 1H NMR (CDCl3) δ 2.01 (t, J ) 2.4 Hz,
3H, -CdC(Ar)CH3), 2.07 (s, 3H, -COCH3), 3.25 (m, 2H, ArCH2-),
3.46 (s, 2H, -CdCCH2CO-), 7.05-7.14 (m, 4H, Ar). 13C NMR
(CDCl3): δ 10.8 (s, -CdC(Ar)CH3), 29.7 (s, -COCH3), 41.3 (s,
ArCH2-), 44.5 (s, -CdCCH2CO-), 119.0, 123.5, 124.8, 126.5, 134.0
(s, vinyl), 136.5 (s, vinyl), 142.9, 146.7, 206.5 (-CO-). HRMS calcd
for C13H14O 186.1045, found m/z 186.1045.
1
also confirmed by H NMR spectra on the reaction mixture. The
reaction might have proceeded via 3 and A. The Ni(0) complex
did not catalyze the reaction of 1a with ZnMe2, analogous to
Scheme 4 under the same condition, but the Ni(0) species was
recovered as 2a, although the addition of ZnMe2 to a solution of
2a in C6D6 at room temperature led to slow reaction to give nickel
black precipitates and an organozinc compound which gave
quantitative yield of 6a by the protonation. This zinc compound is
estimated as the corresponding allyloxy(methyl)zinc, which might
be also formed via Me2Zn-promoted oxidative cyclization of 2a
and transmetalation.
(9) Selected spectral data for 6a: 1H NMR (C6D6) δ 1.50 (s, 3H, -C6H4-
CCH3), 3.35 (s, 2H, -C6H4CH2-), 4.95 (s, 1H, H2CdC-), 5.38 (s, 1H,
H2CdC-), 6.99 (m, 1H, Ar), 7.08 (m, 2H, Ar), 7.35 (m, 1H, Ar). 13C
NMR (C6D6): δ 29.5 (-CH3), 36.3 (benzyl), 80.1 (H2CdC-), 107.6
(H2CdC-), 123.7, 124.7, 127.5, 128.4, 139.4 (-CH2C-), 149.1 (-CC-
(CH3)OH), 158.0 (-C(CH3)OH). HRMS calcd for C11H12O1 160.0888,
found m/z 160.0874.
In conclusion, we demonstrated that AlMe3 promoted the
oxidative cyclization of η2-alkene and η2-ketone on nickel(0) to
give an intriguing nickel-aluminum dinuclear complex. This
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