Direct observation of oxidative cyclization of η2-alkene and η2-aldehyde on Ni(0) center. Significant acceleration by addition of Me3SiOTf

Article abstract of DOI:10.1021/ja0460716

Direct oxidative cyclization of (η²:η²-CH₂CHCH₂C₆H₄CHO)Ni(PR₃) to form the nickelacycle and drastic acceleration of the cyclization by the addition of Me₃SiOTf were ob

Full text of DOI:10.1021/ja0460716

Published on Web 09/03/2004
Direct Observation of Oxidative Cyclization of η2-Alkene and η2-Aldehyde on
Ni(0) Center. Significant Acceleration by Addition of Me3SiOTf
Sensuke Ogoshi,* Masa-aki Oka, and Hideo Kurosawa*
Department of Applied Chemistry, Faculty of Engineering, Osaka UniVersity, Suita, Osaka 565-0871, Japan
Received July 1, 2004; E-mail: ogoshi@chem.eng.osaka-u.ac.jp
Carbonyl compounds are transformed into various organic
compounds having an oxygen functional group by transition metal-
catalyzed or -mediated reactions. Recently, nickel-catalyzed multi-
component coupling reactions involving carbonyl compounds have
received increasing attention.1a-h Among several reaction mecha-
nisms proposed for these processes, the oxidative cyclization
involving metal, CdO, and CdC (or CtC) bonds represents one
of the most often envisaged, yet never directly demonstrated, key
steps.1a-g,2 Here, we report the first direct observation of oxidative
cyclization by η2-aldehyde and η2-alkene ligands with Ni(0). More-
over, we also observed the significant acceleration of such cycli-
zation by electrophilic addition of Me3SiOTf to carbonyl oxygen,
which may have potential relevance to the course of some coupling
reactions involving carbonyl compounds and Lewis acidic sub-
strates.3
The addition of 5-hexenal or o-allylbenzaldehyde to a solution
Figure 1. Molecular structure of 2b-anti.
of Ni(cod)2 and PR3 (1 equiv) gave (η2:η2-CH2dCH(CH2)3CHO)-
Ni(PCy3) (1a) or (η2:η2-CH2dCHCH2C6H4CHO)Ni(PR3) (1b,c)
Scheme 1. Oxidative Cyclization
quantitatively (Scheme 1). The chemical shifts of vinyl and formyl
1
groups in H and 13C NMR of 1a are in much higher magnetic
fields than those of 5-hexenal, which suggests that both CdC and
CdO double bonds coordinate to the nickel(0) center.4 Heating the
solution of 1 at 60 or 80 °C resulted in oxidative cyclization to
give nickelacycle complexes (2).5 Even at room temperature for
16 h, 1c underwent oxidative cyclization in 68% yield. For 2a,
only the syn isomer was obtained, the structure of which was
determined by X-ray diffraction analysis, while 2b and 2c existed
as two isomers. The structure of 2b-anti was also confirmed by
X-ray diffraction analysis (Figure 1). Under a carbon monoxide
pressure (3 atm), a mixture of syn and anti isomers of 2b or 2c
reacted with carbon monoxide to give the corresponding lactone 3
as a sole product quantitatively concomitant with the formation of
6
Ni(CO)n(PR3)4-n
.
To the best of our knowledge, the direct
observation of oxidative cyclization from the η2-carbonyl:η2-olefin
coordination complex to five-membered metallacycle has not been
reported even with early transition metal systems. The addition of
2 equiv of PPh3 to Ni(cod)2 and o-allylbenzaldehyde did not give
1c but instead gave the η2-aldehyde bisphosphine complex (1c′).7
In contrast to 1c, 1c′ did not undergo oxidative cyclization at room
temperature for 24 h at all, which could be attributable to the failure
of simultaneous coordination of both CdC and CdO bonds to
nickel.
Scheme 2. Acceleration by Me3SiOTf
Previously, we reported that Lewis acid (e.g., Me3Al) or Me3-
SiOTf can add to the carbonyl group in enone coordinated to
palladium(0) to enhance the reactivity of the enone toward carbon
nucleophile and disilane.8 We now found the addition of 1 equiv
of Me3SiOTf to η2:η2-enal complexes 1a-c at room temperature
accelerated the cyclization significantly to give η1:η1-3-siloxypropyl
complexes (4a-c) quantitatively (Scheme 2, Figure 2).9 Without
adding Me3SiOTf, cyclization of 1 was much slower (see Scheme
1). Moreover, the reaction of 2b with Me3SiOTf proceeded only
very slowly to generate a trace of 4b at 50 °C for 2 h. These results
suggest that the Si-O bond formation takes place prior to
cyclization, presumably via attack of Me3SiOTf at the oxygen of
the η2-coordinated CdO group. To examine if Me3SiOTf reacts
with the CdO double bond coordinated to nickel(0), the reaction
t
of Me3SiOTf with RCHO (R ) Ph, Bu) under similar reaction
conditions was carried out.
9
11802 J. AM. CHEM. SOC. 2004, 126, 11802-11803
10.1021/ja0460716 CCC: $27.50 © 2004 American Chemical Society

C O M M U N I C A T I O N S
to generate a nickel-carbon bond quantitatively. The observations
in this paper suggest that any reagent having Lewis acidic character
present in the reaction medium could be a promoter for the
cyclization involving CdO and CdC double bonds coordinated to
a nickel(0) center
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.
References
(1) Acetylene: (a) Oblinger, E.; Montgomery, J.; J. Am. Chem. Soc. 1997,
119, 9065-9066. (b) Miller, K. M.; Huang, W.-S.; 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,
39, 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.
Figure 2. Molecular structure of 4b.
(2) Oxidative cyclization of CdO and CdC with Ti(II): Hewlett, D. F.;
Whitby, R. J. Chem. Commun. 1990, 1684-1686. Kablaoui, N. M.;
Buchwald, S. L. J. Am. Chem. Soc. 1995, 117, 6785-6786. Crowe, W.
E.; Rachita, M. J. J. Am. Chem. Soc. 1995, 117, 6787-6788. Quan, L.
G.; Cha, J. K. Tetrahedron Lett. 2001, 42, 8567-8569. Nickelacycles
derived from oxidative cyclization: Hoberg, H.; Peres, Y.; Kru¨ger, C.;
Tasy, Y.-H. Angew. Chem, Int. Ed. Engl. 1987, 26, 771-773. Walther,
D.; Dinjus, E.; Sieler, J.; Andersen, L.; Lindqvist, O. J. Organomet. Chem.
1984, 276, 99-107. Walther, D.; Bra¨unlich, G.; Kempe, R.; Sieler, J. J.
Organomet. Chem. 1992, 436, 109-119. Amarasinghe, K. K. D.;
Chowdhury, S. K.; Heeg, M. J.; Montgomery, J. Organometallics 2001,
20, 370-372.
(3) It was suggested that the coordination of a Lewis acidic reagent to a
carbonyl group on nickel enhances the reactivity of the carbonyl
compound.1f
Figure 3. Molecular structure of 5b.
(4) Selected spectral data for 1a. 1H NMR (C6D6): δ 0.60 (m, 1H), 0.83 (m,
1H), 0.95-2.28 (m, 36H, including 1H of -CHdCH2 at δ 2.00), 2.31 (t,
J ) 8.0 Hz, 1H, -CHdCH2), 2.46 (m, 1H, -CH2CHdCH2), 3.01 (m,
1H, -CHdCH2), 5.54 (m, 1H, -CHO). 31P NMR (C6D6): δ 38.4 (s).
Scheme 3. Addition of Me3SiOTf to η2-RCHO
13C NMR (C6D6): δ 45.8 (d, JCP ) 3.8 Hz, -CHdCH2), 68.2 (d, JCP
)
8.4 Hz, -CHdCH2). 102.9 (d, JCP ) 7.6 Hz, -CHO). Anal. Calcd for
C24H43O1P1Ni1: C, 65.92; H, 9.91. Found: C, 64.99; H, 9.64.
(5) Selected spectral data for 2b-anti: 1H NMR (C6D6): δ -0.51 (m, 1H of
-CH2Ni), 0.90-2.25 (m, 34H, including 1H of -CH2Ni at δ 1.45), 2.45
(m, 1H, -CHCH2C6H4-), 2.98 (dd, J ) 15.1 Hz, J ) 5.7 Hz, 1H,
-CH2C6H4-), 3.01 (m, 1H, -CH2C6H4), 4.55 (m, 1H, -NiCH2CHCHO-),
7.22 (d, J ) 7.6 Hz, 1H), 7.34 (t, J ) 7.0 Hz, 1H), 7.81 (t, J ) 7.3 Hz,
1H), 10.02 (d, J ) 7.3 Hz, 1H). 31P NMR (C6D6): δ 28.6 (s). Anal. Calcd
for C28H43Ni1O1P1(C6H6)0.5 C, 71.01; H, 8.84. Found: C, 70.60; H, 8.91.
(6) Similar carbonylation of titanium complexes has been reported: (a) Crowe,
W. E.; Vu, A. T. J. Am. Chem. Soc. 1996, 118, 1557-1558. (b) Kablaoui,
N. M.; Hicks, F. A.; Buchwald, S. L. J. Am. Chem. Soc. 1996, 118, 5818-
5819.
10
Treatment of (η2-PhCHO)Ni(PCy3)2 with Me3SiOTf gave
(η1:η1-Me3SiOCH(Ph))Ni(PCy3)OTf (5a) quantitatively, concomi-
tant with dissociation of PCy3 (Scheme 3).11 5a was also prepared
by the treatment of PhCHO with Me3SiOTf in the presence of
Ni(cod)2 and PCy3. Similarly to the latter method, (η1:η1-Me3-
SiOCH(tBu))Ni(PCy3)OTf (5b) was prepared, the structure of which
was confirmed by X-ray diffraction analysis (Figure 3). The
complex shows a square planar structure with the siloxymethyl
ligand generated by the electrophilic addition of Me3SiOTf to
carbonyl oxygen. An intermolecular reaction of 5a with styrene or
trimethylvinylsilane was attempted, but in vain. Presumably, the
formation of an intermediate for the cyclization having neighboring
η2-olefin and siloxymethyl ligands from 5 may have been unfavor-
able. On the other hand, the cyclization from 1 to 4 may involve
the preorganized CdC and CdO double bonds on the nickel(0)
center, which are ready to undergo the Me3SiOTf-triggered multi-
bond formation process.
(7) Selected spectral data for 1c′. 1H NMR (C6D6): δ 2.87 (brd, J ) 5.4 Hz,
2H), 3.88 (brd, J ) 14.5 Hz, 1H, -CHdCH2), 4.04 (brd, J ) 10.0 Hz,
1H, -CHdCH2), 5.11 (brm, 1H, -CHdCH2), 6.60 (brs, 1H, -CHO).
31P NMR (C6D6): δ 29.0 (brs). The olefinic proton chemical shifts in 1c′
are apparently different from those of 1c: 1H NMR (C6D6) δ 2.38 (brd,
J ) 13.0 Hz, 1H, -CHdCH2), 2.59 (brd, J ) 8.1 Hz, 1H, -CHdCH2),
2.90 (brs, 2H), 4.11 (brm, 1H, -CHdCH2), 6.80-7.10 (br, 11H, including
-CHO).
(8) Ogoshi, S.; Yoshida, T.; Nishida, T.; Morita, M.; Kurosawa, H. J. Am.
Chem. Soc. 2001, 123, 1944-1950. Ogoshi, S.; Tomiyasu, S.; Morita,
M.; Kurosawa, H. J. Am. Chem. Soc. 2002, 124, 11598-11599.
(9) Selected spectral data for 4b. 1H NMR (C6D6): 0.03 (dt, J ) 10.3 Hz,
1.5 Hz, 1H, -CH2Ni), 0.57 (s, 9H, -OSiMe3), 0.86 (t, J ) 8.9 Hz, 1H,
-CH2Ni), 1.30-1.92 (m, 34H, including 1H of -NiCH2CH- at δ 1.48),
2.67 (d, J ) 15.6 Hz, 1H, -CH2C6H4-), 2.87 (dd, J ) 15.6 Hz, 7.3 Hz,
1H, -CH2C6H4-), 4.83 (d, J ) 6.4 Hz, 1H, -CHOSiMe3), 7.20 (d, J )
7.3 Hz, 1H), 7.34 (t, J ) 7.3 Hz, 1H), 7.53 (t, J ) 7.3 Hz, 1H), 8.12 (d,
J ) 7.6 Hz, 1H). 31P NMR (C6D6): δ 32.9 (s). Anal. Calcd for C32H52F3-
Ni1O4S1Si1P1: C, 54.32; H, 7.41. Found: C, 54.08; H, 7.38.
In conclusion, we have demonstrated the formation of nickela-
cycle by the direct oxidative cyclization of (η2:η2-CH2dCHCH2-
CH2CH2CHO)Ni(PR3) or (η2:η2-o-CH2dCHCH2-C6H4CHO)-
Ni(PR3) and the drastic acceleration of cyclization by the addition
of Me3SiOTf. (η2-PhCHO)Ni(PCy3)2 also reacted with Me3SiOTf
(10) Walther, D. J. Organomet. Chem. 1980. 190, 393-401.
(11) Selected spectral data for 5a. 1H NMR (C6D6): δ 0.31 (s, 9H, -OSiMe3),
0.95-1.95 (m, 33H), 4.34 (d, JHP ) 3.5 Hz, 1H, -CHOSiMe3), 7.00 (m,
3H), 7.47 (d, JHP ) 7.3 Hz, 2H). 31P NMR (C6D6): δ 42.0 (s).
JA0460716
9
J. AM. CHEM. SOC. VOL. 126, NO. 38, 2004 11803