Synthesis, structure, and reactivity of a η3-1-hydroxyallyl complex: Protonation of an α,β-unsaturated carbonyl compound bound to palladium(0) and platinum(0)

Article abstract of DOI:10.1021/ja0361042

The direct addition of a proton to a carbonyl oxygen in an η²-enone complex of palladium and platinum led to the quantitative formation of η³-1-hydroxyallyl complexes of palladium and platinum, of which X-ray diffraction analysis sho

Full text of DOI:10.1021/ja0361042

Published on Web 07/08/2003
Synthesis, Structure, and Reactivity of a η3-1-Hydroxyallyl Complex:
Protonation of an r,â-Unsaturated Carbonyl Compound Bound to
Palladium(0) and Platinum(0)
Sensuke Ogoshi,* Masaki Morita, and Hideo Kurosawa*
Department of Applied Chemistry, Faculty of Engineering, Osaka UniVersity, Suita, Osaka 565-0871, Japan
Received May 13, 2003; E-mail: ogoshi@chem.eng.osaka-u.ac.jp
Although η3-allyl transition metal complexes have been well
Scheme 1
studied, only a limited number of η3-hydroxyallyl complexes have
been reported.1 The potential of η3-hydroxyallyl complexes for
organic synthesis appears very high, because an appropriate
transformation of η3-hydroxyallyl complex would allow us to
introduce a C3 unit bearing oxygen into organic products. So far,
only η3-2-hydroxyallyl complexes have been investigated as a
Scheme 2
derivative of oxatrimethylenemethane (OTMM) complexes, in
which the reversible interconversion between η2-OTMM and η3-
2-hydroxyallyl complexes by addition or abstraction of a proton
has been reported (Scheme 1).1c On the other hand, the regioisomer,
η3-1-hydroxyallyl complex, has not been reported yet.2 In view of
the reaction of η2-enonepalladium complexes with Lewis acid to
give zwitterionic η3-1-metalloxyallylpalladium complexes,3 an
Scheme 3
attractive route to η3-1-hydroxyallyl complexes is the addition of
a proton to η2-enone complexes (Scheme 2). However, a proton
could also undergo electrophilic addition at the metal center to
generate a metal hydride complex, as in the reaction of Pd-
(PMePh2)2(CH2dCHPh) with HCl to give Pd(H)(Cl)(PMePh2)2.4
If hydride is formed, there would be little chance for the formation
of η3-1-hydroxyallyl complex, because the hydride and enone would
give â-ketoalkyl and η3-oxaallyl complexes, as suggested by van
Leeuwen and co-workers (Scheme 3).5 For the development of new
η3-allylmetal chemistry, it seems of fundamental value to examine
how efficiently the method of Scheme 2 works. We describe the
synthesis, structure, and reactivity of η3-1-hydroxyallyl complexes
1b is normal as in the η3-allylpalladium complex, while it is
of palladium and platinum. Moreover, we propose the isomerization
path from η3-1-hydroxyallyl to â-ketoalkyl via tautomerization in
an η1-allyl coordination mode.
somewhat longer in 1c (2.73 Å).8 However, the latter is much
shorter than that in the η2-enonepalladium complex,3 which indicates
significant contribution of the η3-1-hydroxyallyl structure to 1c.
The relatively short distance between the two oxygen atoms in the
carbonyl group and TfO- (2.91 Å for 1b, 2.70 Å for 1c) suggests
the existence of a hydrogen bond. This hydrogen bond would
lengthen the bond between palladium and carbonyl carbon. The
The reaction of η2-enonepalladium complex with TfOH gave a
palladium complex (1a-c) having expected composition in el-
emental analysis (eq 1).6 The 1H, 31P, and 13C NMR spectra indicate
that these complexes have an η3-hydroxyallyl structure or an
intermediate structure between an η3-hydroxyallyl and a proton
coordinated η2-enone structure.3 1a does not transform into its
isomers, â-ketoalkylpalladium 3a or η3-oxaallylpalladium 4a (M
) Pd, L2 ) DPPF in Scheme 3). These complexes 3a and 4a were
reported to undergo mutual isomerization at room temperature via
the insertion of methylvinyl ketone (MVK) into hydridopalladium
species formed by the â-H elimination (Scheme 3).5 During such
interconversion, there was no indication of the formation of η3-1-
hydroxyallyl complex. Moreover, neither 3a nor 4a was observed
in the reaction of Pd(dppf)(mvk) with TfOH. Thus, η3-1-hydroxy-
allyl complexes would not have been formed via hydride palladium
species but via the direct addition of a proton to the carbonyl oxygen
of the coordinated enone.
-
corresponding complex having B(C6F5)4 as a counteranion (1c′:
major/minor ) 65/35) prepared by the treatment of 1b with LiB-
(C6F5)4 shows the larger P-P coupling constant, probably due to
the stronger Pd-C3 bond9 caused by a weaker hydrogen bond
involving B(C6F5)4-. Addition of pyridine (1 equiv) to the solution
of 1b in CD2Cl2 led to the formation of a mixture of (η2-acrolein)-
Pd(PPh3)2 and 1b (56/44), which indicates that the pKa value for
1b is very close to that of pyridine‚H+ (pKa ) 5.22). For
comparison, the pKa of (η3-2-hydroxyallyl)Pd(PPh3)2 in aqueous
MeOH is ca. 7.1c
The analogous η3-1-hydroxyallylplatinum complexes 2a, 2b, and
2c were also prepared by the same method. Complexes 2a and 2c
isomerized slowly to the corresponding â-ketoalkylplatinum com-
plexes (5a, 5c) at room temperature (Scheme 4),10 although complex
2b did not undergo isomerization under the same condition. The
spontaneous isomerization may proceed via an η1-1-hydroxyallyl
The structure of 1b and 1c, determined by X-ray diffraction
analysis, is consistent with the anticipated structure (Figures 1 and
2).7 The complex 1b is the first example of the η3-1-hydroxyallyl
transition metal complex. The Pd-C3 bond distance (2.29 Å) in
9
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J. AM. CHEM. SOC. 2003, 125, 9020-9021
10.1021/ja0361042 CCC: $25.00 © 2003 American Chemical Society

C O M M U N I C A T I O N S
allylpalladium complex did not undergo isomerization to the
corresponding â-ketoalkyl palladium complex. On the other hand,
the η3-1-hydroxyallylplatinum complex isomerized to the corre-
sponding â-ketoalkyl complex, in which tautomerization would
occur in the η1-allyl coordination mode.
Acknowledgment. Partial support of this work through the
Tokuyama Science Foundation (S.O.), Grants-in-Aid for Scientific
Research from the Ministry of Education, Science, and Culture,
Japan, and the Japanese Government’s Special Coordination Fund
for Promoting Science and Technology is gratefully acknowledged.
Figure 1. Molecular structure of 1b.
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) (a) Frey, M.; Jenny, T. A.; Stoeckli-Evans, H. Organometallics 1990, 9,
1806-1812. (b) Frey, M.; Jenny, T. A. J. Organomet. Chem. 1991, 421,
257-264. (c) Ohsuka, A.; Fujimori, T.; Hirao, T.; Kurosawa, H.; Ikeda,
I. J. Chem. Soc., Chem. Commun. 1993, 1039-1040. (d) Huang, T.-M.;
Hsu, R.-H.; Yang, C.-S.; Chen, J.-T.; Lee, G.-H.; Wang, Y. Organome-
tallics 1994, 13, 3657-3663. (e) Hsu, R.-H.; Chen, J.-T.; Lee, G.-H.;
Wang, Y. Organometallics 1997, 16, 1159-1166.
(2) (a) η3-1-Hydroxyallylnickel complex had been described very briefly
without details: Jolly, P. W.; Wilke, G. In The Organic Chemistry of
Nickel; Jolly, P. W., Wilke, G., Eds.; Academic Press: New York, 1974;
Vol. 1, pp 329-401. (b) Protonation of oxygen in (η4-quinone)M(cod)
(M ) Pd, Pt) had been reported with no evidence for η3-hydroxyallyl
formation. Pd: Grennberg, H.; Gogoll, A.; Ba¨ckvall, J.-E. Organometallics
1993, 12, 1790-1793. Pt: Chetcut, M. J.; Howard, J. A. K.; Pfeffer, M.;
Spercer, J. E.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1981, 276-
283.
Figure 2. Molecular structure of 1c.
Scheme 4. Spontaneous Isomerization
(3) Ogoshi, S.; Yoshida, T.; Nishida, T.; Morita, M.; Kurosawa, H. J. Am.
Chem. Soc. 2001, 123, 1944-1950.
(4) Ozawa, F.; Ito, T.; Nakamura, Y.; Yamamoto, A. J. Organomet. Chem.
1979, 168, 375-391.
(5) Zudeveld, M. A.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.; Klusener,
P. A. A.; Stil, H. A.; Roobeek, C. F. J. Am. Chem. Soc. 1998, 120, 7977-
7978.
(6) General procedure for 1b: To a solution of Pd(CH2dCHCHO)(PPh3)2
(119.3 mg, 0.1736 mmol) in 5 mL of THF was added 15.3 µL of TfOH
(26.1 mg, 0.1741 mmol) at room temperature, and the solution color
changed from pale yellow to orange. The reaction mixture was concen-
trated in vacuo to give brown solids quantitatively. The solids were washed
with hexane to give 128.1 mg of the complex 1b in 88% (syn/anti )
18/82) isolated yield. Selected spectral data for syn isomer, 1H NMR (CD2-
Cl2): δ 3.28 (t, J ) 8.6 Hz, 1H), 4.56 (m, 1H), 7.06 (t, J ) 5.2 Hz, 1H).
31P NMR (CD2Cl2): δ 20.36 (d, JPP ) 38.4 Hz), 30.61 (d, JPP ) 38.4
Hz). 13C NMR (CD2Cl2): δ 57.4 (d, JCP ) 29.8 Hz), 88.6 (dd, JCP ) 3.4,
6.1 Hz), 141.1 (dd, JCP ) 3.7, 10.1 Hz, COH). Anti isomer, 1H NMR
(CD2Cl2): δ 2.43 (dt, J ) 2.4, 11.0 Hz, 1H), 3.22 (dt, J ) 3.2, 7.9 Hz,
1H), δ 5.45 (dd, J ) 11.2, 19.6 Hz, 1H), 6.78 (dd, J ) 8.8, 10.8 Hz, 1H),
7.16-7.85 (m, 30H). 31P NMR (CD2Cl2): δ 24.66 (d, JPP ) 34.1 Hz),
27.90 (d, JPP ) 34.1 Hz). 13C NMR (CD2Cl2): δ 59.4 (dd, JCP ) 2.3,
27.9 Hz), 95.9 (dd, JCP ) 3.1, 5.9 Hz), 128.9 (dd, JCP ) 4.4, 10.3 Hz),
130.8 (dd, JCP ) 2.3, 14.6 Hz), 132.1 (dd, JCP ) 1.4, 40.7 Hz), 133.8 (dd,
JCP ) 3.0, 13.3 Hz), 141.4 (dd, JCP ) 2.8, 26.5 Hz, COH). Anal. Calcd
for C40H35F3O4P2Pd1S1 (a mixture of syn and anti isomers): C, 57.39; H,
4.21. Found: C, 56.95; H, 4.37.
Scheme 5. Transformation into the η1-â-Ketoalkyl Complex
intermediate. The occurrence of the η1-allyl coordination mode
would promote tautomerization from enol to keto, which could not
occur in the η3-allyl coordination mode. In fact, addition of Bu4-
NCl to 2a led to the formation of the η1-â-ketoalkylplatinum
complex (6) via the η1-1-hydroxyallyl complex (Scheme 5).11
Because Pt(H)(Cl)(dppf)12 did not react with MVK, an alternative
route from 2a to 6 via formation of Pt(H)(Cl)(dppf) and its reaction
with MVK would be ruled out. The greater ease of the isomerization
for 2c than 2b would be attributed to the larger contribution of
η3-allyl structure in 2b than in 2c, which can be deduced from the
comparison of the X-ray structures of 1b and 1c. Similarly, the
failure of the corresponding palladium complexes, 1a and 1c, to
isomerize to 3 (and 4) could be rationalized by the highly stable
η3-allyl coordination mode of these complexes, because palladium
prefers η3-coordination to η1-coordination of the allyl ligand to a
greater extent than platinum.13
(7) X-ray data for 1b. M ) 837.12, yellow, monoclinic, P21/c (No. 14), a )
11.8091(5) Å, b ) 18.3006(7) Å, c ) 17.807(1) Å, â ) 103.656(1)°, V
) 3739.6(3) Å3, Z ) 4, Dcalcd ) 1.487 g/cm3, T ) 0.0 °C, R (RW) )
0.070 (0.093). X-ray data for 1c. M ) 851.14, yellow, orthorhombic, Pna21
(No. 33), a ) 21.429(1) Å, b ) 12.8667(8) Å, c ) 14.2909(6) Å, V )
3940.3(3) Å3, Z ) 4, Dcalcd ) 1.435 g/cm3, T ) 0.0 °C, R (RW) ) 0.078
(0.126).
(8) A similar influence of the substituent group at C3 on the Pd-C3 bond
distance has been reported.3
(9) A larger coupling constant indicates a shorter Pd-C3 bond length3 (1c,
35.3 and 29.3 Hz; 1c′, 36.9 and 34.1 Hz).
(10) Selected spectral data for 5a, 1H NMR (CD2Cl2): δ 1.49 (m, 2H), 2.24
(s, 3H), 3.20 (m, 2H), 4.06-4.67 (m, 8H), 7.2-8.1 (m, 20H). 31P NMR
(CD2Cl2): δ 10.17 (d, JPP ) 15.5 Hz, JPPt ) 4764.5 Hz), 30.71 (d, JPP
15.5 Hz, JPPt ) 1430.1 Hz). 13C NMR (CD2Cl2): δ(CO) 244.0 (dd, JCP
13.4, 5.4 Hz).
)
)
(11) Selected spectral data for 6, 31P NMR (CD2Cl2): δ 18.46 (d, JPP ) 14.9
Hz, JPPt ) 4613.4 Hz), 21.55 (d, JPP ) 14.9 Hz, JPPt ) 1711.9 Hz).
(12) Pt(H)(Cl)(dppf) was generated in situ by the reaction of Pt(H)(Cl)(PPh3)2
with DPPF.
In summary, we demonstrated that the direct addition of a proton
to a carbonyl oxygen in the η2-enone complex of palladium and
platinum led to the quantitative formation of η3-1-hydroxyallyl
complexes of palladium and platinum, of which X-ray diffraction
analysis showed typical η3-allyl structure. Moreover, η3-1-hydroxy-
(13) Kurosawa, H.; Ogoshi, S. Bull. Chem. Soc. Jpn. 1998, 71, 973-984 and
references therein.
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