Figure 2. 1H NMR spectroscopic comparison of (a) zinc porphyrin 13, (b) free base monoalkenylporphyrin 10, and (c) resulting trimer 2.
Resonances are annotated as per assigned protons and * indicates residual solvent resonances.
sociated with the bis-free-base analogue of 1. Catalytic
hydrogenation of the alkene 1 (H2/Pd/C/THF/48 h) gave the
bisporphyrin 11 in 96% yield (Scheme 1),15 as evinced by
the loss of alkenyl resonances and formation of upfield
1
triplets within the H NMR spectrum of 11.16
Cross-metathesis of the 5,15-dialkenylporphyrin 13 bearing
type I olefins, prepared by Zn(II) metalation of 12,17 with
the type II-containing olefin 10 (4 equiv), was achieved in
48% yield using a stoichiometric amount of 7 (Scheme 1).18
The trimer product 2 comprising a central dibutenylzinc
porphyrin 13 capped by two free base acrylate porphyrins
(5) This is especially important in regioselective mixed metalloporphyrins
systems, which are otherwised formed through statistical metalations post-
multiporphyrin synthesis.
(6) Chatterjee, A. K.; Choi, T.-L.; Sanders, D. P.; Grubbs, R. H. J. Am.
Chem. Soc. 2003, 125, 11360.
(7) This procedure has obvious uses with other olefins. For example,
we have reacted 3 with allylglycine, which acts like a type-II olefin, to
form a porphyrin R-amino acid in good yield. Conversely, we have reacted
type-I olefins such as resin-bound undecenoate esters with protoporphyrin
IX, which in our hands acts as a type-III olefin. These results and their
applications will be published at a later date.
1
10 was characterized by H and 13C NMR spectroscopies
and MALDI TOF mass spectrometry (m/z ) 2477.9 [M+]).
1
A comparison of the H NMR spectra of 10, 13, and 2
(8) Adler, A. D.; Longo, F. R.; Finarelli, J. D.; Goldmacher, J.; Assour,
J.; Korsakoff, L. J. Org. Chem. 1967, 32, 476.
(9) Mainly tetra(p-methoxyphenyl)porphyrin and only a small amount
of the desired monobutenyl porphyrin 2 was isolated using a 3:1 aldehyde
ratio due to the greater reactivity of the p-methoxybenzaldehyde under the
conditions used.
(10) Buchler, J. W. In The Porphyrins; Dolphin, D., Ed.; Academic
Press: New York, 1978; Vol. 1A, p 389.
(11) The lower yield observed for carboxylic acids over esters in CM
has been recently discussed; see: Elaridi, J.; Jackson, W. R.; Robinson, A.
J. Tetrahedron: Asymmetry 2005, 16, 2025.
(12) The acrylate porphyrin 10 was produced in 84% yield by reaction
of an acrylate ester and 5,10,15-tris(p-tolyl)-20-(p-hydroxyphenyl)porphyrin.
See: Nowakowska, M.; Karewicz, A.; Loukine, N.; Guillet, J. E. Polymer
2002, 43, 2003.
(13) The alternative synthesis of 1 employing an esterification procedure
by reacting 5 or 6 and 5,10,15-tris(p-tolyl)-20-(p-hydroxyphenyl)porphyrin
leads to in situ demetalation of the metalloporphyrin.
(14) The reduced yields are thought to result from the formation of a
coordination product between catalyst 7 and porphyrin 4.
(15) Previous reports on the reduction of alkyne porphyrins utilized
palladium on carbon in THF with good effect; see: Bampos, N.; Marvaud,
V.; Sanders, J. K. M. Chem. Eur. J. 1998, 4, 335.
(16) The success of the hydrogenation is important in instances where
both geometric isomers are formed by CM. While not yet attempted, this
last result opens up the possiblity of performing a CM/hydrogenation tandem
reaction to produce flexibly linked porphyrin systems in one pot.
(17) The synthesis of 12 was recently reported by us; see ref 4f. We
have since been able to grow crystals of 12 suitable for X-ray structural
determination by slow diffusion of MeOH into a CHCl3 solution of 12.
Crystal data for 12: C72H98N4, M ) 1019.54, crystal dimensions 0.60 ×
0.08 × 0.05 mm3, a ) 8.675(6) Å, b ) 9.849(10) Å, c ) 19.648(16) Å, R
) 97.46(4)°, â ) 96.67(3)°, γ ) 100.67(4)°, triclinic P-1, Z ) 1, V )
1619(2) Å3, Dc ) 1.046 g/cm3, F000 ) 558, λ ) 0.71073 Å, T ) 123(2) K,
µ ) 0.060 mm-1, Nonius Kappa CCD diffractometer, φ scan data, 11123
data collected, corrected for Lorenz and polarization effects, 4557 unique
(Rint ) 0.1261) and 2886 observed [I >2σ(I)], 471 refined parameters, R
) 0.0851, Rw ) 0.2339, w ) (σ2(F))-1. Crystallographic data for the
structure analyses have been deposited with the Cambridge Crystallographic
Data Centre, CCDC 603983 for structure of 12. Copies of this information
may be obtained free of charge from The Director, CCDC, 12 Union
Road, Cambridge, CB21EZ, UK (fax: +44-1223-336-033; e-mail:
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
(18) The formation of oligomers of 13 is possibile and no doubt
contributes to the reduced yield obtained. For a previous study in this regard,
see ref 4b.
Org. Lett., Vol. 8, No. 12, 2006
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