Suzuki porphyrins: New synthons for the fabrication of porphyrin- containing supramolecular assemblies [6]

Full text of DOI:10.1021/ja982410h

12676
J. Am. Chem. Soc. 1998, 120, 12676-12677
pyridyl ligand lies in van der Waals contact with a second pyridyl
ring (interplanar separation 3.46 Å); the plane defined by this
pyridyl moiety lies parallel to that of the axial ligand. The
noncoordinating pyridine is rotated 60° about its perpendicular
C1 axis with respect to the axial pyridyl moiety and vertically
displaced 3.37 Å from the above-mentioned porphyrin plane; this
positions the π system of each pyridine ring over the positively
charged σ framework of the other, optimizing electronic interac-
tions between the six-membered heteroaromatic rings.9 Consistent
with structural studies of borate ester derivatives of 1-naphtha-
lene,10 the steric interactions between the porphyrin â-hydrogens
and the pinacolborane oxygen atoms enforce large dihedral angles
(60.8 and 69.3°) between the planes defined by the two respective
sets of pinacol ester O-B-O atoms and the four pyrrolyl
nitrogens; the average O-(â-H) nonbonded contact distance is
2.65 Å,11 lying just within the sum of their van der Waals radii
(2.72 Å).12
In I‚(benzene), the Zn atom is centered in the plane of the
porphyrin ligand. The benzene molecule is positioned above the
Zn atom in a π-donor configuration; the interplanar separation
between the two aromatic ring systems is 3.10 Å, with the closest
Zn-Cbenzene distance being 3.16 Å. The orientation of the arene
ring with respect to the porphyrin ligand is similar to that found
in Scheidt’s structure of the bis(toluene) solvate of (5,10,15,20-
tetraphenylporphinato)zinc(II).13 The dihedral angle between the
planes defined by the O-B-O atoms of the meso-boronate group
and the macrocyclic N atoms is 52.0° (O-(â-H) average nonbond-
ed contact distance 2.53 Å); because a sterically unencumbered
aromatic moiety functions as the axial ligand in I‚(benzene), a
more closely packed solid-state arrangement is possible and is
thus the likely cause of reduction of the O-B-O plane-to-porphy-
rin plane dihedral angle with respect to those observed for II‚(pyri-
dine). The B-C [I, 1.575(5) Å; II, 1.565(5) Å] and B-O bond
lengths [(I, 1.364(5) Å; II, 1.362(5) Å] for both complexes are
similar to that previously reported for arylboronic acid esters.10,14
The utility of these air- and water-stable ring-metalated por-
phyrins is exemplified in reactions where I and II function as
transmetalating reagents. An exemplary set of such Suzuki-type
cross-couplings are presented in Scheme 1, which utilize a
compound I synthon;15 a number of principles are illustrated in
these high-yield reactions: (i) Cross-coupling of I with N-(tert-
butoxycarbonyl)-4-iodo-L-phenylalanine gives (5-[N-(tert-butoxy-
carbonyl)-L-phenylalanin-4′-yl]-10,20-diphenylporphinato)zinc-
(II) (III), corroborating the suitability of ring-metalated I with
respect to coupling reactions involving nucleophile-sensitive
substrates. (ii) The synthesis of 3,6-bis[10′,20′-diphenylporphi-
nato(zinc)(II)-5′-yl]-9-H-carbazole (IV) demonstrates I’s value
in the fabrication of porphyrin-spacer-porphyrin systems.16 Such
reactions can be exploited when a dihalogenated spacer moiety
Suzuki Porphyrins: New Synthons for the
Fabrication of Porphyrin-Containing Supramolecular
Assemblies
Alison G. Hyslop, Matthew A. Kellett, Peter M. Iovine, and
Michael J. Therien*
Department of Chemistry, UniVersity of PennsylVania,
Philadelphia, PennsylVania 19104-6323
ReceiVed July 9, 1998
Palladium-catalyzed cross-coupling reactions that employ
halogenated porphyrin templates and a wide range of organome-
tallic moieties have provided synthetic entre´e into new families
of unusually elaborated porphyrin macrocyles.1-3 General,
economic syntheses of porphyryl organometallic reagents4 would
expand the scope of this methodology5,6 and aid in the design of
new classes of porphyrin-containing supramolecular assemblies
and tetraazamacrocycles with unconventional peripheral substit-
uents. Reported herein are the first examples of meso ring-
metalated porphyrin species in which boronic esters are appended
to a (porphinato)zinc(II) framework; we structurally characterize
the archetypal members of this new class of macrocycle-
derivatized porphyrins and briefly illustrate their utility in carbon-
carbon bond-forming reactions.
Masuda recently described a series of reactions in which
pinacolborane functions as a transmetalating reagent in Pd-
catalyzed cross-coupling reactions, enabling the synthesis of a
wide range of arylboronates from aryl halide precursors.7 Ap-
plication of this reaction to halogenated (porphinato)zinc(II)
complexes such as (5-bromo-10,20-diphenylporphinato)zinc(II)
and (5,15-dibromo-10,20-diphenylporphinato)zinc(II)1 gives the
corresponding [5-(4′,4′,5′,5′-tetramethyl[1′,3′,2′]dioxaborolan-2′-
yl)-10,20-diphenylporphinato]zinc(II) (I) and [5,15-bis(4′,4′,5′,5′-
tetramethyl[1′,3′,2′]dioxaborolan-2′-yl)-10,20-diphenylporphinato]-
zinc(II) (II) complexes in respective yields of 86 and 79%.8 These
compounds were structurally analyzed; the results of our single-
crystal X-ray crystallographic studies of I‚(benzene) and II‚
(pyridine) are shown in Figure 1.
In II‚(pyridine), the metal-ligand bond lengths and the
magnitude of the Zn atom displacement from the least-squares
plane defined by the macrocycle’s four Npyrrolyl atoms (0.35 Å)
typify that seen for other crystallographically characterized
(porphinato)zinc(II)‚(py) complexes.1b Interestingly, II’s axial
(1) (a) DiMagno, S. G.; Lin, V. S.-Y.; Therien, M. J. J. Am. Chem. Soc.
1993, 115, 2513-2515. (b) DiMagno, S. G.; Lin, V. S.-Y.; Therien, M. J. J.
Org. Chem. 1993, 58, 5983-5993.
(2) (a) Lin, V. S.-Y.; DiMagno, S. G.; Therien, M. J. Science 1994, 264,
1105-1111. (b) Lin, V. S.-Y.; Therien, M. J. Chem.-Eur. J. 1995, 1, 645-
651. (c) LeCours, S. M.; Guan, H.-W.; DiMagno, S. G.; Wang, C. H.; Therien,
M. J. J. Am. Chem. Soc. 1996, 118, 1497-1503. (d) LeCours, S. M.; DiMagno,
S. G.; Therien, M. J. J. Am. Chem. Soc. 1996, 118, 11854-11864.
(3) (a) Zhou, X.; Tse, M. K.; Wan, T. S. M.; Chan, K. S. J. Org. Chem.
1996, 61, 3590-3593. (b) Shultz, D. A.; Gwaltney, K. P.; Lee, H J. Org.
Chem. 1998, 63, 769-774.
(9) (a) Hunter, C. A.; Sanders, J. K. M. J. Am. Chem. Soc. 1990, 112,
5525-5534. (b) Hunter, C. A. Chem. Soc. ReV. 1994, 101-109.
(10) (a) de Rege, F. M. G.; Davis, W. M.; Buchwald, S. L. Organometallics
1995, 14, 4799-4807.
(11) Note that the O-â-H distance in a hypothetical structure in which the
pinacolborane and porphyrin moieties are coplanar (porphyrin structure
constant) is 2.14 Å.
(12) Pauling, L. The Nature of the Chemical Bond and the Structure of
Molecules and Crystals, an Introduction to Modern Structural Chemistry, 3d
ed.; Cornell University Press: Ithaca, NY, 1960.
(4) Few examples of a ring-metalated porphyrins have been reported; these
species include [2-(triphenylarsonium)-5,10,15,20-tetraphenylporphinato]zinc-
(II) perchlorate and 2,4-bis(chloromercuro)deuteroporphyrin IX dimethyl ester.
See: (a) Shine, H. J.; Padilla, G. A.; Wu, S.-M. J. Org. Chem. 1979, 44,
4069-4075. (b) Minnetian, O. M.; Morris, I. K.; Snow, K. M.; Smith, K. M.
J. Org. Chem. 1989, 54, 5567-5574.
(5) (a) Heck, R. F. Acc. Chem. Res. 1979, 12, 146-151. (b) Kumada, M.
Pure Appl. Chem. 1980, 52, 669-679. (c) Negishi, E.-I.; Luo, F. T.; Frisbee,
R.; Matsushita, H. Heterocycles 1982, 18, 117-122. (d) Stille, J. K. Angew.
Chem., Int. Ed. Engl. 1986, 25, 508-524.
(6) Miyaura, N.; Suzuki, A. Chem. ReV. 1995, 95, 2457-2483.
(7) Murata, M.; Watanabe, S.; Masuda, Y. J. Org. Chem. 1997, 62, 6458-
6459.
(8) Porphyrylboronates such as I and II can also be fabricated using
synthetic approaches reported by Miyaura which utilize the pinacol ester of
diboronic acid as a transmetalating reagent; see: Ishiyama, T.; Murata, M.;
Miyaura, N. J. Org. Chem. 1995, 60, 7508-7510. At least for these
halogenated porphyrinic substrates, this method afforded the porphyrylboronate
products in slightly lower yield with respect to that obtained using the approach
outlined in ref 7.
(13) Scheidt, W. R.; Kastner, M. E.; Hatano, K. Inorg. Chem. 1978, 17,
706-710.
(14) (a) Gupta, A.; Kirfel, A.; Will, G.; Wulff, G. Acta Crystallogr., Sect.
B 1977, B33, 637-641. (b) Schilling, B.; Kaiser, V.; Kaufmann, D. E. Chem.
Ber./Recl. 1997, 130, 923-932.
(15) Reaction conditions are similar to those developed for coupling
reactions utilizing arylboronic acids (see ref 6); details are provided as
Supporting Information.
(16) (a) Osuka, A.; Maruyama, K.; Mataga, N.; Asahi, T.; Yamazaki, I.;
Tamai, N. J. Am. Chem. Soc. 1990, 112, 4958-4959. (b) Helms, A.; Heiler,
D.; McLendon, G. J. Am. Chem. Soc. 1992, 114, 6227-6238. (c) de Rege, P.
J. F.; Williams, S. A.; Therien, M. J. Science 1995, 269, 1409-1413.
10.1021/ja982410h CCC: $15.00 © 1998 American Chemical Society
Published on Web 11/21/1998

Communications to the Editor
J. Am. Chem. Soc., Vol. 120, No. 48, 1998 12677
Figure 1. ORTEP views of (a) [5-(4′,4′,5′,5′-tetramethyl[1′,3′,2′]dioxaborolan-2′-yl)-10,20-diphenylporphinato]zinc(II)‚(benzene) and (b) [5,15-bis-
(4′,4′,5′,5′-tetramethyl[1′,3′,2′]dioxaborolan-2′-yl)-10,20-diphenylporphinato]zinc(II)‚(pyridine) with thermal ellipsoids at 30% probability.
Scheme 1. Examples of Metal-Catalyzed Cross-Coupling
Reactions Utilizing Porphyrylboronate Transmetalating
Reagentsa
congested cross-coupling reactions.17 The close, sub van der
Waals interplanar separation18 between the cofacial aromatic
entities of V is highlighted by the unusual local magnetic
environment experienced by the C-4′′ dimethoxyphenyl proton
(δ ) 2.42 ppm); this nucleus resonates 4.53 ppm upfield from
that observed for the corresponding C-4′ proton of 1-(2′,5′-
dimethoxyphenyl)-8-iodonaphthalene.
Ring-metalated porphyrylboronic acids and their corresponding
esters expand the repertoire of reagents that can be utilized in
metal-catalyzed coupling reactions that form new bonds at the
porphyrin periphery. Given the established, rich chemistry of
boronate, boronic acid, and borane derivatives of aromatic
compounds,19 porphyrylboronates should likely serve as versatile
precursor molecules that enable facile introduction of carbon-
heteroatom bonds directly at the macrocycle skeleton. Further-
more, diboronate-functionalized II and related multiply boronated
porphyryl species constitute a new class of synthons for porphyrin-
based conjugated materials that are formed via metal-catalyzed
carbon-carbon bond-forming reactions1-3 or hydroboration po-
lymerization.20
Acknowledgment. M.J.T. is indebted to the United States Department
of Energy (Grant DE-FG02-94ER14494) for their generous financial
support of this work and thanks the Arnold and Mabel Beckman
Foundation, Searle Scholars Program (Chicago Community Trust), and
E. I. duPont de Nemours, and for young investigator awards, as well as
the Alfred P. Sloan and Camille and Henry Dreyfus Foundations for
research fellowships.
Supporting Information Available: Characterization data and
detailed descriptions of the syntheses of compounds I-V along with tables
of crystal data, structure solution and refinement, atomic coordinates, bond
lengths and angles, and anisotropic thermal parameters for compounds
I‚(benzene) and II‚(pyridine) (36 pages print/PDF). An X-ray crystal-
lographic file, in CIF format, is available through the Internet only. See
any current masthead page for ordering and Web access instructions.
a Reagents and conditions: Ba(OH)2‚8 H2O (0.24 mmol), Pd(PPh3)4
(0.003 mmol), 50:1 DME/H2O, 80 °C. (i) I (0.16 mmol), N-(tert-
butoxycarbonyl)-4-iodo-L-phenylalanine (0.08 mmol); (ii) I (0.2 mmol),
3,6-dibromocarbazole (0.05 mmol); (iii) I (0.08 mmol), 1-(2′,5′-dimeth-
oxyphenyl)-8-iodonaphthalene (0.08 mmol).
JA982410H
(17) While the underlying cause is unclear at present, similar cross-
couplings involving (5-bromo-10,20-diphenylporphinato)zinc(II) with large
excesses of organozinc and organoboronate derivatives of 1-(2′,5′-dimethox-
yphenyl)-8-iodonaphthalene proceed at a fraction of the 74% yield observed
for the stoichiometric coupling of I and 1-(2′, 5′-dimethoxyphenyl)-8-
iodonaphthalene.
bears a functionality incompatible with direct formation of its
corresponding bis(organometallic) derivative or when practical
considerations warrant using porphyrylboronates as an expendable
transmetalating species. Because I is available in two steps from
(5,15-diphenylporphinato)zinc(II), carrying out carbon-carbon
bond-forming reactions with excess I enables the most efficient
use of mono- and dihalogenated organic substrates derived from
multiple synthetic steps. (iii) The synthesis of [10-(8′-(2′′,5′′-
dimethoxyphenyl)-1′-naphthyl)-5,15-diphenylporphinato]zinc-
(II) (V) from I and 1-(2′,5′-dimethoxyphenyl)-8-iodonaphthalene
illustrates the efficacy of this porphyrylboronate in sterically
(18) Clough, R. L.; Kung, W. J.; Marsh, R. E.; Roberts, J. D. J. Org. Chem.
1976, 41, 3603-3609.
(19) (a) Brown, H. C. Organic Syntheses Via Boranes; Wiley: New York,
1975. (b) Mikhailov, B. M.; Bubnov, Yu. N. Organoboron Compounds in
Organic Synthesis; Harwood Academic: New York, 1984. (c) Larock, R. C.
ComprehensiVe Organic Transformations: A Guide to Functional Group
Preparations; VCH: New York, 1989.
(20) Matsumi, N.; Naka, K.; Chujo, Y. J. Am. Chem. Soc. 1998, 120, 5112-
5113.