Excited-State Energy-Transfer Dynamics in Self-Assembled Triads Composed of Two Porphyrins and an Intervening Bis(dipyrrinato)metal Complex

Inorg. Chem. 2003, 42, 6629−6647

Excited-State Energy-Transfer Dynamics in Self-Assembled Triads

Composed of Two Porphyrins and an Intervening Bis(dipyrrinato)metal

Complex

Lianhe Yu,^†Kannan Muthukumaran,^†Igor V. Sazanovich,^‡Christine Kirmaier,^‡Eve Hindin,^‡

,§

,‡

,†

James R. Diers,^§Paul D. Boyle,^†David F. Bocian,* Dewey Holten,* and Jonathan S. Lindsey*

Departments of Chemistry, North Carolina State UniVersity, Raleigh, North Carolina 27695-8204,

Washington UniVersity, St. Louis, Missouri 63130-4889, and UniVersity of California,

RiVerside, California 92521-0403

Received May 23, 2003

The synthesis and characterization of various triads composed of a linear array of two zinc porphyrins joined via

an intervening bis(dipyrrinato)metal(II) complex are reported. The preparation exploits the facile complexation of

dipyrrins with divalent metal ions to give bis(dipyrrinato)metal(II) complexes [abbreviated (dp)₂M]. Copper(II) and

palladium(II) chelates of dipyrrins (available by oxidation of dipyrromethanes) were prepared in 50−80% yield. A

one-flask synthesis of bis(dipyrrinato)zinc(II) complexes was developed by oxidation of a dipyrromethane with DDQ

or p-chloranil in the presence of Zn(OAc)₂‚2H O in THF (∼80% yield). Three routes were developed for preparing

2

porphyrin-dipyrrins: (1) Suzuki coupling of a boronate-substituted zinc porphyrin (ZnP) and bis[5-(4-iodophenyl)-

dipyrrinato]Pd(II) to give the (ZnP-dp)₂Pd triad (50% yield), followed by selective demetalation of the (dp)₂Pd unit

by treatment with 1,4-dithiothreitol under neutral conditions (71% yield); (2) oxidation of a porphyrin-dipyrromethane

with p-chloranil in the presence of Zn(OAc)₂‚2H O followed by chromatography on silica gel (71% yield); and (3)

2

condensation of a dipyrrin-dipyrromethane and a dipyrromethane-dicarbinol under InCl₃catalysis followed by oxidation

with DDQ (10−16% yield). Four triads of form (ZnP-dp)₂Zn were prepared in 83−97% yield by treatment of a

porphyrin-dipyrrin with Zn(OAc)₂‚2H O at room temperature. Free base dipyrrins typically absorb at 430−440 nm,

2

while the bis(dipyrrinato)metal complexes absorb at 460−490 nm. The fluorescence spectra/yields and excited-

state lifetimes of the (ZnP-dp)₂Zn triad in toluene show (1) efficient energy transfer from the bis(dipyrrinato)zinc(II)

chromophore to the zinc porphyrins (98.5% yield), and (2) little or no quenching of the resulting excited zinc

porphyrin relative to the isolated chromophore. Taken together, these results indicate that bis(dipyrrinato)zinc(II)

complexes can serve as self-assembling linkers that further function as secondary light-collection elements in

porphyrin-based light-harvesting arrays.

Introduction

properties of photosynthetic light-harvesting antennas.¹In

the preceding paper, we described a series of porphyrinic

light-harvesting arrays wherein the porphyrins were co-

valently linked via an imine motif. This motif is attractive

because the arrays can be prepared using one-flask reactions.

The imine motif was found to support highly efficient energy

transfer between porphyrins.²

The preparation of light-harvesting arrays requires the

organization of a large number of pigments in well-defined

3-dimensional architectures. Porphyrinic macrocycles have

been widely employed in the construction of synthetic light-

harvesting arrays owing to their desirable optical and

photochemical features, as well as the desire to mimic the

(1) (a) Harvey, P. D. In The Porphyrin Handbook; Kadish, K. M., Smith,

K. M., Guilard, R., Eds.; Academic Press: San Diego, CA, 2003; Vol.

18, pp 63-250. (b) Burrell, A. K.; Officer, D. L.; Plieger, P. G.; Reid,

D. C. W. Chem. ReV. 2001, 101, 2751-2796.

(2) Sazanovich, I. V.; Balakumar, A.; Muthukumaran, K.; Hindin, E.;

Kirmaier, C.; Diers, J. R.; Lindsey, J. S.; Bocian, D. F.; Holten, D.

Inorg. Chem. 2003, 42, 6616-6628.

* To whom correspondence should be addressed. E-mail: holten@

wuchem.wustl.edu (D.H.); jlindsey@ncsu.edu (J.S.L.); David.Bocian@ucr.edu

(D.F.B.).

^†North Carolina State University.

^‡Washington University.

^§University of California.

Published on Web 09/17/2003

Inorganic Chemistry, Vol. 42, No. 21, 2003 6629

Yu et al.

Chart 1

A general limitation of porphyrins for light-harvesting

purposes is that porphyrins have strong absorption only in

the blue region (λ_max∼420 nm), with weak absorption across

the remainder of the visible spectrum. One approach to

increase the spectral coverage of porphyrin-based light-

harvesting arrays has been to include accessory pigments

that absorb in regions where the porphyrins are relatively

transparent and that funnel the resulting excited-state energy

to the porphyrin. The ideal accessory pigment for use with

porphyrins should have the following properties: (1) strong

light absorption in the region between the porphyrin Soret

and Q-bands, (2) a long-lived excited-state, (3) high stability,

(4) high solubility, and (5) synthetic compatibility with a

molecular building block approach.³Accessory pigments that

have been used with porphyrins include boron-dipyrrin

dyes,^4-7carotenoids,⁸coumarin dyes,⁹cyanine dyes,¹⁰perylene-

imide dyes,^7,11,12and xanthene dyes.¹³Meeting all of the

criteria for an ideal accessory pigment is a significant

challenge, and no one class is superior in all aspects. The

carotenoids absorb very strongly but have very short excited-

state lifetimes, requiring very close juxtaposition for energy

transfer to an acceptor. The cyanine dyes can be tuned for

absorption across the visible region but, like the xanthene

dyes, are positively charged, limiting solubility and typically

causing difficulties in purification. The coumarins are neutral

but absorb weakly, and the absorption band is in the vicinity

of the porphyrin Soret band, affording little additional

spectral coverage. The perylene-monoimide dyes have mod-

est absorption intensity, undergo efficient energy transfer,

and are nonpolar, but they require extensive substitution with

bulky groups to achieve adequate solubility.^13,14The boron-

dipyrrin dyes have been widely used as fluorescent labels¹⁵

in biological applications and provide a nice compromise of

all features for use with porphyrins. While the synthesis of

boron-dipyrrins is more straightforward than that of perylene-

imides, the one type of boron-dipyrrin that was used in

conjunction with porphyrins exhibited a biphasic excited-

state decay, with a short component that limits the yield of

energy transfer.⁶Accordingly, there remains a need for new

types of dyes that can be used as accessory pigments with

porphyrins.

Dipyrrins provide the basis for the boron-dipyrrin dyes¹⁶

and also have a rich chemistry with diverse transition metals.

Free base dipyrrins react readily with a wide variety of metal

salts, affording the corresponding bis(dipyrrinato)metal(II)

(or tris(dipyrrinato)metal(III)) complexes. The bis(dipyrri-

nato)metal(II) complexes typically absorb quite strongly in

the blue-green region (λ_max∼ 470-500 nm; ꢀ_λmax50 000-

100 000 M^-1cm^-1). However, the photochemical properties

of bis(dipyrrinato)metal complexes have rarely been studied,

with only anecdotal reports concerning fluorescence of the

complexes.¹⁷The bis(dipyrrinato)metal complexes derived

from a divalent metal such as zinc are fundamentally distinct

from the dipyrrinatoboron difluoride complexes (Chart 1);

the latter comprise only one dipyrrin ligand per boron and

typically are quite fluorescent.

The chemistry of bis(dipyrrinato)metal complexes dates

to the time of Hans Fischer, where dipyrrins (previously

termed pyrromethenes or dipyrromethenes)¹⁸employed as

precursors to naturally occurring porphyrins were found to

form stable complexes with divalent metal ions such as iron,

copper, cobalt, nickel, and zinc.¹⁹The dipyrrins, obtained

by oxidation of dipyrromethanes, typically contained a full

complement of substituents at the R- and â-positions of the

chromophore. In the ensuing years, complexes of diverse

divalent metals (Mg,²⁰Ca,²¹Mn,²¹Fe,²²Co,^23-31Ni,^{21,23-29,31-33}

(3) (a) Wagner, R. W.; Lindsey, J. S. Pure Appl. Chem. 1996, 68, 1373-

1380. (b) Wagner, R. W.; Lindsey, J. S. Pure Appl. Chem. 1998, 70

(8), i.

(4) Wagner, R. W.; Lindsey, J. S. J. Am. Chem. Soc. 1994, 116, 9759-

9760.

(5) Ambroise, A.; Wagner, R. W.; Rao, P. D.; Riggs, J. A.; Hascoat, P.;

Diers, J. R.; Seth, J.; Lammi, R. K.; Bocian, D. F.; Holten, D.; Lindsey,

J. S. Chem. Mater. 2001, 13, 1023-1034.

(6) Li, F.; Yang, S. I.; Ciringh, Y.; Seth, J.; Martin, C. H., III; Singh, D.

L.; Kim, D.; Birge, R. R.; Bocian, D. F.; Holten, D.; Lindsey, J. S. J.

Am. Chem. Soc. 1998, 120, 10001-10017.

(7) Ambroise, A.; Kirmaier, C.; Wagner, R. W.; Loewe, R. S.; Bocian,

D. F.; Holten, D.; Lindsey, J. S. J. Org. Chem. 2002, 67, 3811-3826.

(8) (a) Gust, D.; Moore, T. A.; Moore, A. L. Acc. Chem. Res. 2001, 34,

40-48. (b) Gust, D.; Moore, T. A.; Moore, A. L. Acc. Chem. Res.

1993, 26, 6, 198-205.

(15) (a) Kim, H.; Burghart, A.; Welch, M. B.; Reibenspies, J.; Burgess, K.

Chem. Commun. 1999, 1889-1890. (b) Burghart, A.; Kim, H.; Welch,

M. B.; Thoresen, L. H.; Reibenspies, J.; Burgess, K. J. Org. Chem.

1999, 64, 7813-7819. (c) Chen, J.; Burghart, A.; Derecskei-Kovacs,

A.; Burgess, K. J. Org. Chem. 2000, 65, 2900-2906. (d) Burghart,

A.; Thoresen, L. H.; Chen, J.; Burgess, K.; Bergstro¨m, F.; Johansson,

L. B.-Å. Chem. Commun. 2000, 2203-2204.

(9) Hecht, S.; Vladimirov, N.; Fre´chet, J. M. J. J. Am. Chem. Soc. 2001,

123, 18-25.

(10) Lindsey, J. S.; Brown, P. A.; Siesel, D. A. Tetrahedron 1989, 45,

4845-4866.

(16) Treibs, A.; Kreuzer, F.-H. Liebigs Ann. Chem. 1968, 718, 208-223.

(17) Granick, S.; Gilder, H. In AdVances in Enzymology; Nord, F. F., Ed.;

Interscience Publishers: New York, 1947; Vol. VII, pp 305-368.

(18) Moss, G. P. Pure Appl. Chem. 1987, 59, 779-832.

(19) (a) Fischer, H.; Schubert, M. Ber. Dtsch. Chem. Ges. 1924, 57, 610-

617. (b) Fischer, H.; Klarer, J. Justus Liebigs Ann. Chem. 1926, 448,

178-193.

(11) Just, E. M.; Wasielewski, M. R. Superlattices Microstruct. 2000, 28,

317-328.

(12) Tomizaki, K.-Y.; Loewe, R. S.; Kirmaier, C.; Schwartz, J. K.; Retsek,

J. L.; Bocian, D. F.; Holten, D.; Lindsey, J. S. J. Org. Chem. 2002,

67, 6519-6534.

(13) Lindsey, J. S.; Prathapan, S.; Johnson, T. E.; Wagner, R. W.

Tetrahedron 1994, 50, 8941-8968.

(20) Corwin, A. H.; Melville, M. H. J. Am. Chem. Soc. 1955, 77, 2755-

(14) Loewe, R. S.; Tomizaki, K.-Y.; Youngblood, W. J.; Bo, Z.; Lindsey,

J. S. J. Mater. Chem. 2002, 12, 3438-3451.

2759.

(21) Motekaitis, R. J.; Martell, A. E. Inorg. Chem. 1970, 9, 1832-1839.

6630 Inorganic Chemistry, Vol. 42, No. 21, 2003

Porphyrin-Containing Self-Assembled Triads

Cu,^{20,22-25,27-29,31,34,35}Zn,^{21-24,27,29-31,34}Pd,^23,27Cd,^22,23and

Hg^23,27) have been prepared from similarly substituted

dipyrrins.

porphyrins joined by a bridging bis(terpyridyl)ruthenium (or

iridium) complex.^44-47More generally, the self-assembly

approach is inspired by a rich collection of self-assembled

arrays composed of porphyrins and metal-coordinated

ligands.⁴⁸

In this paper, we describe the synthesis of a number of

bis(dipyrrinato)metal complexes. We then investigate three

routes for forming porphyrin-dipyrrins. The porphyrin-

dipyrrins are used to create triads consisting of two zinc

porphyrins joined by an intervening bis(dipyrrinato)metal

complex. The spectroscopic properties of several all-zinc

triads and their component parts have been characterized.

This work provides the foundation for the use of bis-

(dipyrrinato)metal complexes as self-assembling chro-

mophores in light-harvesting systems.

In the past decade, dipyrromethanes that bear one meso-

substituent and lack any R- or â-substituents have become

available via a simple one-flask synthesis.^36,37Dolphin’s

group³⁸found that exposure of such meso-substituted dipyr-

romethanes to DDQ or p-chloranil afforded the corresponding

dipyrrins. Dolphin also showed that such dipyrrins could be

converted to the corresponding bis(dipyrrinato)metal com-

plex³⁸[(dp)₂M] or tris(dipyrrinato)metal complex³⁹upon

treatment with base and a divalent (M ) Zn, Cu, Ni) or

trivalent (Co, Fe) metal acetate. Dolphin subsequently

showed that a variety of elegant structures could self-

assemble from multimers of the fundamental dipyrrin

motif.^40,41Similar structures have been made by others.^42,43

The ready access to dipyrromethanes/dipyrrins and the facile

self-assembly of bis(dipyrrinato)metal complexes prompted

us to consider the use of this motif as the basis for linking

porphyrins in a self-assembly process. Given the strong

absorption in the blue-green region, we also sought to

examine whether excited-state energy transfer would occur

from the bis(dipyrrinato)metal unit to the attached porphyrin.

Such a process, if viable, would afford a self-assembling

accessory pigment for elaborating multiporphyrin light-

harvesting arrays. This approach closely resembles the

strategy employed by the groups of Collin, Flamigni, and

Sauvage where a terpyridine-porphyrin reacts with a ruthe-

nium (or iridium) reagent to give the array containing two

Results and Discussion

Synthesis. Preparation of 5-Substituted Dipyrro-

methanes. Dipyrromethanes bearing various substituents at

the 5-position are readily available via condensation of the

corresponding aldehyde + pyrrole under TFA catalysis.^36,37

The dipyrromethanes 1a-j were prepared as shown in

Scheme 1.

Preparation of Free Base Dipyrrins and Bis(dipyrri-

nato)metal Complexes. Bru¨ckner et al. reported that oxida-

tion of 5-phenyldipyrromethane (1a) with 2,3-dichloro-5,6-

dicyano-1,4-benzoquinone (DDQ) in benzene at room

temperature affords 5-phenyldipyrrin (2a) in 47% yield.³⁸

We performed the same reaction in THF, a solvent providing

much higher solubility for quinones than benzene.⁴⁹The

reaction with DDQ for 40 min gave 2a in 42% yield, while

the milder oxidant p-chloranil for 18 h gave 2a in 62% yield.

Similarly, oxidation of 1b, 1h, and 1j with DDQ in THF

afforded the corresponding free base dipyrrins 2b, 2h, and

2j in 51%, 57%, and 85% yields, respectively.

(22) Corwin, A. H.; Sydow, V. L. J. Am. Chem. Soc. 1953, 75, 4484-

4486.

(23) Porter, C. R. J. Chem. Soc. 1938, 368-372.

(24) Fergusson, J. E.; Ramsay, C. A. J. Chem. Soc. 1965, 5222-5225.

(25) Murakami, Y.; Sakata, K. Inorg. Chim. Acta 1968, 2, 273-279.

(26) Murakami, Y.; Kohno, Y.; Matsuda, Y. Inorg. Chim. Acta 1969, 3,

671-675.

(27) March, F. C.; Couch, D. A.; Emerson, K.; Fergusson, J. E.; Robinson,

W. T. J. Chem. Soc. A 1971, 440-448.

Bru¨ckner et al. reported two approaches for the formation

of bis(dipyrrinato)metal complexes: (1) the traditional treat-

ment of a purified dipyrrin with a metal acetate,³⁸or (2) a

two-step one-flask approach involving oxidation of a dipyr-

(28) Murakami, Y.; Matsuda, Y.; Sakata, K. Inorg. Chem. 1971, 10, 1734-

1738.

(29) Murakami, Y.; Matsuda, Y.; Sakata, K.; Martell, A. E. J. Chem. Soc.,

Dalton Trans. 1973, 1729-1734.

(30) Murakami, Y.; Matsuda, Y.; Kobayashi, S. J. Chem. Soc., Dalton

Trans. 1973, 1734-1737.

(44) (a) Flamigni, L.; Barigelletti, F.; Armaroli, N.; Collin, J.-P.; Dixon, I.

M.; Sauvage, J.-P.; Williams, J. A. G. Coord. Chem. ReV. 1999, 190-

192, 671-682. (b) Harriman, A.; Sauvage, J.-P. Chem. Soc. ReV. 1996,

25, 41-48.

(45) Flamigni, L.; Barigelletti, F.; Armaroli, N.; Collin, J.-P.; Sauvage, J.-

P.; Williams, J. A. G. Chem. Eur. J. 1998, 4, 1744-1754.

(46) Dixon, I. M.; Collin, J.-P.; Sauvage, J.-P.; Flamigni, L. Inorg. Chem.

2001, 40, 5507-5517.

(47) Flamigni, L.; Marconi, G.; Dixon, I. M.; Collin, J.-P.; Sauvage, J.-P.

J. Phys. Chem. B 2002, 106, 6663-6671.

(31) Johnson, A. W.; Kay, I. T.; Markham, E.; Price, R.; Shaw, K. B. J.

Chem. Soc. 1959, 3416-3424.

(32) Cotton, F. A.; DeBoer, B. G.; Pipal, J. R. Inorg. Chem. 1970, 9, 783-

788.

(33) Ferguson, J.; West, B. O. J. Chem. Soc. A 1966, 1565-1568.

(34) Murakami, Y.; Matsuda, Y.; Kanaoka, Y. Bull. Chem. Soc. Jpn. 1971,

44, 409-415.

(35) Murakami, Y.; Matsuda, Y.; Sakata, K. Inorg. Chem. 1971, 10, 1728-

1734.

(36) Lee, C.-H.; Lindsey, J. S. Tetrahedron 1994, 50, 11427-11440.

(37) Littler, B. J.; Miller, M. A.; Hung, C.-H.; Wagner, R. W.; O’Shea, D.

F.; Boyle, P. D.; Lindsey, J. S. J. Org. Chem. 1999, 64, 1391-1396.

(38) Bru¨ckner, C.; Karunaratne, V.; Rettig, S. J.; Dolphin, D. Can. J. Chem.

1996, 74, 2182-2193.

(48) (a) Alessio, E.; Iengo, E.; Marzilli, L. G. Supramol. Chem. 2002, 14,

103-120. (b) Richeter, S.; Jeandon, C.; Gisselbrecht, J.-P.; Ruppert,

R.; Callot, H. J. J. Am. Chem. Soc. 2002, 124, 6168-6179. (c) Balzani,

V.; Ceroni, P.; Juris, A.; Venturi, M.; Campagna, S.; Puntoriero, F.;

Serroni, S. Coord. Chem. ReV. 2001, 219-221, 545-572. (d)

Swiegers, G. F.; Malefetse, T. J. Chem. ReV. 2000, 100, 3483-3537.

(e) Chambron, J.-C.; Heitz, V.; Sauvage, J.-P. In The Porphyrin

Handbook; Kadish, K. M.;, Smith, K. M., Guilard, R., Eds.; Academic

Press: San Diego, CA, 2000; Vol. 6, pp 1-42. (f) Sanders, J. K. M.

In The Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard,

R., Eds.; Academic Press: San Diego, CA, 2000; Vol. 3, pp 347-

368. (g) Imamura, T.; Fukushima, K. Coord. Chem. ReV. 2000, 198,

133-156. (h) Wojaczynski, J.; Latos-Grazynski, L. Coord. Chem. ReV.

2000, 204, 113-171.

(39) Bru¨ckner, C.; Zhang, Y.; Rettig, S. J.; Dolphin, D. Inorg. Chim. Acta

1997, 263, 279-286.

(40) (a) Zhang, Y.; Thompson, A.; Rettig, S. J.; Dolphin, D. J. Am. Chem.

Soc. 1998, 120, 13537-13538. (b) Thompson, A.; Rettig, S. J.;

Dolphin, D. Chem. Commun. 1999, 631-632. (c) Thompson, A.;

Dolphin, D. J. Org. Chem. 2000, 65, 7870-7877.

(41) Thompson, A.; Dolphin, D. Org. Lett. 2000, 2, 1315-1318.

(42) Zhang, Y.; Ma, J. S. Org. Prep. Proced. Int. 2001, 33, 81-86.

(43) Zhang, Y.; Wang, Z.; Yan, C.; Li, G.; Ma, J. Tetrahedron Lett. 2000,

41, 7717-7721.

(49) Walker, D.; Hiebert, J. D. Chem. ReV. 1967, 67, 153-195.

Inorganic Chemistry, Vol. 42, No. 21, 2003 6631

Yu et al.

Scheme 1

Scheme 2

mixture was filtered to remove quinone species, and the crude

dipyrrin was treated with Pd(OAc)₂in CH₂Cl₂to give Pd-

2c in 47% overall yield upon filtration (Scheme 2). It is

noteworthy that this method did not involve any chroma-

tography.

romethane yielding the dipyrrin followed by treatment of

the crude dipyrrin with triethylamine (TEA) and a metal

acetate.³⁹Our application of the first approach with 2b and

Cu(OAc)₂‚H₂O in CH₂Cl₂/MeOH at room temperature for

10 min afforded the bis(dipyrrinato)copper(II) species Cu-

2b in 82% yield (42% from 1b) after chromatographic

purification (Scheme 2). Similar attempts to metalate 2b

using either Pd(OAc)₂or Pd(NO₃)₂in different solvents over

a range of temperatures gave either a low yield (10%) or

complicated product distributions. However, exposure of 2b

to tris(dibenzylideneacetone)dipalladium(0) (Pd₂(dba)₃) in

CHCl₃/MeOH/TEA at room temperature afforded Pd-2b

after a simple chromatographic purification. The overall yield

from dipyrromethane 1b was 43%.

One-Flask Synthesis of Bis(dipyrrinato)zinc(II) Com-

plexes. The facile formation of bis(dipyrrinato)zinc(II)

complexes prompted us to investigate a one-flask synthesis.

Thus, treatment of 5-phenyldipyrromethane (1a) with an

equimolar amount of DDQ in THF for 30 min at room

temperature in the presence of Zn(OAc)₂‚2H₂O afforded bis-

(5-phenyldipyrrinato)zinc(II) (Zn-2a) in 78% yield after

column chromatography (Scheme 3). With the milder oxidant

p-chloranil, the oxidation/complexation of 1a was complete

in ∼27 h but gave a cleaner reaction than that with DDQ.

The product was obtained in 81% yield after column

chromatography. Under the same conditions, Zn-2b, Zn-

2c, Zn-2d, Zn-2g, Zn-2h, and Zn-2j were prepared in good

yields. The same reaction of 1e (no meso-substituent) or 1i

(containing a meso-alkyl substituent) with DDQ or p-

chloranil failed to give the desired bis(dipyrrinato)zinc(II)

complexes, though in both cases the starting dipyrromethane

was completely consumed. The failure must originate in the

Similar attempts to prepare the desired bis[(5-(4-iodophe-

nyl)dipyrrinato]palladium(II) complex Pd-2c by using Pd₂-

(dba)₃were not successful. In a two-step approach, dipyr-

romethane 1c was treated with p-chloranil, the crude reaction

6632 Inorganic Chemistry, Vol. 42, No. 21, 2003

Porphyrin-Containing Self-Assembled Triads

Scheme 3

Scheme 4

employed for protective purposes during specific synthetic

transformations (vide infra). We first examined the acid-

induced demetalation of Zn-2a to give 5-phenyldipyrrin (2a).

However, only partial demetalation was observed with use

of excess trifluoroacetic acid (TFA, 50 equiv) in CH₂Cl₂for

several hours. Even use of methanolic HCl did not afford

complete demetalation. Because the complexes were resistant

to acid hydrolysis, an alternative method of demetalation was

explored.

Dithiothreitol (threo-1,4-dimercapto-2,3-butanediol, DTT)

is a nonvolatile, thiol-containing ligand capable of coordinat-

ing a variety of metal ions. We examined the use of DTT to

liberate the free base dipyrrins by displacement of the metal

from the bis(dipyrrinato) complexes (Scheme 4). Treatment

of Cu-2b in CH₂Cl₂(5 mM) with 10 molar equiv of DTT at

room temperature gave quantitative demetalation as observed

by TLC and UV-vis spectroscopic analysis. The free base

dipyrrin 2b was obtained in 95% yield after chromatographic

purification. Each zinc(II)-dipyrrin complex that was ex-

amined also was readily demetalated under the same condi-

tions within 30 min. The bis(dipyrrinato)palladium(II) com-

plexes Pd-2b and Pd-2c demetalated much more slowly (17

h) under the same conditions, yet the free base dipyrrins 2b

and 2c were obtained in 79% and 89% yield, respectively.

It is noteworthy that treatment of Zn-1a with ethylene glycol

in place of DTT caused no demetalation, indicating that the

thiols of DTT are essential for the demetalation process.

We examined an alternative method for removing the

metal from the bis(dipyrrinato)metal complexes. Treatment

of Cu-2b with NaBH₄(20 molar equiv) in THF/MeOH (3:

1) at room temperature for 20 min gave complete reduction,

oxidation rather than the complexation process, because in

each case, oxidation (DDQ or p-chloranil) alone failed to

afford the expected free base dipyrrin.

The attempted metalation of 5-phenyldipyrrin (1a) with

CaCl₂, MgBr₂‚OEt₂, or Cd(OAc)₂‚2H₂O was not successful

as evidenced by UV-vis and ¹H NMR spectroscopic analysis

of the crude reaction mixture (see Supporting Information).

The failure in these cases was surprising, because each type

of complex has been prepared from dipyrrins with a full

complement of R- and â-substituents. The conditions for

MgBr₂‚OEt₂were very similar to those used for magnesiation

of porphyrins.⁵⁰

Demetalation of Bis(dipyrrinato)metal Complexes. We

investigated methods for the demetalation of bis(dipyrrinato)-

metal complexes because we wanted to be able to (1)

disassemble self-assembled structures, and (2) remove metals

(50) Lindsey, J. S.; Woodford, J. N. Inorg. Chem. 1995, 34, 1063-1069.

Inorganic Chemistry, Vol. 42, No. 21, 2003 6633

Yu et al.

Scheme 5

affording dipyrromethane 1b in 88% yield after chromato-

graphic purification. However, Zn-2a gave only a 50% yield

of 1a upon similar reduction. Dipyrrins are well-known to

undergo reduction to give the dipyrromethane.⁵¹Indeed,

Dolphin showed that meso-substituted dipyrrins could be

converted to the dipyrromethanes upon reduction with

NaBH₄.³⁸Our results show that the bis(dipyrrinato)metal

complexes undergo reduction to give the dipyrromethane.

Routes to Porphyrin-Dipyrrins. We developed three

routes for the synthesis of porphyrin-dipyrrin systems. The

first two routes employ a porphyrin building block, while

the third route employs a dipyrrin in a porphyrin-forming

reaction.

Route 1: Suzuki Coupling of a Porphyrin and a Bis-

(dipyrrinato)metal Complex. The synthesis of the key

porphyrin building block for use in a Suzuki coupling

reaction is shown in Scheme 5. Treatment of dipyrromethane

1e and mesitaldehyde with BF₃-ethanol cocatalysis (achieved

with BF₃‚OEt₂in CHCl₃containing 0.75% ethanol)⁵²for 0.5

h at room temperature followed by oxidation with DDQ

afforded the target 5,15-dimesitylporphyrin (3) in 28% yield.

No acidolytic scrambling leading to undesired porphyrin

products was detected as evidenced by laser desorption-mass

spectrometry (LD-MS) analysis of the crude reaction mixture.

Metalation with Zn(OAc)₂‚2H₂O afforded Zn-3. Following

a standard procedure,⁵³treatment of 3 with 1 molar equiv

of NBS in CHCl₃/pyridine for 25 min at 0 °C gave the

desired monobrominated product 4 in 73% yield, the

dibrominated byproduct (12% yield), and the unreacted 3

(12%), which were readily separated by chromatography. No

1

â-bromination was observed by H NMR spectroscopic

analysis. Metalation of 4 with Zn(OAc)₂‚2H₂O afforded Zn-4

in 98% yield. Following the conditions used previously for

Suzuki coupling at the porphyrin meso-positions,^54,55reaction

of Zn-4 and 4,4,5,5-tetramethyl-1,3,2-dioxaborolane in the

presence of TEA/Pd(PPh₃)₂Cl₂in 1,2-dichloroethane at 85

°C for 1 h afforded the desired product Zn-5 in 93% yield

after column chromatography.

A number of approaches were explored for the Suzuki

coupling of a porphyrin and a dipyrrin species. Attempts to

couple boronate-porphyrin Zn-5 and iodo-complex Zn-2c,

or bromo-porphyrin Zn-4 and boronate-complex Zn-2d,

under standard Suzuki coupling conditions resulted in failure,

which we attributed to the sequestration of palladium by the

dipyrrins following transmetalation of zinc. A large number

of control experiments showed that Suzuki reactions are

poisoned by the presence of a free base dipyrrin, bis-

(dipyrrinato)zinc(II), or bis(dipyrrinato)copper(II), even if the

dipyrrin has no functional groups to participate as a coupling

partner (see Supporting Information). We turned to the use

of Pd-2c for the Suzuki reaction.

Reaction of Zn-5 and Pd-2c under the conditions em-

ployed previously⁵⁶gave the (ZnP-dp)₂Pd triad 6 in only 6%

yield. We examined the Suzuki coupling of Zn-5 and Pd-

2c under conditions similar to those employed by Therien

et al. for attachment of substituents to the porphyrin meso-

position:⁵⁷Pd[(PPh₃)]₄(15% mol relative to Zn-5); Ba(OH)₂‚

(51) Gossauer, A.; Engel, J. In The Porphyrins; Dolphin, D., Ed.; Academic

Press: New York, 1978; Vol. II, pp 197-253.

(52) Lindsey, J. S.; Wagner, R. W. J. Org. Chem. 1989, 54, 828-836.

(53) (a) Nudy, L. R.; Hutchinson, H. G.; Schieber, C.; Longo, F. R.

Tetrahedron 1984, 40, 2359-2363. (b) DiMagno, S. G.; Lin, V. S.-

Y.; Therien, M. J. J. Org. Chem. 1993, 58, 5983-5993.

(54) Hyslop, A. G.; Kellett, M. A.; Iovine, P. M.; Therien, M. J. J. Am.

Chem. Soc. 1998, 120, 12676-12677.

(55) Murata, M.; Watanabe, S.; Masuda, Y. J. Org. Chem. 1997, 62, 6458-

6459.

(56) Yu, L.; Lindsey, J. S. Tetrahedron 2001, 57, 9285-9298.

6634 Inorganic Chemistry, Vol. 42, No. 21, 2003

Porphyrin-Containing Self-Assembled Triads

Scheme 6

8H₂O (1 equiv relative to Zn-5); 1,2-dimethoxyethane/H₂O

(10:1) at 80 °C under argon; [Zn-5] ) 20 mM and [Pd-2c]

) 10 mM. TLC analysis showed complete consumption of

the starting porphyrin after 2 h. Analytical size exclusion

chromatography (SEC) indicated the desired triad 6 was

formed in ∼50% yield, and a considerable amount of

monomeric porphyrin species was present (∼45%, as indi-

cated by analytical SEC). LD-MS analysis of this latter

product showed that deboronation and phenylation are the

major side reactions in this Suzuki coupling. Purification by

silica gel chromatography, preparative SEC, and silica gel

chromatography afforded the desired (ZnP-dp)₂Pd triad 6 in

50% yield (Scheme 6).

the synthesis of a porphyrin-dipyrromethane, which is then

oxidized to the porphyrin-dipyrrin. The reaction of bromo-

porphyrin 4 and 4-formylphenylboronic acid under standard

Suzuki coupling conditions afforded porphyrin 8a in 91%

yield (Scheme 7). Porphyrin-benzaldehyde 8b was prepared

via the reaction of a dipyrromethane bearing a carboxalde-

hyde group and a dipyrromethane-dicarbinol.⁵⁶Porphyrins

8a and 8b were converted to the zinc chelates Zn-8a and

Zn-8b (Scheme 8).

The availability of porphyrin-benzaldehydes prompted us

to explore the conditions for preparing porphyrin-substituted

dipyrromethanes, following the general method for preparing

dipyrromethanes shown in Scheme 1. In this method, the

aldehyde is dissolved in neat pyrrole and then treated with

a catalytic amount of TFA at room temperature.^36,37We

modified this method slightly.^14,58A solution of porphyrin-

benzaldehyde 8a or 8b (∼15 mM) in dichloromethane was

treated with a large excess of pyrrole (300-400 molar equiv).

When 0.1 equiv of TFA was employed, only a minor amount

of porphyrin-dipyrromethane was formed, but increasing the

Treatment of 6 with DTT at room temperature resulted in

selective demetalation of the bis(dipyrrinato)Pd complex,

affording the Zn-porphyrin-dipyrrin Zn-7a in 71% yield. No

demetalation of the Zn-porphyrin was observed by UV-vis

absorption or LD-MS analysis.

Route 2: Formation and Oxidation of a Dipyr-

romethane-Substituted Porphyrin. The second route entails

(57) Iovine, P. M.; Kellett, M. A.; Redmore, N. P.; Therien, M. J. J. Am.

Chem. Soc. 2000, 112, 8717-8727.

(58) Speckbacher, M.; Yu, L.; Lindsey, J. S. Inorg. Chem. 2003, 42, 4322-

4337.

Inorganic Chemistry, Vol. 42, No. 21, 2003 6635

Yu et al.

Scheme 7

Scheme 8

amount of TFA to 1.1 equiv led to complete consumption

of the porphyrin-benzaldehyde in 2 h. Chromatographic

purification using an eluant containing 1% TEA [silica,

CHCl₃/TEA (99:1)] to minimize acidolysis of the dipyr-

romethane afforded porphyrin-dipyrromethane 9a (86%) or

9b (80%) in good yield (Scheme 8).

The porphyrin-dipyrromethanes were treated under the

conditions for dipyrrin formation, employing p-chloranil in

the presence of Zn(OAc)₂‚2H₂O. The presumed product in

this reaction is the triad composed of two Zn porphyrins

attached to a central bis(dipyrrinato)zinc complex. However,

such triads were not stable upon exposure to the silica

chromatographic purification process, and the zinc porphyrin-

free base dipyrrin compounds Zn-7a and Zn-7b were

obtained in ∼70% yield (Scheme 8).

Route 3: Formation of a Porphyrin from a Dipyrrin-

Dipyrromethane. The reaction of a dipyrromethane and a

dipyrromethane-dicarbinol provides a straightforward route

to meso-substituted porphyrins.⁵⁹This approach is compatible

with diverse substituents, particularly upon attachment to the

dipyrromethane moiety. We sought to employ this method

using a dipyrromethane bearing a dipyrrin. Several routes

are available for the preparation of the precursor dipyrrin-

benzaldehyde 2g. Oxidation of dipyrromethane-benzaldehyde

1g with p-chloranil in the presence of Zn(OAc)₂‚2H₂O

afforded Zn-2g in 81% yield (Scheme 3); however, treatment

with DTT gave the free base dipyrrin 2g in only 31% yield

(Scheme 4). For a more expedient synthesis, 1g was treated

with p-chloranil in THF at room temperature for 24 h, giving

the free base dipyrrin in 60% yield (Scheme 9).

compound 10. Analysis by ¹H NMR spectroscopy indicated

the presence of an impurity, which gave signals consistent

with that for the N-confused dipyrromethane. The ratio of

10 and the N-confused isomer was 96:4; the combined yield

was 41% (Scheme 9). The mixture could not be separated

and was used directly in subsequent condensations.

The condensation of 10 with dipyrromethane-dicarbinol

11a-diol in the presence of TFA (30 mM) in CH₃CN for up

to 30 min followed by oxidation with DDQ failed to give

the porphyrin. We next examined the condensation of 10

and 11a-diol under new catalysis conditions that employ mild

The condensation of 2g (1 equiv) with pyrrole (50 equiv)

in CH₂Cl₂in the presence of TFA (1.2 equiv) afforded

(59) Rao, P. D.; Dhanalekshmi, S.; Littler, B. J.; Lindsey, J. S. J. Org.

Chem. 2000, 65, 7323-7344.

6636 Inorganic Chemistry, Vol. 42, No. 21, 2003

Porphyrin-Containing Self-Assembled Triads

Scheme 9

while a competition experiment of a dipyrrin (2b) and a

dipyrromethane (1a) in the reaction with a dipyrromethane-

dicarbinol (11a-diol) gave the porphyrin derived by exclusive

reaction with the dipyrromethane (see Supporting Informa-

tion). (2) Syntheses employing a mixed condensation of 2g,

mesitaldehyde, and pyrrole with BF₃‚OEt₂/ethanol cocatalysis

did not yield the porphyrin-dipyrrin, even with increased acid

concentration and prolonged reaction time. The success of

the dipyrromethane + dipyrromethane-dicarbinol condensa-

tion/oxidation in the presence of the dipyrrin highlights the

mild conditions of this transformation and the greater

reactivity of the dipyrromethane versus the dipyrrin toward

electrophilic substitution.

Bis(porphyrin-dipyrrinato)metal Triads. Triads com-

posed of two zinc porphyrins and one zinc-dipyrrin complex

were prepared as shown in Scheme 10. Treatment of Zn-

7a, Zn-7b, 7c, or 7d with Zn(OAc)₂‚2H₂O afforded the

desired (ZnP-dp)₂Zn triad 12a, 12b, 12c, or 12d in 83-97%

yield. In each case, the absorption spectral data indicated

the reaction had gone to completion. Attempts to perform

TLC analysis or column chromatography on silica, or SEC

(analytical or preparative), however, resulted in disassembly

of the bis(dipyrrinato)zinc unit and formation of the zinc

porphyrin-free base dipyrrin. The LD-MS spectrum showed

the expected molecule ion peak for the triad. Each triad was

examined by fluorescence spectroscopy, which indicated the

integrity of the zinc porphyrin.

Characterization. Chemical Characterization. The free

base dipyrrins and metal derivatives were generally assessed

for purity by TLC and characterized by absorption spectros-

copy, ¹H NMR spectroscopy, ¹³C NMR spectroscopy (except

Pd-2c), and FAB-MS. Acceptable elemental analyses were

obtained except for 2a-c, 2g, 2h, Pd-2b, Zn-2b, Zn-2g,

and 10. The porphyrins and triads were characterized by

1

absorption and fluorescence spectroscopy, H NMR spec-

troscopy, and LD-MS. Note that the bis(dipyrrinato)zinc(II)

complexes remained intact upon exposure to silica whereas

the all-zinc containing triads (ZnP-dp)₂Zn disassembled upon

exposure to silica (see Supporting Information). The ¹H NMR

spectra of all free base dipyrrins and their metal complexes

display simple coupling patterns derived from the protons

1

on the dipyrrin units. However, the H NMR spectrum (in

CDCl₃) of the free base dipyrrins showed no peak for the

NH proton in the dipyrrin moiety, possibly due to hydrogen

bonding.

The available crystal structure analyses for (dp)₂M com-

plexes include the following: (1) â-substituted dipyrrins

where the metal is palladium²⁷or nickel;³²(2) bis[5-(4-

nitrophenyl)dipyrrinato]nickel;³⁸(3) zinc complexes of dipyr-

rin multimers;^40,43,61and (4) a zinc complex in which each

dipyrrin bears one meso-substituent and one R-substituent.⁶²

A single crystal suitable for X-ray analysis was obtained by

slow evaporation of a solution of Zn-2a in CHCl₃/ethanol.

A summary of the crystal data for Zn-2a is given in Table

Lewis acid catalysts in CH₂Cl₂.⁶⁰Thus, the condensation of

10 and 11a-diol in the presence of InCl₃(0.32 mM) in CH₂-

Cl₂followed by oxidation with DDQ gave the desired

porphyrin 7c in 16% yield. Similarly, compound 7d was

synthesized in 10% yield by condensation of 10 and 11b-

diol. Two points concerning this approach are noteworthy.

(1) Reaction of a dipyrrin (2a) and a dipyrromethane-

dicarbinol (11a-diol) showed only a 2.5% yield of porphyrin,

(61) Subramanian, J.; Fuhrhop, J.-H. In The Porphyrins; Dolphin, D. Ed.,

Academic Press: New York, 1978; Vol. II, pp 255-285.

(62) Hill, C. L.; Williamson, M. M. J. Chem. Soc., Chem. Commun. 1985,

1228-1229.

(60) Geier, G. R., III; Callinan, J. B.; Rao, P. D.; Lindsey, J. S. J. Porphyrins

Phthalocyanines 2001, 5, 810-823.

Inorganic Chemistry, Vol. 42, No. 21, 2003 6637

Yu et al.

Scheme 10

Table 1. Crystal Data for Zn-2a‚CHCl₃

chemical formula

fw

C₃₁H₂₃Cl₃N₄Zn

623.28

cryst syst

space group

a/Å

b/Å

c/Å

â/deg

V, Å³

Z

monoclinic

C2/c (No. 15)

25.478(5)

10.9632(10)

22.143(4)

111.866(16)

5740.0(16)

8

T/°C

λ/Å

-125

Figure 1. ORTEP drawing of a representative molecule in the crystal

structure of Zn-2a. Only the asymmetric part of the structure is labeled.

Anisotropic displacement ellipsoids are drawn at the 50% probability level.

Hydrogen atom radii are set to arbitrary values for clarity.

0.71073

1.443

F/g cm^-1

µ/cm^-1

R^a

11.6

0.064

R_w

0.077

crystallographic 2-fold axis passing through the Zn atom

positions, which gives rise to a columnar structure running

along [010]. The Zn atom positions are separated on the

2-fold axis by approximately a half of the unit cell length

along the b axis. A depiction of one of the molecules is given

in Figure 1. Selected bond lengths and angles from the first

coordination sphere are given in Table 2. In the ensuing

^aDefinitions of R and R_w: R ) ∑|F_o- F_c|/∑F_o; R_w) [∑w(F_o- F_c)²/

∑wF_o]^1/2

.

2

1. The asymmetric unit consists of two symmetry indepen-

dent half molecules as well as a chloroform molecule

occupying a general lattice position, giving a total of eight

Zn-2a molecules per unit cell. Each molecule sits on a

6638 Inorganic Chemistry, Vol. 42, No. 21, 2003

Porphyrin-Containing Self-Assembled Triads

Figure 2. Absorption spectra in CH₂Cl₂at room temperature of free base

dipyrrin 2b and its bis(dipyrrinato)metal complexes.

Table 2. Selected Bond Lengths and Angles (Å, deg)^a

Zn1-N1

Zn1-N2

1.980(5)

1.972(5)

Zn2-N1′

Zn2-N2

1.987(5)

1.973(5)

N1-Zn1-N2

N1-Zn1-N1*

N1-Zn1-N2*

N2-Zn1-N2*

94.2(2)

120.3(2)

114.6(2)

121.0(2)

N1′-Zn2-N2′

N1′-Zn2-N1′*

N1′-Zn2-N2′*

N2′-Zn2-N2′*

94.7(2)

119.0(2)

114.9(2)

120.5(2)

^aThe asterisk indicates atoms related by the 2-fold crystallographic axis.

Figure 3. Electronic absorption spectra (s) and fluorescence spectra (- -

and ‚ ‚ ‚) for the triad 12a (A) and reference porphyrin Zn-8a (B) and bis-

(dipyrrinato)zinc Zn-2a (C) in toluene at room temperature. The absorption

spectra in the 450-650 nm region in parts A and B have been multiplied

by the factors shown. The triad emission in A and B was obtained using

the predominant zinc porphyrin excitation (- -) at 400 nm or bis-

(dipyrrinato)zinc excitation (‚ ‚ ‚) at 453 nm. Spectra in the respective regions

have been normalized to the same peak intensity, and the maxima ((1 nm)

indicated.

discussion, quantities for both symmetry independent mol-

ecules are reported with the quantities for the second

molecule given in parentheses. The following features of the

molecular structure of Zn-2a are pertinent: (1) Each dipyrrin

unit deviates only slightly from planarity. The dihedral angle

between the two pyrrolic rings in each dipyrrin is 1.2(3)°

(4.3(3)°). As expected, owing to conjugation, the dipyrrin

C-C bond lengths range between 1.349 and 1.428 Å. (2)

The dipyrrin ligands are nearly perpendicular to one another

with the dihedral angle between the N-Zn-N chelate planes

being 85.1(3)° (86.0(3))°. (3) The phenyl ring is also roughly

perpendicular to the dipyrrin moiety as evidenced by a

dihedral angle of 77.8(3)° (74.1(3)°). (4) The Zn-N bond

distances range from 1.972 to 1.987 Å.

Electrochemistry. The redox characteristics of a repre-

sentative bis(dipyrrinato)metal complex, Zn-2a, were ex-

amined in the 0-1.5 V range using both square-wave and

cyclic voltammetry. In this window, the complex exhibits

oxidation waves at 0.81 and 0.94 V (vs Ag/Ag⁺; E_1/2(Fc/

Fc⁺) ) 0.19 V). The cyclic voltammetric studies revealed,

however, that the redox process is highly irreversible. In

particular, the reductive waves for the two oxidation pro-

cesses are completely absent in the voltammogram. Scans

that were terminated at a potential between the two oxidation

waves also failed to reveal the reduction analogue of the

first oxidation wave. These results suggest that Zn-2a

demetalates upon formation of either the mono- or dication.

Bulk electrolysis studies of Zn-2a were further consistent

with this view.

ladium. Most striking is the change from the broad-band

absorption of the free base dipyrrin to the more intense, sharp

feature for the metallo complexes. Similar comparisons apply

for a wide variety of dipyrrins and their (dp)₂M com-

plexes,^{17,21,24,25,33}including those synthesized here.

The absorption spectra of (ZnP-dp)₂Zn triad 12a and

reference zinc porphyrin Zn-8a and bis(dipyrrinato)zinc

complex Zn-2a in toluene are shown in Figure 3 (s). The

spectrum of the triad is essentially the sum of the spectra of

the component parts. The ultimate porphyrin absorption

characteristics in the triad derive mainly from the addition

of the aryl ring at the linker site to starting porphyrin Zn-3

to give Zn-8a, with little change upon attachment of the

dipyrrin to give porphyrin-dipyrrin Zn-7a, or upon self-

assembly to produce (ZnP-dp)₂Zn triad 12a. Similar results

are found for triad 12b and its reference compounds, except

for spectral changes expected for porphyrins bearing four

instead of three meso-aryl substituents (see Scheme 10).

Similar findings were also obtained for the compounds in

benzonitrile, except that metal coordination red shifts the zinc

porphyrin absorption bands by 5-10 nm and alters the

Q-band ratios; in contrast, the (dp)₂Zn features are unper-

turbed. The spectral comparisons are given in the Supporting

Information. Thus, the (ZnP-dp)₂M triads display S₀f S₁

absorption of the bis(dipyrrinato)metal complex (∼485 nm)

sandwiched between the strong S₀f S₂Soret band (410-

Absorption Spectra. Figure 2 shows the absorption

spectra in CH₂Cl₂of free base dipyrrin 2b and its bis-

(dipyrrinato)metal(II) complexes with zinc, copper, or pal-

Inorganic Chemistry, Vol. 42, No. 21, 2003 6639

Yu et al.

Table 3. Photophysical Properties^a

zinc porphyrin

430 nm) and weaker S₀f S₁Q vibronic manifold (480-

610 nm) of the porphyrins.

bis(dipyrrinato)zinc

excited-state decay

Φ_f^bτ (ns)^cΦ_Q

Triads

Fluorescence Spectra, Quantum Yields, and Lifetimes.

The emission spectra of (ZnP-dp)₂Zn triad 12a and reference

porphyrin Zn-8a and bis(dipyrrinato)zinc complex Zn-2a in

toluene are shown in Figure 3 (- - and ‚‚‚). The fluores-

cence from reference Zn-2a has rough mirror symmetry to

the absorption with a rather large Stokes shift of ∼660 cm^-1.

The fluorescence quantum yield of Zn-2a is 0.007. The

emission from the triad occurs only from the porphyrin(s),

displaying Q(0,0) and Q(0,1) bands (∼595 and ∼640 nm)

present in reference Zn-8a, using direct excitation of either

the porphyrin (400 nm; - -) or the (dp)₂Zn complex (485

nm; ‚ ‚ ‚). Furthermore, the porphyrin fluorescence yields of

the triad are the same upon excitation of either type of subunit

(0.022 or 0.025). These yields are comparable to those for

the reference porphyrin, as are the lifetimes (∼2.6 ns) of

the excited zinc porphyrin (ZnP*) in the triad and isolated

chromophores in toluene (Table 3). Similar results are

obtained for triad 12b (and its component parts), except for

differences in emission profiles that parallel the absorption

spectra. The results for 12a and 12b in toluene demonstrate

the following. (1) Energy transfer from the excited bis-

(dipyrrinato)zinc complex, denoted [(dp)₂Zn]*, to a zinc

porphyrin to produce ZnP* is basically quantitative, as will

be addressed further below using the transient absorption

data. (2) There is minimal (<10%) quenching of ZnP* due

to the presence of (dp)₂Zn in the triads.

Differences in the fluorescence behavior for the com-

pounds in benzonitrile versus toluene are described in the

Supporting Information and summarized as follows (Table

3). (1) The fluorescence spectra, yields, and lifetimes of the

Zn porphyrin and the (dp)₂Zn complex are altered. The

fluorescence yield of Zn-2a in benzonitrile is 0.002. (2) State

[(dp)₂Zn]* in triads 12a or 12b may be modestly quenched

by a process (e.g., charge transfer) competing with energy

transfer to ZnP. (3) State ZnP* in the triads and ZnP-dp

species (Zn-7a and Zn-7b) is substantially quenched relative

to reference porphyrins (e.g., Zn-8a, Zn-8b). (3) More than

one structural/ligated/electronic form likely contributes to the

photophysics in the triads.

d

f

compd solvent

τ (ps)^e

Φ_EnT

12a

12b

toluene 0.022 (0.025)

PhCN

2.6 <0.1

1.4

0.97

∼0.8

0.97

∼0.8

0.010 (0.012) ∼1^g

∼0.6

2.4 <0.1

∼0.6

0.8

1.4

0.8

toluene 0.043 (0.037)

PhCN

0.030 (0.021) ∼1^g

Reference Compounds

2.5

Zn-7a toluene 0.019

PhCN 0.010

Zn-7b toluene 0.030

PhCN 0.020

toluene 0.024

PhCN 0.023

Zn-8a toluene 0.032

PhCN 0.032

Zn-8b toluene 0.033

1.5

2.4

1.5

2.6

2.7

2.8

2.7

2.8

2.5

0.45

Zn-3

PhCN

Zn-2a^htoluene

PhCN

0.034

9, 93

6.5, 1000ⁱ

^aAll data taken in toluene or benzonitrile (PhCN) at room temperature.

^bPorphyrin fluorescence yield (( 15%) for nondeoxygenated solutions

relative to ZnTPP in toluene (Φ_f) 0.030)⁷⁴obtained with predominant

porphyrin excitation in the Soret region (e.g., 400 nm for 12a and 12b).

The values in parentheses are for predominant excitation of the bis(dipyr-

rinato)zinc subunit at 453 nm for 12a and 487 nm for 12b. ^cZnP* lifetimes

((5%) were measured by fluorescence modulation spectroscopy using

samples deoxygenated by bubbling with dry nitrogen. ^dThe yield of

quenching of ZnP* by a process such as charge transfer derived from the

static and time-resolved optical spectroscopy. See Supporting Information

for the analysis of the data for the triads in benzonitrile, which give yields

of 0.6 ( 0.2. ^e[(dp)₂Zn]* lifetime determined by transient absorption

spectroscopy ((0.2 ps for the triads). ^fQuantum yield of energy transfer

from [(dp)₂Zn]* to ZnP in the [ZnP-dp]₂Zn triads, estimated from the

combined fluorescence and transient absorption data. The results for the

triads in benzonitrile are analyzed in the Supporting Information and give

values of 0.8 ( 0.2. ^gThe ZnP fluorescence profile for 12a in benzonitrile

is dual exponential with time constants of 0.9 ns (52%) and 2.2 ns (48%),

and a time constant of 0.7 ns was obtained by transient absorption, giving

the effective lifetime shown. For 12b in benzonitrile, the respective values

are 0.9 ns (50%), 2.1 ns (50%), and 0.7 ns. Effective time constants of ∼1

ns are listed. ^hThe fluorescence yield of Zn-2a is 0.007 in toluene and

0.002 in benzonitrile. ⁱIn addition to the fast (∼6.5 ps) phase associated

with [(dp)₂Zn]*, and the slower decay phase (∼1 ns) that may derive from

the excited or other (e.g., charge-transfer) states, a considerable (∼30%)

contribution of long-lived state (>5 ns) is also observed (not seen in toluene).

of the central (dp)₂Zn moiety with a 485 nm 130 fs flash.

The spectrum at 0.5 ps can be assigned mainly to [(dp)₂Zn]*

on the basis of the sharp trough in the 500-525 nm region.

This feature primarily reflects excited-state stimulated (by

the white-light probe pulse) emission that coincides with the

red side of the spontaneous emission from reference complex

Zn-2a (Figure 3C, - -). State ZnP* also contributes to the

0.5 ps spectrum on the basis of partial bleaching of the

porphyrin Q(1,0) ground-state band at 545 nm and weak

Q(0,1) stimulated emission at 640 nm. A contribution of

ZnP* at early times likely derives from direct porphyrin

excitation in a fraction of the arrays (in which (dp)₂Zn is

not excited) and the early stage of energy transfer from

[(dp)₂Zn]*. By 6.2 ps (- -), the [(dp)₂Zn]* stimulated

emission has decayed and is replaced by ZnP* excited-state

absorption along with further development of the ZnP*

features noted above.⁶³The kinetic trace and fit in Figure

4b shows decay of [(dp)₂Zn]* stimulated emission and

growth of ZnP* absorption; this time profile combined with

Time-Resolved Absorption Spectra. Triad 12a and the

benchmark bis(dipyrrinato)metal complex Zn-2a have been

characterized by time-resolved absorption spectroscopy in

toluene or benzonitrile. Transient absorption data for the bis-

(dipyrrinato)metal complexes will be described elsewhere.

A finding pertinent to the (ZnP-dp)₂Zn triads is that the

(dp)₂M complexes display multicomponent excited-state

profiles. For Zn-2a in toluene, a fast (∼9 ps) phase likely

represents electronic/conformational/vibrational relaxation in

the excited-state manifold while the slower (∼93 ps)

component reflects population decay of [(dp)₂M*]. The latter

phase is accompanied by substantial ground-state recovery,

indicating little formation of longer-lived transients such as

the triplet excited state. The situation changes to some extent

in benzonitrile (Table 3).

Figure 4 shows representative transient absorption differ-

ence spectra for triad 12a in toluene using primary excitation

6640 Inorganic Chemistry, Vol. 42, No. 21, 2003

Porphyrin-Containing Self-Assembled Triads

methods,⁶⁵energy transfer from [(dp)₂Zn]* to a zinc por-

phyrin subunit has rate constant k_EnT) (2‚1.4 ps)^-1- (93

ps)^-1) (2.8 ps)^-1and yield Φ_EnT) [1-2‚(1.4 ps)/(93 ps)]

) 0.97 (Table 3). The factors of 2 derive from the assumption

that the excited state of the (dp)₂Zn complex can transfer

energy with equal probability to either of the two zinc

porphyrin energy acceptors in each (ZnP-dp)₂Zn triad.

The excited-state dynamics are more complex for 12a or

12b in benzonitrile (Supporting Information), as is also the

case for (dp)₂Zn reference complex Zn-2a, with more than

one structural/ligated/electronic form probably contributing.

For Zn-2a in benzonitrile, the dynamics are different with

some uncertainty in the assignments: a fast (∼6.5 ps) phase

associated with [(dp)₂Zn]*, followed by a slower decay phase

(∼1 ns) that may derive from the excited or other (e.g.,

charge transfer) states, followed by a considerable (∼30%)

contribution of a long-lived state (>5 ns) not seen in toluene.

State [(dp)₂Zn]* in each triad has a lifetime of 0.8 ps,

compared to 1.4 ps in toluene and 6.5 ps for the fast decay

component in Zn-2a. Analysis of these lifetimes, the transient

absorption spectra, and the fluorescence data suggests that

energy transfer from [(dp)₂Zn]* to one of the zinc porphyrins

in each triad has a yield of 80 ( 20% that competes with

alternate routes such as charge transfer. The subsequent

spectral evolution in combination with the fluorescence data

indicates that ZnP* is 60 ( 20% quenched by a process such

as charge transfer (Table 3). Thus, energy transfer in the

self-assembled (Zn-dp)₂Zn triads is somewhat less effective

in polar, ligating solvents compared to the excellent behavior

in nonpolar media.

Outlook. Dyes must meet a number of challenging criteria

for use as accessory pigments with porphyrins. The bis-

(dipyrrinato)zinc complexes (1) are nonpolar (i.e., neutral),

thereby facilitating chemical manipulations, (2) form by self-

assembly from the free base dipyrrin, (3) provide spectral

coverage in the blue-green, a region where porphyrins absorb

poorly, and (4) can be synthesized by oxidation of dipyr-

romethanes with DDQ or p-chloranil in the presence of Zn-

(OAc)₂‚2H₂O. Three different routes to prepare porphyrin-

dipyrrins were developed. Static emission spectroscopy and

time-resolved absorption spectroscopy of two (ZnP-dp)₂Zn

triads indicated efficient energy transfer from the bis-

(dipyrrinato)zinc complexes to the zinc porphyrin. In com-

parison with the boron-dipyrrin complexes, the bis(dipyrrinato)-

zinc complexes have the distinct advantages of efficient self-

assembly and the ability to serve a mechanical role in linking

two porphyrins. Although the excited-state decay of bis-

(dipyrrinato)zinc complexes is shorter than that of boron-

dipyrrin complexes, a high yield of energy transfer can be

achieved in an appropriate architecture as shown herein.

The approach for preparing the self-assembled triads

described herein was inspired by the work of Collin, Sauvage,

and Flamigni aimed at preparing analogous triads based on

Figure 4. Representative time-resolved absorption spectra (A) and a kinetic

profile at 508 nm (B) for the triad 12a in toluene at room temperature using

predominant excitation of the bis(dipyrrinato)zinc subunit with a 485 nm

130 fs flash. The 0.5 ps spectrum (s) was constructed from spectra at closely

spaced time intervals in order to account for the time dispersion of

wavelengths in the white-light probe pulse. The fit to the data in part B is

the convolution of the instrument response with a dual exponential plus a

constant, giving time constants of 1.3 ps and ∼1 ns (inset). The average

(dp)₂Zn* and ZnP* lifetimes, respectively, deduced from measurements at

a number of probe wavelengths are given in Table 3.

those at other probe wavelengths gives a [(dp)₂Zn]* lifetime

of 1.4 ps (Table 3).

The spectrum at 6.2 ps then evolves slowly to 3.4 ns,

showing little remaining ZnP* stimulated emission while

retaining porphyrin Q(1,0) bleaching at 550 nm at about the

same amplitude (Figure 4a, ‚ ‚ ‚). These findings reflect the

decay of ZnP* to give the triplet excited-state ZnP^Tin high

yield, as is found for reference porphyrins (Φ_T∼ 0.9⁶⁴). The

subsequent spectral evolution for ZnP* decay (not shown)

is in keeping with the 2.6 ns fluorescence lifetime (Table

3).

Similar results were obtained for triad 12b in toluene,

including the same [(dp)₂Zn]* lifetime of 1.4 ps found for

12a, which is much shorter than the value of 93 ps for

(dp)₂Zn reference complex Zn-2a (Table 3). Using standard

(63) Rodriguez, J.; Kirmaier, C.; Holten, D. J. Am. Chem. Soc. 1989, 111,

6500-6506.

(64) (a) Gradyushko, A. T.; Sevchenko, A. N.; Solovyov, K. N.; Tsvirko,

M. P.; Photochem. Photobiol. 1970, 11, 387-400. (b) Hurley, J. K.;

Sinai, N.; Linschitz, H. Photochem. Photobiol. 1983, 38, 9-14. (c)

Kajii, Y.; Obi, K.; Tanaka, I.; Tobita, S. Chem. Phys. Lett. 1984, 111,

347-349. (d) Kikuchi, K.; Kurabayashi, Y.; Kokubun, H.; Kaizu, Y.;

Kobayashi, H. J. Photochem. Photobiol. A: Chem. 1988, 45, 261-

263. (e) Bonnett, R. D.; McGarvey, D. J.; Harriman, A.; Land, E. J.;

Truscott, T. G.; Winfield, U. J. Photochem. Photobiol. 1988, 48, 271-

276.

(65) (a) Yang, S. I.; Lammi, R. K.; Seth, J.; Riggs, J. A.; Arai, T.; Kim,

D.; Bocian, D. F.; Holten, D.; Lindsey, J. S. J. Phys. Chem. B 1998,

102, 9426-9436. (b) Prathapan, S.; Yang, S. I.; Seth, J.; Miller, M.

A.; Bocian, D. F.; Holten, D.; Lindsey, J. S. J. Phys. Chem. B 2001,

105, 8237-8248.

Inorganic Chemistry, Vol. 42, No. 21, 2003 6641

Yu et al.

mg, 3.00 mmol) in THF (10 mL) for 1 h at room temperature.

Removal of solvent and chromatography [silica, CHCl₃/MeOH (98:

2)] afforded a brown-black solid (415 mg, 51%): mp 148-150

terpyridyl-metallo complexes bridging two porphyrins in a

linear array.^44-47The synthesis of the latter arrays can be

done in a directed manner, affording unsymmetrical triads

(M¹P-terpy)M(terpy-M²P).^45,46No such directed methods yet

exist for the rational synthesis of unsymmetrical dipyrrin-

metal complexes. On the other hand, the terpy-based triads

generally have been designed to undergo photoinduced

electron transfer among the three components, though some

energy-transfer processes have been elicited with iridium-

terpy complexes upon UV illumination.⁴⁷The bis(dipyrri-

nato)zinc complexes undergo highly efficient energy transfer

following excitation and thus constitute viable accessory

pigments for the attached porphyrins.

1

°C; H NMR δ 1.39 (s, 9H), 6.39 (dd, J¹) 1.6 Hz, J²) 5.6 Hz,

2H), 6.66 (d, J ) 5.6 Hz, 2H), 7.44 (s, 4H), 7.64 (s, 2H); ¹³C NMR

δ 31.3, 34.7, 117.4, 124.5, 128.9, 130.7, 134.3, 140.9, 142.3, 143.3,

152.1; LD-MS obsd 274.8; FAB-MS obsd 277.1707 (M⁺+ H),

calcd 277.1705 (C₁₉H₂₀N₂). Anal. Calcd: C, 82.57; H, 7.29; N,

10.14. Found: C, 82.15; H, 7.37; N, 9.93. λ_abs(CH₂Cl₂, log ꢀ) 327

(3.97), 433 (4.36) nm.

5-(4-Formylphenyl)dipyrrin (2g). A solution of 1g (1.15 g, 4.60

mmol) in THF (46 mL) was treated with p-chloranil (1.13 g, 4.60

mmol). The reaction mixture was stirred at room temperature for

24 h. The mixture was diluted with CHCl₃, washed with water,

and dried (Na₂SO₄). The solvent was evaporated under reduced

pressure to afford a dark residue. The dark residue obtained was

chromatographed [silica, hexanes/ethyl acetate (3:1)], affording an

orange oil (0.68 g, 60%). The analytical data were identical to those

obtained for the product prepared by demetalation of Zn-2g.

5-Mesityldipyrrin (2h). Following the procedure described for

the preparation of 2a, a solution of 1h (264 mg, 1.00 mmol) in

THF (5 mL) was treated with a solution of DDQ (227 mg, 1.00

mmol) in THF (3 mL) for 30 min at room temperature. Removal

of solvent and chromatography [silica, CH₂Cl₂/MeOH (98:2)]

afforded a brown solid (150 mg, 57%): mp 114-116 °C; ¹H NMR

δ 2.08 (s, 6H), 2.35 (s, 3H), 6.32 (d, J ) 4.4 Hz, 2H), 6.40 (d, J

) 4.4 Hz, 2H), 6.91 (s, 2H), 7.62 (s, 2H); ¹³C NMR δ 19.9, 21.1,

117.6, 117.7, 127.3, 127.7, 133.4, 136.6, 137.4, 140.5, 140.9; LD-

MS obsd 261.7, calcd av mass 262.4 (C₁₈H₁₈N₂). Anal. Calcd: C,

82.41; H, 6.92; N, 10.68. Found: C, 81.63; H, 6.97; N, 10.37. λ_abs

(CH₂Cl₂) 431 nm.

Experimental Section

1

General. H NMR spectra (300 or 400 MHz) and ¹³C NMR

spectra (75 or 100 MHz) were collected in CDCl₃. Absorption

spectra and fluorescence spectra were collected in CH₂Cl₂or toluene

at room temperature. Mass spectra of porphyrins were obtained

via laser desorption mass spectrometry (LD-MS) in the absence of

an added matrix,⁶⁶or by high-resolution fast atom bombardment

mass spectrometry (FAB-MS). All reagents were obtained from

Aldrich and were used as received. The known compounds 1a-

c,³⁷1d,⁵⁶1e,^37,671f,⁵⁹1g,⁵⁹1h,³⁷1i,⁶⁸1j,³⁷8b,⁵⁶11a,⁵⁹11b,⁵⁹11a-

diol,⁵⁹and 11b-diol⁵⁹were prepared according to literature

procedures.

Solvents. All solvents were dried by standard methods. Toluene

was distilled from CaH₂. Anhydrous DMF, 1,2-dimethoxyethane,

CH₂Cl₂, and CHCl₃(certified ACS grade stabilized with 0.8%

ethanol) were used as received.

Chromatography. Adsorption column chromatography was

performed using flash silica gel (Baker, 60-200 mesh). Preparative-

scale size exclusion chromatography (SEC) was performed using

BioRad Bio-beads SX-1 in THF (HPLC grade). Analytical SEC⁶⁹

(λ ) 420 nm) was performed to monitor the progress of the coupling

reactions.

Synthesis of Dipyrrins by Oxidation of Dipyrromethane.

5-Phenyldipyrrin (2a). To a solution of 1a (666 mg, 3.00 mmol)

in THF (10 mL) was added dropwise a solution of DDQ (681 mg,

3.00 mmol, one molar equiv) in THF (10 mL). TLC analysis (silica,

CHCl₃) indicated complete consumption of the starting materials

after stirring for 1 h at room temperature. The mixture was poured

into H₂O, extracted with CHCl₃, and dried (Na₂SO₄). Column chro-

matography [silica, CHCl₃/MeOH (99:1)] afforded a brown oil

which partially solidified upon storage overnight at 0 °C (280 mg,

42%): mp 176-178 °C; ¹H NMR δ 6.39 (dd, J¹) 1.2 Hz, J²) 4.2

Hz, 2H), 6.60 (d, J ) 4.2 Hz, 2H), 7.43-7.52 (m, 5H), 7.65 (s, 2H);

¹³C NMR δ 117.5, 127.5, 128.9, 129.1, 130.7, 137.2, 140.5, 143.6;

FAB-MS obsd 221.1068 (M⁺+ H), calcd 221.1079 (C₁₅H₁₂N₂);

λ_abs(CH₂Cl₂, log ꢀ) 309 (3.84), 432 (4.28) nm. See ref 38.

5-(4-tert-Butylphenyl)dipyrrin (2b). Following the procedure

described for the preparation of 2a, a sample of 1b (834 mg, 3.00

mmol) in THF (10 mL) was treated with a solution of DDQ (681

5-(Pentafluorophenyl)dipyrrin (2j). Following the procedure

described for the preparation of 2a, a sample of 1j (624 mg, 2.00

mmol) in THF (5 mL) was treated with a solution of DDQ (454

mg, 2.00 mmol) in THF (5 mL) at room temperature. TLC analysis

[silica, hexanes/CH₂Cl₂(1:1)] after 40 min showed incomplete

oxidation; therefore, an additional amount of DDQ (91 mg, 0.40

mmol) in THF (2 mL) was added and stirred for another 20 min at

room temperature. Removal of solvent and chromatography [silica,

hexanes/CH₂Cl₂(1:1)] afforded a brown-yellowish solid (530 mg,

1

85%): mp 116-117 °C; H NMR δ 6.42 (dd, J¹) 1.2 Hz, J²)

4.0 Hz, 2H), 6.47 (d, J ) 4.0 Hz, 2H), 7.66 (s, 2H); ¹³C NMR δ

118.9, 123.8, 126.8, 140.3, 145.4. Anal. Calcd: C, 58.07; H, 2.27;

N, 9.03. Found: C, 58.21; H, 2.19; N, 9.06 (C₁₅H₇F₅N₂). λ_abs(CH₂-

Cl₂) 430 nm.

Synthesis of Bis(dipyrrinato)metal Complexes by Metalation

of Dipyrrins. Bis[5-(4-tert-butylphenyl)dipyrrinato]copper(II)

(Cu-2b). A solution of 2b (113 mg, 0.410 mmol) in CH₂Cl₂(10

mL) was treated with a suspension of Cu(OAc)₂‚H₂O (204 mg,

1.02 mmol, 2.5 molar equiv) in methanol (∼3 mL). The mixture

was stirred at room temperature for 10 min. UV-vis spectroscopic

analysis showed no remaining free base dipyrrin. The reaction

mixture was then diluted with CH₂Cl₂(30 mL) and washed with

H₂O. The organic layer was separated and dried (Na₂SO₄).

Chromatography (silica, CH₂Cl₂) afforded a brown solid (104 mg,

82%): mp > 280 °C; LD-MS obsd 611.5, FAB-MS obsd 613.2408,

calcd 613.2392 (C₃₈H₃₈CuN₄). Anal. Calcd: C, 74.30; H, 6.24; N,

9.12. Found: C, 74.19; H, 6.37; N, 8.91. λ_abs(CH₂Cl₂, log ꢀ) 342

(4.38), 466 (4.83), 499 (4.54) nm.

(66) (a) Srinivasan, N.; Haney, C. A.; Lindsey, J. S.; Zhang, W.; Chait, B.

T. J. Porphyrins Phthalocyanines 1999, 3, 283-291. (b) Fenyo, D.;

Chait, B. T.; Johnson, T. E.; Lindsey, J. S. J. Porphyrins Phthalo-

cyanines 1997, 1, 93-99.

(67) Wang, Q. M.; Bruce, D. W. SYNLETT 1995, 1267-1268.

(68) Hammel, D.; Erk, P.; Schuler, B.; Heinze, J.; Mu¨llen, K. AdV. Mater.

1992, 4, 737-739.

(69) Wagner, R. W.; Johnson, T. E.; Lindsey, J. S. J. Am. Chem. Soc. 1996,

118, 11166-11180.

Bis[5-(4-tert-butylphenyl)dipyrrinato]palladium(II) (Pd-2b).

A solution of 2b (28 mg, 0.10 mmol) in CHCl₃(2.0 mL) and TEA

(0.50 mL) was treated with Pd₂(dba)₃(228 mg, 0.250 mmol) in

methanol (1 mL) overnight at room temperature. The mixture was

6642 Inorganic Chemistry, Vol. 42, No. 21, 2003

Porphyrin-Containing Self-Assembled Triads

diluted with CHCl₃(5 mL) and filtered through a pad of silica gel

(CHCl₃). Chromatography (silica, CHCl₃) afforded a red-orange

solid (28 mg, 85%): mp > 280 °C; ¹H NMR δ 1.42 (s, 18H), 6.36

(dd, J¹) 1.6 Hz, J²) 4.4 Hz, 4H), 6.77 (dd, J¹) 1.6 Hz, J²)

4.4 Hz, 4H), 7.41 (s, 4H), 7.48 (d, J ) 8.0 Hz, 4H), 7.52 (d, J )

8.0 Hz, 4H); ¹³C NMR δ 31.4, 34.8, 116.6, 124.3, 130.3, 131.3,

134.6, 137.2, 148.2, 151.5, 151.8; FAB-MS obsd 656.2166, calcd

656.2131 (C₃₈H₃₈N₄Pd). Anal. Calcd: C, 69.45; H, 5.83; N, 8.53.

Found: C, 68.74; H, 6.00; N, 7.88. λ_abs(CH₂Cl₂, log ꢀ) 342 (4.42),

376 (4.32), 479 (5.02) nm.

(1 mL) for 40 min at room temperature. The same workup procedure

afforded a yellow solid (99 mg, 78%) with identical analytical data.

See ref 38.

Bis[5-(4-tert-butylphenyl)dipyrrinato]zinc(II) (Zn-2b). A mix-

ture of 1b (115 mg, 0.413 mmol) and Zn(OAc)₂‚2H₂O (227 mg,

1.03 mmol, 2.5 equiv) in THF (5 mL) was treated with p-chloranil

(102 mg, 0.413 mmol) overnight at room temperature. The reaction

mixture was poured into H₂O, extracted with CHCl₃, and dried (Na₂-

SO₄). The solvent was removed, and the residue was collected into

CHCl₃(5 mL) and was treated with Zn(OAc)₂‚2H₂O (227 mg, 0.413

mmol) in methanol (1.0 mL) overnight at room temperature.

Standard workup and chromatography (silica, CH₂Cl₂) afforded a

Bis[5-(4-iodophenyl)dipyrrinato]palladium(II) (Pd-2c). A so-

lution of 2c (140 mg, 0.40 mmol) in CH₂Cl₂(5 mL) was treated

with Pd(OAc)₂(90 mg, 0.40 mmol) at room temperature. UV-vis

and TLC analysis (silica, CHCl₃) indicated complete metalation

after 20 min. Removal of solvent and chromatography (silica, CH₂-

Cl₂) afforded a yellow-orange solid (80 mg, 50%): mp > 280 °C;

¹H NMR δ 6.37 (dd, J¹) 1.2 Hz, J²) 4.0 Hz, 4H), 6.69 (d, J )

4.0 Hz, 4H), 7.32 (d, J ) 8.4 Hz, 4H), 7.39 (m, 4H), 7.83 (d, J )

8.4 Hz, 4H); LD-MS obsd 752.8, calcd 753.9 (C₃₀H₂₀I₂N₄Pd); Anal.

Calcd: C, 45.22; H, 2.53; N, 7.03. Found: C, 45.26; H, 2.51; N,

6.78. λ_abs(CHCl₃, log ꢀ) 333 (br, 4.19), 385 (br, 4.11), 482 (4.78)

nm.

1

yellow solid (105 mg, 82%): mp > 280 °C; H NMR δ 1.41 (s,

18H), 6.39-6.41 (m, 4H), 6.76 (d, J ) 4.2 Hz, 4H), 7.46 (d, J )

8.4 Hz, 4H), 7.50 (d, J ) 8.4 Hz, 4H), 7.53 (s, br, 4H); ¹³C NMR

δ 31.4, 34.7, 116.8, 124.0, 130.6, 133.0, 136.1, 140.7, 149.2, 149.5,

151.6; FAB-MS obsd 614.2392, calcd 614.2388 (C₃₈H₃₈N₄Zn).

Anal. Calcd: C, 74.08; H, 6.22; N, 9.09. Found: C, 73.43; H, 6.18;

N, 8.96. λ_abs(CH₂Cl₂, log ꢀ) 338 (br, 4.30), 482 (5.06) nm.

Bis[5-(4-iodophenyl)dipyrrinato]zinc(II) (Zn-2c). A mixture

of 1c (1.92 g, 5.51 mmol) and Zn(OAc)₂‚2H₂O (3.02 g, 13.8 mmol,

2.5 equiv) in THF (75 mL) was treated with p-chloranil (1.35 g,

5.51 mmol). After stirring overnight at room temperature, the entire

reaction mixture was filtered through a short pad of silica gel, which

was then washed with THF. Solvent was removed, and the residue

was collected in CHCl₃(100 mL). Zn(OAc)₂‚2H₂O (1.21 g, 5.51

mmol) in methanol (10 mL) was added, and the mixture was stirred

overnight at room temperature. The reaction mixture was then

washed with aqueous NaHCO₃and H₂O and dried (Na₂SO₄). The

organic layer was dried (Na₂SO₄), concentrated, and chromato-

graphed (silica, CHCl₃), affording a yellow solid. The solid was

washed (sonicated) with methanol (1.35 g, 65%): mp > 280 °C;

¹H NMR δ 6.42 (dd, J¹) 1.2 Hz, J²) 4.4 Hz, 4H), 6.69-6.70

(m, 4H), 7.30 (d, J ) 8.0 Hz, 4H), 7.53 (s, br, 4H), 7.81 (d, J )

8.0 Hz, 4H); ¹³C NMR δ 117.4, 132.3, 132.7, 136.4, 138.4, 140.2,

147.2, 150.1; LD-MS obsd 756.9, calcd 753.9 (C₃₀H₂₀I₂N₄Zn). Anal.

Calcd: C, 47.68; H, 2.67; N, 7.41. Found: C, 47.83; H, 2.71; N,

7.38. λ_abs(CH₂Cl₂, log ꢀ) 333 (br, 4.29), 485 (5.08) nm

Bis[5-(4-iodophenyl)dipyrrinato]palladium(II) (Pd-2c). A so-

lution of 1c (5.27 g, 15.1 mmol) in THF (150 mL) was treated

overnight with p-chloranil (3.71 g, 15.1 mmol) at room temperature.

Solvent was removed, and the residue was collected in CH₂Cl₂(150

mL), sonicated, and filtered to remove the quinone species. The

filtrate was concentrated, affording a brown solid. This crude

product was dissolved in CH₂Cl₂(150 mL) and was treated with

Pd(OAc)₂(6.78 g, 30.2 mmol) at room temperature. TLC and UV-

vis analysis indicated complete metalation after 20 min. The red-

orange solid precipitated from the reaction mixture. Filtration and

washing with CH₂Cl₂afforded a red-orange solid (2.46 g, 43%).

The analytical data were identical to those obtained for the product

prepared by metalation of the dipyrrin. The one-flask oxidation/

complexation process employed to form zinc-dipyrrin complexes

applied to 1c using p-chloranil and Pd(OAc)₂in THF gave slow

reaction and afforded the product Pd-2c in only 30% yield.

Bis[5-[4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl]-

dipyrrinato]zinc(II) (Zn-2d). A mixture of 1d (348 mg, 1.00

mmol) and Zn(OAc)₂‚2H₂O (549 mg, 2.50 mmol) in THF (14 mL)

was treated overnight with p-chloranil (246 mg, 1.00 mmol) at room

temperature. The mixture was poured into H₂O and extracted with

CHCl₃. The organic layer was dried (Na₂SO₄) and chromatographed

[silica, CHCl₃f CHCl₃/methanol (95:5)], affording a yellow solid.

The solid was dissolved in CHCl₃and precipitated with methanol

(321 mg, 85%): mp 272 °C (dec); ¹H NMR δ 1.40 (s, 24H), 6.40

(dd, J¹) 1.2 Hz, J²) 4.2 Hz, 4H), 6.69 (dd, J¹) 1.2 Hz, J²)

4.2 Hz, 4H), 7.53 (br, s, 4H), 7.58 (d, J ) 8.4 Hz, 4H), 7.90 (d, J

) 8.4 Hz, 4H); ¹³C NMR (100 MHz) δ 24.93, 84.01, 117.08,

129.98, 132.86, 133.42, 140.35, 141.80, 148.59, 149.78; LD-MS

obsd 752.5, calcd exact mass 754.3 (C₄₂H₄₄B₂N₄O₄Zn). Anal.

Calcd: C, 66.74; H, 5.87; N, 7.41. Found: C, 66.87; H, 5.78; N,

7.45. λ_abs(CH₂Cl₂, log ꢀ) 323 (br, 4.26), 483 (5.07) nm.

Bis[5-(4-formylphenyl)dipyrrinato]zinc(II) (Zn-2g). A solution

of 1g (1.15 g, 4.60 mmol) in THF (46 mL) was treated with Zn-

(OAc)₂‚2H₂O (2.52 g, 11.5 mmol) and p-chloranil (1.13 g, 4.60

mmol). The reaction mixture was stirred at room temperature for

20 h. The mixture was diluted with CHCl₃, washed with water,

and dried (Na₂SO₄). The solvent was evaporated under reduced

pressure to afford a dark residue. The dark residue obtained was

chromatographed [silica, CH₂Cl₂/ethyl acetate (9:1)], affording an

orange solid. The orange solid was washed with methanol (to

One-Flask Syntheses of Bis(dipyrrinato)zinc Complexes from

the Dipyrromethane. Bis(5-phenyldipyrrinato)zinc(II) (Zn-2a).

A mixture of 1a (111 mg, 0.500 mmol) and Zn(OAc)₂‚2H₂O (274

mg, 1.25 mmol) in THF (5 mL) was treated all at once with

p-chloranil (123 mg, 0.500 mmol). TLC (silica, CHCl₃) showed

no dipyrromethane remained after stirring for 27 h at room

temperature. Solvent was removed, and the residue was dissolved

in CHCl₃. The organic phase was washed with aqueous NaHCO₃

and H₂O and dried (Na₂SO₄). Chromatography [silica, CHCl₃f

1

CHCl₃/MeOH (98:2)] afforded a yellow solid. H NMR analysis

of this product showed a mixture of the free base dipyrrin and the

zinc(II)-dipyrrin complex. This mixture was dissolved in CHCl₃

(5 mL) and treated with Zn(OAc)₂‚2H₂O (274 mg, 1.25 mmol) in

methanol (1 mL) at room temperature. After stirring overnight,

standard workup and chromatography (silica, CHCl₃) afforded a

1

yellow solid (102 mg, 81%): mp 225-227 °C; H NMR δ 6.40

(dd, J¹) 4.0 Hz, J²) 1.2 Hz, 6H), 6.71 (d, J ) 3.6 Hz, 6H),

7.44-7.50 (m, 4H), 7.55-7.58 (m, 6H); ¹³C NMR δ 117.0, 127.1,

128.4, 130.6, 132.9, 139.0, 140.6, 148.7, 149.7; FAB-MS obsd

502.1172, calcd 502.1136 (C₃₀H₂₂N₄Zn). Anal. Calcd: C, 71.50;

H, 4.40; N, 11.12. Found: C, 71.29; H, 4.56; N, 11.21. λ_abs(CH₂-

Cl₂, log ꢀ) 322 (br, 4.14), 482 (5.06) nm. Alternatively, the same

mixture of 1a and Zn(OAc)₂‚2H₂O in THF (5 mL) was treated

dropwise with a solution of DDQ (114 mg, 0.500 mmol) in THF

Inorganic Chemistry, Vol. 42, No. 21, 2003 6643

Yu et al.

remove any quinone species present) to afford an orange solid (1.05

2b. A solution of Pd-2b (34 mg, 0.052 mmol) in CH₂Cl₂(10 mL)

was treated with DTT (80 mg, 0.52 mmol, 10 molar equiv) at room

temperature. TLC and UV-vis analysis showed complete demeta-

lation after 17 h. The reaction mixture was diluted with CH₂Cl₂,

washed with H₂O, and dried (Na₂SO₄). Removal of solvent and

chromatography [silica, ethyl acetate/hexanes (1:2)] afforded a

slightly brown solid (23 mg, 79%). The analytical data were

identical to those obtained for the product prepared by direct

oxidation of the dipyrromethane.

1

g, 81%): mp 221-223 °C; H NMR δ 6.44 (dd, J¹) 1.2 Hz, J²

) 4.4 Hz, 4H), 6.64 (dd, J¹) 0.8 Hz, J²) 4.4 Hz, 4H), 7.58 (s,

4H), 7.75 (d, J ) 8.0 Hz, 4H), 8.01 (d, J ) 8.0 Hz, 4H), 10.16 (s,

2H); ¹³C NMR δ 117.75, 128.69, 131.40, 132.75, 136.35, 140.00,

145.16, 146.77, 191.91. Anal. Calcd for C₃₂H₂₂N₄O₂Zn: C, 68.08;

H, 3.87; N, 10.24. Found: C, 68.88; H, 3.95; N, 9.99. λ_abs(CH₂-

Cl₂) 486 nm.

Bis[5-mesityldipyrrinato]zinc(II) (Zn-2h). A mixture of 1h

(264 mg, 1.00 mmol) and Zn(OAc)₂‚2H₂O (549 mg, 2.50 mmol)

in THF (10 mL) was treated with p-chloranil (248 mg, 1.00 mmol)

overnight at room temperature. Removal of solvent and chroma-

tography (silica, CH₂Cl₂) afforded an orange solid. The orange solid

was washed with methanol and dried giving an orange solid (253

5-(4-Iodophenyl)dipyrrin (2c) from Demetalation of Zn-2c.

A solution of Zn-2c (227 mg, 0.300 mmol) in CH₂Cl₂(30 mL)

was treated with DTT (462 mg, 3.00 mmol, 10 equiv) at room

temperature. UV-vis analysis indicated complete demetalation after

30 min. Then, the reaction mixture was washed with H₂O three

times and dried (Na₂SO₄). Removal of solvent and chromatography

(silica, CH₂Cl₂) afforded a brown solid (176 mg, 85%): mp 145

1

mg, 86%): mp 254-256 °C; H NMR δ 2.18 (s, 12H), 2.38 (s,

6H), 6.35 (d, J ) 4.0 Hz, 4H), 6.58 (d, J ) 4.0 Hz, 4H), 6.95 (s,

4H), 7.47 (s, 4H); ¹³C NMR (100 MHz) δ 19.9, 21.1, 117.1, 127.6,

131.1, 135.4, 136.4, 137.1, 140.0, 148.2, 149.1; MALDI-MS

(dithranol) obsd 586.5, calcd av mass 588.1 (C₃₆H₃₄N₄Zn). Anal.

Calcd: C, 73.53; H, 5.83; N, 9.53. Found: C, 73.21; H, 5.78; N,

9.47. λ_abs(CH₂Cl₂) 345 (br), 485 nm.

1

°C (dec); H NMR δ 6.41 (dd, J¹) 1.6 Hz, J²) 4.4 Hz, 2H),

6.58-6.59 (m, 2H), 7.23 (d, J ) 8.4 Hz, 2H), 7.67 (s 2H), 7.79 (d,

J ) 8.4 Hz, 2H); ¹³C NMR δ 117.7, 130.5, 132.5, 136.9, 144.0;

LD-MS obsd 345.6; FAB-MS obsd 347.0045 (M⁺+ H), calcd

347.0053 (C₁₅H₁₁IN₂); λ_abs(CH₂Cl₂, log ꢀ) 320 (3.98), 433 (4.33)

nm.

5-(4-Iodophenyl)dipyrrin (2c) from Demetalation of Pd-2c.

A suspension of Pd-2c (159 mg, 0.200 mmol) in CH₂Cl₂(40 mL)

was treated with DTT (308 mg, 2.00 mmol, 10 equiv) at room

temperature. UV-vis analysis indicated complete demetalation after

18 h. Then, the reaction mixture was washed with H₂O three times

and dried (Na₂SO₄). Removal of solvent and chromatography [silica,

ethyl acetate/hexanes (1:2)] afforded a brown solid (124 mg, 89%).

The analytical data were identical to those obtained for the product

prepared from demetalation of Zn-2c.

5-(4-Formylphenyl)dipyrrin (2g) from Demetalation of Zn-

2g. A solution of Zn-2g (0.750 g, 1.34 mmol) in CH₂Cl₂(134 mL)

was treated with DTT (2.06 g, 13.4 mmol) at room temperature.

After 1 h, the TLC examination of the reaction mixture indicated

that the Zn complex was completely consumed. The reaction

mixture was diluted with CH₂Cl₂and washed with water. The

organic layer was dried (Na₂SO₄) and concentrated. Chromatog-

raphy (silica, CHCl₃) afforded a dark oil (204 mg, 31%): ¹H NMR

δ 6.41 (dd, J¹) 1.6 Hz, J²) 4.4 Hz, 2H), 6.52 (dd, J¹) 0.4 Hz,

J²) 4.0 Hz, 2H), 7.67-7.68 (m, 4H), 7.97-7.98 (m, 2H), 10.12

(s, 1H); ¹³C NMR δ 118.20, 128.45, 129.01, 131.40, 136.50, 139.94,

140.55, 143.46, 144.32, 191.82. Anal. Calcd for C₁₆H₁₂N₂O: C,

77.40; H, 4.87; N, 11.28. Found: C, 76.95; H, 4.94; N, 10.95. λ_abs

(CH₂Cl₂) 439 nm.

Synthesis of Porphyrins. 5,15-Dimesitylporphyrin (3). Fol-

lowing a published procedure,⁷⁰a solution of dipyrromethane (1e)

(1.75 g, 12.0 mmol) and mesitaldehyde (1.78 g, 12.0 mmol) in

CHCl₃(1200 mL) was flushed with argon for 5 min and treated

with BF₃‚OEt₂(840 µL, 3.3 mM) at room temperature for 30 min

under argon. DDQ (4.09 g, 18.0 mmol) was added, and the mixture

was stirred for another 1 h. Triethylamine (920 µL, 3.3 mM) was

added, and the entire reaction mixture was filtered through a pad

of alumina. The alumina pad was washed with CHCl₃until the

eluent was colorless. Removal of solvent and chromatography

[silica, CHCl₃/hexanes, (2:1)] afforded a purple solid (922 mg,

28%): ¹H NMR δ -3.08 (s, br, 2H), 1.84 (s, 12H), 2.66 (s, 6H),

7.32 (s, 4H), 8.88 (d, J ) 4.5 Hz, 4H), 9.32 (d, J ) 4.5 Hz, 4H),

10.22 (s, 2H); LD-MS obsd 544.9; FAB-MS obsd 546.2776, calcd

546.2783 (C₃₈H₃₄N₄); λ_abs(toluene) 407, 502, 532, 576, 632 nm;

λ_em(λ_ex) 500 nm, toluene) 632, 701 nm.

Bis[5-(pentafluorophenyl)dipyrrinato]zinc(II) (Zn-2j). A mix-

ture of 1j (312 mg, 1.00 mmol) and Zn(OAc)₂‚2H₂O (549 mg, 2.50

mmol) in THF (10 mL) was treated with DDQ (272 mg, 1.20 mmol)

for 40 min at room temperature. The reaction mixture was filtered

through a pad of silica and washed with CH₂Cl₂. The solvent was

removed, and the residue was dissolved in CH₂Cl₂(30 mL) and

was treated with a solution of Zn(OAc)₂‚2H₂O (549 mg, 2.50 mmol)

in methanol (5.0 mL) overnight at room temperature. The reaction

mixture was washed with aqueous NaHCO₃, H₂O and dried (Na₂-

SO₄). Chromatography [silica, hexanes/CH₂Cl₂(1:1)] afforded an

orange-red solid, which was washed with methanol (190 mg,

1

55%): mp 266-268 °C; H NMR δ 6.46 (d, J ) 4.0 Hz, 4H),

6.67 (d, J ) 4.0 Hz, 4H), 7.59 (s, 4H); ¹³C NMR δ 118.7, 130.4,

131.2, 139.5, 151.7. Anal. Calcd: C, 52.69; H, 1.77; N, 8.19.

Found: C, 52.66; H, 1.73; N, 8.14 (C₃₀H₁₂F₁₀N₄Zn). λ_abs(CH₂Cl₂)

496 nm. Alternatively, the same mixture of 1j (312 mg, 1.00 mmol)

and Zn(OAc)₂‚2H₂O (547 mg, 2.50 mmol) in THF (10 mL) was

treated overnight with p-chloranil (297 mg, 1.20 mmol) at room

temperature. The same workup procedure afforded an orange-red

solid (105 mg, 31%) with identical analytical data.

Synthesis of Dipyrrins via DTT-Mediated Demetalation of

Bis(dipyrrinato)metal Complexes. 5-Phenyldipyrrin (2a). A

solution of Zn-2a (163 mg, 0.323 mmol) in CH₂Cl₂(60 mL) was

treated with DTT (498 mg, 3.23 mmol, 10 molar equiv) at room

temperature. TLC and UV-vis analysis showed complete demeta-

lation after 30 min. The reaction mixture was diluted with CH₂Cl₂,

washed with H₂O, and dried (Na₂SO₄). Removal of solvent and

chromatography [silica, ethyl acetate/hexanes (1:2)] afforded a

slightly brown solid (114 mg, 80%). The analytical data were

identical to those obtained for the product prepared by direct

oxidation of the dipyrromethane.

5-(4-tert-Butylphenyl)dipyrrin (2b) from Demetalation of Cu-

2b. A solution of Cu-2b (50 mg, 0.081 mmol) in CH₂Cl₂(15 mL)

was treated with DTT (125 mg, 0.81 mmol, 10 molar equiv) at

room temperature. TLC and UV-vis analysis showed complete

demetalation after 10 min. The reaction mixture was diluted with

CH₂Cl₂, washed with H₂O, and dried (Na₂SO₄). Removal of solvent

and chromatography [silica, ethyl acetate/hexanes (1:2)] afforded

a slightly brown solid (43 mg, 95%). The analytical data were

identical to those obtained for the product prepared by direct

oxidation of the dipyrromethane.

(70) Littler, B. J.; Ciringh, Y.; Lindsey, J. S. J. Org. Chem. 1999, 64, 2864-

5-(4-tert-Butylphenyl)dipyrrin (2b) from Demetalation of Pd-

2872.

6644 Inorganic Chemistry, Vol. 42, No. 21, 2003

Porphyrin-Containing Self-Assembled Triads

5,15-Dimesitylporphinatozinc(II) (Zn-3). A solution of free

base porphyrin 3 (218 mg, 0.400 mmol) in CHCl₃(30 mL) was

treated overnight with a solution of Zn(OAc)₂‚2H₂O (438 mg, 2.00

mmol) in methanol (5.0 mL) at room temperature. Standard workup

and washing with methanol afforded a red-purple solid (235 mg,

96%): ¹H NMR δ 1.82 (s, 12H), 2.66 (s, 6H), 7.32 (s, 4H), 8.95

(d, J ) 4.5 Hz, 4H), 9.37 (d, J ) 4.5 Hz, 4H), 10.23 (s, 2H); LD-

MS obsd 606.6; FAB obsd 608.1926, calcd 608.1918 (C₃₈H₃₂N₄-

Zn); λ_abs(toluene) 411, 538, 573 nm; λ_em(λ_ex) 540 nm, toluene)

578, 632 nm.

stirred at 80 °C. TLC analysis (silica, CHCl₃) indicated complete

consumption of the starting porphyrin after 2 h. The solvent was

removed, and the residue was chromatographed (silica, CHCl₃)

affording a mixture of porphyrins. This mixture was purified by

preparative SEC (THF) affording four major bands (in order of

elution): (1) unidentified product (t_R) 10.34 min); (2) desired

triad (t_R) 10.89 min); (3) monocoupled byproduct (t_R) 11.52

min, LD-MS obsd at m/z ) 1151, calcd 1153.0 (C₆₈H₅₂N₈PdZn);

and (4) monomeric porphyrin species (t_R) 11.96 min). The second

fraction from the SEC column was chromatographed (silica, CHCl₃),

affording a red-purple solid (18 mg, 50%): ¹H NMR δ 1.87 (s,

24H), 2.67 (s, 12H), 6.61-6.62 (m, 4H), 7.22-7.23 (m, 4H), 7.33

(s, 8H), 7.65 (s, 4H), 8.03 (d, J ) 8.0 Hz, 4H), 8.40 (d, J ) 8.0

Hz, 4H), 8.92 (d, J ) 4.4 Hz, 4H), 8.95 (d, J ) 4.4 Hz, 4H), 9.06

(d, J ) 4.4 Hz, 4H), 9.38 (d, J ) 4.4 Hz, 4H), 10.21 (s, 2H); LD-

MS obsd 1758.6; calcd av mass 1761.0 (C₁₀₆H₈₂N₁₂PdZn₂); λ_abs

5-Bromo-10,20-dimesitylporphyrin (4). Following a known

procedure,⁵³a solution of 3 (328 mg, 0.600 mmol) in CHCl₃(200

mL) and pyridine (250 µL) was treated with NBS (106 mg, 0.600

mmol) at 0 °C. After 25 min, the reaction was quenched with

acetone (10 mL). Then, the reaction mixture was washed with H₂O

and dried (Na₂SO₄). Chromatography [silica, CHCl₃/hexanes (1:

2)] afforded three bands (in order of elution): the first band (purple)

was dibrominated product (51 mg, 12%), the second band (purple)

was the desired product, and the third band (purple) was the starting

material 3 (42 mg, 12%). The second band was rechromatographed

[silica, CHCl₃/hexanes (1:2)] affording a purple solid (274 mg,

73%). Data for the title compound follow: ¹H NMR δ -2.87 (s,

br, 2H), 1.83 (s, 12H), 2.65 (s, 6H), 7.31 (s, 4H), 8.78 (d, J ) 4.4

Hz, 4H), 9.22 (d, J ) 4.4 Hz, 2H), 9.66 (d, J ) 4.4 Hz, 2H), 10.08

(s, 1H); LD-MS obsd 624.7; FAB-MS obsd 624.1902, calcd

624.1889 (C₃₈H₃₃BrN₄); λ_abs(toluene) 417, 511, 543, 589, 646 nm;

λ_em(λ_ex) 515 nm) 647, 711 nm. Data for the dibrominated

porphyrin follow: ¹H NMR δ -2.54 (s, br, 2H), 1.82 (s, 12H),

2.64 (s, 6H), 7.29 (s, 4H), 8.69 (d, J ) 4.4 Hz, 4H), 9.55 (d, J )

4.4 Hz, 4H); LD-MS obsd 702.5, calcd 702.1 (C₃₈H₃₂Br₂N₄Zn).

5-Bromo-10,20-dimesitylporphinatozinc(II) (Zn-4). A solution

of 4 (240 mg, 0.383 mmol) in CHCl₃(50 mL) was treated overnight

with Zn(OAc)₂‚2H₂O (421 mg, 1.92 mmol, 5 equiv) in methanol

(2.0 mL) at room temperature. Standard workup gave a purple solid

(259 mg, 98%): ¹H NMR δ 1.81 (s, 12H), 2.66 (s, 6H), 7.31 (s,

4H), 8.87 (d, J ) 4.5 Hz, 4H), 9.30 (d, J ) 4.5 Hz, 2H), 9.74 (d,

J ) 4.5 Hz, 2H), 10.14 (s, 1H); LD-MS obsd 688.0; FAB-MS obsd

686.1055, calcd 686.1024 (C₃₈H₃₁BrN₄Zn); λ_abs(toluene) 420, 548,

583 nm; λ_em(λ_ex) 550 nm, toluene) 639 nm.

5,15-Dimesityl-10-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-

yl)porphinatozinc(II) (Zn-5). Following a literature procedure,⁵⁴

samples of Zn-4 (482 mg, 0.700 mmol), 4,4,5,5-tetramethyl-1,3,2-

dioxaborolane (122 µL, 0.840 mmol), TEA (780 µL, 5.60 mmol),

and Pd(PPh₃)₂Cl₂(14.7 mg, 0.0210 mmol, 3% mol) were loaded

into a 100 mL Schlenk flask under argon. Then, 1,2-dichloroethane

(35 mL) was added, and the mixture was stirred at 85 °C. TLC

analysis [CHCl₃/hexanes (1:1)] after 1 h showed complete con-

sumption of the starting porphyrin and the presence of a new, polar

spot. The reaction mixture was cooled to room temperature, washed

with water, and dried (Na₂SO₄). Chromatography [silica, CH₂Cl₂/

hexanes (1:1)] afforded a purple solid (479 mg, 93%): ¹H NMR δ

1.80 (s, 12H), 1.85 (s, 12H), 2.66 (s, 6H), 7.30 (s, 4H), 8.90 (d, J

) 4.5 Hz, 2H), 8.96 (d, J ) 4.5 Hz, 2H), 9.36 (d, J ) 4.5 Hz, 2H),

9.87 (d, J ) 4.5 Hz, 2H), 10.24 (s, 1H); LD-MS obsd 735.9; FAB-

MS obsd 734.2794, calcd 734.2771 (C₄₄H₄₃N₄O₂Zn); λ_abs(toluene)

415, 543, 573 nm; λ_em(λ_ex) 540 nm, toluene) 581, 637 nm.

Bis[5-[4-(5,15-dimesitylporphinatozinc(II)-10-yl)phenyl]dipyr-

rinato]palladium(II) (6). Following a standard method,⁵⁷samples

of Pd-2c (16 mg, 0.020 mmol), Zn-5 (29 mg, 0.040 mmol), Ba-

(OH)₂‚8H₂O (13 mg, 0.040 mmol), and Pd(PPh₃)₄(6.9 mg, 0.0060

mmol) were weighed into a 10 mL Schlenk flask. The flask was

pump-purged with argon for three times. Dimethoxyethane (1.8 mL)

and H₂O (0.2 mL) were added under argon, and the mixture was

(toluene, log ꢀ) 419 (5.72), 483 (4.88), 544 (4.70) nm; λ_em(λ_ex

)

485 nm, toluene) 531 (w), 590, 637 nm.

5,15-Dimesityl-10-[4-(dipyrrin-5-yl)phenyl]porphinatozinc-

(II) (Zn-7a) by Demetalation of Triad 6. A sample of triad 6

(14.5 mg, 8.23 µmol) in CHCl₃(3.0 mL) was treated with DTT

(13.0 mg, 82.3 µmol) at room temperature. UV-vis analysis

indicated complete demetalation of the dipyrrin moiety (removal

of palladium) after 2 h. The reaction mixture was washed with H₂O

and dried (Na₂SO₄). Chromatography [silica, CHCl₃f CHCl₃/

MeOH (98:2)] afforded a purple solid (9.6 mg, 70%): ¹H NMR δ

1.84 (s, 12H), 2.66 (s, 6H), 6.57 (d, J ) 3.6 Hz, 2H), 7.04 (d, J )

3.6 Hz, 2H), 7.31 (s, 4H), 7.77 (s, 2H), 7.99 (d, J ) 8.0 Hz, 2H),

8.33 (d, J ) 8.0 Hz, 2H), 8.87 (d, J ) 4.4 Hz, 2H), 8.93 (d, J )

4.4 Hz, 2H), 8.98 (d, J ) 4.4 Hz, 2H), 9.36 (d, J ) 4.4 HZ, 2H),

10.19 (s, 1H); LD-MS obsd 824.0; FAB-MS obsd 827.2864 (M⁺

+ H); calcd 827.2841 (C₅₃H₄₂N₆Zn₄); λ_abs(toluene) 417, 544 nm;

λ_em(λ_ex) 540 nm, toluene) 590, 637 nm.

5,15-Dimesityl-10-[4-(dipyrrin-5-yl)phenyl]porphinatozinc-

(II) (Zn-7a) via Oxidation of 9a. A mixture of 9a (49 mg, 0.064

mmol) and Zn(OAc)₂‚2H₂O (70 mg, 0.32 mmol, 5 equiv) in THF

(5 mL) was treated with p-chloranil (16 mg, 0.064 mmol) at room

temperature. The mixture was stirred overnight. The standard

workup and chromatography [silica, CH₂Cl₂/MeOH (99:1)] afforded

a purple solid (38 mg, 72%). The characterization data were

identical to those obtained for the product prepared from triad 6.

5,15-Bis(3,5-di-tert-butylphenyl)-10-mesityl-20-[4-(dipyrrin-

5-yl)phenyl]porphinatozinc(II) (Zn-7b). A mixture of 9b (41 mg,

0.040 mmol) and Zn(OAc)₂‚2H₂O (44 mg, 0.20 mmol, 5 equiv) in

THF (3 mL) was treated overnight with p-chloranil (9.8 mg, 0.040

mmol) at room temperature. The standard workup and chromatog-

raphy [silica, CH₂Cl₂/MeOH (99:1)] afforded a purple solid (31

mg, 71%): ¹H NMR δ 1.54 (s, 36H), 1.87 (s, 6H), 2.63 (s, 3H),

6.55-6.57 (m, 2H), 7.04-7.05 (m, 2H), 7.29 (s, 2H), 7.76 (s, 2H),

7.80-7.81 (m, 2H), 7.89 (d, J ) 8.1 Hz, 2H), 8.13-8.14 (m, 4H),

8.34 (d, J ) 8.1 Hz, 2H), 8.81 (d, J ) 4.5 Hz, 2H), 8.97-9.05 (m,

6H); LD-MS obsd 1085.8; FAB-MS obsd 1085.5175 (M⁺+ H),

calcd 1085.5188 (C₇₂H₇₂N₆Zn); λ_abs(toluene) 425, 551, 590 nm;

λ_em(λ_ex) 550 nm, toluene) 599, 648 nm.

5,15-Bis(4-methylphenyl)-10-[4-(dipyrrin-5-yl)phenyl]-20-phe-

nylporphyrin (7c). Following a standard procedure,⁶⁰a sample of

diacyldipyrromethane 11a (137 mg, 0.300 mmol) in THF/methanol

(16 mL, 3:1) was treated with NaBH₄(570 mg, 15.0 mmol). After

40 min (TLC showed reaction completion), the reaction was

quenched with aqueous NH₄Cl. The mixture was extracted with

CH₂Cl₂. The combined extracts were washed with water, dried (Na₂-

SO₄), and concentrated. The resulting dicarbinol 11a-diol and

compound 10 (109 mg, 0.300 mmol) were dissolved in CH₂Cl₂

Inorganic Chemistry, Vol. 42, No. 21, 2003 6645

Yu et al.

(120 mL) and treated with InCl₃(8.4 mg, 0.038 mmol, 0.32 mM).

The reaction mixture was stirred at room temperature for 20 min,

then DDQ (204 mg, 0.900 mmol) was added, and the mixture was

stirred for 1 h at room temperature. The mixture was filtered through

a pad of silica [eluted with a mixture of CH₂Cl₂/methanol (95:5)],

and the filtrate was concentrated. Chromatography [silica, CH₂-

Cl₂/methanol (98:2)] afforded a purple solid (38 mg, 16%): ¹H

NMR δ -2.73 (s, 2H), 2.72 (s, 6H), 6.59 (dd, J¹) 0.8 Hz, J²)

4.0 Hz, 2H), 7.06 (d, J ) 3.6 Hz, 2H), 7.57 (d, J ) 8.0 Hz, 4H),

7.65-7.82 (m, 5H), 7.91 (d, J ) 7.6 Hz, 2H), 8.12 (d, J ) 7.6 Hz,

4H), 8.23 (dd, J¹) 1.6 Hz, J²) 7.2 Hz, 2H), 8.32 (d, J ) 7.6 Hz,

2H), 8.80-9.00 (m, 8H); LD-MS obsd 784.6; FAB-MS obsd

785.3379 (M⁺+ H), calcd 785.3393 (C₅₅H₄₀N₆); λ_abs(toluene) 421,

516, 551, 593, 648 nm; λ_em(λ_ex) 550 nm, toluene) 652, 720 nm.

10.38 (s, 1H); FAB obsd 712.2215, calcd 712.2181 (C₄₅H₃₆N₄OZn);

λ_abs(toluene) 418, 544 nm; λ_em(λ_ex) 540 nm, toluene) 593, 640

nm.

5,15-Bis(3,5-di-tert-butylphenyl)-10-(4-formylphenyl)-20-mesi-

tylporphinatozinc(II) (Zn-8b). A solution of free base porphyrin

8b (2.5 mg, 2.7 µmol) in CHCl₃(1.0 mL) was treated with a

solution of Zn(OAc)₂‚2H₂O (3.0 mg, 14 µmol) in methanol (200

µL) for 3 h at room temperature. Standard workup afforded a purple

1

solid (2.3 mg, 88%): H NMR δ 1.53 (s, 36H), 1.86 (s, 6H), 2.63

(s, 3H), 7.28 (s, 2H), 7.79-7.80 (m, 2H), 8.09-8.10 (m, 4H), 8.28

(d, J ) 8.0 Hz, 2H), 8.42 (d, J ) 8.0 Hz, 2H), 8.81 (d, J ) 4.8 Hz,

2H), 8.86 (d, J ) 4.8 Hz, 2H), 8.96 (d, J ) 4.8 Hz, 2H), 9.01 (d,

J ) 4.8 Hz, 2H), 10.39 (s, 1H); LD-MS obsd 970.6; FAB-MS obsd

970.4490, calcd 970.4528 (C₆₄H₆₆N₄OZn); λ_abs(toluene) 425, 551,

592 nm; λ_em(λ_ex) 550 nm, toluene) 601, 649 nm.

5,15-Bis(4-methoxyphenyl)-10-[4-(dipyrrin-5-yl)phenyl]-20-

phenylporphyrin (7d). Following a standard procedure,⁶⁰a sample

of diacyldipyrromethane 11b (147 mg, 0.300 mmol) in THF/

methanol (16 mL, 10:1) was treated with NaBH₄(228 mg, 6.00

mmol). After 40 min (TLC showed reaction completion), the

reaction was quenched by with aqueous NH₄Cl. The mixture was

extracted with CH₂Cl₂. The combined extracts were washed with

water, dried (Na₂SO₄), and concentrated. The resulting dicarbinol

11b-diol and compound 10 (109 mg, 0.300 mmol) were dissolved

in CH₂Cl₂(120 mL) and treated with InCl₃(8.4 mg, 0.038 mmol,

0.32 mM). The reaction mixture was stirred at room temperature

for 20 min, then DDQ (204 mg, 0.900 mmol) was added, and the

mixture was stirred for 1 h. The mixture was filtered through a

pad of silica [eluted with a mixture of CH₂Cl₂/methanol (95:5)],

and the filtrate was concentrated. Chromatography [silica, CH₂-

Cl₂/methanol (98:2)] afforded a purple solid (23 mg, 10%): ¹H

NMR δ -2.72 (s, 2H), 4.11 (s, 6H), 6.60 (d, J ) 3.6 Hz, 2H),

7.06 (d, J ) 4.0 Hz, 2H), 7.31 (d, J ) 8.4 Hz, 4H), 7.72-7.83 (m,

5H), 7.91 (d, J ) 8.4 Hz, 2H), 8.15 (d, J ) 8.0 Hz, 4H), 8.23 (dd,

J¹) 2.0 Hz, J²) 7.6 Hz, 2H), 8.33 (d, J ) 7.6 Hz, 2H), 8.82-

8.98 (m, 8H); LD-MS obsd 815.7; FAB-MS obsd 817.3304 (M⁺

+ H), calcd 817.3291 (C₅₅H₄₀N₆O₂); λ_abs(toluene) 422, 517, 553,

593, 650 nm; λ_em(λ_ex) 550 nm, toluene) 656, 723 nm.

5,15-Dimesityl-10-(4-formylphenyl)porphyrin (8a). Following

a standard procedure for Suzuki coupling,⁵⁶samples of Zn-4 (2.05

g, 3.28 mmol), 4-formylphenyl boronic acid (984 mg, 6.56 mmol),

anhydrous K₂CO₃(3.62 g, 26.2 mmol), and Pd(PPh₃)₄(381 mg,

0.330 mmol, 10 mol %) were weighed into a Schlenk flask. The

flask was pump-purged with argon three times. Toluene/DMF (164

mL, 1:1) was added, and the mixture was heated to 90 °C under

argon. TLC analysis (silica, CHCl₃) after 5 h indicated complete

consumption of the starting porphyrin and the formation of a new

polar spot. Removal of the solvent and chromatography (silica,

CHCl₃) afforded a purple solid (1.94 g, 91%): ¹H NMR δ -2.90

(s, br, 2H), 1.84 (s, 12H), 2.64 (s, 6H), 7.30 (s, 4H), 8.27 (d, J )

8.0 Hz, 2H), 8.41 (d, J ) 8.1 Hz, 2H), 8.74-8.77 (m, 4H), 8.84

(d, J ) 4.8 Hz, 2H), 9.29 (d, J ) 4.8 Hz, 2H), 10.16 (s, 1H), 10.38

(s, 1H); LD-MS obsd 649.7, FAB-MS obsd 650.3058, calcd

650.3046 (C₄₅H₃₈N₄O); λ_abs(toluene) 415, 509, 540, 584, 640 nm;

λ_em(λ_ex) 510 nm, toluene) 642, 709 nm.

5,15-Dimesityl-10-[4-(dipyrromethan-5-yl)phenyl]porphy-

rin (9a). A mixture of 8a (65 mg, 0.10 mmol) and pyrrole (2.7 g,

40 mmol) in CH₂Cl₂(5.0 mL) was treated with TFA (9.6 µL, 0.11

mmol) for 2 h at room temperature. The reaction mixture was

neutralized with TEA. The solvent and the excess pyrrole were

removed under reduced pressure. Chromatography [silica, CHCl₃/

TEA (99:1)] afforded a purple solid (66 mg, 86%): ¹H NMR δ

-2.90 (s, br, 2H), 1.84 (s, 12H), 2.65 (s, 6H), 5.83 (s, 1H), 6.18-

6.19 (m, 2H), 6.30-6.31 (m, 2H), 6.86-6.87 (m, 2H), 7.30 (s,

4H), 7.59 (d, J ) 8.4 Hz, 2H), 8.17 (d, J ) 8.4 Hz, 2H), 8.22 (s,

br, 2H), 8.73 (d, J ) 4.4 Hz, 2H), 8.82-8.84 (m, 4H), 9.27 (d, J

) 4.4 Hz, 2H), 10.11 (s, 1H); LD-MS obsd 765.3, FAB-MS obsd

767.3866, calcd 767.3862 (C₅₃H₄₆N₆); λ_abs(toluene) 414, 508, 584,

640 nm; λ_em(λ_ex) 510 nm, toluene) 642, 710 nm.

5,15-Bis(3,5-di-tert-butylphenyl)-10-[4-(dipyrromethan-5-yl)-

phenyl]-20-mesitylporphyrin (9b). A solution of 8b (227 mg,

0.250 mmol) and pyrrole (5.0 g, 75 mmol) in CH₂Cl₂(12 mL) was

treated with TFA (22 µL, 0.28 mmol, 1.1 equiv) at room

temperature. TLC analysis [silica, CHCl₃/TEA (99:1)] showed

complete consumption of the starting porphyrin-benzaldehyde after

2 h. The reaction mixture was neutralized with TEA. The solvent

and the excess pyrrole were removed under reduced pressure.

Chromatography [silica, CHCl₃/TEA (99:1)] afforded the desired

product as a purple solid (205 mg, 80%): ¹H NMR δ -2.65 (br s,

2H), 1.53 (s, 36H), 1.86 (s, 6H), 2.62 (s, 3H), 5.84 (s, 1H), 6.18

(br s, 2H), 6.29-6.32 (m, 2H), 6.85-6.87 (m, 2H), 7.27 (s, 2H),

7.60 (d, J ) 8.1 Hz, 2H), 7.78-7.79 (m, 2H), 8.08-8.09 (m, 4H),

8.18 (d, J ) 8.1 Hz, 2H), 8.22 (br s, 2H), 8.69 (d, J ) 4.8 Hz, 2H),

8.83-8.88 (m, 6H); LD-MS obsd 1024.8; FAB-MS obsd 1024.6115,

calcd 1024.6131 (C₇₂H₇₆N₆); λ_abs(toluene) 421, 516, 550, 593, 649

nm; λ_em(λ_ex) 515 nm, toluene) 652, 720 nm.

5-[4-(Dipyrrin-5-yl)phenyl]dipyrromethane (10). Following a

standard procedure³⁷with slight modification,^14,58a sample of 2g

(0.320 g, 1.30 mmol) in CH₂Cl₂(4.6 mL) was mixed thoroughly

with pyrrole (4.60 mL, 65.0 mmol). The mixture was treated with

TFA (0.120 mL, 0.156 mmol). The reaction mixture was stirred at

room temperature for 5 min and quenched with 0.1 N aqueous

NaOH. The reaction mixture was extracted with ethyl acetate, dried

(Na₂SO₄), and concentrated. The dark residue obtained was

chromatographed [silica, hexanes/ethyl acetate (3:1)] to give dark

oil. The dark oil was dissolved in hexanes/ethyl acetate (9:1), and

the precipitate that formed was filtered off. The yellow filtrate was

concentrated to afford an orange solid (196 mg, 41%): mp 129-

130 °C; ¹H NMR δ 5.57 (s, 1H), 5.96 (s, 2H), 6.20-6.21 (m, 2H),

6.40 (dd, J¹) 4.0 Hz, J²) 1.2 Hz, 2H), 6.63 (d, J ) 4.0 Hz, 2H),

6.75-6.76 (m, 2H), 7.29 (d, J ) 8.0 Hz, 2H), 7.46 (d, J ) 8.0 Hz,

2H), 7.64 (s, 2H), 8.02 (s, 2H). (In addition, signals consistent with

that for the N-confused dipyrromethane were present in the ¹H NMR

10-(4-Formylphenyl)-5,15-dimesitylporphinatozinc(II) (Zn-

8a). A solution of free base porphyrin 8a (130 mg, 0.200 mmol)

in CHCl₃(10 mL) was treated with a solution of Zn(OAc)₂‚2H₂O

(220 mg, 1.00 mmol) in methanol (2.0 mL) for 3 h at room

temperature. Standard workup afforded a purple solid (138 mg,

96%): ¹H NMR δ 1.82 (s, 12H), 2.65 (s, 6H), 7.30 (s, 4H), 8.27

(d, J ) 8.4 Hz, 2H), 8.42 (d, J ) 8.4 Hz, 2H), 8.84 (s, 4H), 8.93

(d, J ) 4.8 Hz, 2H), 9.36 (d, J ) 4.8 HZ, 2H), 10.21 (s, 1H),

6646 Inorganic Chemistry, Vol. 42, No. 21, 2003

Porphyrin-Containing Self-Assembled Triads

spectrum, indicating a 96:4 ratio of 10/N-confused isomer. All data

reported here were derived from this mixture.) ¹³C NMR δ 43.9,

107.5, 108.6, 117.6, 117.7, 127.7, 129.0, 130.1, 131.3, 132.2, 143.7;

FAB-MS obsd 365.1779 (M⁺+ H), calcd 365.1766 (C₂₄H₂₀N₄);

λ_abs431 nm.

ously described.⁷¹The solvent was CH₂Cl₂and 0.1 M Bu₄NPF₆

(Aldrich, recrystallized three times from methanol and dried under

vacuum at 110 °C) served as the supporting electrolyte. The

potentials were measured versus Ag/Ag⁺; E_1/2Fc/Fc⁺) 0.19 V.

The scan rate was 0.1 V/s.

Bis[5-[4-(5,15-dimesitylporphinatozinc(II)-10-yl)phenyl]dipyr-

rinato]zinc(II) (12a). A solution of Zn-7a (9.60 mg, 0.0116 mmol)

in CHCl₃(3 mL) was treated overnight with Zn(OAc)₂‚2H₂O (12.7

mg, 0.0579 mmol) in methanol (0.2 mL) at room temperature. UV-

vis analysis showed complete metalation. The reaction mixture was

washed with aqueous NaHCO₃and H₂O. The organic layer was

dried (Na₂SO₄) and concentrated, affording a purple solid (9.7 mg,

97%): ¹H NMR (CDCl₃) δ 1.87 (s, 24H), 2.67 (s, 12H), 6.66 (d, J

) 4.4 Hz, 4H), 7.23 (d, J ) 4.4 Hz, 4H), 7.33 (s, 8H), 7.78 (s,

4H), 8.01 (d, J ) 7.6 Hz, 4H), 8.39 (d, J ) 7.6 Hz, 4H), 8.92 (d,

J ) 4.4 Hz, 4H), 8.95 (d, J ) 4.4 Hz, 4H), 9.06 (d, J ) 4.4 Hz,

4H), 9.38 (d, J ) 4.4 Hz, 4H), 10.21 (s, 2H); LD-MS obsd 1720.1,

calcd av mass 1720.4 (C₁₀₆H₈₂N₁₂Zn₃); λ_abs(toluene, log ꢀ) 419

(5.72), 486 (4.93), 544 (4.58) nm; λ_em(λ_ex) 485 nm, toluene) 531

(w), 590, 637 nm.

Static and Time-Resolved Optical Spectroscopy. The spec-

troscopic measurements were performed as described in the

preceding article.²

X-ray Crystallography. Data Collection. All X-ray measure-

ments were made on an Enraf-Nonius CAD4-MACH diffractometer

at -125 °C. The unit cell dimensions were determined by a

symmetry constrained fit of 25 well-centered reflections and their

Friedel pairs with 30° < 2θ < 36°. A quadrant of unique data was

collected using the ω scan mode in nonbisecting geometry. The

adoption of a nonbisecting scan mode was accomplished by

offsetting ψ by 20° for each data point collected. This was done to

minimize the interaction of the goniometer head with the cold

stream.

Structure Solution and Refinement. The data were reduced

using routines from the NRCVAX set of programs.⁷²The structure

was solved using SIR92.⁷³Most non-hydrogen atoms were recov-

ered from the initial E-map. The hydrogen atom positions were

introduced at idealized positions. All non-hydrogen atoms were

refined anisotropically. All hydrogen atoms were allowed to ride

on the parent carbon atoms. The calculated structure factors were

fit to the data using full-matrix least-squares based on F. The

calculated structure factors included corrections for anomalous

dispersion.

Bis[5-[4-[5,15-bis(3,5-di-tert-butylphenyl)-10-mesitylporphi-

natozinc(II)-20-yl]phenyl]dipyrrinato]zinc(II) (12b). A solution

of Zn-7b (31 mg, 0.028 mmol) in CHCl₃(3 mL) was treated

overnight with a solution of Zn(OAc)₂‚2H₂O (22 mg, 0.10 mmol)

in MeOH (0.5 mL) at room temperature. The standard workup and

washing with methanol (sonication and filtration) afforded a purple

solid (28 mg, 87%): ¹H NMR δ 1.49 (s, 72H), 1.81 (s, 12H), 2.57

(s, 6H), 6.58-6.60 (m, 4H), 7.16-7.17 (m, 4H), 7.22 (s, 4H), 7.72-

7.74 (m, 8H), 7.94 (d, J ) 7.8 Hz, 4H), 8.03-8.08 (m, 8H), 8.31

(d, J ) 7.8 Hz, 4H), 8.73-8.76 (m, 4H), 8.86-8.95 (m, 6H), 9.01-

9.02 (m, 6H); LD-MS obsd 2238.2, calcd av mass 2236.9

(C₁₄₄H₁₄₂N₁₂Zn₃); λ_abs(toluene, log ꢀ) 423 (5.85), 486 (4.97), 551

(4.68), 590 (4.04) nm; λ_em(λ_ex) 485 nm, toluene) 597, 647 nm.

Bis[5-[4-[5,15-bis(4-methylphenyl)-10-phenylporphinatozinc-

(II)-20-yl]phenyl]dipyrrinato]zinc(II) (12c). A solution of 7c (24

mg, 0.030 mmol) in CHCl₃(3 mL) was treated overnight with a

solution of Zn(OAc)₂‚2H₂O (49 mg, 0.23 mmol) in MeOH (0.5

mL) at room temperature. The standard workup afforded a purple

solid. The solid was washed with methanol, affording a purple solid

(22 mg, 83%): ¹H NMR δ 2.74 (s, 12H), 6.68 (d, J ) 4.8 Hz,

4H), 7.25 (d, J ) 4.4 Hz, 4H), 7.59 (d, J ) 7.6 Hz, 8H), 7.72-

7.84 (m, 10H), 8.03 (d, J ) 8.0 Hz, 4H), 8.15 (d, J ) 8.4 Hz, 8H),

8.24-8.25 (m, 4H), 8.38 (d, J ) 8.0 Hz, 4H), 8.92-9.14 (m, 16H);

LD-MS obsd 1755.3; calcd 1754.4 (C₁₁₀H₇₄N₁₂Zn₃); λ_abs(toluene)

427, 486, 557, 597 nm; λ_em(λ_ex) 485 nm, toluene) 599, 648 nm.

Bis[5-[4-[5,15-bis(4-methoxyphenyl)-10-phenylporphinatozinc-

(II)-20-yl]phenyl]dipyrrinato]zinc(II) (12d). A solution of 7d (15

mg, 0.018 mmol) in CHCl₃(2 mL) was treated overnight with a

solution of Zn(OAc)₂‚2H₂O (30.0 mg, 0.135 mmol) in MeOH (0.5

mL) at room temperature. The standard workup afforded a purple

solid. The solid was washed with methanol, affording a purple solid

(14 mg, 85%): ¹H NMR δ 4.12 (s, 12H), 6.68 (d, J ) 4.0 Hz,

4H), 7.22-7.38 (m, 12H), 7.72-7.84 (m, 10H), 8.03 (d, J ) 8.0

Hz, 4H), 8.17 (d, J ) 8.0 Hz, 8H), 8.25 (d, J ) 7.2 Hz, 4H), 8.38

(d, J ) 7.6 Hz, 4H), 8.97 (d, J ) 4.0 Hz, 4H), 9.03 (d, J ) 4.4 Hz,

4H), 9.09-9.10 (m, 8H); LD-MS obsd 1820.3, calcd 1818.4

(C₁₁₀H₇₄N₁₂O₄Zn₃); λ_abs(toluene) 426, 486, 551, 591 nm; λ_em(λ_ex

) 485 nm, toluene) 600, 650 nm.

Acknowledgment. This research was supported by a

grant to J.S.L. from the Division of Chemical Sciences,

Office of Basic Energy Sciences, Office of Energy Research,

U. S. Department of Energy. Mass spectra were obtained at

the Mass Spectrometry Laboratory for Biotechnology at

North Carolina State University. Partial funding for the

facility was obtained from the North Carolina Biotechnology

Center and the NSF. The X-ray diffractometer was obtained

by a grant (9509532) from the NSF. We thank Prof.

Sreedharan Prathapan for stimulating discussions.

Supporting Information Available: Description of control

experiments related to synthesis methodology development; ¹H

NMR spectra for all new compounds; ¹³C NMR spectra for all new

non-porphyrin compounds except Pd-2c; LD-MS spectra for all

new porphyrins; X-ray data for Zn-2a; static absorption and

emission spectra and description for triads 12a and 12b, porphyrin-

dipyrrins Zn-7a and Zn-7b, reference porphyrins Zn-8a, Zn-8b,

and Zn-3, and bis(dipyrrinato)zinc complex Zn-2a in toluene and

benzonitrile at room temperature; time-resolved absorption data and

description for triad 12b in toluene and 12a and 12b in benzonitrile.

Crystallographic data in CIF format. This material is available free

of charge via the Internet at http://pubs.acs.org.

IC034559M

(71) Seth, J.; Palanniapan, V.; Wagner, R. W.; Johnson, T. E.; Lindsey, J.

S.; Bocian, D. F. J. Am. Chem. Soc. 1996, 118, 11194-11207.

(72) Gabe, E. J.; LePage, Y.; Charland, J.-P.; Lee, F. L.; White, P. S. J.

Appl. Crystallogr. 1989, 22, 384-387.

(73) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.; Burla,

M. C.; Polidori, G.; Camalli, G. J. Appl. Crystallogr. 1994, 27, 435.

(74) Seybold, P. G.; Gouterman, M. J. Mol. Spectrosc. 1969, 31, 1-13.

Characterization. Electrochemistry. The electrochemical mea-

surements were made using instrumentation and procedures previ-

Inorganic Chemistry, Vol. 42, No. 21, 2003 6647

Article Doi

Excited-State Energy-Transfer Dynamics in Self-Assembled Triads Composed of Two Porphyrins and an Intervening Bis(dipyrrinato)metal Complex

DOI: 10.1021/ic034559m

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