Dendritic iron porphyrins with a tethered axial ligand as new model compounds for heme monooxygenases

Article abstract of DOI:10.1002/1522-2675(200202)85:2<599::AID-HLCA599>3.0.CO;2-V

The novel iron(III) porphyrin dendrimers of generation zero ([1·Fe^III]Cl), one ([2·Fe^III]Cl), and two ([3· Fe^III]Cl) (Fig. 1) were prepared (Schemes 1 and 3) as models of heine monooxygenases. They feature controlled axial ligation at the Fe center by one imidazole tethered to the porphyrin core and possess a vacant coordination site available for ligand binding and catalysis. The high purity of the dendrimers and the absence of structural defects was demonstrated by matrix-assisted laser-desorption-ionization time-of-flight (MALDI-TOF) mass spectrometry (Fig. 3). The electronic properties of the Fe^III porphyrin dendrimers and comparison compounds [4·Fe^III]Cl and [12·Fe^III(1,2-Me:Im)]Cl (1,2-Me₂Im = 1,2-dimethylimidazole) were investigated by UV/VIS and EPR (electronic paramagnetic resonance) spectroscopy, as well as by measurements of the magnetic moments by the Evans-Scheffold method. Epoxidation of olefins and oxidation of sulfides to sulfoxides, catalyzed by the new dendritic metalloporphyrins, were investigated in CH₂Cl₂: with iodosylbenzene as the oxidant (Tables 1 and 2). The total turnover numbers were found to increase with the size of the dendrimer, due to improved catalyst stability at higher dendritic generations (Figs. 4 and 5). The second-generation complex [3.Fe^III]Cl was, therefore, the most efficient catalyst in the series, despite the fact that its active site is considerably hindered by the encapsulation inside the sterically demanding, fluctuating dendritic wedges. Very high product selectivities were observed in all oxidation reactions, regardless of dendrimer generation.

Full text of DOI:10.1002/1522-2675(200202)85:2<599::AID-HLCA599>3.0.CO;2-V

Helvetica Chimica Acta Vol. 85 (2002)
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Dendritic Iron Porphyrins with a Tethered Axial Ligand as New Model
Compounds for Heme Monooxygenases
by Philipp Weyermann and FranÁois Diederich*
Laboratorium f¸r Organische Chemie, ETH-Hˆnggerberg, HCI, CH-8093Z¸rich
The novel iron(III) porphyrin dendrimers of generation zero ([1 ¥ FeIII]Cl), one ([2 ¥ FeIII]Cl), and two ([3 ¥
FeIII]Cl) (Fig. 1) were prepared (Schemes 1 and 3) as models of heme monooxygenases. They feature controlled
axial ligation at the Fe center by one imidazole tethered to the porphyrin core and possess a vacant coordination
site available for ligand binding and catalysis. The high purity of the dendrimers and the absence of structural
defects was demonstrated by matrix-assisted laser-desorption-ionization time-of-flight (MALDI-TOF) mass
spectrometry (Fig. 3). The electronic properties of the FeIII porphyrin dendrimers and comparison compounds
[4 ¥ FeIII]Cl and [12 ¥ FeIII(1,2-Me2Im)]Cl (1,2-Me2Im ˆ 1,2-dimethylimidazole) were investigated by UV/VIS
and EPR (electronic paramagnetic resonance) spectroscopy, as well as by measurements of the magnetic
moments by the Evans-Scheffold method. Epoxidation of olefins and oxidation of sulfides to sulfoxides,
catalyzed by the new dendritic metalloporphyrins, were investigated in CH2Cl2 with iodosylbenzene as the
oxidant (Tables 1 and 2). The total turnover numbers were found to increase with the size of the dendrimer, due
to improved catalyst stability at higher dendritic generations (Figs. 4 and 5). The second-generation complex
[3 ¥ FeIII]Cl was, therefore, the most efficient catalyst in the series, despite the fact that its active site is
considerably hindered by the encapsulation inside the sterically demanding, fluctuating dendritic wedges. Very
high product selectivities were observed in all oxidation reactions, regardless of dendrimer generation.
1. Introduction. Heme-containing monooxygenases such as cytochromes P450 [1],
and peroxidases [2] catalyze a broad variety of important oxidation reactions in nature.
They are the central enzymes in a large number of biosynthetic transformations, as well
as in detoxification of organic toxins and growth regulation in higher organisms. The
catalytic function of these enzymes is exerted by their prosthetic group, an iron
porphyrin complex, which resides in the FeIII form in the resting state. The protein shell
around the heme core controls the access of substrates and oxidizing agent to the active
site, and orients the substrate to favor the desired selective oxidation. In addition, it
prevents the sensitive cofactor at the active site from degradation via undesirable side
reactions. The activation of the oxidant under formation of highly reactive oxoferryl
porphyrin species depends mostly on electronic effects mediated by a −proximal× axial
ligand, provided to the Fe center by the protein shell, and on the nature of −distal× amino
acid side chains on the opposite site of the porphyrin macrocycle where substrate
binding and oxidation occurs.
Catalytic dendrimers have attracted considerable interest recently (for reviews on
catalytically active dendrimers, see [3]), since their large molecular weights and
multinanometer-sized dimensions allow application in membrane reactors without
leaking, as well as versatile catalyst recycling. A variety of porphyrin dendrimers [4][5]
have been prepared, and some of them have been successfully investigated for
monooxygenase activity [4a,g] (for selected examples of other heme monooxygenase
mimics, see [6]).

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Here, we describe the preparation and characterization of the novel FeIII porphyrin
dendrimers [1 ¥ FeIII]Cl, [2 ¥ FeIII]Cl, and [3 ¥ FeIII]Cl of generations zero, one, and two,
featuring a covalently attached imidazole axial ligand to ensure formation of five-
coordinate species with one free axial coordination site (Fig. 1) (for a preliminary
communication on the synthesis and gas-binding properties of these dendrimers, see
[7]). These compounds were expected to be functional mimics of heme-containing
monooxygenases and to perform oxidation reactions along mechanisms similar to those
of their natural counterparts. Axial N-ligands are well-known to enhance reactivity in
metalloporphyrin-catalyzed oxidation reactions [8], and peroxidases also feature
mono-imidazole ligation similar to the dendritic mimics described in this paper. The
higher-generation derivatives include a dendritic shell of respectable size ([3 ¥ FeIII]Cl:
Mr 11588 D), which serves to model the protecting peptide shell of the heme proteins.
We envisaged that the highly reactive iron-oxo species formed by O-atom transfer from
an oxidizing agent to the FeIII center through a peroxide shunt-type mechanism [9]
could be considerably stabilized by encapsulation within a dendritic superstructure.
This should prevent bimolecular degradation pathways, thereby extending the lifetime
of the catalyst. The catalytic efficiency of the novel dendritic heme monooxygenase
mimics in a number of different oxidation reactions is indeed found to be dependent on
the size of the dendritic shell.
2. Results. 2.1. Synthesis and Characterization of the Porphyrin Core. The three
novel porphyrin dendrimers were synthesized by the convergent strategy developed in
our previous work on dendritic cytochrome mimics [5]. The imidazole-appended ZnII
porphyrin core 4 ¥ Zn was prepared (Scheme 1) by a high-yielding Suzuki cross-
coupling (81%) [10] between the meso-brominated ZnII porphyrin 5 ¥ Zn [5b] and the
imidazole-containing boronate 6. The latter was obtained from 5-bromo-2-methylphe-
nol (7) [11] by OH-group protection with MOM-Cl (MOM ˆ methoxymethyl) in
MeCN to give 8, followed by lithiation (BuLi in THF), reaction with B(OMe)3 in THF,
and transesterification with pinacol in PhH to afford 9. MOM Ether deprotection (HCl
in THF/MeOH) provided phenol 10, which was alkylated with 1-(6-bromohexyl)-1H-
imidazole (11) [5b][12] to give 6, in good overall yield with only one chromatographic
1
purification step necessary in the entire sequence. H-NMR spectroscopy of 4 ¥ Zn in
CDCl3 clearly established the strong and complete internal complexation of the
imidazole moiety to the central Zn-atom under formation of a defined five-coordinate
complex. All signals were sharp and well-defined, and the resonances of the aromatic
imidazole protons displayed impressive upfield shifts due to their positioning above the
strongly shielding region of the porphyrin macrocycle, as a result of the internal
coordination (Fig. 2). The signal of these protons appeared at 4.89, 2.15, and 1.97 ppm,
with the extent of the upfield shift correlating with their degree of proximity to the
1
porphyrin plane. When H-NMR measurements were carried out in (D5)pyridine,
which, at the concentration present, efficiently displaces the internal imidazole from
the Zn coordination site, the aromatic imidazole resonances were observed at their
expected positions at 7.70, 7.25, and 7.11 ppm. Complete signal assignments in both
solvents were achieved by means of 2D-NMR spectroscopy at 500 MHz. Acid-induced
demetallation with CF3COOH in benzene yielded the free-base porphyrin 4 ¥ 2 H,
1
which showed a H-NMR spectrum very similar to the one of 4 ¥ Zn in (D5)pyridine,

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Fig. 1. Dendritic Fe porphyrins [1 ¥ FeIII]Cl, [2 ¥ FeIII]Cl, and [3 ¥ FeIII]Cl with mono-imidazole axial ligation as
mimics of heme monooxygenases

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Scheme 1. Synthesis of the Imidazole-Ligated FeIII Porphyrin Core [4 ¥ FeIII]Cl
a) MOM-Cl, K2CO3, MeCN, 08, 2 h; 95%. b) BuLi, TMEDA, THF, À788, 60 min; then B(OMe)3, r.t., 3h; then
pinacol, NH4Cl, PhH, reflux, 4 h; 74%. c) Conc. aq. HCl soln., THF/MeOH, r.t., 1 d; 84%. d) 1-(6-
Bromohexyl)-1H-imidazole (11), Cs2CO3, DMF, r.t., 4 h; 68%. e) [Pd(PPh3)4], Cs2CO3, PhMe, reflux, 6 h;
81%. f) CF3COOH, PhH, 08, 10 min; 92%. g) FeCl2, 2,6-lutidine, THF, reflux, 2 h; then air; then 1% HCl in
CHCl3, r.t., 5 min; then −proton sponge×, THF, r.t., 15 min; 68%. MOM ˆ Methoxymethyl; TMEDA ˆ
N,N,N',N'-tetramethylethylenediamine; −proton sponge× ˆ 1,8-bis(dimethylamino)naphthalene.
with none of the signals displaying unusual chemical shifts (Fig. 2). Despite its
instability towards light and air, which was particularly pronounced in dilute solution,
4 ¥ 2 H could be prepared in almost quantitative yield when workup and product
isolation were carried out under an inert atmosphere.
The corresponding FeIII complex [4 ¥ FeIII]Cl was obtained from 4 ¥ 2 H by insertion
of FeII (FeCl2 in THF) and subsequent air oxidation (Scheme 1). An acidic workup step
with HCl in CHCl3 after the autoxidation led to complete displacement by chloride
of any axial ligands present. Recomplexation of the internal imidazole was
subsequently induced via treatment with 1,8-bis(dimethylamino)naphthalene (−proton

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603
Fig. 2. 300-MHz 1H-NMR Spectra of 4 ¥ Zn (a) and 4 ¥ 2 H (b) in CDCl3. Assignments of the imidazole protons
are shown in a schematic representation of the structures. Signal assignments were obtained by 2D-NMR
spectroscopy at 500 MHz (H,H-COSY (DQFCOSY-45), C,H-COSY (HSQR and HMBC), and ROESY
(mixing time 150 ms)).
sponge×) in THF [5b][13]. The entire workup was performed under anhydrous
conditions to prevent formation of hydroxy complexes. A model compound of very
similar coordination environment, [12 ¥ FeIII(1,2-Me2Im)]Cl with 1,2-Me2Im (1,2-
Me2Im ˆ 1,2-dimethylimidazole) as axial ligand, was prepared by iron insertion into
12 ¥ 2 H [4b], followed by simple addition of a slight excess of 1,2-Me2Im (Scheme 2).
Scheme 2. Synthesis of Model Compound [12 ¥ FeIII(1,2-Me2Im)]Cl
a) FeCl2, 2,6-lutidine, THF, reflux, 2 h; then air; then 1m HCl; then 1,2-Me2Im, CH2Cl2, r.t. 4 h; 69%.

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Both Fe complexes were investigated by a number of physico-chemical techniques
to elucidate the nature of their axial ligation sphere. The UV/VIS spectra of the two
FeIII derivatives were very similar to each other and were characteristic of high-spin
complexes. They compared well with the spectra of similar compounds known from the
literature [14]. The magnetic moments of 4.77 Æ 0.05 mB ([4 ¥ FeIII]Cl and 5.78 Æ 0.05 mB
([12 ¥ FeIII(1,2-Me2Im)]Cl) are consistent with a high-spin configuration possessing five
unpaired electrons [14c][15], although the value for [4 ¥ FeIII]Cl is somewhat lower than
expected. This is possibly due to the formation of head-to-tail dimers at the high
solution concentration required for the measurement or, alternatively, due to weak
complexation of chloride at the second axial coordination site. EPR Measurements on
[4 ¥ FeIII]Cl displayed the dominant axial signal typical for high-spin FeIII porphyrins
[14c][15b][16] and a minor rhombic contribution from a low-spin form. Surprisingly,
the model compound [12 ¥ FeIII(1,2-Me2Im)]Cl was EPR-silent, preventing comparison
of the EPR spectra. The experiments mentioned above clearly demonstrated that the
internal imidazole in [4 ¥ FeIII]Cl is coordinated to the Fe center to form a five-
coordinate high-spin complex, and that the sixth coordination site is either completely
vacant or partially occupied by a weakly bound chloride (which is easily replaced by an
oxidant-donor atom during catalysis of oxidation reactions). Complete internal
imidazole coordination was further confirmed by reduction of [4 ¥ FeIII]Cl and [12 ¥
FeIII(1,2-Me2Im)]Cl to the five-coordinate FeII complexes [4 ¥ FeII] and [12 ¥ FeII(1,2-
Me2Im)], which exhibited UV/VIS spectra typical of five-coordinate high-spin FeII
porphyrins [14][15a]. Their magnetic moments of 4.10 Æ 0.05 mB ([4 ¥ FeII]) and 4.78 Æ
0.05 mB ([12 ¥ FeIII(1,2-Me2Im)]) are consistent with the high-spin state, having four
unpaired electrons, and agree very well with published values for similar complexes
[15a][17]. Collman et al. had previously demonstrated that the sterically demanding
ligand 1,2-Me2Im forms exclusively five-coordinate high-spin FeII porphyrin adducts,
even when present in large excess [18].
The two FeII species formed six-coordinate low-spin adducts with different ligands
extremely easily and were, for this reason, very difficult to obtain in pure form. Only
under rigorously O2-free conditions did the five-coordinate species prevail, and traces
of O2 led immediately to the formation of O2 complexes, which subsequently
underwent autoxidation. Interestingly, [4 ¥ FeII] was considerably more stable than
[12 ¥ FeII(1,2-Me2Im)], as the former could be obtained by reduction with aqueous
Na2S2O4 solution in PhMe, whereas the presence of H2O led to complete decom-
position of the latter compound. Reduction in this case could only be achieved under
anhydrous conditions. The presence of CO gas during the reduction led to the
formation of stable, six-coordinate, low-spin CO complexes, which are diamagnetic and
possess very characteristic UV/VIS spectroscopic properties [19]. These complexes
show a narrow, extremely intense Soret band at 421 nm ([4 ¥ FeII]) and 414 nm ([12 ¥
FeII(1,2-Me2Im)]), while the Q bands appear at 539 nm ([4 ¥ FeII]) and 526 nm ([12 ¥
FeII(1,2-Me2Im)]). These results compared well with data reported previously for
similar complexes [20] and, thus, proved again the presence of a coordinated imidazole
axial ligand and one free coordination site in the reduced FeII state.
2.2. Synthesis and Characterization of the Dendritic Porphyrins. For the synthesis of
the ZnII porphyrin dendrimers of generation zero (1 ¥ Zn), one (2 ¥ Zn) and two
(3 ¥ Zn; Scheme 3), tetraethyl ester 4 ¥ Zn was hydrolyzed to give the core tetraacid

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605
Scheme 3. Synthesis of the Dendritic Heme Monooxygenase Mimics [1 ¥ FeIII]Cl, [2 ¥ FeIII]Cl, and [3 ¥ FeIII]Cl
a) NaOH, dioxane/H2O, r.t., 3d. b) 14, 15, or 16, HATU, Et3N, DMF, 08, 1 d; 91% (1 ¥ Zn); 3d, 70% ( 2 ¥ Zn); 7 d
(reaction temperature: À158); 65% (3 ¥ Zn); all yields starting from 4 ¥ Zn. c) CF3COOH, CHCl3, 08, 5 min;
then FeCl2, 2,6-lutidine, THF, reflux, 2 6 h; then air; then 1% HCl in CHCl3, r.t., 5 min; then −proton sponge×,
THF, r.t., 15 min; 49% ([1 ¥ FeIII]Cl); 53% ([2 ¥ FeIII]Cl); 59% ([3 ¥ FeIII]Cl). HATU ˆ O-(7-azabenzotriazol-1-
yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate.
13 ¥ Zn, which was coupled with the triethyleneglycol-monomethyl-ether-functional-
ized dendritic wedges 14 [21], 15 [22], and 16 [5b], respectively, in DMF with the very
reactive HATU (ˆO-(7-azabenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexa-
fluorophosphate) as the coupling agent.
The dendritic ZnII porphyrins were purified by repeated preparative gel-perme-
ation chromatography (GPC, Bio-Rad Bio-Beads S-X1; CH2Cl2) and fully character-
ized by spectroscopic methods. The isolation of pure 3 ¥ Zn required the combined use
of preparative GPC (Bio-Rad Bio-Beads S-X1; CH2Cl2) and high-performance gel-
permeation chromatography (HP-GPC, NovoGROM 100; THF), but nevertheless, the
target compound was obtained in a remarkable yield of 65%. It was critical to maintain
the reaction temperature below 08 at all times in this case to avoid formation of
inseparable higher-mass by-products in the course of the coupling reaction. The lower-
generation compounds were isolated in 70% (2 ¥ Zn) and 91% yield (1 ¥ Zn), thus
demonstrating a pronounced increase in coupling efficiency with decreasing bulkiness
of the dendritic wedges. UV/VIS and NMR spectroscopic analysis proved the complete
coordination of the tethered imidazole to the ZnII ion, and dendritic purity was
confirmed by MALDI-TOF mass spectrometry. The spectrum of the second-generation
dendrimer 3 ¥ Zn (matrix: 2-(4-hydroxyphenylazo)benzoic acid (HABA)) featured the
‡
sodium complex of the molecular ion [M ‡ Na] (m/z 11586.1 (100%); calc. for
‡
C
524H904N22O249ZnNa: 11584.8) and the molecular ion M (30%) as the only prominent
peaks. Lack of fragmentation and absence of structural defects were apparent from the
absence of signals at lower masses.
Demetallation with CF3COOH in CHCl3 and FeII insertion with FeCl2 and 2,6-
lutidine in THF, followed by autoxidation, gave the air-stable dendritic FeIII porphyrins
[1 ¥ FeIII]Cl, [2 ¥ FeIII]Cl, and [3 ¥ FeIII]Cl, respectively, which were purified by prepara-
tive TLC (SiO2; CH2Cl2/MeOH 90 :10), followed by preparative GPC (Bio-Rad Bio-
Beads S-X3; CH2Cl2). The highly polar compounds were difficult to recover from SiO2
after preparative TLC, which resulted in rather low isolated yields.

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All three dendritic FeIII complexes were shown to be highly monodisperse by
MALDI-TOF mass spectrometry (Fig. 3). They exhibited UV/VIS absorption spectra
characteristic of five-coordinate high-spin FeIII porphyrins [14], and this spin config-
uration was also apparent from EPR measurements. The compounds displayed a
predominant axial signal in the EPR spectrum, typical for high-spin FeIII porphyrins
[16] and a weak rhombic signal indicative of a low-spin FeIII species [23]. These
paramagnetic properties indicate a possible weak coordination of the chloride
counterion at the vacant coordination site of the FeIII porphyrin, as, in these cases,
the formation of head-to-tail dimers is improbable, considering the steric bulkiness of
the dendritic shells (for example, it has been shown previously that m-oxo dimers do not
form with higher-generation dendrimers [7][20]). Overall, the physico-chemical
properties of the FeIII porphyrin moiety in the dendrimers [1 ¥ FeIII]Cl, [2 ¥ FeIII]Cl,
and [3 ¥ FeIII]Cl were quite similar to those of the corresponding FeIII porphyrin core [4 ¥
FeIII]Cl.
Fig. 3. MALDI-TOF Mass spectrum of the dendritic FeIII porphyrin [3 ¥ FeIII]Cl. Matrix: 0.01m 2-(4-
hydroxyphenylazo)benzoic acid (HABA) in MeCN/H2O 4 :1, analyte in CH2Cl2; reflector mode.
2.3. Catalytic Properties of the Dendritic Iron Porphyrins. The catalytic performance
of the new heme monooxygenase mimics was assessed in the epoxidation of olefins
[6][24] and the oxidation of sulfides to sulfoxides [6a] in CH2Cl2 with iodosylbenzene as
the oxidant. Epoxidation reactions were carried out on oct-1-ene (17) and cyclooctene

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607
(18) as substrates with an excess of olefin compared to oxidant and ca. 1 mol-% of
catalyst (Table 1). The oxidations of (methylsulfanyl)benzene (19) and diphenyl
sulfide (20) were performed in a similar way (Table 2).
Table 1. Epoxidation of Alkenes with Iodosylbenzene Catalyzed by the Dendritic FeIII Porphyrins [1 ¥ FeIII]Cl,
[2 ¥ FeIII]Cl, and [3 ¥ FeIII]Cl in CH2Cl2, Tˆ 295 K
Catalyst
Substrate
Yielda) [%]
Selectivityb) [%]
Turnoversc)
[1 ¥ FeIII]Cl
[2 ¥ FeIII]Cl
[3 ¥ FeIII]Cl
17
17
17
2391
24
25
7
94
95
14
25
[1 ¥ FeIII]Cl
[2 ¥ FeIII]Cl
[3 ¥ FeIII]Cl
18
18
18
46
5397
56
97
42
98
28
57
a) Based on iodosylbenzene consumed, as determined by calibrated analytical GC. b) Determined by calibrated
analytical GC. c) Moles of product formed per moles of catalyst used. Determined by calibrated analytical GC.
Table 2. Oxidation of Sulfides with Iodosylbenzene Catalyzed by the Dendritic FeIII Porphyrins [1 ¥ FeIII]Cl,
[2 ¥ FeIII]Cl, and [3 ¥ FeIII]Cl in CH2Cl2, Tˆ 295 K
Catalyst
Substrate
Yielda) [%]
Selectivityb) [%]
Turnoversc)
[1 ¥ FeIII]Cl
[2 ¥ FeIII]Cl
[3 ¥ FeIII]Cl
19
19
19
66
70
59
> 99
> 99
> 99
38
54
77
[1 ¥ FeIII]Cl
[2 ¥ FeIII]Cl
[3 ¥ FeIII]Cl
20
20
20
50
80
63
> 99
> 99
> 99
30
63
87
a) Based on iodosylbenzene consumed, as determined by calibrated analytical GC. b) Determined by calibrated
analytical GC. c) Moles of product formed per moles of catalyst used. Determined by calibrated analytical GC.
Analysis of the crude product mixtures by calibrated quantitative analytical gas
chromatography (GC) indicated that all three dendritic FeIII-porphyrins catalyzed the
formation of the desired oxidation product. The dendritic shell obviously does not
hinder access of substrates or oxidant to the FeIII porphyrin core. Catalyst deactivation
by oxidative degradation processes was identified as the major reason for the rather low
total turnover numbers measured (Tables 1 and 2). All three dendrimers, which are of
intensely brown color, decomposed to nearly colorless degradation products in the
course of the reactions, with the highest-generation derivative being clearly the most
stable one. Contrasting the low total turnover numbers, product selectivities were
excellent in all cases (Tables 1 and 2) and even in sulfide oxidations, where
overoxidation to sulfones is a frequent problem [6a], no products other than the
desired sulfoxide could be detected in significant amounts.
3. Discussion and Conclusions. All oxidation reactions catalyzed by the dendritic
FeIII porphyrins occurred at similar rates, independent of the dendritic generation.
Clearly, all substrates tested as well as the oxidant iodosylbenzene could easily reach

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the active site at the core of the dendrimers. However, the three dendrimers are rather
inferior compared with state-of-the-art metalloporphyrin catalysts [6a] and show only
low total turnover numbers. These are caused by the inherent instability of the
metalloporphyrin core against self-oxidation. The most probable point of attack is the
single free meso-position at the porphyrin macrocycle, which can be readily oxidized
leading to ring-opened oxidative degradation products [25]. This low stability made it
impossible to draw conclusions concerning the beneficial effect of the axial imidazole
ligand on catalysis or regarding the influence of the size of the dendritic shell on shape
selectivity with different substrates.
Despite these limitations, a number of interesting findings were obtained. Thus, in
both olefin epoxidation (Fig. 4) and sulfide oxidation (Fig. 5), the total turnover
numbers increase with increasing size of the dendritic shell. With increasingly shielding
dendritic shells, degradation slows down, and catalyst stability is improved. At the same
time, side reactions are reduced, and the yield of the desired oxidation product based
on consumed iodosylbenzene increases (Figs. 4 and 5). This makes the second-
generation compound [3 ¥ FeIII]Cl the best catalyst in the series, which is rather unusual
in dendritic catalysis whereby a decrease in activity is commonly observed with
increasing dendritic generation [3][22] (for dendrimers with a catalytically active core,
see also [26]).
Sulfide oxidation was more efficiently catalyzed than olefin epoxidation, which
correlates with the observation that sulfides are generally much easier to oxidize than
alkenes. Cyclooctene (18) gave clearly better results than oct-1-ene (17), which is
&
Fig. 4. Epoxidation of oct-1-ene (17; .) and cyclooctene (18; ) with iodosylbenzene in CH2Cl2, catalyzed by the
dendritic FeIII porphyrins [1 ¥ FeIII]Cl, [2 ¥ FeIII]Cl, and [3 ¥ FeIII]Cl. Plot of the total turnover numbers ( ),
yields (
; in %), and selectivities ( ¥¥¥¥¥¥ ; in %) vs. dendrimer generation. Tˆ 295 K.

Helvetica Chimica Acta Vol. 85 (2002)
609
&
Fig. 5. Oxidation of (methylsulfanyl)benzene (19; .) and diphenyl sulfide (20; ) with iodosylbenzene in
CH2Cl2, catalyzed by the dendritic FeIII porphyrins [1 ¥ FeIII]Cl, [2 ¥ FeIII]Cl, and [3 ¥ FeIII]Cl. Plot of the total
turnover numbers ( ), yields (
; in %), and selectivities ( ¥¥¥¥¥¥ ; in %) vs. dendrimer generation.
Tˆ 295 K.
known to be a difficult compound for epoxidation, whereas the former is referred to as
an excellent epoxidation substrate [6a]. On the other hand, the two sulfides 19 and 20
employed in this study are very similar in structure and, expectedly, are oxidized with
similar efficiency.
A positive aspect of our new catalytic dendrimers are the very high product
selectivities observed, particularly in sulfide oxidations, for which by-products resulting
from overoxidation are frequently observed with a variety of other catalysts including
metalloporphyrins [6a].
In summary, we have prepared a series of structurally elaborate mimics for heme
monooxygenases and shown their ability to catalyze olefin epoxidation and sulfide
oxidation reactions. Dendritic encapsulation mimics the function of the protein shell in
the natural heme proteins and significantly enhances the stability of the catalyst. In
future work, catalyst stability (and efficiency) will be further improved by attachment
of electron-withdrawing substituents to the porphyrin macrocycle and by blocking its
fourth meso-position (for examples of improved catalyst stability due to the
introduction of electron-withdrawing substituents, see [27]). This would then allow
full exploitation of the advantages of the dendritic structure, such as excellent solubility,
facile catalyst separation and recycling, and utilization in economically efficient
membrane reactors.
This work was supported by the ETH Research Council and F. Hoffmann-La Roche, Basel.

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Experimental Part
General. See [5b]. Compounds 5 ¥ Zn [5b], 7 [11], 11 ¥ AcOH [5b][12], 12 ¥ 2 H [4b], 14 [21], 15 [22], and 16
[5b] were prepared according to published procedures or by slight modifications of such. Prep. TLC: Merck PSC
glass plates, 2 mm SiO2 with F254, 20 Â 20 cm, visualization by UV light at 254 and 366 nm, as well as by visible
light. Anal. GC: Perkin-Elmer PE Auto System with FID detector and H2 as carrier gas, separation in a temp.
gradient on an OPTIMA-1701 0.25-mm Macherey-Nagel capillary column (0.25 mm  25 m) at a carrier-gas
25o
pressure of 2.6 bar. Magnetic moments m (mB) were determined by the Evans-Scheffold method in deuterated
eff
solvents with 2% Me4Si or t-BuOH as reference compounds [28].
General Procedure 1 (GP 1): Hydrolysis of Porphyrin Tetraethyl Ester to Porphyrin Tetraacid. The
porphyrin tetraethyl ester (0.020 mmol) was dissolved in dioxane (2 ml), and 2m NaOH (2 ml) was added. The
two-phase system was vigorously stirred in the dark at r.t. for 3d. The mixture was extracted with CHCl 3
(10 ml), and the deep purple aq. phase carefully acidified with 0.5m HCl, until a stable, voluminous purple
precipitate formed. The resulting suspension was saturated with NaCl by addition of solid NaCl, upon which the
precipitate aggregated to form black crystals, which were filtered off. The crude porphyrin tetraacid was washed
with H2O (10 ml), acetone (5 ml), and Et2O (25 ml), and dried under h.v. in the dark for 2 h.
General Procedure 2 (GP 2): ZnII-to-FeIII Metal Exchange in the Dendritic Porphyrins. A deep-purple soln.
of the dendritic ZnII porphyrin (0.010 mmol) in abs. CHCl3 (10 ml) was carefully degassed by three −freeze-
pump-thaw× cycles and then cooled to 08 in an ice bath. Subsequently, CF3COOH (23.0 ml, 0.300 mmol) was
added, and the dark-green soln. was stirred at r.t. for 5 min. The resulting mixture was titrated with 2,6-lutidine,
until its color changed to brown-purple and then washed with degassed H2O (3 Â 10 ml). The aq. phase was
removed between washings and, at the end, with a syringe equipped with a long, thin needle. All solvent was
then distilled off under h.v. at r.t., and the residue of free-base porphyrin was dried under h.v. for 2 h. The crude,
amorphous product was dissolved in abs. THF (15 ml), 2,6-lutidine (8.7 ml, 0.075 mmol) was added, and the soln.
was heated to reflux for 15 min. The brown-purple soln. was treated with anh. FeCl2 (19.0 mg, 0.150 mmol) and
heated to reflux for 2 6 h. After cooling the now red-brown soln. to r.t., the mixture was exposed to air with
stirring for 30 min to ensure complete oxidation to the FeIII complex. Subsequently, the mixture was filtered
through a 1-cm layer of Celite, then concentrated in vacuo and dried under h.v. The residue was dissolved in
CHCl3 (5 ml), 1% HCl in CHCl3 (20 ml) was added, and the mixture was stirred at r.t. for 5 min. The solvent was
evaporated in vacuo and the dark-brown residue taken up in abs. THF (10 ml). The resulting soln. was treated
with 1,8-bis(dimethylamino)naphthalene (34.3 mg, 0.160 mmol), upon which its color changed from dark brown
to red-brown. The mixture was stirred at r.t. for an additional 15 min and concentrated in vacuo. The crude, oily
product was subjected to prep. TLC (SiO2; CH2Cl2/MeOH 90 :10), the red-brown porphyrin zone was separated
from the plate, and the product was recovered by soaking the SiO2 in hot MeOH (100 ml) in an ultrasonic bath
for 30 min. After filtration over a 1-cm layer of Celite and concentration of the red-brown filtrate in vacuo, the
product was purified by prep. GPC (Bio-Beads S-X3; CH2Cl2) and dried under h.v. for at least 3d.
4-Bromo-2-(methoxymethoxy)-1-methylbenzene (8). A soln. of 5-bromo-2-methylphenol (7; 2.806 g,
15.0 mmol) in MeCN (60 ml) was cooled to 08 in an ice bath, and anh. K2CO3 (8.800 g, 60.0 mmol) was added.
After 30 min, the green-yellow suspension was treated dropwise with MOM-Cl (2.44 ml, 30.0 mmol) and
subsequently stirred at r.t. for 2 h. MeOH (20 ml) was added, and the mixture was stirred at r.t. overnight. After
evaporation in vacuo, H2O (75 ml) was added to the residue, and the resulting mixture was extracted with Et2O
(3 Â 50 ml). The combined org. phases were washed with 1m NaOH (30 ml) and 25 ml of H2O (25 ml), dried
(MgSO4), and concentrated in vacuo. The resulting orange oil was purified by distillation under h.v. to yield 8
(3.277 g, 95%). Colorless oil. B.p. 1108 (0.50 Torr). TLC (SiO2; hexane/AcOEt 90 :10): Rf 0.59. IR (film):
2955m, 2910m, 2880m, 2840w, 2825w, 1590s, 1485s, 1440m, 1410w, 1385s, 1305w, 1285s, 1205w, 1185s, 1155s, 1125s,
1080s, 1000s, 925m, 870w, 850s, 800m, 760w, 650w. 1H-NMR (300 MHz, CDCl3): 7.22 (d, J ˆ 1.6, 1 H); 6.98 7.07
(m, 2 H); 5.19 (s, 2 H); 3.49 (s, 3H); 2.20 ( s, 3 H). 13C-NMR (75 MHz, CDCl3): 156.1; 131.0; 126.4; 124.5; 119.5;
117.2; 94.5; 56.0; 15.8. EI-MS: 232 (25, M , C9H1181BrO2), 230 (22, M , C9H1179BrO2), 171 (17, [M À
‡
‡
OCH2OMe] , C7H681Br), 169 (18, [M À OCH2OMe] , C7H679Br), 45 (100, CH2OMe ). Anal. calc. for
‡
‡
‡
C9H11BrO2 (231.09): C 46.78, H 4.80, Br 34.58; found: C 46.78, H 4.88, Br 34.47.
2-[3-(Methoxymethoxy)-4-methylphenyl]-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (9). A soln. of TMEDA
(0.24 ml, 16.0 mmol) in abs. THF (20 ml) was cooled to À788 and treated with 1.6m BuLi in hexane (10.00 ml,
16.0 mmol), and the mixture was stirred at this temp. for 30 min. Subsequently, 8 (2.311 g, 10.0 mmol) in abs.
THF (20 ml) was added dropwise, and the soln. was stirred for 60 min at À788. B(OMe)3 (0.57 ml, 50.0 mmol)
was added in one batch, and, after 60 min, the cooling bath was removed, and the white suspension was stirred at
r.t. for 3h. After addition of sat. aq. NH 4Cl soln. (50 ml), the mixture was extracted with CH2Cl2 (3 Â 50 ml).

Helvetica Chimica Acta Vol. 85 (2002)
611
The combined org. layers were dried (Na2SO4) and evaporated in vacuo. The resulting yellow, oily residue was
taken up in benzene (150 ml), and pinacol (11.800 g, 100.0 mmol) and NH4Cl (1.070 g, 20.0 mmol) were added.
After heating to reflux for 4 h with continuous azeotropic removal of H2O by means of a Dean-Stark trap, the
mixture was extracted with H2O (5 Â 50 ml), dried (Na2SO4), and evaporated in vacuo. Distillation of the
residue under h.v. (1508/0.50 Torr) provided 9 (2.056 g, 74%) as a viscous oil, which slowly crystallized at r.t.
Colorless solid. M.p. 44 478. TLC (SiO2; hexane/AcOEt 90 :10): Rf 0.25. IR (CHCl3): 2990m, 2980m, 2930w,
1610w, 1570w, 1510w, 1460w, 1440w, 1420m, 1390s, 1355s, 1310w, 1295w, 1270w, 1235m, 1185m, 1145s, 1090m,
1010s, 965w, 920w, 895w, 855w, 825w, 685w, 665s, 620w. 1H-NMR (300 MHz, CDCl3): 7.40 (s, 1 H); 7.3 8 (d, JAB
ˆ
7.5, 1 H); 7.17 (d, JAB ˆ 7.5, 1 H); 5.25 (s, 2 H); 3.50 (s, 3H); 2.28 ( s, 3H); 1.33( s, 12 H). 13C-NMR (75 MHz,
CDCl3): 155.0; 131.2; 130.5; 128.4; 119.3; 94.4; 83.6; 56.1; 24.7; 16.4; one signal not observed. EI-MS: 278 (100,
‡
‡
‡
‡
‡
M ), 263(10, [ M À Me] ), 248 (67, [M À 2 Me] ), 233 (21, [M À CH2OMe] ), 45 (52, CH2OMe ). Anal. calc.
for C15H23BO4 (278.16): C 64.77, H 8.33; found: C 64.92, H 8.12.
2-(3-Hydroxy-4-methylphenyl)-4,4,5,5-tetramethyl-1,3,2-dioxoborolane (10). To 9 (1.391 g, 5.00 mmol) in
160 ml THF (160 ml) and MeOH (90 ml), conc. aq. HCl soln. (0.25 ml) was added, and the soln. was stirred at
r.t. for 24 h. Ice/H2O (100 ml) was added and the mixture was extracted with CH2Cl2 (3 Â 100 ml). The
combined org. phases were washed with H2O (100 ml), dried (MgSO4), and concentrated in vacuo. The crude,
oily product was purified by bulb-to-bulb distillation under h.v. (1258/0.50 Torr) and the resulting solid
recrystallized (hexane) to give 10 (0.986 g, 84%). Colorless cubes. M.p. 111 1128. TLC (SiO2; hexane/AcOEt
75 :25): Rf 0.36. IR (KBr): 3375s, 2980s, 2925m, 1620m, 1580m, 1530m, 1460m, 1435m, 1410s, 1365s, 1310s, 1280s,
1250s, 1220m, 1190m, 1170m, 1140s, 1110m, 1085s, 990m, 965m, 920m, 890w, 850m, 815m, 785w, 725m, 705w,
685s, 580w, 525w, 43 0w. 1H-NMR (300 MHz, CDCl3): 7.30 (d, JAB ˆ 7.2, 1 H); 7.19 (s, 1 H); 7.14 (d, JAB ˆ 7.2,
1 H); 5.25 (s, 1 H); 2.27 (s, 3 H); 1.34 (s, 12 H). 13C-NMR (75 MHz, CDCl3): 153.5; 130.8; 127.8; 127.3; 120.7;
‡
‡
111.4; 83.8; 24.7; 15.9. EI-MS: 234 (62, M ), 219 (30, [M À Me] ), 134 (100). Anal. calc. for C13H19BO3 (234.10):
C 66.70, H 8.18; found: C 66.91, H 8.18.
2-{[6-(1H-Imidazol-1-yl)hexyl]oxy}-1-methyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxoborolan-1-yl)benzene (6).
A soln. of 11 ¥ AcOH (730 mg, 2.50 mmol) in CH2Cl2 (40 ml) was rapidly extracted with 1m KOH (20 ml) at
08. The org. layer was thoroughly dried (Na2SO4), abs. DMF (5 ml) was added, and, after concentration in vacuo
at r.t., 10 (234 mg, 1.00 mmol) was added. The soln. was treated with anh. Cs2CO3 (652 mg, 2.00 mmol) and
stirred at r.t. for 4 h. The resulting suspension was diluted with CH2Cl2 (20 ml), filtered through a 1-cm layer of
Celite, and the CH2Cl2 was evaporated at r.t. in vacuo. The remaining DMF was distilled off under h.v. at 408. FC
(SiO2 (15 g); AcOEt) and drying under h.v. afforded 6 (522 mg, 68%) as a highly viscous oil, which very slowly
solidified at À208. Colorless, crystalline powder. M.p. 63 64 8. TLC (SiO2; AcOEt/MeOH 99 :1): Rf 0.15. IR
(KBr): 3115w, 2970m, 2935m, 2850w, 1570w, 1540w, 1510w, 1475w, 1445w, 1385m, 1355m, 1250s, 1210w, 1155s,
1145m, 1115m, 1045s, 1030m, 1010m, 995w, 975w, 905w, 845w, 820w, 760m, 73 w5, 710w, 670w. 1H-NMR
(300 MHz, CDCl3): 7.47 (s, 1 H); 7.3 2 (d, JAB ˆ 7.3, 1 H); 7.20 (s, 1 H); 7.15 (d, JAB ˆ 7.3, 1 H); 7.06 (s, 1 H); 6.91
(s, 1 H); 4.00 (t, J ˆ 6.1, 2 H); 3.94 (t, J ˆ 7.0, 2 H); 2.23( s, 3H); 1.74 1.87 ( m, 4 H); 1.43 1.56 ( m, 2 H); 1.3 4
1.42 (m, 2 H); 1.3 4 (s, 12 H). 13C-NMR (75 MHz, CDCl3): 156.7; 137.1; 130.5; 130.2; 129.5; 127.1; 118.8; 116.3;
‡
110.0; 83.7; 67.5; 47.0; 31.1; 29.2; 26.3; 25.7; 24.9; 16.5. FAB-MS: 385.2 (100, MH ). Anal. calc. for C22H33BN2O3
(384.33): C 68.75, H 8.65, N 7.29; found: C 68.79, H 8.46, N 7.28.
(SP-5-13)-({Tetraethyl 4,4',4'',4'''-[10-(3-{[6-(1H-Imidazol-1-yl)hexyl]oxy}-4-methylphenyl)-21H,23H-por-
phine-5,15-diylbis(benzene-2,1,3-triyldioxy)]tetrakis(butanoato)}(2À)-N21,N22,N23,N24,N3)zinc(II) (4 ¥ Zn). A
suspension of 5 ¥ Zn (112.5 mg, 0.100 mmol), 6 (137.6 mg, 0.250 mmol), anh. Cs2CO3 (154.0 mg, 0.800 mmol),
and [Pd(PPh3)4] (96.1 mg, 0.050 mmol) in abs. PhMe (30 ml) was carefully degassed with five −freeze-pump-
thaw× cycles. The mixture was placed in a preheated oil bath and heated to reflux for 6 h in the dark. After
cooling to r.t., the suspension was filtered through a 1-cm layer of Celite, and the residue was washed with PhMe
(100 ml). After evaporation of the combined filtrate and washing soln. in vacuo, the remaining dark-purple solid
was purified by FC (SiO2 À H (25 g); CH2Cl2/MeOH/AcOH 97:2 :1 ! CH2Cl2/MeOH/Et3N 97:2 :1). The
product-containing fraction (ca. 200 ml) was washed with 1m NaOH (200 ml), dried (Na2SO4), and evaporated
to dryness in vacuo. The resulting purple solid was recrystallized (CHCl3/heptane) at À208 to yield 4 ¥ Zn
(105.2 mg, 81%). Fine, purple needles. M.p. 95 978. TLC (SiO2; CH2Cl2/MeOH 95 :5): Rf 0.87. UV/VIS
(CHCl3): 596 (3700), 560 (14400), 521 (2400), 426 (427200), 404 (33100), 313 (17300). IR (KBr): 2930m, 2856w,
1728s, 1583m, 1520w, 1455s, 1378m, 1289w, 1246s, 1179s, 1094s, 1056m, 1028m, 990m, 93 3w, 83 3w, 791w, 780w,
717m, 650w, 628w. 1H-NMR (500 MHz, CDCl3): 9.95 (s, 1 H); 9.20 (d, J ˆ 4.3, 2 H); 8.89 (d, J ˆ 4.3, 2 H); 8.76
(d, J ˆ 4.5, 2 H); 8.73( d, J ˆ 4.5, 2 H); 7.93( d, J ˆ 7.1, 1 H); 7.68 (t, J ˆ 8.5, 2 H); 7.44 (d, J ˆ 7.1, 1 H); 7.08
(s, 1 H); 7.04 (d, J ˆ 8.5, 2 H); 7.00 (d, J ˆ 8.5, 2 H); 4.89 (s, 1 H); 4.05 (t, J ˆ 6.8, 2 H); 3.80 4.01 (m, 8 H);
3.47 3.72 (m, 8 H); 2.51 (t, J ˆ 6.7, 2 H); 2.49 (s, 3H); 2.15 ( s, 1 H); 1.97 (s, 1 H); 1.59 (br. s, 2 H); 1.39 1.48

612
Helvetica Chimica Acta Vol. 85 (2002)
(m, 4 H); 1.29 1.34 (m, 8 H); 1.00 1.19 (m, 4 H); 0.94 (br. s, 2 H); 0.89 (t, J ˆ 7.1, 6 H); 0.73(br. s, 2 H); 0.73
(t, J ˆ 7.1, 6 H); 0.09 (br. s, 2 H). 1H-NMR (500 MHz, (D5)pyridine): 10.14 (s, 1 H); 9.40 (d, J ˆ 4.4, 2 H); 9.28
(d, J ˆ 4.9, 2 H); 9.27 (d, J ˆ 4.9, 2 H); 9.20 (d, J ˆ 4.4, 2 H); 7.89 (d, J ˆ 7.5, 1 H); 7.88 (t, J ˆ 8.5, 2 H); 7.87
(s, 1 H); 7.70 (s, 1 H); 7.49 (s, 1 H); 7.27 (d, J ˆ 8.5, 2 H); 7.26 (d, J ˆ 8.5, 2 H); 7.25 (s, 1 H); 7.11 (s, 1 H); 4.00
4.15 (m, 8 H); 3 .96 (t, J ˆ 6.3, 2 H); 3.78 (t, J ˆ 7.2, 2 H); 3.58 3.76 (m, 8 H); 2.60 (s, 3H); 1.68 1.79 ( m, 2 H);
1.47 1.67 (m, 10 H); 1.30 1.47 (m, 10 H); 1.12 1.20 (m, 2 H); 0.78 (t, J ˆ 7.2, 6 H); 0.72 (t, J ˆ 7.2, 6 H).
13C-NMR (125 MHz, CDCl3): 173.1; 172.7; 160.1; 159.8; 153.0; 150.2; 150.0; 149.4; 148.9; 142.9; 131.8; 131.4;
131.0; 130.7; 130.0; 129.4; 128.4; 125.3; 124.9; 123.4; 122.6; 119.3; 118.9; 115.0; 111.0; 106.1; 105.3; 104.3; 67.6;
67.4; 66.0; 59.8;59.6; 46.1; 29.6; 29.4; 29.4; 26.5; 24.8; 24.0; 24.0; 23.9; 16.3; 13.9; 13.7. 13C-NMR (125 MHz,
(D5)pyridine): 172.6; 172.5; 160.4; 160.3; 155.5; 151.1; 151.1; 143.3; 137.7; 132.1; 131.9; 131.9; 131.1; 129.7; 129.4;
128.6; 127.9; 125.3; 122.3; 120.7; 119.5; 119.1; 112.5; 106.1; 106.0; 105.2; 68.0; 67.9; 67.8; 59.9 (2 Â); 46.7; 31.3;
‡
29.8; 29.8; 29.5; 26.5; 25.9; 24.5; 24.4; 16.5; 14.0; 13.9. FAB-MS: 1300.5 (100, M ). Anal. calc. for C72H80N6O13Zn
(1302.85): C 66.38, H 6.19, N 6.45; found: C 66.24, H 6.27, N 6.46.
Tetraethyl 4,4',4'',4'''-[10-(3-{[6-(1H-Imidazol-1-yl)hexyl]oxy}-4-methylphenyl)-21H,23H-porphine-5,15-
diylbis(benzene-2,1,3-triyldioxy)]tetrakis(butanoate) (4 ¥ 2 H). A purple soln. of 4 ¥ Zn (26.1 mg, 0.02 mmol) in
abs. benzene (5 ml) was degassed by three −freeze-pump-thaw× cycles and then treated dropwise at 08 with
CF3COOH (0.10 ml, 1.30 mmol). The resulting dark-green soln. was stirred at r.t. for 10 min, degassed sat. aq.
Na2CO3 soln. (10 ml) was added, the resulting two-phase system shaken vigorously, and the colorless aq. phase
was separated from the now brown-purple org. layer by means of a syringe with a long, thin needle. The org.
layer was washed 3 Â in a similar fashion with degassed H2O (5 ml) and then directly subjected to FC under N2
(SiO2 (10 g); CH2Cl2 ! CH2Cl2/MeOH 95 :5). The product-containing fractions were pooled and evaporated to
dryness in vacuo in the dark. The resulting residue was recrystallized under N2 from CHCl3/heptane at À208 to
give 4 ¥ 2 H (23.0 mg, 92%), which, in the solid state, was stable towards light and air for a few h. Brown-purple
powder. M.p. 70 728. TLC (SiO2; CH2Cl2/MeOH 95 :5): Rf 0.19. UV/VIS (CHCl3): 639 (1400), 584 (5600), 542
(4800), 509 (18300), 415 (398500), 400 (sh, 84600), 302 (15800). IR (KBr): 3688w, 2977m, 2933m, 1725s, 1589m,
1506w, 1457s, 1411w, 1372w, 1344w, 1320w, 1251m, 1178s, 1104s, 1044w, 967w, 955w, 910m, 850w, 817w, 617w.
1H-NMR (300 MHz, CDCl3): 10.09 (s, 1 H); 9.25 (d, J ˆ 4.6, 2 H); 8.93( d, J ˆ 4.6, 2 H); 8.88 (d, J ˆ 4.8, 2 H);
8.81 (d, J ˆ 4.8, 2 H); 7.76 (d, J ˆ 7.5, 1 H); 7.76 (s, 1 H); 7.72 (t, J ˆ 8.5, 2 H); 7.47 (s, 1 H); 7.46 (s, 1 H); 7.05
(s, 1 H); 7.03( d, J ˆ 8.5, 4 H); 6.90 (s, 1 H); 4.07 (t, J ˆ 6.2, 2 H); 3.82 3.99 (m, 10 H); 3.46 3.70 (m, 8 H); 2.57
(s, 3H); 1.74 1.92 ( m, 4 H); 1.50 1.63( m, 2 H); 1.20 1.46 (m, 18 H); 0.81 (t, J ˆ 7.1, 6 H); 0.76 (t, J ˆ 7.1,
6 H); À2.86 (s, 2 H). 13C-NMR (75 MHz, CDCl3): 172.9; 172.8; 159.7 (2Â); 155.2; 145.0 148.6 (4 Â br.); 141.5;
137.1; 129.6 131.7 (4 Â br.); 130.2; 129.6; 128.5; 127.4; 125.8; 120.3; 119.6; 118.8; 118.3; 111.6; 105.5 (2 Â); 103.7;
67.8; 67.4; 67.4; 59.7 (2Â); 46.9; 31.0; 29.6 (2Â); 29.3; 26.4; 25.8; 23.9; 23.8; 16.4; 13.8; 13.7. FAB-MS: 1239.2
‡
‡
‡
(100, MH ). HR-FAB -MS: 1239.6018 (M , C72H82N6O13; calc. 1239.6018).
(SP-5-13)-({Tetraethyl 4,4',4'',4'''-[10-(3-{[6-(1H-Imidazol-1-yl)hexyl]oxy}-4-methylphenyl)-21H-23H-por-
phine-5,15-diylbis(benzene-2,1,3-triyldioxy)]tetrakis(butanoato)}(2À)-N21,N22,N23,N24,N3)iron(III) Chloride
([4 ¥ FeIII]Cl). To 4 ¥ 2 H (24.8 mg, 0.020 mmol) in abs. THF (5 ml) degassed by three −freeze-pump-thaw×
cycles, 2,6-lutidine (11.6 ml, 0.200 mmol) was added, and the purple soln. was heated to reflux for 15 min. Anh.
FeCl2 (25.3mg, 0.200 mmol) was added, and the mixture was heated to reflux for 2 h. The now red-brown soln.
was left to cool to r.t. and then exposed to air for 30 min. Direct CC of the entire mixture (Al2O3 (10 g); THF !
THF/MeOH 80 :20) provided a red-brown oil, which was dried under h.v. The resulting crude product was
dissolved in CHCl3 (5 ml), treated with 1% HCl in CHCl3 (20 ml), and stirred at r.t. for 5 min. After evaporation
in vacuo, the residue was taken up in abs. THF (10 ml), and 1,8-bis-(dimethylamino)naphthalene (34.3 mg,
0.160 mmol) was added, leading to an immediate color change from dark brown to red-brown. The mixture was
stirred at r.t. for 15 min and then evaporated to dryness in vacuo. The crude, oily product was purified by prep.
GPC (Sephadex LH-20; MeOH), dried under h.v., and recrystallized (CHCl3/heptane) to provide, after drying
under h.v., [4 ¥ FeIII]Cl (18.1 mg, 68%). Red-brown crystalline solid. M.p. 78 798. TLC (Al2O3; THF/MeOH
60 :40): Rf 0.86. UV/VIS (CHCl3): 680 (sh, 1900), 649 (2300), 570 (sh, 3700), 507 (9400), 415 (78200), 385
(sh, 27100). IR (KBr): 2933m, 2867w, 1729s, 1633w, 1585m, 1458s, 1372w, 1250s, 1179m, 1125w, 1099s, 1022w,
995w, 795w, 770w, 718w, 655w, 63 0w. EPR (CHCl3): g? ˆ 5.79; gk ꢀ 1.98; in addition, a weak rhombic signal was
25o
‡
observed. m (CDCl3): 4.77 Æ 0.05 mB. FAB-MS: 1293.0 (100, [M À Cl] ). Anal. calc. for C72H80ClFeN6O13
¥
eff
2H2O (1364.79): C 63.63, H 6.40, N 6.16; found: C 63.42, H 6.07, N 5.96.
To synthesize the reduced FeII complex [4 ¥ FeII], a soln. of [4 ¥ FeIII]Cl in PhMe of appropriate concentration
was degassed by three −freeze-pump-thaw× cycles and then mixed with half its volume of a freshly prepared 0.1m
soln. of Na2S2O4 in degassed H2O, upon which the color changed from red-brown to deep red. The two-phase
system was vigorously stirred for 90 min and then left standing for 30 min to allow for complete phase

Helvetica Chimica Acta Vol. 85 (2002)
613
separation. The org. layer containing the desired [4 ¥ FeII] was then transferred into the vessels for the individual
measurements, or evaporated and the product dried under h.v. Red, amorphous solid. UV/VIS (PhMe): 552
25o
(sh, 11300), 533 (13600), 432 (163400). m (CDCl3): 4.10 Æ 0.05 mB.
eff
(SP-5-12)-({Tetraethyl 4,4',4'',4'''-[21H,23H-Porphine-5,15-diylbis(benzene-2,1,3-triyldioxy)]tetrakis-
(butanoato)}(2À)-N21,N22,N23,N24)(1,2-dimethylimidazolato](0)-N3)iron(III) Chloride ([12 ¥ (1,2-Me2Im)-
FeIII]Cl). To 12 ¥ 2 H (49.0 mg, 0.050 mmol) in abs. THF (10 ml) degassed by three −freeze-pump-thaw× cycles,
2,6-lutidine (25.0 ml, 0.200 mmol) was added, and the purple soln. was heated to reflux for 15 min. Anh. FeCl2
(63.0 mg, 0.500 mmol) was added, and the mixture was heated to reflux for 2 h. The brown soln. was left to cool
to r.t. and was then exposed to air for 30 min. Direct CC of the entire mixture (Al2O3 (15 g); THF) provided a
dark brown oil, which was dried under h.v. The resulting black oil was dissolved in Et2O (20 ml), washed with 1m
HCl (10 ml) and sat. aq. NaCl soln. (10 ml), dried (MgSO4), and concentrated in vacuo. The remaining black
solid was recrystallized (Et2O/pentane) and dried under h.v. to yield a black crystalline solid of [12 ¥ FeIII Cl],
which was taken up in CH2Cl2 (5 ml). The dark-brown soln. was treated with 1,2-Me2Im (5.3mg, 0.060 mmol)
and stirred at r.t. for 4 h, which led to a color change from dark brown to red-brown. Evaporation in vacuo,
crystallization of the crude oily product from MeOH/Et2O, and drying under h.v. gave [12 ¥ (1,2-Me2Im)FeIII]Cl
(40.3mg, 69%). Red-brown, crystalline solid. M.p. 132 8. TLC (Al2O3; THF/MeOH 60 :40): Rf 0.92. UV/VIS
(0.01m 1,2-Me2Im in CHCl3): 629 (sh, 2700), 568 (5900), 498 (9900), 408 (85700), 380 (36500). IR (KBr): 2923m,
2867w, 1726s, 1591m, 1522w, 1458s, 1378w, 1311w, 1289w, 1250s, 1178s, 1103s, 1055w, 1022w, 994s, 855w, 83 3w,
25o
795w, 765w, 715w, 695w, 640w, 63 0w. m (0.01m 1,2-Me2Im in CDCl3): 5.78 Æ 0.05 mB. FAB-MS: 1036.2 (100,
eff
‡
[M À 1,2-Me2Im À Cl] ). Anal. calc. for C61H68ClFeN6O12 (1168.52): C 62.70, H 5.87, N 7.19; found: C 62.64,
H 6.10, N 6.99.
To prepare the reduced, five-coordinate FeII complex [12 ¥ (1,2-Me2Im)FeII], a soln. of appropriate
concentration of [12 ¥ (1,2-Me2Im)FeIII]Cl in 0.01m 1,2-Me2Im in PhMe was degassed by three −freeze-pump-
thaw× cycles and then mixed with an excess of a sat. soln. of Na2S2O4/18-crown-6 in degassed abs. Me2SO, upon
which the color slowly changed from red-brown to deep red. The soln. was stirred for 120 min and then
transferred into the vessels required for the individual measurements, or evaporated and dried under h.v. Red,
25o
amorphous solid. UV/VIS (0.01m 1,2-Me2Im in PhMe): 548 (sh, 7500), 522 (15800) 419 (176900). m (0.01m 1,2-
eff
Me2Im in CDCl3): 4.78 Æ 0.05 mB.
(SP-5-13)-({Tetrakis{2-[2-(2-methoxyethoxy)ethoxy]ethyl} 4,4',4'',4'''-[10-(3-{[6-(1H-Imidazol-1-yl)hexyl]-
oxy}-4-methylphenyl)-21H,23H-porphine-1,15-diylbis(benzene-2,1,3-triyldioxy)]tetrakis[butanamido]}(2À)-
N21,N22,N23,N24,N3)zinc(II) (1 ¥ Zn). Compound 13 ¥ Zn was prepared from 4 ¥ Zn (29.4 mg, 0.020 mmol)
according to GP 1. The black-purple powder was immediately dissolved in abs. DMF (5 ml), and 14
(130.6 mg, 0.800 mmol) was added. The soln. was cooled to 08 in an ice bath, and HATU (45.2 mg, 0.120 mmol)
and Et3N (112.0 ml, 0.800 mmol) were added. After 2 h at 08, the ice bath was removed, and stirring was
continued for 1 d at r.t. in the dark. The solvent was distilled off under h.v. at 408, and the residue was taken up in
CH2Cl2/MeOH 95 :5 (10 ml) and purified by FC (SiO2 (5 g); CH2Cl2/MeOH 95 :5). The porphyrin fraction was
concentrated in vacuo and dried under h.v. overnight. Prep. GPC (Bio-Beads S-X1; CH2Cl2) and drying under
h.v. provided 1 ¥ Zn (32.1 mg, 91%). Purple, amorphous solid. TLC (SiO2; CH2Cl2/MeOH 90 :10): Rf 0.34. UV/
VIS (CHCl3): 596 (4400), 560 (16500), 512 (2400), 427 (389100), 405 (39300), 313 (19400). IR (CHCl3): 3405w,
2933m, 2878m, 1662s, 1583w, 1521m, 1456s, 1378w, 1350w, 1330w, 1290w, 1248m, 1101s, 1050w, 1022w, 992m,
909s, 850m, 650w, 625w. 1H-NMR (500 MHz, CDCl3): 10.03( s, 1 H); 9.28 (d, J ˆ 4.4, 2 H); 8.98 (d, J ˆ 4.4, 2 H);
8.85 (d, J ˆ 4.5, 2 H); 8.80 (d, J ˆ 4.5, 2 H); 7.85 (d, J ˆ 7.1, 1 H); 7.70 (t, J ˆ 8.5, 2 H); 7.47 (d, J ˆ 7.1, 1 H); 7.04
(d, J ˆ 8.5, 2 H); 7.00 (s, 1 H); 6.99 (d, J ˆ 8.5, 2 H); 4.99 (s, 1 H); 4.96 (s, 2 H); 4.01 (t, J ˆ 6.8, 2 H); 3.78 3.99
(m, 8 H); 3.64 (s, 8 H); 3.54 (s, 8 H); 3 .3 4s(, 6 H); 3.18 (s, 4 H); 3.04 (s, 8 H); 3.02 (s, 6 H); 2.78 2.99 (m, 8 H);
2.50 2.70 (m, 8 H); 2.49 (s, 3H); 2.18 ( s, 1 H); 1.99 (s, 8 H); 1.72 (s, 1 H); 1.55 (br. s, 2 H); 1.12 1.38 (m, 8 H);
0.81 1.05 (m, 8 H); 0.73(br. s, 2 H); 0.56 (br. s, 2 H); 0.00 (br. s, 2 H). 13C-NMR (125 MHz, CDCl3): 172.3;
171.4; 159.9; 159.5; 153.3; 150.5; 150.4; 149.2; 149.0; 142.0; 131.6; 131.6; 131.5; 131.1; 130.8; 130.0; 128.8; 125.6;
124.7; 123.1; 121.4; 119.9; 118.5; 115.8; 112.3; 105.7; 104.9; 104.0; 71.9; 71.2; 70.5; 70.5; 70.1; 69.6; 69.6; 69.5; 69.0;
68.9; 67.4; 66.9; 66.0; 59.0; 58.6; 46.3; 38.6; 37.7; 31.2; 31.1; 29.4; 26.5; 24.9; 24.5 (2Â); 23.8; 16.3. FAB-MS: 1770.4
‡
(100, M , C92H124N10O21Zn; calc. 1770.8). MALDI-TOF-MS (10À5 m in CH2Cl2; matrix: 0.02m HABA in MeCN/
‡
‡
H2O 4 :1): 1793.9 (37, [M ‡ Na] , C92H124N10NaO21Zn; calc. 1793.8), 1771.5 (100, M , C92H124N10O21Zn; calc.
1770.8).
(SP-5-13)-({Tetrakis{2-[2-(2-methoxyethoxy)ethoxy]ethyl} 17,17',17'',17'''-[10-(3-{[6-(1H-Imidazol-1-yl)-
hexyl]oxy}-4-methylphenyl)-21H,23H-porphine-1,15-diylbis{benzene-2,1,3-triylbis[oxy(1-oxobutane-4,1-diyl)-
imino]}]tetrakis[12-oxo-17-(5-oxo-2,6,9,12,15-pentaoxahexadec-1-yl)-2,5,8,11,15,19-hexaoxadocosan-22-ato]}(2À)-
N21,N22,N23,N24,N3)zinc(II) (2 ¥ Zn). Compound 13 ¥ Zn was prepared from 4 ¥ Zn (29.4 mg, 0.020 mmol)

614
Helvetica Chimica Acta Vol. 85 (2002)
according to GP 1. The black-purple powder was immediately dissolved in abs. DMF (2 ml), 15 (124.0 mg,
0.160 mmol) was added, and the mixture was cooled to 08 in an ice bath. After addition of HATU (45.2 mg,
0.120 mmol) and Et3N (3 1.8ml, 0.240 mmol) at 08, the soln. was slowly warmed to r.t. during 24 h and stirred at
r.t. for 2 d in the dark. The solvent was distilled off under h.v. at 408, and the residue was taken up in CH2Cl2/
MeOH 95 :5 (10 ml) and purified by FC (SiO2 (5 g); CH2Cl2/MeOH 95 :5). The porphyrin fraction was
concentrated in vacuo and dried under h.v. overnight. Prep. GPC (Bio-Beads S-X1; CH2Cl2) and drying under
h.v. afforded 2 ¥ Zn (59.0 mg, 70%). Purple, viscous oil. TLC (SiO2; CH2Cl2/MeOH 90 :10): Rf 0.42. UV/VIS
(CHCl3): 596 (4400), 560 (17000), 522 (3100), 427 (464000), 405 (sh, 39200), 312 (22600). IR (CHCl3): 3411w,
2930m, 2880m, 1734s, 1669m, 1583w, 1511w, 1456m, 1378w, 1350w, 1316w, 1278w, 1250m, 1183m, 1103s, 1028w,
993w, 950w, 850w, 620w. 1H-NMR (500 MHz, CDCl3): 9.93( s, 1 H); 9.20 (d, J ˆ 4.4, 2 H); 8.90 (d, J ˆ 4.4, 2 H);
8.75 (d, J ˆ 4.5, 2 H); 8.71 (d, J ˆ 4.5, 2 H); 7.88 (d, J ˆ 7.6, 1 H); 7.67 (t, J ˆ 8.5, 2 H); 7.45 (d, J ˆ 7.6, 1 H); 7.05
(d, J ˆ 8.5, 2 H); 7.04 (s, 1 H); 6.98 (d, J ˆ 8.5, 2 H); 5.74 (s, 2 H); 5.61 (s, 2 H); 5.04 (s, 1 H); 4.17 4.19
(m, 12 H); 4.02 (t, J ˆ 6.8, 2 H); 3.98 4.00 (m, 12 H); 3.82 3.88 (m, 8 H); 3.39 3.65 (m, 168 H); 3.33 (s, 18 H);
3.29 (s, 18 H); 2.78 (br. s, 2 H); 2.52 (t, J ˆ 6.4, 12 H); 2.47 (s, 3H); 2.43( t, J ˆ 6.4, 12 H); 2.10 (s, 1 H); 1.88
(s, 1 H); 1.58 (br. s, 2 H); 1.22 1.45 (m, 8 H); 0.97 1.21 (m, 8 H); 0.93(br. s, 2 H); 0.76 (br. s, 2 H); 0.06 (br. s,
2 H). 13C-NMR (125 MHz, CDCl3): 172.6; 171.9; 171.3; 171.3; 160.1; 159.5; 153.1; 150.3; 150.0; 149.2; 148.8;
142.7; 131.8; 131.1; 131.0; 130.9; 130.3; 129.5; 128.5; 124.9; 124.9; 123.6; 121.8; 119.2; 118.7; 115.5; 111.5; 105.6;
105.0; 104.1; 71.8; 71.7; 70.5; 70.5 (2Â); 70.3(2 Â); 70.3; 69.1; 69.0 (2 Â); 68.8; 67.4; 67.2; 66.6; 66.5; 66.0; 63.5;
63.3; 59.7; 59.6; 58.9; 58.9; 46.1; 34.7; 34.6; 32.3; 32.0; 29.6; 26.6; 24.8; 24.6; 24.4; 23.9; 16.2. MALDI-TOF-MS
‡
(10À5 m in CH2Cl2; matrix: 0.5m 2,5-DHB in MeOH): 4245.8 (49, [M ‡ Na] , C200H316N10NaO81Zn; calc. 4245.0),
‡
4222.7 (100, M , C200H316N10O81Zn; calc. 4222.0).
(SP-5-13)-({Octakis{2-[2-(2-methoxyethoxy)ethoxy]ethyl} 13,13',13'',13'''-[10-(3-{[6-(1H-Imidazol-1-yl)-
hexyl]oxy}-4-methylphenyl)-21H,23H-porphine-1,15-diylbis{benzene-2,1,3-triylbis[oxy(1-oxobutane-4,1-diyl)-
imino]}]tetrakis{13-[5,12-dioxo-7,7-bis(5-oxo-2,6,9,12,15-pentaoxahexadec-1-yl)-2,9,13,16,19,22-hexaoxa-6-aza-
tricos-1-yl]-8,18-dioxo-6,6,20,20-tetrakis(5-oxo-2,6,9,12,15-pentaoxahexadec-1-yl)-4,11,15,22-tetraoxa-7,19-di-
azapentacosanedioato}}(2À)-N21,N22,N23,N24,N3)zinc(II) (3 ¥ Zn). Compound 13 ¥ Zn was prepared from 4 ¥ Zn
(29.4 mg, 0.020 mmol) according to GP 1. The black-purple powder was immediately mixed with a soln. of 16
(627.0 mg, 0.240 mmol) in abs. PhMe (10 ml), and the mixture was evaporated to dryness in vacuo and further
dried azeotropically by co-evaporation with abs. PhMe (3 Â 5 ml). The residue was dissolved in abs. DMF (2 ml)
and cooled in an ice/NaCl bath to À158. HATU (45.6 mg, 0.120 mmol) and Et3N (3 1.8ml, 0.240 mmol) were
added, and the soln. was left to warm very slowly to 08 in the dark during 5 d and then stirred for an additional
2 d at 08 in an ice bath in the dark. The entire mixture was directly subjected to prep. GPC (Bio-Beads S-X1;
CH2Cl2). The resulting crude product was filtered through a poly(tetrafluoroethylene) (PTFE) membrane
(Æ ˆ 13mm, pore size 0.45 mm) and then subjected to prep. HP-GPC (NovoGROM 100; THF, 20 mg of mixture
per run). Finally, the product was again purified by prep. GPC (Bio-Beads S-X1; CH2Cl2) and dried under h.v. to
yield 3 ¥ Zn (153.1 mg, 65%). Purple, highly viscous oil. TLC (SiO2; CH2Cl2/MeOH 90 :10): Rf 0.58. UV/VIS
(CHCl3): 595 (4300), 558 (17000), 522 (3500), 426 (442600), 405 (sh, 45900), 312 (21900). IR (CHCl3): 3426w,
2920m, 2880m, 1734s, 1670m, 1585vw, 1517m, 1457m, 1380w, 1350w, 1323w, 1282m, 1245m, 1186s, 1105s, 1031w,
990w, 949w, 854m. 1H-NMR (500 MHz, CDCl3): 9.85 (s, 1 H); 9.12 (d, J ˆ 4.2, 2 H); 8.83( d, J ˆ 4.2, 2 H); 8.68
(d, J ˆ 4.3, 2 H); 8.62 (d, J ˆ 4.3, 2 H); 7.81 (d, J ˆ 7.4, 1 H); 7.63( t, J ˆ 8.5, 2 H); 7.39 (d, J ˆ 7.4, 1 H); 7.07
(d, J ˆ 8.5, 2 H); 6.97 (s, 1 H); 6.96 (d, J ˆ 8.5, 2 H); 6.09 (s, 6 H); 6.08 (s, 6 H); 6.01 (s, 2 H); 5.98 (s, 2 H); 4.99
(s, 1 H); 4.17 (t, J ˆ 6.8, 2 H); 4.14 (t, J ˆ 4.9, 36 H); 4.11 (t, J ˆ 4.9, 36 H); 3.71 3.82 (m, 8 H); 3.38 3.65
(m, 552 H); 3.30 (s, 54 H); 3.27 (s, 54 H); 2.53(br. s, 2 H); 2.49 (t, J ˆ 6.3, 36 H); 2.48 (t, J ˆ 6.3, 36 H); 2.42
(s, 3H); 2.33(br. t, J ˆ 6.1, 12 H); 2.32 (br. t, J ˆ 6.1, 12 H); 1.99 (s, 1 H); 1.00 1.81 (m, 19 H); 0.89 (br. s, 2 H);
0.72 (br. s, 2 H); 0.01 (br. s, 2 H). 13C-NMR (125 MHz, CDCl3): 172.1; 171.7; 171.3(2 Â); 170.8; 170.7; 160.1;
159.3; 153.0; 150.2; 150.0; 149.1; 148.7; 142.7; 131.9; 131.0; 131.0; 130.8; 130.3; 129.5; 128.4; 124.8; 124.7; 123.6;
121.8; 119.1; 118.7; 115.3; 111.4; 105.8; 105.1; 103.9; 71.8; 71.7; 70.4; 70.4 (2 Â); 70.3; 70.3 (2 Â); 69.1 (3Â); 68.9
(2Â) 68.8; 67.9; 67.7; 67.4 (2Â); 66.6; 66.6; 59.9; 63.5; 63.4; 60.3 (2Â); 59.7; 59.7; 58.9; 58.8; 46.0; 37.0; 36.9; 34.6;
34.6; 31.9; 31.9; 29.5; 26.6; 24.7; 24.1; 23.9; 23.7; 16.2. MALDI-TOF-MS (10À5 m in CH2Cl2; matrix: 0.02m HABA
‡
‡
in MeCN/H2O 4 :1): 11586.1 (100, [M ‡ Na] , C524H904N22NaO249Zn; calc. 11584.8), 11562.6 (30, M ,
C524H904N22O249Zn; calc. 11561.8).
(SP-5-13)-({Tetrakis{2-[2-(2-methoxyethoxy)ethoxy]ethyl} 4,4',4'',4'''-[10-(3-{[6-(1H-Imidazol-1-yl)hexyl]-
oxy}-4-methylphenyl)-21H,23H-porphine-1,15-diylbis(benzene-2,1,3-triyldioxy)]tetrakis[butanamido]}(2À)-
N21,N22,N23,N24,N3)iron(III) Chloride ([1 ¥ FeIII]Cl). Compound [1 ¥ FeIII]Cl (13.2 mg, 49%) was prepared from
1 ¥ Zn (26.6 mg, 0.015 mmol) according to GP 2. The reaction time in the metal insertion step was 2 h. Red-
brown, amorphous solid. TLC (SiO2; CH2Cl2/MeOH 90 :10): Rf 0.12. UV/VIS (CHCl3): 646 (2100), 577 (sh,

Helvetica Chimica Acta Vol. 85 (2002)
615
4500), 507 (10400), 415 (90000), 385 (sh, 50300), 350 (sh, 25200). IR (CHCl3): 3428w, 2930w, 2867m, 1662s,
1588m, 1517m, 1458s, 1378w, 1349w, 1290w, 1253m, 1102s, 1017w, 998m, 855w, 840w, 640w. EPR (CHCl3): g? ˆ
‡
5.82; gk ꢀ 1.99; in addition, a weak rhombic signal was observed. FAB-MS: 1761.6 (100, [M À Cl] ; calc. for
C92H124FeN10O21: 1761.8). MALDI-TOF-MS (10À5 m in CH2Cl2; matrix: 0.02m HABA in MeCN/H2O 4 :1):
‡
‡
1786.0 (17, [MÀ Cl ‡ Na] , C92H124FeN10NaO21; calc. 1784.8), 1762.4 (100, [MÀ Cl] , C92H124FeN10O1; calc. 1761.8).
(SP-5-13)-({Tetrakis{2-[2-(2-methoxyethoxy)ethoxy]ethyl} 17,17',17'',17'''-[10-(3-{[6-(1H-Imidazol-1-yl)-
hexyl]oxy}-4-methylphenyl)-21H,23H-porphine-1,15-diylbis{benzene-2,1,3-triylbis[oxy(1-oxobutane-4,1-diyl)-
imino]}]tetrakis[12-oxo-17-(5-oxo-2,6,9,12,15-pentaoxahexadec-1-yl)-2,5,8,11,15,19-hexaoxadocosan-22-
ato]}(2À)-N21,N22,N23,N24,N3)iron(III) Chloride ([2 ¥ FeIII]Cl). Compound [2 ¥ FeIII]Cl (22.5 mg, 53%) was
prepared from 2 ¥ Zn (42.5 mg, 0.010 mmol) according to GP 2. The reaction time in the metal-insertion step was
4 h. Red-brown, viscous oil. TLC (SiO2; CH2Cl2/MeOH 90 :10): Rf 0.24. UV/VIS (CHCl3): 645 (3400), 575
(sh, 5700), 507 (12000), 415 (96000), 385 (sh, 46600), 350 (sh, 27000). IR (CHCl3): 3425w, 2925m, 2880s, 1734s,
1670m, 1591w, 1514m, 1458m, 1378m, 1351m, 1316m, 1252s, 1185s, 1103s, 1028m, 992m, 951w, 853w. EPR
(CHCl3): g? ˆ 5.86; gk ꢀ 2.01; in addition, a weak rhombic signal was observed. MALDI-TOF-MS (10À5 m in
‡
CH2Cl2; matrix: 0.02m HABA in MeCN/H2O 4 :1): 4436.6 (6, [M À Cl ‡ Na] ; calc. for C200H316FeN10NaO81:
‡
4235.0), 4214.6 (100, [M À Cl] ; C200H316FeN10O81; calc. 4212.0).
(SP-5-13)-({Octakis{2-[2-(2-methoxyethoxy)ethoxy]ethyl} 13,13',13'',13'''-[10-(3-{[6-(1H-Imidazol-1-yl)-
hexyl]oxy}-4-methylphenyl)-21H,23H-porphine-1,15-diylbis{benzene-2,1,3-triylbis[oxy(1-oxobutane-4,1-diyl)i-
mino]}]tetrakis{13-[5,12-dioxo-7,7-bis(5-oxo-2,6,9,12,15-pentaoxahexadec-1-yl)-2,9,13,16,19,22-hexaoxa-6-aza-
tricos-1-yl]-8,18-dioxo-6,6,20,20-tetrakis(5-oxo-2,6,9,12,15-pentaoxahexadec-1-yl)-4,11,15,22-tetraoxa-7,19-di-
azapentacosanedioato}}(2À)N21,N22,N23,N24,N3)iron(III) Chloride ([3 ¥ FeIII]Cl). Compound [3 ¥ FeIII]Cl
(44.6 mg, 59%) was prepared from 3 ¥ Zn (86.7 mg, 0.0075 mmol) according to GP 2. The reaction time in the
metal insertion step was 6 h. Red-brown, highly viscous oil. TLC (SiO2; CH2Cl2/MeOH 90 :10): Rf 0.35. UV/VIS
(CHCl3): 645 (sh, 2200), 585 (sh, 5700), 507 (12200), 415 (99900), 395 (sh, 74000), 350 (sh, 27400). IR (CHCl3):
3427w, 2879s, 2822m, 1733s, 1669m, 1590w, 1540w, 1506w, 1485w, 1457m, 1400w, 1372w, 1352w, 1320w, 1284m,
1175m, 1104s, 1022w, 997w, 950w, 862w, 640w. EPR (CHCl3): g? ˆ 5.85; gk ꢀ 2.03; in addition a weak rhombic
signal was observed. MALDI-TOF-MS (10À5 m in CH2Cl2; matrix: 0.02m HABA in MeCN/H2O 4 :1): 11552.0
‡
(100, [M À Cl] , C524H904FeN22O249; calc. 11551.8).
Catalysis Studies. All experiments were carried out with the FeIII forms of the dendritic porphyrins.
Epoxidations. A soln. of alkene (0.250 mmol), dendritic porphyrin (0.001 0.002 mmol), and dodecane
(0.1319 mmol) as an internal standard in abs. CH2Cl2 (2.00 ml) was degassed by three −freeze-pump-thaw× cycles
and then treated with iodosylbenzene (0.200 mmol) in the dark at 295 Æ 2 K. The mixture was stirred for 4 h,
subsequently it was filtered over SiO2 (1.0 g), and the SiO2 was washed with CH2Cl2 (3ml). The filtrate and
washing soln. were combined, and 0.5 ml of this soln. was directly subjected to anal. GC. A temp. program from
508 to 2008 with a gradient of 108 minÀ1 was applied.
Sulfide Oxidations. A soln. of sulfide (0.250 mmol), dendritic porphyrin (0.001 0.002 mmol), and
dodecane (0.1319 mmol) as an internal standard in abs. CH2Cl2 (2.00 ml) was degassed by three −freeze-pump-
thaw× cycles and then treated with iodosylbenzene (0.200 mmol) in the dark. The mixture was stirred at 295 Æ
2 K for 4 h, subsequently it was filtered over SiO2 (1.0 g) and the SiO2 washed with CH2Cl2 (1.0 ml), followed by
Et2O (3.0 ml). The filtrate and washing solns. were combined, and 1.0 ml of this soln. was directly subjected to
anal. GC. A temp. program from 1508 to 3008 with a gradient of 108 minÀ1 was applied. Yields based on
consumed iodosylbenzene and total turnover numbers were calculated by quantification of the anal. GC traces
with help of the internal standard according to established methods [29]. All catalysis reactions were performed
at least in duplicate and showed good reproducibility between experiments. The background reaction in absence
of catalyst was negligibly slow.
Calibration for Anal. GC Quantification. Response factors for reactants and products were determined
from linear regression analysis of anal. GC traces from serial dilutions of these compounds in CH2Cl2 with
dodecane as an internal standard [29]. All calibrations were run in duplicate.
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