Azo-linked corner porphyrin systems: Synthesis, crystal structures and spectroscopic investigation

Journal of Porphyrins and Phthalocyanines

J. Porphyrins Phthalocyanines 2010; 14: 481–493

DOI: 10.1142/S1088424610002318

Published at http://www.worldscinet.com/jpp/

Azo-linked corner porphyrin systems: synthesis, crystal

structures and spectroscopic investigation

Bruno Bašić, John C. McMurtrie and Dennis P. Arnold*^◊

Discipline of Chemistry, Faculty of Science and Technology, Queensland University of Technology, G.P.O. Box 2434,

Brisbane 4001, Australia

Received 9 November 2009

Accepted 25 January 2010

ABSTRACT: 1,2-bis[10,15-di(3,5-di-tert-butyl)phenylporphyrinatonickel(II)-5-yl]diazene was synthe-

sised via copper-catalyzed coupling of aminated nickel(II) 5,10-diarylporphyrin (“corner porphyrin”)

and its X-ray crystal structure was determined. Two different crystals yielded different structures, one

with the free meso-positions in a trans-like orientation, and the other with a cis-like disposition. The

free meso-positions of the obtained dimer have been further functionalized while the synthesis of a

zinc analog has so far been unsuccessful. The X-ray crystal structure of the dinitro derivative of the

dinickel(II) azoporphyrin was determined, and the structure showed a cis-like disposition of the nitro

groups.

KEYWORDS: azo bridge, azoporphyrin, corner porphyrin, crystal structure, dimer.

be affected by coordinating solvents as well as by the

INTRODUCTION

presence of competing coordinating compounds.

Since the crystal structure of the light-harvesting

The use of porphyrins as monomers for larger struc-

antenna complex LH2 of Rhodopseudomonas acido-

phila was elucidated [1–3], efforts have been made to

tures is not a new ﬁeld. However, the investigation of

linker groups, their properties and their overall effect on

synthesize a diverse range of cyclic porphyrin oligomers

the resulting molecule is a developing area. The linker

(CPOs) with the aim of studying excitation energy trans-

groups of special interest are those that do not interrupt

fer (EET) and creating analogs of natural light-harvesting

the conjugation of the porphyrin macrocycle but rather

antennae. However, CPOs have been investigated in other

extend the overall conjugation of the entire system. The

ﬁelds such as host-guest chemistry and single-molecule

ﬁrst such conjugated porphyrin system was a butadiyne-

photochemistry [4].

linked dimer [9]. Since then porphyrin systems that would

While porphyrin systems linked by covalent bonds are

offer the best electronic communication through their

the most robust, they are also difﬁcult to make and so

conjugated linkers have been investigated [4, 10–13].

systems linked by metal coordination bonds, which rely

The butadiyne and other linkers have been studied

to a large degree on the nitrogen atom-metal coordination

extensively, with numerous papers reporting interesting

bond, as well as systems involving non-covalent bonds,

results with justiﬁed promise of potential in various ﬁelds

have also been explored [4–8]. Though the environment

[4, 13–19]. Theoretical work suggested that an azo link-

will inﬂuence all of these systems, the non-covalently

age will provide the optimum degree of interporphyrin

linked porphyrins are more affected by solvents while

conjugation and thus quite possibly the best bridge for

porphyrin systems involving coordination bonds will

electronic communication between the porphyrins [17].

The Arnold group reported the copper-promoted syn-

thesis of the ﬁrst azoporphyrins from 5,10,15-triaryl

substituted and 5,15-diaryl substituted porphyrins [20].

^SPP full member in good standing

Here, we present an extension of that work to include the

5,10-diaryl substituted porphyrin (corner porphyrin). Our

*Correspondence to: Dennis P. Arnold, email: d.arnold@qut.

edu.au, fax: +61 7-3138-1804

´

482

B. BašIC et al.

Ar

M

N

Ar

M

N

Ar

N

Ar

M

Ar

N

Ar

N

Ar

M

Ar

M

N

M

Ar

N

Ar

A

B

Ar

M = 2H, Ni, Zn

Fig. 1. Proposed azo-linked tetramers

objective was the synthesis of more ambitious azo-linked

porphyrin systems. The initial goal was to synthesize an

azo-linked dimer that would still have two meso-positions

left available for further modiﬁcation. We chose to use

the corner porphyrin as our starting material. Though

the synthesis of 5,10-DAP is harder than the synthesis

of 5,15-DAP with notably lower yields, we felt that a

successfully synthesized azo-linked dimer made of two

corner porphyrin units would not only extend the family

of known azo-linked compounds but would also allow

us to explore a more diverse range of porphyrin systems.

In particular, we are interested in preparing new CPOs.

Furthermore, for the purposes of molecular electronics

and nonlinear optics, we are interested in those CPOs in

which ground-state electronic interaction between the

linked porphyrins is substantial [21].

Inspired by work done elsewhere [4, 21] the research

presented here aims towards the synthesis of cyclic azo-

linked tetramers (Fig. 1). Tetramer A would be the azo

analog of the known butadiyne-linked cyclic porphyrin

system [21] while B would be a system that uses both

butadiyne and azo bridges, thus extending the synthesis

possibilities for both linkers.

azo-bridged dimer 5 in 66% yield (Scheme 1). Aside

from being the ﬁrst azo-linked dimer made up of two

corner porphyrin units, this dimer also has two free meso-

positions that could be further modiﬁed. Using the same

AgNO₂/I₂method used for nitration of the monomer we

attempted to nitrate the dimer. On a 5 mg scale the only

product was the meso dinitrated dimer 6 in almost quan-

titative yield. However, the result was not reproducible

when the scale was increased. The main outcome was

the destruction of the dimer where, strangely enough,

the unsubstituted Ni corner porphyrin 12 and the meso

dinitrated monomer 13 were obtained together with some

compound 6 and the mononitrated dimer 7. This was the

ﬁrst indication that the azo link may not be as strong as

we had thought it would be.

Although 6 was not available in great quantities we

tried to reduce the nitro groups to amino groups using

sodium borohydride and 10% palladium on carbon,

mimicking the route in which 4 was obtained from 3.

We considered the synthesis of an azo-linked dimer with

amino groups on the remaining meso-positions a precur-

sor to A as we further expected to induce the aminated

dimer to self-couple. There was of course the possibility

of creating an open oligomer rather than a closed cyclic

tetramer system. However, we wished to investigate

those linear systems, too, and explore reaction condi-

tions that would give one but not the other. The result

of the attempted reduction of the nitro groups was a

complete loss of starting material in favour of uniden-

tiﬁed non-porphyrinic compounds. Thus, once again

we observed the azo-linked porphyrin dimer’s appar-

ent instability. Next, we tried to brominate the dimer

using the same NBS method used for the bromination of

monomer porphyrins [22]. We wanted to create a bromi-

nated dimer that would lend itself to the introduction of

alkynyl groups. From there we thought tetramer B could

be obtained through self-coupling as well as opening up

various other substitution reactions. However, though 8

RESULTS AND DISCUSSION

To approach the synthesis of tetramer A, we decided

ﬁrst to try the synthesis of an azo-linked dimer that would

be further modiﬁed and then self-coupled to form the tar-

get compound. The synthesis of compounds 2, 3 and 4

followed the methods used for the synthesis of analogous

5,15-diaryl substituted porphyrins [22]. All three com-

pounds are obtained in good yields and the crude product

of each can be used in subsequent steps. This is fortuitous

as the recrystallization of 3 and particularly 4 has proved

difﬁcult due to high solubility of these compounds. Fol-

lowing the Cu(OAc)₂method established by our group

[20], compound 4 was successfully coupled to form the

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Ar

Ni

N

NH

N

NH

N

(i)

(ii)

(iii)

NH₂

NO₂

Ni

H

NO₂

Ar

HN

H

2

H

4

1

3

(iv)

Ar

Ni

Ar

Ni

Ar

Ni

Ar

N

(v)

N

Ni

H

N

Ar

Ni

N

Ar

N

Ar

N

NO₂

H

6

5

7

(vi)

Ar

Ni

Br

Ar

N

Ni

N

Ar

Br

8

Scheme 1. Synthesis of azo-linked Ni corner porphyrin dimers: (i) 0.75 eq. I₂, 1.5 eq. AgNO₂, DCM/MeCN; (ii) Ni(acac)₂, toluene

120 °C; (iii) 10% Pd on C, 25 eq. NaBH₄, DCM/MeOH; (iv) 12 mol.% Cu(OAc)₂·H₂O, 4 eq. pyridine, toluene 80 °C; (v) 1.5 eq. I2,

3 eq. AgNO₂, DCM/MeCN; (vi) 2.5 eq. NBS, CHCl₃/pyridine. Ar = 3,5-di-tert-butylphenyl

Table 1. Chemical shifts of the hydrogen atoms for the synthesized azo-linked compounds

Compound

2-H

9.27

8.95

8.90

3-H

10.15

9.88

9.91

7-H

10.08

9.98

9.97

8-H

8.99

9.40

9.90

12-H

8.73

9.11

9.35

13-H

8.71

8.79

8.71

17-H

8.83

8.67

8.63

18-H

9.01

8.65

8.61

20-H

9.71

N/A

5

6

8

was obtained, the yield was low and the reaction has not

proven reproducible.

The ¹H NMR spectra of the azo compounds (5, 6 and

8) showed eight β peaks that were shifted signiﬁcantly

downﬁeld (Table 1). The former is attributed to a lack of

symmetry of the porphyrin macrocycles and the down-

ﬁeld shift to the presence of an electron-withdrawing

group on the adjacent meso-positions.

The absorption spectra of the synthesized azo-linked

dimers (Fig. 2) include a large split in the Soret band and

red-shift of the Q bands. These features are commonly

observed in porphyrin dimers linked with conjugated

bridges and are also very similar to the features of the

ﬁrst azo-linked porphyrin dimer [20]. The overall red-

shift of the absorption bands relative to other porphyrins

is indicative of an efﬁcient p-overlap between the por-

phyrin moieties [17].

Fig. 2. Electronic absorption spectra of azo-linked compounds:

5 (solid), 6 (dotted) and 7 (dashed)

were solved, namely 5a and 5b. The unsubstituted meso-

positions of the two porphyrin rings are in a trans-like

relation to one another in 5a and cis-like in 5b. Pertinent

geometric data for the porphyrin rings and their relative

Single crystals of 5 were grown from DCM/methanol,

and the structures were solved by X-ray crystallographic

analysis (Figs 3–5). For compound 5 two structures

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B. BašIC et al.

Fig. 3. Crystal structure of 5a shown from two different per-

spectives: (a) orthogonal to the mean planes of the porphyrin

rings; (b) parallel to the mean planes. The side view (b) shows

the distortion of the rings and the displacement of the planes

of the rings with respect to each other. The porphyrin rings are

rufﬂed but lie in parallel planes displaced by 2.35 Å

Fig. 5. Crystal structure of 6 shown orthogonal to the mean

planes of the porphyrin rings. The two molecules (a) and (b) in

the asymmetric unit of 6 both have the cis-like arrangement of

the meso nitro groups

of the rings are farthest from the mean plane of the

C₂₀N₄Ni porphyrin atoms in the arrangement described

in the literature as “rufﬂed” [23]. The perpendicular dis-

tances of the meso carbon atoms from the C₂₀N₄Ni mean

plane range between 0.319 Å and 0.778 Å across all the

porphyrin rings in the three structures. These displace-

ments are the best indicator of the extent of the distor-

tion of the porphyrin. The coordination sphere (N₄Ni) in

each porphyrin is almost perfectly square planar. In each

case the N₄Ni plane is almost coincident with the mean

C₂₀N₄Ni plane. The dihedral angles range between 0.62°

and 1.47°. The maximum displacement for the nickel

atoms from the mean plane of their respective C₂₀N₄Ni

plane occurs for 5a at only 0.055 Å.

A key feature of interest in the structures is the rela-

tive orientation of the porphyrin rings with respect to

each other. In 5a the unsubstituted meso carbon atoms

(C5 and C5′) are arranged in a trans-like fashion. In con-

trast to this the unsubstituted meso carbon atoms (C5 and

C53) in 5b and the nitro substituted meso carbon atoms

(C5 and C53 in molecule 1 and C101 and C149 in mol-

ecule 2) of 6 are arranged in the cis-like position. Inter-

estingly, the rufﬂing of porphyrin rings in the trans-like

structure (5a) with an average C_mesodisplacement 0.40

Å is signiﬁcantly less than that observed in the cis-like

structures (5b and 6) with an average C_mesodisplacement

0.56 Å for 5b and 0.64 Å for 6. Intuition based on intra-

molecular steric considerations suggests that the trans

arrangement should be more favorable. However, the

3,5-di-tert-butylphenyl rings through which steric inter-

ference is possible are well separated in space with 11 Å

Fig. 4. Crystal structure of 5b shown from two different perspec-

tives: (a) orthogonal to the mean planes of the porphyrin rings;

(b) parallel to the mean planes. The side view (b) shows the dis-

tortion of the rings and the displacement of the planes of the

rings with respect to each other. The porphyrin rings are rufﬂed

but lie in approximately parallel planes displaced by ca. 2.98 Å

conformational arrangements in each of the structures are

provided in Table 3. All three structures bear resemblance

to the ﬁrst azo-bridged porphyrin structure [20].

In all three structures the porphyrin rings are signiﬁ-

cantly distorted from planarity. The meso carbon atoms

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Table 2. Crystal data for 5a, 5b and 6

Complex

Formula

5a

C_98.5H₁₀₂Cl₅N₁₀Ni₂

1725.61

5b

6

C₉₆H₁₀₂N₁₀Ni₂

1513.30

C₉₆H₁₀₀N₁₂Ni₂O₄

1603.30

M

Crystal system

Space group

a, Å

triclinic

–

P1

11.2769(5)

12.4229(9)

16.2387(9)

100.427(5)

92.641(4)

97.123(5)

2214.6(2)

1.294

16.0280(9)

17.4993(11)

18.7205(11)

114.691(2)

95.295(2)

99.510(2)

4628.2(5)

1.086

19.021(2)

22.330(2)

26.717(3)

111.974(10)

102.900(9)

96.223(9)

10023.6(19)

1.062

b, Å

c, Å

α, °

β, °

γ, °

V, Å³

D_c, g cm^-3

Z

1

2

4

Color

purple/green

prism

purple/green

prism

purple

Habit

prism

Dimensions, mm

µ(MoKα), mm^-1

T_min,max

0.68 × 0.32 × 0.14

0.629

0.10 × 0.09 × 0.04

0.454

0.14 × 0.12 × 0.03

0.426

0.769, 1.000

14643 (0.0451)

8572

0.824, 1.000

16316 (0.0591)

10541

0.518, 1.000

32722 (0.2113)

6924

N_ind(R_int)

N_obs- (I > 2σ(I))

N_var

534

979

919

R1^a, wR2^a

0.0720, 0.1659

0.02, 5

0.0621, 0.2031

0.08, 8

0.1345

A, B

0.08, 1

GoF

1.062

1.183

1.027

∆ρ_min,max, e^-Å^-3

~1.312, 1.001

~0.767, 1.083

~0.656, 0.947

^aReﬂections with [I > 2σ(I)] considered observed. R1 = Σ||F_o| - |F_c||/Σ|F_o| for F_o> 2σ(F_o) and wR2_(all)

=

{Σ[w(F_o²- F_c²)²]/Σ[w(F_c²)²]}^1/2where w = 1/[σ²(F_o²) + (AP)²+ BP], P = (F_o²+ 2F_c²)/3.

between planes of 3,5-di-tert-butylphenyl rings and are

thus unlikely to contribute signiﬁcantly to steric insta-

bility in the cis-like arrangement. Interestingly, the azo-

linked porphyrin in the trans-like structure (5a) has

porphyrin rings arranged such that their respective mean

C₂₀N₄Ni planes are exactly co-planar and separated by

approximately 2.35 Å. This was estimated by the per-

pendicular displacement of the Ni atom associated with

one ring with the mean plane of the other. In the case

of the cis-like structures there is a signiﬁcant twist from

co-planarity of the azo-bridged porphyrin rings with

a 17.9° dihedral angle between C₂₀N₄Ni planes in 5b

and 22.93° and 22.13° in the two molecules of the asym-

metric unit in 6.

conﬁguration in crystals is not conﬁrmation that it is the

most favored arrangement, the fact that it can and does

occur in crystals is strong evidence that it exists to some

extent in solution and that the production of a molecular

square is therefore possible.

The dihedral angles between the azo bridge

(C-N=N-C) and the mean planes of the porphyrin rings

are a measure of out-of-plane twist which, in turn, limits

the potential for electronic communication. The trans-

like structure 5a has an out-of-plane twist of 36.94°

which is virtually identical to that observed for the ﬁrst

azoporphyrin previously synthesized by the Arnold

group [20]. There are two such measurements in 5b

and 6 resulting from the lack of molecular symmetry.

In 5b, the dihedral angles are 30.65° and 42.31°. In 6,

the angles are 24° and 36° for one molecule and 23° and

38° for the other. It is possible that the lower out-of-

plane twist in 6 could lead to more efﬁcient electronic

communication.

The occurrence of both the trans-like and cis-like

forms of the molecules in different crystals clearly sug-

gests that both forms exist in the solution phase. The cis-

like arrangement is required for creation of molecular

squares and while the presence of the molecules in this

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B. BašIC et al.

Table 3. Geometric details for structures 5a, 5b and 6

Geometric parameter (Å or °)

Porphyrin ring associated with

Rufﬂe

5a

5b

6

Ni1

Ni(1)

0.439

Ni(2)

Ni(1)

Ni(2)

Ni(3)

Ni(4)

(Ni1′)

0.319

0.602

(C53)

-0.614

(C58)

0.627

(C63)

-0.720

(C68)

0.62°

0.013

0.674

(C5)

0.633

(C53)

-0.444

(C58)

0.512

(C63)

-0.687

(C68)

0.88°

0.026

0.640

(C101)

0.778

(C149)

-0.666

(C154)

0.693

a

C₂₀N₄Ni_plane- C5_meso

a

C₂₀N₄Ni_plane- C10_meso

-0.369

0.420

-0.478

-0.406

0.514

-0.575

-0.700

-0.523

(C6)

(C106)

a

C₂₀N₄Ni_plane- C15_meso

0.698

0.450

(C15)

(C111)

(C159)

-0.804

(C164)

0.79°

a

C₂₀N₄Ni_plane- C20_meso

-0.733

-0.614

(C20)

(C116)

b

∠C₂₀N₄Ni_plane- N₄Ni_plane

0.92°

0.055

0

0.77°

1.47°

1.36°

0.027

C₂₀N₄Ni(a)_plane- Ni(a) (⊥)^b

∠C₂₀N₄Ni(a)_plane- C₂₀N₄Ni(b)_plane

C₂₀N₄Ni(a)_plane- Ni(b) (⊥)^d

C₂₀N₄Ni(b)_plane- Ni(a) (⊥)^d

0.019

0.033

0.049

c

17.90°

22.93°

22.13°

2.351 2.794 (a = 1, b = 2)

2.351 3.158 (a = 2, b = 1)

3.169 (a = 1, b = 2)

3.122 (a = 2, b = 1)

24.65°

3.318 (a = 3, b = 4)

2.883 (a = 4, b = 3)

38.34°

e

∠C₂₀N₄Ni(a)_plane- CN=NC_plane

36.94°

42.31°

30.65

e

∠C₂₀N₄Ni(b)_plane- CN=NC_plane

36.15°

22.59°

^aThe perpendicular distance of the respective meso carbon atoms from the mean plane of the porphyrin is indicative of the rufﬂed

type [23] and degree of distortion from planarity. ^bThe dihedral angles between the mean plane of the porphyrin and the mean plane

of the coordination sphere combined with the perpendicular displacement of the Ni atom from that ring is indicative of the average

distortion of the porphyrin with respect to the square planar coordination environment. ^cThe dihedral angle between the mean planes

of the two porphyrins in each azo-bridged molecule is a measure of the deviation from coplanarity of the two porphyrin components

in each azo-bridged dimer. ^dThe perpendicular distance of the Ni atom in one porphyrin component to the mean plane of the other

porphyrin in each azo-bridged molecule. This is an estimate of the spatial displacement. ^eThe dihedral angles between the porphyrin

rings and the CN=NC atoms of the azo bridge are indicative of out-of-plane twist of the azo bridge connecting the two porphyrins.

In general, the smaller this angle the greater the potential for electronic communication across the azo bridge.

We have also tried to synthesize zinc and free-base

azo-linked dimers (Scheme 2). The Zn amino monomer

10 was made from 9 in very good yield but the copper-

promoted self-coupling reaction yielded a non-porphy-

rinic material. The free-base aminated monomer 11 was

created from 2 in good yield but the subsequent self-cou-

pling gave only very little of the dimer which had copper

in the porphyrin cores as well as some starting material

with copper inserted. This was not unexpected as the con-

ditions of the copper-catalyzed self-coupling reaction are

similar to those needed to metalate the porphyrin with

the copper. Interestingly, no free-base porphyrins were

isolated even though only 30 mol.% of copper(II) acetate

was used. Due to the paramagnetic nature of the copper

¹H NMR spectra were not obtained and the positive iden-

tiﬁcation of the compounds was supported by MS and

UV-vis analysis. These results led us to consider the pos-

sibility that the synthesis of the desired tetramers would

have to use a route that did not include linking of pre-

formed azo-linked dimers.

In order to obtain A there was the option of attempt-

ing to synthesize 5,10-diamino substituted porphyrin and

then using it to create the tetramer via the same reac-

tion conditions used for the synthesis of the azo-linked

dimer. The reason we did not go this way is we expected

the diaminated porphyrin to be unstable and we needed

a reliable route towards a 5,10-dinitro substituted por-

phyrin. Initially we tried to obtain it by modifying the

AgNO₂/I₂method used for 2. However, that proved fruit-

less as we only ever obtained 2. We then turned to a dif-

ferent method of nitration using nitric acid [24]. After

inserting nickel into 1 thus giving 12, 13 was obtained

reliably and in very good yield by using 30% HNO₃in

chloroform. The compound proved to be very soluble

and so the crude product (pure by ¹H NMR) was used to

make 14 (Scheme 3). As we predicted, 14 was difﬁcult to

handle as it was very soluble and not very stable. A clear

¹H NMR spectrum was obtained only when the sample

was cooled to -50 °C. The presence of amino groups was

veriﬁed by ATR infrared spectrum while the MS analy-

sis supported the conclusion of a successful synthesis.

Compound 14 was then used to attempt synthesis of A

via the route used for the synthesis of the azo-linked

It should be brieﬂy noted that compound 10 can also

be obtained quantitatively from 11 and vice versa by

metalation and acid-assisted demetalation, respectively.

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Ar

NH

N

(ii)

(i)

NO₂

Zn

NO₂

Zn

NH₂

Ar

HN

H

2

9

10

(iii)

Ar

NH

N

NH₂

Ar

HN

H

11

Scheme 2. Synthesis of Zn aminoporphyrin 10 and free-base aminoporphyrin 11: (i) Zn(OAc)₂, chloroform 60 °C; (ii) 10% Pd on

C, 10 eq. NaBH₄, DCM/MeOH; (iii) 10% Pd on C, 4 eq. NaBH₄, DCM/MeOH. Ar = 3,5-di-tert-butylphenyl

Ar

Ni

Ar

Ni

Ar

Ni

N

NH

N

(iii)

(i)

(ii)

NH₂

H

NO₂

Ar

H

Ar

HN

NH₂

H

NO₂

H

1

12

13

14

Scheme 3. Synthesis of Ni diaminoporphyrin 14: (i) Ni(acac)₂, toluene 120 °C; (ii) 30% HNO₃, CHCl₃; (iii) 10% Pd on C, 4 eq.

NaBH₄, DCM/MeOH. Ar = 3,5-di-tert-butylphenyl

dimer, namely Cu(OAc)₂catalyzed coupling. Unfortu-

nately, the attempts have not been successful and A has

remained elusive. The reaction involving 14 resulted in

loss of starting material in favor of very polar unidenti-

ﬁed non-porphyrinic substances. As yet, we are unsure

whether this is due to the instability of 14 or because A

may simply not be viable. We have explored a range of

approaches towards production of cyclic tetramer B with

interesting outcomes and expect to report these experi-

ments in the near future.

plates. For preparative column chromatography, Merck

1

silica gel (230–400 mesh) was used. The H NMR and

¹³C NMR spectra were measured on a Bruker Avance 400

MHz instrument. Samples were prepared in deuterated

chloroform (CDCl₃), unless stated otherwise. The chemi-

cal shifts are reported in ppm and referenced against the

1

residual chloroform (CHCl₃) peak at 7.26 ppm for H

NMR and CDCl₃at 77.16 ppm for ¹³C NMR. Coupling

constants are given in Hz. The UV-visible spectra were

recorded in dichloromethane (DCM) on a Varian Cary

50 instrument. Liquid Secondary Ion (LSI) and Electro-

spray Ionisation (ESI) mass spectra were recorded at the

Organic Mass Spectrometry Facility, University of Tas-

mania, Hobart. LSIMS data were obtained on a Kratos

ISQ double-focusing magnetic sector mass spectrometer

using a direct insertion probe and ﬁtted with an LSIMS

ion source, using 10KV cesium ions as the primary beam,

and m-nitrobenzyl alcohol as the liquid matrix. ESI mass

spectra were obtained on a Thermo Electron LTQ Orbit-

rap mass spectrometer. Samples were dissolved in dichlo-

romethane and then diluted 1/100 in methanol before

being infused into the mass spectrometer at a ﬂow rate

EXPERIMENTAL

General

All reported synthetic work was performed at the

Queensland University of Technology, Brisbane, Austra-

lia. All chemicals used were of analytical reagent grade

and were purchased from Sigma-Aldrich. Solvents were

evaporated under reduced pressure at 40 °C. Analytical

TLC was performed using Merck Silica Gel 60 F254

J. Porphyrins Phthalocyanines 2010; 14: 487–493

´

488

B. BašIC et al.

of 50 μL/min. A voltage of 4500 V was applied at the tip.

The IR spectra were collected using a Nicolet 870 Nexus

Fourier transform infrared (FTIR) system equipped with

an attenuated total internal reﬂectance (ATR) accessory

with a single-bounce diamond cell.

ﬁltered off and the acetone evaporated, leaving behind

a slightly orange oil. The oil was placed in the freezer.

After one day white crystals formed. They were ﬁltered

off and washed with ice-cold acetone. The mother liquor

was collected, the acetone evaporated and the oil stored

in the freezer again. This process was repeated until the

oil stopped yielding crystals.Yield 9.8% (32%). ¹H NMR

(400 MHz; DMSO-d₆): δ_H, ppm 10.52 (bs, 1H, NH), 5.77

(s, 2H, β-H), 4.76 (bs, 2H, OH), 4.33 (s, 4H, CH₂).

Tripyrrane[31].Deionizedwater(700mL)wasplaced

into a 1 dm³round bottomed ﬂask. The ﬂask was shielded

from light and the water was stirred at 5 °C while being

bubbled with argon for 30 min. 2,5-bis(hydroxymethyl)

pyrrole (5 g, 0.039 mol) was added followed by pyrrole

(26.9 mL, 0.39 mol) 10 min later. After 30 min the bub-

bling with argon was stopped and concentrated hydro-

chloric acid (0.5 mL) was added. The solution became

a white emulsion that was stirred for a further 30 min. It

was then neutralized with sodium bicarbonate (15 mL).

The emulsion was stirred for a further 5 min. The prod-

uct was extracted in DCM (3 × 150 mL). The solvent

was removed and the oil was puriﬁed by column chroma-

tography using DCM/TEA (100:1) as eluent. Collection

of the desired fraction was monitored by TLC. The sol-

vent was removed, leaving a yellow-white solid that was

dried under vacuum and stored under argon in the freezer.

Yield: 2.93 g (33%). ¹H NMR (400 MHz; DMSO-d₆): δ_H,

ppm 7.91 (bs, 2H, NH), 7.64 (bs, 1H, NH), 6.66 (m, 2H,

1,14-H), 6.14 (m, 2H, 2,13-H), 5.98 (bs, 2H, 3,12-H),

5.92 (m, 2H, 7,8-H), 3.90 (s, 4H, 5,5′,10,10′-H).

Reﬂection data for 5b were collected at 150(2) K

using an APEX II-FR591 diffractometer employing

graphite-monochromated Mo-Kα radiation generated

from a rotating anode (0.71073 Å). Data integration and

reduction were undertaken with SAINT and XPREP

[25]. A multi-scan empirical absorption correction was

applied using SADABS [26]. Reﬂection data for 5a and

6 were collected under the software control of CrysAlis

CCD [27] at 173(2) K on an Oxford Diffraction Gemini

Ultra diffractometer using Mo-Kα radiation generated

from a sealed tube. Data reduction was performed using

CrysAlis RED [27]. Multi-scan empirical absorption cor-

rections were applied using spherical harmonics, imple-

mented in the SCALE3 ABSPACK scaling algorithm,

within CrysAlis RED [27]. Subsequent computations

for all structures were carried out using the WinGX-32

graphical user interface [28].

The structures were solved by direct methods using

SIR97 [29] and then reﬁned with SHELXL-97 [30].

Ordered non-hydrogen atoms were reﬁned anisotropi-

cally for 5b and 6. Hydrogen atoms attached to carbon

atoms were included in idealized positions and reﬁned

using a riding model. All three structures are triclinic

_

with symmetry P1. Interestingly each one has a different

Z value. In 5a the asymmetric unit comprises half of the

azo-bridged dimer which has crystallographic inversion

symmetry (Z = 1). The asymmetric unit in 5b comprises

one complete azo-bridged dimer (Z = 2) and in 6 the

azo-bridged dimer comprises two full crystallographi-

cally distinct azo-bridged dimers (Z = 4). Crystal data

and reﬁnement details (presented left to right in order of

decreasing symmetry) are reported in Table 2. Depictions

of the molecular structures are provided in Figs 3–5.

5,10-bis(3,5-di-tert-butylphenyl)porphyrin (1) [21,

32]. To a 1 dm³round-bottomed ﬂask DCM (300 mL)

was added which was then bubbled with argon for

30 min. Tripyrrane (270 mg, 1.20 × 10^-3mol), followed by

3,5-di-tert-butylbenzaldehyde (524 mg, 2.4 × 10^-3mol),

pyrrole (83 μL, 1.2 × 10^-3mol) and TFA (55 μL,

7.2 × 10^-4mol) were added. The solution was stirred at

room temperature for 3.5 h. DDQ (708 mg, 3.13 × 10^-3

mol) was added and stirring continued for a further

30 min. The solution was neutralized with TEA (1 mL)

and stirred for an additional 5 min. The solvent was evap-

orated, leaving a dark purple residue that was puriﬁed by

column chromatography using DCM/hexane (1:2) as elu-

ent. A single dark-red fraction was obtained. The solvent

was evaporated once more, leaving a purple residue. It

was recrystallized from DCM/methanol. The recrystal-

lized product was dark-purple shiny needle-like crystals.

Yield: 66 mg (8%). ¹H NMR (400 MHz; CDCl₃): δ_H, ppm

10.22 (s, 2H, 15,20-H), 9.46 (s, 2H, 17,18-H), 9.35 (d, J

4.9 Hz, 2H, 2,13-H), 9.08 (d, J = 4.9 Hz, 2H, 3,12-H),

8.99 (s, 2H, 7,8-H), 8.10 (d, J = 2.0 Hz, 4H, o-H_aryl), 7.82

Synthesis

2,5-bis(hydroxymethyl)pyrrole [31]. Potassium carbo-

nate (62 g, 0.485 mol) was dissolved in deionized water

(200 mL) in a 1 dm³round-bottomed ﬂask. The solu-

tion was stirred in a cold water bath at 5 °C while being

bubbled with argon for 30 min. Formalin (40%, 105

mL, 0.485 mol) and freshly distilled pyrrole (17 mL,

0.240 mol) were added. The resulting solution was bub-

bled with argon for a further 15 min and then the ﬂask was

sealed and shielded from light. The mixture was stirred

for 7 days at 5 °C. The colorless solution was evapo-

rated, leaving a white slurry. To this acetone (300 mL)

was added. The potassium carbonate precipitated out

and was ﬁltered off and washed with acetone (3 × 100

mL). To the collected solution anhydrous sodium sulfate

(300 g) was added. The solution was shielded from light,

sealed, and left in the fridge for 2 h. Sodium sulfate was

t

(t, J = 2.0 Hz, 2H, p-H_aryl), 1.56 (s, 36H, Bu-H), -3.27

(bs, 2H, inner NH).

10,15-bis(3,5-di-tert-butylphenyl)-5-nitroporphy-

rin (2). Compound 1 (357 mg, 5.20 × 10^-4mol) was

dissolved in a DCM/acetonitrile solution (31.5 mL/31.5

mL) and stirred under argon for 10 min. The ﬂask was

J. Porphyrins Phthalocyanines 2010; 14: 488–493

azO-lInkeD COrner POrPhyrIn SyStemS

489

shielded from light. Iodine (99 mg, 0.75 eq., 3.90 × 10^-4

mol) dissolved in DCM (12.5 mL) was added and the

solution was stirred for 30 min. Silver nitrite (120 mg,

1.5 eq., 7.80 × 10^-4mol) dissolved in acetonitrile (12.5

mL) was added. The starting material was consumed

after 1.5 h. The solvents were evaporated, leaving a dark-

purple solid which was redissolved in minimum amount

of DCM and ﬁltered through a cotton wool plug. The sol-

vent was evaporated and the product recrystallized from

DCM/methanol. The product was a grey-purple powder.

Yield: 355 mg (93%), mp > 310 °C. ¹H NMR (400 MHz;

CDCl₃): δ_H, ppm 10.22 (s, 1H, 20-H), 9.47 (d, J = 5.3

Hz, 1H, 3-H), 9.41 (d, J = 5.3 Hz, 1H, 2-H), 9.35 (d,

J = 5.2 Hz, 1H, 7-H), 9.27 (d, J = 5.0 Hz, 1H, 18-H),

9.02 (d, J = 5.0 Hz, 1H, 17-H), 9.00 (d, J = 5.2 Hz, 1H,

8-H), 8.91 (d, J = 5.3 Hz, 1H, 13-H), 8.84 (d, J = 5.3 Hz,

1H, 12-H), 8.05 (d, J = 1.8 Hz, 2H, o-H_aryl), 8.02 (d, J

= 1.8 Hz, 2H, o-H_aryl), 7.83 (t, J = 1.8 Hz, 2H, p-H_aryl),

1.54 (s, 18H, ^tBu-H), 1.53 (s, 18H, ^tBu-H), -2.71 (bs, 2H,

inner NH). ¹³C NMR (100 MHz; CDCl₃): δ_C, ppm 149.1,

148.9, 140.6, 140.0, 134.1, 133.7, 132.8, 132.2, 132.0,

131.0, 129.8, 129.6, 128.5, 127.5, 127.3, 125.9, 124.9,

121.7, 121.6, 107.2, 35.0, 31.7. UV-vis (DCM): λ_max, nm

(ε, 10³M^-1.cm^-1) 418 (149), 514 (9.16), 560 (7.80), 580

(6.45), 643 (4.31). MS (ESI): m/z 754.4098 (calcd. for

C₄₈H₅₃N₅NaO₂[M + Na]⁺754.4097). IR (ATR): ν, cm^-1

1500s (NO_{2 asym}), 1314s (NO_{2 sym}).

(150 mL/150 mL) that was bubbled with argon for

10 min. Argon atmosphere was maintained and then

10% palladium on carbon (255 mg) was added, followed

by stepwise addition of sodium borohydride (454 mg,

25 eq., 1.21 × 10^-3mol). After 1.5 h the starting material

was consumed. The solvent was evaporated and the resi-

due ﬁltered through a cotton wool plug after dissolving

in DCM. The DCM solution was washed with water. The

product was puriﬁed by column chromatography using

DCM/hexane (1:1) as eluent. A single red fraction was

obtained. The solvent was evaporated and the product

was red/purple. Yield: 349 mg (95%). It was recrystal-

lized from DCM/pentane. The product was a purple pow-

der that is very soluble. Yield: 29 mg (8%), mp > 310 °C.

¹H NMR (400 MHz; CDCl₃): δ_H, ppm 9.36 s, 1H, 20-H),

9.09 (d, J = 4.9 Hz, 1H, 3-H), 9.01 (d, J = 4.9 Hz, 1H,

7-H), 8.88 (d, J = 4.9 Hz, 1H, 2-H), 8.85 (d, J = 4.9 Hz,

1H, 18-H), 8.61 (d, J = 4.9 Hz, 1H, 17-H), 8.59 (d, J =

4.9 Hz, 1H, 8-H), 8.57 (d, J = 5.1 Hz, 1H, 13-H), 8.51 (d,

J = 5.1 Hz, 1H, 12-H), 7.78 (t, J = 2.0 Hz, 4H, o-H_aryl),

7.67 (m, J = 2.0 Hz, 2H, p-H_aryl), 5.81 (bs, 2H, NH₂), 1.45

t

(s, 36H, Bu-H). ¹³C NMR (100 MHz; CDCl₃): δ_C, ppm

149.0, 148.9, 145.0, 144.9, 141.5, 141.4, 141.0, 140.9,

140.8, 139.9, 133.2, 133.0, 132.7, 131.7, 131.1, 130.0,

129.2, 128.3, 128.2, 128.0, 124.1, 123.8, 120.8, 120.7,

120.5, 116.0, 104.2, 35.0, 31.5. UV-vis (DCM): λ_max, nm

(ε, 10³M^-1.cm^-1) 422 (160), 537 (9.79), 592 (9.96). MS

(ESI): m/z 780.3542 (calcd. for C₄₈H₅₃N₅NaNi[M + Na]⁺

780.3552). IR (ATR): ν, cm^-13392m, 1255m (NH₂).

1,2-bis{[10,15-bis(3,5-di-tert-butylphenyl)porphy-

rinato]nickel(II)-5-yl}diazene (5). Porphyrin 4 (349 mg,

4.60 × 10^-4mol) was dissolved in 15 mL of toluene.

To this copper(II) acetate (11 mg, 5.52 × 10^-5mol, 12

mol.%) and pyridine (150 μL, 1.84 × 10^-3, 4 eq) were

added. The mixture was stirred at 80 °C for 2 h. The solu-

tion was washed with water and the product extracted

into DCM. The solvent was evaporated and the product

recrystallized from DCM/methanol. The product was an

olive green powder. Yield: 230 mg (66%), mp > 310 °C.

¹H NMR (400 MHz; CDCl₃): δ_H, ppm 10.15 (d, J = 4.8

Hz, 2H, 3,3′-H), 10.08 (d, J = 5.3 Hz, 2H, 7,7′-H), 9.71

(s, 2H, 20,20′-H), 9.27 (d, J = 4.8 Hz, 2H, 2,2′-H), 9.01

(d, J = 4.8 Hz, 2H, 18,18′-H), 8.99 (d, J = 5.3 Hz, 2H,

8,8′-H), 8.83 (d, J = 4.8 Hz, 2H, 17,17′-H), 8.73 (d, J =

5.3 Hz, 2H, 12,12′-H), 8.71 (d, J = 5.3 Hz, 2H, 13,13′-H),

7.90 (d, J = 1.8 Hz, 4H, o-H_aryl), 7.87 (d, J = 1.8 Hz,

4H, o-H_aryl), 7.74 (m, J = 1.8 Hz, 4H, p-H_aryl), 1.50 (s,

36H, ^tBu-H), 1.48 (s, 36H, ^tBu-H). ¹³C NMR (100 MHz;

CDCl₃): δ_C, ppm 149.2, 149.0, 143.3, 143.2, 142.6, 142.5,

141.8, 141.5, 140.5, 140.4, 139.5, 139.4, 134.6, 134.2,

133.6, 133.5, 133.2, 132.9, 132.8, 132.2, 131.7, 128.6,

128.5, 128.4, 122.5, 122.4, 121.3, 106.0, 35.0, 31.7. UV-

vis (DCM): λ_max, nm (ε, 10³M^-1.cm^-1) 402 (78.2), 487

(129), 738 (41.5). MS (LSI): m/z 1510.7024 (calcd. for

C₉₆H₁₀₂N₁₀Ni₂[M]⁺1510.6996). Crystals of 5 for X-ray

data collection were grown by slow diffusion of metha-

nol into a solution of the azo-linked porphyrin in DCM.

[10,15-bis(3,5-di-tert-butylphenyl)-5-nitroporphy-

rinato]nickel(II) (3). Porphyrin 2 (354 mg, 4.84 × 10^-4

mol) was dissolved in 15 mL of toluene and stirred. To

this, Ni(acac)₂(354 mg, 1.38 × 10^-3mol) was added.

The mixture was reﬂuxed for 2 h, after which the start-

ing material was consumed. The product was puriﬁed by

column chromatography using DCM/hexane (1:1) as elu-

ent. A single red fraction was collected. The solvent was

evaporated to give a red residue (yield: 382 mg (100%))

which was recrystallized from DCM/pentane to give a

pale red powder. Yield: 218 mg (57%), mp > 310 °C. ¹H

NMR (400 MHz; CDCl₃): δ_H, ppm 9.84 (s, 1H, 20-H),

9.37 (d, J = 5.1 Hz, 1H, 3-H), 9.24 (d, J = 5.1 Hz, 1H,

7-H), 9.22 (d, J = 5.1 Hz, 1H, 2-H), 9.09 (d, J = 5.1 Hz,

1H, 18-H), 8.92 (d, J = 5.1 Hz, 1H, 8-H), 8.91 (d, J =

5.1 Hz, 1H, 17-H), 8.81 (d, J = 5.1 Hz, 1H, 13-H), 8.78

(d, J = 5.1 Hz, 1H, 12-H), 7.85 (t, J = 2 Hz, 2H, o-H_aryl),

7.83 (t, J = 2 Hz, 2H, o-H_aryl), 7.75 (m, J = 1.9 Hz, 2H,

t

p-H_aryl), 1.48 (s, 18H, Bu-H), 1.47 (s, 18H, Bu-H). ¹³C

NMR (100 MHz; CDCl₃): δ_C, ppm 149.1, 144.0, 143.8,

143.2, 143.0, 142.9, 142.7, 139.2, 139.1, 137.8, 137.5,

134.9, 134.4, 134.0, 133.5, 132.8, 132.3, 129.5, 128.7,

128.6, 126.3, 123.6, 123.0, 121.5, 106.5, 35.0, 31.7. UV-

vis (DCM): λ_max, nm (ε, 10³M^-1.cm^-1) 411 (129), 528

(7.03), 565 (4.53). MS (ESI): m/z 810.3293, (calcd. for

C₄₈H₅₁N₅NiNaO₂[M + Na]⁺810.3294). IR (ATR): ν, cm^-1

1498s (NO_{2 asym}), 1314s (NO_{2 sym}).

[5-amino-10,15-bis(3,5-di-tert-butylphenyl)por-

phyrinato]nickel(II) (4). Compound 3 (382 mg, 4.84

× 10^-4mol) was dissolved in a DCM/methanol solution

J. Porphyrins Phthalocyanines 2010; 14: 489–493

´

490

B. BašIC et al.

Crystals of 5a and 5b came from the same synthesis

experiment. Structure 5a. The crystals, while not par-

ticularly small, diffracted relatively weakly. A reasonable

dataset was obtained by long-frame collection time. The

removal from the mother liquor prior to cooling for data

collection. The best dataset obtainable was characterized

by very weak diffraction to about 1.1 Å and possible non-

merohedraltwinning. Despitethisitwaspossibletoobtain

a solution for the structure that shows very reasonable

atom positions and molecular structure. The asymmetric

unit comprises two full molecules. There are solvent-

accessible voids but the low data quality and resulting

noisy difference map made it impossible to identify any

particular solvents. Reﬁnement was problematic and the

ﬁnal model has been reﬁned isotropically for all atoms

except Ni. Geometric restraints were applied to tert-butyl

groups but proper convergence could not be achieved.

The structure is presented herein despite the aforemen-

tioned shortcomings in the data because the molecular

structure is very reasonable and indicates clearly both the

presence and relative orientation of the meso-positioned

nitro groups as well as the relative orientations of the

azo-bridged porphyrin rings.

ˉ

compound has 1 crystallographic symmetry and as such

the asymmetric unit comprises half of one molecule. Con-

tained within the asymmetric unit are dichloromethane

molecules at two positions: one (comprising atoms C49,

Cl1-2) modelled with occupancy 0.75 and the other (com-

ˉ

prising atoms C50, Cl3) disordered around a 1 site with

occupancy for each position modelled at 0.5. Structure

5b. The crystals were very small and relatively weakly

diffracting (limited data with resolution better than 1 Å).

The asymmetric unit comprises one complete molecule.

The tert-butyl groups associated with C27 and C79 were

modelled with disordered components 0.55:0.45 and

0.65:0.35 for positions A and B, respectively. There are

solvent-accessible voids in the structure but there was no

evidence of occupation of these voids by solvent.

1,2-bis{[15,20-bis(3,5-di-tert-butylphenyl)-10-

nitroporphyrinato]nickel(II)-5-yl}diazene (6). Dimer

5 (29 mg, 1.91 × 10^-5mol) was dissolved in DCM/

acetonitrile solution (2.3 mL/0.7 mL) and stirred under

argon for 10 min. The ﬂask was shielded from light.

Iodine (7.3 mg, 1.5 eq., 2.86 × 10^-5mol) dissolved in

DCM (0.8 mL) was added and the solution stirred for 30

min. Silver nitrite (8.8 mg, 3 eq., 5.73 × 10^-4mol) dis-

solved in acetonitrile (0.8 mL) was added. The starting

material was consumed after 1 h. The solvents were evap-

orated. The dark-red solid was redissolved in minimum

amount of DCM and ﬁltered through a cotton wool plug.

The compound was puriﬁed by two chromatography col-

umns using DCM/hexane (1:1) as eluent. The product

was a red/brown sticky powder. Yield: 15.2 mg (49%).

It was recrystallized from DCM/methanol. Yield: 5.6 mg

1-{[15,20-bis(3,5-di-tert-butylphenyl)-10-nitro-

porphyrinato]nickel(II)-5-yl}-2-{[10,15-bis(3,5-di-tert-

butylphenyl)porphyrinato]nickel(II)-5-yl}diazene (7).

Dimer 5 (100 mg, 6.60 × 10^-5), was dissolved in DCM/

acetonitrile solution (12 mL/4 mL) and stirred under

argon for 10 min. The ﬂask was shielded from light.

Iodine (21 mg, 1.25 eq., 8.27 × 10^-5mol) dissolved in

DCM (4 mL) was added and the solution stirred for

30 min. Silver nitrite (25 mg, 2.5 eq., 1.62 × 10^-4mol)

dissolved in acetonitrile (4 mL) was added. The starting

material was consumed after 1 h. The solvents were evap-

orated. The dark-red solid was redissolved in minimum

amount of DCM and ﬁltered through a cotton wool plug.

The compound was puriﬁed by two chromatography col-

umns using DCM/hexane (1:2) as eluent. Two products

were isolated. The ﬁrst was compound 7. The second

was compound 6. Both were red/brown sticky powders.

They were recrystallized from DCM/methanol. Yield: 11

mg (10%) and 8 mg (7%) respectively. Data for 6 can be

1

(18%), mp > 310 °C. H NMR (400 MHz; CDCl₃): δ_H,

ppm 9.98 (d, J = 4.8 Hz, 2H, 7,7′-H), 9.88 (d, J = 4.8 Hz,

2H, 3,3′-H), 9.40 (d, J = 4.8 Hz, 2H, 8,8′-H), 9.11 (d, J =

4.8 Hz, 2H, 12,12′-H), 8.95 (d, J = 4.8 Hz, 2H, 2,2′-H),

8.79 (d, J = 4.8 Hz, 2H, 13,13′-H), 8.67 (d, J = 4.5 Hz,

2H, 17,17′-H), 8.65 (d, J = 4.5 Hz, 2H, 18,18′-H), 7.84 (d,

J = 1.8 Hz, 4H, o-H_aryl), 7.80 (d, J = 1.8 Hz, 4H, o-H_aryl),

7.75 (t, J = 1.8 Hz, 4H, p-H_aryl), 1.48 (s, 72H, ^tBu-H). ¹³C

NMR (100 MHz; CDCl₃): δ_C, ppm 149.2, 149.1, 143.3,

143.2, 142.6, 142.5, 141.8, 141.5, 140.5, 140.4, 139.5,

139.4, 134.6, 134.2, 133.5, 133.3, 132.9, 132.8, 132.3,

131.7, 128.6, 128.5, 128.4, 122.5, 122.4, 121.3, 106.0,

35.0, 31.7. UV-vis (DCM): λ_max, nm (ε, 10³M^-1.cm^-1) 403

(54.9), 498 (74.6), 716 (26.0). MS (LSI): m/z 1600.6674

(calcd. for C₉₆H₁₀₀N₁₂Ni₂O₄[M]⁺1600.6697). IR (ATR):

ν, cm^-11479s (NO_{2 asym}), 1370s (NO_{2 sym}). Crystals for

X-ray data collection were grown by slow diffusion of

methanol into a solution of the azo-linked porphyrin in

DCM. Structure 6. The crystals of this structure were

very small and poorly formed. In almost all cases the

crystals were clearly twinned and unusable for data col-

lection. The crystals were also structurally unstable after

1

found above. Data for 7 follow. mp > 310 °C. H NMR

(400 MHz; CDCl₃): δ_H, ppm 10.11 (d, J = 4.8 Hz, 1H,

3′-H), 10.06 (d, J = 4.8 Hz, 1H, 7′-H), 10.04 (d, J = 4.8

Hz, 1H, 18′-H), 9.95 (d, J = 4.8 Hz, 1H, 7-H), 9.72 (s, 1H,

20′-H), 9.43 (d, J = 4.8 Hz, 1H, 8′-H), 9.28 (d, J = 4.8 Hz,

1H, 2′-H), 9.15 (d, J = 4.9 Hz, 1H, 3-H), 9.01 (d, J = 4.8

Hz, 1H, 17′-H), 9.00 (d, J = 5.0 Hz, 1H, 12-H), 8.96 (d,

J = 4.8 Hz, 1H, 8-H), 8.83 (d, J = 5.0 Hz, 1H, 13-H), 8.82

(d, J = 4.9 Hz, 1H, 2-H), 8.73 (d, J = 4.8 Hz, 1H, 17-H),

8.71 (d, J = 4.8 Hz, 1H, 18-H), 8.70 (d, J = 4.8 Hz, 1H,

12′-H), 8.67 (d, J = 4.8 Hz, 1H, 13′-H), 7.90 (d, J = 1.8

Hz, 2H, o-H_aryl), 7.88 (t, J = 1.8 Hz, 4H, o-H_aryl), 7.83 (d,

J = 1.8 Hz, 2H, o-H_aryl), 7.76 (m, J = 1.8 Hz, 4H, p-H_aryl),

t

1.50 (s, 72H, Bu-H). UV-vis (DCM): λ_max, nm (ε, 10³

M^-1.cm^-1) 410 (77.6), 497 (109), 731 (39.9). MS (LSI):

m/z 1558.0 (calcd. for C₉₆H₁₀N₁₁Ni₂O₂[M]⁺1555.6847).

IR (ATR): ν, cm^-11480s (NO_{2 asym}), 1369s (NO_{2 sym}).

1,2-bis{[10-bromo-15,20-bis(3,5-di-tert-butylphe-

nyl)porphyrinato]nickel(II)-5-yl}diazene (8). Dimer 5

J. Porphyrins Phthalocyanines 2010; 14: 490–493

azO-lInkeD COrner POrPhyrIn SyStemS

491

(5 mg, 3.30 × 10^-6mol) was dissolved in 1.5 mL of chlo-

roform. The solution was stirred and NBS (2 mg, 2.5 eq,

8.25 × 10^-6) was added, followed by pyridine (20 μL,

2.49 × 10^-4mol). After 30 min the starting material was

consumed and the reaction was quenched with acetone.

The solvent was evaporated and the residue washed

with methanol through a cotton wool plug. The product

was extracted from the plug in DCM. The solvent was

removed and the product dried. It was a dark red/brown

Argon atmosphere was maintained and then 10% palla-

dium on carbon (30 mg) was added, followed by step-

wise addition of sodium borohydride (21 mg, 10 eq.,

5.65 × 10^-4mol). After 10 min the starting material was

consumed. The solvent was evaporated and the residue

ﬁltered through a cotton wool plug after dissolving in

DCM. The DCM solution was washed with water and

the product extracted. The solvent was removed and the

product was puriﬁed by column chromatography using

DCM/pyridine (100:1) as eluent. A single green/blue

fraction was isolated. The solvent was evaporated and

the product was green/purple.Yield: 41 mg (85%). It was

recrystallized from chloroform/pentane. The product was

1

powder residue. Yield: 2.3 mg (39%), mp > 310 °C. H

NMR (400 MHz; CDCl₃): δ_H, ppm 9.97 (d, J = 5.0 Hz,

2H, 7,7′-H), 9.91 (d, J = 4.9 Hz, 2H, 3,3′-H), 9.60 (d, J =

5.0 Hz, 2H, 8,8′-H), 9.35 (d, J = 5.0 Hz, 2H, 12,12′-H),

8.90 (d, J = 4.9 Hz, 2H, 2,2′-H), 8.71 (d, J = 5.0 Hz,

2H, 13,13′-H), 8.63 (d, J = 4.4 Hz, 2H, 17,17′-H), 8.61

(d, J = 4.4 Hz, 2H, 18,18′-H), 7.84 (d, J = 2.1 Hz, 4H,

o-H_aryl), 7.80 (d, J = 2.1 Hz, 4H, o-H_aryl), 7.73 (t, J = 2.1

1

a green powder. Yield: 22 mg (46%), mp > 310 °C. H

NMR (400 MHz, CDCl₃with pyridine-d₅): δ_H, ppm 9.61

(s, 1H, 20-H), 9.23 (d, J = 4.4 Hz, 1H, 3-H), 9.14 (d, J =

4.4 Hz, 1H, 7-H), 9.05 (d, J = 4.4 Hz, 1H, 2-H), 9.01 (d, J

= 4.8 Hz, 1H, 18-H), 8.70 (d, J = 4.8 Hz, 1H, 17-H), 8.67

(d, J = 4.4 Hz, 1H, 8-H), 8.66 (d, J = 4.8 Hz, 1H, 12-H),

8.61 (d, J = 4.8 Hz, 1H, 13-H), 7.98 (d, J = 2.0 Hz, 2H,

o-H_aryl), 7.96 (d, J = 2.0 Hz, 2H, o-H_aryl), 7.73 (t, J = 2.0

Hz, 1H, p-H_aryl), 7.71 (t, J = 2.0 Hz, 1H, p-H_aryl), 6.35 (bs,

t

Hz, 4H, p-H_aryl), 1.48 (s, 72H, Bu-H). ¹³C NMR (100

MHz; CDCl₃): δ_C, ppm 149.3, 149.2, 144.1, 142.8, 142.5,

141.9, 141.1, 140.5, 140.4, 139.0, 138.8, 135.1, 135.0,

134.3, 133.9, 133.5, 133.4, 133.2, 132.7, 132.6, 130.9,

128.7, 128.5, 128.3, 123.5, 122.5, 121.2, 103.8, 35.0,

31.7. UV-vis (DCM): λ_max, nm (intensity ratio) 413 (2.7),

495 (3.4), 761 (1.0). MS (LSI): m/z 1666.5135 (calcd. for

C₉₆H₁₀₀Br₂N₁₀Ni₂[M]⁺1666.5206).

t

2H, NH₂), 1.52 (s, 18H, Bu-H), 1.51 (s, 18H, Bu-H).

¹³C NMR (100 MHz; CDCl₃with pyridine-d₅): δ_C, ppm

153.0, 149.0, 148.8, 148.4, 148.2, 148.1, 147.4, 142.6,

142.4, 140.0, 139.7, 132.6, 132.0, 131.6, 131.0, 130.9,

129.8, 129.6, 129.4, 128.8, 123.1, 122.4, 122.3, 120.3,

120.1, 116.6, 105.1, 35.0, 31.6. UV-vis (DCM): λ_max, nm

(ε, 10³M^-1.cm^-1) 425 (473), 556 (7.40), 5.95 (10.2), 623

(17.4). MS (ESI): m/z 764.3681 (calcd. for C₄₈H₅₄N₅Zn

[M + H]⁺764.3671). IR (ATR): ν, cm^-13302b, 1236m

(NH₂). The reaction was repeated successfully on a

100 mg scale.

[10,15-bis(3,5-di-tert-butylphenyl)-5-nitroporphy-

rinato]zinc(II) (9). Porphyrin 2 (50 mg, 6.83 × 10^-5mol)

was dissolved in 5 mL of chloroform and stirred. To this

Zn(OAc)₂(50 mg, 2.28 × 10^-4) in 1 mL of methanol was

added. The mixture was reﬂuxed at 60 °C. After 20 min

the starting material was consumed. The solution was

washed with water and the product was extracted in DCM.

The solvent was evaporated and the product was dark

brown/green. Yield: 54 mg (100%). It was recrystallized

from chloroform/pentane. The residue was a dark brown/

green sticky powder. Yield: 50 mg (91%), mp > 310 °C.

¹H NMR (400 MHz; CDCl₃with pyridine-d₅): δ_H, ppm

10.19 (s, 1H, 20-H), 9.41 (d, J = 4.8 Hz, 1H, 3-H), 9.39

(d, J = 4.8 Hz, 1H, 2-H), 9.36 (d, J = 4.8 Hz, 1H, 7-H),

9.34 (d, J = 4.8 Hz, 1H, 18-H), 9.14 (d, J = 4.8 Hz, 1H,

17-H), 9.12 (d, J = 4.8 Hz, 1H, 8-H), 9.06 (d, J = 4.6 Hz,

1H, 12-H), 9.01 (d, J = 4.6 Hz, 1H, 13-H), 8.09 (d, J = 2.0

Hz, 2H, o-H_aryl), 8.07 (d, J = 2.0 Hz, 2H, o-H_aryl), 7.86 (t,

J = 2.0 Hz, 2H, p-H_aryl), 1.57 (s, 18H, ^tBu-H), 1.56 (s, 18H,

^tBu-H). ¹³C NMR (100 MHz; CDCl₃with pyridine-d₅):

δ_C, ppm 151.3, 150.7, 150.2, 150.1, 150.0, 148.5, 145.5,

145.4, 141.6, 141.4, 134.4, 133.7, 133.6, 132.8, 132.0,

131.2, 129.7, 129.6, 129.1, 128.0, 126.4, 125.3, 121.0,

106.9, 35.0, 31.7. UV-vis (DCM): λ_max, nm (ε, 10³M^-1.

cm^-1) 417 (378), 546 (27.8), 586 (19.2). MS (LSI): m/z

794.4847 (calcd. for C₄₈H₅₂N₅O₂Zn [M + H]⁺794.3407).

IR (ATR): ν, cm^-11510s (NO_{2 asym}), 1333s (NO_{2 sym}). The

reaction was repeated successfully on a 170 mg scale.

[5-amino-10,15-bis(3,5-di-tert-butylphenyl)por-

phyrinato]zinc(II) (10). Porphyrin 9 (45 mg, 5.65 ×

10^-5mol) was dissolved in a DCM/methanol solution

(18 mL/18 mL) that was bubbled with argon for 10 min.

Attempted synthesis of 1,2-bis{[10,15-bis(3,5-di-

tert-butylphenyl)porphyrinato]zinc(II)-5-yl}diazene.

Porphyrin 10 (88 mg, 1.15 × 10^-4mol) was dissolved in

7 mL of toluene. To this copper(II) acetate (3 mg, 1.37 ×

10^-5mol, 12 mol.%) and pyridine (37 μL, 4 eq., 4.59 ×

10^-3mol) were added. The mixture was stirred at 80 °C

and the starting material was consumed after 3 h. The

dimer was not formed. The main products were non-por-

phyrinic compounds, as shown by ¹H NMR spectroscopy.

The residue was puriﬁed by column chromatography.

Only one porphyrin was isolated, which was found by

NMR spectroscopy to be the unsubstituted Zn corner

porphyrin monomer.

5-amino-10,15-bis(3,5-di-tert-butylphenyl)por-

phyrin (11). Porphyrin 2 (25 mg, 3.41 × 10^-5mol) was dis-

solved in a DCM/methanol solution (10 mL/10 mL) that

was bubbled with argon for 10 min. Argon atmosphere

was maintained and then 10% palladium on carbon

(18 mg) was added followed by a stepwise addition of

sodium borohydride (5 mg, 4 eq., 1.36 × 10^-4mol). After

10 min the starting material was consumed. The solvent

was evaporated and the residue ﬁltered through a cotton

wool plug after dissolving in DCM. The DCM solution

was washed with water and the product extracted. The

J. Porphyrins Phthalocyanines 2010; 14: 491–493

´

492

B. BašIC et al.

solvent was removed and the product was puriﬁed by col-

umn chromatography using DCM/TEA (100:1) as elu-

ent. A single violet fraction was isolated. The solvent was

evaporated and the product was green/purple. Yield: 22

mg (91%). It was recrystallized from chloroform/pentane

To this 30% HNO₃(3 mL) was added. The starting mate-

rial was consumed within 20 min. The reaction mixture

was diluted with water (20 mL). The organic layer was

separated and washed with saturated sodium bicarbonate

solution (20 mL) and water (20 mL) before being dried

over anhydrous potassium carbonate. The organic layer

was decanted and the solvent removed. The compound

was puriﬁed by column chromatography using DCM/

hexane (1:1) as eluent. A single red powder compound

was isolated.Yield: 26 mg (94%), mp > 310 °C. ¹H NMR

(400 MHz, CDCl₃): δ_H, ppm 9.32 (s, 2H, 7,8-H), 9.15 (d,

J = 5.0 Hz, 2H, 3,12-H), 8.89 (d, J = 5.0 Hz, 2H, 2,13-H),

8.76 (s, 2H, 17,18-H), 7.78 (d, J = 1.8 Hz, 4H, o-H_aryl),

7.76 (t, J = 1.8 Hz, 2H, p-H_aryl), 1.47 (s, 36H, ^tBu-H). ¹³C

NMR (100 MHz, CDCl₃): δ_C, ppm 149.0, 144.5, 143.4,

138.3, 138.2, 137.4, 135.9, 134.2, 131.3, 129.3, 129.1,

128.6, 125.5, 122.0, 35.0, 31.3. UV-vis (DCM): λ_max, nm

(ε, 10³M^-1.cm^-1) 426 (96.0), 536 (11.6). MS (LSI): m/z

833.3322 (calcd. for C₄₈H₅₁N₆NiO₄[M + H]⁺833.3325).

IR (ATR): ν, cm^-11510s (NO_{2 asym}), 1345s (NO_{2 sym}).

[5,10-diamino-15,20-bis(3,5-di-tert-butylphenyl)

porphyrinato]nickel(II) (14). Compound 13 (20 mg,

2.39 × 10^-5mol) was dissolved in DCM/methanol solu-

tion (5 mL/5 mL) that was bubbled with argon for 10 min.

Argon atmosphere was maintained and 10% palladium

on carbon (13 mg) was added, followed by addition of

sodium borohydride (3.6 mg, 4 eq., 9.56 × 10^-5mol).

There was an immediate change of color from wine red

to emerald green. The starting material was consumed

within 1 min. The solvent was evaporated and the resi-

due ﬁltered through a cotton wool plug after dissolving

in DCM. The DCM solution was washed with water and

the product extracted. The solvent was removed to leave a

green powder residue. Yield: 18 mg (95%), mp > 310 °C.

¹H NMR (400 MHz, CDCl₃, -50 °C): δ_H, ppm 8.71 (s, 2H,

7,8-H), 8.61 (bs, 2H, 3,12-H), 8.27 (bs, 4H, 2,13,17,18-H),

7.70 (bs, 4H, o-H_aryl), 7.58 (bs, 2H, p-H_aryl), 5.57 (bs, 4H,

NH₂), 1.42 (s, 36H, ^tBu-H). ¹³C NMR (100 MHz, CDCl₃):

unobtainable due to broadness of peaks. UV-vis (DCM):

1

as purple crystals. Yield: 2 mg (8%), mp > 310 °C. H

NMR (400 MHz, CDCl₃): δ_H, ppm 9.67 (s, 1H, 20-H),

9.19 (d, J = 4.6 Hz, 1H, 3-H), 9.07 (d, J = 4.6 Hz, 1H,

7-H), 9.04 (d, J = 4.6 Hz, 1H, 2-H), 9.01 (d, J = 4.6 Hz,

1H, 18-H), 8.68 (d, J = 4.6 Hz, 1H, 17-H), 8.62 (d, J =

5.0 Hz, 1H, 12-H), 8.60 (d, J = 4.6 Hz, 1H, 8-H), 8.58 (d,

J = 5.0 Hz, 1H, 13-H), 7.98 (d, J = 2.0 Hz, 2H, o-H_aryl),

7.97 (d, J = 2.0 Hz, 2H, o-H_aryl), 7.77 (t, J = 2.0 Hz, 1H,

p-H_aryl), 7.74 (t, J = 2.0 Hz, 1H, p-H_aryl), 6.39 (bs, 2H,

t

NH₂), 1.53 (s, 18H, Bu-H), 1.52 (s, 18H, Bu-H), -1.13

(bs, 2H, inner NH). ¹³C NMR (100 MHz, CDCl₃): δ_C,

ppm 149.0, 148.6, 141.6, 140.7, 132.5, 132.0, 130.8,

129.9, 129.5, 129.3, 128.3, 122.2, 121.9, 121.7, 120.9,

120.7, 115.9, 104.5, 35.0, 31.7. UV-vis (DCM): λ_max, nm

(ε, 10³M^-1.cm^-1) 421 (308), 534 (9.52), 572 (20.2), 615

(6.01), 675 (16.6). MS (ESI): m/z 702.4533 (calcd. for

C₄₈H₅₆N₅[M + H]⁺702.4536). IR (ATR): ν, cm^-13360b,

1245s (NH₂). The reaction was repeated successfully on

a 50 mg scale.

Attempted synthesis of 1,2-bis[10,15-bis(3,5-di-tert-

butylphenyl)porphyrin-5-yl]diazene. Porphyrin 11 (25

mg, 3.56 × 10^-5mol) was dissolved in 5 mL of toluene. To

this copper(II) acetate (2 mg, 1.00 × 10^-5mol, 30 mol.%)

and pyridine (6 μL, 4 eq., 7.41 × 10^-5mol) were added.

The mixture was stirred at 80 °C and the starting mate-

rial was consumed after 3 h. The solution was washed

with water and the product extracted into DCM. The resi-

due was puriﬁed by column chromatography. The target

compound was not achieved. The main products were

non-porphyrinic compounds. The main porphyrin prod-

uct was the copper analog of the target compound. Yield:

4 mg (5%). UV-vis (DCM): λ_max, nm (intensity ratio)

400 (3.3), 484 (4.3), 700 (1.0), 753 (1.1). MS (ESI): m/z

1521.6996 (calcd. for C₉₆H₁₀₂Cu₂N₁₀[M]⁺1521.6915).

[5,10-bis(3,5-di-tert-butylphenyl)porphyrinato]

nickel(II) (12) [21]. Porphyrin 1 (200 mg, 2.91 × 10^-4

mol) was dissolved in 12 mL of toluene and stirred.

To this Ni(acac)₂(200 mg, 7.78 × 10^-4mol) was added.

The mixture was reﬂuxed for 2 h after which the start-

ing material was consumed. The product was puriﬁed

by column chromatography using DCM/hexane (1:1) as

eluent. A single red fraction was collected. The solvent

was evaporated and the product was recrystallized from

DCM/methanol to give shiny purple crystals. Yield: 203

mg (94%). ¹H NMR (400 MHz, CDCl₃): δ_H, ppm 9.93 (s,

2H, 15,20-H), 9.29 (s, 2H, 17,18-H), 9.20 (d, J = 4.6 Hz,

2H, 2,13-H), 8.99 (d, J = 4.6 Hz, 2H, 3,12-H), 8.90 (s,

2H, 7,8-H), 7.93 (d, J = 1.8 Hz, 4H, o-H_aryl), 7.77 (t, J =

1.8 Hz, 2H, p-H_aryl), 1.51 (s, 36H, ^tBu-H).

λ

_max, nm (intensity ratio) 430 (9.8), 614 (1.0). MS (LSI):

m/z 772.3763 (calcd. for C₄₈H₅₄N₆Ni [M]⁺772.3763). IR

(ATR): ν, cm^-13375m, 1281m (NH₂).

Attempted synthesis of Ni azo-linked cyclic

tetramer (A). Porphyrin 14 (8 mg, 1.03 × 10^-5mol) was

dissolved in 4 mL of toluene. To this copper(II) acetate (1

mg, 5.00 × 10^-6mol, 50 mol.%) and pyridine (1.7 μL, 2

eq., 2.06 × 10^-5mol) were added. The mixture was stirred

at 80 °C and the starting material was consumed after 1

hour. The solution was washed with water and the product

extracted into DCM. The residue was puriﬁed by column

chromatography. The target compound was not achieved.

The main products were non-porphyrinic compounds.

Acknowledgements

[15,20-bis(3,5-di-tert-butylphenyl)-5,10-dinitropor-

phyrinato]nickel(II) (13). Compound 12 (25 mg, 3.36 ×

10^-5mol) was dissolved in chloroform (10 mL) and stirred.

We thank theAustralian Research Council for ﬁnancial

support through Discovery Grant DP0663774, Prof. K.-i.

J. Porphyrins Phthalocyanines 2010; 14: 492–493

azO-lInkeD COrner POrPhyrIn SyStemS

493

Sugiura for collaboration on the corner porphyrin synthe-

sis and the Crystal Structure Analysis Facility, University

of Sydney, for single-crystal X-ray data collection of 5b.

B.B. thanks the Queensland University of Technology for

post-graduate scholarships and the School of Physical

and Chemical Sciences for continuing support.

13. Hoffmann M, Wilson CJ, Odell B and Anderson

HL. Angew. Chem. Int. Ed. 2007; 46: 3122–3125.

14. Anderson HL. Inorg. Chem. 1994; 33: 972–981.

15. Kuebler SM, Danning RG and Anderson HL. J. Am.

Chem. Soc. 2000; 122: 339–347.

16. Screen TEO, Thorne JRG, Denning RG, Bucknall

DG and Anderson HL. J. Am. Chem. Soc. 2002;

124: 9712–9713.

Supporting information

17. Screen TEO, Blake IM, Rees LH, Clegg W, Bor-

wick SJ and Anderson HL. Perkin Trans. 1 2002;

320–329.

18. Drobizhev M, Stepanenko Y, Dzenis Y, Karotki A,

Rebane A, Taylor PN and Anderson HL. J. Am.

Chem. Soc. 2004; 126: 15352–15353.

19. Balaz M, Collins HA, Dahlstedt E and Anderson

HL. Org. Biomol. Chem. 2009; 7: 874–888.

20. Esdaile LJ, Jensen P, McMurtrie JC and Arnold DP.

Angew. Chem. Int. Ed. 2007; 46: 2090–2093.

21. Sugiura K-i, Fujimoto Y and Sakata Y. Chem.

Commun. 2000; 1105–1106.

Crystallographic data for 5a, 5b and 6 have been

deposited at the Cambridge Crystallographic Data Cen-

ter (CCDC) under deposition numbers 753463-753465.

Copies can be obtained on request, free-of-charge, via

www.ccdc.cam.ac.uk/conts/retrieving.html or from the

Cambridge Crystallographic Data Centre, 12 Union

Road, Cambridge CB2 1EZ, UK (fax: +44 1223-336-033

or email: deposit@ccdc.cam.ac.uk).

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Article Doi

Azo-linked corner porphyrin systems: Synthesis, crystal structures and spectroscopic investigation

DOI: 10.1142/S1088424610002318

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