Synthesis and characterization of Ni(II) and Cu(II) complexes of 6-(b-(3,4-dimethoxyphenylethyl))cyclam (L(1)) and 6-(b-(3,4-dihydroxyphenylethyl))cyclam (H(2)L(2)) (cyclam = 1,4,8,11-tetraazacyclotetradecane). X-ray crystal structures of [Cu(L(1))Br(2)] and [Cu(H(2)(BrL(2)))Br]Br·H(2)O and metal ion templated formation of multinuclear macrocyclic complexes

Article abstract of DOI:10.1016/S0020-1693(99)00554-X

The synthesis of 6-(β-(3,4-dimethoxyphenyl)ethyl)cyclam (L₁) and the corresponding Ni(II) and Cu(II) complexes is described. Demethylation of the complexes of L₁ was carried out with BBr₃ and the corresponding Ni(II) and Cu(II) complexes of H₂L₂ (H₂L₂ = 6-(β-(3,4-dihydroxyphenyl)ethyl)cyclam) have been isolated and characterized. Reaction of [Cu(L₁)Br₂] with Br₂ resulted in bromination of the phenyl group, to yield [Cu(BrL₁)Br₂]. Demethylation of [Cu(BrL₁)Br₂] yielded the corresponding bromo-catechol appended macrocyclic complex [Cu(H₂(BrL₂))]Br₂, where H₂(BrL₂) = 6-(β-(6-bromo-3,4-dihydroxyphenyl)ethyl)cyclam. The crystal structures of [Cu(L₁)Br₂] and [Cu(H₂(BrL₂))Br]Br·H₂O have been determined. In both complexes, the Cu(II) ion is within the macrocyclic cavity with an average Cu-N distance of (2.01 A?). In [Cu(L₁)Br₂], the Cu(II) is pseudo-octahedral, with Cu-Br(1) = 2.9996(3) and Cu- Br(2)= 2.925(3) A? whereas in [Cu(H₂(BrL₂))Br]Br·H₂O, the Cu(II) is square pyramidal with a Cu-Br distance of 2.904(2) A?. Reaction of [M(H₂L₂)]₂₊ (M = Ni²⁺ and Cu²⁺) ions with Fe(III) in basic aqueous media led to the formation of the tetranuclear species [Fe(M(L₂)Br₂)₃]^3-, which has been monitored by UV-Vis and EPR spectroscopy (C) 2000 Elsevier Science S.A.

Full text of DOI:10.1016/S0020-1693(99)00554-X

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Inorganica Chimica Acta 300–302 (2000) 477–486
Synthesis and characterization of Ni(II) and Cu(II) complexes of
6-(b-(3,4-dimethoxyphenylethyl))cyclam (L1) and
6-(b-(3,4-dihydroxyphenylethyl))cyclam (H2L2)
(cyclam=1,4,8,11-tetraazacyclotetradecane). X-ray crystal
structures of [Cu(L1)Br2] and [Cu(H2(BrL2))Br]Br·H2O and metal
ion templated formation of multinuclear macrocyclic complexes
A. McAuley *, S. Subramanian
Department of Chemistry, PO Box 3065, Uni6ersity of Victoria, Victoria, BC, Canada V8W 3V6
Received 30 September 1999; accepted 1 December 1999
Abstract
The synthesis of 6-(b-(3,4-dimethoxyphenyl)ethyl)cyclam (L1) and the corresponding Ni(II) and Cu(II) complexes is described.
Demethylation of the complexes of L1 was carried out with BBr3 and the corresponding Ni(II) and Cu(II) complexes of H2L2
(H2L2=6-(b-(3,4-dihydroxyphenyl)ethyl)cyclam) have been isolated and characterized. Reaction of [Cu(L1)Br2] with Br2 resulted
in bromination of the phenyl group, to yield [Cu(BrL1)Br2]. Demethylation of [Cu(BrL1)Br2] yielded the corresponding
bromo-catechol appended macrocyclic complex [Cu(H2(BrL2))]Br2, where H2(BrL2)=6-(b-(6-bromo-3,4-dihydroxyphenyl)-
ethyl)cyclam. The crystal structures of [Cu(L1)Br2] and [Cu(H2(BrL2))Br]Br·H2O have been determined. In both complexes, the
,
Cu(II) ion is within the macrocyclic cavity with an average CuꢀN distance of (2.01 A). In [Cu(L1)Br2], the Cu(II) is
,
pseudo-octahedral, with CuꢀBr(1)=2.9996(3) and Cuꢀ Br(2)=2.925(3) A whereas in [Cu(H2(BrL2))Br]Br·H2O, the Cu(II) is
2+
,
square pyramidal with a CuꢀBr distance of 2.904(2) A. Reaction of [M(H2L2)]
(M=Ni2+ and Cu2+) ions with Fe(III) in basic
aqueous media led to the formation of the tetranuclear species [Fe(M(L2)Br2)3]3−, which has been monitored by UV–Vis and
EPR spectroscopy. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Crystal structures; Copper complexes; Substituted cyclams; Self-assembly; Multinuclear complexes
chemistry [13]. Among bifunctional ligands, those with
a macrocyclic ring and a chelating pendant arm are
unique in that they offer facile routes to heteronuclear
supramolecular structures through self-assembly [14].
Specifically, such processes can be assisted by metal ion
templates which may be different from the metal ion
present in the macrocycle [15]. Since the reactivity of
metal centers is controlled by their coordination envi-
ronments, such ligands offer a versatile approach to
building unique supramolecular structures of rich
chemistry and application [16].
1. Introduction
The design and syntheses of new ligands with various
functionalities is a key factor in the advancement of the
coordination chemistry [1]. In particular, such strategies
have been useful in modifying: (i) binding constants [2]
for use in selective metal extraction and as therapeutic
agents [3], (ii) the reactivity of metal centers with regard
to biomimetic [4–6] and catalytic functions [7,8] and
recently, (iii) in the self-assembly and formation of
supramolecular structures [9–12] and in materials
As a result of the relative ease of functionalization of
the secondary nitrogens in cyclam [17], the majority of
the ligands derived from cyclam have either chelating
moieties such as 2,2%-bipy [18,19] or mostly monoden-
* Corresponding author. Tel.: +1-250-721 7164; fax: +1-250-721
7147.
E-mail address: amcauley@uvic.ca (A. McAuley)
0020-1693/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0020-1693(99)00554-X

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A. McAuley, S. Subramanian / Inorganica Chimica Acta 300–302 (2000) 477–486
tate pendant arms such as aminoethyl or hydroxy-
ethyl groups on one of the nitrogens [20]. Bridging of
the nitrogens with suitable agents have also been de-
scribed [21]. A variety of pendant arms with groups
such as phenol, pyridyl and other heterocyclic rings
substituted at the C(5) position of cyclam have been
prepared and studied by Kimura [22,23]. In all these
cases, owing to their proximity and orientation, these
monodentate substituents invariably coordinate to the
metal center in the macrocyclic cavity. Tabushi’s cy-
clization method offers a general route to C(6)-substi-
tuted cyclams [24,25]1. However, other methods have
also been described for specific substituents [26,27].
Acros Chemical Co., were used without further purifi-
cation. Non-aqueous solvents and electrolytes were
purified by standard methods [28].
2.2. Preparation of 1,2-dimethoxy-4-(i-tosyloxyethyl)-
benzene (1)
To 20 g (0.109 mol) of 3,4-dimethoxy phenylethanol
dissolved in 250 ml of CH2Cl2, was added 20.76 g
(0.109 mol) of p-toluene sulfonylchloride under stir-
ring. The resulting clear solution was cooled in an ice
bath and 15 ml (0.118 mol) of Et3N was dropped in
slowly over a period of 30 min, while maintaining the
temperature below 10°C. This mixture was stored in a
refrigerator for 16 h. Most of the precipitated
[Et3NH]Cl was filtered off under suction. The filtrate
was concentrated in a rotary evaporator and the re-
sulting oil was dissolved in dry CH3COCH3 and
filtered to remove traces of [Et3NH]Cl. The filtrate
was concentrated and traces of solvents were removed
under vacuum. A clear pale yellow liquid was ob-
tained. Yield: 32 g (97% based on the alcohol). 1H
NMR (CDCl3, ppm): 2.40 (s, 3H, CH3), 2.80 (t, 2H,
PhꢀCH2ꢀ), 3.79, 3.81 (s, 6H, ꢀOCH3), 4.19 (t, 2H,
CH2ꢀOTs), 6.62 (m, 3H, Ar), 7.41 (d of d, 4H, tosyl
group). 13C NMR: 21.5 (CH3ꢀAr) 34.5 (PhCH2), 70.8
(CH2OTs), 55.7 and 55.8 (OCH3), 111.2, 111.9, 120.8,
121.0, 126.0, 127.7, 129.7, 144.7, 147.9 and 148.8
(aromatics). FAB MS: Calc. for C17H20SO5, 336.10.
Found, 336.10%.
In the ligands L1 and H2L2, described here, we
have introduced a 3,4-disubstituted phenylethyl unit
into the C(6) position of cyclam. The 3,4-disubstitu-
tion in the phenyl group and the ethylene bridge con-
necting this group to the 6-position in cyclam, orients
the catecholate oxygens in L2 for exodentate chelation
and hence, makes them available for template assisted
self-assembly of cyclam units on a suitable metal ion
such as Fe(III), Ga(III) and Al(III). We report here
the syntheses of Cu(II) and Ni(II) complexes of L1
and H2L2 and preliminary data on a spectroscopic
investigation of the formation of multinuclear species
on Fe(III).
2.3. Preparation of 1,2-dimethoxy-4-(i-iodoethyl)-
benzene (2)
To a solution of 12.0 g (0.08 mol) of anhydrous
NaI in 100 ml of CH3COCH3, a solution of 22.7 g
(74.5 mmol) of 1 in 100 ml of CH3COCH3 was
added. An immediate reaction occurred with the pre-
cipitation of sodium tosylate. The mixture was
refluxed for 1 h to ensure the completion of the reac-
tion. The precipitated sodium tosylate was filtered off
under suction and the filtrate was concentrated to
remove acetone. The resulting oil was dissolved in
CH2Cl2, washed several times with a solution of
Na2S2O3 until faint yellow in color, filtered, dried
over anhydrous sodium sulfate and filtered. The
filtrate was concentrated and traces of solvents were
removed under vacuum to form a pale yellow oil.
2. Experimental
1
2.1. Materials
Yield: 15.72 g (91% based on the tosylate). H NMR
(CDCl3, ppm): 2.10 (t, 2H, PhꢀCH2), 3.30 (t, 2H,
CH2ꢀI), 3.79, 3.81 (s, 6H, OCH3), 6.75 (m, 3H, aro-
matic). 13C NMR: 6.45 (CH2ꢀI), 39.9 (PhꢀCH2), 55.8
(OCH3), 112.4, 112.9, 121.6, 133.3, 147.8, 148.1 (aro-
matic). FAB MS. Calc. for C10H13O2I: 291.99. Found:
291.9% [M+].
Reagents purchased from Aldrich Chemical Co.,
and 1,4,8,11-tetraazaundecane (97%) purchased from
1 6-(b-(2,3-Dimethoxyphenyl)ethyl cyclam and 6-dipy substituted
cyclams have been prepared.

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479
2.4. Preparation of (i-(3,4-dimethoxyphenyl)ethyl)-
dimethylmalonate (3)
3.73 (s, 6H, ꢀOCH3), 3.46 (d of t, 1H, C(O)ꢀCHꢀC(O)),
6.60 (m, 3H, aromatic). 13C NMR: 33.1 (PhCH2) 38.9
(PhCCH2), 28.5 (CꢀCH2ꢀC), 48.9, 50.5 (NHꢀC) and
54.3 (C(O)ꢀCꢀC(O), cyclam ring carbons), 55.7 and
55.8 (OCH3), 111.0, 111.7, 120.2, 133.7, 147.1 and 148.6
(aromatic carbons), 170.8 (CꢁO). FAB MS (negative
ion). Calc. for C20H32N4O4: 392.24. Observed: 391.2
[M−H]−.
In a 500-ml three-necked flask equipped with a N2
inlet and a condenser, 1.70 g (0.068 mol) of 97% NaH
was suspended in 150 ml of dry CH3OCH2CH2OCH3
and stirred with a magnetic stirrer. Neat dimethyl mal-
onate, 9.0 g (0.0687 mol) was dropped in slowly, brisk
effervescence occurred due to liberation of hydrogen
and a clear solution formed. This solution was heated
to 60–65°C and 20.2 g (0.068 mol) of 2 in 50 ml of
CH3OCH2CH2OCH3 was added dropwise over a period
of 5 h. The reaction mixture was maintained at this
temperature for a further period of 20 h, after which it
was cooled and concentrated to dryness. The residue
was suspended in 200 ml of water and extracted with
2×75 ml of CH2Cl2. The combined extracts were
washed successively with 50 ml of 0.1 M HCl and
2×50 ml of water and dried over anhydrous Na2SO4.
The bulk of the solvent was removed in a rotary
evaporator and final traces under vacuum to obtain a
very pale yellow oil. Yield: 19.4 g (97% based on the
iodide). 1H NMR (CDCl3, ppm): 2.52 (t, 2H,
CH2ꢀCH), 2.64 (t, 2H, PhCH2), 3.68 (s, 6H, OCH3),
4.05, 4.15 (s, 6H, C(O)OCH3), 6.65 (m, 3H, aromatic).
13C NMR: 30.6 (PhCH2) 32.8 (CH2ꢀCH), 50.7 (CH),
52.5 (C(O)OCH3), 55.7, 55.8 (OCH3), 111.2, 111.7,
120.4, 137.0, 147.4, 148.8 (aromatic), 169.7 (CꢁO). MS
(CH4 CI): Calc. for C15H20O6: 296.12. Found: 297
[M+1, 65%], 325 [M+29, 5%] and 337 [M+41, 5%],
165 [dimethoxyphenylethyl, 100%].
2.6. Preparation of 6-(i-(3,4-dimethoxyphenylethyl))-
1,4,8,11-tetraazacyclotetradecane (L1)
To a suspension of 15.7 g (55% pure, 0.022 mol) of
crude 4 in 100 ml of CH3OCH2CH2OCH3, 500 ml of
1.0 M BH3·THF was added under a N2 atmosphere.
The mixture was stirred manually with a spatula and
the crisp white solid that formed was crushed carefully
to form a good suspension. This suspension was stirred
with a magnetic stirrer and refluxed in a N2 atmosphere
for 16–20 h. The mixture was occasionally cooled and
the white solids sticking to the sides and the bottom of
the flask were released with a spatula to maintain a
good suspension. The reaction mixture was cooled and
excess borane was decomposed by dropwise addition of
10% HCl under vigorous stirring. The organic solvents
were removed in a rotary evaporator, the resulting
aqueous solution was made strongly acidic (6 M HCl)
and refluxed for 30 min. The mixture was cooled and
filtered to remove any insoluble material. The filtrate
was made strongly basic (pH 12) with 30% NaOH
solution and the free ligand was extracted with CHCl3
in a continuous extractor for 12 h. The CHCl3 extract
was dried over anhydrous Na2SO4 and concentrated to
dryness. The resulting oily impure ligand (15.1 g) was
dissolved in methanol and acidified with concentrated
HCl until a clear solution was formed. This solution
was concentrated to dryness and the resulting light
brown oil was digested with 100 ml of anhydrous
ethanol and the ethanol was decanted off. This process
was repeated four or more times until the brown oil
was transformed to a light creme colored solid which
was then filtered under suction. This highly hygroscopic
solid weighed 5.56 g. Yield: 46% based on 55% pure
lactam. Anal. Calc. for C20H38N4O2·4HCl·2H2O: C,
43.96; H, 8.12; N, 10.25. Found: C, 43.53; H, 7.92; N,
10.72%. 1H NMR (D2O, ppm): 1.76 (2H, m,
CꢀCH2ꢀC), 2.11 (3H, m, CH2ꢀCHꢀ), 2.58 (2H, t,
ArCH2ꢀ), 3.20 and 3.38 (8H each, m, NHꢀCH2ꢀ), 3.64
and 3.66 (3H, s, CH3Oꢀ), 6.76–6.82 (3H, m, Ar). 13C
NMR: 22.7 (CꢀCH2ꢀC), 33.7, 35.5 (PhꢀCH2ꢀCH2ꢀ),
43.3 (ꢀCHꢀ), 44.1, 44.4, 45.0 and 49.3 (CH2ꢀ NH), 57.5
(CH3Oꢀ), 112.1, 112.4, 121.0, 134.1, 146.6 and 148.1
(aromatic carbons). MS: Calc. for [(C20H36N4O2)H]+,
2.5. Preparation of 6-(i-(3,4-dimethoxyphenyl)ethyl)-
-5,7-dioxo-1,4,8,11-tetraazacyclotetradecane (4)
To a solution of 7.4 g (0.025 mol) of 3 dissolved in
500 ml of freshly distilled anhydrous ethanol, a solution
of 4.0 g (0.025 mol) of 1,4,8,11-tetraazaundecane (2,3,2-
tet) was added and stirred using a magnetic stirrer. A
dry N2 atmosphere was maintained and the mixture
was refluxed gently (85–90°C) for 7 days. Ethanol was
removed in a rotary evaporator and the resulting oil
was further evacuated under vacuum at 60°C to remove
traces of ethanol and other volatile impurities. A sticky
solid (9.80 g) was obtained. This solid was dried under
vacuum and used for reduction without further purifi-
cation. A small quantity of this impure lactam was
purified as follows. A total of 2.00 g of the crude
product in 50 ml of water was diluted with 350 ml of
acetone to yield 1.1 g of pure 4 as a white precipitate,
which was filtered off and dried under vacuum. It was
highly hygroscopic. Yield: 55% based on 3. M.p.:\
210°C. 1H NMR (CDCl3, ppm): 1.5 (m, 2H,
CꢀCH2ꢀC), 2.06 (d of d, 2H, PhCH2), 3.04 (d of d, 2H,
PhꢀCꢀCH2), 2.40 and 2.57 (m, 12H, CH2ꢀN), 3.70 and
365.28.
Observed
365.0.
HRMS:
Calc.
for
[(C20H36N4O2)H]+, 365.2916. Observed 365.2918.

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2.6.1. [Cu(L1)Br2]
N2 atmosphere was maintained. The pink solution of
[Cu(L1)Br2] turned reddish immediately and remained
cloudy throughout the reaction. After 4 h, the solvent
and excess BBr3 were removed under vacuum to give a
dark red fuming solid. Anhydrous methanol (15 ml)
was added and the solution was refluxed for 30 min and
filtered to remove any insoluble materials. The filtrate
was concentrated to dryness under vacuum to yield 50
mg of a red–violet hygroscopic solid. Yield: 53% based
on [Cu(L1)Br2]. HRMS: Calc. for [Cu(L1)Br2]+,
478.1006. Observed 478.0999.
To a solution of 6.73 g of CuBr2 (0.03 mol) in 200 ml
of H2O, a solution of 10.07 g of the crude ligand
dissolved in 130 ml of EtOH was added under stirring.
A dark blue color developed instantaneously. The mix-
ture was refluxed for 16 h and concentrated to dryness.
The resulting solid was dissolved in 200 ml of H2O and
filtered to remove any insoluble materials. The clear
filtrate was acidified with 10 ml of 48% HBr and
extracted with CHCl3 in a continuous extractor. The
CHCl3 extract was dried over anhydrous Na2SO4 and
concentrated to dryness to yield 4.0 g of a crisp dark
pink solid. Yield: 24.7% based on crude ligand. MS
(ES): m/e Calc. for C20H36N4O2CuBr [M−Br]: 506.14.
2.6.5. [Cu(H2(BrL2))Br]Br·H2O
Found: 505.9.
A
peak for the dimeric species
[Cu(BrL1)Br2] (100 mg (0.15 mmol)) was used and
the reaction was carried out exactly as described above
for [Cu(L2)Br]Br. The violet solid obtained was recrys-
tallized from 80% aqueous methanol. Yield: 77 mg
(80% based on [Cu(BrL1)Br2]. Anal. Calc. for
C18H33N4O3CuBr3: C, 32.92; H, 5.06; N, 8.53. Found:
C, 33.68; H, 5.07; N, 8.52%. MS (ES): Calc. for
[C18H33N4O3CuBr2]+, 558.04. Observed 558.0.
[(C20H36N4O2CuBr)···Br···(C20H36N4O2CuBr)]+ at 1095
was
also
observed.
HRMS:
Calc.
for
[C20H36N4O2CuBr]+, 506.1319. Observed 506.1314.
2.6.2. [Cu(BrL1)]Br2
To a solution of 100 mg (17.0×10−5 mol) of
[Cu(L1)]Br2 in 20 ml of CHCl3, 5 ml of a 1% solution of
Br2 in CHCl3 was added and the mixture was stirred for
2 h under nitrogen. Excess Br2 and the solvent was
removed and the resulting solids were carried over for
demethylation. Yield: 100 mg (89% based on
[Cu(L1)]Br2) Anal. Calc. for C20H35N4O2CuBr3: C,
36.03; H, 5.29; N, 8.40; Cu, 9.53. Found: C, 36.75; H,
5.57; N, 8.42; Cu, 9.68%. MS (ES): Calc. for
[C20H35N4O2CuBr2], 586.88. Observed 586.2.
2.6.6. [Ni(H2L2)]Br2
Demethylation was carried out exactly as described
in the above cases except 100 mg (0.17 mmol) of
[Ni(L1)Br2] was used. Soon after the addition of BBr3,
the reaction mixture turned brownish and cloudy. The
dark solid obtained from the reaction mixture upon
dissolution in methanol gave a yellowish–brown solu-
tion. As a dry solid, the complex was very dark in color
and was also found to be very hygroscopic. Yield: 80
mg (85% based on [Ni(L1)Br2]). HRMS: Calc. for
[C18H32N4O2NiBr]+, 473.1062. Observed 473.1074.
2.6.3. [Ni(L1)Br2]
To 0.60 g (2.40 mmol) of Ni(OAc)2·4H2O dissolved
in 100 ml of 50% aqueous ethanol, a solution of 1.00 g
(1.83 mmol) of L1·4HCl·2H2O in 50 ml of H2O was
added and the solution was heated in an oil bath at
60–65°C for 6 h. The solution pH was adjusted to 7.0
by dropwise addition of 1.0 M NaOH solution and
ethanol was removed under vacuum. The resulting
aqueous solution was made acidic with 10 ml HBr and
extracted with CHCl3 in a continuous extractor for 8 h.
The resulting pale yellow solution was dried over anhy-
drous Na2SO4 and concentrated to dryness to give a
pale pink solid. Yield: 0.22 g (83% based on pure
2.6.7. [(Me4N+)3][Fe(M(L2)Br2)3] (M=Cu2+ or Ni2+
)
To a mixture of 10 ml of 8.0×10−4 M [M(H2L2)Br2]
and 0.53 ml of 5×10−3 M [Fe(OH2)6](ClO4)3 or
[Fe(NO3)3]·9H2O in aqueous MeOH (8:2 MeOH:H2O),
was added aliquots of 5 ml of 0.1 M [Me4N][OH]·5H2O
in water with stirring under a N2 atmosphere. The
formation of the Fe–catecholate complex was moni-
tored by UV–Vis spectroscopy at 500 nm for Ni and at
525 nm for the Cu complex, respectively, until the
maximum absorption values were reached. The result-
ing dark purplish–red solutions were stable for only
about 10 min after which they tended to precipitate out.
The individual solutions were diluted with 25 ml of
absolute EtOH and stirred at this point for a further
period of 15 min. The resulting dark purple solids were
removed by centrifugation, washed with 10 ml aliquots
of EtOH and Et2O and dried under vacuum. Yield: 4–5
mg (77–96%). See Tables 4 and 5 for UV–Vis and EPR
spectroscopic characterizations.
1
L1·4HCl·2H2O). H NMR (D2O): 1.04 (1H, m, H(6)),
1.23 (2H, m, H(13)), 1.59 (2H, m, H(a)), 1.81 (H, m,
H(13a)), 2.40 (2H, m, H(9,14)), 2.50 (2H, m, H(b)), 2.59
(2H, m, H(9,14)), 3.13 (4H, m, H(5,7)), 3.64, 3.73 (6H,
s, ꢀOCH3), 6.86 (3H, m, aromatic). HRMS: Calc. for
[C20H36N4O2NiBr]2+, 501.1375. Observed 501.1372.
2.6.4. [Cu(H2L2)Br]Br
To 100 mg (0.17 mmol) of [Cu(L1)Br2] dissolved in 10
ml of CH2Cl2, 0.3 ml (1.19 mmol) of neat BBr3 was
added at room temperature. During addition of BBr3,
the mixture was stirred vigorously and an oxygen free

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481
2.7. Crystallographic data collection and structure
solution
FAB (negative or positive ion mode) and electro-spray
(ES) techniques. In all cases, the theoretical isotopic
distributions of relevant peaks were calculated and were
found to agree with the experimentally observed spec-
tra. All the m/e values observed by HRMS were within
95 ppm of calculated values. UV–Vis spectra were
recorded on a Cary 17 dual beam spectrophotometer.
EPR spectra were recorded in an X-band Varian ES-6
spectrometer at liquid N2 temperatures in solvents as
indicated in the text. EPR spectra of Fe(III) catecholate
species were obtained by preparing a uniform mixture
with MgO and by cooling this matrix in liquid N2
temperatures. Diphenyl picryl hydrazide (DPPH, g=
2.0037) was used as an external standard. A three-elec-
trode cell configuration was used in electrochemical
experiments. Platinum electrodes were used as working
electrodes. Redox potentials in aqueous media were
measured against a saturated calomel electrode (SCE),
(0.244 V versus NHE) and an Ag/Ag+ electrode [30]
was used for measurements in non-aqueous media. The
Fc/Fc+ couple was used either as an external or an
internal standard. Cyclic voltammetry experiments were
performed using a Princeton Applied Research Gal-
vanostat/Potentiostat model 273 instrument interfaced
to an IBM PC. The Coreware version 2 and Corrview,
version 1.5 software packages for Windows (Scribners
Associates, Inc.) were used to collect and process cyclic
voltammetry data. Reversibility of cyclic voltam-
mograms were confirmed as described elsewhere [31].
Dark purple single crystals suitable for X-ray crystal-
lography were obtained by slow diffusion of ether into
a chloroform solution in the case of [Cu(L1)Br2] and
from a solution of aqueous methanol (80%) in the case
of [Cu(BrL2)]Br2·H2O. Experimental factors common
to data collection for both crystals are as follows: a
Siemens SMART/CCD diffractometer equipped with
an LT-II low temperature device was used to collect
diffraction data at 193(2) K using graphite-monochro-
,
mated X-radiation of u=0.71073 A and ꢀ–2q meth-
ods. An index range of −105h510, −145k513,
−145l518 for [Cu(L1)Br2] and −195h522,
−145k515, −165l516 for [Cu(BrL2)]Br2·H2O
was used. Corrections for absorption were made using
the SADABS program. SHELXTL [29] was used for struc-
ture solutions and refinements were based on F2. All
the non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were fixed in calculated positions and
refined isotropically on the basis of corresponding C
atoms [U(H)=1.2 Ueq (C)]. Pertinent crystallographic
information is given in Table 1.
Microanalyses were performed by Canadian Micro-
analytical Services Ltd., Delta, B.C., Canada. HRMS
was used for identification of samples that were hygro-
scopic. Mass spectra were obtained either on a Finni-
gan 3200 GCMS using chemical ionization methods or
on a Kratos Concept Model 2H mass spectrometer by
Table 1
Crystal data and structure parameters
Compound
[Cu(L1)Br]Br·H2O
C20H36Br2CuN4O2
587.89
triclinic
[Cu(H2(BrL2))Br2]
Empirical formula
Formula weight
Crystal system
Space group
Unit cell dimensions
C18H25Br3CuN4O3
648.69
monoclinic
P21/c
(
P1
,
a (A)
8.4572(7)
11.2250(10)
13.9768(12)
97.864(2)
97.087(2)
108.727(2)
1224.8(2)
2
17.054(2)
11.7801(11)
12.6049(12)
90.00
108.790(2)
90.00
2397.4(4)
4
1.797
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
V (A )
3
,
Z
Dcalc (Mg m−3
)
1.594
4.176
598
Absorption coefficient (mm−1
F(000)
)
5.936
1276
q Range (°)
1.49–25.00
0.5×0.3×0.2
6064
4031 [Rint=0.0449]
3745/0/262
0.939
2.14–25.00
0.05×0.05×0.02
11 233
4136 [Rint=0.1279]
4136/0/263
0.965
Crystal size (mm)
Reflections collected
Unique
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I\2|(I)]
R1=0.0785, wR2=0.1880
1.450, −1.778
R1=0.0832, wR2=0.1576
0.737, −0.869
−3
,
Largest difference peak and hole (e A
)

482
A. McAuley, S. Subramanian / Inorganica Chimica Acta 300–302 (2000) 477–486
Scheme 1. Reaction conditions: (i) TsCl–Et3N–CH2Cl2; (ii) NaI–acetone; (iii) NaH–CH2(COOMe)2–MeOCH2CH2OMe; (iv) 2,3,2-tet–EtOH
reflux 7 days; (v) THF–BH3 reflux 24 h; (vi) M2+ (M=Ni or Cu)–HBr extraction; (vii) BBr3–CHCl3–RT.
3. Results and discussion
The cyclic lactam 4 was difficult to purify and hence,
the bulk product was taken to the reduction step with-
out further purification. Only a small quantity was
purified for characterization purposes. The high stabil-
ity of macrocyclic complexes in acidic media [32] was
exploited to extract the complexes, [M(L1)Br2] (M=
Ni(II) and Cu(II)) into chloroform, free of acid un-
stable complexes. Solid cyclam complexes of the type,
[M(cyclam)X2] (M=Cu(II) or Ni(II) and X=Cl−Br−)
are neutral and soluble in CHCl3, but are not easily
extracted into CHCl3 from aqueous media [33]. How-
ever, due to axial coordination, the complexes of L1
described here are neutral and also, the presence of
3,4-dimethoxyphenylethyl moiety renders these com-
plexes more lipophilic, which facilitated their extraction
into CHCl3. The purity of complexes thus obtained
were checked by chromatography on a Sephadex CM
C-25 cation exchange resin using 0.3 M NaCl as eluant.
The complexes of L1 described here are solids, but are
difficult to purify by crystallization. However, the
bromo derivatives were easily crystallized. The com-
plexes of H2L2 are relatively stable in oxygen and were
also difficult to crystallize. Due to their hygroscopic
nature, they tend to form oily layers which solidified to
amorphous solids upon drying in vacuo. Hence, these
3.1. Syntheses of ligands and complexes
The preparation of ligands and complexes is outlined
in Scheme 1. The ligand, L1 was synthesized based on
an extension of the method of Tabushi et al. [24]. The
synthesis of the iodide 2 was best achieved via the
tosylate under very mild conditions. The precursor ester
3 was prepared from a reaction of the carbanion of the
dimethyl malonate ester with 2. Conventional methods
such as refluxing with K2CO3 in THF gave very poor
yields with side products arising from b-elimination.
The method described here with NaH as the base and
CH3OCH2CH2OCH3 as the solvent gave excellent
yields. Syntheses of 1 to 3 proceeded without any side
products and the crude products from these reactions
were found to be very pure and were used without
further purification. The cyclization method was not
efficient and was the critical step that controlled the
overall yield of the complexes. Even under high dilution
conditions, the yields of L1 were only 30–35% and the
products were often contaminated with unreacted 2,3,2-
tet and b-elimination products (3,4-dimethoxystyrene
and corresponding polymeric products) arising from 3.

A. McAuley, S. Subramanian / Inorganica Chimica Acta 300–302 (2000) 477–486
483
Table 3
,
Important bond distances (A) and bond angles (°) for [Cu(BrL2)Br2]
Cu(1)ꢀN(2)
Cu(1)ꢀN(4)
Cu(1)ꢀN(1)
Cu(1)ꢀN(3)
2.008(9)
2.008(8)
2.010(9)
2.039(9)
N(2)ꢀCu(1)ꢀN(4)
N(2)ꢀCu(1)ꢀN(1)
N(4)ꢀCu(1)ꢀN(1)
N(2)ꢀCu(1)ꢀN(3)
N(4)ꢀCu(1)ꢀN(3)
N(1)ꢀCu(1)ꢀN(3)
N(2)ꢀCu(1)ꢀBr(2)c1
N(4)ꢀCu(1)ꢀBr(2)c1
N(1)ꢀCu(1)ꢀBr(2)c1
N(3)ꢀCu(1)ꢀBr(2)c1
175.4(4)
86.3(4)
92.6(4)
95.0(4)
86.1(4)
177.8(4)
89.2(3)
95.3(3)
92.4(3)
89.5(3)
Cu(1)ꢀBr(2)c1 2.904(2)
Br(2)ꢀCu(1)c1 2.904(2)
Br(3)ꢀC(18)
O(1)ꢀC(16)
O(2)ꢀC(15)
N(1)ꢀC(2)
N(1)ꢀC(3)
N(2)ꢀC(4)
N(2)ꢀC(5)
N(3)ꢀC(7)
N(3)ꢀC(8)
N(4)ꢀC(9)
N(4)ꢀC(10)
1.912(14)
1.38(2)
1.36(2)
1.458(14)
1.467(13)
1.474(14)
1.479(14)
1.48(2)
1.485(14)
1.485(13)
1.509(13)
Fig. 1. ORTEP diagram of [Cu(L1)Br2] (30% ellipsoid).
complexes were best analyzed by high resolution mass
spectroscopy using the ES technique.
3.2. Structure of [Cu(L1)Br2]
An ORTEP diagram of [Cu(L1)Br2] is shown in Fig. 1.
Although,
a
bromide bridged dimeric species,
[(C20H36N4O2CuBr)···Br···(C20H36N4O2CuBr)]+ was ob-
served in the mass spectrum, the crystal contained only
the discrete molecules of the neutral dibromo complex.
The Cu(II) ion sits well within the macrocyclic cavity
and in the plane defined by the four nitrogen donors.
,
An average CuꢀN distance of 2.026 A observed in this
compound is typical of such distances observed in
various Cu(II) complexes of cyclam derivatives [34,35].
With two bromide ions occupying the axial sites, the
coordination geometry around the Cu(II) ion is pseudo
octahedral. The CuꢀBr(1) distance is slightly longer
Fig. 2. ORTEP diagram of [Cu(BrL2)Br]Br·H2O (30% ellipsoid).
,
,
(2.9941 A) than the CuꢀBr(2) distance (2.9251 A).
Other structural parameters of the cyclam ring are very
similar to those observed in similar complexes [36–38].
As expected, the OꢀC(Ar) distances, C(15)ꢀO(19) and
adopts a cisoid conformation. Important bond dis-
tances and angles are listed in Tables 2 and 3.
3.3. Structure of [Cu(H2(BrL2))Br]Br·H2O
,
C(16)ꢀO(20) (1.334 and 1.359 A) are distinctly shorter
than the OꢀCH3 distances, O(19)ꢀC(19) and
An ORTEP view of the molecule is shown in Fig. 2. As
in the previous structure, many of the features pertain-
ing to the macrocycle are very similar except the coor-
dination geometry around the Cu(II) ion. Unlike in
[Cu(L1)Br2], the Cu(II) is square pyramidal and with
,
O(20)ꢀC(20) (1.432 and 1.450 A). The ethylene bridge
connecting the cyclam ring and the aromatic ring
Table 2
,
Important bond distances (A) and bond angles (°) for
[Cu(L1)Br]Br·H2O
,
the coordinated bromide (CuꢀBr(1)) at 2.904(2) A. The
other bromide ion and the water molecule do not show
any interaction at all with the metal center. The bulky
bromine at C18 appears to exert an influence on the
conformation of the ethylene bridge linking the aro-
matic ring to the cyclam. Unlike in [Cu(L1)Br2], this
bridge adopts a transoid conformation pushing the
aromatic group away from the macrocycle.
Cu(1)ꢀN(4)
Cu(1)ꢀN(1)
Cu(1)ꢀN(3)
Cu(1)ꢀN(2)
Cu(1)ꢀBr(2)
Cu(1)ꢀBr(1)
N(1)ꢀC(10)
N(1)ꢀC(1)
N(2)ꢀC(3)
N(2)ꢀC(2)
N(3)ꢀC(5)
N(3)ꢀC(6)
N(4)ꢀC(7)
N(4)ꢀC(8)
2.004(7)
2.023(7)
2.024(7)
2.029(7)
N(4)ꢀCu(1)ꢀN(1)
N(4)ꢀCu(1)ꢀN(3)
N(1)ꢀCu(1)ꢀN(3)
N(4)ꢀCu(1)ꢀN(2)
N(1)ꢀCu(1)ꢀN(2)
N(3)ꢀCu(1)ꢀN(2)
N(4)ꢀCu(1)ꢀBr(2)
N(1)ꢀCu(1)ꢀBr(2)
N(3)ꢀCu(1)ꢀBr(2)
N(2)ꢀCu(1)ꢀBr(2)
N(4)ꢀCu(1)ꢀBr(1)
N(1)ꢀCu(1)ꢀBr(1)
N(3)ꢀCu(1)ꢀBr(1)
N(2)ꢀCu(1)ꢀBr(1)
Br(2)ꢀCu(1)ꢀBr(1)
94.5(3)
86.2(3)
178.4(3)
177.9(3)
85.5(3)
93.8(3)
90.7(2)
93.4(2)
85.2(2)
91.4(2)
86.8(2)
86.4(2)
95.1(2)
91.1(2)
177.48(5)
2.9251(16)
2.9941(16)
1.462(11)
1.485(10)
1.462(11)
1.490(12)
1.471(12)
1.499(11)
1.470(11)
1.503(12)
3.4. UV–Vis spectroscopy
The UV–Vis spectroscopic data for the complexes
are listed in Table 4. The complexes of L1 and L2
exhibit features characteristic of cyclam complexes
[39,40] along with the aromatic absorption bands in the

484
A. McAuley, S. Subramanian / Inorganica Chimica Acta 300–302 (2000) 477–486
ultra-violet region. In CHCl3, the bands at 500 nm
(m=30 M− 1cm−1) for [Ni(L1)Br2] and at 530 nm
(m=57 M−1cm−1) for [Cu(L1)Br2] indicate that the
bromide ions are coordinated axially and hence the
metal centers adopt pseudo octahedral geometry. How-
ever, in aqueous medium, a mixture of octahedral and
square planar species was present. In particular, this is
clearly evident from the 1H NMR spectrum of the
[Ni(L1)]2+ species which showed predominantly sharp
lines corresponding to the diamagnetic square planar
species [41]. The aromatic substituents were not ex-
pected to interact with the metal centers in the cyclam
cavity. Such interactions would be obvious, particu-
larly, in the case of [Ni(H2L2)]2+, where deprotonation
of the catecholate rings with bases could be expected to
produce a dramatic change in the spectroscopic fea-
tures. However, no such change was observed. In the
case of [Cu(H2L2)]2+, there was also no change ob-
served under anaerobic conditions. However, it is well
known that in basic medium, Cu(II) is known to cata-
lyze the aerial oxidation of phenolic groups [42] and in
the case of [Cu(H2L2)]2+, a brown insoluble product
was observed. However, this has not been fully investi-
gated at present and will be the subject of a future
report.
CHCl3. This might be compared with the tendency of
[Cu(L1)Br2] to form a dimeric species as observed in
mass spectroscopic experiments. At higher scan rates
(100–1000 mV s−1), particularly when these waves
tend to broaden, the formation of this polymeric species
may be very slow. However, in aqueous medium no
such phenomenon was observed and only a quasi-re-
versible (supplementary figure 2) wave was observed
(E1/2=0.98 V; DEp=135 mV; 100 mV s−1). The re-
versibility improved considerably in acidic medium and
also in the presence of chloride. However, there was no
dramatic lowering of the redox potential as has been
observed in the cyclam complexes [43]. The
[Ni(H2L2)]2+ cation also showed a scan-rate dependent
irreversible wave (Ep,a=1.19 V; Ep,a=0.839 V; DEp=
351 mV; 10–1000 mV s−1; supplementary figure 3).
The Ni(III) species of both L1 and H2L2 were reason-
ably stable when prepared chemically (vide infra). As
might be expected, the Ni(III) complex of L1 was
indefinitely stable compared with that of H2L2 which
decomposed over time owing to internal oxidation of
the catecholate groups.
3.6. EPR spectroscopy
The EPR spectra of the Cu(II) (in 1:1 EtOH–DMF
glass) and Ni(III) species (in aqueous medium) were
recorded with no distinct differences observed between
the complexes of L1 and H2L2. The Cu(II) and Ni(III)
spectra closely resembled those of the Ni(III) and
Cu(II) complexes of cyclam [39,44] with g features as
listed in Table 5. The Ni(III) species were prepared in
aqueous medium with K2S2O8 as the oxidant. The
Ni(III) species of L1 was indefinitely stable compared
with a lifetime of about 1 h at room temperature for the
complex of L2 (3×10−4 M). There was no evidence for
any steric contribution from the aromatic substituents.
Both Ni(III) species formed trans-dichloro species as
clearly demonstrated by the hyperfine interactions.
There is no evidence that coordination of the phenolic
groups to the Ni(III) center with a subsequent dissocia-
tion of protons.
3.5. Electrochemistry
Cyclic voltammograms of complexes of L1 were stud-
ied both in CHCl3 and in aqueous media, and those of
L2 in aqueous methanolic medium. Under the condi-
tions employed, the Cu(II) complexes of both L1 (in
CHCl3 and in H2O) and H2L2 (in aqueous MeOH) did
not show any characteristic redox activity. [Ni(L1)Br2]
in CHCl3 did show a redox wave for the Ni2+/3+
couple. At 10 mV s−1 this wave was very sharp with
Ep,a at 0.780 mV and Ep,c at 0.900 mV suggestive of a
strong tendency of the redox active species to be ad-
sorbed on the electrode surface (supplementary figure
1). This could be due to formation of bromo-bridged
species of the type [···Br[(L1)NiIII]···Br··· [NiIII(L1)]-
Br···]n3n+, which the d7 Ni(III) ion could enhance in
Table 4
UV–Vis spectroscopic data for complexes
Compound
Solvent
u (nm) (m (M−1 cm−1))
[Cu(L1)Br2]
[Ni(L1)Br2]
[Cu(L2)]Br2
CHCl3
CHCl3
8:2 CH3OH–H2O (v/v)
8:2 CH3OH–H2O (v/v)
8:2 CH3OH–H2O (v/v)
8:2 CH3OH–H2O (v/v)
530(57), 285 sh (5980), 279(6700), 240(9500)
500 br sh(30), 350(183), 287(4200), 273(6070)
487(132), 278(6770), 225 sh(12 410)
455(88), 350(320), 281(240), 220 sh(13 600)
500(4045), 359 sh(5270), 295(18 500)
525(5060), 360(32 450), 260(34 350)
[Ni(L2)]Br2
[Fe(Ni(L2))3]3+
[Fe(Cu(L2))3]3+

A. McAuley, S. Subramanian / Inorganica Chimica Acta 300–302 (2000) 477–486
485
Table 5
the range of 3.8–4.4 (see Table 5) suggesting the pres-
ence of an [FeO6]3− chromophore and with S=5/2 for
the Fe(III) [45]. The environment around [FeO6]3− may
not be homogeneous suggesting the orientation of the
cyclam units may vary independently. Considering the
structure of the ligands, one would not expect any direct
interaction between the Fe(III) and the metal ions in the
cyclam units. However, the EPR spectrum of
Fe(Cu(L2)Br2)3]3− was somewhat sharper compared
with that of Fe(Ni(L2)Br2)3]3−. Also, a broad signal
around g=2.067 for the Cu(II) ion was observed in the
case of Fe(Cu(L2)Br2)3]3−. The coordination geometry
of the Ni(II) center may vary depending on the counter
ions present in solution. Also, depending upon the pH
used in the preparation of the Fe(M(L2)Br2)3]3− species,
the conformation of the cyclam rings may differ. The
influence of such factors on the spectroscopic parame-
ters is under further investigation.
EPR spectroscopic data (see Section 2 for conditions)
Complex
gꢀ
gÞ
Aꢀ
[Cu(L1)Br2]
[Cu(L2)Br2]
2.143
2.143
2.022
2.022
2.048
2.048
2.176
2.174
200G
200G
27.5G
27.5G
[Ni(L1)Cl2]+
[Ni(L2)Cl2]+
[Fe(Cu(L2))3]3+
[Fe(Ni(L2))3]3+
4.367, 4.118 and 3.805 (2.067 for Cu(II))
4.396, 4.144 and 3.828
3.7. Formation of template-assisted multinuclear
species on Fe(III)
4. Conclusions
The synthesis and characterization of the Ni(II) and
Cu(II) complexes of L1 and H2L2 are described. The
structures of the Cu(II) complexes, [Cu(L1)Br2] and
[Cu(H2(BrL2))Br]Br·H2O are reported. As has been
shown here, the catecholate groups in the complexes of
L22− are exodentate in nature and available for chelating
suitable metal ions such as Fe(III). A detailed investiga-
tion of the formation of multinuclear species, their
structure and properties are under detailed investigation.
5. Supplementary material
The
formation
of
species
of
the
type
[Fe(M(L2)Br2)3]3− (M=Cu(II) and Ni(II)) were both
Crystallographic information in CIF format for the
two structures, [Cu(L1)Br2] and [Cu(H2(BrL2))Br]Br·
H2O are available from the Cambridge Crystallographic
Data Center (CCDC deposit nos. 134871 and 134872).
Copies of this material may be obtained free of charge
from The Director, CCDC, 12 Union Road, Cambridge,
CB2 1EZ, UK (fax: +44-1223-336-033; e-mail:
deposit@ccdc.cam.ac.uk or www:http//www.ccdc.cam.
ac.uk). Figures (S1–S5) of cyclic voltammograms of
[Ni(L1)Br2] and [Ni(H2L2)]Br2 and UV–Vis spectra for
the formation of multinuclear complexes on Fe(III)
template are available as hard copies. Ordering informa-
tion is given on any masthead page.
studied by UV–Vis spectroscopy (see Table 4). Spec-
trophotometric
titration
of
a
solution
of
[Fe(OH2)6](ClO4)3 or [Fe(NO3)3]·9H2O with solutions of
[M(H2L2)Br2]2+ in aqueous methanol (8:2 MeOH–
H2O) in the presence of a base (at least 6 equivalents of
a strong base such as [Me4N][OH]·H2O) produced in-
tense violet–blue species in solution. However, these
species are only meta-stable in solution and are very
easily precipitated (within 10 min from 1×103 M solu-
tions) out of aqueous solutions in which they were
prepared. They are also sparingly soluble in most sol-
vents. The UV–Vis spectroscopic data, recorded before
such precipitation, are presented in Table 4. The intense
bands observed at 500 nm (m=4045 M−1 cm−1) for the
[Fe(Ni(L2)Br2)3]3− and at 525 nm (m=5060 M−1 cm−1
)
for the [Fe(Cu(L2)Br2)3]3− complex anions are charac-
teristic of the [Fe(catecholate)]3− chromophore [45,46].
EPR spectra of [Fe(Ni(L2)Br2)3]3− and Fe(Cu(L2)-
Br2)3]3− were obtained in a MgO matrix and they both
showed three distinguishable features with g-values in
Acknowledgements
We acknowledge NSERC for financial support. Also,
we thank Drs M.J. Zaworotko and K. Biradha for the
X-ray crystallographic studies reported here.

486
A. McAuley, S. Subramanian / Inorganica Chimica Acta 300–302 (2000) 477–486
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