Conversion of some substituted phenols to the corresponding masked thiophenols, synthesis of a dinickel(n) dithiolate macrocyclic complex and isolation of some metal- And ligand-based oxidation products

Article abstract of DOI:10.1039/b004214p

A modified preparation of the masked thiolate head unit 5-(2, 6-diformyl-4-methyIphenyl) dimethylthiocarbamate 6 is detailed and two new masked thiolate head units, 5-(2, 6-diformyl-4-tert-butylphenyl) dimethylthiocarbamate 7 and S-(2-formylphenyl) dimethylthiocarbamate 8, are prepared by this method. The synthesis, crystal structure, NMR spectra and electrochemical properties of the first macrocyclic complex to be derived from 7, [Ni2Ll](GO4)2, are discussed. Oxidation of [Ni2L2](CF3SO3)2 (L22- is derived from 6 and 1, 3-diaminopropane) with cerium(iv) ammonium nitrate led to the precipitation of the black complex [Ni2L2][Ce(NO3)6], which is believed to contain a single nickel(in) centre. This complex decomposes in DMF over time (24 hours) to form the red dinickel(n) complex [Ni2L2](NO3)2-2DMF which has been structurally characterised. Oxidation of [Ni2L3](CF3SO3)2 (L32- is derived from 6 and 1, 4-diaminobutane) with I2 results in ligand oxidation forming the metal free macrocycle (L3')2t which contains two five membered isothiazole rines. This is confirmed by the X-ray crystal structure determinations of (L3')(I, ), and (L3')(I):(I2)5. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b004214p

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Conversion of some substituted phenols to the corresponding
masked thiophenols, synthesis of a dinickel(II) dithiolate
macrocyclic complex and isolation of some metal- and ligand-
based oxidation products
Sally Brooker,*a Graham B. Caygill,a Paul D. Croucher,a Tony C. Davidson,a
Derrick L. J. Clive,b Stephen R. Magnuson,b Stephen P. Cramercd and Corie Y. Ralstoncd
a Department of Chemistry, University of Otago, PO Box 56, Dunedin, New Zealand.
E-mail: sbrooker@alkali.otago.ac.nz
b Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2
c Department of Applied Science, University of California at Davis, Davis, CA 95616, USA
d Lawrence Berkeley National Laboratory, Energy and Environment Division, Berkeley,
CA 94720, USA
Received 26th May 2000, Accepted 25th July 2000
Published on the Web 23rd August 2000
A modified preparation of the masked thiolate head unit S-(2,6-diformyl-4-methylphenyl) dimethylthiocarbamate 6
is detailed and two new masked thiolate head units, S-(2,6-diformyl-4-tert-butylphenyl) dimethylthiocarbamate 7
and S-(2-formylphenyl) dimethylthiocarbamate 8, are prepared by this method. The synthesis, crystal structure,
NMR spectra and electrochemical properties of the first macrocyclic complex to be derived from 7, [Ni2L1](ClO4)2,
are discussed. Oxidation of [Ni2L2](CF3SO3)2 (L22Ϫ is derived from 6 and 1,3-diaminopropane) with cerium()
ammonium nitrate led to the precipitation of the black complex [Ni2L2][Ce(NO3)6], which is believed to contain a
single nickel() centre. This complex decomposes in DMF over time (≈24 hours) to form the red dinickel() complex
[Ni2L2](NO3)2ؒ2DMF which has been structurally characterised. Oxidation of [Ni2L3](CF3SO3)2 (L32Ϫ is derived
from 6 and 1,4-diaminobutane) with I2 results in ligand oxidation forming the metal free macrocycle (L3Ј)2ϩ which
contains two five membered isothiazole rings. This is confirmed by the X-ray crystal structure determinations of
(L3Ј)(I3)2 and (L3Ј)(I)2(I2)5.
Introduction
Interest in the coordination and redox chemistry of nickel thio-
late complexes is high due to the discovery of bimetallic
thiolate-bridged active sites in metalloproteins such as the [Ni-
Fe] hydrogenases.1–7 Hydrogenase enzymes catalyse the revers-
ible two-electron oxidation of molecular hydrogen, H2
2Hϩ ϩ 2eϪ. Single crystal X-ray diffraction studies of a [Ni-Fe]
hydrogenase1,2 have shown the enzyme to contain a hetero-
binuclear center, where the nickel ion at the active site is bound
by four cysteine residues, two of which bridge to an iron atom.
Nickel is thought to be a redox centre in this enzyme3 and
therefore considerable attention has focused on the redox
chemistry of nickel thiolate complexes.8–17
Fig. 1 Synthesis of the O-dimethylthiocarbamates 1–5 and the S-
dimethylthiocarbamates 6–8.
We,17–24 and others25–39 have used the masked thiolate head
unit S-(2,6-diformyl-4-methylphenyl) dimethylthiocarbamate 6
(Fig. 1) in the production of a wide range of thiophenolate
according to the method of Gagné et al.40 Alternatively the
complexes since the first report, by Robson and co-workers, of
product of the first step of this synthesis, sodium 2,6-bis-
such a complex.25 In this paper we report a modified synthesis
(hydroxymethyl)-4-methylphenolate, could be converted into
of 6 and the extension of this method to the preparation of
2,6-bis(hydroxymethyl)-4-methylphenol (see below) which can
two new masked thiolate head units, 7 and 8 (Fig. 1). A new
then be oxidised in one step to 2,6-diformyl-4-methylphenol by
dinickel() dithiolate macrocyclic complex, [Ni2L1](ClO4)2
the method of Tanigughi.41 Similarly, 2,6-diformyl-4-tert-
(Fig. 2), the first to be prepared from 7, has been prepared and
butylphenol was prepared from 2,6-bis(hydroxymethyl)-4-tert-
characterised. Finally, the results of some chemical oxidations
butylphenol (see below).41 2,6-Diacetyl-4-methylphenol and
of some dinickel() dithiolate macrocyclic complexes (Fig. 2)
2,6-dibenzoyl-4-methylphenol were prepared according to the
are presented and discussed.
literature.42,43 [Ni2L2](CF3SO3)2 and [Ni2L3](CF3SO3)2 were
prepared as previously described.17 1,3-Diaminopropane was
distilled from KOH before use. Activated MnO2 (Aldrich, <5
micron, 85% ϩ grade) was dried at 80 ЊC for 48 h before use.
DABCO [Aldrich, 1,4-diazabicyclo[2.2.2]octane] and BF3ؒOEt2
(Aldrich, redistilled 99% grade) were used as received. If neces-
Experimental
Materials
Almost all of the 2,6-diformyl-4-methylphenol used was made
DOI: 10.1039/b004214p
J. Chem. Soc., Dalton Trans., 2000, 3113–3121
This journal is © The Royal Society of Chemistry 2000
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1
(2 × 25 mL) and dried in vacuo (6.50 g, 66%). H NMR (200
MHz, solvent CDCl3, reference SiMe4) δ 7.11 (2H, s), 4.84 (4H,
s), 1.28 (9H, s). Rf (CH2Cl2) = 0.7.
O-(2,6-Diformyl-4-methylphenyl) dimethylthiocarbamate 1.
2,6-Diformyl-4-methylphenol (3.00 g, 18.3 mmol) was sus-
pended in dry DMF (30 mL) under a nitrogen atmosphere. To
this stirred suspension was added solid DABCO (4.00 g, 35.7
mmol) giving a light brown solution. This solution was left
stirring and brought to 35 ЊC. After 15 min solid dimethyl-
thiocarbamoyl chloride (3.35 g, 26.9 mmol) was added. After
15 h stirring under a nitrogen atmosphere at 35 ЊC a yellow
precipitate had developed. Water (100 mL) was added, the mix-
ture cooled to 0 ЊC and the cream precipitate of 1 collected,
washed with water (500 mL) and dried in vacuo (4.10 g, 90%)
(Found: C, 57.1; H, 5.5; N, 5.5; S, 12.8. Calc. for C12H13NSO3:
C, 57.4; H, 5.2; N, 5.6; S, 12.8%). 1H NMR (200 MHz, solvent
CDCl3, reference SiMe4) δ 10.1 (2H, s), 7.93 (2H, s), 3.47 (3H,
s), 3.45 (3H, s), 2.47 (3H, s). νmax/cmϪ1 (KBr disk) 1685. Rf
(CH2Cl2) = 0.2.
O-(2,6-Diformyl-4-tert-butylphenyl) dimethylthiocarbamate
2. As for 1 except that 2,6-diformyl-4-tert-butylphenol (0.10 g,
0.49 mmol) was suspended in 5 mL dry DMF. Amounts of
other reagents/solvents used: DABCO (0.11 g, 1.00 mmol),
dimethylthiocarbamoyl chloride (0.09 g, 0.75 mmol), water (10
mL). The cream precipitate of 2 was collected by filtration,
washed with water (10 mL) and dried in vacuo (0.50 g, 35%)
(Found: C, 61.4; H, 6.6; N, 4.8; S, 10.8. Calc. for C15H19NSO3:
C, 61.4; H, 6.5; N, 4.8; S, 10.9%). 1H NMR (200 MHz, solvent
CDCl3, reference SiMe4) δ 10.2 (2H, s), 8.2 (2H, s), 3.52 (3H, s),
3.52 (3H, s), 1.4 (9H, s). νmax/cmϪ1 (KBr disk) 1687. Rf (CH2-
Cl2) = 0.3.
Fig. 2 The dinickel() macrocyclic complexes [Ni2L1]2ϩ, [Ni2L2]2ϩ and
[Ni2L3]2ϩ, and the organic oxidation product, the macrocycle (L3Ј)2ϩ
.
sary BF3ؒOEt2 can be redistilled from CaH2 after adding a small
amount of dry diethyl ether (≈2% by weight). Spectrophoto-
metric grade 1,2-dichloroethane was used as received from
Aldrich. Isopropanol (IPA) was stored over CaO, then decanted
off and distilled. Toluene was distilled from sodium. HPLC
grade MeCN and DMF were distilled from CaH2 (DMF in
vacuo) immediately before use. All other reagents were used as
received. Merck silica gel 60 F254 pre-coated TLC plates were
used. Measurements were carried out as previously described.17
CAUTION: Perchlorate salts are potentially explosive and
should therefore be prepared in small quantities only and
handled with appropriate care.
O-(2-Formylphenyl) dimethylthiocarbamate 3. As for 1 except
that salicylaldehyde (0.48 g, 4.0 mmol) was suspended in dry
DMF (10 mL). Amounts of other reagents/solvents used:
DABCO (0.90 g, 8.0 mmol), dimethylthiocarbamoyl chloride
(0.75 g, 6.0 mmol), water (25 mL). The cream precipitate of 3
was collected by filtration, washed with water (250 mL) and
dried in vacuo (0.74 g, 90%) (Found: C, 57.0; H, 5.5; N, 6.8; S,
15.6. Calc. for C10H11SNO2: C, 57.4; H, 5.3; N, 6.7; S, 15.3%).
1H NMR (200 MHz, solvent CDCl3, reference SiMe4) δ 10.09
(1H, s), 7.93 (1H, d), 7.61 (1H, t), 7.44 (1H, t), 7.16 (1H, d), 3.47
(3H, s), 3.42 (3H, s). Rf (CH2Cl2) = 0.5.
Syntheses
Sodium 2,6-bis(hydroxymethyl)-4-tert-butylphenolate. 4-tert-
Butylphenol (25.0 g, 0.17 mol) was added to a stirred solution
of NaOH (9.00 g, 0.22 mol) in boiling water (200 mL) and the
golden brown solution stirred for 10 min. Fresh 37% formalde-
hyde (40.0 g, 0.50 mol) was added to the still warm solution and
the solution went an orange-brown colour. This was stirred for
20 min and then left to stand overnight. The white crystalline
O-(2,6-Diacetyl-4-methylphenyl) dimethylthiocarbamate 4. As
for 1 except that 2,6-diacetyl-4-methylphenol (0.10 g, 0.52
mmol) was suspended in dry DMF (5 mL). Amounts of other
reagents/solvents used: DABCO (0.11 g, 1.0 mmol), dimethyl-
thiocarbamoyl chloride (0.95 g, 0.75 mmol), water (20 mL).
After a few minutes a small amount of orange precipitate was
removed by filtration and washed with water (50 mL). This
material was insoluble in all common solvents and has not been
identified. The combined filtrates yielded tan needles of 4 which
were collected, washed with ice-chilled water and dried in vacuo
(0.05 g, 25%) (Found: C, 60.0; H, 6.4; N, 4.7; S, 11.0. Calc. for
1
product was collected and dried in vacuo (21.0 g, 52%). H
NMR (200 MHz, solvent D2O, reference Me3Si(CH2)3SO3Na)
δ 7.14 (2H, s), 4.60 (4H, s), 1.19 (9H, s).
2,6-Bis(hydroxymethyl)-4-methylphenol. Sodium 2,6-bis-
(hydroxymethyl)-4-methylphenolate (10.0 g, 0.05 mol)40 was
dissolved in hot water (35 mL) and left to cool. Glacial acetic
acid (about 5 mL, to pH ≈ 4) was added dropwise to the solu-
tion at room temperature and the resulting white precipitate
filtered off, washed with water (200 mL) and dried in vacuo
1
C14H17SNO3: C, 60.2; H, 6.3; N, 5.0; S, 11.5%). H NMR (200
MHz, solvent CDCl3, reference SiMe4) δ 7.67 (2H, s), 3.45 (3H,
s), 3.43 (3H, s), 2.68 (3H, s), 2.43 (6H, s).
1
(7.20 g, 88%). H NMR (200 MHz, solvent CDCl3, reference
O-(2,6-Dibenzoyl-4-methylphenyl) dimethylthiocarbamate 5.
As for 1 except that 2,6-dibenzoyl-4-methylphenol (0.32 g, 1.0
mmol) was suspended in dry DMF (5 mL). Amounts of other
reagents/solvents used: DABCO (0.26 g, 2.0 mmol), dimethyl-
thiocarbamoyl chloride (0.19 g, 1.5 mmol), water (25 mL). The
cream precipitate of 5 was collected by filtration, washed with
water (50 mL) and dried in vacuo (0.38 g, 80%) (Found: C, 71.0;
H, 5.6; N, 3.2; S, 7.6. Calc. for C24H21SNO3: C, 71.4; H, 5.3; N,
SiMe4) δ 6.97 (2H, s), 4.55 (4H, s), 2.13 (3H, s).
2,6-Bis(hydroxymethyl)-4-tert-butylphenol. Sodium 2,6-bis-
(hydroxymethyl)-4-tert-butylphenolate (10.0 g, 0.04 mol) was
dissolved in hot water (140 mL) and left to cool. Glacial acetic
acid (about 5 mL, to pH ≈ 4) was added dropwise to the room
temperature solution causing a brown oil to form. This was
separated from the colourless solution, washed with H2O
1
3.5; S, 8.0%). H NMR (200 MHz, solvent CDCl3, reference
3114
J. Chem. Soc., Dalton Trans., 2000, 3113–3121

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SiMe4) δ 7.83 (2H, s), 7.48 (10H, m), 3.0 (3H, s), 2.83 (3H, s),
2.41 (3H, s).
for a 2:1 electrolyte in MeCN).44 FAB mass spectrum: m/z
734 [Ni2L1](ClO4)ϩ, 634 [Ni2L1]ϩ.
[Ni2L2][Ce(NO3)6]. [Ni2L2](CF3SO3)2 (100 mg, 0.134 mmol)
was dissolved in dry MeCN (7 mL), under a nitrogen atmos-
phere (the nitrogen was bubbled into the solution which caused
a stirring effect), giving a red solution which was cooled in an
ice bath. To this solution was added, in a dropwise fashion, an
orange solution of cerium() ammonium nitrate (CAN) (74.0
mg, 0.134 mmol) in dry MeCN (5 mL). A black precipitate of
[Ni2L2][Ce(NO3)6] formed immediately. This was filtered off,
washed with IPA (2 mL) and dried under vacuum (108 mg,
85%) (Found: C, 27.3; H, 2.7; N, 13.4; S, 6.4. Calc. for
S-(2,6-Diformyl-4-methylphenyl) dimethylthiocarbamate 6.
BF3ؒOEt2 (1.32 mL, 11.0 mmol) was slowly injected via a
syringe into a stirred solution of 1 (2.50 g, 10.0 mmol) in dry
toluene (160 mL) held at 60 ЊC. This caused the formation of a
white precipitate and a small amount of brown oil. The tem-
perature was raised to 85 ЊC and the solution stirred for 15 h by
which time the precipitate had disappeared. The yellow solution
was cooled to room temperature, decanted from the oil and
washed with water (5 × 200 mL). The resulting colourless tolu-
ene solution was evaporated to dryness and the resulting cream
powder, 6, dried in vacuo (1.80 g, 72%) (Found: C, 57.4; H,
5.2; N, 5.7; S, 12.8. Calc. for C12H13NSO3: C, 57.4; H, 5.2; N,
C24H26N10S2O18Ni2Ce: C, 27.0; H, 2.5; N, 13.1; S, 6.0%). νmax
/
cmϪ1 (KBr disk) 1625, 1447, 1319, 1031. µ = 3.5 µB per complex
at 292 K. λmax/nm (DMF) (ε/dm3 molϪ1 cmϪ1) 870 (1320), 485
(2950). FAB mass spectrum: m/z 550 [Ni2L2]ϩ.
1
5.6; S, 12.8%). H NMR (200 MHz, solvent CDCl3, reference
SiMe4) δ 10.5 (2H, s), 7.95 (2H, s), 3.24 (3H, s), 3.04 (3H, s),
2.50 (3H, s). 13C NMR (75 MHz, CDCl3 reference SiMe4) δC
(L3Ј)ؒ10I. [Ni2L3](CF3SO3)2 (100 mg, 0.11 mmol) was dis-
solved in MeCN (7 mL) giving a red solution. To this
solution was added an excess of iodine (80.0 mg, 0.32 mmol) in
MeCN (5 mL). The solution immediately turned brown. Over
approximately one day, small brown single crystals and several
small red single crystals developed. These were filtered off,
washed with MeCN (3 mL) and dried in vacuo (24.0 mg, 13%)
(Found: C, 17.8; H, 1.5; N, 3.0; S, 4.1; I, 73.7. Calc. for
190.4, 163.9, 141.2, 138.3, 134.2, 131.9, 37.5. 37.3, 21.2. νmax
/
cmϪ1 (KBr disk) 1687, 1663. FAB mass spectrum: m/z 251. Rf
(CH2Cl2) = 0.1.
S-(2,6-Diformyl-4-tert-butylphenyl) dimethylthiocarbamate 7.
As for 6 except that reagents/solvents used were: BF3ؒOEt2 (0.13
mL, 1.1 mmol), 2 (0.10 g, 0.35 mmol), dry toluene (20 mL),
water wash (5 × 30 mL). The resulting cream powder, 7, was
dried in vacuo (0.30 g, 30%) (Found: C, 60.8; H, 6.6; N, 4.8;
S, 10.5. Calc. for C15H19NSO3: C, 61.4; H, 6.5; N, 4.8; S,
C26H30N4S2I10: C, 18.0; H, 1.8; N, 3.2; S, 3.7; I, 73.3%). νmax
/
cmϪ1 (KBr disk) 1617.
1
10.9%). H NMR (200 MHz, solvent CDCl3, reference SiMe4)
X-Ray crystallography
δ 10.5 (2H, s), 8.2 (2H, s), 3.2 (3H, s), 3.0 (3H, s), 1.3 (9H, s).
13C NMR (75 MHz, CDCl3, reference SiMe4) δC 190.6, 164.2,
154.1, 138.1, 132.6, 130.7, 37.5, 30.9. νmax/cmϪ1 (KBr disk) 1680.
FAB mass spectrum: m/z 293. Rf (CH2Cl2) = 0.1.
Data were collected on a Bruker SMART diffractometer, using
graphite-monochromated Mo-Kα radiation (λ = 0.71013 Å).
The data were corrected for Lorentz and polarisation effects
and semi-empirical absorption corrections were applied. The
structures were solved by direct methods (SHELXS-97)45,46 and
refined against all F2 data (SHELXL-97).47 Hydrogen atoms
were inserted at calculated positions and rode on the atoms to
which they are attached (including isotropic thermal param-
eters which were equal to 1.2 times the equivalent isotropic
displacement parameter for the attached non-hydrogen atom).
S-(2-Formylphenyl) dimethylthiocarbamate 8. BF3ؒOEt2 (0.22
mL, 2.2 mmol) was slowly injected via a syringe into a stirred
solution of 3 (0.42 g, 2.0 mmol) in 1,2-dichloroethane (50 mL)
held at 60 ЊC. This caused the formation of a brown oil. The
temperature was raised to 85 ЊC and the solution stirred for 24
h. The yellow solution was cooled to room temperature,
decanted from the oil and washed with water (5 × 200 mL). The
yellow 1,2-dichloroethane solution was evaporated to dryness
giving a light brown oil, 8, which was dried in vacuo (0.38 g,
90%) (Found: C, 57.3; H, 5.8; N, 6.3; S, 14.9. Calc. for
Crystal data for [Ni2L1](ClO4)2ؒ0.5H2Oؒ0.5Et2O. Space
group Pbcn, a = 20.517(2) Å, b = 27.241(3) Å, c = 15.7733(17)
Å, V = 8815.6(17) Å3, R1 = 0.1374 for 4607 F > 4σ(F);
wR2 = 0.4096 and GOF = 1.173 for all 7768 F2. The data
allowed only the gross structure to be determined.
1
C10H11SNO2: C, 57.4; H, 5.3; N, 6.7; S, 15.3%). H NMR (200
MHz, solvent CDCl3, reference SiMe4) δ 10.3 (2H, s), 7.95 (2H,
s), 3.2 (3H, s), 3.0 (3H, s). 13C NMR (75 MHz, CDCl3, reference
SiMe4) δC 192, 138.0, 133.9, 130.3, 128.9, 37.4. FAB mass
spectrum: m/z 209. Rf (CH2Cl2) = 0.2.
Crystal data for [Ni2L3](CF3SO3)2ؒEt2O. C32H40F6N4O7S4-
Ni2, M = 952.34, monoclinic, space group C2/c, a = 25.0993(16)
Å, b = 10.9758(7) Å, c = 17.1135(11) Å, V = 3972.9(4) Å3, Z = 4,
µ = 1.236 mmϪ1. A total of 13534 reflections were collected at
158 K and the 3887 independent reflections were used in the
structural analysis after correcting for absorption. R1 = 0.036
for 3275 F > 4σ(F); wR2 = 0.096 and GOF = 1.034 for all 3887
F2; 249 parameters, all non-hydrogen atoms except the dis-
ordered diethyl ether molecules anisotropic [C(60) and C(70)
diethyl ether molecules each 0.5 occupancy].
[Ni2L1](ClO4)2. S-(2,6-Diformyl-4-tert-butylphenyl) di-
methylthiocarbamate 7 (293 mg, 1.00 mmol) dissolved in IPA
(80 mL) was brought to reflux under a nitrogen atmosphere.
Ground NaOH (40.0 mg, 1.00 mmol) was added and the result-
ing orange solution refluxed for 5 h. Nickel() perchlorate
hexahydrate (365 mg, 1.00 mmol) in IPA (20 mL) was then
added. To the dark red-brown mixture was added 1,3-diamino-
propane (74.0 mg, 1.00 mmol) in IPA (20 mL). The mixture was
refluxed for 5 h and then filtered whilst hot. The resulting
red-brown solid was recrystallised from MeCN by vapour dif-
fusion of diethyl ether to yield [Ni2L1](ClO4)2 as red single
crystals (116 mg, 28%) (Found: C, 42.8; H, 4.7; N, 6.9; S, 7.7.
Calc. for C30H38N4S2Ni2Cl2O8: C, 43.2; H, 4.6; N, 6.7; S,
Crystal data for [Ni2L2](NO3)2ؒ2DMF. C30H40N8Ni2O8S2,
M = 822.24, monoclinic, space group C2/c, a = 21.884(6) Å,
b = 9.948(3) Å, c = 18.441(5) Å, β = 117.713(3)Њ, V = 3554.0(16)
Å3, Z = 4, µ = 1.237 mmϪ1. A total of 12389 reflections were
collected at 173 K and the 3593 independent reflections were
used in the structural analysis after correcting for absorption.
R1 = 0.0255 for 2636 F > 4σ(F); wR2 = 0.0602 and GOF =
0.931 for all 2636 F2; 229 parameters, all non-hydrogen atoms
anisotropic.
1
7.7%). νmax/cmϪ1 (KBr disk) 1626, 1093, 624. H NMR (500
MHz, CD3NO2, referenced to solvent) δ 7.96 (2H, s), 7.79
(2H, s), 4.35 (2H, t), 3.80 (2H, d), 2.42 (1H, d), 1.85 (1H, q)
1.35 (9H,s). 13C NMR (125 MHz, CD3NO2, referenced to
solvent) δ 168.2, 154.4, 137.0, 135.9, 123.2, 63.1, 36.1, 30.8,
29.3. λmax/nm (MeCN) (ε/LϪ1 molϪ1 cmϪ1
)
510 (1250).
Crystal data for (L3Ј)(I3)2. C26H30N4I6S2, M = 1224.06, tri-
Λm(MeCN) = 235 molϪ1 cm2 ΩϪ1 (cf. 220–300 molϪ1 cm2 ΩϪ1
clinic, space group P1, a = 8.9104(19) Å, b = 9.1521(19) Å,
¯
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c = 12.172(3) Å, α = 70.605(3)Њ, β = 85.336(3)Њ, γ = 68.074(3)Њ,
V = 867.6(3) Å3, Z = 1, µ = 5.514 mmϪ1. A total of 11120 reflec-
tions were collected at 168 K and the 3511 independent reflec-
tions were used in the structural analysis after correcting for
absorption. R1 = 0.0284 for 2969 F > 4σ(F); wR2 = 0.0715 and
GOF = 1.093 for all 3511 F2; 173 parameters, all non-hydrogen
atoms anisotropic.
ably due to it having higher solubility in DMF, and compound 3
in excellent yield (90%). Two phenol diketones were also reacted
in this manner to form O-(2,6-diacetyl-4-methylphenyl) di-
methylthiocarbamate 4 (25% yield) and O-(2,6-dibenzoyl-4-
methylphenyl) dimethylthiocarbamate 5 (80% yield) (Fig. 1). In
summary, all of the parent phenol compounds were successfully
converted into the corresponding O-phenyl dimethylthio-
carbamate derivatives.
Electron-withdrawing groups on the phenyl ring are known
to facilitate the Newman–Kwart rearrangement, which is
believed to occur by nucleophilic attack of the thiocarbamoyl
sulfur at the α-carbon of the aromatic ring (C1), so the presence
of aldehyde and ketone functional groups in the compounds of
interest is advantageous.48 Consistent with this, the thermal
rearrangement of neat 1 to 6 occurs at 178 ЊC which is at the
lower end of the temperature range expected.20 However, the
rearrangement of neat 1 to 6 yields a mixture of both com-
pounds under these conditions, necessitating column chromato-
graphy on a large time and solvent consuming scale. Hence
improvements to the rearrangement reaction were sought for
the conversion of 1 to 6 before extending the synthesis to
include the other O-phenyl dimethylthiocarbamates of interest.
The thermal rearrangement of O-(2-formyl-3-methacryl-
oxymethyl-5-nitrophenyl) dimethylthiocarbamate has been
reported to occur in refluxing toluene (bp = 111 ЊC).50 This
temperature was found to be insufficient to rearrange signifi-
cant quantities of 1 to 6 even after a reaction time of several
days. However, the addition of the Lewis acid boron trifluoride
diethyl etherate to 1 in refluxing dry benzene (bp = 80 ЊC) did
result in rearrangement to 6. Dry toluene, held at 85 ЊC, can be
used in place of dry benzene and was the solvent of choice. The
work up of this reaction is simple and quick: the reaction solu-
tion is allowed to cool, is decanted from a small amount of oily
residue, washed with water and then evaporated to dryness to
give 6 in good yield (72%). It was found that adding the
boron trifluoride diethyl etherate to the solution of 1 in dry
toluene at around 60 ЊC rather than at 85 ЊC resulted in a
smaller amount of oil formation and hence gave better yields.
This method gives cleaner material and is much less labour
intensive than the literature method due to avoiding the need for
column chromatography.20 The reaction can also be scaled up by
a factor of at least four with only a small (≈10%) drop in yield.
The tert-butyl analogue 2 was successfully converted into 7
by this method albeit in a modest yield (30%). The conversion
of 3 to 8 proceeded smoothly and in a high yield (90%), but in
1,2-dichloroethane rather than toluene (as an insoluble precipi-
tate formed on the addition of boron trifluoride diethyl etherate
to the toluene solution of 3 and resulted in the formation of
intractable tars). Other chlorinated solvents were tried but the
boiling points were too low to give complete conversion.
The rearrangement of ketones 4 and 5 (Fig. 1) was tried via
this method but in both cases the reactions were unsuccessful.
Compound 4 was unexpectedly hydrolysed back to 2,6-diacetyl-
4-methylphenol on the addition of boron trifluoride diethyl
etherate, perhaps due to the presence of traces of water. No
rearrangement was observed for compound 5, even in refluxing
toluene, indicating that a higher temperature may be needed,
but this was not explored further.
Crystal data for (L3Ј)(I)2(I2)5. C26H30N4I12S2, M = 1985.46,
monoclinic, space group C2/c, a = 11.854(7) Å, b = 15.450(7) Å,
c = 25.559(14) Å, β = 91.291(10)Њ, V = 4680(4) Å3, Z = 4, µ =
8.053 mmϪ1. A total of 29085 reflections were collected at 183
K and the 4775 independent reflections were used in the struc-
tural analysis after correcting for absorption. R1 = 0.0645 for
3008 F > 4σ(F); wR2 = 0.1854 and GOF = 1.040 for all 4775 F2;
195 parameters, all non-hydrogen atoms anisotropic except
C(10).
CCDC reference number 186/2113.
See http://www.rsc.org/suppdata/dt/b0/b004214p/ for crystal-
lographic files in .cif format.
Results and discussion
Organic synthesis
The synthesis of 6 (Fig. 1) was modified in order to avoid the
need for time-consuming, large-scale column chromato-
graphy.20 In an attempt to improve the solubility of the di-
nickel() thiolate complexes obtained from 6, especially in
non-polar solvents, the new head unit S-(2,6-diformyl-4-tert-
butylphenyl) dimethylthiocarbamate 7, in which the para group
on the aromatic head unit was changed from methyl (6) to tert-
butyl (7), was prepared by this method. The synthesis of
S-(2-formylphenyl) dimethylthiocarbamate 8 was also achieved
by this route but attempts to further extend this method to
include the preparation of the related ketones from 4 and 5
(Fig. 1) was not successful.
Almost all of the 2,6-diformyl-4-methylphenol used was
made according to the method of Gagné et al.40 However, we
have recently switched to utilising an alternative oxidation
pathway which involves a simple one step oxidation of 2,6-
bis(hydroxymethyl)-4-methylphenol (vide infra), using MnO2
as the oxidant, in thoroughly dried chloroform, at room
temperature.41 Tanigughi also reported the preparation of
2,6-diformyl-4-tert-butylphenol41 so in order to utilise this syn-
thesis we prepared the necessary starting material, bis(hydroxy-
methyl)-4-methylphenol, from sodium bis(hydroxymethyl)-4-
methylphenolate. The sodium salt was prepared using a slight
modification (higher temperatures and larger solvent volumes
were necessary in the first step due to the low solubility of
4-tert-butylphenol compared to 4-methylphenol in water) of
the first step of the Gagné synthesis (vide infra).40 Two phenol
diketones, 2,6-diacetyl-4-methylphenol and 2,6-dibenzoyl-4-
methylphenol, were prepared according to the literature.42,43
The conversion of these phenol aldehydes and ketones into
the corresponding masked thiophenol aldehydes and ketones
was attempted via a two step procedure where a Newman–
Kwart rearrangement of the appropriate O-phenyldimethyl-
thiocarbamate derivative should give access to the, thermo-
dynamically more stable, S-phenyl dimethylthiocarbamate
derivative (Fig. 1).20,48
Thin layer chromatography was found to be a sensitive and
quick method for determining the end point of all of these
reactions and was the principle method of checking the purity
of these compounds as the microanalysis is unchanged on
rearrangement.
The first step involves removing the phenol proton with base
and ‘clipping’ on the dimethylthiocarbamate group (Fig. 1). A
minor modification to the literature method20,48 has been made
with the hindered base DABCO being used instead of sodium
hydride.49 In comparison with the previously reported synthesis
of 120 this reaction is more reliable, although the yields are no
higher than the best yields obtained using the previous method.
Compounds 2 and 3 were prepared on a smaller scale but in the
same manner as 1: compound 2 in a lower yield (35%), presum-
Synthesis of [Ni2L1](ClO4)2
In order to prepare the thiolate complexes from the masked
thiolates it is necessary to first remove the dimethylcarbamoyl
group from the sulfur atom. The in situ nucleophilic base
hydrolysis in IPA reported for unmasking 620 was successfully
3116
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Table 1 Selected bond lengths (Å) and angles (Њ) for [Ni2L3](CF3-
SO3)2ؒ Et2O
Ni(1)–N(2)
Ni(1)–N(1)
Ni(1)–S(1)
Ni(1)–S(1)#1
1.924(2)
1.934(2)
2.1535(7)
2.1690(7)
S(1)–C(1)
Ni(1) ؒ ؒ ؒ Ni(1)#1
S(1) ؒ ؒ ؒ S(1)#1
1.766(3)
3.1567(6)
2.7890(12)
N(2)–Ni(1)–N(1)
N(2)–Ni(1)–S(1)
N(1)–Ni(1)–S(1)
N(2)–Ni(1)–S(1)#1
96.91(9)
165.27(7)
95.25(7)
89.79(6)
S(1)–Ni(1)–S(1)#1
C(1)–S(1)–Ni(1)
C(1)–S(1)–Ni(1)#1
Ni(1)–S(1)–Ni(1)#1
80.36(3)
106.57(8)
98.33(8)
93.82(3)
N(1)–Ni(1)–S(1)#1 165.19(7)
Symmetry transformations used to generate equivalent atoms: #1 Ϫx,
y, Ϫz ϩ 1/2.
Fig. 3 Perspective view of the cation of [Ni2L1](ClO4)2ؒ0.5H2Oؒ
0.5Et2O (hydrogen atoms, full occupancy perchlorate ion and diethyl
ether molecule omitted for clarity).
employed for 7. Nickel() template ions were then added
followed by 1,3-diaminopropane yielding a red tetraimine
complex [Ni2L1](ClO4)2 in an acceptable yield (28%) (Fig. 2).
IR spectroscopy showed imine formation (1626 cmϪ1) and
that no unreacted carbonyl or primary amine functional groups
were present. As expected [Ni2L1](ClO4)2 is a 2:1 conductor in
MeCN. The UV/Vis spectrum of the red MeCN solution of
[Ni2L1](ClO4)2 showed an absorption band at 510 nm (ε = 1250
L molϪ1 cmϪ1) which was assigned as a ligand to metal charge
transfer (LMCT) transition, Sπ→Ni.17,51 This complex, with a
para tert-butyl group on each of the aromatic head units, is
more soluble in common solvents such as MeCN and DMF
than the related complexes, [Ni2L2](ClO4)2 and [Ni2L3](ClO4)2,
which have para methyl groups on the aromatic head units.17
[Ni2L1](ClO4)2 has sparing solubility in CHCl3 but this is not
sufficient for further characterisation by techniques such as
NMR spectroscopy or cyclic voltammetry.
Fig. 4 Perspective view of the cation of [Ni2L3](CF3SO3)2ؒEt2O
(hydrogen atoms, triflate ions and diethyl ether molecules omitted for
clarity).
analogue, where a perchlorate anion acted as a template for the
formation of a “star” of four π–π stacked macrocycles, but π–π
stacking is also a feature in the triflate structure.
Crystal structures of [Ni2L1](ClO4)2 and [Ni2L3](CF3SO3)2
NMR studies
The 1H NMR spectra of compounds 1–4 all featured two nearly
superimposed singlets at δ 3.4–3.5, while 5 has two singlets at
δ 3.0 and 2.8, due to the NMe2 groups. In each case the NMe2
Poor quality red crystals of [Ni2L1](ClO4)2ؒ0.5H2Oؒ0.5Et2O
were grown by the slow diffusion of diethyl ether vapour into a
MeCN solution of [Ni2L1](ClO4)2 and the X-ray structure
determined (Fig. 3). The structure is not of sufficient quality to
be published in full and therefore no detailed discussion can be
made but the gross structure has been determined. There is one
complete complex in the asymmetric unit. There are two square
planar nickel() ions within each macrocycle and they are
bridged by two thiolate sulfur atoms from the macrocycle. The
remaining two coordination sites on each nickel atom are occu-
pied by imine nitrogen atoms, giving each nickel() ion a N2S2
coordination sphere. The complex adopts a bowed shape and
there are π–π stacking interactions between adjacent macrocy-
cles with the phenyl ring on one macrocycle lying over the imine
group of another macrocycle.
1
signals in the H NMR spectra of the rearranged compounds
6–8 are split into two clearly separated singlets and the aldehyde
proton resonances are shifted downfield relative to the starting
materials (1–3 respectively).
In the non-coordinating solvent CD3NO2 [Ni2L1](ClO4)2
gave easily assigned diamagnetic 1H NMR and 13C NMR spec-
tra. As observed for related dinickel dithiolate complexes17 the
methylene protons give rise to four resonances, at δ 4.35 and
1
3.80 (H9, H9Ј) and at δ 2.42 and 1.85 (H10, H10Ј), in the H
NMR spectrum. This is consistent with the folded shape
(Fig. 3) being retained in solution.
Red crystals of [Ni2L3](CF3SO3)2ؒEt2O were grown from
MeCN solution by vapour diffusion of diethyl ether and the
structure determined (Fig. 4, Table 1). The asymmetric unit
consists of one half of the complex with the other half gener-
ated by a two fold rotation. Each of the nickel atoms is in a
square planar N2S2 environment [Ni(1) 0.037 Å out of this
plane] although there is a degree of tetrahedral twist in the N2S2
plane (16.4Њ) which is comparable to that observed for the per-
chlorate salt of [Ni2L3]2ϩ (15.4–18.9Њ).17 The complex is folded:
the phenyl rings make an angle of 86.87(7)Њ with each other and
the N2S2 planes intersect at 40.76(3)Њ. The packing of these
macrocycles is different to that observed for the perchlorate
Electrochemical studies on [Ni2L1](ClO4)2
Cyclic voltammetry studies in MeCN show that [Ni2L1](ClO4)2
undergoes two quasi-reversible, approximately one electron,
oxidations at ϩ0.69 and ϩ1.16 V and two quasi-reversible,
approximately one electron, reductions at Ϫ0.96 and Ϫ1.45 V
vs. 0.01 M AgNO3/Ag. These processes are very similar to those
reported for the closely related complex [Ni2L2](ClO4)2.17,20,23
Isolation of metal- and ligand-based redox products from
dinickel(II) dithiolate macrocyclic complexes
Due to the biological significance of the nickel() oxidation
J. Chem. Soc., Dalton Trans., 2000, 3113–3121
3117

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Table 2 Observations from a series of attempted chemical oxidations
of room temperature acetonitrile solutions of the red complex
[Ni2L2](CF3SO3)2
Table 3 Selected bond lengths (Å) and angles (Њ) for [Ni2L2]-
(NO3)2ؒ2DMF
Ni(1)–N(1)
Ni(1)–N(2)
Ni–S(1)
1.9250(16)
1.9351(16)
2.1820(8)
Ni(1)–S(1)#1
Ni(1) ؒ ؒ ؒ Ni(1)#1
S(1) ؒ ؒ ؒ S(1)#1
2.1837(7)
3.2136(9)
2.833(1)
Initial colour
change
Oxidant
Comment
N(1)–Ni(1)–N(2)
N(1)–Ni(1)–S(1)
N(2)–Ni(1)–S(1)
N(1)–Ni(1)–S(1)#1 169.83(5)
N(2)–Ni(1)–S(1)#1 91.91(5)
94.28(7)
92.63(5)
172.70(5)
S(1)–Ni(1)–S(1)#1
C(1)–S(1)–Ni(1)
C(1)–S(1)–Ni(1)#1
Ni(1)–S(1)–Ni(1)#1
80.92(2)
104.14(7)
101.29(7)
94.80(2)
(NH4)2S2O8(s)
HNO3(aq)
NOBF4(s)
No change
Green
Purple
Remains a red solution
Solution quickly goes colourless
Solution quickly goes colourless
Solution stable for minutes
Acidic
Purple
[Co(H2O)6]3ϩ
I2(in MeCN)
(s)
Dark brown
Black
Brown single crystals form
Insoluble black precipitate forms
Symmetry transformations used to generate equivalent atoms: #1 Ϫx,
y, Ϫz ϩ 1/2.
CAN(in MeCN)
state3 and current interest in mixed valent complexes15,16,52–57
the isolation of mixed valent dinickel(/) dithiolate complexes
was targeted. The black complex [Ni2L2][Ce(NO3)6], which we
believe to be a Ni()Ni() complex, has been isolated. Given
the rich redox chemistry of the series of dinickel() dithiolate
complexes17,20,23 the isolation of nickel() products and fully
oxidised Ni()2 complexes was also attempted, but unsuccess-
fully.
There are two approaches, electrochemical and chemical
oxidation, to making nickel() complexes from nickel()
analogues.58–60 Both approaches were explored with complexes
[Ni2L2](CF3SO3)2 and [Ni2L3](CF3SO3)2 (for electrochemical
attempts see ref. 17) but only the products of chemical oxid-
ations could be isolated from solution.
A range of chemical oxidants were tested with the red di-
nickel() dithiolate complexes [Ni2L2](CF3SO3)2 and [Ni2L3]-
(CF3SO3)2. The initial colour changes observed on adding the
oxidant to an MeCN solution of [Ni2L2](CF3SO3)2 under an
argon atmosphere are listed in Table 2. The most promising
oxidants were cerium() ammonium nitrate (CAN) and I2.
The black complex [Ni2L2][Ce(NO3)6] was subsequently isol-
ated in excellent yield (85%) by adding one equivalent of the
strong oxidant CAN to an ice-cooled solution of [Ni2L2]-
(CF3SO3)2 in MeCN. The infrared spectrum of [Ni2L2]-
[Ce(NO3)6] confirmed the presence of an imine stretch {1625
cmϪ1 cf. 1624 cmϪ1 for [Ni2L2](CF3SO3)2} indicating that the
integrity of the macrocycle is retained throughout the oxidation
process. The presence of the cerium hexanitrate anion is indi-
cated by a nitrate band in the infrared spectrum at 1380 cmϪ1 61
and was confirmed by elemental analysis. The black solid,
[Ni2L2][Ce(NO3)6], is not stable indefinitely but slowly changes
to a red colour over a period of weeks. In DMF solution (it is
not soluble enough to be studied in any other solvents) this
colour change occurs much more quickly. The UV/Vis spec-
trum of [Ni2L2][Ce(NO3)6] in DMF is very similar to that of
both the one electron electrochemical oxidation product of
[Ni2L2](CF3SO3)2 (in MeCN) and the product obtained by
adding one equivalent of CAN to a MeCN solution of [Ni2L2]-
(ClO4)2.17 Initially the solution is black and there is a broad
band at 870 nm. The solution decays quite rapidly, over ca. 24
hours, from black to red. The UV/Vis spectrum of the resulting
red solution indicates that the major product of the decay
process is [Ni2L2]2ϩ, with a band at ≈510 nm. The slow diffusion
of diethyl ether vapour into this red DMF solution yields red
single crystals. The infrared spectrum of the red crystals still
features an imine band at 1625 cmϪ1 indicating that the macro-
cycle remains intact. The crystal structure of this red product
was determined and it was found to be the complex [Ni2L2]-
(NO3)2ؒ2DMF (vide infra). Microanalysis of the remaining
crystals is also consistent with this formula.
Fig.
5
Perspective view of the cation of [Ni2L2](NO3)2ؒ2DMF
(hydrogen atoms and nitrate ions omitted for clarity).
crystal were determined. The brown crystal was found to be the
metal free macrocycle salt (L3Ј)(I)2(I2)5 and the red crystal was
found to be (L3Ј)(I3)2 (vide infra). In both cases the macrocyclic
cation (L3Ј)2ϩ is present. Microanalysis of the crystalline prod-
ucts of different oxidation reactions gave iodine contents in the
range 10–12 iodine atoms per macrocycle. The infrared spec-
trum of the mixed material has an imine band at 1617 cmϪ1
indicative of an intact macrocycle. No triflate bands were
present.
These polyiodide salts of the macrocyclic cation (L3Ј)2ϩ are
practically insoluble in common solvents, including H2O,
CHCl3, MeCN and DMF, significantly limiting attempts at
further characterisation. Oxidation of closely related thiolate
ligands to isothiazole ring containing derivatives by the weak
oxidant I2 has been reported.16
Crystal structures of [Ni2L2](NO3)2ؒ2DMF, (L3Ј)(I3)2 and
(L3Ј)(I)2(I2)5
Red crystals of [Ni2L2](NO3)2ؒ2DMF were grown by the slow
diffusion of diethyl ether vapour into a red DMF solution of
[Ni2L2][Ce(NO3)6] and the crystal structure determined (Fig. 5,
Table 3). The asymmetric unit consists of one half of the com-
plex with the other half generated by a two fold rotation. The
crystal structure revealed two square planar nickel() ions with-
in the macrocycle which are bridged by two thiolate sulfur
atoms from the macrocycle. The other two coordination sites on
each nickel ion are occupied by imine nitrogen atoms, thus giv-
ing each nickel() ion an N2S2 coordination sphere. Each nickel
atom has an additional interaction with an oxygen donor atom
from a DMF solvent molecule [Ni(1)–O(51) 2.575 Å] (Fig. 5).
There are two nitrate counter anions, presumably resulting
from the decomposition of Ce(NO3)6. In order to accommodate
the geometries of the two nickel ions the complex adopts a
bowed shape with the two aromatic rings almost perpendicular
The metal free macrocycle (L3Ј)2ϩ was isolated in a number
of forms, in low overall yield (13%), from the slow evaporation
of a solution of [Ni2L3](CF3SO3)2 in MeCN which had been
treated with an excess of the oxidant I2 (Fig. 2). The product
consisted of dark brown single crystals together with a few red
single crystals. The crystal structures of both a brown and a red
3118
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Table 5 Selected bond lengths (Å) and angles (Њ) for (L3Ј)(I)2(I2)5
Table 4 Selected bond lengths (Å) and angles (Њ) for (L3Ј)(I3)2
S(1)–C(1)
S(1)–N(1)
C(1)–C(6)
C(6)–C(8)
C(8)–N(1)
N(2)–C(13)
1.725(4)
1.748(3)
1.397(5)
1.423(5)
1.315(5)
1.281(5)
I(1)–I(2)
I(2)–I(3)
S(1) ؒ ؒ ؒ I(1)
I(3) ؒ ؒ ؒ I(3)#2
S(1) ؒ ؒ ؒ S(1)#1
2.9510(7)
2.9221(7)
3.9463(11)
3.9711(09)
5.0408(19)
S(1)–C(1)
S(1)–N(1)
1.724(19)
1.746(14)
1.43(2)
1.31(2)
1.32(2)
I(5)–I(6)
2.780(2)
I(1) ؒ ؒ ؒ I(2)
I(1) ؒ ؒ ؒ I(3)
I(1) ؒ ؒ ؒ I(4)
I(1) ؒ ؒ ؒ I(5)
I(1) ؒ ؒ ؒ I(6)#4
S(1) ؒ ؒ ؒ I(4)
S(1) ؒ ؒ ؒ S(1)#1
I(1) ؒ ؒ ؒ I(6)#5
3.5008(2)
3.3863(2)
3.4368(2)
3.3175(2)
3.7190(2)
3.9988(5)
4.7730(2)
4.922
C(6)–C(8)
C(8)–N(1)
N(2)–C(13)
C(13)–C(2)#3
I(2)–I(2)#1
I(3)–I(3)#2
I(4)–I(4)#3
1.45(2)
2.751(2)
2.794(2)
2.803(3)
I(3)–I(2)–I(1)
177.004(11)
88.18(16)
113.8(3)
N(1)–C(8)–C(6)
C(8)–N(1)–S(1)
C(13)–N(2)–C(12)
112.8(3)
115.1(3)
119.7(3)
C(1)–S(1)–N(1)
C(6)–C(1)–S(1)
C(1)–C(6)–C(8)
110.2(3)
C(1)–S(1)–N(1)
C(2)–C(1)–C(6)
C(2)–C(1)–S(1)
C(6)–C(1)–S(1)
C(5)–C(6)–C(8)
C(5)–C(6)–C(1)
89.0(7)
C(8)–C(6)–C(1)
N(1)–C(8)–C(6)
C(8)–N(1)–C(9)
C(8)–N(1)–S(1)
C(9)–N(1)–S(1)
108.8(15)
113.8(15)
122.8(15)
115.8(12)
121.0(11)
119.8(17)
127.6(14)
112.6(13)
132.4(16)
118.8(16)
Symmetry transformations used to generate equivalent atoms: #1 Ϫx,
y Ϫ 1, Ϫz ϩ 2; #2 1 Ϫ x, Ϫ3 Ϫ y, 3 Ϫ z.
Symmetry transformations used to generate equivalent atoms: #1
Ϫx ϩ 1, y, Ϫz ϩ 3/2; #2 Ϫx ϩ 2, Ϫy ϩ 1, Ϫz ϩ 1; #3 Ϫx ϩ 2, y,
Ϫz ϩ 3/2; #4 x ϩ 1/2, y ϩ 1/2, z; #5 1 Ϫx, 1 Ϫy, 1 Ϫz.
Fig. 6 Perspective view of (L3Ј)(I3)2 (hydrogen atoms omitted for
clarity).
[81.50(5)Њ] to each other. This lengthens the S ؒ ؒ ؒ S distance
minimising repulsive S ؒ ؒ ؒ S interactions. There are π–π inter-
actions between adjacent macrocycles, with the phenyl rings
being an average of 3.44 Å apart.
Red crystals of the metal free macrocycle (L3Ј)(I3)2 were
grown by slow evaporation of a solution of [Ni2L3](CF3SO3)2
in MeCN treated with an excess of I2 and the crystal structure
determined (Fig. 6, Table 4). The asymmetric unit consists of
one half of the complex with the other half generated by inver-
sion. Ligand oxidation has occurred to form two five membered
isothiazole rings within each macrocycle (Fig. 6). The macro-
cycle adopts a stepped conformation with the two phenyl rings
being parallel to each other, as required by the symmetry
operation.
The anions are triiodide ions, formed from the reaction of
the excess iodine with the iodide formed during the ligand oxid-
ation reaction. The triiodide ions are linear [I(1)–I(2)–I(3)
177.00(1)Њ] and symmetrical [I(1)–I(2) 2.9510(7), I(2)–I(3)
2.9221(7) Å]. These values are typical for discrete triiodide
anions:62 no significant interactions involving these anions are
observed (Table 4, vide infra).
Fig. 7 Perspective view of (L3Ј)(I)2(I2)5 (hydrogen atoms omitted for
clarity). Note that nearest neighbour iodine atoms have been generated
by symmetry (see Table 5) to show the nature of the polyiodide array
and hence this figure does not show the correct ratio of iodine atoms to
macrocyclic complex.
I(4) ؒ ؒ ؒ S(1) 3.9988(5) Å, is much longer than the expected value
for a sulfur iodine bond [I–S ca. 2.6–3.0 Å].66
Brown crystals of the metal free macrocycle (L3Ј)(I)2(I2)5
were grown by slow evaporation of a solution of [Ni2L3]-
(CF3SO3)2 in MeCN treated with an excess of I2 and the crystal
structure determined (Fig. 7, Table 5). The asymmetric unit
consists of one half of the complex with the other half gener-
ated by a two fold rotation. Ligand oxidation has occurred to
form two five membered isothiazole rings within each macro-
cycle (Fig. 7). The macrocycle adopts a bowed shape with the
two aromatic rings almost perpendicular [79.95(5)Њ] to each
other. Two iodide ions act as the anions. The iodide ion, I(1),
formed during the ligand oxidation reaction, interacts with
neighboring iodine molecules (excess iodine was used in the
oxidation) to form a polyiodide array.62,63 Consistent with this,
the iodine bond lengths (I–I 2.751–2.803 Å) are longer than
those observed for free iodine in the vapour phase (2.667 Å)64
or in the solid phase (2.715 Å),65 due to donation of electron
density from the iodide into the σ* antibonding orbital on the
iodine molecule.62 The iodine ؒ ؒ ؒ iodide distances of 3.317–
3.5008 Å are typical of those observed for polyiodides.62,63 There
are no significant interactions between the isothiazole sulfur
and the iodide or iodine (Table 5). The shortest I ؒ ؒ ؒ S distance,
Electrochemical studies on [Ni2L2][Ce(NO3)6]
Due to the low solubility of [Ni2L2][Ce(NO3)6] in common
solvents, electrochemical studies on this complex were limited
to those performed in DMF. The decay of the complex occurs
even faster in the presence of the supporting electrolyte, with
the solutions changing colour from black to red in around 45
min, making a conclusive study (e.g. bulk electrolysis, scan rate
dependence of the E1/2 etc.) impossible.67 The cyclic voltam-
mogram of [Ni2L2][Ce(NO3)6], freshly dissolved in DMF (vs.
0.01 M AgNO3/Ag), revealed a series of four approximately one
electron processes: two reduction processes at Ϫ1.60 (quasi-
reversible) and Ϫ1.10 V (quasi-reversible) and two oxidation
processes at ϩ0.30 V (quasi-reversible) and ϩ0.70 V (irrevers-
ible). Characteristic of cyclic voltammograms run in DMF, the
two oxidation waves have somewhat smaller peak currents than
those observed for the reduction waves.67 These processes are
assigned as largely metal based by comparisons with other din-
ickel dithiolate macrocycles.17 All four processes are translated
approximately Ϫ0.10 V from those observed for [Ni2L2]-
(CF3SO3)2 in DMF and for the electrochemically generated one
J. Chem. Soc., Dalton Trans., 2000, 3113–3121
3119

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this method the range of masked thiolate head units available
can in principle be extended still further to include, for example,
the masked thiols derived from 2,6-diformyl-4-chlorophenol70
and 2,6-diformyl-4-trifluoromethylphenol.71
The first Schiff-base macrocyclic complex to be derived from
the new head unit 7, [Ni2L1](ClO4)2, has been prepared and
characterised. As yet the masked thiolate 8 has not been reacted
to form metal complexes, however, it could provide an attractive
synthetic route to many new ligands as well as an alternative
route to tsalen type complexes.72–75
Both metal and ligand centred oxidation products of the di-
nickel() dithiolate complexes have been successfully isolated in
the course of this work. The unstable black complex [Ni2L2]-
[Ce(NO3)6] proved difficult to characterise and work with,
but taken together the results indicate that this product of
CAN oxidation is primarily nickel centred: (a) the complex
decomposes over time to form the structurally characterised
dinickel() complex [Ni2L2](NO3)2ؒ2DMF with no change to
the ligand, (b) the electrochemistry is similar to that of the
parent dinickel() complex [Ni2L2](CF3SO3)2, (c) the EPR spec-
trum indicates the presence of a nickel() centre, (d) the UV/
Vis spectrum is similar to the electrochemically generated one
electron oxidation product of [Ni2L2](CF3SO3)2, (e) the nickel
L-edge XANES studies indicate the presence of a nickel()
centre. In contrast, the metal free macrocycle (L3Ј)2ϩ is the
product of ligand centred oxidation. It results, in low yields,
from the treatment of the parent dinickel() complex with
excess iodine and has been conclusively identified by X-ray
structure determinations.
Fig. 8 Nickel L-edge XANES spectra of [Ni2L2][Ce(NO3)6] (top) and
[Ni2L2](CF3SO3)2 (bottom).
electron oxidation product of [Ni2L2](CF3SO3)2 in MeCN,17
implying that the nickel centres in [Ni2L2][Ce(NO3)6] experience
a slight change in environment, presumably due to interactions
with the cerium nitrate anions (the macrocyclic ligand is
unchanged).
A controlled potential electrolysis experiment was performed
at Ϫ0.10 V vs. 0.01 M AgNO3/Ag on a fresh black DMF solu-
tion of [Ni2L2][Ce(NO3)6] and 0.64 electron equivalents of
charge were transferred (If = 2% of Ii), yielding a red solution.
This is less than the expected one electron equivalent of charge,
indicating that, as anticipated, some decomposition may have
already taken place.
Acknowledgements
This work was supported by grants from the University of
Otago, including a bridging grant (to T. C. D.) which has greatly
facilitated the preparation of this paper. D. L. J. C. and S. R. M.
thank NSERC for financial support. We are grateful to
Professor W. T. Robinson and Dr J. Wikaira (University
of Canterbury) for the X-ray data collections, B. M. Clark
(University of Canterbury) for the FAB mass spectra,
Dr M. Thomas (University of Otago) for obtaining the NMR
spectra and to Geoffrey S. Dunbar and Paul G. Plieger for their
help (University of Otago). The help and advice given to us by
Professor A. McAuley (Victoria), particularly regarding the
interpretation of the EPR spectra, is greatly appreciated.
EPR spectroscopy of [Ni2L2][Ce(NO3)6]
A fresh sample of [Ni2L2][Ce(NO3)6] was prepared (in MeCN)
immediately before carrying out the EPR experiment. This
black solid was isolated from the reaction mixture, washed and
dried briefly in vacuo, then dissolved in DMF, frozen in liquid
nitrogen and the EPR spectrum promptly obtained on the
DMF glass. The observation of two overlapping axial signals is
consistent with the presence of two different nickel() ions. The
signals at g|| = 2.04 and g⊥ = 2.20 are closely similar to those
derived for the electrochemically oxidised [Ni2L2](CF3SO3)2
reported earlier.17 However, a second species with g⊥ = 2.18 and
a complex multiplet centred near 2.07 is also observed. The ion
is characteristic of d7 nickel(), but with axial coordination of
solvent (DMF/MeCN) molecule or molecules or possibly an
anion present in solution.
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