A streamlined synthesis of extended thiophloroglucinol ligands and their trinuclear NiII3 complexes

Article abstract of DOI:10.1039/c3dt53457j

A protocol for the synthesis of trinucleating C₃-symmetric ligands based on a central meta-phenylene bridging 1,3,5-trimercaptobenzene (thiophloroglucinol) backbone has been established. The key compound turned out to be the trialdehyde obtaine

Full text of DOI:10.1039/c3dt53457j

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A streamlined synthesis of extended
thiophloroglucinol ligands and their trinuclear
Cite this: Dalton Trans., 2014, 43,
4102
NiII complexes†
3
Bastian Feldscher, Hubert Theil, Anja Stammler, Hartmut Bögge and
Thorsten Glaser*
A protocol for the synthesis of trinucleating C3-symmetric ligands based on a central meta-phenylene
bridging 1,3,5-trimercaptobenzene (thiophloroglucinol) backbone has been established. The key com-
pound turned out to be the trialdehyde obtained from the triple nucleophilic attack of dimethyldithiocar-
bamate at 1,3,5-tribromo-2,4,6-triformylbenzene. Reacting this trialdehyde with six equivalents of a
primary amine results in the simultaneous dithiocarbamate cleavage and Schiff-base formation providing
II
the extended thiophloroglucinol ligands H3bertdien, H6bertMe, H6bertt-Bu , and H6habbi. Reaction with Ni
2
Received 9th December 2013,
Accepted 11th January 2014
leads to the formation of the trinuclear NiII complexes [(bertdien)NiII3](X)3 (X = BPh4−, BF4−), [(bertMe)-
3
II
NiII3], [(bertt-Bu )Ni 3], and [(habbi)NiII3], which are characterized spectroscopically, electrochemically, and
DOI: 10.1039/c3dt53457j
2
www.rsc.org/dalton
crystallographically.
triplesalen ligand is slightly antiferromagnetic. This result was
especially unexpected, as the meta-phenylene linkage is a well
Introduction
The discovery of single-molecule magnets (SMMs)1–3 and their established ferromagnetic coupling unit in organic
potential applications4–7 has attracted much interest for new chemistry,15,18,20,34–37 where coupling constants up to
types of SMMs. We have developed the trinucleating ligand 1700–1800 cm−1 have been estimated.38–40
system triplesalen which combines a central phloroglucinol
In order to optimize our ligand system we have to under-
(=1,3,5-trihydroxybenzene) bridging unit with three salen-like stand this discrepancy of efficiency in the spin-polarization
coordination compartments (Scheme 1a) for the rational syn- mechanism in transition metal complexes16,21,22,41–58 vs.
12,13
14
thesis of SMMs.8–11 Trinuclear CuII
and VIV
complexes organic systems. In organic radicals and carbenes as the
3
3
exhibit the anticipated ferromagnetic interactions by the spin-
polarization mechanism15–22 although the interactions are
only weak (+0.5 < J < +3.0 cm−1, H = −2JS1S2). Trinuclear com-
plexes of the triplesalen ligand H6talent-Bu (Scheme 1b) react
2
with hexacyanometallates to heptanuclear complexes [Mt6Mc]n+
t
c
(= [{(talent-Bu )M 3}2{M (CN)6}]n+) by molecular recognition.23–29
2
[MnIII6CrIII]3+ is a SMM with a relatively high anisotropy
barrier of Ueff ∼ 25.4 K and a blocking temperature of TB
∼
1.5 K depending on the counter-anion and the solvate,23,26
while [MnIII6MnIII]3+ is a SMM with a low anisotropy barrier
but which exhibits a hysteretic opening up to 10 T at 0.3 K due
to high molecular and crystal symmetry.27,28
Detailed magnetic studies demonstrated that the coupling
between MnIII 23–28,30,31 and FeIII 32,33 ions through the
Lehrstuhl für Anorganische Chemie I, Fakultät für Chemie, Universität Bielefeld,
Universitätsstr. 25, D-33615 Bielefeld, Germany. E-mail: tglaser@uni-bielefeld.de
†Electronic supplementary information (ESI) available: Thermal ellipsoid plots
and crystallographic data (CIF format) of all structures. CCDC 901451, 901452,
901454 and 901455. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c3dt53457j
Scheme 1
4102 | Dalton Trans., 2014, 43, 4102–4114
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archetype 1,3-dimethylenebenzene (meta-quinodimethane)38,39 trinuclear NiII complexes of the extended thiophloroglucinol
3
there is a strong π overlap of the pz orbitals containing the ligands have been synthesized. The synthesis of the ligand
unpaired electrons and the pz orbitals of the central bridging H6habbi and its trinuclear copper complex [(habbi)CuII3] has
benzene unit. In a simple Hückel-MO-treatment (one-electron only recently been communicated.76
theory), two degenerate π MOs result with one unpaired elec-
tron in each MO. Application of Hund’s rule (as in molecular
O2) leads to the energetically favored parallel orientation of the
Experimental section
Preparation of compounds
two spins (ferromagnetic interaction).59,60 Incorporation of
electron–electron repulsion results in the stabilization of the
triplet, mainly by the exchange integral (which is of course the Solvents and starting materials were of the highest commer-
physical origin of Hund’s rule). Thus, the stronger the π inter- cially available purity and were used as received. 1,3,5-Tri-
action of the pz orbitals the stronger is the spin-polarization bromo-2,4,6-triformylbenzene (1),77 half-units 3,32 and 6,78
effect.
and 2,4,6-triformylphloroglucinol79 were prepared according to
An obvious difference noticed by comparing e.g. 1,3- reported procedures. Trialdehyde 4 and H6habbi were syn-
dimethylenebenzene with a trinuclear transition metal triple- thesized as described previously.76 The assignments of the
salen complex is the localization of the magnetic orbitals. NMR resonances in all products were supported by 2D COSY,
Whereas in the organic radical the magnetic orbital is the pz HMBC, and HMQC spectroscopy and the numbering was done
orbital that is perfectly oriented for a π interaction with the according to the numbering scheme in Fig. 1.
bridging π system, in triplesalen complexes the magnetic orbi-
1,3,5-Tri(tert-butylmercapto)-2,4,6-triformylbenzene
(2).
tals are metal d orbitals. Although the covalent metal–ligand Under standard Schlenk-conditions NaSt-Bu (147 mg,
interaction provides some spin-density on the phloroglucinol 1.31 mmol) and 1 (166 mg, 0.42 mmol) were dissolved in dmf
oxygen atom (for an educational review on spin-density trans- (4 mL) at 0 °C. The resulting mixture was stirred at room temp-
fer from metal d orbitals to ligand orbitals see ref. 19), this erature for 24 h and subsequently Et2O (10 mL) was added.
spin-density is much smaller and is not necessarily as well The precipitating salts were separated and the filtrate was
oriented as in the organic radicals. This comparison implies evaporated to dryness to afford 2 as a yellow powder (143 mg,
that a stronger metal–ligand covalency would transfer more 0.34 mmol, 81% yield). 1H NMR (500.25 MHz, CDCl3): δ =
spin-density to the ligand atom and thus would provide a 10.52 (s, OvCH), 1.28 (s, t-Bu). 13C NMR (125.80 MHz, CDCl3):
more efficient spin-polarization over the meta-phenylene δ = 192.5 (s, CvO), 153.3 (s, CArC), 132.7 (s, CArS), 52.1 (s,
linkage.
C(CH3)3), 31.4 (s, CH3). EI MS (positive ion mode) m/z =
In this respect, biological electron-transfer (ET) sites are a 426 [M]+. IR (KBr) ˜ν/cm−1 = 2964m, 2926w, 2901w, 2858w,
good guide. Nature has solved the problem of a necessary 1707s, 1460m, 1366m, 1161m, 987m. Elemental analysis:
strong metal–ligand covalency for a fast and directed superex- Found: C, 58.49; H, 7.05; N, 0.17. Calc. for C21H30O3S3·0.15dmf
change ET pathway by using metal–thiolate (cysteine) coordi- (C21.45H31.5N0.15O3.15S3) C, 58.81; H, 7.25; N, 0.48.
nation in iron–sulfur clusters and blue copper centers.61–66
t-Bu3H3bertMe. Aldehyde 2 (90 mg, 0.211 mmol) and half-
The metal–sulfur bond has a stronger covalency than a corres- unit 3 (281 mg, 1.28 mmol) were suspended in MeOH (2 mL)
ponding metal–oxygen bond due to the energetically higher and the mixture was stirred for 24 h at 40 °C. The resulting
lying and more diffuse sulfur 3p orbitals than the oxygen 2p solution was evaporated to dryness and the oil was purified via
orbitals.67–71 Based on these considerations, we started a column chromatography with a Sephadex® LH-20 column
project to substitute the central phloroglucinol unit by a (MeOH) yielding the product as a yellow solid (184 mg,
central thiophloroglucinol (=1,3,5-trimercaptobenzene) unit 0.178 mmol, 85% yield). 1H NMR (500.25 MHz, CDCl3): δ =
leading to extended thiophloroglucinol and in particular thio- 16.4 (br s, OH), 8.68 (m, C11H2), 7.30 (m, C103H), 7.07 (d, J =
triplesalen ligands (Scheme 1c).
8 Hz, C105H), 6.83 (d, J = 8 Hz, C106H), 3.72 (m, C13H2), 2.31
Our first synthetic route to thiotriplesalen ligands was (s, C18H3), 2.26 (s, C120H3), 1.47 (s, C15H2), 1.13 (m, C13H3).
based on the Newman–Kwart rearrangement,72–74 which is an 13C NMR (125.80 MHz, CDCl3): δ = 172.3 (s, C17), 162.0
established route from phenols to thiophenols via the thermal (s, C107), 158.7 (s, C11), 153.9 (s, C2), 133.2 (s, C105), 132.0 (s,
rearrangement of the O-thiocarbamate (synthesized from the C1), 128.1 (s, C103), 125.8 (s, C104), 118.8 (s, C102), 118.3 (s,
phenol with carbamoylchloride) to the S-thiocarbamate. Thus, C106), 62.5 (s, CMe3), 60.4 (s, C13), 31.5 (s, C13), 24.8 (s, C15),
we reacted our starting material 2,4,6-triacetyl-1,3,5-trihydroxy- 20.8 (s, C120), 14.8 (s, C18). ESI MS (positive ion mode) m/z =
benzene for the triplesalen ligands H6talenR with 1056 [M + Na]+, 1034 [M + H]+, 539 [M + 2Na]2+, 517
dimethylthiocarbamoyl chloride to afford the tris(O-thiocarba- [M + 2H]2+, 528 [M + H + Na]2+. HRMS (MALDI) for
mate) and rearranged it to the tris(S-thiocarbamate). However, C60H85N6O3S3 [M + H]+ calc.: 1033.58398, found: 1033.58385.
cleavage of the tris(S-thiocarbamate) resulted not in the free IR (KBr) ˜ν/cm−1 = 2964s, 2924m, 2897m, 2866m, 1645m,
thiol, but in the formation of polycyclic products.75
Herein, we present the successful realization of extended 1296m, 1163m, 1069w, 822m, 654w.
1622s, 1585m, 1504m, 1471m, 1456m, 1383m, 1364m, 1325w,
thiophloroglucinol ligands. This proved to be a versatile route
[(bertMe)Ni3]. Trialdehyde 4 (86 mg, 0.165 mmol) and half-
to such ligands with varying pendant arms. Furthermore, the unit 3 (220 mg, 1.00 mmol, 6.2 eq.) were dissolved in CH2Cl2
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Fig. 1 Molecular structures of (a) [(bertMe)Ni3], (b) [(bertt-Bu )Ni3], (c) [(bertdien)Ni3]3+, and (d) [(habbi)Ni3] (molecule 1) and the numbering schemes
2
used. Hydrogen atoms are omitted for clarity.
(15 mL) and stirred for 6 h. The volatiles were removed under 811w. Elemental analysis: Found: C, 56.46; H, 5.56; N, 7.67; S,
vacuum and the resulting yellow solid was redissolved in EtOH 8.62. Calc. for [(bertMe)Ni3]·0.35toluene (C50.45H56.8N6Ni3O3S3)
(15 mL). This solution was added to
Ni(OAc)2·4H2O (258 mg, 1.02 mmol, 6.4 eq.) in EtOH (30 mL)
a
solution of C, 56.76; H, 5.36; N, 7.87; S, 9.01.
[(bertt-Bu )Ni3]. Trialdehyde 4 (73 mg, 0.140 mmol) and half-
2
and heated to reflux for 30 min. The precipitating solid was unit 6 (269 mg, 0.845 mmol, 6 eq.) were dissolved in CH2Cl2
isolated and recrystallized via slow evaporation of a mixture of (10 mL) and stirred for 6 h. The volatiles were removed under
toluene–CHCl3 (80 mg, 0.077 mmol, 47% yield). 1H NMR vacuum and the resulting oil was redissolved in EtOH (10 mL).
(500.25 MHz, C2D2Cl4): δ = 9.13 (s, C11H), 7.24 (s, C103H), This solution was added to a solution of Ni(OAc)2·4H2O
6.95 (dd, JH.H = 1.5 Hz and JH.H = 8.7, CArH), 6.77 (d, JH,H
=
(209 mg, 0.840 mmol, 6 eq.) and heated to reflux for 75 min.
8.5 Hz, CHar), 3.37 (s, C13H2), 2.38 (s, C18H), 2.22 (s, C120H3), The precipitating crude product was recrystallized via slow
1.67 (s, C15H3 + C16H3). 13C NMR (125.75 MHz, C2D2Cl4): δ = evaporation of a mixture of the complex in EtOH and CH2Cl2
1
167.1 (C17), 161.6 (C11), 160.7 (C101), 155.7 (C1), 134.0 (C2), (50 mg, 0.038 mmol, 27%). H NMR (500.25 MHz, CDCl3): δ =
128.7 (C103), 125.3 (C2), 123.6 (C104), 122.1 (C106), 121.1 9.33 (s, C3H), 7.33 (m, C103H), 7.28 (m, C105H), 3.39 (s,
(C102), 70.4 (C13), 65.2 (C14), 26.9 (C15 + C16), 20.5 (C120), C13H), 2.47 (s, C18H), 1.63 (s, C15H + C16H), 1.34 (s,
18.0 (C18). MALDI MS (positive ion mode) m/z = 1035 C111–113H), 1.29 (s, C121–122H). 13C NMR (125.75 MHz,
[M + H]+. IR (KBr) ˜ν/cm−1 = 2965m, 2918w, 2857w, 1616m, CDCl3): δ = 167.6 (C17), 162.5 (C11), 160.8 (C101), 156.6 (C1),
1582s, 1528s, 1458s, 1412s, 1379w, 1325s, 1292m, 1260w, 141.1 (C106), 135.5 (C104), 127.6 (C105), 125.3 (C2), 122.6
1234m, 1209w, 1186m, 1153w, 1140w, 1078m, 943w, 824m, (C104), 120.7 (C102), 70.5 (C14), 65.8 (C13), 35.7 (C110), 34.3
4104 | Dalton Trans., 2014, 43, 4102–4114
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(C120), 31.6 (C121–123), 30.1 (C111–113), 27.3 (C15 + C16), subsequently washed with EtOH and Et2O and recrystallized
19.0 (C18). MALDI MS (positive ion mode) m/z = 1328 [M]+. IR via slow evaporation of a solution of the complex in CH3CN
(KBr) ˜ν/cm−1 = 2951m, 2905m, 2866w, 1582s, 1524m, 1460s, (336 mg, 0.900 mmol, 84%). MALDI MS (positive ion mode)
1422s, 1383w, 1360w, 1333w, 1292w, 1261w, 1248w, 1223w, m/z = 1131 [M + BPh4]+. IR (KBr) ˜ν/cm−1 = 3157w, 3119w,
1186w, 1152w, 1084w, 1067w, 943w, 947w, 785w. Elemental ana- 3053m, 3030m, 2997m, 2982m, 2926m, 2872br, 1948w, 1818w,
lysis: Found: C, 61.23; H, 7.19; N, 6.39. Calc. for [(bertt-Bu )- 1818w, 1591m, 1580m, 1466s, 1432s, 1333m, 1290m, 1267w,
2
Ni3]·0.25CH2Cl2·0.30H2O·0.10EtOH(C69.45H97.78N6Ni3O3.40S3Cl0.5
C, 61.29; H, 7.24; N, 6.18.
)
124m, 1182w, 1167w, 1138m, 1107m, 1089m, 1045m, 1032m,
941m, 887m, 845m, 788m, 734s, 705s, 611s. Elemental analy-
2-2((2-(Dimethylamino)ethyl)(methyl)amino)acetonitrile (10). sis: Found: C, 69.10; H, 6.44; N, 7.82. Calc. for [(bertdien)Ni3]-
Na2S2O5 (11.891 g, 62.55 mmol) was dissolved in water (30 mL) (BPh4)3·CH3CN (C104H117N10Ni3S3B3) C, 68.94; H, 6.51; N, 7.73.
and cooled to 0 °C. To this cold solution a 37% formaldehyde To obtain single crystals suitable for X-ray diffraction, [(bert-
solution in water (9.590 g, 118.16 mmol) was added and dien)Ni3](BPh4)3·CH3CN has been recrystallized from acetone.
heated under reflux for 10 min. At room temperature N,N,N′-
To enhance the solubility in noncoordinating solvents (see
trimethylethylenediamine (15 mL, 12.06 g, 118.03 mmol) was the text for details), [(bertdien)Ni3](BPh4)3 has been converted
slowly added and the reaction mixture was stirred for 3.5 h at into the B(ArF)4-salt (B(ArF)4 = tetrakis[3,5-bis(trifluoromethyl)-
−
room temperature. To the resulting mixture a solution of phenyl]borate) via salt-metathesis. All NMR-spectra have been
NaCN (6.079 g, 124.04 mmol) in water (14 mL) was added and collected from this salt. 1H NMR (500.25 MHz, CDCl3): δ = 8.97
the resulting suspension was stirred overnight. The precipitate (d, J = 10 Hz, HCvN), 8.95 (d, J = 11 Hz, HCvN), 7.75 (s,
and the filtrate were extracted with CH2Cl2 and the combined B(ArF)4−), 7.58 (s, B(ArF)4−), 4.08–2.10 (m, CH2 and CH3).
organic layers were dried over Na2SO4. The solvents have been 13C NMR (125.75 MHz, CDCl3): δ = 167.4 (s, CvN), 167.3 (s,
1
evaporated at 40 °C and 20 mbar yielding the nitrile 10 as a CvN), 162.3 (q, JBC = 50 Hz, B(ArF)4−), 153.8 (s, CAr-S), 153.7
2
colourless liquid (14.462 g, 102 mmol, 87%). 1H NMR (s, CAr-S), 135.4 (s, B(ArF)4−), 129.5 (q, JCF = 32 Hz, B(ArF)4−),
125.8 (m, CArC), 125.2 (q, JCF = 270 Hz, B(ArF)4−), 118.1 (s,
3
1
(500.25 MHz, CDCl3): δ = 3.60 (s, CH2CuN), 2.54 (t, JH,H
=
6.3 Hz, CH2NMe), 2.36 (m, CH2NMe2 and NCH3), 2.21 (s, B(ArF)4−), 64.9, 64.3, 64.0, 59.6, 58.5, 51.8, 50.9.
N(CH3)2). 13C NMR (125.75 MHz, CDCl3): δ = 114.6 (s, CuN),
[(bertdien)Ni3](BF4)3. Trialdehyde 4 (138 mg, 0.265 mmol)
56.9 (s, CH2NMe2), 52.9 (s, CH2NMe), 45.5 (s, N(CH3)2), 45.2 (s, and triamine 9 (305 mg, 2.10 mmol) were dissolved in CH2Cl2
CH2CuN), 42.2 (s, NCH3). ESI MS (positive ion mode) m/z = (10 mL) and stirred for 4 h at ambient temperature. The vola-
142.2 [M + H]+.
tiles were removed under vacuum and the resulting oil was
N′-(2-Aminoethyl)-N′,N,N-trimethylethan-1,2-diamine
(9). redissolved in MeOH (15 mL). This solution was added to a
LiAlH4 (6.512 g, 172.59 mmol) was suspended in dry thf solution of Ni(BF4)2·6H2O (273 mg, 0.802 mmol) in MeOH
(90 mL) and cooled to 0 °C. A solution of nitrile 10 (11.015 g, (50 mL). The resulting red suspension was heated to reflux for
78.60 mmol) in thf (180 mL) was added slowly over a period of
2 min, the solid dissolved and triethylamine (80 mg,
one hour. The resulting suspension was heated under reflux 0.795 mmol) was added. The resulting solution was slowly
for 3 h and stirred overnight at room temperature. At 0 °C, allowed to cool to ambient temperature during which the
water (20 mL) has been slowly added and afterwards a solution product precipitated as a red solid (109 mg, 0.102 mmol,
of KOH (340 g) in water (230 mL). The suspension has been 38%). MALDI MS (positive ion mode) m/z = 810 [M]+. IR (KBr)
vigorously stirred until all solids dissolved. The solution has ˜ν/cm−1 = 2928m, 2884w, 2855w, 2810w, 1593m, 1466s, 1422m,
been extracted with CH2Cl2, the combined organic layers dried 1343w, 1288w, 1250m, 1084s, 1055s, 968w, 947m, 889m,
over Na2SO4 and the volatiles removed at 40 °C and 789m, 766m, 534m, 523m. Elemental analysis: Found: C,
≥200 mbar. The resulting raw product can be distilled under 33.10; H, 5.06; N, 11.35. Calc. for [(bertdien)Ni3](BF4)3·H2O
slight vacuum to yield the product as a colourless liquid (C30H56N9Ni3S3B3F12) C, 33.01; H, 5.17; N, 11.55.
(9.511 g, 65.48 mmol, 83%). 1H NMR (500.25 MHz, CDCl3): δ =
[(habbi)Ni3]. A solution of H6habbi (162 mg, 0.139 mmol)
solution of
3
2.65 (t, JH,H = 6.4 Hz, CH2NH2), 2.38–2.27 (m, CH2), 2.13 (s, in EtOH (20 mL) was slowly added to
a
CH3), 1.35 (bs, NH2). 13C NMR (125.75 MHz, CDCl3): δ = 60.8 Ni(OAc)2·4H2O (208 mg, 0.836 mmol) in EtOH (20 mL) and
(s, CH2CH2NH2), 57.3 (s, CH2NMe2), 55.7 (s, CH2CH2NMe2), heated to reflux for 40 min. The precipitate has been isolated
45.7 (s, N(CH3)2), 42.4 (s, NCH3), 39.4 (s, CH2NH2). ESI MS and recrystallized via slow evaporation of a mixture of EtOH
(positive ion mode) m/z = 146 [M + H]+, 168 [M + Na]+.
and CH2Cl2 yielding crystals suitable for single-crystal
[(bertdien)Ni3](BPh4)3. Trialdehyde 4 (117 mg, 0.225 mmol) X-ray diffractions (55 mg, 0.041 mmol, 30%). 1H NMR
and triamine 9 (240 mg, 1.652 mmol, 7 eq.) were dissolved in (500 MHz, CDCl3): δ = 8.86 (s, H3), 7.10 (s, H15), 6.85 (s, H11),
CH2Cl2 (10 mL) and stirred for 4 h at ambient temperature. 5.71 (m, 1H, H9), 4.32 (m, 1H, H4), 3.48 (m, 1H, H8), 3.03 (m,
The volatiles were removed under vacuum and the resulting oil 2H, H9 + H4), 2.67 (m, 1H, H7), 2.52 (m, 1H, H5), 2.30 (m,
was redissolved in MeOH (15 mL). This solution was added to 1H, H8), 1.95 (m, 1H, H6), 1.88 (m, 1H, H7), 1.60 (m, 1H, H6),
a solution of Ni(OAc)2·4H2O (168 mg, 0.68 mmol, 3 eq.) in 1.32 (s, H14), 1.30 (s, H18). 13C NMR (125.75 MHz, CDCl3): δ =
MeOH (30 mL) and stirred for 2 h. To the resulting red solu- 165.5 (C3), 157.8 (C19), 154.5 (C1), 139.5 (C16), 135.0 (C12),
tion was added a solution of NaBPh4 (231 m, 0.67 mmol, 3 eq.) 125.2 (C2), 123.4 (C11), 123.3 (C15), 120.2 (C10), 68.2 (C4), 66.6
in MeOH (10 mL). The precipitating solid was isolated, (C5), 59.7 (C9), 57.0 (C8), 35.4 (C17), 34.1 (C13), 32.1 (C14),
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29.9 (C18), 27.5 (C6), 23.5 (C7). MALDI MS (positive ion not be properly refined and was therefore removed from the
mode): 1328.7 [M]+. IR (KBr) ˜ν/cm−1 = 2951m, 2903m, 2866m, coordinate set. The SQUEEZE82,83 electron count can be attrib-
1601m, 1462s, 1439s, 1412m, 1358w, 1304m, 1287m, 1240m, uted to ca. two toluene molecules per complex. Approximately
1204w, 1165w, 1128w, 1103w, 1026w, 1005w, 934w, 899w, 1.5 CH2Cl2 and 1.5 EtOH molecules were found in the asym-
874w, 837m, 804w, 766w, 748w, 642w, 550w. [α]D20 = −1255°, metric unit of [(bertt-Bu )Ni3]·1.5EtOH·1.5CH2Cl2 but did not
2
C = 0.014 g/100 mL, CHCl3. Elemental analysis: Found: C, refine properly due to severe disorder. The electron count found
62.36; H, 7.35; N, 6.32. Calc. for [(habbi)Ni3] by SQUEEZE82,83 after removal of the solvent corresponds quite
(C69H96N6S3O3Ni3) C, 62.32; H, 7.28; N, 6.32.
closely to 1.5 CH2Cl2 and 1.5 EtOH molecules. Approximately
0.6 CH2Cl2 and 0.3 H2O molecules per complex can be found
and refined for [(habbi)Ni3]·CH2Cl2·H2O. Together with the
electron density found by SQUEEZE82,83 in the remaining
X-ray crystallography
The single-crystals were coated with oil and measured at low voids, 1 CH2Cl2 and 1 H2O molecules can be attributed to each
temperature on a Bruker Kappa APEX II diffractometer (four complex molecule. The solvent molecules of all structures, deter-
circle goniometer with 4 K CCD detector, Mo-Kα radiation, mined by the above described procedure, are, however, included
focussing graphite monochromator; ω- and φ-scans) ([(bertMe)- in the reported chemical formulae and derived quantities.
Ni3]·2toluene, [(bertt-Bu )Ni3]·1.5EtOH·1.5CH2Cl2), and a Bruker
The ligands in [(bertdien)Ni3](BPh4)3·3acetone and [(bertMe)-
2
X8-Prospector diffractometer (three circle goniometer with 4 K Ni3]·2toluene show partial disorder, which made it necessary
CCD detector, Cu-Kα radiation, IμS microfocus source with to restrain some distances in these ligand areas. Additionally,
multilayer optics) ([(bertdien)Ni3](BPh4)3·3acetone, [(habbi)- in [(habbi)Ni3]·CH2Cl2·H2O the C–Cl distances of the dis-
Ni3]·CH2Cl2·H2O). Empirical absorption corrections using ordered CH2Cl2 molecules were restrained.
equivalent reflections were performed using the program
Crystal data and further details concerning the crystal struc-
SADABS 2008/1.80 The structures were solved using the ture determination are given in Table 1. CCDC 901451 ([bert-
program SHELXS-9781 and refined using SHELXL-97.81
dien)Ni3](BPh4)3), CCDC 901452 ([bertMe)Ni3]), CCDC 901454
In preliminary refinements of [(bertdien)Ni3](BPh4)3 three ([(bertt-Bu )Ni3]), and CCDC 901455 ([(habbi)Ni3]) from the
acetone molecules per formula unit were found to be strongly Cambridge Crystallographic Data Center contain the sup-
disordered over approximately five positions. This is in good plementary crystallographic data for this contribution.
agreement with the number of electrons and the corres-
2
ponding void volume was found by SQUEEZE82,83 after
Other physical measurements
removal of the solvent molecules. Originally 1/3 toluene mole-
cule was found disordered in the asymmetric unit of [(bertMe)- Infrared spectra (400–4000 cm−1) of solid samples were
Ni3]·2toluene (one toluene molecule per complex), but it could recorded on a Shimadzu FTIR-8400S spectrometer as KBr
Table 1 Crystallographic data of compounds
[(bertdien)Ni3](BPh4)3
111H132B3N9Ni3O3S3
[(bertMe)Ni3]
[(bertt-Bu )Ni3]
[(habbi)Ni3]
2
Empirical formula
Formula weight
Crystal system
Space group
a/Å
b/Å
c/Å
C
C62H70N6Ni3O3S3
1219.55
C73.50H108Cl3N6Ni3O4.50S3
1526.32
C70H100Cl2N6Ni3O4S3
1432.77
1945.00
Monoclinic
P21/c
17.7065(11)
33.162(2)
17.0365(10)
90
90.034(3)
90
10 003.7(10)
100(2)
Trigonal
R3
21.4863(17)
21.4863(17)
27.386(3)
90
90
120
10 949.2(16)
100(2)
Triclinic
P1
Trigonal
R3
24.7936(5)
24.7936(5)
89.645(3)
90
90
120
47 724(2)
100(2)
ˉ
ˉ
12.1982(12)
13.1994(15)
24.094(3)
87.884(4)
83.960(4)
88.575(4)
3854.4(7)
100(2)
α/°
β/°
γ/°
V/Å3
T/K
Z
4
6
2
24
Crystal size/mm
Radiation type
μ/mm−1
0.35 × 0.21 × 0.13
CuKα
1.673
0.23 × 0.17 × 0.14
MoKα
0.887
0.5 × 0.08 × 0.05
MoKα
0.961
0.16 × 0.11 × 0.05
CuKα
2.529
ρ/g cm−3
1.291
1.026
1.315
1.196
Θ/range/°
2.50–70.00
89 035
18 244, 0.0355
15 267
18 244, 11, 1027
0.0687, 0.1914
0.0773, 0.1987
1.056
2.31–24.98
38 677
4282, 0.0716
2516
4282, 28, 196
0.0690, 0.1849
0.1097, 0.2093
1.046
2.50–25.00
37 519
13 195, 0.0662
8502
13 195, 0, 760
0.0653, 0.1611
0.1005, 0.1770
0.940
10.80–66.60
79 261
34 119, 0.1052
25 902
34 119, 45, 2074
0.0712, 0.1822
0.0928, 0.1971
1.023
0.004(16)
901455
Measured refl.
Unique refl., Rint
Observed refl. (I > 2σ(I))
Data, restraints, parameters
R1, wR2 (I > 2σ(I))
R1, wR2 (all data)
Goodness-of-fit on F2
Flack parameter
CCDC number
901451
901452
901454
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disks. ESI mass spectra were recorded on a Bruker Esquire
3000 ion trap mass spectrometer equipped with a standard ESI
source. MALDI TOF mass spectra were recorded using a PE
Results and discussion
Synthesis of ligands and complexes
Biosystems Voyager™ DE instrument. 1H and 13C NMR spectra The principal problem in the synthesis of the anticipated thio-
were measured on a Bruker DRX500 or a Bruker Avance III 300 triplesalen ligand is best illustrated by the fact that several
spectrometer using the solvent as an internal standard. complexes of the parent ligand thiosalen are known,84–88 but
Optical rotations were measured using a JASCO DIP-360 polari- the free thiosalen ligand is unstable since it forms bicyclic
meter. The electrochemical experiments were performed on dithiocin derivatives.85,89,90 Thus, a protected ligand precursor
Ar-flushed CH3CN solutions containing 0.1 M [NBu4]PF6 in a is usually used that becomes deprotected during the complex
classical three electrode cell. The working electrode was a plati- formation. A common route to NiII thiolate complexes is by
num electrode, the counterelectrode was a platinum wire and the use of tert-butyl protected sulfides as the starting
the reference electrode was Ag/0.01 M AgNO3–CH3CN. All material.91–96 In this respect, we reacted Rubin’s aldehyde 177
potentials are referenced to the ferrocenium/ferrocene (Fc+/Fc) (Scheme 2) with sodium tert-butylmercaptan and obtained the
couple used as an internal standard. The electrochemical cell trialdehyde 2. The reaction of 2 with half-unit 3 afforded the
was connected to an EG&G potentiostat/galvanostat (model protected thiotriplesalen ligand t-Bu3H3bertMe as a yellow
273 A).
solid. Unfortunately, employing the reaction conditions that
Scheme 2
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have been described for the deprotection in the literature triamine 9 resulted in the formation of the free ligand H3bert-
using Lewis acids like NiII 91–95 or using reductants like Na/ dien again contaminated with the thiourea byproduct 11.
NH3 97,98 afforded no pure products.
Although H3bertdien exhibits no hydrolytically labile terminal
Therefore, we tested other sulfur nucleophiles to introduce imine functions we were not able to find suitable conditions to
the sulfur functionality combined with its facile deprotection. isolate the free ligand. This might be associated with the quite
Sodium dithiocarbamate99 turned out to be the ideal sulfur strong interactions of the nine nitrogen donors with the SiO2
nucleophile to afford trialdehyde 476 (Scheme 2). We thus surface. However, it was again possible to use the crude product
reacted trialdehyde 4 with three equivalents of half-unit 3. without further purification for the reaction with Ni(OAc)2·4H2O
However, we could not isolate the expected triimine still and we obtained after addition of NaBPh4 [(bertdien)Ni3](BPh4)3
having three carbamate protecting groups. Instead, we in good yield. For electrochemical measurements we also pre-
obtained complicated mixtures of compounds. Using NMR, pared the BF4− salt [(bertdien)Ni3](BF4)3.
IR, and MS we could realize that imine condensation and car-
In order to obtain an extended thiophloroglucinol ligand,
bamate deprotection resulting in the thiourea byproduct 7 are which can be purified using column chromatography, i.e. con-
kinetically competing reactions. Thus, we then used six equi- taining neither a hydrolytically labile imine function nor a
valents of half-unit 3 resulting in the simultaneous nucleophi- basic N3 pendant arm, we employed the chiral saturated salan
lic cleavage and Schiff-base formation with the formation of half-unit 12102 in the reaction with 4. The resulting mixture of
H6bertMe and the thiourea byproduct 7. Analogously, we the ligand H6habbi and thiourea 13 can be purified by column
obtained the ligand H6bertt-Bu and the thiourea byproduct 8 chromatography to obtain the free ligand H6habbi.76 Reaction
2
starting from the half-unit 6.
of H6habbi with Ni(OAc)2·4H2O results in [(habbi)NiII3].
The ligands H6bertMe and H6bertt-Bu and their thiourea
byproducts exhibit similar solubilities. Moreover, by using
column chromatography for separation, the ketimine groups
2
Structural characterization
The structures of [(bertdien)NiII3](BPh4)3·3acetone, [(bertMe)-
in the ligands H6bertMe and H6bertt-Bu proved to be sensitive
2
II
NiII3]·2toluene,
[(bertt-Bu )Ni 3]·1.5EtOH·1.5CH2Cl2,
and
2
[(habbi)NiII3]·CH2Cl2·H2O were determined by single-crystal
X-ray diffraction. The molecular structures are displayed in
Fig. 1 (thermal ellipsoid plots are provided in Fig. S1 and S2†)
and selected interatomic distances are summarized in Table 2.
The structure of [(bertdien)Ni3]3+ exhibits the same disorder
against cleavage. Therefore, we applied the crude products
directly in the reaction with Ni(OAc)2·4H2O in ethanol to
II
afford the NiII complexes [(bertt-Bu )Ni 3] and [(bertMe)NiII3].
2
In order to obtain an extended thiophloroglucinol ligand
without terminal imine functions, which prevents the chromato-
graphic workup, we synthesized H3bertdien which requires the
triamine 9 (Scheme 2). Different synthetic procedures have
been published,100,101 but the described multi-step procedures
only provide unsatisfactory yields. We have thus developed a
simple and better yield procedure to afford triamine 9
(Scheme 2). The reaction of trialdehyde 4 with an excess of
phenomenon of one ethylene bridge which has already been
3+
observed in the oxygen analog [(felddien)NiII
]
(Fig. S3†).103
3
The asymmetric unit of [(habbi)NiII3]·CH2Cl2·H2O consists of
two trinuclear complexes (molecule 1: Ni1, Ni2, Ni3, and mole-
cule 2: Ni4, Ni5, Ni6) and of two times a third of a trinuclear
complex (molecule 3: Ni7 and molecule 4: Ni8). The whole
Table 2 Selected interatomic distances [Å]
[(habbi)Ni3]
[(bertMe)Ni3]
2.144(1)
[(bertt-Bu )Ni3]
[(bertdien)Ni3]3+
Molecule 1
Molecule 2a
Molecule 3a
2.127(2)
Molecule 4a
2.130(3)
2
Ni1–S11
Ni2–S21
Ni3–S31
Ni1–N11
Ni2–N21
Ni3–N31
Ni1–N12
Ni2–N22
Ni3–N32
Ni1–O12
Ni2–O22
Ni3–O32
Ni1–N13
Ni2–N23
Ni3–N33
S11–C1
2.146(1)
2.142(1)
2.140(1)
1.852(3)
1.839(4)
1.850(4)
1.870(4)
1.873(3)
1.879(3)
1.822(3)
1.833(3)
1.828(3)
2.124(1)
2.130(1)
2.119(1)
1.844(3)
1.829(3)
1.842(2)
1.951(3)
1.952(3)
1.935(3)
2.146(2)
2.119(2)
2.149(2)
1.814(5)
1.825(6)
1.828(6)
1.933(5)
1.928(5)
1.957(5)
1.827(4)
1.838(4)
1.854(5)
2.147(2)
2.133(2)
2.136(2)
1.817(5)
1.814(6)
1.842(5)
1.936(5)
1.942(5)
1.945(6)
1.846(5)
1.837(5)
1.851(5)
1.831(4)
1.883(4)
1.821(3)
1.818(5)
1.929(5)
1.831(4)
1.829(8)
1.963(8)
1.866(6)
1.979(3)
1.968(3)
1.975(2)
1.734(3)
1.731(3)
1.732(3)
1.740(5)
1.729(4)
1.731(4)
1.725(5)
1.732(6)
1.720(6)
1.747(7)
1.723(7)
1.711(7)
1.710(7)
1.726(6)
1.729(9)
S21–C3
S31–C5
a The labeling scheme has been adapted for molecules 2–4 of [(habbi)Ni3] to account for analogous atoms.
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II
II
Table 3 Selected structural properties of the nickel complexes [(felddien)NiII3](BF4)3,103 [(talent-Bu )Ni 3],9 [(bertMe)NiII3], [(bertt-Bu )Ni 3], [(bertdien)
2
2
NiII3](BPh4)3, and [(habbi)NiII
]
3
[(habbi)Ni3]
[(felddien)Ni3]3+ [(bertdien)Ni3)3+ [(bertMe)Ni3] [(bertt-Bu )Ni3] Molecule 1 Molecule 2 Molecule 3 Molecule 4
2
da [Å]
αb [°]
βc [°]
γd [°]
Ni1 0.43
Ni2 0.07
Ni3 0.13
Ni1 19.9
Ni2 4.4
Ni3 14.1
Ni1
Ni2
Ni3
Ni1
Ni2
0.72
0.52
0.49
19.2
16.7
16.7
0.52
17.2
11.9
25.0
17.6
2.4
−0.22
0.44
−0.40
13.5
13.5
19.7
14.6
15.0
22.7
16.1
1.8
1.02
0.54
0.70
35.7
22.1
22.2
36.0
31.9
30.1
20.8
25.0
17.5
33.2
25.1
23.8
0.92
0.71
0.86
34.3
25.4
29.0
37.4
18.2
32.4
23.7
32.6
17.2
33.1
25.5
26.5
0.92
31.8
36.9
18.7
29.5
0.90
31.8
35.8
22.4
30.0
Ni3
3.3
φ
cent e [°]
Ni1 13.9
Ni2 2.2
Ni3 8.1
17.3
16.4
20.9
21.3
16.5
23.6
1.4
φ
term f [°] Ni1
Ni2
Ni3
9.2
12.8
a d is the shortest distance of an NiII ion from the best plane formed by the six carbon atoms of the central benzene ring of the phloroglucinol
backbone. A negative value corresponds to a displacement to the other side of the plane. b α is the angle between the best planes of (1) N2O2(S)
and (2) benzene of the central phloroglucinol backbone. c β is the angle between the best planes of (1) N2O2(S) and (2) benzene of the terminal
phenolate. d γ is the angle between the best planes of (1) benzene of the central phloroglucinol backbone and (2) benzene of the terminal
phenolate. e Bent angle φcent = 180° − ∠(Ni–XNOcent–XRcent). f Bent angle φterm = 180° − ∠(Ni–XNOterm–XRterm).
trinuclear complexes are generated by C3 axes. Each structure with φcent ∼ 25–33°. However, this effect is mainly attributed to
contains trinuclear complexes in which one ligand coordinates the special diamine bridging unit in this complex.
to three NiII ions. All NiII ions are four-coordinate in a square-
Electrochemical characterization
planar coordination environment.
Trinuclear triplesalen complexes are known to exhibit
various degrees of ligand folding which results in an overall
bowl-shaped molecular structure for the trinuclear NiII and
The electrochemistry of the four new Ni3 complexes was
studied by means of cyclic and square-wave voltammetry. Due
II
to solubility reasons, [(bertt-Bu )Ni 3] and [(habbi)NiII3] have
2
CuII complexes of H6talent-Bu and we applied several para-
been measured in CH2Cl2, [(bertMe)NiII3] in C2H2Cl4, and
[(bertdien)NiII3](BF4)3 in CH3CN solutions. Representative
2
meters for
a
quantitative description of the ligand
folding9,12,33 which have also been determined for the com-
plexes within this study (Table 3). The bent angles φcent and
φterm turned out to be a good indicator of the ligand folding.
examples of the CVs and of the SWs as well as of [(felddien)-
103
NiII3](BF4)3
for comparison are provided in Fig. 2 and 3,
and redox potentials (all referenced vs. Fc+/Fc) are compiled in
Table 4.
The bent angle φ is defined by φ = 180° − ∠(M–XNO–XR) (XNO
:
The two trinuclear complexes [(felddien)NiII3](BF4)3 and
[(bertdien)NiII3](BF4)3 both exhibit three reductions, which
appear to be more reversible for [(felddien)NiII3](BF4)3 than for
[(bertdien)NiII3](BF4)3 (Fig. 2). These may be assigned to the
known reductions of NiII ions to NiI ions in related coordi-
nation environments.104,105 Comparing the potentials for
midpoint of adjacent N and O donor atoms; XR: midpoint of
the six-membered chelate ring containing the N and O donor
atoms).
3+
The previously reported complex [(felddien)NiII
]
provides
3
an opportunity to investigate the differences in ligand folding
by O vs. S substitution as it represents the exact O-analog to
[(bertdien)NiII3]3+.103 The comparison of mean values of φcent
these processes (Table 4), it is interesting to note that the
3+
3+
for [(bertdien)NiII
]
(∼18°) to [(felddien)NiII
]
3
(∼8°) indi-
3+
sulfur complex [(bertdien)NiII
]
is by 0.26–0.28 V easier to
3
3
reduce than the oxygen analog [(felddien)NiII3]3+. This reflects
some flexibility of thiolate ligands in charge donation com-
pared to their oxygen analogs so that the NiI ions are less
destabilized.106 In the oxidative region, only irreversible, less
resolved electron transfer processes are observed.
cates that the sulfur complex exhibits a more severe ligand
folding than its oxygen counterpart. As there is only O vs. S
substitution and no particular crystal packing effects are
evident, the stronger ligand folding in the sulfur complex
should be mainly due to electronic effects. Additionally, the
longer S–Ni and S–C bonds provide even more space in the
sulfur complex so that steric hindrance can be disregarded as
the reason for the stronger ligand folding. An even more pro-
Interestingly, the complexes with terminal phenolate
ligands exhibit no reductive electrochemistry but a rich oxi-
dative electrochemistry (Fig. 3). This reflects the stronger elec-
tron density donation by σ and π donation of the terminal
nounced central ligand folding is observed in [(habbi)NiII
]
3
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103
Fig. 2 CV and SW of (a) [(felddien)Ni3](BF4)3
and (b) [(bertdien)Ni3]-
(BF4)3 measured in CH3CN solution at 20 °C recorded at a platinum
working electrode. Scan rate 200 mV s−1
.
phenolates vs. pure σ donation of the terminal amines. The tri-
II
plesalen complex [(talent-Bu )Ni 3] exhibits three reversible oxi-
2
dative waves with the second wave being a not yet resolved two-
electron oxidation. Spectro-electrochemical measurements
revealed a complicated temperature-dependent equilibrium
between a metal-centered oxidation leading to a NiIII species
and a phenolate-centered oxidation leading to a coordinated
phenoxyl radical. However, the assignment of the oxidation to
the terminal or the central phenolate units was only tentative
at that stage.9
Fig. 3 CV and SW of (a) [(bertMe)Ni3] measured in C2H2Cl4 (solvent
II
The sulfur complex [(bertt-Bu )Ni 3] exhibits quite an analo- decomposition of C2H2Cl4 limits measurements to positive potential),
2
(b) [(bertt-Bu )Ni3] and (c) [(habbi)Ni3] all measured in CH2Cl2 solution at
2
gous electrochemical behavior as its oxygen analog [(talent-Bu )-
2
20 °C recorded at a platinum working electrode. Scan rate 200 mV s−1
.
NiII3]. The second oxidation is partially resolved in the SW,
which manifests its two-electron nature. Furthermore, these
II
oxidations in [(bertt-Bu )Ni 3] are at only slightly higher poten-
2
central phloroglucinol backbone but at the terminal Ni–
phenolate parts. A further argument for the assignment to the
oxidation of the terminal Ni–phenolate units arises from the
II
tials than in [(talent-Bu )Ni 3]. These closely related redox pro-
2
cesses indicate that these oxidations are not centered at the
Table 4 Electrochemical properties of the NiII complexes (E1/2 for processes exhibiting peaks in the forward and back scans, peak potentials for
processes, exhibiting no peak for the back scan (irr), presented in V vs. Fc+/Fc)
Oxidation
+1.53irr
Reduction
Ref.
[(felddien)Ni3](BF4)3
[(bertdien)Ni3](BF4)3
+1.27irr
+1.10irr
+1.00
−1.69
−1.42
−1.88
−1.62
−2.10
−1.82
103
This work
9
This work
This work
This work
[(talent-Bu )Ni3]
+0.55a
+0.22
+0.39irr
+0.33
+0.30
2
[(bertMe)Ni3]
+0.85irr
+0.61irr
[(bertt-Bu )Ni3]
+1.29irr
+1.16irr
+0.56/+0.51b
2
[(habbi)Ni3]
a Presumable 2 electron process which is not resolved. b Separation of two one-electron processes detected by SW.
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irreversibility of these redox waves in [(bertMe)NiII3] as it is well
Having the desired thiotriplesalen ligands in hand, we will
established that coordinated phenolates with tert-butyl groups evaluate their potential to optimize the SMM behavior of
in ortho and para positions can be reversibly oxidized, while a sulfur analogs of [Mt6Mc]n+ complexes. Furthermore, we will
methyl protection is not sufficient for the stabilization of the analyze in detail the differences in electronic structures of the
oxidized phenoxyl radical resulting in irreversible electron ligands and the complexes by the O–S substitution as well as
transfer processes.107–110 The complex [(habbi)NiII3] exhibits a their potential for a more efficient spin-polarization contri-
reversible oxidation at 0.30 V. As three terminal phenolate bution to the exchange interactions.
units are available, this electron transfer wave might even be a
three-electron oxidation without the splitting observed in
II
II
[(talent-Bu )Ni 3] and [(bertt-Bu )Ni 3], indicative of less elec-
tronic communications. The shape of the SW voltammogram
provides a further indication of a non-one-electron step.
2
2
Acknowledgements
Considering all data provided in Table 4 indicate that the This work was supported by the DFG (FOR945 ‘Nanomagnets:
triplesalen complexes with terminal phenolates can be oxi- from Synthesis via Interactions with Surfaces to Function’), the
dized in the 0.2 to 0.6 V region, which is assigned to the term- Fonds der Chemischen Industrie, and Bielefeld University. We
inal phenolates, while in the range above 1 V irreversible would like to thank Dr Andreas Mix (Bielefeld University) for
oxidative waves are observed for all compounds, implying that fruitful discussions on NMR spectroscopy.
the central backbone is oxidized. While all these processes are
irreversible in the Ni complexes, it should be emphasized that
3+
[(felddien)CuII
]
exhibits a reversible one-electron oxidation
3
at 0.80 V.103 Spectroelectrochemistry provided an increase of
absorption intensity around 26 800 cm−1, which is character-
istic of the formation of phenoxyl radicals.107–110 This com-
parison indicates that the potential and the reversibility for
the oxidation of the central phloroglucinol backbone are
metal-dependent.
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Conclusions
We have established a versatile procedure for the synthesis of
extended thiophloroglucinol ligands in general and thiotriple-
salen ligands in particular. Rubin’s aldehyde 1 is nucleophili-
cally substituted by three equivalents of dithiocarbamate to
obtain the tris(dithiocarbamate)trialdehyde 4. This can be
reacted with six equivalents of a primary amine resulting in a
simultaneous three-fold Schiff-base formation and three-fold
deprotection of the dithiocarbamate to obtain the free
trithiols, which are contaminated with three equivalents of a
thiourea derivative as the deprotection byproduct. This
thiourea byproduct could be removed for H6habbi, but not for
H3bertdien, H6bertMe, and H6bertt-Bu . However, reaction of the
2
pure ligand H6habbi or the mixtures of H3bertdien, H6bertMe
,
and H6bertt-Bu with NiII salts resulted in the formation of the
2
−
trinuclear NiII complexes [(bertdien)NiII3](X)3 (X = BPh4
,
3
BF4−) [(bertMe)NiII3], [(bertt-Bu )Ni 3], and [(habbi)NiII3] as evi-
denced by single-crystal X-ray diffraction. The molecular struc-
tures consist of square-plane coordinated NiII ions that are
bridged by a central thiophloroglucinol backbone.
II
2
Comparison of the molecular structures to those of their
oxygen analog phloroglucinol-bridged complexes reveals a
stronger ligand folding at the central Ni–S bond. The electro-
chemical analysis in conjunction with the oxygen-analogs
allows one to assign the reversible oxidations in the nickel
complexes of triplesalen and thiotriplesalen ligands to include
the terminal phenolate units and not the central backbone.
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