Bis(o-iminobenzosemiquinonato)metal Complexes
J. Am. Chem. Soc., Vol. 123, No. 10, 2001 2215
[CuII(LISQ)2] (3). To a solution of the ligand I (0.59 g; 2.0 mmol)
in acetonitrile (30 mL) was added at 40 °C a solid sample of anhydrous
CuICl (0.10 g; 1.0 mmol). Upon addition of 0.5 mL of NEt3 in the
presence of air the color of the solution changed to green. After heating
of the solution for 2 h to reflux, a dark green microcrystalline product
of 3 formed upon cooling which was collected by filtration. Yield:
0.55 g (84%). EI mass spectrum: m/z ) 653 {M - H}+ (100%) {M+}.
Anal. Calcd for C40H50N2O2Cu: C, 73.41;H, 7.70; N, 4.28; Cu, 9.71.
Found: C, 73.3; H, 7.6; N, 4.2; Cu, 9.8.
quinones or o-phenylenediamido(2-), o-diiminobenzosemi-
quinonates(1-), or o-diiminobenzoquinones.5,11 For simple
o-aminophenolates this has not been established previously
although some coordination chemistry of rather similar tert-
butyl-substituted phenoxazinolate semiquinone radicals has been
described by Pierpont and co-workers.5b,c
We describe here a series of complexes containing one, two,
or three O,N-coordinated o-iminobenzosemiquinonato(1-) ligands
(Scheme 1). We present evidence that the neutral, square planar
complexes [MII(LISQ)2] (MII ) Cu, Ni, Pd) and analogous
complexes of type A and B are diradicals with a singlet ground
state.
[NiII(LISQ)2] (4a) and [NiII(ClLISQ)2] (4b). Both compounds were
obtained by using the same procedure: To a solution of the ligand I or
II (2.0 mmol) in acetonitrile (30 mL) or methanol (30 mL) was added
Ni(NO3)2‚6H2O (0.291 g; 1.0 mmol) and 0.5 mL of NEt3. The solution
was heated to reflux in the presence of air for 1 h. Upon cooling, dark
green precipitates of 4a or 4b formed in ∼80% yield. The complexes
were recrystallized from a diethyl ether/methanol (3:1) mixture. Anal.
Calcd for C40H50N2O2Ni (4a): C, 73.97; H, 7.76; N, 4.31; Ni, 9.04.
Found: C, 73.9; H, 7.7; N, 4.3; Ni, 9.0. Calcd for C40H46Cl4N2O2Ni
Experimental Section
The synthesis of the ligand 1,4-dimethyl-1,4,7-triazacyclononane
(dmtacn) was performed according to a literature procedure.13
Preparation of the Ligands I and II. 2-Anilino-4,6-di-tert-
butylphenol (I) and 2-(3,5-dichloroanilino)-4,6-di-tert-butylphenol (II)
were prepared according to a slightly modified procedure described in
ref 12.
1
(4b): C, 61.02; H, 5.89; N, 3.56. Found: C, 60.9, H, 6.1; N, 3.3. H
NMR (400 MHz, CDCl3) of 4a: δ ) 1.03 (s, 18H), 1.06 (s, 18H),
6.46 (d, 2H), 6.88 (d, 2H), 7.38-7.55 (m, 10H). EI-MS of 4a: m/z )
648 {M - H}+ (100%).
[PdII(LISQ)2] (5). To a solution of the ligand I (0.59 g; 2.0 mmol) in
acetonitrile (50 mL) was added anhydrous PdCl2 (0.177 g; 1.0 mmol)
and 0.5 mL of NEt3 under an argon-blanketing atmosphere. The solution
was stirred at 20 °C for 30 min. and then heated to reflux for 20 min.
The solution was then exposed to air and stirred for 3-4 h at ambient
temperature. After storage of the solution at 0 °C for ∼12 h the green
precipitate of 5 was collected by filtration. Recrystallization from
CH3CN solution afforded X-ray-quality crystals. Yield: 0.4 g (60%).
Anal. Calcd for C40H50N2O2Pd: C, 68.90; H, 7.23; N, 4.02, Pd, 15.26.
Found: C, 68.2; H, 7.2; N, 4.3; Pd, 15.0. EI mass spectrum: m/z )
To a solution of 3,5-di-tert-butylcatechol (10 g; 45 mmol) and
triethylamine (0.6 mL) in n-heptane (30 mL) was added dropwise a
solution of aniline or 3,5-dichloroaniline (45 mmol) in n-heptane (15
mL). The resulting mixture was heated to reflux for 5 h. The suspension
was stored at 4 °C for 12 h after which time a white (brownish) solid
was collected by filtration, washed with cold n-heptane, and air-dried.
The compounds were recrystallized from n-hexane yielding colorless
crystalline materials. The yields were in both cases 80-85% based on
1
the starting catechol. H NMR (400 MHz, 300 K): I (CD2Cl2), δ )
1.28 (s, 9H), 1.46 (s, 9H), 4.99 (s, 1H), 6.3-7.05 (arom. H, 7H), mp
145-147 °C; II (CH3OH), δ ) 1.27 (s, 9H), 1.42 (s, 9H), 4.58 (1H),
6.5-7.2 (arom. protons, 5H). 13C {1H} NMR (100.6 MHz): I (CDCl3),
δ ) 29.52, 31.38, 34.35, 34.98, 115.0, 119.76, 121.49, 121.97, 127.73,
129.31, 135.28, 142.18, 146.78, 149.37; II (CH3OH), δ ) 30.11, 32.02,
35.17, 36.04, 113.58, 118.25, 122.16, 122.48, 128.81, 136.35, 137.75,
143.22, 150.34, 151.29. EI mass spectrum for I and II: m/z ) 297
[M+] and 365 [M - H]+, respectively. Anal. Calcd for C20H27NO: C,
80.76; H, 9.15; N, 4.71. Found: C, 80.4; H, 8.9; N, 4.5. To obtain the
electronic spectrum of the o-iminobenzoquinone derivative of I we have
oxidized I in CH2Cl2 solution (1 × 10-4 M) with an excess of
Pb(acetate)4 (5 × 10-4 M) at ambient temperature. The electronic
spectrum displays absorption maxima at λ ) 290 (sh) nm (ꢀ ) 5.8 ×
103 M-1 cm-1), 396 (4.8 × 103), and 488 sh (2.7 × 103).
1
696 {M - H}+ (100%). H NMR (400 MHz, CDCl3): δ ) 1.12 (s,
18H), 1.14 (s, 18H), 6.60 (d, 2H), 6.8 (br, 2H), 7.40-7.42 (m, 10H).
Physical Measurements. Electronic spectra of the complexes and
spectra of the spectroelectrochemical investigations were recorded on
a HP 8452A diode array spectrophotometer (range: 221-1100 nm).
Cyclic voltammograms, square-wave voltammograms, and coulometric
experiments were performed using an EG & G potentiostat/galvanostat.
Simulations of the cyclic voltammograms were obtained using the
program DigiSim 3.0 (Bioanalytical Systems, Inc., West Lafayette, IN).
Temperature-dependent (2-298 K) magnetization data were recorded
on a SQUID magnetometer (MPMS Quantum design) in an external
magnetic field of 1.0 T. The experimental susceptibility data were
corrected for underlying diamagnetism by the use of tabulated Pascal’s
constants.
X-band EPR spectra were recorded on a Bruker ESP 300 spectro-
meter. The spectra were simulated by iteration of the (an)isotropic g
values, hyperfine coupling constants, and line widths. We thank Dr. F.
Neese (Abteilung Biologie der Universita¨t Konstanz) for a copy of his
EPR simulation program. NMR experiments were carried out on a
Bruker ARX 250 (250 and 63 MHz for 1H and 13C NMR, respectively).
The internal shift reference for 1H NMR, with CHD2CN, is δH ) 1.94.
The internal shift reference for 13C NMR, with CD3CN, is δC ) 118.3.
Abbreviations used are the following: s ) singlet; d ) doublet; t )
triplet.
X-ray Crystallographic Data Collection and Refinement of the
Structures. A colorless single crystal of I, dark green crystals of 3
and 5, and black specimens of 2 and 4b were coated with perfluoro-
polyether, picked up with glass fibers, and mounted on diffractometers
equipped with a nitrogen cold stream at 100 K. Graphite-monochro-
mated Mo KR radiation (λ ) 0.710 73 Å) was used. Crystallographic
data of the compounds and diffractometer types used are listed in Table
1. Cell constants were obtained from a least-squares fit of the diffraction
angles of several thousand strong reflections. Intensity data were
corrected for Lorentz and polarization effects. Data sets of I, 2,and 4b
were corrected for absorption using the program SADABS,14 whereas
the intensities of 3 were left uncorrected. Crystal faces of 5 were
Preparation of Complexes. [CoIII(LISQ)3] (1). To a solution of the
ligand I (0.89 g; 3.0 mmol) in acetonitrile (30 mL) was added anhydrous
CoIICl2 (0.13 g; 1.0 mmol) and triethylamine (1.0 mL). The resulting
dark green solution was heated to reflux in the presence of air for 1 h.
Slow evaporation of the solvent within 2-3 d at ambient temperature
from the solution afforded deep brown crystals of 1. Yield: 0.61 g
(65%). Anal. Calcd for C60H75N3O3Co: C, 76.24; H, 7.99; N, 4.45;
Co, 6.23. Found: C, 76.1; H, 7.9; N, 4.3; Co, 6.3.
[CuII(dmtacn)(LISQ)]PF6 (2). A methanol solution (30 mL) of CuCl2‚
6H2O (0.170 g; 1.0 mmol) and 1,4-dimethyl-1,4,7-triazacyclononane
(0.156 g; 1.0 mmol) was stirred for 30 min at 20 °C after which time
the ligand I (0.3 g; 1.0 mmol) and NEt3 (0.5 mL) were added in the
presence of air. The color of the solution changed to dark green (almost
black). The solution was heated to ∼60 °C for 1 h. Addition of tetra-
n-butylammonium hexafluorophosphate (1.94 g; 5 mmol) initiated the
precipitation of dark green crystals of 2 within 2-3 d. Yield: ∼30%.
Anal. Calcd for C28H44CuF6N4OP: C, 50.86; H, 6.71; N, 8.47; Cu,
9.61. Found: C, 51.1; H, 6.7; N, 8.5; Cu, 9.7. Electrospray mass
spectrum (ESI) (CH3OH, positive ion): m/z ) 515.3 {[CuII(dmtacn)-
(LISQ)]+}.
(12) (a) Maslovskaya, L. A.; Petrikevich, D. K.; Timoshchuk, V. A.;
Shadyro, O. I. Russ. J. Gen. Chem. 1996, 66, 1842. Translated from: Zh.
Obsh. Khim. 1996, 66, 1893. (b) FRG Patent No. 1 104522, 1959; Chem.
Abstr. 1962, 56, 5887.
(13) Weisman, G. R.; Vachon, D. J.; Johnson, V. B.; Gronbeck, D. A.
J. Chem. Soc., Chem. Commun. 1987, 886.
(14) Sheldrick, G. M. SADABS; Universita¨t Go¨ttingen: Go¨ttingen,
Germany, 1994.