Substituent Effects of β-Diketiminate Ligands on the Structure and Physicochemical Properties of Copper(II) Complexes

Article abstract of DOI:10.1021/ic0344766

Substituent effects of β-diketiminate ligands on the structure and physicochemical properties of the copper(II) complexes have been systematically investigated by using 3-iminopropenylamine derivatives ^R1L ^R3H, R³-N=CH-C(R¹)=CH-NH-R³, where R¹ is Me, H, CN, or NO₂, and R³ is Ph, Mes (mesityl), Dep (2,6-diethylphenyl), Dipp (2,6-diisopropylphenyl), or Dtbp (3,5-di-tert-butylphenyl). When the ligands with R³ = Ph or Dtbp were treated with Cu^II(OAc)₂, bis(β-diketiminate) copper(II) complexes exhibiting distorted tetrahedral geometries were obtained, the crystal structures of which were nearly the same as each other regardless of the α-substituent (R¹); dihedral angles between the two β-diketiminate coordination planes are 62.5 ± 1.2°, and the Cu-N bond lengths are 1.959 ± 0.008 A. The distorted tetrahedral structures are maintained in solution, but the spectroscopic features, especially g_II values of the ESR spectra and the d-d bands of the absorption spectra, as well as the electrochemical behaviors of the complexes, are significantly affected by the electronic nature of R¹. The ligands with R³ = Mes and Dep, on the other hand, gave di(μ-hydroxo)dicopper(II) complexes, and their crystal structures as well as spectroscopic and electrochemical features have also been explored. Furthermore, the ligand with the more sterically encumbered aromatic substituent (Dipp) provided a mononuclear four-coordinate square planar copper(II) complex supported by one β-diketiminate ligand and one didentate acetate ion. Thus, the β-diketiminate ligands with a variety of substituents (R¹ and R³) have been explored to provide coordinatively unsaturated (four-coordinate) mononuclear and dinuclear copper(II) complexes with significantly different coordination geometry and properties.

Full text of DOI:10.1021/ic0344766

Inorg. Chem. 2003, 42, 8395−8405
Substituent Effects of â-Diketiminate Ligands on the Structure and
Physicochemical Properties of Copper(II) Complexes
Chizu Shimokawa,† Seiji Yokota,† Yoshimitsu Tachi,† Nagatoshi Nishiwaki,‡ Masahiro Ariga,‡ and
,†
Shinobu Itoh*
Department of Chemistry, Graduate School of Science, Osaka City UniVersity, 3-3-138 Sugimoto,
Sumiyoshi-ku, Osaka 558-8585, Japan, and Department of Chemistry, Osaka Kyoiku UniVersity,
4-698-1 Asahigaoka, Kashiwara, Osaka 582-8582, Japan
Received May 7, 2003
Substituent effects of â-diketiminate ligands on the structure and physicochemical properties of the copper(II)
3
complexes have been systematically investigated by using 3-iminopropenylamine derivatives R1LR3H, R sNdCHs
1
3
1
3
C(R )dCHsNHsR , where R is Me, H, CN, or NO , and R is Ph, Mes (mesityl), Dep (2,6-diethylphenyl), Dipp
2
3
(2,6-diisopropylphenyl), or Dtbp (3,5-di-tert-butylphenyl). When the ligands with R ) Ph or Dtbp were treated with
Cu (OAc)2, bis(â-diketiminate) copper(II) complexes exhibiting distorted tetrahedral geometries were obtained, the
crystal structures of which were nearly the same as each other regardless of the R-substituent (R ); dihedral
II
1
angles between the two â-diketiminate coordination planes are 62.5 ± 1.2°, and the Cu−N bond lengths are 1.959
± 0.008 Å. The distorted tetrahedral structures are maintained in solution, but the spectroscopic features, especially
g values of the ESR spectra and the d−d bands of the absorption spectra, as well as the electrochemical behaviors
|
1
3
of the complexes, are significantly affected by the electronic nature of R . The ligands with R ) Mes and Dep,
on the other hand, gave di(µ-hydroxo)dicopper(II) complexes, and their crystal structures as well as spectroscopic
and electrochemical features have also been explored. Furthermore, the ligand with the more sterically encumbered
aromatic substituent (Dipp) provided a mononuclear four-coordinate square planar copper(II) complex supported
by one â-diketiminate ligand and one didentate acetate ion. Thus, the â-diketiminate ligands with a variety of
1
3
substituents (R and R ) have been explored to provide coordinatively unsaturated (four-coordinate) mononuclear
and dinuclear copper(II) complexes with significantly different coordination geometry and properties.
Chart 1
Introduction
â-Diketiminate derivatives function as monoanionic di-
dentate ligands (Chart 1), which have been applied to the
synthesis of a wide variety of transition metal, main group
element, and lanthanide complexes.1 Particular attention has
recently been focused on the roles of â-diketiminate com-
plexes as polymerization catalysts, novel organometallic
compounds, and active site models for metalloenzymes.1 In
these studies, sterically encumbered â-diketiminate ligands
with a bulky aromatic N-substituent (R3 in Chart 1) such as
2,6-diisopropylphenyl (Dipp) have been employed in order
to make the complexes as mononuclear and/or coordinatively
unsaturated.1 However, the substituent pattern of the ligand
framework is rather limited to R1 ) H and R2 ) Me, since
most of the ligands are prepared by the condensation reaction
between commercially available acetylacetone (acac) and
aniline derivatives.2
In order to control the coordination chemistry as well as
the reactivity of â-diketiminate complexes, many recent
efforts have been focused on the substituent effects of the
carbon framework.3-5 The bulky alkyl substituent such as
tert-butyl group at the â-position (R2 in Chart 1) has been
shown to exhibit steric effects on the conformation of
aromatic substituents R3 (torsion angle between the aromatic
* Corresponding author. E-mail: shinobu@sci.osaka-cu.ac.jp.
† Osaka City University.
‡ Osaka Kyoiku University.
(1) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. ReV. 2002,
102, 3031-3065.
10.1021/ic0344766 CCC: $25.00 © 2003 American Chemical Society
Published on Web 11/14/2003
Inorganic Chemistry, Vol. 42, No. 25, 2003 8395

Shimokawa et al.
ring of R3 and the coordination plane of the â-diketiminate
ligand) and on the bite angle of the didentate ligands. Those
steric factors have been shown to induce significant effects
on the structure and reactivity of the â-diketiminate com-
plexes.3 On the other hand, Coates and co-workers have
recently demonstrated that introduction of electron-with-
drawing substituents such as -CN and -CF3 into the carbon
framework improves the catalytic efficiency of the zinc(II)
complexes in the CO2/epoxide copolymerization reaction and
the ring opening polymerization of â-lactones.4 Furthermore,
a nitro group at the R-position (R1) has been demonstrated
to act as a bridging ligand to construct a novel linear polymer
complex of copper(I).5 Thus, further ligand modifications
may have great potential in expanding the chemistry of
â-diketiminate complexes. However, systematic studies on
the substituent effects both of the ligand framework and of
the N-aryl group have yet to be reported.
Chart 2
been employed for the synthesis of copper(II) complexes in
order to get insights into the electronic effects of R1 on the
structures and physicochemical properties of the complexes.
Moreover, steric effects of the N-aryl groups have also been
examined using different aromatic groups (R3 ) Ph, Mes,
Dep, Dipp, Dtbp, see Chart 2) to demonstrate that the N-aryl
group significantly influences the structure of the resulting
copper(II) complexes.
In this study, a series of â-diketiminate ligands carrying a
different R-substituent (R1 ) Me, H, CN, and NO2) have
(2) Some of the recent works dealing with â-diketiminate ligands derived
from acac (R1 ) H, R2 ) Me in Chart 1): (a) Holland, P. L.; Tolman,
W. B. J. Am. Chem. Soc. 2000, 122, 6331-6332. (b) Cheng, M.;
Moore, D. R.; Reczek, J. J.; Chamberlain, B. M.; Lobkovsky, E. B.;
Coates, G. W. J. Am. Chem. Soc. 2001, 123, 8738-8749. (c) Panda,
A.; Stender, M.; Wright, R. J.; Olmstead, M. M.; Klavins, P.; Power,
P. P. Inorg. Chem. 2002, 41, 3909-3916. (d) Eckert, N. A.; Bones,
E. M.; Lachicotte, R. J.; Holland, P. L. Inorg. Chem. 2003, 42, 1720-
1725. (e) Fekl, U.; Goldberg, K. I. J. Am. Chem. Soc. 2002, 124,
6804-6805. (f) Stender, M.; Wright, R. J.; Eichler, B. E.; Prust, J.;
Olmstead, M. M.; Roesky, H. W.; Power, P. P. J. Chem. Soc., Dalton
Trans. 2001, 3465-3469. (g) Jancik, V.; Peng, Y.; Roesky, H. W.;
Li, J.; Neculai, D.; Neculai, A. M.; Herbst-Irmer, R. J. Am. Chem.
Soc. 2003, 125, 1452-1453. (h) Gibson, V. C.; Segal, J. A.; White,
A. J. P.; Williams, D. J. J. Am. Chem. Soc. 2000, 122, 7120-7121.
(i) Stender, M.; Eichler, B. E.; Hardman, N. J.; Power, P. P.; Prust,
J.; Noltemeyer, M.; Roesky, H. W. Inorg. Chem. 2001, 40, 2794-
2799. (j) Willems, S. T. H.; Budzelaar, P. H. M.; Moonen, N. N. P.;
de Gelder, R.; Smits, J. M. M.; Gal, A. W. Chem. Eur. J. 2002, 8,
1310-1320. (k) MacAdams, L. A.; Kim, W.-K.; Liable-Sands, L. M.;
Guzei, I. A.; Rheingold, A. L.; Theopold, K. H. Organometallics 2002,
21, 952-960. (l) Ding, Y.; Ma, Q.; Uso´n, I.; Roesky, H. W.;
Noltemeyer, M.; Schmidt, H.-G. J. Am. Chem. Soc. 2002, 124, 8542-
8543. (m) Yao, Y.; Zhang, Y.; Shen, Q.; Yu, K. Organometallics 2002,
21, 819-824. (n) Burford, N.; Ragogna, P. J.; Robertson, K. N.;
Cameron, T. S.; Hardman, N. J.; Power, P. P. J. Am. Chem. Soc. 2002,
124, 382-383. (o) Cui, C.; Ko¨lpke, S.; Herbst-Irmer, R.; Roesky, H.
W.; Noltemeyer, M.; Schmidt, H.-G.; Wrackmeyer, B. J. Am. Chem.
Soc. 2001, 123, 9091-9098.
(3) (a) Budzelaar, P. H. M.; van Oort, A. B.; Orpen, A. G. Eur. J. Inorg.
Chem. 1998, 1485-1494. (b) Jazdzewski, B. A.; Holland, P. L.; Pink,
M.; Young, V. G., Jr.; Spencer, D. J. E.; Tolman, W. B. Inorg. Chem.
2001, 40, 6097-6107. (c) Spencer, D. J. E.; Aboelella, N. W.;
Reynolds, A. M.; Holland, P. L.; Tolman, W. B. J. Am. Chem. Soc.
2002, 124, 2108-2109. (d) Aboelella, N. W.; Lewis, E. A.; Reynolds,
A. M.; Brennessel, W. W.; Cramer, C. J.; Tolman, W. B. J. Am. Chem.
Soc. 2002, 124, 10660-10661. (e) Spencer, D. J. E.; Reynolds, A.
M.; Holland, P. L.; Jazdzewski, B. A.; Duboc-Toia, C.; Le Pape, L.;
Yokota, S.; Tachi, Y.; Itoh, S.; Tolman, W. B. Inorg. Chem. 2002,
41, 6307-6321. (f) Smith, J. M.; Lachicotte, R. J.; Holland, P. L.
Chem. Commun. 2001, 1542-1543. (g) Smith, J. M.; Lachicotte, R.
J.; Pittard, K. A.; Cundari, T. R.; Lukat-Rodgers, G.; Rodgers, K. R.;
Holland, P. L. J. Am. Chem. Soc. 2001, 123, 9222-9223. (h) Bailey,
P. J.; Coxall, R. A.; Dick, C. M.; Fabre, S.; Parsons, S. Organometallics
2001, 20, 798-801. (i) Caro, C. F.; Hitchcock, P. B.; Lappert, M. F.
Chem. Commun. 1999, 1433-1434. (j) Hayes, P. G.; Piers, W. E.;
Lee, L. W. M.; Knight, L. K.; Parvez, M.; Elsegood, M. R. J.; Clegg,
W. Organometallics 2001, 20, 2533-2544. (k) Hayes, P. G.; Piers,
W. E.; McDonald, R. J. Am. Chem. Soc. 2002, 124, 2132-2133.
(4) (a) Allen, S. D.; Moore, D. R.; Lobkovsky, E. B.; Coates, G. W. J.
Am. Chem. Soc. 2002, 124, 14284-14285. (b) Moore, D. R.; Cheng,
M.; Lobkovsky, E. B.; Coates, G. W. Angew. Chem., Int. Ed. 2002,
41, 2599-2602.
Experimental Section
General. Reagents and solvents used in this study except the
ligands and the complexes were commercial products of the highest
available purity and were further purified by the standard methods,
if necessary.6 Ligands MeLPhH and HLPhH and their copper(II)
complexes were prepared according to the reported procedures.7,8
1-Methyl-5-nitro-1H-pyrimidin-2-one (1) was prepared according
to the reported methods.9 FT-IR spectra were recorded with a
Shimadzu FTIR-8200PC. Mass spectra were recorded with a JEOL
1
JMS-700T Tandem MS station. H NMR spectra were recorded
on a JEOL LMN-ECP300WB or a LMX-GX400. ESR measure-
ments were performed of frozen THF solutions on the copper(II)
complexes using a JEOL JES-ME spectrometer at -150 °C
equipped with a variable temperature cell holder. Electronic spectra
were measured using a Hewlett-Packard HP8453 diode array
spectrophotometer or a Hitachi U-3500L spectrophotometer. The
λmax and ꢀ values were determined by spectral resolution with
Gaussian functions using Igor Pro software (version 4, Hulinks).
Elemental analyses were recorded with a Perkin-Elmer or a Fisons
instruments EA1108 Elemental Analyzer.
X-ray Structure Determination. The single crystal was mounted
on a glass-fiber. X-ray diffraction data were collected by a Rigaku
RAXIS-RAPID imaging plate two-dimensional area detector using
graphite-monochromated Mo KR radiation (λ ) 0.71069 Å) to 2θmax
of 55.0°. All the crystallographic calculations were performed using
Crystal Structure software package of the Molecular Structure
Corporation (version 2.0 and 3.1). The crystal structures were solved
by the direct methods and refined by the full-matrix least-squares
using SIR-92 or SHELX97. All non-hydrogen atoms and hydrogen
atoms were refined anisotropically and isotropically, respectively.
(5) Yokota, S.; Tachi, Y.; Nishiwaki, N.; Ariga, M.; Itoh, S. Inorg. Chem.
2001, 40, 5316-5317.
(6) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of
Laboratory Chemicals, 4th ed.; Pergamon Press: Elmsford, NY, 1996.
(7) Klimko, V. T.; Skoldinov, A. P. Zh. Obshch. Khim. 1959, 29, 4027-
4029.
(8) Tsybina, N. M.; Vinokurov, V. G.; Protopopova, T. V.; Skoldinov,
A. P. J. Gen. Chem. USSR 1966, 36, 1383-1385.
(9) Nishiwaki, N.; Tohda, Y.; Ariga, M. Bull. Chem. Soc. Jpn. 1996, 69,
1997-2002.
8396 Inorganic Chemistry, Vol. 42, No. 25, 2003

â-Diketiminate Cu(II) Complexes
Atomic coordinates, thermal parameters, and intramolecular bond
distances and angles are deposited in the Supporting Information
as in CIF file format.
solution containing CNLDepH. IR (KBr): 3110 (NH), 2201 (CtN),
1638 (CdN) cm-1. 1H NMR (CDCl3, 400 MHz): δ 1.17 (t, 12 H,
J ) 7.6 Hz, CH3), 2.59 (q, 8 H, J ) 7.6 Hz, CH2), 7.10-7.16 (m,
6 H, aromatic H of Ar group), 7.69 (s, 2 H, CH), 12.40 (br, 1 H,
NH). HRMS (EI+): m/z 359.2376, calcd for C24H29N3 359.2361.
Anal. Calcd for C24H29N3: C, 80.18; H, 8.13; N, 11.69. Found: C,
80.01; H, 8.14; N, 11.67.
Electrochemical Measurement. The cyclic voltammetry was
performed on an ALS electrochemical analyzer CHI-630A in
deaerated THF containing 0.10 M n-Bu4NClO4 as supporting
electrolyte. The Pt electrode was polished with BAS polishing
alumina suspension, rinsed with THF, and dried before use. The
counter electrode was a platinum wire. The measured potentials
were recorded with respect to a Fc/Fc+ (2.0 × 10-3 M) reference
electrode. All electrochemical measurements were carried out under
an atmospheric pressure of Ar in a glovebox.
2-Cyano-N-(2,6-diisopropylphenyl)-3-(2,6-diisopropylphenyl)-
amino-2-propeneimine (CNLDippH). This compound was prepared
in a similar manner described for the synthesis of CNLPhH by using
2,6-diisopropylaniline instead of aniline in a 29% isolated yield.
In this case, the reaction of 2,6-diisopropylaniline was carried out
for 96 h. IR (KBr): 3190 (NH), 2210 (CtN), 1647 (CdN) cm-1
.
Theoretical Calculations. The heat of formation (∆Hf) values
1H NMR (CDCl3, 400 MHz): δ 1.20 (d, 24 H, J ) 6.8 Hz, CH3),
3.07 (septet, 4 H, J ) 6.8 Hz, CH), 7.16-7.24 (m, 6 H, aromatic
H of Ar group), 7.66 (s, 2 H, CH), 12.47 (br, 1 H, NH). HRMS
(EI+): m/z 415.2966, calcd for C28H37N3 415.2987. Anal. Calcd
for C28H37N3: C, 80.92; H, 8.97; N, 10.11. Found: C, 80.80; H,
Ar
of NO L H were calculated using the PM3 semiempirical molecular
2
orbital method.10 The calculations were performed using the CAChe
program version 3.2. Final geometries and energetics were obtained
by optimizing the total molecular energy with respect to all
structural variables.
8.94; N, 10.12.
Synthesis. 2-Cyano-N-phenyl-3-phenylamino-2-propeneimine
Ph
2-Nitro-N-phenyl-3-phenylamino-2-propeneimine (NO L H).
2
(
CNLPhH). This compound was prepared by the reported method
Aniline (2.33 g, 25 mmol) was added into a methanol solution (150
by Noguchi and co-workers as follows.11 To a solution of 1,3,3-
tributoxy-2-cyanopropene (50.1 wt % in butanol, 10 mL, 15 mmol)
was added water (10 mL) and concentrated hydrochloric acid (5
mL), and the mixture was stirred at room temperature for 48 h.
The reaction mixture was extracted with methylene chloride (50
mL × 3), and the combined organic layer was dried over anhydrous
MgSO4. Removal of the solvent by evaporation gave an orange
liquid, to which a methanol solution (30 mL) of aniline (2.79 g, 30
mmol) was added. After refluxing the mixture for 24 h, removal
of the volatile organic material under reduced pressure gave a brown
oily material, from which CNLPhH was isolated in a 29% yield by
SiO2 column chromatography by using chloroform as an eluent.
IR (KBr): 3080 (NH), 2208 (CtN), 1641 (CdN) cm-1. 1H NMR
(CDCl3, 300 MHz): δ 7.15 (d, 4 H, J ) 7.5 Hz, aromatic o-proton
of Ph), 7.22 (t, 2 H, J ) 7.5 Hz, aromatic p-proton of Ph), 7.40 (t,
4 H, J ) 7.5 Hz, aromatic m-proton of Ph), 8.07 (s, 2 H, CH),
13.20 (br, 1 H, NH). HRMS (EI+): m/z 247.1100, calcd for
C16H13N3 247.1109. Anal. Calcd for C16H13N3: C, 77.35; H, 5.21;
N, 16.88. Found: C, 77.71; H, 5.30; N, 16.99.
2-Cyano-N-mesityl-3-mesitylamino-2-propeneimine (CNLMesH).
This compound was prepared in a similar manner described for
the synthesis of CNLPhH by using 2,4,6-trimethylaniline instead of
aniline in a 47% isolated yield. In this case, the reaction of 2,4,6-
trimethylaniline was carried out for 48 h. Single crystals suitable
for X-ray crystallographic analysis were obtained by slow diffusion
of liquid methanol into a chloroform solution containing CNLMesH.
IR (KBr): 3070 (NH), 2202 (CtN), 1644 (CdN) cm-1. 1H NMR
(CDCl3, 400 MHz): δ 2.19 (s, 12 H, CH3), 2.28 (s, 6 H, CH3),
6.90 (s, 4 H, aromatic H of mesityl group), 7.67 (s, 2 H, CH),
12.38 (br, 1 H, NH). HRMS (EI+): m/z 331.2046, calcd for
C22H25N3 331.2048. Anal. Calcd for C22H25N3: C, 79.72; H, 7.60;
N, 12.68. Found: C, 79.66; H, 7.67; N, 12.65.
mL) of 1-methyl-5-nitro-1H-pyrimidin-2-one (1) (1.86 g, 12 mmol).
The mixture was refluxed for 24 h. After the reaction, evaporation
NO2 Ph
of the solvent gave a brown oily material, from which
L H
was isolated in a 52% yield by flash SiO2 column chromatography
with chloroform as an eluent. IR (KBr): 3080 (NH), 1645 (CdN),
1
1565, 1317, 1282 (NO2) cm-1. H NMR (CDCl3, 300 MHz): δ
7.23-7.30 (m, 6H, aromatic proton of Ph), 7.45 (t, 4H, J ) 8.0
Hz, aromatic m-proton of Ph), 9.15 (s, 2H, CH), 13.64 (br, 1H,
NH). HR-MS (EI+): m/z 267.0990, calcd for C15H13N3O2 267.1008.
Anal. Calcd for C15H13N3O2: C, 67.41; H, 4.90; N, 15.72. Found:
C, 67.24; H, 4.84; N, 15.67.
N-Mesityl-3-mesitylamino-2-nitro-2-propeneimine (NO
L
MesH).
2
2,4,6-Trimethylaniline (850 mg, 6.3 mmol) was treated with
compound 1 (510 mg, 3.3 mmol) in refluxing methanol (40 mL)
for 4 days. Removal of volatile organic materials under reduced
NO2
pressure gave a brown oily material, from which
L
MesH was
isolated in a 27% yield by SiO2 column chromatography with
chloroform as an eluent. Single crystals suitable for X-ray crystal-
lographic analysis were obtained by slow diffusion of liquid
NO2
methanol into a chloroform solution containing
L
MesH. IR
(KBr): 3100 (NH), 1640 (CdN), 1574, 1305, 1291, 1272 (NO2)
cm-1. 1H NMR (CDCl3, 300 MHz): δ 2.22 (s, 12H, CH3), 2.29 (s,
6H, CH3), 6.93 (s, 4H, aromatic H of Ar group), 8.75 (s, 2H, CH),
12.77 (br, 1H, NH). HRMS (EI+): m/z 351.1957, calcd for
C21H25N3O2 351.1947. Anal. Calcd for C21H25N3O2: C, 71.77; H,
7.17; N, 11.96. Found: C, 71.79; H, 7.21; N, 11.75.
N-(3,5-Di-tert-butylphenyl)-3-(3,5-di-tert-butylphenyl)amino-
L
2-nitro-2-propeneimine (NO DtbpH). 3,5-Di-tert-butylaniline (821
2
mg, 4.0 mmol) in methanol (20 mL) was added to a methanol
solution (20 mL) of 1 (310 mg, 2.0 mmol), and the solution was
refluxed for 2 days. The resulting precipitates were collected by
NO2
filtration to give
L
DtbpH in 45% yield. Single crystals suitable
2-Cyano-N-(2,6-diethylphenyl)-3-(2,6-diethylphenyl)amino-2-
propeneimine (CNLDepH). This compound was prepared in a similar
manner described for the synthesis of CNLPhH by using 2,6-
diethylaniline instead of aniline in a 35% isolated yield. In this
case, the reaction of 2,6-diethylaniline was carried out for 48 h.
Single crystals suitable for X-ray crystallographic analysis were
obtained by slow diffusion of liquid methanol into a chloroform
for X-ray crystallographic analysis were obtained by slow diffusion
NO2
of liquid methanol into a CH2Cl2 solution containing
IR (KBr): 3100 (NH), 1648 (CdN), 1564, 1295, 1274 (NO2) cm-1
L
DtbpH.
.
1H NMR (CDCl3, 300 MHz): δ 1.36 (s, 36H, CH3), 7.09 (s, 4H,
aromatic H of Ar group), 7.35 (s, 2H, aromatic H of Ar group),
9.15 (s, 2H, CH), 13.92 (br, 1H, NH). HRMS (EI+): m/z 491.3504,
calcd for C31H45N3O2 491.3512. Anal. Calcd for C31H45N3O2: C,
75.72; H, 9.22; N, 8.55. Found: C, 75.48; H, 9.27; N, 8.60.
[CuII(CNLPh)2]. Ligand CNLPhH (49.5 mg, 0.2 mmol) in meth-
anol (10 mL) was added into a methanol solution (10 mL) of
(10) Stewart, J. J. P. J. Comput. Chem. 1989, 10, 209, 221-264.
(11) Takamura, S.; Yoshimiya, T.; Kameyama, S.; Nishida, A.; Yamamoto,
H.; Noguchi, M. Synthesis 2000, 5, 637-639.
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Shimokawa et al.
CuII(OAc)2‚H2O (20.0 mg, 0.1 mmol), and the mixture was stirred
for 1 h at room temperature. The resulting precipitates were
collected by filtration and dried to obtain green powder in 94%
yield. Single crystals suitable for X-ray crystallographic analysis
were obtained by slow diffusion of liquid methanol into a
chloroform solution containing the complex. IR (KBr): 2205 (Ct
N), 1605 (CdN) cm-1. HRMS (FAB+): m/z 556.1440, calcd for
C32H25CuN6 556.1436. Anal. Calcd for C32H24CuN6: C, 69.11; H,
4.35; N, 15.11. Found: C, 69.07; H, 4.27; N, 14.98.
Scheme 1
Scheme 2
[CuII CNLMes)2(µ-OH)2]. Ligand CNLMesH (33.1 mg, 0.1 mmol)
(
2
in methanol (10 mL) was added into a methanol solution (10 mL)
of CuII(OAc)2‚H2O (20.0 mg, 0.1 mmol). After addition of
triethylamine (0.1 mmol), the mixture was refluxed for 48 h. The
resulting precipitates were collected by filtration and dried to obtain
brown powder in 73% yield. Single crystals suitable for X-ray
crystallographic analysis were obtained by vapor diffusion of ether
into a CH2Cl2 solution of the complex. IR (KBr): 3650 (µ-OH),
2203 (CtN), 1616 (CdN) cm-1. HRMS (FAB+): m/z 803.2558,
calcd for C44H49Cu2N6O ([(CuIIL)2(µ-OH)]+) 803.2559. Anal. Calcd
for C44H50Cu2N6O2: C, 64.29; H, 6.13; N, 10.22. Found: C, 64.26;
H, 6.13; N, 10.15.
NO2
[CuII
(
2
L L
Mes)2(µ-OH)2]. Ligand NO MesH (35.4 mg, 0.1 mmol)
2
suspended in methanol (10 mL) was added to CuII(OAc)2‚H2O (20.0
mg, 0.1 mmol) in CH3OH (10 mL) at 60 °C. Then, the mixture
was refluxed for 24 h. Removal of the solvent gave brown material,
from which the dicopper complex was isolated by recrystallization
from CH2Cl2/hexane as purple microcrystals in a 95% yield. IR
(KBr) 3640 (µ-OH), 1612 (CdN), 1603, 1531, 1477, 1373, 1299
(NO2) cm-1. MS (FAB+) m/z 845.4 ([(CuL)2(µ-OH)]+). Anal. Calcd
for C42H50N6O6Cu2: C, 58.52; H, 5.85; N, 9.75. Found: C, 58.27;
H, 5.82; N, 9.62.
[CuII CNLDep)2(µ-OH)2]. This compound was prepared in a
(
2
similar manner described for the synthesis of [CuII CNLMes)2(µ-
(
2
OH)2] as brown powder in 73%. Single crystals suitable for X-ray
crystallographic analysis were also obtained by vapor diffusion of
ether into a CH2Cl2 solution of the complex. IR (KBr): 3650 (µ-
OH), 2201 (CtN), 1616 (CdN) cm-1. HRMS (FAB+): m/z
877.3287, calcd for C48H59Cu2N6O2 877.3491. Anal. Calcd for
C48H58Cu2N6O2: C, 65.65; H, 6.66; N, 9.57. Found: C, 65.64; H,
6.66; N, 9.55.
Results and Discussion
Ligand Synthesis and Characterization. Ligands MeLPhH
and LPhH were prepared according to the reported proce-
H
dures.7 The cyano derivatives CNLArH (Ar ) aryl group) were
[CuII(CNLDipp)(AcO)]. Ligand CNLDippH (41.6 mg, 0.1 mmol) in
methanol (10 mL) was added into a methanol solution (10 mL) of
CuII(OAc)2‚H2O (20.0 mg, 0.1 mmol). After addition of triethyl-
amine (0.1 mmol), the mixture was refluxed for 48 h. The mixture
was then concentrated and redissolved into 3 mL of methanol. The
methanol solution was poured into ether (50 mL) to give green
precipitates, which were collected by filtration and dried (77%).
Single crystals suitable for X-ray crystallographic analysis were
also obtained by vapor diffusion of ether into a CH2Cl2 solution of
the complex. IR (KBr): 2185 (CtN), 1616 (CdN) cm-1. HRMS
(FAB+): m/z 478.2294, calcd for C28H37CuN3 ([CuIIL]+) 478.2283.
Anal. Calcd for C30H39CuN3O2: C, 67.08; H, 7.32; N, 7.82.
Found: C, 67.31; H, 7.43; N, 7.67.
synthesized by following Noguchi’s procedure with a little
modification (Scheme 1).11 The nitro derivatives NO L H (Ar
) aryl group), on the other hand, were obtained from the
reaction between 1-methyl-5-nitro-1H-pyrimidin-2-one (1)
and the aniline derivatives (Scheme 2).9 Crystal structures
of CNLMesH, CNLDepH,
Ar
2
NO2
NO2
L
MesH, and
L
DtbpH have been
solved as shown in Figure 1, and their crystallographic data
and selected bond length, bond angles, and angles of the
least-squares planes are presented in Tables 1 and 2.
In the previous paper by Nishiwaki et al., the products of
the reaction between 1 and amines were assigned as diimine
derivatives A shown in Scheme 3. This assignment was based
on magnetic equivalence of the two â-protons on the carbon
framework as well as the two N-aromatic substituents in the
Ph
NO2 Ph
[CuII(NO L )2]. Ligand
L H (53.3 mg, 0.2 mmol) in meth-
2
anol (10 mL) was added into a methanol solution (10 mL) of
CuII(OAc)2‚H2O (20.0 mg, 0.1 mmol), and the mixture was stirred
for 1 h at room temperature. The resulting precipitates were then
collected by filtration and dried to obtain green powder in 88%
yield. Single crystals suitable for X-ray crystallographic analysis
were obtained by slow diffusion of liquid methanol into a CH2Cl2
solution containing the complex. IR (KBr) 1600 (CdN), 1582,
1530, 1490, 1483, 1315, 1274 (NO2) cm-1. HRMS (FAB+): m/z
556.1216, calcd for C30H25CuN6O4 596.1255. Anal. Calcd for
C30H24N6O4Cu: C, 60.45; H, 4.06; N, 14.10. Found: C, 60.06; H,
3.95; N, 13.99.
1H and 13C NMR spectra (for the definition of â-proton, see
Chart 1).9 Structural refinement of
L H in the X-ray
NO2 Ar
analysis [parts c and d in Figure 1], however, has unambigu-
ously indicated that the compounds exist mainly as 3-imino-
2-nitropropenylamine derivatives B (Scheme 3). The disso-
ciable proton of each compound was found to be associated
with one of the nitrogen atoms N(1), and the bond distances
of C(1)-C(3) (1.451(4) and 1.436(3) Å for Ar ) Mes and
Dtbp, respectively) and C(2)-N(1) (1.308(5) and 1.317(3)
Å) are longer than those of C(1)-C(2) (1.420(5) and 1.389
(3) Å) and C(3)-N(2) (1.285(4) and 1.283(3) Å), respec-
tively (see, Table 2). Semiempirical molecular orbital calcu-
lations (PM3) of the compounds indicated that form B is
much more stable than form A; ∆Hf values follow for
[CuII(NO
L
Dtbp)2]. This compound was obtained in a similar
2
manner described for the synthesis of [CuII(NO L )2] as green
powder in 95% yield. Single crystals suitable for X-ray crystal-
lographic analysis were obtained by slow diffusion of liquid
methanol into a CH2Cl2 solution containing the complex. IR (KBr)
1595 (CdN), 1529, 1486, 1364, 1282 (NO2) cm-1. MS (FAB+):
m/z 1044.7 ([CuIIL2 + H]+). Anal. Calcd for C62H90N6O4Cu: C,
71.26; H, 8.49; N, 8.04. Found: C, 71.07; H, 8.53; N, 8.02.
Ph
2
NO2 Ar
L H: Ar ) Ph, form A, 85.7 kcal/mol, form B, 69.4
kcal/mol; Ar ) Mes, form A, 38.5 kcal/mol, form B, 29.5
8398 Inorganic Chemistry, Vol. 42, No. 25, 2003

â-Diketiminate Cu(II) Complexes
Figure 1. ORTEP drawings of (a) CNLMesH (molecule 1), (b) CNLDepH, (c) NO
MesH, and (d) NO DtbpH with 50% probability thermal ellipsoids. Hydrogen
L
2
L
2
atoms except the one at the amino group [H(25) of a, H(29) of b, H(25) of c, and H(45) of d] are omitted for clarity.
NO2
NO2
Table 1. Summary of X-ray Crystallographic Data of CNLMesH, CNLDepH,
CNLMes CNLDep
C22H25N3 C24H29N3
L
MesH, and
L
DtbpH
NO2
NO2
H
H
L
MesH
L
DtbpH
empirical formula
fw
C21H25N3O2
351.45
C31H45N3O2
491.72
monoclinic
P21/n (No. 14)
13.6374(4)
9.2069(3)
331.46
359.51
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
monoclinic
monoclinic
P21/n (No. 14)
8.9281(4)
19.8377(8)
11.7517(5)
triclinic
P21/n (No. 14)
15.4580(3)
15.5024(3)
16.1439(4)
P1h (No. 2)
8.954(2)
14.536(4)
8.220(2)
105.55(1)
109.61(1)
77.70(2)
961.9(5)
2
23.8174(9)
97.2594(9)
97.603(1)
98.942(2)
3837.7(1)
8
2063.1(2)
4
2954.1(2)
4
Z
F(000)
D
T, °C
1424.00
1.147
-115
776.00
1.157
-115
376.00
1.213
-115
1072.00
1.106
-115
calcd, g/cm3
cryst size, mm3
µ(Mo KR), cm-1
radiation
0.20 × 0.25 × 0.30
0.10 × 0.20 × 0.20
0.30 × 0.30 × 0.30
0.20 × 0.30 × 0.30
0.68
0.68
0.79
0.69
Mo KR (0.71069 Å)
55.0
33664
6242 [I > 1.00σ(I)]
502
0.066; 0.081
0.98
Mo KR (0.71069 Å)
54.8
18839
3343 [I > 3.00σ(I)]
290
0.042; 0.048
1.01
Mo KR (0.71069 Å)
54.9
6073
2717 [I > 3.00σ(I)]
261
0.077; 0.089
1.00
Mo KR (0.71069 Å)
55.0
22656
3785 [I > 3.00σ(I)]
371
0.047; 0.053
1.06
2θmax, deg
no. reflns measd
no. reflns obsd
no. variables
b
Ra; Rw
GOF indicator
2
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑w(|Fo| - |Fc|)2/∑wFo ]1/2
.
kcal/mol; Ar ) Dtbp, form A, -0.97 kcal/mol, form B,
-17.9 kcal/mol. Thus, the magnetic equivalence of the
â-proton of the carbon framework and the aromatic protons
of the N-substituents in the NMR spectra can be explained
by a rapid tautmerization within an NMR time scale between
B and B′ in solution as illustrated in Scheme 4.
Compounds CNLArH have a similar structural feature of
the ligand framework. Namely, the amine proton was
found to exist at N(1), and the bond distances of C(1)-C(3)
(1.442(5) and 1.442(2) Å for Ar ) Mes and Dep, respec-
tively) and C(2)-N(1) (1.326(4) and 1.323(2) Å) are longer
than those of C(1)-C(2) (1.386(5) and 1.383(2) Å) and
C(3)-N(2) (1.291(4) and 1.275(2) Å), respectively (see,
Table 2). Detailed comparison of the crystal structures
NO2
between CNLMesH [Figure 1a] and
L
MesH [Figure 1c]
having the same aromatic substituent (Mes) indicates that
the bond lengths of C(1)-C(2) and C(1)-C(3) of NO
L
MesH
2
(1.420(5) and 1.451(4) Å) are longer than those of CNLMes
H
Inorganic Chemistry, Vol. 42, No. 25, 2003 8399

Shimokawa et al.
NO2
NO2
Table 2. Selected Bond Lengths (Å), Angles (deg), and Angles of Least Square Planes (deg) of CNLMesH, CNLDepH,
CNLMes
L
MesH, and
L
DtbpHa
H
NO2
NO2
L
DtbpH
CNLDep
H
L
MesH
molecule 1
molecule 2
N(3)-C(4)
N(1)-C(2)
N(2)-C(3)
N(1)-C(5)
N(2)-C(14)
C(1)-C(2)
C(1)-C(3)
C(1)-C(4)
1.148(4)
1.326(4)
1.291(4)
1.424(4)
1.420(4)
1.386(5)
1.442(5)
1.429(5)
1.148(4)
1.313(4)
1.291(4)
1.437(4)
1.434(4)
1.393(5)
1.424(5)
1.425(5)
N(3)-C(4)
N(1)-C(2)
N(2)-C(3)
N(1)-C(5)
N(2)-C(15)
C(1)-C(2)
C(1)-C(3)
C(1)-C(4)
1.148(2)
1.323(2)
1.275(2)
1.438(2)
1.421(2)
1.383(2)
1.442(2)
1.425(2)
O(1)-N(3)
1.261(4)
O(1)-N(3)
O(2)-N(3)
N(1)-C(2)
N(1)-C(4)
N(2)-C(3)
N(2)-C(18)
N(3)-C(1)
C(1)-C(2)
C(1)-C(3)
C(2)-N(1)-C(4)
C(3)-N(2)-C(18)
O(1)-N(3)-O(2)
O(1)-N(3)-C(1)
O(2)-N(3)-C(1)
N(3)-C(1)-C(2)
N(3)-C(1)-C(3)
C(2)-C(1)-C(3)
N(1)-C(2)-C(1)
N(2)-C(3)-C(1)
plane 1-plane 2
plane 1-plane 3
plane 2-plane 3
1.242(2)
1.239(2)
1.317(3)
1.417(3)
1.283(3)
1.418(3)
1.431(3)
1.389(3)
1.436(3)
128.1(2)
122.8(2)
122.5(2)
119.2(2)
118.3(2)
116.6(2)
118.8(2)
124.6(2)
122.0(2)
119.2(2)
3.62°
O(2)-N(3)
N(1)-C(2)
N(1)-C(4)
N(2)-C(3)
N(2)-C(13)
N(3)-C(1)
C(1)-C(2)
C(1)-C(3)
1.258(4)
1.308(5)
1.444(4)
1.285(4)
1.457(4)
1.416(4)
1.420(5)
1.451(4)
123.3(3)
117.7(3)
122.6(3)
119.1(3)
118.3(3)
116.3(3)
118.6(3)
125.1(3)
121.7(3)
121.2(3)
49.06°
C(2)-N(1)-C(5)
C(3)-N(2)-C(14)
N(3)-C(4)-C(1)
C(2)-C(1)-C(4)
C(3)-C(1)-C(4)
C(2)-C(1)-C(3)
N(1)-C(2)-C(1)
N(2)-C(3)-C(1)
129.1(3)
120.8(3)
178.0(4)
118.9(3)
117.4(3)
123.6(3)
121.7(3)
121.9(3)
123.8(3)
119.7(3)
178.3(4)
118.3(3)
118.7(3)
123.1(3)
123.0(3)
122.6(3)
C(2)-N(1)-C(5)
121.6(1)
118.5(1)
177.8(2)
118.0(1)
118.2(1)
123.7(1)
125.5(1)
122.2(1)
C(2)-N(1)-C(4)
C(3)-N(2)-C(13)
O(1)-N(3)-O(2)
O(1)-N(3)C(1)
O(2)-N(3)-C(1)
N(3)-C(1)-C(2)
N(3)-C(1)-C(3)
C(2)-C(1)-C(3)
N(1)-C(2)-C(1)
N(2)-C(3)-C(1)
plane 1-plane 2
plane 1-plane 3
plane 2-plane 3
C(3)-N(2)-C(15)
N(3)-C(4)-C(1)
C(2)-C(1)-C(4)
C(3)-C(1)-C(4)
C(2)-C(1)-C(3)
N(1)-C(2)-C(1)
N(2)-C(3)-C(1)
plane 1-plane 2
plane 1-plane 3
plane 2-plane 3
32.83°
61.14°
75.74°
84.36°
88.72°
61.93°
plane 1-plane 2
plane 1-plane 3
plane 2-plane 3
71.13°
78.13°
50.30°
65.38°
79.60°
39.11°
40.25°
a Estimated standard deviations are given in parentheses. Definitions of the least-squares planes follow. For CNLMesH: plane 1, N(1)-N(2)-C(1)-
C(2)-C(3); plane 2, C(5)-C(6)-C(7)-C(8)-C(9)-C(10); plane 3, C(14)-C(15)-C(16)-C(17)-C(18)-C(19). For CNLDepH: plane 1, N(1)-N(2)-C(1)-
NO2
C(2)-C(3); plane 2, C(5)-C(6)-C(7)-C(8)-C(9)-C(10); plane 3, C(15)-C(16)-C(17)-C(18)-C(19)-C(20). For
L
L
MesH: plane 1, N(1)-N(2)-
C(1)-C(2)-C(3); plane 2, C(4)-C(5)-C(6)-C(7)-C(8)-C(9); plane 3, C(13)-C(14)-C(15)-C(16)-C(17)-C(18). For NO
C(1)-C(2)-C(3); plane 2, C(4)-C(5)-C(6)-C(7)-C(8)-C(9); plane 3, C(18)-C(19)-C(20)-C(21)-C(22)-C(23).
DtbpH: plane 1, N(1)-N(2)-
2
of Mes and Dep in CNLMesH, CNLDepH and NO
MesH and the
Scheme 3
2
L
â-proton of the ligand framework makes the torsion angle
NO2
larger than that in
L
DtbpH, which does not have the
o-substituents in the N-aryl group (Dtbp). Such a steric effect
also affected the structures of the copper(II) complexes as
discussed in following paragraphs.
Bis(â-diketiminate) Copper(II) Complexes. Treatment
of CuII(OAc)2 with the neutral ligands carrying phenyl (Ph)
or 3,5-di-tert-butylphenyl (Dtbp) groups as the aromatic
Scheme 4
Ph
NO2
substituent (MeLPhH, HLPhH, CNLPhH, NO L H, and
L
DtbpH)
2
in methanol gave the corresponding bis(â-diketiminate)
copper(II) complexes, the crystal structures of which, except
the complex of MeLPhH, have been determined by X-ray
crystallographic analysis as shown in Figure 2. The crystal-
lographic data and selected bond lengths and angles as well
as torsion angles of the two coordination planes defined by
N-Cu-N are given in Tables 3 and 4. Although a number
of bis(â-diketiminate) copper(II) complexes have so far been
reported,8-17 there is only one precedent for the X-ray
structure of bis(â-diketiminate) copper(II) complex, which
is supported by CHOLDmp [R1 ) CHO; R3 ) Dmp (3,5-
dimethylphenyl)].17
(1.386(5) and 1.442(5) Å for molecule 1, 1.393(5) and 1.424-
(5) Å for molecule 2), while bond lengths of N(1)-C(2) and
L
N(2)-C(3) of NO MesH (1.308(5) and 1.285(4) Å) are shorter
2
than those of CNLMesH (1.326(4) and 1.291(4) Å for molecule
1, 1.313(4) and 1.437(4) Å for molecule 2). These results
clearly suggest that, in the nitro derivative, the double bond
character of C(1)-C(2) and C(1)-C(3) decreases while that
of N(1)-C(2) and N(2)-C(3) increases as compared to that
of the corresponding bonds in the cyano derivative. Thus, it
could be concluded that there is some contribution of the
The copper(II) complexes exhibit distorted tetrahedral
geometries, where the dihedral angles between the two
coordination planes are 63.68°, 62.48°, 62.03°, and 61.39°
and the mean values of Cu-N bond length are 1.951, 1.959,
diimine form A (Scheme 3) to the overall structure in the
NO2
nitro derivative
L
MesH.
(12) Honeybourne, C. L.; Webb, G. A. J. Chem. Soc., Chem. Commun.
1968, 739-740.
It is also interesting to note that the angles between the
(13) McGeachin, S. G. Can. J. Chem. 1968, 46, 1903-1912.
(14) Attanasio, D.; Tomlison, A. G.; Alagna, L. J. Chem. Soc., Chem.
Commun. 1977, 618-619.
least-squares plane defined by N(1)-C(2)-C(1)-C(3)-N(2)
and the aromatic rings of the N-aryl groups in NO
L
DtbpH are
2
(15) Nishida, Y.; Oishi, N.; Kida, S. Inorg. Chim. Acta 1979, 32, 7-10.
(16) Kulichenko, A. V.; Kurbatov, V. P.; Kukharicheva, E. S.; Osipov, O.
A. J. Gen. Chem. USSR 1987, 55, 612-615.
smaller than those of other compounds. This could be attrib-
uted to the steric effects of the o-substituents in Mes and
Dep. Namely, the steric repulsion between the o-substituents
(17) Knorr, R.; Zo¨lch, R.; Polborn, K. Heterocycles 1995, 40, 559-576.
8400 Inorganic Chemistry, Vol. 42, No. 25, 2003

â-Diketiminate Cu(II) Complexes
Figure 2. ORTEP drawings of (a) [CuII(HLPh)2], (b) [CuII(CNLPh)2], (c) [CuII(NO
Ph)2], and (d) [CuII(NO Dtbp)2] with 50% probability thermal ellipsoids.
L
2
L
2
Hydrogen atoms are omitted for clarity.
1.952, and 1.966 Å for [CuII(HLPh)2], [CuII(CNLPh)2], [CuII-
(
seen in Table 5, the g| values increase as the electron-
withdrawing nature of R1 increases in the series of [CuII-
(R1LPh)2] (R1 ) Me, H, CN, and NO2, R3 ) Ph), although
the g values are rather constant (2.054-2.056). Thus, it can
be said that the g| values are correlated to the electron-donor
ability of the â-diketiminate ligands, where the more elec-
tron-donor ability of the ligand, the smaller the g| value of
copper(II) ion.19
NO2 Ph
L )2], and [CuII(NO2 Dtbp)2], respectively (Table 4). These
L
structural parameters are nearly the same to those of the bis-
(â-diketiminate) copper(II) complex supported by CHOLDmp
[dihedral angle ) 62.4°; Cu-Nav ) 1.952 Å].17 Thus, the
electronic nature of substituent R1 and the meta-substituents
of the N-aromatic groups (Me in CHOLDmp and t-Bu in
NO2
L
Dtbp) hardly affect the core structure of the bis(â-
diketiminate) copper(II) complexes.
The electronic spectrum in THF is also sensitive to the
electron-donor ability of the ligands (Table 5). Although
complete assignments of the absorption bands have yet to
be accomplished, the following peak assignments are pos-
sible.19 The strong absorption bands (ꢀ > 104 M-1 cm-1)
below 500 nm could be attributed to π-π* transitions of
the â-diketiminate ligands, since similar absorption bands
also exist in the zinc(II) complexes supported by the same
ligands.20 Then, the reasonably intense bands in the visible
Spectral data of the bis(â-diketiminate) copper(II) com-
plexes are summarized in Table 5. The complexes exhibit
ESR spectra having g| ) 2.182-2.214, g ) 2.054-2.056,
and A| ) 125-132 G. These ESR parameters are also nearly
the same to those of the bis(â-diketiminate) copper(II)
complexes so far reported.13,15 The smaller A| values, as
compared to that of square planar copper(II) complexes, are
characteristic of tetrahedrally distorted bis(â-diketiminate)
copper(II) complexes.13,15 Thus, the similarity in the A| value
clearly indicates that the structures of the copper(II) com-
plexes in solution are also very close each other as in the
case of the crystal structures (Figure 2).18 In such a case,
the differences in g| values could mainly be attributed to
the electronic effects of the ligand substituents. As can be
(18) The ESR parameters of the bis(â-diketiminate) copper(II) complexes
in CH2Cl2 are nearly the same as those of the complexes in THF (Table
5), indicating that the solvent molecules do not coordinate to the metal
center in the THF solution.
(19) Theoretical studies are planned to be carried out in order to evaluate
the substituent effects on the spectroscopic features of bis(â-diketimi-
nate) copper(II) complexes in more detail.
Inorganic Chemistry, Vol. 42, No. 25, 2003 8401

Shimokawa et al.
Table 3. Summary of X-ray Crystallographic Data of [CuII(HLPh)2], [CuII(CNLPh)2], [CuII(NO
[CuII CNLDep)2(µ-OH)2], and [CuII(CNLDipp)(AcO)]
Ph)2], [CuII(NO
L (
Dtbp)2], [CuII CNLMes)2(µ-OH)2],
2
2
L
2
(
2
[CuII CNLMes)2-
(
[CuII
(
CNLDep)2-
[CuII CNLDipp)-
(
2
2
2
[CuII(HLPh)2]
empirical formula C30H26CuN4
[CuII(CNLPh)2]
[CuII(NO
L
Ph)2]
[CuII(NO
L
Dtbp)2]
(µ-OH)2]
(µ-OH)2]
(AcO)]
2
2
C32H24CuN6
556.13
C30H24CuN6O4
596.10
C62H88CuN6O4
1044.96
C44H50Cu2N6O2
822.01
C48H58Cu2N6O2
878.12
C30H39CuN3O2
537.20
fw
506.11
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
orthorhombic
Aba2 (No. 41)
14.19(2)
7.087(8)
23.76(4)
monoclinic
C2/c (No. 15)
7.2391(3)
23.0260(9)
15.5591(8)
monoclinic
C2/c (No. 15)
7.64143(4)
23.016(2)
monoclinic
P21/c (No. 14)
15.8197(5)
19.2852(6)
20.0849(5)
monoclinic
P21/n (No. 14)
15.564(2)
14.764(2)
17.723(3)
triclinic
P1h (No. 2)
9.465(1)
11.151(2)
11.601(1)
67.824(4)
83.156(3)
74.441(7)
1092.0(2)
1
orthorhombic
Pnma (No. 62)
12.435(2)
21.398(4)
10.729(2)
14.995(1)
97.720(4)
102.931(3)
98.766(2)
94.324(6)
2388.9(5)
4
2570.0(2)
4
2561.2(3)
4
6056.1(3)
4
4060.8(1)
4
2854.8(9)
4
F(000)
D
1052.00
1.407
1148.00
1.437
1228.00
1.546
2252.00
1.146
1720.00
1.344
462.00
1.335
1140.00
1.250
calcd, g/cm3
T, °C
-115
-115
-115
-115
-115
-115
-115
cryst size, mm3
0.10 × 0.15
× 0.15
9.41
0.10 × 0.10
× 0.30
8.84
0.10 × 0.10
× 0.20
9.04
0.20 × 0.20
× 0.20
4.09
0.30 × 0.30
× 0.30
10.91
0.20 × 0.20
0.20 × 0.20
× 0.30
7.95
× 0.30
µ(Mo KR), cm-1
radiation
10.19
Mo KR
(0.71069 Å)
54.8
11440
1119
Mo KR
(0.71069 Å)
54.9
11271
2208
Mo KR
(0.71069 Å)
55.0
11885
2443
Mo KR
(0.71069 Å)
55.0
25017
8845
Mo KR
(0.71069 Å)
55.0
37161
6019
Mo KR
(0.71069 Å)
55.0
10416
4180
Mo KR
(0.71069 Å)
55.0
27321
2027
2θmax, deg
no. reflns measd
no. reflns obsd
[I > 1.00σ(I)]
[I > 3.00σ(I)]
[I > 3.00σ(I)]
[I > 1.00σ(I)]
[I > 3.00σ(I)]
[I > 3.00σ(I)]
[I > 3.00σ(I)]
no. variables
173
190
199
747
538
292
194
R;a Rw
0.024; 0.048
1.03
0.031; 0.060
1.18
0.030; 0.042
1.04
0.059; 0.065
1.03
0.037; 0.039
0.98
0.030; 0.034
0.95
0.024; 0.036
1.03
b
GOF indicator
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑w(|Fo| - |Fc|)2/∑wFo ]1/2
.
2
region could be assigned to n-π* transitions of the ligands
as well as ligand-to-metal charge transfer transitions (LMCT)
of the copper(II) complex, those of which may overlap with
the d-d bands of copper(II) as discussed in following
paragraphs.
between the d orbitals (dxz and dyz) of copper and the p
orbitals of the ligand causes an increase of the energy level
of dxz and dyz orbitals, which on the other hand decreases
the transition energy of dxz, dyz f dxy. Thus, the ligand with
the electron-donating substituent such as MeLPh- causes the
red-shift of the d-d band as compared to the corresponding
It has been documented that the distorted tetrahedral
2
copper(II) complexes exhibit three d-d bands due to the dz
ligands with the electron-withdrawing substituent such as
f dxy, dx -y f dxy, and dxz, dyz f dxy transitions.21 According
to the previous report by Nishida et al.,15 the weak dz f dxy
CNLPh- and NO
(
L
.
Ph- 19 The red-shift of the d-d band in [CuII-
2
2
2
L
Dtbp)2] (1305 nm) as compared to that of [CuII(NO L )2]
NO2
Ph
2
2
2
2
and dx -y f dxy bands become obscure due to overlap with
the relatively intense LMCT bands around 650-750 nm (ꢀ
∼ 103 M-1 cm-1, Table 5). Thus, only the dxz, dyz f dxy
transition bands in the near-IR region can be evaluated.15
Apparently, the d-d absorption bands in the near-IR region
shift toward a shorter wavelength (blue-shift) as the electron-
withdrawing nature of R1 increases in the series of [CuII-
(R1LPh)2] (R1 ) Me, H, CN, and NO2, R3 ) Ph). On the other
hand, this band shifts toward longer wavelength (red-shift),
when the R3 substituent (Ph) is replaced by the more electron-
(1200 nm) can also be attributed to the increasing electron-
donating ability of Dtbp as compared to that of Ph.19
In Figure 3 is shown the cyclic voltammograms of [CuII-
Ph
(MeLPh)2], [CuII(HLPh)2], [CuII(CNLPh)2], and [CuII(NO L )2] in
2
THF. Complexes [CuII(MeLPh)2] and [CuII(HLPh)2] gave ir-
reversible reduction peak at significantly negative positions
at -1.62 and -1.46 V versus Fc/Fc+, respectively [parts a
Ph
and b in Figure 3], while [CuII(CNLPh)2] and [CuII(NO L )2]
2
exhibited reversible redox couples at -0.97 and -0.68 V
versus Fc/Fc+, respectively [parts c and d in Figure 3]. Com-
Ph
II NO2
donating substituent Dtbp ([CuII(NO L )2] vs [Cu (
L
Dtbp)2],
2
L
plex [CuII(NO Dtbp)2] also provides a reversible redox couple
2
Table 5). Since the coordination geometry of the copper(II)
center is nearly the same among the bis(â-diketiminate)
complexes as demonstrated by the ESR (Table 5) and the
X-ray crystallographic analysis (Table 4), the shifts of the
d-d band can be mainly attributed to the electronic effects
of R1 and R3. We assume that electron donation from the
â-diketiminate ligand through σ-antibonding interactions
at -0.71 V, which is a little negative as compared to that of
Ph
[CuII(NO L )2] (not shown in Figure 3). Apparently, the re-
2
duction potentials as well as reversibility of the redox pro-
cesses are significantly affected by the ligand substituent R1.
The positive shift of the reduction potential on going from
Ph
[CuII(MeLPh)2] to [CuII(NO L )2] can be attributed to the in-
2
crease of electron-withdrawing ability of R1. The slight neg-
ative shift of E1/2 of [CuII(NO
L
Dtbp)2] as compared to that of
2
(20) Synthesis and characterization of the zinc(II) complexes will be
reported elsewhere.
(21) (a) Ferguson, J. J. Chem. Phys. 1964, 40, 822-830. (b) Smith, D. W.
J. Chem. Soc. A 1970, 2900-2902. (c) Smith, D. W. Inorg. Chim.
Acta 1977, 22, 107-110.
[CuII(NO L )2], on the other hand, is due to the increasing
electron-donor ability of the aromatic substituent Dtbp as
already discussed. Irreversibility observed in the redox
Ph
2
8402 Inorganic Chemistry, Vol. 42, No. 25, 2003

â-Diketiminate Cu(II) Complexes
Table 4. Selected Bond Lengths (Å), Angles (deg), and Angles of Least Square Planes (deg) of [CuII(HLPh)2], [CuII(CNLPh)2], [CuII(NO
Ph)2],
2
L
[CuII(NO
L
Dtbp)2][CuII
(
2
CNLMes)2(µ-OH)2], [CuII
(
2
CNLDep)2(µ-OH)2], and [CuII(CNLDipp)(AcO)]a
2
[CuII(HLPh)2]
[CuII(CNLPh)2]
[CuII(NO
2
L
Ph)2]
[CuII(NO Dtbp)2]
L
2
Cu(1)-N(1)
Cu(1)-N(2)
N(1)-C(2)
N(1)-C(4)
N(2)-C(3)
N(2)-C(10)
C(1)-C(2)
C(1)-C(3)
1.971(4) Cu(1)-N(1)
1.931(4) Cu(1)-N(2)
1.321(5) N(1)-C(2)
1.415(5) N(1)-C(5)
1.318(5) N(2)-C(3)
1.415(6) N(2)-C(11)
1.410(6) C(1)-C(2)
1.379(6) C(1)-C(3)
1.954(3) Cu(1)-N(1)
1.944(2) Cu(1)-N(1)
1.959(2) Cu(1)-N(4)
1.308(3) N(1)-C(2)
1.424(3) N(1)-C(4)
1.306(3) C(1)-C(2)
1.427(3) N(1)-Cu(1)-N(2) 94.2(1) N(1)-Cu(1)-N(4) 103.4(1)
1.396(3) N(2)-Cu(1)-N(4) 136.7(1) N(1)-Cu(1)-N(5) 135.5(1)
1.412(3) N(2)-Cu(1)-N(5) 100.7(1) N(4)-Cu(1)-N(5) 93.9(1)
1.975(3) Cu(1)-N(2)
1.957(3) Cu(1)-N(5)
1.310(5) N(2)-C(3)
1.440(4) N(2)-C(18)
1.402(5) C(1)-C(3)
1.946(3)
1.974(3)
1.305(5)
1.445(4)
1.418(5)
1.964(3) Cu(1)-N(2)
1.310(5) N(1)-C(2)
1.431(5) N(1)-C(4)
1.306(4) N(2)-C(3)
1.427(5) N(2)-C(10)
1.406(5) C(1)-C(2)
1.407(5) C(1)-C(3)
N(1)-Cu(1)-N(2) 96.1(2) N(1)-Cu(1)-N(2)* 95.40(12) N(1)-Cu(1)-N(2) 96.20(7) Cu(1)-N(1)-C(2) 124.1(2) Cu(1)-N(1)-C(4) 119.7(2)
Cu(1)-N(1)-C(2) 122.3(3) Cu(1)-N(1)-C(2)
Cu(1)-N(1)-C(4) 118.0(2) Cu(1)-N(1)-C(5)
C(2)-N(1)-C(4)
123.3(3) Cu(1)-N(1)-C(2) 123.3(2) C(2)-N(1)-C(4)
118.9(2) Cu(1)-N(1)-C(4) 118.8(1) Cu(1)-N(2)-C(18) 118.2(3) C(3)-N(2)-C(18) 115.1(3)
117.8(3) C(2)-N(1)-C(4) 117.8(2) Cu(1)-N(4)-C(33) 124.7(2) Cu(1)-N(4)-C(35) 119.4(2)
116.1(3) Cu(1)-N(2)-C(3) 126.3(3)
119.5(3) C(2)-N(1)-C(5)
Cu(1)-N(2)-C(3) 123.5(3) Cu(1)-N(2)*-C(3) 124.3(3) Cu(1)-N(2)-C(3) 123.8(2) C(33)-N(4)-C(35) 115.9(3) Cu(1)-N(5)-C(34) 124.7(3)
Cu(1)-N(2)-C(10) 117.5(3) Cu(1)-N(2)-C(11) 116.9(2) Cu(1)-N(2)-C(10) 117.2(1) Cu(1)-N(5)-C(49) 118.1(2) C(34)-N(5)-C(49) 117.1(3)
C(3)-N(2)-C(10) 118.8(3) C(3)*-N(2)-C(11) 118.4(3) C(3)-N(2)-C(10) 118.8(2) N(3)-C(1)-C(2)
117.1(3) N(3)-C(1)-C(3)
126.8(4) N(1)-C(2)-C(1)
123.4(4) N(1)-C(4)-C(5)
122.2(3) C(5)-C(4)-C(9)
61.39°
115.9(3)
125.1(3)
117.3(3)
120.4(3)
C(2)-C(1)-C(3)
N(1)-C(2)-C(1)
N(2)-C(3)-C(1)
plane 1-plane 2
126.7(3) C(2)-C(1)-C(3)
125.3(4) N(1)-C(2)-C(1)
125.9(3) N(2)*-C(3)-C(1)
126.4(3) C(2)-C(1)-C(3)
126.0(3) N(1)-C(2)-C(1)
124.6(3) N(2)-C(3)-C(1)
128.3(2) C(2)-C(1)-C(3)
124.7(2) N(2)-C(3)-C(1)
123.5(2) N(1)-C(4)-C(9)
63.68°
plane 1-plane 2
62.48°
plane 1-plane 2
62.03°
plane 1-plane 2
[CuII
(
2
CNLMes)2(µ-OH)2]
[CuII
(
2
CNLDep)2(µ-OH)2]
[CuII(CNLDipp)(AcO)]
Cu(1)-Cu(2)
2.981(1)
1.922(2)
1.946(3)
1.920(2)
1.963(3)
1.303(4)
1.309(4)
1.302(4)
1.293(4)
1.408(5)
1.406(5)
76.7(1)
Cu(1)-O(1)
Cu(1)-N(1)
Cu(2)-O(1)
Cu(2)-N(4)
O(1)-O(2)
N(1)-C(5)
N(2)-C(14)
N(4)-C(27)
N(5)-C(36)
C(1)-C(3)
1.905(2)
1.959(3)
1.919(2)
1.961(3)
2.374(3)
1.442(4)
1.443(4)
1.441(4)
1.442(4)
1.411(5)
1.414(4)
94.3(1)
Cu(1)-Cu(1)*
Cu(1)-O(1)
3.045(1)
1.908(1)
1.926(1)
1.955(2)
1.943(2)
2.331(3)
1.312(2)
1.441(2)
1.304(2)
1.447(2)
1.405(3)
1.410(3)
96.02(6)
170.36(6)
93.62(7)
105.13(7)
123.7(1)
120.8(1)
115.5(2)
124.5(1)
119.6(1)
115.9(2)
124.3(2)
125.6(2)
125.1(2)
Cu(1)-O(1)
Cu(1)-N(1)
Cu(1)-C(16)
O(1)-C(16)
N(1)-C(2)
N(1)-C(4)
C(1)-C(2)
2.028(1)
1.944(2)
Cu(1)-O(2)
Cu(1)-N(2)
Cu(1)-O(1)*
2.362(3)
1.265(2)
1.304(2)
1.450(2)
1.418(2)
1.493(4)
Cu(2)-O(2)
Cu(1)-N(1)
Cu(2)-N(5)
Cu(1)-N(2)
N(1)-C(2)
O(1)-O(1)*
N(2)-C(3)
N(1)-C(2)
N(4)-C(24)
N(1)-C(5)
C(16)-C(17)
N(5)-C(25)
N(2)-C(3)
C(1)-C(2)
N(2)-C(15)
C(23)-C(24)
C(23)-C(25)
C(1)-C(2)
O(1)-Cu(1)-O(2)
O(1)-Cu(1)-N(2)
O(2)-Cu(1)-N(2)
O(1)-Cu(2)-O(2)
O(1)-Cu(2)-N(5)
O(2)-Cu(2)-N(5)
Cu(1)-O(1)-Cu(2)
Cu(1)-N(1)-C(2)
C(2)-N(1)-C(5)
Cu(1)-N(2)-C(14)
Cu(2)-N(4)-C(24)
C(24)-N(4)-C(27)
Cu(2)-N(5)-C(36)
C(2)-C(1)-C(3)
N(2)-C(3)-C(1)
N(4)-C(24)-C(23)
O(1)-Cu(1)-N(1)
O(2)-Cu(1)-N(1)
N(1)-Cu(1)-N(2)
O(1)-Cu(2)-N(4)
O(2)-Cu(2)-N(4)
N(4)-Cu(2)-N(5)
Cu(1)-O(2)-Cu(2)
Cu(1)-N(1)-C(5)
Cu(1)-N(2)-C(3)
C(3)-N(2)-C(14)
Cu(2)-N(4)-C(27)
Cu(2)-N(5)-C(25)
C(25)-N(5)-C(36)
N(1)-C(2)-C(1)
C(24)-C(23)-C(25)
N(5)-C(25)-C(23)
C(1)-C(3)
169.5(1)
95.9(1)
76.4(1)
170.8(1)
93.3(1)
173.3(1)
97.2(1)
O(1)-Cu(1)-N(1)
O(1)-Cu(1)-N(2)
N(1)-Cu(1)-N(2)
Cu(1)-O(1)-Cu(1)*
Cu(1)-N(1)-C(2)
Cu(1)-N(1)-C(5)
C(2)-N(1)-C(5)
Cu(1)-N(2)-C(3)
Cu(1)-N(2)-C(15)
C(3)-N(2)-C(15)
C(2)-C(1)-C(3)
N(1)-C(2)-C(1)
N(2)-C(3)-C(1)
O(1)-Cu(1)-O(1)*
O(1)-Cu(1)-N(1)
N(1)-Cu(1)-N(1)*
N(1)-Cu(1)-C(16)
Cu(1)-O(1)-C(16)
Cu(1)-N(1)-C(2)
Cu(1)-N(1)-C(4)
C(2)-N(1)-C(4)
C(2)-C(1)-C(2)*
N(1)-C(2)-C(1)
64.70(8)
98.82(6)
94.79(9)
130.02(5)
88.5(1)
124.2(1)
118.8(1)
116.9(2)
124.54(24)
125.4(2)
93.8(1)
167.7(1)
102.4(1)
121.4(2)
117.3(3)
119.8(2)
122.1(2)
116.5(3)
117.5(2)
124.2(3)
124.6(3)
126.2(3)
92.8(1)
101.8(1)
120.8(2)
122.4(2)
117.6(3)
121.4(2)
123.6(2)
118.8(3)
125.6(3)
123.8(3)
124.7(3)
a Estimated standard deviations are given in parentheses. Definitions of the least-squares planes follow. For [CuII(HLPh)2]: plane 1, N(1)-Cu(1)-N(2);
plane 2, N(1)*-Cu(1)-N(2)*. For [CuII(CNLPh)2]: plane 1, N(1)-Cu(1)-N(2)*; plane 2, N(1)*-Cu(1)-N(2). For [CuII(NO
Ph)2]: plane 1, N(1)-Cu(1)-
2
L
N(2); plane 2, N(1)*-Cu(1)-N(2)*. For [CuII(NO
Dtbp)2]: plane 1, N(1)-Cu(1)-N(2); plane 2, N(4)-Cu(1)-N(5).
2
L
process of [CuII(MeLPh)2] and [CuII(HLPh)2] indicates that the
copper(I) state of the bis(â-diketiminate) complex is unstable
with such ligands. Instability of these copper(I) complexes
could be attributed to the strong electron-donating nature of
complex is stabilized when it takes a tetrahedral geometry.
In fact, the tetrahedral copper complexes supported by a
series of 2,9-disubstituted 1,10-phenanthroline derivatives
have very positive redox potentials around 0.84-1.03 V
versus SCE, 0.36-0.55 V versus Fc/Fc+ in CH2Cl2.23,24 In
the present â-diketiminate ligand systems, the bulky aromatic
N-substituent also reinforces the copper(II) complexes to
exhibit the distorted tetrahedral geometry (Figure 2), which
may cause a positive shift of the reduction potential as in
the case of the former complexes.23,24 However, due to the
H
MeLPh- and LPh-. On the contrary, less electron-donating
ligands having the electron-withdrawing substituents, CNLPh-
,
NO2
2
L
Ph-, and NO Dtbp-, can support the one-electron reduced
L
species [CuI(â-diketiminate)2]-, providing reversible redox
couples.
The electrochemical behavior of the distorted tetrahedral
copper(II) complexes is worth noting in relation to the
ubiquitous type 1 copper biological electron transfer sites,
which also possess significantly distorted tetrahedral cupric
centers.22 In general, four coordinate copper(II) complexes
favor the square planar geometry, while the copper(I)
(22) Randall, D. W.; Gamelin, D. R.; LaCroix, L. B.; Solomon, E. I. JBIC,
J. Biol. Inorg. Chem. 2000, 5, 16-19.
(23) Miller, M. T.; Gantzel, P. K.; Karpishin, T. B. Inorg. Chem. 1999,
38, 3414-3422.
(24) Connelly, N. G.; Geiger, W. E. Chem. ReV. 1996, 96, 877-910.
Inorganic Chemistry, Vol. 42, No. 25, 2003 8403

Shimokawa et al.
Table 5. Absorption Spectral and ESR Data of the Bis(â-diketiminate) Copper(II) Complexes
[CuII(MeLPh)2]
[CuII(HLPh)2]
[CuII(CNLPh)2]
max,a nm (ꢀ, M-1 cm-1
[CuII(NO
L
Ph)2]
[CuII(NO
L
Dtbp)2]
2
2
λ
)
409(14 100)
443(16 700)
471(11 600)
571(840)
717(1050)
1566(283)
401(27 900)
441(11 900)
389(45 400)
369(46 600)
381(51 800)
496(382)
600(145)
671(1580)
1328(234)
439(1880)
590(174)
643(1660)
1200(308)
462(2240)
623(342)
705(1480)
1305(160)
549(394)
697(456)
1422(258)
ESRb
g|
g
A|,G
2.182
2.054
125
2.198
2.055
126
2.205
2.055
128
2.210
2.055
132
2.214
2.056
129
a In THF at 25 °C. In case the absorption bands are overlapped, the λmax and ꢀ values were determined by spectral resolution using Gaussian functions
with Igor Pro (ver 4, Hulinks). b ESR measurements were performed on frozen THF solutions of the copper(II) complexes at -150 °C.
Steric Effects of ortho-Substituents of N-Aromatic
Groups (R3). In contrast to the former complexes supported
by the ligands with R3 ) Ph or Dtbp, the reaction of CNLMes
H
or CNLDepH with CuII(OAc)2 gave a di(µ-hydroxo)dicopper-
(II) complex as shown in Figure 4a,b. A similar di(µ-
hydroxo)dicopper(II) complex was also obtained, when
NO2
L
MesH was treated with CuII(OAc)2 under the same
experimental conditions. The crystal structure of the di(µ-
NO2 Mes-
hydroxo)dicopper(II) complex supported by
L
was
reported in the previous paper.3e In these cases, each copper
ion exhibits a square planar geometry consisting of a N2O2
donor set, which is provided from the didentate ligands and
the bridging OH groups. All the di(µ-hydroxo)dicopper(II)
complexes were ESR silent due to a strong magnetic
interaction between the two cupric ions through the µ-hy-
droxo bridges. Since the Cu-O-Cu angle of the complex
is 102-105° (see Table 4), the magnetic interaction may be
antiferromagnetic. Crawford and co-workers have established
the linear correlation between the Cu-O-Cu angle (θ) of a
series of di(µ-hydroxo)dicopper(II) complexes and their
singlet-triplet exchange parameter J as 2J ) -74.53θ +
7270 cm-1.25 From this correlation, it was concluded that
when θ is larger than 97.55°, the overall magnetic behavior
is antiferromagnetic. Such a large Cu-O-Cu angle in the
di(µ-hydroxo)dicopper(II) complexes supported by the
â-diketiminate ligands may be due to the steric repulsion
between the N-aromatic groups. The complexes [CuII -
2
(
CNLMes)2(µ-OH)2] and [CuII (CNLDep)2(µ-OH)2] also exhibit
2
a strong ligand based π-π* band at 345 nm (ꢀ ) 33 100
M-1 cm-1) and 340 (32 900), respectively, together with an
LMCT band at ∼440 (3900) and n-π* at ∼540 (300-500).
The d-d bands of these complexes ∼800 nm are signifi-
cantly weak and broadened. The di(µ-hydroxo)dicopper(II)
complexes gave two irreversible reduction peaks at sigin-
ificantly negative positions: -2.10 and -2.85 V versus
Figure 3. Cyclic voltammograms of (a) [CuII(MeLPh)2], (b) [CuII(HLPh)2],
(c) [CuII(CNLPh)2], and (d) [CuII(NO
L
Ph)2] (1.0 × 10-3 M) in THF containing
2
0.1 M TBAP; working electrode Pt, counter electrode Pt, pseudoreference
electrode Ag, scan rate 0.1 V s-1
.
negative charge of the â-diketiminate ligands, the redox
potentials of the bis(â-diketiminate) copper(II) complexes
are significantly negative even though they possess nearly
Fc/Fc+ for [CuII (CNLMes)2(µ-OH)2] and -2.05 and -2.81 V
2
versus Fc/Fc+ for [CuII (CNLDep)2(µ-OH)2]. The irreversibility
2
tetrahedral geometry. Nonetheless, the â-diketiminate ligands
in the electrochemical measurements clearly indicates that
the reduction of the dinuclear copper(II) complex induces
degradation of the di(µ-hydroxo)dicopper core.
NO2 Ph-
with the electron-withdrawing substituents, CNLPh-
,
L
,
and NO
L
Dtbp-, can accommodate the copper(I) state, provid-
2
ing the reversible redox couple of copper(II)/copper(I). Thus,
these complexes serve as valuable models for investigating
the electronic structures of tetrahedral copper(II) complexes,
and the results may relate to the active sites of blue copper
proteins.
The steric effect of the ortho-substituents of R3 is more
prominent in the case of CNLDippH. In this case, the mono-
(25) Crawford, V. H.; Richardson, H. W.; Wasson, J. R.; Hodgson, D. J.;
Hatfield, W. E. Inorg. Chem. 1976, 15, 2107-2110.
8404 Inorganic Chemistry, Vol. 42, No. 25, 2003

â-Diketiminate Cu(II) Complexes
Figure 4. ORTEP drawings of (a) [CuII CNLMes)2(µ-OH)2], (b) [CuII CNLDep)2(µ-OH)2], and (c) [CuII(CNLDipp)(AcO)] with 50% probability thermal ellipsoids.
( (
2 2
Hydrogen atoms except the one at the hydroxy group [H(49) and H(50) of a, H(29) and H(29)* of b] are omitted for clarity.
nuclear copper(II) complex supported one â-diketiminate
ligand CNLDipp- and one didentate acetate ion as shown in
Figure 4c. The cupric ion exhibits a distorted square planar
geometry showing an ESR spectrum with g| ) 2.257, g )
2.057, and A| ) 172 G. The UV-vis spectrum of this
complex is similar to that of the di(µ-hydroxo)dicopper(II)
complexes [344 nm (ꢀ ) 20200 M-1 cm-1), 440 (754), 580
(150), ∼700 (120)], and the compound gave an irreversible
reduction peak at -1.17 V vs Fc/Fc+ in THF.
excellent opportunity to examine the electronic effects of
the ligands on the redox functions of the distorted tetrahedral
copper(II) complexes. Chemical functions of the mono-
nuclear and dinuclear copper(II) complexes are now under
investigation.26
Acknowledgment. The authors thank Professor H. Na-
kazawa of Osaka City University for his valuable comments
and discussions. This work was financially supported in part
by Grants-in-Aid for Scientific Research on Priority Area
(11228206) and Grants-in-Aid for Scientific Research
(13480189) from the Ministry of Education, Culture, Sports,
Science and Technology, Japan.
In summary, mononuclear and dinuclear copper(II)
complexes supported by a series of â-diketiminate ligands
have been synthesized, and their structures and physico-
chemical properties have been investigated systematically.
The metal centers of these complexes are all enforced to
have four-coordinate structures, but their coordination ge-
ometries are significantly altered, providing the distorted
tetrahedral copper(II), planar di(µ-hydroxo)dicopper(II), and
distorted square planar copper(II) complexes, depending on
the N-aromatic substituents of the â-diketiminate ligands.
Supporting Information Available: X-ray structural determi-
nation and details of the crystallographic data as a CIF file. This
material is available free of charge via the Internet at http://
pubs.acs.org.
IC0344766
The copper(II) complexes supported by MeLPh-
,
HLPh-
,
NO2
NO2 Dtbp-
CNLPh-
,
L
Ph-, and
L
possess essentially the same
(26) A preliminary study on the reaction of H2O2 and the mononuclear
copper(II)-acetate complex supported by CNLDipp- has suggested
formation of a thermally stable copper(II)-peroxo complex that is a
subject of a separate report.
distorted tetrahedral structure, but different spectroscopic and
electrochemical features. Thus, these complexes provide an
Inorganic Chemistry, Vol. 42, No. 25, 2003 8405