Structural effects on nitratocopper(II) complexes of tris(pyrazolyl)borates

Article abstract of DOI:10.1246/bcsj.74.1065

Some structural influences on nitratocopper(II) complexes ligated by a series of hydrotris(pyrazolyl)borates are described. The 5-position of pyrazole rings as well as the 3-position is important to provide coordination structure.

Full text of DOI:10.1246/bcsj.74.1065

c. Jpn.
Bull. Chem. Soc. Jpn., 74, 1065—1066 (2001) 1065
e Chemical
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Short Articles
e Chemical
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salts of the substituted hydrotris(pyrazolyl)borates in a mixed
solvent, Me2CO/CH2Cl2, at room temperature in high yield
(Scheme 1). The crystal structures of 4 and 6 have been re-
ported.6 All other nitratocopper(II) complexes are character-
ized by an X-ray diffraction method in the present work. An
X-ray characterization of all nitratocopper(II) complexes re-
veals that three nitrogen atoms of the hydrotris(pyrazolyl)-
borate ligand bind the copper(II) atom as a facially coordinat-
ing tridentate ligand, forming a mononuclear structure.
Structural Effects on
Nitratocopper(II) Complexes
of Tris(pyrazolyl)borates
K. Fujisawa et al.
01
65
66
Kiyoshi Fujisawa,* Yoshitaro Miyashita,
Yasunori Yamada, and Ken-ichi Okamoto
SJA8
09-2673
0046
cember
In the case of phenyl substituted ligand at the 3-position
(LPh,iPr), the structural values of 5 (∆Cu–O ꢁ 0.074 Å, τ
value12 ꢁ 0.70) are intermediate between those of 4 with LiPr,iPr
and 6 with LtBu,iPr, which has many differences in their struc-
tural parameters (∆Cu–O, τ value) and physicochemical prop-
erties (Scheme 2 and Table 1).6 This result can be summarized
by the following series according to effective steric bulkiness
at a complexed metal center in the 3-position substituted
ligand system: But > Ph > Pri.
Department of Chemistry, University of Tsukuba,
Tsukuba 305-8571
(Received December 25, 2000)
00
Some structural influences on nitratocopper(II) complexes li-
gated by a series of hydrotris(pyrazolyl)borates are described.
The 5-position of pyrazole rings as well as the 3-position is
important to provide coordination structure.
01
.2
In the methyl substituted complexes at the 5-position (1–3),
1 has a crystallographically imposed plane of symmetry con-
ꢀ
taining one of pyrazole rings, B Cu, N41 and O42 of the NO3
unit. Therefore, two Cu–O distances are exactly the same
(∆Cu–O ꢁ 0). As the substituent in the 3-position (LMe,Me (1),
LPh,Me (2), LtBu,Me (3)) become bulkier, the ∆Cu–O distance is
Tris(pyrazolyl)borate ligands have been applied to inorgan-
ic, bioinorganic, and organometallic chemistry owing to the
fact that these anionic ligands take versatile coordination
modes and are useful for the preparation of complexes of ele-
ments throughout the periodic table.1 In 1986, the bulkier sub-
stitutions were introduced in the 3-position of pyrazole rings,
[HB(3-Rpz)3]ꢀ (R ꢁ Ph, But); the formation of the unreactive
and coordinately saturated complex, [M{HB(3-Rpz)3}2], was
easily inhibited.2 After then, many substituents, aliphatic or ar-
omatic groups, in the 3- and/or 5- (and/or 4-) position(s) were
inserted to obtain novel complexes. We also used this method-
ology by using [HB(3,5-Pri2pz)3]ꢀ (ꢁ hydrotris(3,5-diisopro-
pyl-1-pyrazolyl)borate(1-)) to prepare peroxocopper(II) com-
plexes,3 alkylperoxocopper(II) complexes,4 and thiolato-
copper(II) complexes5 as models for oxy-hemocyanin, copper
containing monooxygenases, and blue copper proteins, respec-
tively. Expanding this ligand system, we introduced tert-butyl
group in the 3-position, [HB(3-But-5-Pripz)3]ꢀ (ꢁ hydrotris(3-
tert-butyl-5-isopropyl-1-pyrazolyl)borate(1-)), to make mono-
nuclear complexes selectively, and recently reported the struc-
tural influences on copper(II) complexes.4,6 In our previous
paper,6 the nitrate ligand exhibited both unidentate and biden-
tate coordination modes. Therefore, observation of the struc-
ture of a nitratocopper(II) complex may provide a good indica-
tion as to the structural effects on tris(pyrazolyl)borate ligands.
We report herein some structural researches on nitratocop-
per(II) complexes ligated by hydrotris(pyrazolyl)borates,
[HB(3,5-Me2pz)3]ꢀ: (LMe,Me) (ꢁ hydrotris(3,5-dimethyl-1-
pyrazolyl)borate(1-)),7 [HB(3-Ph-5-Mepz)3]ꢀ: (LPh,Me) (ꢁ hy-
Scheme 1.
Scheme 2.
a)
LR , R
3
5
Table 1.
Comparison of Structural Data
Cu(NO3)
Complexes
∆Cu–
O (Å)
Cu···N
(Å)
a)
LR , R
3
5
d1 (Å)
d2 (Å)
τe)
LMe,Me (1)
2.030(9)
2.033(2)
2.16(2)
2.030(9)
2.011(2)
1.99(1)
0
0
2.38(2)
2.416(3)
2.47(2)
2.413(4)
2.427(5)
2.493(3)
—
LPh,Me
tBu,Me b)
(2)
(3)
(4)
(5)
(6)
0.022
0.17(2)
0.032
0.074
0.217
0
0.38
0.55(1)
0.22
0.70
0.77
0
L
iPr,iPr c)
L
2.021(4)
2.072(4)
2.206(3)
2.042(3)
1.989(4)
1.998(4)
1.989(3)
2.042(3)
drotris(3-phenyl-5-methyl-1-pyrazolyl)borate(1-)),8
[HB(3-
LPh,iPr
But-5-Mepz)3]ꢀ: (LtBu,Me) (ꢁ hydrotris(3-tert-butyl-5-methyl-
1-pyrazolyl)borate(1-)),9 [HB(3,5-Pri2pz)3]ꢀ: (LiPr,iPr),3 [HB(3-
Ph-5-Pripz)3]ꢀ: (LPh,iPr) (ꢁ hydrotris(3-phenyl-5-isopropyl-1-
pyrazolyl)borate(1-)),10 [HB(3-But-5-Pripz)3]ꢀ: (LtBu,iPr).10,11
The nitratocopper(II) complexes were obtained from the re-
action between copper(II) nitrate trihydrate and potassium
tBu,iPr c)
L
tBu,H d)
L
a) R3, R5 denotes 3- and 5-substitution position at pyrazole
rings, respectively. b) There are two independent molecules
in the unit cell. c) Ref. 6. d) Ref. 13. e) Ref. 12.

1066 Bull. Chem. Soc. Jpn., 74, No. 6 (2001)
© 2001 The Chemical Society of Japan
0.057 and GOF ꢁ 1.26 for 649 variable parameters; 5 triclinic
longer (0, 0.022, 0.17) and the τ value is also larger (0, 0.38,
0.55). Such facts suggest that the bulkiness of the substituent
in the 3-position is effective in coordination environments.
As can be seen from Table 1, some influences on the struc-
tural data in the 5-position substituent (2 vs. 5 and 3 vs. 6) are
also observed. The ∆(∆Cu–O) distances and ∆τ values are
0.052 and 0.32 (2 vs. 5), 0.047 and 0.22 (3 vs. 6), whereas
those are 0.017 and 0.55 (1 vs. 3), and 0.185 and 0.55 (4 vs. 6).
Therefore, the bulkiness of substituent in the 5-posision (2 vs.
5 and 3 vs. 6) is smaller than that in the 3-position (1 vs. 3 and
4 vs. 6). From the τ value and the distance between copper(II)
ion and N41 (Table 1), the coordination of the nitratocopper(II)
ligated by more bulkier substituent(s) in 3 and/or 5 position(s)
has a more distorted geometry. In the case of the difference
between methyl (1) and isopropyl (4) groups in the 3- and 5-
positions, there are slight changes about ∆Cu–O distances and
τ values. In addition, LtBu,H ligand has almost the same bulki-
ness as LMe,Me in nitratocopper(II) complexes. From these re-
sults, the substituent in the 5-position as well as that in the 3-
position are also effective in the metal center environment.
And the bulkiness order of nitratocopper(II) complexes is as
follows: LMe,Me (1) < LiPr,iPr (4) < LPh,Me (2) < LPh,iPr (5) < LtBu,Me
(3) < LtBu,iPr (6). Further research is proceeding on these struc-
tural effects on metal center in other ligand systems.
space group
(No. 2), Z ꢁ 2, Dcalc ꢁ 1.25, 3828 observed re-
P1
flections [I > 2.00σ(I)] used in the refinements, R ꢁ 0.059, Rw ꢁ
0.065 and GOF ꢁ 1.40 for 433 variable parameters using the teX-
san crystallographic software package.14 The final positional and
thermal parameters, full listing of the bond distances and angles,
torsion angles, and ORTEP drawings, and the Fo-Fc table of 1–3
and 5 have been deposited as Document No. 74037 at the Office of
the Editor of Bull. Chem. Soc. Jpn. Crystallographic data have
been deposited at the CCDC, 12 Union Road, Cambridge CB2
1EZ, UK and copies can be obtained on request, free of charge, by
quoting the publication citation and the deposition numbers
159121–159124.
This research was in part supported from the Ministry of
Education, Science, Sports and Culture (No. 11640555) and
from KAWASAKI STEEL 21st Century Foundation.
References
1
For recent book and reviews: S. Trofimenko, “Scorpi-
onates—The Coordination Chemistry of Polypyrazolylborate
Ligands,” Imperial College Press, London (1999); N. Kitajima and
W. B. Tolman, Prog. Inorg. Chem., 43, 419 (1995); G. Parkin,
Chem Commun., 2000, 1971.
2
S. Trofimenko, J. C. Calabrese, and J. S. Thompson, Inorg.
Experimental
Chem., 26, 1507 (1987).
Measurement. Elemental analyses were performed in the an-
alytical facility at the Research Laboratory of Resource Utiliza-
tion, Tokyo Institute of Technology and the Analysis Center of the
University of Tsukuba.
3
N. Kitajima, K. Fujisawa, C. Fujimoto, Y. Moro-oka, S.
Hashimoto, T. Kitagawa, K. Toriumi, K. Tatsumi, and A.
Nakamura, J. Am. Chem. Soc., 114, 1277 (1992).
4
P. Chen, K. Fujisawa, and E. I. Solomon, J. Am. Chem.
Preparation. All the complexes were prepared by the meth-
ods described in previous papers.6 Yield and elemental analyses
of new nitratocopper(II) complexes are as follows: 1 (yield 72%)
Found: C, 42.37; H, 5.40; N, 23.67%. Calcd for C15H22N7BCuO3:
C, 42.62; H, 5.25; N, 23.19%.; 2 (yield 84%) Found: C, 58.74; H,
4.21; N, 16.05%. Calcd for C30H28N7BCuO3: C, 59.17; H, 4.63;
N, 16.10%.; 3 (yield 76%) Found: C, 52.51; H, 7.34; N, 17.86%.
Calcd for C24H40N7BCuO3: C, 52.96; H, 7.27; N, 17.94%.; 5
(yield 79%) Found: C, 62.36; H, 5.89; N, 14.22%. Calcd for
C36H40N7BCuO3: C, 62.38; H, 5.82; N, 14.15%.
Crystallography. The diffraction data were measured on a
Rigaku automated four-circle diffractometer with graphite-mono-
chromated Mo Kα (λ ꢁ 0.71069 Å) radiation. The data were col-
lected at 23 ꢂ 1 ˚C. The unit-cell parameters of each crystal were
obtained from a least-squares refinement. The crystallographic
data and collection details are summarized in Table S1. The non-
hydrogen atoms were refined anisotropically. Refinements were
carried out by a full-matrix least-squares method on F. Some im-
portant crystal data are as follows: 1 orthorhombic space group
Cmc21 (No. 36), Z ꢁ 4, Dcalc ꢁ 1.44, 532 observed reflections [I >
1.00σ(I)] used in the refinements, R ꢁ 0.056, Rw ꢁ 0.061 and
GOF ꢁ 1.59 for 133 variable parameters; 2 triclinic space group
Soc., 122, 10177 (2000).
5
D. W. Randall, S. D. George, B. Hedman, K. O. Hodgson,
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K. Fujisawa, T. Kobayashi, K. Fujita, N. Kitajima, Y.
Moro-oka, Y. Miyashita, Y. Yamada, and K. Okamoto, Bull. Chem.
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7
8
S. Trofimenko, J. Am. Chem. Soc., 89, 6288 (1967).
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9
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12 This τ value is good indicator about coordination mode,
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N. Rao, J. Reedijk, J. van Rijn, and G. C. Verschoor, J. Chem.
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14 teXsan: Single Crystal Structure Analysis Package, Version
1.10b Molecular Structure Corporation, The Woodlands, TX,
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(No. 2), Z ꢁ 2, Dcalc ꢁ 1.41, 3201 observed reflections [I >
P1
2.00σ(I)] used in the refinements, R ꢁ 0.030, Rw ꢁ 0.045 and
GOF ꢁ 1.43 for 379 variable parameters; 3 orthorhombic space
group Pca21 (No. 29), Z ꢁ 8, Dcalc ꢁ 1.28, 4124 observed reflec-
tions [I > 2.00σ(I)] used in the refinements, R ꢁ 0.051, Rw
ꢁ