Imino- and bis-imino-pyridines with N-ter-butyl-N-aminoxyl group: Synthesis, oxidation and use as ligand towards M2+ (Mn, Ni, Zn) and Gd3+

Article abstract of DOI:10.1016/j.jorganchem.2004.09.014

Imino- and bis-iminopyridine ligands bearing N-ter-butylhydroxy groups were synthesized by the condensation reaction between a N-ter-butylhydroxy substituted aniline and 2-formylpyridine, 2-acetylpyridine and 2,6-bis-acetylpyridine. The N-ter-butylaminoxy radicals obtained after oxidation using PbO₂ or Ag₂O were studied by EPR spectroscopy in solution. Indeed, complete decomposition was observed during isolation of these radical derivatives. The N-ter-butylhydroxy substituted ligands obtained were complexed with Mn²⁺, Ni²⁺, Zn²⁺ and Gd ³⁺ salts; the obtained complexes were characterized and oxidized to give the aminoxy analogs, which were studied using IR, UV and EPR spectroscopies.

Full text of DOI:10.1016/j.jorganchem.2004.09.014

Journal of Organometallic Chemistry 690 (2005) 197–210
www.elsevier.com/locate/jorganchem
Imino- and bis-imino-pyridines with N-ter-butyl-N-aminoxyl
group: synthesis, oxidation and use as ligand towards M2+
(Mn, Ni, Zn) and Gd3+
*
Carsten Uerpmann, Bernard J.L. Henner , Christian Guerin, Franc¸is Carre
´
´
´ ´
UMR 5637-Chimie Moleculaire et Organisation du Solide, CC 007 Universite de Montpellier II,
Place E. Bataillon, F-34095 Montpellier Cedex 5, France
Received 1 July 2004; accepted 10 September 2004
Available online 30 November 2004
Abstract
Imino- and bis-iminopyridine ligands bearing N-ter-butylhydroxy groups were synthesized by the condensation reaction between
a N-ter-butylhydroxy substituted aniline and 2-formylpyridine, 2-acetylpyridine and 2,6-bis-acetylpyridine. The N-ter-butylaminoxy
radicals obtained after oxidation using PbO2 or Ag2O were studied by EPR spectroscopy in solution. Indeed, complete decompo-
sition was observed during isolation of these radical derivatives. The N-ter-butylhydroxy substituted ligands obtained were com-
plexed with Mn2+, Ni2+, Zn2+ and Gd3+ salts; the obtained complexes were characterized and oxidized to give the aminoxy
analogs, which were studied using IR, UV and EPR spectroscopies.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Iminopyridines; Metal(II) complexes; Radical
1. Introduction
nate of manganese (II), as lamellar derivatives with an
˚
inter-lamellar distance of 22 A [38].
Much attention has been devoted since several years
to the use of nitroxide free radicals as spin carriers in
the design of molecular magnetic materials [1–14]. In
particular, research have been done in their coordina-
tion chemistry and in the magnetic properties of their
metal complexes [15–31]. This subject has been the topic
of several books [32–36].
One possible way of obtaining these materials is the
organic–inorganic hybrid route with one or more radi-
cals in the organic part. This route was explored by Dril-
lon and coworkers [37] in the case of lamellar
compounds with imino-nitroxide substituted benzoate,
in para and meta position; we also have obtained phenyl
substituted ter-butylnitroxide phosphonate and -sulfo-
We wanted to extend this work to transition metal
ligands bearing ter-butylaminoxyl groups and choose
the imino- and bis-iminopyridine family of compounds.
In this case, this will allow first, the formation of para-
magnetic transition metal complexes bearing organic
radicals and second, open the field of more extended
structures with the possible complexation of the nitrox-
ide group with another transition metal. Indeed, the do-
nor properties of the nitroxide are poor, but
coordination of this group occurs with crowded metal
centres carrying electron-withdrawing groups such as,
for instance, Mn(hfac)2 (hfac: hexafluoroacetyl-
acetonate).
Iminopyridine ligands are known to coordinate easily
to transition metals [39–41]. in the case of bis-iminopy-
ridines, for instance, various complexes were prepared
by Brookhart et al, characterized by X-ray diffraction
*
Corresponding author. Tel.: +33 467 143864; fax: +33 467 143852.
E-mail address: bhenner@univ-montp2.fr (B.J.L. Henner).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.09.014

198
C. Uerpmann et al. / Journal of Organometallic Chemistry 690 (2005) 197–210
Table 1
Physical properties of the radicals
spectroscopy, and used as efficient catalyst for the
polymerisation of ethylene and propylene [42–44].
In this paper, we describe the synthesis of iminopyri-
dines and bis-iminopyridines with ter-butylaminoxyl
groups. These compounds were obtained by the synthe-
sis of ter-butylaminoxylanilines followed by their con-
densation reaction with pyridine substituted aldehydes
or ketones. The as-prepared ligands were reacted with
MXn derivatives (M2+ = Ni2+, Mn2+; X = Cl; n = 2.
Radical
UV (CHCl3) nm
233, 289, 482
IR (CHCl3) cmꢀ1
EPR (CHCl3)
3b
1360 (NO)
3 lines
g = 2.0059
an = 13.1 G
3c
5b
5c
9
233, 288, 479
230, 293, 484
232, 292, 481
230, 291, 379
233, 289, 488
233, 289, 488
230, 291, 345
1359 (NO)
3 lines
g = 2.0061
an = 13.1 G
M3+ = Gd3+
;
X = NO3; n = 3. M2+ = Mn2+
;
Xꢀ ¼
3460, 3390 (NH2)
1603 (NH2)
1363 (NO)
3 lines
g = 2.0053
an = 13 G
ClOꢀ4 ; n ¼ 2. M2+ = Zn2+; Xꢀ ¼ NOꢀ3 ; n ¼ 2).
3466, 3389 (NH2)
1603 (NH2)
1363 (NO)
3 lines
g = 2.0054
an = 13 G
2. Synthesis of imino- and bis-iminopyridine ligands
bearing ter-butylaminoxyl groups: radical formation
1361 (NO)
1641 (C@N)
5 lines
g = 2.0054
2.1. Synthesis of the (N-ter-butyl-hydroxyamino)anilines
an/2 = 6.7 G
13
14
15
1361 (NO)
1641 (C@N)
3 lines
g = 2.0059
an = 12.5 G
Bromoanilines were protected in good yields, in two
steps according to Weisenfeld [45] (Scheme 1): the
monosilylation of the amino group by Me3SiCl in the
presence of Et3N in a first step was followed by the for-
mation of the amino-Grignard reagent and its condensa-
tion with Me3SiCl.
Hydroxylamines 2b and 2c were obtained in 77% and
94% yields, respectively. Oxidation of these derivatives
using PbO2 gave 3-, 3b and 4-[(N-ter-butyl-N-oxy-
amino)-N,N-bis-(trimethylsilyl)]aniline, 3c (Eq. (1))
(Table 1). In contrast, 1a reacted with nBuLi but the
formed organolithium derivative did not react with 2-
methyl-2-nitrosopropane; after hydrolysis, N,N-bis-tri-
methylsilylaniline was only obtained.
361 (NO)
1641 (C@N)
3 lines
g = 2.0057
an = 13.1 G
1364 (NO)
1634 (C@N)
9 lines
g = 2.0036
an/2 = 6.0 G
EPR spectra (CHCl3, ꢁ10ꢀ5 M) were run at room tem-
perature and gave a 1:1:1 triplet due to the coupling of
the radical with nitrogen (3b: g = 2; an = 13.1 G, 3c:
g = 2.0061; an = 13.1 G). We never observe hyperfine
coupling with the hydrogens from butyl and phenyl
groups.
The desilylation of the amino group of 2b and 2c was
performed with aqueous HCl in CHCl3 as solvent. The
results are very different depending on the position
of the substitution group, meta or para (Scheme 2). In
the case of the meta derivative 2b, deprotection led to
the expected 3-(N-ter-butyl-N-hydroxyamino)aniline 4b
in 90% yield. With the para derivative 2c, the deprotec-
tion reaction led to a red coloured mixture characteristic
of the formation of the aminoxyl radical; this was con-
firmed by IR and UV measurements and also by the
EPR spectrum of the red solution showing three lines
Me3Si SiMe3
N
Me3Si SiMe3
N
PbO2
H
CHCl3
N
O
N
O
3b, 3c
2b, 2c
ð1Þ
Unfortunately, when the solutions of 3b and 3c are
concentrated, they decompose readily; however, the rad-
icals 3b and 3c were characterized in the mother liquor
using IR, UV and EPR spectroscopy (Table 1). For in-
stance, the IR spectra of 3c shows the disappearance of
the OH bands at 3595 and 3237 cmꢀ1 and an intense
band at 1359 cmꢀ1 attributed to the N–O group [46].
Me3Si SiMe3
Me3Si SiMe3
N
N
NH2
1) nBuLi, ter-BuNO
1) Me3 SiCl
H
2) H2O
N
O
2) MeMgBr, Me3 SiCl
Br
Br
2
1
a: ortho; b: meta; c: para positions
Scheme 1.

C. Uerpmann et al. / Journal of Organometallic Chemistry 690 (2005) 197–210
199
NH2
NH2
PbO2
H
N
CHCl3
N
O
O
5b
4b
Me3Si SiMe3
N
1) HCl (2M), CHCl3
2) NaOH
H
NH2
N
O
2b, 2c
N
5c
O
Scheme 2.
1
Compounds 6b and 7b were characterized using H
at g = 2.0054 with aN = 13.0 G (Table 1) which corre-
sponds to 5c. These values are analogous to those ob-
tained by Rassat et al. [47]; it must be underlined that
we were unable to prepare in reasonable yields the
parahydroxylaniline 4c using the Grignard procedure
of these authors. After filtration and distillation of the
solution of 5c, N-ter-butyl-phenyl-1,4-diamine 6c was
obtained in 40% yield: deprotection and oxidation
occurred in the same step but decomposition during iso-
lation led to the diamine 6c.
Oxidation of 4b led to 5b which was characterized in
solution (Table 1). Indeed, when we tried to isolate 5b
we observed the decomposition of the radical as in the
case of 5c. Radical 5b gave a mixture of 3-amino-(N-
ter-butyl)aniline 6b and the imino quinone 7b (Eq. (2)).
NMR, IR and UV spectroscopy. These results are in
good accordance with the results obtained by Calder
and Forrester in the case of phenyl-ter-butylnitroxides
Table 2
˚
Selected bond length (A) and angles (ꢁ) of 7b
˚
Bond length (A)
N1–O1
N1–C10
N1–C1
C1–C2
C2–C3
C3–C4
C4–C5
C5–C6
C6–C1
N2–C3
O2–C4
C10–C11
C10–C12
C10–C13
1.290(5)
1.523(4)
1.359(3)
1.419(3)
1.365(4)
1.487(3)
1.449(4)
1.342(3)
1.448(3)
1.358(3)
1.244(3)
1.531(4)
1.542(4)
1.525(4)
NH2
NH2
NH2
O
+
N
N
O
N
O
H
5b
6b
7b
Bonds angles (ꢁ)
C1–N1–O1
C1–N1–C10
O1–N1–C10
N1–C1–C2
N1–C1–C6
C6–C1–C2
ð2Þ
118.0(2)
125.6(2)
116.3(2)
119.4(2)
121.3(2)
119.4(2)
121.3(2)
124.2(2)
115.8(2)
120.0(2)
120.5(2)
122.9(2)
116.5(2)
122.5(2)
120.2(2)
11.4(2)
C1–C2–C3
N2–C3–C2
N2–C3–C4
C2–C3–C4
O2–C4–C3
O2–C4–C5
C3–C4–C5
C4–C5–C6
C5–C6–C1
N1–C10–C11
N1–C10–C12
N1–C10–C13
C11–C10–C12
C12–C10–C13
C13–C10–C11
107.2(2)
107.9(2)
108.0(2)
108.4(2)
113.6(2)
Fig. 1. ORTEP view of 7b.

200
C. Uerpmann et al. / Journal of Organometallic Chemistry 690 (2005) 197–210
[48–50]. Moreover, a red crystal of 7b was obtained and
the structure solved by X-ray analysis. Fig. 1 shows the
ORTEP of the crystal structure of 7b and Table 2 gives
selected bond length and angles of 7b.
compound. We were interested in the preparation of
ter-butyl aminoxide substituted compounds (Scheme 3).
Diazabutadiene derivatives are easily prepared by the
condensation reaction between an amine and glyoxal or
butane-2,3-dione; we tried the reaction of the latter with
the hydroxylamine 4b in order to prepare the first amin-
oxyl-substituted 1,4-diazabutadiene (Scheme 3). The
reaction was performed under acidic catalysis, in hexane
as solvent, which allowed the precipitation of 8 as soon
as formed. Compound 8 is stable under inert atmos-
phere but it oxidizes slowly in air. Oxidation of 8 with
freshly prepared Ag2O in CHCl3 gave 1,4-bis[3-(N-ter-
butyl-N-oxyaminophenyl)]-2,3-dimethyl-1,4-diazabut-
adiene 9 (Scheme 3).
˚
˚
The C2–C3 (1.365 A) and C3–C4 (1.487 A) distances
˚
and the double bond character of C1–N1 (1.359 A) and
˚
C4–O2 (1.244 A) correspond to a iminoquinone struc-
ture, confirmed by the O2–C4–C3 (120.5ꢁ) and N1–
C1–C6 (121.3ꢁ) angles corresponding to sp2 carbons.
In summary, we were able to synthesize the 3-(N-ter-
butyl-N-hydroxyamino)aniline 4b and we shall use it as
a synthesis precursor to a new diazabutadiene and to
Schiff bases in order to use them as transition metal
ligands.
Compound 9 was characterized using IR, UV, and
EPR spectroscopies (Table 1). The IR spectrum shows
the disappearance of the OH bands of 8 at 3591 and
3253 cmꢀ1, which demonstrates that the oxidation was
complete. The EPR spectrum of 9 shows 5 mains lines
2.2. Synthesis of substituted diazabutadiene and Schiff
bases: radical formation
Diazabutadiene, imino- and bis-iminopyridine deriv-
atives are large families of bidentate ligands which are
able to coordinate to transition metal [51]. For instance,
imino- and bis-iminopyridine derivatives are currently
used in the synthesis of, as an example, hydrogenation
catalysts prepared by Brookhart et al. [42–44].
with hyperfine coupling for lines 1,
3 and 5
(g = 2.0054, an/2 = 6.7 G). This pattern is consistent with
spin exchange between the two unpaired electrons, and
with an inter-electronic exchange J > an [52]. This inter-
action is also confirmed by the nitrogen splitting of 6.7
G, that is half of the value observed in the case of a sin-
gle radical. However, we did not observe any EPR signal
The ligands are prepared using the condensation
reaction between an amine derivative and a carbonyl
NH2
O
O
N
O
N
H3C
CH3
R
N
OH
4b
R = H
R = CH3
H+
H+
O
H+
O
H3C
CH3
R
N
N
70 %
Ag2O
8
N
N
N
80 %
60 - 75 %
N
N
N
12
OH
HO
HO
R = H, 10
R = CH3, 11
O
N
Ag2O
Ag2O
N
N
H3C
R
CH3
N
N
N
N
N
N
O
R = H, 13
R = CH3, 14
N
N
N
9
15
O
O
O
Scheme 3.

C. Uerpmann et al. / Journal of Organometallic Chemistry 690 (2005) 197–210
201
corresponding to Dms = 2 at g = 4. The hyperfine cou-
plings were fit by spectral simulation [53] as an/2 = 6.7,
ao = 1.7, am = 0.7 and ap = 1.8 G. (o, m, p correspond
to the hydrogen atoms in ortho, meta and para positions,
respectively).
The iminopyridines 10 and 11 and the bis(iminopyri-
dine) 12 were obtained by condensation of amine
4b with 2-formylpyridine (R = H), 2-acetylpyridine
(R = CH3), and 2,6-diacetylpyridine, respectively. The
reactions were performed in refluxing hexane for 72–96
h, under acidic catalysis; this process allowed the precip-
itation of the derivatives as soon as formed, and the iso-
lation of pure 10–12 by filtration, in good yields. These
iminopyridines and bis(iminopyridine) are stable under
inert atmosphere and were characterized using standard
techniques. The oxidation of 10–12 was performed in
chloroform using freshly prepared Ag2O and led to
13–15 (Scheme 2). The reactions were followed using
IR spectroscopy, by the disappearance of the OH bands
(3588 and 3242 cmꢀ1). The radicals were analysed using
IR, UV and EPR spectroscopies. The results are sum-
marized in Table 1. The infra-red spectra of 13 and 14
show N–O and C@N frequencies at 1361 and 1641
cmꢀ1, respectively, while in 15 these bands are observed
at 1364 and 1634 cmꢀ1. The UV spectra of 13–15 show
3380
3400
3420
3440
3460
3480
H (Gauss)
Fig. 2. EPR spectrum of 15.
As observed in the case of the other radicals (vide su-
pra), 15 is not stable; it decomposes according to Eq. (3).
Indeed, column purification gave a red compound char-
acterized as 7b, already observed in the case of the
decomposition of radical 4b, and diacetylpyridine, iden-
tified by NMR.
the p–p absorption band of the aminoxyl group at 289
*
or 291 nm. Finally, EPR spectra of 13 and 14 gave the
expected triplet at g = 2.0059 with aN = 12.5 G, 13 and
g = 20057, aN = 13.1 G, 14. In the case of the bis(imino-
nitroxide) 15, the EPR spectrum (Fig. 2) shows 9 lines
centred at g = 2.0036 with lines 1, 3, 5, 7 and 9 having
a hyperfine structure, and lines 1, 2 and 8, 9 being less
intense than lines 3, 5 and 7. This EPR spectrum is typ-
ical of a diradical with J ꢁ a [52].
O
NH2
15
+
N
O
O
N
O
7b
ð3Þ
Table 3
Physical properties of the complexes
Ligand
Metal salt
Complex
IR cmꢀ1
MS FAB+ NBA Mz, intensity
10 L
NiCl2 Æ 4H2O
Ni(L)2Cl2 Æ 1H2O
16
1631
1361
1630
1360
1638
1383
633 [M+ ꢀ Cl, 100]
MnCl2 Æ 6H2O
Mn(L)2Cl2 Æ 1H2O
17
628 [M+ ꢀ Cl, 100]
Gd(NO3)3 Æ 5H2O
Gd(L)(NO3)3 Æ 5H2O
24
11 L0
NiCl24 Æ H2O
MnCl2 Æ 6H2O
Ni(L0)2Cl2 Æ 1H2O
18
Mn(L0)2Cl2 Æ 1H2O
19
1630
1598
1633
1592
659 [M+ ꢀ Cl, 100]
656 [M+ ꢀ Cl, 100]
12 L2
Zn(NO3)2 Æ 4H2O
NiCl2 Æ 4H2O
Zn(L2)(NO3)2 Æ 3H2O
25
1638
1383
1626
1590
1633
1592
1629
1590
1633
1383
615 [M+ ꢀ NO3, 100]
580 [M+ ꢀ Cl, 100]
577 [M+ ꢀ Cl, 85]
Ni(L2)Cl2 Æ 1H2O
26
MnCl2 Æ 6H2O
Mn(L2)Cl2 Æ 1H2O
27
Mn(ClO4)2 Æ 6H2O
Gd(NO3)3 Æ 5H2O
Mn(L2)2(ClO4)2 Æ xH2O
31
1129 (M+ ꢀ ClO4, 38)
1029 (M+ ꢀ 2ClO4, 54)
769 (M+ ꢀ NO3, 5)
Gd(L2)(NO3)3 Æ 3H2O
32
707 (M+ ꢀ 2NO3, 15)

202
C. Uerpmann et al. / Journal of Organometallic Chemistry 690 (2005) 197–210
2.3. Complexation of 10, 11, and 12 with M(II) salts
(M = Mn, Ni, Zn) and Gd(NO3)3 and oxidation
reactions
and 1361 cmꢀ1 (m NO) characteristic of the ligand. Mass
spectroscopy and elemental analysis indicated two lig-
ands per metal (Table 3). The complexes 16 and 18
may be described as Ni(10)2Cl2 Æ 1H2O and Ni(11)2-
Cl2 Æ 1H2O, respectively. The possible structure is given
in Scheme 4 with the chlorine atoms in trans positions
in order to minimize steric hindrance.
Using MnCl2 Æ 6H2O and 10 and 11, the two com-
plexes 17 and 19 were obtained. As in the case of the
nickel complexes, IR spectra and elemental analysis sug-
gested complexes with two ligands per metal:
Mn(10)2Cl2 Æ 1H2O, 17 and Mn(11)2Cl2 Æ 1H2O, 19,
whose must have the structure proposed in the case of
the nickel complexes 16 and 18 (Scheme 4).
The ligands 10–12 were synthesized in order to be
complexed with transition metals or lanthanides to en-
hance the total spin number of the molecule. Due to
the low stability of the radicals 9, 13–15, we first pre-
pared the complexes corresponding to the ligands 10–
12 and oxidized the complexes using freshly prepared
Ag2O. The metals used are: Mn(II), Ni(II), Zn(II) and
Gd(III). Table 3 summarizes the observed results.
The complexation reactions of the hydroxylamines 10
and 11 with NiCl2, MnCl2 and Gd(NO3)3 (using the hy-
drate salts) were performed under inert atmosphere, in
THF as solvent and the complexes were obtained as
orange-beige solids in 60–65% yields.
The oxidation of the nickel complexes 16 and 18 were
performed using silver oxide in chloroform as solvent.
The oxidized complexes 20 and 22, at room tempera-
ture, gave exactly the same EPR spectra: in chloroform,
three lines at g = 2.0058 with a hyperfine coupling
In the case of Ni(II) complexes, the IR spectra show
intense bands at 1631 and 1593 cmꢀ1 (m C@N, m C@C)
CH3
CH3
N
Zn(NO3)2
N
N
NiCl2
+
MnCl2
Gd(NO3)3
N
N
OH
OH
12
N
OH
N
Cl
N
R
OH
R
N
N
Ni
+
NiCl2, 4 H2O
N
R
N
N
Cl
R = H 16
R = Me 18
R = H 10
R = Me 11
OH
N
Scheme 4.

C. Uerpmann et al. / Journal of Organometallic Chemistry 690 (2005) 197–210
203
constant an = 12.7 G, characteristic of the aminoxyl
group. This pattern demonstrates that there is no cou-
pling between the two aminoxyl radicals. As very often
noticed, due to a short relaxation time and a broad sig-
nal, the EPR signal of Ni2+ was not observed. The solid
state EPR spectrum of 20 (or 22) is shown in Fig. 3; in
this case, the signal at g = 4, due to the Dms = 2 transi-
tion of the NO group, was observed.
N
N
N
M
X
X
The oxidation of 17 and 19 gave the radicals, 21 and
23, respectively; EPR spectra of 21 and 23 are identical
and show a very broad band due to Mn2+ and the three
lines characteristic of the aminoxyl group. As expected
in the case of the latter group, a signal at g = 4 was also
observed. But, similarly to the nickel complexes 20 and
22, no coupling was observed between the two radicals
of the complex.
In the case of gadolinium, the 1:1 complex obtained
with 10 may be written as Gd(10)(NO3)3 Æ 5H2O, 24.
The EPR spectrum of the oxidized complex 24, prepared
using Ag2O in a 80:20 mixture of chloroform and etha-
nol, shows the superposition of a broad signal with a
peak to peak width of 145 G due to Gd3+, and the three
lines at g = 2.0058 with an = 12.6 G of the nitroxide
group.
Many complexes with a bis-iminopyridine ligand are
known. For instance, Brookhart et al. [54,55]. and Gib-
son and his group [56] have found that this family of
complexes (for instance with cobalt or iron) are very ac-
tive catalysts in the polymerization of olefins. X-ray
analysis of the complexes shows that the metal is penta-
coordinated with the three nitrogen in the same plane
(Fig. 4).
Fig. 4.
In some cases, using different anion Xꢀ, hexacoordi-
nated complexes may be obtained: [MII(Ligand)2X2]
with Xꢀ ¼ PF6ꢀ; ClOꢀ4 or BFꢀ4 . The latter are octahedral
with a distorted square base [57]. In our case, we have
studied the complexation of the bis-iminopyridine 12
with different metal salts (Scheme 4).
In order to characterize the complex by NMR, we
used Zn(NO3)2 as a non-paramagnetic metal salt. The
reaction was performed in THF at room temperature
for 2 h, using Zn(NO3)2 Æ 4H2O and 12 and the complex
25 was obtained in 65% yield. Elemental analysis and
mass spectrum gave a 1:1 metal-to-ligand ratio. The for-
mula of 25 may be written as Zn(12) (NO3)2 Æ 3H2O. In-
fra red spectrum gave the complexed C@N band
frequency at 1638 cmꢀ1. In the NMR spectrum, the
shifts of the aromatic protons (Fig. 5) demonstrate the
formation of the complex. Indeed, in the ligand 12, the
protons of the pyridine group in positions 1 and 2 are
situated at 8.1 and 8.45 ppm, and the aromatic protons
appeared between 6.6 and 7.3 ppm. After complexation,
the pyridine protons are shifted to lower field and ap-
peared as a singlet at 8.75 ppm. Aromatic protons are
also shifted of 0.2–0.5 ppm towards lower field. All these
results are indicative of a hexacoordinated zinc atom
with the three nitrogen atoms of the ligand and two
NOꢀ3 groups, one with monodentate and the second
with bidentate coordinations. Oxidation of 25 gave 28
which shows the EPR spectrum of the aminoxyl group,
i.e., three sharp lines at g = 2.0056 with aN = 13 G.
With NiCl2 Æ 4H2O and 12, the beige coloured com-
plex 26 was prepared in THF, at room temperature
for one hour in 60% yield. IR spectrum gave the ligand
bands at 1626 cmꢀ1 (C@N), 1590 cmꢀ1 (C@C) and 1369
cmꢀ1 (NO). The elemental analysis and the mass spec-
trum indicated a 1:1 metal to ligand ratio. The complex
26 may be described as Ni( 12)Cl2 Æ 1H2O with a penta-
coordinated structure analogous to that described in
Fig. 4. Oxidation of the aminoxyl group using Ag2O
in chloroform gave the complex 29. EPR spectrum of
the latter in solution and at room temperature gave
the aminoxyl signal: g = 2.0056, aN = 12.7 G. As previ-
ously observed, the ESR signal of Ni2+ was not ob-
served. Surprisingly, there is no coupling between the
two nitroxy radicals; indeed, the oxidized ligand 15 itself
gave an EPR spectrum with nine lines (vide supra).
1000
2000
3000
4000
5000
H (Gauss)
3300
3400
3500
3600
3700
3800
H (Gauss)
Fig. 3. Solid state, room temperature EPR spectrum of 20 (identical to
22): (a) around 3500 G; (b) between 1000 and 5000 G.

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C. Uerpmann et al. / Journal of Organometallic Chemistry 690 (2005) 197–210
Ph-H
(a)
++
HO
N
OH
N
N
Py-H1
N
-
Py-H2
2 ClO4
Mn
N
N
N
N
9.0
8.5
8.0
7.5
ppm
7.0
6.5
6.0
N
HO
N
OH
Py
H1+H2
(b)
Fig. 6.
The oxidation of 31 was performed in dichlorometh-
ane using Ag2O as oxidation agent and gave 33. The
EPR spectrum of the latter is reproduced in Fig. 7.
We were unable to interpret this unexpected shape of
this signal.
Ph-H
Using Gd(NO3)3 Æ 5H2O and the ligand 12, the red
complex 32 was obtained and may be described as
Gd(12)(NO3)3 Æ 5H2O. The structure of 32 must corre-
spond to a gadolinium atom with eight coordinations,
i.e., the three nitrogen atoms, two bidentate and one
monodentate NO3 groups.
The oxidation of 32 using silver oxide in a mixture of
THF and ethanol (80:20) gave a red compound; the
EPR spectrum in solution, shows the superposition of
a broad signal due to Gd3+, and the three lines of a nitr-
oxide group (Table 3).
9.0
8.5
8.0
7.5
7.0
6.5
6.0
ppm
Fig. 5. 1HNMR spectra, aromatic part of: (a) ligand 12; (b) complex
25.
An analogous reaction was observed in the case of
MnCl2 Æ 6H2O. The complex obtained, 27, may be de-
scribed as Mn(12)Cl2 Æ 1H2O with a pentacoordinated
structure (Fig. 4). The oxidation reaction performed
with Ag2O in CH2Cl2 as solvent gave complex 30.
EPR spectrum of the latter, in solution and at room
temperature, shows the superposition of two signals:
one at g = 2.01 with six lines corresponding to Mn2+
(S = 5/2) and the second at g = 2.007 with three lines
due to the nitroxy group. As observed in the case of
the nickel complexe, no interaction was observed be-
tween the two radicals of the ligand.
[G]
As said previously, hexacoordinated complexes of
bis-iminopyridines may be obtained by changing the an-
ion of the metal salt. We have performed the complexa-
tion reaction of 12 using Mn(ClO4)2 as metal(II) salt.
Complex 31 was obtained as orange crystals: unfortu-
nately, no crystal was suitable for a X-ray diffraction
study was obtained. The mass spectrum indicated a
1:2, metal to ligand ratio; as observed in the literature
for related compounds, the Mn2+ center must be in a
octahedral environment with the perchlorate anions in
the outer coordination sphere (Fig. 6).
3460
3480
3500
3520
3540
3560
Gauss
Fig. 7. EPR spectrum of 33.

C. Uerpmann et al. / Journal of Organometallic Chemistry 690 (2005) 197–210
205
3. Conclusion
tubes in degassed solvent; concentration range: 10ꢀ5
–
10ꢀ6 mole/L.
In conclusion, imino- and bis-iminopyridines bearing
one or two N-ter-butyl-N-hydroxyamino groups, respec-
tively, were prepared. These derivatives were oxidized
using PbO2 to give the N-ter-butyl-N-aminoxyl com-
pounds; the latter were characterized in solution by
EPR spectroscopy but, they decompose readily when
the solutions are concentrated to give a mixture of ami-
no-(N-ter-butyl)aniline and an iminoquinone. The latter
was characterized by the standard technics and by X-ray
diffraction.
4.2. Crystal data for 7b
Nonius CAD 4 automated diffractometer, crystal of
dimensions 0.30 · 0.10 · 0.06 m3 mounted on a glass fi-
ber with mineral oil at 173 K. C10H14N2O2, M = 194.23,
monoclinic, space group P21/c, a = 10.490(4), b =
˚
8.061(21), c = 11.689(2) A, b = 95.67(2)ꢁ, V = 983.6(26)
3
˚
A , Dcalc. = 1.312, T = 170 K, Z = 4, F (000) = 416,
lMo Ka = 0.09 mmꢀ1, 2541 reflections measured,
2311 unique (Rint = 0.0532) which were used in all calcu-
lations. The structure was solved by direct methods
using SHELXS 86 [62], and refined by least- squares on
F2 with the help of SHELXL 93 [63]. The hydrogen atoms
on the aromatic ring and the t-butyl were positioned by
calculation [63]. The hydrogen atoms on N2 were re-
vealed on a difference Fourier map and their coordinates
were fixed throught the subsequent refinement cycles.
The final R(F) value was 0.0435 for 869 Fo > 4s(Fo)
and wR(F2) = 0.0762.
These imino- and bis-iminopyridines were used as
efficient pincer ligands towards several MII(Mn2+
,
Ni2+, Zn2+) and GdIII salts giving the corresponding
complexes with one or two ligands, depending on
the ligand, the metal and the counter anion. The oxi-
dation of the complexes using Ag2O occurs readily to
give the N-ter-butyl-N-aminoxyl derivatives. These
complexes were characterized by EPR spectroscopy.
In these spectra, the part corresponding to the nitrox-
ide radical are very similar to the oxidized ligands
themselves, indicating that there are no interactions
between the radicals in the complexes through the me-
tal center.
Safety note: Although we have experienced no prob-
lems, perchlorate salts are potentially explosive. They
should be handled with extreme care and used only in
small quantities without heat. [64,65]
4. Experimental part
4.3. 3-, and 4-(N-ter-butyl-N-hydroxyamino)-N,N-
bis(trimethylsilyl)aniline 2b, and 2c
4.1. General
A solution of BuLi (2,2 M, 25 mL, 55 mmol) was
added dropwise to a solution of 1b or 1c (17 g, 54
mmol.) in 150 mL diethylether at ꢀ20 ꢁC and the mix-
ture was stirred for 1 h at that temperature. A solution
of 2-methyl-2-nitrosopropane (5 g, 57 mmol) in 60 mL
of diethylether was added dropwise in 10 min to the
reaction mixture at 0 ꢁC. The mixture was allowed to
reach room temperature and stirred for 1 h. After
hydrolysis at 0 ꢁC and standard work-up, the residue
was crystallized from pentane to give a white crystalline
powder.
All reactions were carried out under argon or nitro-
gen using a vacuum line and Schlenk tubes. Solvent
were dried and distilled before use. The following
compounds were synthesized according to published
methods: 4-bromo-N-(trimethylsilyl)aniline [45], 4-bro-
mo-N,N-bis(trimethylsilyl)aniline [45], 2-methyl-2-nitr-
osopropane [58], 4-(N-ter-butyl-N-oxyamino)aniline [47],
4-N-ter-butyl-phenyl-1,4-diamine [59], 4-bromo-(N-ter-
butyl-N-hy-droxyamino)aniline [60], 4-bromo-(N-ter-
butyl-N-ter-butyldimethylsilyl)aniline [61]. Ag2O was
prepared using the standard procedure: reaction of
AgNO3 with Ba(OH)2. All the metal salts used are hy-
drates: NiCl2 Æ 4H2O; MnCl2 Æ 6H2O; Gd(NO3)2 Æ 5H2O;
Zn(NO3)2 Æ 4H2O; Mn(ClO4)2 Æ 6H2O.
4.3.1. Compound 2b
Yield: 77%, m.p. = 179–181 ꢁC. IR (CCl4), m (cmꢀ1):
3589, 3236 (OH), 1360 (N–OH), 1247 (SiMe3). 1H
NMR (CDCl3), d (ppm): 0.08 (s, 18 H, SiMe3), 1.24 (s,
9 H, ter-Bu), 6.68–7.35 (m, 4H, Ar). MS (FAB+, NBA)
(m/z, intensity): 325 (M+, 60), 252 (M+ ꢀ SiMe3, 50), 73
(SiMe3+, 100). Anal. Calc. for C16H32N2OSi2: C, 59.20;
H, 9.94; N, 8.63. Found: C, 58.84; H, 9.93; N, 8.50%.
1H NMR spectra were obtained on a Bruker DPX
200; chemical shifts, d, are relative to TMS. IR spectra
were recorded on a Perkin–Elmer 1600 with a 4 cmꢀ1
resolution. UV spectra were obtained with a Secaman
Anthelie Advanced instrument using quartz cells (;1
cm); wave lengths are in nm. Mass spectra were recorded
on a Jeol JMS D300 using electronic impact (EI), or
Fast Atom Bombardment in the positive (FAB+) or neg-
ative (FABꢀ) modes with 3-nitro-benzyl alcohol (NBA)
or thioglycerol (GT) as matrixes. EPR spectra were re-
corded on a Bruker 500 (X-band) using standard EPR
4.3.2. Compound 2c
Yield: 94%, m.p. = 176–178 ꢁC. IR (CCl4), m (cmꢀ1):
3595, 3237 (OH), 1348 (N–OH), 1249 (SiMe3). 1H
NMR (CDCl3), (ppm): 0.07 (s, 18H, SiMe3), 1.07 (s, 9
3
H, ter-Bu), 6.81 (d, 2H, JHH = 7.9 Hz), 7.35 (d, 2H,

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C. Uerpmann et al. / Journal of Organometallic Chemistry 690 (2005) 197–210
3JHH = 7.9 Hz). MS (FAB+, NBA) (m/z, intensity): 323
(M+ ꢀ H, 30), 267 (M+ ꢀ ter-Bu, 90), 251 (M+ ꢀ SiMe3,
95), 73 (SiMe3+, 100). Anal. Calc. for C16H32N2OSi2: C,
59.20; H, 9.94; N, 8.63. Found: C, 58.77; H, 9.85; N,
8.45%.
66.64; H, 8.95; N, 15.54. Found: C, 67.21; H, 8.83; N,
15.61%.
4.6. Deprotection of 3c and oxidation
A water solution of HCl (3 M, 10 mL, 6 mmol) was
added dropwise to a solution of 3c (1.9 g, 6 mmol) in
chloroform (25 mL) and the mixture was stirred for 30
min. After phase separation, chloroform, 50 mL, was
added to the water phase and, under stirring a NaOH
solution (3 M, 11 mL, 33 mmol) was added dropwise
up to a pH of 8. The organic phase was separated and
dried over MgSO4 Æ PbO2 (3 g, 12 mmol) was added,
stirred for 30 min and the red solution was filtered over
celite. All the analysis were done using this chloroform
solution. IR (CHCl3), m (cmꢀ1): 3466, 3389 and 1603
(NH2), 1363 (N–O). EPR (CHCl3): g = 2.0054, 3 lines
aN = 13 G. UV (CHCl3), k nm: 232 (p–p* Ph), 292 (p–
p* N–O), 481 (n–p* N–O).
4.3.3. Compound 2a
No reaction was observed, using the same procedure,
between the lithium derivative of 1a and 2-methyl-2-
nitrosopropane. After hydrolysis, N,N-bis(trimethylsi-
lyl)aniline was obtained in 97% yield.
4.4. 3- and 4-(N-ter-butyl-N-oxyamino)-N,N-bis(tri-
methylsilyl)aniline 3b and 3c
PbO2 (1.2 g, 5 mmol) was added to a solution of
2b or 2c (0.52 g, 1.6 mmol) in 50 mL of CHCl3.
The mixture was vigorously stirred for 25 min (up
to the disparition of the OH band in IR spectros-
copy). The red solution was filtrated using celite and
all analyses were performed on this solution, without
evaporation.
The chloroform solution was evaporated under vac-
uum and the residue distillated (80 ꢁC, 0.1 Torr) to give
an orange oil with 40% yield (0.4 g, 2.4 mmol). The com-
pound was characterized as 4-N-ter-butyl-phenyl-1,4-
diamine. IR (CCl4), m (cmꢀ1): 3461, 3384 (NH, NH2).
1H NMR (CDCl3), d (ppm): 1.23 (s, 9H, CH3), 3.25 (s,
4.4.1. Compound 3b
IR (CCl4), m (cmꢀ1): 1360 (N–O), 1247, 970 (SiMe3).
EPR (CHCl3): three lines at g = 2.0059, aN = 13.1 G.
UV (CHCl3), k nm: 233 (p–p* Ph), 289 (p–p* N–O),
482 (n–p* N–O).
3
3H, NH), 6.61 (d, 2H, JHH = 8.1 Hz, Ar), 6.77 (d,
2H,3JHH = 8.1 Hz, Ar). MS (FAB+, NBA) (m/z, inten-
sity): 164 (M+, 100), 149 (M+ ꢀ CH3, 40).
4.4.2. Compound 3c
4.7. 3-(N-ter-butyl-N-oxyamino)aniline 5b
IR (CCl4), m (cmꢀ1): 1359 (N–O), 1249, 974 (SiMe3).
EPR (CHCl3): three lines at g = 2.0061, aN = 13.1 G.
UV (CHCl3), k nm: 233 (p-p* Ph), 288 (p–p* N–O),
479 (n–p* N–O).
PbO2 (2.4 g, 10 mmol) was added to a solution of 4b
(1.2 g, 3.7 mmol) in chloroform (60 mL) under stirring.
The reaction was followed using IR spectroscopy; after
10 min the OH bands have disappeared. The red solu-
tion was filtered over celite and all analysis were done
on that solution. IR (CHCl3), m (cmꢀ1): 3460, 3390
and 1597 (NH2), 137 (N–O). EPR (CHCl3):
g = 2.0053, 3 lines aN = 13.2 G. UV (CHCl3), k nm:
230 (p–p* Ph), 293 (p–p* N–O), 484 (n–p* N–O).
4.5. 3-(N-ter-butyl-N-hydroxyamino)aniline 4b
A deoxygenated water solution of HCl 4M (40 mL,
0.16 mol) was added dropwise to a ethereal solution
(25 mL) of 3b (6.3 g, 20 mmol) and the mixture was stir-
red vigorously for 5 min under inert atmosphere. After
phases separation and extraction of the water phase with
diethylether, a solution of NaOH (4 M solution, 40 mL,
0.16 mmol) was added dropwise to the ethereal solution
under vigorous stirring. The organic phase was sepa-
rated, dried over MgSO4 and the solvent was removed
under vacuum to leave a white powder; recrystallization
from pentane gave 4b in 90% yield. m.p. 130–133 ꢁC. IR
(CCl4), m (cmꢀ1): 3587, 3219 (OH), 3479, 3389 (NH2). 1H
NMR (CDCl3), d (ppm): 1.16 (s, 9H, ter-Bu), 2.08 (s,
2H, NH2), 6.47–6.53 (m, 1H, C5–H), 6.63–6.68 (m, 2
H, C4- and C6–H), 7.02–7.11 (m, 1H, C2–H). 13C
NMR (CDCl3), d (ppm): 26.5 (CH3), 61 (C–CH3), 112
(C2), 113 (C6), 115 (C4), 128 (C5), 146 (C3), 150 (C1).
MS (FAB+, NBA) (m/z, intensity): 181 (M + 1+, 100),
124 (M+ ꢀ ter-Bu, 35). Anal. Calc. for C10H16N2O: C,
4.8. Decomposition of 3-(N-ter-butyl-N-oxyamino)ani-
line 5b: characterization of 3-amino-(N-ter-butyl)aniline
6b and quinone 7b
The solution of 5b was dried under vacuum and the
residue dissolved in diethylether and chromatographed
over silica. A red compound was obtained after evapo-
ration of the solvent. Recrystallization from diethyl-
ether; m.p. 99–101 ꢁC. IR (CHCl3), m (cmꢀ1): 3477,
1
3352 and 1585 (NH2), 1630 (C@O). H NMR (CDCl3),
d (ppm): 7.75 (dd, 1H, J = 3 Hz, J = 10 Hz), 6.9 (d, 1H,
J = 3 Hz), 6.3 (d, 1H, J = 10 Hz), 4.6 (broad, 2H, NH2),
1.75 (s, 9H, ter-Bu). MS (FAB+, NBA) (m/z, intensity):
195 (M+ + 1, 5), 139 (M+ ꢀ ter-Bu, 100). IR and NMR
values are similar to the values observed in the case of

C. Uerpmann et al. / Journal of Organometallic Chemistry 690 (2005) 197–210
207
N-ter-butylated imino quinone 3-(ter-butylamino)-N-
ter-butyl-1,4-benzoquinone imine N-oxide [66]. See Ta-
ble 2 and Fig. 1 for X-ray analysis.
(ppm): 1.18 (s, 9H, ter-Bu), 2.36 (s, 3H, N@C–CH3),
6.62–7.32 (m, 4H, Ar), 7.41 (m, 1H, Py C5–H), 7.82
(m, 1H, Py C3–H or C4–H), 8.28 (m, 1H, Py C4–H or
C3–H), 8.70 (m, 1H, Py C6–H). MS (FAB+, NBA)
(m/z, intensity):284 (M+, 50), 267 (M+ ꢀ OH, 50), 57
(ter-Bu+, 100).
4.9. 1,4-bis-[3-(N-ter-butyl-N-hydroxyamino)phenyl]-
2,3-dimethyl-1,4-diazabutadiene 8
4.12.
N-[3-(N-ter-butyl-N-oxyaminophenyl)]-(2-pyr-
A mixture of 2,3-butanedione (0.35 g, 4 mmol) and 4b
in hexane (80 mL) was heated under reflux in a Dean
Stark apparatus for 30 h, with a few drops of acetic acid
to catalyze the reaction. Precipitation of 8 occurred dur-
ing the reaction. The mixture was cooled to 0 ꢁC, filtered
and the solid washed two times with 30 mL of cold hex-
ane. 8 was obtained as a brown-grey powder with 70%
yield. m.p. 148–151 ꢁC (dec.). IR (CCl4), m (cmꢀ1):
3591,3253 (OH), 1641 (C@N). 1H NMR (CDCl3), d
(ppm): 1.12 (s, 18H, ter-Bu), 2.13 (s, 6H, CH3), 6.57-
6.94 (m, 2H, C5–H), 7.04–7.15 (m, 4H, C4–H and C6–
H), 7.23–7.52 (m, 2H, C2–H). MS (FAB+, NBA) (m/z,
intensity): 411 (M+ + H, 25), 57 (ter-Bu, 100).
idyl)methanimine 13 and N-[3-(N-ter-butyl-N-oxyami-
nophenyl)]-(2-pyridyl)ethanimine 14
Same procedure as for 9.
4.12.1. Compound 13 and 14
IR (CHCl3), m (cmꢀ1): 1641 (C@N), 1361 (N–O). UV
(CHCl3), k nm: 233 (p–p* Ph), 289 (p–p* N–O), 488 (n–
p* N–O). 13: EPR (CHCl3): g = 2.0059, 3 lines, aN = 12.5
G. 14: EPR (CHCl3): g = 2.0057, 3 lines aN = 13.1.
4.13. bis-{1-[3-(N-ter-butyl-N-hydroxyamino)phenyli-
mino]ethyl} pyridine 12
4.10. 1,4-bis-[3-(N-ter-butyl-N-oxyamino)phenyl]-2,3-
dimethyl-1,4-diazabutadiene 9
Same procedure as for 8. 12: Yield: 80%. m.p. 212
–214 ꢁC (dec). IR (KBr), m (cmꢀ1): 3242 (OH), 1638
1
(C@N). H NMR (CDCl3), d (ppm): 1.20 (s, 18H, ter-
PbO2 (2.4 g, 10 mmol) was added to a chloroform
solution (60 mL) of 8 (1.5 g, 3.6 mmol). The mixture
was stirred vigorously for 5 min (disappearance of the
OH bands in IR spectroscopy). The red solution was fil-
tered using celite and the analysis were done on this
solution. IR (CHCl3), m (cmꢀ1): 1641 (C@N), 1361 (N–
Bu), 2.41 (s, 6H, CH3), 6.10 ( s, br, 2H, OH), 6.68 (dt,
2H, 7.7 and 1 Hz, Ph C4–H or C6–H), 6.78 (t, 2H, 2
Hz, Ph C2–H), 7.04 (dt, 2H, 7.7 and 1 Hz, Ph C4–H or
C6–H), 7.30 (t, 2H, 7.9 Hz, Ph C5–H), 7.89 (t, 1H, 7.6
Hz, Py C4–H), 8.35 (d, 2H, 7.8 Hz, Py C3–H and C5–
H). MS (FAB+, NBA) (m/z, intensity):488 (M+ + H,
50), 472 (M+ ꢀ OH, 10), 57 (ter-Bu+, 100). Anal. Calc.
for C29H37N5O2: C, 71.43; H, 7.65; N, 14.36; O, 6.56.
Found: C, 70.99; H, 7.54; N, 13.85; O, 6.65%.
O). EPR (CHCl3): g = 2.0036,
5 principal lines;
aN = 6.7 G, aH = 1.7 (Ho), 0.7 (Hm), 1.8 (Hp). UV
(CHCl3), k nm: 230 (p–p* Ph), 291 (p–p* N–O), 379
(p* N@C–C@N).
4.14. bis-{1-[3-(N-ter-butyl-N-oxyamino)phenylimino]
ethyl} pyridine 15
4.11. N-[3-(N-ter-butyl-N-hydroxyaminophenyl)]-(2-
pyridyl)methanimine 10 and N-[3-(N-ter-butyl-N-
hydroxyaminophenyl)]-(2-pyridyl)ethanimine 11
Same procedure as for 9. IR (CHCl3), m (cmꢀ1): 1634
(C@N), 1364 (N–O). EPR (see text and Table 3). UV
(CHCl3), k nm: 230 (p–p* Ph), 291 (p–p* N–O), 345
(p–p* N@C–C@N).
Same procedure as for 8 but 72 h reaction for 10 and
96 h in the case of 11.
4.11.1. Compound 10
Yield: 75%, m.p. 78–81 (dec.). IR (CCl4), m (cmꢀ1):
3588, 3242 (OH), 1631 (C@N). H NMR (CDCl3), d
5. Complexation reactions
1
(ppm): 1.25 (s, 9 H, ter-Bu), 6.0 (s, br, 1H, OH), 7.05–
7.32 (m, 4H, Ar), 7.41 (m, 1H, Py C5-H), 7.84 (m, 1
H, Py C3–H or C4–H), 8.22 (m, 1H, Py C3–H or C4–
H), 8.63 (s, 1H, N@C–H), 8.75 (m, 1H, Py C6–H).
MS (FAB+, NBA) (m/z, intensity):270 (M+, 100), 213
(M+ ꢀ ter-Bu, 40), 57 (ter-Bu+, 50).
5.1. General procedure
The metal salt was dissolved in THF and added drop-
wise to a solution of the ligand (1.05 equiv.) in THF, un-
der inert atmosphere. The reaction mixture was stirred
for 1 h (case of the ligand 11 and 12) or several hours
(case of 15) and evaporated under vacuum. Addition
of diethylether left a solid which was washed several
times with diethylether and pentane. The solids were
dried under vacuum.
4.11.2. Compound 11
Yield: 60%, m.p. 119–122 (dec). IR (CCl4), m (cmꢀ1):
1
3592, 3281 (OH), 1643 (C@N). H NMR (CDCl3), d

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C. Uerpmann et al. / Journal of Organometallic Chemistry 690 (2005) 197–210
5.2. Case of ligands 10 and 11
sity):615 (M+ ꢀ NO3, 100); 555 (M+ ꢀ 2NO3, 15), 57
(ter-Bu+, 35). Anal. Calc. for Zn(12)(NO3)2 Æ 3H2O,
C29H41N7O11Zn: C, 47.65; H, 5.93; N, 13.40. Found:
C, 47.65; H, 5.92; N, 12.83%.
5.2.1. Dichloro-bis-2-[3-N-ter-butyl-N-hydroxyaminopy-
ridin-2-yl-methylene-phenylamine]nickel(II), 16
Orange-beige powder; Yield: 72% dec. > 260 ꢁC. IR
(KBr), m (cmꢀ1): 3242 (OH), 1631 (C@N), 1593 (C@C).
MS (FAB+, NBA), m/z (intensity): 633 (M+ ꢀ Cl, 100),
596 (M+ ꢀ 2Cl, 100), 57 (ter-Bu+, 100). Anal. Calc. for
Ni(10)2Cl2 Æ 1H2O, C32H40Cl2N6NiO3: C, 56.00; H,
5.87; N, 12.25. Found: C, 56.55; H, 6.14; N, 12.22%.
5.3.2. Dichloro-2,6bis-[1-(3-N-ter-butyl-hydroxylamino-
phenylimino)ethyl]pyridine nickel(II), 26
Orange-beige powder; Yield: 60%, dec. > 280 ꢁC. IR
(KBr), m (cmꢀ1): 3348 (OH), 1627 (C@N). MS (FAB+,
NBA), m/z (intensity):580 (M+ ꢀ Cl, 100); 57 (ter-Bu+,
80). Anal. Calc. for Ni(12)Cl2 Æ 1H2O, C29H39Cl2N5-
NiO3: C, 54.82; H, 6.19; N, 11.02. Found: C, 55.55; H,
6.04; N, 10.57%.
5.2.2. Dichloro-bis-2-[3-N-ter-butyl-N-hydroxyamino-(1-
pyridin-2-yl-ethyl) phenylamine]nickel(II), 18
Orange-beige powder; Yield: 75%, dec. > 260 ꢁC. IR
(KBr), m (cmꢀ1): 3242 (OH), 1629 (C@N). MS (FAB+,
NBA), m/z (intensity): 659 (M+ ꢀ Cl, 100), 624
(M+ ꢀ 2Cl, 70), 57 (ter-Bu+, 40). Anal. Calc. for
Ni(11)2Cl2 Æ 1H2O, C34H44Cl2N6NiO3: C, 57.16; H,
6.21; N, 11.76. Found: C, 57.00; H, 6.31; N, 11.39%.
5.3.3. Dichloro-2,6bis-[1-(3-N-ter-butyl-hydroxylamino-
phenylimino)ethyl]pyridine manganese(II), 27
Beige powder; Yield: 65%, dec. > 280 ꢁC. IR (KBr),
m (cmꢀ1): 3378 (OH), 1633 (C@N). MS (FAB+, NBA),
m/z (intensity):577 (M+ ꢀ Cl, 85); 545 (M+ ꢀ 2Cl,
15);488 (M+ ꢀ 2Cl-ter-Bu, 35); 57 (ter-Bu+, 35). Anal.
Calc. for Mn(12)Cl2 Æ 3H2O, C29H46Cl2MnN5O5: C,
52.17; H, 6.49; N, 10.48. Found: C, 52.93; H, 5.72;
N, 10.44%.
5.2.3. Dichloro-bis-2-[3-N-ter-butyl-N-hydroxyaminopy-
ridin-2-yl- methylene-phenylamine]manganese(II), 17
Orange-beige powder; Yield: 80% dec. > 250 ꢁC. IR
(KBr), m (cmꢀ1): 3400 (OH), 1655 (C@N). MS (FAB+,
NBA), m/z (intensity): 628 (M+ ꢀ Cl, 100), 57 (ter-
Bu+, 55). Anal. Calc. for Mn(10)2Cl2 Æ 1H2O,
C32H40Cl2MnN6O3: C, 56.31; H, 5.91; N, 12.31. Found:
C, 57.82; H, 5.56; N, 11.66%.
5.3.4. Diperchlorato-2,6bis-[1-(3-N-ter-butyl-hydroxyl-
aminophenylimino)ethyl]pyridine manganese(II), 31
Orange crystals. m.p. > 120 ꢁC (the complex was not
heated more than that temperature). (No X-ray diffrac-
tion pattern was obtained). IR (KBr), m (cmꢀ1): 3442
(OH), 1629 (C@N), 1101, 950 (ClO4). MS (FAB+,
NBA), m/z (intensity):1129 (M+ ꢀ ClO4, 38); 1029
(M+ ꢀ 2ClO4, 52).
5.2.4. Dichloro-bis-2-[3-N-ter-butyl-N-hydroxyamino-(1-
pyridin-2-yl-ethyl) phenylamine]manganese(II), 19
Orange-beige powder; Yield: 69%, dec. > 260 ꢁC. IR
(KBr), m (cmꢀ1): 3330 (OH), 1633 (C@N). MS (FAB+,
NBA), m/z (intensity): 656 (M+ ꢀ Cl, 100), 621
(M+ ꢀ 2Cl, 45), 57 (ter-Bu+, 55). Anal. Calc. for
Mn(11)2Cl2 Æ 2H2O, C34H46Cl2MnN6O4: C, 56.05; H,
6.36; N, 11.53. Found: C, 56.42; H, 6.94; N, 11.40%.
5.3.5. Trinitro-2,6bis-[1-(3-N-ter-butyl-hydroxylamino-
phenylimino)ethyl]pyridine gadolinium(III), 32
Beige powder. Yield: 65%, Tdec. > 280 ꢁC. IR (KBr), m
(cmꢀ1): 3378 (OH), 1633 (C@N), 1383 (NO3). MS
(FAB+, NBA), m/z (intensity): 769 (M+ ꢀ NO3, 5); 707
(M+ ꢀ 2NO3, 15); 650 (M+ ꢀ 2NO3-ter-Bu, 60). Anal.
Calc. for Gd(12)(NO3)3 Æ 3H2O, C29H43GdN8O14: C,
39.36; H, 4.90; N, 12.66. Found: C, 39.38; H, 4.72; N,
11.90%.
5.2.5. Trinitro-2-[3-N-ter-butyl-N-hydroxyaminopyridin-
2-yl- methylene-phenylamine]gadolinium(III), 24
Orange-beige powder; Yield: 57%, dec. > 230 ꢁC. IR
(KBr), m (cmꢀ1): 3392 (OH), 1638 (C@N), 1383 (NO3).
Anal. Calc. for Gd(10)(NO3)3 Æ 5H2O, C16H29GdN6O15:
C, 27.35; H, 4.16; N, 11.96. Found: C, 27.45; H, 3.66; N,
11.52%.
5.4. Oxidation of the complexes
5.4.1. General procedure
5.3. Case of ligand 12
Ag2O (2 equiv.) was added to a solution of the com-
plex in chloroform and the mixture was stirred at room
temperature for 30 mn. After filtration over celite, the
solution was evaporated and the obtained solid was
dried under vacuum.
5.3.1. Dinitro-2,6bis-[1-(3-N-ter-butyl-hydroxylamino-
phenylimino)ethyl]pyridine zinc(II), 25
Orange-beige powder; Yield: 65%, dec.: > 280 ꢁC.
IR (KBr), m (cmꢀ1): 3392 (OH), 1638 (C@N), 1383
(NO3). 1H NMR (acetone d6) d (ppm, Hz): 1.17 (s,
18H, N-ter-Bu), 2.72 (s, 6H, @C(CH3)), 6.78 (d, 2H,
6.9 Hz, Ph), 6.95 (s, 2H, Ph), 7.23–7.40 (m, 4H,
Ph), 8.75 (s, 3H, Py). MS (FAB+, NBA), m/z (inten-
5.4.2. Oxidation of 25
EPR spectrum of 28 was run in CHCl3, after filtra-
tion over celite. g = 2.0056, aN = 13 G.

C. Uerpmann et al. / Journal of Organometallic Chemistry 690 (2005) 197–210
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209
5.4.3. Oxidation of 26
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(1994) 575.
Complex 29 was obtained as a red powder. Yield:
90%, EPR: see Table 3. IR (KBr), m (cmꢀ1): 3348
(OH), 1627 (C@N). Anal. Calc. for Ni(15)Cl2 Æ 2H2O,
C29H39Cl2N5NiO4: C, 53.48 H, 6.03; N, 10.74. Found:
C, 53.55; H, 6.91; N, 10.57%.
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5.4.4. Oxidation of 27
Complex 30 was obtained as a red powder. Yield:
95%, EPR: see Table 3. IR (KBr), m (cmꢀ1): 3378
(OH), 1633 (C@N). Anal. Calc. for Mn(15)Cl2 Æ 2H2O,
C29H39Cl2MnN5O4: C, 53.79 H, 6.07; N, 10.81. Found:
C, 52.93; H, 5.72; N, 10.44%.
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The red solution of complex 33, after filtration on cel-
ite was characterized using EPR spectroscopy. See Table
3 and Fig. 6. Thin layer chromatography (TLC) with
CH2Cl2 led to partial decomposition: 3 spots were ob-
tained but the best migrating red spot has the same spec-
trum as the initial solution. This seams to indicate that
the latter corresponds to a single complex.
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5.4.6. Oxidation of 32
Complex 34 was obtained as a red powder. Yield:
93%, EPR: see Table 3. IR (KBr), m (cmꢀ1): 3378
(OH), 1633 (C@N), 1383 (NO3). Anal. Calc. for
Gd(15)(NO3) Æ 3H2O, C29H41GdN8O14: C, 39.45; H,
4.68; N, 12.68. Found: C, 39.26; H, 4.68; N, 11.85%.
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6. Supporting information available
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Center, CCDC No. 238906. Copies of this infor-
mation may be obtained free of charge from The Direc-
tor, CCDC, 12 Union Road, Cambridge, CB2 1EZ,
UK, (fax: + 44-1223-33-336033; e-mail: deposit@ccdc.
cam.ac.uk or www.ccdc.cam.ac.uk).
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M. Drillon, J. Chem. Soc., Chem. Commun. (1994) 741.
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J. Am. Chem. Soc. 118 (1996) 1803.
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Magn. Mater. 154 (1996) 1107.
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Acknowledgement
[31] M.L. Kahn, J.P. Sutter, S. Golhen, P. Guinneau, L. Ouahab, O.
Kahn, D. Chasseau, J. Am. Chem. Soc. 122 (2000) 3413.
[32] F. Mathevet, D. Luneau, J. Am. Chem. Soc. 123 (2001)
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This work was supported by the CNRS, France.
[33] O. Kahn, Molecular Magnetism, VCH, New York, 1993.
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