2-(4′,4′-dimethyl-3′,4′-dihydrooxazol-2′-yl) phenol: Some first-row transition metal complexes of this naturally occurring binding group

Article abstract of DOI:10.1002/1099-0682(200103)2001:3<669::AID-EJIC669>3.0.CO;2-7

The synthesis and characterization of monomeric Mn^III, Co^II, Ni^II, Cu^II, and Zn^II phenolates derived from a biologically relevant ligand, 2-(4′,4′-dimethyl-3′,4′-dihydrooxazol-2′-yl)- phenol (1), are

Full text of DOI:10.1002/1099-0682(200103)2001:3<669::AID-EJIC669>3.0.CO;2-7

FULL PAPER
2
-(4Ј,4Ј-Dimethyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)phenol: Some First-Row Transition
Metal Complexes of This Naturally Occurring Binding Group
[
a]
[a]
[b]
Govindasamy Mugesh, Harkesh B. Singh,* and Ray J. Butcher
Dedicated to Prof. B. L. Khandelwal on the occasion of his 63rd birthday
Keywords: Oxazolines / Metal assisted hydrolysis / Hydrogen bonds / Chirality / Siderophores
III
II
The synthesis and characterization of monomeric Mn , Co ,
techniques. Complexes 2, 3, 5, 6, and 7 were characterized
II
II
II
Ni , Cu , and Zn phenolates derived from a biologically rel- by single crystal X-ray diffraction studies. Complex 2 is six-
evant ligand, 2-(4Ј,4Ј-dimethyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)-
phenol (1), are described. The addition of Mn(OAc) · 4 H
to an ethanolic solution of 1 affords an unexpected 1:3 com-
plex [Mn(OR){O(Ox)} ] (2) [R = C CONHC(Me )CH OH,
Ox = 2-(4,4-dimethyl-2-oxazolinyl)phenyl] in which one of
the five-membered oxazoline rings is partially hydrolyzed.
coordinate whereas complexes 3, 6, and 7 are four-coordinate
with two oxazoline bidentate ligands. The geometry around
the metal center is found to be distorted tetrahedral for all of
the four-coordinate complexes. Complex 5 is octahedral with
four coordination sites occupied by the two bidentate oxazo-
line ligands and the other two are occupied by two neutral
acetic acid molecules. The hydroxy groups of the coordinated
2
2
O
2
6
H
4
2
2
2
The complexes [M{O(Ox)} ] [M = Co (3), Ni (4), Cu (6), or Zn
(
7)] were prepared in good yield by the reactions of 1 with acetic acid are hydrogen-bonded to the phenolate oxygen
1
the corresponding metal acetates. Novel formation of the six- atoms of the oxazoline ligands. The variable-temperature H
coordinate Ni complex 5 with neutral acetic acid was ob- NMR spectroscopic studies of complex 7 indicate that the in-
II
served during the crystallization process. The complexes
were characterized by elemental analysis, magnetic suscept-
ibility, as well as EPR, H NMR, electronic, and mass spectral
terconversion between the (M) and (P) helix is slow at low
temperatures.
1
Introduction
complexes of chiral oxazoline ligands containing N,O and
N,P moieties and Mn complex of 2-(2Ј-hydroxyphenyl)-2-
III
Interest in the biochemistry of 2-(2-hydroxyphenyl)-2-ox-
azoline started with the finding that this ligating moiety is
present as a naturally occurring iron chelator in some
classes of siderophores such as mycobactine, parabactin,
oxazoline have been used for the catalytic epoxidation of
styrene.
[5]
Although a few complexes of 2-(2Ј-hydroxyphenyl)-2-ox-
azolines with trivalent and divalent metal ions are
[
1]
and vibriobactin.
known,[
6Ϫ8]
very little information is available about their
Owing to the strong chelating ability of the oxazoline li-
structural chemistry. As part of our work on intramolecul-
arly coordinated organochalcogens,[ we have recently de-
scribed the synthesis and characterization of Group 12
metal chalcogenolates (S, Se, Te) with bidentate oxazoline
III
gand and its high affinity for Fe , the siderophores have
9]
been shown to be highly potent in the deferration of mam-
malian cell lines and are potentially useful for chelation
[
2]
therapy. The use of oxazoline ligands in a wide range of
catalytic reactions has also been reported in recent years.[
In this regard much effort has been directed towards the
synthesis and catalytic applications of metal complexes con-
taining 2-(2Ј-hydroxyphenyl)-2-oxazoline ligands.[ Re-
[
10]
[10a]
ligands. Interestingly, the (thiolato)-
and (selenolato)-
3]
zinc[
10b]
complexes were found to be chiral at room temper-
ature and interconversion between the (M) and (P) helix
was slow at room temperature. Replacement of the S or Se
by Te led to the faster interconversion between the (M) and
4]
IV
IV
cently, Ti and Zr complexes of 2-(2Ј-hydroxyphenyl)-2-
oxazolines have been used for some homogeneous catalytic
reactions such as Mukaiyama reaction, allylations, hydrocy-
anations, DielsϪAlder reactions.[ In these cases, the bis-
(
P) forms. A similar trend was observed when the central
metal ion was varied. It was observed that the interconver-
sion of enantiomers at small metal ions, such as zinc, was
slower whereas at the larger metal ions, such as mercury, it
was much faster even at low temperature. Since the isolation
of ‘‘helically’’ chiral metal complexes of zinc with lighter
chalcogens (S, Se) was found to be more facile than the
complexes with the heavier chalcogen (Te), it was thought
worthwhile to extend our approach to the lightest chal-
cogen (oxygen) as well. Also, in order to generalize our ob-
servations, we extended our approach to other transition
metals where the isolation of the tetrahedral complexes was
4b]
(oxazoline)-ligated transition metal Lewis acids displayed
activity for almost all commonly encountered Lewis acid
II
II
III
promoted reactions. More recently, Ni , Pd , and Mn
[
[
a]
b]
Department of Chemistry, Indian Institute of Technology
Powai, Bombay 400076, India
Fax: (internat.) ϩ 91-22/572-3480
E-mail: chhbsia@chem.iitb.ernet.in
Department of Chemistry, Howard University
Washington, DC 20059, USA
Eur. J. Inorg. Chem. 2001, 669Ϫ678

WILEY-VCH Verlag GmbH, 69451 Weinheim, 2001
1434Ϫ1948/01/0303Ϫ0669 $ 17.50ϩ.50/0
669

G. Mugesh, H. B. Singh, R. J. Butcher
FULL PAPER
Scheme 1. Synthetic route to the metal complexes 2؊7; reagents and conditions: i) Mn(OAc)
2
· 4 H
2
O, EtOH, room temp., 24 h; ii)
· H O, EtOH, room temp.,
Co(OAc)
2
· 4 H
2
O, EtOH, room temp., 12 h; iii) Ni(OAc)
2
· 4 H
2
O, EtOH, room temp., 18 h; iv) Cu(OAc)
2
2
2
4 h; v) Zn(OAc) , EtOH, room temp. 24 h
2
feasible. In this paper we describe the synthesis and charac-
terization of Mn , Co , Ni , Cu , and Zn complexes is similar to the hydrolysis of the active site of Agrobactin, a
The partial hydrolysis of the oxazoline ring in complex 2
III
II
II
II
II
with the naturally occurring 2-(2Ј-hydroxyphenyl)-2-oxazo- siderophore from Agrobacterium tumefaciens. The oxazoline
line ligating moiety.
ring of the siderophore hydrolyzes in the presence of an acid
to give the open-chain form, Agrobactin A (Scheme 2).[
It has been further reported by Neilands et al. that the re-
placement of the ϪOH group in the 2-position of the ben-
zene ring with ϪOMe or ϪOBz groups in Agrobactin led
to a facile opening of the oxazoline ring.[ Similarly, in
ligand 1 the coordination of the nitrogen atom to the metal
center probably disturbs the co-planarity of the oxazoline
ring leading to hydrolysis of the five-membered ring in the
presence of acetic acid. The partial hydrolysis of the oxazo-
line ring is also noteworthy since acid hydrolysis of the ox-
azoline ring in complex 2 leads to the formation of an
amide instead of the expected acid (ϪCOOH). The mech-
anism of the hydrolysis involves the formation of the oxazo-
lium ion. The oxazolium ion so formed presumably then
1a]
Results and Discussion
1c]
Synthesis
The ligand 2-(4Ј,4Ј-dimethyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)-
phenol (1) was prepared in a one-pot synthesis by following
the published procedure with minor modifications.[5] Since
the proton of the hydroxy group in the oxazoline was acidic
enough to react with the metal salts containing basic anion
acetate, the ligand was treated with various metal acetates
in absolute ethanol to obtain the corresponding metal com-
plexes (Scheme 1). The addition of Mn(OAc) · 4 H O to an
2
2
ethanolic solution of 1 afforded a black-green solution of
complex 2. Elemental analysis of the black-green crystals
obtained upon slow evaporation of the solvent did not
match with the expected 1:2 complex. Instead, it indicated
the formation of a 1:3 complex where manganese was in a
ϩ3 oxidation state. Interestingly, one of the oxazoline rings
undergoes a metal-assisted hydrolysis (vide infra) in the
presence of acetic acid produced during the reaction. How-
ever, no hydrolysis of the oxazoline ring was observed with
the other metal ions.
Scheme 2. Acid-catalyzed hydrolysis of the oxazoline ring present
in the active site of Acrobactin to the open-chain from, Agrobac-
tin A
670
Eur. J. Inorg. Chem. 2001, 669Ϫ678

2-(4Ј,4Ј-Dimethyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)phenol
FULL PAPER
Scheme 3. Proposed mechanism of the hydrolysis of oxazoline ring in complex 2
opens to afford the cleaved product which then undergoes methyl and methylene protons were observed as singlets.
tautomerization to give the open-chain amide However, the signals due to the methyl and methylene pro-
[
1a]
(
Scheme 3).
In order to determine whether the presence of air plays was probably not rigid at room temperature. At Ϫ55 °C,
an important role in the ligand hydrolysis, the synthesis of the ϪCH protons gave rise to two singlets and the ϪCH Ϫ
tons were slightly broad and this showed that the complex
3
2
complex 2 was attempted under nitrogen. In this case, a protons gave an AB quadruplet (Figure 1). When the solu-
very air-sensitive green-colored gummy solid, presumably tion was heated to 50 °C, the two signals observed for the
II
the expected Mn complex, was obtained. All efforts to ob- methyl protons and the AB quadruplet for the methylene
II
tain crystals of the Mn complex were unsuccessful. Isola- protons became sharp singlets. This clearly indicates that
III
tion of the Mn complex under aerobic conditions further the interconversion of the (M) and (P) helix is fast at room
III
demonstrates that both the stability of the Mn oxidation temperature and becomes slow at a low temperature on the
state and its oxophilicity promote the ligand hydrolysis.
NMR spectoscopic time scale. A similar behavior was ob-
The addition of Co(OAc) · 4 H O to an ethanolic solu- served at low temperatures for the cadmium thiolate, selen-
2
2
II
tion of 1 resulted in an immediate formation of Co com- olate, and tellurolate complexes derived from 4,4-dimethyl-
plex 3 as a pink-colored solid. The crystals of the complex 2-phenyloxazoline.[ The C NMR spectrum of 7 was re-
10]
13
were obtained from a CH Cl /methanol (1:1) solution.
2
2
When an ethanolic solution of 1 was added to a solution
of Ni(OAc) · 4 H O, an immediate formation of a green
2
2
precipitate was observed. After 12 h of stirring at room tem-
perature, the pale green solid obtained was filtered and
washed with ethanol. Interestingly, the slow concentration
of the filtrate afforded dark green crystals which were differ-
ent from the compound obtained by filtration of the reac-
tion mixture. Elemental analyses of both the products indic-
ated that the pale green solid was the expected 1:2 complex
4
whereas the dark green crystalline solid (5) obtained from
the filtrate was an acetic acid [produced in the reaction mix-
ture during the reaction of Ni(OAc) · 4 H O with 1] adduct
2
2
of 4 (vide infra). The addition of acetic acid to an ethanolic
solution of complex 4 also afforded complex 5. Although
II
four-coordinate Ni complexes are known to coordinate ex-
tra ligands in solution to set up equilibria between four-,
five-, and six-coordinate complexes,[ the strong bonding
of the acetic acid molecules in this case is surprising since
the recrystallization from methanol did not lead to the ex-
11]
[
11b]
II
II
pected exchange.
The Cu and Zn complexes 6 and 7
were prepared in good yields by the reaction of 1 with the
corresponding metal acetates. All the complexes are quite
soluble in common organic solvents such as CH Cl ,
2
2
CHCl , benzene, etc.
3
NMR Spectroscopy
Complex 7 was studied in solution by NMR spectro-
1
scopy. The H NMR spectrum of 7 in CDCl showed only
3
small chemical shift differences compared with the spec-
trum of 1. We have recently observed an AB spin behavior
of the methylene protons in the corresponding zinc thiolate
and selenolate complexes, and used it as a diagnostic probe
1
Figure 1. Variable-temperature H NMR (CDCl
tra (in part only) of 7 at Ϫ55°C, the signals due to the ϪCH
and ϪCH protons split into an AB quadruplet and two singlets,
3
, 300 MHz) spec-
Ϫ
[
10a,10b]
2
for their chirality.
For complex 7, no such behavior
3
was observed at room temperature and the signals for the respectively
Eur. J. Inorg. Chem. 2001, 669Ϫ678
671

G. Mugesh, H. B. Singh, R. J. Butcher
FULL PAPER
corded in CDCl . The methyl and methylene carbon signal nǞπ* excitation. The electronic spectrum of 2 is dominated
3
were shifted upfield with respect to those of 1. The signals by a peak with medium intensity centering at 303 nm
Ϫ1
Ϫ1
III
for the oxygen-bearing aromatic carbon atom and C(2) of (εmax ϭ 7480  cm ), attributable to the σ(N)ǞMn
the heterocycle were significantly shifted downfield (δ ϭ ligand-to-metal charge-transfer (LMCT) transition. One
Ϫ1
Ϫ1
1
60.2 and 165.3 for 1, δ ϭ 170.0 and 170.5 for 7).
broad band at 658 nm (εmax ϭ 191  cm ) may be attrib-
uted to the ligand field transition. A broad peak centered
Ϫ1
Ϫ1
Magnetic Properties
at 500 nm (εmax ϭ 357  cm ) is also attributed to d-d
transition. Four-coordinate tetrahedral and pseudo-tetra-
hedral Co complexes are commonly intense blue or green
The room-temperature magnetic moment of the black-
green manganese(III) complex 2 is 3.33 BM which indicates
that the complex is low-spin (S ϭ 1). The observed mag-
netic moment of 2 is considerably larger than the spin-only
value of 2.83 BM for two unpaired electrons. This result is
attributable to the presence of the orbital angular mo-
mentum for the ground term ion. MnIII is known to form
low-spin octahedral complexes only with strong donors like
cyanides, oximes, or porphyrins. Complex 2 provides a rare
II
in color. Complex 3 shows pink color in the solid state as
well as in solution. However, this is not surprising since a
few complexes with dipivaloylmethane are known to give a
pink color in solution.[
13,14]
In the tetrahedral Co case,
II
there are three regions of absorption and, therefore, three
spin-allowed electronic transitions are expected. Three d-d
transition bands were observed as weak features at 501 nm
Ϫ1
Ϫ1
Ϫ1
Ϫ1
(
(
εmax ϭ 110  cm ), 563 (εmax ϭ 90  cm ), and 619
III
example of a low-spin Mn complex with N and O donors
εmax ϭ 30 Ϫ1cm ). The splitting of the middle band is
Ϫ1
from the oxazoline ligand. Although the effective magnetic
probably due to spin-orbit coupling. There are four strong
absorption bands in the high-energy region, 244 nm (ε
II
moments for the tetrahedral Co complexes are normally
ϭ
max
observed close to the spin-only values, the observed mag-
Ϫ1
Ϫ1
ϭ 12070  cmϪ1), 312 nm
Ϫ1
3
3850  cm ), 281 nm (ε
II
max
netic moment for the Co complex 3 (µeff ϭ 4.57 BM) is
Ϫ1
Ϫ1
(
ε
ϭ 10000  cm ), and 344 nm (εmax ϭ 11750
max
much higher than the spin-only magnetic moment (µ ϭ 3.87
BM) for three unpaired electrons. This discrepancy may
again be caused by angular momentum introduced to the

Ϫ1cmϪ1), which can be assigned to the ligand transitions
and charge-transfer transitions. For 4, two bands, observed
Ϫ1
Ϫ1
at 689 nm (ε

ϭ 15  cm ) and 591 nm (εmax ϭ 12
max
ground state (A ) by mixing of higher T states. The mag-
2
Ϫ1
Ϫ1
cm ), can be attributed to d-d transitions. There are
netic moment of 3.05 BM determined for the octahedral
three strong absorption bands in the high-energy region,
II
Ni complex 5 is very close to the spin-only value for two
Ϫ1
Ϫ1
2

46 nm (ε
ϭ 12900  cm ), 309 nm (ε
ϭ 4730
max
max
unpaired electrons, whereas the magnetic moment observed
Ϫ1
cm ), and 336 nm (εmax ϭ 2590  cmϪ1), which may
Ϫ1
Ϫ1
II
for tetrahedral Ni complex 4 (3.42 BM) is much higher
be assigned to charge transfer and intra-ligand transitions.
For 5, there are two intense bands in the region between
than the spin-only value. This is in agreement with the gen-
II
eral observation that octahedral Ni complexes have less
2
00 and 340 nm that may be assigned to the intra-ligand
orbital momentum than the tetrahedral complexes. It is
πǞπ* transitions. The band at 340 nm (ε ϭ 1500
II
max
known that the magnetic moment of truly tetrahedral Ni
Ϫ1
Ϫ1

cm ) with medium intensity indicates the charge-trans-
complexes should be about 4.2 BM because of the ground
fer (CT) character. Finally, a weak feature (ε ϭ 12
3
max
state, T (F), which has much inherent orbital angular mo-
1
Ϫ1
Ϫ1

5
cm ) assigned to d-d transition, is present in the
00Ϫ600 nm range. For the Cu complex 6, the ligand field
mentum. However, it is also reported that even slight distor-
tion in the geometry reduces this markedly by splitting the
orbital degeneracy. Thus, fairly regular tetrahedral com-
plexes have moments of 3.5Ϫ4.0 BM, while for the more
distorted ones the moments are 3.0Ϫ3.5 BM, i.e. in the
same range as for six-coordinate complexes. The magnetic
moment observed for 4, therefore, suggests that the geo-
metry around the metal ion is highly distorted. The mag-
netic moment of complex 6 (1.76 BM) is very close to the
spin only value (1.73 BM) for one unpaired electron. The
geometry around the metal center is, therefore, predicated
as planar since a higher orbital contribution to the mag-
II
transition occurs as a single broad band centering at
Ϫ1
Ϫ1
6
53 nm with an εmax of 105  cm . In addition two in-
tense bands appear at higher energies. The peak that ap-
Ϫ1
Ϫ1
pears at 244 nm (ε
σ(N)ǞCu LMCT transition.
ϭ 30600  cm ) is assigned to the
max
II
[15Ϫ17]
The peak with medium
intensity at 343 nm (εmax ϭ 11600 Ϫ1cm ) is too low for
Ϫ1
a charge-transfer transition involving an N donor. For tet-
II
rahedral Cu complexes with phenolate coordination, the
II
Cu Ǟphenolate
MLCT
absorption
occurs
near
[18,19]
3
00 nm.
Therefore, the band at 309 nm (εmax ϭ 10600
Ϫ1
Ϫ1
II

cm ) is assigned as the higher energy Cu Ǟπ*-
II
netic moment is expected for a tetrahedral Cu complex
phenolate transition.
than for a planar one.[
12]
Electrochemistry
Electronic Spectra
The cyclic voltammograms of 2؊6 were recorded at room
The solution-phase electronic spectrum (Ͼ 200 nm) of temperature in acetonitrile in the potential range Ϫ1.5 to
the ligand 1 consists of two relatively intense bands centered ϩ2.0 V vs. Ag/AgCl reference electrode. Complex 2 exhibits
Ϫ1
Ϫ1
at 255 nm (ε

ϭ 47500  cm ) and 303 (εmax ϭ 36600 a quasi-reversible one-electron oxidation-reduction corres-
max
Ϫ1
Ϫ1
IV
III
cm ), involving πǞπ* transitions, and a low-intensity ponding to the Mn /Mn redox process (E1/2 ϭ 1.59 V;
Ϫ1
Ϫ1
ϩ
feature (εmax ϭ 2500  cm ) in the 350Ϫ360 nm region, ∆E ϭ 130 mV vs. Fc/Fc , E ϭ 0.38 V; ∆E ϭ 100 mV
p
1/2
p
Ϫ1
III
II
responsible for the yellow color, and presumably involving at scan rate 50 mVs ). The Mn /Mn couple was not
672
Eur. J. Inorg. Chem. 2001, 669Ϫ678

2-(4Ј,4Ј-Dimethyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)phenol
FULL PAPER
observed up to Ϫ2.2 V, showing high stability of the MnIII where two nitrogen donor atoms of oxazoline rings and one
state in the present environment. Other complexes do not carbonyl oxygen atom of the hydrolyzed oxazoline are co-
show any well-defined response in this potential range.
ordinated to the central metal ion in addition to the aryloxo
groups. Selected bond lengths and angles are summarized
in Table 1. The three MnϪOϪ(Ar) bond lengths are close
to each other but differ significantly from the distance be-
tween Mn and the carbonyl oxygen atom. The MnϪO and
MnϪN bond lengths are comparable with the correspond-
X-ray Crystallography
Crystal Structure of 2
¯
Complex 2 crystallizes in the triclinic space group P1. As
III
ing bond lengths reported for other related Mn pseudo-
can be seen in Figure 2, one of the five-membered oxazoline
octahedral complexes.[ The bond lengths and angles for
19]
rings is partially hydrolyzed to give the open-chain form.
III
the oxazoline ring reflect many similarities with the Agrob-
The Mn ion present in the complex is six-coordinate
actin (Table 2).[
1c]
The intramolecular hydrogen bonds
which are very similar to the ones observed in Agrobactin
efficiently stabilize the molecular structure in the crystalline
state. There are several weak interactions between the atoms
in the crystal structure. Of these interactions, the hydrogen
bonding between the NH proton and oxygen atom of the
˚
hydrolyzed oxazoline ring [O(33)···HϪN(3) 2.266(6) A;
˚
O(33)···N(3) 2.697(4) A] is found to be much stronger than
the others.
Crystal Structure of 3
A perspective view of the molecule with an atom num-
bering scheme is shown in Figure 3. Compound 3 crystal-
¯
lizes as a neutral monomer in the P1 space group of a tri-
II
Figure 2. Crystal structure of complex 2
clinic system. The geometry around the Co center is tetra-
hedral with two bidentate oxazoline ligands. Selected bond
˚
lengths and angles are given in Table 3. The average CoϪO
Table 1. Selected bond lengths [A] and angles [°] for 2
˚
bond length 1.9052 A is significantly shorter than those
˚
[20]
MnϪN(1)
MnϪO(21)
MnϪO(31)
2.086(2)
1.870(2)
1.931(2)
MnϪN(2)
MnϪO(11)
MnϪO(32)
2.250(3)
1.879(2)
2.223(2)
reported for Co(OAc) (imid)2 [1.984(1) A]
and Co-
2
˚
[21]
(
OAc) (2-Me-imid)2 [2.098(1) A].
The average CoϪN
2
˚
O(21)ϪMnϪO(11) 178.39(10) O(21)ϪMnϪO(31) 92.12(10) bond lengths 1.9885 A is also shorter than those observed
O(11)ϪMnϪO(31) 88.86(10)
O(21)ϪMnϪN(1)
O(31)ϪMnϪN(1)
91.69(10)
168.16(9)
˚
for Co(OAc) (imid) [2.0135(1) A] Co(OAc) (2-Me-imid)
[
2
2
2
2
O(11)ϪMnϪN(1)
87.60(9)
˚
2.062(3) A]. The average chelate bite angle of OϪCoϪN
O(21)ϪMnϪO(32) 91.71(9)
O(31)ϪMnϪO(32) 84.07(9)
O(11)ϪMnϪO(32) 89.66(10)
N(1)ϪMnϪO(32)
O(11)ϪMnϪN(2)
N(1)ϪMnϪN(2)
84.62(9)
92.59(10)
99.95(10)
is 94.57°. The larger bite angle leads to relatively smaller
OϪCoϪO and NϪCoϪN angles of 119.23(7)° and
O(21)ϪMnϪN(2)
O(31)ϪMnϪN(2)
O(32)ϪMnϪN(2)
86.11(9)
91.49(10)
174.99(9)
1
21.25(7)°, respectively. The OϪCoϪO angle of 119.23(7)°
is higher than the corresponding value reported for Co-
Table 2. The bond lengths and angles for the oxazoline ring of complex 2 compared with those of the active site of Agrobactin
Agrobactin[a]
Complex 2
1.288(4)
1.503(4)
1.353(3)
1.442(4)
1.526(5)
106.2(2)
107.6(2)
116.3(3)
C(1)ϪN(2)
1.286(5)
1.464(5)
1.327(5)
1.466(5)
1.547(5)
106.6(3)
106.6(3)
118.9(3)
N(1)ϪC(17)
N(2)ϪC(27)
1.286(4)
1.485(4)
1.365(3)
1.428(4)
1.519(5)
106.0(3)
108.2(3)
116.4(3)
C(3)ϪN(2)
N(1)ϪC(19)
N(2)ϪC(29)
C(1)ϪO(5)
O(12)ϪC(17)
O(22)ϪC(27)
C(4)ϪO(5)
O(12)ϪC(18)
O(22)ϪC(28)
C(3)ϪC(4)
C(18)ϪC(19)
C(28)ϪC(29)
C(1)ϪO(5)ϪC(4)
C(1)ϪN(2)ϪC(3)
O(5)ϪC(1)ϪN(2)
C(17)ϪO(12)ϪC(18)
C(17)ϪN(1)ϪC(19)
O(12)ϪC(17)ϪN(1)
C(27)ϪO(22)ϪC(28)
C(27)ϪN(2)ϪC(29)
O(22)ϪC(27)ϪN(2)
[
a]
The atom numbering scheme of the active site of Agrobactin.
Eur. J. Inorg. Chem. 2001, 669Ϫ678
673

G. Mugesh, H. B. Singh, R. J. Butcher
˚
OAc) (2-Me-imid) [105.1(1)°]. The interplanar angle be- C(12b)ϪO(3b) 1.223(3) A] are quite short while the dis-
2 2
FULL PAPER
(
tween CoϪO(11)ϪN(1) and CoϪO(21)ϪN(2) is 94.7°.
tance of the noncoordinated oxygen atoms [C(12a)ϪO(4a)
˚ ˚
1
.302(4) A, C(12b)ϪO(4b) 1.298(3) A] are rather long. The
bonding situation of the acetic acid molecules then allows
for assuming double-bond-coordinated carbonyl groups
C(12a)ϪO(3a) and C(12b)ϪO(3b) and CϪO single bonds
C(12a)ϪO(4a) and C(12b)ϪO(4b). The molecule has eight
rings: two phenyl groups, two oxazoline groups, and four
six-membered chelate rings; the latter are connected by the
˚
metal atom. The Ni(1)ϪN(1a) [2.075(2) A] and
˚
Ni(1)ϪN(1b) [2.074(2) A] distances are larger than those
II
reported for four-coordinate Ni complexes with similar
oxazoline ligands.[ From the bond angle values it is ob-
served that the two nitrogen atoms of the oxazoline five-
membered rings and the two oxygen atoms of neutral acetic
acid molecules form a square planar arrangement and the
two phenolate oxygen atoms lie above and below the plane.
The O(1a)ϪNi(1)ϪO(1b) bond angle of 169.98(7)° indic-
ates that these two atoms lie in the axial positions. The geo-
metrical isomer isolated is, therefore, defined as the cis iso-
mer.
6]
Figure 3. Crystal structure of complex 3
˚
Table 3. Selected bond lengths [A] and angles [°] for 3, 6, and 7
Bond lengths/angles
3
6
7
M ϭ Co
M ϭ Cu
M ϭ Zn
MϪN(1)
1.9770(16)
1.9799(16)
1.9025(15)
1.9075(14)
1.312(2)
1.349(2)
1.442(3)
1.309(2)
1.355(2)
1.451(3)
1.295(2)
1.494(2)
1.288(2)
1.497(2)
119.23(7)
121.25(7)
116.61(6)
94.03(6)
95.13(6)
112.52(7)
1.985(1)
1.986(2)
1.885(2)
1.880(2)
1.308(3)
1.353(3)
1.439(3)
1.309(3)
1.347(3)
1.424(4)
1.298(3)
1.509(3)
1.297(3)
1.501(3)
156.04(9)
160.20(8)
92.05(7)
91.99(7)
91.76(7)
92.38(8)
1.9866(19)
1.992(2)
1.9026(18)
1.9187(18)
1.308(3)
1.356(3)
1.445(4)
1.302(3)
1.353(3)
1.448(4)
1.287(3)
1.488(3)
1.286(3)
1.497(3)
117.73(9)
121.14(9)
116.75(8)
94.16(8)
95.90(8)
112.90(9)
MϪN(2)
MϪO(11)
MϪO(21)
O(11)ϪC(11)
(12)ϪC(17)
O(12)ϪC(18)
O(21)ϪC(21)
O(22)ϪC(27)
O(22)ϪC(28)
N(1)ϪC(17)
N(1)ϪC(19)
N(2)ϪC(27)
N(2)ϪC(29)
O(11)ϪMϪO(21)
N(1)ϪMϪN(2)
N(1)ϪMϪO(21)
N(2)ϪMϪO(21)
O(11)ϪMϪN(1)
O(11)ϪMϪN(2)
Figure 4. Crystal structure of complex 5
˚
Table 4. Significant bond lengths [A] and angles [°] for 5
Crystal Structure of 5
The molecular structure of complex 5 is shown in Fig- Ni(1)ϪO(1a)
1.998(2) Ni(1)ϪO(1b)
2.074(2) Ni(1)ϪN(1a)
2.137(2) Ni(1)ϪO(3a)
2.016(2)
2.075(2)
2.176(2)
Ni(1)ϪN(1b)
ure 4. Selected bond lengths and angles are presented in
Ni(1)ϪO(3b)
Table 4. The unit cell of 5 contains two nonsymmetric O(1a)ϪNi(1)ϪO(1b) 169.98(7) O(1a)ϪNi(1)ϪN(1b) 97.94(8)
O(1b)ϪNi(1)ϪN(1b) 88.22(8) O(1a)ϪNi(1)ϪN(1a) 88.57(7)
equivalent molecules. No significant differences between
these two molecules are observed. The structure of complex
O(1b)ϪNi(1)ϪN(1a) 98.37(7) N(1b)ϪNi(1)ϪN(1a) 98.47(8)
O(1a)ϪNi(1)ϪO(3b) 87.06(7) O(1b)ϪNi(1)ϪO(3b) 85.22(7)
5
is found to be quite interesting. The Ni atom is six-coord- N(1b)ϪNi(1)ϪO(3b) 88.33(8) N(1a)ϪNi(1)ϪO(3b) 172.37(8)
O(1a)ϪNi(1)ϪO(3a) 85.37(7) O(1b)ϪNi(1)ϪO(3a) 87.58(7)
inate and the geometry around the metal center is distorted
octahedral. The Ni ion is bonded to two nitrogen and two
N(1b)ϪNi(1)ϪO(3a) 172.23(8) N(1a)ϪNi(1)ϪO(3a) 87.58(7)
O(3b)ϪNi(1)ϪO(3a) 84.81(8)
oxygen atoms [both pairs are in the cis position (OϪNiϪN Ni(2)ϪO(1c)
2.001(2) Ni(2)ϪO(1cЈ)
2.074(2) Ni(2)ϪN(1cЈ)
2.179(2) Ni(2)ϪO(3cЈ)
2.001(2)
2.074(2)
2.179(2)
Ni(2)ϪN(1c)
angles 88.22Ϫ98.37°)] as well as two oxygen atoms of neut-
Ni(2)ϪO(3c)
ral acetic acid molecules. Interestingly, the acidic protons O(1c)ϪNi(2)ϪN(1c) 88.71(9) O(1cЈ)ϪNi(2)ϪN(1c) 97.67(8)
O(1c)ϪNi(2)ϪN(1cЈ) 97.67(8) O(1cЈ)ϪNi(2)ϪN(1cЈ) 88.71(9)
form strong hydrogen bonds with the aryloxo function of
the ligand. This observation is similar to the one reported
N(1c)ϪNi(2)ϪN(1cЈ) 100.83(12) O(1c)ϪNi(2)ϪO(3c) 87.51(9)
O(1cЈ)ϪNi(2)ϪO(3c) 84.97(9) N(1c)ϪNi(2)ϪO(3c) 170.34(9)
for a binuclear nickel(II) complex in which the neutral N(1cЈ)ϪNi(2)ϪO(3c) 88.49(9) O(1c)ϪNi(2)ϪO(3cЈ) 84.97(9)
O(1cЈ)ϪNi(2)ϪO(3c) 87.51(9) N(1c)ϪNi(2)ϪO(3cЈ) 88.49(9)
acidic acid molecule is involved in a hydrogen bonding with
N(1cЈ)ϪNi(2)ϪO(3cЈ) 170.34(9) O(3c)ϪNi(2)ϪO(3cЈ) 82.32(14)
the alkoxo function.[
11b]
The CϪO bond lengths of the co-
O(1c)ϪNi(2)ϪO(1cЈ) 170.01(12)
˚
ordinated oxygen atoms [C(12a)ϪO(3a) 1.223(3) A,
674
Eur. J. Inorg. Chem. 2001, 669Ϫ678

2-(4Ј,4Ј-Dimethyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)phenol
FULL PAPER
Crystal Structure of 6
than the corresponding angles in bis(N-alkylsalicylaldimin-
ato)copper(II) (94.4 and 95.0°). Significant bond lengths
and angles for 6 are given in Table 3.
An ORTEP view of the copper complex 6 is shown in
Figure 5. Complex 6 crystallizes in the monoclinic space
group P2 /c. The N atoms of the oxazoline five-membered
ring and phenolato O atoms gave a distorted tetrahedral
arrangement. Both tetrahedral and planar configurations
1
Crystal Structure of 7
II
The colorless crystals of Zn complex 7 belong to the
¯
have
been
reported
for
the
related
bis[N- space group P1 of the triclinic system. An ORTEP view of
alkylsalicylaldiminato(OϪN)]copper(II) complexes, de- the structure is shown in Figure 6. Selected bond lengths
pending upon the nature of the alkyl groups.[ For com- and angles for 6 are given in Table 3. The Zn atom has a
parison with 6, the complexes with α-branched N-alkyl distorted tetrahedral coordination configuration. The in-
22]
groups should be considered. In the case of iPr or tBu terplanar
groups, they were found to be pseudo-tetrahedral in the ZnϪO(21)ϪN(2) is 86.2°. The planes between the phenyl
solid state. For example,
bis[N-isopropylsalicyl- ring and the heterocyclic ring are only slightly twisted. The
angle
between
ZnϪO(11)ϪN(1)
and
aldiminato(OϪN)]copper(II) has a tetrahedral structure dihedral angle between C(15)ϪC(16)ϪC(17)ϪO(12) is
with an angle of 60° between the salicylaldiminato planes, Ϫ0.9(3)°, that of C(15)ϪC(16)ϪC(17)ϪN(1) is Ϫ179.8(2)°.
whereas, N-Ph and N-Me substituted complexes are almost The ZnϪO(11), ZnϪO(21), ZnϪN(1), and ZnϪN(2) bond
[
23,24]
planar.
Lehn and co-workers have reported the crystal lengths are 1.9026(18), 1.9187(18), 1.9866(19), and
˚
structure of a chiral bis(dihydrooxazole)copper(II) com- 1.992(2) A. Whereas the ZnϪO distances do not differ sub-
[
25]
plex,
with a dihedral angle of 52° between the two stantially from values reported for similar Schiff base com-
NϪCuϪN planes. Similar to the salicylaldiminato com- plexes,[ the ZnϪN distances are relatively short. However,
plexes, the oxazoline complexes also form both tetrahedral the ZnϪN bond lengths are slightly longer than the values
and square planar complexes depending upon the nature of reported for a similar oxazoline complex.[
the alkyl groups present on the five-membered ring. Bolm
26]
6]
II
et al. have reported a Cu complex with a chiral oxazoline
ligand in which the geometry around the metal center was
found to be almost square planar.[ However, the geometry
around the metal center in complex 6 tends more towards
tetrahedral which is probably due to the presence of the two
methyl groups on the oxazoline ring. Bolm et al. have also
reported that there is an interaction between the Cu atom of
one molecule and the phenolate O atom of the neighboring
molecule which make the Cu atoms pentacoordinate.[
However, in complex 6 no such interactions were observed.
In 6, the angle between O(11)ϪCuϪN(1) and
O(21)ϪCuϪN(2) planes is 30.8°, which indicates a distor-
6]
6]
tion from planar geometry. The CuϪO distances [1.880(2)
Figure 6. Crystal structure of complex 7
˚
˚
˚
A and 1.885(2) A] and the CuϪN distances [1.985(2) A,
˚
6]
II
1
.986(2) A] are similar to those reported for the chiral Cu
[
Conclusion
complex
and bis(N-alkylsalicylaldiminato)copper(II)
complexes. In 6, the angles of 91.76(7)° and 91.99(7)° for
O(11)ϪCuϪN(1) and O(21)ϪCuϪN(2) are slightly smaller
[
24]
In conclusion, we have shown that the 2-(4Ј,4Ј-dimethyl-
3
Ј,4Ј-dihydrooxazol-2Ј-yl)phenol ligand can be conveniently
used to synthesize tetrahedral complexes of the late first
row transition metals. Complexes 3, 6, and 7 crystallize as
racemates in achiral space group, however, for complex 7,
the interconversion between the (M) and (P) helix is slow
at low temperatures. Since the other complexes (Co, Ni, Cu)
are found to be paramagnetic, the variable-temperature
NMR spectroscopy of these complexes, which is used to
study their low-temperature behavior, could not be at-
tempted. The solid-state structures show that none of these
complexes are chiral. Similar to the behavior of Agrobactin,
the ligand 2-(4Ј,4Ј-dimethyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)-
phenol undergoes metal-assisted hydrolysis/oxidation in the
III
presence of oxophilic Mn ions to give the partially hy-
drolyzed oxazoline ring as found in Agrobactin A, forming
II
a novel mononuclear complex. The ability of Ni to form
Figure 5. Crystal structure of complex 6
Eur. J. Inorg. Chem. 2001, 669Ϫ678
six-coordinate complexes with neutral ligands allows the
675

G. Mugesh, H. B. Singh, R. J. Butcher
FULL PAPER
isolation of a novel octahedral NiII complex with a neutral was recrystallized by slow concentration of a solution of 2 in 1:1
mixture of CH Cl (5 mL)/CH OH (5 mL) at room temperature to
acetic acid ligand.
2
2
3
give black-green crystals. Yield: 0.31 g (48%). Ϫ M.p. 180Ϫ182°C.
38MnN (643.6): calcd. C 61.58, H 5.95, N 6.53; found
Ϫ C33
H
3 7
O
ϩ
26 2 5
C 61.52, H 5.10, N 6.13. Ϫ MS; m/z: 453 [C22H N O Mn] , 435
Experimental Section
ϩ
ϩ
ϩ
[C H
22
24
N
2
O
4
Mn] , 293 [C11
H14NO
5 2
Mn] , 244 [C11H12NO Mn] ,
12NO] . Ϫ IR (KBr): ν˜ ϭ 1580
ϩ
ϩ
1
91 [C11H12NO ] , 173 [C11H
2
General Procedures: Solvents were purified by standard proced-
Ϫ1
Ϫ1
3
cm (CϭO), 1609 cm (CϭN). Ϫ EPR (Solid & CDCl , 298 K):
[
27]
ures
and were freshly distilled prior to use. 2-Amino-1-methyl-
Silent.
were also purified prior to use.[
27]
1
2
-propanol (Merck) and ZnCl
-Hydroxybenzonitrile (Merck) was used as received. Ϫ Melting
2
2 2 2
Synthesis of [Co{O(Ox)} ] (3): To a solution of Co(OAc) · 4 H O
points were recorded in capillary tubes and are uncorrected. Ϫ IR
spectra were recorded as KBr pellets with a Nicolet Impact 400
FT-IR spectrometer. Ϫ For 1 and 7, the H, and C spectra were
obtained at 300 and 75.42 MHz in CDCl with a Varian VXR 300S
spectrometer. Chemical shifts are cited with respect to SiMe as an
(
0.25 g, 1.01 mmol) in absolute ethanol (20 mL) was added a solu-
tion of 1 (0.38 g, 1.99 mmol) in ethanol (10 mL). A pink-colored
compound precipitated immediately. The stirring was continued for
1
13
3
1
2 h at room temperature. The resulting crude solid was filtered
4
and dried under vacuum. Pink-colored needle-shaped crystals of
internal standard. Ϫ Elemental analyses were performed with a
CarloϪErba model 1106 elemental analyzer. Ϫ Fast atom bom-
bardment (FAB) mass spectra were recorded at room temperature
with a JEOL SX 102 DA-6000 mass spectrometer/data system us-
ing xenon (6 kV, 10 mV) as the bombarding gas. Ϫ Cyclic Voltam-
metry (CV) experiments were performed with an EPΣG Princeton
Applied Research Potentiostat/Galvanostat Model 273A which
consisted of a one-compartment cell with platinum working and
counter electrodes and an AgϪAgCl electrode (reference electrode).
Tetraethylammonium perchlorate was used as the supporting elec-
trolyte. All solutions were purged with argon or nitrogen and re-
tained under these gases while the CV data were recorded. Ϫ The
EPR spectra of the complexes in chloroform or ethanol were re-
corded with a Varian E-112 EPR spectrometer using tetracyanoe-
thylene as g marker (g ϭ 2.00277) at room temperature and liquid-
nitrogen temperatures. Ϫ Magnetic susceptibilities of powdered
samples were determined at room temperature with a Faraday bal-
the desired compound 3 were obtained by slow concentration of a
CH
room temperature. Yield: 0.37g (85%). Ϫ M.p. 234Ϫ236°C. Ϫ
24CoN (439.4): calcd. C 60.14, H 5.50, N 6.38; found C
0.23, H 5.35, N 6.22. Ϫ MS; m/z (%): 439 [M , C22
2 2
Cl (5 mL)/methanol(5 mL) solution of the crude product at
C
6
22
H
2 4
O
ϩ
ϩ
H
24
N
2
ϩ
O
4
Co]
ϩ
(
100), 364 [C22
H
24
N
2
O
3
] , 249 [C11
H
12NO
2
Co] , 190
ϩ
ϩ
Ϫ1
[C H12NO ] , 177 [C11H
11 2
12NO] . Ϫ IR (KBr): ν˜ , 1618 cm
(
CϭN).
2 2 2
Synthesis of [Ni{O(Ox)} ] (4): To a solution of Ni(OAc) · 4 H O
(0.25 g, 1.01 mmol) in absolute ethanol (20 mL) was added a solu-
tion of 1 (0.38 g, 1.99 mmol) in ethanol (10 mL). The resulting
green solution was stirred for 18 h at room temperature. The pale
green solid formed was filtered and washed with ethanol and dried
under vacuum. The pale green crystals of 4 were obtained by slow
2 2
concentration of a CH Cl (5 mL)/ethanol(5 mL) solution of the
crude product. Slow concentration of the filtrate at room temper-
ance, standardized with mercury tetracyanocobaltate(II) [χ ϭ ature afforded the dark green crystals of 5.
Ϫ6
3
Ϫ1
1
6.44·10 cm mol ]. The molar susceptibilities were corrected
4
: Yield: 0.26g (60%). Ϫ M.p. 224Ϫ226°C. Ϫ C22
24 2 4
H N NiO
for ligand diamagnetism using Pascal’s constants. The effective
(
439.2): calcd. C 60.17, H 5.51, N 6.38; found C 59.84, H 5.32, N
magnetic moments were calculated using the expression µeff
ϭ
ϩ
/2
6.10.
Ϫ
26 32 2 8
MS; m/z (%): 555 [C H N O Ni] , 496
2
.83(χ
CHCl
m
ϫ T)1 . Ϫ Electronic absorption spectra were obtained in
ϩ
ϩ
ϩ
[C
24
H
28
N
2
O
6
Ni] , 439 [C22
H
24
N
2
O
4
Ni] , 424 [C21
H
21
N
2
O
4
Ni] ,
3
at 25 °C in a 1-cm quartz cuvette with a Shimadzu UV-
ϩ
ϩ
ϩ
3
1
6 6 2
67 [C15H20NO Ni] , 352 [C14H17NO Ni] , 248 [C11H12NO Ni] ,
2100 apparatus.
ϩ
Ϫ1
76 [C11H
12NO] (100). Ϫ IR (KBr): ν˜ ϭ 1622 cm (CϭN). Ϫ
Synthesis of 2-(4Ј,4Ј-Dimethyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)phenol (1):
This compound was synthesized by following the published proced-
ure with minor modifications.[ 2-Amino-1-methyl-1-propanol
EPR (Solid, 77 K): geff ϭ 2.18.
5]
32 2 8
5: Yield: 0.17g (30%). Ϫ M.p. 198Ϫ200°C. Ϫ C26H N NiO
(559.3): calcd. C 55.84, H 5.77, N 5.01; found C 55.54, H 5.45, N
(
4
5.99 g, 6.41 mL, 67.20 mmol), 2-hydroxybenzonitrile (5.35 g,
ϩ
4.91 mmol), and ZnCl
2
(0.31 g, 2.24 mmol) were dissolved in chlo- 4.87. Ϫ MS; m/z (%): 555 [M, C26H N O Ni] (100), 498
32 2 8
ϩ
ϩ
ϩ
robenzene (90 mL) and refluxed for 24 h under nitrogen. The re-
sulting reaction mixture was filtered to remove the undissolved im-
[C24
365 [C15
28 2 6 24 2 4 21 2 4
H N O Ni] , 439 [C22H N O Ni] , 424 [C21H N O Ni] ,
ϩ
ϩ
ϩ
H
20NO
6
ϩ
Ni] , 352 [C14
H
17NO
12NO] . Ϫ IR (KBr): ν˜ ϭ 1617 cm (CϭN), 1706 cm
, 298 K): Silent.
6 2
Ni] , 248 [C11H12NO Ni] ,
Ϫ1
Ϫ1
purities. The filtrate was concentrated under reduced pressure to 176 [C11
give a brown oil which was dissolved in 50 mL of CH Cl and
washed with water. The organic layer was separated, dried with
anhydrous Na SO , filtered, and concentrated to give the desired
H
(CϭO). Ϫ EPR (Solid & CDCl
3
2
2
2 2 2
Synthesis of [Cu{O(Ox)} ] (6): To a solution of Cu(OAc) · H O
2
4
(
0.20 g, 1.01 mmol) in absolute ethanol (20 mL) was added a solu-
compound as a light brown oil.
tion of 1 (0.38 g, 1.99 mmol) in ethanol (10 mL). The resulting
green-colored solution was stirred for 24 h at room temperature
and then filtered. The filtrate was concentrated under vacuum to
give a green-colored solid. Recrystallization of the solid from
Synthesis of [Mn(OR){O(Ox)}
2
]
(2): To
a
solution of
2 2
Mn(OAc) · 4 H O (0.25 g, 1.02 mmol) in absolute ethanol (20 mL)
was added a solution of 1 (0.38 g, 1.99 mmol) in ethanol (10 mL).
The reaction mixture was stirred for 24 h at room temperature.
The resulting dark green solution was concentrated under reduced
pressure to give a dark oil. This was dissolved in dry ether (20 mL)
and filtered through Celite to remove the undissolved impurities.
Addition of hexane (20 mL) to the ethereal solution followed by
cooling of the solution overnight afforded a black-green solid. The
solid was filtered off, washed with hexane and dried under reduced
pressure to give 2 as a black-green crystalline solid. Compound 2
CH
forded the dark green crystals of 6. Yield: 0.38g (85%). Ϫ M.p.
190Ϫ192°C. Ϫ C22 24CuN (443.10): calcd. C 59.52, H 5.45, N
6.31; found C 59.27, H 5.23, N 6.14. Ϫ MS; m/z (%): 443 [M,
2 2
Cl (5 mL)/methanol(5 mL) mixture at room temperature af-
H
2 4
O
ϩ
ϩ
C
[C11
22
H
H
24
N
12NO
2
O
4
Cu]
(100),
371
[C22
H
24
N
2
O
H
3
] ,
12NO] .
253
Ϫ
ϩ
ϩ
ϩ
2
Cu] , 191 [C11
H
12NO
2
] , 176 [C11
Ϫ1
IR(KBr): ν˜ ϭ 1614 cm (CϭN). Ϫ EPR (CHCl
, 25 °C): geff ϭ
3
2.31.
676
Eur. J. Inorg. Chem. 2001, 669Ϫ678

2-(4Ј,4Ј-Dimethyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)phenol
FULL PAPER
Synthesis of [Zn{O(Ox)}
.51 mmol) in absolute ethanol (30 mL) was added a solution of 1
0.95 g, 4.97 mmol) in ethanol (10 mL). The reaction mixture was
2 2
] (7): To a solution of Zn(OAc) (0.46 g, Table 6. Crystal data and structure refinement for 6 and 7
2
(
6
7
stirred for 24 h at room temperature during which time a white
solid was formed. The solid was filtered and dried under vacuum.
Colorless crystals of the desired compound were obtained by
Empirical formula
Molecular mass
Crystal system
Space group
C
22
443.97
H
24CuN
2
O
4
C
22
445.80
H
24
N
2
O
4
Zn
monoclinic
P2
triclinic
P1
8.0231(8)
3
recrystallization from CHCl (5 mL)/hexane (5 mL). Yield: 0.40 g
¯
1
/c
˚
(
5
(
(
90%). Ϫ M.p. 210Ϫ212 °C. Ϫ C22 Zn (445.8): calcd. C
H
24
N
2
O
4
a [A]
11.462(2)
9.3919(12)
19.628(2)
90
˚
1
b [A]
11.4838(13)
13.2563(13)
115.582(7)
96.924(6)
94.500(7)
1081.9(2)
2
9.27, H 5.43, N 6.28; found C 59.14, H 5.22, N 6.16. Ϫ H NMR
): δ ϭ 1.38 (s, 12 H, CH ), 4.16(s, 4 H, CH ), 6.52Ϫ6.56
dd, 2 H, Ar-H), 6.84Ϫ6.88 (d, 2 H, Ar-H) 7.25Ϫ7.33 (dd, 2 H,
˚
c [A]
CDCl
3
3
2
α [°]
β [°]
91.726(8)
90
13
Ar-H), 7.67Ϫ7.71 (d, 2 H, Ar-H). Ϫ C NMR (CDCl
3
): δ ϭ 28.34, γ [°]
˚
3
V [A ]
2112.0(4)
4
6
6.39, 77.77, 108.95, 113.86, 123.14, 130.05, 134.99, 168.11, 170.27.
ϩ
ϩ
Z
Ϫ MS; m/z (%): 702 [C33
H
12NO
36
N
3
O
6
Zn
2
] , 445 [M, C22
H
24
N
2
ϩ
O
4
Zn]
3
D(calcd.) [Mg/m ]
1.396
1.368
ϩ
(100), 254 [C11
H
2
Zn] , 238 [C10
H
9
NO
2
Zn] , 191
Ϫ1
Abs. coeff. [mm
]
1.064
1.164
ϩ
Ϫ1
[C
11
H12NO
2
] . Ϫ IR (KBr): ν˜ ϭ 1645 cm (CϭN).
Obsd. reflexions [I Ͼ 2σ]
4800
5969
[
a]
Final R(F) [I Ͼ 2σ(I)]
0.0358
0.0928
4799/0/291
1.03
0.0432
2
X-ray Crystallographic Studies: The diffraction measurements for
compounds 2, 3, 5, 6, and 7 were performed at room temperature
wR(F ) indices [I Ͼ 2σ(I)]
0.1132
Data/restrains/parameters
5968/0/291
1.07
2
Goodness of fit on F
(
293 K) with a Siemens R3m/V diffractometer using graphite-mon-
˚
ochromated Mo-K
α
radiation (λ ϭ 0.71073 A). The unit cell was
[a]
2) ϭ {[w(F
2
Definitions: R(F
o
) ϭ ||F
o
| Ϫ |F
c
||/|F
o
| and wR(F
o
o
Ϫ
2
2
2 2 1/2
determined from 25 randomly selected reflections using the auto-
matic search index and least-squares routine. For 2, the θ range for
data collection was from 2.25 to 27.50° whereas for 3, 5, 6, and 7
the ranges were 2.58Ϫ27.50°, 1.29Ϫ27.50°, 2.40Ϫ27.50°, and
c c
F ) ]/[w(F ) } .
and the rest were fixed at calculated positions. Scattering factors
were from common sources. Some details of data collection and
refinement are given in Table 5 and Table 6. Crystallographic data
[30]
2.58Ϫ50.59°. The index range for 2 was Ϫ13 Յ h Յ 0, Ϫ13 Յ k Յ
13, Ϫ19 Յ l Յ 20 while for 3, 5, 6, and 7 the ranges were 0 Յ h Յ
10, Ϫ13 Յ k Յ 13, Ϫ16 Յ l Յ 17; 0 Յ h Յ 41, Ϫ20 Յ k Յ 0, Ϫ21
(
excluding structure factors) for the structures reported in this pa-
per have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publications nos. CCDC-134052 (2),
Յ l Յ 21; Ϫ14 Յ h Յ 0, 0 Յ k Յ 12, Ϫ25 Յ l Յ 25, and 0 Յ h Յ
1, Ϫ14 Յ k Յ 14, Ϫ18 Յ l Յ 18. The data for 3, 6, and 7 were
1
-
134053 (3), -134054 (5), -134055 (6), -134056 (7). Copies of the
corrected for Lorentz, polarization, and absorption effects. The
maximum and minimum transmission values of the correction fac-
tors for compounds 3 (dimensions 0.48 ϫ 0.50 ϫ 0.49 mm), 6 (0.19
ϫ 0.88 ϫ 0.38 mm), and 7 (0.28 ϫ 0.64 ϫ 0.32 mm) were 0.4733
and 0.3904, 0.2873 and 0.2187, and 0.9181 and 0.8319. The data
were monitored by measuring two standard reflections every 60
min of X-ray exposure time. The structures were solved by routine
heavy-atom (using SHELXS 86[ ) and Fourier methods and re-
fined by full-matrix least squares with the non-hydrogen atoms an-
isotropic and hydrogen atoms with fixed isotropic thermal para-
data can be obtained free of charge on application to CCDC, 12
Union Road, Cambridge CB21EZ, UK [Fax: (internat.) ϩ 44-1223/
3
36-033; E-mail: deposit@ccdc.cam.ac.uk].
Acknowledgments
28]
We are grateful to the Department of Science and Technology
(DST), New Delhi and Board of Research in Nuclear Sciences
(BRNS), Department of Atomic Energy, Bombay for funding this
work. Additional help from the Regional Sophisticated Instru-
mentation Centre (RSIC), Indian Institute of Technology (IIT),
˚
2
[29]
meters of 0.07 A using the SHELXL 93 program. The hydrogen
atoms were partially located from difference electron-density maps
Table 5. Crystal data and structure refinement for 2, 3, and 5
2
3
5
Empirical formula
Molecular mass
Crystal system
Space group
C
33
H
38
N
3
O
7
Mn
C
22
439.36
H
24
N
2
O
4
Co
C
26 32 2 8
H N O Ni
643.60
triclinic
559.25
triclinic
monoclinic
C2/c
¯
¯
P1
P1
˚
a [A]
10.095(2)
10.646(2)
15.734(4)
94.76(2)
108.22(2)
91.14(2)
1598.7(6)
2
8.018(2)
31.690(6)
15.401(2)
16.856(3)
90
˚
b [A]
11.472(3)
13.230(3)
64.581(14
˚
c [A]
α [°]
β [°]
γ [°]
79.358(14)
85.54(2)
1080.2(5)
2
97.083(9)
90
˚
3
V [A ]
8164(2)
12
Z
3
D(calcd.) [Mg/m ]
1.337
1.351
1.365
Ϫ1
Abs. coeff. [mm
]
0.464
0.823
0.763
Obsd. reflexions [I Ͼ 2σ]
7332
4345
9231
[a]
Final R(F) [I Ͼ 2σ(I)]
0.0558
0.1267
0.0344
0.0917
4345/0/291
1.09
0.0427
0.1019
9228/0/567
1.08
2
wR(F ) indices [I Ͼ 2σ(I)]
Data/restrains/parameters
7328/0/447
1.043
2
Goodness of fit on F
[
a]
| and wR(F 2
2
2)2]/[w(F 2)2}1/2.
c
Definitions: R(F
o
) ϭ ||F
o
| Ϫ |F
c
||/|F
o
o
) ϭ {[w(F
o
Ϫ F
c
Eur. J. Inorg. Chem. 2001, 669Ϫ678
677

G. Mugesh, H. B. Singh, R. J. Butcher
FULL PAPER
Chem. Eur J. 1999, 5, 1411. Ϫ [ A. Panda, G. Mugesh, H. B.
Singh, R. J. Butcher, Organometallics 1999, 18, 1986.
10] [10a]
9i]
Bombay, for EPR and 300-MHz NMR spectroscopy is gratefully
acknowledged. R. J. B. wishes to acknowledge the DoD-ONR pro-
gram for funds to upgrade the diffractometer.
[
[
G. Mugesh, H. B. Singh, R. J. Butcher, Eur. J. Inorg. Chem.
[10b]
1
999, 1229. Ϫ
G. Mugesh, H. B. Singh, R. P. Patel, R. J.
[10c]
Butcher, Inorg. Chem. 1998, 37, 2663. Ϫ
G. Mugesh, H. B.
[
1] [1a]
Singh, R. J. Butcher, J. Organomet. Chem. 1999, 577, 243.
S. A. Ong, T. Peters, J. B. Neilands, J. Biol. Chem. 1979,
11] [11a]
[
1b]
M. Schroder, ‘‘Nickel: Inorganic and Coordination Chem-
2
54, 1860. Ϫ
T. Peterson, J. B. Neilands, Tetrahedron Lett.
[1c]
istry’’ in: Encyclopedia of Inorganic Chemistry (Ed.: R. B. King)
1
979, 50, 4805. Ϫ
T. Peterson, K. -E. Falk, S. A. Leong, M.
[
11b]
John Wiley & Sons, New York, 1994, vol. 4, p. 2392. Ϫ
D.
P. Klein, J. B. Neilands, J. Am. Chem. Soc. 1980, 102, 7715. Ϫ
[
1d]
Volkmer, A. Horstmann, K. Griesar, W. Haase, B. Krebs, Inorg.
Chem. 1996, 35, 1132.
12]
Y. Nagao, T. Miyasaka, Y. Hagiwara, E. Fujita, J. Chem.
[
1e]
Soc., Perkin Trans. 1 1984, 183. Ϫ
D. L. Eng-Wilmot, D.
[
van der Helm, J. Am. Chem. Soc. 1980, 102, 7719.
A. Jacobs, G. P. White, G. H. Tait, Biochem. Biophys. Res.
Commun. 1977, 74, 1626.
B. N. Figgis, Nature 1958, 182, 1568.
[
[
2]
[13]
R. L. Carlin Jr., S. L. Holt, Inorg. Chem. 1963, 2, 849.
F. A. Cotton, D. M. L. Goodgame, M. Goodgame, J. Am.
Chem. Soc. 1961, 83, 4690.
[
14]
3] [3a]
H. Brunner, H. Nishiyama, K. Itoh, in: Catalytic Asymmet-
[
15]
ric Synthesis (Ed.: I. Ojima), VCH Publishers, New York, 1993,
H. Yokoi, T. Isobe, Bull. Chem. Soc. Jpn. 1969, 42, 2187.
B. P. Kennedy, A. B. P. Lever, J. Am. Chem. Soc. 1973, 95, 6907.
V. M. Miskowski, J. A. Thich, R. Solomon, H. J. Schugar, J.
Am. Chem. Soc. 1976, 98, 8344.
[
3b]
[16]
[17]
p. 303. Ϫ
metry 1994, 5, 277. Ϫ
Asymmetry 1995, 6, 653. Ϫ
hedron: Asymmetry 1995, 6, 549. Ϫ
Gais, Tetrahedron: Asymmetry 1995, 6, 643. Ϫ
ards, D. E. Hibbs, M. B. Hursthouse, Tetrahedron Lett. 1995,
6, 3745.
J. V. Allen, J. M. J. Williams, Tetrahedron: Asym-
[3c]
H. Brunner, D. Henrichs, Tetrahedron:
[3d]
E. Macedo, C. Moberg, Tetra-
[3e]
H. Eichelmann, H.-J.
[18]
[19]
[20]
A. R. Amundsen, J. Whelan, G. Bosnich, J. Am. Chem. Soc.
[3f]
C. J. Rich-
1
977, 99, 6730.
G. Das, R. Shukla, S. Mandal, R. Singh, P. K. Bharadwaj, J.
Van Hall, K. H. Whitmire, Inorg. Chem. 1997, 36, 323.
W. D. Horrocks, J. N. Ishley, R. R. Whittle, Inorg. Chem. 1982,
3
[
[
4] [4a]
P. G. Cozzi, C. Floriani, A. C. Villa, C. Rizzoli, Inorg.
[4b]
Chem. 1995, 34, 2921. Ϫ
P. G. Cozzi, C. Floriani, J. Chem.
2
1, 3265.
Soc., Perkin Trans.1 1995, 2557.
[
21]
5] [5a]
W. D. Horrocks, J. N. Ishley, R. R. Whittle, Inorg. Chem. 1982,
M. G. Simon, S. Jansat, G. Muller, D. Panyella, M. F. Bar-
[5b]
21, 3270.
dia, X. Soians, J. Chem. Soc., Dalton Trans. 1997, 3755. Ϫ
[
[
22]
23]
P. L. Orioli, L. Sacconi, J. Am. Chem. Soc. 1966, 88, 277.
E. C. Lingafelter, G. L. Simmons, B. Morosin, C. Scheringer,
C. Freiburg, Acta Crystallogr. 1961, 14, 1222.
L. Wei, R. M. Stogsdill, E. C. Lingafelter, Acta Crystallogr.
964, 17, 1058.
J. Hall, J. -M. Lehn, A. DeCian, J. Fisher, Helv. Chim. Acta
991, 74, 1.
R. H. Prince, in: Comprehensive Coordination Chemistry (Eds.:
G. Wilkinson, R. D. Gilliard, J. A. McCleverty), Pergamon
Press, Oxford, 1987, vol. 5, pp. 925.
D. D. Perrin, W. L. F. Armarego, D. R. Perrin, Purification of
Laboratory Chemicals, 2nd ed., Pergamon, Oxford, 1980.
G. M. Sheldrick, Crystallographic Computing 3, Oxford Uni-
versity Press, Oxford, 1985, p. 175.
M. Hoogenraad, K. Ramkisoensing, H. Kooijman, A. L. Spek,
E. Bouwman, J. G. Haasnoot, J. Reedijk, Inorg. Chim. Acta
1
998, 279, 217.
[
[
[
24]
25]
26]
[
[
[
[
6]
7]
8]
H. R. Hoveyda, V. Karunaratne, S. J. Rettig, C. Orvig, Inorg.
1
Chem. 1992, 31, 5408.
C. Bolm, K. Wieghardt, M. Zehnder, D. Glasmacher, Helv.
Chim. Acta 1991, 74, 717.
1
C. Bolm, K. Wieghardt, M. Zehnder, T. Renff, Chem. Ber.
1
991, 124, 1173.
9] [9a]
H. B. Singh, N. Sudha, Coord. Chem. Rev. 1994, 135Ϫ136,
[
[
27]
28]
[
9b]
4
69. ؊
R. Kaur, H. B. Singh, R. J. Butcher, Organometallics
[9c]
1
995, 14, 4755. Ϫ
R. Kaur, H. B. Singh. R. P. Patel, S. K.
[9d]
Kulshreshtha, J. Chem. Soc., Dalton Trans. 1996, 461. Ϫ
S.
C. Menon, H. B. Singh, J. M. Jasinski, J. P. Jasinski, R. J. But-
[9e]
[29]
[30]
cher, Organometallics 1996, 15, 1707. Ϫ
S. C. Menon, H. B.
G. Mugesh, A. Panda, H. B. Singh, N. S. Pune-
G. M. Sheldrick, SHELX 93, Program for Crystal Structure
Determination, University of Göttingen, 1993.
International Tables for X-ray Crystallography, Kynoch Press,
Birmingham, 1974, vol. 4, pp. 99, 149.
Singh, R. P. Patel, K. Das, R. J. Butcher, Organometallics 1997,
[
9f]
1
8, 563. Ϫ
kar R. J. Butcher, Chem. Commun. 1998, 2227. Ϫ
gesh, H. B. Singh, R. J. Butcher, Tetrahedron: Asymmetry 1999,
[9g]
G. Mu-
Received June 30, 2000
[
9h]
1
0, 237. Ϫ
G. Mugesh, A. Panda, H. B. Singh, R. J. Butcher,
[I00259]
678
Eur. J. Inorg. Chem. 2001, 669Ϫ678