Kinetics and mechanism of the copper-catalysed oxygenation of 2-nitropropane

Article abstract of DOI:10.1002/1099-0682(200207)2002:7<1687::AID-EJIC1687>3.0.CO;2-Q

Primary and secondary nitro compounds react with dioxygen in the presence of copper metal and N ligands such as N,N,N′,N′-tetramethylethylenediamine (tmeda), 2,2′-bipyridine (bpy), and 1,10-phenantroline (phen) in various solvents to form aldehydes or ketones. More coordinating solvents as well as donor N ligands accelerate the reaction remarkably. The oxygenolysis of 2-nitropropane (NPH) in the presence of copper and tmeda in DMF results in acetone and acetone oxime. The amount of tmeda influences the chemoselectivity, higher tmeda concentrations preferentially lead to the formation of the oxime. The kinetics of the reaction, measured at 90 °C, resulted in a rate equation of first-order dependence on copper and dioxygen and second-order dependence on 2-nitropropane. The rate constant, activation enthalpy, and entropy at 363.16 K are as follows: k_cat = (5.37 ± 0.34) × 10^-2 Mol^-3 dm⁹ s^-1, E_a = 131 ± 4 kJ mol^-1, ΔH? = 127 ± 4 kJ mol^-1 and ΔS? = 80 ± 13 J mol^-1 K^-1. The catalytically active intermediates Cu^II(NP)₂(tmeda) and Cu^II(NO₂)₂(tmeda) in the catalytic cycle were isolated and their structures determined by X-ray crystallography. The kinetics of the stoichiometric oxygenation of Cu^II(NP)₂(tmeda) to Cu^II(NO₂)₂(tmeda) and acetone resulted in the overall second-order rate equation with a rate constant, activation enthalpy, and entropy at 313.16 K of ks = 0.46 ± 0.02 mol^-1 dm³ s^-1, E_a = 38 ± 1 kJ mol^-1, ΔH? = 35 ± 1 kJ mol^-1 and ΔS? = -142 ± 13 J mol^-1 K^-1, respectively. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.

Full text of DOI:10.1002/1099-0682(200207)2002:7<1687::AID-EJIC1687>3.0.CO;2-Q

FULL PAPER
Kinetics and Mechanism of the Copper-Catalysed Oxygenation of
2-Nitropropane
[a]
[b]
[a]
[a]
´
´
´
´
´
Eva Balogh-Hergovich, Zoltan Greczi, Jozsef Kaizer, Gabor Speier,*
[c]
[c]
[d]
´
´
´ ´ ´
Marius Reglier, Michel Giorgi, and Laszlo Parkanyi
Keywords: 2-Nitropropane / Copper nitronates / Oxygenation / Copper / Kinetics / Dioxygenase
Primary and secondary nitro compounds react with dioxygen
in the presence of copper metal and N ligands such as
N,N,NЈ,NЈ-tetramethylethylenediamine (tmeda), 2,2Ј-bipyr-
idine (bpy), and 1,10-phenantroline (phen) in various solv-
ents to form aldehydes or ketones. More coordinating solv-
ents as well as donor N ligands accelerate the reaction re-
markably. The oxygenolysis of 2-nitropropane (NPH) in the
presence of copper and tmeda in DMF results in acetone and
acetone oxime. The amount of tmeda influences the chemo-
selectivity, higher tmeda concentrations preferentially lead
to the formation of the oxime. The kinetics of the reaction,
measured at 90 °C, resulted in a rate equation of first-order
dependence on copper and dioxygen and second-order de-
pendence on 2-nitropropane. The rate constant, activation
enthalpy, and entropy at 363.16 K are as follows: kcat = (5.37
0.34) × 10−2 mol−3 dm9 s−1, Ea = 131 4 kJ mol−1, ∆H‡ = 127
4 kJ mol−1 and ∆S‡ = 80 13 J mol−1 K−1. The catalytically
active intermediates CuII(NP)2(tmeda) and CuII(NO2)2(t-
meda) in the catalytic cycle were isolated and their structures
determined by X-ray crystallography. The kinetics of the stoi-
chiometric oxygenation of CuII(NP)2(tmeda) to CuII(NO2)2(t-
meda) and acetone resulted in the overall second-order rate
equation with a rate constant, activation enthalpy, and en-
tropy at 313.16 K of ks = 0.46 0.02 mol−1 dm3 s−1, Ea = 38
1 kJ mol−1, ∆H‡ = 35 1 kJ mol−1 and ∆S‡ = −142 13 J
mol−1 K−1, respectively.
( Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany,
2002)
Introduction
There are also a fair number of stoichiometric reagents
for this conversion. Treatment of nitroalkanes with aqueous
TiCl3,[2] cetyltrimethylammonium permanganate,[3] tin
complexes and NaHSO3,[4] activated dry silica gel,[5] 30%
H2O2/K2CO3,[6] KMnO4,[7] ceric ammonium nitrate
(CAN),[8] MoO5/pyridine/HMPA,[9] ozone[10] or singlet
oxygen[11] leads to oxo compounds; tBuOOH and a catalyst
provide a catalytic process for the transformation.[12]
The transformation of primary and secondary aliphatic
nitro compounds to aldehydes or ketones is a reaction often
used in organic chemistry and in biological processes as
well. The Nef reaction, the classical method for this conver-
sion, involves the hydrolysis of the conjugate bases of nitro-
alkanes with sulfuric acid [Equation (1)].[1]
Biochemical degradation of aliphatic nitro compounds is
also known in the literature. Glucose oxidase and - and
L-amino acid oxidase accept nitroalkane anions as sub-
strates.[13] The flavoenzyme-catalysed oxidation of nitroal-
kanes and its mechanism has been established.[14,15] Elec-
tron-deficient flavins also oxidise nitroalkane anions in
model reactions.[16,17]
(1)
[a]
Research Group for Petrochemistry, Hungarian Academy of
Sciences,
´
8201 Veszprem, Hungary
Extracts of Neurospora crassa and pea seedlings oxidat-
ively metabolise nitroethane and nitropropane,[18] and those
from the hyphae of a nitrifying strain of Aspergillus flavus
produce nitrite and nitrate from 2-nitropropane.[19] 2-Nitro-
propane and some other nitroalkanes are oxidatively denit-
rified by an intracellular enzyme of Hansenula mraki.[20] 2-
Nitropropane dioxygenase has been purified and charac-
terised as an iron-containing metalloenzyme.[21] It belongs
to the peculiar class of intermolecular dioxygenases catalys-
ing the reaction according to Equation (2).[22] That means
[b]
[c]
´
Department of Organic Chemistry, University of Veszprem,
´
8201 Veszprem, Hungary
Fax: (internat.) ϩ 36-88/427-492
E-mail: speier@almos.vein.hu
´
´
Universite d’Aix-Marseille 1 et 3, Faculte des Sciences et
Techniques de Saint-Jerome, Chimie, Biologie et Radicaux
´
Libres, UMR CNRS, 6517,
Case 432, Avenue Escadrille Normandie-Niemen, 13397
Marseille Cedex 13, France
[d]
Chemical Research Center, Hungarian Academy of Sciences,
1525 Budapest, Hungary
Supporting information for this article is available on the
WWW under http://www.eurjic.com or from the author.
Eur. J. Inorg. Chem. 2002, 1687Ϫ1696  WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 1434Ϫ1948/02/0707Ϫ1687 $ 20.00ϩ.50/0
1687

G. Speier et al.
FULL PAPER
that the two oxygen atoms of dioxygen are incorporated
into two molecules of the substrate.
(2)
In order to gain more insight into the mechanism of these
reactions we initiated studies on copper- and iron-mediated
oxygenations of nitroalkanes. We could show that isopropyl
nitronate, ligated to a copper ion, can be oxygenated to (ni-
trito)copper species and acetone,[23] and in the presence of
copper metal, as a precursor, nitroalkanes are easily trans-
formed to aldehydes or ketones by dioxygen.[24] In this pa-
per we present kinetic and spectroscopic data on this reac-
tion, the X-ray structures of intermediates and propose a
plausible mechanism for the oxygenation as a 2-nitropro-
pane dioxygenase mimicking reaction.
Figure 1. Time course for the stoichiometric oxygenation of 2-
nitropropane in the presence of copper metal and N-containing
ligands (bpy, phen, tmeda); Cu0 ϭ L ϭ 1.5 mmol, NPH ϭ 3 mmol,
90 °C, 30 mL DMF
Results and Discussion
The presence of the intermediate H2O2 in the reaction
mixture could be demonstrated either by iodometry or ox-
idising triphenylphosphane to triphenylphosphane oxide.
We believe that in the first step copper metal, in the pres-
ence of N ligands, reacts with the aci form of the secondary
nitro compound to give copper nitronate complexes and
H2O2 [Equation (4)]. Similar reactions were reported for the
reaction of copper metal with acidic compounds in the
presence of air.[25]
Stoichiometric Oxygenation
To a 2-nitropropane (NPH) solution in DMF, copper
metal powder was added under dioxygen. The colour of the
solution slowly turned reddish and further dissolution of
the solid copper resulted in a green homogeneous solution.
If coordinating N ligands, such as N,N,NЈ,NЈ-tetramethyl-
ethylenediamine (tmeda), 2,2Ј-bipyridine (bpy), or 1,10-
phenanthroline (phen) were also present, the dissolution of
the copper metal proceeded even faster. According to paral-
lel gas-volumetric (O2), titrimetric (NO3), spectrophoto-
metric (NO2) and GC (acetone) measurements (Table 1),
the stoichiometry of the oxygenation reaction corresponds
to Equation (3). Figure 1 shows typical dioxygen uptake vs.
time curves for the oxidation process obtained by the gas-
volumetric method.
Cu0 ϩ L ϩ 2 NPH ϩ O2 ϭ CuII(L)(NP)2 ϩ H2O2
(4)
In the presence of molecular oxygen both copper(I) and
copper(II) nitronates are probably first formed, the former
is then transformed to CuII(L)(NP)2, which can be oxygen-
ated to the desired products [Equation (5)].
Cu0 ϩ L ϩ 2 NPH ϩ 2 O2 ϭ CuII(L)(NO2)(NO3) ϩ 2
(CH3)2CO ϩ H2O
CuII(L)(NP)2 ϩ O2 ϭ CuII(L)(NO2)2 ϩ 2 (CH3)2CO
(5)
(3)
This is then followed by the fast consecutive formation
of CuII(L)(NO2)(NO3), which is assumed to be obtained as
a product of the oxidative process between CuII(L)(NO2)2
and H2O2 [Equation (6)].
Table 1. Stoichiometric oxygenation of 2-nitropropane in DMF so-
lution in the absence and presence of N ligands
[b]
[c]
Expt. Ligand Conv.[a] NO3
NO2
Conv.[d] Conv.[e]
CuII(L)(NO2)2 ϩ H2O2 ϭ CuII(L)(NO2)(NO3) ϩ H2O
(6)
no.
%
mmol
mmol
%
%
1
2
3
4
Ϫ
12
98
91
73
0.22
0.98
0.89
0.99
0.09
1.20
1.01
1.06
9.3
73
63
68
10
87
78
72
tmeda
phen
bpy
Copper-Catalysed Oxygenation of 2-Nitropropane
Previously we have reported that primary and secondary
nitro compounds in the presence of copper metal and N
ligands can be transformed to aldehydes or ketones and
HNO2. The reaction can also be carried out catalytically in
[a]
[b]
Conversions were determined by gas volumetry.
Yields were
determined by titrimetry. [c] Yields were determined by spectropho-
tometry. [d] Conversions were determined from [b] and [c]
sions were determined by GLC.
.
[e] Conver-
1688
Eur. J. Inorg. Chem. 2002, 1687Ϫ1696

Kinetics and Mechanism of the Copper-Catalysed Oxygenation of 2-Nitropropane
FULL PAPER
the presence of tmeda at high 2-nitropropane/copper ratios
in a very efficient way (Figure 2).
(8)
On addition of ether to the reaction mixture, a green
solid precipitated from which, after recrystallisation from
ethanol, green crystals of CuII(NO2)2(tmeda) were ob-
tained. The presence of CuII(NO2)2(tmeda) in the reaction
mixture clearly suggests that the first step in the catalytic
oxygenation of 2-nitropropane is the formation of the fairly
stable CuII(NP)2(tmeda) complex from copper powder, 2-
nitropropane, tmeda and dioxygen, which further rapidly
reacts with dioxygen to form the more stable nitrito species
CuII(NO2)2(tmeda). The complex CuII(NP)2(tmeda) was
prepared by the stoichiometric reaction of CuII(OMe)2, 2-
nitropropane and tmeda in THF under Ar.
Characterisation of CuII(NO2)2(tmeda)
CuII(NO2)2(tmeda) displays three bands at 1360, 1286
and 808 cmϪ1 in its IR spectrum assigned to the asymmet-
ric and symmetric stretching and bending frequencies of the
nitro group. There are three additional bands at 953, 845
and 593 cmϪ1 due to deformation and bending frequencies
of the nitro group. Three bands at 2983, 2941 and
2899 cmϪ1 can be assigned to the ligand tmeda coordinated
to the copper ion. The electronic absorption spectrum of
CuII(NO2)2(tmeda) in acetonitrile showed two intense
bands at 271 and 222 nm, which were assigned to LMCT
bands. Further, the LMCT bands for the nitro complex at
271 nm may include contributions from the nǞπ* trans-
ition as well.[26] Crystallographic characterisation of CuII-
(NO2)(tmeda) shows that the molecule is monomeric. The
view of the molecule depicted in Figure 4 shows that the
copper(II) centre has an elongated rhombic octahedral geo-
metry with a CuO2N2O2 chromophore and a (4ϩ2*)-type
coordination involving two off-the-z-axis bonds.
Figure 2. Time course for the copper-catalysed oxygenation of 2-
nitropropane (ϩ) [acetone (∆); acetone oxime (o)] in DMF using
tmeda as ligand (Experiment 3, Table 4)
In these experiments Cu0, tmeda, and 2-nitropropane are
first pretreated with O2 to give a homogeneous solution in
about 10Ϫ15 min and thereafter the reaction takes place
in a homogeneous phase. According to simultaneous gas-
volumetric and GC measurements the stoichiometry of the
oxidation reaction corresponds to that shown in Equa-
tion (7).
2 NPH ϩ O2 ϭ 2 HNO2 ϩ 2 (CH3)2CO
(7)
In the reaction mixture the presence of acetone oxime is
also detected (10Ϫ20%). The formation of acetone oxime is
favoured at high tmeda concentrations (Figure 3). We be-
lieve that excess tmeda acts as a base and in the presence
of HNO2 the salt tmeda·HNO2 is formed, which reacts with
2-nitropropane resulting in the oxime [Equation (8)].
Figure 3. Plots of amounts of acetone (∆) and acetone oxime (o)
formed vs. the initial tmeda concentration at the copper-catalysed
oxygenation of 2-nitropropane in DMF (Experiment 15, Table 4)
Figure 4. Molecular structure and numbering scheme of [CuII(N-
O2)2(tmeda)] (1); only one molecule is shown; hydrogen atoms are
omitted for clarity, the ellipsoids represent a probability of 40%
Eur. J. Inorg. Chem. 2002, 1687Ϫ1696
1689

G. Speier et al.
FULL PAPER
Selected bond lengths and angles given in Table 2 show Characterisation of CuII(NP)2(tmeda)
that two N atoms of the bidentate N,N,NЈ,NЈ-tetramethyl-
The green complex CuII(NP)2(tmeda) was prepared in
85% yield. The IR spectrum of the complex shows intense
sharp bands corresponding to the coordinated aci-2-nitro-
propanate ligands at 1612 [ν(CϭN)], 1162 and 1123
[νas(NO2)], and 943 [νs(NO2)] cmϪ1. The electronic spec-
trum of the complex shows an absorption band at 727 nm
due to d-d transitions. A higher energy band at 314 nm is
associated with charge transfer transition. Room-temper-
ature magnetic measurements yielded a value of µeff ϭ 1.92
BM for the complex consistent with a copper(II) ion. The
view of the molecule in Figure 5 shows that the geometry
around the copper(II) centre is similar to that of the CuII-
(NO2)(tmeda) complex with an elongated rhombic octahed-
ral CuO2N2O2 chromophore and a (4ϩ2*)-type coordina-
tion, involving two off-the-z-axis bonds. Selected bond
lengths and angles given in Table 3 show that two N atoms
of the bidentate N,N,NЈ,NЈ-tetramethylethylenediamine li-
ethylenediamine ligand with CuϪN distances of 2.0291(4)
˚
and 2.0242(4) A, and two O atoms of the NO2 ligands with
˚
CuϪO distances of 2.0052(4) and 2.0087(4) A, occupy basal
positions, the other two O atoms of the NO2 ligands with
˚
CuϪO distances of 2.3992(5) and 2.4693(5) A being in ap-
ical positions. This is associated with the bidentate bonding
mode of oxyanions to the copper(II) ion, such as the nitrite
and nitrate anions, all of which form good primary ligands
to the copper(II) ion as in [CuII(pyrazine)2(O2NO)2][27] and
[CuII(bipy)(ONO)2].[28] Asymmetric bidentate copper nitrite
coordination was also found in other complexes with N-
donor ligands.[29,30]
II
˚
Table 2. Selected bond lengths [A] and angles [°] for [Cu (NO2)2-
(tmeda)]
˚
gand, with CuϪN distances of 2.0665(14) A, and two O
Cu1ϪO2
Cu1ϪO3
Cu1ϪO4
Cu1ϪN1
Cu1ϪN2
Cu1ϪO1
O1ϪO2
O1ϪN3
O2ϪN3
O3ϪO4
O3ϪN4
O4ϪN4
N1ϪC1
N1ϪC2
N1ϪC3
N2ϪC4
2.0052(4)
2.3992(5)
2.0087(4)
2.0291(4)
2.0242(4)
2.4693(5)
2.0898(7)
1.2380(7)
1.2700(7)
2.0972(6)
1.2279(7)
1.2784(7)
1.4805(7)
1.4815(8)
1.4851(7)
1.4794(7)
1.4830(7)
1.4766(7)
1.4838(9)
2.3891(10)
86.99(2)
atoms of the nitronate ligands, with CuϪO distances of
1.9997(13) A, occupy basal positions, while the other two
˚
O atoms of the nitronate ligands, with CuϪO distances of
˚
2.3615(13) A, are in apical positions. The carbonϪnitrogen
˚
bond [1.290(2) A] in the nitronate ligand is essentially
[31]
˚
˚
double bond in character (CϪN 1.47 A, CϭN 1.27 A).
This is similar to the findings for the structures of
[23]
CuI(NP)(PPh3)2
and FeIII(NP)3.[32] The CϪN distances
II
˚
are somewhat longer in Cu (NP)2 (1.34Ϫ1.35 A), however,
its structure consists of chains of CuII(NP)2 units.[33]
N2ϪC5
N2ϪC6
C3ϪC4
C5ϪC6
O2ϪCu1ϪO3
O2ϪCu1ϪO4
O2ϪCu1ϪN1
O2ϪCu1ϪN2
O3ϪCu1ϪO4
O3ϪCu1ϪN1
O3ϪCu1ϪN2
O4ϪCu1ϪN1
O4ϪCu1ϪN2
O1ϪCu1ϪO2
O1ϪCu1ϪN1
O1ϪCu1ϪN2
N1ϪCu1ϪN2
O2ϪO1ϪN3
Cu1ϪO2ϪO1
Cu1ϪO2ϪN3
O1ϪO2ϪN3
Cu1ϪO3ϪO4
Cu1ϪO3ϪN4
O4ϪO3ϪN4
Cu1ϪO4ϪO3
Cu1ϪO4ϪN4
O3ϪO4ϪN4
Cu1ϪN1ϪC1
Cu1ϪN1ϪC2
Cu1ϪN1ϪC3
89.602(15)
93.13(2)
166.78(2)
55.98(2)
111.63(2)
105.41(2)
167.18(2)
93.57(2)
54.49(2)
106.08(2)
112.92(2)
86.61(2)
34.06(3)
74.14(2)
107.18(4)
33.09(3)
52.547(15)
86.48(4)
33.96(3)
71.47(2)
103.89(3)
32.45(3)
111.97(3)
109.26(3)
106.23(3)
Figure 5. Molecular structure and numbering scheme of [CuII-
(NP)2(tmeda)] (2); only one molecule is shown; hydrogen atoms are
omitted for clarity, the ellipsoids represent a probability of 40%
Kinetic Measurements
The reaction between 2-nitropropane and dioxygen in the
presence of a catalytic amount of copper and tmeda were
performed in DMF solution and examined in the temper-
ature range 363.16 to 373.16 K with a ratio between initial
concentrations of copper and 2-nitropropane in the range
1690
Eur. J. Inorg. Chem. 2002, 1687Ϫ1696

Kinetics and Mechanism of the Copper-Catalysed Oxygenation of 2-Nitropropane
FULL PAPER
II
˚
A simple rate law for the catalytic reaction between 2-
nitropropane and dioxygen catalysed by copper in the pres-
ence of tmeda is given in Equation (9).
Table 3. Selected bond lengths [A] and angles [°] for [Cu -
(NP2)2(tmeda)]
Cu1ϪO1
Cu1ϪN1
Cu1ϪO2
O1ϪN2
1.9997(13)
2.0665(14)
2.3615(13)
1.3360(18)
1.3205(19)
1.472(2)
Ϫd[NPH]/dt ϭ d[acetone]/dt ϭ kcat[NPH]m[Cu]n[O2]q
(9)
O2ϪN2
In order to determine the rate dependence on the various
reactants, oxygenation runs were performed at different
substrate concentrations (Table 4; Experiments 1Ϫ4), cata-
lyst concentrations (Table 4; Experiments 3, 5Ϫ9), and at
different dioxygen pressures (Table 4; Experiments 10Ϫ14).
Assuming a constant concentration of the catalyst during
each reaction, as well as a constant dioxygen pressure for
the experiments, the pseudo-first-order rate law according
to Equation (10) is obtained, where kcatЈ ϭ kcat[Cu]n[O2]q.
N1ϪC1
N1ϪC2
1.479(2)
N1ϪC3
N2ϪC4
1.481(2)
1.290(2)
C3ϪC3
C4ϪC6
1.508(4)
1.477(3)
C4ϪC5
1.497(3)
98.86(7)
90.64(6)
161.00(5)
161.00(5)
90.64(6)
85.30(8)
93.19(5)
O1ϪCu1ϪO1
O1ϪCu1ϪN1
O1ϪCu1ϪN1
O1ϪCu1ϪN1
O1ϪCu1ϪN1
N1ϪCu1ϪN1
O1ϪCu1ϪO2
O1ϪCu1ϪO2
N1ϪCu1ϪO2
N1ϪCu1ϪO2
O1ϪCu1ϪO2
O1ϪCu1ϪO2
N1ϪCu1ϪO2
N1ϪCu1ϪO2
O2ϪCu1ϪO2
N2ϪO1ϪCu1
N2ϪO2ϪCu1
Ϫd[NPH]/dt ϭ kcatЈ[NPH]m
(10)
Plots of [NPH]Ϫ1 vs. time were linear in Experiments
1Ϫ14, indicating that the reaction is second order with re-
spect to substrate concentration. Columns kcatЈ and R in
Table 4 report slopes and the correlation coefficients ob-
tained by the least-squares method for these linear regres-
sions. From variations of the reaction rates, plots of
Ϫd[NPH]/dt vs. the second exponent of the initial NPH
concentration [NPH]02 (Figure S1, Supporting Information)
were also linear (R ϭ 99.41), reinforcing that the reaction
is indeed second-order with respect to the 2-nitropropane
concentration (Table 4; Experiments 1Ϫ4). This means that
60.51(5)
102.79(5)
105.80(5)
60.51(5)
93.20(5)
105.80(5)
102.79(5)
140.79(7)
100.13(10)
84.51(9)
1:6Ϫ33. Experiments were also carried out at different di- m ϭ 2 in Equation (9).
oxygen concentrations. Experimental conditions are
summarised in Table 4.
Kinetic measurements of the reaction rate with respect to
catalyst concentration (Table 4; Experiments 3, 5Ϫ9) indic-
Table 4. Kinetic data for the copper-catalysed oxygenation of 2-nitropropane in DMF solution
Expt.[a]
no.
Temp.
°C
103[O2]
[Cu]
[NPH]
105 kcatЈ
R[b]
%
102 kcat
105 Ϫd[NPH]/dt
mol dmϪ3
mol dmϪ3
mol dmϪ3
molϪ1 dm3 sϪ1
sϪ1 molϪ3 dm9
mol dmϪ3 sϪ1
1
2
3
4
5
6
7
8
9
10
11
12
13
14
90
90
90
90
90
90
90
90
90
90
90
90
90
90
8.251
8.251
8.251
8.251
8.251
8.251
8.251
8.251
8.251
1.650
4.850
7.686
9.381
11.30
0.086
0.086
0.086
0.086
0.032
0.064
0.114
0.143
0.200
0.086
0.086
0.086
0.086
0.086
0.499
0.853
1.077
1.341
1.077
1.077
1.104
1.077
1.077
1.077
1.077
1.077
1.077
1.077
4.624
4.579
4.629
2.745
1.575
2.992
6.683
6.639
9.141
0.995
3.120
4.251
5.972
7.221
99.87
99.58
99.38
99.70
99.59
99.81
99.63
99.34
99.55
99.59
99.23
98.88
98.54
98.67
6.54 Ϯ 0.19
6.47 Ϯ 0.31
6.55 Ϯ 0.40
3.88 Ϯ 0.10
5.91 Ϯ 0.22
5.66 Ϯ 0.18
7.09 Ϯ 0.30
5.63 Ϯ 0.29
5.54 Ϯ 0.21
7.01 Ϯ 0.31
7.48 Ϯ 0.37
6.45 Ϯ 0.38
7.43 Ϯ 0.63
7.46 Ϯ 0.58
5.37 Ϯ 0.34[c]
11.5 Ϯ 0.35
19.8 Ϯ 0.72
18.3 Ϯ 0.53[d]
21.2 Ϯ 0.67[e]
1.469
3.330
4.843
6.678
15
16
17
18
95
100
100
100
8.562
7.907
7.907
7.907
0.086
0.086
0.043
0.043
1.077
1.077
0.539
0.539
8.455
13.39
6.222
7.208
99.85
99.24
99.85
99.93
[a]
[b]
In 30 mL of DMF, the amount of tmeda is equimolar to copper. Correlation coefficients of least-squares regressions. [c] Mean value
of the kinetic constant k and its standard deviation σ(k) were calculated as k ϭ (Σiwiki/Σiwi) and σ(k) ϭ [Σiwi(ki Ϫ k)2/(n Ϫ 1)Σiwi]1/2
,
where wi ϭ1/σi2. CuII(NO2)2(tmeda) was used as catalyst instead of Cu0. CuII(NP)2(tmeda) was used as catalyst instead of Cu0.
[d]
[e]
Eur. J. Inorg. Chem. 2002, 1687Ϫ1696 1691

G. Speier et al.
FULL PAPER
ate a first-order dependence. Plots of kcatЈ vs. [Cu] for the diate CuII(NP)2(tmeda). The oxygenation of [CuII-
above experiments gave a straight line with a correlation (NP)2(tmeda)] affords a stoichiometry corresponding to
coefficient of 99.10% (Figure S2, Supporting Information). Equation (11) by the use of parallel gas-volumetric and
The experiments performed at different dioxygen concen- GC measurements.
trations (calculated from literature data assuming the valid-
CuII(NP)2(tmeda) ϩ O2 ϭ CuII(NO2)2(tmeda) ϩ 2 (CH3)2CO (11)
ity of Dalton’s law, the dissolved concentration of O2 being
8.25 ϫ 10Ϫ3 mol dmϪ3 at 90 °C and 760 Torr O2 pressure)
show that the reaction is first order with respect to the di-
oxygen concentration (Table 4; Experiments 3, 10Ϫ14).
Plotting kcatЈ against [O2] for the above experiments resulted
in a straight line with a correlation coefficient of 99.61%
(Figure S3, Supporting Information). According to the kin-
etic data obtained the oxygenation of 2-nitropropane obeys
an overall fourth-order reaction rate with m ϭ 2, n ϭ q ϭ
1 in Equation (9), from which a mean value of the kinetic
constant kcat of (5.37 Ϯ 0.34) ϫ 10Ϫ2 molϪ3·3 sϪ1 at
363.16 K was obtained (Table 4).
Figure 6 shows a typical concentration vs. time curve for
[CuII(NP)2(tmeda)] obtained by the measured dioxygen up-
take. The reaction between [CuII(NP)2(tmeda)] and dioxy-
gen was performed in DMF solution and examined in the
temperature range 303.16 to 318.16 K. Experiments were
also carried out at different dioxygen concentrations. The
experimental conditions are summarised in Table 5.
A simple rate law for the stoichiometric reaction between
[CuII(NP)2(tmeda)] and dioxygen is given in Equation (12).
The catalytic oxygenation reactions of 2-nitropropane by
CuII(NO2)2(tmeda) and CuII(NP)2(tmeda) complexes as
catalysts were also carried out (Table 4; Experiments
17Ϫ18). It can be seen that the mean value of the kinetic
constant for CuII(NO2)2(tmeda) and CuII(NP)2(tmeda)
complexes are very similar to those found in the reactions,
where the catalyst was prepared ‘‘in situ’’, suggesting that
the two complexes above were involved in the catalytic pro-
cess when copper metal was used as the catalyst precursor.
The activation parameters for the catalytic oxygenation
reaction were determined from the temperature dependence
of the kinetic constant kcat. The Arrhenius plot of log kcat
vs. 1/T (Figure S4, Supporting information) using the kcat
values at 363.16, 368.16 and 373.16 K (Table 4; Experi-
Ϫd[CuII (NP)2(tmeda)]/dt ϭ ks[CuII(NP)2(tmeda)]m[O2]n
(12)
In order to determine the rate dependence on the various
reactants, oxygenation runs were performed at different
[CuII(NP)2(tmeda)] concentrations (Table 5; Experiments
1Ϫ4), and at different dioxygen pressures (Table 5; Experi-
ments 4Ϫ7). Assuming a constant concentration of the di-
oxygen during each reaction the pseudo-first-order rate law
according to Equation (13) is obtained, where ksЈ ϭ ks[O2]n.
Ϫd[CuII(NP)2(tmeda)]/dt ϭ ksЈ[CuII(NP)2(tmeda)]m
(13)
Plots of log[CuII(NP)2(tmeda)] vs. time were linear in Ex-
ments 1Ϫ14, 15Ϫ16) was linear with a correlation coeffi- periments 1Ϫ10, indicating that the reaction is first-order
cient of 99.27%. From the slope and the ordinate intercept with respect to the CuII(NP)2(tmeda) concentration. Col-
of this line the parameters Ea ϭ 131 Ϯ 4 kJ molϪ1, ∆H‡ ϭ umns ksЈ and R in Table 5 report slopes and the correlation
127 Ϯ 4 kJ molϪ1 and ∆S‡ ϭ 80 Ϯ 13 J molϪ1 KϪ1 were coefficients obtained by the least-squares method for these
calculated.
linear regressions. A typical first-order plot is shown in Fig-
In order to shed light on the kinetic scenery of the ele- ure 6 (Table 5; Experiment 4).
mentary steps of these catalytic reactions we also studied
the kinetics of the oxygenation of the proposed interme- Ϫd[CuII(NP)2(tmeda)]/dt (v0) vs. [CuII(NP)2(tmeda)] (Fig-
ure S5, Supporting Information) were also linear (R ϭ
98.46), reinforcing that the reaction is indeed first-order
with respect to the CuII(NP)2(tmeda) concentration
(Table 5; Experiments 1Ϫ4). This means that m ϭ 1 in
Equation (12).
From variations of the reaction rates, plots of
Experiments carried out at different dioxygen concentra-
tions (calculated from literature data assuming the validity
of Dalton’s law, the dissolved concentration of O2 being
5.36 ϫ 10Ϫ3 mol dmϪ3 at 40 °C and 760 Torr O2 pressure)
show that the reaction is first-order with respect to the di-
oxygen concentration (Table 5; Experiments 4Ϫ7). Plotting
Ϫd[CuII(NP)2(tmeda)]/dt (v0) against [O2] for the above
four experiments resulted in a straight line with a correla-
tion coefficient of 99.41% (Figure S6, Supporting Informa-
tion). According to the kinetic data obtained, the oxygena-
tion of CuII(NP)2(tmeda) obeys an overall second-order
rate equation with m ϭ n ϭ 1 in Equation (12), from which
Figure 6. The time course for the oxygenation of [CuII-
a mean value of the kinetic constant ks of (0.46 Ϯ 0.02)
(NP)2(tmeda)] (o) and plot of log[CuII(NP)2(tmeda)] vs. time for
the oxygenation of [CuII(NP)2(tmeda)] (Experiment 4, Table 5)
molϪ1 dm3 sϪ1, at 313.16 K, was obtained (Table 5).
1692
Eur. J. Inorg. Chem. 2002, 1687Ϫ1696

Kinetics and Mechanism of the Copper-Catalysed Oxygenation of 2-Nitropropane
FULL PAPER
Table 5. Kinetic data for the stoichiometric oxygenation of [CuII(NP)2(tmeda)] in DMF solution
Expt.[a]
no.
Temp.
°C
103[O2]
102[Cu][a]
mol dmϪ3
103ksЈ
R[b]
%
ks
105 Ϫd[Cu]/dt
mol dmϪ3
sϪ1
sϪ1 molϪ1 dm3
mol dmϪ3 sϪ1
1
2
3
4
5
6
7
40
40
40
40
40
40
40
5.36
5.36
5.36
5.36
1.07
2.68
3.75
0.67
1.33
2.00
2.67
2.67
2.67
2.67
2.835 Ϯ 0.166
2.604 Ϯ 0.107
2.422 Ϯ 0.123
2.256 Ϯ 0.107
0.623 Ϯ 0.022
1.283 Ϯ 0.067
0.533 Ϯ 0.041
99.37
99.70
99.45
99.67
99.55
98.44
99.85
0.529 Ϯ 0.031
0.486 Ϯ 0.020
0.452 Ϯ 0.023
0.421 Ϯ 0.020
0.583 Ϯ 0.021
0.479 Ϯ 0.025
0.409 Ϯ 0.011
0.456 Ϯ 0.024[c]
0.217 Ϯ 0.008
0.330 Ϯ 0.015
0.497 Ϯ 0.009
1.901 Ϯ 0.11
3.473 Ϯ 0.14
4.846 Ϯ 0.25
6.015 Ϯ 0.28
1.663 Ϯ 0.06
3.416 Ϯ 0.18
4.090 Ϯ 0.11
8
9
10
30
35
45
4.84
5.10
5.52
2.67
2.67
2.67
1.050 Ϯ 0.038
1.683 Ϯ 0.076
2.743 Ϯ 0.049
98.34
99.60
99.94
2.720 Ϯ 0.10
4.649 Ϯ 0.21
7.314 Ϯ 0.13
[a]
[b]
[c]
In 30 mL of DMF.
Correlation coefficients of least-squares regressions. Mean value of the kinetic constant k and its standard
deviation σ(k) were calculated as k ϭ (Σiwiki/Σiwi) and σ(k) ϭ [Σiwi(ki Ϫ k)2/(n Ϫ 1)Σiwi]1/2, where wi ϭ1/σi2.
The activation parameters for the stoichiometric oxy- radical by EPR spectroscopy failed. The 2-nitropropanate
3
genation reaction were determined from the temperature anion does not react with O2.[34] The absence of the elec-
dependence of the kinetic constant ks. The Arrhenius plot tron transfer from CuII(tmeda)(NP)2 to dioxygen could also
of log ks vs. 1/T (Figure S7, Supporting Information) using be proved by the test for free O2·Ϫ with nitroblue tetrazolium
the ks values at 303.16, 308.16, 313.16 and 318.16 K (NBT), where no reduction of the added dye to the blue
(Table 5; Experiments 4, 8Ϫ10) was linear with a correla- formazan took place excluding the formation of free O2·Ϫ.[35]
tion coefficient of 99.48%. From the slope and the ordinate
intercept of this line the parameters Ea ϭ 38 Ϯ 1 kJ molϪ1
,
∆H‡ ϭ 35 Ϯ 1 kJ molϪ1 and ∆S‡ ϭ Ϫ142 Ϯ 13 J
molϪ1 KϪ1 were calculated. Values of the activation para-
meters indicate that the oxidation of CuII(NP)2(tmeda) is a
bimolecular reaction involving the associative transition
state of CuII(NP)2(tmeda) and molecular oxygen; kcat is
substantially smaller than ks since in the former the pre-
equilibrium constants K1 and K2 are also involved, and K1
and K2 are small. The equilibria according to Equations
(15) and (16) are shifted to the left side. A comparison of
the activation enthalpies and entropies of the catalytic and
stoichiometric reactions clearly shows that the stoichi-
ometric reaction is enthalpy-driven while in the case of the
catalytic reaction the positive ∆S‡ and the larger ∆H‡ values
show a different situation. Here the contribution of the en-
tropy seems to be more and the enthalpy less dominant.
This may be explained by the effect of the pre-equilibrium
according to Equation (15), since K1 is involved in kcat thus
causing this difference.
Based on the kinetic data on the copper-catalysed oxy-
genation of 2-nitropropane to acetone, a probable mechan-
ism is proposed as shown in Scheme 1. According to that,
the first step is the formation of the complex CuII(tmed-
a)(NP)2 (2) from copper powder, 2-nitropropane, tmeda,
and dioxygen [Equation (14)] or from CuII(tmeda)(NO2)2
through substitution of NO2Ϫ by NPϪ in a pre-equilibrium
in the catalytic cycle [Equation (15)]. This is then followed
by an intramolecular electron transfer [Equation (16)] from
the ligand 2-nitropropanate to the copper(II) ion resulting
in
a
(2-nitropropyl
radical)copper(I)
complex
CuI(tmeda)(NP)(NP·) (3). This equilibrium is largely shifted
to the left (K2 is rather small). All attempts to detect the Scheme 1
Eur. J. Inorg. Chem. 2002, 1687Ϫ1696
1693

G. Speier et al.
FULL PAPER
In the complex CuI(tmeda)(NP)(NP·) (3) there are two been proven that valence isomerism plays an important role
redox-active centres, namely the nitropropanyl radical NP· (Scheme 2b). The molecular orbitals involved in this pro-
and the copper(I) ion.
cess are close to each other in energy and so the electron
The biradical dioxygen may react at both redox-active transfer is easily feasible. The equilibrium depends of
sites of the complex CuI(tmeda)(NP)(NP·), in a radical-rad- course on auxiliary ligands as shown in the case of copper
ical reaction with the coordinated radical ligand NP· lead- catecholate complexes, whereas soft ligands prefer the lower
ing to the peroxo intermediate 5, or in an oxidative addition oxidation state of the metal ion.[42] A similar behaviour with
of O2 to the copper(I) ion giving the (superoxo)copper(II) (nitropropane)iron complexes is also to be expected as a
complex 4, as found in the case of many other copper(I) key step in these oxygenations. Further work is in progress
complexes.[36] Both mechanistic assumptions satisfy the kin- on the design and elucidation of iron-containing functional
etic data, but we believe that the reaction of the copper(I) 2-nitropropane dioxygenase models.
centre of 3 with O2 is more probable. We have observed
earlier that radical ligands bound to metal ions that cannot
be oxidised (e.g. CuII, FeIII, etc)[37] do not react with O2 at
Experimental Section
all, or undergo very slow reactions only. The (superoxo)cop-
per(II) complex 4 then undergoes an intramolecular radical-
Materials and Methods: Analytical-grade reagents were used
radical reaction of the coordinated ligands O2·Ϫ and NP·
throughout. Copper powder (Aldrich), 2-nitropropane (Fluka),
N,N,NЈ,NЈ-tetramethylethylenediamine (Aldrich), 2,2Ј-bipyridine
(Aldrich), and 1,10-phenanthroline (Aldrich) were used as sup-
resulting in the peroxide species 6. This then decomposes
to the mixed-ligand copper(II) complex 8 and 1,1-dimethyl-
dioxirane (7). The 1,1-dimethyldioxirane (7) then oxygen
ates the coordinated NPϪ in 8 resulting in CuII(tmeda)-
(NO2)2 and acetone. The 2-nitropropane once again re-
places the nitrito ligand in 1 and so closes the catalytic
cycle. Previous studies have shown, that dimethyldioxirane
oxidation of nitronate anions affords the corresponding car-
bonyl product.[38]
As a conclusion it can be said, that the present work pro-
vides further support to the key role of redox-active ions
in these oxygenation reactions, which may be regarded as
functional models for 2-nitropropane dioxygenase. We be-
lieve that there is a valence tautomerism between CuII(NP)
and CuI(NP·) due to intramolecular electron transfer from
the ligand to the metal ion (Scheme 2a). In this sense of the
activation process the ligand is transformed to a radical and
copper(II) to copper(I). The latter then reacts with dioxygen
to form a peroxidic species, which transforms to the (nitri-
to)copper(II) complex and acetone. At the intradiol cleav-
age of catechols either by iron-[39] or copper-containing[40]
catechol 1,2-dioxygenases along with model studies[41] it has
plied. DMF (Aldrich) was purified by azeotropic distillation with
benzene and water and stored under argon.[43] Gaseous dioxygen
from Messer Griesheim was 99.6% and passed through P2O5 and
Blaugel in order to remove traces of water and other impurities. IR
spectra were recorded with a Specord IR-75 (Carl Zeiss) spectro-
meter on either Nujol or KBr pellets. Electronic spectra were meas-
ured with a Shimadzu UV-160A spectrophotometer using quartz
cells. GC analyses were performed with HP 5830A and HP 5890
gas chromatographs equipped with a flame ionisation detector and
CP SIL 8CB column. GC-MS measurements were recorded with
an HP 5890II/5971 GC/MSD instrument at 75 eV.
Stoichiometric Oxygenation: In a typical stoichiometric reaction 2-
nitropropane (0.36 mL, 3 mmol), copper metal (0.10 mg, 1.5 mmol)
and tmeda (0.225 mL, 1.5 mmol) in DMF (30 mL) were stirred at
90 °C under dioxygen for 60 min. The stoichiometry of the reac-
tions was investigated by gas volumetric (O2), spectrophotometric
(NO2),[44] titrimetric (NO3)[45] and GC measurements (acetone),
and the presence of H2O2 was determined by iodometry[46]
(Table 1.). Then diethyl ether was layered on the solution and left
at Ϫ20 °C for 2 h to afford a green solid, which was filtered off
and recrystallised from acetonitrile to give [Cu(tmeda)(NO3)(NO2)]
as green crystals (0.11 g, 25%). M.p. 172 °C (dec.). C6H16CuN4O5
(287.7): calcd. C, 25.03, H 5.60, Cu 22.07, N 19.46; found C 25.4,
H 5.49, Cu 22.43, N 19.31. UV/Vis (DMF): λmax (log ε/molϪ1
dm3 cmϪ1) ϭ 276 (3.66), 365 (3.16), 642 nm (2.300). IR (KBr):
ν˜max ϭ 2976 m, 2938 w, 2888 w, 1567 m, 1470 vs, 1387 s, 1361 vs,
1284 m, 1161 vs, 1046 s, 1020 s, 1001 m, 956 s, 846 m, 814 s, 769
Ϫ
cmϪ1 m. µeff ϭ 2.07 BM. The ratio NO3Ϫ/NO2 in the complex
was 1:1.2.
Preparation of [CuII(NP)2(tmeda)]: [Cu(OMe)2] (3.14 g, 25 mmol)
was dissolved in MeOH (20 mL); tmeda (3.78 mL, 25 mmol) and
2-nitropropane (4.5 mL, 50 mmol) were added and the mixture was
stirred under argon at room temperature for 20 h. The solvent was
then removed in vacuo and the remaining oily residue was treated
with diethyl ether, filtered off and dried to give a green powder
(7.60 g, 85%). M.p. 95 °C (dec.). C12H28CuN4O4 (355.9): calcd. C
39.88, H 7.45, N 15.49; found C 40.50, H 7.93, N 15.74. IR (KBr):
ν˜ ϭ 2925 w, 1612 vs, 1464 vs, 1393 w, 1291 w, 1162 vs, 1123 vs,
1059 m, 1033 m, 956 m, 943 s, 814 s, 782 m, 634 m, 402 cmϪ1 m.
UV/Vis (DMF): λmax (ε/ molϪ1 cmϪ1) ϭ 314 (978.5), 727 nm
(76.7). µeff ϭ 1.92 BM. On recrystallisation from THF green single
Scheme 2
1694
Eur. J. Inorg. Chem. 2002, 1687Ϫ1696

Kinetics and Mechanism of the Copper-Catalysed Oxygenation of 2-Nitropropane
crystals of [CuII(NP)2(tmeda)] were formed suitable for X-ray dif-
FULL PAPER
Table 6. Crystal data, data collection parameters and structure re-
finement of compounds CuII(NO2)2(tmeda) (1) and CuII-
(NP)2(tmeda) (2)
fraction.
Kinetic Experiments: Kinetic measurement were carried out at at-
mospheric pressure, at constant partial pressure of dioxygen with
vigorous stirring in a thermostatted reaction vessel equipped with
a syringe inlet for taking samples at regular time intervals. The
samples taken were chilled, stored at dry-ice temperature and then
submitted for GC or GC-MS analysis. Dioxygen uptakes were also
measured in a constant-pressure gas-volumetric apparatus. The vol-
1
2
Empirical formula
Crystal system
Space group
Z
C6H16CuN4O4 C12H31CuN4O6
monoclinic
P21/n
tetragonal
P421c
4
293(2)
1.314
11.862(1)
11.862(1)
14.047(1)
90
90
90
1976.5(3)
1.135
832
4
Temperature [K]
293(2)
1.555
ume of absorbed dioxygen was read periodically using a gas bur- dcalcd. [g/cm3]
˚
a [A]
7.5758(2)
12.5094(7)
12.5291(6)
90
102.091(3)
90
1161.0(1)
1.88
564
ette. The amount of nitrous acid was determined spectrophoto-
metrically[44] after diazotization of sulfanylic acid and successive
coupling with 1-aminonaphthalene, and was found in each case to
be nearly equal to that of acetone. The catalytic reactions were
carried out by preparing the catalyst from copper metal, tmeda,
and 2-nitropropane in DMF under dioxygen. After about
10Ϫ15 min, the mixture gave a green homogeneous solution by dis-
solving the copper metal. Thereafter, the reaction was monitored
˚
b [A]
˚
c [A]
α [°]
β [°]
γ [°]
˚
V [A]
µ [mmϪ1
F(000)
]
by analysing the amount of products (acetone and acetone oxime) Index ranges
and the starting 2-nitropropane by GLC. In a typical oxygenation
of 2-nitropropane to acetone and acetone oxime, the copper metal
0 Յ h Յ 8
0 Յ k Յ 15
Ϫ15 Յ l Յ 15
2263
Ϫ19 Յ h Յ 19
Ϫ19 Յ k Յ 19
Ϫ22 Յ l Յ 22
9518
Data collected
(191 mg, 3 mmol), 2-nitropropane (3.6 mL, 40 mmol), tmeda
Reflections [I Ͼ 3σ(I)]
1894
2134
(0.45 mL, 3 mmol) and DMF (30 mL) were stirred under dioxygen
at 95 °C. After dissolution of the copper powder (10 min), samples
were taken at ca. 10-min intervals, cooled to dry-ice temperature
and then subjected to GLC analysis. The solubility of dioxygen in
DMF at 95 °C was taken as 8.56 ϫ 10Ϫ3 .[47] The validity of
Dalton’s law was assumed for the calculation of dioxygen concen-
tration at different partial pressures.[48] Diethyl ether was layered
on the solution and left at Ϫ20 °C for 2 h to afford a green solid,
which was filtered off and recrystallised from ethanol to give [CuII-
(tmeda)(NO2)2] as green crystals. M.p.197 °C (dec.). C6H16CuN4O4
(271.7): calcd. C 26.51, H 5.93, N 20.62; found C 25.7, H 5.72, N
19.91. UV/Vis (DMF): λmax (log ε/molϪ1 dm3 cmϪ1) ϭ 271 (3.66),
222 (3.43) and 648 nm (2.17). IR (KBr): ν˜max ϭ 2983 m, 2941 m,
2899 m, 1477 s, 1468 s, 1360 vs, 1286 m, 1249 m, 1165 vs, 1101 m,
1041 m, 1021 m, 1000 m, 953 s, 845 m, 808 s, 770 m, 593 cmϪ1 m.
The stoichiometric oxygenation of [CuII(NP)2(tmeda)] was carried
out in a thermostatted constant-pressure gas-volumetric apparatus.
The volume of absorbed dioxygen was read periodically using a
gas burette.
Parameters
136
0.032
109
R ϭ Σ||Fo| Ϫ |Fc||/Σ|Fo|
0.0323
0.0682
0.814
wR ϭ [w(F2o Ϫ F2c)2/w(F2c)2]1/2 0.045
GOF
1.537
Supporting Information: Kinetic diagrams for stoichiometric and
catalytic oxygenations are available (see also footnote on the first
page of this article).
Acknowledgments
Financial support of the Hungarian National Research Fund
(OTKA T-30400) and Ministry of Education (FKFP-0446/1999) is
gratefully acknowledged.
[1]
H. W. Pinnick, Org. React. 1990, 38, 655.
[2] [2a]
X-ray Crystallography: Crystallographic and experimental details
of the data collection and refinement of the structures of CuII(N-
O2)2(tmeda) and CuII(NP)2(tmeda) are reported in Table 6, while
the molecular structures are depicted in Figures 4 and 5. The in-
J. E. McMurry, J. Melton, Canad. J. Org. Chem. 1973, 38,
[2b]
[2c]
4367.
J. E. McMurry, Acc. Chem. Res. 1974, 7, 281.
R.
Kirchoff, Tetrahedron Lett. 1976, 17, 2533.
[3]
P. S. Vankar, R. Rathore, S. Chandrasekaran, Synth. Commun.
1987, 17, 195.
tensity data of CuII(NO2)2(tmeda) were collected with
a
[4]
[5]
[6]
F. Urpi, J. Vilarrasa, Tetrahedron Lett. 1990, 31, 7499.
E. Keinan, Y. Mazur, J. Am. Chem. Soc. 1977, 99, 3861.
G. A. Olah, M. Arvanahi, Y. D. Vankar, G. K. S. Prakash,
Synthesis 1980, 662.
KappaCCD single-crystal diffractometer, using the graphite-mon-
ochromated Mo-Kα radiation and ϕ-scan technique. The structure
was solved by direct and difmap methods (SIR92),[49] and refined
on F2 using full-matrix least-squares methods (Maxus).[50] The in-
tensity data of CuII(NP)2(tmeda) were collected with an
EnrafϪNonius CAD-4 single-crystal diffractometer, using graph-
ite-monochromated Mo-Kα radiation and ω/2θ-scan technique. The
structure was solved by direct and difmap methods (SHELXS-
97),[51] and refined with full-matrix least-squares refinement on F2
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