Syntheses and structures of bis(2,6-xylyl-nacnac) copper(I) complexes

Article abstract of DOI:10.1016/j.ica.2008.05.008

The copper(I) complexes {(bis-2,6-dimethylphenyl-penta-2,3-diiminato)Cu}₂(μ-toluene), 3 has been prepared and its reactivity against Lewis bases and nitrous oxide investigated. Complex 3 crystallizes as a toluene-bridged dimer and forms mono- and dinuclear benzene adducts in C₆D₆ solution. It does not coordinate excess THF, but reacts quantitatively with 1 equiv. of acetonitrile. Reaction with 2,6-xylyl isonitrile yields (bis-2,6-dimethylphenyl-penta-2,3-diiminato)Cu(2,6-xylyl isonitrile), 5, (ν_CN = 2123 cm^-1), which was characterized by an X-ray diffraction study. Complex 3 does not react with nitrous oxide in either C₆D₆ solution (5 days 50 °C) or in diethyl ether (13 days at ambient temperature).

Full text of DOI:10.1016/j.ica.2008.05.008

Inorganica Chimica Acta 362 (2009) 570–574
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Syntheses and structures of bis(2,6-xylyl-nacnac) copper(I) complexes
*
Paul O. Oguadinma, Frank Schaper
Département de Chimie, Université de Montréal, Montréal, Québec, Canada H3C 3J7
a r t i c l e i n f o
a b s t r a c t
Article history:
The copper(I) complexes {(bis-2,6-dimethylphenyl-penta-2,3-diiminato)Cu}2(l-toluene), 3 has been pre-
Received 5 May 2008
Accepted 8 May 2008
Available online 15 May 2008
pared and its reactivity against Lewis bases and nitrous oxide investigated. Complex 3 crystallizes as a
toluene-bridged dimer and forms mono- and dinuclear benzene adducts in C6D6 solution. It does not
coordinate excess THF, but reacts quantitatively with 1 equiv. of acetonitrile. Reaction with 2,6-xylyl iso-
nitrile yields (bis-2,6-dimethylphenyl-penta-2,3-diiminato)Cu(2,6-xylyl isonitrile), 5, (m
CN = 2123 cmꢀ1),
Keywords:
Diketiminate ligands
nacnac Ligands
Copper complexes
Nitrous oxide
which was characterized by an X-ray diffraction study. Complex 3 does not react with nitrous oxide in
either C6D6 solution (5 days 50 °C) or in diethyl ether (13 days at ambient temperature).
Ó 2008 Elsevier B.V. All rights reserved.
Isonitrile complexes
X-ray crystal structures
1. Introduction
2. Results and discussion
Nitrous oxide, N2O, is able to oxidize unsaturated carbon–car-
bon bonds, albeit only at elevated pressures and temperatures
[1–5], while reactions involving transition metal complexes as cat-
alysts or reagents proceed under much milder conditions [6–17].
Although coordination of nitrous oxide to the metal centre is prob-
ably involved in all of these reactions, very little is known about
the coordination chemistry of nitrous oxide [18–24].
Recently, coordination of nitrous oxide to copper atoms has
gathered additional interest. The crystal structure of the enzyme
nitrous oxide reductase revealed a unprecedented Cu4S-cluster as
its active centre for the reduction of nitrous oxide (CuZ) [25,26],
and a bridging coordination of nitrous oxide to two copper centres
was proposed as an essential part of the reaction mechanism
[27,28]. We were interested in the reactivity of nitrous oxide with
well defined mononuclear copper complexes, in particular with
copper complexes containing an N,N0-substituted 2,4-pentane-
diketiminato (=‘‘nacnac”) ligand (Scheme 1), which have been
extensively studied as models for the activation of dioxygen in bio-
logical systems [29–34]. We report herein the synthesis and char-
acterization of Cu(I) complexes carrying a bis(2,6-xylyl) nacnac
ligand, which proved, however, unreactive towards nitrous oxide
even at elevated temperatures and increased reaction times.
2.1. Complex synthesis
Several pathways have been described for the synthesis of (nac-
nac)Cu(I) complexes with varying ancillary substituents at the cop-
per centre [29,35–39]. Given the poor coordinative ability of
nitrous oxide, we considered it necessary to avoid strongly coordi-
nating ancillary ligands such as acetonitrile or olefins, thus elimi-
nating the often used [Cu(NCMe)4][OTf] salt as a possible starting
material. Direct reactions of copper iodide with 1Li(THF) or
2Li(THF) failed in our hands to give the desired compound. We at-
tempted to synthesize the desired Cu(I) complex via the corre-
sponding Cu(II) compounds, but neither comproportionation of
the corresponding Cu(II) complex 1Cu(OAc) or 2CuCl [40] with
copper metal, nor reduction with a methyl Grignard reagent,
employing the known instability of Cu(II) alkyls versus reductive
elimination, were successful. We thus turned to a protonation
route using Cu(OtBu), introduced by Warren and coworker as an
economic and soluble starting material for the preparation of cop-
per complexes [38]. Reaction of the protonated ligand 1H with
Cu(OtBu) and recrystallisation from toluene/hexane yielded the
toluene-bridged dimeric complex (1Cu)2(l-toluene), 3, in 90%
yield (Scheme 2). The preparation of derivatives of 3, i.e. (1Cu)2,
lacking the bridging toluene molecule, as well as 1Cu(L) complexes
where L is a more strongly coordinating ligand such as olefin, phos-
phine, lutidine or acetonitrile has been reported previously
[30,35,37,41].
In the absence of more strongly coordinating ligands, nacnac
copper complexes form mono- or dinuclear complexes with the
* Corresponding author. Tel.: +1 5143436683; fax: +1 5143437586.
E-mail address: Frank.Schaper@umontreal.ca (F. Schaper).
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.05.008

P.O. Oguadinma, F. Schaper / Inorganica Chimica Acta 362 (2009) 570–574
571
Table 1
R
N
R
N
Selected bond distances and angles of 3, 4 and related complexes
1
: R = Me
: R = iPrp
4a
Related complexesb
2
3
R
R
Cu–N (Å)
1.932(2)–1.949(2)
2.055(2)–2.084(2)
1.405(3)
1.404(3)
1.437(3)
1.440(3)
1.431(3)
1.361(3)
98.9(1)–100.1(1)
1.922–1.942
2.027–2.078
1.402
1.400
1.438
1.436
1.435
1.361
98.8–99.0
1.903–1.969
2.047–2.119
1.380–1.402
Cu–Carom. (Å)
C44–C45 (Å)
C46–C47 (Å)
C43–C44 (Å)
C45–C46 (Å)
C47–C48 (Å)
C48–C43 (Å)
N–Cu–N (°)
Scheme 1.
1.323–1.423
Ar
N
Cu
N
Ar
Ar
Ar
99.2–100.7
N
N
CNAr
N
+
CuOtBu
Cu CNAr
a
see Ref. [38].
see Refs. [36,37,41,42].
Cu
Ar
- HOtBu
b
NH
Ar
N
N
Ar
Ar
CNAr
6
3
1
H
C6D6
‘‘isolated double bond” C48–C43 (1.405(3) and 1.404(3) Å, com-
pared to 1.361(3) Å, respectively).
Ar
d
6Ar
d6
5b
Ar
N
N
N
1H NMR spectra of 3 in C6D6 display two sets of signals corre-
sponding to a C2v-symmetric nacnac ligand. No signals for coordi-
nated toluene were detected. In analogy to assignments made by
Badiei and Warren for 4, which showed a comparable behaviour
[38], we assign these two species to an equilibrium mixture of
N
N
Cu
2
Cu
Cu
Ar = 2,6-dimethylphenyl
N
Ar
Ar
Ar 5a
Scheme 2.
the benzene adducts {1Cu}2(l-C6D6), 5a, and 1Cu(g
2-C6D6), 5b
(Scheme 2). Irreversible loss of benzene and formation of a ben-
zene-bridged dinuclear copper complex was also reported by Laitar
et al., in this case using a fluorinated nacnac ligand [36]. The ratio of
5a and 5b remained unchanged upon addition of up to 50 equiv. of
toluene, consistent with their assignment as benzene coordinated
complexes. Upon dilution the NMR resonances observed at higher
field diminishes and we thus assign this species to the dinuclear
complex 5a. An equilibrium constant K300 K = [5b]2/[5a] = 130–
220 M was found over a concentration range of 2–36 mM 3 in
C6D6. As expected, no peaks originating from close contacts be-
tween the two species were observed in NOESY spectra of 3 in
C6D6. Cross peaks due to chemical exchange indicate a reasonably
fast interconversion at room temperature, in agreement with the
fact that the original toluene adduct was never observed. This is
in contrast to the behaviour described for 4, where broadened sig-
nals of the original toluene adduct were observed to transform
slowly, over night, into the putative benzene adducts [38].
copper centre coordinated either to an aromatic solvent or to the
aromatic N-aryl substituent [36–38,41,42]. An X-ray diffraction
study confirmed that here a toluene-bridged dimer was obtained
(Fig. 1). Its structure is similar to the related compound {(bis-
2,4,6-trimethylphenyl-nacnac)Cu}2(l-toluene), 4, reported by Ba-
diei and Warren [38]. Complex 3 displays a trigonal coordination
geometry around the copper atom. Bond distances in the ligand
and to the metal centres are comparable to those found in similar
compounds (Table 1). As typically observed in nacnac copper ole-
fin/arene complexes where rotation of the unsaturated ligand is
possible, the coordinated double bond is co-planar with the mean
plane of the nacnac copper fragment. Localisation of the double
bonds in the bridging toluene molecule is evidenced by the alter-
nation of the C–C distances in the aromatic ring. A comparable
alternation was observed for 4, while it is significantly less pro-
nounced in complexes with non-bridging arenes (Table 1). Coordi-
nation of C44–C45 and C46–C47 to the copper centres results in a
significant elongation of these bond distances in comparison to the
2.2. Reactivity towards different ligands
Addition of up to 50 equiv. THF to a C6D6 solution of 3 failed to
have any noticeable influence on its 1H NMR spectrum. In contrast,
formation of the putative complex 1 Cu(NCMe) was observed in
the presence of 1 equiv. of acetonitrile, indicating as expected a
strong coordination of this solvent to nacnac copper complexes.
Addition of 2,6-xylyl isonitrile to 3/C6D6 led to immediate forma-
tion of a single product, which was assigned as 1 Cu{CN(Me2C6H3)},
6. This assignment was supported by direct synthesis of 6 and its
crystal structure analysis. The structure of 6 displays the expected
trigonal coordination of the copper centre. The
g
2-coordinated
nacnac ligand is planar, bond distances indicate complete delocal-
isation of the double bonds in the ligand backbone and the copper
atom is located in the mean ligand plane (\(Cu1,N1,N2)
(Cu1,N1,N2,C2–C4 = 7°)). The structural features of 6 (Table 2) are
similar to those of analogous xylyl isonitrile complexes with the
bis-2,4,6-trimethylphenyl nacnac [38] or bis-2,6-diisopropylphenyl
nacnac ligand [43]. Compound 6 resembles the former particularly
in the symmetric placement of the isonitrile ligand (
and 19 pm, (C–Cu–N) = 6° and 9°, respectively), while the steri-
cally more encumbered isopropyl substituted complex displays a
more asymmetric coordination (Cu–N) = 34 pm, (C–Cu–
D(Cu–N) = 13
D
(
D
D
N) = 22°). The C–N distance (1.157(3) Å) and the N–C–C angle of
the isonitrile (173.8(2)°) are in the middle of the range observed
Fig. 1. Crystal structure of 3. Thermal ellipsoids are drawn at the 50% probability
level. Hydrogen atoms were omitted for clarity.

572
P.O. Oguadinma, F. Schaper / Inorganica Chimica Acta 362 (2009) 570–574
Table 2
Selected bond distances and angles of 6 and other N,N0-bis-aryl-nacnac copper (2,6-
xylyl isonitrile) complexes
Ar = 2,6-Me2C6H2, Ar = 2,4,6-
Ar = 2,6-
iPrp2C6H3
a
b
6
Me3C6H2
Cu1–N1 (Å)
Cu1–N2 (Å)
Cu1–C30 (Å)
C30–N3 (Å)
C30–N3–C22 (°)
N1–Cu1–C30 (°)
N2–Cu1–C30 (°)
\nacnac, Isonitrilec
(°)
1.933(2)
1.946(2)
1.822(2)
1.157(3)
173.8(2)
134.0(1)
127.6(1)
35
1.926(2)
1.945(1)
1.814(2)
1.159(2)
177.0(2)
135.5(1)
126.6(1)
35
1.928(2)
1.962(2)
1.817(2)
1.158(3)
171.4(2)
141.8(1)
120.0(1)
45
a
see Ref. [38].
see Ref. [43].
\(Cu1,N1,N2,C2–C5)(C22–C29).
b
c
Fig. 2. Crystal structure of 6. Thermal ellipsoids are drawn at the 50% probability
level. Hydrogen atoms were omitted for clarity.
for metal complexes containing a
g
1-bound 2,6-xylyl isonitrile li-
gand (1.159(26) Å and 172(6)° [44]) and similar to that of the free
ligand (1.160–1.161 Å [45]) (see Fig. 2). The lack of significant
back-bonding indicated by the structural data is substantiated by
the stretching frequency
of 6 in toluene, which is higher than that of free isonitrile
CN = 2119 cmꢀ1) [46].
m
CN = 2123 cmꢀ1 observed for solutions
3. Conclusion
(m
Nitrous oxide lived up to its reputation as a ‘‘poor” ligand in its
failure to coordinate to nacnac copper complexes under the condi-
tions examined here. Reactions of 1Cu(L) with nitrous oxide in
benzene or diethyl ether solutions, if they occurred at all, were
too slow to be detected next to complex degradation (under nitro-
gen atmosphere and otherwise identical conditions approximately
1–3% per day). Further investigations, e.g. reactions of N2O with
dinuclear copper complexes, are necessary to determine if this lack
of reactivity is related to the fact that coordination to two copper
centres is an essential part of the proposed mechanism of nitrous
oxide reduction in biological systems [28].
2.3. Reactivity towards nitrous oxide
Solutions of 3 in C6D6 under 1 atm of N2O at room temperature
displayed no changes in their NMR spectra, indicating that nitrous
oxide coordination does not occur to a visible extend under these
conditions. More surprisingly, however, neither any noticeable de-
cline in the concentration of 3 (or more precisely: in the concentra-
tions of 5a and 5b, obtained upon dissolution of 3 in C6D6), nor any
colour change was observed when a solution of 3 in C6D6 was kept
for 5 days in presence of an excess of nitrous oxide (1 atm N2O,
exclusion of light, ambient temperature). After heating for 5 days
at 60 °C, the concentration of 3 declined by 10–15%. Approximately
the same ratio of decomposition was observed for the control
experiment (nitrogen atmosphere) under identical conditions and
we have to conclude that there is no evidence for the oxidation
of 3 by nitrous oxide.1
Given the fact that the benzene solvent displaces the bridging
toluene in 3 and could not be replaced by added THF, we investi-
gated reactions of 3 with N2O in diethyl ether solution to minimize
inhibition of nitrous oxide coordination by the solvent. Solutions of
3 in Et2O (3 ꢁ 10ꢀ4–5 ꢁ 10ꢀ3 M) under 1 atm of nitrous oxide (10–
200 equiv.) were kept under exclusion of light at ambient temper-
atures for 6–13 days. No change of the yellowish colour was
observed and UV/Vis spectra, measured for less concentrated solu-
tions, remained significantly different from those of solutions ex-
posed to oxygen. In all experiments, spectral changes were
comparable to those observed for control experiments under nitro-
gen atmosphere and exposure to dry oxygen resulted in an imme-
diate colour change to dark brown even after prolonged storage
under N2O atmosphere. We have to conclude that 3 was not oxi-
dised by N2O in any measurable extend.
4. Experimental
4.1. General
All reactions were carried out under nitrogen atmosphere using
Schlenk or glove box techniques. THF was distilled from sodium/
benzophenone, all other solvents were dried by passage through
activated aluminium oxide (MBraun SPS) and de-oxygenated by
repeated extraction with nitrogen. C6D6 was distilled from Na
and de-oxygenated by three freeze–pump–thaw cycles. 1H [47],
2H [48], and CuOtBu [49] were synthesized as reported. All other
chemicals were obtained from commercial suppliers and used as
received. NMR spectra were recorded on a Bruker ARX 400 MHz
spectrometer and referenced to residual solvent (C6D5H: d 7.15,
C6D6: d 128.02). Elemental analyses were performed by the Labora-
toire d’Analyse Elémentaire (Université de Montréal).
4.2. (N,N0-Bis-2,6-Me2C6H3-nacnac)Cu(OAc), ({1}Cu{OAc})
Following the procedure published for the analogous N,N0-
dimesityl complex [50], 1H (1.50 g, 4.9 mmol) was dissolved in a
mixture of methanol and dichloromethane (4:1, 125 mL) and
added drop-wise to a solution of Cu(OAc)2 (0.17 g, 4.9 mmol) in
the same solvent mixture. On addition the originally blue solution
turned light-green, dark-green and finally black. After stirring for
1.5 h at ambient temperature, the solvent was evaporated and
the obtained precipitate washed twice with water (30 mL) and
dried under vacuum (1.3 g, 84%). Anal. Calc. for C23H28N2O2Cu: C,
64.5; H, 6.5; N, 6.8. Found: C, 64.8; H, 6.6; N, 6.8%.
1
Similar lack of reactivity was observed for C6D6 solutions of the copper
scorpionate complex {HB(3,5-Me2C3N2H)3Cu}2. Again, no noticeable consumption
was observed by NMR for a period of 5 days at ambient temperature or 3 days at 60 °C
under 1 atm of nitrous oxide.

P.O. Oguadinma, F. Schaper / Inorganica Chimica Acta 362 (2009) 570–574
573
4.3. {(N,N0-Bis-2,6-Me2C6H3-nacnac)Cu}2(
l-C7H8) (3)
Table 3
Details of X-ray diffraction studies
To a mixture of 1H (3.28 g, 7.45 mmol) and CuOtBu (1.50 g,
7.50 mmol), toluene (20 mL) was added. After stirring for 2 h, the
yellow-brown solution was filtered through a pad of Celite, con-
centrated to one fifth of its volume and layered with hexane
(20 mL). Yellow crystals of 3 (2.7 g, 90%), formed after 2 days at
room temperature. dH (C6D6): a mixture of a dinuclear, 5a, and a
mononuclear C6D6 adduct, 5b, was observed in C6D6 solution (see
text): 5b: 6.95–7.10 (m, CArH), 4.77 (s, 1H, CH), 2.01 (s, 12H, ArCH3),
1.63 (s, 6H, C(N)CH3). 5a: 7.10–6.95 (m, CArH), 4.74 (s, 2H, CH), 1.89
(s, 24H, ArCH3), 1.55 (s, 12H, C(N)CH3). dC (C6D6): 5a: 159.62, 150.7,
130.6, 128.2 (partially obscured by solvent), 123.3, 93.4, 22.9
(N@CMe), 18.8 (ArMe). 5b: 159.64, 150.6, 130.7, 128.2 (partially
obscured by solvent), 123.2, 93.1, 23.2 (N@CMe), 18.9 (ArMe). Anal.
Calc. for C49H58N4Cu2: C, 70.9; H, 7.0; N, 6.8. Found: C, 70.5; H, 6.9;
N, 6.7%.
3
6
Formula
Mw (g/mol); F(000)
Crystal colour and form
C49H58N4Cu2
830.07; 3504
yellow bloc
0.12 ꢁ 0.12 ꢁ 0.20
150; 1.295
C30H34N3Cu
500.14; 1056
yellow bloc
0.12 ꢁ 0.12 ꢁ 0.12
150; 1.233
monoclinic
P21/c
Crystal size (mm)
T (K); DCalc (g/cm3)
Crystal system
Space group
Unit cell
a (Å)
b (Å)
c (Å)
orthorhombic
Pbca
21.0373(8)
14.8188(6)
27.3128(11)
12.8755(5)
11.3387(5)
19.2722(9)
106.693(2)
2695.0(2); 4
3.6–72.0; 0.944
36248/4991;
0.036
1.293; multi-scan
0.0369; 0.1103
0.0412; 0.1135
1.101
b (°)
V (Å3); Z
8514.7(6); 8
3.2–71.9; 0.970
98923/8101;
0.0594
1.510; multi-scan
0.0345; 0.0906
0.0478; 0.0944
0.953
h Range (°); completeness
Reflections: collected/ independent;
Rint
l
(mmꢀ1); absorption correction
R1 (F); wR (F2) [I > 2
r(I)]
4.4. (N,N0-Bis-2,6-Me2C6H3-nacnac)Cu{CN(2,6-Me2C6H3)} (6)
R1 (F); wR (F2) (all data)
Goodness-of-fit (F2)
Residual electron density (eꢀ/Å3)
0.38
0.25
To a mixture of 3 (200 mg, 0.24 mmol) and 2,6-xylylisonitrile
(33 mg, 0.25 mmol), toluene (1 mL) was added and the resulting
yellow solution was stirred for 1 h, layered with hexane (2 mL)
and kept at ꢀ35 °C. Yellow crystals of 6 (124 mg, 52%) formed after
2 days. dH (C6D6) 6.41–7.16 (m, 9H, CArH), 5.02 (s, 1H, CH), 2.42 (s,
12H, ArCH3), 1.77 (s, 6 H), 1.63 (s, 6 H). dC(C6D6) 162.6, 162.5
(weak), 153.0, 134.9, 130.3, 128.4, 128.3, 127.5, 122.8, (one
aromatic peak missing), 94.3, 22.4, 19.3, 18.0. Anal. Calc. for
C30H34N3Cu: C, 72.0; H, 6.85; N, 8.4. Found: C, 71.9; H, 6.8;
N, 8.4%.
4.7. Reaction of 3 with Lewis bases in C6D6 solution
A J. Young NMR tube was charged with 3 (15 mg, 0.018 mmol)
and C6D6 (0.6–0.8 mL). The required amount of Lewis base (THF:
1.5–75
MeCN: 1.3
l
L, 0.02–0.9 mmol; toluene: 1.9–95
l
lL, 0.02–0.9 mmol;
L, 0.024 mmol) was added in several portions and 1H
NMR spectra were recorded after each addition. No changes were
observed in the case of toluene or THF addition. Addition of MeCN
lead to the formation of a new compound, presumably 1Cu(NCMe):
dH (C6D6) 6.95–7.10 (m, 6H, CArH), 4.81 (s, 1H, CH), 2.08 (s, 12H,
ArCH3), 1.65 (s, 6 H), 0.52 (s, 3H, NCCH3).
4.5. Reaction of 3 with N2O in C6D6 solution
The desired complex 3 (15 mg, 0.018 mmol) was dissolved in
C6D6 (0.8 mL). C6Me6 was added as an internal standard. The
ensuing yellow solution was transferred to a J. Young NMR tube.
Two freeze–pump–thaw cycles were performed to remove N2,
and N2O (2 mL, 1 atm, 0.08 mmol) was introduced to the evacu-
ated tube after warming to room temperature. As a control, an
identical solution was prepared without addition of N2O. NMR
tubes were kept either at room temperature or at 60 °C under
exclusion of light and monitored by 1H NMR at room
temperature.
4.8. X-ray diffraction studies
Crystals suitable for X-ray diffraction studies were obtained di-
rectly in the synthesis. Diffraction data were collected on Bruker/
AXS Smart 6000 (4 K) diffractometer (Mirror Montel 200-mono-
chromated Cu Ka radiation, FR591 Rotating Anode). Cell refine-
ment and data reduction were done using APEX2 [51]. Structures
were solved by direct methods using SHELXS97 and refined on F2
by full-matrix least squares using SHELXL97 [52]. All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were refined
isotropic on calculated positions using a riding model. Further
experimental details are listed in Table 3.
4.6. Reaction of 3 with N2O in Et2O solution
(a) A 25 mL Schlenk flask was charged with
3 (50 mg,
0.06 mmol) and Et2O (12 mL). After two freeze–pump–thaw
cycles, N2O (1 atm, 0.8 mmol) was introduced to the evacu-
ated flask. For control experiments, an identical solution was
left either under nitrogen atmosphere. The solutions were
kept under exclusion of light for 5 days without any visible
colour change. An immediate colour change to brown was
observed on exposure to oxygen.
Acknowledgements
We thank F. Bélanger-Gariépy and Dr. M. Simard for their assis-
tance in X-ray diffraction studies and Dr. T. H. Warren for helpful
discussions. Funding for this research was provided by the Natural
Sciences and Engineering Research Council of Canada and the Uni-
versité de Montréal.
(b) A 25 mL Schlenk flask was charged with 12 mL of a solution
of 3 in Et2O (10 mg in 40 mL). After freeze–pump–thaw
cycles, 1 atm of either nitrogen or nitrous oxide was intro-
duced to the flask. Solutions were stored at ambient temper-
ature under exclusion of light for up to 13 days. UV/Vis
spectra were recorded in regular intervals in the region of
400–800 nm by placing the sealed Schlenk flask directly in
the spectrometer. An immediate colour change to brown
was observed on exposure to oxygen after the end of the
measurement.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2008.05.008.
References
[1] F.S. Bridson-Jones, G.D. Buckley, L.H. Cross, A.P. Driver, J. Chem. Soc. (1951)
2999.

574
P.O. Oguadinma, F. Schaper / Inorganica Chimica Acta 362 (2009) 570–574
[2] F.S. Bridson-Jones, G.D. Buckley, J. Chem. Soc. (1951) 3009.
[3] G.D. Buckley, W.J. Lewy, J. Chem. Soc. (1951) 3016.
[29] D.J.E. Spencer, N.W. Aboelella, A.M. Reynolds, P.L. Holland, W.B. Tolman, J. Am.
Chem. Soc. 124 (2002) 2108.
[4] G.I. Panov, K.A. Dubkov, E.V. Starokon, V.N. Parmon, React. Kinet. Catal. Lett. 76
(2002) 401.
[5] V.N. Parmona, G.I. Panova, A. Uriarteb, A.S. Noskova, Catal. Today 100 (2005)
115.
[30] D.J.E. Spencer, A.M. Reynolds, P.L. Holland, B.A. Jazdzewski, C. Duboc-Toia, L. Le
Pape, S. Yokota, Y. Tachi, S. Itoh, W.B. Tolman, Inorg. Chem. 41 (2002) 6307.
[31] N.W. Aboelella, S.V. Kryatov, B.F. Gherman, W.W. Brennessel, V.G. Young Jr., R.
Sarangi, E.V. Rybak-Akimova, K.O. Hodgson, B. Hedman, E.I. Solomon, C.J.
Cramer, W.B. Tolman, J. Am. Chem. Soc. 126 (2004) 16896.
[32] A.M. Reynolds, B.F. Gherman, C.J. Cramer, W.B. Tolman, Inorg. Chem. 44 (2005)
6989.
[33] W.B. Tolman, J. Biol. Inorg. Chem. 11 (2006) 261.
[34] L.M.R. Hill, B.F. Gherman, N.W. Aboelella, C.J. Cramer, W.B. Tolman, Dalton
Trans. (2006) 4944.
[35] X. Dai, T.H. Warren, Chem. Commun. (2001) 1998.
[36] D.S. Laitar, C.J.N. Mathison, W.M. Davis, J.P. Sadighi, Inorg. Chem. 42 (2003)
7354.
[37] L.D. Amisial, X. Dai, R.A. Kinney, A. Krishnaswamy, T.H. Warren, Inorg. Chem.
43 (2004) 6537.
[6] A. Yamamoto, S. Kitazume, L.S. Pu, S. Ikeda, J. Am. Chem. Soc. 93 (1971) 371.
[7] F. Bottomley, H.H. Brintzinger, Chem. Commun. 234–235 (1978).
[8] G.A. Vaughan, P.B. Rupert, G.L. Hillhouse, J. Am. Chem. Soc. 109 (1987) 5538.
[9] D.J. Berg, C.J. Burns, R.A. Andersen, A. Zalkin, Organometallics 8 (1989) 1865.
[10] J.T. Groves, J.S. Roman, J. Am. Chem. Soc. 117 (1995) 5594.
[11] T. Yamada, K. Suzuki, K. Hashimoto, T. Ikeno, Chem. Lett. 28 (1999) 1043.
[12] R.R. Conry, J.M. Mayer, Inorg. Chem. 29 (1990) 4862.
[13] W.A. Howard, G. Parkin, J. Am. Chem. Soc. 116 (1994) 606.
[14] A.M. Baranger, T.A. Hanna, R.G. Bergman, J. Am. Chem. Soc. 117 (1995) 10041.
[15] M. Dionne, J. Jubb, H. Jenkins, S. Wong, S. Gambarotta, Inorg. Chem. 35 (1996)
1874.
[16] A.V. Leont’ev, O.A. Fomicheva, M.V. Proskurnina, N.S. Zefirov, Russ. J. Org.
Chem. 37 (2001) 496.
[17] J.H. Lee, M. Pink, J. Tomaszewski, H. Fan, K.G. Caulton, J. Am. Chem. Soc. 129
(2007) 8706.
[18] J.N. Armor, H. Taube, J. Am. Chem. Soc. 91 (1969) 6874.
[19] C.B. Pamplin, E.S.F. Ma, N. Safari, S.J. Rettig, B.R. James, J. Am. Chem. Soc. 123
(2001) 8596.
[20] M.H.V. Huynh, R.T. Baker, D.L. Jameson, A. Labouriau, T.J. Meyer, J. Am. Chem.
Soc. 124 (2002) 4580.
[21] X. Jin, G. Wang, M. Zhou, J. Phys. Chem. A 110 (2006) 8017.
[22] G. Wang, X. Jin, M. Chen, M. Zhou, Chem. Phys. Lett. 420 (2006) 130.
[23] K. Molvinger, G.I. Childs, M. Jobling, M. Roper, M.W. George, M. Poliakoff,
Chem. Lett. (2000) 1260.
[38] Y.M. Badiei, T.H. Warren, J. Organomet. Chem. 690 (2005) 5989.
[39] C. Shimokawa, Y. Tachi, N. Nishiwaki, M. Ariga, S. Itoh, Bull. Chem. Soc. Jpn. 79
(2006) 118.
[40] P.L. Holland, W.B. Tolman, J. Am. Chem. Soc. 121 (1999) 7270.
[41] J.T. York, V.G. Young Jr., W.B. Tolman, Inorg. Chem. 45 (2006) 4191.
[42] S.Y. Lee, S.J. Na, H.Y. Kwon, B.Y. Lee, S.O. Kang, Organometallics 23 (2004) 5382.
[43] B.A. Jazdzewski, P.L. Holland, M. Pink, V.G. Young, D.J.E. Spencer, W.B. Tolman,
Inorg. Chem. 40 (2001) 6097.
[44] Determined from 171 structures in the Cambridge Structural Database, which
carry a metal bonded xylyl isonitrile ligand, do not contain any errors and have
an agreement factor R1 < 5%. (b) I.J. Bruno, J.C. Cole, P.R. Edgington, M. Kessler,
C.F. Macrae, P. McCabe, J. Pearson, R. Taylor, Acta Crystallogr., Sect. B 58 (2002)
389.
[24] V.V. Lavrov, V. Blagojevic, G.K. Koyanagi, G. Orlova, D.K. Bohme, J. Phys. Chem.
A 108 (2004) 5610.
[25] K. Brown, K. Djinovic-Carugo, T. Haltia, I. Cabrito, M. Saraste, J.J.G. Moura, I.
Moura, M. Tegoni, C. Cambillau, J. Biol. Chem. 275 (2000) 41133.
[26] T. Haltia, K. Brown, M. Tegoni, C. Cambillau, M. Saraste, K. Mattila, K. Djinovic-
Carugo, Biochem. J. 369 (2003) 77.
[27] P. Chen, S.I. Gorelsky, S. Ghosh, E.I. Solomon, Angew. Chem., Int. Ed. 43 (2004)
4132.
[28] S.I. Gorelsky, S. Ghosh, E.I. Solomon, J. Am. Chem. Soc. 128 (2006) 278.
[45] T. Mathieson, A. Schier, H. Schmidbaur, Dalton Trans. (2001) 1196.
[46] R.W. Stephany, M.J.A. de Bie, W. Drenth, Org. Magn. Reson. 6 (1974) 45.
[47] P.H.M. Budzelaar, N.N.P. Moonen, R. de Gelder, J.M.M. Smits, A.W. Gal, Eur. J.
Inorg. Chem. 2000 (2000) 753.
[48] W. Clegg, E.K. Cope, A.J. Edwards, F.S. Mair, Inorg. Chem. 37 (1998) 2317.
[49] T. Tsuda, T. Hashimoto, T. Saegusa, J. Am. Chem. Soc. 94 (1972) 658.
[50] S. Yokota, Y. Tachi, S. Itoh, Inorg. Chem. 41 (2002) 1342.
[51] APEX2, Release 2.1-0, Bruker AXS Inc., Madison, USA, 2006.
[52] G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112.