Synthesis and structures of isopropyl-β-diketiminato copper(I) complexes

Article abstract of DOI:10.1139/V10-013

The reaction of N,N′-diisopropyl-2-amino-4-iminopent-2-ene (nacnac^i-PrH, 1) either with CuOt-Bu or with a mixture of mesityl copper and 10% CuOt-Bu afforded, in the presence of PPh₃, CN(C ₆Me₂H₃), or MeCN, the Lewis base coordinated complexes nacnac^i-PrCuPPh₃·0.5 C₆H ₁₄ (2), nacnac^i-PrCuCN(C₆Me₂H ₃) (3), and nacnac^i-PrCu(NCMe) (4). Compounds 2, 3, and 4 were characterized by single-crystal X-ray diffraction studies. Compound 4 afforded two species in deuterated benzene in a 2:1 ratio, which were assigned to {nacnac^i-PrCu}₂(μ-NCMe) and nacnac ^i-PrCuNCMe (4). Upon addition of 5 equiv. of MeCN, the two sets collapsed into that of 4. No copper complexes were formed in the presence of styrene, stilbene, or diphenylacetylene.

Full text of DOI:10.1139/V10-013

472
Synthesis and structures of isopropyl-b-
diketiminato copper(I) complexes
Paul O. Oguadinma and Frank Schaper
Abstract: The reaction of N,N’-diisopropyl-2-amino-4-iminopent-2-ene (nacnaci-PrH, 1) either with CuOt-Bu or with a mix-
ture of mesityl copper and 10% CuOt-Bu afforded, in the presence of PPh3, CN(C6Me2H3), or MeCN, the Lewis base co-
ordinated complexes nacnaci-PrCuPPh3Á0.5 C6H14 (2), nacnaci-PrCuCN(C6Me2H3) (3), and nacnaci-PrCu(NCMe) (4).
Compounds 2, 3, and 4 were characterized by single-crystal X-ray diffraction studies. Compound 4 afforded two species
in deuterated benzene in a 2:1 ratio, which were assigned to {nacnaci-PrCu}2(m-NCMe) and nacnaci-PrCuNCMe (4). Upon
addition of 5 equiv. of MeCN, the two sets collapsed into that of 4. No copper complexes were formed in the presence of
styrene, stilbene, or diphenylacetylene.
Key words: diketiminate, copper, coordination chemistry.
i-Pr
´
´
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`
´
Resume : La reaction du N,N’-diisopropyl-2-amino-4-iminopent-2-ene (nacnac H, 1) avec le CuOt-Bu ou un melange du
´
`
´
´
mesityl-cuivre et du CuOt-Bu a 10 % a donne, en presence de PPh3, de CN(C6Me2H3) ou de MeCN, les complexes
nacnaci-PrCuPPh3Á0,5 C6H14 (2), nacnaci-PrCuCN(C6Me2H3) (3), et nacnaci-PrCu(NCMe) (4). Les composes 2, 3 et 4 ont ete
´
´ ´
´
´
´
caracterises par diffraction des rayons-X sur monocristaux. Le spectre RMN de 4 dans C6D6 comporte deux series de si-
i-Pr
i-Pr
´
`
`
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gnaux selon un rapport 2:1, assignes a {nacnac Cu}2(m-NCMe) et a nacnac CuNCMe (4). Apres l’addition de 5 equiv.
´ ´ ´ ´
´
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de MeCN, seuls les signaux de 4 ont ete observes. Aucun complexe de cuivre n’a ete obtenu en presence de styrene, de
`
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stilbene ou de diphenylacetylene.
´
´
Mots-cles : diketiminate, cuivre, chimie de coordination.
syntheses and characterization of N,N’-diisopropyl nacnac
CuI complexes. Just prior to submission of this manuscript,
Arii et al. reported nacnaci-PrCu germylene complexes, using
the same ligand.13
Introduction
Brookhart’s demonstration in the mid 1990s that late tran-
sition-metal a-diimine complexes of Pd and Ni were effec-
tive as catalysts in olefin polymerization1 paved the way for
the synthesis of the corresponding anionic diketiminate ver-
sions of these ligand systems.2 Since then, interest in diketi-
minates has continued unabatedly, and today b-diketiminates
represent one of the most extensively employed nitrogen-
based, bidentate ligands in coordination chemistry.3 The
acronym ‘‘nacnac’’ is often used to describe 2-amino-4-imi-
nopent-2-ene, which is the N-analogue of the ubiquitous
acetylacetonate (acac). The nacnac ligands are monoanionic
spectator ligands, which have assisted in the isolation of
metal complexes in unusual oxidation states and (or) coordi-
nation numbers.4 For copper in particular, Tolman and co-
workers used diketiminate complexes to model the active
site of metalloproteins.5 Warren and co-workers isolated a
nacnac copper carbene complex, which they employed in
catalytic cyclopropanation, and used copper diketiminates
for amination reactions.6–8 While most applications of dike-
timinate ligands revolve around N-aryl substituents, their N-
alkyl derivatives have not been well-exploited. For cop-
per(I), they are limited to applications in atomic layer
deposition9 or analyses of copper–ligand bonding.10 In con-
tinuation of previous work on diketiminate copper com-
plexes with N-alkyl substituents,11,12 we report here the
Results and discussion
Ligand and complex synthesis
Ligand 1 has been obtained previously by a multi-step
protocol, which is generally used to prepare N-alkyl diketi-
minates, either by employing Meerwein salt (32%–60%
yield)14 or dimethylsulfate (74% yield, from the aminoke-
tone)15 as O-alkylating agents. We employed a one-step pro-
cedure for condensation of acetylacetone with isopropylamine
in the presence of equimolar amounts of para-toluenesulfonic
acid,16 which afforded 1 directly, albeit in a relatively low
yield of 23% after 5 days of reflux (Scheme 1). The analo-
gous ligands nacnacBnH and nacnaci-BuH, bearing primary
alkyl groups, have been obtained in 1–2 days using the same
procedure,12,17 while the preparation of nacnacCH(Me)Ph
H
required 5 days.11 Longer reaction times thus seem to be nec-
essary for secondary amines. Complexes 2–4 were obtained
as yellow air- and moisture-sensitive powders or crystals in
26%–84% yield by reaction of 1 in the presence of PPh3,
xylyl isocyanide, or acetonitrile either with CuOt-Bu, a proce-
dure employed by Dai and Warren for preparing N-aryl
nacnacCuI complexes,6 or with mesityl copper and catalytic
Received 15 October 2009. Accepted 6 January 2010. Published on the NRC Research Press Web site at canjchem.nrc.ca on 10 April
2010.
1
´
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P.O. Oguadinma and F. Schaper. Departement de chimie, Universite de Montreal, Montreal, QC H3C 3J7, Canada.
1Corresponding author (e-mail: Frank.Schaper@umontreal.ca).
Can. J. Chem. 88: 472–477 (2010)
doi:10.1139/V10-013
Published by NRC Research Press

Oguadinma and Schaper
473
˚
Scheme 1.
by 0.1 and 0.4 A, respectively, out of the ligand mean plane are
observed (plane defined by N1, N2, C2, and C4). While Cu–P
˚
and Cu–N bond distances (2.191(1) A; 1.978(1) and 1.983(1)
A) are comparable to those in nacnacCH(Me)PhCuPPh3 (2.195(1)
˚
11
˚
˚
A; 1.972(1) and 1.983(1) A), they are longer than in nac-
nac Cu(PPh3) complexes (2.16–2.18 A and 1.94–1.97
Ar
˚
7,22–24
˚
A)
in agreement with increased steric bulk introduced
by a secondary alkyl substituent on the nitrogen atoms.
Spectroscopic properties
The PPh3 resonance in the 31P NMR spectrum of compound
2 in C6D6 was observed at d 4.0. This value is intermediate
between those of nacnacArCuPPh3 complexes (Ar = Me3C6H2:
5.2 ppm,7 Ar = Me2C6H3: 5.4 ppm,23 and Ar = i-Pr2C6H3:
3.6 ppm22) and nacnacRCuPPh3 complexes (R = Bn:
3.5 ppm12 and R = CH(Me)C6H5: 3.9 ppm11). While N-
aryl-substituted diketiminate ligands tend to show 31P reso-
nances at lower field, differences are too small to be corre-
lated to the ligand properties. Similar to the behaviour
observed for nacnacCH(Me)PhCu(NCMe),11 which also carries
a secondary alkyl substituent on N, pure crystals of 4 dis-
solved in C6D6 gave two sets of nacnac resonances in a ratio
amounts of CuOt-Bu (Scheme 1). Mesityl copper in the ab-
sence of CuOt-Bu has been shown to be unreactive.11
Though no major differences in terms of yields were ob-
served between the use of CuOt-Bu or MesCu/CuOt-Bu, the
complexes crystallized easier when MesCu/CuOt-Bu was
used, probably due to the smaller amounts of tert-butanol
present.
1
of 2:1 in its H NMR spectrum; the resonances of the major
species being slightly broadened. Only one resonance was
observed for MeCN. Fast exchange of coordinated and free
Lewis base was observed before in nacnacCuL com-
plexes,11,12,25 and the amount of coordinated MeCN in the
two species thus cannot be derived from NMR. Only one
peak for nCN was observed at 2259 cm–1 in the IR spectrum
of 4 in toluene solution, 5 cm–1 higher than that of free
MeCN.26 Addition of excess MeCN (5 equiv.) caused the
Compound 1 did not react with CuOt-Bu in the presence of
styrene, stilbene, or diphenylacetylene. Identical observations
were made with copper complexes carrying the chiral nac-
nacCH(Me)Ph ligand.11 On the other hand, Cu–styrene complexes
are readily obtained with nacnacMes (Mes = 2,4,6-Me3C6H3)18
or nacnacdipp (dipp = 2,6-i-Pr2C6H3, see Experimental sec-
tion), one of the most sterically encumbered N-aryl diketimi-
1
nates, as well as with nacnacBn or nacnaci-Bu 12,17
.
In-plane
peaks to collapse to one set of resonances in its H and 13C
coordination of the two carbon atoms of an olefin is thus
possible for diketiminate ligands with aryl or primary alkyl
substituents, but not if secondary alkyls are present on the ni-
trogen. The implied increased steric demand of nacnaci-Pr
compared with nacnacdipp has to be set into contrast to obser-
spectra, belonging to the previously minor component.
Changes in the overall concentration, on the other hand, did
not affect the observed ratio, which rules out equilibrium [1]
in Scheme 2. Complete MeCN redistribution (equilibrium [2]
in Scheme 2) also seems unlikely, since bis(acetonitrile)
complexes have not been reported for diketiminate copper
complexes and nacnaci-PrCu complexes could not be ob-
tained in the absence of ancillary ligands. We thus assign
the species favoured at higher acetonitrile concentrations to
the MeCN complex nacnaci-PrCuNCMe (4), observed in the
crystal structure, and the broadened peaks of the major spe-
cies to the bridged complex {nacnaci-PrCu}2(m-NCMe) (4b)
(equilibrium [3] in Scheme 2). While bridging coordination
of acetonitrile is rare, it is not unknown.27 Monomer–dimer
equilibria similar to equilibrium [3] in Scheme 2 have been
observed for nacnacBnCu, which forms a diphenylacetylene-
bridged dimer in the solid state and a monomeric complex
in solution when excess diphenylacetylene is present,12 and
for nacnacArCu complexes, which display an equilibrium be-
tween a monomeric and a dimeric benzene-coordinated
complex in solution.7,25 While single-crystal diffraction stud-
ies confirmed the formation of 4, we were unable to obtain
satisfactory elemental analyses, even from the crystalline
material. Synthesis of 4 was reported at the time of submis-
sion of this article by Arii et al. from the reaction of
[Cu(NCMe)4][CF3SO3] with nacnaci-PrLi.13 Although not
discussed therein, they also observed a variable ratio of two
products in NMR spectra of 4.28
vations for other systems. When compared with nacnacdipp
,
diketiminate ligands with secondary alkyl substituents on the
nitrogen allow additional intramolecular p-coordination in Ti
complexes19 or coordination of a second nacnac to Zr.20
When considering steric congestion imposed by diketiminate
ligands, it is thus important to differentiate between the first
coordination sphere around the metal centre, where nacnaci-Pr
imposes a congested environment, and general steric demand
in the (outer) coordination sphere, where it does not.
Crystal structure studies
All three compounds are monomeric and crystallize in the
P21/c space group with copper in a distorted trigonal-planar
geometry. Complex 2 (Fig. 1) co-crystallizes with half a
molecule of hexane. The methine hydrogen atoms of the i-Pr
substituent point towards the methyl groups in the ligand
backbone, even in the sterically encumbered 2. C–N and
C–C bond lengths of the diketiminate ligand are in agree-
ment with complete delocalization of the double bonds
(Table 1). Cu–N bond distances in 3 and 4 are close to the
average generally observed in nacnacCu complexes (1.94
21
˚
0.06 A), and the copper centre is found in the mean plan
of the ligand. With the bulkier phosphine ligand in 2, longer
Cu–N distances and a displacement of C3 and the copper atom
The stretching frequency nCN = 2105 cm–1 of the isocyanide
Published by NRC Research Press

474
Can. J. Chem. Vol. 88, 2010
Fig. 1. Crystal structures of 2–4. Hydrogen atoms and solvent are omitted for clarity. Thermal ellipsoids are drawn at the 50% probability
level.
˚
product, 5, was obtained. 1H and 13C NMR spectra of 5
showed resonances of the diketiminate ligand and isocya-
nide in a ratio of 1:2, which would suggest the formation of
nacnaci-PrCu(CNC6Me2H3)2. Satisfactory elemental analysis
of 5, however, could not be obtained and, more importantly,
addition of 1 equiv. xylyl isocyanide did not transform 3
into 5. Complex 5 showed the same stretching frequency in
its IR spectrum as 3. Taking also the low solubility of 5 in
toluene into account, assignment as a bisisocyanide adduct
seems improbable and the structure of 5 remains unclear.
Table 1. Selected bond distances (A) and bond angles (8) for 2, 3,
and 4.
2
3
4
˚
Bond distances (A)
Cu1—N1
Cu1—N2
Cu1—Xa
N1—C2
N2—C4
C2—C3
C3—C4
X—Yb
1.978(1)
1.987(1)
2.191(1)
1.323(2)
1.321(2)
1.408(2)
1.411(2)
1.839(2)
1.939(2)
1.935(2)
1.822(2)
1.332(2)
1.331(2)
1.407(3)
1.407(3)
1.161(2)
1.940(1)
1.961(2)
1.893(2)
1.326(3)
1.314(3)
1.413(3)
1.416(2)
1.148(3)
Conclusions
Copper complexes of nacnaci-Pr were readily prepared if
additional Lewis base was present to stabilize the complex.
Bond angles (8)
N1–Cu1–N2
N1–Cu1–Xc
N2–Cu1–Xc
97.7(1)
132.6(1)
129.4(1)
100.2(1)
130.9(1)
128.9(1)
100.6(1)
134.7(1)
124.8(1)
In agreement with observations made for nacnacCH(Me)Ph 11
,
diketiminate ligands with secondary alkyl substituents are
slightly more Lewis-basic, but sterically more demanding in
the first coordination sphere than diketiminates with aryl or
primary alkyl substituents.
aCu1—P1 (2), Cu1—C20 (3), and Cu1—N3 (4).
bAverage of P1—C12, P1—C18, and P1—C24 (2), N3—C20 (3),
N3—C12 (4).
cN1,2–Cu1–P1 (2), N1,2–Cu1–C20 (3), N1,2–Cu1–N3 (4).
Experimental section
Scheme 2.
All reactions, except ligand synthesis, were carried out
under nitrogen atmosphere using Schlenk or glovebox tech-
niques. Solvents were dried by passage through activated
aluminum 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.
CuOt-Bu30 and mesitylcopper31 were synthesized as re-
ported. All other chemicals were obtained from commercial
suppliers and used as received. Elemental analyses were per-
´
´
formed at the Laboratoire d’Analyse Elementaire (Universite
´
de Montreal). NMR spectra were recorded on a Bruker ARX
ligand in 3 is the lowest frequency observed in 2,6-xylyl iso-
cyanide copper complexes with either N-alkyl-substituted
(nCN = 2111–2117 cm–1)11,12,17 or N-aryl-substituted diketi-
minate ligands (nCN = 2121–2126 cm–1),7,25,29 indicating an
increased, but still weak p back-donation (free isocyanide:
nCN = 2119 cm–1).
400 MHz spectrometer and referenced to residual solvent
(C6D5H: d 7.15, C6D6: d 128.02) or external reference (31P,
75% H3PO4).
nacnaci-PrH (1)14,15
In the course of preparing compound 3, a minor side
Acetylacetone (4.0 mL, 38 mmol), para-toluenesulfonic
Published by NRC Research Press

Oguadinma and Schaper
475
Table 2. Details of X-ray diffraction studies.
Complex
CCDC No.
2
3
4
764335
764336
764337
Formula
C29H36CuN2PÁ(C6H14)0.5
550.19; 1.247
150 ; 1172
Monoclinic
P21/c
C20H30CuN3
376.01; 1.239
150; 800
Monoclinic
P21/c
C13H24CuN3
285.89; 1.277
150; 608
Monoclinic
P21/c
Mr (g/mol); dcalcd.(g/cm3)
T (K); F(000)
Crystal system
Space group
Unit cell
˚
a (A)
13.9417(4)
12.4813(4)
17.8496(6)
8.9807(3)
13.3632(4)
16.9799(5)
6.8103(1)
11.4563(3)
19.1252(3)
˚
b (A)
˚
c (A)
b (8)
V (A ); Z
109.348(1)
98.320(1)
94.780(1)
3
˚
2930.60(16); 4
3.36–73.61; 0.99
41989/5843; 0.037
1.72; SADABS
0.0348; 0.0959; 1.052
0.68; –0.38
2016.33(11); 4
4.23–71.45; 0.99
24118/3879; 0.038
1.55; SADABS
0.0413; 0.1128; 1.00
0.32; –0.36
1486.97(5); 4
4.50–67.82; 0.93
23408/2512; 0.034
1.93; SADABS
0.0308; 0.0906; 1.067
0.32; –0.51
q range (8); completeness
Reflections: collec./indep.; Rint
m (mm–1); abs. corr.
R1(F); wR(F2); GoF(F2)a
Residual electron density
aR1(F) based on observed reflections with I > 2s(I), wR(F2) and GoF(F2) based on all data.
acid monohydrate (7.2 g, 38 mmol), and isopropylamine
(6.1 mL, 76 mmol) were added to toluene (200 mL) and re-
fluxed with the help of a Dean–Stark apparatus for 5 days,
during which the yellow suspension turned brown. After
cooling to room temperature, the brown precipitate formed
was filtered. The precipitate was washed with toluene
(100 mL) and transferred to a K2CO3 solution (5 g in
100 mL of water). After stirring for 30 min, the aqueous
phase was extracted with toluene (3 Â 100 mL). The com-
bined organic phases were dried over MgSO4 and then fil-
tered. The filtrate was evaporated to obtain brown oil
(1.6 g, 23%), which was employed without further purifica-
tion in subsequent synthesis.
1H NMR (CDCl3, 400 MHz) d: 11.44 (bs, 1H, NH), 4.38
(s, 1H, HC(C=N)2), 3.64 (sp, J = 6 Hz, 2H, CH(CH3)2), 1.89
(s, 6H, Me(C=N)2), 1.16 (d, J = 6 Hz, 12H, CH(CH3)2). 13C
NMR (CDCl3, 101 MHz) d: 158.5 (C=N), 93.5 (HC(C=N)2),
46.7 (CH(CH3)2), 24.7 (CH(CH3)2), 18.7 (Me(C=N)2). 1H
NMR (C6D6, 400 MHz) d: 11.63 (bs, 1H, NH), 4.46 (s, 1H,
HC(C=N)2), 3.46 (sp, J = 6 Hz, 2H, CH(CH3)2), 1.71 (s, 6H,
Me(C=N)2), 1.11 (d, J = 6 Hz, 12H, CH(CH3)2). 13C NMR
(C6D6, 101 MHz) d: 158.0 (C=N), 94.6 (HC(C=N)2), 47.0
(CH(CH3)2), 25.1 (CH(CH3)2), 18.8 (Me(C=N)2).
(HC(C=N)2), 51.4 (CH(CH3)2), 26.7 (CH(CH3)2), 23.1
(Me(C=N)2). 31P NMR (C6D6, 75 MHz) d: 4.0. Anal. Calcd.
for C29H36N2PCu: C, 68.68; H, 7.15; N, 5.52. Found: C,
67.85; H, 7.48; N, 4.97.
nacnaci-PrCuCN(C6Me2H3) (3)
nacnaci-PrH (200 mg, 1.10 mmol), mesitylcopper (201 mg,
1.10 mmol), CuOt-Bu (15 mg, 0.11 mmol), and xylyl iso-
cyanide (151 mg, 1.15 mmol) were dissolved in toluene
(4 mL). The yellow-brown solution was stirred for 1 h and
then concentrated to half its volume to afford a yellow-
brown suspension. The suspension was filtered, and the fil-
trate was layered with 4 mL of hexanes and kept at –35 8C.
Yellow crystals of 3 formed after 1 day (190 mg, 46%).
IR (toluene) nCN: 2114 cm–1.1H NMR (C6D6, 400 MHz)
d: 6.75 (t, J = 8 Hz, 2H, p-CN(C6Me2H3)), 6.59 (d, J =
8 Hz, m-CN(C6Me2H3), 2H) 4.60 (s, 1H, HC(C=N)2), 4.01
(septet, J = 6 Hz, CH(CH3)2, 2H), 2.11 (s, 6H, Me(C=N)2),
2.08 (s, 6H, CN(C6Me2H3), 1.42 (d, 12H, J = 6 Hz
CH(CH3)2). 13C NMR (C6D6, 101 MHz) d: 160.7 (C=N),
134.8, 94.8 (HC(C=N)2), 50.9 (CH(CH3)2). 27.5
(CH(CH3)2), 22.3 (Me(C=N)2), 18.8 (CN(C6Me2H3)).
(CN(C6Me2H3) and three aromatic resonances were not de-
tected). Anal. Calcd. for C20H30N3Cu: C, 63.88; H, 8.04; N,
11.17. Found: C, 63.83; H, 8.11; N, 11.12.
nacnaci-PrCuPPh3Á0.5 C6H14 (2)
nacnaci-PrH (300 mg, 1.65 mmol), mesitylcopper (301 mg,
1.65 mmol), CuOt-Bu (22 mg, 0.165 mmol), and PPh3
(437 mg, 1.65 mmol) were dissolved in toluene (12 mL) to
give a yellow-brown solution. After stirring for 1 h, the sol-
ution was filtered, concentrated to 1/5 of its volume and lay-
ered with hexane (5 mL). It was then kept at –35 8C. Yellow
crystals together with powder formed after 3 day (700 mg,
84%).
The solid obtained after filtration, 5, gave the following
data: IR (toluene) nCN: 2114 cm–1. 1H NMR (C6D6,
400 MHz) d: 6.69 (t, J = 8 Hz, p-CN(C6Me2H3), 2H), 6.52
(d, J = 8 Hz, m-CN(C6Me2H3), 4H), 4.61 (s, 1H,
HC(C=N)2), 4.02 (septet, J = 6 Hz, CH(CH3)2, 2H), 2.14 (s,
12H, CN(C6Me2H3), 2.08 (s, 6H, Me(C=N)2), 1.43 (d, 12H,
J = 6 Hz, CH(CH3)2). 13C NMR (C6D6, 101 MHz) d: 160.7
(C=N), 135.4, 128.6, 128.1, 127.8, 94.8 (HC(C=N)2), 50.8
(CH(CH3)2), 27.5 (CH(CH3)2), 22.4 (Me(C=N)2), 18.8.
(CN(C6Me2H3)). (CN(C6Me2H3) elusive).
1H NMR (C6D6, 400 MHz) d: 7.66–7.02 (m, 15H, PPh3),
4.67 (s, 1H, HC(C=N)2), 3.86 (sp, J = 6 Hz, 2H CH(CH3)2),
2.10 (s, 6H, Me(C=N)2), 0.98 (d, J = 6 Hz, 12H, CH(CH3)2).
13C NMR (C6D6, 101 MHz) d: 161.3 (C=N), 135.1 (d, J =
30 Hz, ipso PPh3), 134.7 (d, J = 14 Hz, ortho PPh3), 129.7
(para PPh3), 128.6 (d, J = 9 Hz, ortho PPh3), 95.4
nacnaci-PrCuNCMe (4)
nacnaci-PrH (75 mg, 0.41 mmol) and MeCN (41 mg,
Published by NRC Research Press

476
Can. J. Chem. Vol. 88, 2010
0.82 mmol) were mixed and transferred to a vial containing
a yellow solution of CuOt-Bu (69 mg, 0.41 mmol) in tol-
uene (2 mL). The resulting yellow-brown solution was kept
at –30 8C. Colourless crystals formed after 1 h together with
a brown precipitate (mirror) indicative of decomposition.
Decantation of the brown suspension gave, after drying,
31 mg (26%) of yellow crystals, 4.
taining material, refer to cisti-icist.nrc-cnrc.gc.ca/cms/
unpub_e.shtml. CCDCs 764335–764337 contain the X-ray
data in CIF format for this manuscript. These data can be
obtained, free of charge, via www.ccdc.cam.ac.uk/conts/
retrieving.html (Or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax +44 1223 336033; or deposit@ccdc.cam.ac.uk).
Two species were observed in C6D6 solutions of 4 (see
text). IR (toluene) nNC: 2259 cm–1. 4: 1H NMR (C6D6,
400 MHz) d: 4.52 (s, 1H, HC(C=N)2), 4.03 (septet, J =
6 Hz, CH(CH3)2, 2H), 2.11 (s, 6H, Me(C=N)2), 1.38–1.52
(m, 12H, CH(CH3)2), 0.57 (NCMe). 13C NMR (C6D6,
101 MHz) d: 160.6 (C=N), 116.5 (NCMe), 65.9
(HC(C=N)2), 50.7 (CH(CH3)2), 26.9 (CH(CH3)2), 22.3
(Me(C=N)2) and 0.3 (NCMe). 4b: 1H NMR (C6D6,
400 MHz) d: 5.29 (bs, 1H, HC(C=N)2), 3.92–3.99 (feature-
less septet, CH(CH3)2, 2H), 2.56 (bs, 6H, Me(C=N)2), 2.08
(s, 6H, CN(C6Me2H3) and 1.38–1.52 (m, 12H, CH(CH3)2)
overlapping with that of 4. Elemental analysis was unsatisfac-
tory with varying results (DC = 2%–3%), which might be re-
lated to acetonitrile dissociation and complex decomposition.
Acknowledgements
Financial support from the Natural Sciences and Engi-
neering Research Council of Canada (NSERC) and the Uni-
´
´
versite de Montreal is gratefully acknowledged.
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˚
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