Bis(2-phenylethyl)-nacnac: A chiral diketiminate ligand and its copper complexes

Article abstract of DOI:10.1021/om9002279

The chiral diketiminate ligand bis-N, N-(2-phenylethyl)-2,4-diiminopentane, 1H, was synthesized in good yields in a one-step reaction from chiral amine and acetylacetone. Reaction of 1Li(THF) with N-bromosuccinimide yielded the succinimide-substituted lig

Full text of DOI:10.1021/om9002279

Organometallics 2009, 28, 4089–4097 4089
DOI: 10.1021/om9002279
Bis(2-phenylethyl)-nacnac: A Chiral Diketiminate Ligand and Its Copper
Complexes
Paul O. Oguadinma and Frank Schaper*
ꢀ ꢀ ꢀ ꢀ ꢀ
Departement de Chimie, Universite de Montreal, Montreal, Quebec, H3C 3J7, Canada
Received March 25, 2009
The chiral diketiminate ligand bis-N,N0-(2-phenylethyl)-2,4-diiminopentane, 1H, was synthesized
in good yields in a one-step reaction from chiral amine and acetylacetone. Reaction of 1Li(THF) with
N-bromosuccinimide yielded the succinimide-substituted ligand 2H. Copper complexes were ob-
tained by reaction of the ligand with a basic copper source in the presence of coordinating Lewis
bases, and 1Cu(NCMe), 1Cu(DMAP), 1Cu(PPh3), 1Cu(2,6-xylyl isonitrile), 2Cu(PPh3), and 2Cu
(2,6-xylyl isonitrile) have been prepared and, for the most part, characterized by X-ray diffraction
studies. Compared to their more common analogues with aromatic substituents on N, 1 and 2 seem to
be more basic (1 > 2) and sterically more demanding (2 > 1). Their copper complexes are less stable
than those of aryl-substituted diketiminates and tend to decompose by disproportionation, most
probably after dissociation of the coordinated Lewis base. Despite the rotational freedom around the
N-R* bond, the complexes are sterically rigid, a necessary requirement for potential applications in
enantioselective catalysis.
Introduction
with aliphatic substituents on nitrogen.8 During previous
work on biomimetic copper complexes,9 we became inter-
ested in varying the ligand framework of nacnac complexes
by switching from aromatic to aliphatic N,N0-substituents.
In addition to drastically changing the steric environment
around the metal center, aliphatic substituents would be a
very economical way to introduce chirality into diketiminate
ligands. We report here the synthesis of N,N0-bis(2-pheny-
lethyl)-nacnacH, 1H, the first chiral nacnac ligand, and its
copper complexes.
N,N0-Substituted β-diketiminato (“nacnac”)1 ligands have
been gaining increasing interest over the past decade, mainly
due to their suitability as sterically crowded spectator ligands
to stabilize coordinatively unsaturated metal centers and
unusual oxidation states.2 This rekindled interest in a ligand
structure known since the 1960s is mainly due to Brookhart’s
seminal work on late metal complexes for olefin polymeri-
zation.3 β-Diketiminates are the anionic equivalent of the N,
N0-aryl-substituted R-diimine ligands used there, and
research has focused, with only few exceptions, on N,N0-
aryl-substituted ligands, in particular N,N0-bis-2,6-diisopro-
pylphenyl diketiminates. Copper(I) diketiminate complexes,
for example, have been widely studied, in particular by the
groups of Tolman4,5 and Warren,6,7 but only selected com-
plexes investigated for Cu ALD carried diketiminate ligands
Results and Discussion
Ligand Synthesis. Synthesis of β-diketimines with aliphatic
N-substituents has been reported previously by a two-step
procedure.10 Simple condensation of acetyl acetone with a
primary amine yielded the monosubstituted product 4-keti-
minpropan-2-one, which is normally obtained in its enamine
form. Condensation with a second amine required activation
of the ketone, most commonly by alkylation with Meerwein
salt or other alkylating reagents.10 To gain an economic and
fast access to the required ligand, we investigated the possible
one-step synthesis of aliphatic nacnac ligands. Following the
synthetic protocol outlined for aryl-substituted diketi-
mines,11 double condensation of enantiomerically pure phe-
nylethylamine and acetylacetone was achieved in the
presence of 1 equiv of p-toluenesulfonic acid under elimina-
tion of water with a Dean-Stark apparatus for 5 days.
Chiral 1H was obtained in 67-70% yield for RR- and
*Corresponding author. E-mail: Frank.Schaper@umontreal.ca.
(1) Kim, W. K.; Fevola, M. J.; Liable-Sands, L. M.; Rheingold, A. L.;
Theopold, K. H. Organometallics 1998, 17, 4541.
(2) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. Rev. 2002,
102, 3031.
(3) Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc.
1995, 117, 6414.
(4) York, J. T.; Llobet, A.; Cramer, C. J.; Tolman, W. B. J. Am.
Chem. Soc. 2007, 129, 7990. Brown, E. C.; Bar-Nahum, I.; York, J. T.;
Aboelella, N. W.; Tolman, W. B. Inorg. Chem. 2007, 46, 486.
(5) York, J. T.; Young, V. G.Jr.; Tolman, W. B. Inorg. Chem. 2006,
45, 4191.
(6) Badiei, Y. M.; Krishnaswamy, A.; Melzer, M. M.; Warren, T. H.
J. Am. Chem. Soc. 2006, 128, 15056. Kogut, E.; Wiencko, H. L.; Zhang, L.;
Cordeau, D. E.; Warren, T. H. J. Am. Chem. Soc. 2005, 127, 11248.
(7) Badiei, Y. M.; Warren, T. H. J. Organomet. Chem. 2005, 690,
5989.
(9) Oguadinma, P. O.; Schaper, F. Inorg. Chim. Acta 2008, 362, 570.
(10) Dorman, L. C. Tetrahedron Lett. 1966, 459. Bradley, A. Z.; Thorn,
D. L.; Glover, G. V. J. Org. Chem. 2008, 73, 8673.
(11) Budzelaar, P. H. M.; de Gelder, R.; Gal, A. W. Organometallics
1998, 17, 4121.
(8) Park, K.-H.; Bradley, A. Z.; Thompson, J. S.; Marshall, W. J.
Inorg. Chem. 2006, 45, 8480. Thompson, J. S.; Bradley, A. Z.; Park, K.-H.;
Dobbs, K. D.; Marshall, W. Organometallics 2006, 25, 2712.
r
2009 American Chemical Society
Published on Web 07/02/2009
pubs.acs.org/Organometallics

4090 Organometallics, Vol. 28, No. 14, 2009
Oguadinma and Schaper
Table 1. Relative Reactivities in the Formation of Complexes 3
and 4
L
3
4
hexene, styrene
MeCN
pyridine
PPh3
CNC6Me2H3
none
slow
fast, complete
fast, complete
fast, complete
none
none
partial reaction
slow, complete
fast, complete
Figure 1. Crystal structure of SS-1H. Thermal ellipsoids are
drawn at the 50% probability level. Hydrogen atoms, except the
disordered NH, were omitted for clarity.
Scheme 1
Figure 2. Crystal structure of RR-2H. Thermal ellipsoids are
drawn at the 50% probability level. Hydrogen atoms, except
NH, were omitted for clarity.
13
˚
ranged from apparent delocalization (ΔC-C, ΔC-N<0.01 A)
16
˚
˚
to clear bond alternation (ΔC-C = 0.08 A, ΔC-N = 0.06 A).
For 1H, small differences in the C3-C2/C4 and C-N bond
˚
˚
lengths (ΔC-C = 0.02 A, ΔC-N = 0.02 A) indicate an
apparent delocalization (or better, disorder) of the double
bonds. In agreement with this, inspection of the difference
Fourier map yielded two maxima of electron density close to
N1 and N2, which were assigned and refined as the dis-
ordered NH proton. Of special note is the orientation of the
chiral N-substituent, which is rotated in a way to orientate its
hydrogen atom toward the methyl group of the ligand
backbone. Ligand 2H displays, as expected, the same general
geometry (Figure 2, Table 2), with the methine-hydrogen
toward the ligand backbone. In contrast to 1H, the double
bonds are substantially localized, as indicated by differences
SS-1H. While this work was in progress, Buch and Harder
reported the synthesis of SS-1H in a two-step procedure via
alkylation of the corresponding enaminoketone in 36%
yield.12 No metal complexes of this ligand were reported.
Reaction of 1Li(THF) with N-bromosuccinimide yielded the
succinimide-substituted ligand 2H, most probably by initial
bromination at the central carbon atom followed by nucleo-
philic substitution of bromide by lithium succinimide.
Crystals suitable for an X-ray diffraction study of SS-1H
and RR-2H were obtained from ethanol at -20 °C (Figure 1,
Table 2). Ligand 1H shows the expected planar conforma-
tion of an imine-enamine ligand. Bond lengths in previous
solid state structures of 2-amino-4-iminopent-2-enes13-16
˚
in the C3-C2/C4 and C-N bond lengths of ΔC-C = 0.06 A
˚
and ΔC-N = 0.05 A, and H1A was consequently located
bound to N1 only. The introduction of the succinimide
substituent in the ligand backbone did not have any notable
consequences on the overall geometry, as evidenced by
virtually unchanged bond and torsion angles (Table 2).
Complex Syntheses. Protonation of CuOtBu with nacnacH
in aromatic solvents has proved to be a reliable route to
nacnac copper complexes.17 In contrast to aryl-substituted
nacnac ligands, solutions of 1H and CuOtBu in benzene-d6,
however, displayed only signals associated with the starting
material in its NMR spectra, even after several days at
room temperature. Reactions with the stronger base CuMes
(Mes =2,4,6-trimethylphenyl) also did not lead to any
(12) Buch, F.; Harder, S. Z. Naturforsch., B: Chem. Sci. 2008, 63, 169.
(13) Bailey, P. J.; Liddle, S. T.; Parsons, S. Acta Crystallogr., Sect. E
2001, 57, o661.
(14) Stender, M.; Wright, R. J.; Eichler, B. E.; Prust, J.; Olmstead, M.
M.; Roesky, H. W.; Power, P. P. J. Chem. Soc., Dalton Trans. 2001, 3465.
Brownstein, S.; Gabe, E. J.; Prasad, L. Can. J. Chem. 1983, 61, 1410. Hsu, S.
H.; Chang, J. C.; Lai, C. L.; Hu, C. H.; Lee, H. M.; Lee, G. H.; Peng, S. M.;
Huang, J. H. Inorg. Chem. 2004, 43, 6786. Cole, S. C.; Coles, M. P.;
Hitchcock, P. B. Organometallics 2004, 23, 5159.
(15) Aboelella, N. W.; Gherman, B. F.; Hill, L. M. R.; York, J. T.;
Holm, N.; Young, V. G.; Cramer, C. J.; Tolman, W. B. J. Am. Chem.
Soc. 2006, 128, 3445.
(16) Hamaki, H.; Takeda, N.; Yamasaki, T.; Sasamori, T.; Tokitoh,
N. J. Organomet. Chem. 2007, 692, 44.
(17) Dai, X.; Warren, T. H. J. Am. Chem. Soc. 2004, 126, 10085.

Article
Organometallics, Vol. 28, No. 14, 2009 4091
a
˚
Table 2. Selected Bond Distances [A] and Bond Angles [deg] for SS-1H, SS-2H, SS-3a-c, and SS-4d
SS-1H
RR-2H
SS-3a
SS-3bb
SS-3c
SS-4d
N1-C2
1.335(3)
1.312(4)
1.393(4)
1.415(4)
1.455(2)
1.455(4)
1.296(3)
1.348(3)
1.454(3)
1.385(3)
1.462(3)
1.469(3)
1.326(2)
1.326(2)
1.406(2)
1.411(2)
1.473(2)
1.475(2)
1.972(1)
1.983(1)
2.195(1)
1.829-1.844
97.79(5)
129.85(4)
130.37(4)
15 ( 12
1.33 ( 0.02
1.317(2)
1.334(2)
1.416(2)
1.400(2)
1.478(2)
1.476(2)
1.963(1)
1.945(1)
1.890(1)
1.138(2)
101.23(5)
120.63(5)
138.07(5)
14 ( 26
5
1.329(4)
1.329(4)
1.416(4)
1.423(4)
1.474(4)
1.482(4)
1.930(3)
1.944(3)
1.813(4)
1.172(4)
98.09(11)
130.73(13)
130.75(14)
11 ( 1
N2-C4
C2-C3
1.40 ( 0.03
1.50 ( 0.02
1.96 ( 0.04
1.97 ( 0.02
C3-C4
N1-C12
N2-C20
Cu1-N1
Cu1-N2
Cu1-Xc
X-Yc
N1-Cu1-N2
N1-Cu1-Xc
N2-Cu1-Xc
tors. CdN-CBn-Hd
complex bendinge
C2-C3-C4
Me-C-C3f
C2/C4dN-Cg
Cu-N-C12/20h
101.3 ( 0.5
124 - 134
34 ( 10
34 ( 2
17 ( 29
4 ( 2
133.7 ( 1.8
116 ( 1
119 ( 3
122 ( 3
25
3
126.1(2)
118.5 ( 0.9
124.2 ( 0.6
125.4(2)
119.3 ( 2.1
124.0 ( 1.2
129.9(2)
114.8 ( 0.4
118.3 ( 0.4
121.5 ( 0.3
131.1(1)
114.7 ( 0.4
118.4 ( 1.3
121.7 ( 1.6
129.7(3)
118 ( 1
121 ( 1
115.8 ( 0.6
a Errors provided for average values indicate either the biggest deviation from the cited mean value or the highest 3σ, when the latter value was higher.
b Averages of the geometrical data in all four independent molecules. c X, Y = P1, C22/C28/C34 (3a); N3/N6/N8/N11 (3b); N3, C22 (3c); C30, N3 (4d).
d Average of C2-N1-C12-H and C4-N2-C20-H. e Angle between the least-squares planes defined by C2-C4,N1,N2 and N1,N2,Cu1,X. f Average
of C1-C2-C3 and C5-C4-C3. g Average of C2-N1-C12 and C4-CN2-C20. h Average of Cu-N1-C12 and Cu-N2-C20.
Scheme 2
deprotonation of 1H. Reaction of CuOtBu with 1H in C6D6
can be achieved in the presence of coordinating ligands, such
as PPh3, to form the corresponding copper complex (1)Cu
(PPh3), 3a (vide infra), and tert-butanol (1H NMR: δ 1.19
ppm). Surprisingly, CuMes still remains inactive even in the
presence of PPh3, probably due to a kinetically hindered
attack on the CuMes-tetramer.18 CuMes could be employed
as a copper source, however, in the presence of catalytic
Figure 3. Crystal structure of {(2,6-Me2C6H3-NC)Cu(OtBu)}4.
Thermal ellipsoids are drawn at the 50% probability level.
Hydrogen atoms were omitted for clarity.
amounts of either tert-butanol or CuOtBu. We propose a
catalytic cycle, where CuOtBu reacts with 1H and is regen-
erated by reaction of tert-butanol with CuMes (Scheme 2).
While no difference in reactivity between CuOtBu and
CuMes/CuOtBu was observed in any reactions, we found
that products obtained by reaction with CuMes/CuOtBu
were sometimes easier to isolate by crystallization, probably
due to the absence of large amounts of tert-butanol.
start to visibly decompose after 15 min in the presence of
excess MeCN. The lack of any NMR-detectable decomposi-
tion products (apart from small amounts of 1H) and the
formation of a copper mirror indicate disproportionation as
the most probable decomposition pathway. Analogous re-
actions in the presence of 2,6-xylylisonitrile afforded after
crystallization at -30 °C, on standing, or after evaporation
of the volatiles only yellow precipitates, which were insoluble
in benzene or even DMSO. The same results were obtained in
attempts to isolate 1Cu(CNC6Me2H3), 3d, from benzene-d6
solutions, even after the NMR spectrum confirmed the
formation of the copper complex. In one case, attempted
crystallization of 3d yielded a crystalline product, which was
identified as {(2,6-Me2C6H3-NC)Cu(OtBu)}4 by X-ray crys-
tallography (Figure 3). Since reactions were usually complete
Reaction of SS-1H with CuMes/CuOtBu or with CuOtBu
in the presence of PPh3, N,N0-dimethylaminopyridine (DMAP),
or MeCN in toluene at room temperature yielded after
crystallization from toluene/hexane at -30 °C the corre-
sponding ligand-coordinated copper complexes SS-3a-c in
65-80% yield (Scheme 2). While 3aþb were stable in the
presence of excess Lewis base, solutions of 3c in benzene-d6
(18) Meyer, E. M.; Gambarotta, S.; Floriani, C.; Chiesi-Villa, A.;
Guastini, C. Organometallics 1989, 8, 1067.

4092 Organometallics, Vol. 28, No. 14, 2009
Oguadinma and Schaper
when followed via NMR, we believe this to be a minor or
isolated occurrence, and changing the order of reagent
addition did not result in isolation of 3d. Change of the
solvent from toluene to ether finally allowed the isolation of
3d, although we were not able to obtain crystals suitable for
an X-ray structure determination. Reactions of the succini-
mide-substituted ligand SS-2H under analogous conditions
in the presence of PPh3 or 2,6-xylylisonitrile yielded the
Lewis-base-coordinated complexes 2Cu(PPh3), 4a, and
2Cu(CNC6Me2H3), 4d, respectively.
Since copper complexes 3 and 4 could not, in contrast to
their aryl-substituted analogues, be obtained in the absence
of an additional Lewis base ligand, we decided to investigate
the requirement of a coordinating Lewis base in more detail.
Neither complex formation nor decomposition was observed
in reactions of 1H and either CuOtBu or CuMes/CuOtBu in
benzene-d6 in the presence of 1-hexene, styrene, diphenyla-
cetylene, THF, acetone, or benzonitrile. 1H NMR spectra of
the reaction mixtures contained only unreacted starting
materials. In the presence of acetonitrile, signals for 1Cu
(NCMe), 3c, were observed, but the reaction did not go to
completion after 1 h, even if CuMes/CuOtBu was employed
as a copper source. After 1 h, NMR spectra became difficult
to interpret due to the instability of 3c. Complete conversion
to the complexes 3a,bþd and the putative complexes 3eþf
was observed in the presence of PPh3, DMAP, 2,6-xylyliso-
cyanide, pyridine, or PMe3 (Scheme 2). The disappearance of
signals for the starting materials was accompanied by the
appearance of a new set of signals for the nacnac ligand which
lacked a signal for the N-bonded proton and the formation
of 2,4,6-mesitylene (1H NMR: δ 2.15 ppm) and/or tert-
butanol (δ 1.19 ppm).
Salt metathesis reactions of [Cu(NCMe)4][PF6] with 1Li
(THF) in the presence of MeCN or excess styrene did not
yield any Cu(I) complex, but strongly colored suspensions.
In the presence of 2,6-xylylisonitrile, the stable complex 3d
was obtained, albeit in lower yields than via the protonation
route. On the other hand, protonation of CuOtBu in the
presence of styrene by the less sterically demanding N,N0-bis
(benzyl)-nacnacH ligand cleanly generated the stable styrene
complex (nacnacBn)Cu(styrene).19 The differences in reactiv-
ity toward the same Lewis base observed for electronically
comparable, but sterically different diketiminate ligands
indicate that activation of CuOtBu by the Lewis base is not
an essential step in the reaction mechanism. Identical results
obtained using CuMes/CuOtBu, in which tert-butanol is
consistently removed from the reaction mixture, also rule
out negative effects due to the presence of tert-butanol.
Protonation of CuOtBu thus seems to proceed whenever
the resulting copper complex is of sufficient stability. Con-
sequently, salt metathesis reactions in the presence of Lewis
bases that have proved unreactive toward CuOtBu led to
decomposition.
tert-butanol decreased it back to 18%, which indicates
reversible protonation between 2H and tert-butanol in this
case. Surprisingly, no reaction at all occurred when CuOtBu
is replaced by the stronger base CuMes/CuOtBu. This lack of
reaction might have kinetic rather than thermodynamic
reasons, i.e., deactivation of CuMes by pyridine coordina-
tion (cf. Figure 3). Reactions with 2,6-xylylisonitrile and
triphenylphosphine as Lewis bases were complete as in the
case of 1H, but the reaction with triphenylphospine, fast in
the case of 1H, took several hours to reach completion. The
succinimide-substituted ligand 2H thus proved to be slightly
less reactive in complex formation than 1H (Table 1).
Dynamic Processes in Solution. The coordinated Lewis
base in complexes 3a-f exchanges fast on the NMR time
scale at room temperature with excess base present, and only
average signals of free and coordinated Lewis base were
observed in their 1H or 31P NMR spectra. NMR spectra of 3a
in the presence of 5 equiv of PMePh2 also displayed only two
signals in the 31P spectra: the PPh3 signal, which was inter-
mediate between that of 3a and that of PPh3, and the signal of
PMePh2, displaced from the position of the free phosphine.
Fast exchange of phosphine ligands was further confirmed
by the 1H NMR spectrum, which displayed only one set of
signals for the nacnac ligand, slightly displaced from those in
3a. Analogous observations were made when 3a was reacted
with 1 or 5 equiv of 2,6-xylyl isonitrile: only one signal set was
obtained for the nacnac ligand, intermediate between 3a and
3d, and average signals were observed for coordinated and
free Lewis bases. 31P spectra of benzene-d6 solutions of 3a in
the absence of free phosphine did not show any change in the
frequency of the coordinated PPh3 ligand when measured at
complex concentrations of 9-23 mM. Dissociation of the
phosphine ligand from 3a thus does not occur to a notable
extent under these conditions. Taking into account that
ligand exchange is fast on the NMR time scale even for
strongly coordinating ligands such as isonitrile, we believe
the ligand exchange to proceed by an associative mechanism.
Solutions of 3c in C6D6 showed the presence of two signal
sets, A and B, in a 2:1 ratio for the nacnac ligand. Only one
signal was observed for MeCN, corresponding to 1 equiv of
acetonitrile per nacnac, as observed in the crystal structure.
The ratio of A/B is independent from overall complex
concentration. Addition of excess acetonitrile leads to ex-
clusive formation of isomer A, which was assigned to 3c. The
nature of species B is not clear at the moment. Independence
from overall concentration and dependence on MeCN con-
centration suggests an equilibrium between nacnacCu
(MeCN), 3c, and (nacnacCu)2(μ-MeCN) þ free MeCN,
analogous to the one observed for nacnacArCu(C6D6) and
(nacnacArCu)2(μ-C6D6).7,9 IR spectra of toluene solutions of
3c, however, showed one resonance for νCN = 2254 cm-1
,
which does not support a bridging acetonitrile coordination
(free MeCN (toluene): νCN = 2259 cm-1).
When reactions of 2H with CuMes/CuOtBu or CuOtBu in
the presence of Lewis bases in benzene-d6 were followed by
NMR, no reaction was observed with 1-hexene, styrene,
acetone, or even acetonitrile. In the presence of 1 equiv of
pyridine, which yielded 3c fast and quantitatively before,
reaction of 2H with CuOtBu afforded the putative pyridine
adduct 4e in only 8% conversion (compared to unreacted
2H). Further addition of 4 equiv of pyridine increased
the percentage of 4e to 23%, while addition of 2 equiv of
X-ray Diffraction Studies. Crystals suitable for an X-ray
diffraction analysis for 3a-c and 4d were obtained from
toluene/hexane solutions at -30 °C. Complex 3c displays a
trigonal-planar coordination geometry with the copper atom
situated close to the mean plane of the ligand (Figure 4,
Table 2). The nacnac ligand is only very slightly distorted
from the expected planar geometry (mean deviation of all
˚
atoms from the mean plane: 0.05 A), and bond distances
indicate the expected delocalization of the double bonds
˚
˚
(ΔC-C = 0.016 A, ΔC-N = 0.017 A, Table 2). Similar to
the free ligand 1H, the chiral N-substituent orients its
(19) Oguadinma, P. O.; Schaper, F. Unpublished results.

Article
Organometallics, Vol. 28, No. 14, 2009 4093
Figure 5. Crystal structure of SS-3a. Thermal ellipsoids are
drawn at the 50% probability level. Hydrogen atoms were
omitted for clarity.
Figure 4. Crystal structure of SS-3c. Thermal ellipsoids are
drawn at the 50% probability level. Hydrogen atoms were
omitted for clarity.
instead of the sterically rather undemanding acetonitrile
ligand to copper renders the ligand less planar (mean devia-
˚
tion 0.09 A) and significantly displaces the copper center
hydrogen substituent toward the ligand backbone. The acet-
onitrile ligand is found in a slightly bent coordination (Cu1-
N3-C22 171.5(1)°) with geometrical data comparable to
those of other nacnac copper acetonitrile complexes (Cu-
from the ligand mean plane (Figure 5, bending angle in
Table 2). Despite this displacement, the phosphine is coor-
dinated rather symmetrically (Δ(N-Cu-P) = 0.5°) com-
pared to the acetonitrile ligand in 3c (Δ(N-Cu-P) = 17.5°),
resulting in an overall higher symmetry of bond distances
and angles in 3a. Interaction of the sterically bulky phos-
phine and the substituents at the nitrogen atoms resulted in
˚
NMeCN 1.866(3)-1.887(5) A, C-NMeCN 1.122(8)-1.137(4)
A).20 Introduction of a substituted alkyl group at the nitrogen
˚
had noticeable consequences on the ligand structure. The
average CdN-C12/20 angle of 124.2 ( 0.6° in 1H is compar-
able to the corresponding angle found in diketimines with
aromatic N substituents (CdN-CAr 124 ( 3°). Upon coor-
dination of diketiminates to copper, an N-aryl substituent is
pushed toward the ligand backbone (CdN-CAr 117-122°)
with values for CAr-N-Cu of 114-122°.21 Corresponding
values of the average Me-N-C12/22 and the C12/22-N-
Cu angles in 3c (and as well as in 3aþb, vide infra) are at the
extremes of these ranges, 118.4 ( 1.3° and 121.7 ( 1.6°,
respectively. In comparison to aryl substituents, the alkyl
substituent is thus bent further away from the metal center
toward the ligand backbone. Combined with the longer than
˚
an elongation of Cu-N bond lengths by 0.02 A and, conse-
quently, a reduction of the N-Cu-N angle by 3°. Cu-N
˚
(1.972(1) and 1.983(1) A) and Cu-P bond distances (2.195
(1) A) are longer and the out-of-plane coordination of the
˚
phosphine ligand (bending angle in Table 2 25°) is more
pronounced than in (N,N0-Ar2nacnac)Cu(PPh3) complexes
˚
˚
(Cu-N 1.940(2)-1.964(2) A, Cu-P 2.158(1)-2.169(1) A,
complex bending 4-17°),5,7,15,22 in agreement with an in-
creased steric bulk introduced by the aliphatic substituent on
N. It is noteworthy that, despite the steric demand of the
phosphine ligand, the hydrogen atom of the 1-phenylethyl
substituent remains orientated toward the ligand backbone
(see average torsion angle in Table 2) and that average bond
angles in the ligand did not change upon substitution of
acetonitrile by phosphine (Me-C-C3 114.8 ( 0.4° (3a),
114.7 ( 0.4° (3c); C-N-C12/22 118.3 ( 0.4° (3a), 118.4 (
1.3° (3c)). We conclude that the steric interaction of the N-
substituent and the methyl groups of the ligand backbone
governs the conformation of the chiral nacnac ligand and
that its complexes will be sufficiently rigid to provide a
controlled environment for potential applications.
˚
average Cu-N distances of 1.945(1) and 1.963(1) A in 3c
(average in N-Ar-substituted Cu nacnac complexes: 1.94(3)
A), this indicates that 1H should be considered sterically
21
˚
more bulky, at least in the ligand mean plane, than nacnac
ligands with N-aryl substituents, such as the widely employed
bis(2,6-diisopropylphenyl) diketiminate. An increased steric
bulk of diketiminate ligands with secondary alkyl substituents
on N was confirmed by the calculation of the aperture
accessible for coordination to copper in the N2Cu plane.
While xylyl-, mesityl-, and 2,6-bisisopropylphenyl-substituted
diketiminatecopper complexes offered anapertureof40-46°,
a strongly reduced value of 13° was found for 1Cu (see
Supporting Information).
The DMAP-coordinated complex SS-3b crystallizes with
four independent molecules in the asymmetric unit, each
with slightly different torsion angles (Figure 6). The struc-
tural data are of relatively low quality (due to the quality of
the obtained single crystal), and only general structural
features will be discussed (Table 2). Coordination of DMAP
is comparable to acetonitrile coordination in 3c in the rather
While the nacnac ligand in 3a retains the delocalization
of the double bonds, coordination of triphenylphosphine
(20) Hill, L. M. R.; Gherman, B. F.; Aboelella, N. W.; Cramer, C. J.;
Tolman, W. B. Dalton Trans. 2006, 4944. Spencer, D. J. E.; Aboelella, N.
W.; Reynolds, A. M.; Holland, P. L.; Tolman, W. B. J. Am. Chem. Soc. 2002,
124, 2108.
(21) Based on 27 nacnac Cu(I) complexes with nonchelating substit-
uents found in the Cambridge Structural Database. Allen, F. H. Acta
Crystallogr., Sect. B: Struct. Sci. 2002, B58, 380.
(22) Reynolds, A. M.; Lewis, E. A.; Aboelella, N. W.; Tolman, W. B.
Chem. Commun. 2005, 2014.

4094 Organometallics, Vol. 28, No. 14, 2009
Table 3. Details of X-ray Diffraction Studies
Oguadinma and Schaper
SS-1H
RR-2H
SS-3c
SS-3b
SS-3a
SS-4d
{(RNC)Cu (OtBu)}4
formula
Mw (g/mol);
C21H26N2
306.44; 1.093
C25H29N3O2
403.51; 1.218
C23H28CuN3
410.02; 1.310
C28H35CuN4
491.14; 1.248
C39H40CuN2P
631.24; 1.303
C34H37CuN4O2
597.22; 1.308
C52H72Cu4N4O4
1071.30; 1.331
d
calcd (g/cm3)
T (K); F(000)
cryst syst
space group
150; 332
monoclinic
P21
150; 864
orthorhombic
P212121
150; 864
orthorhombic
P212121
150; 2080
monoclinic
P21
150; 1328
orthorhombic
P212121
150; 1256
orthorhombic
P212121
150; 2240
orthorhombic
Aba2
˚
unit cell:a (A)
˚
b (A)
˚
c (A)
10.8574(5)
7.5650(3)
12.5158(6)
115.054(2)
931.27(7); 2
3.9-71.1; 0.99
9.7805(3)
12.5052(4)
17.9988(6)
7.1000(3)
8.6253(4)
33.9399(17)
16.3922(8)
19.2373(9)
18.4203(12)
115.838(1)
5228.0(5); 8
2.7-72.7; 0.99
10.1345(6)
16.2516(9)
19.5435(11)
10.0461(9)
13.1703(11)
22.9287(19)
24.4180(8)
23.1746(9)
9.4477(3)
β (deg)
3
V (A ); Z
˚
2201.4(1); 4
4.3-72.5; 1.00
2078.5(2); 4
1.2-31.4; 0.97
3218.9(3); 4
1.6-31.4; 0.97
3033.7(4); 4
3.9-72.7; 1.00
5346.2(3); 4
3.6-72.6; 0.99
θ range (deg);
completeness
reflns: collec/
indep; Rint
11 088/1929;
8.8%
28 674/2474;
3.2%
48 406/6597;
2.6%
68 189/19992;
4.0%
73 790/10102;
3.5%
39 607/5976;
4.8%
34 639/5249;
4.0%
μ (mm-1); abs corr 0.483; multiscan 0.617; multiscan 1.062; multiscan 1.332; multiscan 0.758; multiscan 1.299; multiscan 2.133; multiscan
R1(F); wR(F2);
GoF(F2) a
4.9%; 13.6%;
1.05
3.73%; 10.4%;
1.05
2.7%; 6.5%;
1.08
0.019(8)
6.1%; 17.5%;
1.0
0.05(3)
3.1%; 6.6%;
0.95
0.015(6)
4.5%; 10.4%;
0.94
3.6%; 8.6%;
1.02
0.01(2)
Flack x-param
residual electron
density
-0.05(3)
0.22; -0.68
0.15; -0.17
0.36; -0.41
0.46; -0.43
0.60; -0.39
0.30; -0.45
0.39; -0.54
a R1(F) based on observed reflections with I > 2σ(I), wR(F2), and GoF(F2) based on all data.
Figure 7. Crystal structure of SS-4d. Thermal ellipsoids are
drawn at the 50% probability level. Hydrogen atoms were
omitted for clarity.
Figure 6. Crystal structure of SS-3b. Only one of four indepen-
dent molecules is shown. Thermal ellipsoids are drawn at the
50% probability level. Hydrogen atoms were omitted for clarity.
The inset displays the orientation of the four independent
molecules in the asymmetric unit.
the ranges observed in analogous copper 2,6-xylylisonitrile
complexes with Ar2nacnac ligands (Cu-C 1.814(2)-1.822(2)
7,9,23
˚
˚
A, C-N 1.157(3)-1.159(2) A).
The observed reduced
reactivity of 2H with CuOtBu to form copper complexes
might be explained by an increased steric crowding of its
copper complexes. Although no geometrical impact of the
substitution at C3 was observed in the structures of the
protonated ligands, it is notable in the geometry of the
respective copper complexes. Coordination of 1 or 2 to
copper widens the C2-C3-C4 angle from 125.4(2)-126.1
(2)° in 1H and 2H to 129.9(2)-135.6(6)° in 3a-c and 4d and
reduces the Me-C2/4-C3 angle by 3-4° in 3a-c (Table 2).
The presence of the succinimide substituent at C3, however,
prevents this reduction in 4d and the Me-C2/4-C3 angle
remains practically unchanged. As a consequence, the alkyl
substituents on the nitrogen atoms are pushed further into
the copper coordination sphere in 4d, evidenced by an
increased average C2/4-N-C angle and a decreased average
unsymmetrical binding of the DMAP ligand (Δ(N-Cu-
NDMAP) = 2-10°). The in-plane coordination of the copper
atom (cf. complex bending angle of 4 ( 2° in Table 2) and the
N1-Cu1-N2 angles (101.3 ( 0.5°) are also strongly com-
parable to those found in 3c.
The lack of strong steric interactions in 4d (Figure 7,
Table 2) results again in a symmetrical coordination of the
nacnac and the isonitrile ligand, with the copper atom in the
mean plane of the complex. Cu-C and C-N distances of
˚
1.813(4) and 1.172(4) A, respectively, are at the extremes of
(23) Jazdzewski, B. A.; Holland, P. L.; Pink, M.; Young, V. G.;
Spencer, D. J. E.; Tolman, W. B. Inorg. Chem. 2001, 40, 6097.

Article
Organometallics, Vol. 28, No. 14, 2009 4095
Cu-N-C12/20 bond angle compared to 3a-c (Table 2),
thus indicating an increased steric crowding around the
copper center in this complex.
Experimental Section
All reactions were carried out under nitrogen atmosphere
using Schlenk or glovebox techniques. THF was distilled from
sodium/benzophenone. All other solvents were dried by passage
through activated aluminum oxide (MBraun SPS) and deoxy-
genated by repeated extraction with nitrogen. C6D6 was distilled
from Na and deoxygenated by three freeze-pump-thaw cycles.
CuOtBu25 and CuMes26 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, δ
7.15; C6D6, δ 128.02) or external reference (31P, 75% H3PO4).
Elemental analyses were performed by the Laboratoire d’Ana-
Spectroscopic Properties. Despite the differences observed
in reactivity with CuOtBu, electronic influences of the ali-
phatic substituent in complexes 3 were subtle at best. The
chemical displacement of the PPh3 ligand in 3a in its 31P
NMR spectra (δ =3.9 ppm) is intermediate between those
of (N,N0-Ar2nacnac)Cu(PPh3) complexes (Ar =Me3C6H2,
5.2 ppm;7 Ar = Me2C6H3, 5.4 ppm;5 Ar= iPr2C6H3,
3.6 ppm22). The signal for the succinimide-substituted com-
plex 4a is observed at 3.6 ppm. Average P-C bond lengths in
3a (Table 2), which should mirror the amount of Cu back-
donation into PPh3,24 are slightly longer (1.836 A) than in
˚
ꢀ
ꢀ
ꢀ
lyse Elementaire (Universite de Montreal).
2-(S-2-Phenylethyl)amino-4-(S-4-phenylethyl)iminopent-2-ene,
SS-1H. Acetylacetone (2.6 mL, 25 mmol), pTsOH (4.7 g,
25 mmol), and S-Ph(Me)CHNH2 (3.0 g, 25 mmol) were com-
bined with toluene (250 mL). The resulting white suspension was
refluxed for 3 h with the help of Dean-Stark apparatus to afford
a yellow solution. After cooling to room temperature, a second
equivalent of S-Ph(Me)CHNH2 (3.0 g, 25 mmol) was added.
The reaction mixture was then refluxed for 5 days. On cooling to
room temperature, a brown precipitate appeared. The suspen-
sion was added to an aqueous KOH solution (5.0 g, 0.45 M) and
stirred for 30 min. The phases were separated, and the aqueous
phase was extracted twice with toluene (400 mL). The combined
organic phases were dried over Na2SO4. Filtration and evapora-
tion of the solvent gave a brown oil, which was dissolved in
EtOH (10 mL). Colorless crystals formed at -20 °C after 1 day
(5.2 g, 70%). 1H NMR (CDCl3 400 MHz): δ 11.89 (bs, 1H, NH),
7.20-7.35 (m, 10H, Ph), 4.68 (q, 2H, J = 7 Hz, CH(Me)Ph),
4.48 (s, 1H, CH(CdN)2), 1.82 (s, 6H, Me(CdN)), 1.49 (d, 6H,
J = 7 Hz CH(Me)Ph). 13C NMR (CDCl3 101 MHz): δ 159.7
(CdN), 146.9 (ipso Ph), 128.4 (ortho Ph), 126.3 (para CH(Me)
Ph), 126.2 (meta Ph), 95.2 (CH(CdN)2), 55.9 CH(Me)Ph), 25.8
(Me(CdN)), 19.5 (CH(Me)Ph). Αnal. Calcd for C21H26N2: C,
82.31; H, 8.55; N, 9.15. Found: C, 81.67; H, 8.38; N, 9.14. Mp:
43.0-43.8 °C. [R]D20 = þ123(1) (c 10-3 g/mL, toluene).
5,7,22
˚
complexes with N-Ar substituents (1.829-1.834 A),
in
agreement with increased back-donation in 3a, but the
differences are hardly significant. Clearer indications of the
electronic differences can be observed in the isonitrile com-
plexes 3d and 4d. The stretching frequency νCN = 2111 cm-1
of the isonitrile ligand in 3d is lower than frequencies ob-
served in 2,6-xylylisonitrile complexes with N-Ar-substituted
nacnac ligands (νCN = 2121-2126 cm-1),7,9,23 indicating an
increased, but still weak back-donation (free isonitrile, νCN
=
2119 cm-1). Introduction of the succinimide substituent in 4d
displaced νCN by 6 to 2117 cm-1, in agreement with the
expected electron-withdrawing effect of this substituent.
Conclusions
Compared to its N-Ar-substituted analogues, ligand 1H is
somewhat more basic, but sterically more demanding. Intro-
duction of a succinimide substituent in 2H slightly decreases
its basicity, which is compensated by an increased steric
crowding in complexes with 2. The decreased stability of
complexes 3 and 4 toward disproportionation, which corre-
lates with their reduced reactivitytowardCuOtBu, seems tobe
of steric rather than of electronic origin. While partial, slow
conversion to the acetonitrile complex 3c and complete con-
version to the pyridine complex 3e was observed with 1H, no
acetonitrile complex and only partial conversion to the pyr-
idine complex 4e was observed for the slightly less basic, but
more bulky succinimide-substituted 2H. Formation of the
triphenylphosphine complex, which was fast in the case of 3a,
required several hours for 4a. In further agreement with steric
rather thanelectronic factorsisthe reported synthesis of stable
vinyltrimethylsilane and bis(trimethylsilane)acetylene copper
complexes of nacnac ligands with simple aliphatic N-substit-
uents8 and that of (nacnacBn)Cu(styrene).19 Overall, diketimi-
nate ligands with chiral aliphatic substituents on nitrogen
provedtobe easily accessibleand, atleast in the caseof1Hand
its derivatives, economically very attractive (<$10/g). Despite
the rotational freedom around the N-C* bond, the ligand
appears to be sufficiently rigid, as evidenced by comparable
torsion angles of the methylbenzyl substituent in all structu-
rallycharacterized complexes. Taking further intoaccount the
increased sterical crowding of the metal center evidenced by
the structural data, chiral diketimines such as 1H might be
interesting ligands for catalytic applications if the problem of
complex stability in the absence of strongly coordinating
ancillary ligands can be addressed. The effects of different
ligand backbone substitutions on complex stability are cur-
rently under investigation.
2-(R-2-Phenylethyl)amino-4-(R-4-phenylethyl)iminopent-2-ene,
RR-1H. Following the same procedure as for the S-enantiomer,
RR-1H was obtained in 67% yield. Αnal. Calcd for C21H26N2:
C, 82.31; H, 8.55; N, 9.15. Found: C, 81.99; H, 8.68; N, 9.07.
[R]2D0 = -123(1) (c 10-3 g/mL, toluene).
2-(S-2-Phenylethyl)amino-3-succinimido-4-(S-4-phenylethyl)-
iminopent-2-ene, SS-2H. n-BuLi (1.5 mL, 2.9 M, 4.4 mmol) was
added dropwise over a period of 45 min at room temperature to
a yellow solution of SS-1H (1.0 g, 3.3 mmol) in THF (50 mL).
After stirring for 6 h, N-bromosuccinimide (0.80 g, 4.5 mmol)
was added, and the resulting yellow suspension was heated for
24 h at 60 °C. The brown suspension obtained was cooled to
room temperature, treated with 1,4-dioxane (1 mL), and stirred
for a further 30 min. The mixture was filtered through a pad of
Celite, the solvent evaporated, and the product extracted into
toluene (50 mL). Evaporation of the solvent gave a brown solid
(0.90 g, 75%). 1H NMR (CDCl3, 400 MHz, 298 K): δ 13.20 (bs,
1H, NH), 7.19-7.32 (m, 10H, Ph), 4.69 (q, 2H, J = 7 Hz, CH
(Me)Ph), 2.76 (s, 4H, CH2C(dO)), 1.58 (s, 6H, MeC(dN)). 1.50
(d, 6H, J = 7 Hz, CH(Me)Ph). 13C NMR (CDCl3, 101 MHz,
298 K): δ 178.2 (CdO), 159.0 (CdN), 146.1 (ipso Ph), 128.5
(ortho Ph), 126.6 (para Ph), 126.1 (meta Ph), 105.1 (C(CN)2 C),
56.3 (CHMePh), 28.0 (MeC(dN)), 25.7 (CHMePh), 14.5
(CH2C(dO)). Anal. Calcd for C25H33N3O2: C, 74.41; H, 7.24;
N, 10.41. Found: C, 74.27; H, 7.27; N, 10.29. (Analogous
reactions with RR-1Li(THF) gave RR-2H.)
(25) Tsuda, T.; Hashimoto, T.; Saegusa, T. J. Am. Chem. Soc. 1972,
94, 658.
(26) Tsuda, T.; Yazawa, T.; Watanabe, K.; Fujii, T.; Saegusa, T. J.
(24) Orpen, A. G.; Connelly, N. G. Chem. Commun. 1985, 1310.
Org. Chem. 1981, 46, 192.

4096 Organometallics, Vol. 28, No. 14, 2009
Oguadinma and Schaper
(SS-1)Cu(PPh3), 3a. SS-1H (250 mg, 0.82 mmol), mesityl
copper (150 mg, 0.83 mmol), CuOtBu (11 mg, 0.082 mmol), and
PPh3 (220 mg, 0.84 mmol) were dissolved in toluene (5 mL) to
give a yellow-brown solution. After stirring for 1 h, the solution
was concentrated to half its volume, layered with hexane (4 mL),
and kept at -35 °C. Yellow crystals formed after 1 day (411 mg,
CH(CdN)2), 2.05 (s, 6H, C(dN)Me), 1.84 (s, 6H, C6H3Me2) 1.
80 (d, 6H, J = 7 Hz, (CH(Me)Ph). 13C NMR (C6D6, 101 MHz,
298 K): δ 163.3 (CdN), 149.0, 134.6, 128.2, 128.1, 127.9, 127.2,
125.9, 95.6 (CH(CdN)2), 59.0 (CHMePh), 27.6 (C(dN)Me),
23.0 (CHMePh), 18.5 (C6H3Me2). Two peaks were elusive.
Anal. Calcd for C30H34N3Cu: C, 72.04; H, 6.85; N, 8.40. Found:
1
80%). H NMR (C6D6, 400 MHz): δ 6.84-7.42 (m, 25H, CH
C, 71.81; H, 7.01; N, 8.13. IR (toluene): νCN = 2114 cm-1
.
(Me)Ph and PPh3), 5.01 (q, 2H, J = 7 Hz, CH(Me)Ph), 4.84 (s,
1H, CH(CdN)2), 2.00 (s, 6H, MeC(dN)), 1.36 (d, 6H, CH(Me)
Ph, J = 7 Hz). 13C NMR (C6D6, 101 MHz): δ 164.0 (CN), 148.3
(ipso CH(Me)Ph), 134.4 (d, JCP = 4 Hz, ortho PPh3), 129.4
(ortho or meta CH(Me)Ph), 128.5 (d, JCP = 2 Hz, meta PPh3),
128.1, 127.1 (ortho or meta CH(Me)Ph), 125.7, 96.4 (CH
(CdN)2), 58.9 (CH(Me)Ph)., 25.4 (MeC(dN)), 23.7 (CH(Me)
Ph) (ipso PPh3 elusive). 31P{1H} NMR (C6D6, 75 MHz): δ 3.9.
Anal. Calcd for C39H40N2P1Cu: C, 74.20; H, 6.39; N, 4.44.
Found: C, 73.89; H, 6.52; N, 4.37.
(SS-2)CuPPh3, 4a. SS-2H (126 mg, 0.31 mmol), CuOtBu (42
mg, 0.31 mmol), and PPh3 (78 mg, 0.30 mmol) were dissolved in
toluene (3 mL) to give a brown solution. After stirring for 15
min, the solution was evaporated. Addition of ether (6 mL) to
the resulting brown oil gave a light brown precipitate. Decanta-
tion, washing with ether (6 mL), and drying yielded 100 mg
(47%) of an off-white powder. 1H NMR (C6D6, 400 MHz, 298
K): δ 6.96-7.48 (m, 25H, CH(Me)Ph and PPh3), 4.89 (q, 2H, J
= 7 Hz CH(Me)Ph), 1.97 (s, 4H, CH2C(dO)), 1.77 (s, 6H, C
(dN)Me), 1.42 (d, 6H, J = 7 Hz, CH(Me)Ph). 13C NMR (C6D6,
101 MHz, 298 K): δ 178.4 (CdO), 163.1 (C=N), 147.5 (ipso CH
(Me)Ph), 134.2 (d, J = 14 Hz, ortho PPh3), 129.5 (ortho or meta
CH(Me)Ph), 128.7 (d, J = 9 Hz, meta PPh3), 127.1 (ortho or
meta CH(Me)Ph), 126.0, 98.3 (CH(CdN)2), 59.3 (CH(Me)Ph),
28.0 (CH2C(dO)), 24.8 (MeC(dN)), 17.7 (CH(Me)Ph). Two
signals missing. 31P{1H} NMR (C6D6, 75 MHz, 298 K): δ 3.6.
Anal. Calcd for C43H43N3O2PCu: C, 70.91; H, 5.95; N, 5.77.
Found: C, 70.26; H, 5.99; N, 5.69.
(SS-2)CuCN(2,6-Me2C6H3), 4d. SS-2H (100 mg, 25.0 μmol),
2,6-xylylisonitrile (32.0 mg, 25 μmol), and CuOtBu (40 mg, 27
μmol) were dissolved in toluene (4 mL) to afford a dark brown
solution. After stirring for 15 min, the solution was layered with
hexane (4 mL). Dark yellow crystals formed after 2 days (68 mg,
47%). 1H NMR (C6D6, 400 MHz, 298 K): δ 6.94-7.48 (m, 10H,
CHMePh), 6.69 (t, 1H, J = 8 Hz, para C6H3Me2), 6.52 (d, 2H,
J = 8 Hz, meta C6H3Me2), 5.00 (q, 2H, J = 7 Hz, CH(Me)Ph),
2.01 (s, 4H, CH2C(dO)), 1.85 (s, 6H, C(dN)Me), 1.78 (s, 6H,
C6H3Me2) 1. 77 (d, 6H, J = 7 Hz, (CH(Me)Ph). 13C NMR
(CDCl3, 101 MHz, 298 K): δ 178.2 (CdO), 159.0 (CdN), 148.3,
134.6, 127.9, 127.1, 126.1, 97.5 (CH(CdN)2), 59.3 (CHMePh),
28.0 (MeC(dN)), 26.7 (CHMePh), 18.5 (CH2C(dO)), 17.2
(C6H3Me2). Four peaks are elusive. Anal. Calcd for
C34H37N4O2Cu: C, 68.38; H, 6.24; N, 19.38. Found: C, 68.12;
H, 6.31; N, 9.05. IR (toluene): νCN = 2117 cm-1
General Experimental Procedure for NMR Experiments. A
vial was charged with SS-1H (10 mg, 33 μmol), CuOtBu (4-5
mg, 33-40 μmol), or 2,4,6-mesityl copper (6 mg, 40 μmol) with
catalytic amounts of CuOtBu (3-4 μmol) and the respective
Lewis base (33-159 μmol). C6D6 (0.6-0.7 mL) was added.
After shaking thoroughly to obtain a homogeneous solution,
the content was transferred to a J. Young tube. 1H NMR (C6D6,
400 MHz) were taken immediately, after1 h, and, in some cases,
after 1 day.
(SS-1)Cu(NCMe), 3c. δ 7.07-7.57 (m, 10H, CH(Me)Ph),
5.01 (q, 2H, J = 6 Hz CH(Me)Ph), 4.60 (s,1H, CH(CdN)2),
2.02 (s, 6H, MeC(dN)), 1.78 (d, 6H, J = 6 Hz, CH(Me)Ph), 0.73
(s, 3H, NCMe). Only 60% conversion was observed before
decomposition.
(SS-1)Cu(DMAP), 3b. CuOtBu (22 mg, 0.17 mmol), SS-1H
(50 mg, 0.17 mmol), and DMAP (20 mg, 0.17 mmol) were
dissolved in toluene (1 mL) to give a yellow solution. After
stirring for 15 min, the solution was evaporated. The resulting
yellow solid was suspended in toluene/hexane 1:1 (2 mL) and
filtered through a plug of Celite, and the filtrate was kept at
-30 C. Yellow crystals formed after 4 h (53 mg, 65%). 1H NMR
(C6D6 400 MHz, 298 K): δ 7.09-7.63 (m, 12H, CH(Me)Ph and
ortho DMAP CH), 5.58 (bs, 2H, meta DMAP) 5.07 (q, 2H, J =
6 Hz CH(Me)Ph), 4.78 (s,1H, CH(CdN)2), 2.12 (s, 6H, DMAP
Me) 1.93 (s, 6H, MeC(dN)), 1.60 (d, 6H, J = 6 Hz CH(Me)Ph).
13C NMR (C6D6 101 MHz, 298 K): δ 162.7 (CdN), 150.0 (ortho
DMAP) 149.1 (ipso Ph), 128.1 (meta Ph), 127.2 (ortho Ph), 125.6
(para Ph), 106.9 (meta DMAP), 102.8 (para DMAP) 94.6 (CH
(CdN)2), 58.9 (CHMePh), 40.0 (DMAP Me), 26.2 (MeC(dN)),
23.1 (CHMePh). Anal. Calcd for C28H35N4Cu: C, 67.68; H,
7.36; N, 11.69. Found: C, 67.24; H, 7.13; N, 11.08.
(SS-1)Cu(NCMe), 3c. (1) Mesitylcopper (60 mg, 0.33 mmol),
CuOtBu (4 mg, 0.03 mmol), and SS-1H (100 mg, 0.33 mmol)
were suspended in acetonitrile (3 mL). Toluene (3 mL) was
added until a clear solution was obtained. The solution was
stirred for 1 h, concentrated to half its volume, and kept at -35
°C. Yellow crystals formed after 1 day (98 mg, 72%).
(2) SS-1H (167 mg, 0.60 mmol), CuOtBu (85 mg, 0.62 mmol),
and MeCN (200 μL) were mixed in Et2O (5 mL) to afford a
yellow solution. The solution was kept at -35 °C. Yellow
1
crystals formed after 1 day (132 mg, 55%). H NMR (C6D6,
400 MHz, 298 K): δ 7.07-7.57 (m, 10H, CH(Me)Ph), 5.01 (q,
2H, J = 6 Hz CH(Me)Ph), 4.60 (s, 1H, CH(CdN)2), 2.02 (s, 6H,
MeC(dN)), 1.78 (d, 6H, J = 6 Hz CH(Me)Ph), 0.73 (s, 3H,
NCMe). 13C NMR (C6D6 101 MHz): δ 163.1 (CdN), 147.6 (ipso
Ph), 128.2 (meta Ph), 127.2 (ortho Ph), 125.8 (para Ph), 116.1
(ΝCCH3) 95.1 (CH(CdN)2), 59.2 (CH(Me)Ph), 27.3 (MeC
(dN)), 23.0 (CH(Me)Ph), 0.2 (ΝCCH3). Anal. Calcd for
C23H28N3Cu: C, 67.37; H, 6.88; N, 10.25. Found: C, 67.14; H,
7.07; N, 10.11. IR (toluene): νCN = 2254 cm-1
.
In acetonitrile-free C6D6 solutions of 3c a second isomer (B) is
observed (see text): 1H NMR (C6D6, 400 MHz, 298 K) δ 7.05-
7.59 (m, 10H, CH(Me)Ph), 4.92 (s,1H, CH(CdN)2), 4.41 (q, 2H,
J = 6 Hz CH(Me)Ph), 2.35 (bs, 6H, MeC(dN)), 1.45 (d, 6H,
J = 6 Hz CH(Me)Ph), 0.50 (s, 3H, NCMe). 13C NMR (C6D6,
101 MHz): δ 167.5 (CdN), 146.4 (ipso Ph), 128.6 (meta or ortho
Ph), 127.1 (ortho or meta Ph), 126.7 (para Ph), 116.1 (ΝCCH3)
95.1 CH(CdN)2), 59.2 (CH(Me)Ph), 30.4 (MeC(dN), 26.1 (CH
(Me)Ph), 0.2 (NCCH3).
(SS-1)CuPy, 3e. δ 6.51-7.40 (m, 15H, CH(Me)Ph and Py),
4.96 (q, 2H, J = 6 Hz CH(Me)Ph), 4.72 (s,1H, CH(CdN)2), 2.09
(s, 6H, MeC(dN)), 1.40 (d, 6H, J = 6 Hz, CH(Me)Ph).
(SS-1)Cu(PMe3), 3f. δ 7.10-7.53 (m, 10H, CH(Me)Ph), 4.94
(q, 2H, J = 6 Hz CH(Me)Ph), 4.72 (s, 1H, CH(CdN)2), 2.04 (s,
6H, MeC(dN)), 1.57 (d, 6H, J = 6 Hz, CH(Me)Ph), 0.35 (bs,
9H, PMe3).
(SS-1)Cu(CNC6H3Me2), 3d. SS-1H (100 mg, 33.0 μmol),
CNC6H3Me2 (43.0 mg, 33 μmol), and CuOtBu (45 mg, 33
μmol) were dissolved in ether (10 mL) to afford a bright yellow
solution. After stirring for 15 min, the solution was evaporated
(SS-2)CuPy, 4e. δ 6.60-8.52 (CH(Me)Ph and Py), 4.93 (q,
2H, J = 6 Hz CH(Me)Ph), 1.86 (s, 4H, C(dO)CH2), 1.51-1.52
(MeC(dN)), 1.38 (d, 6H, J = 6 Hz CH(Me)Ph). Several peaks
overlap with those of 2H.
X-ray Diffraction Studies. Diffraction data were collected on a
Bruker Smart Bruker Smart APEX II with graphite-monochro-
mated Mo KR radiation (3aþc) and a Bruker SMART
6000, equipped with a rotating anode source and Mirror Montel
1
to give a yellow-brown oil (152 mg, 92%) (4 mL). H NMR
(C6D6, 400 MHz, 298 K): δ 6.99-7.56 (m, 10H, CHMe(Ph)),
6.71 (t, 1H, J = 8 Hz, para C6H3Me2), 6.55 (d, 2H, J = 8 Hz,
meta C6H3Me2), 5.03 (q, 2H, J = 7 Hz, CH(Me)Ph), 4.71 (s, 1H,

Article
Organometallics, Vol. 28, No. 14, 2009 4097
200-monochromated Cu KR radiation. Cell refinement and data
reduction were done using APEX2.27 Structures were solved by
direct methods using SHELXS97 and refined on F2 by full-matrix
least-squares using SHELXL97.28 All non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were refined isotropically
on calculated positions using a riding model. Further exp-
erimental details are listed in Table 3 and given in the Supporting
Information. Refinement of the Flack x parameter in 1H and 2H
resulted in unacceptable standard deviations, and Friedel pairs have
thus been merged prior to refinement for this structure.
Acknowledgment. Funding for this research was pro-
vided by the Natural Sciences and Engineering Research
ꢀ
Council of Canada and the Universite de Montreal. We
thank Francine Belanger and Dr. Michel Simard for
ꢀ
ꢀ
their support with the crystal structure determinations,
ꢀ
and Prof. Dr. Andre B. Charette for the use of his
polarimeter.
Supporting Information Available: Details of the X-ray dif-
fraction studies (CIF) and calculation of the lateral aperture
angle. This material is available free of charge via the Internet at
http://pubs.acs.org.
(27) APEX2, Release 2.1-0; Bruker AXS Inc.: Madison, WI, 2006.
(28) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.