The presence of [Ar2Cu]- and [(RC≡C)2Cu]- homocuprate moieties in the neutral mixed cuprate (see abstract)

Article abstract of DOI:10.1021/om030082a

The neutral, mixed 2:2 aryl-alkynyl-cuprates [Cu₂Li₂(C≡CR)₂Ar₂] (Ar = [C₆H₄{CH₂N(Me)CH₂-CH₂ NMe₂}-2]^-; R = C₆H₄Me-4 (3a) or C₆H₄SiMe₃-4 (3b)) are the first examples of cuprates that contain two different organic homocuprate parts ([Ar-Cu-Ar]^- and [(RC≡C)-Cu-(C≡CR)]^-) in one assembled structure. Each part has a two-coordinate Cu atom in linear geometry. They are held together by Li-C_ipso interactions to two Li atoms. Tetrahedral four-coordination at the Li centers is completed by N,N′-chelation of the ortho-diamine substituent of the Ar ligand. Compound 3 is formed as the only reaction product in almost quantitative yield when LiAr and Cu(C≡CR) aggregates are mixed together in equimolar amounts. This cuprate is an example of ion-pairing between two different homocuprate anions and two Li cations.

Full text of DOI:10.1021/om030082a

2312
Organometallics 2003, 22, 2312-2317
Th e P r esen ce of [Ar 2Cu ]- a n d [(RCtC)2Cu ]-
Hom ocu p r a te Moieties in th e Neu tr a l Mixed Cu p r a te
[Cu 2Li2(CtCR)2Ar 2] (Ar )
C6H4{CH2N(Me)CH2CH2NMe2}-2; R ) C6H4Me-4 or
C6H4SiMe3-4)
Claudia M. P. Kronenburg,† J ohann T. B. H. J astrzebski,† Martin Lutz,‡
Anthony L. Spek,‡,# and Gerard van Koten*,†
Debye Institute, Department of Metal-Mediated Synthesis, Utrecht University, Padualaan 8,
3584 CH Utrecht, The Netherlands, and Bijvoet Center for Biomolecular Research, Crystal and
Structural Chemistry, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
Received February 4, 2003
The neutral, mixed 2:2 aryl-alkynyl-cuprates [Cu2Li2(CtCR)2Ar2] (Ar ) [C6H4{CH2N(Me)CH2-
CH2NMe2}-2]-; R ) C6H4Me-4 (3a ) or C6H4SiMe3-4 (3b)) are the first examples of cuprates
that contain two different organic homocuprate parts ([Ar-Cu-Ar]- and [(RCtC)-Cu-
(CtCR)]-) in one assembled structure. Each part has a two-coordinate Cu atom in linear
geometry. They are held together by Li-Cipso interactions to two Li atoms. Tetrahedral four-
coordination at the Li centers is completed by N,N′-chelation of the ortho-diamine substituent
of the Ar ligand. Compound 3 is formed as the only reaction product in almost quantitative
yield when LiAr and Cu(CtCR) aggregates are mixed together in equimolar amounts. This
cuprate is an example of ion-pairing between two different homocuprate anions and two Li
cations.
In tr od u ction
Although the influence of the nature of organic and
inorganic anions, ligands, and solvents on the formation
of pure organocopper(I) compounds has been studied
extensively,1-8 our understanding of the influence of
these factors on the self-assembling process that gives
rise to the actual organocopper(I) species is still in its
infancy. Organocopper species commonly are poly-
nuclear compounds of type CunRn which are formed by
self-assembly of a number of monomeric CuR species.
F igu r e 1. Schematic representation of the arylbromo-
cuprate [CuLi2BrAr2] (1) (Ar ) C6H4{CH2N(Me)CH2CH2-
NMe2}-2) and the hetero-organocopper compound [Cu6Br2-
Aryl4] (2) (Aryl ) C6H4NMe2-2).
* To whom correspondence should be addressed. E-mail:
g.vankoten@chem.uu.nl. Fax: +31 30 2523615.
† Debye Institute.
This process may involve other moieties present in
solution, e.g., a metal salt MX or another organometallic
species MR′, and we have extensively demonstrated that
the formation of self-assembled species such as CuR/
MX or CuR/MR′ may interfere with the preparation of
pure organocopper compounds.9-13 Some examples are
[CuLi2BrAr2] (1)13 (Ar ) C6H4{CH2N(Me)CH2CH2NMe2}-
2) and [Cu6Br2Aryl4] (2)10 (Aryl ) C6H4NMe2-2); see
Figure 1.
‡ Bijvoet Center for Biomolecular Research.
#
To whom correspondence on crystallographic data should be
addressed.
(1) (a) van Koten, G.; Noltes, J . G. In Comprehensive Organometallic
Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Perga-
mon: Oxford, 1981; Vol. II, Chapter 7. (b) J anssen, M. D.; Corsten, M.
A.; Spek, A. L.; Grove, D. M.; van Koten, G. Organometallics 1996,
15, 2810, and references therein.
(2) Hwang, C.-S.; Olmstead, M. M.; He, X.; Power, P. P. J . Chem
Soc., Dalton Trans. 1998, 2599.
(3) Wehman, E.; van Koten, G.; Erkamp, J . C. M.; Knotter, D. M.;
J astrzebski, J . T. B. H.; Stam, C. H. Organometallics 1989, 8, 94, and
references therein.
(4) Kapteijn, G. M.; Wehman-Ooyevaar, I. C. M.; Grove, D. M.;
Smeets, W. J . J .; J astrzebski, J . T. B. H.; Spek, A. L.; van Koten, G.
Angew. Chem., Int. Ed. Engl. 1993, 32, 72.
These species, which are both relevant to the present
study, are neutral and formed directly from the reaction
of the corresponding aryllithium compound with copper
(5) (a) van Koten, G.; Noltes, J . G. J . Organomet. Chem. 1975, 102,
551. (b) Wehman, E.; van Koten, G.; J astrzebski, J . T. B. H.; Rotteveel,
M. A.; Stam, C. H. Organometallics 1988, 7, 1477.
(6) Hope, H.; Olmstead, M. M.; Power, P. P.; Sandell, J .; Xu, X. J .
Am. Chem. Soc. 1985, 107, 4337.
(7) Hwang, H.; Power, P. P. Organometallics 1999, 18, 697.
(8) (a) Gschwind, R. M.; Rajamohanan, P. R.; J ohn, M.; Boche, G.
Organometallics 2000, 19, 2868. (b) J ohn, M.; Auel, C.; Behrens, C.;
Marsch, M.; Harms, K.; Bosold, F.; Gschwind, R. M.; Rajamohanan,
P. R.; Boche, G. Chem. Eur. J . 2000, 6, 3060.
(9) van Koten, G.; Leusink, A. J .; Noltes, J . G. J . Organomet. Chem.
1975, 84, 117.
(10) van Koten, G.; ten Hoedt, R. W. M.; Noltes, J . G. J . Org. Chem.
1977, 42, 2705.
(11) ten Hoedt, R. W. M.; Noltes, J . G.; van Koten, G.; Spek, A. L.
J . Chem. Soc., Dalton Trans. 1978, 1800.
(12) van Koten, G.; Noltes, J . G. J . Chem. Soc., Chem Commun.
1975, 575.
(13) Kronenburg, C. M. P.; Amijs, C. H. M.; J astrzebski, J . T. B. H.;
Lutz, M.; Spek, A. L.; van Koten, G. Organometallics 2002, 21, 4662.
10.1021/om030082a CCC: $25.00 © 2003 American Chemical Society
Publication on Web 04/23/2003

[Ar2Cu]- and [(RCtC)2Cu]- Homocuprate Moieties
Organometallics, Vol. 22, No. 11, 2003 2313
bromide. These reagents have to be used in the proper
2:1 ratio to obtain [CuLi2BrAr2] (1), but [Cu6Br2Aryl4]
(2) is always formed initially, irrespective of the ratio
of the two reactants. The organocopper compound
[CuAryl]n is formed only after prolonged reaction of
copper bromide with aryllithium.
The two bromide ions in 2 can be replaced by other
halide or also alkynyl anions while the overall [Cu6X2-
Aryl4] structure is retained.10 These observations point
to a considerable stability of the [Cu6Aryl4]2+ skeleton,
which obviously can be formed by self-assembly from
various combinations of reagents.
The present paper describes a study of reactions of
[CuLi2BrAr2] (1) with organolithium compounds, in
particular lithium acetylides, which were aimed at
preparing the first examples of organocuprates contain-
ing different organic anions. In fact, 1 is the first
example of a neutral heterocuprate with a CuLi2
structural motif that has been used in computational
studies of reactions of higher-order cuprates.14 Struc-
tural information on related hetero-organocuprates
would greatly assist these latter studies.
upon exposure to air. They are soluble in toluene,
benzene, and THF and slightly soluble in diethyl ether
and pentane.
That the formation of 3 is driven by thermodynamics
became evident from the observation that irrespective
of the ratio of the starting materials, [Li2(C6H4{CH2N-
(Me)CH2CH2NMe2}-2)2] and [CuCtCC6H4R-4], 3 is
always formed, with one of the unreacted starting
materials remaining that was present in excess. This
was furthermore confirmed by the observation that the
attempted substitution of the bromide anion in [CuLi2-
Br(C6H4{CH2N(Me)CH2CH2NMe2}-2)2] (1) with a sto-
ichiometric amount of [LiCtCC6H4R-4] (eq 2) leads to
the formation of 3 and [Li2(C6H4{CH2N(Me)CH2CH2-
NMe2}-2)2]. These observations indicate that among
other aggregates that might be formed during the
synthesis of 3 it is 3 that is thermodynamically the most
stable one.
We here report the synthesis and characterization of
novel mixed cuprate complexes [Cu2Li2(CtCR)2Ar2] (3)
(Ar ) C6H4{CH2N(Me)CH2CH2NMe2}-2), which have
been obtained both from the stoichiometric reaction of
[LiAr] with [Cu(CtCR)] (R ) C6H4Me-4 or C6H4SiMe3-
4) and from the reaction of [CuLi2BrAr2] with [Li(Ct
CR)].
Solid Sta te Str u ctu r e of 3a a n d 3b. Both for 3a
and 3b the crystal structures were determined, showing
that their overall structural geometries are identical;
see Figure 2. Selected bond distances, angles, and
torsion angles are given in Table 1. Only slight but not
significant differences were observed in bond distances
and angles; therefore the structure of 3a is described
below in detail. Corresponding bond distances and
angles for 3b are given in Table 1 and the Supporting
Information.
Compound 3a contains two linear anionic units, [Ar-
Cu-Ar]- and [(RCtC)-Cu-(CtCR)]-, linked together
by two lithium cations. These two lithium cations are
tetrahedral four-coordinated by N,N′-chelate coordina-
tion of the diamine functionalities of the ortho-CH2N-
(Me)CH2CH2NMe2 substituent and by Cipso atoms of one
aryl and one acetylide anion. Thus the alkynyl and aryl
units each bridge one Cu and one Li atom. The cen-
trosymmetric unit cell of the solid state structure of 3a
contains an SNSN/RNRN enantiomeric pair. Figure 2
shows the SNSN stereoisomer (vide infra).18
Resu lts a n d Discu ssion
P r ep a r a tion of th e 2:2 Mixed Bisa r yl-, Bis(a lk yn -
yl)cu p r a tes [Cu 2Li2(CtCC6H4R-4)2Ar 2] (Ar ) [C6H4-
{CH2N(Me)CH2CH2NMe2}-2]-, R ) Me (3a ) or SiMe3
(3b)). Addition of an equimolar amount of [Li2(C6H4-
{CH2N(Me)CH2CH2NMe2}-2)2] (4) to copper(I) p-tolyl-
acetylide [CuCtCC6H4Me-4]15 or copper(I) p-trimeth-
ylsilylphenylacetylide [CuCtCC6H4SiMe3-4] in toluene
at 0 °C gives the 2:2 complexes containing two different
homocuprate units [Cu2Li2(C6H4{CH2N(Me)CH2CH2-
NMe2}-2)2(CtCC6H4R-4)2] (3a and 3b, respectively) as
the only reaction product (eq 1). Complexes 3 are
The two linear anionic units, [Ar-Cu-Ar]- and
[(RCtC)-Cu-(CtCR)]-, are mutually orthogonally
oriented. The two Cu atoms and the two Li atoms are
nearly in one plane ( Cu(1)-Li(1)-Cu(2)-Li(2) )
2.17(13)°). This in-plane position of the metal atoms is
comparable to that found in [Cu2Li2Aryl4] (Aryl ) C6H4-
CH2NMe2-2) ( Cu(1)-Li(1)-Cu(2)-Li(2) ) 0.448°).17
The (aryl)Cipso-Cu bonds are significantly longer than
the (acetylide)CR-Cu bonds (d(mean) 1.933 and 1.869
Å, respectively) which reflects the differences in s-
character (sp2 vs sp) and steric influences of Cipso in the
obtained as off-white powders, which are extremely
sensitive toward air. The solid immediately turns yellow
(15) Castro, C. E.; Caughan, E. J .; Owsley, D. C. J . Am. Chem. Soc.
1966, 31, 4071.
(16) Eaborn, C.; Thompson, A. R.; Walton, D. R. M. J . Chem. Soc. C
1967, 15, 1364.
(17) van Koten, G.; J astrzebski, J . T. B. H.; Mu¨ller, F.; Stam, C. H.
J . Am. Chem. Soc. 1985, 107, 697.
(18) Upon nitrogen to lithium coordination of the -N(Me) group,
this nitrogen atom becomes a stereogenic center. The stereochemistry
of cuprates of type CuLi2BrAr2 is described in ref 13.
(14) (a) Nakamura, E.; Yamanaka, M. J . Am. Chem. Soc. 1999, 121,
8941. (b) Nakamura, E.; Mori, S. J . Am. Chem. Soc. 1998, 120, 8273.
(c) Nakamura, E.; Mori, S.; Nakamura, M.; Morokuma, K. J . Am.
Chem. Soc. 1997, 119, 4887. (d) Nakamura, E.; Mori, S.; Morokuma,
K. J . Am. Chem. Soc. 1997, 119, 4900. (e) Mori, S.; Nakamura, E.
Tetrahedron Lett. 1999, 40, 5319.

2314 Organometallics, Vol. 22, No. 11, 2003
Krononburg et al.
F igu r e 2. (a) Displacement ellipsoid plot (50% probability) of 3a . Hydrogen atoms are omitted for clarity. Only the major
disorder component of the ortho-diamine substituent (N11 f N12) is shown. (b) Displacement ellipsoid plot (50% probability)
of 3b. Hydrogen atoms and benzene solvent molecules are omitted for clarity.
Ta ble 1. Selected Bon d Dista n ces (Å), An gles
(d eg), a n d Tor sion An gles (d eg) for 3a a n d 3ba
Ta ble 2. Cu --Cu Dista n ces (Å) in a Ser ies of Ar yl-,
Alk yl-, a n d Mixed Ar yl-a lk yn ylcu p r a tes.
3a
3b
d(mean)
entry
compound
Cu-Cu
2.47-2.85 11
2.67
ref
C31-C32
C41-C42
Cu1-C11
Cu1-C21
Cu2-C31
Cu2-C41
Li1-C11
Li2-C21
Li1-C31
Li2-C41
Cu1-Cu2
Li1-N11
Li1-N12
Li2-N21
Li2-N22
Cu1-Li1
Cu1-Li2
Cu2-Li1
Cu2-Li2
1.219(3)
1.217(3)
1.932(2)
1.933(2)
1.871(2)
1.868(2)
2.513(4)
2.498(4)
2.219(4)
2.233(4)
2.6723(4)
2.045(4)
2.056(4)
2.094(4)
2.096(4)
2.678(4)
2.764(4)
2.686(4)
2.755(4)
1.218(3)
1.220(3)
1.943(2)
1.940(2)
1.868(2)
1.869(2)
2.432(5)
2.435(4)
2.258(4)
2.241(4)
2.6282(4)
2.102(4)
2.088(4)
2.091(4)
2.095(4)
2.750(4)
2.706(4)
2.903(4)
2.813(4)
1
2
3
4
5
6
7
[Cu6(CtCC6H4Me-4)2Aryl4]
[Cu2Li2(CtCC6H4Me-4)2Ar2] (3)
[Cu3{SC6H4(CH2NMe2)-2}2(CtCt-Bu)]2 2.46-2.84 20a
[Cu3(S-1-C10H6NMe2-8)2(CtCt-Bu)]2
[Cu2Li2(C6H4{CH2NMe2}-2)4]
[CuLi(CN)t-Bu]∞
a
2.47-2.69 20b
2.67
2.71
2.39
17
19
7
[Cu2I2(C6H3Mes2-2,6)][Li(THF)4]
a
Present work.
the Cu-Cu distances in the 1:1 cyanocuprate [(t-Bu)-
Cu(CN)Li(Et2O)2]∞ (ca. 2.71 Å)19 (Table 2).
An interesting aspect of the molecular structure of
3a is the relatively short Cu-CR bond of 1.869 Å (mean),
which is also shorter than the corresponding bonds for
previously reported mixed organoalkynylcopper com-
pounds11,20 (Table 2). In the compounds in entries 3 and
4 of Table 2 two different types of bonding for the
CtCt-Bu units are present. One alkynyl unit in these
cuprates is µ3-η1 coordinated (end-on). The other unit
is µ3-η2 bonded (side-on) to the other Cu atom. Such side-
on coordination results in an elongated Cu-CR distance.
The Cu-Cu distances found, in 3a (2.6723(4) Å) and
3b (2.6282(4) Å) are similar to that in the neutral
arylcuprate [Cu2Li2(C6H4{CH2NMe2}-2)4]17 (2.666 Å)
and somewhat smaller than that found in Boche’s 1:1
C11-Cu1-C21
C31-Cu2-C41
Cu1-C11-Li1
Cu1-C21-Li2
Cu2-C31-Li1
Cu2-C41-Li2
Cu2-C31-C32
Cu2-C41-C42
166.91(9)
173.15(9)
72.76(11)
76.01(11)
81.63(12)
83.90(12)
169.5(2)
165.10(9)
176.43(9)
77.00(12)
75.45(11)
88.91(13)
85.88(13)
175.7(2)
176.1(2)
169.7(2)
Li2-Cu2-Li1-Cu1
2.17(13)
-2.26(12)
a
The estimated standard deviations are given in parentheses.
19
cyanocuprate [CuLi(CN)(t-Bu)]2 (2.713 Å) (entry 6 in
Table 2). Following this author’s view of Cu(d10)-
Cu(d10) bonding in such cuprates,19 which contain a
perpendicular arrangement of two organocopper units,
compound 3a could be another example of a cuprate
containing such Cu(d10) interactions.
Another interesting aspect of the structure of the
mixed 2:2 aryl-alkynyl-cuprate 3a concerns the fact that
the Cipso-Li bond distances in 3a are ca. 0.2 Å larger
(2.498(4) and 2.513(4) Å) than in the aryl-bromo-
cuprates. These observations suggest that the electron-
deficient type of bonding of Cipso between copper and
Cu-C bonding. The two different C-Cu-C units have
bond angles of 166.91(9)° ( Cipso(11)-Cu(1)-Cipso(21))
and 173.15(9)° ( CR(31)-Cu(2)-CR (41)), respectively.
The angle in the [alkynyl-Cu-alkynyl] anion is closer
to 180° than found in the [Ar-Cu-Ar] anion. The (aryl)-
Cipso-Li distances in 3a are longer than those reported
for the related arylcuprate [Cu2Li2(C6H4{CH2NMe2}-
2)4]17 (2.513(4) and 2.498(4) versus 2.385(7) Å) and much
longer than the (acetylide)CR-Li distances (2.219(3) and
2.233(4) Å). The Cu-(aryl)Cipso-Li angles in 3a (72.76-
(11)° and 76.01(11)° are comparable to those in [CuLi2-
BrAr2] (1) (77.63°).13 Finally, the Cu-Cu distance found
in 3a (2.6723(4) Å) is longer than the ca. 2.39 Å found
in the organoiodocuprate [Cu2I2(2,6-Mes2C6H3)][Li-
(THF)4] (Mes ) C6H2Me3-2,4,6)7 but comparable with
(19) Boche, G.; Bosold, F.; Marsch, M.; Harms, K. Angew. Chem.,
Int. Ed. 1998, 37, 1684.
(20) (a) Knotter, D. M.; Spek, A. L.; van Koten, G. J . Chem. Soc.,
Chem. Commun. 1989, 1738. (b) J anssen, M. D.; Donkervoort, J . G.;
van Berlekom, S. B.; Spek, A. L.; Grove, D. M.; van Koten, G. Inorg.
Chem. 1996, 35, 4752.

[Ar2Cu]- and [(RCtC)2Cu]- Homocuprate Moieties
Organometallics, Vol. 22, No. 11, 2003 2315
cuprate 3a shows one resonance pattern with two
distinct singlet resonances (∆δ ca. 1 ppm) for the NMe2
groups of the aryl ligands and one AB pattern for the
benzylic protons. These observations indicate that at
room temperature both the benzylic (NMe) and di-
methylamino (NMe2) nitrogen atoms coordinate to a
lithium atom. The presence of single resonance patterns,
for both the aryl ligands and the p-tolylacetylene
ligands, points to the presence of an inversion center
in 3a in solution, which implies that the structure of
3a found in the solid state is retained in solution. The
13
C
resonance of 3a (benzene-d6, 298 K) has a line
ipso
width of 15 Hz. From this, and data obtained for species
such as 1 (1J (13Cipso-7Li) ) 7 Hz),13 it follows that an
average J (13Cipso-7Li) of about 5 Hz is present in 3a .
1
Both 13C signals of the CtC units are broad (line width
ca. 20 Hz), which is in accord with a 13C nucleus being
coupled to one 7Li nucleus with an average 1J (13CR-
7Li) of about 7 Hz. Attempts to resolve the expected
quartet multiplicity (1:1:1:1 intensity distribution) failed
(toluene-d8, 243 K, 75 MHz).
F igu r e 3. Possible bonding modes of an alkynyl group
bonded to copper and lithium.
lithium is far less pronounced in 3a than in other known
neutral cuprates.13,17 This supports our idea that 3a can
be best seen as consisting of two anionic homocuprate
parts, namely, [Ar-Cu-Ar] and [RCtC-Cu-CtCR],
with the two Li cations acting as bridges between the
anionic parts.
Coordination of the benzylic nitrogen (NMe) to lithium
turns the NMe atom into a stereogenic center. As a
result, 3a may exist as four diastereoisomers and in the
solid state it appears to be the SNSN/RNRN enantiomeric
pair. Since for both the aryl and p-tolylacetylene ligands
only one distinct signal is observed in the NMR spec-
trum, one can conclude that also in solution only one
diastereoisomeric pair is present (no decision can be
made whether this is the racemic or meso compound).
Variable-temperature NMR investigations do not pro-
vide any evidence for interconversion of these stereo-
isomers in solution.13,18 Upon cooling to 233 K, no
significant alterations in the resonance pattern were
The Cu-CR-Li angle is almost rectangular
(81.63(12)° and 83.90(12)°), while the acetylene-copper
(Cu-CR-Câ) units are almost linear (169.5(2)° and
176.1(2)° for Cu(2)-C(31)-C(32) and Cu(2)-C(41)-
C(42), respectively). Bridge-bonding of an alkynyl unit
between copper and lithium can be realized in various
ways21 (Figure 3). The actual interaction may differ in
the number of atoms (one or two) bonded to the CR atom
of the alkynyl group (µ1 or µ2 type) and in the way the
triple bond participates in the bonding to lithium (η1 or
η2 type). At first sight, the bridging of the p-tolylacety-
lene unit between copper and lithium seems to be of 3c-
2e character (µ2-η1, Type I in Figure 3).
1
observed. The H NMR spectrum at elevated tempera-
ture (333 K) shows coalescence of the NMe2 methyl
resonances to one singlet, showing that the NMe2-Li
coordination-dissociation process has become fast on
the NMR time scale. The benzylic protons are still
represented by a distinct AB pattern, even at 333 K,
pointing to NMe-Li coordination, which is rigid on the
NMR time scale. Above 333 K, decomposition of cuprate
3a occurs.
Both in the solid state (Nujol) and in solution (ben-
zene), the IR spectrum of 3 shows a CtC stretching
vibration at 2076 cm-1. This suggests identical struc-
tural features in solution and in the solid state. Con-
clusive evidence for a dimeric structure in solution is
provided by cryoscopic molecular weight determination
in benzene (calcd for 3a , 752.80; found, 670).
In the 13C NMR spectrum (vide infra) of 3a , however,
two distinct broad resonances with a line width of ca.
20 Hz are observed, which point to coupling of both the
CR and Câ with lithium (1J (13C-7Li ) 7 Hz). The
bonding of both CR and Câ to lithium suggests a side-on
coordination mode of the acetylene unit to lithium (as
in Type II and III in Figure 3). Such an interaction
between lithium and p-tolylacetylene would rule out the
possibility of a contact ion pair interaction or electro-
static π-contacts21 (Type IV in Figure 3). Supporting
evidence for at least partial side-on coordination follows
from the solid state structure of 3a , where the distances
between lithium and the CR and Câ atoms of the
p-tolylacetylene group are quite close, i.e. ca. 2.2 and
2.7 Å, respectively. Moreover, the short Cu-CR bond
distances of 1.868(2) and 1.871(2) Å suggest that, despite
the interaction between lithium and CR, the interaction
between copper and CR can be best described in terms
of two-center-two-electron (2c-2e) bonding. This sp-
character also appears from the Cu-CR-Câ angles
(176.1(2)° and 169.5(2)°) (vide supra). In conclusion, the
bridging of the p-tolylacetylene ligand can be considered
to be intermediate between Type II and III (Figure 3).
Str u ctu r e of 3a in Solu tion . The 1H NMR spectrum
(benzene-d6, 298 K) of the mixed 2:2 aryl-alkynyl-
Con clu d in g Rem a r k s
The neutral heterocuprates 3 are the first cuprates
in which two different homocuprate anionic moieties
([Ar-Cu-Ar]-and[RCtC-Cu-CtCR]-)(Ar )[C6H4{CH2-
N(Me)CH2CH2NMe2}-2]-) and [CuCtCR] (R ) C6H4-
Me-4 or C6H4SiMe3-4) are combined. Both lithium
cations function as bridges between the two homo-
cuprate anionic parts and are stabilized by the N,N′-
chelating function of the ortho-diamino substituent of
the Ar ligand.
The intrinsic stabilities of the [Aryl4Cu6]2+ cationic
skeleton as found in [Cu6Br2Aryl4], 2,10 and that of the
[Ar2Cu]- anion in [CuLi2BrAr2], 1,13 critically affect the
(21) The various possibilities involving π-interactions of acetylenes
with alkali metal cations have been discussed earlier; see: Goldfuss,
B.; Schleyer, P. Von R.; Hampel, F. J . Am. Chem. Soc. 1997, 119, 1080.

2316 Organometallics, Vol. 22, No. 11, 2003
Krononburg et al.
Ta ble 3. Exp er im en ta l Da ta for th e X-r a y
type and stability of the copper compounds formed
during substitution reactions. As an example, the
substitution of bromide by acetylide occurs only on a
stable cationic moiety as is seen in compound 2. Another
example is the selective synthesis of the relatively
stable, mixed 2:2 aryl-alkynyl-cuprate 3 from [LiAr] and
different combinations of [CuCtCR]. An alternative
view of the formation of 3 is that it occurs by a
substitution of Br- in 1 by a [RCtC-Cu-CtCR]-
anion.
Diffr a ction Stu d ies of 3a a n d 3b
3a
3b
formula
C
42H52Cu2Li2N4
C
46H64Cu2Li2N4Si2‚
0.56C6H6
Mr
753.84
913.89
cryst size [mm3]
cryst color
temp [K]
cryst syst
space group
a [Å]
0.60 × 0.12 × 0.12 0.63 × 0.18 × 0.18
yellow
yellow
150(2)
150(2)
triclinic
P1h (No. 2)
12.7340(2)
12.8276(1)
14.2614(2)
97.7242(7)
103.7379(6)
114.7861(7)
1980.83(4)
2
triclinic
P1h (No. 2)
11.8848(2)
13.3156(2)
18.6519(3)
81.5370(7)
78.6000(7)
69.5940(6)
2702.06(7)
2
b [Å]
c [Å]
Exp er im en ta l Section
R [deg]
â [deg]
γ [deg]
V [Å3]
Gen er a l Com m en ts. All experiments were carried out
under a completely dry and oxygen-free nitrogen atmosphere,
using standard Schlenk techniques. Solvents were dried and
distilled prior to use. All reactions concerning organocuprate
and -lithium syntheses were carried out in flame-dried Schlenk
flasks. The starting materials [CuLi2Br(C6H4{CH2N(Me)CH2-
CH2NMe2}-2)2] (1),13 [Li2(C6H4{CH2N(Me)CH2CH2NMe2}-2)2]
Z
F [g/cm3]
1.264
1.11
0.65
1.123
0.86
0.65
55 863/12 163
µ [mm-1
]
(sin θ/λ)max [Å-1
]
no. of reflns (measd/ 45 664/9004
unique)
(4),22 [LiCtC(C6H4Me-4)],15 and [CuCtC(C6H4Me-4)]∞ were
15
prepared according to literature procedures. [CuCtC(C6H4-
SiMe3-4)]∞ was prepared starting from HCtC(C6H4SiMe3-4)16
according to the procedure described for [CuCtC(C6H4Me-4)]∞.
Elemental analyses were obtained from Dornis und Kolbe
Mikroanalytisches Laboratorium, Mu¨lheim a.d. Ruhr, Ger-
many. Cryoscopic measurements were carried out using a
S2541 thermolyzer and a metal-mantled Pt-100 sensor. For
calibration, naphthalene was used to give the cryoscopic
constant Kf ) 5.54 K‚kg‚mol-1. IR spectra were recorded on a
Mattson Galaxy FTIR 5000 spectrometer and on a Mettler
Toledo ReactIR 1000 FTIR spectrometer with a K6 conduit, 6
bounce SiComp probe, Nickelson Interferrometer, and MCT
Midband detector.
abs corr
PLATON
(MULABS)
0.78-0.91
469/8
PLATON
(MULABS)
0.76-0.88
559/12
transmn
no. of params/
restraints
R1/wR2 [I>2σ(I)]
R1/wR2 [all reflns]
S
0.0378/0.0867
0.0522/0.0933
1.040
0.0380/0.1284
0.0440/0.1328
1.103
res dens [e/Å3]
-0.41/0.73
-0.57/0.87
[Cu 2Li2(CtCC6H 4SiMe3-4)2(C6H 4{CH 2N(Me)CH 2CH 2-
NMe2}-2)2] (3b). The synthetic procedure is identical to that
described for 3a , starting from [Cu(CtCC6H4SiMe3-4)] (0.53
g; 2.24 mmol) and [Li2{C6H4(CH2N(Me)CH2CH2NMe2)-2}2] (4)
(0.44 g; 2.24 mmol) in toluene (50 mL). Analytically pure 3b
was obtained by crystallization from benzene/pentane at room
temperature. Yield: 0.38 g (39%).
1H NMR (C6D6, 300.105 MHz, 298 K): δ (in ppm) 0.16 (s,
18H, Si(Me3)), 1.04 (bs, 6H, NMe2), 1.38 (m, 4H, N(Me)CH2-
CH2N), 1.75 (t, 2H, N(Me)CH2CH2N), 2.08 (bs, 6H, NMe2), 2.21
(s, 6H, CH2N(Me)), 2.30 (m, 2H, N(Me)CH2CH2N), 2.75 (d, 2H,
2J ) 10.80 Hz, ArCH2), 4.11 (d, 2H, 2J ) 10.80 Hz, ArCH2),
6.94 (d, 2H, ArH(3)), 7.16 (t, 2H, ArH(4)), 7.37 (d, 4H, p-Si-
(Me3)ArH(2,6)), 7.53 (bt, 2H, ArH(5)), 7.74 (d, 4H, p-Si(Me3)-
ArH(3,5)), 9.34 (bs, 2H, ArH(6)). 13C NMR (C6D6, 75.469 MHz,
298 K): δ (in ppm) -1.23 (Si(Me3)), 42.5 (NMe2), 46.1 (N(Me)-
CH2CH2N), 47.5 (NMe2), 51.6 (N(Me)CH2CH2N), 56.6 (N(Me)),
70.9 (ArCH2), 111.1 (b, ArCtC), 121.2 (b, ArCtC), 125.4, 125.8
(Ar(3,4), 127.3, 128.4, 131.5, 133.8 (p-Me3Si-Ar(1-6), 138.3,
144.8, 149.2 (Ar(2,5,6), 166.7 (Ar(Cipso)). Anal. Calcd for
C46H64N4Cu2Li2Si2: C, 63.49; H, 7.41; N, 6.44. Found: C, 63.56;
H, 7.21; N, 6.30.
[Cu 2Li2(CtCC6H4Me-4)2(C6H4{CH2N(Me)CH2CH2NMe2}-
2)2] (3a ). To a stirred suspension of [CuCtCC6H4Me-4]∞ (369
mg; 2.07 mmol based on monomer) in toluene (40 mL) was
slowly added dropwise a solution of [Li2(C6H4{CH2N(Me)CH2-
CH2NMe2}-2)2] (4) (0.41 g; 2.07 mmol of monomer) in toluene
(25 mL) at 0 °C. After additional stirring for 1 h at 0 °C the
temperature was raised to ambient temperature, upon which
the reaction mixture turned into a clear yellow solution. After
stirring for another 30 min at room temperature the solvent
was evaporated in vacuo, leaving the crude product as an off-
white powder. After subsequent washing with pentane (3 ×
15 mL) 3 was obtained as an almost white powder (0.74 g,
95%; 0.98 mmol based on dimer). Crystals (ca. 65%) suitable
for X-ray structure determination were obtained by crystal-
lization from benzene/pentane (1:1) at room temperature.
1H NMR (C6D6, 300.105 MHz, 298 K): δ (in ppm) 1.05 (bs,
6H, NMe2) 1.42 (m, 4H, N(Me)CH2CH2N), 1.79 (m, 2H, N(Me)-
CH2CH2N), 2.04 (s, 12H, NMe2 and CH2N(Me)). 2.20 (s, 6H,
2
C6H4(CH3)), 2.36 (m, 2H, N(Me)CH2CH2N), 2.77 (d, 2H, J )
10.80 Hz, ArCH2N), 4.12 (d, 2H, 2J ) 10.80 Hz, ArCH2N), 6.90
(d, 4H, p-TolH(2,6)), 6.95 (d, 2H, ArH(3)), 7.18 (t, 2H, ArH(4)),
7.51 (bt, 2H, ArH(5)), 7.64 (d, 4H, p-TolH(3,5)), 9.34 (bs, 2H,
ArH(6)). 13C NMR (C6D6, 75.469 MHz, 298 K): δ (in ppm) 21.16
(p-Tol(CH3)), 42.7 (b, NMe2), 46.1 (N(Me)CH2CH2N), 47.5 (b,
NMe2), 52.6 (N(Me)CH2CH2N), 57.3 (N(Me)), 70.9 (ArCH2),
111.6, 120.2 (b, J 1(13C-7Li) ) ca. 6.7 Hz,CtC), 123.54, 124.7
(Ar(3,4), 125.3, 129.1, 131.7 (p-Tol), 135.3, 144.9, 149.2 (Ar),
166.6 (J 1(13C-7Li) ) ca. 5 Hz, Ar(Cipso). IR (3 in Nujol): 2076
cm-1; (3 in C6H6) 2076 cm-1. Anal. Calcd for C42H52Cu2Li2N4:
C, 66.92; H, 6.95; N, 7.43. Found: C, 67.11; H, 6.82; N, 7.34.
Molecular weight determination by cryoscopy (0.44 g in 16.19
g of C6H6). Calcd for C21H26CuLiN2: 376.40. Found: 670.
Str u ctu r e Deter m in a tion s a n d Refin em en t of 3a a n d
3b. X-ray intensities were measured on a Nonius KappaCCD
diffractometer with rotating anode (λ ) 0.71073 Å). The
structures were solved with direct methods (SHELXS9724 for
3a and SIR9723 for 3b) and refined with SHELXL9724 against
F2 of all reflections. One of the ortho-diamine substituents in
3a was refined with a disorder model. There are two crystal-
lographically independent benzene solvent molecules present
in 3b, which were refined with an stoichiometry of 26% and
30% with respect to the main molecule. Molecular illustrations,
(23) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarani, H. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterini, A. G. G.; Polidori, G.; Spagna,
R. J . Appl. Crystallogr. 1999, 32, 115.
(24) Sheldrick, G. M. SHELX-97, Program for crystal strcuture
refinement; University of Go¨ttingen: Germany, 1997.
(22) Rietveld, M. H. P.; Wehman-Ooyevaar, I. C. M.; Kapteijn, G.
M.; Grove, D. M.; Smeets, W. J . J .; Kooijman, H.; Spek, A. L.; van
Koten, G. Organometallics 1994, 13, 3782.

[Ar2Cu]- and [(RCtC)2Cu]- Homocuprate Moieties
Organometallics, Vol. 22, No. 11, 2003 2317
structure checking, and calculations were performed with the
PLATON package.25 Further details are given in Table 3.
Netherlands Organization for Scientific Research (NWO).
Dr. J . Boersma is thanked for critical reading of the
manuscript.
Ack n ow led gm en t. This work was supported in part
(M.L., A.L.S.) by The Netherlands Foundation for
Chemical Sciences (CW) with financial aid from The
Su p p or tin g In for m a tion Ava ila ble: X-ray crystallo-
graphic data of 3a and 3b (also CIF). This material is available
free of charge via the Internet at http://pubs.acs.org.
(25) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool;
Utrecht University: Utrecht, The Netherlands, 2000.
OM030082A