Electronic structure and electrophilic reactivity of discrete copper diphenylcarbenes

Article abstract of DOI:10.1016/j.jorganchem.2005.07.098

The β-diketiminato Cu(I) arene adduct {[Me₃NN]Cu} ₂(μ-toluene) (3) is prepared in 62% isolated yield by addition of the neutral β-diketimine H[Me₃NN] to copper t-butoxide in toluene. An X-ray structure of 3 shows that the bridging toluene ligand exhibits η²-bonding to each Cu center via four contiguous C atoms. Reaction of the dicopper 3 with 1 equiv. N₂CPh₂ provides {[Me₃NN]Cu}₂(μ-CPh₂) (4) as purple crystals in 70% isolated yield. Dicopper carbene 4 possesses a Cu-Cu distance of 2.485(1) A? in the solid state and dissociates a [Me₃NN]Cu fragment in arene solvents to provide low concentrations of [Me₃NN]CuCPh ₂ (2) and [Me₃NN]Cu(arene). DFT calculations performed on terminal carbene 2 and dicopper carbene 4 illustrate relationships between these two bonding modes and suggest electrophilic reactivity at the carbene carbon atom bound to Cu. Dicopper carbene 4 undergoes efficient carbene transfer to HCCPh and PPh₃ resulting in the formation of 1,3,3- triphenylcyclopropene and Ph₃PCPh₂ while reaction with the isocyanide CNAr (Ar = 2,6-Me₂C₆H₃) results in loss of the carbene as Ph₂CCPh₂. In each case, the [Me₃NN]Cu fragment is trapped by the incoming nucleophile as the three-coordinate [Me₃NN]Cu(L). Reaction of 4 with O₂ rapidly generates benzophenone and {[Me₃NN]Cu}₂(μ-OH) ₂.

Full text of DOI:10.1016/j.jorganchem.2005.07.098

Journal of Organometallic Chemistry 690 (2005) 5989–6000
www.elsevier.com/locate/jorganchem
Electronic structure and electrophilic reactivity of discrete copper
diphenylcarbenes
*
Yosra M. Badiei, Timothy H. Warren
Department of Chemistry, Georgetown University, P.O. Box 571227, Washington, DC 20057-1227, USA
Received 22 June 2005; received in revised form 25 July 2005; accepted 26 July 2005
Available online 15 September 2005
Abstract
The b-diketiminato Cu(I) arene adduct {[Me3NN]Cu}2(l-toluene) (3) is prepared in 62% isolated yield by addition of the neutral
b-diketimine H[Me3NN] to copper t-butoxide in toluene. An X-ray structure of 3 shows that the bridging toluene ligand exhibits g2-
bonding to each Cu center via four contiguous C atoms. Reaction of the dicopper 3 with 1 equiv. N2CPh2 provides {[Me3NN]-
˚
Cu}2(l-CPh2) (4) as purple crystals in 70% isolated yield. Dicopper carbene 4 possesses a Cu–Cu distance of 2.485(1) A in the solid
state and dissociates a [Me3NN]Cu fragment in arene solvents to provide low concentrations of [Me3NN]Cu@CPh2 (2) and
[Me3NN]Cu(arene). DFT calculations performed on terminal carbene 2 and dicopper carbene 4 illustrate relationships between
these two bonding modes and suggest electrophilic reactivity at the carbene carbon atom bound to Cu. Dicopper carbene 4 under-
goes efficient carbene transfer to HC„CPh and PPh3 resulting in the formation of 1,3,3-triphenylcyclopropene and Ph3P@CPh2
while reaction with the isocyanide CNAr (Ar = 2,6-Me2C6H3) results in loss of the carbene as Ph2C@CPh2. In each case, the
[Me3NN]Cu fragment is trapped by the incoming nucleophile as the three-coordinate [Me3NN]Cu(L). Reaction of 4 with O2 rapidly
generates benzophenone and {[Me3NN]Cu}2(l-OH)2.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Copper; Carbene; Dicopper; Group transfer; Cyclopropanation; Alkyne; Fisher carbene
1. Introduction
changes in the cyclopropane product distribution as a
function of steric bulk of the P(OR)3 ligand in a
[(RO)3PCuCl] catalyst system [3,4], suggested the inter-
mediacy of a copper–carbene complex.
Over the last 40 years, soluble copper(I) and cop-
per(II) complexes have been used in conjunction with
a-diazoesters N2CHC(O)OR to cyclopropanate alkenes
and have played an important role in the development
of this valuable group transfer reaction [1]. The earliest
successful example of an enantioselective homogeneous
metal catalyst employed chiral copper salicylaldimine
complexes which resulted in asymmetric induction in
the cis/trans cyclopropane mixture formed in the reac-
tion of styrene with N2CHCO2R (R = ethyl, Ph) [2].
This asymmetric induction, as well as systematic
Several mechanistic [5–8] and theoretical [8–11] stud-
ies that implicate Cu(I) carbenes [Cu]@CRR0 as the ac-
tive species in copper-catalyzed cyclopropanation
support these early proposals, though such catalytically
active Cu(I) carbenes have proven elusive. A transient
copper carbene has been identified via time-resolved
FTIR spectroscopy upon addition of N2CHCO2Me to
a cationic bis(oxazoline) Cu(I) precatalyst [12]. Employ-
ing a neutral Cu(I) complex featuring the strongly
donating iminophosphanimide ligand, Hofmann dem-
onstrated that ½But2PðNSiMe3Þ2-j2NꢀCuðethyleneÞ reacts
with N2C(Ph)(C(O)OMe) to give a mixture in which the
carbene ½But2PðNSiMe3Þ2-j2NꢀCu@CðPhÞðCðOÞOMeÞ
*
Corresponding author. Tel.: +1 202 687 6362; fax: +1 202 687
6209.
E-mail address: thw@georgetown.edu (T.H. Warren).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.07.098

5990
Y.M. Badiei, T.H. Warren / Journal of Organometallic Chemistry 690 (2005) 5989–6000
1
could be identified by low temperature H, 13C, and 31P
NMR spectroscopy [13]. Moreover, the presence of two
inequivalent But groups indicated that the carbene is
orthogonal to the backbone of the bidentate N,N-donor
ligand.
second-order cyclopropanation of styrene by terminal
¼
¼
carbene 2 (DH = 10.4(3) kcal/mol and DS = ꢁ32.3(9)
cal/mol K) were identified employing dioxane as solvent
[18].
Herein we report an improved synthesis for a synthon
to the [Me3NN]Cu fragment as well as the isolation of
the dicopper carbene {[Me3NN]Cu}2(l-CPh2) (4) previ-
ously identified in the decomposition of [Me3NN]-
Cu@CPh2 (2) in arene solvents. DFT studies on full
models of 2 and 4 have been performed to illustrate
bonding relationships between these copper carbenes
that interconvert in solution. Reactions with selected
nucleophiles as well as dioxygen have been carried out
to probe the substrate dependence on the ultimate reac-
tivity pathway for the diphenylcarbene functionality.
Barluenga has used copper salts to catalyze carbene
coupling in otherwise thermally stable chromium Fischer
carbene complexes of the type (CO)5Cr@C(OR)(R0) to
give the alkenes R0(OR)C@C(OR)R0 [14,15]. In one case,
a crystallographically copper carbene [Cu{@CR1(OR2)}-
(MeCN)(OEt2)]+ was isolated from addition of
[Cu(NCMe)4][PF6] to (CO)5Cr@CR1(OR2) (R1 = (E)-
CH@CH-2-furyl; R2 = menthyl) [14]. While catalytically
inactive towards cyclopropanation, dimerization of the
carbene in [Cu{@CR1(OR2)}(MeCN)(OEt2)]+ is induced
upon addition of PBu3. As this Fischer copper carbene
com- plex is prepared via transmetallation from
(CO)5Cr@ CR1(OR2), it is reasonable to expect bimetallic
[M](l-CRR0)[Cu] species as intermediates [16]. In fact,
spectroscopic data have been reported for two copper-
containing bimetallic carbenes Cp(CO)Ru(l-CPh2)-
(CuCl)2 and Cp(CO)Ru(l-CPh2)CuCp prepared by
addition of CuCl to Cp(CO)Rh@CPh2 followed by treat-
ment with NaCp [17].
We recently reported the use of strongly donating b-
diketiminato ligands to stabilize the crystallographically
characterized copper carbenes {[Me2NN]Cu}2(l-CPh2)
(1) and [Me3NN]Cu@CPh2 (2) [18]. Dicopper carbene
1 possesses Cu–C distances of 1.922(4) and 1.930(4) A
as well as a Cu–Cu distance of 2.4635(7) A found in
many polynuclear Cu(I) aryls in which the Cu(I) centers
are bridged by sp2-hybridized C atoms [19]. The consid-
erably shortened Cu–C distance of 1.834(3) A in the
2. Results and Discussion
2.1. Improved synthesis of a synthon to the [Me3NN]Cu
fragment
We previously reported that the Cu(I) b-diketiminate
[Me3NN]Cu(toluene) could be prepared by addition of
the thallium derivative Tl[Me3NN] to CuBr suspended
in toluene [18]. We find that the addition of the neutral
b-diketimine H[Me3NN] to copper t-butoxide in toluene
more conveniently provides the colorless {[Me3NN]-
Cu}2(l-toluene) (3) in 62% yield (Scheme 2). The
X-ray structure of 3 (Fig. 1; Table 1) illustrates the
bridging nature of the toluene ligand which coordinates
to each [Me3NN]Cu fragment in an g2-manner through
˚
˚
˚
˚
C49–C52 with Cu–C distances of 2.027(5)–2.077(5) A
terminal carbene 2 supports significant Cu@C multi-
ple-bond character. The dicopper carbene dissociates a
[b-diketiminato]Cu fragment in arene solvents to give
an equilibrium mixture of terminal carbene [Cu]@CPh2
and a solvento species [Cu](arene) (Scheme 1). Solutions
of these copper carbenes are active in the cyclopropana-
tion of styrene derivatives. Activation parameters for the
(Table 2) similar to those found in two other [b-diketim-
inato]Cu(g2-benzene) adducts [20,21]. Each coordinated
C–C bond is roughly coplanar with the b-diketiminate
backbone. Two sets of alternately shorter (1.360(7)–
˚
˚
1.403(7) A) and longer (1.436(7)–1.439(7) A) C–C dis-
tances are found within the bridging toluene ligand, sug-
gesting that coordination to two [Me3NN]Cu fragments
somewhat attenuates the aromaticity of this ring. Con-
sistent with the ability of the [b-diketiminato]Cu frag-
ment to bind alkenes [22], two of the three short C–C
bonds of toluene coordinate to the [Me3NN]Cu frag-
ments in 3. It is curious to note that under similar
synthetic conditions, the slightly smaller Cu(I) b-dike-
timinato fragment [Me2NN]Cu crystallizes as the
Scheme 1. Reversible interconversion of b-diketiminato dicopper and
terminal carbenes.
Scheme 2. Synthesis and solution behavior of 3.

Y.M. Badiei, T.H. Warren / Journal of Organometallic Chemistry 690 (2005) 5989–6000
5991
Table 2
˚
Bond distances (A) and angles (ꢁ) in 3
˚
Bond distances (A)
Cu1–N1
Cu1–N2
Cu2–N3
Cu2–N4
Cu1–C49
Cu1–C50
Cu2–C51
Cu2–C52
C48–C49
C49–C50
C50–C51
C51–C52
C48–C53
C52–C53
1.942(4)
1.922(4)
1.930(4)
1.933(4)
2.027(5)
2.077(5)
2.044(5)
2.072(5)
1.437(7)
1.398(7)
1.436(7)
1.403(7)
1.360(7)
1.439(7)
Bond angles (ꢁ)
N1–Cu1–N2
N3–Cu2–N4
C49–Cu1–C50
99.03(17)
98.79(17)
39.8(2)
39.9(2)
5.5
C51–Cu2–C52
N1–Cu1–N2/C49–Cu1–C50
N3–Cu2–N4/C51–Cu2–C52
N1–Cu1–N2/N3–Cu2–N4
4.4
35.5
Fig. 1. X-ray structure of {[Me3NN]Cu}2(l-toluene) (3).
Dissolution of {[Me3NN]Cu}2(l-toluene) (3) in ben-
zene-d6 results in H NMR spectra that are nearly C2v-
1
Table 1
Crystallographic data, collection parameters, and refinement details
symmetric on the NMR timescale, but indicate the pres-
ence of a second species. After standing overnight, the
somewhat broad N-aryl m-H and backbone C–H sing-
lets first observed at d 6.913 and 4.791 ppm convert to
two sets of sharp singlets at d 6.920 and 6.809 ppm
and d 4.803 and 4.763 ppm. We attribute this to slow,
irreversible conversion to two separate Cu(I) benzene
complexes (Scheme 2). On the basis of the nearly identi-
cal chemical shifts originally observed, we attribute the
signals at d 6.920 and 4.803 ppm to {[Me3NN]Cu}2(l-
benzene). A second species in slightly lower abundance
is tentatively assigned as the monomeric solvento com-
plex [Me3NN]Cu(g2-benzene).
for 3 and 4
Compound
Formula
3
4a
C53H66Cu2N4
886.18
173(2)
C59H68Cu2N4
960.25
173(2)
Molecular weight
Temperature (K)
Crystal description
Crystal color
Crystal size (mm3)
System
Rod
Block
Colorless
0.18 · 0.16 · 0.10
Monoclinic
P2(1)/n
14.417(2)
13.915(2)
23.815(4)
90.00
102.253(3)
90.00
4
1.52–24.75
22637
7897
Dark purple
0.37 · 0.33 · 0.18
Orthorhombic
Pccn
Space group
˚
a (A)
26.213(9)
18.711(7)
22.001(8)
90.00
90.00
90.00
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
Z
2.2. Synthesis and characterization of {[Me3NN]Cu}2-
(l-CPh2) (4)
8
h Range (ꢁ)
Measured reflections
Unique reflections
R(int)
GOF of F2
R1 (I > 2r(I))
wR2 (all data)
Largest difference
1.34–25.00
42494
9224
0.0991
0.979
0.0704
0.1850
1.053 and ꢁ0.799
Careful addition of 1 equiv. of N2CPh2 to {[Me3NN]-
Cu}2(l-toluene) (N2CPh2:Cu ratio = 1:2) in ether leads
to immediate effervescence and formation of a deep pur-
ple solution. Crystallization from pentane leads to the
isolation of {[Me3NN]Cu}2(l-CPh2) in 70% yield
(Scheme 3). The X-ray structure of {[Me3NN]Cu}2(l-
CPh2) Æ 0.75 pentane (Fig. 2; Table 1) is very similar to
0.1000
0.978
0.0606
0.1466
0.577 and ꢁ0.426
ꢁ3
˚
peak and hole (e A
)
a
§
SQUEEZE subroutine of PLATON employed in refinement of 4
which possesses ca. 0.75 equivalents of disordered pentane per mole-
§
cule of 4. A.L. Spek, Acta Crystallogr. A46 (1990), C-34.
{[Me2NN]Cu}2 dimer in which each Cu center engages
in an g2-arene interaction with an opposing N-aryl ring
[23].
Scheme 3. Synthesis of dicopper carbene 4.

5992
Y.M. Badiei, T.H. Warren / Journal of Organometallic Chemistry 690 (2005) 5989–6000
nature of metal–carbene bonding from the dicopper
diphenylcarbenes 1 and 4.
The dicopper carbene {[Me3NN]Cu}2(l-CPh2) (4)
was first observed in solution during the thermal decom-
position of the terminal carbene [Me3NN]Cu@CPh2 (2).
In benzene-d6, the bridging carbene of 4 appears at d
189.0 ppm in the 13C{1H} NMR spectrum of 4 (d
1
189.4 ppm for 1). As with 1, the room temperature H
NMR spectrum of 4 in toluene-d8 indicates a fluxional
process assigned as twisting of the bridging CPh2 ligand
about the vector containing the carbene carbon that bi-
1
sects the Cu–Cu axis. Low temperature (ꢁ70 ꢁC) H
NMR spectra show the presence of a single backbone
C–H resonance at d 4.99 ppm as well as eight N-aryl
and backbone Me resonances from d 2.86–1.18 ppm,
consistent with the approximate C2 conformation ob-
served in the solid state. As the temperature is raised,
both [Me3NN]Cu@CPh2 (2) and [Me3NN]Cu(toluene)
are observed in identical concentrations by their charac-
1
teristic backbone C–H H NMR signals at d 4.92 and
Fig. 2. X-ray structure of {[Me3NN]Cu}2(l-CPh2) (4).
4.76 ppm prior to the onset of thermal loss of the
CPh2 functionality as Ph2C@CPh2. Notably, the relative
ratios of [Cu]2(l-CPh2), [Cu]@CPh2, and [Cu](arene)
species at room temperature do not differ appreciably
between the [Me2NN]Cu and [Me3NN]Cu systems un-
der comparable concentrations (Scheme 1). Thus the ex-
tra steric bulk of the N-aryl p-Me substituents does not
overwhelmingly shift the position of equilibrium, despite
the initial isolation of the terminal carbene employing
the [Me3NN]Cu fragment.
that of {[Me2NN]Cu}2(l-CPh2) (1) with Cu–C bond dis-
tances of 1.931(5) and 1.933(5) A (1.922(4) and 1.930(4)
˚
˚
˚
A in 1 [18]) with a Cu–Cu distance of 2.485(1) A
˚
(2.4635(7) A in 1) (Table 3). As in 1, each [b-diketimi-
nato]Cu fragment is roughly orthogonal to the diphenyl-
carbene functionality as well as orthogonal to each
other. Since the initial report of 1, Gishig and Togni
[24] have shown that N-heterocyclic carbenes (NHCs)
can also adopt a dicopper binding mode in the coordina-
tion of a bis(phosphine)-containaing NHC to copper(I)
iodide. The four-coordinate Cu centers in the [Cu]2(l-
NHC) complex exhibit significantly longer Cu–C dis-
2.2.1. DFT studies – bonding analysis of [Me3NN]Cu@
CPh2 (2) and {[Me3NN]Cu}2(l-CPh2) (4)
DFT calculations (ADF 2002.3–ZORA/TZ2P(+))
were performed on the full systems [Me3NN]Cu@CPh2
(2) and {[Me3NN]Cu}2(l-CPh2) (4) to illustrate the
bonding relationships present between these structurally
characterized terminal and dicopper carbenes, empha-
sizing the nature of the Cu–C p-interactions. Starting
with atomic coordinates from the X-ray structures of 2
and 4, a geometry optimization was carried out in each
case. With the exception of the Cu–C distance in termi-
nal carbene 2, the Cu–ligand distances are marginally
˚
tances (2.113(5) and 2.174(5) A) and a shorter Cu–Cu
˚
distance (2.3561(13) A), suggesting a difference in the
Table 3
˚
Bond distances (A) and angles (ꢁ) in 4
˚
Bond distances (A)
Cu1–C47
Cu2–C47
Cu1–Cu2
Cu1–N1
Cu1–N2
Cu2–N3
Cu2–N4
C47–C48
C47–C54
1.933(5)
1.931(5)
2.485(1)
1.971(4)
1.963(4)
1.981(4)
1.967(4)
1.476(7)
1.469(7)
˚
longer (0.03–0.04 A) in the calculated structures (Tables
4 and 5), but otherwise consistent with the X-ray data.
Figs. 3 and 4 illustrate molecular orbitals resulting
from
r and p-bonding interactions between the
[Me3NN]Cu and CPh2 fragments in the terminal car-
bene [Me3NN]Cu@CPh2 (2). A low-laying filled level
(HOMO-15; ꢁ7.39 eV) constitutes the Cu–C(carbene)
r-bonding interaction (Fig. 3), comprised of a hybrid
Cu orbital (3dz2 ; 3dx2ꢁy2 , and 4 pz; 21.7% total) and the
C(carbene) pz (9.8%) orbital. A filled level (HOMO-2;
ꢁ4.83 eV) within the frontier orbitals represents the cor-
responding r*-antibonding interaction and is predomi-
nantely Cu (48.0%) in character. The Cu–C(carbene)
Bond angles (ꢁ)
N1–Cu1–N2
N3–Cu2–N4
Cu1–C47–Cu2
95.68(18)
96.06(18)
80.1(2)
114.9(4)
88.2
C49–C47–C54
N1–Cu1–N2/C48–C47–C54
N3–Cu2–N4/C48–C47–C54
N1–Cu1–N2/N3–Cu2–N4
85.7
85.9

Y.M. Badiei, T.H. Warren / Journal of Organometallic Chemistry 690 (2005) 5989–6000
5993
Table 4
˚
Bond distances (A) and angles (ꢁ) in 2 (DFT)
˚
Bond distances (A)
Cu–C24
Cu–N1
Cu–N2
1.829
1.940
1.958
Bond angles (ꢁ)
N1–Cu–N2
94.7
Cu–C24–C25
Cu–C24–C31
123.3
119.1
Fig. 3. Selected r-bonding interactions in 2 and 4.
p-molecular orbitals are higher in energy (Fig. 4). The
filled Cu–C(carbene) p-bonding orbital (HOMO-1;
ꢁ4.51 eV) is comprised of 19.1% Cu and 6.3% C(car-
bene) py character. The LUMO (ꢁ3.20 eV) originates
from the p*-interaction between the Cu and carbene
fragments consisting of 32.2% C(carbene) and 14.3%
Cu d character. Including the participation the two car-
bene phenyl rings, the LUMO is over 66% localized on
the CPh2 moiety. The relative Cu and C(carbene) contri-
butions to the HOMO and LUMO of [Me3NN]-
Cu@CPh2 clearly indicate a significant backbonding
interaction from the d10 Cu(I) center to the carbene
acceptor orbital. The substantial energy differences of
these p and p* molecular orbitals as compared to the
Table 5
˚
Bond distances (A) and angles (ꢁ) in 4 (DFT)
˚
Bond distances (A)
Cu1–C47
Cu2–C47
Cu1–N1
Cu1–N2
Cu2–N3
Cu2–N4
Cu1–Cu2
1.964
1.959
2.009
1.998
2.006
2.008
2.521
Bond angles (ꢁ)
N1–Cu1–N2
N3–Cu2–N4
Cu1–C47–Cu2
C49–C47–C54
95.9
95.7
80.0
114.9
Fig. 4. Cu–C(carbene) p-bonding interactions in 2 (left) and 4 (right).

5994
Y.M. Badiei, T.H. Warren / Journal of Organometallic Chemistry 690 (2005) 5989–6000
fragment [Me3NN]Cu HOMO (ꢁ3.82 eV) and CPh2
LUMO (ꢁ3.75 eV) (employing same coordinates from
[Me3NN]Cu@CPh2 calculation) further indicate the
importance of p-backbonding in the overall Cu–C(car-
bene) interaction present in 2.
As a basis for comparison, styrene and a-methylsty-
rene undergo efficient carbene transfer from {[Me2NN]-
Cu}2(l-CPh2) to give the corresponding cyclopropanes.
In contrast, reactions with 1,2-disubstituted olefins such
as trans-b-methylstyrene and cyclooctene are more slug-
gish and result in predominant Ph2C@CPh2 formation
from the thermal decomposition of the copper carbene,
even in the presence of 50 equiv. olefin [18]. It should be
noted that [Me3NN]Cu@CPh2 cleanly decomposes in
dioxane via first-order kinetics to give 1/2 equiv.
In the dicopper carbene {[Me3NN]Cu}2(l-CPh2) (4),
two d10 Cu centers can interact with the CPh2 p-acceptor
orbital. As previously illustrated with the simplified
model {[H5C3N2]Cu}2(l-CH2) [18], a 3-center, 4-elec-
tron p-interaction ensues. The HOMO-3 (ꢁ4.71 eV) rep-
resents the p-bonding interaction involving both Cu
centers (17.0% Cu character) and the carbene acceptor
orbital (6.7% C(carbene) character). The HOMO
(ꢁ4.11 eV) is a Cu2C non-bonding (or weakly Cu–Cu
p-antibonding) interaction involving the two [Me3NN]-
Cu fragments (26.8% Cu d character) in which the
C(carbene) atom lies essentially on a nodal plane. The
LUMO (ꢁ3.18 eV) originates from the Cu2C p*-interac-
tion and is comprised of 26.8% C(carbene) p and 19.2%
Cu character. As with [Me3NN]Cu@CPh2, the relative
Cu and C(carbene) constituencies of the p and p* molec-
ular orbitals of dicopper carbene 4 are consistent with
backbonding from the Cu d10 centers to the diphenylcar-
bene functional group.
¼
Ph2C@CPh2 with activation parameters DH = 21(1)
¼
kcal/mol and DS = ꢁ8(3) cal/mol K [18].
2.4. Reaction of {[Me3NN]Cu}2(l-CPh2) (4) with
phenylacetylene
Reaction of {[Me3NN]Cu}2(l-CPh2) with 10 equiv.
phenylacetylene in benzene-d6 results in a change in col-
or from intense purple to light green over 15 min. GC/
MS analysis indicates that efficient carbene transfer to
phenylacetylene occurs as the major Ph2C-containing
species exhibits an m/z of 268 assigned as 1,3,3-triphe-
nylcyclopropene [25]; little Ph2C@CPh2 was present
1
(Scheme 4). H NMR analysis shows that the resulting
Further inspection of the frontier molecular orbitals
reveals two additional features. While the availability
of a 3-center, 4-electron p-bonding interaction appears
to engender enhanced thermal stability to the dicopper
carbene as compared to a terminal carbene, r-interac-
tions within the Cu2C framework (c.f. HOMO-2) cer-
tainly contribute Cu–Cu bonding. Secondly, the
frontier orbital energy levels of [Me3NN]Cu@CPh2 are
significantly higher than in the pared down system
[H5C3N2]Cu@CH2 (LUMO = ꢁ3.44 eV) [18]. Coupled
with the steric bulk of the b-diketiminato and carbene
substituents, inductive and resonance effects are also
important in allowing the isolation of these reactive spe-
cies. Moreover, the significant involvement of the diphe-
nylcarbene moiety in the LUMO of both 2 and 4
suggests that these copper carbenes should exhibit
marked electrophilic character at the carbene C atom.
[Me3NN]Cu fragment was trapped as the phenylacety-
lene adduct [Me3NN]Cu(g2-HC„CPh) (5) by charac-
teristic signals at d 4.871 and 3.997 ppm attributed to
new backbone C–H and coordinated H–C„CPh reso-
nances. The alkyne adduct 5 can be isolated as colorless
crystals from pentane by addition of 2 equiv. phenyl-
acetylene to {[Me3NN]Cu}2(l-toluene) (Scheme 5).
The X-ray structure of [Me3NN]Cu(g2-HC„
CPh) Æ 0.5 pentane (Fig. 5; Table 6) shows that the phe-
nylacetylene ligand is coplanar with the b-diketiminato
backbone, reminiscent of the structures of [Me2NN]-
Cu(g2-ethylene) [22] and [Me2NN]Cu(g2-styrene) [22]
as well as other cationic Cu(I) alkene and alkyne
complexes supported by chelating diimines such as bipy
[26] and 1,10-phenanthroline [27]. This orientation
2.3. Reactions of {[Me3NN]Cu}2(l-CPh2) (4) with
nucleophiles
We chose to survey the reactivity of the dicopper
carbene {[Me3NN]Cu}2(l-CPh2) (4) owing to its greater
thermal stability as compared to the terminal [Me3NN]-
Cu@CPh2 (2) which slowly decomposes in arene sol-
vents to generate the carbene coupling product
Ph2C@CPh2 as well as 4 and [Me3NN]Cu(arene). In
arene solvents, the dicopper carbenes {[MexNN]-
Cu}2(l-CPh2) are convenient sources of the correspond-
ing terminal carbenes as the former are in equilibrium
with [MexNN]Cu@CPh2 and [MexNN]Cu(arene)
(Scheme 1).
Scheme 4. Reactivity of dicopper carbene 4 with nucleophiles.
Scheme 5. Syntheses of [Me3NN]Cu(L) (5–7) from 3.

Y.M. Badiei, T.H. Warren / Journal of Organometallic Chemistry 690 (2005) 5989–6000
5995
˚
(1.183–1.193 A) [28] (Table 7). In addition, the C–C
bond in 5 is also longer than that reported in the cationic
[(phen)Cu(g2-HCCPh)]+ (1.218(13) A) [27] as well a
˚
neutral Cu(I) phenylacetylene complex supported by a
˚
monoanionic, tripodal Kla¨ui ligand (1.208(7) A) [29].
Further evidence for an enhanced backbonding interac-
tion is provided by variable temperature 1H NMR spec-
tra which reveal inequivalent sets of Ar-H, p-Me, o-Me,
and backbone Me resonances at low temperature. The
¼
value DG = 13.4(3) kcal/mol at ꢁ10 ꢁC was calculated
from the coalescence of the backbone-Me signals, nota-
¼
bly higher than the DG = 10.7(3) kcal/mol at ꢁ58 ꢁC
reported for rotation of the styrene ligand in [Me2NN]-
Cu(g2-H2C@CHPh) [22]. The coordinated alkyne
exhibits a characteristic C„C stretch at 1984 cmꢁ1
.
Table 7
˚
Bond distances (A) and angles (ꢁ) in 5
˚
Bond distances (A)
Cu–N1
Cu–N2
Cu–C24
Cu–C25
C24–C25
C25–C26
1.924(2)
1.914(2)
1.919(2)
1.983(2)
1.236(3)
1.458(3)
Fig. 5. X-ray structure of [Me3NN]Cu(g2-HC„CPh) (5).
Bond angles (ꢁ)
N1–Cu–N2
C24–Cu–C25
C24–C25–C26
C25–C24–H24
N1–Cu–N2/C24–Cu–C25
98.68(7)
36.88(9)
158.5(2)
147.5
allows for efficient overlap of the HOMO of the
[Me3NN]Cu fragment (Fig. 4) with an alkyne C–C p*
˚
orbital. The alkyne C24–C25 distance of 1.236(3) A in
2.5
5 is longer than that reported for free phenylacetylene
Table 6
Crystallographic data, collection parameters, and refinement details for 5–7
Compound
Formula
5
6
7
a
C
33.5H36CuN2
C41H44CuN2P
C32H38CuN2
528.19
173(2)
Block
Yellow
0.45 · 0.41 · 0.36
Monoclinic
P2/n
17.565(7)
7.758(3)
22.375(9)
90.00
107.762(6)
90.00
4
Molecular weight
Temperature (K)
Crystal description
Crystal color
Crystal size (mm3)
System
530.18
173(2)
Block
Colorless
0.39 · 0.34 · 0.18
659.29
173(2)
Chunk
Colorless
0.34 · 0.29 · 0.26
Monoclinic
P2(1)/n
10.9249(19)
16.301(3)
20.081(4)
90.00
Triclinic
ꢀ
Space group
P1
˚
a (A)
8.2895(6)
13.5421(11)
15.1011(12)
113.864(1)
103.487(1)
95.267(1)
2
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
Z
101.108(3)
90.00
4
h Range (ꢁ)
Measured reflections
Unique reflections
R(int)
GOF of F2
R1 (I > 2 (I))
wR2 (all data)
1.54–28.29
16104
6886
0.0269
1.111
0.0400
0.1230
0.721 and ꢁ0.585
1.62–28.32
32022
8509
0.0688
1.074
0.0646
0.1585
0.592 and ꢁ1.066
1.30–28.26
24490
6838
0.0256
1.067
0.0343
0.1028
0.362 and ꢁ0.332
ꢁ3
˚
Largest difference peak and hole (e A
)
a
Some H atoms on the disordered pentane of solvation not included in refinement.

5996
Y.M. Badiei, T.H. Warren / Journal of Organometallic Chemistry 690 (2005) 5989–6000
Table 8
2.4.1. Reaction of {[Me3NN]Cu}2(l-CPh2) (4) with
triphenylphosphine
˚
Bond distances (A) and angles (ꢁ) in 6
˚
Bond distances (A)
Reaction of dicopper carbene 4 with excess PPh3 (ca.
8 equiv.) in benzene-d6 results in a similar color change
over 5 min as described above, indicating consumption
of the dicopper carbene. Two sharp 31P NMR reso-
nances at d 7.36 and ꢁ4.79 ppm signal the presence of
the carbene transfer product Ph3P@CPh2 [30–32] as well
as free PPh3, respectively. In addition, a broad reso-
nance at d 5.20 ppm indicates the formation of
[Me3NN]Cu(PPh3) (6) (Scheme 4) which can be pre-
pared in 92% yield as colorless crystals by addition of
2 equiv. PPh3 to a solution of {[Me3NN]Cu}2(l-toluene)
(Scheme 5). Integration of the Ph3P@CPh2 31P NMR
resonance vs. that of [Me3NN]Cu(PPh3) indicates that
the ylide was formed in 76% yield. GC/MS analysis sug-
gests that Ph2C@CPh2 accounts for the remainder of the
CPh2 fragment lost from dicopper carbene 4.
Cu–N1
Cu–N2
Cu–P
P–C24
P–C30
P–C36
1.955(2)
1.940(2)
2.161(1)
1.830(3)
1.829(3)
1.892(3)
Bond angles (ꢁ)
N1–Cu–N2
N1–Cu–P
97.77(10)
126.79(8)
135.32(8)
N2–Cu–P
2.4.2. Reaction of {[Me3NN]Cu}2(l-CPh2) (4) with
2,6-dimethylphenyl isocyanide
Reaction of dicopper carbene 4 with 2,6-dimethyl-
phenyl isocyanide also induces diphenylcarbene loss
from {[Me3NN]Cu}2(l-CPh2), but GC/MS analysis
indicates that Ph2C@CPh2 is the predominant CPh2-
containing product (Scheme 4). The [Me3NN]Cu frag-
ment is trapped as [Me3NN]Cu(CNAr) (7) (Ar = 2,6-
Me2C6H3) which can be isolated in 91% yield as yellow
crystals yield by addition of 2 equiv. CNAr to
{[Me3NN]Cu}2(l-toluene) (3) (Scheme 5). The X-ray
structure of 7 (Fig. 7; Tables 6 and 9) shows trigonal
coordination at Cu, and is very similar to two b-diketim-
inato Cu(I) adducts reported by Tolman [35,36]. The
isocyanide adduct 7 possesses C2v-symmetry in solution
The X-ray structure of [Me3NN]Cu(PPh3) (Fig. 6;
Table 6) shows trigonal coordination at Cu with a
˚
Cu–P distance of 2.161(1) A (Table 8), similar to
˚
Cu–P distances (2.134(1) and 2.1877(7) A) found in
two other neutral, three-coordinate Cu(I) complexes
supported by chelating anionic N,N-donors [33,34].
˚
The Cu–N distances in 6 (1.940(2) and 1.955(2) A) are
longer than in the phenylacetylene adduct 5 (1.914(2)
˚
and 1.924(2) A) suggestive of a more electron-rich
Cu(I) center. At typical NMR concentrations in ben-
zene-d6 (ca. 0.1 mM), the 31P NMR resonance for the
coordinated PPh3 ligand is always broad, suggesting
that the arene solvent is somewhat competitive with
PPh3 for binding to the [Me3NN]Cu fragment.
1
with a backbone H NMR resonance at d 5.037 ppm
and a CN stretch in its IR spectrum at 2121 cmꢁ1
.
This linear r-donor, p-acid ligand very efficiently in-
duces loss of diphenylcarbene from 4 as Ph2C@CPh2.
Upon addition of 2 equiv. of CNAr to 4 in benzene-
Fig. 6. X-ray structure of [Me3NN]Cu(PPh3) (6).
Fig. 7. X-ray structure of [Me3NN]Cu(CNAr) (7).

Y.M. Badiei, T.H. Warren / Journal of Organometallic Chemistry 690 (2005) 5989–6000
5997
Table 9
3. Conclusion
˚
Bond distances (A) and angles (ꢁ) in 7
˚
Bond distances (A)
The dicopper carbene {[Me3NN]Cu}2(l-CPh2) (4)
has been isolated and crystallographically characterized
from the reaction of {[Me3NN]Cu}2(l-toluene) (3) with
1 equiv. N2CPh2. The structural characterization of
dicopper carbene 4 allows direct comparisons with the
structurally characterized [Me3NN]Cu@CPh2 (2). DFT
calculations performed on full models of 2 and 4 indi-
cate significant Cu–C(carbene) p-bonding in each which
occurs in the dicopper carbene via a 3-center, 4-electron
interaction. In both cases, the phenyl substituents of the
carbene participate in the complexꢀs LUMO which is
predominately diphenylcarbene in character, suggesting
electrophilic reactivity at the carbene carbon. Such reac-
tivity is observed with HC„CPh and PPh3 resulting in
carbene group transfer to give 1,3,3-triphenylcyclopro-
pene and Ph2C@PPh3, while the isonitrile CNAr simply
induces diphenylcarbene loss as Ph2C@CPh2. Further
reactivity studies are required to better understand fac-
tors that control carbene group transfer vs. simple car-
bene loss as Ph2C@CPh2. The ability of a nucleophile
to coordinate to the sterically protected Cu center in
three-coordinate [b-diketiminato]Cu@CPh2 species
may favor carbene dimerization as observed during
the addition of PBu3 to the Fischer alkoxycarbene
[Cu{@CR1(OR2)}(MeCN)(OEt2)]+ [14]. Nonetheless,
the observed electrophilic reactivity of the copper diphe-
nylcarbenes contrasts sharply with that of the isoelec-
tronic (tBu2PCH2CH2PtBu2)Ni@CPh2 which behaves
as a C-centered nucleophile [39]. Dioxygen also rapidly
reacts with the copper carbenes to give benzophenone,
opening the possibility of metathesis reactions between
[Me3NN]@CPh2 and other double bonds E@E0.
Cu–N1
Cu–N2
Cu–C24
C24–N3
N3–C25
1.945(1)
1.926(2)
1.814(2)
1.159(2)
1.396(2)
Bond angles (ꢁ)
N1–Cu–N2
N1–Cu–C24
N2–Cu–C24
Cu–C24–N3
C24–N3–C25
97.85(6)
126.63(7)
135.51(6)
177.41(15)
177.01(16)
d6, the predominant Cu-containing species after 10 min
is [Me3NN]Cu(CNAr) – less than 5% each of copper
carbenes 2 and 4 could be observed by H NMR analy-
1
sis. This is to be contrasted with the significant thermal
stability of these mono and dicopper carbenes in arene
solvents which exhibit cyclopropanation activity after
standing two days at room temperature. In contrast to
HC„CPh and PPh3 which may attack the carbene car-
bon atom leading to group transfer of the carbene moi-
ety, perhaps the linear isonitrile attacks the Cu-center of
[Me3NN]Cu@CPh2 (generated by dissociation of
{[Me3NN]Cu}2(l-CPh2)) with concomitant loss of car-
bene (Scheme 4).
2.4.3. Reaction of {[Me3NN]Cu}2(l-CPh2) (4) with
dioxygen
Reaction of dicopper carbene 4 in ether solvent with
dioxygen results in the instantaneous decoloration of the
intense purple color of 4 to give a brown solution con-
taining a brown precipitate. GC/MS analysis shows
the formation of Ph2C@O as the major Ph2C-containing
product (Scheme 6). In accordance with the dioxygen
reactivity of [Me2NN]Cu(g2-ethylene) which forms
brown {[Me2NN]Cu}2(l-OH)2 (mOH = 3646 cmꢁ1) [22]
via the intermediacy of a CuI2IIðl-OÞ2 species [22,36,37],
the brown precipitate observed in the reaction of 4 with
O2 is likely {[Me3NN]Cu}2(l-OH)2. This is supported
by observation of a sharp IR m(OH) stretch at 3648
cmꢁ1 in the precipitate, identical to that observed upon
oxygenation of a solution of {[Me3NN]Cu}2(l-toluene).
Such [M]@CPh2 reactivity with dioxygen has been previ-
ously observed in the reaction of the aza-macrocycle
supported Fe(II) carbene (tmtaa)Fe@CPh2 with O2 to
give Ph2C@O and (tmtaa)Fe-O-Fe(tmtaa) [38].
4. Experimental
4.1. General experimental details
All experiments were carried out in a dry nitrogen
atmosphere using an MBraun glovebox and/or standard
Schlenk techniques. 4A molecular sieves were activated
in vacuo at 180 ꢁC for 24 h. Dry toluene was purchased
from Aldrich and was stored over activated 4A molecu-
lar sieves. Benzene, diethyl ether, tetrahydrofuran
(THF) and pentane were distilled before use from so-
dium/benzophenone and dichloromethane was distilled
from calcium hydride. All deuterated solvents were
sparged with nitrogen, dried over activated 4A molecu-
1
lar sieves and stored under nitrogen. H, 13C, and 31P
NMR spectra were recorded on a Mercury Varian 300
MHz spectrometer (300, 121.5, and 75.4 MHz, respec-
tively) at 25 ꢁC unless otherwise noted. 1H and 13C
NMR spectra were indirectly referenced to TMS using
residual solvent signals as internal standards, while 31P
Scheme 6. Reactivity of dicopper carbene 4 with dioxygen.

5998
Y.M. Badiei, T.H. Warren / Journal of Organometallic Chemistry 690 (2005) 5989–6000
NMR spectra were referenced against external 85%
H3PO4. GC/MS spectra were recorded on a Fisions
Instruments MD800. Phenylacetylene was passed
through activated alumina prior to use. Copper t-butox-
ide [40] was prepared by addition of 1 equiv. t-butanol
to mesitylcopper [41–43] in toluene. Triphenylphosphine
and 2,6-diphenyl isocyanide were obtained from Aldrich
and used as received. 2,4-bis(2,4,6-dimethylphenyllim-
ido)pentane, (H[Me3NN]) [44] and diphenyldiazome-
thane [45] was synthesized according to literature
procedures.
4.2.2. Preparation of {[Me2NN]Cu}2(l-CPh2) (4)
A chilled (ꢁ35 ꢁC) solution of N2CPh2 (0.015 g, 0.073
mmol) in ether was added in one portion to a chilled
solution of {[Me3NN]Cu}2(l-toluene) (0.068 g, 0.077
mmol) in 5 mL of ether. Evolution of N2 gas was ob-
served with the formation of a dark purple solution.
After stirring for 10 min, the solution was filtered
through Celite and the volatiles were removed in vacuo.
The residue was extracted with pentane, concentrated
and was allowed to stand overnight at ꢁ35 ꢁC. The
product was isolated and recrystallized from pentane
to afford 0.050 g (70%) of dark purple crystals suitable
1
4.2. DFT calculation details
for X-ray diffraction. H NMR (toluene-d8, ꢁ70 ꢁC): d
7.3–6.4 (br m, 6, m and p-CPh2), 7.07 (s, 2, Ar-H),
6.81 (s, 2, Ar-H), 6.61 (br, 2, o-CPh2), 6.33 (br s, 2,
Ar-H), 6.28 (br s, Ar-H), 6.18 (d, 2, o-CPh2), 4.99 (s,
2, backbone-CH), 2.86 (s, 6, Ar-CH3), 2.36 (s, 6, Ar-
CH3), 2.01 (s, 6, Ar-CH3), 1.87 (s, 6, Ar-CH3), 1.86 (s,
6, backbone-CH3), 1.63 (s, 6, backbone-CH3), 1.54 (s,
6, backbone-CH3) 1.18 (s, 6, Ar-CH3); 13C{1H} NMR
(benzene-d6, 25 ꢁC – partial data): d 189.0 (CPh2),
162.95 (imine), 148.69, 144.22, 131.79, 129.36, 128.84,
128.21, 126.78, 96.93 (backbone-CH), 23.45, 23.06,
21.05, 20.81, 19.46, 18.85; Anal. Calc. for C59H68N4Cu2:
C, 73.79; H, 7.14; N, 5.83. Found: C, 73.85; H, 7.66; N,
5.81%.
The DFT calculations employed the Becke–Perdew
exchange correlation functional [46–48] using the
Amsterdam Density Functional suite of programs (ADF
2002.03) [49,50]. Slater-type orbital (STO) basis sets
employed for H, C, and N atoms were of triple-f quality
augmented with two polarization functions (ZORA/
TZ2P – ADF basis V) while an improved triple-f basis
set with two polarization functions (ZORA/TZ2P+)
was employed for the Cu atom. Scalar relativistic effects
were included by virtue of the zero order regular approx-
imation (ZORA) [51–53]. The 1s electrons of C and N as
well as the 1s–2p electrons of Cu were treated as frozen
core. The VWN (Vosko, Wilk, and Nusair) functional
was used for LDA (local density approximation) [54].
The contour plots in Figs. 3 and 4 were rendered with
the MOLEKEL molecular graphics package [55,56].
4.2.3. Preparation of [Me3NN]Cu(g2-HC„CPh) (5)
Phenylacetylene (0.069, 0.67 mmol) was added to a
solution of {[Me3NN]Cu}2(l-toluene) (0.300 g, 0.339
mmol) in 1 mL toluene. The volatiles were removed in
vacuo immediately and the resulting solid residue was
extracted with pentane, concentrated and was allowed
to stand for two days at ꢁ35 ꢁC to give 0.275g (81%)
4.2.1. Preparation of {[Me3NN]Cu}2(l-toluene) (3)
A solution of H[Me3NN] (1.70 g, 5.35 mmol) in 10 ml
of toluene was stirred for 1 h with a solution of copper
(I) t-butoxide. The reaction mixture was filtered through
Celite, and the volatiles were removed in vacuo to give a
brown oil. Addition of pentane (ca. 10 mL) to the brown
residue induced crystallization. After standing at ꢁ35
1
of the product as colorless crystals. H NMR (toluene-
d8, ꢁ70 ꢁC): d 6.730 (m, 2, Ar-H), 6.719 (t, 1, p-Ph),
6.583 (t, 2, m-Ph), 6.435 (d, 2, o-Ph), 6.288 (s, 2, Ar-
H), 4.871 (s, 1, backbone-CH), 3.997 (s, 1, C„C–H),
2.194 (s, 6, Ar-o-CH3), 2.157 (s, 6, Ar-pꢁH), 2.039 (s,
6, Ar-o-CH3), 2.025 (s, 3, Ar-p-H), 1.656 (s, 3, backbone
–CH3), 1.591 (s, 3, backbone –CH3); 13C{1H} NMR
(benzene d6, 25 ꢁC): d 163.14, 148.86, 132.10, 130.26,
129.28, 129.05, 126.66, 124.12, 103.99 (HCCPh), 94.68
(backbone-CH), 86.87 (HCCPh), 22.68, 20.92, 18.74.
IR (cmꢁ1): 3169 (mCH), 1894 (mHC„CPh). Anal. Calc.
for C31H35N2Cu: C, 74.59; H, 7.07; N, 5.61. Found:
C, 74.41; H, 7.01; N, 5.65%.
1
ꢁC, 1.60 g (62%) of colorless crystals were isolated. H
NMR (benzene-d6): d 7.131–7.022 (m, 5, toluene-Ar),
6.913 (br s, 8, Ar-H), 4.791 (s, 2, backbone-CH), 2.264
(br s, 12, Ar-p-CH3), 2.103 (s, 3, toluene-CH3), 2.023
(br s, 24, Ar-p-CH3) (shoulder at 1.922), 1.660 (br s,
12, backbone-CH3). 13C{1H} NMR (benzene d6): d
162.74, 148.27, 131.81, 130.32, 129.29 (tol), 128.91,
128.50 (tol), 125.65 (tol), 94.54 (backbone-CH), 23.16,
21.06, 18.81, 18.71. After standing overnight in ben-
1
zene-d6, 2 species are observed by H NMR in nearly
identical ratios. Species 1 (nearly identical to initial spec-
trum): d 6.920 (s, 4, Ar-H), 4.803 (s, 1, backbone C–H),
2.275 (s, 6, Ar-p-CH3), 2.029 (s, 12, Ar-o-CH3), 1.669 (s,
6, backbone-CH3); Species 2 (becomes more distinct
with time): d 6.809 (s, 4, Ar-H), 4.763 (s, 1, backbone
C–H), 2.239 (s, 6, Ar-p-CH3), 1.901 (s, 12, Ar-o-CH3),
1.585 (s, 6, backbone-CH3). Unable to obtain satisfac-
tory elemental analysis due to extreme air sensitivity.
4.2.4. Preparation [Me3NN]Cu(PPh3) (6)
A solution of triphenylphosphine (0.059 g, 0.226
mmol) in 1 mL toluene was added to a solution of
{[Me3NN]Cu}2(l-toluene) (0.100 g, 0.113 mmol) in 1
mL toluene. The volatiles were removed in vacuo imme-
diately to give an oil which crystallized upon addition of
pentane (2 mL). After standing at ꢁ35 ꢁC, 0.129 g (92%)
colorless crystals were isolated. 1H NMR (benzene-d6): d

Y.M. Badiei, T.H. Warren / Journal of Organometallic Chemistry 690 (2005) 5989–6000
5999
6.98–6.88 (m, 15, Ar-H), 6.690 (s, 4, Ar-H), 5.086 (s, 1,
backbone-CH), 2.198 (s, 6, Ar-p-CH3), 2.154 (s, 12, Ar-
o-CH3), 1.795 (s, 6, backbone-CH3). 13C{1H} NMR
(benzeneꢁd6, partial data): d 162.81, 150.52, 133.57
(JPC = 15.6 Hz), 131.06, 130.21, 129.28, 129.10, 128.72
(JPC = 9 Hz), 128.47 (JPC = 9.6 Hz), 22.84, 21.00,
18.99; 31P NMR (benzene-d6): d 5.20. Anal. Calc. for
C41H44N2CuP: C, 74.69; H, 6.73; N, 4.25. Found: C,
74.54; H, 7.04; N, 4.35%.
4.2.8. Reaction of {[Me3NN]Cu}2(l-CPh2) with CNAr
Approx. 2 equiv. 2,6-dimethylphenyl isocyanide
(0.003 g, 0.02 mmol) was added to a solution of
{[Me2NN]Cu}2(l-CPh2) (0.012 g, 0.011 mmol) in ca. 1
mL benzene-d6. The intense purple color of 4 was dis-
charged to give a much less intense indigo solution.
1
Analysis by H NMR spectroscopy indicates [Me3NN]-
Cu(CNAr) as the major [Me3NN]Cu product with
{[Me3NN]Cu}2(l-CPh2) and [Me3NN]Cu@CPh2 pres-
ent in less than 5 mol%. Ph2C@CPh2 was observed by
1H NMR spectroscopy (multiplets between d 7.16–7.11
and 6.96–6.85 ppm), corroborated by GC/MS analysis
as the sole Ph2C-containing species.
4.2.5. Preparation of [Me3NN]Cu(CNAr) (7)
A solution of 2,6-dimethylphenyl isocyanide (0.030 g,
0.226 mmol) in 1 mL toluene was added to a solution of
{[Me3NN]Cu}2(l-toluene) (0.100 g, 0.113 mmol) in 1
mL toluene. The volatiles were removed in vacuo imme-
diately to give an oil. Addition of pentane (2 mL) fol-
lowed by standing at ꢁ35 ꢁC allowed for the isolation
of 0.100g (91%) yellow crystals. 1H NMR (benzene-
d6): d 6.884 (s, 4, Ar-H), 6.594 (t, 1, Ar-p-H), 6.394 (d,
2, Ar-m-H), 5.037 (s, 1, backbone-CH), 2.405 (s, 12,
Ar-o-CH3), 2.213 (s, 6, Ar-H), 1.810 (s, 6, Ar-H),
1.628 (s, 6, backbone-CH3). 13C{1H} NMR (benzene-
d6): d 163.18, 153.95, 150.94, 135.15, 131.59, 130.23,
129.36, 127.85, (one aromatic resonance missing or ob-
scured), 94.77, 22.76, 21.32, 19.58, 18.39. IR (cmꢁ1):
2121 (mCN). Anal. Calc. for C32H38N3Cu: C, 72.76; H,
7.25; N, 7.96. Found: C, 73.13; H, 7.05; N, 8.05%.
4.2.9. Reaction of {[Me3NN]Cu}2(l-CPh2) with O2
Bubbling O2 gas through a ca. 0.1 mM ether solution
of {[Me3NN]Cu}2(l-CPh2) resulted in the immediate
discharge of the deep purple solution to give a brown
precipitate. Analysis by GC/MS indicates Ph2C@O as
the predominant Ph2C-containing species. IR analysis
of the brown precipitate gives a sharp stretch at 3648
cmꢁ1, identical to that produced by oxygenation of
{[Me3NN]Cu}2(l-toluene) under similar conditions,
consistent with the formation of {[Me3NN]Cu}2(l-
OH)2. (mOH = 3646 cmꢁ1 for {[Me2NN]Cu}2(l-OH)2).
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 279253–279257 for com-
pounds 3–7.
4.2.6. Reaction of {[Me3NN]Cu}2(l-CPh2) with
HC„CPh
10 equiv. phenylacetylene (57 lL, 0.52 mmol) was
added to a solution of {[Me2NN]Cu}2(l-CPh2) (0.050
g, 0.052 mmol) in ca. 1 mL benzene-d6. The intense pur-
ple color of 4 was discharged over 15 min to result in a
greenish solution which revealed [Me3NN]Cu(g2-
HC„CPh) as the only Cu(I) b-diketiminato product.
After standing for 1 h, the solution was pale yellow
and analysis by GC/MS indicated a peak with m/
z = 268 (1,3,3-triphenylcyclopropene) as the major
Ph2C-containing species.
Acknowledgements
We thank Ms. Claire Comfort for first crystallizing
{[Me3NN]Cu}2(l-toluene) (3), Ms. Marie Melzer for
preparing an additional sample of 3, and Mr. Matthew
Varonka for assistance in the DFT calculation of
[Me3NN]Cu@CPh2 (2). T.H.W. thanks the NSF CA-
REER program (CHE-0135057) for financial support
of this work.
References
4.2.7. Reaction of {[Me3NN]Cu}2(l-CPh2) with PPh3
8 equiv. triphenylphosphine (0.057 g, 0.219) was added
to a solution of {[Me2NN]Cu}2(l-CPh2) (0.026 g, 0.027
mmol) in ca. 1 mL benzene-d6. The intense purple color
of 4 was discharged over 10 min to result in a greenish
solution. Analysis by 31P NMR spectroscopy indicates
the presence of Ph3P@CPh2 (d 7.36 ppm), [Me3NN]-
Cu(PPh3) (d 5.20 ppm), and free PPh3 (d ꢁ4.79 ppm).
Integration of the Ph3P@CPh2 resonance against the
[Me3NN]Cu(PPh3) formed indicates a 76% yield of ylide
formation. An authentic sample of Ph3P@CPh2 was pre-
pared by the method of Staudinger from PPh3 and
N2CPh2 to first give colorless Ph3P@N–N@CPh2 which
affords red Ph3P@CPh2 upon extrusion of N2 with
heating of Ph3P@N–N@CPh2 in the melt [30,31].
[1] W. Kirmse, Angew. Chem. Int. Ed. 42 (2003) 1088.
[2] H. Nozaki, S. Moriuti, H. Takaya, R. Noyori, Tetrahedron Lett.
(1966) 5239.
[3] W.R. Moser, J. Am. Chem. Soc. 91 (1969) 1135.
[4] W.R. Moser, J. Am. Chem. Soc. 91 (1969) 1141.
[5] R.G. Salomon, J.K. Kochi, J. Am. Chem. Soc. 95 (1973) 3300.
[6] M.M. D´ıaz-Requejo, P.J. Pe´rez, M. Brookhart, J.L. Templeton,
Organometallics 16 (1997) 4399.
´
´
[7] M.M. Dıaz-Requejo, M.C. Nicasio, P.J. Perez, Organometallics
17 (1998) 3051.
[8] T. Rasmussen, J.F. Jensen, N. Ostergaard, D. Tanner, T. Ziegler,
P.-O. Norrby, Chem. Eur. J. 8 (2002) 177.
[9] J.M. Fraile, J.I. Garcıa, V. Martınez-Merino, J.A. Mayoral, L.
Salvatella, J. Am. Chem. Soc. 123 (2001) 7616.
[10] B.F. Straub, I. Gruber, F. Rominger, P. Hofmann, J. Organomet.
Chem. 684 (2003) 124.
´
´

6000
Y.M. Badiei, T.H. Warren / Journal of Organometallic Chemistry 690 (2005) 5989–6000
[11] M. Buhl, F. Terstegen, F. Lo¨ffler, B. Meynhardt, S. Kierse, M.
[34] L. Bo¨ttcher, D. Walther, H.Z. Go¨rls, Anorg. Allg. Chem. 629
(2003) 1208.
¨
Muller, C. Na¨ther, U. Luning, Eur. J. Org. Chem. (2001) 2151.
¨
¨
[12] T. Ikeno, I. Iwakura, T. Yamada, J. Am. Chem. Soc. 124 (2002)
15152.
[13] B.F. Straub, P. Hofmann, Angew. Chem. Int. Ed. 40 (2001) 1288.
[35] B.A. Jazdzewski, P.L. Holland, M. Pink, V.G. Young Jr., D.J.E.
Spencer, W.B. Tolman, Inorg. Chem. 40 (2001) 6097.
[36] D.J.E. Spencer, A.M. Reynolds, P.L. Holland, B.A. Jazdzewski,
C. Duboc-Toia, L. Le Pape, S. Yokota, Y. Tachi, S. Itoh, W.B.
Tolman, Inorg. Chem. 41 (2002) 6307.
[37] D.J.E. Spencer, N.W. Aboelella, A.M. Reynolds, P.L. Holland,
W.B. Tolman, J. Am. Chem. Soc. 124 (2002) 2108.
[38] A. Klose, E. Solari, C. Floriani, N. Re, A. Chiesi-Villa, C.
Rizzoli, Chem. Commun. (1997) 2297.
´
´
´
[14] J. Barluenga, L.A. Lopez, O. Lo¨ber, M. Tomas, S. Garcıa-
Granda, C. Alvarez-Ru´a, J. Borge, Angew. Chem. Int. Ed. 40
(2001) 3392.
´
´
[15] J. Barluenga, P. Barrio, R. Vicente, L.A. Lopez, M. Tomas, J.
Organometal. Chem. 689 (2004) 3793.
[16] S.-T. Liu, K.R. Reddy, Chem. Soc. Rev. 28 (1999) 315.
[17] H. Werner, P. Schwab, E. Bleuel, N. Mahr, B. Windmuller, J.
¨
[39] D. Mindiola, G.L. Hillhouse, J. Am. Chem. Soc. 124 (2002)
9976.
Wolf, Chem. Eur. J. 6 (2000) 4461.
[18] X. Dai, T.H. Warren, J. Am. Chem. Soc. 126 (2004) 10085.
[19] G van Koten, S.L. James, J.T.B.H. Jastrebeski, in: E.W. Abel,
F.G.A. Stone, G. Wilkinson (Eds.), Comprehensive Organometal-
lic Chemistry II, vol. 3, Pergamon Press, New York, 1995, p. 57.
[20] D.S. Laitar, C.J.N. Mathison, W.M. Davis, J.P. Sadighi, Inorg.
Chem. 42 (2003) 7354.
[40] M. Hakansson, C. Lopes, S. Jagner, Inorg. Chim. Acta 304 (2000)
178.
[41] S. Gambarotta, C. Floriani, A. Chiesi-Vila, C. Guastini, Chem.
Commun. (1983) 1156.
[42] E.M. Meyer, S. Gambarotta, C. Floriani, A. Chiesi-Vila, C.
Guastini, Organometallics 8 (1989) 1067.
˚
[21] S.Y. Lee, S.J. Na, H.Y. Kwon, B.Y. Lee, S.O. Kang, Organo-
metallics 23 (2004) 5382.
[22] X. Dai, T.H. Warren, Chem. Commun. (2001) 1998.
[23] L.D. Amisial, X. Dai, R.A. Kinney, A. Krishnaswamy, T.H.
Warren, Inorg. Chem. 43 (2004) 6537.
[43] H. Eriksson, M. Hakansson, Organometallics 16 (1997) 4243.
[44] P.H.M. Budzelaar, A.B. van Oort, A.G. Orpen, Eur. J. Inorg.
Chem. (1998) 1485.
[45] L.I. Smith, K.L. Howard, Organic Synthesis Collective vol. 3
(1955).
[24] S. Gishig, A. Togni, Organometallics 24 (2005) 203.
[25] M.W. Klett, R.P. Johnson, J. Am. Chem. Soc. 107 (1985)
3963.
[26] H. Masuda, K. Machida, M. Munakata, S. Kitagawa, H.
Shimono, J. Chem. Soc., Dalton Trans. (1988) 1907.
[27] M. Munakata, S. Kitagawa, I. Kawada, M. Maekawa, H.
Shimono, J. Chem. Soc., Dalton Trans. (1992) 2225.
[28] H.-C. Weiss, D. Bla¨ser, R. Boese, B.M. Doughan, M.M. Haley,
Chem. Commun. (1997) 1703.
[46] A. Becke, Phys. Rev. A 38 (1988) 3098.
[47] J.P. Perdew, Phys. Rev. B 34 (1986) 7406.
[48] J.P. Perdew, Phys. Rev. B 33 (1986) 8822.
[49] G. te Velde, F.M. Bickelhaupt, E.J. Baerends, C. Fonseca Guerra,
S.J.A. Van Gisbergen, J.G. Snijders, T. Ziegler, J. Comput.
Chem. 22 (2001) 931.
[50] C. Fonseca Guerra, J.G. Snijders, G. te Velde, E.J. Baerends,
Theor. Chem. Acc. 99 (1998) 391.
[51] J.G. Snijders, E.J. Baerends, P. Ros, Mol. Phys. 38 (1979)
1909.
[29] T.C.H. Lam, W.-L. Mak, W.-L. Wong, H.-L. Kwong, H.H.Y.
Sung, S.M.F. Lo, I.D. Williams, W.-H. Leung, Organometallics
23 (2004) 1247.
[52] T. Ziegler, V. Tschinke, E.J. Baerends, J.G. Snijders, W.K.
Ravenek, J. Phys. Chem. 93 (1989) 3050.
[30] H. Staudinger, J. Meyer, Helv. Chim. Acta 2 (1919) 619.
[31] H. Staudinger, J. Meyer, Helv. Chim. Acta 2 (1919) 635.
[32] R.S. Tewari, N. Kumari, P.S.Z. Kendurkar, Naturforsch 30b
(1975) 513.
[53] E. van Lenthe, E.J. Baerends, J.G. Snijders, J. Chem. Phys. 99
(1993) 4597.
[54] S.H. Vosko, L. Wilk, M. Nusair, Can. J. Phys. 58 (1980)
1200.
[33] G.A. Ardizzoia, S. Cenini, G. La Monica, N. Masiocchi, A.
Maspero, M. Moret, Inorg. Chem. 37 (1998) 4284.
[55] P.F., Flu¨kiger, Ph.D. Thesis, University of Geneva, 1992.
[56] S. Portmann, H.P. Luthi, Chimia 54 (2000) 766.
¨