Synthesis, characterization, and the role of counterion in cyclopropanation of styrene catalyzed by [CuI(2,2′-bpy)(π-CH2{double bond, long}CHC6H5)][A] (A = ClO4-, PF6- and CF3 SO3-) complexes

Article abstract of DOI:10.1016/j.jorganchem.2007.07.045

Copper(I)/2,2′-bipyridine complexes, [Cu^I(bpy)(π-CH₂CHC₆H₅)][A] (A = CF₃ SO₃^- (1), PF₆^- (2)) have been synthesized and characterized. The equilibrium constants for the coordination of styrene to [Cu^I(bpy)]⁺ cations at 300 K were determined to be 4.3 × 10³ (1), 4.4 × 10³ (2) and 3.8 × 10³ M^-1(A = ClO₄^-, 3) . These data suggested that the axial coordination of the counterion in these complexes observed in the solid state (2.4297(11) A? 1, 2.9846(12) A? 2, and 2.591(4) A? 3) did not significantly affect the binding constant of styrene to [Cu^I(bpy)]⁺ cations in solution. In cyclopropanation reactions catalyzed by 1-3, similar product distribution was obtained. The rate of decomposition of EDA in the presence of styrene at room temperature catalyzed by 3 (k_obs = (7.7 ± 0.32) × 10^-3 min^-1) was slower than the rate observed for 1 (k_obs = (1.4 ± 0.041) × 10^-2 min^-1) or 2 (k_obs = (1.0 ± 0.025) × 10^-2 min^-1).

Full text of DOI:10.1016/j.jorganchem.2007.07.045

Journal of Organometallic Chemistry 692 (2007) 5165–5172
www.elsevier.com/locate/jorganchem
Synthesis, characterization, and the role of counterion
in cyclopropanation of styrene catalyzed by
[CuI(2,ꢀ20-bpy)ꢀ(p-CH2@CHCꢀ6H5)][A]
ðA ¼ ClO4 ; PF6 and CF3SO3 Þ complexes
*
Carolynne Ricardo, Tomislav Pintauer
Department of Chemistry and Biochemistry, Duquesne University, 600 Forbes Avenue, Pittsburgh, PA 15282, United States
Received 14 June 2007; received in revised form 28 July 2007; accepted 28 July 2007
Available online 3 August 2007
Abstract
I
ꢀ
ꢀ
Copper(I)/2,20-bipyridine complexes, [Cu (bpy)(p-CH2CHC6H5)][A] ðA ¼ CF3SO3 ð1Þ; PF6 ð2ÞÞ have been synthesized and char-
acterized. The equilibrium constants for the coordination of styrene to [CuI(bpy)]+ cations at 300 K were determined to be 4.3 · 103 (1),
4.4 · 103 (2) and 3.8 · 103 Mꢀ1 ðA ¼ ClO4ꢀ; 3Þ. These data suggested that the axial coordination of the counterion in these complexes
˚
˚
˚
observed in the solid state (2.4297(11) A 1, 2.9846(12) A 2, and 2.591(4) A 3) did not significantly affect the binding constant of styrene to
[CuI(bpy)]+ cations in solution. In cyclopropanation reactions catalyzed by 1–3, similar product distribution was obtained. The rate of
decomposition of EDA in the presence of styrene at room temperature catalyzed by 3 (kobs = (7.7 0.32) · 10ꢀ3 minꢀ1) was slower than
the rate observed for 1 (kobs = (1.4 0.041) · 10ꢀ2 minꢀ1) or 2 (kobs = (1.0 0.025) · 10ꢀ2 minꢀ1).
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Copper(I); 2,20-Bipyridine; Styrene; Crystal structure; Cyclopropanation
1. Introduction and background
So far, cationic copper(I) complexes in conjunction with a
C2-symmetric ligand, such as bis(oxazoline) [15], 2,20-bipyr-
idine (bpy) [16], 2,20:60,200- terpyridine [16–18] and 1,10-phe-
nanthroline (phen) [16,19], and neutral copper(I) complexes
with semicorrin [20], polypyrazolylborates [21–23], imino-
phosphanamidates [24,25] and b-diketiminates [26] have
been successfully used in cyclopropanation reactions. How-
ever, despite a tremendous effort directed towards empirical
catalyst development, mechanism of these very important
synthetic reactions is still not fully understood. It is gener-
ally accepted that the copper catalyzed cyclopropanation
reactions proceed via a copper–carbene complex, as
indicated in Scheme 1 for cyclopropanation catalyzed by
copper(I)/2,20-bipyridine complex [1,2,15]. However, the
details of this process are not well-known.
In recent years, a considerable effort has been devoted to
the development of transition metal catalysts for diastereo-
and enantioselective cyclopropanation [1–4] and aziridin-
ation [5,6] of olefins. Effective catalytic system for the cyclo-
propanation of alkenes with diazo reagents requires the use
of a transition metal complex which facilitates the loss of N2
from the diazo reagent, as well as stabilizes intermediate
carbene species against competing carbene dimerization
[7–10]. A variety of transition metal complexes have been
found to be active in cyclopropanation reactions and they
include the complexes of Fe [11], Rh [12], Ru [13,14] and
Cu [4]. Copper appears to be particularly attractive because
of its low cost relative to other transition metal complexes.
Only, very recently, copper–carbene complexes have
been detected as reaction intermediates in cyclopropana-
tion reactions utilizing low temperature NMR
*
Corresponding author. Tel.: +1 412 396 1626; fax: +1 412 396 5683.
E-mail address: pintauert@duq.edu (T. Pintauer).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.07.045

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C. Ricardo, T. Pintauer / Journal of Organometallic Chemistry 692 (2007) 5165–5172
Scheme 1. Proposed mechanism for copper(I)/2,20-bipyridine catalyzed cyclopropanation of olefins.
measurements [24,25] and X-ray diffraction [26]. Another
key mechanistic feature of these reactions includes the role
of monomer and counterion, both of which are poorly
understood. Mechanistic [15,27] and computational
[28,29] studies have indicated that copper(I)/olefin com-
plexes in these systems might act as either catalytically
active species or resting states. Furthermore, the reactivity
of cationic copper(I) complexes is strongly influenced by
the counterion. Triflates and hexafluorophosphates
[15,30] were found to be highly effective catalysts whereas
halides, cyanides, acetates and perchlorate showed little
or no catalytic activity.
the role of counterion in cyclopropanation of styrene with
ethyldiazoacetate (EDA) catalyzed by these complexes and
[CuI(bpy)(p-CH2@CHC6H5)][ClO4] (3) is also discussed.
Cationic copper(I)/alkene complexes with bidentate
nitrogen based ligands are very rare and so far only two
complexes with nonpolar olefins such as styrene [31] and
cyclohexene [32] have been isolated (Scheme 2). In both
complexes, the geometry around copper(I) atom was found
to be trigonal pyramidal, due to the weak interaction with
the counterion. Recently, we have successfully isolated
and structurally characterized [CuI(bpy)(p-CH2CHCO-
ꢀ
OCH3)][A] ðA ¼ CF3SO3ꢀ; PF6 and ClO4ꢀÞ complexes
(Scheme 2). These complexes represented the first class of
trigonal pyramidal copper(I) complexes with p-coordinated
electron poor olefins. Weak coordination of the counterion
ꢀ
˚
was observed in the case of CF3SO3 (Cu–O = 2.388(4) A)
ꢀ
˚
and PF6 (Cu–F = 2.609(2) A) complexes. The counterion
ClO4ꢀ, on the other hand, was noncoordinating and the
corresponding copper(I) complex was dimeric in the solid
state with oxygen atoms of the carbonyl moieties in methyl
acrylate bridging two copper(I) centers (Cu–O =
˚
2.434(4) A).
In this article, we report the synthesis and characteriza-
tion of copper(I)/bpy complexes [CuI(bpy)(p-CH2@CH-
C6H5)][A] ðA ¼ CF3SO3 ð1Þ; PF6 ð2ÞÞ. Furthermore,
Scheme 2. Structures of cationic copper(I)/alkene complexes with biden-
tate nitrogen based ligands.
ꢀ
ꢀ

C. Ricardo, T. Pintauer / Journal of Organometallic Chemistry 692 (2007) 5165–5172
5167
2. Experimental
dry box refrigerator at ꢀ35 ꢁC. After 24 h, colorless
crystals were formed, which were washed with 10 mL of
pentane and dried under vacuum to yield 0.120 g (68%)
of [CuI(bpy)(p-CH2@CH–C6H5)][CF3SO3]. 1H NMR
(300 MHz, CD2Cl2, 250 K): d 8.39 (d, J = 5.0 Hz, 2H,
H6 + H06), d 8.24 (d, J = 8.1 Hz, 2H, H3 + H03), d 8.11 (t,
J = 7.7 Hz, H4 + H04), d 7.60 (m, 2H, H5 + H05), d 7.51 (d,
J = 7.5 Hz, 2H, Sty), d 7.27–7.36 (m, 3H, Sty), d 6.32
(dd, Jtrans = 16 Hz, Jcis = 10 Hz, 1H, Ha), d 5.06 (d,
Jtrans = 16 Hz, 1H, Hbtrans), d 4.73 (d, Jcis = 10 Hz, 1H,
Hbcis). FT-IR (solid): m(C@C) = 1529 cmꢀ1. Anal. Calc.
for C19H16CuF3N2O3S: C, 48.25; H, 3.41; N, 5.92. Found:
C, 48.36; H, 3.42; N, 5.87%.
2.1. General
[CuI(CF3SO3)]2 Æ C6H5CH3 (99.99%, Aldrich), [CuI-
(CH3CN)4][PF6] (98+%, Strem) and 2,20-bipyridine
(99+%, Acros) were used as received. [CuI(CH3CN)4]
[ClO4] was synthesized according to the literature proce-
dure [33]. Styrene (99%, Acros) was stirred over CaH2 for
24 h and distilled under argon. Solvents (methylene chlo-
ride, pentane, acetonitrile and methanol) were degassed
and deoxygenated using Innovative Technology solvent
purifier. Ethyl diazoacetate (EDA, 99% Aldrich) was
degassed prior to use. All manipulations were performed
under argon atmosphere in a dry box (<1.0 ppm of O2
and <0.5 ppm of H2O) or using standard Schlenk line tech-
niques. 1H NMR spectra were obtained using Bruker
Avance 300 and 400 MHz spectrometers and chemical
shifts are given in ppm relative to residual solvent peaks
(d(CD2Cl2) = 5.32 and d(CDCl3) = 7.26). IR spectra were
recorded in the solid state or solution using Nicolet Smart
Orbit 380 FT-IR spectrometer (Thermo Electron Corpora-
tion). Elemental analyses for C, H and N were obtained
from Midwest Microlab, LLC. Caution: Perchlorate metal
salts are potentially explosive and were handled in small
quantities under argon atmosphere (Fig. 1).
2.3. [CuI(bpy)(p-CH2@CHC6H5)][PF6] Æ
1/2CH2@CHC6H5 (2)
The complex was prepared using the procedure for
[CuI(bpy)(p-CH2@CH–C6H5)][CF3SO3] except that [CuI-
(CH3CN)4][PF6] (0.100 g, 2.68 · 10ꢀ4 mol) was used
instead of [CuI(CF3SO3)]2 Æ C6H5CH3. Yield = 0.105 g
1
(75%). H NMR (300 MHz, CD2Cl2, 180 K): d 8.55 (ddd,
J1 = 5.0 Hz, J2 = 1.5 Hz, J3 = 0.90 Hz, 2H, H6 + H06), d
8.41 (dt, J1 = 8.0 Hz, J2 = 1.0 Hz, 2H, H3 + H03), d 8.32
(dt, J1 = 8.0 Hz, J2 = 1.7 Hz, 2H H4 + H04), d 7.80 (m,
2H, H5 + H05), d 7.5–7.6 (m, 7.5H, Sty), d 6.31 (dd,
Jtrans = 16 Hz, Jcis = 10 Hz, 1.5H, Ha),
d
5.23 (d,
2.2. [CuI(bpy)(p-CH2@CHC6H5)][CF3SO3] (1)
Jtrans = 16 Hz, 1.5H, Hbtrans), d 4.74 (d, Jcis = 10 Hz, 1.5H,
Hbcis). FT-IR (solid): m(C@C) = 1527 cmꢀ1. Anal. Calc.
for C44H40Cu2F12N4P2: C, 50.72; H, 3.87; N, 5.38. Found:
C, 50.57; H, 3.88; N, 5.18%.
[CuI(CF3SO3)]2 Æ C6H5CH3 (0.100 g, 1.93 · 10ꢀ4 mol)
and styrene (1.33 mL, 1.16 · 10ꢀ2 mol) were dissolved in
2.0 mL of dry and degassed methanol and the solution
stirred at room temperature for 20 min. 2,20-Bipyridine
(0.0604 g, 3.86 · 10ꢀ4 mol) was then added and the solu-
tion stirred for additional 30 min. Pentane (2.0 mL) was
layered on top of methanol and the solution placed inside
2.4. [CuI(bpy)(p-CH2@CHC6H5)][ClO4] (3)
The complex was synthesized according to the modified
literature procedure, starting from [CuI(CH3CN)4][ClO4],
2,20-bipyridine and excess styrene [31]. The complex was
obtained in 83% yield. 1H NMR (300 MHz, CD2Cl2,
220 K): d 8.40 (d, J = 4.5 Hz, 2H, H6 + H06), d 8.25 (d,
J = 8.1 Hz, 2H, H3 + H03),
d 8.15 (dt, J1 = 7.8 Hz,
J2 = 1.7 Hz, 2H H4 + H04), d 7.64 (m, 2H, H5 + H05), d
7.51 (d, J = 6.9 Hz, 2H, Sty), d 7.30–7.40 (m, 3H, Sty), d
6.33 (dd, Jtrans = 16 Hz, Jcis = 10 Hz, 1H, Ha), d 5.17 (d,
Jtrans = 16 Hz, 1H, Hbtrans), d 4.75 (d, Jcis = 10 Hz, 1H,
Hbcis). FT-IR (solid): m(C@C) = 1525 cmꢀ1
.
2.5. General procedure for cyclopropanation of styrene
In a 20-mL Schlenk flask, catalyst precursor (0.0250
mmol, 1 equiv.), 2,20-bipyridine (0.0038 g, 0.025 mmol,
1 equiv.) and styrene (1.40 mL, 12.2 mmol, 500 equiv.)
were suspended in CH2Cl2 (1.4 mL) and stirred at room
temperature for 10 min. To the homogenous solution,
EDA (130 lL, 1.24 mmol, 50 equiv.) was added in one por-
tion and stirred for 2 h. Completeness of the reaction was
determined by IR spectroscopy, as indicated by the disap-
pearance of the absorption of the diazo group (–N@N–) at
Fig. 1. 1H NMR labeling scheme.

5168
C. Ricardo, T. Pintauer / Journal of Organometallic Chemistry 692 (2007) 5165–5172
2112 cmꢀ1. The reaction mixture was then exposed to air
and the remaining copper(II) complex was removed by
passing through a basic alumina column. The solvent was
removed by vacuum evaporation and the product distribu-
(k = 0.71073 A) on a Bruker Smart Apex II CCD diffrac-
tometer. Data reduction included absorption corrections
by the multiscan method using SADABS [34]. Crystal data
and experimental conditions are given in Table 1. Struc-
tures were solved by direct methods and refined by full-
matrix least squares using SHELXTL 6.1 bundled software
package [35]. The H atoms were positioned geometrically
˚
1
tion determined by H NMR in CDCl3.
2.6. Kinetic studies
˚
˚
(aromatic C–H = 0.93 A, methylene C–H = 0.97 A and
methyl C–H = 0.96 A) and treated as riding atoms during
subsequent refinement, with Uiso(H) = 1.2Ueq(C) or
1.5Ueq (methyl C). Crystal maker 7.2 was used to gener-
ate molecular graphics.
˚
A solution at time zero was prepared separately by mix-
ing EDA (260 lL, 2.47 mmol), styrene (2.8 mL, 24.4 mmol)
and CH2Cl2 (2.8 mL) and the IR spectrum was recorded
(mN@N = 2112 cmꢀ1). In a 20-mL Schlenk flask, the solu-
tion was prepared by dissolving the catalyst precursor
(0.0100 mmol, 1.0 equiv.) and 2,20-bipyridine (0.0016 g,
0.010 mmol, 1.0 equiv.) in styrene (2.80 mL, 24.7 mmol,
2500 equiv.) and CH2Cl2 (2.80 mL). The solution was stir-
red at room temperature until it became homogeneous
(10 min). EDA (260 lL, 2.47 mmol, 250 equiv.) was then
added in one portion. The consumption of EDA was mon-
itored by collecting 0.2 mL of the reaction solution every
15 min and recording the IR spectrum for a period of 3 h.
3. Results and discussion
3.1. X-ray crystallography
[CuI(bpy)(p-CH2@CHC6H5)][A]
ðA ¼ CF3SO3 ð1Þ;
ꢀ
ꢀ
ꢀ
PF6 ð2Þ and ClO4 ð3ÞÞ were synthesized by reacting
[CuI(CF3SO3)]2 Æ C6H5CH3, [CuI(CH3CN)4][PF6] and [CuI-
(CH3CN)4][ClO4], respectively, with the stoichiometric
amounts of 2,20-bipyridine (bpy) and large excess of styrene
(typically 30 equiv). Slow crystallization from methanol at
ꢀ35 ꢁC afforded colorless crystals of 1–3 in reasonable
yields. Shown in Fig. 2 is the molecular structure of com-
plex 1. Selected bond distances and angles are listed in
2.7. X-ray crystallography
The X-ray intensity data were collected at room temper-
ature using graphite-monochromated Mo Ka radiation
Table 1
Crystallographic data and experimental details for 1 and 2
Compound
[CuI(bpy)(p-CH2@CHC6H5)][CF3SO3] (1)
[CuI(bpy)(p-CH2@CHC6H5)][PF6] Æ 1/2Sty (2)
Formula
Color/shape
C
19H16CuF3N2O3S
C44H40Cu2F12N4P2
Colorless/needles
1041.82
Monoclinic
P2(1)/c
Colorless/needles
472.94
Monoclinic
P2(1)/c
Formula weight
Crystal system
Space group
Temperature (K)
Cell constants
150(2)
150(2)
˚
a (A)
8.36140(10)
22.3107(7)
˚
b (A)
15.6925(2)
14.8425(2)
12.2893(4)
16.5493(5)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
90.
98.4940(10)
90.
1926.14(4)
90.
107.63(4)
90.
4324.5(2)
3
˚
V (A )
Formula units/unit cell
4
4
Dcalc (g cmꢀ3
)
1.631
1.294
960
1.600
1.148
2112
l (mmꢀ1
F(000)
)
Diffractometer
Radiation, graphite-monochromated
Crystal size (mm)
h Range (ꢁ)
Range of h,k,l
Bruker Smart Apex II
Bruker Smart Apex II
˚
˚
Mo Ka (k = 0.71073 A)
0.25 · 0.14 · 0.08
1.90 < h < 30.97
12, 22, 21
Mo Ka (k = 0.71073 A)
0.49 · 0.29 · 0.17
0.96 < h < 32.47
32, 18, 24
53954/14828
0.0476
Full-matrix least-squares on F2
14828/0/577
Reflections collected/unique
Rint
33538/6103
0.0280
Full-matrix least-squares on F2
6103/0/265
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
1.023
0.745
R1 = 0.0288, wR2 = 0.0716
R1 = 0.0391, wR2 = 0.0764
0.426 and ꢀ0.304
R1 = 0.0325, wR2 = 0.0975
R1 = 0.0503, wR2 = 0.1104
0.668 and ꢀ0.461
ꢀ3
˚
Maximum residual peaks (e A
)

C. Ricardo, T. Pintauer / Journal of Organometallic Chemistry 692 (2007) 5165–5172
5169
Table 2
Selected bond distances (A) and angles (ꢁ) for 1 and 2
˚
Distances Angles
[CuI(bpy)(p-CH2@CHC6H5)][CF3SO3] (1)
Cu(1)–N(1)
Cu(1)–N(2)
Cu(1)–C(1)
Cu(1)–C(2)
Cu(1)–O(1)
C(1)–C(2)
1.9998(12)
1.9978(12)
2.0033(14)
2.0304(14)
2.4297(11)
1.383(2)
N(2)–Cu(1)–N(1)
N(2)–Cu(1)–C(1)
N(1)–Cu(1)–C(1)
N(2)–Cu(1)–C(2)
N(1)–Cu(1)–C(2)
C(1)–Cu(1)–C(2)
N(2)–Cu(1)–O(1)
N(1)–Cu(1)–O(1)
C(1)–Cu(1)–O(1)
C(1)–C(2)–C(3)
82.88(5)
156.03(6)
119.27(6)
115.92(6)
153.24(5)
40.11(6)
91.31(4)
94.77(4)
95.49(5)
125.04(13)
[CuI(bpy)(p-CH2@CHC6H5)][PF6] Æ 1/2Sty (2)
Cu(1)–N(1)
Cu(1)–N(2)
Cu(1)–C(1)
Cu(1)–C(2)
C(1)–C(2)
Cu(2)–N(3)
Cu(2)–N(4)
Cu(2)–C(19)
Cu(2)–C(20)
Cu(2)–F(9)
C(19)–C(20)
1.9779(13)
1.9964(13)
2.0144(15)
2.0167(14)
1.378(2)
1.9713(12)
1.9621(12)
1.9706(15)
2.0131(14)
2.9846(12)
1.388(2)
N(1)–Cu(1)–N(2)
N(1)–Cu(1)–C(1)
N(2)–Cu(1)–C(1)
N(1)–Cu(1)–C(2)
N(2)–Cu(1)–C(2)
C(1)–Cu(1)–C(2)
C(1)–C(2)–C(3)
N(4)–Cu(2)–C(19)
N(4)–Cu(2)–N(3)
C(19)–Cu(2)–N(3)
N(4)–Cu(2)–C(20)
C(19)–Cu(2)–C(20)
N(3)–Cu(2)–C(20)
C(19)–C(20)–C(21)
83.40(5)
117.64(6)
158.31(6)
156.27(6)
118.37(6)
39.99(6)
124.80(14)
115.05(6)
84.01(5)
159.80(6)
155.71(6)
40.76(6)
119.75(6)
125.19(14)
Fig. 2. Molecular structure of [CuI(bpy)(p-CH2@CHC6H5)][CF3SO3] (1),
shown with 50% probability displacement ellipsoids. H atoms have been
omitted for clarity.
Table 2. Complex 1 is distorted trigonal pyramidal in
geometry and copper(I) atom is coordinated by two nitro-
gen atoms of bpy ligand, two olefinic carbon atoms of
styrene at the equatorial position, and an oxygen atom of
C6H5)(PF6)]
and
[CuI(bpy)(p-CH2@CHC6H5)][PF6]
(Fig. 3) and styrene solvate. The structure of [CuI(bpy)(p-
CH2@CHC6H5)(PF6)] is very similar to 1. The copper(I)
atom is coordinated by two nitrogen atoms from bpy
ꢀ
CF3SO3 anion at the axial position. The dihedral angle
˚
ligand (Cu(2)–N(3) = 1.9713(12) A, Cu(2)–N(4) = 1.9621
between the planes defined by the copper and two nitrogen
atoms of the bpy molecule and by the copper and two
˚
(12) A), two carbon atoms from styrene in equatorial
carbon atoms of styrene is 19.63(4)ꢁ. The CuI–N bond
˚
position (Cu(2)–C(19) = 1.9706(15) A, Cu(2)–C(20) =
ꢀ
˚
˚
2.0131(14) A), and a fluorine atom from PF6 anion
distances
(Cu(1)–N(1) = 1.9998(12) A,
Cu(1)–N(2) =
˚
˚
(Cu(2)–F(9) = 2.9846(12) A) in the axial position. Rela-
tively long Cu –F(PF5) distance (2.9846(12) A) indicates
that counterion in this complex is weakly coordinated to
the copper(I) center. The C@C bond length of coordinated
1.9978(12) A) are in the range generally found for copper(I)
complexes with bpy containing ligands (1.93–2.16 A) [36].
I
˚
˚
I
˚
The Cu –O(SO2CF3) distance (2.4297(11) A) is lꢀonger than
I
˚
˚
the sum of ionic radii for Cu (0.96 A) and O (1.40 A),
˚
˚
styrene is 1.388(2) A. The dihedral angle between Cu(2)–
and is also longer than 2.388(4) A observed in structurally
related p-methyl acrylate complex, [CuI(bpy)(p-CH2@CH-
C(19)–C(20) and Cu(2)–N(3)–N(4) planes in 2 is 6.34(3)ꢁ,
which is much smaller than 19.63(4)ꢁ and 12.60(5)ꢁ
observed in 1 and [CuI(bpy)(p-CH2@CHC6H5)][ClO4] (3)
[31], respectively. This result indicates that CuI(bpy)
(p-CH2@CHC6H5)+ moiety in 2 is more trigonal planar
in geometry than in 1 and 3. The [CuI(bpy)(p-CH2@
CHC6H5)]+ cations in 2 form p–p stacking interactions
between bpy planes (perpendicular separation between
COOCH3)][CF3SO3] [37]. The two Cu–C bond distances
˚
˚
(Cu(1)–C(1) = 2.0033(14) A, Cu(1)–C(2) = 2.0304(14) A)
are slightly shorter than those found in tetrahedral
CuI(PMDETA)(p-CH2@CHC6H5)][BPh4] (PMDETA =
N,N,N0,N00,N00-pentamethyldiethylenetriamine)
(Cu –C = 2.052(2) and 2.108(2) A) [38]. Furthermore, the
complex
I
˚
C@C double bond distance of the coordinated styrene
˚
˚
least-squares planes = 3.303(5) A).
(1.383(2) A) is slightly longer than those reported for other
˚
In the molecular structure of complex 3, which has been
published previously (Scheme 2) [31], the copper(I) center is
distorted trigonal pyramidal in geometry. Bipyridine ligand
coordinates to the copper(I) atom in a bidentate fashion
(Cu–N = 1.985(4) and 2.014(5) A). Additionally, two
coordination sites are occupied by olefinic carbon atoms
from styrene in equatorial position (Cu–C = 2.014(5)
free olefin molecules (1.355 0.005 A) [38,39]. The crystal
structure of 1 is stabilized by p–p stacking interactions
between bpy units (perpendicular separation between
˚
least-squares planes = 3.304(6) A). Such interactions are
˚
very common in copper(I) complexes with bipyridine based
˚
ligands and are typically in the range 3.30–3.60 A [40,41].
The crystals of complex 2 contain two crystallographi-
cally independent molecules, [CuI(bpy)(p-CH2@CH-
ꢀ
˚
and 1.985(6) A) and an oxygen atom from ClO4 anion

5170
C. Ricardo, T. Pintauer / Journal of Organometallic Chemistry 692 (2007) 5165–5172
Table 3
1H NMR chemical shifts (300 MHz, CD2Cl2, 180 K) of olefinic protons
and C@C stretching frequency (cmꢀ1) for 1–3
1
2
3
dHa(dDHa)a
6.22(0.52)
5.01(0.77)
4.65(0.60)
1529(101)
6.31(0.43)
5.19(0.59)
4.74(0.51)
1527(103)
6.26(0.48)
5.12(0.66)
4.68(0.57)
1525(105)
dHtbrans(dDHtbrans
)
dHcbis(dDHcbis
)
m(C@C)(dDm)b
a
dDHa = dHa (free Sty) ꢀ dHa (observed at 180 K), ppm (Ph–
CHa@CHtbransCHbcis).
b
dDm = m(free Sty) ꢀ m(observed at 298 K), cmꢀ1
.
resonances for bpy ligand were observed at temperatures
as low as 180 K, which is not consistent with solid state
structures. This is most likely induced by the fast rotation
about the alkene–copper(I) bond on the NMR time scale.
Chemical shifts of complexed styrene are summarized in
Table 3 and compared to those of free styrene. For 1–3,
strong shielding of vinyl protons was observed which indi-
cates p-backbonding donation from CuI, although with
different magnitudes [33,42]. The shielding effect is the
weakest with a-carbon, which is also further away from
CuI than is the b-carbon (Table 2). The p-nature of C@C
of styrene is further supported by a decrease in the IR
stretching frequency of C@C by approximately 102 cmꢀ1
upon coordination.
Because complexes 1–3 undergo fast styrene exchange
on the NMR time scale at room temperature, the average
signals for the free and complexed styrene were observed.
Methods for the determination of the equilibrium constant
for styrene coordination to the copper(I) center for such a
reaction from solution NMR data are well-known. Using
previously described methodology [43,44], the equilibrium
constants for the coordination of styrene to [CuI(bpy)]+
cations at 300 K were determined to be 4.3 · 103 (1),
4.4 · 103 (2) and 3.7 · 103 Mꢀ1 (3). These data suggest that
the axial coordination of the counterion in these complexes
˚
˚
observed in the solid state (2.4297(11) A 1, 2.9846(12) A 2,
Fig. 3. Molecular structure of [CuI(bpy)(p- CH2@CHC6H5)][PF6] Æ 1/2Sty
(2), shown with 50% probability displacement ellipsoids. H atoms and
styrene solvate have been omitted for clarity.
˚
and 2.591(4) A 3) does not significantly affect the binding
constant of styrene to [CuI(bpy)]+ cations in solution.
3.3. Cyclopropanation studies
˚
(Cu–O = 2.591(4) A) in the axial position. The dihedral
angle between the planes defined by the copper and two
nitrogen atoms of the bpy molecule and by the copper
and two carbon atoms of styrene is 12.60(5)ꢁ. Similarly
to the structures of 1 and 2, the structure of 3 is stabilized
In order to further investigate the role of counterion in
1–3, cyclopropanation of styrene in the presence of ethyl-
diazoacetate (EDA) was conducted. The reactions were
performed in CH2Cl2 at room temperature using standard
conditions [CuI]0:[Styrene]0:[EDA]0 = 1:500:50 [23,45]. The
˚
by p–p stacking interactions between bpy planes (3.37 A).
1
product distribution was determined by H NMR and the
1
3.2. H NMR and FT-IR characterization
results are summarized in Table 4. For all three complexes,
the relative amounts of EDA decomposition products,
diethyl fumarate and diethyl maleate, ranged between
16.0 and 18.0 mol%. Furthermore, the mole percent of
trans and cis cyclopropane were very similar for complexes
1 and 2. In the case of complex 3, there was a slight increase
in the amount of trans cyclopropane formed (66.9 mol%),
accompanied by a decrease in the amount of cis product
Complexes 1–3 are very stable in the solid state even in
the presence of air. However, they disproportionate in
CD3OD, (CD3)2CO and CD2Cl2 within 10 min at room
temperature, unless excess free styrene is present. The spec-
tra of 1 and 2 in CD2Cl2 (Section 2) indicated 1:1 ratio
between 2,20-bipyridine and styrene. However, only four

C. Ricardo, T. Pintauer / Journal of Organometallic Chemistry 692 (2007) 5165–5172
5171
Table 4
Cyclopropanation of styrene in the presence of EDA catalyzed by 1–3a
Catalyst
Ph
H
H
H
H
EtO2C
H
H
H
H
CO2Et
Ph
CO2Et
CO2Et
EtO2C
CO2Et
1
2
3
58.0
58.7
66.9
27.0
25.3
14.7
8.0
9.9
6.7
7.0
6.1
11.7
a
Solvent = CH2Cl2, reaction time = 2h, [CuI]0:[2,20- bpy]0:[EDA]0:[Styrene]0 = 1:1:50:500, [CuI]0 = 1.7 · 10ꢀ3 M, % yield based on 1H NMR.
(14.7 mol%). However, surprisingly, the diethyl fumarate
to diethyl maleate ratio does not follow the same trend.
Cyclopropanation of styrene catalyze by complex 3 leads
to a 36:64 mol% ratio, favoring the formation of diethyl
maleate, whereas the same ratio for complexes 1 and 2
was determined to be 53:47 mol% and 62:38 mol%, respec-
tively. We are presently conducting kinetic measurements
in the absence of styrene to gain further information on
the effect of counterion on the ratio of EDA decomposition
products. Overall, based on the results presented in this
article, it appears that 1–3 showed similar trans:cis cyclo-
propane selectivity.
The effect of counterion in 1–3 on the cyclopropanation
of styrene in the presence of EDA was additionally exam-
ined by monitoring the rate of decomposition of EDA.
The decomposition of EDA in the presence of 1–3 was very
fast and quantitative conversions were achieved within
2 min at room temperature. However, the presence of
externally added styrene dramatically slowed down the
reaction rate. This result was expected due to the known
fact that the coordination of olefin to the copper(I) center
inhibits the diazocarbene decomposition (Scheme 1)
[45,46]. Shown in Fig. 4 are the plots for the pseudo-first
order decomposition of EDA in the presence of styrene
and 1–3.
Linearity was observed for all three complexes, enabling
the determination of the observed rate constant (kobs). The
observed rate constant (kobs), as pointed out by detailed
kinetic studies with anionic poly(pyrazolyl) borate ligands
[45], is a complex function of the total copper(I) and sty-
rene concentration, equilibrium constant for styrene coor-
dination to the copper(I) center (K0, Scheme 1), and the
rate constant for the formation of copper(I) carbene com-
plex (k1, Scheme 1). The rate of decomposition of EDA
catalyzed by 3 (kobs = (7.7 0.32) · 10ꢀ3 minꢀ1) is slower
than the rate observed for 1 (kobs = (1.4 0.041) ·
10ꢀ2 minꢀ1) or 2 (kobs = (1.0 0.025) · 10ꢀ2 minꢀ1). This
result is consistent with the cyclopropanation of styrene
catalyzed by copper(I) complꢀexes with bis(oxazolines) in
which the presence of ClO4 counterion resulted in a
decrease in the catalytic activity [15,30]. Furthermore, the
decrease in the observed rate constant for EDA decompo-
ꢀ
sition in the case of ClO4 counterion cannot be explained
in terms of equilibrium constant for styrene coordination
1
to the copper(I) center because variable temperature H
NMR measurements have indicated similar binding con-
stant of styrene to 1 (4.3 · 103 Mꢀ1), 2 (4.4 · 103 Mꢀ1
)
and 3 (3.8 · 103 Mꢀ1). We believe that the counterion in
1–3 can also have an effect on the formation of tetrahedral
[CuI(2,20-bpy)2]+ cations [33,36,40,47,48], which are com-
monly present in these systems (Scheme 1), and would
additionally slow down the rate of decomposition of
EDA. This possibility is currently under investigation.
In summary, novel copper(I)/2,2-bipyridine complexes
with p-coordinated styrene have been synthesized and
characterized. These complexes are used as catalysts in
copper(I) mediated cyclopropanation of styrene. The equi-
librium constants for the coordination of styrene to
[CuI(bpy)]+ cations at 300 K were determined to be
4.3 · 103, 4.4 · 103 and 3.8 · 103 Mꢀ1 for 1, 2 and 3, respec-
tively. These data suggested that the axial coordination of
the counterion in these complexes observed in the solid
Fig. 4. Plots of ln([EDA]0/[EDA]t) vs. time for the cyclopropanation of
styrene with EDA in CH2Cl2 at 25 ꢁC catalyzed by
1 (n, kobs =
(1.4 0.041) · 10ꢀ2 minꢀ1), 2 (ꢁ, kobs = (1.0 0.025) · 10ꢀ2 minꢀ1) and
3
(¤, kobs = (7.7 0.32) · 10ꢀ3 minꢀ1). [CuI]0:[EDA]0:[Styrene]0 =
˚
˚
˚
1:250:2500, [CuI]0 = 1.71 · 10ꢀ3 M. Errors are given at 95% confidence
state (2.4297(11) A 1, 2.9846(12) A 2, and 2.591(4) A 3)
did not significantly affect the binding constant of styrene
limits.

5172
C. Ricardo, T. Pintauer / Journal of Organometallic Chemistry 692 (2007) 5165–5172
to [CuI(bpy)]+ cations in solution. In cyclopropanation
reactions catalyzed by 1–3, similar product distribution
was obtained. Furthermore, the rate of decomposition of
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Financial support from Duquesne University (start-up
grant and faculty development grant), NSF X-ray facility
Grant (CRIF 0234872), Petroleum Research Fund (PRF
44542-G7) and NSF NMR Grant (CHE 0614785) is greatly
acknowledged.
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Appendix A. Supplementary material
CCDC No. 649535 and 649536 contain the supplemen-
tary crystallographic data for 1 and 2. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail: depos-
it@ccdc.cam.ac.uk. Supplementary data associated with
this article can be found, in the online version, at
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