Cationic copper(I) and silver(I) nitrile complexes with fluorinated weakly coordinating anions: Metal-nitrile bond strength and its influence on the catalytic performance

Article abstract of DOI:10.1016/j.ica.2005.12.044

Copper(I) and silver(I) complexes of formulae [Cu(NCCH₃)₄]⁺[A]^- ([A]^- = [B(C₆F₅)₄]^- (1), {B[C₆H₃(CF₃)₂]₄} ^- (2), [(C₆F₅)₃B-C₃H₃N ₂-B(C₆F₅)₃]^- (3), and [Ag(NCCH₃)₄]⁺[B(C₆F ₅)₄]^- (4) are examined with particular emphasis on the strength of their M-N bond and its influence on the catalytic performance of these complexes in cyclopropanation and aziridination. To examine the strength of the M-N interactions, vibrational spectra of the related hydrogenated and deuterated species [Cu(NCCH₃)₄]⁺, [Cu(NCCD₃)₄]⁺, [Ag(NCCH₃)₄]⁺, and [Ag(NCCD₃)₄]⁺ are also determined. It is found that the metal-nitrile bond strength is an important factor for the catalytic activity of the respective complexes.

Full text of DOI:10.1016/j.ica.2005.12.044

Inorganica Chimica Acta 359 (2006) 4723–4729
www.elsevier.com/locate/ica
Cationic copper(I) and silver(I) nitrile complexes with
fluorinated weakly coordinating anions: Metal–nitrile bond strength
and its influence on the catalytic performance
a
a
a
a
Yanmei Zhang , Wei Sun , Christelle Freund , Ana M. Santos ,
Eberhardt Herdtweck , Janos Mink b,c, Fritz E. Kuhn
a
a,
*
¨
a
Lehrstuhl fu¨r Anorganische Chemie der Technischen Universita¨t Mu¨nchen, Lichtenbergstrasse 4, D-85747 Garching, Germany
Molecular Spectroscopy Department, Chemical Research Centre of the Hungarian Academy of Sciences, P.O. Box 17, H-1525 Budapest, Hungary
b
c
Faculty of Informational Technology, Research Institute of Chemical and Process Engineering, Analytical Chemistry Research Group of the Hungarian
Academy of Sciences, Veszpre´m University, P.O. Box 158, H-8201 Veszpre´m, Hungary
Received 15 November 2005; accepted 11 December 2005
Available online 14 February 2006
Dedicated to Professor Dr. Dr. h.c. mult. Wolfgang A. Herrmann.
Abstract
Copper(I) and silver(I) complexes of formulae [Cu(NCCH3)4]+[A]ꢀ ([A]ꢀ = [B(C6F5)4]ꢀ (1), {B[C6H3(CF3)2]4}ꢀ (2), [(C6F5)3B–
C3H3N2–B(C6F5)3]ꢀ (3), and [Ag(NCCH3)4]+[B(C6F5)4]ꢀ (4) are examined with particular emphasis on the strength of their M–N bond
and its influence on the catalytic performance of these complexes in cyclopropanation and aziridination. To examine the strength of the
M–N interactions, vibrational spectra of the related hydrogenated and deuterated species [Cu(NCCH3)4]+, [Cu(NCCD3)4]+,
[Ag(NCCH3)4]+, and [Ag(NCCD3)4]+ are also determined. It is found that the metal–nitrile bond strength is an important factor for
the catalytic activity of the respective complexes.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Copper; Silver; Cyclopropanation; Aziridination; Vibrational spectroscopy
1. Introduction
the corresponding sources, comparatively little attention
has been paid to the development of Cu(I) complexes with
WCAs and to their potential catalytic applications. The
[Cu(NCCH3)4]+ cation coordinated with some common
Weakly or non-coordinating anions (WCAs) are of
considerable interest as counterions for the synthesis of
novel ionic compounds as well as counterions for cationic
catalysts, due to their potential in enhancing reactivity of
metal complexes [1]. Among the industrial applications
requiring WCAs is, for example, the so-called metallocene
process for the stereoregular polymerization of olefins [2].
Although copper-based complexes have played a promi-
nent role in the in situ generation of metal carbenes (or
carbenoids) from diazo compounds and of nitrenes from
ꢀ
counterions, such as BF4 ꢀ, ClO4 and PF6 ꢀ, is well
known both with respect to its properties, its structure
and its catalytic activity [3]. Particular attention was given
to Cu(I) compounds, especially as precursors for catalysts
in the asymmetric catalytic cyclopropanation/aziridination
[3b]. Copper(I) complexes bearing anionic polypyrazolylb-
orate ligands have also been reported as catalysts for both
cyclopropanation and aziridination of olefins [3c].
Three-membered carbocyclic rings hold a prominent
position in organic chemistry both due to their interesting
biological properties [4] and to their use as starting materi-
als and intermediates in organic synthesis [5]. However, the
*
Corresponding author. Tel.: +49 0 89 289 13080; fax: +49 0 89 289
13473.
E-mail address: fritz.kuehn@ch.tum.de (F.E. Kuhn).
¨
0020-1693/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.12.044

4724
Y. Zhang et al. / Inorganica Chimica Acta 359 (2006) 4723–4729
synthesis of small rings still poses some challenges. Accord-
ingly, the catalytic cyclopropanation and aziridination of
olefins, forming three-membered rings, have been attract-
ing significant attention [6]. The development of new and
more efficient catalysts for these reactions as well as the
study of their mechanism has been under investigation in
several groups [7].
We recently published our findings about the applica-
tions of Ag(I) and Cu(I) nitrile compounds, associated with
several non-coordinating anions as intermediates in the
synthesis of Mn(II)-based polymerization catalysts [8]. It
had turned out, however, that these synthetic intermediates
were not applicable as catalysts for the polymerization of
isobutene or the copolymerization of isobutene and iso-
prene [8b]. However, Ag(I) compounds with WCAs could
be successfully applied for the coupling of terminal alkynes
with aldehydes and amines [8d] and Cu(I) complexes with
WCAs were applicable for catalytic cyclopropanations
and aziridinations, as we have communicated recently
[8e]. These latter findings are described in this work in more
detail and a comparison of the vibrational spectra of Cu(I)
and Ag(I) complexes with WCAs is given.
2.3. Syntheses
2.3.1. [Cu(NCCH3)4][B(C6F5)4] (1)
CuCl (0.79 g, 7.98 mmol) was added to a 40 mL solution
of Ag[B(C6F5)4] (6.28 g, 7.98 mmol) in dry acetonitrile
under argon atmosphere. The resulting mixture was stirred
overnight at r.t. in darkness. The formed precipitate (AgCl)
was removed and the filtrate was concentrated to ca.
5.0 mL under oil pump vacuum and kept at ꢀ35 ꢁC. The
desired product was obtained as a colorless crystalline
solid. Yield 6.0 g (83%). Anal. Calc. for C32H12BCuF20N4:
C, 42.38; H, 1.33; N, 6.18. Found: C, 42.13; H, 1.28; N,
6.74%. Selected IR (KBr, cmꢀ1) mCN, 2277, 2308. 1H
NMR (400 MHz, CDCl3, r.t., d (ppm)): 1.87 (CH3, 12H).
2.3.2. [Cu(NCCH3)4]{B[C6H3(CF3)2]4} (2)
CuCl (0.052 g, 0.53 mmol) was added to a 20 mL solu-
tion of Ag[B{C6H3(CF3)2}4] (0.6 g, 0.53 mmol) in dry ace-
tonitrile. The resulting solution was stirred overnight in
darkness under an argon atmosphere. The solid (AgCl)
was filtered off and the filtrate was evaporated to dryness
under oil pump vacuum and recrystallized with dichloro-
methane and hexane in an 1:1 ratio. The desired product
was obtained as a colorless crystalline solid. Yield 0.49 g
(85%). Anal. Calc. for C36H18BCuF24N2: C, 44.04; H,
2.22; N, 5.14. Found: C, 43.64; H, 2.45; N, 4.74%. Selected
IR (KBr, cmꢀ1): mCN, 2286, 2317. 1H NMR (400 MHz,
CDCl3, r.t., d(ppm)): 2.02 (CH3, 12H), 7.53–7.68 (C6H3,
12H).
2. Experimental
2.1. Materials
All solvents were dried using standard procedures unless
otherwise stated. All manipulations were carried out using
standard Schlenk techniques. Styrene, a-methylstyrene,
trans-b-methylstyrene, cis-b-methylstyrene, trans-anulene,
1,2-dihydronaphthalene, cis-cyclooctene and ethyldiazoac-
etate (EDA) were purchased from Aldrich. PhI = NTs
was synthesized according to a known literature procedure
[12]. The potassium salts of anions for complexes 1–3 were
prepared according to Ref. [4].
2.3.3. [Cu(NCCH3)4][(C6F5)3B–C3H3N2–B(C6F5)3] (3)
CuCl (0.022 g, 0.22 mmol) was added to a 20 mL solu-
tion of (0.3 g, 0.22 mmol) Ag[(C6F5)3B–C3H3N2–
B(C6F5)3] in dry acetonitrile under argon atmosphere.
The resulting solution was stirred overnight at r.t. in dark-
ness. The formed precipitate of AgCl was removed and the
solution was concentrated to ca. 1 mL under oil pump vac-
uum and kept at ꢀ35 ꢁC. The desired product was obtained
as a colorless crystalline solid. Yield 0.26 g (89%). Anal.
Calc. for C47H15BCuF30N6: C, 42.81; H, 1.15; N, 6.37.
Found: C, 42.76; H, 1.34; N, 6.47%. Selected IR (KBr,
2.2. Physical measurements and calculations
IR spectra were recorded on a Perkin–Elmer FT-IR
1
spectrometer using KBr pellets as matrix. H NMR exper-
1
iments were performed on a Bruker AVANCE-DPX-400
spectrometer. Elemental analyses were performed at the
cmꢀ1) mCN, 2286, 2318. H NMR (400 MHz, CDCl3, r.t.,
d (ppm)): 2.13 (CH3, s, 12H), 6.74 (C2H2, s, 2H) 7.43
Mikroanalytisches Labor of the TU Munchen (M. Barth).
¨
(CH, s, 1H).
The MIR spectra were recorded on a Digilab FTS-60A
spectrometer with a KBr beamsplitter and a MCT detec-
tor. FIR spectra were recorded on a Digilab FTS-40 spec-
trometer with high pressure Hg-lamp, wiremesh
beamsplitter and DTGS detector. Raman spectra were
recorded on a Digilab and partially on a Nicolet FT-
Raman 950 spectrometer equipped with NdYAG laser
(wavelength: 1064 nm; power: 50–150 mW). Some of the
Raman spectra were measured on a Renishaw System
RM1000 spectrometer equipped with a Leica DMLM
microscope, a diode laser (782 nm) and a Peltier-cooled
CCD detector. Calculations were performed using a pub-
lished program [13].
2.3.4. Typical procedure for cyclopropanation
(114 mg, 1.0 mmol) EDA in 2.0 mL dichloromethane
was added slowly to a 2 mL dichloromethane solution
of styrene (208.0 mg, 2.0 mmol) and
1
(18.0 mg,
0.02 mmol) over 30 min. The reaction was completed
within 1 h. The structure of the product was determined
by GC–MS and the conversion of styrene was deter-
mined by GC (FID) from a calibration curve recorded
prior to the reaction course with dodecane as internal
standard. Since no by-products containing styrene were
found, the conversion can be considered as equivalent
to the yield.

Y. Zhang et al. / Inorganica Chimica Acta 359 (2006) 4723–4729
4725
2.3.5. Typical procedure for aziridination
were corrected for Lorentz, polarization, and, arising from
the scaling procedure, for latent decay and absorption
effects. After merging (Rint = 0.047) a sum of 6267 (all
data) and 5744 [I > 2r(I)], respectively, remained and all
data were used. The structure was solved by a combination
of direct methods and difference Fourier syntheses. All
non-hydrogen atoms were refined with anisotropic dis-
placement parameters. All hydrogen atoms were placed
in ideal calculated positions and treated as riding atoms
using SHELXL-97 default parameters. Full-matrix least-
squares refinements with 527 parameters were carried out
(130.0 mg, 1.25 mmol) styrene, (94.0 mg, 0.25 mmol)
PhI = NTs and (18.0 mg, 0.02 mmol) 1 were stirred in
4.0 mL acetonitrile for 20 h. The product was then purified
by silica gel column chromatography (hexane:ethyl ace-
tate = 5:1) and the yields were determined by weighing
the isolated product. The composition of the pure product
1
was determined by H NMR and GC–MS.
2.4. X-ray crystallographic studies on
[Cu(NCCH3)4][B(C6F5)4] (1)
P
2
by minimizing
wðF 2o ꢀ F 2cÞ with the SHELXL-97 weight-
Crystal data and details of the structure determination
are presented in Table 1. Suitable single crystals for the
X-ray diffraction study were grown by standard cooling
techniques from a saturated solution of freshly prepared
complex 1 in acetonitrile. A clear colorless fragment was
stored under perfluorinated ether, transferred in a Linde-
mann capillary, fixed, and sealed. Preliminary examination
and data collection were carried out on an area detecting
system (NONIUS, MACH3, j-CCD) at the window of a
rotating anode (NONIUS, FR951) and graphite mono-
ing scheme and stopped at shift/err <0.001. The final resid-
ual electron density maps showed no remarkable features.
Neutral atom scattering factors for all atoms and anoma-
lous dispersion corrections for the non-hydrogen atoms
were taken from International Tables for Crystallography.
All calculations were performed on an Intel Pentium IV
PC, with the STRUX-V system, including the programs
PLATON, SIR92, and SHELXL-97 [14].
3. Results and discussion
˚
chromated Mo Ka radiation (k = 0.71073 A). The unit cell
parameters were obtained by full-matrix least-squares
refinement of 6517 reflections. Data collections were per-
formed at 123 K (OXFORD CRYOSYSTEMS) within a
h-range of 1.67ꢁ < h < 25.34ꢁ and measured with 10 data
sets in rotation scan modus with Du/Dx = 1.0ꢁ. A total
number of 82913 reflections were integrated. Raw data
3.1. Syntheses and characterizations
3.1.1. Syntheses and structures
The WCAs for complexes 1 and 2 were prepared res-
pectively from pentafluorobenzene bromide and 3,5-bis-
(trifluoromethyl)-bromobenzene treated successively with
n-butyllithium, borontrichloride and potassium chloride
(Chart 1, Scheme 1). The resulting salts were then trans-
formed to silver salts by reaction with silver nitrate. The
WCA of complex 3 was synthesized according to the liter-
ature procedures [4] and then transferred to the respective
silver salt with silver nitrate as in the case of the anions
of complexes 1 and 2.
Table 1
Crystallographic data for complex 1
Formula
C32H12BCuF20N4
Formula weight
Color/habit
906.82
colorless/fragment
0.53 · 0.61 · 0.81
monoclinic
P21/n (no. 14)
11.4125(1)
16.2928(1)
19.1983(1)
106.4778(2)
3423.15(4)
4
Crystal dimensions (mm3)
Crystal system
Space group
The copper(I) complexes 1–3 were synthesized by react-
ing copper(I) chloride with the silver salts of the corre-
sponding anions in acetonitrile (anion exchange) (Eq.
˚
a (A)
˚
b (A)
˚
c (A)
b (ꢁ)
3
˚
V (A )
Z
T (K)
123
1.760
0.779
1784
Dcalc (g cmꢀ3
)
l (mmꢀ1
F(000)
)
h Range (ꢁ)
Index ranges (h,k,l)
1.67–25.34
13, 19, 23
82913
6267/0.047
5744
6467/0/527
0.0280/0.0715
0.0314/0.0736
1.046
Number of reflections collected
Number of independent reflections/Rint
Number of observed reflections (I > 2r(I))
Number of data/restraints/parameters
R1/wR2 (I > 2r(I))a
R1/wR2 (all data)a
Goodness-of-fit (on F2)a
ꢀ3
˚
Largest diff peak and hole (e A
)
+0.26/ꢀ0.25
P
P
P
P
2
2
1=2
a
R1
¼
ðjjF oj ꢀ jF cjjÞ= jF oj; wR2 ¼ f ½wðF 2o ꢀ F c2Þ ꢁ= ½wðF o2Þ ꢁg
;
P
2
1=2
Goodness-of-fit ¼ f ½wðF 2o ꢀ F c2Þ ꢁ=ðn ꢀ pÞg
.
Chart 1.

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Y. Zhang et al. / Inorganica Chimica Acta 359 (2006) 4723–4729
Table 2
Selected bond lengths (A) and angles (ꢁ) for complex 1
˚
Cu–N(1)
Cu–N(2)
Cu–N(3)
Cu–N(4)
2.000(2)
2.021(2)
2.001(2)
2.029(2)
N(1)–Cu–N(2)
N(1)–Cu–N(3)
N(1)–Cu–N(4)
N(2)–Cu–N(3)
N(2)–Cu–N(4)
N(3)–Cu–N(4)
Cu–N(1)–C(1)
Cu–N(2)–C(2)
Cu–N(3)–C(3)
Cu–N(4)–C(4)
103.13(7)
106.26(7)
119.81(7)
120.57(7)
104.28(7)
103.89(7)
175.8(2)
161.8(2)
170.0(2)
170.1(2)
Scheme 1.
(1)). The solvent stabilized complexes are stored at ꢀ35 ꢁC
under argon atmosphere to prevent decomposition and
oxidation over long storage periods. However, they can
be stored at room temperature for short periods of time
and handled in laboratory atmosphere briefly.
The X-ray structure of a closely related Ag complex,
namely of [Ag(NCCH2CH3)4]+[B(C6F5)4]ꢀ, had been
described previously. In this case, the Ag(I)–N bond dis-
tances range between 2.265(3) and 2.298(3) A, the N–Ag–
N bond angles between 98.77(12)ꢁ and 125.53(12)ꢁ [8b].
ð1Þ
˚
The copper(I) complexes were characterized by IR spec-
troscopy, X-ray crystallography, elemental analysis and 1H
NMR. Suitable crystals were obtained from acetonitrile
solution. The molecular structure of complex 1 was deter-
mined by single-crystal X-ray crystallography (Fig. 1).
The crystallographic data are listed in Table 1, and selected
bond lengths and angles are tabulated in Table 2.
3.1.2. Infrared spectra
Due to the interest in vibrational spectra of transition
metal nitrile complexes [3d,3e] in general and due to the
importance of such nitrile complexes as starting materials
for a wide range of syntheses and catalyses in particular
[9,10], the infrared spectra of copper(I) complexes 1–3 were
investigated in detail and the bands are listed in Table 3.
The IR shifts of the mCN absorption are observed at 2277
and 2308 cmꢀ1 for complex 1, 2286 and 2317 cmꢀ1 for
complex 2 and 2286 and 2318 cmꢀ1 for complex 3. Based
on these IR data and the examinations on its analog con-
taining only two (instead of four) nitrile ligands [9], it can
As expected, the coordination environments around the
monovalent copper ions in 1 are slightly distorted tetrahe-
˚
dral, with Cu(I)–N bond distances (2.000(2)–2.029(2) A)
and bond angles (N–Cu–N angles range from 103.13(7)ꢁ
to 120.57(7)ꢁ). The acetonitrile ligands form nearly linear
bonds to the copper atoms, and the bond distances of the
acetonitrile ligands are longer than theꢀanalogs with com-
mon counterions such as BF4 ꢀ, ClO4 and PF6 ꢀ. There
is nothing surprising about this slightly distorted tetrahe-
dral geometry of the d10 cation. Table 2 gives the Cu–N
bond lengths and N–Cu–N and Cu–N–C bond angles.
Table 3
Infrared bands of the [Cu(NCCH3)4]+ complexes with different
counterions
[B(C6F5)4]ꢀ
(1)
[B(C6H3(CF3)2)4]ꢀ
(2)
[(C6F5)3B–C3H3-
N2–B(C6F5)3]ꢀ (3)
Assignment
3028 w
2954 s
2308 s
3022w
2946 s
2317 w
2286 s
1416 w
1380 sh
1094 w
1071 sh
1001 vw
933 w
3030 w
2950 w
2318 w
2286 s
CH3 asym str
CH3 sym str
933 + 1380
CN str
CH3 asym def
CH3 sym def
2277 vs
1420 sh
1384 m
1093 m
1037 vw
1000 sh
933 vw
545 vw
402 w
1408 sh
1380 sh
1100 m, sh
1031 vw
1000 sh
935 vw
530 w,b
403 vw
390 sha
375 sh
CH3 rocking
C–C str
545 w
405 sh
395 sa
d(CCN)
ma(CuN)
389 m
345 sh
350 w
318 m
252 m
203 m
b
227 w
154 m
147 m
92 w
230 w
105 m
146 w
88 m
d(MCN)
d(CMC)
b
b
74 w
70 w
s, strong; m, medium; w, weak; v, very; sh, shoulder.
Fig. 1. ORTEP-style representation of the cationic part of the molecular
structure of complex 1 as determined by single-crystal X-ray crystallog-
raphy. The thermal ellipsoids are given at a 50% probability level.
a
Overlapping with anion bands.
b
No FIR spectrum is available.

Y. Zhang et al. / Inorganica Chimica Acta 359 (2006) 4723–4729
4727
be concluded that compounds 2 and 3 bind their nitrile
ligands slightly stronger than compound 1. This assump-
tion is supported by the H NMR data of the acetonitrile
gram system [13]. As expected, the frequencies of
[Cu(NCCH3)4]+ are closely related to those of the
[Cu(NCCD3)4]+ cation.
1
ligands of complexes 1–3. The chemical shift of the aceto-
nitrile protons in CDCl3 of compound 1 (d = 1.87 ppm)
is closer to the shift of free acetonitrile (d = 1.83 ppm) than
the nitrile proton shift of the nitrile ligands of compounds 2
and 3 (d = 2.02 and 2.13 ppm, respectively).
In order to aid the assignments, the spectra of acetoni-
trile-d3 copper(I) complexes of compound 1 (1a) prepared
by the same method were recorded. Table 4 contains the
measured and the calculated fundamental vibrations of
related species such as hydrogenated [Cu(NCCH3)4]+ and
deuterated [Cu(NCCD3)4]+. The force constant calcula-
tions have been performed with an updated computer pro-
The vibrational spectra of the corresponding silver com-
pounds, [Ag(NCCH3)4]+ (4) and [Ag(NCCD3)4]+ (4a) (with
the same counterion as 1 and 1a), have been recorded for
the sake of completeness. The results for [Ag(NCCH3)4]+
and [Ag(NCCD3)4]+ are summarized in Table 5. The two
bands corresponding to the CN stretching vibrations of
the Ag(I) complexes 4 and 4a (2296 and 2295 cmꢀ1) show
a stronger frequency shift from the vibration of the free ace-
tonitrile (2261 cmꢀ1) than that observed for the Cu com-
pounds 1 and 1a (2294 and 2293 cmꢀ1, see Table 4),
indicating a stronger metal–ligand interaction compared
to the Cu(I) complex.
Table 4
Experimental and calculated frequencies of the Cu(I) complexes 1 and 1a (cmꢀ1) (counterion BðC6F5Þ
)
ꢀ
4
[Cu(NCCH3)4]+ (1)
[Cu(NCCD3)4]+ (1a)
Potential energy distribution (PED)
Experimental
Calculated
Experimental
Calculated
A1
m1
m2
m3
2294*
948
2294
949
326
2293
901
343
2293
899
314
40mCN + 30mCC + 10mCuN
50mCC + 40mCuN + 5mCN
80mCuN + 12mCC + 3mCN
368
E
m4
m5
m6
401
256
92
401
255
91
400
250
88
401
255
89
52dCCN + 41dCCuC
100dCuNC
80dCCuC + 10dCCN
F2
m7
m8
m9
m10
m11
m12
2277
933
402
389
227
147
2277
933
402
386
221
119
2276
882
402
370
220
143
2276
880
401
375
217
116
60mCN + 30mCC + 5mCuN
50mCC + 25 mCuN
100dCCN
50mCuN + 40mCN + 4mCC
70dCuNC + 10mCuN + 4mCC
60dCCuC + 10dCuNC
*
Fundamental bands for the A1 and E species were observed in the Raman spectra.
Table 5
Experimental and calculated frequencies of the Ag(I) complexes 4 and 4a (cmꢀ1) (counterion BðC6F5Þ
)
ꢀ
4
[Ag(NCCH3)4]+ (4)
[Ag(NCCD3)4]+ (4a)
Potential energy distribution (PED)
Experimental
Calculated
Experimental
Calculated
A1
m1
m2
m3
2296*
948
2296
948
343
2295
901
334
2295
901
319
93mCN + 8mCC + 4mAgN
81mCC + 16mAgN
80mAgN + 12mCC + 6mNC
359
E
m4
m5
m6
394
296
118
394
290
109
393
290
114
392
290
106
52dCCN + 41dCAgC
100dAgNC
70dCAgC + 20dCCN
F2
m7
m8
m9
m10
m11
m12
2286
932
403
350
230
88
2286
932
403
339
213
85
2285
880
403
338
226
85
2285
879
403
327
211
82
90mCN + 10mCC + 4mAgN
80mCC + 10mAgN
100dCCN
80mAgN + 10mCN + 4mCC
70dAgNC + 10mAgN + 4mCC
60dCAgC + 10dAgNC
*
Fundamental bands for the A1 and E species were observed in the Raman spectra.

4728
Y. Zhang et al. / Inorganica Chimica Acta 359 (2006) 4723–4729
Table 6
From these data, it is obvious that compound 1 is more
efficient in the cyclopropanation reaction than its deriva-
tives 2 and 3. As a possible reason for this observation,
the slightly weaker Cu–N bond in compound 1 in compar-
ison to its derivatives 2 and 3 has been assumed. According
to the vibrational spectroscopic results presented above, it
is to be expected that the silver complex 4 also shows a
lower catalytic activity than the copper complex 1. This is
indeed the case. Applied under the same reaction condi-
tions as compound 1, compound 4 shows no catalytic activ-
ity for olefin cyclopropanation reactions.
Infrared valence force constantꢀs of [M(NCCH3)4]+ complexes of the types
1 and 4 (counterion BðC6F5Þ4
)
[Cu(NCCH3)4]ꢀ (1)
[Ag(NCCH3)4]+ (4)
Unit
a
a
a
a
a
a
b
b
b
c
K(CN)
K(CC)
K(MN)
F(CN,CN)
F(CC,CC)
F(MN,MN)
H(CNC)
H(MNC)
H(CMC)
18.803
4.989
2.224
ꢀ0.021
ꢀ0.020
0.307
0.859
0.077
0.402
0.060
0.091
0.001
18.873
4.960
2.347
ꢀ0.020
ꢀ0.049
0.405
0.102
0.942
0.436
0.041
0.087
0.129
h(CNC,CNC)
h(MNC,MNC)
h(CMC,CMC)
c
c
ð2Þ
K, stretch; F, stretch–stretch; H, bend; h, bend–bend force constants.
a
102 N mꢀ1
10ꢀ18 N m radꢀ2
10ꢀ8 N radꢀ1
.
b
c
The aziridination of olefins has been very often consid-
ered to be a similar reaction to cyclopropanation, in the
sense that a nitrene group is transferred to the olefin, gen-
erating the three-membered ring. We also compared the
complexes 1 and 4 as catalysts for olefin aziridination reac-
tions (Eq. (3)). Again, while 1 proved to be an active cata-
lyst as communicated previously [8e], compound 4 was
found to be catalytically inactive.
.
.
The Cu–N stretching vibrations (m1 = 368 and m10
=
389 cmꢀ1) are observed at higher wave numbers than those
for the Ag–N stretching modes (Table 5). Based on these
latter frequency differences, it could be easily misinter-
preted that in the Cu(I) complexes the CH3CN ligands
are more strongly coordinated. The real explanation, how-
ever, results from force constant calculations where the
Ag–N stretching force constants (2.347 N cmꢀ1) are higher
than the Cu–N force constant (2.224 N cmꢀ1). As it can be
seen in Table 6, the CN stretching force constant is higher
in the Ag(I) complexes [13].
ð3Þ
As a first step in such catalytic reactions, the removal
(dissociation) of one or two ligands has been assumed in
the literature [8e,11], to create an empty coordination site
for the entry of a substrate molecule (Eq. (4)). It is interest-
ing to note that a copper compound of composition
[Cu(NCCH3)2]+[B(C6F5)4]ꢀ (5) has been described in the
literature [9], while the corresponding Ag complex could
not be isolated [8d]. Furthermore, compound 5 displays
3.2. Influence of the M–N bond strength on the catalytic
behavior
The use of complexes with weakly coordinated, easily
displaceable ligands, has a positive effect on the catalytic
activity, by rendering the intermediate species more acces-
sible to substrate coordination. The negative effect of
excess ligand in cyclopropanation catalysis with copper(I)
complexes has been observed previously [3c]. It has been
shown in the literature that nitrile ligated complexes may
lose one or more of their acetonitrile ligands quite easily
forming an under-coordinated, linear [Cu(NCCH3)2]+-
complex [9]. As we have communicated previously [8e]
complexes 1–3 were tested as catalysts for cyclopropana-
tion reactions using styrene as olefin (Eq. (2), Table 7).
˚
ca. 0.15 A shorter copper–nitrile bond distances than com-
pound 1.
ð4Þ
4. Conclusions
Acetonitrile ligated copper(I) complexes 1–3 bearing
weakly or non-coordinating anions are catalytically active
toward cyclopropanation and aziridination of olefins. The
related silver complex 4, however, is inactive in both cata-
lytic reactions. The catalytic activity corresponds very well
with the strength of the metal–nitrile interaction as deduced
from vibrational spectroscopic data. The stronger the
metal–nitrogen interaction is, the lower is the catalytic
activity of the complexes. This supports the assumption that
the catalytic reaction starts with a metal–ligand dissocia-
tion, opening a free coordination site for the entry of a
substrate.
Table 7
Cyclopropanation of styrene catalyzed by complexes 1–4 (reaction time
1 h)
Complexesa
Yieldb
cis:transc
[Cu(NCCH3)4]+[B(C6F5)4]ꢀ (1)
71
42
25
0
49:51
36:64
37:63
[Cu(NCCH3)4]+{B[C6H3(CF3)2]4}ꢀ (2)
[Cu(NCCH3)4]+[B(C6F5)3–C3H3N2–B(C6F5)3]ꢀ (3)
[Ag(NCCH3)4]+[B(C6F5)4]ꢀ (4)
a
Styrene: EDA = 2:1.
b
Yield determined by GC (FID) with dodecane as standard.
Determined by GC (FID) and GC–MS.
c

Y. Zhang et al. / Inorganica Chimica Acta 359 (2006) 4723–4729
4729
[8] (a) M. Vierle, Y. Zhang, E. Herdweck, M. Bohnenpoll, O. Nuyken,
Acknowledgments
F.E. Kuhn, Angew. Chem., Int. Ed. Engl. 42 (2003) 1307;
¨
(b) M. Vierle, Y. Zhang, A.M. Santos, K. Ko¨hler, C. Haeßner, E.
Herdtweck, M. Bohnenpoll, O. Nuyken, F.E. Ku¨hn, Chem. Eur. J.
10 (2004) 6323;
The authors are grateful to the DFG (DFGKK1265/4-
1) and the Fonds der Chemischen Industrie for financial
support.
(c) A. Sakthivel, A.K. Hijazi, H.Y. Yeong, K. Ko¨hler, O. Nuyken,
F.E. Kuhn, J. Mater. Chem. 15 (2005) 4441;
¨
(d) Y. Zhang, A.M. Santos, E. Herdtweck, J. Mink, F.E. Kuhn,
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New J. Chem. 29 (2005) 366;
Appendix A. Supplementary data
(e) Y. Zhang, W. Sun, A.M. Santos, F.E. Kuhn, Catal. Lett. 101
¨
(2005) 35;
Crystallographic data (excluding structure factors) for
the structures reported in this paper have been deposited
with the Cambridge Crystallographic Data Centre as Sup-
plementary Publication No. CCDC 296400 for 1. Copies of
the data can be obtained free of charge on application to
CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK, fax:
+44 1223 366 033, e-mail: deposit@ccdc.ac.uk or on the
web www: http://www.ccdc.cam.ac.uk. Supplementary
data associated with this article can be found, in the online
version, at doi:10.1016/j.ica.2005.12.044.
(f) S. Gago, Y. Zhang, A.M. Santos, K. Ko¨hler, F.E. Kuhn, J.A.
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