Copper(I)-olefin complexes: The effect of the trispyrazolylborate ancillary ligand in structure and reactivity

Article abstract of DOI:10.1021/om1002705

The spectroscopic and structural characteristics and the relative reactivity of several Tp^MsCu(olefin) (olefin = ethylene, 1, 1-hexene, 2, allyl ethyl ether, aee, 3, cyclohexene, 4, and styrene, 5) complexes bearing the bulky hydrotris(3-mesitylpyrazolyl)borate ligand have been examined. Experimental data, including an unusual high-field chemical shift in the ¹H and ¹³C NMR spectra, and DFT theoretical calculations support the proposal that the copper-olefin linkage is mainly sustained by σ-donation, lacking a substantial degree of π-back-donation.

Full text of DOI:10.1021/om1002705

Organometallics 2010, 29, 3481–3489 3481
DOI: 10.1021/om1002705
Copper(I)-Olefin Complexes: The Effect of the Trispyrazolylborate
Ancillary Ligand in Structure and Reactivity
†
Carmen Martın, Jose Marıa Munoz-Molina, Abel Locati, Eleuterio Alvarez,
†
§
‡
ꢀ
Feliu Maseras, Tomas R. Belderrain,* and Pedro J. Perez*
~
§
,†
,†
ꢀ
ꢀ
†
ꢀ
ꢀ
´
Laboratorio de Catalisis Homogenea, Departamento de Quımica y Ciencia de los Materiales,
ꢀ
´
Unidad Asociada al CSIC, Centro de Investigacion en Quımica Sostenible (CIQSO), Campus de El Carmen
s/n, Universidad de Huelva, 21007 Huelva, Spain, §Institute of Chemical Research of Catalonia (ICIQ),
‡
Avenida Paisos Catalans 16, 43007 Tarragona, Spain, and Instituto de Investigaciones Quımicas,
ꢀ
CSIC-Universidad de Sevilla, Avenida Americo Vespucio 49, 41092 Sevilla, Spain
´
Received April 6, 2010
The spectroscopic and structural characteristics and the relative reactivity of several TpMsCu-
(olefin) (olefin=ethylene, 1, 1-hexene, 2, allyl ethyl ether, aee, 3, cyclohexene, 4, and styrene, 5)
complexes bearing the bulky hydrotris(3-mesitylpyrazolyl)borate ligand have been examined.
Experimental data, including an unusual high-field chemical shift in the 1H and 13C NMR spectra,
and DFT theoretical calculations support the proposal that the copper-olefin linkage is mainly
sustained by σ-donation, lacking a substantial degree of π-back-donation.
Introduction
[HB{3,5-(CF3)2pz}] (e),9 or [MeB(3-(CF3)pz)3]10 (f) ligands.
The latter compounds have been described as air-stable
solids, which do not lose ethylene under reduced pressure.
The copper-olefin bonds of the above and other com-
plexes have been rationalized by means of the Dewar-
Chatt-Duncanson model.11 The ancillary ligands bonded
to the metal center affect the relative energy of the σ- and π-
type metal orbitals and subsequently exert a certain influence
on the metal-olefin bond. Thus, the π-back-bonding inter-
action can be enhanced with strongly Lewis-basic ancillary
ligands, whereas weakly donating (electron-withdrawing)
ligands will decrease such interaction, lowering the energy
of the empty Cu 4s and 4p orbitals. In the latter case, a
stronger metal-olefin σ-interactions arises.12 Usually, the
donating properties of the ancillary ligands Ln can be eval-
uated by means of IR studies with the corresponding carbo-
nyl complexes LnCu(CO).
The interaction between copper(I) centers and ethylene is
crucial in plants.1,2 In addition, copper(I)-alkene complexes
have been used as catalyst precursors and proposed as the
resting state in several copper-catalyzed reactions.3 It is well
known that such binding is reversible, and therefore, most
copper(I)-ethylene complexes are labile. The first stable
copper(I) ethylene complex, Tp*Cu(η2-C2H4) (Tp* = [HB-
(3,5-Me2pz)3], Scheme 1a), was reported by Thompson and
co-workers.4 Although stable in the solid state toward
ethylene loss,5 the coordinated olefin was easily removed
under vacuum. The most stable systems described to date
usually contain anionic ligands (Scheme 1) such as imino-
phosphinamide (b),6 β-diketiminato (c),7 the highly fluori-
nated 1,3,5-triazapentadienyl (d),8 tris(pyrazolyl)borate
In the past decade, we have described the use of TpxCuL
(Tpx = trispyrazolylborate ligand;13 L (leaving group) =
olefin, acetonitrile) complexes as catalysts for several reactions
involving olefins as the substrate: cyclopropanation,14 aziridi-
nation,15 epoxidation,16 atom transfer radical addition,17
*To whom correspondence should be addressed. E-mail: perez@
dqcm.uhu.es (P.J.P), trodri@dqcm.uhu.es (T.R.B.).
(1) Khan, N.A. Ethylene Action in Plants; Springer-Verlag: Berlin,
2006.
(2) (a) Schaller, G. E.; Bleecker, A. B. Science 1995, 270, 1809–1811.
(b) Rodríguez, F. I.; Esch, J. J.; Hall, A. E.; Binder, B. M.; Schaller, G. E.;
Bleecker, A. B. Science 1999, 283, 996–998. (c) Ecker, J. R. Science 1995,
268, 667-675, and references therein.
ꢀ
(3) Perez, P. J.; Dıaz-Requejo, M. M. Copper Organometallics.
(10) Dias, H. V. R.; Wang, X.; Diyabalanage, H. V. K. Inorg. Chem.
2005, 44, 7322–7324.
(11) Wang, X.-S.; Zhao, H.; Li, Y.-H.; Xiong, R.-G.; You, X.-Z. Top.
In Comprehensive Organometallic Chemistry III, Vol. 2; Elsevier:
Amsterdam, 2007.
(4) Thompson, J. S.; Harlow, R. L.; Whitney, J. F. J. Am. Chem. Soc.
Catal. 2005, 35, 43–61.
1983, 105, 3522–3527.
(12) Sullivan, R. M.; Liu, H.; Smith, D. S.; Hanson, J. C.; Osterhour,
D.; Ciraolo, M. F.; Grey, C. P.; Martin, J. D. J. Am. Chem. Soc. 2003,
125, 11065–11079.
(13) (a) Trofimenko, S. Scorpionates: The Coordination of Poly-
(pyrazolyl)borate Ligands; Imperial College Press: London, 1999.
(b) Pettinari, C. Scorpionates II: Chelating Borate Ligands; Imperial
College Press: London, 2008.
(5) (a) Dias, H. V. R.; Wu J. Eur. J. Inorg. Chem. 2008, 509-522, and
references therein. (b) Dias, H. V. R.; Lovely, C. J. Chem. Rev. 2008, 108,
3223–3238.
(6) Straub, B. F.; Eisentrager, F.; Hofmann, P. Chem. Commun. 1999,
2507–2508.
(7) Dai, X.; Warren, T. H. Chem. Commun. 2001, 1998–1999.
(8) Dias, H. V. R.; Singh, S.; Flores, J. A. Inorg. Chem. 2006, 45,
8859–8861.
(14) (a) Dıaz-Requejo, M. M.; Belderrain, T. R.; Trofimenko, S.;
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Perez, P. J. J. Am. Chem. Soc. 2001, 123, 3167–3168. (b) Díaz-Requejo,
(9) Dias, H. V. R.; Lu, H.-L.; Kim, H.-J.; Polach, S. A.; Goh, T. K. H.
M. M.; Caballero, A.; Belderrain, T. R.; Nicasio, M. C.; Trofimenko, S.;
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H.; Browning, R. G.; Lovely, C. J. Organometallics 2002, 21, 1466–1473.
Perez, P. J. J. Am. Chem. Soc. 2002, 124, 978–983.
r
2010 American Chemical Society
Published on Web 07/22/2010 pubs.acs.org/Organometallics

´
Martın et al.
3482 Organometallics, Vol. 29, No. 16, 2010
and atom transfer radical addition and cyclization.18 Since the
formation of olefin adducts has been proposed along the
catalytic cycles in those transformations, we decided to investi-
gate the stability of such complexes by preparing a series of
compounds of general formula TpxCu(olefin) and performing a
spectroscopic, structural, and reactivity study. A second factor
that was taken into account is the well-known ability of the
substituents located at the distal-to-boron position in these
ligands, which exert a fundamental role in the definition of the
catalytic pocket around the metal center. Because of this, we
chose the hydrotris(3-mesitylpyrazolyl)borate (TpMs) as the
ligand on the basis of the steric effect of the Ms groups, which
provides the biggest cone angles known for TpxM complexes.13
Scheme 1. Stable Copper-Ethylene Complexes
Results and Discussion
Synthesis and Characterization of the Ethylene Complex
TpMsCu(C2H4) (1). When ethylene was bubbled through a
solution of Tolman’s complex19 TpMsCu(THF) (TpMs= hydro-
tris(3-mesityl)pyrazolylborate) in dichloromethane for 1 h, a
white crystalline solid came out of the solution upon addition of
diethyl ether. This compound has been identified as TpMsCu-
(C2H4), 1 (eq 1), on the basis of 1H and 13C NMR data, IR data,
elemental analysis, and X-ray crystallography. This compound is
remarkably stable, in a similar manner to the already mentioned
fluorinated hydrotris(pyrazolyl)borate copper complexes:5 solid
samples of 1 were stable under air for days, and when exposed to
reduced pressure, ethylene loss was not observed.
copper-to-ethylene π-back-donation.20 However, collected
data did not support this proposal for the case of 1.
The electronic properties of the Tpx ligands can be estimated
using the ν(CO) frequencies5b,21 of the carbonyl add-
ucts TpxCu(CO). The values for the Tp* and TpMs derivatives
have been reported as 2056 and 2079 cm-1, respectively. If there
were a correlation between the chemical shift of coordinated-
ethylene protons and the electron density at the metal center,
the chemical shift of such hydrogen nuclei for 1 should appear
at a higher chemical shift than Tp*Cu(C2H4), that is, the
opposite of the experimental observations. Therefore, we be-
lieve that the observed upfield shift of the ethylene resonances
of 1 is better, and correctly, explained as a consequence of the
anisotropy generated by the π-systems of the mesityl aromatic
rings.22 A similar effect was found in the 13C NMR spectra: the
ethylene carbons resonated at δ 77.4 (C6D6, 298 K) with an
upfield shift of 46 ppm compared to free ethylene (δ 123.5
ppm). That chemical shift is slightly different than expected by
comparison with experimental and calculated values in other
copper complexes containing poor electron donor trispyrazo-
Importantly, no free ethylene was detected in the solutions of 1
by 1H NMR spectroscopy, even at þ70 °C, assessing the high
stability of this complex. The 1H NMR resonance of the ethylene
protons appeared as a sharp singlet at δ 3.03 (C6D6, 298 K) or
2.72 (CDCl3, 298 K) shifted to higher field than the ethylene
signals reported for the majority of copper(I)-olefin com-
plexes.5 For instance, Thompson’s complex4 Tp*Cu(C2H4)
showed the corresponding peak at a higher chemical shift,
δ 4.41 ppm (in CD2Cl2). Some authors have attributed the
upfield shift of the 1H NMR resonance of ethylene protons
of copper(I) adducts to the increased shielding caused by the
1
lylborate ligands.23 Moreover, the JCH coupling constant
value of 161 Hz suggests a sp2-character of the C2H4 carbons
in 1. This constant for free ethylene is 156 Hz,24 from which we
can estimate that π-back-bonding in 1 is quite weak.
The structure of the molecules of 1 was confirmed by a X-ray
single-crystal diffraction study. This compound crystallizes in the
triclinic space group P1. When data were acquired at 173 K, the
double carbon-carbon bond distance, C(37)-C(38), was found
˚
to be 1.299(8) A, shorter than that for free ethylene (1.3369(16)
A).25 A similar situation has been described by Dias et al. for the
˚
complex [HB(3-(CF3),5-(C6H5)pz)3]Cu(C2H4),9 where a 1.30(1)
˚
A distance was found for coordinated CdC. This observation
(15) Mairena, M. A.; Dıaz-Requejo, M. M.; Belderraın, T. R.;
ꢀ
Nicasio, M. C.; Trofimenko, S.; Perez, P. J. Organometallics 2004, 23,
was explained in terms of the existence of disorder of the ethylene
unit, with the ethylene group in these adducts placed in a pocket
with a significant amount of vibrational/rotational freedom. In
our case, when a second set of data was collected at 100(2) K,
the CdC distance of coordinated ethylene was found to be
253–256.
ꢀ
(16) Dıaz-Requejo, M. M.; Belderraın, T. R.; Perez, P. J. Chem.
Commun. 2000, 1853–1854.
~
(17) Munoz-Molina, J. M.; Caballero, A.; Dıaz-Requejo, M. M.;
ꢀ
Trofimenko, S.; Belderraın, T. R.; Perez, P. J. Inorg. Chem. 2007, 46,
7725–7730.
~
ꢀ
(18) Munoz-Molina, J. M.; Belderraın, T. R.; Perez, P. J. Adv. Synth.
Catal. 2008, 350, 2365–2372.
(19) Schneider, J. L.; Carrier, S. M.; Ruggiero, C. E.; Young, V. G.,
Jr.; Tolman, W. B. J. Am. Chem. Soc. 1998, 120, 11408–11418.
(20) Hertwig, R. H.; Koch, W.; Schroeder, D.; Schwarz, H.; Hrusak,
J.; Schwerdtfeger, P. J. Phys. Chem. 1996, 100, 12253–12260.
(21) (a) Fujisawa, K.; Ono, T.; Ishikawa, Y.; Amir, N.; Miyashita,
Y.; Okamoto, K.; Lehnert, N. Inorg. Chem. 2006, 45, 1698–1713.
(22) Abraham, R. J.; Canton, M.; Griffiths, L. Magn. Reson. Chem.
2001, 39, 421–431.
(23) Kazi, A. B.; Dias, H. V. R.; Tekarli, S. M.; Morello, G. R.;
Cundari, T. R. Organometallics 2009, 28, 1826–1831.
(24) Friebolin, H. Basic One- and Two-Dimensional NMR Spectros-
copy; VCH: Cambridge, 1992.
ꢀ
(b) Mairena, M. A.; Urbano, J.; Carbajo, J.; Maraver, J. J.; Alvarez, E.;
(25) Bartell, L. S.; Roth, E. A.; Hollowell, C. D.; Kuchitsu, K.;
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Día-Requejo, M. M.; Perez, P. J. Inorg. Chem. 2007, 46, 7428–7435.
Young, J. E., Jr. J. Chem. Phys. 1965, 42, 2683–2686.

Article
Organometallics, Vol. 29, No. 16, 2010 3483
Table 1. Selected NMR Data of TpMsCu(olefin) Complexesa
TpMsCu[olefin]
1H
13C
TpMsCu(C2H4), 1b
CH2 olef 3.08 (5.28)c
Colef 77.4 (123.5)
TpMsCu(1-hexene), 2b
TpMsCu(aee), 3d
CHolef 4.00 (5.80)
CH2 olef 3.28 and
3.21 (4.96 and 4.92)
CHolef 101.5 (137.9)
CH2 olef 78.5 (114.4)
CHolef 3.66 (5.91) CHolef 93.6 (134.4)
CH2 olef 2.92 and 2.78 CH2 olef 70.2 (116.4)
(5.27 and 5.17)
TpMsCu(cyclohexene), 4b CHolef 4.70 (5.66)
CHolef 99.4 (127.3)
CHolef 98.0 (135.8)
CH2 olef 3.75 and 3.56 CH2 olef 77.9 (111.3)
TpMsCu(styrene), 5b
CHolef 5.18 (6.55)
(5.59 and 5.00)
a Chemical shift in ppm. b C6D6. c Free olefin proton’s chemical shift
between brackets. CDCl3. d CD2Cl2.
appeared significantly shifted upfield when compared to
the resonances of the free olefins (1-hexene or aee) and
other R-olefin copper complexes.26 Accordingly, the che-
mical shift of the CR (CH2dCH) and Cβ (CH2dCH) olefin
carbon also emerged shifted to lower frequencies com-
pared to free olefins. Yet the rest of the protons resonances
corresponding to both 1-hexene and aee were shifted,
probably due, as proposed for 1, to the anisotropy caused
by the π-systems of the mesityl rings. For instance, the
methylene CH2dCH-CH2 protons in 2 resonated at δ
2.42 and 1.73 ppm (3.95 ppm in free 1-hexene), whereas
the methylene OCH2CH3 in 3 appeared at δ 2.81 and 2.71
(3.47 ppm in free aee).
Figure 1. Molecular structure of TpMsCu-(C2H4), 1 (30% dis-
placement ellipsoids; hydrogen atoms have been omitted except
for that bound to the boron atom).
˚
1.345(6) A, very similar but longer than that for the free molecule
25
1
˚
(1.3369(16) A), in good agreement with the observed JCH
coupling constant. As observed in Figure 1, the ethylene mole-
cule coordinates to copper(I) in a typical η2-fashion. The
distances for Cu(1)-C(37) and Cu(1)-C(38), 2.034(4) and
˚
˚
2.029(4) A, respectively, fall in the range (1.93-2.07 A) pre-
viously observed for related complexes.5a As found for other
structures with the TpMsCu core,19 the mesityl rings lie ortho-
gonal to their respective pyrazolyl rings, providing a sort of
pocket with aromatic walls, i.e., a “nest” to accommodate the
alkene ligand. Due to the steric pressure of the mesityl groups,
complex 1 displays a mononuclear nature, similar to that
Complex 2 was isolated as good X-ray quality colorless
crystals from CH2Cl2 solutions. The solid-state structure is
shown in Figure 2 (data collected at 173 K). The CdC
distance of coordinated 1-hexene, C(37)-C(38), determined
˚
for 2, 1.278(7) A, is quite similar to that reported for [Cu-
(dien)(1-hexene](BPh4) by Floriani and co-workers27 and to
the average values of the free olefin.28 As in other R-olefin
complexes,29 the Cu(I) atom is located closer to the unsub-
described for the parent complex TpMsCu(THF)19 and in con-
0
trast with other copper complexes containing TpR,R ligands
(R = R0 = H, CH3, or Ph; R = tBu, R0 = H or CH3), which
0
preferred the dinuclear [TpR,R Cu]2 geometry.
˚
stituted carbon atom (Cβ) (Cu(1)-C(37), 2.002(4) A) than
˚
the substituted carbon atom (CR) (Cu(1)-C(38), 2.095(5) A).
Synthesis and Characterization of the Olefin Complexes
TpMsCu(olefin) (olefin = 1-hexene, 2; allyl ethyl ether (aee), 3;
cyclohexene, 4; styrene, 5). In order to expand the study to
other olefins with different electronic and steric properties, we
have prepared a series of olefin complexes upon addition of an
excess of the corresponding olefin to a solution of TpMsCu-
(THF) in dichloromethane. Following this procedure, com-
plexes TpMsCu(1-hexene) (2), TpMsCu(aee) (3), TpMsCu(cyclo-
hexene) (4), and TpMsCu(styrene) (5) were isolated (eq 2) and
characterized by 1H and 13C NMR, IR, and elemental analysis,
as well as by X-ray crystallography in the case of 2 and 4.
This difference found for the two Cu-C distances is in good
accord with the chemical shifts of the olefin protons and
carbons in the 1H and 13C NMR spectra already discussed.
Complexes 2 and 3 have been found to be very stable,
lacking olefin loss under vacuum. However, a different
behavior has been observed with the copper complexes
containing the bulkier olefins styrene and cyclohexene.
Because of this, complexes 4 and 5 had to be isolated in the
presence of excess olefin. Both complexes also showed
different NMR spectra when compared with 1-3. Thus,
the 1H NMR spectrum of 4 in C6D6 showed CHolefin protons
as a broad singlet centered at 4.57 ppm. Similarly, the
(26) (a) Allen, J. J.; Barron, A. R. Dalton Trans. 2009, 878–890.
(b) Braunecker, W. A.; Pintauer, T.; Tsarevsky, N. V.; Kickelbick, G.;
Matyjaszewski, K. J. Organomet. Chem. 2005, 690, 916–924.
(27) Pasquali, M.; Floriani, C.; Gaetani-Manfredotti, A.; Chiesi-
Villa, A. Inorg. Chem. 1979, 18, 3535–3542.
(28) The more reliable overage determination of the double-bond
length for free olefin was retrieved from the Cambridge Structural
Database. See: Allen, F. H. Acta Crystallogr. Sect. B: Struct. Sci.
2002, 58, 380–388.
(29) Pintauer, T.; Matyjaszewski, K. Coord. Chem. Rev. 2005, 249,
1155–1184.
Table 1 displays NMR data for complexes 1-5. Signals
due to the coordinated CH2dCH protons of 2 and 3

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Martın et al.
3484 Organometallics, Vol. 29, No. 16, 2010
Figure 3. Molecular structure of TpMsCu(cyclohexene), 4 (30%
displacement ellipsoids; hydrogen atoms have been omitted
except for that bound to the boron atom).
Figure 2. Molecular structure of TpMsCu(1-hexene), 2 (30%
displacement ellipsoids; hydrogen atoms have been omitted
except for that bound to the boron atom).
back-bonding, the CdC double bond distance of the co-
˚
1
resonances corresponding to the olefinic protons in the H
ordinated cyclohexene of C(37)-C(42) (1.368(2) A) is
ca. 0.03 A longer than that reported for the free olefin,
˚
NMR spectrum of 5 in C6D6 appeared at δ 5.18 (CβH, dd,
JHH = 15.3 Hz, JHH = 9.4 Hz), 3.75 (CRH2, d, JHH = 9.5 Hz),
and 3.56 (CRH2, d, JHH = 15.2 Hz). Although these reso-
nances are also upfield shifted with respect to those of the
free olefins, the degree of shifting was not as pronounced as
in the case of complexes 1-3. The origin of this difference
may lie in the steric interaction of cyclohexene or styrene with
the mesityl rings in TpMsCu(cyclohexene) and TpMsCu-
(styrene), weakening the copper-olefin interaction. Since
back-bonding in these copper-olefin adducts is relatively
weak, a facile rotation about the Cu-olefin bond is expected.
Indeed, the rotational barrier for the olefin ligand has been
calculated by VT 1H NMR (through coalescence of the sign-
als of mesityl aromatic CH protons at -40 °C) as ΔG‡ =
10.9(3) kcal mol-1. This value is similar to that reported by
Warren and co-workers for the β-diketiminato copper(I)
styrene complex.7
32
˚
1.335(3) A.
Olefin Exchange Reactions. In order to compare the
stability of the olefin adducts, we decided to investigate
the olefin exchange reactions and determine the exchange
equilibrium constants. Thus, when 1 equiv of styrene was
added to a solution of TpMsCu(C2H4) in a NMR scale
(C6D6), no exchange was observed after 5 h, and therefore
we could not estimate the exchange equilibrium constant.
Consequently, ethylene complex 1 is much more thermo-
dynamically favored over the styrene adduct 5. However,
when 1 equiv of aee, a less bulky olefin compared with
styrene, was added to a solution of TpMsCu(C2H4), the
formation of TpMsCu(aee) (eq 4) was observed by NMR
spectroscopy along with the appearance of free ethylene.
After 5 h, an equilibrium mixture of 1 and 3 in the ratio of
2.55:1 was attained. On the basis of this ratio and the
concentration of both olefins, the equilibrium constant
Keq has been estimated as 0.12(1) at room temperature:
again, the ethylene adduct 1 seems to be more stable than
the aee complex, 3.
The structure of 4 was confirmed by X-ray crystallo-
graphy, an Ortep drawing being shown in Figure 3. The bond
distances Cu(1)-C(37) and Cu(1)-C(42), 2.1146(14) and
˚
(2.1110(13) A, in 4 are larger than those found in 1, in good
agreement with the already proposed weaker metal-olefin
bond in 4 as inferred from NMR studies. The observed
elongation could be explained as the result of steric inter-
actions between the olefin and the mesityl groups. Indeed,
these Cu-carbon distances are longer that those reported
by Thompson and Whitney30 for the dinuclear cyclo-
hexene adduct 1-chloro-2-(η2-cyclohexene)-μ-[hydrotris-
(1-pyrazolyl)borato-N:N0,N0’]dicopper(I), 2.039(2) and
2.022(2) A, or Stamp and Dieck31 for the mononomeric com-
˚
pound (cyclohexene)[glyoxalbis(2-diisopropylphenylimine)-
˚
trifluoromethanesulfonatocopper(I), 2.00(2) and 2.06(2) A.
In addition, as expected for a negligible copper-to-olefin
In an attempt to evaluate the effect of electronic factors,
we have carried out the exchange reactions of TpMsCu(1-
hexene) (2) with aee, since 1-hexene and aee are similar from
a steric point of view but differ substantially in electronic
density. When 1 equiv of aee was added to a solution of 2,
(30) Thompson, J. S.; Whitney, J. F. Acta Crystallogr. 1984, C40,
756–759.
(31) Stamp, L.; Dieck, H. T. Inorg. Chim. Acta 1987, 129, 107–114.
(32) Chiang, J. F.; Bauer, S. H. J. Am. Chem. Soc. 1969, 91, 1898–
1901.

Article
Organometallics, Vol. 29, No. 16, 2010 3485
Scheme 2. Possible Olefin Exchange Mechanisms
Figure 4. Influence of the entering olefin concentration on kobs
in the exchange reaction of 3 and 1-hexene.
the associative mechanism a pentacoordinated 20 e- species
(or alternatively an unlikely 18-electron κ2-TpxCu(aee)(1-
hexene)) would be formed, and in this case a certain effect of
the olefin concentration should be expected.
a ca. 1:1 mixture of 2 and 3 was observed after the equili-
brium was reached (eq 5). Finally, TpMsCu(cyclohexene) (4)
reacted with 1 equiv of aee to afford compound 3 quantita-
tively (eq 6).
With the aim of elucidating the actual mechanism we have
carried out a kinetic study of the exchange reaction of
TpMsCu(aee) with different amounts of 1-hexene. Monitor-
ing the reaction by 1H NMR at room temperature provided
no useful information since equilibrium was reached imme-
diately. However, at 0 °C the process was slow enough to
carry out the desired study. Thus, to five solutions of
TpMsCu(aee) (0.02 M) in 0.7 mL of CD2Cl2, variable
amounts of 1-hexene (1 to 5 equiv) were added. The values
of kobs at those different olefin concentrations were obtained
by first-order linear plots of ln([3]e/[3] - [3]e) vs time (see
Supporting Information). As shown in Figure 4, kobs re-
mained almost unchanged with the increase of entering
olefin concentration, in good accord with the existence of
a dissociative mechanism (Scheme 2a). Therefore, the global
equilibrium is controlled by the ratio of k1 vs k-2, being
shifted to the olefin with the less steric influence.
DFT Calculations for the Exchange Reactions. We have
carried out DFT studies to evaluate the steric influences on
the TpMsCu backbone after ligation of ethylene, 1-hexene,
allyl ethyl ether, and cyclohexene and, therefore, on the
stabilities of the corresponding olefin adducts. The B3LYP
functional applied is sufficient to describe the problem at
hand, because it properly describes the stability trends ob-
served experimentally in the exchange reactions. The stron-
gest coordination free energy corresponds to ethylene, fol-
lowed by allyl ethyl ether, 1-hexene, and cyclohexene, which
have weaker binding, by 2.6, 3.5, and 8.7 kcal mol-1, respec-
tively, relative to ethylene (see Supporting Information). The
calculation seems to exaggerate the energy differences, but
the order of stabilities is reproduced. The experimental
equilibrium constant of 2.55 in favor of the ethylene coordi-
nation with respect to aee is reflected in a computed free
energy difference of 2.6 kcal mol-1. The smallest free energy
difference of 0.9 kcal mol-1 between AEE and 1-hexene corres-
ponds to the almost 1:1 experimental equilibrium, while the
largest difference of 6.1 kcal mol-1 between aee and cyclohex-
ene corresponds to the experimental case where the reactions is
completely shifted. The computed energy values clearly con-
firm that the weakest coordination corresponds to the bulkier
olefin, cyclohexene, whereas the strongest one corresponds to
the smallest olefin, the ethylene. The adducts of linear olefins,
From experimental data, we can conclude at this stage that
the relative stability of the different TpMsCu(olefin) com-
plexes is mainly governed by steric factors. The bulkier ole-
fins such as cyclohexane or styrene were easily replaced by
smaller olefins, whereas in the cases of similar size (e.g.,
1-hexene and allyl ethyl ether) the equilibrium mixture con-
tains equimolar amounts of both complexes. The ethylene
complex seemed to be the most stable, probably due to the
lowest size that allows a better packing of the olefin between
the aromatic walls. Indeed, when ethylene is bubbled
through a solution of TpMsCu(styrene), 5, the equilibrium
is totally shifted to the formation of the ethylene adduct, 1
(eq 7). In order to check if 1 was stable in the presence of
styrene even in the absence of free ethylene, N2 was bubbled
through the above solution. After 48 h, the 1H NMR spec-
trum of the mixture remained unchanged with 1 as the only
observable olefin adduct.
Kinetic Studies of the Exchange of TpMsCu(aee) with
1-Hexene. The observed exchange process may occur by
a dissociative (Scheme 2a) or an associative mechanism
(Scheme 2b). In the dissociative mechanism, the rate-
determining step would be the formation of a 16-electron spe-
cies, the olefin concentration having no effect on kobs. In

´
Martın et al.
3486 Organometallics, Vol. 29, No. 16, 2010
a
˚
Table 5. Calculated Colefin-Cu Distances (A)
complex
C-Cu distance
C-C distance
TpMsCu(C2H4), 1
2.079/2.08
2.141/2.081
2.120/2.077
2.149/2.143
1.376
1.376
1.375
1.376
TpMsCu(1-hexene), 2
TpMsCu(AEE), 3
TpMsCu(cyclohexene), 4
a Values calculated using the B3LYP functional.
Scheme 3. Olefin Cyclopropanation Catalytic Cycle Proposed
for TpxCu As the Catalyst
Figure 5. Cu-N and C-Cu distances and C-C-Cu angle
employed to evaluate the steric distortion of the TpMsCu frag-
ment. Hydrogen atoms have been removed for clarity.
Table 2. Values of the Cu-N Distances (A) for the TpMsCu(olefin)
˚
Complexes (see Figure 4)
complex
average
Cu-N distances
TpMsCu(C2H4), 1
2.155
2.166
2.162
2.218
2.069
2.156
2.152
2.114
2.081
2.078
2.072
2.102
2.314
2.264
2.262
2.437
TpMsCu(1-hexene), 2
TpMsCu(AEE), 3
TpMsCu(cyclohexene), 4
˚
Table 3. Values of the Cu-Cpara-mesityl Distances (A)
(see Figure 4)
that there are no electronic differences for the four olefins in
the type of interaction with the metal, being almost identical.
Effect of Olefin Coordination in TpMsCu-Catalyzed Olefin
Cyclopropanation. Our group has previously reported33 the
catalytic capabilities of the complex TpMsCu for several
catalytic transformations involving the transfer of the carbene
moiety :CHCO2Et from ethyl diazoacetate (N2CHCO2Et,
EDA), including the olefin cyclopropanation reaction.14 We
proposed (Scheme 3) the existence of an equilibrium involving
the olefin adducts TpxCu(olefin) as the resting state of the
catalyst.14b Such equilibrium controls the amount of the real
catalytic species, TpxCu, in the reaction mixture. Hence, if the
equilibrium constant of formation of the olefin adduct, KL,
were very high, a very stable adduct would be formed and the
reaction rate would significantly decrease.
complex
average
C-Cu distances
TpMsCu(C2H4), 1
5.754
5.860
5.857
5.960
5.677
5.832
5.827
5.901
5.680
5.795
5.792
5.912
5.905
5.953
5.952
6.091
TpMsCu(1-hexene), 2
TpMsCu(AEE), 3
TpMsCu(cyclohexene), 4
Table 4. Values of the Cu-Cipso-Cpara-mesityl Angles (deg)
(see Figure 4)
complex
average
Cipso-Cpara-mesityl-Cu angles
TpMsCu(C2H4), 1
TpMsCu(1-hexene), 2
TpMsCu(AEE), 3
120.3
122.3
122.6
120.6
122.0
123.2
125.4
119.8
123.1
122.0
120.8
120.4
121.9
121.9
124.7
TpMsCu(cyclohexene), 4 123.6
allyl ethyl ether and 1-hexene, show similar stabilities, which
again points toward the lack of a significant electronic effect in
the interaction of the olefin with copper.
DFT Calculations for the Structures. All structures can be
viewed like an upside-down nest shaped by the TpMsCu
backbone (Figure 5). The steric effects should show up in
distortions of this nest, which we evaluated with the three
magnitudes shown in Figure 5: the Cu-N and Cu-
Cpara-mesityl distances and the Cu-Cipso-Cpara-mesityl angles,
which are collected in Tables 2, 3, and 4.
As can be seen in Tables 2-4, the results of these calcula-
tions always indicate the same trend: two extreme values,
corresponding to ethylene and cyclohexene, and two inter-
mediate values close to each other for 1-hexene and aee. The
bulkier olefin cyclohexene induced a higher degree of aper-
ture of the TpMsCu nest, whereas for the ethylene adduct this
pocket is the smallest. It is also worth mentioning that
1-hexene and allyl ethyl ether provoked a similar distortion,
in spite of their differences in electronics.
When complex TpMsCu(THF) was employed as the cata-
lyst for the reaction of allyl ethyl ether and ethyl diazoace-
tate, at room temperature, no consumption of the diazo
compound was observed after 24 h. This is in contrast with
the well-known capabilities of this compound to induce the
cyclopropanation of styrene in quantitative yield and with
high reaction rates (250 h-1).14b The use of the isolated
complex TpMsCu(aee) as catalyst precursor did not make
any difference, until the reaction was performed at 70 °C.
Under those conditions, EDA was consumed and the mix-
1
ture of products shown in Scheme 4 was detected by H
NMR. In addition to the cyclopropane derivative,34 the
carbene group was, copper-mediated, inserted into the
C-H bonds vicinal to the oxygen atoms as well as to the
oxygen atom to give an ylide intermediate that underwent a
2,3-sigmatropic rearrangement.35
ꢀ
(33) Dıaz-Requejo, M. M.; Perez, P. J. J. Organomet. Chem. 2005,
The bond distances corresponding to the olefin coordina-
tion to the metal are not so informative in terms of steric/
electronic terms, because both factors are involved. In any
case, the calculated Colefin-Cu distances (Table 5) in the
cyclohexene complex are longer than for the rest of the
complexes studied, in good agreement with the X-ray data.
Finally, the calculated CdC bond distances (Table 5) show
690, 5441–5450.
(34) (a) Dıaz-Requejo, M. M.; Belderrain, T. R.; Nicasio, M. C.;
Trofimenko, S.; Perez, P. J. J. Am. Chem. Soc. 2002, 124, 896–897.
(b) Caballero, A.; Díaz-Requejo, M. M.; Belderraín, T. R.; Nicasio, M. C.;
Trofimenko, S.; Perez, P. J. Organometallics 2003, 22, 4145–4150.
(35) (a) Doyle, M. P.; McKervey, M. A.; Ye, T. Modern Catalytic
Methods for Organic Synthesis with Diazo Compounds; John Wiley &
Sons: New York, 1998.
ꢀ
ꢀ

Article
Organometallics, Vol. 29, No. 16, 2010 3487
Scheme 4. Reaction of Allyl Ethyl Ether with Ethyl Diazoacetate
Using TpMsCu(aee) As the Catalyst
Synthesis of TpMsCu[C2H4] (1). This complex was synthesized
by bubbling C2H4 for 30 min through a dichloromethane
solution of TpMsCu(THF) (0.11 g, 0.16 mmol). Complexes were
obtained as crystalline solids in the solution in 80% yield. Anal.
Calcd for BC41H50N6O10Cu 1/3CH2Cl2: C 66.91, H 6.44, N
3
12.22. Found: C 67.18, H 6.52, N 12.06. IR (KBr): ν(B-H) 2440
cm-1, ν(CdC) 1518 cm-1. 1H NMR (400 MHz, CDCl3): δ 7.78
(d, J = 2.1 Hz, 3H), 6.82 (s, 6H), 6.03 (d, J = 2.3, 3H), 2.72 (s,
4H), 1H), 2.26 (s, 9H), 1.91 (s, 18H). 13C NMR (100 MHz,
CDCl3): δ 151.04 (Cq pyrazol), 137.79 (Cq mesityl), 137.49 (Cq
mesityl), 134.91 (CH pyrazol), 131.77 (Cq mesityl), 127.79 (CH
mesityl), 104.74 (CH pyrazol), 77.43 (CH2 olefin), 21.3 (CH3),
20.57 (CH3).
General Synthesis Procedure for TpMsCu[olefin]. To a stirred
solution of TpMsCu(THF) (0.1 g, 0,16 mmol) in CH2Cl2 (10 mL)
was added the olefin (30 mmol). The mixture was stirred for 1 h
at room temperature. After the removal of the volatiles under
reduced pressure, a white solid was obtained in quantitative
yield. The complex was purified by recrystallization. All com-
plexes were obtained as crystalline solids in 80% yield.
TpMsCu(1-hexene) (2). Anal. Calcd for BC41H50N6O10-
The low catalytic activity of TpMsCu(aee) reminded us of
the results reported by our group in a study on the insertion
of the carbene fragment :CHCO2Et into the OH bonds of
unsaturated alcohols using several TpxCu complexes as the
catalyst.36 When allyl alcohol was employed as the substrate,
the ether derived from the insertion reaction (eq 8) was
obtained in almost quantitative yields for an array of cata-
lysts, with the exception of TpMsCu, for which the yield was
low at room temperature. Such anomalous behavior can now
be explained in terms of the formation of an allylic alcohol
copper complex that should be quite stable, precluding olefin
decoordination and therefore blocking diazo compound
coordination and further metallocarbene formation.
Cu 3/2CH2Cl2: C 61.94, H 6.52, N 9.97. Found: C 62.41, H
3
6.41, N 10.17. IR (KBr): ν(B-H) 2441 cm-1, ν(CdC) 1520
cm-1. 1H NMR (400 MHz, C6D6): δ 7.76 (d, J = 2.1 Hz, 3H),
6.79 (s, 6H), 5.99 (d, J = 2.3, 3H), 4.00 (dddd, J = 15.0, 9.6, 8.7,
3.5 Hz, 1H), 3.28 (d, J = 8.3, 1H cis), 3.21 (d, J = 15, 1H trans),
2.16 (s, 9H), 1.12 (s, 18H), 1.07-0.88 (m, 2H), 0.8 (m, 3H),
0.6-0.55 (m, 2H), 0.37-0.32 (m, 2H). 13C NMR (100 MHz,
C6D6): δ 151.64 (Cq pyrazol), 137.82 (Cq mesityl), 137.33 (Cq
mesityl), 135.34 (CH pyrazol), 132.37 (Cq mesityl), 128.08 (CH
mesityl), 104.95 (CH pyrazol), 101.65 (CH olefin), 78.59 (CH2
olefin), 33.52 (3CH2), 21.03 (CH3), 20.79 (CH3), 14.25 (CH3).
TpMsCu(aee) (3). Anal. Calcd for BC41H50N6O10Cu 1/4CH2-
3
Cl2: C 67.15, H 6.90, N 11.39. Found: C 66.97, H 6.83, N 11.34.
1
IR (KBr): ν(B-H) 2425 cm-1, ν(CdC) 1516 cm-1. H NMR
(400 MHz, CD2Cl2): δ 7.81 (d, J = 2.1 Hz, 3H), 6.84 (s, 6H),
6.03 (d, J = 2.3, 3H), 3.66 (dddd, J = 15.0, 9.6, 8.7, 3.5 Hz,
1H), 2.92 (d, J = 8.3, 1H cis), 2.81 (qd, J = 9.1, 7.01 Hz, 1H),
2.78 (d, J = 15, 1H trans), 2.71 (dq, J = 9.1, 7.01 Hz, 1H), 2.42
(dd, J = 9.6, 3.6, 1H), 2.25 (s, 9H), 1.90 (s, 18H), 1.73 (t, J =
9.6 Hz, 1H), 0.89 (t, J = 7.01 Hz, 3H). 13C NMR (100 MHz,
CD2Cl2): δ 151.54 (Cq pyrazol), 137.85(Cq mesityl), 137.69
(Cq mesityl), 135.18 (CH pyrazol), 131.73 (Cq mesityl), 127.88
(CH mesityl), 104.97 (CH pyrazol), 93.57 (CH olefin), 79.89
(CH2), 70.12 (CH2 olefin), 64.51 (CH2), 20.95 (CH3), 20.40
(CH3), 15.20 (CH3).
Conclusion. We have collected experimental as well as
theoretical data relevant to the nature of the copper-olefin
bond in a series of TpMsCu(olefin) complexes. We have
found that the impact of steric factors is more relevant in
the stability of these complexes than that of the electronic
ones (small olefins, as ethylene, afford more stable complexes
than styrene or cyclohexene). We have also shown that
extracting conclusions about the copper-olefin bonding
only from chemical shifts of the olefin protons and carbons
TpMsCu(cyclohexene) (4). Anal. Calcd for BC41H50N6O10Cu:
C 70.73, H 7.07, N 11.78. Found: C 70.47, H 6.78, N 11.75. IR
(KBr): ν(B-H) 2449 cm-1, ν(CdC) 1519 cm-1. 1H NMR (400
MHz, toluene-d8): δ 7.67 (d, J = 2.1 Hz, 3H), 6.70 (s, 6H), 5.87
(d, J = 2.3, 3H), 4.57 (s, 2H), 2.08 (s, 9H), 2.04 (s, 18H), 1.06 (m,
4H), 0.70 (m, 4H). 13C NMR (100 MHz, toluene-d8): δ 151.88
(Cq pyrazol), 137.73 (Cq mesityl), 137.18 (Cq mesityl), 135.60
(CH pyrazol), 132.47 (Cq mesityl), 127.88 (CH mesityl), 104.87
(CH pyrazol), 99.04 (CH olefin), 25.35 (CH2), 22.40 (CH2),
20.90 (CH3), 20.50 (CH3).
1
in H or 13C NMR spectra can be misleading, since the
substituents on the other ligands (in our case, the mesityl rings
of the TpMs ligand) may have an influence on those data.
Experimental Section
General Methods. All reactions and manipulations were
carried out under an oxygen-free nitrogen atmosphere with
standard Schlenk techniques. All substrates were purchased
from Aldrich. Solvents were dried and degassed before use.
TpMsCu(THF)19 complex was prepared according to the re-
ported method. NMR spectra were recorded on a Varian
Mercury 400 MHz spectrometer using deuterated solvents. IR
data were collected in a Varian Scmitar 1000 Fourier transform
IR spectrophotometer. Elemental analyses were performed in
TpMsCu(styrene) (5). Anal. Calcd for BC41H50N6O10Cu: C
71.39, H 6.53, N 11.35. Found: C 71.34, H 6.66, N 10.92. IR
(KBr): ν(B-H) = 2433 cm-1, ν(CdC) = 1513 cm-1. 1H NMR
(400 MHz, C6D6): δ 7.65 (d, J = 2.1 Hz, 3H), 6.64 (s, 6H), 5.86
(d, J = 2.3, 3H), 5.18 (dd, J = 15.3, 9.4 Hz, 1H), 3.75 (d, J = 9.5,
1H cis), 3.56 (d, J = 15.2 Hz, 1H trans), 2.05 (s, 9H), 2.00 (s,
18H). 13C NMR (100 MHz, C6D6): δ 151.95 (Cq pyrazol),
137.55(Cq mesityl), 137.29 (Cq mesityl), 135.51 (CH pyrazol),
131.78 (Cq mesityl), 127.98 (CH mesityl), 105.23 (CH pyrazol),
98.04 (CH olefin), 77.89 (CH2 olefin), 21.00 (CH3), 20.40 (CH3).
Activation Barriers for Styrene Rotation in 5. The activation
barrier for styrene rotation in 5 was calculated using the
ꢀ
Unidad de Analisis Elemental at the Instituto de Investigaciones
Quımicas, CSIC-Universidad de Sevilla.
(36) Morilla, M. E.; Molina, M. J.; Dıaz-Requejo, M. M.; Belderraın,
ꢀ
1
following partial H NMR data (toluene-d8, 193 K): δ 6.65 (s,
3, aromatic mesityl-CH), 6.33 (s, 3, aromatic mesityl-CH).
T. R.; Nicasio, M. C.; Trofimenko, S.; Perez, P. J. Organometallics 2003,
22, 2914–2918.

´
Martın et al.
3488 Organometallics, Vol. 29, No. 16, 2010
Coalescence of these peaks at δ 6.51 (Δv = 129.43 Hz, Tc =
233 K) corresponds to an activation barrier of ΔG‡ = 10.9(3) kcal
mol-1 at 233 K.
(SHELXTL-6.14)43 minimizing w[Fo2 - Fc2]2. All non-hydrogen
atoms were refined with anisotropic displacement parameters.
The hydrogen atoms were introduced into geometrically calcu-
lated positions and refined riding on the corresponding parent
atoms.
Olefin Exchange Reactions. One equivalent of olefin-R2 was
added to a solution of TpMsCu(olefin-R1) in 0.6 mL of deuter-
ated solvent, and the solution was transferred to an NMR tube
that was sealed with a Teflon stopper. The reaction mixture was
monitored every hour at room temperature until an equilibrium
mixture was reached. Accounting for the relative concentrations
of olefin-R1 and olefin-R2 in solution afforded the equilibrium
constant Keq at room temperature for the exchange reaction
below.
Crystal data for 1: C38H44BCuN6, Mw=659.14, colorless
prism crystal of dimensions 0.19 ꢀ 0.15 ꢀ 0.08 mm3, monoclinic,
˚
˚
space group P1 (no. 2), a = 9.1125(14) A, b = 11.1306(16) A,
˚
c=17.644(3) A, R=102.973(5)°, β=96.970(6)°, γ= 94.440(6)°,
3
3
˚
V = 1720.9(5) A , T = 100(2) K, Z = 2, D = 1.272 Mg/m ,
F = 0.670 mm-1, F(000) = 696; 38 117 reflections measured, of
which 13 102 were unique (Rint = 0.0502). The asymmetric unit
of the structure is formed by two equivalent but symmetrically
independent complexes of 1. Refined parameters 830, final R1 =
0.0473 for reflections with I >2σ(I), wR2 = 0.1052 (all data),
GOF = 1.002. Final largest diffraction peak and hole: 0.557 and
-3
˚
-0.656 e A
Crystal data for 2: C42H52BCuN6, Mw = 715.25, colorless
.
Kinetic Study of the Exchange Reaction of TpMsCu(aee), 3,
with 1-Hexene. At 0 °C, 1, 2, 3, 4, and 5 equiv of 1-hexene (from a
stock 1.6 M solution in CD2Cl2) were added to five solutions of
10 mg of TpMsCu(aae) (0.02 M) in 0.7 mL of CD2Cl2. The
reaction was monitored by 1H NMR until the equilibrium was
reached. The kobs at different olefin concentrations were ob-
tained by first-order linear plots of ln([3]e/[3] - [3]e) vs time (see
Supporting Information).
plate crystal of dimensions 0.16 ꢀ 0.13 ꢀ 0.08 mm3, triclinic,
˚
space group P1 (no. 2), a = 9.0845(7) A, b = 12.6099(9) A, c =
˚
˚
17.7141(12) A, R = 97.856(2)°, β = 97.736(2)°, γ = 102.926(2),
3
3
˚
V = 1930.4(2) A , T = 100(2) K, Z = 2, D = 1.231 Mg/m , F =
0.603 mm-1, F(000) = 760; 71 663 reflections measured, of
which 11521 were unique (Rint = 0.0680). Refined parameters
451, final R1 = 0.0547 for reflections with I > 2σ(I), wR2 =
0.1547 (all data), GOF = 1.044. Final largest diffraction peak
Reaction of Allyl Ethyl Ether and EDA Catalyzed by TpMsCu-
(THF). A solution of ethyl diazoacetate (0.114 g, 1 mmol) in 10
mL of 1,2-dichloroethane was added to a solution of TpMsCu-
(THF) (8.6 mg, 0.0125 mmol) and allyl ethyl ether (0.76 g,
8.8 mmol) in 10 mL of 1,2-dichloroethane. The reaction mixture
was heated at 70 °C. The consumption of EDA was monitored
by IR. After 24 h, volatiles were removed under vacuum and the
-3
˚
and hole: 1.073 and -1.043 e A
.
Crystal data for 4: C42H50BCuN6, Mw = 713.23, colorless
prism crystal of dimensions 0.49 ꢀ 0.47 ꢀ 0.46 mm3, ortho-
˚
rhombic, space group Pna21 (no. 33), a = 16.3641(9) A, b =
˚
˚
11.8396(6) A, c = 19.3116(10) A, R = β = γ = 90°, V =
3
3
˚
3741.5(3) A , T = 100(2) K, Z = 4, D = 1.266 Mg/m , F = 0.622
mm-1, F(000) = 1512; 87 199 reflections measured, of which
11 153 were unique (Rint = 0.0341). Refined parameters 466,
final R1 = 0.0300 for reflections with I > 2σ(I), wR2 = 0.0778
(all data), GOF = 1.055. Absolute structure parameter (Flack x
parameter): 0.007(6). Final largest diffraction peak and hole:
1
reaction crude was analyzed by H NMR spectroscopy. The
products have been identified by comparison with data pre-
viously reported.37-39 The addition of 1,4-dimethoxybenzene as
internal reference provided both mass balance, referred to initial
EDA, and the ratio of products formed in each transformation.
Purification of products was performed with neutral silica gel as
described previously.5
-3
˚
0.706 and -0.544 e A
.
Computational Details. Calculations were carried out with
DFT using the B3LYP functional44-46 as implemented in
Gaussian 03.47 The 6-31G(d) basis set48,49 was used for all
atoms except copper, which was treated with SDD and the
associated effective core potential.50 Frequency calculations
X-ray Crystal Structure Analyses of 1, 2, and 4. A single
crystal, of each representative compound, of suitable size
was mounted on a glass fiber using perfluoropolyether oil
(FOMBLIN 140/13, Aldrich) in the cold N2 stream of a low-
temperature device attachment. Full crystallographic data
and structure refinement are given in the Supporting Infor-
mation. Intensity data were performed on a Bruker-AXS X8
Kappa diffractometer equipped with an Apex-II CCD area
detector, using a graphite monochromator Mo KR1 (λ =
(44) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5652.
(45) Lee, C. T.; Yang, W. T.; Parr, R. G. Phys. Rev. B 1988, 37, 785–
789.
(46) Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J.
J. Phys. Chem. 1994, 98, 11623–11627.
˚
0.71073 A) and a Bruker Cryo-Flex low-temperature device.
(47) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken,
V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.;
Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas,
O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.;
Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.;
Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
Gonzalez, C.; Pople, J. A. Gaussian 03, Revision C.02; Gaussian, Inc.:
Wallingford, CT, 2004.
The data collection strategy used in all instances was phi and
omega scans with narrow frames. Instrument and crystal
stability were evaluated from the measurement of equivalent
reflections at different measuring times, and no decay was
observed. The data were reduced (SAINT)40 and corrected
for Lorentz and polarization effects, and a semiempirical
absorption correction was applied (SADABS).41 The struc-
ture was solved by direct methods (SIR-2002)42 and refined
against all F2 data by full-matrix least-squares techniques
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Article
Organometallics, Vol. 29, No. 16, 2010 3489
were performed to characterize the stationary points as minima.
Free energy corrections were introduced for a pressure of 1 atm
and a temperature of 298 K.
ICIQ Foundation for financial support. C.M. thanks the
ꢀ
Ministerio de Educacion for a research fellowship.
Supporting Information Available: CIF files for 1, 2, and 4,
kinetic data for olefin exchange processes, and 1H and 13C NMR
spectra of complexes 1-5. Cartesian coordinates for all com-
puted structures. This material is available free of charge via the
Internet at http://pubs.acs.org.
Acknowledgment. We thank the MICINN (Proyecto
CTQ2008-00042BQU, CTQ2008-06866-CO2-02/BQU
and Consolider Ingenio 2010 grant CSD2006-0003), the
Junta de Andalucıa (Proyecto P07-FQM-02794), and the