Hydrotris(3-mesitylpyrazolyl)borato-copper(i) alkyne complexes: Synthesis, structural characterization and rationalization of their activities as alkyne cyclopropenation catalysts

Article abstract of DOI:10.1039/c2dt11951j

The use of the bulky hydrotris(3-mesitylpyrazolyl)borate anionic ligand has allowed the synthesis of stable Tp^MsCu(alkyne) complexes (alkyne = 1-hexyne, 1, phenylacetylene, 2, and ethyl propiolate, 3). The spectroscopic and structural features of these compounds and their relative reactivity have been examined, indicating the existence of a low π back-bonding from the copper(i) centre to the alkyne. Ligand exchange experiments have shown that terminal alkyne adducts are more stable than internal alkyne analogues. In good accordance with this, the previously reported alkyne cyclopropenation reaction catalysed by the Tp^xCu complexes can be rationalized and correlated with their relative stability.

Full text of DOI:10.1039/c2dt11951j

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PAPER
Hydrotris(3-mesitylpyrazolyl)borato-copper(I) alkyne complexes: synthesis,
structural characterization and rationalization of their activities as alkyne
cyclopropenation catalysts†‡
Carmen Martín,a Marta Sierra,a Eleuterio Alvarez,b Tomás R. Belderrain*a and Pedro J. Pérez*a
Received 16th October 2011, Accepted 16th January 2012
DOI: 10.1039/c2dt11951j
The use of the bulky hydrotris(3-mesitylpyrazolyl)borate anionic ligand has allowed the synthesis of
stable TpMsCu(alkyne) complexes (alkyne = 1-hexyne, 1, phenylacetylene, 2, and ethyl propiolate, 3).
The spectroscopic and structural features of these compounds and their relative reactivity have been
examined, indicating the existence of a low π back-bonding from the copper(I) centre to the alkyne.
Ligand exchange experiments have shown that terminal alkyne adducts are more stable than internal
alkyne analogues. In good accordance with this, the previously reported alkyne cyclopropenation reaction
catalysed by the TpxCu complexes can be rationalized and correlated with their relative stability.
in cationic complexes of group 11 elements have more electro-
static than covalent character. Nevertheless, the covalent contri-
Introduction
Group 11 metals complexes containing alkynes are involved in
butions to the bonding is mainly due to the metal←acetylene σ
donation.10
important transformations, such as the addition of alkynes to het-
eroatom–hydrogen bonds,1 cycloaddition,2 cyclopropenation3
Recently, we have reported the synthesis and characterization
and coupling reactions.4 Copper–alkyne adducts are also
employed as volatile metal precursors for chemical vapour depo-
sition (CVD) of high-purity copper films.5 Furthermore, these
alkyne adducts have been proposed as reaction intermediates,
providing insights into the mechanisms of catalytic processes.6
But surprisingly, since the first report of an X-ray diffraction
structure of an acetylene complex7 by Thompson and Whitney
nearly three decades ago, only a few mononuclear alkyne copper
complexes have been isolated and structurally characterized.6a,8
Therefore, the synthesis of coinage metal complexes containing
metal–alkyne bonds constitutes an important area of interest.
Copper–alkyne bonding can be described by the Dewar–
Chatt–Duncanson model in a similar manner to metal–alkene
bonding.9 The bond is explained as a consequence of a synergis-
tic metal←acetylene σ-donation from the occupied π-orbital of
the alkyne into the empty d(σ) atomic orbital of the metal, and
metal→acetylene π-back-donation from the occupied d(π) orbital
of the metal into the empty π* orbital of the ligand. However,
theoretical studies have shown that the metal–alkyne interaction
of several TpMsCu(olefin) complexes (Fig. 1).11 The experimen-
tal as well as theoretical data collected were relevant to the
nature of the copper–olefin bond. Thus, the impact of steric
factors had a higher effect on the stability of those complexes
than that of the electronic ones: small olefins, as ethylene,
afforded more stable complexes than styrene or cyclohexene. We
proposed that the three aromatic “walls” of mesityl substituents
of pyrazolyl rings provide a somewhat protective pocket
for the olefin. In addition, we showed that the stability of the
olefin adducts clearly influenced the catalytic capabilities of
the complex TpMsCu for the transfer of the carbene moiety
: CHCO2Et from ethyl diazoacetate (N2CHCO2Et, EDA), to
olefins in the cyclopropanation reactions. On the basis of the
aforementioned interest of copper–alkyne complexes and our
previous study with copper–olefin complexes, we decided
to study a series of terminal and internal alkyne complexes:
1-hexyne, phenylacetylene, ethyl propiolate and 3-hexyne.
Herein, we describe the synthesis and characterization of
TpMsCu(alkyne) complexes as well as the study of their relative
stabilities and reactivities.
aLaboratorio de Catálisis Homogénea, Departamento de Química y
Ciencia de los Materiales, Unidad Asociada al CSIC, Centro de
Investigación en Química Sostenible (CIQSO), Universidad de Huelva,
Campus de El Carmen, 21007 Huelva, Spain. E-mail: perez@
dqcm.uhu.es, trodri@dqcm.uhu.es
bInstituto de Investigaciones Químicas, CSIC-Universidad de Sevilla,
Avenida Américo Vespucio 49, 41092 Sevilla, Spain
†In memoriam to Prof. Purificación Escribano
‡Electronic supplementary information (ESI) available. CCDC reference
numbers 849107–867111. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c2dt11951j
Fig. 1 TpMsCu(alkene) complexes.
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8a
[(phen)Cu(CHuCPh)]ClO4
and
[H2B(3,5-(CF3)2Pz)2]
Results and discussion
Cu(CHuCPh)6a appear at δ 5.21, 5.14 and 4.60 ppm, respect-
ively. The smaller values found for 1–3 could be a consequence
of the anisotropy generated by the π-systems of the mesityl
aromatic rings which avoid the downfield shift of those
resonances. However, in the 13C{1H} NMR spectra of 1–3 the
chemical shifts of acetylenic carbons CuC of the coordinated
alkyne are similar to those of the above examples, with small
differences in the chemical shifts of alkyne carbon atoms for
coordinated and free alkyne molecule. This is at variance with
d10 metal–alkyne complexes of group 10 elements, where the
Δδ(CuC) is considerably higher.12 The ν(CuC) values
observed in 1–3 have also provided useful information about the
metal–alkyne interaction.6a,8,13 Such absorptions appear at 1957,
1923, 1901 cm−1 for 1, 2 and 3, respectively, differing from
those of the free alkynes (2120, 2110 and 2115 cm−1, respect-
ively), and resembling data already reported for other copper–
alkyne adducts. Thus, the 1-pentyne complex [Cu(bpy)
(HCuCCH2CH2CH3)]+,13a shows the ν(CuC) band at
1932 cm−1, similar to the value observed for 1. The reported
Synthesis and spectroscopic characterization of TpMsCu(alkyne)
complexes
TpMsCu(alkyne) adducts (alkyne = 1-hexyne, 1, HCuCPh, 2,
and HCuCCO2Et, 3) were synthesized using the procedure pre-
viously reported for the TpMsCu(olefin) complexes.11 An excess
of alkyne was added to a solution of TpMsCu(THF) in CH2Cl2 to
give the corresponding copper–alkyne adducts in 80–90% yields
(eqn (1)). All three compounds were stable under vacuum and in
the air in the solid state. Internal alkynes such as 3-hexyne have
also been employed, but isolation of pure compounds has been
elusive, although the adducts have been detected in solution.
Indeed, the addition of 2 equiv of 3-hexyne to a solution of
TpMsCu(THF) in C6D6 did not lead to complete conversion to
the alkyne adduct and a mixture of THF and alkyne adducts was
1
observed in a 1 : 5 ratio (see H NMR spectrum in the ESI),‡
whereas that equilibrium is totally shifted to the formation of the
alkyne complex in the case of 1-hexyne with only 1 equiv of
alkyne added. Similarly to the TpMsCu(olefin) case,11 the stab-
ility TpMsCu(alkyne) might be controlled by steric factors (see
below).
value of ν(CuC) for the complex [(phen)Cu(HCuCPh)]
13b
ClO4
(1921 cm−1) is close to the value of complex TpMsCu
(HCuCPh), 2. The Δν(CuC) between the free and the coordi-
nated alkyne in complexes 1–3 is smaller than that for other
alkyne adducts of other low oxidation state metals like Pt, Ni, Ir,
Nb and W, which show much higher Δν(CuC) values (around
410–540 cm−1).14 This fact could be related to the existence of a
lower metal→alkyne π back-donation contribution in these
TpMsCu(alkyne) complexes. In the case of TpMsCu(ethyl propio-
late) (3) Δν(CuC) = 214 cm−1 is slightly higher than in 1 or 2,
assessing a higher degree of such interaction in this compound
due to the presence of the electron attracting substituent –CO2Et.
ð1Þ
Selected spectroscopic NMR and IR data of complexes 1–3
are shown in Table 1. In the 1H NMR spectra of these three com-
pounds the corresponding CuCH acetylenic proton resonances
appear at lower fields than those corresponding to the free
alkynes. The alkyne chain hydrogens are affected by the pres-
ence of the π system of the mesityl ring of the ligand, with their
signals shifted to higher fields than those for free 1-hexyne, as
described for the adduct of 1-hexene.11 Interestingly, the CuCH
resonance shifts found for 1–3 are small (Δδ = 1.0–1.3 ppm)
compared with those described for other copper–terminal alkyne
complexes. For example, the chemical shifts of the acetylene
protons in the complexes [Cu{NH(C5H4N)2}(HCuCH)]BF4,7b
Structural characterization of complexes 1–3
The structures of complexes 1–3 were confirmed by means of
single-crystal X-ray diffraction studies (Fig. 2). In the three com-
pounds the TpMs ligand is coordinated in a κ3-N,N,N fashion and
the alkyne molecules are bonded to the metal in a η2 mode, the
two Cu–Cα and Cu–Cβ distances being slightly different
(Table 2). The unit cell contains more than one independent mol-
ecule, as well as alkyne crystallization molecules that have been
omitted in Fig. 2 (see ESI for complete ORTEP).‡
The Cu–Calkyne bond distances found for 1–3 are similar to
those reported for other copper complexes of the same alkynes
For example, Cu–C(37) and Cu–C(38) bond lengths in 2, 1.967
Table 1 Selected NMR and IR data for 1–3a,b
(2) and 2.0284(18) Å, respectively, compare well with those pub-
6a
lished for BpCF ,CF Cu(HCuCPh) (1.936(4) and 2.003(4) Å),
[ClCu(HCuCPh)]14b (1.999(4) and 2.066(3) Å) and [(phen)Cu
(HCuCPh)]ClO414b (1.922(12) and 1.995(10) Å). In the case of
complex 3 the Cu–C(78) and Cu–C(79) distances, 1.956(4) and
1.964(4), are slightly longer than those found for the complex
[(phen)(CuHCuCCO2Et)]ClO4,8a 1.925(9) and 1.934(7) Å.
The values of the CuC–C angle for 1, 2 and 3 are 163.5(2)°,
159.9(2)° and 151.9(4)°, respectively, with a deviation from line-
arity in each case of 16.5°, 20.1° and 28.1°. These data can be
related with the degree of π back-bonding contribution, and, con-
sequently, in good agreement with spectroscopic data, the
3
3
δ(1H)
CuCH
δ(13C)
RCuCH
TpMsCu(alkyne)
ν(CuC)
TpMsCu(1-hexyne), 1c
2.79 (1.75) 70.1 (68.5) 1957 (2120)
93.4 (83.9)
TpMsCu(phenylacetylene), 2c 3.94 (2.66) 79.0 (77.9) 1923 (2110)
94.2 (83.9)
TpMsCu(ethyl propiolate), 3d 3.89 (2.92) 85.4 (74.7) 1901 (2115)
87.1 (75.0)
a Chemical shift in ppm, at room temperature, and IR data in cm−1
b Values for metal-free alkynes are given in brackets. c C6D6. d CDCl3.
.
5320 | Dalton Trans., 2012, 41, 5319–5325
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Fig. 2 The molecular structures of complexes (a) TpMsCu(1-hexyne), 1, (b) TpMsCu(phenylacetylene), 2, and (c) TpMsCu(ethyl propiolate), 3 (30%
displacement ellipsoids; hydrogen atoms have been omitted except for the acetylenic one and that bound to the boron atom; crystallization solvent has
been also omitted for clarity).
Table 2 Selected bond parameters for complexes TpMsCu(alkyne),
1–3
Alkyne exchange reactions
Experimental data obtained for the olefin exchange reactions in
TpMsCu(olefin) indicated that the relative stability of such
adducts depends mainly on steric factors.11 With the aim of
examining the role of those effects in the stability of alkyne com-
plexes, we decided to study the related exchange reactions with
alkynes. Thus, the addition of 1 equiv of phenylacetylene to a
solution of the complex TpMsCu(1-hexyne) (1) in C6D6 led to an
equilibrium mixture of 1 and 2 immediately (eqn (2)). The equi-
Bond lengths (Å)
Complex CuC Cu–Cα
Angles (°)
Cu–Cβ
CuC–H
CuC–C
1
2
3
1.213 (3) 1.991(2) 2.0127(18) 162.3 (18) 163.5 (2)
1.218 (3) 1.967(2) 2.0284(18) 161.4 (15) 159.9 (2)
1.212 (6) 1.956 (4) 1.964 (4)
166 (3)
151.9 (4)
1
librium constant Keq has been estimated by H NMR as 0.23(1)
greatest deviation is observed for the HCuCCO2Et adduct. As
already mentioned, theoretical studies have indicated that the
copper–acetylene interaction occurs mainly through the com-
ponent σ, with a rather low Cu+–HCuCH π contribution.10
Accordingly, the CuC distance found for 2, 1.218(3) Å, is only
slightly longer than that for free phenylacetylene, 1.19(2) Å.8a
at room temperature by the integration of the coordinated acety-
lenic protons signals. The Keq value indicates that 1 is more
stable than 2, and suggests, once again, that steric interactions
between substituents of the acetylene and mesityl groups of the
TpMs control the stability of the adduct: reducing the size of the
alkyne ligand confers a certain stability to the copper adduct. As
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expected from that, when 1 equiv of 3-hexyne was added to a
solution of complex TpMsCu(1-hexyne) (1) no formation of the
internal alkyne adduct was observed (eqn (3)).
the cyclopropenation reactions of 1-hexyne and 3-hexyne using
EDA as a carbene source. Table 3 displays the reaction outcome,
showing substituted cyclopropene yields and the time required in
each case for the total consumption of EDA. It is worth mention-
ing that these experiments have been carried out adding both the
alkyne and the diazo in one portion, the use of slow addition
devices would infer higher conversions. For the sake of compari-
son of activities, it is preferable to operate at moderate conver-
sions. The reaction of EDA with the terminal alkyne, 1-hexyne
using TpMsCu as the catalyst is significantly slower for TpMsCu,
followed by TpPhCu and TpBr3Cu, the latter inducing a similar
yield only in 1 h. This is the order of stabilities of the corre-
sponding TpxCu(1-hexyne) adducts, and therefore it is in good
agreement with the proposal shown in Scheme 1: those com-
plexes favouring the formation of alkyne adducts will display
lower catalytic activities as the result of a certain decrease of the
concentration of the catalytic species TpxCu. For 3-hexyne as the
substrate, reaction times were considerably shorter for the three
complexes employed. These data can be reasoned in terms of the
less favoured formation of internal alkyne adducts due to the
steric interaction between the substituents of the Tpx ligand and
those of the alkyne.
ð2Þ
ð3Þ
Rationalization of catalyst activity in the alkyne
cyclopropenation reactions
The reaction of diazo compounds and alkynes catalysed by tran-
sition metal complexes has been employed in the synthesis of
cyclopropenes (eqn (4)).3,15 In such processes there exists a side
reaction, the carbene dimerization, that competes with the cyclo-
propenation reaction. In our group we have previously reported
that a series of TpxCu complexes efficiently catalyses this
transformation,16,17
The bulkiness of the Tpx ligand also influences the catalyst
chemoselectivity. Thus, in the 1-hexyne cyclopropenation reac-
tion catalysed by TpMsCu, although slow, cyclopropene was
obtained in moderate yields (49%), whereas for 3-hexyne diethyl
fumarate and maleate (92%), from the dimerization reaction of
ð4Þ
using ethyl diazoacetate (EDA) as the carbene source, with
excellent results for both internal and terminal alkynes.
However, some exceptions were found: the complexes TpMsCu,
TpPhCu and Tpα-NtCu (TpPh = hydrotris(3-phenylpyrazolyl)
borate; Tpα-Nt = hydrotris(3-α-naftylpyrazolyl)borate) did not
provide good yields. The behaviour of these complexes in the
case of terminal alkynes can be explained by means of the exist-
ence of an equilibrium of the alkyne adducts and the real cataly-
tic species, TpxCu, in the reaction mixture (Scheme 1). In the
case of high KL (equilibrium constant of alkyne adduct for-
mation) values a very stable adduct would be formed and the
reaction rate would significantly decrease. On the other hand,
very active catalysts for carbene transfer in cyclopropenation
such as TpBr3Cu(NCCH3),17 with low steric hindrance, do not
form alkyne adducts.
With the aim of comparing the catalytic capabilities of
Scheme 1 Proposed mechanism for the cyclopropenation reactions
catalysed by TpxCu complexes.
TpMsCu, TpBr3Cu and TpPhCu complexes, we have carried out
Table 3 Cyclopropenation of 1-hexyne and 3-hexyne with EDA using TpxCu complexesa
Catalyst
Substrate
1-Hexyne
Product
TpMsCu
TpPhCu
TpBr3Cu
50%/1 h
49%/48 h
29%/24 h
3-Hexyne
8%/1 h
18%/2 h
43%/1 h
a Catalyst : EDA : alkyne ratio of 1 : 30 : 90, 0.1 mmol of TpxCu employed. Percentage of cyclopropenes and reaction time required for total
consumption of EDA. The remaining initial EDAwas converted in mixtures of diethyl fumarate and maleate.
5322 | Dalton Trans., 2012, 41, 5319–5325
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were prepared according to the reported methods. All other
chemicals were purchased from the Sigma-Aldrich Chemical Co.
and purified before use. NMR spectra were recorded on a
400 MHz Varian Mercury. Infrared spectra were recorded on a
Nicolet FTIR 200 spectrophotometer. Elemental analyses were
performed in Unidad de Análisis Elemental at the Instituto de
Investigaciones Químicas, CSIC-Universidad de Sevilla.
General synthesis of TpMsCu(alkyne) adducts
Fig. 3 Steric interactions between the mesityl groups of the TpMs
ligand and the alkyne during the carbene transfer step: (a) 1-hexyne; (b)
3-hexyne.
30 mmol of the alkyne were added to a solution of 0.10 g of
complex TpMsCu(THF) (0.14 mmol) in 10 mL of dichloro-
methane. After 1 h, the solvent was removed under vacuum and
a solid was obtained. The complexes were purified by recrystalli-
zation using a mixture of CH2Cl2–alkyne. All complexes were
isolated as crystalline solids in 80–90% yields.
EDA, were obtained as the major products (Table 3). This behav-
iour may be due to steric repulsions between the mesityl groups
of the TpMs ligand and 3-hexyne, which would prevent the
approach of the alkyne to the carbene ligand and hindering the
process of carbene transfer (Fig. 3b). For internal alkynes the
formation of diethyl fumarate and maleate is faster (k3,
Scheme 1) than the cyclopropenation reaction (k2, Scheme 1),
even in the presence of an excess of alkyne. In good agreement
with this proposal, for 3-hexyne the yields of the cyclopropene
derivative increase as the steric effect of the ligand decreases, in
the order TpMs < TpPh < TpBr3. In the case of 1-hexyne, cyclo-
propenation using TpMsCu(THF) as catalyst, the less bulky
alkyne molecule can approximate more easily to the carbenic
moiety since the steric repulsion with the mesityl groups is
reduced (Fig. 3a), and, consequently, the cyclopropenation step
rate becomes comparable or even higher than the EDA dimeriza-
tion process, with the corresponding enhancement of cyclopro-
pene products.
TpMsCu(1-hexyne), 1. 1H NMR (400 MHz, C6D6) δ 7.66 (d,
3J(HH) = 2.1 Hz, 3H, CHpyrazol), 6.67 (s, 6H, CHmesityl),
3
3
5.92 (d, J(HH) = 2.1 Hz, 3H, CHpyrazol), 2.79 (t, J(HH) = 2.3
Hz, 1H, CHacetylene), 2.58 (s, 18H, CH3(mesityl)), 2.05 (s, 9H,
CH3(mesityl)), 0.76–0.87 (m, 4H, CH2), 0.57–0.71(m, 4H, CH2),
0.65 (t, 3J(HH) = 7.2 Hz, 3H, CH3). 13C NMR (100 MHz,
C6D6) δ 151.24 (Cpyrazol), 137.81 (Cmesityl), 137.06 (Cmesityl),
135.35 (CHpyrazol), 132.27 (Cmesityl), 128.01 (CHmesityl), 104.92
(CHpyrazol), 92.73 (HCuC), 69.40 (HCuC)), 32.09 (CH2),
21.31(CH2), 20.93 (CH3(mesityl)), 20.82 (CH3(mesityl)), 13.64
(CH3). IR (KBr, cm−1): 2443 [ν(BH)], 1957 [ν(CuC)]. Anal.
Calcd. for BC42H50N6Cu: 70.75 C, 7.02 H, 11.79 N. Found:
70.91 C, 7.01 H, 11.94% N.
TpMsCu(phenylacetylene), 2. 1H NMR (400 MHz, C6D6) δ
3
3
7.71 (d, J(HH) = 2.1 Hz, 3H, CHpyrazol), 6.69 (t, J(HH) = 7.4
3
Hz, 1H, CHp-phenyl), 6.59 (t, J(HH) = 7.7 Hz, 2H, CHm-phenyl),
6.47 (s, 6H, CHmesityl), 6.43 (d, 3J(HH) = 7.1 Hz, 2H,
CHo-phenyl), 5.96 (d, 3J(HH) = 2.1 Hz, 3H, CHpyrazol), 3.94
(s, 1H, CHacetylene), 2.06 (s, 18H, CH3(mesityl)), 1.90 (s, 9H,
CH3(mesityl)). 13C NMR (100 MHz, C6D6) δ 151.84 (Cpyrazol),
137.32 (Cmesityl), 136.83 (Cmesityl), 135.36 (CHpyrazol), 131.54
(Cmesityl), 131.38 (CHo-phenyl), 128.04 (CHmesityl), 126.98
(CHp-phenyl), 126.07 (CHm-phenyl), 122.76 (Cphenyl), 105.44
(CHpyrazol), 94.05 (HCuC), 78.82 (HCuC), 21.22
(CH3(mesityl)), 20.84 (CH3(mesityl). IR (KBr, cm−1): 2440
Conclusion
We have prepared and characterized a series of TpMsCu(alkyne)
complexes. Data collected indicate that steric interactions
between the mesityl groups and the substituents of the alkyne
clearly influences the stability of the adducts. Thus, terminal
alkyne adducts are more stable that internal alkyne analogues.
This is an important issue when using these compounds as cata-
lyst precursors in the alkyne cyclopropanation reaction with
ethyl diazoacetate as the carbene source. Under catalytic con-
ditions, metal centres with a low steric hindrance (such as
TpBr3Cu) do not form alkyne adducts and display high catalytic
activities. In the opposite case, stable alkyne adducts can be
formed and the reaction rate lowered. This study provides the
information to choose the appropriate Tpx ligand for a given
alkyne to be converted into cyclopropenes.
[ν(B-H)],
1923
[ν(CuC)].
Anal.
Calcd.
for
BC44H46N6Cu.2/3HCuC-Ph: 74.00 C, 6.25 H, 10.50 N. Found:
73.93 C, 6.28 H, 10.12% N.
TpMsCu(ethyl propiolate), 3. 1H NMR (400 MHz, C6D6) δ
7.77 (d, 3J(HH) = 2.1 Hz, 3H, CHpyrazol), 6.76 (s, 6H, CHmesityl),
6.02 (d, 3J(HH) = 2.1 Hz, 3H, pyrazol CH), 3.81 (s, 1H,
CHacetylene), 3.61 (q, 3J(HH) = 7.1, 2H, CH2), 2.02 (s, 9H,
3
CH3(mesityl)), 1.91 (s, 18H, CH3(mesityl)), 0.98 (t, J(HH) = 7.1,
3H, CH3). 13C NMR (100 MHz, C6D6) 153.09 (COpropiolate),
151.58 (Cpyrazol), 137.82 (Cmesityl), 137.38 (Cmesityl), 135.20
(CHpyrazol), 131.28 (Cmesityl), 127.85 (mesityl CH), 105.32
(CHpyrazol), 86.68 (HCuC), 86.06 (HCuC), 61.35 (CH2), 21.29
(CH3(mesityl), 20.85(CH3(mesityl), 14.05 (CH3). IR (KBr, cm−1):
2447 [ν(B-H)], 1901 [ν(CuC)], 1727 [ν(CuO)]. Anal. Calcd.
for BC40H44N6O2Cu: 67.10 C, 6.16 H, 11.75 N. Found:
66.84 C, 5.84 H, 11.71% N.
Experimental
General
Solvents were dried and deoxygenated before use. All reactions
and manipulations were carried out under an oxygen-free nitro-
gen atmosphere with standard Schlenk techniques. TpMsCu
(THF),18 TpPhCu(NCCH3)19 and TpBr3Cu(NCCH3)20 complexes
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In situ preparation of TpMsCu(3-hexyne), 4.
2
2 2
minimizing w[Fo −Fc ] . All non-hydrogen atoms were refined
with anisotropic displacement parameters. The hydrogen atoms
were introduced into geometrically calculated positions and
refined riding on the corresponding parent atoms.
3.8 μL of 3-hexyne (0.032 mmol) was added to a solution of
10 mg of TpMsCu (0.016 mmol) in 0.7 mL of C6D6. H NMR
1
3
(400 MHz, C6D6) δ 7.71 (d, J(HH) = 2.1 Hz, 3H, CHpyrazol),
6.75 (s, 6H, CHmesityl), 5.93 (d, 3J(HH) = 2.1 Hz, 3H, CHpyrazol),
Crystal data for 1. C87H106B2Cl6Cu2N12, M = 1681.26, tricli-
nic, P1, a = 11.1908(5), b = 12.0506(5), c = 16.6731(7) Å, α =
3
2.11 (s, 18H, CH3(mesityl))), 2.07 (s, 9H, CH3(mesityl)), 1.14 (q, J
ˉ
(HH) = 7.3, 4H, CH2), 0.52 (t, 3J(HH) = 7.2, 6H, CH3).
77.7080(9)°, β = 83.1730(10)°, γ = 89.2120(10)°, V = 2181.19
(16) Å3, Z = 1, Dc = 1.280 Mg m−3, absorption coefficient
0.722 mm−1, T = 173(2) K, colourless prisms; 13 139 indepen-
dent measured reflections (Rint = 0.0266), F2 refinement, final R
indices [I > 2σ(I)] R1 = 0.0481, wR2 = 0.1287, R indices (all
data) R1 = 0.0664, wR2 = 0.1437.
General procedure for the study of exchange equilibrium
between alkynes
1 equiv of HCuCR2 was added to a solution of the adduct
TpMsCu(HCHuCR1) in 0.6 mL of C6D6. The solution was
transferred to an NMR tube that was sealed with a Teflon
Crystal data for 2. C52H52BCuN6 [C44H46BCuN6, C8H6],
M = 835.35, monoclinic, P21/n, a = 9.1406(6), b = 20.6632(15),
c = 23.8733(17) Å, α = 90°, β = 97.186(2)°, γ = 90°, V = 4473.6
(5) Å3, Z = 4, Dc = 1.240 Mg m−3, absorption coefficient
0.531 mm−1, T = 173(2) K, colourless prisms; 13 516 indepen-
dent measured reflections (Rint = 0.0652), F2 refinement, final R
indices [I > 2σ (I)] R1 = 0.0463, wR2 = 0.1001, R indices (all
data) R1 = 0.0769, wR2 = 0.1142.
1
stopper. The reaction mixture was monitored by H NMR spec-
troscopy. The equilibrium was reached immediately. Accounting
for the relative concentrations of HCuCR2 and HCHuCR1 in
solution afforded the equilibrium constant Keq at room tempera-
ture for the exchange reaction below.
Crystal data for 3. : C165H186B4Cl2Cu4N24O8 [4
ˉ
(C41H46BCuN6O2), CH2Cl2], M = 3001.68, triclinic, P1, a =
9.0009(7), b = 11.2392(9), c = 38.765(3) Å, α = 97.899(2)°, β =
97.186(2)°, γ = 90°, V = 3875.5(5) Å3, Z = 1, Dc = 1.286 Mg
m−3, absorption coefficient 0.641 mm−1, T = 100(2) K, colour-
General procedure for the alkyne cyclopropenation reactions
4.5 mmol of alkyne (1-hexyne or 3-hexyne) and 1.5 mmol of
EDA were simultaneously added to a solution of 0.05 mmol of
the TpxCuL (L = THF or CH3CN) in 20 mL of dichloromethane
(ratio catalyst–EDA–alkyne 1 : 30 : 90). The reaction mixture
was stirred at room temperature until the total consumption of
diazo compounds was observed by IR and/or GC. The reaction
time (1–48 h) depended on the substrate and catalyst used.
Solvent was removed under vacuo and the reaction crude was
less prisms; 23 921 independent measured reflections (Rint
=
0.0544), F2 refinement, final R indices [I > 2σ (I)] R1 = 0.0776,
wR2 = 0.1802, R indices (all data) R1 = 0.1021, wR2 = 0.1900.
Acknowledgements
We thank the MICINN (CTQ2008-00042/BQU) and the Junta
de Andalucía (Proyecto P07-FQM-02794). C.M. thanks the Min-
isterio de Educación for a research fellowship.
1
analysed by H NMR spectroscopy. The reaction products were
identified by comparison with the reported data.21 Reaction con-
versions and yields of the products were determined by using
1,4-dimethoxybenzene as internal standard.
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