Fluorinated N-heterocyclic carbenes rhodium (I) complexes and their activity in hydrosilylation of propargylic alcohols

Article abstract of DOI:10.1016/j.jorganchem.2011.11.005

The synthesis of three rhodium complexes with fluorinated N-heterocyclic carbenes of general formula [RhCOD(NHC)Cl] where COD = 1,5-cyclooctadiene, NHC = N-heterocyclic carbene [1-butyl-3-pentafluorobenzyl-imidazol-2-ylidene (1), 1-benzyl, 3-pentafluorobe

Full text of DOI:10.1016/j.jorganchem.2011.11.005

Journal of Organometallic Chemistry 699 (2012) 82e86
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Fluorinated N-heterocyclic carbenes rhodium (I) complexes and their activity in
hydrosilylation of propargylic alcohols
,
a
a
a
b
Guillermina Rivera a , Oscar Elizalde , Gerarldine Roa , Israel Montiel , Sylvain Bernès
*
a Laboratorio de Química Inorgánica, Unidad de Investigación Multidisciplinaria, Facultad de Estudios Superiores Cuautitlán, Universidad Nacional Autonóma de México,
Cuautitlan Izcalli, Estado de México 54714, Mexico
b Facultad de Ciencias Químicas, UANL, Ciudad Universitaria, San Nicolás de los Garza, Nuevo León 66451, Mexico
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of three rhodium complexes with fluorinated N-heterocyclic carbenes of general formula
[RhCOD(NHC)Cl] where COD ¼ 1,5-cyclooctadiene, NHC ¼ N-heterocyclic carbene [1-butyl-3-pentafluor-
obenzyl-imidazol-2-ylidene (1), 1-benzyl, 3-pentafluorobenzyl-imidazol-2-ylidene (2) and 1,3-Bis(pentaflu-
robenzyl)-imidazol-2-ylidene (3)], and their respective NHC ligands as imidazolium salts are reported. The
catalytic activity inhydrosilylation of two propargylicalcohols gives mainly isomers E and gem; howeverwhen
cationic form of the catalysts with triphenylphosphine as an additional ligand are used, only the E isomer is
observedforallthe complexes. Thex-raystructures of twocomplexes(1 and 2)showsquareplanargeometries
with rhodium-carbene bond lengths in the short range 2.025(5)-2.028(5) Å indicating little influence of the
NHC’s arms.
Received 1 October 2011
Received in revised form
3 November 2011
Accepted 4 November 2011
Keywords:
N-Heterocyclic carbenes
Rhodium
Hydrosilylation
Propargyl alcohol
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
different chain sizes. Also, we report the synthesis of three new
rhodium complexes; two of them were characterized by X-ray
N-Heterocyclic carbenes have been very successful compounds
since Arduengo isolated the first example [1]. Coordination to
metals generates stable compounds which make them competitive
with phosphines [2]. Particularly, fluorinated N-heterocyclic car-
benes have been barely explored, even though used in the study of
electronic properties in reactions such as activation of bonds [3e5]
and metathesis [6], among others [7]
In order to favor molecular recognition in catalysis we worked in
the synthesis of fluorinated N-heterocyclic carbenes which, once
coordinated to rhodium could have the role of molecular recogni-
tion group, considering the fluorine as hydrogen bond acceptor. In
this way, we performed the hydrosilylation of propargylic alcohols
which behave as hydrogen bond donors. It is important to point out
that after the useful contributions of Crabtree et al. [8], few works
[9] have been developed in molecular recognition applied to
organometallic catalysis.
crystallography.
2. Results and discussion
2.1. Ligands
The synthesis of ligands was carried out following the Welton’s
method [10] and they were fully characterized by 1H, 13C and 19F
Nuclear Magnetic Resonance spectroscopy, Elemental analysis and
Mass spectrometry. NHC-1 and NHC-4 were isolated as brown oils,
while NHC-2 and NHC-3 were white solids. The ligands are labeled
according to their rhodium compounds so, complex 1 bears ligand
NHC-1; complex 2, ligand NHC-2; complex 3, ligand NHC-3 and
complex 4, ligand NHC-4 (see Fig. 1).
2.2. Rhodium complexes
For this reason, we probed three rhodium complexes with
fluorinated N-substituents and one non-fluorinated as control
experiment in hydrosilylation of two propargylic alcohols with
The rhodium complexes studied in this work are illustrated in
Fig. 1. They were prepared by a combination of the appropriate
silver salt generated in situ by the metalation of imidazolium salt
and silver oxide, and the rhodium dimer [Rh(cod)Cl]2 using the
transmetalation procedure similar to that reported by Crabtree [11]
and Wang and Lin [12]. The compounds were purified by column
chromatography affording yellow or orange crystals which were
fully characterized.
* Corresponding author. Universidad Nacional Autonóma de México, Facultad de
Estudios Superiores Cuautitlán, Unidad Multidsciplinaria de Investigación, primer
piso, Laboratorio de Química Inorgánica, Campo Cuatro, Carretera Cuautitlán-Teo-
loyucan Km 2.5, Col. San Sebastián Xhala, Cuautitlán Izcalli, Estado de México,
54714 México. Tel.: þ525 555623 1999x39403.
E-mail address: grm@unam.mx (G. Rivera).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.11.005

G. Rivera et al. / Journal of Organometallic Chemistry 699 (2012) 82e86
83
N
N
F
Rh
Rh
N
N
F
Cl
Cl
1
2
F
N
N
Rh
N
Rh
N
Cl
F
Cl
4
3
Fig. 1. Rhodium complexes.
The crystal structures of two complexes (1 and 2) were deter-
mined. Selected bond and angles are given in Fig. 2 (complex 1) and
Fig. 3 (complex 2) with the corresponding ORTEP representations.
Crystal data and structure refinement details are listed in Table 1.
Both compounds show the slightly distorted square planar geometry
catalysis, taking into account that the control experiment gave
almost identical results, and even better yields than the experi-
ments with molecular fluorinated recognition groups.
In order to improve our catalytic system, we generated in situ
the cationic form of the complexes 1e4 by using silver tetra-
fluoroborate and triphenylphosphine. These experiments were run
just for substrate B, under the same experimental conditions as
those with the neutral catalyst, affording the E isomer as single
product with the four catalysts. However, using just silver tetra-
fluoroborate, without triphenylphosphine, and the same experi-
mental conditions than the other cases, a mixture of the three
isomers was obtained, but we saw irreproducible reaction times.
So, getting high selectivity involves the use of triphenylphosphine
as an additional ligand, not just a cationic form of the catalyst in this
system.
typical for rhodium (I) complexes, considering the h2 2-COD ligand
, h
as bidentate. The nature of the NHC ligand has very little influence, if
any, on the rhodium-carbene bond length, 2.025(5) Å in 1 and
2.028(5) Å in 2. These distances compare well with those observed in
related non-fluorinated Rh(I) carbene complexes for which the x-ray
structures have been reported (distance range ¼ 2.020e2.052 Å for
four structures) [13]. In both complexes, substituents at N atoms are
oriented below and above the heterocycle plane, an arrangement
previously described in some structures bearing symmetrically-
substituted NHC ligands [13a,c].
2.3. Catalysis
3. Conclusions
The catalytic reactions were carried out under inert atmosphere
in refluxing dried THF over 48 h., for each of the catalyst shown in
Fig.1 following Equation (1). Reproducibility was established on the
basis of three run experiments.
Three new Rh(I) complexes were synthesized and fully charac-
terized. The experiments show mainly isomers E and gem as
products of the hydrosilylation of two propargylic alcohols with the
four complexes in the neutral form, indicating not recognition
OH
HO
1% mol of catalyst
THF reflux
OH
HO
R
SiEt3
+
+
Et3SiH
+
R
R
R
SiEt3
SiEt3
(E)
(Z)
gem
SUBSTRATE A: R=Ph
SUBSTRATE B: R=H
The results are given in Table 2. The isomer E predominates over
the other isomers in all experiments. When substrate A is used,
traces of hexaethyldisiloxane are also detected. However no
significant molecular recognition process was obtained during the
behavior with the fluorinated groups. However, a highly selective
system was obtained when triphenylphosphine was used as an
additional ligand in a cationic form of the catalysts, leading to the
formation of the E isomer with the four catalysts.

84
G. Rivera et al. / Journal of Organometallic Chemistry 699 (2012) 82e86
Table 1
Crystal data and structure refinement details for rhodium complexes 1 and 2.
[Rh(COD)(NHC-1)Cl] (1) [Rh(COD)(NHC-2)Cl] (2)
Empirical formula
Fw, g/mol
C22H25ClF5N2Rh
550.80
C25H23ClF5N2Rh
584.81
Colour, habit
Space group
Unit cell
Yellow, prism
C2/c
Orange, irregular
C2/c
a ¼ 26.430(9)
b ¼ 10.439(4)
c ¼ 19.823(7)
a ¼ 25.757(7)
b ¼ 10.842(4)
c ¼ 20.149(5)
dimensions (Å, ꢂ
)
b
¼ 124.114(17)
b
¼ 123.45(2)
Volume (Å3)
Z, Z0, calc.
4528(3)
4695(2)
8, 1, 1.616
8, 1, 1.655
density (g cmꢁ3
)
)
Abs. coeff. (mmꢁ1
Cryst. Dimens. (mm)
qmax (ꢂ), completeness
0.925
0.897
0.60 ꢀ 0.22 ꢀ 0.20
0.3 ꢀ 0.3 ꢀ 0.3
2
50, 0.999
50, 0.996
Data/parameters/restraints 4008/300/4
4138/308/0
R1 ¼ 5.21%, wR2
¼ 13.41%
Final R indices, [I > 2
s
(I)]
R1 ¼ 4.97%, wR2
¼ 12.29%
Final R indices (all data)
R1 ¼ 6.99%, wR2
¼ 14.06%
R1 ¼ 7.25%, wR2
¼ 15.76%
Largest diff peak
0.997, ꢁ0.743
1.304, ꢁ1.046
hole (e Åꢁ3
)
Fig. 2. ORTEP representation of the molecular structure of [Rh(COD)(NHC-1)Cl] (1),
with displacement ellipsoids shown at the 25% probability level. Selected bond (Å) and
angles (ꢂ) for 1: Rh1eC1: 2.025(5), Rh1eCl1: 2.3740(15), Rh1eC17: 2.204(6), Rh1eC18:
2.213(7), Rh1eC21: 2.096(6), Rh1eC22: 2.095(5); C1eRh1eCl1: 88.50(16).
solvents, which were used as received, isolated yields are given for
all products. 1H, 13C and 19F NMR spectra were obtained at 300 K
using a Varian Mercury spectrometer operating at 200 MHz.
Chemical shifts are reported in ppm with the residual solvent peak
as an internal reference and referenced to SiMe4 (d in ppm, J in Hz).
Mass spectra and elemental analyses were performed by the USAI
at Facultad de Química, UNAM, Mexico.
4. Experimental
4.1. General considerations
4.2. Synthesis of ligands
All reactions were carried out under a nitrogen atmosphere
using standard Schlenk techniques. THF was distilled from sodium-
benzophenone. All reagents were purchased from Aldrich Chem,
Co. and used as received. Complex 4 (control catalyst) was prepared
as reported [14]. All syntheses were performed using reagent grade
The alkyl or aryl halide (35.4 mmol) was reacted with alkyl or
benzylimidazol (17.7 mmol) at overnight toluene reflux. Purifica-
tion was carried out with silica gel chromatography column and
acetone/hexane 3:1 as eluent (ligand NHC-3) or by washing
(5 ꢀ10 mL) with the same mixture (ligands NHC-1 and NHC-2). The
ligand NHC-1 was isolated as brown oil, while NHC-2 and NHC-3
were white solids. The procedure is similar to the method re-
ported by Welton [10]. The spectroscopic data are as follows.
4.2.1. 1-Butyl, 3-pentafluorobenzyl-imidazolium bromide (NHC-1)
Yield 95%. 1H NMR (CDCl3): 0.9 (t, 3H, CH3-but, J ¼ 11), 1.4 (m,
2H, CH2-but), 1.9 (m, 2H, CH2-but), 4.4 (t, 2H, NCH2-but, J ¼ 11), 5.9
(s, 2H, CH2-N), 7.7 (d, 1H, CHbackbone, J ¼ 5.3), 7.8 (d, 1H, CHbackbone
,
J ¼ 5.3), 10.2 (s, 1H, NCHN). 19F NMR (CDCl3): ꢁ137.7 (dd, 2F,
ortho), ꢁ149.4 (pt, 1F, para), ꢁ158.2 (m, 2F, meta). 13C NMR (CDCl3):
13.4 (CH3-but),19.5 (CH2-but), 32.1 (CH2-but), 41.0 (NCH2-but), 50.2
(NCH2), 107.4 (C aromatic), 122.6, 123.5 (CH-backbone NHC), 135.4,
140.5, 143.1, 145.1, 148.2 (CF, aromatic), 137.0 (CH-carbene). Anal.
Table 2
Hydrosilylation results.
Catalyst
1
Substrate
Ratio E:gem
Yield (%)
A
B
A
B
A
B
A
B
2:1
2:1
3:1
2:1
2:1
2:1
3:1
2:1
70
75
100
75
85
100
100
100
2
3
4
Fig. 3. ORTEP representation of the molecular structure of [Rh(COD)(NHC-2)Cl] (2),
with displacement ellipsoids shown at the 25% probability level. Selected bond (Å) and
angles (ꢂ) for 2: Rh1eC1: 2.028(5), Rh1eCl1: 2.3941(16), Rh1eC20: 2.219(6), Rh1eC21;
2.200(6), Rh1eC24: 2.110(7), Rh1eC25: 2.104(6); C1eRh1eCl1: 86.77(18).
Reaction conditions:
atmosphere.
1
mol% catalyst, dried THF reflux for 48
h
under inert

G. Rivera et al. / Journal of Organometallic Chemistry 699 (2012) 82e86
85
Calcd. for C14H14N2F5Br (MW ¼ 385.17): C, 43.65; H, 3.66; N, 7.27.
Found: C, 41.45; H, 3.46; N, 7.58. Mass spectrum: m/z ¼ 284
(C14H14N2F4), m/z ¼ 248 (C10H5N2F5), m/z ¼ 227 (C10H5N2F4), 181
(C7H2F5), 161 (C7H2F4).
benzyl); 5.1 (broad, 2H, CHCOD-trans carbene); 3.4 (broad, 2H,
CHCOD-trans Cl); 2.4 (m, 4H, CH2COD-trans carbene); 1.9 (m, 4H,
CH2COD-trans Cl). 19F NMR (acetone-d6): ꢁ140.3 (pd, 2F,
ortho); ꢁ152.3 (pt, 1F, para), ꢁ150.9 (m, 2F, meta). 13C NMR
(acetone-d6): 28.9, 33.2 (CH2-COD); 42.6 (CH2-benzyl); 55.1 (CH2-
fluorinated benzyl); 64.5 (CH, COD); 128.9 (CH-backbone-NHC);
140.5, 136.3, 121.3 (CH aromatic); 149.9, 148.5, 143.5 (CF aromatic);
185.0 (carbene, JRh-C ¼ 51.64 Hz). Anal. Calcd. for C25H23ClF5N2Rh
(MW ¼ 584.81): C, 51.38; H, 3.94; N, 4.80. Found: C, 50.79; H, 4.18;
N, 4.28 Mass spectrum: m/z ¼ 549 (-Cl ¼ C25H23F5N2Rh), m/z ¼ 440
(-COD ¼ C17H11F5N2Rh), m/z ¼ 476 (C17H11F5N2ClRh), m/z ¼ 339.1
(single ligand C17H12F5N2), m/z ¼ 91 (C7H7).
4.2.2. 1-Benzyl, 3-pentafluorobenzyl-imidazolium bromide (NHC-
2)
Yield 91.61%. 1H NMR (acetone-d6): 10.6 (s, 1H, NCHN); 8.0 (s,
1H, CHbackbone); 7.9 (m, 1H, CHbackbone); 7.9, 7.4 (m, 5H, benzyl), 5.9
(s, 2H, pentafluorobenzyl); 5.8 (s, 2H, benzyl). 19F NMR (acetone-
d6): ꢁ143.1 (pd, 2F, ortho); ꢁ154.7 (pt, 1F, para); ꢁ163.6 (m, 2F,
meta). 13C NMR (acetone-d6): 40.8 (CH2-benzyl); 52.7 (CH2-penta-
fluorobenzyl); 129.2 (CH-backbone-NHC); 138.0, 135.0, 123.1 (CH-
aromatic); 148.6, 143.8, 141.0 (CF-aromatic); 200.8 (CH-carbeno).
Anal. Calcd. for C17H12N2F5Br (MW ¼ 419.19): C, 48.76; H, 2.87; N,
6.69. Found: C, 48.53; H, 3.20; N, 6.44. Mass spectrum: m/z ¼ 339
(C17H12F5N2); m/z ¼ 180 (C7F5H2); m/z ¼ 91(C7H7).
5.3. [{1,3-Bis-(pentaflurobenzyl)-imidazol-2-ylidene}(
tadiene) chloro rhodium (I)] (3)
h
4-1,5-cyclooc-
Yield: 74% 1H NMR (CDCl3): 2.0 (m, 4H, CH2-COD), 2.4 (m, 4H,
CH2-COD), 3.5 (broad, 2H, CH-COD), 5.1 (broad, 2H, CH-COD), 5.7
4.2.3. 1,3-Bis-(pentafluorobenzyl)-imidazolium bromide (NHC-3)
Yield: 78.25%. 1H NMR (acetone-d6): 6.0 (s, 4H, CH2), 8.0 (s, 2H,
CHbackbone), 10.6 (s, 1H, NCHN). 19F NMR (acetone-d6): ꢁ163.7 (m, 2F,
meta), ꢁ154.8 (pt, 1F, para), ꢁ142.7 (pd, 2F, ortho). 13C NMR (acetone-
d6): 41.0 (CH2-N); 108.2 (Car), 123.3 (d, CHbackbone NHC); 138.8 (C
aromatic); 135.7, 140.7, 143.7, 145.0, 148.7 (CF-aromatic). Anal. Calcd.
for C17H7N2F10Br (MW ¼ 509.15): C, 40.10; H, 1.39; N, 5.50. Found: C,
39.38; H, 1.48; N, 6.18. Mass spectrum: m/z ¼ 409 (C17H7N2F9), m/
z ¼ 248 (C10H5N2F5), m/z ¼ 181 (C7H2F5), m/z ¼ 161 (C7H2F4).
(pt, 2H, CH2-Bz), 5.9 (pt, 2H, CH2-Bz), 6.8 (s, 2H, CHbackbone NHC). 19
F
NMR (CDCl3): ꢁ160.7 (m, 2F, meta), ꢁ152.0 (m,1F, para), ꢁ140.1 (pd,
2F, ortho). 13C NMR (CDCl3): 26.6 (CH2-COD), 29.1 (CH2-COD), 30.9
(CH2-COD), 33.5 (CH2-COD), 42.8 (CH2-N), 45.6 (CH2-N), 67.1 (CH-
COD), 70.3 (CH-COD), 99.1 (C aromatic), 119.3 (CHback), 123.3
(CHback), 135.5, 139.5, 140.6, 143.5, 148.5 (CF aromatic), 186.3 (Rh-C,
JRh-C
¼
50.08). Anal. Calcd. for C25H18ClF10N2Rh.(CH3)2CO
(MW ¼ 732.85): C, 45.89; H, 3.30; N, 3.82. Found: C, 45.14; H, 2.99,
N, 3.39. Mass spectrum: m/z ¼ 674 (C25H18F10N2ClRh); m/z ¼ 639
(-Cl¼C25H18F10N2Rh); m/z ¼ 531 (-COD ¼ C17H6F10N2Rh); m/
z ¼ 429.1 (just ligand C17H6N2F10).
5. Synthesis of rhodium complexes
The metalation followed by the transmetalation procedure used
was that described previously [11], itself a modification of the
procedure of Wang and Lin [12]. The appropriate [imidazol-2-
ylidene] silver chloroargentate (0.840 mmol) generated in situ
from the imidazolium salt and silver oxide were combined with
[Rh(cod)Cl]2 (0.420 mmol) in acetone (20 mL). The mixture was
stirred at room temperature for 2 h, followed by TLC and filtered
through Celite. The product was purified by silica gel chromatog-
raphy column. All the compounds so obtained were yellow solids,
then, recrystallized from acetone/hexane. The spectroscopic data
for the new compounds are as follows:
6. Hydrosilylation reactions
All experiments and manipulation were carried out under inert
atmosphere using Schlenk techniques. In a round Schlenk flask 1-
phenylprop-2-yn-1-ol or 2-propyn-1-ol (1.48 mmol), triethylsi-
lane (1.48 mmol), 10 mL of dried THF and the rhodium complex (1%
mol) were mixed. The reactions were kept under THF reflux for
48 h. Additionally, for the second system (cationic) we also used
triphenylphosphine and silver tetrafluoroborate in the same molar
amount that the one for each catalyst. And, for the third system,
only silver tetrafluoroborate was added to the initial reactants in
the same molar amount as each catalyst. All experiments were run
three times. Organic fractions were separated from the mixed
reaction by chromatography silica gel and analyzed by gas/mass
chromatography. 1H NMR spectra were compared with literature
data for all products [15].
5.1. [(1-Butyl-3-pentafluorobenzyl-imidazol-2-ylidene)(
cyclooctadiene) chloro rhodium (I)] (1)
h
4-1,5-
Yield: 82%. 1H NMR (CDCl3): 1.0 (t, 3H, CH3-but, J ¼ 7.4), 1.4 (m,
2H, CH2-but),1.8 (m, 2H, CH2-but),1.9 (m, 4H, 2CH2-COD), 2.4 (m, 4H,
2CH2-COD), 3.3 (m, 2H, NCH2-but), 4.5 (m, 2H, 2CH-COD), 5.0 (broad,
2H, 2CH-COD), 6.5 (dd, 2H, NCH2), 6.8 (d, CHbackbone NHC), 6.7 (d,
CHbackbone NHC). 19F NMR (CDCl3): ꢁ140.3 (pd, 2F, ortho), ꢁ152.6 (pt,
1F, para), 161.0 (m, 2F, meta). 13C NMR (CDCl3): 13.8 (CH3-but); 20.1
(CH2-but); 28.7 (CH2-COD); 29.7 (CH2-but); 33.0 (CH2-COD); 42.2
(NCH2-but); 50.9 (NCH2); 67.5 (CH-COD); 68.6 (CH-COD); 98.8
(CHbackbone NHC); 99.4 (CHbackbone NHC); 99.9, 109.1, 136.0, 139.4,
144.1, 147.4 (CF, aromatic); 183.7 (C-Rh, JRh-C ¼ 51.31). Anal. Calcd. for
C22H25F5N2ClRh.(CH3)2CO (MW ¼ 680.88): C, 49.32; H, 5.13; N, 4.60.
Found: C, 49.30; H, 4.94; N, 4.35. Mass spectrum: 550.1
(C22H25F5N2ClRh), 515.1 (-Cl¼C22H25F5N2Rh), 405.0 (-COD and
2H ¼ C14H13F5N2Rh), 305.1 (single ligand C14H13F5N2).
7. X-ray crystallography
The diffraction data were collected on a Bruker P4 diffractom-
eter [16] using graphite monochromated Mo Ka radiation
(
l
¼ 0.71073 Ǻ) and
q
/2
q
or
u
scan mode with variable scan speed.
-scans data. Structures
Absorption corrections were applied using
j
were solved and refined using routine procedures [17]. In the case
of 1, the butyl group has the terminal eCH2eCH3 group disordered
over two positions, with occupancies fixed to 1/2, and the corre-
sponding CeC bond lengths were restrained to 1.54(1) Å.
5.2. [(1-benzyl, 3-pentafluorobenzyl-imidazol-2-ylidene) (
cyclooctadiene) chloro rhodium (I)] (2)
h
4-1,5-
Acknowledgments
Yield: 68.00%. 1H NMR (acetone-d6): 7.4 (m, 5H, benzyl); 6.8 (s,
1H, CHbackbone NHC); 6.7 (s, 1H, CHbackbone NHC); 5.8 (m, 4H, 2CH2-
We gratefully acknowledge financial support from DGAPA-
UNAM-IN217011.

86
G. Rivera et al. / Journal of Organometallic Chemistry 699 (2012) 82e86
[2] R.H. Crabtree, J. Organomet. Chem. 690 (2005) 5451e5457.
Appendix A. Supplementary material
[3] A. Acosta-Ramírez, D. Morales-Morales, J.M. Serrano-Becerra, A. Arévalo,
W.D. Jones, J.J. García, J. Mol. Catal. A: Chem. 288 (2008) 14e18.
[4] S. Burling, M.F. Mahon, S.P. Reade, M.K. Whittlesey, Organometallics 25 (2006)
3761e3767.
[5] S. McGrandle, G.C. Saunders, J. Fluorine Chem. 126 (2005) 451e455.
[6] (a) T. Ritter, M.W. Day, R.H. Grubbs, J. Am. Chem. Soc. 128 (2006) 11768e11769;
(b) G.C. Vougioukalakis, R.H. Grubbs, Chem. Eur. J. 14 (2008) 7545e7556.
[7] (a) L. Xu, W. Chen, J.F. Bickley, A. Steiner, J. Xiao, J. Organomet. Chem. 598
(2000) 409e416;
CCDC 846531 and 846532 contain the supplementary crys-
tallograpic data for 1 and 2 for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via http://www.ccdc.cam.ac.uk/cgi-bin/catreq.cgi.
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