Alkenyl-functionalized NHC iridium-based catalysts for hydrosilylation

Article abstract of DOI:10.1039/b707280e

A family of alkenyl-functionalized N-heterocyclic-carbene-iridium(i) complexes has been synthesized, providing a series of mono-coordinated, bis-chelate and pincer alkenyl-NHC species. Olefin coordination is highly influenced by the nature of the substitu

Full text of DOI:10.1039/b707280e

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PAPER
www.rsc.org/njc | New Journal of Chemistry
Alkenyl-functionalized NHC iridium-based catalysts for hydrosilylationw
Alessandro Zanardi, Eduardo Peris and Jose A. Mata*
Received (in Montpellier, France) 14th May 2007, Accepted 10th August 2007
First published as an Advance Article on the web 7th September 2007
DOI: 10.1039/b707280e
A family of alkenyl-functionalized N-heterocyclic-carbene–iridium(I) complexes has been
synthesized, providing a series of mono-coordinated, bis-chelate and pincer alkenyl-NHC species.
Olefin coordination is highly influenced by the nature of the substituents on the NHC ring, and
on the length of the alkenyl branch. A fluxional process involving coordination/decoordination of
the olefin in bis-allyl-NHC complexes has been studied, and the activation parameters have been
determined by means of VT-NMR spectroscopy. The mono-coordinated complexes are highly
active in the hydrosilylation of terminal alkynes, showing high selectivity for the Z-isomers, with
no a-isomers or dehydrogenative silylation processes being observed. The molecular structures
reported that are representative of the species have been determined by means of X-ray
crystallography.
The original idea of our work came from the interesting recent
Introduction
reports of Hahn et al., who described a series of Ir complexes
The hydrosilylation of unsaturated organic molecules is one of
with allyl- and bis-allyl-NHC ligands, some of them tested in
transfer hydrogenation to cyclohexanone (Scheme 1).10,11 We
the most powerful tools for the transformation of organic
compounds, providing a wide range of industrial applica-
thought that changing the nature of the NHC ligand by
tions.1 Organosilicon compounds are important functional
substituting the 4 and 5 positions of the azole ring, and
groups because their derivation into other functionalities
modifying the length of the terminal alkenyl groups may
through the oxidative cleavage of the carbon–silicon bond is
provide an interesting opportunity to systematically study
easily achieved.2 The versatility of catalytic hydrosilylation
the reactivity pattern of the system. In our study, we observed
towards the reduction of carbon–carbon, carbon–oxygen and
that some of the complexes obtained showed a fluxional
carbon–nitrogen multiple bonds is a 100% atom-economical
behaviour, which we studied by means of variable temperature
and efficient process. The search for catalysts that can promote
NMR (VT-NMR) experiments. More remarkably, the
hydrosilylation processes under mild and aerobic conditions is
NHC–Ir(I) complexes are highly active and selective catalysts
one of the main aims of industry.3 An important drawback of
in the hydrosilylation of terminal alkynes.
the hydrosilylation process in the laboratory is that there
remain no clear patterns in the design of highly selective
catalysts, so the search for new complexes providing selective
Results and discussion
processes is highly desirable.
N-Heterocyclic carbene (NHC) ligands are finding increas-
ing use in organometallic chemistry and homogeneous cata-
lysis.4 Part of this success is due to the electron donor ability of
NHC ligands, which is higher than that of phosphines.5 We
have been interested in the use of polydentate NHCs and their
application in catalysis,6 as well as the influence of their
anisotropic nature in the reactivity patterns of their com-
plexes.7 As part of our research, we focused our attention on
the preparation of M–NHC complexes as hydrosilylation
catalysts,8 and also studied the mechanism of the process by
means of electrospray mass spectroscopy.9 Based on our
previous results, we now report the syntheses of a series of
NHC–Ir(I) complexes functionalized with terminal alkenes.
Syntheses and characterization
Transmetallation of the corresponding silver–NHC com-
pounds to [IrCl(COD)]2 afforded complexes 1a, 1b and 1c
(60–90%). A compound similar to 1a, but with a bromine
ligand instead of a chlorine, had been previously obtained by
the direct reaction of 1,3-bis(2-propenyl)imidazolium bromide
with [Ir(m-OMe)(COD)]2.11 The addition of AgBF4 to corre-
sponding solutions of 1 in acetone provided the corresponding
carbene-bisolefin pincer species 2. All compounds obtained
were characterized by the usual spectroscopic techniques,
elemental analysis and/or high resolution mass spectroscopy.
´
`
`
Departament Quımica Inorganica i Organica, Universitat Jaume I,
Av. Vicent Sos Baynat s/n, E-12071 Castello´, Spain. E-mail:
jmata@qio.uji.es; Fax: +34 964728214; Tel: +34 964728234
w Electronic supplementary information (ESI) available: Description
of general procedures, ligand precursor syntheses, catalytic studies,
NMR characterization (1H, 13C, COSY), VT-NMR experiments and
experimental crystallographic data collection. See DOI: 10.1039/
b707280e
Scheme 1
ꢀc
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Scheme 2
Complexes 1a, 1b and 1c show interesting examples of
fluxional behavior. In the case of 1a, we were able to obtain
the activation barrier parameters by means of VT-NMR
studies. The room temperature 1H NMR spectrum of complex
1a shows a different environment for the two azole ring
protons at 6.89 and 6.67 ppm. This observation and the low
frequency alkene resonances are consistent with the coordina-
tion of one of the olefinic fragments. The upper and lower
sides of the iridium complex are different, making all the
residences magnetically inequivalent. The signals due to the
olefinic protons at room temperature are broad (e.g. 6.89 ppm,
species was obtained, with both alkenyl branches being out of
the coordination sphere of the metal. The addition of
AgBF4 to the complex did not afford the desired carbene–
olefin chelating species, thus suggesting that olefin co-
ordination must be an unfavorable process due to the
formation of the more unstable seven membered ring. We
recently observed a similar behaviour for other alkenyl-NHC
species of Cp*Ir(III).16 For comparative reasons, in the
catalytic studies (see below), we found it convenient to obtain
complexes 413 and 511 by following the procedures mentioned
above (Scheme 3).
1
2
1
2
w = 9.43 Hz; solvent CDCl3, w = 0.98 Hz), suggesting that a
fluxional process is operating that involves the chemical ex-
change of the coordinated and uncoordinated olefins. Metal–
carbene rotation is not feasible, as previously observed in
analogous rhodium complexes.12,13 Previous studies by Enders
and co-workers showed that hindered rotation is found for
NHC–rhodium(I) complexes with bulky cyclooctadiene or
norbornadiene ligands.14 A combination of linewidth analysis
and the coalescence temperature of the signals corresponding
to the protons of the imidazolylidene ring (see the ESIw)
Scheme 3
allowed us to establish the kinetic parameters as DHa
20.9 Kcal molꢁ1 and DSa = 17.4 cal molꢁ1 ꢁ1. The
=
K
X-Ray diffraction studies
decoordination of the olefin being the main factor governing
the process, we estimate that the DHa value of 20.9 kcal molꢁ1
is a good estimation of the Ir–olefin bond energy. This analysis
is in good agreement with experimental and theoretical data
for olefin-coordinated complexes.15 The high positive value of
DSa may suggest a highly disordered transition state com-
pared to the ground state, probably as a consequence of the
decoordination of the olefinic branch. A variable temperature
study of complex 1a was carried out by 13C NMR spectro-
scopy, confirming the above mentioned kinetic parameters.
In order to check whether longer alkenyl branches would
provide chelating Ir(I) species, we decided to obtain the related
complex, using 1,3-bis(4-pentenyl)imidazolium bromide as the
carbene precursor. The coordination of this imidazolium salt
to [IrCl(COD)]2 was achieved by the same methodology as the
one shown in Scheme 2, but in this case only the monodentate
Crystals of 2a, 2b ꢂ PF6 and 3 suitable for X-ray diffraction
analysis were obtained by slow evaporation from correspond-
ing concentrated dichloromethane–hexanes solutions. The
structures of 2a and 2b ꢂ PF6 confirm the pincer coordination
of the NHC ligand, a result of the binding of the two olefins.z
The geometry at the iridium center (Fig. 1 and Fig. 2) is best
described as distorted trigonal bipyramidal. The equatorial
plane is defined by the two olefinic fragments from the NHC-
bis-allyl ligand and one CQC from COD, while the axial axis
is occupied by the other CQC from COD and the carbene
carbon. The relative orientation of the olefin fragments of the
z CCDC 656989–656991. For crystallographic data in CIF or other
electronic format see DOI: 10.1039/b707280e
ꢀc
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Fig. 1 The ORTEP diagram of complex 2a, showing 50% probability
ellipsoids. Hydrogen atoms and the counterion (BF4ꢁ) have been
omitted for clarity. Selected bond lengths (A) and angles (1):
Ir(1)–C(1) = 1.934(9), Ir(1)–C(5) = 2.214(8), Ir(1)–C(9) = 2.261(9),
Ir(1)–C(8) = 2.308(8), Ir(1)–C(6) = 2.225(9), C(5)–C(6) = 1.404(12),
C(8)–C(9) = 1.373(13); N(1)–C(1)–Ir(1) = 123.9(7), N(1)–C(4)–
C(5)–C(6) = 57.7(11).
Fig. 3 The ORTEP diagram of complex 3, showing 35% probability
ellipsoids. Hydrogen atoms have been omitted for clarity. Selected
bond lengths (A) and angles (1): Ir(1)–C(1) = 2.030(10); N(1)–
Ir(1)–C(1) = 127.6(7), N(1)–C(4)–C(5)–C(6) = ꢁ173.6(9); a = 84.2
(a = angle between the imidazolium ring plane and the xy plane of the
metal complex).
bis-allyl ligand is syn, with the two olefins being symmetry-
related by a plane perpendicular to the azole ring.
Catalytic hydrosilylation
The structure of compound 3 confirms that the olefin
fragment of the NHC remains unbound (Fig. 3).z The geo-
metry at the iridium center is pseudo-square planar. The plane
angle defined by the azole ring is almost perpendicular to the
iridium coordination plane (a = 84.21 for 3).
The pincer coordination of the NHC-bis-allyl ligand
seems to push the azole ring closer to the metal center,
shortening the Ir–Ccarbene distance by ca. 0.1 A. As a
consequence, the iridium–carbene distance is in the expected
range for complex 3 (Ir–Ccarbene = 2.030(10) A), but slightly
shorter for complexes 2a (1.934(9) A) and 2b ꢂ PF6 (1.944(12)
A). All metal-coordinated olefins show a longer CQC
distance compared to the free alkene (dCQC, 1.337 A)
as a consequence of metal back-bonding into the olefin
p* orbital.
Table 1 summarizes the catalytic results for the hydrosilylation
of 1-hexyne with phenylacetylene using catalysts 1 and 3–5 at
room temperature after 1 h of reaction. All the compounds
showed some activity under the reaction conditions used
(1 mol% cat. loading), the best conversions (68–92%) being
obtained for catalysts 1a and 5. In general, the reaction
proceeded with higher yields for the reduction of phenylace-
tylene, as has previously been reported,17 although catalysts 3
and 4 seemed to present the reverse tendency. The 4,5-sub-
stituted azoles (1b and 1c) presented a lower activity than their
unsubstituted analogue (1a), although this behaviour did not
seem to follow a logical tendency if we consider the electronic
modification of the ligands implied.18 In this sense, we believe
that the 4,5-substituents may have had some steric influence
on the reaction’s outcome. The high selectivity of the products
obtained is noteworthy, with a clear preference for the
Z-isomer, which in some cases was obtained as the only
product. This selectivity was higher when catalysts 1 (1a, 1b
Table 1 Hydrosilylation of alkynes at room temperature (hydro-
silane = HSiMe2Ph)a
Entry Catalystb Substrate
Conversion (%)c
a
E
Z
1
2
3
4
5
6
1b
1a
1c
3
4
5
1b
1a
1c
3
4
5
1-Hexyne
1-Hexyne
1-Hexyne
1-Hexyne
1-Hexyne
1-Hexyne
Phenylacetylene 57
Phenylacetylene 92
Phenylacetylene 45
Phenylacetylene 18
21
68
25
71
46
55
—
—
—
—
—
—
—
—
—
—
—
7
—
100
93
100
12 88
91
9
17 83
34 66
28 72
20 80
7
8d
9
Fig. 2 The ORTEP diagram of complex 2b ꢂ PF6, showing 50%
10
11
12d
a
7
93
ꢁ
probability ellipsoids. Hydrogen atoms and the counterion (PF6
)
Phenylacetylene
Phenylacetylene 80
0
have been omitted for clarity. Selected bond lengths (A) and angles (1):
Ir(1)–C(1) 1.944(12), Ir(1)–C(5) 2.221(14), Ir(1)–C(6)
—
20 80
=
=
=
b
Temperature 25 1C, time 1 h, solvent CHCl3. Catalyst loading
2.248(18), Ir(1)–C(8) = 2.247(12), Ir(1)–C(9) = 2.203(12), C(5)–C(6) =
1.38(2), C(8)–C(9) = 1.41(2); N(1)–C(1)–Ir(1) = 124.5(9), N(1)–C(4)–
C(5)–C(6) = ꢁ56.8(17).
(1 mol%). Yields determined by 1H NMR. Catalyst active for at
least three runs.
c
d
ꢀc
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Table 2 Hydrosilylation of phenylacetylene at 60 1C (hydrosilane =
NHC ligand. Further studies related to the electronic and
steric effects of olefin-functionalized NHC spectator ligands
are in progress.
HSiMe2Ph)a
Entry
Catalystb
Time/h
Conversion (%)c
a
E
Z
1
2
3
4
5
6
7
8
1b
1a
1c
3
4
5
1b
1a
1c
3
1
1
1
1
1
1
2
2
2
2
2
2
2
2
70
100
67
36
55
—
—
—
—
—
—
—
—
—
—
—
—
—
—
10 90
23 77
12 88
21 79
26 74
27 73
23 76
17 83
20 80
20 80
31 69
35 65
30 70
35 65
Experimental section
General procedure
Ligand precursors were prepared according to literature metho-
dologies.20 Experimental conditions and characterization data
can be found in the ESI.w NMR Spectra were recorded on
Varian Inova 300 and 500 MHz instruments using CDCl3 as
the solvent. Elemental analyses were carried out in a Euro EA
3000 Eurovector Analyser. Electrospray Mass Spectra
(ESI-MS) were recorded on a Micromass Quatro LC instru-
ment, nitrogen being employed as the drying and nebulising
gas. All other reagents were used as received from commercial
suppliers.
100
100
100
100
100
100
100
85
9
10
11
12
13
14
a
4
5
1ad
1ae
45f
b
Temp 60 1C, Solvent CHCl3. Catalyst loading (1 mol%) unless
otherwise stated. Yields determined by 1H NMR. Catalyst loading
c
d
e
f
(0.1 mol%). Catalyst loading (0.01 mol%). Full conversion was
achieved after 24 h.
1,3-Bis(2-propenyl)-imidazolin-2-ylidene
[(1,2,5,6-g)-1-5-
cyclooctadiene]chloro iridium (1a). Silver oxide (63 mg, 0.27
mmol) was added to a solution of 1,3-bis(2-propenyl)imida-
zolium bromide (55 mg, 0.3 mmol) in MeOH. The solution
was stirred at room temperature for 1 h and filtered through
Celites. The solution was concentrated under reduced pres-
sure and redissolved in dichloromethane. [IrCl(COD)]2
(100 mg, 0.15 mmol) was added and the mixture was stirred
for 1 h at 45 1C. After solvent removal, the crude product was
purified by flash chromatography using CH2Cl2/MeOH (7 : 3)
as the eluent (yield 117 mg, 80%).
and 1c) were used, compared to the selectivities shown by 5
(i.e., compare entries 1–3 and 6 in Table 1). We believe that the
second alkenyl branch of catalyst in 1 may have had some
steric influence on the selectivity of the reaction. Compound 5,
with a small methyl group as a wingtip, had a reduced steric
influence that seemed to reduce the selectivity of the process
(although still high). In general, the selectivities obtained when
using these catalysts were the highest we have obtained
compared to similar Ir(I)– and Rh(I)–NHC species,19 and lie
among the highest reported to date for Ir complexes. Remark-
ably, the a-isomer was not obtained in any experiment.
Degradation of the catalytically-active species was not ob-
served in the hydrosilylation process, even at the end of the
catalytic reaction. After the initial batch, two more runs using
catalyst 1a were carried out without any measurable deactiva-
tion of the system, confirming the high stability of the
NHC–metal complexes (Table 1, entries 8 and 12).
1H NMR (500 MHz, CDCl3, T = ꢁ15 1C): d 6.89 (s, 1H,
NCHCHN), 6.67 (s, 1H, NCHCHN), 5.92 (m, 1H,
3
NCH2CHQCH2, not coordinated), 5.52 (dd, JHH = 4.5
Hz, 2JHH = 17.0 Hz, 1H, NCHHCHQCH2, not coordinated),
3
5.13 (d, JHH = 10.5 Hz, 1H, NCH2CHQCHHcis, not co-
ordinated), 4.89 (d, 3JHH = 17 Hz, NCH2CHQCHHtrans, not
coordinated), 4.66 (m, 2H, NCHHCHQCH2, not coordinated
and COD), 4.23 (m, 2H, NCHHCHQCH2, coordinated and
3
Table 2 shows the results of the catalytic hydrosilylation of
phenylacetylene at 60 1C. As expected, an increase of the
reaction temperature resulted in an increase in reaction yields,
with catalysts 1a and 5 again achieving the highest efficiencies
in terms of conversion (full in all cases). The selectivity for the
Z-hydrosilylated isomer was reduced, but the reaction re-
mained highly selective. Conversions between 65–90% lead
to this reaction product, and only the b-isomers were obtained.
Catalyst loadings as low as 0.1 and 0.01 mol% also provided
high activities at 60 1C, although slow kinetics were found
(Table 2, entries 13 and 14).
NCH2CHQCH2, coordinated), 3.70 (d, JHH = 15 Hz,
NCHHCHQCH2, coordinated), 3.54 (m, 1H, COD), 3.44
(m, 1H, COD), 2.93 (m, 1H, COD), 2.70 (m, 2H, COD),
2.49 (m, 1H, COD), 2.39 (m, 2H, COD), 2.08 (d, 1H, 3JHH
=
cis
7.5 Hz, NCH2CHQCHH, coordinated), 1.93 (m, 2H, COD),
3
1.89 (d, 1H, JHH
= 9.0 Hz, NCH2CHQCHH), 1.61 (m,
trans
1H, COD). 13C NMR (75 MHz, CDCl3): d 161.9 (NCN),
135.4 (NCH2CHQCH2, not coordinated), 122.2 (NCHCHN),
118.0 (NCHCHN), 117.5 (NCH2CHQCH2, not coordinated),
99.0, 97.7, 60.6, 55.6 (COD), 52.89 (NCH2CHQCH2, coordi-
nated), 52.5 (NCH2CHQCH2, not coordinated), 47.27
According to the results of this catalytic survey,
olefin-functionalized NHC–iridium complexes constitute a
new family of catalysts for the addition of Si–H to alkynes.
The high activity and selectivity indicate the potential of these
catalysts for future applications. VT-NMR studies revealed
that the olefin coordination/decoordination fluxional process
is enthalpy driven. The thermodynamic parameters are in
agreement with the experimental and theoretical data for
olefin coordination. Compound 1a is a highly active and
robust catalyst for the hydrosilylation of alkynes because it
combines the high activity of iridium with the stability of the
(NCH2CHQCH2,
coordinated),
41.0
(COD),
35.9
(NCH2CHQCH2, coordinated), 33.4, 29.6, 28.1 (COD).
ESI-MS (cone 25 V): m/z (fragment): 449.4 [M ꢁ Cl+].
4,5-Dichloro-1,3-bis(2-propenyl)imidazolin-2-ylidene [(1,2,5,6-g)-
1-5-cyclooctadiene]chloro iridium (1b). The synthesis of com-
plex 1b was carried out using the same general procedure as
described for complex 1a using silver oxide (76 mg, 0.33
mmol), 4,5-dichloro-1,3-bis(2-propenyl)imidazolium hexa-
fluorophosphate (89 mg, 0.30 mmol) and [IrCl(COD)]2
(100 mg, 0.15 mmol) (yield 114 mg, 70%).
ꢀc
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1H NMR (500 MHz, CDCl3): d 5.97 (d, 1H, 2JHH = 17 Hz,
NCHHCHQCH2, not coordinated), 5.78 (m, 1H, NCH2CHQ
CH2, not coordinated), 5.08 (m, 1H, NCH2CHQCH2, not
coordinated), 4.68 (m, 2H, NCH2CHQCH2, not coordi-
nated), 4.46 (m, 1H, NCHHCHQCH2, not coordinated),
3JHH = 5.0 Hz, 2JHH = 13.0 Hz, 2H, NCHHCHQCH2), 4.40
2
(d, 2H, JHH = 13.5 Hz, NCHHCHQCH2), 3.52 (m, 2H,
COD), 3.47 (d, 3JHH = 9.0 Hz, 2H, NCH2CHQCHHcis), 2.85
3
(m, 2H, COD), 2.75 (d, JHH
=
11.5 Hz, 2H,
NCH2CHQCHHtrans), 2.72 (m, 2H, COD), 2.29 (m, 4H,
COD). 13C NMR (75 MHz, CDCl3): d NCN not observed,
120.6 (NCHCHN), 93.7, 74.0 (COD), 64.9 (NCH2CHQCH2),
51.6 (NCH2CHQCH2), 42.6 (NCH2CHQCH2), 32.8, 31.4
(COD). ESI-MS (cone 25 V): m/z (fragment) 449.1 [M]+.
4.13 (m, 2H, NCHHCHQCH2, coordinated and
= 11 Hz,
2
NCH2CHCH2, coordinated), 3.77 (d, JHH
NCHHCHQCH2, coordinated), 3.59 (m, 1H, COD), 3.46
(m, 1H, COD), 3.34 (m, 1H, COD), 2.87 (m, 2H, COD),
2.68 (m, 1H, COD), 2.38 (m, 2H, COD), 2.28 (m, 1H,
NCH2CHQCHH, coordinated), 2.00 (m, 2H, COD), 1.91
(m, 1H, NCH2CHQCHH), 1.58 (m, 2H, COD).
4,5-Dichloro-1,3-bis(2-propenyl)imidazolin-2-ylidene [(1,2,5,6-g)-
.
1-5-cyclooctadiene]iridium hexafluorophosphate (2b PF6). The
13C NMR (75 MHz, CDCl3): d 161.61 (NCN), 134.05
(NCH2CHQCH2, not coordinated), Cl–C not observed,
115.87 (NCH2CHQCH2, not coordinated), 99.41, 97.96,
61.20, 56.06 (COD–CH), 52.36 (NCH2CHQCH2, coordi-
nated), 50.55 (NCH2CHQCH2, not coordinated), 44.55
(NCH2CHQCH2, coordinated), 40.96 (COD–CH2), 35.54
(NCH2CHQCH2, coordinated), 33.15, 28.80, 27.48 (COD).
ESI-MS (cone 25 V): m/z (fragment) 517.1 [M ꢁ Cl]+.
synthesis of complex 2b was carried out using the same general
procedure as described for complex 2a but followed by anion
exchange (PF6ꢁ) using complex 1b (75 mg, 0.13 mmol) and
AgBF4 (25 mg, 0.13 mmol) (yield 68 mg, 92%).
1H NMR (500 MHz, CDCl3):
NCH2CHQCH2), 4.91 (m, 2H, COD), 4.55 (dd, JHH = 4.5
Hz, 2JHH = 13.5 Hz, 2H, NCHHCHQCH2), 4.35 (d, 2JHH
d
5.22 (m, 2H,
3
=
13.0 Hz, 2H, NCHHCHQCH2), 3.59 (m, 2H, COD), 3.51 (d,
3JHH = 6.5 Hz, 2H, NCH2CHQCHHcis), 2.88 (d, 3JHH = 10
Hz, 2H, NCH2CHQCHHtrans), 2.86 (m, 2H, COD), 2.73 (m,
2H, COD), 2.26 (m, 4H, COD). 13C NMR (125 MHz,
4,5-Dimethyl-1,3-bis(2-propenyl)imidazolin-2-ylidene [(1,2,5,6-g)-
1-5-cyclooctadiene]chloro iridium (1c). The synthesis of com-
plex 1c was carried out using the same general procedure as
described for complex 1a using silver oxide (94 mg, 0.45
mmol), 4,5-dimethyl-1,3-bis(2-propenyl)imidazolium chloride
(95 mg, 0.45 mmol) and [IrCl(COD)]2 (150 mg, 0.22 mmol)
(yield 148 mg, 66%).
acetone):
d 161.25 (NCN), 114.6 (Cl–C), 94.82, 74.53
(COD), 63.71 (NCH2CHQCH2), 51.11 (NCH2CHQCH2),
42.60 (NCH2CHQCH2), 32.26, 30.87 (COD). ESI-MS (cone
25 V): m/z (fragment) 517.0 [M]+.
4,5-Dimethyl-1,3-bis(2-propenyl)imidazolin-2-ylidene [(1,2,5,6-g)-
1-5-cyclooctadiene]iridium hexafluorophosphate (2cPF6). The
synthesis of complex 2c was carried out using the same general
procedure as deꢁscribed for complex 2a but followed by anion
exchange (PF6 using complex 1c (40 mg, 0.08 mmol) and
AgBF4 (15 mg, 0.08 mmol) (yield 30 mg, 68%).
1H NMR (500 MHz, CDCl3):
d
5.85 (m, 2H,
NCHHCHQCH2, NCH2CHQCH2, not coordinated), 5.03
2
(d, JHH = 15.5 Hz, 1H, NCH2CHQCH2, not coordinated),
4.60 (m, 1H, NCH2CHQCH2, not coordinated), 4.18 (m, 2H,
COD, NCHHCHQCH2, not coordinated), 4.01 (m, 2H,
NCHHCHQCH2, coordinated and COD), 3.61–3.43 (m,
4H, NCHHCHQCH2, NCH2CHQCH2, coordinated and
COD), 3.30 (m, 1H, COD), 2.95 (m, 2H, COD), 2.85 (m,
2H, COD), 2.38 (m, 1H, COD), 2.28 (m, 1H,
NCH2CHQCHH, coordinated), 2.06 (s, 3H, CH3), 1.91 (m,
1H, NCH2CHQCHH, coordinated), 1.89 (s, 3H, CH3), 1.54
(m, 2H, COD). 13C NMR (75 MHz, CDCl3): d 158.9 (NCN),
136.1 (NCH2CHQCH2, not coordinated), 125.8 (C–CH3),
122.2 (C–CH3), 114.5 (NCH2CHQCH2, not coordinated),
98.3, 96.7, 60.1, 55.3 (COD), 50.3 (NCH2CHQCH2, coordi-
nated), 49.4 (NCH2CHQCH2, not coordinated), 46.1
1H NMR (500 MHz, CDCl3):
NCH2CHQCH2), 4.74 (m, 2H, COD), 4.44 (dd, JHH = 4.5
Hz, 2JHH = 13.0 Hz, 2H, NCHHCHQCH2), 4.21 (d, 2JHH
d
5.17 (m, 2H,
3
=
12.5 Hz, 2H, NCHHCHQCH2), 3.47 (m, 2H, COD), 3.44 (d,
3JHH = 8.0 Hz, 2H, NCH2CHQCHHcis), 2.85 (m, 2H, COD),
2.77 (d, 3JHH = 12.0 Hz, 2H, NCH2CHQCHHtrans), 2.70 (m,
2H, COD), 2.29 (m, 4H, COD), 1.98 (s, 6H, CH3). 13C NMR
(125 MHz, CDCl3): d NCN not observed, 124.7 (C–CH3),
93.3, 74.2 (COD), 63.9 (NCH2CHQCH2), 49.2 (NCH2CH
QCH2), 42.2 (NCH2CHQCH2), 32.7, 31.3 (COD), 9.4 (CH3).
ESI-MS (cone 25 V): m/z (fragment) 477.3 [M]+.
(NCH2CHQCH2,
coordinated),
41.2
(COD),
35.8
(NCH2CHQCH2, coordinated), 33.3, 29.0, 27.5 (COD), 9.7
(CH3), 8.9 (CH3). ESI-MS (cone 25 V): m/z (fragment) 477.2
[M ꢁ Cl]+.
1,3-Bis(4-pentenyl)-imidazolin-2-ylidene
[(1,2,5,6-g)-1-5-
cyclooctadiene]chloro iridium (3). Silver oxide (63 mg, 0.27
mmol) was added to a solution of 1,3-bis(4-pentenyl) imida-
zolium bromide (85 mg, 0.30 mmol) in MeOH. The mixture
was stirred at room temperature for 1 h and filtered through
Celites. The solution was concentrated under reduced pres-
sure and redissolved in dichloromethane. [IrCl(COD)]2 (100
mg, 0.15 mmol) was added and the mixture was stirred for 1 h
at 45 1C. The volatiles were removed under reduced pressure.
Compound 3 was obtained as a yellow oil (yield 122 mg, 77%).
1H NMR (500 MHz, CDCl3): d 6.83 (s, 2H, CH imidazole),
5.86 (m, 2H, –CHQCH2), 5.14 (m, 4H, –CHQCH2), 4.58
(s, 2H, COD), 4.36 (m, 2H, –NCH2–), 4.30 (m, 2H, –NCH2–),
2.88 (s, 2H, COD), 2.19 (m, 4H, COD), 2.0 (m, 4H, COD),
1,3-Bis(2-propenyl)-imidazolin-2-ylidene
[(1,2,5,6-g)-1-5-
cyclooctadiene]iridium tetrafluoroborate (2a). To a solution of
complex 1a (44 mg, 0.09 mmol) in acetone was added AgBF4
(18 mg, 0.09 mmol), and the mixture was stirred at room
temperature for 4 h. The suspension was filtered through
Celites and the solution concentrated under reduced pressure.
Precipitation with diethyl ether (6 mL) afforded a solid (yield
40 mg, 82%).
1H NMR (500 MHz, CDCl3): d 6.88 (s, 2H, NCHCHN),
5.19 (m, 2H, NCH2CHQCH2), 4.73 (m, 2H, COD), 4.60 (dd,
ꢀc
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124 | New J. Chem., 2008, 32, 120–126

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Table 3 Crystal data and structure refinement for complexes 2a, 2b ꢂ PF6 and 3
2a
2b ꢂ PF6
C17H22Cl2F6IrN2P
662.44
293(2)
3
Empirical formula
Molecular weight
Temperature/K
C17H24BF4IrN2
535.39
293(2)
C21H32ClIrN2
540.14
293(2)
Radiation (l/A)
Crystal system
Space group
a/A
b/A
c/A
a/1
Mo-Ka monochromated (0.71069)
Monoclinic
P2(1)/c (no 14)
15.2900(11)
10.7009(8)
12.7347(10)
90
Monoclinic
P2(1)/c (no 14)
8.1277(4)
36.568(2)
12.0502(6)
90
99.5350(10)
90
3532.0(3)
8
2.014
Triclinic
P-1 (no 2)
12.0233(11)
13.9740(14)
14.7666(15)
64.168(2)
85.560(3)
89.213(2)
2225.8(4)
4
b/1
96.789(2)
90
2069.0(3)
4
2.127
g/1
Volume/A3
Z
Calc. density/g cmꢁ3
Absorption coefficient/mmꢁ1
F(000)
1.612
6.124
7.602
2064
6.848
1272
1064
0.13 ꢃ 0.11 ꢃ 0.09
Crystal size/mm
Reflections collected
Independent reflections
0.19 ꢃ 0.12 ꢃ 0.10
0.12 ꢃ 0.11 ꢃ 0.08
24 448
8122
8374
3109
12 840
7842
Rint = 0.0742
8122/0/451
1.047
R1 = 0.0448
wR2 = 0.0778
R1 = 0.0953
1.281/ꢁ1.175
Rint = 0.0518
3109/36/262
1.117
R1 = 0.0525
wR2 = 0.1315
R1 = 0.0750
2.075/ꢁ2.127
Rint = 0.0421
7842/32/448
1.005
R1 = 0.0468
wR2 = 0.1019
R1 = 0.0898
1.104/ꢁ0.768
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I 4 2s(I)]a
R indices (all data)b
Max./min. residual electron densities/e Aꢁ3
1
P
P
P
P
R = ||Fo| ꢁ |Fc||/ |Fo| for all I 4 2s(I). wR = [ w(|Fo| ꢁ |Fc|)2/ wFo ]2.
a
b
2
1.95 (m, 2H, –CH2–), 1.87 (m, 2H, –CH2–), 1.71 (m, 2H,
–CH2–), 1.67 (m, 2H, –CH2–). 13C NMR (75 MHz, CDCl3): d
180.2 (NCN–Ir), 137.5 (–CHQCH2), 120.2 (–NCHCHN–),
115.8 (–CHQCH2), 84.3 (COD), 51.6 (COD), 50.8
(2C, NCH2), 33.8 (COD), 31.0 (COD), 30.2 (–CH2–), 29.7
(–CH2–). ESI-MS (cone 25 V): m/z (fragment) 505.3
[M ꢁ Cl+].
Acknowledgements
We gratefully acknowledge financial support from the MEC
(CTQ2005-05187) and Bancaixa (P1.1A2005-04). We would
also like to thank the Generalitat Valenciana for a fellowship
(A. Z.), and J. M. thanks the Ramon y Cajal program.
´
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