Novel quasi-scorpionate ligand structures based on a bis-N-heterocyclic carbene chelate core: Synthesis, complexation and catalysis

Article abstract of DOI:10.1002/aoc.1773

A series of novel quasi-scorpionate CNC donor ligands, MeC(2-C ₅H₄N){CH₂(imidazole-R)} (R = methyl, n-butyl, n-propenyl), in which a chelating bis(NHC) core is supplemented by a hemi-labile pyridyl donor, were prepared. The coordination chemistry of these ligands was investigated with silver, palladium, rhodium and iridium. The single crystal X-ray structures of [Rh(NC₂^Me)(COD)]Cl 8a and [Ir(NC ₂^Pr)(COD)]Br 9b were determined. The catalytic potential of the rhodium and iridium complexes was assessed in the transfer hydrogenation of ketones; the iridium complexes, which show superior performance, form very effective and stable catalysts.

Full text of DOI:10.1002/aoc.1773

Full Paper
Received: 20 October 2010
Revised: 25 November 2010
Accepted: 7 December 2010
Published online in Wiley Online Library: 29 March 2011
(wileyonlinelibrary.com) DOI 10.1002/aoc.1773
Novel quasi-scorpionate ligand structures
based on a bis-N-heterocyclic carbene chelate
core: synthesis, complexation and catalysis
Sedat Yasara,b, Kingsley J. Cavella∗, Benjamin D. Warda and Benson Kariukia
A series of novel quasi-scorpionate CNC donor ligands, MeC(2-C5H4N){CH2(imidazole-R)} (R = methyl, n-butyl, n-propenyl),
in which a chelating bis(NHC) core is supplemented by a hemi-labile pyridyl donor, were prepared. The coordination
chemistry of these ligands was investigated with silver, palladium, rhodium and iridium. The single crystal X-ray structures
of [Rh(NC2Me)(COD)]Cl 8a and [Ir(NC2Pr)(COD)]Br 9b were determined. The catalytic potential of the rhodium and iridium
complexes was assessed in the transfer hydrogenation of ketones; the iridium complexes, which show superior performance,
c
form very effective and stable catalysts. Copyright ꢀ 2011 John Wiley & Sons, Ltd.
Supporting information may be found in the online version of this article.
Keywords: CNC donor ligands; bis-N-heterocyclic carbene; metal-complexes; catalysis
Introduction
As part of our ongoing investigation into novel functionalized
N-heterocyclic carbene ligands as supporting environments
for metal complexes and their application in catalysis, we
herein report the synthesis and coordination chemistry of
chelating bis(NHC) ligands, possessing a pyridyl-donor, with silver,
palladium, rhodium and iridium. Catalytic transfer hydrogenation
reactions employing the rhodium and iridium complexes are
reported. The pyridyl ring is seen as an interesting structural
feature of this ligand; in square-planar complexes the hemi-labile
pyridyl donor is well placed to coordinate to the metal center to
stabilize a catalyst resting state, whilst easily decoordinating to
allow a reaction to proceed when a lower coordination number is
required.
The rational design of functional, yet robust molecular complexes
relies heavily on the availability of kinetically inert chelating
ligands. Metal complexes thus prepared have found widespread
application in many diverse areas, from catalysis to biomedical
imaging. Consequently, the continued search for new functional
complexes must also incorporate the design of novel, readily
adaptable supporting ligand environments. Scorpionate ligands
are one such group that have an important role in this field.[1–3]
Scorpionate ligands possessing two amide donors, and a third
(and possibly a fourth) pyridine or amine donor (Scheme 1),[4–8]
have been shown to support metal complexes which exhibit a
range of unusual reactivity, often allowing catalytic intermediates
to be isolated and studied to an unprecedented level of
detail.[9] Peris and coworkers prepared an interesting tripodal
bis(imidazolylidene) with a phenoxy moiety providing the third
donor (Scheme 1).[10a] Such a ligand is extremely strongly bound,
andforoctahedralmetalsprovidesthreecis-arrangedcoordination
sites available for further chemistry. In a second paper Peris
and coworkers also reported a bis-carbene ligand containing a
pyridine donor on the backbone.[10b] However, the rigid structure
of this ligand would probably preclude it from coordinating in
a tridentate fashion. Other tridentate NHC based ligands with
labile donors have also been reported, for example see Hahn and
coworkers.[10c,11]
Results and Discussion
Ligand Synthesis
The ligands MeC(2-C5H4N){CH2(imidazole-R)} (R = methyl, n-
butyl, n-propenyl) were prepared according to the procedure
depicted in Scheme 2. The di-hydroxy species, 2, was synthe-
sized by the hydroxymethylation of 2-ethylpyridine with aqueous
formaldehyde, following the method of Gade;[4] this gave a
mixture of the monohydroxymethylation product 1 and the di-
hydroxymethylation product 2. The yield of 2 was increased
by reacting 1 with further equivalents of formaldehyde un-
der identical conditions. Treatment of a solution of 2 with
N-Heterocyclic carbenes (NHCs) are now well established as
powerful coordinating ligands that provide a very effective base
on which to build new polydentate ligands. Many publications
describing NHC ligands and their application in catalysis have
appeared in the past 20 years; a number of excellent reviews
have now appeared outlining the synthesis and chemistry of
these ligands and their multidentate derivatives.[11] The field is
vibrant and novel developments in NHC ligand design appear
regularly.[12,13]
∗
Correspondence to: Kingsley J. Cavell, School of Chemistry, Cardiff University,
Main Building, Park Place, Cardiff CF10 3AT, UK. E-mail: CavellKJ@Cardiff.ac.uk
a
School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff CF10
3AT, UK
b
Gaziosmanpasa University, Faculty of Science and Arts, Department of
Chemistry, 60150, Tokat, Turkey
c
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Novel quasi-scorpionate ligand structures
Scheme 1. Selected amido- and NHC-based scorpionate ligands.
Scheme 2. Synthesis of the bis-imidazolium ligand precursors.
methanesulfonyl chloride gave the product, 3, as a red oil in
nearly quantitative yield (93%); further reaction of 3 with dry
lithium bromide yielded 4 as pale yellow oil (56% yield). The
bis-imidazolium salts were synthesized by reaction of 4 with
selected N-substituted imidazoles to give the imidazolium salts
[H2NC2R]Br2 (R = Me, Bu, Pr) 5a–c, shown in Scheme 2 (75–80%
yields).
Synthesis of Metal Complexes
Scheme 3. Synthesis of the Ag-bis-NHC complexes 6a–c.
Silver complexes of the new ligands were prepared by dissolving
the bis-imidazolium salts in CH2Cl2 (DCM) to which Ag2O was
added (Scheme 3). The resulting suspension was stirred at room
temperature overnight, yielding a grey precipitate and red
solution. After filtration and washing, the silver complexes 6a–c
were obtained as white powders (in 65–80% yield), which rapidly
discolored on standing (the structure depicted in Scheme 3 is
based on the molecular formulae obtained from high-resolution
MS data).
c
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S. Yasar et al.
Scheme 4. Synthesis of transition metal complexes of the bis-imidazole ligands.
A common function of Ag-NHC complexes is to act as a ligand
transfer agent. To demonstrate the feasibility of such an approach
for the current ligands, a square-planar bis-NHC–Pd complex was
prepared by treating the Pd precursor [PdCl2(NCCH3)2] with a
solution of the Ag complex as shown in equation (2) (Scheme 4);
complex 7 was obtained in good yield as a stable yellow
compound. Rh and Ir complexes were readily prepared from
the bis-imidazolium salt, KN(SiMe3)2 and the appropriate metal
precursor complex, according to equation (3) (Scheme 4).
Structural Characterization
The structure of complexes [Rh(NC2Me)(COD)]Cl, 8a, and
[Ir(NC2Pr)(COD)]Br, 9b, were confirmed by crystallographic analy-
ses. The molecular structures of the two complexes are depicted
in Figs 1 and 2, respectively, with selected bond lengths and
angles provided in Table 1. The precision in the bond lengths
and angles is somewhat low. Nevertheless, the two structures
confirm the overall connectivity of the ligands, and indicate the
coordination mode via the two NHC moieties. In these cases it
can be seen that the pyridyl arm remains pendant, presumably
owing to the preference for a square planar coordination geom-
etry in these d8 complexes. However, it can be clearly seen that
the pyridyl donor lies in a position which makes coordination
likely, should the metal require further coordinative saturation,
for example in octahedral complexes, or should coordination be
required to stabilize a catalyst resting state. The principal bond
lengths and angles (i.e. those associated with the central coordina-
tion sphere) are comparable to those reported in the Cambridge
Structural Database: Rh–CNHC = 1.901–2.224, mean 2.038 for
161 examples; Rh–CCOD = 1.998–2.397, mean 2.160 for 1098
examples; Ir–CNHC = 1.907–2.115, mean 2.040 for 111 exam-
ples; Ir–CCOD = 1.984–2.363, mean 2.165 for 509 examples.[14]
Complex 9b crystallizes with two independent molecules in the
asymmetric unit; the two show no significant differences (the
Figure 1. Molecular structure of [Rh(NC2Me)(COD)]Cl (8a). H atoms and
anion omitted for clarity; thermal ellipsoids are drawn at 25% probability.
corresponding metric parameters are provided in parentheses in
Table 1). Complex 8a crystallizes with a chloride anion, whereas 9b
crystallizes with a bromide. Since both complexes were prepared
usingananalogousroute, andbothhalideionswerepresent(chlo-
ride being derived from the metal precursor and bromide being
derived from the imidazolium salt), we ascribe this phenomenon
to subtle differences in crystal packing. However, neither structure
indicates any evidence of interaction between the anion and the
cationic complex, and we therefore deem this difference to be
of little consequence in relation to the coordination motif of the
ligand or the catalytic ability of the complexes.
Catalytic Studies
To explore the effectiveness of these new ligands in catalysis,
preliminary catalytic investigations were undertaken into the
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Novel quasi-scorpionate ligand structures
30 min (and ∼100% conversion) an additional 1 mmol of p-
bromoacetophenone was added and the reaction monitored,
and then after 100 min a third aliquot of substrate was added
(results are shown Fig. 5). A similar procedure was also followed
usingp-methylacetophenoneassubstrate.Importantly,theresults
indicate that there is little diminution in catalyst performance with
time, despite the reduced catalyst concentration and increasing
product concentration.
The catalytic performance of the chelating NHC-Ir complexes,
although not optimized in terms of ligand substituents or reaction
conditions, generally compare quite favorably with previously
reported systems for transfer hydrogenation.[15–20] The catalyst
systems showed good stability and activity for the range of
substrate tested.
Figure 2. Molecular structure of [Ir(NC2Bu)(COD)]Br (9b). H atoms, the
second crystallographically independent molecule and anion omitted for
clarity, thermal ellipsoids are drawn at 25% probability.
Conclusions
Table 1. Selected bond lengths (Å) and angles (deg) for 8a and 9b.
Values in parentheses are for the crystallographically independent
molecule
A new series of bis(carbene)pyridine ligands have been shown
to provide valuable supporting environments for a range of late
transition metals. The complexes have been applied as catalysts
in transfer hydrogenation, and they exhibit good activity and
excellent catalyst stability. It is clear that there is potential for
these ligands to find applications with many other metals and
catalytic processes other than those described here; the CNC
coordination motif is expected to facilitate the development of
novelorganometalliccomplexesforbothfundamentalstudiesand
in catalytic applications. Further studies are currently underway to
determine the efficacy of the pyridyl coordination with a variety
of transition metals, and also in the development of new donor-
functionalized ligand structures based on a related bis-NHC core.
8a
9b
M(1)–C(1)
2.163(12)
2.036(11)
2.170(12)
2.240(13)
1.998(12)
1.916(12)
106.7(9)
109.6(9)
85.1(4)
2.168(9) [2.189(10)]
2.185(9) [2.186(9)]
2.182(9) [2.177(10)]
2.185(9) [2.178(9)]
2.033(9) [2.027(9)]
2.059(9) [2.047(9)]
104.2(8) [104.9(7)]
104.7(7) [104.7(7)]
87.1(3) [84.7(3)]
M(1)–C(2)
M(1)–C(5)
M(1)–C(6)
M(1)–C(17)
M(1)–C(21)
N(2)–C(17)–N(3)
N(4)–C(21)–N(5)
C(17)–M(1)–C(21)
Experimental
transfer hydrogenation of ketones. Initial results were very
promising and good catalytic activity, and catalyst stability was
observed.
All manipulations were performed using standard Schlenk tech-
niques under an argon atmosphere, except where otherwise
noted. Complexes [Rh(COD)Cl]2 and [Ir(COD)Cl]2 were synthesized
according to literature methods.[21] NHC salts and the Rh and Ir
complexes were prepared as previously reported.[13l] Solvents of
analyticalgradewerefreshlydistilledfromsodium/benzophenone
(THF, hexane) or from calcium hydride (CH2Cl2) or dried using
a Braun SPS-800 system (hexane, CH2Cl2) or a Vacuum Atmo-
spheres recirculating SPS system (THF). Deuterated solvents for
NMR measurements were distilled from the appropriate drying
agents under N2 immediately prior to use, following standard
literature methods. Air-sensitive compounds were stored and
weighed in a glovebox. All reagents [1,3-dibromopropane, 1,4-
diiodobutane, 2-aminopyridine, o-anisidine, 2,6-dimethylaniline,
2,6-diisopropylaniline, triethylorthoformate, sodium tetrafluorob-
orate and potassium bis(trimethylsilyl)amide] were obtained from
commercial suppliers and used as received. 1H and 13C NMR
spectra were obtained on Bruker Advance AMX 400, 500 or Jeol
Eclipse 300 spectrometers. Chemical shifts (δ) were expressed in
ppm downfield from tetramethylsilane using the residual protio
solvent (1H) or solvent (13C) as an internal standard (CDCl3, 1H
7.26 ppm and 13C 77.0 ppm; benzene-d6 1H 7.15 ppm and 13C
128.0 ppm). Coupling constants J are expressed in Hertz. HRMS
were obtained on a Waters LCT Premier XE instrument and are
reported as m/z (relative intensity). Infrared spectra were recorded
using a Jasco FT/IR-660 Plus spectrometer and analyzed in solution
(dichloromethane).
The performances of iridium(I) and rhodium(I) complexes, 8 and
9, [M(NC2R)(COD)]+X−, were tested using a variety of substrates.
The complexes catalyze the hydrogen transfer from PrOH with
i
potassium tert-butoxide as the base, according to equation (4). As
previously observed,[15] the Ir(I)–NHC complexes show higher
catalytic activity than their rhodium analogues. With 1 mol%
catalyst loading, each of the Ir complexes gave 100% conversion in
60 min or less for all substrates tested; hence lower concentrations
of catalyst (0.3 and 0.01 mol%) were also investigated, and results
for the lower loadings are reported in Table 2. [Rh(NC2Me)(COD)]Cl
8a (0.3 mol%; the only Rh complex tested) required over 16 h
to yield 100% conversion of 4-bromoacetophenone into the
corresponding alcohol (entry 19, Table 2). Although all iridium
complexes gave rise to very effective catalysts, complexes with
ligands bearing the longer chain, propenyl and n-butyl groups
show better performance than the methyl bearing catalyst system.
Plots of conversion vs time for Ir(I)–NHC complex 9c, with
different substrates, were investigated using a concentration
of 0.3 mol% catalyst and the results are shown in Figs 3
and 4. Reactions were monitored by taking aliquots from the
reaction mixture at set intervals and the percentage conversion
determined. Complete conversion of 4-bromoacetophenone to
the alcohol is achieved after approximately 30 min (Fig. 4).
To test the stability of the catalyst system, catalyst 9c
was tested under normal operating conditions; however, after
c
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S. Yasar et al.
Table 2. Results of hydrogen transfer reactions
Catalyst
Entry
Catalyst
Substrate (1 mmol)
concentration (mol%)
Time (min)
Conversion (%)
1
9c
9c
9b
9b
9a
9a
9c
9c
9b
9b
9a
9a
9c
9c
9b
9b
9a
9a
8a
p-Bromoacetophenone
p-Bromoacetophenone
p-Bromoacetophenone
p-Bromoacetophenone
p-Bromoacetophenone
p-Bromoacetophenone
p-Methylacetophenone
p-Methylacetophenone
p-Methylacetophenone
p-Methylacetophenone
p-Methylacetophenone
p-Methylacetophenone
Cyclohexanone
0.3
0.01
0.3
30
30
30
30
30
30
60
60
60
60
60
60
30
30
30
30
30
30
16 h
100
60
2
3
100
55
4
0.01
0.3
5
100
45
6
0.01
0.3
7
100
50
8
0.01
0.3
9
100
46
10
11
12
13
14
15
16
17
18
19
0.01
0.3
80
0.01
0.3
30
100
100
100
100
100
90
Cyclohexanone
0.01
0.3
Cyclohexanone
Cyclohexanone
0.01
0.3
Cyclohexanone
Cyclohexanone
0.01
0.3
p-Bromoacetophenone
100
Catalyst (0.3 mol%, 0.01 mol%; substrate 1 mmol), iPrOH (5 ml), KOBut (10 mol%), 80 ◦C, 0.5–1 h. Products were determined by NMR spectroscopy
and yields are based on the corresponding aryl ketone or cyclo ketone.
Time (min)
Figure 4. Plot of conversion vs time for p-methylacetophenone (1 mmol)
catalysed by 9c (0.3 mol%).
of formaldehyde under the same reaction conditions. 1H NMR
(400.1 MHz, CDCl3, 293 K) δ 1.16 (s, CCH3, 3 H), 3.74 (d, J = 11.1 Hz,
CCH3CH2, 2 H), 3.94 (d, J = 11.1 Hz, CHCH3CH2, 2 H), 7.14 (d,
Time (min)
J = 7.6 Hz, C5H4N, 1 H), 7.27 (m, C5H4N, 1 H), 7.66 (m, C5H4N, 1 H),
1
8.43 (d, C5H4N, 1 H) ppm. 13C{ H} NMR (100.6 MHz, CDCl3, 293 K)
Figure 3. Plot of conversion vs time for p-bromoacetophenone (1 mmol)
catalyzed by 9c (0.3 mol%).
δ 19.7, 45.7, 69.3, 121.5, 121.7, 137.0, 147.8, 165.1 ppm.
Synthesis of 2-(1,3-Dibromo-2-methylpropan-2-yl)pyridine, 4
Synthesis of 2-(1,3-Dihydroxy-2-methylpropan-2-yl)pyridine,
2
This compound was synthesized in a two-step process.
Compound 2 was synthesized following the method of Gade
et al.[4] using a mixture of 2-ethylpyridine (37.5 ml, 35.2 g,
0.327 mol) and an aqueous solution of formaldehyde (37%,
115.5 ml, 1.60 mol). As described by Gade, the total yield of 2
was increased to 48% by reaction of 1 with a further 4 equiv.
Part a: synthesis of 2-[bis-1,3-methylsulfonate-2-methylpropan-2-
yl)]pyridine, 3
A solution of 2 (16.7 g, 0.1 mol) and triethylamine (62.6 ml,
0.45 mol) in dichloromethane (200 ml) was cooled to −2 ◦C,
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Novel quasi-scorpionate ligand structures
overnight. The resulting hygroscopic brown solid was washed
with diethyl ether and dried under vacuum to give the pure salt
5a (3.65 g, 80%). 1H NMR (400.1 MHz, D2O, 293 K): δ 1.43(s, CCH3,
3H), 3.82 (s, NCH3, 6H), 4.61–4.86 (dd, AB, J = 11.2 Hz, CCH3CH2,
4H), 7.25 (s, NCHCHN, 2H), 7.65 (s, NCHCHN, 2H), 7.21 (m, C5H4N,
1H), 7.38 (m, C5H4N, 1H), 7.85 (m, C5H4N, 1H), 8.7 (t, J = 3.2 Hz,
1
C5H4N, 1H), 9.06 (s, NCHN, 2H) ppm. 13C{ H} NMR (100.6 MHz, D2O,
293 K): 17.8, 35.8, 46.6, 56.2, 122.7, 123.4, 124.3, 138.6, 139.0, 148.9,
149.8, 156.9 ppm. HR-MS (ES), m/z = 376.1127 [M + Br]+ (calcd
for C17H23BrN5: 376.1137).
Synthesis of 2-[1,3-bis(3-Butylimidazolidin-1-yl)-2-
methylpropan-2-yl]pyridine bromide, 5b
Thiscompoundwaspreparedananalogousmannerto 5a, using1-
butylimidazole (2.98 g, 24 mmol). The resulting hygroscopic white
solid was washed with diethyl ether and dried under vacuum
to give the salt 5b (4 g, 75%). 1H NMR (400.1 MHz, DMSO-d6,
293 K): δ 0.84 (t, J = 7.6 Hz, NCH2CH2CH2CH3, 6H), 1.09 (m,
NCH2CH2CH2CH3,4H),1.42(s,CCH3,3H),1.66(m,NCH2CH2CH2CH3,
4H), 4.11(t, J = 7.2 Hz, NCH2CH2CH2CH3, 4H), 4.65–4.85 (dd, AB,
J = 13.6 Hz, CCH3CH2, 4H), 7.37 (s, NCHCHN, 2H), 7.4 (m, C5H4N,
1H), 7.6 (s, C5H4N, 1H), 7.74 (s, NCHCHN, 2H), 7.85 (m, C5H4N, 1H),
Time (min)
Figure 5. Lifetime studies for catalyst 9c (0.3 mol%) with
p-bromocetophenone as substrate.
and a solution of methanesulfonyl chloride (19.3 ml, 0.25 mol)
in dichloromethane (50 ml) added dropwise, taking care that the
temperature did not exceed +2 ◦C. The resulting suspension was
warmed to room temperature and stirred for 1 h. The reaction
product was washed successively with hydrochloric acid (1 M,
1×50 ml), water(1×50 ml), sodiumcarbonatesolution(1×50 ml),
brine (1 × 50 ml) and finally again with water (1 × 50 ml). After
drying over Na2SO4 and evaporating the solvent, the residue was
driedinvacuotoyield3asaredoil, whichwasusedwithoutfurther
purification (29.3 g, 93%). 1H NMR (400.1 MHz, CDCl3, 293 K): δ 1.50
(s,CCH3,3H),2.96(s,CH2SO2CH3,6H),4.63–4.52(dd,AB,J = 8.8 Hz,
CCH3CH2, 4H), 7.21 (d, J = 7.9 Hz, C5H4N, 1H), 7.27 (d, J = 7.9 Hz,
C5H4N, 1H), 7.70 (t, J = 8.0 Hz, C5H4N, 1H), 8.49 (d, J = 8.0 Hz,
1
8.7(d, J = 1.2 Hz, C5H4N, 1H), 8.97(s, NCHN, 2H)ppm. 13C{ H}NMR
(100.6 MHz, DMSO-d6, 293 K): δ 13.8, 19.4, 23.9, 31.1, 38.9, 51.48,
55.8, 113.7, 121.4, 123.0, 123.4, 136.0, 148.1, 159.7, 160.2 ppm.
Synthesis of 2-[1,3-Bis(3-propenylimidazolidin-1-yl)-2-
methylpropan-2-yl]pyridine bromide, 5c
This compound was prepared an analogous manner to 5a, from
1-propenylimidazol (2.6 g, 24 mmol). The resulting hygroscopic
brown solid was washed with diethyl ether and dried under
vacuum to give the salt 5c (3.97 g, 78%). 1H NMR (400.1 MHz,
DMSO-d6, 293 K): δ 1.43 (s, CCH3, 3H), 4.82 (d, J = 6.8 Hz,
NCH2CHCH2, 4H), 4.63–4.89 (dd, AB, J = 13.6 Hz, CCH3CH2, 4H),
5.32 (d, J = 0.8 Hz, NCH2CHCH2, 4H), 5.97 (m, NCH2CHCH2, 2H),
6.9 (s, NCHCHN, 2H), 7.34 (s, NCHCHN, 2H), 7.38 (m, C5H4N, 1H),
7.68 (s, C5H4N, 1H), 7.82 (m, C5H4N, 1H), 8.7 (t, J = 1.2 Hz, C5H4N,
C5H4N, 1H) ppm. 13C{ H} NMR (100.6 MHz, CDCl3, 293 K) δ 19.1,
1
36.7, 36.8, 45.1, 72.7, 119.1, 137.5, 158.4, 163.3 ppm.
Part b: synthesis of 4
Compound3(31.6 g,0.1 mol)wasdissolvedinanhydrousdimethyl
sulfoxide (150 ml) and heated to 70 ◦C. Vigorously dried (in vacuo,
100 ◦C, 3 days)lithiumbromide(21.75 g, 0.25 mol)wasthenadded
in one portion, and the solution stirred for 2 days at 70 ◦C. After
cooling to room temperature, water (200 ml) was added, and
the mixture stirred for 30 min. The milky solution was extracted
with diethyl ether (7 × 70 ml), and the combined ether extracts
washed with water (3 × 50 ml) to remove residual dimethyl
sulfoxide. The organic phase was separated, dried with Na2SO4,
and the solvent evaporated to give an oily, crude product. Column
chromatography (SiO2, 0.060–0.200 mm, pore diameter ca 6 nm)
using a combination of ethyl acetate and hexane (3 : 1) as eluent
1
1H), 9.03 (s, NCHN, 2H) ppm. 13C{ H} NMR (100.6 MHz, DMSO-d6,
293 K): δ 20.6, 39.5, 46.6, 51.3, 56.0, 120.3, 122.8, 123.7, 124.2, 132.2,
137.6, 149.3, 149.8, 158.5 ppm.
Synthesis of Ag(I)–NHC Complexes
Synthesis of 2-[2-methyl-1,3-bis(3-methylimidazolidin-1-yl)
propan-2-yl]pyridine silver(I) bromide, 6a
2-[2-Methyl-1,3-bis(3-methylimidazolidin-1-yl)propan-2-yl]pyri-
dine bromide, 5a (0.45 g, 1 mmol) was dissolved in dried DCM
(20 ml) and Ag2O (0.271, 1 mmol) added. The resulting suspension
was stirred at room temperature for overnight, yielding a gray
precipitate and red solution. The supernatant was separated
and stripped in vacuo and the red solid washed with ether and
hexane. The resultant white powder was dried invacuo but rapidly
discolored, giving 6a (0.37 g, 75%), a red creamy powder that
showed no further signs of decomposition at room temperature.
1H NMR (400.1 MHz, D2O, 293 K): δ 1.55 (s, CCH3, 3H), 3.76 (s,
NCH3, 6H), 4.73–4.93 (dd, AB, J = 13.6 Hz, CCH3CH2, 4H), 6.8 (s,
NCHCHN, 2H), 7.3 (d, J = 3.2 Hz, C5H4N, 1H), 7.42 (s, NCHCHN,
2H), 7.43 (m, C5H4N, 1H), 7.80 (t, J = 2.4 Hz, C5H4N, 1H), 8.75
1
yielded compound 4 as a light yellow oil (16.4 g, 56%). H NMR
(400.1 MHz, CDCl3, 293 K): δ 1.63 (s, CCH3, 3H), 4.00–3.86 (dd, AB,
J = 10.0 Hz, CCH3CH2, 4H), 7.18 (d, J = 7.9 Hz, C5H4N, 1H), 7.23
(d, J = 7.9 Hz, C5H4N, 1H), 7.66 (t, J = 7.9 Hz, C5H4N, 1H), 8.54
1
(d, J = 8.0 Hz, C5H4N, 1H) ppm. 13C{ H} NMR (100.6 MHz, CDCl3,
293 K): δ 23.1, 42.1, 46.0, 118.3, 118.4, 137.1, 160.0, 164.1 ppm.
HR-MS (ES), m/z = 291.9345 [M + H]+ (calcd for C9H12Br2N:
291.9336).
Synthesis of 2-[2-Methyl-1,3-bis(3-methylimidazolidin-1-yl)
propan-2-yl]pyridine Bromide, 5a
1
(d, J = 1.6 Hz, C5H4N, 1H) ppm. 13C{ H} NMR (100.6 MHz, D2O,
293 K), 19.7, 34.8, 46.7, 54.9, 58.4, 64.9, 122.5, 122.6, 122.8, 137.5,
149.5, 160.0, 181.7 ppm. ES-MS: m/z = 484 (20%) [M + H]+, 402
(100%) [M − Br]+.
2-(1,3-Dibromo-2-methylpropan-2-yl)pyridine (2.93 g, 10 mmol)
and 1-methylimidazole (1.97 g, 24 mmol) were stirred at 100 ◦C
c
Appl. Organometal. Chem. 2011, 25, 374–382
Copyright ꢀ 2011 John Wiley & Sons, Ltd.
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S. Yasar et al.
Synthesis of 2-(1,3-bis(3-butylimidazolidin-1-yl)-2-methylpropan-2-
yl)pyridine silver(I) bromide, 6b
[Rh(COD)Cl]2 (0.24 g, 0.5 mmol). An immediate color change was
observed from light yellow to dark orange and after 5 minutes
yellow solid precipitated out. After the reaction mixture was
stirred at room temperature for 2 h, the volatiles were removed
in vacuo. The yellow solid obtained was washed with cold hexane
(2 × 10 ml) and dried under vacuum. Yield: 65%, 164 mg. The
This compound was prepared an analogous manner to
6a, from 2-[1,3-bis(3-butylimidazolidin-1-yl)-2-methylpropan-2-
yl]pyridine bromide, 5b (0.54 g, 1 mmol) and Ag2O (0.27 g,
1 mmol). The resultant solid was dried in vacuo giving 6b
(0.37 g, 66%) as a grey creamy powder. 1H NMR (400.1 MHz,
DMSO-d6, 293 K): δ 0.74 (t, J = 6 Hz, NCH2CH2CH2CH3, 6H),
1.09 (m, NCH2CH2CH2CH3, 4H), 1.43 (s, CCH3, 3H), 1.55 (m,
NCH2CH2CH2CH3, 4H), 3.90 (t, J = 4.8 Hz, NCH2CH2CH2CH3, 4H),
4.55–4.76 (dd, AB, J = 13.6 Hz, CCH3CH2, 4H), 6.95 (s, NCHCHN,
2H), 7.2 (m, C5H4N, 1H), 7.4 (s, C5H4N, 1H), 7.45 (s, NCHCHN, 2H),
1
structure of complex characterized by X-ray diffraction. H NMR
(500.1 MHz, CDCl3, 293 K): δ 1.2 (s, CCH3, 3H), 2.1–2.6 (m, CHCH2,
8H), 3.99 (s, NCH3, 6H), 4.01 (d, J = 15 Hz, CHCH2, 2H), 4.5 (dd,
AB, J = 13.2 Hz, CCH3CH2, 4H), 5.62 (d, J = 24.5 Hz, CHCH2, 2H),
6.99 (s, NCHCHN, 2H), 7.02 (s, NCHCHN, 2H), 7.27 (m, C5H4N, 1H),
7.64 (d, J = 8 Hz, C5H4N, 1H), 7.78 (t, J = 6 Hz, C5H4N, 1H), 8.58
1
(d, J = 1 Hz, C5H4N, 1H) ppm. 13C{ H} NMR (125.7 MHz, CDCl3,
1
7.65 (m, C5H4N, 1H), 8.5 (d, J = 1.2 Hz, C5H4N, 1H) ppm. 13C{ H}
293 K): δ 14.2, 17.23, 27.0, 29.7, 30.1, 37.1, 45.1, 54.5, 62.6, 64.8,
87.6, 89.2, 118.9, 121.5, 123.7, 127.6, 136.6, 148.1, 162.2, 182.0 (d,
J = 52.5 Hz) ppm. HR-MS (ES): m/z = 506.1813 [M]+ (calcd for
C25H33N5Rh: 506.1791).
NMR (100.6 MHz, DMSO-d6, 293 K): δ 14.3, 17.6, 18.5, 31.5, 54.6,
57.5, 63.5, 120.8, 121.3, 121.9, 122.5, 136.4, 148.5, 158.8, 179.4 ppm.
Synthesis of 2-(1,3-bis(3-propenylimidazolidin-1-yl)-2-
methylpropan-2-yl)pyridine silver(I) bromide, 6c
Synthesis of 2-[1,3-bis(3-Butylimidazolidin-1-yl)-2-
methylpropan-2-yl]pyridine Rhodium(I) Cyclooctadiene
Chloride, 8b
This compound was prepared an analogous manner to
6a, from 2-[1,3-bis(3-propenylimidazolidin-1-yl)-2-methylpropan-
2-yl]pyridine bromide, 5c (0.51 g, 1 mmol) and Ag2O (0.27 g,
1 mmol). The resultant solid was dried in vacuo, giving 6c (0.4 g,
77%) as a grey creamy powder, which rapidly discolored on stand-
Complex 8b was prepared from 2-[1,3-bis(3-butylimidazolidin-
1-yl)-2-methylpropan-2-yl]pyridine bromide, 5b (0.54 g, 1 mmol),
KN(SiMe3)2 (0.4 g, 1 mmol) and [Rh(COD)Cl]2 (0.24 g, 0.5 mmol)
according to the method described for 8a. A yellow solid was
obtained in 75% yield, 221 mg. 1H NMR (500.1 MHz, CDCl3, 293 K):
δ 0.95 (t, J = 6.2 Hz, NCH2CH2CH2CH3, 6H), 1.10 (s, CCH3, 3H),
1.40–2.3 (m, NCH2CH2CH2CH3, 8H and CHCH2, 8H), 3.77 (m,
NCH2CH2CH2CH3, 4H), 3.97 (s, CCH3CH2, 4H), 4.04 (d, J = 11.5 Hz,
CHCH2, 2H), 5.30 (d, J = 14 Hz, CHCH2, 2H), 6.95 (s, NCHCHN, 2H),
7.15 (s, NCHCHN, 2H), 7.26 (m, C5H4N, 1H), 7.70 (m, C5H4N, 1H), 7.75
1
ing. H NMR (400.1 MHz, CDCl3, 293 K): δ 1.40 (s, CCH3, 3H), 4.6
(d, J = 2 Hz, NCH2CHCH2, 4H), 4.65–4.75 (dd, AB, J = 13.2 Hz,
CCH3CH2, 4H), 5.08 (d, J = 4 Hz, NCH2CHCH2, 4H), 5.7 (m,
NCH2CHCH2, 2H), 6.26 (s, NCHCHN, 2H), 6.64 (s, NCHCHN, 2H),
6.95 (d, J = 3.2 Hz, C5H4N, 1H), 7.32 (m, C5H4N, 1H), 7.5 (t,
J = 0.8 Hz, C5H4N, 1H), 8.6 (d, J = 1.6 Hz, C5H4N, 1H) ppm. 13C{ H}
1
NMR (100.6 MHz, CDCl3, 293 K): δ 15.2, 47.4, 59.2, 65.8, 120.4, 121.7,
122.5, 122.9, 132.6, 132.9, 137.5, 150.1, 160.1, 183.6 ppm.
1
(m, C5H4N, 1H), 8.50 (d, J = 4.8 Hz, C5H4N, 1H) ppm. 13C{ H} NMR
(125.7 MHz, CDCl3, 293 K): δ 13.8, 18.8, 26.6, 30.0, 31.7, 44.7, 49.3,
59.5, 64.4, 66.5, 86.8, 88.9, 118.4, 121.7, 123.4, 127.2, 136.4, 147.8,
161.6, 180.9 (d, J = 62.5 Hz) ppm. HR-MS (ES), m/z = 590.2734
[M]+ (calcd for C31H45N5Rh: 590.2730).
Synthesis of 2-[2-Methyl-1,3-bis(3-propenylimidazolidin-1-
yl)propan-2-yl)pyridine Acetonitrile Palladium(II) Chloride, 7
2-[2-Methyl-1,3-bis(3-methylimidazolidin-1-yl)propan-2-yl]pyri-
dine silver(I) bromide 6c (0.24 g, 0.05 mmol) was dissolved in
20 ml DCM, and PdCl2(CH3CN)2 (129.7 mg, 0.05 mmol) was added
to the solution of 6c. The mixture was stirred in the dark at room
temperature overnight. The solution was filtered to remove AgBr.
All volatiles were removed under vacuum. The yellow solid was
washed with ether (2 × 10 ml) and dried under vacuum. Yield:
75%, 180 mg. 1H NMR (500.1 MHz, DMSO-d6, 293 K): δ 1.15 (s,
CCH3, 3H), 4.22 (d, J = 14.5 Hz, NCH2CHCH2, 4H), 5.12–5.26 (m,
CCH3CH2, 4H), 5.57 (d, J = 14.5 Hz, NCH2CHCH2, 4H), 6.15 (m,
NCH2CHCH2, 2H), 7.21 (s, NCHCHN, 2H), 7.47 (s, NCHCHN, 2H), 7.4
(m, C5H4N, 1H), 7.77 (d, J = 8 Hz, C5H4N, 1H), 8.01 (t, J = 6 Hz,
Synthesis of 2-[1,3-bis(3-propenylimidazolidin-1-yl)-2-
methylpropan-2-yl]pyridine Rhodium(I) Cyclooctadiene
Chloride, 8c
Complex 8c was prepared from 2-[1,3-bis(3-propenylimidazolidin-
1-yl)-2-methylpropan-2-yl]pyridine bromide, 5c (0.51 g, 1 mmol),
KN(SiMe3)2 (0.4 g, 1 mmol) and [Rh(COD)Cl]2 (0.24 g, 0.5 mmol)
according to the method for 8a. A yellow solid was obtained
1
in 55% yield, 163 mg. H NMR (500.1 MHz, CDCl3, 293 K): δ 1.34
(s, CCH3, 6H), 1.63–2.3 (m, CHCH2, 8H), 4.2–4.6 (m, CCH3CH2, 4H,
NCH2CHCH2,4HandCHCH2,2H),5.65(d, J = 14.2 Hz,NCH2CHCH2,
4H), 5.85 (m, CHCH2, 2H), 6.90–7.45 (m, NCHCHN, 2H, C5H4N, 1H,
NCHCHN, 2H), 7.86 (m, C5H4N, 2H), 8.59 (d, J = 3.2 Hz, C5H4N, 1H)
1
C5H4N, 1H), 8.79 (d, J = 3.5 Hz, C5H4N, 1H) ppm. 13C{ H} NMR
(125.7 MHz, DMSO-d6, 293 K): δ 16.4, 44.5, 51.9, 59.6, 117.4, 118.1,
118.6, 120.0, 125.4, 134.1, 137.6, 148.9, 160.4, 163.1 ppm. CNHC
not observed. HR-MS (ES), m/z = 486.0851 [M − Cl]+ (calcd for
C21H2535ClN5104Pd: 486.0839).
1
ppm. 13C{ H} NMR (125.7 MHz, DMSO-d6, 293 K): δ 13.2, 16.6, 23.6,
26.0, 28.5, 44.3, 59.2, 66.0, 87.4, 88.9, 119.4, 122.8, 123.5, 125.8,
126.7, 135.9, 147.0, 161.0, 183.1 (d, J = 75 Hz) ppm. HR-MS (ES),
m/z = 558.2103 [M]+ (calcd for C29H37N5Rh: 558.2104).
Synthesis of 2-[2-Methyl-1,3-bis(3-methylimidazolidin-1-yl)
propan-2-yl]pyridine Rhodium(I) Cyclooctadiene Chloride, 8a
Synthesis of 2-[2-Methyl-1,3-bis(3-methylimidazolidin-1-yl)
propan-2-yl]pyridine Iridium(I) Cyclooctadiene Chloride, 9a
2-[2-Methyl-1,3-bis(3-methylimidazolidin-1-yl)propan-2-yl]pyri-
dine bromide, 5a (0.457 g, 1 mmol) and KN(SiMe3)2 (0.4 g, 1 mmol)
were placed into a Schlenk tube followed by the addition of THF
(10 ml). The solution was stirred for 2 h and subsequently filtered
into another Schlenk tube containing 10 ml of a THF solution of
2-[2-Methyl-1,3-bis(3-methylimidazolidin-1-yl)propan-2-yl]pyri-
dine bromide, 5a (0.457 g, 1 mmol) and KN(SiMe3)2 (0.4 g, 1 mmol)
were placed in a Schlenk tube followed by the addition of THF
(10 ml). The solution was stirred for 2 h and subsequently filtered
c
wileyonlinelibrary.com/journal/aoc
Copyright ꢀ 2011 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2011, 25, 374–382

Novel quasi-scorpionate ligand structures
into another Schlenk tube containing a 10 ml THF solution of
[Ir(COD)Cl]2 (335 mg, 0.5 mmol). An immediate color change was
observed from light orange to dark orange and after half an hour
orange solid formed. The reaction mixture was stirred at room
temperature for 2 h, and the volatiles were removed in vacuo. The
yellow solid obtained was washed with cold hexane (2 × 10 ml)
and dried under vacuum. Yield: 60%, 178 mg. The complex was
characterized by X-ray diffraction. 1H NMR (500.1 MHz, CDCl3,
293 K): δ 1.17 (s, CCH3, 3H), 1.9–2.4 (m, CHCH2, 8H), 3.36 (s, NCH3,
6H), 3.95 (d, J = 4.5 Hz, CHCH2, 2H), 4.1 (s, CCH3CH2, 4H), 5.4 (d,
J = 14.5 Hz, CHCH2, 2H), 7.02 (s, NCHCHN, 2H), 7.07 (s, NCHCHN,
2H), 7.27 (m, C5H4N, 1H), 7.61 (d, J = 8 Hz, C5H4N, 1H), 7.77 (t,
Table 3. Details of the crystal structure determinations for 8a and 9b
8a
9b
Empirical formula
Mr
C25H33ClN5Rh
541.93
150
C31H45BrIrN5
759.86
150
T (K)
λ (Å)
0.71073
Monoclinic
P21/a
0.71073
Triclinic
P-1
Crystal system
Space group
a (Å)
14.885(3)
13.167(3)
13.902(3)
90
14.109(3)
15.263(3)
16.214(3)
117.13(3)
90.52(3)
95.31(3)
3088.9(14)
4
b (Å)
c (Å)
1
J = 7.5 Hz, C5H4N, 1H), 8.58 (d, J = 1 Hz, C5H4N, 1H) ppm. 13C{ H}
α (deg)
β (deg)
γ (deg)
V (Å3)
NMR (125.7 MHz, CDCl3, 293 K), δ 17.1, 24.6, 27.0, 30.3, 36.9, 45.7,
59.6, 67.0, 74.9, 76.6, 118.9, 121.2, 121.6, 123.4, 127.7, 136.7, 148.1,
162.2, 177.8 ppm. HR-MS (ES), m/z = 594.2350 [M]+ (calcd for
C25H33N5Ir: 594.2342).
115.41(3)
90
2461.1(11)
4
Z
Dc (mg m−3
)
1.462
1.634
Synthesis of 2-[1,3-bis(3-butylimidazolidin-1-yl)-2-
methylpropan-2-yl]pyridine Iridium(I) Cyclooctadiene
Bromide, 9b
µ(MoKα) (mm−1
)
0.825
5.644
F000
1120
1512
Crystal dimensions (mm)
θ range (deg)
0.10 × 0.10 × 0.05 0.10 × 0.10 × 0.05
8–21
−13 ≤ h ≤ 12
0 ≤ k ≤ 12
0 ≤ l ≤ 14
3401
4–26
Complex 9b was prepared from 2-[1,3-bis(3-butylimidazolidin-
1-yl)-2-methylpropan-2-yl]pyridine bromide, 5b (0.54 g, 1 mmol),
KN(SiMe3)2 (0.4 g, 1 mmol) and [Ir(COD)Cl]2 (0.33 g, 0.5 mmol)
according to the method of 9a. Orange solid was obtained
in 60% yield, 200 mg. The complex was characterized by
X-ray diffraction. 1H NMR (400.1 MHz, CDCl3, 293 K): δ 0.99 (t,
J = 6 Hz, NCH2CH2CH2CH3, 6H), 1.15 (s, CCH3, 3H), 1.45–2.4 (m,
NCH2CH2CH2CH3, 8H and CHCH2, 8H), 3.87 (m, NCH2CH2CH2CH3,
4H), 4.05 (s, CCH3CH2, 4H), 4.1 (d, J = 12 Hz, CHCH2, 2H), 5.36
(d, J = 14 Hz, CHCH2, 2H), 7.0 (s, NCHCHN, 2H), 7.22 (s, NCHCHN,
2H), 7.27 (m, C5H4N, 1H), 7.78 (m, C5H4N, 1H), 7.8 (m, C5H4N,
Index ranges h, k, l
−17 ≤ h ≤ 17
−19 ≤ k ≤ 16
0 ≤ l ≤ 20
17730
Reflections measured
Unique reflections [Rint
]
2026 [0.054]
0.96, 0.92
2024/0/289
1.1528
12416 [0.058]
0.75, 0.57
Max, min trans.
Data/restraints/parameters
GOF on F2
12379/42/685
0.9728
R indices [F > 4σ(F)] R(F),
wR (F2)
0.074, 0.134
0.062, 0.133
1
1H), 8.55 (d, J = 4.4 Hz, C5H4N, 1H) ppm. 13C{ H} NMR (100.6 MHz,
R indices (all data) R(F), wR
(F2)
0.093, 0.141
0.089, 0.146
CDCl3, 293 K):δ 14.1, 18.7, 20.6, 30.1, 31.6, 31.8, 33.5, 47.1, 50.7, 61.0,
75.6, 77.7, 120.0, 120.9, 123.0, 125.7, 138.2, 149.3, 163.6, 178.2ppm.
HR-MS (ES), m/z = 680.3282 [M]+ (calcd for C31H45N5Ir: 680.3304).
Largest residual peak (e
0.74, −0.84
2.31, −2.10
Å−3
)
Synthesis of 2-[1,3-bis(3-propenylimidazolidin-1-yl)-2-
methylpropan-2-yl]pyridine Iridium(I) Cyclooctadiene
Chloride, 9c
Reaction progress was monitored by 1H NMR and GC-MS:
aliquots (0.1 ml) were taken every 3 or 5 min for the first hour, and
finally another two samples were taken after 2 h. The samples were
filteredthroughashortpadofsilica, andthesilicawaswashedwith
DCM (2×2 ml), and the sample subsequently analyzed. Yields and
substrateidentitiesweredeterminedbyGC-MSanalysisofreaction
mixtures using an Agilent Technologies 6890N GC system with
Agilent Technologies 5973 inert MS detector with MSD. Column:
Agilent 190915-433 capillary, 0.25 mm × 30 m × 0.25 µm. Initial
temperature, 50 ◦C, held for 4 min, ramp 5 ◦C min−1; then 100 ◦C,
ramp 10 ◦C min−1; then 240 ◦C held for 15 min. The temperature
of the injector and detector were held at 240 ◦C. The retention
times for analytes (minutes) were 4-bromoacetophenone 18.3 and
1-(4-bromophenyl)ethanol 18.7.
Complex 9c was prepared from 2-[1,3-bis(3-propenylimidazolidin-
1-yl)-2-methylpropan-2-yl]pyridine bromide, 5c (0.51 g, 1 mmol),
KN(SiMe3)2 (0.4 g, 1 mmol) and [Ir(COD)Cl]2 (0.33 g, 0.5 mmol)
accordingtothegeneralmethodfor9a.Orangesolidwasobtained
1
in 55% yield, 180 mg. H NMR (500.1 MHz, CDCl3, 293 K): δ 1.32
(s, CCH3, 6H), 1.63–2.3 (m, CHCH2, 8H), 4.0–4.22 (m, CCH3CH2, 4H
and NCH2CHCH2, 4H), 4.26 (d, J = 14.4 Hz, NCH2CHCH2, 2H), 5.34
(d, J = 14.4 Hz, NCH2CHCH2, 2H), 5.57 (m, CHCH2, 2H), 6.94 (d,
J = 8 Hz, CHCH2, 2H), 7.0 (s, NCHCHN, 2H), 7.27 (m, C5H4N, 1H),
7.44 (s, NCHCHN, 2H), 7.82 (m, C5H4N, 2H), 8.52 (d, J = 3.2 Hz,
1
C5H4N, 1H) ppm. 13C{ H} NMR (125.7 MHz, DMSO-d6): δ 11.6, 17.4,
27.0, 30.2, 45.9, 59.9, 75.6, 75.7, 77.2, 118.8, 119.8, 121.6, 123.6,
125.7, 137.0, 147.7, 162.0, 179.4 ppm. HR-MS (ES), m/z = 648.2676
[M]+ (calcd for C31H45N5Ir: 648.2678).
Crystallographic Studies
Crystal data and details of the structure determinations are listed
in Table 3. Intensity data were collected at low temperature with
an Enraf-Nonius Kappa CCD diffractometer. Data were corrected
for air and detector absorption, Lorentz and polarization effects;
absorption by the crystal was treated with a semiempirical multi-
scan method. The structures were solved by direct methods and
refined by full-matrix least squares methods based on F2 against
Catalytic Transfer Hydrogenation
The Ir/Rh catalyst precursor (1, 0.3, 0.01 mol%) was dissolved in
a solution of KtBuO (10 mmol) in 2-propanol (5 ml) and substrate
(1 mmol) in a Schlenk tube. The solution was heated to 80 ◦C for
30 min, the final conversion being determined by 1H NMR.
c
Appl. Organometal. Chem. 2011, 25, 374–382
Copyright ꢀ 2011 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

S. Yasar et al.
all unique reflections (8a). Owing to unsatisfactory refinement,
the structure of 9b was refined against all data with I > −5σ(I).
All non-hydrogen atoms were given anisotropic displacement pa-
rameters. Hydrogen atoms were input at calculated positions and
were refined with the riding model.
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Acknowledgments
¨
We would like to thank the EPSRC and TUBYTAK, Turkey (DB2219,
postdoctoral fellowship for S. Y.) for funding this work. We would
also like to thanks Johnson Matthey for the loan of precious
metals.
[12] For example: a) V. Lavallo, Y. Canac, C. Prasang, B. Donnadieu,
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Angew Chem., Int. Ed. 2006, 45, 3488; e) V. Lavallo, Y. Canac,
B. Donnadieu, W. W. Schoeller, G. Bertrand, Science 2006, 312, 722R;
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Supporting information
Supporting information may be found in the online version of this
article.
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