Rhodium and iridium complexes with chelating C-C′-imidazolylidene- pyridylidene ligands: Systematic approach to normal, abnormal, and remote coordination modes

Article abstract of DOI:10.1021/om3005096

A series of linked imidazolium-pyridinium salts ([Him-pyH](X)₂) have been used as imidazolylidene-pyridylidene ligand precursors for the preparation of rhodium(III) and iridium(III) complexes. The relative configuration of the [Him-pyH](X)₂ salts determines whether the coordination of the pyridylidene occurs through the normal, abnormal, or remote form. In order to obtain complexes with the imidazolylidene part of the ligand coordinated through the abnormal form, salts with the C2 position of the imidazolium blocked with a methyl group were used, although the products resulting from the C-H aliphatic activation of the methyl group or the C-C cleavage of the C2-Me bond were obtained instead. The crystallographic study of three molecules allowed us to evaluate the relative trans influence of the normal, abnormal, and remote coordination forms of the pyridylidene and also to compare it to the trans influence provided by the imidazolylidene.

Full text of DOI:10.1021/om3005096

Article
pubs.acs.org/Organometallics
Rhodium and Iridium Complexes with Chelating C−C′-
Imidazolylidene−Pyridylidene Ligands: Systematic Approach to
Normal, Abnormal, and Remote Coordination Modes
Candela Segarra, Elena Mas-Marza,* Jose A. Mata, and Eduardo Peris*
́
́
́ ́ ́
Departamento de Química Inorganica y Organica, Universitat Jaume I, Avenida Vicente Sos Baynat s/n, Castellon E-12071, Spain
S
* Supporting Information
ABSTRACT: A series of linked imidazolium−pyridinium salts
([Him-pyH](X)2) have been used as imidazolylidene−
pyridylidene ligand precursors for the preparation of rhodium-
(III) and iridium(III) complexes. The relative configuration of
the [Him-pyH](X)2 salts determines whether the coordination
of the pyridylidene occurs through the normal, abnormal, or
remote form. In order to obtain complexes with the
imidazolylidene part of the ligand coordinated through the
abnormal form, salts with the C2 position of the imidazolium
blocked with a methyl group were used, although the products
resulting from the C−H aliphatic activation of the methyl
group or the C−C cleavage of the C2−Me bond were
obtained instead. The crystallographic study of three molecules allowed us to evaluate the relative trans influence of the normal,
abnormal, and remote coordination forms of the pyridylidene and also to compare it to the trans influence provided by the
imidazolylidene.
ligands with novel stereoelectronic properties, we found it
interesting that only a very few examples of linked
imidazolylidene (or triazolylidene)−pyridylidenes have been
described so far.9−11 Interestingly, the strong σ-donor proper-
ties of this type of ligand have been used for the preparation of
iridium(III) complexes with excellent activity in catalytic water
oxidation,11 thus exemplifying the interesting potential
applications of these ligands.
In response to the above background we sought to make and
investigate the chemistry of transition metal complexes
incorporating linked imidazolylidene−pyridylidene (C,C′-im-
py) ligands, in which the relative configuration of the
imidazolium−pyridinium ligand precursors facilitates the
systematic coordination of the chelate ligand in all possible
combinations of normal, abnormal, and remote modes
(Scheme 1). We herein report the systematic preparation and
full characterization of a series of Ir and Rh complexes with a
full set of chelate C,C′-im-py ligands. All complexes are
obtained by a base-free C−H activation route under mild
reaction conditions. The molecular structures of three
representative complexes are also described.
INTRODUCTION
■
The coordination chemistry of N-heterocylic carbenes (NHCs)
has experienced an explosive development in the past few years
not only due to the extremely large number of their catalytic
applications1,2 but also due to the easy access to a large library
of ligands with almost “on-demand” stereoelectronic proper-
ties.2,3 Azolium salts are often found to be excellent NHC
precursors because they are generally easy to make and they
provide a variety of topologies that may facilitate the
preparation of metal complexes with different architectures.
This versatility comes not only from the different structures
available from the NHC precursors but also from the
coordination modes that these preligands can afford depending
on whether the “expected” (normal) or “unexpected”
(abnormal) coordination modes may occur. Since Crabtree
and co-workers described for the first time the abnormal (or
C4) coordination of imidazolium-based NHCs, the number of
such types of “wrong way”, “unusual”, or “nonclassical”
imidazolylidenes has enormously increased.4,5 Abnormal
carbenes not only are limited to imidazolylidenes or other
five-membered ring NHCs but are also easy to find in pyridine-
based NHCs, where remote carbenes (without a heteroatom
adjacent to the carbene carbon) are also accessible.4,6,7 Because
the chemical functionalization of imidazoles and pyridines is
very well established, both imidazolylidenes and pyridylidenes
can be connected to a variety of functionalities that allow them
to be embedded in chelating environments.4,8 With NHC
chemistry in continuous growth, and with the increasing
interest in finding new coordination modes that can facilitate
RESULTS AND DISCUSSION
The [Him-pyH](X)2 salts were prepared by a two-step
procedure implying the Ullmann coupling of the imidazole to
■
Received: June 8, 2012
Published: July 5, 2012
© 2012 American Chemical Society
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a
Scheme 1. Imidazolium−Pyridinium Salts Used in This Work
a
Arrows indicate the potential coordination sites.
Scheme 2
the 3- or 4-bromopyridine, followed by addition of an excess of
MeI (or nBuI, in the case of 1-nBu). Anion metathesis in
methanol with ammonium hexafluorophosphate allowed the
precipitation of the [Him-pyH](PF6)2 salt, in the case of [1-
Me](PF6)2. Because, in general, pyridiniums are considered less
acidic than imidazoliums, we reasoned that all salts 1−4 should
first coordinate to the metal via the imidazole ring and then
facilitate the pyridinium C−H activation at the ortho position
by chelation assistance.
The reaction of 1 with [MCl(COD)]2 (M = Rh, Ir) in
acetonitrile in the presence of an excess of KI affords the
corresponding [(C,C′-im-py)MIIII2(CH3CN)2]+ complexes, in
which the pyridylidene unequivocally coordinates to the metal
center through the para carbon atom, affording the remote
coordination mode rather than the coordination through the
carbon adjacent to the nitrogen atom. This selectivity is
remarkable, especially if we consider that previous studies with
N-butyl-3-(2-pyridyl)pyridinium iodide show that the reactions
with [IrCl(COD)]2 afford a mixture of two complexes,
probably due to the presence of the two possible carbene
types.12 Scheme 2 displays the preparation of complexes 5 and
6 as iodide salts. The hexafluorophosphate analogues were also
obtained starting from [1-Me](PF6)2. All yields were above
50%.
and not for the iodides. The reason for this may be due to the
high trans effect provided by the pyridylidene, which facilitates
the rapid exchange between the CH3CN ligand trans to the
metalated pyridine and the iodide counterion, an effect that
cannot be produced with a noncoordinating anion such as
hexafluorophosphate. The signals due to the pyridylidene
carbene carbons display a big difference depending on whether
the remote pyridylidene is coordinated to rhodium or iridium,
as seen by the resonances at δ 183.9 (d, 1JRh−C = 28 Hz) for the
rhodium complex 5 and at δ 164.7 and 164.8 for the iridium
compounds 6-Me and 6-nBu, respectively. This almost 20 ppm
shift is also displayed for the signals attributed to the carbene
carbons of the imidazolylidene, which appear at δ 167.4 (d,
1JRh−C = 43 Hz) for 5 and at δ 149.3 and 149.4 for 6-Me and 6-
nBu, respectively. These findings should not be considered as
surprising, if we take into account similar chemical shift
differences for the same type of coordinated imidazolylidene
(or triazolylidene)−pyridylidene complexes of iridium10,11 and
rhodium.9
When 1 reacts with [RhCl(NBD)]2 in acetonitrile in the
presence of an excess of KI, under exactly the same reaction
conditions as those used for the preparation of 5, a new Rh(III)
complex with the normal coordination of the pyridylidene is
obtained as the only isolable product, in 66% yield (compound
7 in Scheme 2). The normal coordination of the pyridylidene is
confirmed by the hyperfine structure of the signals due to the
pyridine ring in the 1H NMR spectrum. The 13C NMR
spectrum shows the signal due to the carbene carbon atom of
the pyridylidene as a doublet at 175.7 ppm (1JRh−C = 36 Hz),
while the doublet due to the carbene carbon atom of the
Compounds 5 and 6 were characterized by NMR spectros-
copy, elemental analysis, and mass spectrometry. The
assignation of the remote coordination of the pyridylidene
can be easily determined by the evaluation of the hyperfine
structure of the signals attributed to the protons of the pyridine
ring in the corresponding 1H NMR spectra. The most
representative 13C NMR signals are the ones attributed to the
metalated carbons. It is important to point out that for all the
rhodium complexes reported in this work the 13C NMR
chemical shifts attributed to the carbene carbon of the
1
imidazolylidene appears at 162.7 (d, JRh−C = 42 Hz).
The preparation of the rhodium and iridium complexes with
the chelate C,C′-im-py ligands in which the pyridylidene is
bound by the abnormal position could be achieved by using the
[Him-pyH]2(I)2 salt 3 (Scheme 3). For the reactions with
−
pyridylidene could be observed only for the PF6 derivatives
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Scheme 3
Scheme 4
[MCl(COD)]2 (M = Rh, Ir), the expected M(III) complexes
with the abnormal coordination of the pyridylidene were
obtained in moderate yields (above 50%). Again, the
coordination of the chelate ligand and the type of coordination
of the pyridylidene can be unambiguously determined by NMR
spectroscopy. The 13C NMR spectra display the resonance due
to the carbene carbon of the pyridine ring at δ 169.3 (d, 1JRh−C
= 47 Hz) for 8 and δ 160.8 for 9. The signals assigned to the
carbene carbon of the imidazolylidene are shown at δ 139.6 (d,
1JRh−C = 34 Hz) and δ 152 for 8 and 9, respectively.
In order to facilitate the coordination of the imidazolylidene
by an abnormal coordination mode, we decided to use one
[Him-pyH]2(I)2 salt with the C2 position of the imidazolium
blocked with one methyl group (2, in Scheme 4). This strategy
for the preparation of C4-bound imidazolylidenes has been
successfully used previously.13−15 While the reaction of 2 with
[RhCl(COD)]2 afforded mixtures of compounds that we were
unable to indentify, the reaction with [IrCl(COD)]2 allowed
the formation in good yield (65%) of an iridium(III) complex,
in which the chelate ligand is coordinated through the
pyridylidene and a methylene group resulting from the C−H
activation of the C2-Me group at the imidazolium ring (10,
Scheme 4). Although this was not our expected result, we may
rationalize this result as a consequence of the kinetic preference
of the aliphatic (methyl) C−H activation over the aromatic
(imidazole) one in the formation of methylene-bound versus
abnormally bound imidazoliums, as we have previously
described.15 In our case this observation can also be supported
by the kinetic preference for the formation of a seven-
membered iridacycle versus the themodynamic preference for
the formation of a six-membered iridacycle, as previously
described for the reactions of [IrCl(COD)]2 with C2-
substituted imidazoliums.16
In order to prepare complexes with the bis-abnormally
bound C,C′-im-py ligand, we decided to use the [Him-pyH](I)2
salt 4, which differs from 3 by the presence of a methyl group
blocking the C2 position of the imidazolium ring. Surprisingly,
when the reaction between 4 and [MCl(COD)]2 (M = Rh, Ir)
is carried out under similar reaction conditions to those
described for the coordination of 1−3, we obtained compounds
8 and 9, as the only isolable products (Scheme 3), although this
time the yields were low (20−24%). This unexpected C−C
cleavage in the metalation of C2-substituted imidazoliums was
first described by Crabtree for reactions implying silver oxide,14
and we are unaware of any other similar examples of such type
of process regarding any other transition metals. Very recently
Albrecht and co-workers described that the demethylation of a
C2-Me-substituted imidazolium may take place in the presence
of CsOH, forming a cyclic urea,17 which actually supports the
idea previously reported by Crabtree that this demethylation
may take place via an initial four-electron oxidation of the
imidazolium 2-methyl to give a 2-formyl ion, followed by the
hydrolytic cleavage to give the NHC,14 in our case trapped by
the rhodium or iridium centers. Although we have not studied
the fate of the leaving methyl group, we believe that these two
previous studies may give some important mechanistic
clues.14,17 Crabtree suggested that 2-Me can be an unreliable
blocking group for imidazolium/Ag2O,14 but our results widen
the warning to other transition metals such as Rh and Ir. While
this C−C cleavage at the C2-substituted imidazolium is rare,
there are many examples in which C2−H or C2−X (X = I, Cl)
activations are observed.18
The molecular structures of 6-nBu, 7, 8, and 10 were
confirmed by means of X-ray diffraction studies. Unfortunately,
the molecular structure of complex 7 presents some disorder
due to the presence of two molecules with a different
orientation of the C,C′-im-py ligand, so an averaged structure,
not suitable for a detailed analysis, was obtained. The
crystallographic data of complex 7 can be found in the
Supporting Information of this article.
Compound 10 was characterized by NMR spectroscopy,
elemental analysis, and mass spectrometry. The remote
coordination of the pyridylidene can be easily confirmed by
looking at the pattern of the resonances coming from the
pyridylidene ring. The 13C NMR spectrum shows significant
signals at 168.9 (carbene carbon) and −25.5 (metalated
methylene) ppm.
The molecular structure of 6-nBu (Figure 1) displays a
pseudo-octahedral arrangement about the iridium center. Two
iodide ligands in a relative trans configuration occupy the axial
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Figure 1. Molecular diagram of complex 6-nBu. Ellipsoids are at the
50% probability level. Hydrogens and counterion (iodide) are omitted
for clarity. Selected bond lengths [Å] and angles [deg]: Ir(1)−I(1)
2.6585(4), Ir(1)−C(1) 1.981(5), Ir(1)−I(2) 2.6610(4), Ir(1)−N(4)
2.086(4), Ir(1)−N(5) 2.122(5), Ir(1)−C(8) 1.989(5), I(1)−Ir(1)−
I(2) 177.548(14), C(1)−Ir(1)−C(8) 79.7(2).
Figure 3. Molecular diagram of complex 10. Ellipsoids are at the 50%
probability level. Hydrogens, counterion (iodide), and solvent
(acetonitrile) are omitted for clarity. Selected bond lengths [Å] and
angles [deg]: Ir(1)−I(2) 2.6608(7), Ir(1)−I(3) 2.6881(6), Ir(1)−
N(2) 2.102(6), Ir(1)−N(4) 2.111(8), Ir(1)−C(5) 2.003(7), Ir(1)−
C(7) 2.083(8), I(2)−Ir(1)−I(3) 178.00(2), C(5)−Ir(1)−C(7)
89.0(3).
axis of the molecule. A chelate C,C′-im-py ligand and two
acetonitriles complete the coordination sphere. The pyridyli-
dene is coordinated to the metal via the remote form. The Ir−
Cimz and Ir−Cpyr distances are 1.981 and 1.989 Å, respectively.
The structure provides an excellent opportunity to evaluate the
relative trans influence of the two different carbene ligands
within the same molecule, by comparing the Ir−N distances of
the acetonitriles trans to the imidazolylidene (2.086 Å) and to
the pyridylidene (2.122 Å), therefore suggesting the stronger
trans influence of the latter one.
iodides occupying a transoid disposition (I(2)−Ir(1)−I(3) =
178.00°). The structure confirms that the chelate ligand is
coordinated through the remote position of the pyridylidene
and the methylene group at the C2 position of the imidazolium,
forming a distorted six-membered iridacycle. The chelate bite
angle is 89.0°. The Ir−N distance of the acetonitrile trans to the
remote pyridylidene is 2.102 Å, similar to that found for the
analogous bond in 6-nBu.
The evaluation of the NMR spectroscopy and crystallo-
graphic data of the complexes described in this work reveal
some features that are worth mentioning. With regard to the
13C NMR spectroscopy, we observed that the resonances due
to the carbene carbons of the pyridylidenes decrease in the
order
Figure 2 shows the molecular structure of complex 8. The
molecule consists of a distorted octahedral structure with two
Rhodium: remote (δC = 183.9) > normal (δC = 175.7)
> abnormal (δC = 169.3)
Iridium: remote (δC = 164.7) > abnormal (δC = 160.8)
This trend is along the same lines as that found by Albrecht
and co-workers for a series of palladium complexes with
normal, abnormal, and remote pyridylidenes.7 When these 13C
NMR resonances of the coordinated carbenes are compared to
the corresponding resonances in the precursor pyridiniums, it is
observed that abnormal bonding induces the smallest chemical
shift difference.
Figure 2. Molecular structure of compound 8. Ellipsoids are at the
50% probability level. Hydrogens and counterion (iodide) are omitted
for clarity. Selected bond lengths [Å] and angles [deg]: Rh(1)−I(2)
2.6666(6), Rh(1)−I(3) 2.6504(6), Rh(1)−N(18) 2.096(5), Rh(1) −
C(11) 1.995(6), Rh(1)−C(4) 1.962(6), Rh(1)−N(21) 2.127(5),
I(3)−Rh(1)−I(2) 177.99(2), C(4)−Rh(1)−C(11) 79.6(2).
On the basis of bond length analyses of the crystal structures
that we have described in this work, we can clearly state that
pyridylidenes provide a larger trans influence than imidazoly-
lidenes. By comparing the bond lengths of a series of Pd and Ni
complexes with different pyridylidenes and imidazolylidenes, it
was previously stated that remote pyridylidenes exhibit larger
trans influence than imidazolylidenes.19,20 It was also suggested
that carbene ligands with remote heteroatoms display a greater
trans influence than those with the N atom adjacent to the
carbene carbon.20 However, we did not find any studies in
which a clear comparison between remote and abnormal
pyridylidenes was made. By evaluating the bond distances of
complexes 6-nBu and 8, we can now confirm that both
transoid iodides. The chelate C,C′-im-py ligand is coordinated
through the abnormal position of the pyridylidene and forms a
five-membered rhodacycle, with a chelate bite angle of 79.6°.
The Ir−Cimz and Ir−Cpyr distances are 1.962 and 1.995 Å,
respectively. Again, the structure offers a good opportunity to
evaluate the relative trans influence of the two types of
carbenes, by comparing the Rh−N distances of the acetonitriles
trans to the imidazolylidene (2.096 Å) and pyridylidene (2.127
Å), therefore confirming the stronger trans influence of the
latter one.
The molecular structure of 10 is shown in Figure 3. The
molecule consists of a distorted octahedral structure with two
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dide precipitated in the reaction media as a pale yellow solid. The
compound was isolated by filtration, washed with diethyl ether (3 × 5
mL), and dried under vacuum. Yield: 4.90 g (71%). For 1-(3′-
pyridyl)imidazole: 1H NMR (500 MHz, DMSO-d6, 303 K): δ 8.95 (s,
abnormal and remote pyridylidenes provide a larger trans
influence that normal imidazolylidenes. Although the remotely
bound complex 6-nBu and the abnormally bound compound 8
contain different metals (iridium and rhodium, respectively),
we can estimate the relative trans influence between these two
types of pyridylidenes by comparing with the trans influence
provided by the imidazolylidene in each complex. In this regard,
the Ir−N bond distance of the acetonitrile trans to the remote
pyridylidene is larger by 1.7% than the Ir−N distance of the
acetonitrile trans to the imidazolylidene in complex 6-nBu. The
analogous comparison for the Rh−N distances in complex 7
affords a similar bond length increase (1.5%), which may be
interpreted as a consequence of a similar trans influence
provided by the remote and abnormal pyridylidenes.
3
1H, CHpyr), 8.57 (d, JHH = 4 Hz, 1H, CHpyr), 8.35 (s, 1H, CHimz),
8.11 (d, 3JHH = 8 Hz, 1H, CHpyr), 7.84 (s, 1H, CHimz), 7.57 (dd, 3JHH
=
3
4 Hz, JHH = 8 Hz, 1H, CHpyr), 7.16 (s, 1H, CHimz). For [1-(3′-(1′-
methylpyridiniumyl)-3-methyl]imidazolium diiodide: 1H NMR
(500 MHz, DMSO-d6, 303 K): δ 9.94 (s, 1H, CHpyr), 9.72 (s, 1H,
3
3
CHimz), 9.18 (d, JHH = 6 Hz, 1H, CHpyr), 8.97 (d, JHH = 8 Hz, 1H,
3
3
CHpyr), 8.46 (dd, JHH = 6 Hz, JHH = 8 Hz, 1H, CHpyr), 8.35 (s, 1H,
CHimz), 8.06 (s, 1H, CHimz), 4.45 (s, 3H, CH3pyr), 4.03 (s, 3H,
CH3imz). 13C{1H} NMR (125 MHz, DMSO-d6, 303 K): δ 145.9, 140.5,
138.0, 137.3, 133.6, 128.2, 124.9, 121.1 (s, CHimz, Cpyr and CHpyr), 48.7
(s, CH3pyr), 36.7 (s, CH3imz). ESI-MS (20 V, CH3OH): m/z 174.1 [M
− 2I − H]+, m/z 87.8 [M − 2I]2+. Anal. Found (calcd) for
C10H13N3I2: C, 28.43 (27.99); H, 2.75 (3.05); N, 9.50 (9.79).
CONCLUSIONS
Synthesis of [1-(3′-(1′-Methylpyridiniumyl)-3-methyl]-
imidazolium Di(hexafluorophosphate), [1-Me](PF6)2. NH4PF6
(1.14 g, 7 mmol) was added slowly to a solution of 1-Me (1.00 g,
2.33 mmol) in methanol (25 mL). The mixture was stirred at room
temperature for 2 h. During this time [1-Me](PF6)2 precipitated in the
reaction media as a colorless solid. The compound was isolated by
filtration, washed with cold methanol (3 × 5 mL) and diethyl ether (3
× 5 mL), and dried under vacuum. Yield: 0.83 g (77%). 1H NMR (500
MHz, DMSO-d6, 303 K): δ 9.95 (s, 1H, CHpyr), 9.73 (s, 1H, CHimz),
■
In this work we have shown the systematic preparation of the
series of imidazolylidene−pyridylidene complexes of rhodium-
(III) and iridium(III) with the three possible types of
coordination of the pyridylidene (normal, abnormal, and
remote). Attempts to obtain analogous complexes with the
abnormal coordination of the imidazolylidene by using a C2-
Me-substituted imidazolium resulted in the aliphatic C−H
activation of the methyl group, affording the methylene-bound
imidazolium, or C−C bond cleavage, affording the demethy-
lated products, which are similar to the products obtained when
nonsubstituted imidazoliums were used. Although the aliphatic
C−H activation of the methyl group in C2-Me-substituted
imidazoliums has already been described for iridium and
rhodium complexes,15,16 this is the first time that the
demethylation is observed for these two metals. In any case,
the difficulties in achieving the abnormal coordination of the
imidazolylidene when a pyridylidene is bound to the metal are
remarkable and may deserve further studies.
3
3
9.18 (d, JHH = 6 Hz, 1H, CHpyr), 8.97 (d, JHH = 8 Hz, 1H, CHpyr),
3
3
8.45 (dd, JHH = 6 Hz, JHH = 8 Hz, 1H, CHpyr), 8.35 (s, 1H, CHimz),
8.05 (s, 1H, CHimz), 4.45 (s, 3H, CH3pyr), 4.02 (s, 3H, CH3imz).
13C{1H} NMR (125 MHz, DMSO-d6, 303 K): δ 146.1, 140.6, 138.2,
137.4, 133.9, 128.3, 125.1, 121.2 (s, CHimz, Cpyr and CHpyr), 48.7 (s,
CH3pyr), 36.7 (s, CH3imz). ESI-MS (20 V, CH3OH): m/z 174.1 [M −
2(PF)6 − H]+, m/z 87.7 [M − 2(PF6)]2+. Anal. Found (calcd) for
C10H13N3P2F12: C, 26.13 (25.82); H, 2.93 (2.82); N, 9.31 (9.03).
Synthesis of [1-(3′-(1′-n-Butylpyridiniumyl)-3-n-butyl]-
imidazolium Diiodide, 1-nBu. The same procedure and quantities
as compound 1-Me were used, except with the use of 1-iodobutane
(5.5 mL, 48 mmol). Yield: 4.0 g (50%). 1H NMR (500 MHz, DMSO-
d6, 303 K): δ 10.06 (s, 1H, CHpyr), 9.84 (s, 1H, CHimz), 9.31 (d, 3JHH
=
The evaluation of the crystal structures of complexes 6-nBu,
8, and 10 allows us to evaluate the relative trans influence of the
pyridylidene and the imidazolylidene. Both remote and
abnormal coordinations of the pyridylidene provide similar
trans influence, this being larger than the one provided by the
imidazolylidene.
6 Hz, 1H, CHpyr), 9.04 (d, 3JHH = 8 Hz, 1H, CHpyr), 8.50 (dd, 3JHH = 6
Hz, 3JHH = 8 Hz, 1H, CHpyr), 8.45 (s, 1H, CHimz), 8.18 (s, 1H, CHimz),
3
3
4.72 (t, JHH = 7 Hz, 2H, CH2pyr), 4.35 (t, JHH = 7 Hz, 2H, CH2imz),
2.01 (m, 2H, CH2CH2pyrCH2), 1.90 (m, 2H, CH2CH2imzCH2), 1.36
(m, 4H, CH2CH3), 0.94 (t, JHH = 7 Hz, 6H, CH3). 13C{1H} NMR
3
(125 MHz, DMSO-d6, 303 K): δ 145.0, 139.6, 138.4, 136.7, 134.4,
128.5, 123.7, 121.5 (s, CHimz, Cpyr and CHpyr), 61.4 (s, CH2pyr), 49.5 (s,
CH2imz), 32.2 (s, CH2CH2pyrCH2), 30.9 (s, CH2CH2imzCH2), 18.7 (s,
CH2pyrCH3), 18.6 (s, CH2imzCH3), 13.3 (s, CH3pyr), 13.2 (s, CH3imz).
ESI-MS (20 V, CH3OH): m/z 202.1 [M − 2I − nBu]+, m/z 258.0 [M
− 2I − H]+. Anal. Found (calcd) for C16H25N3I2: C, 37.67 (37.45); H,
5.02 (4.91); N, 8.03 (8.19).
EXPERIMENTAL SECTION
■
General Procedures. All manipulations were performed under a
nitrogen atmosphere using standard Schlenk techniques. Solvents and
reagents are commercially available and were used as received from
commercial suppliers. NMR spectra were recorded on Varian Innova
300 and 500 MHz spectrometers, using CDCl3, CD3CN, and DMSO-
d6 as solvents (Merck and Aldrich). Elemental analyses were carried
out in an EA 1108 CHNS-O Carlo Erba analyzer. Electrospray mass
spectra (ESI-MS) were recorded on a Micromass Quattro LC
instrument, and nitrogen was employed as drying and nebulizing
gas. A solution of leucine enkephalin (m/z = 556.2771) was employed
Synthesis of [1-(3′-(1′-Methylpyridiniumyl)-2,3-dimethyl]-
imidazolium Diiodide, 2. A 50 mL Schlenk flask was charged
with 2-methylimidazole (1.04 g, 12.66 mmol), 3-bromopyridine (0.61
mL, 6.33 mmol), CuSO4 (40 mg, 0.25 mmol), and K2CO3 (1.31 g,
9.49 mmol). The reaction mixture was heated for 48 h to 185 °C
under a nitrogen atmosphere. The reaction mixture was then allowed
to cool to room temperature, and the resulting brown solid was
dissolved in 50 mL of H2O and extracted with ethyl acetate, to obtain
1-(3′-pyridyl)-2-methylimidazole and unreacted 2-methylimidazole.
This mixture, without further purification, was refluxed with
iodomethane (1.18 mL, 19 mmol) in CH3CN (20 mL) for 24 h.
During this time [1-(3′-(1′-methylpyridiniumyl)-2,3-dimethyl]-
imidazolium diiodide precipitated in the reaction media as a pale
yellow solid. The compound was isolated by filtration, washed with
ether (3 × 5 mL), and dried under vacuum. Yield: 1.12 g (35%). For
as standard. [IrCl(COD)]2,21 [RhCl(COD)]2,22 and [RhCl(NBD)]2
23
were prepared according to literature procedures.
Synthesis of [1-(3′-(1′-Methylpyridiniumyl)-3-methyl]-
imidazolium Diiodide, 1-Me. Imidazole (2.18 g, 32 mmol), 3-
bromopyridine (1.54 mL, 16 mmol), CuSO4 (100 mg, 0.60 mmol),
and K2CO3 (2.95 g, 21 mmol) were heated in a 50 mL Schlenk flask at
150 °C for 48 h under a nitrogen atmosphere. After this time, the
reaction mixture was cooled to room temperature, and the resulting
brown solid was dissolved in 50 mL of H2O and extracted with ethyl
acetate to obtain 1-(3′-pyridyl)imidazole and unreacted imidazole.
This mixture, without further purification, was refluxed with
iodomethane (3 mL, 48 mmol) in CH3CN (20 mL) for 24 h. During
this time [1-(3′-(1′-methylpyridiniumyl)-3-methyl]imidazolium diio-
1
1-(3′-pyridyl)-2-methylimidazole: H NMR (300 MHz, CDCl3, 303
K): δ 8.67 (m, 1H, CHpyr), 8.62 (m, 1H, CHpyr), 7.65 (m, 1H, CHpyr),
7.45 (m, 1H, CHpyr), 7.07 (d, 3JHH = 1.5 Hz, 1H, CHimz), 7.02 (d, 3JHH
= 1.5 Hz, 1H, CHimz), 2.37 (s, 3H, C−CH3imz). For [1-(3′-(1′-
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1
methylpyridyl)-2,3-dimethyl]imidazolium diiodide: H NMR (300
MHz, DMSO-d6, 303 K): δ 9.54 (s, 1H, CHpyr), 9.24 (d, 3JHH = 6 Hz,
Synthesis of Compound [5]PF6. The same procedure and
quantities as compound 5 were used, except with the use of [1-(3′-(1′-
methylpyridiniumyl)-3-methyl]imidazolium di(hexafluorophosphate)
([1-Me](PF6)2; 94 mg, 0.2 mmol). The compound was purified by
column chromatography. Elution with CH2Cl2 separated a yellow
band containing [RhCl(COD)]2. Further elution with CH2Cl2/
CH3CN (9:1) afforded the separation of an orange band that
contained compound [5]PF6. Compound [5]PF6 was obtained as an
orange solid by precipitation from CH3CN/Et2O. Yield: 85 mg (56%).
3
3
1H, CHpyr), 8.86 (d, JHH = 8 Hz, 1H, CHpyr), 8.43 (dd, JHH = 8 Hz,
3JHH = 6 Hz, 1H, CHpyr), 8.01 (d, 3JHH = 2.4 Hz, 1H, CHimz), 7.95 (d,
3JHH = 2.4 Hz, 1H, CHimz), 4.44 (s, 3H, CH3pyr), 3.90 (s, 3H, CH3imz),
2.67 (s, 3H, C−CH3imz). 13C{1H} NMR (75 MHz, DMSO-d6, 303 K):
δ 146.7, 146.5, 144.3, 142.6, 133.6, 128.4, 123.4, 122.0 (s, Cimz, CHimz
,
Cpyr and CHpyr), 48.6 (s, CH3pyr), 35.5 (s, CH3imz), 11.1 (s, C-CH3imz).
ESI-MS (20 V, CH3OH): m/z 94.5 [M − 2I]2+. Anal. Found (calcd)
for C11H15N3I2: C, 29.67 (29.82); H, 3.19 (3.41); N, 9.42 (9.48).
Synthesis of [1-(4′-(1′-Methylpyridiniumyl)-3-methyl]-
imidazolium Diiodide, 3. Imidazole (0.70 g, 10.28 mmol), 4-
bromopyridine hydrochloride (1.00 g, 5.14 mmol), CuSO4 (32.8 mg,
0.21 mmol), and K2CO3 (2.13 g, 15.43 mmol) were heated in a 50 mL
Schlenk flask at 185 °C for 72 h under a nitrogen atmosphere. After
this time, the reaction mixture was cooled to room temperature, and
the resulting brown solid was dissolved in 50 mL of H2O and extracted
with ethyl acetate, to obtain 1-(4′-pyridyl)imidazole and unreacted
imidazole. This mixture, without further purification, was refluxed with
1-iodomethane (1 mL, 15,42 mmol) in CH3CN (20 mL) for 24 h.
During this time [1-(4′-(1′-methylpyridiniumyl)-3-methyl]imidazolium
diiodide precipitated in the reaction media as a yellow solid. The
compound was isolated by filtration, washed with ether (3 × 5 mL),
and dried under vacuum. Yield: 1.17 g (53%). For 1-(4′-pyridyl)-
3
1H NMR (300 MHz, CD3CN, 303 K): δ 8.42 (d, JHH = 6 Hz, 1H,
CHpyr), 8.34 (s, 1H, CHpyr), 7.87 (d, 3JHH = 6 Hz, 1H, CHpyr), 7.80 (d,
3
3JHH = 2 Hz, 1H, CHimz), 7.34 (d, JHH = 2 Hz, 1H, CHimz), 4.22 (s,
3H, CH3pyr), 3.99 (s, 3H, CH3imz). 13C{1H} NMR (75 MHz, CD3CN,
303 K): δ 183.9 (d, 1JRh−C = 28 Hz, Rh-Cpyr), 167.4 (d, 1JRh−C = 43 Hz,
Rh-Cimz), 147.5 (s, Cpyr), 136.9 (s, CHpyr), 136.4 (s, CHpyr), 127.0 (s,
CHimz), 124.8 (s, CHpyr), 117.2 (s, CHimz), 47.8 (s, CH3pyr), 38.3 (s,
CH3imz). ESI-MS (20 V, CH3CN): m/z 570.9 [M − PF6 − CH3CN]+,
m/z 529.9 [M − PF6 − (CH3CN)2]+. Anal. Found (calcd) for
C14H17N5I2RhPF6: C, 22.43 (22.21); H 2.25 (2.26); N 9.43 (9.25).
Synthesis of Compound 6-Me. A mixture of [1-(3′-(1′-
methylpyridiniumyl)-3-methyl]imidazolium diiodide (1-Me; 64 mg,
0.15 mmol), [IrCl(COD)]2 (50 mg, 0.075 mmol), and KI (25 mg,
0.15 mmol) was dissolved in CH3CN (50 mL) and stirred for 12 h at
65 °C. After cooling to room temperature, the reaction mixture was
filtered over Celite, and all volatiles were removed under reduced
pressure. The crude solid was purified by column chromatography.
Elution with CH2Cl2 separated a minor red band containing
[IrCl(COD)]2. Further elution with CH2Cl2/CH3CN (1:1) afforded
the separation of an orange band that contained compound 6-Me.
Compound 6-Me was obtained as an orange solid by precipitation
from CH3CN/Et2O. Yield: 74 mg (60%). 1H NMR (300 MHz,
1
imidazole: H NMR (300 MHz, CDCl3, 303 K): δ 8.68 (m, 2H,
CHpyr), 8.01 (s, 1H, CHimz), 7.38 (s, 1H, CHimz), 7.33 (m, 2H, CHpyr),
7.23 (s, 1H, CHimz). For [1-(4′-(1′-methylpyridyl)-3-methyl]-
1
imidazolium diiodide: H NMR (300 MHz, DMSO-d6, 303 K): δ
3
10.28 (s, 1H, CHimz), 9.33 (d, JHH = 6.5, 2H, CHpyr), 8.62 (s, 1H,
CHimz), 8.57 (d, 3JHH = 6.5 Hz, 2H, CHpyr), 8.09 (s, 1H, CHimz), 4.40
(s, 3H, CH3pyr), 4.01 (s, 3H, CH3imz). 13C{1H} NMR (75 MHz,
3
DMSO-d6, 303 K): δ 148.0, 146.1, 138.2, 125.4, 120.0, 118.1 (s, CHimz
,
CD3CN, 303 K): δ 8.75 (s, 1H, CHpyr), 8.23 (d, JHH = 7 Hz, 1H,
CHpyr), 7.92 (s, 1H, CHimz), 7.78 (d, 3JHH = 7 Hz, 1H, CHpyr), 7.32 (s,
1H, CHimz), 4.22 (s, 3H, CH3pyr), 4.00 (s, 3H, CH3imz). 13C{1H} NMR
(75 MHz, DMSO-d6, 303 K): δ 164.7 (s, Ir-Cpyr), 148.1 (s, Ir-Cimz),
146.8 (s, Cpyr), 136.2 (s, CHpyr), 133.8 (s, CHpyr), 126.3 (s, CHimz),
123.6 (s, CHpyr), 115.3 (s, CHimz), 46.0 (s, CH3pyr), 42.6 (s, CH3imz).
ESI-MS (15 V, CH3CN): m/z 701.9 [M − I]+, m/z 660.9 [M − I −
CH3CN]+. Anal. Found (calcd) for C14H17N5I3Ir: C, 20.46 (20.30); H,
1.99 (2.07); N, 8.50 (8.46).
Cpyr and CHpyr), 47.9 (s, CH3pyr), 36.9 (s, CH3imz). Anal. Found (calcd)
for C10H13N3I2: C, 27.89 (27.99); H, 2.98 (3.05); N, 9.70 (9.79).
Synthesis of [1-(4′-(1′-Methylpyridiniumyl)-2,3-dimethyl]-
imidazolium Diiodide, 4. The same procedure and quantities as
compound 3 were used, except with the use of 2-methylimidazole
(0.84 g, 10.28 mmol). Yield: 0.757 g (33%). For 1-(4′-pyridyl)-2-
1
methylimidazole: H NMR (300 MHz, CDCl3, 303 K): δ 8.66 (m,
2H, CHp3yr), 7.20 (m, 2H, CHpyr), 7.02 (d, 3JHH = 1.5 Hz, 1H, CHimz),
6.98 (d, JHH = 1.5 Hz, 1H, CHimz), 2.39 (s, 1H, C−CH3imz). For [1-
(4′-(1′-methylpyridyl)-2,3-dimethyl]imidazolium diiodide: 1H NMR
Synthesis of Compound [6-Me]PF6. The same procedure and
quantities as compound 6-Me were used, except with the use of [1-(3′-
( 1′ - m e t h y l p y r i d i n iu m y l ) - 3 - m e t h y l] i m i d a z o li u m d i -
(hexafluorophosphate) ([1-Me](PF6)2; 70 mg, 0.15 mmol). The
compound was purified by column chromatography. Elution with
CH2Cl2 separated a red band containing [IrCl(COD)]2. Further
elution with CH2Cl2/CH3CN (9:1) afforded the separation of a yellow
band that contained compound [6-Me]PF6. Compound [6-Me]PF6
was obtained as a yellow solid by precipitation from CH3CN/Et2O.
Yield: 70 mg (55%). 1H NMR (300 MHz, CD3CN, 303 K): δ 8.32 (s,
3
(300 MHz, DMSO-d6, 303 K): δ 9.32 (d, JHH = 6 Hz, 2H, CHpyr),
3
8.44 (d, JHH = 6 Hz, 2H, CHpyr), 8.13 (s, 1H, CHimz), 7.99 (s, 1H,
CHimz), 4.46 (s, 3H, CH3pyr), 3.91 (s, 3H, CH3imz), 2.72 (s, 3H, C−
CH3imz). 13C{1H} (75 MHz, DMSO-d6, 303 K): δ 148.0, 146.9, 146.4,
124.1, 123.9, 121.2 (s, Cimz, CHimz, Cpyr and CHpyr), 48.2 (s, CH3pyr),
35.6 (s, CH3imz), 11.8 (s, C-CH3imz). Anal. Found (calcd) for
C11H15N3I2: C, 29.73 (29.82); H, 3.06 (3.41); N, 9.24 (9.48).
Synthesis of Compound 5. A mixture of [1-(3′-(1′-methylpyr-
idiniumyl)-3-methyl]imidazolium diiodide (1-Me; 87 mg, 0.2 mmol),
[RhCl(cod)]2 (50 mg, 0.1 mmol), and KI (34 mg, 0.2 mmol) were
dissolved in CH3CN (50 mL) and stirred for 12 h at 65 °C. After
cooling to room temperature, the reaction mixture was filtered over
Celite, and all volatiles were removed under reduced pressure. The
crude solid was purified by column chromatography. Elution with
CH2Cl2 separated a yellow band containing [RhCl(COD)]2. Further
elution with CH2Cl2/CH3CN (1:1) afforded the separation of a red
band that contained compound 5. Compound 5 was obtained as a red
3
3
1H, CHpyr), 8.20 (d, JHH = 6 Hz, 1H, CHpyr), 7.72 (d, JHH = 6 Hz,
1H, CHpyr), 7.68 (s, 1H, CHimz), 7.30 (s, 1H, CHimz), 4.17 (s, 3H,
CH3pyr), 4.01 (s, 3H, CH3imz). 13C{1H} NMR (75 MHz, CD3CN, 303
K): δ 164.6 (s, Ir-Cpyr), 149.3 (s, Ir-Cimz), 145.7 (s, Cpyr), 138.0 (s,
CHpyr), 134.8 (s, CHpyr), 125.7 (s, CHimz), 124.2 (s, CHpyr), 116.7 (s,
CHimz), 47.5 (s, CH3pyr), 37.7 (s, CH3imz). ESI-MS (20 V, CH3CN):
m/z 701.9 [M − PF6]+, m/z 660.8 [M − PF6 − CH3CN]+. Anal.
Found (calcd) for C14H17N5I2IrPF6: C, 19.93 (19.87); H, 2.07 (2.02);
N, 8.41 (8.28).
1
solid by precipitation from CH3CN/Et2O. Yield: 72.5 mg (50%). H
Synthesis of Compound 6-nBu. Same procedure and quantities
as compound 6-Me, but using [1-(3′-(1′-n-butylpyridiniumyl)-3-n-
butyl]imidazolium diiodide (1-nBu; 77 mg, 0.15 mmol). Compound
purified by column chromatography. Elution with CH2Cl2 separated a
red band containing [IrCl(COD)]2. Further elution with CH2Cl2/
CH3CN (7:3) afforded the separation of an orange band that
contained compound 6-nBu. Compound 6-nBu was obtained as an
orange solid by precipitation from CH3CN/Et2O. Crystals suitable for
X-ray crystallography were obtained from a concentrated solution of
NMR (300 MHz, CD3CN, 303 K): δ 8.86 (s, 1H, CHpyr), 8.45 (d,
3
3JHH = 6 Hz, 1H, CHpyr), 8.08 (d, JHH = 2 Hz, 1H, CHimz), 7.95 (d,
3
3JHH = 6 Hz, 1H, CHpyr), 7.37 (d, JHH = 2 Hz, 1H, CHimz), 4.28 (s,
3H, CH3pyr), 3.99 (s, 3H, CH3imz). 13C{1H} NMR (75 MHz, CD3CN,
303 K): the signal corresponding to Rh-Cimz could not be observed, δ
1
183.6 (d, JRh−C = 28 Hz, Rh-Cpyr), 147.5 (s, Cpyr), 137.0 (s, CHpyr),
136.4 (s, CHpyr), 126.9 (s, CHimz), 125.2 (s, CHpyr), 117.8 (s, CHimz),
47.7 (s, CH3pyr), 38.3 (s, CH3imz). ESI-MS (20 V, CH3CN): m/z 611.7
[M − I]+, m/z 570.7 [M − I − CH3CN]+. Anal. Found (calcd) for
C14H17N5I3Rh: C, 28.43 (28.76); H, 2.75 (2.32); N, 9.50 (9.48).
1
compound 6-nBu in CH3CN. Yield: 68 mg (50%). H NMR (500
3
MHz, CD3CN, 303 K): δ 8.59 (s, 1H, CHpyr), 8.24 (d, JHH = 6 Hz,
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3
1H, CHpyr), 7.86 (s, 1H, CHimz), 7.80 (d, JHH = 6 Hz, 1H, CHpyr),
7.33 (s, 1H, CHimz), 4.40 (t, 3JHH = 7.5 Hz, 2H, NCH2pyr), 4.35 (t, 3JHH
= 7.5 Hz, 2H, NCH2imz), 1.98 (m, 4H, CH2CH2CH2), 1.42 (m, 2H,
CH2pyrCH3), 1.37 (m, 2H, CH2imzCH3), 0.98 (m, 6H, CH3). 13C{1H}
NMR (125 MHz, CD3CN, 303 K): δ 164.8 (s, Ir-Cpyr), 149.4 (s, Ir-
Cimz), 146.8 (s, Cpyr), 137.1 (s, CHpyr), 134.9 (s, CHpyr), 124.7 (s,
CHimz), 123.4 (s, CHpyr), 117.3 (s, CHimz), 60.9 (s, CH2pyr), 49.9 (s,
CH2imz), 33.5 (s, CH2CH2pyrCH2), 32.4 (s, CH2CH2imzCH2), 20.4 (s,
CH2pyrCH3), 20.1 (s, CH2imzCH3), 14.1 (s, CH3pyr), 13.7 (s, CH3imz).
ESI-MS (15 V, CH3CN): m/z 786 [M − I]+, m/z 745 [M − I −
CH3CN]+. Anal. Found (calcd) for C20H29N5I3Ir: C, 26.45 (26.33); H
3.00 (3.20); N 7.80 (7.68).
CH3CN (50 mL) and stirred for 12 h at 65 °C. After cooling to room
temperature, the reaction mixture was filtered over Celite and all
volatiles were removed under reduced pressure. The crude solid was
purified as explained in method a. Yield: 29 mg (20%). 1H NMR (300
MHz, DMSO-d6, 303 K): δ 9.12 (s, 1H, CHpyr), 8.74 (d, 3JHH = 11 Hz,
1H, CHpyr), 8.44 (d, 1H, 3JHH = 4 Hz, CHimz), 8.12 (d, 3JHH = 11 Hz,
3
1H, CHpyr), 7.72 (d, JHH = 4 Hz, 1H, CHimz), 4.29 (s, 3H, CH3pyr),
4.03 (s, 3H, CH3imz). 13C{1H} NMR (75 MHz, DMSO-d6, 303 K): δ
1
169.3 (d, JRh−C = 47 Hz, Rh-Cpyr), 157.9 (s, Cpyr), 153.5 (s, CHpyr),
1
143.1(s, CHpyr), 139.6 (d, JRh−C = 34 Hz, Rh-Cimz), 127.0 (s, CHpyr),
117.5 (CHimz), 109.0 (s, CHimz), 47.3 (s, CH3pyr), 35.9 (s, CH3imz).
ESI-MS (20 V, CH3CN): m/z 570.7 [M − I − CH3CN]+, m/z 529.7
[M − I − (CH3CN)2]+. Anal. Found (calcd) for C14H17N5I3Rh: C,
22.89 (22.76); H, 2.26 (2.32); N, 9.36 (9.48).
Synthesis of Compound 7. A mixture of [1-(3′-(1′-methylpyr-
idiniumyl)-3-methyl]imidazolium diiodide (1-Me; 93 mg, 0.22 mmol),
[RhCl(NBD)]2 (50 mg, 0.11 mmol), and KI (36 mg, 0.22 mmol) was
dissolved in CH3CN (50 mL) and stirred for 12 h at 65 °C. After
cooling to room temperature, the reaction mixture was filtered over
Celite, and all volatiles were removed under reduced pressure. The
crude solid was purified by column chromatography. Elution with
CH2Cl2 separated a yellow band containing [RhCl(NBD)]2. Further
elution with CH2Cl2/CH3CN (1:1) afforded the separation of a red
band that contained compound 7. Compound 7 was obtained as a red
solid by precipitation from CH3CN/Et2O. Slow diffusion of Et2O into
a concentrated solution of compound 7 in CH3CN gave crystals
Synthesis of Compound 9. Method a. A mixture of [1-(4′-(1′-
methylpyridiniumyl)-3-methyl]imidazolium diiodide (3; 64 mg, 0.15
mmol), [IrCl(COD)]2 (50 mg, 0.075 mmol), and KI (25 mg, 0.15
mmol) was dissolved in CH3CN (50 mL) and stirred for 12 h at 65
°C. After cooling to room temperature, the reaction mixture was
filtered over Celite, and all volatiles were removed under reduced
pressure. The crude solid was purified by column chromatography.
Elution with CH2Cl2 separated a red band containing [IrCl(COD)]2.
Further elution with CH2Cl2/CH3CN (9:1) afforded the separation of
a yellow band that contained compound 9. Compound 9 was obtained
as a yellow solid by precipitation from CH3CN/Et2O. Yield: 70 mg
(56%). Method b. A mixture of [1-(4′-(1′-methylpyridiniumyl)-2,3-
dimethyl]imidazolium diiodide (4; 66 mg, 0.15 mmol), [IrCl(COD)]2
(50 mg, 0.075 mmol), and KI (25 mg, 0.15 mmol) was dissolved in
CH3CN (50 mL) and stirred for 12 h at 65 °C. After cooling to room
temperature, the reaction mixture was filtered over Celite, and all
volatiles were removed under reduced pressure. The crude solid was
purified as explained in method a. Yield: 30 mg (24%). 1H NMR (500
1
suitable for X-ray crystallography. Yield: 107 mg (66%). H NMR
3
(500 MHz, DMSO-d6, 303 K): δ 8.60 (d, JHH = 6 Hz, 1H, CHpyr),
3
3
8.30 (d, JHH = 2 Hz, 1H, CHimz), 8.17 (d, JHH = 8 Hz, 1H, CHpyr),
7.63 (d, 3JHH = 2 Hz, 1H, CHimz), 7.54 (dd, 3JHH = 6 Hz, 3JHH = 8 Hz,
1H, CHpyr), 4.52 (s, 3H, CH3pyr), 4.04 (s, 3H, CH3imz). 13C{1H} NMR
(125 MHz, DMSO-d6, 303 K): δ the signals corresponding to the two
Rh-C could not be observed, 147.7 (s, Cpyr), 143.0 (s, CHpyr), 127.2 (s,
CHimz), 121.1 (s, CHpyr), 119.1 (s, CHpyr), 117.0 (s, CHimz), 51.6 (s,
CH3pyr), 37.1 (s, CH3imz). ESI-MS (20 V, CH3CN): m/z 571.0 [M − I
− CH3CN]+, m/z 529.9 [M − I − (CH3CN)2]+. Anal. Found (calcd)
for C14H17N5I3Rh: C, 28.43 (28.76); H, 2.75 (2.32); N, 9.50 (9.48).
Synthesis of Compound [7]PF6. The same procedure and
quantities as compound 7 were used, except with the use of [1-(3′-(1′-
methylpyridiniumyl)-3-methyl]imidazolium di(hexafluorophosphate)
([1-Me](PF6)2; 101 mg, 0.22 mmol). The compound was purified
by column chromatography. Elution with CH2Cl2 separated a yellow
band containing [RhCl(NBD)]2. Further elution with CH2Cl2/
CH3CN (9:1) afforded the separation of an orange band that
contained compound [7]PF6. Compound [7]PF6 was obtained as an
orange solid by precipitation from CH3CN/Et2O. Yield: 88 mg (54%).
3
MHz, CD3CN, 303 K): δ 8.42 (s, 1H, CHpyr), 8.04 (d, JHH = 6 Hz,
3
3
1H, CHpyr), 7.80 (d, 1H, JHH = 2 Hz, CHimz), 7.69 (d, JHH = 6 Hz,
3
1H, CHpyr), 7.33 (d, JHH = 2 Hz, 1H, CHimz), 4.21 (s, 3H, CH3pyr),
4.04 (s, 3H, CH3imz). 13C{1H} NMR (125 MHz, CD3CN, 303 K): δ
160.8 (s, Ir-Cpyr), 152.0 (s, Ir-Cimz), 148.4 (s, CHpyr), 142.4 (s, CHpyr),
128.5 (s, Cpyr), 125.4 (s, CHpyr), 116.6 (s, CHimz), 107.6 (s, CHimz),
47.1 (s, CH3pyr), 36.9 (s, CH3imz). ESI-MS (20 V, CH3CN): m/z 701.9
[M − I]+, m/z 660.8 [M − I − CH3CN]+. Anal. Found (calcd) for
C14H17N5I3Ir: C, 20.18 (20.30); H, 2.32 (2.07); N, 8.72 (8.86).
Synthesis of Compound 10. A mixture of [1-(3′-(1′-methylpyr-
idiniumyl)-2,3-dimethyl]imidazolium diiodide (2; 67 mg, 0.15 mmol),
[IrCl(COD)]2 (50 mg, 0.075 mmol), and KI (25 mg, 0.15 mmol) was
dissolved in CH3CN (20 mL) and refluxed for 18 h. After cooling to
room temperature, the reaction mixture was filtered over Celite, and all
volatiles were removed under reduced pressure. The crude solid was
purified by column chromatography. Elution with CH2Cl2 separated a
red band containing [IrCl(COD)]2. Further elution with CH2Cl2/
CH3CN (1:1) afforded the separation of an orange band that
contained compound 10. Compound 10 was obtained as an orange
solid by precipitation from CH3CN/Et2O. Slow diffusion of Et2O into
a concentrated solution of compound 10 in CH3CN gave crystals
suitable for X-ray crystallography. Yield: 78 mg (62%). 1H NMR (300
MHz, CD3CN, 303 K): δ = 8.51 (d, 3JHH = 6 Hz, 1H, CHpyr), 8.21 (s,
1H NMR (300 MHz, CD3CN, 303 K): δ 8.36 (d, JHH = 6 Hz, 1H,
CHpyr), 7.93 (d, JHH = 8 Hz, 1H, CHpyr), 7.85 (s, 1H, CHimz), 7.47
3
3
(m, 1H, CHpyr), 7.34 (s, 1H, CHimz), 4.52 (s, 3H, CH3pyr), 4.03 (s, 3H,
CH3imz). 13C{1H} NMR (75 MHz, CD3CN, 303 K): δ 175.7 (d, 1JRh−C
= 36 Hz, Rh-Cpyr), 162.7 (d, 1JRh−C = 42 Hz, Rh-Cimz), 148.1 (s, Cpyr),
143.7 (s, CHpyr), 127.8 (s, CHimz), 122.7 (s, CHpyr), 121.5 (s, CHpyr),
117.4 (s, CHimz), 54.7 (s, CH3pyr), 39.0 (s, CH3imz). ESI-MS (20 V,
CH3OH): m/z 529.8 [M − PF6 − (CH3CN)2]+. Anal. Found (calcd)
for C14H17N5I2RhPF6: C, 22.38 (22.21); H, 2.33 (2.26); N, 9.20
(9.25).
Synthesis of Compound 8. Method a. A mixture of [1-(4′-(1′-
methylpyridiniumyl)-3-methyl]imidazolium diiodide, (3; 87 mg, 0.2
mmol), [RhCl(COD)]2 (50 mg, 0.1 mmol), and KI (34 mg, 0.2
mmol) was dissolved in CH3CN (50 mL) and stirred for 12 h at 65
°C. After cooling to room temperature, the reaction mixture was
filtered over Celite and all volatiles were removed under reduced
pressure. The crude solid was purified by column chromatography.
Elution with CH2Cl2 separated a yellow band containing [RhCl-
(COD)]2. Further elution with CH2Cl2/CH3CN (7:3) afforded the
separation of an orange band that contained compound 8. Compound
8 was obtained as an orange solid by precipitation from CH3CN/Et2O.
Slow diffusion of Et2O into a concentrated solution of compound 8 in
CH3CN gave crystals suitable for X-ray crystallography.Yield: 79 mg
(54%). Method b. A mixture of [1-(4′-(1′-methylpyridiniumyl)-2,3-
dimethyl]imidazolium diiodide (4; 90 mg, 0.2 mmol), [RhCl(COD)]2
(50 mg, 0.01 mmol), and KI (34 mg, 0.2 mmol) was dissolved in
3
3
1H, CHpyr), 7.63 (d, JHH = 6 Hz, 1H, CHpyr), 7.52 (d, JHH = 2 Hz,
3
1H, CHimz), 7.16 (d, JHH = 2 Hz, 1H, CHimz), 4.10 (s, 3H, CH3pyr),
3.99 (s, 2H, Ir−CH2imz), 3.72 (s, 3H, CH3imz). 13C{1H} NMR (75
MHz, CD3CN, 303 K): δ 168.9 (s, Ir-Cpyr), 163.5 (s, Cimz), 145.6 (s,
CHpyr), 144.8 (s, Cpyr), 135.1 (s, CHpyr), 130.0 (s, CHpyr), 122.2 (s,
CHimz), 118.7 (s, CHimz), 46.8 (s, CH3pyr), 35.8 (s, CH3imz), −25.5 (s,
Ir-CH2imz). ESI-MS (20 V, CH3CN): m/z 674.0 [M − I − CH3CN]+,
m/z 633.9 [M − I − (CH3CN)2]+. Anal. Found (calcd) for
C15H19N5I3Ir: C, 21.43 (21.39); H, 2.35 (2.27); N, 8.23 (8.31).
X-ray Crystal Structure Determinations. Diffraction data were
collected on a Agilent SuperNova diffractometer equipped with an
Atlas CCD detector using Mo Kα radiation (λ = 0.71073 Å). Single
crystals were mounted on a MicroMount polymer tip (MiteGen) in a
random orientation. Absorption corrections based on the multiscan
method were applied.24 Structures were solved by direct methods in
5175
dx.doi.org/10.1021/om3005096 | Organometallics 2012, 31, 5169−5176

Organometallics
Article
SHELXS-97 and refined by the full-matrix method based on F2 with
the program SHELXL-97 using the OLEX software package.25
Crystal Data and Structure Refinement for Complex 6-nBu.
C20H29N5I3Ir, M = 912.38, triclinic, a = 8.1564(4) Å, b = 13.2101(6)
Å, c = 14.2977(7) Å, α = 108.985(4)°, β = 102.089(4)°, γ = 98.667(4)
G.; Kruger, G. J.; Otte, R.; Van Zyl, W. E.; Olivier, P. J. Organomet.
Chem. 1994, 466, 291.
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Tosh, E.; Albrecht, M.; Frenking, G.; Raubenheimer, H. G.
Organometallics 2010, 29, 5821.
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1700. Normand, A. T.; Cavell, K. J. Eur. J. Inorg. Chem. 2008, 2781.
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Inorg. Chem. 2012, 51, 2191. McSkimming, A.; Bhadbhade, M.;
Colbran, S. B. Dalton Trans. 2010, 39, 10581.
°, V = 1383.96(11) Å3, T = 293(2), space group P1 (no. 2), Z = 2,
̅
μ(Mo Kα) = 8.185, 17 980 reflections measured, 6199 unique (Rint
=
0.0321), which were used in all calculations. The final wR2 was 0.0769
(all data), and R1 was 0.0322 (>2σ(I)).
Crystal Data and Structure Refinement for Complex 8.
C14H17I3N5Rh, M = 738.94, monoclinic, a = 11.3673(4) Å, b =
24.5851(7) Å, c = 7.6286(3) Å, β = 100.612(3)°, V = 2095.48(12) Å3,
T = 199.95(10), space group P21/c (no. 14), Z = 4, μ(Mo Kα) =
5.240, 24 019 reflections measured, 5217 unique (Rint = 0.0414), which
were used in all calculations. The final wR2 was 0.1056 (all data), and
R1 was 0.0417 (>2σ(I)).
(10) Lalrempuia, R.; Muller-Bunz, H.; Albrecht, M. Angew. Chem., Int.
Ed. 2011, 50, 9969.
(11) Lalrempuia, R.; McDaniel, N. D.; Muller-Bunz, H.; Bernhard, S.;
Albrecht, M. Angew. Chem., Int. Ed. 2010, 49, 9765.
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W. Organometallics 2008, 27, 6193.
(13) Chianese, A. R.; Kovacevic, A.; Zeglis, B. M.; Faller, J. W.;
Crabtree, R. H. Organometallics 2004, 23, 2461. Alcarazo, M.;
Roseblade, S. J.; Cowley, A. R.; Fernandez, R.; Brown, J. M.;
Lassaletta, J. M. J. Am. Chem. Soc. 2005, 127, 3290. Bacciu, D.; Cavell,
K. J.; Fallis, I. A.; Ooi, L. L. Angew. Chem., Int. Ed. 2005, 44, 5282.
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253.
Crystal Data and Structure Refinement for Complex 10.
C17H22I3IrN6, M = 883.31, triclinic, a = 10.1810(6) Å, b =
11.0855(5) Å, c = 12.6852(7) Å, α = 107.112(4)°, β = 94.167(4)°,
γ = 112.461(5)°, V = 1236.42(11) Å3, T = 220(2), space group P1
̅
(no. 2), Z = 2, μ(Mo Kα) = 9.158, 27 397 reflections measured, 6297
unique (Rint = 0.0658), which were used in all calculations. The final
wR2 was 0.1252 (all data), and R1 was 0.0462 (>2σ(I)).
ASSOCIATED CONTENT
* Supporting Information
Crystallographic information files for compound 6-nBu, 7, 8,
and 10 are available free of charge via the Internet at http://
pubs.acs.org.
(14) Chianese, A. R.; Zeglis, B. M.; Crabtree, R. H. Chem. Commun.
2004, 2176.
(15) Viciano, M.; Feliz, M.; Corberan, R.; Mata, J. A.; Clot, E.; Peris,
E. Organometallics 2007, 26, 5304.
■
S
(16) Song, G. Y.; Li, X. W.; Song, Z. C.; Zhao, J.; Zhang, H. J.
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̈
AUTHOR INFORMATION
Corresponding Author
*E-mail: emas@uji.es, eperis@uji.es.
Notes
2012, DOI: 10.1039/c2cc32843g.
■
(18) Hahn, F. E.; Naziruddin, A. R.; Hepp, A.; Pape, T.
Organometallics 2010, 29, 5283. Kosterke, T.; Pape, T.; Hahn, F. E.
̈
J. Am. Chem. Soc. 2011, 133, 2112. Viciano, M.; Poyatos, M.; Sanau,
M.; Peris, E.; Rossin, A.; Ujaque, G.; Lledos, A. Organometallics 2006,
25, 1120. Viciano, M.; Mas-Marza, E.; Poyatos, M.; Sanau, M.;
Crabtree, R. H.; Peris, E. Angew. Chem., Int. Ed. 2005, 44, 444. Fraser,
P. J.; Roper, W. R.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1974,
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Furstner, A.; Seidel, G.; Kremzow, D.; Lehmann, C. W. Organo-
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The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We gratefully acknowledge the financial support from the
́
Ministerio de Economia y Competitividad of Spain (CTQ2011-
24055/BQU) and Bancaixa (P1.1B2010-02). C.S. thanks the
́
Ministerio de Economia y Competitividad for a doctoral
fellowship. E.M.-M. thanks the Juan de la Cierva program. We
also want to thank the SCIC-UJI for the instrumental facilities.
(19) Schneider, S. K.; Roembke, P.; Julius, G. R.; Loschen, C.;
Raubenheimer, H. G.; Frenking, G.; Herrmann, W. A. Eur. J. Inorg.
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Puschmann, H. J. Appl. Crystallogr. 2009, 42, 339. Sheldrick, G. M.
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