Triazoles from N-alkynylheterocycles and their coordination to iridium

Article abstract of DOI:10.1021/om201157g

N-alkynylheterocycles (benzimidazole and indazole) are converted to triazoles by click chemistry, and the resulting triazoles react with [IrCl ₂Cp*]₂. The benzimidazole-triazole coordinates in a monodentate fashion through the benzimidazole, whereas the indazole-triazole is bidentate through coordination of both heterocycles. Reaction of the benzimidazole-triazole with methyliodide gives a benzimidazolium salt that deprotonates on coordination to afford a rare example of a bidentate NHC-triazole.

Full text of DOI:10.1021/om201157g

Article
pubs.acs.org/Organometallics
Triazoles from N-Alkynylheterocycles and Their Coordination to
Iridium
Glenn A. Burley,*,† Youcef Boutadla, David L. Davies,* and Kuldip Singh
University of Leicester, Leicester, U.K., LE1 7RH
S
* Supporting Information
ABSTRACT: N-alkynylheterocycles (benzimidazole and indazole) are
converted to triazoles by click chemistry, and the resulting triazoles react
with [IrCl2Cp*]2. The benzimidazole-triazole coordinates in a monodentate
fashion through the benzimidazole, whereas the indazole-triazole is
bidentate through coordination of both heterocycles. Reaction of the
benzimidazole-triazole with methyliodide gives a benzimidazolium salt that
deprotonates on coordination to afford a rare example of a bidentate NHC−
triazole.
The luminescence of pyridine triazoles is sensitive to the
INTRODUCTION
■
presence of metal ions,9 and the ease of tuning the electronic
properties of these ligands has been used to control the
luminescence of biscyclometalated iridium complexes.5d,10
Amido-triazoles have been used in luminescent copper
complexes.11 Recently, chelating triazoles have been applied
to the modification of half-sandwich ruthenium complexes to
try and improve their anticancer activity.6
Triazoles have received a lot of interest in the past decade due
to their easy synthesis by the copper-catalyzed Huisgen [3 + 2]
cycloaddition reaction between a terminal alkyne and an azide
(“click chemistry”),1 and this chemistry has been applied in a
wide range of fields, including material science, chemical
biology, and drug discovery.2 The application of click chemistry
to the synthesis of chelate ligands was first described in 2006
using amino acid derived alkynes or azides.3 The resultant
ligands are bound through a primary amine and either the N(3)
or, in some cases, the N(2) of the triazoles (see Figure 1). Since
Perhaps surprisingly, the use of the click-to-chelate approach
has not yet been explored greatly for use in homogeneous
catalysis, though some phosphine-triazole chelates have been
studied.12 The first example of a chelate formed from an N-
heterocyclic carbene and a triazole synthesized via click
chemistry was only reported in 2010.13 In addition, triazoles
themselves can also be alkylated and function as precursors to
triazolylidenes.14 We and others have shown that, in the
absence of a N or P chelating atom using triazoles derived from
phenylalkynes, the triazoles can act as a directing group to
facilitate CH activation to form cyclometalated N,C chelates.
Thus, triazoles provide a range of opportunities to develop new
ligand systems where the electronic and steric properties can be
easily tuned by virtue of the types of alkynes and azides
utilized.10c,15
In all the cases described above, the alkynes used are terminal
with one carbon substituent. Azide cycloadditions to ynamides
are also known;16 however, the corresponding reactions with
N-alkynyl heterocycles have not been studied. Having recently
reported a convenient route to N-alkynyl heterocycles,17 we
decided to test the click reactivity of these and investigate the
coordinating ability of the resulting triazoles.
Figure 1. Chelating triazoles derived from 2-ethynyl pyridine (A), 2-
picolylethyne (B), and 2-azidomethylpyridine (C).
then, several further examples of this “click-to-chelate”
approach have been reported, and the field has been reviewed.4
The majority of examples use either 2-ethynyl pyridine,5 which
tends to give five-membered chelates of type A (Figure 1), or 2-
picolylethyne,6 which gives six-membered chelates of type B
(Figure 1). Both of these ligands coordinate through N(3) as
expected, since DFT calculations have shown that N(3) is a
better donor than N(2).3,7 However, coordination through
N(2) is also possible using ligands of type C,8 but the
complexes are less stable than those of type A, as has been
confirmed experimentally and computationally for a series of
palladium complexes.8c
RESULTS AND DISCUSSION
N-alkynylbenzimidazole 1 and N-alkynylindazole 2 were
reacted with the appropriate azide in the presence of copper
■
Received: November 19, 2011
Published: January 25, 2012
© 2012 American Chemical Society
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to give triazoles 3 and 4, respectively (Scheme 1). The click
reaction between each N-alkynylheteroarene and the appro-
Scheme 1. Preparation of Triazoles from N-
Alkynylheterocycles
priate azide was extremely facile, with the reaction complete in
less than 5 min using 20 mol % Cu2+ and 40 mol % sodium
ascorbate, affording 3 and 4 as white waxy solids in good yield.
Having synthesized the triazoles, we decided to explore their
coordination by reaction with [IrCl2Cp*]2. Our previous results
have shown that the triazole N(3) can act as a directing group
for CH activation of a 4-phenyl group by acetate-assisted
cyclometalation with [IrCl2Cp*]2.15a Additionally, acetate-
assisted cyclometalation of heterocycles, such as pyrrole and
thiophene, is also known.18 Hence, synthesis of 6 by
cyclometalation of the benzimidazole of 3b was attempted by
reaction with [IrCl2Cp*]2 in the presence of sodium acetate
Figure 2. Ortep plot of 5b. Thermal ellipsoids are drawn at the 50%
probability level, and hydrogen atoms are omitted for clarity. Selected
bond lengths [Å] and bond angles [deg]: M−N(1) 2.135(5), M−
Cl(1) 2.4191(18), M−Cl(2) 2.4124(18), Ir(1)−C(21) 2.144(7),
Ir(1)−C(20) 2.162(7), Ir(1)−C(19) 2.152(6), Ir(1)−C(18)
2.155(7), Ir(1)−C(17) 2.156(7); N(1)−M−Cl(1) 88.52(15),
N(1)−M−Cl(2) 85.71(16).
benzimidazole proton being observed at δ 9.35 and the NCH2
protons being equivalent giving rise to a triplet at δ 4.13.
Hence, although coordination through the triazole is feasible, it
appears that the benzimidazole is a better donor.
1
(Scheme 2). The H NMR spectrum of the reaction mixture
showed the presence of only one Cp*Ir complex (δ 1.66);
however, 13 additional proton signals were observed,
suggesting that no CH activation had occurred. Three singlets
were observed at δ 9.39(1H), 8.01(1H), and 5.31(2H); the
latter is clearly due to the benzylic CH2 group. Moreover,
because these protons are equivalent, it suggests that the ligand
is not bidentate since this would make the iridium a chiral
center, and hence, these protons would be diastereotopic.
Hence, the compound is assigned as 5b. The NOESY spectrum
showed a correlation between the singlet at δ 8.01 and a
doublet at δ 8.02; hence, this singlet is assigned to the triazole
proton. Therefore, the singlet at δ 9.39 is the benzimidazole
proton, which is 0.89 ppm downfield from the free ligand,
consistent with coordination through the benzimidazole rather
than the triazole. This was confirmed by an X-ray structure
determination (see Figure 2).
To prevent coordination of the benzimidazole, and to
examine the conversion of the ligand to an NHC−triazole
chelate, alkylation of 3a with methyl iodide was attempted.
Reaction with methyl iodide proceeded selectively to alkylate
the more electron-rich benzimidazole, giving 7a (Scheme 3);
there was no evidence for competing alkylation at the triazole
even though this reaction is known.14c To our knowledge, this
is the first imidazolium directly attached to a triazole. The only
previous examples of imidazolium-functionalized triazoles were
reported in 201013 and have a CH2 linker between the two
heterocycles. Note, in our case, construction of the triazole,
followed by alkylation of the benzimidazole, works well;
however, in the previous cases, the imidazolium salts had to be
made first, followed by cycloaddition to form the triazoles. Even
then, click coupling of the imidazolium salts was not very
efficient, stoichiometric amounts of copper being required to
give good yields.13 Hence, our procedure provides a novel and
facile synthetic method for the preparation of imidazolium-
functionalized triazoles.
This result suggests that acetate is not required for the
reaction, and indeed, if the reaction is repeated omitting the
sodium acetate, the same product is formed. A similar reaction
with 3a gives the corresponding hexyl substituted product 5a.
1
This shows similar features in the H NMR spectrum with the
Scheme 2. Coordination of Triazoles 3a and 3b
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Scheme 3. Preparation of NHC−Triazole Complex 8a and NMR Labeling Scheme
Scheme 4. Coordination of Indazole-Triazole 4a
Subsequently, the benzimidazolium salt 7a was reacted with
[IrCl2Cp*]2 in the presence of sodium acetate. After 20 h, the
1H NMR spectrum showed complete reaction, with one set of
signals for the ligand and a Cp*, suggesting that the reaction
selectively produced one compound. The 1H NMR spectrum of
the product showed signals integrating for 38 H (i.e., loss of
one H) with only one singlet, at δ 10.94, similar to that of the
imidazolium proton H7 in the free ligand (at δ 10.09).
However, in the NOESY spectrum, the singlet at δ 10.94 shows
cross peaks with both H5 and the hexyl chain and hence is
assigned as the triazole proton H9, confirming the loss of H7
and the formation of carbene complex 8a. The chemical shift
for H9 in 8a (δ 10.94, c.f. δ 8.83 in 7a) is consistent with
coordination of the triazole to form a cationic complex with
hydrogen bonding of H9 to the counterion (Cl−, I−), causing
the low-field NMR shift. The other protons are in typical
positions, and NOE correlations between the methyl signal and
the Cp* and the methyl and H2 confirm the assignments. The
13C NMR spectra show the expected number of carbons with
the carbene C7 at δ 173.00, which is slightly deshielded (about
15 ppm) compared with other Cp*Ir NHC complexes.19 The
ES-MS spectrum of 8a shows one peak at m/z 738, which
suggests that iodide is coordinated to the metal with chloride as
a counterion. The elemental analysis is also consistent with this
formulation.
complex making H9 more acidic. It is not as low field as in 8a (δ
10.94), possibly reflecting less hydrogen bonding to PF6 than to
chloride in 8a. The other aromatic protons are observed as two
doublets at δ 7.86 (H6) and 7.88 (H3) and two doublets of
doublets at δ 7.37 (H4) and 7.66 (H5). The 13C NMR spectra
show the expected number of C−H and quaternary carbons
with the imine carbon C1 at 138.68. The elemental analysis
confirmed that the product contains PF6 as a counterion.
In conclusion, we have shown that N-alkynylbenzimidazole 1
and indazole 2 are easily converted to triazoles 3 and 4,
respectively, by copper-catalyzed addition of azide. The
coordination behavior of these triazoles suggests that triazoles
are not very strong ligands. Hence, for 1, coordination via the
benzimidazole is preferred; as a result, cyclometalation is not
possible. As we observed previously,15a in cyclometalation
reactions with [IrCl2Cp*]2 in the presence of sodium acetate, if
a second N or O donor can coordinate to provide a bidentate
N,N or N,O ligand, then cyclometalation does not occur. This
is the case with the indazole-triazole 4a, which forms the
chelate complex 9a. Benzimidazole-triazole 3a is easily
methylated (to 7a), and this reacts with [IrCl2Cp*]2 in the
presence of sodium acetate to form an NHC−triazole chelate
complex 8a. In contrast to the only previous report on NHC−
triazole ligands, in our case, the click reaction can be performed
before alkylation; hence, ligands with different substituents can
easily be accessed from a common precursor through use of
different alkylating agents. In addition, in 7a, the carbene is
directly linked to the triazole rather than with a CH2 spacer. In
conclusion, we have shown than N-alkynyl-derived triazoles can
be used to make chelate ligands. Further applications of these
ligands in catalysis and in labeling biomolecules are being
investigated.
Next, we examined coordination of indazole-triazole 4a. In
principle, this can act as an N−N chelate; however, if
coordination of the indazole occurs first, then subsequent C−
H activation of the triazole may also be possible to form 10a
(Scheme 4). The reaction of 4a with [IrCl2Cp*]2 and sodium
1
acetate was carried out, and after 23 h, the H NMR spectrum
showed one Cp* signal and one set of signals for the ligand
integrating to 19 protons, suggesting that no C−H activation
had occurred and 10a was not formed. The ES-MS and FAB-
MS showed a peak at m/z 632 assigned as the cation
[IrCl(4a)Cp*]+. Hence, the reaction was repeated without
sodium acetate in the presence of KPF6, to afford 9a as a PF6
salt.
EXPERIMENTAL SECTION
■
All reactions were carried out at room temperature under nitrogen;
however, the workup was carried out in air, unless stated otherwise.
Solvents were dried by passage through activated alumina and
degassed prior to use. 1H, 13C-{1H} NMR spectra were obtained
using a Bruker ARX 400 MHz spectrometer, with CDCl3 as a solvent,
unless otherwise stated. Chemical shifts were recorded in parts per
1
The H NMR spectrum of 9a shows two singlets at δ 8.46
and 8.59, which are assigned to H1 and H9, respectively. H9 is
0.7 ppm downfield from the corresponding signal in 4a (δ
7.85), consistent with coordination of the triazole in a cationic
1
million (on the δ scale for H NMR, with tetramethylsilane as an
internal reference), and coupling constants are reported in hertz. FAB
mass spectra were obtained on a Kratos concept mass spectrometer
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using NOBA as a matrix, and electrospray (ES) mass spectra were
recorded using a micromass Quattro LC mass spectrometer in
acetonitrile. Microanalyses were performed by the Elemental Analysis
Service (London Metropolitan University). Starting alkynes 1 and 2
were prepared from TIPS-protected alkynes, which were prepared by
the literature method.17 [IrCl2Cp*]2,20 hexyl azide,21 and benzyl
azide22 were prepared by literature methods; other compounds were
obtained from Aldrich and Alfa Aesar.
133.8 (C-ipso), 141.2 (CH), 142.7 (C-ipso), 143.8 (C-ipso). HR-MS
(FAB): calculated for C16H14N5 , 276.12437; found, 276.12454
+
Preparation of 4a. To a solution of 1-ethynyl-1H-indazole 2
(0.062 g, 434 μmol) and n-hexyl azide (0.110 g, 867 μmol) in EtOH
(2.0 mL) was added an aqueous solution of CuSO4·5H2O (0.011 g, 43
μmol in 2.0 mL), followed by solid sodium ascorbate (0.017 g, 88
μmol) in air. The reaction mixture was stirred at room temperature
until complete consumption of 2 (typically 5 min, as monitored by
tlc). The reaction mixture was then diluted with ethyl acetate (250
mL) and the organic layer washed with dilute ammonia solution (1%,
1 × 100 mL), followed by brine (2 × 100 mL) and finally water (1 ×
100 mL). The organic layer was dried (MgSO4) and concentrated in
vacuo. Column chromatography (flash SiO2, EtOAc/hexane 1:1)
afforded the desired compound 4a as a white solid (0.098 g, 84%). 1H
NMR (500 MHz): δ 0.89 (t, 3H, J = 9.00 Hz, Me), 1.35 (m, 6H, 3 ×
CH2), 1.98 (p, 2H, J = 7.5 Hz, NCH2CH2), 4.48 (t, 2H, J = 7.5 Hz,
NCH2), 7.25 (td, 1H, J = 7.00, 0.5 Hz, CHin), 7.53 (td, 1H, J = 7.5, 1.5
Hz, CHin), 7.77 (dd, 1H, J = 7.5, 1.5 Hz, CHin), 7.87 (s, 1H, CHtr),
8.17 (s, 1H, CHN), 8.48 (dd, 1H, J = 8.5, 1.0 Hz, CHin). 13C NMR
(125.8 MHz): 14.0 (Me), 22.4, 26.1, 30.1, 31.2 (4 × CH2), 51.1
(NCH2), 112.8 (CHtr), 113.0, 120.8, 122.2 (3 × CHin), 124.8 (ipso-C),
128.0 (CHin), 136.4 (NCH), 138.8 (ipso-C), 148.2 (ipso-C). HR-MS
(FAB, +ve mode): calcd for C15H20N5, 270.17132; found, 270.17134
[M + H]+.
Preparation of 1. To a solution of 1-((triisopropylsilyl)ethynyl)-
1H-benzo[d]imidazole17 (0.060 g, 0.200 mmol.) in THF (10 mL) was
added a solution of tetrabutylammonium fluoride (1.0 M, 200 μL) at
room temperature in air. The reaction was stirred for 30 min, followed
by concentration in vacuo in the dark. Column chromatography (10%
EtOAc in Petroleum Spirit 40/60) and concentration in vacuo
1
afforded 1 (0.042 g, 74%) as a white crystalline solid. H NMR (500
MHz): δ 3.32 (s, 1H, CC-H), 7.38 (dt, 1H, J = 7.9, 0.6 Hz, Ar-H),
7.44 (dt, 1H, J = 8.2, 1.0 Hz, Ar-H), 7.62 (dd, 1H, J = 7.9, 0.8 Hz, Ar-
H), 7.84 (dd, 1H, J = 8.2, 0.8 Hz, Ar-H), 8.11 (s, 1H, Ar-H). 13C NMR
(125.8 MHz): δ 62.1 (CC-H), 70.3 (CC−H), 110.9 (Ar-C-H),
120.9 (Ar-C-H), 124.2 (Ar-C-H), 124.9 (Ar-C-H), 134.4 (Ar-Cipso),
141.8 (Ar-Cipso), 143.6 (Ar-C-H). MS (FAB, +ve mode): calcd for
+
C9H7N2 , 143.06037; found, 143.06079 [M + H]+.
Preparation of 2. This was prepared similarly, starting from 1-
((triisopropylsilyl)ethynyl)-1H-indazole17 (0.207 g, 0.695 mmol.).
Column chromatography (10% EtOAc in Petroleum Spirit 40/60)
and concentration in vacuo afforded 2 (0.096 g, 97%) as a white
Preparation of 5a. A mixture of [IrCl2Cp*]2 (60.0 mg, 0.076
mmol) and 3a (43.0 mg, 0.17 mmol) in CH2Cl2 (5 mL) was stirred for
4 h. The mixture was filtered through Celite and evaporated to
dryness. The product was washed with hexane and precipitated from
CH2Cl2/hexane to give 5a as a yellow powder (31.0 mg, 73%). Anal.
Calcd for C25H34Cl2N5Ir: C, 44.97; H, 5.13; N, 10.49. Found: C,
1
crystalline solid. H NMR (400 MHz): δ 3.47 (s, 1H, CC-H), 7.29
(dt, 1H, J = 7.9, 0.6 Hz, Ar-H), 7.52 (dt, 1H, J = 7.2, 1.1 Hz, Ar-H),
7.61 (dd, 1H, J = 8.1, 0.8 Hz, Ar-H), 7.74 (dd, 1H, J = 8.1, 0.8 Hz, Ar-
H), 8.11 (s, 1H, Ar-H). 13C NMR (125.8 MHz): δ 62.7 (CC-H),
73.7 (CC-H), 110.6 (Ar-C-H), 121.6 (Ar-C-H), 123.4 (Ar-C-H),
123.5 (Ar-Cipso), 128.6 (Ar-C-H), 138.3 (Ar-C-H), 142.4 (Ar-Cipso).
Preparation of 3a. To a solution of 1-ethynyl-1H-benzo[d]-
imidazole 1 (0.390 g, 2.75 mmol) and n-hexyl azide (0.699 g, 5.50
mmol) in EtOH (1.0 mL) was added an aqueous solution of
CuSO4·5H2O (0.274 g, 1.10 mmol in 10.0 mL), followed by solid
sodium ascorbate (0.436 g, 2.20 mmol) in air. The reaction mixture
was stirred at room temperature until complete consumption of 1
(typically 5 min, as monitored by tlc). The reaction mixture was then
diluted with ethyl acetate (500 mL) and the organic layer washed with
dilute ammonia solution (1%, 1 × 250 mL), followed by brine (2 ×
250 mL) and finally water (1 × 250 mL). The organic layer was dried
(MgSO4) and concentrated in vacuo. Column chromatography (flash
SiO2, EtOAc/hexane 1:1) afforded the desired compound 3a as a
white solid (0.512 g, 80%). 1H NMR (500 MHz): 0.91 (t, 3H, J = 7.5
Hz, Me), 1.37 (m, 6H, 3 × CH2), 2.01 (m, 2H, NCH2CH2), 4.47 (t,
2H, J = 7.5 Hz, NCH2), 7.37 (m, 2H, 2 × CHbi), 7.69 (d, 1H, J = 7.5
Hz, CHbi), 7.83 (s, 1H, CHtr), 7.88 (d, 1H, J = 7.5 Hz, CHbi), 8.38 (s,
1H, NCHN). 13CNMR (125.7 MHz): 13.9 (Me), 22.4, 26.1, 30.2, 31.1
(4 × CH2), 51.4 (NCH2), 111.0 (CHtr), 113.8, 120.7, 123.3, 124.2 (4
× CHbi), 132.6 (C-ipso), 141.3 (NCHN), 142.3 (C-ipso), 143.8 (C-
1
44.46; H, 5.05; N, 10.44%. H NMR: δ 0.85 (t, 3H, J = 7 Hz, Me),
1.22 (m, 6H, 3 × CH2), 1.66 (m, 17H, C5Me5 + NCH2CH2), 4.13 (t,
2H, J = 7.5 Hz, NCH2), 7.36 (m, 2H, 2 × CHbi), 7.97 (d, 1H, J = 8.0
Hz, CHbi), 7.98 (s, 1H, CHtr), 8.10 (d, 1H, J = 7.5 Hz, CHbi), 9.35 (s,
1H, NCHN). 13C NMR: δ 8.16 (C5Me5), 12.97 (Me), 21.38, 24.96,
29.21, 30.14 (4 × CH2), 49.95 (NCH2), 84.94 (C5Me5), 112.94
(CHtr), 114.00, 119.26, 122.95, 124.55 (4 × CHbi), 130.80, 138.99 (2
× Cbi), 139.92 (Ctr), 142.46 (NCHN).
Preparation of 5b. A mixture of [IrCl2Cp*]2 (50.0 mg, 0.063
mmol) and 3b (38.0 mg, 0.14 mmol) in CH2Cl2 (5 mL) was stirred
for 4 h. The mixture was filtered through Celite and evaporated to
dryness. The product was washed with hexane and precipitated from
CH2Cl2/hexane to give 5b as a yellow powder (60.0 mg, 63%). The
product was recrystallized from CH2Cl2/hexane. Anal. Calcd for
C26H28Cl2N5Ir: C, 46.36; H, 4.19; N, 10.40. Found: C, 46.48; H, 4.06;
N, 10.42%. 1H NMR: δ 1.66 (s, 15H, C5Me5), 5.31 (s, 2H, CH2), 7.32
(m, 7H, Ph + 2CHbi), 8.01 (s, 1H, CHtr), 8.02 (d, 1H, J = 7.5 Hz,
CHbi), 8.14 (d, 1H, J = 7.5 Hz, CHbi), 9.39 (s, 1H, NCHN). 13C
NMR: δ 9.16 (C5Me5), 54.15 (CH2), 86.01 (C5Me5), 114.21 (CHtr),
114.76, 120.21, 124.12, 125.59 (4 × CHbi), 128.51, 128.55, 128.85 (3
× CHPh), 131.71 (CPh), 134.65, 139.96 (2 × Cbi), 141.26 (Ctr), 143.51
(NCHN). FAB-MS: 673 [M]+, 638 [M − Cl]+
+
ipso). HR-MS (FAB +ve mode): calculated for C15H19N5 , 269.16405;
found, 269.16367 [M]+.
Preparation of 7a. 3a (150 mg, 0.55 mmol) was dissolved in
MeCN (5 mL), and MeI (140 mg, 0.99 mmol) was added. The
mixture was heated at 60 °C for 24 h in a sealed tube. The mixture was
then filtered through Celite and evaporated to dryness. The product
was washed with hexane and precipitated from CH2Cl2/hexane to give
7a as a white powder (170 mg, 75%). The product was recrystallized
from CH2Cl2/hexane. Anal. Calcd for C16H22N5I: C, 46.72; H, 5.39;
Preparation of 3b. To a solution of 1-ethynyl-1H-benzo[d]-
imidazole 1 (0.031 g, 218 μmol) and benzyl azide (0.035 g, 262 μmol)
in EtOH (1.0 mL) was added an aqueous solution of CuSO4·5H2O
(0.011 g, 44 μmol in 1.0 mL), followed by solid sodium ascorbate
(0.017 g, 87 μmol) in air. The reaction mixture was stirred at room
temperature until complete consumption of 1 (typically 5 min, as
monitored by tlc). The reaction mixture was then diluted with ethyl
acetate (250 mL) and the organic layer washed with dilute ammonia
solution (1%, 1 × 100 mL), followed by brine (2 × 100 mL) and
finally water (1 × 100 mL). The organic layer was dried (MgSO4) and
concentrated in vacuo. Column chromatography (flash SiO2, EtOAc/
hexane 1:1) afforded the desired compound 3b as a white solid (0.037
1
N, 17.03. Found: C, 46.63; H, 5.29; N, 16.99%. H NMR: δ 0.91 (t,
3H, J = 7.0 Hz, H15), 1.38 (m, 6H, 3 × CH2), 2.03 (m, 2H,
NCH2CH2), 4.28 (s, 3H, Me), 4.58 (t, 2H, J = 7.0 Hz, NCH2), 7.79
(m, 2H, 2 × CHbi), 8.07 (m, 1H, CHbi), 8.13 (m, 1H, CHtrCHbi), 8.83
(s, 1H, CHtr), 10.09 (s, 1H, NCHN). 13C NMR: δ 12.32 (Me), 21.50,
25.13, 29.11, 30.27 (4 × CH2), 32.75 (NMe), 50.64 (NCH2), 112.82,
113.44 (2 × CHbi), 118.03 (CHtr), 126.92, 127.35 (2 × CHbi), 129.79,
131.48, 138.23 (Ctr, 2 × Cbi), 140.78 (NCHN).
1
g, 61%). H NMR (500 MHz): 5.65 (s, 2H, CH2), 7.36 (m, 4H, Ph),
7.45 (m, 3H, Ph), 7.66 (m, 1H, CHbi), 7.72 (s, 1H, CHtr), 7.87 (m,
1H, CHbi), 8.36 (s, 1H, NCHN). 13C NMR (CDCl3, 125.7 MHz):
55.20 (CH2), 111.00 (CH), 113.7 (CH), 120.7 (CH), 123.3 (CH),
124.3 (CH), 128.2 (2CH), 129.2 (CH), 129.4 (2CH), 132.5 (C-ipso),
Preparation of 8a. A mixture of [IrCl2Cp*]2 (60 mg, 0.076
mmol), 5a (68 mg, 0.17 mmol), and NaOAc (15 mg, 0.19 mmol) in
CH2Cl2 (5 mL) was stirred for 20 h. The mixture was filtered through
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Celite and evaporated to dryness. The product was washed with
hexane and precipitated from CH2Cl2/hexane to give a yellow powder
(50 mg, 40%). Anal. Calcd for IrC26H36ClIN5Ir: C, 40.39; H, 4.69; N,
9.06. Found: C, 40.28; H, 4.60; N, 9.03%.1H NMR: δ 0.87 (t, 3H, J =
7.0 Hz, Me), 1.33 (m, 6H, 3 × CH2), 2.03 (s, 15H, C5Me5), 2.13 (m,
2H, NCH2CH2), 4.07 (s, 3H, NMe), 4.77 (t, 2H, J = 7.0 Hz, NCH2),
7.44 (t, 1H, J = 8.0 Hz, H3), 7.50 (d, 1H, J = 8.0 Hz, H2), 7.59 (t, 1H, J
= 8.0 Hz, H4), 8.70 (d,1H, J = 8.0 Hz, H5), 10.94 (s, 1H, H9). 13C
NMR: δ 10.30 (C5Me5), 13.99 (Me), 22.51, 26.02, 29.97, 31.07 (4 ×
CH2), 35.54 (NMe), 53.55 (NCH2), 93.18 (C5Me5), 110.85 (C2),
114.00 (C5), 115.89(C9), 125.10 (C3), 126.76 (C4), 129.27 (C1),
135.35(C6), 144.91 (C8), 173.00 (C7). FAB-MS: m/z 738 [M]+, 611
[M − I]+. ES-MS: m/z 738 [M]+.
trichloride. We thank Amelia Beiling for some experimental
work.
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4.48; N, 8.93%. 1H NMR: δ 0.89 (m, 3H, Me), 1.34 (m, 6H,3 × CH2),
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X-ray Crystal Structure Determinations. Data for 5b were
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̅
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ASSOCIATED CONTENT
* Supporting Information
Crystallographic data in CIF format for 5b. This material is
■
S
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AUTHOR INFORMATION
Corresponding Author
*E-mail: glenn.burley@strath.ac.uk (G.A.B.), dld3@le.ac.uk
(D.L.D.).
■
(13) Warsink, S.; Drost, R. M.; Lutz, M.; Spek, A. L.; Elsevier, C. J.
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†Department of Pure and Applied Chemistry, University of
Strathclyde, 295 Cathedral Street, Glasgow, U.K. G11 7JU.
̈
Kohn, U.; Altuntas, E.; Baumgaertel, A.; Hager, M. D.; Winter, A.;
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ACKNOWLEDGMENTS
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D.L.D. thanks the EPSRC for funding (EP/D055024/1).
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E055095/1) and Johnson Matthey for a loan of iridium
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