Synthesis, characterization and catalytic activity of saturated and unsaturated N-heterocyclic carbene iridium(I) complexes

Article abstract of DOI:10.1039/b814234c

Both saturated and unsaturated N-benzyl substituted heterocyclic carbene (NHC) iridum(i) complexes were synthesized. The unsaturated carbene complex [(un-NHC-Bn)Ir(CO)₂Cl] in the cis form was prepared via the carbene transfer from the corresponding silver complex to [Ir(COD)₂Cl] ₂ followed by ligand substitution with CO, whereas the saturated complex was obtained via the transfer from (sat-NHC-Bn)W(CO)₅. The treatment of phosphines with (NHC)Ir(CO)₂Cl complexes yielded the products with the phosphine ligand trans to the carbene moiety via substitution. X-Ray structural determination shows that distances of Ir-C_(carbene) in both (un-NHC-Bn)Ir(CO)(PR₃)Cl and (un-NHC-Bn)Ir(CO)(PR ₃)Cl are essentially the same. Analyses of spectroscopic and crystal structural data of iridium complexes [(NHC)Ir(CO)(PR₃)Cl] and Vaska's complex show similar corresponding data in both types of complexes, suggesting that the studied NHC ligands and phosphines have similar bonding with Ir(i) metal center. All iridium complexes studied in this work illustrated their catalytically activity on N-alkylation of amine with alcohol via hydrogen transfer reduction. It appears no dramatic difference on the catalytic activity among these iridium carbene complexes; but the saturated carbene complex (sat-NHC-Bn)Ir(CO)(PR₃)Cl appears to be slightly more active. For example, the reaction of benzyl alcohol with aniline in the presence of catalyst (1 mol%) under basic conditions at 100 °C provided the secondary amine (N-benzylaniline) in 96% yield.

Full text of DOI:10.1039/b814234c

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www.rsc.org/dalton | Dalton Transactions
Synthesis, characterization and catalytic activity of saturated and unsaturated
N-heterocyclic carbene iridium(I) complexes†
Yung-Hung Chang, Ching-Feng Fu, Yi-Hong Liu, Shei-Ming Peng, Jwu-Ting Chen and Shiuh-Tzung Liu*
Received 15th August 2008, Accepted 20th October 2008
First published as an Advance Article on the web 5th December 2008
DOI: 10.1039/b814234c
Both saturated and unsaturated N-benzyl substituted heterocyclic carbene (NHC) iridum(I) complexes
were synthesized. The unsaturated carbene complex [(un-NHC-Bn)Ir(CO)2Cl] in the cis form was
prepared via the carbene transfer from the corresponding silver complex to [Ir(COD)2Cl]2 followed by
ligand substitution with CO, whereas the saturated complex was obtained via the transfer from
(sat-NHC-Bn)W(CO)5. The treatment of phosphines with (NHC)Ir(CO)2Cl complexes yielded the
products with the phosphine ligand trans to the carbene moiety via substitution. X-Ray structural
determination shows that distances of Ir–C(carbene) in both (un-NHC-Bn)Ir(CO)(PR3)Cl and
(un-NHC-Bn)Ir(CO)(PR3)Cl are essentially the same. Analyses of spectroscopic and crystal structural
data of iridium complexes [(NHC)Ir(CO)(PR3)Cl] and Vaska’s complex show similar corresponding
data in both types of complexes, suggesting that the studied NHC ligands and phosphines have similar
bonding with Ir(I) metal center. All iridium complexes studied in this work illustrated their catalytically
activity on N-alkylation of amine with alcohol via hydrogen transfer reduction. It appears no dramatic
difference on the catalytic activity among these iridium carbene complexes; but the saturated carbene
complex (sat-NHC-Bn)Ir(CO)(PR3)Cl appears to be slightly more active. For example, the reaction of
benzyl alcohol with aniline in the presence of catalyst (1 mol%) under basic conditions at 100 ◦C
provided the secondary amine (N-benzylaniline) in 96% yield.
metal complexes and their phosphine substituted species. In partic-
ular, we make comparison of donating ability between phosphines
and NHCs toward iridium(I) by means of crystallographic and
spectroscopic analyses. In addition, the preparation of secondary
amines from alcohols and primary amines by using iridium
carbene complexes as the catalyst was investigated.
Introduction
Recently, transition metal catalyzed reactions involving the use
of N-heterocyclic carbenes (NHCs) as ligands have received
considerable attention due to their strong s-donor property.1 It
is believed that the donation property of NHCs, stronger than
phosphines, are able to increase the stability of the catalysts or
pre-catalysts.2–6 Through the analysis of uCO for (NHC)M(CO)x to
estimate the Tolman electronic parameters (TEP) of ligands, N-
heterocyclic carbenes have been considered to be stronger electron
donors than the basic phosphine ligands.6 Like other ligand
systems, the modification of NHCs to fine-tune their coordination
ability and catalytic activity has been amply demonstrated.3 Along
Results and discussion
this context, the difference between saturated and unsaturated N-
heterocyclic carbene (NHC) ligands was also one of the features
to investigate. Nolan and co-workers reported that 1,3-bis(2,4,6-
Iridium carbene complexes
Iridium carbene complexes were prepared via the carbene transfer
method.7 The saturated iridium carbene complex was from the
reaction of (sat-NHC-Bn)W(CO)5 with [Ir(COD)Cl]2,7b whereas
the unsaturated complex was from the reaction of the [(un-NHC-
Bn)AgI]2 complex with [Ir(COD)Cl]2.
trimethylphenyl)-4,5-dihydroimidazol-2-ylidene, a saturated car-
bene donor, appeared to be a better donor than its unsaturated
analogue in Cp*Ru(NHC)Cl, but showing little difference in the
catalytic activity in the olefin metathesis.4 Few other studies on
various metal complexes reveal similar results.5
Tungsten carbene, complex 1, was prepared according to the
previously reported procedure, by a deoxygenation reaction of
In this work, we report the preparation of both saturated and
unsaturated N-benzyl substituted heterocyclic carbene (NHC)
iridum(I) complexes via carbene transfer reactions from different
=
W(CO)6 with NH2(CH2)2N PPh3 to form the corresponding
isocyanide complex, which subsequently underwent intramolec-
ular cyclization to give the un-substituted NHC complex 1.7a
Deprotonation of 1 with an excess of NaH followed by treatment
of benzyl bromide yielded the desired tungsten carbene complex
2.7c The reaction of 2 with an equal molar amount of [Ir(COD)Cl]2
resulted in the formation of the iridium carbonyl complex 3
(Scheme 1). Apparently, both the carbene and the carbonyl
Department of Chemistry, National Taiwan University, Taipei 106, Taiwan.
E-mail: stliu@ntu.edu.tw; Fax: +886 2 2363 6359
† Electronic supplementary information (ESI) available: ORTEP plot
of 7a. CCDC reference numbers: 698437 4a and 698438 7a. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/b814234c
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ability of carbene is stronger than that of chloride, the down-field
13C chemical shifts of the carbonyl groups of the compounds 3 and
6 are assigned to those trans to carbene.9
The stereoisomers of phosphine substituted complexes
[(NHC)Ir(CO)Cl(PR3)] were identified by both spectroscopic
analyses and X-ray structural determination. The trans relation-
ship of phosphine to the carbene ligand is supported by the
13C NMR spectrum, in which the phosphorus–carbon coupling
constants for (JP–C(carbene)) and (JP–C(carbonyl)) are around 100 and
10 Hz, respectively. The carbonyl stretching frequencies for 4a
and 7a are 1944 and 1945 cm-1, respectively, which are essentially
identical to the corresponding data for Vaska’s complex.10 These
data also verify that the carbonyl ligands are trans to the chloride
in 4a and 7a. The detail coordination configurations of 4a and 7a
were confirmed by the X-ray crystal structural analysis.
The crystal structures of 4a and 7a are isomorphous. Fig. 1
displaystheORTEPplotsof 4a. Thestructuresofbothcompounds
4a and 7a show that the metal is in a square planar geometry
and clearly displays the trans relationship between carbene and
phosphine donors. Selected bond lengths and bond angles are
summarized in Table 2 and all are in the normal range as
compared to those of the related species. Bond lengths of Ir–
Scheme 1
ligands readily transfer from the tungsten metal center to the
iridium(I). This carbonyl substitution was expected due to the
strong donating of NHC ligand leading the enhancement of back-
bonding to the carbonyls, which was also observed in the platinum
complexes.7c In probing the donating ability of carbene ligands,
the corresponding phosphine complexes were prepared for the
investigation. Substitution of a carbonyl ligand by phosphine
proceeded smoothly to yield the substituted product 4, which
the phosphine was seated trans to the carbene moiety. Both
triphenylphosphine and tricyclohexylphosphine behave similarly.
For the unsaturated NHC complex, the carbene moiety transfer
from silver to iridium was employed to deliver the desired
species.8 Treatment of 1,3-dibenzylimidazolium bromide with
Ag2O in the presence of NaI smoothly afforded silver-(un-NHC-
Bn) complexes, which was subsequently reacted with [Ir(COD)Cl]2
to provide 5. Under an atmospheric pressure of carbon monoxide,
the COD was completely replaced by carbonyl ligands to form
6. The synthetic route for the silver and iridium complexes is
illustrated in Scheme 2. The phosphine substituted complexes 7
were obtained similarly as described for 4.
˚
C(carbene) [4a:1.807(4) and 7a: 1.813(4) A, respectively] lie in the
same range for other iridium NHC complexes.6,11 There is no
significant difference in both structures in all aspect except the
distances of C(3)–C(4) [single vs. double bond], thus indicating
that the introduction of saturated or unsaturated NHC ligand has
little effect on the structural parameters around metal center.
Scheme 2
The NMR spectroscopic data for the iridium complexes pre-
pared in this work are consistent with their proposed formulations
and selected data are summarized in Table 1. The 13C NMR signals
of the carbene carbons appear down-field in the range of 174–
Fig. 1 ORTEP plot of complex 4a (drawn with 30% probability
ellipsoids).
205 ppm of these iridium complexes, consistent with C(carbene)
-
The iridium phosphine carbene complexes and Vaska’s complex
are compared as illustrated in Tables 1 and 2. 31P NMR shifts for
these species do not show any significant difference, neither are the
carbonyl stretching frequencies. According to Table 2, there is no
substantial difference in either bond distances or bond angles for
bound toward metal center. 13C chemical shifts of carbonyls
appeared at 181.4 and 168.3 ppm for 3 as well as 181.1 and
167.9 ppm for 6, respectively. The carbonyl stretching frequencies
for both 3 and 6 are essentially identical. Based on the donating
862 | Dalton Trans., 2009, 861–867
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Table 1 Selected spectral data for iridium carbene complexesa
b
Complex
13C NMR, C(carbene)–Ir
198.6
13C NMR, C(carbonyl)–Ir
181.4, 168.3
31P NMRa
—
IR (uC )
=
O
3
2064, 1979 (KBr)
2067, 1983 (CH2Cl2)
1944 (KBr)
4a
4b
5
202.1 (JP–C = 108.2)
204.9 (JP–C = 99.4)
181.0
171.7(JP–C = 9.8)
172.0 (JP–C = 10.6)
—
24.6
29.5
—
1932 (KBr)
—
6
174.2
181.1, 167.9
—
2064, 1978 (KBr)
2065, 1983 (CH2Cl2)
1945 (KBr)
7a
7b
177.6 (JP–C = 116)
171.3 (JP–C = 10.4)
171.6 (JP–C = 10.5)
24.7
29.3
23.4
30.5
181.0 (JP–C = 105.8)
1932 (KBr)
[trans-(PPh3)2IrCl(CO)]
[trans-(PCy3)2IrCl(CO)]
1945 (KBr)c
1931 (KBr); 1922 (CH2Cl2)c
a In CDCl3, ppm, J in Hz. b Units are cm-1. c Ref. 10a.
◦
˚
their abilities to catalyze N-alkylation of amine with alcohol were
examined.
Table 2 Selected bond distances (A) and bond angles ( ) for 4a, 7a and
Vaska’s complex
In a typical experiment for the reaction, aniline (1 mmol),
benzyl alcohol (3 mmol), base and 1 mol% of the iridium catalyst
were placed in the flask. An excess amount of alcohol was
used for not only as the reactant, but also as the solvent. The
mixture was heated to 100 ◦C for a certain period. The organic
product was isolated by extraction and then analyzed by both
Complex
4a
7a
Vaska’s complexa
˚
Bond lengths/A
Ir(1)–C(1)
Ir(1)–C(2)
Ir(1)–P(1)
Ir(1)–Cl(1)
C(1)–O(1)
C(3)–C(4)
1.807(4)
2.070(3)
2.3204(8)
2.3680(9)
1.128(5)
1.505(5)
1.813(4)
2.069(3)
2.3075(8)
2.3655(8)
1.127(4)
1.338(5)
1.791(13)
—
2.330(1)
2.382(3)
1.161(18)
—
1
GC and H NMR spectroscopy. The results are summarized in
Table 3.
Besides the N-benzylaniline, we found the un-reduced imine
intermediate presented in each reaction. However, the mono-
alkylated product was formed selectively; no formation of di-
alkylated N,N-dibenzylaniline was observed. When the reac-
tion was carried out without a base, N-benzylaniline and N-
benzylideneaniline were formed in low yields (entry 1). The
production of amine and imine was considerably accelerated by
the addition of base. It was noticed that the amount and nature of
base also affected the product distribution. Both KOH and CsOH
gave excellent conversions of the reactions, but CsOH provided
more N-benzylaniline than KOH did. When the reaction was
carried out in the presence of 50 mol% CsOH, N-benzylaniline was
formed in an excellent yield (96%) with 4a as the catalyst (Table 3,
entry 14), which can be considered the best reaction conditions
for this particular transformation. It was noticed that the use of
organic bases gives poor yields, but the hydroxide salts provide
better results. Presumably, the dissolution of hydroxide salts in
alcohols generates the corresponding alkoxide, which facilitates
the reactions. In these catalytic studies, we found that there is
no dramatic difference among iridium complexes prepared in this
work (Table 3, entries 9, 10, 15, 16 and 17).
We also explored the N-alkylation of other primary amines
(Table 4). The reactions of substituted anilines with benzyl alcohol
proceeded in excellent yields (Table 4, entries 1–3). In the reaction
of hexylamine with benzyl alcohol, a low yield was obtained.
However, we found that the amine was completely consumed and
converted into other unidentified products. When the reaction
of cyclohexylamine with benzyl alcohol proceeded under similar
conditions, only the corresponding imine was obtained. The use of
a secondary amine or secondary alcohol gave poor yields for the
corresponding product. However, the use of pyridinyl derivatives
gave satisfactory results in the production of the corresponding
amine (entries 11 and 12).
Bond angles/◦
C(1)–Ir(1)–C(2)
P(1)–Ir(1)–C(2)
P(1)–Ir(1)–C(1)
C(1)–Ir(1)–Cl(1)
92.0(1)
175.10(9)
91.84(11)
177.6(1)
92.3(1)
174.77(8)
91.78(10)
178.1(1)
—
—
90.81(40)
178.08(40)
a Ref. 10b.
4a, 7a and Vaska’s complex, except the bond length corresponding
to C(1)–O(1) is slightly shorter than that in the Vaska’s complex
by about 0.04 A. From the above observation, we conclude that
the donating ability of both NHC ligands are quite similar, and
appear to be comparable to phosphine.
By adopting the analysis of Tolman electronic parameter (TEP)
for carbene ligands developed by Crabtree and co-workers,6
TEP values for un-NHC-Bn and sat-NHC-Bn were estimated.
Since both complexes 3 and 6 have similar carbonyl stretching
frequencies, their TEP values are comparable and are evaluated
as 2054 and 2055 cm-1, respectively. These values are very close to
that for tricyclohexylphosphine. Such an outcome is in agreement
with an earlier conclusion obtained from a qualitative comparison
using IR data of (NHC)Ir(CO)2Cl reported by Crabtree.6 This
trend is consistent, with a very limited distinct, to that observed
for the related Vaska’s complex as discussed in the previous section.
˚
Catalytic N-alkylation of amine with alcohol
Few reports have demonstrated that iridium complexes are good
catalysts for N-alkylation of amine with alcohols.12 It has also
been established that the introduction of a NHC ligand to the
metal center would enhance the catalytic activity on the hydrogen
transfer reaction.13 Thus, with the new carbene complexes in hand,
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Table 3 Results of N-alkylation of aniline with benzyl alcohola
Yield (%)b
Amount of base
(mol%)
=
Entry
Catalyst
Base
PhNHCH2Ph
PhN CHPh
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
4a
4a
4a
4a
4a
4a
4a
4a
3
4b
4a
4a
4a
4a
4b
7a
7b
4a
—
—
15
15
15
15
15
15
15
15
15
50
75
50
50
50
50
50
75
5
Trace
20
25
Trace
5
11
29
30
39
20
36
15
32
61
50
7
11
29
3
3
15
4
K2CO3
NaOEt
KOtBu
Et3N
DBU
DMAP
KOH
KOH
KOH
KOH
KOH
LiOH
CsOH
CsOH
CsOH
CsOH
CsOH
0
47
24
17
85
68
37
96
82
81
89
73
19
a Aniline (1 mmol) and catalysts (1 mol% based on aniline) in benzyl alcohol (3 mmol) at 100 ◦C for 24 h. b Yield based on 1H NMR integration.
Table 4 N-alkylation reactions catalysed by the iridium complex 4aa
Entry
1
Substrates
t/h
Product (yield)b
p-ClC6H4NH2
C6H5CH2OH
C6H5CH2OH
C6H5CH2OH
C6H5CH2OH
C6H5CH2OH
20
(99%)
(96%)
(99%)
2
3
4
5
p-BrC6H4NH2
p-tBuC6H4NH2
CH3(CH2)5NH2
20
24
24
24
(17%)
(62%)
6
7
C6H5NH2
C6H5NH2
p-MeOC6H5CH2OH
p-ClC6H5CH2OH
24
24
(72%)
(87%)
(18%)
(7%)
8
9
C6H5NH2
C6H5NH2
CH3(CH2)7OH
Cyclohexanol
C6H5CH2OH
24
24
24
C8H17NHC6H5 (67%)
Cyclohexanone (< 5%)
10
(< 8%)
11
12
C6H5NH2
24
24
(90%)
C6H5CH2OH
(99%)
a Amine (1 mmol), CsOH (0.5 mmol) and 4a (1 mol% based on amine) in alcohol (3 mmol) at 100 ◦C. b Isolated yield.
Summary
carbene transfer methods. In having these complexes, substitu-
tion reactions by phosphine ligands were studied. The proper-
ties of the obtained complexes [trans-(NHC)Ir(PR3)COCl] are
quite similar to those of Vaska’s complexes in many aspects,
We have reported the synthesis of both saturated and unsat-
urated N-heterocyclic carbene iridium complexes via different
864 | Dalton Trans., 2009, 861–867
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indicating that both carbene ligands and phosphine have com-
parable coordinating ability. Iridium complexes prepared in this
work showed good catalytic activities on N-alkylation of aniline
with benzyl alcohol. However, there is no significant difference
among these iridium carbene complexes on this catalytic reaction.
We are currently performing methods for investigation of the
mechanistic pathway for the catalysis, and the selectivity in the
processes.
(ArCH2N), 48.1 (d, JP–C = 3.8 Hz, NCH2–CH2N). Anal. calcd for
C36H33ClIrN2OP: C 56.28, H 4.33, N 3.65. Found C 55.70, H 4.56,
N 3.38.
Complex [(sat-NHC-Bn)Ir(CO)(PCy3)Cl] 4b. This procedure
was similar to that for 4a except for the phosphine ligand.
Tricyclohexyl phosphine (37.9 mg, 0.135 mmol) and 3 (72 mg,
0.135 mmol) in anhydrous CH2Cl2 (5 mL) was placed in a flask
under nitrogen atmosphere. After stirring at room temperature for
2.5 h, the solvent was removed and the residue was washed with
diethyl ether (3 ¥ 2 mL). The phosphine substituted complex 4b
was obtained as a yellow solid (98 mg, 92%). IR (KBr)/cm-1: 1932
Experimental
General information
1
1
(uCO). 31P{ H} (161.9 MHz, CDCl3) d/ppm: 29.5 (s). H NMR
(400 MHz, CDCl3) d/ppm: 7.51 (d, J = 7.4 Hz, 4H, ArH), 7.39–
7.26 (m, 6H, ArH), 5.52 (d, J = 14.6 Hz, 2H, ArCH2N), 5.01 (d,
J = 14.6 Hz, 2H, ArCH2N), 3.43–3.38 (m, 4H, NCH2–CH2N),
2.32–1.13 (m, 33H, Cy). 13C NMR (100 MHz, CDCl3) d/ppm:
204.9 (d, JP–C = 99.4 Hz, Ir=C), 172.0 (d, JP–C = 10.6 Hz, CO),
136.8, 128.6, 128, 127.62, 127.61 (phenyl), 54.5 (ArCH2N), 48.1
(d, JP–C = 3.5 Hz, NCH2–CH2N), 33.6 (d, JP–C = 25.4 Hz, Cy),
30.1 (s, Cy), 27.7 (d, JP–C = 10.4 Hz, Cy), 26.8 (s, Cy). Anal. calcd
for C36H51ClIrN2OP: C 54.98, H 6.54, N 3.56. Found: C 54.71, H
6.61, N 3.23.
All reactions, manipulations and purification steps were per-
formed under a dry nitrogen atmosphere. Tetrahydrofuran
was distilled under nitrogen from sodium benzophenone ketyl.
Dichloromethane and acetonitrile were dried over CaH2 and
distilled under nitrogen. Other chemicals and solvents were
of analytical grade and were used after degassing. Tungsten
carbene complex 27a and 1,3-dibenzylimidazolium bromide14 were
prepared accordingly to the method reported previously.
Nuclear magnetic resonance spectra were recorded in CDCl3 on
either a Bruker AM-300 or AVANCE 400 spectrometer. Chemical
shifts are given in parts per million (ppm) relative to Me4Si for
1H and 13C NMR and relative 85% H3PO4 for 31P NMR. Infrared
spectra were measured on a Nicolet Magna-IR 550 spectrometer
(Series-II) as KBr pallets, unless otherwise noted.
Complex [(un-NHC-Bn)AgI]2. To a solution of 1,3-dibenzyl-
imidazolium bromide (2.2 g, 6.59 mmol), silver oxide (0.8 g,
3.30 mmol) and sodium iodide (0.99 g, 6.59 mmol) in CH2Cl2
(50 mL) were stirred at room temperature under nitrogen atmo-
sphere for 48 h. Filtration of the reaction mixture through Celite
gave a colourless solution. Upon the addition of hexane to the
filtrate, the desired silver complex was precipitated and isolated as
a white solid (1.8 g, 72%). 1H NMR (400 MHz, CDCl3) d/ppm:
Complex [(sat-NHC-Bn)Ir(CO)2Cl] 3. A mixture of 2 (100 mg,
0.174 mmol) and [Ir(COD)Cl]2 (117 mg, 0.174 mmol) in a 50 mL
flask capped with a septum was evacuated and flashed with
nitrogen three times. CH2Cl2 (6 mL) was syringed into the mixture
and the resulting solution was stirred at room temperature for
72 h. The reaction mixture was filtered through Celite to remove
the tungsten species. The residue was chromatographed on silica
with elution of hexane–ethyl acetate (3 : 1) and the yellow band was
collected. Upon concentration, the desired product was obtained
as a yellow solid (72 mg, 77%). IR (KBr)/cm-1: 2064, 1979 (uCO).
1H NMR (400 MHz, CDCl3) d/ppm: 7.40–7.31 (m, 10H, ArH),
5.17 (d, J = 14.8 Hz, 2H, ArCH2N), 4.93 (d, J = 14.8 Hz, 2H,
ArCH2N), 3.47 (s, 4H, NCH2–CH2N). 13C NMR (100 MHz,
CDCl3) d/ppm: 198.6 (Ir=C), 181.4, 168.3 (CO), 135.0, 128.9,
128.24, 128.23 (phenyl), 54.7 (ArCH2N), 48.3 (NCH2–CH2N).
Anal. calcd for C19H18ClIrN2O2: C 42.73, H 3.40, N 5.25. Found:
C 42.75, H 3.67, N 5.00.
=
7.33–7.23 (m, 20H, ArH), 6.87 (s, 4H, C CHN), 5.30 (s, 8H,
ArCH2N). 13C NMR (100 MHz, CDCl3) d/ppm: 185.0 (Ag=C),
136.0, 128.9, 128.3, 128.0 (phenyl), 121.2 (NCH=CHN), 55.6
(ArCH2N). Anal. calcd for C17H16AgIN2: C 42.27, H 3.34, N 5.80.
Found C 42.00, H 3.09, N 5.56.
Complex [(un-NHC-Bn)Ir(COD)Cl] 5. A mixture of sil-
ver complex [(un-NHC-Bn)AgI]2 (100 mg, 0.128 mmol) and
[IrCl(COD)]2 (86 mg, 0.128 mmol) in dichloromethane (6 mL)
was stirred at room temperature for 10 h. The resulting solu-
tion was filtrated through Celite followed by concentration and
chromatographed on silica gel with elution of CH2Cl2–hexane
to afford yellow crystalline solids upon concentration (69 mg,
1
92%). H NMR (400 MHz, CDCl3) d/ppm: 7.38–7.28 (m, 10H,
=
ArH), 6.65 (s, 2H, C CHN), 5.76 (d, J = 14.8 Hz, 2H, ArCH2N),
Complex [(sat-NHC-Bn)Ir(CO)(PPh3)Cl] 4a. Triphenyl phos-
phine (35.4 mg, 0.135 mmol) and 3 (72 mg, 0.135 mmol) in
anhydrous CH2Cl2 (5 mL) was placed in a flask under nitrogen
atmosphere. After stirring at room temperature for 2.5 h, the
solvent was removed and the residue was washed with diethyl ether
(3 ¥ 2 mL). The phosphine substituted complex was obtained as a
5.60 (d, J = 14.8 Hz, 2H, ArCH2N), 4.67–4.61 (m, 2H, COD),
2.98–2.94 (m, 2H, COD), 2.18–2.10 (m, 4H, COD), 1.72–1.68
(m, 2H, COD), 1.57–1.51 (m, 2H, COD). 13C NMR (100 MHz,
CDCl3) d/ppm: 181.0 (Ir=C), 136.3, 128.9, 128.2, 128.1 (phenyl),
120.5 (NCH=CHN), 85.1 (COD), 54.3 (ArCH2N), 52.0, 33.5,
29.5 (COD). Anal. calcd for C25H28ClIrN2: C 51.40, H 4.83, N
4.80. Found: C 51.17, H 5.15, N 4.49.
1
yellow solid (90 mg, 87%). IR (KBr)/cm-1: 1944 (uCO). 31P{ H}
(161.9 MHz, CDCl3) d/ppm: 24.6 (s). 1H NMR (400 MHz,
CDCl3) d/ppm: 7.65–7.63 (m, 6H, ArH), 7.48 (d, J = 7.4 Hz,
4H, ArH), 7.34–7.30 (m, 15 H, ArH), 5.59 (d, J = 14.7 Hz,
2H, ArCH2N), 5.08 (d, J = 14.7 Hz, 2H, ArCH2N), 3.47–3.43
(m, 4H, NCH2–CH2N). 13C NMR (100 MHz, CDCl3) d/ppm:
202.1 (d, JP–C = 108.2 Hz, Ir=C), 171.7 (CO), 136.4, 134.7, 134.6,
133.7, 133.2, 129.8, 128.7, 128.5, 128.0, 127.9, 127.7 (phenyl), 54.9
Complex [(un-NHC-Bn)Ir(CO)2Cl] 6. A solution of 5 (100 mg,
0.171 mmol) in CH2Cl2 (6 mL) was stirred under an atmosphere of
carbon monoxide at room temperature overnight. Upon removal
of organic molecules, the residue was washed with a small portion
of hexane (0.5 mL) to yield 6 as a yellow solid (87 mg, 95%).
1
IR (KBr)/cm-1: 2064, 1978 (uCO). H NMR (400 MHz, CDCl3)
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Table 5 Crystal data for 4a and 7a
Complex
4a
7a
Formula
FW
C36H33ClIrN2OP
768.26
C36H31ClIrN2OP
766.25
Crystal system
Space group
Monoclinic
P21/n
10.2700(3)
32.3955(7)
10.8716(3)
90
117.397(1)
90
3211.3(2)
4
1.589
1520
0.25 ¥ 0.20 ¥ 0.15
22 873
Monoclinic
P21/n
10.1220(5)
32.2279(14)
10.7193(6)
90
117.211(6)
90
3109.8(3)
4
1.637
1512
0.25 ¥ 0.20 ¥ 0.15
18 105
6807 (Rint = 0.0265)
2.59–27.50
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
V/A
Z
D
calcd/Mg m-3
F(0,0,0)
Crystal size/mm
Reflections collected
Independent reflections
q range/◦
Refinement method
Goodness of fit on F2
R indices [I > 2s(I)]
R indices (all data)
7295 (Rint = 0.0436)
1.26–27.50
Full-matrix least-squares on F2
1.006
1.074
R1 = 0.0277, wR2 = 0.0680
R1 = 0.0266, wR2 = 0.0470
R1 = 0.0363, wR2 = 0.0728
R1 = 0.0373, wR2 = 0.0485
=
d/ppm: 7.38–7.32 (m, 10H, ArH), 6.82 (s, 2H, C CHN), 5.53 (dd,
J = 14.8 Hz, 4H, ArCH2N). 13C NMR (100 MHz, CDCl3) d/ppm:
181.1(Ir–CO), 174.2 (Ir–Ccarbene), 167.9 (Ir–CO), 135.2, 129.0,
128.6, 128.3 (phenyl), 121.6 (NCH=CHN), 55.1 (ArCH2N). Anal.
calcd for C19H16ClIrN2O2: C 42.89, H 3.03, N 5.27. Found C 42.57,
H 3.35, N 5.65.
Then, alcohol (3 mmol), amine (1 mmol) and base were added
subsequently to the above iridium complex. The mixture was
stirred at room temperature for 10 min, and then heated
and kept at 100 ◦C by an oil bath. The reaction was then
monitored by 1H NMR. After completion of the reaction,
brine (3 mL) and CH2Cl2(5 mL) were added. The organic
layer was separated and the aqueous layer was extracted
with CH2Cl2. The combined organic extracts were dried over
magnesium sulfate, filtered and then concentrated in vacuo.
The residue was chromatographed on silica gel with the
elution of a mixture of hexane and ethyl acetate. Products
obtained in this work were characterized by spectral methods
Complex [(un-NHC-Bn)Ir(CO)(PPh3)Cl] 7a. The preparation
of 7a is similar to that of 4a. Yield 80%. IR (KBr)/cm-1: 1945
(uCO). 31P{ H} (161.9 MHz, CDCl3) d/ppm: 24.7 (s). H NMR
(400 MHz, CDCl3) d/ppm: 7.69–7.65 (m, 6H, phenyl), 7.44–
7.42 (m, 4H, phenyl), 7.35–7.31 (m, 15H, phenyl), 6.76 (s, 2H,
1
1
=
C CHN), 5.90 (d, J = 14.8 Hz, 2H, ArCH2N), 5.66 (d, J = 14.8
1
particularly with H NMR, and the data were consistent with
Hz, 2H, ArCH2N). 13C NMR (100 MHz, CDCl3) d/ppm: 177.6
(d, JP–C = 116 Hz, Ir=C), 171.3 (d, JP–C = 10.4 Hz, CO), 136.5,
134.7, 134.6, 133.8, 133.3, 129.8, 128.8, 128.5, 128.1, 128.0, 127.9
(phenyl), 120.6 (d, JP–C = 3.5 Hz, NCH=CHN), 54.9 (ArCH2N).
Anal. calcd for C36H31ClIrN2OP: C 56.43, H 4.08, N 3.66. Found:
C 56.52, H 4.24, N 3.45.
those reported: N-(4-chlorophenyl)benzenemethanamine,15a N-
(4-bromophenyl)benzenemethanamine,15b N-(4-t-butylphenyl)-
benzenemeth-anamine,15c N-hexylbenzenemethanamine,15a ben-
zylidene-cyclohexylamine,15d 4-methoxy-N-phenylbenzene-me-
than-amine,15a N-[(4-methoxyphenyl)methylene]benzen-amine,15e
4-chloro-N-phenyl-benzenemethanamine,15a N-[(4-chloro-phe-
nyl)methylene]benzenamine,15e N-octylbenzen-amine,15f 1-[(4-
chlorophenyl)methyl]piperidine,15g N-phenyl-2-pyrid-inemetha-
namine,15a N-(phenylmethyl)-4-pyridinamine.15h
Complex [(un-NHC-Bn)Ir(CO)(PCy3)Cl] 7b. The preparation
of 7b is similar to that of 4a. 90% yield, IR (KBr)/cm-1: 1932
(uCO). 31P{ H} (161.9 MHz, CDCl3) d/ppm: 29.3 (s). H NMR
1
1
(400 MHz, CDCl3) d/ppm: 7.46 (d, J = 7.0 Hz, 4H, phenyl), 7.35–
Crystallography. Crystals suitable for X-ray determination
were obtained for 4a and 7a by recrystallization from
dichloromethane/ether at room temperature. Cell parameters
were determined using a Siemens SMART CCD diffractometer.
The structure was solved using the SHELXS-97 program16 and
refined using the SHELXL-97 program17 by full-matrix least-
squares on F2 values. The crystal data of these complexes are listed
in Table 5. An ORTEP plot of 4a is drawn with 30% probability
ellipsoids and partial labelling for clear view in Fig. 1, whereas an
ORTEP plot of 7a is deposited as ESI.† Other crystallographic
data are deposited as ESI.†
=
7.28 (m, 6H, phenyl), 6.76 (s, 2H, C CHN), 5.85 (d, J = 14.7 Hz,
2H, ArCH2N), 5.59 (d, J = 14.7 Hz, 2H, ArCH2N), 2.34–1.16 (m,
33H, Cy). 13C NMR (100 MHz, CDCl3) d/ppm: 181.0 (d, JP–C
=
105.8 Hz, Ir=C), 171.6 (d, JP–C = 10.5 Hz, CO), 136.9, 128.7,
128.5, 127.9 (phenyl), 120.3 (d, JP–C = 3.1 Hz, NCH=CHN), 54.4
(ArCH2N), 33.7 (d, JP–C = 25.7 Hz, Cy), 30.1 (s, Cy), 27.7 (d,
JP–C = 10.4 Hz, Cy), 26.8 (s, Cy). Anal. calcd for C36H49ClIrN2OP:
C 55.12, H 6.30, N 3.57. Found: C 54.98, H 6.11, N 3.19.
Catalysis general procedure. A mixture of 1 mol% iridium
complex was placed in a flask under a nitrogen atmosphere.
866 | Dalton Trans., 2009, 861–867
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Lee and S.-M. Peng, Organometallics, 1998, 17, 993–995; (c) R.-Z.
Ku, J.-C. Huang, J.-Y. Cho, F.-M. Kiang, K. R. Reddy, Y.-C. Chen,
K.-J. Lee, J.-H. Lee, G.-H. Lee, S.-M. Peng and S.-T. Liu,
Organometallics, 1999, 18, 2145–2154; (d) F. E. Hahn, V. Langenhahn,
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2005, 5390–5392.
Acknowledgements
We thank the National Science Council for financial support
(NSC96-2113-M-002-009).
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©