Simple and reactive Ir(i) N-heterocyclic carbene complexes for alkyne activation

Article abstract of DOI:10.1039/c9dt00313d

Two simple unsymmetrical monometallic Ir(i) complexes with an N-heterocyclic carbene ligand and an analogous bimetallic Ir(i) complex were synthesised. These complexes were found to be extremely active catalysts for a range of C-X (X = N or O) and Si-N bond forming reactions involving alkyne and imine activation for dihydroalkoxylation, hydroamination and hydrosilylation reactions. These catalysts exhibited reaction rates far exceeding those of other Rh(i) and Ir(i) complexes previously reported. In addition, a small change to the ligand design (phenyl vs. mesityl) substantially affected both the reactivity and product selectivity of the catalyst. The Ir(i) complex bearing a mesitylene wingtip provided unprecedented regioselectivity in the dihydroalkoxylation reaction and a new kinetic product from the typical hydrosilylation protocol of 2-benyzlpyrroline to produce an N-silylaminoalkene. Our mechanistic studies indicated that this transformation proceeded via a dehydrogenative coupling mechanism.

Full text of DOI:10.1039/c9dt00313d

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Efficient extraction of sulfate from water using
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DOI: 10.1039/C9DT00313D
Journal Name
ARTICLE
Simple and Reactive Ir(I) N-Heterocyclic Carbene Complexes for
Alkyne Activation
feReceived 00th January 20xx,
Accepted 00th January 20xx
a
a
a
a
Mark R. D. Gatus , Indrek Pernik , Joshua A. Tompsett , Samantha C. Binding , Matthew B.
a,b
a
Peterson and Barbara A. Messerle *
DOI: 10.1039/x0xx00000x
www.rsc.org/
Two simple unsymmetrical monometallic Ir(I) complexes with an
Late transition metal complexes containing N-heterocyclic
N-heterocyclic carbene ligand and an analagous bimetallic Ir(I) carbenes (NHCs) are used for many different catalytic
3
4
complex were synthesised. These complexes were found to be applications such as transfer hydrogenation, hydrosilylation
5
extremely active catalysts for a range of C-X (X = N or O) and Si-N and hydroamination reactions. Recently there have been
bond forming reactions involving alkyne and imine activation for reports of Ir(I) NHC complexes that exhibit interesting
dihydroalkoxylation,
hydroamination
and
hydrosilylation structural properties due to interactions between the metal
reactions. These catalysts exhibited reaction rates far exceeding and aromatic substituents of the NHC ligand. These have led to
those of other Rh(I) and Ir(I) complexes previously reported. In surprisingly effective catalytic reactivity and selectivity. Dorta
addition, a small change to the ligand design (phenyl vs mesityl) and co-workers were the first to report the catalysed
substantially affected both the reactivity and product selectivity of intramolecular hydroamination of aminoalkenes using an Ir(I)
6
the catalyst. The Ir(I) complex bearing a mesitylene wingtip complex with a monodentate NHC ligand. The 14 electron Ir(I)
provided
unprecedented
regioselectivity
in
6
the complex, [Ir(dinapthyl)COD][PF ], used for the reaction
dihydroalkoxylation reaction and a new kinetic product from the resulted in excellent enantioselectivity as well as reactivity
typical hydrosilylation protocol of 2-benyzlpyrroline to produce an (Figure 1a) yielding products with enantiomeric excesses of 87-
N-silylaminoalkene. Our mechanistic studies indicated that this 99 %. Oro and co-workers investigated the hydroalkynylation
transfromation proceeded via
mechanism.
a
dehydogenative coupling of imines using an Ir(II) bimetallic NHC complex that was
generated by halide abstraction and hydrogenation from a
simple Ir(I) NHC complex (Figure 1b), the catalyst exhibited
exceptional tolerance towards a variety of different alkyne and
imine substrates.
Introduction
7
The examples given above are based on complexes with
C2-symmetric NHC ligands where the two N-wingtips are
identical. Such systems are the most commonly studied as the
ligands are isolable and commercially available as free NHCs
due to the stability provided but bulkier wingtips protecting
the free NHC, and are therefore benchtop stable for extended
The success of late transition metals as catalysts for organic
transformations of N- and O- containing compounds including,
imines, furans, and ketals, has allowed industry and academia
to access many useful pharmaceuticals, agro- and fine
2
chemicals. Obtaining a fundamental understanding of the
roles and the pathways these transition metal complexes take
during catalysis makes it possible to make informed decisions
on what type of metal centre and ligand would be the most
beneficial for a selected catalysed reaction. One outcome of
this can, however, be complex ligand structures, which in turn
can lead to the ligand itself becoming more expensive to
synthesise than the cost of the precious metal precursor.
8
periods of time. Complexes containing unsymmetrical NHC
ligands can be challenging to synthesise, particularly when
a.Department of Molecular Sciences, Macquarie University, North Ryde, NSW,
Australia, 2109, E-mail: barbara.messerle@mq.edu.au Address here.
b.
School of Chemistry, University of New South Wales, Kensington, NSW, Australia,
2
052
†
Electronic Supplementary Information (ESI) available: Experimental procedure
and characterisation data of new compounds. CCDC 1885417-1885418 For ESI and
crystallographic data in CIF or other electronic format see
DOI: 10.1039/x0xx00000x
Figure 1 IrNHC complexes for catalysing a) intramolecular hydroamination of
alkene amines, and b) hydroalkynylation of imines reactions.
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targeting asymmetric systems and/or two sp -hybridised was synthesised in four steps from 2,7-ditertbutyl-4,5-
View Article Online
DOI: 10.1039/C9DT00313D
13
substituents as the two N-wingtips of an NHC. As the synthesis dibromo-9,9-dimethylxanthene (12) (see SI Section 2.2).
of unsymmetrical NHCs can be more challenging than the The solid-state structures obtained for the complexes
protocol developed by Arduengo for symmetrical NHCs they Ir(COD)Cl(PhNHC) (COD 1,5-cyclooctadiene), the
bearing a COD ligand (see SI Section 2) and
) were as expected. Both Ir(I) centres of
exhibit a four-coordinate square planar geometry about
many research groups reporting superior reactivity and the metal centre (Figure 3). The carbon monoxide co-ligands of
selectivity for a range of reactions catalysed by complexes with exist in a cis arrangement with one being trans disposed to
(9
)
=
are in some cases not as well studied as their symmetric precursor to
4
9
counterparts. However, using unsymmetrical NHC complexes Ir(CO)
2
Cl(MesNHC) (
5
5
for catalytic transformations has proven to be fruitful, with and
9
5
unsymmetrical NHC ligands compared to the symmetrical the carbenic carbon, while the other is situated trans to the
counterparts, partly due to the change in the electronic and chloride. The complexes do not exhibit any metal-arene
10
structural parameters of the NHC ligand.
interaction in the solid-state structures, unlike the examples
We have recently reported both mono- and bimetallic Rh(I) given in Figure 1, as we did not attempt chloride abstraction.
and Ir(I) complexes containing N,N-donor ligands as highly We were unable to obtain crystallographic quality crystals for
active catalysts for C-X (X= O or N) and N-Si bond formation the Ir bimetallic complexes
6 or the analogous Ir(I) bimetallic
reactions with the bimetallic complexes outperforming the complex bearing COD coligands (15, See SI Section 2).
1
1
monometallics in terms of the rate of reaction. We have also
reported the same catalysed reactions using relatively simple Catalysis - Dihydroalkoxylation
mono- and bimetallic Rh(I) NHC complexes (Figure 2, 1-3) as
The complexes 4, 5 and 6 were initially tested as catalysts
catalysts, however, the catalytic activity of these complexes for the intramolecular dihydroalkoxylation reaction of the
was much lower than those of the Rh(I) complexes containing alkynediols, 16a
,
17a
, 18a and 19a (Table 1) with the addition
1
N,N-donor ligands.
of
sodium
F
tetrakis[3,5-bis(trifluoromethyl)phenyl]borate
Obtaining complexes that catalyse a specific C-X bond (Na[BAr ]), allowing for the replacement of the chlorido
4
formation chemo- or regioselectively is highly desirable. Due ligands with a weakly coordinating anion. Both monometallic
to the unusual reactivity of Ir NHC complexes discussed above, Ir(I) complexes catalysed the dihydroalkoxylation reaction of
we were interested in synthesising and determining the 16a to completion (Table 1, entries 1 and 2), in much shorter
activity of the analogous monometallic Ir(I) complexes (
4
and time frames than the analogous Rh(I)NHC(CO) Cl complex (
1
).
) was previously shown to be a poor catalyst
for this particular reaction requiring 5 hours to achieve 90 %
2
5
) as well as the homobimetallic Ir(I) complex
6
which contain RhNHC(CO) Cl (
1
2
unsymmetrical NHC ligands.
-
1 1
conversion of the substrate (TOF = 35 h ). Unexpectedly, the
Ir(I) bimetallic complex took >4 times longer than the
6
Results and discussion
Complex Synthesis
monometallic analogues to complete the reaction (Table 1,
entry 3).
Interestingly, we observed a significant change to the
regioselectivity in the formation of the two products (16b and
The Ir(I) NHC complexes
4
and
5
(Figure 2) can be accessed
following two different methodologies. The complex
Ir(CO) Cl(PhNHC)] ( ) can be synthesised in two steps from 1-
methyl-3-phenyl-1H-imidazolium, while [Ir(CO) Cl(MesNHC)]
) was synthesised in three steps from 1-methyl-3-(2,4,6-
1
6c) when catalysing the cyclisation of alkynediol 16a using
complex as a catalyst (Table 1, entry 2) compared to that
reported previously using other catalysts.
complex favoured the formation of 16c, yielding the
[
2
4
5
2
1, 11a, 14
The Ir(I)
(5
12
5
trimethylphenyl)-1H-imidazolium iodide (see SI Section 2.1).
The bimetallic complex [(Ir(CO) ClLNHC/Ir(CO) ClLNHC) Xan] (6)
2 2
t
products 16b and 16c in a ratio of 1:14. The reaction in this
particular case would proceed initially via a 5-exo-dig
hydroalkoxylation, followed by an aliphatic 6-endo-trig
hydroalkoxylation. This is the highest selectivity of formation
of 16c reported to date. The highest selectivity observed
previously for this reaction was a 1:2 ratio of 16b:16c, reported
by Hashmi and co-workers, using Au(I) phosphite complexes as
15
catalysts. We have previously reported an Ir(I) bimetallic
Figure 2 Previous work; Mono- and bimetallic Rh(I)NHC complexes 1-31 and, this
work; mono- and bimetallic Ir(I)NHC complexes 4-6.
Figure 3 ORTEP depictions of the Ir(I)NHC complexes 5 and 9 with thermal ellipsoids
shown at 50 % probability. Hydrogen atoms have been omitted for clarity.
2
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species favouring the production of 16c resulting in a mixture
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DOI: 10.1039/C9DT00313D
13
of the two products in a ratio of 1:2 for 16b
:16c.
Complexes and (Table 1, entries 4-6) were also highly
4
,
5
6
reactive for the cyclisation of 17a, with all three catalysts
promoting the completion of the reaction within 15 minutes.
Scheme 1 Proposed initial exo-cyclic ring formation/isomerisation observed during
the catalysed dihydroalkoxylation reaction of 18a using complex 5.
In comparison, the rhodium analogue (
1
) stopped turning over
1
after 3.4 hours yielding just 41 % of the product (17b).
the rate at which the substrate 19a was converted to 19b
and promoted 98% conversion of the substrate to
product after 5.9 min and 7.4 min respectively (Table 1, entries
completing the reaction within 48 minutes (Table 1, entries 7 10 and 11) while the bimetallic complex took 33 minutes to
and 8), while the bimetallic catalyst
was again ca. four times catalyse the reaction to 98% conversion (Table 1, entry 12).
slower, completing the reaction in 180 minutes (Table 1, entry
In summary, the monometallic Ir(I) complex significantly
). Interestingly when complex
was used as a catalyst for the outperformed other reported transition metal catalysts in
dihydroalkoxylation of 18a we observed the formation of terms of reaction times, including a NAC-Au(I) complex (NAC =
.
Similar results were obtained for the dihydroalkoxylation of Catalysts
4
5
diol 18a with both monometallic complexes and
4
5
6
6
4
9
5
1
17
18
reaction intermediate 18ai (Scheme 1) by
spectroscopy. That once again demonstrated the preferential hydride complex. As an example, for 16a, 98% conversion
selectivity achieved using complex
as a catalyst towards was obtained after only 4.2 minutes when using (60 °C),
H
NMR N-acyclic carbene), a silver zeolite complex and an Ir
19
5
4
initial exo-dig cyclisation (Table 1, entry 6). The reaction whereas 40 hours was required for the NAC-Au(I) (r.t.), 22
intermediate 18ai was proposed to be the 5,7-spiroketal hours for the silver zeolite (60 °C) and 5 hours for the Ir
(
Scheme 1) based on the identification of a pair of resonances hydride (60

C). Similarly,
4
outperformed the same silver
1
attributed to diastereotopic protons in the H NMR spectrum zeolite catalyst and Ir-H complex for 18a (47 min vs. 24 h) and
2
at 5.0 and 5.1 ppm (doublets, JH-H = 12.4 Hz). While we did not 19a (6 min vs. 24 h). What really made both
4 and 5 stand out
1
fully assign the H NMR spectrum due to the transient nature was that complex
4 is comparable to the best reported Ir(I)
1
3
of the intermediate, the diastereotopic set of proton homobimetallic complexes, while complex
5 displayed novel
resonances did match well to that of the proposed reported product selectivity, particularly for 16c. The simplicity of the
16
structure. The reaction profile (see SI Section 5) shows the structure and ease of synthesis of the monometallic complexes
initial rapid formation of intermediate 18ai, accounting for
and far outweighs the benefit of synergistic effects
0% of the components of the reaction mixture at its obtained for reported Rh(I) and Ir(I) bimetallic complexes, as
4
5
8
1
, 13-14
maximum, quickly followed by the formation of the desired these catalysts are just as effective.
6
,6-spiroketal (18b) as the intermediate is consumed.
The Ir(I) NHC complexes and were extremely active
catalysts for the dihydroalkoxylation reaction of the aliphatic
alkynediol 19a. Kinetic studies were performed at 60
Catalysis – Hydroamination/hydrosilylation
4
5
Given the prevalence of N-containing structural motifs
C as we within pharmaceuticals and agrochemicals, the ability to easily
°
were unable to obtain any informative data at 100
°C due to promote the formation of new carbon-nitrogen bonds using
20
transition metal catalysts is highly desirable. Transition metal
catalysed hydroamination reactions are an ideal way to form
nitrogen-carbon bonds either intra- or intermolecularly as they
Table 1 Catalysed dihydroalkoxylation reaction of alkynediols (16a-19a) using
complexes 4-6
Dihydroalkoxylationa
are highly atom efficient.
21
Complexes
intramolecular hydroamination reactions of 4-pentyn-1-amine
20a) and 5-phenyl-4-pentyn-1-amine (21a), and for the
intermolecular hydroamination reaction of phenylacetylene
22a) with aniline (22b) (Table 2). Following the intramolecular
4, 5 and 6 were tested as catalysts for the
Entry Cat. Substrate
Product(s)
98 % conv. TOF
-
1 a
(min)
(h )
(
1
2
3
4
5
6
4.2 (1:0.5)c 2950
3.0 (1:14)c 2143
16.8 (1:2)c 1360
(
hydroamination of alkynamines 20a and 21a, a subsequent
catalysed hydrosilylation reaction of the cyclised pyrroline
products (20b and 21b) was carried out using diphenylsilane as
the hydrosilylating agent.
4
5
6
4
5
6
4.2
12.0
14.6
2018
648
1283
Complexes 4, 5 and 6 catalysed the hydroamination of 4-
pentyn-1-amine (20a) at a significantly faster rate than the
hydroamination of 5-phenyl-4-pentyn-1-amine (21a). The
7
8
9
4
5
6
47.4
42.0
180
255
132
210
complex [Ir(CO)
efficiently than
(Ir(CO) ClLNHC/Ir(CO)
Surprisingly, when using
4
4
2
Cl(PhNHC)] (
4
) catalysed both reactions more
Cl(MesNHC)] and
) (Table 2, entries 1-6).
as a catalyst, the hydroamination of
-pentyn-1-amine (20a) reached complete conversion within
5 seconds, compared to complexes and which required 35
[Ir(CO)
2
(5)
b
b
b
1
1
1
0
1
2
4
5
6
5.9
7.4
32.7
817
647
676
ClLNHC)tXan] (
[
2
2
6
4
F
Conditions – 1 mol % cat for 4 and 5 and 0.5 mol % for 6, 1 mol % Na[BAr
4
],
5
6
4
a
2
x10- mol substrate, 1,1,2,2-tetrachloroethane-d
2
, 100 °C; TOFs (Turn
and 47 minutes respectively to complete the reaction. Longer
Over Frequency) was calculated at the point of 50% conversion of substrate
to product(s); Reactions were carried out at 60 °C. cRatio of product
formation of 16b:16c
b
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To achieve the subsequent reduction of the imine products
Table 2 Catalysed two-step intramolecular hydroamination/hydrosilylation of
alkynamines 20a and 21a and the catalysed intermolecular hydroamination of
phenylacetylene (23a) with aniline (23b) using complexes 4-6.
View Article Online
: 10.1039/C9DT00313D
SiH were added
2 2
DO
I
(
20b and 21b), two molar equivalents o
to the reaction mixtures after the hydroamination step had
reached >95% conversion. Complexes and were extremely
f
P
h
4
5
Hydroamination/Hydrosilylation
active catalysts for the hydrosilylation reaction of 2-
methylpyrroline (20b) (Table 2, entries 7-8), with both
complexes promoting the completion of the reaction within 4
-
1 i
Entry Cat.
Substrate
Product(s)
95 % conv. TOF (h )
min)
<0.6
34.8
47.4
(
a
1
2
3
4
5
6
>2123
674
1682
-1
-1
minutes (
4
; TOF > 1833 h ,
5; TOF = 698 h ), while the
a
b
bimetallic complex
6
was not very effective, requiring 23
minutes to complete the reaction (Table 2, entry 9). The same
reactivity
trend was observed for the hydrosilylation of 2-benzylpyrroline
a
a
b
4
5
6
4
5
6
21.6
180
>1440
136
73
112
(
21b) using complex
completing in less than 12 seconds with a TOF > 9050 h . The
bimetallic complex did not promote the reaction cleanly,
4 (Table 2, entry 10) with the reaction
-1
c
7
8
9
4
5
6
<1
4
23
>1833
698
391
c
c
6
resulting a in a mixture of products.
There are no reports by other groups of the catalysed
hydrosilylation reactions of 20b and 21b to gauge the
efficiency of 4-6. However, complex 4 was able to catalyse the
1
1
0c
1
4
6
<0.2
N/A
>9050
N/A
reactions in under one minute, which was substantially faster
than the monometallic complexes and comparable to
bimetallic Rh(I) and Ir(I) complexes reported previously.1
1
2d
5
33
104
3, 31
e
1
1
1
3
4
5
6
<1
N/A
110
>1336
<30
331
2
Interestingly, when the [Ir(CO) Cl(MesNHC)] complex (5)
4f
g
was used to promote the hydrosilylation of 2-benzyl-1-
pyrroline (21b) the reaction formed a mixture of the desired
product (21c) and a second product (21d) in a 1:1.6 ratio. The
product 21d could be selectively produced with small amounts
of 21c produced by carrying out the reaction at the lower
h
5
a
F
-4
Conditions – 2 mol % cat, 2 mol % Na[BAr
, 100 °C; 1 mol % cat, 2 mol % Na[BAr
00 °C; Conditions – 4x10 mol of Ph
of Ph
substrates, toluene-d
.3x10 mol substrates in toluene-d8, 110 °C; The reaction plateaued at 46
conversion, TOF based on 46 % conversion. Conditions – 1 mol % cat, 2
mol % Na[BAr ], 3.3x10 mol substrates, toluene-d , 80 °C TOFs (Turn Over
4 8
4
], 2x10 mol substrate, toluene-
], 2x10 mol substrate, toluene-d
b
F
-4
d
1
8
4
8
,
c
-4
d
-4
2
SiH
2
, 100 °C; Conditions - 4x10 mol
e
F
-4
2
SiH
2
, 70 °C; Conditions – 2 mol % cat, 2 mol % Na[BAr
4
], 3.3x10 mol
f
F
8
, 80 °C; Conditions – 2 mol % cat, 2 mol % Na[BAr
4
],
temperature of 70 C (see SI Section 3). Effervescence of H
2
-
4
g
3
%
was observed during the hydrosilylation reaction of 21b
identified by a singlet proton resonance at 4.5 ppm in the H
,
h
1
F
-4
i
Frequency) were calculated at the point of 50% conversion of substrate to
product(s).
8
NMR spectrum using toluene-d as the solvent, and suggests
that the reaction could be proceeding via a dehydrogenative
time periods were also required for converting 21a to 21b with hydrosilylation mechanism (see SI Section 4a). Similar
complex taking up to 9 times longer than (21 vs 180 mins, reactions which produce enamines by dehydrogenative
5
4
respectively) while
conversion.
6
took more than a day to reach 95% coupling mechanism using hydrosilanes have been observed
using a ruthenium(II) thiolate complex as catalyst.32
To the best of our knowledge complexes
4
and
5
are the
While it was not possible to isolate the new product (21d
)
most efficient complexes that have been reported for formed during the hydrosilylation reaction of 21b complex
5
catalysing the hydroamination reactions of 20a and 21a. For was used as the catalyst, we were able to identify the new
the cyclisation of 20a, complex (<0.6 min) outperforms a compound in situ as N-diphenylsilyl-2-benzylidenepyrrolidine
range of other complexes including a samarium (>151 h),
4
2
2
1
2
13
21d (Table 2, entry 12) using 1D and 2D H, H and C NMR
copper(4 h) and a gold organoboron complex (1 h at r.t). spectroscopy. Numerous attempts were made to isolate the
Similarly for 21a (22 min) and (180 min) performed compound either by purification (chromatography) which
extremely well compared to complexes containing a range of resulted in decomposition, or by derivatisation (hydrolysis,
2
3
24
,
4
5
2
5
26
27
lanthanides (>22 h), zinc (16h), tantalum (16h) and gold iodination) which resulted in inseparable mixtures of products.
2
8
1
(
2h).
involving 22a and 22b complex
than gold ylide complexes (3 h at 50
For the intermolecular hydroamination reaction The H NMR spectrum of the product (21d) had similarities to
4
(< 1 min) was more reactive that of N-diphenylsilyl-2-benzylpyrrolidine (21c), with the
2
9

C), a gold organoboron exception of the diastereotopic benzylic proton resonances
2
4
1
complex (24 h at r.t.) and a palladium complex (2 h at 100 which were only present in the H NMR spectrum of 21c. One
3
0
1

C). The monometallic complex
Rh(I) bimetallic complexes we have reported previously for was the appearance of a poorly resolved triplet resonance at
catalysing the hydroamination reactions of 20a and 21a. This 5.87 ppm in the
H NMR spectrum (see SI Section 3), which
4 also outclassed Ir(I) and of the characteristic features of the H NMR spectrum of 21d
1
again demonstrates that the simplicity of this complex was assigned to the benzylic alkene proton. Additionally, we
outshines any synergistic effects obtained by similar bimetallic were able to identify the carbon that is directly bound to the
13, 31
systems due to its highly active characteristics.
alkene proton due to the characteristic chemical shift of this
species (99.2 ppm) in the C NMR spectrum, while the second
13
4
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quaternary carbon resonance of the alkene was observed at
COMMUNICATION
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NHC =
Cl
1
3
1
1
51.6 ppm. 2D C- H correlations supported the assignment
NHC Ir CO
N
N
of these two carbons. The analogous N-silylaminoalkene was
not observed when carrying out the hydrosilylation of 2-
methylpyrroline (20b) under the same reaction conditions.
CO
5
A Na[BArF4]
To probe the reaction mechanism, we used Ph
silylating agent for the catalysed hydrosilylation reaction of 2-
benzylpyrrolidine (21b). When Ph SiD was used as the
reducing agent production of HD gas was observed, identified
2 2
SiD as the
Ph SiD
2
2
2
2
NHC Ir CO
CO
B
D
H
1
1
F
as 1:1:1 triplet at 4.5 ppm ( JH-D = 42.7 Hz) in the H NMR
NHC
SiPh D
1
2
spectrum (Figure 4a) and a doublet at 4.5 ppm ( JD-H = 42.7 Hz)
Ir
NHC
OC
H
D
OC
D
Ir
CO
CO
Ph
2
in the H NMR spectrum (Figure 4b). Formation of a broad
1
singlet at 5.9 ppm in the H NMR spectrum, which was slightly
N
C
2 2
downfield from the Ph SiD resonance at 5.1 ppm, and which
2
1b
increased in intensity as the reaction progressed was indicative
of the formation of the silane bound to the nitrogen of the
Ph
H
Ph
H
E
N
N
H
pyrroline ring (Ph
when using Ph SiD
reaction mechanism leading to proton/deuterium scrambling.
The observation of HD gas and not D gas during the
2 2
DSi-N) (Figure 4b). H gas was also observed
NHC
OC
SiPh D
2
SiDPh2
Ir
Ph
2
2
indicating there is a reversible step in the
D
2
1d
Ph DSi
2
N
CO
NHC
OC
H
D
H
Ir
CO
D
2
hydrosilylation reaction indicates that there is elimination of a
proton from the substrate, hence, the reaction is not
proceeding via the general Chalk-Harrod mechanism typically
Scheme 2 Proposed catalytic cycle for the hydrosilylation of 2-benzylpyrroline (21b)
with Ph SiD using complex 5 and forming N-silylalkeneamine (21d). For simplicity, no
2
2
equilibrium arrows have been used in this scheme.
observed for the hydrosilylation of imines.33
With this information in hand we have proposed a
mechanism for the formation of 21d (Scheme 2). Initially, the
active catalyst is formed by salt metathesis of the chloride co-
F
ligand with Na[BAr
SiD Ph
4
] (Step A), oxidative addition of the silane
2
2
follows generating an Ir(III) deuteride species (Step B).
The nitrogen of the pyrroline substrate then binds to the
vacant coordination site on the Ir(III) centre (Step C). This is
followed by a 1,1-migratory insertion of Ph SiD onto the
2
pyrroline ring generating the silylamine intermediate, while
the benzylic protons on the substrate align themselves
towards the Ir(III) centre (Step D). This facilitates
elimination and release of the N-silylaminoalkene product
21d). Finally, reductive elimination of HD gas regenerates the
active catalyst (Step F). As noted earlier, when using
Ph SiD there was still some production of H gas (Figure 4b)
-hydride
(
2
2
2
which we attributed to reversibiliy at some step of the reaction
mechanism. We propose that this occurs at step D where it is
most likely that a deuterium atom can exchange with one of
the methylene hydrogen atoms of the substrate proior to -
hydride elimination (Scheme 3). Likely step D is not the only
reversible step durng the catalytic cycle, but we remain
cautious interpreting these data further. In addition to the
proposed mechanism here, there has been some studies
suggesting that these types of hydrosilylation reactions can
proceed via an outer sphere mechanism recently discussed by
1
2
Figure 4. HD/H
spectrum for the hydrosilylation reaction of 21b using complex 5 as a catalyst and
Ph SiD as the silylating agent with both products shown as green (21c) and red
21d).
2
(4.5 ppm) gas region of a) The H NMR spectrum and, b) H NMR
2
2
(
N
Ph
STEP D
Ph
H
Ph2DSi
Ph
Ph
H
D
H H
Ph2DSi
NHC
OC
N
Ph2DSi
NHC
OC
N
N
H
H
D
H
D
H
NHC
OC
SiPh2D
NHC
OC
H
H
Ir
Ir
CO
Ir
CO
Ir
NHC Ir CO
CO
D
CO
CO
Scheme 3. Hydrogen/deuterium exchange during the proposed catalytic cycle for the hydrosilylation of 21b using complex 5 as a catalyst
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
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Dalton Transactions
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COMMUNICATION
Journal Name
bimetallic complex
catalyst for the reactions investigated here than the two
monometallic counterparts
6
, however, was typically less effective as a
View Article Online
DOI: 10.1039/C9DT00313D
Table 3. 13C NMR data of carbene carbon and infrared data of carbonyl
stretching frequencies of complexes 4, 5 and 6
4 and 5. This was unexpected, as
Complex
13C NMR
Ir-Carbene-C
5
6
4
previously we have observed substantial catalytic
enhancement by the bimetallic complexes when compared to
broadly similar monometallic analogues.
The investigation of electronic parameters indicated that
both the chemical shift of the carbene carbon and carbonyl
stretching frequency of the Ir complexes correlated well with
their catalytic activity (5<6<4). This suggests that for these
catalyst motifs, an electron poor iridium metal centre results in
a more effective catalyst. For example, the most electron-poor
1
75.1 ppm
174.6 ppm
173.7 ppm
-
-
1
-1
-1
2
1
054.5 cm
974.2 cm
2056.4 cm
1972.0 cm
2066.9 cm
1984.6 cm
IR CO
1
-1
-1
monometallic Ir(I) complex
4 showed extremely high catalytic
activity for the dihydroalkoxylation of alkynediols. It
significantly outperformed other reported transition metal
catalysts in terms of reaction times. At the same time the
three Ir(I) complexes exhibited exemplary catalytic activity for
the inter- and intramolecular hydroamination of alkynamines,
Figure 5. Complexes 4, 5 and 6 ranked in order of increasing catalytic activity observed
for dihydroalkoxylation reactions 17a, 18a and 19a, and hydroamination reactions 20a,
21a and 22a/b.
Oro and co-workers.34 Based on the data available, we are still
1
, 11, 13, 17-19, 36 1, 11,
compared to other catalysts reported to date.
confident that our reaction goes through the proposed inner-
sphere route, however, we cannot exclude that the reaction is
also proceeding via an outer sphere mechanism.
13, 17-19, 35
The cyclic imines formed during the hydroamination
step were subsequently hydrosilyalated. These hydrosilylation
reactions exhibited reaction rates that far exceeded those
observed on using other Rh(I) and Ir(I) complexes previously
investigated.
In summary the simplest of the three complexes, the Ir(I)
monometallic complex (
the homobimetallic complex
followed by the other monometallic complex 5. The reactivity
trend was apparent when the complexes were used for
promoting the synthesis of the majority of alkynediols (17a
8a 19a) and aminoalkynes (20a 21a and 22a/b) tested. The
4
) was the most active catalyst with
6
being slighty less reactive,
In addition to high activity, impressive product selectivity
was also observed. The Ir(I) complex
5 exhibited unique regio-
4>6>5
and chemoselectivity in the promotion of hydroelementation
reactions. For these transformations we observed selective
exo-dig cyclisation of an alkynediol and a silylation reaction of
an imine. This was shown to proceed via a dehydrogenative
coupling reaction mechanism which is not the usual behaviour
of an Ir(I) complex for this type of reaction. The unique
reactivity and high activity of these Ir(I) complexes has spurred
our interest in expanding the scope and applicability of their
use in other catalytic processes.
,
1
,
,
exception was for diol 16a where the reactivity trend was
found to be 4>5>6, due in part to the change in selectivity of
the products 16b and 16c when complex
5 was used. To gain a
better undertsanding of what contributed to the general trend
in catalytic activity for the majority of substrates tested we
examined the carbene carbon using 13C NMR spectroscopy and
the IR spectra of the carbonyl co-ligands of each of the
complexes. Interestingly, the trend in the chemical shift of the
carbene carbon for each complex mimics the trend in catalytic
Acknowledgements
activity of the complexes, with more active catalysts (5<6<4
)
having a more upfield chemical shift of carbene carbon
This research was supported under the Australian Research
1
3
resonance in the C NMR spectrum (Table 3). A similar trend Council’s Discovery Projects funding scheme (project number
was observed in the IR spectra, with more efficient catalysts DP110101611). We thank Macquarie University for financial
having stronger C-O bonds. While these observations suggest support. We acknowledge Macquarie NMR Facilities (including
that the more effective catalysts have an electron poor iridium Yves De Deen’s research facility) and the University of New
metal centre; a part may also be played by the steric South Wales NMR Facility located within the Mark Wainwright
constraints about the metal centres with the iridium in Analytical Centre. There are no conflicts to declare.
compound
compound
4 being the least encumbered and the iridium in
3
5
5
the most.
Notes and references
1
V. Diachenko, M. J. Page, M. R. D. Gatus, M. Bhadbhade and B. A.
Messerle, Organometallics, 2015, 34, 4543-4552.
(a) J. F. Hartwig, Nature, 2008, 455, 314-322; (b) R. Hili and A. K.
Yudin, Nat. Chem. Biol., 2006, 2, 284-287.
D. Wang and D. Astruc, Chem. Rev., 2015, 115, 6621-6686.
(a) A. J. Huckaba, T. K. Hollis and S. W. Reilly, Organometallics,
Conclusion
2
In conclusion, three Ir(I) complexes containing relatively
simple unsymmetrical NHC ligands were synthesised and
evaluated as catalysts. The monometallic complexes
were significantly more active catalysts than the previously
reported monometallic N,N-donor ligand containing Ir(I)
dicarbonyl bis(pyrazol-1-yl)methane (bpm) complexes. The
3
4
4 and 5
2
2
013, 32, 6248-6256; (b) Y. Nakajima and S. Shimada, RSC Adv.
015, 5, 20603-20616.
6
| J. Name., 2012, 00, 1-3
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Dalton Transactions
Journal Name
COMMUNICATION
5
6
7
L. Huang, M. Arndt, K. Gooßen, H. Heydt and L. J. Gooßen, Chem.
Rev. 2015, 115, 2596-2697.
G. Sipos, A. Ou, B. W. Skelton, L. Falivene, L. Cavallo and R. Dorta,
Chem. - Eur. J. 2016, 22, 6939-6946.
L. Rubio-Pérez, M. Iglesias, J. Munárriz, V. Polo, P. J. Sanz Miguel,
J. J. Pérez-Torrente and L. A. Oro, Chem. Comm. 2015, 51, 9860-
28 C. Sarcher, A. Lühl, F. C. Falk, S. Lebedkin, M. Kühn, C. Wang, J.
View Article Online
Paradies, M. M. Kappes, W. Klopper andDPO. IW: 1.0R.1o0e39sk/Cy,9DEuT.0J0.313D
Inorg. Chem. 2012, 2012, 5033-5042.
29 T. Scherpf, C. Schwarz, L. T. Scharf, J.-A. Zur, A. Helbig and V. H.
Gessner, Angew. Chem. 2018, 57, 12859-12864.
30 Q. Chen, L. Lv, M. Yu, Y. Shi, Y. Li, G. Pang and C. Cao, RSC Adv.
2013, 3, 18359-18366.
9863.
8
9
(a) X. Bantreil and S. P. Nolan, Nat. Protocols, 2011, 6, 69-77; (b) A. 31 M. R. D. Gatus, M. Bhadbhade and B. A. Messerle, Dalton Trans.
J. Arduengo, H. V. R. Dias, R. L. Harlow and M. Kline, J. Am. Chem.
Soc. 1992, 114, 5530-5534.
P. Queval, C. Jahier, M. Rouen, I. Artur, J.-C. Legeay, L. Falivene, L.
Toupet, C. Crévisy, L. Cavallo, O. Baslé and M. Mauduit, Angew.
Chem. 2013, 52, 14103-14107.
2017, 46, 14406-14419.
32 J. Hermeke, H. F. T. Klare and M. Oestreich, Chem. - Eur. J. 2014,
20, 9250-9254.
33 (a) A. J. Chalk and J. F. Harrod, J. Am. Chem. Soc. 1965, 87, 16-21;
(b) Y. Corre, W. Iali, M. Hamdaoui, X. Trivelli, J. P. Djukic, F.
Agbossou-Niedercorn and C. Michon, Catal. Sci. Technol. 2015,
5, 1452-1458.
1
1
0 J. Tornatzky, A. Kannenberg and S. Blechert, Dalton Trans. 2012,
41, 8215-8225.
1 (a) J. H. H. Ho, R. Hodgson, J. Wagler and B. A. Messerle, Dalton
Trans., 2010, 39, 4062-4069; (b) L. D. Field, B. A. Messerle and S.
L. Wren, Organometallics, 2003, 22, 4393-4395; (c) S. Burling, L.
D. Field, B. A. Messerle and S. L. Rumble, Organometallics, 2007,
34 J. J. Pérez-Torrente, D. H. Nguyen, M. V. Jiménez, F. J. Modrego,
R. Puerta-Oteo, D. Gómez-Bautista, M. Iglesias and L. A. Oro,
Organometallics, 2016, 35, 2410-2422.
35 L. D. S. Field, S.; Kalman, J. R. , Organic Structures from Spectra,
WIley, 2008.
26, 4335-4343.
1
2 C. M. Wong, M. Fekete, R. Nelson-Forde, M. R. D. Gatus, P. J.
Rayner, A. C. Whitwood, S. B. Duckett and B. A. Messerle, Catal.
Sci. Technol. 2018, 8, 4925-4933.
36 (a) S. Burling, L. D. Field, B. A. Messerle and P. Turner,
Organometallics, 2004, 23, 1714-1721; (b) Y. Zhang, J. Xue, Z.
Xin, Z. Xie and Y. Li, Synlett, 2008, 2008, 940-944.
1
1
3 M. R. D. Gatus, R. T. McBurney, M. Bhadbhade and B. A.
Messerle, Dalton Trans., 2017, 46, 7457-7466.
4 (a) J. H. H. Ho, S. W. S. Choy, S. A. Macgregor and B. A. Messerle,
Organometallics, 2011, 30, 5978-5984; (b) M. G. Timerbulatova,
M. R. D. Gatus, K. Q. Vuong, M. Bhadbhade, A. G. Algarra, S. A.
Macgregor and B. A. Messerle, Organometallics, 2013, 32, 5071-
5
081.
1
5 M. C. Blanco Jaimes, F. Rominger, M. M. Pereira, R. M. B.
Carrilho, S. A. C. Carabineiro and A. S. K. Hashmi, ChemComm.
2
014, 50, 4937-4940.
6 K. Iio, S. Sachimori, T. Watanabe and H. Fuwa, Org. Lett. 2018,
0, 7851-7855.
1
1
1
1
2
2
7 M. C. Blanco Jaimes, C. R. N. Boehling, J. M. Serrano-Becerra and
A. S. K. Hashmi, Angew. Chem. 2013, 52, 7963-7966.
8 S. Borghèse, P. Drouhin, V. Bénéteau, B. Louis and P. Pale, Green
Chem. 2013, 15, 1496-1500.
9 X. Li, A. R. Chianese, T. Vogel and R. H. Crabtree, Org. Lett., 2005,
7
, 5437-5440.
0 (a) E. Vitaku, D. T. Smith and J. T. Njardarson, J. Med. Chem.
2
014, 57, 10257-10274; (b) C. Lamberth, Pest Manage. Sci., 2013,
6
9, 1106-1114.
2
2
2
1 (a) T. E. Mueller and M. Beller, Chem. Rev. 1998, 98, 675-703; (b)
F. Pohlki and S. Doye, Chem. Soc. Rev. 2003, 32, 104-114.
2 A. Zulys, T. K. Panda, M. T. Gamer and P. W. Roesky, ChemComm.
2
3 M. J. Pouy, S. A. Delp, J. Uddin, V. M. Ramdeen, N. A. Cochrane,
G. C. Fortman, T. B. Gunnoe, T. R. Cundari, M. Sabat and W. H.
Myers, ACS Catalysis, 2012, 2, 2182-2193.
004, 22, 2584-2585.
2
2
2
2
4 L. Kong, R. Ganguly, Y. Li and R. Kinjo, Chem. Sci. 2015, 6, 2893-
2902.
5 T. K. Panda, A. Zulys, M. T. Gamer and P. W. Roesky,
Organometallics, 2005, 24, 2197-2202.
6 M. A. Chilleck, L. Hartenstein, T. Braun, P. W. Roesky and B.
Braun, Chem. - Eur. J., 2014, 21, 2594-2602.
7 T. R. Helgert, X. Zhang, H. K. Box, J. A. Denny, H. U. Valle, A. G.
Oliver, G. Akurathi, C. E. Webster and T. K. Hollis,
Organometallics, 2016, 35, 3452-3460.
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N
N
CO
Ir CO
Cl
Ir Catalysis:
Dalton TransactionsPage 8 of 8
C-X bond formation
N
N
CO
FAST
Ir CO
Cl
CO
CO
OC Ir
Cl
N
N
N
N
CO
N
Ir CO
Cl
Ir CO
Cl
N
O
SELECTIVE
NO BENEFIT