An unprecedented iridium(III) catalyst for stereoselective dimerisation of terminal alkynes

Article abstract of DOI:10.1002/adsc.200700406

A novel iridium(III) hydride complex, IrHCl(TIMP₃) (HTIMP ₃, = tris[1 -(diphenylphosphino)-3-methyl-1 H-indol-2-yl]methane) was prepared and fully characterized in both the solid state and in solution. Chloride abstraction by silver

Full text of DOI:10.1002/adsc.200700406

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DOI: 10.1002/adsc.200700406
An Unprecedented Iridium
A
T
E
N
(III) Catalyst for Stereoselective
Dimerisation ofTerminal Alkynes
a
b
b,
b,c,
Marco Ciclosi, Francisco Estevan, Pascual Lahuerta, * Vincenzo Passarelli, *
a,
b
Julia PØrez-Prieto, * and Mercedes Sanaffl
Departamento de Química Orgµnica/ICmol, Universidad de Valencia, Polígono La Coma s/n, 46980 Paterna, Valencia,
a
Spain
Fax : (+34) 96-354-3274; E-mail: julia.perez@uv.es
Departamento de Química Inorgµnica, Universidad de Valencia, Doctor Moliner 50, 46100 Burjassot, Valencia, Spain
E-mail: lahuerta@uv.es
Present address: ICMA-CSIC, Facultad de Ciencias, Universidad de Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain
E-mail: vincenzo.passarelli@poste.it
b
c
Received: August 20, 2007; Published online: January 4, 2008
Supporting information for this article is available on the WWW under http://asc.wiley-vch.de/home/.
Abstract: A novel iridium
A
H
R
U
G
defined Ir
sation.
A
T
E
N
(III) complex that catalyses alkyne dimeri-
IrHCl(TIMP ) {HTIMP =tris[1-(diphenylphos-
ACHTREUNG
3
phino)-3-methyl-1H-indol-2-yl]methane} was pre-
pared and fully characterized in both the solid state
and in solution. Chloride abstraction by silver cat-
ions provides a more reactive compound, [IrH-
In this context, here we report the synthesis of the
(III) hydride derivative, IrHCl(TIMP ) (1), starting
from the P-tripodal ligand HTIMP3, and its deriva-
tives [IrH(TIMP )]
[BF ] (2), [Ir(PhCH=CÀCH=
CHPh)(TIMP )]
Ir
A
H
R
U
G
ACHTREUNG
3
[
4]
A
H
R
U
G
ACHTREUNG
3
4
A
C
H
T
R
E
U
N
G
(TIMP )]
A
C
H
T
R
E
U
N
G
[BF ], which can react with pyridine (py)
A
H
R
U
G
A
H
R
U
G
A
T
E
N
A
C
H
T
R
E
U
N
G
3
4
3
4
3
and phenylacetylene to yield the complexes [IrH-
(4) (Scheme 1, reaction i). We also report preliminary
catalytic studies which demonstrate the activity of 4
in the stereoselective dimerisation of model terminal
alkynes (Scheme 1, reaction ii).
A
C
H
T
R
E
U
N
G
(TIMP )(py)]
A
C
H
T
R
E
U
N
G
[BF ] and [Ir(PhCH=CÀCH=CHPh)-
3
4
A
C
H
T
R
E
U
N
G
(TIMP )][BF ], respectively. Interestingly, IrH-
A
C
H
T
R
E
U
N
G
3 4
A
C
H
T
R
E
U
N
G
(TIMP )(py)][BF ] efficiently catalyses the stereose-
A
C
H
T
R
E
U
N
G
3
4
lective dimerisation of model terminal alkynes to
To assess the binding ability of HTIMP to iridium,
3
the 1,4-disubstituted (E)-but-1-en-3-yne only.
it was refluxed in deaerated toluene containing [IrCl-
A
T
E
N
Keywords: alkyne dimerisation; catalyst design; dia-
non-symmetrical complex was obtained; whose struc-
1
stereoselectivity; iridium
A
H
R
U
(III) complexes
ture in solution was compatible with 1, based on H
3
1
and P NMR spectroscopy, and fully in agreement
with its solid state structure (see below, X-ray analy-
3
1
1
sis). Thus, its P{ H} NMR spectrum shows three sig-
nals (1:1:1 ratio) at 31.7, 38.1, and 43.5 ppm. More-
1
The transition metal-catalysed dimerisation of termi- over, its H NMR spectrum evidences the disappear-
nal alkynes is an efficient method for the synthesis of ance of the Csp
branched and linear enynes, which are versatile inter- three non-equivalent methyl groups (1.6, 1.7 and
3
ÀH methyne hydrogen and shows
[
1,2]
mediates in organic synthesis.
iridium complexes appears to involve an Ir(I)/Ir
This process for the 2.0 ppm), as well as a doublet of triplets at À8.4 ppm
2
2
A
H
R
U
G
=142.5 Hz,
J
=15.9 Hz], which can
H,P(cis)
H,P(trans)
cycle consisting of i) oxidative addition of the alkyne clearly be assigned to the hydride. The X-ray analysis
CÀH bond to the Ir(I) complex, which leads to an (Figure S1 in Supporting Information) of a single crys-
RCꢀCÀIr(III)ÀH compound, ii) insertion of a second tal of 1 shows the distorted square pyramidal geome-
A
C
H
T
R
E
U
N
G
alkyne molecule into the IrÀH or the IrÀC bond, try of the complex, in which the three P atoms, the
which affords a vinyl-Ir(III) species, and iii) reductive deprotonated methylene carbon and a chloride ligand
AHCTREUNG
elimination, which regenerates the iridium(I) com- are coordinated to thconditionse metal centre. The
pound and produces a linear (E)-enyne, a (Z)-enyne, hydride is not located in the structure refinement but
[
2b,3]
1
or a mixture of both in most cases.
To our knowl- is visible in the H NMR spectrum.
Compound 1 was found to be unreactive towards
edge, there is no example in the literature of a well-
[5]
phenylacetylene under a variety of reaction. To
234
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2008, 350, 234 – 236

Iridium(III) Catalyst for Stereoselective Dimerisation of Terminal Alkynes
A
C
H
T
R
E
U
N
G
COMMUNICATIONS
stable in air and in non-chlorinated solvents, but
again leads to complex 1 in the presence of trace
amounts of CHCl or CH Cl .
3
2
2
Cationic complex 2 does react with phenylacetylene
in methanol and quantitavely gives rise to a new com-
pound, identified as the butadienyl species
3
[
6]
19
(
Scheme 1, reaction i). The F NMR spectrum of 3
shows a singlet at À154.6 ppm, indicating an uncoor-
À
dinated BF anion. The presence of three non-equiv-
4
alent phosphorus atoms in a pseudo T-shaped ar-
3
1
1
rangement can be assumed from its P{ H} NMR
spectrum (three signals at 30.3, 46.2, and 50.4 ppm).
1
Regarding the butadienyl moiety, its main H NMR
spectrum features are the three 1:1:1 signals at 5.3,
5
1
.5, and 5.55 ppm. A quaternary carbon is observed at
33.7 ppm (from the H C HMBC spectrum), corre-
1
13
sponding to the carbon atom directly bonded to the
metal. The X-ray analysis of a single crystal of 3
shows that the Ir centre is coordinated to three phos-
phorus atoms and to a carbon atom from the TIMP3
ligand (Figure 1), the coordination sphere being com-
pleted by the butadienyl moiety, with an Ir(1)ÀC
bond distance of 2.052 Š. Interestingly, C(101) and C-
(102) of the butadienyl residue are weakly bound to
the metal [Ir(1)ÀC(101)=2.427 Š and Ir(1)ÀC
(102)
.751 Š]. Thus, these distances are shorter than those
A
C
H
T
R
E
U
N
G
(100)
AHCTREUNG
AHCTREUNG
A
H
R
N
ACHTREUNG
Scheme 1. i) Synthesis of Ir(III) complexes 1–4 containing
A
H
E
N
2
the tripodal HTIMP phosphine ligand, and ii) the catalysed
2
3
reported for the h -butadienyl Ir
formula Ir
A
T
E
N
dimerisation of model terminal alkynes.
A
H
R
U
G
[L=
3
2
PhC=CHÀC(=O)CH ], where they are 2.509 and
3
[
7]
obtain a more reactive complex, a methanol solution 3.092 Š, respectively. Furthermore, the CÀC bond
of 1 was treated with AgBF at room temperature for distances along the C chain in 3 exhibit an irregular
4
4
12 h. Under these conditions the chloride groupfrom
short-long-short pattern [C
A
T
E
N
A
T
E
N
(100), 1.30; C-
1
was efficiently abstracted and the resulting product
A
H
R
U
G
A
H
R
U
G
A
H
R
U
G
ACHTREUNG
was assigned the structure [IrH
A
H
R
U
G
A
H
R
U
1
19
31
the basis of its H, F and P NMR data (see Sup- above-mentioned compound of reference (1.33, 1.47
porting Information). This compound is thermally and 1.32 Š).
Figure 1. (Left) Molecular structure of 3 (only the ipso carbon atoms are reported for the PPh moieties) and (right) its coor-
2
ACHTREUNG ACHTREUNG
A
C
H
T
R
E
U
N
G
dination polyhedron. Selected bond distances [Š] and angles [8] are: Ir(1)ÀC
2
8
.134(16), Ir(1)ÀP(1) 2.397(5), Ir(1)ÀP(2) 2.374(5), Ir(1)ÀP(3) 2.305(5), C
A
H
R
U
G
ACHTREUNG
6.4(5), C(01)ÀIr(1)ÀP(2) 81.8(5) C(01)ÀIr(1)ÀP(1) 77.8(5), P(2)ÀIr(1)ÀP(1) 99.76(17).
Adv. Synth. Catal. 2008, 350, 234 – 236
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
235

Marco Ciclosi et al.
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Since the b-hydrogen elimination from 3 could give Representative Procedure for Catalytic Tests
rise to highly unsaturated four-carbon derivatives,
which are nowadays compounds of great relevance,
the capacity of 3 to undergo b-hydrogen elimination
was investigated: i) no decomposition occurs even
To a solution of 4 (6 mg; 5 mmol) in CD OD (0.7 mL), the
alkyne (500 mmol) was added. The reaction was conducted
[
8]
3
in a sealed tube, and the mixture was heated at 808C. The
1
reaction evolution was followed by H NMR, showing the
after 3 days in refluxing CHCl or MeOH, but ii) 3 clean and progressive conversion of the alkyne into the (E)-
3
readily reacts with stoichiometric amounts of pyridine enyne.
in refluxing MeOH, releasing the butadienyl moiety
as (E)-1,4-diphenylbut-1-en-3-yne and yielding the Supporting Information
hexacoordinated complex 4 (Scheme 1, reaction i). In
Data for 1–4, X-ray structure of 1, and time evolution of the
catalytic reactions.
addition, 4 converts to 3 when reacted with phenyla-
cetylene (PhCꢀCH/Ir=2/1 molar ratio).
In view of this, the capacity of 4 to catalyse the di-
merisation of model terminal alkynes [PhCꢀCH, t-
BuCꢀCH and (CH ) SiCꢀCH] was tested. Interesting-
3
3
Acknowledgements
ly, complex 4 (2% mol Ir) cleanly and selectively led
to the corresponding (E)-but-1-en-3-yne after heating
the reaction mixture in sealed tube at 808C. The evo-
This project was supported by the European Community
(
(
Project: HPRN-CT-2001–00187), and Spanish Government
Project CTQ2005–08351).
1
lution of all these reactions was followed by H NMR
(
see Figures S2 and S3 in the Supporting Informa-
tion), which showed shorter reaction times for both
(
(
9
CH ) SiCꢀCH (24 h, 98% yield) and t-BuCꢀCH
3
3
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31
5%). Moreover, P NMR spectra obtained at differ-
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[
2
-yl]methane (HTIMP ) leads to the non-symmetrical
3
IrHCl
converts to the more reactive Ir
(TIMP )(py)][BF ], which behaves as a catalyst for
A
C
H
T
R
E
U
N
G
(TIMP ) Ir
A
C
H
T
R
E
U
N
G
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3
AHCTREUNG
(III) compound [IrH-
A
C
H
T
R
E
U
N
G
ACHTREUNG
3
4
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AHCTREUNG
AHCTREUNG
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[
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Experimental Section
Synthesis of1
[
A toluene solution of [IrCl(COE) ] (565 mg, 1.26 mmol of
A
H
R
U
G
2 2
Ir) and HTIMP (1.20 g, 1.26 mmol) was refluxed for 5 d
3
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2
1
31
1
1
183.71). H and P { H} NMR spectra were recorded.
236
asc.wiley-vch.de
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2008, 350, 234 – 236