Unusual 1-Alkyne Dimerization/Hydrogenation Sequences Catalyzed by [Ir(H)2(NCCH3)3(P-i-Pr3)]BF 4: Evidence for Homogeneous-Like Mechanism in Imidazolium Salts

Article abstract of DOI:10.1002/adsc.200390023

The reaction of complex [Ir(H)₂(NCCH₃) ₃(P-i-Pr₃)]BF₄ (1) with excess of 1-alkynes such as t-BuC ≡ CH and PhC ≡ CH gave the butadiene compounds Ir[η⁴-(R)₂C₄H₄

Full text of DOI:10.1002/adsc.200390023

FULL PAPERS
Unusual 1-Alkyne Dimerization/Hydrogenation Sequences
Catalyzed by [Ir(H)2(NCCH3)3(P-i-Pr3)]BF4: Evidence for
Homogeneous-Like Mechanism in Imidazolium Salts
a
b
a
a
¬
¬
Janeth Navarro, Maria Sagi, Eduardo Sola, Fernando J. Lahoz,
a
b
b,
a,
¬
¬
¬
Isabel T. Dobrinovitch, Agnes Katho, Ferenc Joo, * Luis A. Oro *
Departamento de QuÌmica Inorganica, Instituto de Ciencia de Materiales de Aragon, Universidad de Zaragoza CSIC,
50009 Zaragoza, Spain
a
À
¬
¬
Fax: ( ‡ 34)-976-761143, e-mail: oro@posta.unizar.es
b
Department of Physical Chemistry, University of Debrecen, and Research Group of Homogeneous Catalysis, Hungarian
Academy of Sciences, 4010 Debrecen, P.O.B. 7, Hungary
Fax: ( ‡ 36)-52-512 915, e-mail: jooferenc@tigris.klte.hu
Received: July 31, 2002; Accepted: October 7, 2002
Abstract:
The
reaction
of
complex sequence has been found to be the major reaction of
[Ir(H)2(NCCH3)3(P-i-Pr3)]BF4 (1) with excess of 1- t-BuC ꢀ CH under conditions of homogeneous hydro-
alkynes such as t-BuC ꢀ CH and PhC ꢀ CH gave the genation whereas that of PhC ꢀ CH produced styrene
butadiene compounds Ir[h4-(R)2C4H4](NCCH3)2(P-i- and ethylbenzene as major products. Similar selectiv-
Pr3)}BF4 (R ˆ t-Bu, 5; R ˆ Ph, 6). Compound 5 was ity was observed for these hydrogenations using
obtained as a single isomer containing a 1,3-disub- organic/ionic liquid biphasic conditions with toluene/
stituted butadiene ligand, whereas 6 was formed as a BMIM ¥ BF4, suggesting reaction mechanisms similar
7:1 mixture of isomers containing 1,3- and 1,4- to those operating under homogeneous conditions.
disubstituted butadienes, respectively. Spectroscopic This conclusion is also supported by the spectroscopic
observations showed alkenyl hydride reaction inter- observation of alkenyl hydride intermediates during
mediates, consistent with a double insertion/C-C the formation of 6 in BMIM ¥ BF4 as solvent.
coupling sequence. Complexes 5 and 6 were found
to react with dihydrogen to give 1 and alkenes
resulting from the partial hydrogenation of the Keywords: alkynes; biphasic catalysis; homogeneous
butadiene moieties. This dimerization/hydrogenation catalysis; hydrogenation; ionic liquids, iridium
Introduction
on the features of the ionic liquid,[3] evidencing possible
non-innocent roles of these immobilizing media during
The investigation of biphasic catalytic systems based on catalysis.[4] Due to the latter traits and the lack of
ionic liquids has demonstrated that most homogeneous mechanistic studies on these biphasic systems, whether
catalytic reactions can be transferred to such biphasic or not the catalytic mechanisms in solution can be
media without requiring substantial modification of the extrapolated to ionic liquids remains open to discussion.
catalyst precursors or the reaction conditions.[1] This
In this paper, we present experimental evidence
lack of special requirements enhances the attractiveness indicating that similar mechanisms are operating in
of using ionic liquids as immobilizing agents allowing both organic solvents and in 1,3-dialkylimidazolium-
facile catalyst recycling whilst maintaining the charac- based ionic liquids, during the hydrogenation of 1-
teristic selectivity of molecular catalysts. In addition, it alkynes
catalyzed
by
the
compound
has been observed that the ligand effects typical of some [Ir(H)2(NCCH3)3(P-i-Pr3)]BF4 (1). This hydrogenation
homogeneous processes remain operative under such system has been found to be highly diagnostic, due to the
biphasic conditions,[2] suggesting the occurrence of spectroscopic accessibility of its reaction intermediates
similar reaction mechanisms in both media, and indicat- and to the occurrence of an unusual hydrogenative
ing that our current understanding of structure/function dimerization reaction, which is competitive with alkyne
relationships in solution could also be used for catalyst hydrogenation, and strongly dependent upon the al-
improvement in ionic liquids. Nevertheless, other stud- kyne×s features.
ies have found reaction selectivities strongly dependent
280
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1-Alkyne Dimerization/Hydrogenation Sequences Catalyzed by [Ir(H)2(NCCH3)3(P-i-Pr3)]BF4
FULL PAPERS
Results and Discussion
Ir-H bonds of 1. The reaction pathway opened by this
double insertion was found to be non-productive given
Recently, we have reported on the catalytic activity of that the hydrogen b-elimination from 3 to reform 2
complex 1 in alkene hydrogenation reactions.[5] This seems to be kinetically favored over the reductive
compound has also been found to facilitate the spectro- elimination of butane.
scopic observation and characterization of labile species
In an attempt at exploiting the potential of these
likely involved in the catalytic cycles, as illustrated by double insertions in C-C coupling reactions, we have
the intermediates of ethene hydrogenation depicted in explored the reactivity of 1 towards alkynes. In refer-
Scheme 1. A noticeable feature of this cycle is the ence to well-established trends in organometallic reac-
formation of the bis-ethyl compound 3, which results tivity, such substrates are likely to provide favorable
from an unusual double insertion of ethene into the two relationships between b-elimination and C-C reductive
elimination rates. In fact, to the best of our knowledge,
the facile b-elimination of hydrogen from an alkenyl
ligand has never been reported, and the reductive
coupling of two sp2 carbons has been found to be favored
over that of sp3 ones.[6] In agreement with these expect-
ations, the reaction of 1 with an excess of 1-alkynes such
as PhC ꢀ CH or t-BuC ꢀ CH has been found to afford
butadiene complexes (Scheme 2).
The stereoselectivity of these reactions has been
found to be dependent on the 1-alkyne substrate.
Thus, the reaction with t-BuC ꢀ CH selectively gave
compound
{Ir[h4-1,3-(t-Bu)2C4H4](NCCH3)2(P-i-
Pr3)}BF4 (5) in quantitative yield. The structure of 5
determined by X-ray diffraction is shown in Figure 1.[7]
Under the same conditions, the reaction with PhC ꢀ CH
was less selective, leading to the compound {Ir[(h4-
(Ph)2C4H4](NCCH3)2(P-i-Pr3)}BF4 (6) as a 7:1 mixture
of isomers which contain 1,3- (6a) and 1,4-diphenylbu-
tadiene (6b) ligands, respectively. The major isomer was
isolated in an analytically pure state by crystallization of
the product mixture in CH2Cl2/diethyl ether.
The NMR investigation of the course of these
reactions in CDCl3 at low temperature allowed obser-
vation of alkenyl hydride intermediates which are
consistent with the expected double insertion/C-C
coupling reaction sequence.[8] Thus, the treatment of 1
with one equivalent of PhC ꢀ CH at 253 Kreadily
afforded an equimolar mixture of two isomeric alkenyl
hydride complexes, 7a and 7b, which have a- and b-(Z)-
alkenyl ligands, respectively (Scheme 3). Both isomers
were found to be stable towards the reductive elimi-
nation of styrene at room temperature. The reactivity of
these two isomers towards a second equivalent of the
alkyne was found to be different. Thus, 7b readily
Scheme 1.
Scheme 2.
Adv. Synth. Catal. 2003, 345, 280 288
281

Janeth Navarro et al.
FULL PAPERS
Figure 1. Molecular structure of the cation of complex 5
(ORTEP). Selected bond distances [ä] and angles [0]: Ir P
2.3559(12), I N1 2.1000(4), Ir N2 2.090(4), Ir C1 2.111(4),
Ir C2 2.193(4), Ir C3 2.179(4), Ir C4 2.151(4); C1 C2 C3
113.3(4), C2 C3 C4 118.6(4), C3 C4 C9 118.1(4).
reacted with an excess of the alkyne at 253 Kgiving 6,
whereas the disappearance of the a-alkenyl hydride 7a
was slow even at temperatures above 273 K. In both
Scheme 3.
cases, the spectroscopic observations did not allow the the selective formation of the 1,3-disubstituted buta-
detection of additional intermediates of this second diene complex 5, suggesting a sequence of two com-
reaction step. This suggests that once the second pletely stereoselective insertions of b-(Z)- and a-stereo-
insertion takes place, the subsequent C-C reductive chemistry, respectively. In this case, the formation of the
coupling is fast.
butadiene complex could not be carried out stepwise
The isomeric distribution of 6 resulting from the since the first and second insertion steps seem to have
evolution of each alkenyl hydride intermediate revealed comparable rates. In consequence, intermediate 8 was
interesting stereochemical features. Thus, 7b afforded detected only as a minor component in the reaction
6a and 6b in a 3:1 molar ratio respectively, indicating that mixture (10%).
for the second alkyne insertion step, a-stereochemistry
The reaction of the butadiene compounds 5 and 6 with
is preferred. On the contrary, the intermediate 7a dihydrogen, in CDCl3 and in excess of acetonitrile, has
exclusively produced the isomer 6a, most likely through been found to give alkenes thus regenerating the
a selective second insertion step of b-(Z)-stereochem- starting complex 1 (Scheme 4). This reaction closes a
istry. In the latter case, both the relative inertness of 7a possible cycle for hydrogenative dimerization of termi-
and its proclivity to undergo selective b-(Z)-insertions nal alkynes which may operate at room temperature in
could be rationalized on the basis of the steric hindrance dihydrogen at atmospheric pressure. The alkenes
introduced by the a-alkenyl ligand. However, we still formed from hydrogenation of complex 5 were those
cannot offer a plausible rationale for the preferential shown in Scheme 4 and have been identified by mass
a-stereochemistry of the second alkyne insertion in spectrometry and NMR spectroscopy. Isomer 9 was
the b-(Z)-alkenyl hydride 7b. Moreover, the use of found to be the main kinetic product of the reaction,
t-BuCꢀCH seems to enhance this latter stereochemical although, at room temperature and in the presence of
preference. Only one alkenyl hydride intermediate of b- stoichiometric amounts of 1, it was readily isomerized to
(Z)-stereochemistry (8) could be detected along with 10 (major) and 11 (minor). The subsequent hydro-
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1-Alkyne Dimerization/Hydrogenation Sequences Catalyzed by [Ir(H)2(NCCH3)3(P-i-Pr3)]BF4
FULL PAPERS
Scheme 4.
genation of these alkenes to the alkane was not observed dihydride species and double insertion/C-C coupling
under such mild conditions. The hydrogenation of sequences. In addition, considering that both the extent
isomers 6 under the same conditions also produced 1 of this reaction under catalytic conditions and the
together with a complicated mixture of organic products stereochemistry of its products are strongly dependent
which was not analyzed in detail.
on the alkyne features, it seems likely that small changes
Interestingly, the reaction sequence leading to prod- in the steric or electronic properties of the active species
ucts 9 11 was found to be the major reaction path when would lead to changes in the reaction outcome.
t-BuCꢀCH and dihydrogen were treated with catalytic
Despite the likely sensitivity of this hydrogenation
amounts of complex 1 in 1,2-dichloroethane (Figure 2a). system, the selectivity of the catalytic reactions re-
As a contrast and under the same catalytic conditions, mained essentially the same when the processes were
phenylacetylene mostly afforded simple hydrogenation carried out in toluene/1-butyl-3-methylimidazolium
products: styrene and ethylbenzene, amounting to 90% tetrafluoroborate (BMIM ¥ BF4) biphasic solvent mix-
of all products at 90% conversion. With regard to the tures. Thus, as in homogeneous conditions, PhCꢀCH
aforementioned experimental observations and mech- produced styrene and ethylbenzene (with C-C coupled
anistic proposals, this dependence on the alkyne of the products less than 4%), whereas t-BuCꢀCH was trans-
selectivity may arise from the competition of substrates formed into a mixture of products similar to that
for the alkenyl hydride reaction intermediates. Thus, obtained in 1,2-dichloroethane at low alkyne concen-
under the actual catalytic conditions, the second in- trations (Figure 2c). This would indicate that the
sertion of t-BuCꢀCH in intermediate 8 seems to be changes in the active species provoked by variations of
kinetically favored over its reaction with dihydrogen, the reaction media are if any, very minor.
whereas for intermediates 7 this latter reaction seems to
The minor differences in rate and selectivity of these
be faster than the second PhCꢀCH insertion. Such latter reactions with respect to those in the homoge-
rationalization based on substrate competition, would neous phase can be readily rationalized as a conse-
imply a dependence of the reaction selectivity upon the quence of the expected low solubility of the substrates in
relative concentration of the reactants. In agreement the ionic liquid and mass transfer limitations. Thus, we
ˆ
with this, the proportion of t-BuCH CH2 and t- observed that the increase of the initial alkyne concen-
BuCH2CH3 hydrogenation products was found to tration in the biphasic system had little effect on the
increase at low alkyne concentrations (Figure 2b). reaction rate; a likely consequence of the limited
Under the latter conditions, the lower substrate/catalyst solubility of this substrate in the ionic liquid. Similarly,
ratio led to a faster isomerization of the kinetic product 9 the low solubility of the reaction products in the ionic
into its internal isomers 10 and 11, and a faster hydro- liquid is expected todiminish the extent of isomerization
ˆ
ˆ
genation of t-BuCH CH2 to t-BuCH2CH3. The decrease of 9 and the hydrogenation of t-BuCH CH2, as was
in the initial alkyne concentration also resulted in higher observed under biphasic conditions. In this way the
initial hydrogenation rates. A similar substrate inhib- partition of the primary (kinetic) products and the
ition effect has been observed with PhCꢀCH, revealing catalyst into their respective organic and ionic liquid
a complex dependence of the hydrogenation rate upon phases, provides protection against further reduction or
the alkyne concentration and is currently under study.
isomerization and this may be a useful feature for
To the best of our knowledge, a catalytic hydro- selective syntheses.
genative dimerization such as that leading to 9 11 has
The similarity of the active species suggested by the
not been previously reported. With regard to this lack of above catalytic experiments is also in agreement with
precedent and the aforementioned mechanistic obser- the conclusions of our spectroscopic observations on
vations, the occurrence of such a transformation in the stoichiometric reactions of 1 with PhCꢀCH and t-
presence of iridium catalyst precursors could be consid- BuCꢀCH in BMIM ¥ BF4 as solvent. In fact, the
ered as a sound indication for the participation of 31P NMR spectra under off resonance conditions (allow-
Adv. Synth. Catal. 2003, 345, 280 288
283

Janeth Navarro et al.
FULL PAPERS
Figure 3. 31P NMR spectra of compound mixtures obtained
by treatment of 1 with PhCꢀCH at room temperature:
(above) 31P off resonance spectrum in CDCl3; (center) 31P{1H}
spectrum in BMIM ¥ BF4; (below) 31P off resonance spectrum
in BMIM ¥ BF4.
tion and insertion remain unaltered despite the signifi-
cant change in the solvent properties.
Attempted recycling of the catalyst in the ionic
liquid phase was met with fair success. In the case of
t-BuCꢀCH, the selectivity has been found to be
maintained, although each recycling step brought about
a progressive decrease in the activity (ca. 30%). When
PhCꢀCH was hydrogenated in toluene/BMIM ¥ BF4
(293 K, substrate/catalyst ˆ 100), the total conversion
of the substrate in 2 hours first reached 57% (styrene/
ethylbenzene ˆ 6:1), but then decreased to 25, 20 and
11% in the subsequent 2 hour runs, respectively, with an
increase in the proportion of styrene over the fully
hydrogenated product (10:1 ratio in the fourth run). In
some cases, the catalyst-containing ionic liquid phase
was washed with toluene between successive runs but
this was found detrimental to the catalytic activity. It is
conceivable that acetonitrile originating from the facile
dissociation of the catalyst is removed as a result of the
repeated removal of the organic phase (especially when
Figure 2. Reaction profiles for t-BuCꢀCH hydrogenations
catalyzed by 1. Conditions: (a) 1,2-dichloroethane (8 mL),
293 K, [1]o ˆ 0.010 mmol, [t-BuCꢀCH]o ˆ 5.0 mmol, P(H2) ˆ
1.1 bar; (b) 1,2-dichloroethane (8 mL), 293 K, [1]o ˆ
0.015 mmol, [t-BuCꢀCH]o ˆ 1.5 mmol, P(H2) ˆ 1.1 bar; (c)
toluene (6 mL), BMIM ¥ BF4 (2 mL), 293 K, 1 ˆ 0.019 mmol,
[t-BuCꢀCH]o ˆ 1.19 mmol, P(H2) ˆ 1.1 bar.
ing hydride coupling) are indicative of the sequential the ionic liquid phase is washed with toluene between
formation of the alkenyl hydrides 7 and the butadiene the runs), nevertheless, simple addition of acetonitrile to
complexes 6 on treatment of BMIM ¥ BF4 solutions of 1 the toluene phase did not restore the catalytic activity.
with PhCꢀCH at room temperature (Figure 3). Inter- Although these latter findings show the limits of the use
estingly, the isomeric distributions of 6 and 7 obtained in of [Ir(H)2(NCCH3)3(P-i-Pr3)]BF4 (1) in toluene/BMI-
this solvent were similar to those observed in CDCl3, M ¥ BF4 biphasic systems, the unchanged selectivity of
suggesting that the factors governing alkyne coordina- the hydrogenations together with the spectroscopic
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1-Alkyne Dimerization/Hydrogenation Sequences Catalyzed by [Ir(H)2(NCCH3)3(P-i-Pr3)]BF4
FULL PAPERS
conditions, the large J(H,P) coupling constants (19 21 Hz)
due to hydride coupling were clearly observed, whereas
smaller ones (2 3 Hz) due to possible couplings with alkenyl
protons were not resolved. Spectral assignments were achieved
observations reveal that no major changes in the hydro-
genation mechanisms are brought about by the presence
of the ionic liquid. This gives space to catalyst design.
According to our preliminary results, the compound
[Ir(H)2(C6H6)(P-i-Pr3)]BF4[9] shows similar activity and
selectivity but is substantially more robust than 1 under
the same biphasic conditions.
1
by H COSY, NOESY, and 13C DEPT experiments. Infrared
spectra were recorded as Nujol mulls on polyethylene sheets
with use of a Bruker Equinox 55 spectrometer. IR frequencies
are reported in cmÀ1. C, H, N analyses were carried out using a
Perkin-Elmer 2400B CHNS/O analyzer. MS data were re-
corded on a VG Autospec double-focusing mass spectrometer
operating in the positive mode; ions were produced with the
Conclusions
‡
Cs gun at ca. 30 kV, and 3-nitrobenzyl alcohol (NBA) was
used as the matrix. Conductivities were measured in ca. 3 Â
10À4 M solutions with a Philips PW 9501/01 conductivity meter.
GC analyses were preformed either on an Agilent 6890 Series
gas chromatograph equipped with an Agilent 5973 mass
selective detector and a 30 m (0.25 mm i. d.; 0.25 mm FT) HP-
5MS column, or on a Hewlett-Packard HP 5890 Series II gas
chromatograph equipped with a flame ionization detector and
a 25 m (0.32 mm i. d., 0.17 mm FT) HP Ultra 1 column.
Calibration of the detector response to the substrates and
products was made by comparing the GC integrals with those
obtained in the same samples by 13C{1H} NMR, setting the
relaxation delay between pulses to 30 s.
Under hydrogenation conditions, the dihydride com-
plex [Ir(H)2(NCCH3)3(P-i-Pr3)]BF4 catalyzes unprece-
dented hydrogenative dimerizations of terminal al-
kynes. Such catalytic reactions involve butadiene iridiu-
m(I) intermediates, which are most likely formed
through a reaction sequence comprising double inser-
tion and C-C reductive coupling steps. The extent of this
reaction under homogeneous catalytic conditions is
strongly dependent on the alkyne features and the
concentrations of the substrates. Despite this sensitivity,
the selectivity of the catalytic reactions remains essen-
tially the same for homogeneous (1,2-dichloroethane)
or biphasic (toluene/BMIM ¥ BF4) systems, suggesting a
common mechanism under both experimental condi-
tions. This conclusion is supported by the spectroscopic
observation of similar alkenyl hydride and butadiene
complexes, likely catalytic intermediates, in both 1,2-
dichloroethane and BMIM ¥ BF4 solutions.
Synthesis of {Ir[h4-1,3-(t-Bu)2C4H4](NCCH3)2(P-i-
Pr3)}BF4 (5)
A solution of 1 (100 mg, 0.18 mmol) in acetone (5 mL) at 273 K
was treated with t-BuCꢀCH (43.4 mL, 0.35 mmol), and al-
lowed to react for 2 h at room temperature. The resulting red
solution was concentrated to ca. 0.5 mL, layered with diethyl
ether, and stored at 273 Kfor 24 h to yield pale yellow crystals.
The crystals were separated by decantation and washed with
diethyl ether; yield: 111 mg (90%). Anal. calcd. for
Experimental Section
General Remarks
Reactions were carried out under exclusion of air by using
standard Schlenk techniques. Solvents were dried by known
procedures and distilled under argon just prior to use. PhC ꢀ
CH (Aldrich), was distilled under argon and stored over
molecular sieves. t-BuCꢀCH (Lancaster) was used as received
without further purification. 1-Butyl-3-methylimidazolium
tetrafluoroborate (BMIM ¥ BF4),[10] and the complex
[Ir(H)2(NCCH3)3(P-i-Pr3)]BF4 (1),[5] were prepared as previ-
ously reported. BMIM ¥ BF4 was dried by azeotropic distilla-
tion with benzene several times, followed by prolonged
evacuation. NMR spectra were recorded on Varian UNITY,
Varian GEMINI 2000, or Bruker ARX, 7.04 T spectrometers,
operating at 300 MHz (1H), 121 MHz (31P), and 75.2 MHz
(13C). 1H and 13C NMR chemical shifts were measured relative
to partially deuterated solvent peaks but are reported in ppm
relative to tetramethylsilane. 31P NMR chemical shifts were
measured relative to H3PO4 (85%). The samples dissolved in
BMIM ¥ BF4 were examined without the addition of any
deuterated compound or TMS. A capillary containing ace-
tone-d6 was added to provide a lock signal and an approximate
reference. As a result of this referencing method, the chemical
shifts are subject to a significant error due to susceptibility
effects.[4a] 31P off resonance spectra were recorded under
continuous decoupling of the P-i-Pr3 protons. Under these
C25H49N2BF4IrP: C 43.67, H 7.18, N 4.07%; found: C, 43.63;
À1
ˆ
H, 7.49; N, 4.36%; IR: nÄ ˆ 1629 (C C), 1054 cm (BF4);
1H NMR (CDCl3, 293 K): d ˆ 0.16 [ddd, J(H,H) ˆ 5.4, 0.9 Hz,
ˆ
ˆ
J(H,P) ˆ 6.9 Hz, 1H, CH2 C(t-Bu)CH CH(t-Bu)], 0.52 [dd,
ˆ
J(H,H) ˆ 7.2 Hz,
J(H,P) ˆ 5.7 Hz,
1H,
CH2 C(t-
ˆ
Bu)CH CH(t-Bu)], 0.95 [s, 9H, C(CH3)3], 1.25 [dd, J(H,P) ˆ
13.5 Hz, J(H,H) ˆ 7.5 Hz, 9H, PCHCH3], 1.26 [s, 9H, C(CH3)3],
1.27 [dd, J(H,P) ˆ 13.5 Hz, J(H,H) ˆ 7.8 Hz, 9H, PCHCH3],
ˆ
2.42, (s, 3H, NCCH3), 2.43 [d, J(H,H) ˆ 5.4 Hz, 1H, CH2 C(t-
ˆ
Bu)CH CH(t-Bu)], 2.49 (s, 3H, NCCH3), 2.69 (m, 3H,
PCHCH3), 5.12 [ddd, J(H,H) ˆ 7.2, 0.9 Hz, J(H,P) ˆ 3.0 Hz,
1H, CH2 C(t-Bu)CH CH(t-Bu)]; 31P{1H} NMR (CDCl3,
293 K): d ˆ 27.77 (s); 13C{1H} NMR (CDCl3, 293 K ):d ˆ 3.09,
ˆ
ˆ
ˆ
ˆ
3.36 (both s, NCCH3), 11.64 [br, CH2 C(t-Bu)CH CH(t-Bu)],
18.76, 19.51 (both s, PCHCH3), 27.13 [d, J(C,P) ˆ 24.8 Hz,
ˆ
ˆ
PCHCH3], 30.08 [s, CH2 C(t-Bu)CH CH(t-Bu)], 30.10, 30.90
[both s, C(CH3)3], 33.38, 34.18 [both s, C(CH3)3], 82.77 [d,
ˆ
ˆ
J(C,P) ˆ 4.6 Hz, CH2 C(t-Bu)CH CH(t-Bu)], 110.62 [d,
ˆ
ˆ
J(C,P) ˆ 6.0 Hz, CH2 C(t-Bu)CH CH(t-Bu)], 121.76, 124.11
‡
(both s, NCCH3); MS (FAB ‡ ): m/z (%) ˆ 599 (5) [M ], 560
‡
‡
ˆ
(15) [M NCCH3], 517 (100) [M CH2 C(tBu)]; LM (4.8 Â
10À5, acetone) ˆ 114 WÀ1 cm2 molÀ1 (1:1).
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Janeth Navarro et al.
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Synthesis of {Ir[h4-(Ph)2C4H4](NCCH3)2(P-i-Pr3)}BF4
(6)
heated to 293 Kand the stability of the reaction mixture was
monitored for 4 hours during which periodic recordings of
1H NMR spectra were made. Even though the sample decom-
posed partially (ca. 20%) throughout this period to give several
unidentified products, such decomposition reactions did not
produce styrene.
The same procedure described for 5 but starting from PhCꢀCH
(48.6 mL, 0.44 mmol) led to a pale yellow microcrystalline
solid; Yield: 104 mg (80%). The NMR analysis of this
mixture of complexes {Ir[h4-1,3-
Partial data for 7a: 1H NMR (CDCl3, 293 K): d ˆÀ 22.29 [d,
J(H,P) ˆ 22.2 Hz, 1H, Ir-H], 0.87 [dd, J(H,P) ˆ 13.8 Hz,
J(H,H) ˆ 7.2 Hz, 9H, PCHCH3], 1.08 [dd, J(H,P) ˆ 13.8 Hz,
J(H,H) ˆ 6.9 Hz, 9H, PCHCH3], 1.91 (br, 3H, NCCH3), 2.17
(m, 3H, PCHCH3), 2.36 (s, 3H, NCCH3), 2.42 (br, 3H, NCCH3),
solid revealed
a
(Ph)2C4H4](NCCH3)2(P-i-Pr3)}BF4 (6a) and {Ir[h4-1,4-
(Ph)2C4H4](NCCH3)2(P-i-Pr3)}BF4 (6b) in a 7:1 molar ratio.
The solid was dissolved in ca. 1 mL of CH2Cl2, layered with
diethyl ether, and stored at room temperature for 24 h. The
yellow solid formed was separated by decantation, washed
with diethyl ether and dried under vacuum. This solid was
found to be 6a in purity > 98% (NMR). The yield of the
recrystallization step was 31%.
ˆ
5.10, 5.45 [both d, J(H,H) ˆ 2.4 Hz, 1H each, Ir-C(Ph) CH2];
31P{1H} NMR (CDCl3, 293 K): d ˆ 13.98 (s); 13C{1H} NMR
(CDCl3, 293 K): d ˆ 1.91 (br, NCCH3), 3.04, 3.66 (both s,
NCCH3), 18.51, 19.30 (both s, PCHCH3), 24.22 [d, J(C,P) ˆ
33.0 Hz, PCHCH3], 117.54 [d, J(C,P) ˆ 16.5 Hz, NCCH3],
Data for 6a: Anal. calcd. for C29H41N2BF4IrP: C 47.87, H
5.68, N 3.85%; found: C 47.71, H 6.04, N 3.94%; IR: nÄ ˆ 1604
ˆ
119.76 (s, NCCH3), 121.20 (s, Ir-C(Ph) CH2), 125.41, 127.71,
À1
1
ˆ
(C C), 1064 cm (BF4); H NMR (CDCl3, 293 K): d ˆ 0.73
ˆ
127.82 (all CH), 135.35 [d, J(C,P) ˆ 8.2 Hz, Ir-C(Ph) CH2],
[ddd,
J(H,H) ˆ 4.5,
0.8 Hz,
J(H,P) ˆ 5.1 Hz,
1H,
156.11 (s, C).
ˆ
ˆ
Partial data for 7b: 1H NMR (CDCl3, 293 K ):d ˆÀ 22.20 [d,
J(H,P) ˆ 21.0 Hz, 1H, Ir-H], 6.43 [d, J(H,H) ˆ 16.2 Hz, 1H, Ir-
CH2 C(Ph)CH CH(Ph)], 1.08, 1.10 [both dd, J(H,P) ˆ
14.1 Hz, J(H,H) ˆ 7.2 Hz, 9H each, PCHCH3], 1.93, (br, 3H,
NCCH3), 2.00 [dd, J(H,H) ˆ 6.6 Hz, J(H,P) ˆ 5.1 Hz, 1H,
ˆ
CH CHPh], 7.75 [dd, J(H,H) ˆ 16.2 Hz, J(H,P) ˆ 2.7 Hz, 1H,
ˆ
ˆ
Ir-CH CHPh]; 31P{1H} NMR (CDCl3, 293 K): d ˆ 17.30 (s);
CH2 C(Ph)CH CH(Ph)], 2.44 (m, 3H, PCHCH3), 2.45 (s,
ˆ
13C{1H} NMR (CDCl3, 293 K): d ˆ 137.65 [d, J(C,P) ˆ 6.9 Hz,
3H,
NCCH3),
2.61
[d,
J(H,H) ˆ 4.5 Hz,
1H,
ˆ
ˆ
CH2 C(Ph)CH CH(Ph)], 6.21 [ddd, J(H,H) ˆ 6.6, 0.8 Hz,
ˆ
Ir-CH CHPh].
ˆ
ˆ
J(H,P) ˆ 3.0 Hz, 1H, CH2 C(Ph)CH CH(Ph)], 7.13 7.19
(m, 5H, Ph), 7.36 7.44 (m, 3H, Ph), 7.66 (m, 2H, Ph);
31P{1H} NMR (CDCl3, 293 K): d ˆ 28.87 (s); 13C{1H} NMR
(CDCl3, 293 K): d ˆ 2.38 (br, NCCH3), 3.48 (s, NCCH3), 13.64
ˆ
{Ir(H)[Z-CH CH(t-Bu)](NCCH3)3(P-i-Pr3)}BF4 (8)
ˆ
ˆ
[d, J(C,P) ˆ 2.3 Hz, CH2 C(Ph)CH CH(Ph)], 18.67, 18.78
The procedure described for the observation of isomers 7, but
using t-BuCꢀCH (44 mL, 0.36 mmol), led to mixtures contain-
ing complexes 1, 5, and 8 in a 9:9:1 molar ratio, respectively.
Partial data for 8: 1H NMR (CDCl3, 293 K): d ˆÀ 22.01 [d,
J(H,P) ˆ 21.0 Hz, 1H, Ir-H], 5.26 [d, J(H,H) ˆ 16.0 Hz, 1H, Ir-
(both s, PCHCH3), 26.37 [d, J(C,P) ˆ 26.3 Hz, PCHCH3],
ˆ
ˆ
29.05 [d, J(C,P) ˆ 1.4 Hz, CH2 C(Ph)CH CH(Ph)], 85.68 [d,
ˆ
ˆ
J(C,P) ˆ 6.0 Hz, CH2 C(Ph)CH CH(Ph)], 100.20 [d,
ˆ
ˆ
J(C,P) ˆ 5.1 Hz, CH2 C(Ph)CH CH(Ph)], 121.22 (br,
NCCH3), 121.62 (s, NCCH3), 125.08, 126.73, 128.53, 128.64,
128.65, 129.03 (all CH), 136.41 [d, J(C,P) ˆ 1.8 Hz, C], 143.66
ˆ
CH CH(t-Bu)], 6.18 [dd, J(H,H) ˆ 16.0 Hz, J(H,P) ˆ 3.0 Hz,
1H, Ir-CH CH(t-Bu)]; 31P{1H} NMR (CDCl3, 293 K): d ˆ
ˆ
‡
(s, C); MS (FAB ‡ ): m/z (%) ˆ 557 (100) [M Ph]; LM (4.8 Â
14.88 (s).
10À5, acetone) ˆ 109 WÀ1 cm2 molÀ1 (1:1).
Partial data for 6b (from the 6a/6b mixture): 1H NMR
(CDCl3, 293 K): d ˆ 1.26 [dd, J(H,P) ˆ 12.3 Hz, J(H,H) ˆ
7.2 Hz, 9H, PCHCH3], 1.30 [dd, J(H,P) ˆ 13.8 Hz, J(H,H) ˆ
Catalytic Reactions
ˆ
7.2 Hz, 9H, PCHCH3], 2.26 [m, 5H, PCHCH3 ‡ CH(Ph) CH-
ˆ
The equipment consisted of a 25 mL two-necked flask fitted
with a septum (to allow sampling without opening the system),
and connected through a condenser to a conventional Schlenk
manifold that used dihydrogen instead of inert gas. Magnetic
stirring (1000 rpm) was used during the reactions. The progress
of the reactions was followed by GC. Dry solvents should be
used throughout. In a typical procedure for homogeneous
reactions, complex 1 and octane (10 mL for internal reference)
were dissolved in 8 mL of 1,2-dichloroethane. The solution was
degassed and the system was refilled with dihydrogen at
1.1 bar, to exclude the penetration of air during sampling.
Then, the substrate was injected through the septum. In the
biphasic reactions, the catalyst was previously dissolved in
2 mL of BMIM ¥ BF4 under argon. Then, 6 mL of toluene
containing the internal reference was added. The reaction
mixture was degassed, put under dihydrogen and the substrate
was added as in the homogeneous case. After completion of the
reaction, the ionic liquid was separated by decantation. For
recycling experiments, the products and the unreacted sub-
strate were removed in the toluene phase through a cannula by
applying a positive pressure of dihydrogen, and then reduced
CH CH(Ph)], 2.33 (s, 6H, NCCH3), 4.00 [dd, J(H,H) ˆ 8.8 Hz,
ˆ
ˆ
J(H,P) ˆ 3.7 Hz,
2H,
CH(Ph) CH-CH CH(Ph)];
31P{1H} NMR (CDCl3, 293 K): d ˆ 19.71 (s); 13C{1H} NMR
(CDCl3, 293 K): d ˆ 2.80 (s, NCCH3), 19.15 (s, PCHCH3), 24.65
[d, J(C,P) ˆ 24.6 Hz, PCHCH3], 48.66 [d, J(C,P) ˆ 2.2 Hz,
ˆ
ˆ
CH(Ph) CH-CH CH(Ph)], 80.42 [d, J(C,P) ˆ 26.1 Hz,
ˆ
ˆ
CH(Ph) CH-CH CH(Ph)], 112.96 (s, NCCH3), 125.58,
127.66, 128.62 (all CH), 135.92 (s, C).
ˆ
{Ir(H)[C(Ph) CH2](NCCH3)3(P-i-Pr3)}BF4 (7a)and
ˆ
[Ir(H)(Z-CH CHPh)(NCCH3)3(P-i-Pr3)]BF4 (7b)
PhCꢀCH (40 mL, 0.36 mmol) was slowly added to a stirred
solution of complex 1 (200 mg, 0.36 mmol) in CDCl3 (2 mL) at
253 K. 0.5 mL of this solution was transferred under argon to
an NMR tube also cooled at 253 K. The NMR spectra of the
solution recorded at 253 Krevealed the formation of com-
plexes 7a and 7b in equimolar amounts, together with minor
amounts of complex 6a and traces of styrene. The sample was
286
Adv. Synth. Catal. 2003, 345, 280 288

1-Alkyne Dimerization/Hydrogenation Sequences Catalyzed by [Ir(H)2(NCCH3)3(P-i-Pr3)]BF4
FULL PAPERS
pressure was used to introduce a new toluene solution
prepared under dihydrogen. The pressure of the system was
reset to 1.1 bar and the magnetic stirring started.
1.470; m ˆ 4.055 mmÀ1; minimum and maximum transmission
factors 0.1682 and 0.3211; 2qmax ˆ 52.08; temperature 173(1) K;
8094 reflections measured, 6607 unique [R(int) ˆ 0.0276];
number of data/restrains/parameters 6607/0/393; final R1(F)
(F2 ꢁ 4s(F2)) ˆ 0.0324, wR(F2) (all data) ˆ 0.0848; final GoF
1.045; largest diff. peak 1.029 e.äÀ3; extinction coefficient
0.00081(11).
Crystallographic data (excluding structure factors) for the
structure(s) reported in this paper have been deposited with
the Cambridge Crystallographic Data Centre as supplemen-
tary publication no. CCDC-186454. Copies of the data can be
obtained free of charge on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK[Fax: int. code ‡ 44-(1223)-
336-033; E-mail: deposit@ccdc.cam.ac.uk].
Isolation of 2-tert-Butyl-5,5-dimethyl-1-hexene (9),
2,2,3,6,6-Pentamethyl-E-3-heptene (10), and 2,2,5,6,6-
Pentamethyl-E-3-heptene (11)
After completion of the catalytic reactions with t-BuC ꢀ CH in
1,2-dichloroethane described above, the solvent and the
volatile products were removed by distillation at 356 K. The
remaining residue was distilled under reduced pressure to give
a mixture of compounds 9 11. Each individual product was
separated from the mixture by column chromatography on
silica gel (70 230 mesh) with hexane. The yields based on the
reaction of Figure 2a (410 mg of t-BuC ꢀ CH) were: 39 mg of 9
(9%), 129 mg of 10 (31%), 12 mg of 11 (3%). Purity of the
compounds were confirmed by GC-MS. Mass spectra indicated
the empirical formula C12H24 for all compounds.
Acknowledgements
¬
Thanks are due to Plan Nacional de Investigacion, MCYT
(Project BQU2000-1170) and CSIC Hungarian Academy of
Sciences (Project 2001HU0006). J. N. thanks Universidad del
Zulia for a grant, and M.S. thanks the E.C. for a fellowship at the
1
NMR data for 9: H NMR (CDCl3, 293 K): d ˆ 0.89, 1.05
[both s, 9H each, C(CH3)3], 1.30, 1.96 (both m, 2H each, CH2),
ˆ
ˆ
4.65 [dt, J(H,H) ˆ 1.2, 1.2 Hz, 1H, CH2], 4.81 (m, 1H, CH2);
¬
Marie Curie Training Site MPMT-CT-2000-00200. A. K. is
13C{1H} NMR (CDCl3, 293 K): d ˆ 25.98 (CH2), 30.35, 36.24
grateful for a grant from the Hungarian Ministry of Education
(FKFP 0416). I. J. D. thanks DGA for a grant.
ˆ
[C(CH3)3], 30.25, 32.77 [C(CH3)3], 44.27 (CH2), 105.87 ( CH2),
ˆ
159.24 ( C).
1
NMR data for 10: H NMR (CDCl3, 293 K): d ˆ 0.85, 1.01
[both s, 9H each, C(CH3)3], 1.56 [dt, J(H,H) ˆ 1.2, 0.6 Hz, 3H,
CH3], 1.85 [brd, J(H,H) ˆ 7.7 Hz, 2H, CH2], 5.26 [tq, J(H,H) ˆ
7.7, 1.2 Hz, 1H, CH]; 13C{1H} NMR (CDCl3, 293 K): d ˆ 25.43
References and Notes
ˆ
[C(CH3)3], 27.38 (CH3), 29.13, 29.19 [C(CH3)3], 31.69
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ˆ
[C(CH3)3], 41.79 (CH2), 44.24 [C(CH3)3], 118.22 ( CH),
144.24 ( C); The E-stereochemistry has been confirmed by
ˆ
1H NOE measurements.
NMR data for 11: 1H NMR (CDCl3, 293 K): d ˆ 0.81 [s, 9H,
C(CH3)3], 0.88 [d, J(H,H) ˆ 6.9 Hz, 3H, CH3], 0.97 [s, 9H,
C(CH3)3], 1.80 [dq, J(H,H) ˆ 8.7, 6.9 Hz, 1H, CH], 5.21 [dd,
ˆ
J(H,H) ˆ 15.6, 8.7 Hz, 1H, CH], 5.36 [d, J(H,H) ˆ 15.6 Hz,
1H, CH]; 13C{1H} NMR (CDCl3, 293 K): d ˆ 15.68 (CH3),
ˆ
29.35, 29.81 [C(CH3)3], 36.73, 44.39 [C(CH3)3[, 47.01 (CH),
ˆ
127.98, 141.22 ( CH).
X-Ray Crystallographic Study
Crystals of 5 suitable for a crystallographic study were obtained
from solutions in acetone layered with diethyl ether. X-ray data
were collected on a four-circle Siemens P4 diffractometer with
graphite monochromated Mo-Ka radiation (l ˆ 0.71073 ä)
using w/2q scan. Data were corrected for absorption by using a
psi-scan method at 108 y-intervals.[11] The structure was solved
by direct methods with SHELXS-97.[12] Refinement, by full-
matrix least-squares on F2 with SHELXL-97, included aniso-
tropic displacement parameters for all non-hydrogen atoms. A
solvation acetone molecule was included in the refinement
without hydrogen atoms. Hydrogen atoms for the metal
complex were found from difference Fourier maps and refined
as isotropic atoms with coordinates riding on carbon atoms.
Crystal data for 5.(CH3)2CO: C25H49BF4IrN2P.(CH3)2CO; M ˆ
745.72; colorless prismatic block, 0.44 Â 0.40 Â 0.28 mm;
monoclinic, P21/c; a ˆ 18.360(3), b ˆ 14.714(1), c ˆ
13.176(2) ä, b ˆ 108.83(1)8; Z ˆ 4; Vˆ 3369.0(8) ä3; d ˆ
Adv. Synth. Catal. 2003, 345, 280 288
287

Janeth Navarro et al.
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P. F. P. Fichtner, S. R. Teixeira, J. Am. Chem. Soc. 2002,
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Organometallics 1994, 13, 1165 1173; for recent work
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Lopez, F. J. Lahoz, L. A. Oro, Organometallics 2001, 20,
[7] The structural parameters of 5 are intermediate between
those expected for Ir(I) butadiene (h4-p coordination)
and Ir(III) metallacyclopentene (s2-p coordination)
resonant forms. For a complete structural discussion on
a similar complex, see: C. Bohanna, M. A. Esteruelas,
2716 2724.
[10] J. Dupont, C. S. Consorti, P. A. Z. Suarez, R. F. de Souza,
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[11] C. T. North, D. C. Phillips, F. S. Matheus, Acta Crystal-
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ƒ
F. J. Lahoz, E. Onate, L. A. Oro, E. Sola, Organometal-
[12] SHELXTL Package v. 6.10, 2000, Bruker-AXS, Madison,
WI; G. M. Sheldrick, SHELXL-97, University of Gˆt-
tingen, Germany, 1997.
lics 1995, 14, 4825 4831.
[8] For a precedent of this reaction sequence, see: a) C.
Bianchini, M. Graziani, J. Kaspar, A. Meli, F. Vizza,
288
Adv. Synth. Catal. 2003, 345, 280 288