Pseudo-tetrahedral Rhodium and Iridium Complexes: Catalytic Synthesis of E-Enynes

Article abstract of DOI:10.1002/chem.201803878

The reactions of the rhodium(I) and iridium(I) complexes [M(PhBP₃)(C₂H₄)(NCMe)] (PhBP₃=PhB(CH₂PPh₂)₃^?) with alkynes have resulted in the synthesis of a new family of p

Full text of DOI:10.1002/chem.201803878

A Journal of
Accepted Article
Title: Pseudo-Tetrahedral Rhodium and Iridium Complexes: Catalytic
Synthesis of E-Enynes
Authors: Ana M. Geer, Alejandro Julian, José Antonio López, Miguel
Ángel Ciriano, and Cristina Tejel
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Pseudo-Tetrahedral Rhodium and Iridium Complexes: Catalytic
Synthesis of E-Enynes
Ana M. Geer, Alejandro Julián, José A. López, Miguel A. Ciriano, and Cristina Tejel*
Dedicated In Memoriam to Professor Dr. Pascual Royo
Abstract: Reactions of rhodium(I) and iridium(I) complexes
M(PhBP )(C )(NCMe)] with alkynes result in the synthesis of a
Bianchini proposed a π-alkyne metal complex as the first step in
the mechanism for alkyne cyclotrimerization when using rhodium
and iridium compounds with the tripodal neutral phosphine
triphos as the catalyst, and described the cationic complexes
[
3
2 4
H
new family of pseudo-tetrahedral complexes, [M(PhBP
3
)(RC≡CR’)]
−
(
M = Rh, Ir; PhBP
3
2
= PhB(CH PPh
)
2 3
), which contain an alkyne as a
four-electron donor. Reactions of these unusual compounds with
[Rh(MeCP
3
)(RC≡CR)]BPh
4
(R
=
CO
2
Me, Ph; MeCP
3
=
t
[13]
two-electron donors (L = PMe
3
, CN Bu) produces a change in the
MeC(CH PPh ) ).
2
2 3
Unfortunately, the lack of crystallographic
‘
donicity’ of the alkyne from a 4e− to a 2e− donor to give five-
studies prevented their full characterization, and they were
assumed to be in a fast equilibrium in solution between trigonal-
bipyramidal and square-pyramidal species on the basis of
coordinate complexes. These are the final products for iridium while
further reactions take place for the rhodium complexes. In particular,
C(sp)−H bond activation of the alkyne leading to hydrido-alkynyl
complexes occurs. This process is essential in a further reactivity of
the alkynes, and thus if the alkyne itself is used as a ligand, E-enyne
complexes are obtained. As a consequence of this chemistry, we
spectroscopic studies.
2
A
survey on the literature revealed that η -alkyne
coordination to rhodium is dominated by a two-electron donicity
stabilizing both, trigonal bipyramid (TBPY) and square-planar
(SP) complexes. From the few examples crystallographically
characterized, electronically saturated TBPY complexes are
3 2 4
showcase that complex [Rh(PhBP )(C H )(NCMe)] is a very efficient
precatalyst for the regioselective dimerization and trimerization of
terminal alkynes to E-enynes. Interestingly, acetonitrile significantly
enhances the catalytic activity facilitating the C(sp)−H bond
activation step. A hydrometallation mechanism to account for these
experimental observations is proposed.
[
14
]
derived from metal fragments such as ‘RhCl(PMe
3 3
) ’,
i
[
15
]
[ ]
16
‘RhCp’PPr
3
or ‘RhTp(L)’,
while the metallic fragments
i
[
17
]
[ ]
18
‘Rh(X)(PPr
3
)
2
’ (X = Cl, I) and ‘Rh(acac)(olefin)’ are suitable
to to bind alkynes to electronically unsaturated 16 ev SP-
compounds. More recently, SP-complexes with functionalized
alkynes like thioether-alkynylborates,
[
19
]
and P(C≡C)P pincer
20
[ ]
type ligands have been described.
Introduction
Herein we report the synthesis, full characterization,
reactivity studies, and electronic structure of the neutral
Alkynes play a pivotal role in the synthesis of a wide range of
organics derived from the high versatility of the ‘C≡C’
functionality. They include the well-known Sonogashira
−
[M(PhBP
3
)(RC≡CR’)] (M = Rh, Ir; PhBP
3
= PhB(CH
2
PPh
)
2 3
)
complexes with a unique pseudo-tetrahedral geometry, which
give an insight into this very unusual coordination environment
[
1
]
[
2
]
[
3
]
]
]
couplings,
dimerizations,
metathesis,
hydroaminations
oxidative alkynylations,
hydroacylations,
8
for mononuclear d -metal complexes of the second and third row.
[
4
]
[
5
redox-neutral α-amine alkynylations,
hydrogenations,
Indeed, tetrahedral or pseudo-tetrahedral geometries are
[
6
]
[
7
]
[
8
hydrosilylations,
[ 21 ]
unknown in rhodium(I) chemistry so far,
and they are
[
9
]
[ ]
10
cycloisomerizations,
as well as three-
[ 22 ]
restricted to rhodium(−I) and rhodium(0) oxidation states.
Nonetheless, despite of the strong propensity of d -RhL
[
11
]
component couplings including [2+2+2] cycloadditions.
8
4
Coordination of the alkyne to a metal center is often one of the
initial steps in these types of transformations; therefore a
fundamental knowledge of the metal-alkyne interaction is
essential for the development of new processes and catalysis.
Moreover, from a theoretical point of view, analysis of the
bonding between an alkyne and a transition metal complex is
also interesting because the ambivalent character of alkynes as
complexes to adopt square-planar geometries, rare sawhorse
[23]
(SH) environments have also been reported,
while the unique
compound [Rh(trop SiMe)(C )] remains the sole example for
2
2 4
H
[24]
the related trigonal pyramid (TP) geometry.
Moreover, we have studied the chemistry of these
complexes and, as a consequence, we have uncovered that the
rhodium complexes are efficient precatalysts for terminal alkyne
dimerization with a high selectivity to E-enynes, which is a long
pursued proposal. Part of this work has been previously
−
−
[ ]
12
ligands, behaving either as 2e or 4e donors.
Accordingly,
[25]
communicated.
.
[
a]
Dr. A. M Geer, A. Julián, Dr. J. A. López, Prof. Dr. M. A. Ciriano, Dr.
C. Tejel
Departamento de Química Inorgánica
Instituto de Síntesis Química y Catálisis Homogénea-ISQCH, CSIC-
Universidad de Zaragoza
Results and Discussion
Pedro Cerbuna 12, 50009-Zaragoza (Spain)
E-mail: ctejel@unizar.es
Synthesis and Characterization of [M(PhBP )(CR≡CR’)] (M =
Rh, Ir).
3
The iridium monoolefin complex [Ir(PhBP
PhBP = [PhB(CH PPh ]) was synthesized in order to prepare
iridium alkyne complexes, since it contains two labile
3 2 4
)(C H )(NCMe)] (1)
Supporting information for this article is given via a link at the end of
the document.
(
3
2
2 3
)
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2
(
acetonitrile and ethylene) ligands, as observed for the
analogous rhodium complex [Rh(PhBP )(C )(NCMe)]•2MeCN
(μ-Cl)} ] was treated with 1
PPh ] (tmen = N,N,N’,N’-
phenylacetylene in a η fashion. The short iridium−carbon and
long C46−C47 bond distances (2.001 Å in average and 1.32 Å,
3
2 4
H
[
26]
2
(2).
With this purpose, [{Ir(C
2
H
4
)
2
2
respectively) of the η coordinated alkyne are consistent with the
alkyne acting as a four-electron donor in 3.
[
12a,29]
mol-equiv. of [Li(tmen)][PhB(CH
2
2
)
3
Also the C≡C−C
tetramethylethane-1,2-diamine) in an ethylene saturated solution
of acetonitrile to provide 1, which precipitated in the reaction
medium as a pure white solid (Scheme 1). Noticeably, no
activation of C−H bonds was observed in our case, in contrast to
angle is considerably bent up to 137°. The three P−Ir−Ct angles
(Ct is the middle point of the C≡C bond) were found to be
different while the topology of the tripodal ligand impose P−Ir−P
[30]
angles close to 90º.
similar metathesis reactions of the phosphine with [{Ir(coe)
Cl)} ] (coe = cyclooctene) and [{Ir(H C=CHMe) (μ-Cl)} ], which
result in hydrideallyliridium(III) complexes.
2
(μ-
2
2
2
2
[27]
Complex 1 is pentacoordinate with a trigonal bipyramidal
geometry (TBPY), analogous to the rhodium complex 2, but they
1
31
1
differ in that the H and P{ H} NMR spectra of the iridium
complex correspond to a static species. Thus, according to the
31
1
proposed structure, the P{ H} NMR spectrum displays a
doublet for the two equivalent equatorial phosphorus nuclei and
a triplet for the axial phosphorus atom. The C=C bond of the
coordinated ethylene is located within the equatorial plane and it
1
does not rotate, as evidenced by two distinct signals in the H
NMR spectrum due to the protons on both sides of the
equatorial plane. The lack of rotation of ethylene is
a
consequence of a strong metal-olefin π-interaction, which occurs
Figure 1. Structure (ORTEP at 50% level) of the complex,
8
[ 28 ]
[Ir(PhBP )(HC≡CPh)] (3). Hydrogen atoms have been omitted and only the
3
at the equatorial position for TBPY d -ML
5
complexes.
In
ipso
C
3
atoms of the phenyl groups from PhBP are shown for clarity. Selected
sharp contrast, the ethylene in the rhodium counterpart 2
displays free rotation at r.t., suggesting thus that ethylene is
more tightly bound to iridium than rhodium.
angles (°) and bond distances (Å) for complex 3: Ir−P1, 2.242(2); Ir−P2,
2.334(2); Ir−P3, 2.280(2); Ir−C46, 1.979(8); Ir−C47, 2.019(8); Ir−Ct, 1.888(8);
C46−C47, 1.318(10); C47−C48, 1.464(10); P1−Ir−Ct, 129.1(2); P2−Ir−Ct,
127.8(2); P3−Ir−Ct, 123.4(2); C46−C47−C48, 137.1(8). (Ct is the middle point
between C46 and C47).
PhB
P
PhB
P
Ir
[
{Ir(C
2
H
4
)
2
(μ-Cl)}
2
]
MeCN
PhCCH
P
P
+
Ir
H
P
Additionally, the three Ir−P bond distances are unequal.
Assuming that the C≡C bond occupies one coordination position,
P
[
3
Li(tmen)][PhBP ]
NCMe
Ph
1
3
the ‘Ir(PhBP
distorted from C3v, in which the atoms of boron and iridium would
define the C axis. In this structure, Ct is somewhat shifted from
3
)’ fragment possesses a local symmetry slightly
3
Scheme 1. Synthesis of complexes 1 and 3.
the C3v axis (axis(B,Ir)−Ct, 176.78(2)º). This off-axis distortion
makes the P2−Ir−Ct angle smaller than the other two P−Ir−Ct
angles. These structural features are very similar to those found
for one independent molecule in the crystal and in the DFT
calculated structures of the analogous rhodium complex
Reactions of phenylacetylene, propargyl alcohol and methyl
propiolate with complex 1 in toluene were easily detected by a
color change of the solution from colorless to orange at room
temperature. They proceed with the corresponding replacement
of both the ethylene and acetonitrile ligands by the alkyne to
[
25]
3
[Rh(PhBP )(HC≡CPh)] (6), although the C≡C bond distance is
longer for iridium as a consequence of a stronger π-back
donation.
yield the corresponding complexes [Ir(PhBP
; CH OH, 4; CO Me, 5) (Scheme 1). However, no reaction was
observed
dimethylacetylenedicarboxylate
3
)(HC≡CR)] (R = Ph,
2
There are only two η -alkyne-iridium(I) tetracoordinated
3
2
2
complexes
Ir(PMe Ph)
roughly square-pyramidal with the alkyne acting as a four-
characterized
crystallographically:
with
the
internal
(dmad). Noticeably,
alkyne
the
[
31 ]
[
2
3
(MeC≡CMe)]BF described by Caulton
4
,
as
–
replacement of two 2-e ligands by one triple C≡C bond is a first
clear indication that the alkyne behaves as a four-electron ligand.
Complexes 3-4 were isolated as orange crystalline solids in
good yields and were fully characterized while complex 5 was
characterized in situ. In addition, the structure of 3 was
determined by X-ray diffraction methods. An ORTEP diagram of
the complex is shown in Figure 1.
electron
tolyl) (MeO
donor
CC≡CCO
and
Me)], with
[Ir(COCH
distorted tetrahedral
2 3
Me )(P(p-
3
)
2
2
2
a
geometry, where the authors propose that the alkyne is a two-
electron donor considering the lack of signals for the multiple-
[
32 ]
bonded carbon atoms.
However, both complexes possess
similar geometrical features to those of 3. Consequently, these
three species can be described as 18-electron complexes with a
pseudo-tetrahedral geometry, which is very uncommon for
rhodium(I) and iridium(I) compounds. Some fluxional fac-triphos-
rhodium and -iridium complexes with alkynes reported by
The geometry around the iridium atom was found to be
pseudo-tetrahedral with the iridium center bound to the three
phosphorus atoms of the PhBP ligand and to the C≡C bond of
3
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Bianchini can also be included into this category on the basis of
mentionable that the rhodium complex 2 reacts with styrene to
[
13]
spectroscopic studies.
Treatment of
Rh(PhBP )(C )(NCMe)]•2MeCN (2) in toluene with terminal
and internal alkynes gave directly the complexes
Rh(PhBP )(RC≡CR’)] (R = H; R’ = Ph (6), p-MeC (7), p-
Me (11); R = R’= CO Me,
2), which were isolated as reddish-brown solids after work up.
give [Rh(PhBP
3 2
)(H C=CHPh)(NCMe)] (13), with an axial
the
rhodium
complex
acetonitrile ligand (see Experimental Section). Since the styrene
[
3
2
H
4
complex
13
and
the
hypothetical
compound
3
[Rh(PhBP )(HC≡CPh)(NCMe)] (A) only differ in two protons,
[
3
6
H
4
steric effects are not the origin for the formation of the
tetracoordinate [Rh(PhBP )(HC≡CPh)] (6). Consequently,
t
n
BuC
6
H
4
(8), Bu (9), CH
2
OH (10), CO
2
2
3
1
electronic effects arising from the change of the ‘donicity’ of the
−
The reaction is similar to the above described for the iridium
complex 1 and it is clearly detected by a color change of the
solution from yellow to red-brown.
alkyne (from 2 to 4 e ) along with the entropy change associated
to acetonitrile dissociation (on going from A to 6) seems to be
the main factors that govern the result of this reaction.
The spectroscopic data of the iridium and rhodium
complexes are comparable (Table 1) to those reported for the
In theory, tetrahedral complexes of Rh(I) and Ir(I) should be
paramagnetic with two unpaired electrons according to the
complex [Rh(PhBP
show equivalent phosphorus nuclei and give a singlet (Ir) or
doublet (Rh) in the
3
)(HC≡CPh)] (6). Thus, compounds 3-12
classical d-orbital splitting. However, on decreasing the T
d
symmetry to C3v by closing three angles, the dz -based orbital is
lowered in energy while a low-energy hybrid sp orbital (2a )
1
2
31
1
P{ H} NMR spectra even at low
temperature. This feature requires a fast rotation of the alkyne
around the M-Ct axis, which has a very low energy barrier as
calculated for the rhodium complex 6 (ca. 1 kcal mol ). The
facile rotation of the alkyne results from an almost continuous
overlap of the orbitals involved in the metal−alkyne bond along
the axis of rotation, thus avoiding a bond cleavage.
becomes available for bonding.
8
DFT analysis of the d -M{MeB(CH
2
PMe
2
)
3
} (M = Rh, Ir)
−
1 [25]
fragments indicates a small difference in energy in favor of the
triplet versus the singlet state (3.0 and 2.0 kcal mol− for Rh and
Ir, respectively). However, this difference can be meaningless
because of the tendency of the B3LYP functional to stabilize
1
[33]
Aside from the equivalence of the phosphorus nuclei, other
noticeable spectroscopic characteristics of these compounds are
the large shift to low-field of the proton of the terminal alkynes in
high-spin species. Consequences of the spin-pairing are: a) a
distortion of the framework that results in distinct M−P bond
distances and P−M−P bond angles that reduces the symmetry
1
the H NMR spectra as well as the signals of the bound
from C
(2.36 and 2.13 eV for Rh and Ir, respectively) between the
HOMO (2e ) and LUMO (2e ) that stabilizes the singlet state and
leaves empty the orbital 2e
The two empty frontier orbitals (2a
3
(triplet) to Cs (singlet); b) a drastic energy difference
13
1
acetylene carbons ca. 160 ppm in the C{ H} NMR spectra.
Both features are typical for alkynes behaving as four-electron
a
s
[
12b-d]
donors.
s
of parentage dyz
.
1
s
, and 2e ) in the singlet
8
state of the d -M{MeB(CH
2 2 3
PMe ) } fragment match those filled π||
Table 1. Selected NMR spectroscopic data (δ (ppm)) for complexes
and π orbitals of the bent C≡C bond. They form thus two
⊥
[
M(PhBP
3
)(RC≡CR’)] (M = Rh, Ir).
bonding MOs, namely σ and π, which are filled with four
electrons given by the alkyne, stabilizing a pseudo-tetrahedral
geometry for an 18 electron complex. A further match of the
1
13
1
31
1
Complex
H (HC≡)
C{ H}(RC≡, ≡CH)
P{ H}
filled 2e
a
orbital with the empty π||* orbital of the C≡C bond
3
4
5
6
7
8
9
11.77 (q)
10.91 (qt)
11.08 (q)
10.04 (qd)
10.11 (qd)
10.18 (qd)
9.52 (qd)
9.36 (qd)
9.46 (q)
179.8, 166.3
182.2, 157.8
167.1, 164.8
164.9, 151.8
165.0, 152.2
164.9, 152.4
167.7, 144.8
166.4, 144.1
154.0, 148.4
152.7
14.6 (s)
16.5 (s)
17.7 (s)
47.7 (d)
47.2 (d)
47.6 (d)
47.6 (d)
48.6 (d)
51.6 (d)
53.1 (d)
[25]
corresponds to a π-backdonation.
This picture supports a
mayor contribution of the pseudo-tetrahedral M(I)−alkyne
canonical form. The alternative pseudo-square-pyramidal
M(III)−metallacyclopropene description could be also considered
to give account for the proton and carbon low-field shifts.
However, the equivalence of the three P atoms in the P{ H}
NMR spectra would require an easy P-donor exchange through
either trigonal bipyramidal structures or P−M bond dissociation,
which in our experience for Rh(III) and Ir(III) complexes involve
energy barriers quite larger than that calculated (1 kcal mol ).
The DFT-computed optimized geometries of the model
complexes [M{MeB(CH PMe }(HC≡CPh)] (M = Ir, 3’; Rh, 6’) as
closed-shell species reproduce quite well the experimental data
found for 3 and 6. In particular, the agreement of the M−P bond
distances and P−M−P bond angles with the experimental data is
31
1
−
1 [34]
10
11
12
2
2 3
)
-
remarkable. This geometric irregularity characteristic of the
8
metallic fragments d -M{MeB(CH
2
PMe
2 3
) } in the singlet state is
retained in the complexes while the HOMO–LUMO gap
increases to 3.48 and 3.81 eV in 6’ and 3’, respectively. The
representations and composition of the MOs of the model
A common and noticeable characteristic of all reactions is
that neither ethylene nor acetonitrile remain coordinated to the
metal. Indeed, complexes of the type [M(PhBP )(RC≡CR’)(L)] (L
or MeCN) have not been observed. With this in mind it is
3
=
2 4
C H
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Chemistry - A European Journal
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complexes show strong mixing, therefore a direct comparison
with the MOs of the fragment is difficult.
(B), analogous to the iridium counterpart 14. However, this
species was not detected even monitoring the reaction at −70 ºC.
2
Further evidence for the participation of η -alkyne
Reactions of complexes [M(PhBP
electron donor ligands.
3
)(HC≡CPh)] with two-
pentacoordinated intermediates in the C−H bond activation
process was obtained from the reaction of 6 with BuNC, a
t
[
35]
Reactivity studies on these novel complexes was initiated with
M(PhBP )(HC≡CPh)] (M = Ir, 3; Rh, 6). Although they are
slightly weaker donating ligand than PMe
detection of the intermediate [Rh(PhBP )(HC≡CPh)(CN Bu)] (16)
by H and P{ H} NMR spectroscopy at −50 ºC. However, the
3
,
which allowed the
t
[
3
3
1
31
1
electronically saturated (18 electron), both compounds present a
low-lying energy LUMO pointing out towards a possible vacant
site (Figure 2).
t
complex evolves very quicky to [Rh(PhBP
(17) on raising the temperature. Selected spectroscopic data of
6 and 17 can be found in Table 2 and are in agreement with
3
)(C≡CPh)(H)(CN Bu)]
1
the proposed formulation.
[a]
Table 2. Selected NMR spectroscopic data (δ (ppm)) for complexes 14-21.
1
13
1
31
1
Complex
H
C{ H}
P{ H}
(
HC≡ / Rh−H)
(RC≡, ≡CH)
3
6
11.77 (q)
10.04 (qd)
6.13 (t)
−8.74 (ddt)
5.97 (dd)
−7.19 (ddt)
6.80 (t)
−8.74 (ddt)
−
179.8, 166.3
164.9, 151.8
89.0, 83.1
14.6 (s)
47.7 (d)
2 2 3
Figure 2. LUMO of complex [Ir{MeB(CH PMe ) }(HC≡CPh)] (3').
1
4
5
−7.7, −17.8, −39.6, −47.6
28.4, 21.1, 4.7, −11.6
25.5, 22.2,15.1
Thus, good σ-donor ligands such as PMe
give [Ir(PhBP )(HC≡CPh)(PMe )]
Rh(PhBP )(C≡CPh)(H)(PMe )] (15) in very high yields (Scheme
). There is a notable influence of the metal center on the
3
react with 3 and 6
1
111.5, 109.5
to
[
2
3
3
(14) and
[
b]
3
3
16
− , 84.6
17
18
19
110.6, 103.4
111.3, 87.9
28.9, 25.8, 4.3
products obtained, yielding a pentacoordinate complex for
iridium but a hydrido alkynyl compound for rhodium.
22.0, 18.0, 12.8, −11.2
27.4, 19.7, 5.4, −11.6
45.8 (d)
[
b]
[b]
−
, −
PhB
P
PhB
P
PhB
P
Ph
PMe
3
PMe3
P
Ph
P
P
20
21
167.4, 161.8
168.1, 163.3
Ir
M
Rh
Ph
P
Me
P
P
H
M = Ir
M = Rh
H
3
P
PMe
3
−
45.2 (d)
H
1
4
M = Ir, 3; Rh, 6
15
[a] The pseudrotetrahedral complexes 3 and 6 have also been included for
comparative purposes. [b] Not detected.
Scheme 2. Synthesis of complexes 14 and 15 from reactions of PMe
and 6, respectively.
3
with 3
Although a decrease of the electronic density at the metal
slightly slows down the C−H oxidative addition reaction,
releasing electronic density in the alkyne showed a more
The most significant spectroscopic features observed for 14
are the chemical shifts of the acetylenic proton and carbon
atoms, which are substantially shifted towards higher field
relative to 3 (Table 2). These shifts indicate a clear change in
the ‘donicity’ of the phenylacetylene from a 4-electron donor (in
noticeable effect. Thus, addition of PMe
3
to the complex which
acceptor alkyne
Me)] (11) allowed the isolation of
Me)(PMe )] (18) as an orange solid in
contains
the
)(HC≡CCO
)(HC≡CCO
electron
[Rh(PhBP
Rh(PhBP
3
2
[
3
2
3
excellent yields. Spectroscopic data of 18 confirm the presence
of the alkyne as a two-electron donor (Table 2). This complex
slowly transforms in solution into the corresponding hydrido
3
) to a 2-electron donor (in 14). The result contrasts with that
obtained for the rhodium species 6, where addition of PMe
enables a C(sp)−H bond activation reaction to give the hydrido
alkynyl complex [Rh(PhBP )(C≡CPh)(H)(PMe )] (15) (Scheme 2).
Relevant signals for 15 corresponds to the hydride ligand (δ =
8.74 ppm, dddt) and to the acetylide carbon atoms (δ = 111.5
3
alkynyl derivative [Rh(PhBP
3
2 3
)(C≡CCO Me)(H)(PMe )] (19)
3
3
quantitatively, but this reaction requires one week at room
temperature to reach completion. From these solutions complex
−
1
9 was isolated as colorless microcrystals whose molecular
1
1
13
(≡CPh), 109.5 ppm (RhC≡)) in the H and H, C-hmbc NMR
structure is depicted in Figure 3.
spectra, respectively. The expected ABCMX spin system (M =
In 19, the rhodium atom is bound to four phosphorus atoms
103
31
1
PMe
3
, X =
Rh) is clearly observable in the P{ H} NMR
−
(PMe
3
and the three from the [PhBP
3
] ), the hydrido, and the
spectrum (see Supporting Information). Formation of the
rhodium-hydrido-alkynyl complex most likely involves the
alkynyl ligand through a σ-Rh−C bond in a slightly distorted
octahedral geometry. The strong trans influence of the hydrido
ligand is clearly reflected in a longer Rh−P2 bond distance (trans
pentacoordinated intermediate, [Rh(PhBP
3 3
)(HC≡CPh)(PMe )]
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Chemistry - A European Journal
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to it) when compared with the other three that are almost equal.
between [Ir(PhBP
3
)(HC≡CPh)] (3) and phenylacetylene, even
2
The methylcarboxylate group (CO Me) was found to be
when added in excess.
disordered over two positions (only one of them, labelled with
the letter ‘a’ with a relative occupancy’ of 85.2(7)% is shown in
Figure 3). The C49−C50 bond distance falls in the range for
terminal alkynyl ligands and is practically linear, with
Rh−C49−C50 and Rh−C49−C51a/b angles close to 180º.
DFT
[Rh(MeBP
calculations
)(PhC≡C−CH=CHPh)]
2 2 3
MeB(CH PMe ) ) confirm the proposed structure (Figure 4, right).
on
the
(20’,
model
complex
3
MeBP
3
=
Noticeably, rhodium retains the pseudotetrahedral geometry
even in the presence of the close C=C bond. These calculations
also indicate that from a thermodynamic perspective, a value of
-
1
ΔGº298 = −0.4 kcal mol is obtained for the alkyne exchange
reaction:
2
0’ + PhC≡CH → 6’ + PhC≡C−CH=CHPh
Therefore, substitution of the enyne by phenylacetylene is
possible, closing thus plausible catalytic cycle for the
a
dimerization of phenylacetylene. Indeed, preliminary assays
indicated the reaction to be catalytic.
Figure
Rh(PhBP
3.
Structure
Me)(H)(PMe
(ORTEP
)] (19). Hydrogen atoms have been omitted
are shown for clarity.
at
50%
level)
of
[
3
)(C≡CCO
2
3
Figure 4. Left: synthesis of the E-enyne complexes 20 and 21. Right: DFT
ipso
and only the C atoms of the phenyl groups from PhBP
Selected angles (°) and bond distances (Å): Rh−P1, 2.367(1); Rh−P2,
3
calculated structure for the model complex [Rh(MeBP
(20’, MeBP = MeB(CH PMe ).
3
)(PhC≡C−CH=CHPh)]
3
2
2 3
)
2
1
.460(1); Rh−P3, 2.355(1); Rh−P4, 2.345(1); Rh−C49, 2.017(4); C49−C50,
.212(5); C50−C51a, 1.438(5); C50−C51b, 1.440(7); P1−Rh−P4, 167.4(4);
P2−Rh−H, 174(2); P3−Rh−C49, 166.0(1).
Catalytic synthesis of enynes.
A first test for the dimerization of phenylacetylene by using
Rh(PhBP mol% catalyst loading)
)(HC≡CPh)] (6) (in
[
3
a 5
Reactions leading to complexes 14−19 indicate that subtle
resulted in the conversion to the corresponding enyne (1,4-
diphenyl-but-3-en-1-yne) with good regioselectivity to the E
isomer (Table 3, entry 1). However, the reaction was found to be
very slow. Remarkably, we found that the reaction time can be
significantly reduced if the rhodium(I) derivative 2 was used as a
catalyst precursor (entry 2). A comparison of both reactions by
NMR spectroscopy indicated that the only difference is the
presence of free acetonitrile in the reaction media when using 2
as precatalyst, since this complex crystallizes with two
molecules of acetonitrile. Therefore, acetonitrile was responsible
for the increase in catalytic activity. Indeed, if the catalysis was
carried out in the presence of 10 equivalents of acetonitrile (per
mol of 2), the time of the reaction was reduced to 40 min (entry
changes in both, the substituent on the alkyne ligand or the two-
t
electron ligand (L = PMe
3
, CN Bu) on the metal can result in
significant differences in reactivity for rhodium. Moreover, the
most surprising difference is the lack of C−H bond activation for
the iridium complex 14 since this metal is thought to be more
[36]
suitable for this type of reactions than rhodium. In our opinion,
this lack of reactivity of the iridium complex 3 can be mainly
attributed to kinetic reasons. In addition, it is also noticeable the
long reaction time for the C−H bond activation in
3 2 3
[Rh(PhBP )(HC≡CCO Me)(PMe )] (18), with an electron
withdrawing group on the alkyne.
Interestingly, if the alkyne itself is used as a ligand, E-enyne
complexes are obtained. In this manner, the reaction of
3). Moreover, if the catalysis is performed in neat acetonitrile the
[
Rh(PhBP
phenylacetylene
Rh(PhBP
)(PhC≡C−CH=CHPh)] (20), while a similar reaction
with p-tolylacetylene gives [Rh(PhBP
)(p-tolC≡C−CH=CHtol-p)]
21). Complexes 20 and 21 represent two new examples of
3
)(C
2
H
4
)(NCMe)]•2MeCN (2) with two mol-equiv. of
quantitative conversion of the phenylacetylene is considerably
reduced (15 min) even at 60 ºC, maintaining the regioselectivity
to the E isomer (entry 4) (Figure 5). Nonetheless, lowering the
temperature to r.t. increased the reaction time considerably
gives the complex
[
3
3
(
(
entry 5).
The catalysts work equally well with a wider variety of
alkynes, such as the arylic p-tolC≡CH, the functionalized
rhodium(I) species in a pseudotetrahedral geometry with the
triple C≡C bond bound to the metal. They were isolated as dark
red solids fully characterized by analytical and spectroscopic
methods according to the formulation shown in Figure 4.
Remarkably, both reactions were found to be regioselective,
observing the formation of the E isomer, as indicated by the
n
Me SiC≡CH or the alkylic BuC≡CH. Using complex 2 as
3
precatalyst in neat acetonitrile at 60 ºC, the corresponding
enynes were obtained with a high selectivity to the E isomers
and with short reaction times (Table 3, entries 6-8). Under these
conditions complex 2 is one of the fastest catalysts reported so
3
large coupling constant of the olefinic protons ( J(H,H) = 15.7-
15.9 Hz). On the contrary, no further reaction was observed
[
37]
far with the advantage that no additives are necessary.
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Chemistry - A European Journal
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selectivities to the E isomer (up to 95 %). In fact, when using this
alkyne the catalyst loading can be lowered to 0.1 % in a reaction
which is completed in 72 min (entry 14).
As commented before, such short reaction times in alkyne
dimerization are quite unusual; other known rhodium catalysts,
2
[
RhCl(IPr)(η -coe)(py)]/py
(IPr
=
1,3-bis(2,6-
[
39
]
diisopropylphenyl)imidazol-2-ylidene, py
=
pyridine),
[RhCl(PR ] (R =
and [Rh(CNC-
i
i
[38]
[
40
[
]
[
Rh(POCOPPr)SPr
2
)],
[Rh(PNP)(H)
2
)],
3 3
)
[
41
]
[
42
]
3
i
43
]
Ph,
Me)(C
Me,
)][BArF
), [Rh(η -C
3
H
5
)(PPr
)
3 2
],
[
44
]
2
H
4
4
]
require longer reaction times (3-24 h)
under comparable reaction conditions to those described here.
Reaction times are in general longer for other metal catalysts.
Figure 5. Left: Conversion (%) vs time for the synthesis of PhC≡C–CH=CHPh
45
]
[
(
E+gem) using complex 2 as precatalyst showing the beneficial effect of
acetonitrile. Right: Details of this reaction in neat CD CN at 60 º.
3
Nevertheless, the use of microwave radiation has permitted a
remarkable improvement in the activity of a palladium catalyst,
obtaining high yields after 30 min, but with harsher reactions
[
46]
The results of lowering the catalyst loading to 1 mol%,
entries 9-12) have been also included in Table for
conditions (130 ºC and addition of an external base).
More
2
(
3
recently, an iron(II) polyhydride catalyst, [Fe(PNP)(H) (η -H )]
2 2
comparative purposes. Good reaction times (11-82 min) are still
(PNP = 2,6-di(diphenylphosphanyl-methylamine)pyridine), has
maintained and similar high selectivities towards the E-enyne
are again obtained.
been reported to promote efficiently alkyne dimerization to
[38]
[47]
enynes in comparable times.
In addition, selective and very
fast cross-dimerization of alkynes to 1,3-enynes catalyzed by
[48]
titanium complexes has been also reported. Our attempts to
produce cross-dimerization of alkynes to 1,3-enynes were fully
unselective resulting in a mixture of the three possible E-enynes.
Two main mechanistic pathways are recognized for alkyne
Table 3. Catalytic dimerization of alkynes to enynes mediated by complexes 6
or 2.
[
a]
Cat
mol%)
T (ºC) /
Solvent
% Convers.
(E/gem)
[39],[45e],[45f],[ 49 ]
Entry
Alkyne
Time
[b]
dimerization.
The first one involves oxidative
(
addition of the C−H bond generating a rhodium-alkynyl-hydride
complex, followed by coordination of a second alkyne and either
insertion of the coordinated alkyne into the M−H bond
1
2
PhC≡CH
PhC≡CH
6 (5)
2 (5)
80 / [D
8
8
]tol
]tol
30 h
> 99 (85:15)
> 99 (82:18)
80 / [D
90 min
(hydrometallation) or into the M−C bond (carbometallation) and
subsequent reductive elimination to afford the enyne. The
second alternative involves the isomerization of the alkynyl-
hydride species to the corresponding vinylidene isomer. This
vinylidene mechanism leads to E/Z isomers while the hydro- or
carbometallation paths generate E or gem enynes. Since the Z
isomer is absent in all of the reported experiments here,
catalysis with complex 2 as precatalyst most likely takes place
via insertion reactions.
8
0 / [D ]tol:
8
3
PhC≡CH
2 (5)
[c]
40 min
> 99 (83:17)
3
CD CN
4
5
6
7
8
9
PhC≡CH
PhC≡CH
p-tolC≡CH
2 (5)
2 (5)
2 (5)
2 (5)
2 (5)
2 (1)
2 (1)
2 (1)
2 (1)
60 / CD
25 / CD
60 / CD
60 / CD
60 / CD
60 / CD
60 / CD
60 / CD
60 / CD
60 / CD
60 / CD
3
3
3
3
3
3
3
3
3
3
3
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
CN
15 min
9 h
> 99 (85:15)
> 99 (83:17)
> 99 (84:16)
> 99 (95:5)
> 99 (88:12)
> 99 (85:15)
> 99 (84:16)
> 99 (95:5)
> 99 (86:14)
68 (85:15)
> 99 (95:5)
1
10 min
[
d]
Me
3
SiC≡CH
4 min
A
plausible mechanism for alkyne dimerization using
n
BuC≡CH
PhC≡CH
p-tolC≡CH
10 min
82 min
58 min
11 min
52 min
15 h
complex 2 as catalyst precursor is shown in Scheme 3. Only the
hydrometallation path has been considered since this step is
[39],[45e],[45f] ,[49b]
typically lower in energy than the carbometallation.
The beneficial effect of acetonitrile has also been taken into
account in the C(sp)−H bond activation and the reductive-
10
11
12
13
14
Me
3
SiC≡CH
elimination steps, through species
Scheme 3). Experimental evidence for the positive role of
acetonitrile in the first one arises from the observation of the
CPh)(NCMe)] (22, Scheme 3)
A and D, respectively
(
n
BuC≡CH
PhC≡CH
2 (0.1)
2 (0.1)
intermediate [Rh(PhBP
after dissolving complex [Rh(PhBP
6 6
CD CN, while no reaction was observed in neat C D .
3
)(H)(C
≡
)(HC≡CPh)] (6) in neat
3
Me
3
SiC≡CH
72 min
3
[
a] Reaction conditions: 0.5 mL of solvent. [b] Determined by H NMR
3
spectroscopy. [c] 10 mol of CD CN per mol of 2. [d] Minimum time required for
lock and shim optimization.
It is interesting to mention that the reactions using the
bulkiest and most electron-donating alkyne Me SiC≡CH (entries
and 11) displayed the greatest activity along with the best
3
7
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[
Rh](C
C
2
H
4
)(NCMe) + RC CH
the alkyne to the corresponding enyne. However, it was found to
be a good catalyst for the [2+2+2] cycloaddition reaction of
methyl propiolate to tri(carboxymethyl)benzene (Scheme 4).
C H NCMe
2
4,
H
NCMe
Rh]
H
CR
[
R
H
R
NCMe
H
[
Rh]
Catalytic synthesis of trisubstituted benzenes.
R
A
RC CH
Complex 2 was also found to be an appropriate precatalyst for
the synthesis of trisubstituted benzenes. Scheme 4 and Table 4
summarize the results obtained for this reaction under several
reaction conditions. In all the cases the reaction is almost
quantitative with a good regioselectivity towards the 1,3,5-isomer
relative to the 1,2,4-isomer.
NCMe
R
H
R
[
Rh]
H
− NCMe
Rh]
[
Rh]
R
[
H
R
2
2 (R = Ph)
NCMe
H
R
H
RC CH
NCMe
H
NCMe
[Rh]
R
NCMe
H
[Rh]
R
[
Rh]
R
H
R
H
R
R
CO Me
2
2
CO Me
H
H
C
[Rh]
CO
2
Me
3
HC CCO
2
Me
+
D
MeO
2
C
2
CO Me
Scheme 3. Plausible catalytic cycle for the synthesis of enynes catalyzed by
complex 2. A different orientation of the π-alkyne in species C would give the
gem isomer. [Rh] = ‘Rh(PhBP )’.
3
2
CO Me
1
,3,5-C
6
H
3
(CO
2
Me)
3
1,2,4-C
6
H
3
(CO
2
Me)
3
Scheme 4. Cyclotrimerization of methyl propiolate catalyzed by complexes 2
and 11.
Moreover, DFT-calculations of intermediates I1 and I2,
previous to the cleavage of the C−H bond, revealed that I2 with
coordinated MeCN is 8.6 kcal mol lower in energy that the
−
1
The reaction is thermally activated as deduced from
comparison of entries 1 and 2, which demonstrate considerable
acceleration of the reaction on raising temperature from 25 to 80
ºC. No appreciable changes were observed when using complex
related I1 without MeCN (Figure 6). Since a change in the
2
2
coordination-mode of the alkyne from Rh-(η )C≡C to Rh-(η )C−H
is required to achieve intermediates I1 or I2, this is reasonably
easier in [Rh(PhBP
alkyne acting
Rh(PhBP
)(HC≡CPh)] (6) where it is tightly bound because of
3
)(HC≡CR)(NCMe)] (A, Scheme 3) −with the
as two-electron donor− than in
1
1 as catalyst (entries 2 and 3). More remarkable, and in clear
contrast to the dimerization of alkynes commented before, is that
the presence of acetonitrile in the reaction media only slightly
enhances the activity of the catalysis in the cyclotrimerization
process (entry 4). This observation strongly supports a catalytic
cycle in which the oxidative-addition reaction of the C−H bond is
[
3
the four-electron donicity. In addition, the observed selectivity
towards the E-isomers can be easily understood considering the
–
steric overcrowding provided by the [PhBP
3
]
ligand in
intermediates of type C in Scheme 3.
not
MeO
involved. Internal
CC≡CCO
Me did not trimerize if complexes 2, 6 and 11
2
activated
alkynes
such
as
On the other hand, the iridium complex [Ir(PhBP
3
)(HC≡CPh)]
2
(3) is not catalytically active for this reaction, most probably due
were used as catalyst precursors.
to its reluctance to undergo the C−H bond activation reaction as
commented before.
Table 4. Catalytic cyclotrimerization of methyl propiolate (HC≡CCO
mediated by 2 or 11.
Me)
2
[
a]
%
Conver.
[b]
Entry
Cat.
T (ºC) / Solvent
Time
(
1,3,5:1,2,4)
1
2
3
2
2
25 / [D
80 / [D
80 / [D
8
8
8
]tol
]tol
]tol
12 h
98 (86:14)
> 99 (82:18)
> 99 (83:17)
16 min
21 min
11
8
CD
0 / [D
8
]tol:
4
5
11
11
[c]
13 min
55 min
> 99 (83:17)
> 99 (82:18)
3
CN
Figure 6 Calculated (DFT) molecular structures for intermediates I1 and I2.
Values of ΔGº298 are given in kcal mol− and relative to [Rh(PhBP
1
)(HC≡CPh)]
60 / CD
3
CN
3
(
3
6) and [Rh(PhBP )(HC≡CPh)] (6) + NCMe, respectively.
[
a] Reaction conditions: 5% Catalyst load, 0.8 M substrate, 0.5 mL of
1
solvent. [b] Determined by H NMR spectroscopy. [c] 15 mol per mol of 2.
Furthermore,
Rh(PhBP
)(HC≡CCO
the
rhodium
compound
[
3
2
Me)] (11), for which the C−H bond
activation process is slow, is also inactive for the dimerization of
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Chemistry - A European Journal
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FULL PAPER
For this type of [2+2+2] cycloadditions, the most accepted
Catalytic reactions
to
enynes
by
using
[50]
mechanism implies the coordination of two alkyne molecules,
which would lead to an intermediate species,
Rh(PhBP ]. Oxidative coupling of the two
)(HC≡CCO
alkynes to form metallacyclopentadiene followed by
[Rh(PhBP )(C H )(NCMe)]•2MeCN (2) as precatalyst proceed
3
2 4
under smooth conditions and high regioselectivities to the E
isomers. The reactions work very well in acetonitrile, which is
expected according to the above comments. Remarkably,
complex 2 is one the faster precatalyst for alkyne-dimerization
reported up to date. For the particular case of
[
3
Me)
2 2
a
subsequent coordination of a third alkyne and its insertion into
the Rh−C bond to form either a rhodacycloheptatriene (Schore’s
51
[ ]
mechanism ) or give an intramolecular [4+2] cycloaddition to
[Rh(PhBP
is slow, cyclotrimerization of methyl propiolate to the arene
1,3,5-C (CO Me) was observed.
Finally, this report highlights the notable versatility of the
Rh(PhBP )’ platform in C−C bond formation either through
3 2
)(HC≡CCO
Me)] , where C−H bond activation process
[
52]
render a 7-rhodanorbornadiene.
In both cases a reductive
elimination would lead to the corresponding arene.
6
H
3
2
2
‘
3
Summary and Conclusions
insertion or cycloaddition reactions for the synthesis of E-enynes
or arenes, respectively. The E selectivity in the synthesis of
enynes can be attributed to the steric crowding provided by the
In summary, we have synthesized a family of rhodium and
iridium pseudo-tetrahedral alkyne complexes of formula
−
[PhBP
3
] ligand, while the nature of the alkyne tips the balance
towards dimerization vs cycloaddtion reactions. We believe that
the findings reported here will help the improvement of existing
catalytic methods, as well as the development of new catalysts
for organic transformations.
[
3
M(PhBP )(HC≡CR)] (M = Ir, Rh), in which the alkyne ligand
behaves as a four-electron donor. This unique coordination
environment is achievable by the combination of a strongly
donating and strong-field tripodal [PhBP
−
3
]
ligand with alkyne
ligands acting as four electron donors. Further reactions of these
t
compounds with two-electron donor ligands (L = BuNC and
PMe
metal. For rhodium, the hydrido alkynyl complexes
Rh(PhBP
)(C≡CR)(H)L] are the final result from these reactions.
3
) lead to noticeably contrasting reactivity depending on the Experimental Section
[
3
General methods: All operations were carried out under an argon
atmosphere using standard Schlenk techniques. Organic solvents were
dried by standard procedures and distilled under argon prior to use or
obtained oxygen- and water-free from a Solvent Purification System.
These compounds are formed through a C−H bond activation in
2
the terminal η -alkyne pentacoordinated intermediates
[
Rh(PhBP
temperature NMR studies or even isolated, as in the case of
Rh(PhBP )(HC≡CCO Me)(PMe )].
Other weaker ligands such as acetonitrile also promote the
C−H bond cleavage of terminal alkynes, as confirmed by the
observation of [Rh(PhBP
)(H)(C≡CPh)(NCMe)] on dissolving
Rh(PhBP
)(HC≡CPh)] in acetonitrile. In this line, DFT-
3
)(HC≡CR)L], which have been observed by low-
[
53
]
[
54
]
Complexes
[{Ir(coe)
2
(μ-Cl)}
2
],
[{Ir(C
2
H
4
[26]
)
2
2
(μ-Cl)} ],
[
[
Rh(PhBP
Li(tmen)][PhB(CH
3
)(C
2
H
4
)(NCMe)]
•
[27]
2MeCN
(2),
and
[
3
2
3
2 2 3
PPh ) ]
were prepared according to the literature
methods. Phenylacetylene was distilled under vacuum. Other reagents
were commercially available and were used as received. Carbon,
hydrogen, and nitrogen analyses were carried out with a Perkin-Elmer
3
2
400 CHNS/O microanalyzer. Mass spectra of complexes were acquired
[
3
on an Esquire3000 plus (ESI+) spectrometer in acetonitrile. NMR spectra
were recorded on Bruker AV 300, AV 400 and AV 500 spectrometers
operating at 300.13, 400.13 and 500.13 MHz, respectively, for H.
calculations on intermediates I1 and I2 having the alkyne
coordinated through the C−H bond (previous to the C−H bond
cleavage step) revealed that I2 is stabilized by 9.3 kcal mol−
upon acetonitrile coordination. These results support the
relevant role of pentacoordinated intermediates of the type
1
1
Chemical shifts are reported in ppm and referenced to SiMe
4
, using the
internal signal of the deuterated solvent ( H and C) and external H PO
P). IR spectra of solid samples were recorded with a Perkin-Elmer 100
1
13
3
4
31
(
−1
[
Rh(PhBP
3
)(HC≡CPh)(L)] in which the alkyne undergoes a
FT-IR spectrometer (4000−400 cm ) equipped with attenuated total
reflectance (ATR).
2
2
change of the coordination mode from η -C≡C to η -C−H
−
behaving as a 2e donor.
C−H activation for iridium complexes is highly disfavoured
Synthesis of representative complexes (see the Supporting
Information for the compounds not included here):
even with the basic PMe
3
ligand, and the reaction stops at the
pentacoordinate complex [Ir(PhBP
3
)(HC≡CPh)(PMe )]. This
3
[
[
[
Ir(PhBP
{Ir(C
Li(tmen)][PhB(CH
3
)(C
2
H
4
)(NCMe)] (1). A Schlenk tube was charged with solid
(120.0 mg, 0.211 mmol) and solid
PPh (338.0 mg, 0.423 mmol). Addition of
divergence in the reactivity of rhodium vs iridium complexes is
associated to the strength of the M−alkyne bond, which prevents
the slippage of the alkyne to get the C−H coordination mode in
iridium complexes.
The hydrido alkynyl rhodium complexes having the labile
acetonitrile as coligand are suitable to bind a new molecule of
alkyne, which promotes hydride insertion and C−C bond
H
2 4
)
2
(μ-Cl)}
2
]
2
2 3
) ]
degassed acetonitrile (3 mL) dissolved the starting materials while a
white crystalline solid precipitated almost immediately. After stirring for 30
min, the solid was separated by decantation, washed with a mixture of
water/acetonitrile (1:2, 3 x 3 mL) and vacuum-dried. Yield: 407.6 mg
1
o1
M
(58%). H NMR (300.13 MHz, CD
2
Cl
2
, 25 ºC): δ = 7.92 (br s, 4H, Ph
2
P ),
3
o
(m+p)1
M
m
7
7
1
.63 (br d, J(H,H) = 7.1 Hz, 2H, BPh ), 7.33 (m, 8H, Ph
2
P
+ BPh ),
formation
to
give
the
E-enyne
compounds
p
(o+m+p)2
2
M
p
A
(o+m)
A
.04 (m, 13H, BPh + Ph
P
+ Ph
2
P ), 6.80 (m, 8H, Ph
P), 1.56 (s, 3H, NCMe), 1.41
). P{ H} NMR (121.5 MHz, CD Cl , 25
ºC): δ = −10.4 (t, 1P, J(P,P) = 23 Hz, P ), −12.5 (d, 2P, J(P,P) = 23 Hz,
2
P ),
[
Rh(PhBP
3
)(RC≡C−CH=CHR)] (R
= Ph; p-tol). In these
3
.86 (br d, J(H,H) = 6.2 Hz, 4H, C
2
H
4
1
+ CH
2
complexes rhodium was found to be again in a pseudo-
3
1
2
(m, 4H, CH
2
P), 1.15 (m, 2H, C
H
2 4
2
2
tetrahedral environment η -C≡C bound to the enyne, despite the
2
A
2
close C=C bond suitable for coordination.
M
13
1
2 2
P ). Selected C{ H} NMR (75.5 MHz, CD Cl , 25 ºC) resonances
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201803878
FULL PAPER
1
13
1
13
obtained from H, C-hsqc and H, C-hmbc spectra: δ = 113.9 (NCMe),
[Ir(PhBP
3
)(HC≡CPh)(PMe
3
)] (14). Trimethylphosphane (1M in toluene,
+
+
1
6.6 (C
Anal. Calcd (%) for C49
found: C 61.98, H 5.17, N 1.55.
H
2 4
), 3.2 (NCMe). MS (ESI ): m/z (%): 878 (100) [(PhBP
3
)Ir] .
86.7 μL, 0.087 mmol) was added to a solution of [Ir(PhBP
3
)(HC≡CPh)]
H
48NBP
3
Ir (946.86): C 62.16, H 5.11, N 1.48;
(3) (85.0 mg, 0.087 mmol) in toluene (5 mL) producing an immediate
color change from red to yellow. The solution was evaporated to ca. 0.5
mL and precipitated with hexane (6 mL) yielding a beige solid. The
solution was decanted and the solid was washed with hexane (2 x 2 mL)
[
Ir(PhBP
3
)(HC≡CPh)] (3). Freshly distilled PhC≡CH (7.6μL, 0.070 mmol)
)(C )(NCMe)] (1) (65.8 mg, 0.070
1
31
and vacuum-dried. Yield: 77.8 mg (85%). H{ P} NMR (400.13 MHz,
was added to a solution of [Ir(PhBP
3
2 4
H
3
o
3
6 6
C D , 25 ºC): δ = 8.19 (d, J(H,H) = 7.6 Hz, 2H, BPh ), 8.13 (d, J(H,H) =
mmol) in toluene (5 mL). An immediate color change of the solution to
orange took place. After stirring for 45 min, the volatiles were evaporated
to ca. 1 mL under vacuum and the solution was carefully layered with
hexane to render orange microcrystals in two days. The solution was
decanted and the crystals were washed with hexane and vacuum-dried.
Yield: 54.18 mg (79%). H NMR (500.13 MHz, CD
q, J(H,P) = 7.2 Hz, 1H, HC≡), 7.78 (d, J(H,H) = 7.2 Hz, 2H, BPh ), 7.59
m, 2H, ≡CPh ), 7.37 (m, 5H, BPh , ≡CPh
8.8 Hz, 12H, Ph
o1
2
C
3
o
3
7
.4 Hz, 2H, Ph
P ), 7.82 (d, J(H,H) = 6.8 Hz, 2H, Ph ), 7.66 (t, J(H,H)
m
3
o2
C
=
7.4 Hz, 2H, BPh ), 7.63 (d, J(H,H) = 7.0 Hz, 2H, Ph
2
P ), 7.44 (m, 9H,
p
o(1+2)
A
o(1+2)
B
3
m
BPh + Ph
2
P
+ Ph
2
P ), 7.24 (t, J(H,H) = 7.6 Hz, 2H, Ph ), 7.10
p
3
p1 C
(
m, 1H, Ph ), 7.02 (t, J(H,H) = 7.1 Hz, 1H, Ph
2
C
P ), 6.79 (m, 13H,
(
m+p)1
B
(m+p)2
+ Ph2
B
p(1+2)
A
m(1+2)
+ Ph2
3
p2 C
1
Ph
P
P
+ Ph
2
P
P + Ph2 P ), 6.61 (t,
2
Cl
2
, 25 ºC): δ = 11.77
2
3
m1
A
m2 A
3
3
o
2
J(H,H) = 7.5 Hz, 2H, Ph2 P ), 6.59 (t, J(H,H) = 8.0 Hz, 2H, Ph P ),
(
C
2
o
o
(m+p)
3
3
6.13 (s, 1H, HC≡), 2.45 (br s, 2H, CH P ), 2.36 (d, J(H,H) = 15.6 Hz, 1H,
(
=
Ph
6
), 7.33 (t, J(H,H) = J(H,P)
2
B
2
B
2
o
2
3
4
CH P ), 2.10 (d, J(H,H) = 15.6 Hz, 1H, CH P ), 1.89 (d, J(H,H) = 14.7
P), 7.03 (tt, J(H,H) = 7.3, J(H,H) = 1.2 Hz, 1H,
2
2
A
2
A
p
3
m
2
2
2 2
Hz, 1H, CH P ), 1.47 (d, J(H,H) = 14.7 Hz, 1H, CH P ), 0.25 (s, 9H,
2
P), 6.92 (t, J(H,H) = 7.3 Hz, 12H, Ph
P), 1.65 (d, J(H,P) = 11.2 Hz,
P). P{ H} NMR (202.5 MHz, CD Cl , 25 ºC): δ = 14.6 (s).
, 25 ºC) resonances obtained
from H, C-hsqc and H, C-hmbc spectra: δ = 179.8 (≡CPh), 166.3
3
1
1
2
3
1
1
(PMe3). P{ H} NMR (162.0 MHz, C D , 25 ºC): δ = –7.7 (td, J(P,P) =
H, CH
2
2
2
6
6
2
2
C
2
13
1
27 Hz, J(P,P) = 19 Hz, P ), –17.8 (td, J(P,P) = 26 Hz, J(P,P) = 19 Hz,
2 2
Selected C{ H} NMR (125.8 MHz, CD Cl
B
2
2
A
2
1
13
1
13
P ), –39.6 (dt, J(P,P) = 424 Hz, J(P,P) = 26 Hz, P ), –47.6 (dt, J(P,P) =
2
13
1
ipso
o
m
p
3
424 Hz, J(P,P) = 19 Hz, PMe ). Selected C{ H} NMR (100.6 MHz,
(
HC≡), 138.7 (≡CPh ), 131.2 (≡CPh ), 128.3 (≡CPh ), 127.8 (≡CPh ).
1
13
1
13
−
1
+
6 6
C D , 25 ºC) resonances obtained from H, C-hsqc and H, C-hmbc
spectra: δ = 131.6 (C ), 131.1 (Ph ), 127.6 (Ph ), 125.6 (Ph ), 89.0
IR (ATR): ν(C≡C)/cm : 1664. MS(ESI ): m/z (%): 979.1 (15) [M−H]. Anal.
Calcd (%) for C53 Ir (979.89): C 64.96, H 4.83; found: C 66.50, H
.98.
ipso
o
m
p
H47BP
3
−
1
(
≡CPh), 83.1 (HC≡), 14.7 (PMe
Calcd. (%) for C56 Ir (1055.97): C 63.70, H 5.35; found: C 63.86, H
.30.
3
). IR (ATR): ν(C≡C)/cm : 1669 (w). Anal.
4
H56BP
4
5
[
Rh(PhBP
)(HC≡CPh)] (6). Freshly distilled PhC≡CH (7.7 μL, 0.07 mmol)
was added to a solution of [Rh(PhBP )(C )(NCMe)] 2MeCN (65.8 mg,
.07 mmol) in toluene (5 mL). An immediate color change of the solution
from orange to dark-red took place. After stirring for 15 min, the volatiles
were evaporated under vacuum to ca. 1 mL and the solution was
carefully layered with hexane to render dark-red microcrystals in two
days. The solution was decanted, and the crystals were washed with
3
3
2
H
4
•
[
Rh(PhBP
toluene, 126.1 μL, 0.126 mmol) was added to
Rh(PhBP Me)] (11) (110.0 mg, 0.126 mmol) in toluene (5
)(HC≡CCO
3 2
)(HC≡CCO Me)(PMe
3
)] (18). Trimethylphosphane (1M in
0
a
solution of
[
3
2
mL), producing an immediate color change from red to orange. The
solution was evaporated to ca. 0.5 mL and the product was precipitated
with hexane (6 mL) as an orange solid. The solution was decanted and
the solid was washed with hexane (2 x 2 mL) and vacuum-dried. Yield:
1
hexane and vacuum-dried. Yield: 47.4 mg (76%). H NMR (400 MHz,
3
2
6 6
C D , 25 ºC): δ = 10.04 (qd, J(H,P) = 10.5 Hz, J(H,Rh) = 1.7 Hz, 1H,
3 o 3
1
31
89.7 mg (75%). H{ P} NMR (400.13 MHz, C D , 25 ºC): δ = 8.45 (br s,
6
6
o
HC≡), 8.22 (d, J(H,H) = 7.3 Hz, 2H, BPh ), 7.75 (t, J(H,H) = 7.5 Hz, 2H,
o1
B
3
3
m
o
2H, Ph2 P ), 8.21 (d, J(H,H) = 6.3 Hz, 2H, BPh ), 8.03 (d, J(H,H) = 6.6
BPh ), 7.66 (dd, J(H,H) = 8.5, 1.6 Hz, 2H, ≡CPh ), 7.49 (tt, J(H,H) = 7.3,
.4 Hz, 1H, BPh ), 7.38 (t, J(H,H) = J(H,P) = 8.5 Hz, 12H, Ph
tt, J(H,H) = 7.5, 1.2 Hz, 2H, ≡CPh ), 7.11 (tt, J(H,H) = 7.2, 1.3, 1H,
CPh ), 6.74 (td, J(H,H) = 7.1, 1.2 Hz, 6H, Ph
o1
C
3
m
3
p
3
3
o
Hz, 2H, Ph2 P ), 7.66 (t, J(H,H) = 7.2 Hz, 2H, BPh ), 7.62 (d, J(H,H) =
1
(
≡
1
2
P), 7.19
o2
B
3
o1 A
m
2
7.0 Hz, 2H, Ph2 P ), 7.41 (d, J(H,H) = 7.6 Hz, 2H, Ph P ), 7.38 (m,
p
3
o2
C
3
p
p
2
1H, BPh ), 7.33 (d, J(H,H) = 6.3 Hz, 2H, Ph P ), 7.24 (t, J(H,H) = 7.2
2
P), 6.68 (td, J(H,H) = 7.9,
m1
B
3
p1
A
3
m
3
31
1
2
Hz, 2H, Ph2 P ), 7.12 (t, J(H,H) = 7.3 Hz, 1H, Ph P ), 7.04 (d, J(H,H)
.3 Hz, 12H, Ph
2
P), 1.88 (d, J(H,P) = 10.9 Hz, 6H, CH
, 25 ºC): δ = 47.7 (d, JP,Rh = 110 Hz). Selected C NMR
2
P). P{ H} NMR
o2
A
m1
C
p1
B
13
= 7.03, 2H, Ph P ), 6.98 (m, 3H, Ph P + Ph2 P ), 6.80 (m, 4H, HC≡
(
162 MHz, C
6
D
6
2
2
(
2
m+p)2
B
(m+p)2
A
(m+p)2
C
p1 C
1
13
1
13
P ), 6.74 (m, 7H, Ph
2
P
+ Ph2
P + Ph2 P ), 6.62 (t,
+
Ph
resonances obtained from H, C-hsqc and H, C-hmbc spectra: δ =
64.9 (≡CPh), 151.8 (HC≡), 138.1 (≡CPh ), 130.2 (≡CPh ), 128.2
≡CPh ), 127.5 (≡CPh ). IR (ATR): ν(C≡C)/cm : 1661 (w). MS (ESI ):
m/z (%): 890.6 (100) [M] . Anal. Calcd (%) for C53
3
m1 A
ipso
o
J(H,H) = 7.4 Hz, 2H, Ph P ), 3.69 (s, 3H, CO Me), 2.25 (m, 3H,
1
(
2
2
B
C
2
C
m
p
−1
+
CH P + CH P ), 1.88 (br d, J(H,H) = 14.6 Hz, 1H, CH P ), 1.68 (br s,
2
2
2
A
31
1
+
2 3 6 6
H, CH P ), 0.34 (s, 9H, PMe ). P{ H} NMR (162.0 MHz, C D , 25 ºC):
2
3
H47BP Rh (890.58): C
2
2
C
δ = 22.0 (ddt, J(P,Rh) = 117 Hz, J(P,P) = 37 Hz, J(P,P) = 27.0 Hz, P ),
7
1.48, H 5.32; found: C 71.74, H 5.31.
2
2
B
1
8.0 (ddd, J(P,Rh) = 107 Hz, J(P,P) = 37 Hz, J(P,P) = 31 Hz, P ), 12.8
2
2
A
(
dt, J(P,P) = 454 Hz, J(P,Rh) = 84 Hz, J(P,P) = 37 Hz, P ), −11.2 (dddd,
2 2 M
[
Rh(PhBP
styrene in excess (84.1 μL, 0.734 mmol) to
Rh(PhBP )(C )(NCMe)]•2MeCN (115.0 mg, 0.122 mmol) in toluene (2
3
)(H
2
C=CHPh)(NCMe)] (13) was prepared by addition of
2
J(P,P) = 454 Hz, J(P,Rh) = 94 Hz, J(P,P) = 31 Hz, J(P,P) = 27 Hz, P ).
a
yellow solution of
13
1
Selected C{ H} NMR (100.6 MHz, C
D
6 6
, 25 ºC) resonances obtained
from H, C-hsqc and H, C-hmbc: δ = 166.3 (CO
Me), 111.3 (HC≡),
Me), 15.7 (PMe ). IR (ATR):
1664. Anal. Calcd. (%) for
[
3
2 4
H
1
13
1
13
2
mL). An immediate color change to dark orange took place. After 4
vacuum/argon cycles in order to displace the equilibrium to complex 13,
and 40 min. at room temperature, hexane (8 mL) was added producing
the precipitation of an orange solid. The solid was washed with cold
hexane (4 x 2 mL), decanted and vacuum dried. Yield: 89.4 (82%).
NMR (300.13 MHz, C
8
7.9 (≡CCO
2
−
Me), 51.2 (CO
2
3
1
−1
2
ν(CO CH
3
)/cm
:
1708, ν(C≡C)/cm :
52 4 2
C H54BP O Rh (948.60): C 65.84, H 5.74; found: C 66.04, H 5.30.
1
H
[Rh(PhBP
3 2 3
)(C≡CCO Me)(H)(PMe )] (19). was prepared ‘in situ’ by
D
6 6
, 25 ºC): δ = 8.49-6.51 (40H, Ph), 4.43 (q,
=CHPh), 3.12 (m, J(H,H) = 10.9 Hz, 1H,
3
3
complete conversion of a solution of [Rh(PhBP )(HC≡CCO Me)(PMe )]
(18) (25.0 mg, 0.029 mmol) into 19 after 7 days at room temperature.
Single monocrystals for X-ray diffraction studies were grown in C D .
J(H,H) = 8.3 Hz, 1H, CH
2
3
2
3
C
A
CH
CH
CH
2
2
2
=CHPh), 2.45 (m, 1H, CH
P ), 1.92 (m, 1H, CH
=CHPh), 0.46 (br s, 3H, NCMe). P{ H} RMN (121.5 MHz, C
2
P ), 2.25 (m, 1H, CH
2
P ), 2.09 (m, 1H,
C
B
B
P ), 1.82 (m, 1H, CH
2
P ), 1.76 (m, 1H,
6
6
2
1
31
3
31
1
H{ P} NMR (300.13 MHz, C D , 25 ºC): δ = 8.19 (d, J(H,H) = 6.7 Hz,
D
6 6,
6
o1
6
o
A
o1
B
o1 C
2
A
2
), 8.13 (m, 2H, Ph2 P ), 8.01 (m, 6H, Ph P
+ Ph2
P
+
2
H, BPh
2
5º): δ = 43.9 (dt, J(P,Rh) = 122 Hz, J(P,P) = 33 Hz, 1P, P ), 18.8 (ddd,
2 2 C
o2
A
3
m
o2 B
2
Ph2 P ), 7.68 (t, J(H,H) = 7.5 Hz, 2H, BPh ), 7.48 (m, 2H, Ph P ),
J(P,Rh) = 83 Hz, J(P,P) = 51 Hz, J(P,P) = 33 Hz, 1P, P ), 5.90 (ddd,
3
p
o2 C
2
2
B
2
7.42 (t, J(H,H) = 7.3 Hz, 1H, BPh ), 7.20 (m, 2H, Ph P ), 6.98 (m, 6H,
Ph
J(P,Rh) = 106 Hz, J(P,P) = 50 Hz, J(P,P) = 33 Hz, 1P, P ).
(
2
m+p)1
A
(m+p)1
2
B
(m+p)2
2
B
P
+
Ph
P ), 6.86 (m, 3H, Ph
P ), 6.71 (m, 9H,
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201803878
FULL PAPER
(
m+p)2
C
(m+p)1
C
3
(m+p)2
A
Ph
2
2
P
+ Ph
2
P
+ Ph
2
P ), 3.58 (s, 3H, CO
2
CH
3
), 2.30 (m,
Selected crystallographic data can be found in the Supporting
Information. The structures were solved by direct methods and refined by
(
B+C)
B
3
H, CH
2
P
), 2.13 (d, J(H,H) = 15.5 Hz, 1H, CH
2
P ), 1.97 (d, J(H,H) =
B
2
A
[ 58 ]
1
4.4 Hz, 1H, CH
2
P ), 1.91 (d, J(H,H) = 14.6 Hz, 1H, CH
2
P ), 1.32 (d,
), –8.74 (d, J(H,Rh) =
4.5 Hz, 1H, Rh−H). P{ H} NMR (121.5 MHz, C , 25 ºC): δ = 27.4
full-matrix least-squares, with the program SHELXL-2016
in the
2
A
[59]
J(H,H) = 14.5 Hz, 1H, CH
2
P ), 0.65 (s, 9H, PMe
3
WINGX package. Hydrogen atoms were geometrically calculated and
refined by the riding mode, including the isotropic displacement
parameters. All non-hydrogen atoms were refined with anisotropic
displacement parameters except the ones of the minor fraction
3
1
1
1
6 6
D
2
2
C
(
ddt, J(P,Rh) = 90 Hz, J(P,P) = 36 Hz, J(P,P) = 23 Hz, P ), 19.7 (ddt,
J(P,P) = 341 Hz, J(P,Rh) = 82 Hz, J(P,P) = 35 Hz, P ), 5.4 (ddt,
J(P,Rh) = 72 Hz, J(P,P) = 35 Hz, J(P,P) = 23 Hz, P ), –11.6 (ddt,
J(P,P) = 341 Hz, J(P,Rh) = 87 Hz, J(P,P) = 23 Hz, P ).
2
2
A
2
2
B
(occupancy 0.148(7)) of a disorder modelled in (19·2C
ligand was refined with geometrical constrains. CCDC 1855476 (3·C
and 1855269 (19·2C ) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
6 6
H ); this disorder
2
2
M
7 8
H )
6 6
H
[
Rh(PhBP
mg, 0.03 mmol) was dissolved in C
3
)(PhC≡C−CH=CHPh)] (20). [Rh(PhBP
(0.5 mL) and freshly distilled
3 2 4
)(C H )(NCMe)] (22.7
Cambridge
Crystallographic
Data
Centre
via
6
D
6
www.ccdc.cam.ac.uk/data_request/cif.
PhC≡CH (5.8 μL, 0.05 mmol) was added. An immediate color change of
the solution from orange to dark-red was observed. The course of the
1
reaction was monitored by H NMR spectroscopy and the complete
Selected crystallographic data for [Ir(PhBP
3
(3·C ). Crystal data for 3·C 55BIrP , Mr = 1071.96, triclinic,
3
)(HC≡CPh)]•C
7 8
H
conversion was reached after ca. 8h at rt. The solution was then
evaporated to ca. 0.1 mL and layered with hexane to render dark-red
microcrystals in two days. The crystals were decanted, washed with
hexane and vacuum-dried. Yield: 16.3 mg (62%). H{ P} NMR (300 MHz,
, 25 ºC) (integrals were taken from the usual H NMR spectrum): δ =
.21 (d, J(H,H) = 8.8 Hz, 2H, BPh ), 8.09 (dd, J(H,H) = 15.7 Hz,
J(H,Rh) = 1.8 Hz, 1H, Ph CH=CH–C≡C–Ph ), 7.74 (t, J(H,H) = 7.3 Hz,
H, BPh ), 7.71 (dd, J(H,H) = 6.9, 1.3 Hz, 2H, Ph ), 7.48 (tt, J(H,H) =
2
.2, 1.4 Hz, 1H, BPh ), 7.40 (dd, J(H,H) = 6.8, 1.7 Hz, 12H, Ph P), 7.30
dd, J(H,H) = 8.4, 1.4 Hz, 2H, Ph ), 7.25 (tt, J(H,H) = 7.7, 1.4 Hz, 2H,
Ph ), 7.14 (t, J(H,H) = 7.4 Hz, 1H, Ph ), 7.09 (t, J(H,H) = 7.1, 2H,
Ph ), 7.07 (d, J(H,H) = 15.7 Hz, 1H, Ph CH=CH–C≡C–Ph ), 7.05 (t,
J(H,H) = 7.0 Hz, 1H, Ph ), 6.76 (tt, J(H,H) = 7.4, 1.4 Hz, 6H, Ph
.69 (tt, J(H,H) = 6.9, 1.7 Hz, 12H, Ph
H
7 8
7 8
H : C60H
space group P-1, a = 10.9698(12), b = 13.1865(14), c = 16.7637(18) Å, α
3
= 87.958(2), β = 80.720(2), γ = 87.178(2)º, V = 2389.3(4) Å , Z = 2, ρcalcd
1
31
-3
= 1.490 g cm , F(000) = 1084, T = 100(2) K, MoK
α
radiation (λ = 0.71073
1
-1
C
D
6 6
Å, μ = 2.935 mm ). Data were collected with a dark orange irregular
block (0.46 × 0.08 × 0.01 mm). Of 13086 measured reflections (2θ: 3.1-
52.0º), 9239 were unique (Rint = 0.0430). Final agreement factors were
= 0.0575 (7610 observed reflections) and wR2 = 0.1129.
Data/restrains/parameters 9239/0/586; GOF = 1.081. Largest peak and
3
o
3
8
4
B
A
3
m
3
Ao
3
2
7
(
R1
p
3
o
3
Bo
3
–3
hole in the final difference map 1.456 and -2.001 e Å
.
Am
3
Ap
3
Bm
3
B
A
Selected
Rh(PhBP
9·2C
a = 18.1205(13), b = 10.1578(7), c = 30.375(2) Å, β = 106.3300(10), V =
crystallographic
Me)(H)(PMe )]•2C
Rh, Mr = 1104.76, monoclinic, space group P2
data
for
3
Bp
3
p
2
P),
P).
[
)(C≡CCO
H
6 6
(19·2C H
6 6
). Crystal data for
/c,
3
2
3
3
m
2
6
P), 1.91 (br s, 6H, CH
2
1
6 6 2
H : C64H66BO P
4
1
31
1
P{ H} NMR (121 MHz, C
6
D
6
, 25 ºC): δ = 45.8 (d, J(P,Rh) = 110 Hz).
1
3
Selected C NMR resonances obtained from hsqc and hmbc spectra: δ
167.4 (Ph CH=CH–C≡C–Ph ), 161.8 (Ph CH=CH–C≡C–Ph ), 136.3
Ph CH=CH–C≡C–Ph ), 128.8 (Ph ), 128.7 (Ph ), 128.16 (Ph ),
3
-3
5
365.4(7) Å , Z = 4, ρcalcd = 1.368 g cm , F(000) = 2304, T = 100(2) K,
MoK radiation (λ = 0.71073 Å, μ = 0.483 mm ). Data were collected with
α
a pale yellow irregular block (0.35 × 0.12 × 0.08 mm). Of 60721
measured reflections (2θ: 3.1-54.0º), 11694 were unique (Rint = 0.0415).
Final agreement factors were R1 = 0.0578 (10460 observed reflections)
and wR2 = 0.1301. Data/restrains/parameters 11694/37/673; GOF =
B
A
B
A
=
(
1
-1
B
A
Am
Ao
Bm
Bp
Bo
Ap
B
A
28.15 (Ph ), 127.2 (Ph ), 127.1 (Ph ), 123.6 (Ph CH=CH–C≡C–Ph ).
1 + +
−
IR (ATR): ν(C≡C)/cm : 1665. MS (ESI ): m/z (%): 994.2 (6) [M+2H] ,
+
7
89.2 (62) [M–enyne+H] . Anal. Calcd (%) for C61
3
H53BP Rh (992.71): C
7
3.80, H 5.38; found: C 73.61, H 5.30.
1
0
.100. Largest peak and hole in the final difference map 1.433 and -
–3
.859 e Å
.
Catalytic essays.
Catalytic alkyne dimerization reactions: A NMR tube containing a solution
of the catalyst with loads of 5%, 1% or 0.1% mol% in either [D ]-toluene
or CD CN (0.5 mL) was treated with the alkyne (1.00 mmol) and warmed
to the indicated temperature. The reaction course was monitored by
NMR spectroscopy, and the conversion was determined by integration of
the corresponding resonances of the alkyne and the enynes. Catalytic
cyclotrimerization of methyl propiolate: A NMR tube containing a solution
Acknowledgements
8
3
1
The generous financial support from MINECO/FEDER (Projects
CTQ2014-53033-P and CTQ2017-83421-P, C.T.), and Gobierno
H
de
Aragón/FEDER
(GA/FEDER,
Inorganic
Molecular
Architecture Group E08_17R; C.T.) is gratefully acknowledged.
The Centro de Supercomputación de Galicia (CESGA) is also
gratefully acknowledged for generous allocation.
8 3
of catalyst (0.01 mmol) in either [D ]-toluene or CD CN (0.5 mL) was
treated with methyl propiolate (0.20 mmol) and warmed to the indicated
1
temperature. The reaction course was monitored by
H NMR
spectroscopy, and the conversion was determined by integration of the
corresponding resonances of the alkyne and tri(carboxymethyl)benzene.
Keywords: rhodium • iridium • pseudotetrahedral • C−C
coupling • enynes
DFT geometry optimizations. The DFT geometry optimizations and
[
55]
calculations were carried out with the Gaussian 09 program package,
using the B3LYP-D3 hybrid functional.
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Geometry optimizations were
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Pseudo-Tetrahedral Rhodium and
Iridium Complexes: Catalytic
Synthesis of E-enynes
Eighteen-electron pseudo-tetrahedral Rh(I) and Ir(I) complexes are generated with
alkynes as four-electron donors. On addition of two-electron ligands the rhodium
complexes undergo a C−H bond activation via pentacoordinate intermediates while
these are the final products with iridium. Stoichiometric reactions with alkynes give
2
new pseudo-tetrahedral rhodium complexes with η -C≡C coordinated enynes while
these reactions are catalytic with highly enhanced activity in MeCN.
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