Synthesis and Reactivity of Phosphine-Quinolinolato Rhodium Complexes: Intermediacy of Vinylidene and (Amino)carbene Complexes in the Catalytic Hydroamination of Terminal Alkynes

Article abstract of DOI:10.1021/acs.organomet.6b00853

We report here on the syntheses of rhodium(I) complexes bearing a phosphine-quinolinolate ligand and the isolation of two classes of important intermediates in the anti-Markovnikov hydroamination of terminal alkynes with secondary amines: vinylidene-bridged dirhodium complexes and (amino)carbene complexes. We first prepared various rhodium(I) complexes bearing a phosphine-quinolinolate ligand and found that some of these complexes had catalytic activity for the anti-Markovnikov hydroamination of terminal alkynes with secondary amines. The reaction of stoichiometric amounts of a (PNO)Rh complex with terminal alkynes provided vinylidene-bridged dirhodium complexes. When the resulting vinylidene complexes were reacted with secondary amines, (amino)carbene complexes were generated, which gave the hydroamination product upon heating with an additive. These results suggest that this anti-Markovnikov hydroamination catalyzed by (PNO)Rh complexes proceeds via vinylidene and (amino)carbene complexes.

Full text of DOI:10.1021/acs.organomet.6b00853

Article
pubs.acs.org/Organometallics
Synthesis and Reactivity of Phosphine-Quinolinolato Rhodium
Complexes: Intermediacy of Vinylidene and (Amino)carbene
Complexes in the Catalytic Hydroamination of Terminal Alkynes
Shotaro Takano, Takuya Kochi, and Fumitoshi Kakiuchi*
Department of Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa
223-8522, Japan
S
* Supporting Information
ABSTRACT: We report here on the syntheses of rhodium(I)
complexes bearing a phosphine-quinolinolate ligand and the
isolation of two classes of important intermediates in the anti-
Markovnikov hydroamination of terminal alkynes with secondary
amines: vinylidene-bridged dirhodium complexes and (amino)-
carbene complexes. We first prepared various rhodium(I) complexes
bearing a phosphine-quinolinolate ligand and found that some of
these complexes had catalytic activity for the anti-Markovnikov
hydroamination of terminal alkynes with secondary amines. The
reaction of stoichiometric amounts of a (PNO)Rh complex with
terminal alkynes provided vinylidene-bridged dirhodium complexes.
When the resulting vinylidene complexes were reacted with
secondary amines, (amino)carbene complexes were generated, which gave the hydroamination product upon heating with an
additive. These results suggest that this anti-Markovnikov hydroamination catalyzed by (PNO)Rh complexes proceeds via
vinylidene and (amino)carbene complexes.
of a low-valent late-transition-metal complex with a terminal
alkyne gives a vinylidene complex. The high electrophili-
city of the vinylidene carbon center that is directly bound
to the metal facilitates the nucleophilic attack to the car-
bon atom, which was originally the terminal carbon of
the alkyne. The corresponding alkenyl or carbene complex
formed by the addition of a nucleophile then releases the
anti-Markovnikov addition product (Figure 1). The mecha-
nism of the anti-Markovnikov addition to terminal alkynes via
vinylidene intermediates has been widely accepted and has
been proposed for many transformations. However, direct
evidence of the involvement of vinylidene and alkenyl or
carbene intermediates has not been presented for most of the
reactions.3−6
Our group has been studying transformations of terminal
alkynes using 8-quinolinolato rhodium catalysts (Figure 2).7
For example, the anti-Markovnikov addition of alcohols to form
enol ethers was developed using an 8-quinolinolato carbonyl
rhodium catalyst (Figure 2a).7a In addition, combinations of
phosphines with an 8-quinolinolato rhodium complex bearing a
COD ligand were found to be effective catalysts for the anti-
Markovnikov addition of secondary amines to arylacetylenes
at room temperature (Figure 2b).7b In these reactions, we
speculated that one of the reaction intermediates is a vinyli-
dene rhodium complex, because these reactions gave only
1. INTRODUCTION
Anti-Markovnikov addition reactions to terminal alkynes have
been studied extensively using transition-metal catalysts,
because they are otherwise difficult to achieve. The use of
late transition metals in anti-Markovnikov additions is par-
ticularly effective, not only because of the extensive functional
group tolerance but also because vinylidene intermediates can
be readily produced from terminal alkynes. Since the pio-
neering work by Dixneuf and co-workers in 1986,1 vinylidene
complexes have been considered to be key intermediates in
many anti-Markovnikov additions that are catalyzed by late-
transition-metal catalysts.2
Figure 1 shows a general scheme for the anti-Markovnikov
addition of weak nucleophiles to terminal alkynes, which
proceeds via a vinylidene intermediate. First, the reaction
Figure 1. General scheme of the anti-Markovnikov addition of
nucleophiles to terminal alkynes via vinylidene intermediates.
Received: November 12, 2016
© XXXX American Chemical Society
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To examine this hypothesis, rhodium complexes with a
phosphine-quinolinolate ligand were prepared. A few transition-
metal complexes possessing a phosphine-quinolinolate-type
ligand have been reported in previous studies.9,10 In 1995, the
Grotjahn group synthesized transition-metal complexes bearing
the same PNO tridentate ligand as that depicted in Figure 3
(Ar = Ph), and a rhodium(III) complex was prepared by the
oxidative addition of an acyl−oxygen bond of the acylated PNO
ligand to a rhodium(I) complex.9 Vigalok and co-workers,
in 2014, also synthesized a PNO Pd(II) complex using a
phosphine-quinolinol ether ligand.10 However, these complexes
were not employed in catalytic reactions, and the synthesis of a
rhodium(I) complex bearing a PNO ligand has not been
reported. Following Grotjahn’s procedure,9 we prepared the
PNO ligand precursor 2-((diphenylphosphaneyl)methyl)qui-
nolin-8-ol (1), which was then used for the synthesis of a series
of rhodium(I) complexes.
Figure 2. anti-Markovnikov hydroalkoxylation and hydroamination
catalyzed by 8-quinolinolato rhodium catalysts.
2.1.1. Synthesis of Dinuclear PNO Rhodium Complex 2.
We first examined the synthesis of an alkene rhodium complex
following the procedure used to prepare the 8-quinolinolato
rhodium complex bearing a COD ligand. Treatment of
[Rh(OMe)(cod)]2 with 1 in benzene at room temperature
gave the dinuclear rhodium(I) complex 2 in 61% yield (eq 1).
anti-Markovnikov products and did not proceed when internal
alkynes were used as a substrate. In 2013, Wang and co-workers
carried out DFT calculations of the above hydroalkoxylation
and concluded that the reaction proceeds via a vinylidene
rhodium complex.8 They also concluded that the mechanism of
the reaction involved a 1,2-β-H shift from a carbene complex,
which is more favorable than reductive elimination from an
alkenyl hydride complex.
Here we provide evidence to suggest that both vinylidene
and (amino)carbene complexes are formed as intermediates in
the anti-Markovnikov addition of secondary amines to terminal
alkynes catalyzed by our newly synthesized rhodium complexes
bearing a tridentate phosphine-quinolinolate ligand. Various
phosphine-quinolinolato rhodium(I) complexes were synthe-
sized and examined as catalysts for the anti-Markovnikov
hydroamination. We also investigated the reactivities of the
rhodium complexes toward terminal alkynes and secondary
amines and succeeded in the first structural determination of
both of the two catalytically relevant intermediates that are
involved in the anti-Markovnikov hydroamination of terminal
alkynes: namely, vinylidene complexes and (amino)carbene
complexes.
The 31P{1H} NMR spectrum of complex 2 exhibited two
doublets of doublets coupled with the rhodium and phosphorus
nuclei at 46.1 (1JP−Rh = 175.9 Hz, 2JP−P = 44.6 Hz) and 54.3 ppm
2
(1JP−Rh = 184.3 Hz, JP−P = 44.6 Hz). A single-crystal X-ray
diffraction analysis of complex 2 showed that one of the PNO
ligands is bound to a rhodium center in a tridentate fashion
but that the other PNO ligand bridges two rhodium centers
(see Figure S1 in the Supporting Information).
2.1.2. Synthesis of PNO Rhodium Complexes Bearing
Various Monodentate Ligands via PNO Rhodium Complex
2. Complex 2 can be used as a precursor for (PNO)Rh com-
plexes with various monodentate ligands (Scheme 1). When
2. RESULTS AND DISCUSSION
2.1. Synthesis of Rhodium Complexes Bearing a
Phosphine-Quinolinolate Ligand. As mentioned in the
Introduction, our group developed the anti-Markovnikov
hydroamination of terminal alkynes with secondary amines
using a combination of an 8-quinolinolato rhodium catalyst
with a phosphine.7b In this catalyst system, we hypothesized
that rhodium complexes bearing an 8-quinolinolate and a
phosphine were the catalytically active species (Figure 3, left).
Therefore, we envisioned that rhodium complexes bearing a
PNO tridentate ligand containing both a phosphine and an
8-quinolinolate moiety may also catalyze anti-Markovnikov
hydroamination reactions (Figure 3, right).
Scheme 1. Synthesis of (PNO)Rh Complexes 3−7
complex 2 was generated in situ by the reaction of [Rh(OMe)
(cod)]2 with 1 and treated with triphenylphosphine, a (PNO)
Rh complex possessing a triphenylphosphine ligand (3) was
obtained in 58% yield. The molecular structure of complex 3
was also confirmed by X-ray diffraction analysis (see Figure S2
in the Supporting Information). Similarly, (PNO)Rh complexes
with other phosphines, P(4-MeOC6H4)3 and P(4-CF3C6H4)3,
were prepared in 89 (4) and 25% (5) yields, respectively.
Figure 3. Working hypothesis: synthesis of rhodium complexes
bearing a phosphine-quinolinolate ligand.
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The relatively low yield of 5 is due to the difficulty in
reprecipitating highly soluble complex 5 from a benzene
solution with hexane, and quantitative formation of 5 under
these conditions was confirmed by NMR analyses of the
reaction performed in an NMR tube. In addition to phosphine
complexes, the corresponding pyridine (6) and carbonyl (7)
complexes were synthesized in excellent yields by a similar
procedure. The reaction of 2 with carbon monoxide to give 7
proceeded particularly smoothly at room temperature. The IR
spectrum of complex 7 exhibited a carbonyl stretching vibration
at 1945 cm−1. The structure of 7 was also confirmed by single-
crystal X-ray diffraction analysis, which clearly showed that
the PNO ligand and the carbonyl ligand coordinate to the
rhodium center in a square-planar fashion (see Figure S3 in the
Supporting Information). Complex 7 was also synthesized
by reacting PNO ligand precursor 1 with in situ generated
[RhCl2(CO)2]−.11
Table 1. Reaction of Phenylacetylene with Piperidine
Catalyzed by (PNO)Rh Complexes
a
b
entry
solvent
temp (°C)
catalyst
yield (%)
1
2
3
4
benzene-d6
toluene-d8
DMA
room temp
3
3
3
3
2
7
trace
25
13
42
5
80
80
toluene-d8
toluene-d8
toluene-d8
110
110
110
c
5
6
95
a
Reaction conditions unless specified otherwise: phenylacetylene
(0.2 mmol), piperidine (0.6 mmol), catalyst (0.02 mmol), solvent
b
c
1
(0.6 mL), 24 h. Determined by H NMR analysis. Performed using
5 mol % of the catalyst.
2.2. Anti-Markovnikov Hydroamination Reactions
Catalyzed by (PNO)Rh Complexes. The catalytic activities
of the (PNO)Rh complexes in the anti-Markovnikov hydro-
amination of terminal alkynes with secondary amines were
examined. Only a few late-transition-metal catalysts for anti-
Markovnikov hydroamination of terminal alkynes have been
reported in addition to the phosphine/8-quinolinolato rhodium
system reported by our group.12 In 2007, Fukumoto and
co-workers reported on the anti-Markovnikov addition of both
primary and secondary amines to terminal alkynes using a
TpRh(C2H4)2/PPh3 catalyst system.13 Lau and co-workers also
reported on the catalytic activity of TpRu[4-CF3C6H4N-
(PPh2)2](OTf) in anti-Markovnikov hydroamination reac-
tions.14 In these reactions, only aliphatic amines were used
as secondary amines. The use of secondary amines in anti-
Markovnikov hydroamination was reported by Bhattacharjee
and co-workers by employing [Ru(dppe)(PPh3)(CH3CN)2Cl]-
(BPh4) as a catalyst.15 In all of these reactions, vinylidene
complexes were proposed to be formed as intermediates but
were not actually observed for these systems.
The anti-Markovnikov hydroamination of piperidine to
phenylacetylene was first investigated using complexes 2, 3,
and 7. Considering that a combination of an 8-quinolinolato
rhodium complex with 2 equiv of triarylphosphine was used as
a catalyst for our original anti-Markovnikov hydroamination,7b
triphenylphosphine complex 3 was employed as a catalyst in
the beginning. When the reaction of phenylacetylene with 3
equiv of piperidine in the presence of 10 mol % of complex 3
was performed in benzene-d6 at room temperature, only trace
amounts of the corresponding hydroamination product 8a were
obtained (Table 1, entry 1). Accordingly, the reaction was
performed at higher temperatures to improve the product yield.
The reaction at 80 °C in toluene-d8 gave a 25% yield of 8a with
complete E selectivity (entry 2). The use of DMA as a solvent
lowered the product yield of 8a to 13% (entry 3). The reaction
temperature was further examined using toluene-d8 as a solvent
at 110 °C to give 8a in 42% yield (entry 4). The use of
dinuclear complex 2 and carbonyl (PNO)Rh complex 7 as
catalysts under these reaction conditions was also examined,
and 8a was obtained in 5% (entry 5) and 95% (entry 6) yields,
respectively.
Table 2. Reactions of Terminal Alkynes with Piperidine
Catalyzed by (PNO)Rh Complexes
a
b
entry
R
catalyst
8
yield (%)
c
1
C6H13
2
3
7
2
3
7
8b
8b
8b
8c
8c
8c
10
14
66
52
36
90
2
3
C6H13
C6H13
c
4
ferrocenyl
ferrocenyl
ferrocenyl
5
6
a
Reaction conditions unless specified otherwise: terminal alkyne
(0.2 mmol), piperidine (0.6 mmol), catalyst (0.02 mmol), toluene-d8
b
c
(0.6 mL), 110 °C, 24 h. Determined by 1H NMR analysis. Performed
using 5 mol % of the catalyst.
The reaction of ethynylferrocene gave no less than 36% yield of
the corresponding hydroamination product 8c regardless of
the choice of catalyst 2, 3, or 7 (entries 4−6), and carbonyl
complex 7 provided the highest yield (90%) of 8c (entry 6).
In all cases, only E isomers were obtained as products.
2.3. Formation of Vinylidene-Bridged Dirhodium
Complexes from Terminal Alkynes. As mentioned above,
the formation of vinylidene complexes as intermediates has
been proposed for many anti-Markovnikov additions catalyzed
by late-transition-metal complexes, but the observation of the
vinylidene complexes formed from the catalysts and the sub-
strates has not often been achieved. Therefore, the reactivity
of the (PNO)Rh complexes toward terminal alkynes was
investigated.
2.3.1. Reactivity of (PNO)Rh Complex 2 with Terminal
Alkynes: Formation of Vinylidene-Bridged Dirhodium Com-
plexes. Treatment of dinuclear (PNO)Rh complex 2 with an
excess amount of 1-octyne at 110 °C gave vinylidene-bridged
dirhodium complex 9a in 78% yield (eq 2). The structure of
Reactions of other terminal alkynes were also investigated
(Table 2). The use of complexes 2 and 3 as catalysts for the
reaction of 1-octyne with piperidine resulted in low product
yields (entries 1 and 2), but when carbonyl complex 7 was
used as a catalyst, 8b was produced in 66% yield (entry 3).
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complex 9a was confirmed by NMR spectra. In the 13C{1H}
NMR spectrum, a signal corresponding to the bridging carbon
of the vinylidene ligand appeared at 266.0 ppm (tt, J = 34.7,
16.4 Hz). Complexes possessing a μ2-vinylidene ligand have
been synthesized using various metals,16 and many researchers
have conducted studies dealing with their reactivities,17
including recent detailed studies by the groups of Cowie and
Antonova and Rubaylo.18,19 However, only a few reports of
catalytic reactions using the bridging vinylidene complexes have
appeared.20
Other terminal alkynes can be used as substrates for the syn-
thesis of the vinylidene-bridged dirhodium complexes (Table 3).
Table 3. Synthesis of Various Vinylidene-Bridged Dirhodium
a
Complexes 9
Figure 4. Molecular structure of complex 9e. Hydrogen atoms are
omitted for clarity. Selected bond lengths (Å) and angle (deg): Rh1−
Rh2 2.6395(11), C1−C2 1.368(12), Rh1−C1 1.976(10), Rh2−C1
1.934(10); Rh1−C1−Rh2 84.9(4).
entry
R
9
yield (%)
1
2
Cy
9b
9c
9d
9e
78
82
74
33
CyCH2
tBu
b
mononuclear vinylidene complexes. In 1982, Green and
co-workers reported on the synthesis of a vinylidene-bridged
dirhodium complex by the reaction of acetylene with a
rhodium complex bearing η5-indenyl and ethylene ligands,
and it was suggested to have been generated via a mono-
nuclear vinylidene complex.21 There have also been reports of
the synthesis of vinylidene-bridged heterometallic complexes
by the reaction of a mononuclear vinylidene complex with a
complex of another metal.25 Accordingly, complex 9 may also
be generated via a mononuclear vinylidene complex. The car-
bene carbon of the vinylidene ligand is generally susceptible
to nucleophilic attack, and that of the mononuclear vinylidene
(PNO)Rh complex generated by the dissociation of dinuclear
complex 2 may be attacked by the mononuclear (PNO)Rh
complex to form the vinylidene-bridged dirhodium complex
(Scheme 2).
3
c
4
ferrocenyl
a
Reaction conditions unless specified otherwise: [Rh(OMe)(cod)]2
(0.05 mmol), 1 (0.10 mmol), terminal alkyne (0.50 mmol), toluene
(1.0 mL), 110 °C, 1 h. Performed at 40 °C for 24 h. Performed with
b
c
2 equiv of ethynylferrocene.
The reactions of cyclohexylacetylene and 3-cyclohexyl-1-propyne
afforded the corresponding complexes in 78% (9b) and 82%
(9c) yields, respectively (entries 1 and 2). The reaction of tert-
butylacetylene with complex 2 was performed at 40 °C for 24 h
because the alkyne has a low boiling point (38 °C), and com-
plex 9d was obtained in 74% yield (entry 3). Ethynylferrocene
also reacted with complex 2 to give the corresponding
vinylidene complex 9e, but separation of complex 9e from
byproducts formed from ethynylferrocene was not a trivial
process. Therefore, the reaction was conducted using 2 equiv of
ethynylferrocene to give complex 9e in 33% yield in pure form
(entry 4). The structures of these complexes were also deter-
mined by various NMR spectra. A single-crystal X-ray dif-
fraction analysis of complex 9e showed that the two PNO
ligands as well as the vinylidene ligand bridge two rhodium
centers and the quinolinolate moiety and the phosphine in
PNO ligands bind to different rhodium centers (Figure 4). The
distance between two rhodium atoms of complex 9e (2.6395(11)
Å) was similar to those of the other reported vinylidene-bridged
dirhodium complexes [Rh2(η5-C9H7)2(μ-CCH2)(CO)2]
(2.691(1) Å),21 [Rh2(η5-C5Me5)(μ-CCMe2)(CO)2]
(2.684(0) Å),22 [Rh2(η5-C5H5)2{μ-η4-C4(CF3)2HtBuCO}(μ-
CCHtBu)] (2.625(2) Å),23 and [Rh2(μ-OOCMe)(μ-C
CHPh)(CO)2(PCy3)2]BF4 (2.6557(5) Å),24 all of which are
considered to possess a single bond between the rhodium
centers. The distance between the C1 and C2 of the vinylidene
ligand in complex 9e (1.368(12) Å) was longer than the values
for previously reported vinylidene-bridged dirhodium com-
plexes.21−24
Scheme 2. Possible Mechanism for Formation of Vinylidene-
Bridged Dirhodium Complex 9
2.3.3. Reversibility of the Formation of the Vinylidene-
Bridged Dirhodium Complexes. The reaction of vinylidene-
bridged dirhodium complex 9a with terminal alkynes was
performed, in an attempt to examine the reversibility of the
vinylidene formation (Table 4). The reaction of complex 9a
with 5 equiv of cyclohexylacetylene at 80 °C in benzene-d6 did
not give cyclohexylvinylidene complex 9b (entry 1). The use
of other common organic solvents was also not effective
for producing complex 9b (see Table S1 in the Supporting
Information). The reaction using trimethylamine as an additive
provided a 3% yield of complex 9b (entry 2). Additives were
then screened for the exchange reaction. While the use of
2.3.2. Possible Pathway for the Formation of the
Vinylidene-Bridged Dirhodium Complexes. Bridging vinyl-
idene complexes are usually considered to be formed from
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Table 4. Exchange Reaction of Complex 9a with
a
Cyclohexylacetylene
b
NMR yield (%)
recovered 9a
entry
additive
9b
1
2
3
4
5
6
7
8
9
10
none
Et3N
100
97
100
100
90
0
3
DABCO
0
2.4. Formation of (Amino)carbene Complexes. The
nucleophilic attack on the carbene carbon of the vinylidene
ligand is regarded as a key step in anti-Markovnikov addition
reactions. Therefore, we examined the possibility that a
carbon−nitrogen bond could be formed via the nucleophilic
attack of secondary amines to vinylidene complexes.
2.4.1. Reactions of Vinylidene-Bridged Dirhodium Com-
plexes 9 with Secondary Amines. When complex 9a was
reacted with 5 equiv of piperidine in benzene-d6 at 90 °C, a
mononuclear (PNO)Rh complex bearing an (amino)carbene
ligand (10aa) was obtained in 88% NMR yield, on the basis of
the amount of the vinylidene ligand in complex 9a (eq 5).
N-methylpiperidine
pyridine
0
9
DMAP
30
62
0
PPh3
0
TMEDA
97
0
2,2′-bipyridyl
4,4′-bipyridyl
96
0
80
15
a
Reaction conditions: 9a (0.01 mmol), cyclohexylacetylene (0.05 mmol),
additive (0.05 mmol), benzene-d6 (0.75 mL), 80 °C, 12 h. Determined
by H NMR analysis.
b
1
DABCO and N-methylpiperidine failed to provide complex 9b
(entries 3 and 4), a 9% yield of 9b was obtained when the
reaction was carried out in the presence of pyridine (entry 5).
The exchange reaction was facilitated further in the presence of
DMAP as an additive, with complex 9b being produced in 62%
yield (entry 6). In contrast, the use of triphenylphosphine as an
additive did not provide complex 9b but gave triphenylphos-
phine complex 3 and 1-octyne (entry 7). Additives possessing
two coordinating groups were also examined. While TMEDA
and 2,2′-bipyridyl were not effective as additives for the exchange
reaction (entries 8 and 9), the reaction using 4,4′-bipyridyl
provided complex 9b in 15% yield (entry 10).
Similar effects of additives were also observed for conversion
of complex 9b to complex 9a. While the reaction of complex 9b
with 5 equiv of 1-octyne in the presence of pyridine and DMAP
gave complex 9a in 11 and 68% yields, respectively (eq 3), the
use of additives such as Et3N, DABCO, and N-methylpiperidine
did not provide complex 9a from complex 9b.
Because, in theory, one molecule of 9a can produce only one
molecule of 10aa, at least 50% of the rhodium atoms in 9a
are not contained in 10aa after the reaction is complete. An
unidentified insoluble precipitate was detected in the reaction
mixture, which may be some form of (PNO)Rh complex.
The structure of complex 10aa was consistent with various
NMR spectra. The 13C{1H} NMR spectrum of complex 10aa
showed a signal corresponding to a carbene carbon spin−spin-
coupled with rhodium and a phosphorus nuclei at 260.3 ppm
(dd, J = 43.4, 13.5 Hz). The synthesis of (amino)carbene com-
plexes by reacting mononuclear vinylidene complexes of various
transition metals with amines has been achieved by many
researchers.26,27
The reaction of bridging vinylidene complex 9 with various
secondary amines also gave the corresponding (amino)carbene
complex 10 (Table 5). Using cyclic secondary amines such as
morpholine, 3,5-dimethylmorpholine, N-methylpiperazine, and
isoindoline, the (amino)carbene complexes (10ab−ae) were
obtained in 82−93% yields (entries 1−4). Other bridging
vinylidene complexes, including 9b,c,e, were also reacted with
piperidine. The reactions of 9b,c with piperidine afforded the
corresponding (amino)carbene complexes in 95 (10ba) and
89% (10ca) yields, respectively (entries 5 and 6). In the case of
ferrocenyl-substituted complex 9e, however, the reactivity was
lower than that for the other complexes 9 (48% conversion)
and complex 10ea was obtained in only 26% yield (entry 7).
In the reactions of complexes 9 with secondary amines,
insoluble precipitates were detected, and it was difficult to isolate
(amino)carbene complexes 10 in pure form. The reaction of
dirhodium complex 9 with an amine should produce equal
When complex 9a was reacted with DMAP in the absence of
an additional terminal alkyne in benzene-d6, 1-octyne and a
(PNO)Rh complex bearing a DMAP ligand were generated in
18 and 15% yields, respectively (eq 4). These results indicate
that the formation of vinylidene-bridged dirhodium complex 9
is reversible, and the vinylidene ligand can be dissociated
from the metal as a terminal alkyne or exchanged with another
alkyne molecule via an associative pathway. The reversible
vinylidene formation process may be accelerated by using
nucleophilic nitrogen additives.
E
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a
Table 5. Synthesis of Various (Amino)carbene Complexes 10
Figure 5. Molecular structure of complex 10ae. Hydrogen atoms are
omitted for clarity. Selected bond angles (Å) and dihedral angles
(deg): Rh1−C1 1.966(3), C1−N1 1.328(3); O1−Rh1−C1−N1
−71.0(29), P1−Rh1−C1−N1 114.2(2).
a
Reaction conditions: complex 9 (0.01 mmol), amine (0.05 mmol),
b
benzene-d6 or toluene-d8 (0.75 mL), 90 °C, 24 h. Determined by 1H
NMR analysis using 1,3,5-trimethoxybenezene as an internal standard.
complex 10ae was determined to be 1.966(3) Å, which
indicates a relatively strong back-donation from the electron-
rich Rh(I) center bearing the electron-donating PNO ligand.
The bond length between the carbene carbon and the nitrogen
atoms of the complex (1.328(3) Å) is comparable to that of
Bertrand’s (alkyl)(amino)carbene rhodium(I) complex, [RhCl-
{C(tBu)(NiPr2)}(cod)] (1.317(3) Å).28
2.4.2. Investigations into the Possible Pathway for the
Formation of (Amino)carbene Complexes 10. As discussed
earlier, it was indicated that the formation of bridging
vinylidene complexes 9 is reversible in the presence of nitrogen
nucleophiles, and this process is considered to proceed via
mononuclear vinylidene intermediates. Secondary amines react
with complexes 9 but are also nitrogen nucleophiles, which may
facilitate the formation of mononuclear vinylidene complexes
from complexes 9 and the alkyne exchange reaction. These
speculations prompted us to examine the reaction of complex
9a with piperidine in the presence of cyclohexylacetylene
(eq 7). As a result, (amino)carbene complexes 10aa,ba were
amounts of mononuclear (amino)carbene complex 10 and a
(PNO)Rh unit, which may be part of the insoluble precipitate.
We speculated that the reaction of complex 9 with an amine in
the presence of a terminal alkyne may convert the extra amount
of the (PNO)Rh unit to a vinylidene complex, which may
eventually be transformed into an (amino)carbene complex.
Treatment of complex 9a with isoindoline in the presence of
1-octyne did not produce a precipitate and gave the
corresponding (amino)carbene complex 10ae in 58% isolated
yield (based on the rhodium center) after recrystallization
(eq 6). The structure of 10ae was confirmed by a single-crystal
X-ray diffraction analysis, which showed that the (amino)-
carbene ligand is not oriented parallel to the square-planar
plane of the rhodium complex, and the dihedral angle between
the phosphorus−rhodium bond and the carbon−nitrogen bond
of the (amino)carbene ligand was 114.2° (Figure 5).
While several rhodium(I) complexes bearing N−Ccarbene
−
C-type (amino)carbene ligands including ylide-stabilized
carbene ligands have been prepared,28−31 only one report
includes the preparation of rhodium(I) complexes possess-
ing an (alkyl)(amino)carbene ligand.28 In the paper on the
synthesis of the first stable (alkyl)(amino)carbene, C(tBu)-
(NiPr2), by Bertrand and co-workers in 2004, they also
reported on the synthesis of (alkyl)(amino)carbene rhodium(I)
complexes using the carbene itself as a ligand source. While
all of the previously reported rhodium(I) (amino)carbene
complexes possess Rh−C bonds longer than 2 Å,28−31 the
distance between the rhodium and the carbene carbon atoms of
obtained in 44 and 52% yields, respectively, and 1-octyne
was also generated in 8% yield. The observation of 1-octyne
suggested that the reversible formation of bridging vinyli-
dene complexes 9 via mononuclear vinylidene intermediates
and the alkyne exchange reaction occur under these reaction
F
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Article
conditions, and secondary amines may facilitate the conversion
of bridging vinylidene complexes 9 to mononuclear vinylidene
complexes as well as other nitrogen nucleophiles, such as DMAP.
A proposed mechanism for the generation of (amino)-
carbene complexes 10 from vinylidene-bridged dirhodium
complexes 9 is shown in Scheme 3. Complexes 9 may be
Scheme 3. Proposed Mechanism for the Formation of
(Amino)carbene Complex 10 from Vinylidene-Bridged
Complex 9
converted to mononuclear vinylidene complexes in the
presence of a secondary amine, and the nucleophilic attack of
a secondary amine followed by proton transfer gives (amino)-
carbene complex 10.
Generation of complex 10aa by the reaction of dinuclear
(PNO)Rh complex 2 with 1-octyne and piperidine was
monitored to determine whether or not the bridging vinylidene
complex 9a is involved in the process to form (amino)carbene
complex 10aa (eq 8 and Figure 6). When complex 2 was
Figure 6. Time dependence for the transformation of complexes 2
◆
■
▲
), 9a ( ), and 10aa ( ). The upper part shows the reaction up to
(
30 min, and the lower part shows the reaction after 30 min. Reaction
conditions: complex 2 (0.01 mmol), 1-octyne (0.02 mmol), piperidine
(0.05 mmol), benzene-d6 (0.75 mL), 80 °C.
Table 6. Generation of Hydroamination Product Form
a
Complex 10aa
b
b
entry
additive
conversion (%)
yield (%)
reacted with 2 equiv of 1-octyne and 5 equiv of piperidine in
benzene-d6 at 80 °C, both complexes 9a and 10aa were
observed. The yields of 9a and 10aa gradually increased up to
30 min. After 30 min, most of the 2 was consumed, and 10aa
was formed in 60% yield along with a 27% yield of 9a. Complex
9a was then gradually converted to 10aa, and after 24 h, only a
small amount of 9a was detected, while the yield of 10aa
increased to 81%. These results indicate that the conversion
between bridging vinylidene complexes 9 and mononuclear
vinylidene complexes is reversible under these reaction con-
ditions, and complex 9 functions as an intermediate in the
generation of (amino)carbene complex 10.
2.5. Generation of Hydroamination Products 8 from
(Amino)carbene Complex 10. Finally, the generation of the
hydroamination products from (amino)carbene complex 10
was examined. A 1,2-β-H shift to generate the corresponding
alkene products from carbene complexes is a known pathway.32
A similar reaction pathway for our anti-Markovnikov hydro-
alkoxylation of terminal alkynes with alcohols using an
8-qionolinolato rhodium catalyst was proposed by Wang and
co-workers on the basis of theoretical calculations.8
c
1
none
Et3N
26
5
7
4
2
3
pyridine
4
2
4
PPh3
38
36
47
84
100
100
4
33
34
40
77
91
95
3
5
P(4-MeC6H4)3
P(4-MeOC6H4)3
P(4-FC6H4)3
P(4-CF3C6H4)3
P[3,5-(CF3)2C6H4]3
OPPh3
6
7
8
9
10
11
P(OPh)3
100
100
69
51
d
12
CO
a
Reaction conditions unless specified otherwise: 10aa (ca. 0.01 mmol;
generated by the reaction of 9a with 5 equiv of piperidine), additive
b
(0.05 mmol), benzene-d6 (0.75 mL), 80 °C, 24 h. Determined by
1H NMR analysis using 1,3,5-trimethoxybenezene as an internal
c
d
standard. Performed at 110 °C in toluene-d8 (0.75 mL). Peformed at
room temperature for 5 min.
When complex 10aa was generated in situ by the reaction of 9a
with 5 equiv of piperidine in toluene-d8 and heated at 110 °C
for 24 h, only a 7% yield of hydroamination product 8b was
The generation of the hydroamination product 8b was examined
using in situ generated (amino)carbene complex 10aa (Table 6).
G
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Article
obtained (entry 1). Using Et3N and pyridine as an additive
at 80 °C in benzene-d6, 8b was obtained in less than 4% yield
(entries 2 and 3). Treatment of complex 10aa with tri-
phenylphosphine gave a 33% yield of 8b, and triphenylphos-
phine complex 3 was detected in 1H and 31P{1H} NMR spectra
(entry 4). The use of a phosphine ligand to dissociate an
(amino)carbene ligand has been reported by Michelin and
co-workers, and in their study, a bis(amino)carbene Pt(II)
complex was reacted with a bidentate phophine at room tem-
perature to give a formamidine and a Pt(II) complex bearing
the bidentate phosphine ligand.33 The results for the reaction of
complex 10aa with triarylphosphines containing electron-
donating substituents on the phenyl groups were similar to
that with triphenylphosphine (entries 5 and 6). In contrast, the
use of phosphines containing electron-withdrawing groups
accelerated the reaction (entries 7−9), and 8b was produced in
yields in excess of 90% in the reactions with P(4-CF3C6H4)3
and P[3,5-(CF3)2C6H4]3 (entries 8 and 9). While triphenyl-
phosphine oxide was less effective than triarylphosphines as an
additive (entry 10), the reaction in the presence of triphenyl
phosphite reached completion and 8b was obtained in 69%
yield (entry 11). As the (PNO)Rh carbonyl complex 7 showed
a high catalytic activity in anti-Markovnikov hydroaminations,
the reaction was also carried out under an atmosphere of
carbon monoxide (entry 12). In this case, the color of the
reaction mixture changed immediately at room temperature,
and complex 10aa disappeared, with 8b being generated in 51%
yield. In the reactions described in Table 6, (PNO)Rh
complexes bearing an additive as the fourth ligand on the rho-
amine, the mononuclear vinylidene complex B reacts with
another (PNO)Rh complex to form vinylidene-bridged dirho-
dium complex 9. The interactions among complexes A, B, and 9
are reversible and alkyne exchange reactions can also proceed for
the terminal alkyne complex A. Coordination of a nucleophile
to one of the rhodium centers appears to be important for the
conversion of complex 9 to complex B, which reacts with
the secondary amine to form (amino)carbene complex 10.
The formation of the hydroamination products 8 occurs from
complex 10, and this process is facilitated by additives such as
triarylphosphines and CO.
2.7. Proposed Mechanism for the Anti-Markovnikov
Hydroamination by (PNO)Rh Complexes. To examine the
relevance of complexes 9 and 10 to the catalytic hydroamin-
ation, the reaction of ethynylferrocene with piperidine cata-
lyzed by complex 2 was monitored by NMR spectroscopy (eq 9
and Figure 8). When 5 mol % of complex 2, ethynylferrocene,
1
dium center were detected in H and 31P{1H} NMR spectra,
when the hydroamination product 8b was obtained in high
yield. In contrast, other products generated in this reaction
1
appeared to be complicated small signals in the H NMR
spectrum. As a result, it was not possible to determine them at
this point.
2.6. Summary of the Reactivity of (PNO)Rh Complex 2
toward Terminal Alkynes and Secondary Amines. The
reactivity of (PNO)Rh complex 2 with terminal alkynes and
secondary amines is summarized in Figure 7. A terminal alkyne
first coordinates to complex 2 and is transformed into a
vinylidene ligand. If there is an insufficient amount of the
Figure 8. Results of the monitoring of catalytic reaction of
◆
ethynylferrocene with piperidine catalyzed by complex 2: (
complex 2; ( ) 8c; ( ) complex 10ea.
)
●
▲
and piperidine were mixed in toluene-d8 at room temperature,
complex 2 was rapidly consumed and 27% of complex 10ea and
unidentified rhodium complexes were formed. After the
reaction mixture was heated to 110 °C, more than 80% of 2
was converted into 10ea within 1 h, and the corresponding
hydroamination product 8c was generated in 3% yield. While
the amount of 10ea remained essentially unchanged for 24 h, the
rate of formation of 8c appears to be independent of the
substrate concentrations, and after 24 h, 8c was generated in 62%
yield.
The reaction of ethynylferrocene with piperidine catalyzed
by carbonyl complex 7 was also monitored by 1H NMR
spectroscopy (eq 10 and Figure 9). The hydroamination
reaction with complex 7 was faster than that with complex 2.
The yield of the hydroamination product 8c reached 70% in
2 h, but after this period, the reaction slowed down. (Amino)-
carbene complex 10ea was observed during this reaction, and 29%
Figure 7. Summary of the reaction for (PNO)Rh complex 2 toward
terminal alkyne and secondary amine.
H
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Figure 10. Proposed catalytic cycle for the anti-Markovnikov
hydroamination of terminal alkynes catalyzed by (PNO)Rh complexes.
alkynes to form enamines, and the intermediacy of both
vinylidene and (amino)carbene complexes is strongly suggested
for this hydroamination. We first synthesized various rhodium-
(I) complexes bearing a phosphine-quinolinolate ligand. Some
of these complexes showed catalytic activities in the anti-
Markovnikov hydroamination of terminal alkynes with secondary
amines. Stoichiometric reactions of a (PNO)Rh complex with
terminal alkynes provided vinylidene-bridged dirhodium
complexes. The reaction of the vinylidene complexes with
secondary amines gave (amino)carbene complexes. Finally, the
(amino)carbene complexes generated the hydroamination
products via a 1,2-β-H shift, when heated in the presence of
an additive such as a phosphine or CO. These experimental
results essentially show that the hydroamination catalyzed by
(PNO)Rh complexes proceeds via vinylidene and (amino)-
carbene intermediates. This is the first structural determination
of both of the two important intermediates, namely vinylidene
and (amino)carbene complexes in catalytic hydroamination
reactions. Further improvement in the hydroamination reaction
and additional developments on the basis of this mechanistic
information are currently in progress.
Figure 9. Result of the monitoring of catalytic reaction of
●
ethynylferrocene with piperidine catalyzed by complex 7: ( ) 8c;
▲
(
) complex 10ea.
of the rhodium complexes was observed as complex 10ea, the
amount of which then gradually decreased and eventually
disappeared after 24 h. Complex 7 was present throughout the
reaction, as observed by 31P{1H} NMR spectroscopy, but
estimating the amount of 7 was difficult because of its low
solubility in toluene-d8. A catalytic amount of carbon monoxide
might accelerate the generation of 8c from (amino)carbene
complex 10ea in the hydroamination reaction using carbonyl
complex 7. These monitoring results for the hydroamination
reaction strongly indicate that the (amino)carbene complex 10
is one of the important intermediates in this reaction.
Figure 10 shows a proposed catalytic cycle for the anti-
Markovnikov hydroamination of terminal alkynes catalyzed by
(PNO)Rh complexes on the basis of the experimental results
presented herein. First, the reaction of the (PNO)Rh complex
with the terminal alkyne generates the alkyne complex A, which
is then transformed into the mononuclear vinylidene rhodium
complex B. Complex B then reacts with another (PNO)Rh
species to form vinylidene-bridged dirhodium complex 9, which
is a resting state but can also react with the secondary amine to
form (amino)carbene complex 10. At high temperatures, the
interactions among complexes A, B, and 9 are reversible, and in
the presence of a secondary amine, complex 9 is converted back
to complex B, which can then be converted into complex 10.
Finally, the hydroamination product 8 was formed by reaction
with a ligand such as a triarylphosphine, thus regenerating the
catalytically active (PNO)Rh complex. The results of the
monitoring of the catalytic reaction suggest that the formation
of hydroamination product 8 from (amino)carbene complex 10
is turnover-limiting in the catalytic hydroamination.
4. EXPERIMENTAL SECTION
1
4.1. General Information. H, 13C{1H}, 19F{1H}, and 31P{1H}
NMR spectra were recorded on a JEOL ECX-400, AL-400, or
1
ALPHA-400 spectrometer. Chemical shifts in H and 13C{1H} NMR
spectra are reported in ppm relative to residual solvent peaks such as
1
chloroform (δ 7.26 for H and δ 77.00 for 13C), benzene (δ 7.16 for
1H and δ 128.00 for 13C), toluene (δ 2.08 for 1H NMR), or the
internal reference tetramethylsilane (δ 0.00 for both 1H and 13C).
Chemical shifts in 19F{1H} and 31P{1H} NMR spectra are reported in
ppm relative to an external reference, CFCl3 and 85% H3PO4 (δ 0.00
for both 19F and 31P), respectively. Melting points were determined on
a Stanford Research Systems MPA100 instrument. IR spectra were
recorded on a JASCO FT/IR-410 infrared spectrometer. GCMS
analysis was performed using a Shimadzu GCMS QP-5000 instrument
equipped with a CBP-10 capillary column (25 m × 0.22 mm, film
thickness 0.25 μm). The temperature for GCMS analysis was
programmed from 70 to 250 °C at a 10 °C/min ramp with a final
hold time of 40 or 60 min (injection temperature, 250 °C; detector
temperature, 250 °C). ESI-MS and APCI-MS analyses were performed
on a JEOL JMS-T100LCS. Flash chromatography was carried out with
3. CONCLUSIONS
In conclusion, rhodium(I) complexes bearing a phosphine-
quinolinolate ligand prepared here showed catalytic activity for
the anti-Markovnikov addition of secondary amines to terminal
I
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Kanto silica gel 60N (40−50 μm), Merck aluminum oxide 90 active
neutral, or Merck aluminum oxide 90 standardized. In addition to
NMR analyses, elemental analyses were performed to establish the
purity of the new compounds, except for complexes 3−5 and
compound 8c, which were not stable enough to obtain elemental
analysis using our facility.
1095 m, 1029 w, 998 w, 915 w, 839 w, 742 m, 695 s, 618 w, 543 m,
523 m, 513 m cm−1; HRMS (ESI-TOF) m/z [M + Na]+ calcd for
C40H32NNaOP2Rh 730.0911, found 730.0903. Red single crystals
suitable for X-ray diffraction analysis were obtained by recrystallization
from benzene.
4.4.2. Complex 4. The reaction was performed for 1 h to give
1
4.2. Solvents and Materials. Unless otherwise noted, all
manipulations involving air- and/or moisture-sensitive compounds
were carried out using the standard Schlenk technique under nitrogen
and all commercial reagents were used without further purification.
Benzene was distilled from Na/benzophenone ketyl. Dry toluene,
hexane, and CH2Cl2 were purchased from Kanto Chemical Co., Inc.,
and passed through solvent purification columns (Glass Counter
Solvent purification system). Dry Et2O, THF, and DMF were
purchased from Kanto Chemical Co., Inc., and used without further
purification. [Rh(OMe)(cod)]2 was prepared according to the
literature procedure.34 Phenylacetylene was distilled from CaSO4.
1-Octyne was distilled from NaBH4. Ethynylferrocene was purified by
sublimation. Other terminal alkynes were purified by bulb-to-bulb
distillation. Triethylamine and piperidine were distilled from CaH2.
N-Methylpiperidine, morpholine, 3,5-dimethylmorpholine, and N-meth-
ylpiperazine were distilled from NaOH. Pyridine was distilled from Na.
4.3. Synthesis of Dinuclear (PNO)Rh Complex 2 (Eq 1). In a
glovebox, 96.8 mg of [Rh(OMe)(cod)]2 (0.20 mmol) was placed in an
oven-dried 50 mL Schlenk tube containing a magnetic stirring bar, and
137.3 mg of PNO ligand precursor 1 (0.40 mmol) and 1.5 mL of
benzene were placed in the tube. The mixture was stirred at room
temperature for 5 min and cooled to 0 °C. Hexane was added to the
mixture to form a precipitate, which was then collected by filtration in
air, washed with cold hexane, and dried in vacuo to afford 122 mg
(61% yield) of dinuclear (PNO)Rh complex 2 as an orange solid: mp
complex 4 in 89% yield as an orange solid: mp 135−140 °C dec; H
2
NMR (C6D6, 391.8 MHz) δ 3.18 (s, 9 H, OCH3), 3.54 (d, JH−P
=
9.8 Hz, 2 H, PCH2), 6.53−6.60 (m, 7 H, ArH), 6.84 (dd, J = 7.4, 1.2
Hz, 1 H, ArH), 6.90−7.00 (m, 6 H, ArH), 7.46−7.64 (m, 7 H, ArH),
7.94−7.99 (m, 6 H, ArH); 31P{1H} NMR (C6D6, 158.6 MHz) δ 54.6
(dd, 1JP−Rh = 187.6 Hz, 2JP−P = 45.5 Hz), 38.4 (dd, 1JP−Rh = 169.5 Hz,
2JP−P = 45.5 Hz); IR (KBr) 3402 w, 3052 w, 2952 w, 2834 w, 2541 w,
2047 w, 1898 w, 1669 w, 1636 w, 1594 s, 1556 s, 1499 s, 1437 s,
1396 w, 1375 w, 1338 w, 1310 m, 1287 s, 1252 s, 1181 s, 1097 s, 1027
m, 915 w, 836 m, 799 m, 746 m, 717 w, 696 m, 668 w, 648 w, 617 w,
535 m, 503 m cm−1; HRMS (ESI-TOF) m/z [M + Na]+ calcd for
C43H38NNaO4P2Rh 820.1229, found 820.1213.
4.4.3. Complex 5. The reaction was performed for 2 h to give
1
complex 5 in 25% yield as an orange solid: mp 127−133 °C dec; H
2
NMR (C6D6, 391.8 MHz) δ 3.47 (d, JH−P = 10.2 Hz, 2 H, PCH2),
6.49 (d, J = 9.0 Hz, 1 H, ArH), 6.82−6.87 (m, 5 H, ArH), 6.92−6.96
(m, 2 H, ArH), 7.15 (overlapped with the signal of residual benzene, 6
H, ArH), 7.36−7.41 (m, 4 H, ArH), 7.46−7.47 (m, 2 H, ArH), 7.54 (d,
J = 8.6 Hz, 1 H, ArH), 7.76 (t, J = 8.6 Hz, 6 H, ArH); 19F{1H} NMR
(C6D6, 368.6 MHz) δ −62.6 (s); 31P{1H} NMR (C6D6, 158.6 MHz) δ
1
2
1
54.6 (dd, JP−Rh = 179.0 Hz, JP−P = 44.6 Hz), 45.6 (dd, JP−Rh
=
2
175.9 Hz, JP−P = 44.6 Hz); IR (KBr) 3053 w, 1924 w, 1607 w,
1557 m, 1501 w, 1479 w, 1440 m, 1398 m, 1376 w, 1324 s, 1284 w,
1167 s, 1124 s, 1110 m, 1061 s, 1017 m, 957 w, 917 w, 837 m, 780 w,
747 m, 701 m, 679 w, 634 w, 617 w, 600 w, 573 w, 549 m, 524 m,
502 w cm−1; HRMS (APCI-TOF) m/z [M + H]+ calcd for
C43H30F9NO4P2Rh 912.0714, found 912.0728.
148−154 °C dec; 1H NMR (C6D6, 391.8 MHz) δ 1.47 (br s, 4 H, CH2
2
of cod ligand), 2.04 (br s, 4 H, CH2 of cod ligand), 3.45 (d, JH−P
=
2
10.2 Hz, 2 H, PCH2 of PNO ligand), 3.90 (d, JH−P = 11.4 Hz, 2 H,
PCH2 of PNO ligand), 4.08 (br s, 2 H, CH of cod ligand), 4.81 (br s,
2 H, CH of cod ligand), 6.51 (d, J = 8.6 Hz, 1 H, ArH), 6.59 (dd, J =
7.1, 1.6 Hz, 1 H, ArH), 6.68 (td, J = 7.8, 1.6 Hz, 4 H, ArH), 6.85−6.91
(m, 9 H, ArH), 7.09−7.14 (m, 4 H, ArH), 7.24−7.31 (m, 2 H, ArH),
7.37 (d, J = 8.6 Hz, 1 H, ArH), 7.52−7.61 (m, 7 H, ArH), 9.33 (d, J =
8.6 Hz, 1 H, ArH); 31P{1H} NMR (C6D6, 158.6 MHz) δ 54.3
(dd, 1JP−Rh = 184.3 Hz, 2JP−P = 44.6 Hz), 46.1 (dd, 1JP−Rh = 175.9 Hz,
2JP−P = 44.6 Hz); IR (KBr) 3433 w, 3052 w, 2926 w, 2878 w, 2831 w,
1945 w, 1805 w, 1593 w, 1555 s, 1503 m, 1436 s, 1395 m, 1374 m,
1326 m, 1312 m, 1281 m, 1209 w, 1178 w, 1154 w, 1118 m, 1096 m,
1028 w, 996 w, 944 w, 909 w, 840 m, 740 s, 694 s, 650 w, 618 w,
586 w, 539 m, 507 m cm−1. Red single crystals suitable for X-ray
diffraction analysis were obtained by recrystallization from toluene/
hexane. The crystals were also used for elemental analysis. Anal. Calcd
for C59H54N2O2P2Rh2 (2·toluene): C, 64.96; H, 4.99; N, 2.57. Found:
C, 64.67; H, 5.03; N, 2.43.
4.5. Synthesis of (PNO)Rh Pyridine Complex 6 (Scheme 1). In
a glovebox, 48.4 mg of [Rh(OMe)(cod)]2 (0.10 mmol) was placed in
an oven-dried 50 mL Schlenk tube containing a magnetic stirring bar,
and 68.7 mg of PNO ligand precursor 1 (0.20 mmol) and 1.0 mL of
benzene were placed in the tube. The mixture was stirred at room
temperature for 5 min, and 1.61 mL of pyridine (158.2 mg, 2.00
mmol) was added. The reaction mixture was heated in an oil bath at
60 °C for 4 h and cooled to 0 °C. Hexane was added to the mixture to
form a precipitate, which was then collected by filtration, washed three
times with hexane at 0 °C, and dried in vacuo to afford 103.1 mg (98%
yield) of pyridine complex 6 as a brown solid: mp 141−147 °C dec;
1H NMR (C6D6, 391.8 MHz) δ 3.38 (d, 2JH−P = 10.2 Hz, 2 H, PCH2),
6.17 (m, 2 H, ArH), 6.48 (d, J = 8.6 Hz, 1 H, ArH), 6.56 (tt, J = 7.4,
1.6 Hz, 1 H, ArH), 6.86 (dd, J = 7.8, 1.2 Hz, 1 H, ArH), 7.08−7.10 (m,
6 H, ArH), 7.54−7.58 (m, 2 H, ArH), 7.65 (dd, J = 7.8, 1.2 Hz, 1 H,
ArH), 7.84−7.89 (m, 4 H, ArH), 9.11−9.12 (m, 2 H, ArH); 31P{1H}
1
NMR (C6D6, 158.6 MHz) δ 50.5 (d, JP−Rh = 214.1 Hz); IR (KBr)
4.4. Synthesis of (PNO)Rh Triarylphosphine Complexes 3−5
(Scheme 1). In a glovebox, 48.4 mg of [Rh(OMe)(cod)]2
(0.10 mmol) was placed in an oven-dried 50 mL Schlenk tube
containing a magnetic stirring bar, and 68.7 mg of PNO ligand
precursor 1 (0.20 mmol) and 1.0 mL of benzene were placed in the
tube. The mixture was stirred at room temperature for 5 min, and PAr3
(0.20 mmol) was added. The reaction mixture was heated in an oil
bath at 60 °C for 1−2 h and cooled to 0 °C. Hexane was added to the
mixture to form a precipitate, which was then collected by filtration in
air, washed with cold hexane, and dried in vacuo to afford
triarylphosphine complexes 3−5.
3410 m, 3049 m, 2955 w, 2926 w, 1968 w, 1907 w, 1605 m, 1554 s,
1500 m, 1482 m, 1436 s, 1389 m, 1375 m, 1335 m, 1315 m, 1286 s,
1215 w, 1184 w, 1154 w, 1108 s, 1070 m, 1048 w, 1026 w, 998 w,
948 w, 918 w, 841 m, 831 m, 751 s, 695 s, 650 w, 616 w, 597 w, 560 w,
536 s, 504 w cm−1. In order to improve the stability of the complex,
the brown solid was further recrystallized from benzene/hexane to
form black crystals, which were used for elemental analysis. Anal.
Calcd for C28H73/3N2O1P1Rh1 (6·1/6(hexane)): C, 62.43; H, 4.55; N,
5.20. Found: C, 62.46; H, 4.57; N, 4.99.
4.6. Synthesis of (PNO)Rh Carbonyl Complex 7 (Scheme 1).
In a glovebox, 48.4 mg of [Rh(OMe)(cod)]2 (0.10 mmol) was placed
in an oven-dried 50 mL Schlenk tube containing a magnetic stirring
bar, and 68.7 mg of PNO ligand precursor 1 (0.20 mmol) and 1.0 mL
of benzene were placed in the tube. The mixture was stirred at room
temperature for 5 min. A balloon filled with CO gas was attached to
the flask, which was then briefly evacuated and back-filled with CO gas
three times. The reaction mixture immediately turned dark green and
was stirred at room temperature for 1 h. Hexane was added to the
mixture to form a precipitate, which was then collected by filtration,
washed three times with hexane, and dried in vacuo to afford 86.4 mg
4.4.1. Complex 3. The reaction was performed for 1 h to give
1
complex 3 in 58% yield as an orange solid: mp 162−166 °C dec; H
2
NMR (C6D6, 391.8 MHz) δ 3.51 (d, JH−P = 10.2 Hz, 2 H, PCH2),
6.52 (d, J = 8.6 Hz, 1 H, ArH), 6.81−6.98 (m, 17 H, ArH), 7.43−7.45
(m, 1 H, ArH), 7.48−7.56 (m, 5 H, ArH), 7.93−7.99 (m, 6 H, ArH);
1
31P{1H} NMR (C6D6, 158.6 MHz) δ 54.3 (dd, JP−Rh = 184.4 Hz,
1
2
2JP−P = 45.5 Hz), 43.3 (dd, JP−Rh = 171.6 Hz, JP−P = 45.5 Hz); IR
(KBr) 3051 w, 1699 w, 1654 w, 1588 w, 1557 s, 1500 w, 1481 w,
1435 s, 1395 w, 1375 w, 1338 w, 1312 w, 1289 w, 1182 w, 1108 w,
J
DOI: 10.1021/acs.organomet.6b00853
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Organometallics
Article
(92% yield) of carbonyl complex 7 as a brown solid: mp 206−209 °C
and then Et2O or CH2Cl2) to afford vinylidene-bridged dirhodium
complex 9.
4.9.1. Complex 9a. Following the general synthetic procedure
1
2
dec; H NMR (CDCl3, 391.8 MHz) δ 4.45 (d, JH−P = 11.0 Hz, 2 H,
PCH2), 6.94 (d, J = 8.2 Hz, 1 H, ArH), 7.16 (d, J = 8.2 Hz, 1 H, ArH),
7.31 (d, J = 8.6 Hz, 1 H, ArH), 7.42−7.46 (m, 7 H, ArH), 7.79 (ddd,
J = 12.1, 7.8, 2.0 Hz, 4 H, ArH), 8.09 (d, J = 8.2 Hz, 1 H, ArH);
31P{1H} NMR (CDCl3, 158.6 MHz) δ 56.9 (d, 1JP−Rh = 163.2 Hz); IR
described above, complex 9a was obtained in 78% yield as a brown
1
solid: mp 206−210 °C dec; H NMR (C6D6, 391.8 MHz) δ 0.89 (t,
3JH−H = 6.7 Hz, 3 H, CH3), 1.27−1.36 (m, 6 H, CH2), 1.53−1.71 (m, 2
H, CH2), 2.75−2.84 (m, 1 H, CH2), 2.89−2.96 (m, 2 H, PCH2),
(KBr) 3045 w, 3008 w, 2982 w, 2944 w, 2899 w, 1945 s (CO), 1557 s,
1501 s, 1479 m, 1440 s, 1392 s, 1379 m, 1338 m, 1315 s, 1281 s,
1180 w, 1158 w, 1127 m, 1108 s, 1069 w, 1027 w, 996 w, 948 w,
919 w, 844 s, 818 m, 784 w, 744 s, 719 s, 695 s, 618 m, 589 s, 560 m,
537 m, 516 s, 450 m cm−1. The carbonyl complex 7 was also
synthesized by reaction of PNO ligand precursor 1 with in situ
generated [RhCl2(CO)2]−, following Buzina’s method.11 A 273 mg
portion of RhCl3·nH2O (38.5 wt % Rh, 1.02 mmol) and 8.0 mL of
DMF were reacted in a three-neck round-bottom flask equipped with a
reflux condenser at 170 °C for 30 min and cooled in an ice bath to give
a yellow solution. A solution of 425 mg of PNO ligand precursor 1
(1.24 mmol) in 2.0 mL of DMF was transferred to the resulting
mixture via a cannula, and the obtained mixture was stirred at room
temperature for 1 h. The resulting suspension was poured into water.
The precipitate was collected by filtration in air and washed with
water. The resulting solid was dissolved in CH2Cl2, dried over Na2SO4,
filtered through a Celite pad, and concentrated in vacuo. Purification
of the crude solid by reprecipitation from CH2Cl2/hexane afforded
407 mg (84% yield) of carbonyl complex 7 as a dark green solid.
Orange single crystals suitable for X-ray diffraction analysis were
obtained by recrystallization from CH2Cl2/hexane. The crystals were
also used for elemental analysis. Anal. Calcd for C23H17NO2PRh: C,
58.37; H, 3.62; N, 2.96. Found: C, 58.23; H, 3.64; N, 2.88.
3
3.02−3.12 (m, 1 H, CH2), 5.01 (t, JH−H = 7.1 Hz, 1 H, C =
CH(C6H13)), 5.35 (t, J = 12.1 Hz, 1 H, PCH2), 5.54 (t, J = 11.8 Hz, 1
H, PCH2), 6.01−6.07 (m, 2 H, ArH), 6.55 (d, J = 7.1 Hz, 2 H, ArH),
6.74−6.78 (m, 3 H, ArH), 6.82−6.88 (m, 3 H, ArH), 6.90−6.95 (m, 2
H, ArH), 7.01−7.14 (m, 5 H, ArH), 7.18−7.23 (m, 5 H, ArH), 8.02−
8.11 (m, 8 H, ArH); 13C{1H} NMR (C6D6, 98.5 MHz) δ 266.0 (tt, J =
34.7, 16.4 Hz, C = CH(C6H13)); 31P{1H} NMR (C6D6, 158.6 MHz) δ
1
1
40.8 (d, JP−Rh = 184.2 Hz), 43.1 (d, JP−Rh = 184.4 Hz); IR (KBr)
3428 w, 3052 w, 2920 m, 2849 w, 1597 w, 1558 s, 1501 m, 1483 w,
1442 s, 1407 m, 1372 m, 1318 s, 1282 s, 1174 w, 1130 m, 1101 s,
1027 w, 999 w, 847 m, 825 m, 798 w, 741 s, 691 s, 665 w, 618 m,
509 s cm−1. In order to improve the stability of the complex, the
brown solid was further recrystallized from toluene/hexane to form
black crystals, which were used for elemental analysis. Anal. Calcd for
C55.5H52N2O2P2Rh2 (9a·1/2(toluene)): C, 63.68; H, 5.01; N, 2.68.
Found: C, 63.83; H, 5.01; N, 2.72.
4.9.2. Complex 9b. Following the general synthetic procedure
described above, complex 9b was obtained in 78% yield as a brown
solid: mp 223−227 °C dec; 1H NMR (C6D6, 391.8 MHz) δ 1.03−1.36
3
(m, 4 H, CH2), 1.42−1.51 (m, 1 H, CH2), 1.61 (d, JH−H = 10.2 Hz,
3
3
2 H, CH2), 1.73 (d, JH−H = 11.4 Hz, 1 H, CH2), 1.95 (d, JH−H
=
3
12.5 Hz, 1 H, CH2), 2.35 (d, JH−H = 12.5 Hz, 1 H, CH2), 2.91−3.04
(m, 3 H, PCH2 and CH), 4.81 (d, 3JH−H = 8.2 Hz, 1 H, C = CH(Cy)),
5.36 (t, J = 10.6 Hz, 1 H, PCH2), 5.72 (t, J = 11.4 Hz, 1 H, PCH2),
6.01−6.06 (m, 2 H, ArH), 6.54 (t, J = 7.4 Hz, 2 H, ArH), 6.72−6.78
(m, 3 H, ArH), 6.82−6.91 (m, 4 H, ArH), 6.95 (d, J = 7.4 Hz, 1 H,
ArH), 7.01−7.28 (overlapped with the signal of residual benzene, 10
H, ArH), 8.03−8.20 (m, 8 H, ArH); 13C{1H} NMR (C6D6, 98.5 MHz)
δ 265.0 (tt, J = 34.4, 16.5 Hz, CCH(Cy)); 31P{1H} NMR (C6D6,
158.6 MHz) δ 43.0 (d, 1JP−Rh = 184.4 Hz), 40.5 (d, 1JP−Rh = 185.4 Hz);
IR (KBr) 3432 w, 3053 w, 2916 m, 2846 w, 1596 w, 1559 s, 1502 m,
1483 w, 1442 s, 1434 s, 1410 w, 1373 m, 1326, m, 1318 m, 1283 m,
1246 w, 1186 w, 1129 w, 1102 m, 1028 w, 999 w, 962 w, 890 w,
848 m, 826 m, 799 w, 741 m, 692 m, 621 w, 505 m cm−1. In order to
improve the stability of the complex, the brown solid was further
recrystallized from toluene/hexane to form black crystals, which were
used for elemental analysis. Anal. Calcd for C52H46N2O2P2Rh2: C,
62.54; H, 4.64; N, 2.81. Found: C, 62.76; H, 4.67; N, 2.97.
4.7. General Procedure for Anti-Markovnikov Hydroamina-
tion of Terminal Alkynes with Piperidine Catalyzed by (PNO)
Rh Complexes (Tables 1 and 2). In a glovebox, 10 mol % of the
(PNO)Rh complex and 1,3,5-trimethoxybenzene (internal standard)
were placed in an NMR tube, and 0.6 mL of benzene-d6 or toluene-d8,
59.3 μL of piperidine (51.1 mg, 0.60 mmol), and the terminal alkyne
(0.20 mmol) were placed in the tube. The reaction mixture was heated
in an oil bath for 24 h. The NMR tube was cooled to room
temperature, and the NMR yield of hydroamination product 8 was
1
determined by H NMR analysis.
4.8. Synthesis of (E)-1-(2-Ferrocenylethenyl)piperidine 8c. In
a glovebox, 10 mol % of (PNO)Rh complex 7 was placed in an oven-
dried 20 mL Schlenk tube containing a magnetic stirring bar, and
0.6 mL of toluene, 59.3 μL of piperidine (51.1 mg, 0.60 mmol), and
42.0 mg of ethynylferrocene (0.20 mmol) were placed in the tube.
The reaction mixture was stirred in an oil bath at 110 °C. After 24 h,
the resulting mixture was diluted with 10 mL of CH2Cl2 to stop the
reaction, and then the volatile materials were removed in vacuo.
Purification by bulb-to-bulb distillation afforded 27.9 mg of 8c (47%
isolated yield) as an orange solid: bp 226 °C (1.1 × 102 Pa); 1H NMR
(C6D6, 391.8 MHz) δ 1.20−1.26 (m, 2 H, NCH2CH2CH2), 1.31−1.36
(m, 4 H, NCH2CH2), 2.63−2.65 (m, 4 H, NCH2), 4.08−4.09 (m, 7 H,
FeCp), 4.24 (t, 3JH−H = 2.0 Hz, 2 H, FeCp), 5.10 (d, 3JH−H = 14.1 Hz,
1 H, FeCpCH), 6.28 (d, 3JH−H = 14.1 Hz, 1 H, NCH); 13C{1H} NMR
(C6D6, 98.5 MHz) δ 24.5, 25.5, 49.8, 65.0, 67.5, 69.4, 88.1, 96.6, 139.0;
IR (KBr) 3428 w, 3087 w, 3075 w, 3057 w, 2939 s, 2849 m, 2816 m,
1720 w, 1643 s, 1454 m, 1440 m, 1408 m, 1387 s, 1365 m, 1343 m,
1314 w, 1296 w, 1276 m, 1243 s, 1195 m, 1180 m, 1161 w, 1118 s,
1103 m, 1069 w, 1044 m, 1023 m, 1003 s, 964 w, 930 s, 861 m,
811 m, 786 m, 731 w, 636 w, 586 w, 508 m cm−1; HRMS (ESI-TOF)
m/z [M + H]+ calcd for C17H22FeN 296.1102, found 296.1096.
4.9. Synthesis of Vinylidene-Bridged Dirhodium Complex 9
(Eq 2 and Table 3). In a glovebox, 24.2 mg of [Rh(OMe)(cod)]2
(0.05 mmol) was placed in an oven-dried 50 mL Schlenk tube
containing a magnetic stirring bar, and 1.0 mL of toluene and 34.3 mg
of PNO ligand precursor 1 (0.10 mmol) were placed in the tube. The
mixture was stirred for 5 min, and the terminal alkyne (0.50 mmol)
was added. The resulting mixture was heated in an oil bath at 110 °C
for 1 h. After the volatile materials were removed in vacuo, the crude
material was purified by Al2O3 gel column chromatography (hexane
4.9.3. Complex 9c. Following the general synthetic procedure
described above, complex 9c was obtained in 82% yield as a brown
solid: mp 243−244 °C dec; 1H NMR (C6D6, 391.8 MHz) δ 0.87−1.01
(m, 2 H, CH2), 1.14−1.38 (m, 3 H, CH2), 1.45−1.55 (m, 1 H, CH),
1.70−1.71 (m, 2 H, CH2), 1.81−1.85 (m, 3 H, CH2), 2.71−2.78 (m, 1
3
H, CyCH2), 2.90−2.98 (m, 3 H, CyCH2 and PCH2), 5.00 (t, JH−H
=
7.4, 1 H, CCH(CH2Cy)), 5.28 (dd, J = 10.6, 12.5 Hz, 1 H, PCH2),
5.45 (t, J = 11.8, 1 H, PCH2), 6.03 (t, J = 8.2 Hz, 2 H, ArH), 6.54−6.57
(m, 2 H, ArH), 6.73−6.96 (m, 8 H, ArH), 7.06−7.13 (m, 4 H, ArH),
7.18−7.26 (m, 6 H, ArH), 8.01−8.15 (m, 8 H, ArH); 13C{1H} NMR
(C6D6, 98.5 MHz) δ 266.1 (tt, J = 34.1, 17.2 Hz, CCH(CH2Cy));
31P{1H} NMR (C6D6, 158.6 MHz) δ 43.4 (dd, 1JP−Rh = 184.4, 2JP−Rh
=
3.3 Hz), 40.6 (dd, 1JP−Rh = 184.4, 2JP−Rh = 3.3 Hz); IR (KBr) 3390 w,
3052 m, 2917 s, 2846 m, 1949 w, 1898 w, 1807 w, 1596 m, 1557 s,
1501 s, 1434 s, 1372 s, 1318 s, 1280 s, 1213 w, 1177 w, 1125 s, 1101 s,
1027 w, 999 w, 967 w, 938 w, 890 w, 848 s, 825 s, 798 m, 742 s, 693 s,
619 s, 585 w, 507 s cm−1. In order to improve the stability of the
complex, the brown solid was further recrystallized from toluene/
hexane to form black crystals, which were used for elemental analysis.
Anal. Calcd for C166/3H152/3N2O2P2Rh2 (9c·1/3(toluene)): C, 63.69;
H, 4.89; N, 2.68. Found: C, 63.45; H, 4.90; N, 2.68.
4.9.4. Complex 9d. The reaction was performed at 40 °C for 24 h,
and complex 9d was obtained in 74% yield as a brown solid: mp 235−
240 °C dec; 1H NMR (C6D6, 391.8 MHz) δ 1.44 (s, 9 H, CCH3), 2.98
(td, J = 13.7, 3.5 Hz, 1 H, PCH2), 3.12 (td, J = 13.7, 3.5 Hz, 1 H,
K
DOI: 10.1021/acs.organomet.6b00853
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Organometallics
Article
1
PCH2), 4.99 (s, 1 H, CCH(tBu)), 5.40 (dd, J = 9.8, 12.9 Hz, 1 H,
PCH2), 5.75 (dd, J = 11.4, 12.9 Hz, 1 H, PCH2), 6.14 (t, J = 8.2 Hz,
2 H, ArH), 6.50 (d, J = 6.7 Hz, 1 H, ArH), 6.55 (d, J = 7.1 Hz, 1 H,
ArH), 6.69−6.77 (m, 3 H, ArH), 6.85−6.90 (m, 5 H, ArH), 7.06
(dt, J = 5.1, 7.8 Hz, 2 H, ArH), 7.10−7.16 (overlapped with the signal
of residual benzene, 2 H, ArH), 7.18−7.28 (m, 6 H, ArH), 8.01−8.06
(m, 2 H, ArH), 8.10−8.24 (m, 6 H, ArH); 13C{1H} NMR (C6D6, 98.5
MHz) δ 261.5 (tt, J = 33.8, 15.9 Hz, CCH(tBu)); 31P{1H} NMR
complex 10 was confirmed on the H and 31P{1H} NMR spectra, the
1
NMR yield of (amino)carbene complex 10 was determined by H
NMR analysis using the signals given in Table S2 in the Supporting
Information.
4.13. Synthesis of (Amino)carbene Complex 10ae (Eq 6). In a
glovebox, 50.0 mg of complex 9a (0.05 mmol) was placed in an oven-
dried 50 mL Schlenk tube containing a magnetic stirring bar, and
5.0 mL of toluene, 7.4 μL of 1-octyne (5.51 mg, 0.05 mmol), and
22.7 μL of isoindoline (23.8 mg, 0.20 mmol) were placed in the tube.
The resulting mixture was heated in an oil bath at 100 °C for 12 h, and
the volatile materials were removed in vacuo. Recrystallization of the
crude material from toluene/hexane afforded 40.7 mg (58% yield) of
(amino)carbene complex 10ae as red crystals, which were suitable for
X-ray diffraction analysis: mp 160−165 °C dec; 1H NMR (C6D6, 391.8
MHz) δ 0.88 (t, 3JH−H = 7.1 Hz, 3 H, CH3), 1.17−1.30 (m, 8 H, CH2),
2.03−2.11 (m, 2 H, CH2), 2.42 (t, J = 7.4 Hz, 2 H, CH2), 3.56 (d,
2JH−P = 9.8 Hz, 2 H, PCH2), 4.15 (s, 2 H, NCH2), 6.08 (s, 2 H,
NCH2), 6.67−6.69 (m, 2 H, ArH), 6.74 (d, J = 7.1 Hz, 1 H, ArH), 6.87
(dd, J = 7.4, 1.2 Hz, 1 H, ArH), 6.92−7.01 (m, 2 H, ArH), 7.03−7.06
(m, 6 H, ArH), 7.47 (dd, J = 8.2, 1.6 Hz, 1 H, ArH), 7.50−7.57 (m, 5
H, ArH), 7.70 (dd, J = 8.6, 1.2 Hz, 1 H, ArH); 13C{1H} NMR (C6D6,
98.5 MHz) δ 263.6 (dd, J = 43.2, 13.5 Hz, RhC); 31P{1H} NMR
(C6D6, 158.6 MHz) δ 51.4 (d, 1JP−Rh = 215.0 Hz); IR (KBr) 3416 m,
3053 m, 2926 m, 2855 m, 1956 w, 1897 w, 1825 w, 1639 m, 1604 m,
1553 s, 1496 m, 1436 s, 1395 m, 1375 m, 1336 m, 1316 m, 1286 m,
1191 m, 1152 w, 1108 m, 1027 w, 998 w, 915 w, 841 m, 744 s, 698 m,
668 w, 615 w, 533 m, 502 m cm−1. Anal. Calcd for C38H40N2OPRh: C,
67.65; H, 5.98; N, 4.15. Found: C, 67.53; H. 5.91; N, 4.06.
1
(C6D6, 158.6 MHz) δ 42.9 (dd, JP−Rh = 184.3, 2JP−Rh = 3.2 Hz), 39.0
1
2
(dd, JP−Rh = 185.4, JP−Rh = 3.2 Hz); IR (KBr) 3435 w, 3053 w,
3004 w, 2949 w, 2890 w, 2857 w, 1899 w, 1806 w, 1589 w, 1559 s,
1502 m, 1482 w, 1456 s, 1443 s, 1434 s, 1400 w, 1373 m, 1326 m,
1319 m, 1283 m, 1234 w, 1214 w, 1171 w, 1147 w, 1127 w, 1103 m,
1070 w, 1027 w, 999 w, 940 w, 894 w, 848 m, 826 w, 797 w, 741 m,
694 m, 621 w, 587 w, 573 w, 539 w, 504 m cm−1. In order to improve
the stability of the complex, the brown solid was further recrystallized
from toluene/hexane to form black crystals, which were used for
elemental analysis. Anal. Calcd for C50H44N2O2P2Rh2: C, 61.74; H,
4.56; N, 2.88. Found: C, 61.72; H, 4.56; N, 2.76.
4.9.5. Complex 9e. The reaction was performed with 2 equiv of
ethynylferrocene, and complex 9e was obtained in 33% yield as a
1
brown solid: mp 243−244 °C dec; H NMR (CDCl3, 399.7 MHz) δ
3.11 (dt, J = 4.0, 14.0 Hz, 1 H, PCH2), 3.39 (dt, J = 4.0, 14.0 Hz, 1 H,
PCH2), 3.70 (br d, 1 H, FeCp′), 3.84 (s, 5 H, FeCp), 4.01−4.03 (m,
1 H, FeCp′), 4.08−4.10 (m, 1 H, FeCp′), 5.00 (br t, 1 H, FeCp′),
5.12 (dd, J = 9.6, 13.6 Hz, 1 H, PCH2), 5.75 (br s, 1 H, C
CH(ferrocenyl)), 5.79 (dd, J = 11.1, 13.2 Hz, 1 H, PCH2), 6.52
(dd, J = 0.8, 7.6 Hz, 1 H, ArH), 6.59 (dd, J = 0.8, 7.6 Hz, 1 H, ArH),
6.67−6.70 (m, 2 H, ArH), 6.77 (d, J = 7.2 Hz, 1 H, ArH), 6.89 (d, J =
8.4 Hz, 1 H, ArH), 7.09−7.22 (m, 8 H, ArH), 7.24−7.31 (overlapped
with the signal of residual chloroform, 5 H, ArH), 7.42−7.46 (m, 3 H,
ArH), 7.73 (d, J = 8.4 Hz, 1 H, ArH), 7.75−7.80 (m, 2 H, ArH), 7.87
(d, J = 8.0 Hz, 1 H, ArH), 8.15−8.24 (m, 4 H, ArH); 13C{1H} NMR
(CDCl3, 98.5 MHz) δ 272.1 (tt, J = 35.1, 15.7 Hz, C =
CH(ferrocenyl)); 31P{1H} NMR (CDCl3, 161.9 MHz) δ 42.1 (dd,
4.14. Reaction of Complex 9a with Cyclohexylacetylene and
Piperidine (Eq 7). In a glovebox, 1.68 mg of 1,3,5-trimethoxybenzene
(0.01 mmol), 10.0 mg of complex 9a (0.01 mmol), and 0.75 mL of
benzene-d6 were placed in a screw-cap NMR tube. After the amount of
complex 9a was determined by 1H NMR analysis, 6.5 μL of
cyclohexylacetylene (5.41 mg, 0.05 mmol) and 4.9 μL of piperidine
(4.26 mg, 0.05 mmol) were added. The tube was heated in an oil bath
at 80 °C for 12 h and cooled to room temperature. The NMR yields of
2
1
2
1JP−Rh = 179.3, JP−Rh = 3.1 Hz), 41.9 (dd, JP−Rh = 181.1, JP−Rh
=
1
complexes 10aa, 10ba, and 1-octyne were determined by H NMR
3.6 Hz); IR (KBr) 3430 w, 3051 w, 1559 s, 1502 m, 1436 s, 1373 m,
1319 m, 1283 m, 1131 w, 1103 m, 1020 w, 999 w, 848 m, 825 m,
800 w, 740 m, 693 m, 666 w, 621 w, 586 w cm−1. In order to improve
the stability of the complex, the brown solid was further recrystallized
from CH2Cl2 to form black crystals, which were used for elemental
analysis as well as X-ray diffraction analysis. Anal. Calcd for
C56.25H44.5Cl0.5Fe1N2O2P2Rh2 (9e·1/4CH2Cl2): C, 60.22; H, 4.00;
N, 2.50. Found: C, 60.45; H, 4.02; N, 2.41.
analysis.
4.15. Reaction of Complex 10aa with Additives (Table 6). In
a screw-cap NMR tube, (amino)carbene complex 10aa was generated
in situ by the reaction of 10.0 mg of complex 9a (0.01 mmol) with
4.9 μL of piperidine (4.26 mg, 0.05 mmol) in 0.75 mL of benzene-d6 at
100 °C, and the amount of complex 10aa was determined by 1H NMR
analysis. The additive (0.05 mmol) was then placed in the tube in a
glovebox, and the resulting mixture was heated in an oil bath for 24 h.
When CO was used as an additive, the NMR tube was charged with
CO gas by repeating the cycle of evacuation and refilling after freezing
the reaction mixture in a liquid N2 bath and the tube was warmed to
room temperature. The NMR yields of hydroamination product 8b
and (amino)carbene complex 10aa were determined by 1H NMR
analysis.
4.16. Stoichiometric Reaction of Complex 2 with 1-Octyne
and Piperidine (Eq 8 and Figure 6). In a glovebox, 1.68 mg of
1,3,5-trimethoxybenzene (0.01 mmol, internal standard), 10.0 mg of
complex 2 (0.01 mmol), and 0.75 mL of benzene-d6 were placed in a
screw-cap NMR tube. After the amount of complex 2 was determined
by H NMR analysis, 3.0 μL of 1-octyne (2.20 mg, 0.02 mmol) and
4.9 μL of piperidine (4.26 mg, 0.05 mmol) were added. The tube was
4.10. Exchange Reaction of Complex 9 with Terminal
Alkynes (Table 4 and Eq 3). In a glovebox, 1.68 mg of 1,3,5-
trimethoxybenzene (0.01 mmol, internal standard), vinylidene-bridged
complex 9 (0.01 mmol), and 0.75 mL of solvent were placed in a
screw-cap NMR tube. After the amount of complex 9 was determined
by 1H NMR analysis, the terminal alkyne (0.05 mmol) and the
additive (0.05 mmol) were added. The tube was heated in an oil bath
at 80 °C for 12 h and cooled to room temperature. The NMR yield of
vinylidene-bridged complexes 9 was determined by 1H NMR analysis.
4.11. Reaction of Complex 9a with DMAP (Eq 4). In a
glovebox, 1.68 mg of 1,3,5-trimethoxybenzene (0.01 mmol, internal
standard), vinylidene-bridged dirhodium complex 9a (0.01 mmol),
and 0.75 mL of benzene-d6 were placed in a screw-cap NMR tube.
After the amount of complex 9a was determined by 1H NMR analysis,
6.11 mg of DMAP (0.05 mmol) was added. The tube was heated in an
oil bath at 80 °C for 12 h and cooled to room temperature. The NMR
yields of 9a, 1-octyne, and the (PNO)Rh DMAP complex were
1
heated in an oil bath at 80 °C. The NMR yields of complex 2, 9a, and
10aa were determined by H NMR analysis.
4.17. Monitoring of the Reaction of Ethynylferrocene with
Pipridine using Catalyst 2 (Eq 9 and Figure 8). In a glovebox,
1.68 mg of 1,3,5-trimethoxybenzene (0.01 mmol, internal standard),
10.0 mg of complex 2 (0.01 mmol) and 0.60 mL of toluene-d8 were
placed in a screw-cap NMR tube. After the amount of complex 2
1
1
determined by H NMR analysis.
4.12. Reaction of Complex 9 with Secondary Amines (Eq 5
and Table 5). In a glovebox, 1.68 mg of 1,3,5-trimethoxybenzene
(0.01 mmol, internal standard), complex 9 (0.01 mmol), and 0.75 mL
of benzene-d6 or toluene-d8 were placed in a screw-cap NMR tube.
1
was determined by H NMR analysis, 42.0 mg of ethynylferrocene
1
After the amount of complex 9 was determined by H NMR analysis,
(0.20 mmol) and 59.3 μL of piperidine (51.1 mg, 0.60 mmol) were
added. The tube was heated in an oil bath at 110 °C. The NMR yields
of complex 2, 10ea, and hydroamination product 8c were determined
the secondary amine (0.05 mmol) was added. The tube was heated
in an oil bath at 90 °C for 24 h and cooled to room temperature.
After the presence of the signals corresponding to the (amino)carbene
1
by H NMR analysis.
L
DOI: 10.1021/acs.organomet.6b00853
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
4.18. Monitoring of the Reaction of Ethynylferrocene with
Pipridine using Catalyst 7 (Eq 10 and Figure 9). In a glovebox,
1.68 mg of 1,3,5-trimethoxybenzene (0.01 mmol, internal standard),
9.47 mg of complex 7 (0.02 mmol), and 0.60 mL of toluene-d8 were
placed in a screw-cap NMR tube. Then, 42.0 mg of ethynylferrocene
(0.20 mmol) and 59.3 μL of piperidine (51.1 mg, 0.60 mmol) were
added. The tube was heated in an oil bath at 110 °C. The NMR yields
of complex 10ea and hydroamination product 8c were determined by
1H NMR analysis.
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the ACS
Publications website at DOI: 10.1021/acs.organomet.6b00853.
■
S
Crystallographic data (CIF)
Experimental details, characterization data, and crystallo-
graphic data (PDF)
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32, 2804−2813.
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14.
AUTHOR INFORMATION
Corresponding Author
*E-mail for F.K.: kakiuchi@chem.keio.ac.jp.
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ORCID
(12) (a) Muller, T. E.; Hultzsch, K. C.; Yus, M.; Foubelo, F.; Tada,
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Fumitoshi Kakiuchi: 0000-0003-2605-4675
M. Chem. Rev. 2008, 108, 3795−3892. (b) Evano, G.; Gaumont, A.−
C.; Alayrac, C.; Wrona, I. E.; Giguere, J. R.; Delacroix, O.; Bayle, A.;
Jouvin, K.; Theunissen, C.; Gatignol, J.; Silvanus, A. C. Tetrahedron
2014, 70, 1529−1616. (c) Yim, J. C.−H.; Schafer, L. L. Eur. J. Org.
Chem. 2014, 2014, 6825−6840. (d) Huang, L.; Arndt, M.; Gooβen, K.;
Heydt, H.; Gooβen, L. J. Chem. Rev. 2015, 115, 2596−2697.
(13) Fukumoto, Y.; Asai, H.; Shimizu, M.; Chatani, N. J. Am. Chem.
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported, in part, by a Grant-in-Aid for Scientific
Research (B) from the Ministry of Education, Culture, Sports,
Science and Technology of Japan (16H04150). We are grateful
to Professor Yoshio Aso and Associate Professor Yutaka Ie (The
Institute of Scientific and Industrial Research, Osaka University)
for their assistance with the elemental analyses. We also thank
Professor Sensuke Ogoshi and Associate Professor Masato
Ohashi (Division of Applied Chemistry, Graduate School of
Engineering, Osaka University) for their assistance with
collecting elemental analysis data and FAB-MS spectrum
measurements.
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