Cationic Dirhodium Complexes Bridged by 2-Phosphinopyridines Having an Exquisitely Positioned Axial Shielding Group: A Molecular Design for Enhancing the Catalytic Activity of the Dirhodium Core

Article abstract of DOI:10.1021/acs.organomet.1c00314

This report describes a strategy to create highly electrophilic dirhodium catalysts. The electrophilicity of lantern-Type dirhodium complexes is generally decreased by the coordination of a ligand to the axial site, which often causes a reduction in the catalytic activity. We designed and synthesized a series of cationic dirhodium complexes bridged by 2-diarylphosphinopyridines having a bulky 2,4,6-Triisopropylphenyl (Tip) group that can prevent the attack of external molecules to the closest axial site. Theoretical calculations indicated that the Tip group weakly interacts with the axial site but hardly reduces the electrophilicity of the dirhodium core. The complexes served as excellent catalyst precursors for the dehydrogenative silylation of alcohols using hydrosilanes under mild conditions and a low metal loading, producing the silyl ethers in higher yields in comparison to conventional dirhodium complexes.

Full text of DOI:10.1021/acs.organomet.1c00314

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Article
Cationic Dirhodium Complexes Bridged by 2‑Phosphinopyridines
Having an Exquisitely Positioned Axial Shielding Group: A Molecular
Design for Enhancing the Catalytic Activity of the Dirhodium Core
Ryuhei Ohnishi, Hidetoshi Ohta,* Shigeki Mori, and Minoru Hayashi*
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ABSTRACT: This report describes a strategy to create highly
electrophilic dirhodium catalysts. The electrophilicity of lantern-type
dirhodium complexes is generally decreased by the coordination of a
ligand to the axial site, which often causes a reduction in the catalytic
activity. We designed and synthesized a series of cationic dirhodium
complexes bridged by 2-diarylphosphinopyridines having a bulky 2,4,6-
triisopropylphenyl (Tip) group that can prevent the attack of external
molecules to the closest axial site. Theoretical calculations indicated that
the Tip group weakly interacts with the axial site but hardly reduces the
electrophilicity of the dirhodium core. The complexes served as excellent
catalyst precursors for the dehydrogenative silylation of alcohols using
hydrosilanes under mild conditions and a low metal loading, producing the silyl ethers in higher yields in comparison to
conventional dirhodium complexes.
for improving the catalytic performance.9 However, in most
cases, the coordination of axial ligands, usually solvents
containing N and O atoms, diminishes the catalytic activity
useful catalysts for various organic transformations: e.g., Lewis
INTRODUCTION
Lantern-type dirhodium complexes, shown in Figure 1A, are
■
for the following reasons (Figure 1B). (i) The ligands quickly
occupy both axial sites and prevent the generation of a
coordinatively unsaturated and catalytically active rhodium
center.5c,10,11 (ii) The active rhodium center is electronically
influenced by the axial ligand on the opposite rhodium atom,
resulting in a decrease in the electrophilicity in comparison
with the corresponding dirhodium core without axial
ligands.10,12 These imply that a rational catalyst design for
preventing the coordination of axial ligands to the dirhodium
core may lead to the development of highly active dirhodium
complex catalysts.13
Figure 1. (A) Structural representation of lantern-type dirhodium
complexes. (B) Coordination of axial ligands to the Rh2 core and the
2-Phosphinopyridine derivatives constitute an important
influence on the catalytic activity. Lax′ is a molecule that is in a
class of bridging ligands for the construction of various homo-
coordination equilibrium with Rh2.
and heteronuclear dimetal complexes.14 A few reports for the
preparation of lantern-type dirhodium complexes with
diphenylphosphinopyridine (1) as a ligand are known (Figure
̈
2A). Kuhn et al. reported that the reaction of commercially
available Rh2(OAc)4 with 1 gave the diaxial adduct 2, whereas
the preparation of the monoaxial adduct and 1-bridged
acid catalysis and rhodium carbenoid mediated reactions.1−6
The electrophilic nature and the surrounding steric environ-
ments of the dirhodium core greatly influence the catalytic
properties.1,2a−d,3b,c,4d,e,6a,b These factors can be adjusted by
changing the bridging ligands, leading to an improvement in
the catalytic activity, selectivity, and stability in various
reactions. Therefore, dirhodium complexes with various
bridging ligands such as carboxylates, carboxamidates,
phosphonates, 1,8-naphthyridines, ortho-metalated phosphines,
thienylphosphines, and oxothioethers have been synthesized
and their catalytic properties investigated.1b,5a,7,8 The axial
ligand modification has also been studied as another strategy
Received: May 28, 2021
Published: July 12, 2021
https://doi.org/10.1021/acs.organomet.1c00314
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acetonitrile ligand. The complexes have electrophilic cationic
character and weakly coordinating counteranions (X = BF4,
PF6, SbF6). In addition, the electronic tuning of the dirhodium
core is possible by changing the substituents (R = H, OMe,
CF3) on the phosphorus atom in LR. Therefore, the designed
complexes are expected to become highly electrophilic catalyst
precursors. [CR(MeCN)][X] were successfully prepared from
Rh2(OAc)4 and LR as starting materials in a few steps. The
experimental and quantum chemical studies revealed that the
Tip group weakly interacts with the dirhodium core and
protects the axial site from the coordination of external
molecules but it hardly reduces the electrophilicity. The
complexes were more effective catalyst precursors for the
dehydrogenative silylation of alcohols using hydrosilanes in
comparison to conventional dirhodium complexes.
RESULTS AND DISCUSSION
■
Synthesis of Ligands. In order to achieve the synthesis of
the novel cationic dirhodium complexes [CR(MeCN)][X], we
prepared 2-phosphinopyridine ligands LR from 2-bromo-6-
(2,4,6-triisopropylphenyl)pyridine (9) and diaryl-
(hydroxymethyl)phosphine sulfides 5R (R = H, OMe, CF3)
as shown in Scheme 1. First, 5H was obtained from
triphenylphosphine through in situ generation and reaction of
lithium diphenylphosphide (Scheme 1A). 5OMe and 5CF3 were
produced by the Pd-catalyzed P−C cross-coupling19 of
bis(hydroxymethyl)(tert-butyldimethylsilyl)phosphine sulfide
(6) with aryl iodides 7OMe and 7CF3 followed by the
deprotection of the silyl groups (Scheme 1B). The P−C
cross-coupling between 9 and 5R into thiophosphinopyridines
10R and the subsequent reduction by tris(dimethylamino)-
phosphine proceeded to give LR in good yields (Scheme 1C).
Synthesis of Dirhodium Complexes. LR-bridged dirho-
dium complexes CRCl were prepared as precursors for
[CR(MeCN)][X] through a one-pot reaction shown in Scheme
2. Thus, the treatment of Rh2(OAc)4 with an equimolar
amount of LR in acetic acid under reflux conditions yielded the
LR-bridged complexes CROAc.20 After the solvent was
removed under vacuum, the crude CROAc was dissolved
Figure 2. Lantern-type dirhodium complexes with 2-phosphinopyr-
idines.
complexes was not successful.15 Cotton et al. found that their
complexation in the presence of lithium chloride afforded
doubly 1-bridged dirhodium complex 3.16 Piraino et al. also
synthesized complex 4 from 1 and a specially prepared
dirhodium precursor.17 Further molecular conversions and the
catalytic properties of this class of dirhodium complexes are of
interest; however, they have not been explored.
Herein, we wish to report the synthesis, characterization, and
catalytic application of novel lantern-type dirhodium com-
plexes [CR(MeCN)][X] bridged by 2-diarylphosphino-6-
(2,4,6-triisopropylphenyl)pyridines18 LR (Figure 2B). The
bridging ligands LR are selected to enhance the electrophilicity
of the dirhodium core. Thus, a bulky 2,4,6-triisopropylphenyl
(Tip) group on the pyridine ring shields the closest rhodium
atom from the axial coordination which reduces the electro-
philicity of the dirhodium core. On the other hand, the axial
site of the opposite rhodium atom can work as a catalytic
center after the dissociation of the initially coordinated
Scheme 1. Synthesis of 2-Phosphinopyridine Ligands LR
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Scheme 2. Synthesis of Cationic Dirhodium Complexes [CR(MeCN)][X]
Figure 3. X-ray crystal structures of (A) CHCl and (B) [CH(MeCN)][PF6] with thermal ellipsoids drawn at the 50% probability level. Hydrogen
atoms and solvent molecules (CH2Cl2) are omitted for clarity. Partial structures showing the coordination geometry around Rh1 center for (C)
CHCl and (D) [CH(MeCN)][PF6].
with chloroform and reacted with ammonium chloride to give
CRCl in 65−78% isolated yields. The anion exchange of CRCl
with AgX (X = BF4, PF6, SbF6) proceeded efficiently in
acetonitrile at room temperature, affording [CR(MeCN)][X]
in 97−98% isolated yields. The isolated complexes were
Scheme 3. Synthesis of Dicationic Dirhodium Complex 11
1
characterized by H, 13C{1H}, and 31P{1H} NMR, FAB-MS,
and elemental analysis. Furthermore, the molecular structures
of CHCl and [CH(MeCN)][PF6] were successfully determined
by X-ray crystallographic analyses, as shown in Figure 3 (the
details are described in the next section).
To evaluate the influence of the axial shielding Tip group of
[CR(MeCN)][X] on the catalytic activity, we attempted to
synthesize singly 1-bridged dirhodium complexes by the same
synthetic procedure for [CR(MeCN)][X]. However, the
reactions using 1 and Rh2(OAc)4 (1−3 equiv) as the starting
materials did not give singly 1-bridged complexes, and
mixtures containing doubly 1-bridged complexes were
obtained. The results suggest that the Tip group controls the
coordination behavior of LR toward the dirhodium core and is
important to produce singly LR-bridged complexes. Therefore,
instead of singly 1-bridged complexes, we prepared the doubly
1-bridged dicationic complex 11 from 3 for comparison in
catalytic activity testing (Scheme 3).
crystal structures showed that LH bridges two rhodium centers
via both nitrogen and phosphorus atoms by occupying the
equatorial positions. The Rh1−Rh2 bond lengths of CHCl and
[CH(MeCN)][PF6] are 2.4401(5) and 2.4246(4) Å, respec-
tively. These bond lengths are similar to those of reported
dirhodium triacetate complexes (2.405−2.439 Å).4d,5a,21 The
Rh2−P1 bond length of CHCl (2.209(1) Å) is shorter than
that of [CH(MeCN)][PF6] (2.2270(10) Å), suggesting that
the rhodium atom of [CH(MeCN)][PF6] is more electron
deficient than that of CHCl and has lower back-donating ability
toward the phosphine moiety. The most noteworthy structural
feature of these complexes is that the rhodium atom Rh2 has
an axial acetonitrile ligand, whereas no ligand coordinates to
the axial position of Rh1 near the Tip group.22 The carbon
atoms C1, C2, and C6 in the Tip group are close to Rh1, and
the interatomic distances are shorter than the sum of the van
Structural Evaluation. The X-ray crystal structures of
CHCl and [CH(MeCN)][PF6] are shown in Figure 3. The
crystallographic data and selected structural parameters are
given in Tables S1 and S2 (Supporting Information). The
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der Waals radii of Rh and C atoms (4.21 Å),23 suggesting the
existence of interactions between Rh1 and the Tip group.
Density functional theory (DFT) calculations for the
[CH(MeCN)]+ cation at the M06-L/Def2TZVP//ωB97XD/
Def2SVP level of theory were performed to elucidate the
interactions between the Rh1 and the Tip group (Figure 4 and
The above results indicate that the Tip group in
[CH(MeCN)][PF6] weakly interacts with the dirhodium core
and can protect the axial site of Rh1 from the coordination of
an external polar molecule such as acetonitrile.
Evaluation of Electrophilic Nature. Lewis acidity and
electrophilicity are crucial factors for determining the catalytic
performance of dirhodium complexes. We employed the
Gutmann−Beckett method25 for the evaluation of the Lewis
acidity of [CR][X] ,in which the structure of the cation part
[CR]+ is shown in Figure 6. For the tests, [CR(MeCN)][X]
Figure 4. Frontier orbitals of the [CH(MeCN)]+ cation: HOMO
(left) and LUMO (right) (isovalue 0.013). Hydrogen atoms are
omitted for clarity.
Figure 6. Structures of dirhodium cations bridged by LR or 1.
Table 1. Stabilization Energies of Selected NBO Pairs as
Given by Second-Order Perturbation Theory Analysis of the
a
Fock Matrix in NBO Basis for [CH(MeCN)]+
were reacted with an equimolar amount of triethylphosphine
oxide (TEPO) in CD2Cl2 at room temperature to form the
Lewis acid−base adducts [CR(TEPO)][X], and the 31P{1H}
NMR chemical shifts for the phosphorus atom of the TEPO
were measured (Figure 7 and Table 2). The stronger the Lewis
donor NBO
ED (e)
acceptor NBO
ED (e)
E(2) (kcal/mol)
π(C1−C2)
LP(Rh1)
LP(N2)
σ(N2−C39)
LP(Rh2)
LP(Rh2)
1.65807
1.96967
1.79940
1.99633
1.95502
1.95502
σ*(Rh1−Rh2)
π*(C1−C2)
σ*(Rh1−Rh2)
σ*(Rh1−Rh2)
π*(N2−C39)
π*(N2−C39)
0.44164
0.40259
0.44164
0.44164
0.07251
0.07257
1.01
0.52
52.38
2.13
3.23
0.99
a
The atom numbering is shown in Figure 3. Abbreviations: LP, lone
pair orbital; ED, electron density; E(2), stabilization energy (energy of
delocalization).
Table 1). Figure 4 shows that the calculated highest occupied
molecular orbital (HOMO) and lowest unoccupied molecular
orbital (LUMO) are delocalized over the dirhodium core and
the Tip group. A natural bond orbital (NBO) analysis revealed
the existence of weak donor−acceptor interactions between
them: π(C1−C2) → σ*(Rh1−Rh2) and LP(Rh1) → π*(C1−
C2).24 The total stabilization energy is 1.53 kcal/mol, which is
much lower than the energy between the dirhodium core and
the axial acetonitrile ligand, 58.73 kcal/mol.
Figure 7. 31P{1H} NMR spectra of (A) TEPO and (B−F) 1:1 molar
mixtures of TEPO and [CR(MeCN)][X] in CD2Cl2 at rt.
acid, the more downfield the signal for the corresponding
adduct appears from that of free TEPO and the larger the
Gutmann−Beckett acceptor number (AN). As a result, this
method provided the order of the relative Lewis acidity as
follows: [CCF3][SbF6] > [CH][SbF6] = [CH][PF6] ≈ [CH]-
[BF4] > [COMe][SbF6]. This result indicates that the electron-
To confirm the axial shielding effect of the Tip group, we
1
measured a series of H NMR spectra of [CH(MeCN)][PF6]
in the absence and presence of excess acetonitrile. As shown in
Figure 5, the addition of acetonitrile increased the signal
intensity of free acetonitrile, and no new signals derived from
the acetonitrile coordinated to Rh1 were observed.
Table 2. Experimental Evaluation of the Lewis Acidity of
a
[CR][X] by the Gutmann−Beckett Method
b
c
d
Lewis acid
δRh‑TEPO (ppm)
Δδ (ppm)
AN
[CH][BF4]
71.3
71.4
71.4
71.1
72.3
20.4
20.5
20.5
20.2
21.4
67.2
67.4
67.4
66.7
69.4
[CH][PF6]
[CH][SbF6]
[COMe][SbF6]
[CCF3][SbF6]
a
[CR(TEPO)][X] were generated in situ by mixing a 1:1 molar ratio
of [CR(MeCN)][X] and TEPO in CD2Cl2 at rt, then the 31P{1H}
b
NMR spectra were recorded at rt. 31P{1H} NMR chemical shift for
c
the phosphorus atom of the coordinated TEPO. The difference in
chemical shifts between coordinated and free TEPO. AN = (δRh‑TEPO
d
Figure 5. 1H NMR spectra of [CH(MeCN)][PF6] in the absence (A)
and presence of 2 (B) and 18 (C) equiv of MeCN in CDCl3 solution.
− 41.0) × {100/(86.1−41.0)}.
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withdrawing p-trifluoromethylphenyl groups on the phospho-
with typical solvents were calculated. 15, the cation of 11
without the acetonitrile ligands, has a high ω′ value (123%)
that is probably due to the dicationic character; however, the
ω′ value (78%) of the monoacetonitrile adduct 16 is lower
than that of [CR]+. Similarly, the ω′ values of Rh2(OAc)4
(69%), Rh2(tfa)4 (109%), and Rh2(pfb)4 (109%) are greatly
reduced by the axial coordination of polar molecules. These
results suggest that [CR(MeCN)][SbF6] would serve as a more
effective catalyst precursor in comparison to 11 and the
commonly used dirhodium complexes in a catalytic reaction.
Catalysis. Doyle et al. reported that electrophilic Rh2(pfb)4
was an effective catalyst precursor for the dehydrogenative
silylation of alcohols with hydrosilanes to afford silyl ethers
under mild conditions (room temperature, 1.0 mol % Rh2
loading).5f Therefore, we evaluated [CR(MeCN)][X] as a
catalyst precursor for the dehydrogenative silylation of 1-
phenylethanol (17a) using triethylsilane (18a) in dichloro-
methane at room temperature for 1 h with a lower Rh2 loading
of 0.1 mol % (Table 4). As shown in entries 1−3,
+
rus atom in [CCF3
]
increase the Lewis acidity of the
dirhodium core. For reference, the ANs of typical Lewis
acids are shown: SnCl4 (AN = 59), BPh3 (AN = 66), B(C6F5)3
(AN = 78).25b
To investigate the effect of the axial shielding Tip group in
[CR]+ on the electrophilic nature of the dirhodium core, we
compared [CR]+ and 1-bridged dirhodium cations 12−14
(Figure 6) by the global electrophilicity index (GEI, ω)26
calculated from the HOMO and LUMO energies obtained at
the M06-L/Def2TZVP(SMD,CH2Cl2)//ωB97XD/Def2SVP
level of theory (Table 3). GEI is used to estimate the
Table 3. GEI Value (ω) Calculated from the Energies of the
HOMO and LUMO (EHOMO, ELUMO) for Electrophilic
a
Dirhodium Complexes
b
c
Rh2 complex
EHOMO (eV) ELUMO (eV) ω (eV)
ω′ (%)
+
[CCF3
]
−5.172
−5.087
−5.015
−5.140
−5.013
−4.964
−5.943
−5.788
−4.438
−4.209
−4.161
−4.259
−5.530
−5.269
−5.213
−5.296
−5.566
−5.311
−5.259
−5.335
−3.875
−3.776
−3.706
−3.838
−3.238
−3.113
−4.473
−3.821
−3.073
−2.489
−2.419
−2.382
−4.106
−3.484
−3.409
−3.364
−4.131
−3.520
−3.451
−3.398
7.884
7.494
7.265
7.741
4.793
4.405
9.224
5.866
5.165
3.261
3.108
2.936
8.151
5.363
5.151
4.851
8.191
5.444
5.245
4.922
105
100
97
103
64
59
123
78
69
44
42
39
109
72
69
65
109
73
[CH]+
+
[COMe
12
]
a
Table 4. Dehydrogenative Silylation of 17a with 18a
13
14
15
16
b
entry
Rh2 complex
Rh2(OAc)4
Rh2(tfa)4
yield (%)
Rh2(OAc)4
1
2
0
1
Rh2(OAc)4(H2O)
Rh2(OAc)4(MeOH)
Rh2(OAc)4(MeCN)
Rh2(tfa)4
Rh2(tfa)4(H2O)
Rh2(tfa)4(MeOH)
Rh2(tfa)4(MeCN)
Rh2(pfb)4
3
4
Rh2(pfb)4
CHCl
4
0
5
6
7
8
9
10
11
[CH(MeCN)][BF4]
[CH(MeCN)][PF6]
[CH(MeCN)][SbF6]
[COMe(MeCN)][SbF6]
[CCF3(MeCN)][SbF6]
11
2
87
94
91
99
82
94
Rh2(pfb)4(H2O)
Rh2(pfb)4(MeOH)
Rh2(pfb)4(MeCN)
c
[CCF3(MeCN)][SbF6]
70
66
a
Reaction conditions unless specified otherwise: 17a (1.0 mmol), 18a
(1.1 mmol, 1.1 equiv), Rh2 complex (0.1 mol %), CH2Cl2 (1.0 mL),
a
b
Abbreviations: tfa, trifluoroacetate; pfb, perfluorobutyrate. ω = χ2/
2η, χ = −(EHOMO + ELUMO)/2, η = ELUMO − EHOMO. ω′ = 100(ω of
c
b
c
rt, 1 h. GC yield. The reaction was performed at 60 °C for 1 h using
DMF (1.0 mL) as a solvent.
the Rh2 complex)/(ω of [CH]+).
electrophilicity of a molecule without considering the influence
of a Lewis base, and a stronger electrophile has a larger ω
value. In Table 3, we also give ω′, which is a relative
percentage of the ω value of an electrophile over that of [CH]+.
First, the order of electrophilicity between [CR]+ cations was
found to be [CCF3]+ > [CH]+ > [COMe]+, which is consistent
with the above results for Lewis acidity by the Gutmann−
Beckett method.26a,b 12 is the derivative of [CH]+ without a
Tip group, and the ω′ value (103%) is slightly higher than that
of [CH]+. However, the actual electrophilic species formed
during catalytic reactions using 12 is considered to be
complexes such as 13 and 14 having one axial ligand, and
the ω′ values are 64% and 59%, respectively. These results
indicate that axial-ligand-free 12 is highly electrophilic but axial
coordination to the dirhodium core significantly reduces the
electrophilicity. On the other hand, [CH]+ retains an
electrophilicity similar to that of 12, although the Tip group
is weakly interacting with the axial site as mentioned above. To
further evaluate the electrophilicity of [CR]+, the GEI values of
15 and 16 (Figure 6), commonly used dirhodium catalysts
(Rh2(OAc)4, Rh2(tfa)4, Rh2(pfb)4), and their monoadducts
representative dirhodium complexes such as Rh2(OAc)4,
Rh2(tfa)4, and Rh2(pfb)4 did not work as effective catalyst
precursors under the conditions. CHCl, having no available
axial sites, gave no product (entry 4), and thus we performed
the reaction with [CH(MeCN)][X] (entries 5−7). The
−
−
−
complexes having BF4 , PF6 , and SbF6 anions gave the
silyl ether 19a in 2%, 87%, and 94% yields, respectively. The
much lower yield by [CH(MeCN)][BF4] is probably due to
the stronger affinity of [CH]+ with BF4 than with PF6 and
−
−
27
SbF6 . Next, we compared the reactions of [CR(MeCN)]-
−
[SbF6] having different aryl groups on the phosphorus atom
(entries 7−9). The complexes having [CH]+, [COMe]+, and
+
[CCF3
]
cations exhibited a difference in yield, and
[CCF3(MeCN)][SbF6] was found to be the best catalyst
precursor. Doubly 1-bridged complex 11 having SbF6 anions
−
also provided 19a in 82% yield (entry 10). Interestingly, the
product yields obtained with the cationic dirhodium complexes
are well explained by the order of electrophilicity of the species
having one available axial site described above ([CCF3 +
] >
[CH]+ > [COMe]+ > 16). Another noteworthy point is that
[CCF3(MeCN)][SbF6] worked well in the reaction using N,N-
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a
Table 5. Dehydrogenative Silylation of Various Alcohols
b
entry
alcohol 17
hydrosilane 18
18a
product 19
solvent
temperature (°C)
time (h)
yield (%)
1
2
3
4
5
benzyl alcohol (17b)
2-phenylethanol (17c)
3-phenyl-1-propanol (17d)
1-phenyl-1-propanol (17e)
3-phenyl-2-propanol (17f)
2-methyl-4-phenyl-2-butanol (17g)
2-methyl-3-phenyl-2-propanol (17h)
4-propylphenol (17i)
4-phenylphenol (17j)
17b
19b
19c
19d
19e
19f
19g
19h
19i
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
DCE
DCE
DCE
DCE
DCE
rt
rt
rt
rt
1
1
1
1
1
9
9
25
25
24
24
99
99
(99)
(99)
(98)
97
(91)
99
(96)
(99)
(24)
18a
18a
18a
18a
18a
18a
18a
18a
rt
c
6
60
60
40
40
60
60
c
7
8
c
c
9
19j
19k
19l
c
t
10
11
HSiMe2 Bu (18b)
c
17a
18b
DCE
a
Reaction conditions unless specified otherwise: 17 (1.0 mmol), 18 (1.1 mmol, 1.1 equiv), [CCF3(MeCN)][SbF6] (0.1 mol %), CH2Cl2 (1.0 mL)
b
c
or DCE (0.5 mL). GC yield of 19. Isolated yields are given in parentheses. 1.5 mmol (1.5 equiv) of 18 was used.
dimethylformamide (DMF) as a solvent at 60 °C, although the
activity of conventional dirhodium catalysts is usually sup-
pressed by coordinating solvents.5c It is known that Biffis’s
monocationic dirhodium complexes bridged by oxothioether
ligands are one of the most effective dirhodium catalyst
precursors for the dehydrogenative silylation of alcohols, which
proceeds at 50 °C with a Rh2 loading of 0.1 mol % or below.5a
The catalyst generated from [CCF3(MeCN)][SbF6] has quite
high activity, comparable to that of the Biffis catalysts.
EXPERIMENTAL SECTION
■
General Information. Reagents were obtained from commercial
suppliers (Aldrich, Kanto, TCI, Wako) and used without further
purification unless otherwise noted. Toluene, tetrahydrofuran (THF),
DMF, and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) were refluxed
over drying agents and purified by distillation under an inert gas (Na
for toluene under Ar; Na/benzophenone for THF under N2; BaO for
DMF under Ar; CaH2 for DBU under Ar). Superdehydrated
dichloromethane (Wako) and DCE (Kanto) were used for catalytic
reactions. Oily alcohols were dried over MS4A and purified by
distillation. 6 (CAS registry number 1420040-42-1) was prepared
according to our previous report.19b 1H NMR (400 MHz), 31P{1H}
NMR (162 MHz), and 13C{1H} NMR (101 or 126 MHz) spectra
were measured with Bruker AVANCE 400 and Bruker AVANCE III
The efficacy of [CCF3(MeCN)][SbF6] was further inves-
tigated by the reaction of various alcohols using dichloro-
methane or 1,2-dichloroethane (DCE) as a solvent (Table 5).
Primary alcohols 17b−d and secondary alcohols 17e,f reacted
with 18a at room temperature for 1 h, giving the
corresponding products 19b−f in excellent yields (entries 1−
5). Although the silylation of tertiary alcohols hardly proceeds
by conventional dirhodium catalysts,5a,f the reaction of 17g,h
using [CCF3(MeCN)][SbF6] afforded 19g,h in high yields by
optimizing the reaction conditions (entries 6 and 7). Phenol
derivatives 17i,j were converted to 19i,j at 40 °C after 25 h
(entries 8 and 9). tert-Butyldimethylsilane (18b) could be used
for the silylation of 17b and 17a to form 19k and 19l in 99%
and 24% isolated yields, respectively (entries 10 and 11).
1
HD 500 spectrometers. The H NMR chemical shifts are reported
relative to tetramethylsilane (TMS, 0.00 ppm) or residual protiated
solvent (7.26 ppm for CDCl3; 5.32 ppm for CD2Cl2; 1.94 ppm for
CD3CN).28 The 13C{1H} NMR chemical shifts are reported relative
to CDCl3 (77.16 ppm), CD2Cl2 (53.84 ppm), and CD3CN (1.32
ppm).28 Fast atom bombardment (FAB) low-resolution mass spectra
(LRMS) and high-resolution mass spectra (HRMS) were measured
on a JEOL JMS-700V instrument by using 3-nitrobenzyl alcohol as a
matrix. X-ray diffraction data collections were performed with a
Rigaku VariMax SaturnCCD724/α diffractometer using multilayer
mirror monochromated Mo Kα radiation (λ = 0.71073 Å) at −173
°C. Elemental analyses were performed on a J-SCIENCE LAB
MICRO CORDER JM10T instrument. Gas chromatographic (GC)
analyses were performed on a Shimadzu GC-2014 instrument with a
flame ionization detector (FID) equipped with a capillary column
(DB-FFAP, 0.25 mm i.d. × 30 m, df 0.25 μm). Analyses by GC
coupled to electron impact mass spectrometry (EI-MS) were
conducted on a Shimadzu GCMS-2020 NX instrument (capillary
column: DB-FFAP, 0.25 mm i.d. × 30 m, df 0.50 μm). Column
chromatography was performed on Kanto silica gel 60 (spherical, 40−
50 μm).
CONCLUSION
■
In conclusion, novel cationic lantern-type dirhodium com-
plexes [CR(MeCN)][X] bridged by 2-diarylphosphinopyri-
dines having an axial shielding Tip group at the 6-position were
designed, synthesized, and evaluated as catalyst precursors for
the dehydrogenative silylation of alcohols using hydrosilanes. It
was found that the Tip group weakly interacts with the
dirhodium core and prevents the closest axial site from the
coordination of external molecules. Experimental and quantum
chemical studies suggested that the unique structural features
and the electron-withdrawing p-trifluoromethylphenyl groups
on the phosphorus atom make the complexes highly
electrophilic. Actually, [CCF3(MeCN)][SbF6] was a superior
catalyst precursor for the dehydrogenative silylation of various
alcohols in comparison with conventional dirhodium com-
plexes. Currently, studies on further catalytic reactions using
[CR(MeCN)][X] are ongoing in our laboratory.
Synthesis of 5H. A mixture of triphenylphosphine (9.97 g, 38.0
mmol, 1.0 equiv), lithium (0.673 g, 97.0 mmol, 2.6 equiv), and THF
(38 mL) was stirred at room temperature for 24 h under Ar. Then,
the solution was placed in another reactor containing paraformalde-
hyde (5.14 g, 171 mmol as the monomer, 4.5 equiv) under Ar by
cannula transfer. After completion of the addition, water (Ar bubbled,
10 mL), 1 N HCl(aq) (Ar bubbled, 90 mL), and S8 (2.73 g, 85.1
mmol as S, 2.2 equiv) were successively added to the mixture, and the
resulting mixture was stirred at room temperature for 3 h under Ar.
The mixture was extracted with ethyl acetate, and the combined
organic layers were washed successively with water, saturated
NaHCO3(aq), and brine. After the solution was dried over Na2SO4,
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the solvent was removed in vacuo. The residue was purified by column
chromatography on silica gel (eluent: ethyl acetate/n-hexane 1/3).
The obtained solid was recrystallized from ethyl acetate/n-hexane to
give the product as a white solid (7.10 g, 28.6 mmol, 75%). CAS
registry number: 96620-51-8. 1H NMR (400 MHz, CDCl3): δ 2.95−
3.00 (m, 1H, OH), 4.33−4.35 (m, 2H, CH2), 7.46−7.57 (m, 6H,
PhH), 7.79−7.85 (m, 4H, PhH). 13C{1H} NMR (101 MHz, CDCl3):
δ 63.1 (d, J = 60.7 Hz, CH2), 128.9 (d, J = 12.2 Hz, m-C of Ph × 4),
130.4 (d, J = 79.1 Hz, ipso-C of Ph × 2), 131.6 (d, J = 9.9 Hz, o-C of
Ph × 4), 132.2 (d, J = 2.9 Hz, p-C of Ph × 2). 31P{1H} NMR (162
MHz, CDCl3): δ 42.9.
Synthesis of 5CF3. The compound was prepared by following the
synthetic procedure for 5OMe, using 8CF3 (1.50 g, 3.00 mmol, 1.0
equiv), acetyl chloride (4 mL), and ethanol (38 mL). Isolation by
column chromatography (eluent: ethyl acetate/n-hexane 1/5) gave
the product as a white solid (1.10 g, 2.87 mmol, 96%). 1H NMR (400
MHz, CDCl3): δ 2.90−2.92 (br, 1H, OH), 4.43 (br s, 2H, CH2), 7.76
(dd, J = 8.3 and 2.0 Hz, 4H, o-H of p-CF3C6H4), 7.97 (dd, J = 12.3
and 8.2 Hz, 4H, m-H of p-CF3C6H4). 13C{1H} NMR (101 MHz,
CDCl3): δ 63.5 (d, J = 62.1 Hz, CH2), 123.5 (q, J = 273.0 Hz, CF3 ×
2), 125.9 (dq, J = 12.0 and 3.9 Hz, m-C of p-CF3C6H4 × 4), 132.2 (d,
J = 10.4 Hz, o-C of p-CF3C6H4 × 4), 134.4 (qd, J = 32.9 and 3.0 Hz,
p-C of p-CF3C6H4 × 2), 134.4 (d, J = 76.6 Hz, ipso-C of p-CF3C6H4 ×
2). 31P{1H} NMR (162 MHz, CDCl3): δ 41.0. HRMS (FAB+): m/z
calcd for C15H12F6OPS, 385.0251 [M + H]+; found, 385.0267.
Synthesis of 9. 9 was prepared by a modified procedure described
in the literature.18b A solution of 2-bromo-1,3,5-triisopropylbenzene
(2.39 g, 8.43 mmol, 1.2 equiv) in THF (8 mL) was slowly added to a
suspension of magnesium (0.223 g, 9.18 mmol, 1.3 equiv) in THF (3
mL) at room temperature under Ar. The resulting mixture was stirred
at reflux for 3 h under Ar. The Grignard reagent prepared was
cannulated into a solution of 2,6-dibromopyridine (1.66 g, 7.00 mmol,
1.0 equiv) and NiCl2(PCy3)2 (14.5 mg, 0.021 mmol, 0.3 mol %) in
toluene (14 mL). After the resulting mixture was stirred at room
temperature for 43 h under Ar, the reaction was quenched
successively by dilution with toluene, saturated NH4Cl(aq), and
dichloromethane. Then, the mixture was extracted with dichloro-
methane. The combined organic layers were washed successively with
saturated NH4Cl(aq), water, and brine. After the solution was dried
over Na2SO4, the solvent was removed in vacuo. The resulting solid
was recrystallized from toluene/diethyl ether. The precipitate that
formed was filtered, washed with diethyl ether/ethanol, and dried
under vacuum to give the product as a white solid (1.87 g, 5.19 mmol,
74%). CAS registry number: 833453-21-7. 1H NMR (400 MHz,
Synthesis of 8OMe. A solution of Pd2(dba)3·CHCl3 (41.4 mg,
0.040 mmol, 2 mol %) and 1,1′-bis(diphenylphosphino)ferrocene
(dppf; 44.4 mg, 0.080 mmol, 4 mol %) in toluene (8 mL) was stirred
at room temperature for 15 min under Ar. To the solution were added
successively 6 (0.542 g, 2.00 mmol, 1.0 equiv), 7OMe (1.04 g, 4.42
mmol, 2.2 equiv), toluene (12 mL), and DBU (1.22 g, 8.00 mmol, 4.0
equiv). The mixture was stirred at 60 °C for 3 h under Ar. After it was
cooled to room temperature, the resulting mixture was quenched with
1 N HCl(aq) and extracted with ethyl acetate. The combined organic
layers were washed with brine and dried over Na2SO4. After the
solvent was removed in vacuo, the residue was purified by column
chromatography on silica gel (eluent: ethyl acetate/n-hexane 1/29) to
give the product as a white solid (0.827 g, 1.96 mmol, 98%). 1H NMR
(400 MHz, CDCl3): δ −0.09 (s, 6H, Si-CH3), 0.81 (s, 9H, tBu), 3.84
(s, 6H, OCH3), 4.37 (d, J = 4.8 Hz, 2H, CH2), 6.95 (dd, J = 8.8 and
2.2 Hz, 4H, m-H of p-An), 7.83 (dd, J = 12.0 and 8.6 Hz, 4H, o-H of
p-An). 13C{1H} NMR (101 MHz, CDCl3): δ − 5.8 (s, Si-CH3 × 2),
18.3 (s, quat C of tBu), 25.8 (s, CH3 of tBu × 3), 55.5 (s, OCH3 × 2),
67.5 (d, J = 72.7 Hz, CH2), 114.0 (d, J = 13.2 Hz, m-C of p-An × 4),
122.4 (d, J = 86.8 Hz, ipso-C of p-An × 2), 134.2 (d, J = 11.1 Hz, o-C
of p-An × 4), 162.5 (d, J = 2.9 Hz, p-C of p-An × 2). 31P{1H} NMR
(162 MHz, CDCl3): δ 37.8. HRMS (FAB+): m/z calcd for
C21H32O3PSSi, 423.1579 [M + H]+; found, 423.1574.
i
CDCl3): δ 1.09 (d, J = 6.9 Hz, 6H, CH3 of Pr), 1.14 (d, J = 6.8 Hz,
6H, CH3 of iPr), 1.26 (d, J = 6.9 Hz, 6H, CH3 of iPr), 2.47 (sep, J =
6.8 Hz, 2H, CH of iPr), 2.91 (sep, J = 6.9 Hz, 1H, CH of iPr), 7.05 (s,
2H, m-H of Tip), 7.24 (d, J = 7.4 Hz, 1H, PyH), 7.45 (d, J = 7.9 Hz,
1H, PyH), 7.56−7.60 (m, 1H, PyH). 13C{1H} NMR (101 MHz,
CDCl3): δ 24.0 (CH3 of iPr × 2), 24.2 (CH3 of iPr × 2), 24.3 (CH3 of
Synthesis of 8CF3. The compound was prepared by following the
synthetic procedure for 8OMe, using Pd2(dba)3·CHCl3 (0.104 g, 0.10
mmol, 2 mol %), dppf (0.111 g, 0.20 mmol, 4 mol %), toluene (20
mL), 6 (1.35 g, 5.01 mmol, 1.0 equiv), 7CF3 (2.86 g, 10.5 mmol, 2.1
equiv), toluene (30 mL), and DBU (3.04 g, 20.0 mmol, 4.0 equiv).
Isolation by column chromatography gave the product as a white solid
(2.31 g, 4.63 mmol, 92%). 1H NMR (400 MHz, CDCl3): δ −0.06 (s,
i
i
iPr × 2), 30.6 (CH of Pr × 2), 34.6 (CH of Pr × 2), 120.9 (m-C of
Tip × 2), 124.1 (5-C of Py), 126.1 (3-C of Py), 135.0 (ipso-C of Tip),
138.1 (4-C of Py), 141.6 (2-C of Py), 146.3 (o-C of Tip × 2), 149.4
(p-C of Tip), 161.5 (6-C of Py).
t
6H, Si-CH3), 0.82 (s, 9H, Bu), 4.49 (d, J = 4.6 Hz, 2H, CH2), 7.74
(dd, J = 8.3 and 2.2 Hz, 4H, o-H of p-CF3C6H4), 8.06 (dd, J = 12.2
and 8.1 Hz, 4H, m-H of p-CF3C6H4). 13C{1H} NMR (101 MHz,
CDCl3): δ −5.8 (s, Si-CH3 × 2), 18.2 (s, quat C of tBu), 25.7 (s, CH3
of tBu × 3), 67.0 (d, J = 72.0 Hz, CH2), 123.6 (q, J = 273.2 Hz, CF3 ×
2), 125.4 (dq, J = 12.1 and 3.9 Hz, m-C of p-CF3C6H4 × 4), 132.8 (d,
J = 10.3 Hz, o-C of p-CF3C6H4 × 4), 134.0 (qd, J = 32.9 and 3.0 Hz,
p-C of p-CF3C6H4 × 2), 135.1 (d, J = 78.6 Hz, ipso-C of p-CF3C6H4 ×
2). 31P{1H} NMR (162 MHz, CDCl3): δ 38.7. HRMS (FAB+): m/z
calcd for C21H26F6OPSSi, 499.1115 [M + H]+; found, 499.1133.
Synthesis of 5OMe. 8OMe (1.91 g, 4.52 mmol, 1.0 equiv) was
dissolved in a small amount of ethyl acetate. To the solution was
added a solution of acetyl chloride (5.3 mL) in ethanol (50 mL). The
mixture was stirred at room temperature for 24 h in air, neutralized
with KOH, and extracted with ethyl acetate. The combined organic
layers were washed with brine and dried over Na2SO4. After the
solvent was removed in vacuo, the residue was purified by column
chromatography on silica gel (eluent: ethyl acetate/n-hexane 1/2) to
give the product as a white solid (1.15 g, 3.73 mmol, 83%). 1H NMR
(400 MHz, CDCl3): δ 3.09−3.11 (br, 1H, OH), 3.81 (s, 6H, OCH3),
4.24 (br s, 2H, CH2), 6.95−6.96 (m, 4H, m-H of p-An), 7.72 (dd, J =
12.0 and 8.7 Hz, 4H, o-H of p-An). 13C{1H} NMR (101 MHz,
CDCl3): δ 55.4 (s, OCH3 × 2), 63.5 (d, J = 62.2 Hz, CH2), 114.4 (d,
J = 13.2 Hz, m-C of p-An × 4), 121.4 (d, J = 85.6 Hz, ipso-C of p-An
× 2), 133.4 (d, J = 11.3 Hz, o-C of p-An × 4), 162.5 (d, J = 2.9 Hz, p-
C of p-An × 2). 31P{1H} NMR (162 MHz, CDCl3): δ 41.0. HRMS
(FAB+): m/z calcd for C15H17O3PS: 308.0636 [M]+; found:
308.0636.
Synthesis of 10H. A solution of Pd(OAc)2 (18.9 mg, 0.084 mmol,
2 mol %) and dppf (140 mg, 0.25 mmol, 6 mol %) in toluene (20
mL) was stirred at room temperature for 0.5 h under Ar. To the
solution were added successively 5H (1.25 g, 5.05 mmol, 1.2 equiv), 9
(1.51 g, 4.20 mmol, 1.0 equiv), toluene (30 mL), and DBU (1.54 g,
10.1 mmol, 2.4 equiv). The mixture was stirred at reflux for 3 h under
Ar. After it was cooled to room temperature, the resulting mixture was
quenched with water and extracted with ethyl acetate. The combined
organic layers were washed with brine and dried over Na2SO4. After
the solvent was removed in vacuo, the residue was purified by column
chromatography on silica gel (eluent: ethyl acetate/n-hexane 1/29) to
give the product as a white solid (2.05 g, 4.13 mmol, 98%). 1H NMR
(400 MHz, CDCl3): δ 0.90 (d, J = 6.8 Hz, 6H, CH3 of iPr), 1.01 (d, J
= 6.8 Hz, 6H, CH3 of iPr), 1.29 (d, J = 6.9 Hz, 6H, CH3 of iPr), 2.29
i
(sep, J = 6.8 Hz, 2H, CH of Pr), 2.93 (sep, J = 6.9 Hz, 1H, CH of
iPr), 7.03 (s, 2H, m-H of Tip), 7.27−7.30 (m, 1H, ArH), 7.36−7.31
(m, 4H, ArH), 7.39−7.43 (m, 2H, ArH), 7.86−7.89 (m, 1H, ArH),
7.91−7.96 (m, 4H, ArH), 8.70−8.74 (m, 1H, ArH). 13C{1H} NMR
(101 MHz, CDCl3): δ 24.0 (s, CH3 of iPr × 4), 24.2 (s, CH3 of iPr ×
2), 30.5 (s, CH of iPr × 2), 34.4 (s, CH of iPr), 120.7 (s, m-C of Tip
× 2), 126.6 (d, J = 3.1 Hz, 5-C of Py), 126.9 (d, J = 26.0 Hz, 4-C of
Py), 128.2 (d, J = 12.7 Hz, m-C of Ph × 4), 131.4 (d, J = 3.0 Hz, p-C
of Ph × 2), 132.5−133.4 (m, ipso-C × 4 and o-C of Ph × 2), 135.7 (s,
ipso-C of Tip), 136.2 (d, J = 11.1 Hz, 3-C of Py), 146.3 (s, o-C of Tip
× 2), 149.1 (s, p-C of Tip), 155.7 (d, J = 111.0 Hz, 2-C of Py), 160.5
(d, J = 17.9 Hz, 6-C of Py). 31P{1H} NMR (162 MHz, CDCl3): δ
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36.0. HRMS (FAB+): m/z calcd for C32H37NPS, 498.2384 [M + H]+;
found, 498.2369.
(d, J = 4.5 Hz, 2-C of Py). 31P{1H} NMR (162 MHz, CDCl3): δ
−4.91.
Synthesis of 10OMe. The compound was prepared by following
the synthetic procedure for 10H, using Pd(OAc)2 (4.5 mg, 0.020
mmol, 2 mol %), dppf (33.3 mg, 0.060 mmol, 6 mol %), toluene (4
mL), 5OMe (0.370 g, 1.20 mmol, 1.2 equiv), 9 (0.360 g, 1.00 mmol,
1.0 equiv), toluene (6 mL), and DBU (0.366 g, 2.41 mmol, 2.4
equiv). Isolation by column chromatography (eluent: ethyl acetate/n-
hexane 1/9) gave the product as a white solid (0.466 g, 0.835 mmol,
83%). 1H NMR (400 MHz, CDCl3): δ 0.93 (d, J = 6.8 Hz, 6H, CH3
of iPr), 1.01 (d, J = 6.8 Hz, 6H, CH3 of iPr), 1.29 (d, J = 6.9 Hz, 6H,
CH3 of iPr), 2.30 (sep, J = 6.8 Hz, 2H, CH of iPr), 2.93 (sep, J = 6.9
Hz, 1H, CH of iPr), 3.77 (s, 6H, OCH3), 6.83−6.86 (m, 4H, m-H of
p-An), 7.03 (s, 2H, m-H of Tip), 7.25−7.28 (m, 1H, PyH), 7.83−7.88
(m, 5H, ArH), 8.67−8.71 (m, 1H, PyH). 13C{1H} NMR (101 MHz,
CDCl3): δ 24.01 (s, CH3 of iPr × 2), 24.04 (s, CH3 of iPr × 2), 24.2
(s, CH3 of iPr × 2), 30.4 (s, CH of iPr × 2), 34.4 (s, CH of iPr), 55.4
(s, OCH3 × 2), 113.8 (d, J = 13.8 Hz, m-C of p-An × 4), 120.7 (s, m-
C of Tip × 2), 124.3 (d, J = 92.3 Hz, ipso-C of p-An × 2), 126.3 (d, J
= 2.7 Hz, 5-C of Py), 126.5 (d, J = 26.0 Hz, 4-C of Py), 134.3 (d, J =
11.8 Hz, o-C of p-An × 4), 135.8 (s, ipso-C of Tip), 136.1 (d, J = 11.1
Hz, 3-C of Py), 146.3 (s, o-C of Tip × 2), 149.0 (s, p-C of Tip), 156.5
(d, J = 111.7 Hz, 2-C of Py), 160.3 (d, J = 18.2 Hz, 6-C of Py), 162.1
(d, J = 3.1 Hz, p-C of p-An × 2). 31P{1H} NMR (162 MHz, CDCl3):
δ 34.6. HRMS (FAB+): m/z calcd for C34H41NO2PS, 558.2596 [M +
H]+; found, 558.2586.
Synthesis of LOMe. The compound was prepared by following the
synthetic procedure for LH, using 10OMe (0.413 g, 0.740 mmol, 1.0
equiv) and tris(dimethylamino)phosphine (1.5 mL). Isolation by
reprecipitation gave the product as a white solid (0.2897 g, 0.551
mmol, 74%). 1H NMR (400 MHz, CDCl3): δ 1.01 (d, J = 6.8 Hz, 6H,
CH3 of iPr), 1.07 (d, J = 6.8 Hz, 6H, CH3 of iPr), 1.25 (d, J = 6.9 Hz,
6H, CH3 of iPr), 2.48 (sep, J = 6.8 Hz, 2H, CH of iPr), 2.89 (sep, J =
6.9 Hz, 1H, CH of iPr), 3.80 (s, 6H, OCH3), 6.87 (d, J = 8.5 Hz, 4H,
m-H of p-An), 6.97 (d, J = 7.7 Hz, 1H, PyH), 7.01 (s, 2H, m-H of
Tip), 7.11 (d, J = 7.7 Hz, 1H, PyH), 7.31−7.35 (m, 4H, o-H of p-An),
7.54−7.58 (m, 1H, PyH). 13C{1H} NMR (101 MHz, CDCl3): δ 24.1
(s, CH3 of iPr × 2), 24.2 (s, CH3 of iPr × 2), 24.3 (s, CH3 of iPr × 2),
i
i
30.47 (s, CH of Pr × 2), 34.53 (s, CH of Pr), 55.3 (s, OCH3 × 2),
114.3 (d, J = 8.0 Hz, m-C of p-An × 4), 120.8 (s, m-C of Tip ×2),
123.6 (s, 5-C of Py), 125.3 (d, J = 15.3 Hz, 3-C of Py), 128.0 (d, J =
8.0 Hz, ipso-C of p-An × 2), 135.3 (s, 4C of Py), 135.9 (d, J = 21.2
Hz, o-C of p-An × 4), 136.5 (d, J = 1.3 Hz, ipso-C of Tip), 146.3 (s, o-
C of Tip × 2), 148.8 (s, p-C of Tip), 160.4 (s, p-C of p-An × 2), 160.7
(d, J = 12.6 Hz, 6-C of Py), 164.7 (d, J = 4.4 Hz, 2-C of Py). 31P{1H}
NMR (162 MHz, CDCl3): δ −8.1. HRMS (FAB+): m/z calcd for
C34H41NO2P, 526.2875 [M + H]+; found, 526.2875.
Synthesis of LCF3. The compound was prepared by following the
synthetic procedure for LH, using 10CF3 (0.507 g, 0.800 mmol, 1.0
equiv) and tris(dimethylamino)phosphine (1.5 mL). Isolation by
reprecipitation gave the product as a white solid (0.349 g, 0.579
mmol, 72%). 1H NMR (400 MHz, CDCl3): δ 0.91 (d, J = 6.8 Hz, 6H,
CH3 of iPr), 0.99 (d, J = 6.8 Hz, 6H, CH3 of iPr), 1.19 (d, J = 6.9 Hz,
6H, CH3 of iPr), 2.33 (sep, J = 6.7 Hz, 2H, CH of iPr), 2.83 (sep, J =
6.8 Hz, 1H, CH of iPr), 6.95 (s, 2H, m-H of Tip), 7.09−7.14 (m, 2H,
PyH), 7.43−7.51 (m, 8H, ArH), 7.61−7.57 (m, 1H, PyH). 13C{1H}
NMR (101 MHz, CDCl3): δ 24.0 (s, CH3 of iPr × 2), 24.2 (s, CH3 of
iPr × 2), 30.6 (s, CH of iPr × 2), 34.5 (s, CH of iPr), 120.9 (s, m-C of
Tip × 2), 124.1 (q, J = 272.4 Hz, CF3 × 2), 124.9 (s, 5-C of Py),
125.4 (dq, J = 7.2 and 3.6 Hz, m-C of p-CF3C6H4 × 4), 126.9 (d, J =
24.5 Hz, 3-C of Py), 131.3 (br q, J = 32.4 Hz, p-C of p-CF3C6H4 × 2),
134.5 (d, J = 19.9 Hz, o-C of p-CF3C6H4 × 4), 135.8 (d, J = 5.4 Hz, 4-
C of Py), 136.0 (s, ipso-C of Tip), 141.2 (d, J = 14.2 Hz, ipso-C of p-
CF3C6H4 × 2), 146.2 (s, o-C of Tip × 2), 149.1 (s, p-C of Tip), 161.0
(d, J = 3.2 Hz, 2-C of Py), 161.7 (d, J = 11.1 Hz, 6-C of Py). 31P{1H}
NMR (162 MHz, CDCl3): δ −5.7. HRMS (FAB+): m/z calcd for
C34H35F6NP, 602.2411 [M + H]+; found, 602.2412.
Synthesis of 10CF3. The compound was prepared by following the
synthetic procedure for 10H, using Pd(OAc)2 (4.5 mg, 0.020 mmol, 2
mol %), dppf (33.3 mg, 0.060 mmol, 6 mol %), toluene (4 mL), 5CF3
(0.461 g, 1.20 mmol, 1.2 equiv), 9 (0.360 g, 1.00 mmol, 1.0 equiv),
toluene (6 mL), and DBU (0.366 g, 2.41 mmol, 2.4 equiv). Isolation
by column chromatography gave the product as a white solid (0.606
g, 0.957 mmol, 96%). 1H NMR (400 MHz, CDCl3): δ 0.89 (d, J = 6.8
Hz, 6H, CH3 of iPr), 1.02 (d, J = 6.8 Hz, 6H, CH3 of iPr), 1.30 (d, J =
i
i
6.9 Hz, 6H, CH3 of Pr), 2.22 (sep, J = 6.8 Hz, 2H, CH of Pr), 2.94
(sep, J = 6.9 Hz, 1H, CH of iPr), 7.04 (s, 2H, m-H of Tip), 7.34−7.36
(m, 1H, PyH), 7.61−7.62 (m, 4H, ArH), 7.93−7.98 (m, 1H, PyH),
8.06−8.11 (m, 4H, ArH), 8.68−8.72 (m, 1H, PyH). 13C{1H} NMR
(101 MHz, CDCl3): δ 23.9 (s, CH3 of iPr × 2), 24.0 (s, CH3 of iPr ×
i
i
2), 24.1 (s, CH3 of Pr × 2), 30.6 (s, CH of Pr × 2), 34.5 (s, CH of
iPr), 120.9 (s, m-C of Tip × 2), 123.7 (q, J = 273.4 Hz, CF3 × 2),
125.2 (dq, J = 12.8 and 3.8 Hz, m-C of p-CF3C6H4 × 4), 127.2 (d, J =
26.5 Hz, 4-C of Py), 127.3 (d, J = 3.3 Hz, 5-C of Py), 133.0 (d, J =
10.7 Hz, o-C of CF3C6H4 × 4), 133.5 (qd, J = 32.9 and 3.0 Hz, p-C of
CF3C6H4 × 2), 135.2 (s, ipso-C of Tip), 136.6 (d, J = 11.5 Hz, 3-C of
Py), 136.9 (d, J = 84.2, ipso-C of CF3C6H4) 146.2 (s, o-C of Tip × 2),
149.5 (s, p-C of Tip), 154.3 (d, J = 113.0 Hz, 2-C of Py), 161.1 (d, J =
18.3 Hz, 6-C of Py). 31P{1H} NMR (162 MHz, CDCl3): δ 34.3.
HRMS (FAB+): m/z calcd for C34H35F6NPS, 634.2132 [M + H]+;
found, 634.2134.
Synthesis of CHCl. A solution of Rh2(OAc)4 (0.442 g, 1.00 mmol,
1.0 equiv) and LH (0.466 g, 1.00 mmol, 1.0 equiv) in acetic acid (40
mL) was stirred at reflux for 24 h under Ar. After the solvent was
removed in vacuo, the residue was dissolved with chloroform (50 mL)
at room temperature. Saturated NH4Cl(aq) (100 mL) was added to
the solution, and the mixture was stirred at room temperature for 2 h
in air. Then, the resulting mixture was extracted with chloroform, and
the combined organic layers were washed successively with saturated
NaHCO3(aq) and brine. After the solution was dried over Na2SO4,
the solvent was removed in vacuo. The residue was purified
successively by washing with diethyl ether/n-hexane (1/2) and
recrystallizing from dichloromethane/diethyl ether, giving the product
as a green solid (0.690 g, 0.780 mmol, 78%). Single crystals suitable
for X-ray crystallographic analysis were obtained by slow diffusion of
diethyl ether into a dichloromethane solution of CHCl. 1H NMR (400
MHz, CDCl3): δ 1.04 (d, J = 6.6 Hz, 6H, CH3 of iPr), 1.31−1.33 (m,
12H, CH3 of iPr and OAc), 1.40 (d, J = 6.8 Hz, 6H, CH3 of iPr), 2.09
(s, 3H, OAc), 2.31 (sep, J = 6.5 Hz, 2H, CH of iPr), 3.09 (sep, J = 6.8
Synthesis of LH. A mixture of 10H (0.372 g, 0.747 mmol, 1.0
equiv) and tris(dimethylamino)phosphine (1.5 mL) was stirred at
140 °C for 15 h under Ar. After the volatiles were removed in vacuo,
the reactor was cooled to room temperature. The residue was purified
twice by reprecipitation using degassed chloroform and degassed
methanol under Ar, giving the product as a white solid (0.268 g, 0.576
mmol, 77%). CAS registry number: 919091-19-3. 1H NMR (400
MHz, CDCl3): δ 1.03 (d, J = 6.8 Hz, 6H, CH3 of iPr), 1.09 (d, J = 6.9
Hz, 6H, CH3 of iPr), 1.27 (d, J = 6.9 Hz, 6H, CH3 of iPr), 2.51 (sep, J
i
i
= 6.9 Hz, 2H, CH of Pr), 2.91 (sep, J = 6.9 Hz, 1H, CH of Pr),
7.00−7.03 (m, 1H, PyH), 7.03 (s, 2H, m-H of Tip), 7.15−7.17 (m,
1H, PyH), 7.32−7.35 (m, 6H, PhH), 7.38−7.45 (m, 4H, PhH),
7.57−7.61 (m, 1H, PyH). 13C{1H} NMR (101 MHz, CDCl3): δ 24.1
(s, CH3 of iPr × 2), 24.2 (s, CH3 of iPr × 2), 24.3 (s, CH3 of iPr × 2),
i
Hz, 1H, CH of Pr), 7.29−7.32 (m, 1H, ArH), 7.32−7.41 (m, 6H,
ArH), 7.47−7.51 (m, 3H, ArH), 7.58−7.63 (m, 4H, ArH), 7.84−7.88
(m, 1H, ArH). 13C{1H} NMR (101 MHz, CDCl3): δ 22.1 (s, CH3 of
iPr × 2), 23.1 (s, CH3 of OAc × 2), 23.7 (d, J = 3.6 Hz, CH3 of OAc),
24.0 (s, CH3 of iPr × 2), 26.5 (s, CH3 of iPr × 2), 31.3 (s, CH of iPr ×
2), 34.7 (s, CH of iPr), 121.8 (s, m-C of Tip × 2), 127.6 (s, ipso-C of
Tip), 128.1−128.7 (m, m-C of Ph × 4 and ipso-C of Ph × 2), 128.4
(br s, 5-C of Py), 130.06−130.14 (m, 3-C of Py), 131.5 (d, J = 2.6 Hz,
p-C of Ph × 2), 134.4 (d, J = 10.3 Hz, o-C of Ph × 4), 135.6 (d, J =
i
i
30.5 (s, CH of Pr × 2), 34.5 (s, CH of Pr), 120.8 (s, m-C of Tip ×
2), 123.9 (s, 5-C of Py), 125.7 (d, J = 15.6 Hz, 3-C of Py), 128.6 (d, J
= 7.2 Hz, m-C of Ph × 4), 129.0 (s, p-C of Ph × 2), 134.4 (d, J = 19.7
Hz, o-C of Ph × 4), 135.4 (d, J = 2.5 Hz, 4-C of Py), 136.5 (s, ipso-C
of Tip), 136.8 (d, J = 11.1 Hz, ipso-C of Ph × 2), 146.3 (s, o-C of Tip
× 2), 148.8 (s, p-C of Tip), 160.9 (d, J = 12.6 Hz, 6-C of Py), 163.6
2685
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Article
4.7 Hz, 4-C of Py), 148.6 (s, o-C of Tip × 2), 152.5 (s, p-C of Tip),
165.8−166.4 (m, 2-C and 6-C of Py), 187.0 (d, J = 4.2 Hz, CO2 of
OAc), 190.9 (s, CO2 of OAc × 2). 31P{1H} NMR (162 MHz,
CDCl3): δ 34.1 (dd, JP−Rh = 143.5 and 2.1 Hz). HRMS (FAB+): m/z
calcd for C38H4535ClNO6PRh2, 883.0783 [M]+; found, 883.0797.
Synthesis of COMeCl. The compound was prepared by following
the synthetic procedure for CHCl, using Rh2(OAc)4 (0.177 g, 0.400
mmol, 1.0 equiv), LOMe (0.219 g, 0.416 mmol, 1.0 equiv), acetic acid
(16 mL), CHCl3 (40 mL), and saturated NH4Cl(aq) (50 mL).
Isolation by recrystallization gave the product as a green solid (0.270
g, 0.286 mmol, 72%). 1H NMR (400 MHz, CDCl3): δ 1.03 (d, J = 6.7
Hz, 6H, CH3 of iPr), 1.32 (d, J = 6.4 Hz, 6H, CH3 of iPr), 1.37 (s, 6H,
(s, CH3 of CH3CN), 21.8 (s, CH3 of iPr × 2), 23.2 (s, CH3 of OAc ×
2), 23.4 (d, J = 3.4 Hz, CH3 of OAc × 2), 24.0 (s, CH3 of Pr × 2),
i
26.7 (s, CH3 of iPr × 2), 31.4 (s, CH of iPr × 2), 34.8 (s, CH of iPr),
116.4 (s, CN of CH3CN), 121.9 (s, m-C of Tip × 2), 125.6 (s, ipso-C
of Tip), 126.1 (d, J = 55.9 Hz, ipso-C of Ph × 2), 129.6 (d, J = 11.3
Hz, m-C of Ph × 4), 130.1 (br s, 5-C of Py), 131.5−131.6 (m, 3-C of
Py), 132.8 (d, J = 2.6 Hz, p-C of Ph × 2), 133.7 (d, J = 10.5 Hz, o-C
of Ph × 4), 138.2 (d, J = 5.6 Hz, 4-C of Py), 149.0 (s, o-C of Tip × 2),
153.2 (s, p-C of Tip), 163.1 (d, J = 71.9 Hz, 2-C of Py), 165.6−165.7
(m, 6-C of Py), 187.8 (d, J = 3.8 Hz, CO2 of OAc), 192.0 (s, CO2 of
OAc × 2). 31P{1H} NMR (162 MHz, CDCl3): δ 30.1 (dd, JP−Rh
=
138.6 and 3.3 Hz). LRMS (FAB+) m/z calcd for C38H45NO6PRh2,
848 [M − CH3CN − BF4]+); found, 848. Anal. Calcd for
C40H48BF4N2O6PRh2·0.5CH2Cl2·H2O: C, 46.91; H, 4.96; N, 2.70.
Found: C, 46.98; H, 4.91; N, 2.53.
i
OAc), 1.40 (d, J = 6.9 Hz, 6H, CH3 of Pr), 2.09 (s, 3H, OAc), 2.30
i
(sep, J = 6.5 Hz, 2H, CH of Pr), 3.09 (sep, J = 6.5 Hz, 1H, CH of
iPr), 3.82 (s, 6H, OCH3), 6.92 (br d, J = 7.6 Hz, 4H, m-H of p-An),
7.32−7.36 (m, 3H, ArH), 7.46−7.48 (m, 1H, ArH), 7.50−7.55 (m,
4H, ArH), 7.78−7.82 (m, 1H, ArH). 13C{1H} NMR (101 MHz,
Synthesis of [CH(MeCN)][PF6]. The compound was prepared by
following the synthetic procedure for [CH(MeCN)][BF4] using CHCl
(0.106 g, 0.120 mmol, 1.0 equiv), AgPF6 (33.3 mg, 0.132 mmol, 1.1
equiv), and acetonitrile (3 mL). Isolation by recrystallization gave the
product as a blue solid (0.121 g, 0.117 mmol, 98%). Single crystals
suitable for X-ray crystallographic analysis were obtained by slow
diffusion of diethyl ether into a dichloromethane solution of
i
CDCl3): δ 22.2 (s, CH3 of Pr × 2), 23.1 (s, CH3 of OAc × 2), 23.7
(d, J = 4.2 Hz, CH3 of OAc), 24.1 (s, CH3 of iPr × 2), 26.5 (s, CH3 of
iPr × 2), 31.3 (s, CH of iPr × 2), 34.7 (s, CH of iPr), 55.5 (s, OCH3 ×
2), 114.3 (d, J = 12.3 Hz, o-C of p-An × 4), 119.3 (d, J = 62.0 Hz,
ipso-C of p-An × 2), 121.8 (s, m-C of Tip × 2), 127.8 (s, ipso-C of
Tip), 128.1−128.2 (m, 5-C of Py), 129.8−129.9 (m, 3-C of Py),
135.3 (d, J = 5.9 Hz, 4-C of Py), 136.1 (d, J = 11.8 Hz, o-C of p-An ×
4), 148.6 (s, o-C of Tip × 2), 152.5 (s, p-C of Tip), 162.2 (d, J = 2.8
Hz, p-C of p-An × 2), 166.2−167.3 (m, 6-C of Py), 167.1 (d, J = 65.3
Hz, 2-C of Py), 186.9 (d, J = 3.8 Hz, CO2 of OAc), 190.8 (s, CO2 of
1
[CH(MeCN)][PF6]. H NMR (400 MHz, CDCl3): δ 1.06 (d, J =
6.8 Hz, 6H, CH3 of iPr), 1.31 (d, J = 6.5 Hz, 6H, CH3 of iPr), 1.38−
1.40 (m, 12H, CH3 of iPr and OAc), 2.12 (s, 3H, OAc), 2.26 (sep, J =
6.5 Hz, 2H, CH of iPr), 2.37 (s, 3H, CH3CN), 3.09 (sep, J = 6.9 Hz,
i
1H, CH of Pr), 7.36−7.42 (m, 6H, ArH), 7.48−7.51 (m, 1H, ArH),
OAc × 2). 31P{1H} NMR (162 MHz, CDCl3): δ 32.2 (dd, JP−Rh
=
7.53−7.57 (m, 4H, ArH), 7.62−7.65 (m, 2H, ArH), 7.70−7.72 (m,
1H, ArH), 8.14−8.18 (m, 1H, ArH). 13C{1H} NMR (101 MHz,
CDCl3): δ 3.1 (s, CH3 of CH3CN), 21.8 (s, CH3 of iPr × 2), 23.3 (s,
CH3 of OAc × 2), 23.5 (d, J = 2.8 Hz, CH3 of OAc), 24.0 (s, CH3 of
iPr × 2), 26.7 (s, CH3 of iPr × 2), 31.5 (s, CH of iPr × 2), 34.8 (s, CH
of iPr), 116.3 (s, CN of CH3CN), 121.9 (s, m-C of Tip × 2), 125.7 (s,
ipso-C of Tip), 126.0 (d, J = 56.1 Hz, ipso-C of Ph × 2), 129.7 (d, J =
11.4 Hz, m-C of Ph × 4), 130.0 (br s, 5-C of Py), 131.5−131.6 (m, 3-
C of Py), 132.9 (d, J = 2.6 Hz, p-C of Ph × 2), 133.7 (d, J = 10.7 Hz,
o-C of Ph × 4), 138.1 (d, J = 5.9 Hz, 4-C of Py), 149.1 (s, o-C of Tip
× 2), 153.3 (s, p-C of Tip), 163.2 (d, J = 72.1 Hz, 2-C of Py), 165.7−
165.8 (m, 6-C of Py), 187.9 (d, J = 3.6 Hz, CO2 of OAc), 192.1 (s,
CO2 of OAc × 2). 31P{1H} NMR (162 MHz, CDCl3): δ −144.4 (sep,
JP−F = 712.2 Hz, PF6), 30.1 (dd, JP−Rh = 138.6 and 3.5 Hz). HRMS
(FAB+): m/z calcd for C38H45NO6PRh2, 848.1095 [M − CH3CN −
PF6]+; found, 848.1073. Anal. Calcd for C40H48F6N2O6P2Rh2·H2O: C,
45.64; H, 4.79; N, 2.66. Found: C, 45.53; H, 4.73; N, 2.47.
142.5 and 2.7 Hz). HRMS (FAB+): m/z calcd for
C40H4935ClNO8PRh2, 943.0994 [M]+; found, 943.1003.
Synthesis of CCF3Cl. The compound was prepared by following
the synthetic procedure for CHCl, using Rh2(OAc)4 (0.177 g, 0.400
mmol, 1.0 equiv), LCF3 (0.248 g, 0.412 mmol, 1.0 equiv), acetic acid
(16 mL), CHCl3 (40 mL), and saturated NH4Cl(aq) (50 mL).
Isolation by recrystallization gave the product as a green solid (0.267
g, 0.261 mmol, 65%). 1H NMR (400 MHz, CDCl3): δ 1.05 (d, J = 6.8
Hz, 6H, CH3 of iPr), 1.34 (d, J = 6.6 Hz, 6H, CH3 of iPr), 1.36 (s, 6H,
i
OAc), 1.41 (d, J = 6.9 Hz, 6H, CH3 of Pr), 2.11 (s, 3H, OAc), 2.26
i
(sep, J = 6.7 Hz, 2H, CH of Pr), 3.11 (sep, J = 6.9 Hz, 1H, CH of
iPr), 7.32−7.35 (m, 1H, ArH), 7.38 (s, 2H, m-H of Tip), 7.57−7.59
(m, 1H, ArH), 7.68−7.70 (m, 4H, ArH), 7.78−7.83 (m, 4H, ArH),
7.85−7.90 (m, 1H, ArH). 13C{1H} NMR (101 MHz, CDCl3): δ 22.1
i
(s, CH3 of Pr × 2), 23.3 (s, CH3 of OAc × 2), 23.7 (d, J = 3.9 Hz,
CH3 of OAc), 24.1 (s, CH3 of iPr × 2), 26.6 (s, CH3 of iPr × 2), 31.5
Synthesis of [CH(MeCN)][SbF6]. The compound was prepared by
following the synthetic procedure for [CH(MeCN)][BF4] using CHCl
(0.354 g, 0.400 mmol, 1.0 equiv), AgSbF6 (0.139 g, 0.404 mmol, 1.0
equiv), and acetonitrile (10 mL). Isolation by recrystallization gave
i
i
(s, CH of Pr × 2), 34.8 (s, CH of Pr), 122.0 (s, m-C of Tip × 2),
123.6 (q, J = 272.7 Hz, CF3 × 2), 125.6 (dq, J = 11.3 and 3.7 Hz, m-C
of p-CF3C6H4 × 4), 127.0 (s, ipso-C of Tip), 129.0 (br s, 5-C of Py),
130.1−130.2 (m, 3-C of Py), 132.6 (d, J = 54.1 Hz, ipso-C of p-
CF3C6H4 × 2), 133.8 (qd, J = 33.1 and 2.3 Hz, p-C of p-CF3C6H4 ×
2), 134.9 (d, J = 10.8 Hz, o-C of p-CF3C6H4), 135.8 (d, J = 4.8 Hz, 4-
C of Py), 148.6 (s, o-C of Tip × 2), 153.1 (s, p-C of Tip), 164.5 (d, J
= 67.2 Hz, 2-C of Py), 167.3−167.4 (m, 6-C of Py), 187.7 (d, J = 3.9
Hz, CO2 of OAc), 191.3 (s, CO2 of OAc × 2). 31P{1H} NMR (162
MHz, CDCl3): δ 35.1 (br d, JP−Rh = 145.5 Hz). HRMS (FAB+): m/z
calcd for C40H4437ClF6NO6PRh2, 1022.0580 [M + H]+; found,
1022.0608.
1
the product as a blue solid (0.437 g, 0.388 mmol, 97%). H NMR
(400 MHz, CDCl3): δ 1.06 (d, J = 6.8 Hz, 6H, CH3 of iPr), 1.31 (d, J
= 6.5 Hz, 6H, CH3 of iPr), 1.38−1.40 (m, 12H, CH3 of iPr and OAc),
2.12 (s, 3H, OAc), 2.27 (sep, J = 6.6 Hz, 2H, CH of iPr), 2.35 (s, 3H,
i
CH3CN), 3.09 (sep, J = 6.9 Hz, 1H, CH of Pr), 7.36−7.42 (m, 6H,
ArH), 7.46−7.49 (m, 1H, ArH), 7.53−7.57 (m, 4H, ArH), 7.62−7.66
(m, 2H, ArH), 7.69−7.70 (m, 1H, ArH), 8.09−8.13 (m, 1H, ArH).
13C{1H} NMR (101 MHz, CDCl3): δ 3.1 (s, CH3 of CH3CN), 21.8
Synthesis of [CH(MeCN)][BF4]. A solution of CHCl (0.106 g,
0.120 mmol, 1.0 equiv) and AgBF4 (25.3 mg, 0.130 mmol, 1.1 equiv)
in acetonitrile (3 mL) was stirred at room temperature for 1 h under
Ar. The resulting mixture was filtered through a pad of Celite. The
filtrate was evaporated to dryness, and the residue was recrystallized
from dichloromethane/diethyl ether to give the product as a blue
i
(s, CH3 of Pr × 2), 23.3 (s, CH3 of OAc × 2), 23.5 (d, J = 2.8 Hz,
CH3 of OAc), 24.1 (s, CH3 of iPr × 2), 26.7 (s, CH3 of iPr × 2), 31.5
i
i
(s, CH of Pr × 2), 34.8 (s, CH of Pr), 116.1 (s, CN of CH3CN),
121.9 (s, m-C of Tip × 2), 125.7 (s, ipso-C of Tip), 126.0 (d, J = 55.9
Hz, ipso-C of Ph × 2), 129.7 (d, J = 11.4 Hz, m-C of Ph × 4), 129.9
(br s, 5-C of Py), 131.4−131.5 (m, 3-C of Py), 132.9 (d, J = 2.7 Hz, p-
C of Ph × 2), 133.7 (d, J = 10.6 Hz, o-C of Ph × 4), 137.9 (d, J = 5.9
Hz, 4-C of Py), 149.1 (s, o-C of Tip × 2), 153.3 (s, p-C of Tip), 163.3
(d, J = 72.2 Hz, 2-C of Py), 165.8−165.9 (m, 6-C of Py), 187.9 (d, J =
3.5 Hz, CO2 of OAc), 192.1 (s, CO2 of OAc × 2). 31P{1H} NMR
(162 MHz, CDCl3): δ 30.1 (dd, JP−Rh = 138.5 and 3.6 Hz). HRMS
(FAB+): m/z calcd for C38H45NO6PRh2, 848.1095 [M − CH3CN −
SbF6]+; found, 848.1076. Anal. Calcd for C40H48F6N2O6PRh2Sb·
1
solid (0.114 g, 0.117 mmol, 98%). H NMR (400 MHz, CDCl3): δ
1.06 (d, J = 6.7 Hz, 6H, CH3 of iPr), 1.30 (d, J = 6.4 Hz, 6H, CH3 of
i
iPr), 1.38−1.40 (m, 12H, CH3 of Pr and OAc), 2.12 (s, 3H, OAc),
i
2.26 (sep, J = 6.5 Hz, 2H, CH of Pr), 2.41 (s, 3H, CH3CN), 3.09
(sep, J = 6.8 Hz, 1H, CH of iPr), 7.36−7.42 (m, 6H, ArH), 7.51−7.57
(m, 5H, ArH), 7.62−7.66 (m, 2H, ArH), 7.72−7.74 (m, 1H, ArH),
8.22−8.26 (m, 1H, ArH). 13C{1H} NMR (101 MHz, CDCl3): δ 3.1
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Article
0.5CH2Cl2·H2O: C, 41.02; H, 4.34; N, 2.36. Found: C, 41.21; H,
4.21; N, 2.28.
5. 1H NMR (400 MHz, CD2Cl2): δ 1.14 (s, 6H, OAc), 6.91−6.96 (m,
4H, ArH), 7.02−7.06 (m, 2H, ArH), 7.20−7.26 (m, 6H, ArH), 7.43−
7.47 (m, 2H, ArH), 7.47−7.57 (m, 6H, ArH), 7.63−7.67 (m, 2H,
ArH), 8.14−8.19 (m, 4H, ArH), 9.51−9.53 (m, 2H, ArH). 13C{1H}
NMR (126 MHz, CD2Cl2): δ 22.9 (d, J = 2.6 Hz, CH3 of OAc × 2),
126.0 (d, J = 54.4 Hz, ipso-C of Ph × 2), 127.6 (br s, 5-C of Py × 2),
128.7 (d, J = 10.9 Hz, m-C of Ph × 4), 129.0 (d, J = 10.3 Hz, m-C of
Ph × 4), 129.4 (d, J = 50.7 Hz, ipso-C of Ph × 2), 131.1 (d, J = 2.6
Hz, p-C of Ph × 2), 131.7 (d, J = 2.7 Hz, p-C of Ph × 2), 132.7 (d, J =
9.1 Hz, o-C of Ph × 4), 134.1−134.2 (m, 3-C of Py × 2), 135.3 (d, J =
9.9 Hz, o-C of Ph × 4), 135.7 (d, J = 5.0 Hz, 4-C of Py × 2), 160.7 (d,
J = 10.4 Hz, 6-C of Py × 2), 166.4 (d, J = 71.7 Hz, 2-C of Py × 2),
189.6 (d, J = 3.0 Hz, CO2 of OAc × 2). 31P{1H} NMR (162 MHz,
CD2Cl2): δ 30.6-31.6 (m). HRMS (FAB+): m/z calcd for
C38H3435ClN2O4P2Rh2, 884.9792 [M − Cl]+; found, 884.9821.
LRMS (FAB+): m/z 885 [M − Cl]+, 850 [M − 2Cl]+. Anal. Calcd
for C38H34ClN2O4P2Rh2·H2O: C, 48.59; H, 3.86; N, 2.98. Found: C,
48.87; H, 3.74; N, 2.99.
Synthesis of [COMe(MeCN)][SbF6]. The compound was prepared
by following the synthetic procedure for [CH(MeCN)][BF4] using
COMeCl (0.142 g, 0.150 mmol, 1.0 equiv), AgSbF6 (53.5 mg, 0.156
mmol, 1.0 equiv), and acetonitrile (4 mL). Isolation by recrystalliza-
tion gave the product as a blue solid (0.175 g, 0.147 mmol, 98%). 1H
i
NMR (400 MHz, CDCl3): δ 1.05 (d, J = 6.8 Hz, 6H, CH3 of Pr),
1.31 (d, J = 6.5 Hz, 6H, CH3 of iPr), 1.39 (d, J = 6.9 Hz, 6H, CH3 of
iPr), 1.43 (s, 6H, OAc), 2.10 (s, 3H, OAc), 2.26 (sep, J = 6.5 Hz, 2H,
i
CH of Pr), 2.37 (s, 3H, CH3CN), 3.09 (sep, J = 6.9 Hz, 1H, CH of
iPr), 3.87 (s, 6H, OCH3), 7.04−7.06 (m, 4H, m-H of p-An), 7.28−
7.34 (m, 4H, o-H of p-An), 7.36 (s, 2H, m-H of Tip), 7.45−7.48 (m,
1H, PyH), 7.64−7.65 (m, 1H, PyH), 8.04−8.09 (m, 1H, PyH).
13C{1H} NMR (101 MHz, CDCl3): δ 3.1 (s, CH3 of CH3CN), 21.8
i
(s, CH3 of Pr × 2), 23.3 (s, CH3 of OAc × 2), 23.5 (d, J = 2.0 Hz,
CH3 of OAc), 24.1 (s, CH3 of iPr × 2), 26.7 (s, CH3 of iPr × 2), 31.5
(s, CH of iPr × 2), 34.8 (s, CH of iPr), 55.8 (s, OCH3 × 2), 115.4 (d,
J = 12.5 Hz, m-C of p-An × 4), 116.1−116.7 (m, ipso-C of p-An × 2
and CN of CH3CN), 121.9 (s, m-C of Tip × 2), 125.9 (s, ipso-C of
Tip), 129.6 (br s, 5-C of Py), 131.0−131.1 (m, 3-C of Py), 135.5 (d, J
= 12.1 Hz, o-C of p-An × 4), 137.6 (d, J = 5.7 Hz, 4-C of Py), 149.1
(s, o-C of Tip × 2), 153.2 (s, p-C of Tip), 163.1 (d, J = 2.7 Hz, p-C of
p-An × 2), 164.4 (d, J = 71.4 Hz, 2-C of Py), 165.5−165.6 (m, 6-C of
Py), 187.7 (d, J = 2.7 Hz, CO2 of OAc), 191.9 (s, CO2 of OAc × 2).
31P{1H} NMR (162 MHz, CDCl3): δ 28.1 (dd, JP−Rh = 136.6 and 1.8
Hz). HRMS (FAB+): m/z calcd for C40H49NO8PRh2, 908.1300 [M −
Synthesis of 11. A solution of 3 (93.9 mg, 0.102 mmol, 1.0 equiv)
and AgSbF6 (70.0 mg, 0.204 mmol, 2.0 equiv) in acetonitrile (30 mL)
was stirred at room temperature for 2 h under Ar. The resulting
mixture was filtered through a pad of Celite. Then, the filtrate was
evaporated to dryness in vacuo to give the product as an orange solid
1
(0.142 g, 0.101 mmol, 99%). H NMR (400 MHz, CD2Cl2): δ 1.43
(s, 6H, OAc), 2.37 (s, 6H, CH3CN), 6.81−6.86 (m, 4H, ArH), 7.32−
7.39 (m, 6H, ArH), 7.44−7.52 (m, 6H, ArH), 7.54−7.59 (m, 6H,
ArH), 7.62−7.66 (m, 2H, ArH), 7.92−7.97 (m, 2H, ArH), 8.53−8.54
(m, 2H, ArH). 13C{1H} NMR (101 MHz, CD2Cl2): δ 3.3 (d, J = 1.8
Hz, CH3 of CH3CN × 2), 23.2 (d, J = 1.7 Hz, CH3 of OAc × 2),
119.6 (d, J = 2.3 Hz, CN of CH3CN × 2), 125.3 (d, J = 53.4 Hz, ipso-
C of Ph × 4), 129.7 (d, J = 11.4 Hz, m-C of Ph × 4), 130.1 (br s, 5-C
of Py × 2), 130.7 (d, J = 10.9 Hz, m-C of Ph × 4), 132.0 (d, J = 9.8
Hz, o-C of Ph × 4), 132.8 (d, J = 2.8 Hz, p-C of Ph × 2), 132.9 (d, J =
2.9 Hz, p-C of Ph × 2), 133.8 (d, J = 10.1 Hz, o-C of Ph × 4), 135.7
(d, J = 7.9 Hz, 3-C of Py × 2), 138.6 (d, J = 5.4 Hz, 4-C of Py × 2),
158.5 (d, J = 9.7 Hz, 6-C of Py × 2), 163.3 (d, J = 75.0 Hz, 2-C of Py
× 2), 190.6 (d, J = 3.1 Hz, CO2 of OAc × 2). 31P{1H} NMR (162
MHz, CD2Cl2): δ 25.7−26.7 (m). HRMS (FAB+): m/z calcd for
C38H34N2O4P2Rh2, 850.0104 [M − 2CH3CN − 2SbF6]+; found,
850.0130. Anal. Calcd for C42H40F12N4O4P2Rh2Sb2: C, 35.93; H,
2.87; N, 3.99. Found: C, 35.65; H, 3.11; N, 3.83.
General Procedure for the Dehydrogenative Silylation of
Alcohols with Hydrosilanes. The dehydrogenative silylation of
alcohols with hydrosilanes was performed under Ar in a 10 mL
Schlenk flask for the reaction at room temperature or a closed system
using a 10 mL borosilicate glass screw-top vial sealed by a melamine
plastic screw cap with Teflon liner (screw-top test tube, NR-10:
Maruemu Corporation) for the reaction with heating. A Rh2 complex
(1.0 μmol, 0.1 mol %) was placed in the reaction vessel and dissolved
with a solvent (0.50 or 0.25 mL) under Ar. Then, the vessel was
charged successively with an alcohol (1.0 mmol, 1.0 equiv), the
solvent (0.50 or 0.25 mL), and a trialkylsilane (1.1 or 1.5 mmol, 1.1 or
1.5 equiv) via syringe. After the resulting mixture was stirred under
the reaction conditions indicated in each case (Tables 4 and 5), n-
tridecane (0.10 mmol, as an internal standard for GC analysis) and
the solvent (4.0−4.5 mL, for dilution) were added to the mixture in
atmospheric air. Then, the liquid part was analyzed by GC/FID to
determine the GC yield of the product. The isolation of the product
was performed by column chromatography on silica gel (eluent: ethyl
acetate/n-hexane 1/9) without adding the internal standard. All of the
reaction products are known compounds, and the CAS registry
numbers and analytical data are given in the Supporting Information.
Computational Details. DFT calculations were performed with
the Gaussian 16 (Revision C. 01) program package.29 All structures
were optimized as a singlet state in the gas phase with the ωB97XD
functional30 using the Def2SVP basis set31 for all atoms. All obtained
stationary points were confirmed by frequency calculations at the
same level of theory as geometry optimization. Single-point energy
calculations of the optimized structures were conducted with the
M06-L functional32 using the Def2TZVP basis set31 for all atoms. All
CH3CN
−
SbF6]+; found, 908.1345. Anal. Calcd for
C42H52F6N2O8PRh2Sb·CH2Cl2: C, 40.66; H, 4.28; N, 2.21. Found:
C, 40.61; H, 4.33; N, 2.19.
Synthesis of [CCF3(MeCN)][SbF6]. The compound was prepared
by following the synthetic procedure for [CH(MeCN)][BF4] using
CCF3Cl (0.204 g, 0.200 mmol, 1.0 equiv), AgSbF6 (68.8 mg, 0.200
mmol, 1.0 equiv), and acetonitrile (5 mL). Isolation by recrystalliza-
tion gave the product as a blue solid (0.246 g, 0.195 mmol, 97%). 1H
i
NMR (400 MHz, CDCl3): δ 1.06 (d, J = 6.8 Hz, 6H, CH3 of Pr),
1.32 (d, J = 6.5 Hz, 6H, CH3 of iPr), 1.39 (d, J = 6.9 Hz, 6H, CH3 of
iPr), 1.42 (s, 6H, OAc), 2.12 (s, 3H, OAc), 2.24 (sep, J = 6.4 Hz, 2H,
i
CH of Pr), 2.41 (s, 3H, CH3CN), 3.09 (sep, J = 6.9 Hz, 1H, CH of
iPr), 7.37 (s, 2H, m-H of Tip), 7.55−7.64 (m, 5H, PyH and o-H of p-
CF3C6H4), 7.73−7.75 (m, 1H, PyH), 7.81−7.83 (m, 4H, m-H of p-
CF3C6H4), 8.14−8.18 (m, 1H, PyH). 13C{1H} NMR (101 MHz,
CDCl3): δ 3.1 (s, CH3 of CH3CN), 21.7 (s, CH3 of iPr × 2), 23.3 (s,
CH3 of OAc × 2), 23.5 (d, J = 2.3 Hz, CH3 of OAc), 24.1 (s, CH3 of
iPr × 2), 26.8 (s, CH3 of iPr × 2), 31.6 (s, CH of iPr × 2), 34.9 (s, CH
i
of Pr), 116.4 (s, CN of CH3CN), 122.0 (s, m-C of Tip × 2), 123.3
(q, J = 274.1 Hz, CF3 × 2), 125.1 (s, ipso-C of Tip), 126.5 (dq, J =
11.5 and 3.7 Hz, m-C of p-CF3C6H4 × 4), 130.0−130.5 (m, ipso-C of
p-CF3C6H4 × 2 and 5-C of Py), 132.1−132.2 (m, 3-C of Py), 134.0−
135.1 (m, p-C of p-CF3C6H4 × 2 and o-C of p-CF3C6H4 × 4), 138.5
(d, J = 5.7 Hz, 4-C of Py), 149.3 (s, o-C of Tip × 2), 153.5 (s, p-C of
Tip), 161.7 (d, J = 74.1 Hz, 2-C of Py), 166.1−166.2 (m, 6-C of Py),
188.2 (d, J = 4.1 Hz, CO2 of OAc), 192.3 (s, CO2 of OAc × 2).
31P{1H} NMR (162 MHz, CDCl3): δ 30.6 (br d, JP−Rh = 141.0 Hz).
HRMS (FAB+): m/z calcd for C40H43F6NO6PRh2, 984.0837 [M −
CH3CN
−
SbF6]+; found, 984.0885. Anal. Calcd for
C42H46F12N2O6PRh2Sb: C, 39.99; H, 3.68; N, 2.22. Found: C,
39.68; H, 3.73; N, 2.07.
Synthesis of 3. 3 was prepared by a modified procedure described
in the literature.16 A solution of Rh2(OAc)4 (0.177 g, 0.400 mmol, 1.0
equiv), 1 (0.316 g, 1.20 mmol, 3.0 equiv), and lithium chloride (0.170
g, 4.01 mmol, 10 equiv) in toluene (8 mL) was stirred at reflux for 24
h under Ar. After the mixture was cooled to room temperature, the
resulting precipitate was collected by filtration. Then, the product in
the obtained solid was extracted with dichloromethane until the
washings became colorless. The organic liquid was washed with brine
and dried over Na2SO4. After the solvent was removed in vacuo, the
residue was washed with diethyl ether to give the product as a pink
solid (0.253 g, 0.275 mmol, 69%). CAS registry number: 114411-83-
2687
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Organometallics 2021, 40, 2678−2690

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pubs.acs.org/Organometallics
Article
of the calculations shown in Figure 4 and Table 1 were performed in
the gas phase, while the results shown in Table 3 were obtained by
single-point energy calculations with the SMD solvation model,33
where dichloromethane was selected as the solvent to consider the
results of the Gutmann−Beckett tests and catalytic reactions
described above. On the basis of the optimized structure, NBO
calculations were performed at the M06-L/Def2TZVP level of theory
using the NBO 7.034 program in Gaussian 16.
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.1c00314.
■
sı
Crystallographic and additional computational data,
characterization data of silyl ethers, and NMR spectra
(PDF)
Cartesian coordinates for the calculated structures
(XYZ)
(3) (a) Cheng, Q.-Q.; Deng, Y.; Lankelma, M.; Doyle, M. P.
Cycloaddition reactions of enoldiazo compounds. Chem. Soc. Rev.
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Accession Codes
CCDC 2084570−2084571 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
■
Hidetoshi Ohta − Department of Materials Science and
Biotechnology, Graduate School of Science and Engineering,
Ehime University, Matsuyama 790-8577, Japan;
orcid.org/0000-0002-8767-5689;
Email: ota.hidetoshi.mx@ehime-u.ac.jp
Minoru Hayashi − Department of Materials Science and
Biotechnology, Graduate School of Science and Engineering,
Ehime University, Matsuyama 790-8577, Japan;
orcid.org/0000-0001-9672-1758; Email: mhayashi@
ehime-u.ac.jp
Authors
Ryuhei Ohnishi − Department of Materials Science and
Biotechnology, Graduate School of Science and Engineering,
Ehime University, Matsuyama 790-8577, Japan
Shigeki Mori − Division of Material Science, Advanced
Research Support Center (ADRES), Ehime University,
Matsuyama 790-8577, Japan; orcid.org/0000-0001-
6731-2357
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.organomet.1c00314
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the Division of Applied Protein Research (APR), the
Advanced Research Support Center (ADRES), Ehime
University for the measurements of NMR spectra.
(5) (a) Biffis, A.; Basato, M.; Brichese, M.; Ronconi, L.; Tubaro, C.;
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(II) with 1,8-naphthyridine: Catalysis of reactions involving silanes. J.
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