Silica-supported tripod triarylphosphane: Application to transition metal-catalyzed C(sp3)-H borylations

Article abstract of DOI:10.1002/adsc.201301147

A silica-supported tripod triarylphosphane (Silica-3p-TPP), containing a triphenylphosphane-type core tripodally immobilized on the silica surface, allows rhodium- and iridium-catalyzed C(sp³)-H borylations of amide, urea and alkylpyridine derivatives. The ³¹P CP/MAS NMR studies for the coordination behavior of the tripod phosphane towards a rhodium complex indicate efficient site isolation of the each phosphane center, allowing independent mono-P-coordination to the metal center.

Full text of DOI:10.1002/adsc.201301147

FULL PAPERS
DOI: 10.1002/adsc.201301147
Silica-Supported Tripod Triarylphosphane: Application to
3
À
Transition Metal-Catalyzed C
A
H
U
G
E
N
N
(sp ) H Borylations
a
a
a
a
Tomohiro Iwai, Ryo Murakami, Tomoya Harada, Soichiro Kawamorita,
a,
and Masaya Sawamura *
Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan
a
E-mail: sawamura@sci.hokudai.ac.jp
Received: December 19, 2013; Revised: March 8, 2014; Published online: May 6, 2014
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201301147.
Abstract: A silica-supported tripod triarylphosphane a rhodium complex indicate efficient site isolation of
(
Silica-3p-TPP), containing a triphenylphosphane- the each phosphane center, allowing independent
type core tripodally immobilized on the silica sur- mono-P-coordination to the metal center.
3
face, allows rhodium- and iridium-catalyzed C
A
H
U
G
R
N
U
G
H borylations of amide, urea and alkylpyridine deriv-
31
atives. The P CP/MAS NMR studies for the coordi- Keywords: borylation; CÀH activation; phosphanes;
nation behavior of the tripod phosphane towards rhodium; silica-supported catalysts
Introduction
a simple Ph P-type core tripodally immobilized on
3
[4–6]
a silica surface.
The tripodal immobilization con-
Heterogenized catalysts have advantages over their strained the mobility of the phosphane molecule effi-
homogeneous counterparts in their easy separation, ciently, turning its P lone pair upwards. This resulted
efficient reusing, and applicability towards flow reac- in selective formation of a 1:1 metal-phosphane spe-
[1]
tor systems. Recent significant developments in the cies that was free from unfavorable steric repulsions
area of solid-phase chemistry have resulted in re- caused by the surface. This tripod phosphane Silica-
markable progress on selective heterogeneous cataly- 3p-TPP enabled room temperature Pd-catalyzed
sis. However, in many cases, the catalytic activity was cross-coupling reactions with unactivated chloroar-
only comparable with that of the homogeneous sys-
tems or was even decreased, owing to limited accessi-
bility of the active sites of the heterogenized cata-
[2]
lyst. In this regard, our ongoing program for devel-
oping active heterogeneous catalysts based on silica-
[
3]
supported monophosphane ligands, Silica-SMAP
[3]
and Silica-TRIP, (Figure 1) has provided novel ex-
amples of increased catalytic activity due to surface
immobilization. The silica-supported phosphanes, fea-
turing compact cage structures with a bridgehead P
atom and a cage-to-surface direct linkage through
a disiloxane bond, can produce metal/P 1:1 species
with a range of transition metal species. We have
demonstrated the usefulness of this strategy in
a number of catalytic molecular transformations.
We then started to seek for a further generalization
of this strategy, such that similar or more active and
selective catalyst systems can be produced by easier
and hence more practical ways. To achieve this goal,
recently we developed a silica-supported tripod triar-
ylphosphane (Silica-3p-TPP, Figure 1), comprising of Figure 1. Silica-supported monophosphanes.
Adv. Synth. Catal. 2014, 356, 1563 – 1570
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Tomohiro Iwai et al.
FULL PAPERS
3
enes, for which the corresponding homogeneous li- Table 1. Ligand effects in Rh-catalyzed N-Adjacent C
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(sp )
À
[a]
[
6,7]
H borylation of 1a with 2.
gands such as Ph P were not effective.
3
Herein we report that Silica-3p-TPP was also effec-
3
tive for Rh- and Ir-catalyzed borylation of C
A
H
U
G
E
N
N
(sp )ÀH
bonds, for which Silica-SMAP or Silica-TRIP were
successfully used in our previous studies. This paper
also reports the results of comparative experiments
with less symmetrical, bipod- and monopod-supported
phosphanes and with soluble triarylphosphanes. The
bipod and monopod phosphanes showed ligand per-
formances comparable with that of the tripod phos-
phane in some cases while the soluble phosphanes
were totally ineffective.
[b]
Entry
Ligand
Yield of 3a [%]
Results and Discussion
[
[
c]
c]
[d]
1
2
3
4
5
6
7
8
9
Silica-SMAP
Silica-TRIP
Silica-3p-TPP
Silica-2p-TPP
Silica-1p-TPP
Silica-1p-EtTPP
3p-TPP
0
[d,e]
3
126
Rh-Catalyzed N-Adjacent C
A
T
N
T
N
U
G
[e]
69[ (50)
e]
70
3
Transition metal-catalyzed direct C
offers a versatile strategy for obtaining alkylboronates
from easily available starting materials.
A
H
U
G
R
N
N
(sp )ÀH borylation
[c]
[d]
5
3
0
0
0
[
8–11]
Recently,
[
c]
[d]
we reported Rh-catalyzed borylations of N-adjacent
Ph P
3
3
[c]
[d]
C
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(sp )ÀH bonds of amide, urea, and aminopyridine
XPhos
SIPr
[
c]
[d]
derivatives using the cage-type supported phosphane 10
0
[
3k]
Silica-TRIP as a ligand. Silica-TRIP was a particu-
larly effective ligand, and no homogeneous ligands in-
duced this challenging transformation. Remarkably,
even Silica-SMAP, which features a cage structure
like Silica-TRIP but has different electronic and steric
natures, was not effective. On the other hand, the Rh
catalyst with the monopodally immobilized triaryl-
phosphane Silica-1p-TPP showed a trace of catalytic
activity. These results suggested the importance of
a triarylphosphane-type core structure for electronic
or steric reasons. Accordingly, we envisaged that mul-
[a]
Conditions: 1a (0.50 mmol), 2 (0.25 mmol), [Rh
AHCTUNGTREG(NNUN cod)] (0.00063 mmol, 0.5 mol% Rh), ligand ([P] 0.07–
.09 mmolg , 0.0017 mmol, 0.7 mol% P), hexane
ACHTUNGTRENNUNG( OMe)-
2
À1
0
(
1 mL), 608C, 1 h.
[
b]
1
Yields based on 2 were determined by H NMR and GC
analysis. Isolated yield is given in parenthesis. Yield in
excess of 100% indicates that HBpin formed during cata-
lytic turnover also worked as a borylating reagent
(
1
theoretical maximum yield is 200%).
:1 Rh/ligand.
Data taken from ref.
[
[
c]
d]
[3k]
[e]
A geminal bisborylation product was also detected by
H NMR and GC analysis of the crude product mixture
tipodal immobilization of Ph P-based ligands may be
an effective means for producing active catalysts for
the Rh-catalyzed N-adjacent C
1
3
(
entry 2, 9%; entry 3, 5%; entry 4, 7%).
3
A
H
U
G
R
N
U
G
Various Rh catalyst systems (0.5 mol% Rh loading)
with different ligands were prepared in situ from effective ligand, giving 3a in 70% yield (entry 4). The
Rh(OMe)(cod)] in hexane for evaluation of their ac- monopod ligand Silica-1p-TPP, which has a direct disi-
tivities toward the C
dimethylacetamide (1a, 0.50 mmol) with bis(pinacola- core and the silica surface, was far less effective (5%
[
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
ACHTUNGTRENNUNG
2
3
A
H
U
G
R
N
U
G
ACHTUNGTRENNUNG
to)diboron (2, 0.25 mmol) at 608C over 1 h. The re- yield, entry 5) than the tripod and bipod ligands. Fur-
sults are summarized in Table 1. To our delight, thermore, the other silica-supported phosphane Silica-
À1
Silica-3p-TPP ([P] 0.09 mmolg , 0.7 mol% P) in- 1p-EtTPP, which has a longer and more flexible
duced catalytic activity to afford the N-adjacent C- linker chain, was even less effective (3% yield,
3
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(sp )ÀH borylation product 3a in 69% yield (based on entry 6). No reaction occurred with the corresponding
[
12,13]
[6a]
2
, entry 3).
TRIP gave the product in a yield exceeding 100% accordance with our previous observations
126%, entry 2) due to the reaction of the by-product experiments with Ph P, bulky biarylphosphane X-
Under the same conditions, Silica- soluble ligand [4-(i-PrO)Me Si-C H ] P (3p-TPP) in
2 6 4 3
[3k]
in the
(
3
[
14]
[15]
H-Bpin. The difference in the ligand performance be- Phos, and bulky NHC ligand SIPr (entries 7–10).
tween Silica-TRIP and Silica-3p-TPP may be attribut- Thus, the catalytic function of the Rh catalyst based
ed to the steric natures around the P centers.
on Silica-TRIP could mostly be reproduced by immo-
Table 1 also shows the effect of the number of link- bilizing a non-caged triarylphosphane in tripodal or
ages. The bipod phosphane Silica-2p-TPP was also an bipodal modes. The reduced performance of the con-
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Silica-Supported Tripod Triarylphosphane
3
[a]
Table 2. N-Adjacent C
A
H
U
G
E
N
N
(sp )ÀH borylation of 1 with 2 by the Silica-3p-TPP/Rh system.
[
b]
Entry
1
Substrate
1
Temp. [8C]
Time [h]
2
Product
3
Yield [%]
[c]
1b
60
3b
116 (106)
[
c]
2
3
1c
40
80
1
3c
100 (75)
1d
24
3d
154 (117)
[
[
a]
b]
Conditions: 1 (0.50 mmol), 2 (0.25 mmol), [Rh
A
H
U
G
R
N
U
G
A
H
U
G
R
N
U
G
2
À1
0
.09 mmolg , 0.0017 mmol, 0.7 mol% P), hexane (1 mL).
1
Yields based on 2 were determined by H NMR and GC analysis. Isolated yields are given in parentheses. Yield in excess
of 100% indicates that HBpin formed during catalytic turnover also worked as a borylating reagent (theoretical maxi-
mum yield is 200%).
[
c]
The geminal bisborylation product was also detected by H NMR and GC analysis of the crude product mixture (entry 1,
3
%; entry 2, 3%).
ventional heterogeneous catalysts monopodally im- observed with the Silica-TRIP ligand, but with signifi-
mobilized via a silylene linkage confirmed it to be in- cantly reduced substrate conversion and product yield
sufficient for suppressing mobility of the P center (46% for 5a) (entry 2). To our delight, the use of the
(
vide infra).
tripod phosphane Silica-3p-TPP resulted in the im-
The catalyst system with Silica-3p-TPP allowed effi- provement of the yield of 5a up to 74% (entry 3).
cient borylation at the N-methyl groups of lactam 1b Unlike the case of the Rh-catalyzed borylation of
and cyclic urea 1c as well as at the N-adjacent methyl- N,N-dimethylacetamide 1a (Table 1), the bipod phos-
ene group of 2-piperidinopyridine 1d (Table 2).
phane Silica-2p-TPP was much worse than the tripod
phosphane in ligand performance, giving 5a in only
4
3% yield (entry 4). To our surprise, however, the
3
Ir-Catalyzed C
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(sp )ÀH Borylation of 2-Alkylpyridines
more flexible monopod phosphanes such as Silica-1p-
TPP and Silica-1p-EtTPP also promoted the boryla-
In our previous study, Silica-SMAP was the most ef- tion to afford 5a in 48% and 33% yields, respectively
3
fective ligand for the Ir-catalyzed C
A
H
U
G
R
N
N
(sp )ÀH borylation (entries 5 and 6). No reaction occurred with the solu-
[
3i]
of 2-alkylpyridines (4). However, the present study ble ligand 3p-TPP or in the absence of a phosphane
revealed that the silica-supported Ph P-based ligands ligand at 258C, confirming the importance of the im-
3
exhibited comparable or even better performances mobilization (entries 7 and 8). At higher temperature
than Silica-SMAP and Silica-TRIP. Results of the (608C), 4a underwent efficient borylation in the ab-
room-temperature borylation (258C, 12 h) of 2-ethyl- sence of any phosphane ligand, with 3a and 4a ob-
pyridine (4a, 0.90 mmol) with 2 (0.30 mmol) in the tained in 99% and 15% yields, respectively (en-
[
3i,10b]
presence of [Ir
ACHTUNGTRENNUNG( OMe) ACHTUNGTRENNUNG( cod)] (2 mol% Ir) and various try 9).
2
ligands (2–2.3 mol% P) are summarized in Table 3.
The complementary utility of the silica-supported
Under these conditions, Silica-SMAP caused com- non-cage-type phosphanes (Silica-3p-TPP, Silica-2p-
plete conversion of diboron 2, but the yield of mono- TPP and Silica-1p-TPP) with the cage-type supported
borylation product 5a was only 66% due to the for- phosphanes (Silica-SMAP and Silica-TRIP) for the Ir-
3
mation of geminal bisborylation product 6a in 21% catalyzed C
A
H
U
G
R
N
U
G
yield (entry 1). More selective formation of 5a was pyridine derivatives is summarized in Table 4. In the
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Tomohiro Iwai et al.
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3
Table 3. Ligand effects in Ir-catalyzed C
of 4a with 2.
A
H
U
G
R
N
U
G
[a]
borylation (Table 3). This is difficult to explain at
present. The catalyst prepared from the soluble phos-
phane ligand 3p-TPP was virtually inactive for the
borylation of 4b–d (entries 7, 14, 21).
Coordination with a Rh(I) Complex
To gain an insight into the ligand performance of the
silica-supported triarylphosphanes in the metal cataly-
sis, their coordinating properties were investigated for
Entry
Ligand
Yield of
Yield of
[b]
the reaction with [RhCl
tion of an excess amount of [RhCl AHCTUNGTERNNUGN( cod)] (27.6 mg,
2
ACHTUNGTNRENUNG( cod)] . Specifically, the reac-
2
[b]
5a [%]
6a [%]
À1
[
[
c]
c]
[d]
[d]
0.056 mmol) with Silica-3p-TPP ([P] 0.18 mmolg ,
400 mg, 1.5:1 Rh/P) in benzene was conducted at
room temperature. The resulting yellow solids were
collected by filtration, washed with CH Cl and Et O,
1
2
3
4
5
6
7
8
9
Silica-SMAP
Silica-TRIP
Silica-3p-TPP
Silica-2p-TPP
Silica-1p-TPP
Silica-1p-EtTPP
3p-TPP
66
46
21
0
[d]
[d]
[e]
74 (64)
13
1
1
43
48
33
0
2
2
2
and dried, giving a yield of 411 mg. Unreacted
[RhCl(cod)] was recovered from the filtrate, and its
0
A
H
U
G
R
N
N
ACHTUNGTRENNUNG
2
0
0
15
weight measured (13.8 mg). These procedures allowed
an estimation of the amount of Rh loaded onto the
[
d]
[d]
none
none (at 608C)
0
[d]
[d]
99
silica gel as a 1:1 Rh/P complex RhCl ACHUTNGRNENUG( cod)(Silica-3p-
[
a]
À1
Conditions:
2-ethylpyridine
4a
(0.90 mmol),
2
TPP), which was calculated to be 0.14 mmolg . Sur-
prisingly, this was significantly lower than that expect-
(0.30 mmol), [Ir
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(OMe)(cod)] (0.0030 mmol, 2 mol% Ir),
ACHTUNGTRENNUNG
2
À1
[16]
ligand ([P] 0.07–0.09 mmolg , 0.0068 mmol, 2.3 mol%
ed from the [P] value of the starting Silica-3p-TPP.
P), t-BuOMe (3 mL), 258C, 12 h.
Yields based on 2 were determined by H NMR analysis.
This strongly suggests that some P atoms in Silica-3p-
TPP were not used for metal coordination, in contrast
[
b]
1
The isolated yield is given in parenthesis.
[
6a]
[c]
[d]
[e]
to the case of previous Pd coordination.
[RhCl(cod)] may be more inaccessible than the steri-
cally less demanding monomeric PdCl
Dimeric
1
:1 Ir/P.
[3i]
ACHTUNGTRENNUNG
2
Data taken from ref.
Isolated 5a was contaminated with small quantity of im-
[17]
AHCTUNGTERNNUG( PhCN) .
2 2
3
1
In fact, the P CP/MAS NMR spectrum of the Rh-
modified complex showed signals for both
purities.
RhCl ACHUTNGRENNUG( cod)(Silica-3p-TPP) (31 ppm) and free phos-
reaction of 6-methyl-2-ethylpyridine (4b), Silica-TRIP phane (À5 ppm) (Figure 2 a). This observation indi-
gave the highest catalytic activity causing nearly com- cated an inhomogeneity of Silica-3p-TPP with regard
plete conversion of 4b into 2-(6-methylpyridyl)ethyl- to the environment surrounding the P center and
boronate 5b, while Silica-SMAP and the silica-sup- some of the P atoms existed in relatively buried sites
ported non-caged phosphanes gave 5b in 29–46% in the silica gel that the Rh complex cannot access.
yields (entries 1–7). The relatively low efficiency of This situation is in sharp contrast to the homogeneity
[
3a,b]
the reaction with Silica-SMAP compared to that with of Silica-SMAP.
Nevertheless, it was confirmed
Silica-TRIP may be due to less favorable coordination that the 1:1 Rh/P complex was formed selectively
of the sterically demanding 2-substituted pyridine to even when excess P was present (1:4 Rh/P) and the
the less electrophilic Ir center coordinated with the mixture was heated at 608C for 1 h (Figure 2b).
more electron-donating trialkylphosphane ligand
In contrast, the reaction of [RhCl
nopod-type silica-supported phosphane Silica-1p-TPP
(sp )ÀH bonds of (1:4 Rh/P) at 608C for 1 h afforded two overlapping
P signals at 30 and 23 ppm, which were assigned to
cage-type phosphanes and the non-cage-type phos- a 1:1 Rh/P complex RhCl(cod)(Silica-1p-TPP) and
phanes exhibited nearly the same ligand effect except a 1:2 Rh/P complex [Rh(cod)(Silica-1p-TPP) ] , along
ACHTUNGTNERNGNU( cod)] with mo-
2
(
SMAP).
3
In the borylation of secondary CACHTNUGTRENNUNG
3
1
2-propylpyridine (4c) or 2-pentylpyridine (4d), the
AHCTUNGTRENNUNG
+
AHCTUNGTRENNUNG
2
for Silica-1p-EtTPP, which was apparently inferior to with the signal for free phosphane at À5 ppm (Fig-
the other suppoorted ligands (Table 4, entries 8–13 ure 2c). The 1:2 complex was assigned on the basis of
and 15–20). These results obtained in the secondary the homogeneous reaction between [Rh
CÀH borylation are rather contradictory in that such and
the corresponding soluble
more challenging reactions were enabled even [4-(i-PrO)Me Si-C H ]PPh (1p-TPP) (1:3 Rh/P) in
through the conventional modes (bipod and monop- benzene, which gave a P NMR (CDCl ) signal for
ACHTUNGTNERUNNG( cod) ]BF
2 4
ligand
[
6a]
AHCTUNGTRENNUNG
2
6
4
2
3
1
3
od) of ligand immobilization while the superiority of bis(phosphane)-Rh complex [Rh CAHTUNGTERNNN(UG cod) ACHTUNGTRENUNNG( 1p-TPP) ]BF
2 4
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Silica-Supported Tripod Triarylphosphane
3
[a]
Table 4. Silica-supported phosphane-Ir-catalyzed CACHTUNGTRENNUNG
[b]
Entry
Substrate 4
Ligand
Temp. [8C]
Product 5
Yield [%]
[
[
[
[
[
[
[
c,d]
c,d]
c]
[e]
1
2
3
4
5
6
7
Silica-SMAP
Silica-TRIP
Silica-3p-TPP
Silica-2p-TPP
Silica-1p-TPP
Silica-1p-EtTPP
3p-TPP
70
70
70
70
70
70
70
46
[e]
[f]
94 (81)
[e]
40
30
37
29
c]
[e]
c]
[e]
c]
[e]
c]
1
[
[
d]
d]
[g]
8
9
1
1
1
1
1
Silica-SMAP
Silica-TRIP
Silica-3p-TPP
Silica-2p-TPP
Silica-1p-TPP
Silica-1p-EtTPP
3p-TPP
70
70
70
70
70
70
70
69
[g]
73[
g]
[f]
0
1
2
3
4
85[ (71)
g]
84
[g]
69[
g]
19
0
[
[
d]
d]
[g,h]
15
16
17
18
19
20
21
Silica-SMAP
Silica-TRIP
Silica-3p-TPP
Silica-2p-TPP
Silica-1p-TPP
Silica-1p-EtTPP
3p-TPP
60
60
60
60
60
60
60
106
[g,h]
89
[f]
91 (82)
83
74
46
0
[
a]
À1
Conditions: 4 (0.90 mmol), 2 (0.30 mmol), [Ir
ACHTUNGTRENNUNG( OMe) CAHTUNGTRNEUNNG( cod)] (0.0030 mmol, 2 mol% Ir), ligand ([P] 0.07–0.09 mmolg ,
2
0
.0068 mmol, 2.3 mol% P), t-BuOMe (3 mL), 15 h.
[
b]
1
Yields based on 2 were determined by H NMR analysis. Yield in excess of 100% indicates that HBpin formed during
catalytic turnover also worked as a borylating reagent (theoretical maximum yield is 200%).
Hexane (3 mL) was used as a solvent.
[
[
[
[
[
c]
d]
e]
f]
1
:1 Ir/P.
Geminal diborylation products (6) were produced in entries 1, 2, 3, 4, 5, 6 (15%, 4%, 11%, 10%, 12% and 3% yields).
Isolated 5b–d were contaminated with small quantity of impurities.
g]
2
C
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(sp )ÀH borylation products were produced in entries 8, 9, 10, 11, 12, 13, 15, 16 (20%, 3%, 8%, 13%, 13%, 2%, 11%
and 11% yields).
Data taken from ref.
[
h]
[3i]
[18]
at 26.4 ppm.
The bidentate P-coordination by the kylpyridine derivatives. The Silica-3p-TPP comple-
monopod silica-supported phosphane indicated that mented the performance of the reported cage-type
the P center of the monopod phosphane Silica-1p- silica-supported phosphanes (Silica-SMAP and Silica-
TPP was flexible and the monopodal immobilization TRIP) in these reactions, for which homogeneous li-
3
1
via a dimethylsilylene (-SiMe -) linker was not an ef- gands were not effective. The P CP/MAS NMR
2
fective method for inhibiting bidentate P-coordination analysis for coordination behavior of the Silica-3p-
[
19,20]
on the silica gel surface.
TPP ligand towards an Rh complex indicated efficient
site isolation of each phosphane center, regardless of
the inhomogeneity of the surface structure of the
tripod phosphane, allowing independent coordination
to the metal center to form mono(phosphane)-metal
Conclusions
The silica-supported tripod triarylphosphane Silica- complexes (1:1 M/P). The tripod immobilization of li-
p-TPP, which features a Ph P-type core tripodally gands is a simple and useful strategy to construct
3
3
immobilized on the silica surface, allows Rh- and Ir- highly active heterogeneous catalyst.
3
catalyzed C
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(sp )ÀH borylations of amide, urea and al-
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31
Figure 2. P CP/MAS NMR spectra obtained from (a) [RhCl
A
H
U
G
R
N
U
G
A
H
U
G
R
N
U
G
2
2
Silica-3p-TPP (1:4 Rh/P) and (c) [RhCl(cod)] and Silica-3p-TPP (1:4 Rh/P). Asterisks (*) indicate spinning side bands.
AHCTUNGTRENNUNG
2
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Silica-Supported Tripod Triarylphosphane
Experimental Section
References
3
[1] For selected books, see: a) New Avenues to Efficient
Typical Procedure for the N-Adjacent C
A
H
U
G
R
N
U
G
Chemical Synthesis: Emerging Technologies, (Eds.:
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Borylation Catalyzed by the Silica-3p-TPP-Rh
System (Table 1, Entry 3)
In
0
a
nitrogen-filled glove box, Silica-3p-TPP ([P]
.09 mmolg , 18.8 mg, 0.0017 mmol P, 0.7 mol% P), and
bis(pinacolato)diboron (2, 63.5 mg, 0.25 mmol), were placed
in a 10-mL glass tube containing a magnetic stirring bar. A
À1
solution of [Rh
.5 mol% Rh) in hexane (1 mL) and N,N-dimethylacetamide
1a, 43.6 mg, 0.50 mmol) were added. The tube was sealed
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
(OMe)
A
H
U
G
R
N
U
G
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0
(
with a screw cap and was removed from the glove box. The
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moved under reduced pressure. An internal standard
(
1,1,2,2-tetrachloroethane) was added to determine the yield
1
of the product by H NMR and GC analysis (69%). The
crude material was then purified by silica gel chromatogra-
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a white solid; yield: 26.6 mg (0.12 mmol, 50%).
3
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3
Typical Procedure for the C
A
H
U
G
R
N
U
G
Alkylpyridines Catalyzed by the Silica-3p-TPP-Ir
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2
007, 119, 5477; Angew. Chem. Int. Ed. 2007, 46, 5381;
In
0
a
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.09 mmolg , 75.0 mg, 0.0068 mmol P, 2.3 mol% P), bis(pi-
nacolato)diboron (2, 76.2 mg, 0.30 mmol), and anhydrous,
degassed t-BuOMe (1 mL) were placed in a 10-mL glass
tube containing a magnetic stirring bar. A solution of
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À1
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[ ACHTUNGTRENNUNG( OMe) ACHTUNGTRENNUNG( cod)] (2.0 mg, 0.0030 mmol, 2 mol% Ir) in t-
Ir
BuOMe (2 mL) and 2-ethylpyridine (4a, 96.4 mg,
.90 mmol) were added. The tube was sealed with a screw
2
5
Org. Chem. 2010, 75, 3855; e) K. Yamazaki, S. Kawa-
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0
cap and was removed from the glove box. The mixture was
stirred at 258C for 12 h, and filtered through a glass pipette
equipped with a cotton filter. Solvent was removed under
reduced pressure. An internal standard (1,1,2,2-tetrachloro-
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3
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1
H NMR (74%). The crude material was then purified by
Kugelrohr distillation (1 mmHg, 65–708C) to give 5a as col-
orless oil; yield: 44.7 mg (0.19 mmol, 64%). Isolated 5a was
contaminated with a small quantity of impurities.
2
Iwai, M. Sawamura, J. Am. Chem. Soc. 2013, 135, 2947;
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Supporting Information
Experimental details and characterization data for new com-
pounds are available as Supporting Information.
[3g]
also ref.
[
[
4] Corriu and co-workers developed organic-inorganic
hybrid materials incorporating free tripodal phos-
phanes bearing tris(trialkoxysilyl)aryl groups via a sol-
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Acknowledgements
This work was supported by Grants-in-Aid for Scientific Re-
search on Innovative Areas “Organic Synthesis Based on Re-
action Integration” from MEXT, and by CREST and ACT-C
from JST. T. I. is grateful for the Grant-in-Aid for Young Sci-
entists (B).
3
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[10d,e]
[
[
[
12] The Silica-3p-TPP-Rh and Silica-3p-TPP-Ir catalysts
were readily removed from the products by Celite fil-
tration, but attempts to reuse the catalysts were unsuc-
cessful.
1
0.11246/cl.131161.
7] The three-fold cross-linked polystyrene-Ph P hybrid
3
[
13] The three-fold cross-linked polystyrene-Ph P hybrid
3
PS-Ph P, which had a monocoordinating property, was
3
[7]
(
ref. ) did not produce an active catalyst under other-
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[
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[
8] I. A. Mkhalid, J. H. Barnard, T. B. Marder, J. M.
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[
15] N. Marion, S. P. Nolan, Acc. Chem. Res. 2008, 41, 1440.
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[
9] Selected references on transition metal-catalyzed pri-
3
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ACHTUNGTNERNUNG( acac)(CO)
2
1
instead of [RhCl(cod)] increased metal coordination
AHCTUNGTRENNUNG
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À1
0
.16 mmolg . See the Supporting Information for de-
2
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[
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1
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3
3
[
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1570
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Adv. Synth. Catal. 2014, 356, 1563 – 1570