Carboranyl phosphites: The electronic effect in the Suzuki-Miyaura reaction

Article abstract of DOI:10.1007/s11172-010-0292-z

Isomeric carborane-containing phosphite ligands possessing different electronic properties have been synthesized. Their use in the Pd-catalyzed Suzuki-Miyaura reaction involving activated aryl bromides showed that phosphite with 9-o-carborane substituent

Full text of DOI:10.1007/s11172-010-0292-z

Russian Chemical Bulletin, International Edition, Vol. 59, No. 8, pp. 1665—1667, August, 2010
1665
Carboranyl phosphites: the electronic effect in the Suzuki—Miyaura reaction
S. E. Lyubimov, T. A. Verbitskaya, E. G. Rys, P. V. Petrovskii, M. M. Il´in, V. A. Davankov, and V. N. Kalinin
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
2
8 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 6471. Eꢀmail: vkalin@ineos.ac.ru
Isomeric carboraneꢀcontaining phosphite ligands possessing different electronic properties
have been synthesized. Their use in the Pdꢀcatalyzed Suzuki—Miyaura reaction involving
activated aryl bromides showed that phosphite with 9ꢀoꢀcarborane substituent has proved more
efficient, with carboranyl phosphite having 1ꢀmꢀcarborane fragment being more efficient in the
reactions with nonactivated aryl bromides.
Key words: carboranes, crossꢀcoupling, phenylboronic acid, aryl halides, phosphites.
Activity of a metal complex catalyst considerably
carborane fragment on the phosphorus atom. In this work,
we report on the results of testing isomeric phosphite
ligands containing 9ꢀoꢀcarborane and 1ꢀmꢀcarborane
groups in the Suzuki—Miyaura reaction, which is a conꢀ
venient method for the creation of carbon—carbon bonds,
in particular, in biaryls widely used for the preparation
of biologically active drugs, as well as in polymeric mateꢀ
depends on the steric and electronic structure of the
ligands used. Bulky ligands can have a positive effect on
the catalytic process.1 Usually, it is more difficult to
evaluate electronic effect of the ligand, which also affects
—4
5
—7
properties of the catalyst,
since introduction of elecꢀ
tronꢀdonating or electronꢀwithdrawing substituents into
it is frequently accompanied by the change in the ligand
shape and size.
1
4,15
rials.
Dicarbaꢀclosoꢀdodecaboranes, existing in the orthoꢀ,
metaꢀ, and paraꢀisomeric forms, are bulky spherical strucꢀ
tures, whose electronic properties change within a wide
range depending on position of boron atoms in the
Results and Discussion
The reaction of phosphorylating agent 1 with 1ꢀhydroxyꢀ
mꢀcarborane 2 and 9ꢀhydroxyꢀoꢀcarborane 3 afforded new
carboraneꢀcontaining phosphites 4 and 5 (Scheme 1).
Compounds 4 and 5 are white powders stable on proꢀ
longed standing.
8
carborane framework. In this case, spatial structure of
the isomers remains virtually unchanged, that makes them
attractive objects for the study of electronic effects of
9
—13
ligands. Recently,
we have reported on the synthesis
and use in metal complex catalysis of a series of monoꢀ
and bidentate phosphiteꢀtype ligands containing isomeric
carborane substituents. It was shown that catalytic charꢀ
acteristics of the ligands can be optimized by varying a
Their efficiency as ligands was studied in the Pdꢀcataꢀ
lyzed crossꢀcoupling reactions of phenylboronic acid 6
with aryl bromides 7—12, leading to the formation of
biaryls 13—18 (Scheme 2, Table 1).
Scheme 1
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1620—1622, August, 2010.
066ꢀ5285/10/5908ꢀ1665 © 2010 Springer Science+Business Media, Inc.
1

1
666
Russ.Chem.Bull., Int.Ed., Vol. 59, No. 8, August, 2010
Lyubimov et al.
Table 1. PdꢀCatalyzed crossꢀcoupling of phenylboronic
acid with aryl bromides*
Experimental
31
1
31
1
P and H NMR spectra ( P, 121.49 MHz; H, 300.13 MHz)
were recorded on an Avance 400 spectrometer, 11B NMR spectra
128.4 MHz), on an Avance 300 spectrometer, relatively to 85%
aqueous H PO in D O, Me Si, and BF •OEt , respectively
Entry
Ligand
Substrate Conversion of ArBr (%)
(
1
2
3
4
5
6
7
8
9
4
5
4
5
4
5
4
5
4
5
4
5
7
7
60
45
62
35
75
97
43
60
97
99
55
80
3
4
2
4
3
2
(
for solutions in CDCl ). Elemental analysis was performed in
3
8
8
9
9
the Laboratory of Microanalysis of the A. N. Nesmeyanov
Institute of Organoelement Compounds, Russian Academy of
Sciences.
All the reactions were carried out under dry argon in
anhydrous solvents. Bis(2,6ꢀdimethylphenyl) chlorophosphite
10
10
11
11
12
12
16
17
(
(
1), 1ꢀhydroxyꢀmꢀcarborane (2), 9ꢀhydroxyꢀoꢀcarborane
18
3) were obtained according to the known procedures. Phenylꢀ
1
1
1
0
1
2
boronic acid 6, aryl bromides 7—12, and palladium acetate were
commercially available from Aldrich.
Synthesis of ligands 4 and 5. Hydroxycarborane 2 or 3
(
160 mg, 1 mmol) and triethylamine (0.135 mL, 1 mmol) were
*
1.0 equiv. of ArBr, 1.4 equiv. of PhB(OH) , 3 equiv.
2
added to a solution of phosphorylating agent 1 (309 mg, 1 mmol)
in benzene (20 mL) with stirring. The reaction mixture was
heated to boiling point and cooled to ~20 °C. A precipitate of
of K PO , 5 mL of toluene, 0.01 equiv. of Pd(OAc) ,
0
3
4
2
.02 equiv. of L, 100 °C, 4 h.
HNEt Cl was filtered off. A solution obtained was subjected to
3
Scheme 2
flashꢀchromatography on silica gel (benzene). The solvent was
evaporated in vacuo to obtain ligand 4 or 5 as an oil solidified on
standing.
Pd(OAc)2 (1 mol.%)/2L
Bis(2,6ꢀdimethylphenyl)ꢀmꢀcarboranꢀ1ꢀyl phosphite (4). The
yield was 380 mg (88%). Found (%): C, 49.80; H, 6.92; P, 7.02.
C H B O P. Calculated (%): C, 49.99; H, 6.78; P, 7.16.
1
8
29 10
3
1
H NMR, δ: 7.12—6.91 (m, 6 H, Ar); 2.72 (s, 1 H, CH carb.);
.30 (s, 12 H, 4 Me); 3.74—1.02 (m, 10 H, BH). P{ H} NMR,
δ: 141.8. B{H} NMR, δ: –4.89 (s, 1 B); –11.67 (s, 1 B); –12.93
Ar = Ph (7, 13), 4ꢀMeC H (8, 14), 4ꢀMeC(O)C H (9, 15),
6
4
6
4
31
1
2
11
4
ꢀFC H (10, 16), 3,5ꢀ(CF ) C H (11, 17),
(12, 18)
6
4
3 2
6
3
(
s, 2 B); –14.70 (s, 1 B); –15.98 (m, 5 B).
Bis(2,6ꢀdimethylphenyl)ꢀoꢀcarboranꢀ9ꢀyl phosphite (5). The
yield was 302 mg (70%). Found (%): C, 50.12; H, 6.85; P, 7.06.
The reaction outcome depends on the donorꢀacceptor
C H B O P. Calculated (%): C, 49.99; H, 6.78; P, 7.16.
1
8
29 10
3
characteristics of the ligands. In the reaction with
involvement of bromobenzene 7 and 4ꢀbromotoluene 8,
the conversion in the presence of phosphite 4 containing
1
H NMR, δ: 7.02—6.85 (m, 6 H, Ar); 3.25 (s, 2 H, CH carb.);
.29 (s, 12 H, 4 Me); 3.11—0.98 (m, 9 H, BH). P{ H} NMR,
31
1
2
δ: 141.8 (q, JP,B = 16.7 Hz). 11B{H} NMR, δ: 12.14 (s, 1 B);
–3.80 (s, 1 В); –10.51 (s, 2 В); –13.45—19.50 (m, 6 В).
Suzuki—Miyaura crossꢀcoupling reaction. Palladium diacetate
(2 mg, 0.01 mmol), ligand 4 or 5 (8 mg, 0.02 mmol), and toluene
8
electronꢀwithdrawing 1ꢀmꢀcarboranyl group (δ = +0.21)
i
was higher than in the presence of ligand 5 bearing elecꢀ
8
tronꢀdonating 9ꢀoꢀcarborane fragment (δ = –0.23)
i
(
5 mL) were placed into a Schlenk vessel, followed by addition
(
Table 1, entries 2, 4). In the reactions with involvement
of aryl bromides containing electronꢀwithdrawing
substituents, i.e., 4ꢀbromoacetophenone (9), 1ꢀbromoꢀ
ꢀfluorobenzene (10), and 1ꢀbromoꢀ3,5ꢀbis(trifluoroꢀ
methyl)benzene (11), as well as 2ꢀbromotoluene (12),
another situation was observed (see Table 1, entries 5—12).
In these cases, when ligand 5 with a donating 9ꢀoꢀcarꢀ
borane group was used, higher conversion was observed
than upon use of carboranyl phosphite 4.
of the corresponding haloarene 7—12 (1 mmol), phenylboronic
acid (6) (171 mg, 1.4 mmol), and K PO (637 mg, 3 mmol). The
3
4
mixture was stirred for 4 h at 100 °C, cooled to 20 °C, diluted
4
with hexane (10 mL), filtered through a layer of silica gel, and
1
analyzed by GC and H NMR spectroscopy after isolation of the
reaction products by column chromatography.
References
In conclusion, we have synthesized isomeric carboranyl
phosphite ligands containing electronꢀdonating 9ꢀoꢀcarꢀ
borane and electronꢀwithdrawing 1ꢀmꢀcarborane group.
The use of these ligands in the Pdꢀcatalyzed crossꢀ
coupling reaction of phenylboronic acid with activated
aryl bromides showed higher efficiency of phosphite with
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in revised form March 31, 2010