New class of pincer ligands: Phosphite esters of 1,3-di(hydroxy)arenes in cyclopalladation reaction [5]

Full text of DOI:10.1007/s11172-005-0134-6

Russian Chemical Bulletin, International Edition, Vol. 53, No. 10, pp. 2355—2356, October, 2004
2355
✾
New class of pincer ligands:
phosphite esters of 1,3ꢀdi(hydroxy)arenes in cyclopalladation reaction
ꢀ
V. I. Sokolov and L. A. Bulygina
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
2
8 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5085. Eꢀmail: sokol@ineos.ac.ru
The cyclometallation reaction consists in the replaceꢀ
product isolated after repeated reprecipitations was no
higher than 90%, whereas chromatography afforded phosꢀ
phate and metallic Pd. Under conventional conditions,
cyclopalladation with palladium chloride or acetate gave
rise to a mixture, with products of P →P oxidation
predominating.
ment of the hydrogen atom with a metal atom proceeding
with retention of coordination of the metal atom by an
electronꢀdonating atom in the same molecule. Ligands
containing two electronꢀdonating atoms in positions suitꢀ
able for the simultaneous closure of two fiveꢀ or sixꢀmemꢀ
bered rings are referred to as pincer ligands. Cycloꢀ
metallation of pincer ligands is well studied for arenes
containing benzylꢀtype metaꢀsubstituents with the sulfide
sulfur atom, the R P or R N groups as ligating centers.
III
V
Alkyl phosphite ester of 5ꢀRꢀsubstituted resorcinol 2b
(phloroglucinol, R = OH) behaves analogously.
2
2
Palladium, platinum, and rhodium are most often used of
1
all metals (see the review ).
Recently, Pd complexes with 2,5ꢀdi(dialkylphosphinoꢀ
2
methyl)ferrocenes as pincer ligands have been described.
In the present study, we report the synthesis of a new class
of pincer ligands for cyclometallation, viz., bis(phosphite)
3
,4
esters of 1,3ꢀdihydroxyarenes. Earlier, we have develꢀ
oped a new synthetic method, viz., cyclopalladation of
alkyl aryl phosphites, which makes it possible to perform
this reaction with phenols belonging to an important and
abundant class of compounds and provides a way of modiꢀ
fying natural phenols. We studied cyclopalladation of reꢀ
sorcinol bis(alkoxyphosphite) 2a under various conditions
and found that the reaction with the cationic reagent,
viz., bis(acetonitrile)palladium fluoroborate, involves seꢀ
lective palladation at position 2 to form pincer cycloꢀ
palladated fluoroborate 3a. We failed to isolate the anaꢀ
lytically pure product even after its transformation into
more stable chloride 4a, because the process was compliꢀ
cated by competitive hydrolysis and oxidation of the phosꢀ
R = H (1a—4a), OH (1b, 3b), OP(OEt) (2b, 4b)
2
phorus atom. The 3 P and H NMR spectra of comꢀ
pound 4a confirm the pincer structure of the product.
Both phosphorus atoms are equivalent, the signal for the
P atom (δ(P) 142) being typical of cyclopalladated phenol
1
1
To summarize, we constructed a new class of ligands
for pincer metallation, in which phosphite P atoms are
III
involved in coordination bonds. Cyclopalladated phosꢀ
phites have attracted recent attention as active catalysts
4
phosphites. The signals for the aryl protons appear as one
doublet and one triplet with an intensity ratio of 2 : 1. In
5
for the Heck reaction. However, a few pincer ligands
1
the H NMR spectrum of compound 4a, splitting of the
described earlier contain a phosphinite fragment rather
than a phosphite group (i.e., they contain one P—O bond
and two P—C bonds).
signal on the phosphorus atom is observed only for the
H(5) proton, but not for H(4) and H(6) due to collinearꢀ
3
The H and 31P NMR spectra were recorded on Bruker
1
ity of the C—H(5) and O—P bonds ( J
= 8.28 Hz,
H,H
5
JH,P = 1.92 Hz). The maximum purity of the "pincer"
WPꢀ200 SY and Bruker 400 HX instruments in CDCl3 and
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2253—2254, October, 2004.
066ꢀ5285/04/5310ꢀ2355 © 2004 Springer Science+Business Media, Inc.
1

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Russ.Chem.Bull., Int.Ed., Vol. 53, No. 10, October, 2004
Sokolov and Bulygina
CD CN. The solvents were purified according to standard proꢀ
cedures.
discarded. The filtrate was concentrated to dryness. Comꢀ
3
1
pound 4a was obtained in 55% yield. H NMR (CDC1 ), δ: 1.4
3
3
ꢀ[(Diethoxyphosphino)oxy]phenyl diethyl phosphite (2a).
(t, 12 H, (CH CH O) P, J = 7.0 Hz); 4.32—4.41 (m, 8 H,
3
2
2
A mixture of resorcinol (0.51 g, 4.88 mmol) and (EtO) PNEt
(CH CH O) P); 6.67 (d, 2 H, C H , J = 8.0 Hz); 7.12 (t, 1 H,
2
2
3
2
2
6
3
(
1.88 g, 9.76 mmol) in anhydrous acetonitrile (2 mL) was heated
C H , J = 8.0 Hz). 1,3,5ꢀTris[(diethoxyphosphino)oxy]phenylꢀ
6 3
1
on an oil bath in an argon stream at 100 °C for 5 h and then at
the same temperature in vacuo for 5 h. Compound 2a was obꢀ
tained in a yield of 1.58 g (98%). Found (%): C, 48.17; H, 6.70;
P, 17.45. C H P O . Calculated (%): C, 48.00; H, 6.91;
P, 17.69. H NMR (CD CN), δ: 1.33 (t, 12 H, (CH CH O) P,
J = 7.2 Hz); 4.02—4.11 (m, 8 H, (CH CH O) P); 6.83 (d, 3 H,
C H , J = 8.1 Hz); 7.27 (t, 1 H, C H , J = 8.1 Hz). P NMR
(
ethyl phosphite (2b) was synthesized analogously. Found (%):
C, 44.35; H, 6.91; P, 19.05. C H P O . Calculated (%):
palladium chloride (4b): was prepared analogously. H NMR
(CDC1 ), δ: (t, 18 H, (CH CH O) P, J = 7.1 Hz); 4.35 (m,
3
3
2
2
12 H, (CH CH O) P); 6.25 (s, 2 H, C H ).
3
2
2
6
3
1
4
24
2
6
1
We thank A. S. Peregudov for recording the NMR
spectra.
This study was financially supported by the Russian
Foundation for Basic Research (Project Nos 99ꢀ03ꢀ32978
and 02ꢀ03ꢀ33355).
3
3
2
2
3
2
2
31
6
3
6
3
CD CN), δ: 134. 3,5ꢀBisꢀ[(diethoxyphosphino)oxy]phenyl diꢀ
3
1
8
33
3
9
1
C, 44.43; H, 6,84; P, 19.11. H NMR (CDC1 ), δ: 1.27 (t, 18 H,
(
6
3
References
CH CH O) P, J = 7.2 Hz); 3.98 (m, 12 H, (CH CH O) P);
3 2 2 3 2 2
31
.50 (s, 3 H, C H ). P NMR (CDC1 ), δ: 134.
6 3 3
1
,3ꢀBis[(diethoxyphosphino)oxy]phenylpalladium chloride
1
. M. Albrecht and G. van Koten, Angew. Chem., Int. Ed. Engl.,
2001, 40, 3750.
(
4a). A suspension of PdCl (0.2268 g, 1.28 mmol) in anhydrous
acetonitrile (35 mL) was refluxed in an argon stream until PdCl2
was completely dissolved. Then a solution of AgBF4 (0.5 g,
.57 mmol) in anhydrous CH CN (12 mL) was added. The
3
reaction solution was refluxed for 2 h and cooled to room temꢀ
perature. The precipitate of AgCl that formed was filtered off.
The filtrate was added to compound 2a (0.45 g, 1.28 mmol) and
the mixture was refluxed under argon for 4 h. Then the precipiꢀ
tate was filtered off, the solvent was removed, and solid white
product 3a was obtained in a yield of 1.0 g. Compound 3a was
2
2. A. A. Koridze, A. S. Kuklin, A. M. Sheloumov, M. V.
Kondrashov, F. M. Dolgushin, A. S. Peregudov, and P. V.
Petrovskii, Izv. Akad. Nauk, Ser. Khim., 2003, 2607 [Russ.
Chem. Bull., Int. Ed., 2003, 52, 2754].
3
4
5
2
. V. I. Sokolov and L. A. Bulygina, Izv. Akad. Nauk, Ser. Khim.,
998, 1268 [Russ. Chem. Bull., 1998, 47, 1235 (Engl. Transl.)].
1
. V. I. Sokolov, L. A. Bulygina, O. Ya. Borbulevich, and O. V.
Shishkin, J. Organometal. Chem., 1999, 582, 246.
. F. Miyazaki, K. Yamaguchi, and S. Shibasaki, J. Tetrahedron
Lett.,1999, 40, 7379.
dissolved in anhydrous CH Cl , a saturated aqueous NaCl soluꢀ
2
2
tion was added, and the mixture was stirred for 24 h. The orꢀ
ganic layer was separated, dried over K CO , and concentrated
2
3
to a small volume, after which hexane was added. The solid
white precipitate that immediately formed was filtered off and
Received June 17, 2004;
in revised form September 29, 2004