Niew bidentate diphosphine ligands on the basis of diphenyl ether

Article abstract of DOI:10.1023/A:1013808220187

A new procedure has been developed for the preparation of new bidentane diphosphine ligands, 2,2′-diphosphinodiphenyl ethers containing various substituents on the phosphorus, which differ in both electron-donor and steric parameters.

Full text of DOI:10.1023/A:1013808220187

Russian Journal of Organic Chemistry, Vol. 37, No. 11, 2001, pp. 1583 1586. Translated from Zhurnal Organicheskoi Khimii, Vol. 37, No. 11, 2001,
pp. 1657 1660.
Original Russian Text Copyright
2001 by Veits, Mutsenek, Neganova, Beletskaya.
Niew Bidentate Diphosphine Ligands
on the Basis of Diphenyl Ether
Yu. A. Veits, E. V. Mutsenek, E. G. Neganova, and I. P. Beletskaya
Faculty of Chemistry, Moscow State University, Vorob’evy gory, Moscow, 119899 Russia
Received January 31, 2001
Abstract A new procedure has been developed for the preparation of new bidentane diphosphine ligands,
2,2 -diphosphinodiphenyl ethers containing various substituents on the phosphorus, which differ in both
electron-donor and steric parameters.
In the recent years, bidentate P,P- and P,N-ligands
derived from o,o -disubstituted aromatic and hetero-
aromatic compounds (such as biphenyl, binaphthyl,
ferrocene, and diphenyl ether and its analogs linked
through positions 6 and 6 by a heteroatom bridge),
have become of specific importance [1 3] for metal-
complex catalysis. These ligands are capable of
forming complexes with transition metals, which
possess a rigid skeleton having 4 5 units between
the donor atoms. As compared with monophosphine
ligands, as well as with those based on , -diphos-
phinoalkanes, the above complexes turned out to be
more effective; they ensured mild conditions and
high conversion and regio- and stereoselectivity of
a number of reactions, e.g., hydroformylation [4] and
hydrocyanation of alkenes [5, 6], allylic alkylation [7]
and arylation of amines [8, 9], etc. Sagighi et al. [8]
studied cross coupling of aniline with 4-bromo-N,N-
dimethylaniline and found that replacement of the
diphenylphosphino groups in the catalyst, 2,2 -bis-
(diarylphosphino)diphenyl ether complex with Pd(0),
by di(o-tolyl)phosphino groups increases the conver-
sion from 30 to 80%. The effect of steric properties
of such ligands on the catalytic activity and selectivity
of metal complexes in the arylation of amines was
discussed in [10 12]. It was presumed [10] that
complexes with sterically hindered ligands favor the
oxidative addition stage due to ready dissociation of
one of the phosphine centers; however, in the reac-
tions with fatty amines -hydride reduction of allyl
bromide is considerably accelerated [11].
known [13] ligand with diphenylphosphino groups,
we obtained its analogs having secondary or tertiary
radicals or both these on the phosphorus, as well as
petafluorophenyl group which is a stronger electron
acceptor than phenyl. Comparison of the catalytic
activities of palladium complexes with ligands in
which both steric and donor parameters of the phos-
phorus atom are varied could allow us to estimate the
role of key stages (such as oxidative addition of
aromatic substrate and, especially, the subsequent
nucleophile replacement in the palladium complex)
in cross coupling reactions.
2,2 -Diphosphinodiphenyl ethers IIa IIg were syn-
thesized by a modified procedure [13]. Diphenyl ether
was treated with butyllithium in the presence of
N,N,N ,N -tetramethylethylenediamine (TMEDA), and
the resulting dilithium derivative I was treated with
appropriate chlorophosphine (Scheme 1). Our proce-
dure differed from that reported in [13] by the follow-
ing. First of all, we used 2 equiv of butyllithium
instead of 2.2 equiv of more difficultly accessible
s-butyllithium. Second, the phosphorylation of salt I
was also effected with 2 rather than 2.2 equiv (as in
[13]) of halophosphine. Under optimal conditions, the
yields of products II were almost quantitative (accord-
ing to the 31P NMR data), except for ligand IIe (72%,
31P NMR); moreover, our procedure ensured easier
isolation of the target products. The yields of the
isolated products were 55 75% because of their ready
oxidation in solution. However, often there is no need
of isolating pure ligands, for palladium complexes can
be prepared from crude products II.
The lack of sufficient data on the effect of steric
parameters of complexes on their catalytic activity
prompted us to synthesize a number of new bidentate
ligands on the basis of diphenyl ether. Unlike the
The reaction of butyllithium with TMEDA is ac-
companied by a strong exothermic effect (the mixture
warms up to 50 55 C) and formation of a colorless
1070-4280/01/3711-1583$25.00 2001 MAIK Nauka/Interperiodica

1584
VEITS et al.
Scheme 1.
R1 = R2 = Ph (a), cyclo-C6H12 (b), i-Pr (c), t-Bu (d), C6F5 (e); R1 = i-Pr, R2 = t-Bu (f); R1 = t-Bu, R2 = Ph (g).
precipitate. The latter dissolves completely by the
end of addition of TMEDA. After cooling to room
temperature, 1 equiv of diphenyl ether was added,
and the mixture was stirred for 16 24 h at 20 C.
Salt I thus obtained was treated with 2 equiv of
appropriate chlorophosphine in hexane. The reactions
with dialkylchlorophosphines having secondary and
especially tertiary alkyl radicals required elevated
temperature because of reduced electrophilicity and
(what is more important) increased steric hindrance
at the phosphorus atom. For example, diphenylchloro-
phosphine reacts with salt I at 20 C in several hours,
whereas reactions with branched dialkylchlorophos-
phines occurred at 60 C (reaction time 2 4 h); the
conversion of diisopropylchlorophosphine at 20 C
in 24 h was 70%. The most electrophilic bromobis-
(pentafluorophenyl)phosphine reacts with salt I very
vigorously even at room temperature; the reaction is
accompanied by strong heat evolution and profound
tarring, presumably as a result of reaction of butyl-
lithium with fluorine atoms in the pentafluorophenyl
groups. By carrying out the reaction at low tempera-
ture ( 50 C) we succeeded in obtaining ligand IIe
in a good yield.
R1R2PPh. When R1
signals from diastereoisomeric ligands are broadened.
The signal width is about 5 ppm; it is consistent with
the difference between the 31P chemical shifts of the
R2 (compounds IIf and IIg),
meso-form and racemate (
0.5 to 10 ppm) [12].
The spectrum of IIe containsPan anomalously upfield
multiplet signal at
fluorine nuclei.
56.2 ppm due to coupling with
P
The synthesis of palladium complexes with ligands
IIa IIg and study of their catalytic activity in the
amination of aryl halides are now in progress.
EXPERIMENTAL
The 31P NMR spectra were obtained on Varian FT-
80A (32.2 MHz) and Varian VXR-400 (161.9 MHz)
instruments using 85% H3PO4 as external reference.
1
The H NMR spectra were measured on Varian VXR-
400 spectrometer relative to tetramethylsilane as
internal reference. All operations were performed
under dry argon. The solvents were purified by stand-
ard procedures. Chlorodiisopropylphosphine [14], di-
tert-butylchlorophosphine [14], dicyclohexylchloro-
phosphine [14], chlorodiphenylphosphine [15], bromo-
bis(pentafluorophenyl)phosphine [16], tert-butyl-
(chloro)phenylphosphine [17], and tert-butyl(chloro)-
isopropylphosphine [18] were synthesized by known
methods.
General procedure for preparation of ligands II.
A two-necked flask equipped with a dropping funnel
and a reflux condenser was filled with argon and
charged with 4.5 ml of a 2.64 N solution of butyl-
lithium (11.8 mmol). N,N,N ,N -Tetramethylethylene-
diamine, 1.36 g (11.8 mmol), was added dropwise
with stirring. The mixture spontaneously warmed up
to 50 60 C, and a colorless material separated. The
mixture became homogeneous by the end of addition
of TMEDA. It was cooled to room temperature, and
a solution of 1 g (5.9 mmol) of diphenyl ether in 3 ml
of tetrahydrofuran was slowly added. The mixture
was stirred for 16 h at 20 C. Further procedures were
different for each particular ligand.
When treating the reaction mixtures and isolating
products II, thoroughly degassed solvents and distilled
water should be used; otherwise, ligands II undergo
fast oxidation in solution. The isolation procedures
and solvents for crystallization of the products were
different for particular compounds II (see Experi-
mental). Pure ligands II are colorless or light pink
solid, amorphous, or finely crystalline substances
(except for IIf). They are readily soluble in methylene
chloride and chloroform and poorly soluble in ethanol.
Solid ligands II can be stored for a long time under
argon. The melting points of compounds II increase in
going from tert-alkyl- to secondary alkyl-substituted
derivatives and with rise in the number of phenyl
groups on the phosphorus.
Ligands II (R1 = R2 = Alk) show in the 31P NMR
spectra narrow singlets in the range from 20 to
+12 ppm, which are typical of tertiary phosphines like
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 11 2001

NIEW BIDENTATE DIPHOSPHINE LIGANDS
1585
2,2 -Bis(diphenylphosphino)diphenyl ether (IIa).
A solution of 2.6 g (11.8 mmol) of chlorodiphenyl-
phosphine in 3.5 ml of petroleum ether was added
dropwise with stirring to a mixture containing
5.9 mmol of dilithium salt I (see above). After
10 min, a colorless material began to separate from
the solution. The mixture was stirred for 24 h at 20 C,
10 ml of degassed distilled water and 10 ml of
methylene chloride were added, and the organic phase
was separated, dried over sodium sulfate, and the
solvent was removed under reduced pressure. After
1 h, the residue crystallized. It was dissolved in 10 ml
of acetone at 40 45 C, the solution was cooled to
room temperature, and the colorless precipitate was
filtered off through a glass filter and dried under
reduced pressure. Yield 2.4 g (78%), mp 183 184 C.
1.4 g (58%), mp 81.5 82 C. 1H NMR spectrum
(CDCl3), , ppm: 1.08 d.d (24H, J = 7.2, 14.0 Hz),
2.28 2.36 m (4H), 1.84 d.m (4H), 6.73 d.d (2H, J =
2.9, 8.1 Hz), 7.08 d.t (2H, J = 0.7, 8.0 Hz), 7.24 d.t
(2H, J = 0.7, 8.2 Hz), 7.50 d.t (2H, J = 0.6, 6.8 Hz).
31P NMR spectrum (CH2Cl2):
1.48 ppm. Found,
P
%: C 72.29; H 9.12. C24H36OP2. Calculated, %:
C 71.64; H 8.96.
2,2 -Bis(di-tert-butylphosphino)diphenyl ether
(IId). Following the above procedure, from 2.12 g
(11.8 mmol) of di-tert-butylchlorophosphine and
a solution of salt I (2.5 h at 60 C) we obtained 1.9 g
(72%) of ligand IId as a yellow noncrystallizable oily
1
substance, bp 170 175 C (1 mm). H NMR spectrum
(CDCl3), , ppm: 1.10 1.22 m (36H); the aromatic
region of the spectrum was almost identical to that
of ligand IIc. 31P NMR spectrum (CH2Cl2):
11.23 ppm. Found, %: C 72.95; H 9.57. C28H44OP2P.
Calculated, %: C 73.36; H 9.61.
31P NMR spectrum (CH2Cl2):
lished data [13]: mp 175 176 PC;
(in CHCl3).
18.0 ppm. Pub-
16.4 ppm
P
2,2 -Bis(dicyclohexylphosphino)diphenyl ether
(IIb). A solution of 2.7 g (11.8 mmol) of chlorodi-
cyclohexylphosphine in 3 ml of petroleum ether was
added dropwise with stirring at 10 C to a solution of
salt I. The mixture was heated for 4 h at 60 C, cooled,
and treated as described above for ligand IIa. A light
brown oily substance was isolated. It was treated
with 5 ml of methanol, and the mixture was kept for
a long time at 50 C for crystallization. The product
was quickly filtered off through a glass filter, washed
with acetone and petroleum ether cooled to 50 C
(2 ml each), and dried under reduced pressure. Yield
1.9 g (59%), mp 159 160 C. 1H NMR spectrum
(CDCl3), , ppm: 1.07 1.26 m (24H), 1.54 1.73 m
(16H), 1.84 d.m (4H), 6.73 d.d (2H, J = 2.9, 8.1 Hz),
7.07 d.t (2H, J = 0.7, 7.3 Hz), 7.25 d.t (2H, J = 1.1,
2,2 -Bis[bis(pentafluorophenyl)phosphino]di-
phenyl ether (IIe). A solution of 2.6 g (5.88 mmol)
of bromobis(pentafluorophenyl)phosphine in 3 ml of
petroleum ether was added dropwise at 50 C to
a mixture containing 2.94 mmol of salt I. When the
entire amount of bromobis(pentafluorophenyl)phos-
phine was added, the mixture was allowed to slowly
warm up to room temperature and was stirred for
1.5 h. We isolated 1.85 g (72%) of ligand IIe as
an oily substance which crystallized on addition of
3 ml of acetone and cooling to 60 C. mp 151 154 C
(decomp.). 31P NMR spectrum (CH2Cl2):
56.2 ppm. Found, %: C 48.72; H 1.09. C36H8F20OP2P.
Calculated, %: C 48.11; H 0.89.
2,2 -Bis[tert-butyl(isopropyl)phosphino]diphenyl
ether (IIf). Following the procedure described above
for ligand IId, from 1.96 g (11.8 mmol) of tert-butyl-
(chloro)isopropylphosphine (4 h at 60 C) we obtained
a light yellow mobile oily substance. It was subjected
to vacuum distillation to isolate 1.5 g (65%) of ligand
IIf, bp 162 168 C (1 mm) as a light yellow viscous
oil which did not crystallize on prolonged storage at
20 C. 1H NMR spectrum (CDCl3), , ppm: 0.98
1.38 m (32H); the aromatic region of the spectrum
was almost identical to that of IId. 31P NMR spec-
8.9 Hz), 7.52 d.t (2H, J = 1.1, 7.0 Hz). 31P NMR spe-
ctrum (CH2Cl2):
7.06 ppm. Found, %: C 76.22;
H 9.11. C36H52OP2P. Calculated, %: C 76.87; H 9.25.
2,2 -Bis(diisopropylphosphino)diphenyl ether
(IIc). A solution of 1.83 g (11.8 mmol) of chlorodi-
isopropylphosphine in 2 ml of petroleum ether was
added to a solution of salt I on cooling with water.
The mixture was heated for 40 min at 55 C and
cooled to room temperature, 10 ml of distilled water
and 10 ml of methylene chloride were added, and
the organic phase was separated and dried over
magnesium sulfate. The solvent was removed under
reduced pressure to leave an oily residue which was
treated with 3 ml of methanol and 0.3 ml of ether. The
mixture was kept for a long time at 10 to 15 C,
and the colorless precipitate was filtered off, washed
on a filter with methanol and acetone (2 ml) cooled
to 20 C, and dried under reduced pressure. Yield
trum (CH2Cl2):
1.90 6.90 ppm. Found, %:
P
C 71.97; H 9.15. C26H40OP2. Calculated, %: C 72.59;
H 9.30.
2,2 -Bis[tert-butyl(phenyl)phosphino]diphenyl
ether (IIg). In a similar way, by reaction of 2.6 g
(11.8 mmol) of tert-butyl(chloro)phenylphosphine
with salt I on heating for 4 h at 55 C and appropriate
treatment we obtained a brown oily substance which
crystallized on addition of 3 ml of acetone and cooling
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 11 2001

1586
VEITS et al.
to 0 C. The colorless precipitate of ligand IIg was
7. Kranenburg, M., Kamer, P.C.J., and van Leeu-
wen, P.W.N.M., Eur. J. Inorg. Chem., 1998,
pp. 25 27.
filtered off, washed on a filter with 1 ml of acetone,
1
and dried. Yield 1.55 g (54%), mp 134 135 C. H
NMR spectrum (CDCl3), , ppm: 1.23 1.26 d (9H,
J = 12.5 Hz), 6.47 d.d (2H, J = 2.7, 8.0 Hz), 6.83 d.t
(2H, J = 0.7, 7.6 Hz), 7.03 d.t (2H, J = 0.5, 7.4 Hz),
7.15 d.t (2H, J = 0.8, 7.5 Hz), 7.28 m (6H), 7.50 m
8. Sagighi, J.P., Harris, M.C., and Buchwald, S.L.,
Tetrahedron Lett., 1998, vol. 39, pp. 5327 5330.
9. Hamann, B.C. and Hartwig, J.F., J. Am. Chem. Soc.,
1998, vol. 120, pp. 3694 3703.
(4H). 31P NMR spectrum (CH2Cl2):
0.2 1.3 ppm.
P
10. Hamann, B.C. and Hartwig, J.F., J. Am. Chem. Soc.,
Found, %: C 77.53; H 7.32. C32N36OP2. Calculated,
%: C 77.11; H 7.23.
1998, vol. 120, pp. 7369 7370.
11. Wolfe, J.P., Wagaw, S., and Buchwald, S.L., J. Am.
Chem. Soc., 1996, vol. 118, pp. 7215 7216.
REFERENCES
12. Driver, M.S. and Hartwig, J.F., J. Am. Chem. Soc.,
1. Wolfe, J.P. and Buchwald, S.L., J. Org. Chem., 2000,
1996, vol. 118, pp. 7217 7218.
vol. 65, pp. 1144 1157.
13. Kranenburg, M., van der Burgt, Y.E.M., Ka-
mer, P.C.J., and van Leeuwen, P.W.N.M., Organo-
metallics, 1995, vol. 14, pp. 3081 3089.
2. Van der Veen, L.A., Keeven, P.H., Schoemaker, G.C.,
Reek, J.N.H., Kamer, P.C.J., van Leeuwen, P.W.N.M.,
Lutz, M., and Spek, A.L., Organometallics, 2000,
vol. 19, pp. 872 883.
14. Voskuil, W. and Arens, J.F., Recl. Trav. Chim.
Pays Bas, 1963, vol. 82, pp. 302 310.
3. Bei, X., Uno, T., Norris, J., Turner, H.W., Wein-
berg, W.H., Guram, A.S., and Petersen, J.L., Organo-
metallics, 1999, vol. 18, pp. 1840 1853.
15. Kabachnik, M.I., Medved’, T.Ya., Polikar-
pov, Yu.M., and Yudina, K.S., Izv. Akad. Nauk
SSSR, Ser. Khim., 1961, no. 11, pp. 2029 2031.
4. Meessen, P., Vogt, D., and Keim, W., J. Organomet.
Chem., 1998, vol. 551, pp. 165 170.
16. Magnelli, D.D., Tesi, G., Lowe, J.U., and Mequis-
tion, W.E., Inorg. Chem., 1966, vol. 5, pp. 457 461.
5. Kranenburg, M., Kamer, P.C.J., van Leeu-
wen, P.W.N.M., Vogt, D., and Keim, W., J. Chem.
Soc., Chem. Commun., 1995, pp. 2177 2178.
17. Hoffmann, H. and Schellenbeck, P., Chem. Ber.,
1966, vol. 99, pp. 1134 1142.
6. Goertz, W., Kamer, P.C.J., van Leeuwen, P.W.N.M.,
and Vogt, D., J. Chem. Soc., Chem. Commun., 1997,
pp. 1521 1522.
18. Foss, V.L., Solodenko, V.A., Veits, Yu.A., and
Lutsenko, I.F., Zh. Obshch. Khim., 1979, vol. 49,
no. 8, pp. 1724 1729.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 11 2001