Facile syntheses of 1,8-bis(diphenylphosphino)anthracene and 1,8-bis(dimethylamino)anthracene by nucleophilic substitution of 1,8-difluoroanthracene

Article abstract of DOI:10.1055/s-1998-1627

1,8-Bis(diphenylphosphino)anthracene (1) was prepared in a three-step synthesis in 51 % overall yield starting from 1,8-dichloro-9,10-anthraquinone (8). Compound 8 was converted by chlorine-fluorine exchange and reduction with zinc into 1,8-difluoroanthracene (7) from which 1 was obtained by reaction with potassium diphenylphosphide. The conversion of 7 with lithium dimethylamide to 1,8-bis(dimethylamino)anthracene (10) clearly showed that in the case of 7 direct nucleophilic displacement (addition-elimination mechanism) dominates over aryne formation (elimination-addition mechanism). Single crystal X-ray structure analyses are reported for 1 and 10.

Full text of DOI:10.1055/s-1998-1627

March 1998
SYNLETT
301
Facile Syntheses of 1,8-Bis(diphenylphosphino)anthracene and 1,8-Bis(dimethylamino)anthracene by
1
Nucleophilic Substitution of 1,8-Difluoroanthracene
Matthias W. Haenel*, Stephan Oevers, Joachim Bruckmann, Jörg Kuhnigk and Carl Krüger
Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der Ruhr, Germany
Fax +49-208-306-2980; E-mail Haenel@mpi-muelheim.mpg.de
Received 11 December 1997
Abstract: 1,8-Bis(diphenylphosphino)anthracene (1) was prepared in a
three-step synthesis in 51 % overall yield starting from 1,8-dichloro-
9,10-anthraquinone (8). Compound 8 was converted by chlorine-
fluorine exchange and reduction with zinc into 1,8-difluoroanthracene
step synthesis. Following a literature procedure 8 was converted by
reaction with cesium fluoride in dimethyl sulfoxide under anhydrous
conditions into 1,8-difluoro-9,10-anthraquinone (9) [m.p. = 228°C
7
7
(DSC, lit. m.p. = 228-229°C), 71 %]. Reduction of 9 with zinc powder
in aqueous ammonia (75°C, 4 h) followed by an acidic treatment
(aqueous HCl, 2-propanol, reflux, 3 h) yielded 7 [yellow needles, m.p. =
(7) from which
1
was obtained by reaction with potassium
diphenylphosphide. The conversion of 7 with lithium dimethylamide to
1,8-bis(dimethylamino)anthracene (10) clearly showed that in the case
of 7 direct nucleophilic displacement (addition-elimination mechanism)
dominates over aryne formation (elimination-addition mechanism).
Single crystal X-ray structure analyses are reported for 1 and 10.
8,9
142°C (DSC), 84%]. As anticipated compound 7 proved to be highly
reactive for nucleophilic displacement of the fluoro substituents by
alkali metal phosphides. Reaction with two equivalents potassium
10
diphenylphosphide (Ph PK, dioxane/THF 5:1 reflux, 3 h) converted 7
2
in excellent yield to the diphosphine 1 [yellow needles, m.p. = 234°C
2
(lit. m.p. = 233-235°C), 86 %]. For the three-step synthesis starting
from commercial 8 the overall yield of the diphosphine 1 was 51 %.
Previously
we
reported
the
synthesis
of
the
1,8-
bis(diphenylphosphino)anthracene (1) and its reaction with nickel or
palladium dichloride forming cyclometallated and hence extremely
2
stable complexes 2 and 3. As a result of the cyclometallation at the
anthracene C-9 atom, the diphosphine 1 is acting as a tridentate PCP
ligand in these complexes. Whereas we first had failed to prepare the
diphosphine 1 from either 1,8-dichloro- or 1,8-dibromoanthracene, 1
was obtained in moderate yield of 33 % by reaction of potassium
anthracenedisulfonate (4) with two equivalents potassium
diphenylphosphide (Ph PK) in diethylene glycol diethyl ether
2
2,3
(DEGDEE) under harsh reaction conditions (180°C, 20 h).
The
disulfonate 4 needed for this conversion was prepared by zinc reduction
4
of potassium 9,10-anthraquinone-1,8-disulfonate. However, since the
latter compound apparently is not commercially available anymore, it
was desirable to search for a new and improved synthesis of the
diphosphine 1.
The fact that 7 is converted efficiently into 1 without forming 1,7- or
2,7-substituted isomers rules out that the elimination-addition
mechanism (aryne mechanism) is involved. Hence it must be assumed
that the direct nucleophilic displacement 7 → 1 proceeds by the
11
addition-elimination mechanism.
However, in the case of the
nucleophilic substitution of 1-fluoronaphthalene by different alkali
metal amides (amide, diethylamide, piperidide) the corresponding 1-
and 2-naphthylamines were formed in varying ratios which were
11,12
interpreted by a competition of both mechanisms.
This gave us
reason to attempt the nucleophilic substitution of 7 by alkali metal
amides in order to see whether the direct nucleophilic displacement of
the fluoro substituents is restricted to special nucleophiles such as alkali
metal phosphides or represents a reaction of more general use. Treating
7 with 12 equivalents of lithium dimethylamide [(CH ) NLi, prepared
from dimethylamine and n-butyllithium] in dioxane/THF (1:1)
3 2
In a recent paper we described the reaction of 4,5-difluoroacridine (5)
10
with
potassium
diphenylphosphide
(Ph PK)
giving
4,5-
2
yielded the unknown 1,8-bis(dimethylamino)anthracene (10, red
5
bis(diphenylphosphino)acridine (6) in 79 % yield. This prompted us to
attempt the synthesis of 1 from 1,8-difluoroanthracene (7) and to
investigate the use of fluoro substituted polycyclic aromatic
hydrocarbons in nucleophilic aromatic substitution reactions with alkali
13,14
crystals, m.p. = 128°C, 65 %).
As analysed by GC and GC-MS, the
crude product of the reaction contained two isomers of the major
component 10. Their yields with respect to 10 amounted to < 5 % and <
0.5 %. Considering the relative ratios, it is tempting to assume that the
two isomers possibly are 1,7- and 2,7-bis(dimethylamino)anthracene
formed by a small contribution of the elimination-addition mechanism.
However, no matter what their structures are, direct nucleophilic
displacement also is found to be the major pathway in the reaction of 7
and lithium dimethylamide. The observation, that the direct nucleophilic
displacement of fluoro substituents apparently is more favourable for
anthracene than for naphthalene compounds, can be interpreted by
considering the relative energies of the negatively charged σ-complexes
which are formed as intermediates by the addition-elimination
6
metal phosphides and other nucleophiles.
The unknown 1,8-difluoroanthracene (7) was prepared from the
commercially available 1,8-dichloro-9,10-anthraquinone (8) in a two-

302
LETTERS
SYNLETT
mechanism. Delocalisation of the negative charge over an additional
condensed aromatic ring is expected to further lower the energy of the
σ-complex.
currently underway to further explore the coordination chemistry of the
PCP ligand 1 and to investigate the properties of 10 as NCN-ligand in
corresponding transition metal complexes.
15
When 7 was treated with only two equivalents of lithium dimethylamide
10
under the same conditions as in the previous reaction, a product
In conclusion, we have shown that fluoro-substituted polycyclic arenes
and heteroarenes such as 7 and 5 can serve as synthetically useful
intermediates which are capable of direct nucleophilic displacement
mixture was obtained which according to GC and GC-MS analyses
contained 50 % of a dimethylaminofluoroanthracene besides 36 % educt
7 and traces of 10. Based on the structural characterisation of 10 it can
be anticipated that the compound obviously is 1-dimethylamino-8-
fluoroanthracene (11). Using compound 11 the preparation of 1-amino-
8-phosphinoanthracenes such as 12 is feasible by reaction with
potassium diphenylphosphide. This will enable us to extend our
investigations of the PCP ligand 1 to NCN and NCP ligands of types 10
and 12.
5,17
reactions by various strong nucleophiles.
Acknowledgement: We thank the Fonds der Chemischen Industrie,
Frankfurt am Main, for financial support. For the NMR spectra we
thank Dr. R. Mynott, Mrs. B. Gabor and Mr. R. Ettl, MPI für
Kohlenforschung.
References and Notes
5
(1) Phosphine ligands, 8; for part 7 see ref. ; this work is part of the
diploma thesis of S. Oevers, University of Düsseldorf, 1997.
(2) Haenel, M. W.; Jakubik, D.; Krüger, C.; Betz, P. Chem. Ber. 1991,
124, 333.
(3) For nucleophilic substitution of alkali metal arenesulfonates by
alkali metal phosphides see: Zorn, H.; Schindlbaur, H.; Hagen, H.
Chem. Ber. 1965, 98, 2431.
In the context of our interest to use the diphosphine 1 and the diamine
10 as potential polydentate ligands in transition metal compounds, the
molecular structures of both compounds were determined by single
16
(4) Lampe, B. Ber Dtsch. Chem. Ges. 1909, 42, 1413.
crystal X-ray structure analyses (Figure 1).
(5) Hillebrand, S.; Bartkowska, B.; Bruckmann, J.; Krüger, C.;
Haenel, M. W. Tetrahedron Lett. 1998, 39, in press.
(6) For recent examples describing the conversion of fluoro-
substituted benzene derivatives to phosphines see: McFarlane, H.
C. E.; McFarlane, W. Polyhedron 1988, 7, 1875. - McFarlane, H.
C. E.; McFarlane, W.; Muir, A. S. Polyhedron 1990, 9, 1757. -
Herd, O.; Langhans, K. P.; Stelzer, O.; Weferling, N.; Sheldrick,
W. S. Angew. Chem. 1993, 105, 1097; Angew. Chem. Int. Ed.
Engl. 1993, 32, 1058. - Herd, O.; Heßler, A.; Langhans, K. P.;
Stelzer, O.; Sheldrick, W. S. Weferling, N. J. Organomet. Chem.
1994, 475, 99. - Bitterer, F.; Herd, O.; Heßler, A.; Kühnel, M.;
Rettig, K.; K. P.; Stelzer, O.; Sheldrick, W. S.; Nagel, S.; Rösch,
N. Inorg. Chem. 1996, 35, 4103. - Allen, J. V.; Dawson, G. J.;
Frost, C. G.; Williams, J. M. J.; Coote, S. J. Tetrahedron, 1994,
50, 799. - Peer, M; de Jong, J. C.; Kiefer, M.; Langer, T.; Rieck,
H.; Schell, H.; Sennhenn, P.; Sprinz, J.; Steinhagen, H.; Wiese B.;
Helmchen, G. Tetrahedron, 1996, 52, 7547. In almost all these
examples the benzene ring was activated by an additional electron
withdrawing substituent in ortho or para position.
(7) Echegoyen, L.; Hafez, Y.; Lawson, R. C.; de Mendoza, J.; Tores,
T. J. Org. Chem. 1993, 58, 2009.
(8) Procedure analogous to the reduction of
8
to 1,8-
dichloroanthracene: House, H. O.; Ghali, N. I.; Haack, J. L.;
VanDerveer, D. J. Org. Chem. 1980, 45, 1807.
-1
As expected both ligands contain essentially planar anthracene
skeletons. The bond distances between the heteroatoms and the
substituted anthracene carbon atoms are 1.826(3) Å (P1-C1) and
1.813(3) Å (P2-C11) in 1 and 1.422(2) Å (N1-C1) and 1.424(2) Å (N2-
C11) in 10. The valence angles at the substituted anthracene carbon
atoms show small deformations which cause the substituents to be
inclined somewhat towards each other [1: C2-C1-P1: 122.8(2)°; C14-
C1-P1: 118.2(2)°; C10-C11-P2: 122.9(2)°; C12-C11-P2: 117.3(2)°; 10:
C2-C1-N1: 123.4(2)°; C14-C1-N1: 117.1(1)°; C10-C11-N2: 122.9(2)°;
C12-C11-P2: 117.7(1)°]. This results in distances P1···P2 of 4.925(5) Å
for 1 and N1···N2 of 4.960(3) Å for 10. The phosphorus atoms of 1 and
the nitrogen atoms of 10 show tetrahedral geometries. Experiments are
(9) 7: C H F (214.21 g mol ): calcd. 78.50 % C, 3.76 % H, 17.74
14
8 2
% F; found: 78.56 % C, 3.70 % H, 17.63 % F. - MS (EI, 70 eV):
m/z (%) = 214 (100, M ), 213 (6), 194 (6), 107 (20), 94 (10).-
NMR (282 MHz, CDCl , external standard CFCl ): δ = −122.4
ppm (s). - H NMR (200 MHz, CDCl3): δ = 8.94 (s, 1 H, 9-H),
+
19
F
3
3
F
1
8.47 (s, 1 H, 10-H); 7.79, 7.42, 7.15 [ABCX spin system with X =
19
3
4
3
4
F, J = 8.6 Hz, J
= 1.1 Hz, J = 7.5 Hz, J
BX
= 11.0 Hz, each 2 H for 4-,5-H (A), 3-,6-H (B), 2-,7-H (C)]. -
= 5.4 Hz,
13
AB
AC
BC
3
J
C
CX
1
NMR (50 MHz, CDCl ): δ (multiplicity with respect to
coupling with F) = 159.0 (s, d with J = 256.2 Hz, C-1,-8),
133.1 (s, d with J = 5.2 Hz, C-4a,-10a), 126.0 (d, t with J
3.5 Hz, C-10), 125.4 (d, d with J = 8.2 Hz, C-3,-6), 124.0 (d, d
J
,
3
CH
19
1
CF
3
4
=
CF
CF
3
CF

March 1998
SYNLETT
303
4
2
with J = 4.9 Hz, C-4,-5), 122.8 (s, d with J = 17.5 Hz, C-
(15) A recent ab initio computational study of the C H F + F– gas
6 5
CF
CF
3
2
8a,-9a), 113.2 (d, t with J = 4.5 Hz, C-9) 108.2 (d, d with J
phase S Ar reaction shows
a
minimum of the energy
CF
CF
N
= 19.7 Hz, C-2,-7).
hypersurface for the C H F σ-complex: Glukhovtsev, M. N.;
6
5 2–
Bach R. D.; Laiter, S. J. Org. Chem. 1997, 62, 4036.
(10) A solution of Ph PK in THF or (CH ) NLi in THF was added at
2
3 2
room temp. to a solution of 7 in dioxane and subsequently the
(16) Single crystal X-ray structure analyses: 1 · CH Cl (crystallized
2
2
mixture was stirred under reflux for 3 h [Ph PK] or 1 h
from dichloromethane): Empirical formula: C
molecular mass: 631.47 g mol , crystal size: 0.21 x 0.35 x 0.80
H
P
· CH Cl ,
2
38 28
2
2
2
-1
[(CH ) NLi], respectively.
3 2
mm, monoclinic, P2 /n (no. 14), a = 8.3420(6) Å, b = 21.384(2)
(11) Huisgen, R.; Sauer, J. Angew. Chem. 1960, 72, 91. - Sauer, J.;
Huisgen, R. Angew. Chem. 1960, 72, 294.
1
3
Å, c = 17.8822(13) Å, β = 963170(10)°, V = 3170.6(4) Å , T =
-1
-1
293 K, d
= 1.323 g • cm , µ = 0.333 mm , F(000) = 1312 e, Z
calcd
(12) Gilman, H.; Crounse, N. N.; Massie, Jr., S.P.; Benkeser, R. A.;
Spatz, S. M. J. Am. Chem. Soc. 1945, 67, 2106. - Urner, R. S.;
Bergstrom, F. W. J. Am. Chem. Soc. 1945, 67, 2108. Bunnett, J.
F.; Brotherton, T. K. J. Am. Chem. Soc. 1956, 78, 6265. - Sauer,
J.; Huisgen, R.; Hauser, A. Chem. Ber. 1958, 91, 1461. - Huisgen,
= 4, λ= 0.71073 Å, 7880 measured reflections [±h,+k,+l], [sinθ/
-1
λ]
max
= 0.65 Å , 7415 independent and 3977 observed reflections
[I>2σ(I)], 388 refined parameters, H atoms were calculated and
not refined in the final refinement by least squares, R = 0.0688,
2
2
2
R
= 0.1839 [w = 1/σ (F )+(0.100P) + 0.000P) with P =
o
w
R.; Sauer, J.; Mack, W.; Ziegler, I. Chem. Ber. 1959, 92, 441.
2
2
-3
(F +2F )/3], residual electron density 0.615 e • Å .
o
c
-1
(13) 10: C
H
N
(264.37 g mol ): calcd. 81.78 % C, 7.63 % H,
18 20
2
10 (crystallized from n-octane): Empirical formula: C
molecular mass: 264.36 g mol , crystal size: 0.12 x 0.38 x 0.47
H N ,
18 20 2
10.60 % N; found: 80.83 % C, 7.38 % H, 10.41 % N. - MS (EI, 70
-1
+
eV): m/z (%) = 264 (100, M ), 263 (8), 249 (12), 234 (14), 218
mm, orthorhombic, Pbca (no.61), a = 13.505(3) Å, b = 15.318(2)
1
(11), 204 (5). - H NMR (200 MHz, CDCl3): δ = 9.18 (s, 1 H, 9-
3
Å, c = 14.054(2) Å, V = 2907.5(8) Å , T = 100 K, d
= 1.208 g
calcd
H), 8.34 (s, 1 H, 10-H); 7.62, 7.35, 6.97 [ABC spin system with
-3
-1
cm , µ = 0.071 mm , F(000) = 1132 e, Z = 8, λ = 0.71069 Å,
3794 measured reflections [+h,+k,+l], [sinθ/λ]
3
3
J
= 8.5 Hz, J = 7.2 Hz, each 2 H for 4-,5-H (A), 3-,6-H (B), 2-
AB
BC
-1
= 0.65 Å ,
13
max
,7-H (C)], 3.00 (s, 12 H, CH3).- C NMR (50 MHz, CDCl ): δ =
3
3315 independent and 2153 observed reflections [I>2σ(I)], 261
refined parameters, H atoms were found and refined in the final
151.3 (s, C-1,-8), 133.0 (s, C-4a,-10a), 127.0 (s, C-8a,-9a), 126.8
(d, C-10), 125.4 (d, C-3,-6), 122.6 (d, C-4,-5), 120.0 (d, C-9),
refinement by least squares, R = 0.0550, R = 0.1451 [w = 1/
w
112.2 (d, C-2,-7), 45.3 (q, CH ).
3
2
2
2
2
2
σ (F )+(0.100P) + 0.000P) with P = (F +2F )/3], residual
o
o
c
(14) Recently 1,8-diaminoanthracene has been prepared from 1,8-
dinitroanthraquinone: Staab, H. A.; Kirsch, P.; Zipplies, M. F.;
Winges, A.; Krieger, C. Chem. Ber. 1994, 127, 1653. - Sessler, J.
L.; Mody, T. D.; Ford, D. A.; Lynch, V. Angew. Chem. 1992, 104,
461; Angew. Chem. Int. Ed. Engl. 1992, 31, 452.
-3
electron density 0.330 e • Å . Atomic coordinates and e.s.d.'s
have been deposited at the Cambridge Crystallographic Data
Centre.
(17) See also: Sheikh, Y. M.; Ekwuribe, N.; Dhawan, B.; Witiak, D. T.
J. Org. Chem. 1982, 47, 4341.