Synthesis of functional 1,4-diphosphaindenes and their related anions

Article abstract of DOI:10.1039/a900086k

Treatment of a 1-zircona-4-phosphaindene complex with PBr₃ affords a 1-bromo-1,4-diphosphaindene, which can be used as a convenient precursor for the preparation of the related 1,4-diphosphaindenyl mono- and tri-anions and (1R)-functional derivatives.

Full text of DOI:10.1039/a900086k

Synthesis of functional 1,4-diphosphaindenes and their related anions
Patrick Rosa, Louis Ricard, François Mathey* and Pascal Le Floch*
Laboratoire ‘Héteroéléments et Coordination’, UMR CNRS 7653, Ecole Polytechnique, 91128 Palaiseau Cedex,
France. E mail: lefloch@mars.polytechnique.fr
Received (in Liverpool, UK) 4th January 1999, Accepted 16th February 1999
Treatment of a 1-zircona-4-phosphaindene complex with
R
PBr3 affords a 1-bromo-1,4-diphosphaindene, which can be
Zr
P
used as a convenient precursor for the preparation of the
Et
i
ii
Et
Zr
Me
related 1,4-diphosphaindenyl mono- and tri-anions and
P
P
P
(1R)-functional derivatives.
Et
Et
The search for new sophisticated ligands including sp2-
hybridised phosphorus atoms as bonding sites is a current and
topical field of investigation.1 Among these ligands, phosphi-
nines play a significant role and continuous efforts have been
made to improve the synthesis of their functional derivatives.2
Whereas several routes towards polyfunctional mono-, bis- and
tris-phosphinine based ligands3 and macrocycles4 have been
developed, fused aromatic and non-aromatic ring systems have
received much less attention. Although some polyaromatic
systems are known,5 only two examples of heterocyclic-fused
ring systems incorporating the phosphinine nucleus have been
described so far.6 In view of the importance of phospholes and
their related phospholide anions in coordination chemistry,7 we
decided to investigate the synthesis of 1,4-diphosphaindene
species, a new type of ligand which could combine the
chemistries of phosphinines and phospholes. Herein we report
on these investigations.
1
2
3 R = Ph
4 R = Br
Scheme 1 Reagents and conditions: i, hex-3-yne, 80 °C, 3 h; ii, PhPCl2,
CH2Cl2, 5–10 d, then PBr3, CH2Cl2, 1 h.
that a substantial delocalization of the negative charge occurs in
5a. As expected, anion 5a can be used as a convenient source of
functional derivatives via reaction of electrophiles at the
nucleophilic P atom of the phospholide unit (Scheme 2).
Reactions of 5a with Br(CH2)2CN and MeI afford compounds
6 and 7 which were isolated in modest yields (40 and 50%
respectively).† The corresponding PSiMe3 derivative 8 was too
sensitive towards hydrolysis to be isolated. An X-ray crystal
structure analysis (Fig. 1) was carried out on the sulfide 9‡
which was obtained by treating 7 with elemental sulfur in
toluene. The structure of 9 deserves no special comment.
Apparently, the phosphinine unit is not perturbed by the
presence of the fused phosphole moiety as shown by the
equivalency of the two CNP sp2 bonds and by the value of the
internal C–P–C angle, which is close to that recorded for other
phosphinines.
Another interesting observation concerns the reduction of
anion 5a. We found that care must be taken to avoid over-
reduction. Indeed, a prolonged contact with excess lithium or
sodium cleanly affords a new species whose structure was
ascribed to trianions 10a,b on the basis of NMR data.12
Evidence supporting the formulation proposed for 10 was given
by oxidation with one equivalent of iodine, which leads back to
the monoanions 5a,b (Scheme 3). Further experiments aimed at
developing the use in coordination chemistry of ligands such as
monoanions 5, whose synthesis was the real aim of this work,
are currently under progress in our laboratories.
Among the different synthetic approaches conventionally
used for the synthesis of phospholes, metallacycle transfer
reactions from zirconacyclopentadiene complexes appear very
attractive.8 Indeed, this simple process was used for the
2
preparation of 1-phosphaindene ligands from h -benzyne
zirconocene complexes, alkynes and PCl3.9 The recent discov-
2
ery of h -phosphabenzyne zirconocene complexes10 prompted
us to investigate the corresponding transformation. All the
experiments were conducted with the 1-zircona-4-phosphain-
dene complex 2 whose synthesis was previously reported from
2
the reaction of the PMe3 adduct of the h -phosphabenzyne
complex with hex-3-yne. As a prelude to this work we found
that the use of the Zr–Me complex 1 as precursor provided a
more straighforward access to 2. This complex turns out to be
less reactive than that of its corresponding carbon counterpart.
It seems likely that the decrease of electron density at the b
positions of the phosphinine is responsible for this situation.11
Preliminary experiments with PCl3 only led to the recovery of
starting material after several hours of reaction in CH2Cl2.
Better results were obtained using PhPCl2 as transfer reagent
since the 1-phenyl-1,4-diphosphaindene 3 could be prepared
after 5 to 10 days reaction, depending on the concentration used,
in 15% yield. Finally, we found that the use of PBr3
dramatically increased the rate of the reaction as well as the
yield. After 1 h, the 1-bromo-1,4-diphosphaindene 4 was
isolated in 80% yield as a slightly moisture- and oxygen-
sensitive yellow oil after extraction with hexanes (Scheme 1).
The reaction of 4 with lithium is of particular interest. With a
stoichiometric amount of lithium in THF at 25 °C, the
monoanion 5a is formed quantitatively according to 31P NMR
We are grateful to the CNRS and the Ecole Polytechnique for
the financial support of this work.
R
Li+
P
P
ii
i
Et
Et
4
P
P
Et
Et
5a
6 R = CH2CH2CN
7 R = Me
8 R = SiMe3
Me
S
P
iii
Et
7
1
P
analysis. All available data (31P, H, 13C NMR) support the
Et
structure proposed for 5a. Whereas the 31P NMR chemical shift
of 5a is comparable to those recorded for other phosphaindenyl
anions, that of the phosphinine subunit experiences a dramatic
upfield shift (d 146.6 in 5a vs. 176 in 4). This observation shows
9
Scheme 2 Reagents and conditions: i, Li, THF, 30 min; ii, BrCH2CH2CN
or MeI or Me3SiCl, THF 280 to 25 °C; iii, 1/8 S8, toluene, 40 °C, 4 h.
Chem. Commun., 1999, 537–538
537

1
3
1
1
(dd, JP,C 43.3, JP,C 4.2, C9), 144.9 (d, JP,C 41.6, C5), 139 (dd, JP,C 40,
2JP,C 10.4, C8), 114.7 (dd, 2JP,C 12, 2JP,C 7.5, C3), 61.1 (dd, 3JP,C 24.2, 2JP,C
8.4, C7). For 10b: dP(C4D8O) 39.3 (d, 3JP,P 12.2, P1), 20.4 (P4).
‡ Crystal data for 9: Crystals of 9 (C14H20P2S) were grown from MeOH.
Data were collected at 123 ± 0.5 K on an Enraf-Nonius CAD4 dif-
fractometer using Mo-Ka radiation (l
= 0.71073 Å) and a graphite
monochromator. The crystal structure was solved and refined using the
Enraf-Nonius MOLEN package. The compound crystallises in space group
P21/n (14), a = 9.861(1), b = 15.219(2), c = 10.715(1) Å, b = 110.95(1)°,
V = 1501.89(59) Å3, Z = 4, Dc = 1.249 g cm23, m = 4.0 cm21, F(000) =
600. A total of 4725 unique reflexions were recorded in the range 2 @ 2q @
60.0 of which 1153 were considered as unobserved [F2 < 2.0s(F2)],
leaving 3572 for solution and refinement. Direct methods yielded a solution
for all atoms. The hydrogen atoms were refined with isotropic temperature
factors in the final stages of least-squares while using anisotropic
temperature factors for all other atoms. A non-Poisson weighting scheme
was applied with a p factor equal to 0.08. The final agreement factors were
R = 0.033, Rw = 0.053, GOF = 1.10. CCDC 182/1177. Crystallographic
data are available in CIF format from the RSC web site, see:
http://www.rsc.org/suppdata/1999/537/
Fig. 1 Molecular structure of 9 showing the atomic number scheme. The
numbering is arbitrary, not the systematic system used in the spectroscopic
data. Selected interatomic distances (Å) and angles (°): P(1)–C(2) 1.734(2),
C(2)–C(3) 1.377(3), C(3)–C(4) 1.419(2), C(4)–C(5) 1.388(3), C(5)–C(6)
1.417(3), C(6)–P(1) 1.730(2), C(6)–C(7) 1.480(2), C(7)–C(8) 1.349(2),
C(8)–P(9) 1.797(2), P(9)–C(5) 1.813(2), C(6)–P(1)–C(2) 99.65(9), C(5)–
P(9)–C(8) 93.40(8), P(9)–C(5)–C(6) 107.6(1), C(5)–C(6)–C(7) 113.9(1).
1 K. B. Dillon, F. Mathey and J. F. Nixon, in Phosphorus: The carbon
copy, Wiley, Chichester, 1998.
2 G. Märkl, in Multiple Bonds and Low Coordination in Phosphorus
Chemistry, ed. M. Regitz and O. J. Scherer, Thieme, Stuttgart, 1990; F.
Mathey and P. Le Floch, Chem. Ber., 1996, 129, 263.
3 N. Avarvari, P. Le Floch, L. Ricard and F. Mathey, Organometallics,
1997, 16, 4089.
4 N. Avarvari, N. Mézailles, L. Ricard, P. Le Floch and F. Mathey,
Science, 1998, 280, 1587.
3 M+
P
i
ii
5a
4
2
Et
iii
5a or 5b
P
5 See, for example: P. De Koe and F. Bickelhaupt, Angew. Chem., Int. Ed.
Engl., 1967, 6, 567; Dimroth and H. Odenwälder, Chem. Ber., 1971,
104, 2984; G. Märkl and K. H. Heier, Angew. Chem., Int . Ed. Engl.,
1972, 11, 1017; K. H. Dötz, A. Tiriliomis, K. Harms, M. Regitz and U.
Annen, Angew. Chem., Int. Ed. Engl., 1988, 27, 713.
6 Two types of heterocyclic-fused phosphinines have been previously
reported: an indolo derivative (see G. Märkl, G. Habel and H. Baier,
Phosphorus Sulfur, 1979, 5, 257) and two isostructural phoshabenzo-
furan and thiophene compounds (see K. H. Dötz, A. Tiriliomis and K.
Harms, Tetrahedron, 1993, 46, 5577).
Et
10a M = Li
b M = Na
Scheme 3 Reagents and conditions: i, Li (excess), 1 h; ii, Na (excess),
20 min; iii, I2 (1 equiv.), THF.
Notes and references
7 F. Mathey, Coord. Chem. Rev., 1994, 137, 1.
† All isolable compounds (3, 6 and 9) gave analytical data consistent with
the proposed structures. Selected data for 3: dP(81 MHz, CDCl3 unless
otherwise stated) 171.5 (P4), 6.5 (P1). For 4: dP 176.5 (P4), 59.6 (P1); dH(200
MHz, CDCl3) 8.42 (d, 1H, 2JH,P 39.75, H5); dC(50 MHz, CDCl3) 172.7 (d,
1JP,C 50.6, C9), 155.10 (d, 1JP,C 48.8, C5). For 5a: dP(C4D8O) 146.6 (d, 3JP,P
8 P. J. Fagan and W. A. Nugent, J. Am. Chem. Soc., 1988, 110, 2310.
9 F. Nief and L. Ricard, J. Organomet. Chem., 1994, 464, 149.
10 P. Le Floch, A. Kolb and F. Mathey, J. Chem. Soc., Chem. Commun.,
1994, 2065; P. Rosa, P. Le Floch, L. Ricard and F. Mathey, J. Am.
Chem. Soc., 1997, 119, 9417.
11 L. Nyulaszi and T. Veszpremi, J. Phys. Chem., 1996, 100, 6456.
12 Mono radical, di- and even tri-anions of phosphinines exist. Dianions
have been reported as diamagnetic species although no NMR data are
available, see: K. Dimroth and F. W. Steuber, Angew. Chem., Int. Ed.
Engl., 1967, 6, 445; H. Weber, Dissertation, Universität Marburg, 1975,
quoted in ref. 2.
2
10.5, P4), 63.7 (P1); dH(C4D8O) 7.66 (d, 1H, JH,P 38.05, H5); dC(C4D8O)
1
2
1
3
157.1 (dd, JP,C 36.2, JP,C 14, C8), 156.5 (dd, JP,C 38.6, JP,C 6.8, C2),
153.8 (dd, 1JP,C 42.4, 2JP,C 2.1, C9); 143.9 (d, 1JP,C 36.9, C5), 135.7 (dd, JP,C
16.5, JP,C 17.2, C6 or C7), 132.6 (dd, 2JP,C 23, 2JP,C 3.6, C3), 122.6 (dd, JP,C
10.5, JP,C 17, C7 or C6). For 5b: dP 153.6 (d, 3JP,P 10.3, P4), 53.7 (P1). For
6: dP 174 (P4), 21.8 (P1). For 7: dP 171.3 (P4), 210.8 (P1). For 8: dP 170
(P4), 243.6 (P1). For 9: dP 174 (P4), 50.8 (P1). For 10a: dP(C4D8O) 34.7 (d,
3JP,P 13.8, P1), 24 (P4); dH(C4D8O) 7.20 (d, 1H, 2JH,P 40.1, H5); dC(C4D8O)
150.6 (dd, 2JP,C 17.6, 3JP,C 3.9, C6), 150 (dd, 1JP,C 37.1, 2JP,C 6.8, C2), 146
Communication 9/00086K
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Chem. Commun., 1999, 537–538