Simple access to α-functional phospholide ions. 2. Application to the synthesis of 1-methyl-2-pyrrolyl and 2-(diphenylphosphino)phenyl derivatives

Article abstract of DOI:10.1021/om980081w

Heating 1-Z-3,4-dimethylphospholes with potassium tert-butoxide in THF at ca. 150-160 °C affords the corresponding potassium 2-Z-3,4-dimethylphospholides (Z = 1-methyl-2-pyrrolyl and 2-(diphenylphosphino)phenyl) via a [1,5]-sigmatropic shift of Z. The first anion can be used to prepare the corresponding bis(pyrrolyl)-1,1′-diphosphaferrocene, and the second anion is able to chelate palladium(II) between its phospholide and PPh₂ functionalities.

Full text of DOI:10.1021/om980081w

2996
Organometallics 1998, 17, 2996-2999
Sim p le Access to r-F u n ction a l P h osp h olid e Ion s. 2.
Ap p lica tion to th e Syn th esis of 1-Meth yl-2-p yr r olyl a n d
2-(Dip h en ylp h osp h in o)p h en yl Der iva tives
Serge Holand, Nicole Maigrot, Claude Charrier, and Franc¸ois Mathey*
Laboratoire “He´te´roe´le´ments et Coordination” UMR 7653 CNRS, DCPH, Ecole Polytechnique,
F-91128 Palaiseau Cedex, France
Received February 6, 1998
Heating 1-Z-3,4-dimethylphospholes with potassium tert-butoxide in THF at ca. 150-160
°C affords the corresponding potassium 2-Z-3,4-dimethylphospholides (Z ) 1-methyl-2-
pyrrolyl and 2-(diphenylphosphino)phenyl) via a [1,5]-sigmatropic shift of Z. The first anion
can be used to prepare the corresponding bis(pyrrolyl)-1,1′-diphosphaferrocene, and the
second anion is able to chelate palladium(II) between its phospholide and PPh2 functionalities.
In tr od u ction
stands for phenyl, 2-pyridyl, and ethoxycarbonyl. In
fact the scope of this scheme is much broader. In this
paper, we report on two additional examples of special
interest for coordination chemists.
Among the numerous carbon-phosphorus hetero-
cycles which are presently known,1 two of the simplest,
i.e., the phospholide ion and phosphinine, play a special
role as a result of their high aromaticity. The aromatic
stabilization energy (ASE) of phosphinine has been
evaluated at 88% of that of benzene,2 whereas the ASE
of the phospholide ion has been estimated between 90%
and 100% of that of the cyclopentadienide ion.3,4
Whereas the chemistry of phosphinines is now highly
developed,1,5,6 presently this is not the case for phospho-
lide ions if we exclude coordination chemistry.7 Indeed,
all of the classical reagents react with these ions at
phosphorus, and no chemistry at the carbons of the ring
has been described until now. Very recently, we were
able to devise the first simple access to R-functional
phospholides8 whose principle is depicted in eq 1.
Resu lts a n d Discu ssion
2-(1-Me t h yl-2-p yr r olyl)-3,4-d im e t h ylp h osp h o-
lid e. The starting product was 1-(1-methyl-2-pyrrolyl)-
3,4-dimethylphosphole (1) prepared from 1-methyl-2-
lithiopyrrole and 1-cyano-3,4-dimethylphosphole10 as
shown in eq 2. The two most noteworthy spectral
features of 1 are its 31P NMR resonance at high field
δ31P (1) -32 vs -2.5 for the P-Ph analogue, and the
large coupling of the â carbon in the pyrrole ring with
the phosphole P. An unambiguous assignment of the
The two prerequisites for applying this scheme are a
good migratory aptitude of Zsthis is the case for sp2-C,
sp-C, Si, P, S...sand a good compatibility of Z with the
base, generally tBuOK, which is used to deprotonate the
transient 2H-phosphole.9 Three examples have been
described in our preliminary communication, where Z
1
corresponding resonance was made using H-13C cor-
2
related spectra. The J (C-P) value of 37.8 Hz can be
compared with 18.3 Hz for the o-C6H5 carbon in the
P-Ph analogue.11 This high value suggests that the
pyrrole ring is lying almost perpendicular to the phos-
phole plane with a Câ-CR-P-lone pair dihedral angle
close to 0°.12 The [1,5] shift of the pyrrole substituent
around the phosphole ring proved to be rather difficult.
The migration needs 3 days at 160 °C to go to comple-
tion. Under such extreme conditions, the resulting
(1) A good overview of carbon-phosphorus heterocyclic chemistry
is provided in Comprehensive Heterocyclic Chemistry II; Katritzky, A.
R., Rees, C. W., Scriven, E. F. V., Eds.; Pergamon: Oxford, U.K., 1996.
(2) Baldridge, K. K.; Gordon, M. S. J . Am. Chem. Soc. 1988, 110,
4204.
(3) Padma Malar, E. J . J . Org. Chem. 1992, 57, 3694.
(4) Goldfuss, B.; Schleyer, P. v. R.; Hampel, F. Organometallics 1996,
15, 1755.
(5) Ma¨rkl, G. In Multiple Bonds and Low Coordination in Phospho-
rus Chemistry; Regitz, M., Scherer, O. J ., Eds.; Georg Thieme Verlag:
Stuttgart, Germany, 1990; p 220.
(6) Dillon, K. B.; Mathey, F.; Nixon, J . F. Phosphorus: The Carbon
Copy; Wiley: Chichester, U.K., 1998.
(9) For a review on 2H-phospholes, see: Mathey, F.; Mercier, F. C.
R. Acad. Sci. Paris, Ser. IIb 1997, 324, 701. Under drastic conditions,
3H-phospholes may also intervene as intermediates in the reaction
mechanism, see: Bachrach, S. M. J . Org. Chem. 1993, 58, 5414.
(10) Holand, S.; Mathey, F. Organometallics 1988, 7, 1796.
(11) Gray, G. A.; Nelson, J . H. Org. Magn. Reson. 1980, 14, 14.
(12) Quin, L. D. In Phosphorus-31 NMR Spectroscopy In Stereo-
chemical Analysis; Verkade, J . G., Quin, L. D., Eds.; VCH: Deerfield
Beach, FL, 1987; p 396.
(7) Mathey, F. Coord. Chem. Rev. 1994, 137, 1.
(8) Holand, S.; J eanjean, M.; Mathey, F. Angew. Chem., Int. Ed.
Engl. 1997, 36, 98.
S0276-7333(98)00081-8 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 06/11/1998

Simple Access to R-Functional Phospholide Ions
Organometallics, Vol. 17, No. 14, 1998 2997
phospholide was nevertheless obtained in g65% yield,
as measured on its alkylation product 3 (eq 3). This
temperature. The resulting o-lithiophenyl derivative 6
was then reacted with diphenylchlorophosphine to give
7 (eq 6).
3
The diphosphine 7 displays a huge J (P-P) coupling
(110 Hz) which is characteristic of a cis P-CdC-P
link.15 When compared to the pyrrole case, the phos-
phinophenyl substituent of 7 migrates under less drastic
conditions (eq 7).
satisfactory result emphasizes the extraordinary ther-
mal stability of phospholide ions. From 3, it is possible
to get back 2 by treatment with a base (tBuOK, BuLi)
or a metal (Na). We have observed a significant
variation of the 31P shift of 2 with the nature of the
counterion: δ31P 74 (K+), 61.7 (Na+), and 56.5 (Li+) in
THF. This phenomenon suggests that the structure of
2 involves a more or less labile coordination of the
pyrrole nitrogen with the counterion. The reaction of
2 with FeCl2 affords, as expected,13 the corresponding
1,1′-diphosphaferrocene 4 as a mixture of meso and rac
diastereomers (eq 4).
The phospholide ion 8 is thus obtained almost quan-
titatively as monitored by 31P analysis of the crude
reaction mixture. The 31P NMR data of 8 are highly
characteristic: δ31P (THF) +86.2 (P-), -14.7 (PPh2),
4J (P-P) ) 25 Hz. The anion was also characterized by
1
negative-ion mass spectrometry and H and 13C NMR
spectroscopy. The phospholide C2 resonance occurs at
148.96 as a doublet of doublets: 1J (C-P) ) 40.8 Hz and
3J (C-P) ) 9 Hz. The strong 1J (C-P) coupling is a
constant feature of the phospholide ions.16
In order to demonstrate the chelating ability of this
species, 8 was allowed to react with (cyclooctadiene)-
palladium dichloride (eq 8). Unfortunately, we were
The major meso diastereomer displays a simple first-
1
order H NMR spectrum, and its 31P resonance appears
at -55.7 in CD2Cl2. The minor rac diastereomer
1
displays a complex second-order H NMR spectrum, and
its phosphorus resonates at -57.8. Due to its two
pyrrole rings, 4 might be incorporated into polypyrrole
macrocycles and oligomers. Finally, it must be men-
tioned here that previous attempts to build the R-linked
pyrrole-phosphole subunit failed.14
2-[2-(Dip h en ylp h osp h in o)p h en yl]-3,4-d im eth yl-
p h osp h olid e. Here our aim was to incorporate the
phospholide ion into a chelating diphosphorus ligand.
In the first step, 3,4-dimethylphospholide was allowed
to react with 1,2-dibromobenzene. Even in the presence
of a nickel catalyst, only the monosubstitution product
was observed (eq 5).
unable to crystallize complex 9, but its formulation was
unambiguously established by a combination of NMR
spectroscopy and mass spectrometry, including a com-
parison between the observed and simulated isotopic
patterns of the molecular ion. The A2X2 31P spectrum
of 9 implies that the geometry of this square-planar Pd-
(II) complex is trans. The availability of phospholide
ions such as 2 and 8 offers numerous synthetic pos-
sibilities that we are currently exploring.
Exp er im en ta l Section
All reactions were routinely performed under an inert
atmosphere of nitrogen by using Schlenk techniques and dry
deoxygenated solvents. Nuclear magnetic resonance spectra
were obtained at 25 °C on a Bruker AC 200 SY spectrometer
Bromine to lithium exchange readily takes place when
5 is allowed to react with butyllithium in THF at low
1
operating at 200.13 MHz for H, 50.32 MHz for 13C, and 81.01
(13) De Lauzon, G.; Deschamps, B.; Fischer, J.; Mathey, F.; Mitschler,
A. J . Am. Chem. Soc. 1980, 102, 994.
(14) Deschamps, E.; Mathey, F. J . Org. Chem. 1990, 55, 2494.
(15) Carty, A. J .; J ohnson, D. K.; J acobson, S. E. J . Am. Chem. Soc.
1979, 101, 5612.
(16) Charrier, C.; Mathey, F. Tetrahedron Lett. 1987, 28, 5025.

2998 Organometallics, Vol. 17, No. 14, 1998
Holand et al.
MHz for 31P. Chemical shifts are expressed in parts per
million downfield from external TMS (1H and 13C) and 85%
H3PO4 (31P), and coupling constants are given in hertz. Mass
spectra were obtained at 70 eV with an HP 5989 B spectrom-
eter coupled with a HP 5890 chromatograph by the direct inlet
method. The following abreviations are used: s, singlet; d,
doublet; t, triplet; m, multiplet; b, broad. Elemental analyses
were performed by the Service d’analyse du CNRS at Gif sur
Yvette, France.
major meso isomer which was eluted first. Meso 4. 31P NMR
(CD2Cl2): δ -55.7. 1H NMR (CD2Cl2): δ 2.09 (s, 3H, Me-C),
2.18 (s, 3H, Me-C), 3.39 (s, 3H, Me-N), 3.83 (d, J (H-P) )
2
36.1, CH-P), 5.97 (m, 2H, Hââ′ pyrrole), 6.58 (m, 1H, HR′
pyrrole). 13C NMR (CD2Cl2): δ 14.95 (s, Me-C), 16.71 (s, Me-
C), 35.39 (d, 4J (C-P) ) 9.5, Me-N), 83.01 (d, 1J (C-P) ) 59.1,
1
CH-P), 94.74 (d, J (C-P) ) 58.0, P-C-pyrrole), 95.32 (s, Câ
phosphole), 93.37 (d, Câ phosphole), 107.15 (s, Câ′ pyrrole),
111.39 (s, Câ pyrrole), 123.57 (s, CR′ pyrrole), 129.80 (m, CR
1-(1-Meth yl-2-p yr r olyl)-3,4-d im eth ylp h osp h ole (1). A
solution of n-butyllithium (1.6 M in hexane; 3.8 mL, 6 × 10-3
mol) was added dropwise to 1-methylpyrrole (0.8 mL, 9 × 10-3
mol) and TMEDA (0.9 mL, 6 × 10-3 mol) in 15 mL of dry THF
at 0 °C. The reaction mixture was then warmed to room
temperature and stirred for 1 h. A solution of 1-cyano-3,4-
dimethylphosphole10 (0.82 g, 6 × 10-3 mol) in 5 mL of THF
was added dropwise to the reaction mixture at room temper-
ature. After evaporation of the solvent, the residue was
chromatographed on alumina with toluene as the eluent: yield
0.75 g (65%).
pyrrole). MS: m/z 436 (M+, 100). Anal. Calcd for C22H26
-
FeN2P2: C, 60.57; H, 6.01. Found: C, 60.43; H, 6.17.
1-(2-Br om op h en yl)-3,4-d im eth ylp h osp h ole (5). A mix-
ture of lithium 3,4-dimethylphospholide (3.2 × 10-2 mol),
prepared from lithium metal and 1-phenyl-3,4-dimethylphos-
phole,10 1,2-dibromobenzene (7.55 g, 3 × 10-2 mol), and
anhydrous nickel bromide (0.35 g, 1.6 × 10-3 mol) in THF (100
mL) was heated to reflux for 4 h. After evaporation of the
solvent, the residue was chromatographed on silica gel first
with hexane and then hexane:toluene (80:20) giving 5 as a
colorless oil (4.4 g, 54.9%). 31P NMR (CDCl3): δ 0.9. 1H NMR
31P NMR (CD2Cl2): δ -32. 1H NMR (CD2Cl2): δ 2.17 (dd,
4
4
(CDCl3): δ 2.15 (dd, J (H-P) ) 3.7, J (H-H) ) 0.7, 6H, Me),
6.66 (dd, 2J (H-P) ) 37.3, 4J (H-H) ) 0.7, 2H, dCH), 7.09-
7.26 (m, 3H), 7.53-7.59 (m, 1H, Ph). 13C NMR (CDCl3): δ
17.90 (d, 3J (C-P) ) 3.7, Me), 126.90 (d, 1J (C-P) ) 2.3, dCH),
149.43 (d, 2J (C-P) ) 9.2, dC-), 127.40 (s, C5 Ph), 129.02 (d,
2J (C-P) ) 27.3 Hz, C2-Br Ph), 129.53 (s, C4 Ph), 132.35 (s,
4
4J (H-P) ) 3.8, J (H-H) ) 0.8, 6H, Me-C), 3.2 (s, 3H, Me-
N), 6.21 (m, 3J (H-H) ) 3.3 and 2.4, 4J (H-P) ) 3.4, Hâ′
pyrrole), 6.56 (dd, 2J (H-P) ) 37, 4J (H-H) ) 0.8, 2H, HR
4
3
3
phosphole), 6.69 (ddd, J (H-H) ) 1.7, J (H-H) ) 3.3, J (H-
P) ) 5.1, Hâ pyrrole), 6.88 (dd, 3J (H-H) ) 2.4, 4J (H-H) )
1.7, HR′ pyrrole). 13C NMR (CD2Cl2): δ 18.3 (d, 3J (C-P) ) 3.9,
Me-C), 34.05 (s, Me-N), 108.9 (d, 3J (C-P) ) 12.6, Câ′
pyrrole), 118.0 (d, 1J (C-P) ) 18.5, CR pyrrole), 123.4 (d, 2J (C-
P) ) 37.8, Câ pyrrole), 129.0 (d, 1J (C-P) ) 13.2, CR phosphole),
2
1
C3 Ph), 132.80 (d, J (C-P) ) 38.4, C6 Ph), 136.65 (d, J (C-P)
) 10.8, C1 Ph). MS: m/z (relative intensity), isotope pattern
for M: calcd 266 (100), 267 (14), 268 (98), 269 (13); found 266
(100), 267 (20), 268 (98), 269 (15). Anal. Calcd for C12H12
-
2
129.1 (s, CR′ pyrrole), 148.6 (d, J (C-P) ) 12, Câ phosphole).
BrP: C, 53.96; H, 4.53; Br, 29.91; P, 11.60. Found: C, 54.02;
H, 4.63; Br, 30.01; P, 11.46.
MS of the dimeric oxide: m/z 414 (M+, 26), 208 (M/2 + H, 100).
Anal. Calcd for C11H14NP: C, 69.10; H, 7.38. Found: C, 69.41;
H, 7.39.
1-[2-(Dip h en ylp h osp h in o)p h en yl]-3,4-d im et h ylp h os-
p h ole (7). A solution of bromophenylphosphole 5 (5.34 g, 2
× 10-2 mol) in THF (100 mL) was cooled to -60 °C. Butyl-
lithium (1.5 M) in hexane (14.6 mL, 2.2 × 10-2 mol) was added,
followed by chlorodiphenylphosphine after 15 min (4.85 g, 2.2
× 10-2 mol). The mixture was stirred for 0.5 h. After
evaporation of THF, the residue was dissolved in a small
quantity of CH2Cl2, deposited on silica gel, and chromato-
graphed, first with hexane and then with hexane:CH2Cl2 (50:
50). Phosphole 7 was obtained as a white solid: mp 138 °C,
yield 4.8 g (65%). 31P NMR (CH2Cl2): δPA -7.0 (phosphole)
and PB -10.5 (PPh2), 3J (PA-PB) ) 110. 1H NMR (CDCl3): δ
1-(â-Cya n oet h yl)-2-(1-m et h yl-2-p yr r olyl)-3,4-d im et h -
ylp h osp h ole (3). A solution of phosphole 1 (0.76 g, 4 × 10-3
t
mol) in 20 mL of THF with BuOK (0.56 g, 5 × 10-3 mol) was
heated for 3 days at 160 °C to cleanly give the phospholide 2
2
(K+) (δ31P 74, J (P-H) ) 40). Then, BrCH2CH2CN (0.42 mL,
5 × 10-3 mol) was added at room temperature to instanta-
neously give the phosphole 3. After evaporation of the solvent,
the residue was chromatographed on alumina with dichlo-
romethane as the eluent: yield 0.64 g (65%). 31P NMR (C6D6):
δ -0.2. 1H NMR (C6D6): δ 1.65 (m, 4H, P-CH2CH2CN), 1.92
(d, 4J (H-P) ) 3.4, 3H, Me-C3), 2.02 (dd, 4J (H-P) ) 2.8, 4J (H-
H) ) 1.4, 3H, Me-C4), 3.28 (s, 3H, Me-N), 6.22 (dd, 4J (H-H)
) 1.8, 3J (H-H) ) 3.5, Hâ pyrrole), 6.25 (dq, 2J (H-P) ) 39,
4
2
1.99 (d, J (H-P) ) 3.4, 6H, Me), 6.13 (ddd, J (H-PA) ) 35.5,
5J (H-PB) ) 1.6, 4J (H-H) ) 0.6, 2H, dCH), 6.91 (m, 1H), 7.08
(m, 3H, phenylene), 7.30 (m, 10H, Ph). 13C NMR (CDCl3): δ
17.79 (d, 3J (C-P) ) 6.4, Me), 128.59 (d, 3J (C-P) ) 6.4, Ph
o-C), 128.75 (s, Ph p-C), 129.02 (s, phenylene C4 and C5), 129.25
3
4J (H-H) ) 1.4, HR′ phosphole), 6.44 (dd, J (H-H) ) 2.6 and
3.5, Hâ′ pyrrole), 6.65 (dd, 4J (H-H) ) 1.8, 3J (H-H) ) 2.6, HR′
pyrrole). 13C NMR (C6D6): δ 13.44 (d, 2J (C-P) ) 3.1, CH2-
1
3
(d, J (C-P) ) 5.0, dCH), 132.49 (d, J (C-P) ) 5.9, C3 or C6),
3
CN), 15.87 (s, Me-C), 18.99 (d, J (C-P) ) 2.8, Me-C), 20.27
133.19 (d, 3J (C-P) ) 7.8, C6 or C3), 134.13 (d, 2J (C-P) ) 18.6,
(d, 1J (C-P) ) 24.4, P-CH2), 35.23 (d, 4J (C-P) ) 7.8, Me-N),
2
Ph o-C), 137.07 (pseudo q, Ph ipso C), 138.72 (dd, J (C-P) )
3
109.29 (s, Câ′ pyrrole), 110.97 (d, J (C-P) ) 4.5, Câ pyrrole),
31.8, 1J (C-P) ) 7.6, C1 or C2), 143.30 (dd, 2J (C-P) ) 30.2,
1J (C-P) ) 7.0, C2 or C1), 148.65 (d, 2J (C-P) ) 8.8, dC-). MS:
m/z (relative intensity): 372 (M, 100). Anal. Calcd for
3
120.29 (d, J (C-P) ) 5.4, CN), 124.42 (s, CR′ pyrrole), 126.76
1
(d, J (C-P) ) 5.7, CR′ phosphole), 129.23 (CR pyrrole, partly
1
masked), 136.85 (d, J (C-P) ) 2.1, CR phosphole), 146.32 (d,
C
24H22P2: C, 77.41; H, 5.95; P, 16.64. Found: C, 77.31; H, 5.94;
P, 16.41.
P ot a ssiu m 2-[2-(Dip h en ylp h osp h in o)p h en yl]-3,4-d i-
2
2J (C-P) ) 12.5, Câ phosphole), 153.00 (d, J (C-P) ) 4.5 Hz,
Câ′ phosphole). MS: m/z 244 (M+, 100), 204 (M - CH2CN, 56),
190 (M - CH2CH2CN, 50). Anal. Calcd for C14H17N2P: C,
68.84; H, 7.01. Found: C, 68.42; H, 7.01.
m eth ylp h osp h olid e (8). A solution of phosphole 7 (0.5 g,
1.3 × 10-3 mol) and potassium tert-butoxide (0.17 g, 1.56 ×
10-3 mol) in THF (3 mL) was heated for 4 h at 150 °C in a
pressure tube, leading to the phospholide ion 8. 31P NMR
(THF): δA 86.2 (P-), δX -14.7 (PPh2), 4J (PA-PX) ) 25. 13C NMR
Bis(η5-[2-(1-m et h yl-2-p yr r olyl)-3,4-d im et h ylp h osp h o-
lyl])ir on (4). A solution of n-butyllithium (1.6 M in hexane;
1.25 mL, 2 × 10-3 mol) was added dropwise to phosphole 3
(0.44 g, 1.8 × 10-3 mol) in 10 mL of THF at -80 °C. The
reaction mixture was warmed to room temperature and
anhydrous FeCl2 (0.11 g, 0.9 × 10-3 mol) was added. The
mixture was heated at 45 °C for 30 min. After evaporation of
the solvent, the residue was chromatographed on alumina with
dichloromethane as the eluent. A mixture of meso and rac 4
was obtained: yield 0.09 g (23%). Further careful chromatog-
raphy on alumina with CH2Cl2 provided a pure sample of the
1
(THF): δ 15.52 (s, Me), 18.50 (s, Me), 148.96 (dd, J (C-PA) )
3
2
40.8, J (C-PX) ) 9.0, CR phospholide), 154.29 (dd, J (C-PX)
) 33.2, 2J (C-PA) ) 20.6, C ipso-C6H4). MS (negative ion, NH3,
70 eV): m/z 371 (M-, 35), 197 (100).
Bis[2-(2-(diph en ylph osph in o)ph en yl)-3,4-dim eth ylph os-
p h olyl]p a lla d iu m (9). To a solution of anion 8 (0.67 × 10-3
mol) in THF (4 mL) was added cyclooctadienepalladium

Simple Access to R-Functional Phospholide Ions
Organometallics, Vol. 17, No. 14, 1998 2999
1
dichloride (0.15 g, 0.4 × 10-3 mol). After evaporation of the
solvent (T e 30 °C), the residue was dissolved in toluene and
the solution filtrated on a short column of silica gel. The
evaporation yielded 9 as a red microcrystalline solid: 0.1 g
(33%). 31P NMR (C6D6): δA 60.1 (P-), δX 24.2 (PPh2), J (PA-
PX) ) 24.2. MS m/z for 106Pd (relative intensity): 848 (M, 25),
371 (M - Pd /2, 100); isotope pattern for M+ (relative intensity
calcd; found) 846 (27.2; 30), 847 (68.9; 69.5), 848 (100.0; 100),
849 (44.7; 46.5), 850 (76.3; 76.5), 851 (37.3; 37), 852 (38.4; 37.5),
853 (17.3; 16), 856 (4.4; 4.5).
OM980081W