658
I. BEZKISHKO ET AL.
predominantly bridging µ:η1,η1-coordination to form binuclear or polymeric metal com-
plexes. Recently we have demonstrated for the first time that the 3,4,5-triaryl-1,2-
diphosphacyclopentadienide anion forms bimetallic manganese complexes that exhibit
large anti-ferromagnetic exchange interaction due to metal-to-ligand charge transfer.9 Thus,
the 3,4,5-triaryl-1,2-diphosphacyclopentadienide anion may be considered as a novel type
of non-innocent ligand combining the ability of both the metal-to-ligand charge transfer
and the exchange interaction between the metals.
Two different methods are employed for preparation of alkali metal 1,2-diphos-
phacyclopentadienides. One is based on the cleavage of a P-C bond of 1-phosphetene by
lithium, followed by reaction with PCl3 and finally reduction of the formed 1,2-diphos-
phole by lithium.10 However, this method does not allow isolation of the pure lithium
1,2-diphosphacyclopentadienide. A more convenient synthesis of sodium 1,2-diphos-
phacyclopentadienide is based on reaction of triphenylcyclopropenyl nickel complexes
with sodium polyphosphides.11,12 However, this method demands the use of expensive
[Ni(cod)2] and does not allow the isolation of large amounts of sodium 3,4,5-triphenyl-
1,2-diphosphacyclopentadienide. Recently, we have found that sodium 3,4,5-triphenyl-
1,2-diphosphacyclopentadienide can be easily obtained by reaction of 1,2,3-triphenyl-
cyclopropenylphosphonium bromides with sodium polyphosphides in high yield.13
This method is scalable and allows preparation of sodium 3,4,5-triphenyl-1,2-
diphosphacyclopentadienide in significant amounts (up to 20 g) from common starting
materials. In continuation of this work we were interested in the possibility of using the same
method for the preparation of other derivatives of sodium 1,2-diphosphacyclopentadienide.
For this purpose we have synthesized a series of 1,2,3-triarylcyclopropenylphospho-
nium bromides (1), containing both acceptor or donor substituents in the para-position of
the aryl group, by reaction of the corresponding 1,2,3-triarylcyclopropenyl bromides with
PPh3. The structure of compounds 1a–f was confirmed by NMR spectroscopy. Thus, the
1
31P{ H}-NMR spectrum of 1a contains a singlet at +33 ppm typical for phosphonium
1
salts. The 13C{ H}-NMR spectrum consists of a doublet for the carbon atom C1 at +26
1
ppm, characteristic for sp3-hybridized carbon atoms, with a coupling constant JCP
=
72 Hz.
The phosphonium salts (1) were treated with a mixture of polyphosphides obtained
in situ from sodium and white phosphorus containing mainly NaP5 and Na3P7.14
Only the signals of sodium 3,4,5-triaryl-1,2-diphosphacyclopentadienides (2a–d) and
1
PPh3 were detected in the 31P{ H}-NMR spectrum of the reaction mixture after refluxing
for 3 h (Scheme 1). Compounds 2a–d can easily be isolated from the reaction mixture by
filtration. After washing with n-hexane, 2a–d were obtained in good purity and can be used
for following reactions without further purification.
However, no 1,2-diphosphacyclopentadienide anions were formed in the reaction
of sodium polyphosphides with 1,2,3-tri(tert-butyl)- or 1,2,3-tri-isopropylcyclopropenyl-
1
phosphonium bromides (1e,f); the 31P{ H}-NMR spectra of the reaction mixtures contain
only signals in the range of +50 to −100 ppm typical for sodium polyphosphides such as
Na3P21, Na3P19, and others.15
In summary, we have found that reactions of cyclopropenylphosphonium bromides
with sodium polyphosphides can be successfully used for the preparation of sodium 3,4,5-
triaryl-1,2-diphosphacyclopentadienides containing acceptor or donor substituents in the
para-position of an aryl group.