| dc.description.abstract | Reactions involving nucleophilic attack of
tertiary phosphines and related compounds upon
acetylenic systems have been reviewed and the
literature has been covered to the end of 1970.
In an extension of some of the work outlined
in the above review, the bisphosphines 1,2-
bis (diphenylphosphino)ethane, bis(diphenylphosphino)
methane, o'is 1,2-bis (diphenylphosphino)-
ethylene and trans 1,2-bis(diphenylphosphino)-
ethylene and the biphosphine derivative tetraphenyibiphosphine
were treated with the powerful
electrophile dimethyl acetylenedicarboxylate in
attempts to synthesize new cyclic phosphonium
ylides containing two phosphorus atoms. On reaction with the acetylenic ester, the
first three of these bisphosphosphines produced
in high yield, cyclic phosphonium ylides character
ized as dimethyl 1,1,4,4-tetraphenyl-l,4-
diphosphacyclohexa-1,3-diene-2,3-dicarboxylate,
dimethyl 1,1,3,3-tetraphenyl-5^-l,3-diphosph(V)ole
4,5-dicarboxylate and dimethyl 1,1,4,4-tetraphenyl 1,4-diphosphorin-2,3-dicarboxylate respectively.
The adducts were found to be extremely sensitive
to water and they were characterized largely by
extensive spectroscopic (mainly NMR) investigations
although certain cheinical reactions assisted in
the structure determinations« Dimethyl 1,1,4,4-
tetraphenyl-1,4-diphosphorin-2,3-dicarboxylate
showed some evidence of aromatic character.
The fourth of the bisphosphines, trans 1,2-
bis(diphenyiphosphino)ethylene, was found to
react with dimethyl acetylenedicarboxylate to
give a 1:1 adduct. NMR evidence suggests that
this adduct has a zwitterionic rather than an
ylidic structure while protonation experiments,
hydrolyses and deuterolyses are consistent with
an ylidic structure. The sum of the evidence
suggested that the adduct in solution is an
equilibrium of two or more isomers in which a
zwitterionic form is the major component while
an ylidic form is the most reactive component
of the mixture. Hydrolysis of the adduct led
to an unusual reaction in which one of the
diphenyiphosphino groups was eliminated to give
a product identical to the 1:1:1 adduct formed
from diphenylvinyIphosphine, dimethyl acetylenedicarboxylate
and water. A mechanism has been postulated for this reaction and deuterium labelling
studies gave some support to this mechanism.
Tetraphenylbiphosphine gave a derivative of
the o'ls 1,2-bis (diphenylphosphino) ethylene
system on reaction with the acetylenic ester. | |
