My PhD dissertation - Institut Fresnel

10
Although the most frequently employed method for the preparation of tertiary
phosphines i.e. the reaction of phosphorus trihalide with Grignard reagents
[ , ] 68 69 or
organolithium species [48, 66, 67] is efficient in most cases, this method does not always give
satisfactory yields [51] o
-1 [ 70 ]
. Since the lower reactivity of the P−O bonds ( D298
≈ 596 kcal·mol )
o
compared to the P−Cl bonds ( D 289 kcal·mol
298 ≈
demonstrated by different research groups
-1 ) [ ]
71 towards organometallic reagents was
[ - ] 72 76 , the use of phosphites instead of phosphorus
trichloride was believed to give cleaner reactions and thus, should allow performing reactions
on larger scale without any special care. Since the use of phosphorus trichloride was thought
to produce, in situ, molecular chlorine and could cause partial oxidation of the phosphine
formed, its substitution by a phosphite constituted an additional advantage. As a matter of
fact, depending on its structure, the phosphine formed can be prone to rapid oxidation and
form, to some extent, the corresponding tertiary phosphine oxide which usually causes tedious
purification procedures. Although the use of phosphite for the preparation of tertiary
phosphines had already been mentioned in few reports from the beginning of the 20 th century
until now
[49 - 51, , ] 77 78 , no rational arguments were given to explain the failure of other
classical preparation procedures nor the better yields obtained with phosphites. Furthermore,
in most cases the yields were relatively low. Therefore, several already described
triarylphosphines were prepared by means of triethyl phosphite to evaluate and compare the
efficiency of this method compared to more classical ones. Once the "phosphite pathway"
procedure had been well established, new furyl and pyrrolylphosphines have been prepared.
2.1 Uniformly Substituted Triarylphosphines
Triarylphosphines were formed in excellent yields when triethyl phosphite was
condensed with three equivalents of aryllithiums (Table 1). The latter were generated from the
corresponding bromoarene by halogen/metal permutation using butyllithium. In the case of
tris(3,5-dimethylphenyl)phosphine (7), 1-iodo-3,5-dimethylbenzene
material.
R
X
1) LiC 4H 9, THF, - 75 °C
2) P(OEt) 3, - 75 °C to 25 °C
P
[ ] 79 served as the starting
R
3