Abstract
The reductive cleavage of phenylalkylphosphines Ph~2~PR, PhPR~2~ (R = Bu, iPr) with Na/NH~3~ is unselective: both phenyl and alkyl groups can be cleaved and Birch reduction may occur. Reaction of Ph~2~tBuP gives a high yield of diphenylphosphide. Polar groups (CO~2~Na, SO~3~,Na) at the ω position of primary alkyl groups may lead to an increase in selectivity; Birch reduction is suppressed and a functionalised secondary phosphide is obtained.
From diarylbenzyl‐ and diarylallylphosphines, the benzyl and allyl groups are selectively removed; Ar~2~PH and ArRPH are formed in high yield after hydrolytic work‐up unless the aryl group bears F, CF~3~, or (CH~3~)~2~N substituents. From the reaction mixture of Ph~2~PCH~2~Ph we have isolated 1,2‐ ‐diphenylethane.
2‐Methoxyphenyl and 2,6‐dimethoxyphenyl groups are selectively removed from Ar~2~BuP, ArPhBuP and Ar~2~P(CH~2~)~3~PAr~2~, forming ArBuPH, PhBuPH and ArP(H)(CH~2~)~3~(H)PAr, respectively. A double‐cleavage reaction of Ar~2~RP may occur in low yield. 2,6‐(Dimethoxyphenyl‐dibutylphosphine gives dibutylphosphine in moderate yield. When compounds with a 2,6‐dimethoxyphenyl moiety are allowed to react with Li/THF, removal of a methyl group leads to novel phosphinophenols. It is concluded that cleavage of alkyl groups R selectively occurs when R° is relatively stable (tBu, PhCH~2~ > iPr > Bu).