Contribution to the chemistry of boron. CCXXV[1]: Reactions of monomeric phosphanylboranes with acyl chlorides : 1-oxa-3-oxonia-5-phospha-2-borata-3,5-cyclohexadienes

Monomeric B-[bis(trimethylsilyl)phosphanyl]-9-borabicyclo-[3.3.1]nonane (1) reacts with acyl chlorides 2 in a 1:2 ratio to afford deep red derivatives of six-membered oxaoxonia-σ 2 ,λ 3 -phosphaboratacyclohexadienes 3. In contrast, the (ditert-butylboryloxy)phosphaethene 5 is obtained from tBu 2 BP-(SiMe 3 ) 2 (4) and PhC(O)Cl. It is assumed that both reactions proceed via a common intermediate, an (acylphosphanyl)borane 6. The color of compounds 3, which feature a flat boat conformation, is due to a π-π * transition