PREPARATION AND ISOMERIZATION OF 3,4-BIS(2,4,6-TRI-TERT-BUTYLPHENYLPHOSPHINIDENE)CYCLOBUTENES

(E,E)- and (E,Z)-3,4-Bis(2,4,6-tri-t-butylphenylphosphinidene)cyclobutenes were prepared by desilylation reaction of the corresponding 1,2-bis(trimethylsilyl)cyclobutenes or by thermal isomerization reaction of 1,6-bis(2,4,6-tri-t-butylphenyl)-1,6-diphospha-1,2,4,5-hexatetraene. Optimized structures and total energies of various parent compounds C4H4P2 were calculated by ab initio method and the effect of steric congestion on the valence isomerization is discussed.