Structures of dibenzocycloheptenylidene- and fluorenylidene-(2,4,6-tri-t- butylphenyl)phosphines and their reactions with sulfur

Dibenzocycloheptenylidene(2,4,6-tri-t-butylphenyl)- phosphine and fluorenylidene(2,4,6-tri-t-butylphenyl)- phosphine were prepared by the reactions of lithium silylphosphide with benzosuberenone and fluorenone, respectively. The reactions of the phosphines with sulfur were carried out to compare the results with those of the corresponding diphenyl derivative, and the new findings are discussed in terms of steric hindrance based on the results of the X-ray crystallographic analyses for dibenzocycloheptenylidenephosphine and its sulfide and the computational structure for the fluorenyl derivative.