Reaction of Triarylphosphines with Tetramethyl-1,2-dioxetane: Kinetics of Formation and Decomposition of 2,2-Dihydro-4,4,5,5-tetramethyl-2,2,2-triaryl-1,3,2-dioxaphospholanes

Article abstract of DOI:10.1021/jo01306a010

The reaction of a series of triarylphosphines <(XC6H4)3P> with tetramethyl-1,2-dioxetane (1) in C6D6 produced a series of 2,2-dihydro-4,4,5,5-tetramethyl-2,2,2-triaryl-1,3,2-dioxaphospholanes in high yield.Thermal decomposition of the phosphoranes produced tetramethylethylene oxide and the corresponding triarylphosphine oxides in all cases.The kinetics of phosphorane formation and decomposition in benzene was investigated.The rate data for phosphorane formation showed a reasonable correlation with ?⁺ constants (correlation coefficient ca 0.98: ρ = -0.82).Theresults are not consistent with nucleophilic attack on oxygen by phosphorus but rather with a concerted (biphilic) insertion into the peroxy bond of the dioxetane.Phosphorane decomposition (at 38 deg C) was found to be substantially more sensitive to substituent effects than phosphorane formation.A good correlation of phosphorane decomposition with Hammett ? constants was obtained (correlation coefficient = 0.997, ρ = -3.51 +/- 0.24).This result is consistent with a mechanism that involves heterolytic cleavage of a phosphorus-oxygen bond followed by the irreversible internal displacement of triarylphosphine oxide.