Acid-Induced Reactions of 1,2-Oxaphosphetane Complexes

Abstract

Selective P–O bond activation of 1,2-oxaphosphetane complexes [(OC)5W(P{CH(SiMe3)2}CH2CRR′O)] (R/R′ = H/H (1a), H/CH3 (1b), H/CF3 (1c), CF3/CF3 (1d)) was achieved using different Bronsted acids. In case of acids with nucleophilic anions, such as HCl and HBF4·OEt2, the corresponding halophosphane complexes [(OC)5W(XP{CH(SiMe3)2}CH2CRR′OH] (X = Cl (2a–c), F (3c,d)) resulted as ring-opened products; 2b could be closed again with tBuLi/12-crown-4. In contrast, trifluoromethanesulfonic acid could be used to initiate either a ring-opening hydrolysis with a subsequent cleavage of the P–M bond to yield PH(O){CH(SiMe3)2}{CH2C(CF3)2OH} (7) or, in the presence of nitriles, a ring expansion yielding [(OC)5W(P{CH(SiMe3)2}CH2CH2OCR═N)] (R = CH3 (5a), Ph (5b), C(CH3)3 (5c)). P–O bond cleavage in 1a was achieved using the Lewis acidic catechol(chloro)borane to give [(OC)5W(P{CH(SiMe3)2}CH2CH(CH3)OBcat}Cl)] (8; cat = catechol).