Synthesis and characterization of R2PN=P(iBuNCH2CH2)3N: a new bulky electron-rich phosphine for efficient Pd-assisted Suzuki-Miyaura cross-coupling reactions.

Pro-azaphosphatrane 1a [P(iBuNCH2CH2)3N] reacts with iodine under mild conditions to give [IP(iBuNCH2CH2)3N]I in excellent yield, which on subsequent reaction with ammonia followed by deprotonation with KOtBu provided HN=P(iBuNCH2CH2)3N (3a) in quantitative yield. Reaction of 3a with R'2PCl afforded sterically bulky electron-rich phosphines of the type R'2PN=P(iBuNCH2CH2)3N (4) [R'=Ph (4a), iPr (4b), tBu (4c)]. The Pd(OAc)2/4c catalyst system was particularly efficient for the coupling of arylboronic acids with aryl bromides as well as aryl chlorides to give biaryls in excellent yields.