Reactivity of a Sterically Unencumbered α-Borylated Phosphorus Ylide towards Small Molecules

The influence of substituents on alpha-borylated phosphorus ylides (alpha-BCPs) has been investigated in a combined experimental and quantum chemical approach. The synthesis and characterization of Me3PC(H)B(iBu)(2) (1), consisting of small Me substituents on phosphorous and iBu residues on boron, is reported. Compound 1 is accessible through a novel synthetic approach, which has been further elucidated through DFT studies. The reactivity of 1 towards various small molecules was probed and compared with that of a previously published derivative, Ph3PC(Me)BEt2 (2). Both alpha-BCPs react with NH3 to undergo heterolytic N-H bond cleavage. Different di- and trimeric ring structures were observed in the reaction products of 1 with CO and CO2. With PhNCO and PHNCS, the expected insertion products [Me3PC(H)(PhNCO)B(iBu)(2)] and [Me3PC(H)(PhNCS)B(iBu)(2)], respectively, were isolated.