Conjugate phosphination of cyclic and acyclic acceptors using Rh(I)–phosphine or Rh(I)–carbene complexes. Probing the mechanism with chirality at the silicon atom or the phosphorus atom of the Si–P reagent

The Rh(I)-catalyzed conjugate phosphinyl transfer from an Si–P reagent to an electron-deficient acceptor requires individual protocols for cyclic and acyclic α,β-unsaturated carbonyls and carboxyls. While 1,4-addition to cyclic acceptors is catalyzed by a Rh(I)–phosphine complex, a Rh(I)–carbene complex is needed to promote conjugate phosphination of acyclic acceptors. General procedures for both systems are reported. Aside from monophosphine-derived Si–P reagents as phosphinide sources, dppe- as well as dppp-derived reagent having two Si–P units do also participate in this reaction. The mechanism of this Rh(I)-catalyzed activation of the Si–P reagent is still under debate. Control experiments with enantiopure silicon-stereogenic and racemic phosphorus-stereogenic Si–P reagents support a catalysis commencing with transmetalation rather than oxidative addition. Preparation and full characterization data of the Si–P compounds used in this investigation is included.