Abstract Unprecedented C [BOND] P systems: Me 3 SiX (X= Br, I) catalyses rearrangements of P III esters R′ R′′ P [BOND] OR into the corresponding phosphoryl systems, providing a simple, mild and efficient route to a variety of structures containing P [BOND] C bonds. The mechanism has been found to be fundamentally different from that of the Arbuzov–Michaelis reaction and includes three definite steps a, b and c (see scheme).