Synthesis of New Metallacycles of Rhenium(VII) Oxides: Migration of a Me3Si Group to Form the cis-Dioxo Cyclometallaphosphoranimino Phosphane Cyclic NPPh2CH2PPh2Re(O)2(OSiMe3)2 and Arsane Cyclic NPPh2(CH2)2AsPh2Re(O)2(OSiMe3)2.