synthesis of newdiphosphenes TbtPPTbt and BbtPPBbt having extremely bulky substituents, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (Tbt) and 2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl groups (Bbt). Their x-ray crystallographic analysis revealed their unique structures in the solid state. Furthermore, the configurations of these extremely overcrowded diphosphenes, TbtPPTbt