Diphenylglycoluril as a novel ligand architecture for dirhodium(II) carboxamidates

1,6-Bis-(N-benzyl)-diphenylglycoluril (1,6-BPGlyc) was used as a ligand in the synthesis of a dinuclear rhodium(II) paddlewheel complex. The ligand exchange reaction from Rh2(OAc)4 was remarkably selective for the formation of Rh2(1,6-BPGlyc)2(OAc)2 with a cis-(1,3) ligand arrangement in 46% isolated yield. The bis-substitution pattern and diastereoselective ligand exchange is attributed to the steric bulk of the glycoluril backbone that prevents further ligand substitution. Rh2(1,6-BPGlyc)2(OAc)2 catalyzes cyclopropanation reactions via decomposition of diazoacetates with reactivities and selectivities that were comparable to those of dirhodium(II) tetrakis-μ-carboxamidates.