Bend the Coin Your Way: Ligand Design and Main Group Element Chemistry

The dibenzo[a,d]cycloheptatrienyl residue is introduced as platform for the high-yield synthesis of new rigid phosphanes (tropp ligand system) and phosphiranes (BABAR-phos); strained three-membered heterocycles. With tropp as ligands, transition metal complexes with unusual low oxidation states at the metal center could be prepared and isolated. Especially mononuclear paramagnetic rhodium(O) and iridium(O) complexes could be studied in detail. The BABAR-phos compounds show very high thermal and chemical stability, i.e. they are remarkably stable against oxygen, sulfur, strong alkylating agents, and aqueous acid and base. Rhodium(l) complexes with BABAR-phos proved to be highly stable active catalyst precursors for hydroborations.