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 pho sphiranes (BABAR-phos); strained three-membered heterocycles. With tropp as ligands, transition metal complexes with unusual low oxidation states at t he metal center could be prepared and isolated. Especially mononuclear para magnetic rhodium(0) and iridium(0) complexes could be studied in detail. Th e 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(I) complexes with BABAR-phos proved to be highly stable active catalyst precursors for hydroborations.