Design, synthesis and coordination chemistry of sidearm substituted bisoxazoline ligands

We describe herein the design, synthesis and coordination chemistry of a novel ligand motif that combines a bisoxazoline with a third flexible chelating substituent (“tail”). Four such ligands (6-9) were synthesized from phenylglycine in 4–5 steps each in ca. 20% overall yield. Coordination of 6 and 7 to [Re(CO)4Cl]2 yielded crystals suitable for X-ray analysis. Likewise, crystals were obtained from coordination of 6 to FeCl2. The solid state structures of the resulting complexes (10–12) reveal κ2 binding of the bisoxazoline motif; however, the structures of complexes 10 and 12 show that the “tail” is poised above the metal center, demonstrating the potential for alternate binding modes in solution. The complexes exhibit a relatively planar 6-membered chelate structure, in contrast to the boat conformation typical of trispyrazolylborate complexes.