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)(4)Cl](2) yielded crystals suitable for X-ray analysis. Likewise, crystals were obtained from coordination of 6 to FeCl(2). The solid state structures of the resulting complexes (10-12) reveal kappa(2) 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. (C) 2009 Elsevier B. V. All rights reserved.