Diphosphino-Functionalized 1,8-Naphthyridines: a Multifaceted Ligand Platform for Boranes and Diboranes

A 1,8-naphthyridine diphosphine (NDP) reacts with boron-containing Lewis acids to generate complexes featuring a number of different naphthyridine bonding modes. When exposed to diborane B2Br4, NDP underwent self-deprotonation to afford [NDP-B2Br3]Br, an unsymmetrical diborane comprised of four fused rings. The reaction of two equivalents of monoborane BBr3 and NDP in a non-polar solvent provided the simple phosphine-borane adduct [NDP(BBr3)2], which then underwent intramolecular halide abstraction to furnish the salt [NDP-BBr2][BBr4], featuring a different coordination mode from that of [NDP-B2Br3]Br. Direct deprotonation of NDP by KHMDS or PhCH2K generates mono- and dipotassium reagents, respectively. The monopotassium reagent reacts with one or half an equivalent of B2(NMe2)2Cl2 to afford NDP-based diboranes with three or four amino substituents.