Octaboraneyl Complexes of Nickel: Monomers for Redox-Active Coordination Polymers

Herein, we establish the preparation, characterization, and reactivity of a new diphosphine ligand, 1,2-bis(di(3-dicyclohexylboraneyl)propylphosphino)ethane (P2B4Cy), a scaffold that contains four pendant boranes. An entryway into the coordination chemistry of P(2)B(4)(Cy)is established by using nickel, providing the octaboraneyl complex [Ni(P2B4Cy)(2)]-this species contains a boron-rich secondary coordination sphere that reacts readily with Lewis bases. In the case of 4,4 '-bipyridine, an air-sensitive coordination polymer is obtained. Characterization of this material by solid-state NMR and EPR spectroscopy reveals the presence of a charge-transfer polymer, which forms as a function of intramolecular Ni -> 4,4 '-bpy electron transfer (ET), providing an array of oxidized nickel sites and reduced 4,4 '-bpy radical anion sites. Notably, the related intermolecular reaction between the model fragments [Ni(dnppe)(2)] (dnppe=1,2-bis(di-n-propylphosphino)ethane) and a bis(boraneyl)-protected 4,4 '-bpy, provides no ET. Overall, the P(2)B(4)(Cy)fragment provides a unique opportunity for Lewis base activation, in one case allowing for the facile construction of monomers for incorporation into redox-active macromolecules.