A tetraanionic diphosphine borate ligand: Complexation with platinum

Charge is a property that is inherent to most chemical phenomena. In coordination chemistry, charge can be conferred through targeted ligand design. Notwithstanding, examples of ligands containing greater than a single pendant point charge remain sparse. This report describes a new diphosphine framework that hosts four tetraborate units, accessed from borane alkylation of 1,2-bis(di(3-dicyclohexylpropylboranyl)phosphino)ethane (P2BCy4) using alkyllithium reagents. The coordination chemistry of this ligand was developed using the platinum(II) starting material, [Pt(COD)(CH3)2] (COD = 1,5-cyclooctadiene) providing the corresponding tetraanionic Pt(II) compound. Despite its high negative 4- charge, this species (and its ligand) are soluble in common non-polar organic solvents such as pentane and toluene, complementing previously examined sulfonate or carboxylate-containing diphosphine ligands, developed for chemistry in aqueous media. This work additionally outlines the effect of ligand charge state on spectroscopic observables, such as NMR chemical shift, coupling constant, and infrared stretching frequency.