Our research goal is to design palladium compounds bonded to negatively charged diphosphorus compounds and to test them for catalysis. We have explored two ways to synthesize these compounds. The first plan involves forming the negatively charged diphosphorus compound then bonding it to palladium. Here, palladium acts as a catalyst that promotes two diphosphine units to react with each other to form new tetraphosphine compounds that do not contain palladium.The second plan uses the same steps in reverse: first, the neutrally charged diphosphorus compound is bonded to palladium; then, while it is on palladium, the diphosphorus compound is converted to the negatively charged form. We have found that this procedure generally forms new palladium-diphosphine dimers in which symmetric diphosphines remain neutral. Similar compounds are known, and they have been shown to demonstrate catalytic activity for organic transformations. A modification to our procedure in which an unsymmetric diphosphine compound was tested and found to yield a palladium complex that contains negatively charged diphosphorus units. Therefore, our research has focused on the synthesis of new unsymmetric diphosphine compounds. Our more recent results suggest that when all four phosphine substituents are aromatic, the diphosphine compound can react to become negatively charged. However, with alkyl substituents present, the diphosphine compound remains neutral. We have narrowed our focus on unsymmetric diphosphine ligands that contain only aromatic substituents with different electronic and/or spatial character to further examine conditions that favor the diphosphine to become negatively charged.

Dimerization reactions of palladium with symmetric and unsymmetric diphosphinomethane compounds

248th National Meeting (2014)

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