Chelating diphosphines are an important class of ligands in a wide range of catalytic processes.  Bidentate phosphines provide several structural features that can be modified to optimize catalyst activity including the backbone structure, bite angle, and the substituents on the phosphorus centers.  Symmetrically substituted diphosphines, in which both phosphorus atoms have the same substituents, are the most common class of chelating phosphine ligands.  Asymmetrically substituted diphosphines, where the phosphorus centers have different steric and/or electronic properties, are less widely studied.  The differently substituted diphosphine would offer the ability to fine tune ligand steric and electronic properties at each phosphorus center. Herein we describe the synthesis, isolation, and catalytic application of a series of asymmetrically substituted 1,3-diphosphine ligands. The target 1,3-diphosphines were achieved through sequential substitution of 1,3-dibromoalkanes.  Reaction of a secondary borane phosphide with 1,3-dibromopropane affords 1-borane dialkylphosphino-3-bromopropanes.  A second nucleophilic substitution with a different borane phosphide the borane protected asymmetrically substituted 1,3-diphosphines.  Following borane deprotection with DABCO, the free phosphines are isolated and converted into either phosphonium salts or complexed to palladium.  The resulting complexes have been applied to carbonylation reactions.

Synthesis and catalytic application of asymmetrically substituted 1,3-diphosphines

255th National Meeting (2018)

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