Our research focuses on the synthesis of palladium complexes containing unsymmetrical diphosphine ligands. Our previous findings show that when all four phosphine substituents are aromatic, the methylene carbons can be deprotonated.  For example, when the ligand is Ph2PCH2P(2-methylphenyl)2, the dianionic palladium complex, [Li(Et2O)]2[Pd(Ph2PCHP(2-methylphenyl)]2, forms, where the each diphosphino ligand is tridentate, bonding to three metals (two Pd atoms and Li) through the phosphorus atoms and its central methanide atom. However, when alkyl substituents are present, deprotonation does not occur, and the ligands are bidentate. It appears that electron-donating properties, and possibly steric hindrance, of the alkyl groups prevent deprotonation of the methylene backbone.  Our current study focuses on the synthesis of unsymmetric Ph2PCH2PR2 ligands, where R = 3,5-dimethylphenyl, 2-methoxyphenyl, or 3,5-bis(trifluoromethyl)phenyl, and their preferred bonding mode when treated with base in the presence of palladium. These compounds have been analyzed by 1H and 31P{1H} NMR spectroscopy.

Synthesis, characterization, and reactivity of unsymmetric diphosphinomethane ligands

243rd National Meeting (2012)

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