Palladium catalyzed cross-coupling reactions have become an invaluable tool in synthetic organic chemistry. Catalytic systems involving trialkylphosphine ligands in particular have been extensively developed. Despite the widespread adoption of this methodology several drawbacks remain including the air-sensitivity of the phosphine ligands and a limited understanding of the active species. A series of air-stable trialkylphosphine palladium dichloride dimers ([Pd(PR3)Cl(�-Cl)]2) and trialkylphosphine allyl palladium chloride complexes (Pd(?3-allyl)(PR3)Cl) containing neopentylphosphine ligands were prepared and shown to provide active catalysts for cross-coupling reactions. Effective steric profiles of the neopentylphosphines were probed by measuring the binding equilibria of the phosphines to [Pd(PR3)Cl(�-Cl)]2 to give Pd(PR3)2Cl2. These results suggest that conformational flexibility of the neopentyl substituent plays a key role in the steric demand of neopentylphosphines. The effect of varying allyl substitution on the stability of Pd(?3-allyl)(PR3)Cl complexes and their conversion to catalytically active species was investigated.

Structural studies and activation mechanisms for air-stable neopentylphosphine palladium pre-catalysts

245th National Meeting (2013)

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