Organic ligands provide a highly flexible platform that can be used to modulate the course of metal-catalyzed reactions. Through fine control of ligand steric and electron properties, reactions with multiple possible outcomes can be selectively driven to desired products. Our group has a long-standing interest in developing an understanding of the role of steric and electronic properties of ligands in catalyst performance. Phosphine ligands with conformationally flexible substituents, such as neopentyl or benzyl, have proven to afford catalysts with interesting synthetic applications. The highly flexible trineopentylphosphine ligand affords catalysts that are highly active for the C–C and C–N coupling of sterically demanding substrates. In contrast to sterically rigid ligands, such as tri-tert-butylphosphine, trineopentylphosphine provides a highly active catalyst for coupling of sterically demanding aryl halides and aryl amines. The neopentylphosphine family of ligands provides for fine control of the product selectivity of Heck couplings of cyclic alkenes to afford either the kinetically or thermodynamically preferred olefin product. Neopentylphosphines readily form metallacyclic complexes by C–H activation of the neopentyl substituent. The [Pd(µ-κ2-O,O-OAc)( κ2-C,P-(t-Bu)2PCH2C(Me)2CH2)]2 complex selectively affords E-5-aryl-2-en-4-yn-1-ol products in good yields under mild conditions with high chemo-, regio-, and stereoselectivity.

Conformational flexibility as a design element in ligand design for palladium-catalyzed bond-forming reactions

253rd National Meeting (2017)

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