A combined synthetic-theoretical study has been undertaken to determine the factors that influence transannulation in azaphosphatranes. The commonly used proazaphosphatrane P­(i-BuNCH2CH2)3N and several of its oxidized congeners are used as model systems. The haloazaphosphatranes of P­(i-BuNCH2CH2)3N were synthesized, including a rare fluoroazaphopshatrane, and used as references for computational investigations. Comparisons of the experimental and theoretical observations highlight the flexibility observed in transannulated atranes and the potential for multiple local energetic minima depending on the identity of the equatorial substituents for a given azaphosphatrane. Theoretical calculations also identify the role of the ethylene linker in azaphosphatrane bonding, the influence of transannulation on P–electrophile interactions, and the contribution of electrostatic interactions to transannulation.

The preparation and reactivity of elusive palladium proazaphosphatrane complexes that represent putative intermediates in C−N cross-coupling reactions are described. Variable transannulation in these compounds, as determined by X-ray crystallography, validates the previously untested hypothesis that proazaphosphatranes undergo conformational changes to stabilize catalytic intermediates. The competence of these complexes as catalytic intermediates is supported through stoichiometric and catalytic coupling reactions, providing the first examples of discrete proazaphosphatrane complexes employed in cross-coupling.