Cyclodiphosphazanes, of the form, [(RNH)P(µ-NR)]2 are four-membered, P- and N-containing ring systems. In the cis geometric configuration, they serve as a unique class of ligands for transition metals; however, for most substituents, the preferred geometry is trans. An assortment of cyclodiphosphazanes have been modeled using the PBE0 DFT functional and the 6–311++G** basis sets for all atoms to ascertain the driving forces that lead to the generally favored trans versus cis configurations. Global energy minima for cis and trans configurations have been calculated for R = Me, Bz, tBu, o-tol, Ph, Phf, CF3, 2-py, and 2-CH2py as well as a common precursor motif for the class, [ClP(µ-NR)]2. Thermodynamics as well as kinetics (via transition state analyses) for the established [2+2] cycloaddition pathway for their formation has been explored in order to determine their relative significance in selecting for the preferred configuration. Isomerization from cis to trans is frequently observed, thus two plausible pathways for this phenomenon, pyramidal inversion and decyclization, have been modeled.

Computational modeling of the formation and cis-trans isomerization of cyclodiphosphazanes

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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