Ladderenes and polyladderenes are highly strained fused carbocycles, accessed via photochemical [2+2] cycloadditions. [3]- And [5]-ladderanes have been isolated from living organisms, making them important targets for synthetic chemists. Polyladderenes are precursors to polyacetylene–a valuable but unstable conductive polymer. are anticipated to have improved stabilities relative to polyacetylenes, but straightforward methodologies towards fluoropolyacetylene are largely absent from the literature. The Burns and Lopez groups have collaborated to map the potential energy surfaces (PESs) corresponding to a photochemical pericyclic cascade reaction. Perfluorobenzene and [2]-ladderene are continuously irradiated with 254 nm light to promote a [2+2]-cycloaddition followed by a 4π-disrotatory ring closing reaction to form [5]-hexafluoroladderene. For this reaction, exploratory complete active space self-consistent field (CASSCF) calculations with an active space of 8 orbitals and 8 electrons, and the 6-31G(d) basis set were performed to locate the stationary points on the PES.  The previous results where refined by including 3p functions to the standard Pople 6-31G(d) basis set. This basis set, 6-31G(d)+3p, was then used to generate oscillator orbitals to account for electron correlation. Finally, restricted active space self-consistent field (RASSCF) calculations using an active space defined by the correlating orbitals were performed at the Franck-Condon geometries found with the CASSCF(8,8)/6-31G(d) level of theory.  Further improvements to the CASSCF energies due to electron correlation effects will be explored using perturbative corrections, (<i>i.e.</i>,) CASPT2. Computations on reactions involving substituted [2]-ladderenes are currently underway to broaden our understanding of this photochemical cascade.

Multireference computations elucidate the mechanism of a photochemical cascade reaction  towards fluoropolyacetylene

2019 Spring National Meeting

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