Hexahapto metal coordination to cyclic conjugated trienes was first reported in 1958. It is therefore surprising that no unambiguous reports of hexahapto complexes of acyclic conjugated trienes have appeared in the literature. In this presentation we describe the synthesis, structures, and chemical reactivity of the first hexahapto complexes of acyclic conjugated trienes. Significant structural differences are found between cyclic and acyclic conjugated trienes due in part to the existence of the multiple conformations available to acyclic triene ligands. Computational studies establish the relative energies of the three possible hexahapto hexatriene ligands in CpRu(triene)+ complexes (I-cis/cis, I-trans/cis, and I-trans/trans). The s-cis/s-cis isomer I-cis/cis is shown computationally to undergo a concerted disrotatory ring closure to a CpRu(cyclohexadiene)+ complex. In solution, [CpRu(NCMe)3]BF4 is shown to catalyze the disrotatory electrocyclic ring closure of conjugated trienes that fail to undergo thermal or photochemical 6π electrocyclizations. Mechanistic and computational studies support a ruthenium-catalyzed 6π electrocyclization mechanism.

Transition-metal complexes of acyclic conjugated trienes: Synthesis, structure and chemical reactivity

ACS Fall 2020 Virtual Meeting

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