Exploiting the o-Quinodimethane Nature of Naphthalene: Cycloaddition Reactions with η2-Coordinated Tungsten–Naphthalene Complexes

Naphthalene, when bound to the complex {TpW(NO)(PMe₃)}, is shown to be activated toward Diels–Alder cycloaddition in the bound ring with N-methylmaleimide (NMM). In its most stable form, the tungsten in this complex binds C1 and C2. However, the cyclization reaction is thought to proceed through an intermediate in which the metal binds C2 and C3, rendering the uncoordinated portion of the hydrocarbon similar to a quinodimethane. The reaction rates and regio- and stereochemistry are investigated for a series of substituted naphthalene ligands, and these observations support the proposed mechanism. An X-ray structure of the complex TpW(NO)(PMe₃)(η²-L), where L is the cycloadduct of NMM and 1,4-dimethylnaphthalene, confirms the endo stereochemistry of the cycloaddition.