Synthesis, reactions, and structural and NMR features of [2.2]metacyclophane monoenes and their tricarbonylchromium and cyclopentadienyliron(+) complexes

8,16-Dimethyl-, 5,8,13,16-tetramethyl, and 4,6,8,12,14,16-hexamethyl[2,2]me tacyclophanene have been synthesized from the corresponding methyl-substitu ted 3-thia[3.2]metacyclophane precursors via a Wittig rearrangement-Hofmann elimination procedure. Simple addition of bromine or similar electrophiles to the bridge double bond of the cyclophane monoenes did not occur; rather , the methyl-substituted dihydropyrenes were formed. However, mono- and bis -tricarbonylchromium and monocyclopentadienyliron complexes were obtained u sing ligand-exchange reactions. Addition of bromine to the cyclophane bridg e double bond of the iron complex did occur, but unusually slowly. Surprisi ngly, debromination rather than dehydrobromination occurred when the dibrom o addition product was treated with a variety of bases. Photoisomerization of the monoenes and nucleophilic substitution of the metal complexes was al so investigated. The geometries of the monoenes and their complexes were co mpared to the cyclophanes and the cyclophanedienes and to the monothia- and dithiacyclophanes, by comparison of X-ray and calculated structural data a nd NMR spectroscopic data. Introduction of double bonds into the cyclophane bridges causes the cyclophane step to be less steep but increases distorti on of the internal atoms out of the plane of the benzene rings. Making the bridges nonidentical also causes a sideways twist of the step.