Summary The synthesis and chemistry of the cycloaddition products formed by reaction of various dienes with nickel bis(1,2-ethenedithiolate) is reported An orbital correlation model previously proposed in describing these and the related olefin reactions is supported by an X-ray diffraction study of the 2,3-dimethylbutadiene/nickel bis(1,2-ethenedithiolate) structure. This study confirms that the products formed by olefins and dienes are close structural relatives. Briefly the structures show a tetradentate sulfur ligand coordinated to square planar nickel. The central ring of the three chelate ring structure is formed in the cycloaddition reaction, and in the present case of a seven membered ring is completely strain free. Bond lengths and molecular properties suggest that reaction is redox in nature with nickel bis(1,2-ethenedithiolate) being the oxidant or acceptor molecule. The crystals studied were monoclinic P2 1/ c with a=7.393(9), b=13.624(21), c = 20.003(26)Å and β=90.80(5)°. The unit cell contains 4 formula units and the structure was solved using 1333 diffractometer measured intensities and refined to a final R factor of 0.094 based on F.