Cyclobutadiene-silver nitrate complex

It had been thought that a cyclobutadiene silver nitrate complex resulted from the reaction shown in the equation below [51, 52]. However, subsequent spectral studies suggest that the product should be formulated as the dimeric complex, 3.16 [53, 54]. 

The best known of these complexes was cyclobutadiene silver nitrate prepared by Nenitzescu et al. (5). It was assigned structure (LXXXIX) on the basis of its method of preparation and some incorrect proton NMR data (4). A careful repetition of this work (3), however, show ed the complex to be the di(silver nitrate) complex of ryn-tricyclooctadiene (XC). In solution this complex isomerized to a cyclooctatetraene-silver nitrate complex which gave the originally observed (4) single proton resonance. 

A silver-cyclobutadiene complex is obtained when the mercury-containing, bromine-free oil, obtained by treatment of 1,2,3,4-tetrabromo-cyclobutane with lithium amalgam, is treated with silver nitrate (5). The complex forms colorless crystals which, on treatment with steam, evolve... 

On treatment with aqueous silver nitrate it forms a stable crystalline complex (78), from which 75 can be recovered almost quantitatively by addition of ammonia ". Anhydrous nickel(ii) bromide converts cyclooctyne into the trimer (79) with a quantitative yield . However, when the reaction was carried out in the presence of a trace of water, the dimeric cyclobutadiene-nickel bromide complex (80) was obtained in 9-4% yield, together with 79 (85%) . The spectroscopic properties of 80 showed close similarity with those of the tetramethylcyclobutadiene-nickel chloride complex . 

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