The reaction of nitrous oxide (N2O) with Nheterocyclic olefins (NHOs) results in cleavage of the N-O bond and formation of azo-bridged NHO dimers. The latter represent very electron-rich compounds with a low ionization energy. Cyclic voltammetry studies show that the dimers classify as a new organic super-electrondonors, with a reducing power similar to what is found for tetraazafulvalene derivatives. Mild oxidants are able to convert the neutral dimers into radical cations, which can be isolated. Further oxidation gives stable dications.

Reactions of [(C2H4)2RhCl]2 or [(coe)2RhCl]2 (coe = cyclooctene) with AgPF6 and arenes, followed by addition of 3-hexyne, give the cyclobutadiene complexes [(C4Et4)­Rh­(arene)]+ in 40–65% yield (arene = tert-butylbenzene, p-xylene, mesitylene, 4-mesitylbutanoic acid). In the absence of arenes, the hexaethylbenzene complex [(C4Et4)­Rh­(C6Et6)]+ is formed in 70% yield as a result of cyclotrimerization of 3-hexyne in the coordination sphere of rhodium. Similar reaction of [(coe)2IrCl]2 with AgPF6 and 3-hexyne leads to [(C4Et4)­Ir­(C6Et6)]+, which is apparently the first reported cyclobutadiene iridium complex. DFT calculations suggest that formation of the model cyclobutadiene complex [(C4Me4)­Rh­(C6H6)]+ from bis­(alkyne) intermediate [(C2Me2)2Rh­(C6H6)]+ can proceed via a metallacycle transition state with a low energy barrier of 14.5 kcal mol–1.

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