Microwave synthesis of mono- and bis-tetrazolato complexes via 1,3-dipolar cycloaddition of organonitriles with nickel(II)-bound azides: Isolation of 5-substituted tetrazoles from parent complex

[2 + 3] Cycloaddition reaction of diazidonickel(II) complexes cis-[Ni(N3)2(phen)2] 1 with organonitriles NCR 2 under microwave irradiation give the bis(tetrazolato) complexes cis-[Ni(N4CR)2(phen)2] [R = Ph (3a), 4-NC5H4 (3b), 3-NC5H4 (3c), 4-CNPh (3d)]. Treatment of the tetrazolato complexes with excess of NaN3 liberates the free tetrazoles from the parent metal complexes. Reaction of 2-cyanopyridine with cis-[Ni(N3)2(phen)2] 1 in presence of NaClO4 gives a mono(tetrazolato) complex [Ni{5-(2-pyridyl)-tetrazolato}(phen)2](ClO4) 3e along with formation of pure 2-(1H-tetrazol-5-yl)-pyridine. Reaction of tetracyanoethylene with cis-[Ni(N3)2(bipy)2] 4 at room temperature produced a bis(tetrazolato) complex [Ni{2-cyano-3-(tetrazolato-5-yl)-but-2-enedintrile}2(bipy)2] 5. A monoazidonickel complex [Ni(N3)(H2O)(phen)2]ClO4 6 was isolated as a minor product during the synthesis of cis-[Ni(N3)2(phen)2] 1. All the complexes obtained were characterized by IR, elemental analyses and ESI-MS apart from single crystal X-ray crystallography.