Microwave synthesis of mono- and bis-tetrazolato complexes via1,3-dipolar cycloaddition of organonitriles with platinum(ii)-bound azides

Abstract

[2 + 3] Cycloaddition reactions of the diazidoplatinum(II) complexes cis-[Pt(N₃)₂(PPh₃)₂] 1 and cis-[Pt(N₃)₂(2,2′-bipy)] 4 with organonitriles NCR 2 give the bis(tetrazolato) complexes trans-[Pt(N₄CR)₂(PPh₃)₂] 3 [R = Me (3a), Et (3b), Pr (3c), Ph (3d), 4-ClC₆H₄ (3e)] and cis-[Pt(N₄CR)₂(2,2′-bipy)] 5 [R = Me (5a), Et (5b), Pr (5c), Ph (5d)]. The reaction of cis-[Pt(N₃)₂(PPh₃)₂] 1 with propionitrile also affords, apart from 3b, the unexpected mixed cyano-tetrazolato complex trans-[Pt(CN)(5-ethyltetrazolato)(PPh₃)₂] 3b′ which is derived from the reaction of the bis(tetrazolato) 3b with propionitrile, with concomitant formation of 5-ethyl-1H-tetrazole, via a suggested unusual oxidative addition of the nitrile to Pt^II. All these reactions are greatly accelerated by microwave irradiation and this method also shows a higher selectivity in the case of the reaction of propionitrile with 1, leading only to the formation of 3b. All the complexes obtained were characterized by IR, ¹H, ¹³C and ³¹P{¹H} (for complexes 3) NMR spectroscopies, FAB-MS and elemental analyses. Complexes 3b′, 3d, 3e and 5d were also characterized by X-ray structural analyses.