Synthesis of (1,2,4‐Oxadiazole)palladium( II ) Complexes by [2 + 3] Cycloaddition of Nitrile Oxides to Organonitriles in the Presence of PdCl 2

The reaction between the nitrile oxides 2,4,6‐R 3 C 6 H 2 CNO (R = Me, OMe) and trans ‐[PdCl 2 (RCN) 2 ], or RCN (R = Me, Et, CH 2 CN, NMe 2 , Ph) in the presence of PdCl 2 , proceeded smoothly under mild conditions and allowed the isolation of the 1,2,4‐oxadiazole complexes trans ‐[PdCl 2 {N a =C(R)‐ON=C b (C 6 H 2 R 3 )( N a –C b )} 2 ] ( 1 – 8 ) in 40–85 % yields. In CH 2 Cl 2 , the reaction between 2,4,6‐R 3 C 6 H 2 CNO and [PdCl 2 (MeCN) 2 ] furnishes [PdCl 2 (ONCC 6 H 2 R 3 ) 2 ] ( 9 and 10 ), which are the first representatives of metal compounds where nitrile oxides act as ligands. The 1,2,4‐oxadiazole complexes 1 – 8 were characterized by elemental analysis, FAB mass spectrometry, and IR, 1 H and 13 C{ 1 H} NMR spectroscopy, while 2 , 3 , 7 , and 8 were additionally characterized by X‐ray crystallography. The liberation of the heterocyclic species from 1 – 8 was successfully performed by substitution reaction either with 1,2‐bis(diphenylphosphanyl)ethane or with an excess amount of Na 2 S · 7H 2 O in MeOH; the liberated 1,2,4‐oxadiazoles ( 11 – 18 ) were characterized by positive‐ion FAB mass spectrometry and 1 H and 13 C{ 1 H} NMR spectroscopy. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)