Platinum(II)‐Promoted [2+3] Cycloaddition of Azide with 4‐Cyanobenzaldehyde, a Schiff Base Derivative or Dicyanobenzenes To Give Formyl‐, Amino(imino)‐ or Cyano‐Functionalized Tetrazolato Complexes

Abstract

The [2+3] cycloaddition reaction (which is greatly accelerated by microwave irradiation) of the bis(azido)platinum(II) compound cis-[Pt(N 3 ) 2 (PPh 3 ) 2 ] (1) with 4-cyanobenzaldehyde (2) furnishes the N 2 N 2 -bonded isomer of bis[5-(4-formylphenyl)tetrazol-2-ate] platinum(II) trans-(Pt{N 4 CC 6 H 4 -(4-CH=O)} 2 (PPh 3 ) 2 ] (3a) as the major product, along with the N 1 N 2 -bonded isomer 3b. Treatment of 3a with 2-dimethylaminoethylamine (4), in refluxing methanol, gives the corresponding N 2 N 2 -bonded bis[(E)-5-(4-{[2-(dimethylamino)-ethylimino]methyl}phenyl)tetrazol-2-ate] platinum(II) complex trans-[Pt{N 4 CC 6 H 4 (4-CH=NCH 2 CH 2 NMe 2 )} 2 (PPh 3 ) 2 ] (6) in good yield. An alternative route involves the reaction of 4-cyanobenzaldehyde (2) with diamine 4 to give the E isomer of 4-{[2-(dimethylamino)ethylimino]methyl)benzonitrile N≡CC 6 H 4 (4-CH=NCH 2 CH 2 NMe 2 ) (5), followed by the reaction of the latter with bis(azido)platinum(II) complex 1 to afford 6 in similar yield. The reaction of 6 with MCl 2 (M = Pd, Ni, Zn, Cu), at room temperature for 3 h regenerates complex 3a as a result of the Schiff base hydrolysis, along with the diamine complex [MCl 2 (NH 2 CH 2 CH 2 NMe 2 )] (7). Treatment of 6 with ZnCl 2 for 36 h affords a mixture of 3a with its substitution products [Pt{HN 4 CC 6 H 4 (4-CH=O)}(NH 2 CH 2 CH 2 -NMe 2 )(PPh 3 )]Cl 2 (9; isolated in the tetrazole form) and cis-[PtCl 2 (PPh 3 ) 2 ] (10) and diamine complex 7 (M = Zn). The [2+3] cycloaddition reactions of cis-[Pt(N 3 ) 2 (PPh 3 ) 2 ] (1) with unsubstituted dicyanobenzenes 11 [1,2-C 6 H 4 (CN) 2 (11a), 1,3-C 6 H 4 (CN) 2 (11b), 1,4-C 6 H 4 (CN) 2 (11c)] occur regioselectively and give the corresponding N 2 N 2 -bonded bis[5-(cyanophenyl)tetrazol-2-ate] trans-[Pt(N 4 CC 6 H 4 R) 2 (PPh 3 ) 2 ] complexes 12 (R = 2-CN 12a, 3-CN 12b, 4-CN 12c). The isolated compounds were characterized by IR, 1 H NMR, 13 C NMR and 31 P{ 1 H} NMR (metal complexes) spectroscopy, elemental analyses, ESI-MS and X-ray structural analyses (for 3a, 5·HCl, 7, 9 and 12a).