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

摘要

The [2+3] cycloaddition reaction (which is greatly acceleratedby microwave irradiation) of the bis(azido)platinum( II) compound cis-[Pt(N3)2(PPh3)2] (1) with 4-cyanobenzaldehyde (2) furnishes the N2N2-bonded isomer of bis[5-(4- formylphenyl)tetrazol-2-ate] platinum(II) trans-[Pt{N4CC6H4- (4-CH=O)}2(PPh3)2] (3a) as the major product, along with the N1N2-bonded isomer 3b. Treatment of 3a with 2-dimethylaminoethylamine (4), in refluxing methanol, gives the corresponding N2N2-bonded bis[(E)-5-(4-{[2-(dimethylamino)- ethylimino]methyl}phenyl)tetrazol-2-ate] platinum(II) complex trans-[Pt{N4CC6H4(4-CH=NCH2CH2NMe2)}2(PPh3)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 NCC6H4(4-CH=NCH2CH2NMe2) (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 MCl2 (M = Pd, Ni, Zn, Cu), at room temperature for 3 h regenerates complex3a as a result of the Schiff base hydrolysis, along with the diamine complex [MCl2(NH2CH2CH2NMe2)] (7). Treatment of 6 with ZnCl2 for 36 h affords a mixture of 3a with its substitution products [Pt{HN4CC6H4(4-CH=O)}(NH2CH2CH2- NMe2)(PPh3)]Cl2 (9; isolated in the tetrazole form) and cis- [PtCl2(PPh3)2] (10) and diamine complex 7 (M = Zn). The [2+3] cycloaddition reactions of cis-[Pt(N3)2(PPh3)2] (1) with unsubstituted dicyanobenzenes 11 [1,2-C6H4(CN)2 (11a), 1,3- C6H4(CN)2 (11b), 1,4-C6H4(CN)2 (11c)] occur regioselectively and give the corresponding N2N2-bonded bis[5-(cyanophenyl) tetrazol-2-ate] trans-[Pt(N4CC6H4R)2(PPh3)2] complexes 12 (R = 2-CN 12a, 3-CN 12b, 4-CN 12c). The isolated compounds were characterized by IR, 1H NMR, 13C NMR and 31P{1H} NMR (metal complexes) spectroscopy, elemental analyses, ESI-MS and X-ray structural analyses (for 3a, 5·HCl, 7, 9 and 12a)