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

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 ). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)