Alkoxy‐1,3,5‐triazapentadien(e/ato) Copper(II) Complexes: Template Formation and Applications for the Preparation of Pyrimidines and as Catalysts for Oxidation of Alcohols to Carbonyl Products

Template combination of copper acetate (Cu(AcO) 2 ⋅H 2 O) with sodium dicyanamide (NaN(C≡N) 2 , 2 equiv) or cyanoguanidine (N≡CNHC(=NH)NH 2 , 2 equiv) and an alcohol ROH (used also as solvent) leads to the neutral copper(II)–(2,4‐alkoxy‐1,3,5‐triazapentadienato) complexes [Cu{ N HC(OR)NC(OR) N H} 2 ] (R=Me ( 1 ), Et ( 2 ), n Pr ( 3 ), i Pr ( 4 ), CH 2 CH 2 OCH 3 ( 5 )) or cationic copper(II)–(2‐alkoxy‐4‐amino‐1,3,5‐triazapentadiene) complexes [Cu{ N HC(OR)NHC(NH 2 ) N H} 2 ](AcO) 2 (R=Me ( 6 ), Et ( 7 ), n Pr ( 8 ), n Bu ( 9 ), CH 2 CH 2 OCH 3 ( 10 )), respectively. Several intermediates of this reaction were isolated and a pathway was proposed. The deprotonation of 6 – 10 with NaOH allows their transformation to the corresponding neutral triazapentadienates [Cu{ N HC(OR)NC(NH 2 ) N H} 2 ] 11 – 15 . Reaction of 11 , 12 or 15 with acetyl acetone (MeC(O)CH 2 C(O)Me) leads to liberation of the corresponding pyrimidines NC(Me)CHC(Me)NC NHC(NH)OR, whereas the same treatment of the cationic complexes 6 , 7 or 10 allows the corresponding metal‐free triazapentadiene salts {NH 2 C(OR)NC(NH 2 )NH 2 }(OAc) to be isolated. The alkoxy‐1,3,5‐triazapentadiene/ato copper(II) complexes have been applied as efficient catalysts for the TEMPO radical‐mediated mild aerobic oxidation of alcohols to the corresponding aldehydes (molar yields of aldehydes of up to 100 % with >99 % selectivity) and for the solvent‐free microwave‐assisted synthesis of ketones from secondary alcohols with tert ‐butylhydroperoxide as oxidant (yields of up to 97 %, turnover numbers of up to 485 and turnover frequencies of up to 1170 h −1 ).