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)center dot H2O) with sodium dicyanamide (NaN(C N)(2), 2 equiv) or cyanoguanidine (N CNHC(=NH)NH2, 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{NH=C(OR)NC(OR)=NH}(2)] (R=Me (1), Et (2), nPr (3), iPr (4), CH2CH2OCH3 (5)) or cationic copper(II)(2-alkoxy-4-amino-1,3,5-triazapentadiene) complexes [Cu{NH=C(OR)NHC(NH2)=NH}(2)]-(AcO)(2) (R=Me (6), Et (7), nPr (8), nBu (9), CH2CH2OCH3 (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{NH=C(OR)NC(NH2)=NH}(2)] 11-15. Reaction of 11, 12 or 15 with acetyl acetone (MeC(=O)CH2C(=O)Me) leads to liberation of the corresponding pyrimidines NC(Me)CHC(Me)NCNHC(=NH)OR, whereas the same treatment of the cationic complexes 6, 7 or 10 allows the corresponding metal-free triazapentadiene salts {NH2C(OR)=NC(NH2)=NH2}(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)).