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

Abstract

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{NH=C(OR)NC(OR)=NH}(2)] (R = Me (1), Et (2), nPr (3), iPr (4), CH(2)CH(2)OCH(3) (5)) or cationic copper(II)-(2-alkoxy-4-amino-1,3,5-triazapentadiene) complexes [Cu{NH=C(OR)NHC(NH(2))=NH}(2)](AcO)(2) (R = Me (6), Et (7), nPr (8), nBu (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{NH=C(OR)NC(NH(2))=NH}(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)NCNHC(=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)).

Oxidovanadium complexes with tridentate aroylhydrazone as catalyst precursors for solvent-free microwave-assisted oxidation of alcohols

“…Addition of TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) radical, an efficient mediator for the aerobic oxidation of alcohols [23,24,[61][62][63][64][65], although scarcely used for the peroxidative oxidation [35,43,66,67] of those substrates, provided almost quantitative formation of acetophenone (Fig. 3) and a significant increase in cyclohexanone yield (from 38 to 58% (2), Fig.…”

“…Hence, aerobic [10][11][12][13] and peroxidative [14][15][16] selective oxidations of secondary alcohols are regarded as simple and very useful synthetic methods for the preparation of ketones, this conversion being of a pivotal significance in organic synthesis. Moreover, it is known that microwave (MW) irradiation can provide a much more efficient synthetic method than conventional heating, allowing to achieve similar (or higher) yields in a shorter time and/or to improve the selectivity [17][18][19][20][21][22][23][24][25][26][27].…”

Platinum(II)‐Mediated Double Coupling of 2,3‐Diphenylmaleimidine with Nitrile Functionalities To Give Annulated Pentaazanonatetraenate (PANT) Systems

“…[8][9][10][11] Metal- [12][13][14][15][16][17][18] or boron-containing [18] TAPDs exhibit luminescence properties and they also serve as components of catalytic systems. [19,20] In addition, as we recently established by combined X-ray crystallographic and theoretical methods, metal-TAPD complexes are useful for studies of weak molecular interactions, such as hydrogen [21][22][23][24] and halogen bonding, [21,24] or clustering [21][22][23] in the solid state.…”

“…their generation, [5,15,16,20] phosphorescence properties, [15,16] and application for studies of weak molecular interactions [23,24] ) and relevant phthalocyanines (E), [25] we focused our attention on an almost unexplored type of TAPD ligands that includes two annulated triazapentadiene rings, 1,3,5,7,9-pentaazanona-1,3,6,8-tetraenate (PANT; D). Indeed, to the best of our knowledge, only four examples of compounds with PANT ligands have been reported, and methods for the facile generation of PANT ligand systems have not been developed.…”

A convenient Pd-mediated oxidation of 4-methylbenzyl alcohol

“…[3] Of the reported oxidations, basic N-donor ligands [4][5][6] such as Et 3 N in combination with Pd(OAc) 2 have generally provided active catalyst. Here, we have applied the catalytic system Pd(OAc) 2 /Et 3 N to the oxidation of 4-methylbenzyl alcohol because generally, benzylic alcohols with electron-donating groups showed good reactivity [3,7,8]. We have investigated the dependence of conversion percentage on temperature and time.…”