Pd^II‐Promoted Single‐Pot Template Transformations of Benzonitriles, Cyanoguanidine and Sodium Dicyanamide with the Formation of Symmetrical and Asymmetrical (1,3,5‐Triazapentadienate)palladium(II) Complexes

Abstract

Treatment of benzonitriles 4‐XC6H4CN (1) [X = H (1a), F (1b), Cl (1c), Br (1d), I (1e)] with an excess of 2‐butanone oxime (Me)(Et)C=NOH (as a reagent and solvent) in the presence of PdCl2 at 100 °C for 12 h affords the symmetrical cationic 2,4‐diaryl‐1,3,5‐triazapentadiene (Htap) palladium(II) complexes [Pd(Htap)2]Cl2 (2′) [Htap = HN=C(4‐XC6H4)NHC(4‐XC6H4)=NH]. Recrystallization of 2′ from MeOH/CHCl3 with two equivalents of n‐propylamine gives the corresponding neutral triazapentadienate (tap) complexes [Pd(tap)2] (2) [tap = HN=C(4‐XC6H4)NC(4‐XC6H4)=NH; X = H (2a), F (2b), Cl (2c), Br (2d), I (2e)] in good yields. When cyanoguanidine, HN=C(NH2)N(H)C≡N (3), or sodium dicyanamide NaN(C≡N)2 (5) are treated with an excess of primary alcohols, ROH [R = Me, Et, nPr, nBu or (CH2)2OMe] in the presence of PdCl2, while being heated for 12 h, the corresponding asymmetrical 2‐amino‐4‐alkoxy‐1,3,5‐triazapentadienate‐PdII complexes [Pd{HN=C(NH2)NC(OR)=NH}2] (4) [R = Me (4a), Et (4b), nPr (4c), nBu (4d)] or the symmetrical 2,4‐dialkoxy‐1,3,5‐triazapentadienate‐PdII complexes [Pd{HN=C(OR)NC(OR)=NH}2] (6) [R = Me (6a), Et (6b), nPr (6c), (CH2)2OMe (6d)], respectively, are formed and isolated as a mixture of isomers in good yields. All these compounds have been characterized by IR, 1H and 13C NMR spectroscopy, ESI‐MS, elemental analyses and, in the case of 2c, by XRD.

Metal-Involving Synthesis and Reactions of Oximes

“…O -Iminoacylated oximes were hydrolytically split in ketoxime-catalyzed syntheses of 1,3,5-triazapentadienate complexes. In the presence of acetoxime and butan-2-one oxime, excess R 2 CN ( 92 ) reacting with either NiCl 2 or PdCl 2 followed by addition of 2 equiv of a base (typically Et 3 N) at 100 °C for 12 h gave the neutral complexes 93 (Scheme ; 47–88%, a). − These reactions did not proceed under the above-mentioned conditions in the absence of the oxime, suggesting that the reaction is oxime-catalyzed. The reactions are believed to start from electrophilic activation of a nitrile by its ligation to the metal center (b), followed by nucleophilic addition of the oxime (c), subsequent hydrolysis of the coupling product generating ammonia in the reaction mixture (d), and regenerating the oxime species (e).…”

Metal-mediated generation of triazapentadienate-terminated di- and trinuclear μ2-pyrazolate NiIIspecies and control of their nuclearity

“…Co III , 22 Ni II , 22b Cu II , 22,23 Zn II , 22b,23a,b,24 and Pd II . 25 These chelates were obtained either through a chelation-driven reaction of the dicyanimides, (NC) 2 NNa or (NC) 2 NH, with alcohols in the presence of a transition metal salt (Cu II , 14 . The reactions were performed in all possible combinations of the reactants and molar ratios between NiX 2 ÁnH 2 O and NCNR 2 that range from 1 : 2 to 1 : 6 and between NCNR 2 and the azoles that are in the interval from 1 : 0.5 to 1 : 4 and two temperatures, i.e.…”

Amidoximes Provide Facile Platinum(II)-Mediated Oxime–Nitrile Coupling

“…In particular, reactions between ligated nitriles at kinetically inert metal centers (e.g., platinum − or rhodium , ) and HON species such as “simple” oximes, − vic -dioximes, and functionalized oximes ,− lead to the formation of the C–O­{N} bond upon addition of the OH group at the CN moiety. Moreover, when these reactions were performed at kinetically labile metal centers (e.g., Co II , Ni II , ,,− and Zn II ), they acquired an applied significance insofar as they opened some efficient routes to syntheses of important classes of nitrile-derived organic compounds such as amidines, acylamides, 1,3,5-triazapentadienes, − ,, carboxamides ,− and related species, , and phthalocyanines. , The latter findings made a strong impact on the further exploration of the nitrile reactions with HON-type nucleophiles.…”