Complex Compounds Based on 1-Isopropenylimidazoles and -pyrazole

Abstract

With respect to Co 2+ , Ni 2+ , Zn 2+ , Cd 2+ , Cu 2+ , Pd 2+ , and Sn 4+ salts, 1-isopropenyl-substituted imidazole, 2-methylimidazole, and pyrazole behave as monodentate ligands with only one coordination center on the N 1 and N 2 atoms, respectively; 1-isopropenylpyrazole under complex-formation conditions is dealkylated to form pyrazole complexes. The reaction with HCl leaves the unsaturated substituent in 1-isopropenylimidazole intact and yields corresponding hydrochlorides by the N 3 atom of the heterocycle. The least basic 1-isopropenylpyrazole takes up HCl also by the double bond of the alkenyl group.Earlier [1, 2] we have synthesized coordination compounds of Lewis (M = Co 2+ , Ni 2+ , Zn 2+ , Cd 2+ , Cu 2+ , Pd 2+ , and Sn 4+ ) and Brøns+ed (HCl) acids with 1-propadienylimidazoles, -pyrazoles and -triazoles, the donor3acceptor bond in which involves the lone electron pair of the N 3 , N 2 , and N 4 atoms of the heterocycle, respectively. Depending on the basicity of 1-propadienylazole, either monodentate or polymeric metal complexes are formed [2]. The exocyclic unsaturated group in the least basic 1-propadienylimidazole participates in the electrophilic addition of HCl. Proceeding with the research into the behavior of nitrogen-containing heterocycles with unsaturated exocyclic groups in complex formation with metals salts [133], in this work we have studied for the first time reactions of 1-isopropenyl derivatives of imidazole (I), 2-methylimidazole (II), and pyrazole (III), which became accessible recently [4], with Co 2+ , Ni 2+ , Zn 2+ , Cd 2+ , Cu 2+ , Pd 2+ , and Sn 4+ chlorides and Zn 2+ acetate. Like 1-allylazoles [5310], 1-isopropenylazoles can form n-and p-type complexes [8310], as well as polymeric chains in such reactions. This extends the possibilities for further practical application of azole systems with unsaturated exocyclic groups, which play an important role in coordination chemistry as perspective ligands for metal complexes. There is information in literature about the creation on the basis of vinyl derivatives of azoles and of their complexes of effective pharmaceuticals [11313], biologically active materials of broad-spectrum action [3,14,15], and materials with high technological and operation properties [16318].The composition and structure of the complexes synthesized in this work were established by elemental analysis, 1 H and 13 C NMR, and IR spectra of free and coordinated ligands I3III, and by potentiometric titration.To find out possible directions of complex formation and to estimate quantitatively the proton-donor power of azoles I3III, we determined the dissociation constants (pK a ) of their by nonaquoeus potentiometric titration in acetonitrile. Comparison of out present results with those reported for 1-vinyl-and 1-propadienylazoles [2] showed that introduction of the isopropenyl substitution scarcely affects the basicity of the [pyridine] nitrogen atom of the cycle: The pK a values for pyrazole I and imidazoles II and III are 6.78, 13.29, and 15.66, respectively. ...

Unexpected formation of pyrazolecarbaldehyde dithioacetal hydrochlorides

“…If pyrazole molecule contains another nucleophilic center, e.g., double C=C bond, their reactions with hydrohalic acids could follow two pathways. Hydrochlorination of 1-alkenylpyrazoles occurs at the N 2 atom only on cooling (-70°C), whereas at room temperature the process involves the alkenyl substituent [5,6].We were the first to reveal that acetalization of pyrazole-4-carbaldehydes Ia-Ic with 2-sulfanylethanol in the presence of 5-6 equiv of chlorotrimethylsilane at room temperature leads to the formation of the corresponding dithioacetal hydrochlorides IIa-IIc in good yield. Protonation of the N 2 atom in the heteroring of compounds IIa-IIc is indicated by the presence in their IR spectra of a broadened NH + absorption bands at 2500-2800 cm -1 .…”

“…If pyrazole molecule contains another nucleophilic center, e.g., double C=C bond, their reactions with hydrohalic acids could follow two pathways. Hydrochlorination of 1-alkenylpyrazoles occurs at the N 2 atom only on cooling (-70°C), whereas at room temperature the process involves the alkenyl substituent [5,6].…”

Dichloridobis(3,4,5-trimethyl-1H-pyrazole-κN2)cobalt(II)

“…For a similar tetrahedral complex with pyrazole, see: Zyryanova et al (2005). For thermal decomposition studies, see: Petrovic et al (1993).…”

10.1007/s11178-008-2003-x

“…Monodentate ligands with the coordination center on the nitrogen atom in complex with metals were described [15]. Monodentate ligands with the coordination center on the nitrogen atom in complex with metals were described [15].…”