The new ligand bis(2-picolyl)(2-hydroxy-3,5-di-tert-butylbenzyl)amine (HL) was prepared from bis(2-picolyl)amine and 2,4-di-tert-butyl-6-(chloromethyl)phenol. It acts as a tetradentate N,N,O tripod ligand ensuring 5-fold coordination in all its zinc complexes L.Zn-X. The central complex of the series was [L.Zn(OH(2))]ClO(4) (1) obtained from zinc perchlorate. Together with the more labile complex L.Zn-C(2)H(5) (2), obtained from diethyl zinc, it was used as a starting material for ligand substitutions. In the presence of bases, 1 was converted to L.Zn-OH (3), [L.Zn(py)]ClO(4) (4), and [(L.Zn)(3)(mu(3)-CO(3))]ClO(4) (5). Metathetical reactions produced the neutral complexes L.Zn-X with X = Br (6), OAc (7), OC(6)H(5) (8), SC(6)H(5) (9), OP(O)(OPh)(2) (10), p-nitrophenolate (11), 1-methyluracilate (12), o-formylphenolate (13), and o-hydroxymethylphenolate (14). Structure determinations of 1, 5, 7, 10, 11, 13, and 14 confirmed the strictly monodentate attachment of all units X in L.Zn-X. The hydrolytic cleavage of tris(p-nitrophenyl) phosphate by 1 was investigated preparatively and kinetically. L.Zn-OH was found to be the hydrolytically active nucleophile. The second-order rate constant for the cleavage reaction was found to be slightly lower than the values for related systems, reflecting the steric hindrance in the tert-butyl-substituted ligand L.
Der dreizähnige Ligand N, N(2‐Dimethylaminoethyl)‐3, 5‐di‐tert.‐butyl‐salicylaldimin (LH) bildet sich aus dem entsprechenden Salicylaldehyd und N, N‐Dimethylethylendiamin. Mit Zinksalzen bildet er die einkernigen Halogenokomplexe [LZnCl˙CH3OH] (1) und [LZnI˙CH3OH] (2) und das vermutlich polymere Acetat [LZnOCOCH3] (3). Mit Diethylzink und Phosphorsäurediphenylester entsteht der Phosphatkomplex [LZn‐OPO(OPh)2˙CH3OH] (4). Die zwischen trigonal‐bipyramidal und quadratisch‐pyramidal liegende Koordination der Komplexe und die Art der fünf Donoren im Phosphatkomplex repräsentieren den Übergangszustand der hydrolytischen Substratspaltung in einem Zinkenzym.
Professor Ernst-G. Ja Èger zum 65. Geburtstag gewidmet Inhaltsu È bersicht. Durch eine verbesserte Synthese des Titelliganden MBPA±H wurde dessen Komplexchemie zuga È nglich gemacht. Mit Diethylzink liefert er den reaktiven Ethylkomplex (MBPA)Zn±C 2 H 5 (1), dessen Reaktion mit Phenol zu (MBPA)Zn±OC 6 H 5 (2) fu È hrt. Mit Zinknitrat entsteht die labile Verbindung (MBPA)Zn±ONO 2 (3), die ihrerseits mit Thiophenolat in den Komplex (MBPA)Zn±SC 6 H 5 (4) u È bergeht. Strukturanalysen haben fu È r 2 und 3 stark verzerrte trigonal-bipyramidale Koordinationen des Zinkatoms belegt, deren Koordinationsmuster denen in einigen hydrolytischen Zinkenzymen entsprechen.
Zinc Complexes of the N,N,S-Ligand 2-Mercaptobenzyl-bis-(2-pyridylmethyl)amineAbstract. An improved synthesis of the title ligand MBPA±H has made its complex chemistry accessible. With diethyl zinc it forms the reactive ethyl complex (MBPA)-Zn±C 2 H 5 (1) whose reaction with phenol leads to (MBPA)-Zn±OC 6 H 5 (2). With zinc nitrate the labile compound (MBPA)Zn±ONO 2 (3) is formed which in turn is converted with thiophenolate into (MBPA)Zn±SC 6 H 5 (4). Structure determinations of 2 and 3 have confirmed severely deformed trigonal-bipyramidal coordinations of the zinc atom whose ligation patterns correspond to those in some hydrolytic zinc enzymes.
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