2‐Iminoimidazoline — starke Stickstoffbasen als Koordinationspartner in der Anorganischen Chemie

Abstract

Abstract2‐Iminoimidazoline weisen, bedingt durch die Tendenz des Fünfringfragments zur Übernahme einer positiven Formalladung und die hieraus resultierende Ylid‐artige Bindungssituation, eine hohe Stickstoff‐Basizität auf; sie können als Neutral‐liganden, als 2+2‐Elektronendonatoren fungieren. Durch Deprotonierung sind hieraus die zugehörigen Anionen als potentielle 2+4‐Elektronendonatoren zugänglich.Wir beschreiben zunächst die Synthese und Charakterisierung der Titelverbindung 2‐Imino‐1, 3‐dimethylimidazolin (ImNH, 8) und ihres Anions 9. Nachfolgend werden deren Ligandeigenschaften an ausgewählten Beispielen der Koordinationsverbindungen der Haupt‐ und Nebengruppenelemente demonstriert. In einem dritten Abschnitt stellen wir Versuche zur Funktionalisierung der Iminoimidazoline vor in der Absicht, durch die Konstruktion hemilabil koordinierender Neutralliganden einen Beitrag zur katalyseorientierten Komplexchemie zu leisten.Die Ergebnisse von MO‐Berechnungen zur Interpretation der Bindungssituation werden experimentellen Befunden gegenübergestellt.

Advances in guanidine ligand design: synthesis of a strongly electron-donating, imidazolin-2-iminato functionalized guanidinate and its properties on iron

“…The Im R N- ligand class, largely pioneered by Tamm [1–12], has experienced a notable rise in popularity over recent years as these ligands enjoy the modularity of NHCs while exhibiting interesting electronic features [1, 13, 14]. The exocyclic nitrogen of these neutral imines have been shown to be highly basic [1, 15]; yet, Im R NH can be deprotonated using strong alkyl lithium bases to give the monoanionic imidazolin-2-iminato ligands Im R N − [16].…”

Functionalisation of Imidazolin-2-imine to Corresponding Phosphinamine, Chalcogenide (O, S, Se, Te), and Borane Compounds

“…It allows us to observe the effect of different chalcogenides on the basicity of a system. The computational investigation will help us to make a comparative study of the electronic environment around the exocyclic (5), Te(1)-P(1) 2.3720 (15), P(1)-C(12) 1.839 (6), P(1)-C(18) 1.836 (6), N(1)-C(1) 1.338 (7), N(3)-C(1) 1.380 (7), N(3)-C(4) 1.493 (7), N(3)-C(2) 1.382 (8), N(2)-C(1) 1.392 (7) nitrogen with the changing electronegativity of the chalcogenides. An earlier study [10e] emphasised the importance of protonation energy and charge on exocyclic nitrogen atoms to predict the basicity of these types of compounds.…”

“…The study presented in this paper on these compounds enables us to understand the electronic environment at the exocyclic heteroatom as well as the attached phosphorus atom or further at the chalcogen atom. We now wish to give a full account of the synthesis and structural characterisation of 1,3-di-tert-butyl-imidazolin-2-ylidine-1,1-diphenylphosphinamine (2) and its resulting chalcogenides compounds: 1,3-di-tert-butyl-imidazolin-2-ylidine-P,P-diphenylphosphinicamide (3), 1,3-di-tert-butyl-imidazolin-2-ylidine-P,Pdiphenyl-phosphinothioicamide (4), 1,3-di-tert-butyl-imidazolin-2-ylidine-P,P-diphenyl-phosphinoselenoicamide (5), 1,3-di-tertbutyl-imidazolin-2-ylidine-P,P-diphenyl-phosphinotelluroicamide (6), and 1,3-di-tert-butyl-imidazolin-2-ylidine-P,P-diphenylphosphinaminoborane (7), used for the preparation of transition metal complexes currently under investigation in our laboratory. We also report a comparative theoretical study of the electronic structure of compound 2 and the protonation energy among compound 2 and related model compounds.…”

“…Using this concept, numerous ligands, such as 2-methylene-, 2-imino-, 2-oxoimidazolines, and heavier 2-chalcogenoimidazoline have been reported. [4][5][6] In all of these ligands, the resulting accumulated negative charge at the exocyclic heteroatom affords the compound significantly enhanced basicity and nucleophilicity. Recently, Tamm et al exploited this concept to synthesise various 2-trimethylsilyl-iminoimidazolines and imidazolin-2-imines.…”

Synthesis and characterization of homoleptic imidazolin-2-iminato rare earth metal complexes

“…For the latter ligands, Dehnicke has proposed a pseudo-isolobal relationship with the cyclopentadienyl system because of their ability to act as 2s,4p-electron donors [6e9]. Similar considerations apply to related imidazolin-2-iminato ligands (Im R N) [10,11], which can be described by the two limiting resonance structures A and B (Scheme 1), indicating that the ability of the imidazolium ring to efficiently stabilize a positive charge affords highly basic ligands with a strong electron-donating capacity toward early transition metals or metals in a higher oxidation state [12,13]. In our hands, these ligands proved to be viable systems for the preparation of catalytically active transition metal complexes [14] and also for the stabilization of mononuclear rare earth metal complexes, in which the terminal imidazolin-2-iminato ligands exhibit exceptionally short metalenitrogen bonds [15].…”