Expanding Bismuth Trihalide Coordination Chemistry with Trimethyltriazacyclohexane and Trimethyltriazacyclononane

Bismuth(III)-Catalyzed Regioselective Selenation of Indoles with Diaryl Diselenides: Synthesis of 3-Selanylindoles

Heterocyclic aryl selenides have recently attracted considerable research interest owing to their applications in biological and pharmaceutical fields. Herein, we describe a simple and general synthesis of 3-selanylindoles via a novel regioselective C-H selenation of indoles using a bismuth reagent as a catalyst. The reactions of indoles with diselenides in the presence of 10 mol% BiI3 at 100 °C in DMF afforded the corresponding 3-selanylindoles in moderate-to-excellent yields. The reaction proceeded efficiently under aerobic conditions by adding only a catalytic amount of BiI3, which was non-hygroscopic and less toxic, and both selanyl groups of the diselenide were transferred to the desired products.

Tridentate Nitrogen Ligand as a Tool for the Construction of Well-Defined Rare Earth Trichloride Complexes

LnCl3(THF)3 (Ln = Y, La ÷ Nd, Sm ÷ Lu) readily react with the tridentate 1,3,5-trimethyl-1,3,5-triazacyclohexane (Me3tach) ligand to form mono- or binuclear lanthanide trichloride complexes, depending on the stoichiometry of the reaction and the ionic radius of the metal: mononuclear pseudosandwich [LnCl3(Me3tach)2], (Ln = Y, La ÷ Ho) or binuclear complexes [Ln2Cl6(Me3tach)3], or [LnCl3(Me3tach)(THF)]2 (Ln = Sm, Tb). Detailed analysis of the NMR data of [LnCl3(Me3tach)2] complexes with paramagnetic lanthanide ions showed that their structures remained unchanged in the toluene solution. A series of isomorphous complexes [LnCl3(Me3tach)(Py)2] (Ln = La, Sm, Tb, Er, Lu; Py = pyridine) have been obtained by the recrystallization of either mononuclear or binuclear complexes from pyridine. Complexes of terbium and europium ions with the Me3tach ligand exhibit relatively high quantum yields of metal-centered luminescence (0.39 and 0.32, respectively).

Trimethyltriazacyclohexane coordination chemistry of simple rare-earth metal salts

Reactions of 1,3,5-trimethyl-triazacyclohexane (Me₃tach) with common rare-earth metal iodide, chloride, and triflate salts were examined to determine the capacity of this inexpensive chelate to provide alternative precursors for THF-free reactions. The reaction of LaI₃(THF)₄ and CeI₃(THF)₄ with 1,3,5-trimethyl-triazacyclohexane in THF generated toluene soluble (Me₃tach)₂LnI₃, 1-Ln, in which the Ln center has a tri-capped trigonal prismatic geometry with two eclipsed Me₃tach rings. Reaction with NdI₃(THF)_3.5 forms the analogous 1-Nd, but a different structure with one outer sphere iodide, [(Me₃tach)₂NdI₂][I], 2-Nd, is also accessible and has a structure reminiscent of bent metallocenes. The reaction of LaCl₃ and Me₃tach forms the less soluble (Me₃tach)₂LaCl₃, which has a structure analogous to 1-Ln with eclipsed Me₃tach rings. The mono-ring yttrium complex, (Me₃tach)YCl₃(THF)₂, could be isolated from the reaction of YCl₃ with Me₃tach. Reactions of La(OTf)₃ with Me₃tach were sensitive to the presence of residual proton sources as exemplified by the isolation of {[(Me₃tach)La(μ-OH)(μ-OTf)]₂(μ-OTf)₂}₂, 5-La, and [HMe₃tach][(Me₃tach)₂La-(OTf)₄], 6-La. SmI₂ reacts with Me₃tach to produce the Sm(II) complex, (Me₃tach)₂SmI₂(THF), 7-Sm, but 2-Sm can also form in this reaction. Complexes of the larger 1,4,7-trimethyltriazacyclononane (Me₃tacn) ligand, namely (Me₃tacn)LaI₃(THF), (Me₃tacn)YCl₃, and (Me₃tacn)SmI₂(THF) were synthesized for comparison. Several examples of the protonated ligands with simple counteranions, [HMe₃tach][X] (X = Cl, Br, I) and [HMe₃tacn][OTf], were identified in the course of these studies.

Synthesis of Trimethyltriazacyclohexane (Me3tach) Sandwich Complexes of Uranium, Neptunium, and Plutonium Triiodides: (Me3tach)2AnI3

1,3,5-Trimethyl-1,3,5-triazacyclohexane (Me₃tach) readily complexes uranium triiodide to form (Me₃tach)₂UI₃. The complex is soluble in THF and arenes and can function as a source of UI₃ to form organometallic U(III) complexes. When dissolved in pyridine (py), (Me₃tach)₂UI₃ forms (Me₃tach)UI₃(py)₂. A related complex with the larger 1,4,7-trimethyl-1,4,7-triazacyclononane (Me₃tacn) ligand, namely (Me₃tacn)UI₃(THF), was synthesized for comparison. Since X-ray quality crystals of (Me₃tach)₂UI₃ can be synthesized in high yield even with small-scale reactions, the system is ideal for extension to transuranium elements. Accordingly, the neptunium and plutonium complexes (Me₃tach)₂NpI₃ and (Me₃tach)₂PuI₃ were synthesized in an analogous manner from NpI₃(THF)₄ and PuI₃(THF)₄, respectively.