Trimethyltriazacyclohexane coordination chemistry of simple rare-earth metal salts

Abstract

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.