Mechanochemical Synthesis of Tripodal Tris4-(1,2,3-triazol-5-ylidene)methylamine Mesoionic Carbene Ligands and Their Complexation with Silver(I)

Ang, Z.Z., Laxmi, S., León, F. , Kooij, J.E.M., García, F. and England, Jason (2021) Mechanochemical Synthesis of Tripodal Tris4-(1,2,3-triazol-5-ylidene)methylamine Mesoionic Carbene Ligands and Their Complexation with Silver(I). Inorganic Chemistry, 60 (6). pp. 3556-3564. ISSN 0020-1669

Full content URL: https://doi.org/10.1021/acs.inorgchem.0c02429

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Mechanochemical Synthesis of Tripodal Tris4-(1,2,3-triazol-5-ylidene)methylamine Mesoionic Carbene Ligands and Their Complexation with Silver(I)
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Abstract

The conjugate acids of 1,2,3-triazolylidene mesoionic carbenes can be prepared in a straightforward fashion by alkylation of 1-substituted 1,2,3-triazoles. However, this becomes a much more challenging proposition when other nucleophilic centers are present, which has curtailed the development of ligands containing multiple 1,2,3-triazolylidene donors. Herein, methylation of a series of tris[(1-aryl-1,2,3-triazol-4-yl)methyl]amines possessing both electron-rich and electron-deficient aromatic substituents, using Me3OBF4, is shown to proceed with much higher chemoselectivity under mechanochemical conditions than when conducted in solution. This provides a means to reliably access a series of tricationic tris[4-(1,2,3-triazolium)methyl]amines in good yields. DFT calculations suggest that a potential reason for this change in regioselectivity is the difference between the background dielectric of the DCM solution versus the solid state, which is predicted to have a large effect on the relative thermodynamic driving force for alkylation of the tertiary amine center versus the triazole rings. Homoleptic silver complexes of the triazolylidene ligands derived therefrom, of formulas [Ag3(1a-d)2](X)3 (X- = BF4-, TfO-), have been isolated and fully characterized. In the case of the ligand bearing the smallest aryl substituents, 1b, argentophilic interactions yield a triangular Ag3 core. The [Ag3(1a-d)2](X)3 silver salts are viable agents for transmetalation to other transition metals, demonstrated here for cobalt. In the case of 1a, the complex [CoII(1a)(NCMe)](OTf)2 was obtained. Therein, the bulky mesityl substituents enforce a tetrahedral geometry, in which only the triazolylidene donors of 1a coordinate (i.e., it acts as a tridentate ligand). Transmetalation of the less sterically encumbered ligand 1b yields six-coordinate cobalt(III) complexes, [CoIII(1b)(Cl)(NCMe)](OTf)2 and [CoIII(1b)(NCMe)2](OTf)3, in which the ligand coordinates in a tetradentate fashion. These are the first examples of tris(1,2,3-triazolylidene) ligands containing an additional coordinating heteroatom and, more generally, of tetradentate 1,2,3-triazolylidene ligands. Crucially, we believe that the divergent chemoselectivity under mechanochemical conditions (vs conventional solution-based chemistry) demonstrated herein offers a pathway by which other challenging synthetic targets, including further multidentate carbene ligands, can be prepared in superior yields.

Keywords:Alkylation, Amines, Chelation, Cobalt compounds, Complexation, Salts, Silver halides, Substitution reactions, Transition metals, Argentophilic interaction, Cobalt complexes (III), Ligand coordinates, Mechanochemical synthesis, Mesityl substituents, Nucleophilic centers, Tetrahedral geometry, Thermodynamic driving forces, Ligands
Subjects:F Physical Sciences > F120 Inorganic Chemistry
F Physical Sciences > F100 Chemistry
F Physical Sciences > F161 Organometallic Chemistry
Divisions:College of Science > School of Chemistry
ID Code:51889
Deposited On:04 Oct 2022 09:15

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