Heterometallic [M_nPt_n(L)_2n]^x+ Macrocycles from Dichloromethane-Derived Bis-2-pyridyl-1,2,3-triazole Ligands

There is continued interest in the assembly of heterometallic metallosupramolecular assemblies due to the potential for new structural types and/or interesting chemical and physical properties. Two novel methylene-linked bis-2-pyridyl-1,2,3-triazole ligands (1a, 1b) were synthesized through CuAAC "click" chemistry between dichloromethane (DCM), sodium azide, and the appropriate ethynylpyridine, giving the shortest possible "regular" bis-pyridyl-1,2,3-triazole. The first example of bis-coordination of two 2-pyridyl-1,2,3-triazoles (Rpytri) around one Pt(II) center is reported, giving exclusive formation of head-to-tail [Pt(Rpytri)₂]²⁺ complexes with vacant binding sites suitable for complexation with other metals and the formation of heterometallic assemblies. The concentration-dependent formation of an equilibrium mixture of a heterometallic [Pd₂Pt₂(L)₄]⁸⁺ [4 + 4] square and [Pd₃Pt₃(L)₆]¹²⁺ [6 + 6] hexagon was observed, and at lower concentrations ([reactants] = 1.5 mM) hexamer formation was negligible. The [Pt(L)₂]²⁺ building block could also be utilized in the synthesis of a concentration-independent [Cu₂Pt₂(L)₄]⁶⁺ metallomacrocyle. These compounds were characterized with ¹H, ¹³C, and ¹H DOSY NMR spectroscopies, elemental analysis, mass spectrometry, and in some cases X-ray crystallography.