Coordination driven self-assembly of metallamacrocycles using ambidentate linkers and self-selection of single linkage isomer

Nicotinate-N-oxide and isonicotinate-N-oxide have been employed to synthesize four heterometallic metallamacrocycles [(dppf)2Pd2(nicotinate-N-oxide)2](OTf)2 (1), [(dppf)2Pt2(nicotinate-N-oxide)2](OTf)2 (2), [(dppf)2Pd2(isonicotinate-N-oxide)2](OTf)2 (3) and [(dppf)2Pt2(isonicotinate-N-oxide)2](OTf)2 (4). The complexes represent the first examples of metallamacrocycles driven by solely Pd(II)/Pt(II)–O coordination using carboxylate-N-oxide donor. All the complexes 1–4 are characterized by IR, UV–Vis, multinuclear NMR spectroscopic and ESI-MS studies. The molecular structures of the complexes 1 and 3 are unambiguously determined by single crystal X-ray diffraction analysis. Despite the possibility of formation of several linkage isomers due to ambidentate nature of the donors, exclusive formation of [2 + 2] self-assembled single isomeric metallamacrocycle in each case is interesting observation.

Four metallamacrocycles [(dppf)2Pd2(nicotinate-N-oxide)2](OTf)2 (1), [(dppf)2Pt2(nicotinate-N-oxide)2](OTf)2 (2), [(dppf)2Pd2(isonicotinate-N-oxide)2](OTf)2 (3) and [(dppf)2Pt2(isonicotinate-N-oxide)2](OTf)2 (4) have been synthesized via Pd/Pt–O coordination driven self-assembly. Complexes 1–4 represent the first examples of metallamacrocycles of these metal ions using carboxylate-N-oxide linkers.Figure optionsDownload as PowerPoint slideHighlights
► For soft-hard combination dxygen-donors are not suitable for Pd(II)/Pt(II).
► We report here the use of oxygen-donor ambidentate linkers in synthesis of Pd(II)/Pt(II) macrocycles.
► Selective formation of a single linkage isomer is also established.