N-Coordinated tellurenium(ii) and telluronium(iv) cations: synthesis, structure and hydrolysis

A set of N-coordinated tellurium(ii) compounds containing either C,N-chelating ligands CN (R) (where CN = 2-(RN 00000000 00000000 00000000 00000000 11111111 00000000 11111111 00000000 00000000 00000000 CH)C6H4, R = tBu or Dipp; Dipp = 2,6-iPr(2)C(6)H(3)) or N,C,N pincer ligands NCN (R) (where NCN = 2,6-(RNCH)(2)C6H4, R = tBu or Dipp) were synthesized. In the case of C,N-chelated compounds, the reaction of (CNLi)-Li-Dipp with Te(dtc)2 (where dtc = Et2NCS2) in a 1 : 1 molar ratio smoothly provided the carbamate (CNTe)-Te-Dipp(dtc) which upon treatment with 2 eq. of HCl provided the chloride CNDippTeCl. In contrast, the analogous conversion of NCN (R) Li with Te(dtc)2 surprisingly furnished ionic bromides [NCN (R) Te]Br as a result of the exchange of dtc by Br coming from nBuBr present in the reaction mixture. Furthermore, the reaction of (CNTeCl)-Te-Dipp or [NCNRTe]Br with silver salts AgX (X = OTf or SbF6) provided the expected tellurenium cations [(CNTe)-Te-Dipp]SbF6 and [NCN (R) Te]X. To further increase the Lewis acidity of the central atom, the oxidation of selected compounds with 1 eq. of SO2Cl2 was examined yielding stable compounds [(CNTeCl2)-Te-tBu]X and [(NCNTeCl2)-Te-tBu]X. The oxidation of the Dipp substituted compounds proved to be more challenging and an excess of SO2Cl2 was necessary to obtain the oxidized products [(CNTeCl2)-Te-Dipp]SbF6 and [(NCNTeCl2)-Te-Dipp]SbF6, which could solely be characterized in solution. Compounds [(CNTeCl2)-Te-tBu]OTf and [(NCNTeCl2)-Te-tBu]OTf were shown to undergo a controlled hydrolysis to the corresponding telluroxanes. All compounds were studied by multinuclear NMR spectroscopy in solution and for selected compounds solid state Te-125 NMR spectroscopy and single-crystal X-ray diffraction analysis were performed. The Lewis acidity of the studied cations was examined by the Gutmann-Beckett method using Et3PO as the probing agent. The Te-N chalcogen bonding situation of selected compounds has also been examined computationally by a set of real-space bonding indicators.

Automated summary

A set of N-coordinated tellurium(ii) compounds containing either C,N-chelating ligands CN (R) or N,C,N pincer ligands NCN (R) were synthesized. Different forms of compounds were obtained through chemical reactions, and their characterization was performed using multinuclear NMR spectroscopy and single-crystal X-ray diffraction analysis. The Lewis acidity and chalcogen bonding of the compounds were also studied.