Synthesis and Structure of Group 14 Element Derivatives of Carbotelluroates

Group 14 element derivatives of carbotelluroates, RCOTeMPh₃ (M = Ge, Sn, Pb), were synthesized as stable compounds by reacting sodium carbotelluroates with Ph₃MCl and were characterized by IR and ¹³C and ¹²⁵Te NMR spectra. Their molecular structures were revealed by X-ray molecular analysis. The CO···Sn distance in RCOTeSnPh₃ was found to be shorter than the CO···Ge distance in RCOTeGePh₃, despite the fact that the atomic radius of Sn is larger than that of Ge. A similar shortening of the nonbonding distance was observed for the corresponding selenium derivatives. Molecular orbital calculations of model compounds, i.e., CH₃COEM(CH₃)₃ (E = Se, Te; M = Ge, Sn, Pb), at the B3LYP/LANL2DZ+p level also supported this shortening of the CO···Sn distance. NBO (natural bond orbital) analyses of the model compounds showed that two types of orbital interactions, n_O→σ*_ME and n_O→σ*_MC (E = S, Se, Te; M = Ge, Sn, Pb), are important in these carbochalcogenoates. Furthermore, the former interaction has a greater role in the case of carbothioates, whereas the latter is dominant in carbotelluroates.