Oxo and Imido Complexes of Rhenium and Molybdenum in Catalytic Reductions

Strong π-interactions between tantalum and apical ligands in square pyramidal complexes supported by a rigid tetradentate spectator ligand

“…Characteristic 1 H NMR resonances for the methylene and methyl protons of the ethoxide ligand were observed at δ 4.27 and 1.08 ppm, respectively, in benzene-d 6 . The olefinic carbon resonates at δ 117.2 ppm, comparable to that observed for TPO(H) 4 and indicative of no change in hybridisation of the carbon atoms and of no coordination to the metal. Complex 1 is thermally stable, with no decomposition observed upon prolonged heating at 70 °C.…”

“…The dimethylamide group resonates at δ 3.40 and 43.8 ppm in benzene-d 6 in the 1 H and 13 C NMR spectra, respectively. The olefinic carbon resonates at δ 117.1 ppm, comparable to that observed for complex 1 and for TPO(H) 4 , further indicating no change in hybridisation of the carbon atoms and no interaction of the alkene with the metal. Similar to the ethoxide analogue 1, complex 2 showed no sign of decomposition upon prolonged heating at 70 °C in benzene-d 6 .…”

“…For instance, metal oxo complexes have been extensively used in epoxidation of alkenes [2], atom-transfer reactions to compounds containing C=O, C=N, C=C and C≡C bonds [3,4], C-H bond activation [5], and other important transformations [6,7]. The analogous metal imido complexes have been used in related reactions, including aziridination of alkenes [8,9], selective reduction of compounds containing C=X multiple bonds [4], C-H activation of hydrocarbons [10], and more [6,11,12]. Transition metal nitrido complexes have been used in a wide range of stoichiometric and catalytic reactions [6,11,13].…”

“…Synthetic methodologies have been developed to functionalise and tailor calixarenes for specific applications [26,27]. p-tert-Butylcalix [4]arene however remains the most studied for its cone conformation and the quasiplanar arrangement of the four phenolic oxygen atoms [28], with its first transition metal complex reported 30 years ago [29]. Since then, many groups have used calixarenes as spectator ligands in transition metal chemistry [27,28,30,31].…”

Oxidorhenium(V) Complexes with Tridentate and Tetradentate Phenol‐Based Ligands

“…[21,22] Subsequently, several rhenium(V) catalysts for the reduction of various substrates were developed. [23] The scope of these transformations has only begun to be explored. Last but not least, due to the water stability and the occurrence of the radioactive isotopes 186/188 Re, oxidorhenium(V) compounds have been applied in therapeutic nuclear medicine.…”