Molecular and electronic structure of MM quadruply bonded complexes containing O2CC6H4N(Ph)2 supporting ligands

The complexes trans-M2(TiPB)2(O2CC6H4-4-NPh2)2 where M = Mo (I), and M = W (II) were prepared from the reaction between M2(TiPB)4 and the carboxylic acid Ph2N-4-C6H4CO2H (∼2 equiv.) in toluene (TiPB = 2,4,6-triisopropylbenzoate). The compounds were isolated as microcrystalline powders that are yellow, I or purple II, and are air-sensitive. Compound I was characterized by single-crystal X-ray crystallography and shown to have a centrosymmetric structure and a planar central C6H4-CO2M2O2C-C6H4 unit. Calculations indicate that the HOMO is principally M2δ with mixing of the filled π-orbitals of the N,N-diphenyl-4-aminobenzoate. Oxidation of I and II yield cationic species that have been characterized by EPR and UV–Vis–NIR spectroscopy. The radical cations show EPR spectra characteristic of M25+ centers having the MM configuration σ2π4δ1 and compound I+ shows a low energy NIR transition assignable to a ligand to metal charge transfer transition. The homoleptic compound Mo2(O2CC6H4-4-N-Ph2)4, III, was prepared from the reaction between Mo(CO)6 and Ph2N-4-C6H4CO2H in refluxing ortho-dichlorobenzene and is shown to exhibit similar spectroscopic features to those of I.

Graphical abstractThe complexes trans-M2(TiPB)2(O2CC6H4N-Ph2)2 where M = Mo (I), and M = W (II) and (TiPB = 2,4,6-triisopropylbenzoate) were prepared. Calculations indicate that the HOMO is principally M2δ with mixing of the filled π-orbitals of the diphenylaminocarboxylate. Oxidation of I and II yield cationic species that have been characterized by EPR and UV–Vis–NIR spectroscopy. The radical cations show EPR spectra characteristic of M25+ centers having the MM configuration σ2π4δ1 and compound I+ shows a low energy NIR transition assignable to a ligand to metal charge transfer transition. The homoleptic compound Mo2(O2CC6H4-4-N-Ph2)4, III, exhibits similar spectroscopic features to those of I.Figure optionsDownload full-size imageDownload as PowerPoint slide