Structural, spectroscopic, and computational characterization of the cleavage product of dimolybdenum(II) core under aerobic conditions

Abstract

Full characterization of the adduct isolated in crystalline form from a solution of tetrakis(μ-trifluoroacetato) dimolybdenum(II) and (2S,3S)-butane-2,3-diol is reported herein. For this purpose X-ray crystallographic, spectroscopic, and computational methods were conducted. The single crystal X-ray diffraction analysis clearly indicates the cleavage of the MoMo quadruple bond in the chiral complex initially formed in situ after mixing the components. Cleavage product 2 shows two coordinated, symmetrically unequivalent (2S,3S)-butane-2,3-diol ligands associated with one Mo atom with different MoO bond lengths and MoOC bond angles. This inequivalence most likely reflects the engagement of the coordinated butanediol ligands in an intermolecular hydrogen bonding interaction with solvating butanediol molecules leading to the formation of an infinite helical chain pattern. Density functional theory (DFT) and time-dependent DFT calculations were used to provide support for the proposed structural assignment of 2 in acetonitrile and chloroform solutions, which were made on the basis of experimental CD and NMR results. Additional studies under anaerobic conditions have shown that the cleavage of the quadruple MoMo bond takes place only under aerobic conditions. Thus, it has been demonstrated that the changes in the shapes of the ECD curves observed over time are associated with spontaneous, air-oxidative cleavage of the quadruple MoMo bond and conversion of the Mo(II) to Mo(VI) centers.