Applications of 95Mo NMR to inorganic and bioinorganic chemistry

Abstract

A variety of dinuclear Mo(V), Mo(IV), Mo(III) and Mo(I) complexes, and tri- and tetranuclear homo- and heterometallic complexes of molybdenum have been studied by 95Mo NMR. The Mo(V) complexes, Cp′ 2Mo 2Y 2(μ-X) 2 (Y = O or S, X = S or Se, Cp′ = η 5-C 5Me 5), exhibit resonances in the −93 to 478 ppm region, the chemical shifts being sensitive to changes in the oxygen, sulfur and selenium content of the coordination spheres. The Mo(IV) complexes, Cp′ 2Mo 2(μ-X) 2(μ-X 2) (X = S or Se), and their derivatives exhibit resonances in the 382–790 ppm region: isomers of Cp′ 2Mo 2(μ-S) 2(μ-SH) 2 which differ in the arrangement of the bridging ligands were also detected. Dinuclear Mo(III) complexes of the form Mo 2L 6 (L = amido, alkoxy or alkyl ligand) exhibit very deshielded resonances (2430–3624 ppm). The complexes Cp 2Mo 2{μ-S 2C 2(CF 3) 2} 2 and Cp 2Mo 2(CO) 2{μ-S 2C 2(CF 3) 2} 2 (Cp = η 5-C 5H 5) exhibit resonances consistent with their formulation as distinct Mo(III) and mixed-valence Mo(IV-II) complexes, respectively. The Mo(I) complexes exhibit resonances which are very sensitive to the bond order of the MoMo bond: the resonances of the L 2Mo 2(CO) 6 complexes (L = Cp, −1856 ppm; L = Cp′, −1701 ppm) are more than 1800 ppm more shielded than the triply metalmetal bonded complexes, L 2Mo 2(CO) 4 (L = Cp, 182 ppm; L = Cp′, 133 ppm). The molybdenum containing homo- and heterometallic complexes exhibit resonances in the −133 to −1619 ppm region. The Fe 2Mo 2 cubane complex, Cp′ 2Mo 2Fe 2(μ 3-S) 4(CO) 4, exhibits a resonance at −506 ppm. The ease of observation of the sulfurized complexes suggests that 95Mo NMR may be a valuable technique for the study of hydro-desulfurization processes.