SPECTROSCOPIC AND ELECTROCHEMICAL STUDIES OF MONOMERIC OXOMOLYBDENUM(V) COMPLEXES WITH 5-MEMBERED CHELATE RINGS AND ALKOXO OR ALKANETHIOLATO LIGANDS

A series of monomeric oxomolybdenum(V) complexes of the type LMoO[X-CHR'-CHR"-Y] (L = hydrotris(3,5-dimethyl-1-pyrazolyl)borate; X = O, Y = S, R' = Me, R" = H or R' = R" = H, Me; X = Y = O, S, R' = R" = Me) have been synthesized. Several monoalkoxo and monoalkanethiolato complexes with the general formula of LMoO(Cl)(XR) (X = O, R = Me, Et, (n)Pr; X = S, R = Et, (n)Pr, (i)Pr) also have been prepared. All of these complexes have been characterized by elemental analyses, mass spectrometry, infrared and UV-visible spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, and cyclic voltammetry. The electronic absorption spectra for chelate complexes with X = Y = O or S show two transitions with similar extinction coefficients in the range 400-900 nm. The energy difference between these two bands is approximately 3400 and 3600 cm-1 for X = Y = O and S, respectively. In the potential window +2.0 to -2.0 V, all of these complexes exhibit one quasi-reversible reduction wave, corresponding to forming the analogous monoxomolybdenum(IV) species. The reduction potentials shift to the negative direction with an increase in the number of methyl groups on the chelate rings and with an increase in the number of methylene units in the monodentate alkoxo or alkanethiolato ligands.