SYNTHESIS AND CHARACTERIZATION OF MONONUCLEAR OXOMOLYBDENUM(V) COMPLEXES WITH ALIPHATIC DIOLATO, DITHIOLATO, OR ALKOXO LIGANDS - EFFECT OF CHELATE RING SIZE ON THE PROPERTIES OF THE METAL CENTER

A series of mononuclear (diolato)- or (dithiolato)oxomolybdenum(V) complexes, LMoO[E-(CH2)n-E] (L = hydrotris(3,5-dimethyl-1-pyrazolyl)borate; E = O, S; n = 2-4), and bis(alkoxo) complexes, LMoO(OR)2 (R = Me, Et, nPr), have been synthesized and characterized by elemental analysis, mass spectrometry, electron paramagnetic resonance spectroscopy (EPR), cyclic voltammetry, and IR and electronic absorption spectroscopy. The lowest energy electronic absorption bands for the diolato complexes can be assigned as d → d transitions. However, the lowest energy electronic absorptions for the dithiolato complexes have substantial charge-transfer character. Hypsochromic and bathochromic effects are observed upon increasing the ring size for the dithiolato and diolato complexes, respectively. The value of 〈g〉 becomes smaller with increasing ring size in the diolato complexes, which correlates with the red-shift data obtained from the electronic spectra. All of these complexes exhibit quasi-reversible one-electron reduction waves. The diolato complexes with six- and seven-membered metallacycle rings and bis(alkoxo) complexes also show one-electron oxidation waves. The dithiolato complexes are more easily reduced than analogous diolato complexes. Both series of complexes show remarkable decreases in the Mo(V)/Mo(IV) reduction potential with increasing chelate ring size (0.12-0.22 V/additional CH2 group). © 1990, American Chemical Society. All rights reserved.