Molybdenum complexes. 1. Acceptor behavior and related properties of Mo^VIO₂(tridentate) systems

Abstract

Molybdenum(VI) complexes of the type MoO₂(L). where L is a tridentate dianionic Schiff base ligand, are reported. Infrared data suggest oligomerization via a Mo=0→Mo bridge which is cleaved by a wide variety of donors (D): aldehyde, amide, amine. N-oxide, sulfoxide, phosphine oxide, water, alcohol, and phosphinetroducing Mo0₂(L)(D). The tendency of adduct formation by the molybdenyl systems increases in a particular way as L is changed. Mo0₂(L)(D) usually shows two IR absorptions attributable to cis-Mo0₂ stretches, and on the average, species with oxygen donors vibrate at higher frequencies than those with nitrogen donors. On the basis of ligand displacement reactions D binding increases in the order CH₃CHO < C₆H₅CHO < Et0H < p-anisaidehyde < dmf < pic < Me₂S0 < im < py-N-0. On being heated. Mo0₂(L)(D) is readily converted to Mo0₂(L) in a single endothermic step. Thermal analysis data together with NMR data support the weak binding of the D ligands. The electron transfer characteristics of a number of the MoO₂(L)(dmf) species are studied with use of voltarmmetric techniques. In general two to three reduction waves are obsened, all !mated at potentials more negative than —0.9 V vs. SCE. The chemistry and electrochemistry of a dinuclear molybdenum V) species resulting from hydrazine reduction of one Mo0₂(L) is also briefly described.