Synthesis, electrochemistry, and electron spin resonance spectra of some seventeen-electron complexes containing the {Mo(NO)}2+ core and the molecular structure of [Mo(NO){HB(Me2pz)3}(pyr)2]

Abstract

The reactions between [Mo(NO)LI₂][L = hydrotris(3,5-dimethylpyrazol-1-yl)borate] and several neutral, unsaturated nitrogen-heterocyclic ligands have been investigated in order to establish the nature of the paramagnetic species produced. The complexes [Mo(NO)L(A)₂]⁺(A = imidazole, N-methylimidazole, pyrazole, 3,5-dimethylpyrazole, or pyridine) have been isolated as their [BPh₄]^– salts from such reactions with an excess of A. These complexes are paramagnetic and exhibit room-temperature e.s.r. signals in which hyperfine coupling to molybdenum isotopes is apparent. In the cases where A = pyridine or N-methylimidazole the complexes exhibited a reversible one-electron reduction process in their cyclic voltammograms. However, where an exchangeable proton was bound to a nitrogen atom in A, irreversible reduction was observed. The neutral diamagnetic complex [Mo(NO)L(pyr)₂](pyr = pyrrol-1-yl) was also prepared, and was found to undergo a reversible one-electron reduction at more anodic potentials than its cationic counterparts. An X-ray diffraction study of [Mo(NO)L(pyr)₂] revealed a linear nitrosyl ligand and an average Mo–N(pyrrolyl) distance of 2.040 Å.