cis-Dioxo- and cis-(Hydroxo)oxo-Mo(V) Complexes Stabilized by Intramolecular Hydrogen-Bonding

• Published in: Inorganic chemistry Vol. 49; no. 20; pp. 9460 - 9469
• Main Authors: Ng, Victor W. L, Taylor, Michelle K, White, Jonathan M, Young, Charles G
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 18.10.2010
• Subjects: Crystallography, X-Ray; Electrochemistry; Hydrogen Bonding; Models, Molecular; Molecular Conformation; Molybdenum - chemistry; Organometallic Compounds - chemistry; Protons; Stereoisomerism
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic1011428

The reactions of Tp iPrMoVIO2Cl with salicylanilides and NEt3 produce cis-Tp iPrMoVIO2(2-OC6H4CONHR) (Tp iPr = hydrotris(3-isopropylpyrazol-1-yl)borate, R = Ph, 4-C6H4Cl, 4-C6H4OMe). The N-methyl complex, Tp iPrMoO2{2-OC6H4CON(Me)Ph}, is similarly prepared. Reduction of the amido complexes by cobaltocene produces green, EPR-active compounds, [CoCp2][Tp iPrMoVO2(2-OC6H4CONHR)], that exhibit strong, low energy, ν(MoO2) IR bands at ∼ 895 and 790 cm−1 (cf. ∼ 935 and 900 cm−1 for the Mo(VI) analogues). The X-ray structures of all seven complexes have been determined. In each case, the Mo center exhibits a distorted octahedral coordination geometry defined by mutually cis oxo and phenolate ligands and a tridentate fac-Tp iPr ligand. The Mo(V) anions exhibit greater MoO distances (av. 1.738 Å vs 1.695 Å) and OMoO angles (av. 112.4° vs 102.9°) than their Mo(VI) counterparts, indicative of the presence of a three-center (MoO2), π* semioccupied molecular orbital in these d1 complexes. The amido Mo(VI) and Mo(V) complexes exhibit an intramolecular hydrogen-bond between the NH and O phenolate atoms. Protonation of [CoCp2][Tp iPrMoVO2(2-OC6H4CONHR)] by lutidinium tetrafluoroborate is quantitative and produces EPR-active, cis-(hydroxo)oxo-Mo(V) complexes, Tp iPrMoVO(OH)(2-OC6H4CONHR), related to the low pH Mo(V) forms of sulfite oxidase.