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Structural Studies of Mono‐ and Dimetallic Mo VI Complexes − A New Mechanistic Contribution in Catalytic Olefin Epoxidation Provided by Oxazoline Ligands
Author(s) -
Brito José A.,
Gómez Montserrat,
Muller Guillermo,
Teruel Helena,
Clinet JeanClaude,
Duñach Elisabet,
Maestro Miguel A.
Publication year - 2004
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200400331
Subject(s) - chemistry , catalysis , norbornene , molybdenum , denticity , oxazoline , ligand (biochemistry) , epoxide , cyclooctene , medicinal chemistry , stereochemistry , nuclear magnetic resonance spectroscopy , olefin fiber , crystal structure , selectivity , crystallography , organic chemistry , polymerization , biochemistry , receptor , polymer
New seven‐coordinate oxo(peroxo)molybdenum( VI ) complexes with bidentate chiral oxazolines, anionic κ 2 ‐ N , O ( V ) and neutral κ 2 ‐ N , N ( VI ), have been prepared and fully characterised by NMR spectroscopy and single‐crystal X‐ray diffraction studies. Dimetallic dioxo(μ‐oxo)molybdenum( VI ) compounds containing oxazolinylpyridine ligands II − IV have also been synthesised. NMR studies showed the presence of several isomers (up to six species) due to the Mo−O−Mo bridge angle and the unsymmetrical nature of the N,N ligand. The roles of mono‐ ( I , V and VI ) and dimetallic ( II ) oxomolybdenum( VI ) complexes in the catalytic epoxidation of cyclooctene, norbornene and ( R )‐limonene have been studied. The high activity of the oxomono(peroxo) precursor V containing the hemilabile oxazolinylphenolate, in contrast to the unexpected low activity for the oxobis(peroxo) species VI , could be justified by the inertness observed for the oxazolinylpyridine ligand. In addition, the dimetallic system II afforded high selectivity towards limonene epoxide formation ( trans / cis ‐ 10 ratio up to 9:1). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)