Tris(3,5-di-tert-butylcatecholato)molybdenum(VI): Lewis Acidity and Nonclassical Oxygen Atom Transfer Reactions

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• 作者：Amanda H. Randolph ; Nicholas J. Seewald ; Karl Rickert ; and Seth N. Brown
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：November 4, 2013
• 年：2013
• 卷：52
• 期：21
• 页码：12587-12598
• 全文大小：536K
• 年卷期：v.52,no.21(November 4, 2013)
• ISSN：1520-510X

文摘

In the solid state, tris(3,5-di-tert-butylcatecholato)molybdenum(VI) forms a dimer with seven-coordinate molybdenum and bridging catecholates. NMR spectroscopy indicates that the dimeric structure is retained in solution. The molybdenum center has a high affinity for Lewis bases such as pyridine or pyridine-N-oxide, forming seven-coordinate monomers with a capped octahedral geometry, as illustrated by the solid-state structure of (3,5-^tBu₂Cat)₃Mo(py). Structural data indicate that the complexes are best considered as Mo(VI) with substantial 蟺 donation from the nonbridging catecholates to molybdenum. Both the dimeric and the monomeric tris(catecholates) react rapidly with water to form free catechol and oxomolybdenum bis(catecholate) complexes. Monooxomolybdenum complexes are also obtained, more slowly, on reaction with dioxygen, with organic products consisting mostly of 3,5-di-tert-butyl-1,2-benzoquinone with minor amounts of the extradiol oxidation product 4,6-di-tert-butyl-1-oxacyclohepta-4,6-diene-2,3-dione. The pyridine-N-oxide complex reacts on heating (with excess pyO) to form initially (3,5-^tBu₂Cat)₂MoO(Opy) and ultimately MoO₃(Opy), with quinone and free pyridine as the only organic products. The decay of (3,5-^tBu₂Cat)₃Mo(Opy) shows an accelerated, autocatalytic profile because the oxidation of its product, (3,5-^tBu₂Cat)₂MoO(Opy), produces an oxo-rich, catecholate-poor intermediate which rapidly conproportionates with (3,5-^tBu₂Cat)₃Mo(Opy), providing an additional pathway for its conversion to the mono-oxo product. The tris(catecholate) fragment Mo(3,5-^tBu₂Cat)₃ deoxygenates Opy in this nonclassical oxygen atom transfer reaction slightly less rapidly than does its oxidized product, MoO(3,5-^tBu₂Cat)₂.