Reactivity of Cyclopentadienyl Molybdenum Compounds towards Formic Acid: Structural Characterization of CpMo(PMe3)(CO)2H, CpMo(PMe3)2(CO)H, [CpMo(μ-O)(μ-O2CH)]2, and [Cp*Mo(μ-O)(μ-O2CH)]2

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• 作者：Michelle C. NearyGerard Parkin
• 刊名：Inorganic Chemistry
• 出版年：2017
• 出版时间：February 6, 2017
• 年：2017
• 卷：56
• 期：3
• 页码：1511-1523
• 全文大小：708K
• ISSN：1520-510X

文摘

The molecular structures of CpMo(PMe₃)(CO)₂H and CpMo(PMe₃)₂(CO)H have been determined by X-ray diffraction, thereby revealing four-legged piano-stool structures in which the hydride ligand is trans to CO. However, in view of the different nature of the four basal ligands, the geometries of CpMo(PMe₃)(CO)₂H and CpMo(PMe₃)₂(CO)H deviate from that of an idealized four-legged piano stool, such that the two ligands that are orthogonal to the trans H–Mo–CO moiety are displaced towards the hydride ligand. While Cp^RMo(PMe₃)_3–x(CO)_xH (Cp^R = Cp, Cp*; x = 1, 2, 3) are catalysts for the release of H₂ from formic acid, the carbonyl derivatives, Cp^RMo(CO)₃H, are also observed to form dinuclear formate compounds, namely, [Cp^RMo(μ-O)(μ-O₂CH)]₂. The nature of the Mo···Mo interactions in [CpMo(μ-O)(μ-O₂CH)]₂ and [Cp*Mo(μ-O)(μ-O₂CH)]₂ have been addressed computationally. In this regard, the two highest occupied molecular orbitals of [CpMo(μ-O)(μ-O₂CH)]₂ correspond to metal-based δ* (HOMO) and σ (HOMO–1) orbitals. The σ²δ*² configuration thus corresponds to a formal direct Mo–Mo bond order of zero. The preferential occupation of the δ* orbital rather than the δ orbital is a consequence of the interaction of the latter orbital with p orbitals of the bridging oxo ligands. In essence, lone-pair donation from oxygen increases the electron count so that the molybdenum centers can achieve an 18-electron configuration without the existence of a Mo–Mo bond, whereas a Mo═Mo double bond is required in the absence of lone-pair donation.