Bonding and Activation of N2 in Mo(0) Complexes Supported by Hybrid Tripod Ligands with Mixed Dialkylphosphine/Diarylphosphine Donor Groups: Interplay of Steric and Electronic Factors

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• 作者：Ludger S枚ncksen ; Christian Gradert ; Jan Krahmer ; Christian N盲ther ; Felix Tuczek
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：June 3, 2013
• 年：2013
• 卷：52
• 期：11
• 页码：6576-6589
• 全文大小：526K
• 年卷期：v.52,no.11(June 3, 2013)
• ISSN：1520-510X

文摘

Molybdenum dinitrogen complexes are presented which are supported by novel hybrid tripod ligands of the type Me-C(CH₂PPh₂)₂(CH₂PⁱPr₂) (trpd-1) and H鈥揅(CH₂PPh₂)(CH₂PⁱPr₂)₂ (trpd-2) having mixed dialkylphosphine/diarylphosphine donor groups. Reaction of the ligand trpd-1 with [MoI₃(thf)₃] followed by sodium amalgam reduction in the presence of the dppm gives the dinitrogen complex [Mo(N₂)(trpd-1)(dmpm)] where trpd-1 is coordinated in a 魏³ fashion. The complex exhibits a moderate activation of N₂ which enables its protonation under retention of the pentaphosphine ligation. Replacement of dmpm by the sterically more demanding coligand dppm is found to hamper coordination of N₂ and leads to [Mo(trpd-1)(dppm)], the first structurally characterized five-coordinate Mo(0) complex with a phosphine-only ligand sphere. Employing the ligand trpd-2 along with the diphosphines dmpm and dppm in an analogous synthetic route results in a mixture of the bis(dinitrogen) complexes trans-[Mo(N₂)₂(魏²-trpd-2)(diphosphine)] and trans-[Mo(N₂)₂(iso-魏²-trpd-2)(diphosphine)] where the tripod ligand trpd-2 coordinates with two phosphine arms and one phosphine group (PPh₂ or PⁱPr₂, respectively) is free. Similar results are obtained with the pure alkyl- and arylphosphine tripod ligands H鈥揅(CH₂PⁱPr₂)₃ (trpd-3) and H鈥揅(CH₂PPh₂)₃ (tdppmm), leading to trans-[Mo(N₂)₂(魏²-trpd-3)(diphos)] and trans-[Mo(N₂)₂(魏²-tdppmm)(dmpm)], respectively. The electronic and steric reasons for the experimental findings are considered, and the implications of the results for the area of synthetic nitrogen fixation with molybdenum phosphine systems are discussed.