Triazenide Complexes of the Heavier Alkaline Earths: Synthesis, Characterization, And Suitability for Hydroamination Catalysis

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• 作者：Anthony G. M. Barrett ; Mark R. Crimmin ; Michael S. Hill ; Peter B. Hitchcock ; Gabriele Kociok-Kö ; hn ; Panayiotis A. Procopiou
• 刊名：Inorganic Chemistry
• 出版年：2008
• 出版时间：August 18, 2008
• 年：2008
• 卷：47
• 期：16
• 页码：7366-7376
• 全文大小：372K
• 年卷期：v.47,no.16(August 18, 2008)
• ISSN：1520-510X

文摘

A series of triazenide complexes of the heavier alkaline earths, Ca, Sr and Ba, have been synthesized by either protonolysis or salt metathesis routes. Although complexes of the form [{Ar<sub>2sub>N<sub>3sub>}M{N(SiMe<sub>3sub>)<sub>2sub>}(THF)<sub>nsub>] (M = Ca, n = 2; M = Sr, n = 3; Ar = 2,6-diisopropylphenyl) and [{Ar<sub>2sub>N<sub>3sub>}Ca(I)(THF)<sub>2sub>]<sub>2sub> could be isolated and characterized by X-ray crystallography, solution studies revealed the propensity of these species to undergo Schlenk-like redistribution with the formation of [{Ar<sub>2sub>N<sub>3sub>}<sub>2sub>M(THF)<sub>nsub>] (M = Ca, n = 1; M = Sr, n = 2). The latter compounds have been synthesized independently. In the case of the large barium dication, attempts to synthesize the heaviest analogue of the series, [{Ar<sub>2sub>N<sub>3sub>}<sub>2sub>Ba(THF)<sub>nsub>], failed and led instead to the isolation of the potassium barate complex [K{Ar<sub>2sub>N<sub>3sub>}Ba{N(SiMe<sub>3sub>)<sub>2sub>}<sub>2sub>(THF)<sub>4sub>]. Single crystal X-ray diffraction studies demonstrated that, although in all the aforementioned cases the triazenide ligand binds to the electrophilic group 2 metal centers via symmetrical κ<sup>2sup>-N,N-chelates, in the latter compound an unprecedented bridging mode is observed in which the triazenide ligand coordinates through both terminal and internal nitrogen centers. A series of density-functional theory computational experiments have been undertaken to assist in our understanding of this phenomenon. In further experiments, the calcium and strontium amide derivatives [{Ar<sub>2sub>N<sub>3sub>}M{N(SiMe<sub>3sub>)<sub>2sub>}(THF)<sub>nsub>] (M = Ca, n = 2; M = Sr, n = 3) proved to be catalytically active for the intramolecular hydroamination of 1-amino-2,2-diphenylpent-4-ene to form 2-methyl-4,4-diphenylpyrrolidine, with the calcium species demonstrating a higher turnover number than the strontium analogue (<b>2ab>, TOF = 500 h<sup>−1sup>; <b>2bb>, TOF = 75 h<sup>−1sup>). In these instances, because of ambiguities in the structural charcterization of the precatalyst in solution, such quantification holds little value and detailed catalytic studies have not been conducted.