Reactivity of Mg(AlMe4)2 towards neutral tris(pyrazolyl)alkanes
Felix Kracht1, Christoph Stuhl1, Cäcilia Maichle-Mössmer1
1Institut für Anorganische Chemie, Eberhard Karls Universität Tübingen (EKUT), Auf der Morgenstelle 18, 72076, Germany. reiner.anwander@uni-tuebingen.de.
Abstract:
Various new tris(pyrazolyl)alkanes of the class R'CTp3-R (R' = Me, Et, nPr, iBu; R = Et, cyPr, Cy, p-tBuPh, Ph; cyPr = cyclopropyl, Cy = cyclohexyl, p-tBuPh = para-tert-butylphenyl) were synthesised and their reactivity towards Mg(AlMe4)2 was examined. Along with new examples of recurring structural motifs, such as separated ion pairs and "metal in a box" complexes, e.g., [(MeCTp3-Et)2Mg][AlMe4]2, several magnesium complexes with new structural features/compositions were obtained. Treatment of the "metal in a box" species [(MeCTp3-R)Mg][AlMe4]2 with THF donor gave the terminal methyl complex [(MeCTp3-)MgMe(thf)2][AlMe4]. Variation of the backbone alkyl substituent R' in the tris(pyrazolyl)alkane R'CTp3-Ph gave ionic liquids (R' = Et, nPr) and the methyl-bridged dimagnesium complex [({iBuCTp3-Ph}Mg{AlMe4})2(μ-Me)][AlMe4]. The bulky Cy and p-tBuPh moieties at the pyrazolyl 3 position gave the new structural motif [MeCTp3-RMg(η-AlMe4)][AlMe4] (η3, R = Cy; η2, R = p-tBuPh), stabilising a "[Mg(AlMe4)]+" entity. The AlMe3 group can be reversibly displaced under reduced pressure affording the new separated ion pair [(MeCTp3-)MgMe][AlMe4] with a terminal "[MgMe]+" moiety. Moderate thermal treatment of both [(MeCTp3-)MgMe][AlMe4] and [(MeCTp3-)Mg(η2-AlMe4)][AlMe4] resulted in selective C-H-bond activation in the 5 position of one of the pyrazolyl moieties and the formation of an AlMe3-modified anionic tris(pyrazolyl)alkane and hence the neutral complex [MeC(pz3-)2(pz3-)]MgMe.
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