| Abstract
| - 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 [{Ar2N3}M{N(SiMe3)2}(THF)n] (M = Ca, n = 2; M = Sr, n = 3; Ar = 2,6-diisopropylphenyl) and [{Ar2N3}Ca(I)(THF)2]2 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 [{Ar2N3}2M(THF)n] (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, [{Ar2N3}2Ba(THF)n], failed and led instead to the isolation of the potassium barate complex [K{Ar2N3}Ba{N(SiMe3)2}2(THF)4]. 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 κ2-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 [{Ar2N3}M{N(SiMe3)2}(THF)n] (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 (2a, TOF = 500 h−1; 2b, TOF = 75 h−1). 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.
- A series of triazenide complexes of the heavier alkaline earths, Ca, Sr, and Ba, have been synthesized and characterized by X-ray crystallography and by solution NMR studies. Although heteroleptic silylamido species are catalytically active for the intramolecular hydroamination of 1-amino-2,2-diphenylpent-4-ene, this process is ill-defined because of solution equilibration.
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