Aminotroponiminate Complexes of the Heavy Alkaline Earth and the Divalent Lanthanide Metals as Catalysts for the Hydroamination/Cyclization Reaction

Abstract

Reaction of SrI2, EuI2(THF)2, and YbI2(THF)2 with KN(SiMe3)2 and [{(iPr)2ATI}K] ((iPr)2ATI = N-isopropyl-2-(isopropylamino)troponiminate) led to monoaminotroponiminate complexes of the heavier alkaline earth elements and the related divalent lanthanides of composition [{(iPr)2ATI}M{N(SiMe3)2}(THF)2)] (M = Sr, Eu, Yb). Diaminotroponiminate complexes of composition [{(iPr)2ATI}2M(THF)2)] (M = Sr, Ba) were obtained by the reaction of SrI2 and BaI2 with 2 equiv of [{(iPr)2ATI}K]. All new compounds were characterized by single-crystal X-ray diffraction. Independent of the ionic radius of the center metal all monoaminotroponiminate complexes [{(iPr)2ATI}M{N(SiMe3)2}(THF)2] including the previously reported Ca analogue are isostructural. The same phenomenon is observed for [{(iPr)2ATI}2M(THF)2)]. The heterolepetic compounds [{(iPr)2ATI}M{N(SiMe3)2}(THF)2)] were used as catalysts for the intramolecular hydroamination/cyclization reaction of nonactivated aminoalkenes. A decrease in the rate with increasing ion radius of the center metal is observed for the alkaline earth elements. The ytterbium complex, which is oxidized during the catalytic conversion, is also an efficient precatalyst for the hydroamination/cyclization reaction.

New Perspectives for Aminotroponiminates: Coordination Chemistry, Redox Behavior, Cooperativity, and Catalysis

“…This is remarkable, since the opposite trend (i.e. increasing activity with increasing ionic radius of the metal center) has been reported for lanthanoid complexes as olefin hydroamination catalysts , . For more challenging substrates 23 (e.g.…”

“…ATI complexes [M(ATI i Pr/ i Pr ){N(SiMe 3 ) 2 (thf) 2 }] ( 25‐M ) of the heavier alkaline earth metals Ca and Sr have been tested as catalysts in intramolecular hydroamination reactions and compared to their Yb II analogs (Scheme ) . The ATI ligand presumably serves as a spectator ligand in these transformations, while the {N(SiMe 3 ) 2 } – group undergoes transamination with the substrate 23 . Near quantitative yields of regioselectively cyclized products 24 were observed in most cases, with catalyst loadings of 2–10 %, reaction times of 0.25–40 h and reaction temperatures of 23–60 °C, depending on the substrate.…”

Highly Fluorinated Tris(indazolyl)borate Silylamido Complexes of the Heavier Alkaline Earth Metals: Synthesis, Characterization, and Efficient Catalytic Intramolecular Hydroamination

“…With the N-bound aminotroponiminate or 2,5-bis-[N-(aryl)iminomethyl]-pyrrolyl Ca and Sr silylamido complexes, the activity of the catalysts decreased with increasing atomic number of the metal. [16][17][18] Asymmetric versions of these reactions have also been reported. [19][20][21] Some of us have recently described new Ca, Sr, and Ba heteroleptic [(LO)Ae{N(SiMe 2 R) 2 }(thf) x ] (R= H, Me) complexes bearing different types of N-and O-based amino-phenolate ligands (LO À ).…”

Synthesis and Characterization of Strontium Bis(N-isopropylanilide) and Comparison with the Lighter Magnesium and Calcium Congeners

“…The interest in the amides of strontium has increased also due to the fact that these complexes showed catalytic activity [36,37] in the Tishchenko reaction [38], intramolecular [39,40] and intermolecular hydroamination of alkenes and alkynes [41], and hydrophanylation of carbodiimides [42]. For the calcium complexes we could show that the catalytic reactivity of N-alkyl substituted anilides is significantly enhanced compared to the diphenylamides (N-phenylanilides) [43] whereas the strontium bis[bis(trimethylsilyl)amide] exhibited a higher catalytic activity than the homologous calcium congener [39 -41].…”