16486-74-1Relevant articles and documents
Alkaline Earth Metal Aluminates as Catalysts for Imine Hydrogenation
Elsen, Holger,Langer, Jens,Wiesinger, Michael,Harder, Sjoerd
, p. 4238 - 4246 (2020)
Alkaline earth (Ae) metal complexes with the alanate anion AlH4-have been prepared by salt metathesis between NaAlH4and AeCl2in THF and could be isolated as Mg(AlH4)2·(THF)4, Ca(AlH4)2·(THF)4, and Sr(AlH4)2·(THF)5. The previously reported crystal structure of the Mg alanate complex shows bonding of AlH4-with one bridging hydride, H3Al-(μ-H)-Mg, while the Ca and Sr alanates show a combination of H3Al-(μ-H)-Ae and H2Al-(μ-H)2-Ae bridging. The heteroleptic β-diketiminate complexes (DIPPBDI)Mg(AlH4)·THF and (DIPPBDI)Ca(AlH4)·(THF)2have been prepared by reaction of the corresponding Ae hydride complexes with AlH3·(THF)2[DIPPBDI = DIPP-NC(Me)C(H)C(Me)N-DIPP, where DIPP = 2,6-diisopropylphenyl]. Crystal structures show H2Al-(μ-H)2-Ae bridging. The Ca complex decomposes at room temperature by reduction of the β-diketiminate anion. Density functional theory calculations (B3PW91/def2tzvpp) show that the formation of Ae(AlH4)2from AeH2and AlH3is exothermic by δH (kilocalories per mole): Be, -68.8; Mg, -66.1; Ca, -95.4; Sr, -100.9; Ba, -112.3. Calculations of NPA charges on LiAlH4and the Ae alanate complexes (Ae = Mg, Ca, or Sr) show that these are highly ionic salts in which the charge on AlH4-of approximately -0.95 is hardly dependent on the countercation. Compared to LiAlH4, the Ae alanates are very efficient catalysts for imine hydrogenation, clearly extending the substrate scope. In addition to aldimines RC(H)=NR′ (R/R′ = Ph/tBu, tBu/tBu, nPr/tBu, or Ph/Ph), ketimine PhC(Me)=NtBu could be reduced. The salt [Bu4N+][AlH4-] is catalytically not active, which shows that the s-block metal is crucial. The highest activities were found for the heterobimetallic Ca and Sr alanates.
Stabilization of the hindered urea bond through de-tert-butylation
Yang, Yingfeng,Ying, Hanze,Jia, Yunchao,Chen, Yingying,Cheng, Jianjun
supporting information, p. 3812 - 3815 (2021/04/21)
We report the discovery of an acid-assisted de-tert-butylation reaction that can instantly “turn off” the dynamicity of hindered urea bonds (HUBs) and thus broaden their applications. The reaction is demonstrated to be widely applicable to different hindered urea substrates, leading to improved chemical stabilities and mechanical properties of HUB-containing materials.
Catalytic hydrogenation with frustrated lewis pairs: Selectivity achieved by size-exclusion design of lewis acids
Eroes, Gabor,Nagy, Krisztina,Mehdi, Hasan,Papai, Imre,Nagy, Peter,Kiraly, Peter,Tarkanyi, Gabor,Soos, Tibor
scheme or table, p. 574 - 585 (2012/03/08)
Catalytic hydrogenation that utilizes frustrated Lewis pair (FLP) catalysts is a subject of growing interest because such catalysts offer a unique opportunity for the development of transition-metal-free hydrogenations. The aim of our recent efforts is to further increase the functional-group tolerance and chemoselectivity of FLP catalysts by means of size-exclusion catalyst design. Given that hydrogen molecule is the smallest molecule, our modified Lewis acids feature a highly shielded boron center that still allows the cleavage of the hydrogen but avoids undesirable FLP reactivity by simple physical constraint. As a result, greater latitude in substrate scope can be achieved, as exemplified by the chemoselective reduction of α,β-unsaturated imines, ketones, and quinolines. In addition to synthetic aspects, detailed NMR spectroscopic, DFT, and 2H isotopic labeling studies were performed to gain further mechanistic insight into FLP hydrogenation. Copyright
