133622-02-3Relevant articles and documents
Cationic Aluminium Complexes as Catalysts for Imine Hydrogenation
Friedrich, Alexander,Eyselein, Jonathan,Elsen, Holger,Langer, Jens,Pahl, Jürgen,Wiesinger, Michael,Harder, Sjoerd
, p. 7756 - 7763 (2021)
Strongly Lewis acidic cationic aluminium complexes, stabilized by β–diketiminate (BDI) ligands and free of Lewis bases, have been prepared as their B(C6F5)4? salts and were investigated for catalytic activity in imine hydrogenation. The backbone (R1) and N (R2) substituents on the R1,R2BDI ligand (R1,R2BDI=HC[C(R1)N(R2)]2) influence sterics and Lewis acidity. Ligand bulk increases along the row Me,DIPPBDIMe,DIPePBDI≈tBu,DIPPBDItBu,DIPePBDI; DIPP=2,6-C(H)Me2-phenyl, DIPeP=2,6-C(H)Et2-phenyl. The Gutmann-Beckett test showed acceptor numbers of: (tBu,DIPPBDI)AlMe+ 85.6, (tBu,DIPePBDI)AlMe+ 85.9, (Me,DIPPBDI)AlMe+ 89.7, (Me,DIPePBDI)AlMe+ 90.8, (Me,DIPPBDI)AlH+ 95.3. Steric and electronic factors need to be balanced for catalytic activity in imine hydrogenation. Open, highly Lewis acidic, cations strongly coordinate imine rendering it inactive as a Frustrated Lewis Pair (FLP). The bulkiest cations do not coordinate imine but its combination is also not an active catalyst. The cation (tBu,DIPPBDI)AlMe+ shows the best catalytic activity for various imines and is also an active catalyst for the Tishchenko reaction of benzaldehyde to benzylbenzoate. DFT calculations on the mechanism of imine hydrogenation catalysed by cationic Al complexes reveal two interconnected catalytic cycles operating in concert. Hydrogen is activated either by FLP reactivity of an Al???imine couple or, after formation of significant quantities of amine, by reaction with an Al???amine couple. The latter autocatalytic Al???amine cycle is energetically favoured.
Square-planar diacetatopalladium complexes with trans-configured secondary amine ligands that avoid orthometalation: Ligand synthesis, coordination, molecular structure and catalytic potential for Suzuki cross-coupling reactions
Chahen, Ludovic,Therrien, Bruno,Suess-Fink, Georg
, p. 5045 - 5051 (2008/09/17)
The trans-configured square-planar palladium complexes [Pd(OAc) 2(LNtBu)2] (1), [Pd(OAc)2(η2- LN∩NtBu)] (2), [Pd(OAc)2(LNPh)2] (3), and [Pd(OAc)2(η2-LN∩NPh)] (4), have been synthesized by treating palladium acetate with the amines NHtBuCH2-2,4,6-Me 3C6H2 (LNtBu) or NHPhCH2-2,4,6- Me3C6H2 (LNPh) or with the diamines NHtBuCH2-2,4,6-Me3C6H-CH2-2,4,6- Me3C6H-CH2-NHtBu (LN∩NtBu) or NHPh-CH 2-2,4,6-Me3C6H-CH2-2,4,6-Me 3C6H-CH2-NHPh (LN∩NPh). The single-crystal X-ray structure analysis of complexes 1-3 confirms a trans arrangement of the two acetato groups and of the two nitrogen atoms. Orthometalation leading to palladacycles is impossible in all cases as the ortho positions in the benzylic rings are blocked by methyl substituents. All complexes are found to catalyze Suzuki cross-coupling reactions of deactivated and even sterically hindered arene substrates. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.