RESUMEN
An easily prepared iron(ii) amide precatalyst enables the selective hydroboration of carbonyls with HBpin (pinacolborane) in the absence of any additive. The reactions proceed with low catalytic loading (1-3 mol%) under mild reaction conditions and display wide functional group compatibility. Aldehydes are selectively hydroborated in the presence of other reducible functional groups, such as ketones, alkenes, nitriles, esters, amides, acids and halides.
RESUMEN
A series of structurally characterized magnesium and zinc complexes of the form L4-tBuPh-M{N(SiMe3)2}2 [M = Mg (1) and Zn (2); L4-tBuPh = 1,3-diethyl-4,5-dimethylimidazolium-2-{N,N'-bis(4-tert-butylphenyl)amidinate}], L4-iPrPh-M{N(SiMe3)2}2 [M = Mg (3) and Zn (4); L4-iPrPh = 1,3-diethyl-4,5-dimethylimidazolium-2-{N,N'-bis(4-isopropylphenyl)amidinate}], and L4-iPrPh-ZnEt2 (5) bearing a zwitterionic-type neutral amidinate or N-heterocyclic carbene-carbodiimide ("NHC-CDI") adduct and monoanionic amido or alkyl ligands have been reported. The synthesis of compounds 1-5 was achieved by the direct addition of a "NHC-CDI" adduct to a corresponding metal bis(amide) or dialkyl reagent. All compounds 1-5 exist as monomers in the solid state. In all cases, the metal (magnesium or zinc) centers adopt a distorted four-coordinate tetrahedral geometry bonded to one N,N'-chelated neutral zwitterionic ligand and two monoanionic amido or alkyl moieties. In contrast, sterically bulky zwitterionic amidinate 1,3-diethyl-4,5-dimethylimidazolium-2-{N,N'-bis(2,6-diisopropylphenyl)amidinate} (LDipp) upon treatment with lithium bis[(trimethylsilyl)amide], Li{N(SiMe3)2}, affords the NHC-lithium complex MeIEt-[Li{N(SiMe3)2}]2 (6), in which one molecule of NHC (MeIEt = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene) coordinates to one of the two lithium centers. In a similar way, the reaction between LDipp and Mg{N(SiMe3)2}2 allowed the formation of a NHC adduct of metal bis(amide), MeIEt-Mg{N(SiMe3)2}2 (7), instead of a zwitterionic adduct of metal bis(amide). Alternatively, the synthesis of both compounds 6 and 7 was achieved by the direct addition of 1 equiv of NHC, i.e., MeIEt to Li{N(SiMe3)2} (2.0 equiv) and Mg{N(SiMe3)2}2 (1.0 equiv) in benzene-d6, respectively. All compounds (1-7) were characterized by multinuclear {1H, 13C, and 29Si (for 1-4, 6, and 7) and 7Li (for compound 6)} magnetic resonance spectroscopy, mass spectrometry, elemental analysis, and single-crystal X-ray structural analysis. In addition, preliminary reactivity studies of zwitterion-supported metal complexes have been investigated. Furthermore, density functional theory calculations have been carried out to obtain the energetics of zwitterion-supported lithium and magnesium complexes.
RESUMEN
The synthesis of novel heteroleptic organomagnesium(ii) amide complexes [IMesMg(Ar){N(SiMe3)2}]; (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), Ar = 2,6-Me2C6H3 (Xyl) (1) and 2,4,6-Me3C6H2 (Mes) (2) is reported. Both compounds 1 and 2 were confirmed by multinuclear (1H, 13C and 29Si) magnetic resonance spectroscopy, elemental analysis and single crystal X-ray structural analysis. Furthermore, the organomagnesium amide pre-catalyzed cross-dehydrogenative coupling of organosilanes with amines has been investigated.
RESUMEN
Magnesium amide complexes such as Mg{N(SiMe3)2}2 (1) xylLMgN(SiMe3)2·THF (2) [xylL = ArNC(NiPr2)NAr; (Ar = 2,6-Me2-C6H3)] and dippLMgN(SiMe3)2·THF (3) [dippL = ArNC(NiPr2)NAr; (Ar = 2,6-iPr2-C6H3)] are reported as highly efficient pre-catalysts for the hydroboration of a wide range of esters using pinacolborane (HBpin) under mild reaction conditions. Moreover, we have shown compound 1 catalyzed chemoselective reduction of esters in the presence of other reducible functional groups such as alkene, alkyne and nitro.