Chemoselective hydrosilylation of functionalized alkenes is difficult to achieve using base-metal catalysts. Reported herein is that well-defined bis(amino)amide nickel pincer complexes are efficient catalysts for anti-Markovnikov hydrosilylation of terminal alkenes with turnover frequencies of up to 83,000 per hour and turnover numbers of up to 10,000. Alkenes containing amino, ester, amido, ketone, and formyl groups are selectively hydrosilylated. A slight modification of reaction conditions allows tandem isomerization/hydrosilylation reactions of internal alkenes using these nickel catalysts.
[Fe]-Hydrogenase catalyzes the hydrogenation of a biological substrate via the heterolytic splitting of molecular hydrogen. While many synthetic models of [Fe]-hydrogenase have been prepared, none yet are capable of activating H2 on their own. Here, we report the first Fe-based functional mimic of the active site of [Fe]-hydrogenase, which was developed based on a mechanistic understanding. The activity of this iron model complex is enabled by its unique ligand environment, consisting of biomimetic pyridinylacyl and carbonyl ligands, as well as a bioinspired diphosphine ligand with a pendant amine moiety. The model complex activates H2 and mediates hydrogenation of an aldehyde.
Iron-catalyzed hydrogenation has drawn much attention, yet the scope and chemoselectivity of iron catalysis warrant further improvement. Here we report new iron pincer complexes as chemoselective hydrogenation and transfer hydrogenation catalysts. Several Fe(II) complexes supported by a 2,6-bis(phosphinito)pyridine ligand (PONOP) have been synthesized. Fe(II) hydride complexes [( i PrPONOP)Fe(CO)-(H)Br] (2) and [( i PrPONOP)Fe(CO)(H)(CH 3 CN)](OTf) ( 3) can activate H 2 at room temperature. Complexes 2 and 3 are hydrogenation catalysts at room temperature, and the hydrogenation is selective for aldehyde in the presence of ketone and alkene groups. 2 and 3 are also chemoselective transfer hydrogenation catalysts using sodium formate as the hydride source.
A new series of half-sandwich ruthenium(II) complexes containing p-aminobenzoic acids (4-aminobenzoic acid and 4-aminocynnamic acid) and different arene ligands (benzene, p-cymene, and indane) have been synthesized and fully characterized giving particular attention to the analysis of the generated crystalline supramolecular architectures. A careful design of the molecular building blocks allows a perfect match to be reached between hydrogen bond donors and acceptors thus leading to the construction of crystalline wheel-and-axle metal–organic (WAAMO) systems, where the wheels are the half-sandwich units [(arene)RuCl2] and the axles are based on the cyclic dimerization of the COOH functions of the aminobenzoic ligands. The R
2
2(8) cyclic pattern is however conserved only in absence of hydrogen bond donor crystallization solvents, which, when present, tend to insert between the COOH group and a Cl–Ru moiety with formation of hydrates or solvates. Far more robust is the supramolecular synthon based on the coupling involving the Ru–NH2 function as donor and the RuCl2 group as acceptor, which has been found in five out of seven X-ray structures reported in this work. The porosity of the WAAMOs can be modulated acting on the steric requirements of the arene ligand and on the length of the covalent segment of the central supramolecular axle.
Chemoselective hydrosilylation of functionalized alkenes is difficult to achieve using base-metal catalysts. Reported herein is that well-defined bis(amino)amide nickel pincer complexes are efficient catalysts for anti-Markovnikov hydrosilylation of terminal alkenes with turnover frequencies of up to 83 000 per hour and turnover numbers of up to 10 000. Alkenes containing amino,e ster,a mido,k etone,a nd formyl groups are selectively hydrosilylated. As light modification of reaction conditions allows tandem isomerization/hydrosilylation reactions of internal alkenes using these nickel catalysts.
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