Abstract
The complex [Cp*RuCl(COD)] reacts with LH2Cl2 (L = bis(3-methylimidazol-2-ylidene)) and LiBun in tetrahydrofuran at 65 °C furnishing the bis-carbene derivative [Cp*RuCl(L)] (2). This compound react...
Highlights
The catalytic transfer hydrogenation (TH) of carbonyl groups to afford their corresponding alcohols is considered a useful synthetic tool to produce valuable building blocks for the pharmaceutical industry.[1−3] This methodology has as an advantage the use of alcohols,[4] water,[5] or formic acid[6] instead of molecular hydrogen or metal hydrides as sources of the hydrogen atoms transferred in the reaction
Article linked bis(NHC) ligand bis(3-methylimidazol-2-ylidene)methane (L),[21] we focused our attention in the preparation of homologous pentamethylcyclopentadienyl (Cp*) ruthenium complexes with the same ligand in order to compare the effect of the replacement of the supporting ligand Tp by Cp*
We have found that this modification enhances reactivity, and that several of the new complexes prepared in this way are efficient catalyst precursors for TH reactions of carbonyl groups
Summary
The catalytic transfer hydrogenation (TH) of carbonyl groups to afford their corresponding alcohols is considered a useful synthetic tool to produce valuable building blocks for the pharmaceutical industry.[1−3] This methodology has as an advantage the use of alcohols,[4] water,[5] or formic acid[6] instead of molecular hydrogen or metal hydrides as sources of the hydrogen atoms transferred in the reaction. NHC ligands have been successfully used as ancillary ligands in the design and synthesis of homogeneous catalysts.[11] These ligands are considered an alternative to phosphine ligands due to their stronger sigma-donor properties that confer a greater stability to the corresponding metallic complexes, and facilitate the modulation of their stereoelectronic properties.[12] Chelation is a strategy used to stabilize the M−NHC bond and provide more robust complexes with different topological properties, namely steric hindrance, bite angle, or fluxional behavior.[13] In contrast to their monodentate counterparts, the chemistry of transition-metal complexes based on bis(NHC) ligands have been far less explored.[14] Ruthenium(II)−NHC complexes have been recently used in a wide range of organic reactions[15] including TH reactions.1,11a,16−18 the synthesis and catalytic application of their related hydrocarbon chain-linked bis(NHC) complexes is scarce in the literature and their potential synthetic applicability still needs to be studied. To the best of our knowledge, only a few reports have been described about the use of hydrocarbon chain-linked bis(NHC) complexes of ruthenium in TH of ketones[19] and hydrogenation of olefins.[20]
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