Alternative Metals for Homogeneous Catalyzed Hydroformylation Reactions

Transition‐metal‐catalyzed hydroformylation reactions constitute one of the most powerful tools for C? C bond formation in organic synthesis and represent an outstanding example of the application of homogeneous catalysis on an industrial scale. This process allows for the straightforward conversion of inexpensive chemical feedstock into broadly applicable aldehydes, which serve as major building blocks for numerous chemical products. These products are highly valuable for the chemical industry and used as plasticizers, detergents, and surfactants on a million ton scale. Moreover, aldehydes serve as versatile chemical intermediates for the production of fine chemicals and pharmaceuticals. Currently, most of the bulk hydroformylation processes rely on rhodium‐based catalysts. The increasing demand and resulting high cost of this precious metal has resulted in alternative transition‐metal catalysts becoming highly desirable. The following Review summarizes the progress achieved utilizing Ru, Ir, Pd, Pt, and Fe catalysts in hydroformylation reactions.     

Heteroleptic Alkyl and Amide Iminoanilide Alkaline Earth and Divalent Rare Earth Complexes for the Catalysis of Hydrophosphination and (Cyclo)Hydroamination Reactions

[{N^N}M(X)(thf)_n] alkyl (X=CH(SiMe₃)₂) and amide (X=N(SiMe₃)₂) complexes of alkaline earths (M=Ca, Sr, Ba) and divalent rare earths (Yb^II and Eu^II) bearing an iminoanilide ligand ({N^N}^?) are presented. Remarkably, these complexes proved to be kinetically stable in solution. X‐ray diffraction studies allowed us to establish size–structure trends. Except for one case of oxidation with [{N^N}Yb^II{N(SiMe₃)₂}(thf)], all these complexes are stable under the catalytic conditions and constitute effective precatalysts for the cyclohydroamination of terminal aminoalkenes and the intermolecular hydroamination and intermolecular hydrophosphination of activated alkenes. Metals with equal sizes across alkaline earth and rare earth families display almost identical apparent catalytic activity and selectivity. Hydrocarbyl complexes are much better catalyst precursors than their amido analogues. In the case of cyclohydroamination, the apparent activity decreases with metal size: Ca>Sr>Ba, and the kinetic rate law agrees with R_CHA=k[precatalyst]¹[aminoalkene]¹. The intermolecular hydroamination and hydrophosphination of styrene are anti‐Markovnikov regiospecific. In both cases, the apparent activity increases with the ionic radius (Ca<Sr<Ba) but the rate laws are different, and obey R_HA=k[styrene]¹[amine]¹[precatalyst]¹ and R_HP=k[styrene]¹[HPPh₂]⁰[precatalyst]¹, respectively. Mechanisms compatible with the rate laws and kinetic isotopic effects are proposed. [{N^N}Ba{N(SiMe₃)₂}(thf)₂] ( 3 ) and [{N^N}Ba{CH(SiMe₃)₂}(thf)₂] ( 10 ) are the first efficient Ba‐based precatalysts for intermolecular hydroamination and hydrophosphination, and display activity values that are above those reported so far. The potential of the precatalysts for C? N and C? P bond formation is detailed and a rare cyclohydroamination–intermolecular hydroamination “domino” sequence is presented.     

离子色谱法同时分析中药中的碱金属与碱土金属离子

用离子色谱法简单快速地分析了中药中的阳离子。分析结果表明,川芎和酸枣仁中5种常见阳离子Na~+,NH~+_4,K~+,Mg~2+和Ca~2+的含量比例不同。各离子的检出限（S/N=3）为0.001～0.013mg／L,线性范围达3个数量级。     

When bigger is better: intermolecular hydrofunctionalizations of activated alkenes catalyzed by heteroleptic alkaline Earth complexes

New alkaline-earth amido complexes catalyze the regioselective intermolecular hydroamination (see scheme; Ae=alkaline earth) and hydrophosphination of styrene and isoprene with unprecedented activities. The catalytic performances increased linearly with the size of the metal.     

Enantioselective Addition of Boronates to Acyl Imines Catalyzed by Chiral Biphenols

On the big screen : A chiral biphenol catalyst screening protocol was developed for the rapid identification of enantioselective nucleophilic boronate reactions with acyl imines (see scheme). The approach successfully identified a unique catalyst for the reaction of aryl, vinyl, and alkynyl boronates. Mechanistic studies demonstrate boronate ligand exchange with the catalyst is necessary for activation towards nucleophilic addition.

     

稀土金属在不对称催化中的应用:从均相催化到异相催化

稀土金属的配位数较高,可通过容纳大型手性配体,构筑手性环境,催化不对称反应的定向发生,在工业生产特别是制药工程中具有重要应用价值.本文以Henry反应、Mannich反应和Strecker反应为例,总结回顾了稀土金属催化剂在此类反应中的设计思路、性能特点与应用前景,旨在展现稀土金属催化剂兼具融合均相催化与异相催化的优势...     

Atom‐Transfer Radical Addition Reactions Catalyzed by RuCp* Complexes: A Mechanistic Study

Kinetic and spectroscopic analyses were performed to gain information about the mechanism of atom‐transfer radical reactions catalyzed by the complexes [RuCl₂Cp*(PPh₃)] and [RuClCp*(PPh₃)₂] (Cp*=pentamethylcyclopentadienyl), in the presence and in the absence of the reducing agent magnesium. The reactions of styrene with ethyl trichloroacetate, ethyl dichloroacetate, or dichloroacetonitrile were used as test reactions. The results show that for substrates with high intrinsic reactivity, such as ethyl trichloroacetate, the oxidation state of the catalyst in the resting state is +3, and that the reaction is zero‐order with respect to the halogenated compound. Furthermore, the kinetic data suggest that the metal catalyst is not directly involved in the rate‐limiting step of the reaction.     

Computational Mechanistic Elucidation of the Intramolecular Aminoalkene Hydroamination Catalysed by Iminoanilide Alkaline‐Earth Compounds

A comprehensive computational exploration of plausible alternative mechanistic pathways for the intramolecular hydroamination (HA) of aminoalkenes by a recently reported class of kinetically stabilised iminoanilide alkaline‐earth silylamido compounds [{N^N}Ae{N(SiMe₃)₂} ? (thf)_n] ({N^N}=iminoanilide; Ae=Ca, Sr, Ba) is presented. On the one hand, a proton‐assisted concerted N?C/C?H bond‐forming pathway to afford the cycloamine in a single step can be invoked and on the other hand, a stepwise σ‐insertive pathway that involves a fast, reversible migratory olefin 1,2‐insertion step linked to a less rapid, irreversible metal?C azacycle tether σ‐bond aminolysis. Notably, these alternative mechanistic avenues are equally consistent with reported key experimental features. The present study, which employs a thoroughly benchmarked and reliable DFT methodology, supports the prevailing mechanism to be a stepwise σ‐insertive pathway that sees an initial conversion of the {N^N}Ae silylamido into the catalytically competent {N^N}Ae amidoalkene compound and involves thereafter facile and reversible insertive N?C bond‐forming ring closure, linked to irreversible intramolecular Ae?C tether σ‐bond aminolysis at the transient {N^N}Ae alkyl intermediate. Turnover‐limiting protonolysis accounts for the substantial primary kinetic isotope effect observed; its DFT‐derived barrier satisfactorily matches the empirically determined Eyring parameter and predicts the decrease in rate observed across the series Ca>Sr>Ba correctly. Non‐competitive kinetic demands militate against the operation of the concerted proton‐assisted pathway, which describes N?C bond‐forming ring closure triggered by concomitant amino proton delivery at the C?C linkage evolving through a multi‐centre TS structure. Valuable insights into the catalytic structure–activity relationships are unveiled by a detailed comparison of [{N^N}Ae(NHR)] catalysts. Moreover, the intriguingly opposite trends in reactivity observed in intramolecular (Ca>Sr>Ba) and intermolecular (Ca<Sr<Ba) HA catalysis for the studied family of iminoanilide alkaline‐earth amido catalysts are rationalised.     

Catalytic Direct‐Type Addition Reactions of Alkylarenes with Imines and Alkenes

Catalytic addition reactions of very weakly acidic nonactivated alkylarenes such as toluene and its derivatives were developed by using a strongly basic mixed catalyst system under mild reaction conditions. The addition reactions with imines and alkenes proceeded smoothly under proton‐transfer conditions to afford the desired products in good to high yields, and high levels of regio‐ and stereoselectivity were achieved. It was also revealed that the asymmetric addition reaction of an alkylarene was possible.     

Highly Efficient Organosuperbase-Catalyzed Mannich-type Reactions of Sulfonylimidates with Imines: Successful Use of Aliphatic Imines as Substrates and a Unique Reaction Mechanism

First walk, then run! Highly efficient organosuperbase-catalyzed Mannich-type reactions of sulfonylimidates with readily prepared Boc-protected imines have been developed. The desired products were obtained in high yield and with high anti selectivity. Mechanistic studies show an induction period for the catalyzed reaction, and that the organosuperbase works as an initiator.     

Decarboxylative Mannich Reactions with N-Alkyl Imines

The use of N-alkyl imines in decarboxylative Mannich reaction with substituted malonic acids half oxyesters (SMAHOs) has been developed to afford a direct access to secondary β^2,3-aminoesters. The transformation occurs under very practical conditions (DABCO as a catalyst in bulk toluene and open to air) and can be performed with a broad range of each substrate in yields of 36 to 97 %. Importantly, the reaction was found to require the use of acidic additives in combination with the organocatalyst to limit the competitive olefination reaction.