Oxidation of alcohols by transition metal complexes—iv : The rhodium catalysed synthesis of esters from aldehydes and alcohols

Both RhH(CO)PPh₃)₃ and a catalyst made in _situ from RhCl₃·3H₂O, PPh₃ and Na₂CO₃ catalyse the reaction of a range of aldehydes with simple primary alcohols to give esters together with alcohols formed by reduction of the aldehydes. The proportion of ester can be increased by adding an efficient hydrogen acceptor. The reaction can also be used to produce 5- and 7-membered lactones from aromatic dialdehydes. Propan-2-ol and the _{in situ} catalyst reduce some aromatic aldehydes to the corresponding alcohols without concomitant ester formation.     

Efficient solvent-free selective monoalkylation of arylacetonitriles with mono-, bis-, and tris-primary alcohols catalyzed by a Cp*Ir complex

Our objectives were to develop catalytic atom-economic processes accessing and/or incorporating versatile functionality using aryl/heteroaryl acetonitriles as substrates. We report essentially solvent-free [Cp*IrCl2]2 catalyzed redox neutral processes whereby substituted acetonitriles react with primary alcohols to deliver monosubstituted aryl/heteroaryl acetonitriles in excellent yield. We further demonstrate that such processes can be achieved by conventional or microwave heating and that bis- and tris-primary alcohols are also processed efficiently.     

Calculation of catalytic activity of transition metal complexes

A method is proposed for calculation of the catalytic activity of the complexes of transition metals. An effective Hamiltonian describing the behavior of the reagents in the presence of the catalyst is formulated, and a catalytic activity index tan2 is introduced. The isomerization of quadricyclane to norbornadiene is considered. It is shown that the index in the case of the catalytically active low-spin complex CoTPP is two orders of magnitude larger than in the case of the catalytically inactive high-spin complex MnTPP and the analogous Fe(III)TPP and MnPc complexes.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 4, pp. 398–406, July–August, 1988.     

Molecular orbital calculations on transition metal complexes part VII

INDO SCF Molecular Orbital Calculations have been made for manganocene (MnCp₂), its molecular cation (MnCp ₂ ⁺ ) and the ferricenium ion FeCp ₂ ⁺ . The computations yield a high spin ⁶ A _1g (e _2g ² a _1g ¹ e _1g ² ) ground state for MnCp₂, contrary to that which was assumed to interpret the photoelectron spectrum. The lowest energy ionisations from the ⁶ A _1g state have been obtained by differences in total energies of the ion and the neutral molecule. These are in very good agreement with the experimental values. The use of the eigen-values of the neutral molecule to obtain ionisation energies (Koopmans' Theorem) is shown to be inappropriate due to the considerable electronic redistribution which accompanies the formation of the molecular ion from the neutral molecule. The main factor which influences this charge rearrangement is found to be the covalency within the e _1g (d _xz , d _yz ) orbitals.     

Selective,catalytic carbon-carbon bond activation and functionalization promoted by late transition metal catalysts

The selective catalytic activation and functionalization of carbon-carbon bonds in a series of substituted cyclopropane substrates has been developed using commercially available transition metal catalysts. Catalytic hydrogenation and olefination procedures, tolerant of a range of functional groups, have been discovered. Introduction of a chelate-assisting substituent such as [PPh2] is effective in altering the kinetic selectivity and lowering the activation barrier for the catalytic processes.     

Mechanistic considerations on catalytic H/D exchange mediated by organometallic transition metal complexes

The purpose of this review is to analyze the different reaction mechanisms of the H/D exchange on organic substrates catalyzed by transition metal complexes in homogeneous phase. The metal-catalyzed H/D exchange is a multifaceted reaction whose mechanism depends strongly on the reaction conditions and on the metal complex used as a catalyst. It is possible to group the different mechanisms into three main families depending on the “role” and behavior of the catalyst: (i) Lewis acid–base catalysis; (ii) CH activation (iii) insertion/β-elimination. For each macro-group, several representative examples are discussed and critically evaluated in order to provide the reader with keys to the understanding of how the different catalytic systems act and how their modification may affect their performance in terms of activity and selectivity. This knowledge is fundamental for designing improved organometallic H/D catalysts for labeling organic products in greener conditions with more cost-effective processes.     

Allylic alcohols as synthetic enolate equivalents: isomerisation and tandem reactions catalysed by transition metal complexes

Allylic alcohols can be isomerised into carbonyl compounds by transition metal complexes. In the last few years, catalyst design and development have resulted in highly efficient isomerisations under mild reaction conditions, including enantioselective versions. In addition, the isomerisation of allylic alcohols has been combined with C-C bond forming reactions when electrophiles such as aldehydes or imines were present in the reaction mixture. Also, C-F bonds can be formed when electrophilic fluorinating reagents are used. Thus, allylic alcohols can be treated as latent enol(ate)s. In this article, we highlight the latest developments concerning the isomerisation of allylic alcohols into carbonyl compounds, focusing in particular on tandem isomerisation/C-C or C-heteroatom bond formation processes. Significant attention is given to the mechanistic aspects of the reactions.     

Oxidation of alcohols by metal nitrates supported on silica gel

Many metal nitrates, especially zinc(II) and copper(II) nitrates, supported on silica gel, oxidized secondary and benzylic alcohols to the corresponding ketones and aldehydes efficiently.     

Selective transition metal extraction by reverse micelles

In this report we have studied the extraction of a series of heavy metals ions (Cu2+, Ni2+, Fe3+, Cr3+, CrO4(2-)) from water bulk solutions by means of reverse micelles. The parameters explored are the nature and concentration of the accompanying electrolyte, as well as the surfactant nature and its concentration. The extracted metals can be recovered and eventually concentrated in a new water solution carrying out a back extraction. The extracted amount of metal is strongly dependent on the charge of the metal to be extracted. Therefore the extracted water solution is enriched in higher charge metal. Anions of amphoteric metals, like the chromate ions, can be quantitatively separated from their positive cations, like Cr3+ by properly choosing the cationic or the anionic surfactants. The transfer of the metal is essentially controlled by electrostatic forces. A model based on the Poisson-Boltzmann distribution allow us to get the potential profile inside the water pool by determining the concentrations of the surfactant counter ions. From the potential profile and mass balance it is possible calculate the extraction percentage.     

不对称席夫碱过渡金属配合物的合成和催化性能

用乙二胺、乙酰丙酮与水杨醛反应合成了一种不对称四齿席夫碱配体(H2L)及其铜、钴、镍、锌配合物,通过元素分析、摩尔电导、红外光谱、紫外光谱、X-射线光电子能谱等手段对配体及其配合物进行了表征,并推测所有配合物均为烯醇式四配位结构,确定新配合物的组成为MC14H16N2O2(M=Cu,Co,N i,Zn)。并研究了配合物对双氧水的催化分解性能。     

Oxidation of alcohols by electrochemically regenerated nickel oxide hydroxide. Selective oxidation of hydroxysteroids

Primary alcohols, α,ω-diols and secondary alcohols are easily transformed into carboxylic acids, dicarboxylic acids or ketones, respectively, by heterogeneous oxidation with nickel oxide hydroxide electrochemically regenerated at a nickel hydroxyde electrode. The results are discussed in comparison to those of the nickel peroxide and chromic acid oxidation. The oxidation rate decreases with increasing steric hindrance of the alcohol, thus allowing the selective oxidation of the 3-position in hydroxysteroids.     

Dinitrogen activation by low-coordinate transition metal complexes

In this article, several avenues in the ongoing computational study of first row transition metal β-diketiminate dinitrogen complexes are discussed. Analysis of monometallic N–N bond length changes reveals that upon complexation of free N₂, side-bound N₂ is 0.018–0.054?Å longer than analogous end-bound N₂. Although the same isomeric preferences across the 3-D series were calculated for bimetallic β-diketiminate N₂ complexes, the N–N bond lengths and hence N₂ activation was found to be greater compared to the monometallic species. This present research demonstrates that a useful starting point for activated dinitrogen complexes is the choice of bimetallic supporting ligands, which unlike monometallic ligands allow both metals to activate N₂ in a concerted fashion.     

Oxidation states, atomic charges and orbital populations in transition metal complexes

The differences and similarities between calculated atomic charge and formal oxidation state in transition metal complexes are discussed in the light of density functional theory calculations on a variety of four-coordinate complexes. It is shown that the oxidation state formalism provides a framework for the classification of families of compounds related by ligand substitution or redox processes, and can neither be replaced by nor deduced from net atomic charges.     

Oxidation and photooxidation of sulfide and thiosulfate ions catalyzed by transition metal chalcogenides and phthalocyanine complexes

The catalytic and photocatalytic activities of supported cobalt or zinc phthalocyanine complexes, bulk MoS₂, MoS₂ deposited on Al₂O₃, potassium intercalated MoS₂ (K_0.33 H₂O_0.66 MoS₂), CdS and polycrystalline nickel phosphorus trisulfide (NiPS₃) have been investigated in the oxidation of sodium sulfide and Na₂S₂O₃. The phthalocyanine complexes and the metal chalcogenides do not catalyze, in the absence of light, the complete oxidation of the sulfide ion to sulfate ion. The final product of the catalytic oxidation is the formed thiosulfate. No oxidation of Na₂S₂O₃ has been registered in the dark in the presence of any of the catalytic samples. Their activity was enhanced upon irradiation with visible light. Thiosulfate appears to be the final product also of the photooxidation of the sulfide ion catalyzed by metal chalcogenides. They do not catalyze the further photooxidation of Na₂S₂O₃. The only photocatalysts which favour with their presence the oxidation of the sulfide and thiosulfate ions to sulfate ion, are the zinc phthalocyanine complexes. In this case, the photooxidation process involves singlet oxygen.     

Hydrophosphination of alkoxyalkenes catalyzed by transition metal complexes

Diphenylphosphine adds to alkyl vinyl ethers in the presence of Ni(II) and Pd(II) complexes with a high regioselectivity, leading to exclusive formation of the corresponding Markownikoff adducts which were isolated as 1-alkoxyalkyl(diphenyl)phosphine oxides via oxidation with hydrogen peroxide.