Pyridine-type complexes of transition metal halides

Formation of nitrogen ligated complexes of types NiL₆X₂, NiL₄X₂, NiL₂X₂ and NiL₁X₂ (whereL=pyridine, 2-, 3- and 4-methyl-pyridine andX=F, Cl, Br, I) have been studied by traditional preparative methods, i.e. from solutions and by solid-gas phase chemisorption. Quaternary mixed complexes were obtained by chemisorption from heated intermediates. The complexes thus formed were further analysed by simultaneous TG-DTG-DTA. Effects of the ligands on stoichiometry and thermal properties of the complexes are discussed.     

Computational mechanistic studies of acceptorless dehydrogenation reactions catalyzed by transition metal complexes

Acceptorless dehydrogenation (AD) that uses non-toxic reagents and produces no waste is a type of catalytic reactions toward green chemistry. Acceptorless alcohol dehydrogenation (AAD) can serve as a key step in constructing new bonds such as C-C and C-N bonds in which alcohols need to be activated into more reactive ketones or aldehydes. AD reactions also can be utilized for hydrogen production from biomass or its fermentation products (mainly alcohols). Reversible hydrogenation/ dehy-drogenation with hydrogen uptake/release is crucial to realization of the potential organic hydride hydrogen storage. In this article, we review the recent computational mechanistic studies of the AD reactions catalyzed by various transition metal complexes as well as the experimental developments. These reactions include acceptorless alcohol dehydrogenations, reversible dehydrogenation/hydrogenation of nitrogen heterocycles, dehydrogenative coupling reactions of alcohols and amines to construct C-N bonds, and dehydrogenative coupling reactions of alcohols and unsaturated substrates to form C-C bonds. For the catalysts possessing metal-ligand bifunctional active sites (such as 28, 45, 86, 87, and 106 in the paper), the dehydrogenations prefer the "bifunctional double hydrogen transfer" mechanism rather than the generally accepted-H elimination mechanism. However, methanol dehydrogenation involved in the C-C coupling reaction of methanol and allene, catalyzed by the iridium complex 121, takes place via the-H elimination mechanism, because the Lewis basicity of either the-allyl moiety or the carboxyl group of the ligand is too weak to exert high Lewis basic reactivity. Unveiling the catalytic mechanisms of AD reactions could help to develop new catalysts.     

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.     

Cross-combination of magnesium diacetylenides with organic halides catalyzed by transition metals complexes

Conclusions The cross-combination of magnesium diacetylenides of the type (R-CC)₂Mg (R=C₅H₁₁, Ph) with alkyl-, allyl-, propargyl-, and arylhalides, catalyzed by Cu(I), Ni, and Pd complexes, gives mono- and disubstituted acetylenes with high yields.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2037–2041, September, 1987.     

4-Cyanoaniline complexes with transition metal(II) halides

Summary Coordination compounds formed by the interaction of manganese(II), cobalt(II), nickel(II) and copper(II) chloride and bromide with 4-cyanoaniline (4-CA) have been prepared and characterized by molar conductance, magnetic susceptibilities, electronic and i.r. spectral measurements down to 200 cm^–1 in the solid state. The isolated complexes are M(4-CA)₂X₂ except for nickel(II) bromide which is NI(4-CA)₄Br₂. I.r. spectra, indicate that 4-CA, though a potentially bidentate ligand, nevertheless acts only as a terminally aniline (NH₂) bonded monodentate ligand in all the complexes. Tentative stereochemistries of the complexes have been suggested in the solid state.     

ESR studies on reactions of dicyclopentadienyl dicarbonyl titanium with organic halides

ESR method was used to elucidate the mechanism of the reactions of alkyl, allyl or benzyl halides with dicyclopentadienyldicarbonyl titanium. The paramagnetic [intermediates of the reactions were identified during the course of the reactions. The reaction mechanism based on ESR findings and the products analyses is postulated to operate on radical pathways. When alkyl halides were used to react with the organometallic compound 1, the intermediate found was [Cp₂Ti(CO)X] (C), and the main product was identified to be dicyclopentadienyl-acyl-halo titanium (3), an insertion of TiCO into R-X, i.e. [Cp₂Ti-C(0)R] X. When allyl or benzyl halides were used, the intermediate found was [Cp₂TiX] (B), and the main products were identified to be the dicyclopentadienyl titanium dihalides and the coupling products of allyl or benzyl groups.     

Solid,Primary aliphatic amine complexes of transition metal halides

The thermal decomposition of some new primary aliphatic amine RNH₂ (R=methyl-, ethyl-,n-propyl,i-propyl,n-butyl-,i-butyl-,n-amyl-,i-amyl-, cyclohexyl-andi-allyl-) complexes with cadmium(II) chloride, prepared by solid-gas phase chemisorption, have been investigated by simultaneous TG-DTG-DTA. The enthalpy changes during the degradation were followed by DSC. The course of the thermal decomposition is described in detail. The thermal properties observed were compared to the more recently reported nickel(II) analogues. The changes in thermal parameters in the series of cadmium(II) chloride aliphatic amine complexes are discussed on the basis of the inductive releasing effect of the aliphatic chain and the steric hindrance of the ligands. Part I: J. Thermal Anal. 39 (1993) 333.     

New reactions of 1-alkynes catalyzed by transition metal complexes

Recently discovered catalytic reactions with ruthenium and lanthanide metal complexes have extended the scope of 1-alkynes as useful reagents. The specific formation of aryl-substituted (Z)-1,3-enzymes via the dimerization of HC(triple bond) CR(1) (R(1) = aryl) has been attained using dimeric lanthanide complexes, the catalytic activity of which appears to be unaffected by time. The dimerization of HC(triple bond) CR(2) (R(2) = t-Bu, SiMe(3)) catalyzed by Ru(cod)(cot)/PR(3) or RuH(2)(PPh(3))(3) produces a good yield of butatrienes (Z)R(2)CH=C=C=CHR(2) with a high degree of selectivity. Under certain conditions, HC(triple bond) C=SiMe(3) dimerizes to yield exclusively (Z)-M(3)Si-C(triple bond) C-CH=CH-SiMe(3). The hydration of HC(triple bond)CR(3) (R(3) = alkyl, aryl) catalyzed by RuCl(2)/PR'(3) or CpRuCl(PR"(3))(2) has realized the first example of anti-Markovnikov regioselectivity in an addition reaction of water that produces aldehydes R(3)CH(2)bond;CHO. The application of this reaction to propargylic alcohols has lead to their formal isomerization to alpha,beta-unsaturated aldehydes. In contrast, the addition of amines R(4)bond;NH(2) (R(4) = aryl) to HCtbond;CR(5) (R(5) = alkyl, aryl) conforms to Markovnikov's rule to produce ketimines R(5)bond;(C=NR(4))bond;CH(3) when catalyzed by a Ru(3)(CO)(12)/additive. Since the reaction can be performed in air without the need for any solvents, it enables the practical synthesis of aromatic ketimines, which are difficult to prepare by conventional methods. The synthesis of indoles using deactivated anilines is one practical application of this reaction. The mechanisms of some of these reactions have been analyzed in detail with the aid of theoretical calculations.     

Oxidative-addition reactions of nitronium tetrafluoroborate with unsaturated transition metal complexes

The oxidative-addition reaction of nitronium tetrafluoroborate to unsaturated species such as Ru(O), Rh(I), Ir(I), Pt(O) has been used to prepare nitrosyl and nitro complexes of these transition metals. In the case of Ru(O), a nitro-nitrosyl complex is also found. The use of nitronium ion, NO₂⁺ to introduce the nitrosyl group into coordination complexes is novel. The reaction of NO₂⁺ with coordinatively unsaturated species appears to be analogous with that of NO⁺. The preparation and some chemical and physical properties of the complexes are discussed.     

Addition reactions to cyclopolyolefin transition metal π complexes

The non-coordinated double bonds of (η⁴-1,2,3,4-cycloheptatriene)Fe(CO)₃ and (η⁴-1,2,5,6-cyclooctatetraene)Co(η⁵-C₅H₅) add methylene generated from the Simmons-Smith reaction to yield (η⁴-2,3,4,5-bicyclo[5.1.0]octa-2,4-diene)Fe(CO)₃ and (η⁴-2,3,7,8-tricyclo[7.1.0.0^4,6]deca-2,7-diene)Co(η⁵-C₅H₅). An analogous reaction of (η⁴-1,2,3,4-cyclooctatetraene)Fe(CO)₃ yields (η⁴-6,7,8,9-tricyclo[8.1.0.0^3,5]undeca-6,8-diene)Fe(CO)₃, a product of the addition of three equivalents of methylene in which a cyclopropyl ring opening is proposed to occur. Dichlorocatbene, generated from C₆H₅HgCCl₂Br, would not react in a similar fashion. A BH₃ · THF solution would react with these starting materials but unusual products were produced.     

Investigation of exchange reactions between alkaline earth metal oxides and some transition metal halides

DTA and the simultaneous recording of electrical conductivity were applied for the investigation of exchange reactions between alkaline earth metal oxides and some lead, copper and nickel halides. Although the possibility of the gaseous phase is not excluded for the majority of the reactions investigated, it is either the appearance of a liquid phase or the polymorphous transformation of CaO that has the decisive effect on the interaction mechanism.     

Mechanistic studies on ethylene silylation with chlorosilanes catalysed by ruthenium complexes

Silylation of ethylene by chlorosilanes is catalysed by ruthenium complexes. Mechanistic investigations reveal the presence of a complicated network of reactions leading to new sigma-silane, ethylene and silyl complexes.     

Ring-opening reactions of methylenecyclopropanes promoted by metal halides

The methylenecyclopropanes (MCPs) react with various metal chlorides or bromides to give the corresponding homoallylic chlorides or bromides in good yields. [reaction: see text]     

Effect of the nature of organic solvents on their interaction with metal halides. Further investigations on antimony

A study is given on the extraction of trivalent antimony halides by nonpolar solvents, nitrobenzene, Amberlite LA-2 from sulphuric and orthophosphoric acids. These two acids, because of their dehydration action, were found to have an enhancing effect on the extraction of Sb(III) halides. Extraction by nonpolar solvents and nitrobenzene was also studied as a function of the antimony concentration.