Reductive coupling of carbonyl compounds to pinacols by using low-valent cerium

Aldehydes and ketones, on treatment with a low-valent cerium reagent, undergo reductive dimerization to produce the corresponding pinacols in high yield.     

Reductive dimerization and reduction of imines using lanthanum metal

The treatment of N‐benzylideneaniline ( 1a ) with a half‐equivalent of lanthanum metal and a catalytic amount of iodine gave the reductive dimerization product of 1a , a vic‐diamine, in good yield. Various vic‐diamines were synthesized from aldimines in this manner in moderate to good yields. Our findings suggest that electrons of a zero‐valent lanthanum metal were efficiently utilized in this reductive dimerization. In the reaction of ketimines, however, a similar reductive dimerization did not take place, and the corresponding amines were formed as the sole products. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:131–135, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10007     

Reductive coupling of allylic acetates with carbonyl compounds by using Pd(0)-SmI2 system

Reductive coupling of allylic acetates with carbonyl compounds proceeded by SmI₂ in the presence of catalytic Pd(0) to yield homoallylic alcohols.     

Reductive coupling of metal triangles in sandwich complexes

The one-electron reduction of [Pd3(C7H7)2(CH3CN)3][BF4]2 in acetonitrile resulted in the formation of the dimer dication [Pd6(C7H7)4(CH3CN)4][BF4]2, whose structure containing a novel bitriangle hexapalladium skeleton was determined by X-ray crystallographic analysis. The dimer is stable in CD3CN at ambient temperature for several days but is highly air-sensitive. Similarly, the cycloheptatriene tripalladium complex [Pd3(C7H7R)2(CH3CN)3][BF4]2 (R = H, t-Bu) dimerized upon one-electron reduction. Both monomer and dimer of cycloheptatriene complexes were structurally determined by X-ray crystallographic analyses.     

Perspectives in the syntheses of novel organometallic compounds using metal carbonyl anions

The molecular structure of [(C₆H₅)₃P]₂Pt(C₅H₈) has been determined from three-dimensional X-ray diffraction data (R = 0.045 for 6033 reflections). The crystal belongs to the triclinic system, space group P$\text{1}$, with two formula units in a cell of dimensions: a = 18.557(2), b = 10.216(2), c = 9.647(2) Å, α = 98.29 (3), β = 73.44(2), and γ = 88.34(2)°.One of the olefinic bonds of dimethylallene, which has no adjacent methyl groups, is coordinated to the platinum atom: PtC(1) = 2.108(8), PtC(2) = 2.049(7) Å. The coordinated dimethylallene molecule is no longer linear, the C(1)C(2)C(3) angle being 140.8(8)°, which is significantly smaller than that found in [(C₆H₅)₃P]₂Pd(C₃H₄). The C(1)C(2) distance is 1.430(11) Å, whereas the uncoordinated bond distance is normal [C(2)C(3) = 1.316(11)Å].     

Gallium-induced Barbier coupling of carbonyl compounds with allyl iodide

Gallium metal readily prompted the allylation of aldehydes and ketones with allyl iodide. α, β-Unsaturated carbonyl compounds underwent only 1,2-addition.     

Preparation of some metal carbonyl cluster formyl compounds

The reduction of H₂Os₃(CO)₁₀S or HOs₃(CO)₁₀(O₂CMe) with KBH(OPr-i)₃ at low temperatures yields unstable formyl complexes which have been identified by ¹H NMR spectroscopy; at higher temperatures conversion into stable hydridoanions is observed.     

Base-free dehydrogenative coupling of enolizable carbonyl compounds with silanes

A dehydrogenative coupling between enolizable carbonyl compounds and equimolar amounts of triorganosilanes catalyzed by a tethered ruthenium complex with a Ru-S bond is reported. The complex is assumed to fulfill a dual role by activating the Si-H bond to release a silicon electrophile and by abstracting an α-proton from the intermediate silylcarboxonium ion, only liberating dihydrogen as the sole byproduct. Reaction rates are exceedingly high at room temperature with very low loadings of the ruthenium catalyst.     

Novel and efficient Ni-mediated pinacol coupling of carbonyl compounds

It was firstly found that the Rieke Ni generated in situ was able to promote the pinacol coupling of various carbonyls efficiently. Based on this information, another catalytically effective, cheaper and more convenient NiCl₂(Cat.)/Mg/TMSCl system was designed and developed further successfully. The interesting single-electron transfer (SET) mechanisms for the coupling reactions were proposed. Additionally, the dl/meso diastereoselectivity and some additive effects were also explained in terms of the proposed mechanisms.     

Reductive amination of carbonyl compounds in the presence of cobalt and rhodium complexes

Summary The reductive amination of carbonyl compounds in the presence of some cobalt and rhodium complexes has been studied, The selectivity and efficiency of the process is discussed using the interaction of cyclohexanone with ammonia as an example. The possible mechanism for the reaction is considered.Abbreviation DMG dimethylglyoxime - IDSA indigodisulphoacid - Fl flourescein - DBG dibenzylglyoxime     

FTIR-screening of carbonyl compounds in metal working fluid aerosols

Due to the complex composition of metal working fluids (MWF) the determination of all individual compounds is sometimes difficult and very expensive. Today the widely used method for the quantification of airborne MWFs consists of a non specific IR analysis of their C-H valence bands. With a new design of sample cell this inexpensive technique was extended to a more detailed screening of the MWF composition, especially the detection of carbonyl compounds in MWFs and their aerosols and vapors. The screening method was evaluated for the determination of concentrations of the aldehyde nonanal and the ketone diacetone alcohol in air in laboratory experiments. In preliminary workplace studies the applicability of this method to the (semi-)quantitative determination of carbonyl compounds in airborne MWFs is shown. The screening method was found to be very useful, specially to detect alterations in the composition of the MWF due to industrial use. Received: 16 January 1997 / Revised: 9 April 1998 / Accepted: 14 April 1998     

Reductive coupling of carbon monoxide in a rhenium carbonyl complex with pendant Lewis acids

Phosphinoborane ligands impart unique reactivity to a rhenium carbonyl cation relative to simple phosphine complexes. Addition of either triethylborohydride or a platinum hydride (that can be formed from H2) forms a rhenium boroxycarbene. This carbene, which crystallizes as a dimer, disproportionates over a period of days to afford the starting cation and a structurally unprecedented boroxy(boroxymethyl)carbene, in which a new C-C bond has been formed between two reduced CO ligands. This product of C-C bond formation can be independently synthesized by addition of 2 equiv of hydride to the rhenium carbonyl cation.     

Reductive amination of carbonyl compounds using NaBH4 in a Brønsted acidic ionic liquid

Reductive amination of carbonyl compounds using sodium borohydride is conducted in the Brønsted acidic ionic liquid, 1-methyl imidazolium tetrafluoroborate ([HMIm][BF₄]). The ionic liquid plays the dual role of solvent as well as catalyst for efficient conversion of aldehydes and ketones to amines in excellent yields without the formation of side products.     

Reductive coupling of (azulen-1-yl)carbonyl compounds by low-valent titanium; pinacol/pinacolone rearrangement versus pinacol and alkene generation

The azulen-1-yl group strongly influences the course of the TiCl₄-Zn promoted McMurry coupling of 1-acetylazulene which afforded, along with the normal coupling products, pinacol 2dl and alkene 3, the pinacolone 4. The latter was likely formed via rearrangement of the pinacolate intermediate. An improved, microwave-assisted protocol was developed for this reaction that provided high yields of products in a short reaction time. The steric reaction route is consistent with the proposed mechanism.     

Selective isomerization of 1-alkenes by binary metal carbonyl compounds

An efficient and selective isomerization of 1-alkenes to their corresponding 2-alkenes is achieved by using binary metal carbonyls such as Ru₃(CO)₁₂ as catalysts. Possible mechanisms are discussed. Substituents on the 1-alkene have a significant effect on the isomerization.     

Synthesis and structures of substituted tetramethylcyclopentadienyl dinuclear metal carbonyl compounds

Cyclopentadienes (C₅Me₄R) [R = Allyl (1), n-Butyl (2), Benzyl (3), and PhMe-2 (4)] reacted with Fe(CO)₅ in refluxing xylene to give new substituted tetramethylcyclopentadienyl dinuclear iron carbonyl complexes [(η ⁵-C₅Me₄R)Fe(CO)(μ-CO)]₂ [R = Allyl (5), n-Butyl (6), Benzyl (7), and PhMe-2 (8)], respectively. The four new complexes 5–8 were characterized by elemental analysis, IR, and ¹H NMR spectra. The crystal structures of complexes 5–7 were determined using single crystal X-ray diffraction. The crystal structure of complex 5 showed that allyl underwent isomerization to give the corresponding methyl-vinyl. A possible mechanism is discussed. The X-ray crystal structures of complexes 5, 6, and 7 confirm the structure with bridging and terminal CO groups. They show that the steric effects of substituents influence the Fe–Fe bond distances of the complexes.     

Palladium-catalyzed and samarium-promoted coupling of stereochemically-biased allylic acetates with carbonyl compounds

Stereochemically-biased bicyclic allylic acetates endo- and exo-1 were shown as being allyl donors for Pd-catalyzed carbonyl allylation using stoichiometric quantities of samarium diodide. Cyclopentenyl acetate and bicyclic derivatives 1 react with cyclic ketones in the presence of SmI₂ without requirement of palladium catalysis. Use of enantiomerically enriched substrate suggests that the reaction goes through a π-allyl samarium complex. However, this reactivity appears to be restricted to strained cyclopentenyl acetates since other linear and cyclic allylic acetates do not give the carbonyl allylation product.