Stereocontrolled acylation of (η4-cycloheptatriene)iron tricarbonyl

The anion derived by deprotonating (cycloheptatriene)Fe(CO)₃ reacts with acid chlorides to give exo C-7 substitution. The acyl group is readily isomerized to C-5 on treatment with base. The C-7 acylated products can be deprotonated; the resulting anions react at oxygen with acyl chlorides and Me₃SiCl, and at carbon with MeI.     

Iridium pentahydride complex catalyzed formation of CC bond by CH bond activation followed by olefin insertion

The formation of carbon-carbon bond was found to occur by first carbon-hydrogen bond activation followed by olefin insertion under the catalysis of an iridium pentahydride complex.     

Allyldialkyl complexes of ruthenium(IV): Preparation and reductive CC bond formation followed by CH bond activation

New η³-allyldimethyl complexes Ru(η⁵-C₅R₅)(η³-C₃H₅)(CH₃)₂, where R = H or CH₃, are prepared from Ru(η⁵-C₅R₅)(η³-C₃H₅)Br₂ by alkylation with trimethyl-aluminium. The Ru^IV dimethyl complex is thermally converted to the Ru^II 1-methylallyl compound, Ru(η⁵-C₅R₅)(η³-CH₂CHCHCH₃)L, where L = CO or t-C₄H₉NC, with evolution of methane. Kinetic and deuteration studies on the reductive process are also discussed.     

The use of iron carbonyls in the C—C bond formation reactions

Russian Chemical Bulletin - The review systematizes material by key types of reactions promoted by iron carbonyls. The reaction types are subdivided into several principal directions, focusing...     

Stereoselective synthesis of a new enantiopure tricyclic β-lactam derivative via a tricarbonyl(η6-arene)chromium(0) complex

The tricyclic β-lactam 5 has been synthesized both in racemic and enantiopure form starting from the enantiomerically pure tricarbonylchromium(0) complex 1. The synthetic sequence involves the stereoselective [2+2] cycloaddition of 1 with acetoxyacetylketene, followed by intramolecular aromatic nucleophilic substitution of the fluorine atom. Mechanistic pathways leading to 5 are discussed.     

Rhodium-catalyzed CC bond formation by ring-opening of alkylidenecyclopropanes and insertion of 3-butenoic acid

Diphenylmethylenecyclopropane reacts with 3-butenoic acid in the presence of RhCl(PPh₃)₃ to give products resulting from insertion of one or two molecules of butenoic acid. Insertion of the first molecule of butenoic acid is not regioselective, whereas insertion of the second is highly regioselective.     

Synthesis of benzoindoloquinolizines via a Cu(I)-mediated C–N bond formation

An effective synthesis of the multi ring-fused benzoindoloquinolizines has been accomplished by Cu(I)-mediated and MW-assisted C–N_amide bond formation of benzo[a]quinolizin-4-ones. The deamination of tetrahydro-2H-pyrido[2,1-a]isoquinolines was also studied and was found to give benzoquinolizines. The benzo[a]quinolizin-4-ones were prepared based on the annulations of C-1 substituted 3,4-dihydroisoquinolines and azlactones.     

Dissociation potential for breaking a CH bond in methane

The potential energy along the dissociation coordinate for CH₄ → CH₃ + H is calculated by the multi-reference configuration interaction method, including all single and double excitations, with a triple-split-plus-diffuse-and-extended-polarization basis set. The three-parameter Lippincott and Varshni potential curves provide better approximations to the dissociation potential than does the Morse model.     

ESR study of reversible complex formation between bis(η5-cyclopentadienyl)vanadium and fullerene C60 in solution

Using the ESR method, equilibrium complex formation of fullerene C₆₀ with bis-(⁵-cyclopentadienyl)vanadium in solutions in aromatic solvents was found to occur. Based on an analysis of isotropic (g _i = 2.0008;A _i ,(V⁵¹)=–45.7 mT) and anisotropic (g _i =1.9808;g ₂ = 2.0135; <g ₃> = 2.0060;A ₁(⁵¹V)=–7.85 mT;A ₂(⁵¹V) = –6.50 mT; <A ₃(⁵¹V)> = 0.61 mT) ESR spectra parameters, it was established that the complex formed, Cp₂V(²-C₆₀), corresponds to vanadocene d¹-complexes with ²-bonded ligands.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1945–1947, November, 1994.     

The CF bond as a tool in the conformational control of amides

The conformation of 2-fluoro-N-(2-fluoroethyl)-propionamide 4 in the solid state indicates the influence of both a β-fluorine-amide gauche effect and an α-fluoroamide effect. The structure reveals the influence of two recently observed stereoelectronic effects associated with the CF bond, which has resulted in the successful prediction of the solid state conformation of amide 4. A gauche relationship (−69.9°) was observed for atoms N(1)C(4)C(5)F and a syn planar (2.0°) relationship was observed for N(1)C(3)C(2)F. The paper demonstrates the predictive power of using the CF bond as a tool in influencing the conformation of amides and peptides.     

Use of a bis-lithium amide base in asymmetric metallation of tricarbonyl(η6-1,3-dihydroisobenzothiophene)chromium(0)

Enantiomerically enriched tricarbonyl(η⁶-arene)chromium complexes derived from tricarbonyl(η⁶-1,3-dihydroisobenzothiophene)chromium(0) can be obtained in up to 95% ee by means of an enantioselective metallation reaction using the bis-lithium amide base 8.     

An exceptionally stable cis-(hydride)(η2-dihydrogen) complex of iron

The cis-(H)(H₂ complex [(PP₃)Fe(H)(H₂)]BPh₄ (PP₃  P(CH₂CH₂PPh₂)₃) has been made by reaction of the chloride [(PP₃)FECl]BPh₄ in THF with NaBH₄ under 1 atm of H₂. In the solid state and in solution at low temperature the complex is octahedral, and the hydride and dihydrogen ligands occupy mutually cis positions. At ambient temperature in solution the complex is trigonal-bipyramidal, and an “H₃” unit occupies an axial position trans to the bridgehead phosphorus atom of PP₃; this results in exceptional thermal and chemical stability of the complex.     

Novel coupling between tricarbonyl(7-azabenzonorbornadiene)iron complexes and cyclohexene to form stereospecifically a (C-5 substituted η4-cyclohexadiene)Fe(CO)3 moiety

Novel coupling between tricarbonyl(7-azabenzonorbornadiene)iron complexes 1 and cyclohexene occurs thermally and photochemically. Complexes 2 were formed stereospecifically with a yield of 21–34% via C-C bond formation from the exo-face of 7-ABND accompanied by the generation of (⁴η-cyclohexadiene)Fe(CO)₃ moieties with Fe(CO)₃ syn to the new C-C bond. At the same time, C-5 of this moiety was functionalized with a bulky 7-ABND heterocycle.     

Phenyl directing groups in the demethoxylation route to tricarbonyl(η5-cyclohexadienyl)iron(1 +) complexes

Acid catalysed demethoxylation of tricarbonyl(η⁴-2-methoxy-6-phenyl-1,3- cyclohexadiene)iron(0) leads to the exclusive formation of a 3-phenyl salt, rather than the product of minimum rearrangement, a 1-phenyl salt. With an additional 2-methyl substituent present, the competing directing influence is overcome by the phenyl group. The importance of the phenyl substituent in promoting regioselectivity is demonstrated by the demethoxylation of a 2,5-dimethyl-3-methoxy substituted complex, which led to a mixture of products.     

Temperature-dependent in situ ligand cyclization via C═C coupling and formation of a spin-crossover iron(II) coordination polymer

The reaction of N(1),N(2)-bis(pyridin-4-ylmethylene)ethane-1,2-diamine (L) with Fe(NCS)(2) under various temperatures gave rise to three iron(II) coordination polymers, namely, one-dimensional [Fe(L')(NCS)(2)] (1), two-dimensional [Fe(L)(2)(NCS)(2)]·H(2)O (2), and one-dimensional [Fe(L)(2)(NCS)(2)]·2CH(2)Cl(2)·4MeOH (3). The formation of 1 involved an in situ C═C coupling reaction, L to L' [L' = 5,6-di(pyridin-4-yl)-1,2,3,4-tetrahydropyrazine], which was catalyzed by cyanide ions decomposed from thiocyanates; the manganese(II) (1a) and zinc(II) (1b) analogues of 1 were also synthesized for comparison. Magnetic studies showed that complex 1 underwent a pressure-dependent one-step incomplete spin transition whereas complexes 2 and 3 were paramagnetic in the whole temperature range.     

Theoretical exploration of structure-reactivity relationships in organometallic chemistry: butadiene insertion into the organyltransition-metal bond and conversion of the allyltransition-metal fragment in the [Ni(η-Cp)(η-phenyl)(η-butadiene)] complex

We have theoretically examined the reaction course of the butadiene insertion into the arylNi^II bond in the [Ni^II(η⁵-Cp)(η¹-phenyl)(η²-butadiene)] complex (1), by employing a gradient-corrected DFT method. Critical elementary processes have been scrutinized, viz. monomer insertion, rotational allylic isomerization and allylic η¹-σ→η³-π rearrangement. The first mechanism suggested by Lehmkuhl et al. was refined and supplemented with important details. The critical factors that determine the generation of anti-η³- and syn-η³-allyl isomers of the [Ni^II(η⁵-Cp)(1-benzyl-allyl)] product have been elucidated. This let us to rationalize the experimentally observed, almost exclusive formation of the anti-η³-allyl isomer. Butadiene preferably inserts in η²-mode into the η¹-phenylNi^II bond, initially giving rise to the η¹(C³)-allyl product species, 3σ. The direct formation of the η³-allyl product species, 3π, along the alternative path for η⁴-butadiene insertion, however, is found to be almost entirely disabled kinetically. The thermodynamically favorable η²-trans form of 1 is also shown to be more reactive in accomplishing CC bond formation. Species 3σ is indicated to be a metastable intermediate, occurring in an appreciable stationary concentration. Its respective anti and syn isomeric forms are likely to be in equilibrium, due to the facile rotational isomerization. The subsequent allylic rearrangement into the thermodynamically strongly favorable η³-allylNi^II coordination mode is shown to be the crucial elementary step that discriminates which of the isomeric η³-allyl forms is preferably generated. The higher reactivity of the anti isomer in this process decisively determines the almost exclusive formation of the anti-η³-allyl product species under kinetic control. The requirement of elevated temperatures for the anti-η³-allyl→syn-η³-allyl isomerization to occur, as revealed from experiment, is attributed to the pronounced thermodynamic stability of the η³-allylNi^II coordination.     

Homogeneous decarbonylation of ethyl formate at rhodium. Evidence for the formation of a cis-hydride(ethoxycarbonyl) intermediate through CH bond cleavage

The 16-electron fragment [(NP₃)Rh]⁺ inserts into the sp² CH bond of ethyl formate to give the octahedral complex cation [(NP₃)Rh(H)(CO₂Et)]⁺ which can be isolated in the solid state as SO₃CF₋3 salt. Thermal decomposition of the cis-hy-dride(ethoxycarbonyl) complex in benzene gives EtOH and the carbonyl [(NP₃)RhCO](SO₃CF₃) (NP₃ = N(CH₂CH₂PPh₂)₃).     

Crystal structure of a μ-oxo-bridged dimeric iron(III) complex

A dimeric [{Fe(5-ClL1)}₂(μ-O)], [H₂-5-ClL1 = N,N′-bis(5-chloro-2-hydroxybenzylidene)-2-methylpropane-1,2-diamine] tetradentate Schiff-base complex, 1, has been synthesized and its crystal structure has been determined by single crystal X-ray diffraction analysis. Structural analysis of complex 1 shows that the complex is a centrosymmetric dimer. Each of the Fe(III) ions has a five-coordinate geometry and one oxygen atom bridges two Fe(III) ions to form a μ-oxo structure. The geometry around iron atom can be described as a square based pyramid with the FeN₂O₂ coordination plane and oxo ligand.