Kinetische und mechanistische untersuchungen von übergangsmetallkomplex-reaktionen : IX. Substitution von CO durch PPh3 in aminocarbinkomplexen: Präparative und kinetische untersuchungen

Pentacarbonyl(diethylaminocarbyne)chromium tetrafluoroborate, [(CO)₅₋ CrCNEt₂]BF₄ (I), reacts with PPh₃ with substitution of CO and formation of trans-tetracarbonyl(diethylaminocarbyne)triphenylphosphanechromium tetra-fluoroborate, trans-[PPh₃(CO)₄CrCNEt₂]BF₄ (III). Substitution of CO by PPh₃ in neutral trans-tetracarbonyl(halo)(diethylaminocarbyne)chromium complexes, trans-X(CO)₄CrCNEt₂ (IVa: X = Br, IVb: X = I), leads in a reversible reaction to the corresponding tricarbonyl complexes, mer-X(PPh₃)(CO)₃₋ CrNEt₂ (V), PPh₃ occupying the cis-position to the carbyne ligand. With PPh₃ in large excess both reactions follow a first-order rate law. This as well as the activation parameters (ΔH≠ = 104–113 kJ mol⁻¹, ΔS≠ = 64–71 J mol⁻¹ K⁻¹) indicate a dissociative mechanism.     

Chemistry of metal hydrides : XXI. Insertion of acetylenes into palladium hydrides

trans-Pd(NO₃)H(PCy₃)₂ (I) when treated with Et₄NCl forms the hydride trans-PdClH(PCy₃)₂ which in turn reacts with AgPF₆ in acetonitrile to give trans-[PdH(CH₃CN)(PCy₃)₂]PF₆ (III). Both I and III react smoothly with acetylenes containing one electron-withdrawing group to give alkenyl products. The geometry of the resulting alkenyl ligand implies that cis addition has occurred and that the hydridic hydrogen adds to the acetylenic carbon containing the electron-withdrawing group.Acetylenes containing two electron-withdrawing groups give mixtures from which both alkenyl and zerovalent acetylene compounds can sometimes be isolated. In the presence of proton sponge, monosubstituted acetylenes still give alkenyl products while those substituted with two electron-withdrawing groups give the zerovalent products in good yield. The relevance of these results to an understanding of the nature of the migratory insertion reaction is discussed.     

Oxythallation of norbornene derivatives with thallium(III) acetate in methanol

Treatment of norbornene, norbornadiene, benzonorbornadiene, and chloro- and methoxy-benzonorbornadiene with thallium(III) acetate in methanol affords only the corresponding cis-exo-acetoxythallation adducts in a sharp contrast to oxymercuration of such strained olefins where methoxymercuration prevails. In the cases of substituted benzonorbornadienes the products are obtained as the regioisomeric mixtures, the isomer ratio being determined by ¹³C NMR. In the cases of 5-norbornene-2,3-dicarboxylic anhydride, 5-norbornene-2-methyl-2,3-dicarboxylic anhydride, and 5-norbornen-2-endo-carboxylic acid, lactonization occurs to give a trans-oxythallation adduct having a lactone ring, no introduction of either methoxy or acetoxy groups being observed. ¹H and/or ¹³C NMR data for several new oxythallation adducts are provided. The alkaline sodium borohydride reduction of adducts in methanol affords mainly the parent olefin together with 10–16% yields of the corresponding exo-alcohol.     

Durene-rhodium(I) complexes. Crystal structures of the complexes [Rh(durene)(diolefin)]ClO4 (diolefin  tetrafluorobenzobarrelene or trimethyltetrafluorobenzobarrelene)

The crystal structures of [Rh(durene)(diolefin)ClO₄ (diolefin  tetrafluorobenzobarrelene (TFB) and trimethyltetrafluorobenzobarrelene (Me₃TFB)) have been solved by standard X-ray single crystal methods. The compounds crystallize in the space groups R₃c for the unmethylated TFB compound and P2₁/n for the methylated one. The cell dimensions are 25.7586(5), 17.0059(4) Å and 12.6686(6), 11.5565(3), 16.7269(8) Å, β  104.023(5)°, respectively. The refinement was taken to R values of 0.04 and 0.06, respectively. The arene in the TFB derivative has a distorted inverted boat conformation which becomes a skew one in the Me₃TFB compound. These puckering seems to be related to the tendency of rhodium(I) to achieve square-planar coordination.     

Complexes dinucleaires pontes des metaux d8: VII. Reactions d'addition oxydante d'halogenures d'alkyle et d'acycle aux complexes μ-halogenes du rhodium(i) [RhX(CO)(PR3)]2. Structure cristalline de [RhCl(CO)(PMe2Ph)(Me)(Br)]2

The halogen bridged binuclear complexes of rhodium(I) [RhCl(CO)(PR₃)]₂ undergo oxidative addition with methyl halides to yield the complexes [RhCl(CO)(PR₃)(Me)(X)]₂ (X = Cl, Br). The crystal and molecular structures of [RhCl(CO)(PMe₂Ph)(Me)(Br)]₂ have been determined from a single crystal by use of X-ray crystallographic methods. The space group is Pca2₁ or Pacm with a 19.501(5), b 10.381(4), c 13.641(5) e? Z = 4. Parameters of 30 nonhydrogen atoms in the space group Pca2₁ were refined by the full-matrix least squares technique to a conventional R factor of 0.073. In a binuclear unit, each rhodium atom is in an octahedral environment being bonded to a carbonyl group, a methyl group and a tertiary phosphine ligand and three halogen atoms for which, due to a disorder phenomenon, the diffusion factors have been determined as the average between those of chlorine and bromine atoms. In solution the cis-migration of the methyl groups occurs, leading to the acetyl complexes. In the case of CH₃I, it is shown that an equilibrium is present in solution: [RhCl(CO)(PR₃(Me)(I)]₂ ? [RhCl(COMe)(PR₃)(I)(solvant)]₂] Carbonylation reactions shift this equilibrium to give the complexes [RhCl(CO)(COMe)(PR₃(I)]₂. Such complexes are readily prepared by direct oxidative addition of acyl halides to the compounds [RhCl(CO)(PR₃)]₂.     

The behaviour of an electrochemical detector used in liquid chromatography and continuous flow voltammetry: Part III. Potential dependent current

The potential dependence of the steady-state current at a channel electrode has been calculated approximately. Six regions of behavior can be described from a consideration of the characteristic times of diffusion, fluid flow and electrochemical reaction. Wave shapes and half-wave potential shifts are as expected for amperometric cells under all values of the heterogeneous reaction rate constant, and for reversible electrochemical reactions in a coulometric cell. The wave adopts a peculiar shape for irreversible reactions at a coulometric electrode. This is caused by the inapplicability of the concept of mass transfer control in these systems.     

Cleavage by halogens of carbon—cobalt bonds in organometallic complexes of cobalt(III) : III. Kinetics and mechanism of the reactions of organobis(dimethylglyoximato)cobalt(III) complexes with iodine in chloroform

The kinetics of the reaction between organocobaloximes, RCo(DH)₂H₂O, and iodine have been investigated. They reveal the participation of an RCo(DH)₂H₂O · I₂ intermediate which undergoes intramolecular transalkylation and acts as an electrophile towards a second organocobaloxime molecule. The trend in reactivity as the R group is varied is discussed.     

Metall-π-komplexe von benzolderivaten : III. Bis(diphenylphosphino-h6-benzol)-chrom(0)

Rhodium complexes containing poly(pyrazolyl)borate ligands are described, and the fluxional nature of some of them considered.     

Titrimetric determination of vanadium(IV) with DCTA

Vanadium(IV) has been determined by DCTA titration conductometrically, spectrophotometrically and visually (with Alizarin Red S, Gallein and Catechol Violet as indicators at pH 4.0, 4.2 and 4.5-4.6 respectively). The interference of nickel, copper, lead, aluminium and thorium can be removed, and the method utilized for the analysis of binary mixtures of vanadium(IV) with nickel, copper or thorium.     

Prototropic rearrangements of unsaturated hydrocarbons promoted by iron carbonyls

Results from the thermal and photochemical reactions of $\text{cis}$-1,3-pentadiene and 4-methyl-1,3-pentadiene with iron pentacarbonyl are described together with those obtained from the thermolysis and photolysis of their η²-iron tetracarbonyl and η⁴-iron tricarbonyl complexes. Consideration of these results, and some recent related work of others, allows a new reaction path to be formulated for alkene and diene isomerizations promoted by iron carbonyls.     

Olefin complexes of rhodium(I) containing the ligands but-3-enyldiphenylphosphine and diphenylpent-4-enylphosphine

But-3-enyldiphenylphosphine (mbp) and diphenylpent-4-enylphosphine (mpp) react with Rh₂Cl₂(C₂H₄)₄ (molar ratio $\text{2}\text{1}$ to form the four coordinate dimeric complexes Rh₂Cl₂(mbp)₂ and Rh₂Cl₂(mpp)₂ respectively, while but-3-enyldiphenylphosphine reacts with Rh₂Cl₂(C₂H₄)₄ (molar ratio $\text{4}\text{1}$) to form RhCl(mbp)₂, a five coordinate complex in the solid state. The dimers further react with sodium tetraphenylborate to give the π-bonded tetraphenylborate complexes Rh[mbp][C₆H₅)₄B] and Rh[i-mpp][(C₆H₅)₄B] where i-mpp = (C₆H₅)₂P(CH₂CH₂CHCHCH₃). RhCl(CO)(mbp)₂ reacts with sodium tetraphenylborate to form the five coordinate cationic complex [Rh(CO)(mbp)₂][(C₆H₅)₄B]. Both RhCl(CO)(mbp)₂ and RhCl(mbp)₂ react with hydrogen in methanol saturating the olefin to form RhCl[CO][(C₆H₅)₂P(C₄H₉)]₂ and Rh₂Cl₂[(C₆H₅)₂P(C₄H₉)]₂ respectively.     

A kinetic study of the ortho-mercuration of 2-methylazobenzene

The kinetics of the mercuration of 2-methylazobenzene in methanol were studied. The thermodynamic data found were ?E_act = 22.7 kcal mol^?1, ?H¹ = 22.0 kcal mol^?1, and ?S¹ = ?12.3 eu. In comparison with a value of ?S¹ ? ?20 eu for the mercuration of benzene, this lowered entropy is taken as evidence for complex formation between mercuric acetate and 2-methylazobenzene before and during the rate determining step of electrophilic substitution.     

Gehinderte ligandenbewegungen in übergangsmetallkomplexen : V. 1H-NMR-untersuchung der bewegungen des olefinliganden in cyclopentadienyl-mangan-dicarbonyl-tetramethoxyäthylen

The methoxy signals in the ¹H NMR spectrum of cyclopentadienylmanganese dicarbonyl tetramethoxyethylene, C₅H₅Mn(CO)₂[C₂(OCH₃)₄], show a definite temperature-dependence. In CS₂ solution the variations of the signals are observed within a single temperature range, while in toluene-d₈ two regions of change are found to exist. These data are explained on the basis of two mutually independent ligand movements: a hindered rotation of the olefin ligand around the metalligand bond (ΔG³₁₉₄ = 9.8 ± 0.6 kcal/mol), and a hindered movement of the four methoxy groups (ΔG³₂₆₃ = 13.8 ± 0.3 kcal/mol, both in toluene-d₈. Chiral conformations of the ligand are assumed to be formed when the movement of the methoxy substituents ceases.     

Copper(II)-cetyltrimethylammonium chloride-chromal blue G ternary complex and its application to the spectrophotometric determination of copper(II)

A sensitive spectrophotometric method for the determination of copper(II) based on a ternary complex with chromal blue G, a triphenylmethane reagent in the presence of cetyltrimethylammonium chloride, is described. The sensitivity of color reaction between copper and chromal blue G has been greatly increased by the sensitizing action of cetyltrimethylammonium chloride, a cationic surfactant. The color development of the ternary complex can be utilized in the highly sensitive spectrophotometric determination of copper. The molar absorptivity of the binary complex between copper and chromal blue G ε_630nm = 9.56 × 10³liters · mol⁻¹ · cm⁻¹ is enchanced on ternary complex formation to ε_{542 nm} = 4.78 × 10⁴liters · mol⁻¹ · cm⁻¹. The ternary complex gave a maximal absorbance at 542 nm in the pH range 9.8–11. Beer's law is obeyed up to at least 1.2 ppm of copper. The maximal absorbance of the ternary complex was found to develop within 5 min and then it remains constant for several hours. The formation constant of the ternary complex is calculated to be 8.6 × 10¹⁰ under these conditions.     

The formation of lithium diarylargentates from arylsilver compounds and the corresponding aryllithium compounds

Diarylsilverlithium compounds of the type Ar₂AgLi are formed by treating arylsilver compounds with the corresponding aryllithium compounds. Cryoscopy in benzene shows that the Ar₂AgLi compounds are associated into dimers. NMR spectroscopic data indicate that only one type of aryl group is present in these dimers, and that each aryl group is bridging between one silver and one lithium atom.     

Synthesis and properties of some 2-(dimethylamino)methyl-substituted arylcopper compounds

The synthesis and isolation of 2-[(dimethylamino)methyl]phenylcopper and its 5-methyl, 5-methoxy, 5-chloro and 3-chloro derivatives are described. These hydrocarbon-soluble arylcopper compounds are appreciably more thermally stable than phenylcopper (e.g. 2-[(dimethylamino)methyl]phenylcopper decomposes only at 175–185°). They also show improved hydrolytic and oxidative stability.Lithiation of 1-methoxy-4-[(dimethylamino)methyl]naphthalene with butyllithium occurs at the 5-position. Metathesis of 1-methoxy-4-[(dimethylamino)methyl]-5-lithionaphthalene with cuprous bromide affords the corresponding organocopper compound.     

Cycloaddition of diphenylnitrilimine to coumarins. The synthesis of 3a,9b-dihydro-4-oxo-1H-benzopyrano [4 ,3-c]pyrazole derivatives

The cycloaddition of diphenylnitrilimine to a series of coumarins occurs with the same regioselectivity in all cases, regardless the nature of the substituent present, to yield the corresponding 3a,9b-dihydro-4-oxo-lH-benzopyrano [4,3-c]pyrazoles $\text{4}$a–f. Dehydrogenation of $\text{4a}$ yields 4-oxo-1H-benzopyrano [4,3-c]-pyrazole $\text{6}$. In ethanolic sodium ethoxide solution, the reaction between coumarin and diphenylnitrilimine precursor, namely N-phenylbenzohydrazidoyl chloride $\text{1}$, affords no cycloadducts, but yields o-(β-ethoxycarbonylvinyl)phenyl N-phenylbenzohydrazidate $\text{10}$. The regiochemistry of the cycloadducts $\text{4}$a–f and the reaction sequence leading to $\text{10}$ are outlined. The structures of the products have been established by spectroscopic methods and independent syntheses wherever possible.     

Elektronenstoss-induzierter zerfall von benzol-tricarbonyl-chrom- und -wolfram-derivaten; ein vergleich

The Electron impact mass spectra of (CO)₃ MC₆H₅—X complexes (M = Cr, W; X = OCH₃, OC₄H₉, CO₂CH₃, CO₂C₄H₉) were recorded. From metastable transitions and by high-resolution measurements complete fragmentation diagrams were obtained; in some cases comparative structure determinations of fragment ions were carried out by collisional activation. The fragmentation of the tungsten complexes considerably differs from that of the chromium compounds. The differences may be attributed to the stronger-electrophilic character as well as to the more pronounced tendency of tungsten to attain higher oxidation states.     

Beiträge zur chemie des bors LXXX. Pentacarbonylchromkomplexe von diorganylmethylthioboranene und von 2-diäthylboryl-5-methylthiophen

Substitution of THF by diorganylmethylthiboranes in (CO)₅Cr · THF yields the rather unstable complexes (CO)₅Cr · CH₃SBR₂ (R = CH₃, C₆H₅). In contrast to the σ-thiophene complex (CO)₅Cr · SC₄H₄ the pentacarbonylchromium complex of the σ-S-bonded 2-diethylboryl-5-methylthiopene is quite stable due to interaction of the boryl group with CO ligands.