Alkyl complexes of cobalt in catalytic cycles for hydrogenation of alkenes

The potential of several alkylcobalt complexes as catalysts for hydrogenation and isomerization of alkenes has been investigated. The complexes CH₃Co(CO)₂(Pom-Pom) (Pom-Pom = 1,2 bis(dimethoxyphosphino)ethane), CH₃Co(CO)₃P(OMe)₃ and C₆H₅CH₂Co(CO)₃PPh ₃ are compared to CH₃Co(CO)₂(P(OMe)₃)₂, for their ability to function in catalytic cycles. Each is active for hydrogenation and isomerization of alkenes under conditions where the carbonylation-decarbonylation equilibrium is readily established. The lifetime for the complexes is much shorter than for CH₃Co(CO)₂ (P(OMe)₃)₂ suggesting that two phosphorus donors in trans positions in an intermediate is a requirement for catalyst stability in these alkylcobalt complexes.     

Heterogeneous reactions of solid nickel(II) complexes. XVIII

The Stoichiometry of thermal decomposition was studied for the following compounds: Ni(NCS)₂(2-Mepy)₂ (I), (Me=methyl, py=pyridine), Ni(NCS)₂(2-Etpy)₂ (II) (Et=ethyl), Ni(NCS)₂(2-Clpy)₂ (III), Ni(NCS)₂(2-Brpy)₂ (IV), Ni(NCS)₂(2-NH₂py)₂ (V), Ni((NCS)₂(2-NH₂py)₂·3/4 (C₂H₅)₂O (VI). The release of volatile ligands 2-Rpy is a one-step process for complexes I, II, III and IV, while for V and VI it is a two-step process, Ni(NCS)₂(2-NH₂py)₁ (VII) being formed as an intermediate complex. It was found that complexes I and II are square-planar; the others exhibited pseudo-octahedral geometry. The differences in stereochemistry of the above complexes are explained by the different electronic properties of 2-Rpy.     

Protonation of a series of diphosphazane- and diphosphine-bridged derivatives of iron and ruthenium: dependence of the nature of the hydride ligand on the metal and the bridging diphosphorus ligand

Protonation of the dinuclear compounds [M₂(μ-CO)(CO)₄(μ-R₂PYPR₂)₂] by HBF₄ or HPF₆ leads to the formation of crystalline cationic hydrido products [M₂H(CO)₅(μ-R₂PYPR₂)₂]X and [M₂(μ-H)(μ-CO)(CO)₄(μ-R₂PYPR₂)₂]X (X = BF₄ or PF₆) in which the hydride ligand is terminal for M = Ru, Y = N(Et) and R = OMe or OPrⁱ and bridging for M = Fe, Y = CH₂ and R = Me or Ph, for M = Fe, Y = N(Et) and R = OMe, OEt, OPrⁱ or OPh and for M = Ru, Y = CH₂ and R = Ph; the fluxional behaviour of [Ru₂H(CO)₅{μ-(RO)₂PN(Et)P(OR)₂}₂]⁺ (R = Me or Prⁱ) in solution is described.     

A new understanding of the co-catalytic activity of alumoxanes: The opening of a black box!

The isolation of non-fluxional alumoxane compounds, [(^tBu)₂Al{OAl(^tBu)₂}]₂ and [(^tBu)AlO]_n (n = 6, 7, 8, 9), has allowed for an investigation of the mode of activity observed for alumoxanes as co-catalysts for the zirconocene polymerization of olefins. [(^tBu)₂Al{OAl(^tBu)₂}]₂, which contains two three-coordinate aluminum centers, shows no reaction with Cp₂ZrMe₂, and no catalytic activity towards ethylene polymerization. In contrast, the closed cage compound [(^tBu)AlO]₆ reacts reversibly to give the ion pair complex, [Cp₂ZrMe][(^rBu)₆Al₆O₆Me], which is active as a catalyst for the polymerization of ethylene. Polymerization is also observed for mixtures of Cp₂ZrMe₂ with [(^tBu)AlO]_n (n = 7, 9). A new concept, “latent Lewis acidity”, is proposed to account for the reactivity of the cage alumoxanes, [(^tBu)AlO]_n.     

Polymerization of propadiene. IV. Kinetics and mechanism of polymerization under the influence of rhodium(I) complexes

The kinetics and mechanisms of propadiene polymerization under the influence of [Rh(CO)₂Cl]₂, Rh(CO)₂P(C₆H₅)₃Cl, Rh(CO)₃Cl are reported. The reaction rates are first-order in Rh(CO)₂P(C₆H₅)₃Cl and Rh(CO)₃Cl and half-order in [Rh(CO)₂Cl]₂. They are second-order in the substrate for Rh(CO)₃Cl and [Rh(CO)₂Cl]₂ and first-order for Rh(CO)₂P(C₆H₅)₃Cl. The data are interpreted in terms of a common intermediate mechanism. The formation of this common intermediate is the rate-determining step. A solvent effect is also discussed.     

A spectroscopic study of the hydrolysis products of aryltellurium trihalides

The hydrolysis of aryltellurium trihalides to aryltellurium oxide halides in neutral aqueous media is considered to proceed in a stepwise manner in which the first stage involves the formation of a monomeric species. In alkaline media the initially isolated hydrolysis product analyses as (p-EtOC₆H₄)TeO(OH) and on treatment with dilute acid, affords the known (p-EtOC₆H₄TeO)₂O.The infrared spectra are assigned in the low frequency region for the compounds RTe(O)X (X = halogen), RTeO(OH) and (RTeO)₂O. It is argued that the probable coordination number for tellurium in RTe(O)X is four, and that a ring structure is likely. The preparation of the salts(C₅H₅NH⁺)(RTeCl₄^?) is reported and the anions are considered to have square-based pyramidal structures of approximately C_4v symmetry. The reaction of (C₅H₅NH⁺)(PhTeCl₄^?) with acetone affords Ph(CH₃COCH₂)TeCl₂.     

Reactions of dicobalt octacarbonyl and related compounds with gem-dihalides

Dicobalt octacarbonyl and some of its derivatives (NaCo(CO)₄, Co₄(CO)₁₂, Hg[Co(CO)₄]₂, [Co(CO)₃PPh₃]₂, NaCo(CO)₃PPh₃) react with activated gem-dihalides, R₂CX₂, such as dichlorodiphenylmethane, 9,9-dihalofluorenes and dimethyl dibromomalonate, to give the ‘dimer’ olefin, R₂CCR₂. The course of this conversion involves formation of the coupling product, R₂XCCXR₂, followed by dehalogenation of the latter. These separate steps have been confirmed for activated monohalides (bromodiphenylmethane, 9-bromofluorene, dimethyl bromomalonate) which were readily coupled by cobalt carbonyls, and for activated vicinal dihalides (D,L and meso-dibromostilbene, 9,9′-dichlorobisfluorenyl) which cobalt carbonyls readily dehalogenated. A radical mechanism is favored for these processes, and indirect evidence in its favor is presented.     

A neutron-diffraction study of the tetragonal-monoclinic crystal structures of some uranium-thorium dicarbides

Crystal-structure line profile refinements have been made for neutron powder diffraction data collected at room temperature from the ternary uranium-thorium dicarbide U_0.1Th_0.9C₂ and the two binary dicarbides UC₂ and ThC₂. U_0.1Th_0.9C₂ is monoclinic, with unit cell dimensionsa = 6.630(2), b = 4.183(1), c = 6.690(2)A˚, β = 103.86(1)°, isostructural with ThC₂, a = 6.684(2), b = 4.220(1), c = 6.735(2)A˚, β = 103.91(1)°. The tetragonal structure for UC₂ is confirmed, witha = 3.522(1), c = 5.988(1)A˚. U_0.1Th_0.9C₂ contains discrete C-C groups 1.297(8)A˚long; more precise values for C-C lengths have been determined for UC₂ (1.322(4)A˚) and ThC₂ (1.304(6)A˚).     

Kinetics and mechanism of the aminolysis of O-ethyl S-aryl dithiocarbonates in acetonitrile

The aminolysis reactions of O-ethyl S-(Z-phenyl) dithiocarbonates (Z=p-CH₃, H, p-Cl, and p-NO₂) with anilines (AN) and N,N-dimethylanilines (DMA) in acetonitrile at 30.0°C are investigated. Relatively small values of β_X (β_nuc,0.4 ca. 0.7) and β_Z (β_lg −0.1 ca. −0.4) for both ANs and DMAs, significantly large k_H/k_D values (1.1 ca. 1.9) involving deuterated anilines, and large negative ρ_XZ values for ANs (−0.56) are interpreted to indicate a concerted mechanism for both ANs and DMAs but with a hydrogen bonded four-center type transition state (TS) for ANs. The relative leaving ability, k(Z=p-NO₂)/k(Z=p-CH₃), is smaller for ANs than for DMAs, especially for a weaker nucleophile (1.9 and 4.7 for AN and DMA, respectively, with X=p-Cl). This suggests that the rate enhancement by the hydrogen-bond formation in the four-center type TS for AN is greater for a weaker nucleofuge (Z=p-CH₃), especially when the nucleophile (X=p-Cl) is weaker. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 419–423,1998     

Metal-thiophen derivatives. Organometallic compounds of palladium and platinum

Thienylmercury(II)chloride reacts with [Pd(PPh₃)₂Cl₂], [Pd(PPh₃)₄] and [Pt(PPh₃)₄] to afford new compounds containing a metal-2-thienyl linkage. The compound [Pd(PPh₃)₂(2-C₄H₃S)Cl] probably has trans stereochemistry.2-Bromothiophen undergoes oxidative addition with [Pd(PPh₃)₄] and [Pt(PPh₃)₄], probably via a radical mechanism. With [Pd(CO)(PPh₃)₃], a carbonyl inserted product is obtained. The bromo-metal(II) complexes have trans stereochemistry. The course of the reaction between 3-methyl-2-bromothiophen and Pd(PPh₃)₄ is more complex. Thus, there is evidence of some cis bromopalladium(II) compounds amongst the products, also there is good evidence to support the view that some isomerisation of 3-methyl-2-thienyl to 4-methyl-2-thienyl occurs during the reaction, thus giving greater molar quantities of [Pd(PPh₃)₂(4-CH₃-2-C₄H₂S)Br] than can be accounted for from any initial 4-methyl-2-bromothiophen impurity.The metallation of the thiophen ring, probably in the 4-position, with palladium(II) is described for 3-theylidene-4-methylaniline.     

Kinetics of ammoniation of some halobis(ethylenediamine)-rhodium(III) perchlorates in liquid ammonia

Summary The ammoniation ofcis-[Rh(en)₂Cl₂] · (ClO₄) in liquid NH₃ was studied at constant ionic medium of 0.20 m perchlorate in the 0 to 35° range. The complex reacts in two distinct steps to givecis-[Rh(en)₂(NH₃)₂] · (ClO₄)₃, with the intermediate formation ofcis-[Rh(en)₂(NH₃)Cl] · (ClO₄)₂. Both steps follow a conjugate-base mechanism. Activation parameters were obtained for the acid-base preequilibrium and the rate-determining step. The entropies of activation for the rate-determining step are 0 and –42 JK^–1mol^–1 for the first and second ammoniations respectively. These values are considerably lower than those found for the cobalt(III) analogues. The entropy changes for the acid-base equilibria are –84 and –36 JK^–1mol^–1 respectively, which is less negative than those values found for the cobalt(III) analogues. Trans-[Rh(en)₂I₂] · (ClO₄) ammoniates totrans-[Rh(en)₂(NH₃)I] · (ClO₄)₂. The contribution of spontaneous ammoniation to the overall reaction oftrans-[Rh(en)₂I₂] · (ClO₄) is negligible, so the uniqueness oftrans-[Co(en)₂Cl₂] · (ClO₄) among cobalt(III) complexes in this respect is not reproduced for thetrans-dihalotetraamine structure in rhodium(III) complexes. A comparison of cobalt(III) and rhodium(III) amines with respect to activation parameters and the influence of formal charge of the metal complex on reactivity indicates a more associative type of activation for rhodium(III).     

The mechanism of a redox indicator reaction: The kinetics of oxidation of ferrocyphen by nitrous acid

Summary The oxidation of [Fe(phen)₂(CN)₂] and [Fe(bipy)₂(CN)₂] by nitrous acid in sulphuric acid follows the kinetic equation rate = k[H⁺] [HNO₂] [complex] at low acidities. The mechanism is a diffusion controlled reaction between NO⁺ and the complex. Reaction is too slow for satisfactory use as a redox indicator for nitrite titrations at low acidities (0.1 M) [H⁺]. The variation of rate with acidity in more concentrated sulphuric acid (up to 6 M) is interpreted in terms of protonation of the complex to form [Fe(phen)₂(CNH)₂]²⁺.We thank the British Council for a maintenance award for P.R., and the Universidad Tecnica Federico Santa Maria, Valparaiso, Chile, for study leave.     

Structure and UV-Vis spectroscopy of nitrosylthiolatoferrate mononuclear complexes

Density functional calculations for the [(RS)_xFe(NO)_4−x]⁻ (R=CH₃) compounds are carried out using the DFT method with the B3LYP functional. The results can be verified by the experimental data only in the case of the [(RS)₂Fe(NO)₂]⁻ complex. The experimentally characterised molecular structure of [(RS)₂Fe(NO)₂]⁻ (where (RS)₂=(SCH₂CH₂NMeCH₂CH₂CH₂NMeCH₂CH₂S) is properly reproduced by the RB3LYP method. The discrepancy between the calculated spin densities with the integral spin observed experimentally is interpreted in terms of antiferromagnetic coupling between the Fe(III) centre and the NO⁻ ligands. The theoretical analysis gives a good account of some properties observed in these compounds. In particular, the electronic spectrum calculated by the TDDFT method for [(CH₃S)₂Fe(NO)₂]⁻ is similar in shape to the experimental one, although is hypsochromically shifted. The LLCT (S_π→π^*_NO), LMCT (S_π→d) or (π^*_NO→d+S_π→d) and MLCT (d→π^*_NO) transitions are mostly responsible for absorption of the [(RS)_xFe(NO)_4−x]⁻ complexes within UV-Vis. The chemical reactivity of [(RS)₂Fe(NO)₂]⁻ is interpreted basing on the calculated effect of a polar solvent on the ligand polarity and on the character of the HOMO and LUMO orbitals.     

Studies of chelation : II. Phosphine complexes of molybdenum and manganese

Activation parameters have been obtained for the chelation of Mo(CO)₅dpe (dpe = Ph₂PCH₂CH₂PPh₂) and of Mo(CO)₅dmpe (dmpe = Me₂PCH₂CH₂PMe₂) to give cis-Mo(CO)₄dpe and cis-Mo(CO)₄dmpe respectively. The results are compared with those for the analogous chromium complexes and show that the enthalpy contribution determines the more rapid chelation in the molybdenum complexes. The preparation and properties of the chelate-bridged hetero-metallic complex (CO)₅ModmpeMn(CO)₄Br are reported. The reaction between Et₄N[Mn(CO)₄X₂] (X = Cl, Br) and bidentate ligands dpe, dmpe and ape (ape = Ph₂PCH₂CH₂AsPh₂) in the presence of either silver(I) tetrafluoroborate or Et₃OBF₄ produces cis-Mn(CO)₄X(bidentate) which is identified by infrared and mass spectrometry. At room temperature the Mn(CO)₄X(bidentate) complex is rapidly converted to the chelated fac-Mn(CO)₃X(bidentate) complex. The chelation process is approximately 10⁴ times more rapid than in the isoelectronic chromium(O) complexes. The preparation and characterisation of fac-Mn(CO)₃Br(dmpe), cis-Mn(CO)₄Br(PMe₃) and fac-Mn(CO)₃Br(PMe₃)₂ are reported.     

Evolution of (GaAl) n Clusters and Chemisorptions of H2 on (GaAl) n Clusters

The growth behavior of (GaAl) _n (n = 1–12) and the chemisorptions of hydrogen on the ground state geometries have been studied with the three-parameter hybrid generalized gradient approximation due to Becke-Lee–Yang–Parr (B3LYP). The dissociation energy, the second-order energy differences, and the HOMO–LUMO gaps indicate that the magic numbers of the calculated (GaAl) _n clusters are n = 4 and 6. To my knowledge, this is the first time that a systematic study of chemisorptions of hydrogen on gallium aluminum clusters. The onefold top site of aluminum atom is identified to be the most favorable chemisorptions site for one hydrogen chemisorptions on most (GaAl) _n clusters. In general, dissociative chemisorptions of a hydrogen molecule on a top site of aluminum atom is found common for all sizes clusters considered here except for (GaAl) _n (n = 1–3) clusters. The stability of the (GaAl) _n H _m complexes shows that both large second-order difference and large fragmentation energies for (GaAl)₁₀H₂ and (GaAl)₁₁H₂ make these species behaving like magic clusters.     

Structural Systematics of Rare Earth Complexes. XXII 4‐Methylpyridinium Salts of Diverse Complex Aqua/Chloro/Lanthanoid(III) Species

4‐Methylpyridinium cations, mpyH⁺, crystallized with complex aqua/chloro/lanthanoid(III) species for the gamut of the rare earth series, have ‘domains of existence’ defined for the following forms:

• (a) The triclinic series (mpyH)₂[{(H₂O)₃Cl₃Ln(μ‐Cl)_(2|2)}₂], previously defined for the Ln = La–Nd members (those for La, Pr characterized by full structure determinations);
• (b) The triclinic series (mpyH)₂[(H₂O)₃LnCl₄]Cl, previously defined for the Ln = Eu, Ho members by full structure determinations, is here augmented by the Ln = Nd, Sm examples (full structure determinations, the latter a new ‘light’ Ln extremum);
• (c) A new monoclinic C2/c series (mpyH)₂[(H₂O)₄LnCl₃]Cl₂, defined for the Ln = Er–Yb extrema (full structural characterizations for the Ln = Er, Tm, Yb members); the lanthanoid‐containing entity (which, with the cations, exhibits some disorder) is a neutral molecule of a new type. For the Ln = Lu case, a fully ordered derivative monoclinic C2 form has been obtained in a cell one half the size.

Other types have also been characterized, thus:

• (i) For Ln = La, (mpyH)₈[{(H₂O)₃Cl₃La(μ‐Cl)_(2|2)}₂]‐[{(H₂O)₄Cl₂La(μ‐Cl)₂La(OH₂)₂Cl₂(μ‐Cl)_(2|2)}₂]Cl₄·6H₂O·mpy has been defined by a full structural determination; the binuclear anion is similar to that in (a), albeit with some disorder, with the tetranuclear anion derivative of it.
• (ii) For Ln = Lu, (mpyH)₂[(H₂O)₅LuCl₂]Cl₃ is defined by a full structure determination.
• (iii) For Ln = Y, (mpyH)₂[(H₂O)₇YCl]Cl₄ is defined by a full structure determination; here, and in (ii), the complex component is cationic.

     

Implications of Nitrogen Doping on Geometrical and Electronic Structure of the Fullerene Dimers

Because of its unsaturated bonds, C₆₀ is susceptible to polymerize into dimers. The implications of nitrogen doping on the geometrical and electronic structure of C₆₀ dimers have been ambiguous for years. A quarter‐century after the discovery of azafullerene dimer (C₅₉N)₂, we reported its single crystallographic structure in 2019. Herein, the unambiguous crystal structure information of (C₅₉N)₂ is elucidated specifically, revealing that the inter‐cage C—C single bond length of (C₅₉N)₂ is comparable with that of an ordinary C(sp³)‐C(sp³) single bond, and that the most stable conformer of (C₅₉N)₂ is gauche‐conformer with a dihedral angle of 66°. To amend the structural deviations, geometrical structure of (C₅₉N)₂ is optimized by a B3LYP‐D3BJ function, which is proved to be more consistent with its single crystal structure than those by the commonly used B3LYP function. Moreover, the calculation method is also suitable for other representative fullerene dimers, such as (C₆₀)₂ and its divalent anion. Additionally, the dissociation of (C₅₉N)₂ at 473 K under mass spectrometric conditions suggests the inter‐cage C—C bond is relatively weaker than an ordinary C—C single bond, which can be explained by the interaction energies of inter‐cages.     

Direct Observation of the Binding Mode of the Phosphonate Anchor to Nanosized Polyoxotitanate Clusters

The structures of three newly synthesized phosphonate‐substituted polyoxotitanates are reported. The Ti/O core of [Ti₄O(OEt)₁₂(PhenylPO₃)] ( 1 ) is the building block for two larger phosphonate‐substituted nanoclusters, [Ti₂₅O₂₆(OEt)₃₆(PhenylPO₃)₆] ( 2 ) and [Ti₂₆O₂₆(OEt)₃₉(PhenylPO₃)₆]Br ( 3 ). All compounds exhibit a not previously recognized triply bridging binding mode of the phosphonate anchor with short connecting Ti? O bonds, the average of which is 2.010(7) Å. Comparison with previously reported work suggests that the binding mode of the phosphonate anchor is strongly dependent on the structure of the underlying substrate.     

Cyclic voltammetry of iron dimine complexes in acetonitrile

The electrochemical behavior of iron diimine complexes, (H₃C?N=C(R)?C(R′)=N?CH₃)₃Fe(II) (R, R′=H,H;H, CH₃; CH₃, CH₃), and (C₅H₄N?C(R₁)=N(R₂))₃Fe(II) (R₁, R₂=H, CH₃; CH₃, CH₃) on a platinum working electrode in acetonitrile is described, and compared to that of the parent aromatic complex, tris-(2,2′-bipyridine)Fe(II). One-electron reversible oxidations were found for all the compounds studied. The electrochemical reductions show 2–3 reduction waves in the potential range studied. Only for the complexes of mixed diimine ligands or 2,2′-bipyridine, a pre-adsorption wave is also observed. It is possible to stabilize low valence states with all ligands studied. A formal iron(I) state is described for the first time for all aliphatic diimine complexes, thus showing that the acceptor properties of the diimine complexes do not depend on the presence of the aromatic rings, but on the iron-diimine chromophore.     

Polynuclear carbonyltrialkylphosphine complexes of zerovalent palladium

The synthesis of three new polynuclear carbonyltrialkylphosphine complexes of Pd⁰ is described. The formulae Pd₁₂(CO)₁₅ (PEt₃)7, Pd₁₂ (CO)₁₂ (PBu₃)₇ and Pd₁₂(CO)₁₇ (PBu3)₅ are proposed for the new complexes.