Mechanism of the formation of palladium complexes serving as catalysts in hydrogenation reactions : I. Reactions of complexes with molecular hydrogen

The interaction of Ph₃PPD(OAc)₂₂ with molecular H₂ yields a binuclear complex of zero-valent palladium, (Ph₃P)₂Pd₂. This complex interacts reversibly with H₂ in CH₂Cl₂, yielding (Ph₃P)₂Pd₂H₂. In argon atmosphere (Ph₃P)₂Pd₂ reacts with [Ph₃PPd(OAc)₂₂ to form a binuclear complex of Pd^I with a metal—metal bond. These data, as well as the results of kinetic studies of the reactions between [Ph₃PPd(OAc)₂₂ and H₂, are in agreement with an autocatalytic mechanism for the process, including catalysis of the reduction of Pd^II complexes by the Pd⁰ compounds. It has been established that the synthesized compound of Pd^II, Pd^I and Pd⁰ with the ratio P/Pd?1, are inactive in the hydrogenation of unsaturated compounds. The catalytically active complex (PPh)₂Pd₅ is formed when palladium acetate reacts with (Ph₃P)₂Pd₂ in the presence of H₂. The same compound is formed when a solution of (Ph₃P)₂Pd₂ is treated with a mixture of H₂ and O₂ (or H₂O₂ in an atmosphere of H₂). (PPh)₂Pd₅ is an effective catalyst for the hydrogenation of olefins, dienes, acetylenes, aldehydes, organic peroxides, quinones, O₂, Schiff bases, and nitro, nitroso, and azo compounds.     

Antiferromagnetic complexes involving metalmetal bonds IV. Synthesis,molecular structure and magnetic properties of the heterotrinuclear cluster, (C5H5Cr)2(μ2-SCMe3)(μ3-S)2Fe(CO)3, with direct and indirect exchange between CrIII and FeI centers

The photochemical reaction between the antiferromagnetic complex (C₅H₅-CrSCMe₃)₂S (I) (containing a CrCr bond 2.689 Å long) and Fe(CO)₅ results in the elimination of two carbonyl groups and one tert-butyl radical to give (C₅H₅Cr)₂(μ²-SCMe₃)(μ³-S)₂ · Fe(CO)₃ (III). As determined by X-ray diffraction, III contains a CrCr bond of almost the same length as in I (2.707 Å), together with one thiolate and two sulphide bridges. The latter are also linked with the Fe atom of the Fe(CO)₃ moiety (average FeS bond length 2.300 Å). Fe also forms a direct bond, 2.726 Å long, with one of the Cr atoms, whereas its distance from the other Cr atom (3.110 Å) is characteristic for non-bonded interactions. Complex III is antiferromagnetic, the exchange parameter, ?2J, values for CrCr, Cr(1)Fe and Cr(2)…Fe are 380, 2600 and 170 cm^?1, respectively. The magnetic properties of III are discussed in terms of the “exchange channel model”. The contributions from indirect interactions through bridging ligands are shown to be insignificant compared with direct exchange involving metalmetal bonds. The effects of steric factors and of the nature of the M(CO)_n fragments on the chemical transformations of (C₅H₅CrSCMe₃)₂S · M(CO)_n are discussed.     

Reactions of manganese π-acetylenic, η-vinylidenic,and η-allenylidenic complexes with Fe2(CO)9. Crystal and molecular structure of Cp(CO)2Mn(μ2-CCHCOOCH3)Fe(CO)4

The interaction between Cp(CO)₂Mn(CCHCOOMe) (I), Cp(CO)₂Mn(π-HCCCOOMe) (II), Cp(CO)₂Mn(CCCPh₂) (III), and Fe₂(CO)₉ in hexane gives rise to the complexes Cp(CO)₂Mn(μ²-CCHCOOMe)Fe(CO)₄ (IVa,b) and Cp(CO)₂Mn(μ²-CCCPh₂)Fe(CO)₄ (VIII). The structure of IVb was determined by X-ray analysis. This compound is a binuclear complex with the Fe(CO)₄ and Cp(CO)₂Mn fragments linked by a FeMn bond and a carbomethoxyvinylidenic ligand. Compound IVa is a geometrical isomer of IVb.     

Reactivity of palladium(II) complexes supported on carbon toward molecular hydrogen

The reactivity of Pd(II) complexes supported on carbon toward H₂ was studied. For the carboxylate complexes Pd(RCOO)₂ (R = Me, Me₃C, F₃C), it decreases upon decrease in the basicity of the acid RCO₂H. The reactivity of Pd(II) η³-allyl complexes increases with increase in the Mulliken charges on the C atom of the allyl ligand connected to the substituent R. The results are in line with the heterocyclic mechanism of H-H bond activation in the hydrogen molecule and can be used for optimization of the composition of the initial compounds for the preparation of palladium catalysts.     

Cationic palladium(II) complexes of ferrocenylphosphines as homogeneous hydrogenation catalysts for olefins

Cationic palladium(II) complexes of ferrocenylphosphines [(L-L′)Pd(S)₂][ClO₄]₂ ((L-L′) = Fe(η⁵-C₅H₄P (C₆H₅)₂)₂ 1, or Fe(η⁵-C₅H₅)(η⁵C₅H₃(CHMeNMe₂)P(C₆H₅)₂-1,2) 2a: S=pyridine or dimethylformamide) were prepared and characterized. The derivatives of 2a are effective catalysts for the hydrogenation of simple olefins at 30°C (1 atm H₂). The rate of reduction of styrene depends on the substrate concentration, catalyst concentration and the solvent, and is only slightly inhibited (16%) by the addition of mercury. These observations are conistent with a homogeneous catalytic system.     

Rhodium phosphine complexes as homogeneous catalysts. part 3. Homogeneous ssymmetric hydrogenation of schiffs bases

Summary Complexes formed from [Rh(norbornadiene)Cl]₂ and tertiary phosphines under hydrogen are active catalysts for the homogeneous hydrogenation of Schiff bases at 30–80° and 1-70 bars. Using chiral phosphines some optical induction can be achieved, but the optical yields are rather low.     

Reactivity of diacetylplatinum(II) complexes: Oxidative addition of halogens and hydrogen halides

Diacetylplatinum(II) complexes [Pt(COMe)₂()] ( = bpy, 3a; 4,4′-t-Bu₂-bpy, 3b), obtained by the reaction of [Pt(COMe)₂X(H)()] with NaOH in CH₂Cl₂/H₂O, were found to undergo oxidative addition reactions with halogens (Br₂, I₂) yielding the platinum(IV) complexes (trans, OC-6-13)/(cis, OC-6-32) [Pt(COMe)₂X₂()] ( = bpy, X = Br, 4a/4b; I, 4c/4d;  = 4,4′-t-Bu₂-bpy, X = Br, 4e/4f; I, 4g/4h). The diastereoselectivity of the reactions proved to be strongly dependent on the solvent. The oxidative addition of (SCN)₂ resulted in the formation of (OC-6-13)-[Pt(COMe)₂(SCN)₂()] ( = bpy, 4i; 4,4′-t-Bu₂-bpy, 4j). In a reaction the reverse of their formation, the diacetylplatinum(II) complexes 3 underwent oxidative addition with anhydrous HX (X = Cl, Br, I), prepared in situ from Me₃SiX/H₂O, yielding diacetyl(hydrido)platinum(IV) complexes [Pt(COMe)₂X(H)()] ( = bpy, X = Cl, 5a; Br, 5b; I, 5c;  = 4,4′-t-Bu₂-bpy, X = Cl, 5d; Br, 5e; I, 5f). Furthermore, diacetyldihaloplatinum complexes 4 were found to undergo reductive elimination reactions in boiling methanol yielding acetylplatinum(II) complexes [Pt(COMe)X()] ( = bpy, X = Br, 6b; I, 6c;  = 4,4′-t-Bu₂-bpy, X = Br, 6e; I, 6f). All complexes were characterized by microanalysis, IR and ¹H and ¹³C NMR spectroscopy. Additionally, the bis(thiocyanato) complex 4j was characterized by single-crystal X-ray diffraction analysis.     

Template reactions with polynuclear complexes. The reaction of octachlorodimolybdate(II) with 2-aminobenzaldehyde

The binuclear molybdenum(II) anion [Mo₂Cl₈]^4? acts as a template for the self-condensation of 2-aminobenzaldehyde. The dimolybdenum unit is retained in the molybdenum(IV) product, [Mo₂(A)₂(H₂O)⁴⁺.4Cl^?, where A is a macrocyclic tetradentate ligand containing two Schiff base nitrogen donors. The product forms as two isomers, whose ¹H nmr spectra are discussed.     

Selenium-ligated palladium(II) complexes as highly active catalysts for carbon-carbon coupling reactions: the Heck reaction

Three selenium-ligated Pd(II) complexes were readily synthesized and shown to be extremely active catalysts for the Heck reaction of various aryl bromides, including deactivated and heterocyclic ones. The catalytic activity of the selenide-based Pd(II) complexes not only rivals but vastly outperforms that of the corresponding phosphorus and sulfur analogues. Practical advantages of the selenium-based catalysts include their straightforward synthesis and high activity in the absence of any additives as well as the enhanced stability of the selenide ligands toward air oxidation.     

Cationic organometallic complexes with hexaalkylborazines: I. Synthesis and reactivity of cationic hexamethylborazinerhodium complexes with carbonyl,ethylene and diolefins as ligands

The PF₆ salts of the new cationic hexamethylborazinerhodium(I) complexes of general formula [Rh(Me₃B₃N₃Me₃)(LL′)]⁺ (LL′= 1,5-cyclooctadiene, norbornadiene, tetrafluorobenzobarrelene, trimethyltetrafluorobenzobarrelene, L = L′ = ethylene, CO) have been prepared from the reaction between [RhCl(LL′)]₂, Me₃B₃NMe₃, and AgPF₆ in dichloromethane. These complexes are very labile, undergoing rapid ring ligand exchange in solution with σ and π-donor ligands. The synthesis of [Rh(η⁶-naphthalene)(COD)]PF₆ is also described. The properties and NMR and IR spectroscopic characteristics of the new compounds are briefly discussed.     

Poly(vinylpyridine) complexes of palladium as hydrogenation catalysts. Effect of polymeric ligand structure

The title complexes exhibit high catalytic activity, selectivity and stability in hydrogenation of allyl alcohol. The structure of a polymeric ligand (i.e. the position of the nitrogen atom in the pyridine ring) affects catalyst activity. According to the hydrogenation rates of allyl alcohol, the complexes studied are arranged in the sequence: P4VP-Pd>P2VP-Pd>P2M5VP-Pd.

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, - - . ( ) . : 4->2-Pd>25-.

     

Identification of Cu(II)/Cu(III) couples in binuclear copper(II) complexes

A new series of binuclear copper(II) complexes were synthesised and studied by magnetic, spectral, ESR and cyclic voltammetry methods. The μ_eff values per copper atom correspond to the values observed for mononuclear copper(II) complexes. ESR spectral data in solution indicate weak interactions resulting from the electron delocalisation through the ligand system. Two nearly reversible red-ox couples are identified at $\text{+}\text{?}$0.50 V and $\text{+}\text{?}$0.75 V vs SCE. They correspond to Cu(II)αCu(III) red-ox processes, successively occurring at the two copper sites in the binuclear complexes.     

Unusual metalloporphyrins : thorium and uranium complexes of octaethylporphyrin.

The action of thorium or uranium tetrachloride with octaethylporphyrin [(oep)H₂] affords the dichlorometal (IV) complexes [M(IV)(oep)Cl₂, L_n] (M(IV) = Th or U, L = benzonitrile, tetrahydrofuran or pyridine). Spectral properties of these complexes are in good agreement with a cis octa-coordination.     

Reactivity of cyclopalladated compounds: VIII. Synthesis of cyclometallated compounds with an oxygen as the donor atom. Crystal and molecular structure of (8-methylquinoline-C,N)-(1-methoxynaphthalene-8-C,O)palladium(II)

Treatment of 1-methoxynaphthalene (MXNH) with n-butyllithium in a diethyl ether/n-hexane solution gives 1-methoxynaphthalene-8-lithium (MXNLi) in 30% yield as an insoluble material. This compound reacts with PdCl₂(SEt₂)₂ to give bis(1-methoxynaphthalene-8-C,O)palladium(II) (I)_and with PtCl₂(SEt₂)₂ to give cis- and trans-(1-methoxynaphthalene-8-C,O)(1-methoxynaphthalene-8-C)(diethylsulfide)platinum(II) (II), which are non-rigid molecules in solution. With the cyclopalladated dimers [{$\text{Pd(CN}$)Cl₂}₂], MXNLi gives the palladobicyclic compounds: ($\text{N∩C)P}$$\text{d(C∩O}$) (III). An X-ray diffraction study of compound IIIa where N∩N = 8-methylquinoline-C,N reveals the planarity of the molecule, shows that it has a cis configuration with respect to the PdC bonds, and confirms that the oxygen atom of MXN is bonded to palladium: PdO 2.236(4) Å. The geometry of IIIa is maintained in solution, whereas the corresponding compounds IIIb and IIIc in which N∩C is benzo[h]quinoline-9-C,N and N,N-dimethyl-1-naphthylamine-8-C,N, respectively, appear to be mixtures of cis and trans isomers in solution. With PMe₂Ph I and II give trans-Pd(MXN)₂(PMe₂Ph)₂ and cis-Pt(MNX)₂(PMe₂Ph)₂, respectively, in which the methoxynaphthalene is bound to the metals via the 8-carbon of the naphthalene ring. Only one phosphine ligand adds to compounds IIIb and IIIc with displacement of the O → Pd bond. One carbon monoxide ligand can be added to the platinum compound II to give Pt(MXN)₂(SEt₂)CO which in solution exists as two isomers in equilibrium.     

Hydrido- and hydroxo-cyanoalkyl complexes of platinium(II). Reactivity of the PtH and PtOH bonds towards nucleophiles and electrophiles

Reactions of the PtH and/or PtC bonds of the hydridocyanoalkyl complexes cis- or trans-PtH[(CH₂)_nCN]L₂ (n = 1, 3; L₂ = 2 PPh₃, Ph₂PCHCHPPh₂) are described, viz. reductive elimination induced by CO, PhCCPh, PEt₃, PPhMe₂, cis-Ph₂PCHCHPPh₂ to give Pt(CO)₂L₂, PtL₂(PhCCPh), PtL₂, PtL(PPhMe₂)₃, PtL₂(Ph₂PCHCHPPh₂) (L = PPh₃), respectively, and cleavages by acids, halogens and alkyl halides.The monomeric hydroxo complexes cis-Pt(OH)[(CH₂)_nCN]L₂ were shown to be intermediates in the synthesis of PtH[(CH₂)_nCN]L₂ from cationic cyanoalkyl complexes in alcoholic NaOH. Their characterisation and the reactions of the PtOH bond with activated methyl groups are reported.     

Spectrophotometric determination of palladium by solvent extraction as the Pd(II)-biacetylmonoxime 2-pyridylhydrazone complex

Determination of trace levels of palladium(II) is described. The method relies upon the extraction of palladium(II)-biacetylmonoxime 2-pyridylhydrazone (BMPH) from aqueous acidic solution into chloroform to form a purple-reddish complex. The molar absorptivity of the Pd-BMPH complex is about 7500 liters mol^?1 cm^?1 at 560 nm in the chloroform extract. The highly colored chloroform extract is suitable for spectrophotometric determination. The method devised has been applied to the determination of palladium in $\text{Pd}\text{CaCO}{}_3$ catalyst with good results.     

Rhodium(I) phosphine complexes containing bidentate unsaturated thio ligands: II. Reactions with O2 and H2

The rhodium(I) complexes (Ph₃P)₂Rh[Me₂NC(S)NC(S)NMe₂], (Ph₃P)₂Rh[SC(S)NMe₂] and (Ph₃P)₂Rh[PhNC(S)NMe₂] react with O₂ to give 1/1 dioxygen adducts. In solution, trans-(Ph₃P)₂Rh(O₂)[Me₂NC(S)NC(S)NMe₂], cis- and trans-(Ph₃P)₂Rh(O₂)[SC(S)NMe₂] and cis- and trans-(Ph₃P)₂Rh(O₂)[PhNC(S)NMe₂] are observed. For (Ph₃P)₂Rh(O₂)[PhNC(S)NMe₂], there is a solvent effect on the initial cis—trans ratio and the rate of O=PPh₃ formation. In C₆H₆, O=PPh₃ formation from (Ph₃P)₂Rh(O₂)[PhNC(S)NMe₂] is inhibited by additional PPh₃.The reaction of (Ph₃P)₂Rh[Ph₂PC(S)NPh] with O₂ in the presence of additional PPh₃ gives O=PPh₃ and cis-(Ph₃P)₂Rh(O₂)[Ph₂P(O)C(S)NPh] as the only products. The same complex also can be prepared from (Ph₃P)₂Rh[Ph₂P(O)C(S)NPh] and O₂.Only (Ph₃P)₂Rh[PhNC(S)NMe₂] reacts with H₂ at room temperature to give (Ph₃P)₂RhH₂[PhNC(S)NMe₂], which is a catalyst for cyclohexene hydrogenation.     

Organolanthanoids V. The crystal and molecular structure of DI-η5-cyclopentadienyl-1,2-dimethoxyethaneytterbium(II)

Crystals of di-η⁵-cyclopentadienyl-1,2-dimethoxyethaneytterbium(II) are mono-clinic, space group Cc, with a 9.25(2), b 23.49(5), c 8.23(2) Å, β 123.59(4)° and Z  4. The ytterbium ion is pseudo-tetrahedrally coordinated by two cyclopentadienyl groups and a bidentate 1,2-dimethoxyethane ligand, and there is no inter-molecular association. The sites of the cyclopentadienyl ligands are disordered.