The preparation and electrochemistry of manganese(II) complexes of an unsaturated pentadentate macrocyclic ligand

The preparation of a series of six and seven coordinate manganese(II) complexes [Mn^(II)(L)X]⁺, and [Mn^(II)(L)X₂]^2? (X = halide, water, triphenylphosphine oxide, imidazole, 1-methyl imidazole and pyridine) incorporating the pentadentate planar macrocylic ligand L is described. Cyclic voltammetry of these complexes in acetonitrile each shows a reversible one-electron reduction wave near - 1.4 V vs a Ag/AgNO₃ reference electrode. Quantitative reduction of these complexes by controlled potential electrolysis at a platinum gauze at - 1.4 V yields the corresponding one-electron reduction products which have been shown by ESR spectroscopy to be manganese(II)-ligand radical species, the electron being thought to reside on the di-imino pyridine moiety of the macrocyclic ligand. No metal reduced species could be isolated even in the presence of π-acceptor ligands such as CO or phosphines.     

Fast atom bombardment mass spectra of [(diars)Fe(CO)2(C(O)Me)(P-donor)]+ BF4− salts

Characteristic fast atom bombardment (FAB) mass spectra (8 keV, argon, glycerol matrix) have been obtained for an isostructural series of organometallic cations of the form cis,trans[(diars)Fe(CO)₂(C(O)Me)L]⁺ Bf₄ (L = phosphorus donor). The fast atom bombardment mass spectra (FABMS) obtained show relatively abundant fragments corresponding to the cationic portion of the complex [C⁺]. Extensive fragmentation also occurs via successive CO loss, phosphorus donor ligand cleavage, and ligand decomposition. Evidence for a rearrangement fragmentation corresponding to the process [Fe(C(O)Me)]⁺ → [FeMe]⁺ + CO is presented.     

Katalytische oxidation von cyclohexen mit IrCl(CO)(PPh3)2 und kritische hydroperoxidkonzentration

Cyclohexene, dissolved in benzene is homogeneously oxidised with IrCl(CO)(PPh₃)₂ as catalyst. No induction period is observed if the concentration of hydroperoxide has a critical value. The reaction rate r increases with the concentration of cyclohexene from r = 1 to 15 mMol O₂ l^?1 min^?1 in pure cyclohexene with turnover numbers of 3000. Product composition is practically independent of the catalyst and cyclohexene concentrations.     

Spectroscopic and structural properties of homonuclear Fe(II) pyrazine-bridged polymeric complexes [Fe(pyrazine)2X2]n. (X = Cl,Br or I)

The reactions of FeX₂ (X = Cl, Br or I) with pyrazine (pyz) yield the Fe(pyz)₂X₂ compounds. Examination of IR and Raman spectra in the medium- and far-IR region as well as studies of electronic and Mössbauer spectra suggests that the complexes contain six-coordinate high-spin Fe(II) in the FeN₄X₂ chromophore. The complexes have a polymeric pseudo-octahedral pyz-bridged structure. The magnetic moments are independent of temperature and low-temperature magnetic measurements do not indicate any magnetic ordering above 4.2 K in these compounds. The π-acceptor properties of pyz are reflected both in the electronic spectra evaluated in terms of the angular overlap model and the Mössbauer parameters.     

On the molecular structure and nmr spectrum of cis-[PtPh2(Ph2PCH2PPh2)]

The X-ray crystal structure analysis of cis-[PtPh₂(Ph₂PCH₂PPh₂)] suggests that the unusually low PtP coupling constant is a consequence of distortion of the valency angles at the platinum and phosphorus atoms; the restrictive geometry of the chelate ring does not effect the lengths of the metal—ligand bonds.     

Kinetics of nucleophilic attack on coordinated organic moieties: XXVI. An extended nucleophilicity scale for nucleophilic addition to the cation [Fe(CO)3(1-5-η-C6H7)]+

A nucleophilicity scale is established for the addition of ca. 40 different nucleophiles to the cyclohexadienyl ring of the cation [Fe(CO)₃(1-5-η-C₆H₇)]⁺ (I). The factors controlling nudeophilicity towards cation I are discussed, and comparisons made with data for reactions of the nucleophiles with other model organic and inorganic substrates such as MeI and trans-[PtCl₂py₂].     

Photochemistry of planar four-co-ordinate palladium(II) complexes—III. Photosynthesis and crystal structure of [Pd2(PPr3n2(NCS)(SCN)2(μ-CN)]

U.V. irradiation of MeOH and CH₃CN solutions of trans-[Pd(PPr₃ⁿ)₂(NCS)₂] causes a stepwise photochemical reaction. When the solvent is CH₃CN the photoproduct can be conveniently isolated in a crystalline form. This compound has been shown, by X-ray analysis, to be a cyano bridged palladium(II) complex.     

Synthesis of two dibenzo-3, 2, 3-tetramines and their Ni(II), Zn(II) and Cd(II) complexes. The X-ray structure of diiodo-[2, 3:10, 11-dibenzo-1, 5, 8, 12-tetraazadodecane]cadmium(II)

Convenient syntheses of the tetramines 2, 3:10, 11-dibenzo-1, 5, 8, 12-tetraazadodecane, (L1, and 3, 4:9, 10-dibenzo-1, 5, 8, 12-tetraazadodecane (L2), are described. Both ligands form complexes with Ni(II), Zn(II) and Cd(II). The X-ray structure of [Cd(L1)I₂), confirms a five coordinate geometry for the Cd atom, where the two iodines are bonded to the metal and (L1) acts as a tridentate ligand. The complex crystallises in the monoclinic space group P2₁/c with a = 19.741(4) Å, b = 8.726(3) Å, c = 12.221(4) Å, and β = 104.55(3)°. The structure was refined to R = 0.062 for 1051 reflections.     

Redox properties of NN′-X-phenylenebis(Y-salicyli-deneiminato)iron(II) complexes and reactivity of the corresponding iron(III) complexes towards catecholates

The electrochemical behaviour of a series of iron(II) complexes with the tetradentate ligand NN′-1,2-phenylenebis(salicylideneimine), [Fe(II)L], was studied in non-aqueous solvents. The redox properties of the complexes were related to the nature of the substituents in the aromatic rings. Attention was devoted to dioxygen reactivity of the complexes. The electrode activity of the catechol—[NN′-1,2-phenylenebis(salicylidene-iminato) iron(III)] system, [Fe(III)L(catH)], was also studied; the results gave evidence that both the electrochemical oxidation and the chemical oxidation by dioxygen of [Fe(II)L] in the presence of catechol lead to the complex [Fe(III)L(catH)].     

Zinc(II), cadmium(II) and mercury(II) complexes of 4,6-dimethyl-pyrimidine-2(1H)-one

The following zinc(II), cadmium(II) and mercury(II) complexes of 4,6-dimethylpyrimidine-2(1H)-one (L) have been prepared and investigated by conductometric,IR and Raman methods: MX₂L₂ (M = Zn, X = Cl, Br(CHCl₃, I(CHCl₃, CF₃COO; M = Cd, X = Cl, Br CF₃COO; M = Hg, X = Cl, CF₃COO), Cd₂I₄L₃, Hg₃X₆L₂ (X = Cl, Br), Hg₃X₆L₄(X = Br, I), MX₂L₄·6H₂O (M = Zn, Cd, X = CIO₄, BF₄; M = Hg, X = CIO₄. The ligand is principally bonded through the unprotonated nitrogen atom and in some complexes also through the carbonylic oxygen atom. The zinc halide complexes are tetrahedrally coordinated, the trifluoroacetate ion is coordinated as a monodentate ligand.     

Low oxidation state ruthenium chemistry : IV. The reactions of M(CO)2(PPh3)3 complexes (M = Fe,Ru) and the hydrogenation and isomerization of alkenes catalyzed by RuL(CO)2(PPh3)2 (L = H2, PPh3)

The complexes M(CO)₂(PPh₃)₃ (I, M = Fe; II, M = Ru) readily react with H₂ at room temperature and atmospheric pressure to give cis-M(H)₂(CO)₂(PPh₃)₂ (III, M = Fe;IV,M = Ru). I reacts with O₂ to give an unstable compound in solution, in a type of reaction known to occur with II which leads to cis-Ru(O₂)(CO)₂(PPh₃)₂(V). Even compound IV reacts with O₂ to give V with displacement of H₂; this reaction has been shown to be reversible and this is the first case where the displacement of H₂ by O₂ and that of O₂ by H₂ at a metal center has been observed. III and IV are reduced to M(CO)₃(PPh₃)₂ by CO with displacement of H₂; Ru(CO)₃- (PPh₃)₂ is also formed by treatment of IV with CO₂, but under higher pressure. Compounds II and IV react with CH₂CHCN to give Ru(CH₂CHCN)(CO)₂- (PPh₃)₂(VI) which reacts with H₂ to reform the hydride IV.cis-Ru(H)₂(CO)₂(PPh₃)₂(IV) has been studied as catalyst in the hydrogenation and isomerization of a series of monoenes and dienes. The catalysts are poisoned by the presence of free triphenylphosphine. On the other hand the ready exchange of H₂ and O₂ on the “Ru(CO)₂(PPh₃)₂” moiety makes IV a catalyst not irreversibly poisoned by the presence of air. It has been found that even Ru(CO)₂(PPh₃)₃(II) acts as a catalyst for the isomerization of hex-1-ene at room temperature under an inert atmosphere.     

Siliconcarbon multiple-bonded (pπpπ)intermediates : II. Chemical reactivity and selectivity of thermally generated 1,1-dimethyl-1-silaethene (Me2SiCH2)

The order of reactivity and the selectivity of 1,1-dimethyl-1-silaethene (Me₂SiCH₂), generated from 1,1-dimethylsilacyclobutane at 611°, toward a variety of substrates was determined using standard competition experiments. The observed reactivity order was Ph₂CO>ROH, ArOH ? m-ClPhNH₂ CH₃CN, which indicates that with these substrates and under the reaction conditions used, Me₂SiCH₂ is behaving like an electrophilic species. Within a given class of substrates, polar effects were found to be generally unimportant, while increased steric effects caused a decrease in rate (up to 50%).     

Cu(II) complexes of N-propyl-2-picolinamine N-oxide

Cu(II) complexes have been prepared with N-propyl-2-picolinamine N-oxide(PA) employing the perchlorate, tetrafluoroborate, nitrate, chloride and bromide salts. The following unique solids have been isolated and characterized: Cu(PA)₂X₂ (X = ClO₄^?, BF₄^? and NO₃^?) and Cu(PA)X₂ (X = Cl^?, Br^?). Characterization has been accomplished primarily by IR, electronic and ESR measurements of the solid state since considerable alteration of the complexes occurs on dissolution. PA bonds as a bidentate ligand via its N-oxide oxygen and amine nitrogen in all of the complexes. Anion coordination occurs in the halogen complexes and the nitrate ions appear to be bound to Cu(II) as monodentate ligands in Cu(PA)₂(NO₃)₂. In addition, there appears to be a rhombic distortion of the CuO₂N₂ chromophore of the perchlorate and tetrafluoroborate solids which is probably due to the steric requirements of the propyl substituents.     

Studies on the thermal decomposition of salicylhydroxamic acid and its metal complexes with Ni(II), Co(II), Fe(II), Mn(II) and Zn(II)

The thermal decomposition of salicylhydroxamic acid and its metal complexes with Ni(II), Co(II), Fe(II), Mn(II) and Zn(II) has been studied by TG, DTG, DTA and IR spectroscopy. All the compounds investigated decompose to yield intermediate N-hydroxylactams.Decomposition schemes have been proposed and reaction enthalpies and kinetic parameters have been calculated.     

Transition metal-main group metal bond. VI. 199Hg NMR and 57Fe mössbauer study of (η5-C5H5)(CO)2FeHgX [X = Cl,Br,I,S2COC2H5, S2CN(C2H5)2, S2P(OC2H5)2 and Fe(CO)2(η5-C5H5)]complexes.

The ¹⁹⁹Hg NMR and ⁵⁷Fe Mössbauer spectra of iron-mercury bounded complexes are reported, compared with the ¹⁹⁹Hg NMR data for analogous molybdenum and tungsten compounds and discussed in terms of the polarization of the metal-metal bonds.     

Synthesis and characterisation of ReOCl3(DTO)2 and ReOCl3(MBT)2 complexes

New complexes of Re(V) with dithiooxamide and 2-mercaptobenzothiazole with the general formula ReOCl₃L₂, were prepared starting from potassium perrhenate. The compounds were characterised by chemical analysis, optical spectra and magnetic susceptibilities.     

Synthesis of low-valent thiocarbonyl complexes via 1,2-elimination of methylthiol from cis-metal-hydrido-dithiomethylester complexes. Os(cs)(CO)2(PPh3)2 and IrCl(CS)(PPh3)2.

[OS(η²-CS₂Me)(CO)₂(PPH₃)₂]⁺ and [Ir(η²-CS₂Me)Cl(CO)(PPh₃)₂)⁺ react with NaBH₄ giving OsH(CS₂Me)(CO)₂(PPh₃)₂ and IrH(CS₂Me)Cl(CO)(PPh₃)₂ respectively; These compounds contain mutually $\text{cis}$ hydride and η¹-dithiomethylester ligands and upon heating undergo 1,2-elimination of MeSH producing Os(CS)(CO)₂(PPh₃)₂ and IrCl(CS)(PPh₃)₂.     

Formation of Cu(II)—dicyandiamide complexes in neutral and acidic aqueous solutions

This work presents spectroscopic studies and electrochemical characterization of Cu(II)—dicyandiamide (DCDA) complex formation. The range of conditions leading to the precipitation of the complex is significantly larger than that presented in the literature. In all cases the stoichiometry of the compound is: [Cu(DCDA)₂(SO₄)(H₂O)₅). The spectroscopic data suggest that DCDA is a monodentate ligand forming a bond with Cu²⁺ via the nitryl nitrogen. Electroreduction of this complex is a two-step process occurring through a Cu(I)—DCDA intermediate.     

Formation equilibria of copper(II) complexes with some pyridinols in various solvents

Complexation of copper(II) with two different pyridinols in three solvents has been studied by visible spectrophotometry and flow-microcalorimetry. The influence of the solvent on tautomeric equilibrium of the ligand, on distribution, on stability and on formation enthalpies of the main complex species is discussed.     

Carbonyl-organocobalt(I) and -(II) complexes

Passage of CO through solutions of complexes (C₆F₅)₂CoL₂ gives carbonyl derivatives (C₆F₅)₂CoL₂(CO) (L₂ = 2 PEt₃, 2 P-n-Bu₃, 2 PPh₃, Ph₂PCH₂CH₃PPh₂). The properties of these compounds are described.The compounds are also produced by treating solutions of (C₆F₅)₂Co-(dioxane)₂ with CO, but a simultaneous reduction to (C₆F₅)Co(CO)₄ takes place. Treatment of the latter complex with monodentate ligands gives substitution products (C₆F₅)Co(CO)₃L (L = PEt₃, P-n-Bu₃, PPh₃) all of which are monomeric, whereas the addition of Ph₂PCH₂CH₂PPh₂ gives the dimer (C₆F₅)(CO)₂CoLLCo(CO)₂(C₆F₅). The properties of these compounds are discussed.