Michal Wilgocki

PHOTOCHEMICAL SYNTHESIS, SPECTROSCOPIC PROPERTIES AND BARRIERS TO ALKENE ROTATION IN THE NOVEL BIS(ALKENE) TETRACARBONYL COMPLEXES OF TUNGSTEN

Abstract Photolysis of W(CO) 6 in the presence of twentyfold alkene excess (1-pentene, 1-hexene, 2-hexene, 3-hexene, 1-heptene, 1-octene, 1-decene, cyclopentene, cyclohexene cycloheptene and cyclooctene) in n -hexane leads to the formation of the corresponding bis(alkene)tetracarbonyl complexes of tungsten via the less stable [( ν 2 -alkene)W(CO) 5 ] complexes; the products have been isolated and characterized by their IR, UV-visible and NMR spectra. Bis(alkene)tetracarbonyl complexes of tungsten exhibit fluxional behaviour on the NMR time scale due to rotation of the alkene ligands around the axis defined by the metal and the midpoint of the C 2 linkage. The barriers to alkene rotation, which reflects the energy difference between the ortogonal and the parallel arrangement of the two C=C units, of a number of bis(alkene) complexes, have been determined using variable-temperature 13 C NMR spectroscopy.

Polarographic Studies of Dimeric and Monomeric Rhodium(II) and Rhodium(III) Complexes

Abstract The polarographic behaviour of [Rh2(O− 2)(OH)2(H2O)n]3+, [I], [Rh2(H2O)10]4+ (Rh2 4+ (aq)), [II], [Rh(H2O)6]3+, [III], in 3 M HCIO4 and Rh2(CH3CO2)4(H2O)2, [IV], and [Rh2(CH3CO2)4(H2O)2]+, [V], in 3 M HC1O4 and 3 M NaCIO4 has been investigated at a Pt (planar) electrode. The cation [I], which is the reaction product of [II] with molecular oxygen, produced a single electron cyclic polarogram, while cations [II], Rh2 4++(aq), and [III] do not show any wave. Formal potentials of the following couples were evaluated: [Rh2(O2)(OH)2(H2O)n]3+/[Rh2(O2 2-)(OH)2(H2O)n]2+, Eo f = 1.032 ± 0.002 V in 3M HCIO4; [Rh2(CH3CO2)4(H2O)2]+/[Rh2(CH3CO2)4(H2O)2], Ef o = 1.208 ± 0.002 V in 3M HCIO4, Ef o = 1.228 ± 0.002 V vs SHE in 3 M NaCIO4.

STABILITY CONSTANTS OF PROTONATED NON-AND PARTLY-CHELATED COMPLEXES IN THE ZINC 1,2-ETHANEDIAMINE SYSTEM

Abstract Complex formation between Zn(II) ion and 1,2-ethanediamine (en) or 2-aminoethylammonium cation (enH+) has been studied in 3 M (Na,H)ClO4 at 25°, by measuring the e.m.f. of glass and Zn(Hg) electrodes. At low initial acid concentration range and relatively high initial Zn(II) concentration the formation of a precipitate (for n < 1.9) was observed. From e.m.f. measurements of the solutions with high initial 1,2-ethane-diammonium diperchlorate concentrations (CenH2(ClO4)2 =0.75 or 0.50 M) and a low initial Zn(II) concentration (CZn(ClO4)2 =4.79 × 10−3 M) the values for the cumulative stability constants of the following complexes were evaluated: Zn(en)2+, β10=106.49±0.02; Zn(en)2 2+, β20=1012.44±0.01; Zn(en)3 2+, β30=1014.88±0.12; Zn(enH)3+, β01=101.03±0.06; Zn(en)(enH)3+, β11=107.47±0.13; Zn(en)2(enH)3+, β21=1012.81±0.03.

The evaluation of stability constants of protonated zinc -1,2-ethanediamine complexes using iso-concentration functions

Abstract A detailed study of complex formation between Hg(II) and 1,2-ethanediamine (en) and 2-aminoethylammonium cation (enH+) has been performed with high initial 1,2-ethanediammonium diperchlorate concentrations (CenH2(ClO4)2 =0.3333 M, 0.25 M, 0.15 M or 0.05 M) and low initial Hg(II) concentration (CHg(ClO4)2 =9.51 × 10−4 M) in 3M (Na, H)ClO4 at 25°C, by measuring the e.m.f. of glass and mercury electrodes. The data for each constant level of p[en], p[enH+] and pH were treated separately by an iso-concentration function of complexation procedure or by a generalized weighted least-squares computer method. The values for the cumulative stability constants of the following complexes were evaluated: Hg(en)2+, β10=1016.749±0.006; Hg(enH)3+, β01=108.82±0.02; Hg(en(enH)3+, β11=1020.751±0.007; Hg(en)2 2+, β20=1025.970±0.003.

Reactivity of bis(alkene) tetracarbonyl complexes of tungsten: evidence for alkene to π-allyl hydride rearrangement

Abstract The bis(alkene)tetracarbonyl complexes of tungsten were identified as olefin isomerization and metathesis catalyst precursors whose activities are based on the formation of a π-allyl hydride intermediate. It has been observed that the β-hydrogen atom of coordinated olefin may migrate to the metal giving η3-allylic hydrides which have been characterized by their 1H NMR spectra. This is the first case where the rearrangement of tungsten(0) alkenes coordinated to a π-allylic hydrides intermediate, fundamental to many catalytic mechanisms, can be observed directly. In the presence of Lewis acid the same alkene complexes are catalytically active toward olefin metathesis. It seems reasonable that the catalystically active alkylidene compounds are formed from the coordinated alkene via π-allylic hydride and metallacyclobutane precursors.

Electrochemical oxidation of basic aqueous solutions of rhodium(III)

Abstract The electrochemical oxidation of yellow basic solutions containing hydrolysed Rh 3+ results in the formation of blue superoxo-rhodium(III). The products of oxidation (electrochemical and chemical) of aqueous rhodium(III) are rationalized.

REFINEMENT OF COMPLEXATION EQUILIBRIA MODELS FOR THE MERCURY(II)-ETHANEDIAMINE SYSTEM

Abstract The three existing models for mercury(II)-ethanediamine equilibria are in considerable disagreement. It has been demonstrated that all three sets of experimental data (obtained by different authors) can be best explained on the basis of the same model of complexation: Hg(en)f°, Hg(en)(enH)3+, Hg(en)2+, Hg(enH)3+, while the formation of the latter complex for pH<4 may be neglected. Refined stability constants for chelated and protonated mercury(II)-ethanediamine complexes are presented.

Interpretation of stability constants obtained from electrometric data for zinc triad cation-ethanediamine complexes in aqueous solution. The paradox of complex equivalence, their acid properties and chelation effects.

Abstract Some basic elements have been developed for the interpretation of stability constants of metal-ion complexes obtained from electrometric data alone. Zinc triad cation-1,2-ethanediamine systems have been considered. The paradox of electrometric equivalence of complexes has been discussed. Relations for electrometric apparently indistinguishable complexes have been derived and acid properties of the protonated complexes and chelation effects have been estimated on the basis of Bjerrums and Schwarzenbachs empirical relations. The precision of the basic electrometric methods (potentiometry with amalgam and Hg electrodes, DC and tast polarography) and its influence on the possibility of the selection of a statistically unique model for complexation equilibria has been evaluated. Models including complexation with the monoprotonated form of 1,2-ethanediamine have been refined. A definitive model for complexation equilibria of zinc family cations in acid and near neutral aqueous solutions of 1,2-ethan...

DYNAMIC ELECTROCHEMISTRY OF CIS-[Co(EN)2(ENH)Cl]Cl3 · H2O AND [Co(EN)3]Cl3 COMPLEXES

Abstract The polarographic and voltammetric behaviour of cis-[Co(en)2(enH)Cl]Cl3 · H2O and [Co(en)3]Cl3 in water and dimethylsulphoxide has been investigated at a dropping mercury electrode, a hanging mercury drop electrode and a Pt planar electrode. The mechanism for electrochemical conversion of the protonated, partly-chelated cis-[Co(en)2(enH)Cl]3 + complex into [Co(en)3]3+ was established on the basis of dynamic electrochemistry investigations. For the second step of the reduction, [Co(en)ienH]3+ to Co(Hg), the electrode reaction mechanism varies with changes in the degree of complcxation. Reduction of Co(II) in ethanediamine/2-aminoethylammonium buffer solution in the presence of a small amount of human blood serum at nearly neutral pH is catalytic in nature.

Low Temperature Electrochemistry and Spectroelectrochemistry of Catalytically Important Tungsten(O) Complexes

The construction of the variable temperature electrochemical cryostat equipped with non-aqueous reference half-cell with liquid junction and its utilization for the characterization of organometallic complexes is reported. New tetracarbonylbis(olefine) tungsten(O) complexes of the formula trans-W(CO)4L2 have been synthetized (where L is terminal or cyclic olefine). The electrochemical oxidation of W0/+1 mplexes have been studied by the low temperature: cyclic voltammetry, micro bulk-electrolysis and in situ ESR spectroelectrochemistry.