Attila Sisak

Pair-wise interactions by gas chromatography. VII. Interaction free enthalpies of solutes with secondary alcohol groups

A polar type liquid having a secondary alcohol substituent on a branched alkane skeleton, SOH, was used as stationary phase. The molecules of this stationary phase are nearly isomorphous and isochor with those of the branched alkane, C78, elected as standard, i.e., the molecules of both solvents have nearly the same form and the same size. Partition properties of 158 chosen molecular probes were measured by gas chromatography on SOH and on an SOH-C78 mixture having a volume fraction of thetaOH = 0.5. Based on the resulting data an interaction free enthalpy could be calculated, i.e., the additional effect of the secondary alcohol to partition. Comparison with data determined earlier on another member of this solvent family, POH, having a primary alcohol as interacting group gives information about the effect of steric hindrance on polar type solute-solvent interaction free energies.

The formation of catalytically active species by the reduction of palladium carboxylate phosphine systems: i. Hydrogenations

Abstract Palladium carboxylates were hydrogenated in the presence of tertiary phosphines (P/Pd = 1 1 ) under ambient conditions. Phenyl-substituted phosphines gave benzene and palladium clusters with P—Pd covalent bonds, e.g. [Pd5(PPh)2(PPh3)2], while the products from more basic trialkylphosphines proved to be palladium hydride clusters. The former systems were active hydrogenation catalysts for various alkynes and conjugated dienes, and the latter catalysed the hydrogenation of 1-alkenes as well. Only traces of alkanes could be detected as long as alkynes or dienes were present, and internal alkynes gave cis-alkenes selectively.

Mechanistic studies on the disproportionation of dicobald octacarbonyl with hard Lewis bases

Abstract The disproportionation of Co 2 (CO) 8 and pyridine are fractional, and depend on the partial CO pressure. A radical mechanism with partial chain character is proposed. The reaction appears to involved inner sphere electron transfer processes.

The reaction of alkoxides with dicobalt octacarbonyl: Trapping of the Co(I) intermediate in the disproportionation (“base reaction”) with a hardLewis base

Dicobalt octacarbonyl reacts with alcoholates (RO−) yielding alkoxycarbonylcobalt tetracarbonyls,ROC(O)Co(CO)4.ZusammenfassungDicobaltoctacarbonyl reagiert mit Alkoxiden (RO−) zu Alkoxycarbonylcobalt tetracarbonylen,ROC(O)Co(CO)4.

Darstellung und Eigenschaften Heterobimetallischer Komplexe — Kristallstruktur von [(acac)3ZrOCCo3(CO)9]

Abstract ‘Early–late’ bimetallic complexes of the type [(acac) 3 M–OCCo 3 (CO) 9 ] (M=Zr ( 1 ), Hf ( 2 )) are formed in reactions between (acac) 3 MCl and NaCo(CO) 4 . These complexes exhibit a remarkable stability. They were characterized by their IR, 1 H- and 13 C-NMR spectra. The crystal structure of 1 was determined.

Reaction of silylcobalt tetracarbonyls with oxiranes. Kinetics and mechanism

It has been shown that (β-silyloxyacyl)cobalt tetracarbonyls are formed in the reaction between silylcobalt tetracarbonyl, terminal oxirane, and carbon monoxide. The linear acyl isomer is obtained with a regioselectivity of about 80%, which is practically independent of the nature of the substituents in the silyl group. Kinetic studies have revealed a first order dependence on Ph3SiCo(CO)4, an increasing order with respect to ethyloxirane, and zero order with respect to [Co(CO)4]− and CO. A mechanism involving a rapid formation of a tight ion pair, rate-determining internal SN2 type substitution, and fast insertion of CO is suggested.

Kinetics of the ring-opening carbonylation of ethyloxirane with hydrido tetracarbonyl cobalt

Abstract The rate of CO uptake in the reaction of HCo(CO) 4 with ethyloxirane, which gives (3-hydroxypentanoyl)cobalt tetracarbonyl as the major product in an n-octane/methyl isobutyl ketone solvent mixture at 15° C, is first order with respect to HCo(CO) 4 and ethyloxirane, and independent of the concentration of CO(CO) 4 − 4 or CO. The reaction is faster with DCo(CO) 4 . A preequilibrium ion pair formation and a subsequent rate-determining internal substitution, followed by fast CO insertion, accounts for these results.

Stoichiometric hydrogenations using tetracarbonylcobaltate(—I)

Abstract Methanolic solutions of tracarbonylcobaltate(—I) in the presence of an acid are simple and useful reducing agents for the selective hydrogenation of conjugated carbon-carbon double bonds. The reaction has the following stoichiometry:

Silylations of α,β-unsaturated and aromatic carbonyl compounds with cobalt carbonyls

Abstract [η 3 -η 5 -(Silyloxy–alkenyl)]-cobalt carbonyls and various silyl ethers were formed in the cobalt carbonyl mediated silylations of α,β-unsaturated and aromatic carbonyl compounds. A silyloxonium tetracarbonylcobaltate tight ion pair was suggested as a common intermediate, which provides the products through a radical pair in the cases of aromatic aldehydes and ketones.

O-silylation of acylcobalt tetracarbonyls: synthesis of a new type of dinuclear µ2-hydroxycarbene cobalt carbonyl derivatives

O-Silylation of acylcobalt tetracarbonyls, RC(O)Co(CO)4, gives the dinuclear carbene complexes [{µ2-RC(OSiR′3)}(µ2-CO)Co2(CO)6], of which one derivative (R = Me, R′= Ph) was characterized by X-ray diffraction.