Übergangsmetall-Organoverbindungen in superkritischem Kohlendioxid: Löslichkeiten,Reaktionen, Katalysen

Organometallics of Transition Metals in Supercritical Carbon Dioxide: Solubilities, Reactions, Catalysis Monomeric compounds of the type Cp₂M (p. e. M = Fe, Co, Ni) are soluble in liquid or supercritical CO₂ (”︁scCO₂”︁”︁) without any reaction with the solvent. The polymeric compounds zincocene or manganocene form with CO₂ insoluble CO₂ insertion products. As well homoleptic metal carbonyls as a number of ligand-stabilized metal carbonyls are also soluble in scCO₂. Fe(CO)₅ reacts photochemically in this solvent to Fe₂(CO)₉ and thermically to Fe₃(CO)₁₂. The highly reactive (cdt)Ni(0) (cdt: cyclododeca-1,5,9-triene) is soluble in liquid CO₂. A reaction with the solvent could not been observed. Solved in scCO₂ (cdt)Ni reacts thermically to form Ni after a short time. CpCo(cod) catalyzes slowly the cyclo-cooligomerization of hex-3-yne with acetonitrile to form 2,3,4,5-Tetraethyl-6-methylpyridine. Propargylic alcohol reacts under formation of cyclotetrameres with a selectivity of 90% using (cod)₂Ni or (cdt)Ni as catalysts, hex-3-yne in and with carbon dioxide under selective formation of tetraethyl-2-pyrone when the catalyst system R₃P/(cod)₂Ni (R: Me, Et) is used. In situ IR measurements show that the catalytically active species will be desactivated by formation of nickel carbonyl complexes. The catalytic oxidation of cyclooctene to form cycloocteneoxid with t-BuOOH using Titan(IV)-isopropylate as soluble catalyst proceeds less selectively, however in the presence of Mo(CO)₆ the epoxid is formed in good yields and in a highly selective reaction.