Ulrich Kölle

Oxidation of Alcohols by [Cp*Rh(ppy)(OH)]+

Rh(III) polypyridine complexes ([Cp*Rh(ppy)(O2H)]2+; ppy = 2,2′-bipyridine, 2,2′-bipyridine-4,4′-dicarboxylate, o-phenanthroline, tetrahydro-4,4′-dialkyl-bis-oxazole) oxidize in organic or aqueous alkaline solution primary and secondary alcohols to aldehydes or ketones and are thereby reduced to the Rh(I) complexes Cp*Rh(ppy). The Rh(III) form can be regenerated by oxidants like pyruvate or oxygen, making the reaction quasi-catalytic. The reaction follows an autocatalytic pathway; hydrogen transfer from the α-CH2 group of an alcoholate complex [Cp*Rh(ppy)(OR)]+ to Cp*Kh(I)(ppy) is suggested to yield the Rh(II) intermediate Cp*Rh(ppy)H as the key and rate determining step. The knowledge of Rh(III)/Rh(I) redox potentials allows to estimate the thermodynamic driving force of the reaction which is not more than about 300 mV.

Übergangsmetallkomplexe instabiler Ylide, X [1] Chemische und elektrochemische Untersuchungen zu den Redox-Eigenschaften cyclischer Tetracarbonylchrom-Ylidchelatkomplexe / Transition Metal Complexes of Unstable Ylides, X [1] Chemical and Electrochemical Investigations of the Redox Properties of Cyclic Tetracarbonylchromium-Ylide-Chelate-Complexes

Abstract Treatment of the ylide chelate complexes (CO)4 (1) with (C5H5)2Fe+PF6- leads to the organometallic radical cations 2. The oxidation process of 1 is also checked electrochemically by means of cyclovoltammetry, which exhibits a reversibel one electron oxidation between -0.1 and +0.3 V vs. SCE. These potentials are more negative than in any other complex of the general type Cr(CO)4L2 (L e.g. = PR3, CNR).