Reactions of ¹³CO with Ethoxycarbonylcarbene‐Bridged Dicobalt Carbonyl Complexes: [μ₂‐{Ethoxycarbonyl(methylene)}‐μ₂‐(carbonyl)bis(tricarbonylcobalt)(<i>Co</i>–<i>Co</i>)] and [Di‐μ₂‐{ethoxycarbonyl(methylene)}bis(tricarbonylcobalt)(<i>Co</i>–<i>Co</i>)]

Abstract

Abstract In a CH 2 Cl 2 solution, under an atmospheric pressure of 13 CO, the bridging and terminal CO ligands of the cobalt complex[μ 2 ‐{ethoxycarbonyl(methylene)}‐μ 2 ‐(carbonyl)bis(tricarbonylcobalt)( Co – Co )] ( 1 ) exchange with external 13 CO at the same rate. The overall rate of CO exchange is k obs (10 °C) = 9.4 × 10 –3 s –1 and k obs (25 °C) = (20.1 ± 1.2) × 10 –3 s –1 . In the presence of excess ethanol diethyl malonate (DEM), EtO 2 13 CCH 2 CO 2 Et is formed from 1 at a much smaller rate [ k DEM (10 °C) = 0.40 × 10 –5 s –1 and k DEM (25 °C) = (1.2 ± 0.1) × 10 –5 s –1 ]. On the other hand, the complex [di‐μ 2 ‐{ethoxycarbonyl(methylene)}bis(tricarbonylcobalt)( Co – Co )]( 2 ) does not exchange its CO ligands for 13 CO at all at 10 or 25 °C. In the presence of excess ethanol, diethyl malonate with natural isotopic distribution, and 13 CO, ligands containing complex 1 are formed simultaneously and at the same rate, which is k obs (10 °C) = (15.2 ± 1.1) × 10 –5 s –1 and k obs (25 °C) = (33.5 ± 1.8) × 10 –5 s –1 . Variable temperature 13 C NMR spectra of 1 and 2 reveal fluxional behavior for both complexes.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2006)