Reactions of 13CO with Ethoxycarbonylcarbene-Bridged Dicobalt Carbonyl Complexes: [μ2-{Ethoxycarbonyl(methylene)}-μ2-(carbonyl)bis(tricarbonylcobalt)(Co-Co)] and [Di-μ2-{ethoxycarbonyl(methylene)}bis(tricarbonylcobalt)(Co-Co)]

In a CH2Cl2 solution, under an atmospheric pressure of 13CO, the bridging and terminal CO ligands of the cobalt complex[μ2‐{ethoxycarbonyl(methylene)}‐μ2‐(carbonyl)bis(tricarbonylcobalt)(Co–Co)] (1) exchange with external 13CO at the same rate. The overall rate of CO exchange is kobs (10 °C) = 9.4 × 10–3 s–1 and kobs (25 °C) = (20.1 ± 1.2) × 10–3 s–1. In the presence of excess ethanol diethyl malonate (DEM), EtO213CCH2CO2Et is formed from 1 at a much smaller rate [kDEM (10 °C) = 0.40 × 10–5 s–1 and kDEM (25 °C) = (1.2 ± 0.1) × 10–5 s–1]. On the other hand, the complex [di‐μ2‐{ethoxycarbonyl(methylene)}bis(tricarbonylcobalt)(Co–Co)](2) does not exchange its CO ligands for 13CO at all at 10 or 25 °C. In the presence of excess ethanol, diethyl malonate with natural isotopic distribution, and 13CO, ligands containing complex 1 are formed simultaneously and at the same rate, which is kobs (10 °C) = (15.2 ± 1.1) × 10–5 s–1 and kobs (25 °C) = (33.5 ± 1.8) × 10–5 s–1. Variable temperature 13C NMR spectra of 1 and 2 reveal fluxional behavior for both complexes.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)