Reactions of ~(13)CO with Ethoxycarbonylcarbene-Bridged Dicobalt Carbonyl Complexes:[mu_2-{Ethoxycarbonyl(methylene)}-mu_2-(carbonyl)-bis(tricarbonylcobalt)(Co-Co)] and [Di-mu_2-{ethoxycarbonyl(methylene)} -bis(tricarbonylcobalt)(Co-Co)]

摘要

In a CH_2Cl_2 solution,under an atmospheric pressure of ~(13)CO,the bridging and terminal CO ligands of the cobalt complex [mu_2-{ethoxycarbonyl(methylene)}-mu_2-(carbonyl)bis(tricarbon-ylcobalt)(Co-Co)] (1)exchange with external ~(13)CO at the same rate.The overall rate of CO exchange is k_(obs)(10 deg C)=9.4x10~-3)s~(-1)and k_(obs)(25 deg C)=(20.1 +-1.2)x 10~(-3)s~(-1).In the presence of excess ethanol diethyl malonate (DEM),EtO_2~(13)CCH_2CO_2Et is formed from 1 at a much smaller rate [k_(DEM)(10deg C)=0.40x10~(-5)s~(-1)and k_(DEM)(25 deg C)=(1.2+-0.1)x10~(-5)s~(-1)].On the other hand,the complex [di-mu_2-{ethoxycarbonyl(methylene)}bis(tricarbonylcobalt)(Co-Co)] (2)does not exchange its CO ligands for ~(13)CO at all at 10 or 25 deg 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 deg C)=(15.2+-1.1)x 10~(-5)s~(-1)and k_(obs) (25 deg C)=(33.5+-1.8)x 10~(-5) s~(-1).Variable temperature ~(13)C NMR spectra of 1 and 2 reveal fluxional behavior for both complexes.