Synthesis and Characterization of Neutral Cyano-Bridged Dicobaloximes. (Alkyl)cobaloxime-μ-cyano-(ligand)cobaloxime
The reaction of an alkylaquocobaloxime, Co(dmgH)2(R)(H2O), with a cyano(ligand)cobaloxime, Co(dmgH)2(CN)(B), has been found to produce a series of cyano-bridged dicobaloximes of the general formula R-Co(dmgH)2-NC-Co(dmgH)2-B (I). A series of 30 such cyano-bridged dicobaloximes where R = CF3, CH3, C2H5, n-C3H7, i-C3H7, or C6H11 and B = py, py-4-NH2, py-3-Cl, NH3, or pip have been synthesized and isolated as crystalline solids. The complexes are characterized as dicobaloximes by means of elemental analysis and molecular weight data for selected compounds. Evidence for formulation as dicobaloximes containing a cyano ligand bridge is obtained from infrared data which show a 28-51-cm-1 increase in vex upon formation of the dicobaloxime from the corresponding terminal cyanocobaloxime Co(dmgH)2(CN)(B). Characterization of I as the exclusive linkage isomer formed in all 30 compounds is based on electronic spectra of selected compounds and regular variations in vCN with variations in the ligands R and B. Further characterization of the bonding in the cyano-bridged dicobaloximes described here is obtained from 1H NMR data. The relative stabilities of the cyano-bridged dicobaloximes with respect to dissociation were found to vary with the σelectron donating ability of the ligands R and B; the most stable cyano-bridged compounds are formed when R and B have a relatively small electron donating ability, as measured by the pKb and σ* values for the free ligand. © 1976, American Chemical Society. All rights reserved.
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