Stereoisomeric products of electrochemical reduction of heterocyclic Fischer aminocarbene Cr(0) complexes. Development of the electrochemistry-mass spectrometry tandem approach using biphasic (acetonitrile-hexane) preparative electrolysis
Abstract
Preparative electrolyses of a series of newly synthesized Cr(0) Fischer aminocarbene complexes bearing furane, thiophene or N-methylpyrrole rings attached by position 2 or 3, have been performed in acetonitrile. For the more friendly isolation of products and for better removal of conducting salt a biphasic preparative electrolysis was developed, where the electrolyzed acetonitrile solution is overlaid by hexane.
This arrangement enables direct interconnection of the electrolyzed solution with a mass spectrometer. In all cases the only dominating products were dimeric species of the type N, N, N', N'-tetramethyl-1,2-di(hetaren-yl) ethane-1,2-diamine formed from two aminocarbene ligands after reductive splitting of the metallic part.
Neither the type of heterocycle, nor its position of attachment influences the final products. Dimeric products of all studied aminocarbene complexes are electrochemically formed as a mixture of meso-and d,l- stereoisomers in a comparable representation.
The stereoisomers were proved and characterized by MS and NMR, their separation was achieved by HPLC. The present contribution evidences the pure electrosynthetic approach to the above mentioned stereoisomers.