Catalyzed M-C coupling reactions in the synthesis of s-(pyridylethynyl)dicarbonylcyclopentadienyliron complexes

Abstract

The reactions between terminal ethynylpyridines, (trimethylsilyl)ethynylpyridines and cyclopentadienyliron dicarbonyl iodide were studied under Pd/Cu-catalyzed conditions to develop a synthetic approach to the s-alkynyl iron complexes Cp(CO)2Fe-C?C-R (R =ortho-,meta-,para-pyridyl). Depending on the catalyst and reagents used, the yields of the desired s-pyridylethynyl complexes varied from 40 to 95%. In some cases the reactions withortho-ethynylpyridine gave as byproduct the unexpected binuclear FePd µ-pyridylvinylidene complex [Cp(CO)Fe{µ2-?1(Ca):?1(Ca)-?1(N)-Ca?Cß(H)(o-C5H4N)}(µ-CO)PdI]. The conditions, catalysts, and reagents that provide the highest yields of the desired s-pyridylethynyl iron compounds were determined. The methods developed allowed the synthesis of the corresponding s-4-benzothiadiazolylethynyl complex Cp(CO)2Fe-C?C-(4-C6H3N2S) as well. Eventually, synthetic approaches to s-alkynyl iron complexes of the type Cp(CO)2Fe-C?C-R (R =ortho-,meta-,para-pyridyl, 4-benzothiadiazol-2,1,3-yl) based on the Pd/Cu-catalyzed cross-coupling reactions were elaborated.