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

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 σ-alkynyl iron complexes Cp(CO) 2 Fe-C[triple bond, length as m-dash]C-R (R = ortho -, meta -, para -pyridyl). Depending on the catalyst and reagents used, the yields of the desired σ-pyridylethynyl complexes varied from 40 to 95%. In some cases the reactions with ortho -ethynylpyridine gave as byproduct the unexpected binuclear FePd μ-pyridylvinylidene complex [Cp(CO)Fe{μ 2 -η 1 (C α ):η 1 (C α )-κ 1 (N)-C α [double bond, length as m-dash]C β (H)( o -C 5 H 4 N)}(μ-CO)PdI]. The conditions, catalysts, and reagents that provide the highest yields of the desired σ-pyridylethynyl iron compounds were determined. The methods developed allowed the synthesis of the corresponding σ-4-benzothiadiazolylethynyl complex Cp(CO) 2 Fe-C[triple bond, length as m-dash]C-(4-C 6 H 3 N 2 S) as well. Eventually, synthetic approaches to σ-alkynyl iron complexes of the type Cp(CO) 2 Fe-C[triple bond, length as m-dash]C-R (R = ortho -, meta -, para -pyridyl, 4-benzothiadiazol-2,1,3-yl) based on the Pd/Cu-catalyzed cross-coupling reactions were elaborated.