Synthesis of (1-alkynyl)dicarbonylcyclopentadienyliron complexes by palladium-catalyzed Sonogashira-type carbon–iron bond formation

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)₂Fe–C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> 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{μ₂-η¹(C_α):η¹(C_α)-κ¹(N)-C_α Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C_β(H)(o-C₅H₄N)}(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)₂Fe–CC–(4-C₆H₃N₂S) as well. Eventually, synthetic approaches to σ-alkynyl iron complexes of the type Cp(CO)₂Fe–CC–R (R = ortho-, meta-, para-pyridyl, 4-benzothiadiazol-2,1,3-yl) based on the Pd/Cu-catalyzed cross-coupling reactions were elaborated.

Two approaches were developed for the synthesis of iron σ-pyridylethynyl complexes based on Pd/Cu- and Pd-catalyzed Fe–C coupling reactions.

Crystal structure of μ-carbonyl-1:2κ2C:C-carbonyl-1κC-(1η5-cyclo-penta-dien-yl)iodido-2κI-[μ-2-(pyridin-2-yl)ethene-1,1-diyl-1κC1:2κ2N,C1]ironpalladium(Fe-Pd) benzene monosolvate

The reaction of Cp(CO)2FeI with 2-ethynyl-pyridine under Sonogashira conditions [5% PdCl2(PPh3)2, 10% CuI, THF-NEt3 (2:1)] afforded the title binuclear μ-pyridyl-vinyl-idene FePd complex (FePd1) as a benzene solvate, [FePd(C5H5)(C7H5N)I(CO)2]·C6H6, in a very low yield rather than the expected iron o-pyridyl-ethynyl complex Cp(CO)2Fe-C≡C-(2-C5H4N). The Fe and Pd atoms in FePd1 are bridged by carbonyl and pyridyl-vinyl-idene ligands, the pyridyl N atom being bonded to the palladium atom. The use of equimolar amounts of PdCl2 increases the yield of FePd1 to 12%. The reaction pathway leading to FePd1 is proposed.

Iron(0) mediated C–H activation of 1-hexyne: a mechanistic study using time-resolved infrared spectroscopy

Photolysis of an iron tricarbonyl complex in the presence of 1-hexyne results in the formation of an intermediate Fe-(η²-1-hexyne) species which converts to the C–H activated Fe–CCR product.