The possibility to alter properties of metal complexes without significant steric changes is a useful tool to tailor the reactivity of the complexes. Herein we present the synthesis of iron complexes with the tripodal phosphane ligands Triphos and Triphos(Si) and report on their different coordination properties. Whereas reaction of Triphos(Si) and FeX2 (X = Cl, Br) exclusively afforded (Triphos(Si))FeX2 with a κ(2)-coordinated ligand, the homologous C-derived Fe complexes show rapid conversion in solution to afford [(Triphos)Fe(CH3CN)3][Fe2Cl6] or [(Triphos)Fe(CH3CN)3][FeBr4], respectively. The structural conversion was found to be temperature- and solvent-dependent and was accompanied by a linear change of the overall magnetization. The different ligand influence was shown to have a significant effect on the ability of (Triphos(Si))FeCl2 and (Triphos)FeCl2 to perform the Sonogashira cross-coupling reaction of 4-iodotoluene and phenyl acetylene as well as the hydrosilylation of acetophenone. The results presented herein show the different coordination properties of two structurally homologous tripodal ligands and demonstrate the importance of geometrically controlled ligand field splitting on the stability and reactivity of metal complexes. The C/Si exchange therefore provides a simple and straightforward tool to manipulate properties and reactivity of metal complexes.

Herein, we present the synthesis of nickel complexes with tripodal phosphine ligands, CH3Si(CH2PPh2)3 and CH3C(CH2PPh2)3, and their application as catalysts in Sonogashira cross‐coupling reactions in water. Although both types of nickel complexes are based on similar tripodal ligands, the Si‐derived compounds adopt stable tetrahedral coordination geometries, whereas the C‐derived counterparts adopt a square‐planar coordination environment. This structural and electronic difference has an important effect on the catalytic properties of the complexes. Our study demonstrates that C‐derived complexes are catalytically inactive, whereas the complexes [CH3Si(CH2PPh2)3NiX2] (X = Cl–, Br–) are competent catalysts for cross‐coupling reactions of aryl halides with phenylacetylenes. This investigation reveals the importance of structural tuning on catalysis and strongly supports the theory that tetrahedral (PR3)2NiCl2 complexes are the active species in Sonogashira cross‐coupling reactions.

Herein, we report on the versatile reactions of CHC(CHPPh) as well as CHSi(CHPPh) derived Ni-complexes. While Ni[CHC(CHPPh)] complexes reveal high stability, the Ni[CHSi(CHPPh)] analogs show rapid decomposition at room temperature and afford the unprecedented pseudo-tetrahedral phosphino methanide complex 5. We provide a detailed electronic structure of 5 from X-ray absorption and emission spectroscopy data analysis in combination with DFT calculations, as well as from comparison with structurally related complexes. A mechanistic study for the formation of complex 5 by reaction with BF is presented, based on a comparison of experimental data with quantum chemical calculations. We also show a simple route towards isolable Ni(i)-complexes on the gram scale.

Herein we report on the cross-coupling reaction of phenylmagnesium bromide with aryl halides using the well-defined tetrahedral Ni(I) complex, [(Triphos)Ni I Cl] (Triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane). In the presence of 0.5 mol % [(Triphos)Ni I Cl], good to excellent yields (75-97%) of the respective coupling products within a reaction time of only 2.5 h at room temperature were achieved. Likewise, the tripodal Ni(II)complexes [(κ 2 -Triphos)Ni II Cl 2 ] and [(κ 3 -Triphos)Ni II Cl](X) (X = ClO 4 , BF 4 ) were tested as potential pre-catalysts for the Kumada cross-coupling reaction. While the Ni(II) complexes also afford the coupling products in comparable yields, mechanistic investigations by UV/Vis and electron paramagnetic resonance (EPR) spectroscopy indicate a Ni(I) intermediate as the catalytically active species in the Kumada cross-coupling reaction. Based on experimental findings and density functional theory (DFT) calculations, a plausible Ni(I)-catalyzed reaction mechanism for the Kumada cross-coupling reaction is presented.