Ni–Fe and Pd–Fe Interactions in Nickel(II) and Palladium(II) Complexes of a Ferrocene-Bridged Bis(imidazolin-2-imine) Ligand
datasetposted on 2015-12-21, 00:00 authored by Kristof Jess, Dirk Baabe, Thomas Bannenberg, Kai Brandhorst, Matthias Freytag, Peter G. Jones, Matthias Tamm
The bis(imidazolin-2-imine) ligand N,N′-bis(1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene)-1,1′-ferrocenediamine, fc(NIm)2 (1) was prepared. Its reaction with [NiCl2(dme)] (dme = 1,2-dimethoxyethane) or [PdCl2(MeCN)2] afforded the tetrahedral, paramagnetic complex [(1-κ2N,N′)NiCl2] (6a) or the diamagnetic, square-planar complex [(1-κ2N,N′)PdCl2] (6b), respectively. For the latter, slow rearrangement to the ionic complex [(1-κFe,κ2N,N′)PdCl]Cl, Cl, was observed, which was followed by 1H NMR and UV/vis spectroscopy. Treatment of Cl with NaBF4 afforded BF4; the palladium atoms in both cations adopt square-planar environments with short Fe–Pd bonds (ca. 2.65 Å). In addition, a series of dicationic complexes of the type [(1-κFe,κ2N,N′)ML](BF4)2 (8a: M = Ni, L = MeCN; 8b: M = Pd, L = MeCN; 9a: M = Ni, L = PMe3; 9b: M = Pd, L = PMe3) was prepared from 6a (M = Ni) or BF4 by chloride abstraction with NaBF4 or AgBF4 in the presence of acetonitrile or trimethylphosphine, respectively. In the presence of triphenylphosphine, the palladium(II) complex [(1-κFe,κ2N,N′)Pd(PPh3)](BF4)2 (10) was isolated. Iron–nickel and iron–palladium bonding in these complexes was studied experimentally by NMR, UV/vis, and Mössbauer spectroscopy and by cyclic voltammetry. Detailed DFT calculations were carried out for the cations [(1-κFe,κ2N,N′)M(MeCN)]2+ in the 8a/8b couple, with Bader’s atoms in molecules theory revealing the presence of noncovalent, closed-shell metal–metal interactions. Potential energy surface scans with successive elongation of the Fe–M bonds allow an estimation of the iron–metal bond dissociation energies (BDE) as BDE(Fe–Ni) = 11.3 kcal mol–1 and BDE(Fe–Pd) = 24.3 kcal mol–1.