Ni-Fe and Pd-Fe Interactions in Nickel(II) and Palladium(II) Complexes of a Ferrocene-Bridged Bis(imidazolin-2-imine) Ligand

作者：Jess Kristof; Baabe Dirk; Bannenberg Thomas; Brandhorst Kai; Freytag Matthias; Jones Peter G; Tamm Matthias^*

来源：Inorganic Chemistry, 2015, 54(24): 12032-12045.

DOI：10.1021/acs.inorgchem.5b02457

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-kappa N-2,N')NiCl2] (6a) or the diamagnetic, square-planar complex [(1-kappa N-2,N')PdCl2] (6b), respectively. For the latter, slow rearrangement to the ionic complex [(1-kappa Fe,kappa N-2,N')PdCl]Cl, [7]Cl, was observed, which was followed by H-1 NMR and UV/vis spectroscopy. Treatment of [7]Cl with NaBF4 afforded [7]BF4; the palladium atoms in both cations adopt square-planar environments with short Fe-Pd bonds (ca. 2.65 angstrom). In addition, a series of dicationic complexes of the type [(1-kappa Fe,kappa N-2,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 [7]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-kappa Fe,kappa N-2,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 Mossbauer spectroscopy and by cyclic voltammetry. Detailed DFT calculations were carried out for the cations [(1-kappa Fe,kappa N-2,N')M(MeCN)](2+) in the 8a/8b couple, with Baders 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).

• 出版日期2015-12-21