A Joint Experimental and Theoretical Study of Cation−π Interactions: Multiple-Decker Sandwich Complexes of Ferrocene with Alkali Metal Ions (Li + , Na + , K + , Rb + , Cs + )
ABSTRACT A systematic study of cation-pi interactions between alkali metal ions and the cyclopentadienyl ring of ferrocene is presented. The alkali metal (Li+, Na+, K+, Rb+, Cs+) salts of the ditopic mono(pyrazol-1-yl)borate ligand [1,1'-fc(BMe2pz)2]2- crystallize from dimethoxyethane as multiple-decker sandwich complexes with the M+ ions bound to the pi faces of the ferrocene cyclopentadienyl rings in an eta5 manner (fc = (C5H4)2Fe; pz = pyrazolyl). X-ray crystallography of the lithium complex reveals discrete trimetallic entities with each lithium ion being coordinated by only one cyclopentadienyl ring. The sodium salt forms polyanionic zigzag chains where each Na+ ion bridges the cyclopentadienyl rings of two ferrocene moieties. Linear columns [-CpR-Fe-CpR-M+-CpR-Fe-CpR-M+-](infinity) (R = [-BMe2pz]-) are established by the K+, Rb+, and Cs+ derivatives in the solid state. According to DFT calculations, the binding enthalpies of M+-eta5(ferrocene) model complexes are about 20% higher as compared to the corresponding M+-eta6(benzene) aggregates when M+ = Li+ or Na+. For K+ and Rb+, the degree of cation-pi interaction with both aromatics is about the same. The binding sequence along the M+-eta5(ferrocene) series follows a classical electrostatic trend with the smaller ions being more tightly bound.
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ABSTRACT: Mit dem Periodensystem als „Baukasten” sind Elementensembles zugänglich, die Theoretiker und Anwender inspirieren. Die klassischen Arbeitsfelder der Koordinationschemie erhalten neue Impulse. Ein Leitmotiv der bioanorganischen Chemie sind hochvalente Eisenverbindungen.Nachrichten aus der Chemie 03/2006; 54(3):214 - 233. DOI:10.1002/nadc.20060540306 · 0.20 Impact Factor
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ABSTRACT: Cited By (since 1996): 13, Export Date: 14 February 2013, Source: ScopusAngewandte Chemie International Edition 02/2007; 46(35):6732-4. DOI:10.1002/anie.200702148 · 11.26 Impact Factor
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ABSTRACT: This work describes a systematic experimental and theoretical study of the properties of two series of isoelectronic and largely isosteric ligands, namely PPh2Me, PPh2BH3–, and SiPh2Me– and SPtBu3, SPtBu2BH3–, and SSitBu3–. In addition, we have also investigated the oxo derivatives OPPh2BH3– and OSiPh2Me–. Based on X-ray crystal structure determinations (Fe–CO and C–O bond lengths) as well as NMR [e.g. δ(13CO)] and IR [ν(CO)] spectroscopic investigations of the corresponding [CpFe(CO)2]+ complexes, we can conclude that, with respect to electron donor strength, phosphanyl borohydrides occupy an intermediate position between phosphanes (weakest donors) and silyl ligands (strongest donors). The same is true for the thio derivatives, although the differences are smaller. In the reaction with [CpFe(CO)2]+, the oxo derivative OPPh2BH3– transfers a hydride ion rather than forming a stable [CpFe(CO)2(OPPh2BH3)] complex. The tendency to undergo hydride-transfer reactions was studied by density functional calculations for the series PtBu2BH3–, OPtBu2BH3–, and SPtBu2BH3–. The results reveal that OPtBu2BH3– is the strongest and SPtBu2BH3– the weakest hydride donor, in accordance with the experimental observations. Theoretical analysis indicates that the three derivatives PPh2Me, PPh2BH3–, and SiPh2Me– are truly isolobal species despite variations in their charge distributions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)Berichte der deutschen chemischen Gesellschaft 05/2007; 2007(14):1989 - 2003. DOI:10.1002/ejic.200601207