Complexes of Iron(II) with silylated pentalene ligands; building blocks for homo- and heterobimetallics

A range of iron(II) complexes incorporating the silylated pentalene ligands (Pn†H = 1,4-{SiiPr3}2C8H5 and Pn† = 1,4-{SiiPr3}2C8H4) have been investigated as model molecules/building blocks for metallocene-based polymers. Six complexes have been synthesised and extensively characterised by a range of techniques, including by cyclic voltammetry and X-ray diffraction studies. Amongst these compounds are the homobimetallic [Cp∗Fe]2(μ-Pn†) which is a fused analogue of biferrocene, and the 3d/4s heterobimetallic [Cp∗Fe(η5-Pn†)][K] which forms an organometallic polymer in the solid state. DFT calculations on model mono-Fe(η5-Pn) compounds reveal the charge densities on the uncoordinated carbon atoms of the pentalene ligand, and hence the potential for incorporating these units into heteronuclear bimetallic complexes is assessed

Electronic communication through unsaturated hydrocarbon bridges in homobimetallic organometallic complexes.

Metal-metal interactions have been studied in a large number of different carbon bridged homobinuclear complexes. The bridging ligands considered are sp2- and/or sphydrocarbon chains, bridging aromatic rings linked directly as fulvalene and fulvalene-like; and fused aromatic spacers as indenyl, permethylpentalene-diide, and permethylfluorene between others. The efficiency of the intramolecular electronic communication between the metal centers depends on the nature of the metals, their oxidation state, the strength of the coupling between the acceptor and the donor sites, the ancillary ligands and the structure of the bridging ligand. Generally, the electronic communication decreases with increasing the distance between the donor and the acceptor sites. Also, electronic coupling and other donor-acceptor interactions are stronger through alkene than alkyne bridges. Bridging aromatic rings and fused aromatic linkers are also suitable spacers to promote metal-metal interactions. However, if their planarity is broken due to steric effects, the loss of aromaticity decreases the electronic communication between the metal centers. Metal-metal interactions have been mainly evaluated on the basis of IR, EPR, optical, and electrochemical measure-ments of the mixed-valence species. According to these data, the numerous complexes presented on this review have been categorized following the Robin and Day classification. © 2010 American Chemical Society

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Synthesis, Structure, and Ligand Exchange Reactions of Tetramethyleneethane Complexes of Cobalt

The synthesis of (η3:η3-TME)[Co(CO) 3]2 (1) was achieved using 2,3-bis(bromomethyl)-1,3- butadiene (TMEBr2) as the tetramethyleneethane (TME) ligand precursor and Na[Co(CO)4]. Solution NMR studies suggested an η3:η3-configuration, which has been confirmed in the solid state by single-crystal X-ray diffraction studies. The series of complexes (η3:η3-TME)[Co(CO)2PR 3]2 (R = Me, 2; R = Et, 3; R = n-Bu, 4; R = Ph, 5; R = OPh, 6) were also synthesized by ligand exchange reactions, demonstrating that only one carbonyl may be exchanged for a phosphine group on each metal center. The η3:η3-configuration of the tetramethyleneethane ligand in these complexes was determined by crystallographic studies. The effect of the electron-donating properties of PR3 was studied by cyclic voltammetry (CV) and infrared spectroscopy. The greatest degree of electron donation was seen when R = Et (3) and lowest when R = Ph (5) or R = OPh (6). Electronic communication between the metal centers was observed by CV. The chemical oxidation of 1 resulted in a highly unstable species that decomposed to {[(CO)2Co]TME[Co(CO) 3]}+[BF4]- (1+d), determined by its crystal structure. The synthesis of (η4: η4-TME)[CoCp*]2 (7) has been achieved using a dipotassium 2,3-bis(methylene)-1,3-butanediyl (TMEK2) synthon. NMR studies suggested that 7 adopts an unusual η4:η4- configuration, which was confirmed with the aid of crystallographic studies. DFT calculations were performed in order to rationalize the bonding for 1, 7, and hypothetical (η4:η4-TME)[CoCp]2 (8). The large energy difference between the two coordination isomers 1 and 1a confirmed the η3:η3-configuration. For isomers 7/7a and 8/8a, the energy difference between the two isomers (ca. 15 kJ mol -1) is in favor of the η4:η4- configuration. For complexes 1+ and 8+, the calculations suggested complete delocalization on the system when one electron was removed. © 2010 American Chemical Society