Dimeric structures transition metals

The solvated sulfenamides [Li2( BuNSC6H4Me-4)2(THF)n] (n = 2,4) have dimeric structures with a central Li2N2 ring. The coordination mode is determined by the extent of solvation of the Li" ions monosolvation allows for rj -N,S coordination whereas disolvation restricts the coordination mode to // -M Variable temperature NMR studies indicated that a dynamic exchange between these two structural types occurs in THF solution (Scheme 10.10). The dihapto coordination mode is observed exclusively in transition-metal complexes and the... 

The determination of structural properties of dimeric transition metal ion complexes from e.p.r. spectra. T. D. Smith and J. R. Pilbrow, Coord. Chem. Rev., 1974, 13,173-278 (186). 

In an earlier work, we have proposed a theoretical procedure for the spectroscopy of antiferromagnetically (AF) coupled transition-metal dimers and have successfully applied this approach to the electronic absorption spectrum of model 2-Fe ferredoxin. In this work we apply this same procedure to the [Fe2in - 82) P o - CeH48)2)2 complex in order to better understand the electronic structure of this compound. As in our previous work" we base our analysis on the Intermediate Neglect of the Differential Overlap model parameterized for spectroscopy (INDO/S), utilizing a procedure outlined in detail in Reference 4. 

The first transition metal isonitrilate complex reported was the tetrahedral Co-1 complex [Co(C=NPh )4] where Ph = 2,6-Me2C6H3,96 characterized by a crystal structure analysis. Oxidation yields the zerovalent dimer Co2(C=NPh )8, which features two bridging isonitrile groups. 

A kinetically stabilized diarylgermylene, Tb(Tip)Ge, is also stable in hexane solution with no tendency to dimerize. The structure has not yet been measured but it was characterized as the base-free mononuclear transition metal complex formed with the reactive M(CO)s. THF adduct (M = Mo,W). The crystal structure of the W complex466 shows Ge=W = 259.3 pm, Ge-Tb = 198.8 pm, Ge-Tip = 199.9 pm, CGeC = 108.4°, TbGeW = 138.9° and TipGeW = 112.2°. Thus the Ge is pyramidal and the structure is obviously the result of a balance of steric repulsions between the carbonyls, Tb, and Tip. Older work on similar Ge=W compounds, RR,Ge=W(CO)5 with RR = Cp (Cl) or (Bsi)2467, show Ge=W lengths of 251.1 and 263.2 pm, respectively, indicating the combined steric and electronic effects. 

Iminoboranes (continued) in transition metal complexes, 31 165-167 X-ray structural studies, 31 135 Iminofluorosulfinamide ions, 19 206-208 Iminofluorosulfonylamide ions, 19 200 Iminolithium complexes, solid-state structures, 37 67-75 dimers, 37 68-70 trimers, 37 68-70... 

In practice, however, already with a comparatively small number of metal atoms it is no longer feasible to investigate all possible spin states with all potential realizations by various local spin distributions. Assumptions on the interaction of the metal centers on the basis of their structural arrangement and experimental susceptibility measurements have to be made. For example, for the BS state of a tetranuclear transition-metal cluster, one has to decide which of the four metal atoms couple in an antiferromagnetic fashion with each other. Prominent coupling schemes are, e.g., the dimer-of-dimers 2-plus-2-type or the 3-plus-... 

This then was the first report of a compound in which alkyl C—H bond activation by a transition metal had occurred. In the solid state, this equilibrium is also in favor of the hydrido complex (V), and its crystal structure has recently been determined (15). It shows compound V to be a dimer (VI), the oxidative addition of the methyl group of a ligand on each ruthenium atom being to a second ruthenium atom. Presumably one reason why this occurs is because the product of intramolecular ring closure would contain a highly strained three-membered Ru—P—C ring (i.e., in monomer V). 

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