Transition-metal complexes chemical structures

Diphenyl cyclopropenone and Ni(CO)4 were reported278) to give a transition-metal complex of structure 453, which was recently re-evaluated in favor of formulation 454 from spectral and chemical evidence199 ... 

The scopes outlined above limit the purpose of this chapter, which will not cover (1) the transition metal complexation by protonated or functionalized forms of calix[4]arenes (2) the metalation of calix[4]arenes using non-transition metals and (3) chemical curiosities derived from the metalation of calix[4]arenes (some recent reviews cover these areas very well).1 In addition, the authors have been particularly careful to report only those compounds which have a well-established synthesis and a full spectroscopic and structural characterization. 

In view of the abundant experimental studies on the boration reactions catalyzed by transition metal complexes summarized above, theoretical studies to the detailed reaction mechanisms have also been carried out [25-28]. The main focus of these quantum chemical calculations has been to provide detailed structural and energetic information on the proposed reaction mechanisms. 

The number of theoretical investigations of transition metal complexes with carbodiphosphoranes and related divalent carbon(O) ligands is rather small. Quantum chemical calculations of the nickel complexes (CO) Ni-C(PPh3)2 with n = 2, 3 have been pubhshed together with experimental work which describes the S3mthesis and X-ray structure analyses of the compounds [107]. The first systematic... 

Scheme 5 Chemical structures of transition metal complexes of organic conductors...

For quantum chemistry, first-row transition metal complexes are perhaps the most difficult systems to treat. First, complex open-shell states and spin couplings are much more difficult to deal with than closed-shell main group compounds. Second, the Hartree—Fock method, which underlies all accurate treatments in wavefunction-based theories, is a very poor starting point and is plagued by multiple instabilities that all represent different chemical resonance structures. On the other hand, density functional theory (DFT) often provides reasonably good structures and energies at an affordable computational cost. Properties, in particular magnetic properties, derived from DFT are often of somewhat more limited accuracy but are still useful for the interpretation of experimental data. 

It is evident from the above table that a considerable spread of chemical shift values is observed in tellurium-transition metal complexes, but the factors that determine the chemical shift are still poorly understood and data are not available for all known structural types. The most extensive compilations of data have been provided by Rauchfuss (187) and Herrmann (191), with the point being made in the former reference that chemical shifts are extremely sensitive to changes in cluster geometry. In principle, 12sTe NMR spectroscopy is a valuable method for studying tellurium-transition metal clusters in solution, but it is clear that more data are required before unambiguous structural assignments can be inferred. 

Transition metal complexes containing fluorinated ligands date back to the initial explosive development of organometallic chemistry in the period from 1950 to 1970, and some early reviews contain a great deal of useful and relevant information (3,6,7). Early work clearly established that these compounds do indeed exhibit dramatically different structural, bonding, and chemical... 

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