Carbyne complexes properties

The carbyne complexes [Mo(=CBu )(SAr)3] (SAr = TMT, TIPT) have been synthesized by adding 3 eq of Li[SAr] to [Mo(=CBu )Cl3(dme)] (dme = dimethoxyethane). The analogous W derivatives were made by a slightly modified route (32). The initial aim was to probe the acetylene metathesis catalytic properties of the complexes [M ( Bu KSArlg] (M = Mo, W SAr = TMT, TIPT). However, none of the complexes were active for metathesis, which was in contrast to the high activity of the analogous alkoxide compounds for metathesis. This was attributed to the stronger electron donation power of thiolate, which reduces the electrophilic nature of the metal center (32). 

Stable paramagnetic carbynes have also been obtained, usually by electrochemical methods which proved to be successfully applicable to the investigation of the electronic properties of the carbyne ligands (which are shown to behave as rather strong net electron acceptors) and to their activation, in particular towards N-H or C-H bond cleavage. Although electrochemical studies of carbyne complexes have been reported only very rarely, this study illustrates some of their potentialities in this field. 

In a study by Brower, Templeton, and Mingos the electronic properties of bis-oxo, oxo-carbyne, and bis-carbyne metal complexes were compared... 

Alkylidyne-metal complexes have traditionally been divided into two categories, according to the oxidation state of the metals, in a manner directly analogous to the classification of the very large number of known alkylidene-metal species (19a,b). Hence Fischer-type alkylidyne complexes involve metals in low oxidation states, while Schrock-type complexes generally involve more electropositive metals with higher oxidation states (13). However, the properties of some of the numerous carbyne-metal complexes that have been characterized since the early days have in many cases blurred the distinction between the two classes (12a). 

Veillard [19] covers a similar range of molecules but from the Hartree-Fock and post-HF view. The discussion is organised more in terms of molecular properties. Thus, he deals with metal carbonyls, carbides, cyanides, C02 complexes, alkyls, carbenes, carbynes, alkenes, alkynes and metallocenes under the headings of electronic states, electronic spectra, optimised geometries, binding energies, Ionisation Potentials and Electron Affinities, nature of M-L bonding and other properties (e.g. vibrational spectra, dipole moments and electron distributions). 

A similar dichotomy of bonding models exists for other classes ofTM compounds where the chemical bond can be discussed either in terms of electron-sharing interactions TM-R or as donor-acceptor bond TM-L. Examples are TM compounds with carbenes CR2 or carbynes CR as ligands, which can be considered as either Fischer-type complexes or as Schrock-type alkylidenes and alkylidynes [31, 32). We want to emphasize that the two bonding models should be considered as sketches of two extreme situations, whereas the electronic situation of real molecules has components of both forms. The value of such dichotomic models lies in the fact that they establish an ordering scheme, which is very useful for describing the physical and chemical properties of molecules. 

ABSTRACT. The redox properties of a variety of isocyanide, rutrile arvj alkyne-derived vinylidene and phenylatlene complexes, commonly with an electron-rich Re(l) or Fe(ll)-phosphinic centre, as well as of the derived protonated species (with aminocarbyne, methyteneamido, carbyne, i vinyl or hydride ligands), as studied by < dic voltammetry and controlled potential electrolysis in aprotic media, are discussed in terms of ligand and metal site effects on the redox potential, and the values of the electrochemical parameter which measures the ligand net etectron-donor/acceptor character are also presented for these ligands. Expressions are indicated which allow to predict the oxidation potential for the octahedral-type 18-electron complexes or 3) or [MsU-1-... 

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