Tetrakis complexes transition metals

Biuret (bu) co-ordinates transition metals in both neutral and anionic forms. Compounds containing neutral bu include both bis- and tetrakis-complexes. The latter are limited to the larger cations of the group II [e.g., [Sr(bu)4]2+ [9] and lanthanide groups e.g., [Sm(bu)4]2+ [ 10,11]. Only the former are considered in detail in this review, together with bis-complexes containing anionic bu as they have the greater potential for formation of 1-D chains and 2-D sheets. 

At the time of our investigation the only known coordination compounds of chlorophosphines (aside from phosphorus trichloride complexes) were the nickel-(0) compounds, tetrakis(methyldichlorophosphine)nickel-(0) (20) and tetrakis-phenyldichlorophosphine) nickel- (0) (17). Tetrakis (methyldichlorophosphine) -nickel-(0) is noteworthy in that it represents a still rare example of the direct reaction of a ligand with an elemental transition metal to give a complex, while tetrakis (phenyldichlorophosphine) nickel- (0), like tetrakis (trichlorophosphine) -nickel-(0), was obtained readily via the carbonyl. AD chlorophosphine-nickel-(O) complexes, including the phosphorus trichloride complex, Ni(PCl3)4, are compounds relatively stable in the atmosphere, but show poor stability in almost any organic solvent, even under strictly anaerobic conditions. 

The problem of terminal addition (anti-Markovnikov) of HCN to isolated unactivated double bonds was not solved until carbon monoxide-free, low-valent transition metal complexes became available. During the mid 1960s, W. C. Drinkard allowed 1-hexene to react with HCN in the presence of tetrakis(triethylphosphite)nickel(0) and the resulting product mixture contained a small amount of the terminal addition product n-heptanenitrile, and Drinkard and Lindsey found that the reaction with 3-pentenenitrile produced ADN (7). 

A recent report 121) on the reactions of tetrakis(trimethylphosphine) iron, Fe(PMe3)4, with carbon dioxide reveals a rich and varied chemistry, illustrating many of the reaction modes of C02 with low-valent transition metal complexes. Two primary reactions of C02 with Fe(PMe3)4 are noted, as a consequence of the two isomers in equilibrium (49). 

The third order optical susceptibility was measured for a series of transition metal tetrakis(cumylphenoxy)phthalocyanines at 1.064 pm. Metal substitution caused a dramatic variation in the third order susceptibility. The largest s were found in the Co, Ni, and Pt complexes. Metal substitution introduces low lying electronic states which can enhance the susceptibility in these phthalocyanines. A strategy for enhancing the figure of merit, x(3)/a> of centrosymmetric nonlinear optical materials is suggested. 

ECL from inorganic chromophores has been observed from a variety of transition metal complexes of ruthenium, osmium, palladium, platinum, and a few other transition metal chromophores, some of which are listed in Tables 2 and 3. For example, ECL has been observed from tetrakis(pyrophosphito)diplatinate(II),... 

Pyrazine derivatives were again popular as ligands in crystallographic studies of transition metal complexes. These complexes included silver(I) alkylpyrazine sulfonates 83 <07IC7299>, tetrakis[3-(pyrazin-2-yloxy)pyridinc-AiVJdithiocyanatomanganese <07AX(E)m441>,... 

Under remarkably mild conditions aromatic cyanides can be prepared from halogen compounds with alkali metal cyanides in the presence of transition metal complexes. Complexes of palladium and nickel are particularly useful, for instance tetrakis(triphenylphosphine)palladium(0) (6), tris(triphe-nylphosphine)nickel(O) (7) or trun -dichlorobis(triphenylphosphine)nickel(II) (8 Scheme 7). 

Dialkyl metallocenes and other dialkyl Group 4 transition metal complexes are useful as precatalysts in combination with co-catalysts such as tris(perfluoro-aryl)boranes or tetrakis(periluoroaryl)borate salts [18]. Recently, an expedient procedure for the production of dimethyl metallocenes and Cp-amido dimethyl metal complexes in high yields and purity has been reported. The direct synthesis of Group 4 dimethylmetallocenes [19] consists of the one-pot reaction between the r-ligand, a 2-fold excess of MeLi, and MtCU. This simple method produces the dimethylated complexes in higher overall yield, and saves on reaction time and solvents, compared to the classic two-step route, which consists in the synthesis of the metallocene dichloride followed by its methylation with 2 equiv. MeLi. 

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