Metal tetraalkyl compounds

Recently, we have demonstrated that hydrogen preadsorbed on pla tinum or nickel can react with tin or lead tetraalkyl compounds re suiting in the formation of bimetallic surface entities with metal -metal interaction [5-8]. CSRs leading to the formation of bimetal lie surface species can be written as follows ... 

Diarsines and Diarsenes. Under certain conditions, the reduction of compounds with two organic groups attached to arsenic may give rise to tetraalkyl-or tetraaryldiarsines. Thus a number of diarsines have been obtained by the reduction of arsinic acids with phosphorous or hypophosphorous acid (100). Diarsines can also be prepared by the treatment of a metal dialkyl- or diarylarsenide with iodine (101) or a 1,2-dihaloethane (102). 

Cobalt provides only a few examples of this oxidation state, namely some fluoro compounds and mixed metal oxides, whose purity is questionable and, most notably, the thermally stable, brown, tetraalkyl, [Co(l-norbomyl)4]. Prepared by the reaction of C0CI2 and Li(l-norbomyl), it is the only one of a series of such compounds obtained for the first row transition... 

Chemical reactivity of unfunctionalized organosilicon compounds, the tetraalkylsilanes, are generally very low. There has been virtually no method for the selective transformation of unfunctionalized tetraalkylsilanes into other compounds under mild conditions. The electrochemical reactivity of tetraalkylsilanes is also very low. Kochi et al. have reported the oxidation potentials of tetraalkyl group-14-metal compounds determined by cyclic voltammetry [2]. The oxidation potential (Ep) increases in the order of Pb < Sn < Ge < Si as shown in Table 1. The order of the oxidation potential is the same as that of the ionization potentials and the steric effect of the alkyl group is very small. Therefore, the electron transfer is suggested as proceeding by an outer-sphere process. However, it seems to be difficult to oxidize tetraalkylsilanes electro-chemically in a practical sense because the oxidation potentials are outside the electrochemical windows of the usual supporting electrolyte/solvent systems (>2.5 V). 

Tetraalkyl titanates are the most commonly used catalysts for PBT polymerization [8], The varieties of titanates include tetraisopropyl titanate (TPT), tetrabutyl titanate (TBT) and tetra(2-ethylhexyl) titanate (TOT). Titanates effectively speed the reaction rate with few detrimental effects on the resin. Alkoxy zirconium and tin compounds, as well as other metal alkoxides, may also be used in PBT polymerization. 

On the other hand, TV-tetraalkyl derivatives151 152 are quite well known (equation 2) but only in one case have ligands of this type been reported to bind in the bidentate chelating mode to a central atom153 to form a four-membered ring. The more normal use of such compounds, as ligands, is in carbene formation154 via metal-central carbon atom bond. 

Similarly to the low chemical reactivity of (simple) alkylsilanes devoid of functional groups, the electrochemical reactivity of simple alkylsilanes is quite low. Klingler and Kochi measured the oxidation potentials of tetraalkyl derivatives of group-14-metal compounds by using cyclic voltammetry3. These compounds exhibit an irreversible anodic peak in acetonitrile. The oxidation potential (7 p) decreases in the order of Si>Ge>Sn>Pb as illustrated in Table 1. This order is the same as that of the gas-phase ionization potentials (7p). The absence of steric effects on the correlation of Ev with 7p indicates that the electron transfer should take place by an outer-sphere mechanism. Since tetraalkylsilane has an extremely high oxidation potential (>2.5 V), it is generally difficult to oxidize such alkylsilanes anodically. 

Gilman and his co-workers, however, found469 that all the lead of lead(n) salts can be converted into tetraalkyl or tetraaryl derivatives if the corresponding organic iodide (RI) was present during the reaction with the organometallic compound the metallic lead formed in the reaction is finely divided and reacts with the iodide thus ... 

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