Metalloids, organometallic compounds

A quite surprising development, even to experienced workers in elemental-fluorine chemistry, has been the synthesis of trifluoromethyl organometallic compounds by direct fluorination of metal alkyls (25). Even more surprising is the fact that, for certain metal and metalloid systems, such as the reaction of elemental fluorine with tetramethyl-germane, this t5rpe of low-temperature synthesis is a practical method 26) for the laboratory preparation of the perfluoro analog. 

Organometallic compounds can be hydrolyzed by acid treatment. For active metals such as Mg, Li, and so on, water is sufficiently acidic. The most important example of this reaction is hydrolysis of Grignard reagents, but M may be many other metals or metalloids. Examples are SiRs, HgR, Na, and B(OH)2- Since aryl Grignard and aryllithium compounds are fairly easy to prepare, they are often used to prepare salts of weak acids, for example,... 

There are distinct structural types of organic compounds containing metals and metalloids. The first contain covalent carbon-metal bonds and are strictly organometallic compounds, for example, the alkylated compounds of Hg, Sn and Pb, and of Li, Mg, and A1 (and formerly Hg), which have been extensively used in laboratory organic synthesis, and A1(C2H5)3 that is a component of the... 

The chemistry of a class of organometallic compounds that contain a linkage between two different metallic and/or metalloidal elements has recently been the subject of considerable study (195, 207), but only very little interest has been shown in such compounds with the silicon-silicon-metal bond. Only a few derivatives of mercury and alkali metals are known. 

A major group of organometallic compounds has carbon-metal covalent single bonds in which both the C and metal (or metalloid) atoms contribute one electron each to be shared in the bond (in contrast to ionic bonds, in which electrons are transferred between atoms). The bonds produced by this sharing arrangement are sigma-covalent bonds, in which the electron density is concentrated between the two nuclei. Since in all cases the more electronegative atom in this bond is carbon... 

Is tetramethyldiarsine an organometallic compound By definition, arsenic is a so-called metalloid or semi-metal , not a metal, and thus organoarsenic compounds like the organic compounds of boron or silicon are not per se organometallics. There is no doubt that the preparation of tetramethyldiarsine and the elucidation of its structure may in retrospect be linked to the development of organometallic chemistry, but it would be far beyond the scope of this book, if the chemistry of the organic compounds of the metalloids in its entirety was discussed. 

There are several recent texts dealing with NMR spectroscopy in general and the reader is referred to these texts for further information 117,135, 171,186, 214). The purpose of this review is to cover only the NMR spectroscopy of organometallic compounds, paying particular attention to the chemical shifts and coupling constants of carbon atoms directly attached to metals and metalloids. 

R. Varma Characterisation of metalloid and organometallic compounds by microwave spectroscopy, pp. 277-314 (73). 

Organometallic compounds of less active metals and metalloids (e.g., silicon," antimony, and bismuth, are quite inert to water. Organomercury compounds (RHgX or R2Hg) can be reduced to RH by H2, NaBITj, or other reducing agents." The reduction with NaBH4 takes place by a free-radical mechanism." Alkyl-Si... 

The more comprehensive definitions have grown to include metalloids and even what were considered only a few decades ago to be nonmetals. Furthermore, some are of the opinion that the so-called metals need not always be attached formally to carbon in order to have compounds with organometallic characteristics. An extreme case is the concept that carbon itself may partake of the characteristics of a metal and on such a classification simple compounds such as ethane or benzene are in and of themselves, organometallic compounds. 

Natural particles suspended in the air can be transported to regions far from their sources. This is important for transporting many metals and metalloids in the ecosystem. A few metals and metalloids, most notably Hg, As, and Se, can exist not only in the solid and liquid phases but also as gases in ambient environments. The loss of Hg from the aqueous phase can result from reduction of Hg " " to Hg and alkylation to form methyl- or dimethylmercury. Through microbial activity, the methylated forms can be converted to Hg, which is more volatile and less toxic. Microbial mediation can also transform several other trace elements (e.g., As, Se) to organometallic compounds (Gadd, 1993). These volatile organometallic compounds can dominate the transport of these trace elements in local environments. However, bacterial mediation of alkylation of metals such as Hg is influenced substantially by Hg speciation. Mineral colloids vary in their ability to affect the bioavailability and methylation of Hg(II) in aqueous systems... 

The availability of the aluminum alkyls in pure state makes their use as alkylating agents for the synthesis of other organometallic compounds quite feasible. One of the general approaches is the interaction of the metal or metalloid halide with the trialkylaluminum (105) ... 

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