Organometallic methyl-metal compounds

In addition to these supported transition-metal catalysts, some soluble transition-metal compounds exhibit considerable activity in polymerization without added aluminum alkyls.292 The most active compounds are a-organometallics of Ti and Zr with methyl, benzyl, and halogen ligands. jt-Allyl compounds of Ti, Zr, and Cr are also useful catalysts. 

Organometallic Niobium ) and Tantalum ) Compounds. Reports this year have concerned two main areas of interest the preparation of alkyl-niobium and tantalum halides and their reactions with donor ligands, and insertion reactions into methyl-metal bonds. The first examples of monomethyl niobium and tantalum compounds have been prepared by the low-temperature methylation of the appropriate halides... 

Therefore, if you use methylammonium chloride you will produce Cl3BN(CHj)3 (i.e., R = CH3). This product can be converted to the desired one by treating it with an organometallic methyl compound of a metal that is more electropositive than boron. Either methyllithium or methymagnesium bromide could be used, as shown below ... 

As with preparing allyl complexes, direct reaction of benzyl halides and alkali metals is not a generally useful route to benzylalkali metal compounds due to R-R coupling. Benzylalkali metal compounds can be prepared by (1) addition of organometallic reagents to arylalkenes, (2) cleavage of benzyl ethers (equation 28), (3) transmetallation (equations 29-31), and (4) metallation of methyl substituted aromatics. Q, Q -Bis(trimethylsilyl)benzyl potassium can be prepared by metallation with a mixture of butyllithium and potassium 3-methyl-3-pentanolate in THF. ... 

Analysis of liver, kidney and brain provide the most widely accepted diagnosis of metal concentrations that may produce toxicosis (26, 30, 72). Liver and kidney accumulate most inorganic forms of metals, and organometallic forms of compounds such as methyl mercury may concenti ate in the brain (72). The route of exposure can be evaluated through food item analysis. Food samples can be collected, identified, and separated for residue analysis. The concentration data will provide a distribution of metal(s) in the dietary components (73). Regurgitation samples from some species can also provide food samples to quantify metal exposure 57, 60). 

D. Synthesis of Methyl Organometallic Compounds by Cocondensation of Methyl Radicals and Metals... 

In this review we shall not deal with the synthesis of this coordination complex, but we shall deal with the chemical properties of B 12-coenzymes with special emphasis on how these properties relate to Bi2-enzyme mechanisms. Also, we shall show how B -catalyzed methyl-transfer reactions have special significance in the biosynthesis of methylated heavy metals in the aqueous environment, and how the synthesis of these organometallic compounds has special relevance to problems concerned with continuing global environmental health hazards. 

Synthesis with sacrificial electrodes is employed as a direct method in several other preparations of organometallic compounds and complexes. 3-Hydroxy-2-methyl-4-pyrone derivatives of Sn 1 (and of Zn, Cu, In and Cd as well) were prepared using the metal as an anode. The low oxidation state Sn(II) compound is obtained by direct electrolysis134. 

Metallic tin, Sn(0), is even more effectively employed. For example, in the presence of Sn(0), allyl bromide and a-halocarbonyl compounds afford nucleophilic organometallic species, which add to aldehydes in good yields to give homoallylic alcohols (12) and g-hydroxycarbonyl compounds (13,14) respectively. a-Diketones could be reduced by activated Sn(0), to give tin(II) enediolates which in turn undergo aldol reaction to form a,g-dihydroxyketones (15,16). This reaction was successfully applied to a stereoselective synthesis of methyl D-glucosaminate (17). 

The organometallic compounds of the group I and II metals are strongly basic and nucleophilic. The main limitation on alkylation reactions is complications from electron-transfer processes which can lead to radical reactions. Methyl and other primary iodides usually give good results in alkylation reactions. HMPA can accelerate the reaction and improve yields when electron transfer is a complication.64... 

---