Organometallic chemistry electropositive metals

Transmetallation is probably the most frequently employed preparative procedure in organometallic chemistry, and perhaps the commonest variant on this route to new metal-carbon bonds is the interaction of a transition-metal halide MX and a hydrocarbyl derivative of a (usually) more electropositive metal M R ... 

It appears reasonable from organometallic chemistry that Fischer-Tropsch catalysts containing electropositive metals (e.g., potassium, lanthanoids) activate carbon monoxide better than do pure metals. For example, the structurally characterized complex 11 [25] exhibits quite a long C-0 bond (155.0 pm vCO = 1667 cm ). 

Soft bases have lone pairs on atoms of the second or later row of the periodic table (e.g., Cl , Br , PPh3> or have double or triple bonds (e.g., CN", C2H4, benzene). Soft acids can also come finom the second or later row of the periodic table (e.g., Hg ) or contain atoms that are relatively electropositive (e.g., BH3) or are metals in a low (<2) oxidation state [e.g., Ni(0), Re(I), Pt(II), 11(11)]. An important part of organometallic chemistry is dominated by soft-soft interactions (e.g., metal carbonyl, alkene, and arene chemistry). 

This result is of considerable significance and suggests that, particularly on supports activated at relatively high temperatures (perhaps >500°C), transfer of a hydrocarbyl group from electropositive transition metal centres to exposed support cations must be considered. Certainly these reactions have their counterparts in solution organometallic chemistry. Ignoring them may lead to erroneous conclusions based upon the sole expectation of protonolysis of M-C bonds as the surface reaction. A further point is the clear distinction between the major species formed on dehydroxylated and partially dehydroxylated surfaces (Fig. 9). 

Before we can study the complexes, we have to isolate them in a pure form. The methods used resemble those of organic chemistry. Most organometallic complexes are involatile crystalline materials, although. some are liquids [e.g., CH3CsH4Mn(CO)3l, or even vapors [e.g., Ni(CO)4l at room temperature and pre.ssure. They normally have solubilities similar to those of organic compounds. The main difference from organic chemistry is that many organometallic compounds are air sensitive, which usually means that they react with O2 and sometimes- with water. Tlie electropositive /-block, and early rf-block metals are the most reactive. Crystalline material is usually more stable than are solutions, but in many cases both mast be kept under dry Nj or At, and air and water must... 

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