Organotransition metal reagents
The chemistry of organometallic transition-metal compounds is marked by the tendency of the metal to achieve an electronic configuration corresponding to that of the next highest noble gas. This equates to a total of 18 electrons in the outermost d, s, and p orbitals. The product of oxidative addition can often undergo reductive elimination with the release of an organic product. The carbon atom bonded to titanium is strongly negatively polarized and, as in a Grignard reagent, the organic group behaves as a nucleophile. However, the reagents are significantly more selective than Grignard reagents in two important respects. The process is superior to the Wittig reaction in two circumstances: first, if an asymmetric carbon atom with an enolizable proton is adjacent to the carbonyl group, it retains its stereochemical integrity; second, highly hindered carbonyl compounds react more efficiently. Tebbe's reagent reacts with the carbonyl group in aldehydes, ketones, esters, lactones, and amides to replace oxygen by methylene.