Transition metals specialized routes

Aminopyridinato ligands form a special class of anionic ligands in which an aromatic ring is part of an amidinate system. These ligands have frequently been employed in early transition metal and lanthanide coordination chemistry. Their diverse and interesting chemistry has been described in detail by Kempe et al. ° and will thus be covered here only briefly. Typical reaction pathways leading to titanium aminopyridinato complexes are outlined in Scheme 169. Metathetical as well as salt-free routes have been developed. 

The high oxophilicity of early transition metal catalysts (titanium, zirconium, or chromium) causes them to be poisoned by most functionalized olefins, particularly the commercially available polar comonomers. However, there are examples of copolymerizations with special substrates or with very high levels of a Lewis acid incorporated into the polymerization system to protect the polar functionality through complexation. " Alternative routes to polar copolymers involving metathesis of cyclic olefins and functionalization of the resulting unsaturated polymer or metathesis of polar cycloolefins followed by hydrogenation to remove the resulting unsaturation have been published.The cost of these multistep... 

Transition metal catalyzed hetero-annulation provides a useful and convenient tool for the construction of N-heterocycles [1]. Quinolines are of special interest in that they display attractive applications in pharmaceuticals and are synthetic building blocks [2, 3]. Catalytic processes employing palladium [4—6], rhodium [7-9], ruthenium [10-14], and iron [15] have been studied and developed to synthesize quinoline skeletons. There are five common methods used to prepare substituted quinolines the Skraup reaction [16], the Doebner-Von Miller reaction [17], the Conrad-Limpach reaction [18], the Friedlaender reaction [19, 20], and the Pfitz-inger reaction [21, 22]. All five of the reactions require environmentally unfriendly acids or bases, high temperatures, or harsh conditions. Quinoline yields are usually low due to numerous side reactions. Even though much work has been done to find catalytic routes to quinolines, the use of non-precious metals remains an active area of research. 

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