Polymeric metal complexes adducts

Chain growth differs from step growth in that it involves initiation and usually also termination reactions in addition to actual growth. This makes its kinetic behavior similar to that of chain reactions (see Chapter 9). However, the chain carriers in chain-growth polymerization need not be free radicals, as they are in ordinary chain reactions. Instead, they could be anions, cations, or metal-complex adducts. While the general structure of kinetics is similar in all types of chain-growth polymerizations, the details differ depending on the nature of the chain carriers. 

Metallation of anthracyclines releases protons, and using a of 10.0 for the first phenolic group, Martin calculated log values (for M + H2L M(HL) + H", where H2L refers to the neutral ligand) of 11.0 and 7.3 for Fe " and Cu ", respectively [81]. Metal ion binding must take into account possible formation of hydroxo and polymeric metal complexes at basic pH, and such events make analysis difficult, e.g. a polymeric 1 1 complex CuL forms at high pH [84]. With variation of pH and molar ratio, various complexes are formed between the ligand and these metals. The 2 1 Cu(HL)2 adduct predominates at 5 < pH < 8 [84, 86], with a reported log P = 16.66 [84], which seems high in comparison to the value of 7.3 reported [81]. Resonance Raman spectroscopy has been particularly useful in analysis of these systems and studies on the Cu(II)— adriamycin—DNA adduct indicated that an intercalated adduct could be formed [87]. 

Adduct formation of the present type has been shown to provide a potentially useful method for separation of transition metals. Thus, 18-crown-6 selectively precipitates the Cu(n) tetrammine complex (as a polymeric 1 1 adduct) in the presence of a corresponding concentration of Co(iii) stabilized as its hexammine complex. 

The fact that NHCs form stable compounds with beryllium, one of the hardest Lewis acids known and without p-electrons to back donate, shows the nu-cleophilicity of these ligands. Reaction of l,3-dimethylimidazolin-2-ylidene with polymeric BeCl2 results in the formation of the neutral 2 1 adduct 23 or the cationic 3 1 adduct 24. The first NHC-alkaline earth metal complex to be isolated was the 1 1 adduct 25 with MgEt2- Whereas l,3-dimesitylimidazolin-2-ylidene results in the formation of a dimeric compound, the application of sterically more demanding l,3-(l-adamantyl)imidazolin-2-ylidene gives a monomeric adduct. ... 

In coordination polymerization, monomer forms an adduct with a transition-metal complex, and further monomer is then successively inserted between metal and carbon. Termination occurs when the metal complex splits off from the polymer or the chain is broken intentionally by hydrogenolysis. Since the initiator is restored to its original form, the process is catalytic. The most important industrial processes are Ziegler-Natta polymerizations of a-olefins and employ solid catalysts. Most catalysts for coordination polymerization are hydride complexes of transition metals. An important example is the Shell Higher Olefin Process (SHOP) for homogeneous oligomerization of ethene with a complex nickel catalyst. The molecular-weight distribution is a Schulz-Flory distribution. The rate is first order in the catalyst metal. 

MA Diels-Alder adducts, 118, 119, 158, 159 MA ene reaction, 119, 158, 159 MA equimolar copolymerization, 270, 273 MA-metal complex polymerization, 212 maleate and fumarate copolymerization, 365, 369 maleimide copolymerization, 266, 365 MA nonequimolar copolymerization, 270-298 MA reactivity ratios, 302 methyl methacrylate copolymerization with MA CTC, 370... 

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