Ligand substitutions overview

This section reviews copolymerization studies and aims to give an overview of research on ethylene-1-olefin copolymerization, the role of ligand substitution in copolymerization and the polymerization mechanisms involved. The copolymerization behavior of a group of siloxy-substituted complexes is discussed because they have the ability to be activated at low MAO ratios and some of them provide excellent comonomer respraise. 

There are several recent reviews on the topic as well as a vast number of original research reports. Marcus (1981) in the Gmetin Handbook gives an authoritative overview on solution studies related to aqua complex formation the literature is covered up to 1978. Carnall (1979) in this Handbook covers approximately the same period, emphasizing spectroscopic studies. Since the late 1970 s a few additional reviews have appeared. Grenthe (1978) discusses briefly the thermodynamics and kinetics of R complex formation in aqueous solutions, while Williams (1982) focuses his review on the NMR methods and biological systems. The most comprehensive of the recent reviews is that of Lincoln (1987), which discusses the ligand substitution processes and includes data from nonaque-ous solutions. 

A key objective on our part was to complement material that had already been reviewed as well as to provide an overview of the key developments. Several reviews and commen-taries have appeared since the 1980 book and almost half of these have been published since 2000. These have dealt with, either fully or in part, derivatives of specific types of amido and related ligands, the applications of amido substituted complexes in chemical transformations, and the use of amido complexes as precursors for electronic materials or catalysis. The increasing interest in the use of multidentate amido and similar ligands of various types, which had been a notable development of mainstream amide chemistry since 1980, has resulted in the largest numbers of reviews. These cover ligands such as... 

CoCp unit C-C bond activation, 7, 80 CoCp unit CH activation, 7, 79 in ethylene polymerization, 7, 81 substituted ligands, 7, 71 synthetic applications, 7, 74 with )4-cyclobutadiene applications, 7, 66 new ligand preparation, 7, 70 with )4-(cyclobutadiene) ligands, 7, 59 dendrimeric cobaltocenium derivatives, 7, 88 with fullerenes, 7, 51 HP-NMR and HP-IR studies, 1, 488 with rj -hydrocarbyl units, 7, 8 immobilized, as polymer support, 12, 681 kinetic studies, 1, 520 with )3-ligands, 7, 56 with metallaboranes, 3, 158 overview, 7, 1-119... 

The data in Tables 1-3 probably constitute the most extensive overview available for solution M-H BDE data that have been obtained by a single method. The effect of ancillary ligands on the M-H BDEs in series of related complexes can be studied in some detail. It was pointed out in Section 3.3.1 that the BDEs are remarkably insensitive to certain changes in the ligands. For example, within each of the following groups from Table 1, BDE differences are smaller than 8 kJ moL CpCr(CO)2(L)H (entries 1-4) CpW(CO)2(L)H (entries 12 and 13) Mn(CO)4(L)H (entries 17 and 18) Co(CO)3(L)H (entries 24-26) CpM(CO)3H compared with Cp M(CO)3H (M = Cr, entries 1 and 5 Mo, entries 8 and 9). Similar effects are found in Table 2 less than 5 kJ mol differences within the series CpIr(CO)(L)H+ (entries 32-39) Cp Ir(COD)H+ (entries 41-45) Cp Ir(CO)(L)H+ (entries 46-51, where the dicarbonyl differs somewhat more from the substituted compounds). 

An extensive and well-organized overview of the synthesis of tpy ligands by Thompson appeared in 1997.2 It reviewed the synthetic methodologies, as well as various substitution... 

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