Diketiminate complexes

Complexes of these ligands have not yet been developed into commonly used catalysts, although early metal p-diketiminate complexes with co-catalysts do catalyze the polymerization of ethylene. More striking, these ligands have led to the synthesis of a number of unusual low-coordinate complexes. Examples of such complexes are described later in this section. Other examples are shown in later chapters of this text.  

The steric, as well as electronic, properties of these ligands can be tuned by the choice of substituent at nitrogen. The renaissance of 3-diketiminate chemistry resulted from the synthesis of p-diketiminate complexes in which the substituents on nitrogen were steri-cally demanding. This steric effect led to the predominant formation of monomeric complexes and to the formation of unsaturated early and late metal complexes. The earlier p-diketiminate complexes containing smaller substituents at nitrogen tended to be stable and saturated. 

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The complexation of a range of tridentate monoanionic ligands has been examined across the transition metal series and (98) was shown to catalyze the polymerization of ethylene with an activity of 500 gmmol-1 h-1 bar-1.264 Bis(iminopyrrolide) complexes, such as (99),265 display moderate ethylene polymerization activities (70 gmmol-1 h-1 bar-1), as does the /3-diketiminate complex (100).2 6... 

Seven-coordinate Co(n) complexes are known, and eight-coordinate Co(II) is found in both (Ph4As)2[Co(02NO)4] and the diazapyridinophane complex [CoL2]BPh4 Et20 (L = (6)). The three-coordinate /3-diketiminate complexes (7) and (8) are also known. ... 

Since Piers and coworkers [80] reported the first scandium P-diketiminate complexes by using category B ligands in 1999, a few scandium P-diketiminate complexes have been revealed to be highly active catalysts for the polymerization of ethylene and the intramolecular hydroamination [81,82]. 

FIGURE 9.25 Complexes with Coordination Number 2. (a) Linear Au in [EtjPAuTilCOjg]". Note that this structure features 2-coordinate gold and 7-coordinate titanium, (b) A )3-diketiminate complex of thallium, (c) The result of a novel strategy for low coordinate iron that features dative Fe—Fe bonding. (Molecular structure drawings created from CIF data with hydrogen atoms omitted for clarity.)... 

Transition metal p-diketiminate complexes are typically prepared by one of three routes. In one, these complexes are prepared by the reaction of a metal halide with an alkali metal P-diketiminate generated from the reaction of the p-diketiminate with an alkali metal base. An example of this synthesis is shown for the scandium system in Equation 4.51 In a second method, these complexes are prepared by the reaction of a transition metal complex containing a basic ligand, such as an alkyl or amido group, with the neutral p-diketimine. Two examples of this route for zirconium systems are shown in Equations 4.52 and 4.53, 3... 

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