Diketiminate

Alkali metal derivatives of 2-(trimethylsilyl)aminopyridines can be further derivatized by insertion of 1,3-dicyclohexylcarbodiimide. Functionalized guani-dinates are formed in this reaction via a 1,3-silyl shift. Scheme 170 illustrates the reaction sequence as well as the preparation of an aluminum complex of the modified ligand, which exhibits pseudo jS-diketiminate binding of the metal center, thus exemplifying the coordinative versatility of this new multi-N-donor system. ... 

Diketimines can be prepared by condensation of 1,2-diketones with 2 equiv of an amine, or 1 equiv of a 1,2-diamine, by azeotropic removal of water. Either a chiral diketone or a chiral amine/diamine can be used in order to obtain a chiral diimine. In both cases, the use of 1,2-diamines is expected to provide better stereocontrol, because of the rigidity of the derived cyclic diimines. For example, the reaction of camphor 1,2-diketone 275 and racemic 1,2-diphenylethylenediamine (d,l)-26 gave the diimine 276 as a mixture of two diastereomers (Scheme 45) [138]. Reduction of 276 with sodium borohydride followed by hydrogenolysis of the N substituents afforded the camphordiamine, which was isolated as the dihydrochloride... 

By an alternative approach, the enantioselective reduction of 1,2-diketimines was achieved by using hydride reagents in the presence of stoichiometric amounts or an excess of enantiopure carboxylic acids. An... 

With the same tactic, a meta-stable 3-coordinate iron(III) imido complex was reported by Holland and coworkers [40]. Using the diketiminate-supported dinitrogen iron(I) complex [L T eNNFeU ] as a source of iron(I) precursor [L = 2,4-bis (2,6-diisopropylphenylimino)pent-3-yl], the addition of adamantyl azide (AdN3) in... 

Fig. 4.3 Ranges of isomer shifts observed for Fe compounds relative to metallic iron at room temperature (adapted from [24] and complemented with recent data). The high values above 1.4-2 mm s were obtained from Co emission experiments with insulators like NaCl, MgO or Ti02 [25-28], which yielded complex multi-component spectra. However, the assignment of subspectra for Fe(I) to Fe(III) in different spin states has never been confirmed by applied-field measurements, or other means. More recent examples of structurally characterized molecular Fe (I)-diketiminate and tris(phosphino)borate complexes with three-coordinate iron show values around 0.45-0.57 mm s [29-31]. The usual low-spin state for Fe(IV) with 3d configuration is 5 = 1 for quasi-octahedral or tetrahedral coordination. The low-low-spin state with S = 0 is found for distorted trigonal-prismatic sites with three strong ligands [30, 32]. Occurs only in ferrates. There is only one example of a molecular iron(VI) complex it is six-coordinate and has spin S = 0 [33]...

Synthesis of 3-diketiminate stabilized phosphenium salts (R Dipp, C6F3 X=Br, Cl)... 

Scheme 19 Reduction of a P-diketiminate stabilized phosphenium salt...

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... 

A more active zinc catalyst has been developed containing a /3-diketiminate ancillary ligand.823 Complex (272) converts 200 equivalents rac-LA. in less than 20 min at room temperature to highly heterotactic PLA (the probability of a racemic junction between monomer units, PR = 0.90 at 25 °C and 0.94 at 0°C) of narrow polydispersity (Mn = 37,900, Mn calc = 28,800, Mw/Mn= 1.10). Kinetic studies reveal that the zinc initiators display a fractional rate law order (1.56 0.06). In accord with the observation that kR/ss > kR/RR (or ks/RR > ks/ss), the polymerization of L-LA proceeds significantly slower than rac-LA (kapp L-LA = 0.031 min-1 kapp rac-LA = 0.22 min-1).824... 

The substituents on the ancillary /3-diketiminate ligand play a crucial role in determining the activity of these catalysts. Hence, although (335) and (336) are highly active, the less bulky (337) and (338) are inactive. The most active example reported is (339) which produces 558 g polymer/g [Zn]/h. 

Figure 45 The structure of the base-free /3-diketiminate species 94.

Organozinc diiminates of various ligand platforms (particularly /2-diketiminates (BDIs)) have been used extensively in catalysis, especially for the polymerizations of lactides and epoxides and the co-polymerization of epoxides with carbon dioxide. 

Aluminum compounds with Schiff bases and /3-diketiminates 22,23... 

A review of complexes of /3-diketiminate ligands (155) contains little material on iron complexes. ... 

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