Diketimines, reduction

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... 

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

A stable crystalline heterocycle 51 was prepared in two steps by treatment of the /3-diketimine 118 with butyllithium and PCl2Ph followed by the reductive dechlorination of the intermediate product 119 (Scheme 9) <2003CC1142>. 

A substantial body of C-H activation chemistry can be initiated by reductive elimination from Pt(IV) species either of ethane from stable, five-coordinate (p-diketiminate)Pt Me3 or of alkane from six-coordinate TpPt HR2. In some cases, usually involving arene activation, new stable Pt(IV) products are obtained the course of benzene activation by the TpPt system has been examined theoretically [80]. For alkane activation, the final product is often a Pt(II)-olefin hydride... 

It is probable that the aforementioned reduction reactions proceed via an initial coordination of the substrate to one or both of the Mg centers of the dimer before its reduction or reductive coupling. Therefore, these reductions need to be carried out in noncoordinating solvents, as competitive coordination of a donor solvent (e.g., THF) at the Mg centers effectively blocks nucleophilic attack at those centers by the reaction substrate. For similar reasons, it has been found that the reactivity of p-diketiminato-coordinated Mg dimers toward unsaturated substrates is inversely proportional to the steric bulk of the p-diketiminate ligand involved. 

In 2012, a Mnj compound [Mn(q q -Af C3-( Bu)C(NDipp)2) 2 was made from the reduction of a Mn(II) bromide precursor using a Mg(I) dimer as reductant (Scheme 7.7) [17], The molecular structure of the compound is shown in Hgure 7.9 and the Mn-Mn bond length is 2.7170(9) A. Magnetic susceptibility studies in the solid state surest high-spin Mn(I) centers, like that in the p-diketiminate compound in Scheme 7.5. And DFT calculations also suggest antiferromagnetic... 

In contrast to 53, reduction of 3,5- Pr2-Ar FeCl 2 in the presence of benzene afforded the orange half-sandwich complex 54. The iron is coordinated to the ipso carbon of the terphenyl ligand and a benzene in an ti fashion. The C( 1 )-Fe-centroid is strictly linear and the Fe(l)-centroid distance of 1.6427(13)A is similar to the Fe-centroid distance of 1.6245(8) A in the related P-diketiminate Fe(I) complex [ (C6H3-2,6-Pr2)NC(Me) 2CH]Fe(Ti -C6H6) [94], but is shorter than the 1.733(2) and 1.763(2) A in Ar FeFeAr (42). Magnetic studies showed that the Fe(I) center adopts a high-spin configuration with three unpaired electrons. 

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