Saturated nitrogen ligands

A similar observation is noted for complexes containing partially (salalen) and completely (salan) saturated nitrogen centers (Fig. 8) [28]. Metal complexes of these ligands generally exhibit a c -p configuration and the metal center of these derivatives is chiral (A or A) (Fig. 9) [29, 30], Figure 10 depicts the structure of a (salalen)CrCl(H20) complex as determined by X-ray analysis. 

These compounds are the first examples for the stabilization of the LS state of iron(II) with saturated nitrogen as the most abundant donors this has been ascribed by the authors to the enhanced ligand field strength due to the constrictive effect of the mechanically confining in-plane macrocyclic ligand . Six-coordinate iron(II) complexes are formed with relatively weak axial ligands such as X = CH3C002 >... 

Ni1 complexes (944)-(950) with various different saturated polyaza macrotricyclic ligands having noncoordinated nitrogen atoms in the ligand framework have been prepared by reduction of the Ni11 complexes with Na/Hg in acetonitrile. The crystal and molecular structures of (948), (946), and (945) were determined.1582,2333 Both complexes were found to have essentially square... 

Placing a proton on the X group presumably weakens the Cr-X bond. The enhanced lability is due to a reduced enthalpy of activation, compared with that associated with the step. Normally, the removal of unidentate ammonia or amine ligands from metal complexes is not accelerated by acid, since the nitrogen is coordinately saturated. This situation changes when we consider multidentates (Sec. 4.4.2). 

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