Macrocyclic tetradentate

The indirect electrochemical reduction of alkyl halides is also possible by use of nickel(I) complexes which may be obtained by cathodic reduction of square planar Ni(n)-complexes of macrocyclic tetradentate ligands (Table 7, No. 10, 11) 2 4-248) Comparable to the Co(I)- and Ni(O)-complexes, the Ni(I)-species reacts with the alkyl halide unter oxidative addition to form an organo nickel(III) compound. The stability of the new nickel-carbon bond dominates the overall behavior of the system. If the stability is low, the alkyl group is lost in form of the radical and the original Ni(II)-complex is regenerated. A large number of regenerative cycles is the result. 

Busch and coworkers193) have also synthesized and characterized six-coordinate iron(II) complexes [Fe([14]aneN4)X2], where [14]aneN4 refers to the 14-membered fully saturated macrocyclic tetradentate ligand meso-5,5,7,12,12,14-hexamethyl-l,4,-8,11-tetraazacyclotetradecane. The complexes are found to be predominantly low-spin, when the axial ligands X are relatively strong examples, in spectrochemical order, are CN" > N02 > NCS" > CH3CN. 

Several methods have been used to distinguish between diastereoisomers in more complex systems. Thus, stereoisomers resulting from the coordination of linear tetradentate ligands have often been identified as trans, cis-a, or c/s-( S,10 and those resulting from coordination of macrocyclic tetradentate ligands have their own system.11 The scope of most of these nomenclatures is generally quite limited, but a proposal with wider application in the description of complexes of polydentate ligands has been made more recently.12... 

Wuest. J.D. Zacharie, B. Multidentate Lewis acids. Complex of macrocyclic tetradentate organomercuric perfluoroglutarate. J. Am. Chem. Soc. 1987, 109, 4714-4715. 

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