Coordination chemistry nitrogen donor

Structural aspects and coordination chemistry of metal porphyrin complexes with emphasis on axial ligand binding to carbon donors and mono- and di-atomic nitrogen and oxygen donors. P. D. Smith, B. R. James and D. H. Dolphin, Coord. Chem. Rev., 1981,39, 31-75 (170). 

The study of [4.4.0] ring systems has resulted primarily from the study of various other aspects of phosphorus chemistry. An investigation into the effect of nitrogen donor action on the increase in coordination at phosphorus in a series of oxyphosphoranes led Holmes and co-workers <1998IC4945> to compounds 24 and 25. The compounds were fully characterized by NMR spectroscopy and X-ray diffraction. Compound 24 was heated for 30 min at 140°C in an NMR tube. The reaction was followed by 31P NMR spectroscopy which indicated that conversion to a phosphorane 26 and a small amount of phosphate had taken place (Equation 4). The pentaoxyphosphorane 25 was successfully produced via an oxidative addition reaction between the diol 27 and triphenyl phosphate in the presence... 

The coordination chemistry of macrocyclic ligands has been extensively studied and aspects of isomerism have been considered in numerous systems.241 Methods whereby two diastereomers of complexes of tetra- N-methylcyclam may be isolated have been discussed previously.184 This, however, is a relatively simple system and it is usually necessary to consider isomerism due to the presence of asymmetric atoms in the chelate arms, as well as that due to asymmetric donor atoms that may be rendered stable to inversion by coordination. An example of a system exhibiting this level of complexity is afforded by the nickel(II) complexes of the macrocyclic ligands generated by reduction of the readily prepared macrocycle (46). These ligands contain two asymmetric carbon atoms and four asymmetric nitrogen atoms but, because AT-inversion is rapid, it is conventional to consider that only three separable stereoisomers exist. There is an enantiomeric pair, (47a) and (47b), which constitutes the racemic isomer (R, R ), and an achiral (R, S ) diastereomer (47c), the meso isomer. 

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