Nitrogen donor

Multidentate ligands contain more than two coordinating atoms per molecule, e.g. 1,2-diaminoethanetetra-acetic acid (ethylenediaminetetra-acetic acid, EDTA),f which has two donor nitrogen atoms and four donor oxygen atoms in the molecule, can be hexadentate. 

Cytochromes. A cytochrome is a protein containing a heme with an iron cation bonded to four donor nitrogen atoms in a square planar array. Figure 20-29a shows the structure of cytochrome c, in which a histidine nitrogen atom and a cysteine sulfur atom occupy the fifth and sixth coordination sites of the octahedral iron center. 

The geometry of the assembly can be altered by using a 3-pyridyl substituent on the porphyrin periphery. The donor nitrogen atom is oriented at an angle with respect to the porphyrin plane, and this has been exploited in the assembly of oblique dimeric, trimeric, and penta-meric structures from free base mono- (13 (12) and 14 (23), Fig 4a), bis-... 

Figure 3.33 The dative sigma bond aB N of F3B NH3, showing the NBO (left) and the donor nitrogen nN NHO (right).

The first successful axially chiral phosphinamine ligand in asymmetric catalysis was QUINAP 60 (Figure 8) reported by Brown in 1993 and the original synthesis has since been modified.94 The donor nitrogen atom is incorporated in an isoquinoline unit to form a six-membered chelate ring. 

Figure 2.6. Examples of donor-acceptor fluoroionophores in which the electron-donating character of the donor (nitrogen atom of the crown) is cation-controlled.

The bleomycins (50) are hardly simple amines, but they do have two NH2 groups and a CONH2 group at the N-terminal domain, as well as potential donor nitrogens in pyrimidine and imidazole, which can complex metal ions." " The complexing of iron to bleomycin" " " has a significant effect on bleomycin-DNA interactions—metal complexes can mediate strand scission—and on alkene oxidation. Both may involve hydroperoxide intermediates." " " " ... 

The first total synthesis of morphine [115] involves hydration of a tetracyclic intermediate. The attack of water from the more hindered face of the double bond could hardly have been predicted. However, the donor nitrogen atom of the molecule may have been responsible for the protonation at C-7 in favor of C-6 via a polarity alternation mechanism. 

Intramolecular interception of an Af-alkoxy-AT-acylnitrenium ion by an aromatic ring results in a spirocyclic species [203], There follows a C-migration (instead of N-migration) to restore aromaticity. This migration is assisted by the stabilization of the incipient carbocation by the resident donor nitrogen atom N-migration would not profit from this favorable electronic interaction. 

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