Nitrogen precursors pyrrole derivatives

Reynolds et al. (1985, 1987) examined petroleum porphyrin and nonporphyrin metals independently with EPR after methanol extraction of porphyrins from the petroleum. Table IV shows the EPR-derived coordination spheres of vanadyl nonporphyrin fractions of various crudes. The Ni and V coordinated to four nitrogens (N4 type) could be petropor-phyrin precursors and derivatives as previously discussed or tetradentate-mixed ligands in which N does not necessarily come from a pyrrole group. Considerable variability in the vanadyl coordination among different crude oils is evident. Figure 4 illustrates some proposed metal complexes that may exist in petroleum (Yen, 1975). 

The Phillips catalyst, based on a Cr/2,5-dimethylpyrrole precursor and TEA as a cocatalyst, is the only commercial catalytic system for ethylene trimerization [164] and has thus been extensively studied [139, 140]. Based on DFT calculations, a redox mechanism involving a Cr(ll)/Cr(lV) couple has been proposed [154, 165]. Also, the pyrrole derivative ligand, able to interact with one or two metal centers through the nitrogen lone pair and/or the aromatic Jt-system, may play a key role for the stabilization of heterodinuclear Cr/Al species formed after activation. 

In 2014, Yu and coworkers used the hydroxylamine derivative Af,0-ditosyl-JV-methylhydroxylamine 273 as a tunable nitrogen source for the direct C-H amida-tion of heteroarenes through a visible-light-mediated photocatalytic method (Eq. (13.28)) [77a]. A variety of heteroarenes, such as indoles, furans, and pyrroles, smoothly underwent this amidation reaction at room temperature. Very recently, Studer successfully introduced Af-aminopyridinium salts, which are readily prepared from cheap starting materials, as efficient Af-centered radical precursors. These novel Af-radical precursors can be used for the direct C-H amidation of... 

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