Donor carbon

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 simplest example of oxygen spillover is found in the adsorption of oxygen on carbon. The spillover oxygen migrates from the basal carbon (donor) to carbon atoms exposed at steps between layers of the graphite surface, where it reacts with the edge carbons (acceptor).71 In this case the donor and acceptor phase consist of the same material with different surface properties. 

A series of novel l-substituted-4-phenyl-l,2,3-triazolo(4,3-a)quinazolin-5(4H)-ones 1 were synthesized by the cyclization of 2-hydrazino-3-phenyl-quinazolin-4(3H) 2 with various one carbon donors. The starting material 2-hydrazino-3-phenylquinazolin-4(3H)-one 2, was synthesized from aniline 7 by a novel innovative route. When tested for their in vivo Hi-antihistaminic activity on conscious guinea pigs all the test compounds protected the animals from histamine-induced bronchospasm significantly, whereas the compound l-methyl-4-phenyl-l,2,3-triazolo(4,3-a)quinazolin-5(4H)-one lb (percentage protection 70.7%) was found to be equipotent with the reference standard chlorpheniramine maleate (percentage protection 71%). These compounds show negligible sedation (5%) when compared to the reference standard (26%). Hence they could serve as prototype molecules for future development [1,4,5]. 

The title compounds la-e were obtained in fair to good yields through the cyclization of 2 with a variety of one carbon donors such as formic acid, acid acetic, propionic acid, buturic acid, and chloroacetyl chloride at reflux (Scheme 1). 

Scheme 9.1. Homologation and Coupling of Organoboranes by Carbon Monoxide and Other One-Carbon Donors...

Methyl transferases are responsible for methylation of a nucleophile, typically using SAM as the carbon donor. They are known to accept a wide range of nucleophiles such as halides (eq. 1 in Figure 13.22) [64], amines (eq. 2 in Figure 13.22) [65], hydroxyls, and enolates. As expected, the reactivity of methyl transfer to halides follows the order of iodide, bromide, and chloride, with chloride being the poorest acceptor. Methylation of amines in nucleotides and proteins plays important roles in biological activities. 

Also, the Fe methyl contact distance of 3.005(2) A in 34 shortens to 2.085(5) A when the Fe—C-l bond is formed. The most dramatic feature of this rearrangement is that the two acyl carbon donor atoms of 34 have undergone a transannular, interligand C—C coupling reaction. 

Lippard et al. have demonstrated a reductive C—C coupling between the carbon donor atoms of terminal isocyanide ligands [Eq. (11)] (48,49). 

Because the interligand C—C coupling of the acyl carbon donor atoms in metalla-/3-diketonate complexes [Eq. (8)] is such a general (though unusual) reaction that occurs very facilely, we have proposed (without proof) a formal description of how this type of coupling might take place (44,50). This formalism has been adopted by others to explain the C—C coupling shown in Eq. (10) (47). 

Scheme 3. Proposed mechanism for the formation of pivaloin by an interligand C—C coupling of two carbon donor atoms.

---