Amines donor-acceptor

H-bond donor/acceptors water, alcohols, carboxylic acids, amines, amides. 

Eullerene-based donor-acceptor complexes and ion-radical salts with tetrathia-fulvalenes, metalloporphyrins, and cyclic amines as donors 99UK23. 

In nature, aminotransferases participate in a number of metabolic pathways [4[. They catalyze the transfer of an amino group originating from an amino acid donor to a 2-ketoacid acceptor by a simple mechanism. First, an amino group from the donor is transferred to the cofactor pyridoxal phosphate with formation of a 2-keto add and an enzyme-bound pyridoxamine phosphate intermediate. Second, this intermediate transfers the amino group to the 2-keto add acceptor. The readion is reversible, shows ping-pong kinetics, and has been used industrially in the production ofamino acids [69]. It can be driven in one direction by the appropriate choice of conditions (e.g. substrate concentration). Some of the aminotransferases accept simple amines instead of amino acids as amine donors, and highly enantioselective cases have been reported [70]. 

Electron density is transferred from a Lewis donor to a Lewis acceptor, here shown for an amine (donor) interacting with a phosphenium cation (acceptor). The lone pair orbital at the amine dives into the emptyp-orbital of the phosphenium cation, hollowing the ideas of Mulliken the donation towards an acceptor can be viewed as sketched in Scheme 2. 

The donor-acceptor formation can be considered by transfer of electrons from the donor to the acceptor. In principle one can assume donor-acceptor interaction from A (donor) to B (acceptor) or alternatively, since B (A) has also occupied (unoccupied) orbitals, the opposite charge transfer, from B to A. Such a view refers to mutual electron transfer and has been commonly estabUshed for the analysis of charge transfer spectra of n-complexes [12]. A classical example for a donor-acceptor complex, 2, involving a cationic phosphorus species has been reported by Parry et al. [13]. It is considered that the triaminophosphines act as donor as well as an acceptor towards the phosphenium cation. While 2 refers to a P-donor, M-donors are in general more common, as for example amines, 3a, pyridines, 3b, or the very nucleophilic dimethylaminopyridine (DMAP) [ 14], 3c. It is even a strong donor towards phosphorus trichloride [15]. 

In practice one can differentiate between two kinds of donors, the resulting donor-acceptor bonds can be largely ionic (class I) or covalent (class II) [16]. Donors of the first type (class I) stem from the first row of the periodic table of elements, such as amines, ethers, in detail structures in which the Lewis basis centre possessing the non-bonding lone pair is strong electronegative. Donors of the second type are constituted from elements of the second row of the periodic table of elements, such as phosphines, thioethers, etc. (class II). These Lewis donors are... 

Blackstock, S. C., J. P. Lorand, and J. K. Kochi. 1987. Charge Transfer Interactions of Amines with Tetrahalomethanes. X-ray Crystal Structures of the Donor-Acceptor Complexes of Quinuclidine and Diazabicyclo-[2.2.2]octane with Carbon Tetrabromide. J. Qrg. Chem. 52,1451. 

It is most likely that this difference of the Ee0 values is caused by the CTC formation due to the donor-acceptor interactions between peroxyl oxygen with a free valence and amine nitrogen of the type... 

At low temperature, this equilibrium shifts to the right, and only a small fraction of free peroxyl radicals participate in the reaction, whereas at a high temperature the equilibrium is shifted to the left, and the fraction of bound radicals is small. If we assume that at 210-260 K almost all R02 radicals are bound in complexes with amines, then it can be shown that the difference of low- and high-temperature Ee0 values is close to the enthalpy of this donor-acceptor interaction in the CTC complex AEe0 AHDA = 66.7 - 59.1 = 7.6 kJ mol-1. 

The C-H insertion a to nitrogen can be extended to acyclic systems. The reaction with jY-benzyl-iV-methylamine is an excellent example of the interplay between steric and electronic effects. The benzylic position would be electronically the most activated, but due to the steric crowding, the C-H insertion occurred exclusively at the iV-methyl site (Equation (27)).86 This is a general method for generating a-aryl-/5-amino acid derivatives. The N,N-dimethylamino group undergoes a very favorable C-H insertion by the donor/acceptor-substituted carbenoids. Indeed, the reaction is so favorable that double C-H insertion was readily achieved to form the elaborated -symmetric amine 10 (Equation (28)).87... 

Aniline may complex (as a proton donor) not only with tertiary amines (proton acceptors) such as 7V,7V-dimethylaniline, pyridine or A,A-diethylcyclohexylamine, but also with apparently neutral molecules such as CCI492, benzene93 or chloroform, which acts as proton donor toward amines94. 

Some complications arise from the presence of proton donor-acceptor interactions134 when the donor is a protic amine. The separate evaluation of the two kinds of interactions may be a difficult problem. Similarly, if the electron acceptor is also a proton donor, the overlapping of salification and complexation processes makes the separate investigation of the interactions very difficult. This is the case in the complexes between amines and picric acid or other related phenols. For complexes of 2,4,6-trinitro-3-hydroxypyridine135 and... 

Charge transfer complexes between amines and discharged substances were investigated extensively (mainly by spectroscopic methods). The choice of more simple models excludes the presence of proton donor-acceptor interactions which complicate the investigations of other interactions by overlapping different interactions. 

Interactions between aliphatic amines (n-donors) and benzonitrile139 or dicyanoben-zenes140,141 (jr-acceptors), in n-hexane, are mainly electron donor-acceptor interactions. It is reasonable to assume that the lone-pair of the donor is perpendicular to the plane of the acceptor as reported in 42 for 1,4-dicyanobenzene. 

The long known132 electron donor-acceptor complexes between tertiary amines and carbon tetrahahdes are simple systems. Thus, l,4-diaza[2,2,2]bicyclooctane (DABCO) or quinuclidine afford solid complexes with carbon tetrabromide142. 

In principle, aliphatic amines may interact as n electron donor molecules towards electron acceptor centres such as aromatic substrates, both homocyclic and heterocyclic, containing electron-withdrawing groups, usually nitro groups. These interactions are mainly electron donor-acceptor (EDA) interactions, in which aromatic amines are considered n or/and tt electron donors. 

Weak donor acceptor Alcohol, organic acid, phenol, primary and secondary amines, oxime, nitro and nitrile compounds having hydrogen at a-position, hydrazine, HF, and HCN... 

The photolysis of donor-acceptor systems shows a reaction pattern of unique synthetic value. Direct irradiation of the donor-acceptor pairs, such as arene-amine, leads by intramolecular electron transfer, to amine radical cations and arene radical anions. The generated radical cation and radical anion intermediates undergo cyclization reactions providing efficient synthetic routes to N-heterocycles with a variety of ring sizes. 

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