4- Phenylimidazole, complexes with

Correlations between pK,d values and the equilibrium constants for the formation of iodine complexes with imidazoles suggest that the charge transfer complexes are of the /j-type involving donation of the unshared electron pair at N-3. For examples of K and pK3 values are imidazole, 202, 6.95 1-methylimidazole, 333, 7.33 4-phenylimidazole, 152, 6.10 4,5-diphenylimidazole, 141, 5.90 (83BSB923). 

Values of molar Kerr constants and dipole moments of nitrogen azoles and their complexes with phenols have been obtained. " These complexes are formed by an intermolecular hydrogen bond between the pyridine-type nitrogen of the azole and the phenolic proton. " The use of dipole moments in conformational studies has shown that A-aryl- and C-aryl- and A-furyl- and C-furyl imidazoles (and benzimidazoles) are nonplanar, but l-(a-furyl)-4,5-diphenylimidazoles do have a planar bicyclic fragment. The dipole moments and conformations of azolides (A-acylazoles) have been studied. In the 1-arylimidazoles the dipole is toward the aryl group. In 4,5-di-t-butylimidazole the molecule is essentially planar, but the C-4—C-5 bond is slightly stretched. Among other imidazole derivatives which have been studied by X-ray are histidine hydrochloride, 4-acetyl-amino - 2 - bromo - 5 - isopropyl -1 - methylimidazole, 4- acetyl - 5 - methyl - 2 -phenylimidazole, and imidazole-4-acetic acid hydrochloride. 

Crystal structures have been reported for the enzyme with several bound drugs. Metyrapone- and 1-, 2- and 4-phenylimidazole-inhibited complexes of cytochrome P-450cam have each been refined to 2.1 A resolution. Except in the 2-phenylimidazole complex, each complex forms an N Fe interaction to the heme iron atom. In the 2-phenylimidazole complex, water or hydroxide coordinates the heme iron atom and the inhibitor binds in the camphor pocket. Details of the inhibitor binding are shown in Figure 17.25. Eukaryotic cytochrome P-450 is membrane bound and has a different structure from the soluble... 

Figure 3.20. Ligand-induced conformational changes in CYP119. Compared to the phenylimidazole complex (dark shading), the C-terminal end of the F-helix in the imidazole complex unfolds which lengthens the F/G loop thus allowing the F/G loop to dip into the active site and interact with the iron-linked imidazole. Since phenylimidazole is larger than imidazole, the F/G loop cannot remain positioned in the active site complex. Therefore, the F/G helical region and loop shapes itself around the ligand bound in the active site.

The kinetically best characterized system for which a bimolecular reductive elimination has been proposed is a neutral hydrido porphyrin derivative of Ru(III) [4]. Cyclic voltammetry and double potential step chronoamperometry afford data that are more consistent with a second order than with a first order decay for the 17-electron RuH(OEP)(L) (OEP = octaethylporphyrin L = THE, 1 -tert-bytyl-S-phenylimidazole) complexes in THF as solvent. The second order dependence of the rate constant and the independence on the parent 18-electron anion concentration exclude the proton transfer mechanism. The possibility of a disproportionation mechanism (which would afford the same second order dependence, see section 6.5.2), however, has not been considered, nor were studies in solvents other than THF carried out. In the light of the gathered information, the mechanism shown in Scheme 17 was proposed. 

Diphenylimidazole with palladium acetate forms the cyclometallated complex 80 (X = OAc) (97AOC491). The acetate group is replaced by chloride or bromide when 80 (X = OAc) reacts with sodium chloride or lithium bromide, respectively, to give 80 (X = C1, Br). Bromide with diethyl sulfide forms the mononuclear complex 81. Similar reactions are known for 1 -acetyl-2-phenylimidazole (96JOM(522)97). 1,5-Bis(A -methylimidazol-2-yl)pen-tane with palladium(II) acetate gives the cyclometallated complex 82 (OOJOM (607)194). 

The N-coordinated compound [AuCljL] (L= l-ethyl-2-phenylimidazole) with silver tetrafluoroborate gives the cycloaurated species 102, which on further reaction with triphenylphosphine and sodium tetrafluoroborate or ammonium hexafluorophosphate forms the cationic complexes 103 (X = BF., PF,) (00JCS(D)271). 

Involvement of AModo species in electrophilic C-iodinations needs to be considered since a number of imidazoles are known to form such compounds in basic medium. Charge-transfer complexes, too, are quite well known. They seem to be of the n -type through the unshared electron pair at N-3. Equilibrium constants for their formation are known to increase regularly in line with electron-donating powers of substituents (or vice versa). Some KCT values at 20°C (L M are imidazole (200), 1-methylimidazole (333), 1,2-dimethylimidazole (1165), 4-phenylimidazole (152), and 4,5-diphenylimidazole (141) (83BSB923). The charge-transfer complexes formed between iodine and imidazole-2-thiones appear to involve the sulfur atoms (88JA2586). 

---