The reactions of substituted 1-phenylpyrazoles (phpyz-H) at [MCl 2 Cp*] 2 dimers (M = Rh, Ir; Cp* = C 5 Me 5 ) in the presence of NaOAc to form cyclometalated Cp*M(phpyz)-Cl were studied experimentally and with density functional theory (DFT) calculations. At room temperature, time-course and H/D exchange experiments indicate that product formation can be reversible or irreversible depending on the metal, the substituents, and the reaction conditions. Competition experiments with both para-and meta-substituted ligands show that the kinetic selectivity favors electron-donating substituents and correlates well with the Hammett parameter giving a negative slope consistent with a cationic transition state. However, surprisingly, the thermodynamic selectivity is completely opposite, with substrates with electron-withdrawing groups being favored. These trends are reproduced with DFT calculations that show C−H activation proceeds by an AMLA/CMD mechanism. H/D exchange experiments with the meta-substituted ligands show ortho-C−H activation to be surprising facile, although (with the exception of F substituents) this does not generally lead to orthocyclometalated products. Calculations suggest that this can be attributed to the difficulty of HOAc loss after the C−H activation step due to steric effects in the 16e intermediate that would be formed. Our study highlights that the use of substituent effects to assign the mechanism of C−H activation in either stoichiometric or catalytic reactions may be misleading, unless the energetics of the C−H cleavage step and any subsequent reactions are properly taken into account. The broader implications of our study for the assignment of C−H activation mechanisms are discussed.

C–H activation processes may show contradictory substituent effects depending on the reaction conditions: under kinetic control ligands with electron-releasing substituents are favoured, whereas the opposite trend is seen under thermodynamic control.

No abstract

No abstract

The current study includes mercuration and telluration of some sulpha compounds; these compounds were prepared by reaction of 4-aminobenzenesulfonic acid and 4,4'-sulfonyldianiline with mercuric(II) acetate reagent to produce Arylmercuric(II)chloride, which was subjected to transmetallation reactions by using TeBr4 to form the Aryltellurium(IV) tribromide. Additionally, the reactions between (2-amino-5-sulfophenyl)mercury(II) chloride and 3,4-dihydroxybenzaldehyde on one hand, and 4,4'-sulfonylbis[2-chloromercuric aniline] with benzaldehyde, on the other, produce mercurated sulpha compounds containing azomethine-group. These obtained compounds react with TeBr4 to form new tellurated sulpha compounds containing azomethine-group. These newly created compounds were subjected to various analyses, including C.H.N.S analysis, proton-NMR, FT-IR, and Carbon-13 NMR. The synthesised compounds were tested for cytotoxicity using in-vitro analyses on two human cancer cell lines, PC3 (prostate cancer cell) and T24 (bladder cancer cell). The prepared organotellurium compounds are effective, especially 4 and 6 compounds. DFT calculations of HOMO and LUMO energy levels and certain quantum parameters indicate that the organomercury compounds are relatively stable and exhibit lesser reactivity when compared to their organotellurium counterparts. Additionally, theoretical results validate the results obtained by the measurement of cancer effectiveness.