A variety of nickel and copper complexes bearing the trifluoromethyl ligand have been prepared in order to quantify by electrochemical methods the redox potentials relative to their chloro and methyl counterparts. The effects of coordination number and geometry, as well as the oxidation state of the metal, on the relative ease with which trifluoromethyl complexes can be oxidized have for the first time been identified. In the d10 system [(NHC)Cu(X)] (NHC = N-heterocyclic carbene, X = methyl or trifluoromethyl), a single substitution of methyl for trifluoromethyl raised the oxidation potential of the organometallic complex by approximately +0.6 V versus the ferrocene/ferrocenium (Fc/Fc+) couple, a testament to the extreme electron-withdrawing properties of the trifluoromethyl ligand. The ΔE ox (methyl vs trifluoromethyl) for d8 nickel complexes were of similar magnitude; however the absolute oxidation potentials were dramatically dependent on the ligand (dippe = 1,2-bis(diisopropylphosphino)ethane vs BOXAM = bis(4-isopropyl-4,5-dihydrooxazol-2-yl)phenyl)amine).

Catalytic amounts of the compounds [(dippe)- NiH] 2 (1), [(dcpe)NiH] 2 (2), and [Ni(PEt 3 ) 4 ] (3) (1-0.1 mol %) with alkyl Grignard reagents promoted the desulfurization of dibenzothiophene, 4-methyldibenzothiophene, and 4,6-dimethyldibenzothiophene, to produce the corresponding biphenyls (90-100%) in toluene or mixtures of biphenyls and thiols favored in THF. Also, the thianickelacycle [(dippe)Ni(η 2 -C,S-C 12 H 8 )] ( 4) was used as a catalyst precursor to test its participation as an active intermediary in the catalytic cycle.

II oxidation states containing mono-and diphosphines ligands, in conjunction with alkyl Grignard reagents, promoted the desulfurization of dibenzothiophene (DBT), 4-methyldibenzothiophene (4-MeDBT), and 4,6-dimethyldibenzothiophene (4,6-Me 2 DBT), to produce the corresponding substituted and unsubstituted biphenyls. It was also observed that the use of polar solvents such as THF yielded thiols, while the use of nonpolar solvents allowed the complete desulfurization of these substrates.

The reactivity of the nickel(I) dimer [(dippe)Ni(mu-H)](2) (1) with biphenyl-2-thiol was explored with the aim of clarifying the key step of sulfur extrusion during the hydrodesulfurization process using dibenzothiophene (DBT). These reactions were monitored by variable temperature NMR experiments which allowed the complete characterization and isolation of [(dippe)(2)Ni(2)(mu-H)(mu-S-2-biphenyl)] (3). The latter compound evolves to the terminal nickel-hydride [(dippe)Ni (eta(1)-C-2-biphenyl)(H)] (4) and transient [(dippe)NiS] (5), to ultimately yield [(dippe)(2)Ni(2)(mu-S)] (2) and biphenyl as the resulting HDS products. The reactivity of 1 and biphenyl-2-thiol was examined using different ratios of reactants, which allowed preparation of [(dippe)Ni(eta(1)-S-biphenyl-2-thiolate)(2)] (6) when using an excess of this substrate. The reactivity of 6 with 1 was addressed, yielding compound 2 and an equivalent amount of biphenyl.

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