- Transition metal complexes with sulfur ligands. 117. A reaction cycle for nickel mediated thioester formation from alkyl, CO, and thiolate groups modeling the acetyl-coenzyme A synthase function of CO dehydrogenase
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In quest of nickel complexes with sulfur ligation that model the acetyl-CoA synthase function of CO dehydrogenase (CODH), [Ni('S4C3Me2')] (1, 'S4C3Me2'2- = 1,3-bis(2-mercaptophenylthio)-2,2-dimethyl-propane-(2-)) was synthesized by template alkylation of Na2[Ni('S2')2] ('S2'2- = benzene-1,2-dithiolate(2-)) with CMe2(CH2Br)2. Acidic hydrolysis of 1 yielded the thiol "S4C3Me2"-H2 (2). Reduction of 1 with Na/Hg resulted in cleavage of the 'S4C3Me2'2- ligand and formation of the thermally stable trinuclear nickel(II) alkyl thiolato complex [Ni('μ-S2C3Me2')]3 (3, 'S2C3Me2' 2- = 1-(2-mercaptophenylthio)-2,2-dimethylpropyl(2-)). Treatment of 3 with L = Py, THF, or PMe3 afforded the mononuclear compounds [Ni('S2C3Me2')(L)] (4, L = Py; 5, L = PMe3). The stoichiometric reaction of [Ni('S2C3Me2')(L)] with CO led to the cyclic thioester 'S2C3Me2CO' (6, 'S2C3Me2CO' = 2,3-benzo-6,6-dimethyl-8-oxo-1,4-dithia-cyclooctane) and Ni(CO)4. In the analogous reaction of 5 with CO the intermediate nickel(II) acyl thiolato complex [Ni('S2C3Me2CO')(PMe3)] (7, 'S2C3Me2CO'(2-) = 1-(2-mercaptophenylthio)-2,2-dimethyl-3-oxobutyl(2-)) could be intercepted and fully characterized. The reaction of Ni(CO)4 with the thiol 2 yielded the starting Ni(II) complex 1 and allowed to close the reaction cycle that comprises the CODH sequence: [Ni] → [Ni-alkyl] → [Ni-acyl] → [Ni] + thioester. The net reaction can be formulated as 'S4C3Me2'-H2 (2) + CO → 'S2C3Me2CO' (6) + 'S2'-H2 and represents the first example of nickel mediated thioester formation in a complete reaction cycle. X-ray structure determinations of complexes 1,3,4, and 7 revealed approximately square planar coordination geometry for all Ni centers.
- Sellmann, Dieter,H?ussinger, Daniel,Knoch, Falk,Moll, Matthias
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