Reaction of a polydentate cysteine-based ligand and its nickel(ii) complex with electrophilic and nucleophilic methyl-transfer reagents - from S-methylation to acetyl coenzyme A synthase reactivityElectronic supplementary information (ESI) available: 1H NMR, 13C NMR, ATR-FTIR and mass spectra of the synthesized compounds as well as a UV-vis absorption spectrum of [(MeLNi)3I]I2 (3). CCDC 1414764 (2) and 1414763 (3). For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1

The l -cysteine derived N 2 S 2 ligand precursor H 2 L and its nickel( ii ) complex L 2 Ni 2 were investigated with respect to their behaviour in contact with electrophilic and nucleophilic methylation reagents (H 2 L = ( N , N ′-dimethyl-(2 R ,5 R )-bis-(sulfanylmethyl)-piperazine). Treatment of deprotonated L 2− with MeI led to the selective methylation of the thiolate groups thus generating a novel potential ligand, Me 2 L, which is neutral and contains two thioether donors. The coordinating properties of Me 2 L were demonstrated by the synthesis of a first nickel( ii ) complex: reaction with NiBr 2 led to a mononuclear complex 2 where all donor atoms coordinate to the nickel ion, which completes its octahedral coordination sphere by the two bromide ligands. If, however, the complex [LNi] 2 ( 1 ) is treated with MeI only one thiolate function per ligand moiety is methylated, while the other one remains a thiolate. This leads to [MeLNi] + complex metal fragments, which trimerize including a μ 3 -bridging iodide ion to give the compound 3 that was tested with regards to ACS reactivity. While it behaved inert towards CO, attempts to replace the bridging iodide ligand by methyl units in reactions with nucleophilic methylation reagents led to a product, which could not be identified but reacted with CO. Work-up showed that this protocol had converted the thiolate function of MeL − into a thioester function, which corresponds to an ACS-like reactivity. A cysteine-based nickel( ii ) complex reacts with methylating reagents followed by CO treatment via acetylation of the thiolate function corresponding to the ACS reactivity.