Thiolate Coordination vs C–S Bond Cleavage of Thiolates in Dinickel(II) Complexes

A detailed study for the synthesis of dinickel(II)–thiolate and dinickel(II)–hydrosulfide complexes and the complete characterization of the relevant intermediates involved in the C–S bond cleavage of thiolates are presented. Hydrated Ni(II) salts mediate the hydrolytic C–S bond cleavage of thiolates (NaSR/RSH; R = Me, Et, nBu, tBu), albeit inefficiently, to yield a mixture of a dinickel(II)–hydrosulfide complex, [Ni2(BPMP)(μ-SH)(DMF)2]2+(1), and the corresponding dinickel(II)–thiolate complexes, such as [Ni2(BPMP)(μ-SEt)(ClO4)]1+(2) (HBPMP is 2,6-bis[[bis(2-pyridylmethyl)amino]methyl]-4-methylphenol). A systematic study for the reactivity of thiolates with Ni(II) was therefore pursued which finally yielded 1as a pure product which has been characterized in comparison with the dinickel(II)–dichloride complex, [Ni2(BPMP)(Cl)2(MeOH)2]1+(3). While the reaction of thiolates with anhydrous Ni(OTf)2in dry conditions could only yield [Ni2(BPMP)(OTf)2]1+(5) instead of the expected dinickel(II)–thiolate compound, the C–S bond cleavage could be suppressed by the use of a chelating thiol, such as PhCOSH, to yield [Ni2(BPMP)(SCOPh)2]1+(6). Finally, with the suitable choice of a monodentate thiol, a dinickel(II)–monothiolate complex, [Ni2(BPMP)(SPh)(DMF)(MeOH)(H2O)]2+(7), was isolated as a pure product within 1 h of reaction, which after a longer time of reaction yielded 1and PhOH. Complex 7may thus be regarded as the intermediate that precedes the C–S bond cleavage and is generated by the reaction of a thiolate with an initially formed dinickel(II)–solvento complex, [Ni2(BPMP)(MeOH)2(H2O)2]3+(4). Selected dinickel(II) complexes were explored further for the scope of substitution reactions, and the results include the isolation of a dinickel(II)–bis(thiolate) complex, [Ni2(BPMP)(μ-SPh)2]1+(8).