Definition of Reaction Sequences Resulting in Self-Assembly of 2- Cluster from Simple Reactants

Article abstract of DOI:10.1021/ja00404a013

Several reaction systems which result in the assembly of the biologically relevant ^2- cluster (1) from simple reactants have been examined by spectrophotometry and 1H NMR spectroscopy in order to define reaction sequences and identify intermediates.Systems I and II were based on the reactant mole ratios PhS^-/FeCl3/S = 3.5/1/1 and >=5/1/1, respectively, and were conducted in acetonitrile and methanol solutions.In system I the first identifiable intermediate is the adamantane-like species ^2- (4), which reacts with sulfur in an all-or-nothing process in both solvents to afford 1.No other intermediates were identified in this system.In system II the first recognizable species formed is tetrahedral ^2- (2).Reaction of 2 with sulfur in acetonitrile yields binuclear ^2- (3), but in methanol 3, which also results from 2 and sulfur, spontaneously forms 1 in a slow reaction.Thus system II provides the first demonstrated instance of elaboration of a tetranuclear cluster through mononuclear and binuclear intermediates.In methanol the overall reactions affording 1 from initial reactants are quantitative when assayed spectrophotometrically.Salts of intermadiates 2, 3, and 4 have been independently synthesized, and the reactions 4 + S -> 1 and 2 + S -> 3 have been executed in good yield on a preparative scale.Reaction system III, having the reactant mole ratio PhS^-/FeCl3/S^2- = 1.5/1/1, affords 1 in 82percent spectrophotometric yield but proceeds too rapidly for detection of intermediateds by the methods employed.The results are used to interpret reaction sequences in previously reported preparative methods for ^2- clusters.Certain limitations of the investigation are noted.