Transition metal complexes with sulfur ligands. Part CLV. Structural and spectroscopic characterization of hydrogen bridge diastereomers of [μ-N2H2{Fe(PR3)(‘tpS4’)}2] diazene complexes (‘tpS4’ 2−=1,2-bis(2-mercaptophenylthio)phenylene(2−))

New diazene complexes of the type [μ-N2H2{Fe(PR3)(‘tpS4’)}2] (R=Pr (1), Bu (2)) have been synthesized from FeCl2·4H2O, PR3, ‘tpS4’ 2− in THF–MeOH solution and N2H2 generated in situ by hydrolysis of K2N2(CO2)2 with acetic acid. The deuterated complexes [μ-N2D2{Fe(PR3)(‘tpS4’)}2] (R=Pr (3), Bu (4)) were obtained by using D2O, CH3OD and CH3CO2D. The complexes 1–4 each form as a mixture of two diastereomers. Fractional crystallization of 1 from either toluene or CH2Cl2 afforded single crystals of 1a·2toluene and 1b·4CH2Cl2 that were characterized by X-ray structure determination and permitted to establish unambiguously the hydrogen bridge diastereoisomerism of 1a and 1b. Complexes 1a and 1b differ from each other mainly with respect to the orientation of NH⋯S(thiolate) bridges, but are nearly identical otherwise. The reactivity of 1–4 was investigated with respect to H+/D+ exchange, reversible oxidation and PR3 exchange reactions. The PPr3 ligands of 1 can be exchanged reversibly for PBu3 to give 2 under retention of the [FeNHNHFe] cores. The PR3 exchange is rationalized by dissociation of the PR3 ligands yielding intermediates with five-coordinate iron centers. Such intermediates also account for the isomerization of 1a and 1b and related diazene complexes, for which a mechanism is proposed.