Synthesis and Characterization of Bridging-Diazene Diiron Half-Sandwich Complexes: The Role of Sulfur Hydrogen Bonding.

We report two bridging-diazene diiron complexes [Cp*Fe(8-quinolinethiolate)] 2 (μ-N 2 H 2 ) ( 1-N 2 H 2 ) and [Cp*Fe(1,2-Cy 2 PC 6 H 4 S)] 2 (μ-N 2 H 2 ) ( 2-N 2 H 2 ), synthesized by the reaction of hydrazine with the corresponding thiolate-based iron half-sandwich complex, [Cp*Fe(8-quinolinethiolate)] 2 ( 1 ) and Cp*Fe(1,2-Cy 2 PC 6 H 4 S) ( 2 ). Crystallographic analysis reveals that the thiolate sites in 1-N 2 H 2 and 2-N 2 H 2 can engage in N-H···S hydrogen bonding with the diazene protons. 1-N 2 H 2 is thermally stable in both solid and solution states, allowing for one-electron oxidation to afford a cationic diazene radical complex [ 1-N 2 H 2 ] + at room temperature. In contrast, 2-N 2 H 2 tends to undergo N 2 H 2 /N 2 transformation, leading to the formation of a Fe(III)-H species by the loss of N 2 . In addition to stabilizing HN=NH species through the hydrogen bonding, the thiolate-based ligands also seem to facilitate proton-coupled electron transfer, thereby promoting N-H cleavage.