Configuration Control in the Synthesis of Homo- and Heteroleptic Bis(oxazolinylphenolato/thiazolinylphenolato) Chelate Ligand Complexes of Oxorhenium(V): Isomer Effect on Ancillary Ligand Exchange Dynamics and Implications for Perchlorate Reduction Catalysis

This study develops synthetic strategies for N,N-<i>trans</i> and N,N-<i>cis</i> Re­(O)­(<i>L</i><sub>O–N</sub>)<sub>2</sub>Cl complexes and investigates the effects of the coordination spheres and ligand structures on ancillary ligand exchange dynamics and catalytic perchlorate reduction activities of the corresponding [Re­(O)­(<i>L</i><sub>O–N</sub>)<sub>2</sub>]<sup>+</sup> cations. The 2-(2′-hydroxyphenyl)-2-oxazoline (H<i>hoz</i>) and 2-(2′-hydroxyphenyl)-2-thiazoline (H<i>htz</i>) ligands are used to prepare homoleptic N,N-<i>trans</i> and N,N-<i>cis</i> isomers of both Re­(O)­(<i>hoz</i>)<sub>2</sub>Cl and Re­(O)­(<i>htz</i>)<sub>2</sub>Cl and one heteroleptic N,N-<i>trans</i> Re­(O)­(<i>hoz</i>)­(<i>htz</i>)­Cl. Selection of <i>hoz</i>/<i>htz</i> ligands determines the preferred isomeric coordination sphere, and the use of substituted pyridine bases with varying degrees of steric hindrance during complex synthesis controls the rate of isomer interconversion. The five corresponding [Re­(O)­(<i>L</i><sub>O–N</sub>)<sub>2</sub>]<sup>+</sup> cations exhibit a wide range of solvent exchange rates (1.4 to 24,000 s<sup>–1</sup> at 25 °C) and different <i>L</i><sub>O–N</sub> movement patterns, as influenced by the coordination sphere of Re (<i>trans</i>/<i>cis</i>), the noncoordinating heteroatom on <i>L</i><sub>O–N</sub> ligands (O/S), and the combination of the two <i>L</i><sub>O–N</sub> ligands (homoleptic/heteroleptic). Ligand exchange dynamics also correlate with the activity of catalytic reduction of aqueous ClO<sub>4</sub><sup>–</sup> by H<sub>2</sub> when the Re­(O)­(<i>L</i><sub>O–N</sub>)<sub>2</sub>Cl complexes are immobilized onto Pd/C. Findings from this study provide novel synthetic strategies and mechanistic insights for innovations in catalytic, environmental, and biomedical research.