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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

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posted on 19.02.2016, 00:00 authored by Jinyong Liu, Dimao Wu, Xiaoge Su, Mengwei Han, Susana Y. Kimura, Danielle L. Gray, John R. Shapley, Mahdi M. Abu-Omar, Charles J. Werth, Timothy J. Strathmann
This study develops synthetic strategies for N,N-trans and N,N-cis Re­(O)­(LO–N)2Cl 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)­(LO–N)2]+ cations. The 2-(2′-hydroxyphenyl)-2-oxazoline (Hhoz) and 2-(2′-hydroxyphenyl)-2-thiazoline (Hhtz) ligands are used to prepare homoleptic N,N-trans and N,N-cis isomers of both Re­(O)­(hoz)2Cl and Re­(O)­(htz)2Cl and one heteroleptic N,N-trans Re­(O)­(hoz)­(htz)­Cl. Selection of hoz/htz 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)­(LO–N)2]+ cations exhibit a wide range of solvent exchange rates (1.4 to 24,000 s–1 at 25 °C) and different LO–N movement patterns, as influenced by the coordination sphere of Re (trans/cis), the noncoordinating heteroatom on LO–N ligands (O/S), and the combination of the two LO–N ligands (homoleptic/heteroleptic). Ligand exchange dynamics also correlate with the activity of catalytic reduction of aqueous ClO4 by H2 when the Re­(O)­(LO–N)2Cl 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.