Ligand Design for Isomer-Selective Oxorhenium(V) Complex Synthesis
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https://figshare.com/articles/dataset/Ligand_Design_for_Isomer-Selective_Oxorhenium_V_Complex_Synthesis/4542673
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Recently, N,N-trans Re(O)(LN–O)2X (LN–O = monoanionic N–O chelates;
X = Cl or Br prior to being replaced by solvents or alkoxides) complexes
have been found to be superior to the corresponding N,N-cis isomers in the catalytic reduction of perchlorate
via oxygen atom transfer. However, reported methods for Re(O)(LN–O)2X synthesis often yield only the N,N-cis complex or a mixture of trans and cis isomers. This study reports
a geometry-inspired ligand design rationale that selectively yields N,N-trans Re(O)(LN–O)2Cl complexes. Analysis of the crystal structures revealed
that the dihedral angles (DAs) between the two LN–O ligands of N,N-cis Re(O)(LN–O)2Cl complexes are less than 90°,
whereas the DAs in most N,N-trans complexes are greater than 90°. Variably sized alkyl groups
(−Me, −CH2Ph, and −CH2Cy)
were then introduced to the 2-(2′-hydroxyphenyl)-2-oxazoline
(Hhoz) ligand to increase steric hindrance in the N,N-cis structure, and it was found that substituents
as small as −Me completely eliminate the formation of N,N-cis isomers. The generality of the
relationship between N,N-trans/cis isomerism and DAs is further established from a literature
survey of 56 crystal structures of Re(O)(LN–O)2X, Re(O)(LO–N–N–O)X, and Tc(O)(LN–O)2X congeners. Density functional theory
calculations support the general strategy of introducing ligand steric
hindrance to favor synthesis of N,N-trans Re(O)(LN–O)2X and Tc(O)(LN–O)2X complexes. This study demonstrates the promise of
applying rational ligand design for isomeric control of metal complex
structures, providing a path forward for innovations in a number of
catalytic, environmental, and biomedical applications.
创建时间:
2017-01-12



