p-Tolylimido rhenium(v) complexes – synthesis, X-ray studies, spectroscopic characterization, DFT calculations and catalytic activity

Abstract

Novel p-tolylimido rhenium(V) complexes trans-(Cl,Cl)-[Re(p-NC₆H₄CH₃)Cl₂(py-2-COO)(PPh₃)]·MeCN (1a), trans-(Cl,Cl)-[Re(p-NC₆H₄CH₃)Cl₂(py-2-COO)(PPh₃)] (1b), trans-(Br,Br)-[Re(p-NC₆H₄CH₃)Br₂(py-2-COO)(PPh₃)] (2), cis-(Cl,Cl)-[Re(p-NC₆H₄CH₃)Cl₂(py-2-COO)(PPh₃)] (3), cis-(Br,Br)-[Re(p-NC₆H₄CH₃)Br₂(py-2-COO)(PPh₃)]·H₂O (4), trans-(Cl,Cl)-[Re(p-NC₆H₄CH₃)Cl₂(OMe)] (5) and trans-(Br,Br)-[Re(p-NC₆H₄CH₃)Br₂(OMe)(PPh₃)₂]·1/2H₂O (6) were synthesized. The compounds were identified by elemental analysis, IR, NMR (¹H, ¹³C and ³¹P), UV-Vis spectroscopy and X-ray crystallography. Calculations at the DFT level were undertaken in order to elucidate the structural, spectroscopic and bonding properties of the trans-(Cl,Cl) and cis-(Cl,Cl) isomers of [Re(p-NC₆H₄CH₃)Cl₂(py-2-COO)(PPh₃)]. In the first step, extended tests of the ability of different DFT methods (B3LYP, BP86, and PBE1PBE) were performed to find the best overall performer in describing the geometry of the imido Re(V) complexes; then, the electronic spectra of the trans and cis isomers of [Re(p-NC₆H₄CH₃)Cl₂(py-2-COO)(PPh₃)] were investigated at the TDDFT level employing the PBE1PBE functional. Additional information about bonding in the compounds [Re(p-NC₆H₄CH₃)Cl₂(py-2-COO)(PPh₃)] was obtained by NBO analysis. The catalytic activity of the complexes incorporating the picolinate ligand was studied and compared in the synthesis of N-substituted ethyl glycine esters from ethyl diazoacetate and amines.