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]·½H2O (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, 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 PBE1PBE functional. Additional information about bonding in the compounds [Re(p-NC6H4CH3)Cl2(py-2-COO)(PPh3)] were obtained by NBO analysis. The catalytic activity of the complexes incorporating picolinate ligand was studied and compared in the synthesis of N-substituted ethyl glycine esters from ethyl diazoacetate and amines.