Complexes of cis-dioxomolybdenum(VI) with a chiral tetradentate tripodal-like ligand system: Syntheses, structures and catalytic activities. (29th March 2017) - Ghosh, Sabari
Graphical Abstract: Racemic complexes of formula cis -[MoO2 (bzacL n )] ((bzacL n ) 2− represents a tetradentate tripodal-like transformed ligand) synthesized from [MoO2 (bzac)2 ] (bzac − = benzoylacetonate) and 4/5-R-2-(2-pyridylaldimine)phenols (HL n ) are reported. Molecular structures of the diamagnetic and redox-active complexes are established by spectroscopic and X-ray crystallographic studies. The bromoperoxidase activities of cis -[MoO2 (bzacL n )] and the analogous cis -[MoO2 (acacL n )] are demonstrated. Abstract: Racemic complexes with the general formula cis -[MoO2 (bzacL n )] (1 –4 ) (H2 bzacL n = 2-((4/5-R-2-hydroxyphenylamino)(pyridin-2-yl)methyl)-1-phenylbutane-1, 3-dione, where n = 1–4 for R = H, 5-Me, 5-Cl and 4-Me, respectively and 2Hs represent the dissociable phenolic proton and the active tertiary CH proton) have been synthesized in 75–82% yields by reacting [MoO2 (bzac)2 ] (Hbzac = benzoylacetone) with the potentially N2 O-donor 5, 5-membered fused chelate rings forming Schiff bases 4/5-R-2-(2-pyridylaldimine)phenols (HL n ; n = 1–4 for R = H, 4-Me, 4-Cl and 5-Me, respectively) in hot methanol. The chiral ligand system (bzacL n ) 2− in1 –4 is formed via metal assisted Mannich-type addition of benzoylacetonate methine to the azomethine fragment of HL n . All four complexes have been characterized by elemental (CHN) analysis, solution conductivity, magnetic susceptibility, spectroscopic (IR, UV–Vis and NMR) and electrochemical measurements. The molecular structures of1 –3 have been established by single crystal X-ray crystallography. In each complex, the chiral (bzacL n ) 2− acts as a tetradentate, N2 O2 -donor, tripodal-like ligand system and along with the two mutually cis oxo groups forms a distorted octahedral N2 O4 coordination environment around the molybdenum(VI) center. All four complexes are diamagnetic and non-electrolytic. The infrared spectra are generally consistent with the structural formulas of1 –4 . The electronic spectra of1 –4 in dimethylformamide display two strong absorption bands in the range 245–300 nm. The cyclic voltammograms of1 –4 in dimethylformamide exhibit a metal centered one-electron reduction response within −0.64 to −0.74 V. All these complexes (1 –4 ) and the analogous cis -[MoO2 (acacL 1–4 )] (5 –8 ) synthesized from [MoO2 (acac)2 ] (Hacac = acetylacetone) and HL 1–4 have been evaluated for their bromoperoxidase activities.