Synthesis, structural elucidation, and catalytic activity of bimetallic rhenium-tin complexes containing Schiff base ligand

Novel bimetallic systems with Re and Sn metals, containing Schiffbase linker were designed and explored for their cooperative effect in the catalysis. ReSn bimetallic complexes were prepared by adopting a two-step synthesis procedure, which includes covalent binding of Sn with the Schiffbase and then with the Re(CO)(5)Br. The Schiffbase, (E)- N'-(2, 3-dihydroxybenzylidene)isonicotinohydrazide (H2L, 1) was used in the preparation of three Schiffbase diorganotin (IV) complexes; Diphenyltin(IV) Schiffbase complex (DPTC, (2a)), Dimethyltin(IV) Schiffbase complex (DMTC, (2b)); and Dioctyltin(IV) Schiffbase complex (DOTC, (2c)). The Schiffbase organotin (IV) complexes, 2a-2c were used as precursors to synthesize bimetallic ReSn complexes. The ReSn bimetallic complexes; ReDPTC (3a), ReDMTC (3b) and ReDOTC (3c) were prepared by treating respective organotin(IV) Schiffbase complex, DPTC (2a), DMTC (2b), DOTC (2c) with the rhenium pentacarbonyl bromide (Re(CO)(5)Br). All the three ReSn bimetallic complexes 3a, 3b and 3c were characterized by FTIR, HRMS, EDX, and UV-Vis spectroscopy. DFT studies were employed to rationalize the ground state structure of the synthesized bimetallic complexes. The catalytic activity of compounds 3a, 3b, 3c were investigated for selective oxidation of anthracene to 9,10 anthraquinone under mild reaction conditions by employing H2O2 as an oxidizing agent. The catalyst 3a (ReDPTC) with the phenyl substituent on the Sn has shown excellent catalytic activity (96.9 % conversion with 100% selectivity) in comparison to 3b (with methyl substituent) and 3c (with octyl substituent). (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Novel bimetallic complexes with Re and Sn metals were designed and synthesized using a Schiffbase linker, demonstrating cooperative catalytic effects. The catalyst with a phenyl substituent on the Sn metal showed the highest catalytic activity compared to those with methyl and octyl substituents.