Silicon (IV) complexes containing bidentate ligands; Syntheses, Characterization and Catechol oxidase activity

Two silicon complexes, [SiIV(Quin)(Sal)]Cl2 (1) and [SiIV(Quin)(Naf)]Cl2 (2), containing bidentate ligands have been synthesized and characterized by elemental analysis, IR and UV–vis spectral measurements. In both complexes, silicon is four-coordinated with oxidation state 4. Catecholase activity was measured against 3,5-di-tert-butylcatechol (3,5-DTBC) in methanol saturated with oxygen. By comparison with the enzyme itself (Kcat= 2.29 sec-1), complexes 1 and 2 show moderate catecholase activity (Kcat= 1.15 and 1.354 sec-1), respectively with the activated 3,5-DTBC. The KM (19 and 17 mM for complexes 1 and 2, respectively), is rather large. Large KM values seem typical of the faster model complexes, and indeed the enzyme itself. The reaction rate for both complexes is linearly dependent on the concentration of the complex, indicating a first-order dependence on catalyst concentration.