Chitosan-Silica as a Cheap Carrier and Green Soft Ligand for Improved Ru-catalyzed Hydroformylation

Abstract

[EN] Dodecacarbonyltriruthenium Ru-3(CO)(12) has been immobilized onto a biopolymer (chitosan) supported on SiO2 (Ch@SiO2) to give Ru-Ch@SiO2. Ch@SiO2 behaves as a soft, recoverable and bulky ligand allowing the stabilization of released Ru active species and preventing its irreversible reduction to Ru-0. Under these conditions very high activity (TOF= 1086 h(-1); TON=2749) and regioselectivity (n:iso=92 : 8) are obtained, surpassing that of the homogeneous Ru-3(CO)(12) counterpart.Spectroscopic studies have shown that Ru-3(CO)(12) transforms into a mononuclear Run+ (n=2,3) di o try carbonyl species by interacting with the amido/amino groups of the biopolymer, being released into the reaction media whilst stabilized by the chitosan functional groups.The herein 0.5 Ru-Ch@SiO2 catalyst can operate be operated under a semi-continuous mode for at least 14 h without deactivation, representing providing a starting point in the search for a green catalyst with definitive industrial application in hydroformylations. In particular in the search for a heterogeneous catalyst away from the use of phosphines and their known drawbacks (i. e. tedious synthesis, facile oxidation of phosphor center, ..) as well as expensive Rh as active site.