A Heterogeneous Recyclable Rhodium-based Catalyst for the Reduction of Pyridine Dinucleotides and Flavins

Reduced pyridine nucleotides and flavins are important enzyme cofactors that require continuous regeneration for biotechnological development of the corresponding enzymes. This can be achieved with the assistance of a dehydrogenase system or by reduction with formate catalysed by a soluble organometallic {[Cp*Rh(bpy)(H2O)](2+)} (Cp*=pentamethylcyclopentadienyl; bpy=bipyridine) complex. Here, we report that this Rh complex, once immobilized on bypiridine-periodic mesoporous organosilica, displays catalytic activity for flavin (including FAD, FMN and riboflavin) and NAD(P)(+) reduction by formate. The recyclability of this solid catalyst makes it possible to achieve up to 20 cycles of FAD reduction without activity loss. This recyclable heterogeneous catalyst can also be used to assist a complex NADH-, FAD- and O-2-dependent monooxygenase system, allowing several cycles of transformation of a phenol into the corresponding catechol.