Nanoparticles (NP) of Au, Ir, Pd, Pt, and Rh are synthesized by benzimidazo[1',2':1,2]quinolino-[4,3-b][1,2,5]oxodiazolo[3,4-f]quinoxaline (BIQOQ)-mediated electrochemical reduction of AuCl, K3[IrCl6], PdCl2, PtCl2, RhCl3, respectively, in the presence of poly(N-vinylpyrrolidone) (PVP) and nanocellulose (NC) at the potential controlled in the region of generation of BIQOQ.– anion radicals in the DMF/0.1 M Bu4NBF4 medium at room temperature. The efficiency of electrosynthesis is shown to be determined by the nature of the substrate to be reduced. K3[IrCl6] is virtually unreducible, whereas the other substrates are reduced to form NP–M. As the theoretical charge is passed, the generated metal is formed in the solution volume rather than as the cathodic deposit. NP–Au particles are formed in the quantitative amount, the mediator is retained in the process. In the other cases, the process consumes from ~50 (Ir, Pd, Pt) to 80% (Rh) of the mediator with the corresponding decrease in the NP–M yield. The synthesis produces individual spherical NP–Pd (4 ± 1 nm) and agglomerates of nanoparticles of gold (78 ± 27 nm), platinum (34 ± 14 nm), and rhodium (33 ± 20 nm) all stabilized in PVP shells. In contrast to the earlier described Ag@PVP nanoparticles which decorated NC in the extremely dense way, these particles are bound only partly with NC. The nanocomposites of Pd, Pt, and Au exhibit catalytic activity in the reactions of reduction of nitroaromatic compounds by sodium borohydride in aqueous media.