Kinetic investigations of the mechanism of dihydrogen driven catalytic reduction of methylene blue, safranine O, methyl viologen and ferricyanide using platinum carbonyl cluster anions (Chini-clusters) as catalyst

[Bu4N]2[Pt12(CO)24] (1) catalyses the selective reduction of electron acceptors (S), methylene blue (MB+), safranine O (Saf+), methyl viologen (MV2+) and ferricyanide by dihydrogen. Macroscopic rate investigations for the cationic substrates in DMF, and for ferricyanide in DMSO have been carried out. In all cases, kobs is given by k1 [S] + k2, indicating that there are two catalytic cycles. In one of them, the formation of a complex between S and [Pt12(CO)24]2- in the rate determining step (rate constant k1) is followed by electron transfer and/or other fast steps. In the other catalytic cycle, the rate determining step (rate constant k2) involves formation of the solvated cluster anion [Pt12(CO)24]2-. The solvated cluster then undergoes fast reduction by dihydrogen and other reactions. The relative contributions of these two cycles depend on the substrate, and for MB+, Saf+, MV2+ and [Fe(CN)6]3- the contribution of the second cycle is about 99%, 55%, 77% and 97%, respectively. Both k1 and k2 of ferricyanide are about three orders of magnitude smaller than those of the cationic electron acceptors. The rates of reduction of MB+ and Saf+ have also been studied in the presence of added water. Rates increase as the presence of water provides an additional pathway for the reduction of [Pt12(CO)24]2- to [Pt9(CO)18]2-

4,7,13,18-Tetra­oxa-1,10-diazo­nia­bicyclo­[8.5.5]icosane bis­(hexa­fluorido­phosphate)

The asymmetric unit of the title structure, C14H30N2O4 2+·2PF6 −, contains the anion and half of the cation, the latter being completed by a crystallographic twofold axis. The cation has a cage structure with the ammonium H atoms pointing into the cage. These H atoms are shielded from inter­molecular inter­actions and form only intra­molecular contacts. There are short inter­molecular C—H⋯F inter­actions in the structure, but no conventional inter­molecular hydrogen bonds

4,7,13,18-Tetra­oxa-1,10-diazo­nia­bicyclo­[8.5.5]icosane hexa­fluorido­silicate

The asymmetric unit of the title molecular salt, C14H30N2O4 2+·SiF6 2−, contains half of both the anion and the cation, both ions being completed by a crystallographic twofold axis passing through the Si atom. The cation has a cage structure with the ammonium H atoms pointing into the cage. These H atoms are shielded from inter­molecular inter­actions and form only intra­molecular contacts. There are short inter­molecular C—H⋯F inter­actions in the structure, but no conventional inter­molecular hydrogen bonds

Kinetic investigations of the mechanism of dihydrogen driven catalytic reduction of methylene blue, safranine O, methyl viologen and ferricyanide using platinum carbonyl cluster anions (Chini-clusters) as catalyst

[Bu4N]2[Pt12(CO)24] (1) catalyses the selective reduction of electron acceptors (S), methylene blue (MB+), safranine O (Saf+), methyl viologen (MV2+) and ferricyanide by dihydrogen. Macroscopic rate investigations for the cationic substrates in DMF, and for ferricyanide in DMSO have been carried out. In all cases, kobs is given by k1 [S] + k2, indicating that there are two catalytic cycles. In one of them, the formation of a complex between S and [Pt12(CO)24]2− in the rate determining step (rate constant k1) is followed by electron transfer and/or other fast steps. In the other catalytic cycle, the rate determining step (rate constant k2) involves formation of the solvated cluster anion [Pt12(CO)24]2−. The solvated cluster then undergoes fast reduction by dihydrogen and other reactions. The relative contributions of these two cycles depend on the substrate, and for MB+, Saf+, MV2+ and [Fe(CN)6]3− the contribution of the second cycle is about 99%, 55%, 77% and 97%, respectively. Both k1 and k2 of ferricyanide are about three orders of magnitude smaller than those of the cationic electron acceptors. The rates of reduction of MB+ and Saf+ have also been studied in the presence of added water. Rates increase as the presence of water provides an additional pathway for the reduction of [Pt12(CO)24]2− to [Pt9(CO)18]2−.© Elsevie