Reduced and superreduced diplatinum complexes

Abstract

A d8-d8 complex [Pt2(μ-P2O5(BF2)4]4- (abbreviated Pt(pop-BF2)4-) undergoes two 1e- reductions at E1/2 = -1.68 and Ep = -2.46 V (vs Fc+/Fc) producing reduced Pt(pop-BF2)5- and superreduced Pt(pop-BF2)6- species, respectively. The EPR spectrum of Pt(pop-BF2)5- and UV- vis spectra of both the reduced and the superreduced complexes, together with TD-DFT calculations, reveal successive filling of the 6pσ orbital accompanied by gradual strengthening of Pt-Pt bonding interactions and, because of 6pσ delocalization, of Pt-P bonds in the course of the two reductions. Mayer-Millikan Pt- Pt bond orders of 0.173, 0.268, and 0.340 were calculated for the parent, reduced, and superreduced complexes, respectively. The second (5-/6-) reduction is accompanied by a structural distortion that is experimentally manifested by electrochemical irreversibility. Both reduction steps proceed without changing either d8 Pt electronic configuration, making the superreduced Pt(pop-BF2)6- a very rare 6p2 σ-bonded binuclear complex. However, the Pt-Pt σ bonding interaction is limited by the relatively long bridging-ligand-imposed Pt-Pt distance accompanied by repulsive electronic congestion. Pt(pop-BF2)4- is predicted to be a very strong photooxidant (potentials of +1.57 and +0.86 V are estimated for the singlet and triplet dσ∗pσ excited states, respectively).