Electronic Communication in Binuclear Osmium- and Iridium-Polyhydrides

Abstract

Reactions of polyhydrides OsH6((PPr3)-Pr-i)(2) (1) and IrH5((PPr3)-Pr-i)(2) (2) with rollover cyclometalated hydride complexes have been investigated in order to explore the influence of a metal center on the MHn unit of the other in mixed valence binuclear polyhydrides. Hexahydride 1 activates an ortho-CH bond of the heterocyclic moiety of the trihydride metal-ligand compounds OsH3{kappa(2)-C,N-[C5RH2N-py]}((PPr3)-Pr-i)(2) (R = H (3), Me (4), Ph (5)). Reactions of 3 and 4 lead to the hexahydrides ((PPr3)-Pr-i)(2)H3Os{mu-[kappa(2)-C,N-[C5RH2N-C5H3N]-N,C-kappa(2)]}OsH3((PPr3)-Pr-i)(2) (R = H (6), Me (7)), whereas 5 gives the pentahydride ((PPr3)-Pr-i)(2)H3Os{mu-[kappa(2)-C,N-[C5H3N-C-5(C6H4)H2N]-C,N,C-kappa(3)]}OsH2((PPr3)-Pr-i)(2) (8). Pentahydride 2 promotes C-H bond activation of 3 and the iridium-dihydride IrH2{kappa(2)-C,N-[C5H3N-py]}((PPr3)-Pr-i)(2) (9) to afford the heterobinuclear pentahydride ((PPr3)-Pr-i)(2)H3Os{mu-[kappa(2)-C,N-[C5H3N-C5H3N]-N,C-kappa(2)]}IrH2 ((PPr3)-Pr-i)(2) (10) and the homobinuclear tetrahydride ((PPr3)-Pr-i)(2)H2Ir{mu-[kappa(2)-C,N-[C5H3N-C5H3N]-N,C-kappa(2)]}-IrH2((PPr3)-Pr-i)(2) (11), respectively. Complexes 6-8 and 11 display HOMO delocalization throughout the metal-heterocycle-metal skeleton. Their sequential oxidation generates mono- and diradicals, which exhibit intervalence charge transfer transitions. This notable ability allows the tuning of the strength of the hydrogen-hydrogen and metal-hydrogen interactions within the MHn units.