Electronic Communication in Binuclear Osmium- and Iridium-Polyhydrides

Reactions of polyhydrides OsH6(PiPr3)2 (1)
and IrH5(PiPr3)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{κ2-C,N-[C5RH2N-py]}­(PiPr3)2 (R = H (3), Me (4), Ph (5)). Reactions of 3 and 4 lead to the hexahydrides
(PiPr3)2H3Os­{μ-[κ2-C,N-[C5RH2N-C5H3N]-N,C-κ2]}­OsH3(PiPr3)2 (R = H (6), Me (7)),
whereas 5 gives the pentahydride (PiPr3)2H3Os­{μ-[κ2-C,N-[C5H3N-C5(C6H4)­H2N]-C,N,C-κ3]}­OsH2(PiPr3)2 (8).
Pentahydride 2 promotes CH bond activation of 3 and the iridium-dihydride IrH2{κ2-C,N-[C5H3N-py]}­(PiPr3)2 (9)
to afford the heterobinuclear pentahydride (PiPr3)2H3Os­{μ-[κ2-C,N-[C5H3N-C5H3N]-N,C-κ2]}­IrH2(PiPr3)2 (10) and the homobinuclear tetrahydride (PiPr3)2H2Ir­{μ-[κ2-C,N-[C5H3N-C5H3N]-N,C-κ2]}­IrH2(PiPr3)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.