Luminescent and redox-active ruthenium(II) and osmium(II) complexes with a rigid allene-bridged polyphosphine†

Abstract

A series of monometallic and homo- and hetero-bimetallic Ru^II and Os^II complexes with the polyphosphines 1,1′-bis(diphenylphosphino)ethene (bppe) and 1,1′,3,3′-tetrakis(diphenylphosphino)allene (tppa) have been prepared and characterized by ³¹P-{¹H} NMR spectroscopy, elemental analysis and fast atom bombardment mass spectral analysis. Their ground-state properties (including electrochemical behavior and electronic absorption) and excited-state properties (including luminescence, quantum yields and MLCT excited state lifetimes) are reported herein. All complexes exhibit room-temperature luminescence, with long-lived ³MLCT excited states observed for monometallic and homobimetallic Os^II complexes with both bppe and tppa ligands. In the heterobimetallic Ru^II–Os^II complex [Ru(bpy)₂(µ-tppa)Os(bpy)₂][PF₆] (bpy = 2,2′-bipyridine) the luminescence of the Ru(bpy)₂-based unit is quenched by the connected Os(bpy)₂-based unit via energy transfer across the tppa spacer containing the allene bridge. Two overlapping one-electron oxidations, corresponding to the two M^II-based moieties (M = Ru or Os) bridged by the tppa spacer, are observed in the homobimetallic complexes.