Osmium(II) Complexes Containing a Dianionic CCCC-Donor Tetradentate Ligand

Abstract

The preparation of osmium(II) complexes containing a C C 6 H 4 ,C BzIm ,C BzIm ,C C 6 H 4-tetradentate ligand with a-CH 2 CH 2link between the benzimidazolidene (BzIm) groups is described and the influence of the link on their structures and emissive properties is analyzed. The hexahydride complex OsH 6 (P i Pr 3) 2 (1) reacts with 1,1'-diphenyl-3,3'-ethylenedibenzimidazolium bromide in dimethylformamide to afford OsBr{κ 3-C,C,C-(C 6 H 4-BzIm-CH 2 CH 2-BzIm-Ph)}(CO)(P i Pr 3) 2 (2), as a result of the direct metalation of both benzimidazolium moieties of the salt, the ortho-CH bond activation of a phenyl substituent, and the carbonylation of the metal center by action of the solvent. Treatment of 2 with Na[BH 4 ] leads to the hydride derivative OsH{κ 3-C,C,C-(C 6 H 4-BzIm-CH 2 CH 2-BzIm-Ph)}(CO)(P i Pr 3) 2 (3) which evolves into Os{κ 4-C,C,C,C-(C 6 H 4-BzIm-CH 2 CH 2-BzIm-C 6 H 4)}(CO)(P i Pr 3) 2 (4) as a consequence of the assisted C-H bond activation of the second phenyl substituent. The use of dimethylsulfoxide instead of dimethylformamide allows the generation of the tetradentate ligand in one pot. Stirring of dimethylsulfoxide solutions of 1 leads to Os{κ 4-C,C,C,C-(C 6 H 4-BzIm-CH 2 CH 2-BzIm-C 6 H 4)}(DMSO) 2 (5). The solvent molecules of 5 can be displaced by 1,2bis(diphenylphosphino)ethylene (bdppe), 1,2-bis(diphenylphosphino)benzene (dppbz) and tetrafluorobenzobarrelene (TFB) to yield the [4+2]-derivatives Os{κ 4-C,C,C,C-(C 6 H 4-BzIm-CH 2 CH 2-BzIm-C 6 H 4)}L 2 (L 2 = bdppe (6), dppbz (7), TFB (8)). The X-ray structures of 4, 6 and 7 reveal that in these compounds, the tetradentate ligand adopts a mer three-planar disposition of a phenyl and two benzimidazolidene groups with the other phenyl group situated in a perpendicular direction trans-disposed to L. The reason of this preference is electronic. Thus, the stereochemistry of 7 is the same as that found in the related complexes Os{κ 2-C,C-(MeBzIm-C 6 H 4)} 2 (dppbz) (13) and Os{κ 2-C,C-(MeBzIm*-C 6 H 4)} 2 (dppbz) (14) containing two free orthometalated Nphenylbenzimidazolidene ligands. Complexes 7, 13 and 14 are phosphorescent. The first of them shows emissions narrower and bluer than those of 13 and 14.

Pyridyl-Directed C–H and C–Br Bond Activations Promoted by Dimer Iridium-Olefin Complexes

“…The structure of 9 (Figure ) reveals that the C–Br bond activation is a concerted oxidative addition, which takes place along the olefin-Ir-Cl axis of 8 with the bromine on the chloride ligand . Thus, the coordination polyhedron around the iridium atom can be rationalized as a distorted octahedron with the bromide anion disposed trans to the C(1)–C(2) olefinic bond (Br–Ir–M(1) = 175.21(9)°; M(1) = midpoint between C(1) and C(2)), whereas the chloride ligand lies trans to the metalated phenyl substituent (Cl–Ir–C(9)) = 159.80(8)°), and the pyridyl group is situated trans to the olefinic C(5)–C(6) bond (N–Ir–M(2) = 174.8(1)°; M(2) = midpoint between C(5) and C(6)).…”

Racemic NHC–Iridium Complexes with Electron-Poor Diene Ligands and Their Reactivity in the Intramolecular Hydroamination Reaction

“…Coming back to our interest in the development of NHC–metal chemistry, we note that studies that incorporate both an NHC ligand and such dienes (TFB, TCB, BB) are almost entirely absent from the literature. In fact and to the best of our knowledge, the only NHC–metal complex ever prepared with such dienes was reported a couple of years ago and features a cyclometalated bis-NHC osmium motif ([Os­{κ 4 - C , C , C , C -(C 6 H 4 -BzIm-CH 2 CH 2 -BzIm-C 6 H 4 )}­TFB], BzIm = benzimidazolidene) …”

Recent Advances in Synthesis of Molecular Heteroleptic Osmium and Iridium Phosphorescent Emitters

“…[36] The hexahydride complex 1 also promotes the metalation of the benzimidazolium units and the ortho-CH bond activation of the phenyl substituents of 1,1'-diphenyl-3, Complex 44 is emissive in the orange region (550-600 nm) with a photoluminescence quantum yield of 0.05 in PMMA film. [38] Compounds related to 44, bearing two free phenylbenzimidazolylidene groups, were also prepared to gain insight into the influence of the ethylene linker on the disposition of the donor atoms of the tetradentate ligand and on the photophysical properties. They were obtained according to Scheme 13, starting from the tetrakis(solvento) complexes 45 and 46 via a two steps procedure.…”

“…A deeper comparison of the spectra indicates that the À CH 2 CH 2 À chain favors narrower and bluer emissions. [38]…”