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

The preparation of
osmium­(II) complexes containing a CC6H4,CBzIm,CBzIm,CC6H4-tetradentate ligand with a −CH2CH2– link between the benzimidazolidene
(BzIm) groups is described, and the influence of the link on their
structures and emissive properties is analyzed. The hexahydride complex
OsH6(PiPr3)2 (1) reacts with 1,1′-diphenyl-3,3′-ethylenedibenzimidazolium
bromide in dimethylformamide to afford OsBr­{κ3-C,C,C-(C6H4-BzIm-CH2CH2-BzIm-Ph)}­(CO)­(PiPr3)2 (2), as a result of the
direct metalation of both benzimidazolium moieties of the salt, the o-CH bond activation of a phenyl substituent, and the carbonylation
of the metal center by action of the solvent. Treatment of 2 with Na­[BH4] leads to the hydride derivative OsH­{κ3-C,C,C-(C6H4-BzIm-CH2CH2-BzIm-Ph)}­(CO)­(PiPr3)2 (3), which evolves
into Os­{κ4-C,C,C,C-(C6H4-BzIm-CH2CH2-BzIm-C6H4)}­(CO)­(PiPr3)2 (4) as a consequence
of the assisted C–H bond activation of the second phenyl substituent.
The use of dimethyl sulfoxide instead of dimethylformamide allows
the generation of the tetradentate ligand in one pot. Stirring of
dimethyl sulfoxide solutions of 1 leads to Os­{κ4-C,C,C,C-(C6H4-BzIm-CH2CH2-BzIm-C6H4)}­(DMSO)2 (5). The solvent molecules of 5 can be displaced
by 1,2-bis­(diphenylphosphino)­ethylene (bdppe), 1,2-bis­(diphenylphosphino)­benzene
(dppbz), and tetrafluorobenzobarrelene (TFB) to yield the [4 + 2]
derivatives Os­{κ4-C,C,C,C-(C6H4-BzIm-CH2CH2-BzIm-C6H4)}­L2 (L2 = 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 disposed
trans to L. The reason for this preference is electronic. Thus, the
stereochemistry of 7 is the same as that found in the
related complexes Os­{κ2-C,C-(MeBzIm-C6H4)}2(dppbz)
(13) and Os­{κ2-C,C-(MeBzIm*-C6H4)}2(dppbz)
(14) containing two free ortho-metalated N-phenylbenzimidazolidene ligands. Complexes 7, 13, and 14 are phosphorescent. The first of them
shows emissions narrower and bluer than those of 13 and 14.

本文报道了含CC₆H₄、CBzIm、CBzIm、CC₆H₄型四齿配体的锇(II)配合物的合成方法，该配体在苯并咪唑卡宾（benzimidazolidene, BzIm）基团之间带有−CH₂CH₂−桥联结构，并分析了该桥联结构对配合物结构与发光性能的影响。六氢合配合物OsH₆(三(异丙基)膦（PiPr₃）)₂（1）与1,1'-二苯基-3,3'-亚乙基二苯并咪唑鎓溴化物在N,N-二甲基甲酰胺（dimethylformamide, DMF）中反应，生成OsBr{κ³-C,C,C-(C₆H₄-BzIm-CH₂CH₂-BzIm-Ph)}(CO)(PiPr₃)₂（2）；该反应过程涉及该盐的两个苯并咪唑鎓单元的直接金属化、一个苯基取代基的邻位C-H键活化，以及溶剂参与的金属中心羰基化反应。用硼氢化钠（Na[BH₄]）处理配合物2，得到氢化物衍生物OsH{κ³-C,C,C-(C₆H₄-BzIm-CH₂CH₂-BzIm-Ph)}(CO)(PiPr₃)₂（3）；该衍生物可发生辅助型C-H键活化，转化为Os{κ⁴-C,C,C,C-(C₆H₄-BzIm-CH₂CH₂-BzIm-C₆H₄)}(CO)(PiPr₃)₂（4）。若使用二甲基亚砜（dimethyl sulfoxide, DMSO）替代N,N-二甲基甲酰胺，则可通过一锅法生成该四齿配体。将配合物1的二甲基亚砜溶液搅拌，得到Os{κ⁴-C,C,C,C-(C₆H₄-BzIm-CH₂CH₂-BzIm-C₆H₄)}(DMSO)₂（5）。配合物5中的溶剂分子可被1,2-双(二苯基膦)乙烯（1,2-bis(diphenylphosphino)ethylene, bdppe）、1,2-双(二苯基膦)苯（1,2-bis(diphenylphosphino)benzene, dppbz）以及四氟苯并降冰片烯（tetrafluorobenzobarrelene, TFB）取代，生成[4+2]型衍生物Os{κ⁴-C,C,C,C-(C₆H₄-BzIm-CH₂CH₂-BzIm-C₆H₄)}L₂（L₂ = bdppe (6)、dppbz (7)、TFB (8)）。对配合物4、6和7的X射线晶体结构分析表明，在这些化合物中，该四齿配体采取面式三平面排布：一个苯基与两个苯并咪唑卡宾基团共面，另一个苯基则处于垂直于该平面的方向，且与配体L处于反位。该空间取向偏好的原因源于电子效应。配合物7的立体化学结构与相关配合物Os{κ²-C,C-(MeBzIm-C₆H₄)}₂(dppbz)（13）和Os{κ²-C,C-(MeBzIm*-C₆H₄)}₂(dppbz)（14）一致，后两者均包含两个游离的邻位金属化N-苯基苯并咪唑卡宾配体。配合物7、13和14均具有磷光发射特性，其中配合物7的发射峰相较于13和14更窄且蓝移程度更高。