A series of halogen-substituted biphenyl chromium tricarbonyl complexes has been synthesized and characterized. Heating (2-X-biphenyl), (3-X-biphenyl), or (4-X-biphenyl) (X = F, Cl, Br) with Cr(CO)6 led to formation of biphenyl chromium tricarbonyl complexes where the non-halogenated ring is ligated to Cr(CO)3. X-ray studies show a trend in increasing arene-arene dihedral angles that is consistent with halogen size and carbon-halogen bond length. Special emphasis was placed on single-crystal X-ray diffraction characterizations of the fluorinated derivatives and their respective free ligands. While the dihedral angle for the ortho-fluoro complex is not unexpected, the angles for the meta- and para-fluoro complexes are surprisingly large, since their free ligands are almost completely planar in the solid state. Packing diagrams suggest that the presence of intermolecular C-H…F non-classical hydrogen bonding may be the basis for the observed large dihedral angles. While these interactions may be seen in the solid state, NMR studies using variable temperature, variable concentration, and investigation of nuclear Overhauser effect reveal no evidence for C-H…F hydrogen bonding in solution.

Non-classical hydrogen bonding in halobiphenyl chromium tricarbonyl complexes

ACS Spring 2022

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