Synthesis, Characterization, and H-Bonding Abilities of Ruthenium(II) Complexes Bearing Bidentate NR,NH-Carbene/Phosphine Ligands

Two new diphenylphosphine-substituted benzimidazoles featuring
an ethylene (2) or a methylene linker (5) between the benzimidazole and the phosphine have been prepared.
These precursors for bidentate carbene/phosphine ligands react with
[RuCp*(μ3-Cl)]4 under tautomerization
with formation of complexes of type [RuCp*Cl(L)] ([6]
and [7], L = NR,NH-carbene/phosphine ligand). The crystal
structures of [6] and [7] have been determined
by X-ray diffraction. These studies revealed that the length of the
bridge between the benzimidazol-2-ylidene and the phosphine determines
the geometric parameters of the carbene/phosphine chelate ring and
the donor properties of the phosphine. A 1H NMR titration
of complex [6] with DMPU revealed the formation of a
(carbene)N−H···O(DMPU) hydrogen bond in solution.