Cationic acetyl complexes of iron(II) and ruthenium(II) bearing neutral N,O ligands: Synthesis, characterization, and interionic solution structure by NOESY NMR spectroscopy

The reactions of complexes trans, cis-M(PMe₃)₂(CO)₂(Me)I (M = Fe (1a), Ru (1b)) with N,O ligands [2-acetylpyridine (2-apy), 2-benzoylpyridine (2-bzpy), and 2,2′-dipyridyl ketone (2,2′-dpk)] in the presence of NaBPh₄ afford a mixture of the two possible stereoisomers trans-[M(PMe₃)₂(CO)(COMe)(N, O)]BPh₄ having the N arm cis (A) or trans (B) to the acetyl group. The stereochemistry of the complexes was determined by ¹H NOESY NMR spectra. For all the iron complexes the major stereoisomer is B, while for ruthenium complexes it is A. When A/B mixtures are left in methylene chloride, the concentration of A increases, indicating that A and B are the thermodynamic and kinetic reaction products, respectively. Furthermore, the more basic the N,O ligands, the more B stereoisomer that forms. The solid-state structure of 4b was obtained using single-crystal X-ray diffraction. For all the complexes, the ion-pair structures and the localization of the counterion in solution with respect to the organometallic moiety were investigated by the detection of interionic contacts in the ¹H NOESY NMR spectra. Specific interactions were observed that indicate that the counterion is localized in solution in front of the face determined by PMe₃ and the two arms of the N,O ligands.