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 H-1 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 H-1 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.