Detection of a Ruthenabenzene, Ruthenaphenoxide, and Ruthenaphenanthrene Oxide: The First Metalla Aromatics of a Second-Row Transition Metal

Recent Advances in Metallabenzene Chemistry

“…Most of the ruthenabenzenes that have been synthesized are either short-lived at room temperature or can be isolated only if coordinated to a transition-metal center to which some of the electron density can be donated. [18,31] This stability trend between the 4d and 5d metallabenzenes is generally true, in …”

“…The 31 P NMR spectra reveal sharp singlets for the phosphines, even when samples were cooled to À80 8C, thus demonstrating that the axial and basal phosphines exchange rapidly in solution by the well-known Berry pseudorotation process. 31 P-13 C coupling is observed for the substituted carbon atom C1 but not for the unsubstituted C5. This observation demonstrates that while the ligand sphere in solution is dynamic, the smaller CO ligand spends a disproportionate amount of time near substituted C1, probably as a result of steric crowding.…”

“…[19,20,30] The first ruthenabenzene 5 to be observed spectroscopically was reported by Jones, Allison, and co-workers in 1995. [31] Utilizing a method similar to what Ferede and Allison had previously reported for a suspected ferrabenzene, [32] 13 C NMR spectrum of the 13 C-enriched complex exhibited a label-enhanced singlet at d = 291 ppm, which was attributed to the ring carbon atom in the {RuC(OEt)} moiety. Complex 5 subsequently decomposed above À50 8C to an h 1 -cyclopentadienyl complex.…”

“…Complex 5 subsequently decomposed above À50 8C to an h 1 -cyclopentadienyl complex. [31] Additionally, a similar reaction sequence was proposed to proceed through a ruthenaphenanthrene complex, although no direct observation of the metallaphenanthrene was made. This was the first, and to date remains one of the very few, second-row metalla-aromatic molecules to be reported.…”

Selective Activation of Ar-Cl and Ar-C Bonds with Iron(II) Complexes

“…[7] We assume that the ethoxide ion initially adds to the carbene center and that the intermediate complex 9 then rearranges by Ar ± C a bond cleavage, that is, a-aryl elimination. Examples of hydride, alkyl, and aryl migration to a carbene ligand are known; [11,12] the reverse reaction is probably induced by the presence of the labile ligand [13] and/ or the instability of the acetal complex (see above). Exchange of the alkyl group of the carbene ligand occurs in the presence of an excess of EtO À /EtOH, a behavior already observed for vinyl ether complexes.…”