Electrophilic Substitution Reactions at the Phenyl Ring of the Chelated 2-(2‘-Pyridyl)phenyl Ligand Bound to Ruthenium(II) or Osmium(II)

Reaction between (PyPh)2Hg (PyPh = 2-(2‘-pyridyl)phenyl) and MHCl(CO)(PPh3)3 proceeds smoothly to form M(η2-PyPh)Cl(CO)(PPh3)2 (M = Ru (1a); M = Os (1b)). In both complexes the PyPh ligand is bound as a stable five-membered chelate ring. The chloride ligand in these complexes can be removed through reaction with a silver salt and other ligands then introduced. In this way the compounds M(η2-PyPh)I(CO)(PPh3)2 (M = Ru (2a); M = Os (2b)), [M(η2-PyPh)(CO)2(PPh3)2]SbF6 (M = Ru (3a); M = Os (3b)), and M(η2-PyPh)(η2-S2CNMe2)(CO)(PPh3) (M = Ru (4a); M = Os (4b)) have been prepared. The coordinated PyPh ligand in 1a and 1b is activated by the metal toward electrophilic substitution at the phenyl ring. Nitration occurs in both the phenyl 4- and 6-positions of 1a or 1b, i.e., ortho and para to the metal, to give M(η2-PyPh-4,6-(NO2)2)Cl(CO)(PPh3)2 (M = Ru (5a); M = Os (5b)). Under appropriate conditions the mono-nitrated derivative, Os(η2-PyPh-4-NO2)Cl(CO)(PPh3)2 (5c), can also be isolated. Bromination of 1a or 1b occurs in the phenyl 4-position, i.e., para to the metal, to give M(η2-PyPh-4-Br)Cl(CO)(PPh3)2 (M = Ru (6a); M = Os (6b)). With excess brominating agent ([PyrH][Br3]) and a longer reaction time the unusual mixed triphenylphosphine/pyridine complex, Os(η2-PyPh-4-Br)Cl(CO)(Pyr)(PPh3) (6c) (Pyr = pyridine), is formed. The brominated osmium substrate (6b) can be lithiated through reaction with BuLi. Although this intermediate has not been isolated, further treatment with the electrophiles CO2/H+ or Bu3SnCl forms Os(η2-PyPh-4-CO2H)Cl(CO)(PPh3)2 (7a) or Os(η2-PyPh-4-SnBu3)Cl(CO)(PPh3)2 (7b), respectively. The functionalized pyridylphenyl ligand in 6a can be removed by heating with acid, to give 2‘-(3-bromophenyl)pyridine, in modest isolated yield. The structures of [Os(η2-PyPh)(CO)2(PPh3)2]SbF6 (3b), Os(η2-PyPh)(η2-S2CNMe2)(CO)(PPh3) (4b), Os(η2-PyPh-4-NO2)Cl(CO)(PPh3)2 (5c), Os(η2-PyPh-4-Br)Cl(CO)(PPh3)2 (6b), and Os(η2-PyPh-4-Br)Cl(CO)(Pyr)(PPh3) (6c) have all been determined by X-ray crystal structure analyses.