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) 2 Hg (PyPh = 2-(2‘-pyridyl)phenyl) and MHCl(CO)(PPh 3 ) 3 proceeds smoothly to form M(η 2 -PyPh)Cl(CO)(PPh 3 ) 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(η 2 -PyPh)I(CO)(PPh 3 ) 2 (M = Ru ( 2a ); M = Os ( 2b )), [M(η 2 -PyPh)(CO) 2 (PPh 3 ) 2 ]SbF 6 (M = Ru ( 3a ); M = Os ( 3b )), and M(η 2 -PyPh)(η 2 -S 2 CNMe 2 )(CO)(PPh 3 ) (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(η 2 -PyPh-4,6-(NO 2 ) 2 )Cl(CO)(PPh 3 ) 2 (M = Ru ( 5a ); M = Os ( 5b )). Under appropriate conditions the mono-nitrated derivative, Os(η 2 -PyPh-4-NO 2 )Cl(CO)(PPh 3 ) 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(η 2 -PyPh-4-Br)Cl(CO)(PPh 3 ) 2 (M = Ru ( 6a ); M = Os ( 6b )). With excess brominating agent ([PyrH][Br 3 ]) and a longer reaction time the unusual mixed triphenylphosphine/pyridine complex, Os(η 2 -PyPh-4-Br)Cl(CO)(Pyr)(PPh 3 ) ( 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 CO 2 /H + or Bu 3 SnCl forms Os(η 2 -PyPh-4-CO 2 H)Cl(CO)(PPh 3 ) 2 ( 7a ) or Os(η 2 -PyPh-4-SnBu 3 )Cl(CO)(PPh 3 ) 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(η 2 -PyPh)(CO) 2 (PPh 3 ) 2 ]SbF 6 ( 3b ), Os(η 2 -PyPh)(η 2 -S 2 CNMe 2 )(CO)(PPh 3 ) ( 4b ), Os(η 2 -PyPh-4-NO 2 )Cl(CO)(PPh 3 ) 2 ( 5c ), Os(η 2 -PyPh-4-Br)Cl(CO)(PPh 3 ) 2 ( 6b ), and Os(η 2 -PyPh-4-Br)Cl(CO)(Pyr)(PPh 3 ) ( 6c ) have all been determined by X-ray crystal structure analyses.