Synthesis and Characterization of Cycloruthenated 2-(Phenylimino)phenyls:  A Useful Probe for the Elucidation of the Tautomeric Process in 2-Hydroxyphenyl-Schiff Bases

Abstract

Treatment of [RuHCl(CO)(PPh 3 ) 3 ] with a 1:1 molar ratio of Hg{ o -C 6 H 4 C(H) NC 6 H 4 -4-R} 2 in refluxing toluene afforded the new compounds [RuCl(CO){η 2 - C,N -C 6 H 4 C(H) NC 6 H 4 -4-R}(PPh 3 ) 2 ] (R = NMe 2, 1a; Me, 1b; I, 1c; NO 2, 1d ) in good yield. The new compounds have been fully characterized by elemental analysis, IR spectroscopy, and 1 H, 13 C{ 1 H}, and 31 P{ 1 H} NMR spectroscopy. A linear correlation in a Hammett plot of the metalated carbon resonance of the imine ligand versus σ + -values is observed, and this is used to comment on, along with the reported ν(CO) data and data previously reported for analogous azo-containing complexes, the keto/enol tautomerization undergone by 2-hydroxyphenyl-Schiff bases. These data suggest that the position of the tautomeric equilibrium is affected by electron-withdrawing or -releasing substituents in the same way as for the analogous 2-phenylazophenols. During the purification of 1a and 1b small amounts of the bis-cyclometalated imine-containing complexes [Ru(CO){η 2 - C,N -C 6 H 4 C(H) NC 6 H 4 -4-R} 2 (PPh 3 )] (R = NMe 2, 2a; Me, 2b ) were isolated. These compounds have been subsequently synthesized and fully spectroscopically characterized. The compounds 1a, 1b, 2a, and 2b have also been further characterized by single-crystal X-ray diffraction studies.