REACTIVITY OF CYCLOMANGANATED 2-PHENYLPYRIDINE DERIVATIVES TOWARD ORGANOLITHIUM REAGENTS - SYNTHESIS OF NOVEL CHELATED TRICARBONYL(ETA(3)-BENZYL)MANGANESE(I) COMPLEXES

Ortho-manganated 2-arylpyridine and -quinoline derivatives were treate d with aryllithium reagents and subsequently with alkyl triflates to y ield air-stable chelated (eta(3)-benzyl)-tricarbonylmanganese complexe s. Addition of PhLi to the cyclomanganated complex of 2-phenylpyridine [NC5H4-C6H4-Mn(CO)(4)], 1, followed by methylation with MeOTf afforde d a red air-stable chelated eta(3)-benzyl, tricarbonyl{2-[(1,2-eta(2)) ,kappa -alpha-2-(phenylmethoxymethylene)-phenyl]pyridine- kappa N}mang anese(I), complex 4a. The molecular structure of lia was established b y single-crystal X-ray diffraction analysis. The study of this structu re indicates a helical shape in which the manganese center adopts an o ctahedral configuration. Spectroscopic analysis indicates that the add ition of the aryllithium reagent to 1 generates a new temperature-and air-sensitive benzoylmanganate species. The latter and other anionic a cylmanganese species generated from different substrates readily decom pose above a temperature of 0 degrees C to yield ketones and a formal [Mn(CO)(3)](-) species which is believed to remain coordinated to the ancilliary pyridinyl group. The latter anionic tricarbonylmanganese sp ecies was trapped by reaction with Me3SnCl and 2 equiv of PPh3 to yiel d a mixture of mer and fac isomers of Me3SnMn(CO)(3)(PPh3)(2). The the rmal decomposition of the benzoylmanganates into ketones via a reducti ve elimination step was exploited as a new synthetic route of aromatic ketones bearing a pyridyl, quinolinyl, or benzo[h]quinolinyl substitu tion pattern.