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 treated with aryllithium reagents and subsequently with alkyl triflates to yield air-stable chelated (eta(3)-benzyl)-tricarbonylmanganese complexes. Addition of PhLi to the cyclomanganated complex of 2-phenylpyridine [NC5H4-C6H4-Mn(CO)(4)], 1, followed by methylation with MeOTf afforded a red air-stable chelated eta(3)-benzyl, tricarbonyl{2-[(1,2-eta(2)),kappa C-alpha-2-(phenylmethoxymethylene)-phenyl]pyridine- kappa N}manganese(I), complex 4a. The molecular structure of lia was established by single-crystal X-ray diffraction analysis. The study of this structure indicates a helical shape in which the manganese center adopts an octahedral configuration. Spectroscopic analysis indicates that the addition of the aryllithium reagent to 1 generates a new temperature-and air-sensitive benzoylmanganate species. The latter and other anionic acylmanganese species generated from different substrates readily decompose 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 species was trapped by reaction with Me3SnCl and 2 equiv of PPh3 to yield a mixture of mer and fac isomers of Me3SnMn(CO)(3)(PPh3)(2). The thermal decomposition of the benzoylmanganates into ketones via a reductive elimination step was exploited as a new synthetic route of aromatic ketones bearing a pyridyl, quinolinyl, or benzo[h]quinolinyl substitution pattern.