Redox isomerization of allylic alcohols catalyzed by osmium and ruthenium complexes containing a cyclopentadienyl ligand with a pendant amine or phosphoramidite group: X-ray structure of an η~3-1-hydroxyallyl- metal-hydride intermediate

摘要

Complexes [MCl_2(η~6-p-cymene)]_2 (M = Os (1a), Ru (1b)) react with Li(C_5H_4CH_2CH _2NHMe) (LiCp~N) and KPF_6 to give the sandwich derivatives [M(η~5-Cp~N)(η~6-p-cymene)] PF_6 (M = Os (2a), Ru (2b)). Treatment of 2a and 2b with (2,2--biphenol)PCl leads to [M(η~5-Cp~P) (η~6-p-cymene)]PF_6 (M = Os (3a), Ru (3b); Cp ~P = C_5H_4CH_2CH_2N(Me)P(2,2- -biphenol)). The photolysis of 2a, 2b, 3a, and 3b in acetonitrile produces the release of the p-cymene group and the coordination of the cyclopentadienyl pendant substituent to the metal center to afford [M(η~5-C _5,κ-N-Cp~N)(CH_3CN)_2]PF _6 (M = Os (4a), Ru (4b)) and [M(η~5-C _5,κ-P-Cp~P)(CH_3CN)_2]PF _6 (M = Os (5a), Ru (5b)). Complex 4a, which has been characterized by X-ray diffraction analysis, is a more efficient catalyst precursor than 4b for the redox isomerization of primary allylic alcohols, while the latter is more efficient than the former for the redox isomerization of secondary allylic alcohols. From the catalytic solutions containing 4a and 2-methyl-2-propen-1-ol, the η~3-1-hydroxyallyl complex [OsH(η~5-C _5,κ-N-Cp~N){η~3-CH_2C(CH _3)CHOH}]PF_6 (6) has been crystallized and characterized by spectroscopic methods and X-ray diffraction analysis. The structure shows a N-HO hydrogen bond (2.22 ?) between the NH-hydrogen atom of the coordinated pendant amine group and the oxygen atom of the hydroxy substituent of the allyl ligand.