Synthesis of Bench-Stable (CO)₅Mn(I)–Aryl Compounds by Transmetalation of Arylboronic Esters

To explore arylboron transmetalation at manganese(I), reactions of 4-fluorophenylborates with pentacarbonylmanganese(I) hexafluorophosphate cation (CO)5Mn(MeCN)(PF6) were evaluated for the formation of 4-fluorophenylmanganese(I) pentacarbonyl (CO)5Mn(4-F–C6H4). The optimal reagent was neopentylglycol 4-fluorophenylboronic ester activated with n-butyllithium, which reacted with (CO)5Mn(MeCN)(PF6) to give (CO)5Mn(4-F–C6H4) in 58% yield. These conditions were extrapolated to reactions involving other neopentylglycol esters to yield a scope of seven (CO)5Mn(I)–aryls with varied substitutions on the aryl ring. The bench-stable, diamagnetic (CO)5Mn(I)–aryl compounds were purified by flash column chromatography on silica and were characterized by IR spectroscopy and by 1H, 13C, 19F, and 55Mn NMR spectroscopies, with solid-state molecular structures verified by X-ray crystallography. Finally, (CO)5Mn(4-F–C6H4) was explored as a synthetic arylating reagent in reactions with various electrophiles and nucleophiles, with organic products including those from aryl C(sp2)–X and aroyl C(sp2)CO–X bond formation.