Understanding Precatalyst Activation and Speciation in Manganese-Catalyzed C–H Bond Functionalization Reactions

An investigation into species formed following precatalyst activation in Mn-catalyzed C–H bond functionalization reactions is reported. Time-resolved infrared spectroscopy demonstrates that light-induced CO dissociation from precatalysts [Mn(C^N)(CO)4] (C^N = cyclometalated 2-phenylpyridine (1a), 1,1-bis(4-methoxyphenyl)methanimine (1b)) a toluene solution of (2a) or (2b) results the initial formation solvent complexes fac-[Mn(C^N)(CO)3(toluene)]. Subsequent substitution on nanosecond time scale then yields fac-[Mn(C^N)(CO)3(κ1-(N)-2a)] and fac-[Mn(C^N)(CO)3(κ1-(N)-2b)], respectively. When experiments are performed presence phenylacetylene, fac-[Mn(C^N)(CO)3(toluene)] followed by competitive reaction to give fac-[Mn(C^N)(CO)3(2)] fac-[Mn(C^N)(CO)3(η2-PhC2H)]. The fate mixture depends nature nitrogen-containing substrate used. In case 2-phenylpyridine, migratory insertion alkyne Mn–C occurs, remains unchanged. contrast, when 2b used, η2-bound phenylacetylene occurs microsecond scale, fac-[Mn(C^N)(CO)3(κ1-(N)-2b)] sole product reaction. Calculations with density functional theory indicate this difference behavior may be correlated different affinities 2a for manganese. This study therefore speciation immediately kinetically controlled event. most dominant (the solvent) initially binds metal. subsequent metal-bound also (on ns scale) prior thermodynamic distribution products being obtained.