Oxidative Addition of C-Cl Bonds to a Rh(PONOP) Pincer Complex.

Straightforward procedures for the generation of rhodium(I) κ-chlorocarbon complexes of the form [Rh(PONOP-Bu)( -ClR)][BAr ] [R = CHCl, ; Ph, ; Cy, ; Bu, ; PONOP-Bu = 2,6-bis(di--butylphosphinito)pyridine; Ar = 3,5-bis(trifluoromethyl)phenyl] in solution are described, enabling isolation of analytically pure and crystallographic characterization of the new complexes and . Complex was found to be stable at ambient temperature, but prolonged heating in chlorobenzene at 125 °C resulted in formation of [Rh(PONOP-Bu)(Ph)Cl][BAr ] with experimental and literature evidence pointing toward a concerted C(sp)-Cl bond oxidative addition mechanism. C(sp)-Cl bond activation of dichloromethane, chlorocyclohexane, and 2-chloro-2-methylpropane by the rhodium(I) pincer occurred under considerably milder conditions, and radical mechanisms that commence with chloride atom abstraction and involve generation of the rhodium(II) metalloradical [Rh(PONOP-Bu)Cl][BAr ] are instead proposed. For dichloromethane, [Rh(PONOP-Bu)(CHCl)Cl][BAr ] was formed in the dark, but facile photo-induced reductive elimination occurred when exposed to light. Net dehydrochlorination affording [Rh(PONOP-Bu)(H)Cl][BAr ] and an alkene byproduct resulted for chlorocyclohexane and 2-chloro-2-methylpropane, consistent with hydrogen atom abstraction from the corresponding alkyl radicals by . This suggestion is supported by dynamic hydrogen atom transfer between and on the H NMR time scale at 298 K in the presence of TEMPO.