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

Straightforward procedures for the generation of rhodium(I) κ Cl -chlorocarbon complexes of the form [Rh(PONOP- t Bu)( κ Cl -ClR)][BAr F 4 ] [R = CH 2 Cl, A ; Ph, 1 ; Cy, 2 ; t Bu, 3 ; PONOP- t Bu = 2,6-bis(di- tert -butylphosphinito)pyridine; Ar F = 3,5-bis(trifluoromethyl)phenyl] in solution are described, enabling isolation of analytically pure A and crystallographic characterization of the new complexes 1 and 2 . Complex 1 was found to be stable at ambient temperature, but prolonged heating in chlorobenzene at 125 °C resulted in formation of [Rh(PONOP- t Bu)(Ph)Cl][BAr F 4 ] 4 with experimental and literature evidence pointing toward a concerted C(sp 2 )-Cl bond oxidative addition mechanism. C(sp 3 )-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- t Bu)Cl][BAr F 4 ] 6 are instead proposed. For dichloromethane, [Rh(PONOP- t Bu)(CH 2 Cl)Cl][BAr F 4 ] 5 was formed in the dark, but facile photo-induced reductive elimination occurred when exposed to light. Net dehydrochlorination affording [Rh(PONOP- t Bu)(H)Cl][BAr F 4 ] 7 and an alkene byproduct resulted for chlorocyclohexane and 2-chloro-2-methylpropane, consistent with hydrogen atom abstraction from the corresponding alkyl radicals by 6 . This suggestion is supported by dynamic hydrogen atom transfer between 6 and 7 on the 1 H NMR time scale at 298 K in the presence of TEMPO.