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Updated: Aug 16, 2025

Combining Solid-state and Solution-based Techniques: Synthesis and Reactivity of ChalcogenidoplumbatesII or IV
Published on: December 29, 2016
Oxidative Addition of C-Cl Bonds to a Rh(PONOP) Pincer Complex
Alexandra Longcake1, Martin R Lees2, Mark S Senn1
1Department of Chemistry, University of Warwick, Gibbet Hill Road, CoventryCV4 7AL, U.K.
Abstract:
Straightforward procedures for the generation of rhodium(I) κCl-chlorocarbon complexes of the form [Rh(PONOP-tBu)(κ Cl-ClR)][BArF 4] [R = CH2Cl, A; Ph, 1; Cy, 2; tBu, 3; PONOP-tBu = 2,6-bis(di-tert-butylphosphinito)pyridine; ArF = 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-tBu)(Ph)Cl][BArF 4] 4 with experimental and literature evidence pointing toward a concerted C(sp2)-Cl bond oxidative addition mechanism. C(sp3)-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-tBu)Cl][BArF 4] 6 are instead proposed. For dichloromethane, [Rh(PONOP-tBu)(CH2Cl)Cl][BArF 4] 5 was formed in the dark, but facile photo-induced reductive elimination occurred when exposed to light. Net dehydrochlorination affording [Rh(PONOP-tBu)(H)Cl][BArF 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 1H NMR time scale at 298 K in the presence of TEMPO.
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