Work

Light-Induced Palladium(IV)–Carbon Bond Homolysis

Year: 2025

Type: article

Abstract: Palladium chemistry has been widely studied since the 1950s, particularly for cross-coupling reactions. It facilitates breaking C-X bonds through oxidative addition and forming C–C bonds through reductive elimination. These 2 electrons’ elementary steps are the key features to construct highly elaborated molecules and explain their exceptional versatility. While Pd(0)/Pd(II) catalytic cycles are well understood, the behavior of Pd(IV) alkyl complexes is less studied, particularly due to their instability. Here, we report the synthesis and characterization by X-ray diffraction, solid-state magnetism, and 1 H NMR of several Pd(Alkyl) 4 fragments, which demonstrate unusual stability thanks to a Cp* 2 Yb(bipym) fragment (Cp* is for pentamethylcyclopentadienyl and bipym for 2,2′bipyrimidine). As such, the Cp* 2 Yb(bipym)Pd(Me) 3 (R) (R = Me, 3 Me; Et, 3 Et ) complexes have a room temperature half-life of more than 17 h, while the one-electron reduction of 3 Me leads to a Pd(Me) 4 fragment, 3 @crypt, which does not degrade over time. This unusual stability allowed us to study the original reactivities of these Pd(Alkyl) 4 fragments other than classical reductive elimination. Thus, we report the first light-induced Pd(IV)–C bond homolysis, which leads to the formation of alkyl radicals. The Cp* 2 Yb(bipym)PdMe 4 complex, 3 Me, reacts under irradiation at 370 nm to form the Cp* 2 Yb(4Me,4H-bipym)PdMe 4, 4, and the Cp* 2 Yb(4Me,4H-bipym)PdMe 2, 5, in which the methyl radical couples with the bipym radical. The mechanism of this peculiar reaction has been determined by DFT. Similar reactivity with 3 @crypt leads to the formation of a free methyl radical, as shown by EPR reaction trapping.

Source: Journal of the American Chemical Society

DOI: 10.1021/jacs.5c12686