Unexpected activation of carbon–bromide bond promoted by palladium nanoparticles in Suzuki C–C couplings

Abstract

Dihydroanthracene derivatives (1–6) containing imide (1–3) and amine (4–6) functions have been used for the stabilization of palladium nanoparticles, starting from Pd(0) and Pd(II) organometallic precursors. Well-dispersed nanoparticles of mean size in the range ca. 1.9 to 3.6 nm could be obtained using Pd(0) precursors (PdLc and PdLd, where L = 1–6 and c and d mean the organometallic precursor involved, [Pd₂(dba)₃] and [Pd(ma)(nbd)] respectively). With the aim to evaluate the behaviour of homogeneous species and nanoparticles used as catalytic precursors, palladium complex coordinated to the diamine 6, [Pd(OAc)₂(κ²-N,N-6)], was prepared, reporting for the first time the X-ray diffraction structure of a metallic complex containing a ligand with a 9,10-dihydroanthracene backbone. Palladium systems were evaluated in Suzuki C–C coupling reactions and relevant differences were observed comparing the reactivity of the homogeneous systems in relation to that obtained using palladium nanoparticles as starting catalyst in relation to the activation of the C–Br bonds for deactivated substrates.