N-Heterocyclic-Carbene Complexes Readily Prepared from Di-μ-hydroxopalladacycles Catalyze the Suzuki Arylation of 9-Bromophenanthrene

Abstract

New cyclometalated palladium complexes of general formula [Pd(Bmim)(X)(C∧N)] have been synthesized by a novel reaction route involving di-μ-hydroxo-palladacycles [{Pd(μ-OH)(C∧N)}2] (C∧N = 2-benzoylpyridine (Bzpy), I, previously unreported, or C∧N = 2-phenylpyridine (Phpy), II)] and 1,3-butylmethylimidazolium salts [HBmim]X (X: Cl, Br, I, or saccharinate (Sacc); a, b, c, or d complexes, respectively). This simple acid–base reaction could not be achieved under identical conditions when corresponding di-μ-acetate complexes were used as starting materials. An alternative pathway to NHC/imidate complexes has also been explored by reacting IIb with [Ag(Phthal)(SMe2)]2 (Phthal = phthalimidate, e) to obtain [Pd(Bmim)(Phthal)(Phpy)], IIe. Structural characterization by X-ray diffraction of complexes Id, IIb, IId, and IIe has confirmed the proposed formulas. The mononuclear complexes have shown to catalyze the scalable Suzuki–Miyaura cross-coupling of 9-bromophenanthrene with a wide scope of aryl boronic acids, irr...