Reactivity of 2-(2-hydroxyphenyl)benzoxazole and 2-(2-hydroxyphenyl)benzothiazole towards group 10 transition metals. Evaluation in palladium catalyzed Suzuki–Miyaura C–C couplings

Abstract

A series of group 10 transition metal complexes based on 2-(2-hydroxyphenyl)benzoxazole (HPBO) and 2-(2-hydroxyphenyl)benzothiazole (HPBT) have been prepared. Reactions of nickel or palladium acetates with HPBT and HPBO produce chelate N–O coordinated compounds respectively. Whilst reaction of [K2PtCl4] with HPBT affords organometallic species product of a C–H bond activation of the phenolic moiety at room temperature. The molecular structures of the three complexes were unambiguously determined by means of single crystal X-ray diffraction analyses. The nickel compound [{Ni(κ2-N,O-HPBT)}2(μ2-O-HPBT)2(μ2-OOCCH3)] (1) showing to be binuclear with the nickel ions found in six-coordinated distorted octahedral environments. Conversely, compound [Pd(κ2-N,O-HPBO)2] (2) is a tetracoordinated monomer with the Pd center having a slightly distorted square planar geometry. Similarly, platinacycle [Pt(κ1-N-HPBT)(κ2-N,C-HPBT)Cl] (3) shows the Pt center into a slightly distorted square planar geometry, exhibiting ligand HPBT in two different coordination modes, as single κ1-N coordinated and as κ2-N-C metalated chelate bidentate ligand, completing the coordination sphere with a chloride ligand. The catalytic activity of the palladium complex (2) was evaluated in Suzuki–Miyaura cross couplings, showing good activity.