Selenated Schiff bases of 2-hydroxyacetophenone and their palladium(II) and platinum(II) complexes: Syntheses, crystal structures and applications in the Heck reaction

Selenated Schiff bases 2-HO-C6H4C(CH3)N(CH2)nSePh (n = 2, L1; n = 3, L2) and their complexes with Pd(II) and Pt(II), viz [Pd(L1–H)Cl] (1), [Pt(L1–H)Cl] (2), [Pd(L2–H)Cl] (3) and [PtL2Cl2] (4), have been synthesized and characterized with proton, carbon-13 and 77Se{1H} NMR spectra. In the 77Se{1H} NMR spectrum of 2 the signal at δ 387.4 ppm appears as a triplet due to 1J(195Pt–Se) coupling (2043 Hz). The single-crystal structures of L1, L2, 1 and 2 were solved. The C–Se–C bond angles in L1 and L2 have been found to be around 99°. The geometry around Pd and Pt is square planar. The Pd–Se and Pt–Se bond distances are 2.3669(11) and 2.3543(16) Å, respectively. Complexes 1 and 2 are the first examples of crystal structures of Pd and Pt complexes of a (Se, N, O−) ligand. Complex 1 has been explored as a homogeneous catalyst for a Heck type C–C coupling reaction between methyl acrylate and p-iodonitrobenzene (yield ∼80%; reaction time 14 h).

Selenated Schiff bases 2-HO-C6H4C(CH3)N(CH2)nSePh (n = 2, L1; n = 3, L2) and their complexes, [Pd(L1–H)Cl] (1), [Pt(L1–H)Cl] (2), [Pd(L2–H)Cl] (3) and [Pt(L2)Cl2] (4), have been synthesized and characterized with proton carbon-13 and selenium-77 NMR spectra. On coordination of L1 and L2 the signals in the 77Se{1H} spectra undergo deshielding (by up to ∼158 ppm). The single-crystal structures of L1, L2, 1 and 2 were solved. In the square planar complexes 1 and 2, Pd/Pt–Se bond distances are 2.3683(11)–2.3654(10)/2.3549(15)–2.3536(17) Å. Complexes 1 and 2 are the first examples of crystal structures of Pd and Pt complexes of a (Se, N, O−) ligand. Complex 1 catalyzes the Heck type C–C coupling reaction.Figure optionsDownload as PowerPoint slide