A novel coordination mode of κ1-N-Br-pyridylbenz-(imida, oxa or othia)-zole to Pt(ii): synthesis, characterization, electrochemical and structural analysis

Abstract

Herein, three novel Pt(ii) complexes with formula [trans-Pt(Br-PyBenz-X)(Cl)₂(DMSO)] (1-3) having Br-pyridylbenz-(imida, oxa or othia)-zole (L_1-3) derivatives as potential bidentate ligands, under an unusual κ¹-N-coordination mode are reported. All compounds were obtained straightforwardly via reaction of corresponding L_PB1-3 and [Pt(Cl)₂(DMSO)₂] (DMSO = dimethyl sulfoxide), at 100 °C in acetonitrile, respectively. 1-3 complexes were characterized by analytical and spectroscopic data: melting point, FT-IR, Raman, UV/Vis and NMR experiments. Cyclic voltammetry studies show an irreversible two-electron process at -0.50 and -0.51 V, which was ascribed to the Pt(ii)/Pt(iv) couple, for complexes 2 and 3. The crystal structure of complex 2 was elucidated by single-crystal X-ray diffraction, where the platinum atom exhibits a square plane geometry, where L_PB2 adopts an unusual mono-coordinated mode via an N-κ¹-benzoxazole ring. According to DFT calculations the first N-coordination exchanging one DMSO molecule is favourable, while the second N-coordination is highly impeded.

Chart 1

Scheme 1. Synthetic route of [trans-PtCl₂(DMSO)(L_PB1–3)], 1–3, species.

Fig. 1. The molecular structure of complex 2 (the thermal ellipsoids are drawn at 60% probability). Selected bond lengths [Å] and angles (°); Cl(1)–Pt(1) 2.2990(12); Cl(2)–Pt(1) 2.3022(12); N(1)–Pt(1) 2.051(3); Pt(1)–S(1) 2.2108(11); N(1)–Pt(1)–S(1) 179.52(10); N(1)–Pt(1)–Cl(1) 87.00(10); S(1)–Pt(1)–Cl(1) 93.47(4); N(1)–Pt(1)–Cl(2) 89.68(10); S(1)–Pt(1)–Cl(2) 89.84(4); Cl(1)–Pt(1)–Cl(2) 174.85(5).

Fig. 2. Cyclic voltammograms of (a) PtCl₂(DMSO)₂; (b) L_PB1 free ligand and complex 1; (c) L_PB2 free ligand and complex 2; (d) L_PB3 free ligand and complex 3. Scan rate 300 mV s⁻¹ cathodic direction.

Fig. 3. Platinum complexes having ligand L_BP1–3 in a mono-coordination mode κ¹-N.