Cyclopalladated complexes with pincer-like ONC-donor N-(4-R-benzoyl)-N′-(9-phenanthrylidene)hydrazines: Regioselective peri‑palladation of the 9-phenanthryl group

Abstract

Two series of cyclopalladates [Pd(HL1–5)Cl] (1–5) and [Pd(L1–5)(PPh3)] (6–10) with the Schiff bases N-(4-R-benzoyl)-N′-(9-phenanthrylidene)hydrazines (H2Ln, where n = 1–5 for R = H, Cl, OMe, NO2 and NMe2, respectively and 2 Hs represent the amide and the ortho or peri H-atom of the 9-phenanthryl group) are reported. All the complexes were characterized by mass spectrometric and spectroscopic (IR, UV–Vis and fluorescence) measurements. Molecular structures of two Schiff bases (H2L1 and H2L4) and three representative complexes from each series [Pd(HL1,3,5)Cl] (1, 3 and 5) and [Pd(L1,2,4)(PPh3)] (6, 7 and 9) were confirmed by single crystal X-ray crystallographic studies. In each of the two types of complexes (HLn)– or (Ln)2– acts as ONC-donor pincer-like ligand. In [Pd(HL1,3,5)Cl], the metal center is in square-planar ONCCl environment assembled by amide-O, azomethine-N and 9-phenanthryl peri‑C coordinating (HL1,3,5)– and the Cl-atom. On the other hand, in [Pd(L1,2,4)(PPh3)], (L1,2,4)2– coordinate through amidate-O, azomethine-N and 9-phenanthryl peri‑C and the P-atom of PPh3 satisfies the fourth coordination site to form a square-planar ONCP coordination geometry around the metal center. The mass spectrometric and infrared and electronic spectroscopic characteristics of all the complexes are complementary to their molecular structures. All the Schiff bases and the complexes are emissive in solution. Theoretical calculations were carried out with a representative complex to comprehend the regioselective peri‑palladation of the 9-phenanthryl fragment of the tridentate ligand.