Regioselective cyclometallation with some platinum group metal ions

• Cyclometallates of 4-R-Nʹ-(1-arylidene)benzohydrazides (H2Ln) were synthesized.
• These are trans-[M(Ln)(PPh3)2H] (M = Rh/Ir), [M(HLn)Cl] and [M(Ln)(PPh3)] (M = Pd/Pt).
• Characterization was done by microanalysis, spectroscopic and electrochemical measurements.
• X-ray structures showed CNO pincer like coordination of (Ln)2− and (HLn)−.
• Polycyclic aryl is peri- or ortho-metallated in the complexes of 4d or 5d metal ions, respectively.

Reactions of [Rh(PPh3)3Cl], [Ir(PPh3)3Cl], Li2[PdCl4] and K2[PtCl4] with the corresponding 4-R-Nʹ-(arylidene)benzohydrazides (H2Ln; n = 1 and 2 for arylidene = 1-pyrenylidene and R = H and Cl, respectively and n = 3 for arylidene = 1-naphthylidene and R = H) in presence of NaOAc·3H2O in methanol/toluene provide the complexes with general formula trans-[Rh(Ln)(PPh3)2H] (1 and 2), trans-[Ir(Ln)(PPh3)2H] (3 and 4), [Pd(HLn)Cl] (5) and [Pt(HLn)Cl] (6), respectively. Reactions of 5 and 6 with PPh3 in acetone produce the complexes [Pd(Ln)(PPh3)] (7) and [Pt(Ln)(PPh3)] (8), respectively. All the complexes have been characterized with the help of microanalysis (CHN), spectroscopic (infrared, NMR, electronic and emission) and cyclic voltammetric measurements. Molecular structures of 1–5 and 8 have been confirmed with single crystal X-ray crystallography. In 5 and 6, (HL1)− acts as a monobasic CNO-donor ligand, whereas in each of 1–4, 7 and 8, the (Ln)2− acts as a dibasic CNO-donor ligand. In 1, 2, 5 and 7, metallation at the peri position of the 1-pyrenyl moiety of the pincer like ligand leads to the formation of 6,5-membered fused chelate rings, whereas in 3, 4, 6 and 8 metallation takes place at ortho position of the 1-pyrenyl/1-naphthalenyl moiety of the ligand with the formation of 5,5-membered fused chelate rings.

Cyclometallated complexes of Rh(III), Ir(III), Pd(II) and Pt(II) with 4-R-Nʹ-(1-pyrenylidene/naphthylidene)benzohydrazides (H2Ln) are reported. These complexes demonstrate a metal ion depenedent regioselective cyclometallation process. The polycyclic aryl moiety of the ligand (Ln)2− or (HLn)− undergoes exclusive peri- and ortho-metallation with 4d and 5d metal ions, respectively.Figure optionsDownload as PowerPoint slide