Synthesis of Binuclear Platinum Complexes Containing the Ligands 8-Naphthyridine, 2-Aminopyridine, and 7-Azaindolate. An Experimental Study of the Steric Hindrance of the Bulky Pentafluorophenyl Ligands in the Synthesis of Binuclear Complexes

N,C,N-Pincers in Platinum Bimetallic Complexes: Influence of the Pincer and Bridging Ligands on the Metal-Metal Bond and the Photophysical Properties

Precursors PtCl{κ3-N,C,N-[py-C6HMe2-py]} (1), PtCl{κ3-N,C,N-[py-O-C6H3-O-py]} (2), Pt(OH){κ3-N,C,N-[py-C6HMe2-py]} (3), and Pt(OH){κ3-N,C,N-[py-O-C6H3-O-py]} (4) were used to prepare d8-platinum bimetallic complexes. Precursors 1 and 2 react with AgBF4 and 7-azaindole (Haz) to give [Pt{κ3-N,C,N-[py-C6HMe2-py]}{κ1-N-[Haz]}]BF4 (5) and [Pt{κ3-N,C,N-[py-O-C6H3-O-py]}{κ1-N-[Haz]}]BF4 (6) and 3 and 4 with indolo[2,3-b]indole (H2ii) to generate Pt{κ1-N-[Hii]}{κ3-N,C,N-[py-C6HMe2-py]} (7) and Pt{κ1-N-[Hii]}{κ3-N,C,N-[py-O-C6H3-O-py]} (8). Subsequent addition of 3 and 4 to 5-7 affords bimetallic derivatives [{Pt[κ3-N,C,N-(py-C6HMe2-py)]}2{μ-N,N-[az]}]BF4 (9), [{Pt[κ3-N,C,N-(py-O-C6H3-O-py)]}2{μ-N,N-[az]}]BF4 (10), and {Pt[κ3-N,C,N-(py-C6HMe2-py)]}2{μ-N,N-[ii]} (11). X-ray structures of 9-11 reveal separations between the metals in sequence 9 (3.0515(4) Å) < 10 (3.2689(9) Å) < 11 (3.2949(2) Å). DFT calculations support σ overlap of the dz2 orbitals of platinum atoms, for 9 and 10. Accordingly, their absorption spectra show a MMLCT transition. Complex 9 is a red emitter. The excited state has 3MMLCT characteristics and a Pt-Pt separation of 2.763 Å. Complex 11 is a dual emitter in the red and NIR regions, in solid. Both excited states have a 3LC/LMCT characteristic and platinum-platinum separations of 3.290 and 3.202 Å. Intermediate 5 is a green emitter that achieves quantum yields close to unity, when diluted in PMMA and 1,2-dichloroethane at low concentrations.

Utilising a Proton-Responsive 1,8-Naphthyridine Ligand for the Synthesis of Bimetallic Palladium and Platinum Complexes

We present four proton-responsive palladium and platinum complexes, [MCl2 (R PONNHO)] (M=Pd, Pt; R=i Pr, t Bu) synthesised by complexation of PdCl2 or PtCl2 (COD) with the 1,8-naphthyridine ligand R PONNHO. Deprotonation of [MCl2 (tBu PONNHO)] switches ligand coordination from mono- to dinucleating, offering a synthetic pathway to bimetallic PdII and PtII complexes [M2 Cl2 (tBu PONNO)2 ]. Two-electron reduction gives planar MI -MI complexes [M2 (tBu PONNO)2 ] (M=Pd, Pt) containing a metal-metal bond. In contrast to the related nickel system that forms a metallophosphorane [Ni2 (tBu PONNOPONNO)], an unusual phosphinite binding mode is observed in [M2 (tBu PONNO)2 ] containing close phosphinite-naphthyridinone P⋅⋅⋅O interactions, which is investigated spectroscopically, crystallographically and computationally. The presented proton-responsive and structurally-responsive R PONNHO and bimetallic R PONNO complexes offer a novel platform for future explorations of metal-ligand and metal-metal cooperativity with palladium and platinum.

Synthesis of 1,8-Naphthyridines by the Ionic Liquid-Catalyzed Friedlander Reaction and Application in Corrosion Inhibition

A several of basic ionic liquids (ILs) were synthesized as green solvents and catalysts for the preparation of 1,8-naphthyridyl derivatives via the Friedlander reaction. [Bmmim][Im] exhibited remarkable catalytic activity to achieve the synthetic targets, and the reaction conditions were optimized. The model product 2,3-diphenyl-1,8-naphthyridine (1,8-Nap), with carboxyethylthiosuccinic acid (CETSA) to form an IL corrosion inhibitor ([1,8-Nap][CETSA]), and its corrosion inhibition performance for Q235 steel in 1 M HCl were researched by weight loss measurements, and the results showed that the inhibition efficiency was 96.95% when the concentration of [1,8-Nap][CETSA] was 1 mM at 35 °C. The electrochemical test verified that [1,8-Nap][CETSA] acted as a mixed-type inhibitor but mainly exhibited cathodic behavior. The inhibitor adsorbed on the metal surface was further proved by surface topography analysis.

Two Four-Coordinate and Seven-Coordinate CoII Complexes Based on the Bidentate Ligand 1, 8-Naphthyridine Showing Slow Magnetic Relaxation Behavior

For a long time, the cobalt(II) complex ([Co(napy)₄ ](ClO₄ )₂ ) (napy=1, 8-naphthyridine) has been considered as an eight-coordinate complex without any structural proof. After careful considerations, two complexes [Co(napy)₂ Cl₂ ] (1) and [Co(napy)₄ ](ClO₄ )₂ (2) based on the bidentate ligand napy were synthesized and structurally characterized. X-ray single-crystal structural determination showed that the cobalt(II) center in [Co(napy)₂ Cl₂ ] (1) is four-coordinate with a tetrahedral geometry (T_d ), while [Co(napy)₄ ](ClO₄ )₂ (2) is seven-coordinate rather than eight-coordinate with a capped trigonal prism geometry (C_2v ). Direct-current (dc) magnetic data revealed that complexes 1 and 2 possess positive zero-field splitting (ZFS) parameters of 11.08 and 25.30 cm^-1 , respectively, with easy-plane magnetic anisotropy. Alternating current(ac) susceptibility measurements revealed that both complexes showed slow magnetic relaxation behaviour. Theoretical calculations demonstrated that the presence of easy-plane magnetic anisotropy (D>0) for complexes 1 and 2 is in agreement with the experimental data. Furthermore, these results pave the way to obtain four-coordinate and seven-coordinate cobalt(II) single-ion magnets (SIMs) by using a bidentate ligand.

Enhanced kinetic stability of [Pd2L4]4+ cages through ligand substitution

[Pd₂(tripy)₄]⁴⁺ cage architectures (where tripy = 2,6-bis(pyridin-3-ylethynyl)pyridine) were made more kinetically robust in the presence of range of nucleophiles by the addition of amino groups in either the 2-(2A-tripy) or 3-(3A-tripy) positions of the tripy ligands' terminal pyridines, with the [Pd₂(2A-tripy)₄]⁴⁺ cage proving the most stable.