Structural diversity in Cu(i) complexes of the PNP ligand: from pincer to binuclear coordination modes and their effects upon the electrochemical and photophysical properties

Monoanionic Anilidophosphine Ligand in Lanthanide Chemistry: Scope, Reactivity, and Electrochemistry

We present the synthesis of a series of new lanthanide(III) complexes supported by a monoanionic bidentate anilidophosphine ligand (N-(2-(diisopropylphosphanyl)-4-methylphenyl)-2,4,6-trimethylanilide, short PN^-). The work comprises the characterization of a variety of heteroleptic complexes containing either one or two PN ligands as well as a study on further functionalization possibilities. The new heteroleptic complexes cover selected examples over the whole lanthanide(III) series including lanthanum, cerium, neodymium, gadolinium, terbium, dysprosium, and lutetium. In case of the two diamagnetic metal cations lanthanum(III) and lutetium(III), we have furthermore studied the influence of the lanthanide ion (early vs. late) on the reactivity of these complexes. Thereby we found that the radius of the lanthanide ion has a major influence on the reactivity. Using sterically demanding, multidentate ligand systems, e.g., cyclopentadienide (Cp^-), we found that the lanthanum complex La(PN)₂Cl (1-La) reacts well to the corresponding cyclopentadienide complex, while for Lu(PN)₂Cl (1-Lu) no reaction was observed under any conditions tested. On the contrary, employing monodentate ligands such as mesitolate, thiomesitolate, 2,4,6-trimethylanilide or 2,4,6-trimethylphenylphosphide, results in the clean formation of the desired complexes for both lanthanum and lutetium. All complexes have been studied by various techniques, including multi nuclear NMR spectroscopy and X-ray crystallography. ³¹P NMR spectroscopy was furthermore used to evaluate the presence of open coordination sites on the complexes using coordinating and noncoordinating solvents, and as a probe for estimating the Ce-P distance in the corresponding complexes. Additionally, we present cyclic voltammetry (CV) data for Ce(PN)₂Cl (1-Ce), La(PN)₂Cl (1-La), Ce(PN)(HMDS)₂ (8-Ce) and La(PN)(HMDS)₂ (8-La) (with HMDS = hexamethyldisilazide, (Me₃Si)₂N^-) exploring the potential of the anilidophosphane ligand framework to stabilize a potential Ce(IV) ion.

Luminescent phosphine copper(i) complexes with various functionalized bipyridine ligands: synthesis, structures, photophysics and computational study

A new series of luminescent phosphine copper(i) complexes with cyano- and hydroxyl-substituted 2,2′-bipyridine ligands have been synthesized and structurally characterized. Their luminescent properties have also been investigated in detail.

[Cu(POP)(N^S)][PF6] and [Cu(xantphos)(N^S)][PF6] compounds with 2-(thiophen-2-yl)pyridines

A series of [Cu(POP)(N^S)][PF₆] and [Cu(xantphos)(N^S)][PF₆] compounds (POP = bis(2-(diphenylphosphino)phenyl)ether, xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene) in which the N^S ligand is a 2-(thiophen-2-yl)pyridine (1), 2-(thiophen-2-yl)-6-methylpyridine (2), 2-(5-methylthiophen-2-yl)pyridine (3) or 2-(5-methylthiophen-2-yl)-6-methylpyridine (4) have been prepared and characterized in solution and the solid state. Single crystal structures of [Cu(POP)(1)][PF₆], [Cu(xantphos)(1)][PF₆], [Cu(xantphos)(2)][PF₆], [Cu(POP)(3)][PF₆]·CH₂Cl₂, and [Cu(xantphos)(4)][PF₆] confirm chelating N^S and P^P ligands, and distorted tetrahedral copper(i) centres. There is close cation⋯anion association, particularly in [Cu(xantphos)(1)][PF₆]. Although the compounds are stable over days in CH₂Cl₂ solution, they are susceptible to the effects of competing ligands such as chloride ion and MeCN. Analysis of the NMR spectroscopic data of a solution of [Cu(POP)(3)][PF₆] with added Cl⁻, gives a K_d value of 0.14 ± 0.03 mM, indicative of ion-pairing. [Cu(POP)(N^S)][PF₆] and [Cu(xantphos)(N^S)][PF₆] exhibit quasi-reversible or irreversible Cu⁺/Cu²⁺ oxidations. They are blue emitters in solution, and the presence of the 5-methyl group in the thiophene ring in 3 and 4 leads to a red-shift in the emission. The highest photoluminescence quantum yields are for [Cu(POP)(2)][PF₆] (30.8%) and [Cu(POP)(4)][PF₆] (33.2%), both of which have a 6-methyl-substituted pyridine ring in the N^S ligand. Excited-state lifetimes are <5 ns. On going from solution to powder samples, red-shifts of 133 to 163 nm are observed leading to yellow emitters. The brightest emitter, [Cu(xantphos)(1)][PF₆], was tested in a LEC device but showed poor electroluminescence and poor charge transporting characteristics.

[Cu(P^P)(N^S)][PF₆] with N^S = 2-(thiophen-2-yl)pyridines show close cation⋯anion association in the solid-state; complex cation association with Cl⁻ occurs in solution. The compounds are blue-emitters in solution with a red-shift of the emission on going to the solid.