N2.3−: eine Lücke in der N2n−-Reihe gefüllt

Structural and Oxidation State Alternatives in Platinum and Palladium Complexes of a Redox-Active Amidinato Ligand

Reaction of [Pt(DMSO)₂ Cl₂ ] or [Pd(MeCN)₂ Cl₂ ] with the electron-rich LH=N,N'-bis(4-dimethylaminophenyl)ethanimidamide yielded mononuclear [PtL₂ ] (1) but dinuclear [Pd₂ L₄ ] (2), a paddle-wheel complex. The neutral compounds were characterized through experiments (crystal structures, electrochemistry, UV-vis-NIR spectroscopy, magnetic resonance) and TD-DFT calculations as metal(II) species with noninnocent ligands L^- . The reversibly accessible cations [PtL₂ ]⁺ and [Pd₂ L₄ ]⁺ were also studied, the latter as [Pd₂ L₄ ][B{3,5-(CF₃ )₂ C₆ H₃ }₄ ] single crystals. Experimental and computational investigations were directed at the elucidation of the electronic structures, establishing the correct oxidation states within the alternatives [Pt^II (L^- )₂ ] or [Pt^. (L )₂ ], [Pt^II (L^0.5- )₂ ]⁺ or [Pt^III (L^- )₂ ]⁺ , [(Pd^II )₂ (μ-L^- )₄ ] or [(Pd^1.5 )₂ (μ-L^0.75- )₄ ], and [(Pd^2.5 )₂ (μ-L^- )₄ ]⁺ or [(Pd^II )₂ (μ-L^0.75- )₄ ]⁺ . In each case, the first alternative was shown to be most appropriate. Remarkable results include the preference of platinum for mononuclear planar [PtL₂ ] with an N-Pt-N bite angle of 62.8(2)° in contrast to [Pd₂ L₄ ], and the dimetal (Pd₂ ⁴⁺ →Pd₂ ⁵⁺ ) instead of ligand (L^- →L ) oxidation of the dinuclear palladium compound.

Metal-Chelating N,N'-Bis(4-dimethylaminophenyl)acetamidinyl Radical: A New Chromophore for the Near-Infrared Region

A new non-innocent ligand redox system, N,N'-bis(4-dimethylaminophenyl) substituted acetamidinato/acetamidinyl, has been designed and described by example of structurally and spectroscopically characterized ruthenium complexes. The hitherto unreported ligand is responsible for rather intense and narrow absorptions in the near-infrared region of the one- and two-electron oxidized forms. The spectroscopic, computational, and first structural characterization of an amidinyl radical complex adds to the list of established N-based radical ligands.

Discovering more non-innocence: triazenido versus triazenyl radical ligand function, and a comment on [NO2]n as a "suspect" ligand

The unusual suspects: Depending on co-ligands L(n) and the effects of substituents (R), the well-known triazenides [N(NR)2](-) may act as EPR detectable coordinated triazenyl ligands, [N(NR)2](·). They are thus new non-innocent ligands and are related to the hitherto unused non-innocent nitrogen dioxide ligand, [NO2](·).

Manifestations of noninnocent ligand behavior

The potential of redox-active ligands to behave "noninnocently" in transition-metal coordination compounds is reflected with respect to various aspects and situations. These include the question of establishing "correct" oxidation states, the identification and characterization of differently charged radical ligands, the listing of structural and other consequences of ligand redox reactions, and the distinction between barrierless delocalized "resonance" cases M(n)/L(n) ↔ M(n+1)L(n-1) versus separated valence tautomer equilibrium situations M(n)/L(n) ⇌ M(n+1)L(n-1). Further ambivalence arises for dinuclear systems with radical bridge M(n)(μ-L(•))M(n) versus mixed-valent alternatives M(n+1)(μ-L(-))M(n), for noninnocent ligand-bridged coordination compounds of higher nuclearity such as (μ(3)-L)M(3), (μ(4)-L)M(4), (μ-L)(4)M(4), or coordination polymers. Conversely, the presence of more than one noninnocently behaving ligand at a single transition-metal site in situations such as L(n)-M-L(n-1) or L(•)-M-L(•) may give rise to corresponding ligand-to-ligand interaction phenomena (charge transfer, electron hopping, and spin-spin coupling) and to redox-induced electron transfer with counterintuitive oxidation-state changes. The relationships of noninnocent ligand behavior with excited-state descriptions and perspectives regarding material properties and single-electron or multielectron reactivity are also illustrated briefly.