Quadratisch‐planare Iridium(II)‐ und Iridium(III)‐Amidokomplexe mit einem PNP‐Pinzettenliganden

Abstract

Koordinationsverbindungen der Edelmetalle nehmen eine zentrale Stellung in der homogenen Katalyse ein. Die Präfe-renz zur geschlossenschaligen elektronischen Struktur prä-destiniert solche Komplexe zu formalen Zwei-ElektronenRedoxreaktionen (oxidative Addition/reduktive Eliminierung).[1] Die Bedeutung von Ein-Elektronen-Reaktionen der Platinmetalle, z. B. bei radikalischen H 2 -, C-H-und C-C-Aktivierungen oder bei katalytischen Oxidationen, wurde bereits demonstriert, [2][3][4][5] dennoch sind voll charakterisierte Metalloradikale noch immer selten.[ [8]Ebenso sind Platinmetallkomplexe mit gerader Valenzelektronenzahl und elektronischer High-Spin-Konfiguration wegen der generell hçheren Ligandenfeldaufspaltung der 4d/ 5d-Metallionen als bei 3d-Metallen sehr selten. Eine Ausnahme bilden quadratisch-planare d 6 -Disilylamidokomplexe vom Typ [MX (L 5 )] (M = Ru, Os; X = F, Cl, I, Trifluormethansulfonat (OTf); L 5 = N(SiMe 2 CH 2 PtBu 2 ) 2 ), die in Analogie zu Eisen(II) eine elektronische Intermediate-SpinKonfiguration aufweisen. [9,10] [Ir(H)Cl(C 8 H 13 )(HL 1 )] (3; R = tBu) [13] wird in situ mit Benzochinon (2.5 ¾quiv.) zum türkisfarbenen 1 in Ausbeuten an isoliertem Produkt von bis zu 60 % oxidiert (Schema 2). [14] Im 31 P-NMR-Spektrum von 1 werden keine Signale beobachtet. Die drei breiten Signale im 1 H-NMR-Spektrum sind stark paramagnetisch verschoben und kçnnen den tBu-Substituenten (d = 10.5 ppm) und je einem Satz von Ligand-

Thionitrosyl‐ and Selenonitrosyliridium Complexes

“…The Ir(PNP) fragments exhibit similar structural features, as expressed, for example, in the Ir–N PNP bond lengths [ 2 : 1.991(2) Å, 3 : 1.995(2) Å, 4 : 1.997(3) Å]. These values are in the same range as that found in [IrCl(PNP)] [1.985(2) Å],9 yet they are shorter relative to that found in parent 1 [2.041(4) Å]3c as a consequence of the stronger nitride trans influence. All three Ir–N–E moieties are almost linear (Table 1).…”

Electron-Spin Structure and Metal–Ligand Bonding in Open-Shell Systems from Relativistic EPR and NMR: A Case Study of Square-Planar Iridium Catalysts

“…To establish a quantitative link between the electronic spin structure and the relativistic magnetic resonance parameters, we performed a detailed analysis of the three square-planar iridium complexes 20,21 shown in Figure 1. The X-ray crystallographic structure available for compound 1 (CCDC-822068) 20 was used as a starting point for the optimizing geometry.…”

“…To establish a quantitative link between the electronic spin structure and the relativistic magnetic resonance parameters, we performed a detailed analysis of the three square-planar iridium complexes 20,21 shown in Figure 1. The X-ray crystallographic structure available for compound 1 (CCDC-822068) 20 was used as a starting point for the optimizing geometry. Molecular geometries for 2 and 3 were then constructed based on that of compound 1 by substituting −N3 or ≡N for chlorine followed by full optimization of geometry (for additional geometry benchmarking calculations, see Tables S2-S4 in Supporting Information).…”

“…Open-shell square-planar iridium amido complexes based on the PNP pincer and containing terminal −Cl, −N3, or ≡N ligands are particularly promising candidates (Figure 1), and have been prepared and structurally characterized by diffraction experiments, EPR, and 1 H NMR spectroscopy. 20,21 The electronic structures of these compounds were analyzed in detail in the original papers, and the oxidation state +II was assigned to iridium in compounds 1 and 2 with an Ir (+II) -L (−I) bond. In contrast, the formal oxidation state +IV was ascribed to iridium in compound 3 as shown in Figure 1, with the Ir (+IV) ≡ N‫|‬ (−III) fragment having a significant amount of nitrido radical character as expressed by the resonance structure Ir (+III) However, no quantitative analysis of the magnetic response parameters was attempted for these systems.…”

“…This is partly due to the fact that such open-shell 5d transition-metal complexes represent a challenge for computational chemistry because of the large effects of spin-orbit (SO) coupling. The authors of the original papers 20,21 even noted that "with large SO coupling spin is not a good quantum number to quantitatively describe electronic structure 22 ".…”