Synthetic access to a phosphorescent non-palindromic pincer complex of palladium by a double oxidative addition – comproportionation sequence

Abstract

A highly luminescent non-palindromic [(C^C^N)Pd] pincer complex forms upon reacting 3-pyridine-substituted 2,2’-diiodo-biphenyl with [Pd(PPh3)4]. This case study establishes for the first time that the title compound is formed via a...

Luminescent Pd(II) Complexes with Tridentate − Aryl‐pyridine‐(benzo)thiazole Ligands

“…From the viewpoint of the choice of design cyclometalated tetradentate ligand fit perfectly to the square planar geometry of d 8 ‐configured metal cations and conform with the requested rigidity [2,4,7–9,14,15,21,27,49–53] . Nevertheless, tridentate cyclometalating ligands have been very successfully used in luminescent Pt(II), [2,13,20,26,28–31,45,51–53] Pd(II) [5,12,19,20,24,28,31,43,45] and especially Au(III) complexes, [2,51,54–56] as their synthesis is easier than for the complex scaffolds related to tetradentate ligands, whereas the fourth coordination site allows for fine‐tuning of the electronic properties.…”

“…d 8 ‐configured Pt(II) and Pd(II) complexes containing π‐accepting ligand moieties with low lying π* orbitals have allowed to design and tune long‐lived metal‐to‐ligand charge transfer (MLCT) or mixed MLCT/π–π* (LC) excited states for efficient triplet emission [1–24] . Moreover, rigidity of both the organic ligand and the square planar coordination environment around the metal centre help suppressing competitive radiationless decay paths [6,7,10,11,13,17–20,23–31] . Cyclometalating heteroaromatic ligands have been frequently used for luminescent Pt(II) or Pd(II) complexes as they provide rigidity, a strong ligand field and suitable LC excited states [2,4–25,31] .…”

“…Cyclometalating heteroaromatic ligands have been frequently used for luminescent Pt(II) or Pd(II) complexes as they provide rigidity, a strong ligand field and suitable LC excited states [2,4–25,31] . Combined experimental/theoretical studies on such complexes have previously related structural features with photoluminescence (PL) properties [11,18,19,23–31] . While structural effects on the emission energy can be rationally predicted via density functional theory (DFT) modelling, the PL efficiency, expressed as PL quantum yields, is less predictable [13,22,25–27] .…”

“…Moreover, rigidity of both the organic ligand and the square planar coordination environment around the metal centre help suppressing competitive radiationless decay paths [6,7,10,11,13,17–20,23–31] . Cyclometalating heteroaromatic ligands have been frequently used for luminescent Pt(II) or Pd(II) complexes as they provide rigidity, a strong ligand field and suitable LC excited states [2,4–25,31] . Combined experimental/theoretical studies on such complexes have previously related structural features with photoluminescence (PL) properties [11,18,19,23–31] .…”

Non-palindromic (C^C^D) gold(iii) pincer complexes are not accessible by intramolecular oxidative addition of biphenylenes – an experimental and quantum chemical study

“…38 In addition, we could show that 2,2'-dihalobiphenyls may be applied to palladium using a double oxidative additioncomproportionation sequence. 39 However, in the course of searching new variants for introducing (C^C^D)-based pincer ligands, we followed a different idea as well: In 2015, Dean Toste and co-workers showed a gold(I) NHC complex to be able to undergo an oxidative addition into the strained ring of biphenylene, thereby forming the corresponding cyclometalated [(C^C)Au III ] complex 1 (Chart 1 A), 40 a reaction which was already shown to happen for the group 10 metals. [41][42][43][44][45] Only shortly thereafter, the group of Didier Bourissou succeeded in a similar reaction employing a bidentate 1,2-diphosphano-1,2-dicarba-closo-dodecaborane ligand (Chart 1 B).…”