# Platinum Complexes of Tetradentate NCCN-Coordinating Ligands: Structures and Photophysical Properties of PtII, Pt2 III and PtIV Compounds

## TL;DR

This paper studies the synthesis and properties of platinum complexes with tetradentate ligands, revealing structural and photophysical characteristics of Pt(II), Pt(III), and Pt(IV) compounds.

## Contribution

The paper reports the synthesis and structural characterization of novel platinum complexes with unique photophysical behaviors.

## Key findings

- PtL1 exhibits intense green phosphorescence with a quantum yield of 67%.
- PtL2–3 show deep-red emission with suppressed radiative rates and faster nonradiative decay.
- Pt(IV) complexes emit only at 77 K with lifetimes of around 300 μs.

## Abstract

Tetradentate proligands
based on biphenyl appended at
the 3 and
3′ positions with pyridin-2-yl rings (H2L1), quinoline-8-yl (H2L3) heterocycles, or one
such pyridine and quinoline (H2L2), have been
synthesized by palladium-catalyzed cross-coupling. These compounds
were expected to undergo cyclometalation with K2PtCl4 to generate Pt­(II) complexes, PtL1–3, featuring NCCN-coordinated ligands. For H2L2 and H2L3, the corresponding Pt­(IV) compounds
PtL2–3Cl2 were initially isolated, from
which PtL2–3 could be obtained by reduction with
zinc. In contrast, H2L1 gave an unusual Pt­(III)
dimer, Pt2L1
2Cl2, and
subsequently PtL1 upon reduction. All of the complexes
have been structurally characterized in the solid state by X-ray diffraction.
The quinoline-containing complexes of L2 and L3 feature one or two 6-membered chelates, respectively, with an accompanying
twisting of the quinoline ring(s) relative to the biphenyl unit to
allow the metal ion to achieve its preferred square-planar coordination.
PtL1 displays intense green phosphorescence in solution
at room temperature with a quantum yield of 67%. The deep-red emission
of PtL2–3 is weaker due to suppressed triplet radiative
rate constants as well as faster nonradiative decay. The Pt­(IV) complexes
emit only at 77 K, with long lifetimes of around 300 μs, while
the Pt­(III) dimer shows no detectable emission.