Phosphorescent Thiazol-2-ylidene Platinum(II) Complexes with β‑Ketoiminates: Single Isomer Formation by Ligand Architecture

We present the synthesis and photophysical
properties of six novel N-phenyl-1,3-thiazol-2-ylidene
platinum­(II) complexes with
sterically demanding N-aryl-β-ketoiminate ligands.
Diverse aryl substituents at the coordinating nitrogen atom (phenyl,
mesityl, 2,6-diisopropylphenyl, 4-cyanophenyl, 1-naphthyl, and 2,4-difluorophenyl)
of the N-aryl-(3Z)-4-amino-3-penten-2-ones
exclusively yielded the SP-4-3 coordinated C∧C*
cyclometalated platinum­(II) complexes as single isomers as a consequence
of the low steric demand of the C∧C* cyclometalating
thiazole ligand and the bulkiness of the β-ketoiminate ligands.
The formation of this isomer was confirmed by 195Pt NMR
and extensive 2D NMR experiments, two solid-state structures, and
the results of DFT calculations. As a proof of principle, two complexes
with the sterically less demanding β-ketoiminate ligands (3Z)-4-amino-3-penten-2-onato and (2Z)-3-amino-1-phenyl-2-buten-1-onato
were synthesized and isolated as an isomeric mixture.