On the Geometrical Stability of Square‐Planar Platinum(0) Complexes That Bear a PNP‐Pincer‐Type Phosphaalkene Ligand (Eind2‐BPEP).

The four‐coordinate Pt0 complex [Pt(PPh3)(Eind2‐BPEP)] (Eind=1,1,3,3,5,5,7,7‐octaethyl‐1,2,3,5,6,7‐hexahydro‐s‐indacen‐4‐yl; BPEP=2,6‐bis(1‐phenyl‐2‐phosphaethenyl)pyridine), which bears a PNP‐pincer‐type phosphaalkene ligand (Eind2‐BPEP; PNP=N,N‐bis(diphenylphosphine)‐2,6‐diaminopyridine), were found to adopt a square‐planar configuration around the Pt center (τ4=0.11). This coordination geometry is very uncommon for formal d10 complexes. In this study, a series of ligands with different electronic properties (i.e. DMAP, 2,6‐lutidine, PMe3, tBuNC, and CO) were introduced in place of PPh3, and their effects on the coordination geometry were examined. X‐ray diffraction analysis revealed that all complexes adopted a square‐planar configuration (τ4=0.20–0.27). In contrast, DFT calculations indicated that the geometrical stability towards distortion around Pt varied with the ligand. The complexes with pyridine‐based ligands had rigid planar structures, whereas those with π‐accepting ligands, such as CO, were relatively flexible towards distortion. The electronic effects of the ligands were reflected in the spectroscopic properties of the complexes, which showed a large color change in the near‐infrared region. π‐Accepting ligands cause geometrical distortion: The four‐coordinate Pt0 complexes [Pt(L)(Eind2‐BPEP)] (Eind2‐BPEP; Eind=1,1,3,3,5,5,7,7‐octaethyl‐1,2,3,5,6,7‐hexahydro‐s‐indacen‐4‐yl; BPEP=2,6‐bis(1‐phenyl‐2‐phosphaethenyl)pyridine) that bear a pincer‐type phosphaalkene ligand adopt a square‐planar configuration around Pt; this coordination geometry is very uncommon for formal d10 complexes. These complexes have extremely narrow HOMO–LUMO gaps and show strong absorption in the near‐infrared region. [ABSTRACT FROM AUTHOR]