Synthesis, Structural Characterization, and Photophysical Properties of Palladium and Platinum(II) Complexes Containing 7,8-Benzoquinolinate and Various Phosphine Ligands

A series of mononuclear cyclometalated benzo[h]quinolinate platinum and palladium(II) complexes with phosphine
ligands, namely, [M(bzq)ClL] (L = PPh2H, Pt 1, Pd 2; PPh2C⋮CPh, Pt 3, Pd 4), [Pt(bzq)(PPh2H)(PPh2C⋮CPh)]ClO4
5, [Pt(bzq)(PPh2C(Ph)C(H)PPh2)]ClO4 6, and [Pt(bzq)(C⋮CPh)(PPh2C⋮CPh)] (7a, 7b), were synthesized. The
X-ray crystal structures of 1, 6·CH3COCH3·1/2CH3(CH2)4CH3, and 7b·CH3COCH3 have been determined. In 1, the
metalated carbon atom and the P atom are mutually cis, whereas in 7b they are trans located. For complex 6, C
and N are crystallographically indistinguishable. Reaction of [Pt(bzq)(μ-Cl)]2 with PPh2H and excess of NEt3 leads
to the phosphide-bridge platinum dimer [Pt(bzq)(μ-PPh2)]2 8 (X-ray). Moderate π−π intermolecular interactions
and no evident Pt−Pt interactions are found in 1, 7b, and in 8. All of the complexes exhibit absorption bands at
high energy due to the intraligand transitions (1IL π → π*) and absorptions at lower energy which are attributed
to MLCT (5d) π → π* (CΛN) transition. Platinum complexes show strong luminescence in both solid state and
frozen solutions. The influence of the coligands on the photophysics of the platinum complexes has been examined
by absorption and emission spectroscopy.