Synthesis and structures of platinum diphenylacetylene and dithiolate complexes bearing diphosphinidenecyclobutene ligands (DPCB-Y)

Abstract

A series of platinum complexes of the type [Pt(D)(A)] having two kinds of π-conjugated ligand systems with donor and acceptor properties are prepared, using p-substituted diphenylacetylenes (tolan-X; X = OMe, H, CF₃), 1,2-benzenedithiolato (bdt) and 1,3-dithia-2-thione-4,5-dithiolato (dmit) as π-donor ligands (D), and 1,2-diaryl-3,4-bis[(2,4,6-tri-tert-butylphenyl)phosphinidene]cyclobutenes (DPCB-Y; diaryl = 2C₆H₄-p-Y (Y = OMe, H, CF₃), biphenyl-2,2′-diyl) as π-acceptor ligands (A). The electronic structures of the resulting complexes are examined in detail to investigate π-orbital interaction occurring in DPCB-Y complexes with a low-coordinate phosphorus ligand. The ³¹P NMR chemical shifts are highly sensitive to the Pt–P distances of the complexes, and linearly correlated with the bond lengths. The UV-vis absorption spectra of [Pt(tolan-X)(DPCB-Y)] display π–π* transitions in the visible region, which are shifted to longer wavelengths as the electron-donating ability of X and electron-withdrawing ability of Y increase, respectively. The complex [Pt(tolan-OMe)(DPCB-CF₃)] with a donor–acceptor combination of substituents exhibits particularly low-energy absorption. The absorption is further red-shifted for [Pt(bdt)(DPCB-phen)] and [Pt(dmit)(DPCB-phen)] having dithiolates as strong π-donor ligands.