Sterically Encumbered 4,5-Bis(diphenylphosphino)acenaphthene Ligand and Its Ni(II), Pd(II), Pt(II), and Cu(I) Complexes

A new sterically encumbered symmetrically substituted 4,5-bis(diphenylphosphino)acenaphthene ligand (L) has been prepared. The ligand readily forms distorted square-planar complexes with group 10 metal ions [Ni(II), Pd(II), Pt(II)] and a dimeric tetrahedral complex with Cu(I). The X-ray structures of the ligand and of the complexes show a notably short distance between the two phosphorus atoms, well below than twice the van der Waals radius of P, due to the steric requirements of the rigid acenaphthene backbone. Moreover, in the complexes a stabilizing π–π interaction between two phenyl rings belonging to the two P atoms is present. The [LCuCl]₂ complex is weakly fluorescent both in solution and in the solid state with higher quantum yield as a solid where it exhibits thermally-activated delayed fluorescence and phosphorescence. [LPdCl₂] and [LCuCl]₂ behave as chloride transporters across a liposomal phospholipid membrane with the Pd(II) complex displaying a very high activity.