Tris(2-pyrimidyl)- and tris(5-pyrimidyl)phosphines: new multidentate ligands with diverse coordination chemistry

Tris(2-pyrimidyl)- and tris(5-pyrimidyl)phosphines, previously inaccessible multidentate ligands, have been synthesized and introduced into coordination chemistry. Theoretical studies indicate that both ligands are weak σ-donors and strong π-acceptors, exhibiting electronic properties comparable to those of trialkyl phosphites. Positional isomerism of the pyrimidyl groups induces a pronounced difference in steric profile, with the 5-isomer adopting a more open conformation and the 2-isomer a significantly more compact geometry, reflected in their Tolman cone angles of 157° and 148°, respectively. Reactions with Cu(I), Cu(II), Ag(I), Au(I), Co(II), and Pt(II) salts afforded a series of molecular complexes together with 1D and 2D coordination polymers. Tris(5-pyrimidyl)phosphine acts predominantly as a P-monodentate or P,N-/N,N'-bridging ligand, yielding extended frameworks, whereas tris(2-pyrimidyl)phosphine forms both discrete complexes and coordination polymers through P,N,N'- and P,N,N',N″-modes. Selected Cu(I) and Ag(I) complexes exhibit short-lived luminescence with emission maxima between 460 and 605 nm. These findings demonstrate the potential of symmetric tris(pyrimidyl)phosphines as versatile ligands for coordination chemistry.