Synthesis of binuclear platinum complexes containing the ligands 8-naphthyridine, 2-aminopyridine, and 7-azaindolate.: An experimental study of the steric hindrance of the bulky pentafluorophenyl ligands in the synthesis of binuclear complexes

The bidentate N-donor ligands 2-aminopyridine (2-ampy), 7-azaindolate (aza) and 1,8-naphthyridine (napy) have been used to study the steric effect of pentafluorophenyl groups in the synthesis of binuclear platinum(II) complexes. The 2-ampy and aza ligands bridge two Pt(C6F5)(2) fragments with Pt center dot center dot center dot Pt distances of 4.1 and 3.4 angstrom, respectively (complexes 1 and 3). Under the same reaction conditions the napy ligand shows chelating behavior and makes the mononuclear complex (A) highly reactive because of its strained coordination. One of the Pt-N bonds of the chelating complex is broken on reaction with HX {X = Cl (4), Br (5)) because of protonation while the anion X- occupies a created vacant site. The resulting mononuclear complex eliminates C6F5H when refluxed, and a binuclear complex (6) with two napy ligands bridging two Pt(C6F5)Cl fragments is obtained. The reaction of A with HPPh2 affords a mononuclear complex (7) analogous to complexes 5 and 6, but reflux gives a binuclear complex (8) with the two napy ligands terminally bound and the PPh2 groups bridging the Pt(C6F5)napy moieties. The reaction of A with HC CPh gives a binuclear complex; moreover, the final product does not depend on the ratio of complex A to HC CPh. Complexes 1, 4, 6, 9 have been structurally characterized by X-ray diffraction.