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···Pt distances of 4.1 and 3.4 Å, 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.