Syntheses, molecular structures and electrochemical behavior of two isomeric Ru(PhNpy)₂(PPh₃)₂ complexes

Abstract

The title compounds, isomers of Ru(PhNpy)₂(PPh₃)₂ (PhNpy = the anion of 2-(N-anilino)-pyridine), having C₁ and C₂ symmetry, were prepared by reacting RuCl₂(PPh₃)₃ with LiPhNpy in toluene. The crystal and molecular structures of these compounds have been determined from three-dimensional X-ray study. Both compounds crystallize in the monoclinic space group P2₁/c with the following unit cell dimensions: C₁-isomer: A = 13.852(3), B = 18.872(3), C = 18.206(3), β = 84.32(5), V = 4736(2) and Z = 4. C₂-isomer: A = 11.166(9), B = 20.404(8), C = 20.716(16), β = 97.14(7), V = 4683(10) and Z = 4. The structures were refined to R = 0.053 (Rw = 0.083) for the C₁-isomer and R = 0.055 (R_w = 0.063) for the C₂-isomer. In the C₁-isomer, the coordinating atoms N-py, N-Ph and PPH₃ are all in cis-arrangement. In the C₂-isomer, the py-rings are trans to each other. The complexes are six-coordinate with four-membered chelate rings. The N---Ru---N angle in the chelate rings is ca. 62° in each case. The Ru---P bond lengths lie in the range 2.286(3)-2.337(1) Å. The average Ru---N(py), and Ru---N(Ph) bond lengths are 2.083 Å and 2.171 Å, respectively. Dichloromethane solutions of the C₁ and C₂ isomers display two quasireversible oxidation waves at 0.480, 1.175 V and 0.290, 1.040 V, respectively. The responses have one-electron stoichiometry and are assignable to Ru_III/Ru_II and Ru_IV/Ru_III couples.