Synthesis of Bis(6-methylquinolin-8-yl)phenylarsine and tris(6-methylquinolin-8-yl)-arsine and certain of their bivalent palladium and zerovalent molybdenum complexes. Crystal and molecular structures of Dichloro- and Diiodo-[bis(6-methylquinolin-8-yl)phenylarsine]palladium(II)

Abstract

The potentially tridentate chelating agent bis(6-methylquinolin-8-yl)phenylarsine (AsN₂) and quadridentate tris(6-methylquinolin-8-yl)arsine (AsN₂) have been prepared from 6-methyl-8-lithio-quinoline and dichlorophenylarsine or arsenic trichloride, respectively. Both ligands behave as bidentates in complexes of the type [PdX₂(AsN₂)] and [PdX₂(AsN₂)] (where X = Cl or I) and as tridentates in [Mo(CO)₃(AsN₂)] and [Mo(CO)₃(AsN₂)]. The crystal and molecular structures of [PdCl₂(AsN₂)],CH₂Cl₂ and [PdI₂(AsN₂)] have been determined by single-crystal X-ray analysis. The dichloro complex crystallizes in space group P1 (C_i¹; No.2) with a 9.963(3), b 8.555(3), c 16.102(7) Å; α 86.64(3), β 82.13(3), γ 85.84(3)º; U 1354.3(9) ų and Z = 2. The structure was solved by heavy-atom methods and refined by least squares to R 0.044 for 2530 'observed' reflections with 1>3σ(I). The coordination geometry of the palladium(II) atom is pseudo-square-planar in which the potentially tridentate AsN₂ is behaving as a bidentate only. There is no evidence of interaction of the remaining 6-methylquinolin-8-yl group with the metal centre, although a weak interaction between the solvent of crystallization and the metal may be present. The diiodo complex similarly crystallizes in the centrosymmetric triclinic space group P1 (C_i^l ; No.2) with a 13.590(5), b 10.035(2), c 9.435(2) Å; α 102.68(2), β 90.10(2), γ 92.99(2)º; U 1253.5(6) ų and Z = 2. Least- squares refinement led to a convergence with R 0.038 for 3461 'observed' reflections. The structure of this complex was similar to that of the dichloro analogue.