Synthesis and characterization of Ni-, Pd- and Pt-complexes of functionalized, tripodal phosphine ligands

Abstract

The tripodal ether, ester and cyano functionalized phosphine ligands (tdppcymome) ( a), (tdppcyme) ( b), and (tdppcycn) ( c), respectively, of the cyclohexane backbone type cis,cis-1,3,5-(PPh 2) 3-1,3,5-(R) 3-C 6H 5 (tdppcyR) (with R=–CH 2OCH 3, –COOCH 3, –CN) are each treated with the cyclooctadiene complexes M(COD)Cl 2 ( 1, 2) (M=Pt, Pd) and NiCl 2 ( 3). The potentially tridentate ligands form with these transition metals four-coordinated, bidentate dichloro complexes cis-M II(η 2-tdppcyR)Cl 2 ( 1a– c, 2a– c, 3a– c), in which two diphenylphosphino donor groups are bound to the metal center, and one phosphorus remains uncoordinated. Treatment of the ether functionalized complex 1b with SnCl 2 a bimetallic platinum tin complex cis-Pt(tdppcyme)Cl(SnCl 3) ( 1e) is obtained. Detailed NMR investigations were undertaken to characterize structural properties. The platinum and palladium complexes have square-planar coordination geometries, whereas the nickel compounds show a different behavior with a temperature-dependent change from square-planar to tetrahedral arrangements. For Ni(tdppcyme)Cl 2 ( 3b) a single-crystal X-ray structure determination was performed which established the η 2-coordination of the phosphine ligand and the square-planar geometry of the nickel complex in the solid state. The cyclohexane backbone of the ligand prefers the boat conformation.