Ferrocenylated imine- and amine(secondary/tertiary)- phosphine P^N ligands and their Pd(II) complexes: Synthesis and structural characterization

Abstract

A new family of ferrocenylated P^N ligands where the nitrogen donor is either of an imine or amine (secondary/tertiary), was synthesized. The condensation reaction between diphenylphosphino propylamine and formyl ferrocene led to the formation of imine ligand [(η5-C5H5)Fe{(η5-C5H4)CH=N-(CH2)3-PPh2)}] (1), which on reduction with NaBH4 gave secondary amine ligand [(η5-C5H5)Fe{(η5-C5H4)CH2-NH-(CH2)3-PPh2)}] (2). Additionally, nucleophilic substitution reaction of diphenylphosphino ethyl/propyl amine with [FcCH2NMe3+][I−] salt leads to tertiary-amine ligand [(η5-C5H5)Fe(η5-C5H4)CH2]2-N-(R-PPh2) where R= C2H4 (3) and C3H6 (4). The newly synthesized ferrocenylated ligands were then complexed with Pd(II) giving [cis(κ2-P^N)PdCl2] type complexes (5-8), where imine, secondary amine, and tertiary amine ligands act as a bidentate ligand. The molecular structures of ligand (3), and complexes (5), (6), and (7) have also been determined by X-ray crystallography. In the molecular structures of these complexes, the Pd(II) center presents a distorted square-planar geometry. During the isolation of ligand (4), corresponding phosphine oxide (4A) along with a phosphonium salt (4B) was also isolated as by-products and were characterized by X-ray crystallography. The preliminary catalytic evaluation of complex (7) in the Suzuki-Miyaura cross-coupling reaction of arylboronic acids with aryl bromides was performed.