Synthesis and catalytic properties of palladium(ii) complexes with P,π-chelating ferrocene phosphinoallyl ligands and their non-tethered analogues

Abstract

Hybrid phosphines usually combine a phosphine moiety with another heteroatom secondary donor group in their structures while compounds equipped with hydrocarbyl π–donor moieties remain uncommon. This contribution reports the synthesis and structural characterization of the first P/π-allyl-chelating complexes that were obtained using the structurally flexible and redox-active ferrocene unit as the scaffold, viz. [PdCl(R₂PfcCHCHCH₂-η³:κP)] (1^R; R = Ph and cyclohexyl (Cy); fc = ferrocene-1,1′-diyl). These compounds were synthesized from the respective phosphinoferrocene carboxaldehydes R₂PfcCHO via reaction with vinylmagnesium bromide to generate 1-(phosphinoferrocenyl)allyl alcohols, which were subsequently acetylated. The resulting allyl acetates reacted smoothly with [Pd₂(dba)₃]/[Et₃NH]Cl (dba = dibenzylideneacetone) to produce the target compounds. Complexes 1^R and their nontethered analogues [PdCl(η³-C₃H₅)(FcPR₂-κP)] (5^R; Fc = ferrocenyl) were evaluated as pre-catalysts for the Pd-catalysed allylic amination of cinnamyl acetate with aliphatic amines and Suzuki–Miyaura-type cross-coupling of 4-tolylboronic acid with benzoyl chloride. In these reactions, better results were achieved with compounds 5^R (particularly with 5^Ph), presumably because they form more stable LPd(0)-type catalysts.