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

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, . [PdCl(RPfcCHCHCH-η:κ)] (1R; R = Ph and cyclohexyl (Cy); fc = ferrocene-1,1'-diyl). These compounds were synthesized from the respective phosphinoferrocene carboxaldehydes RPfcCHO reaction with vinylmagnesium bromide to generate 1-(phosphinoferrocenyl)allyl alcohols, which were subsequently acetylated. The resulting allyl acetates reacted smoothly with [Pd(dba)]/[EtNH]Cl (dba = dibenzylideneacetone) to produce the target compounds. Complexes 1R and their nontethered analogues [PdCl(η-CH)(FcPR-κ)] (5R; 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 5R (particularly with 5Ph), presumably because they form more stable LPd(0)-type catalysts.