Structural, Computational, and Spectroscopic Investigation of [Pd(κ³‑1,1′-bis(di-tert-butylphosphino)ferrocenediyl)X]⁺ (X = Cl, Br, I) Compounds

The reaction of [Pd­(dtbpf)­Cl₂] (dtbpf = 1,1′-bis­(di-tert-butylphosphino)­ferrocene) with sodium bromide yields [Pd­(dtbpf)­Br]­[Br], which displays an interaction between the iron and palladium atoms. The structure of this compound has been obtained and is compared to those of the previously reported [Pd­(dtbpf)­X]⁺ (X = Cl, I) analogues. Similar to [Pd­(dtbpf)­Cl]⁺, [Pd­(dtbpf)­Br]⁺ appears to undergo a solid-state isomerization at low temperature to a species in which the Fe–Pd interaction is disrupted. In addition to ¹H and ³¹P­{¹H} NMR and visible spectroscopy, the [Pd­(dtbpf)­X]⁺ (X = Cl, Br) compounds were also characterized by zero-field ⁵⁷Fe Mössbauer spectroscopy. DFT calculations on [Pd­(dtbpf)­X]⁺ (X = Cl, Br, I) show that the Fe–Pd interaction is weak and noncovalent and that the strength of the interaction decreases as the halide becomes larger. A related trend is noted in the potential at which oxidation of the iron center occurs; the larger the halide, the less positive the potential at which oxidation occurs. Finally, the catalytic activity of [Pd­(dtbpf)­X]⁺ (X = Cl, Br, I) in the arylation of an aromatic ketone was examined and compared to the activity of [Pd­(dtbpf)­Cl₂].