Study of the conformationally flexible, wide bite-angle diphosphine 4,6-bis(3-diisopropylphosphinophenyl)dibenzofuran in rhodium(I) and palladium(II) coordination complexes

The diphosphine 4,6-bis(3-diisopropylphosphinophenyl)dibenzofuran (abbreviated as ^iPrDPDBFphos) was prepared and studied for its potential as a trans-chelating ligand in transition-metal coordination complexes. In the rhodium norbornadiene complex [(^iPrDPDBFphos) Rh(NBD)]BF₄, which has been characterized with multinuclear NMR spectroscopy, X-ray crystallography, and electrochemical studies, the ligand binds in cis fashion. In the bis(acetonitrile) complexes of rhodium and palladium [(^iPrDPDBFphos)M(CH₃CN)₂](BF ₄)_n (M = Rh, Pd; n = 1, 2), the ligand adopts a trans coordination geometry. Density functional theory (DFT, M06-L) calculations predict that the trans conformer is energetically more favorable than the cis by 3.5 kcal/mol. Cyclic voltammograms of the bis(acetonitrile) Pd(II) and Rh(I) complexes contain reversible and quasi-reversible reduction events, respectively, which are preliminarily assigned as metal-based redox reactions.