Synthesis and Ligand Properties of Chelating Bis(-heterocyclic carbene)-Stabilized Bis(phosphinidenes).

NHC-phosphinidene (NHCP) adducts are an emerging class of ligands with proven binding ability for main group and transition metal elements. They possess electron-rich P atoms with two lone pairs (LPs) of electrons, making them interesting platforms for the formation of multimetallic complexes. We describe herein a modular, high-yielding synthesis of bis(NHCP)s, starting from alkylidene-bridged bis(NHC)s ((IMe)CH; = 1,3) and triphosphirane (PDip) (Dip = 2,6-PrCH) as phosphinidene transfer reagent. The coordination chemistry of [{DipP(IMe)}CH], , was studied in detail, and complexes [·FeBr] and [·Rh(cod)]Cl were prepared, showing that the ligand has a flexible bite angle. The dicarbonyl complex [·Rh(CO)]Cl, with an average value for the CO stretching frequency of 2029 cm, indicates a strongly donating ligand when compared to related complexes. The binding ability of the remaining two phosphorus LPs was demonstrated with AuCl(SMe), giving the heterotrimetallic complex [·(AuCl)·Rh(cod)]Cl. Moreover, [·Rh(cod)]X (X = Cl, B(3,5-(CF)-CH)) was tested in the catalytic hydrogenation of methyl--α-acetamidocinnamate (MAC) and dimethyl itaconate (ItMe), revealing that the chloride complex was inactive, while the BAr complex demonstrated moderate activity. Additionally, [·Rh(cod)]Cl was shown to be moderately air- and moisture-stable, slowly decomposing to the corresponding NHC-stabilized bis-dioxophosphorane, which was independently synthesized by treating the free ligand with dry O.