Synthesis and Ligand Properties of Chelating Bis( N -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)2 Cn H2n ; n = 1,3) and triphosphirane (PDip)3 (Dip = 2,6- i Pr2 C6 H3 ) as phosphinidene transfer reagent. The coordination chemistry of [{DipP(IMe)}2 CH2 ], 1 , was studied in detail, and complexes [ 1 ·FeBr2 ] and [ 1 ·Rh(cod)]Cl were prepared, showing that the ligand has a flexible bite angle. The dicarbonyl complex [ 1 ·Rh(CO)2 ]Cl, with an average value for the CO stretching frequency of 2029 cm-1 , indicates a strongly donating ligand when compared to related complexes. The binding ability of the remaining two phosphorus LPs was demonstrated with AuCl(SMe2 ), giving the heterotrimetallic complex [ 1 ·(AuCl)2 ·Rh(cod)]Cl. Moreover, [ 1 ·Rh(cod)]X (X- = Cl, B(3,5-(CF3 )2 -C6 H3 )4 ) was tested in the catalytic hydrogenation of methyl- Z -α-acetamidocinnamate (MAC) and dimethyl itaconate (ItMe2 ), revealing that the chloride complex was inactive, while the BArF complex demonstrated moderate activity. Additionally, [ 1 ·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 O2 .