A Cationic Terminal Methylene Complex of Ir(I) Supported by a Pincer Ligand

A rare example of a cationic methylene complex of Ir­(I), [(PONOP)­Ir­(CH₂)]⁺, <b>2</b> (PONOP = 2,6-bis­(di-<i>tert</i>-butylphosphinito)­pyridine), has been prepared by α-hydride abstraction from the previously described neutral methyl complex [(PONOP)­Ir­(CH₃)]. The intrinsic high reactivity of the compound prevented both the isolation of a pure solid and its full characterization in the solid state. Nevertheless, the proposed molecular structure finds unequivocal support in multinuclear NMR spectroscopy and in reactivity studies that include reactions with Lewis bases, dihydrogen, and ethyl diazoacetate. An ylide compound, <b>3</b>, resulted from the reaction between [(PONOP)­Ir­(CH₂)]⁺ and PMe₃, while the η²-alkene complex <b>5</b> formed in a CC coupling reaction involving the methylene ligand of <b>2</b> and ethyl diazoacetate. Hydrogenolysis of the IrCH₂ linkage of <b>2</b> led to several, previously known, hydride and dihydrogen iridium complexes

Terphenyl Complexes of Molybdenum and Tungsten with Quadruple Metal–Metal Bonds and Bridging Carboxylate Ligands

Mono- and bis-terphenyl complexes of molybdenum and tungsten with general composition M₂(Ar′)­(O₂CR)₃ and M₂(Ar′)₂(O₂CR)₂, respectively (Ar′ = terphenyl ligand), that contain carboxylate groups bridging the quadruply bonded metal atoms, have been prepared and structurally characterized. The new compounds stem from the reactions of the dimetal tetracarboxylates, M₂(O₂CR)₄ (M = Mo, R = H, Me, CF₃; M = W, R = CF₃) with the lithium salts of the appropriate terphenyl groups (Ar′ = Ar^Xyl₂, Ar^Mes₂, Ar^Dipp₂, and Ar^Trip₂). Substitution of one bidentate carboxylate by a monodentate terphenyl forms a M–C σ bond and creates a coordination unsaturation at the other metal atom. Hence in M₂(Ar′)₂(O₂CR)₂ complexes the two metal atoms have formally a low coordination number and an also low electron count. However, the unsaturation seems to be compensated by a weak M–C_arene bonding interaction that implicates one of the aryl substituents of the terphenyl central aryl ring, as revealed by X-ray studies performed with some of these complexes and by theoretical calculations