X-ray Crystal Structure and Homonuclear ³¹P-³¹P δ/J-Resolved NMR Spectroscopic Studies of [AgIr₂(dimen)₄(PPh₃)₂](PF₆)3. Observation of a Statistical Mixture of “Head/Tail” Isomers

The reaction of [AgIr₂(dimen)₄(PF₆)₃(dimen = 1,8-diisocyanomenthane) with 2 equiv of triphenylphosphine results in the coordination of triphenylphosphine to the iridium atoms and forms a linear P-Ir-Ag-Ir-P unit. Recrystallization of the compound from acetone/hexane solutions afforded crystals of [AgIr₂(dimen)₄(PPh₃)₂](PF₆)₃(AgIr₂C₈₄H₁₀₂F_l8N₈P₅) that were the subject of X-ray structural characterization. The complex crystallizes in the monoclinic space group C2/c (No. 15) with Z = 4, a = 26.6 (1) Å, b = 4.67 (1) Å, c = 27.49 (6) Å, β = 117.8 (3)°, and V= 9496 ų. At convergence, R = 0.108 and R_w= 0.123 for 1251observed reflections. The structure features an encapsulated two-coordinate Ag⁺ion with Ir⁺−Ag⁺distances of 2.642 (1) Å. The dimen ligands are disordered in a “head to tail” fashion about the iridium metal centers. Homonuclear ³¹P{¹H) δ/J-resolved NMR data for solutions of the [AgIr₂(dimen)₄(PPh₃)₂]³⁺cation show that a statistical distribution of four different geometrical isomers with different “head to tail” orientations of the dimen ligand occurs in the complex.