Chemistry of an (η⁶-Metallabenzene)metal Complex,[formula omitted]

“Iridabenzene”, [formula omitted] (1), displaces p-xylene from (η⁶-p-xylene)Mo(CO)₃ in tetrahydrofuran solvent, producing (η⁶-iridabenzene)Mo(CO)₃ (2). The solid state structure of 2 has been determined by a single-crystal X-ray diffraction study (monoclinic, P2₁/n, a = 9.897 (1) Å, b = 16.213 (3) Å, c = 20.937 (3) Å, β = 96.68 (1)°, V = 3336.7 (9) ų, Z = 4, R = 0.036, R_w = 0.042). The iridium center in 2 retains the square-pyramidal coordination geometry of parent compound 1, but the Mo(CO)₃ moiety now occupies the formerly “open face” of the pyramid. In solution, the iridabenzene ring rotates with respect to the Mo(CO)₃ fragment. The barrier for this process (ΔG^‡) is estimated to be less than 8 kcal/mol. Treatment of 2 with PMe₃ or CO (L) results in clean replacement of one basal PEt₃ ligand and production of [formula omitted]Mo(CO)₃ (3, L = CO). The solid state structure of 3 (monoclinic, P2₁/n, a = 10.005 (2) Å, b= 18.012 (3) Å, c = 17.055 (4) Å, β = 93.33 (2)°, V= 3068.3 (11) ų, Z = 4, R = 0.031, R_w = 0.041) confirms the basal coordination position of the PMe₃ ligand. As in 2, solution-phase arene ring rotation in 3 and 4 is facile. Treatment of 2–4 with HBF₄·OEt₂ leads to protonation of the metal centers and production of the novel μ-H heterobimetallic complexes, [formula omitted] (5, L = PEt₃; 6, L = PMe₃; 7, L = CO). In the solid state structure of 6-tetrahydrofuran (orthorhombic, P2₁2₁2₁, a = 10.200 (4) Å,b= 16.467 (9) Å, c = 22.023 (7) Å, V = 3699 (3) ų, Z = 4, R = 0.022, R_w = 0.029), the hydride ligand resides approximately trans to the axial phosphine on iridium but bends in slightly toward molybdenum, generating a P_ax-Ir-H angle of 173 (2)°. The Ir-H and Mo-H bond lengths are 1.77 (6) and 1.97 (7) Å, respectively. While solution-phase arene ring rotation still occurs in 5–7, the barrier for this process (ΔG^‡) increases to ~ 13.5–15 kcal/mol.