Synthesis of a New Family of Metallafurans from (Oxapentadienyl)metal Precursors

Treatment of ((1,2,5-η)-4-methyl-5-oxapentadienyl)Ir(PMe₃)₃(1) with HBF₄·OEt₂leads to protonation at carbon C3 and production of [((1,2,5-η)-4-methyl-5-oxapenta-1,4-diene)Ir-(PMe₃)₃]⁺BF₄^-(4). At room temperature, this species rearranges to the iridafuran complex (5). Similar treatment of the five-membered iridacycle, (3) with HBF₄·OEt2 results in direct electrophilic attack at carbon C1 and production of the mer isomer of 5, (6). In the tris(PEt₃) reaction system, treatment of the six-membered ring compound, (7), with HBF₄·OEt₂leads to protonation at C3 and production of (9). Upon heating in tetrahydrofuran at reflux, this species rearranges to the iridafuran complex, (10). Protonation of the five-membered-ring compound, (8), with HBF₄· OEt₂ also produces iridafuran 10 via direct electrophilic addition to C1. Excess I₂reacts with compound 10 exclusively at the metel center to produce the neutral diiodide compound, (11), while excess Br2 reacts with 10 at both the iridium center and C3 of the ring to form the electrophilic aromatic substitution product, (12). Molecular structures of (the PF₆- salt of 10), (11), and (12) have been determined by single-crystal X-ray diffraction studies.