Syntheses of Amino-Substituted Iridabenzofurans and Subsequent Selective N-Functionalisation

The first examples of amino-substituted fused-ring metallabenzenes, the cationic iridabenzofuran [Ir(C₇ H₄ O{NH₂ -2}{OMe-7})(CO)(PPh₃ )₂ ][O₃ SCF₃ ] (5) and neutral analogue Ir(C₇ H₄ {NH₂ -2}{OMe-7})Cl(PPh₃ )₂ (6), can be prepared by reduction of the corresponding nitro-substituted iridabenzofurans with zinc and concentrated hydrochloric acid. N-functionalised derivatives of 5 and 6 are formed through alkylation, sulfonylation or acylation. Thus, consecutive treatments with methyl triflate and base gives the corresponding trimethylammonium-substituted iridabenzofurans while sulfonamide derivatives are formed with p-toluenesulfonyl chloride. N-Acylation of 5 or 6 with acid chlorides, however, selectively form either amide or imide products depending on the charge on the metal and the steric size of the acid chloride. Cationic 5 gives amide substituted products regardless of the conditions whereas neutral 6 rapidly undergoes di-N-acylation with excess benzoyl chloride under mild conditions to give the imide-substituted product Ir(C₇ H₄ O{N[C(O)Ph]₂ -2}{OMe-7})Cl(PPh₃ )₂ (13). Selective mono-acylation of 6 can be achieved with one equivalent of benzoyl chloride or with excess of the sterically congested pivaloyl chloride.