Oxidative-addition of organic monochloro derivatives to dinuclear iridium complexes: The detection of tautomeric equilibria and their implications onthe reactivity

Reactions of MeCOCH2Cl, MeCO2CH2Cl, and (-)-methyl(S)-2-chloropropionate wi th [(Ir-mu -Pz)(CNBut)(2)}(2)] (Pz = pyrazolate, 1) gave the metal-metal bo nded diiridium(II) complexes [(CNBut)(2)(Cl)Ir(mu -Pz)(2)Ir(eta (1)-CH2R)(C NBut)(2)] (R = COMe (2), CO2Me (3)) and the two enantiomers of [(CNBut)(2)( Cl)Ir(mu -Pz)(2)Ir(eta (1)-CH(Me)CO2Me)(CNBut)(2)] (4). Similar reactions o f 1 with equimolar amounts of benzyl chloride and allyl chloride rendered [ (CNBut)(2)(Cl)Ir(mu -Pz)(2)Ir(eta (1)-CH2R)(CNBut)(2)] ((R = Ph (5), CH=CH2 (7)), which were found to be the metal-metal bonded complexes in the solid state, but in equilibrium with the mixed-valence Ir(I)Ir(III) complexes [( CNBut)(2)Ir(mu -Pz)(2)Ir(Cl)(eta (1)-CH2R)(CNBut)(2)] in solution. Replacem ent of chloride by iodide in 5 affords only the diiridium(II) complex [(CNB ut)(2)(I)Ir(mu -Pz)(2)Ir(eta (1)-CH2Ph)(CNBut)(2)] (6). Complexes 5 and 7 r eacted further with a second molar equivalent of chloro derivative to rende r dialkyldiiridium(III) complexes [{Ir(mu -Pz)(eta (1)-CH2R)(CNBut)(2)}(2)( mu -Cl)] Cl, ((R = Ph (8), CH=CH2 (10a)), while those showing a single stat ic species in solution (2-4 and 6) were inactive. The reaction of 7 with al lyl chloride gave also the isomer [(CNBut)(2)(Cl)Ir(eta (1),eta (2)-CH2CH=C H2)(mu -Pz)(2)Ir(eta (1)-allyl)(CNBut)(2)]Cl (10b), in which one allyl grou p bridges the two iridium atoms in an unsymmetrical fashion. This complex i somerizes into the thermodynamic product [{Ir(mu -Pz)(eta (1)-allyl)(CNBut) (2)}(2)(mu -Cl)]Cl, an stereoisomer of 10a. The structures of 10b and 5 wer e solved by single-crystal X-ray diffraction methods.