Selective C-C coupling of Ir-ethene and Ir-carbenoid radicals.

The reactivity of the paramagnetic iridium(II) complex [Ir(II)(ethene)(Me(3)tpa)](2+) (1) (Me(3)tpa=N,N,N-tris(6-methyl-2-pyridylmethyl) amine) towards the diazo compounds ethyl diazoacetate (EDA) and trimethylsilyldiazomethane (TMSDM) was investigated. The reaction with EDA gave rise to selective C--C bond formation, most likely through radical coupling of the Ir-carbenoid radical species [Ir(III){CH.(COOEt)}(MeCN)(Me(3)tpa)](2+) (7) and (the MeCN adduct of) 1, to give the tetracationic dinuclear complex [(MeCN)(Me(3)tpa)Ir(III){CH(COOEt)CH(2)CH(2)}Ir(III)(MeCN)(Me(3)tpa)](2+) (4). The analogous reaction with TMSDM leads to the mononuclear dicationic species [Ir(III){CH(2)(SiMe(3))}(MeCN)(Me(3)tpa)](2+) (11). This reaction probably involves a hydrogen-atom abstraction from TMSDM by the intermediate Ir-carbenoid radical species [Ir(III){CH.(SiMe(3))}(MeCN)(Me(3)tpa)](2+) (10). DFT calculations support pathways proceeding via these Ir-carbenoid radicals. The carbenoid-radical species are actually carbon-centered ligand radicals, with an electronic structure best described as one-electron-reduced Fischer-type carbenes. To our knowledge, this paper represents the first reactivity study of a mononuclear Ir(II) species towards diazo compounds.