Selective CC Coupling of Ir–Ethene and Ir–Carbenoid Radicals

Abstract

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.

Carbene Radicals in Cobalt(II)–Porphyrin‐Catalysed Carbene Carbonylation Reactions; A Catalytic Approach to Ketenes

“…It is also worth noting that with dispersion forces, the carbonbound methyl diazoacetate (MDA) adduct B was calculated to be more stable than the nitrogen-bound MDA adduct B ′, while this was reversed in previous calculations without dispersion corrections. [8] Apart from this interesting effect of inclusion of dispersion forces in the calculations, this part of the catalytic mechanism is in fact identical to carbenoid formation in the calculated mechanism for olefin cyclopropanation. [8] Carbene radicals C are in equilibrium with “bridging carbenes” C ′ according to these calculations (nearly thermoneutral), and both C - and C ′-type species were previously detected by EPR spectroscopy after reacting [Co II ( P3 )] with ethyl diazoacetate.…”

“…[7, 8] In this respect, we envisioned that similar intermediates might well be effective in carbene carbonylation reactions, which can be considered as an attack of a nucleophilic cobalt–carbene radical ( C ) at the π-accepting CO substrate. At the same time, both the [Co(Por)] catalyst and the carbenoid intermediates are expected to interact only weakly with amines, alcohols, imines and the ketene reaction products.…”

Cyclopropanation Reactions Mediated by Group 9 Metal Porphyrin Complexes

“…[96] The synthetic strategy reported in Scheme 14 has already been employed to trap iridium radical species. [101] Scheme 14. Reaction of Co(TPP) with ethyl styryldiazoacetate to yield 35.…”

Computational Study on the Intramolecular Carbene-CO Coupling in M(CH2)(CO)3 Radicals (M = Co, Rh, Ir)

“…In particular, De Bruin and coworkers have reported various transition metal carbene radicals of the cobalt group, with catalytic applications, such as cyclopropanation [11,12], carbonylation [13], and selective carboncarbon bond formation by coupling of Ir-ethene complexes with Ir-carbenoid radicals [14]. The structure and the spin density distribution of mononuclear Rh(0) radical complexes were also examined experimentally and computationally [15].…”