A molecular orbital analysis of Cu(I)-catalysed cyclopropanation using diazoalkanes with CH3 and CF3 substituents |
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Authors: | Howell James A S |
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Institution: | School of Chemistry and Physics, Lennard Jones Laboratories, Keele University, Keele, Staffordshire, UK ST5 5BG. j.a.s.howell@keele.ac.uk |
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Abstract: | The mechanism of cyclopropanation catalysed by Cu(I) complexes has been investigated by calculation using a series of diazoalkanes containing inductive electron donating (methyl) and withdrawing (CF3) substituents and a range of metal fragments (Cu+, (DAB)Cu]+, ClCu and (triflate)Cu). Copper-diazoalkane complexes exist as an equilibrium of C- and N-bonded isomers. Catalysis occurs through lowering of the activation energy for rate determining C-N bond cleavage of the C-bonded isomer; this is most marked for (triflate)Cu. Direct reaction of the copper-carbene complex occurs to yield stable cupracyclobutanes in all but one case. Associative substitution of the cupracyclobutane by diazoalkane completes the catalytic cycle. |
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