Kinetics of the BpCu-catalyzed carbene transfer reaction (Bp equals dihydridobis(1-pyrazolyl)borate).: Is a 14-electron species the real catalyst for the general copper-mediated olefin cyclopropanation?

Kinetic studies of the ethyl diazoacetate (EDA) decomposition reaction in the presence of BpCu (1) and in the presence or absence of olefin have led to the determination of several kinetic and thermodynamic parameters, and a consistent mechanism has been proposed for the olefin cyclopropanation reaction. Related studies with the complexes [Cu(bipy)(2)]I (bipy = bipyridine) and [Cu(bis(oxazoline))(2)]OTf have shown strong similarities with the results obtained with 1. A general mechanism covering the copper-based systems reported in the literature has been proposed, the real catalyst (i.e., the species to be reacted with EDA) in all cases being a neutral, 14-electron fragment of composition (L-L)Cu (L-L = Bp- and Tp-like ligands, semicorrins, salicylaldehyde derivatives) or, alternatively, the isoelectronic, cationic [(L-L)Cu](+) (for L-L = bis(oxazoline), bipyridine).