Catalytic Aziridination of Styrene with Copper Complexes of Substituted 3,7‐Diazabicyclo[3.3.1]nonanones

Abstract

AbstractThe copper(II) complexes of five bispidine‐type ligands {3,7‐diazabicyclo[3.3.1]nonanone; three tetradentate ligands with 2‐pyridyl (L1), 6‐methyl‐2‐pyridyl (L2) or 2‐imidazolyl‐3‐methyl (L3) substituents in 2,4‐positions; two pentadentate derivatives of L1 with an additional 2‐methylpyridine substituent at N3 (L4) or N7 (L5)} have, with one co‐ligand (Cl−), a ligand‐enforced square pyramidal (L1,2,3) or octahedral (L4,5) geometry. The main structural properties of three of the five [Cu(L)(Cl)]+ complexes (L1,2,3) are very similar, with Cu−N3 < Cu−N7 and Cu−Cl ≈︁ 2.25 Å (trans to N3); with L2 Cu−N3 ≈︁ Cu−N7 and Cu−Cl = 2.22 Å (trans to N7); with L5 Cu−N3 < Cu−N7 and Cu−Cl = 2.72 Å (trans to N7). These structural patterns lead to considerable differences in ligand field and electrochemical properties (range of E° of approx. 500mV), and the reactivities of the copper(II) complexes as aziridination catalysts (styrene, PhINTs, CH3CN) are strikingly different. While the complex with L2 is very efficient, the activities of those with L1 and L3 are reduced to approx. 50% and 30%, respectively, and those with L4 and L5 are inactive. The fact that the maximum TON (maximum turnover number) of CuIIL2 (19) is much smaller than the maximum TON of CuIL2 (47) suggests that in the active form the catalysts are in the CuI oxidation state, and that the differences in reduction potentials are of major importance for catalysis. The result that CuL4,5 have no activity in the CuII state and only a small activity in the reduced form indicates that, apart from the reduction potentials, steric effects might also be of importance. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)