Catalytic aziridination of styrene with copper complexes of substituted 3,7-diazabicyclo[3.3.1]nonanones

The copper(n) complexes of five bispidine-type ligands (3,7-diazabicyclo[3.3. I]nonanone; three tetradentate ligands with 2-pyridyl (L-1), 6-methyl-2-pyridyl (L-2) or 2-imidazolyl-3-methyl (L-3) substituents in 2,4-positions; two pentadentate derivatives of L-1 with an additional 2-methylpyridine substituent at N3 (L-4) or N7 (L-5)) have, with one co-ligand (Cl-), a ligand-enforced square pyramidal (L-1,L-2,L-3) or octahedral (L-4,L-5) geometry The main structural properties of three of the five [Cu(L)(CI)](+) complexes (L-1,L-2,L-3) are very similar, with Cu-N-3 < Cu-N7 and Cu-Cl approximate to 2.25 Angstrom (trans to N3); with L-2 Cu-N3 approximate to Cu-N7 and Cu-Cl = 2.22 Angstrom (trans to N7); with L-5 Cu-N3 < Cu-N7 and Cu-Cl = 2.72 Angstrom (trans to N7). These structural patterns lead to considerable differences in ligand field and electrochemical properties (range of Edegrees of approx. 500mV), and the reactivities of the copper(n) complexes as aziridination catalysts (styrene, PhINTs, CH3CN) are strikingly different. While the complex with L-2 is very efficient, the activities of those with L-1 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 (CuL2)-L-II (19) is much smaller than the maximum TON of (CuL2)-L-I (47) suggests that in the active form the catalysts are in the Cu-I 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 Cu-II state and only a small activity in the reduced form indicates that, apart from the reduction potentials, steric effects might also be of importance. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).