Structural variation in the copper(II) complexes with a tetradentate bis-6-methylpyridine-substituted bispidine ligand

The Mechanism of the (Bispidine)copper(II)‐Catalyzed Aziridination of Styrene: A Combined Experimental and Theoretical Study

“…This was achieved by tuning the reduction potential on the basis of subtle structural modifications, which enforce a stabilization of the less-common "Jahn-Teller isomers". [36][37][38] Both experimental and DFT-based results indicate that the reduction of the copper(II) precursors is an inner-sphere process to yield a catalytically active copper nitrene species. In contrast with earlier results, [30] there is no significant difference between complexes of tetra-and pentadentate bispidine ligands.…”

“…[36] Although there still is the usual elongation along N7ÀCu with the "sterically innocent" monoA C H T U N G T R E N N U N G dentate co-ligand acetonitrile in combination with the methylated ligand L 5 or the less sterically demanding quinoline donors in L 6 , larger co-ligands such as Cl À ions lead to a partially quenched Jahn-Teller elongation along N3 À Cu and, with the chelating NO 3 À ions, longer bonds to the aromatic donors are observed with L 5 . With the large Br substituents of L 7 , the latter type of structure is already observed with acetonitrile as the co-ligand.…”

“…With (bispidine)copper(II) complexes, isomers with Jahn-Teller-type elongations along one of the three axes (N7-Cu-X ax , N3-Cu-X eq , Ar1-Cu-Ar2) have been observed, and the stabilization of a particular geometry has been found to be a subtle combination of ligand-induced steric strain and electronic effects owing to the bispidine and the co-ligands. [21,[36][37][38] The most commonly observed elongation is along the N7-Cu-X ax axis, and for the tetradentate ligands, this geometry can be destabilized with sterically demanding substituents at the ortho position of the aromatic…”

“…Selected structural parameters of (bispidine)copper(II) complexes. [a] Ligand Co-ligand(s) X,Y (trans-N3, trans-N7) [36,37] An interesting possibility emerging from these observations is to tune the electronic and, specifically, the electrochemical properties. That is, the destabilization of the preorganized "Jahn-Teller isomer" with an N7-Cu-X ax elongation is the design principle used herein for the optimization of the aziridination reactivity (see the Introduction).…”

“…Structural data, also including published structures, [23,25,30,[35][36][37] are listed in Table 1, and the structural plots of the copper(II) complexes with the new ligands appear in Figure 1. With (bispidine)copper(II) complexes, isomers with Jahn-Teller-type elongations along one of the three axes (N7-Cu-X ax , N3-Cu-X eq , Ar1-Cu-Ar2) have been observed, and the stabilization of a particular geometry has been found to be a subtle combination of ligand-induced steric strain and electronic effects owing to the bispidine and the co-ligands.…”