Copper(II)-Promoted Chemical Transformations of 3-Substituted 5-(2′-Pyridyl)-1,4-benzodiazepin-2-one Derivatives. Crystal Structures and Spectroscopic Characterisation of Metal Complexes

Abstract

Enantiomerically pure 7-bromo-1,3-dihydro-3-hydroxymethyl-1-methyl-5-(2′-pyridyl)-2H-1,4-benzodiazepin-2one, (+)-1, affords the dichloro adduct 3, [CuCl2(1)], when treated with a solution of CuCl2·2H2O in ethanol. Complex 3 is isolated as a racemic compound. The replacement of one chlorine atom with DMSO gives complex 4, [CuCl(1-H)(DMSO)]. The C(3)-oxygenated product appears as a racemic N,N,O-tridentate ligand in the square-pyramidal complex 5. Oxidative ring contraction of (+)-1 yields 6-bromo-4-ethoxy-1,4-dihydro-1-methyl-4-(2′-pyridyl)-1,3-quinazoline, which acts as an N,N-bidentate ligand in the tetrahedral complex 6. Reaction of 3-acetoxymethyl-7-bromo-1,3-dihydro-1-methyl-5-(2′-pyridyl)-2H-1,4-benzodiazepin-2-one, (±)-2, with CuCl2·2H2O, affords the square-pyramidal complex 7, [CuCl2(2)]. In this complex the lactam oxygen atom of a neighbouring molecule binds to the fifth coordination site, hence forming an infinite chain of connected polyhedra in the crystal. Oxidative ring contraction of 2 leads to 6-bromo1,4-dihydro-4-hydroxy-1-methyl-4-(2′pyridyl)-1,3-quinazoline, which acts as an N,N-bidentate ligand in the centrosymmetric binuclear five-coordinate CuII complex 8. In this complex the di-μ-chloro bridges are asymmetrical: one Cl atom is in an apical position [Cu−Cl, 2.820 (7) Å], whereas the other is in an equatorial position [Cu−Cl, 2.252 (5) Å]. The complexes are characterised by IR spectroscopy and X-ray structure analysis. Mechanisms of racemisation, oxygenation and ring contraction are discussed.