Divalent Cobalt and Copper Coordination Complexes of κ2-N, O-Derivatives of (Z)-1-R-2-(2’-oxazolin-2’-yl)-eth-1-en-1-ates: Structure and Reactivity Patterns

Abstract

The synthesis and characterisation of a small library of Co and Cu derivatives (29 examples) incorporating the (Z)-1-R1-2-(4’,4’-R2-2’-oxazolin-2’-yl)-eth-1-en-1-ate (L: R1 = alkyl or aryl; R2 = H or Me) skeleton is described. This work includes six new derivatives of “Tohda’s Ligands”. In the case where R2 = H, solid-state stable Co(II) materials of formula Co(κ2-N,O-L)2 could, in some cases, be obtained following base-induced deprotonation of L+H and treatment with hydrated CoX2 salts. These complexes display redox induced solution decomposition behaviour giving Co(κ2-N,O-L)3 as one isolable product. Stable Cu(II) complexes could only be obtained in the case of for R1 = Ph and R2 = H. In the case of R2 = Me, distorted tetrahedral Co(II) compounds (also Co(κ2-N,O-L)2) are obtained as above (twelve examples). Square planar derivatives of Cu(II), of similar stoichiometry, are likewise isolated (eleven new examples). In contrast to the R2 = H reactions, all of these latter materials were found to be air-stable in solution or the solid phase. In total, 18 complexes have been characterised by single crystal X-ray diffraction. Molecular modelling (PM6(tm) and DFT) are also used to elucidate the molecular properties of selected complexes. Only a single Co complex (R1 = t-butyl and R2 = Me) of the library displays reversible one-electron redox properties.<br>