The structural and electrochemical properties of new bis-imido transition metal salen complexes

The reaction between [M(NtBu)2(NHtBu)2](M = Mo or W) and dianionic N2O2 coordinating salen ligands afforded new bis-imido salen Mo(VI) and W(VI) transition metal complexes [W(NtBu)2{(3,5-tBu2)2salen}]1, [W(NtBu)2{(3-MeO)2salen}]2, [W(NtBu)2{(4-MeO)2salen}] 3, [W(NtBu)2{(5-MeO)2salen}]4, [W(NtBu)2(salen)]5, [Mo(NtBu)2{(3,5-tBu2)2salen}]6, [Mo(NtBu)2{(4-MeO)2salen}]7 and [Mo(NtBu)2 (salen)]8. Compounds 1-8 were characterised by NMR, IR and FAB mass spectrometry while compound 6 was additionally characterised by X-ray crystallography. Both the Mo and W series adopt structures having the Schiff bases in the strained (beta)-cis configuration and the structural parameters suggest that this is dictated by steric rather than electronic factors while the cis configuration of the imido groups results from expected electronic preferences. The redox chemistry of all these compounds has been studied by cyclic voltammetry and additionally by chemical routes and controlled current electrolytic routes in the case of 1. EPR and density function calculations on oxidised 1 confirmed that the oxidation process is imido centred.