Synthesis, Spectroscopic Characterization and Reactivity Studies of Oxovanadium(IV) Complexes With Bulky N,N′-Polymethylenebis(3,5 Tbu2salicylaldimine) Ligands

Abstract

A series of new sterically hindered N,N′-polymethylenebis(3,5- tBu<inf>2</inf>salicylaldimine) ligands (H<inf>2</inf>L<inf>x</inf>) VO(IV) complexes, [VO{(2-O-3,5-tBu<inf>2</inf>C<inf>6</inf>H <inf>2</inf>)CH-N-R-N-CH-(3,5-tBu<inf>2</inf>-C<inf>6</inf>H <inf>2</inf>O-2)] (X), where R= -(CH<inf>2</inf>)<inf>3</inf>- (3), -(CH <inf>2</inf>)<inf>4</inf>- (4), -(CH<inf>2</inf>)<inf>5</inf>- (5), -(CH <inf>2</inf>)<inf>6</inf>- (6) and -CH<inf>2</inf>C(CH<inf>3</inf>) <inf>2</inf>CH<inf>2</inf>- (7) and early reported -(CH<inf>2</inf>) <inf>2</inf>- (1) and -CH<inf>2</inf>CH(CH<inf>3</inf>)- (2), has been synthesized and characterized by spectroscopic (IR, UV/vis, 1H NMR, EPR), electrochemical and magnetic susceptibility measurements. Complexes 1-7 are described a trigonal distorted pyramids. All seven compounds give nearly the same parallel hyperfine coupling constant {A<inf>z</inf>) regardless that the geometry of VO(IV) changes from square pyramidal to trigonal distorted pyramids. Chemical oxidation of 1-7 by one equiv Ce(IV) leads to the formation of stable [VO(V)L<inf>x</inf>]+ complexes. Cyclic voltammograms of 2-6 in DMSO along with a quasi-reversible VO(IV)/VO(V) redox couple also showed irreversible phenolate/phenoxyl responses. Each 1 and 7 shows only one reversible VO(IV) centered oxidation waves. Chemical oxidation of H<inf>2</inf>L<inf>x</inf> forms the stable [H<inf>2</inf>L<inf>x</inf>]+ radical species. © 2010 Elsevier B.V. All rights reserved.