Triphenylantimony(V) 6-alkoxymethyl-3,5-di-tert-butylcatecholates. Structure and redox-properties

A number of mononuclear triphenylantimony(V) 3,5-di-tert-butylcatecholates of the type (6-AlkOCH2-3,5-DBCat)SbPh3 functionalized with alkoxymethyl group in the 6th position of aromatic ring in catecholato ligand, where Alk = Me (1), Et (2), iPr (3), tBu (4), n-Hexyl (5), and binuclear bis-catecholate Ph3Sb(3,5-DBCat-CH2OCH2-3,5-DBCat)SbPh3 (6) have been synthesized and characterized in details. The molecular structures of 1·0.5 (n-hexane), 2, 3, 4, 5·2MeOH, 6·2 (n-hexane) and 6·acetone have been determined by means of single-crystal X-ray analysis. The presence of alkoxymethyl-group in catecholate ligand does not lead to its coordination to the central antimony atom. Complexes 1–4 and 6 possess pentacoordinated environment of the central antimony atoms varying from the trigonal bipyramidal to the distorted tetragonal pyramidal. In crystal, molecules of complexes 1–5 form pairs where the “CPh–H … π-system” interactions were found. The coordination environment of the central antimony atom in 5∙2MeOH is a distorted octahedral with coordinated methanol; the second methanol molecule is fixed between thehydroxyl group of coordinated methanol and the oxygen atom of hexyloxymethyl-group in the 6th position of catecholate ligand through the intramolecular hydrogen bonding. The electrochemical oxidations of complexes 1–4 proceed as two one-electron oxidations (the quasireversible oxidation “catecholate/o-semiquinolate” and the irreversible oxidation “o-semiquinolate/o-benzoquinone”). The first half-wave potential (E11/2) depends weakly on the alkyloxy substituent in AlkO-CH2 group due to a weak inductive effect of AlkO group to the catecholate aromatic ring through the methylene linker. For binuclear bis-catecholate 6, the first redox stage is two-electronic quasi-reversible peak without the separation of two stages into two one-electron processes, which indicates the absence of the electronic interaction between the two catecholate fragments.