Triphenylantimony(v) Catecholates and o‐Amidophenolates: Reversible Binding of Molecular Oxygen

Abstract

Novel neutral antimony(V) complexes were isolated as crystalline materials and characterized by IR and NMR spectroscopy: o-amidophenolate complexes [4,6-di-tert-butyl-N-(2,6-dimethylphenyl)-o-amidophenolato]triphenylantimony(V) (Ph3Sb[AP-Me], 1) and [4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-amidophenolato]triphenylantimony(v) (Ph3Sb[AP-iPr], 2); catecholate complexes (3,6-di-tert-butyl-4-methoxycatecholato)triphenylantimony(V) (Ph3Sb[(MeO)Cat], 3), its methanol solvate 3CH3OH (4); (3,6-di-tert-butyl-4,5-di-methoxycatecholato)triphenylantimony(V) (Ph3Sb[(MeO)2Cat], 5) and its acetonitrile solvate 5CH3CN (6). Complexes 1-7 were synthesized by oxidative addition of the corresponding o-iminobenzoquinones or o-benzoquinones to Ph3Sb. In the case of the phenanthrene-9,10-diolate (PhenCat) ligand, two different complexes were isolated: Ph3Sb[PhenCat] (7) and [Ph4Sb]+[Ph2Sb(PhenCat)2]- (8). Complexes 7 and 8 were found to be in equilibrium in solution. Molecular structures of 2, 4, 6, and 8 were determined by X-ray crystallography. Complexes 1-7 reversibly bind molecular oxygen to yield Ph3Sb[L-Me]O2 (9), Ph3Sb[L-iPr]O2 (10), Ph3Sb[(MeO)L']O2 (11), Ph3Sb[(MeO)2L']O2 (12) and Ph3Sb[PhenL']O2 (13), which contain five-membered trioxastibolane species (where L is the O,O',N-coordinated derivative of a 1-hydroperoxy-6-(N-aryl)-iminocyclohexa-2,4-dienol, and L' the O,O',O''-coordinated derivative of 6-hydroperoxy-6-hydroxycyclohexa-2,4-dienone). Complexes 9-13 were characterized by IR and 1H NMR spectroscopy and X-ray crystallography.

Geometrical and energetical aspects of structure of 3,6-di-tert-butyl-o-benzoquinones

“…2) shows that the inequivalent O…C(Me) cis-distances always lead to twist distortion of the O=C-C=O fragments (2)(3)(4) whereas the equivalent O…C(Me) cis-distances lead to ring puckering of cyclohexadiene ring (1). Apparently, completely equivalent O…C(Me) distances in 3,6-Q stabilize the planarity O=C-C=O and cyclohexadiene fragments (5). Consequently, from the geometrical point of view, the inequivalent positions of the Me groups in these 3,6-Q become the driving force for ring puckering and nonplanarity of the O=C-C=O fragments.…”

“…3,6-Di-tert-butyl-o-benzoquinones (3,6-Q) are particularly interesting due to the possibility of the red-ox processes [3,6-Q] [semiquinone] •-[catecholate] 2-in the metal coordination sphere that influence the structure and properties of the metal complexes. Recently, the catecholate and closely related o-amidophenolate antimony(V) complexes were demonstrated to reversibly bind dioxygen [5][6][7], which makes these compounds even more important. Despite these results, there are no publications focused exclusively on the structural aspects of the 3,6-Q compounds.…”

Analysis of the supramolecular structures of Sb(III) and Sb(V) catecholate complexes from the viewpoint of ligand solid angles

“…From the chemical point of view, the interest in investigating the antimony catecholate complexes stems from the possibility of redox reactions ([catecholate] 2-$ [semiquinone] •-) that, in turn, defines the properties and composition of these compounds [5][6][7][8]. Additionally, the catecholates and their related amidophenolate structural analogs were demonstrated to reversibly bind dioxygen, which enhances the interest in this class of compounds [9][10][11].…”

Dopamine complexes of iron in the etiology and pathogenesis of Parkinson’s disease

“…The mechanism may follow the steps described by Que and co-workers with the formation of an iron-bound peroxosemiquinone species (II) [27]. Support for a structure of this type comes from structural characterization on complexes of Rh, Ir, and Sb [38][39][40], and for the ironbound peroxysemiquinone intermediate formed during ring cleavage by an extradiol dioxygenase enzyme [41].…”