ESR investigation of paramagnetic derivatives of [6-tert-butyl-4-(5-tert-butyl-2-methyl-3,4-dioxocyclohexa-1,5-dien-1-yl)-3-methylcatecholato]triphenylantimony(V)

Abstract

A number of paramagnetic derivatives of [6 tert butyl 4 (5 tert butyl 2 methyl 3,4 dioxocyclohexa 1,5 dien 1 yl) 3 methylcatecholato]triphenylantimony(V) were investigated by ESR spectroscopy. The reactions of this complex with Cр 2 Cо or LiCl in the presence of Hg metal. lead to the formation of free (nonchelated) radical anion semiquiones. Chelated complexes are formed in the case of Tl(Hg), Mn 2 (CO) 10 , Re 2 (CO) 10 , Sn 2 Ph 6 , Cu(met.), and CuCl + dppfc (dppfc is bis diphenylphosphinoferrocene). Key words: ESR spectroscopy, di o quinone, o semiquinonato metal complexes, catecholatotriphenylantimony(v).An important and promising line of research in the chemistry of о semiquinone metal complexes is the study of intramolecular electronic interactions (metal-ligand, metal-metal, ligand-ligand), depending on the molecu lar geometry and the system behavior. The topicality of the studies in this field is related to the search for new approaches to the design of molecular electronic de vices 1-3 and molecular magnets, 4-6 being developed in tensively in recent years. Of particular interest in this respect are di о quinones, able to form bi and poly nuclear complexes with bridging paramagnetic ligands. Their use provides new opportunities for the synthesis of high spin systems and bi stable metal complexes. Two types of derivatives of this sort are now known. A series of homometal binuclear di o semiquinone complexes (1a,b) have been reported. 7,8 In these complexes, the ligand ex ists as so called "nonalternate biradical" whose structure ensures the ferromagnetic type of the exchange between the radical centers.Previously, 9-11 we reported the synthesis and the structures of a number of mono , bi , and polynuclear complexes derived from 4,4´ di (6 tert butyl 3 methyl benzo 1,2 quinone) (2). The reduction of 2 may yield three paramagnetic species: radical monoanion, radical dianion, and radical trianion. A number of examples have been reported for the first two species, quinone semi quinone and di semiquinone derivatives. 9,10 For the third type, i.e., the catecholato semiquinone form, only one example is known: the tripotassium salt. 11Heteronuclear complexes derived from 2 have not been described until recently. Recently, we obtained, by oxi dative addition, quinone catecholate (3), 12 which served as the starting synthon for the synthesis of catecholato semiquinone derivatives.This communication presents a ESR study of para magnetic heteronuclear complexes obtained by the re duction of quinone catecholate (3).

The binuclear trimethyl/triethylantimony(V) bis-catecholate derivatives of four-electron reduced 4,4′-di-(3-methyl-6-tert-butyl-o-benzoquinone)

“…3. On the other hand, these spectral data are very close to those observed on salts with anion of [Ph 3 Sb(Cat-SQ)] À type [29] ( Table 2). Worthy of note is that EPR spectra of 2a and 2b do not reveal any h.f.c.…”

ESR study of paramagnetic derivatives of sterically hindered di-o-quinone with the tetrathiafulvalene bridge

“…19) at a reactant ratio of 1 : 1. The resulted blue green solution was used for the preparation of the semiquinone catecholate complexes 21-27 according to the previously described procedures.…”

“…The resulted blue green solution was used for the preparation of the semiquinone catecholate complexes 21-27 according to the previously described procedures. 19 Triphenylantimony dicatecholate 28 was prepared accord ing to the analogous procedure 19 upon mixing of solutions of 1 and triphenylantimony in THF at a 1 : 2 molar ratio. The addi tion of slight amounts of the oxidizing reagents to the resulted diamagnetic solution led to the change in the solution color from green yellow to deep brown and the ESR spectrum displayed an intense singlet corresponding to the radical cation 29.…”

“…To date, a variety of mono and binuclear metal complexes based on di o quinones with different bridges between the ligand cen ters has been studied. [15][16][17][18][19][20] However, in all known examples, the bridge is not redox active. The introduction of a redox active spacer, which can also undergo a reversible oxidation, into the di o quinone molecule of fers additional opportunities for control of the channel connecting the metal centers.…”

“…A number of paramagnetic heteronuclear complexes containing the three reduced form of ligand 1 was suc cessfuly prepared by analogy with triphenylantimony(V) 6 (tert butyl) 4 [5 (tert butyl) 2 methyl 3,4 dioxocyclo hexa 1,5 dienyl] 3 methylcatecholate. 19 The oxidative addition of triphenylantimony to 1 at an equimolar reac tant ratio led to in situ formation of a diamagnetic quino ne catecholate 20, from which the bimetallic complexes 21 27 were generated following Scheme 4; the parameters of their isotropic ESR spectra are given in Table 1. The patterns of the ESR spectra of all semiquinone catecho late derivatives is analogous to those of the monosemi quinone complexes with the same magnetic centers.…”