Triarylboron anion radicals and the reductive cleavage of boron compounds

Abstract

depend strongly on solution conditions, there is little reason to expect much similarity between UOzz+-ATP complexes and monatomic cation-ATP complexes in which all three phosphate groups are involved, since ligands attached to the uranyl ion are restricted to positions close to its equatorial plane. On the other hand, one might look for relationships between UOzz+-ATP chelates and those monatomic cation-ATP complexes, like Cu2+-ATP, in which only two phosphate groups are involved, but it is apparent that much more extensive and systematic studies, e.g., over wider pH and concentration ranges, are needed for systems containing monatomic cations than are now available. It is of interest to this point that BrintzingerZ9 in 1961 claimed that his pH titrations showed involvement of the ribose hydroxyl group in the complexation of Mn2+, Co2+, Ni2+, Znz+, and Cu2+ by ATP in basic solution. However, he believed that, unlike the binding in our suggested UOz2+-ATP structures, there was an intervening water molecule attached by its oxygen atom to the metal and by hydrogen bridges to the two ribose hydroxyl oxygens.(29) H. Brintzinger, Helu. Chim. Acta, 44, 1199 (1961). and Ni2+ interact simultaneously with all three phosphateThe latter two ions were studied only at p H 8.5-9. At pH -7 all four paramagnetic ions bind to the adenine ring of ATP also,2",2bb the latter three all the time they are bound to the phosphate."'To resolve apparent disagreement between these conclusions and previous ultravioletz6 and temperature-jump27 studies which involved solutions containing only M ATP, Sternlicht, et U E . ,~~ performed nmr experiments on Mnz+-ATP solutions with only = 5 X M ATP. These authors claim to have shown that at low ATP concentration, = 5 X M , primarily 1 : 1 complexes are present, but that 1 : 2 complexes predominate at high ATP concentration, =0.1 M , i.e., with only = M Mn2+ in each case. Sternlicht, et al., believe that in the 1 :2 complex the Mn2+ binds simultaneously to the phosphate of one nucleotide and to the adenine of the second nucleotide, but that the metal is bound only to the phosphate in the 1 : 1 complex.Abstract: The boron nuclear spin coupling constant of the triphenylboron anion radical is positive. The assignment of coupling constants to the ortho, meta, and para protons has been confirmed by a study of the tris(p-deu-teriopheny1)-and tris(3,5-dideuteriophenyl)boron esr spectra. The lines corresponding to mB = f 3/? are selectively broadened either by incomplete averaging of the anisotropic hyperfine coupling or by an unidentified reaction that modulates the boron coupling constant. Prolonged reaction of triphenylboron anion radical with alkali metals in DME degrades it to biphenyl anion radical, both halves of which comefrom the same triphenylboron. The behavior o f tris(p-chlorophenyl)boron, tris(p-methoxyphenyl)boron, tris(p-dimethylaminophenyl)boron, tris(p-tolyl)boron, several trialkylborons, diphenylboron chloride, and dimesitylboron fluoride with alkali metals is also described.ost triarylbor...

The Reduction Chemistry of Ferrocenylborole

“…Indeed, simulation of the EPR signal shows that the unpaired electron is coupled to one 11 B nucleus giving a hyperfine-coupling constant of A( 11 B) = 3.73 G, which is comparable to that observed for 9-arylborafluorene radical anions (between 3.1 and 4.5 G). [11] We note that this value is smaller than that observed for triarylborane radical anions, such as [Ph 3 B]C À (7.84 G) or [Mes 3 B]C À (10.32 G), [19] because of a stronger electronic delocalization within the C 4 B ring. The relatively low value of A( 11 B) in [1]C À indicates that the unpaired electron density is associated with boron 2p orbital and that the geometry is planar rather than pyramidal.…”

Electrochemistry and Photophysics of Donor‐Substituted Triarylboranes: Symmetry Breaking in Ground and Excited State

“…In addition, TABs are isoelectronic to triphenylmethane cations and can therefore provide further information about this important class of dyes. Although the electrochemistry [14][15][16] and photophysics [17][18][19] of simple TABs, such as triphenylborane or trimesitylborane, have been the subject of various publications in the past decades, some aspects of the properties of their donor-substituted analogues still demand further investigation. Especially, the symmetry of the ground state, which has been studied intensively for triphenylborane and related model compounds [18,[20][21][22][23] and for triphenylmethane dyes, [24,25] is still a controversial topic.…”

“Umpolung” at Boron by Reduction of [B(CN)4]− and Formation of the Dianion [B(CN)3]2−

“…[8,9] Only the radical anion with mesityl ligands at boron can be isolated, because its dimerization is kinetically hindered. [10,11] The blue [Li( [12]crown-4) 2 ][BMes 3 ] is stable up to 230 8C, and its structure was determined by single crystal X-ray diffraction.…”