Abstract:The intriguing (m-hydrido)diboranes(4) with their prominent pristine representative [B 2 H 5 ] À have mainly been studied theoretically.W en ow describe the behavior of the planarizedt etraaryl (m-hydrido)diborane(4) anion [1H] À in cycloaddition reactions with the homologous series of heterocumulenes CO 2 ,i PrNCO,a nd iPrNCNiPr.W es how that a C = Obond of CO 2 selectively activates the B À Bbond of [1H] À , while the m-H ligand is left untouched( [ 2H] À ). The carbodiimide iPrNCNiPr,i nc ontrast, neglects … Show more
“…[ 31 , 47a ] To test this proposal, we treated 4 with 1 equiv of Li[ 2 H], which here served as a storage form of [ 8 ] − (Scheme 6 ). [ 23 , 32 , 33 ] Indeed, Li[ 5 ] and the byproduct 1 ⋅thf were obtained in equimolar amounts and with perfect selectivity. [56] Scheme 6 Reaction of Li[ 2 H] with 4 in THF gives Li[ 5 ] and 1 ⋅thf, likely via the Li[ 8 ]⋅ 1 adduct, which liberates a borafluorenyl anion [ 8 ] − (green) for insertion into one B−C bond of 4 (blue; carbon atoms marked with asterisks bear t Bu substituents).…”
Section: Resultsmentioning
confidence: 99%
“…[ 31 , 47a ] To test this proposal, we treated 4 with 1 equiv of Li[ 2 H], which here served as a storage form of [ 8 ] − (Scheme 6 ). [ 23 , 32 , 33 ] Indeed, Li[ 5 ] and the byproduct 1 ⋅thf were obtained in equimolar amounts and with perfect selectivity. [56]…”
Two subvalent, redox‐active diborane(4) anions, [3]4− and [3]2−, carrying exceptionally high negative charge densities are reported: Reduction of 9‐methoxy‐9‐borafluorene with Li granules without stirring leads to the crystallization of the B(sp3)−B(sp2) diborane(5) anion salt Li[5]. [5]− contains a 2,2′‐biphenyldiyl‐bridged B−B core, a chelating 2,2′‐biphenyldiyl moiety, and a MeO substituent. Reduction of Li[5] with Na metal gives the Na+ salt of the tetraanion [3]4− in which two doubly reduced 9‐borafluorenyl fragments are linked via a B−B single bond. Comproportionation of Li[5] and Na4[3] quantitatively furnishes the diborane(4) dianion salt Na2[3], the doubly boron‐doped congener of 9,9′‐bis(fluorenylidene). Under acid catalysis, Na2[3] undergoes a formal Stone–Wales rearrangement to yield a dibenzo[g,p]chrysene derivative with B=B core. Na2[3] shows boron‐centered nucleophilicity toward n‐butyl chloride. Na4[3] produces bright blue chemiluminescence when exposed to air.
“…[ 31 , 47a ] To test this proposal, we treated 4 with 1 equiv of Li[ 2 H], which here served as a storage form of [ 8 ] − (Scheme 6 ). [ 23 , 32 , 33 ] Indeed, Li[ 5 ] and the byproduct 1 ⋅thf were obtained in equimolar amounts and with perfect selectivity. [56] Scheme 6 Reaction of Li[ 2 H] with 4 in THF gives Li[ 5 ] and 1 ⋅thf, likely via the Li[ 8 ]⋅ 1 adduct, which liberates a borafluorenyl anion [ 8 ] − (green) for insertion into one B−C bond of 4 (blue; carbon atoms marked with asterisks bear t Bu substituents).…”
Section: Resultsmentioning
confidence: 99%
“…[ 31 , 47a ] To test this proposal, we treated 4 with 1 equiv of Li[ 2 H], which here served as a storage form of [ 8 ] − (Scheme 6 ). [ 23 , 32 , 33 ] Indeed, Li[ 5 ] and the byproduct 1 ⋅thf were obtained in equimolar amounts and with perfect selectivity. [56]…”
Two subvalent, redox‐active diborane(4) anions, [3]4− and [3]2−, carrying exceptionally high negative charge densities are reported: Reduction of 9‐methoxy‐9‐borafluorene with Li granules without stirring leads to the crystallization of the B(sp3)−B(sp2) diborane(5) anion salt Li[5]. [5]− contains a 2,2′‐biphenyldiyl‐bridged B−B core, a chelating 2,2′‐biphenyldiyl moiety, and a MeO substituent. Reduction of Li[5] with Na metal gives the Na+ salt of the tetraanion [3]4− in which two doubly reduced 9‐borafluorenyl fragments are linked via a B−B single bond. Comproportionation of Li[5] and Na4[3] quantitatively furnishes the diborane(4) dianion salt Na2[3], the doubly boron‐doped congener of 9,9′‐bis(fluorenylidene). Under acid catalysis, Na2[3] undergoes a formal Stone–Wales rearrangement to yield a dibenzo[g,p]chrysene derivative with B=B core. Na2[3] shows boron‐centered nucleophilicity toward n‐butyl chloride. Na4[3] produces bright blue chemiluminescence when exposed to air.
“…The resulting intermediate Na[ 10 ] can be regarded as adduct between a Lewis basic 9‐borafluorenyl anion [ 8 ] − and a Lewis acidic 9‐butyl‐9‐borafluorene (compare the related adduct Li[ 8 ]⋅ 1 in Scheme 6). In a follow‐up step, [ 8 ] − inserts into the C α −H bond of the n ‐butyl chain to form Na[ 9 ] [30, 32, 33] . The vigorous reactivity of Na 2 [ 3 ] also became apparent when we tried to record cyclic voltammograms of the compound, since the initial blue‐green color of the THF solution quickly faded on contact with the supporting electrolyte [ n Bu 4 N][PF 6 ].…”
Section: Resultsmentioning
confidence: 99%
“…[22][23][24] In the recent past, we have investigated in detail the alkali-metal reduction of the 9H-9-borafluorene dimer (1) 2 or of the THF adduct 1•thf (Scheme 2). [25][26][27][28][29][30][31][32][33][34] Specifically,w e found that treatment of 1•thf with an excess of Li granules in THF leads to ap roduct mixture from which Li 2 [2], ad oubly boron-doped analogue of dibenzo[g,p]chrysene (C), could be isolated in approximately 45 %yield (Scheme 2). [35] Asecond major product is the borafluorene-dianion salt Li 2 [1](approx.…”
Section: Introductionmentioning
confidence: 99%
“…High-yield syntheses of M 2 [1]( M = Li-K) were developed in the meantime and the role of [1] 2À as boroncentered nucleophile was established. [23,[30][31][32][33] We have now succeeded in identifying at hird reaction product, the unique tetraanion salt Li 4 [3]( approx. 5%;S cheme 2).…”
Two subvalent, redox‐active diborane(4) anions, [3]4− and [3]2−, carrying exceptionally high negative charge densities are reported: Reduction of 9‐methoxy‐9‐borafluorene with Li granules without stirring leads to the crystallization of the B(sp3)−B(sp2) diborane(5) anion salt Li[5]. [5]− contains a 2,2′‐biphenyldiyl‐bridged B−B core, a chelating 2,2′‐biphenyldiyl moiety, and a MeO substituent. Reduction of Li[5] with Na metal gives the Na+ salt of the tetraanion [3]4− in which two doubly reduced 9‐borafluorenyl fragments are linked via a B−B single bond. Comproportionation of Li[5] and Na4[3] quantitatively furnishes the diborane(4) dianion salt Na2[3], the doubly boron‐doped congener of 9,9′‐bis(fluorenylidene). Under acid catalysis, Na2[3] undergoes a formal Stone–Wales rearrangement to yield a dibenzo[g,p]chrysene derivative with B=B core. Na2[3] shows boron‐centered nucleophilicity toward n‐butyl chloride. Na4[3] produces bright blue chemiluminescence when exposed to air.
The synthesis of element−carbon double bonds is of great importance for the development and understanding of reactive π‐bonded systems in chemistry. The seven‐membered heterocyclic system 4 b is readily made by internal C−H activation at a pendent isopropyl methyl group of the respective [(IPr)C6F5BH]+ borenium ion. Subsequent deprotonation with the IMes carbene gives the neutral cyclic boraalkene system 5 b. The B=C double bond in compound 5 b adds carbon dioxide, CS2, sulfur dioxide, phenyl isocyanate, an acetylenic ester or two NO molecules to give the corresponding four‐membered ring annulated heterocycles. With sulfur or selenium 5 b gives the respective three‐membered ring systems. N2O reacts with 5 b to give a mixture of the related oxaborirane 18 and a unique [B]OH containing diazoalkane product 19.
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