Synthesis,Characterization And Property Studies Of Diboriranes And Boron And Chalcogen Analogues Of Carboxylic Acids

In this dissertation,two projects were studied:(1)Neutral diborirane derivatives were synthesized for the first time by rearrangement reaction of alkylideneborane.Joint experimental and computational studies revealed their structural and bonding characters.In addition,their elementary reactions including ring-opening and oxidative functionalization have been revealed.(2)Anionic boron and chalcogen analogues of carboxylic acids were synthesized by deprotonation of boronodithioic acid or boronodiselenoic acid with organic base,which feature typical boron and chalcogen multiple bonds.Detail studies are as the following:(1)1-bromo-1,2-bis(dimethylamino)-2-fluorenyldiborane[(Me2N)(FluH)B-BBr(NMe2)](FluH=fluorenyl)reacted with two equivalents of Br3B·SMe2 to afford Me2S-ligated tribromofluorenyldiborane(Me2S)(FluH)BrB-BBr2(SMe2)(2-1).Subsequent dehydrobromination and ligand exchange reaction of 2-1 with three equivalents NHC(NHC=IPr2Me2=1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene)proceeded smoothly to give an boryl-substitunted alkylideneborane Flu=B(NHC)-BBr2(NHC)(Flu=fluorenylidene)(2-2).A complete conversion to a diborirane-NHC complex Flu[BBr(NHC)]2(2-3)was observed upon dissolving 2-2 in chloroform at room temperature or heating a toluene solution of 2-2 at 80℃.Reduction of 2-3 with LiAlH4 at ambient temperature afforded a new diborirane Flu[BH(NHC)]2(2-4)featuring B-H bonds.As the diboron analogues of cyclopropanes,both 2-3 and 2-4 feature van’t Hoff-Le Bel geometry and strained B2C rings formed by 2c-2e bent σbonds.Consequently,the B-B and B-C bonds in 2-3 are cleaved in the presence of hydride,proton,and chalcogens.The former two reactions gave NHC-coordinated fluorenyldihydridoborane 2-5 and dichlorofluorenylborane 2-6,respectively,whereas the latter transformations afforded novel thiaborirane 2-8 and selenaborirane 2-9.In addition,transfer hydrogenation of 2-3 with ammonia borane(H3N·BH3)led to the formation of(μhydrido)diborane 2-7 via selective cleavage of the B-B bond.(2)Reaction of dimeric borane[DmpBH(μ-H)]2[Dmp=2,6-bis(2,4,6trimethylphenyl)phenyl]with sulfur and selenium resulted in the formation of trithiadiborolane and triselenadiborolane DmpB(μ-Ch)(μ-η2-Ch2)BDmp(2-10:Ch=S;2-15:Ch=Se).Both 210 and 2-15 could be cleaved by the strong reductant potassium graphite(KC8)to afford ring opening products sulfide salt[DmpB(SK)2](2-11)and diselenide salt[DmpB(SeSeK)(SeK)](2-16).Protonation of 2-11 with triethylamine hydrochloride[Et3NH]Cl yielded boronodithioic acid DmpB(SH)2(2-12),which readily deprotonated with one equivalent of NHC to give the boron and sulfur analogues of carboxylic acids 2-13 and 2-14.Comparatively,2-16 directly reacted with[Et3NH]Cl to afford boron and selenium analogue of carboxylic acid via salt elimination reaction.