Borane tris

FLATffiRETARDANTS - PHOSPHORUS FLATffi RETARDANTS] (Vol 10) Tris(dimethylamino)borane [4375-83-1]... 

The reactions of trialkylboranes with bromine and iodine are gready accelerated by bases. The use of sodium methoxide in methanol gives good yields of the corresponding alkyl bromides or iodides. AH three primary alkyl groups are utilized in the bromination reaction and only two in the iodination reaction. Secondary groups are less reactive and the yields are lower. Both Br and I reactions proceed with predominant inversion of configuration thus, for example, tri( X(9-2-norbomyl)borane yields >75% endo product (237,238). In contrast, the dark reaction of bromine with tri( X(9-2-norbomyl)borane yields cleanly X(9-2-norbomyl bromide (239). Consequentiy, the dark bromination complements the base-induced bromination. 

Vinylboranes are interesting dienophiles in the Diels-Alder reaction. Alkenylboronic esters show moderate reactivity and give mixtures of exo and endo adducts with cyclopentadiene and 1,3-cyclohexadiene (441). Dichloroalkenylboranes are more reactive and dialkylalkenylboranes react even at room temperature (442—444). Dialkylalkenylboranes are omniphilic dienophiles insensitive to diene substitution (444). In situ formation of vinyl-boranes by transmetaHation of bromodialkylboranes with vinyl tri alkyl tin compounds makes possible a one-pot reaction, avoiding isolation of the intermediate vinylboranes (443). Other cycloadditions of alkenyl- and alkynylboranes are known (445). 

Amine Boranes. Trialkylamine and dialkylamine boranes, such as tri-Z-butylamine borane and dimethylamine borane, are mainly used in... 

Synthesis. One of the more common routes for the synthesis of aminoboranes involves the aminolysis of the appropriate boron hahde. Trisaminoboranes are most convenientiy prepared by adding BCI3 to an excess of amine in an inert solvent at low temperatures (42). For example for tris(dimetby1amino)borane [4375-83-1]. ... 

Imidazole reacts with dimethylzirconocene in the presence of a strong Lewis base, tris(pentafluorophenyl)borane, to yield the betaine species 22 (96JOM(518)17), which when exposed to the atmosphere is hydrolyzed to 23. 

Reduction of 3,5,5-tris-aryl-2(5// )-furanones 115 (R, R, R = aryl) with dimethyl sulfide-borane led to the formation of the 2,5-dihydrofurans 116 in high yields. However, in the case of 3,4-diaryl-2(5//)-furanones 115 (R, R = aryl R = H or r = H R, R = aryl), the reduction led to a complicated mixture of products of which only the diarylfurans 117 could be characterized (Scheme 36) (88S68). It was concluded that the smooth conversion of the tris-aryl-2(5//)-furanones to the corresponding furan derivatives with the dimethylsulfide-borane complex in high yields could be due to the presence of bulky aryl substituents which prevent addition reaction across the double bond (88S68). 

In the next step, one of the borane-hydrogens is transferred to a sp -carbon center of the alkene and a carbon-boron bond is formed, via a four-membered cyclic transition state 6. A mono-alkyIborane R-BH2 molecule thus formed can react the same way with two other alkene molecules, to yield a trialkylborane R3B. In case of tri- and tctra-substituted alkenes—e.g. 2-methylbut-2-ene 7 and 2,3-dimethylbut-2-ene 9—which lead to sterically demanding alkyl-substituents at the boron center, borane will react with only two or even only one equivalent of alkene, to yield a alkylborane or mono alky Iborane respectively ... 

Biphenylcarboxylic acid [[1,1 -Biphenyl] -2-carboxylic acid], 83 Boron tnfluonde, etherate, [Borane, tri-fluoro-, compd. with l,l -oxybis-[ethane] (11)], 10 Bromine, 108... 

Tris-[2-methyI-propyl]-boran (S. 52) und Benzo-l,3,2-dioxaborol (S. 53) dienen zu Regioselcktiven Hydro-borierungen, letzteres ist ein ausgezeichnetes Reduktionsmittel (s.S. 87, 370f., 466)6. 

Die Kalium-trialkyl-hydrido-boratezersetzen sich an der Luft und werden daher ohne Isolierung eingesetzt. Kalium-triathyl-hydrido-borat ist z.B. aus Kaliumhydrid und Triathyl-boran erhaltlich1 und hat ein ahnliches Reduktionsvermogen wie Lithium-tri-athyl-hydrido-borat (s.S. 14). 

Diese Tatsache hat in erster Linie bei der Hydroborierung mittelstandiger Olefine Be-deutung1. So werden tri- und tetrasubstituierte Athylene mit unverzweigten Seitenketten durch Diboran bei 20° geniigend rasch nur in Di- bzw. Monoalkyl-borane uberfiihrt2. 

AuBerst selektive 1,2-Reduktionsmittel sind Bis-[2-methyl-propyl]-aluminiumhydrid1, Tris-[2-methyl-propyl]-aluminium2, Natrium-bis-[2-methyl-propyl]-dihydrido-aluminat3 und besonders 9-Bora-bicyclo[3.3. ljnonan4 (9-BBN, S. 7). Letzteres ergibt zuerst ein Alkoxy-boran, das zweckmaRig mit 2-Amino-athanol gespalten wird. 

Die Reaktion kann auch mit Lithiumhydrid in Gegenwart katalytischer Mengen Tri-athyl-boran durchgefiihrt werden. Bei 1,1-Dibrom-cyclopropanen tritt Ringspaltung zu Allenen ein z. B.2 ... 

Vinyl-chlorid reagiert mit Diboran auCerst heftig zu Tris-f2-chlor-athyl]-boran, das sofort in 2-C.hlor-athyl-bordichlorid und Alhylen zerfallt1 (nahcres s. Bd. XIII/3). 

Zur Spaltung von Tetrahydrofuran-Ringen kann auch Lithium-tri-tert.-butyl-oxy-hydrido-aluminat/Triathyl-boran verwendet werden. Die Reaktion wird in Tetrahydropyran durchgefiihrt, das vom Reagens nur langsam angegriffen wird. 

When E = P, R = 2,4,6-trimethylphenyl, and R = 2,4,6-tri-f-butylphenyl (Eq. 26), the same reduction can be accomplished using BH3-SMe2.59 The borane addition product is also obtained (Mes2GeH—PArBH2). 

Suchy, H. Uber Alan, Aluminiumboranate und Tris(N,N-dimethyl-hydrazino)-boran. Dissertation, Univ. Miinchen, 1966. 

V. Polymers Derived from tris(A]kylamino)boranes 169... 

Figure 14 rr-Conjugated dendritic polymers (18 and 19) obtained from tri-9-anthrylborane. The branched conducting polymer 20 was obtained from tris(JV-pyrrolyl)borane. (Adapted from refs. 38 and 39.)... 

A. tris(Alkylamino)boranes-Derived Poly Z -(alkylamino)borazines]... 

Poly[/i-(alkylamino)borazines] can be prepared through a multistep thermolysis process involving tris(monoalkylamino)boranes of the type B(NHR)3 (R = Me, Pr ). Heating these molecular precursors under reduced pressure or in an inert atmosphere... 

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