Roland Köster

A Convenient Preparation of Trimethylborane and Triethylborane

Abstract A convenient, high yield preparation of Me3B on a laboratory scale from (n-BuO)3B and Me3Al2Cl3 is described. The preparation of Et3B from Al3Et and Et2O[sbnd]BF3 on a laboratory scale and from AlEt3 and KBF4 on a pilot plant scale are also given.

Organo-1,2-Phosphaboretene

Abstract Sodium trialyl-1-alkynylborates (I) react with chlorodiorganophosphanes to give organo-1,2-phosphaboret-3-enes (II) in high yields. However, organo-1,2- azaboret-3-ines cannot be prepared from I and e.g. chlorodiethylamine. Some reactions of the phosphaboretenes (II), such as transmetallation using triethylalane, oxidation with trimethylamine- N -oxide and protolyses to give E -alkenyl-phosphanes are described.

Boron Compounds. XLIV The Influence of Silicon on the Formation of (Z/E)-Tetrasubstituted Ethylenes via 1-Alkynylborates2

Abstract Sodium triethyl- (I) and triphenyl-trimethylsilylethynylborate (II), when treated with electrophilic reagents give (Z/E)-mixtures of tetrasubstituted alkenes III and IV. The influence of the trimethylsilyl group, incorporated in the borates I and II, on the stereoselectivity of the reaction was studied with the aid of 1H and 11B nmr. A novel rearrangement of bis-trimethylsilylalkenes IIId and IVd was also investigated.

Condensation route from 1,1,1-tris(diethylboryl)propane to pentaethyl-1,5-dicarba-closo-pentaborane(5)via arachno-CB4(10) and nido-C2B4(8) carbaboranes

Diethyl(prop-1-ynyl)borane 1 reacts, in the presence of a large excess of tetraethyldiborane(6), to give the new substituted 1-carba-arachno-pentaborane(10)4 as the first intermediate which can be isolated; 4 rearranges via the nido-C2B4(8) carbaboranes A and Bto the known pentaethyl-1,5-dicarba-closo-pentaborane(5)5which is characterized by single crystal X-ray analysis.

An outline of the chemistry of bis(9-borabicyclo[3.3.1]nonane)

- The distinctive features in the reactivity of (9H-9-BBN), compared to other tetraakyldiboranes(6) arise primarily from the rigid and usually very stable bicydic structure of the 1,5-cyclooctanediyl residue, which prevents the facile dismutation of the organic groups often observed in the latter, especially at elevated temperatures. - The 1,s-cyclooctanediylboryl group (9-BBN) has gained manifold importance in chemistry for a number of reasons: 1. Highly selective reaction pathways. 2. Enhanced reactivity of exocyclic BC-bond over the endocyclic BC-bonds in the bicyclic C8HI4B system. - 3. Facile preparations of various pure 9X-9-BBN borane reagents. - 4. New informative, easily isolable 9-BBN crystalline solids.

1,1-ORGANOBORATION OF MONO-1-ALKYNYLTIN COMPOUNDS USING DIALKYL(N-AZOLYL) BORANES-STEPWISE RING ENLARGEMENT OF BORON HETEROCYCLES

Abstract Mono-1-alkynyltin compounds 1–4 (Me3Sn-C ≡ CR1; R1 = H (1), Me (2), Ph (3), SnMe3 (4)) react with various dialkyl(N-azolyl)boranes 5–9 (azolyl = pyrrolyl (a), 2,5-dimethylpyrrolyl (b), indolyl (c), carbazolyl (d)) stereospecifically by 1,1-organoboration to give organometallic-substituted alkenes 10–20, 22–25, with the trimethylstannyl and the boryl group in cis-positions at the C=C bond. These reactions proceed via an alkynylborate-like zwitterionic intermediate ZI, and exchange of the azolyl against the 1-alkynyl group may compete (Eq. (1)(b)) with the 1,1-organoboration (Eq. (1)(a)), depending on the reactivity of the boron carbon bonds and the steric requirements. It is also shown that in addition to the products formed in the reactions with 1:1 stoichiometry other products result from the reaction of two equivalents of 1 with one equivalent of the borane. These products may be either 1,3-butadiene derivatives or allenes formed by allylic rearrangement. All products were characterized by 1H, 11B, 13C and 119Sn NMR. The molecular structure of the allene 24a was determined by X-ray structural analysis.

Synthesis of new chiral macrocyclic polyhydroxy ethers by reduction of cyclodextrins

The new chiral macrocyclic polyhydroxy ethers (5) and (8) were prepared by treatment of β- and α-cyclodextrins with diethylborane and 9-borabicycle[3.3.1]nonan-9-yl methanesulphonate as catalyst.

Boron compounds. 47. Quantitative determination of hydroxyl groups in lignites using activated triethylborane

Abstract A method for the quantitative determination of hydroxyl groups in lignites by means of activated triethylborane is described. The ethane evolved during the O-diethylborylation is determined volumetrically. This newly developed method is compared with other known procedures for the determination of hydroxyl groups; it is able to determine the hydroxyl group content in lignites both more exactly and more rapidly than any other known procedure.

2,5‐Dihydro‐1,2,5‐phosphasilaborole Derivatives: Determination of Signs of Coupling Constants [1J(31P,29Si), 2J(31P,31P), J(31P,13C), J(31P,1H)]

2,5‐Dihydro‐1,2,5‐phosphasilaborole derivatives 1–3, 5 and 6 and the 1,2,5,6‐tetrahydro‐1,2,5‐phosphasilaborin derivative 4 were studied with respect to the signs of coupling constants 1J(31, P29Si), 2J(31P,31P), nJ(31P,13C) (n = 1, 2, 3) and nJ(31P,1H) (n = 2, 3, 4). The determination of relative coupling signs was achieved either by 1D selective 1H{31P} heteronuclear double resonance or by various types of 2D X‐detected X/1H or 1H‐detected 1H/X heteronuclear shift correlations (X = 13C, 29Si). The absolute signs were related to 1J(13C,1H)>0, using 2D 1H‐detected 1H/31P(13C) or 1H/29Si(13C) pseudo‐BIRD HMQC experiments. The sign of 1J(31P,29Si) is positive [1K(31P,29Si)<0] in the phosphane adduct 2 where the ring phosphorus atom is three‐coordinate. It becomes negative [1K(31P,29Si)>0] for tetracoordinate phosphorus atoms as in the dimer 1, in the AlCl3 adduct 5 and in the transition metal complexes 3, 4 or 6, 6′, 6″. The molecular structure of the Me3P adduct 2 in solution can be deduced on the basis of the large and positive coupling constant 2J(31P,31P) (+160.0 Hz) together with evidence from NOE difference spectra. All coupling constants nJ(31P,13C) and nJ(31P,1H) in 1–6 possess a positive sign except 2J(31P,1HPMe) in 2, 2J(31P,1H  PCH 2 ) in 4 and 2J(31P,1H  PCH 2 ) in 6′.

Produkte der Carbodiimid-Hydroborierung mit (9H -9-BBN)2 [1] / Hydroboration Products of Carbodiimides with (9H-9-BBN)2 [1]

The hydroboration of H11C6N=C=NC6H11(A) with (9H-9-BBN)2 (C2) gives H11C6N= C(H)N(C6H11)BC8H14 (1), which reacts with 9H-9-BBN to form the six-membered heterocycle mixed dimer (2). Compound 2 crystallizes in the monoclinic space group C 2/c, a = 27.776(3). b = 17.140(2), c = 12.302(2) Å, β = 113.31° (at 120 K). - On heating. 2 is transformed by intramolecular hydroboration into H2C[N(C6H11)B(C8H14)]2 (3a). - 1 reacts with Et2O-BF3 to give 9F-9-BBN (4) and (5). - The total hydroboration of H5C6N=C=NC6H5 (B) with C2 affords H2C[N(C6H5)B(C8H14)]2 (3b).