Peter Paetzold

Boron-Nitrogen Analogues of Cyclobutadiene, Benzene and Cyclooctatetraene

Abstract Iminoboranes RB [tbnd] NR′, isoelectronic with alkynes, cyclooligomerize to give B-N rings (RBNR′)n that are either analogues of cyclobutadienes (n = 2) or benzenes or Dewar benzenes (n = 3) or cyclooctatetraenes (n = 4), depending on the ligand set R/R′ and on conducting the oligomerization either thermally or catalytically. Cyclodimers and cyclotetramers may either undergo reversible interconversions or cyclotetramers are formed irreversibly from cyclodimers. The (4+2) cycloaddition of cyclodimers and iminoboranes yields cyclotrimers. Cyclotrimers may thermally be converted into cyclodimers, and poly(iminoboranes), isoelectronic with polyalkynes, can thermally be depolymerized into cyclotrimers. nido-Cluster derivatives of N2B4H6, arachno-cluster derivatives of N2B3H7, four-membered rings N2B2R3R′, or five-membered rings N2B3R4R′ are isolated, when three-membered rings NB2R3, isoelectronic with cyclopropenyl cations, either dimerize or add aminoboranes H2B=NR′2 or insert nitrenes R′N (from R′N3...

Undecaborates M2[B11H11]: Facile Synthesis, Crystal Structure, and Reactions

closo-Undecaborates were synthesized by the deprotonation of B11H13(SMe2) with LitBu in thp or K[BHEt3] in thf, [Li(thp)3]2[B11H11] and K2[B11H11] being obtained in 83 and 93% yield, respectively. K2[B11H11] can be transformed into A2[B11H11] with the corresponding ammonium chlorides in aqueous solution (A = [NMe3Ph], [NBzlEt3], [N(PPh3)2]). The crystal structure analysis of [Li(thp)3]2[B11H11] (space group P21/c) reveals a rather distorted octadecahedron for the [B11H11]2– anion, whereas the corresponding octadecahedron in [NBzlEt3]2[B11H11] (space group P212121) exhibits a structure close to C2v symmetry, expected for the free anion. The protonation of [B11H11]2– at low temperature gives [B11H12]–, whose structure could be elucidated by NMR methods; it is formed, apparently, by the opening of the B1–B4 edge of [B11H11]2– in the course of its known degenerate skeletal rearrangement, followed by the protonation of the B2–B4 edge. The reaction of [B11H12]– with a second molecule of the acid HX (X = CF3COO) gives nido-[B11H13X]–. The addition of BH3 to [B11H11]2– yields closo-[B12H12]2– under loss of H2. Two [B11H11]2– units are fused by the aid of FeCl3, with the known anion [B22H22]2– as the product, whose 11B-NMR signals could completely be assigned on the basis of Cs symmetry. The compound [NBzlEt3][N(PPh3)2][B22H22] crystallizes in the space group Pna21. Undecaborate M2[B11H11]: Einfache Synthese, Kristallstruktur und Reaktionen closo-Undecaborate kann man durch Deprotonierung von B11H13(SMe2) mit LitBu in thp oder K[BHEt3] in thf erhalten, und zwar [Li(thp)3]2[B11H11] mit 83 und K2[B11H11] mit 93% Ausbeute. K2[B11H11] last sich mit entsprechenden Ammoniumchloriden in wasriger Losung in A2[B11H11] uberfuhren (A = [NMe3Ph], [NBzlEt3], [N(PPh3)2]). Die Kristallstrukturanalyse von [Li(thp)3]2 · [B11H11] (Raumgruppe P21/c) zeigt, das das Anion [B11H11]2– ein stark verzerrtes Octadecaeder darstellt, wahrend das entsprechende Octadecaeder in [NBzlEt3]2[B11H11] (Raumgruppe P212121) nahezu die fur das freie Anion erwartete C2v-Symmetrie aufweist. Die Protonierung von [B11H11]2– fuhrt bei tiefer Temperatur zu [B11H12]–, dessen Struktur sich aus NMR-Messungen ergibt; es entsteht offenkundig durch Offnen der Kante B1–B4 von [B11H11]2– im Zuge von dessen bekannter entarteter Gerustumlagerung mit nachfolgender Protonierung der Kante B2–B4. Die Reaktion von [B11H12]– mit einem zweiten Molekul der Saure HX (X = CF3COO) ergibt nido-[B11H13X]–. Die Addition von BH3 an [B11H11]2– erbringt closo-[B12H12]2– unter Verlust von H2. Die oxidative Fusion zweier [B11H11]-Einheiten mit Hilfe von FeCl3 fuhrt zum schon bekannten Anion [B22H22]2–, dessen NMR-Signale unter Zugrundelegung von Cs-Symmetrie vollstandig zugeordnet werden konnten. Die Verbindung [NBzlEt3][N(PPh3)2][B22H22] kristallisiert in der Raumgruppe Pna21.

Hydro(trisyl)borane (Me3Si)3CBHX und -borate M[H3BC(SiMe3)3]x

Abstract Dimethoxy(trisyl)borane A 3 (CB(OMe) 2 ( 1a : “trisyl” = A 3 C; A = Me 3 Si) can be hydridated to the borate (Et 2 O) 2 LiH 3 BCA 3 ( 2a ) by the action of LiAlH 4 in ether. Hydro(trisyl)boranes A 3 C-BH(OR) ( 3a–d ; R = Me, Et, i-Pr, H) are formed from 2a with ROH by oxidative removal of two H-atoms. The removal of only one H-atom from 2a can be achieved with either Me 3 NHCl or I 2 , yielding bis(trisyl)di-borane(6) (A 3 CBH 2 ) 2 ( 4 ; space group P 1 ; molecular symmetry C i ), which forms the adduct A 3 CBH 2 · PMe 3 ( 5 ) with PMe 3 . Starting from 2a , the borates (tmeda)LiH 3 BCA 3 ( 2b ) and ClZr(H 3 BCA 3 ) 3 · 0.5Et 2 O ( 2c ; space group P 2 1 / c ) can be prepared by the reaction with tmeda and ZrCl 4 , respectively; the trisylborate groups are bonded to the Zr atom via H 3 -triple bridges.

The chemistry of the undecaborates

Abstract The formation, structure, and reactivity of the nido-11-vertex species B11H15, B11H14−, B11H132−, B11H123− and of the closo-12-vertex species B11H12−, B11H112− are reviewed. The reactivity includes the behavior towards acids, bases, and oxidants as well as cluster expansion reactions, giving closo-11-vertex species of the type EB11H11n− or [B11H11M]n−.

Beiträge zur chemie der borazide VII. Darstellung und eigenschaften von diorganylboraziden

Abstract The preparation and some properties of diorganylboron azides R′RBN 3 and of some of their pyridinates R′RBN 3 ·Py are described.

MOLECULAR AND CRYSTAL STRUCTURE OF ZIRCONIUM HYDROBORATES

Two new zirconium tetrakis(alkyltrihydroborate) complexes have been prepared and characterized by single crystal X-ray diffraction: Zr(H3BtBu)4 crystallizes in the cubic space group P43m (No. 215), a = 8.666(3) A with Z = 1 and site symmetry 43m (Td). The approximately tetrahedral molecules of Zr{H3B(C(SiMe3)3}4 occupy the threefold axes in the cubic space group Pa3 (No. 205), a = 23.886(4) A with Z = 8. Space filling and packing of these new and the two previously described and crystallographically established zirconium hydroborates are compared and the relation between their molecular and crystal structures is discussed.

Pyridin-Borabenzol und Pyridin-2-Boranaphthalin als Liganden von Metallen der Chromgruppe / Pyridine-borabenzene and Pyridine-2-boranaphthaline as Ligands of Group 6 A Metals

Pyridine-borabenzene (1) and pyridine-2-boranaphthalene (2) can be coordinated to group 6A metals M to form compounds of the type (OC)3M·1 and (OC)3M·2, respectively. X-ray structure determinations prove the ligands to be η6-bonded to the metal via the boron-containing six-membered ring.

1,3,5-Tri-tert-butyl-2,4,6-triisopropyl-3,5-diaza-1-azonia-2,6-dibora- 4-borata[2.2.0]bicyclohexan, der erste Vertreter der Dewarborazine/ 1,3,5-Tri-tert-butyl-2,4,6-triisopropyl-3,5-diaza-1-azonia-2,6-dibora- 4-borata[2.2.0]bicyclohexane, the First Dewar Borazine

Abstract The iminoborane iPr-B ≡ N -tBu (1a), metastable at -78 °C, trimerizes to form (iPrBNtBu)3 (4a) at elevated temperatures. The determination of the molecular and crystal structure reveals 4a to be a Dewar-borazine-type molecule with two short peripheral BN-double-bonds (136 and 138 pm) and an extra-long bridge BN-single-bond (175 pm). The same trimer 4a is formed by addition of la to the diazadiboretidine-type dimer (iPrBNtBu)2, prepared independently. The ethyloboration and the azidoboration of la with BEt3 and Me3SiN3, respectively, and the cycloaddition of PhN3 to 1a follow expected patterns.

Formation of the novel neopentylidenoborane Me3Si(But)NBCHBut from the tantalum neopentylidene complex [(η-C5H5)Cl2TaCHBut] by metathesis

The aminoiminoborane Me3Si(But)NB[graphic omitted]NBut reacts with the alkylidene complex [(η-C5H5)Cl2TaCHBut] at –50 °C to give a (2 + 2) cycloadduct containing a [graphic omitted] ring; on warming to 0 °C cleavage occurs, affording the metathesis products Me3Si(But)NBCHBut and [(η-C5H5)Cl2TaNBut].

Hydrometallation of the IminoboranestBuB(NtBu) and [tBu(Me3Si)N]B(NtBu)

The hydrometallation of the iminoboranes XB(NtBu) (1 a: X = tBu; 1 b: X = tBu(Me3Si)N) with Cp2ZrHCl and Cp2HfHCl gives products of the type X–BH=N(tBu)–MCp2–Cl (7 a, b: M = Zr; 8 a, b: M = Hf). There is a B–H–M (3c2e) bond interaction. The BN multiple bond of the iminoboranes is more or less side-on bound to the metal. Hence, iminoboranes again turn out to behave as analogues of alkynes.