Preparation, Reactions, and Structure of tert-Butyl(tert-buty1imino)boraneThe iminoborane t BuB = Nt Bu (1) is formed from the aminoborane Cl(t Bu)B-N(t Bu)SiMe, by the elimination of Me,SiCI in the gas phase at 530°C. Compound 1 slowly dimerizes to the diazadiboretidine [tBuBNtBu], (2). In a way typical for iminoboranes, the borane 1 undergoes a? ethyloboration with BEt,, a [2 + 31-cycloaddition with PhN,, and an azidosilation with Me3SiN3. The crystal and molecular structure of 1 and 2 are described; there is a linear central CBNC-chain in 1 with a BN-bond distance of 125.8 pm; the ring-skeleton of 2 deviates from planarity by the influence of the bulky ring ligands. The structural properties of the iminoborane 1 are comparable to those of the isoelectronic alkyne fBuC=CtBu (3). and the properties of the cyclodimer 2 are comparable to those of the isoelectronic cyclobutadiene [t BuC = Ct Bu], (4). The strength of the triple bond decreases from 3 to 1 in a similar manner as by going from N, to CO. Darstellung und Reaktionen von tert-Butyl(tert-buty1imino)boran (1)Aus dem Aminoboran Cl(tBu)B -N(tBu)SiMe,, das aus dem Chlorboran C1,BtBu und dem Lithiumamid LiN(tBu)SiMe, zuganglich ist, laBt sich in der bekannten 0

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Iminoboranes RB = NtBu (R = Me, Et, Pr; 1a-c) undergo a catalytic cyclodimerisation to 2a-c at -10 to -20 °C, but a thermal cyclotrimerisation to 3a-c at 50 °C. The cyclodimer 2a and the cyclotetramer 4a (R = Me) are reversibly transformed into each other at 20 to 70 °C. The cyclodimer 2d (R = Bu), kinetically stable with respect to the cyclotrimer 3d, yields 3d when reacted with the monomer 1d . The ethyloboration of the new monomer 1a , its cycloaddition with PhN3, and its azidosilation by Me3SiN3 are described. The coordination compounds (OC)4Cr[(RBNtBu)2] (9a-c) are formed from Cr(CO)5(THF) or from Cr(CO)4(COD) either with 1a-c or with 2a-c.

AbstractThe 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.

[2 + 21-Cycloaddition Products from lminoborane and IminophosphaneThe iminoborane Bu -B = N-tBu (la) and the iminophosphanes R2N -P = N -R' (2a, b) undergo a cyclisation to the corresponding 1,3,2,4-diazaphosphaboretidines (3a, b). Wie anhand zweier Diazadiboretidine vom Typ 4 mittels Rontgenstrukturanalyse nachgewiesen wurde, liegt bei dieser Verbindungsklasse wohl im allgemeinen ein planarer Vierring mit koplanaren Nachbaratomen vor. Auch die NPNP-Vierring-Verbindung 5a ist planar gebaut, die beiden Nachbaratome Si sind hierzu koplanar angeordnet, nicht jedoch die P-gebundenen Gruppen NR,, die aus der Vierringebene in trans-Stellung zueinander herausragen. Es liegt nahe, den Verbindungen 3a, b einen planaren NPNB-Vierring mit koplanaren Nachbaratomen zuzuschreiben mit Ausnahme des nicht koplanaren N-Atoms der NR2-Gruppe. Hierfur spricht die Verwandtschaft der NMR-Signale von 4a und der Iminoboran-Halfte von 3a, b (Tab. 1) sowie von Sa, b und der Iminophosphan-Halfte von 3a, b (Tab. 2,3). Aus den NMR-Daten von 5a wurde eine unerwartet hohe Barriere fur die Rotation der N(SiMe3)2-Gruppe um die PN-Achse abgeleitet3). Wir finden jetzt ebenfalls im NMR-Spektrum bei Raumtemperatur eine Nichtaquivalenz der beiden Reste R 0 Verlag

Abstract The iminoboranes RB≡NR′, 2a-f, are formed by the elimination of Me3SiHal from the corresponding aminoboranes 1a-f. Stabilization occurs either through cyclodimerisation (→3b-d,f), cyclotrimerisation (→4e), bicyclotrimerisation (→5b) or cyclotetramerisation (→6a). Trialkylboranes BX3 are added to give the diboryl amines . 7a-f. The Δ2:-tetraazaborolines . 8a-f, are the (3+2)-cycloaddition products from 2a-f and azides X′N3. A CH-bond of cyclopentadiene adds to one of the BN bonds of 2f, giving a mixture of the corresponding 1,3- and 1,4-cyclopentadienyl boranes. 9f, 9′f.

Das aus dem Amin (I) und dem Boran (II) dargestellte Aminoboran (III) läßt sich thermisch unter Bildung der Titelverbindung (IV) (Röntgenstrukturanalyse: Pnma; Z=4), einer farblosen Flüssigkeit, zersetzen.

Protic reagents XH (X = Cl, RO, R2N) were added to the triple bond of the iminoboranes iPrB ≡ NiPr and BuB ≡ NtBu, in a rapid and uncatalyzed reaction