Beiträge zur Chemie des Bors, 159. [2 + 2]‐Cycloadditionen von ( tert ‐Butylimino)(2,2,6,6‐tetramethylpiperidino)boran mit Kohlenstoffdichalkogeniden

Abstract

COz. COS, CS2 und CSe2 reagieren rnit dem Aminoiminoboran 1 unter [2 + 21-Cycloaddition zu den Azaboretidinen 2-5. Diese zerfallen thermisch oder photolytisch unter Abspaltung von (CHJ3C -N = C = E (E' = 0, S, Se) und Bildung der dimeren (Tetramethylpiperidin0)borchalkogenide 7 -9. Die Rontgenstrukturanalyse der schwefelhaltigen Heterocyclen 4 und 8 zeigt planare Vierringe auf. In 4 bildet das C2N-Strukturelement der Tetramethylpiperidino-Gruppe mit der Vierring-Ebene einen Winkel von 72 ' , in 8 sind die beiden Ebenen dagegen nur um 17" verdrillt. Contributions to the Chemistry of Boron, 159')[2 + 23 Cycloadditions of (iert-Butylimino)(2,2,6,6-tetramethylpiperidino)borane with Carbon Dichalcogenides[2 + 21 Cycloadditions of C02, COS, CS2, and CSez and the aminoiminoborane 1 give access to the azaboretidines 2-5. These decompose thermally or photolytically with formation of (CH3)$Z-N=C=E' ( E = 0, S, Se) and the dimers of the (tetramethylpiperidino)boron chalcogenides 7-9. The X-ray structure analyses of the sulfur containing heterocycles 4 and 8 reveal the presence of planar four-membered rings. The C2N-unit of the tetramethylpiperidino group in 4 approaches a perpendicular arrangement with four-membered ring (interplanar angle 72"), in 8 however, the two planes are twisted to each other by 17 only.Iminoborane sind nach Untersuchungen von Paetzold gute Cycloadditionsreagenzien2); dies gilt insbesondere fur [2 + 31-Cycloadditionen. Ursache der hohen Reaktivitat der Iminoborane ist ihr den Acetylenen vergleichbarer ungesattigter Charakter, wahrend die Regiospezifitat der Cycloaddition auf die Polaritat der BN-Bindung zuriickgeht. Als typische [2 + 21-Cycloaddition der Iminoborane kann ihre Dimerisierung zu 1,3,2,4-Diazadiboretidinen gelten3*4).Die chemische Reaktivitat der Aminoiminoborane, R2N -B = N -R', ist im Vergleich mit Iminoboranen, RB = NR', um die funktionelle Aminogruppe erweitert. So ist etwa mit ungesattigten Systemen, wie COz, nicht nur eine Reaktion an der BN-Dreifachbindung zu erwarten, sondern auch eine Insertion von C 0 2 in die Aminoboran-BN-Bindung. Derartige Einschiebungsreaktionen sind ausfuhrlich untersucht5'.

Oxidative Addition at a Carbene Center: Synthesis of an Iminoboryl–CAAC Adduct

“…This compound formally results from the [2+2] cycloaddition of CO 2 with the BN fragment of iminoboryl 4 I with concomitant formation of a covalent boron-iodine bond or, alternatively, does not involve 4 I but the iodoiminoborane form 3 c. Indeed, when 3 a and 3 b were exposed to CO 2 the corresponding adducts 5 a and 5 b, were isolated in 91 and 83 % yields, respectively. The These results are consistent with reports by the groups of Nçth [3] and Cui [19] on the reactivity of an amino iminoborane and a p-conjugated iminoborane stabilized by an intramolecu- lar imine group, respectively, with carbon dioxide. The lack of reactivity observed with 4 BPh 4 and 4 B(C 6 F 5 ) 4 is most probably due to the unavailability of the lone pair on nitrogen.…”

“…The reactivity of these systems has been studied and they were shown to undergo several transformations including [2+2] cycloaddition reactions across the BN linkage, [1e, 2] where, for example, reactions between an amino iminoborane and molecules of the form CX 2 (X = O, S, Se) were reported. [3] Despite the large number of known transition metal alkynyl complexes [L n MÀCCÀR], [4] it was only as recently as 2006 that Braunschweig and co-workers reported the isolation of transition metal iminoboryl complexes A (Scheme 1). [5] The trans-[(Br)(PCy 3 ) 2 M(BNÀSiMe 3 )] (M = Pd, Pt) complexes were obtained upon oxidative addition of the BÀBr bond in (Me 3 Si) 2 NBBr 2 to [M(PCy 3 ) 2 ] and subsequent facile intramolecular elimination of Me 3 SiBr at room temperature.…”

“…[3] Despite the large number of known transition metal alkynyl complexes [L n MÀCCÀR], [4] it was only as recently as 2006 that Braunschweig and co-workers reported the isolation of transition metal iminoboryl complexes A (Scheme 1). [5] The trans-[(Br)(PCy 3 ) 2 M(BNÀSiMe 3 )] (M = Pd, Pt) complexes were obtained upon oxidative addition of the BÀBr bond in (Me 3 Si) 2 NBBr 2 to [M(PCy 3 ) 2 ] and subsequent facile intramolecular elimination of Me 3 SiBr at room temperature. Notably, the transition metal iminoboryl systems were found to be stable against oligomerization, yet reactive towards a variety of substrates.…”

The Doubly Base‐Stabilized Diborane(4) [HB(μ‐hpp)]2 (hpp = 1,3,4,6,7,8‐hexahydro‐2H‐pyrimido[1,2‐a]pyrimidinate): Synthesis by Catalytic Dehydrogenation and Reactions with S8 and Disulfides

“…The B-S bond lengths in these molecules measure 181.0(10)/178.9(14) pm in 1, [34] 179.5(9)/180.6(9) pm in 2, [35] 182.4(2) pm in 3, [36] and 186.1(2) pm in 4. [37] As anticipated, these distances are shorter than the 188.6(2)/189.4(2) pm determined for [HB(µ-hpp)] 2 (µ-S), for which boron-sulfur π-bonding is not significant (four-coordinate B atoms). Scheme 1.…”

1,3,2,4-Diselenastannaboretane, a novel selenium-containing four-membered boracycle: synthesis, structure and thermal cycloreversion into a selenoxoborane

“…8 Although the synthesis and structure of 1,3,2,4-diselenadiboretane, a dimer of a selenoxoborane, has already been reported by Nöth and coworkers, no description was given for the intermediary selenoxoborane. 9 The reaction of an overcrowded trihydroborate 2, synthesized by the reaction of (Tbt)B(OMe) 2 1 with LiAlH 4 , 2 with titanocene pentaselenide followed by treatment with Ph 2 SnCl 2 gave a novel five-membered boracycle, 1,2,4,3,5-triselenastannaborolane 3, as yellow crystals in 20% yield from 1 (Scheme 1). Although we have attempted the thermolysis of 3 in the hope of cycloreversion into the selenoxoborane (Tbt)BNSe, no change was observed even at 150 °C in the presence of 2,3-dimethylbuta-1,3-diene as a trapping reagent for a selenoxoborane.…”