Ein stabiles neutrales Radikal in der Koordinationssphäre des Aluminiums

Abstract

Das neuartige neutrale Radikal (Me 2 -cAAC) 2 AlCl 2 (2)w ird durch cyclische Alkylaminocarbene (cAACs) stabilisiert. Die Synthese erfolgte in Gegenwart eines weiteren ¾quivalents Me 2 -cAACd urch Reduktion des Addukts Me 2 -cAAC:AlCl 3 (1)m it KC 8 .A nhand der Kristallstruktur zeigt sich, dass die beiden Carbene,d ie an das Aluminiumatom gebunden sind, deutlichu nterschiedlicheA l-C-Bindungen aufweisen. Dies lässt sich vermutlich auf die intermolekularen Wechselwirkungen zurückführen. Quantenmechanische Rechnungen ergaben dagegen eine Gleichgewichtsstruktur mit identischen Al-C-Bindungslängen. Verbindung 2 weist einen Monoradikalcharakter auf,d er durch eine ESR-Messung bestätigt werden konnte.Die Bindungsanalyse deutet darauf hin, dass das ungepaarte Elektron hauptsächlich am Carbenkohlenstoffatom lokalisiert ist. Somit ist 2 ein Beispiel füre in ungewçhnliches neutrales Al-Radikal.

Electronic and Ligand Properties of Skeletally Substituted Cyclic (Alkyl)(Amino)Carbenes (CAACs) and Their Reactivity towards Small Molecule Activation: A Theoretical Study

“…However,t he change in p-acidity is not very significant despite the presence of the electron-withdrawing boron centre. Based on the calculated E s values, ylide stabilized carbenes (5)(6)(7)(8)(9)(10)(11)(12)(13)a re found to have significantly enhanced electron-donation ability comparedt on on-ylidic ones, which is in agreement with earlier findings. [16a-d,j] It is evidentf rom Ta ble 3 that installation of the benzene ring in the backbone of ring Chem.…”

“…We calculated their N and w values using the equations N = E HOMO ÀE HOMO(TCNE) (considering tetracyanoethylene (TCNE) as the reference) [23] and w = m 2 /2h where m = (E HOMO + E LUMO )/2 and h = (E HOMO ÀE LUMO ), [24] respectively.T he calculated nucleophilicity and electrophilicity index values of these carbenes (Table 3) are in accord with their respective E s and E p* values. In agreement with their better electron-donation ability,y lide substituted carbenes (5)(6)(7)(8)(9)(10)(11)(12)(13)a re found to be more nucleophilic compared to non-ylidic ones (1)(2)(3)(4)14). We obtained an excellent correlation between N and E s values( R 2 = 1; Figure 4a)a sw ell as between E p* and w values (R 2 = 0.95, Figure4b).…”

“…[12] Furthermore, Roeskya nd co-workers employed this ligandf or the stabilization of an eutral radical within the coordination sphere of aluminium. [13] Recently,t he group of Bertrand isolated as eries of hemilabile bidentatec yclic (alkyl)(amino) carbenesw herein their gold and copperc omplexes showed unusualr eactivity toward the oxidative addition of biphenylene (Au), catalytic hydroarylationo fa lkenes (Cu and Au) and anti-Markovnikov hydrohydrazination of alkynes (Cu). [14] In addition, Braunschweig and co-workers were successful in the isolation of the first beryllium(0)c ompound by incorporation of two CAAC ligands.…”

Hydride Amide and Hydride Phenolate Complexes of NHC Coordinated Aluminum

“…Most common is the synthesis by salt elimination following the reaction of a NHC with lithium aluminum hydride or by base substitution of (NMe 3 ) · AlH 3 . The application of NHCs and cAACs in aluminum chemistry enabled recently the synthesis of interesting substances with new structural motifs such as the neutral aluminum dimer (Dipp 2 Im) · H 2 Al–AlH 2 · (Dipp 2 Im) reported by Jones et al, a neutral compound {( i Pr 2 Im Me2 )Al( t Bu 2 MeSi)} 2 with an aluminum–aluminum double bond reported by Inoue et al, or cAAC stabilized neutral aluminum radicals as presented by Roesky et al…”

“…NHC aluminum chemistry has been explored in more and more detail over the last few years . For NHC stabilized AlH 3 a variety of synthetic routes are established meanwhile in the literature .…”