The combination of (AlCp*)4, a source of monomeric :AlCp* at elevated temperatures, with DipTerPnPMe3 (Pn = P, As), so-called pnicta-Wittig reagents, at 80 °C cleanly gives the pnictaalumenes DipTerPnAlCp* with polarized Pn–Al double bonds and intramolecular stabilization through interactions of Al with a flanking aryl group of the terphenyl substituent on Pn. In contrast, using MesTerPPMe3, the reaction with 2 equiv of :AlCp3t or :AlCp* afforded the three-membered 2π-aromatic ring systems MesTerP(AlCp x )2 (x = 3t, *).
Theoretical studies predicted the planar cyclopenten-4-yl cation to be aclassical carbocation, and the highest-energy isomer of C 5 H 7 + .H ence,i ts existence has not been verified experimentally so far.W ew ere now able to isolate two stable derivatives of the cyclopenten-4-yl cation by reaction of bulky alanes Cp R AlBr 2 with AlBr 3 .E lucidation of their (electronic) structures by X-raydiffraction and quantum chemistry studies revealed planar geometries and strong hyperconjugation interactions primarily from the CÀAl s bonds to the empty p orbital of the cationic sp 2 carbon center.Aclose inspection of the molecular orbitals (MOs) and of the anisotropyofcurrent (induced) density (ACID), as well as the evaluation of various aromaticity descriptors indicated distinct aromaticity for these cyclopenten-4-yl derivatives,w hich strongly contrasts the classical description of this system. Here,strong delocalization of p electrons spanning the whole carbocycle has been verified, thus providing rare examples of p aromaticity involving saturated sp 3 carbon atoms.
Heterocycles containing group 13 and 15 elements such as borazines are an integral part of organic, biomedical and materials chemistry. Surprisingly, heterocycles containing P and Al are rare. We have now utilized phosphaalumenes in reactions with alkynes, alkenes and conjugated double bond systems. With sterically demanding alkynes 1,2‐phosphaalumetes were afforded, whereas the reaction with HCCH or HCCSiMe3 gave 1,4‐phosphaaluminabarrelenes. Using styrene saturated 1,2‐phosphaalumates were formed, which reacted further with additional styrene to give different regio‐isomers of 1,4‐aluminaphosphorinanes. Using ethylene, a 1,4‐aluminaphosphorinane is obtained, while with 1,3‐butadiene a bicyclic system containing an aluminacyclopentane and a phosphirane unit was synthesized. The experimental work is supported by theoretical studies to shed light on the mechanism governing the formation of these heterocycles.
Using the Al I precursor Cp 3t Al in conjunction with triphosphiranes (PAr) 3 (Ar = Mes,Dip,Tip) we have succeeded in preparing Lewis base-free cyclic diphosphadialanes with both the Al and Patoms bearing three substituents.U sing the sterically more demanding Dip and Tips ubstituents the first 1,2-diphospha-3,4-dialuminacyclobutanes were obtained, whereas with Mes substituents [Cp 3t Al(m-PMes)] 2 is formed. This divergent reactivity was corroborated by DFT studies, which indicated the thermodynamic preference for the 1,2diphospha-3,4-dialuminacyclobutane form for sterically more demanding groups on phosphorus.U sing Cp*Al we could extend this concept to the corresponding cyclic diarsadialanes [Cp*Al(m-AsAr)] 2 (Ar = Dip,T ip) and additionally add the phosphorus variants [Cp*Al(m-PAr)] 2 (P = Mes,D ip,T ip). The reactivity of one variant [Cp 3t Al(m-PPh)] 2 towards NHCs was tested and resulted in double NHC-stabilised [Cp 3t -(IiPr 2 )Al(m-PPh)] 2 .
Bei Umsetzungen der Al I -Verbindung Cp 3t Al mit Triphosphiranen (PAr) 3 (Ar = Mes,D ip,T ip) ist es gelungen, Lewis-basenfreie cyclische Diphosphadialane herzustellen, bei denen sowohl das Al-als auchdas P-Atom drei Substituenten tragen. Mit den sterischa nspruchsvolleren Dip-und Tip-Substituenten wurden die ersten 1,2-Diphospha-3,4-dialuminacyclobutane erhalten, während mit Mes-Substituenten [Cp 3t Al(m-PMes)] 2 gebildet wird.D iese abweichende Reaktivitätwurde durchDFT-Studien bestätigt, die auf eine thermodynamische Präferenz fürd ie 1,2-Diphospha-3,4-dialuminacyclobutane fürs terischa nspruchsvollere Gruppen am Phosphor hinwiesen. Mithilfe von Cp*Al konnten wir dieses Konzept auf die entsprechenden cyclischen Diarsadialane [Cp*Al(m-AsAr)] 2 (Ar = Dip,T ip) ausdehnen und zusätzlich die Phosphorvarianten [Cp*Al(m-PAr)] 2 (P = Mes,D ip,T ip) synthetisieren. Die Reaktivitätv on [Cp 3t Al(m-PPh)] 2 gegenüber NHCs wurde untersucht und führte zu doppelt NHCstabilisiertem [Cp 3t (IiPr 2 )Al(m-PPh)] 2 . 2021 Die Autoren. AngewandteChemie verçffentlichtv on Wiley-VCH GmbH. Dieser Open Access Beitrag steht unter den Bedingungen der Creative Commons AttributionN on-CommercialL icense, die eine Nutzung, Verbreitung und Vervielfältigung in allen Medien gestattet, sofern der ursprünglicheBeitrag ordnungsgemäß zitiert und nicht fürkommerzielle Zwecke genutzt wird.
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