Pnictaalumenes and Pn,Al-Heterocycles

C. Hering-Junghans1
1 Leibniz Institute for Catalysis e.V., Albert-Einstein-Straße 29a, 18059 Rostock.

Email: christian.hering-junghans@catalysis.de

Heavier element–element multiple bonds had been long considered inaccessible but have now moved beyond the status of lab curiosities. The number of heteroatomic Al═E multiple bonds is still limited,[1] and only recently terminal aluminium-imides have been structurally characterized, obtained by the reaction of potassium aluminyls or neutral alanediyls with azides.[2] Examples of unsupported aluminium phosphorus or arsenic multiple bonds have not been reported. Su theoretically investigated compounds of the type R–P≡Al–R and stated: “...sterically bulky ligands can greatly stabilize the R–P≡Al– R species”.[3] Due to alternating Lewis acidic and Lewis basic centers, AlP species are prone to oligomerize. Oligomerization should be suppressed by either kinetic stabilization, acceptor stabilization of the group 15 element, or by intra- or intermolecular interaction of the Lewis acidic metal center with a donor.

In this lecture the facile synthesis of pnictaalumenes and -gallenes is described, afforded by the combination of Pnicta-Wittig reagents of the type ArPn(PMe3) (Ar = terphenyls; Pn = P, As) with sources of Al(I) opr Ga(I), respectively. This afforded DipTerPnAlCp*, compounds with Pn-Al multiple bond character.[4] Furthermore, the steric influence of the group attached to phosphorus was investigated, as the reaction of Cp*Al or Cp3tAl with the sterically less demanding MesTerP(PMe3) afforded 2π- aromatic P2Al-ring systems. The reactivities of DipTerPnAlCp* towards small molecules such as CO2, C2H4, C2H2,[5] N2O and azides were studied and insights into their reactivity are discussed. Lastly, the reversible, photochemically induced formation of gallaphosphenes will be described.[6]

References:
[1] P. Bag, C. Weetman, S. Inoue, Angew. Chem., Int. Ed. 2018, 57, 14394.
[2] M. D. Anker, R. J. Schwamm, M. P. Coles, Chem. Commun. 2020, 56, 2288; b) A. Heilmann, J. Hicks, P. Vasko, J. M. Goicoechea, S. Aldridge, Angew. Chem., Int. Ed. 2020, 59, 4897; c) J. D. Queen, S. Irvankoski, J. C. Fettinger, H. M. Tuononen, P. P. Power, J. Am. Chem. Soc. 2021, 143, 6351.
[3] J.-S. Lu, M.-C. Yang, M.-D. Su, Chem. Phys. Lett. 2017, 686, 60.
[4] M. Fischer, S. Nees, T. Kupfer, J. T. Goettel, H. Braunschweig, C. Hering-Junghans, J. Am. Chem. Soc., 2021, 143, 4106.
[5] S. Nees, T. Wellnitz, F. Dankert, M. Härterich, S. Dotzuaer, M. Feldt, H. Braunschweig, C. Hering- Junghans, Angew. Chem. Int. Ed. 2023, 62, e202215838.
[6] T. Taeufer, D. Michalik, J. Pospech, J. Bresien, C. Hering-Junghans, Chem. Sci. 2023,14, 3018.