Valinate and SiMe2 – An interesting couple in pentacoordinate Si-complexes: Templated generation of the dipeptide val-val and formation of an organosilicon-ammonia-adduct

Lewis Acid-Base Adducts of α-Amino Acid-Derived Silaheterocycles and N-Methylimidazole

“…Nonetheless, compounds such as (Phe)SiMe2 [17] or (His)SiMe2 [18] (with Phe and His being the di-anions of phenylalanine and histidine, respectively) were reported in the literature more than two decades ago as intermediates in reactions such as amide formation [17] and the functionalization of a trityl type resin [18]. Ammonia adduct XVII decomposes when dissolved in chloroform with dissociation of the Si-NH3 bond In this rather limited portfolio, our recently reported compound XVII [16] takes on a prominent role as it represents the first crystallographically characterized ammonia adduct of an organosilicon compound (and, moreover, the first adduct of an α-amino acid derived silaheterocycle with a neutral Lewis base). So far, there is no crystallographic evidence for the isolation and structural characterization of silacycles with di-anionic chelators of the α-amino acid type which feature tetracoordinate silicon.…”

“…In some classes of oligodentate O,N-chelators the α-amino acid motif is contained, e.g., in silatranes with a carboxylate moiety (such as I and II [9,10], Figure 1) and in amino acid-derived Schiff base complexes (such as III and IV [11,12]). As many α-amino acids themselves are available from the natural chiral pool, it is noteworthy that only a comparatively small number of silicon complexes with their mono-or di-anionic α-amino acid ligands have been crystallographically characterized so far (compounds V-XVII) [13][14][15][16].…”

“…Molecules 2023, 28, x FOR PEER REVIEW 2 of 20 and in amino acid-derived Schiff base complexes (such as III and IV [11,12]). As many αamino acids themselves are available from the natural chiral pool, it is noteworthy that only a comparatively small number of silicon complexes with their mono-or di-anionic α-amino acid ligands have been crystallographically characterized so far (compounds V-XVII) [13][14][15][16]. In this rather limited portfolio, our recently reported compound XVII [16] takes on a prominent role as it represents the first crystallographically characterized ammonia adduct of an organosilicon compound (and, moreover, the first adduct of an α-amino acid derived silaheterocycle with a neutral Lewis base).…”

“…As many αamino acids themselves are available from the natural chiral pool, it is noteworthy that only a comparatively small number of silicon complexes with their mono-or di-anionic α-amino acid ligands have been crystallographically characterized so far (compounds V-XVII) [13][14][15][16]. In this rather limited portfolio, our recently reported compound XVII [16] takes on a prominent role as it represents the first crystallographically characterized ammonia adduct of an organosilicon compound (and, moreover, the first adduct of an α-amino acid derived silaheterocycle with a neutral Lewis base). So far, there is no crystallographic evidence for the isolation and structural characterization of silacycles with di-anionic chelators of the α-amino acid type which feature tetracoordinate silicon.…”

“…Nonetheless, compounds such as (Phe)SiMe 2 [17] or (His)SiMe 2 [18] (with Phe and His being the di-anions of phenylalanine and histidine, respectively) were reported in the literature more than two decades ago as intermediates in reactions such as amide formation [17] and the functionalization of a trityl type resin [18]. Ammonia adduct XVII decomposes when dissolved in chloroform with dissociation of the Si-NH 3 bond and formation of a wealth of decomposition products with tetracoordinate Si atoms [16]. Thus, we conclude that this adduct formation, which enhances the Si coordination num-Molecules 2023, 28, 7816 3 of 19 ber, stabilizes these particular five-membered silacycles and, vice versa, this stabilizing effect gave rise to the formation of such a rare ammonia adduct of an organosilicon compound.…”