Chiral M3L2 Self-Assembled Capsules through Metal Coordination of Enantiopure Ligating Benzocyclotrimers: NMR Spectroscopic and ESI Mass Spectrometric Investigation

• Published in: Chemistry : a European journal 2013-04, Vol.19 (18), p.5701-5714
• Main Authors: Tartaggia, Stefano, De Lucchi, Ottorino, Gambaro, Andrea, Zangrando, Roberta, Fabris, Fabrizio, Scarso, Alessandro
• Format: Article
• Language: English
• Subjects: Chemistry; cyclotrimerization; Heck reaction; Ligands; platinum; self- assembly; silver; Software
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201203598

The synthesis of enantiopure (+)‐benzotricamphor syn‐5, an important chiral C3‐symmetric rigid building block for supramolecular applications, was studied in detail to reduce the number of steps and to increase the diastereoselectivity and overall yield. The new synthetic procedure allowed larger amounts of syn‐5 to be obtained and used for the preparation of new derivatives, such as the corresponding tris‐trifluoromethanesulfonate syn‐12, which was efficiently transformed into (+)‐benzotribornenetrinitrile syn‐1 and (+)‐benzotribornenetris(ethynyl‐4‐pyridine) syn‐2. The previously reported (+)‐benzotricamphortrioxime syn‐6 was transformed into tris‐nitrile syn‐3 by Beckman reaction. Compounds syn‐1–3 were employed as multidentate ligands for silver(I) and platinum(II) centres in apolar solvents. The linear coordination geometry of AgI and square‐planar geometry of cis‐chelated PtII in combination with the chiral tripodal ligands syn‐1–3 led to the formation of chiral enantiopure capsules with M3L2 stoichiometry, as confirmed by 2D NMR NOESY and DOSY experiments as well as ESI mass spectrometry. Platinum cages: Chiral tridentate ligands (+)‐benzotribornenetrinitrile and (+)‐benzotribornenetris(ethynyl‐4‐pyridine) (syn‐1) were prepared and employed for coordination of silver(I) and platinum(II) in apolar solvents to give chiral enantiopure capsules with M3L2 stoichiometry, as confirmed by 2D NMR NOESY and DOSY experiments as well as ESI mass spectrometry (see scheme; dppp=1,3‐bis(diphenylphosphino)propane, dippe=1,2‐bis(diisopropylphosphino)ethane).