Internal Adduct Formation of Active Intramolecular C4‑bridged Frustrated Phosphane/Borane Lewis Pairs

• Published in: Journal of the American Chemical Society 2014-02, Vol.136 (8), p.3293-3303
• Main Authors: Wang, Xiaowu, Kehr, Gerald, Daniliuc, Constantin G, Erker, Gerhard
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja413060u

The tetramethylene-bridged PMes2/B(C6F5)2 frustrated Lewis pair (FLP) 8 was prepared by hydroboration of Mes2P–(CH2)2CHCH2 with HB(C6F5)2. It is an active FLP that splits dihydrogen under mild conditions and, consequently, serves as a metal-free hydrogenation catalyst for a variety of substrates. It also reacts typically with terminal acetylenes. The C4-bridged FLP 23 was prepared by HB(C6F5)2 hydroboration of 1-dimesitylphosphino-2-vinylferrocene. It represents a rare example of a FLP where the equilibrium between the open form and the closed internal P/B adduct form is experimentally observable. It also shows a variety of typical FLP reactions, including dihydrogen splitting. The FLPs 8 and 23 (open form) and many precursors and products were characterized by X-ray diffraction.