Frustrated Lewis Pairs and Ring-Opening of THF, Dioxane, and Thioxane

Abstract

The reaction of tBu2PH and B(p-C6F4H)3 in THF afforded tBu2(H)P(CH2)4OB(p-C6F4H)3 (1). Similarly, reactions of N-bases with a THF solution of B(C6F5)3 led to the formation of the THF-ring-opening products C5H3Me2N(CH2)4OB(C6F5)3 (2), C6H5CH2NMe2(CH2)4OB(C6F5)3 (3), and Me2NC6H4NMe2(CH2)4OB(C6F5)3 (4). THF-ring-opening also occurs with aliphatic amines to form the compounds Me3N(CH2)4OB(C6F5)3 (5), Et3N(CH2)4OB(C6F5)3 (6), Me2N(CH2)2NMe2(CH2)4OB(C6F5)3 (7), and tBuHN(CH2)2NHtBu(CH2)4OB(C6F5)3 (8). In related chemistry, reactions of B(C6F5)3, 1,4-dioxane, and the appropriate base yielded tBu3P(CH2)2O(CH2)2OB(C6F5)3 (10), C6H5CH2NMe2(CH2)2O(CH2)2OB(C6F5)3 (11), ((tBuN)2C3H2)(CH2)2O(CH2)2OB(C6F5)3 (12), Me2NC6H4NMe2(CH2)2O(CH2)2OB(C6F5)3 (13), and C5H3Me2N(CH2)2O(CH2)2OB(C6F5)3 (14). In a related fashion, the thioxane adduct (C6F5)3B(SC4H8O) (15) reacted with N,N-dimethylbenzylamine, N,N,N′,N′-tetramethyl-p-phenylenediamine, 2,6-lutidine, or tBu3P to give the corresponding ring-opened products L(CH2)2S(CH2)2OB(C6F5)3 (L = tBu3P (16), C6H5CH2NMe2 (17), Me2NC6H4NMe2 (18), and C5H3Me2N (19)). The crystal structures of 1−7, 10−12, 14, 18, and 19 are reported.