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Synthesis and Reactivity of Alkynyl-Linked Phosphonium Borates

Authors

  • Xiaoxi Zhao,

    1. Department of Chemistry, University of Toronto, 80 St. George St., Toronto, Ontario, M5S 3H6 (Canada), Fax: (+1) 416-978-7551
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  • Dr. Alan J. Lough,

    1. Department of Chemistry, University of Toronto, 80 St. George St., Toronto, Ontario, M5S 3H6 (Canada), Fax: (+1) 416-978-7551
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  • Prof. Dr. Douglas W. Stephan

    Corresponding author
    1. Department of Chemistry, University of Toronto, 80 St. George St., Toronto, Ontario, M5S 3H6 (Canada), Fax: (+1) 416-978-7551
    • Department of Chemistry, University of Toronto, 80 St. George St., Toronto, Ontario, M5S 3H6 (Canada), Fax: (+1) 416-978-7551
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Abstract

The phosphine tBu2PC[TRIPLE BOND]CH (1) was reacted with B(C6F5) to give the zwitterionic species tBu2P(H)C[TRIPLE BOND]CB(C6F5)3 (2). The analogous species tBu2P(Me)C[TRIPLE BOND]CB(C6F5)3 (3), tBu2P(H)C[TRIPLE BOND]CB(Cl)(C6F5)2 (4), tBu2P(H)C[TRIPLE BOND]CB(H)(C6F5)2 (5), and tBu2P(Me)C[TRIPLE BOND]CB(H)(C6F5)2 (6) were also prepared. The salt [tBu2P(H)C[TRIPLE BOND]CB(C6F5)2(THF)][B(C6F5)4] (7) was prepared through abstraction of hydride by [Ph3C][B(C6F5)4]. Species 5 reacted with the imine tBuN[DOUBLE BOND]CHPh to give the borane–amine adduct tBu2PC[TRIPLE BOND]CB[tBuN(H)CH2Ph](C6F5)2 (8). The related phosphine Mes2PC[TRIPLE BOND]CH (9; Mes=C6H2Me3) was used to prepare [tBu3PH][Mes2PC[TRIPLE BOND]CB(C6F5)3] (10) and generate Mes2PC[TRIPLE BOND]CB(C6F5)2. The adduct Mes2PC[TRIPLE BOND]CB(NCMe)(C6F5)2 (11) was isolated. Reaction of Mes2PC[TRIPLE BOND]CB(C6F5)2 with H2 gave the zwitterionic product (C6F5)2(H)BC(H)[DOUBLE BOND]C[P(H)Mes2][(C6F5)2BC[TRIPLE BOND]CP(H)Mes2] (12). Reaction of tBu2PC[TRIPLE BOND]CB(C6F5)2, a phosphine–borane generated in situ from 5, with 1-hexene gave the species [tBu2PC[TRIPLE BOND]CB(C6F5)2](CH2CHnBu)[tBu2PC[TRIPLE BOND]CB(C6F5)2] (13) and subsequent reaction with methanol or hexene resulted in the formation of [tBu2P(H)C[TRIPLE BOND]CB(C6F5)2](CH2CHnBu)[tBu2PC[TRIPLE BOND]CB(C6F5)2](OMe) (14) or the macrocycle {[tBu2PC[TRIPLE BOND]CB(C6F5)2](CH2CH2nBu)}2 (15), respectively. In a related fashion, the reaction of 13 with THF afforded the macrocycle [tBu2PC[TRIPLE BOND]CB(C6F5)2](CH2CHnBu)[tBu2PC[TRIPLE BOND]CB(C6F5)2][O(CH2)4] (16), although treatment of tBu2PC[TRIPLE BOND]CB(C6F5)2 with THF lead to the formation of {[tBu2PC[TRIPLE BOND]CB(C6F5)2][O(CH2)4]}2 (17). In a related example, the reaction of Mes2PC[TRIPLE BOND]CB(C6F5)2 with PhC[TRIPLE BOND]CH gave {[Mes2PC[TRIPLE BOND]CB(C6F5)2](CH[DOUBLE BOND]CPh)}2 (18). Compound 5 reacted with AlX3 (X=Cl, Br) to give addition to the alkynyl unit, affording (C6F5)2BC(H)[DOUBLE BOND]C[P(H)tBu2](AlX3) (X=Cl 19, Br 20). In a similar fashion, 5 reacted with [Zn(C6F5)2]C7H8, [Al(C6F5)3]C7H8, or HB(C6F5)2 to give (C6F5)3BC(H)[DOUBLE BOND]C[P(H)tBu2][Zn(C6F5)] (21), (C6F5)3BC(H)[DOUBLE BOND]C[P(H)tBu2][Al(C6F5)2] (22), or [(C6F5)2B]2HC[DOUBLE BOND]CH[P(H)tBu2] (23), respectively. The implications of this reactivity are discussed.

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