Synthesis and reactivity of alkynyl-linked phosphonium borates.

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