Chloro- and phenoxy-phosphines in frustrated Lewis pair additions to alkynes.

The reaction of tBu(C(6)H(4)O(2))P, with the borane B(C(6)F(5))(3) gives rise to NMR data consistent with the formation of the classical Lewis acid-base adduct tBu(C(6)H(4)O(2))P(B(C(6)F(5))(3)) (1). In contrast, the NMR data for the corresponding reactions of tBu(C(20)H(12)O(2))P and Cl(C(20)H(12)O(2))P with B(C(6)F(5))(3) were consistent with the presence of equilibria between free phosphine and borane and the corresponding adducts. Nonetheless, in each case, the adducts tBu(C(20)H(12)O(2))P(B(C(6)F(5))(3)) (2) and Cl(C(20)H(12)O(2))P(B(C(6)F(5))(3)) (3) were isolable. The species 1 reacts with PhCCH to give the new species tBu(C(6)H(4)O(2))P(Ph)C=CHB(C(6)F(5))(3) (4) in near quantitative yield. In an analogous fashion, the addition of PhCCH to solutions of the phosphines tBu(C(20)H(12)O(2))P, tBuPCl(2) and (C(6)H(3)(2,4-tBu(2))O)(3)P each with an equivalent of B(C(6)F(5))(3) gave rise to L(Ph)C=CHB(C(6)F(5))(3) (L = tBu(C(20)H(12)O(2))P 5, tBuPCl(2)6 and (C(6)H(3)(2,4-tBu(2))O)(3)P 7). X-Ray data for 1, 2, 6 and 7 are presented. The implications of these findings are considered.

Probing substituent effects on the activation of H(2) by phosphorus and boron frustrated Lewis pairs.

The impact of substituent changes on phosphorus and boron-containing frustrated Lewis pairs (FLPs) has been examined. The phosphites (RO)(3)P R = Me, Ph form classical Lewis acid-base adducts of the formula (RO)(3)PB(C(6)F(5))(3) R = Me ; R = Ph , whereas P(O-2,4-(t)Bu(2)C(6)H(3))(3) and P(O-2,6-Me(2)C(6)H(3))(3) generate FLPs. Nonetheless, these latter combinations do not react with H(2). The more basic phosphinite tBu(2)POR, R = tBu reacts with B(C(6)F(5))(3) to give (tBu(2)(H)PO)B(C(6)F(5))(3). The related species tBu(2)POR, R = Ph ; 2,6-Me(2)C(6)H(3) showed no reaction with B(C(6)F(5))(3) but the FLPs react under H(2) (4 atm) to give [tBu(2)P(OR)H][HB(C(6)F(5))(3)] R = Ph and 2,6-Me(2)C(6)H(3). Similarly, tBu(2)PCl in combination with B(C(6)F(5))(3), generates an FLP that upon addition of H(2), gives [tBu(2)PH(2)][ClB(C(6)F(5))(3)] albeit in low yield. The diborane 1,4-(C(6)F(5))(2)B(C(6)F(4))B(C(6)F(5))(2) in combination with either tBu(3)P or (C(6)H(2)Me(3))(3)P generates FLPs that react with H(2) to give [R(3)PH](2)[1,4-(C(6)F(5))(2)HB(C(6)F(4))BH(C(6)F(5))(2)] (R = tBu , C(6)H(2)Me(3)). Similarly PhB(C(6)F(5))(2) and tBu(3)P react with H(2) giving [tBu(3)PH][HBPh(C(6)F(5))(2)] . The combination of B(OC(6)F(5))(3) and PtBu(3) also generate an FLP which reacts with H(2) to give [HPtBu(3)][B(OC(6)F(5))(4)] , the product of substituent redistribution. The boronic esters, (C(6)H(4)O(2))BC(6)F(5), (C(6)H(3)FO(2))BC(6)F(5) and (C(6)F(4)O(2))BC(6)F(5), and the borate esters B(OC(6)H(3)(CF(3))(2))(3), B(OC(6)H(2)F(3))(3) and B(OC(6)H(4)CF(3))(3) were prepared and shown to generate FLPs with tBu(3)P or (C(6)H(2)Me(3))(3)P. Nonetheless, no reaction with H(2) was observed for . Collectively these data suggest that there is a threshold of combined Lewis acidity and basicity that is required to effect the splitting of H(2).

New strategies to phosphino-phosphonium cations and zwitterions.

By employing strategies based on frustrated Lewis pair chemistry, new routes to phosphino-phosphonium cations and zwitterions have been developed. B(C(6)F(5))(3) is shown to react with H(2) and P(2)tBu(4) to effect heterolytic hydrogen activation yielding the phosphino-phosphonium borate salt [(tBu(2)P)PHtBu(2)] [HB(C(6)F(5))(3)] (1). Alternatively, alkenylphosphino-phosphonium borate zwitterions are accessible by reaction of B(C(6)F(5))(3) and PhC[triple chemical bond]CH with P(2)Ph(4), P(4)Cy(4), or P(5)Ph(5) affording the species [(Ph(2)P)P(Ph)(2)C(Ph)=C(H)B(C(6)F(5))(3)] (2), [(P(3)Cy(3))P(Cy)C(Ph)=C(H)B(C(6)F(5))(3)] (3), and [(P(4)Ph(4))P(Ph)C(Ph)=C(H)B(C(6)F(5))(3)] (4). A related phosphino-phosphonium borate species-[(Ph(4)P(4))P(Ph)C(6)F(4)B(F)(C(6)F(5))(2)] (5) is also isolated from the thermolysis of B(C(6)F(5))(3) and P(5)Ph(5).