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Issue 37, 2013
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Activation of H2 using P/Al based frustrated Lewis pairs and reactions with olefins

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Abstract

The activation of H2 using Mes3P–AlX3 (X = Cl, Br, I) FLPs was investigated. Heating a 1 : 2 mixture of Mes3P–AlI3 under H2 afforded [Mes3PH][H(AlI3)2] 1. The alane Al(p-C6F4H)32 was prepared and a 1 : 2 solution of (otol)3P and 2 under H2 generated the salt [(otol)3PH][(μ-H)(Al(p-C6F4H)3)2] which could not be isolated. However, the bulky anion salt [Li(OEt2)][FAl(C12F9)3] was readily converted to [Et4N][FAl(C12F9)3] 3 and subsequently to the hydride salt [Et4N][HAl(C12F9)3] 4. Further reaction of 4 with [CPh3][B(C6F5)4] generated the free alane, Al(C12F9)3 which in the presence of Mes3P and exposure to H2 resulted in the formation of [Mes3PH][(μ-H)(Al(C12F9)3)2] 5. Exposing a solution of 1 in C6D5Br with ethylene, propylene or cyclohexene followed by quenching with water resulted in liberation of ethane, propane, or cyclohexane, respectively. In contrast, exposure of 5 to an atmosphere of ethylene showed no evidence of reaction. In related chemistry, protonation of [Et4N][EtAl(C6F5)3] by the phosphonium salts [R3PH][Al(C6F5)4] (R = otol (6), Mes (7), tBu (8)) and [(2,6-Cl2C6H3)3PH][AlCl4] (9) was also examined. In the case of the reaction of 6 and 9 ethane was liberated whereas with 7 and 8, no reaction occurred. The implications for transition metal-free hydrogenation catalysis are considered.

Graphical abstract: Activation of H2 using P/Al based frustrated Lewis pairs and reactions with olefins

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Publication details

The article was received on 28 Jun 2013, accepted on 22 Jul 2013 and first published on 23 Jul 2013


Article type: Paper
DOI: 10.1039/C3DT51739J
Citation: Dalton Trans., 2013,42, 13685-13691
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    Activation of H2 using P/Al based frustrated Lewis pairs and reactions with olefins

    G. Ménard, L. Tran and D. W. Stephan, Dalton Trans., 2013, 42, 13685
    DOI: 10.1039/C3DT51739J

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