Issue 37, 2013

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

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

Supplementary files

Article information

Article type
Paper
Submitted
28 Jun 2013
Accepted
22 Jul 2013
First published
23 Jul 2013

Dalton Trans., 2013,42, 13685-13691

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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