Issue 5, 2016

Hydroalumination of alkynyl-aminophosphines as a promising tool for the synthesis of unusual phosphines: P–N bond activation, a transient phosphaallene, a zwitterionic AlP2C2 heterocycle and a masked Al/P-based frustrated Lewis pair

Abstract

Treatment of the new alkynyl-chlorophosphine, Mes-P(Cl)–C[triple bond, length as m-dash]C–CMe3, with LiNR2 afforded various unprecedented aminophosphines, Mes-P(NR2)–C[triple bond, length as m-dash]C–CMe3, which showed a fascinating diversity in their reactivity towards H-AltBu2. NMe2 and NEt2 derivatives yielded the hydroalumination products Mes-P(NR2)–C(AltBu2)[double bond, length as m-dash]C(H)–CMe3 which have an Al–N and an activated P–N bond. Elimination of aluminium amide yielded the transient 3H-phosphaallene, Mes-P[double bond, length as m-dash]C[double bond, length as m-dash]C(H)-CMe3, which finally afforded a five-membered AlP2C2 heterocycle with an Al–P bond and two exocyclic C[double bond, length as m-dash]C bonds. This heterocycle is directly formed with the sterically shielded iPr2N- and dimethylpiperidinophosphines. A unique R2AlH adduct resulted from the NPh2 and N(SiMe3)2 substituted phosphines. It may be viewed as an Al/P-based frustrated Lewis pair (FLP) which coordinates an R2AlH moiety. The heterocyclic AlP2C2 compound is formed in the final step of this reaction. Hydroalumination with Et2AlH yielded [Mes-P(H)–C(AlEt2)[double bond, length as m-dash]C(H)–CMe3]2 which features an Al2P2C2 heterocycle and two Al–P bonds. This dimer resembles the class of hidden or masked FLPs which show a reactivity similar to uncoordinated FLPs. Its unique structural motif is a P–H bond which may result in a new type of FLP chemistry.

Graphical abstract: Hydroalumination of alkynyl-aminophosphines as a promising tool for the synthesis of unusual phosphines: P–N bond activation, a transient phosphaallene, a zwitterionic AlP2C2 heterocycle and a masked Al/P-based frustrated Lewis pair

Supplementary files

Article information

Article type
Paper
Submitted
24 Jul 2015
Accepted
14 Sep 2015
First published
22 Sep 2015

Dalton Trans., 2016,45, 2031-2043

Author version available

Hydroalumination of alkynyl-aminophosphines as a promising tool for the synthesis of unusual phosphines: P–N bond activation, a transient phosphaallene, a zwitterionic AlP2C2 heterocycle and a masked Al/P-based frustrated Lewis pair

H. Klöcker, M. Layh, A. Hepp and W. Uhl, Dalton Trans., 2016, 45, 2031 DOI: 10.1039/C5DT02825F

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