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Issue 31, 2009
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Mixed donor-functionalised phosphinomethanide complexes of the alkali metals; synthesis, structures, and solution dynamics

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Abstract

The mixed donor tertiary phosphine {(Me3Si)2CH}P(C6H4-2-CH2NMe2)(C6H4-2-CH2OMe) (11) is accessible via the stepwise addition of [Li(C6H4-2-CH2NMe2)] followed by [Li(C6H4-2-CH2OMe)] to the dichlorophosphine {(Me3Si)2CH}PCl2. Phosphine 11 is readily deprotonated by BunLi to give the lithium phosphinomethanide [[{(Me3Si)2C}P(C6H4-2-CH2NMe2)(C6H4-2-CH2OMe)]Li] (15), which undergoes metathesis reactions with the alkoxides MOBut [M = Na, K] to give the heavier alkali metal phosphinomethanides [[{(Me3Si)2C}P(C6H4-2-CH2NMe2)(C6H4-2-CH2OMe)]M(L)n]x in good yield [M = Na (12), (L)n = Et2O, x = 1; M = K (13), n = 0, x = 2]. Compounds 12 and 13 adopt monomeric and dimeric structures, respectively, in the solid state. Variable-temperature NMR studies indicate that compounds 12 and 13 are highly fluxional in solution; this fluxionality arises from a dynamic equilibrium between two conformers, which differ in the orientation of the aromatic rings of the ligand. The nature of these conformers and their relative energies have been probed by DFT calculations, which show the two principal conformers to differ in energy by just 1.6 kcal mol−1. Calculation of the 1H NMR shielding tensors using the GIAO method reveals that the low field chemical shifts of one benzylic and one aromatic proton in the ground state conformer are due to their close proximity to the carbanion centre.

Graphical abstract: Mixed donor-functionalised phosphinomethanide complexes of the alkali metals; synthesis, structures, and solution dynamics

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Publication details

The article was received on 16 Feb 2009, accepted on 05 May 2009 and first published on 18 Jun 2009


Article type: Paper
DOI: 10.1039/B903119G
Citation: Dalton Trans., 2009, 6159-6165
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    Mixed donor-functionalised phosphinomethanide complexes of the alkali metals; synthesis, structures, and solution dynamics

    C. Wills, K. Izod, J. Young, W. Clegg and R. W. Harrington, Dalton Trans., 2009, 6159
    DOI: 10.1039/B903119G

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