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Issue 29, 2009
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Neutral ligand induced methane elimination from rare-earth metal tetramethylaluminates up to the six-coordinate carbide state

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Abstract

The reaction of 1,3,5-trimethyl-1,3,5-triazacyclohexane (TMTAC) with [La{Al(CH3)4}3] resulted in C–H activation, leading to the formation of [(TMTAC)La{Al(CH3)4}{(μ3-CH2)[Al(CH3)22-CH3)]2}] (1) containing a bis(aluminate) dianion and subsequent extrusion of methane. A similar reaction with [Y{Al(CH3)4}3] led to the formation of CH4, [TMTAC{Al(CH3)3}2] (2) and {[(TMTAC)Y][Y22-CH3)][{(μ6-C)[Al(μ2-CH3)2(CH3)]3}{(μ3-CH2)(μ2-CH3)Al(CH3)2}2] (3), containing a six-coordinate carbide ion and two [CH2Al(CH3)3]2 anions. Compound 3 is a product of multiple C–H activation. This reaction was monitored by in situ1H NMR spectroscopy. The analogous reaction with [Sm{Al(CH3)4}3] led to the formation of 2, of [(TMTAC)Sm{(μ2-CH3)(CH3)2Al}2{(μ3-CH2)2Al(CH3)2}2] (4), which contains a tris(aluminate) trianion, and [{(TMTAC)Sm}{Sm22-CH3)}{(μ6-C)[Al(μ2-CH3)2(CH3)]3}{(μ3-CH2)(μ2-CH3)Al(CH3)2}2] (5), which is isostructural to 3. The products were characterised by elemental analyses (except 4, 5), 1 by multinuclear NMR spectroscopy and compounds 1, 2, 3, 4 and 5 by X-ray crystallography. Quantumchemical calculations were undertaken to support the crystallographic data analysis and confirm the structure of 3 and to compare it with an analogous compound where the central six-coordinate carbon has been replaced by oxygen. The investigations point to a mechanism of sterically induced condensation of [Al(CH3)4]groups in close proximity in the coordination spheres of the rare-earth metal atoms, which is dependent on the size of these metal atoms.

Graphical abstract: Neutral ligand induced methane elimination from rare-earth metal tetramethylaluminates up to the six-coordinate carbide state

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Publication details

The article was received on 16 Mar 2009, accepted on 01 May 2009 and first published on 16 Jun 2009


Article type: Paper
DOI: 10.1039/B905271B
Dalton Trans., 2009, 5755-5765

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    Neutral ligand induced methane elimination from rare-earth metal tetramethylaluminates up to the six-coordinate carbide state

    A. Venugopal, I. Kamps, D. Bojer, R. J. F. Berger, A. Mix, A. Willner, B. Neumann, H. Stammler and N. W. Mitzel, Dalton Trans., 2009, 5755
    DOI: 10.1039/B905271B

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