Neutral ligand induced methane elimination from rare-earth metal tetramethylaluminates up to the six-coordinate carbide state.
The reaction of 1,3,5-trimethyl-1,3,5-triazacyclohexane (TMTAC) with [La{Al(CH(3))(4)}(3)] resulted in C-H activation, leading to the formation of [(TMTAC)La{Al(CH(3))(4)}{(mu(3)-CH(2))[Al(CH(3))(2)(mu(2)-CH(3))](2)}] (1) containing a bis(aluminate) dianion and subsequent extrusion of methane. A similar reaction with [Y{Al(CH(3))(4)}(3)] led to the formation of CH(4), [TMTAC{Al(CH(3))(3)}(2)] (2) and {[(TMTAC)Y][Y(2)(mu(2)-CH(3))][{(mu(6)-C)[Al(mu(2)-CH(3))(2)(CH(3))](3)}{(mu(3)-CH(2))(mu(2)-CH(3))Al(CH(3))(2)}(2)] (3), containing a six-coordinate carbide ion and two [CH(2)Al(CH(3))(3)](2)(-) anions. Compound 3 is a product of multiple C-H activation. This reaction was monitored by in situ(1)H NMR spectroscopy. The analogous reaction with [Sm{Al(CH(3))(4)}(3)] led to the formation of 2, of [(TMTAC)Sm{(mu(2)-CH(3))(CH(3))(2)Al}(2){(mu(3)-CH(2))(2)Al(CH(3))(2)}(2)] (4), which contains a tris(aluminate) trianion, and [{(TMTAC)Sm}{Sm(2)(mu(2)-CH(3))}{(mu(6)-C)[Al(mu(2)-CH(3))(2)(CH(3))](3)}{(mu(3)-CH(2))(mu(2)-CH(3))Al(CH(3))(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and confirm the structure of 3 and to compare it with an analogous compound where the central six-coordinate carbon has been replaced by oxygen.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(CH(3))(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.
Venugopal
Ajay
A
Universität Bielefeld, Fakultät für Chemie, Anorganische Chemie und Strukturchemie Universitätsstrasse 25, 33615, Bielefeld, Germany.
Kamps
Ina
I
Bojer
Daniel
D
Berger
Raphael J F
RJ
Mix
Andreas
A
Willner
Alexander
A
Neumann
Beate
B
Stammler
Hans-Georg
HG
Mitzel
Norbert W
NW
D000535:Aluminum / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008024:Ligands; D008674:Metals, Rare Earth / Q000737:chemistry*; D008697:Methane / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*
D008024:Ligands; D008674:Metals, Rare Earth; D009942:Organometallic Compounds; D000535:Aluminum; D008697:Methane