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and confirm the structure of 3 and to compare it with an analogous compound where the central six-coordinate carbon has been replaced by oxygen.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.

The reaction of 1,3,5-triisopropyl-1,3,5-triazacyclohexane (TiPTAC) with [Y(AlMe(4))(3)] resulted in the formation of [(TiPTAC)Y(Me(3)AlCH(2)AlMe(3))(μ-MeAlMe(3))] by C-H activation and methane extrusion. In contrast, the presence of bulkier cyclohexyl groups on the nitrogen atoms in 1,3,5-tricyclohexyl-1,3,5-triazacyclohexane (TCyTAC) led to the formation of the cationic dimethyl complex [(TCyTAC)(2)YMe(2)][AlMe(4)]. The investigations reveal a dependency of the reaction mechanism on the steric bulk of the N-alkyl entity and the solvent employed. In toluene C-H activation was observed in reactions of [Y(AlMe(4))(3)] with 1,3,5-trimethyl-1,3,5-triazacyclohexane (TMTAC) and TiPTAC. In THF molecular dimethyl cations, such as [(TCyTAC)(2)YMe(2)][AlMe(4)], [(TMTAC)(2)YMe(2)][AlMe(4)] and [(TiPTAC)(2)YMe(2)][AlMe(4)], could be synthesised by addition of the triazacyclohexane at a later stage. The THF-solvated complex [YMe(2)(thf)(5)][AlMe(4)] could be isolated and represents an intermediate in these reactions. It shows that cationic methyl complexes of the rare-earth metals can be formed by donor-induced cleavage of the rare-earth-metal tetramethylaluminates. The compounds were characterised by single-crystal X-ray diffraction or multinuclear and variable-temperature NMR spectroscopy, as well as elemental analyses. Variable-temperature NMR spectroscopy illustrates the methyl group exchange processes between the cations and anions in solution.

Spontaneous reduction of samarium(III) to samarium(II) is observed upon addition of bulky cyclic triaminals to [Sm(AlMe4)3] (see scheme). The methyl groups of the organometallic precursor act as reductant, and CH activation is found as a side reaction. This reaction is the first base‐induced reduction of a lanthanide(III) complex to lanthanide(II) in the complete absence of stabilizing cyclopentadienyl systems.

The reaction of Pr(AlMe4)3 with 1,3,5‐trimethyl‐1,3,5‐triazacyclohexane (TMTAC) leads to the formation of two isomeric products by C–H activation of the AlMe4– ligands: [(η3‐TMTAC)Pr{η4‐(Me3AlCH2AlMe2CH2AlMe3)}] (1), containing a linear tris(aluminate) trianion, and [(η3‐TMTAC)Pr(η4‐{CH(AlMe3)3})] (2), containing a branched tris(aluminate) trianion. The analogous reaction with the more bulkily substituted 1,3,5‐tri‐tert‐butyl‐1,3,5‐triazacyclohexane (TtBuTAC) leads selectively to [(η3‐TtBuTAC)Pr{η4‐(Me3AlCH2AlMe2CH2AlMe3)}] (3). The reaction of La(AlMe4)3 with TtBuTAC affords [(η3‐TtBuTAC)La{η4‐(Me3AlCH2AlMe2CH2AlMe3)}] (4). All compounds were characterised by elemental analysis and crystal‐structure determination. Isomers 1 and 2 could not be separated and form a cocrystalline product with a 1/2 ratio of 1:2 with two slightly different structures of 2 (2a and 2b). In compounds 2, 3 and 4 the tris(aluminate) ligand [Me3AlCH2AlMe2CH2AlMe3]3– is bonded to the lanthanide ions in an η4‐mode through two CH2 units and two terminal Me groups.

The reaction of the tripodal 1,3,5-trialkyl-1,3,5-triazacyclohexanes (L=cyclo-[N(R)CH(2)](3) , R=Et, iPr, tBu), with [Sm(AlMe(4))(3)] resulted in the formation of divalent samarium complexes of the constitution [{L(n)Sm(AlMe(4))(2)}(m)] (n, m=1,2) under ethane extrusion. These compounds were characterised by single-crystal X-ray diffraction and elemental analyses. Simultaneous occurrence of Lewis base induced reduction and C--activation reactions is observed. The ratio of products depends on the bulkiness of the N-alkyl substituent R. The reaction of [Sm(AlMe(4))(3)] with 1,3,5-triisopropyl-1,3,5-triazacyclohexane (TiPTAC) in benzene afforded the inversion-symmetric dimer [{(TiPTAC)(η(3)-AlMe(4))Sm}(2)(μ(2)-AlMe(4))(2)], whereas in toluene the pseudo-samarocene [(TiPTAC)(2)Sm(η(1)-AlMe(4))(2)] was obtained. The trisaluminate [(TiPTAC)Sm{(μ(2)-Me)(Me(2) l)}(2)(μ(3)-CH(2))(2)AlMe(2))] was found to be the C--activation product. In the case of the particular bulky 1,3,5-tri-tert-butyl-1,3,5-triazacyclohexane (TtBuTAC), the reaction led to the formation of the dimeric [{(TtBuTAC)(η(3)-AlMe(4))Sm}(2)(μ(2)-AlMe(4))(2)] even in toluene in comparably high yields. The decrease of the steric demand to ethyl groups in 1,3,5-triethyl-1,3,5-triazacyclohexane (TETAC) afforded the samarocene-like [(TETAC)(2) Sm(η(1)-AlMe(4))(2)] in lower yields. The resulting divalent samarium compounds are found to be stable with respect to reagents like dinitrogen, conjugated olefins and polycyclic aromatic systems.