Substituent Size Effects in Lewis Base Induced Reductions in Organolanthanide Chemistry

Abstract

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.

CH Activation versus Yttrium–Methyl Cation Formation from [Y(AlMe4)3] Induced by Cyclic Polynitrogen Bases: Solvent and Substituent‐Size Effects

“…[13] The angle enclosed by the two nitrogen atom planes of the ligands (46.08) is comparable to that of the divalent samarium compounds [(TiPTAC) 2 SmA C H T U N G T R E N N U N G (AlMe 4 ) 2 ] (47.58) [21] and results in a compressed…”

Subtle Size Effects in C–H Activation Reactions of Lanthanum and Praseodymium Tetramethylaluminates by Neutral Trinitrogen Bases

“…The triazacyclohexane derivatives were prepared according to our earlier reports. [15][16][17][18] [La(AlMe 4 ) 3 ] and [Pr(AlMe 4 ) 3 ] were synthesised by a literature method. [12] NMR measurements were recorded with Bruker DRX 500 and Avance 600 spectrometers.…”

“…Closer investigation of this reaction with variation of R showed that the isomeric tris(aluminate) ion with two methylidene units had formed in C-H activation reactions besides BIR, namely [(TiPrTAC)La(AlMe 4 )({μ 3 -CH 2 }{AlMe 2 (μ 2 -Me)} 2 )] in the case of R = iPr. [17] A third type of reaction between Ln(AlMe 4 ) 3 and TRTAC ligands was observed for the combinations Ln = Y and R = Cy: in this case the formation of methyl cations of the formula [(TCyTAC) 2 YMe 2 ]…”

“…[14] In a series of contributions on the reactions of 1,3,5-trialkyl-1,3,5-triazacyclohexanes (TRTAC with R = alkyl) with Ln(AlMe 4 ) 3 reagents we have found a variety of reactivities. [15][16][17][18] These are unlike the reactions of TRTAC bases with butyllithium, where deprotonation reactions occur, [19] leading to unusual dinitrogen-substituted carbanions. The products of TRTAC/Ln(AlMe 4 ) 3 reactions depend on the size of the TRTAC ligands, the size of the rare earth metal (Ln) atoms involved, and the ability of these metal ions to undergo reduction reactions.…”

Methylidenkomplexe der Seltenerdmetalle

“…[23,24] Bei der Reaktion von [La{Al(CH 3 ) 4 } 3 ] mit TiPTAC wurden keine weiteren Produkte erhalten, [23] wogegen bei der Reaktion von [Sm{Al-(CH 3 ) 4 } 3 ] mit TiPTAC [(TiPTAC)Sm{Al(CH 3 ) 4 }{m 2 -Al-(CH 3 ) 4 }] 2 (16) als weiteres Produkt gebildet wird (Schema 10). [24] In den Verbindungen 15 betragen die Ln-CH 2 -Abstände 2.542(4) und 2.521 (4) [25] Die Reaktionen von [Ln{Al(CH 3 ) 4 } 3 ] (Ln = Y, Sm) mit anderen 1,3,5-Trialkyl-1,3,5-triazacyclohexanen (Alkyl = Ethyl, tert-Butyl, Cyclohexyl) führten nicht zur Bildung von Methylidenkomplexen. [24][25][26] .…”