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Issue 8, 2013
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Dehydrogenation of secondary amines: synthesis, and characterization of rare-earth metal complexes incorporating imino- or amido-functionalized pyrrolyl ligands

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Abstract

The dehydrogenation of pyrrolyl-functionalized secondary amines initiated by rare-earth metal amides was systematically studied. Reactions of the rare-earth metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with pyrrolyl-functionalized secondary amines 2-tBuNHCH2-5-R-C4H2NH (R = H (1), R = tBu (2)) led to dehydrogenation of the secondary amines with isolation of imino-functionalized pyrrolyl rare-earth metal complexes [2-tBuN[double bond, length as m-dash]CH-5-R-C4H2N]2REN(SiMe3)2 (R = H, RE = Y (3a), Dy (3b), Yb (3c), Eu (3d); R = tBu, RE = Y (4a), Dy (4b), Er (4c)). The mixed ligands erbium complex [2-tBuNCH2-5-tBu-C4H2N]Er[2-tBuN[double bond, length as m-dash]CH-5-tBuC4H2N]2ClLi2(THF) (4c′) was isolated in a short reaction time for the synthesis of complex 4c. Reaction of the deuterated pyrrolyl-functionalized secondary amine 2-(tBuNHCHD)C4H3NH with yttrium amide [(Me3Si)2N]3Y(μ-Cl)Li(THF)3 further proved that pyrrolyl-amino ligands were transferred to pyrrolyl-imino ligands. Treatment of 2-(tBuNHCH2)C4H3NH (1) with excess (Me3Si)2NLi gave the only pyrrole deprotonated product {[η521-2-(tBuNHCH2)C4H3N]Li2N(SiMe3)2}2 (5), indicating that LiN(SiMe3)2 could not dehydrogenate the secondary amines to imines and rare-earth metal ions had a decisive effect on the dehydrogenation. The reaction of the rare-earth metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with 1 equiv. of more bulky pyrrolyl-functionalized secondary amine 2-[(2,6-iPr2C6H3)NHCH2](C4H3NH) (6) in toluene afforded the only amine and pyrrole deprotonated dinuclear rare-earth metal amido complexes {(μ–η51):η1-2-[(2,6-iPr2C6H3)NCH2]C4H3N]LnN(SiMe3)2}2 (RE = Nd (7a), Sm (7b), Er (7c)), no dehydrogenation of secondary amine to imine products were observed. On the basis of experimental results, a plausible mechanism for the dehydrogenation of secondary amines to imines was proposed.

Graphical abstract: Dehydrogenation of secondary amines: synthesis, and characterization of rare-earth metal complexes incorporating imino- or amido-functionalized pyrrolyl ligands

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Supplementary files

Article information


Submitted
21 Oct 2012
Accepted
16 Nov 2012
First published
19 Nov 2012

Dalton Trans., 2013,42, 2861-2869
Article type
Paper

Dehydrogenation of secondary amines: synthesis, and characterization of rare-earth metal complexes incorporating imino- or amido-functionalized pyrrolyl ligands

Q. Li, S. Zhou, S. Wang, X. Zhu, L. Zhang, Z. Feng, L. Guo, F. Wang and Y. Wei, Dalton Trans., 2013, 42, 2861
DOI: 10.1039/C2DT32513F

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