Redox Chemistry between Europium(III) Amide and Pyrrolyl-Functionalized Secondary Amines. Synthesis and Structural Characterization of Lithium and Novel Lanthanide Complexes Incorporating Functionalized Pyrrolyl Ligands

Abstract

The redox reaction between the europium(III) amide [(Me 3 Si) 2 N] 3 Eu III (μ-Cl)Li(THF) 3 and pyrrolyl-functionalized secondary amines was found for the first time. The interactions of 2-(2,6-R 2 C 6 H 3 NHCH 2 )C 4 H 3 NH (R = CH 3 ( 1 ), R = i Pr ( 2 )) with 2 equiv of europium(III) amide [(Me 3 Si) 2 N] 3 Eu III (μ-Cl)Li(THF) 3 led to oxidation of the secondary amine with isolation of imino-functionalized pyrrolyl lithium complexes {[η 2:η 1 -2-(2,6-R 2 C 6 H 3 N═CH)C 4 H 3 N]Li(THF)} 2 (R = CH 3 ( 4 ), R = i Pr ( 5 )). When the deuterated compounds 2-(2,6-R 2 C 6 H 3 NHCHD)C 4 H 3 NH (R = CH 3 ( 1a ), R = i Pr ( 2a )) were respectively treated with 2 equiv of europium(III) amide [(Me 3 Si) 2 N] 3 Eu III (μ-Cl)Li(THF) 3, the corresponding mixture of deuterated imino-functionalized pyrrolyl lithium complexes {[η 2:η 1 -2-(2,6-Me 2 C 6 H 3 N═CD)C 4 H 3 N]Li(THF)} 2 ( 4a ) and 4 and {[η 2:η 1 -2-(2,6- i Pr 2 C 6 H 3 N═CD)C 4 H 3 N]Li(THF)} 2 ( 5a ) and 5 were produced upon analyses of the NMR spectra of the complexes. Treatment of 2-(2,6- i Pr 2 C 6 H 3 NHCHD)C 4 H 3 NH ( 2a ) with excess (Me 3 Si) 2 NLi gave the only pyrrole deprotonated product, {[η 5:η 2:η 1 -2-(2,6- i Pr 2 C 6 H 3 NHCHD)C 4 H 3 N]Li 2 N(SiMe 3 ) 2 } 2 ( 6 ). When 2-(2,6- i Pr 2 C 6 H 3 NHCH 2 )C 4 H 3 NH ( 2 ) was treated with ytterbium(III) amide [(Me 3 Si) 2 N] 3 Yb III (μ-Cl)Li(THF) 3, a dinuclear ytterbium(III) amide with formula {[(μ-η 5:η 1 ):η 1 -2-[(2,6- i Pr 2 C 6 H 3 )NCH 2 ]C 4 H 3 N]YbN(SiMe 3 ) 2 } 2 ( 7 ) was isolated and no oxidation of the secondary amine was observed. Reduction of ytterbium or imino-functionalized pyrrolyl compound was not observed by refluxing the toluene solution of complex 7 for 2 days. Treatment of equal equivalents of grease (Me 2 SiO) 3, 2-(2,6- i Pr 2 C 6 H 3 NHCH 2 )C 4 H 3 NH ( 2 ), and europium(III) amide [(Me 3 Si) 2 N] 3 Eu III (μ-Cl)Li(THF) 3, after workup, afforded the europium(II) complex {[μ - η 5:η 1:η 1 - 2-(ArN(Me 2 SiO)CH 2 )C 4 H 3 N]Eu II [η 5 - 2-(ArN═CH)C 4 H 3 N]Li 2 [N(SiMe 3 ) 2 ]} 2 (Ar = 2,6- i Pr 2 C 6 H 3 ) ( 8 ) with reduction of europium(III) to europium(II) and oxidation of the secondary amine to an imino group. Reaction of a pyrrolyl-functionalized linked secondary diamine [5- t Bu-C 4 H 2 NH-2-CH 2 NHCH 2 ] 2 ( 3 ) with [(Me 3 Si) 2 N] 3 Eu III (μ-Cl)Li(THF) 3 produced a novel centrosymmetric macrocyclic complex with six europium(II) ions and six lithium ions, {[(5- t Bu-C 4 H 2 N-2-CH═NCH 2 ) 2 ] 4 [(5- t Bu-2-CH 3 N═CH(C 4 H 2 N)]Eu 3 Li 3 } 2 ( 9 ) with observation of redox chemistry between europium(III) and the linked secondary amine. When the linked secondary diamine [5- t Bu-C 4 H 2 NH-2-CH 2 NHCH 2 ] 2 ( 3 ) was treated with [(Me 3 Si) 2 N] 3 Dy III (μ-Cl)Li(THF) 3 to produce a novel four-sandwiched-lithium-supported tetranuclear dysprosium(III) complex, {η 2:η 2 -[η 1:η 1 -(μ-η 5:η 5 -[5- t Bu-C 4 H 2 N-2-CH 2 NCH 2 CH 2 N-2-CH 2 -5- t Bu-C 4 H 2 N]Li) 2 ]Dy 2 (μ 3 -Cl)Li} 2 ( 10 ), no redox chemistry was observed. All compounds were characterized by spectroscopic methods and elemental analyses; complexes 4 − 10 were also characterized by X-ray structure analyses.