Study Of Novel Sterically Crowded Induced One-Electron Reductive Reaction

All experiments were performed under an atmosphere of dry argon with the rigid exclusion of air and moisture using standard Schlenk techniques. Reaction of Me2Si(Me2NCH2CH2C9H6)Cl with 1 equiv of 'BuNHLi in diethyl ether yielded Me:Si(Me2NCH2CH2C9H6)CBuNH) (1) in 80.3% yield. Interaction of Me2NCH2CH2C9Hf,Li with excess Me.SiCl in THF yielded Me2NCH2CH2C9HhSiMe, (2) in 78.8% yield; Treatment of anhydrous YbCl, with 3 equiv of (Me Si NLi in refluxed THF produced, after recrystallization from hot toluene, a tetracoordinate ytterbium(Ill) amide [(Me:,Si)2N],Yb(-Cl)Li(THF), (3) in 85.0% yield. Interaction between 3 and 2 equiv of 1 in refluxed toluene gave, after recrystallization from toluene, an ytterbium( II) complex rac-Rp-[ n?: H '-Me,Si(Me1NCH2CH2C9H,)(lBu NH)]2Yb(4) in 58.5% yield. Treatment of 3 with 2 equiv of 2 in refluxed toluene produced, after recrystallization from toluene, an ytterbium( II) complex [ n": n '-(Me2NCH2CH2C9H5SiMe:,)]2Ybn (6) in 51.8% yield; Reaction of 3 with 1 equiv of 1 in refluxed toluene yielded, after recrystallization from toluene, an ytterbium( II) complex rac-Sp-[ n5: n '-Me2Si (Me2NCH2H2C9H5)CBuNH)]2Ybll(5) in 30.8% yield. The formation of complexes 4, 5 6 clearly indicated that these reactions go through one-electron reductive process. To get some more information about the reaction mechanism, several reactions were initated to study the effect of substituted groups of indene compound and metal ionic radius on one-electron reductive reaction. Reaction of 3 with 2 equiv of Me,NCH2CH2C9H7 in refluxed toluene yielded, after recrystallization from foluene, an ytterbium( II) complex[ n: n l-(Me2NCH2CH-,C H,)LYb(7) in 62.9% yield. Interac-rion between [(Me,Si)2N],Eu'"( u -Cl)Li(THF), and 2 equiv of Me2NCH2CH2C9H7 in refluxed toluene gave, after recrystallization from toluene, an Europium(II) complex [ n5: n 1-(Me2NCH2CH2C9Hr,)]2Eu1(8) in 56.9% yield. These results suggested that silyl groups and ionic radius have no influence on the above one-electron reductive reaction. To get some information about the effects of coordinate ClLi(THF), in 3 and the condition of heating, the following reactions were studied. Interaction of [(Me,Si)2N],Ybul with 2 equiv of Me2NCH2CH2C9H7 in refluxed toluene gave, after recrystallization from toluene, an ytterbium( II) complex 7in 62.0% yield. Treatment of 3 with 2 equiv of indene(C9H8) in refluxed toluene afforded, after recrystallization from n-hexane, an ytterbium(III) complex( n 5-7)2YbN(SiMe3)2 (9) in 61.2% yield. The results indicated that (1) coordination ClLi(THF), has no effect on one-electron reductive reaction; (2) heating is not responsible for the reductive reaction; (3) the one-electron reductive reaction may involve ytterbium( Til) amide (Indenyr)2YbN(SiMe3)2 as intermediate. GC-MS analysis of hydrolysis of the reaction for preparation 7 showed no indene coupling product, instead [(Me3Si)2N]2 was detected, suggesting that the reductive reaction does not go through triindenyl ytterbium( 111) path. All the complexes were fully characterized by spectrosopic methods, elemental analyses. 3 4 5, 6, 7 and 8 were also characterized by single-crystal X-ray diffraction study.Based on the above experimental results, the pathway for the formation of the ytterbium( II) complexes is proposed as follows: interaction of indene compound with 3 or [(Me3Si)2N]3Ybm produced bis(indenyr)YbniN(SiMe)2 as intermediates via silylamine elmination reaction, coordination of nitrogen atom of N,N-dimethylaminoethyl groups of indenyl ligand to ytterbium metal leading to sterically crowding around the Yb metal center, which led to the Yb-N bond cleavage with one-electron reduction giving the final ytterbium( II) complexes and [(Me3Si)2N]2.hi summary, A new Yb-N bond cleavage with one-electron reductive reaction was developed. This work not only provides the first evidence to that the reduction chemistry of sterically crowded trivalent lanthanide complexes goes through lanthanide( II) intermediate, but also provides a new methodology for preparation of y...