The Presence and Absence of Agostic Electrostatic Si-H···M Interactions in [M{Me2Si(H)N-t-Bu}] (M = Li, Mg1/2) Species
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- 作者：Bernd Goldfuss ; Paul von Ragué ; Schleyer ; Sandra Handschuh ; Frank Hampel ; and Walter Bauer
- 刊名：Organometallics
- 出版年：1997
- 出版时间：December 23, 1997
- 年：1997
- 卷：16
- 期：26
- 页码：5999 - 6003
- 全文大小：230K
- 年卷期：v.16,no.26(December 23, 1997)
- ISSN：1520-6041
文摘
Agostic Si-H···Li contacts (i.e.significantly less than ~3.0 Å) are not present in thesolvent-free X-ray structure of[Li{Me2Si(H)N-t-Bu}]3;shorter(t-Bu)CH3···Lidistances (~2.8 Å) areobserved instead. The situation in solution is different.While the 1H-6Li HOESYspectrumof[Li{Me2Si(H)N-t-Bu}]in toluene at -80 
C evidently detects the same trimericspecies(lacking Si-H···Li interactions, but with short(t-Bu)CH3···Licontacts), two major specieswith strong Si-H···Li interactions also are present.In the Li-HN-SiH3 computationalmodel system, Si-H···Li interactions are favoredenergetically and result in increased Si-Hdistances and decreased Si-H frequencies. AgosticSi-H···metal contacts in the solid stateare found in the X-ray crystal structure of[Mg2{Me2Si(H)N-t-Bu}4],where Li"+" is replacedby the more highly charged Mg"2+". The two shortagostic Si-H···Mg interactions (2.2, 2.5Å) which result also are shown by the two low 
(Si-H)frequencies (2040, 1880 cm-1) intheIR spectrum (Nujol mull) of[Mg2{Me2Si(H)N-t-Bu}4].
C evidently detects the same trimericspecies(lacking Si-H···Li interactions, but with short(t-Bu)CH3···Licontacts), two major specieswith strong Si-H···Li interactions also are present.In the Li-HN-SiH3 computationalmodel system, Si-H···Li interactions are favoredenergetically and result in increased Si-Hdistances and decreased Si-H frequencies. AgosticSi-H···metal contacts in the solid stateare found in the X-ray crystal structure of[Mg2{Me2Si(H)N-t-Bu}4],where Li"+" is replacedby the more highly charged Mg"2+". The two shortagostic Si-H···Mg interactions (2.2, 2.5Å) which result also are shown by the two low (Si-H)frequencies (2040, 1880 cm-1) intheIR spectrum (Nujol mull) of[Mg2{Me2Si(H)N-t-Bu}4].