Alkali Metal Cation -Interactions in Metalated and Nonmetalated Acetylenes: 
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- 作者：Bernd Goldfuss ; Paul von Ragué ; Schleyer ; and Frank Hampel
- 刊名：Journal of the American Chemical Society
- 出版年：1997
- 出版时间：February 5, 1997
- 年：1997
- 卷：119
- 期：5
- 页码：1072 - 1080
- 全文大小：422K
- 年卷期：v.119,no.5(February 5, 1997)
- ISSN：1520-5126
文摘
The X-ray crystal structure of[Li-C
C-SiMe2-C6H4-OMe]6(14)6 features nearly symmetric
-interactions between the lithium ions and the acetylide anions(Li1-C
= 2.353(9) Å,Li1-C
= 2.292(9) Å).These -contacts are facilitated by the chelatingo-anisyl methoxy groups(Li1-C-C =77.6(4)
, Li1-O1 =2.169(9)Å). The Li-C distances in the(LiC)6 core of (14)6differ significantly (Li1-C =2.132(9) Å, Li1b-C =2.205(11) Å). This Li-C distancedifferentiation is unique in organolithium hexamers, and is due toLi(CC-R)"side-on-" and "end-on-
" contacts, as is showncomputationally in H-CC-Li(LiH)2(20). A second X-raycrystal structure,[Li-O-CMe2-CC-H]6(22)6, reveals electrostatic -interactionsbetween the lithiums in the(LiO)6 core and the nonmetalated acetylene groups(Li1-C2 = 2.443(5) Å,Li1-C3 = 2.749(6) Å). TheseLi-C-contacts shorten upon acetylene lithiation, as is showncomputationally in Li-O-CH2-CC-(H/Li)(24-H/Li).Additional computations reveal that the -interactions in(HCC)M2H (26-Li-Cs) complexes (modellingoligo- andpolymeric M-CC-R) are weak (only 0.7 kcal/mol for Li), butsubstantial in M+(H-CC-H)(27-Li-Cs) species(20.2 kcal/mol for Li+). In 26-Li-Cs, the-contacts increase the CC bond lengths slightly (0.005 Å for Li)andlower the CC stretching frequencies (33 cm-1 for Li),they polarize charge density from C towardC and henceresult in counterion-induced charge delocalizations. The degreesof -interactions both in (26-Li-Cs) and in(27-Li-Cs) decrease with increasing size of the alkalications.
C-SiMe2-C6H4-OMe]6(14)6 features nearly symmetric-interactions between the lithium ions and the acetylide anions(Li1-C = 2.353(9) Å,Li1-C = 2.292(9) Å).These -contacts are facilitated by the chelatingo-anisyl methoxy groups(Li1-C-C =77.6(4), Li1-O1 =2.169(9)Å). The Li-C distances in the(LiC)6 core of (14)6differ significantly (Li1-C =2.132(9) Å, Li1b-C =2.205(11) Å). This Li-C distancedifferentiation is unique in organolithium hexamers, and is due toLi(CC-R)"side-on-" and "end-on-" contacts, as is showncomputationally in H-CC-Li(LiH)2(20). A second X-raycrystal structure,[Li-O-CMe2-CC-H]6(22)6, reveals electrostatic -interactionsbetween the lithiums in the(LiO)6 core and the nonmetalated acetylene groups(Li1-C2 = 2.443(5) Å,Li1-C3 = 2.749(6) Å). TheseLi-C-contacts shorten upon acetylene lithiation, as is showncomputationally in Li-O-CH2-CC-(H/Li)(24-H/Li).Additional computations reveal that the -interactions in(HCC)M2H (26-Li-Cs) complexes (modellingoligo- andpolymeric M-CC-R) are weak (only 0.7 kcal/mol for Li), butsubstantial in M+(H-CC-H)(27-Li-Cs) species(20.2 kcal/mol for Li+). In 26-Li-Cs, the-contacts increase the CC bond lengths slightly (0.005 Å for Li)andlower the CC stretching frequencies (33 cm-1 for Li),they polarize charge density from C towardC and henceresult in counterion-induced charge delocalizations. The degreesof -interactions both in (26-Li-Cs) and in(27-Li-Cs) decrease with increasing size of the alkalications.