"Lithio-Aversion" of Thiophene Sulfur Atoms in the X-ray Crystal Structures of [Li-O-SiMe2(2-C4H3S)]6 and [Li-O-CH(i-Pr)(2-C4H3
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- 作者：Bernd Goldfuss ; Paul von Ragué ; Schleyer ; and Frank Hampel
- 刊名：Organometallics
- 出版年：1997
- 出版时间：November 11, 1997
- 年：1997
- 卷：16
- 期：23
- 页码：5032 - 5041
- 全文大小：805K
- 年卷期：v.16,no.23(November 11, 1997)
- ISSN：1520-6041
文摘
Although lithium-sulfur interactions should result if thethienyl groups in [Li-O-SiMe2(2-C4H3S)]6((6)6) and in[Li-O-CH(i-Pr)(2-C4H3S)]6((9)6) were rotated, no shortdistancesbetween the lithiums of the (LiO)6 cores and the thiopheneS atoms (Li-S > 3 Å) are apparentin their X-ray crystal structures. Instead, the thienylconformations in (9)6 benefit fromLi(C=C) 
-interactions (Li1-C2 =2.631(7) Å, Li1-C3 = 2.845(7)Å). DFT (B3LYP) computationsshow Li-S contacts to be only slightly favored over Li-C binding inLi-O-SiH2(2-C4H3S)(7) (1.4 kcal/mol) and inLi-O-CH2(2-C4H3S)(8) (1.7 kcal/mol). Semiempirical PM3conformational analyses of thienyl groups on the (LiO)6cores of the model hexamers [Li-O-SiH2-(2-C4H3S)]6(7)6 and[Li-O-CH2(2-C4H3S)]6((8)6) show preferences forpyramidalLi-S(thiophene) contacts, whereas planar Li-O arrangements arefavored for the furanylanalogues. Due to the higher aromaticity of thiophene, the 
"in-plane" Li+-S(thiophene)coordination energy (Li+-SC4H4,16.9 kcal/mol) is reduced relative to that of theLi+-SMe2reference (29.5 kcal/mol) more than is the less aromatic furan(Li+-OC4H4, 29.2kcal/mol)relative to Li+-OMe2 (39.1 kcal/mol).Consistently, the Li+ -coordination affinityofthiophene (32.1 kcal/mol) is higher than that of furan (29.6 kcal/mol).The electrostaticpotential (EP) of thiophene is only slightly negative in the ring planeat sulfur butconsiderably more negative in the "out-of-plane" -region.This rationalizes the "lithio-aversion" of thienyl sulfur atoms in the X-ray crystal structures of(6)6 and of(9)6:electrostatic metal-thiophene interactions favor the thiophene-system rather than the"in-plane" sulfur region.
-interactions (Li1-C2 =2.631(7) Å, Li1-C3 = 2.845(7)Å). DFT (B3LYP) computationsshow Li-S contacts to be only slightly favored over Li-C binding inLi-O-SiH2(2-C4H3S)(7) (1.4 kcal/mol) and inLi-O-CH2(2-C4H3S)(8) (1.7 kcal/mol). Semiempirical PM3conformational analyses of thienyl groups on the (LiO)6cores of the model hexamers [Li-O-SiH2-(2-C4H3S)]6(7)6 and[Li-O-CH2(2-C4H3S)]6((8)6) show preferences forpyramidalLi-S(thiophene) contacts, whereas planar Li-O arrangements arefavored for the furanylanalogues. Due to the higher aromaticity of thiophene, the "in-plane" Li+-S(thiophene)coordination energy (Li+-SC4H4,16.9 kcal/mol) is reduced relative to that of theLi+-SMe2reference (29.5 kcal/mol) more than is the less aromatic furan(Li+-OC4H4, 29.2kcal/mol)relative to Li+-OMe2 (39.1 kcal/mol).Consistently, the Li+ -coordination affinityofthiophene (32.1 kcal/mol) is higher than that of furan (29.6 kcal/mol).The electrostaticpotential (EP) of thiophene is only slightly negative in the ring planeat sulfur butconsiderably more negative in the "out-of-plane" -region.This rationalizes the "lithio-aversion" of thienyl sulfur atoms in the X-ray crystal structures of(6)6 and of(9)6:electrostatic metal-thiophene interactions favor the thiophene-system rather than the"in-plane" sulfur region.