标题：13C nuclear magnetic resonance study of five- and six-coordinated carbon in nonclassical organometallic compounds: Dimeric trialkyl-, tricyclopropyl-, and triarylaluminums and some nido and closo carboranes
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1977
卷号：74
期号：12
页码：5217-5221
DOI：10.1073/pnas.74.12.5217
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：A 13C nuclear magnetic resonance spectroscopic study of dimeric trimethyl-, triethyl-, tricyclopropyl-, and triarylaluminums is reported. The five-coordinated bridging carbons are found consistently more shielded than the terminal carbons, in accordance with the increased p-character of the former. The nature of bridging two-electron three-centered Al--C--Al bonds is discussed. 13C nuclear magnetic resonance shifts of several nido and closo carboranes containing five and six coordinated carbons and their 13C-1H spin-spin coupling constants were also obtained. The relationship between the carbon chemical shifts and coordination number of the carbon atom is discussed. There is approximately a 20- to 40-ppm shielding of the 13C chemical shifts of five- and six-coordinated carbons, compared with those of four valent carbons, with a simultaneous general increase of JC-H coupling constants.
