Henry P. DeGroot, Isaiah R. Speight, William W. Brennessel, Timothy P. Hanusa
{"title":"t-Butyl and Trimethylsilyl Substituents in Nickel Allyl Complexes: Similar but Not the Same","authors":"Henry P. DeGroot, Isaiah R. Speight, William W. Brennessel, Timothy P. Hanusa","doi":"10.1021/acsorginorgau.4c00044","DOIUrl":null,"url":null,"abstract":"Metal complexes with <i>t</i>-Bu-substituted allyl ligands are relatively rare, especially compared to their conceptually similar trimethylsilyl-substituted analogs. The scarcity partially stems from the few general synthetic entry points for the <i>t</i>-Bu versions. This situation was studied through a modified synthesis for the allyl ligand itself and by forming several mono(allyl)nickel derivatives. After 2,2,6,6-tetramethyl-4-hepten-3-one was converted to the related 5-bromo-2,2,6,6-tetramethylhept-3-ene (A<sup>2t</sup>Br), a mixture of Ni(COD)<sub>2</sub> and A<sup>2t</sup>Br in the presence of a neutral donor ligand such as MeCN was found to produce the dark red dimeric π-allyl complex [{A<sup>2t</sup>NiBr}<sub>2</sub>]. Both NMR and X-ray crystallographic data confirmed that the <i>t</i>-Bu substituents are in a <i>syn</i>, <i>syn</i>-conformation, like that in the previously described [{A′NiBr}<sub>2</sub>] (A′ = 1,3-(TMS)<sub>2</sub>C<sub>3</sub>H<sub>3</sub>) complex. [{A<sup>2t</sup>NiBr}<sub>2</sub>] will form adducts with neutral donors such as PPh<sub>3</sub> and IMes (IMes = 1,3-dimesitylimidazol-2-ylidene), but the resulting [A<sup>2t</sup>Ni(PPh<sub>3</sub>)Br] complex is not as stable as its trimethylsilyl analog. The [A<sup>2t</sup>Ni(IMes)Br] complex crystallizes from hexanes as a monomer, with an η<sup>3</sup>-coordinated [A<sup>2t</sup>] ligand, and in contrast to the starting arrangement in [{A<sup>2t</sup>NiBr}<sub>2</sub>], the <i>t</i>-Bu groups on the A<sup>2t</sup> ligand are in a <i>syn</i>, <i>anti-</i>relationship. This structure is paralleled in the trimethylsilyl analog [A′Ni(IMes)Br]. DFT calculations were used to compare the structures of <i>t</i>-Bu- and related trimethylsilyl-substituted complexes.","PeriodicalId":29797,"journal":{"name":"ACS Organic & Inorganic Au","volume":null,"pages":null},"PeriodicalIF":3.3000,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"ACS Organic & Inorganic Au","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.1021/acsorginorgau.4c00044","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"CHEMISTRY, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
Abstract
Metal complexes with t-Bu-substituted allyl ligands are relatively rare, especially compared to their conceptually similar trimethylsilyl-substituted analogs. The scarcity partially stems from the few general synthetic entry points for the t-Bu versions. This situation was studied through a modified synthesis for the allyl ligand itself and by forming several mono(allyl)nickel derivatives. After 2,2,6,6-tetramethyl-4-hepten-3-one was converted to the related 5-bromo-2,2,6,6-tetramethylhept-3-ene (A2tBr), a mixture of Ni(COD)2 and A2tBr in the presence of a neutral donor ligand such as MeCN was found to produce the dark red dimeric π-allyl complex [{A2tNiBr}2]. Both NMR and X-ray crystallographic data confirmed that the t-Bu substituents are in a syn, syn-conformation, like that in the previously described [{A′NiBr}2] (A′ = 1,3-(TMS)2C3H3) complex. [{A2tNiBr}2] will form adducts with neutral donors such as PPh3 and IMes (IMes = 1,3-dimesitylimidazol-2-ylidene), but the resulting [A2tNi(PPh3)Br] complex is not as stable as its trimethylsilyl analog. The [A2tNi(IMes)Br] complex crystallizes from hexanes as a monomer, with an η3-coordinated [A2t] ligand, and in contrast to the starting arrangement in [{A2tNiBr}2], the t-Bu groups on the A2t ligand are in a syn, anti-relationship. This structure is paralleled in the trimethylsilyl analog [A′Ni(IMes)Br]. DFT calculations were used to compare the structures of t-Bu- and related trimethylsilyl-substituted complexes.
期刊介绍:
ACS Organic & Inorganic Au is an open access journal that publishes original experimental and theoretical/computational studies on organic organometallic inorganic crystal growth and engineering and organic process chemistry. Short letters comprehensive articles reviews and perspectives are welcome on topics that include:Organic chemistry Organometallic chemistry Inorganic Chemistry and Organic Process Chemistry.