{"title":"Anisotropic π Bonding in Bis(iminoxolene)ruthenium: Consequences for Alkene and Alkyne Binding","authors":"Patricia Rose H. Ayson, and , Seth N. Brown*, ","doi":"10.1021/acs.organomet.4c0025910.1021/acs.organomet.4c00259","DOIUrl":null,"url":null,"abstract":"<p >Orientational preferences in alkene and alkyne complexes arise from differences in the π backbonding capabilities of the relevant dπ orbitals, which typically are engendered by an unsymmetrical arrangement of ancillary ligands. The metal <i>trans</i>-bis(iminoxolene) fragment is <i>C</i><sub>2</sub>-symmetric but discriminates between perpendicular dπ orbitals because only one of them has a strong π interaction with the iminoxolenes. To assess this effect, square pyramidal bis(iminoxolene) alkene and alkyne complexes (Diso)<sub>2</sub>Ru(L) (Diso = <i>N</i>-(2,6-diisopropylphenyl)-4,6-di-<i>tert</i>-butyl-<i>o</i>-iminobenzoquinone) are prepared via the bis-acetonitrile complex <i>cis</i>-(Diso)<sub>2</sub>Ru(NCCH<sub>3</sub>)<sub>2</sub>. The alkenes and alkynes align roughly along the O–Ru–O axis but are turned slightly toward the cleft between the iminoxolene ligands, which orients the ligand π* orbital with the <i>d</i>π orbital that is not engaged in bonding with the iminoxolenes. In the alkyne complexes, π donation from the alkyne competes effectively with the ruthenium-iminoxolene π bonding, forming a favorable four-electron, three-orbital system. The barrier to rotation in the 1-hexyne complex is 19.0 kcal mol<sup>–1</sup>, while allylbenzene dissociates more readily than it undergoes rotation, with a barrier of 17.4 kcal mol<sup>–1</sup>. The strong orientational preference leads to high facial selectivity of alkene binding, with only one diastereomer of the 1-alkene adducts observed by NMR (>30:1 selectivity).</p>","PeriodicalId":56,"journal":{"name":"Organometallics","volume":null,"pages":null},"PeriodicalIF":2.5000,"publicationDate":"2024-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Organometallics","FirstCategoryId":"92","ListUrlMain":"https://pubs.acs.org/doi/10.1021/acs.organomet.4c00259","RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"CHEMISTRY, INORGANIC & NUCLEAR","Score":null,"Total":0}
引用次数: 0
Abstract
Orientational preferences in alkene and alkyne complexes arise from differences in the π backbonding capabilities of the relevant dπ orbitals, which typically are engendered by an unsymmetrical arrangement of ancillary ligands. The metal trans-bis(iminoxolene) fragment is C2-symmetric but discriminates between perpendicular dπ orbitals because only one of them has a strong π interaction with the iminoxolenes. To assess this effect, square pyramidal bis(iminoxolene) alkene and alkyne complexes (Diso)2Ru(L) (Diso = N-(2,6-diisopropylphenyl)-4,6-di-tert-butyl-o-iminobenzoquinone) are prepared via the bis-acetonitrile complex cis-(Diso)2Ru(NCCH3)2. The alkenes and alkynes align roughly along the O–Ru–O axis but are turned slightly toward the cleft between the iminoxolene ligands, which orients the ligand π* orbital with the dπ orbital that is not engaged in bonding with the iminoxolenes. In the alkyne complexes, π donation from the alkyne competes effectively with the ruthenium-iminoxolene π bonding, forming a favorable four-electron, three-orbital system. The barrier to rotation in the 1-hexyne complex is 19.0 kcal mol–1, while allylbenzene dissociates more readily than it undergoes rotation, with a barrier of 17.4 kcal mol–1. The strong orientational preference leads to high facial selectivity of alkene binding, with only one diastereomer of the 1-alkene adducts observed by NMR (>30:1 selectivity).
期刊介绍:
Organometallics is the flagship journal of organometallic chemistry and records progress in one of the most active fields of science, bridging organic and inorganic chemistry. The journal publishes Articles, Communications, Reviews, and Tutorials (instructional overviews) that depict research on the synthesis, structure, bonding, chemical reactivity, and reaction mechanisms for a variety of applications, including catalyst design and catalytic processes; main-group, transition-metal, and lanthanide and actinide metal chemistry; synthetic aspects of polymer science and materials science; and bioorganometallic chemistry.